Premature ageing of a blast furnace taphole clay containing resole resin and liquid pitch as binder

Abstract

The cause of reduction in workability and increased ageing of a blast furnace taphole clay was examined. The investigated taphole clay contained 60 mass% alumina, with phenol-formaldehyde resole resin and liquid pitch as the binder system. The workability and Marshall extrusion pressure of as-manufactured clay samples were evaluated to identify the extent of ageing of the clay. The wettability of all the raw materials was investigated to confirm compatibility between the dry raw materials and both the resin and liquid pitch, while the dry raw materials were analysed using XRF, XRD and SEM-EDS. The characterisation of the resin and liquid pitch, as well as the analysis of their interaction, was performed using viscosity measurements, Fourier-transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. Analyses confirmed a chemical interaction between the resole resin and liquid pitch, where the chemical structure of the resole resin changed when mixed with pitch, preventing the typical curing behaviour of the resin. After ageing of the resin and liquid pitch mixtures, the resin prematurely cross-linked, causing the curing process to move to lower temperatures, i.e., an earlier onset of curing. The premature cross-linking of the resole resin was likely due to secondary amines present in the liquid pitch that acted as a catalyst for the resin curing process. This reduction in curing temperature after ageing was confirmed by an increase in binder viscosity, which was the primary cause of the reduced workability, increased ageing and increasing Marshall extrusion pressure of the taphole clay.