When an organic chemical is prepared, it is checked against known materials for purity and stability. One of the easiest ways of doing this is to determine its melting point! This cannot be done by TG, since it involves no mass change! This also applies to solid-solid phase transitions and to some solid-state reactions. We therefore need a technique that identifies these transitions. Such a technique will give us a simple way of identifying and assessing the quality of materials that may be applied across a large range of substances, from polymers to metals.

Multiple differential thermal analysis

Differential thermal analysis and differential scanning calorimetry

This paper presents a rigorous new theory of differential thermal analysis, taking account of the temperature gradient in the sample. From this consideration, a new quantitative method is proposed, where a solid-cell holder of low thermal conductivity is set between a sample cell and a metal block, and a thermocouple is inserted tightly between the outside wall of the cell and the cell holder. By means of this arrangement, the peak area becomes proportional to the heat of transformation, irrespective of the kinds and the states of samples and operational variables. The experimental verification using various samples and the effect of several operational variables, such as the heating rate, the concentration of a diluent, the packing density, and the depth of the packing sample, are also shown; satisfactory results are obtained. Two new concepts, the sensitivity and the response time of the system, are proposed and evaluated. Conventional methods are criticized, and the inherent limitations of differential...

A New Method of Quantitative Differential Thermal Analysis

The weathering of Stone Mountain Granite (adamellite) forms kaoiinite, endellite, allophane and gibbsite of which kaolinite is the most stable. Bulk density ranges from 2.65 in fresh rock to a minimum of 1.48 in saprolite. It is a good index of weathering. Abrasion pH ranges from 5.0 in saprolite to 9.3 in fresh rock, and is directly related to bulk density and the amount of clay mineral. Among the original minerals, biotite is least stable, followed by oligoclase. Residual microcline fragments occur at the base of the B horizon indicating that it is not completely weathered. Muscovite weathers slightly and quartz appears quite stable. Evidence shows that solution and reconstitution is necessary in the formation of some if not all clay minerals. This is particularly evident in the formation of endellite veins. Expansion of the rock in the early phases of weathering occurs but does not produce a significant increase in volume.

Weathering of Stone Mountain Granite

If a series of rock samples with granitic composition in various stages of chemical weathering is ground in a mortar with distilled water and the pH of the slurry produced is determined, it will be evident that the pH declines as the weathering increases. This relationship can be made useful by plotting abrasion pH against some other index of weathering such as the percentage of clay mineral or the bulk density of the weathered rock. Factors controlling abrasion pH are the cations such as K, Na, Ca, and Mg and the amount of clay mineral present.

ABRASION pH, AN INDEX OF CHEMICAL WEATHERING

Clay minerals are of non uniform composition and particle size. Also their identification and nomenclature have given much confusion. Examples are given. Quantitative analysis of clay minerals from deposits and soils, by X-ray, thermo- and infrared analysis is treated. Examples are given of the large variability in the results; even for X-ray and electron microscope pure- and 85 to 90% chemical pure samples of kaolinite a well defined clay mineral. They are caused mainly by varying conditions of crystal growth from which result differences in isomorphous replacements, structure, ordering and strain. An amorphous weathering substance coating the mineral particles (Beilby layer) upsets in particular quantitative analyses of the finer kinds of clay minerals. Clay minerals from soils have, as compared to those from pure deposits, in particular formed by hydrothermal action, only poor characteristics of small intensity. Examples are given. Quantitative analyses are further hindered by specific characteristics for a certain mineral being masked by those of other minerals which usually occur in the same sample. Examples are given.

Multiple differential thermal analysis

Citations

Differential thermal analysis and differential scanning calorimetry

A New Method of Quantitative Differential Thermal Analysis

Weathering of Stone Mountain Granite

ABRASION pH, AN INDEX OF CHEMICAL WEATHERING

Quantitative analysis of clay minerals and their admixtures

Related Papers (5)

Critical study of the differential thermal method for the identification of the clay minerals

Differential Thermal Analysis

A Theory of Differential Thermal Analysis and New Methods of Measurement and Interpretation

Minerals Present in Soil Colloids

The stability relations of the silica minerals