Ceramic powders of carbides, oxides, solid solutions of oxides, magnetic and non-magnetic spinels, superconductors and composites have been successfully synthesized in a thermal plasma jet reactor using a novel counter-flow liquid injection plasma synthesis (CF LIPS) method developed to overcome the problems associated with solid injection and to realize the benefits of gas phase reactions and counter-flow injection. Standard material characterization techniques have been used for powder analysis.

The Electrical Dispersion Reactor (EDR) allows the continuous production of composite oxide ceramic precursor materials. Silica particles in the form of highly porous shells are produced by the hydrolysis of tetraethylorthosilicate as the continuous phase and water-ammonia as the disperse phase, reflecting the diffusion of the silicon moiety into the dispersed phase. Alternately, denser silica particles result when aqueous solutions of sodium metasilicate are dispersed in a continuous phase containing acetic acid in 2-ethyl-1-hexanol. Additionally, spherical particles in the size range 0.1 to 2 microns are produced from the dispersion of aqueous solutions containing cupric chloride or a mixture of cupric chloride, yttrium nitrate, and barium nitrate (3:1:2 molar ratio) into a continuous organic phase containing ammonia.

A novel Triple DC Torch Plasma Reactor (TTPR) has been developed for the plasma synthesis of fine ceramic powders. The reactor consists of three identical plasma torches. The plasma jets from these torches form a converging plasma volume into which the starting powder is fed. Thermodynamic equilibrium calculations have been performed for predicting the behavior of an aluminum-nitrogen system. Aluminum nitride has been synthesized by using the TTPR operating in the non-transferred mode. Product characterizations indicate that single hexagonal phase AIN ceramic powder has been obtained.

The addition of nitrous oxide (N2O) gas in the hot-filament chemical vapor deposition of carbon film from mixtures of methane and hydrogen was found to increase remarkably the content of diamond structure in the film. Increased particle size and crystal orientation parallel to the (111) direction were also obtained by the N2O addition. Mass spectrometry revealed that the vapor phase reaction was scarcely affected by the N2O addition.

A variety of anhydrous Y, Ba and Cu carboxylates were synthesized and screened for utility as spinnable precursors to 123 superconducting fibers. Simple extrusion studies demonstrate that THF solutions of mixtures of Y, Ba and Cu isobutyrates with some Ba 2-ethyl- hexanoate can be used to form 70 μm dia. precursor fibers. Following a curing at 150°C for 24–48 h, pyrolysis of these fibers in air to 900°C, with controlled heating rates, gives dense, flexible ceramic fibers 15–20 μm in dia. These fibers have the appropriate orthorhombic phase. Flux exclusion measurements indicate the fibers are superconducting; but ΔTc is not optimal.

Superconducting films in the Bi-Sr-Ca-Cu-O system were fabricated using metal alkoxides. To make a mixed alkoxide solution into a dip-coating solution, insoluble Cu alkoxide was modified with 2-dimethylaminoethanol and insoluble Bi alkoxide was dissolved in the presence of Ca and/or Sr alkoxides. The structures of these alkoxide derivatives were studied by FT-IR, 1 H-NMR, and EXAFS. The film with Tc(zero)=115K was fabricated using the alkoxide solution with a nominal composition of Bi:Sr:Ca:Cu=2:2:3:4.

The suitability of several polyfunctional carboxylic acids as coprecipitating agents for Ba, Y, and Cu was investigated. Essentially complete precipitation from alcoholic solutions was achieved for all three metals when tartaric acid was employed as the precipitating agent. The amorphous precipitate formed under these conditions was composed of uniform particles about 50 nm in diameter, and was converted readily to high purity Ba2YCu3O7−x.

The discovery of high critical temperature superconducting oxides 1,2 has stimulated intensive research activities aimed not only at understanding the physical mechanisms of superconductivity, but also developing techniques to produce these ceramics in useful forms. A promising application for superconductors is in electronic components industry which has given rise to an interest in the various ways of producing thin films of superconducting materials.

Samples of Bi1.4Pb0.6Sr2 Ca2Cu3Oy were prepared by sol-gel technique. The formation of polymeric chelate was made possible by oxalic acid in which metal cations are homogeneously distributed. The functional groups in the chelating agent determine the cation absorption rate that pH value is no more critical. XRD and SQUID showed that the compound has a nearly pure 2223 phase and Tc was measured at 110 K. The synthesis is reproducible and the process is amenable for scaling up.

The synthesis of the superconducting perovskite YBa2Cu3O7 using hydroxides as starting precursors has been investigated. Hydroxides are homogeneously coprecipitated from mixed alcohol-water solutions without loss of barium. Upon heat-treatment the perovskite phase rapidly forms around 750°C. However, it remains tetragonal even after long time annealing in oxygen ambient. This is related to an unusual microtwinning in the (ac) plane.

Superconducting YBa2Cu3O7−x fibers were fabricated by the sol-gel method using modified metal alkoxides. To prepare precursors of a homogenous and viscous sol, Y and Cu alkoxides were modified with ethyl acetoacetate(EAA) and ethylenediamine(en), respectively. Their structures were determined by FT-IR and EXAFS. The sol prepared from modified alkoxides was spun into gel fibers by the spinning apparatus. They were subsequently fired to obtain superconducting fibers.

An alkoxide Sol-Gel system was developed to produce bulk powders of the TI2Ca1Ba2Cu2O8+x high Tc superconducting phase. Methoxyethoxide and Cu(II) ethoxide precursors were used for the formation of homogeneous sols. Solubility of the Cu(II) ethoxide was aided by using a 2-methoxyethanol/methyl ethyl ketone/toluene solvent system. The sols were characterized by small angle x-ray scattering (SAXS) and TEM. Powders were produced by rotary evaporation followed by thermal treatment in a closed container with thallium metal present at 900°C for various calcination times. Powders were characterized by x-ray diffraction, resistivity and magnetic susceptibility measurements, and chemical analysis. Samples exhibited transition onsets between 100 and 110K depending upon the processing conditions.

The starting sols were prepared by addition of ammonium hydroxide to acidic solutions of Y-Ba-Cu acetates or by dissolving solid Ba9CO9 or CuCO9.CuCOH)2H2O in acetates of the remaining components. The sols were then gelled to spherical particles with diameter below 50μm by extracting water with 2-ethyl-l-hexanol or to shard by evaporation of water. After thermal treatment of both powders amorphous and then crystalline YBa2Cu,9O7−x were obtained. Formation of these compounds is strongly improved by aging the gel at 200°C. Green and sintered pellets exhibit excellent superconductivity properties.

Soluble resins were prepared by controlled hydrolysis of yttrium isopropoxide, barium isopropoxide and copper ethylhexanoate. The resins were converted to cohesive, viscous, fluid and precipitated states by the addition of different combinations of binary polar and non-polar organic solvents. Viscosity and spinnability of the resins were critically dependent on the solvent constituents. Continuous pre-ceramic fibers were spun from these resins and single phase YBa2Cu3Oy superconducting fibers with Tc=91.5K and ΔT=1.5K have been obtained.

High-Tc superconducting Bi-Pb-Sr-Ca-Cu oxide with zero resistance temperature at above lOOK has been synthesized via the use of ethylenediamine-tetra-acetate(EDTA) colloid and corresponding metal nitrates. Remarkable sinterability of the precursor requires shorter time to achieve superconducting phases than conventional solid-state reactions. Superconducting properties were measured electrically and magnetically. The thermal decomposition, X-ray diffraction and microstructural characteristics of the precursor and the sintered samples were also discussed.

Attempts to identify intermediates in an alkoxide-based solution route to films of the high temperature superconductor YBa2Cu3O7 reported by Fahrenholtz et al.[1] have led to the isolation of the first molecular barium-copper cluster, Ba2Cu2(OR)4(acac)4·2 HOR, R = CH2CH2OCH3. The extension of this route to the preparation of the bismuth superconductors has necessitated the investigation of bismuth alkoxide chemistry. Two separate routes to bismuth alkoxides have been examined: the metathesis of the metal halides with NaOR, (R = t-butyl, and diisopropylphenoxide) and the alcoholysis of bismuth amides, Bi(NR2)3, [R = N(SiMe3)2] The alcoholysis preparation gives high yields of several alkoxides suitable as precursors to the high Tc materials. A monomeric bismuth phenoxide, which is targeted as a volatile precursor, and a bismuth t-butoxide cluster have been isolated and stucturally characterized. Solubility and volatility studies have also been undertaken.

By studying the Bi-Pb-Sr-Ca-Cu-O system, we have found that the sintering time to form high Tc Bi-Pb-Sr-Ca-Cu-O systems was quite different as the compositions of the starting materials varied. Especially, the ratio of Sr/Ca played an important role in determining the sintering time.

DTA study already showed that partial melting occurred during the reaction. The temperature of the partial melting was also related to the ratio of Sr/Ca. Our results supported the existence of a reactive liquid phase in sintering process.

Hydrolyzed metal alkoxide solutions were spin-coated on Si substrates with subsequent thermal processing. Barrier layers of alkaline earth oxides, perovskites, Y2O3, ZrO2 and others were produced. Characterization was performed via SEM, XRD, ESCA, Auger depth profiling and resistivity measurements. Barrier layer films were fairly smooth with some cracking and pitting present. Si migration was severe for alkaline earth thin films on Si wafers. Some perovskite films on Si showed formation of Ba-Si-O phases at the Si interface. Thin films of 1–2–3 on barrier layers of SrTiO3 or ZrO2 on Si showed Ba pileup at the Si interface and were not superconducting. 1–2–3 layers deposited on single crystal ZrO2 were superconducting and showed onset temperatures of 90 K with zero resistance reached at about 55 K.

Solutions of Y, Ba and Cu nitrate were spray-frozen. Very small particles consisting of atomic mixtures of these salts remained after the water was sublimed. These YBCO precursors were characterized and their behavior was studied in detail while they were thermally decomposed by a variety of techniques. Kilogram size batches are routine. The final YBCO products were obtained as powders and sintered bars. Sintered materials exhibited excellent phase purity (>99%) and super-conducting characteristics (Tc = 92 K), while powdered materials had secondary phases present. Some of these samples having high percentages of second phases exhibited sudden drops in resistivity to a few micro-ohms at 200 or 240 K followed by a zero resistance transition at 92 K. Coincident with this drop in resistance was a discontinuity in the magnetization.

High quality bulk YBa2CuOx−7 was synthesized by fusing stoichiometric amounts of yttrium and copper nitrates and barium hydroxide, in air, using an ordinary Bunsen burner. The starting materials go through a short-lived liquid phase yielding a solid black product which was subsequently heat treated, (900 C, 18–24 h, in air, followed by 500 C, 5 h., in O2). These materials were greater than 99% phase pure with CuO as the only other phase and they exhibited a transition temperature of 92 K, a 15.5% perfect diamagnetic response (field cooled), 76% (zero field cooled). This synthesis represents an improvement over the much more labor and time intensive conventional methods in that it allows high quality materials of various compositions to be prepared quickly