H. G. Midgley

Bio: H. G. Midgley is an academic researcher. The author has an hindex of 1, co-authored 1 publication(s) receiving 21 citation(s).

Interstratified Clay Minerals

Abstract: Interstratification is a phenomenon that was first observed on studying clay minerals by X-ray diffraction. It was noted that the majority of them had basal reflections (001), which did not form a regular series. It was verified that this irregularity was due to the interstratification of different types of crystalline layers.

X-ray diffraction studies of the thermal behaviour of commercial vermiculites

Abstract: For the purpose of knowing the vermiculites which would have larger capability to retain contaminating substances heating commercial samples from different places have been identified and their thermal behaviour at several temperatures has been investigated by X-ray diffraction (XRD), electron microprobe, thermal analysis (TG and DTA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The commercial vermiculites can be divided into two types: type 1 (Sta. Olalla, Piaui and Goias) with Mg2+ and K+ ( 1) and/or Na+ and/or Ca2+ with or without Mg2+ as the principal interlayer cations. The process of dehydration in situ with the temperature seems restricted to interlamellar water monolayers of 1-WLHS type-1 of vermiculites, without dehydration to a zero-water-layer-hydration state (0-WLHS) and the dehydroxylation starts at lower temperatures than in vermiculites of type 2. The maximum hydration state exhibited by the type-2 samples at ambient temperature was equal or lower than the monolayer hydrate, the dehydration process in situ with the temperature was slower and the dehydrated vermiculite coexists with a mica-like structure. The behaviour of vermiculites at elevated temperature examined in situ can be understood considering that the vermiculites constitute a complex system not necessarily in equilibrium and where kinetics plays an important role. Commercial vermiculites heated abruptly at 1000 °C during 1 min transform to mica-like or mica-like coexisting with enstatite, in contrast to the purest Sta. Olalla vermiculite, with only magnesium interlayer cations, which changes to enstatite.

On the mechanism of exfoliation of ‘Vermiculite’

Abstract: Six samples of 'Vermiculite' have been studied to investigate the mechanism of its well known but poorly understood property to exfoliate. The samples were analysed quantitatively by XRD to determine their precise mineralogical composition. Electron microprobe methods, including elemental mapping of native potassium and of caesium (introduced by cation exchange) were used to examine variation in the chemical composition of the particles. Most of the samples examined show heterogeneous mineralogical compositions which occur as distinct zones within the volume of individual particles, presenting a mosaic texture. Exfoliation is related to this mosaic distribution of the different mineral phases within the particles. Lateral phase boundaries between vermiculite and mica layers, or vermiculite and chlorite layers are postulated to prevent or impede the escape of gas from a particle, resulting in exfoliation when the pressure exceeds the interlayer bonding forces that hold the layers together. This mechanism provides a common explanation for the exfoliation of 'Vermiculite' by thermal methods or by treatment with H2O2. Paradoxically, one sample which consists of pure vermiculite, in the mineralogical sense of the term, demonstrates that pure vermiculite does not and should not exhibit the property of exfoliation. Our explanation of the mechanism of exfoliation explains the commonly observed particle size dependence of exfoliation and the tendency for obviously poly-phase 'Vermiculite' samples to show the largest coefficients of expansion.

Expansion behaviour of commercial vermiculites at 1000 °C

Abstract: Commercial vermiculites from different places were studied in order to know the cause of their different behaviour after abrupt heating at 1000 °C. Mossbauer spectroscopy provided Fe 2+ and Fe 3+ contents and allowed identification of both tetrahedral and octahedral iron. The Fe 2+ content was higher in type-2 vermiculites (with K + − or > 1 and/or Na + and/or Ca 2+ with or without Mg 2+ as the principal interlayer cations) than in type-1 vermiculites (with Mg 2+ or Mg 2+ and K + (

Expansibility of some vermiculites

Abstract: The thermal expansion of four samples of “vermiculite”, one sample containing both vermiculite and mica and one sample containing vermiculite and mica/vermiculite interstratification from various geological origins have been studied. All samples yield good pyro-expanded products. However, minerals containing mica or mica/vermiculite interstratification have the highest expansibilities. It is suggested that the sudden release of interlayer water is not the only factor influencing the thermal expansion of these samples, e.g. the presence of relicts of altered mica, loss of OH groups or chemical composition.