Intrinsic Kinetics of Carbon Dioxide Degradation of YBa2Cu3O7-x

The intrinsic kinetics, unaffected by diffusional and masstransfer effects, of the CO₂ degradation of superconducting particles have been determined using a nonisothermal technique. Below 900°C, the carbonization of YBa₂Cu₃O_{7- x} leads to formation of BaCO₃, Y₂Cu₂O₅, CuO, and Cu₂O. A further increase in temperature results in formation of BaCuO₂ from BaCO₃ and CuO. The carbonization rate shows the 1.5th-order dependence on the amount of unreacted YBa₂Cu₃O_{7- x} for the temperature range of 550° to 815°C. The activation energy of carbonization was determined to be 95.1 kJ · mol⁻¹.     

Kinetics of Anatase TiO2 Surface Area Reduction in a Mixture of HCl, H2O, and O2: l, Experimental Study

Changes in the surface area of anatase TiO₂ were investigated at 690 K as a function of the gas composition in mixtures of hydrogen chloride, water vapor, and oxygen. The chlorine content on the catalyst support was not dependent on the annealing time, which indicates that the adsorption equilibrium is reached very quickly. The kinetics of surface area were obtained as a function of partial pressure of HCI (from 0.1 to 40 kPa), water vapor (from 0.05 to 10 kPa), and oxygen (from 0.4 to 20 kPa). A mathematical expression for the rate of surface area loss was obtained which includes the partial pressure of water and the chlorine content at the surface of anatase.     

Microcrystalline BaTiO3 by Crystallization from Glass

The properties and composition of glasses suitable for crystallization of BaTiO₃ are described. The crystallization of certain glasses results in a nearly complete recovery of BaTiO₃, besides the feldspar BaAl₂SiO₃ as a minor phase. The mechanism of crystallization was investigated by thermal analysis, viscosity, and grainsize measurements as a function of the temperature whereas density data were used for evaluation of the BaTiO₃ content. Within the range 30 to 60% by volume of BaTiO₃ at about 1μ grain size, the measured dielectric constant increased from 100 to 1200. The calculated partial dielectric constant of the Titanate phase at this grain size was about 3500. As the grain size approached 0.1μ, the dielectric constant decreased and became nearly independent of the temperature because of the predominance of surface states. Other effects were attributed to special structural characteristics, such as absence of porosity and clamping of the titanate particles within the microcrystalline matrix. Data are also presented on dielectric constant and loss tangent at different frequencies, dc breakdown strength, dc resistivity, and ferroelectric properties as a function of the grain size of the crystallized material.     

Kinetics of Anatase TiO2 Surface Area Reduction in a Mixture of HCI, H2O, and O2: II, Quantitative Modeling

From the experimental rate for surface area reduction of anatase TiO₂, expressed versus the partial pressure in H₂O and the surface content of chloride ion, a kinetic model is proposed in which two parallel mechanisms are involved. Two ways of material transport appear to contribute to the surface area loss: in the vapor phase and at the surface of the oxide. The related rate-determining steps are attributed to the formation of the volatile compound Ti(OH)₂Cl₂ in the first case, and to the diffusion of hydroxyl ions in the second one. At high partial pressure of water, the rate is enhanced by surface interactions between water molecules and chlorine-containing species.     

Increase of Annealing Point of 96% SiO2 Glass on Incorporation of Carbon

The annealing point of reconstructed 96% SiO² glasses is markedly increased by incorporating carbon in porous glass and firing in a dry, nonoxidizing atmosphere. Numerous pyrolyzable organic compounds can be used as a source of carbon. Furfuryl alcohol, which is miscible in water, is preferred since it can be readily polymerized in the porous glass into a nonvolatile resin by heating. Relatively low concentrations of furfuryl alcohol are sufficient to markedly increase the viscosity of the final fired glasses. Infrared spectra show that carbon is an excellent dehydroxylating agent, removing silanol and boranol groups which, if left in the structure, soften the final glasses.     

Pressureless Sintering of SiC-Whisker-Reinforced Al2O3 Composites: I, Effect of Matrix Powder Surface Area

Pressureless sintering of SiC-whisker-reinforced Al₂O₃ composites was investigated. In Part I of the study, the effect of the matrix (Al₂O₃) powder surface area on densification behavior and microstructure development is reported. Compacts prepared with higher surface area Al₂O₃ powder showed enhanced densification at lower whisker concentrations (5 and 15 vol%). Samples with 15 vol% whiskers could be pressureless sintered to ∼97% relative density with zero open porosity and ∼1.6-μm matrix average grain intercept size.     

Low-Fire Processing of Microwave BaTi4O9 Dielectric with BaO–ZnO–B2O3 Glass

The effects of BaO—ZnO–B₂O₃ (BZB) glass addition on the densification and dielectric properties of BaTi₄O₉ (BT4) have been investigated. With increasing BaO content in the BZB glass, the softening and melting points of the resulting BZB glass decrease, but the wetting between BZB and BT4 improves cosiderably. Although the densification temperature is reduced from 1300°C for pure BT4 to 925°C for BT4+BZB dielectric ceramics, the enhancement in densification becomes less significant with increasing BaO content in the BZB glass. The above result is attributed to a chemical reaction taking place at the interface of BZB/BT4 during firing, which becomes less extensive with increasing BaO content in the BZB glass. For the BZB glass with a BaO content in the range of 0–20 mol%, the resulting 90 vol% BT4+10 vol% BZB microwave dielectric has a dielectric constant of 28–33, and a product ( Q × f _r) of quality factor ( Q ) and a resonant frequency ( f _r) of 15 000–20 000 GHz at 6.6 GHz.     

Influence of Glass Additions on Particle-Size-Distribution Effects in Tape Casting of BaTiO3

In earlier work it was shown that, by mixing a narrow-particle-size-distribution BaTi03 powder and a wide-distribution BaTiO₃ powder, lower slurry viscosities and higher green densities were obtained. In the present work, the particle size distribution of a narrow-distribution BaTiO₃ powder was broadened by adding a bismuth borate glass phase. This broadened distribution resulted in lower slurry viscosities and higher tape green densities.     

Carbon coating of anatase-type TiO2 through their precipitation in PVA aqueous solution

Fine particles of photocatalytic anatase-type TiO₂ prepared through hydrolysis of titanium-tetraisopropoxide were coated by carbon through their precipitation in poly(vinyl alcohol) (PVA) aqueous solution, followed by heat treatment at high temperatures of 400-1000 °C in a flow of high purity Ar. Without carbon coating, the phase transformation from anatase to rutile started above 600 °C, but it was suppressed up to 800 °C with carbon coating. Suppression of the phase transformation depended on the amount of carbon coated, apparent suppression being observed with carbon content above 5 mass%. The amount of carbon coated on anatase was controlled by changing the concentration of PVA in the solution. In order to have a carbon content of about 5 mass%, a PVA solution with more than 2 mass% had to be used.     

以不同沥青焦为原料制备活性炭的特性分析

以沥青焦、煤沥青以及氧化沥青为原料，采用KOH活化法制备高比表面积活性炭。试验分别考察了不同原料及预处理工艺对活性炭孔径分布与比表面积的影响。发现采用不同原料所制备活性炭的孔径分布呈现出正态分布的特点，孔径分布范围介于0～5．0nm之间，峰的位置介于1．0～1．5nm附近。活性炭主要由1-1．5nm范围的微孔构成，大于2nm的中孔很少。在煤沥青不熔化处理过程中，其挥发分与H／C原子比要适中，挥发分过高与过低均不利于制备高比表面积活性炭。     

Sub-Sub-Tg Enthalpy Relaxation in a B2O3 Glass

Enthalpy relaxation processes in a B,O₃ glass were investigated calorimetrically in the temperature region from well below to near the glass-transition temperature T_g . The low-temperature ( T_aT_g- 100 K) or sub-sub- T_g anneals stabilize the glass structure. On heating, the annealed sample shows an excess endothermic peak above the annealing temperature T_a , and gradually recovers the original enthalpy without heating through T_g . The enthalpy relaxation evolves in a continuous manner with annealing time as seen in the recovery process. As T_a approaches T_g , a gradual transformation of the sub-sub- T_g behavior to that characteristic of the sub- T_g anneal occurs. The relaxation spectrum exhibits a broad distribution of relaxation times with activation energies of ∼ 10⁵ J/mol. The so-called β distribution commonly used in the analysis of the sub- T_g relaxation processes is seen to be too narrow to describe the sub-sub- T_g behavior. Possible mechanisms for the sub-sub- T_g relaxation phenomena are proposed.     

Processing and Tribological Properties of Si3N4/Carbon Short Fiber Composites

Si₃N₄/carbon fiber composites were fabricated using several types of fiber. All the composites had higher fracture toughness compared with monolithic Si₃N₄ ceramics. Tribological properties were investigated by a ball-on-disk method under unlubricated conditions. The composite containing fibers with a high orientation of graphite layers and high graphite content indicated a low friction coefficient. It was identified, by Raman spectroscopy, that graphite was transferred from the composite to the Si₃N₄ ball of the counterbody during the wear test. This transferred layer was effective for producing the low friction behavior of the composite.     

Carbon materials as catalyst supports for SO2 oxidation: catalytic activity of CuO-AC

Copper catalysts supported on acid treated activated carbon (AC) were prepared, characterized and tested in terms of their SO₂ oxidation activity. Reactions of CuO-AC in flow systems with sulfur dioxide, oxygen and nitrogen streams were investigated to determine the types of chemical interactions that occur on the sorbent surface. The effects of reaction temperature, acid treatment, metal loading, support particle size, SO₂ concentration and O₂ concentration on SO₂ oxidation activity were evaluated. It was found that carbon materials used as catalyst supports for copper oxide catalysts provided a high catalytic activity for adsorbing SO₂ from flue gas and oxidizing it. Acid pretreatment of the carbon supports increased the content of specific surface chemical groups to enhance the catalytic activity for SO₂ oxidation. Metal loading, as well as support particle size, have a significant influence on the SO₂ activity. The supported metals rather than surface oxygen functional groups on AC may be the active sites for adsorbing SO₂.     

Light Scattering from a Metastable Immiscible Na2O-CaO-SiO2 Glass

Light scattering was measured for samples of a metastable immiscible Na₂O-CaO-SiO₂ glass which had been heat-treated to develop a droplet microstructure. The angular scattering profiles obtained were fitted to scattering curves generated using the model of Shetterly and Stubler. The results indicate that, even at fairly short times, the mechanism of growth in this glass is ripening.     

Influence of Processing Conditions on the Electrical Properties of CaCu3Ti4O12 Ceramics

The electrical properties of a series of CaCu₃Ti₄O₁₂ ceramics prepared by the mixed oxide route and sintered at 1115°C in air for 1–24 h to produce different ceramic microstructures have been studied by Impedance Spectroscopy. As-fired ceramics are electrically heterogeneous, consisting of semiconducting grains and insulating grain boundaries, and can be modelled to a first approximation on an equivalent circuit based on two parallel RC elements connected in series. The grain boundary resistance and capacitance values vary as a function of sintering time and correlate with the ceramic microstructure based on the brickwork layer model for electroceramics. The large range of apparent high permittivity values for CaCu₃Ti₄O₁₂ ceramics is therefore attributed to variations in ceramic microstructure. The grain-boundary resistance decreases by three to four orders of magnitude after heat treatment in N₂ at 800°–1000°C but can be recovered to the original value by heat treatment in O₂ at 1000°C. The bulk resistivity decreases from ∼80 to 30 Ω·cm with increasing sintering time but is independent of heat treatment in N₂ or O₂ at 800°–1000°C. The origin of the bulk semiconductivity is discussed and appears to be related to partial decomposition of CaCu₃Ti₄O₁₂ at the high sintering temperatures required to form dense ceramics, and not to oxygen loss.     

平板玻璃工业燃料燃烧二氧化碳排放量计算方法探讨

随着平板玻璃产量的增加,化石燃料燃烧产生的温室气体CO2排放量逐年增加,本文就平板玻璃工业燃料燃烧CO2排放计算方法进行了探讨。     

微波辐射甘蔗渣制造活性炭的试验研究

以ZnCl2为活化剂，采用微波辐射甘蔗渣制备活性炭，研究了微波功率、活化时间、ZnCl2用量与甘蔗渣质量比、干燥功率对活性炭性能的影响。试验的最佳反应条件：ZnCl2与甘蔗渣质量比为2．5：1．0、炭化及活化微波有效功率为35W／g（甘蔗渣，干重）、炭化及活化时间为25min、干燥有效功率为12W／g（活性炭，干重）。在上述条件下制得的活性炭的比表面积为1250m^2／g以上。     

Effect of As2O3 and NaNO3 on the Solution of O2 in Soda-Lime Glass

The rate at which soda-lime glass absorbed oxygen increased with the addition of arsenious oxide to the batch; the absorption rate increased further when sodium nitrate was substituted for part of the sodium carbonate in the batch. There was little difference, however, between the rate of absorption in melts in a gas furnace and melts in an electric furnace. The rate of absorption increased in all cases as the temperature increased in the range 1065° to 1280°C.