Thermal shock resistance of refractories

The classical research on the thermal shock resistance of refractories and brittle solids was made by D. P. H. Hasselman [109, 110]. For samples of a simple shape (thin plate, hollow cylinder, sphere), which are cooled in a liquid medium, the... 

ASTM 38-89. Standard test method for the thermal shock resistance of refractory brick (withdrawn). 

There are two standard methods for determining the thermal shock resistance of refractory materials. For brick shapes, thermal shock resistance is measured by Ribbon Thermal Shock Testing (ASTM C-1100), and for monolithic refractories the standard method is ASTM C-1171. These tests clearly differentiate among refractory materials about their resistance to thermal shocks. 

Semler CE, Hawisher TH. Evaluation of thermal shock resistance of refractories using the ribbon burner method. Am Ceram Soc Bull 1980 59(7) 732. 

Experience indicates that there exist substantial differences in thermal shock resistance of one type of refractory due to particle size of grog, its amount and to firing temperature. In agreement with the above concepts, the shock resistance is usually higher when the grog is coarse, the ware porous and the glass content low. 

The crystalline phases—corundum, albite, nepheline, and carnegieite —all possess a high thermal expansion coefficient. (This is typical of most alkali compounds.) As these phases form in increasingly higher amounts, the thermal shock resistance of the reacted portion of the fireclay refractory will decrease significantly. 

A relatively new development is the combination of metals and ceramic in compacts called cermets. The purpose is to combine the high refractoriness, resistance to osidation, electrical insulation, and retention of compression strength on heating—all properties d ceramic bodies—with the ductibility and thermal shock resistance of metals. ... 

The question of a good method for estimating the thermal shock resistance of carbon materials is still open. Due to high thermal conductivity and semibrittle mode of deformation, carbon cathode materials are more thermal shock-resistant compared to refractories. Yet it doesn t mean that there is no problem with thermal shock resistance in carbon cathode materials. We discuss it in Sect. 2.3. 

Drying and preheating of furnaces are very important operations. If the furnace is lined with bricks, it is recommended to make the preheating after at least 24 h, so that the lining mortar and the plastic masses will become dry and become more or less rigid. In order to diminish the tensions, it is recommended to do a 24-h exposure at 800 °C after that, the heating rate is determined by the thermal shock resistance of the refractory. 

Steel fibers improve the thermal shock resistance of the refractory. If a crack forms it is arrested. The thermal limit of the refractories will depend upon the particular alloy used. Under reducing atmospheres, some of the alloys can be effective above 1600°C. Under normal or oxidizing atmospheres, castables containing Cr-Ni-alloyed steel fibers should not be exposed to greater than 1200°C. There could be reactions among the oxides formed by the elements in steel and by those in the refractory. The effect of steel fibers on the properties of refractory castables is summarized in Table 20.5. 

Hu, R, Wang, Z., Sun, X. (2010). Effect of surface oxidation on thermal shock resistance of ZrB2-SiC-G composite. Int. Journal of Refractory Metals and Hard Materials, 28, 280-285. doi 10.1016/j.ijrmhm.2009.10.013. 

The resistance against thermal spalling of fireclay and high alumina brick is indicated in Table 5. No standard test has been adopted for basic brick. Refractories composed of 100% magnesia exhibit poor thermal shock resistance, which is improved by addition of chrome ore. So-called direct bonded basic brick, composed of magnesia and chrome additions, exhibits good thermal shock resistance. 

Alumina—graphite refractories, almost all continuous casting ware, have come into much greater use as continuous casting has spread in steelmaking. These refractories are used in shrouds that conduct the molten metal from the ladle to the tundish, in the subentry tubes that take the metal from the tundish to the mold, in isostatically pressed stopper rods, and in shroud tubes for slab and bloom casters. The alumina—graphite compositions are used in these products because of the thermal-shock resistance and corrosion resistance they impart to the product. 

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