Amorphous Coatings on Mineral Surfaces

Abstract--Electron microscope microprobe analysis (EMMA) has been applied to the determination of the elemental compositions of the kaolinite particles (Mg, A1, Si, K, Ti and Fe) contained in the 0.~0-3 Izm e.s.d., the 0.9-1.0/~m e.s.d, and the 1.9-2.0/am e.s.d, fractions of an English kaolin and an American kaolin. Particles with masses as small as 10-13 g were analysed. An EMMA-4 instrument (A.E.I. Ltd.) equipped with linear fully focussing spectrometers was used. The ratio method of analysis was employed. The operating procedures used to obtain the required high experimental precision in the measurement of AI:Si atom ratio are discussed.Statistical analysis of the results gives the estimated mean and spread of the AI:Si atom ratios. In the English kaolin the mean AI: Si atom ratio differs from the ideal 1:1 at the 0.05 significance level. There is evidence for a variation in composition from kaolinite particle to kaolinite particle in the 1.9-2.0~m fraction of each kaolin. In the 0.9-l.0#m fractions, the mean Fe:Si atom ratio was close to 0.002 showing the presence of iron in the kaolinite structure. The mean K:Si ratio was about 0.002 which would be equivalent to 1 unit muscovite layer associated with a 0.175 #m thick kaolinite particle. In the American clay the Ti:Si atom ratio was 0.002 suggesting that some 12 per cent of the 'titania' found by conventional chemical analysis was associated with the kaolinite particles either as titania itself or as an isomorphous substituent.

Section: Discussionmentioning

confidence: 99%

The Composition of Kaolinite—an Electron Microscope Microprobe Study

Jepson

1975

“…Samples were prepared by dropping a dilute clay suspension onto Formvar-coated copper grids. Exposure of specimens to the electron beam was held to a minimum to avoid adverse effects of specimen-beam interaction (Jones and Uehara, 1973). DTA analyses of Mg-saturated clays equilibrated at 54% RH were done using a DuPont Model 900 Differential Thermal Analyzer.…”

Section: Methodsmentioning

confidence: 99%

Alteration of Andesite in Wet, Unstable Soils of Oregon's Western Cascades

Glasmann

1982

Abstract--Alteration products of andesite cobbles from wet soils formed in volcanic colluvial material were studied using petrographic, electron microscope, X-ray powder diffraction, and thermal techniques. Augite phenocrysts altered by congruent dissolution leaving voids which were subsequently filled with smectite. Plagioclase also altered to produce micrometer-size spheroidal aggregates of smectite. Halloysite was not observed within the altered cobbles, although it was abundant in the soil matrix. The formation of smectite in the altered cobbles was probably favored by the restrictive drainage of the microenvironment in combination with wet soil conditions.

“…This results from the general assumption that noncrystalline materials and reactive components occur only in this fraction, The relatively few studies of the noncrystalline matethe observed differences, however, Follett et al (1965a) and Jones and Uehara (1973) showed that most noncrystalline soil materials exist as coatings that bind aggregates of minerals together, rather than as separate particles. …”

Section: Comparison Of the Noncrystalline Materials Content Of Whole Smentioning

confidence: 99%

Determination of Noncrystalline Soil Components by Weight Difference after Selective Dissolution

Hodges

Zelazny

1980

Abstraet--A procedure based on loss of weight after selective dissolution analysis (SDA) and washing with (NH4)zCO3 was developed for estimating the noncrystalline material content of soils derived from widely different parent materials. After extracting with 0.2 N ammonium-oxalate or boiling 0.5 N NaOH solutions, samples were washed with 1 N (NH,)2CO3 to remove excess dissolution agents and to prevent sample dispersion. The amount of noncrystalline material removed from the sample by the extracting solution was estimated by weighing the leached products dried to constant weight at 110~ The results match closely with those obtained by chemical analyses of the dissolution product and assignment of the appropriate water. The proposed weight-loss method is less time-consuming than the chemical method, and no assumptions need be made concerning sample homogeneity or water content of the noncrystalline material.Extractions of whole soil and dispersed clay fractions indicated that noncrystalline material determinations on the clay fractions underestimated the noncrystalline material content for whole soils from 0 to 34%. Acid ammonium oxalate was found to be a much more selective extractant for noncrystalline materials than NaOH.