Investigations of perlites by modified differential thermogravimetry

Abstract

Perlites from large-scale deposits in the USER were investigated by a modified DTG method. The technique permits an essentially higher DTG curve resolution in comparison with that of conventional DTG curves obtained with a derivatograph. The investigated perlites are classified into two groups: dense and porous. Elimination of water from perlites occurs in from 3 to 5 stages. The content of water lost at low temperature is higher in the dense perlites than in the porous ones.In the past two decades, perlites have found diverse industrial applications. The term "perlite" generally denotes an acid volcanic rock which undergoes expansion at 1000--1150 ~ a highly porous pumiceous product being obtained. The ability of perlites to expand is their most important technological property, which warrants studies of perlite behaviour at elevated temperatures. This property of perlites is governed by various factors, such as the rock formation conditions, the volcanic glass structure, the content of impurities in the material and, above all, the content of water and hydroxyl groups and the conditions of perlite thermal treatment. The data concerning the content of water in perlites are generally obtained by chemical analysis, but this analytical technique provides information on the overall water content only, without differentiating between the molecular water and hydroxyls, let alone between various molecular water types. IR and NMR spectroscopic studies yield information on the types of HOH groups, but permit only approximate evaluations of the amount of each water type present [1,2].In this context, thermal analysis is of great promise, insofar as, a part from revealing separate stages of perlite dehydration which are likely to be somehow associated with various H20 types, this method allows determination of the quantity of water evolved during each stage.So far only a limited number of thermal analyses of perlites have been reported [3], probably due to the fact that the thermal curves of perlites are of relatively little values because of the poor resolution with conventional equipment; this can be attributed to the closeness of the kinetic characteristics inherent in the separate stages of perlite dehydration. In order to obtain reliable data on perlit dehydration, it is essential to employ either a high-resolution instrument or a conventional instrument

Expanded obsidian as a soil aerator, its porosity, physical and mechanical characteristics

“…Obsidian is a volcanic rock consisting of volcanic glass in which the water content does not exceed 1%. A characteristic feature of this stone is the ability to expand under heat treatment [1][2][3][4].…”

“…The expansion of obsidian is possible to implement at temperatures of 1050… 1150 o C. It has been shown that due to obsidian expansion it is possible to obtain a light porous filler with an average density of 200… 350 kg/m 3 , where the heat treatment of 5… 10 mm particles should be performed under temperatures from 1050 to 1150 o C, during 3…5 minutes. The studies revealed that in order to obtain obsidian with high expansion coefficient or with low medium density (200…350kg/m 3 ), it is necessary to expand grains The thickness of the intercalations is irregular, some unexpanded parts of obsidian are noticed.…”