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The feasibility of transforming shaped Mg–Al2O3-bearing precursors into monolithic spinel (MgAl2O4) bodies with a retention of shape and dimensions has been demonstrated.Dense, shaped precursors (disks, bars) were fabricated by the pressureless infiltration of molten Mg into porous Al2O3 preforms. After solidification (and machining, in the case of bar-shaped specimens), the Mg-bearing precursors were oxidized in flowing O2 (g) at 430–700 °C. Postoxidation annealing at 1200 °C resulted in the conversion of MgO and Al2O3 into MgAl2O4. After sintering at 1700 °C, spinel bodies that retained the precursor dimensions (to within 0.65%) were produced. Phase and microstructural analyses at various stages of processing are discussed.

Analytical TEM and HREM have been used to examine the structure of BaAl2Si2O8 crystals produced within oxidized Ba–Al–Al2O3–SiO2 precursors upon annealing: (i) at ≤650 °C and (ii) up to 1650 °C. A BaAl2Si2O8 polymorph with a c-axis parameter of 15.6 Å was detected after annealing at ≤650 °C. Stacking faults and antiphase boundaries were detected within this polymorph after the 650 °C treatment. After a 15 h heat treatment at 1650 °C, convergent beam diffraction patterns and HREM confirmed that the predominant phase was β–hexacelsian. Although antiphase boundaries were absent in the β–hexacelsian crystals, dislocations and stacking faults were detected after the 1650 °C anneal. The generation of defects in BaAl2Si2O8 crystals within specimens annealed at ≤650 °C and at 1650 °C is discussed in light of prior structural analyses.

The grain growth of dense, fine-grained Nd1+xBa2−xCu3Oy (x = 0.1−0.4) specimens has been examined in pure O2(g) at 938 °C and 967 °C. No detectable change in average grain size was observed for Nd1.4Ba1.6Cu3Oy within 72 h at 967 °C; however, a significant increase in average grain size developed between 18 and 24 h at 967 °C for Nd1.3Ba1.7Cu3Oy, and within 8−12 h at ≤967 °C for Nd1.2Ba1.8Cu3Oy and Nd1.1Ba1.9Cu3Oy. Microstructural analyses revealed that sudden changes in average grain size coincided with the formation of relatively large (abnormal) grains. A broadening of the grain size distribution was also observed. TEM analyses revealed that grain boundaries were free of second phases. The possible role of anisotropy in grain boundary energy and/or mobility on grain growth is discussed.

The conversion of Ba–Al2O3 –Si–SiO2, Ba–Al–Al2O3 –SiO2, and Ba–Sr–Al–Al2O3 –SiO2 precursors into monolithic, monoclinic celsian has been examined. The relative amounts of metal and oxide in each type of precursor were adjusted so that the overall stoichiometry and molar volume were similar to those of the desired product, celsian. Metal + oxide mixtures were mechanically alloyed and then uniaxially pressed to yield 84–92% dense precursor disks. The precursors were converted into celsian by exposure to a series of heat treatments from 300–1500 °C in oxygen-bearing gases. Differences and similarities in the phase evolution of the various precursors are discussed. Celsian disks were produced that retained the precursor shape, dimensions, and relative (% theoretical) density.

Silver-sheathed powder-in-tube processed tapes and thick films of the Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub 8/spl plusmn//spl delta//-type (Bi-2212) superconductor have been annealed under high temperature, high oxygen fugacity (i.e.fO/sub 2/>0.1 MPa) conditions. At sufficiently high temperatures and oxygen fugacities, the Bi-2212 phase decomposes into a mixture of solid oxides: a Bi/sub 2/(Sr,Ca)/sub 2/Cu/sub 1/O/sub 8/spl plusmn//spl delta//-type (Bi-2201) phase, an alkaline-earth bismuthate Bi/sub 9/Sr/sub 1/1Ca/sub 5/O/sub y/-type (Bi-91_1_5) phase and CuO. Subsequent reformation of Bi-2212 in pure, flowing oxygen at 0.1 MPa and 860/spl deg/C has yielded plate-like grains with enhanced 00l texture (as discerned from X-ray pole figure analyses and electron microscopy). The values of oxygen fugacity leading to sub-solidus decomposition and reformation of Bi-2212 at 500 to 860/spl deg/C are given. XRD and SEM analyses, as well as preliminary critical current measurements of decomposed and reformed Bi-2212 tapes, are presented.

The synthesis of zinc silicate-coated microparticles with well-controlled three-dimensional (3D) shapes, via chemical modification of the surfaces of diatom microshells, is demonstrated. ZnO nanoparticle-based coatings were first applied by exposing the microshells to a zinc acetate-bearing solution and then firing at 700 °C. The ZnO nanoparticles were then allowed to react with the underlying SiO2 micro-shells at 1050 °C. Thin (submicron), compact, and continuous Zn2SiO4 coatings were generated that conformed to the microshell surfaces. The Zn2SiO4-coated microparticles retained the starting 3D microshell shape. Given the wide range of microshell shapes available among different species of diatoms (or other SiO2-forming organisms), this simple and scalable microshell coating method may be used to synthesize functional microparticles with a variety of well-controlled 3D shapes and tailored silicate chemistries. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Metallic Ba-Al-Si bonding agents have been used to produce all-ceramic, BaO-Al{sub 2}O{sub 3}-SiO{sub 2} bonds between plates of mullite (Al{sub 6}Si{sub 2}O{sub 13}). Ba-Al-Si tapes (200 {micro}m thick) were fabricated by compaction and rolling of mechanically alloyed powder. The Ba-Al-Si tapes were placed between mullite plates and then oxidized by heating to a peak temperature of 1,230 C in air. The oxidized tapes strongly adhered to the mullite plates at 25 and 1,000 C, as indicated by the fracture morphologies obtained from compressive shear tests. Electron microscopy (EPMA, TEM) revealed that the bulk of the oxidized Ba-Al-Si tapes (away from the interfaces with mullite) consisted largely of the compound BaAl{sub 2}Si{sub 2}O{sub 8}, along with some BaSiO{sub 3} and an amorphous, barium-rich aluminosilicate. The interface between the oxidized bonding agent and bulk mullite consisted of a mixture of BaAl{sub 2}Si{sub 2}O{sub 8}, Al{sub 6}Si{sub 2}O{sub 13}, Al{sub 2}O{sub 3}, BaAl{sub 2}O{sub 4}, and an amorphous, barium-bearing aluminosilicate.

Some rare-earth-doped alkaline-earth cerates (e.g., Nd2O3-doped BaCeO3) are proton conductors that can act as solid state electrolytes in hydrogen or steam sensors, hydrogen pumps, steam electrolyzers, and fuel cells. In the present study, dense tapes of neodymia-doped barium cerate were produced by the oxidation of malleable Ba-CeH3-Nd2O3precursor tapes. Precursor tapes were produced by cold-rolling either blended or milled mixtures of Ba, CeH3, and Nd2O3 within a silver can. X-ray diffraction, electron microprobe analyses, and thermogravimetric analyses were used to study the phase transformations resulting from heat treatments conducted at 300° to 900°C in pure, flowing oxygen. Barium peroxide and cerium dioxide, produced during oxidation at ≤300°C, reacted at ≤500°C to form barium cerate. The rate of formation of barium cerate depended on the degree of milling of the solid metal-bearing precursor powder. Dense barium cerate tapes were obtained after heat treatment at 1080°C.

A simple method for fabricating TiO2-based sensors of CO(g) is demonstrated: the oxidation of Ti-bearing foils. Metallic foils (35 μm thick) were converted into free-standing, porous rutile foils (60 μm thick) by exposure to O2(g) at 800°—965°C. The oxidized foils contained thin (0.5—1 μm thick), regularly spaced oxide layers oriented parallel to the external surface. The exposure of such porous foils to increasing concentrations of CO(g) resulted in a monotonic increase in the steady-state electrical resistance. Rutile foils sensitive to 50 ppm changes in CO(g) content with response times of a few minutes were produced. The effects of oxidation conditions and copper doping on sensing performance are discussed.

A novel VIMOX (volume identical metal oxidation) route to near-net-shaped calcium hydroxyapatite, Ca 10 (PO 4 ) 6 (OH) 2 , is demonstrated: the oxidation of machinable Ca-Ca 2 P 2 O 7 precursors. Mechanically alloyed mixtures of Ca and β-Ca 2 P 2 O 7 were compacted into disk- and bar-shaped preforms. The latter preforms could be machined into cylinders using a metalworking lathe (200 rpm, hardened steel tooling). After oxidation at 600°C in O 2 , and then postoxidation annealing in H 2 O/O 2 mixtures at 850°C and 1150°C, phase-pure hydroxyapatite was obtained. Because of offsetting volume changes from calcium oxidation and hydroxyapatite formation, porous hydroxyapatite bodies were produced that retained the shapes and dimensions (within 1%) of the machined precursors.

Dense, near-net-shaped, carbide-rich, carbide/tungsten composites have been produced at modest temperatures by the displacive compensation of porosity (DCP) method. Porous, freestanding WC preforms were infiltrated and reacted with a Zr2Cu liquid at 1300°C and ambient pressure. The carbon in the WC was displaced by zirconium in the melt to yield ZrCxand tungsten. The increase in solid volume associated with this displacement reaction was compensated by the prior pore volume of the preform. Dense ZrCx/WC/W composites that possessed

The stability of the (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10{+-}{delta}}-type compound has been evaluated under conditions of elevated temperature (500--860 C) and elevated oxygen fugacity (i.e., in O{sub 2}/Ar gas mixtures containing {le}20% O{sub 2} at total pressures of {le}207 MPa). At sufficient high oxygen fugacities and temperatures, the (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10{+-}{delta}}-type compound transformed into a mixture of a strontium-rich (Bi, Pb){sub 1}(Sr,Ca,Cu){sub 2}O{sub y}-type compound, a calcium-rich (Bi,Pb){sub 1}-(Sr,Ca,Cu){sub 2}O{sub y}-type compound, CuO, and a small amount of (Sr,Ca)O. The decomposition of the (Bi,Pb){sub 2}Sr{sub 2}Ca-Cu{sub 3}O{sub 10{+-}{delta}}-type compound was accompanied by a 2%--3% weight gain, which was consistent with an oxidation reaction. The conditions of oxygen fugacity and temperature leading to decomposition, and the resulting decomposition products, are compared for the (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10{+-}{delta}}-type and Bi{sub 2}Sr{sub 2}Ca{sub 1}Cu{sub 2}O{sub 8{+-}{Psi}}-type compounds.

Bi{sub 2}Sr{sub 2}Ca{sub 1}Cu{sub 2}O{sub 8{+-}{delta}}-type compound thick films were exposed to oxygen--argon-gas mixtures (1% to 20% oxygen gas) at elevated pressures (up to 207 MPa) and temperatures (500 to 940 C) for times ranging from 5 to 96 h. At a sufficiently high oxygen fugacity and temperature, Bi{sub 2}Sr{sub 2}Ca{sub 1}Cu{sub 2}O{sub 8{+-}{delta}} decomposed via a solid-state reaction. Room-temperature X-ray diffractometry and electron probe microanalysis of decomposed films revealed the presence of Bi{sub 2}(Sr,Ca){sub 2}-Cu{sub 1}O{sub 6{+-}{omicron}}-type compound, Bi{sub 9}Sr{sub 11}Ca{sub 5}O{sub {Psi}}-type compound, and CuO. Bi{sub 2}Sr{sub 2}Ca{sub 1}Cu{sub 2}O{sub 8{+-}{delta}} decomposition was accompanied by a modest weight gain, which was consistent with an oxidation reaction. The solid-state decomposition reaction could be reversed by heat treatment of decomposed films at 860 C in pure, flowing oxygen at ambient pressure.

Celsian (monoclinic BaO · A12O3 · 2SiO2) is being considered as a matrix material for ceramic composites used in high-temperature structural applications. The present article describes the synthesis of celsian by the oxidation and annealing of solid, malleable, metallic Ba-Al-Si precursors. The phase and microstructural evolution after various stages of oxidation at 300 °C to 1260 °C in pure oxygen at 1 atm pressure have been examined by X-ray diffraction (XRD) and electron microprobe analyses (EPMA). Barium peroxide, BaO2, formed rapidly during oxidation at 300 °C, with aluminum and silicon remaining largely as unoxidized particles in a BaO2 matrix. Between 300 °C and 500 °C, barium orthosilicate, Ba2Si04, formed by a solid-state reaction between barium peroxide and unoxidized silicon. Further exposure to temperatures between 500 °C and 1200 °C resulted in the oxidation of aluminum and of residual silicon. The oxidized silicon reacted with the barium orthosilicate matrix to yield higher silica-containing barium silicates that, in turn, reacted with alumina or mullite to form metastable hexacelsian (hexagonal BaO-A12O3 · 2SiO2). Celsian was then obtained by further exposure to peak temperatures ≤1260°C.

In this paper we demonstrate the design and development of a family of low-cost, self-powered, wireless sensor solutions utilizing both analog and digital principles. The sensors will utilize Graphene-based thin films integrated directly into the structure. For an immediately deployable digital sensing solution compatible with current commercial technologies we will utilize the Intel WISP platform, which can be read with current COTS products. Our thin films are produced from water-based, inkjet printed graphene oxide (GO) on paper/Kapton, developed using both conventional thermal and laser reduction techniques. In addition to reporting the first ever integration of inkjet-printed water soluble GO inks into low cost, flexible RF electronics, we also bring gas sensing capabilities to RFID tags relying on purely wireless digital transmission. The introduction of low cost, mass producible, eco-friendly, reduced graphene oxide (RGO) films on paper substrates lays the foundation for the development of a wide range of new low-cost, high performance Graphene-based electronic devices.

Surface micro- and nanostructural modifications of dental and orthopedic implants have shown promising in vitro, in vivo and clinical results. Surface wettability has also been suggested to play an important role in osteoblast differentiation and osseointegration. However, the available techniques to measure surface wettability are not reliable on clinically relevant, rough surfaces. Furthermore, how the differentiation state of osteoblast lineage cells impacts their response to micro/nanostructured surfaces, and the role of wettability on this response, remain unclear. In the current study, surface wettability analyses (optical sessile drop analysis, environmental scanning electron microscopic analysis and the Wilhelmy technique) indicated hydrophobic static responses for deposited water droplets on microrough and micro/nanostructured specimens, while hydrophilic responses were observed with dynamic analyses of micro/nanostructured specimens. The maturation and local factor production of human immature osteoblast-like MG63 cells was synergistically influenced by nanostructures superimposed onto microrough titanium (Ti) surfaces. In contrast, human mesenchymal stem cells cultured on micro/nanostructured surfaces in the absence of exogenous soluble factors exhibited less robust osteoblastic differentiation and local factor production compared to cultures on unmodified microroughened Ti. Our results support previous observations using Ti6Al4V surfaces showing that recognition of surface nanostructures and subsequent cell response is dependent on the differentiation state of osteoblast lineage cells. The results also indicate that this effect may be partly modulated by surface wettability. These findings support the conclusion that the successful osseointegration of an implant depends on contributions from osteoblast lineage cells at different stages of osteoblast commitment.

Surface structural modifications at the micrometer and nanometer scales have driven improved success rates of dental and orthopaedic implants by mimicking the hierarchical structure of bone. However, how initial osteoblast-lineage cells populating an implant surface respond to different hierarchical surface topographical cues remains to be elucidated, with bone marrow mesenchymal stem cells (MSCs) or immature osteoblasts as possible initial colonizers. Here we show that in the absence of any exogenous soluble factors, osteoblastic maturation of primary human osteoblasts (HOBs) but not osteoblastic differentiation of MSCs is strongly influenced by nanostructures superimposed onto a microrough Ti6Al4V (TiAlV) alloy. The sensitivity of osteoblasts to both surface microroughness and nanostructures led to a synergistic effect on maturation and local factor production. Osteoblastic differentiation of MSCs was sensitive to TiAlV surface microroughness with respect to production of differentiation markers, but no further enhancement was found when cultured on micro/nanostructured surfaces. Superposition of nanostructures to microroughened surfaces affected final MSC numbers and enhanced production of vascular endothelial growth factor (VEGF) but the magnitude of the response was lower than for HOB cultures. Our results suggest that the differentiation state of osteoblast-lineage cells determines the recognition of surface nanostructures and subsequent cell response, which has implications for clinical evaluation of new implant surface nanomodifications.

The Displacive Compensation of Porosity (DCP) method is a novel, reactive infiltration approach for fabricating dense, near net-shaped, ceramic/metal composites with high ceramic contents at modest temperatures. In this process, a metallic liquid is pressureless infiltrated into a porous, shaped ceramic preform and allowed to undergo a displacement reaction with the ceramic phase in the preform. Unlike other reactive infiltration approaches, a larger volume of ceramic is produced than is consumed, so that the prior pore volume within the preform becomes filled (i.e. reaction-induced densification). In this paper, the DCP method is used to fabricate MgO/Fe-Al intermetallic composites. Dense MgO/FeAl-based composites were produced by the pressureless infiltration of Mg(1) into, and then reaction with, porous MgAl 2 O 4 /MgO/Fe-bearing preforms within 2 h at 1000°C.

We demonstrate microring resonators using a thin layer of porous silicon (pore size ~30 nm) as the cladding. With a loaded Q factor of 25,000, this new type of resonators is promising for bio/chemical sensing.

Multilayer capacitors with thin, dielectric BaTiO3 layers can possess a relatively high capacitance per unit volume. A solid metallic precursor method has recently been developed for preparing thin BaTiO3/noble metal laminates. In the present paper, the phase and microstructural evolution of Ba-Ti metallic precursors were examined after oxidation at 300° to 900°C in pure oxygen at 1 atm pressure. Barium peroxide, BaO2, formed rapidly during oxidation at 300°C, with titanium largely remaining as unoxidized particles in the peroxide matrix. Between 375° and 500°C, the solidstate reaction of barium peroxide with metallic titanium yielded barium orthotitanate, Ba2TiO4. Further exposure to temperatures between 500° and 900°C resulted in the oxidation of residual metallic titanium. The oxidized titanium then reacted with the orthotitanate matrix to form barium metatitanate, BaTiO3. The rate of formation of BaTiO3 was found to be strongly dependent on the degree of milling of the Ba-Ti precursors and on the heating rate between 300° and 500°C.

The design, fabrication, and characterization of novel integrated optical sensors comprised of nanoporous silicon are presented. This work lays foundation for a new class of planar integrated photonic sensors with high sensitivity.

A complementary metal-oxide-semico-nductor (CMOS)-compatible method for the direct fabrication of arbitrary-shaped Pb(Zr0.52 Ti0.48)O3 and PbTiO3 ferroelectric/piezoelectric nanostructures on plastic, silicon, and soda-lime glass substrates is reported. Thermochemical nanolithography is used to induce nanoscale crystallization of sol-gel precursor films. Ferroelectric lines with width ≥30 nm, spheres with diameter ≥10 nm, and densities up to 213 Gb in(-2) are produced.

Whereas considerable interest exists in self-assembly of well-ordered, porous "inverse opal" structures for optical, electronic, and (bio)chemical applications, uncontrolled defect formation has limited the scale-up and practicality of such approaches. Here we demonstrate a new method for assembling highly ordered, crack-free inverse opal films over a centimeter scale. Multilayered composite colloidal crystal films have been generated via evaporative deposition of polymeric colloidal spheres suspended within a hydrolyzed silicate sol-gel precursor solution. The co-assembly of a sacrificial colloidal template with a matrix material avoids the need for liquid infiltration into the preassembled colloidal crystal and minimizes the associated cracking and inhomogeneities of the resulting inverse opal films. We demonstrate that this co-assembly approach allows the fabrication of hierarchical structures not achievable by conventional methods, such as multilayered films and deposition onto patterned or curved surfaces, and can be transformed into various materials that retain the morphology and order of the original films. We show that colloidal co-assembly represents a simple, low-cost, scalable method for generating high-quality, chemically tailorable inverse opal films for optical applications.

A novel and attractive method for preparing multicomponent electronic ceramics and ceramic-metal composites is the oxidation of solid metallic precursors (SMP). This metallurgical processing route consists of the following steps: (i) preparation of a solid metallic precursor containing the proper ratio of elements for the final ceramic or ceramic-metal composite, (ii) compaction and forming of the metallic precursor into a desired shape, and (iii) oxidation to produce a monolithic ceramic or ceramic-metal composite. While the SMP method has been used to prepare wires and tapes containing a variety of superconducting oxides, this method has not been widely used to synthesize other electronic ceramics. In this paper, the synthesis of dielectric BaTiO3/noble metal laminates from solid metallic precursors is discussed. Ba–Ti precursor powders have been produced by solid-state mechanical alloying. The precursor powder was sealed inside noble metal tubes and rolled to form thin Ba–Ti/noble metal laminates. Exposure of the Ba–Ti core in such tapes to temperatures ≥ 300 °C in pure oxygen resulted in rapid oxidation. Post-oxidation annealing at elevated temperatures (≥900 °C) yielded dielectric BaTiO3/Ag or BaTiO3/Pd laminates.

We report on the fabrication and performance of polymer-based inverted solar cells utilizing amorphous indium zinc oxide (a-IZO) as the electron-collecting electrode. Amorphous IZO films of 200 nm thickness were deposited by room temperature sputtering in a high-purity argon atmosphere. The films possessed a high optical transmittance in the visible region (≥ 80%), a low resistivity (3.3 × 10−4 Ωcm), a low surface roughness (root mean square = 0.68 nm), and a low work function (4.46 ± 0.02 eV). Inverted solar cells with the structure a-IZO/P3HT: PCBM/PEDOT:PSS/Ag exhibited a power conversion efficiency of 3% estimated for AM 1.5G, 100 mW/cm2 illumination.

Multilayer capacitors with thin, dielectric BaTiO3 layers can possess a relatively high capacitance per unit volume. A solid metallic precursor method has recently been developed for preparing thin BaTiO3/noble metal laminates. In the present paper, the phase and microstructural evolution of Ba-Ti metallic precursors were examined after oxidation at 300° to 900°C in pure oxygen at 1 atm pressure. Barium peroxide, BaO2, formed rapidly during oxidation at 300°C, with titanium largely remaining as unoxidized particles in the peroxide matrix. Between 375° and 500°C, the solidstate reaction of barium peroxide with metallic titanium yielded barium orthotitanate, Ba2TiO4. Further exposure to temperatures between 500° and 900°C resulted in the oxidation of residual metallic titanium. The oxidized titanium then reacted with the orthotitanate matrix to form barium metatitanate, BaTiO3. The rate of formation of BaTiO3 was found to be strongly dependent on the degree of milling of the Ba-Ti precursors and on the heating rate between 300° and 500°C.

Tapes of the hard magnetic ferrite, BaFe12O19, were synthesized by the oxidation of metallic barium and iron precursors. Milled mixtures of barium flakes and iron powder (Ba:Fe atomic ratio = 1:12) were sealed within fugitive silver tubes and then compacted and formed into tapes by rolling at room temperature. Oxidation and postoxidation heat treatments were conducted over the temperature range 300°–1250°C (the silver was removed after heat treatment at 900°C). Phase-pure BaFe12O19 tapes were produced after heat treatments at peak temperatures of is greater than or equal to $1080°C. Such tapes exhibited room-temperature magnetization values of is greater than or equal to $65.0 emu/g in an applied field of 16.5 kOe (1.32 × 106 A/m). A coercivity of 3.44 kOe (2.75 × 105 A/m) was achieved in a fine-grained (submicrometer) BaFe12O19 tape that had been annealed for 24 h at a peak temperature of 1080°C.

A simple method for fabricating TiO2-based sensors of CO(g) is demonstrated: the oxidation of Ti-bearing foils. Metallic foils (35 μm thick) were converted into free-standing, porous rutile foils (60 μm thick) by exposure to O2(g) at 800°—965°C. The oxidized foils contained thin (0.5—1 μm thick), regularly spaced oxide layers oriented parallel to the external surface. The exposure of such porous foils to increasing concentrations of CO(g) resulted in a monotonic increase in the steady-state electrical resistance. Rutile foils sensitive to 50 ppm changes in CO(g) content with response times of a few minutes were produced. The effects of oxidation conditions and copper doping on sensing performance are discussed.

Textured superconducting films of YbBa2Cu3O7−δ were grown on single crystals of MgO (100) and SrTiO3 (100) by oxidation of a liquid alloy precursor. The substrates were coated by dipping them in molten YbBa2Cu3 (m.p. ~870 °C). After removal from the melt, the liquid layers on the substrates were oxidized in pure oxygen to form the tetragonal oxide phase, i.e., YbBa2Cu3O7−δ, then annealed at 500 °C to obtain the superconducting orthorhombic phase of the same compound. The microstructure of the films obtained in this way was found to be related to the nature of the substrate as well as to processing variables that included oxidation temperature and oxidation time. Films grown on MgO (100) showed c-axis texture as well as a random growth structure. Films prepared on SrTiO3 (100) showed either a c-axis texture or a mixture of c-axis and a-axis texture. The superconducting properties of the as-prepared films and the effects of key process parameters on film quality and microstructure are presented and discussed.

The stability of the Bi2−xPbxSr2Ca2Cu3O10 (Pb‐2223) phase contained in silver‐sheathed oxide‐powder‐in‐tube specimens has been investigated by x‐ray diffraction, transmission electron microscopy, and energy dispersive x‐ray analysis. Silver tubes loaded with Pb‐2223 precursor powders were processed into tapes using established metallurgical techniques. The tapes were heat‐treated in a specially designed equilibration apparatus at selected temperatures (800–845 °C) for a range of times (10–5500 min) and quenched in liquid gallium held at ∼40 °C. The results showed that the Pb‐2223 phase is stable in a limited temperature interval between 810 and 830 °C in 7.5% oxygen. At 800 °C, this phase decomposes to Bi2Sr2CaCu2O8 (2212), Ca2PbO4, and CuO; while at temperatures ≥840 °C it partially melts with precipitation of Bi2Sr2CuO6 (2201) and Ca2CuO3. The effects of the silver cladding on the Pb‐2223 phase stability and microstructure are also discussed.

Oscillations in temperature and oxygen partial pressure were introduced during the oxidation of melt-spun YBa{sub 2}Cu{sub 3}Ag{sub 29} ribbons to produce superconducting microlaminate tapes consisting of alternating YBa{sub 2}Cu{sub 3}O{sub 7{minus}y}-rich and silver-rich layers oriented parallel to the tap plane. In this paper microstructural and microchemical evolution during oxidation, with and without such oscillations, is discussed. Isothermal oxidation (400{degrees} C, O{sub 2}) of YBa{sub 2}Cu{sub 3}Ag{sub x} (x = 21, 29, 46) ribbons occurred at a parabolic rate, and the oxidized zone consisted of oxide particles dispersed in silver. No significant chemical segregation was observed during isothermal oxidation. However, significant chemical segregation was produced when sudden oscillations in temperature and oxygen partial pressure were introduced during oxidation. Such chemical segregation resulted in the formation of YBa{sub 2}Cu{sub 3}O{sub 7{minus}y}-rich and silver-rich layers after post-oxidation annealing. The number and thicknesses of these layers could be varied by controlling the number and duration of oscillations introduced during oxidation.

Textured superconducting films of YbBa 2 Cu 3 O 7–δ supported on both single and polycrystalline MgO substrates were prepared by oxidation of a liquid precursor alloy. The substrates were coated by dipping them into the molten alloy (YbBa 2 Cu 3 , melting point ≈870°C). After withdrawal from the melt, the adhering metal was oxidized to the corresponding oxide phase, i.e., Y YbBa 2 Cu 3 O 7−δ , which exhibited a superconducting transition at ≈80 K following annealing in pure O 2 at 500°C. With MgO(1 0 0) substrates, evidence was seen for the epitaxial growth of YbBa 2 Cu 3 O 7−δ crystals having their c -axis parallel to the [1 0 0] direction of the substrate. For polycrystalline MgO, X-ray diffraction and microstructural examination showed that the high- T c crystallites in the films were also oriented with their c -axis perpendicular to the substrate surface, but the directions of the a and b axes were disordered rather than epitaxial. The superconducting properties of as-prepared films are discussed together with the effects of key processing parameters on composition and microstructure.

Colloidal self-assembly holds promise for photonic applications as a solution-based, low-cost alternative to top-down photolithography, if significant control of uniformity and defects can be achieved. Herein we demonstrate a new evaporative co-assembly method for highly-uniform inverse opal thin films that involves the self-assembly of polymer colloids in a solution containing a silicate precursor. Nanoporous inverse opal films can be made crack-free and with highly uniform orientation at the cm scale. The silicate between the colloids appears to increase the strength against cracking. This control of defects makes this method well-suited for the low cost fabrication of such films as sensors and photonic devices.

Titania sol-gel and silver electro-less deposition processes were utilized to apply conformal coatings to multiphoton lithographically fabricated polymer photonic crystal templates, resulting in enhanced refractive index and stop band reflectivity.

The dissolution of (Al, Cr)2O3 into CaO—MgO—Al2O3—SiO2 melts, under static and forced-convective conditions was investigated at 1550°C in air. With sufficient MgO in the melt, or sufficient Cr2O3 in (Al, Cr)2O3, a layer consisting of a spinel solid solution, Mg(Al, Cr)2O4, formed at the (Al, Cr)2O3/melt interface. The dissolution kinetics of 1.5 and 10 wt% Cr2O3 specimens were determined as a function of immersion time, specimen rotation rate, and magnesia content of the melt. Electron microprobe analysis was used to characterize concentration gradients in the (Al, Cr)2O3 sample, the Mg(Al, Cr)2O4 spinel, or in the melt after immersion of specimens containing 1.5 to 78 mol% Cr2O3. The dissolution kinetics and microprobe analyses indicated that a steady-state condition was reached during forced-convective, indirect (Al, Cr)2O3 dissolution such that spinel layer formation was rate limited by solid-state diffusion through the spinel layer and/or through the specimen, and spinel layer dissolution was rate limited by liquid-phase diffusion through a boundary layer in the melt. This is consistent with a model previously developed for the indirect dissolution of sapphire in CMAS melts.

The copper-free superconducting oxide BaPb 1- x Bi x O 3 was synthesized by oxidation of Ba 1 Pb 1.04 Bi 0.20 and Ba 1 Pb 0.81 Bi 0.26 Ag 1.28 metallic precursor alloys. Analysis of the resulting oxide and oxide/noble metal composite by X-ray diffractometry and electron microprobe analysis showed the presence of the superconducting phase; silver (in the composite), and small amounts of lead-bismuth oxides and impurity containing phases. Electrical resistivity measurements of the oxide and oxide/normal metal composite produced critical temperature onsets of 10.5 K and 12 K, and zero resistance temperatures of 8.5 K and 9 K, respectively.

The oxide-powder-in-tube (OPIT) method has produced superconducting wires or tapes that exhibit high critical current densities in high magnetic fields when the superconducting oxide is the two-layer compound Bi2Sr2Ca1Cu2Oy or the three-layer compound Bi2−xPbxSr2Ca2Cu3Oy. For good properties to be obtained, however, numerous critical processing issues must be addressed.

Peptides isolated from a phage library have been effective in promoting the precipitation of amorphous germanium oxide from a precursor solution. The morphologies of germania formed under the influence of these library-isolated peptides were shown to be distinct from the GeO 2 formed under similar conditions with homo poly-amino acids. The appearance of germanium oxide hollow spheres or core/shell nanostructures created under the influence of peptide Ge8 is clearly linked to the unique amphiphilic character of the peptide. The appearance of these unique structures represents the first time such morphologies have been seen in germania or created utilizing only an unmodified peptide. The ease of creating these interesting inorganic materials makes this system attractive for the possible fabrication of materials appropriate for catalysis, optical and controlled release applications.

In this paper, the silica-based microshells of diatoms (planktonic micro-algae) have been used as biologically-replicable (i.e., scalable) 3-D templates for synthesizing functional multicomponent microparticles of controlled shape. Three shape-preserving chemical conversion approaches have been explored for the conversion of diatom microshells (frustules) into functional multicomponent oxides: sol-gel, acetate precursor, and hydrothermal routes. For the sol-gel approach, SiO 2 frustules were first converted by gas/solid reaction into MgO microparticles of similar shape. A conformal and continuous coating of BaTiO 3 was then applied, via sol-gel processing, to the MgO microparticles. The underlying MgO templates were then selectively dissolved away to yield BaTiO 3 microparticles that retained the overall shape of the starting frustules. In the acetate precursor route, a zinc acetate precursor solution was used to apply a coating of /nO nanoparticles to SiO 2 frustules. The ZnO nanoparticles were then allowed to react at elevated temperature with the underlying SiO 2 to form Zn 2 SiO 4 -hcaring microparticles with the frustule shape. Finally, a metathetic gas/solid reaction was used to convert SiO 2 frustules into TiO 2 . The titania microparticles were then converted into HaTiO 3 -based microparticles that retained the frustule shape via hydrothermal reaction with a barium hydroxide-bearing solution. These results demonstrate that several shape-preserving chemical approaches may be used to convert biologically-replicable 3-D nanostructured microteinplates into microparticles with functional multicomponent chemistries and with controlled morphologies.

A novel, hybrid route to chemically-tailored oxide nanostructures with complex, three-dimensional (3D) shapes is introduced: the Bioclastic* and Shape-preserving Inorganic Conversion (BaSIC) process. This process couples the massively-parallel and precise replication of biological organisms with rapid, shape-preserving chemical conversion via fluid/solid reactions, so that large numbers (billions) of identical 3D nanostructures can produced with desired (non-natural) compositions. The BASIC process is demonstrated by converting ornate, SiO 2 -based diatom frustules (microshells) into MgO nanostructures that retain the frustule shapes and fine features. Such MgO nanostructures are attractive for biomedical and environmental applications (e.g., drug delivery, water purification). By choosing among the numerous shapes and fine features available in bioclastic structures (from diatoms, radiolaria, sponges, silicoflagellates, etc.), and by using other reactive gases, meso/nanostructures with a wide variety of shapes features, and compositions may be mass produced by the BaSIC process.

An astounding variety of self-assembled, rigid (bioclastic) micro/nanostructures are generated by micro-organisms known as diatoms (single-celled algae). Each diatom species assembles an intricate silica nanoparticle-based microshell (frustule) with a particular three-dimensional (3-D) shape and with specific patterns of nanoscale features (pores, channels, ridges, protuberances, etc.). Sustained reproduction of a single diatom can yield enormous numbers of intricate frustules with identical 3-D shapes and fine features. The massive parallelism and genetic precision of such 3-D nanoparticle self-assembly are highly attractive for device applications. However, in order to expand the use of such micro/nanostructures into a broad range of applications, processes need to be developed to change the silica-based chemistry of diatom frustules into other compositions, so as to achieve a wider variety of properties. Displacement reactions can be used to convert SiO 2 -based diatom frustules into other oxides while preserving the 3-D morphology of the starting frustule. In this paper, an oxidation-reduction reaction between Mg gas and SiO 2 frustules has been used to convert the frustules into MgO-bearing replicas. The influence of processing parameters (reaction temperatures, times, and reactant ratios) on the nanostructural evolution, and on the final product phases (particularly the secondary Si-bearing phases), has been examined. Nanocrystalline MgO-bearing replicas of diatom frustules have been synthesized at temperatures as low as 650°C within a few hours.

This collaborative research project has focused on the integrated use of robust biomimetic or biological silica assembly processes with shape-preserving chemical conversion reactions to produce freestanding 3-D structures with selectable microscale morphologies, nanoscale features, and tailored, non-silica chemistries. Biomimetic 3-D silica structures have been synthesized through Direct-Write Assembly using polyamine-based inks, followed by templated conformal silicification. With proper selection of ink composition and silicification conditions, robust silica structures were formed that retained the patterned morphology after firing to 1000 C. Such 3-D biomimetic silica and biological silica (diatom frustule) structures were converted into freestanding 3-D silica-free replicas comprised of other oxides or metals through the use of gas/solid reactions. For example, these 3-D silica structures were converted into high surface area, microporous Si replicas through reaction with Mg gas (to yield MgO and Si products) and then selective MgO dissolution. Such Si replicas have, in turn, been converted into noble metal replicas through electroless deposition and selective Si dissolution. The reaction kinetics and micro/nanostructural evolution during such reactions have been examined.

The dissolution rate of sapphire into CaO-MgO-Al2O3-SiO2 (CMAS) melts was investigated at 1450° and 1550°C. The effects of immersion time, specimen rotation rate, and magnesia concentration in the bulk melt on the sapphire dissolution rate and on the growth rate of magnesium aluminate spinel at the sapphire/melt interface were determined. The processes of direct and indirect sapphire dissolution into CMAS melts are discussed, with the support of kinetic and microprobe data.1 A model of indirect sapphire dissolution1,2 is used along with the equations of Tedmon3 to describe the kinetics of indirect dissolution and spinel layer growth during forced-convective and static sapphire dissolution.