Papers by Keyword: Solid Solution

Abstract: Formation of the Ti₃(Al,Sn)C₂ solid solutions was studied by combustion synthesis from elemental powder compacts with Al₄C₃ and TiC additions. Combustion temperatures of 1590–1700 °C and flame-front speeds of 14.2–18.8 mm/s were measured for the Al₄C₃-added samples. Due to the dilution effect of TiC, the combustion temperature and flame velocity were significantly reduced to 1220–1280 °C and 7.1–9.6 mm/s, respectively, for the TiC-adopted samples. The XRD analysis indicated that MAX solid solutions Ti₃(Al_1–xSn_x)C₂ with x = 0.2, 0.4, and 0.6 were produced from the Al₄C₃-adopted samples. Because of the low reaction temperature, the extent of Sn substitution for Al in Ti₃(Al_1–ySn_y)C₂ was narrowed down to y = 0.4 for the TiC-containing samples. The as-synthesized Ti₃(Al,Sn)C₂ grains were plate-like and closely stacked into a laminated microstructure.

Abstract: Hydrothermal processes have the potential for the direct preparation of crystalline ceramic powders and offer a low-temperature alternative to conventional powder synthesis techniques in the production of oxide powders. These processes can produce fine, high-purity, stoichiometric particles of single and multi-component metal oxides. Furthermore, if process conditions such as solute concentration, reaction temperature, reaction time and the type of solvent are carefully controlled, the desired shape and size of particles can be produced. Uniform distribution of the particles is key for optimal control of grain size and microstructure in order to maintain high reliability. It has been demonstrated that such powders are composed of much softer agglomerates and sinter much better than those prepared by calcination decomposition of the same oxides. These powders could be sintered at low temperature without calcination and milling steps. The objective of this study was to synthesis TiO₂-CeO₂ nanosized crystalline particles by a hydrothermal process.TiO₂-CeO₂ nanosized powders were prepared under high temperature and pressure conditions by precipitation from metal nitrates with aqueous potassium hydroxide. The TiO₂-CeO₂ nanosized powder was obtained at 185°C and 6 h. The average size and size distribution of the synthesized particles were below 10±5 nm and narrow, respectively. The XRD diffraction pattern shows that the synthesized particles were crystalline. This study has shown that the synthesis of TiO₂-CeO₂ nanosized crystalline particles is possible under hydrothermal conditions in aqueous solution.

Abstract: The crystal structure of GdFeMn alloy has been investigated by using X-ray powder diffraction (XRD) followed by Rietveld refinement technique, differential thermal analysis (DTA) and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) techniques. XRD results showed that annealed GdFeMn alloy was a single phase of Gd₆(Fe_0.5Mn_0.5)₂₃ compound, with Th₆Mn₂₃-structure. SEM/EDS results and Rietveld refinement revealed that GdFeMn alloy was not really a new ternary compound as reported, but a solid solution Gd₆(Fe_0.5Mn_0.5)₂₃ which was only a point between Gd₆Fe₂₃ and Gd₆Mn₂₃. It was also found from DTA measurement that a reaction, Gd (Fe_0.5Mn_0.5)₂ → liquid (rich Gd) + Gd₆(Fe_0.5Mn_0.5)₂₃, had taken place above 650.81 ^oC, and the educed Gd existed in educed part of GdFeMn sample. The results demonstrated the real structure of the GdFeMn compound as reported was Gd₆(Fe_0.5Mn_0.5)₂₃ compound.

Abstract: Manganese-rich austenitic twinning-induced plasticity (TWIP) steels with high strength and superior ductility have received much attention in the past two decades. Tremendous efforts have been made to explore their unusual hardening behaviour which includes contributions from twins, dislocations, grain boundaries and solid solution. Nevertheless, the individual hardening effects of twins, dislocations, grain boundaries and solid solution on the high strength of TWIP steels are still unclear. In the present work, the flow stress of a TWIP steel was experimentally decomposed into the respective contributions of twins, dislocations, grain boundaries and solid solution. For the forest hardening, synchrotron X-ray diffraction experiments with line profile analysis were carried out to measure the dislocation density. It is found that the yield stress of the present TWIP steel is controlled by solid solution and grain boundary hardening, which contribute to 238.3 and 238.5 MPa, respectively. After yielding, the work-hardening rate is dominated by dislocation multiplication which accounts for up to 922 MPa at a true strain of 0.4, equal to about 60% of the flow stress. In comparison, twins contribute to only 118 MPa at the same true strain, equal to about 8% of the flow stress. In other words, twins have minor effect on the flow stress, in contrast to the current understandings in the literature.

Abstract: Supersaturated titanium-aluminum nitride (Ti_1-xAl_xN) is a very attractive material for a wide range of applications due to its high oxidation and wear resistance accompanied by high strength, hardness, thermal conductivity and thermal shock resistance. Currently, its applications are limited to coatings obtained by physical or chemical deposition. Bulk materials based on Ti_1-xAl_xN may be fabricated by powder metallurgy approach using powders synthesized by high-energy ball milling (HEBM), which composition corresponds to supersaturated Ti_1-xAl_xN solid solution. In the present study, thermal stability of the supersaturated Ti_1-xAl_xN solid solution was investigated. According to the quasi-binary TiN-AlN phase diagram, constructed using density functional theory (DFT) analysis, the concentration ranges, where decomposition takes place through spinodal decomposition or through nucleation and growth, were determined. Experimental study on thermal stability of solid Ti_1-xAl_xN solution powder was conducted by means of differential scanning calorimetry (DSC), Brunauer-Emmited-Teller (BET) and XRD. The results indicated that spinodal decomposition of Ti_1-xAl_xN starts at 800°C, while at temperature higher than 1300°C regular decomposition (nucleation and growth) is occur.

Abstract: Series of the mixed cobaltites-ferrites RCo_1−xFe_xO₃ (x = 0.1–0.9) and cobaltites-chromites RCo_0.5Cr_0.5O₃ (R = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er) with the orthorhombic perovskite structure (space group Pbnm) have been prepared from stoichiometric amounts of rare earth oxides, Co₃O₄, Fe₂O₃ and Cr₂O₃ by solid-state reaction in air at 1473–1573 K. In situ high-temperature X-ray synchrotron powder diffraction revealed anomalous lattice expansion of both series, which is reflected in a sigmoidal dependence of the unit cell dimensions and in abnormal anisotropic increase of the thermal expansion coefficients (TEC). Depending on the composition, several broad maxima in the temperature range of 500−1000 K are observed, which are evidently connected with the transitions of Co³⁺ cations to the higher spin states. The observed anomalies in the mixed cobaltites-ferrites and cobaltites-chromites are less pronounced compared with the corresponding “pure” cobaltites.

Abstract: s. Tb³⁺-doped LiYb_1-xTb_x(MoO₄)₂ (x = 0.01-1) solid solutions were prepared by solid state reaction. Structural of the solid solution series was carried out by X-ray powder diffraction. By increasing the Tb³⁺concentration, the XRD results reveal that LiYb_1-xTb_x(MoO₄)₂ adopt a tetragonal structure with space group of I4(No. 82) and transfer to tetragonal structurewith space group of P41/a (No.88) systemically. The emission and excitation spectra were employed to characterize the synthesized phosphors. Theexcitation spectra showed that LiYb_1-xTb_x(MoO₄)₂ can be efficiently excited by the lights of 250-500 nm, which well match with the emission wavelength of near-UV and blue LEDs chips. The phosphor showed bright green luminescence peaking at around 545 nm under the excitation at 266 nm and 490 nm.The Luminescence intensities are investigated under different Tb³⁺ concentrations. The luminescence decay and the color coordinates were also discussed in order to further investigate the potential applications.

Abstract: Chromium and molybdenum exhibit continuous solubility in the solid phase region at temperatures of 908°C and above [1]. At lower temperatures, the system exhibits a miscibility gap. Furthermore a congruent minimum in the liquidus boundary exists at 1854°C. Chromium and molybdenum powders with different particle morphologies were mixed and porous green parts were produced by pressing. Sintering experiments were performed at different temperatures and for different chromium to molybdenum ratios. To investigate the evolution of the microstructure, sintering was interrupted at different temperatures and points in time. The microstructure and morphology of the sintered parts was investigated by scanning electron microscopy as well as light optical microscopy. It was found that during sintering, a Cr-Mo solid solution is formed. Depending on the molybdenum content, this induces either shrinking or swelling of the porous parts. Samples exhibited a linear expansion of up to 10% and final porosities of up to 65%.

Abstract: . In this paper, L-alanine crystal was crystallized in the presence and absence of glycine additive using slow evaporation method, in association with a simulation technique using ab-initio quantum mechanical method used to predict the crystal morphology of L-alanine. Comparison between the experimental and simulated lattice energies have shown a good agreement with the 8% error, thus validating the set of force field and the partial atomic charges used. Attachment energy method used by the simulation to predict the morphology of L-alanine crystal, revealed a prismatic crystal morphology bounded with 10 dominant faces: (110), ( 0), ( 10), (1 0), (020), (0 0) (011), (0 ), (0 1) and (01 ), which is in good agreement with the experimental morphology. Crystallization of L-alanine in the presence of glycine in the solution also resulted in prismatic crystal morphology, but elongated in the z-axis direction. This result was further explained by intermolecular bonding analysis of glycine on the morphological faces of L-alanine crystal, which suggested that glycine was preferentially adsorbed on the (0 ) and (1 0) faces of L-alanine crystal morphology.

Abstract: A study of liquid mixing route to synthesize high purity Mg_0.8Zn_0.2TiO₃ nanopowder, a candidate dielectric ceramics, has been successfully performed. Formation of the phases on the dried powder was studied using TG/DTA, XRD and FT-IR data. Rietveld analysis on the collected XRD patterns confirmed the formation of solid solution in the system. Such solid solution can be obtained from the powder calcined at 500 °C, but calcination at 550 °C gave rise to the most optimum molar purity up to 98.5% without intermediate phases. The role of Zn ions on the formation of solid solution was also discussed. Homogeneity of particle size distribution and nano-crystallinity of the system was verified from the particle size analyzer data, TEM image and the Rietveld analysis output.