Papers by Keyword: Crystalline

Abstract: Gray cast iron has been one of the most widely used engineering materials since a long time ago. However, the development of casting techniques and methods to produce various models of cast iron products for the domestic market is not followed by improvements in product quality. The intriguing aspect of gray iron products is the diverse morphologies that graphite can assume, leading to distinct variations in mechanical and physical properties. Quenching is a typical heat treatment procedure performed to improve the mechanical properties of a material that entails the rapid cooling of the material from a high temperature to a low temperature. The aim of this study is to investigate the effect of water quenching effects on microstructure, crystal structure, hardness, and wear of gray iron, which undergoes quenching from the austenitizing temperature. Gray cast iron was obtained from the local foundry industry, then thermally treated at 900°C, held for 15 minutes, and rapidly quenched by water. The quenching procedure induces a significant alteration in the overall microstructure, where transition of most dendrite arms to the eutectic phase microstructure is observed. Moreover, the quenching process is attributed to the reduction of crystal size and growth of carbon crystal. The average crystal size of the sample was reduced from 47.833 nm to 17.97 nm, hence improving the hardness from 16.375 HRC to 48.04 HRC, which in turn improved wear resistance under high loading condition from 0.014 g/sec to 0.00042 g/sec.

Abstract: This paper demonstrates the transport of electron and hole carriers in two distinct hydrogenated amorphous semiconductor materials at different temperatures. Compared to crystalline materials, the amorphous semiconductors differ structurally, optically and electrically, hence the nature of carrier transport through such amorphous materials differ. Materials like hydrogenated amorphous silicon and amorphous IGZO have been used for the study of temperature dependent carrier transport in this paper. Simulation results have been presented to show the variation of free electron and hole concentration, trapped electron and hole concentration with energy at 300K for both the materials. The change in mobility with a change in the Fermi level has been plotted for different temperatures. The effect of temperature on Brownian motion mobility of electrons and holes in hydrogenated amorphous silicon and amorphous IGZO has been demonstrated towards the end of this paper.

Abstract: Understanding the microstructure evolution of metal thin films on various substrates is essential for developing thin films that need specific requirements. The microstructure of thin films has been identified to be related to the mobility of the adatoms during growth. Recently, the theory of non-classical crystallisation of thin films has been introduced to explain the structure formation in chemical vapor deposition (CVD) and physical vapor deposition (PVD) processes. Much work has been conducted on CVD deposited thin films, while little data appears on PVD techniques. The effect of substrate material on the microstructure of the deposited nickel-titanium (NiTi) thin film and its optical absorbance is studied in this work. Three different substrates with identified surface conditions were used to deposit thin films of NiTi in the same chamber under the same processing conditions. The NiTi thin film was deposited using radio frequency (RF) PVD sputtering process on stainless steel (SS), aluminium (Al) and copper (Cu) substrates. The results were analysed in view of state of art structure models and mechanisms. The microstructure was studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The optical absorbance was measured by spectrophotometery. The results have shown that the structure and morphology of the grown films have varied in all conditions. Amorphous structures were obtained for Al and Cu substrates, while crystalline structures were obtained for the stainless-steel substrate at the same sputtering conditions.

Abstract: Copolyether ketones based on 4,4′-dioxydiphenylpropane and n-dihydroxybenzene were synthesized with 4,4′-difluorodiphenyl ketone by high-temperature polycondensation in diphenylsulfone. The structure and structures of the synthesized polymers are studied. The method of IR spectroscopy proved the formation of copolymers of a given structure.

Abstract: The paper deals with two problems in the field of cement-based crystalline coating: The uncertainties about the depth effect of crystalline coating and the influence of curing on resulting waterproofing effect. For coating depth effect investigation the authors used a method based on the analysis of surface hydrophobicity (contact angle method). The depth effect of crystalline coating can be detected on the basis of the different surface hydrophobicity in various distances from the coated surface. The results of measurement showed that the tested crystalline coatings affect concrete microstructure to depth of approximately 50 - 60 mm (measured 4 months after the coating application). But it turned out that used method is not appropriate for this purpose because the results can be affected by a lot of influences and it is necessary be cautious about the conclusions. Another part of experimental program showed that the curing of crystalline coating during its ageing is absolutely necessary for the consequent waterproofing effect. This fact is also the risk factor for the using of crystalline coatings because the waterproofing effect is dependent on a consistent technological discipline.

Abstract: Stability is one of the most important criterions to judge the quality of products, especially for the phase-change memory (PCM), which is regarded as the most promising candidate for next-generation non-volatile memory. Due to the lack of resistance stability, read errors can occur easily and the reliability of PCM will be influenced. Using Sb₂Te as a base material, the resistance stability of Sb₂Te was studied, and the results indicated that in the whole cooling process, the resistance of Sb₂Te crystalline film was extremely steady under different annealing temperatures and different cooling rates. To unravel the reason why the resistance of Sb₂Te crystalline film has good stability, further study was carried out and the results showed that there was no new diffraction peak in the XRD pattern, and the HRTEM images showed the similar hexagonal phase for the films under different annealing temperatures. Moreover, it was observed that the resistance in Sb₂Te-based PCM device was still stable for crystalline state and amorphous state. These results revealed that the stability of Sb₂Te crystalline films at a micro level and the stability of microscopic structure resulted in the stability of resistance. Therefore, based on the present study, the stability of phase-change material Sb₂Te can be applied to exploit more reliable PCM for near-future application.

Abstract: Crystalline silicon and amorphous silicon are main materials of solar cell. Under prolonged exposure to light, silicon will degrade in quality. Hydrogenation is believed can minimize this degradation by reduce the number of dangling bond. These Molecular dynamics simulations are aimed to elaborate the hydrogenation process of crystalline silicon and amorphous silicon and to elucidate effect of temperature on distribution of hydrogen atoms. Reactive Force Field is selected owing to its capability to describe forming and breaking of atomic bonds as well as charge transfer. Hydrogenation is performed at 300 K, 600 K, 900 K, and 1200 K. Hydrogenated silicon surface hinders further hydrogen atoms to be absorbed such that not all deposited Hydrogen atoms are absorbed by silicon surface. Generally, the higher hydrogenation temperature the more hydrogen atoms are absorbed. Increment of temperature from 900 K to 1200 K only enhances a few numbers of absorbed hydrogen atoms. However, it can enable hydrogen atoms to penetrate into deeper silicon substrate. It is also observed that hydrogen atoms can penetrate into amorphous silicon deeper than into crystalline silicon.

Abstract: K_1-xNa_xNb_1-ySb_yO₃ lead-free piezoelectric ceramic powders were prepared by hydrothermal route. The samples were sintered under normal pressure at 1060 °C for 2 h. The structure of piezoelectric ceramics is perovskite and crystalline grain shows a block shape. With the different ceramics component and microstructure, piezoelectric constant d₃₃ varies from 20 to 73. When x=0.54, y=0.04, reached the maximum.

Abstract: ZnO nanometer materials were synthesized by microwave reaction from ZnO micrometer powders with different C aids. Effect of C style on the morphology of ZnO products was studied. The result show that ZnO nanometer materials can not be formed by using directly high temperature evaporation from ZnO micrometer powders without C aids. Fine ZnO nanometer crystals can be obtained by using carbon black as aids. In this sample, most ZnO grains were nanometer particles with a size of about 100nm. And a small amount of ZnO grains were short rods with a length of 1~2μm and a average diameter of 100nm. Amounts of short columnar and long zigzag ZnO crystals can be obtained by using graphite as aids. One effect mechanism of ZnO crystalline was proposed. ZnO reacted C to form CO and CO₂ gas. Concentration of CO/CO2 directly effects the morphology of ZnO in the products.

Abstract: Yttrium iron garnet (Y₃Fe₅O₁₂) films were prepared by a sol-gel method followed by an annealing process at 500,600,700,800, and 900°C in oxygen atmosphere for 2 hours. The microstructure characterization carried out by an X-ray diffractometer showed that the film started to crystalline into YIG phase at 700°C. The average grain size of the films measured using a field emission scanning electron microscope gave the average value of 20 to 70 nm. The magnetic properties measured by a vibrating sample magnetometer showed that all of the films were soft magnetic materials. The saturation magnetization values increased with the increment of annealing temperature. However, the coercivity values were independence with temperatures.Keywords: Thin films; Crystalline; Sol-gel method;