碳化硅陶瓷烧结助剂的作用机制与研究进展

碳化硅(SiC)陶瓷由于其优异的高温强度、抗氧化性和化学稳定性,在石油化工、航空航天和热交换器等众多领域有广泛的用途.此外,SiC及其复合材料被认为是先进裂变反应堆和未来聚变反应堆的重要结构材料.由于Si-C键的高共价键合性和低自扩散性,纯SiC的烧结极为困难,只能通过高温高压的方式进行致密化.添加烧结助剂对促进SiC的致密化、缓和烧结条件至关重要.本文阐述了烧结助剂存在条件下碳化硅陶瓷致密化的热力学条件,总结了不同烧结机制下烧结助剂的作用机理.从助剂种类的角度综述了目前碳化硅陶瓷烧结领域的常用助剂体系及其研究进展,并展望了碳化硅致密化研究的发展方向.     

纳米碳化硅基复相陶瓷的分散和烧结技术研究进展

碳化硅陶瓷是一种高性能的陶瓷,具有高强度、高硬度、耐高温、耐化学腐蚀、高热导率、低热膨胀以及低密度等性能,广泛应用于各个工业领域以及航空航天领域.从纳米复相陶瓷制备过程中的分散方法以及碳化硅基陶瓷的烧结方法与烧结助剂等方面详细论述了目前有关碳化硅基纳米复相陶瓷的研究进展.     

熔盐辅助合成Dy3Si2C2包裹SiC粉体及其陶瓷的烧结行为

碳化硅陶瓷因自身优良的物理化学性能而具有广泛的应用前景.碳化硅的化学键结合特性决定了其难以烧结成型,因此如何制备高质量碳化硅陶瓷是领域内的难点之一.本研究以三元稀土碳化物Dy3Si2C2作为新型SiC陶瓷的烧结助剂,依据Dy-Si-C体系的高温相转变原位促进碳化硅的烧结致密化.采用放电等离子烧结技术,利用金属Dy与Si...     

碳化硅泡沫陶瓷浆料成分与烧结性能

将用于制备碳化硅泡沫陶瓷的浆料烘干、制粉、干压、烧结,从而探讨浆料的成分与 烧结性能的关系.样品的抗弯强度与烧结助剂的含量之间存在最佳搭配关系,烧结对强度的贡 献主要来自于新相莫来石的生成和玻璃相对碳化硅颗粒的包覆、连接作用.同种成分的样品开 气孔率随着烧结温度的升高表现出单调下降的趋势,而抗弯强度与开气孔率的变化并没有表现 出完全相反趋势;不同成分样品的耐火度均保持在1730℃没有变化.采用最佳配方的浆料和 最佳烧结温度制备的碳化硅泡沫陶瓷抗弯强度可达到0.72MPa.     

锆英石多孔陶瓷烧结助剂的研究

研究了加入各种反应烧结助剂对锆英石质多孔陶瓷反应烧结过程的影响。试验结果表明,以NaF作为反应烧结助剂可改变锆英石质材料的反应烧结机理,促进了其反应烧结过程。在1150°×2h的烧成条件下可获得具有较高强度的锆英石质多孔陶瓷。     

以Al-B-C为烧结助剂的SiC陶瓷热压烧结工艺

以SiC超细粉末为原料,Al粉、B粉和碳黑为烧结助剂,采用热压烧结工艺制备了SiC陶瓷,重点研究了烧结助剂含量(4～13 wt％)对SiC陶瓷物相组成、致密度、断面结构及力学性能的影响.除SiC主晶相外,X射线衍射图还显示了Al8B4C7相的存在;当烧结助剂的含量从4 wt％增至13 wt％时,扫描电镜照片显示陶瓷断面形貌从疏松结构变成致密结构,存在晶粒拔出现象;陶瓷力学性能随着烧结助剂含量的增加先升高后降低.当烧结助剂含量为10 wt％时,SiC陶瓷的力学性能达到最高,抗弯强度为518.1 MPa,断裂韧性为4.98 MPa·m1/2.Al、B和C烧结助剂在1850℃烧结温度下形成的Al8B4C7液相促进晶粒间的重排和传质,并填充晶粒间的气孔,提高了陶瓷致密度.     

碳化硅纳米粉体的合成、分散与烧结工艺技术研究进展

碳化硅陶瓷具有高强度、高硬度、高耐磨性等优异的机械性能以及耐化学腐蚀等,已广泛应用于各个工业领域以及航空航天领域.本文从纳米碳化硅粉体的合成、分散方法以及碳化硅基陶瓷的烧结方法与烧结助剂等方面综合评述了目前有关碳化硅纳米复相陶瓷的研究进展.     

两面顶低温超高压烧结纳米碳化硅的研究

采用两面顶低温超高压（LT-HP）技术在压力4．5GPa、温度（1250±50）℃、烧结时间20min的条件下烧结制备了纳米碳化硅（SiC）陶瓷，研究了烧结体的物相组成、化学成分、微观结构、显微硬度、纳米压痕力学性能等。结果表明，不添加烧结助剂且在较低温度下获得的SiC烧结体的相对密度高达98．4％，其显微硬度达到HV3520；纳米压痕测试硬度高达H31．74GPa、弹性模量E313GPa；烧结体的晶粒尺寸约为89nm，结构致密，无气孔。     

AlN陶瓷的高压烧结研究

以自蔓延高温合成的AlN粉体为原料,用六面顶压机在高压(3.1～5.0GPa)下实现了未添加烧结助剂的AlN陶瓷体的烧结.研究了烧结工艺参数对AlN烧结性能的影响.用XRD、SEM对AlN高压烧结体进行了表征.研究表明:高压烧结能够有效降低AlN陶瓷的烧结温度并缩短烧结时间,烧结体的结构致密.在5.0GPa/1300℃条件下高压烧结50min的AlN陶瓷的相对密度达94.9%.在5.0GPa/1700℃/125min条件下制备的AlN陶瓷晶格常数比其粉体减小了约0.09%.     

不同含量PEG对固相烧结碳化硅陶瓷性能的影响EI北大核心

在以碳黑、碳化硼为烧结助剂的碳化硅陶瓷烧结过程中,通过引入聚乙二醇(PEG)为粘结剂,研究了不同PEG含量对碳化硅陶瓷密度和力学性能的影响。结果表明随着PEG含量的增加,碳化硅陶瓷的密度和力学性能表现为先增加后减小的规律。另外在碳化硅陶瓷烧结过程中增加保温时间,由于晶粒长大过快导致其密度和力学性能迅速下降,同时棒状晶粒的形成没有增加碳化硅陶瓷的韧性。     

粉末材料的爆炸烧结

论述了爆炸烧结的方法及装置，讨论了烧结过程的机理及影响其过程的主要参数。     

Kinetics and sintering mechanisms of hydro-thermally obtained hydroxyapatite

In this paper, the kinetics and sintering mechanism of hydro-thermally synthesized hydroxyapatite in the temperature range 900–1100 °C are presented. It was found that at 900 °C, the sintering process is very slow, whereas at 1000, 1050, and 1100 °C is much faster, caused by activated sintering with liquid phase/phase of solution on spots with concentrated material impurity and the formation of reaction/polyeutectic mixtures dominates. The activation energies of sintering were also determined. At all the investigated sintering temperatures, an approximate value of 90 kJ mol⁻¹ was found.     

Activated sintering of tungsten alloys through conventional and spark plasma sintering process

The sintering temperature of pure tungsten can be reduced through the addition of small amounts of transition elements. The present study deals with the activated sintering of tungsten with 1.0?wt% additions of copper, cobalt, molybdenum, iron and nickel using the spark plasma sintering (SPS) technique. The alloys were sintered at 1200°C and the mechanical properties and microstructures were compared with those of conventionally sintered alloys, sintered under vacuum condition. The high-rate sintering of SPS has led to an overall reduction in process time and also to a better densification of alloys compared with the conventional sintering process. In both the processes, nickel addition is found to be the best activator, followed by cobalt, iron, molybdenum and copper. The addition of copper and molybdenum showed only a meager increase in the relative density. The alloys, with nickel, cobalt and iron additions, sintered through the SPS process offered much higher density compared with the conventionally sintered alloys. The highest density is observed for the nickel-doped tungsten alloy, which is found to be around 90% of the theoretical density. The microhardness of the sintered alloys is found to depend on its sintered density.     

Cold sintering of ceramics and glasses: A review

Traditionally ceramic artifacts are processed at high temperatures (>1000 °C) by classical sintering techniques such as solid state, liquid phase and pressure-assisted sintering. Recently, inspired from the geology, novel sintering approaches that allow the densification of ceramic components at relatively low temperatures ≤400 °C have been proposed. While initial efforts for such low temperature densification concept were developed in the mid-70s, the topic has become increasingly prominent in the last decade. Currently, these low temperature methods can be classified into four main groups: (i) hydrothermal reaction sintering (HRS), (ii) hydrothermal hot pressing (HHP), (iii) pressure-assisted densification techniques: room-temperature densification (RTD), cold sintering (CS), warm press (WP), and finally no-pressure assisted method called (iv) reactive hydrothermal liquid phase densification (rHLPD). Above named techniques are commonly assisted by an aqueous solution used as either reactant or transient liquid phase to assist densification. Starting from the background in traditional sintering processes, this review aims to explore in depth the existing literature about low temperature densification approaches along with their advantages & disadvantages, and probable application areas.     

Computer simulation of pressure sintering

The densification process during pressure sintering has been analyzed using finite element analysis. This analysis uses an iterative solution algorithm. With this the densification process in complex geometries with complex boundary conditions can be analyzed and this technique is particularly suited for tackling material nonlinearity. Evolution of dense structures with gradual closure of pores is described for two typical geometries.     

烧结对共沉淀预烧料制备MnZn高导铁氧体磁性能的影响

以共沉淀法预烧粉为原料,研究了烧结温度及烧结气氛对MnZn高导铁氧体磁性能的影响,采用SEM对其微观结构进行了表征。结果表明,随着烧结温度升高,MnZn高导铁氧体的μi增加;合适的烧结条件能促进晶粒生长,减少气孔产生,增大烧结密度,使晶界变细,提高初始磁导率和改善频率特性。当温度为1380℃,保温气氛为3.0%时,MnZn高导铁氧体的μi为13000,且有较好的频率特性,在150kHz时μi能维持在10000以上。     

Densification of pure magnesium by spark plasma sintering-discussion of sintering mechanism

In this study, high-quantity pure magnesium was prepared by SPS, and the sintering densification mechanism was discussed by using numerical simulation and simultaneous experiment. Results show that a layer of dense magnesium oxide was formed at the surface of Mg particles, and the oxide reduction can be observed owing to the effect of oxide film removal in SPS. The high energy pulsed current flows preferentially through particle contact surfaces, which provides the conditions for the generation of micro-arc between particles and the temperature at the particles contact point can be up to 1979 °C. With the low pressure at the initial sintering stage, local high temperature induced by micro-arc makes the melting (even evaporation) appearance. At the same sintering temperature of 570 °C, the obvious difference in bending strength also demonstrates the significance of spark discharge in SPS. The formation process of sintering neck demonstrates that sintering process is the reflection of melting (even evaporation), diffusion and plastic deformation. In order to realize tiny area and high-quality connection between powder particles, an innovative powder sintering technology using high-frequency pulse electric current (High frequency pulse current assisted sintering) is proposed based on the enlightenment of the skin, proximity and arc discharge effect of high-frequency pulse current. This technology is also instructive for other alloys and engineering materials.     

纳米Cu粉末的SPS烧结与晶粒长大行为的研究

为了研究金属材料在放电等离子烧结(SPS)过程中晶粒的长大行为和激活能的变化情况,利用SEM、FESEM、TEM等技术分析测定了纳米Cu粉坯体在SPS过程中组织形貌和晶粒尺寸的变化情况.研究表明:特定的工艺和烧结制度下,应用SPS技术可以得到均匀、致密的组织;脉冲电流的作用使晶粒表面大大活化,晶粒长大激活能大大降低,材料在迅速烧结的同时,晶粒也迅速长大.     

Fabrication of transparent silica glass by powder sintering

Transparent silica glasses were obtained by sintering a green compact (fabricated by slip-casting methods for high-purity silica glass powder) in diverse atmospheres. The relationships between sintering atmosphere and sintering temperature that result in transparent, sintered silica glass were shown. The results indicate that there are four forming phases for each sintering atmosphere and temperature: (1) nontransparent glass resulting from an overabundance of pores (2) crystal, such as cristobalite or β-quartz, (3) moganite, and (4) transparent glass. Optimum sintering temperature for fabricating transparent silica glass was above 1673 K in a high-vacuum (10^–4 Pa: p(O₂) = 10^–14) atmosphere. We investigate the fabrication of transparent and hydroxyl-free silica glass by a powder-sintered method. After studying the effect of sintering schedule on residual [OH^–] concentration for transparent, sintered silica glasses, we sintered a green compact prepared by silica powders with a mean particle size of 1.6 µm, first heating it to 1523 K for dehydration and then to 1873 K for densification. This typical fabricated condition resulted in a transparent, sintered silica glass with <1 ppm [OH^–] concentration.     

A study of diffusion mechanisms in sintering by shrinkage measurements

Shrinkage measurement is important in the study of sintering to ascertain the operative mechanism. Surface area reduction is related to shrinkage with the help of which operative mechanisms at different temperatures are inferred. Densification during sintering is mainly related to volume diffusion, grain boundary diffusion and plastic flow.