Expansion illite

Figure 3.9. Schematic of the illite structure showing one gibbsite sheet between two silicate sheets. Potassium holds the layers together in a 12-fold coordination, preventing expansion. Isomorphous substitution can occur in the layers marked with an asterisk (from Taylor and Ashcroft, 1972, with permission).

There are inconsistencies in the model for the calculation of activity products for the "clays. Exchangeable cations are disregarded for the low exchange capacity kaolinite, halloysite, chlorite, and moderate capacity illite. For certain expansible layer silicates and two zeolites, the logjo of the activity of selected cations is added into the sum of the activity products. 

Micas are abundant in soils as primary minerals inherited from parent materials. Micas are not known to form to any significant extent in soils. Micas are precursors for other 2 1 layer silicates, notably venniculites. Micas are commonly present in soils as components of particles that have been partially transformed to expansible 2 1 minerals. As a result, mica is often interstratified with other minerals. Altered mica containing less K and more water than well-ordered mica is called hydrous mica (formerly illite). 

Kaolinite Al2Si2 05(0H)4 and illite, which is structurally similar to montmorillonite, belong to the most important non-expanding minerals. The bonds between the layers with K are much stronger, so that they do not allow expansion. 

An alkali-carbonate reaction may takes place if an argillaceous (illitic) dolomitic hmestone is used as concrete aggregate. Here expansion takes place as the consequence of swelling of the illite eonstituent, following a de-dolomitization of the dolomitic... 

Clay deposits are composed principally of fine quartz and clay minerals. The three major clay minerals are kaolinite, illite and montmorillonite. Both kaolinite and illite have non-expansive lattices, whereas that of montmorillonite is expansive. In other words, montmorillonite is characterized by its ability to swell and by its notable cation exchange properties. 

Sodium montmorillonite binds copper and manganese ions without any preference. The restriction of the interlayer expansion by calcium ions seems to be one of the prerequisites for selectivity of montmorillonite. Sposito and L Vesque [68] illustrated that the adsorption of sodium ions by illite eliminated the preference of the clay minerals for Ca over Mg ions. 

Alkali-carbonate reaction. The alkali-carbonate reaction is different from the alkali-silica reaction in forming different products. Expansive dolomite contains more calcium carbonate than the ideal 50 % (mol) proportion and frequently also contains illite and chlorite clay minerals. 

Data for illite (not shown in Fig. 9) indicate a slight expansion in the temperature range 450-800°C followed by a rapid continuous shrinkage. PO] Expansion is attributed to the development of the anhydrite structure, and the shrinkage to loss of structure of the phase. The high rate of shrinkage correlates with the relatively lower development of high temperature crystalline phases. 

Thermal dilatometric curves obtained for six bricks extruded from different raw materials are shown in Fig. Curves for those manufactured from similar raw materials, but made by different forming methods, i.e., soft mud, dry press, and stiff extrusion, are shown in Fig. 23. From room temperature up to 500°C, the dimensional change is approximately linear and is due to thermal expansion. The abrupt increase in expansion (500-800°C) is due to phenomena such as quartz inversion, exfoliation of the illitic, and chloritic minerals due to dehydroxylation, and, possibly, the escape of CO2 under pressure. 

Several workers (Mehra and Jackson [1959], Manghani and Hower [1964]), present evidence that the content of potassium in illite and glauconite is inversely proportional to the number of expansible (smectite or vermiculite) layers within the particles. 

In contrast to the homogeneous mica distribution in weakly podzolised sod-podzolic soils, higher illite contents and accumulation of expansible minerals have been found in a medium podzolised sod-podzolic soil by Labenets [1968]. In strongly podzolised acid soils, weathering of micas, especially of biotites, produces mixed-layered minerals, vermiculite, and soil mont-morillonite. These processes lead to a decrease of illite contents in the upper parts of the... 

As has been shown by Mortland et al [1956], biotite can be altered to vermiculite if interlayer potassium is used as a nutritional source by plants. In a long-term field experiment, the exchange capacity of the soil from plots that received no potassium over an 80-yr period was found to be increased by about 10% (Scheffer et al. [I960]). This effect, which was attributed to partial expansion of illites, was especially marked where heavy dressings of N fertilizer had been used, and the strain on the natural potassium sources was consequently high. 

To take an example, Rg—C—M is a regular interstratification of chlorite with mont-morillonite Rm—I—HI is a random interstratification of illite with hydrated illite. Hydrated illite is a mineral, which shows partial expansion with ethylene glycol and glycerol (Sudo et al. [1962]). 

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