Alcan International Limited

Luc Parent

Mukesh K Jain

Guy Peloquin

Jean Perron

Marc Auger

Daniel Baril

Andre Vaillancourt

Gilles Tremblay

Apparatus for and a method of measuring the temperature of molten aluminum or aluminum alloys. The apparatus comprises a temperature measuring device, usually a thermocouple, contained within a protective tubular sheath, the sheath enclosing the temperature measuring device at least to a point above the point of maximum immersion in molten aluminum during use of the apparatus. The sheath comprises at least one inner layer closed at one end, and an outer layer, the outer layer being made of steel or cast iron, and the inner layer being made of a continuous refractory material. The outer layer and the at least one inner layer are free of discontinuous (refractory) refractory materials between them. The continuous refractory material may be, for example, a carbon fiber-reinforced carbon or graphite fiber-reinforced calcium silicate refractory, and is resistant to failure in, i.e. penetration by, molten aluminum or aluminum alloy. The apparatus is long-lived and durable and does not contaminate the molten metal when it fails.

Method and apparatus for measurement of temperatures of molten aluminum

An ultrasonic device for detecting concentrations of solids or positions of solid/liquid interfaces in liquid media, particularly Bayer process liquids. The device comprises at least one piezoelectric element provided with electrodes; electrical circuit elements connected to the electrodes for conveying electrical signals, in use, to and from control apparatus; an ultrasound-transparent window, made of glassy carbon, positioned adjacent to the or each piezoelectric element; a protective matrix, preferably of epoxy resin, embedding and surrounding said the or each piezoelectric element and the electrodes while allowing ultrasonic waves to pass through the or each adjacent window to or from the piezoelectric element, and an external protective cover, preferably comprising an elastomer that is resistant to caustic alkali and has a smooth and non-porous surface, forming an exterior of the device except at the or each window. The use of glassy carbon for the windows makes the probes resistant to corrosion and scaling without impeding the effectiveness of the device. Further improved scaling resistance is provided by an elastomeric material preferably used as the external protective cover.

Ultrasonic probes for use in harsh environments

A temperature measuring device for measuring the temperature of an abrasive particulate material of the type found, for example, in rotary calcining kilns and the like. The device comprises a temperature sensor producing an indication of a temperature to which the sensor is exposed, circuitry or the like for connecting the temperature sensor to remote equipment for converting the indication to a recognisable form and a protective element shielding the temperature sensor from damage by the abrasive particulate material. The protective element comprises a layer of ceramic material having a matrix of alumina reinforced with 5 to 50% by volume (based on the total volume of the ceramic material) of particles of silicon carbide having an average size, at least in two dimensions, within the range of about 5 to 60 microns. The protective element provides good abrasion, heat-shock and mechanical resistance while exhibiting sufficient thermal conductivity to avoid undue inaccuracies in the temperature measurements.

High temperature and abrasion resistant temperature measuring device

A process for producing silicon carbide platelets having a size of 20 .mu.m or less, and the platelets so produced. The process comprises reacting particles of carbon from a source containing less than 0.2% by weight of iron, with silica or a silica precursor at a temperature in the range of 1800.degree.-2100.degree. C. under an inert atmosphere in the presence of 0.2-10% by weight of an oxide or oxide precursor of Ca, Mg, Al, W, Ce or Cu; 0.1-10% by weight of boron, relative to the weight of SiO.sub.2, and preferably 0.1-10% by weight of the reaction mixture of alpha silicon carbide particles having a size of 5 .mu.m or less. The carbon is preferably in the form of particles of less than 50 .mu.m and the silica or precursor is preferably in the form of particles of less than about 45 .mu.m. The weight ratio of silica to carbon is greater than 1.76:1. The carbon source is preferably a pure form of carbon, e.g. graphite or amorphous carbon. The resulting small SiC platelets are substantially unagglomerated, have a high percentage (up to 95%) of small (&lt; 20 .mu.m) platelets and preferably have an aspect ratio greater than 5. The platelets can be used as reinforcements for ceramic, metal and polymeric matrix materials.

Process for producing silicon carbide platelets

A process for producing small particles of aluminum nitride suitable for sintering and the particles thus-produced. The process comprises reacting particles of gamma alumina, or a precursor thereof, of less than 1 micron in size with a stoichiometrical excess of finely divided carbon in the presence of nitrogen, or a precursor which provides nitrogen in the reaction conditions, first at a temperature in the range of 1550.degree. to 1700.degree. C. for a period of between 1 and 6 (preferably 1 to 4) hours and then at a temperature in the range of 1750.degree. to 1850.degree. C. for a period of 1 to 4 (preferably 1 to 2) hours, followed by cooling said reaction mixture and reheating to a temperature in the range of 500.degree. to 700.degree. C. in an oxygen-containing atmosphere, and maintaining the temperature until excess unreacted carbon is removed. The alumina or precursor preferably has a particle size of less than 400 nm and the carbon source preferably contains iron as an impurity, and is preferably petroleum coke. The AlN product is particularly suited for use in forming a substrate for electronic components by a process involving sintering of the AlN particles because of the small size (less than 2 microns) and narrow size distribution of the particles.

Process for producing small particles of aluminum nitride and particles

A process for producing unagglomerated single crystals of aluminum nitride of low oxygen content having a size of at least 10 microns suitable for the reinforcement of metal, ceramic and polymeric matrix composite materials, and especially metal matrix materials. The process involves producing a reaction mixture of alumina (or a precursor), carbon (or a precursor), and an alkali metal oxide (or precursor such as a carbonate) as a crystal growth promoter or catalyst. The alkali metal oxide is present in an amount required for the formation of crystals of the required size, preferably in the range of 10-60 microns. The reaction mixture is subjected to a preheating step under nitrogen at a temperature in the range of 1600.degree.-1700.degree. and is then subjected to a heating step under nitrogen at a temperature in the range of 1800.degree.-1950.degree. C. This two-stage heating process ensures that the resulting crystals are of low oxygen content and thus good thermal conductivity. Particularly desirable crystals are produced if electrostatic precipitator dust is used as a source of the alumina, if petroleum coke or calcined anthracite coal is used as a source of the carbon and if the reaction is carried out in the presence of a porosity enhancer for the reaction mass, especially short cellulose fibres. The particles produced by the invention are in the form of large single crystals for good matrix reinforcement and have low oxygen and carbon contents. The invention extends to the particles produced by the process and to matrix composites reinforced with the particles.

Process for producing unagglomerated single crystals of aluminum nitride

A process for producing silicon carbide platelets having a size of 20 .mu.m or less, and the platelets so produced. The process comprises reacting particles of a non-graphitizable form of hard carbon containing 0.5-1.5% by weight of aluminum and at least 0.2% by weight of iron (preferably anthracite coal, most preferably Pennsylvania anthracite), with silica or a silica precursor at a temperature in the range of 1800.degree.-2100.degree. C. under an inert atmosphere. If the carbon contains 0.2-1.0% by weight of iron, 0.1-10% by weight of boron, relative to the weight of SiO.sub.2, is added (if not already present). In the invention, 0.1-10% by weight of the reaction mixture of alpha silicon carbide particles having a size of 5 .mu.m or less are added to the reaction mixture to control the size of the platelets so that a majority have a size of less than 20 .mu.m. The carbon is in the form of particles of less than 50 .mu.m and the silica or precursor is preferably in the form of particles of less than about 1 .mu.m. The weight ratio of silica to carbon is greater than 1.67:1. The resulting small SiC platelets are substantially unagglomerated, have a high percentage (up to 95%) of small (&lt;20 .mu.m) platelets and preferably have an aspect ratio greater than 5. The platelets can be used as reinforcements for ceramic and metal matrix materials.

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Chicoutimi, Canada

Luc Parent