Zirconia in the context of "Diamond simulant"

An oxygen sensor is an electronic component that detects the concentration of oxygen molecules in the air or a gas matrix such as in a combustion engine exhaust gas.

For automotive applications, an oxygen sensor is referred to as a lambda sensor, where lambda refers to the air–fuel equivalence ratio, usually denoted by λ). It was developed by Robert Bosch GmbH during the late 1960s under the supervision of Günter Bauman. The original sensing element is made with a thimble-shaped zirconia ceramic coated on both the exhaust and reference sides with a thin layer of platinum and comes in both heated and unheated forms. The planar-style sensor entered the market in 1990 and significantly reduced the mass of the ceramic sensing element, as well as incorporating the heater within the ceramic structure. This resulted in a sensor that started sooner and responded faster.

Ceramography is the art and science of preparation, examination and evaluation of ceramic microstructures. Ceramography can be thought of as the metallography of ceramics. The microstructure is the structure level of approximately 0.1 to 100 μm, between the minimum wavelength of visible light and the resolution limit of the naked eye. The microstructure includes most grains, secondary phases, grain boundaries, pores, micro-cracks and hardness microindentations. Most bulk mechanical, optical, thermal, electrical and magnetic properties are significantly affected by the microstructure. The fabrication method and process conditions are generally indicated by the microstructure. The root cause of many ceramic failures is evident in the microstructure. Ceramography is part of the broader field of materialography, which includes all the microscopic techniques of material analysis, such as metallography, petrography and plastography. Ceramography is usually reserved for high-performance ceramics for industrial applications, such as 85–99.9% alumina (Al₂O₃) in Fig. 1, zirconia (ZrO₂), silicon carbide (SiC), silicon nitride (Si₃N₄), and ceramic-matrix composites. It is seldom used on whiteware ceramics such as sanitaryware, wall tiles and dishware.

• Ceramographic microstructures
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  Fig. 1: Thermally etched 99.9% alumina
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  Fig. 2: Thin section of 99.9% alumina