Influence of Atmosphere on the Bloating of Artificial Light Weight Aggregate from Fly Ash and Pulp Waste Liquor

Abstract

The cylindrical compacts of fly ash, pulp waste liquor being used as a binder were heated at a temperature between 1000°C and 1300°C in an atmosphere of O2, N2, CO2, CO2 (+2 vol% O2) and CO2 (+4 vol% O2), then subjected to chemical analysis, especially on carbon content and iron valency, and also measurement of magnetic susceptibility, apparent density, water absorption and compressive strength. As a result, there were seen remarkable influences of atmosphere on the sintering and bloating characteristics of the compacts, that is, 1) in oxygen, bloating began to occur at about 1200°C, where no carbon was found to remain, and therefore, the thermal decomposition of ferric oxide to release oxygen gas might lead to bloating, 2) carbon dioxide atmosphere facilitate sintering of the compact and bloating was effected by the reaction of ferric oxide with carbon at a temperature above 1100°C, where the favourable mole ratio of Fe2O3/C for bloating was likely to be from 1/1 to 5/1 and 3) there occured no bloating in N2 and CO atmosphere and substantial amount of carbon was found to remain and thereby about half of iron content was reduced to metal.In addition, the compressive strength (S) of the specimen after heating at a temperature (T) in sintering stage prior to bloating was examined, and In S∝ 1/T relation could virtually be verified, the discussion being made for this relation in view of the sintering mechanism based on viscous flow.