Papers by Keyword: Rietveld Refinement

Abstract: We reported on a convenient route to synthesize rhombohedra boron nitride (r-BN) micro-rod using urea (CO(NH₂)₂) and sodium borohydride (NaBH₄) through thermal treatment at 1300 °C. The structure, morphology, and chemical composition of the obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). In order to determine the phase composition and abundance of the as-synthsized simples, Rietveld refinement has been performed to analyze the XRD data using the Rietan-2000 program. The results show that the abundance of r-BN is about 90.6 wt % and h-BN is 9.4 wt % deduced from Reitveld refinement.

Abstract: Magnesium and strontium both play important roles in the growth of bone and so are desirable ions for substitution into hydroxyapatite (HA) intended for use as bioinstructive bone substitutes. A range of compositions were prepared by a solid state method based on the nominal composition of HA (Ca₁₀(PO₄)₆(OH)₂), with various levels of strontium and/or magnesium substitution: strontium-substituted HA (Ca₈Sr₂(PO₄)₆(OH)₂), magnesium-substituted HA (Ca_9.8Mg_0.2(PO₄)₆(OH)₂ and Ca₉Mg (PO₄)₆(OH)₂), and strontium and magnesium co-substituted HA (Ca_7.8Sr₂Mg_0.2(PO₄)₆(OH)₂ and Ca₇Sr₂Mg (PO₄)₆(OH)₂). Materials were characterised by powder X-ray diffraction, Fourier-transform infrared spectroscopy and Raman spectroscopy. These analyses indicated that the co-substituted materials were composed of mixtures of strontium-substituted hydroxyapatite and magnesium and strontium co-substituted β-tricalcium phosphate. In the magnesium-substituted materials, increased magnesium content was related to increased proportion of β-tricalcium phosphate phase, both with and without strontium co-substitution. The unsubstituted and strontium mono-substituted materials, however, were pure apatite phase, suggesting that magnesium was the destabilising factor in the phase compositions of the magnesium mono-substituted and magnesium and strontium co-substituted materials.

Abstract: Na0.5Bi0.5TiO3 (NBT) ceramics were synthesized by conventional solid state reaction method. Structural and dielectric properties of these ceramics were investigated. Crystalline phase of sintered ceramics was investigated by X-ray diffraction (XRD). The Rietveld refinement of powder X-ray diffraction revealed that the prepared ceramics exhibit the rhombohedral space group R3c. Dielectric properties of Na0.5Bi0. analyzer.5TiO3 (NBT) ceramics were studied at different temperatures in a wide frequency range using impedance

Abstract: Potassium Sodium Niobate, Na0.5K0.5NbO3 is a promising base material for lead free piezoceramics. The polycrystalline sample Na0.5K0.5NbO3 was synthesized using solid state reaction method. The crystal structure and phase purity was studied by XRD and analysed using Rietveld refinement method. Good agreement was observed between the observed and calculated patterns in Rietveld refinement. The refinement inferred orthorhombic crystal structure with Amm2 space group. The impedance spectroscopy of the sample was performed in frequency range 10 Hz to 7 MHz in temperature range 573K to 703K. The activation energy was obtained to be 0.67eV from the reciprocal temperature variation of dc conductivity which follows the Arrhenius law.

Abstract: The zirconia in its cubic phase (C-ZrO2) has gained scientific and technological interest because it has high ionic conductivity and is useful in applications where the transport of oxygen ions prevails, for example, in the oxygen sensors and solid oxide fuel cells [1,. In the pure zirconia, the Zr4+ ion is too small to sustain the fluorite structure at low temperatures, so it has to be partially replaced by a higher atomic radius cation and lower valence number, for example, the Y3 +, Mg2 +, Ca2 + and the rare earth cations TR3 +, [. Currently there are several synthesis methods used to obtain cubic zirconia, the most popular being the mixture of oxides and coprecipitation used industrially in the research labs, but these methods provide powders with different characteristics which will be decisive for a specific application. In this context, the objective of this study was the preparation of homogeneous mixtures of zirconia-rare earth in different concentrations in order to stabilize the C-ZrO2, using the technique of heterogeneous coprecipitation for potential applications in oxygen sensors.

Abstract: The zinc-based aerogel was synthesized via a sol-gel route that it was processed using Zinc chloride as precursor, polyacrylic acid as the template and propylene oxide as the gelation agent. The Zn-based aerogel is formed the length and cross-link of the zinc chloride hydroxide chain, owing to a dominant influence of PAA on the nucleation and growth position of sol nucleus. Nevertheless, ZnO aerogel was prepared with the method that the zinc-based aerogel was calcined at 400°C. Consequently, the R_WP value was in reasonable 7.35% according to X-ray diffraction pattern (XRD) refinement. The crystal system of the ZnO aerogel was monoclinic.

Abstract: This paper investigates the evolution of the deformation mechanisms in a homogenized Mg-10Gd-2Y-0.5Zr alloy ingot compressed at 300-500 °C and 0.1-20 s^-1. It can be found that the basal slip and mechanical twinning are the major deformation mechanisms in the alloy compressed at 300 and 0.1-20 s^-1. Increasing the testing temperature to 350 °C, basal slip, non-basal slip and mechanical twinning control the plastic deformation of the alloy compressed at 0.1-20 s^-1. When the testing temperatures increase further to 400-500 °C, the mechanical twinning is replaced gradually by the local shear bands which are formed by dynamic recrystallization (DRX) grains (referred as transformation bands). The transformation bands have the trend to form the typical DRX microstructure with increasing the temperatures (might be caused by increasing testing temperatures or strain rates). Besides, the transformation bands can also be found in the sample compressed at 350 °C and 20 s^-1 when the temperature in the deformation alloy is high enough to activate non-basal slip and form DRX grains at local zone.

Abstract: In this paper, an as-extruded Mg-10Gd-2Y-0.5Zr alloy was compressed at 3265 s^-1 and -20 °C using a split Hopkinson pressure bar (SHPB) machine. Details about the initial texture and the lattice parameters of the as-extruded alloy were obtained by pole figures combined by orientation distribution function (ODF) and X-ray diffraction (XRD) Rietveld refinement method, respectively. It can be obtained that the maximum average orientation factor being 0.297 can be obtained at 45^o angled to the extruded direction that is the force axis, resulting in the fracture of the impact compressed sample along a plane orientated at an angle of ~45^o to the compression axis. Analysis of the fracture reveals that the fracture forms near the periphery of one face of the specimen and then penetrates into the bulk material subsequently meet near the other face. Even though the local shear deformation exists in the compressed sample, the fracture of the as-extruded Mg-10Gd-2Y-0.5Zr alloy compressed at 3265 s^-1 and -20 °C is not caused by forming the adiabatic shear band (ASB).

Abstract: This paper investigated the twinning mode in a homogenized Mg-10Gd-2Y-0.5Zr ingot compressed at 300 oC and 1 s-1 using transmission electron microscopy observation and schematic method. Details about the primary twinning mode was studied based on the minimum sear criterion by comparing the values of the four major twinning modes in the magnesium alloys. The results show that the twins are formed first by {10-11} primary twinning being step characteristics, and then the secondary twins are formed later around the step by {10-12}secondary twinning. The results also show that the XRD Rietveld refinement method is an effective means to obtain the lattice parameter and to calculate the twinning shear that has important effect on the primary twinning mode in a h.c.p alloy.

Abstract: The phase evolution during the sintering of metal injection moulded stainless steel, 316Land 17-4PH, has been observed using in situ neutron diffraction and Rietveld analysis. The formationof the ferrite phase in the final product is associated with the production of -ferrite at high temperatures.Coexistence of phases at high temperature is thought to allow the segregation of alloyingelements, stabilising the ferrite to lower temperature. To prevent ferrite in the final products the sinteringmust occur at a lower temperature than that at which -ferrite is formed. An alternative regimeis proposed in which the temperature would be cycled around the formation temperature of -ferrite.