Ceramic components

All the pyrolyzed samples were XRD amorphous. Weight loss ( 28 weight-%) and linear shinkage ( 29%) associated to the pyrolysis treatment were found to be 

6 Polymer to Ceramic Transformation Processing of Ceramic Bodies and Thin Films 

The open porosity of the PAlCs-derived ceramic samples shows a weak dependence from the amount of aluminum and falls in the range f 8-13%. It increases up to w20% for the PCS-derived component. Such low values of open porosity have been already reported in the literature for similar polymer-derived ceramics [56] and indicate that this processing route is suitable for the fabrication of dense (up to 92% of theoretical density) covalent ceramics at low temperature. The porosity values measured for the ceramic products are comparable with the starting pre-ceramic samples. Indeed, results of the mercury infiltration experiments indicate that the pyrolysis process leads to the removal of the finer pore fraction (below lOnm) leaving almost unchanged the amount and the size of the coarser pores. 

The evolution of the MOR and E with the Al/Si ratio is reported in Figs 10 and 11. Surprisingly, contrary to the behavior of all the other studied parameters, these 

Al/Si (Atom ratio) Batch number Bulk density Pb (gcm ) Porosity P(%) Flexural strength (MOR) (MPa) Elastic modulus (GPa) 

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Generally, tlie last step in ceramic component manufacturing is tliennal processing [60, 61, 62 aiid 65]. This is tlie stage where tlie weakly-bound particulate body produced during shape fonning is heat treated to produce a... 

Presentiy, multilayer capacitors and packaging make up more than half the electronic ceramics market. For multilayer capacitors, more than 20 biUion units are manufactured a year, outnumbering by far any other electronic ceramic component. Multilayer ceramics and hybrid packages consist of alternating layers of dielectric and metal electrodes, as shown in Figures 5 and 6, respectively. The driving force for these compact configurations is miniaturization. 

Principal producers of ferroelectric capacitors are (110) Murata Manufacturing Co., Ltd., Kyoto, Japan Kyocera Corp., Kyoto, Japan Philips Electronics, N.V., Eindhoven, the Netherlands and NEC Corp., Tokyo, Japan. Principal piezoelectric ceramic component producers are (110) Murata Manufacturing Co., Ltd., Kyoto, Japan Motorola, Inc., Schaumburg, lU. EDO Corp., College Point, N.Y. Morgan Matroc, Inc., Bedford, Ohio Kyocera Corp., Kyoto, Japan and Philips Electronics, N.V., Eindhoven, the Netherlands. 

In order to test the strength of a ceramic, cylindrical specimens of length 25 mm and diameter 5 mm are put into axial tension. The tensile stress a which causes 50% of the specimens to break is 120 MPa. Cylindrical ceramic components of length 50 mm and diameter 11 mm are required to withstand an axial tensile stress with a survival probability of 99%. Given that m = 5, use eqn. (18.9) to determine oh... 

Most ceramics (as we have seen) contain flaws holes and cracks left by processing, cracks caused by thermal stress, corrosion or abrasion. Even if there are no cracks to start with, differences in elastic moduli between phases will nucleate cracks on loading. And most of these flaws have a size which is roughly that of the powder particles from which the ceramic was made. If the flaw size can be reduced, or if samples containing abnormally large flaws can be detected and rejected, the mean strength of the ceramic component is increased. 

Ceramics cannot be bolted or riveted the contact stresses would cause brittle failure. Instead, ceramic components are bonded to other ceramic or metal parts by techniques which avoid or minimise stress concentrations. 

Why are special precautions necessary when joining ceramic components to metal components What methods are available for the satisfactory joining of ceramics to metals ... 

Uniform microstractuie is cracial to the superior performance of advanced ceramics. In a cerantic material, atoms are held in place by strong chentical bonds that ate impervious to attack by corrosive materials or heat. At the same time, these bonds are not capable of much "give." When a ceramic material is subjected to mechanical stresses, these stresses concentrate at minute imperfections in the microstmcture, initiating a crack. The stresses at the top of the crack exceed the threshold for breaking the adjacent atomic bonds, and the crack propagates throughout the material causing a catastrophic brittle failure of the ceramic body. The rehability of a ceramic component is directly related to the number and type of imperfections in its microstmcture. 

A PCT thermistor is an electrical ceramic component that has a low resistivity at the normal operating temperature of the equipment. Under these circumstances current is allowed to flow to the machinery. The current passing through the thermistor heats it. If an unusually high current passes, the temperature rise causes the resistivity of the thermistor to increase manyfold, and the device switches abruptly to a high-resistivity state. This effectively switches off the current flow and so protects the equipment from damage. 

Manufacturing technology for the ceramic components (especially firing of the thin flat plates)... 

ITSOFC The intermediate temperature solid oxide fuel cell combines the best available attributes of fuel cell technology development with intermediate temperature (600-800°C) operation. Ceramic components are used for electrodes and electrolytes carbon does not... 

Fitzer. E., Fritz. W. and Gadow, R. (1984). Carbon fiber reinforced silicon carbide. In Proc. International Symp. on Ceramic Components for Engineering (S. Somiya, E. Kanai and K. Ando, eds.), Elsevier. London, pp. 505-518. 

Additional information required to evaluate a sensor includes specifications on the bake-out temperature (during measurement or with the cathode or SEMP switched off), materials used and surface areas of the metal, glass and ceramic components and the material and dimensions for the cathode data is also needed on the electron impact energy at the ion source (and on whether it is adjustable). These values are critical to uninterrupted operation and to any influence on the gas composition by the sensor itself. 

When the powder is isostatically compacted at elevated temperatnres, the process is called hot isostatic pressing (HIP). In this case, the flexible dies are often made of thin metals, and high-pressnre gases snch as argon are nsed to heat the part rapidly and rednce thermal losses. Pressnre np to 100 MPa and temperatnres in excess of 2000°C are possible nsing HIP, and parts up to 600 kg can be fabricated. A schematic diagram of a typical HIP apparatus is shown in Figure 7.18. Metals that are processed commercially by HIP include various specialty steels, superalloys, hard metals, refractory alloys, and beryllium. We will see in Section 7.2 that HIP is also particularly useful for the densification of ceramic components. 

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