Thermolysis and Photolysis of C60 Diozonides

Ozonation of C₆₀ in o-xylene produced three C₆₀(O₃)₂ diozonides that were separated from one another and from two C₆₀(O₃)₃ triozonides by High Performance Liquid Chromatography (HPLC). Upon thermolysis at 10, 15, and 16.6°C, each of the diozonides dissociated sequentially, first to a C₆₀O(O₃) oxyozonide, then to a C₆₀O₂ diepoxide. The three diepoxides were stable in solution for at least 3 weeks. The mean lifetimes of the three diozonides were 52 ± 5, 62 ± 6, and 17.3 ± 1.8 min, respectively (all at 15°C). The mean lifetimes of the three oxyozonides were 69.7 ± 0.7 and 58 ± 6 min at 16.6°C, respectively and about 240 min at 10°C. Photolysis of the diozonides yielded two dioxidoannulenes with UV-Vis adsorption maxima at 333 and 332 nm, and what appeared to be an epoxide-oxidoannulene with UV-Vis adsorption maximum at 327 nm. These annulenes were observed to form dimers. We have synthesized and characterized six C₆₀O₂ dioxides, at least three and possibly four of which were hitherto unknown. We report the discovery of oxyozonides that form during the dissociation of diozonides.     

Study on EB-PVD Zirconia Thermal Barrier Coatings for Gas Turbine Blade Protection

Thermal barrier coatings on hollow turbine blades of DD3 were studied. The DD3 single crystal alloy has excellent mechanical properties, equivalent to that of PWA 1480. The results show that ZrO₂ coatings consist of oriented columnar grains. The coating is composed of t' cubic and tetragonal phases and there is an alumina layer at the ZrO₂-NiCrAlY alloy interface after aging for 30 min. at 1050°C. No degradation occurred to the EBPVD ceramic coatings after 200 thermal cycles at 1100°C for 10 min., air cooling and 100 hours high temperature oxidation at 1100°C.     

SPINNING FIBERS FROM POWDER SUSPENSIONS

Green ceramic fibers from Al₂O₃, Si₃N₄, Ce-ZrO₂, SiC, and other ceramics can be prepared by dry spinning of powder-loaded suspensions. The green fibers contain 54 to 64 vol. % ceramic powder in an ethyl methacrylate polymer base. Continuous fibers with an average diameter of 60 to 175 µm were spun at rates of 10 to 40 meters/minute. Spinnable dope compositions are defined for simple ternary powder + polymer + solvent systems, and are compared for several powders in MEK-based solvents. Spinnability is related to extrusion pressure, and drying conditions, and the shear rheological behavior of the dope. Fiber preparation by suspension dry spinning is compared with melt spinning of powder-loaded thermoplastics.     

Electrochromic properties of nanocrystalline MoO3 thin films

Electrochromic MoO₃ thin films were prepared by a sol–gel spin-coating technique. The spin-coated films were initially amorphous; they were calcined, producing nanocrystalline MoO₃ thin films. The effects of annealing temperatures ranging from 100 °C to 500 °C were investigated. The electrochemical and electrochromic properties of the films were measured by cyclic voltammetry and by in-situ optical transmittance techniques in 1 M LiClO₄/propylene carbonate electrolyte. Experimental results showed that the transmittance of MoO₃ thin films heat-treated at 350 °C varied from 80% to 35% at λ = 550 nm (ΔT =  45%) and from 86% to 21% at λ ≥ 700 nm (ΔT =  65%) after coloration. Films heat-treated at 350 °C exhibited the best electrochromic properties in the present study.     

Piroxicam benzoate--synthesis,HPLC determination,and hydrolysis

An improved method of piroxicam benzoate synthesis was described, and an isocratic reversed-phase high-performance liquid chromatography method for its determination was developed and fully validated. The method was found to be specific, precise (relative standard deviation 0.3%), accurate (mean recovery 99.9%), and robust. Limit of detection was estimated at 0.055 µg mL^-1 and limit of quantification at 0.185 µg mL^-1. The kinetics of piroxicam benzoate hydrolysis in aqueous buffer solutions (pH 1.1 and 10), simulated gastric and intestinal fluids was studied. The hydrolysis followed first-order kinetics. The following rate constants were obtained at pH 10: k = 1.8 × 10^-3 hr^-1 at 37°C and k = 3.4 × 10^-2 hr^-1 at 60°C. In acidic media, no significant hydrolysis was observed after 24 hr. During the 24-hr period in simulated intestinal fluid, only 10.9% of the starting ester was hydrolyzed.     

前驱体热解氮化硼/碳化硅复相泡沫陶瓷的抗氧化与高温隔热性能研究

以聚碳硅烷(PCS)和三甲胺基环硼氮烷聚合前驱体(PBN)进行共聚合制得复合前驱体, 以此为原料采用高压裂解发泡技术制备了一种氮化硼/碳化硅(BN/SiC)复相开孔泡沫陶瓷. 由包含不同比例组分的起始前驱体所制得的泡沫陶瓷的孔隙直径在1~5 mm, 体积密度在0.44~0.73 g/cm³之间. 对该陶瓷材料的微观结构和性能的研究表明, 由于BN相的引入使得BN/SiC复相泡沫陶瓷在800~1100℃的抗氧化性能有了显著的提高; 其压缩强度随着引入BN比例的增加而提高, 约为纯SiC泡沫陶瓷的5~10倍. 其中以组分重量比为1:1的起始复合前驱体所制备BN/SiC复相多孔陶瓷在1500℃时的导热系数仅为4.0 W/(m·K); 对其进行隔热性能测试, 材料热面中心温度为1400℃时, 其背面中心温度仅为280℃; 采用有限差分法数值模拟背部升温历程, 将其有效导热系数代入计算模型, 得到材料背部中心温度升温历程的数值模拟结果, 与实际升温历程基本一致.     

Melt flow and solidification during infiltration in making steel matrix syntactic foams

Steel matrix syntactic foam is a promising lightweight and energy absorbing material. In this study, an infiltration casting technology is developed to prepare syntactic foams, which brings in alumina hollow spheres with an average size of around 3.97?mm to make the pores and enhance the properties of the foams. During the process, melt flow along with heat transfer during the infiltration is investigated. The study shows that melt flow and velocity distribution of molten steel are significantly unstable; the critical solid fraction of the steel is 0.67; and the alumina ceramic mould in which the foams are prepared must be preheated to at least 1000°C to prevent incomplete infiltration. Finally, the microstructure of syntactic foams is studied.     

Annealing effects on microstructure and mechanical properties of chromium oxide coatings

Reactive radio frequency magnetron sputter-deposited chromium oxide coatings were annealed at different temperatures and times. The influence of annealing temperature on the microstructure, surface morphology and mechanical properties was examined by X-ray diffraction, nanoindentation, pin-on-disc wear and scratch tests, respectively. X-ray results show that the chromium oxide sputtered at room temperature in low oxygen flux is primarily amorphous. Annealing below 400 °C did not cause much change, while annealing at higher temperature of 500 °C caused a significant change in microstructure and mechanical properties. Hardness increased from 12.3 GPa to 26 GPa, and the wearability improved with higher annealing temperature due to the formation of crystalline Cr₂O₃ phase, which occurs at 470 °C. Annealing time had little effect on mechanical properties and microstructure, although coating surface roughness increased with a longer annealing time. Coating adhesion was improved by annealing, due to residual stress relief and possible interfacial interdiffusion.     

Surface Preparation of Aluminum Nitride for Metallization: Effect of Temperature on Surface Reactivity

The current aqueous cleaning step in the surface preparation of aluminum nitride (AlN) prior to metallization causes performance and reliability issues for the substrates used for microelectronic packaging due to surface reactions. These issues limit the use of AlN and its replacing of BeO, an environmentally hazardous material currently used. The aim of this investigation was to determine the effects of different solutions on the surface of AlN substrates under varying conditions at times up to 2419.2 ks (28 days). Concentration of the solutions, temperature, and immersion time were varied for the AlN samples in the solutions. Both elevated temperatures (50°C and 90°C) and low temperatures (5°C) were investigated.

Four general types of behavior were observed: minor changes in average surface roughness and microstructure, linear change in average surface roughness and pitted grains, nonlinear change in average surface roughness and product formation on AlN surface, and miscellaneous change in average surface roughness with surface product formation.

The surface roughening kinetics were very complex due to changes in both the reaction product morphology and reaction mechanism with temperature, solvent, and pH for a specific solvent. Minor changes in average surface roughness and microstructure were observed for HCl pH = 5, H₂ SO₄ pH = 5, NaOH pH = 8, NaOH pH = 10, NaOH pH = 12, deionized water and Alfred tap water at 5°C, HCl pH = 3 and oleic acid at 50°C and citric acid and oleic acid at 90°C. Linear changes in average surface roughness and pitted grains were observed for HCl pH = 2 and H₂SO₄ pH = 3 at 50°C and HCl pH = 2, H₂SO₄ pH = 3, and deionized water at 90°C. Non-linear change in average surface roughness and product formation on AlN surface was observed for HCl pH = 5, NaOH pH = 8 and Alfred tap water at 50°C and HCl pH = 5 and H₂SO₄ pH = 2 at 90°C. Miscellaneous changes in average surface roughness with surface product formation were observed for H₂SO₄ pH = 2, H₂SO₄ pH = 5, NaOH pH = 10, NaOH pH = 12, citric acid, Micro-90 and deionized water at 50°C and HCl pH = 3, H₂SO₄ pH = 5, NaOH pH = 8, NaOH pH = 10, NaOH pH = 12, Micro-90 and Alfred tap water at 90°C.     

Fabrication of ferrous metallic foams by reduction of ceramic foam precursors

A process has been developed for obtaining closed cell metallic foams using a ceramic foam precursor. In the present study, the major constituent of the ceramic foam precursor was iron oxide (Fe₂O₃), which was mixed with various foaming/setting additives. The mixture set rapidly at room temperature, stabilizing the foam generated by hydrogen release. The oxide foam was then reduced by annealing at 1240^∘C in a non-flammable hydrogen/inert gas mixture to obtain a metallic foam with a relative density of 0.23 ± 0.017, and an average cell diameter of 1.32 ± 0.32 mm. The iron foams were tested in compression and yielded an average compressive strength of 29 ± 7 MPa. The compressive stress-strain curves obtained were typical of cellular metals. The normalized strengths of the metal foams obtained in the present study compare favorably with those of steel foams produced by other techniques.     

MASS TRANSFER OF SULFUR DIOXIDE TO CONDENSING AQUEOUS AEROSOLS

Sodium chloride aerosols were generated from a 1.0 percent solution and passed through a tubular furnace, then recondensed at 29°C in a cooling section in the presence of SO₂. The dry particles ranged from 0.711 to 0.843 µm and the condensed droplets were in the 1.66 to 2.88 µm range. Final droplet size was varied by controlling the temperature of the nebulizer solution between 17 and 50°C. The SO₂ concentration in the gas phase of the condensing cloud was varied between 0.5x10 - ³ and 2.5 xl0 - ³ atm.

Cloud droplets were separated from the gas stream in a point-to-plane electrostatic precipitator and the droplets analyzed colorimetrically for total sulfur content.

Concentrations of SO₂ in the aqueous phase were about one order of magnitude greater than values obtained from equilibrium constants. The collection rate of SO₂ at 29°C appeared to be first order in SO₂ gas phase concentrations.

A model for this process was constructed, based on the hydrate formation in the gas-water interface[SO₂]_g + n[H₂O]ℓ ⇋ [SO₂ · n(H₂O)]ℓ

The order of the hydrate n was estimated to be 4.0.     

Stability-indicating spectrophotometric and densitometric methods for determination of aceclofenac

Three methods were developed for the determination of aceclofenac in the presence of its degradation product, diclofenac. In the first method, third-derivative spectrophotometry (D₃) is used. The D₃ absorbance is measured at 283 nm where its hydrolytic degradation product diclofenac does not interfere. The suggested method shows a linear relationship in the range of 4-24 µg mL^-1 with mean percentage accuracy of 100.05±0.88. This method determines the intact drug in the presence of up to 70% degradation product with mean percentage recovery of 100.42±0.94. The second method depends on ratio-spectra first-derivative (RSD₁) spectrophotometry at 252 nm for aceclofenac and at 248 nm for determination of degradation product over concentration ranges of 4-32 µg mL^-1 for both aceclofenac and diclofenac with mean percentage accuracy of 99.81±0.84 and 100.19±0.72 for pure drugs and 100.17±0.94 and 99.73±0.74 for laboratory-prepared mixtures, respectively. The third method depends on the quantitative evaluation of thin-layer chromatography of aceclofenac using chloroform:methanol: ammonia (48:11.5:0.5 v/v/v) as a mobile phase. Chromatograms were scanned at 274 and 283 nm for aceclofenac and diclofenac, respectively. The method determined aceclofenac and diclofenac in concentration ranges of 2-10 and 1-9 µg spot^-1 with mean percentage accuracy of 100.20±1.03 and 100.14±0.98 for pure drugs and 99.77±0.74 and 100.07±0.78 for laboratory-prepared mixtures, respectively. This method retains its accuracy in the presence of up to 80% degradation product for the studied drug.

The suggested procedures were checked using laboratory-prepared mixtures and were successfully applied for the analysis of their pharmaceutical preparation. The validity of the proposed methods was further assessed by applying a standard addition technique. The obtained results agreed statistically with those obtained by the reported method.     

Porous Titania Thin Films Grown by Anodic Oxidation for Hydrogen Sensors

Porous titanium dioxide (Titania) thin films were grown by anodic oxidation using high purity (99.7%) titanium foil in a dilute sulphuric acid (1 M) medium. The anodization process was carried out for 30 minutes with 20 mA/cm² and 50 mA/cm² current densities. The samples were characterized by XRD, SEM, and AFM techniques. It was found that the grown porous titania films were less sensitive to 500 ppm hydrogen in air ambient below 300°C; however, the sensitivity and response behavior of the film at 300°C are very much dependent on the growth conditions. Particularly, the films grown at current density 50 mA/cm² and 1 M acid concentration exhibited the lowest response time of 151 sec at 300°C.     

Atmospheric pressure chemical vapour deposition of SnSe and SnSe2 thin films on glass

Atmospheric pressure chemical vapour deposition of tin monoselenide and tin diselenide films on glass substrate was achieved by reaction of diethyl selenide with tin tetrachloride at 350–650 °C. X-ray diffraction showed that all the films were crystalline and matched the reported pattern for SnSe and/or SnSe₂. Wavelength dispersive analysis by X-rays show a variable Sn:Se ratio from 1:1 to 1:2 depending on conditions. The deposition temperature, flow rates and position on the substrate determined whether mixed SnSe–SnSe₂, pure SnSe or pure SnSe₂ thin films could be obtained. SnSe films were obtained at 650 °C with a SnCl₄ to Et₂Se ratio greater than 10. The SnSe films were silver–black in appearance and adhesive. SnSe₂ films were obtained at 600–650 °C they had a black appearance and were composed of 10 to 80 μm sized adherent crystals. Films of SnSe only 100 nm thick showed complete absorbtion at 300–1100 nm.     

Alkoxide route to La0.5Sr0.5CoO3 epitaxial thin films on SrTiO3

An all alkoxide based sol–gel route was investigated for preparation of epitaxial La_0.5Sr_0.5CoO₃ (LSCO) films on 100 SrTiO₃ (STO) substrates. Films with 20–30 to 80–100 nm thickness were prepared by spin-coating 0.2–0.6 M (metal) solutions on the STO substrates and heat treatment to 800 °C at 2 °C min^− 1, 30 min, in air. The films were epitaxial with a cube-on-cube alignment and the LSCO cell was strained to match the STO substrate of 3.905 Å closely; a and b = 3.894 Å and 3.897 Å for the 20–30 and 80–100 nm films, respectively. The c-axis was compressed to 3.789 Å and 3.782 Å for the 20–30 and 80–100 nm films, respectively, which resulted in an almost unchanged cell volume as compared to polycrystalline film and nano-phase powders prepared in the same way. The SEM study showed mainly very smooth, featureless surfaces, but also some defects. A film prepared in the same way on an -Al₂O₃ substrate was dense and polycrystalline with crystallite sizes in the range 10–50 nm and gave cubic cell dimensions of a_c = 3.825 Å. The conductivity of the ca 30–40 nm thick polycrystalline film was 1.7 mΩcm, while the epitaxial 80–100 nm film had a conductivity of around 1.9 mΩcm.     

Aluminum Melt Foam Processing for Light-Weight Structures

Aluminum foam was prepared by two routes, namely, gas injection technique and by the decomposition of TiH₂ blowing agent. The foam structure can be largely controlled by the amount of degassing agent and duration of foaming. The heterogeneity in cell structure could be explained on the basis of foam stability, drainage in the cell walls, and heat transfer during quenching. The variation in cell size and drainage is negligible when the holding time is around 120 s at 750°C. The constant strain rate compression tests indicate that the Young's modulus, plateau stress, and energy absorption capacity increases with relative density of the foam, while the densification strain reduces with increase in relative density.     

Effect of negatively charged species on the growth behavior of silicon films in hot wire chemical vapor deposition

The deposition behavior of silicon in hot wire chemical vapor deposition was investigated, focusing on the generation of negatively charged species in the gas phase using a gas mixture of 20% SiH₄ and 80% H₂ at a 450 °C substrate temperature under a working pressure of 66.7 Pa. A negative current of 6–21 µA/cm² was measured on the substrate at all processing conditions, and its absolute value increased with increasing wire temperature in the range of 1400 °C–1900 °C. The surface roughness of the films deposited on the silicon wafers increased with increasing wire temperature in the range of 1510 °C–1800 °C. The film growth rate on the positively biased substrates (+ 100 V, + 200 V) was higher than that on the neutral (0 V) and negatively biased substrates (− 100 V, − 200 V, − 300 V). These results indicate that the negatively charged species are generated in the gas phase and contribute to deposition. The surface roughness evolved during deposition was attributed to the electrostatic interaction between these negatively charged species and the negatively charged growing surface.     

CHEMICAL VAPOR DEPOSITION OF TiB2 FOR TiN-TiB2 LAMINAR COMPOSITES

TiB₂ is a material with very interesting properties with respect to erosion and corrosion resistance. Deposition on metallic substrates using TiCI₄, BBr₃ or BCI₃ and H₂ at temperatures around 900° C results in coronation of the substrate, which is most severe when using BBr₃. Therefore, a TiN diffusion barrier is applied. Here we discuss the deposition of TiB₂ using BCI₃ on molybdenum and TiN and compare the results with those of the thermodynamically more favorable reaction with BBr₃. Smooth TiB₂ layers are formed when using BCI₃, with faceting occurring above 900° C. The morphology seems to be independent of the BCI₃/TiCl₄ ratio in the gas phase for values between 0·5 and 4. With an excess of boron in the gas phase - BCI₃/TiCl₄ = 8, depletion occurs already at 800° C. An apparent activation energy of 210 KJ/mol has been determined for a stoichiometric gas phase with BCl₃/TiCI₄ = 2. When the supply of boron is limiting - BCl₃/TiCl₄ = 0·5, the activation energy is 120 KJ/mol.     

AC impedance spectroscopy of porous silicon thin films containing metallic cations

Thin porous silicon (PS) films were prepared by HF/HNO₃ vapor etching on silicon wafers. The infiltration of metallic cations inside the porous silicon matrix followed by slow heating in air leads to an interesting electrical and optical physical phenomena. Al³⁺, Cu⁺, K⁺, Li⁺ metallic cations as chloride or as nitrate solutions are infiltrated inside the silicon porous matrix. After annealing in air at 500 °C during 2 h a structure was achieved in order to measure the Nyquist diagram corresponding to the cations embedded in PS/silicon. The real and imaginary parts of the whole structure depend on the voltage bias and on the frequency. Those signify that the junction is a Schotky-barrier junction.

From the variation of Ln(σT) versus absolute temperature T, where σ is the conductivity, we have deduced the activation energy of the metallic impurities in the [100 °C–400 °C] temperature range. We have found that the activation energies are of about 0.19 eV, 0.25 eV, 0.49 eV and 0.71 eV for Cu⁺, K⁺, Al³⁺ and Li⁺ cations respectively. These kinds of structures are suitable for gas sensing, optical sensing or for the fabrication of fuel cell membranes.     

Microstructural, photocatalysis and electrochemical investigations on CeTi2O6 thin films

The properties of sol–gel derived CeTi₂O₆ thin films deposited using a solution of cerium chloride heptahydrate and titanium propoxide in ethanol are discussed. The effect of annealing temperature on structural, optical, photoluminescence, photocatalysis and electrochemical characteristics has been examined. Lowest annealing temperature for the formation of crystalline CeTi₂O₆ phase in these samples is identified as 580 °C. The optical transmittance of the films is observed to be independent of the annealing temperature. The optical energy bandgap of the 600 °C annealed film for indirect transition is influenced by the presence of anatase phase of TiO₂ in its structure. Fourier transform infrared spectroscopy investigations have evidenced increased bond strength of the Ti–O–Ti network in the films as a function of annealing temperature. The photoluminescence intensity of the films has shown dependence on the annealing temperature with the films fired at 450 °C exhibiting the maximum photoluminescence activity. The decomposition of methyl orange and eosin (yellow) under UV–visible light irradiation in the presence of crystalline CeTi₂O₆ films shows the presence of photoactivity in these films. The photocatalytic response of CeTi₂O₆ films is found to be superior to the TiO₂ films. In comparison to crystalline films, the amorphous films have shown superior electrochemical characteristics. The 500 °C annealed amorphous films have exhibited the most appropriate properties for incorporation in electrochromic devices comprising tungsten oxide as the primary electrochromic electrode.