BROWN-COAL DERIVED CARBONACEOUS GELS .1. SHEAR ELASTIC-MODULUS AND ELECTROSTATIC INTERACTIONS

The strength of brown coal-water gels has been assessed by the measure ment of the shear elastic modulus of the gels during drying. The stren gth of the coal-water gel materials has been shown to be related to pH and the exchangeable cation content of the brown coal forming the gel . Manipulation of the coal pH into the alkaline region was found to ca use an increase in the shear elastic modulus and rigidity of the coal- water gel, this being due to an increase in the degree of solubility o f the coal material. The soluble coal material, humates, are able to f orm an increased number of entanglements and hence a stronger, more ri gid network is built up which exhibits an increased shear elastic modu lus.