Abstract: A ceramic having a relatively high proportion of an alpha prime SiAlON phase and exhibiting high hardness and toughness. In a particularly preferred embodiment, a cation of Gd is used as a modifying cation.

Abstract: Novel partially stabilized zirconia ceramic compositions exhibiting improved toughness comprising: a major component consisting of ZrO.sub.2, a minor stabilizing component Y.sub.2 O.sub.3 and an effective amount of a toughening agent (e.g., Ta.sub.2 O.sub.5). The toughness of the tetragonal zirconia polycrystal (e.g., 96% ZrO.sub.2, 3 mole % Y.sub.2 O.sub.3) can be increased nearly three-fold by replacing 1% of the ZrO.sub.2 with Ta.sub.2 O.sub.5. Empirical equations based on ratios of fundamental lattice parameters (e.g. c/a) quantitatively relating to the stability/instability of tetragonal zirconia oxide are disclosed and used in a novel method for improving the toughness of the ceramic compositions.

Abstract: Novel transformation toughened ceramic compositions comprising finely divided ZrO.sub.2 -HfO.sub.2 solid solution particles dispersed in a Al.sub.2 O.sub.3 -Cr.sub.2 O.sub.3 (alumina) or 3Al.sub.2 O.sub.3.2SiO.sub.2 -3Cr.sub.2 O.sub.3.2SiO.sub.2 (mullite) solid solution matrix phase. It is found that increased hardness and modulus associated with higher relative Cr.sub.2 O.sub.3 content (e.g. 20 mole %) in the matrix phase and increased fracture toughness associated with higher relative HfO.sub.2 content (e.g. 10 to 20 mole %) in the disperse phase represent viable and improved ceramic compositions. Such transformation toughened ceramic compositions are considered useful in superhot light diesel engine applications, high temperature gas turbines and ultrahigh temperature ceramic heat exchangers.

Abstract: An oxygen sensor utilizes a chrome oxide compensating resistor (5) in series with a titania sensing resistor (3). The chrome oxide resistor (5) not only compensates for the effects of temperature on the titania sensing (3) resistor, but since it exhibits (p) type behavior while the titania exhibits (n) type behavior in the presence of gaseous oxygen, the sensitivity of the sensor is increased. The resistors (3, 5) can be applied as a film to a substrate (7) or they can be formed as discrete chips. Substantial quantities of alumina and glass can be added to the chrome oxide without affecting oxygen sensitivity although the electrical resistance rises substantially.

Abstract: An oxygen sensing device particularly suited as a sensor for the exhaust gases of internal combustion engines, the sensing device comprising an electrically insulative ceramic element having bonded on the surface thereof a layer of an oxygen sensing metal oxide, preferably titania, and a pair of electrical leads for the oxygen sensing metal oxide, the device also having a layer of electrical resistance heating material adjacent to the layer of oxygen sensing metal oxide but separated therefrom by a layer of the electrically insulative ceramic, a pair of electrical leads for the electrical resistance heating material, and a layer of ceramic covering the layer of electrical resistance heating material.

Abstract: A transducer operative to generate an electrical signal proportional to the partial oxygen pressure in a gas consists of a tube, closed at one end, of zirconia stabilized with yttria. The outer surface of the tube is coated with a porous electronic conductor and a porous platinum layer is coated over the porous conductor so that the platinum contacts the zirconia tubes at the voids in the conductor coating. Electrodes attached to the inner and outer surfaces of the tube sense the potential difference generated across the tube as a result of galvanic action. The open end of the tube is encased within a ceramic cylinder having an outer metal threaded sleeve. Electrodes attached to the inner and outer surfaces of the tube are joined to a connector fixed at the far end of the ceramic tubes.

Abstract: A gas sensor, and its method of manufacture, particularly useful as an exhaust gas sensor for an internal combustion engine air/fuel ratio system, is disclosed. The sensor is comprised of a sintered ceramic body of transition metal oxide, such as titania, and includes a pair of spacedapart electrodes. As the partial pressure of oxygen in the gas being sensed varies in response to variations in the inlet air/fuel mixture ratio, the resistance of the ceramic material varies. The active portion of the sensor body is a substantially uniform body of porous ceramic material having a density of less than about 85% of theoretical density and a modulus of rupture in excess of 11,000 psi. The sensor is fabricated from a very pure transition metal oxide powder having a very fine and highly uniform particle size. The transitional metal oxide is selected so that the operating temperature of the resulting device is less than about 75% and preferably less than about 50% of the melting temperature of the metal oxide.