Defects Analysis of Large Size Silicon Nitride Balls Sintered by Gas Pressure Sintering

2010 ◽  
Vol 434-435 ◽  
pp. 61-63
Author(s):  
Feng Sun ◽  
Wei Ru Zhang ◽  
Ting Yan Tian ◽  
Xiang Hong Teng ◽  
Min Chao Ru ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Silicon Nitride ◽  
Temperature Gradient ◽  
Raw Materials ◽  
Gas Pressure ◽  
Sintering Process ◽  
The Core ◽  
Large Size ◽  
Defects Analysis ◽  
Gas Pressure Sintering

The sections of Φ55mm silicon nitride balls, sintered by gas pressure sintering were analyzed. The results show that temperature gradient during of the sintering process from the surface to the core of large size silicon nitride balls occurred because of the lower thermal conductivity of Si3N4. With the diameter increasing, the temperature gradient was more visible. The impurity of raw materials, such as free Si, free C and other metal oxides, like the SiO2 could produce gas, such as SiO, CO and so on, during the sintering process through the thermodynamic analysis. The producing gas exhausted more difficultly with the diameter of silicon nitride balls increasing. These factors were the most important to the defects of large size silicon nitride balls during the sintering process and made cracks and crescent on the surface of balls.

Influence of YAG-Based Composite Sintering Aids on Gas Pressure Sintered BNw/Si3N4 Composites

2015 ◽  
Vol 655 ◽  
pp. 53-57
Author(s):  
Xian Li Wang ◽  
Hong Yu Gong ◽  
Yu Jun Zhang ◽  
Song Wei Che
Keyword(s):  
Dielectric Properties ◽  
Bending Strength ◽  
Mechanical Performance ◽  
Raw Materials ◽  
Gas Pressure ◽  
Apparent Porosity ◽  
Sintering Process ◽  
Sintering Aids ◽  
Liquid Phases ◽  
Gas Pressure Sintering

BNw/Si3N4composites were fabricated by gas pressure sintering process using α-Si3N4powder and self-made BN whisker as principal raw materials. The effects of different sintering additives such as YAG, MgO+YAG and RE2O3+YAG(RE=La, Sm, Dy) on the apparent porosity, microstructure, phase composition, mechanical performance and dielectric properties of the composites were analysed. The results revealed that composite sintering aids at certain ratio (MgO/RE2O3:YAG=1:5) was more conducive to ceramic densification than single YAG additive. The BNw/Si3N4sintered with La2O3+YAG acquired the highest density and the maximum bending strength (272.46 MPa) and fracture toughness(4.9 MPa·m1/2). It was speculated that ceramic densification process was related to formation of different eutectic liquid phases with different viscosity. Additionally, when the apparent porosity of BNw/Si3N4composites was 20% or less, dielectric properties of the material were mainly influenced by the porosity and the value of the permittivity and dielectric loss decreased with the increase of ceramic porosity.

Thermal Conductivity of Si₃N₄ Ceramics Fabricated From Carbothermal-reduction-derived Powder

2021 ◽  
Author(s):  
Yuelong Wang ◽  
Xingyu Li ◽  
Haoyang Wu ◽  
Baorui Jia ◽  
Deyin Zhang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Fracture Toughness ◽  
Grain Size ◽  
Flexural Strength ◽  
Grain Boundaries ◽  
Carbothermal Reduction ◽  
Secondary Phase ◽  
Gas Pressure ◽  
Gas Pressure Sintering

Abstract Si3N4-based ceramic (Si3N4-5wt%Y2O3-3wt%MgO) was obtained from carbothermal-reduction-derived powder combined with gas pressure sintering. The phase, microstructure, thermal conductivity and mechanical properties of Si3N4 ceramics were comprehensively analyzed. Dense Si3N4 ceramic with uniform grain size was obtained after sintering at 1900°C for 7 h under a N2 pressure of 1.2 MPa. The secondary phase consisted of Y4Si2O7N2 and Y2Si3O3N4 was found to gather around triangular grain boundaries. The thermal conductivity, flexural strength, hardness and fracture toughness of the Si3N4 ceramics were 95.7 W·m-1·k-1, 715 MPa, 17.2 GPa and 7.2 MPa·m1/2, respectively. The results were compared with product derived from commercial powder, the improvement of thermal conductivity (~8.3%) and fracture toughness (~4.3%) demonstrating the superiority of Si3N4 ceramics prepared from carbothermal-reduction-derived powder.

Si3N4-BN-SiO2 Based Microwave-Transparent Materials

2008 ◽  
Vol 368-372 ◽  
pp. 913-916 ◽  
Author(s):  
Wei Ru Zhang ◽  
Chong Hai Wang ◽  
Ling Li ◽  
Jian Liu ◽  
Wen Chen
Keyword(s):  
Dielectric Constant ◽  
Dielectric Properties ◽  
Technological Parameter ◽  
Bending Strength ◽  
Raw Materials ◽  
Gas Pressure ◽  
Loss Angle ◽  
Transparent Materials ◽  
Gas Pressure Sintering ◽  
N Wave

The Si-B-O-N microwave-transparent materials were prepared by gas pressure sintering (GPS).The effect of BN and nano-SiO2 contents on the mechanical and dielectric properties of the composites was studied. The microstructural characteristic and reinforced mechanism of the composites were also investigated. The results showed that a series of Si-B-O-N wave-transparent materials could be obtained by controlling the contents of raw materials and technological parameter. The bending strength of composites is from 74.7MPa to 174.83MPa, the dielectric constant is from 3.5 to 4.2 and the tangent of loss angle is from 0.5×10-3 to 4.5×10-3.

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