陶瓷注射成型研究进展

陶瓷注射成型是一种近净尺寸陶瓷可塑成型方法，是当今国际上发展最快、应用最广的陶瓷零部件精密制造技术。清华大学新型陶瓷与精细工艺国家重点实验室近十年一直致力于陶瓷注射成型的研究，本文将介绍我们在这一领域取得的进展。     

陶瓷注射成型的研究

注射成型是可批量制备形状复杂陶瓷部件的一种先进技术,本工作研究了陶瓷注射成型悬浮体的流变特性,考察了不同注射工艺参数对成型过程和坯体质量的影响,对脱脂过程中有机物的热分解和热失重特性进行了分析,研究了脱脂机理及陶瓷部件的实际脱脂过程,制备了完好的大尺寸陶瓷涡轮转子和叶片。     

陶瓷微注射成型技术的研究与进展

本文介绍了陶瓷微注射成型工艺过程的新特点和新技术;探讨了陶瓷微注射成型充模流动模拟所采用的理论模型及其应用研究现状;最终指出微注射成型技术研究应该着重于陶瓷微注射模拟新方法、微尺寸型腔内的流动机理、微型零件的质量控制方法、微注射成型工艺和设备研制上.     

陶瓷现代成型技术的研究进展

分析了成型工艺在陶瓷制备中的重要作用和高质量的陶瓷坯体对成型工艺的基本要求，评述了国内外陶瓷现代成型技术，着重介绍了离心沉积成型、电泳沉积成型、离心注浆成型、注射成型、胶态成型和快速自动成型等新工艺，讨论了上述成型方法的基本原理和特点，指出了陶瓷成型技术的发展思路。     

陶瓷注射成型有机载体的选择及相容性研究

对数种陶瓷注射成型常用的有机载体，通过ＤＳＣ，ＳＥＭ，溶度参数计算和高温金相显微镜观察，定性和定量地研究了有机载体之间的相容性及它们与Ｓｉ３Ｎ４粉体的润湿性，在此基础上的考察了配方不同的注射成型混合物料的流变特性，确定了适于陶瓷注射成型的有机载体。     

高温合金精密铸造用陶瓷型芯成型技术研究进展

介绍了高温合金在航空发动机部件中的重要地位，以及高温合金熔模铸造用陶瓷型芯的应用背景，概述了陶瓷型芯成型技术的研究现状和重要意义。系统综述了先进陶瓷型芯成型技术的发展历史、特点及其最新研究进展，其中包括注射冷冻成型技术、无模成型技术、负复型技术以及充芯材料灌浆成型技术。重点介绍了立体光刻成型和三维打印成型等无模成型技术，并分析了目前无模成型技术所具有的独特优势和当前产业化所面临的问题与挑战。     

陶瓷的注射成型技术

陶瓷注射成型技术可解复杂形状的高性能陶瓷元件的大批量生产难题,并且产品尺寸精度高,表面条件好,论述了瓷注射成型工艺中粘结剂选取,注射成型,脱脂等步骤,并提出了将来的研究方向。     

陶瓷注射成型粘结剂现状及发展趋势

本文重点介绍了陶瓷注射成型粘结剂的种类，特性及脱脂技术，比较了目前几种粘结剂体系的优缺点，指出了今后粘结剂发展方向和趋势。     

浅析我国塑料成型技术的发展

随着人们对塑料制品品质要求的提高、应用领域的不断扩展，新的塑料制品成型技术不断涌现，本文综述了近年被进一步研发的动态注射成型、流体辅助注射成型(GAIM和WAIM)、微孔发泡注射成型、高速低压注射成型、交变注射成型、熔芯注射成型、旋转成型及反应挤出成型技术，简介了吹塑技术和模压技术的发展，并描述了其各自的特点。塑料制品的成型技术仍有广阔的发展空间，能更进一步地提高制品各种性能、制造成本，并拓宽应用领域。     

工艺参数对陶瓷注射成型的影响与分析

本研究通过改变注射温度，注射压力，保压压力等几个主要参数，对形状，体积不同的注射成型体，试条，圆柱及子部件进行了一系列注射工艺实验。相应地对成型体的密度，弯曲强度及烧结体的密度和强度进行测量，并从陶瓷注射成型混合物的流动行为，热物理特性方面对注射这一复杂过程进行分析，探讨工艺参数对成型过程的内在影响，从而确定合理的注射工艺条件。     

Scale-up of fluidized-bed hydrodynamics

The scale-up of fluidized beds is not an exact science. However, using proven techniques based on experience and mathematical and/or design models can minimize risk and uncertainty when scaling up fluidized beds. Scaling, which maintains that certain dimensionless groups be matched in different sized units for hydrodynamic similarity to be achieved, is different than scale-up, and generally can not be applied to pilot plants used for scale-up. Scaling is typically more useful to be applied to cold model studies that can be used to improve the operation of an existing plant. Deep fluidized beds of Group A materials can cause significant gas bypassing leading to poor gas-solids contacting. Because commercial beds are generally deeper than beds used in pilot plants, care must be taken to ensure that beds that do not exhibit gas bypassing in smaller units, do not have gas bypassing in commercial systems.     

Some observations on failure of quasi brittle materials under thermal stress

The behaviour of a panel of a strain softening material is examined as it is heated to high temperature. It is noted that overall failure can occur due to instability and that this will be the usual mode of compression failure in such structures. It is seen that a limited amount of cracking due to tensile stress can be a stabilising influence and it is suggested that this should be recognized in design.     

The Use of SI Units

It is intended that, generally, the SI system of units shall be used in the Society's publications, in accordance with accepted rules. It is important to appreciate that SI units have evolved, that further additions and amendments may be made, and, particularly, that there is still lack of uniformity in interpretation and application of the system. It may be argued that the Society, through its Publications Committee, should take a lead in proposing and adopting one well-considered procedure. On the other hand, it can be maintained that what is required is a clear exposition of the “state of the art”, and that it is this that the Society can and should provide to guide readers of its publications and contributors to them. This paper, sponsored by the Publications Committee, is designed to serve as a guide to SI units and the use of the SI system. It owes its inception to MrR. Murphy of the Department of Industrial Chemistry, The Queen's University, Belfast. It was his “Notes on the Use of SI Units”, submitted to the Committee, which led to the decision that a more general paper on SI units should be produced. A large part of the information regarding SI equivalents for cgs (centimetre-gram-second) and ft-lb-sec (foot-pound-second) units is taken from his paper. The Committee is much indebted to him for this. It is also much obliged to him for the many helpful and instructive comments he made following very thorough reading of the paper in draft.     

Sonocrystallization and crystallization with gassing of adipic acid

Sonocrystallization is widely used to control nucleation and, therewith, improve the product quality. For this purpose, power ultrasound is turned on within the metastable zone during the crystallization process. But the mechanism by which power ultrasound induces nucleation is still unclear. Efforts have been made to identify the mechanism. It is assumed that nucleation is induced due to the bubble surface provided acting itself as nucleation center so that the mechanism seems to be a heterogeneous one. To prove this assumption, gassing has been investigated to induce nucleation during batch cooling crystallization. The gas bubbles are just expanding not collapsing. This study focuses on the investigation of the crystallization behavior of adipic acid during sonocrystallization and, furthermore, during the crystallization with gassing. During sonocrystallization experiments the insonation period, the ultrasonic frequency and the initial supersaturation ratio were varied. The results show that the metastable-zone width can be reduced and the crystal-size distribution, which turns out to be bimodal, can be narrowed the longer the insonation period and the higher the initial supersaturation ratio is. The crystals formed were identified as agglomerates, whereas the agglomeration can be reduced by power ultrasound. The gassing experiments demonstrated that the crystallization behavior of adipic acid can be affected similar to the application of power ultrasound. It can be concluded that gassing is an alternative to power ultrasound.     

Some basic aspects of flame resistance of polymeric materials

For a better insight into flame resistance and flame extinction it is useful to split the combustion process into its constituent elements. It then appears that the thermal decomposition is the first link in a series of reactions and therefore a better understanding of this decomposition is a prerequisite. Further, it is found that the amount of char and the amount of incombustible gases that may be formed in thermal decomposition are very important quantitative measures of flame resistance. For a large number of model substances the char residue upon pyrolysis has been determined. The residue is found to be very clearly related to the chemical structure of the polymer, so much so that the amount of char can be predicted from the structure. Finally, it has been demonstrated that there is a very significant relation between the pyrolysis residue (%) and the (limiting) oxygen index.     

Science and technology of catalytic diesel particulate filters

During the last few decades, concerns have grown on the negative effects that diesel particulate matter has on health. Because of this, particulate emissions were subjected to restrictions and various emission-reduction technologies were developed. It is ironic that some of these technologies led to reductions in the legislated total particulate mass while neglecting the number of particles. Focusing on the mass is not necessarily correct, because it might well be that not the mass but the number of particles and the characteristics of them (size, composition) have a higher impact on health. To eliminate the threat of diesel particulate matter, essentially absolute filtration in combination with the oxidation of all emitted hydrocarbons is what will be required.

After two decades of development, the first filters will soon be introduced on a large scale. Many different problems had to be overcome; it was especially important that the filter was robust and its regeneration was controllable. The key technology to controllable regeneration is oxidation catalysis, which is the main area of focus in this review. Catalytic filter regeneration is very complex, something which is apparent in the main aspects of catalysis (i.e., activity, stability, and selectivity). Complications are that the process conditions can be very transient and that the temperatures are usually low. It is shown that the oxidation catalyst cannot be examined isolated from the total system. Within the margins of size restrictions and an engine's service life, essentially all particulate matter should be trapped, the filter should be regenerated safely, no toxic by-products should be formed, and the catalyst should not alter the filtration characteristics, and vice versa.

The exhaust conditions of passenger cars are not favorable for continuous regeneration strategies, because the best strategy seems to be periodic regeneration with the aid of a catalyst. This concept is not passive, which makes it complex and expensive. The best technology for filter regeneration with trucks and buses seems to be continuous regeneration. Using the NO_x present in the exhaust gas for soot oxidation amounts to a simple and robust concept. A future limitation might be the minimal required NO_x:soot ratio; it is not sure if this will be met in future engines. Alternatively, a low-temperature catalyst may be developed that does not require NO_x. Developing such an advanced catalytic trap will be one of the major challenges of catalytic filter engineering.     

关于几种形式封头特点的比较

压力容器封头的选型和制造一定要兼顾成本和制作的难易程度,一般优选椭圆型封头和蝶形封头。采用标准椭圆形封头,其封头壁厚近似等于筒体壁厚,这样简体和封头就可采用同样厚度的钢板来制造。这不仅可以给选材带来方便,也便于简体和封头的焊接。蝶形封头的主要优点是便于手工加工成型,且可以安装现场制造。它的主要缺点即受力情况不如椭圆形封头好。     

Theory of glasses

It is argued that is possible to define a ‘perfect glass’ which is both preparable experimentally and understandable theoretically. Some basic conditions and statistical thermodynamics are derived. Polymerized glasses are complex substances but it is argued that progress may be possible by considering them to have short range properties, and long range properties. Examples are given of models of glasses with such properties and their behaviour is shown to be amenable to theory.     

The role of surface tension in microgravity slug flow

In the analysis of slug flow under gravity conditions surface tension is usually neglected. The liquid slug is treated as a homogeneous mixture and the liquid film adjacent to the wall, in the Taylor bubble zone behind the slug, is treated using the one-dimensional approach (channel flow theory). Although the use of the one-dimensional approach is not accurate, especially close to the bubble cap, it is considered as a valid approximation and it yields reasonable results for the modeling of pressure drop, bubble length and void fraction in slug flow. Since for the case of microgravity flow, surface tension is expected to be a dominant force that should not be overlooked, one may be tempted to use the same procedure for the analysis of slug flow under microgravity conditions with the surface tension included (this can be done also for non-microgravity conditions). In this work, it is shown that the inclusion of the surface tension in the one-dimensional approach for the film analysis leads to erroneous and unacceptable results near the bubble cap that cannot be used even as an approximation. It is also shown that far away from the cap the solution with and without the surface tension is practically the same. Thus, a simplified model for slug flow in microgravity is suggested that assumes a spherical shape of the bubbles at the nose that is matched with the conventional one-dimensional viscous solution far downstream. In this procedure the effect of surface tension at the nose is in fact taken into account indirectly by the imposition of a spherical cap. That is, the assumption that the bubble nose behaves similar to the behavior of small size bubbles that are controlled by surface tension.