Cyclic swelling of clays

Changes in free swelling and swelling pressure of different types of clays in response to varying cycles of wetting and drying have been studied. It can be shown that cyclic tests lead to a gradual destruction of the durable contacts in the clay structure and their transformation into less durable ones. At the same time, a reconstruction of the structure of the clays takes place, manifested by the destruction of large micro-aggregates and by disorientation of structural elements. All these phenomena result in great swelling with increase in the number of wetting cycles. Between cycles 3 and 20 the expansibility is at its maximum and may be 1.3–10 times as much as that after one wetting cycle. Cyclic swelling leads to an overall equilibrium in the system, when the internal energy of the clay is minimal and the bound water content is at its maximum. Clay in this state exhibits its maximum moisture uptake (W′_s), the meaning of which is of thermodynamic character and depends neither on the initial soil density and moisture, nor on the scheme of cyclic tests adopted.     

The meaning of surface area and porosity measurements of clays and pillared clays

Pillared clays (PC) generally present textural complexity, geometrical constraints and possible chemical heterogeneity by pillaring. As far as surface area and porosity measurements by physical adsorption of nitrogen are concerned, this overall complexity introduces interpretation difficulties. We consider two aspects of this problem in pillared clays.The textural complexity stems from the distribution of charge density, from the deformation of the host layers and from their entanglement. The microtexture is controlled by the wet preparation chemistry, to a large extent by the drying method as examplified by the titanium pillared montmorillonites.The geometrical constraints arise from the fact that the interlamellar space of the PC is (so far) microporous or just mesoporous. The small distance between the layers, of the order of one or a few molecular diameters, is therefore expected to perturb the arrangement of the pore filling molecules. The molecular confinement is a major source of underestimation of the total pore volume in the interlamellar space. It makes the surface area determination difficult and of little physical significance. Probably microporosity values are more valuable criterion of pillaring as shown in the titanium pillared samples.In addition to these two aspects, one has also to consider a possible chemical heterogeneity arising from the simultaneous presence of pillars, exchangeable ions and precipitated species. This can lead to a complex behaviour of surface area and microporosity as examplified by the mixed aluminium-iron pillared laponites.     

Color characteristics of low-melting clays

An unconventional method of determining the color of clay and ceramic materials in air-dry and calcined states in equal-color coordinates of the color space using the color characteristics (saturation, hue, yellow hue, lightness, color coordinate) is employed to classify clays from the Gzhel’ deposit. The method is recommended for adjusting the color range of ceramic articles.     

Refractory clays of Stepnyi deposit

Conclusions The investigated sample of Stepnyi deposit clay is suitable for production of type ShA normal-purpose chamotte parts. The use of this clay in the production of certain forms of chamotte parts such as bottom teeming, open hearth, and other parts is possible. Being quite plastic, such clays may serve as a binder refractory raw material and be used for production of more critical parts in combination with chamotte from more refractory clays (bauxite and others). Chamotte of Stepnyi deposit clay may be used in combination with enriched Eltai kaolin. This in full measure refers to Stepnyi deposit clays of the better grades corresponding to types VGO-1 and VGM. Taking into consideration the low content of the coloring oxides, Stepnyi deposit clays may also be used as a white-firing raw material in the production of various ceramics.Translated from Ogneupory, No. 4, pp. 24–26, April, 1993.     

Roles of clays in soils

In soil science, the term clay refers to all particles less than 2 μm in diameter. Thus it includes layer silicates, oxides and other minerals. Clays are the source of many of the chemical and physical properties of soils that make them a useful medium for the growth of plants and for the less common uses such as a medium for the disposal of wastes. Clays add much of the diversity found in soils. The minerals in soil clays frequently differ from their counterparts in commercial deposits. Also, the behavior of soil clays is influenced by the associated minerals in the coarser fractions. Organic matter is an important reactant with clays of some soils, but it is beyond the scope of this review.The cation exchange properties of clays are among their most important properties in retaining plant nutrient ions (e.g., NH₄⁺, K⁺, Ca²⁺, Mg²⁺, etc.). Cation selectivity of clays influences soils as a plant growth medium and as a disposal medium for wastes (e.g., radioactive and toxic metal ions). Native K in layer silicates of soils is the most important element provided to plants by illites and other micas. Clays contribute to the formation of soil structure by undergoing seasonal shrinking and swelling. Also, they are transported and form clay films that coat natural aggregates that characterize many friable soils. The dispersion and flocculation of clays are important reactions in the physical behavior of soils which in turn influence friability, water infiltration rate, erodibility and other behavioral properties.Vermiculite and smectite in soils frequently have Al³⁺ or polymeric Al on the cation exchange sites. Thus the behavior of these minerals is different from structurally similar minerals in natural deposits. The Fe oxides in soils occur largely as goethite and hematite. Yet they contain Al substituted in their structures, consequently the crystals are smaller and less soluble than their ideal counterparts. Iron oxides contribute to the color, aggregation, and adsorptive properties of soils. Manganese oxides in soils contribute to the retention of trace metals (Co, Zn, Ba, Ni, etc.) and to the oxidation of Fe. Lithiophorite forms in acid soils thus marking another group of minerals that occurs in soils and that is influenced by Al in the structure or in interlayer positions as a result of weathering.     

Self-assembly behavior of polymer-assisted clays

Layered silicate clays are natural crystallites that are well recognized for their practical uses, but little is known about their self-assembly behavior. In this review, we summarize the recent literature on clay interactions with organic polymers as well as clay self-assembly with organic involvement. We place emphasis on two aspects of these non-covalent interactions: first, plate-like clays can have a considerable impact on polymer properties such as hydrogels and clay films, and also on the encapsulation of bio-molecules. Second, through ionic intercalation with polymeric amine-salts, the clay layered structure units can be modified and enabled to self-assemble into ordered arrays such as rod-, dendrite-, and fiber-like microstructures. The silicate self-assembled morphologies such as worm-like and hollow microspheres were obtained in epoxy matrices and during spray drying, respectively. A mechanism was proposed for the clay self-assembly in two orientations, platelet face-to-face (ionic attraction) and edge-to-edge (organic hydrophobic effect). Further, the layered clays after the exfoliation into random platelets (1 nm in thickness) had strong propensity toward self-piling without any organic influence. Formation of lengthy rods or fibrils up to 5 μm in length and their hierarchical transformation under transmission electron microscope (TEM) electron beam bombardment and ultrasonication were observed. The clay thin-platelet geometric shape and surface ionic charge are two important parameters for the self-assembling tendency. The high surface of clay platelet has a significant impact on polymer interactions and drives the self-organization of inorganic-organic structures.     

Ladle brick from semiacid clays

Conclusions The main feature of the technology developed for the production of high-density ladle brick which expands in service, made from semiacid clay from Chasov Yar and Druzhkov sources, is the regular firing cycle for the chamotte and the finished products, namely completion of firing in the temperature range in which we can guarantee sintering of the material, but in which bloating has not yet begun.The life of the ladle brick in service made from semiacid clays is greater than that of high-chamotte ladle brick owing to the high density of the structural joints, governing the expansion of the working layer of the brick coming into contact with metal and slag.Mass production of semiacid ladle brick using the technology developed by VIO should be organized in refractory plants of the UkrSSR.Deceased.Translated from Ogneupory, No.2, pp.14–17, February, 1967.     

Geochemical effects of electro-osmosis in clays

Geochemical effects of electro-osmosis in bentonite clay are studied in the laboratory, where a 6 mm thick bentonite layer is subjected to direct current. Acidification and alkalization near anode and cathode are expected, possibly causing mineral deterioration, ion mobilization and precipitation of new solids. Afterwards the clay is analysed by XRF and anolyte and catholyte are analysed by ICP-MS. In addition, as a preliminary experiment treated bentonite is analysed by high resolution μ-XRF. Electro-osmotic flow is observed. Due to its carbonate content the bentonite is pH-buffering. Alkalization in the catholyte is substantial. Ca, Na and Sr are significantly removed from the clay and accumulate in the catholyte. Recovery in the catholyte accounts for a small fraction of the element-loss from the clay. The rest will have precipitated in undetected solid phases. μ-XRF indicates the loss of Ca-content throughout the bentonite layer.     

Sintering studies on plastic clays

Plastic clays are essential ingredients for ceramic body manufacture as binding agents for imparting plasticity, workability and green strength to raw materials. Seven clay samples which are mainly kaolinitic were chosen for the present studies. The mineralogy and crystallinity of the raw materials and the phase changes taking place during their sintering under different conditions were examined. The properties of the fired samples, such as water absorption, linear shrinkage and MOR were determined and a correlation of the strength of the sintered material with the microstructure was attempted. The observed variation in the properties was explained as a function of mineralogy, crystallinity and the amount and nature of the impurities present in the clays. The effect of the blending of an aluminosilicate gel and other mineral constituents with clays on their properties after sintering was also studied.