Thermal Conductivity Of Silicon Carbide Research Articles

Molecular dynamics study of effects of point defects on thermal conductivity in cubic silicon carbide

Silicon carbide (SiC) has been widely used in nuclear technology due to its excellent properties. In the irradiation environment, the energetic incident particles can cause the atoms in the material to deviate from the position of the crystal lattice, thereby producing the vacancies, interstitial atoms, anti-site atoms and other point defects. These defects will change the thermal properties of the material and degrade the service performance of the material. Therefore, in this work the equilibrium molecular dynamics method (Green-Kubo method) is used to study the effect of point defects on the heat transfer properties of cubic SiC (<i>β</i>-SiC or 3<i>C</i>-SiC) with the help of the Tersoff-type potential. The point defects considered include Si interstitial atoms (Si<sub>I</sub>), Si vacancies (Si<sub>V</sub>), Si anti-site atoms (Si<sub>C</sub>), C interstitial atoms (C<sub>I</sub>), C vacancies (C<sub>V</sub>) and C anti-site atoms (C<sub>Si</sub>). It is found that the thermal conductivity (<i>λ</i>) decreases with the increase of the point defect concentration (<i>c</i>). The excessive thermal resistance (Δ<i>R</i> = <i>R</i><sub>defect </sub>– <i>R</i><sub>perfect</sub>, <i>R</i> = 1/<i>λ</i>, <i>R</i><sub>defect</sub> is the thermal resistance of the defective material, and <i>R</i><sub>perfect</sub> is the thermal resistivity of the material without defects) has a linear relation with the concentration of point defects in the considered range (0.2%–1.6%), and its slope is the thermal resistivity coefficient. It can be found that the thermal resistivity coefficient of vacancy and interstitial atoms are higher than that of anti-site atoms; the thermal resistivity coefficient of point defects at high temperature is higher than at low temperature; the thermal resistivity coefficient of Si vacancies and Si interstitial atoms are higher than that of C vacancies and C interstitial atoms. These results are helpful in predicting the thermal conductivity of silicon carbide under irradiation and controlling the thermal conductivity of silicon carbide.

The Effect of SiC Polytypes on the Heat Distribution Efficiency of a Phase Change Memory.

The amorphous to crystalline transition of germanium-antimony-tellurium (GST) using three types of silicon carbide’s structure as a heating element was investigated. Simulation was done using COMSOL Multiphysic 5.0 software with separate heater structure. Silicon carbide (SiC) has three types of structure; 3C-SiC, 4H-SiC and 6H-SiC. These structures have a different thermal conductivity. The temperature of GST and phase transition of GST can be obtained from the simulation. The temperature of GST when using 3C-SiC, 4H-SiC and 6H-SiC are 467K, 466K and 460K, respectively. The phase transition of GST from amorphous to crystalline state for three type of SiC’s structure can be determined in this simulation. Based on the result, the thermal conductivity of SiC can affecting the temperature of GST and changed of phase change memory (PCM).

Tuning the thermal conductivity of silicon carbide by twin boundary: a molecular dynamics study

Silicon carbide (SiC) is a semiconductor with excellent mechanical and physical properties. We study the thermal transport in SiC by using non-equilibrium molecular dynamics simulations. The work is focused on the effects of twin boundaries and temperature on the thermal conductivity of 3C-SiC. We find that compared to perfect SiC, twinned SiC has a markedly reduced thermal conductivity when the twin boundary spacing is less than 100 nm. The Si–Si twin boundary is more effective to phonon scattering than the C–C twin boundary. We also find that the phonon scattering effect of twin boundary decreases with increasing temperature. Our findings provide insights into the thermal management of SiC-based electronic devices and thermoelectric applications.

Effect of Biofield Treatment on Structural and Morphological Properties of Silicon Carbide

Silicon carbide (SiC) is a well-known ceramic due to its excellent spectral absorbance and thermo-mechanical properties. The wide band gap, high melting point and thermal conductivity of SiC is used in high temperature applications. The present study was undertaken to investigate the effect of biofield treatment on physical, atomic, and structural characteristics of SiC powder. The control and biofield treated SiC powder was analysed using X-ray diffraction (XRD), particle size analyzer, surface area analyzer, and Fourier transform infrared (FT-IR) spectroscopy techniques with respect to control. The XRD pattern revealed that crystallite size was significantly increased by 40% in treated SiC as compared to control. The biofield treatment has induced changes in lattice parameter, density and molecular weight of atoms in the SiC powder. Particle size was increased upto 2.4% and the surface area was significantly reduced by 71.16% in treated SiC as compared to control. The FT-IR results indicated that the stretching vibrations frequency of silicon-carbon bond in treated SiC (925 cm -1 ) was shifted towards lower frequency as compared to control (947 cm -1 ). These findings suggest that biofield treatment has substantially altered the physical and structural properties of SiC powder.

On a porous medium combustor for hydrogen flame stabilization and operation

In this study, the characteristics of hydrogen flame stabilization in porous medium combustor were investigated. The flame was observed in a quartz tube. The porous medium was oxide-bonded silicon carbide (OB-SiC) or aluminum oxide (Al2O3) with 60 PPI and 30 PPI pore size distributions. The results indicated that under a low equivalence operation, the flame would transform from surface combustion to interior combustion with an increased heating value. Under a high equivalence ratio, both interior combustion and flashback transition existed at the same time. The thermal conductivity of silicon carbide is higher than that of aluminum oxide. Thus, interior combustion region was more extensive under a low equivalence ratio operation with a high premixed gas velocity. Flashback was apparent for Al2O3 under high an equivalence ratio with low a premixed gas velocity. Consequently, hydrogen flame stability could be controlled by the pore size distribution and thermal conductivity of the porous media, input heating value and input equivalence ratio.

Microstructure and Thermal Conductivity of Silicon Carbide with Yttria and Scandia

A fully dense SiC ceramic with high thermal conductivity was obtained by conventional hot pressing, with 1 vol% Y2O3–Sc2O3 additives. The ceramic had a bimodal microstructure consisting of large and small equiaxed SiC grains. Observation with high‐resolution transmission electron microscopy (HRTEM) showed two kinds of homophase (SiC/SiC) boundaries, that is crystallized and clean boundaries, and a fully crystallized junction phase. The thermal conductivity of the SiC ceramic was 234 W (m·K)−1 at room temperature. The high thermal conductivity was attributed to a clean SiC lattice and good contiguity between SiC grains.

Design of a high temperature cavity receiver for residential scale concentrated solar power

A scalable and modular solar thermal dish-Brayton system is proposed in response to growing demand for renewable energy and distributed power generation. The operating temperature of materials limits the conversion efficiency of existing Concentrated Solar Power (CSP) systems, rendering small-scale systems for residential use too expensive to be marketed. This work proposes a low cost, high efficiency solar receiver as the core of a dish-Brayton CSP system with the capability to achieve much higher operating temperatures than existing receivers. The proposed receiver is fabricated from silicon carbide for its high absorptivity and thermal conductivity. The manufacturing process consists of a simple casting and sintering procedure called co-firing. A heat exchanger is integrated into the walls of the receiver, taking advantage of the high thermal conductivity of silicon carbide. The entire solar energy receiver is designed to heat air up to 1500 K, which is found to be the optimal operating temperature for the proposed output and practical component selection. This operating temperature improves energy conversion efficiency over concentrated solar power generation based on 1270 K by 20%. The optimization of the operating temperature for residential scale, along with experimental test results on a scaled device, is presented.

A miniaturized microtiter plate protocol for the determination of in selenized yeast via enzymatic hydrolysis of protein-bound.

This paper describes a simple/low volume enzymatic extraction method for selenomethionine (SeMet) determination in selenized yeast samples. In contrast to traditional methods which generally utilize large sample volumes consuming significant amounts of costly enzymes, the modified protocol employs a microtiter plate format allowing a reduction of the required sample volumes to 1 mL per extract. The extraction is performed in a parallel (5 × 4 = 20 position microtiter plate) reaction platform made out of sintered silicon carbide, fitted with standard disposable glass HPLC/GC vials. Due to the high thermal conductivity of silicon carbide, this set-up can be placed on a standard hotplate to accurately maintain the desired extraction conditions (37 °C, 20 h) for all positions of the microtiter plate. Hydrolysis of selenium-enriched yeast with a combination of protease XIV and lipase VII (ratio 2 : 1, w/w) using these low-volume conditions provided identical results to the more traditional high-volume method. The amount of SeMet was determined by HPLC/ICPMS and confirmed a high recovery rate for SeMet (93 ± 2%, n = 3) for the certified reference material SELM-1.

Characterization, Modeling and Design Parameters Identification of Silicon Carbide Junction Field Effect Transistor for Temperature Sensor Applications

Sensor technology is moving towards wide-band-gap semiconductors providing high temperature capable devices. Indeed, the higher thermal conductivity of silicon carbide, (three times more than silicon), permits better heat dissipation and allows better cooling and temperature management. Though many temperature sensors have already been published, little endeavours have been invested in the study of silicon carbide junction field effect devices (SiC-JFET) as a temperature sensor. SiC-JFETs devices are now mature enough and it is close to be commercialized. The use of its specific properties versus temperatures is the major focus of this paper. The SiC-JFETs output current-voltage characteristics are characterized at different temperatures. The saturation current and its on-resistance versus temperature are successfully extracted. It is demonstrated that these parameters are proportional to the absolute temperature. A physics-based model is also presented. Relationships between on-resistance and saturation current versus temperature are introduced. A comparative study between experimental data and simulation results is conducted. Important to note, the proposed model and the experimental results reflect a successful agreement as far as a temperature sensor is concerned.

Enhanced Thermal Conductivity for LWR Fuel

The thermal conductivity of the fuel in today’s light water reactors, uranium dioxide (UO2), can be improved by incorporating a uniformly distributed heat-conducting network of a higher-conductivity material: silicon carbide (SiC). The higher thermal conductivity of SiC along with its other prominent reactor-grade properties makes it a potential material to address some of the related issues when used in UO2 (97% theoretical density). This ongoing research, in collaboration with the University of Florida, aims to investigate the feasibility and development of a formal methodology for producing the resultant composite oxide fuel. Calculations of the effective thermal conductivity (ETC) of the new fuel as a function of percent SiC for certain percentages and as a function of temperature are presented as a preliminary approach. The ETCs are obtained at different temperatures from 600 to 1600 K. The corresponding polynomial equations for the temperature-dependent thermal conductivities are given based on the simulation results. The heat transfer mechanism in this fuel is explained using a finite volume approach and validated against existing empirical models. FLUENT 6.1.22 was used for the thermal conductivity calculations and to estimate the reduction in centerline temperatures achievable within such a fuel rod. Later, the computer codes COMBINE-PC and VENTURE-PC were employed to estimate the fuel enrichment required to maintain the same burnup levels corresponding to a volume percent addition of SiC.

Parallel microwave chemistry in silicon carbide reactor platforms: an in-depth investigation into heating characteristics

The heating behavior of silicon carbide reaction platforms under 2.45 GHz microwave irradiation was investigated with the aid of online thermoimaging cameras and multiple-channel fiber-optic probe temperature sensors placed inside the wells/vials of the silicon carbide microtiter plates. Microwave irradiation leads to a rapid and homogeneous heating of the entire plate, with minimal deviations in the temperature recorded at different positions of the plate or inside the wells. In temperature-controlled experiments using dedicated multimode reactors, solvents with different microwave absorption characteristics can be heated in parallel in individual wells/vials of the silicon carbide plate reaching the same set temperature. Due to the large heat capacity and high thermal conductivity of silicon carbide, the plates are able to moderate any field inhomogeneities inside a microwave cavity. Although the heating of the plates can be performed extremely efficiently inside a microwave reactor, heating and synthetic applications can alternatively be carried out by applying conventional conductive heating of the silicon carbide plates on a standard hotplate. Due to the slower heating of the silicon carbide material under these conditions, somewhat longer reaction times will be required.

04/01119 Study on the mechanical properties and thermal conductivity of silicon carbide-, zirconia- and magnesia aluminate-based simulated inert matrix nuclear fuel materials after cyclic thermal shock: Lee, Y. W. et al. Journal of Nuclear Materials, 2003, 319, (1), 15–23

04/01119 Study on the mechanical properties and thermal conductivity of silicon carbide-, zirconia- and magnesia aluminate-based simulated inert matrix nuclear fuel materials after cyclic thermal shock: Lee, Y. W. et al. Journal of Nuclear Materials, 2003, 319, (1), 15–23

Thermal conductivity of silicon carbide densified with rare-earth oxide additives

In order to fabricate SiC ceramics of high thermal conductivity, a submicrometer-size β–SiC powder doped with various amounts of combinations of Y 2O 3 and La 2O 3 as sintering additives was hot-pressed at 2000 °C under 40 MPa for 2 h in Ar, and some hot-pressed specimens were subsequently annealed at 1900 °C for 4 h in Ar. The phase compositions and microstructures of the hot-pressed and the annealed SiC ceramics were characterized, and their thermal conductivities were measured by a laser-flash technique. By adding 1 mol% or more additives, full densification was achieved and the materials had thermal conductivities in excess of 166 W/(m K). The thermal conductivities further improved to over 200 W/(m K) after annealing. An explanation on the correlation between thermal conductivity, phase composition, and microstructure was proposed.

Study on the mechanical properties and thermal conductivity of silicon carbide-, zirconia- and magnesia aluminate-based simulated inert matrix nuclear fuel materials after cyclic thermal shock

Modification of thermo-mechanical properties of simulated (SiC) silicon carbide-, (ZrO 2) zirconia- and (MgAl 2O 4) spinel-based inert matrix nuclear fuels after cyclic thermal shock was analyzed in terms of Vickers hardness ( H V), fracture toughness ( K IC) and thermal conductivity. Three different simulated specimens were used for the experiment; a solid solution of yttria-stabilized zirconia and ceria (composition: Er 0.07Y 0.10Ce 0.15Zr 0.68O 1.915, 92.0% TD, specimen hereafter called Ce–ZrO 2), a CeO 2-dispersed Mg-spinel (composition: 15wt%CeO 2–MgAl 2O 4, 93.7% TD, specimen hereafter called Ce-spinel) and a CeO 2-dispersed silicon carbide (composition: 80.8 wt% SiC, 6.9 wt% Al 2O 3, 5.1 wt% Y 2O 3 and 5.0 wt% CeO 2, specimen hereafter called Ce–SiC), CeO 2 being surrogate materials for PuO 2. Cyclic thermal shock experiment and thermal conductivity measurements were simultaneously carried out by heating disc-shaped specimens up to maximum temperature ranging from 1073 to 1673 K and then cooling down to 343 K with Ar gas during 20–25 min. The Vickers hardness of the three different thermally shocked specimens showed nearly constant values with increasing number of cycles, except for the specimen heated at 1673 K. The K IC values of the corresponding specimens increased with the increasing number of cyclic thermal shock at 1673 K. For Ce–ZrO 2 heated at 1673 K, however, it decreases considerably due to the combined effects of formation of second phase and modification of the matrix composition thereby. The calculated thermal conductivity of Ce-spinel decreases as the number of cycles in thermal shock increases in the temperature range between 1073 and 1673 K, and Ce–SiC slightly decreased with the number of cycles in cyclic thermal shock and the variations in thermal conductivity are almost the same for the temperature increases of 1073 and 1373 K, whereas, in Ce–ZrO 2, it remains nearly constant.

Analysis of the temperature dependent thermal conductivity of silicon carbide for high temperature applications

The temperature dependent thermal conductivity of silicon carbide has been calculated taking into account the various phonon scattering mechanisms. The results compared very well with available experimental data. The inclusion of four-phonon processes is shown to be necessary for obtaining a good match. Several important phonon scattering parameters have been extracted in this study. Dislocations are shown to have a strong effect at 300 K, but not as much at the higher temperatures.

Microwave and millimeter-wave power generation in silicon carbide avalanche devices

Silicon carbide (SiC), due to its thermal and electronic properties, has long been considered an excellent device material for microwave and millimeter-wave power generation. Numerical simulations were performed to study the typical power generating capabilities of SiC impact avalanche transit-time (IMPATT) diodes utilizing the recent experimental data available. Operating characteristics of double-drift IMPATT devices at 10, 35, 60 and 94 GHz are compared. Both pulsed mode and continuous-wave (cw) mode operation are studied. Finally, a comparison among SiC, Si, and GaAs double-drift IMPATT devices is made at various frequencies. It is shown that, for the pulsed mode of operation, SiC double-drift IMPATT devices can produce significantly higher powers than Si and GaAs devices at comparable frequencies. In the cw mode of operation, SiC devices can produce significantly more power than GaAs devices at all frequencies. However, a comparison at 94 GHz indicates that SiC IMPATT diodes in the cw mode of operation produce power levels comparable to Si IMPATT devices. At lower frequencies the performance of SiC diodes operating in the cw mode is expected to be better than the performance of Si devices due to the better thermal conductivity of SiC.

Thermal conductivity of silicon carbide at high temperatures

A study was made of the thermal conductivity of silicon carbide, produced by reactive sintering, over the range 200–1650°C. It is shown that the thermal conductivity of dense specimens increases with rise in temperature. The increase of thermal conductivity is caused by additional heat transfer due to radiation and to excitons.