Abstract: This work reports on effect of magnesium addition on the Ti6Si2B stability in Ti-xMg-22Si-11B (x = 2 and 6 at.-%) alloys prepared by high-energy ball milling and subsequent sintering. Ball milling was conducted under Ar atmosphere in stainless steel vials and balls, 300 rpm, and a ball-to-powder weight ratio of 10:1. Following, the powders milled for 10 h were axially compacted in order to obtain cylinder samples with 6 mm diameter. To obtain the equilibrium structures the green samples were sintered at 1100°C for 4 h under Ar atmosphere. X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry were used to characterize the as-milled powders and sintered samples. Extended Ti solid solution were found in the Ti-2Mg-22Si-11B and Ti-7-Mg-Si-B powders milled for 20 min and 60 min, respectively, whereas an amorphous halo was produced on Ti-2Mg-22Si-11B powders milled for 420 min. The increase of Mg amount in the starting powder mixture has inhibited the Ti6Si2B formation in the mechanically alloyed and sintered Ti-7Mg-22Si-11B alloy.
Abstract: Tungsten carbide is potentially attractive for development of catalysts and widely used for fabrication of cutting tools due to its high hardness and wear resistance while the ball milling can improve the mechanical properties from the metastable structures and nanomaterials. The aim of this work was to evaluate the phase transformations during milling of the W-50at%C elemental powder mixture under argon atmosphere in a planetary P-5 ball mill using WC-Co balls (10 mm diameter) and vials (225 mL), 200 rpm, and a ball-to-powder weight ratio of 10:1. Samples were collected into the vial after different times: 20, 60, 300 and 600 min. The as-milled W-50at%C powders were characterized by X-ray diffraction (XRD). Only peaks of W were identified in W-50at%C powders milled up to 600 min, which were broadened and moved to the direction of smaller diffraction angle. In addition, the lattice parameter and cell volume of W were reduced during ball milling of W-50at%C powders, indicating that the C atoms dissolved into the W lattice in order to form metastable structures. Carbon atoms were interstitially dissolved into the W lattice during the initial milling times, and its preferential substitutional dissolution was identified for longer times due to the larger amounts of crystallographic defects during ball milling.
Abstract: The aim of this work is to investigate the influence of some processes variables on the microstructure and hydrogen absorption kinetics of MgH2 - X wt.% TiFe composites. Samples were synthesized by high-energy ball milling in a planetary (X = 40, 50, 60) and shaker mill (X = 40) under high-purity argon atmosphere. Commercial MgH2 instead of Mg powder was used in order to reduce adherence on the vial and balls. TiFe powder was previously produced by ball milling a mixture of TiH2 and Fe powders followed by a reaction synthesis at 600oC. Milled composites samples were characterized by XRD and SEM analysis. Milling time was preliminary investigated (X = 40) in the planetary ball mill (6 to 36h). TiFe particle size reduction was shown to be difficult since they are surrounded by MgH2 matrix. Strong particle reduction was obtained by using a shaker mill only for 2 hours and adding cyclohexane as process control agent. No reaction between MgH2 and TiFe compound was observed in any milled sample. Hydrogen absorption kinetics measurements of the as-milled samples were conducted on an Sieverts' type apparatus at room temperature after hydrogen desorption at 350oC under vacuum. The best hydrogen kinetics (3 wt% at the first hour) was attained by the planetary milled sample (36 h). Higher hydrogen capacity was observed for the sample milled in the shaker mill (4.0 wt.%), but only after 13h.
Abstract: The present work reports on the microstructure and oxidation resistance of Ni-25Nb, Ni-20Nb-5Ta and Ni-15Nb-10Ta alloys produced by high-energy ball milling and subsequent sintering. The sintered samples were characterized by optical microscopy, scanning electron microscopy, X-ray diffraction, energy dispersive spectrometry, and static oxidation tests. Homogeneous microstructures of the binary and ternary alloys indicated the major presence of the β-Ni3Nb compound as matrix, which dissolved large amounts of tantalum. Consequently, the β-Ni3Nb peaks moved toward the direction of smaller diffraction angles. Iron contamination lower than 6.7 at.-% was detected by EDS analysis, which were picked-up during the previous ball milling process. After the static oxidation tests (1100°C for 4 h) the sintered Ni-25Nb, Ni-20Nb-5Ta and Ni-15Nb-10Ta alloys presented mass gains of 31.5%, 30.5% and 28.8%, respectively. Despite the higher densification of the Ni-15Nb-10Ta alloy, the results suggested that the tantalum addition contributed to improve the oxidation resistance of the β-Ni3Nb compound.
Abstract: Aluminum alloy metal matrix composites are a class of materials object of large and intensive research during the last years. In this study an AA2124 aluminum alloy were processed by means of mechanical alloying added by 10, 20 and 20 percent of silicon carbide (SiC) in vibratory SPEX type mill during 60 and 120 minutes. After this the composites powders obtained were characterized by means of Scanning Electron Microscopy (SEM) plus Energy Dispersive Spectroscopy (EDS) to determine the powders morphology. In order to consolidate the AA2124 aluminum alloy composites reinforced by silicon carbide (SiC) composites, the powders processed by high energy ball milling technique were hot extruded and the billets were characterized by SEM to determine the microstructure and the distribution of the reinforced ceramic phase of silicon carbide throughout the aluminum matrix and at last the microhardiness Vickers technique were used to evaluate the mechanical properties.
Abstract: The carbides of refractory metals like tungsten carbide (WC), tantalum carbide (TaC) and niobium carbide (NbC), has been extensively studied due to their applications in several areas of industry, because of their specific properties; such as high melting point, high hardness, wear resistance, oxidation resistance and good electrical conductivity. The tungsten carbide, particularly, is generally used at hardmetal industries due to its high hardness and wear resistance. New synthesis techniques have been developed to reduce the synthesis temperature of refractory metal carbides using more reactive precursors and gas-solid reactions for carbon reduction. The result is producing pure carbides suitable properties for production of high quality cemented carbides and more selective catalysts. In this work, pure and nanostructured WC was obtained from the ammonium paratungstate hydrate (APT), at low temperature and short reaction time. Hydrogen (H2) and methane (CH4) were used as a reducing gas and carbon source, respectively. The precursor and obtained product were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results obtained by diffraction of X-rays showed that complete reduction and carburization of APT have been took place resulted in pure WC formation. The average crystallite size was in nanometer order reaching values of approximately 20.8 nm and a surface area (BET) of 26.9 m2/g.
Abstract: A major challenge in the manufacture of films for polymeric packaging is the definition and setting of the friction coefficient (FCO) for the film surfaces. The FCO values are established with the incorporation of additives during the processing of the polymeric films. But, the homogenization of these additives in the polymeric matrix is very difficult. The additives have different polarity that the matrix polymeric and not are mixable. So, these additives migrate for the surface of the polymeric films easily. Several molecules are used as sliding additives, but among the most efficient are the amides molecules, highlighting the erucamide. This molecule promotes the decrease of the FOC but due its quick migration for the polymeric film surface provides numerous problems for the manufacture of the polymeric packaging and during its application as the product. In this work a nanocomposite (MMT-ERU) was obtained by an intercalation process to improve the compatibility between the polymeric materials and the erucamide molecules. The results shown in this work refers to the studies about the intercalation processes of the erucamide molecules into nanoclays (montmorillonite) to obtain the nanocomposite MMT-ERU. The effect of the temperature and the percentage of the nanoclay in the intercalation processes were studied. The results of x-ray diffraction and differential scanning calorimetry shown that erucamide molecules were intercalated in the nanoclay structures and that intercalation efficiency depends positively of the temperature and percentage amount of the nanoclay in the reaction medium.
Abstract: Transmission infrared spectroscopy (FTIR) was used to study the effect of the temperature and concentration of octadecylamine (surfactant) in the conformation state of amine chains incorporated in a bentonite matrix by organophilization process. The temperature is the most important factor in conformational changes-gauche/trans. Whereas the simultaneous increase of the temperature and concentration of surfactant favors the disordered conformation-gauche. This result is very important in the development of organo-bentonite based polymeric nanocomposites because the intercalation of the polymer in the galleries of the organo-bentonite is dependent on the conformation of the alkyl chains.
Abstract: Nanostructured Mn-Zn ferrites were synthesized using co-precipitation in alkaline solution with different pH. The samples were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), thermal analysis (TG-DTA), dynamic light scattering (DLS) and scanning electron microscopy (SEM) techniques. Monophasic nanoparticles were formed when synthesized with pH 10.5. This sample was heat-treated and its XRD data was refined by the Rietveld method. Mean crystallite sizes and microstrains were determined from X-ray line profile analysis using Single-Line and Warren-Averbach methods, which revealed a mean crystallite size of approximately 10 nm and negligible microstrains. Zn content was estimated using refined cell parameters, giving a value of 33 at %, in accordance with XRF result. TG-DTA revealed that the incorporation of α-Fe2O3 occurs around 1130 °C and 1200 °C with recrystallization of the Mn-Zn ferrite spinel phase. DLS showed that mean particle size increase with temperature up to 1159 nm at 800 °C. SEM analysis showed the samples agglomerate and present similar morphology with negligible size changing when calcined between 280 °C and 800 °C. However, the sample calcined at 1200 °C presents larger agglomerates due to the sintering process.