Adsorption properties of the corundum surface in corundum-based refractories

Abstract

Distribution of the adsorption sites in fused corundum is studied depending on the fractional composition of the material and specific surface of its finely ground fractions. Treatment of the corundum surface with a phenolic resin is shown to affect, both quantitatively and qualitatively, the distribution of acid-base adsorption sites.Corundum-carbon refractories have found wide application as material for blow-off nozzles in the extra-furnace steel processing technology owing to the superior qualities of their constituents: electrofused corundum as filler and phenol resins as binder. The argon blowdown at different steps of the steelmaking process is done at a different rate, which places strict requirements on the operation of blow-off nozzles [1,2].Adsorption ability of fused corundum plays a major role in the buildup of a strong refractory material. Most processes in which the surface of solids is involved, are local in character and in many respects are controlled by the energetic parameters of particular active sites.By construction-and-use regulations, a mixture of polyfractional composition with the grain size from 2 to <0.063 mm should be used. Therefore it was thought of interest to identify active sites on the surface of a solid filler that could adsorb the binder molecules and thus to what role may play a particular fraction in the buildup of the refractory material.The reactivity of active aluminum oxide is controlled by the acid-basic properties of the surface formed. In an acid medium, the Al 2 O 3 surface develops a positive charge, which allows ions of opposite sign to adsorb. In this case, Al 2 O 3 acts as an anion adsorbent. In an alkaline medium, Al 2 O 3 develops a negative charge, which results in the adsorption of cations [3].Generally, three types of sites involved in adsorption are distinguished on the surface of solid aluminum oxide: (i) electron accepting orbitals of metal cations, (ii) electron donating orbitals of oxygen ions; (iii) hydroxyl hydrate shell formed by the different adsorption of water molecules [4].The acid-basic properties of a solid surface are controlled by the concentration and strength of active sites involvedacidic, basic, and their distribution. In this work, we use an indicator method to study the acid-basic properties of corundum surface; the method is based on the surficial adsorption of an indicator and the change of its color which is taken to be a measure of acidity (basicity) of the surface [5].The distribution of acid-base sites over the surface was studied in the range of -0.29 to 8.8 of the dissociation constant pK a of the indicator. For this purpose, 100 ml solutions of each indicator were prepared in water or water/ethanol mixture. Relevant characteristics are given in Table 1.The adsorption sites of particular acid strength were quantified in terms of the q pK a index (mmole/g) using a spectrophotometric method in the UV and visible range of the spectrum. The solutions were measured photometrically on an SF-26 spectrophotometer using cells with l = 1...