Effect of Initial Alpha-SiC Content on Thermal Conductivity of Silicon Carbide Ceramics

2014 ◽  
Vol 616 ◽  
pp. 23-26 ◽  
Author(s):  
Kwang Young Lim ◽  
Tae Young Cho ◽  
Young Wook Kim ◽  
Seung Jae Lee
Keyword(s):  
Thermal Conductivity ◽  
Grain Size ◽  
Room Temperature ◽  
Phase Content ◽  
Sic Ceramics ◽  
Α Phase ◽  
Average Grain Size ◽  
Carbide Ceramics ◽  
Equiaxed Grains ◽  
Silicon Carbide Ceramics

By using α-and/or β-SiC powders, the effects of initial α-phase content on the microstructure and thermal properties of the SiC ceramics sintered with Y2O3 and Sc2O3 were investigated. When α-SiC powder was used, the microstructure consisted of large equiaxed grains and small equiaxed grains. The average grain size decreased with increasing α-SiC content in the starting composition. The thermal conductivity decreased with increasing α-SiC content in the starting composition. Such results suggest that the grain growth of SiC ceramics is beneficial in increasing the thermal conductivity of liquid-phase sintered SiC ceramics. The thermal conductivity of SiC ceramics processed from a 90% β-SiC-10% α-SiC powder mixture was 159 W/m∙K at room temperature.

High thermal conductivity of pure dense SiC ceramics prepared via HTPVT

2019 ◽  
Vol 12 (03) ◽  
pp. 1950032 ◽  
Author(s):  
Yuchen Deng ◽  
Yaming Zhang ◽  
Nanlong Zhang ◽  
Qiang Zhi ◽  
Bo Wang ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Silicon Carbide ◽  
Grain Size ◽  
Phase Composition ◽  
Room Temperature ◽  
Vapor Transport ◽  
Physical Vapor Transport ◽  
Growth Substrate ◽  
Sic Ceramics ◽  
Evolution Of Microstructure

Pure dense silicon carbide (SiC) ceramics were obtained via the high-temperature physical vapor transport (HTPVT) method using graphite paper as the growth substrate. The phase composition, the evolution of microstructure, the thermal diffusivity and thermal conductivity at RT to 200∘C were investigated. The obtained samples had a relative density of higher than 98.7% and a large grain size of 1[Formula: see text]mm, the samples also had a room-temperature thermal conductivity of [Formula: see text] and with the temperature increased to 200∘C, the thermal conductivity still maintained at [Formula: see text].

Influence of Additives on Mechanical Properties in Liquid-Phase Sintered Silicon Carbide Ceramics

2008 ◽  
Vol 403 ◽  
pp. 185-188 ◽  
Author(s):  
Young Wook Kim ◽  
Toshiyuki Nishimura ◽  
Mamoru Mitomo
Keyword(s):  
Mechanical Properties ◽  
Liquid Phase ◽  
Room Temperature ◽  
Trade Off ◽  
Molar Ratios ◽  
Sic Ceramics ◽  
Cationic Radius ◽  
Carbide Ceramics ◽  
Silicon Carbide Ceramics ◽  
Sintered Silicon

The effect of sintering additives comprising AlN and RE2O3 (RE=Lu, Yb, Er and Y) in 2:3 and 3:2 molar ratios on mechanical properties of liquid-phase-sintered (LPS) and subsequently annealed SiC ceramics was investigated. The toughness vs cationic radius curve had a maximum in both 2:3 and 3:2 molar ratios; Yb-doped specimens showed maximal toughness of 5.8 and 6.6 MPa..m1/2 in 2:3 and 3:2 molar ratios, respectively. There was no correlation between room temperature (RT) strength and cationic radius. In contrast, the high temperature (HT) strength vs cationic radius curve had a minimum in both 2:3 and 3:2 molar ratios; Yb-doped specimens showed minimal strength of 520 MPa and 550 MPa in 2:3 and 3:2 molar ratios, respectively. The present results suggest that there is a trade-off in improving both RT toughness and HT strength in LPS-SiC ceramics.

Silicon carbide ceramics prepared by pulse electric current sintering of β–SiC and α–SiC powders with oxide and nonoxide additives

1999 ◽  
Vol 14 (8) ◽  
pp. 3363-3369 ◽  
Author(s):  
You Zhou ◽  
Kiyoshi Hirao ◽  
Motohiro Toriyama ◽  
Hidehiko Tanaka
Keyword(s):  
Electric Current ◽  
Weight Percent ◽  
Total Processing Time ◽  
Pulse Electric Current ◽  
Sic Ceramics ◽  
Α Phase ◽  
Interfacial Bonding Strength ◽  
Carbide Ceramics ◽  
Pulse Electric ◽  
Silicon Carbide Ceramics

Using a pulse electric current sintering (PECS) method, β–SiC and α–SiC powders doped with a few weight percent of Al2O3–Y2O3oxide or Al4C3–B4C–C nonoxide additives were rapidly densified to high densities (95.2–99.7%) within less than 30 min of total processing time. When Al2O3–Y2O3additive was used, both ceramics resulting from β–SiC and α–SiC had fine, equiaxed microstructures. In contrast, when Al4C3–B4C–C additive was used, the ceramic resulting from α–SiC had a coarse, equiaxed microstructure, whereas the ceramic resulting from β–SiC was composed of large elongated grains whose formation was accompanied by the β →?α phase transformation of SiC. Compared with the Al2O3–Y2O3-doped SiC ceramics, the Al4C3–B4C–C-doped SiC ceramics had higher densities, lower fracture toughness, and higher hardness. The fracture mode of the oxide-doped SiC was mainly intergranular, whereas the nonoxide-doped SiC exhibited almost complete intragranular fracture that was attributed to the higher interfacial bonding strength.

scholarly journals Effects of initial α-phase content on the electrical, thermal, and mechanical properties of pressureless solid-state sintered SiC ceramics

2021 ◽  
Author(s):  
Rohit MALIK ◽  
Young-Wook Kim
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Solid State ◽  
Impurity Content ◽  
Coarse Grained ◽  
Bandgap Energy ◽  
Phase Content ◽  
Thermal And Mechanical Properties ◽  
Sic Ceramics ◽  
Α Phase

Abstract αand β-SiC starting powders of similar particle sizes were used to investigate the effect of initial α-phase content on the electrical, thermal, and mechanical properties of pressureless solid-state sintered (PSS) SiC ceramics with B4C and C. For β-SiC starting powders, a coarse-grained microstructure with elongated platelet grains formed by the 3C to 6H to 4H-SiC phase transformation was obtained. In contrast, α-SiC powders exhibited a fine-grained microstructure with platelet grains. The electrical resistivity decreased by an order of magnitude with increasing initial α-phase content presumably due to (1) an increased 6H-SiC content causing a decrease in bandgap energy and (2) the low soluble impurity content (Fe and V) of the α-SiC powders. The thermal conductivity increased by approximately 32% with increasing initial α-phase content due to (1) an increased 6H-SiC content, which has a higher intrinsic thermal conductivity compared to 4H and (2) the low impurity content of the α-SiC powders. The flexural strength increased by approximately 16% with increasing initial α-phase content due to a decreased flaw size with decreasing grain size. However, the fracture toughness and hardness were insensitive to the change in initial α-phase content.

scholarly journals Preparation and Characterization of Pure SiC Ceramics by HTPVT Induced by Seeding with SiC Nanoarrays

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6317
Author(s):  
Yu-Chen Deng ◽  
Nan-Long Zhang ◽  
Qiang Zhi ◽  
Bo Wang ◽  
Jian-Feng Yang
Keyword(s):  
Grain Size ◽  
Room Temperature ◽  
Chemical Vapor ◽  
Second Step ◽  
Anodic Aluminum ◽  
Sic Ceramics ◽  
Average Grain Size ◽  
Amorphous Sic ◽  
Sic Films

Dense SiC ceramics were fabricated by high-temperature physical vapor transport (HTPVT) growth process using SiC nanoarrays as the crystal seeds, which was obtained by vacuum heat treatment of amorphous SiC films prepared by plasma-enhanced chemical vapor deposition (PECVD) with a porous anodic aluminum oxide (AAO) template. In the HTPVT process, two-step holding was adopted, and the temperature at the first step was controlled at 2100 and 2150 °C to avoid SiC nanoarrays evaporation, and the grain size of SiC crystal increased with the increase in temperature and decrease in the pressure of Ar. The temperature of the second step was 2300 °C, and rapid SiC grain growth and gradual densification were achieved. The prepared SiC ceramics exhibited a relative density of more than 99%, an average grain size of about 100 μm, a preferred orientation along the (0 0 0 6) plane, a Vickers hardness of about 29 GPa, a flexural strength of about 360 MPa, and thermal conductivity at room temperature of more than 200 W·m−1·K−1.

Synthesis and Thermal Properties of Nanoscale Skutterudite via Cross-Coprecipitation

2007 ◽  
Vol 336-338 ◽  
pp. 831-833
Author(s):  
Ying Chu ◽  
Xin Feng Tang ◽  
Ling Wan ◽  
Qing Jie Zhang
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Grain Size ◽  
Room Temperature ◽  
Single Phase ◽  
Antimony Oxide ◽  
Hydrogen Atmosphere ◽  
Plasma Sintering ◽  
Average Grain Size ◽  
Spark Plasma

CoSb3 with nanoscale was synthesized by Cross-coprecipitation. A precursor consisting of antimony oxide and cobalt hydrate was prepared by the reaction of CoCl2, SbCl3 and both precipitators at room temperature. The precursor was reduced in thermal treatment under hydrogen atmosphere whereby the CoSb3 was thus obtained. The parameters especially reducing temperature and atmosphere (content of H2) influence the constituent phases and particle size of product significantly. The single phase CoSb3 with the average grain size of 60~70 nm was obtained after reduced at 723 K for 2 h with pure H2. Nanoscale CoSb3 powder was used as starting materials, and bulk CoSb3 compound was prepared by spark plasma sintering (SPS). The effect of grains size on thermal conductivity was investigated.

scholarly journals Experimental and Numerical Investigation of the ECAP Processed Copper: Microstructural Evolution, Crystallographic Texture and Hardness Homogeneity

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 607
Author(s):  
A. I. Alateyah ◽  
Mohamed M. Z. Ahmed ◽  
Yasser Zedan ◽  
H. Abd El-Hafez ◽  
Majed O. Alawad ◽  
...  
Keyword(s):  
Grain Size ◽  
Equal Channel Angular Pressing ◽  
Cross Section ◽  
Room Temperature ◽  
Pure Copper ◽  
High Density ◽  
Ecap Processing ◽  
Heterogeneous Distribution ◽  
Angular Pressing ◽  
Average Grain Size

The current study presents a detailed investigation for the equal channel angular pressing of pure copper through two regimes. The first was equal channel angular pressing (ECAP) processing at room temperature and the second was ECAP processing at 200 °C for up to 4-passes of route Bc. The grain structure and texture was investigated using electron back scattering diffraction (EBSD) across the whole sample cross-section and also the hardness and the tensile properties. The microstructure obtained after 1-pass at room temperature revealed finer equiaxed grains of about 3.89 µm down to submicrons with a high density of twin compared to the starting material. Additionally, a notable increase in the low angle grain boundaries (LAGBs) density was observed. This microstructure was found to be homogenous through the sample cross section. Further straining up to 2-passes showed a significant reduction of the average grain size to 2.97 µm with observable heterogeneous distribution of grains size. On the other hand, increasing the strain up to 4-passes enhanced the homogeneity of grain size distribution. The texture after 4-passes resembled the simple shear texture with about 7 times random. Conducting the ECAP processing at 200 °C resulted in a severely deformed microstructure with the highest fraction of submicron grains and high density of substructures was also observed. ECAP processing through 4-passes at room temperature experienced a significant increase in both hardness and tensile strength up to 180% and 124%, respectively.

ATOMIC FORCE MICROSCOPY AND XRD ANALYSIS OF SILVER FILMS DEPOSITED BY THERMAL EVAPORATION

2006 ◽  
Vol 20 (02) ◽  
pp. 217-231 ◽  
Author(s):  
MUHAMMAD MAQBOOL ◽  
TAHIRZEB KHAN
Keyword(s):  
Atomic Force Microscopy ◽  
Grain Size ◽  
Surface Characterization ◽  
Room Temperature ◽  
Thermal Evaporation ◽  
Xrd Analysis ◽  
Force Microscopy ◽  
Atomic Force ◽  
Average Grain Size ◽  
20 Nm

Thin films of pure silver were deposited on glass substrate by thermal evaporation process at room temperature. Surface characterization of the films was performed using X-ray diffraction (XRD) and atomic force microscopy (AFM). Thickness of the films varied between 20 nm and 72.8 nm. XRD analysis provided a sharp peak at 38.75° from silver. These results indicated that the films deposited on glass substrates at room temperature are crystalline. Three-dimension and top view pictures of the films were obtained by AFM to study the grain size and its dependency on various factors. Average grain size increased with the thickness of the deposited films. A minimum grain size of 8 nm was obtained for 20 nm thick films, reaching 41.9 nm when the film size reaches 60 nm. Grain size was calculated from the information provided by the XRD spectrum and averaging method. We could not find any sequential variation in the grain size with the growth rate.

Thermal Diffusivity and Conductivity of La0.7Ca0.3-xSrxMnO3 (x=0 to 0.10)

2012 ◽  
Vol 501 ◽  
pp. 319-323
Author(s):  
Hasan A. Alwi ◽  
Lay S. Ewe ◽  
Zahari Ibrahim ◽  
Noor B. Ibrahim ◽  
Roslan Abd-Shukor
Keyword(s):  
Thermal Conductivity ◽  
Electrical Conductivity ◽  
Grain Size ◽  
Transition Temperature ◽  
Thermal Diffusivity ◽  
Electrical Properties ◽  
Room Temperature ◽  
Electronic Contribution ◽  
Insulator Metal Transition ◽  
Thermal And Electrical Properties

We report the room temperature thermal conductivity κ and thermal diffusivity α of polycrystalline La0.7Ca0.3-xSrxMnO3 for x = 0 to 0.1. The samples were prepared by heating at 1220 and 1320oC. The insulator-metal transition temperature, TIM and thermal diffusivity increased with Sr content. Phonon was the dominant contributor to thermal conductivity and the electronic contribution was less than 1%. Enhancement of electrical conductivity σ and thermal diffusivity for x ≥ 0.08 was observed in both series of samples. The grain size of the samples (28 to 46 µm) does not show any affect on the thermal and electrical properties.

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