Paula Rojas

Adolfo Ibáñez University · Faculty of Engineering and Sciences

This study evaluated the behavior of three paint systems exposed to the Antarctic marine environment for 45 months compared to a control of uncoated carbon steel with a determined corrosion rate. At the study site, all environmental conditions, solar radiation, and the concentration of environmental pollutants (Cl− and SO2) were evaluated. The pain...

We studied atmospheric corrosion on Rapa Nui Island, using galvanized and non-galvanized SAE 1020 steel samples exposed on racks. We also added Charpy samples of both materials to directly determine the effect of corrosion rate on these materials' impact toughness. The results indicated a correlation between corrosion rate and toughness loss in the...

Atmospheric corrosion of copper, exposed on a tropical island in the South-Central Pacific Ocean, was reported and compared with those of a very similar study at the same site conducted 20 years earlier. The new measurements—taken over three years of exposure, from 2010 to 2013—quantified corrosion by mass loss, characterized corrosion products by...

We present a bottom-up experimental research to address evidence of internal curing of mortars using randomly distributed pig-hair as water reservoirs. Plain and reinforced mortars with pig hair ranging from 0 to 8 kg of fibers per cubic meter of mortar were prepared. The microstructures of plain and reinforced mortars were scanned using electron m...

Several commercial alloys use silicon (Si) to improve titanium (Ti) resistance to creep and oxidation at high temperatures and to improve Ti corrosion resistance in acid media. According to the Ti-Si phase diagram, reported stable solid phases in the Ti-rich region are β-Ti, α-Ti, Ti3Si, and Ti5Si3. Nevertheless, very few works in the literature di...

Nanocrystalline Ni (Ninc) obtained by mechanical milling may present improved mechanical properties paired with high abrasion resistance. Different sintering processes were used to consolidate Nanocrystaline Ni: hot pressed (HP) and hot-isostatic pressed (HIP). The microstructure, mechanical properties, and tribological were evaluated to compare th...

The use of adobe blocks (sun dried bricks made with clayey soil) as construction material has been resurged in late years attracting the interest of the research community due to its thermal properties and, compared to concrete and steel, low CO2 emissions associated with the manufacturing process [1], [2]. Yet, earthen materials compressive and fl...

This paper describes a study exploring milling and subsequent heat treatments of pure IrO2 and Ta2O5 powders. Reactants were milled under Ar atmosphere in a SPEX 8000D mill, with structural, morphological, and compositional characterizations (during milling and after subsequent heat treatments) by X-ray diffraction, energy-dispersive spectroscopy,...

Ag–CdO composites are still one of the most commonly used electrical contact materials in low-voltage applications owing to their excellent electrical and mechanical properties. Nevertheless, considering the restriction on using Cd due to its toxicity, it is necessary to find alternative materials that can replace these composites. In this study, t...

El cobre es actualmente, el producto más importante en la economía chilena, de hecho, su producción equivale al 20% del PIB total y al 60% de las exportaciones mineras chilenas. A nivel mundial, Chile lidera los rankings de producción de cobre, con un 31% del total mundial y sus reservas representan el 30% de las reservas mundiales. Sin embargo, la...

The aim of this work was to study the synthesis and electrochemical properties of Ti 2 wt %-Si alloys prepared by mechanical alloying (MA) and heat treatment. The MA process was performed under Ar atmosphere. The structural, morphological, and compositional evolutions during the milling and subsequent heat treatment were investigated by X-ray diffr...

This work presents the effects of high energy milling with different Ni and Zr ratios on the amorphization of ternary Cu-Ni-Zr alloys (initially, Cu-43Ni-7Zr, Cu-12Ni-31Zr, Cu-33Ni-7Zr, and Cu-12Ni-23Zr; and later, Cu-23Ni-15Zr and Cu-11Ni-7Zr). Microstructure was determined using X-Ray diffraction and electron microscopy. Results were compared to...

Addition of fibers to cement-based materials improve tensile and flexural strength, fracture toughness, abrasion resistance, delay cracking, and reduce crack widths. Natural fibers have recently become more popular in the construction materials community. This investigation addresses the characterization of a new animal fiber (pig hair), a massive...

Elemental powders of Cu and Ni, binary alloys (Cu-Ni and Cu-Zr) and ternary alloy (Cu-Ni-Zr) obtained by mechanical alloying and uniaxial compaction hot microstructure and mechanical properties were investigated. The alloys studied were: pure Cu, pure Ni, binary alloys (Cu-Ni; Cu-Zr) and ternary alloys (Cu-Ni-Zr) under the same mechanical milling a...

Mechanical alloying and uniaxial compaction were used to obtain configurations of: elemental powders of Cu and Ni; binary alloys (Cu-Ni and Cu-Zr); and a ternary alloy (Cu-Ni-Zr) under the same mechanical milling and hot pressing conditions. Microstructure and mechanical properties of these were investigated. According to XRD results, hot pressing...

Este trabajo presenta la evolución microestructural del compuesto Mg2Ni0,5Co0,5 obtenido mediante aleado mecánico y el estudio de sus propiedades de hidruración. Los polvos elementales de Mg, Ni y Co con una relación atómica 2:0,5:0,5 se alearon mecánicamente en un molino de alta energía Spex 8000D por 36 h (muestra amorfa) y posteriormente se real...

The manufacture of alloys in solid state has many differences with the conventional melting (casting) process. In the case of high energy milling or mechanical alloying, phase transformations of the raw materials are promoted by a large amount of energy that is introduced by impact with the grinding medium; there is no melting, but the microstructu...

In this study materials were manufactured using powder metallurgy, by mechanically milling Cu and Ni and mechanically alloying Cu-Ni (at 50-50 and 60-40% in weight). In order to consolidate samples at the lowest possible temperature, after the milling cold sintering was used at 300°C and 900 MPa. This type of sintering does not always give high den...

The unprecedented increase in human life expectancy have produced profound changes in the prevailing patterns of disease, like the observed increased in degenerative disc diseases, which cause degradation of the bones. Ti-Nb-Ta alloys are promising materials to replace the damaged bone due to their excellent mechanical and corrosion resistance prop...

En este estudio se fabricaron diferentes materiales (base cobre) bajo las mismas condiciones de molienda: molino empleado fue un SPEX 8000D, atmósfera de argón, acido esteárico, RBP=10:1, con tiempos variables desde 1 hasta 120 horas, con el objetivo de comparar los cambios microestructurales durante el proceso de: Cobre puro, Aleaciones Cu-Ni, Ale...

Research by this working group's takes as a principal aim the study and manufacture of bulk metal glass based copper (Cu-Ni-Zr) by mechanical alloying. First, the characterization of the milled pure copper, Cu-Ni and Cu-Zr binary alloys and Cu-Ni-Zr ternary alloys in the same conditions of high energy millings. In this work, the microstructural cha...

Development of titanium foams with low Young's modulus as a potential implant material has attracted significant attention. In this work, the effect of manganese on the mechanical properties in compression of Ti-13Ta-30Nb-xMn foams (x52-6 wt-%) has been studied. Titanium based alloys produced by mechanical alloying were processed to obtain foams us...

Nowadays, Ag-CdO alloys are widely used in electrical contact applications, because of their good electrical and thermal conductivity is as well as high resistance to arc erosion and contact welding. Considering the restricted use of Cd due to its toxicity, it is necessary to find a material that can replace those alloys. The objective of this work...

In this study, SAE 1020 steel Charpy's samples, with and without galvanization, were exposed to a large variety of environmental conditions throughout Chile in order to ascertain the degree of deterioration due to environmental corrosion. The levels of Cl-, SO2 and time of wetness were also registered in order to be able to correlate the data with...

In this work the relationship between the chemical composition and atomic volume in the Ag-x % Zn (x ≤ 20) system was studied. For this purpose, 10 solid solutions were obtained by means of casting and mechanical alloying. The microstructural characterization was carried out by means of X ray diffraction. The lattice parameter was obtained using th...

The microstructural evolution of Mg and Co in a 2: 1 atomic ratio was investigated during mechanical alloying and subsequent heat treatments. Microstructural characterization was determined using X-ray diffraction and scanning electron microscopy, while thermal stability was studied by means of differential scanning calorimetry. The results show th...

Microstractural evolution during mechanical alloying of Ag and Zn, and subsequent heat treatments were investigated. The mechanical alloying was carried out in a SPEX 8000D miller. The microstructural characterization was obtained by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The thermal...

Galvanized steel behavior in concretes of different types of cement is very important for new mega construction projects with requirements of durability in highly aggressive environments such as sea water, in harbor structures as in mining projects that use sea water in their processes. To emulate conditions of this type of project, it was used W/C...

Galvanized steel behavior in concretes of different types of cement is very important for new mega construction projects with requirements of durability in highly aggressive environments such as sea water, in harbor structures as in mining projects that use sea water in their processes. To emulate conditions of this type of project, it was used W/C...

Energy values that are transferred as crystalline defects during the mechanical alloying process on powder of the Cu-Cr and Cu-Mo systems and energy dissipated by heat flow of vials in SPEX mill were estimated. The results indicate that the transferred energy values to metallic powders for creating crystalline defects are rather smaller (around two...

This work show the first part of a research project towards the development of a corrosion map for Chile. In order to develop this map, the research group considered carbon steel, galvanized carbon steel, copper and aluminum as testing materials. All these materials were exposed to the atmosphere in 31 places along the country. In each one of these...

Metallic corrosion is a problem that is intensified by exposure to certain atmospheres, decreasing the life of the metal or alloy, creating operational inefficiencies in industrial plants, resulting in high repair costs, arrests and/or replacements. In Chile there are marked geographic, demographic and industry, making it necessary to produce maps...

In this work the effect of mechanical activation on the barite carbothermic reduction has been investigated. The mechanical activation of barite and coke was carried out in a SPEX 8000 D mill. The microstructural and morphological characterization of the powders was obtained by X-ray diffraction and scanning electron microscopy. The kinetics of bar...

This work show the first part of a research project towards the development of a corrosion map for Chile. In order to develop this map, the research group considered carbon steel, galvanized carbon steel, copper and aluminum as testing materials. All these materials were exposed to the atmosphere in 31 places along the country. In each one of these...

The objective of this work is proposing a simple thermodynamic model to explain the increase in the solubility limit of the powders of the Cu–Mo systems or other binary systems processed by mechanical alloying. In the regular solution model, the effects of crystalline defects, such as; dislocations and grain boundary produced during milling were in...

Composite Mg2Ni (25wt.%) amorphous Mg50Ni50 was prepared by mechanical milling starting with nanocrystalline Mg2Ni and amorphous Mg50Ni50 powders, by using a SPEX 8000 D mill. The morphological and microstructural characterization of the powders was performed via scanning electron microscopy and X-ray diffraction. The hydriding characterization of...

In order to study the effect of mechanical activation on the sulphuric acid leaching of CuFeS2, four samples were milled using an Atritor mill during 1, 5, 8, and 15 h. The powders were microstructural and morphologically characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The samples were leached...

Amorphous Mg50Ni50 alloy was produced by mechanical alloying (MA) of the elemental powders Mg and Ni using a SPEX 8000D mill. The alloyed powders were microstructurally characterized by X-ray diffraction (XRD). The thermal transformation of amorphous Mg50Ni50 into stable intermetallics (Mg50Ni50→remaining amorphous+Mg2Ni→Mg2Ni+MgNi2) was analyzed u...

In order to study the relationship between the milling time used in the production of Mg₅₀Ni₅₀ amorphous alloy and its thermal stability, seven amorphous alloys were produced by milling for 20, 25, 30, 35, 40, 50 and 60 h each sample. The obtained powders were morphological and structurally characterized by scanning electron m...

This work studies the evolution of the microstrucutre of a mechanically alloyed Cu-8 wt. % Cr powder mixture by X-Ray profiles analysis. The process was carried out using a SPEX8000D upon mix with stainless steels containers and balls, keeping a constant powder to balls weight ratio of 10. Increasing the milling time, crystallite size and stacking...

An oversaturated solid solution of H in a nanocomposite material formed mainly by nanocrystalline Mg2Ni, some residual nanocrystalline Ni and an Mg rich amorphous phase has been found for the first time. The nanocomposite was produced by mechanical alloying starting from Mg and Ni elemental powders, using a SPEX 8000D mill. The hydriding characteri...

In the present work was investigated the effect of two milling parameters, atmosphere and milling time, on the morphology and microstructure of pure copper powder and a mixture of copper-2,5 wt. % lithium. The mechanical alloying was performed in a SPEX 8000D mill, using steel containers and balls. The two control atmospheres were argon and nitroge...

The effect of milling energy on the amorphisation process and subsequent thermal crystallization of Mg50Ni50 was investigated. The amorphous Mg50Ni50 was produced using a planetary mill (medium energy) with a ball to material weight ratio of 13:1, and a SPEX mill (high energy) with a ball to material weight ratio of 20:1. The results obtained by me...

Aluminum-embedded polymethylmethacrylate (PMMA) composites were produced by using different aluminum concentrations in the polymer matrix. The aluminum particles were spherical with a particle size of 80 nm. The hot compression molding method in inert atmosphere for all the composites was used in their preparation. The PMMA matrix was analyzed usin...

In the present work the effect of milling parameters, such as the ball-to-powder ratio and milling time, on the formation of supersaturated Cu–Li solid solutions produced by mechanical alloying was investigated. The microstructural changes and the phases present after milling were analyzed using scanning electron microscopy and X-ray diffraction, w...

A nanocrystalline Ti alloy with a uniform distribution of grains was synthesized using cryogenic mechanical milling. The effects of cryomilling parameters, such as milling time and ball to powder ratio (BPR), on the particle size, grain size, chemistry, and structure of cryomilled Ti powders were investigated using X-ray diffraction (XRD), scanning...

The grain growth, thermal stability, and recrystallization behavior of a cryomilled Ti alloy with a grain size of about 21.2 nm were examined using differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy. Isochronal heat treatments at different temperatures were applied to study the thermal stability and recrystal...

This study investigates the microstructural evolution during mechanical alloying of Mg and Ni, and during subsequent heat treatments of SPEX milled powders. The milling was performed under an inert argon atmosphere, employing two different ball-to-powder ratios (BPR): 10:1 and 20:1. It was observed that a large number of defects were produced durin...

Nanostructured metals and alloys have been the subject of considerable scientific and technological interest, as a result of their potential in structural and other applications. However, inspection of the scientific literature reveals that only limited work has been reported on nanocrystalline Ti Alloys. The objective of this research is to study...

In the Mg-Ni system, one of the best hydrogen absorbers is the intermetallic compound Mg2Ni. This compound can be easily activated and it forms the Mg2NiH4 ternary hydride with a 3.6 wt% H/M ratio. The production of a high purity, single phase Mg2Ni, is made possible through special techniques such as the vapor exchange diffusion reaction of the el...

Mg is considered one of the prospective materials for the storage of hydrogen as hydride, but unfortunately the activation of Mg requires more effort than other hydride-forming metals and the kinetics of hydriding and dehydriding is rather slow. However, alloying Mg with metals such as Ni introduces positive changes in the kinetics of hydrogen abso...