The interaction of ammonia with Na—, NH4—, Ca—, Cu—, and Mg— forms of two vermiculites has been investigated by infrared spectroscopy and chemical analysis. Both NH4 ions and co-ordinated NH3 are produced in the interlayer space in amounts which depend on the exchangeable cation and the particle size of the vermiculite. With the exception of that in Cu-vermiculite, the co-ordinated NH3 is rapidly displaced by atmospheric water vapour. NH4 ions are slowly decomposed at normal humidity and more rapidly and completely at high humidity. The co-ordinated NH3 in Cu-vermiculite is converted to NH4. Relative amounts of NH4 and co-ordinated NH3 are influenced by particle size, smaller particles favouring NH4. The stabilities of both species to water vapour increase with particle size.

The plastic properties of clays are sufficiently variable to offer a simple but practical aid to identification. This can be done by using their Atterberg 'plastic limit' and 'plasticity index' values as parameters for an identification chart. The advantages and disadvantages of the technique are discussed, and results for a wide variety of clay minerals, particularly industrial clay types, are illustrated. A brief summary is also given of the effect of non-clay impurities, and reference is made to the correlation of Atterberg limit values with other physical properties of clays.

The partial and apparent molal volumes of K-bentonite in pure water and in 0·5 M KCl were determined using pycnometer density data. The values obtained were found to increase with particle concentration. Theoretical values of the electrostatic contribution to the volume of particles calculated from an assumed model based on the electric double layer theory, gave values different from those found experimentally. This is explained as due largely to the uncertainties in the value of the clay specific surface area as well as to the assumed ideality of the model used.

More than twenty new organic complexes of halloysite have been prepared and one hundred and twenty-seven compounds were tested. Results are compared with those of earlier studies and use is made of recent findings concerning particle morphology and interstratification effects to interpret the results. The compounds which form complexes with halloysite are polar, and are usually either acids or bases. Their molecules usually contain two functional groups (preferably —OH and/or —NH2), are relatively small and have one functional group per two carbon atoms, but do not usually include cyclic or aromatic types. The best explanation of the existence of these metastable complexes seems to lie in the ability of some organic molecules to form hydrogen bonds with the halloysite structure, about which insufficient knowledge is available to allow quantitative evaluations to be made.

Adsorption and desorption of cationic surfactants, cetyl pyridinium bromide, cetyl trimethyl ammonium bromide, dodecyl pyridinium bromide on bentonite, kaolinite and illite, and their diffusion through a bentonite membrane have been studied.

The binding of these compounds on the mineral surface takes place much beyond the exchange capacity. For excessive saturations with long chain compounds like these, the chains stand erect to the surface. A correlation of area per exchange site and area associated with surfactant molecule on clay surface also supports this view. The increase in the extent of adsorption with the size of the organic cation is due to an increase in the van der Waal's forces between clay and surfactant molecule. Isosteric heats of adsorption at different stages of surface covered with surfactant have also been determined and the same was found to pass through a minimum point. Larger ions desorb less, owing to the lesser solubility and larger contribution of dispersion forces.

Permeability of these surfactants and energy of activation of the diffusion process through the H- bentonite membrane has also been investigated. Diffusion of these cations takes place via exchange positions through the membrane and the order is exactly the reverse of their adsorption on the clay surface.

Following the work of Davis & Worrall (1971) the adsorption of glucose from aqueous solution on sodium kaolinite has been re-examined. Colorimetric and radiochemical methods were used for glucose assay. Adsorption is very small and is probably positive.

A new method of measuring the water evolved on thermal dehydration of a variety of clay minerals and related hydrated compounds is described. By placing the substance in a tubular furnace and passing over it a dry inert gas, water released on heating is carried to a sensitive electrolytic hygrometer for measurement. The heating is programmed to give a uniform rate of temperature rise, so that continuous monitoring of the evolved water permits discrimination between successive dehydration processes occurring at different temperatures. The procedure is appropriately termed thermohygrometric analysis (THA).

The applications described include investigations of the thermal decomposition behaviours of hydrated aluminas and hydrated iron oxides, and of clay minerals such as kaolin, montmorillonite, chrysotile and micas. The relations between the results given by thermohygrometric analysis and those obtained by differential thermal analysis are discussed. As with DTA, the record trace from a THA examination gives a graphical representation of the dehydration process, but THA has an advantage in providing a quantitative measurement of the water evolved.

Complexes formed by straight chain, primary, aliphatic alcohols from methanol to n-decanol with Ca- and Na-montmorillonite from the liquid and vapour phases, have been investigated by X-ray techniques. Satisfactory complexes are formed more readily by the Ca-mineral and from the liquid phase rather than from the vapour phase. Molecular configurations of the adsorbed molecules are suggested consistent with the experimental data. The importance of cation-dipole interactions for the lower members of the series is stressed.

Ceramic clays are characterized by a method that stems from the IL/MA procedure proposed by Keeling (1958a, b) but which is more rapid to perform and more basic in concept. By thermogravimetric methods an estimate is made of both OH water and interlayer plus physically adsorbed water. These are plotted against each other in a manner similar to the IL/MA plot. The composition of the clay can be characterized uniquely on such a diagram by estimating either the quartz or the free silica contents of a sample, its silt, and < 2μ fraction, and plotting for each on a 100% clay basis their OH water, and interlayer and physically adsorbed water. Simple methods are given for assessing these factors. The determination of interlayer water content could form the basis of a method of plant control of clay composition in a way similar to that proposed by Keeling using moisture adsorption determinations.

A study of the weathering of micaceous clays in some Norwegian podzols, includes semiquantitative estimates of minerals in the concentrated clay fractions which show a decrease in the amounts of illite and chlorite, and an increase in vermiculite and mixed-layer minerals upward in the profile. Illite, the dominant mineral at depth, weathers to hydrobiotite in the surface horizon of the profile. Subsequent weathering of hydrobiotite in this portion of the profile produces trioctahedral vermiculite and smectite, or intergrade smectite-chlorite.

Partial molal voltmae of Ca-montmorillonite, apparent molal volume of silica gel in water and of Ca-montmorillonite in ethanol-water mixtures, were determined using pycnometer density measurements. No electrostriction of water was observed with silica gel but took place in Ca-montmorillonite thus indicating the principle role of surface charges in stricting water. In ethanol-water mixtures alcohol molecules were salted out at low alcohol concentration, but they started reaching inner zones near the clay surfaces when their mole fraction in solution was increased beyond the value of 0·55.

Volcanic ash soils were studied with the scanning electron microscope to observe the morphology and occurrence of allophane, imogolite and halloysite. Allophane and imogolite in general were randomly distributed indicating a process of dissolution and recrystallization. Halloysite is typically associated with feldspars showing that it is formed by direct alteration.

The imogolite fibres studied with the SEM show them to be much thicker than currently reported in the literature and it is thought that pretreatment of the clays for TEM measurements results in a partial destruction. Halloysite consists typically of short rigid tubes and thus differs from imogolite which tends to curl.

A variety of stevensite was collected at the Obori mine, Yamagata Prefecture, Japan. Analysis shows close agreement with published data for stevensite. Chemical composition: SiO2 52·76%; A1203 trace; Fe203 0·38%; MgO 23·67%; MnO 1·57%; CaO 2·19%; Na2O 0·37%; K2O 0·00%; H2O+ 6·52%; H2O− 12·38%; Total 99·84%. The structural formula is (Fe0·04 Mg5·31 Mn0·02) Si80·1 020·00 (OH)4·00·Ca0·36, Na0·10.

This specimen shows an interstratified structure of dehydrated and hydrated layers, the former caused by dehydration of the interlayer water, although stevensite essentially contains a non-swelling layer and shows interstratification. The intensities and spacings of the 00l reflections change successively with changes in humidity. When treated with water and glycerol, the 00l reflections are similar to those of montmorillonite. The DTA and TG curves are similar to those of stevensite and an interstratified mineral of talc and saponite.

The spatial arrangement of platy particles in a clay is defined by an orientation ratio which can be derived analytically from optical birefringence as well as from X-ray diffraction data. Measurements on kaolin slurries consolidated by increasing loads were used to verify that orientation ratios obtained experimentally by these two methods are in fact equivalent. In contrast it was found that particle orientation cannot be assessed objectively from electronmicrographs alone. A combined optical-X-ray study of two natural clays (London Clay and Lias Clay) revealed that the kaolinite crystals are oriented only slightly more than the illite crystals, and showed that the correspondence between optical and X-ray measurements is also valid for natural clays.

Fixation of K by some West Indian soil clays was proportional to their montmorillonite contents. Reductions in c.e.c. and surface areas occurred after fixation. The reductions in c.e.c. were equivalent to the amounts of K fixed, suggesting that an ion exchange mechanism was operative. Reductions in c.e.c. were proportionately greater than reductions in surface area.

Release of native K from the clays was greater from the < 0-2 μm fractions than those from 0·2−2·0 μm. Appreciable amounts of'recently fixed' K were not released after extraction with 0·03 N NaCl solution. Removal of 'free' iron increased the release of: (i) native K from the 0·2−2·0 μm fractions ; and (ii) 'recently fixed' K from both fractions. The presence of NH4 ions decreased the release of 'recently fixed' K.

The release pattern of the clays indicates that intra-particle diffusion rather than film diffusion or mass action exchange, is the rate-limiting mechanism.

Calculated diffraction profiles for interstratified kaolinite and montmorillonite have been used to determine the composition of clays reported from Poland, Japan and Mexico. The predicted layer proportions determined from the curves and by other methods are in close agreement for the first two but a higher kaolinite content than that originally proposed is obtained for the Mexican clays.

Vermiculite single crystals swell to the gel state as a consequence of treatment with concentrated solutions of γ-aminobutyric acid.

The amount of swelling was determined, by measuring by X-ray diffraction the separation of the elementary silicate layers in the gel-like crystals.

By application of pressures into the gels along the swelling direction, a direct measure of the swelling pressure is obtained. The relation between swelling pressures and equilibrium interlayer distances is a function of both cationic concentration and dielectric constant of the solution. Measured swelling pressures are consistent with a model based on formation and interaction of diffuse double layers of aminoacid cations around the silicate particles, these having a Stern layer of an approximate thickness of 5 Å. The specific chemical adsorption potential of the system has been estimated as φ = 3·3 + 0·2 Kcal/mol.

X-ray powder diffraction patterns of kaolinites have been studied with especial reference to the region of the 02, 11, band. Satisfactory correlations with calculated patterns based on the layer structure of dickite can be achieved for a range of kaolinites if account is taken of disorder between and within layers. Some indication of the amount of disorder within a kaolinite can be obtained.

X-ray analyses indicate that illite, smectite, loughlinite (Na20.3Mg0.6SiO2.8H2O) and chlorite are present in the < 2 μm fraction of the lacustrine Green River Formation (Eocene) of Wyoming. Material amorphous to X-rays and random mixed-layer structures are present in subordinate amounts. Individual crystals vary from pure, well-ordered structures to poorly crystallized forms.

Illite is ubiquitous, occurring in all the samples studied. It is generally associated with other clay minerals but frequently occurs as the only clay mineral found in the 'oil shales'. Smectite is present in all three members of the Green River Formation, but its presence frequently shows an inverse relationship to both analcime and loughlinite. Loughlinite is restricted to the saline facies of the Wilkins Peak Member. Chlorite occurs only in the silty and sandy beds of the Tipton Shale Member. The distribution of random mixed-layer structures and amorphous material is irregular. Several independent lines of evidence favour an in situ origin for many of the clay minerals reported in this investigation.

The 'oil shales', which are in most cases varved, kerogenous, dolomitic marls, have a variable clay mineral composition. There is a marked tendency, however, for illite to be the dominant or the only clay mineral present. Apparently the geochemical conditions favouring the accumulation of the oil shales also favoured in situ generation of illite.

The construction is described of a heating stage for examining oriented clay specimens in a Philips' diffractometer. The stage, which is simple and cheap to make, is interchangeable with standard specimen holders, operates over the range 20—265°C and does not require the diffractometer to be specially modified. The maximum temperature attained at the surface of the specimen collapses freely-expanding Mgsaturatcd vermiculite and prevents re-expansion of layer silicate minerals once they have been collapsed.