Papers by Keyword: Phase Evolution

Abstract: This study explores the phase and structural transformations of new lanthanum substituted sodium lead phosphate composite, Pb_(8-x)La_xNa₂(PO₄)₆ with x=0.00 to 0.30. The main focus is to establish the limits of substitution of La³⁺ in the apatite lattice and to understand its effect after substitution. The apatite composite specimen was prepared through a solid–state reaction at 830 °C and characterized using Rietveld–XRD, FT IR and SEM techniques. The statistics suggest that the structure mostly remains a constant up to x = 0.20. However, when the amount of lanthanum exceeds the limit, secondary phases exist and become dominant showing the limit of lanthanum entry. The insertion leads to changes in the host-cation lattice; namely a nonlinear variation along the a-axis, while there is a linear variation along the c-axis in lead-apatite. FT-IR data further confirms that PO₄³⁻ is a tetrahedral ion in the structure. Microstructure is more densely packed what is new in this work is the study of the structural changes which lead to the formation of larger amounts of lead-apatite composites with a wider range of La³⁺ range. The structural changes seen in this study shed light on the structural changes that must occur for effective integration of lead-apatite composites. A fresh perspective on how this study contributes to your submission.

Abstract: In this research, the carbothermal reduction of Langkawi ilmenite ore, FeTiO₃ had been conducted by using coke as carbon reductant. All samples were grinded into size of ≤ 63 µm and pelletized using 2.5 g mixture of ilmenite ore with coke based on C/O molar ratio of 1:3 (carbon to reducible oxygen). The carbothermal reduction was conducted in a horizontal tube furnace using 0.1 L/min of argon gas flow at temperature of 1200°C. The ultimate and proximate analysis of carbon reductant was investigated using carbon, hydrogen, oxygen, nitrogen and sulfur (CHONS) analyzer. The phase evolutions and chemical composition analysis was conducted using X-ray diffraction (XRD) and X-ray fluorescence (XRF) for raw ilmenite and reduced ilmenite with coke, respectively. The reduction time was set with 2, 3 and 4 hours to understand the phase evolutions. It was found that Langkawi ilmenite ore contained mainly higher TiO₂ and hematite, Fe₂O₃ where the phases of FeTiO₃ and titanomagnetite, (Fe₂TiO₄-Fe₃O₄) were detected using XRD. The phase of FeTiO₃ evolved into the production of Fe, FeO, TiC, TiO₂ and Fe₃C when increased the reduction time from 2 to 4 hours. The amount of Fe₂O₃ production was decreased from 59.16 to 47.02 wt%, while higher value of TiO₂ was obtained, increasing from 25.2 to 29.1 wt% due to the reduction of TiO₂ to Ti₃O₅ as the reduction time increased. TiC content is also detected when the reduction time increased by reducing TiC_xO_y into TiC.

Abstract: An investigation of the electrical and microstructural properties of gold (Au)/p-type silicon (Si) contact was performed as a function of rapid thermal annealing (RTA) temperatures. Au films reacted with Si and produced Au₂Si and Au₃Si phases during the deposition of the films at room temperature. The electrical properties of the Au contact to p-type Si degraded with increasing RTA temperature. Such a degradation of the electrical properties could be associated with the degradation of the surface and interface morphology caused by the formation of Au-silicide clusters. The RTA process at 500 °C led to an increase in the size of the Au-silicide Island. This led to the further degradation of the electrical properties after annealing at 500 °C.

Abstract: Sulfate-ion pillared layered hydroxide of Eu₂(OH)₄SO₄·nH₂O (n~2, SO₄^2--LEuH) was synthesized through controlled hydrothermal reaction, and the phase evolution of which upon calcination in the air and hydrogen was studied in detail. It was found that annealing in the air produced orthorhombic Eu₂O₂SO₄ in the temperature range of 300-1000 °C while in flowing H₂ hexagonal Eu₂O₂S was resulted in the 600-1000 °C range. Strong red emissions were found at 621 nm for the SO₄^2--LEuH and 627 nm for Eu₂O₂S under excitation at 396 nm (the ⁷F₀-⁵L₆ transition of Eu³⁺). Improved luminescence intensity was also observed for the Eu₂O₂S powder calcined at a higher temperature.

Abstract: The effects of calcination temperature varying from 700 to 1100°C on the phase evolution and crystallite size of Ni_0.25Zn_0.75Fe₂O₄ synthesized using Sol-Gel technique have been investigated. XRD results showed that the Fe₂O₃ phase was formed in Ni_0.25Zn_0.75Fe₂O₄ in the lower calcination temperature. The crystallization increased as the calcination temperature increased and the crystallite sizes of the Ni_0.25Zn_0.75Fe₂O₄ calculated from Scherrer equation were found to be ranged from 16 to 62 nm which increased when calcination temperature increase. Raman results further confirmed the presence of spinel structure in the samples.

Abstract: Recently photocatalytic materials have been used in variety of industrial applications. TiO₂ is the only suitable photocatalytic material for industrial usage due to its benefits such as non-toxicity, stability, and low cost. TiO₂ nanoparticles were successfully synthesized from titanium alkoxide precursor by sol-gel method. Effects of nitrogen doping on the microstructure and phase evolution of the TiO₂ nanoparticles were investigated. The X-ray diffraction results of doped samples confirm the presence of anatase as the only crystalline phase. The addition of nitrogen in titania matrix leads to disappearance of rutile traces. The scanning electron microscopy show that TiO₂ nanoparticle size decreases by increasing nitrogen doping. Furthermore, DSC-TG results reveal that the crystallization temperature of doped sample shifts to higher temperatures of about 100 °C.

Abstract: Two types of metallic precursors used for the growth of Cu (In,Ga)Se₂ were deposited from a single CuInGa ternary target and binary alloy CuGa and CuIn targets, respectively. Phase evolutions in the precursors of the ternary copper-indium-gallium system were investigated over the temperature range from room temperature to 500°C. Grazing incidence X-ray diffraction (GIXRD) and scanning electron microscopy (SEM) were applied to characterize evolution of phases and surface morphology in the precursor layers. With annealing temperatures increased, phase evolutions of Cu₉Ga₄, Cu₁₁In₉, Cu₁₆In₉ and CuIn were observed. Surface morphology of the two types of precursors changed significantly, which could support the phase evolutions in the ternary Cu-In-Ga system for reactive annealing processes. The existence of the final Cu₁₁In₉ phase, which is the most favorable intermetallic phase for the formation of CuInSe₂ and Cu (In,Ga)Se₂ thin films, may be transformed by a speculated peritectoid reaction of In and Cu₁₆In₉ to Cu₁₁In₉ under In-rich condition.

Abstract: Ultrafine TiC powders with a grain size of about 25 nm were synthesized from nanoanatase TiO₂/carbon black mixtures by mechanical activation-assisted vacuum carbothermal reduction (MCR) reaction. The effects of mechanical activation and carbon sources on TiO₂ carbothermal reduction (CR) were also investigated. Results indicated that the CR of nanoTiO₂ was enhanced after pre-milling of the starting powders. The synthesis temperature and holding time of TiC decreased from 1500 °C to 1300 °C and from 4 h to 2 h, respectively. However, phase evolution analysis of the reaction showed that mechanical activation did not alter the phase evolution sequences of the TiO₂ CR. In addition, the relative weight loss of powders in increasing temperatures indicated that nanoTiO₂ MCR can be divided into three stages, in which the reaction rate of the second stage is found to be the fastest. The study on the effect of different carbon sources on the MCR of nanoTiO₂ showed that the use of nanocarbon black as carbon source can cause MCR to react more thoroughly than the use of graphite and active carbon.

Abstract: Ti(C,N) powder was prepared via carbothermal reduction nitridation (CRN) using rutile and carbon black as the raw material. The phase evolution and the reaction mechanism during the CRN synthesis of Ti(C,N) were investigated, and the effect of reaction temperature and C/TiO₂ molar ratio on the phase composition and x value in TiC_1–xN_x was analyzed. The XRD and SEM results show that: Ti(C,N) powder was synthesized at 1500°C for 4h with the C/TiO₂ molar ratio of 2.2, under the nitrogen pressure of 0.2MPa. Irregular granular structure and the growth stripes were observed in the final products. The growth of Ti(C,N) grains in CRN process was followed by the gas-solid mechanism.The phase compositions of the products were quite dependent on the reaction temperature and the C/TiO₂ molar ratio. The TiN content in Ti(C,N) decreased with the increase of reaction temperature. TiC_1–xN_x powder with different x values can be synthesized by optimizing the experiment conditions including the synthesis temperature and the C/TiO₂ molar ratio.

Abstract: Aluminizing processes are a well-known set of techniques industrially adopted to enrich in aluminum the surface layers of Ni-based alloys, thus improving their resistance to environmental interactions at high temperature. The results of aluminizing are described in terms of the presence, compositions and thickness of the sequence of the resulting surface diffusion layers. A combination of difficulties arising both from the mathematical and the material side restricted the number of available user-friendly models and their applicability to specific alloys or process conditions. The aim of the research work here presented is to overcome part of these difficulties. A synthesis of some well-established models was implemented in a robust numerical algorithm, that automatically prevents instabilities and convergence problems. Such numerical algorithm has been experimentally validated by comparing the results to the experimentally measured composition of profiles obtained for a set of vapor-phase aluminized samples of commercially pure Ni. The model was then applied to predict the effects of the process temperature and of the chemical composition of the surface.