Gas Pressure Sintering Process Research Articles

Review on the thermal characteristics and applications of silicon nitride ceramics

As the heat generation problem is predicted to intensify due to the trend of integration and high density of the power semiconductor power module responsible for the electric drive of the electric vehicle, which has recently been in full swing, high-reliability materials and It is essential to secure large-area heat dissipation substrate manufacturing process technology, and technical obstacles to maintain reliability even in environmental changes such as severe cold/excessive heat are becoming issues.In the case of silicon nitride ceramic material, which is in the spotlight as a heat dissipation substrate material, a balance that meets the user’s needs is required. In order to realize excellent heat dissipation performance, it is necessary to reduce the thickness of the silicon nitride substrate, increase the thickness of the metal junction, and improve the thermal conductivity of the silicon nitride material. Therefore, the task of technological progress beyond the complementary relationship between heat conduction-intensity still remains.In this paper, various technical considerations for increasing the thermal conductivity of silicon nitride ceramics are described, and the direction of technological progress is described along with detailed examples. In order to improve thermal conductivity, it is necessary to minimize the inflow of impurities into the raw material powder, appropriately select sintering additives required for liquid phase sintering, and optimize the microstructure through minimization of the amorphous glass phase and control of grain growth by the gas pressure sintering process.

The effect of T-ZnOw addition on the microstructure, mechanical and antibacterial properties of Si3N4 ceramics for biomedical applications

Si3N4 ceramics with constant proportion of sintering aids and different mass percentages of tetra-needle-like ZnO whisker (T-ZnOw) added were prepared by gas pressure sintering process at 1700 °C under an applied pressure of 4 MPa for 2 h. The microstructure, mechanical and antibacterial properties of Si3N4 ceramics were characterized and investigated. The results indicated that T-ZnOw could be well- dispersed in the sintered ceramic matrix and grain size of Si3N4 ceramics became larger with the addition of T-ZnOw. Moreover, the mechanical properties of Si3N4 ceramics with T-ZnOw added were slightly lower than those of samples without T-ZnOw added for the unnoticeable negative effects of T-ZnOw. Additionally, Si3N4 ceramics with T-ZnOw added possessed superior antibacterial rate against both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) compared with samples without T-ZnOw added owing to generation and release of reactive oxygen and Zn2+ ions that could inhibit the growth of bacteria.

Wear behaviour and electrical conductivity of β-Sialon-ZrN composites fabricated by reaction bonding and gas pressure sintering process

β-Sialon-ZrN composites with different levels of substitution and ZrN content have been formed by a process of reaction bonding and post gas pressure sintering, and the wear properties and electrically conductive properties have been investigated. The results showed that an appropriate higher sintering temperature was beneficial for increasing wear resistance, and the composites with β-Sialon (Z = 1) had better wear properties than those with β-Sialon (Z = 4). The incorporation of the ZrN particles was observed to have an effect on the wear properties of the composites. The best wear properties was observed for the composites sintered at 1700 °C with lowest wear rate of 2.4 × 10−5 mm3N−1m−1 for β-Sialon (Z = 1)-20 wt% ZrN and 5.0 × 10−4 mm3N−1m−1 for β-Sialon (Z = 4)-30 wt% ZrN, respectively. The wear resistance was influenced by numerous factors, including phase composition, microstructure, hardness and fracture toughness, and the material was mainly removed by delamination, micro-fracture and micro-cracks. At a given ZrN content, a continuous electrically conductive network was formed and had an effect on the electrical resistivity of the composites, where the electrical resistivity decreased from around 1012 Ω∙m for monolithic β-Sialon to around 10 Ω∙m for 23 vol% ZrN.

Effect of Applied Pressure on Densification and Mechanical Properties of Sialon-ZrN Composites Fabricated Through a Reaction Bonding / Gas Pressure Sintering Process

Sialon-ZrN composites have been produced by reaction bonding and gas pressure sintering, and the effects of applied pressure on the sintering and properties has been investigated. The results showed that composites were mainly composed of β-Sialon and ZrN, with intermediate phases (including Y2SiAlO5N, Al2SiO5 and Y2Si2O7) for 0.4 MPa and Y5Si4Al2O17N for 1.0 MPa. The mass loss decreased with pressure increase due to suppression of thermal decomposition of the Sialon. Composites sintered under 1.0 MPa had better densification than those sintered under 0.4 MPa, and presented greater mechanical properties. Under 1.0 MPa, compared to the monolithic Sialon, the addition of ZrN resulted in an increased hardness up to 30% ZrN, with the highest hardness of 16.16 GPa being observed with 20% ZrN. The hardness decreased with higher ZrN content due to the weak bonding between the ZrN particles and the Sialon matrix. However this resulted in a continuous increase in fracture toughness, reaching a maximum of 5.41MPa·m1/2 with 50% ZrN.

Influence of YAG-Based Composite Sintering Aids on Gas Pressure Sintered BN<sub>w</sub>/Si<sub>3</sub>N<sub>4</sub> Composites

BNw/Si3N4 composites were fabricated by gas pressure sintering process using α-Si3N4 powder 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/Si3N4 sintered 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/Si3N4 composites 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.

A route to increase fracture toughness of layered Si3N4/SiC composite using interlocked interfaces

Multilayer Si3N4/SiC composite with interwoven interfaces was designed and prepared via the aqueous tape casting and gas pressure sintering process. This composite had relatively uniform layer thickness, high strength (~564MPa), toughness (~16.8MPam1/2) and work-of-fracture (~4411J/m2). The first-level toughening mechanism started from the fracture surface of the multilayer composite. Obvious crack deflection was found in the Si3N4 and SiC layers. At the same time, the pullout and fractured rodlike β-Si3N4 grains were detected along the interfaces of the composite. The growth of the rodlike β-Si3N4 grains (the grain size>50μm) along the interfaces was determined by the vapor phase transport mechanism. Both rich SiO2 on the surfaces of the SiC/Si3N4 particles and high porosity of the SiC layers were contributed to the growth of β-Si3N4 grains.

Sintered-reaction Bonded Silicon Nitride Densified by a Gas Pressure Sintering Process - Effects of Rare Earth Oxide Sintering Additives

Reaction-bonded silicon nitrides containing rare-earth oxide sintering additives were densified by gas pressure sintering. The sintering behavior, microstructure and mechanical properties of the resultant specimens were analyzed. For that purpose, Lu₂O₃-SiO₂ (US), La₂O₃-MgO (AM) and Y₂O₃-Al₂O₃ (YA) additive systems were selected. Among the tested compositions, densification of silicon nitride occurred at the lowest temperature when using the La₂O₃-MgO system. Since the Lu₂O₃-SiO₂ system has the highest melting temperature, full densification could not be achieved after sintering at 1950℃. However, the system had a reasonably high bending strength of 527 ㎫ at 1200℃ in air and a high fracture toughness of 9.2 ㎫·m 1/2 . The Y₂O₃-Al₂O₃ system had the highest room temperature bending strength of 1.2 ㎬.

Microstructure refinement of alumina: Optimisation by gas pressure sintering process

This paper investigates densification and grain growth evolutions during gas pressure sintering of alumina. Isothermal sintering runs are performed under different nitrogen pressures: atmospheric pressure and 2 MPa. Experimental data are fitted thanks to constitutive laws in order to understand nitrogen pressure effect on densification and grain growth mechanisms of a fine-grained alumina. An optimal run of densification is proposed as an application of these results.

Evaluation of the reliability of Si3N4-Al2O3 -CTR2O3 ceramics through Weibull analysis

The objective of this work has been to compare the reliability of two Si3N4 ceramics, with Y2O3/Al2O3 or CTR2O3/Al2O3 mixtures as additives, in regard to their 4-point bending strength and to confirm the potential of the rare earth oxide mixture, CTR2O3, produced at FAENQUIL, as an alternative, low cost sinter additive for pure Y2O3 in the sintering of Si3N4 ceramics. The oxide mixture CTR2O3 is a solid solution formed mainly by Y2O3, Er2O3, Yb2O3 and Dy2O3 with other minor constituents and is obtained at a cost of only 20% of pure Y2O3. Samples were sintered by a gas pressure sintering process at 1900 °C under a nitrogen pressure of 1.5 MPa and an isothermal holding time of 2 h. The obtained materials were characterized by their relative density, phase composition and bending strength. The Weibull analysis was used to describe the reliability of these materials. Both materials produced presented relative densities higher than 99.5%t.d., b-Si3N4 and Y3Al5O12 (YAG) as cristalline phases and bending strengths higher than 650 MPa, thus demonstrating similar behaviors regarding their physical, chemical and mechanical characteristics. The statistical analysis of their strength also showed similar results for both materials, with Weibull moduli m of about 15 and characteristic stress values s o of about 700 MPa. These results confirmed the possibility of using the rare earth oxide mixture, CTR2O3, as sinter additive for high performance Si3N4 ceramics, without prejudice of the mechanical properties when compared to Si3N4 ceramics sintered with pure Y2O3.

Substitution of Y 2O 3 by a rare earth oxide mixture as sintering additive of Si 3N 4 ceramics

The objective of this work was to compare the sinterability, the microstructures and the mechanical properties of Si 3N 4 ceramics with additive mixtures based on yttrium oxide, Y 2O 3, and a mixed concentrate of yttrium and rare earth oxides. The RE 2O 3 samples were prepared by a two-step gas-pressure sintering process. No significant differences between the samples have been found, thus demonstrating the potential of this low cost alternative sinter additive.

Corrosão de cerâmicas à base de Si3N4 em soluções aquosas de HCl 0,1 N

O comportamento à corrosão de cerâmicas à base de Si3N4 contendo misturas de Y2O3/SiO2 e RE2O3/SiO2 como aditivos nas proporções de 14 e 21% em volume ambos na estequiometria dos dissilicatos Y2Si2O7 e RE2Si2O7, respectivamente, foi estudado em soluções aquosas de HCl 0,1N a 100 °C. A resistência à corrosão foi avaliada pela perda de massa das amostras e análise química das soluções após os testes. As análises por microscopia eletrônica das amostras atacadas revelou que basicamemte a fase vítrea intergranular foi dissolvida pela solução ácida, deixando um esqueleto de grãos de b-Si3N4 entrelaçados.

Preparation of High‐Density Si3N4 by a Gas‐Pressure Sintering Process

Si3N4 compacts, containing ≅7 wt% of both BeSiN2 and SiO2 as densification aids, can be reproducibly sintered to relative densities >99% by a gas‐pressure sintering process. Nearly all densification takes place via liquid‐phase sintering of transformed β‐Si3N4 grains at T=1800° to 2000°C. Compacts with high density are produced by first sintering to the closed‐pore stage (≅92% relative density) in 2.1 MPa (20 atm) of N2 pressure at 2000°C and then increasing the N2 pressure to 7.1 MPa (70 atm) where rapid densification proceeds at T= 1800° to 2000°C. The experimental density results are interpreted in terms of theoretical arguments concerning the growth (coalescence) of gas‐filled pores and gas solubility effects. Complex chemical reactions apparently occur at high temperatures and are probably responsible for incomplete understanding of some of the experimental data.