M.J. van Bommel

Hydrolysis-condensation processes of the tetra-alkoxysilanes TPOS, TEOS and TMOS in some alcoholic solvents

Abstract The effects of methanol, ethanol, 1-propanol and 2-propanol on the kinetics and the mechanisms of the hydrolysis-condensation reactions of the silanes TPOS, TEOS and TMOS were studied. Also, the influence of the amount of water on the hydrolysis-condensation processes of TMOS and TPOS was investigated. Accordingly, hydrolysis time versus condensation time curves were recorded and 29 Si-NMR investigations were performed. The hydrolyzability of the silanes in an acidic environment was found to decrease in the sequence TMOS > TEOS > TPOS. The effect of the alcohols, in the sequence methanol > ethanol, 1-propanol > 2-propanol, upon the hydrolysis rate of each of the silanes is explained by differences in degree of dissociation of HCl in the different alcohols. Also, the exchange of alkoxy groups, observed when an alcoholic solvent was used with an alkoxy group different from the alkoxy group of the silane, may influence the hydrolysis rate of the silane. Differences in dimerization are ascribed to differences in base strength of the activated silanol complexes with regard to those of the protonated alcohols.

Drying of silica aerogel with supercritical carbon dioxide

For applications of monolithic silica aerogels, drying without cracking is an important issue. By extracting alcohol with supercritical CO2, crack-free aerogels can be obtained at 35°C and 85 bar. This opens the possibility for a large-scale aerogel drying process. Besides some technical information about the process, the economics of this process are also discussed. It appears that an aerogel plate with a thickness of 1 cm can be dried at a cost of

The influence of the addition of alkyl-substituted ethoxysilane on the hydrolysis—condensation process of TEOS

2/m2. The price will increase exponentially with thickness because diffusion of the alcohol in the alcogel solvated by CO2 molecules is the rate-determining step of the drying process.

Drying of silica gels with supercritical carbon dioxide

Abstract The effect of methyltriethoxysilane, dimethyldiethoxysilane or phenyltriethoxysilane on the hydrolysis-condensation process of TEOS was investigated using hydrolysis time-condensation time curves. Viscosity measurements and 29 Si-NMR investigations were also performed. It is found that the gelation process of such mixtures is slower than that of TEOS itself although, compared with TEOS, both the hydrolysis rate and the condensation rate of each of these compounds are higher.

The electrical and optical properties of thin layers of nano-sized antimony doped tinoxide particles

Results of drying experiments of aerogels with supercritical carbon dioxide are reported. In addition to the results of experiments with a pilot extracting apparatus, a preliminary design is also given of a large-scale supercritical carbon dioxide extraction plant to be used for drying of aerogels. From the experiments it was found that crack-free aerogels could be obtained when drying with carbon dioxide under supercritical conditions. The lowest temperature and pressure at which crack-free aerogel samples were obtained was at 35 °C and 85 bar, respectively. The temperature had a minor influence on the drying time. It was also found that the diffusion of ethanol into the aerogel pores limits the drying time. This limitation implies that the thickness of the aerogel tiles will have a large influence on the cost of drying of an aerogel.Results of drying experiments of aerogels with supercritical carbon dioxide are reported. In addition to the results of experiments with a pilot extracting apparatus, a preliminary design is also given of a large-scale supercritical carbon dioxide extraction plant to be used for drying of aerogels. From the experiments it was found that crack-free aerogels could be obtained when drying with carbon dioxide under supercritical conditions. The lowest temperature and pressure at which crack-free aerogel samples were obtained was at 35 °C and 85 bar, respectively. The temperature had a minor influence on the drying time. It was also found that the diffusion of ethanol into the aerogel pores limits the drying time. This limitation implies that the thickness of the aerogel tiles will have a large influence on the cost of drying of an aerogel.

A 6Li, 7Li and 59Co MAS NMR study of rock salt type LixCoO2 (0.48≤x≤1.05)

For the use in anti-static films on glass or polymeric substrates, transparent conductive layers can be prepared by spinning an aqueous suspension of nano-sized antimony-doped tinoxide (ATO) particles. These layers have a resistivity which is substantially higher than that of homogeneous ATO layers which are deposited by physical vapour deposition techniques. By curing the films to temperatures up to 700 °C, the resistivity of the particle layer can be decreased by two or three decades. Because the nano-sized particles are prepared by a low-temperature process a different mechanism can contribute to this decrease in resistivity. Possible effects which may influence the conductivity are sintering of the particles, change of the bulk material and the presence of an insulating layer at the outside of the particles. This decrease can be explained by the presence of an insulating antimony-rich layer on the outside of the particles, the thickness of which is reduced when the layer is cured. At temperatures above 350 °C, sintering of the particles also highly influences the decrease in resistivity. At temperatures above 700 °C, the resistivity is increased due to segregation of the antimony to the surface of the particle.

11-Megapixel CMOS-Integrated SiGe Micromirror Arrays for High-End Applications

Abstract Low temperature (LT, 400°C) and high temperature (HT, 900°C) Li x CoO 2 samples were synthesised with Li/Co ratios between 0.8 and 1.05. These samples were characterised by XRD, chemical analysis, 6 Li, 7 Li and 59 Co MAS NMR. 7 Li MAS NMR of the Li x CoO 2 -T 400 samples (LT) showed a single resonance line at −0.9 ppm, characteristic of lithium in an octahedral coordination. A somewhat narrower resonance at the same position was observed in the 7 Li MAS NMR spectra of the Li x CoO 2 -T 900 samples synthesised with a Li/Co ratio ≤0.95. The Li x CoO 2 -T 900 samples synthesised with a Li/Co ratio >0.95 showed several new lithium resonances, containing up to 35% of the signal intensity. The resonance positions of these new resonances indicate the presence of a paramagnetic cobalt species in the material. The 59 Co MAS NMR spectra of the Li x CoO 2 -T 900 samples revealed a spinning sideband manifold centred at ≈14 250 ppm for x ≤0.95 and three overlapping spinning sideband manifolds at ≈14 285, ≈14 260 and ≈14 230 ppm for Li/Co ratios >0.95. Compared to the Li x CoO 2 -T 900 samples the Li x CoO 2 -T 400 samples all showed one resonance with an increased line width. These resonance positions are typical for Co 3+ octahedrally coordinated by oxygen. No quadrupole induced shift is observed as a function of the external field (measurements performed at 14.1 and 7.05 T), indicating an undistorted octahedral coordination of cobalt in the materials studied. Chemical extraction of lithium with H 2 SO 4 leads to the formation of lithium that can not be detected with NMR. Electrochemical extraction of lithium, on the other hand, leads to a low field shift of the lithium resonance of 60–120 ppm, depending on the amount of lithium removed. Electrochemical intercalation (discharging) of the samples results in the reappearance of the original lithium spectra, showing the excellent reversibility of the charge/discharge process. Partly charged samples are characterised by signals in the range of 120–60 ppm and a signal at −0.9 ppm, indicating that part of the lithium remains in an unchanged environment. The dependence of the chemical shift on the amount of lithium removed is due to an rapid exchange process.

Structure and topology of silica aerogels

In this paper, we report on the design, fabrication, packaging, and testing of very reliable CMOS-integrated 10-cm2 11-megapixel SiGe-based micromirror arrays on top of planarized six-level metal 0.18-¿m CMOS wafers. The array, which is to be used as a spatial light modulator (SLM) for optical maskless lithography, consists of 8 ¿m × 8 ¿m pixels, which can be individually addressed by an analog voltage to enable accurate tilt angle modulation. Due to very stringent requirements on mounted-die flatness (< 0.01 mrad), the first level packaging of SLM die is done using specially designed SiC holders. To avoid trapped particles between the die and holder, which would jeopardize the flatness spec, special backside cleaning of the dies (less than or equal to one 0.8-¿m particle/cm2) is needed before mounting the SLM die on the holder. To enable this backside cleaning and to avoid front-side particles during dicing, handling, and wire bonding, a temporary waferor zero-level packaging cap, which can be placed and removed at room temperature, was developed. The dynamic white light interferometer measurements of packaged dies showed that 99.5% of the 123 648 mirrors tested are within the spec. In addition, a stable average cupping of below 7 nm, an rms roughness of below 1 nm, and a stable actuation of over 2.5 teracycles are demonstrated.

A Thermoporometry Study of Fumed Silica/aerogel Composites

Neutron spin-echo spectroscopy is used to study the topology of aerogels. Topology or connectivity is varied through precursor chemistry and thermal annealing. Topology is characterized using the concept of fractons (the vibrational excitations of a fractal network). A qualitative difference is observed in the spectrum of polymeric vs. colloidal aerogels, the latter showing a peak in the density of vibrational states. For colloidal aerogels whose structure appears to arise from phase separation in the solution precursor, low-energy excitations were only observed in the lowest density material studied. Finally, a transition from fractal to colloidal microstructure was observed during the sintering of polymeric aerogels. This transformation revealed itself as a transition from a fracton-like to a peaked density of states function.

17O-NMR of Sol-Gel Processes of TEOS and TMOS

The porous texture of fumed silica/aerogel composite materials is studied by thermoporometry. The effect of fumed silica (Aerosil) powder in aerogels, added during the sol-gel processing is investigated. The textural change due to the autoclave drying process as a function of the fumed silica/aerogel ratio of the systems is investigated. The meso- and macro porosity of the fumed silica/aerogel composites is mainly influenced by the ratio fumed silica/aerogel and only slightly by the autoclave drying process. Addition of fumed silica powder results in an increase of the mean pore radius of the system and in a decrease of the meso- and macro-pore volume. By contrast, the micro-porosity is hardly affected by the addition of the fumed silica powder; it is only influenced by the autoclave drying process.