ALUMINA SINTERED COMPACT FOR PROTECTIVE TUBE OF THERMOCOUPLE AND PRODUCTION THEREOF

• Main Authors: TAKESHITA MASAAKI, OGAWA YUKIMI, KURITA SUMIHIKO
• Format: Patent
• Language: English
• Published: 13.08.1996
• Edition: 6
• Subjects: ARTIFICIAL STONE; CEMENTS; CERAMICS; CHEMISTRY; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDINGMATERIALS; CONCRETE; LIME, MAGNESIA; MEASURING; MEASURING QUANTITY OF HEAT; MEASURING TEMPERATURE; METALLURGY; PHYSICS; REFRACTORIES; SLAG; TESTING; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR; TREATMENT OF NATURAL STONE

PURPOSE: To obtain excellent heat resistance, corrosion resistance and characteristics against high temp. creeping and low sintering temp. which decreases the production cost, by forming a specified alumina sintered compact comprising a mixture crystal structure of coarse grains and fine grains. CONSTITUTION: The alumina sintered compact contains >=99.5% aluminum oxide and a sintering aid as the essential component and its crystalline structure consists of coarse grains of >=5μm grain diameter and fine grains of <=3μm grain size. The sintering aid (e.g. alkaline earth metal oxide such as magnesium oxide) is added by <=0.5wt.% to the start source material containing 2-20wt.% fine particles of aluminum oxide having <=1μm average grain diameter. The mixture is compacted into a tube of a specified dimension and then sintered to obtain the mixture structure as above described. The compacted body is sintered in an electric furnace or gas furnace at <=300 deg.C/hr temp. rising rate and <1500 deg.C, preferably <=1400 deg.C sintering temp., then kept for 1-4 hours at this temp. and then cooled in the furnace. It is necessary that the purity of the alumina source be >=99.5%.