Abstract

Slags from iron and steel production are important byproduct, which can be processed to be used for instance in road construction or as fertilizer in agriculture. For application in the production of cement, amorphous solidified blast furnace slag is used, also referred to as slag sand. The blast furnace slag exhibits a tapping temperature up to 1700°C, however this stored thermal energy cannot be retrieved yet. In order to develop industrial facility for the heat recovery, the selection of corrosion resistant refractory materials is crucial.

Different refractory castable materials were tested in contact of molten blast furnace slag in order to describe the mechanisms of corrosion and their suitability for the application process. Materials based on alumina as well as SiC based castables have been examined. A thermodynamic model, by using the software package FactSage, was worked out and applied on the different refractory and slag compositions to predict phase formation and corrosion. The microstructural properties of the monolithic samples were characterized after firing by means of porosimetry and permeability measurements and Scanning Electron Microscopy (SEM) examinations. Static as well as dynamic corrosion test have been performed on the refractory materials, in particular finger test methodology as described in the European standard (DIN 15418). Time and temperature coordinates have been changed as well as the rotation speed to examine kinetic data and dissolution and erosion behavior. The corrosion experiments were applied on the matrix materials (cements, calcium aluminates, SiC fines) as well as on grog aggegates and full castable mixes. Subsequent to the macroscopic evaluation performed on the infiltrated samples, microscopic characterization and structural changes of the corroded microstructure have been carried out with SEM/EDS and XRD.

The SiC based refractory product was strongly infiltrated, while the high alumina specimen exhibited a high resistance against the molten slag. The microstructural analyse of the high alumina sample revealed the dissolution of the matrix and precipitation of new phases in the blast furnace slag, however with slower kinetics than the SiC based sample. For SiC and other carbon constituents the oxidation behaviour was of importance. Finally the impregnation and the microstructural change are discussed in regard of changing thermal properties such as expansion, permeability and strength.