Alcalá M.D

• University of Seville

Biochars obtained via the pyrolysis of biomass are very attractive materials from the point of view of their applications and play key roles in the current energy context. The characterization of these carbonaceous materials is crucial to determine their field of application. In this work, the pyrolysis of a non-conventional biomass (solid wastes i...

From nanostructured mechanically synthesized powder a set of FeCoNiCrMn,(Al) based (Ti,Ta,Nb)(C,N) cermets were fabricated and sintered by a pressureless procedure. Highly dense cermets were obtained, and the nature of chemical change, microstructure, mechanical properties and coarsening kinetic of ceramic phase were characterized by image analysis...

The synthesis of TiCxN1-x from Ti/C mixtures in a N2 atmosphere performed in a high-energy planetary mill was used as example to study the influence of the use of additives in mechanically induced self-sustaining reaction (MSR) processes. In particular, the effect of the addition of TiN, TiC, Si3N4 and SiC was analyzed. The self-sustaining reaction...

SiC-Si3N4 composites have been obtained by carbothermal reduction of rice husk under a nitrogen-argon atmosphere at 1450 °C, which is a lower temperature than those used by other authors. On the other hand, tailoring the argon/nitrogen ratio led to the obtained of SiC-Si3N4 composites across the whole range of compositions. Phosphoric acid treatmen...

FeCoNiCrMn(Al)-based powdered high entropy alloys were synthesized by a short time mechanical alloying process in a high energy planetary ball milling from mixtures of elemental powders, and subsequently sintered by a pressureless procedure. The composition and microstructure of the HEA phases before and after the sintering process were studied by...

A high entropy alloy (HEA, CoCrFeNiMn) synthesized by mechanical alloying was used as the binder for the densification of WC by a pressureless high temperature procedure. Three different WC were used by modifying its microstructure with a high energy ball milling treatment. The alloy content in the HEA-WC mixture was varied from 10 to 30% vol. The...

The synthesis of a titanium carbonitride solid solution (TiCxN1 − x) performed in a high-energy planetary mill by a solid-gas Mechanically induced Self-sustaining Reaction (MSR) was used to study the influence of a full set of experimental milling parameters on the ignition time (tig) as a measure of the mechanical dose rate provided by the mill. T...

Vanadium carbonitrides (VCxN1−x) were prepared via mechanosynthesis from mixtures of elemental vanadium and carbon with different V/C atomic ratios under a nitrogen atmosphere using a high-energy ball mill. We obtained the full composition range of carbonitrides at room temperature. The products were characterized using X-ray diffraction, scanning...

Congreso de la Asociacion Nacional de Quimicos de España. ANQUE

In the present manuscript the authors have systematically investigated the composition and microstructure of a series of ternary nitrides (TixV1−xNy) (0.0≤x≤1.0) prepared by mechanosynthesis, using XRD, SEM, EELS, XAS and TGA. The ternary titanium–vanadium nitride (TixV1−xNy) has been obtained in all range of compositions by the mechanical treatmen...

En el presente trabajo se aborda la síntesis del nitruro ternario de titanio y vanadio por reducción carbotérmica de una mezcla de óxidos o bien por nitruración directa de la mezcla de metales, en todo el rango de composiciones empleando el método de análisis térmico a velocidad controlada (ATVC). La caracterización de los productos obtenidos se ha...

Titanium-Vanadium nitride (TiVN) has been prepared from carbothermal reduction of corresponding oxides and also by direct nitridation of a mix of two metals employing the ATVC method. The characterization of the final product by X-ray diffraction, scanning electron microscopy, electron energy loss (EELS), and X-ray absorption spectroscopy (XAS) is...

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Vanadium nitride (VN) has been prepared by mechanosynthesis from vanadium metal under a pressurized nitrogen atmosphere in a short milling time. The characterization of the final product by X-ray diffraction, scanning electron microscopy, electron energy loss (EELS), and X-ray absorption spectroscopy (XAS) is presented. The final product, VN with 9...

TiCxNy/Ti–Ni and TiCxNy/Ti–Co composites formed by ceramic and intermetallic binder phases were produced by pressureless sintering at 1400 °C from powders synthesized by a mechanically induced self-sustaining reaction (MSR) process. Four different composites were characterized using high-resolution electron microscopic techniques, in both scanning...

The synthesis of solid solutions in the HfB2–ZrB2 system was conducted by mechanically induced self-sustaining reaction (MSR) processes under an inert atmosphere from elemental mixtures of Hf, Zr, and B. The stoichiometry of the Hf1−xZrxB2 solid solution phase was controlled by adjusting the Hf/Zr/B atomic ratio in the starting mixture. Composite m...

The machinability of materials is a dynamic field with enormous implications in different industrial sectors because manufacturers are constantly looking for improvements that can increase the overall productivity. Manufacturers of cutting tool inserts need to develop products that can perform at higher speeds and last longer under increasingly rig...

The properties of TiCxN1−x/(Ni or Co) cermets sintered by a pressureless method from powder mixtures, and obtained for the first time by a mechanically induced self-sustaining reaction process (MSR), were studied. The hardness, toughness, friction and wear coefficients, and oxidation resistance were determined. It was shown that cermets obtained fr...

TiCxN1−x-based powdered cermets were synthesized by a one step mechanically induced self-sustaining reaction (MSR) process from mixtures of elemental powders, and subsequently sintered by a pressureless method. The composition and microstructure of the ceramic and binder phases before and after the sintering process were studied by X-ray diffractio...

Titanium and silicon powder blends were ball-milled under an inert atmosphere and subsequently annealed in a nitrogen atmosphere. Ti62.5Si37.5, Ti55.6Si44.4, and Ti50Si50 mixtures suffered a mechanically induced self-propagating reaction during milling. The products of the combustion were Ti5Si3 for the Ti62.5Si37.5 mixture and a combination of int...

Sample controlled reaction temperature (SCRT) has been used for the first time to study the kinetics of the carbothermal reduction of silica in nitrogen to obtain silicon nitride (Si3N4). It is noteworthy to point out that SCRT method allows both a good control of pressure in the sample surroundings and the use of reaction rates low enough to keep...

The transition metal nitrides such as chromium nitride (CrN) show interesting properties that make them suitable for many technological uses. In the present work, pure nanocrystalline CrN has been directly prepared by mechanical alloying, from chromium metal under a pressurized nitrogen atmosphere, in a short milling time and without post-heating t...

Titanium silicon carbide (Ti3SiC2) and Ti3SiC2-based composite powders were synthesized by isothermal treatment in an inert atmosphere as a function of initial compositions (mixtures). A high content of TiC was obtained in the final product when the initial mixtures contained free carbon. The use of TiC as a reagent was unsuccessful in obtaining Ti...

It is suggested that further improvement of the properties of nitride and carbonitride-based hard alloys and cermets requires systems exclusively constituted of solid solutions. The use of pre-made complex carbonitrides as the raw materials makes it necessary to search for new production methods in preparing the original powders. This work is the f...

Niobium, tantalum, and hafnium carbonitride nanopowders were obtained by high-energy ball milling of elemental metal and graphite in a nitrogen atmosphere. By adjusting milling parameters, a mechanically induced self-propagating reaction was observed during the formation of carbonitride phases. The stoichiometry of transition metal carbonitrides wa...

β-SiALON has been obtained from carbothermal reduction of kaolinite by applying the sample controlled reaction temperature (SCRT) method. By using this technique for the synthesis it has been possible to obtain composites with different percentages of SiALON and with different microstructures.

The present work describes an easy procedure for the preparation of iron-silica and iron oxide-silica composites using the wet impregnation method and subsequent heat treatment in different atmospheres. In this way, a specific composite can be produced with a high content of iron or an iron oxide phase (about 24wt.%) uniformly dispersed in the sili...

Preliminary leaching of rice husks with a solution of hydrochloric acid before their combustion at 600°C is shown to be required to obtain relatively pure silica (∼99.5%) with a high specific surface area (∼260 m2/g) that is maintained even after heating at 800°C. Transmission electron microscopy observations indicate that this material has a homog...

Titanium carbonitride (TiCxN1−x) powders were obtained by high-energy ball milling of elemental titanium and carbon (activated carbon or graphite) in a nitrogen atmosphere. The formation of the carbonitride phase was controlled by adequately choosing the experimental conditions of the milling process. The stoichiometry of TiCxN1−x powders was modif...

TiN/Si3N4 composite powders were obtained by a process that combines the mechanical activation of titanium and silicon powders at room temperature through high-energy milling with an isothermal annealing in a nitrogen atmosphere to complete the synthetic reaction. Mechanical activation has allowed us to complete the synthesis at 1350 °C only. The β...

The crystal growth kinetics of GeS2 in Ge0.38S0.62 glass has been studied by Differential Scanning Calorimetry (DSC) and microsopy. The linear crystal growth kinetics of both high temperature α-GeS2 and low temperature β-GeS2 polymorphs has been observed over a relatively broad range of temperatures, i.e. 420 < T < 494 °C that correspond to viscosi...

Ceramics based on silicon nitride have unusual physical and mechanical properties that make them materials of technological importance for their use as structural material. Silicon nitride has been prepared by carbothermal reduction of silica under nitrogen atmosphere using the control rate thermal analysis (CRTA). The employ of this method allows...

Silicon nitride (Si3N4) has been obtained from the carbothermal reduction of rice husks by applying the constant-rate-thermal-analysis (CRTA) method. Under this method, the reaction rate of carbothermal reduction can be controlled and at the same time the CO concentration generated is maintained constant at a previously selected value by the user....

The synthesis of magnetite has been studied by mechanical alloying in an inert atmosphere of a stoichiometric mixture of micrometric particle size iron and hematite powders. The final products have been characterised by chemical analysis, SEM, TEM, XRD, Mssbauer spectroscopy as well as specific surface and magnetic measurements. The magnetite obtai...

Ceramics based on silicon nitride have unusual physical and mechanical properties that make them materials of technological importance for their use as structural material. Silicon nitride has been prepared by carbothermal reduction of silica under nitrogen atmosphere using the control rate thermal analysis (CRTA). The employ of this method allows...

Carbothermal reduction of silica is one of the most common methods of producing Si3N4 powders. The experimental conditions have an important influence on the structure of the final product, especially the balance of α- to β- Si3N4. The Sample Controlled Reaction Temperature method describes here has permitted to conclude that the phase composition...

A planetary ball-mill device that enables one to perform solid-gas reactions at constant pressure was developed. Titanium powders were ball milled under nitrogen at a spinning rate of 960 rpm. The influence of the nitrogen pressure on the mechanochemical reactivity of titanium was analyzed at 1.5 and 11 bars. A spontaneous combustion took place dur...

The synthesis processes of Si3N4 from the carbothermal reduction of SiO and SiO2, respectively, are studied. It has been concluded that the reaction temperature is lower if SiO instead of silica is used as raw material. The use of the Constant Rate Thermal Analysis (CRTA) method allows a silicon nitride to be obtained with an average crystallite si...

The synthesis processes of Si 3 N 4 from the carbothermal reduction of SiO and SiO 2 , respectively, are studied. It has been concluded that the reaction temperature is lower if SiO instead of silica is used as raw material. The use of the Constant Rate Thermal Analysis (CRTA) method allows a silicon nitride to be obtained with an average crystalli...

In the present paper we report the formation of CNx phases during mechanical treatment of graphite in a nitrogen atmosphere. Samples containing approximately 25 wt.% of CNx phases have been obtained with the experimental conditions presented in this work. The formation of carbon–nitrogen bonds has been proved by infrared (IR) and X-ray photoelectro...

Silicon nitride has been obtained by carbothermal nitridation of silica using Constant Rate Thermal Analysis (CRTA) method. This method permits to maintain the CO concentration generated in the reaction in a constant value previously selected by the user. The results obtained have shown that the synthesis of α-Si3N4 is improved by increasing the pa...

It has been shown that the grinding of Rutile reduces the starting sintering temperature of compacted bodies. A compactness close to full density has been obtained for both the ground and the whole set of Rutile ground samples. SEM observations have shown that the grain size of the compacted bodies decreases by increasing the grinding time of the p...

An equipment for thermally stimulated current (TSC) analysis has been developed. The system can be operated at temperatures from 90 up to 1273 K. The cryogenic system developed for measuring the electrical properties of materials below room temperature is described. The reactor containing the sample is hermetically closed and can be operated from h...

CNx amorphous films have been prepared by reactive magnetron sputtering in a pure N2 discharge. The films grown on NaCl have been characterised by Fourier transform infrared spectroscopy (IR), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). C/N atomic ratios have been determined by EELS with values in the range...

Magnetic properties of magnetite powder prepared by ball-milling of stoichiometric mixture of hematite and iron in an inert atmosphere are reported. Hysteresis loops, isothermal remanence acquisition curves and temperature dependence of magnetic susceptibility measurements are used to characterise this material and to examine the effects of heating...

Some examples of the use of the CRTA method for the synthesis of materials with controlled texture and structure are given. BaTiO3 has been obtained from the thermal decomposition of Barium Titanyl Oxalate (BTO) and Barium Titanyl Citrate (BTC) by controlling the reaction temperature in such a way that the partial pressure of the gases generated in...

The thermal decomposition of a series of lepidocrocite samples has been monitored by means of the Constant Rate Thermal Analysis (CRTA). This method allows controlling the reaction temperature in such a way that both the reaction rate and the partial pressure of the water vapor generated in the reaction are maintained constant at values that can be...

AlN powders have been submitted to mechanical attrition in air. X-ray diffraction (XRD) and transmission electron microscopy (TEM) show that mechanical treatments are producing the fracture of primary particles and the incorporation of microstructural defects. At the same time, Bremsstrahlung excited Auger electron spectroscopy (AES) in conjunction...

The Si K-edge X-ray absorption spectra of three samples obtained from rice husk have been recorded to investigate changes in medium and short range order that could explain the drastic differences in surface area of the samples, from 1 to 260 m2/g. The recorded differences are similar to those detected in densified silica, where they have been asso...

A grinding vial has been developed to be used with a high grinding energy swinging mill under the pressure of selected gases. This tool has been used for the study of titanium with nitrogen gas. Nanometric titanium nitride with a crystallite size around 10 nm has been obtained. A mechanism for the mechanochemical conversion of titanium into titaniu...

Nanocomposite powders (Fe or Fe-Cr alloy)/α-Al2O3 (75 and 85 vol.%) were obtained by room-temperature high-energy milling powder mixtures of hematite (and chromium oxide) with aluminum and alumina in a high-capacity mill for 8-10 h. The composition of iron and iron alloys was followed by Mössbauer spectroscopy, while the appearance of other phases...

New Constant Rate Thermal Analysis (CRTA) equipment has been developed that permits the synthesis of SiC from carbothermal reduction of silica under both constant reaction rate and constant partial pressure of the CO generated in the reaction. It has been suggested that this method improves the formation of whiskers.

A new “incipient-wetness” method is proposed for the synthesis of chemically stabilized β-cristobalite (CSC) that avoids the need to handle liquid phases as required by the sol-gel routes proposed in the literature. Stoichiometric compounds with the composition Si1–xAl*xCa1/2O2 have been investigated. ×= 0.07 represents the optimal composition for...

Preliminary leaching of rice husks with a solution of hydrochloric acid before their combustion at 600 C is shown to be required to obtain relatively pure silica ({approximately}99.5%) with a high specific surface area ({approximately}260 m{sup 2}/g) that is maintained even after heating at 800 C. Transmission electron microscopy observations indic...

Nanocomposites -Al2O3-Fe containing 75 vol% Al2O3 have been obtained by reaction milling, in a vibratory ball mill, a stoichiometric excess of alumina with aluminum and hematite. The kinetics of synthesis of the nanocomposite has been studied for milling times between 15min. and 8h. The reduction reaction is completed in about 2h with formation of...

A CI electronic microbalance which allowed sample weights up to 5 g to be measured with a maximum sensitivity of 1 μg has been used to develop a new constant rate thermal analysis (CRTA) technique. This permitted a constant rate of change of weight |C| ≥ 10 μg min−1. Moreover, it has been extended to constant rate jump thermal analysis (CRJTA). The...

The influence of grinding in a high planetary ball-mill on the texture and thermal stability of Pb3O4 has been studied. The results obtained show that the crystallite size decreases while the level of microstrains increases upon increasing the grinding time. The Pb3O4-->PbO conversion temperature decreases by increasing the grinding time of the pre...

A new equipment has been developed in order to apply the constant rate thermal analysis method (CRTA) to Temperature Programmed Oxidation (TPO) processes. The exhausted gases flow through an electrochemical oxygen sensor after leaving the reactor in order to monitor the oxygen consumption in the reaction. The control of the sample temperature is ca...

The carbothermal reduction of silica under flowing nitrogen at a pressure of 1 atm has been followed by means of a CO IR detector attached to the gas output of a high temperature tubular furnace. The control of the reaction temperature is carried out by interfacing the analogical output of the IR detector to a controller that allows to monitor the...

A theoretical analysis of the influence of mass-transfer phenomena on the shape of EGA traces of the thermal decompositions of solids has been carried out by assuming that the partial pressures of the gases generated in the reactions are proportional to the reaction rate. It has been shown that the EGA curves move to higher temperatures and the app...