Ceramic materials mechanical strength

SiHcon nitride (see Nitrides) is a key material for stmctural ceramic appHcations in environments of high mechanical and thermal stress such as in vehicular propulsion engines. Properties which make this material uniquely suitable are high mechanical strength at room and elevated temperatures, good oxidation and creep resistance at high temperatures, high thermal shock resistance, exceUent abrasion and corrosion resistance, low density, and, consequently, a low moment of inertia. Additionally, siHcon nitride is made from abundant raw materials. 

Crockery preferably is made from ceramic materials, although it is brittle and can break rather easily. Properties of ceramics, such as resistance to absorb flavours and low heat conductivity, however, are superior compared to metals and plastics. Therefore, we defined a task to design crockery with improved mechanical strength. 

The carbides and nitrides are well known for their hardness and strength, and this section will briefly compare a number of these properties with those of the pure metals. Concentration will be placed here on the first row compounds, since these constitute a complete series, and Mo and W, since these are the most commonly studied metals. As will be shown, the physical and mechanical properties of carbides and nitrides resemble those of ceramics not those of metals. Comparisons will be made with boron carbide (B4C), silicon carbide (SiC), aluminium nitride (AIN), silicon nitride (Si3N4), aluminium oxide (A1203), and diamond, as representative ceramic materials. 

In view of the bio-compatibility the composition of glass cannot be altered in such a way that its mechanical strength becomes equally good as that of the glass ceramics of, e.g., a ceramic cooking plate. Consequently, the material is unsuited for important load-bearing implants... 

The use of proven catalyst recipes would greatly curtail development times, and the absence of extraneous material avoids unwanted catalytic effects and enhances thermal stability. The fixation of catalyst on ceramic substrates such as washcoats is a well-known, reliable, and relatively straightforward procedure. The fabrication of complex small-scale ceramic structures is, however, more awkward than for metals or plastics, and they exhibit relatively poor mechanical strength. Furthermore, the porous ceramic nanostructure must be sealed to prevent contact between the reaction medium and coolant. 

Aluminum hydroxide is used in stomach antacids (including Maalox , Mylanta , and Delcid ), as a desiccant powder in antiperspirants and dentifrices in packaging materials as a chemical intermediate as a filler in plastics, rubber, cosmetics, and paper as a soft abrasive for brass and plastics as a glass additive to increase mechanical strength and resistance to thermal shock, weathering, and chemicals and in ceramics (HSDB 1995). Aluminum hydroxide is also used pharmaceutically to lower the plasma phosphorus levels of patients with renal failure (Budavari et al. 1989 Sax and Lewis 1987). 

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