碳化硅陶瓷的液相烧结及其研究进展

本文对碳化硅液相烧结添加系统及其烧结机理作了论述。有氧化物参与的碳化硅的液相烧结可以降低碳化硅的烧结温度，促进碳化硅的致密化，提高碳化硅陶瓷的性能。沿晶断裂和穿晶断裂混合断裂机理是液相烧结碳化硅陶瓷强度和韧性提高的原因，表面强化和韧化可以进一步提高碳化硅陶瓷材料的性能。     

Liquid-Phase Sintering of Ceramics

Expressions for the sintering rate in liquid-phase sintering are derived for coupled-interface dissolution and liquid-phase diffusion. The analysis reveals the important role of stress gradients in the grain boundary phase and also shows that such gradients cannot be supplied by liquid-phase flow. Stress-supporting structure in the grain boundary phase is thus implied. The probable existence of such structure is revealed by diffuse dark-field scattering studies, using transmission electron microscopy, on partially sintered alumina/anorthite bodies.     

3Y-TZP材料的液相烧结

通过在3Y-TZP(Tetragonal Zirconia Polycrystals stabilized with 3mol% Y2O3)中加入适当含量的硅酸盐玻璃添加剂,使其烧结温度明显降低,并且制备出具有细晶粒、高强度的四方相氧化锆增韧陶瓷材料.本文分析了添加剂对3Y-TZP材料烧结特性及显微结构的影响.发现液相烧结的3Y-TZP具有良好的抗弯强度,但韧性有待于提高.     

Liquid-Phase Bonding of Silicon Nitride Ceramics

Mg-Si-O-N glasses were used to bond dense Si₃N₄ ceramic pieces by a liquid-phase diffusion bonding mechanism. In this case, it was difficult to achieve defect-free bonding because, at low nitrogen content in the glass, a large mismatch in thermal expansion coefficient produced cracks perpendicular to the bonding glass layer. With an increase in nitrogen content, the glass layer became frothy and contained "bubbles." However, when a small amount of elemental silicon was added to the glass, volatile reaction was suppressed and intimate bonding was achieved without thermal cracks.     

Silicon Carbide Liquid-Phase Sintering with Various Activating Agents

Refractories and Industrial Ceramics - Silicon-carbide materials with 5 – 10 wt.% additions of oxides were prepared by liquid-phase sintering at 1860 – 2100 °C. The highest...     

Semiconducting Barium Titanate Ceramics Prepared by Boron-Containing Liquid-Phase Sintering

Semiconducting BaTiO₃ ceramics have been prepared by adding BN as a sintering aid. Density as high as 93% of theoretical and grain size as large as 16 μm are obtained after sintering at 1160°C. Most significant is that the semiconducting BaTiO₃ is obtained at sintering temperatures as low as 1100°C. The low-temperature-sintered BaTiO₃ exhibits a positive temperature coefficient. (PTC) anomaly above 120°C with a resistivity maximum at a temperature as high as 400°C, which is much higher than that of the conventional BaTiO₃. The incorporation of B into the perovskite structure is negligible. Also, the presence of B at a grain boundary after sintering is believed to enhance the PTC effect.     

Sintering Silicon Nitride Ceramics in Air

Silicon nitride (Si₃N₄) ceramics, prepared with Y₂O₃ and Al₂O₃ sintering additives, have been densified in air at temperatures of up to 1750°C using a conventional MoSi₂ element furnace. At the highest sintering temperatures, densities in excess of 98% of theoretical have been achieved for materials prepared with a combined sintering addition of 12 wt% Y₂O₃ and 3 wt% Al₂O₃. Densification is accompanied by a small weight gain (typically <1–2 wt%), because of limited passive oxidation of the sample. Complete α- to β-Si₃N₄ transformation can be achieved at temperatures above 1650°C, although a low volume fraction of Si₂N₂O is also observed to form below 1750°C. Partial crystallization of the residual grain-boundary glassy phase was also apparent, with β-Y₂Si₂O₇ being noted in the majority of samples. The microstructures of the sintered materials exhibited typical β-Si₃N₄ elongated grain morphologies, indicating potential for low-cost processing of in situ toughened Si₃N₄-based ceramics.     

Homogeneous Distribution of Sintering Additives in Liquid-Phase Sintered Silicon Carbide

The addition of sintering additives to silicon carbide particles by electrostatic adsorption of colloidal A1₂O₃ and Y₂O₃ sols has been studied as a way to achieve an optimum homogeneity in the microstructure. The adsorption behavior of the sol particles was examined by electrophoretic measurements and X-ray fluorescence analysis. Both A1₂O₃ and Y₂O₃ sols could simultaneously be adsorbed on the SiC particle surfaces. Viscosity measurements showed that the colloidal sol particles had a stabilizing effect on the slip, and hence slips with relatively high solid loadings could be prepared without adding extra dispersing agent. Liquid-phase-sintered silicon carbide materials (LPS-SiC) with 2 wt% A1₂O₃ and 1 wt% Y₂O₃ were prepared by freeze granulation/ pressing and sintering at 1880^deg;C for 4 h. The homogeneity of the green compacts was quantified using a spot analysis technique in an electron probe microanalyzer. It was clearly shown that the addition of sols gave a more homogeneous microstructure than the reference sample with Y₂O₃ and A1₂O₃ added as powders. The addition of sintering additives as sols also enhanced the sintering behavior.     

烧结温度对放电等离子烧结氮化硅陶瓷显微结构和力学性能的影响

以亚微米级氮化硅为原料、Al_2O_3–Y_2O_3为烧结助剂,利用放电等离子烧结(spark plasma sintering,SPS)烧结技术制备氮化硅陶瓷。用X射线衍射和扫描电子显微镜对试样的物相组成和显微结构进行分析,研究了烧结温度对氮化硅陶瓷力学性能和显微结构的影响。结果表明,采用SPS烧结技术可在较低温度下获得致密度较高、综合力学性能较好的β相氮化硅陶瓷。随着烧结温度的提高,样品致密度、抗弯强度、断裂韧性均不断增大,在1 550℃时,其抗弯强度和断裂韧性分别达到973.74 MPa和8.23 MPa?m1/2。在1 550℃以下,陶瓷样品中β相氮化硅含量可达到98%,显微结构均匀,晶粒发育良好、呈长柱状,晶间紧密连接,晶间气孔较少。继续升高温度,部分晶粒发生异常长大,产生了更多的显微孔洞,抗弯强度急剧下降。     

Si3N4陶瓷烧结中烧结助剂的研究进展

研究了多种烧结助剂对氮化硅烧结性能和烧结过程的影响.研究表明,多组分助剂比单一组分助剂对氮化硅的助烧效果好,其中稀土氧化物和MgO-Al2O3-SiO2体系比较受重视.     

无压烧结制备表面微孔碳化硅陶瓷

以碳化硅（SiC）微粉为骨料,Al2O3-Y2O3为烧结助剂,氯化钙（CaCl2）作为造孔剂,采用无压液相烧结制备了表面微孔SiC陶瓷,分析了不同CaCl2含量对SiC陶瓷的烧结性能、显微结构和摩擦性能的影响。结果表明：加CaCl2会降低SiC陶瓷的体积密度、硬度和抗弯强度;可以有效地细化SiC陶瓷晶粒;能在SiC陶瓷...     

氮化硅常压烧结研究进展

本文着重论述了氮化硅陶瓷常压烧结过程中助烧剂的选择、烧结机理和高温性能的改善方面的研究进展。     

Effect of Sintering Additives on Microstructure and Mechanical Properties of Porous Silicon Nitride Ceramics

Porous silicon nitride (Si₃N₄) ceramics with about 50% porosity were fabricated by pressureless sintering of α-Si₃N₄ powder with 5 wt% sintering additive. Four types of sintering aids were chosen to study their effect on the microstructure and mechanical properties of porous Si₃N₄ ceramics. XRD analysis proved the complete formation of a single β-Si₃N₄ phase. Microstructural evolution and mechanical properties were dependent mostly on the type of sintering additive. SEM analysis revealed the resultant porous Si₃N₄ ceramics as having high aspect ratio, a rod-like microstructure, and a uniform pore structure. The sintered sample with Lu₂O₃ sintering additive, having a porosity of about 50%, showed a high flexural strength of 188 MPa, a high fracture toughness of 3.1 MPa·m^1/2, due to fine β-Si₃N₄ grains, and some large elongated grains.     

Thermochemical Analysis of the Silicon Carbide-Alumina Reaction with Reference to Liquid-Phase Sintering of Silicon Carbide

The stabilities of different phases in the Si-Al-C-O system are calculated from thermodynamic considerations with the objective of identifying the liquid phases formed during sintering of SiC in the presence of Al₂O₃. It is shown that a liquid phase can form at the sintering temperatures by the reaction of SiC with Al₂O₃. Depending on the carbon activity, the liquid can be either of the following: Al₂O₃+ Al₄C₃, SiC + Al₄C₃, or molten aluminum. The stability of the aluminosilicate melts that can form by the reaction of Al₂O₃ with the surface silica layer on SiC powders is also evaluated. Several factors that influence liquid-phase sintering, such as the solubility of SiC in the melts and the generation of gases during sintering, are discussed. The results of the thermodynamic analysis are compared with the observed sintering behavior for SiC.     

低温放电等离子烧结法制备氮化硅陶瓷

分别以MgO-Al2O3或MgO-AlPO4作为烧结助剂,采用放电等离子体低温快速烧结方法制备了主相为α相的Si3N4陶瓷材料.采用X射线衍射和扫描电子显微镜分析了样品的物相组成和显微结构;研究了烧结助剂及其含量、烧结温度对陶瓷样品的相对密度与力学性能的影响.结果表明:当采用4%质量分数,下同)MgO-4%Al2O3烧...     

无压烧结氮化硅陶瓷的物理性能研究

以α-Si₃N₄粉末为原料,Y₂O₃和MgAl₂O₄体系为烧结助剂,采用无压烧结方式,研究了烧结温度、保温时间、烧结助剂含量以及各组分配比对氮化硅致密化及力学性能的影响。结果表明:以Y₂O₃和MgAl₂O₄为烧结助剂体系,氮化硅陶瓷在烧结温度为1 600 ℃,保温时间为4 h,烧结助剂含量为12.5%(质量分数),Y₂O₃和MgAl₂O₄质量比为1∶1时,综合性能最好;氮化硅陶瓷显气孔率为0.21%,相对密度为98.10%,抗弯强度为598 MPa,维氏硬度为15.55 GPa。     

Effect of Liquid-Phase Sintering on the Breakdown Strength of Barium Titanate

A glass used to liquid-phase sinter BaTiO₃ was developed and its properties were tested to determine the feasibility of using this glass to aid densification behavior. Glass was added to pure BaTiO₃ powder and pressed into dimpled pellets with glass contents varying from 4 to 20 vol%. The breakdown strength was measured and compared with pure BaTiO₃ and two commercially available dielectric materials. Liquid-phase sintering increased the breakdown strength of pure BaTiO₃ for all the compositions tested. The breakdown strength of the samples containing 20 vol% glass additions was increased by a factor of 2.8 compared with pure BaTiO₃.     

Fabrication of Dense Nanostructured Silicon Carbide Ceramics through Two-Step Sintering

SiC powder compacts were prepared with Al₂O₃, Y₂O₃, and CaO powders. By two-step sintering, fully dense nanostructured SiC ceramics with a grain sizes of ∼40 nm were obtained. The grain size–density trajectories are compared with those of conventional sintering processes.     

烧结助剂对氮化硅陶瓷显微结构和性能的影响

氮化硅中氮原子和硅原子的自扩散系数很低，致密化所必需的扩散速度和烧结驱动力都很小，在烧结过程中需采用烧结助剂。烧结助剂是影响氮化硅陶瓷的显微结构和性能的关键因素之一。有效的烧结助剂不但可以改善氮化硅陶瓷的显微结构，而且可以提高氮化硅陶瓷的高温性能和抗氧化性能。