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.     

Small-angle scattering studies of PVC and PVC blends

Small-angle X-ray and small-angle neutron scattering studies have been carried out on poly(vinyl chloride) (PVC), and blends of PVC with solution-chlorinated polyethylene (SCPE) and poly(butyl acrylate) (PBA). The PVC used was commercial (suspension-polymerized) or bulk-polymerized. The blends of PVC with PBA were prepared by solvent-casting and those with SCPE by in situ polymerization. PVC samples show shoulders in the scattering spectra, presumably due to crystallites, which persist even in samples which have been solvent cast. Blends of PVC with PBA also show a peak but at a higher ‘d’ spacing. The blends with SCPE which were prepared by in situ polymerization show no such peak. This suggests that the method of preparation prevents the formation of crystallites. An increase in scattering of the PBA blends was observed when the samples were heated to the temperature of phase separation. Neutron scattering studies were also carried out using 2% deuterium labelled PVC in PVC and in the blends. In the PVC this showed chain dimensions in good agreement with predicted values. In the blends, dimensions of the same order were obtained, confirming a molecular dispersion of chains in the single phase, but there was an apparent reduction in the chain dimensions. This could be explained by a true reduction in dimensions or a non-zero A₂ value in the blends.     

PVC加工业对PVC树脂的需求及发展前景

简述了世界合成树脂的生产状况及目前国内PVC加工企业的概况，提出了加工企业对树脂的要求，介绍了几种对我国关系重大的特种树脂，分析了PVC树脂加工企业的发展动态，并对其发展前景进行了展望。     

PVC的升级换代产品--纳米PVC复合树脂

在杭州华纳化工有限公司开发的纳米CaCO3微乳液存在下采用原位聚合方法制备纳米PVC复合树脂,在云南盐化股份天塑分公司30m^3聚合釜上实现了产业化。该项目研究了纳米CaCO3团聚体的解离技术及原位聚合过程中的继续分散情况。透射电子显微镜(TEM)图像显示：纳米CaCO3在PVC基体内呈微胶束结构和微曝炸崩解结构,聚合过程崩解后的纳米CaCO3颗粒直径为5～10nm,呈良好的分散分布。在剪切速率为50rad/s的剪切流变实验中,纳米PVC比普通PVC切变黏度降低了一个数量级。在ThennoHaake上进行塑化实验,实验温度185℃、转速50r／min,纳米PVC的塑化时间为2.5min,普通PVC的塑化时间则需要6min。     

Miscibility of PVC with chlorinated PE and chlorinated PVC

Miscibility of PVC with chlorinated PE and chlorinated PVC was reviewed. The miscible region of chlorine content ranged from 44 wt% to 65 wt%, which was not symmetric to the chlorine content of PVC, 56.7 wt%. Two group contribution methods were used to calculate solubility parameters of polymers. The results of solubility parameters showed a more symmetric miscible region with respect to the value of PVC. However, the ranges of miscibility were different. It was 2.3 (J/cm 3 ) 0.5 in a three-dimensional method and was 1.5 (J/cm 3 ) 0.5 in the Fedors method.     

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。     

Recycling of PVC

Recycling of used PVC needs a careful characterization of PVC waste. The analysis of the scrap, especially with respect to the thermal stability and the molecular weight, is useful before reprocessing. Additional stabilization of used PVC can be done by up to 10 wt% fillers, e.g. chalk, which does not change the mechanical properties. A literature survey on the proposed concepts and methods for material and chemical recycling of PVC is given.     

Cyclopentadienylation of PVC

Summary Cyclopentadienylation of PVC with alkaline (NaCPD, LiCPD) and acidic (Me₂CPDAl) cyclopentadienylating agents has been investigated. In terms of product quality (absence of discoloration, gelation) Me₂ CPDAl was found to be a superior cyclopentadienylating agent than NaCPD and LiCPD.     

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…     

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.     

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.     

Microcellular PVC

Novel microcellular PVC foams with a very homogenous cell distribution and cell densities ranging from 10⁷ to 10⁹ cells/cm³ have been created using carbon dioxide as the nucleating gas. Microcellular foams with relative densities (density of foam divided by the density of unfoamed polymer) ranging from 0.15 to 0.94 have been produced. It was found that the bubble nucleation density has and Arrhenius-type dependence on temperature, while the average bubble diameter is relatively independent of the foaming temperature. A majority of the cell growth was found to occur in the early stages of foaming.     

聚氯乙烯生产过程中聚氯乙烯粉末回收探讨

介绍了聚氯乙烯生产过程中离心母液水及干燥外排尾气中聚氯乙烯粉末的回收情况。以30万t/a聚氯乙烯装置为例,回收离心母液水中的聚氯乙烯粉末约352.8 t/a,回收干燥后外排尾气中的聚氯乙烯粉末约131.2 t/a。     

纳米晶PVC在PVC／CaCO3复合材料中的作用

研究了不同粒径的纳米晶PVC的增韧、增强作用及对纳米CaCO3改性时偶联剂对材料力学性能的影响。结果表明：两种粒径的纳米晶PVC均能起到显著的增韧和增强作用，且粒径小的纳米晶PVC作用更明显。材料拉伸强度、冲击强度随偶联剂含量的增加而提高。纳米晶PVC和纳米CaCO3使复合材料达到工程材料的标准。     

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.