A melt-spinnable precursor of aluminum nitride fibers derived from triethylaluminum and ammonia contains AlNH, AlNH2 groups, and a small number of AlN units characteristic of aluminum nitride. The molecular weight of a spinnable composition is 070, corresponding to an average molecular weight of 13 organoaluminum groups. Ammonia, a curing agent for the fibers, accelerates elimination of ethane from the material, and decreases its solubility in toluene.

Metallic Aluminum is dissolved anodically in an electrolyte, containing a primary amine, an aprotic solvent and a tetraalkylammonium salt. Removal of the solvent and subsequent heating lead to a polymer network. Initial drying causes a more viscous liquid, further drying up to 150°C accelerates the polymerization process and a gel-like consistency is obtained. Pyrolysis is carried out under NH3 or inert gas atmosphere. X-ray diffraction data show amorphous products up to 800°C, treatment above 800°C leads to the desired ceramic product aluminum nitride. Peak broadening indicates extremely small crystallite sizes. Pressureless sintering without additives gives a compact product, having densities up to nearly 100% of the theoretical density.

Compression molded bodies fabricated from commercial Si3N4 powder using a polysilazane precursor to Si3N4 as a preceramic binder have been characterized. The process has been partially optimized and can produce green bodies with densities approaching 75% theoretical and considerable mechanical strength. Microstructural development during binder pyrolysis and high-temperature treatment indicate significant interactions and bonding between the commercial powder and the polymer-derived material.

Pyrolyses of a set of silicon and nitrogen substituted polysilazancs arc conducted under a set of standard conditions (5°C/min to 900°C in a nitrogen atmosphere). The apparent ceramic compositions and ceramic yields for pyrolyzed samples of the polysilazancs -[Ph(H)SiNH]x-, -[C6H13(H)SiNH]x-, -[Me(H)SiNH]x-, and -[H2SiNMc]x- arc determined. Preliminary conclusions concerning structure/reactivity relationships are discussed based on the pyrolysis results.

Various routes to silicon (oxy)nitrides are described, using both low-temperature solution chemistry and high temperature gas-solid reactions. The latter approach has led to a convenient synthesis of high-surface-area (e.g. 130 m g) silicon oxynitride, Si2N2O, from gaseous ammonia and commercially available, finely divided amorphous silica.

A variety of reactions employing organometallic precursors have been explored for the synthesis of ZnS. One of the most successful routes involves the reaction of [EtZn(SButS)]5 with H2S at ambient or sub-ambient temperature to yield a precipitate which is subsequently heated under flowing H2S at 500°C to yield a mixture of sub-micron particles and single-crystal ZnS whiskers. Transmission electron micrographs of the [EtZn(SBut)]5 products indicate that the ZnS morphology is critically dependent upon the rate of H2S reaction. Corresponding x-ray/ electron diffraction, electron microscopy, elemental analysis, NMR and infrared spectroscopies have been conducted. A summary of the chemical methods, product characterization results, and proposed synthesis mechanisms will be presented.

The authors gratefully acknowledge the Office of Naval Research for the support of this research under Contract N0014–86-K-0191.

It is proposed that solutions of arsenic trisulfide and ethylenediamine consist of arsenic-sulfur rings (As4S6) which are interlinked through sulfur-sulfur bridges. The Raman spectra of the solutions exhibit an intense band at 438 cm-1 which is attributed to the stretching resonances of these bridges. The bridges are not present in a-As2S3 glass, and thus, the intensity of the band has been used to characterize the molecular connectivity of sols and gels. This band is most intense in the highest viscosity gels, whereas the relative intensity of the band is diminished in the dry gels. The intensity of the band further decreases during vacuum heat-treatment of fibers drawn directly from the gel. TEM analysis of the fibers verify the creation of a dense amorphous structure, while SIMS depth profiles of the films further verify their composition. Altogether, these observations confirm the structural model proposed for the solution, and suggest a relaxation/ recombination process for the molecular gel-to-network glass transition.

BaTiO. thin films deposited on pyrex supportsby dip-coating technique and powders have been prepared by the sol-gel route from sols containing a mixture of tetraisopropyl orthotitanate, iso propanol, barium acetate and glacial acetic acid. The thickness of the films is proportional to the first power of the withdrawal speed. Gelled sols have been dried hypercritically and by natural evaporation. Films and powders have been characterized by X-ray diffraction during their heat treatment. Tetragonal BaTiO structure is observed for T ≥ 600°C.

High field Silicon-29 NMR is used to study the structural intermediates in tetramethyl and tetraethyl orthosilicate (TMOS and TEOS) low pH sol-gel reactions. Linear oligomers as well as ring components of various sizes are identified and their evolution in the sols is followed. Differences in the number of compact ring structures are related to differences in gel times. Reactions are followed for various silicon alkoxide:water:acid molar ratios.

Porous silica glasses have been prepared using an HF-catalyzed tetraethoxysilane(TEOS)-ethanol-water formulation. The optical and physical properties of these glasses, which find use as host matrices for optical organic dyes, can be further improved with the addition of 1,3,5-trioxane to the sol-gel chemical system. In order to understand the effect of trioxane, the time-dependent concentrations of the species involved in TEOS hydrolysis and condensation have been followed by Raman, FT-IR, and NMR spectroscopie methods in both HF-catalyzed TEOS-ethanol-water systems with and without trioxane.

Reactions of C5H6 and BCl3 at 800°C yields a metallic graphite-like material of composition BCx (3.0 ≤ x ≤ 4.00) while reactions of BCl3, NH3 and C2 produces a B/C/N graphitic semiconductor of approximate stoichiometry B2CN2. Both materials were shown to be homogeneous using Auger electron spectroscopy and extensively characterized by electron energy-loss spectroscopy. Single loss profiles of the EELS data were obtained using the fourier-log deconvolution method. Compositions were determined using hydrogenic cross-sections. A careful study of the plasmon resonance energies and the fine structures of the core-loss edges of these materials has been invaluable in demonstrating that the boron, carbon and nitrogen atoms are all sp2 hybridized. Therefore, these new materials are in-sheet graphite hybrids and not intercalations.

Silicon-29 NMR spectroscopy has been widely applied to characterize the development of molecular complexity of silicon alkoxide sols. In the present study, the progression of molecular complexity of partially hydro-lyzed/condensed tetraethoxysilane (TEOS) sols with increasing H2O/TEOS ratio is demonstrated by the study of a carefully prepared set of solutions. Intriguing trends in the 29si NMR spectra of increasingly hydro-lyzed sols are discussed. In an set of samples, TEOS is replaced in part by tetraethoxytitane, Ti(OEt)4 (TEOT). The effects on the 29Si NMR spectrum due to the presence of TEOT are presented and interpreted in terms of changes in the distribution of siloxane monomers and oligomers in solution. Preliminary data on the stability of these solutions with time are reported.

The preparation of homogeneous gels from liquid solutions necessitates the prevention of precipitation. This becomes increasingly difficult in multicomponent systems. Currently, there are no systematic considerations on precipitation in sol-gel solutions. This paper is concerned with the methods to control precipitation in alkoxide solutions. Each method is applied to specific systems, containing alkoxides of various metals, such as yttrium, lanthanum, barium, and titanium, in alcoholic solutions.

As part of an investigation of the dynamics that occur in the plume of a typical thermal spray torch, an analytical and experimental study of the plasma spraying of alumina is being performed; preliminary results are reported here. Numerical models of the physical processes in the torch column and plume were used to determine the temperature and flow fields. Computer simulations of particle injection (15, 34, and 53 μm alumina particles) are also presented. The alumina experiments were conducted at a 35 kW power level using a 100 scfh argon and 15 scfh hydrogen gas mixture for two alumina powders. The quality of the coatings is discussed with respect to porosity, sample metallography, and microhardness.

Tantalum pentoxide (Ta2O5) films are candidates for application as storage capacitors in high density memory cells and as gate insulators in MOS devices because of their large dielectric constant. Thin Ta2O5 films deposited by reactive DC magnetron sputtering of a pure Ta target using an argon/oxygen mixture have been characterized using TEM, glancing angle X-ray diffraction and RBS. The films are amorphous in the as-deposited condition but crystallize after high temperature (> 600 °C) annealing. Numerous pores and significant grain boundary grooving were observed in the crystallized film. A high level (∼2 at. %) of argon was detected in both as-deposited and annealed films formed by Ar/O2 sputtering. The effects of sputtering and annealing conditions on the structure of the films were investigated.

The Sol-Gel process was used to deposit WO3 on Ni substrates. These materials as well as the synthetic methods used have application in electronic devices.

In an effort to quantify the oxidation/reduction chemistry of such materials, electrochemistry was performed in both aqueous and non-aqueous (CH3CN, DMF) solutions. Different intercalation cations such as protons, Li and Na, were used. This paper discusses the synthesis, characterization, and electrochemistry of these materials.

The nature and the composition of the surface and near surface region of A1N films plays a significant role in determining their chemical and thermal stability. A1N thin films were deposited by reactive RF magnetron sputtering of Al in argon and nitrogen atmosphere. Transmission and scanning electron microscopy indicated that these films have a dense columnar microstructure with columns oriented along the c-axis of the A1N crystallites. X-ray photo-electron spectroscopy (XPS) revealed a graded oxygen-rich surface layer about 5–10 nm thick which is formed when the film is exposed to the atmosphere. This oxide is limited to the surface and does not grow even when the film is annealed at 600°C for 10 hours in dry oxygen. It is expected that this passivating oxygen rich surface layer will, to a large extent, determine the oxidation resistance of the fresh underlying AIN. A surface chemistry model is proposed for this protection behavior.

Use of micron-size particles of synthetic diamond in oxide matrices prepared by sol-gel processing is explored. Alumina and borosilicate-diamond composite coatings are deposited on soda-lime microscope glass and fused silica substrates using dipping technique and thermophoresis. By varying the thermal gradient between the substrate and the solution, the quality of the films and the concentration of the particles can be controlled.

Further capability of silazane dehydrocoupling polymerization catalyzed by ruthenium carbonyl (20–200 ppm) is demonstrated in a series of reactions. Ammonia and monomethylamine are used as reactants to bridge oligomers and polymers containing Si-H bonds to provide higher molecular weight polymers with higher latent reactivity and to increase the ceramic yields and the nitrogen-to-carbon ratio in the final ceramic compositions. New types of tractable polymers containing cyclomers having [MeSiHNH] units with molecular weights over 2000 d are formed. Various polymeric properties (e.g., viscosities, softening and melting points) and ceramic yields up to 80–85 wt% are obtained by controlling the catalytic reaction conditions.

Transparent monolithic pieces of gel have been prepared from the hydrolysis of a mixture of dimethyldiethoxysilane (DEDMS) and tetraethoxysilane (TEOS). The characterization of this gel has been done by infrared and shows that a copolymerization between the two precursors has occurred during the hydrolysis-condensation process. Pyrolysis of this gel lead to the formation of β-SiC at 1550°C. The characterization of the pyrolysing process has been investigated. The Si-CH3 bonds are broken during the heat treatment, leading to a mixture of silica and carbon. The formation of β-SiC is therefore due to a carbothermal reduction of this silica matrix.