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ABSTRACTRefractories subject to loading and unloading repeatedly because of physical effects and thermal stress attack in the service process, which is an important issue shortening the service life of the thermal equipment. Therefore, researches of predicting the service life of refractories under cyclic loading have the guiding significance. The present work investigated the synthesis of ZnAl2O4 and discussed its effects on the alumina castables. The results show that the optimized generation temperature of ZnAl2O4 phase is 1400°C and the hysteresis loop in the curves of cyclic loading reveals a general trend of first sparse and then dense. The cycle times of the specimen with 3 wt.% ZnAl2O4 is 50 times, and the time from starting to loop to fracture is about 4300 s. The fatigue resistance of the specimen with 3 wt.% ZnAl2O4 is superior to ZA-0 and ZA-1.5. The new method of cyclic loading was innovatively adopted in refractories, which provide data and theoretical support for the thermal shock evaluation methods.

Refractories subject to loading and unloading repeatedly because of physical effects and thermal stress attack in the service process, which is an important issue shortening the service life of the thermal equipment. Therefore, researches of predicting the service life of refractories under cyclic loading have the guiding significance. The present work investigated the synthesis of ZnAl2O4 and discussed its effects on the alumina castables. The results show that the optimized generation temperature of ZnAl2O4 phase is 1400°C and the hysteresis loop in the curves of cyclic loading reveals a general trend of first sparse and then dense. The cycle times of the specimen with 3 wt.% ZnAl2O4 is 50 times, and the time from starting to loop to fracture is about 4300 s. The fatigue resistance of the specimen with 3 wt.% ZnAl2O4 is superior to ZA-0 and ZA-1.5. The new method of cyclic loading was innovatively adopted in refractories, which provide data and theoretical support for the thermal shock evaluation methods. [ABSTRACT FROM AUTHOR]

To reduce the brittleness of cement-bonded alumina castables for purging plug, different gradations (5-3, 3-1 and 1-0 mm) of calcium hexaluminate aggregates are introduced to replace the tabular alumina aggregates. The interfacial microstructure and fracture behavior with or without calcium hexaluminate aggregates are systematically analyzed. The results show that the large (5-3/3-1 mm) and small (1-0 mm) particle sizes of calcium hexaluminate contributed to the interfacial bonding and prolonged crack propagation path of cement-bonded alumina castables, respectively. Accordingly, the strength is promoted and the fracture mode is significantly affected under tensile stress. Specifically, the proportion of cracks propagating along the interface can be reduced by introducing 5-3-or 3-1 mm calcium hexaluminate particles. Besides, the introduction of 1-0 mm particles reduces the proportion of cracks propagating within the aggregate. Cement-bonded alumina castables containing three particle sizes (5-3/3-1/1-0 mm) of calcium hexaluminate have simultaneously better strength and toughness than castables containing a single particle size. [ABSTRACT FROM AUTHOR]

Mono-aluminium phosphate [MAP, Al(H2PO4)3] is a widely used chemical binder in the refractory industries due to its higher water solubility and greater bonding strength at low temperatures as it reacts with both basic and amphoteric oxides and has higher application temperature. In the present work, commercial-grade MAP is used in high-alumina castables, with different particle size distributions, as the sole binder. The effect of addition of 1 mass-% MgO as a setting accelerator to the castable compositions is also studied. Castables are processed as per conventional processing methods and heat treated after drying at 1000 and 1600 °C. Dried and fired compositions were evaluated for density and strength. Also micro-structural study of the 1600 °C sintered samples was carried out. Addition of MgO resulted in a marginal decrease in density values which may be due to a greater amount of hydrated phase formation and their decomposition at higher temperatures; but it significantly increased crushing strength for all the heat treatment temperatures. Greater bonding from faster reaction at low temperature and the formation of a liquid phase at higher temperatures are the reasons for such an enhancement. [ABSTRACT FROM AUTHOR]