Mechanical characteristics of microwave sintered silicon carbide

The present work deals with the sintering of SIC with a low melting additive by microwave technique, The mechanical characteristics of the products were compared with that of conventionally sintered products. The failure stress of the microwave sintered products, in biaxial flexure, was superior to that of the products made by conventional sintering route in ambient condition. In firing of products by conventionally sintered process, SiC grain gets oxidized producing SiO2 (-32 wt%) and deteriorates the quality of the product substantially. Partially sintered silicon carbide by such a method is a useful material for a varieties of applications ranging from kiln furniture to membrane material

Mechanical characterization of microwave sintered zinc oxide

The mechanical characterization of microwave sintered zinc oxide disks is reported. The microwave sintering was done with a specially designed applicator placed in a domestic microwave oven operating at a frequency of 2.45 GHz to a maximum power output of 800 Watt, These samples with a wide variation of density and hence, of open pore volume percentage, were characterized in terms of its elastic modulus determination by ultrasonic time of flight measurement using a 15 MHz transducer, In addition, the load dependence of the microhardness was examined for the range of loads 0.1-20 N, Finally, the fracture toughness data (K-IC) was obtained using the indentation techniqu

Effect of carbon content on the mechanical properties of ternary boron-nitrogen-carbon compound

BNC films have been deposited on Si (100) and fused silica substrates by inductively coupled plasma chemical vapour deposition (ICP-CVD) technique using a mixture of borane-ammonia, nitrogen and methane as precursor gases. Carbon content in the films is varied by changing the concentration of methane in the precursor gases. The films are amorphous in nature. The films, thus, deposited have been characterized by using Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction and Secondary Ion Mass Spectroscopy (SIMS). Microstructural information has been obtained from SEM studies. Microhardness has been seen to decrease with the increase in carbon content and the highest microhardness observed in these films has been found to be similar to 5.3 GPa

Mechanical and microstructural properties of cordierite-bonded porous SiC ceramics processed by infiltration technique using various pore formers

Cordierite-bonded porous SiC ceramics were prepared by air sintering of cordierite sol infiltrated porous powder compacts of SiC with graphite and polymer microbeads as pore-forming agents. The effect of sintering temperature, type of pore former and its morphology on microstructure, mechanical strength, phase composition, porosity and pore size distribution pattern of porous SiC ceramics were investigated. Depending on type and size of pore former, the average pore diameter, porosities and flexural strength of the final ceramics sintered at 1400 A degrees C varied in the range of similar to 7.6 to 10.1 A mu m, 34-49 vol% and 34-15 MPa, respectively. The strength-porosity relationship was explained by the minimum solid area (MSA) model. After mechanical stress was applied to the porous SiC ceramics, microstructures of fracture surface appeared without affecting dense struts of thickness similar to 2 to 10 A mu m showing restriction in crack propagation through interfacial zone of SiC particles. The effect of corrosion on oxide bond phases was investigated in strong acid and basic salt medium at 90 A degrees C. The residual mechanical strength, SEM micrographs and EDX analyses were conducted on the corroded samples and explained the corrosion mechanisms

Ultrasonic evaluation of gypsum plaster

Ultrasonics have been used for the characterization of set plaster in the water ratio range 0.3 to 1. The variation of ultrasonic velocity with porosity has been studied. The elastic modulus and strength of plaster have also been evaluated. The study indicates both elastic modulus and strength properties correlate well with the ultrasonic velocity. Thus the ultrasonic velocity can be used as a predictor of strength and elastic moduli of these materials

Synthesis of Pd/SnO

Pd/SnO2 composite films were obtained by wet chemical route using SnCl2:2H2O as tin containing precursor and PdCl2 as palladium containing precursor. The bilayer structures were subjected to rapid thermal annealing for the incorporation of Pd in SnO2 matrix. Pd/Sn was varied between 6 to 20% for optimizing the Pd concentration for improved sensitivity. Liquid Petroleum Gas (LPG) sensing properties were also investigated. The films thus obtained were subjected optical, microstructural, FTIR and Raman studies both before and after LPG exposure

High magneto-Seebeck effect at room temperature in Bi1.8_{1.8}Sb0.2_{0.2}Te3−y_{3-y}Sey_y crystal

We report thermoelectric and electrical transport properties of Bi$_{1.8}$Sb$_{0.2}$Te$_{3-y}$Se$_y$ by tuning y. In contrast to the reported p-type conductivity of the end compounds with y = 0 and 3, a dominant n-type conduction mechanism is observed for y = 1.5 from the Hall measurement. Intriguingly, the magneto-Seebeck consequence is enhanced up to ∼ 20 times for y = 1.5 compared to the end members. The reasonable value of magnetoresistance with an anisotropic character with respect to the direction of the magnetic field is observed at low temperature, which decreases with increasing temperature. The density of state at the Fermi level near room temperature correlates high Seebeck coefficient as well as magneto-Seebeck effect. High magneto-Seebeck effect at room temperature is promising for the application

A novel technique for fabrication of near-net-shape CMCs

A sol-gel vacuum infiltration technique has been developed for the fabrication of near-net-shape ceramic matrix composites (CMCs) using discontinuous mullite fibre preform with 15 vol.% of fibre content and ZrO(2)(.)10 Wt-% Y2O3 sol as the infiltrant. Effect of sol viscosity, number of infiltration and calcination temperature on physico-mechanical properties of fabricated CMCs were examined. Characterization of the fibre preform, matrix material (in the form of ceramic specimen without fibre) and the developed CMCs were performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD indicated the presence of cubic (c) and tetragonal (t) zirconia in both the CMCs and the ceramic specimens calcined even at 1400degreesC. Flexural strength of the CMCs and the ceramic specimens (calcined at 1400degreesC), determined by the three-point bending test, was found to be about 14 mPa and 1(.)40 mPa, respectively. SEM indicated multiple fracture of the matrix which gave rise to pseudo elasticity. This is also evident from the load-displacement curve of the three-point bend test. SEM studies also indicated fibre pull-out in the fracture surface of the CMCs

Coexisting ferromagnetic component and negative magnetoresistance at low temperature in single crystals of the VdW material GaGeTe

We report magnetoresistance and magnetization studies of single-crystal GaGeTe, which has been proposed as a Van der Waals material. Semi-metallic character is observed in the temperature (T) variation of resistivity (ρ), following ρ(T) ​$∝$ ​T$^2$ ​at low temperature with a slope compatible with the usual spin-fluctuating system. Magnetoresistance (MR) at 2 ​K is negative and strongly dependent on the direction of the magnetic field (H) with respect to the crystallographic c-axis. MR changes sign with increasing temperature above ∼ 100 ​K, when H is applied along the c-axis. Hall measurements indicate the p-type conductivity with a considerable hole concentration of ∼ 8.7 ​× ​10$^{19}$ ​cm$^{−3}$. Angle-resolved photoemission spectroscopy reproduces the reported results and confirms a peculiar dispersion shape of the hole-like band at the bulk high-symmetry T point near the Fermi energy indicating band inversion. Magnetic hysteresis measurement at 2 ​K shows diamagnetic behaviour at high-H, whereas a ferromagnetic (FM)-like magnetic hysteresis loop is observed at low-H in between ​± ​4 ​kOe. The FM component disappears close to 3 ​K. Signature of spin-fluctuation in ρ(T), negative MR, and low-T FM component without 3d or 4f impurities in GaGeTe is attractive for the fundamental interest

Magnetic order and surface state gap in (Sb0.95Cr0.05)2Te3(Sb_{0.95}Cr_{0.05})_{2}Te_{3}

Magnetic transition element doping in topological insulators, which breaks the time-reversal symmetry, gives rise to the diverse range of exotic consequences, though proper understanding of the magnetic order has rarely been attempted by using any microscopic experiments. We report the occurrence of the magnetic order in $(Sb_{0.95}Cr_{0.05})_{2}Te_{3}$ using the muon spin relaxation studies. The asymmetry curve at low temperature ($T$) shows an evidence of a damped oscillation, providing a clue about the internal magnetic field ($H_{int}$), which follows $H_{int}$($T$)=$H_{int}$(0)[1−$T$/$T_C$]$^β$ with ordering temperature $T_C$≈6.1 K and critical exponent $β$≈0.22. The critical exponent is close to the two-dimensional XY-type interaction. The magnetization curves at low $T$ exhibit a ferromagnetic behavior at low field ($H$) and the de Haas–van Alphen (dHvA) effect at high $H$. The analysis of the dHvA oscillation proposes the charge carrier that acts like a massive Dirac fermion. The Berry phase, as obtained from the Landau-level fan diagram, suggests a surface state gap at the Dirac point. The complex electronic structure is discussed by correlating the magnetic order attributed to the Cr doping in $Sb_2Te_3$