Controlled precipitation conditions allow the formation of highly porous, spheroidal aggregates of hydrotalcite. The aggregate structure resembles a house-of-cards, being composed of interconnected thin plates. The aggregate size can vary over a range of about 1 to 60 μm by altering precipitation conditions such as mixing shear, temperature, addition rates and addition order. These materials are low in bulk density and highly absorptive. The aggregate structure is maintained during calcination. The micro and meso-pore size distribution is very similar to conventionally prepared hydrotalcite, but the macroporosity is dominated by the voids between spheroids. The characteristics of these aggregates point to potential applications in areas such as catalysis and separation.

Montmorillonite was pillared with Al2O3-NiO mixed oxide by ion-exchange combined with titration process; the interlayer Na ions of montmorillonite were first exchanged with aluminum hydroxide polycations, and then nickel hydroxide was precipitated between the layers by a titration method. The aluminum hydroxide pillars reacted with the nickel hydroxide at room temperature, and the microporous structure was much stabilized against heating. The specific surface area as high as 300 m2/g was maintained up to 700°C.

The intercalation of Keggin-type [X(H2O)W11SiO39]6−(X=Co2+, Mn2+) heteropolyanions by aqueous anion exchange of 10 Å in a synthetic hydrotalcite-like Mg2Al(OH)6(NO3) results in products with interlayer spacing of ca. 10 Å. The layered array of the product and the integrity of the intercalated heteropolyanion are stable below 623 K in air as examined by XRD and IR analyses, respectively. UV-vis Diffuse Reflectance spectroscopy indicates that the water ligand in the intercalated [Co(H2O)W11SiO39]6− can be removed by thermal evacuation at 473 K leaving a coordinatively unsaturated site (in the transition metal) which reversibly coordinates water,methanol, ethanol or ammonia. ESR analysis of the intercalated [Mn(H2O)W11SiO39]6− shows that the shape of a signal at g = 2.00, arising from six-coordinated Mn2+ strongly depends on adsorption-desorption of the water ligand.

A new strategy to prepare alumina pillared α-zirconium phosphate with enhanced surface area and narrow pore size distribution is reported. The required precursor, a highly expanded single phase intercalate, is obtained in two steps. In the first one, the oligomeric solution of aluminium, prepared by dissolving aluminium in a solution of A1C13 at 95°C, is contacted with colloidal α-zirconium phosphate under reflux, in the presence of fluoride. Subsequently, the resulting intercalation compound is treated again with a diluted solution of fluoride under hydrothermal conditions at 200°C. It is thought that fluoride ions complex aluminium monomers present in the pillaring solutions, and remove aluminium from the external surface of the phosphate. The pillared materials obtained by calcination in the range 400-600°C present BET surface areas between 184-140 m2g−1 and basal spacings between 17.3-15.4 Å. These results contrast with those reported using classical methods, which systematically lead to materials with BET surface areas <80m2g−1.

The electrical relaxation and charge motion in porous solids (Lithium exchanged alumina pillared layered cc-tin phosphates (Li-PLP)) have been studied on the basis of the coupling model. The static dielectric constant and the dielectric susceptibility show a dependence on the basal distance which is correlated with the ion mean square displacement.

Rectorite clay was pillared with an Al/Ce-cluster pillaring agent made from aluminum chlorhydrol and cerium nitrate. The resulting product had an interlayer distance of 15.7 Å, which was significantly larger than the interlayer distance obtained using conventional aluminum chlorhydrol as the pillaring agent (8.4 Å). Argon adsorption analysis indicates that the pores of the AL/Ce-cluster pillared rectorite are non-uniform, with pore diameters ranging from 5 to 16Å. 29Si MAS NMR studies showed that calcining the natural rectorite changes the silicon environment, while the pillared rectorite clays are much more resistant to such changes upon calcination. It is suggested that pillaring reactions enhance the thermal stability of the rectorite by stabilizing the local silicon environment in the clay.

Aqueous suspensions of exfoliated Li0.25MoO3 and Na-montmorillonite have been combined and dried to form interstratified solids. X-ray diffraction patterns of ethylene glycol treated films show that the d-spacing of restacked materials varies with composition between the limits established by the two end members. Based on these data, we conclude that the new materials are composed of individual layers from each of the precursor compounds, arranged in a random fashion. It is likely that other layered solids can be exfoliated and restacked to form new interstratified materials.

Aerogels are highly porous solids having unique morphology among materials because both the pores and particles making up the material have sizes less than wavelengths of visible light. Such a unique morphology modifies the normal molecular transport mechanisms within the material, resulting in exceptional thermal, acoustical, mechanical, and electrical properties. For example, aerogels have the lowest measured thermal conductivity and dielectric constant for any solid material. Special methods are required to make aerogel films with high porosity. In this paper, we discuss the special conditions needed to fabricate aerogel films having porosities greater than 75% and we describe methods of processing inorganic aerogel films having controllable thicknesses in the range 0.5 to 200 micrometers. We report methods and results of characterizing the films including thickness, refractive index, density (porosity), and dielectric constant. We also discuss results of metallization and patterning on the aerogel films for applications involving microminiature electronics and thermal detectors.

Very highly porous (aerogel) silica films with refractive index in the range 1.006-1.05 (equivalent porosity 98.5-88%) were prepared by an ambient-pressure process1,2. It was shown earlier using in situ ellipsometric imaging1 that the high porosity of these films was mainly attributable to the dilation or “springback” of the film during the final stage of drying. This finding was irrefutably reconfirmed by visually observing a “springback” of >600% using environmental scanning electron microscopy (ESEM). Ellipsometry and ESEM also established the near 100% reversibility of aerogel film deformation during solvent intake and drying. Film thickness profile measurements (near the drying line) for the aerogel, xerogel and pure solvent cases are presented from imaging ellipsometry. The thickness of these films (crack-free) were controlled in the range 0.1-3.5 μm independent of refractive index.

Anhydrous sol-gel condensation of triethyl phosphate [(CH3CH2O)3PO] with boron trichioride (BCl3), triethyl aluminum [(CH3CH2)3Al] or silicon tetrachloride [SiCI4] in organic solvents led to rigid gels. The pore fluid of the gels was removed under supercritical conditions in a pressurized vessel to form porous solids. The condensation chemistry prior to the gel point was monitored by solution 1H, 13C, 31P, and 11B NMR. The materials were then calcined at progressively higher temperatures to produce high surface area phosphates. Nitrogen gasphysisorption was used to determine the surface areas, total pore volume, and average pore radius of the products. FT-IR was used to determine functional groups in the materials. The microstructure was also examined by scanning electron microscopy.

High surface area ethyltrimethoxysilane (ETMS) modified silica aerogels and xerogels were synthesized by cohydrolyzing the mixtures of ETMS and tetramethylorthosilicate (TMOS). The effects of ETMS content, pH value and solvent addition were investigated. The surface area, pore structure and hydrophobicity were studied using nitrogen and water sorption measurements. By ETMS modification of TMOS gels, high surface area, density and hydrophobicity were achieved. The 25 mole% ETMS-75 mole% TMOS was found to be the best composition for both aerogel and xerogel, which are hydrophobic and have surface areas of 1221 and 832 m2/g, respectively.