DOI 10.1007/s11148-016-9924-7 Refractories and Industrial Ceramics
Vol. 57, No. 1, May, 2016
MECHANOCHEMICALLY ACTIVATED PHOSPHATE-CONTAINING REFRACTORY COMPOSITE MATERIALS1 Yu. N. Trepalina,2 E. I. Evtushenko,2 and V. A. Doroganov2,3 Translated from Novye Ogneupory, No. 1, pp. 39 – 42, January, 2016.
Original article submitted March 6, 2015. Development of new highly efficient composite materials is an important area for effective activity of refractory enterprises. It is established that use of binder suspensions as both a mix component, and as an independent material, makes it possible to expand the field of developed material application. The efficiency of using corundum coatings increases heating unit service life. Keywords: mechanochemical activation, phosphate-containing binder, electromelted corundum, orthophosphoric acid, ultimate strength in compression, open porosity, corrosive atmosphere resistance.
In view of a reduction in the volume of refractory production in the Russian Federation a requirement arises for developing new highly efficient composite materials capable of replacing existing materials. The field of application of vibration thixotropic mixes, apart from monolithic refractories, is most promising for preparing large shaped concrete objects. A disadvantage of these concretes based on phosphates is reduced thermomechanical properties. It is possible to improve them by using mechanochemical phosphate-containing binders. Concretes based on binder suspensions have a low (~1.8%) P2O5 content. This aim of this research is to develop refractory mixes used for preparing objects with improved operating properties. The possibility has been studied of using binder suspensions as protective coatings [1], preventing refractory breakdown during action upon them of high temperature and corrosive media. In order to achieve the stated purpose the following were carried out: – combined study of structural and mechanical properties of binders based on phosphate-containing materials, development of molding conditions, and evaluation of material physicochemical properties; – development of compositions and technology for corundum binder suspensions and coatings with a limited phos1 2 3
phate-ion content for refractory protection during action on them of high temperature and corrosive media; – study of the resistance to corrosive media of the material developed and coatings based on binder suspensions. The starting materials used for study were substances of natural (refractory clay) and engineering origin (electromelted corundum). According to GOST 28874 refractory unfired unmolded powder, mixes, and masses include refractory filler and binder that are capable of setting and hardening at quite low temperature with formation of a structure retaining strength properties on heating. Phosphate binders are heterogeneous systems. Aluminate binders form with reaction between alumina materials and orthophosphoric acid. A change in preparation conditions may affect powder activity [2, 3]. We consider an example of reaction of finely milled electrocorundum fraction finer than 0.5 mm with orthophosphoric acid at 20 – 25°C, when acid aluminum phosphate soluble in water forms whose amount increase during suspension. A titration method was used to determine reaction kinetics for H3PO4 with dispersed phase in relation to milling duration. Result of studies showed that the amount of reacted acid depends on milling conditions (combined or separate followed by suspension). Reaction intensity for orthophosphoric acid with corundum shows that formation of aluminum phosphate proceeds more actively in the initial stage o combined milling, i.e., up to 23% in the first 8 h (Fig. 1). With separate milling followed suspension the reaction proceeds slowly, and 5 – 11% of acid reacts in the initial period of mixing time, comparable with the combined mill-
Proceedings of the International Conference of Refractory Workers and Metallurgists (19 – 20 March, 2015, Moscow). FGBOU VPO V. G. Shukhov Belgorod State Technological University, Belgorod, Russia.
[email protected]
42 1083-4877/16/05701-0042 © 2016 Springer Science+Business Media New York
Mechanochemically Activated Phosphate-Containing Refractory Composite Materials
43
Fig. 1. Effect of mechanochemical activation on reaction kinetics for H3PO4 (3.75% P2O5) with a dispersed phase (electromelted corundum) at 20 (l, q) and 40°C (r, ¡): C is combined milling; P is separate milling with suspension.
ing time. The structure of binder is shown in Fig. 2, obtained by different methods; zones are seen of unreacted acid breakdown on heating to 200 – 250°C. In the course of work the effect of orthophosphoric acid concentration on binder suspension properties from electrocorundum was studied. It was established by experiment that use of acid at 25% concentration makes it possible to obtain better physicomechanical properties for specimens of suspensions based on corundum. Binders were prepared with combined milling of components in orthophosphoric acid with a density of 1140 kg/m3. The amount of H3PO4 was determined for achieving a suspension viscosity of 0.09 – 0.10 Pa·sec. the fineness of binders was specified by the content of particle residue on a screen No. 0063 (
