Search

Amorphous silicon–germanium alloys with 70% Si and 30% Ge have been formed by rapid heating in a pure E-field in a single mode 2.45 GHz microwave cavity. The synthesis of amorphous Si–Ge alloy by all conventional processing is difficult. This polarized microwave process provides another striking example of its unique abilities: producing bulk amorphous Si–Ge alloys. The microwave fabricated amorphous Si0.7Ge0.3 alloy composition exhibited relatively high Seebeck coefficient with high potential of its application in high efficient thermoelectric materials.

A new device designed by the senior author of the current paper was examined and tested in the Materials Research Laboratory of The Pennsylvania State University. The device consists of an unconventionally driven magnetron whose directional output is conditioned by filters and a tailored horn antenna. Although the origin of the radiation is an ordinary 600 W magnetron, the modified radiation is not contained by either a Faraday cage or by microwave shielding. It interrupts the operation of electronic devices, shutting them off without apparent harm to the circuitry. The radiation was observed to pass through or circumvent a one inch block of aluminium. Lastly, it unexpectedly attenuated in the building ventilation ducts which were completely outside of the directional field, resulting in the heating of and off-gassing from sealant in the duct flanges.

Silicon and germanium alloys have been formed for the first time by heating powdered mixtures of 75%Si and 25%Ge in just 2 min in the H field in a single mode 2˙45 GHz microwave cavity. As is well known, alloy formation in conventionally heated silicon–germanium mixtures is difficult, even when processed for much longer time durations at the same temperature. Further, any oxide contaminants, if present in the starting material or formed during heating, somehow, appear on the surface of the specimen after microwave treatment.

Most natural waters are probably “ultra dilute”: aquasols. While the composition of such waters is routinely characterized thoroughly with respect to composition, very little attention has been paid to the solid phases which are certainly suspended in most, if not all, such. Our recent work having established the importance of the structure of water on its properties, [[1]; R. Roy, W.A. Tiller, I. Bell, M.R. Hoover; Mater Res Innov. 9 (2005) 577.] we have examined the structures of many waters with easily demonstrated (e.g. silver aquasols) or long-claimed (e.g. homeopathic remedies) biological effects. The results show that such materials can be easily distinguished from the pure solvent, and from each other, by the use of UV–VIS and Raman spectroscopy, while FTIR is insensitive to these differences. This opens up a whole new field of endeavor for inorganic materials scientists interested in biological effects.

We first establish the literature on the use of ultradilute aquasols as extraordinary, powerful, bactericidal inorganic agents equal to most commercial antibiotics. These findings provide the rationale for a major role for inorganic materials scientists to contribute the insights unique to their field for new, safer health vectors. The focus of this preliminary paper is exclusively on the materials science of 2-phase stable sols at ultradilute concentrations near 1 at.-ppm. We analyze the solid and liquid phases for the first time in detail using standard materials science analysis tools. The solid phase is analyzed using DTA, TGA, XRD, SEM, and TEM, and the liquid water phase is analyzed using FTIR, UV–VIS, and Raman spectroscopy. There are at least three crystalline phases in the system Ag–O: Ag, Ag2O, and Ag4O4, which are stable in air. In an aqueous environment between 0 and 100uC there is evidence that various combinations of metal, oxides, and possible ‘oxy-hydroxide’ complexes exist. Similarly, data from Raman and UV–VIS spectroscopy show definite changes in the structure of the water host. These results, in a preliminary way, are parallel to the many empirical observations made by physicians for the last 100 years on the use of metallic silver and water in various combinations for human health.

Beside chromium carbide and chromium nitride, chromium sesquioxide Cr 2 O 3 is a new candidate for hard and protective coatings. The reported bulk microhardness of Cr 2 O 3 is 29.5 GPa according to Samsonov (1982) and 28GPa according to Robertson and Manning (1990), making it second among all oxides, even above sapphire. The Mohs hardness is 8. The hardest oxide is the high pressure form of SiO 2 , stishovite, with 35 GPa (Haines and Lager (1998).

This paper provides an interdisciplinary base of information on the structure of liquid water. It begins with a synthesis built on the information base on the structure 5 of noncrystalline, inorganic, covalently-bonded condensed liquid phases, such as SiO2, S, Se, P, and H2O, which exists in the materials science literature. The data for water are analyzed through the prism of well-established algorithms in materials research: the connection of properties to structure; the pressure-temperature (P-T) phase diagrams; the phenomenon of epitaxy; the phenomenon of liquid-liquid phase separation; the stability of two phase colloids; and, the recently discovered effects of weak magnetic and electric fields on the structure of simple inorganic oxides. A thorough combing of the literature of the condensed matter properties reflecting structural features of essentially pure water obtained via the normal processes of preparing homeopathic remedies, provides another rich data base. The examination of these data through the standard materials science paradigms leads to the following conclusion: Many different structures of liquid water must exist within the range of observations and processes encountered near ambient conditions. A typical sample of water in these experimental ranges no doubt consists of a statistical-mechanical-determined assemblage of monomers and oligomers (clusters) of various sizes up to at least several hundred H2O units. The importance of the structural similarity of SiO2 and OH2 is very relevant to the structure of the latter as well as to the probability of epitaxy in controlling at least the region contiguous to the silicate glass surfaces of many common containers. The most distinctive feature of bonding in liquid water is not only the “well-known hydrogen bonds, but the necessary presence of a wide range” of van der Waals bonds between and among the various oligomeric (cluster) structural units. It is this range of very weak bonds that could account for the remarkable ease of changing the structure of water, which in turn could help explain the half-dozen well-known anomalies in its properties. In its subtler form, such weak bonds would also allow for the changes of structure caused by electric and

Fine, monophasic silicon carbide powder has been synthesized by direct solid-state reaction of its constituents namely silicon and carbon in a 2.45 GHz microwave field. Optimum parameters for the silicon carbide phase formation have been determined by varying reaction time and reaction temperature. The powders have been characterized for their particle size, surface area, phase composition (X-ray diffraction) and morphology (scanning electron microscope). Formation of phase-pure silicon carbide can be achieved at 1300 °C in less than 5 min of microwave exposure, resulting in sub-micron-sized particles. The free energy values for Si + C → SiC reaction were calculated for different temperatures and by comparing them with the experimental results, it was determined that phase-pure silicon carbide can be achieved at around 1135 °C.

The application of microwave technology to a diverse range of materials and processes has resulted in a wide spectrum of materials that are commercially processed using microwaves, from the heating of food to the vulcanisation of rubber to the sintering of specialty ceramics. Microwave sintering of elemental or alloy metal powders has gained significance in recent times as a novel processing method since it offers many advantages over the conventional sintering method. Despite substantial R&D investment in this area in the past two decades, no competitive microwave technology has yet emerged for powder metallurgy (PM) sintering. In sharp contrast, because it is 'obvious' that microwaves are reflected by metals, it is not uncommon to be unable to locate many journal papers or literature, wherein metal powders have been sintered in a microwave field. This paper reports the improved mechanical properties and microstructural development of microwave sintered copper and nickel steel PM parts as compare...

WC/Co samples sintered in a microwave field differ radically in terms of phases, chemistry, and microstructure when compared with conventionally sintered samples. Microstructural investigations by TEM showed that in microwave sintered material the cobalt phase dissolved nearly no tungsten, whereas in conventionally sintered samples up to 20 wt.% tungsten was dissolved in the cobalt binder phase. Besides, smaller WC grains and finer and more uniform distribution of cobalt binder were observed in microwave sintered samples. This resulted in a harder material, which also exhibited better resistance towards both corrosion and erosion. Microwave sintered samples also have a three-dimensional uniform shrinkage, whereas conventionally sintered samples showed a greater vertical shrinkage. It is possible to microwave sinter WC/Co at lower surface temperature and in much shorter times than normally needed in a conventional furnace to obtain the same degree of densification.

Highly doped n-type silicon powder responds aggressively to a 2.45-GHz microwave E-field, whereas it remains unperturbed in the H-field. In the E-field, after about 30 s of treatment, the silicon powder attained submelting temperatures and thus coagulated to a bulk solid piece. X-ray diffraction analysis of the surface and the cross section of this solid material failed to show any detectable peaks, ascertaining the fact that the material had decrystallized. The Raman spectra of the material had broad and shallow peaks quite different from the thin, sharp lines exhibited by Si wafer. It appears that the E-field treatment has considerably distorted the lattice structure creating lattice strains throughout the sample. These lattice strains were relieved by grinding (recrystallized).

Ultralow dielectric constant values were measured on Ni–Zn ferrites prepared using Fe2O3 as a starting material and sintered in a microwave field. Significant differences in microstructure, magnetic, and dielectric properties were observed between microwave-sintered Ni–Zn ferrites prepared using Fe3O4 (T34) and those starting with Fe2O3 (T23) ingredients. Higher magnetization values observed in T23 ferrite are attributed to large grain size, possibly containing abundant domain walls and the presence of fewer Fe2+ ions. The ultralow dielectric constant values observed on T23 ferrites show that this procedure is highly suitable to prepare Ni–Zn ferrites for high-frequency switching applications.

Ni1−xZnxFe2O4 with x=0.0–1.0 in steps of 0.2 have been densified to >95% of theoretical both by conventional and microwave sintering procedures. Comparison studies were performed on these samples sintered at 1275 °C for 30 min. Microstructural study revealed large, but fewer pores in the microwave sintered specimens and small, but substantially more pores in the case of conventionally sintered specimens. Magnetic properties measurements showed lower coercivity and higher magnetization values for microwave sintered specimens. Lower coercivity values observed in microwave sintered specimens are attributed to larger grain size and higher magnetization values may be explained by the contribution of the ‘microwave field’ to the ‘uncoupling spin effect’. Most significantly samples sintered in a microwave field, generally, showed lower dielectric constant values compared with the samples sintered conventionally, making microwave sintering particularly suitable for high frequency applications.

We demonstrate in this paper that common crystalline phases can be made noncrystalline and hard magnets can be converted to soft magnets in the solid state in several seconds at temperatures far below the melting points. New crystal structures and magnetic structures of ferromagnetic oxides (ferrites such as BaFe12O19, CoFe2O4, Fe3O4, and ZnFe2O4, etc.) are formed by reacting either the stoichiometric mixture of oxides or the preformed phase-pure crystalline material in a pure H field (or E field) at microwave (2.45 GHz) frequencies. These major changes in the magnetic properties as well as major structural phase changes are caused by the magnetic field.

Transparent alumina samples have been successfully prepared by microwave sintering processing. In comparison to the conventional sintering processing, microwave sintering to transparent alumina can be achieved at lower sintering temperature and shorter sintering time. It was also found that the microwave heating could substantially increase the conversion rate of polycrystalline alumina to single crystalline sapphire, to improve the transparency and other properties of the transparent alumina samples.

Inspite of overwhelming evidence showing that a variety of solid state reactions were radically different when performed in a multimode microwave chamber compared to conventional heating some still question whether there is direct link to the radiation field. The present study has been conducted, for the first time ever, in a single mode TE103 cavity at 2.45 GHz. A large variety of materials have been reacted as ≈1 cm φ, 2 mm thick samples within the same cavity, at the positions of the E field and H field maxima. Enormous differences are shown to occur for certain families of common ceramic phases depending only on which of the E or H fields were used. The most extraordinary effects and sharpest differences (noted to date) between reactions at the E and H nodes have been found in ferroic oxides. Phases such as Fe3O4 or binary compounds such as BaFe12O19 are rendered non-crystalline to XRD in a few seconds in the H field, although they show no bulk evidence for melting. The microstructures are unique, showing smooth glass-like regions with regular waves parallel to each other. In the E field node the identical pellet components react completely and form large euhedral crystals of a single phase. The phenomenon of de-crystallization or formation of nano-glasses was confirmed for all the 3d ferrite phases. The magnetic properties of these decrystallized ferro-magnetic phases also show remarkable changes from the original very hard, transforming to very soft, magnets.

While the enormous increase in kinetics during the synthesis and sintering of complex ceramics in a microwave field is now well established, there are less examples where synthesis and sintering to high density have been demonstrated in one single step. In this communication, we report the simultaneous synthesis and sintering of NiAl 2 O 4 from NiO+Al 2 O 3 powder mixture in just 15 min in a 2.45-GHz microwave field. The “anisothermal reaction” condition that was achieved in a microwave field appears to be responsible for the observed enhancement in the reaction kinetics of NiAl 2 O 4 formation.

Using a 2.45 GHz wave-guided cavity, in a single mode TE103 excitation, we were able to physically locate compacted 5 mm pellets of samples separately at the H (magnetic) node (where the E field is nearly zero), or the E (electric) node (where H field is nearly zero). A preliminary survey of a variety of metals, (Cu, Fe, Co..) ceramics (ZnO, etc.), and composites, (WC-Co, ZnO-Co) showed remarkable differences in their heating behaviors. The results establish conclusively that the magnetic field interaction contributes greatly to microwave heating of common materials in a manner, previously neglected in most theories of microwave heating, albeit still to be understood.

Pure aluminum nitride (AIN) has been successfully sintered to highly translucent form by microwave sintering at 1850°C with a dwelling time of 30–60 minutes. The results showed that the sintering temperature should be at least 1850°C or higher to get reasonable translucency in the AIN sample by the microwave sintering process. On the other hand, the conventional sintering method requires much longer sintering time to obtain a translucent AIN ceramics.

The experimental achievement of reacting two phases that are held at two different temperatures—the anisothermal reaction condition—is a radical innovation in materials chemistry. Details on the synthesis of Yttrium Iron Garnet (Y3Fe5O12), Barium Ferrite (BaFe12O19), and Nickel Aluminate (NiAl2O4) in 1–10 min in a microwave field are provided. The starting precursor oxides were chosen such that they include a low and a high microwave absorbing phases. When these mixtures are exposed to a 2.45-GHz multimode microwave field the highly absorbing powder particles act as (micro)heat sources and the low absorbing powder particle act as (micro)heat sinks, and create the “anisothermal heat distribution,” a hitherto never attained phenomenon in materials science. A comparison study carried out comparing conventional reactions of the same phases suggested that the “anisothermal heating phenomenon” is also responsible for the very rapid reactions and product formations. Model experiments performed with an Y2O3/Fe3O4 diffusion couple showed a unidirectional diffusion of Fe species into Y2O3, forming a different sequence of intermediate phases.

Microwave processing has gained worldwide acceptance as a novel method for heating and sintering a variety of materials from food to rubber to specialty ceramics, as it offers specific advantages in terms of speed, energy efficiency, process simplicity, novel and improved properties, finer microstructures, and lower environmental hazards. In the present paper, microwave sintering of modulus of rupture (MOR) bar samples of PM copper steel (MPIF FC-0208 composition) and the comparative evaluation of the mechanical properties using both microwave and conventional sintering techniques has been reported.The starting powder characteristics and the processing details of copper steel bar samples sintered in a conventional furnace and in an in house modified commercial microwave oven has been covered at length. In this study, the sintering temperature used typically ranged between 1100 and 1300°C, soaking time ranged from 5 to 20 min, and the atmosphere was controlled using flowing forming gas (mixture of ...

Simultaneous treatment by three pulsed lasers (excimer, Nd-YAG, and CO 2 ) of a ferrosilicon alloy in the QQC process resulted in a 50-μm layer of a non-crystalline phase in the middle of the workpiece.

Nanocomposites based upon framework zirconium phosphates with supported WO 3 , MoO 3 and Pt nanoparticles were synthesized via the incipient wetness impregnation of high-surface-area mesoporous phosphate samples with water solutions of corresponding salts followed by drying and calcination. The structure and surface properties of nanocomposites were studied by using combination of structural and spectral methods. Due to a strong interaction between supports and supported species, the structure of the latter differs considerably from that of the bulk phases. Surface acid centers typical for zirconium phosphates disappear suggesting their participation in bonding nanoparticles of promoters. Instead, new types of strong acid sites associated with tungsten oxide clusters emerge. The effect of these promoters on performance of zirconium phosphates in the reaction of pentane and hexane isomerization is considered.

The application of microwave–hydrothermal (M–H) heating has been evaluated in the decomposition of chlorinated organic compounds such as dichloroethane, trichloroethylene, and pentachlorophenol. This study also focused on the comparison of M–H with conventional–hydrothermal (C–H) treatment on the decomposition of the chlorinated organic compounds. Within 5 min, more than 98% of dichloroethane was decomposed at 180 psi (approximately 190°C) in 2.5 M NaOH solution by M–H treatment. The decomposition rates of the chlorinated compounds were accelerated by four to six times by M–H treatment compared to C–H treatment. No significant difference in reaction products between M–H and C–H treatment was observed, based on the analysis by gas chromatography. This study demonstrates that the application of M–H treatment leads to greatly accelerated kinetics in the decomposition of chlorinated compounds when compared to C–H treatment.

A novel and simple microwave-assisted combustion procedure for the synthesis of a number of technologically important metal nitrides was demonstrated. The method involves the combustion reaction of a porous metal powder compact with N2 gas in the microwave field and provides phase-pure metal nitride products (consisting of fine particles, fibers, and whiskers) within minutes. The ignition and combustion temperatures of the reaction were found to vary as a function of compaction pressure. The microwave-prepared nitrides were characterized using x-ray diffraction, scanning electron microscopy energy dispersive spectroscopy, thermogravimetric analysis, and infrared spectroscopy. The present microwave-assisted hybrid-heating procedure allows the preparation of nitrides with good crystallinity, structural uniformity, and phase purity, and appears to have general applicability for the preparation of metal nitrides (using the respective metals or even their oxides).

This is a review and an overview on hydrothermal synthesis of fine oxide powders. The term hydrothermal today includes methods which involve water at pressures (from 1 atm-several kilobars) and high temperatures from 100–10,000°C. Hydrothermal is one of the best methods to produce pure fine oxide powders. The authors describe (i) hydrothermal decomposition, (ii) hydrothermal metal oxidation, (iii) hydrothermal reaction, (iv) hydrothermal precipitation and hydrothermal hydrolysis, (v) hydrothermal electrochemical, (vi) reactive electrode submerged arc, (vii) hydrothermal microwave, (viii) hydrothermal sonochemical, etc and also ideal and real powders

A key innovation in materials processing of pre-formed metal parts is reported herein. The ”QQC Process” involves the judicious selection of exposure parameters to three pulsed lasers (excimer, Nd-YAG and CO2) simultaneously for treatment of the work piece. Pre-formed commercial steel parts are hardened and/or toughened, and/or clad with TiC improving performance by at least one order of magnitude. Two examples are detailed: a punch for aluminum can production and a fuel injector nozzle. In the latter case it has been shown that some tens of microns of the metal are transformed to a noncrystalline phase, in the middle of the workpiece.

High-power ball mill activation of the mixture of hydrated zirconium and lanthanum salts (oxonitrates, oxochlorides) with ammonium phosphate followed by hydrothermal treatment at temperatures not exceeding 200°C and a nearly neutral pH was found to yield crystalline dispersed phase of a cubic NH4Zr2(PO4)3 type along with admixtures of disordered orthorhombic compounds of a zirconium orthophosphate type. In the same conditions and at the same Zr/P ratio, hydrothermal treatment of gels obtained by reacting mixed zirconium and lanthanum nitrates solutions with ammonium phosphates yields no crystalline products, and only treatment in acid media generates a phase of the α-ZrPO4(OH) type coexisting with the NH4Zr2(PO4)3 phase if polyethylene oxide is present. X-ray powder diffraction, transmission electron microscopy, 31MAS-NMR, FTIRS and thermal analysis were applied to elucidate factors affecting crystallization of complex zirconium phosphates in the hydrothermal conditions. The most essential factor appears to be generation of some nuclei of zirconium phosphates under high pressures developed in the course of mixed solids mechanical activation. These nuclei are embedded into matrix of such well-crystallized solid products as ammonium nitrate or chloride. Hence, metastable cubic or orthorhombic structure of the phases obtained via mechanical activation route can be assigned to the nuclei-matrix orientation relationship. Due to easily scaled-up synthesis procedure, these results appear to be very promising for manufacturing of dispersed framework zirconium phosphates as acid catalysts or fast proton conductors.

Mixed oxides containing La, Mg and Ta were prepared by the sol–gel method. A pure phase, La(Mg2/3Ta1/3)O3 was formed by calcining the gel at a low temperature (

A solution sol–gel method for preparing Ba(Mg 1/3 Ta 2/3 ) 1− x Sn x O 3 [ x =0.0, 0.2] powders was developed. Single phase Ba(Mg 1/3 Ta 2/3 ) 1− x Sn x O 3 [ x =0.0, 0.2] oxide powders formed at temperature as low as 600°C. The calcined powders sintered at 1500°C for 24 h resulted in ≥95% of the theoretical density. The dielectric constant and tangent loss were determined to be 24 and 10 −4 at 10 kHz respectively.

We describe herein a new process for the synthesis of diamond in the presence of various metals and atomic H in a microwave plasma. Along with the traditional high pressure high temperature (HPHT) process and the chemical vapor deposition (CVD) process, for diamonds synthesis this makes it a third route for this purpose. Starting materials used are intimate mixtures of various forms of carbon with one of many metals. These are exposed to a pure H2 microwave-assisted plasma at temperatures in the range 600–1100o C. Novel amorphous alloys are formed containing 40 to 70 atomic percent of carbon. From these liquid alloys diamonds are precipitated with temperature change and/or with possible evaporation of complex, hydrogen-rich Me−C−H species. The carbon content of the metallic liquid drops sequentially down to 5–6%C as more and more diamonds are precipitated therefrom. Au, Ag, Fe, Cu, Ni, and many other metals are used in most runs. Others e.g. La, Mn, Sn, each give distinctive habits or morphology to the diamonds grown. Single crystals have been grown from these MexCyHz metallic liquids on natural diamond substrates, using the same low pressure solid state source (LPSSS) technique. They show high perfection. A mechanism is proposed quite analogous to the HPHT process, to explain this precipitation from metallic solutions, with atomic hydrogen ”substituting” for high pressure.

Two refractory phosphors, BaMg2Al16O27: Eu2+ (BAM) and MgAl11O17.5: Ce3+, Tb3+ (MAO), have been synthesized both by the conventional solid-state processing route (using oxides as the starting materials) and by reacting precursors made by the sol-gel process using organic precursors. The phases formed were reacted at 1000 °C in (a) steam and (b) steam + AlF3. The phosphors were well crystallized with particle sizes in the range of 1–10 μm. The emission spectra showed the characteristic broad band blue emission of Eu2+ for BAM and a narrow band green luminescence of Tb3+ for MAO. The melting points of BAM and MAO were measured to be 1920 ± 20 °C and 1950 ± 20 °C, respectively, using an Ir-strip furnace and optical pyrometer. BAM and MAO phosphor materials are congruently and incongruently melting, respectively. Excellent crystallization via the sol-gel route was found even at 1220 °C. Enhancement of the luminescent output by the steam treatment by some 25% was determined.

Dense and translucent ceramics were prepared by sintering of cylindrical preforms of hydroxyapatite extruded from xerogels. Extruded specimens were dried as monoliths and then consolidated by applying cold isostatic pressure, ranging from 500 to 1500 MPa. Upon heating the samples began to densify at 610 °C, and the densification/sintering was completed at 870 °C as was evidenced by the dilatometry plot indicating no further shrinkage. The sintered specimens thus formed were translucent in appearance. Further heating of the samples up to 1200 °C resulted in their “bloating” or creation of pores in the originally dense matrix. Pore creation within the structure is reproducible, it proceeds from the surface to the interior of the sample, and its spreading can be thermally controlled. Pore evolution within the single phase dense polycrystalline material is not related to the frequently occurring phenomenon of microcracking in ceramics during cooling.

Various ceramic-matrix composites containing zirconia were sintered using a 2.45 GHz microwave field. The effects of the addition of zirconia and the processing parameters on the sintering and microstructure development were investigated. The results showed that microwave processing enhanced the densification of these composites considerably. The enhancement in sintered density was up to 46% over conventional sintering, depending on the systems.

The precipitation of calcium carbonate and calcium phosphates from solutions with and without additives such as hydroxyethyl cellulose, colloidal silica and potato starch, has been studied by X-ray diffraction and scanning electron microscopy. A constant rate of 10−6 mol s−1 of reactant was added into the mixed solutions with and without additives. Nucleation frequency and morphology were dramatically altered by the addition of colloidal potato starch. It was found to be effective for non-specific nucleation of calcite and hydroxyapatite and specific nucleation of monetite. The nucleation frequency of calcite is increased by adding starch by about a factor of 104. Starch also alters the shape of hydroxyapatite to fibre-like.

Transparent mullite ceramics were developed by both microwave and conventional sintering of compacts starting with a diphasic aerogel near 1300°C. Both sintering processes were carried out in air at ambient pressure. The conventionally sintered sample was essentially non-crystalline, whereas the microwave sintered sample was highly crystalline mullite. Using a xerogel of the same composition, no transparency was achieved under the same conditions. The results indicate that the agglomeration-free microstructure of the starting aerogel was the key for achieving the transparency. The achievement of transparent mullite ceramics by microwave processing is attributed to the rapid-heating, accelerated-mullitization, enhanced densification, and limited grain-growth of the diphasic mullite gel in the microwave field.

We have compared the microwave-hydrothermal (M-H) processing with conventional hydrothermal (C-H) processing in the preparation of two layered anion exchangers, i.e., Mg3Al(OH)8NO3 · nH2O and Ni1-xZn2x(OH)2(CH3COO)2x · nH2O. Both these phases can be crystallized more rapidly (an order of magnitude) under M-H processing compared to C-H processing. The above layered mixed basic salt of Ni and Zn was found to exhibit very high selectivity for PO4= (Kd = 15,000). Its order of selectivity for various anions in the presence of 0.1 N̲ NaC1 (ratio of C1- to anion in question is 100) increases as follows: PO4= ≫ SO4= > NO3-.

Phase pure Ba(Mg13Ta23O3 (BMT) powders were prepared using Ba metal, Mg(OC2H5)2, and Ta(OC2H5)5 as metal-organic precursors. Thin films of BMT were spin coated onto Pt-coated Si(100) substrates using the prepared solution and then fired at various temperatures. The X-ray diffraction patterns show that the films crystallize to a single disordered perovskite phase on Si (100) at ~600 °C. Scanning electron microscopy reveals that the films 0.3 μm in thickness and approximately 0.1 μm in grain size were essentially crack-free.

Powder x-ray diffraction (XRD) and Raman evidence are presented for the formation of crystalline diamond in the “hydrothermal” pressure-temperature regime 1–5 kbars, 2O at, say, 800 °C and 1 kbar. The other includes pyrolysis of highly selected organic solid/liquid precursors (halogenated aliphatics such as iodoform) onto similar diamond seeds. In all the cases, powder x-ray diffraction evidence shows a marked increase of the diamond XRD peaks, likewise the Raman spectrum shows a strong increase of the 1331 cm−1 line. However, the crystals apparently are too small to be seen in the SEM. TEM diffraction data, on the other hand, seem to lend support to the possibility of all the grown diamonds being very small.

Condensed silica fume, a by-product from the production of silicon alloys, was sintered by (i) conventional heating in a dilatometric furnace, both at constant heating rate and isothermal heating, and (ii) by the microwave heating. The dense products with relative density up to 95% of theoretical can be obtained only by short runs at high heating rates, preferentially accomplished by the microwave treatment. Prolonged heating leads to the devitrification of the original glassy phase to cristobalite, accompanied by an arrest of densification.

Eu and Tb3+ doped Y2O3, Y2SiO5 and Y3Al5O12(YAG) phosphor materials were prepared by different routes to investigate their effect on luminescent characteristics in micron and submicron particle size powders. Both amorphous low temperature co-precipitate reacted and crystalline high temperature solid state reacted (reference) powders were further crystallized in steam(S) and fluoriferous steam (SF) atmospheres at 1000\ghC for 8 hours, respectively. In spite of sharp XRD peaks in S, SF treated samples, all SEM images exhibited “soft” aggregates of about 3 μm in average diameter consisting of 0.2–0.3 μm small particles. The powder samples characterized by XRD, SEM and luminescence spectra indicated that low temperature reacted samples which were further crystallized in steam or fluoriferous steam have greater improvements in the luminescent intensity than solid state reacted Y2O3, Y2SiO5 based phosphors after S, SF treatments.

Pure and Mn-doped willemite, Zn2SiO4 of different morphologies and particle sizes were prepared with and without NH4OH under different hydrothermal conditions. Pure willemite was synthesized at a temperature as low as 165 °C using autogeneous pressure. The nature of the anion, silica source and the NH4OH∶Zn2+ ratio played an important role in the size and morphology of the willemite phase. The presence of SO 4 2− anions resulted in mainly equiaxed grains. Such powders are expected to be good for consolidation and in the processing of phosphors.

Sol-gel processing was employed to fabricate multilayered SrTiO3 thin films onto fused silica, Si (100) and SrTiO3 (110) substrates. A Sr-Ti alkoxide precursor solution, chemically modified with diisopropanolamine, was hydrolyzed and spin-coated onto these substrates. These films were annealed at 300 °C and then heated to 650 °C for 1 h in air, which resulted in the formation of phase pure crystalline SrTiO3. X-ray diffraction analysis indicated that partially oriented films were deposited onto fused silica and Si (100), while highly oriented film was formed on SrTiO3 (110). A typical microstructure of the film deposited on SrTiO3 (110) and heated at 650 °C for 1 h showed the presence of submicrometer grains on the order of 0.05 to 0.1 μm. The thickness of a single coating measured from the cross section of the SEM micrograph was about 0.1 to 0.2 μm.

For the first time, transparent hydroxyapatite ceramics were fabricated by microwave processing as well as by conventional sintering at ambient pressure. This was achieved essentially using a fine crystalline hydroxyapatite powder synthesized hydrothermally as a starting material. The sintered hydroxyapatite ceramic was phase pure and the average grain size was around 0.2 μm.

Single-crystal fibres of modified strontium aluminium tantalum oxide (1-x)Sr(Al1/2Ta1/2) O3·xLaAlO3(SAT-LA) and (1-x)Sr(Al1/2Ta1/2)O3·xNdGaO3 (SAT·NG), and modified strontium aluminum niobium oxide (1-x)Sr(Al1/2Nb1/2)O3·xNdGaO3(SAT·NG) and (1-x)Sr (Al1/2Nb1/2)O3·xLaAlO3 (SAN·LA) were grown using a laser-heated pedestal growth technique. 0.7SAT·0.3LA grows congruently and retains a twin free simple cubic perovskite structure (as the SAT) when cooled down to room temperature. 0.7SAT·0.3LA crystals have a moderate dielectric constant (κ = 21.7) and low dielectric loss (tan δ = 7.5 × 10−5) at 10 kHz and 90 K. The reduction problem of Ta5+ is eliminated (which is common in the case of SAT growth). 0.7SAT·0.3NG and 0.7SAN·0.3NG have lower melting temperatures and crystal growth is easier. NdGaO3 addition to the SAT and SAN enhances the potential of SAT and SAN as large-area substrates for high-Tc superconductor growth. However, the dielectric constants increased from κ∼-12 to κ∼-16(0.7SAT·0.3NG) and from κ∼18 to κ∼23 (0.7SAN·0.3NG) as a result of NdGaO3 incorporation.

Ca0.5Sr0.5Zr4P6O24 (CSZP) powders were prepared by the decomposition/combustion method using Ca(NO3)2 · 4H2O, Sr(NO3)2, ZrO(NO3)2 · xH2O, NH4H2PO4, urea, and NH4NO3 as starting materials. The homogenized slurries of the mixture were heated at 500 °C for 5 min to obtain CSZP powders. The as-synthesized powders were amorphous and crystallized after heating 800 °C for 2 h. The specific surface area of the powder was varied with the batch weight of starting materials or the amount of urea and ammonium nitrate. Powders with high specific surface area (150 m2/g) could be produced by this method. The sinterability of the powders was comparable to that of sol-gel derived powders. The sintered density of the compacts was 99% of theoretical after firing in air at 1350 °C for 6 h.

A review and some case studies on the interatomic distances of candidate substrates in comparison to the highTcsuperconductor (HTSC) phase YBa2Cu3O7−δ(YBCO) is presented, in an attempt to enhance the basis for substrate selection for YBCO film epitaxy. This preliminary study was carried out by examining a variety of interatomic distances in the structure rather than merely matching the lattice parameters. Interatomic structure matching planes of selected YBCO orientations in contact with substrates were identified. The surface termination of the substrate was found to be a crucial parameter in determining the oriented or epitaxial growth. Possible composition dependence of the orientation of the films at the nucleation stage was also anticipated depending on the comparison. Several currently most commonly used substrates are discussed in some detail.

Monolithic composite aerogels have been prepared from silica/boehmite, silica/montmorillonite, silica/mullite and silica/ kaolinite, with 1 and 10 mol% or wt% of the mineral in the final product. The aerogels were sintered at 1000°C for different durations to determine their thermal stability. The various samples lost 50 to 60% of their initial surface area after this treatment but still retained very high surface areas compared to the sintered aerogels prepared from silica only. The incorporation of small amounts of second phases of different morphologies in silica aerogels prevented their densification leading to high surface area materials with high thermal stability.