Gas thermal conductivity sensor based on SAW

An uncoated surface acoustic wave (SAW) delay line integrated with a suitable film heater is used as a gas sensitive element based on thermal conductivity change. It detects concentrations from 0.1-100% of H₂, O₂, He, and Ar in N₂ in the temperature range from 20-150°C. The value and sign of the SAW gas response are controlled by substrate material and reference gas     

Carbon Nanotubes Grown on the Surface of Cathode Deposit by Arc Discharge

Carbon nanotubes prepared by de arc discharge of graphite electrodes in He and CH₄ gas took markedly different morphology. Thick nanotubes embellished with many carbon nanoparticles were obtained by evaporation under high CH₄ gas pressure and high arc current. Thin and long carbon nanotubes were obtained under a CH₄ gas pressure of 50Torr and an arc current of 20A for the anode with a diameter of 6mm.     

Kinetics of Carbon Multi-wall Nanotube Synthesis by Catalytic Pyrolysis of Methane

By method of isothermal gravimetry at 600-700°C, CH₄ concentration 32-100% in Ar and 91-100% in H₂ under atmospheric pressure the kinetics of CH₄ pyrolysis under Ni/La₂O₃ catalysts is studied. Estimated apparent activation energy of reaction is 73 kJ/mol for fresh catalyst and 71 kJ/mol for aged one. The reaction order on CH₄ changes from 1.05 at 600°C to 1.3 at 700°C. The influence of H₂ concentration on the reaction rate is more complicated. On the basis of kinetics measurements continuously working laboratory-scale reactor with gas and catalyst counter-flow is constructed and tested.     

Gas Storage in Fullerenes

Fullerenes and in particular C₆₀ have been shown to store effectively a wide range of gases from simple monatomic rare gases to diatomics and polyatomics. A review of the research in this area conducted at ANSTO is given. The trapping of Ar, Kr, Xe, and CO₂ are discussed in detail whilst preliminary results pertaining to N₂O, CH₄, CF₄, C₂H₆ and SF₆ are also reported. A range of techniques have been used to elucidate both the structure of the new fullerene intercalated solid and the trapped gas itself. The preponderant techniques used, include infra-red absorption spectroscopy (IR), X-ray powder diffraction a (XRD), neutron powder diffraction (NRD), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA).     

DIAMOND FILMS FROM CH3OH SYSTEMS

Polycrystalline diamond films were obtained on silicon (111) substrates by the microwave plasma-assisted chemical-vapour-deposition (CVD) method from theCH₃OH+H₂ systems.When CH₃OH,CH₃COCH₃, H₂ were used as the source gases.the diamond epitaxial films were obtained on the synthesized single-crystal diamond (100), (110) and (111) substrates too. From the experimental results, we could discover that: CH₃OH, CH₃COCH₃ and other hydrocarbon gases could also be used as suitable source gases for the growth of diamond films.     

CHEMICAL VAPOR DEPOSITION OF TITANIUM CARBIDE ON AISI M2 TOOL STEELS AND Si3N4-TiC CERAMIC COMPOSITE

TiC deposition experiments were performed on high speed steel and on Si₃N₄-TiC composite ceramic cutting tools through chemical vapor deposition (CVD) using gaseous mixture of TiCl₄, CH₄, and H₂. The effects of the deposition temperature and the composition of reactant gases on deposition rate, structure and microhardness of the TiC film were investigated. Experimental apparatus and deposition procedures are also presented. Deposition at 1323K with (CH₄/TiCl₄) ratio of 1.2 gives the optimum mechanical properties of the film for AISI M2 steel substrate while Si₃ N₄-TiC composite shows its maximum strength at 1373K and 1.3(CH₄/TiCl₄).     

Effects of oxygen on multiwall carbon nanotubes growth by PECVD

Multiwall carbon nanotubes (MWCNTs) were grown by dielectric barrier discharge (DBD)-type plasma enhanced chemical vapor deposition (PECVD) method in downstream. The temperature was 973 K and the compositions of gases were methane, hydrogen and oxygen in the total pressure of 0.05 MPa. The effect of O₂ concentration in the mixture on the configuration of carbon nanotubes (CNTs) was investigated in detail. Results from scanning electron microscope (SEM) and transmission electron microscope (TEM) showed that CNTs grown in CH₄/H₂ (38.6%/61.4%, volume) mixture have many defects and contained disordered graphitic materials. With the addition of appropriate amount of O₂ (∼ 0.67%), high-purity CNTs could be obtained. However, no CNT, even no carbon matrix existed under the condition of an excessive oxygen concentration (> 1.0%, volume) in the mixture. In order to understand the role of O₂ during CNTs growth, optical emission spectroscopy (OES) was in-situ employed and the results predicted that the improvement of CNTs quality in O₂ addition was attributed to the effect of OH oxidation from the reaction of atomic oxygen with hydrogen in the plasma.     

Characterization of multilayer films of Ti---Al---O---C---N system prepared by pulsed d.c. plasma-enhanced chemical vapor deposition

TiAlN/TiN, TiAlCN/TiAlN/TiN and TiAlON/TiAlN/TiN multilayer films were prepared on steel substrates by pulsed d.c. plasma-enhanced chemical vapor deposition (PECVD) at 823 K using gas mixtures of TiCl₄, AlCl₃, H₂, N₂, CH₄, O₂ and Ar. We studied the structural, compositional, mechanical and chemical properties of these films. Fracture cross-sections of the TiAlN and TiAlCN films showed columnar structure. On the other hand, those of the TiAlON films showed amorphous-like dense structure. X-Ray diffraction (XRD) analyses showed that the TiAlN, TiAlCN and TiAlON films had NaCl structure. The XRD peaks of the TiAlON films were broad. Glow discharge optical emission spectroscopy (GDOS) analyses proved that these films had multilayer structure. The Vickers hardness of the TiAlN/TiN, TiAlCN/TiAlN/TiN and TiAlON/TiAlN/TiN multilayer films were 2608, 2815 and 1444 Hv, respectively. These multilayer films had higher oxidation resistance and better tribological properties than the TiN single-layer films. The TiAlCN/TiAlN/TiN multilayer films showed the best wear resistance. Furthermore, these multilayer films demonstrated superior corrosion resistance in a molten aluminum alloy at 953 K. The TiAlON/TiAlN/TiN multilayer films indicated the best corrosion resistance.     

FTIR spectroscopy of hydrogen, carbon monoxide, and methane adsorbed and co-adsorbed on zinc oxide

Adsorption of dihydrogen, carbon monoxide and methane, and co-adsorption of H₂/CO, H₂/CH₄ and CO/CH₄ on zinc oxide was studied by means of Fourier transform infrared spectroscopy. Besides the already known dissociation of dihydrogen and molecular adsorption of CO, methane was found to be adsorbed molecularly on coordinatively unsaturated Zn²⁺ ions. Adsorption lowers the CH₄ symmetry from T_d to C_3v, which is reflected in activation of the v₁ (symmetric stretching) mode and discrete frequency shifts of the v₃ (antisymmetric stretching) and ν₄ (bending) modes. Co-adsorption of the above gases on ZnO having pre-adsorbed hydrogen results, in all cases, in a bathochromic shift of the v(Zn–H) band and a hypsochromic shift of the v(O–H) band, which originally appear at 1710 and 3492 cm⁻¹, respectively. The magnitude of these shifts depends upon the nature of the co-adsorbed gas.     

On the Evaporation of C60 in Vacuum and Inert Gases at Temperatures Between 830 K and 1050 K

The binary diffusion coefficient D_AB of subliming C₆₀ in He, N₂ and Ar gas has been determined at a gas pressure between 5 and 10 kPa. It resulted D_AB/(cm^2/s)=D_o(P_o/P_t(T/T_o)ⁿ as a function of the total pressure P_t of the vapor phase and temperature T. At T_o=273 K and P_o=1.0133×10⁵ P_a, the values D_o = (0.059±0.004) cm²/s, (0.011±0.003) cm²/s, (0.012±0.007) cm²/s, n = 1.77±0.06, 2.02±0.18, 1.77±0.37 were obtained for He, N₂, Ar and (830-1000) K, (800-1020) K, (875-1095) K, respectively. Only 40 wt% of the initial C₆₀ material yielded reliable D_AB where the vapor pressure of C₆₀ followed log₁₀(P/Pa) = -(8976±60)/T/K+(11.05±0.07) for T between 640 and 1055 K.     

掺氮金刚石电极性能及其氧化降解硝基苯研究

采用热阴极直流辉光等离子体化学气相沉积法制备亚微米晶氮掺杂金刚石膜(NDD), 采用SEM分析样品的表面形貌, 分别用Hall测试和循环伏安法测试氮掺杂金刚石电极的电学和电化学性能。实验结果表明, 当氮气流量低于30 sccm时, 膜的电导率随氮气流量的增大略有提高; 氮气流量继续增大则电导率迅速下降, 电导率最大为5.091 S/cm。氮掺杂金刚石电极具有较好的伏安性能, 在酸性、中性和碱性介质中均具有较宽的电位窗口和较低的背景电流。以硝基苯为目标污染物测试NDD材料作为阳极氧化降解的电催化性能。在0.1 mol/L Na₂SO₄溶液的支持电解质中, 以氮掺杂金刚石为阳极降解0.5 mmol/L的硝基苯, 反应时间300 min, 硝基苯的降解率达到94%, 化学需氧量(COD)去除率约68%。     

Hysteresis effects in the sputtering process using two reactive gases

The reactive sputtering process involving two reactive gases has been investigated. Sputtering titanium in the presence of oxygen and nitrogen in argon was studied by means of optical emission and mass spectrometries. The experiments reveal the mechanism of the mixed target poisoning. Increasing the nitrogen supply in the presence of a constant oxygen supply forces the reactive sputtering system to avalanche from a high-rate metal-sputtering mode to a low-rate compound-sputtering mode at a lower N₂-to-Ar ratio as compared with the single reactive gas Ar/N₂ reactive sputtering process. The amount of the oxygen admixture, however, also affects the character of the avalanche and the corresponding hysteresis effect. At a definite level of constant oxygen supply the Ar/N₂ processing behaviour becomes irreversible, successive decreasing of the nitrogen supply to zero in this case is not sufficient to force the process to return back to the high-rate metal-sputtering mode. A “process trapping” effect appears.

The coupling effect between the consumption of both reactive gases N₂ and O₂ during increase and successive decrease of N₂ in the presence of a constant O₂ supply is reflected in the dependencies of the respective partial pressures. The cause of the observed trapping effect, the shift and the change of the character of the sputtering rate hysteresis curve may be explained in terms of the link between the consumption of the reactive gases and the corresponding target condition. The experimental findings support the theoretical model of the two-gases reactive-sputering process recently presented by the authors.     

Characterization of indium zinc oxide thin films prepared by pulsed laser deposition using a Zn3In2O6 target

Using a Zn₃In₂O₆ target, indium-zinc oxide films were prepared by pulsed laser deposition. The influence of the substrate deposition temperature and the oxygen pressure on the structure, optical and electrical properties were studied. Crystalline films are obtained for substrate temperatures above 200°C. At the optimum substrate deposition temperature of 500°C and the optimum oxygen pressure of 10⁻³ mbar, both conditions that indeed lead to the highest conductivity, Zn₃In₂O₆ films exhibit a transparency of 85% in the visible region and a conductivity of 1000 S/cm. Depositions carried out in oxygen and reducing gas, 93% Ar/7% H₂, result in large discrepancies between the target stoichiometry and the film composition. The Zn/In (at.%) ratio of 1.5 is only preserved for oxygen pressures of 10⁻²–10⁻³ mbar and a 93% Ar/7% H₂ pressure of 10⁻² mbar. The optical properties are basically not affected by the type of atmosphere used during the film deposition, unlike the conductivity which significantly increases from 80 to 1400 S/cm for a film deposited in 10⁻² mbar of O₂ and in 93% Ar/7% H₂, respectively.     

初始压力和富氧系数对CH4/O2/N2预混气体爆炸特性的影响

为了探究甲烷CH4在富氧和非常压条件下的爆炸危险性,确保CH₄气体在不同工况下的安全使用,借助5 L圆柱形爆炸装置,研究了初始压力p₀和富氧系数E对CH₄/O₂/N₂爆炸特性的影响。包括最大爆炸压力p_max、最大压力上升速率（dp/dt）_max和最大压力到达时间t_c等衡量CH₄爆炸安全性的指标。结果表明:当E为 0.21、0.25和0.30时,p_max随p₀的增加始终线性上升;而当E为 0.35和0.40时,p_max随p₀的增加先缓慢线性上升、后快速线性上升;（dp/dt）_max随p₀的增加分为线性上升和一阶指数快速上升。在E为0.21和0.25时,t_c随p₀的增加而线性增大,因为在燃烧初始阶段CH₄活化自由基的销毁速率增加,降低了反应速率和燃速,引起预混气体t_c的延长;但随着E的增加,氧气的促进作用与自由基销毁的抑制作用形成新的竞争效应,使得t_c先增加、后下降。     

Cubic Boron Nitride Formation by PECVD in the B-N-Cl-H System: Ionic and Chemical Aspects

BN thin films have been synthesized by r.f. Plasma Enhanced Chemical Vapor Deposition (PECVD) from BCl₃ / N₂ /H₂ / Ar mixtures. c-BN formation has been studied through correlations between gas phase characterization (by Optical Emission Spectroscopy, Mass Spectrometry and electrical measurements) and thin film analysis (by Fourier Transformed Infra Red Spectrometry for structure determination).

In particular, the occurrence of physical and possible chemical mechanisms is studied with the help of post-treatments of as-deposited BN coatings in pure Ar, Ar/H₂ and Ar/Cl_b plasma mixtures. It is shown that, in addition to the well known ion-induced formation of the cubic phase, chemical etching also occurs, due to the presence of hydrogen and chlorine species, which leads to a relative increase in the cubic content of the thin film.     

Ozone-enhanced molecular beam deposition of nickel oxide (NiO) for sensor applications

For the deposition of nickel oxide (NiO) a molecular beam deposition process in an ozone atmosphere was developed. Pure gaseous ozone is received from a cooling system, which stores only O₃ at −78°C from a O₂/O₃ gas mixture stream, created with an ozone generator. The ozone is released by heating up the system to room temperature. For the deposition process nickel is evaporated while a constant ozone partial pressure is adjusted in the growth chamber. The reactive species of ozone reacts on the substrate surface with the impinging metal atoms to form the compound. This process was carried out in an ultra high vacuum (UHV) chamber to create pure nickel oxide films at room temperature and to study the fundamental layer properties for sensor applications. These films were characterized with respect to their stoichiometric and optical properties by Auger Electron spectroscopy and ellipsometry. The gas sensitivity of the films (as deposited and annealed) on various gases (H₂, NH₃, NO₂, SO₂, CO) was investigated by work function measurements.     

PRODUCTION OF CARBON NANOTUBES IN AIR

Carbon nanotubes were produced by plasma discharging of graphite electrodes in air at 1 atm. The combined yield of CNTs and carbon nanoparticles is ∼20 wt % relative to the mass of cathode deposits or 14 wt% of graphite electrode consumed. The yields of CNTs and carbon nanoparticles under different inert gas atmospheres, such as He, Ar, N₂, and air were compared.     

高导电性热电池正极材料Ni-NiCl2复合物的原位合成与放电性能研究

作为高电位化合物, NiCl₂是高功率热电池的理想正极材料, 但是其比表面积小、导电性差, 影响了其热电池的应用。采用升华和原位合成技术, 制备具有大比表面积和高导电性的热电池正极材料Ni-NiCl₂复合粉体: 首先将市售含结晶水的NiCl₂·6H₂O经过低温干燥处理, 脱水后形成黄色粉体, 然后在Ar气氛下, 经850~900℃进行升华处理, 将收集的升华粉体置于Ar+H₂还原气氛中, 300~500℃温度下还原热处理1 h, 得到Ni-NiCl₂复合粉体。论文讨论并分析了粉体的热力学、晶体结构、原位合成过程和初步的电化学性能。结果表明: 升华过程中, NiCl₂晶体沿着垂直于c轴的方向生长为直径200~300 µm的层状结构; 与纯NiCl₂作为正极材料的LiSi︱LiCl-LiBr-LiF︱NiCl₂热电池组的放电曲线相比, Ni-NiCl₂复合粉体(5wt%单质Ni)为正极材料的热电池放电曲线更加平稳, 激活时间更短。     

Optical emission spectroscopy study of positive direct current bias enhanced diamond nucleation

High nucleation density and crystalline diamond films were deposited on a mirror-polished Si(100) substrate by horizontal microwave plasma chemical vapor deposition using a two step process consisting of positive direct current (dc) bias enhanced nucleation and growth. Optical emission spectroscopy was employed to investigate in situ the plasma emission characterization during positive biasing process. Emission lines from the Balmer series of atomic hydrogen, molecular hydrogen, CH, C₂, and Ar were observed in the visible and ultraviolet ranges when CH₄, H₂, and Ar were used as the reactant gases. The dependence of plasma emission spectra on the deposition parameters, such as biasing voltage, methane concentration and working pressure was investigated. The relative concentrations of neutral atomic hydrogen were estimated by using the Ar emission at 750.4 nm as an actinometer. A significant variation in the emission intensity of the radicals was measured with a change in the biasing voltage. The correlation between the spectra of some species and the quality of diamond films was studied. The results show that CH and C₂ both were important precursor in the diamond deposition, while C₂ was associated with the presence of amorphous phase in the films during positive dc biasing process.     

Rare-Gas Intercalation Into Fullerene Interstices

We review our neutron diffraction studies of the intercalation of the rare gases into the interstices of C60 at pressures ranging from 0 to 6 kbar, primarily at room temperature, but also at other temperatures. Room temperature compressibilities of C₆₀ for both the face-centered-cubic and simple-cubic phases using Ar, which does not intercalate, as the pressure medium are in excellent agreement with the earlier work of David et al, while the values for He and Ne are slightly smaller than those using Ar. The rates of intercalation and release of Ne, at a number of different temperatures, have been measured and show that, at a given temperature, intercalation is much slower than release. Structural refinements of the Ne intercalated C₆₀ have been carried out for room temperature samples at many different pressures. These data suggest that Ne only intercalates into the octahedral hole and that the occupancy increases smoothly with pressure.