Influence of pore water chemistry on the swelling behavior of compacted clays

The influences of the exchange complex and pH of the solution used for cation saturation on Atterberg limits, compaction, and swelling potential of a compacted clay were investigated. The study involved transforming the exchange complex from a heterogeneous to a homogeneous one so that a frame of reference can be set for the clay behavior under such an ideal condition. The employed method for altering the exchange complex successfully yielded homo-ionic clay. The introduction of different species of cations gave rise to different particles associations. When introduced to the tested clay, potassium cations bond its particles with a rather strong bond (K-linkage), causing a drastic decrease in the specific area of the clay (about one-fourth of its untreated specific area), a decrease in the CEC, as well as a drastic decrease in the swell potential. For example, the swell pressure decreased from 1.87 kg/cm² for the untreated samples to 0.4 kg/cm² for the K-treated samples (under the same conditions). Also, the swell potential vs. time relationships can be modeled accurately using a rectangular hyperbola.     

Synthesis and characterization of novel swelling tunable oligomeric poly(styrene‐co‐acrylamide) modified clays

The oligomeric poly(styrene‐acrylamide‐vinylbenzylchloride) (P(St‐AM‐VBC)) quaternary ammonium salts have been prepared from the reactions of trimethylamine with the corresponding P(St‐AM‐VBC)s, which were synthesized by free‐radical polymerization of a mixture of styrene, acrylamide, and vinylbenzylchloride. Then the swelling tunable oligomeric poly(styrene‐co‐acrylamide) modified clays have been prepared through cation exchange of the sodium ions in the clay with the corresponding P(St‐AM‐VBC) quaternary ammonium salts. The P(St‐AM‐VBC) and its modified clays have been characterized by infrared spectra (IR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA), proton nuclear magnetic resonance (¹H NMR), X‐ray diffraction (XRD), and transmission electron microscopy (TEM). The solvent‐swelling capacity of poly(styrene‐co‐acrylamide) modified clays have also been tested, and the experimental results have indicated that these clays are novel swelling tunable organic clays. XRD and TEM studies have shown that these novel swelling tunable clays are well‐intercalated or exfoliated. Furthermore, TGA analysis shows that these polymerically modified clays have high thermal stability for nanocomposites by melt blending. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Study on superabsorbent composites. IX: Synthesis,characterization and swelling behaviors of polyacrylamide/clay composites based on various clays

A series of clay-based superabsorbent composite from acrylamide (AM) and various clays, such as attapulgite, kaolinite, mica, vermiculate and Na⁺-montmorillonite, was prepared by free-radical aqueous polymerization, using N,N′-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator, and then saponified with sodium hydroxide solution. In this paper, the reaction mechanism and thermal stability of the superabsorbent composites incorporated with various clays were characterized by FTIR, XRD and TGA, respectively. The effects of clay kind and clay content on equilibrium water absorbency of these composites were also investigated and compared. In addition, the influences of clay kind on comprehensive swelling behaviors of the PAM/clay superabsorbent composites were studied. The results indicated that the introduced clays could influence physicochemical properties of obtained superabsorbent composites. Mica could improve thermal stability of corresponding superabsorbent composites to the highest degree comparing with the other clays. The PAM/clay superabsorbent composites incorporated with 10 wt% clay of various kinds were all endowed with equilibrium water absorbency of more than 1300 g g⁻¹. The equilibrium water absorbency decreases with increasing clay content and correlates with the kind of clay. Attapulgite-based superabsorbent composite was endowed with higher water absorbency in univalent cationic saline solution, however, the vermiculite- and the kaolinite-based ones acquired the highest water absorbency in CaCl₂ and FeCl₃ aqueous solution, respectively. Moreover, the superabsorbent composites incorporated with Na⁺-montmorillonite have higher swelling rate and that of doped with mica was endowed with higher reswelling capability.     

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.     

溶剂与溶胀促进剂对神华煤溶胀行为的影响

采用体积法研究了甲苯、四氢萘、甲醇、二甲亚砜、N,N-二甲基甲酰胺(DMF)和乙醇胺(MEA)5种纯溶剂及1∶1的MEA-DMF混合溶剂对神华烟煤的溶胀行为,考察了Fe(NO3)3、Fe2(SO4)3和FeSO4添加量为0.5%(以铁占煤质量计)作为溶胀促进剂的性能。结果表明:MEA-DMF混合溶剂的溶胀效果优于5种单一溶剂。铁盐Fe(NO3)3明显促进煤溶胀,在80℃,24h和剂煤比5∶1条件下MEA-DMF混合溶剂与Fe(NO3)3协同可使溶胀率超过3.0。对溶胀处理后的神华煤FT-IR表明DMF、DMF-MEA溶胀处理以及与Fe(NO3)3协同溶胀处理后明显削弱了煤羟基氢键间的缔合作用,其中,经DMF-MEA与Fe(NO3)3协同溶胀处理的这一变化最为明显。