Comparative Study on Decomposition of CFCl<Subscript>3</Subscript> in Thermal and Cold Plasma

Decomposition of CFCl₃ was investigated in an RF inductively coupled thermal reactor in neutral, oxidative and reductive conditions, and in a silent electric discharge (cold plasma) in neutral and oxidative conditions, respectively. In RF thermal plasma reactor, in neutral conditions, mainly gaseous products and minor amount of solid soot was formed. About 50% the soot could be extracted by toluene. Both the gas phase and the extract contained a wide range of aliphatic and aromatic compounds including chlorine and fluorine containing polyaromatic hydrocarbons (PAHs). In oxidative conditions much less soot was formed as compared to the neutral case. The solid product contained about 45% extractable fraction even in oxidative conditions. However, the extract contained less PAHs than in neutral conditions. In reducing atmosphere the soot yield was similar to the neutral case, but the soot contained 29% extractable fraction only. The extract consisted of polyhalogenated aromatic and polyaromatic hydrocarbons as main components. In neutral conditions different chlorofluorocarbons (CFCs) and chlorine were detected as gaseous products in cold plasma. In oxidative conditions, as final products of decomposition CO₂, CFCs and Cl₃ were formed.     

Comparative Study of the Decomposition of CCl4 in Cold and Thermal Plasma

Decomposition of carbon tetrachloride was studied in an inductively coupled thermal plasma reactor and in a low temperature, non-equilibrium plasma reactor, in neutral and oxidative conditions, respectively. In neutral conditions formation of solid soot, aliphatic- and cyclodienes was observed in equilibrium, and products, such as Cl₂ and C₂Cl₆ were detected in non-equilibrium plasma. Feeding of oxygen into the thermal plasma reactor depressed both soot and dienes formation and induced the formation of oxygen containing intermediates and products. GC-MS analyses of the gaseous products and the extract of the soot referred to as complex decomposition and recombination mechanism at given conditions. Presence of oxygen in the low temperature plasma reactor results in the formation of carbonyl compounds as intermediers. CO₂ and Cl₂ revealed as final products of CCl₄ decomposition in cold plasma.     

Difference in Conversions Between Dimethyl Sulfide and Methanethiol in a Cold Plasma Environment

This study compared the conversion of two malodorous substances, dimethyl sulfide (CH₃SCH₃, DMS) and methanethiol (CH₃SH) in a cold plasma reactor. The DMS and CH₃SH were successfully destroyed at room temperature. DMS decomposed less than CH₃SH at the same conditions. In oxygen-free condition, CS₂ and hydrocarbons were the major products, while SO₂ and CO_x were main compounds in oxygen-rich environments. The DMS/Ar plasma yielded more hydrocarbons and less CS₂ than that of CH₃SH/Ar plasma. In the CH₃SH/O₂/Ar plasma, rapid formation of SO and CO resulted in the yields much more amounts of SO₂ and CO₂ than those in the DMS/O₂/Ar plasma; and remained only a trace of total hydrocarbons, CH₂O, CH₃OH, CS₂, and OCS. The major differences between the reaction mechanisms of DMS and CH₃SH were also proposed and discussed.     

Effects of Precursors and Plasma Parameters on Fullerene Synthesis in RF Thermal Plasma Reactor

Synthesis of fullerenes from graphite powders of different grade was studied in a radiofrequency (RF) plasma reactor. Dependence of fullerene yield on the properties and feed rate of precursors and on the helium content of plasma gas was studied in details. The fullerene yield was influenced by the mean size and the thermal conductivity of graphite particles on the one hand, and the helium content of the gas phase on the other. Soot containing fullerene mixture of 5.9% was produced in best conditions found in this work. The main component of the fullerene mixture was C₆₀. In addition, it contained about 30% of C₇₀ (corresponding to a C₆₀/C₇₀ mass ratio of 2.64). Higher fullerenes such as C₈₄ were also detected by mass spectroscopy (MS) and high performance liquid chromatography (HPLC).     

Kinetic Modeling of the Decomposition of Carbon Tetrachloride in Thermal Plasma

Decomposition of carbon tetrachloride in a RF thermal plasma reactor was investigated in argon atmosphere. The net conversion of CCl₄ and the main products of its decomposition were determined from the mass spectrometric analysis of outlet gases. Flow and temperature profiles in the reactor were calculated and concentration profiles of the species along the axis of the reactor were estimated using a newly developed chemical kinetic mechanism, containing 12 species and 34 reaction steps. The simulations indicated that all carbon tetrachloride decomposed within a few microseconds. However, CCl₄ was partly recombined from its decomposition products. The calculations predicted 70\% net conversion of CCl₄, which was close to the experimentally determined value of 60\%. A thermodynamic equilibrium model also simulated the decomposition. Results of the kinetic and thermodynamic simulations agreed well above 2000 K. However, below 2000 K the thermodynamic equilibrium model gave wrong predictions. Therefore, application of detailed kinetic mechanisms is recommended for modeling CCl₄ decomposition under thermal plasma conditions.     

Study of The Mechanism and Kinetic Parameters of The Thermal Decomposition of Cobalt Sulphate Hexahydrate

Thermogravimetry (TG-DTG), and differential thermal analysis (DTA) were used in the study of the kinetics of decomposition of cobalt sulphate hexahydrate under an air atmosphere. The kinetics of the particular stages of CoSO₄ 6H₂ O decomposition were evaluated from the dynamic mass loss data. The values of the kinetic parameters for each stage of the thermal decomposition were calculated from the α(T) data by using the integral method, applying the Coats-Redfern approximation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Methane Decomposition in a Barium Titanate Packed-Bed Nonthermal Plasma Reactor

The behavior of lattice oxygen species of the ferroelectric material during methane oxidation was investigated using a nonthermal plasma reactor packed with BaTiO ₃ pellets. Lattice oxygen species in BaTiO ₃ play an important role in the formation of N ₂ O and the oxidation of CH ₄ . The oxidation products such as CO and CO ₂ were formed from independent reaction pathways. Lattice oxygen species were able to preferentially oxidize the carbon species deposited on the pellet surface into CO. Also, N ₂ O and NO _x were independently formed in the N ₂–O ₂ reaction, suggesting that different oxygen species give N ₂ O and NO _x. N ₂ O was produced by the oxidation of molecular nitrogen with lattice oxygen species.     

Recent Studies on the Decomposition of n-Hexane and Toluene in RF Thermal Plasma

Thermal decomposition of volatile organic compounds (VOCs) such as n-hexane and toluene has been studied in an inductively coupled thermal plasma reactor, at atmospheric pressure, in neutral and oxidative conditions, respectively. Thermodynamic calculations were performed for predicting the product distribution due to thermal decomposition. Based on these calculations formation of the products observed in the gas phase and in the extract of soot could be interpreted. In neutral conditions formation of soot and PAH was detected to different extent for the different models. The presence of oxygen in the plasma reactor depresses both soot and PAH formation. GC-MS analyses of the gaseous products and the extract of the soot, respectively, refer to as complex decomposition and recombination mechanism in given conditions.     

BaPbO3与BaTiO3多晶态陶瓷缺陷结构对比

BaPbO，是具有类金属导电特性的钙钛矿结构导电陶瓷，其晶体结构由Ba2＋和O^2-离子紧密堆积形成，pb^4＋离子占据由O^2-离子形成的八面体空隙。BaTiO3同为钙钛矿结构的陶瓷材料，由Ba^2＋和O^2-离子紧密堆积形成，Ti^4＋离子占据由O^2-离子形成的八面体空隙。BaPbO3和BaTiO3的A位离子相同,B位离子都为可变价离子。     

Thermal Plasma Synthesis of BaFe12O19 (BaM) Films

Barium Ferrite (BaFe₁₂O₁₉) films have been successfully deposited on high silica glass substrates using an inductively coupled plasma source. Precursor of the metals used was a barium acetate and ferric nitrate solution of controlled concentration which was injected into the hot region of the plasma using a nebulizer. Variables studied included molar ratio of precursor liquid, substrate to plasma distance, plasma torch power, and oxygen concentration in plasma and carrier gas. Films were characterized for microstructure, composition and magnetic properties using scanning and transmission electron microscopy with energy dispersive spectroscopy, X-ray diffraction, and vibrating sample magnetrometry. Results indicate that barium ferrite forms under certain conditions of oxygen content in the plasma and substrate temperature above 800°C. Magnetic properties indicate that there is some degree of preferred orientation of the barium ferrite crystals on the substrate, and coercivity and magnetization correspond to that of a hard magnetic material.     

超级铝热剂Al/Fe2O3的制备、表征及对环三亚甲基三硝胺热分解的影响

采用水热法制备了中空短棒状纳米Fe2O3,并用超声分散法将其与纳米Al颗粒复合为单金属氧化基超级铝热剂.利用X射线粉末衍射(XRD)、傅里叶变换红外(FTIR)光谱、扫描电镜及能量散射光谱仪(SEM-EDS)对样品进行表征.并运用差示扫描量热法(DSC)对比研究了超级铝热剂Al/Fe2O3、Al粉和纳米Fe2O3对环三亚甲基三硝胺(RDX)热分解特性的影响.结果表明:超级铝热剂的加入改变了RDX的热分解过程,并加剧了RDX的二次气相反应;随着超级铝热剂含量的增加,RDX的分解峰峰形发生了明显的改变;Al/Fe2O3、Al粉和Fe2O3对RDX热分解的作用主要表现为二次分解峰逐渐明显且峰温降低.     

H2S and NH3 Removal by Silent Discharge Plasma and Ozone Combo-System

Treatment of H₂S and NH₃ using the non-thermal plasma (NTP) methods was investigated. Two NTP systems were used in this study, one consisting of a multi-cell plate-to-wire reactor (PTW), and the other consisting of an ozonization chamber and the multi-cell PTW reactor. Each cell of the PTW reactor had a sheet of copper foil embedded in dielectric layers as its high voltage electrode and a wired rack as its gounded electrode. Use of the wired rack type electrode allowed large flow throughput, and promoted intense local electric fields. The experiments showed that under constant energy input, the decomposition efficiency of H₂S or NH₃ decreased with increasing initial concentration of the gas, and increased with increasing injected ozone and relative humidity. Injection of NH₃ into H₂S stream did not improve the H2S decomposition efficiency but was necessary for removal of sulfite-containing compounds in the discharge air.     

Thermal Plasma Chemical Vapor Deposition of Si-Based Ceramic Coatings from Liquid Precursors

In this paper a process based on the use of rf inductively coupled plasma is applied for the synthesis and deposition of Si-base ceramic materials (i.e., SiC, Si₃N₄, SiO₂). The starting materials are low-cost liquid disilanes. The atomization process is first investigated and the structure of the resulting coatings is characterized by means of X-ray diffraction, scanning electron microscopy as well as with transmission electron microscopy. Results of the influence of some processing parameters (i.e., chamber pressure, spray distance, substrate cooling, plasma gas nature and composition, precursor composition and atomization parameters) on the phase and microstructure of the coating is reported. Control of the microstructure (or nanostructure) as well as the phase content, namely the / ratio of the phases for SiC and Si3N4, can be achieved with such a synthesis and deposition technique.     

Mg-Al-CO3与Zn-Al-CO3水滑石热稳定性差异的研究

层状双金属氢氧化物（Ｌayered double hydroxides,简称ＬＤＨs）是一种类近年来发展迅速的阴离了型粘土,又称水滑石,其组成通式为[M（II）1－xM(III)x(OH)2]x(OH)2]^x＋Ax/n^n-mH2O,其中M（II）是二介金属离子,M（III）是三价金属离子,A^n-是阴离子,这种材料是由相互平行的层板组成,层板带有永在电荷,层间具有可交换的阴离子以维持电荷平衡,通过离子交换可在层间嵌入不同的基团,制备许多功能材料,被广泛作催化剂、吸附剂及油田化学品等,已引起人们的关注^[1-4]。有关Mg-Al-CO3与Zn-Al-CO3水滑石的合成及性能研究国内外已有大量报道^[1,2],本文对两者热稳定性存在的差异进行了研究,这对深化此类材料的认识具有参考作用。     

Catalytic Effect of Some Chromites on the Thermal Decomposition of KClO4. Mechanistic and non-isothermal kinetic studies

The catalytic effect of two different groups of chromites on the non-isothermal decomposition of KClO₄was studied. TG and DSC curves of the thermal behaviour obtained for KClO₄-alkaline earth chromites (Series 1) mixtures indicate the formation of K₂Cr₂O₇, through a solid-solid interaction, before accelerating the decomposition stage of KClO₄. Such an accelerating effect becomes more pronounced in the case of admixing KClO₄ with some transition metal chromites (Series 2). The results were discussed taking into consideration the electronic configuration of cations and the electrical properties of the chromite catalysts. The presence of coordinatively active cations, able to form surface complex with the oxygen of the perchlorate anion, was proved to be necessary for obtaining an active catalyst. The kinetic parameters and models describing the catalyzed thermal decomposition process of KClO₄ were evaluated by using a computer program that allows the analysis using five different methods. It was found that the adopted kinetic model for pure KClO₄ and that mixed with catalysts from Series 1 is one-dimensional movement of phase boundary. On the other hand, random nucleation mechanism was achieved in the presence of catalysts from Series 2. Finally, a tentative reaction mechanism consistent with the obtained results was suggested. This revised version was published online in July 2006 with corrections to the Cover Date.     

硝酸镁在γ-Al2O3上的热分解及MgO/γ-Al2O3

研究了不同载量时Mg(NO     

SiO_2/Co_3O_4核壳催化剂对AP热分解的催化性能研究

采用改良的St觟ber法制备粒径约为200 nm的单分散球形SiO2颗粒,以此为内核,分别通过液相沉淀法和尿素均匀沉淀法制备包覆形式不同的新型SiO2/Co3O4核壳式纳米催化剂。采用X-射线衍射分析(XRD)、透射电子显微镜(TEM)、红外光谱分析(IR)、拉曼光谱分析(Raman)、BET比表面积测试等手段对产物进行表征,利用差式扫描量热仪(DSC)考察SiO2/Co3O4复合物对高氯酸铵(AP)热分解反应的催化作用,探讨不同包覆形式对其催化活性的影响。结果表明,两种方法制备得到的SiO2/Co3O4复合物分别为层包覆和粒子包覆,比表面积大,具有明显的核壳结构,且粒子包覆形式的SiO2/Co3O4对AP热分解反应的催化效果最好,使AP的高温分解温度降低了110℃,放热量增加了662 J·g-1。     

SiO2/Co3O4核壳催化剂对AP热分解的催化性能研究

采用改良的Stöber法制备粒径约为200 nm的单分散球形SiO₂颗粒,以此为内核,分别通过液相沉淀法和尿素均匀沉淀法制备包覆形式不同的新型SiO₂/Co₃O₄核壳式纳米催化剂。采用X-射线衍射分析(XRD)、透射电子显微镜(TEM)、红外光谱分析(IR)、拉曼光谱分析(Raman)、BET比表面积测试等手段对产物进行表征,利用差式扫描量热仪(DSC)考察SiO₂/Co₃O₄复合物对高氯酸铵(AP)热分解反应的催化作用,探讨不同包覆形式对其催化活性的影响。结果表明,两种方法制备得到的SiO₂/Co₃O₄复合物分别为层包覆和粒子包覆,比表面积大,具有明显的核壳结构,且粒子包覆形式的SiO₂/Co₃O₄对AP热分解反应的催化效果最好,使AP的高温分解温度降低了110 ℃,放热量增加了662 J·g^-1。     

The Influence of the Thermal Behaviour of AgGaS2 on the Crystal Growth Process

Differential thermal analysis has been carried out on AgGaS₂ samples in order to investigate the relationship between the superheating of the melt and the supercooling behaviour of the material leading to an improvement of crystal growth conditions. The knowledge gained will be correlated to the crystal growth experiments which had been carried out by using the gradient freezing method.This revised version was published online in November 2005 with corrections to the Cover Date.     

Deposition of Diamondlike Carbon Film and Mass Spectrometry Measurement in CH4/N2 RF Plasma

The deposition of diamondlike carbon (DLC) film and the measurements of ionic species by means of mass spectrometry were carried out in a CH₄/N₂ RF (13.56 MHz) plasma at 0.1 Torr. The film deposition rate greatly depended on both CH₄/N₂ composition ratio and RF power input. It was decreased monotonically as CH₄ content decreased in the plasma and then rapidly diminished to negligible amounts at a critical CH₄ content, which became large for higher RF power. The rate increased with increasing RF power, reaching a maximum value in 40% CH₄ plasma. The predominant ionic products in CH₄/N₂ plasma were NH⁺ ₄ and CH₄N⁺ ions, which were produced by reactions of hydrocarbon ions, such as CH⁺ ₃, CH⁺ ₂, CH⁺ ₅, and C₂H⁺ ₅ with NH₃ molecules in the plasma. It was speculated that the production of NH⁺ ₄ ion induced the decrease of C₂H⁺ ₅ ion density in the plasma, which caused a reduction in higher hydrocarbon ions densities and, accordingly, in film deposition rate. The N⁺ ₂ ion sputtering also plays a major role in a reduction of film deposition rate for relatively large RF powers. The incorporation of nitrogen atoms into the bonding network of the DLC film deposited was greatly suppressed at present gas pressure conditions.