烧结温度对气压烧结氮化硅铁显微结构及性能的影响

以微米级氮化硅铁为原料、Al_2O_3–Y_2O_3为烧结助剂,采用气压烧结制备氮化硅铁复相陶瓷。通过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了表征,研究了烧结温度对氮化硅铁复相陶瓷成分、显微结构和力学性能的影响。结果表明:烧结温度对于氮化硅铁陶瓷的显微结构和力学性能具有显著影响。随着烧结温度的升高,样品致密度、抗弯强度、断裂韧性先增大后降低,在1 770℃时均达到最大值,密度、抗弯强度和断裂韧性分别达到3.31 g/cm~3、435 MPa和6.97 MPa?m~(1/2)。在1 770℃以下时,陶瓷样品中主晶相为长柱状的β-Si3N4,晶粒彼此间结合紧密,陶瓷气孔率较低。温度继续升高,含铁相和氮化硅发生反应,气孔率增大,抗弯强度和断裂韧性开始下降。如果进一步提高硅铁的氮化率,采用游离硅低、铁含量低及纯度较高的氮化硅铁粉末制备氮化硅铁陶瓷,材料的性能有望得到进一步的提高。     

放电等离子烧结SiC/BN复相陶瓷的制备及力学性能

以高纯h-BN和SiC纳米粉体为原料、B_2O_3为烧结助剂,利用放电等离子烧结技术(SPS)快速烧结制备了h-BN–25%SiC复相陶瓷。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h-BN–SiC复相陶瓷的SPS低温烧结行为及烧结温度对烧结试样的致密度、微观结构及力学性能的影响。结果表明:采用SPS烧结技术,在较低温度下即可获得致密度较高的烧结样品,烧结温度的升高,促进了h-BN晶粒的方向性排列,提高了烧结样品的相对密度。随着烧结温度的提高,晶粒尺寸增大,抗弯强度、断裂韧性和弹性模量增大,并具有相同的变化趋势。样品晶粒细小均匀,不同烧结温度样品的断裂方式相同,主要为沿晶断裂,细小SiC颗粒的钉扎效应、晶粒拔出和裂纹偏转提高了复相陶瓷的断裂强度和断裂韧性。在1 600℃烧结所得试样的综合性能较好,其抗弯强度、断裂韧性和弹性模量分别为289.2 MPa、3.45 MPa·m1/2和150.9 GPa。     

烧结温度对不同Yb_2O_3含量的氮化硅陶瓷结构和性能的影响

在不同烧结温度、30 MPa压力下保温1h制备了不同Yb_2O_3含量的氮化硅陶瓷,通过XRD、SEM、阿基米德排水法、三点抗弯强度法、Vickers压痕法等手段测定了氮化硅陶瓷的物相组成、显微结构、致密度、抗弯强度、断裂韧性和硬度。研究了烧结温度对不同Yb_2O_3含量的氮化硅陶瓷的相变、显微结构和力学性能的影响。研究表明,Yb_2O_3含量的变化导致了Yb_2O_3和氮化硅表面SiO_2反应配比的变化,从而在Yb_2O_3-SiO_2二元体系和Yb_2O_3-SiO_2-Si3_N_4三元体系中,晶界第二相生成物也发生了变化。这些第二相生成物种类与烧结温度共同影响氮化硅陶瓷材料的显微结构和力学性能。5 wt%Yb_2O_3含量的Si_3N_4陶瓷在1850℃获得所有9个样品中最大的抗弯强度和断裂韧性,分别为874 MPa和5.83 MPa·m1/2;15 wt%Yb_2O_3含量Si_3N_4陶瓷中出现的第二相Yb_4Si_2O_7N_2,抑制了氮化硅晶粒在高温下的异常长大。     

烧结助剂(Y_2O_3、Al_2O_3、La_2O_3)对β-Si_3N_4自增韧陶瓷的性能研究

利用氮化硅陶瓷的自增韧技术,使用复合烧结助剂和在氮化硅基体中添加长柱状β-Si_3N_4晶种,制备高断裂韧性的氮化硅陶瓷。采用X射线衍射、扫描电镜、阿基米德法、三点抗弯曲强度、单边切口梁法等测试方法对陶瓷的组成、显微结构、显气孔率以及抗弯强度和断裂韧性等进行了分析与表征。首先研究了无压烧结制备氮化硅陶瓷过程中,烧结助剂(Y_2O_3、Al_2O_3)对其烧结性能和力学性能的影响,当Y_2O_3含量为8wt%,Al_2O_3含量为4wt%时,氮化硅陶瓷的相对密度达95%以上,抗弯强度为674MPa,断裂韧性为6.34MPa·m~(1/2)。再通过引入La_2O_3提高氮化硅晶粒的长径比,使氮化硅陶瓷的抗弯强度和断裂韧性分别达到686MPa和7.42MPa·m~(1/2)。通过无压烧结工艺,在1750℃制备了长柱状的β-Si_3N_4晶种,晶种的平均长度为2.82μm,平均粒径为0.6μm,平均长径比为4.7。笔者着重研究了晶种对氮化硅陶瓷烧结性能和力学性能的影响。在氮化硅陶瓷中加入晶种后,其烧结性能和抗弯强度略有降低,但断裂韧性却得到了很大的提高;且随着晶种添加量的增加,断裂韧性先升高再降低,掺入量为2wt%时断裂韧性达到最大(7.68MPa·m~(1/2)),提高了20%以上。     

添加剂B_2O_3对SiC/h-BN复相陶瓷低温烧结行为及性能的影响

以乱层结构h-BN(t-BN)和SiC纳米粉体为原料,B_2O_3为烧结助剂,利用放电等离子烧结技术(SPS)制备出SiC/h-BN复相陶瓷。采用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,研究烧结助剂含量对SiC/h-BN复相陶瓷的低温烧结行为、致密化、微观结构及力学性能的影响。结果表明:利用SPS低温烧结方法,添加少量B_2O_3添加剂,可有效地提高复相陶瓷的致密度和力学性能。与无添加剂烧结样品相比,烧结助剂的添加降低了样品烧结收缩起始温度,促进样品中片状h-BN晶粒的移动和重排,提高了颗粒间的结合强度。随着烧结助剂添加量的增加,复相陶瓷致密度显著增加,强度和韧性均呈现先增加后降低的趋势,在B_2O_3添加量为5%时,复相陶瓷相对密度和各项力学性能较高,其相对密度、抗弯强度、断裂韧性和弹性模量分别为96.92%、274.7MPa、2.91MPa·m1/2和127.2GPa,但添加过多B_2O_3,则不利于提高复相陶瓷的力学性能。     

添加Mg-Al-Si体系烧结助剂的氮化硅陶瓷的无压烧结

以MgO-Al2O3-SiO2体系作为烧结助剂,研究了氮化硅陶瓷的无压烧结。着重考察了烧结温度、保温时间以及烧结助剂用量等工艺因素对氮化硅陶瓷材料力学性能和显微结构的影响,通过工艺调整来设计材料微观结构以提高材料的力学性能。在烧结助剂质量分数为3.2％的情况下,经1 780℃,3 h无压烧结,氮化硅大都呈现长柱状β-Si3N4晶粒,具有较大的长径比,显微结构均匀。样品的相对密度达99%,抗弯强度为956.8 MPa,硬度HRA为93,断裂韧性为6.1 MPa·m1/3。具有较大长径比晶粒构成的显微结构是该材料表现较高力学性能的原因。     

MgO–Al_2O_3–CeO_2复合烧结助剂对放电等离子烧结氮化硅陶瓷致密化和性能的影响

以MgO–Al_2O_3–CeO_2复合体系为烧结助剂,采用放电等离子烧结工艺制备氮化硅陶瓷。研究了MgO–Al_2O_3–CeO_2含量、烧结温度对氮化硅陶瓷显微结构及力学性能的影响;探讨了复合烧结助剂作用下氮化硅陶瓷的烧结机理。结果表明:当混合粉体中Si_3N_4、MgO、Al_2O_3和CeO_2的质量比为91:3:3:3、烧结温度为1600℃时,氮化硅烧结体相对密度(99.70%)、硬度(18.84GPa)和断裂韧性(8.82MPa?m1/2)达最大值,晶粒以长柱状的β相为主,α-Si_3N_4→β-Si_3N_4相转变率达93%;当混合粉体中Si_3N_4、MgO、Al2O3和CeO_2的质量比为88:4:4:4、烧结温度为1600℃时,烧结体抗弯强度(1086MPa)达到最大值。     

热压烧结制备原位复合（TiB2+TiC）/Ti3SiC2复相陶瓷

采用热压烧结法制备了原位复合(TiB2+TiC)/Ti3SiC2复相陶瓷。采用X射线衍射、扫描电镜和透射电镜对材料的物相组成和显微结构进行了表征,研究了烧结温度对材料物相组成、烧结性能、显微结构与力学性能的影响。结果表明:烧结温度在1 350～1 500℃范围内,随着烧结温度的升高,合成反应进行逐渐完全,材料的密度、抗弯强度和断裂韧性显著提高。1 500℃烧结可得到致密的原位复合(TiB2+TiC)/Ti3SiC2复相陶瓷,材料晶粒发育较完善,层片状Ti3SiC2、柱状TiB2与等轴状TiC晶粒清晰可见,增强相晶粒细小,晶界干净,材料的抗弯强度、断裂韧性和Vickers硬度分别达到741 MPa,10.12 MPa.m1/2和9.65 GPa。烧结温度达到1 550℃时Ti3SiC2开始发生分解,材料的密度和力学性能又显著下降。     

自增韧氮化硅陶瓷的制备与性能研究

氮化硅陶瓷具有优异的物理机械性能和化学性能,被广泛应用于高温、化工、冶金、航空航天等领域。在结构陶瓷中氮化硅陶瓷虽具有相对较高的断裂韧性,但为了进一步拓宽氮化硅陶瓷的运用领域和提高其使用可靠性,改善其断裂韧性一直是该材料研究的重要课题。笔者通过利用氮化硅陶瓷的自增韧技术,使用复合烧结助剂和在氮化硅基体中添加长柱状β-Si_3N_4晶种,制备高断裂韧性的氮化硅陶瓷。采用X射线衍射、扫描电镜、阿基米德法、三点抗弯曲强度、单边切口梁法等测试方法对陶瓷的组成、显微结构、显气孔率以及抗弯强度和断裂韧性等进行了分析与表征。首先研究了无压烧结制备氮化硅陶瓷过程中,烧结助剂(Y_2O_3和Al_2O_3)对其烧结性能和力学性能的影响,当Y_2O_3含量为8wt%,Al_2O_3含量为4wt%时,氮化硅陶瓷的相对密度达95%以上,抗弯强度为674 MPa,断裂韧性为6.34 MPa·m~(1/2)。再通过引入La_2O_3提高氮化硅晶粒的长径比,使氮化硅陶瓷的抗弯强度和断裂韧性达到686 MPa和7.42 MPa·m~(1/2)。笔者通过无压烧结工艺,在1 750℃制备了长柱状的β-Si_3N_4晶种,晶种的平均长度为2.82μm,平均粒径为0.6μm,平均长径比为4.7,着重研究了晶种对氮化硅陶瓷烧结性能和力学性能的影响。氮化硅陶瓷中加入晶种后,其烧结性能和抗弯强度略有降低,但断裂韧性得到了很大的提高;且随着晶种添加量的增加,断裂韧性先升高再降低,掺杂量为2wt%时,断裂韧性达到最大(7.68 MPa·m~(1/2)),提高了20%以上。     

浆料直写成形ZrO_2陶瓷制备及烧结

为浆料直写成形工艺制备了一种高固相含量的水基ZrO_2陶瓷浆料,并用该工艺打印陶瓷坯体,1350～1550℃烧结后制备ZrO_2陶瓷样品。研究烧结温度对样品收缩率、密度、气孔率、相结构、力学性能、微观形貌和表面质量的影响,并与其他制造工艺进行性能比较。结果表明:在1550℃烧结2 h,直写成形ZrO_2陶瓷综合性能最佳,其晶粒细小、显微结构均匀、致密性好,相对密度、抗弯强度、硬度和断裂韧性分别为99.2%、676MPa、12.5 GPa和6.2 MPa·m~(1/2)。在挤出增材制造工艺中,烧结样品具有高的致密度和优异的力学性能。     

Differential Sintering by Improper Selection of Sintering Parameters during Pulse Electric Current Sintering

Recently, we reported on the retention of fine-grained micro-structure in Al₂O₃/3 vol% 3Y-ZrO₂ composites using the pulse electric current sintering (PECS) technique. It was demonstrated that a high heating rate is beneficial for the retention of fine grains and homogeneous microstructure. As there are few reports on microstructural inhomogeneity and excessive grain growth in compacts densified by the PECS technique, we carried out a series of experiments on monolithic alumina by varying the sintering parameters and discussed the characteristic results. All specimens that were densified under selective sintering conditions attained high density (∼99% of the theoretical density) at 1250°3C in > 5 min. The average fracture strength of monolithic alumina was observed to be 741 ± 25 MPa and the fracture toughness was 2.2 MPa.m <^1/2, and these were reasoned out to small grains. However, compacts sintered under very low compaction pressure attained ∼92%-93% of the theoretical density, and these specimens had undesirable microstructural inhomogeneity owing to differential sintering. Hence, in the present study, we address the problem of differential sintering.     

碳化硅泡沫陶瓷烧结温度和烧结机理的研究

将制备碳化硅泡沫陶瓷的浆料通过烘干、制粉、干压成型、烧结来探讨烧结温度对制品性能的影响。试验结果表明样品的最高抗弯强度出现在1400℃、保温2h的工艺条件下，而不是更高的烧结温度1450℃。主要原因在于过高的烧结温度导致碳化硅氧化严重，生成了大量的方石英，方石英在随后的冷却过程中出现微裂纹所致。而碳化硅泡沫陶瓷的烧结机理主要是玻璃相对碳化硅颗粒的包覆、连接作用和新相莫来石的生成。     

Sintering of dolomites

A sampling of data on the density of dolomites fired at 1750°C as a function of their chemical composition and structure is presented, and the coefficients of linear correlation are calculated. The most significant coefficients were obtained for the apparent density after firing, the sums of mass fractions CaO+MgO and Fe₂O₃+Al₂O₃, and the fraction of SiO₂ in the dolomite.     

陶瓷卫生洁具烧成技术

1引言80年代窑炉设备、保温耐火砖的进一步发展,纤维材料的引入以及高速烧嘴的改进,采用轻质窑炉也可进行复杂陶瓷制品（形状、体积和重量）的快速烧成（8～12h）。随着辊道窑的引进,卫生洁具的快速烧成技术获得突破。随后的几年,具有全纤维衬的隧道窑、梭式窑也得到发展。目前纤维衬的宽体隧道窑和间歇窑已用于卫生洁具的快速烧成。同时,随着全自动存储系统的发展,轻质全纤维衬隧道窑解决了“周末问题”,周末期间允许窑炉温度降低、关闭或转换后重烧,出现了间歇操作的隧道窑。操作证明,具有全纤维窑衬的间歇式窑（室式窑、梭式窑…     

Diffusion Sintering: II, Initial Sintering Kinetics of Alumina

The initial sintering kinetics of alumina have been studied by measuring the isothermal shrinkage of compacts of several alumina powders in air. The shrinkage of these compacts can best be described by a grain-boundary vacancy diffusion model for the temperature range 1200° to 1600°C. The behavior of the compacts is consistent with the model after an initial shrinkage has occurred. The magnitude of this initial shrinkage is constant for identical specimens and is independent of the sintering temperature.     

Sintering of Glass

It has been shown by a simple experiment on the closing of capillary glass tubes on heating that the final stage of sintering of glass particles, manifesting itself in densification of the compact, proceeds by viscous flow caused by surface tension. This effect has been predicted theoretically by Frenkel.     

Sintering of PVC

Although PVC is counted as one of the amorphous plastics it possesses a distinct powder grain structure. This structure is responsible for various effects; for example it is impossible to sinter thick pieces of rigid PVC dryblend possessing satisfactory mechanical properties. For this application, it is necessary to break down this powder structure into smaller parts, called primary particles, by mechanical shearing and covering these particles with processing auxiliaries enabling it to be sintered. PVC can then be melted by the influence of temperature and pressure in the same way as other thermoplastic materials. For this reason, tests were carried out to determine the best material configuration and the necessary data for the compounding and shearing process, and the sinter conditions. A continuously working roll mill was used to break down the structure. The rolls of this equipment are provided with grooves inclined at a certain angle. With this construction it is possible to achieve a high shearing rate at a low mass-temperature. Furthermore, all additives can be added during the rolling process, so that no additional mixing process is necessary. These gelable pellets, made by the roll mill, can thus be formed in a die into plates of different thicknesses. Samples were pressed by varying compounding and sintering conditions and these were tested for mechanical properties.     

Sintering of Fine Oxide Powders: II, Sintering Mechanisms

Conventional and new sintering mechanisms have been investigated using fine powders of CeO₂ and Y₂O₃ of excellent sinterability. We have verified the validity of Herrings scaling law for 60%–84% relative density and found that it is consistent with grain-boundary-diffusion control. At lower densities, we have found that pores larger than the critical size, in the sense of Kingery and Francois, can still be sintered readily. This is rationalized by a new sintering mechanism based on particle repacking concurrent with particle coarsening, resulting in a higher packing factor. Very fine, surface-active powders that coarsen rapidly are uniquely capable of taking advantage of this new sintering mechanism, which along with their propensity to homogenization, accounts for their remarkable sinterability even at very low green densities.