Corundum concretes based on modified phosphate-containing binders

Abstract

Physicotechnical properties are provided for concretes based on mechanically-activated phosphate suspensions previously modified with magnesium and aluminum hydroxides and silicic acid. The results obtained demonstrate the efficiency of using modifying additions in order to increase the strength and heat resistance of corundum concretes. Development and improvement of the manufacturing technology for refractory materials using phosphate binders has promoted high physicotechnical and engineering properties for these refractories, strong adhesive bonds between particles of the filler within them, simplicity of production, not requiring significant energy and capital expenditure.Analysis of results of studies in the field of forming the material structure, the technology and properties of refractory concretes based on phosphate binders has revealed the efficiency of their use. Use of phosphate binders makes it possible to prepare high quality components [1]. Of the many forms of refractory concretes the best properties are exhibited by corundum concretes based on orthophosphoric acid, magnesium-and aluminophosphate binders. With the optimum content of 80% H 3 PO 4 these concretes after heat treatment at 800°C have high strength (ultimate strength in compression 60 MPa) and the greatest heat resistance (>50 thermal cycles). Addition of 9 -40% alumina hydrate does not improve the properties of corundum concrete, the strength is reduced, and there is an increase in its shrinkage and porosity. Corundum concretes based on magnesium phosphate binders with addition of 10% raw ground technical grade alumina are distinguished by high apparent density, strength and heat resistance [1].The properties and operating characteristics of corundum refractories are improved by introducing into their composition small amounts of modifiers [2]. In refractory concrete technology based on phosphate binders there is use not only of orthophosphoric acid, but also mechanically activated binding suspensions with different modifiers. Here a combination of mechanical activation and chemical reaction markedly improves the strength of castings with an increase in concentration of the phosphate-ion in the surface layer of corundum crystals [3].Mechanical activation of corundum charges with heat treatment at 180°C of an aluminoborophosphate binder reduces open porosity to 23% and increases the ultimate strength in compression to 115 MPa for corundum concretes after firing at 1300°C [4].The hardening mechanism for refractory concrete mixes based on phosphate binders is quite complicated. Within them there is chemical reaction of phosphates with the filler, polymerization and polycondensation, and also adhesion [5]. Here hardening processes change from chemical reaction of phosphate binders with the surface of filler grains to their simple adhesive gluing. Hardening of the main oxides (MgO, BeO, Y 2 O 3 ) is due to primarily to their chemical reaction with phosphate binders that leads to formation of new chemical compounds. The hardening mechanism f...

Refractory concretes and coatings based on modified binder suspensions

“…Not only orthophosphoric acid, but also mechanically activated binder suspension with different modifying addition agents, are used in refractory phosphate binder concretes. Simultaneous implementation of the process of mechanical activation and chemical reaction substantially increases the strength of the blanks as a consequence of an increase in the concentration of the phosphate ions in the surface layer of the corundum crystals [4].…”

Development and study of composite refractory materials based on modified dispersed systems

“…The strength of specimens based on dispersed systems, containing a modifying addition of aluminum and magnesium hydroxides, increased by a factor of 1.5 -2.0 after 20 thermal cycles. A phosphate-containing mechanically-activated dispersed system, modified with alumino-magnesia reagents, that increases the mechanical strength and thermal shock resistance of corundum concretes [18]. This makes it possible to them as coatings (Fig.…”