Papers by Keyword: Amorphous

Abstract: (Ti_69.7Nb_23.7Zr_4.9Ta_1.7)_100-xFe_x (x=0, 2, 6, and 10) nanocrystalline, nanocomposite and amorphous powders were synthesized by mechanical alloying from blended element powder. The structural transition for the milled powders was confirmed by X-ray diffraction (XRD). Results shows with the increasing Fe content in alloy system, the glass forming ability become larger. Only for x=10, it can obtain nearly completely amorphous structure with wide super cooled liquid region (△T_x =122 K). For x=2 and 6, residual nanocrystals of the β-Ti structure dispersed in the amorphous matrix. For x=0, the milled powder has full nanocrystalline structure. These as-milled powders offer the potential to fabricating the bulk glass material or nanocrystal/glass matrix composites by powder metallurgy for biomedical use.

Abstract: The work shows the main results on the development at NRNU MEPhI of rapidly quenched amorphous and nanocrystalline ribbon-type and powder brazing filler metals based on Al, Cu, Ni, Ti and Zr and their application for brazing of a wide range of materials in nuclear, thermonuclear, aerospace, automotive, aircraft and other industries: from steels, alloys and refractory metals to various ceramics without metallization of their surfaces.

Abstract: Since the first synthesis of an amorphous phase in Au-Si system from liquid, a great number of amorphous alloys have been prepared by rapid solidification. Almost all amorphous alloys require high cooling rates and a lot of studies have been carried out for these metallic glasses. In this study, metallic glass of Nd60Al10Cu20Ni10 have been fabricated, and experimental research was carried out to reflect thermal features. It indicates that the Nd-based amorphous has shown a distinct glass transition and stable super-cooled liquid region. The research results show that the paramagnetic performance of Nd60Al10Cu20Ni10 metallic glass is different from other hard magnetic alloys at ordinary temperature. From the DSC experiment, it is found that the glass transition temperature is increasing with the heating temperature.

Abstract: Freestanding FeCrAl-Y₂O₃ amorphous/crystalline composite coating with a thickness of about 200μm has been produced from electron-beam physical vapor deposition of FeCrAl and yttria materials with a substrate temperature of 500 oC around. The microstructure was composed of columnar grains near the substrate side and an amorphous top layer. Local crystallization occurred during room temperature preservation. It is inferred that the crystallization activation energy of the material is very low.

Abstract: We fabricated mono-dispersed β-quartz GeO₂ by microemulsion synthesis at room temperature. The obtained particles were 300 nm sized GeO₂ walnut and hollow waxberry shaped GeO₂ which were consisted of nanosphere with average size of 20 nm. The evolution of high pressure studies were devoted in a diamond anvil (DAC) cell by Angle Dispersed X-ray Diffraction (ADXD) at room temperature. A phase transformation of β-GeO₂ to amorphous GeO₂ was detected in walnut GeO₂, while the waxberry GeO₂ was found to transform to monoclinic phase directly. It is strongly suggested that size effect played a key role in the high-pressure transformation from the amorphous and monoclinic phase. By fitting the compression data to the BirchMurnaghan equation of state, the bulk moduli of the walnut and waxberry shaped β-GeO₂ particles were determined to be 33±5, and 38±4 GPa with B₀ = 3, respectively.

Abstract: The internal friction of a cold-rolled Fe-Mn-Si alloy has been investigated using a multifunctional internal friction apparatus though forced vibration method from room temperature to 950 °C. It has been shown that an internal friction peak is found on the IF-T curves during first heating at around 640 °C for the cold-rolled Fe-Mn-Si alloy. The internal friction peak is confirmed to be crystallizing peak of amorphous. The amorphous is resulted from the cold-rolling of the Fe-Mn-Si alloy.

Abstract: Scorodite is an important arsenic carrier for the immobilization of arsenic generated in the metallurgical industries. The transformation of the amorphous ferric arsenate into scorodite was investigated in a mixed sulfate media (pH 1-2) and elevated temperature (80-95 °C). This transformation process has been traced via scanning electron microscopy (SEM) and X-ray diffraction (XRD). Thus, it was found that lower pH and higher temperature was favored to generate more stable scorodite. The scorodite with TCLP leachability of 3.58 mg/L As was produced at 95 °C and initial pH 1.2 for 12 h.

Abstract: High-energy electron, proton, neutron, photon and ion irradiation of semiconductor diodes and solar cells has long been a topic of considerable interest in the field of semiconductor device fabrication. The inevitable damage production during the process of irradiation is used to study and engineer the defects in semiconductors. In a strong radiation environment in space, the electrical performance of solar cells is degraded due to direct exposure to energetically charged particles. A considerable amount of work has been reported on the study of radiation damage in various solar cell materials and devices in the recent past. In most cases, high-energy heavy ions damage the material by producing a large amount of extended defects, but high-energy light ions are suitable for producing and modifying the intrinsic point defects. The defects can play a variety of electronically active roles that affect the electrical, structural and optical properties of a semiconductor. This review article aims to present an overview of the advancement of research in the modification of glassy semiconducting thin films using different types of radiations (light, proton and swift heavy ions). The work which has been done in our laboratory related to irradiation induced effects in semiconducting thin films will also be compared with the existing literature.

Abstract: A Zr-based amorphous composite coating was fabricated by laser cladding and remelting on plain carbon steel. The amorphous phase contents of coatings were tailored by controlling the power density. The effect of amorphous phase content along the depth direction on the microhardness and corrosion resistance of the coating was studied. The results showed that the content of amorphous phase significantly decreased from the remelted layer to the cladded layer. In addition, it was found that the maximum microhardness of the coating were about 1061 HV_0.1, observed 200 μm beneath the surface. Potentiodynamic polarization studies in 3.56 wt.% NaCl solution indicated that the remelted layer exhibited excellent corrosion resistance due to the high amount of amorphous phase.

Abstract: Recently, foamed concrete has become a popular construction material that can be used in wide range of constructions application. Whilst the Rice Husk Ash (RHA) as agro-waste is contain high amount of silicon dioxide. RHA is produced in significant amount every year from agriculture countries. RHA has potential as a material to produce foamed concrete. In this research RHA has been used as a replacement for fine aggregate which used in construction as ordinary concrete material. In this study, foamed concrete with target density 1400, 1600 and 1800 kg/m³ has been produced. The compressive strength of foamed concrete with RHA has been tested. Concrete with Ratio 1:3 of RHA/Sand has higher compressive strength than ratios 3:1 and 2:2 of RHA/sand for every density. XRD and XRF test has been used to determinate chemical composition and crystalline structure of RHA. The result showed that RHA is an amorphous material which amorphous is important thing to pozzolanic process when hydration of cement paste. SEM and EDS test has been conducted to determine microstructure and chemical composition on microstructure of RHA foamed concrete. Amorphous RHA incorporating cement paste produces pozzolanic reaction. It is reduces the porosity and width of interfacial zone in such a way the density is increase.