助熔剂法制备硼酸铝晶须

以Al（OH）3和H3BO3为原料,分别以MnO2、Fe2O3为助熔剂制备硼酸铝晶须,研究助熔剂对晶须形貌的影响。研究发现,在1350℃煅烧6h,试样的物相为硼酸铝（9Al2O3·2B2O3）。以MnO2为助熔剂的试样晶须的直径为1μm～6μm,长径比较小;以Fe2O3为助熔剂的试样晶须的直径为0．2μm～1μm,长径比〉10。     

Thermophoretic Deposition of Small Particles in the Modified Chemical Vapor Deposition (MCVD) Process

Thermophoresis is conclusively established as the particulate deposition mechanism in the MCVD process by comparing experimental measurements and quantitative theoretical predictions. The deposition efficiency, E , is defined as the fraction of the silica in the gas stream (initially as SiCl₄) that is deposited. For normal MCVD operating conditions, the deposition efficiency is only a function of the equilibrium temperature, T_e , at which the gas and walls equilibrate downstream of the torch and the temperature, T_r , at which reaction occurs. The deposition efficiency is ∼0.8[1-( T _e/ T _r)]. It is determined that T_e is a strong function of the torch traverse velocity, the traverse length, the temperature of the ambient environment, and the tube wall thickness but only a weak function of the gas flow rate. At high gas flow rates, the efficiency is limited by incomplete reaction.     

Formation and Sintering Characteristics of Aluminum Borate Whiskers

A boric acid-stabilized aluminum acetate powder was decomposed to aluminum borate (Al₁₈B₄O₃₃) by calcining at 1000°C. The powder was then ball-milled, compacted, and fired to temperatures of 1500°, 1600°, and 1700°C for a period of 1 h. The resulting aluminum borate ceramic had a whiskerlike grain morphology, with the whisker length approaching 20 μm and a diameter of 2–3 μm. The sintered compact showed no shrinkage upon firing, had a porosity of ∼50%, a narrow pore size distribution, and an average pore size of 1–3 μm.     

Aluminum Silicate Films Obtained by Low-Pressure Metal-Organic Chemical Vapor Deposition

Amorphous alumina-silica films with film thickness of 0.41–2.69 μm were prepared on glass and silicon substrates by metal-organic chemical vapor deposition using a mixture of aluminum tri-sec-butoxide (ATSB), hexamethyldisilazane (HMDSN), and argon. By controlling the inputs of ATSB and HMDSN, alumina-silica thin films could contain varied compositions and adjustable properties. Basically, the codeposition of alumina and silica to form alumina-silica using ATSB and HMDSN had a faster growth rate than their individual components. The internal stress could be adjusted by deposition temperature and reactant inputs. Adhesion could be improved by having a silicon-rich thin film, whereas an aluminum-rich film could have slightly higher hardness. Optical properties, e.g., refractive index and optical transmittance, were also measured.     

Effect of Cobalt(II) Oxide and Manganese(IV) Oxide on Sintering of Tin(IV) Oxide

Additions of 0. 5 to 2. 0 mol% of CoO or MnO₂ onto SnO₂ promote densification of this oxide up to 99% of theoretical density. The temperature of the maximum shrinkage rate ( T_M ) and the relative density in the maximum densification rate (p*) during constant sintering heating rate depend on the dopant concentration. Thus, dopant concentration controls the densifying and nondensifying mechanisms during sintering. The densification of SnO₂ witih addition of CoO or MnO₂ is explained in terms of the creation of oxygen vacancies.     

Characterization of Lead Oxide Thin Films Produced by Chemical Vapor Deposition

As a step toward creating a chemical vapor deposition (CVD) process for PbTiO₃ thin films, lead oxide films were deposited and then examined. The reaction was oxidation controlled, with an apparent activation energy of 97 kJ/mol in this low-temperature, low-pressure metalorganic CVD (MOCVD) process. Across the deposition parameters examined, several distinct types of morphology were observed. Growth occurred as a combination of layer-on-layer and island formation. The structural and chemical properties of the lead oxide were examined by Auger electron spectroscopy, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and electron diffraction. Various forms of lead oxide were produced (litharge, massicot, and scrutinyite, singly or in combination with each other). The deposition parameters used in this work showed a tendency to maintain the same crystalline form from the initial nucleation stages through post-deposition annealing. Lead oxide formed readily on SiO₂ surfaces (contrary to studies by other researchers) and, indeed, reacted with the underlying SiO₂ layer.     

化学沉积法制备功能性化学镀锡层的研究

在紫铜表面制备了功能性化学镀锡层。用扫描电镜观察了化学镀锡层的表面形貌,用X射线衍射仪分析了化学镀锡层的物相,并用电化学工作站对化学镀锡层的耐蚀性进行了测试。结果表明:化学镀锡层表面比较致密,呈不规则的柱状结构;化学镀锡层的XRD图谱中出现了六个明显的锡衍射峰;化学镀锡层能为紫铜提供有效的保护,提高紫铜在质量分数为3.5%的氯化钠溶液中的耐蚀性。     

Simultaneous Chemical Vapor Deposition of Boron Nitride and Aluminum Nitride

Two chemically different phases, hexagonal BN and AIN, were simultaneously produced by chemical vapor deposition (CVD) using an impinging jet reactor and the BCl₃─AlCl₃─NH₃─Ar reagent system. The microstructure of the BN + AIN composite coatings was strongly dependent on temperature, pressure, and BCl₃ and AlCl₃ concentrations. The growth characteristics of BN and AIN in the codeposition system were similar to those expected from the single-phase deposition processes (i.e., BN-CVD and AIN-CVD), except the growth of AIN whiskers was accentuated, and competition between BN and AIN deposition in the composites was suspected to be the cause of less-crystalline deposits. In both BN + AIN-CVD and AIN-CVD, the growth of AIN whiskers became more apparent with increasing pressure or temperature. The codeposition behavior observed experimentally was compared with thermodynamic predictions.     

氧化铝陶瓷表面化学气相沉积钛涂层的制备及性能

利用卤化物还原原理,以Ti粉和I2粉为反应原料,通过化学气相沉积的方法在Al2O3陶瓷基体上制备了金属Ti涂层。考察了原料配比、加热温度及保温时间等工艺参数对涂层沉积的影响。通过X射线衍射仪分析了涂层的物相组成。利用扫描电子显微镜及能谱仪对涂层的微观组织形貌及成分进行了分析。采用座滴法考察铜与沉积了涂层的氧化铝陶瓷间的润湿性。研究结果表明,化学气相沉积法在氧化铝陶瓷表面制备Ti涂层的适宜工艺参数为:Ti与I2的质量比=1∶3,沉积温度为1 100℃,沉积时间为60min。所获得的Ti涂层纯度较高,具有明显的(110)晶面择优取向性,涂层与陶瓷结合良好。铜与涂层间的润湿角在1 113℃时为57°。     

Effect of Pressure on Plasma-Assisted Chemical Vapor. Deposition of Silicon Oxide(s)

In most chemical vapor deposition processes, the film growth rate increases with the concentrations of the reactant gases. However, in the plasma-assisted chemical vapor deposition of silicon oxide films, the deposition rate decreases when the concentrations of silane and nitrous oxide are increased by enhancing the reactor pressure from 0.5 to 2 torr (66 to 270 Pa). The deposition rate and the plasma properties have been examined for various reactor pressures to seek an improved understanding of the deposition process. Photo emissions from the plasma were monitored to determine the species present in the plasma and to calculate electron energy and density. With the increase in pressure, both the electron temperature and density decreased, and, consequently, the concentration of active species decreased. Although the concentrations of both silane and nitrous oxide increased with total pressure, the deposition rate decreased. The results emphasize the crucial importance of electron energy and density to generate sufficient concentration of active species responsible for film growth.     

化学气相沉积六方氮化硼涂层的制备及应用

六方氮化硼(h-BN)涂层是一种性能优异的功能陶瓷材料,介绍了化学气相沉积( CVD)六方氮化硼涂层的制备工艺,综述了h-BN涂层的优异性能和应用现状,并对其研究发展趋势进行了展望.认为先驱体性能存在缺陷、沉积机理复杂、工艺可控性差、生产成本高是目前CVD制备h-BN涂层存在的主要工艺问题,指出今后还需在新型先驱体的研发和使用、沉积机理的深入探究、工艺优化和放大等方面开展深入研究,以实现h-BN涂层的大规模工业化生产和应用.     

Thermodynamic and Experimental Study of High-Purity Aluminum Nitride Formation from Aluminum Chloride by Chemical Vapor Deposition

Thermodynamic calculations in the systems Al-Cl, Al-Cl-N, and H-Al-Cl-N were used to assess the capabilities of AlCl₃ or mixtures of AlCl₃ with Al to produce AlN by chemical vapor deposition (CVD) techniques. Direct nitridation (N₂ as reaction agent) is possible only at high temperatures (≥1500 K), using AlCl₃–Al mixtures. Reaction with NH₃ at equilibrium gives low yields but the suppression of NH₃ dissociation yields near 100%, which makes the method suitable for powder production, coating, and single-crystal growth. AlN with less than 1 wt% oxygen was obtained from technical grade AlCl₃ by this process. The formation of both amorphous AlN powder and crystalline AlN coatings was observed. It is assumed that the formation of AlCl₃· x NH₃ adducts by mixing of Al-Cl vapor and NH₃ at temperatures ≤1273 K prevents NH₃ dissociation and favors the production of amorphous AlN.     

Kinetic and Thermodynamic Analyses of Chemical Vapor Deposition of Aluminum Nitride

AIN coatings were prepared by chemical vapor deposition from the AlCl₃—NH₃—Ar reagent system using an impinging jet reactor in the temperature range of 700° to 1100°C. A mass transfer model and thermodynamic calculations were used to analyze the deposition data. The AIN-CVD process could be approximated by calculating mass transfer—thermodynamic limits at low AlCl₃ concentrations. The AIN deposition rate decreased drastically with increasing temperature above 1000°C in agreement with thermodynamic predictions. At high AlCl₃ concentrations, a surface kinetic mechanism involving AlCl₃ adsorbed on the deposition surface appeared to be the rate-limiting step. The AIN deposition rate decreased on increasing the AlCl₃ concentration or total pressure. The crystalline structure of AIN was strongly influenced by the processing parameters. The AIN coatings became highly crystalline and preferentially oriented with an increase in the AlCl₃ concentration or pressure.     

Composition and Conductivity of Tin Oxide Films Prepared by Pyrohydrolytic Decomposition of Tin(IV) Compounds

The conductivity of thin poly crystalline Sn oxide films prepared by spraying solutions of Sn(IV) compounds onto glass or quartz substrates was studied. Conductivity was decreased by increasing the temperature or prolonging the time of heating after hydrolysis, by substituting SnBr₄ for SnCl₄, and by substituting O₂ for N₂ during spraying. These effects are explained in terms of nonstoichiometry of the sample and the presence of residual halogens in the crystal lattice as detected by ion-probe analysis.     

Tungsten Oxide Nanorods Array and Nanobundle Prepared by Using Chemical Vapor Deposition Technique

Tungsten oxide (WO₃) nanorods array prepared using chemical vapor deposition techniques was studied. The influence of oxygen gas concentration on the nanoscale tungsten oxide structure was observed; it was responsible for the stoichiometric and morphology variation from nanoscale particle to nanorods array. Experimental results also indicated that the deposition temperature was highly related to the morphology; the chemical structure, however, was stable. The evolution of the crystalline structure and surface morphology was analyzed by scanning electron microscopy, Raman spectra and X-ray diffraction approaches. The stoichiometric variation was indicated by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy.     

Formation and Characterization of Amorphous Aluminum Nitride Powder and Transparent Aluminum Nitride Film by Chemical Vapor Deposition

Based on thermodynamic predictions that, in the gas-phase system AlCl₃/NH₃, AlN can be produced up to the theoretical yield, the performance of a chemical vapor deposition (CVD) reactor suitable for continuous powder production is investigated. Under the applied reaction conditions and reactor configuration, fine spherical AlN powders and transparent AlN films could be preferentially obtained. The generated amorphous CVD AlN powder is characterized by a BET surface area of 23.5 m²/g. The powder deposition rate was determined to be 3.5 g/h.     

Rapid Formation of Zinc Oxide Films by an Atmospheric-Pressure Chemical Vapor Deposition Method

Zinc oxide films were prepared by an atmospheric-pressure chemical vapor deposition method using (acetylacetonato)-zinc as a source material. Transparent and uniform ZnO films of considerable area (20 × 70 mm, ∼0.3 μm thick) could be obtained easily on a crown glass (CGW #200) with a high deposition rate. The deposition rate first remained constant with increasing substrate temperature ( T _s), then increased abruptly from 120 nm/min at T _s= 550°C to 220 nm/min at T _s= 600°C, and finally stopped increasing above T _s= 600°C. The maximum preferred orientation and best crystallinity of the films were obtained at T _s= 550°C.     

Combustion Synthesis of Aluminum Nitride Particles and Whiskers

Aluminum nitride (AlN) was produced via the combustion synthesis of loosely packed aluminum powder (pore fraction of ∼0.8) in a graphite reactor that was lined with permeable carbon felt. Almost-complete conversion was achieved with a forced flow of nitrogen for beds 50-150 mm deep (mass of 200-650 g). The product was in the form of a loosely aggregated bed, with regions of distinct morphology, and had a predominantly whisker morphology. Some control over the microstructure was possible by changing the processing parameters. The addition of 5% of ammonia to the nitrogen resulted in a uniform production of whiskers, whereas a 50% solid-phase dilution with AlN favored the production of particles.