Nm For SiC Research Articles

Comparative Study of Tensile Properties of Hybrid AA6061/SIC/Carbonized Coconut Shell Micro and Nano Composites

This study synthesized a hybrid aluminium 6061 matrix composite with particulates of silicon carbide, SiCp and carbonized coconut shell (CCSP as reinforcements), and determined the effect of combining SiCp and CCSp reinforcements of different sizes and weight fractions on the strength properties and microstructure of the developed composite. The hybrid aluminium matrix composites were developed using the stir casting method. Several samples of the composites consisting of AA6061 alloy with 3, 6, 9, 12 and 15% by wt. each of CCSp and SiCp with average particle sizes of 38μm and 42.3nm for SiC, and 63μm and 50.01nm for CCSp were produced and characterized for strength. The microstructures of the developed composite materials revealed uniform distribution of reinforcement particles in the base matrix and excellent bonding between the base matrix and reinforcements after casting. The results obtained showed that addition of CCSp and SiCp reinforcement to the alloy increased the tensile strength and hardness. Also, a mathematical model was proposed for predictive tensile strength of nano-composite and validated by comparison with results of the physical experiment and those of other authors. The proposed model is in excellent agreement with experimental data. The nano-particulates reinforced composite presented maximum improvement in ultimate tensile strength value (53.4% and 8.5% of that for the unreinforced matrix and micro-composite respectively) at reinforcement level of 15wt.% nSiC/nCCS.

Power and energy performance of porous silicon carbide anode in lithium-metal battery

Abstract Recently, silicon-based next-generation lithium batteries possessed the main core of storage devices to store reversibly electrical energy. For this issue, the interesting silicon and silicon carbide anodes have been synthesized via magnesiothermic reduction. The result of the X-ray diffraction confirms a crystallinity of 2 nm for SiC and 70 nm for silicon. The porous structure is characterized by FESEM and TEM analysis. The power and energy performance of silicon show the 420 W Kg−1 and 200 Wh Kg−1 in the first cycle at 125 mA g−1. While power and energy performance for SiC anode increase to 400 W Kg−1 and 350 Wh Kg−1 in the first cycle at 125 mA g−1. Moreover, at the highest current rate of 1.25 A g−1 specific power and energy for SiC anode become more than 3000 W Kg−1 and 130 Wh Kg−1 after 130th cycles. Furthermore, the electrolyte resistance and charge transfer resistance for SiC anode is measured to be 24.5 and 250 Ω. Nevertheless, the lithiation processes are controlled through the diffusion of Li+ ions because of a low diffusion coefficient of 6.54 × 10 - 19 cm2 s−1.

Fractal analysis of collision cascades in pulsed-ion-beam-irradiated solids

The buildup of radiation damage in ion-irradiated crystals often depends on the spatial distribution of atomic displacements within collision cascades. Although collision cascades have previously been described as fractals, the correlation of their fractal parameters with experimental observations of radiation damage buildup remains elusive. Here, we use a pulsed-ion-beam method to study defect interaction dynamics in 3C-SiC irradiated at 100 °C with ions of different masses. These data, together with results of previous studies of SiC and Si, are analyzed with a model of radiation damage formation which accounts for the fractal nature of collision cascades. Our emphasis is on the extraction of the effective defect diffusion length from pulsed beam measurements. Results show that, for both Si and SiC, collision cascades are mass fractals with fractal dimensions in the range of ~1–2, depending on ion mass, energy, and the depth from the sample surface. Within our fractal model, the effective defect diffusion length is ~10 nm for SiC and ~20 nm for Si, and it decreases with increasing cascade density. These results demonstrate a general method by which the fractal nature of collision cascades can be used to explain experimental observations and predict material’s response to radiation.

Effect of Mg/B2O3 molar ratio and furnace temperature on the phase evaluation and morphology of SiC–B4C nanocomposite prepared by MASHS method

In this study, SiC–B4C nanocomposite has been synthesized in situ successfully by Mechanical activated combustion synthesis method (MASHS). Initially Si, C, B2O3 and Mg powders as raw materials were weighed according to different molar ratio of Mg to B2O3. In next step theses materials were milled in a planetary mill under Ar atmosphere. The synthesis step was performed in a tube furnace equipped with controlled atmosphere system. The different furnace temperature was investigated on the phase synthesis and morphology of the products. The specimens in the various steps were studied by XRD analysis for evaluation of the phase compositions and calculation of the average crystallite size of them. The morphology of synthesized products was investigated by scanning and transmission electron microscopes (SEM&TEM). The final product contains main phases MgO, B4C and SiC. Also, In this sample byproducts were characterized such as Mg3B2O6, Mg2B2O5 and remaining carbon. XRD pattern of synthesized sample showed the considerable effect of increasing Mg to B2O3 molar ratio on reducing the amount of Mg3B2O6, Mg2B2O5 and remaining carbon. SiC–B4C composite was synthesized with more homogenous morphology by reducing the furnace temperature from 1000 to 900 °C, but reduction of temperature up to 800 °C give rise to uncompleted reaction whereas some unreacted Si remains. Average crystallite sizes of optimal sample were calculated 10.5 and 8 nm for SiC and B4C respectively. These values are consisted of the TEM results somehow while grain size was less than 70 nm. Also SEM observation showed fine grains with sizes falling in the nanometer range.

Tailoring the Relative Si3N4 and SiC Contents in Si3N4/SiC Nanopowders through Carbothermic Reduction and Nitridation of Silica Fume

This study demonstrates the synthesis of nanostructured Si3N4/SiC composite powders from silica fume, for the first time. The processing approach to convert the waste silica fume to advanced nanocomposites is based on the integrated mechanical and thermal activation (IMTA) process. The synthesized nanostructured Si3N4/SiC powders have crystallite sizes as small as 17 nm for SiC and 42 nm for Si3N4. It has been shown that the carbothermic reduction and nitridation temperature, as well as the graphite concentration in the starting SiO2 + C mixture are the important parameters to obtain Si3N4 and SiC nanopowders and control their crystal sizes. The synthesis conditions to tailor the relative contents of α‐Si3N4 and α‐SiC (changing from as high as 49 vol.% to as low as 21 vol.% α‐SiC) in the final powder mixture have been investigated, and the mechanisms responsible for the observed relationship between processing conditions and the characteristics of the final powder have been identified.

Fabrication and mechanical properties of silicon carbide–silicon nitride nanocomposites

A powder mixture of ultrafine β –SiC–35 wt% α –Si3N4 containing 6 wt% Al2O3 and 4 wt% Y2O3 as sintering additives were liquid–phase sintered at 1800°C for 30 min by hot–pressing. The hot–pressed composites were subsequently annealed at 1920°C under nitrogen–gas–pressure to enhance grain growth. The average grain–size of the sintered bodies were ranged from 96 to 251 nm for SiC and from 202 to 407 nm for Si3N4, which were much finer than those of ordinary sintered SiC–Si3N4 composites. Both strength and fracture toughness of fine–grained SiC–Si3N4 composites increased with increasing grain size. Such results suggested that a small amount of grain growth in the fine–grained region (≤250 nm for SiC and ≤400 nm for Si3N4) was beneficial for mechanical properties of the composites. The room–temperature flexural strength and fracture toughness of the 8–h annealed composites were 698 MPa and 4.7 MPa · m1/2, respectively.

脆性材料の高温における理想強度

Ideal Strength, aid as a function of temperature was found to be approximated by the following formula:σid≥σid=∫TxT3αE/(1-2μ)dT=3αE(Tx-T)/(1-2μ)where Tx stands for the minimum value of transformation points (melting, sublimation, solid to solid, and brittle to ductile), and α, E, μ respectively for the coefficient of linear thermal expansion, Young's modulus and Poisson's ratio. The formula's error is less than 20%, expressed in the term of error compared with whisker's strength at RT. It was also compared with literature data on high temperature strength of sapphire monofilament, which proved the compatibility of the formula.σid is estimated as 9 GPa for SiC and 3.5 GPa for Si3N4 at 1, 400°C, 1 GPa at 2, 200°C for SiC, and 1 GPa at 1, 700°C for Si3N4. These values prove the usefulness of the materials as high temperature gas turbine components. The formula tells also us that the ideal strength can be well approximated by a straight line regardless of material.The Young's modulus plotted against temperature can be converted to Young's modulus plotted against strain, e, by using e=3∫α/(1-2μ)dT, which can not be given directly from experimental measurement due to the occurrence of fracture in the material. The tangent of the curve for MgO was proved to agree well with the value given by a classical solid state theory. The range of binding force acting across material surface was estimated by using the ideal strength, giving 0.5-1 nm for SiC and Si3N4 and 0.1-0.5 nm for MgO and Al2O3. The allowable atomic distance difference between neighboring layerd material in coherently multilayered films, which has no defect was also estimated to be less than 3% from the ideal fracture strain.