Surface-treated clay

Inks. Refined kaolin is a common ingredient in a large variety of printing inks (qv). In addition to extending the more expensive polymers present, ka olin also contributes to improved color strength, limits the penetration of the ink into the paper, controls rheology, and improves adhesion. Kaolin for this appHcation must usually be as white as possible and free from oversize particles. Surface treated clays are used to improve compatibiHty with oil-based ink. Clays can also be an ingredient in the newer water-based or uv-cured inks. 

Clays vary in price from only a few doUars per ton for common clay to > 0.25/kg for some of the specialty surface treated clays. For clays that are used in large quantities such as kaolins for paper coatings, transportation to the point of use may be the primary cost component. 

Clay hllers were surface modihed with TMPTA or triethoxyvinyl silane (TEVS) followed by EB irradiation by Ray and Bhowmick [394]. Both the untreated and treated fillers were incorporated in an ethylene-octene copolymer. Mechanical, dynamic mechanical, and rheological properties of the EB-cured unfilled and filled composites were studied and a significant improvement in tensile strength, elongation at break, modulus, and tear strength was observed in the case of surface-treated clay-filled vulcanizates. Dynamic mechanical studies conducted on these systems support the above findings. 

Layered silicate nanoparticles have also been used to prepare PEN-based nanocomposites through the direct intercalation of PEN polymer chains from the melt into the surface-treated clay. An internal mixer was used and exfoliated silicate layers within a PEN matrix were obtained. Mechanical and barrier properties measnred by dynamic mechanical and permeability analysis showed significant improvanents in the storage modulus and water permeabihty when compared to neat PEN (Wu and Liu, 2005). 

Surface-treated clay - This is processed kaolin diat has been surface modified (e.g., with stearates or silanes) to improve compatibility with and performance in organic matrices. 

Preparation of Pillared Clay Catalysts. PAG products are used for the preparation of zeolite-like catalysts by intercalation, the insertion of Al polycations molecules between the alurninosiHcate sheets of clay (3,33). Aqueous clay suspensions are slowly added to vigorously stirred PAG solutions, and the reaction mixture is aged for several hours. The clay is separated from the PAG solution and washed free of chloride ion. The treated clay is first dried at low temperature and then calcined in air at 450—500°G, producing a high surface area material having a regular-sized pore opening of about 0.6 to... 

In the corresponding text, the authors emphasize the important trends clay-rich soils show lower adsorption, clay-poor (sandy) soils show higher adsorption, and soils with medium clay content show intermediate adsorption, when compared to their untreated counterparts. Moreover, the unexpected behavior of the clay-rich soils is highlighted. The authors first state the expected behavior ( An increase in water sorption was expected after RAMEB addition to all soils. ) and then point out the unexpected behavior ( However, the isotherms for RAMEB-treated clay-rich S6 and S7 soils show lower adsorption than the original soils. ). Because this is a combined R D section, the authors also offer a tentative interpretation for the unexpected finding ( that RAMEB decreases the amount of water-available surfaces in clay-rich soils ). 

The technology primarily treats clays because their physical and chemical properties, such as external and internal active surfaces produced by their fine crystalline structure, make them difficult to decontaminate. ARC asserts that pilot studies showed that the technology works well on perchloroethylene (PCE), xylene, phenols, and polychlorinated biphenyls (PCBs). 

Figure 15.6A Scanning electron micrographs (SEM) of fractured surfaces of (a) TPS-natural MMT nanocomposite containing 9.8 wt% clay, and (b) TPS-NH4MMT nanocomposite containing 10.7 wt% clay, (c) is the enlarged image for (b) showing spontaneously formed regular foam structures with 84% porosity in TPS-ammonium-treated clay.

Mesoporous solids including silicas and acid-treated clays can be functionalised at their surfaces so as to provide high local concentrations of active sites. These sites can be introduced by post-modification or via sol-gel preparations. In this way a range of novel materials with useful catalytic and other properties can be prepared. One of the most valuable applications for these materials is as replacements for environmentally hazardous reagents including corrosive mineral and Lewis acids, caustic bases and toxic metallic compounds. 

The procedure for preparing supported aluminium chloride relies on the small but significant solubility of aluminium chloride in aromatic hydrocarbons (typically toluene) and the slow reaction of the dissolved A1C13 with the surface hydroxyls of a commercial silica gel or acid-treated clay (Figure 1). One mole equivalent of HC1 is produced during the catalyst preparation consistent with the formation of mostly -OAlCl2 units on the surface and the use of hot solvent is essential so as to force the reaction and to ensure that the HC1 is driven from the system. 

Lewis Acid Sites. Many other mechanisms (66, 85) are best described in terms of the more general concept of aprotic, or Lewis acidity which is defined in terms of the capacity to donate or share pairs of electrons. Aprotic acid sites are commonly derived from the coordinatively unsaturated cations at crystal edges or adsorbed on crystal faces, from deydration of hydroxylated surfaces, and from deamination or deamination and dehydration of silica-aluminum catalysts or similarly treated clays having extensive tetrahedral substitution (130, 132). Formation of Lewis acid sites by deamination or deamination-dehydration is dependent on inversion of the basal oxygens of the aluminum-substituted tetrahedron away from the surface, in order to expose the aluminum (131). 

Diatomaceous earth is composed of the siliceous skeletons of microorganisms. It is pozzolanic, but its use in concrete is much restricted by its very high specific surface area, which greatly increases the water demand. Some clays react significantly with lime at ordinary temperatures, but while this property can be of value for soil stabilization, their physical properties preclude their use in concrete. Many clay minerals yield poorly crystalline or anrorphous decomposition products at 600-900 C (Section. 3.3.2), and if the conditions of heat treatment are properly chosen, these have enhanced pozzolanic properties. Heat-treated clays, including crushed bricks or tiles, can thus be used as pozzolanas in India, they are called surkhi. Other examples of natural rocks that have been used as pozzolanas, usually after heat treatment, include gaize (a siliceous rock containing clay minerals found in France) and moler (an impure diatomaceous earth from Denmark). The heat-treated materials are called artificial pozzolanas, and this term is sometimes used more widely, to include pfa. 

Increased severity of acid treatment continuously increases the surface area and porosity of the clay, but cracking activity shows a maximum at intermediate treating severity (223,325). Mild acid treatment removes a large part of the alkali and alkaline-earth metals. More-severe acid treatment removes increasing quantities of aluminum and iron, as well as other metals still remaining after mild treatment. It has been reported that treatment of clay with ammonium chloride solution, instead of acid, also results in an active cracking catalyst (70). The ammonium ion displaces some of the metal constituents of the clay by base exchange the treated clay is then calcined to drive out ammonia. 

The Claisen rearrangement can be effectively catalyzed by Lewis acids, Bronsted acids, bases, Rh(I) and Pt(0) complexes as well as by silica . Several reviews were published recently in which the application of zeolites and acid-treated clays as catalysts for the Claisen rearrangement was described Thus, it was shown that the rearrangement conditions for phenolic allyl ethers can be dramatically milder if this reaction is carried out by thermolysis of a substrate immobilized on the surface of previously annealed silica gel for chromatography. For example, the thermolysis of ether 159 on silica gel (in a 159 Si02 ratio of 1 10 w/w) at 70°C gives the phenol 160 in 95% yield after 3.5 hours (equation 70). An additional example is shown in equation 71. ... 

Fig. 12 Changes in properties of isothermally cured epoxy monomer and montmorillonite surface-treated with methyl, tallow, bis-2-hydroxyethyl ammonium cations at 10wt% clay (a) d-spacing at a range of temperatures and (b) oscillatory rheological parameters and d-spacing at 70 °C [63]...

Activated carbon surface area 1000 to 1500 m /g pore volume 0.6 to 0.8 cm /g, temperature < 540 °C loading very dependent on molar mass of target solute, solubility in the carrier liquid and pH. Example loading 0.01 kg organic molar mass 100/kg dry solid. The value varies with the molar mass . Carbon usage expressed as kg carbon required/m liquid increases with increase in the TOC in the feed and depends on the type of species present. A gross approximation is that 1 kg/m is required for 300 mg TOC/L with n = 1.0 for the range 200-30000 TOC, mg/L. acid treated clay surface area 225 to 300 m /g. 

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