Shaping in ceramic technology

In his contribution entitled Shaping in ceramic technology - an overview , Andrea Bresciani, who is with the world s largest ceramic plant equipment contractor SACMI, describes and compares the three most important ceramic shaping methods. 

This chapter focuses on the chemical processing of ceramic membranes, which has to date constituted the major part of inorganic membrane development. Before going further into the ceramic aspect, it is important to understand the requirements for ceramic membrane materials in terms of porous structure, chemical composition, and shape. In separation technologies based on permselective membranes, the difference in filtered species ranges from micrometer-sized particles to nanometer-sized species, such as molecular solutes or gas molecules. One can see that the connected porosity of the membrane must be adapted to the class of products to be separated. For this reason, ceramic membrane manufacture is concerned with macropores above 0.1 pm in diameter for microfiltration, mesopores ranging from 0.1 pm to 2 nm for ultrafiltration, and nanopores less than 2 nm in diameter for nanofiltration, per-vaporation, or gas separation. Dense membranes are also of interest for gas... 

But CMCs will be commercially successful only when they are produced cost-effectively. Polymer-derived ceramic (PDC) technology is one of the most promising low cost fabrication methods for ceramic matrix composites, particularly for large, complex shapes. In PDC technology, a silicon-based polymer (siloxane, carbosilane, silazane, etc) with fiber or particle reinforcement is shaped and cured in the polymer condition and then pyrolyzed in a controlled atmosphere to form a stable silicon-based ceramic, such as silicon carbide, sihcon nitride, silicon oxycarbide, or silicon oxynitride. 

In Section 1.4.4, the erosion test was outlined in the list of hardness determination methods and it was concluded that it was of minimal practical importance. However, solid particle erosion is a serious problem in gas turbine operations and in plants where powders are handled and it is of course used as a secondary shaping method in ceramic technology. Therefore it is more useful to consider how a knowledge of ceramic hardness contributes to an assessment of erosion. Figure 5.19 outlines how a knowledge of the process has developed through models taken from the types of indentation test damage already discussed in this chapter. 

Suspensions or dispersions of particles in a liquid medium are ubiquitous. Blood, paint, ink, and cement are examples that hint at the diversity and technological importance of suspensions. Suspensions include drilling muds, foodstuffs, pharmaceuticals, ointments and cremes, and abrasive cleansers and are precursors of many manufactured goods, such as composites and ceramics. Control of the structure and flow properties of such suspensions is often vital to the commercial success of the product or of its manufacture. For example, in consumer products, such as toothpaste, the rheology of the suspension can often determine consumer satisfaction. In ceramic processing, dense suspensions are sometimes molded (Lange 1989) and then dried and sintered or fired into optical components, porcelin insulators, turbine blades, fuel cells, and bricks (Rice 1990 Simon 1993). Crucial to the success of the processing is the ability to transform a liquid, moldable suspension into a solid-like one that retains its shape when removed from the mold. These examples could be multiplied many times over. 

Major advances in ceramic extrusion technology and processing have enabled substantial advances in product quality. In consequence a wide range of shapes, sizes and cell dimensions are available (ref. 27). 

Tho objectives of the program "Dispersion-Toughened Silicon Nitride" carried out within the scope of the Ceramic Technology for Advanced Heat Engines (CTAHE) program are to develop an advanced toughened silicon nitride composite and a process for near net shape part fabrication. The work on this program was Initiated In 1985. 

K. A. Blakely, The Critical Role of Raw Material Suppliers in Market Development pp. 21-27 in Ceramic Transactions, Vol. 62, Science, Technology and Commercialization of Powder Synthesis and Shape Forming Processes. Edited by J. J. Kingsley, C. H. Schilling, and J. H. Adair. The American Ceramic Society, Westerville, OH, 1996. 

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