Ceramic technical requirements

Innovation process Unlike silencers, a substitute for ceramic fibres in catalytic converters is not yet available because very stringent technical requirements have to be met. The test cycles and clarification of the technical and other properties (occupational health and safety and environmental protection) are also correspondingly extensive. Solutions are being developed in cooperation with manufacturers, users and official bodies. 

All shaping methods (also called molding ) mentioned are well-known in the ceramic industry [244, 247], Selection criteria depend on economical and technical requirements. Simple shaped parts mainly produced by uniaxial pressing, cold isostatic pressing, casting and especially injection moulding are favoured for components with complex geometry [263]. 

A promising area is the design of modem ceramic and glass ceramic materials based on high purity elementorganic compounds Si(OR)4, Al(OR)3, B(OR)3, etc.), because traditional materials (metals, metal-based alloys, plastics, etc.) do not meet contemporaiy technical requirements to products designed to operate under extreme conditions. 

In the field of technical ceramics, these requirements are usually satisfied. Extrusion is practiced with well-prepared, homogeneous compounds conducive to constant, uniform production. On the other hand, extrusion involves very high pressures, often in excess of 200 bar, and, frequently, body that is difficult to extrude. This calls for extrusion tools - inch everything from the extruder itself to the die exit - of hydraulically optimized design. Moreover, the extrudates and honeycomb elements for technical applications must display high levels of exactitude. For example, the engineering of a honeycomb die for thin-walled honeycombs, i.e., ceramic monoliths, with web thicknesses of 0.15 mm and less demands a degree of precision that can only be achieved with state-of-the-art machine tools. 

The final applications discussed here are electrodes and metallizations for fine ceramics. This includes ohmic contact pastes for varistors and thermistors as well as materials for complex multilayer components. Figure 8.105 illustrates a cross-sectional view of a ceramic chip capacitor. The internal electrode can be Pt, Pd, or Ag-Pd depending on the type of ceramic formulation and its respective firing temperature. The end termination may be Ag or Ag-Pd and is typically required to be platable. The technical requirements of these materials are extremely challenging. 

Only a very few crystal structures accomplish the following technical requirements for ceramic pigments ... 

X-ray tubes are used in a broad variety of technical applications the classical application certainly is the radiographic inspection. For the penetration of high-Z materials, relatively high power is required. This lead to the development of X-ray tubes for laboratory and field use of voltages up to 450 kV and cp power up to 4,5 kW. Because of design, performance and reliability reasons, most of these maximum power stationary anode tubes are today made in metal-ceramic technology. 

Electric tube furnaces of appropriate dimensions are available from various manufacturers. A model RO 4/25 by Heraeus GmbH, Hanau, FRG is suitable. However, a very satisfactory furnace can be built by any well equipped laboratory workshop at little cost and effort. The material required consists of thin walled ceramic tubing, 3.5 cm i.d., nichrome resistance wire, heat resistant insulation, and ordinary hardware material. A technical drawing will be provided by the submitters upon request. The temperature of the furnace can be adjusted by an electronic temperature controller using a thermocouple sensor. A 1.5 kW-Variac transformer and any high temperature thermometer would do as well for the budget-minded chemist. 

The membrane areas needed in these plants are not huge, but the technical challenges are substantial. Defect-free, anisotropic composite ceramic membranes that are 1-5 pm thick, able to operate continuously at 800-1000 °C, nonpoisoning, nonfouling and low-cost are required—not impossible, but difficult. Conceptual designs of the type of reactor required are beginning to appear. 

In order to improve this situation, studies have been made of the individual isolated ceramic phases, and also of their formation and distribution in the ceramic material. The method has proved satisfactory for both classical and new types of ceramic materials, and still represents a significant proportion of both physical and chemical research in the field of ceramics. It has yielded many positive results, in particular with respect to ceramics of simple phase and chemical composition. From this point of view, it is also clear that development of new ceramics for technical applications, with the strict requirements for properties and tolerances involved, is based on the use of synthetic raw materials, which allow for improved control of the respective manufacturing processes. 

The casting of fluid suspensions into piaster moulds is one of the traditional ceramic forming techniques which is used in particular for asymmetrical and complicated thin-walled shapes. The process is economical even with small series of ware, since the moulds are not costly and minimum technical equipment is required. 

An important step in the manufacture of ceramic products is their thermal treatment at relatively high temperatures > 800°C. This step, known as firing , leads to strengthening of the unsintered molded articles into durable final products with the required form. The processes which take place are collectively known by the technical term sintering . 

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