Clay-like Materials Research Articles

Uses of clay minerals in semisolid health care and therapeutic products

Clay minerals are included in several health care formulations. In particular, they are presented in many semisolid preparations with different functions, including stabilization of suspensions and emulsions, viscosizing and other special rheological tasks, protection against environmental agents, adhesion to the skin, adsorption of greases, control of heat release, etc. These functions are possible because of the special disposition of clay mineral particles when dispersed in polar solvents, due to their high surface areas and colloidal dimensions. When necessary, clays are processed or even modified to exalt or change some properties and new clay-like materials with special features are also synthesized. Finally, clays are frequently used concomitantly with other rheological modifiers to obtain synergic effects, influencing the stability and/or other technical properties of the health care products. This paper reviews the properties of clay mineral dispersions and the different functions derived from those properties, providing examples of applications in products intended to fulfil health care aims.

Pillared clay mimics from dicarboxylic acids and flexible diamines

Three dicarboxylic acids – 3,5-pyrazoledicarboxylic acid, 3,5-pyridinedicarboxylic acid and isophthalic acid – are examined for their ability to participate in lamellar hydrogen-bonded networks upon reaction with alkyl diamines. The use of flexible diamines stems from a desire to mimic the structure and eventually the intercalative abilities of naturally occurring clays. Six structures are reported, with the carbon chain length varying from 3 to 12, and the relative ability of each of the diacids (in combination with flexible diamines) to construct clay-like materials is discussed.

Diagnostic accuracy in sinus fungus balls: CT scan and operative findings.

A fungus ball may be characterized by its radiologic and operative gross findings. Computed tomography (CT) revealed a rim of soft tissue attenuation of variable thickening along the bony walls of the isolated paranasal sinus, or mottled hyperdense foci of variable size. A small amount of friable muddy mass surrounded by purulent secretions or dirty brown clay-like materials provide highly pathognomonic findings. However, these characteristics may induce clinical misdiagnosis. During the last four years we experienced 11 cases of chronic paranasal sinusitis in which pathologic examination failed to confirm fungal hyphae, despite clinical suspicion of a fungus ball based on operative or CT findings. During the same period, we also experienced another 52 patients who were diagnosed with fungus ball at pathologic examination. To evaluate the diagnostic accuracy of CT scans and operative gross findings in sinus fungus balls, we reviewed the medical records of these 63 patients and also reviewed CT scans and operative records of another 1127 patients who received endoscopic sinus surgery for chronic rhinosinusitis. The sensitivity of CT evaluation was 62%, and specificity was 99%. The false-positive and false-negative rate were 22% and 2%, respectively. With regard to operative findings, such as clay-like inspissated mucus, the sensitivity, specificity, and predictive value positive rate were 100%, 99%, and 83%, respectively. To make a diagnosis of fungus ball, a high index of suspicion is necessary and a pathologic confirmation is mandatory.

Successive Inclusion of Water, [H3NCH2CH2NH3]2+ and [H3NCH2CH2NH2]+ in the Aromatic Cavity of (p-Sulfonato)calix[4]arene

Titration of the sulfonic protons of (p-sulfonato)calix[4]arene (H8L) with two equivalents of ethylenediamine affords [H3NCH2CH2NH3]2[H4L(H2O)3]·H2O, a molecular complex in which water is included inside the macrocycle. Deprotonation of one of the phenolic groups expels the water molecules from the aromatic cavity, leading to the formation of [H3NCH2CH2NH3]1.5[(H3L)(H3NCH2CH2NH3)]·(H2O)5.5, which represents an unprecedented example of the inclusion of a dication in a calixarene. Further addition of ethylenediamine affords the mixed salt [H3NCH2CH2NH3]2[(H3L)(H3NCH2CH2NH2)]·(H2O)4.5 in which the monocation [H3NCH2CH2NH2]+ is preferentially bound to the cavity through a non-classical hydrogen bond involving an N-H···π facial aromatic contact. Inclusion phenomena are indicated both by NMR and X-ray structure determinations. In the same way as their inorganic-organic counterparts, these clay-like materials are organised into parallel organic-organic layers.

Weathering of MSWI bottom ash with emphasis on the glassy constituents

Municipal solid waste incinerator (MSWI) bottom ash is predominantly composed of high temperature solids. In a natural atmospheric environment many of these solids are metastable and will alter to form thermodynamically stable assemblages of minerals. Results of our research have revealed that the weathering products of MSWI bottom ash, which has been disposed of in the open, are similar to those found in weathered volcanic ashes and scoriae. The most obvious change is the transformation of glassy constituents into clay-like materials. These secondary products may have a significant influence on the leaching characteristics of contaminants such as heavy metals. Although the influence of this alteration process on total leaching is yet to be determined, our results suggest new topics of future research on geochemical engineering concepts, where natural weathering processes are exploited to minimize deleterious effects of ash disposal and utilization.

High-pressure differential thermal analysis (HP-DTA)

High-pressure differential thermal analysis results are used to describe dehydration reactions for the clay-like materials of Na-rich montmorillonite, K-, Ca-, and Mg-exchanged montmorillonite, kerolite, and a high-pressure phase resembling talc/mica with excess water. Because sealed capsules may be used to contain fluids, it is possible to evaluate the role of H 2 O in these reactions. A separate paper (Part II) addresses the use of HP-DTA to understand dehydroxylation reactions in these materials

High-pressure differential thermal analysis (HP-DTA)

High-pressure differential thermal analysis results are used to describe dehydration reactions for the clay-like materials of Na-rich montmorillonite, K-, Ca-, and Mg-exchanged montmorillonite, kerolite, and a high-pressure phase resembling talc/mica with excess water. Because sealed capsules may be used to contain fluids, it is possible to evaluate the role of H2O in these reactions. A separate paper (Part II) addresses the use of HP-DTA to understand dehydroxylation reactions in these materials.

Olefin isomerization over an alumina-pillared fluoromica catalyst

In the recent past, research on pillared clays has centered on materials made from smectites, such as montmorillonite and hectorite. We have extended the range of pillared clay-like materials to micas, 2:1 layered silicates with higher layer charge density, by pillaring tetrasilicic fluoromica (NaMg 2.5Si 4O 10F 2) with aluminum chlorhydrate solution. The resultant microporous alumina pillared mica can be used as an acid catalyst to effect the isomerization of 2-methylpent-2-ene. Analysis of the activity of the pillared mica as well as its selectivity as compared to γ-alumina demonstrates that the pillared mica has a high concentration of moderately strong acid sites, with a relatively narrow acid strength site distribution.

ChemInform Abstract: Pillared Clays and Micas

The interest in the petroleum industry in converting heavier feeds to liquid fuels has led to a search for microporous materials with pore sizes larger than those found in the faujasitic zeolites which form the basis of many petroleum processing catalysts. Materials with zeolite-like pores in the 10 A range can be synthesized by intercalating large polyoxocations between the layers of smectite clays. Subsequent calcination dehydrates the cations and converts them into oxide pillars that prop the clay layers apart, resulting in permanent microporosity in the interlayer region. Pillared clays have been studied extensively during the last decade due to their potential use in petroleum processing as cracking and hydrocracking catalysts. Previous workers have primarily utilized smectite clays such as montmorillonite and hectorite as the starting layered material for pillared clay. We now report that synthetic fluoromicas, clay-like materials of layer charge density higher than that of smectites, can also be pillared with polyoxoaluminum cations to form aluminapillared fluoromicas that are thermally stable up to 700°C.

Pillared clays and micas

The interest in the petroleum industry in converting heavier feeds to liquid fuels has led to a search for microporous materials with pore sizes larger than those found in the faujasitic zeolites which form the basis of many petroleum processing catalysts. Materials with zeolite-like pores in the 10 A range can be synthesized by intercalating large polyoxocations between the layers of smectite clays. Subsequent calcination dehydrates the cations and converts them into oxide pillars that prop the clay layers apart, resulting in permanent microporosity in the interlayer region. Pillared clays have been studied extensively during the last decade due to their potential use in petroleum processing as cracking and hydrocracking catalysts. Previous workers have primarily utilized smectite clays such as montmorillonite and hectorite as the starting layered material for pillared clay. We now report that synthetic fluoromicas, clay-like materials of layer charge density higher than that of smectites, can also be pillared with polyoxoaluminum cations to form aluminapillared fluoromicas that are thermally stable up to 700°C.

A New Insight into the Nature of the Leached Layers Formed on Basaltic Glasses in Relation to the Choice of Constraints for Long Term Modelling

ABSTRACTExperimental basaltic glass dissolution in fresh water is compared with analyses made on subglacial hyaloclastites from Iceland. The dissolution is initially selective and remains selective if the solution is renewed, whereas it becomes apparently congruent in non-renewed conditions. The congruent dissolution is ascribed to a pH increase (up to 7.0–7.5) which is hampered in the former conditions. The palagonite hydrated layer on the Icelandic basaltic glasses is made up of amorphous to crystallized clay-like materials. The chemical composition of palagonite is close to that of the intergranular clayey material, thus, it is inferred that in most cases no significant chemical gradient exists in the solution between the reaction zone, namely the glass/palagonite interface, and the intergranular solution. We conclude that the dissolution of basaltic glass under subglacial conditions is controlled by thermodynamics and that kinetic constraints, such as the diffusion of species through the altered layers, do not play a major role.

Pillared Clays and Micas

AbstractThe interest in the petroleum industry in converting heavier feeds to liquid fuels has led to a search for microporous materials with pore sizes larger than those found in the faujasitic zeolites which form the basis of many petroleum processing catalysts. Materials with zeolite-like pores in the 10 Å range can be synthesized by intercalating large polyoxocations between the layers of smectite clays. Subsequent calcination dehydrates the cations and converts them into oxide pillars that prop the clay layers apart, resulting in permanent microporosity in the interlayer region. Pillared clays have been studied extensively during the last decade due to their potential use in petroleum processing as cracking and hydrocracking catalysts. Previous workers have primarily utilized smectite clays such as montmorillonite and hectorite as the starting layered material for pillared clay. We now report that synthetic fluoromicas, clay-like materials of layer charge density higher than that of smectites, can also be pillared with polyoxoaluminum cations to form aluminapillared fluoromicas that are thermally stable up to 700°C.

Clays as Catalysts for Natural Processes

Clay minerals are important constituents of the earth's crust not only because of their abundance but merely because of their chemical activity. Clays found in soils and in sediments are distributed among three main mineralogical groups: the kaolin, hydrated micas, and smectite groups. Allophanes derived from volcanic glasses and amorphous Al-Si or Fe-Si mixed oxide gels are also abundant in large areas. These clays and clay-like materials share two common characteristics: a high specific surface area and the presence of exposed cations on their surface. In the natural environment these cations are either Na +, K +, Ca2+, or Mg2+, and/or polynucleic Al or Fe basic cations such as [AI(OH-)x(H20)yJ�+ or [Fe(OH-)x(H20)yJ�+. They balance the excess negative charge of the lattice, generated by isomorphic substitutions (for instance substitution of Si4+ by AI3+ in tetrahedral position, or AI3+ by Mg2+ in octahedral position). A clay microcrystal may thus be considered as the salt of a weak acid, whose anion (i.e. the lattice) has an infinite radius of curvature. In this situation the electrical charges of the cations generate a high electrostatic field because of the very incomplete screening of the positive charges by the anionic lattice charges. Since the lattice charges have fixed positions, the electrical neutrality is easily achieved by monovalent alkali cations, while for divalent cations the situation is much less favorable. Oxygen atoms or hydroxyl groups are the main surface constituents. They may play an important role by forming hydrogen bonds with proton donor or acceptor molecules. In addition, van der Waals (or dispersion) forces are expected to be quite active because of the magnitude of the surface area. In the natural environment a variable number of layers of water molecules but also polar organic molecules do form an adsorbed phase in which many kinds of chemical transformations may occur. The surface constituents and the adsorbed water may show a high catalytic activity in these transformations. The aim of this contribution is to review the recent progress of our knowledge in this field. After a paragraph in which the surface properties of clays and clay-like minerals