Integral degree of blackness of fibrous refractory materials

Abstract

In contemporary metallurgy the role of refractories is extremely important, both technologically and also from the point of view of accelerating the heat processes and rational utilization of energy.This makes it necessary to conduct all-round investigations into refractories, including their radiation characteristics, which have a substantial influence on the heat exchange in the working space of the furnace.The present work deals with an experimental investigation of the integral normal degree of blackness ~tn of fibrous refractories during heating to 1500 K in oxidizing and in inert gas atmospheres.Measurements were made on experimental equipment described in [i]. Specimens were heated in the radiation optical URAN-I furnace in which the source of intensive thermal radiation consisted of a xenon high-pressure lamp, DKsR-10000, located at the first focus of an elliptical mirror reflector.The temperature of the materials being studied was measured with chromel-alumel thermocouples 0.2 mm in diameter, the hot joints of which were attached to the surface of the specimens with refractory cement, and the cold ends were thermostatically controlled at 0~The source of radiation energy consisted of a semiconductor bolometer BKM-5 placed in a thermostatically controlled frame with an automatically maintained temperature (303 • I)K. The temperature of the specimen and the bolometer signal were measured on a digitial metering complex F30K.The rate of heating the specimens was fixed and regulated with an automatic potentiometer KSP-4.The bolometer was graduated with respect to a model of an absolutely black body, consisting of a graphite cone with an opening angle of 13 ~ , pressed in a molybdenum block, which was heated in vacuum in a tungsten resistance furnace.The integral normal degree of blackness etn in the case of equality of the resulting currents of radiation of specimen and black body was calculated from the equation T0--T~2t~t"~ where T0, TI, and T z are respectively the temperature of the black body, the specimen, and the heat receiver.The total error of the determination of ~tn was 12-13%.The investigations were made on the following fibrous materials: ShVP-350 from 75% aluminosilicate fibers (SiO z 49-50%, AIzO 3 48-49%, FezO 3 0.8-1.3%, CaO 0.6-0.8%, MgO 0.3-0.9%, S 0.2-0.8%) and 25% clay bond; ShVP-350 with a coating about 0.5 mm thick of 10% silica sol (water solution of SiOz) ; high-temperature refractory made of 95% mullite-silica fiber (SiO z 46-47%; AIzO 3 46-48%, CaO 2.8-3.5%, NazO 0.9-1.2%, FezO 3 0.9-1.1%) and 5% silica sol bond. The surface of the latter refractory was coated with a layer of 22% silica sol, about 0.5 mm thick.The apparent density of the fibrous material ShVP-350 was 350-380 kg/m 3, and of the high temperature refractory 240-260 kg/m 3. The diameter of the fibers for these materials did not exceed 8-10 ~m. The specimens of diameter 30 and thickness 4-5 mm were cut so that their working (radiating) surfaces formed the face of a standard brick.The thickness of the specimens was selecte...