Azmi Rahmat currently works at the School of Materials Engineering, Universiti Malaysia Perlis. Azmi does research in Materials Engineering. Their current project is 'Synergistic Analysis and CFD Modelling of Sustainable Porous Clay-Synthesized Calcium Carbonate for Gas Adsorbent Applications..'
Skills and Expertise
Mar 2011 - Apr 2014
Universiti Malaysia Perlis · School of Materials Engineering
Feb 1987 - Feb 2011
University of Science Malaysia · School of Material and Mineral Resources Engineering
Nibong Tebal, Malaysia
Global warming resulted from the emission of greenhouse and industrial gases have received widespread attention. Hydrogen sulfide gas became one of the most problematic gas in the industry especially petroleum and waste treatment industries. Even though various capture technologies including physical absorption, chemical absorption and membrane exist, they are not matured yet for post combustion power plants. This is because that huge amount of flue gas is needed to treat and significant mass transfer limitations exist in the processes. Among these technologies, chemical absorption using aqueous alkanolamine solutions is proposed to be the most applicable technology for hydrogen sulfide capture. However, the alkanolamine aqueous solutions possess some drawbacks such as high equipment corrosion rate, high energy consumption in regeneration, and a large absorber volume required. As a result, solid adsorption processes are suggested and studied to overcome those inherent problems in chemical absorption. Therefore, the potential novel porous local clay-synthesized nano calcium carbonate is proposed particularly to adsorb carbon dioxide gas.
This study aims to modify the practice of using over-voltage concept of polarization process in cathodic protection to the potential of zero charges (Epzc) as a new technique of corrosion prevention. At Epzc, a metal surface is not in contact with an aqueous solution due to the absence of electrical charge and no electrostatic attraction. A chemical adsorption caused by oxidation reaction does not occur at Epzc. The removal of electrical charges at the electrode-electrolyte interface leads the desorption of ionic charges which causes the metal surface suffers no longer a corrosion reaction due to the absence of a charge transfers.
This study aims to modify the practice of using over-voltage concept of polarization process in cathodic protection to the potential of zero charges (Epzc) as a new technique of corrosion prevention. At Epzc, a metal surface is not in contact with an aqueous solution due to the absence of electrical charge and no electrostatic attraction. A chemical adsorption caused by oxidation reaction does not occur at Epzc. The removal of electrical charges at the electrode-electrolyte interface leads the desorption of ionic charges which causes the metal surface suffers no longer a corrosion reaction due to the absence of a charge transfers.
Research Items (78)
The consumption of potentiostatic polarization current on austenitic type 304 stainless steel in 3.5 wt.% NaCl solution was studied at pH 4 to 7. The H2SO4 droplet was used to control the solution pH. To obtain the Epzc effect, the sample potential was scanned repeatedly just below Ecorr with magnitude between -3 to -0.3 mV vs Ecorr. The potential scanning was done at the lowest rate 0.01 mV/ min. Potentiostatic polarization shows a lower and steadily stable current consumption on lower potential scanning magnitudes as well as at solution pH that nearly to neutral (pH 7). As predicted, the higher current consumption was found at pH 4 and the highest scanning magnitude (-3 mV to Ecorr) was -9.30 × 10-7 A/cm2, whereas the lowest current consumption occurs at pH 7 at the lowest scanning magnitude (-0.3 mV to Ecorr) was just -0.03 × 10-7 A/cm2. The pH level displays a predictable finding at all potential scanning magnitude. The averages of current consumption were found to reduce with the increasing of studied pH as a manifestation of the passive film on stainless steel surface in the presence of Clˉ ions. The current spikes were clearly observed at lower pH (pH 4) resulted by the passivation and the breakdown of the passive film repeatedly. The current spikes gradually disappear as the increasing of the studied pH.
The corrosion behaviour of austenitic AISI 304 stainless steel was studied in 3.5 wt. % NaCl at pH 4 to pH 7. The pH of the solution was modified by adding H2SO4 accordingly. It was observed that open circuit potential of stainless steel at various pH 4 to pH 7 in 3.5 wt. % NaCl solutions can be obtained within 2 hours of immersion. The OCP values were observed to remain stable during the 120 hours immersion test. The OCP of stainless steel in the solution decreases with an increase in pH. The polarization curves of stainless steel indicated the typical characteristic of corrosion followed by passivation and the breaking down of the passive film due to the pitting in the presence of SO4 2-ions. The corrosion rate at pH 4 was 0.0675 µm/year and correspondingly decreases with an increase in pH. The corrosion rate at pH 7 was 0.0196 µm/year. The stereo microscopic images showing the worst pitting surface of stainless steel at pH 4 and becoming less susceptible to pitting at pH 7.
Aims: Since the 19th century, there has been considerable research effort in the fabrication, and characterization of nanoporous materials. These nanoporous materials are highly scientifically and technologically relevant as a result of the surface openings that have controllable dimensions at both the micrometer and nanometer scales. Nanoporous alumina foil has been a template of choice in various applications due to its simplicity and ease of fabrication. Purpose: The purpose of this review is to provide an insight into the aluminum anodization steps and the different types of electrolytes that have been used to fabricate nanoporous alumina template. Results: In this paper we also briefly review the developments in the anodization of aluminum foil in relation to its mechanical properties, and the various ordered and disordered nano pores that are likely to be obtained from the surface morphology.
This paper presents the results of corrosion studies between Fly Ash Geopolymer (FG) paste and Fly Ash-Slag Geopolymer (FSG) paste. Geopolymer was made from aluminosilicate inorganic polymers mixed with the alkaline activator in order to reduce the carbon dioxide (CO2) to the ecosystem. Samples then were cured at 60ºC for 24 hours in the oven. Reinforcement bar is placed at the center of the paste. The samples were examined after 7, 14 and 28 days in terms of Open Circuit Potential (OCP) test, phase analysis and morphology analysis. The potential values regarding OCP test for FSG paste from 7 days until 28 days are 0.464 V, 0.474 V and 0.498 V more positive than FG paste which the potential values are 0.087 V, 0.133 V and 0.206 V respectively. From the Pourbaix diagram, all the potential values for FG paste and FSG paste were located in the same Fe2O3, passivity region. Passive layer which is the oxide form exists in this region to protect the reinforcement bar from corrosion agents. It can be proved from phase analysis results which iron oxide hydroxide (FeOOH), hematite (Fe2O3) and magnetite (Fe3O4) peaks exist. The differences of morphological structures of these pastes were observed by Scanning Electron Microscope (SEM). It shows that FSG paste had good corrosion resistance and low corrosion rate compared to FG paste.
Activation pretreatment with nickel acetate solution at various concentrations was performed prior to the phosphating step to enhance the corrosion resistance of carbon steel substrates. The activation solution was studied over various concentrations: 10, 50, and 100 g/L. The effects of these concentrations on surface characteristics and microstructural evolution of the coated samples were characterized by scanning electron microscopy and energy-dispersive spectroscopy. The electrochemical behavior was evaluated using potentiodynamic polarization curves, electrochemical impedance spectroscopy, and immersion test in a 3.5 pct NaCl solution. Significant increases in the nucleation sites and surface coverage of zinc phosphate coating were observed as the concentration of activation solution reached 50 g/L. The electrochemical analysis revealed that the activation treatment with 50 g/L nickel acetate solution significantly improved the protection ability of the zinc phosphate coating. The corrosion current density of activated phosphate coating with 50 g/L was reduced by 64.64 and 13.22 pct, compared to the coatings obtained with activation solutions of 10 and 100 g/L, respectively.
This study has been conducted to understand the hardness behavior of geopolymer paste in different conditions; with and without being immersed in water. Geopolymer paste has been used nowadays as an alternative way to reduce global warming pollution by carbon dioxide (CO2) released to the air caused from the production of Ordinary Portland Cement (OPC). Geopolymer has many advantages such as high compressive strength, lower water absorption and lower porosity. Geopolymer paste in this study was made from a mixture of fly ash and alkaline activators. The alkaline activators that have been used were sodium hydroxide (NaOH) solution and sodium silicate (Na2SiO3) solution. Then the mixture was allowed to harden for 24hrs at ambient temperature and then placed in the oven for 24hrs with 60ºC for the curing process. The hardness testing was conducted after a few months when the samples already achieved the optimum design. The samples were divided to two conditions; without immersion which was placed at ambient temperature (S1) and immersed in water for one week (S2). The samples then are divided into two at the center and testing was conducted into 4 parts which are part 1, part 2, part 3 and part 4. Various methods of non-destructively testing concrete and mortar have been in use for many years such as Vickers hardness test, Rockwell hardness test, Brinell hardness test and many more. The Rockwell hardness test method as defined in ASTM E-18 is the most commonly used hardness test method which is also used in this study. From the results, S1 has higher hardness value than S2 for all parts with the maximum value of S1 is 118.6 and the minimum value is 71.8. The maximum value of S2 is 114.4 and the minimum value is 0. The central part of the geopolymer paste also showed greater hardness values than the edge area of the samples.
In this present study, the porous anorthite ceramics were prepared from white clay and precipitated calcium carbonate via polymeric foam replication method. The effects of various precipitated calcium carbonate additions (0, 10, 15, and 25 wt.%) on the properties of porous anorthite ceramics have been studied. The main phase that revealed after the additions of 20 and 25 wt.% of precipitated calcium carbonate was anorthite (CaO·Al2O3·2SiO2). The porosity of the porous anorthite ceramics was increased (from 67 to 77 percent) with the increasing amount of precipitated calcium carbonate. Meanwhile, the density of the porous anorthite ceramics was increased (from 0.463 to 0.703 g/cm3) with the increasing amount of precipitated calcium carbonate. The flexural strength of porous anorthite ceramics consisting of predominantly anorthite phase are ranged from 0.24 to 1.23 MPa. Finally, the correlation between the flexural strength on the foam density has been studied. The flexural strength was increased when the foam density increases.
This study has been conducted to understand the hardness behavior of geopolymer paste in different conditions; with and without being immersed in water. Geopolymer paste has been used nowadays as an alternative way to reduce global warming pollution by carbon dioxide (CO2) released to the air caused from the production of Ordinary Portland Cement (OPC). Geopolymer has many advantages such as high compressive strength, lower water absorption and lower porosity. Geopolymer paste in this study was made from a mixture of fly ash and alkaline activators. The alkaline activators that have been used were sodium hydroxide (NaOH) solution and sodium silicate (Na 2SiO3) solution. Then the mixture was allowed to harden for 24hrs at ambient temperature and then placed in the oven for 24hrs with 60°C for the curing process. The hardness testing was conducted after a few months when the samples already achieved the optimum design. The samples were divided to two conditions; without immersion which was placed at ambient temperature (S1) and immersed in water for one week (S2). The samples then are divided into two at the center and testing was conducted into 4 parts which are part 1, part 2, part 3 and part 4. Various methods of non-destructively testing concrete and mortar have been in use for many years such as Vickers hardness test, Rockwell hardness test, Brinell hardness test and many more. The Rockwell hardness test method as defined in ASTM E-18 is the most commonly used hardness test method which is also used in this study. From the results, S1 has higher hardness value than S2 for all parts with the maximum value of S1 is 118.6 and the minimum value is 71.8. The maximum value of S2 is 114.4 and the minimum value is 0. The central part of the geopolymer paste also showed greater hardness values than the edge area of the samples.
Cobalt-hydroxyapatite (Co-HA) composites was successfully prepared by simple electroless deposition process of Co on the surface of hydroxyapatite (HA) particles. Co deposition was carried out in an alkaline bath with sodium hypophosphite as a reducing agent. The electroless process was carried out without sensitization and activation steps. The deposition of Co onto HA was characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The Co-HA composite powder was compacted and sintered at 1250°C. The Co particles were homogeneously dispersed in the HA matrix after sintering and the mechanical properties of composites was enhanced to 100 % with 3 % wt Co and gradually decreased at higher Co content.
Ceramic foams, a porous material with a gyroid structures, are becoming highly demanded for various applications such as heat insulation, bone implantation and filtration, because of their unique properties such as high specific surface area, high porosity and low heat transfer rate. In this study, the development of ceramic foam utilised white clay with a combination of precipitated calcium carbonate (PCC). The ceramic foam was successfully developed using this combination after the sample was sintered at 1250 °C for 2 hours holding time. The various compositions of PCC (10.0, 12.5, 15.0, 17.5, 20.0, 22.5 and 25.0 wt.%) affected the chemical composition and compressive strength of the ceramic foam. The chemical composition of ceramic foam was analysed by using X -ray fluorescence (XRF) and the result indicated that the PCC was successfully transformed into calcium oxide (CaO) after the sintering process. The mineralogical composition of the ceramic foam was evaluated using X-ray diffraction (XRD) and has shown the presence of mullite (3Al2O3.2SiO2), gehlenite (Ca2Al2SiO7) and anorthite (2CaAl2Si2O8) after the sintering process. The scanning electron microscope (SEM) analysis showed that the presence of porosity on the strut of the ceramic foam. Meanwhile, the compressive strength of the ceramic foam increased from 0.03 to 1.31 MPa, which is directly proportional to the increased amount of PCC.
A method for controlling and protecting corrosion is disclosed, according to an illustrative embodiment of a present invention. The method includes immersing a metal in a solution for reaching a steady state of corrosion potential of the metal. The corrosion potential of the metal is measured. The method includes fixing potential of the metal with respect to a reference electrode and forming a circuit. The circuit is interrupted when current flow direction changes. The corrosion can be controlled and prevented by bringing the potential of the metal to a potential of zero charge.
This paper presents an experimental study of the electrical resistivity of geopolymer paste by using a non-destructive test employing Wenner four probe method. Geopolymer is produced from a combination mixture of aluminosilicate materials which is rich in Si and Al such as fly ash with an alkaline activator. Geopolymer paste in this study was made from a mixture of class F fly ash, sodium hydroxide (NaOH) solution and sodium silicate (Na 2 SiO 3) solution. An alkaline activator was prepared 24 hrs prior to use with the ratio mixture of Na 2 SiO 3 /NaOH being 2.5. Then, the prepared alkaline activator was mixed with the fly ash for about 30 minutes. After that, the mixture was placed in a 100 mm x 103 mm x 495 mm mould. After 24 hrs, the sample was taken out from the mould and cured at 60°C in the oven for 24 hrs. The sample was then tested after 7, 14 and 28 days. The current applied in this study was from 0.01 mA to 1.00 mA and the electrode spacing used were 0.02 m, 0.04 m, 0.06 m, 0.08 m and 0.10 m. The results showed that the geopolymer paste after 28 days with the current of 0.01 mA and 0.10 m electrode spacing showed the highest resistivity with 61575 Ω.m while the geopolymer paste after 7 days with 0.95 mA and 0.02 m electrode spacing showed the lowest resistivity with 537 Ω.m. Hence, the corrosion rate of geopolymer paste in this study was negligible and if occur, was very low. 1. Introduction Currently, geopolymer based on analogous and aluminosilicates materials is used to replace the Ordinary Portland Cement (OPC) as binders for concretes in building materials. Other than that, geopolymer is a potential material that could be used in a lot of applications for instance construction, aerospace, automotive and many more. It has excellent chemical, physical and thermal properties. Geopolymer material is a cost effective and sustainable solution by recycling the waste material and treating it under green chemistry technique. Geopolymerization process involves the combination mixture of aluminosilicate from industrial waste or natural minerals such as fly ash, slag or rice husk ash with an alkaline activator . One of the methods to measure the durability of the concrete is electrical resistivity or concrete resistivity. Concrete resistivity influences the durability and effectiveness of cathodic protection (CP) of concrete structures . Concrete resistivity measurement is a very important parameter concerning determination of intensity of the initiated corrosion process. Furthermore, it is also a useful measurement to aid in identifying problem areas or confirming concerns about poor quality concrete. Measurements can only be considered alongside other measurements. Reinforcement bar will interfere with resistivity measurements. In concrete materials, the corrosion process will be
Greenhouse effects were generated from anthropogenic emissions of carbon dioxide (CO2) into the atmosphere. High concentration of CO2 has recognised as major causes of global warming. In order to keep CO2 at a manageable level, adsorptions of these gases from the flue gases is necessary. Developing a low cost porous solid adsorbent as adsorption media become a great attention due to environmental and economic concerns. This paper has reviewed the cost effective materials with a suitable methods to fabricate the porous solid adsorbent. This paper also has discussed the adsorption mechanisms of CO2 on the selective cost effective materials.
The effect of small tool pin profiles on the microstructures and mechanical properties of 6061 aluminum alloy joints using friction stir welding (FSW) technique was investigated. Three different tool pin profiles: threaded tapered cylindrical (T1), triangular (T2) and square (T3) were used to produce the joints. The results indicate that the weld joints are notably affected by joining with different tool pin profiles. The triangular tool pin profile produces the best metallurgical and mechanical weld properties compared with other tool pin profiles. Besides, the lowest tensile strength and microhardness are obtained for the joint friction stir welded with square tool pin profile. It is observed that the smaller tool pin profile and shoulder diameter lead to narrow region of heat affected zone (HAZ) and a desired level of softening. The fracture surface examination shows that the joints are also affected when welding with different types of tool pin profiles. The fracture surface shows that the triangular specimen fails with a ductile fracture mode during the tensile test, while the brittle fracture modes are observed in the joints fabricated with other tool pin profiles (T1 and T3). 摘 要：研究小搅拌针形状对6061铝合金搅拌摩擦焊接头的显微组织和力学性能的影响。采用3种不同形状的搅拌针：螺纹锥形圆柱形(T1)、三角形(T2)和正方形(T3)。结果表明：不同形状的搅拌针会显著地影响焊接接头的性能。相对于使用其他形状的搅拌针，使用三角形搅拌针能获得最好的冶金和力学焊接性能。此外，使用正方形搅拌针制备的搅拌摩擦焊接头具有最低的拉伸强度和显微硬度。更小的搅拌针形状和轴肩直径导致热影响区域变窄和一定程度的软化。断口分析结果表明，不同形状的搅拌针焊接也能影响接头。断裂面显示三角形搅拌针制备的样品在拉伸试验中以韧性断裂形式失效，而在用其他形状的搅拌针(T1和T2)制备的接头中观察到了脆性断裂。关键词：搅拌摩擦焊；小搅拌针形状；力学性能；铝合金；晶粒尺寸
The interlayer mixing of layered rock salt cathode materials LiNi0.7Mn0.1Co0.2O2 that prepared by mixed hydroxide method at various temperatures (750-950°C) has been studied. X-ray Diffraction (XRD) was used to determine a suitable temperature range to obtain the fully reacted sample. Phase of pure sample was obtained at high temperature above 850°C. The results of XRD show that the LiNi0.7Mn0.1Co0.2O2 samples are iso-structural with α-NaFeO2 with space group of R-3m.The sample that heated at 900°C exhibits a well-ordered and lower cation mixed layered structure than others. Rietveld refinement using XRD data was used to determine the amount of interlayer mixing vary as a function of temperature. Refinements data showed that the interlayer mixing varies depend upon the synthesis temperature and the optimum temperature to prepare LiNi0.7Mn0.1Co0.2O2 with the lowest amount of interlayer mixing was 900°C.
A failure analysis of a broken multi strand wire rope from an offshore platform crane was performed. The wire rope was operated for less than 5 years. The wire consists of seven strands, one central strand and six strands around it. The diameter of the small wires was about 0.78 -0.94 mm and the larger wires was a round of 1.52 - 1.78 mm. The large size wires were found fractured by cyclic torsional stresses as characterized by the presence of fatigue cracking originating from the outer surface of the wire. Meanwhile the smaller wires were fractured in a ductile manner under excessive load after the larger wire broken out due to the fatigue mechanism.
AISI type 316L stainless steel was used as a heat exchanger tube material in an inter-cooler column. After less than a year of operation, severe corrosion failures occurred and a transverse opening leakage was observed on one of the heat exchanger tubes. The failed tube was carefully analyzed using various metallurgical laboratory equipments. The root cause of the tube leakage was believed due to the presence of horizontal micro and macro pores as a hydrogen gas entrapment during casting of the parent ingot. The overlapped and gaping pores formed notch on the shell side of the tube surface, and it increasingly evident when the use of a high-energy water-jet and metal brush as cleaning procedure results in an establishment of pitting type localaction corrosion cells penetrated the tube wall. As a result, corrosive fluid in the tube side dissolved into the cooling water, accelerating the corrosion process.
In the present study, four pairs of 6061 aluminium alloy workpieces with different surface roughness were prepared for welding. The friction stir welding (FSW) technique was used for a butt-joint configuration of a single pass. The influence of different surface roughness of the workpieces coincided with a small welding tool shoulder diameter, and the tool pin was examined. The results demonstrated that spherical nano-sized grains of the joints were produced. The mechanical properties of the joints were significantly better at the least possible workpiece surface roughness. The experimental results also indicated that the tensile strength of FSW 6061 aluminium alloy was notably affected by joining at the different workpiece surface roughness selected. However, an improvement of the Vickers microhardness in the heat affected zone (HAZ) was also observed. The microhardness in the nugget zone (NZ) for the welded joint fabricated at the lowest value of the workpiece surface roughness was higher than that of the base metal (BM). The fractural surface of the cross-section of the tensile specimens has a gradient to change from brittle fracture to ductile fracture.
In this study, dissimilar sheets of commercially available pure aluminium and copper, were butt joined by friction stir welding (FSW) with a thickness of 3mm to explore the effect of tool rotational speeds on microstructures and mechanical properties experimentally. Three rotational speeds of 1000, 1750 and 2000 rpm were applied. The transverse speed and the axial force were kept constant at 30 mm/min and 7.5 KN, respectively. The cylindrical shoulder and conical pin tool was used to produce the joints. Macrostructures, microstructures, X-ray diffraction (XRD), Vickers microhardness and tensile strength were investigated at these different rotational speeds. The joint welded at 1750 rpm was compared with their counterparts and observed significantly better. The formation of relatively hard brittle intermetallic compounds (Al2Cu and Al4Cu9) were observed with the joint fabricated at rotational speed of 2000 rpm. The results of microhardness (HV) at the nugget zone (NZ) were superior to those of thermomechanically affected zone (TMAZ), heat affected zones (HAZ) and the base metal (BM). At the rotational speed of 1750 rpm, the tensile strength was higher than other joints. The examination of fractural surface showed that when the dissimilar joints were affected with increasing rotational speeds or heat input; the fracture mode had a tendency to change from ductile to brittle mode.
Abstract: In this study, the dependence of gamma-ray absorption coefficient on the particulate matter sizes of steel slag, iron fillings and steel balls incorporated concrete were examined. The contents of these fillers in concrete mix was kept constant to 35 wt. %. Only the filler particle size was varied during the tests. The particle size ranged from 0.2mm to 1mm for steel slags and the iron fillings and from 2.5mm to 10mm for the steel balls. The concrete samples were assessed for their anti-radiation attenuation coefficient properties. The attenuation measurements were performed using gamma spectrometer of NaI (Tl) detector with Genie 200 software. The utilized radiation source was 137 Cs radioactive element with photon energy of o.662 MeV. The results showed that gamma-ray attenuation coefficient was inversely proportional to the filler particulate matter size. Likewise the mean free paths for the tested samples were obtained. Maximum linear attenuation coefficient of 1.102±0.263cm -1 was attained for the iron filling. The iron balls and the steel slags showed much inferior values. The concrete incorporates iron fillings afforded the best shielding effect. The density, microstructure, homogeneity and particulate distribution of the concrete samples were examined and evaluated using different metallographic, microscopic and measurement facilities.
This paper presents an experimental study on corrosion of carbon steel as reinforcement bar in artificial solution of geopolymer paste by Open Circuit Potential (OCP). The OCP measurements have been used in reinforcement bar concrete studies for many years to determine the corrosion behavior of materials. OCP is the potential of the working electrode relative to the reference electrode when no current or potential is being applied to cell. The OCP of reinforcement bar was recorded with time and this experiment has been done for 30 days. A copper/copper sulfate (Cu/CuSO 4) reference electrode with a potential V-SHE of +0.318 V (at 25ºC) was used in this study. The pH of geopolymer concrete was observed to be in the range of 11.5 to 12.5 depending on the formulations. Thus, in this study the artificial solutions of geopolymer paste that were used are pH 11, pH 12 and pH 13. It has been found that the potential values of three solutions were fluctuated from the beginning until day 30. The highest potential value was indicated by pH 13 whereas the maximum value is 0.542 V and minimum value is 0.205 V while pH 11 shows the lowest potential value with the maximum value 0.356 V and the minimum value-0.047 V. However, all the redox potential values for pH 11, pH 12 and pH 13 were located at passivity region, Fe 2 O 3. The Fe 2 O 3 is the stable phase in which this oxide acts as a protective film or passive layer in this region. It would be expected to provide some protection against corrosion.
In this study, the dependence of gamma-ray absorption coefficient on amount and particle size of tungsten (W) in W-brass sintered compacts was investigated. To attain this goal, two sets of different W wt. % were prepared (W 65wt. %, W75wt. % and W85 wt. %). One set has compacts of as received powder and the other set has compacts of ball milled powder. The results showed that gamma-ray attenuation coefficient is inversely proportional to the particle size of the tested sintered compacts and directly proportional to the W content. Vickers microhardness, attenuation properties and microstructural characterization were carried out on the sintered samples. The attenuation test was conducted using gamma spectrometer with Genie 200 software. The samples of ball milled powder and of the highest volume fraction of W showed the highest hardness and attenuation values.
An innovative and novel technology method of processing called Turbo-Mixing Reactive Precipitation (TMRP) design proposed as an alternative to this current processing or conventional productions of fine precipitated calcium carbonate (Nano-PCC) in turbo-mixing conditions. In this paper, the effect of the stirring rate onto morphology, particle sizes and reaction time of the precipitated CaCO 3 particles was discussed. CaCO 3 nano-particles with an average particle size of approximately 15.75 nm were successfully obtained by stirring rotation speed at 900 rpm. The structural analysis was conducted using a Scanning Electron Microscope (SEM) and a Field Emission Scanning Electron Microscope (FESEM). The results showed that the increasing of the multiple's impeller stirring rotation speed is in favor of the formation of the spherical vaterite.
In this study, nanocrystalline Al–Ni intermetallic compounds were synthesized by mechanical alloying (MA) of elemental powders. In all MA runs, the ball-to-powder weight ratio was 10:1, the rotation speed was 350 rpm, and the milling time ranged from 4 h to 12 h. The phase evolution and microstructural changes of the powders during MA were investigated by x-ray diffraction (XRD), scanning electron microscopy, and energy-dispersive x-ray spectroscopy. The crystallite sizes of the milled powders were estimated based on the broadening of the XRD peaks using the Williamson–Hall formula. Results showed that an optimum MA time of 12 h resulted in the formation of an Al–Ni intermetallic phase with a crystallite size of <40 nm.
Abstract: In this study, the effect of barite mineral (BaSO4) loading rates and its dispersive manner within two types of heavy constructive concrete matrix on anti radiation attenuation coefficients was investigated. To attain this goal geopolymer concrete based on fly ash and Ordinary Portland cement concrete of different barite additions were fabricated and examined. Similar proportions of natural mineral rocks (Hematite) rich in iron acquired from the north part of Iraq (Al-Sulaimanya site) as aggregates was added to the two concrete mixtures to enhance their density. Then fabricated cured and dried samples were assessed for their anti radiation attenuation properties. The attenuation measurements were performed using gamma spectrometer of NaI (Tl) detector. The utilized radiation sources comprised 137Cs and 60 Co radioactive elements with photon energies of 0.662 MeV for 137Cs and average energy level about 1.25 MeV for the 60Co. Likewise, the linear attenuation coefficient μ (cm-1), mean free path mfp (cm), half value layer HVL(cm), Compressive Strength (Mpa), Density (kg/m 3), Water Absorption (%) for the tested samples were obtained. The maximum linear attenuation coefficients (µ) were attained for ordinary concrete incorporates barite of 75 wt. %. They were of 0.459 ± 4.7 × 10Cs and 0.371 ± 3.3× 10 −2 for 60 Co. For geopolymer they were of 0.396 ± 4.9 × 10 −2 for 137Cs and0.316 ± 4.7 × 10−2 for60Co. Substantial improvement inattenuation performance by 15%–20% was achieved for concrete samples incorporate barite at different (15%–75%) loading rates. The microstructure, concrete density, homogeneity and particulate dispersion were examined using different metallographic, microscopicand measurement facilities. It was found that as the loading barite level is increased within the concrete mix the linear attenuationcoefficient is improved for both the geopolymer and ordinary samples.
In this research, comparative study of corrosion resistance of aluminum based alloys and Al-alloys with nickel have been investigated. Several processes are conducted for the Al-Zn-Mg-Cu alloys and Al-Zn-Mg-Cu-0.5%Ni alloys were homogenized, aged then retrogressed and reaged; also, alloys were homogenized then the extruded thereafter heat treated. Al-Zn-Mg-Cu alloy and AlZn-Mg-Cu-Ni alloy samples after different treatments were subjected to corrosive media (acidic: 1.0M HCl) using weight loss method to evaluate their corrosion resistance. The consequences present that the precipitation for the base alloy samples treated led to enhance their resistance of corrosion. Furthermore, the gain of corrosion resistance for the Al-Zn-Mg-Cu-Ni alloy samples after the RRA treatment and thermomechanical with the RRA about of 52 and 75 %, respectively, more than what the Al-Zn-Mg-Cu alloy samples under same conditions. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to show the corroded surfaces.
Zinc phosphating is a chemical conversion process that has been widely used in industry for corrosion protection and primer for painting. In this investigation, the effect of activation treatment with nickel acetate on the microstructural evolution and corrosion resistance of the zinc phosphate coating on mild steel was studied. The chemical composition and morphology of the coatings were analyzed via scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The corrosion resistance of the coatings was evaluated using polarization curves and electrochemical impedance spectroscopy (EIS) in an aerated 3.5% NaCl solution. Surface morphology observations revealed that the activation treatment increased the population density and refined the grain size of the coating. The electrochemical results showed better barrier protection characteristics and corrosion resistance for activated phosphate coatings compared with inactivated coatings.
Mechanical alloying was employed to synthesize Al-Zn-Mg-Cu alloys with nickel additives from elemental powders via high-energy ball milling. The milled powders were cold compacted and sintered thereafter. The sintered compacts underwent homogenization treatments at various temperatures conditions and aged at 120 °C for 24 h (T6). Subsequently, the compacts were retrogressed at 180 °C for 30 min and reaged at 120 °C for 24 h (RRA). The milled powders and heat-treated products were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The crystallite sizes and microstrains of the alloy powder were estimated with the broadening of XRD peaks by using the Williamson-Hall equation. The results show that Zn, Mg, Cu atoms are soluble in the Al matrix after milling for 5 h. The Vickers hardness of Al-alloys was enhanced following retrogression and re-aging treatments. The addition of nickel influenced the hardness of compacted powders.
A failure analysis of a broken multi strand wire rope from an offshore platform crane was performed. The wire rope was operated for less than 5 years. The wire consists of seven strands, one central strand and six strands around it. The diameter of the small wires was about 0.78-0.94 mm and the larger wires was a round of 1.52-1.78 mm. The large size wires were found fractured by cyclic torsional stresses as characterized by the presence of fatigue cracking originating from the outer surface of the wire. Meanwhile the smaller wires were fractured in a ductile manner under excessive load after the larger wire broken out due to the fatigue mechanism. Introduction Wire rope consists of one or more numbers of strands, laid spirally around one core of steel core. It consists of three basic components; the wires, strands and core. Wire ropes are identified by classifications based upon the number of strands and nominal number of wires in each strand. It allows the production of different design of wire rope for specific purposes or with specific characteristics .The wire, for rope, is made from several materials such as steel, iron, and/or stainless steel. High carbon steel is the most widely used material, available in a variety of grades, each of which has the properties related to the basic curve for steel wire rope. Common defects of the wire rope are corrosion, excessive heat or chemical damage. However, most of the failure case history; the rope is going to fail in the zone, which has been subjected to the greatest amount of fatigue and abrasion [2, 3, 4]. The wire rope has been operated on platform crane and failed on November 2013. It used to lift and lower materials and to move them horizontally. It is mainly used for lifting heavy things and transporting them to other places beyond the normal capability of a human.The rope has a capacity to break at 60,000 lbs (261kN). The boom weight is less than 3 tonnes (30 kN). The wire rope examined in this analysis failed after it had performed one-fourth of its expected total service life. Detailed metallurgical tests were carried out on the failed wire rope, and the findings were summarized in this case study. Methodology On-site visit was commenced to inspect the failure condition of the crane wire rope. Some personnel were interviewed and all important information such as the design and operational parameters were recorded. The photograph the failed rope was captured by a digital camera. The diameter of each wire was measured by vernier calliper. The dirt and lubricant residues were removed by washing alcoholand additional cleaning in an ultrasonic bath was performed prior to microscopic analysis. Fractography study was carried out by scanning electron microscope (FEI Quanta 400).The outer wire (1.52 mm diameter) of the strand and outer wire (0.88 mm diameter) from core were selected for the investigation purpose were represented " strand wire " and " core wire " respectively. Samples for optical microscopy were prepared by grinding, polishing and etching by 2% of nital solution. A macroscopic survey of the wire rope was carried out by optical microscopes.
The utilization of waste rubber powder in polymer matrices provides an attractive strategy for polymer waste disposal. In this study lead free composite material samples for anti– radiation purposes were produced. To attain this goal, 15 wt. % of recycled acrylonitrile-butadiene rubber (NBRr) were added to Naturalrubber (NR) to prepare the composite's matrix part. Then the matrix was incorporated with various hard materials wastes such as iron particulates, iron fillings and slags brought from different industry zones. The amounts of the added particulates were ranged from 15–75 wt%. All fabricated samples were assessed for their anti-radiation attenuation properties. The attenuation measurements were performed using gamma spectrometer of NaI (Tl) detector. The utilized radiation sources comprised 137 Cs and 60 Co radioactive elements with photon energies of 0.662 MeV for 137 Cs and two energy levels of 1.17 and 1.33MeV for 60 Co. Likewise theHalf-Value Layer (HVL) and the mean free paths (Mfp) for the tested samples were obtained. The aim of this work is to investigate the effects of the waste loading rates, the particulate types and their dispersive manner within the rubber blends on the attenuation coefficients. The maximum linear attenuation coefficient (μ)was attained for rubber incorporates iron particulates wastes of 65 wt. %. They were of 0.0510± 3.2123 ×10 -3 for 137 Cs and 0.0346± 6.973×10 -3 and 0.0182±1.297×10 -3 for 60 Cofor the energies of 0.662, 1.17and 1.33 MeV respectively. A Significant improvement of attenuation performance was achieved by 25%–30% for rubber samples incorporate iron particulate. The tested samples were examined using different techniques, metallographic facilities, optical microscopy, scanning electron microscopy (SEM), Fourier Transform Infrared (FTIR) Spectroscopy, and hardness and measurement facilities. The microstructure, homogeneity, particulate dispersion, porosity and structure defects, and the mechanical properties of the fabricated samples were studied and evaluated.
This paper presents an experimental study of the relationship between water absorption and porosity for geopolymer paste. In order to reduce the carbon dioxide (CO2) emissions to the environment, alternatively fly ash was used as binders in making concrete paste. Fly ash is a waste materials produced by combustion of coal at power plant. Geopolymer paste prepared from class F fly ash was obtained from coal power plant and mixed with an alkaline activator. The combination of sodium silicate (Na2SiO3) solution and sodium hydroxide (NaOH) solution were used as alkaline activator. The alkaline activator was prepared 24 hrs prior to use with the ratio of the mixture of Na2SiO3/NaOH is 2.5. Mixed fly ash and alkaline activator placed in moulds and compacted. The samples were kept at ambient temperature in the moulds until it hardened. All the samples were removed from the moulds after 24 hrs. Then, the samples were cured at 60˚C in the oven for 24 hrs. All twelve samples were prepared for water absorption and porosity measurement. The samples were examined after 7, 14, 28 and 90 days in terms of water absorption test and porosity test. It was observed that after day 90 the sample had the lowest water absorption of 3.81% and porosity 3.77%. The sample had the highest water absorption and porosity of 4.65% and 11.95% respectively at day 7. The pore size decreases and the structures became denser. The morphological structure of geopolymer paste pores can be observed by Scanning Electron Microscope (SEM). The porosity and permeability also decreased hence the durability potentially improved.
Abstract Lead metal proved to be toxic. Its lethal effect became eminent. Many developed countries have banned lead usage in various applications. Seeking alternative material to replace lead is a crucial goal. As density concerns, tungsten-brass composite is a good candidate for lead replacement. In this study the radiation shielding effects of tungsten-brass composites were evaluated. To attain this goal, four tungsten-brass sets were prepared. The tungsten (W) wt. % in these specimens was ranged from 50 to 80, the balance is brass. The specimens were sintered at 1050⁰C in alumina tube furnace under protective environment. To evaluate the radiation shielding performance of these specimens, two gamma ray sources, 137 Cs and 60 Co were utilized. The photon energy levels for these sources were of o.662MeV and 1.25MeV respectively. The measurements were performed using gamma spectrometer contains NaI (Tl) detector. The anti-radiation performance of the tungsten-brass was correlated to that of lead under similar conditions. Vickers micro hardness, relative sintered density, micro structural characterisation and linear attenuation coefficient (µ) were carried out. Samples with the highest Weight percentage of W has the highest hardness value while the one with the lowest Weight percentage of W. The linear attenuation coefficients of the specimens were significantly improved by increasing the W wt. % of the specimen. The linear attenuation coefficients of the tested specimens ranged from 0.85±0.010cm 60 Co and0.73±0.012 cm -1 to 0.97±0.027 cm -1 for 137 -1 1,2,g to 1.12±0.049cm Cs. This result indicates that W-brass composites are suitable material for lead replacement as a shielding barrier.
In this work, one stage and two stages compaction technique were used to fabricate the tungsten-copper composite powder. Liquid infiltration technique was used to consolidate the W-Cu green compact and a low concentration iron powder was added as activation material to enhance the sintering behavior. In addition, two-steps compaction process was developed for improving mechanical properties of W-Cu composite as well as segregation of Fe around W grain. The green compact was directly infiltrated at 1250 °C for about 2 hours under vacuum conditions. The microstructure, inter-boundary layer and the contamination levels of the infiltrated compacts were characterized using the scanning electron microscope (SEM) and the energy dispersive X-ray analysis (EDX). Relative sintering density varied in the range of 97.1 to 99.3 % of theoretical density, and it was highly depended on Fe concentration and method of compaction. In contrast to one stage compaction, the experimental results showed that the composites fabricated by the two stages of compact ion had better homogeneous structure, high densification and a clear segregation of inter-boundary layer of Fe-W around W grains.
In order to understand the importance of the retrogression and re-aging as a heat treatment for improving microstructural and mechanical properties of the Al-Zn-Mg-Cu powder metallurgy alloys, Al-Zn-Mg-Cu-Fe-Cr alloys were fabricated from the elemental powders. Green compacts are compressed under compaction pressure about 370 MPa. The sintering process carried out for the samples of aluminum alloys at temperature was 650°C under argon atmosphere for two hours. The sintered compacts were subjected into homogenizing condition at 470°C for 1.5 hours and then aged at 120°C for 24 hours (T6 temper) after that it carried out the retrogressed at 180°C for 30 min., and then re-aged at 120°C for 24 hours (RRA). Observations microstructures were examined using optical, scanning electron microscopy coupled with energy dispersive spectroscopy and X-ray diffraction. Density and porosity content was conducted for the samples of alloys. The result showing that the highest Vickers hardness exhibited for an Al-Zn-Mg-Cu alloy after underwent the retrogression and reaging treatment. Increasing in hardness was because of the precipitation hardening through precipitate the (Mg Zn) and (Mg2 Zn 11) phases during matrix of aluminum-alloy.
In this study, influence cobalt additives on the microstructural and hardness properties of an Al-Zn-Mg-Cu-Fe-Cr-Ni PM alloy undergone the retrogression and re-aging treatment were carried out. Green compacts pressed at 370 MPa were then sintered at temperature 650°C in argon atmosphere for two hours. The sintered compacts subjected to a homogenizing treated at 470°C for 1.5 hours then aged at 120°C for 24 hours and retrogressed at 180°C for 30 minutes, and then re-aged at 120°C for 24 hours. Microstructural results of the Al-Zn-Mg-Cu-Fe-Cr-Ni-Co alloys introduced an intermetallics compound in the matrix of alloy, identified as the Al 5Co2, Al 70Co20 Ni 10 and Al 4 Ni 3 phases besides to the MgZn2 and Mg2Zn11 phases which produced of the precipitation hardening during heat treatment. These compounds with precipitates provided strengthening of dispersion that led to improved Vickers’s hardness and dinsifications properties of the alloy. The highest Vickers hardness of aluminum alloy containing cobalt was gotten after applying the retrogression and re-aging treatment.
In this work, a comparative study between microstructure and mechanical properties of aluminum-zinc- magnesium-copper alloys with different additives of nickel; tin; cobalt was investigated. Al-Zn-Mg-Cu alloys which containing Nickel; Nickel plus tin and Nickel plus Cobalt were homogenized at different temperature conditions, aged at 120°C for 24 h
Concrete is a complex material of construction that enables the high compressive strength of natural stone to be used in any configuration. Nevertheless, concrete which consist of bonding between cured cement and the surfaces of the aggregates has poor tensile properties. Because of that, the reinforcement bar is used to improve the tensile strength of concrete structures. In this study, carbon steel or mild steel was used as the reinforcement bar. The reinforcement bar embedded in concrete tends to have corrosion problem when it exposed to corrosive agents such as salt, acid, chloride, carbonation and even air. Meanwhile, corrosion is the crucial factors for million dollars loss in construction industry. The solution for this problem, the fly ash based geopolymer paste was evaluated as a protective coating material that suitable used to prevent the reinforcement bar in concrete from corrosion. In this paper the study on corrosion behavior of reinforcement bar has been conducted in several geopolymer environments such as geopolymer paste without curing process, geopolymer paste which undergoes curing process, soaked in tap water by using the open circuit potential (OCP) method. The results have shown that the samples which undergo curing process had more positive potential values than samples without curing process because the curing process had made the paste becomes harden in a short time. From Pourbaix diagram, all the samples of geopolymer paste were in passivity region which mean the passive layer was formed to protect the reinforcement bar from corrosion. This paper will focus on corrosion behavior of reinforcement bar embedded in geopolymer paste. Keywords: Corrosion, reinforcement bar, fly ash, geopolymer
The effects of nickel and nickel combined tin additions on mechanical properties and microstructural evolutions of aluminum-zinc-magnesium-copper alloys produced by semi-direct chill casting were investigated. Aluminum alloys contained Ni and Sn additives were homogenized at different temperatures conditions then aged at 120 °C for 24 h (T6) and retrogressed at 180 °C for 30 min and then re-aged at 120 °C for 24 h (RRA). Comparison of the ultimate tensile strength (UTS) of as quenched Al-Zn-Mg-Cu-Ni and Al-Zn-Mg-Cu-Ni-Sn alloys with that of similar alloys underwent aging treatment at T6 temper showed that gains in tensile strengths by 385 MPa and 370 MPa were attained respectively. These improvements are attributed to the precipitation hardening effects of the alloying element within the base alloy and the formation of nickel/tin-rich dispersoid compounds such as Al7Cu4Ni, Al4Ni3, Al50Mg48Ni7 Al75Ni10Fe15, Al3Ni2, Al4Ni15Sn and Al3Cu12Sn. The intermetallic compounds of nickel and tin retard the grain growth, led to grain refinement and result in further strengthening effects. The outcomes of the retrogression and re-aging process which were carried on aluminum alloys indicate to that the mechanical strength and Vickers hardness have enhanced much better than under the aging at T6 temper. The formation of these Ni rich and/or Ni-Sn rich dispersoids, their morphology and distribution within the matrix were examined and analyzed. Mechanical properties characterization, scanning electron microscopy (SEM), X‐ray diffraction analysis (XRD) and energy dispersive X ray analysis (EDX) were utilized for this purpose.
Ni deposited on HA powder was prepared by electroless plating process without sensitization and activation treatment. The deposited powder obtained was characterized by energy dispersive spectroscopy (EDX) and x-ray diffraction (XRD). The microstructure and hardness of the sintered powder were examined by scanning electron microscopy (SEM) and Vickers hardness respectively. From the result, the nickel existence in the deposition was confirmed by the EDX analysis. The diffraction peaks at 44.5 and 64.7 o (2θ) of planes (111) and (211) respectively were belong to nickel. Nickel are homogeneously dispersed in HA matrix with grain size between 0.25-2µm after sintered at 1250 o C. The improvement of 93% and 180% in average hardness and flexural strength respectively were achieved with nickel presence in HA compared to pure HA.
HA-Ni composites were fabricated by uniaxial pressing from coated powders, in which HA particles were successfully coated with nickel precursor by the electroless deposition method. The compacted powders sintered at temperature 1200°C for 1h. Decomposition of hydroxyapatite into α-TCP (α tricalcium phosphate) and TTCP (tetracalcium phosphate) were not occured in any different nickel content before and after sintering. The Ni peaks sharply increased with increasing of Ni content indicate that high crystallinity of metal and confirmed the existence of nickel in the composites. Compared with that of pure HA, the fracture strength of HA inproved by almost 200% by adding 1wt% Ni due to the increase of the composites density. The enhancement in mechanical properties of HA-Ni composites was found to decrease with increase of Ni content, which attributed to the size effect of nickel grains and higher porosity percentage of composites.
Co-HA composite produced using electroless deposition without conventional sensitization and activation treatment was studied with varying sintering temperature (1100 o C, 1200 o C and 1250 o C). The particles size, bulk density, porosity, hardness measurements and the flexural strength are performed in order to find the optimum sintering temperature. After the electroless process for 1 H, the particle size of HA increase to 3.9% and finally the value bulk density percentage of 93.08%, percentage porosity of 6.89%, hardness value of 291.8HV and flexural strength value of 42.4MPa have been achieved after pressing and sintering Co-HA composite at 1250 o C. Observations were supporting the idea that Co-HA produced by modified electroless method was improving the mechanical properties with increasing the sintering temperature.
C0-HA composite produced by simple electroless deposition method was studied. From the particle size analysis by Malvern particles analyzer its shows that 19% increment in average of the particle size powder increase after the electroless process with higher cobalt (II) chloride and reduction agent concentration. By EDX and XR-D analysis it was confirmed that cobalt metal was deposited onto HA and contribute to uniform distribution in morphologies by SEM analysis. The Vickers hardness result of up to 430HV was achieved after sintering process at 1250 o C. The experimental results demonstrated that the Co-HA powder was successfully prepared by using this method and provide distinct advantages such as uniformity of deposition at lower cost and simple process.
The basic concept of Gibbs standard state free energy predicts a favorable condition for both room and high temperature fabrication of nanoporous alumina in phosphoric acid electrolyte. The anodization of aluminum foil in acidic electrolytes is made possible by the well known process parameters that have been studied over the years. These parameters i.e. voltage, current density, type of electrolyte etc have been very effective when anodizing aluminum at freezing temperatures. When the operating temperature is raised above the freezing temperature, additional process parameters would be required to make the pore formation possible. The fabrication of the aluminum foil was carried out using phosphoric acid as the electrolyte source. The electrolyte pH was adjusted to 1, 3 and 5 in order to simulate different anodizing conditions. A potential of 50 V from a dc power supply was applied across the electrochemical cell, while a power regulating device with different power rating was attached to the electrochemical cell to provide the operating system with additional parameters that could influence the surface structure of the alumina. The micrographs obtained show that the propagation and growth of the pores at both room and high temperatures was made possible by the power regulating device attached to the cell.
The aim of the study is to identify the effect of Ca in Mg-Mn alloy on electrochemical corrosion behavior for the development of high performance sacrificial anode. Mg alloys were fabricated by casting technique under an inert atmosphere. 0.35 ~ 1.11 wt.% of Ca were added as alloying element. The finding shows that the addition of small Ca in Mg-Mn anodes was found not significantly affecting the corrosion rate. However, small content of Ca was as much as necessary improving electronegativity of open circuit potential and modifying anodic polarization in promoting the instabilities of surface passive layer hence results in the further dissolution process between ion and alloy species underneath. No passivation occurs on the standard samples. Pitting profile only occur on Mg-Mn anode that has lower Ca content (0.35 wt. %). An XRD result shows no present of Mg 2 Ca phase on the as-cast anode containing 1.11 wt. % Ca. As a conclusion, the influence of small content of Ca was profoundly modifying electrochemically behaviour of Mg containing Mn anodes except corrosion rate.
This paper presents a study on the relationship between porosity and compressive strength for geopolymer paste. In this research, geopolymer paste was made from fly ash class F based geopolymer mixed with alkaline activator; sodium hydroxide solution and sodium silicate solution. Twelve mixes were cast in 50mm x 50mm x 50mm moulds and the samples were cured for 24 hrs at 60˚C in the oven. The samples were examined after 7, 14, 28 and 90 days in terms of porosity test, pulse velocity test and compressive strength test. It was concluded that the sample at day 90 had the highest compressive strength of 56.50 N/mm 2 had porosity 3.77%. Thus, the sample with lowest porosity had highest pulse velocity 3303 m/s during ultrasonic testing with lowest transmission time 15.17 µs.
This paper presents the results of a study on anti-corrosion coating using geopolymerization method. Geopolymerization is synthesis of a fly ash and alkaline activators which are sodium silicate (Na2SiO3) solutionand sodium hydroxide (NaOH) solution.Fly ash is one of the residues produced during the combustion of coal in coal power plant. In this study, fly ash class F based geopolymer was used as a source material. The alkaline activators then were mixed with the fly ash to produce the geopolymer paste which act as a coating material. The mixtures were placed in a 50 mm x 50 mm x 50 mm moulds. Then, the carbon steels were embedded in geopolymer paste as reinforcement bars. The samples were cured at 60˚C for 24hrs in the oven whereby the processplays important role on durability and strength development of concrete. Afterwards, the corrosion behaviours of reinforcement bar for all samples were observed by using Open Circuit Potential (OCP) testing. Besides,Scanning Electron Microscopy (SEM) testing was evaluatedaccording to the corresponding ASTM C1723 standardin order to observe the surface before and after applied the coating material to ordinary concrete. Referring the Pourbaix diagram regarding the OCP testing, all the potential values were located in passivity region. The oxide formed the passive layer that protects the reinforcement bar from corrosion. From the SEM images, itcan be seen that geopolymer coating produce smoother surface compared to the uncoated surface. Keywords:corrosion, geopolymer, geopolymerization
Anodic aluminium oxide fabricated at ambient temperature and low potential in phosphoric acid electrolyte was used as the working electrode for the electrochemical measurement of phosphate buffer saline under different pH conditions using the cyclic voltammetry tool. We investigate the reversibility of the electrochemical reaction as a redox reaction from the cyclic graphs that were obtained. We observed that the ratio of the peak current passed at both the reduction and oxidation when measured was very close to unity in all the pH but except one which produced a none reversible reaction with a non cyclic graph. The peak potential for both reduction and oxidation reactions using phosphate buffer saline as the analyte under different pH of 3, 5, 7, and 9 was also obtained.
Nowadays, many researchers have been studying on the layered rock salt-type structure as cathode materials for the lithium ion batteries. LiCoO2 is the most commonly used cathode material but Co is costly and toxic. Thus, alternative cathode materials which are cheaper, safer and having higher capacity are required. Replacing Co with Ni offered higher energy density battery but it raised interlayer mixing or cation disorder that impedes electrochemical properties of batteries. This paper has reviewed some recent research works that have been done to produce better and safer cathode materials from the structural perspective.
In this study the evolution of the retrogression and reaging (RRA) heat treatment process on microstructure and mechanical properties of AA 7075 Al-alloys which produced by semi-direct chill (DC) casting process were investigated. Al-Zn-Mg-Cu alloys were homogenized at different heat treatment conditions, aged at 120°C for 24 h (T6), and retrogressed at 180°C for 30 min then re-aged at 120°C for 24 h (RRA). The results showed that this three-step process of the heat treatments, the mechanical properties of alloys was substantially improved. The highest ultimate tensile strength and Vickers hardness attained for the retrogression and re-aging about 530 MPa and 223 HV respectively. The precipitation strengthening is responsible about improve the strength under impact the retrogression and re-aging process.
The effect of retrogression and reaging heat treatment on microstructure evolution andmechanical properties of 7075 Al alloy in direct chilling casting process was investigated. The subsequent heat treatment process comprised pre-aging at 120°C for 24 h, retrogression at 180°C for 30 min, and then reaging at 120°C for 24 h. By this three-step process, the mechanical properties of the chilled casted samples were substantially improved. The samples retain their high strength at T6 level. They gave yield strength up to 290 MPa, ultimate tensile strength of 386 MPa and elongation of 5.9%. The average value of multiple Vickers hardness tests results were in the range of 210 Hv. The direct chilling process followed by retrogression and reaging heat treatment yielded casts of fine and uniform microstructure as opposed to the microstructure of samples casted by the conventional process.
Shielding concretes of different iron filling contents were assessed for their anti radiation attenuation properties. The measurements have been performed by using gamma spectrometer of NaI (Tl) detector, the sources were Cs 137 and Co 60 radioactive elements with photon energies of o.662 MeV, for Cs 137 and the two 1.17MeV, 1.33 MeV energy levels for the Co 60 . Likewise, the mean free path of the tested samples was obtained as well. From the measurement of the linear attenuation coefficients for these different shielding materials, it was found that as the iron filings within the concrete are increased the linear attenuation coefficient is increased also. It can be concluded from this work that the Iron filings content in concrete is very effective in augmentation of the anti-radiation shielding capability. It can be used as shelters' material for secure storing of the nuclear wastes.
Green compacts of W–bronze were encapsulated in shells of bronze powder, placed in a ceramic mold and sintered in alumina tube furnace at 1150 °C. Throughout the sintering cooling stage the differential coefficient of thermal expansion ΔCTE of W–bronze was employed to induce an external compressive densification action. The process included simultaneous sintering, hot isostatic pressing (HIP) and infiltration act to enhance densification. By this technique, pilot sintered compacts of different W50–80 wt.%–pre-mix bronze of 97–99% theoretical density were produced. This process resulted in compacts of higher hardness, higher sintered density and better structure homogeneity as opposed to similar compacts densified by the conventional sintering process. The results showed a gain in hardness by 10–20% and in density by 5–15%. The impact of different cooling rates of 3, 4, 8 and 30 °C min−1 on sintered density, microstructure and densification mechanisms was examined and evaluated. Low cooling rates of 3 and 4 °C min−1 gave the best results.
Since decades ago, corrosion is the crucial factors for million dollars loss in construction industry. Corrosion of reinforcement bar in ordinary Portland cement (OPC) concrete is mainly due to chloride and acid attack and also due to carbonation process. The degradation of geopolymer (GP) concrete is still widely studied and the mechanisms of degradation are still not conclusive. However, reinforcement bar in GP concrete is reported having lower corrosion rate than in OPC concrete. The fly ash geopolymer has high alkalinity which provides the passivity of the reinforcement bar. The superior properties of GP have encouraged researchers to do further investigation on its performance. This review paper will focus on corrosion performance of reinforcement bar in GP compared to OPC.
The miscibility of W in Sn and Cu is extremely poor. Sintering of W–bronze composites to their full density is proved to be difficult. To tackle this problem, the ball milling process of the W–bronze powder mixture proposed in this study was split into two steps. In the first step, the softness of Sn powder was exploited to modify the surface morphology of W particles. In the second step, Cu was added to the ball milled mixture. To achieve this goal, four 50 wt% W–bronze compact sets of different powder precursors and activator additions were produced. The sintering process was performed at 1150 °C. The two-step ball milled powder yielded sintered compacts of homogeneous microstructure of fine polygonal W grains dispersed in bronze matrix. They showed the highest hardness and densification levels. The sintered density, microstructure, hardness and densification mechanisms of the sintered compacts were investigated, examined and evaluated using different metallographic, microscopic and measurement facilities.
In this study, anodic aluminum oxide (AAO) fabricated from phosphoric acid electrolyte at ambient temperature was used as the porous template, while a sol gel procedure was used for the preparation of the TiO2 sol with the addition of 0.1, 0.3, and 0.5 g of polyethylene glycol (PEG). The addition of PEG to the TiO2 sol prevents surface cracks and improves the adhesion of the sol to the template to produce different surface morphologies which were visible under the scanning electron microscope (SEM). Although, complete degradation of the methyl orange (MO) dye was not achieved initially with the TiO2 coated template, until an oxidizer in the form of H2O2 with different concentrations of 0.029M, 0.088M, and 0.147M were added during the photocatalysis process to shorten the degradation time and to ensure complete mineralization of the MO dye.
The influence of phosphating temperature on the surface morphology and corrosion resistance of zinc phosphate coatings on mild steel was investigated. The phosphate layers were deposited on steel from phosphating bath at different temperatures (45 ~ 75 ◦C). The surface morphology and composition of phosphate coatings were investigated via scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX). The corrosion resistance of the coatings was evaluated by polarization curves (anodic and cathodic) in an aerated 3.5% NaCl solution. The results showed that the increase in temperature of the phosphating bath up to 55 ◦C caused an increase in surface coverage and in turn resulted in better corrosion resistance. At high temperature (65 °C and 75 °C) the deposition coverage decreased indicating that the best coverage for the phosphate layer on the metal surface was achieved at 55 °C
Zinc phosphate coating is commonly used for corrosion protection of metallic materials, mainly mild steel. In this study, influence of the pH of phosphating bath on the surface morphology and corrosion resistance of zinc phosphate coatings on mild steel was investigated. The phosphate layers were deposited on steel from phosphating bath at different pH values (1.75 ~ 2.75). The surface morphology and composition of phosphate coatings were investigated via scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX). The corrosion resistance of the coating was evaluated by polarization curves (anodic and cathodic) in an aerated 3.5% NaCl solution. The results showed that better surface coverage and corrosion resistance for the steel phosphated at pH 2.75.
Corrosion is an undesirable effect which could lead to the loss of billions of dollars in construction industry all over the world. Generally, Ordinary Portland Cement (OPC) is used as construction materials. Fly ash based geopolymer may replace the OPC because it is more environmental friendly. In this paper the study on corrosion behavior of reinforcement bar has been conducted in several geopolymer environments such as geopolymer paste without curing process, geopolymer paste which undergoes curing process, soaked in tap water by using the open circuit potential (OCP) method. The OCP of reinforcement bar was recorded with time. The reinforcement steel bar in cured geopolymer has showed more positive potential values compared with samples without curing process. However, for sample soaked in tap water, the potential value fluctuated. From the Pourbaix diagram, all the potential values were located in passivity region. The oxide formed the passive layer to protect the reinforcement bar from corrosion.
Full-density of consolidated W–Cu composites produced via conventional sintering method is difficult to achieve. In this work, fully-dense W–Cu composites were developed via the combination of the liquid phase sintering (LPS) and the liquid infiltration (LI) methods, which hereinafter is named as Cu-MI technique. It operates at the low sintering temperature of 1150 °C, and maximum densification was possible without requiring a sintering activator such as Ni, Co or Fe. A comparison was also made between the sintering response of W–(13–27 wt.%) Cu composites consolidated using LPS and Cu-MI techniques. The samples were characterized using SEM, EDX and XRD. It was observed that the samples prepared via the Cu-MI method demonstrated a high relative density (> 99% theoretical density). Contrary to the composite sample prepared by the LPS method, the Cu-MI technique accounted for a homogeneous microstructure almost without any pores. The significance of this finding has major industrial implications and has potential to reduce the production costs of composite materials with improved mechanical and electrical properties.
In this study, the effect of Co and sintering temperature on microstructure of W-25Cu composites prepared via copper melt infiltration has been investigated. The concentration of Co addition used ranged from 0.5 to 3wt. %. The infiltration temperatures were performed at 1150°C and 1250°C for 2 hr under vacuum. The microstructure and sintering density of W-25Cu composites are discussed. Results indicated that, the relative density (RD) and microstructure of W-25wt. % Cu were greatly affected by the addition of low Co concentration and sintering temperature. The concentration of 3 wt. % Co to tungsten-copper compact and infiltration temperature of 1250°C give high sintering density of 98.6% theoretical density (TD). The concentration of Co and infiltrating temperature have strong effects on the densification of W-Cu composite materials. The sintered compact microstructures and density were obtained using scanning electron microscope (SEM) coupled with EDX and Archimedes technique respectively.
During sintering of Wbronze metal matrix composites, the difference in the interdiffusuion path, sintering atmosphere and alloying element might be the source of the swelling phenomenon. In this study, the factors lead to swelling of Wbronze sintered compacts were investigated. To achieve this goal, two swelled groupes of Wbronze sintered compacts were examined. The first group was compacts of ball milled powder with activator additions and the second group was compacts of ball milled powder infiltrated by bronze melt. The latter type showed the severest level of swelling. Sintered density measurements, X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were incorporated to clarify and predict the reasons standing behind the swelling of the Wbronze sintered compacts. Key words: swelling, diffusion path, grain size, sintering activator
In this study, the effects of 1–3 wt.% Fe and Co additions on the sintering of W 40–80wt.%–pre-alloy bronze Sn 10 wt.%–Cu compacts were examined. The isothermal part of the sintering process was conducted at temperatures ranging from 920 °C to 1300 °C for 3 h. Relative sintered densities in the range of 70–90% were achieved. The gain in the sintered densities due to activator addition was 5–15%. The sintering activation effects started at temperatures as low as 600 °C below the bulk eutectic temperature. SEM, XRD and EDX tests proved that Fe and Co-rich crystalline interboundary layers completely wet the tungsten grain boundaries in the solid state and act as a short-circuit diffusion path for mass transportation. These outcomes seem to follow the classical activated sintering model and contrast with some other recently proposed models, whereby a detected nanometer-thick, activator-enriched disordered film at W grain boundary is considered fully responsible for the solid-state activated sintering.
Nanoporous alumina was produced by anodic oxidation of aluminum in both acidic and alkaline electrolytes. Previous reports indicate that nanoporous alumina is mainly produced from strongly acidic electrolytes, and with the use of a low freezing temperature controlled bath to control the propagation and growth of the pores. We design an in-house electrochemical cell with an electronic circuit box attached, to control the anodization of aluminum at room temperature. The electrolytes used were phosphoric acid solution and sodium hydroxide solution. The pH of the acidic electrolyte was adjusted to 1, 3 and 5 with an applied potential of 50V and anodization time of 1 and 3 hrs, respectively, while the alkaline electrolyte pH was adjusted to 9, 11 and 13 with an applied potential of 40V and the templates anodized for 5 hrs. The micrographs of the nanoporous alumina formed from these electrolytes confirm that the nucleation and growth of nanoporous alumina films is achievable with the aid of the electronic circuit box connected to the electrochemical cell.
Zinc phosphate coating is widely used for corrosion protection of metallic materials, mainly mild steel. In the present study, the effect of pretreatment with copper acetate solution on zinc phosphate layer properties was investigated via scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The corrosion resistance of the coating was evaluated using polarization curves and electrochemical impedance spectroscopy (EIS) in a 3.5% NaCl solution. The pretreatment resulted in a compact and uniform phosphate coating with smaller crystal size and greater surface coverage. Electrochemical results showed better corrosion resistance for the pretreated phosphate layer compared with the unpretreated one.
The miscibility of W in Sn and Cu is extremely poor. The wettability of W by those two elements is limited. To tackle this problem, two step ball milling process of the W-bronze elemental powders was proposed in this study. The softness of Sn in the first step was exploited to modify the surface morphology of the W particles. In the second step Cu was added to the ball milled mixture. To achieve this goal, two different sets of W50wt. %-pre mix bronze compacts of ball milled and of as received powders were utilized. Sintering process was performed at 1150°C. The two-step ball milled powders yielded sintered compacts of fine polygonal and homogeneous W network skeletal dispersed in bronze matrix. Sintered compacts of about 95% theoretical density were produced by this technique.
The effect of Mg, Si and Cu content on the microstructural development during ageing treatment of dilute 6000 series alloys have been investigated using transmission electron microscopy (TEM). Four dilute alloys were used in this study. These alloys were subjected to quenching and artificial ageing at 100 °C, 185 °C and 300 °C. The microstructural developments of the precipitates formed were monitored by TEM. The ageing temperature of 100 °C was found to be too low to form precipitates. It was found that needle or rod-shaped precipitates were formed in the alloys after ageing at 185 and 300 °C. Prolong ageing up to 1000 h at 300 °C resulted in the formation of Mg2Si precipitate that coexists with the type of AlFeSi and Si precipitates. The results show a correlation between the Mg2Si, Si and Cu content on the microstructure of the four dilute alloys after ageing treatment.
In this investigation, experiments were conducted to evaluate the effects of Fe additives in the range of 1–5wt.% on the densification of different compositions of W–pre-alloy bronze compacts sintered isothermally at temperatures ranging from 900°C to 965°C for 2.30h. The results showed that substantial improvement in hardness by a factor of two folds and density by 10% was achieved for the W–pre-alloy bronze sintered compacts by the addition of 2–3wt.% Fe as an activator.
This study investigates the wetting behavior of 63Sn-37Pb and Pb-free solders Sn-3Ag-0.5Cu on Cu substrate. The contact angles were measured in order to study the wetting behavior during soldering at 250 degree Celsius under a constant flux (zinc chloride based). The measurements were performed according to the sessile-drop method. Furthermore, the contact angles were also investigated in these two alloys using the optical-microscope technique. It is found that the average values of wetting angles were at 14.720 degree for Sn-37Pb and at 22.010 degree for Sn--3Ag-0.5Cu. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analyses were conducted in order to study the intermetallic compound (IMCs) through the identification of the microstructure interface of these alloys. The X-ray diffraction (XRD) facilitates more accurate measurements and hence was used to confirm the obtained results and from this analysis it is found that the structure of IMCs at the interface presence was Cu6Sn5 phase for each alloys.
Squeeze cast metal matrix composites based on Al 6061 alloy matrix reinforced with 50% alumina-silica continuous fibres were studied from the point of view of their response to heat treatment as compared to the unreinforced Al 6061 matrix alloy. The changes were monitored by following the electrical resistivity of the composite and microhardness of the matrix composite examined. It was observed that the matrix of the composites showed considerably more hardening effect than the matrix of unreinforced alloy. The resistivity changes in the composites during the ageing process indicated that appreciable internal stress remained in the composite material after overageing and decrease in hardness value.
High performance composites on the basis of aluminium al Ioy matrix and alumina-silica continuous fibres were studied from the point of view of their response to age hardening treatment as compared to the unreinforced matrix alloy. The changes were monitored by following the microhardness of the matrix and the electrical resistivity of the materials examined. It was observed that the matrix of the composites showed considerably more hardening effect than the matrix of the unreinforced alloy inspite of the fibre being innert to the matrix alloy. The resistivity changes in the composites during the ageing process indicated that appreciable internal stress continued to persist in the composite material weIl after overageing and hardness decline took place. EDX evaluation of regions close to the fibres indicated a higher magnesium content as compared to the regions away from the fibres.
Continuous alumina-silica fibre (Altex of Sumitomo) which yields high performance composites with some aluminium alloys was tried for squeeze cast 6061 based composites with volume fraction of 0.5 and 0.32 and the matrix microhardness and resistivity changes during age hardening were studied. The matrix in the composites hardened more than the unreinforced alloy. Microhardness increases of upto 70VPN above the solution treated condition at various ageing temperatures were observed. The resistivity variation indicated an appreciable state of internal stress which continued to persist even when hardness fail by overageing set in. Energy dispersive x-ray analysis indicated that the region close to the fibres had a higher silicon content than the matrix, and amorphous silica in the fibre may help the bond and strength in the composite
The paper describes a study of the reaction between lime and amorphous silica obtained from rice-husk (93–94% SiO2) under hydrothermal conditions, in the range 80–140°C. The progress of the reaction, conducted in stainless steel bombs was followed by analysing unreacted lime. It was observed that the reaction follows two-stage progress pattern similar to the one reported earlier for lime-quartz hydrothermal reactions. X-ray diffractometry and DTA on the reaction products of both stage 1 and stage 2 indicated the formation of CSH (1), calcium-silicate-monohydrate in both the stages. An earlier model by Bezjak and coworkers developed for two-stage transformation observed in lime-quartz hydrothermal reaction was examined for a possible application to the data from the present work. Calculations were made following the general assumptions of the model, which could be applied satisfactorily to the first stage, but not the second stage, possibly because of the relatively more rapid reaction between lime and amorphous silica in the first-stage, creating sluggishness in the second stage.