Various methods of unfired periclase-containing refractories are known [1, 2]. Work on organization of production and introduction of unfired refractories has shown the necessity of concentration of efforts in the direction of selection of the optimum binder providing stable properties of the parts in production and in service and with low toxicity [3].Magnesite Corporation has introduced a method of production of type PShGB unfired periclase parts with a phosphate binder and addition of alumina to the charge. The basic characteristics of the parts are 85 wt. % min. MgO, &0-6.3 wt. % A1203, 0.5 wt. % min. P205, compressive strength 50 N/ram 2 min., and open porosity 16% max.This form of refractories has been developed in connection with the poorer mineral composition of the raw material and the sharp increase in energy costs. In 1991-1992 several experimental production lots of parts were produced for testing under various conditions. After service, specimens of the parts were subjected to chemical, petrographic, and X-ray diffraction analyses and certain physicomechanical tests.In the foundry of the Kama Automobile Plant parts were tested in the wall lining of a 50-ton arc furnace above the level of the sills (25 rows of the lining). During the tests high-strength, malleable, and gray irons were melted in the furnace. The time of a heat was 230 min. The metal temperature at tapping varied from 1450 to 1570~ During service, depending upon the condition of the lining, the banks and partially the walls opposite the phases were patched with magnesite powder.The furnace was shut down for repair after 148 heats with a remaining thickness of the parts of 130 mm (initially 348 mm). The campaign preceding the experimental one lasted for 147 heats, that is, the unfired periclase-spinel refractories showed practically the same life as standard fired periclase-spinel parts. After service, the unftred parts had a compressive strength of 45.2 N/mm 2 and an open porosity of 18.3%.During service, zonality was formed in the parts. In the cross section, black reaction, lighter transition, and yellowishgray least changed zones were clearly distinguished. Their thicknesses and chemical compositions are given in Table 1 and mineral compositions in Table 2. The working surfaces of the parts were rough with traces of fusion.The least changed zone is dense, but direct contacts between the periclase and finely ground binder particles are very rare (Fig. la). The silicates are monticellite, merwinite, and larnite.In service the transition zone is subjected to some compaction as the result of weakly expressed additional sintering and the cementing action of the impurity minerals in heating (Fig. lb). Migration of silicates into the transition zone is insignificant and occurs primarily at the boundary with the reaction zone. The silicates are merwinite and monticellite. Periclase is partially replaced by magnesiowiistite.The reaction zone is characterized by a microstructure with a multitude of rounded isolated pores and metallic inclusio...
