Technological properties of high alumina refractories with different phosphoric acid contents

Basel Nour El-Din Ali Shalaby,Ali Ismail Mohamed Ismail,Mohamed Saad El-Maghraby

doi:10.1186/s42269-018-0030-5

Basel Nour El-Din Ali Shalaby, Ali Ismail Mohamed Ismail + Show 1 more

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https://doi.org/10.1186/s42269-018-0030-5

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Abstract

BackgroundHigh alumina refractory batches were prepared from Egyptian clay and imported China calcined bauxite. Three concentrations of phosphoric acid 3, 5, and 7%, were added to study their effects on some of their technological properties. Designed batches tend to form a composition of 76% alumina and ~ 17% silica in addition to the other fluxing and alkali oxides. Chemical and mineralogical composition as well as density and plasticity of both clay and calcined bauxite was performed.ResultsThree batches of different phosphoric acid concentrations were fired at 1350 °C for 1 h. Densification parameters of the fired batches as well as the cold crushing strength and thermal shock resistance were carried out. The mineral composition and microstructure of the selected batch were done using XRD as well as SEM and EDAX. It is concluded that by increasing phosphoric acid percentages, the porosities slightly increase and the cold crushing strengths drastically decrease; however, densities and shrinkages exhibit no remarked effects.ConclusionsThe mineral composition of the selected fired batch exhibits mullite as a main phase with subordinate amount of corundum, while berlinite, quartz, and cristobalite are in less frequent contents. Microstructure of the selected batch ensures that mullite and corundum are the main mineral phases, in addition to minor phases of phosphate minerals. The fluxing and alkali oxides together with some alumina and silica form a liquid phase, which is responsible for the densification of the batch, while mullite and corundum are the essential formed minerals.

Highlights

Refractory materials are inorganic, non-metallic, and brittle crystalline solid materials, fired at optimum temperature according to their uses
The chemical composition of the clay shows that the major oxide content is silica (52.97%) and alumina (29.07%), with less frequent amounts of TiO2 (1.48%), Fe2O3 (3.92%), and alkali oxides (CaO, MgO, Na2O, and K2O) all together less than 1.0%; the sum of these oxides together is less than 6.0%
Mineral and chemical composition of the clay confirms that the kaolinite and halloysite are the main clay minerals, while quartz is the non-clay mineral, and the alumina and silica contents are 29.07% and 52.97%, respectively

Summary

Introduction

Refractory materials are inorganic, non-metallic, and brittle crystalline solid materials, fired at optimum temperature according to their uses They are used as face- and back-linings of industrial furnaces at high temperature for thermal insulations. They are classified according to their chemical composition and resistance to attack by the fired materials in contact under service conditions into acidic, neutral, and basic refractories (Shaw 1972 and Chesters 1973). Kaolinitic clays are considered as acidic refractories due to their Al2O3/SiO2 ratio, as well as their limited total fluxing and alkali oxide contents, namely, Fe2O3, TiO2, CaO, MgO, Na2O, and K2O. These clays include fireclays, ball clays, and kaolins (Grim 1968). Chemical and mineralogical composition as well as density and plasticity of both clay and calcined bauxite was performed

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