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Showing papers in "Clay Minerals in 1955"


Journal ArticleDOI
TL;DR: Brown and MacEwan as mentioned in this paper made proposals for the nomenclature of clay minerals and these proposals were presented in part at a C.I.A. meeting in Paris in July, 1954, where some useful discussion ensued.
Abstract: This sub-committee consisting of Mr G. Brown (Chairman), Dr M. H. Hey, Dr D. M. C. MacEwan and Dr R. C. Mackenzie was asked to make proposals for the nomenclature of clay minerals and these proposals were presented in part at a C.I.P.E.A. meeting in Paris in July, 1954, where some useful discussion ensued. The outcome of that meeting was a suggestion that the proposals be published more fully. It is important to remember that these are proposals for consideration and not a set of rules. The Clay Minerals Group would welcome comments on these proposals (adverse or otherwise) or the comments may equally well be sent to C.I.P.E.A. Addresses to which comments, suggestions, criticisms, etc., should be sent are : For the Clay Minerals Group : Mr G. Brown, Pedology Department, Rothamsted Experimental Stn., Harpenden, Herts., England. For C.I.P.E.A. : Dr W. F. Bradley, Illinois State Geological Survey, Urbana, Illinois, U.S.A.

40 citations


Journal ArticleDOI
TL;DR: In this paper, the authors discuss whether differential thermal analysis can be used to confirm or refute the first-order hypothesis of Murray and White, and the most important result concerns the effects of sample size and dilution on the position of the turning point.
Abstract: AKt;TRACT From their isothermal experiments, Murray and White drew the conclusion that the dehydration reaOions of clays are first-order with a rate factor of Arrhenius form. The object of this paper is to discuss whether differential thermal analysis can be used to confirm or refute this hypothesis. The problem, previously considered by Murray and White, of a sample heated at a constant rate throughout is recalled. Particular attention is drawn to the effect of heating rate on the temperature at which the maximum rate of reaction occurs. To apply to differential thermal analysis, the treatment must be extended to take account of thermal gradients; as the mathematics involved is cumbersome, only results are considered. The most important result concerns the effects of sample size and dilution on the position of the turning-point. A disagreement with the results of experiments on kaolinite is pointed out; it is argued that only a small part of this disagreement is due to simplifications made in developing the theory, and it is concluded that the hypothesis that the clay reactions are first-order, with a rate factor of Arrhenius form, is only approximate.

22 citations


Journal ArticleDOI
TL;DR: In this paper, the authors show how, by a consideration of the energy changes involved, some insight may be gained into the reactions occurring when kaolin minerals are heated, and they suggest that the most probable explanation of the exothermic reaction is the simultaneous production of mullite, A1203 and SiO2.
Abstract: The work outlined in this paper was undertaken to show how, by a consideration of the energy changes involved, some insight may be gained into the reactions occurring when kaolin minerals are heated. Activation energies have been determined experimentally for the dehydration of various kaolin minerals. The fireclay mineral is distinctive and it is suggested that it does not form part of a halloysitekaolinite series. It is further thought possible that there is a series of fireclay minerals. From thermochemical and thermodynamic considerations the heat of formation of kaolinite has been calculated approximately and enthalpy and free energy changes have been estimated for the exothermic reaction at 980~ These indicate that, if a compound is produced during dehydration, the most probable explanation of the exothermic reaction is the simultaneous production of mullite, ),A1203 and SiO2. Finally the lattice energies of kaolinite and its thermal decomposition products have been calculated. INTRODUCTION An extensive literature testifies to the considerable research that has been carried out on the thermal decomposition of kaolinite and related minerals. Nevertheless a complete picture has not yet been obtained of the various changes that occur on heating. (A) Dehydration. In less well-crystallized kaolin minerals sorbed water is removed in an initial endothermic reaction at about 100~ All minerals in the kaolin group undergo dehydration within the temperature range 400-700~ but the dehydration temperatures differ for the various members, being highest for dickite and nacrite. The start of dehydration is also determined by other factors. The precise nature of the dehydration product is still not settled but most workers consider it to be either a poorly-organized compound, A12Si20 v, or a mixture of alumina and silica. A minority think it to be similar to a solid solution, and various other theories, not now seriously held, have been propounded. The literature has been reviewed by Pieters (1928), Mellor (1938) and others. The dehydrated material is essentially amorphous, but pseudomorphs after the parent mineral are common; a few may persist to very high temperatures (1,300-1,400~ although other reactions must have occurred within them. The researches of both Nelson and Hendricks (1944) and Brown and Gregg (1952) suggest that the loss of combined water results in a smaller increase of surface area than might be expected. In this connection, it is interesting to note that Slawson and Vaughan (1954), using the electron microscope, have observed that, in the absence of deflocculating agents, there is an aggregation of the pseudomorphs

22 citations


Journal ArticleDOI
TL;DR: In this paper, the first order nature of the dehydration reaction is shown to be the underlying basis of the type of curve obtained in differential thermal analysis, and the effect of heating at a constant rate on the progress of a reaction for which the isothermal velocity constants are known.
Abstract: Kinetic studies have shown that the isothermal dehydration of the clay minerals proceeds according to a first ordcr law enabling velocity constants to be evahmted for different temperatures. From these, the Arrhenius parameters have been determined and on this basis, the clay minerals may be classified into three main groups, viz., kaolinites, secondary mica clays and montmorillonites. No significant difference is shown by comparison of the Arrhenius plots for the kaolinites and halloysites but the secondary mica clays decompose more rapidly than the kaolinites at comparable temperatures. Evidence is provided to illustrate that the constants obtained are associated with the basic process involving interaction of hydroxyl groups in the clay mineral lattice, Indirect evidence also suggests tnat the irreversibility of the dehydration is due to lattice collapse resulting in the formation of highly stable configurations of Si4q, AP ,and 02atoms. The first order nature of the dehydration reaction is shown to be the underlying basis of the type of curve obtained in differential thermal analysis. Two important conclusions are that:--(a) 'Ihe clay mineral is only approximately 70,~-o decomposed at the peak on the thermal analysis crave. (b) Heating rate has a mar~ed effect on the peak temperature. Mathematical equations have been developed to obtain the effect of heating at a constant rate on the progress of a reaction for which the isothermal velocity constants are known. The effect of sample weight and dilution factors are discussed, together with the kinetic problems associated with mixtures of clay minerals.

21 citations


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14 citations





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5 citations


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4 citations




Journal ArticleDOI
TL;DR: In the case of the argille scagliose clays of the Modenese Apennines as discussed by the authors, the results showed that the clays contained red and grey clays, both of which contain arenaceous foraminifera of Upper Cretaceous age.
Abstract: Samples of the argille sca.eliose from various localities in the Modenese Apennines have been studied by optical, X-ray and d.t.a, methods as part of an investigation into the composition and origin of this remark- able allochthonous formation. Illite, chlorite and a kaolinitic mineral of "fireclay" type are widespread. Samples from one locality contain also a conspicuous 22-28 .~ swelling chlorite, the origin of which is discus- sed. It is as yet mlcertain whether this mineral is confined *.o clays containing exotic blocks of ophiolite (grcenstone) or whether it is more widely distributed. A programme of work on the allochthonous clays of the Apennines, financed by the National Research Council of Italy, has been under- taken in order to investigate the composition and characteristics of these sediments; and if possible to determine their age and the con- ditions under which they were originally deposited. This work, started in 1942, has involved two separate lines of research. The palaeontological side has been largely developed by E. M. Gallitelli, the mineralogical-petrological aspects by the author and his co- workers (see Gallitelli and Gallitelli 1949). The allochthonous formation known as the argille scagliose con- sists of a shaly matrix in which are enveloped exotic blocks of basic igneous material ("ophiolites"), limestones, sandstone and other rocks. The whole sequence is regarded by Merla (1951) as material which has slid eastwards in gigantic "'orogenic landslips" during the elevation of the Apennines. Neither its original position in the geosyncline nor its age are known with certainty. The investigations described in this paper were made on samples of the argille scagliose from Varana, Sassomorello and Castelvecchio in the Modenese Apennines. They were collected close to enveloped blocks of ophiolite (gabbro, diabase or serpentine) and consist of red and grey clays both of which contain arenaceous foraminifera of Upper Cretaceous age (E. M. Gallitelli 1943 (a) and (b), 1947). These clays have been separated by suspension in water into fractions with a particle size of 30-12tz, 12-5/z, 5-1tz and 1-0.1t, for optical, X-ray and d.t.a, examination. RESULTS