Yttria-stabilized zirconia was prepared by (i) coprecipitation and (ii) alkoxide hydrolysis. The thermal and X-ray diffraction data were compared. The coprecipitation method yields microporous materials after calcination at 500°C for 4 hours with a narrow pore size distribution at a radius of 2–2.5 nm. Similar results were also seen with the alkoxide hydrolysis.

Porous inorganic SiO2 glasses obtained by the sol-gel route represent a unique matrix for encapsulation of biomolecules wherein the pores act as enclosures for high molecular weight proteins. These hybrid materials are characterized by a pore-biomolecule interface between the pore walls and the protein surface. As a specific model protein, cytochrome c (cyt c) is used to elucidate the nature of physical and chemical interactions between the pores of the matrix and the protein. Evidence from optical absorption, and resonance Raman (RR) spectroscopy methods indicates that the dopant protein alters the structural features of the pore walls. The optical and vibrational measurements strongly suggest that the pores that contain the trapped protein undergo little or no structural change during aging and drying as compared to protein-free pores. Vibrational RR analysis of the trapped cyt c also suggests that the protein resides in a pore where the pore dimensions conform to the shape of the protein. The results indicate that noncovalent interactions between the surface of the protein and the pore walls govern the dynamics of pore formation during gelation and individual biomolecules act as structural templates to design local pore structure.

The advent of ambient pressure aerogel technology may offer process advantages compared to supercritical drying. Since low density is required for most applications of interest, precursor gels must be very dilute (e.g. 6–8% SiO2). The remaining 92–94% is solvent which must be carried along for the entire process, then evaporated, condensed, separated, and recycled to be reused. These steps and associated unit operations represent a major cost (capital and operating). The drying step is problematic because of the large mass of solvent and the inherently low thermal conductivity of the gel. A new approach for drying aerogels is described whereby a wet gel containing a solvent is submerged in hot water or similar fluid which results in removal of the solvent without the drying fluid penetrating the gel. This results in a dried gel with aerogel properties but with the advantages of having a high heat transfer rate without using large temperature gradients as well as providing inherent separation of the dried material. We explore the effects of different solvents and drying temperature gradients on resulting gel microstructure.

Silica aerogels are a special class of porous materials in which both the pore size and interconnected particle size have nanometer dimensions. This structure imparts unique optical, thermal, acoustic, and electrical properties to these materials. Transmission electron microscopy and small angle x-ray scattering show that this nanostructure is sensitive to variations in processing conditions that influence crosslinking chemistry and growth processes prior to gelation. Recently, Lawrence Livermore National Laboratory (LLNL) has demonstrated that a Rapid Supercritical Extraction (RSCE) process can be used to prepare near-net shape silica aerogels in hours rather than days. Preliminary data from RSCE silica aerogels show that they have improved mechanical properties and slightly lower surface areas than their conventionally dried counterparts, while not compromising their optical and thermal performance.

A new approach to porous-silica doping is via ion bombardment and exposure of thedamaged structure to a controlled atmosphere. As a case study, SiO2 samples, bombarded with Ar2+ in a CO2 ambient and suitably processed, underwent an infrared spectroscopic investigation. The resulting data could be interpreted by assuming the addition of CO2 to the SiO2 skeleton at the diradical silicon defects produced by the bombardment. This addition takes place first via the formation of a carboxylate group, which evolves after heattreatment to an ester-like center, and eventually to a carboxilic acid after exposure to water vapour. Ab initio molecular-dynamics simulations of the interaction between CO2 and a silicon diradical are consistent with the above picture and suggest also the existence of anintermediate, in which tetrahedral carbon is bonded to the two silicon atoms and to two oxygen atoms.

A thin upper layer on a SiC-A12O3 porous substrate was formed by spray deposition of a Si-C composite or SiC fine powder 55.0 wt% total powder suspension. The formation of a compact layer of Si3N4 whisker or a SiC smaller pore size than the porous substrate was obtained under thermal treatment up to 1400°C for 3–4 h in a nitrogen or argon gas environment, respectively. SEM microstructure observations and a qualitative (DRX-EDAX) analysis of both sintered porous bodies were performanced to confirm the nature of both layers.

A ceramic membrane of porous, sintered aluminum nitride (AIN) is under consideration for use as a separator in a Lithium-Metal Sulfide battery due to the corrosion resistance and thermal stability of AlN. The pore structure and electrolytic permeability of the membrane must be appropriate if AlN is to be used. Commercialization of these membranes can occur only after repeatability in the processing conditions can be assured. In this study, extensive permeability and porosity testing was performed on membranes prepared under various processing conditions. Attempts to correlate processing conditions with permeability were made in order to determine the optimum method for fabrication of the membranes. It was determined that membranes produced with a lower molecular weight binder will have a higher permeability, higher porosity, and a larger pore structure than membranes produced with a higher molecular weight binder.

While the sol-gel polymerizations of tetraalkoxy- and organotrialkoxysilanes have been extensively studied, there have been few reports of similar investigations with the analogous tetraalkoxygermanium and organotrialkoxygermanium compounds. Germanium alkoxides have received less attention due, in part to their higher cost, but also their greater reactivity towards hydrolysis and condensation reactions. Germanium oxide materials are potentially interesting because the Ge-O-Ge linkage is labile (compared with the siloxane bond in silica gels and polysilsesquioxanes) opening up the possibility of further chemical modification of the polymeric architecture. This may permit hydrolytic reorganization of germanium oxide networks under relatively mild conditions. In this paper, we will present the results of our investigations of the solgel polymerizations of tetraethoxygermanium 1, tetraisopropoxygermanium 2, and methyltriethoxy-germanium 3 to afford network materials as both xerogels and aerogels.

The high cost of materials prepared by sol-gel processing and the loss of useful surface properties at elevated temperature has prevented the application of sol-gel processed materials in automotive exhaust reduction catalyst formulations. In this report, we briefly describe the important developments needed in the next generation automotive catalysts and the role of sol-gel processed materials. We will also discuss the application of heterometallic alkoxides as sol-gel precursors to achieve the molecular distribution of lanthanides and alkaline earths in alumina matrices needed for the stabilization of alumina based materials at elevated temperatures.

Some synthesis parameters like R-OH/OBu, H20/OBu and composition (Al/Ti) ratios influence the textural and catalytic properties of the mixed Al2O3 -TiO2 oxides. The Radial Distribution Function of the pure and mixed oxides shows that Ti4+ incorporation favors the long-range-order in the mixed aggregates as well as the surface area loss at high temperatures, i.e. 900 °C. The catalytic dehydration of isopropanol towards propylene and the HDS of light gasoils indicate that catalytic properties of the sol-gel mixtures are comparable to the activity of reference catalysts, i.e. Al2O3and Ni/Al2O3.

This paper investigates microporous amorphous silica membranes prepared using an organic template sol-gel approach. We find that the introduction of organic methacryloxypropyl ligands results in a reduced average condensation rate and a lower extent of branching that promotes the collapse of the hybrid network upon drying leading to relatively dense hybrid organic-inorganic xerogels and films. Microporous silica xerogels and membranes, prepared by oxidative pyrolysis of the organic templates at 300 °C for 5 hours in oxygen, contained pores with constrictions of approximately 0.35 nm in diameter with a very narrow size distribution, as evidenced by single gas permeation measurements of a series of probe molecules.

The application of sol-gel processed materials in a variety of sensors has been proposed. We describe microcalorimeter sensor devices employing sol-gel processed alumina based materials which can be used to monitor pollutants in automotive exhaust. These sensors operate by measuring changes in resistance upon catalysis and are economically acceptable for automotive applications. It is important to point out that automobiles will be required to have a means of monitoring exhaust gases by on-board sensors as mandated by the EPA and the California Air Resources Board (OBD-II).

Nanochannel glass replica membranes are thin metallic films containing patterned arrays of uniform, nanometer-scale voids whose sizes, positions, geometric patterns, and packing densities may be controlled to a high degree. These membranes have been prepared from refractory and noble metals and are well suited for use as shadow masks in a variety of substrate patterning applications. Here we describe their use in the sub-micron, parallel patterning of Si and GaAs by materials deposition and reactive-ion etching respectively.

Si nanoclusters with average size of a few nanometers have been synthesized by thermal vaporization of Si in an Ar buffer gas, and passivated with oxygen or atomic hydrogen. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) revealed that these nanoclusters were crystalline. All samples showed strong infrared and/or visible photoluminescence (PL) with varying decay times from nanoseconds to microseconds depending on synthesis conditions. Absorption mainly in the Si cores was observed by photoluminescence excitation (PLE) spectroscopy. The visible components of PL spectra were noted to blue shift and broaden as the size of the Si nanocrystals (nc-Si) was reduced, and there were differences in PL spectra for hydrogen and oxygen passivated nc-Si. Our data can be explained best by a model involving absorption between quantum confined states in the Si cores and emission by surface/interface states.

We have fabricated high-pass optical filters from thin nanochannel glass (NCG) wafers coated with sputtered and evaporated gold films. The near-infrared (IR) transmission spectra of these filters have a sharp cutoff at a wavelength that scales linearly with the channel diameter, as expected for hollow metallic waveguides. Cutoff wavelengths approaching 1 μm have been achieved to date using NCG materials with sub-micron channel diameters. The spectra are dominated by a strongly resonant transmission peak just above the cutoff wavelength, where the peak transmission can be as much as twice that predicted based on the geometrical open area of the NCG structure. The NCG wafers were typically less than 20 μm thick, and the Au films ranged in thickness up to 600 nm.

Porous silicon (PS) layers can easily be formed by an electrochemical etch process using a mixture of hydrofluoric acid (HF) and ethanol. The microstructure and porosity of the layers depend on the HF concentration, the doping level of the substrate and the current density applied during the etch process. Changing the current density during the etch process will result in a well defined layer structure consisting of layers with different porosities. Each single layer can be treated as an effective medium exhibiting a refractive index depending mainly on the porosity of the layer. Using reflectance measurements we have investigated the dependence of the refractive index of PS layers on the formation current density for different substrates. In addition the etch rate was determined by thickness measurements with an electron microscope. Based on these results various kinds of optical interference filters were studied. We have formed samples consisting of discrete single layers with different porosities (e.g. Bragg reflectors) as well as samples with continuous variation of the refractive index (rugate filters). Combining these PS filters with standard photolithography steps, microoptical devices such as spectral sensitive photodiodes can be realized.

In this work we report the synthesis of Ni/SiO2 catalysts promoted by group 2 (IIA) cations (calcium and barium) which are currently used as hydrogenation catalysts. The effect of the preparation parameters aging, base agent, and type of cation, on the surface area of catalysts is evaluated. Catalysts were prepared by precipitation of the precursor silicic acid, along with nickel nitrate and calcium and barium carbonates, with NaOH, NH4OH and Na2CO3as precipitating agents. Catalysts were characterized by diffuse reflectance spectra (DRS) and by BETsurface area measurements. Results are discussed in terms of solgel chemistry (1).

Indium arsenide wires have been fabricated in a glass host consisting of a high density array of uniformly shaped channels in a matrix glass. Reactions between organoindium compounds and arsine have produced polycrystalline InAs with crystallite sizes of approximately 10 nanometers when annealed at 400°C. At higher annealing temperatures, the wires exhibit an increase in surface porosity and grain size.

Activated carbon filaments of diameter ∼ 0.1 μm, mean pore size (BJH) 65 Å, specific surface area 1540 m2/g and burn-off 64% (yield 36%) were obtained by activating carbon filaments of diameter ∼ 0.1 μm in CO2 + N2 (1:1) at 970°C for 100 min. Prior to this activation, the filaments were surface oxidized by exposure to ozone (0.3 vol.% in air) at 150°C for 3 min.

The microstructure of carbonaceous materials strongly affect their ability to electrochemically intercalate lithium [1]. The fractional intercalation capacity (x in LixC 6) for various types of amorphous and graphitic carbons can vary over a range between 0 to 1. Capacities exceeding that of graphite (372 mAh/g or LiC6) can be obtained from chemically doped (i.e., with phosphorous [2]) materials or from carbonized organic precursors pyrolyzed at low temperatures (<900°C) [3]. Additional chemical effects apparently influence the carbon electrochemical behavior in these cases.