Method for treating refractory block

#The present invention relates generally to methods for manufacturing refractory blocks used in lining a furnace in which is conducted a process which produces slag, and more particularly to a method for treating a refractory block to improve its resistance to slag penetration.

#In a typical manufacturing operation for forming a refractory block, a mixture of coarse and fine grains of uncured refractory material are initially formed into a block consisting essentially of relatively coarse grains in a matrix of relatively fine grains located in the interstices between the coarse grains. The fine grains are composed of a refractory material which is either the same as the refractory material of which the coarse grains are composed or of a refractory material which is compatible with the refractory material in the coarse grains, or both. A refractory material is compatible with another refractory material if it does not flux or reduce the melting point of the other refractory material during high temperature operating conditions.

#The uncured block of refractory material has pores extending from the surface of the block inwardly along the matrix in the interstices between the coarse grains.

#In one embodiment in accordance with the present invention, a block of refractory material is formed from relatively coarse grains of alumina in a matrix of relatively fine grains of alumina and chromia. The coarse grains of alumina constitute about 70-80% of the refractory block and have a particle size of plus 100 mesh. The fine grains of alumina in the matrix constitute about 10-15% of the refractory block and have a particle size of minus 100 mesh. The fine grains of chromia in the matrix constitute about 10-15% of the refractory block and have a particle size of minus 200 mesh.

#The coarse grains of alumina and the fine grains of alumina and chromia are formed into a porous block of uncured refractory material and then sintered in a conventional manner to form a fully cured block which is less permeable than the unsintered block, but which still has some pores extending from the surface of the block inwardly along the matrix between the coarse grains, and these pores have cross-sectional spaces which are sufficiently large to permit slag to penetrate through the pores into the interior of the refractory block. Penetration of slag is reduced by subjecting the block to a pair of impregnating steps.

#In the first impregnating step, the block is soaked in phosphoric acid having a concentration in the range 50-95% (85% preferred). The phosphoric acid enters the pores of the refractory block and reacts with the fine grains of alumina in the matrix and with adjacent surface portions of coarse alumina grains to form an aluminum ortho-phosphate reaction product which is compatible with both the alumina and chromia in the block and which, upon formation, reduces the cross-sectional area of the pores to decrease the penetrability of the pores by the slag. The aluminum ortho-phosphate reaction product replaces some of the fine alumina particles entirely and other of the fine alumina particles partially and also forms along the outer surface portions of the coarse alumina particles adjacent the pores.