Modeling and Spectroscopic Investigations on the Evaporation of Zirconia in a Thermal rf Plasma

The evaporation process of zirconia powders injected in a thermal rf plasma is investigated. Both model calculations and optical emission spectroscopy are used to study the evaporation behavior. Gas temperatures and velocity distributions are determined numerically from conservation laws and Maxwell equations. The influence of plasma and particle parameters on the thermal history of entrained particles is discussed. Asymmetric Abel inversion is applied to detect asymmetric emission profiles in the plasma source. Spectroscopic measurements reveal that evaporated zirconium is concentrated near the axis of the plasma. Numerical calculations show that line-integrated emission profiles can be used to distinguish the cases of complete and incomplete evaporation. Axial emission profiles confirm that the evaporation zone is shifted upstream of the plasma when smaller precursor particles are used.     

RF Plasma Deposition of PEO-Like Films: Diagnostics and Process Control

Organic thin films deposited by means of radio-frequency glow discharges fed with Triglyme vapors have been investigated to explore the feasibility for deposition of organic thin films with polyethylene oxide-like features. The film chemical composition has been analyzed by means of X-ray Photoelectron Spectroscopy and FT Infrared Absorption Spectroscopy. Plasma phase diagnostics has been accomplished by means of Optical Emission Spectroscopy. It is shown that the surface density of ether carbon, which is considered the marker of the content of ethylene oxide units in the coating, decreases as the power input is increased. It is also shown that the retention of monomer structure in the film can be easily controlled in situ by actinometric optical emission spectroscopy.     

Flash Evaporation and Headspace Solid-phase Microextraction for the Analysis of the Essential Oils in Traditional Chinese Medicine, Houttuynia Cordata Thunb

We have investigated the use of flash evaporation, headspace solid-phase microextraction (HS-SPME) and steam distillation (SD) as sample concentration and preparation techniques for the analysis of volatile constituents present in Houttuynia cordata Thunb. The samples were analyzed by gas chromatography (GC) and identified by mass spectrometry (MS). Comparison studies were performed. It was found that the results obtained between Headspace solid-phase microextraction HS-SPME and SD techniques were in good agreement, Seventy-nine compounds in Houlluynia cordata Thunh were identified by MS. In flash evaporation, thirty-nine compounds were identified. Discrimination in the response for many constituents studied was not observed, which can be clearly observed in SD and HS-SPME techniques. As a conclusion, HS-SPME is a powerful tool for determining the volatile constitutes present in the Houttuynia cordata.     

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).     

Rf plasma processing of silica

The processing of silica in an rf plasma was studied with a new experimental system, the process being carried out entirely in the vapor phase. SiO and Si were obtained by either thermal decomposition of SiO₂ or reduction by H₂. No other reducing material (which, like C, may become a contaminant) was used. The products were collected along the reactor length and analyzed afterward. Temperatures in the reaction zone were measured spectroscopically. The high reaction rates occurring in the gas phase did compensate for the low residence times. A diffusional model for the buildup of solid reaction products is discussed. Vapor phase plasma reduction of silica with hydrogen proved to be more effective than thermal decomposition and nuch more effective than heterogeneous processing. The efficiency evaluation was made on the laboratory-scale level.Nomenclature c _SiO ^d SiO content, % by wt - c _Si ^t Total Si content, % by wt - cSiO ₂ ^e Experimental SiO₂ content, % by wt - cSiO ₂ ^t Theoretical SiO₂ content, % by wt - D Species diffusivity, cm² · sec^–1 - F Rate of species deposition, mol · cm^–2 · sec^–1 - MSiO₂ Molar flow of SiO₂, mmol · sec^–1 - n Species concentration, cm^–3 - P Anode power, kW - r Reaction radius, cm - R ^* Radius of quartz tube, cm - T Temperature, K - T _av Average temperature, K - USiO ₂ ^t Total extent of SiO₂ decomposition, % - V _Ar ^a Molar flow of axial Ar, mmol · sec^–1 - V _Ar ^p Molar flow of peripheral Ar, mmol · sec^–1 - VH₂ Molar flow of H₂, mmol · sec^–1 - y Molar fraction - Z Position of a plane normal to the plasma axis down the lower turn of rf coil, cm Greek Letters Molar ratio of SiO over SiO₂ in deposit     

Diagnostics and Application of the High Frequency Plasma Pencil

The so called high frequency plasma pencil is a source of highly active environment (electrons, ions, reactive radicals, excited atoms, and molecules) which can be generated at atmospheric, reduced or increased pressure, preserving a good control of the performance. The discharge can be either unipolar or bipolar. The properties of unipolar atmospheric pressure discharges are discussed on the basis of simple theoretical considerations and electric probe measurements. The plasma pencil discharge is studied by optical emission spectroscopy in the gas phase at atmospheric pressure as well as immersed in liquid using argon as a working gas. From the emission spectra the electron, vibrational and rotational temperatures are calculated for various distances from the plasma pencil electrode. Several technological applications like restoration of archaeological glass and metal artifacts, fragmentation of molecules for microelectrophoresis and plasma polymerization are summarized. An advantage of the plasma pencil is that it can be easily operated and controlled.     

Reduction of Metallurgical Wastes in an RF Thermal Plasma Reactor

Recovery of metals from iron and zinc oxides, as well as from zinc-containing metallurgical wastes, such as flue dust from the Siemens–Martin process and sludge from hot galvanizing, has been studied in an rf thermal plasma reactor under reducing conditions. The product composition was estimated by thermodynamic calculations based on the minimization of the Gibbs free enthalpy. Effects of the plate power of rf generator and the feed rate of powder on the chemical and phase composition of products have been investigated in detail. It has been proved that the rf thermal plasma treatment makes possible to produce unstable species in thermodynamic terms: metallic zinc was gained in the reaction of ZnO and hydrogen. The gradient cooling along the plasma reactor led to the segregation of the iron and zinc compounds. Valuable products were made from the particular wastes by a single step thermal plasma processing.     

Fast Imaging of Laser-induced Plasma Emission from a ZnO Target

The spatio-temporal evolution of plasma plume laser ablation zinc oxide target was investigated by ICCD camera fast imaging. The plasma was created by a KrF excimer laser of 248 nm wavelength and 25 ns pulse. The laser fluence was set at 2 J/cm². This study was performed under vacuum and oxygen atmosphere at a pressure range of 10^− 6 to 10 mbar.Free expansion, splitting and stopping of the plume were observed at different pressures and time delays following the laser pulse. Moreover, depending on the gas pressures, the photography shows some turbulence for given time delays in the front edge of the plasma while at 5 and 10 mbar the whole plasma edge is perturbed. Rayleigh–Taylor instability is proposed as an explanation to this observed effect. A time integrated emission spectroscopy diagnostic has been also used to identify plasma species. A plasma emission spectrum shows the presence of Zn⁺, Zn and O emission lines both in vacuum and in O₂ atmosphere. As the distance from the target surface increases the Zn⁺ emission line disappears.     

Depolymerization of Polyethylene Using Induction-Coupled Plasma Technology

A significant, valuable percentage of today's municipal solid wastestream consists of polymeric materials, for which almost no economicrecycling technology currently exists. This polymeric waste is incinerated,landfilled, or recycled via downgraded usage. Thermal plasma treatment is apotentially viable means of recycling these materials by converting themback into monomers or into other useful compounds. The technical, laboratoryscale, feasibility of using an induction-coupled RF plasma (ICP) heatedreactor for this purpose has been demonstrated in the presentstudy. Polyethylene powder was injected axially through the center of anICP torch. Results from the initial set of experiments, analyzed using astatistical design of experiment technique, showed that plasma plate power,central gas flow rate, probe gas flow rate, powder feed rate, and theinteraction between the quench gas flow rate and power input were the keyprocess parameters affecting the yield of ethylene in the product gasstream. The gaseous products obtained were mainly mixtures of ethylene andpropylene. The amount of propylene obtained was significantly higher thananticipated and was believed to be due to -scission reactionsoccurring at the higher plasma temperatures.     

Using Ion-velocity Map Imaging Technique to Study Photodissociation of 2-Bromopentane

The photodissociation dynamics of 2-bromopentane at -234 nm has been investigated by utilizing ion-velocity map imaging technique. The mapped images of Br（2P3/2） （denoted as Br） and Br（2p1/2） （denoted as Br＊） fragments were analyzed by means of the speed and angular distributions, respectively. The speed distributions can be fitted with two Gaussian components which are correlated to the two independent reaction paths on the excited po- tential energy surfaces （PES）. The high-energy component is from the prompt dissociation along the C-Br stretching mode, while the low-energy one is related to the dissociation from the coupling of the C-Br stretching and bending modes. Relative quantum yield is measured to be 0.892 for Br in the photodissociation of 2-bromopentane at 234 nm. Combining the anisotropy parameter with the relative quantum yield of Br and Br fragments, the contributions of the excited 3Q0, 3Q1, and 1Q1 states to the products Br and Br were derived. The effect of alkyl branching on the mechanism of photodissociation was discussed by comparing the photodissociation processes of four isomers of bromopentane.     

Separation of Gold from Sulfide Using a Plasma Arc Fuming Process

Transferred-arc plasma treatment of iron sulfides containing gold is examined from both thermodynamic and experimental points of view. Three cases are analyzed: argon plasma with sulfide, argon plasma with a carbon–sulfide mixture, and argon–methane plasma with sulfide. The carboreduction of the materials appears to be well adapted for gold separation by fuming, but experimentally the process is limited by the poor mixing of graphite with molten material. The reduction with a CH₄ (10%) plasma is a proved alternative to the aforementioned process. A gold extraction efficiency of 90% is achieved for batch smelting operations.     

Investigation of Changes in Conductivity of Juice during the Evaporation Process

The creation of this article was the necessity of experimental determination of the electric conductivity of juice depending on the concentration of solids, expressed by the empirical formula, in order to more precisely control specific power supplied to the machine and foaming. Authors of the article held staged experimental studies using apple juice, the juice of red mountain ash, buckthorn and black currant. Found that the relationship between the conductivity of the juice solids content corresponds to the empirical formula of Kohlrausch, however, this formula does not represent the contribution juice acidity value of conductivity, and allows to correlate the specific power input to the device with the concentration of solids. The empirical formulas for the distribution of electrical juice conductivity depending on the acidity and for calculation of the specific power depending on the concentration of dry matter, allows to keep the speed of the foam below its destruction speed in the zone of vigorous reflux.     

A study of chromic oxide decomposition in an RF argon plasma

Vapor-phase thermal decomposition of chromic oxide in an rf argon plasma was studied using a new experimental system. Homogeneous and heterogeneous modes of reaction were compared, the overall process efficiency being substantially higher for the process carried out entirely in the vapor phase. Reaction products were collected along the reactor wall and studied by chemical methods as well as SEM, X-ray, and IR absorption. The collected powder was highly reactive, fine-grained, and of semiamorphous nature, the average particle size being well below 100 nm. Temperature profiles recorded below the coupling coil by spectroscopic methods were typical of an rf plasma, showing maxima slightly exceeding 5000 K, with the presence of off-axis peaks. Local Cr contents and concentration ratio (Cr)/(Cr₂O₃) in the plasma were determined from the deposition data obtained. A diffusion process was assumed for the wall-deposit buildup. The results obtained confirmed the advantages of using plasma vapor-phase systems, these being higher-efficiency processes and more reliable models than those obtained in the case of gas-solid plasma reactors, where solid particles are injected into the plasma. The thermal decomposition conversion of Cr₂O₃ into Cr was about 8 times higher in the homogeneous gas phase than in the plasma solid phase, all other conditions being equal.Nomenclature c velocity of light, cm × s^–1 - C _Cr ^m metallic Cr content, % by wt. - C _Cr ^t total Cr content, % by wt. - D species diffusivity, cm² · s^–1 - E energy of excited level, eV - f oscillator strength - F rate of species deposition, mol · cm^–2 · s^–1 - g statistical weight - h Planck's constant, J · s^–1 - I radial emission intensity for a given spectral line at a given radius in the plasma, W · sr^–1 · cm^–3 - k Boltzmann's constant, J · K^–1 - l length of collected deposit, cm - m mass of collected deposit, g - M molar weight of Cr - M _Ar ^a molar flow of axial argon, mmol · s^–1 - M _Ar ^p molar flow of peripheral argon, mmol · s^–1 - M _{Cr 2}O₃ molar flow of evaporated Cr₂O₃, mmol · s^–1 - Cr(I) concentration, cm^–3 - Q _T partition function at temperatureT - r reaction radius, cm - R radius of quartz tube, cm - t duration of deposition, s - T temperature, K - total extent of Cr₂O₃ decomposition into Cr, % - Z position of a plane normal to the plasma axis downward the lower turn of rf coil, cm Greek Letters molar ratio of Cr and Cr₂O₃ in deposit - wavelength, nm - species concentration, mol · cm^–3     

A Study on Thermal Degradation of Organic LEDs Using IR Imaging

In this paper, we present a correlation study between the working temperature of OLEDs (Organic Light Emitting Diodes) and the electroluminescence and driving voltage changes. The aim is to investigate the relationship between the operating temperature and the aging mechanisms. We have found that performances degradation of devices is strictly related to the glass transition temperature (T_g) of organic layers, and that electrical failure is reached only for temperatures higher than T_g.     

多格错仁盐湖卤水冷冻、日晒两步法浓缩制卤研究

藏北无人区的多格错仁盐湖水化学类型为氯化物型,该湖水钾、锂资源品位好;结合自然条件制定该低矿化度卤水在高寒区冬季制卤工艺路线。通过冷冻、日晒两步法成功制得了富含钾、锂的精制卤水;对硫酸钙在该卤水蒸发过程中的过饱和溶解度与石膏缓析现象进行了解析。     

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.     

Influence of the Electromagnetic Forces on Momentum and Heat Transfer in a 3-Phase ac Plasma Reactor

A new 3-phase ac plasma reactor has been developed within the framework of research on hydrocarbon cracking for the production of carbon black and hydrogen. ^(1,2) One of the main characteristics of the system is related to the 3-phase, 50 Hz ac current plasma generator which induces a very particular arc motion affecting the heat and mass transfer inside the reactor. In a first step, the general flow inside the reactor in the absence of hydrocarbon injection has been studied. A simplified approach to characterize the heat and mass transfer inside the reactor is presented in this paper. The arc zone analysis is carried out simultaneously by a theoretical analysis of the electromagnetic forces and by an ultrahigh-speed cine-camera analysis. The flow in the reactor is modeled with a CFD commercial code. Results are compared with experimental temperature measurements.     

Comparison of Simple Particle-Radiation Coupling Models Applied on a Plasma Black Process

The effect of soot formation on the radiative heat transfer inside a plasma reactor for carbon black synthesis has been modelled. For this purpose, three methods to quantify the soot volume fraction have been tested and evaluated: (1) Assuming local thermodynamic equilibrium, (2) assuming instantaneous conversion of the hydrocarbon and (3) using a single-step soot model. These approaches have been studied using a two-dimensional axis-symmetric and a three-dimensional steady computational fluid dynamics (CFD) model based on the commercial software FLUENT (v.5.6). The CFD model includes turbulence effects (by standard k– model), an electric arc sub-model to describe the time-average and spatial-average Lorentz forces and ohmic heating generated by the three-phase power-supply, methane transport in a nitrogen plasma and radiation calculations. The calculations show that for the simulated operating conditions the resulting temperature distributions obtained are very similar with the three methods in spite of major differences in the treatment of particle formation in the different methods.     

过氧化氢激活的纳米药物用于原位自生磁共振成像和热成像

恶性肿瘤的早期检测在降低死亡率方面发挥着关键作用。双模态生物医学成像策略能够为癌症的精确诊断提供更多的可用信息,成为当前研究热点。该文通过简便的一锅水热法制备了高度生物相容的多功能纳米粒子（CuSSe NPs）,可以特异性响应肿瘤部位过量的过氧化氢（H2O2）,实现Cu（Ⅰ）向Cu（Ⅱ）的转化,可作为原位自生磁共振成像（MRI）造影剂用于肿瘤诊断。此外,由于近红外（NIR）区域的强吸收,CuSSe NPs表现出良好的光热转换性能,可作为体内实时癌症监测的光热成像剂。血液分析结果表明CuSSe NPs具有较好的生物相容性,无急性、长期毒性。该纳米材料已被证明是一种潜在的纳米探针,可用于临床癌症治疗中具有高肿瘤对比度的双模态成像。     

激光剥蚀-电感耦合等离子体质谱实现黄铁矿中多元素原位成像

采用激光剥蚀-电感耦合等离子体质谱( LA-ICP-MS)建立了单粒黄铁矿的多元素原位成像方法。在1mm×1mm的扫描区域内,获得有效计数点信息约5万个,总分析时间仅为1.5h。结果表明,此粒黄铁矿表面Fe、S元素的信号强度分布均匀,Fe/S比值数据集中,相对标准偏差仅为11.6%,这表明黄铁矿均质性较好,也表明本分析方法的稳定性较高。相对于围岩,黄铁矿表面的微量元素表现出的富集或亏损特征,可能与黄铁矿形成时的氧化还原环境和后期的次生改造作用有关。本方法将有助于LA-ICP-MS在单颗粒矿物分析中的推广应用,可为古环境、烃源岩和流体成藏等研究提供更直接、更准确的可视化实验数据。