Slowness surfaces study of the ferroelastic phase transition of LiCsSO4 crystal
The method of slowness surface is used to study the ferroelastic phase transition of LiCsSO4. The slowness surfaces of the crystal have been plotted between 202K and 293K. The direction of the maximum slowness is on the XZ plane and the angle of it and X axis is -49.5 degree when temperature is above 206K. At 206K, the direction of the maximum slowness is along X axis. As the temperature decreases from 206K to 202K, the direction of the maximum slowness doesn't change anymore but the slowness surfaces change dramatically. According to the soft mode theory and the elastic constitutive relations, we obtained that LiCsSO4 crystal is in the same symmetry between 202K and 206K.
Laser Raman spectroscopic study of ferroelastic
Abstract. Lithium caesium sulphate has been reported to undergo a phase transition from the room temperature orthorhombic phase with space group P cmn to a final phase With space group P 2,111. Though a sharp anomaly in its physical properties has been found at 202OK, it was found that there was a need for careful investigations in the vicinity of 240 and 210°K. Since the changes in the crystal structure involve primarily a rotation of the SO4 tetrahedron about the c-axis and as this may be reflected both in the intensity and polarisation of the internal as well as external phonon modes, the laser Raman spectra of oriented single crystals of LiCsSQ at different temperatures were investigated. For correlation and definite identification of the spectral features, its infrared absorption spectrum was also studied. An analysis of the intensities and polarizations of the internal modes of the sulphate ions reveals the change in symmetry of the crystal. The integrated intensity and peak height of the v , line, plotted against temperature show anomalous peaks in the region of the phase transition. Differential scanning calorimetric study gives the enthalpy change AH across the phase transition to be 0.213 kJ/mol.
Evolution of carbide precipitates in Hastelloy N joints during welding and post weld heat treatment
Abstract The effects of welding and post weld heat treatment (PWHT) on the morphology, composition and lattice parameter of the precipitates in the welding joints of Hastelloy N alloy have been investigated. Joint samples were prepared using a gas tungsten arc welding process with ERNiMo-2 fillers, and then solid-solution treated at 1100 °C for 20 min. After welding, eutectic M6C carbides can be observed in the heat affected zones (HAZ) and weld zones (WZ). These eutectic M6C carbides become spheroidized during the following PWHT. The concentration of Si decreases during the transformation from the primary ones to eutectic ones, and then increases during the spheroidizing process. The total concentration of Si + Cr in M6C carbides remains stable during welding and PWHT. At the same time, the heat leads to the outward diffusion of Mo from the M6C carbides, which results in a decrease of the lattice parameter.