Processing and Characterization of Thin Films of the Two-Layer Superconducting Phase in the Bi─Sr─Ca─Cu─O System: Evidence for Solid Solution

Thin films in the Bi─Sr─Ca─Cu─O system have been synthesized from liquid ethylhexanoate precursors by spin pyrolysis. An extensive solid-solution range was found for the two-Cu-layer phase through the study of c -axis-oriented, single-phase thin films fabricated on single-crystal, (100)-oriented, MgO substrates. All two-layer compositions were excess in Bi and deficient in Sr + Ca relative to the ideal 2212 composition and showed an overall cation deficiency. The solidus temperature and c lattice parameter were found to vary systematically with composition. Sharp superconductive transitions were obtained in the case of a number of different compositions with T _c varying between 72 and 84 K. Evidence for significant compositional heterogeneities within single-phase two-layer thin films was found and the implications for superconductivity are discussed. Compositions within the solid-solution range gave single-phase, c -axis-oriented films over a wide temperature range extending from 730°C to an upper, solidus (or peritectic) temperature (780° to 840°C) which is dependent on the initial starting composition. A model has been developed that describes the formation of the two-layer phase from a fugitive liquid.     

Production of B4C coatings by CVD method in a dual impinging‐jet reactor: Chemical yield,morphology, and hardness analysis

β‐rhombohedral boron carbide (B₄C) was deposited on a tungsten substrate from a BCl₃? H₂? CH₄ gas mixture in a dual impinging‐jet chemical vapor deposition reactor. On‐line FTIR analysis of the product stream proved the formation of BHCl₂ and HCl as by products, in a competing parallel reaction. A maximum of 13% chemical yield of boron carbide was observed, and the yield was found to have increasing trend with an increase in temperature. XRD analysis proved the existence of rhombohedral B₄C phase at 1300°C without any other B₄C phases or impurities. At this temperature, the formation of 5‐fold icosahedral boron carbide crystals up to 30 micron sizes was observed. Such highly symmetric crystalline regions were observed to have a very high hardness value of 4750 kg/mm² as revealed from the microhardness analysis. The change in product morphology at low substrate temperatures resulted in a decrease in the hardness values. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Carbon Nitride-Related Nanomaterials from Chemical Vapor Deposition: Structure and Properties

Nanoscale-sized carbon nitride-related materials exhibit a wealth of interesting structural, electronic, and optical property behaviors. Chemical vapor deposition technology allows almost unlimited freedom to produce films with compositions and structures approaching the nanometer scale among light elements. Aligned polymerized carbon nitride (CN) nanobells have been grown on a large scale and provide excellent field electron emission properties, as described by a side-emission mechanism. Separation of single CN nanobells and fabrication of heterojunctions between CN nanobells and pure carbon nanotubes have been achieved. Boron carbonitride (BCN) nanofibers with controlled orientation and composition have been synthesized; these nanofibers show strong blue-violet photoluminescense at room temperature. Recent progress also has been made on nitrogen-containing diamond, CN, and BCN films. The purpose of this paper is to survey the work that has been conducted and to detail the level of understanding that has been attained in the research on nitride-related materials.     

1000°C Phase Relations and Superconductivity in the (Nd-Ce-Cu)-O Ternary System

The phase relations involving the 24 K n -type Nd_{2- x} Ce _x CuO₄ superconductor were investigated at 1000°C in air. The terminal solid solubility was confirmed to be x = 0.2. This solid solution is the only ternary phase in the Nd₂O₃–CeO₂–CuO diagram. A binary (1 − y )CeO₂– y NdO_1.5 solid solution exists out to y = 0.4. Phase diagrams for NdO_1.5–CeO₂–CuO (1000°C) and NdO_1.5–CeO₂ (900° to 1500°C) are presented.     

SiC14-CH4-H2系统沉积碳化硅动力学与微结构

Silicon carbide was prepared from SiCl4-CH4-H2 gaseous precursors by isothermal, isobaric chemical vapor deposition (CVD) at atmospheric pressure and temperatures ranging from 900°C to 1100°C. Kinetic studies showed that carbosilane of SiH2Cl2, SiHCl3 and SiCl2 formed from decomposition of SiCl4 and CH4 contributed to the deposition of hexangular facet and granular pebble structured SiC. An average apparent activation energy of 152 kJ•mol－1 was determined. The overall CVD process was controlled not only by the surface reactions but also by complex gas phase reactions. The as-deposited thin film was characterized using scanning electron microscopy, X-ray diffraction and transmission electron microscopy, these analysis showed that the deposited thin film consisted of pure phase of the β-SiC, the growth morphology of β-SiC differs from hexangular facet to granular pebble struc-tures, which varied with substrate length and CVD temperature.     

Phase Composition and Compatibilities in the Bi-Sr-Ca-Cu Quaternary Oxide System at 800°C in Air

Subsolidus phase relations in the system (Bi-Sr-Ca-Cu)-O at 800°C were investigated via powder X-ray diffraction and electron probe microanalysis of solid-state reaction products. Two recently reported (Bi-Sr-Ca)-O phases were detected in quaternary assemlages and had the approximate cation stoichiometries of 9 11 5 and 825. The only truly quaternary compound detected is the superconducting phase with the cation stoichiometry 2212. Tie lines, tie triangles, and compatibility tetrahedra involving this phase and the 2201 superconducting phase were determined. Both superconducting compounds exhibit small but detectable Sr-to-Ca solubility and are Sr-deficient with respect to the "ideal" formulas.     

Activity–Composition Relations in NiAl2O4─MnAl2O4 Solid Solutions and Stabilities of NiAl2O4 and MnAl2O4 at 1300° and 1400°C

Activities of NiO were measured in the oxide and spinel solutions of the system MnO–NiO–Al₂O₃ at 1300° and 1400° C with the aim of deriving information on the thermodynamic properties of the spinel phases. Synthetic samples in selected phase assemblages of the system were equilibrated with metallic nickel and a gas phase of known oxygen partial pressures at a total pressure of 1 atm. The data on NiO activities and directions of conjugation lines between coexisting oxide and spinel phases were used to establish the activity–composition relations in spinel solid solutions at 1300° and 1400°C. The MnAl₂O₄–NiAl₂O₄ solid solutions exhibit considerable negative deviations from ideality at these temperatures. The free energy of formation of MnAl₂O₄ from its oxide components (MnO + Al₂O₃) at 1300° and 1400°C is calculated to be −24.97 and −26.56 kJ. mol⁻¹, respectively. The activities determined in the stoichiometric spinel solid solutions are more negative as compared with those predicted from cation distribution models.     

Deposition mechanism of pyrolytic carbons at temperature between 800–1200 °C

The textures, growth features, microstructures and binding of carbon atoms of pyrolytic carbons prepared by chemical vapor deposition (CVD) at a temperature between 800–1200 °C on graphite substrate and carbon fibers were studied. The intermediate product phase of pyrolytic carbons was also investigated. Based on the present study a deposition model of viscous droplet was proposed in this paper. The viscous droplet here refers to all kinds of fine spheroids that are more or less viscous. The mechanism of the formation of three typical textures namely, smooth laminar, rough laminar and isotropic carbons can be satisfactorily explained by this model.     

Synthesis and Structural Characterization by X-ray Absorption Spectroscopy of Tin-Doped Mullite Solid Solutions

The formation of solid solutions between tin cations and mullite by calcination at 1400°C of amorphous precursors prepared by pyrolysis of aerosols is reported. The oxidation state of the tin cations and the position that they occupy in the mullite structure have been analyzed using XAS (XANES and EXAFS) spectroscopy, which shows that the tetravalent tin cations are located at the octahedral positions of the Al³⁺ ions, which induces cell expansion. The limit of tin incorporation under the experimental conditions reported here correspond to a tin/mullite mole ratio of ∼5%, which is within the range previously reported for other tetravalent cations (4%–6%).     

Solubility Limits of α'-SiAION Solid Solutions in the System Si,Al,Y/N,O

The solubility limit of α'-SiAION solid solutions on the Si₃N₄─YN:3AIN composition join in the system Si₃N₄─YN─AIN has been determined at 1800°C. The end members of these solid solutions are Y_0.43Si_10.7Al_1.3N₁₆ and Y_0.8Si_9.6Al_2.4N₁₆. Unit-cell dimensions of the α'-SiAION solid solutions in the system Si,Al,Y/N,O can be expressed as follows: a _o(Å) = 7.752 + 0.045 m + 0.009 n , c _o(Å) = 5.620 + 0.048 m + 0.009 n , where the α'-SiAION solid solution has the formula Y _x Si_{12-( m+n )}Al _m+n N_{16- n} O _n . The single-phase boundary of the solid solution α'-SiAION on the composition triangle Si₃N₄─YN:3AIN─AIN:Al₂O₃ is delineated. The present paper also reports the phase relationships involving α'-SiAION.     

Microstructure and Mechanical Properties of Heat-Treated Silicon Carbide–Aluminum Nitride Solid Solutions

Nanophase-structured composites were fabricated by heat treating hot-pressed 2H-wurtzite SiC-AlN solid-solution specimens of 25, 50, and 75 mol% AlN within the spinodal decomposition zone. Heat-treatment conditions were 1750°C for 150 h, in flowing nitrogen gas. The hot-pressed specimens contained 2H-wurtzite equiaxed grains, and the grain size increased with AlN content. Lattice parameters followed Vegard's law. Nanoprecipitates with typical modulated tweed-type structures were observed along the [2 1 1 0] zone axis and were orthogonal to the {01 1 2} planes that make angles of 46.70°, 46.90°, and 47.11° to the [0001] for the three compositions. The microhardness, flexural strength, and fracture-toughness values of the heat-treated specimens were not significantly different from the hot-pressed values.     

煤基聚苯胺制掺N碳微纳米管的实验研究

我国煤炭资源丰富,以煤为原料制备碳纳米管,可以实现煤炭资源的高效利用,减少环境污染,为煤炭行业的发展提供新途径。以煤基聚苯胺为碳氮源,分别以乙酸镍或柠檬酸铁为碳源热解催化剂,以二茂镍、乙酸镍或二茂铁为碳管生长催化剂,采用催化热解-化学气相沉积耦合法成功制备出了三种高石墨化程度的掺N碳微纳米管。并对其进行了SEM、TEM、XRD、Raman、XPS等结构测试和甲醇氧化电催化剂载体应用测试,结果发现：三种掺N碳微纳米管的微观形态多样,有直立管、弯曲管、竹节状管等。二茂镍和二茂铁适合生长长而直的碳管,乙酸镍适合生长短而弯的碳管。二茂镍和乙酸镍所长碳管收率相当,约为5.8%（质量）;二茂铁所长碳管收率较高,为21.2%（质量）。N元素主要以石墨型N掺入三种碳微纳米管中,乙酸镍所长碳管的掺N量最高,为1.17%（质量）,且表现出良好的电催化剂载体性能。     

Synthesis of multiwalled carbon nanotubes on Al2O3 supported Ni catalysts in a fluidized‐bed

Multiwalled carbon nanotubes (MWNTs) were synthesized on Al₂O₃ supported Ni catalysts from C₂H₂ and C₂H₄ feedstocks in a fluidized bed. The influence of the ratio of superficial gas velocity to the minimum fluidization velocity (U/U_mf), feedstock type, the ratio of carbon in the total quantity of gas fed to the reactor, reaction temperature, the ratio of hydrogen to carbon in the feed gas, and nickel loading were all investigated. Significantly, the pressure drop across the fluidized‐bed increased as the reaction time increased for all experiments, due to the deposition of MWNTs on the catalyst particles. This resulted in substantial changes to the depth and structure of the fluidized bed as the reaction proceeded, significantly altering the bed hydrodynamics. TEM images of the bed materials showed that MWNTs, metal catalysts, and alumina supports were predominant in the product mixture, with some coiled carbon nanotubes as a by‐product. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Activity–Composition Relations in FeCr2O4–FeAl2O4 and MnCr2O4–MnAl2O4 Solid Solutions at 1500° and 1600°C

Activity–composition relations of FeCr₂O₄–FeAl₂O₄ and MnCr₂O₄–MnAl₂O₄ solid solutions were derived from activity–composition relations of Cr₂O₃–Al₂O₃ solid solutions and directions of conjugation lines between coexisting spinel and sesquioxide phases in the systems FeO–Cr₂O₃–Al₂O₃ and MnO–Cr₂O₃–Al₂O₃. Moderate positive deviations from ideality were observed.     

Solid Solutions of Lindbergite–Glushinskite Series: Synthesis,Ionic Substitutions,Phase Transformation and Crystal Morphology

To clarify the crystal chemical features of natural and synthetic oxalates Me²⁺(C₂O₄)∙2H₂O (Me²⁺ = Fe, Mn, Mg, Zn), including minerals of the humboldtine group, solid solutions of lindbergite Mn(C₂O₄)∙2H₂O–glushinskite Mg(C₂O₄)∙2H₂O were precipitated under various conditions, close to those characteristic of mineralization in biofilms: at the stoichiometric ratios ((Mn + Mg)/C₂O₄ = 1) and non-stochiometric ratios ((Mn + Mg)/C₂O₄ < 1), in the presence and absence of citrate ions. Investigation of precipitates was carried out by powder X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Thermodynamic modelling was performed in order to evaluate the lindbergite–glushinskite equilibrium. It was shown that glushinskite belongs to the orthorhombic β-modification (sp. Gr. Fddd), while lindbergite has a monoclinic α-modification (sp. gr. C2/c). Mg ions incorporate lindbergite in much higher quantities than Mn ions incorporate glushinskite; moreover, Mn glushinskites are characterized by violations of long-range order in their crystal structure. Lindbergite–glushinskite transition occurs abruptly and can be classified as a first-order isodimorphic transition. The Me²⁺/C₂O₄ ratio and the presence of citric acid in the solution affect the isomorphic capacity of lindbergite and glushinskite, the width of the transition and the equilibrium Mg/Mn ratio. The transition is accompanied by continuous morphological changes in crystals and crystal intergrowths. Given the obtained results, it is necessary to take into account in biotechnologies aimed at the bioremediation/bioleaching of metals from media containing mixtures of cations (Mg, Mn, Fe, Zn).     

Thermal Stability of a Chemically Vapor Deposited Multilayer Coating Containing Amorphous Silica and Rutile Titania on Hi-Nicalon Fiber

A multilayer coating consisting of consecutive layers of amorphous-silica, rutile-titania, and amorphous-silica was prepared on Hi-Nicalon fiber by chemical vapor deposition at 1050°C. It appeared that the silica and titania layers were strongly bonded to each other with no evidence of detachment and crack deflection at the interface region. The layered structure became morphologically unstable because of the growth of titania grains, the crystallization of the silica layers, and the oxidation of the fiber on exposure to 1200°C in air for 92 h.     

Effect of N doping on properties of diamond-like carbon thin films produced by RF capacitively coupled chemical vapor deposition from different precursors

In this paper, we report results concerning properties of diamond-like carbon (DLC) thin films obtained in different experimental conditions: various RF power values and different precursors (methane, acetone and toluene or in combination with nitrogen). The deposition rate of DLC thin films obtained from precursors with low ionizing energy and high number of carbon atoms in molecule as acetone and toluene was higher (142 nm/min for acetone and 607 nm/min for toluene as compared with 79 nm/min for methane at 400 W input power). The highest value of hardness was obtained from methane (18 GPa). In the case of acetone and toluene precursors, the hardness increased with input power to the highest values of 16.8 and 14.8 GPa. By utilizing nitrogen as doping element, the resistivity of DLC thin films obtained from methane and acetone decreased from values higher than 10⁷ Ω cm to lower values of 12.5×10³ Ω cm for 3.79% nitrogen atomic concentration in the case of films obtained from methane and 40×10³ Ω cm for 4.26% nitrogen atomic concentration in the case of films obtained from acetone.     

Adhesion Measurement of Amorphous C : H Films Deposited onto Stainless Steel. Spectroscopic Investigation of Interfaces

Amorphous hydrogenated carbon films obtained by the Plasma Assisted Chemical Vapor Deposition (PACVD) process, have been extensively studied by many authors^1,2,3 because of their interesting properties (hardness, optical transparency, chemical inertness, high electrical resistivity). In the present work, carbon films were deposited on stainless steel from glow-discharge polymerization of methane at reduced pressure, using an RF generator operating at 13.56 MHz.

These thin protective films are able to play the role of a primer to which another polymer (adhesive, paint, lacquer …) can subsequently be adhered. Surface treatments of the substrate and of the polymeric film were developed in order to obtain suitable adhesion properties, firstly of the film on the metal substrate, secondly of an adhesive on the hydrogenated carbon film. These treatments were monitored by two spectroscopic methods, viz. X-ray photoelectron spectroscopy (XPS) and (Low Energy Electron Induced X-ray Spectrometry) (LEEIXS). Mechanical measurements were made using a three-point flexure test⁴ (Norm AFNOR T 30 010).     

Oxygen Storage Capacity, Specific Surface Area, and Pore-Size Distribution of Ceria–Zirconia Solid Solutions Directly Formed by Thermal Hydrolysis

The oxygen storage capacity (OSC) of CeO₂–ZrO₂ solid solutions that were directly formed as nanocrystals by thermal hydrolysis of acidic aqueous solutions of (NH₄)₂Ce(NO₃)₆ and ZrOCl₂ at 150°C increased from 94 μmol of O₂/g for pure CeO₂ to >400 μmol of O₂/g for compositions of CeO₂/ZrO₂ with molar ratios (C/Z) from 74.1/25.9 to 41.7/58.3 (maximum value of 431 μmol O₂/g was reached at the composition C/Z = 51.7/48.3) and then decreased with increased ZrO₂ content in the solid solutions. As compared with pure CeO₂, the CeO₂–ZrO₂ solid solutions that contained <84.8 mol% ZrO₂ maintained high specific surface area and large pore volume with nanosized pores (pore size at maximum pore volume) <10 nm in diameter after heat treatment at 700°C.     

Optical and Mechanical Properties of Thin PTFE Films,Deposited from a Gas Phase

Thin polytetrafluoroethylene (PTFE) films are produced by deposition from a gas phase by two methods: electron-enhanced vacuum deposition (EVD) and EVD + low-temperature plasma (LTP). Structure, morphology, and composition of the films are studied by IR spectroscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. They are close to the structure of bulk PTFE. The roughness of the films’ surface is changed with gas pressure and LTP power variations. Films are transparent from UV to near-infrared regions. Refractive and extinction indices and their anisotropy are measured by spectral ellipsometry. They are tuned by variations of deposition conditions. Hardness and Young modulus of the films are increased if EVD + low power LTP is used for film deposition. Use of EVD + LTP also increases thermal stability of the films. Contact angle of the films corresponds to the bulk PTFE. The PTFE molecules oriented are preferentially in perpendicular direction to the substrate surface.