常压等离子体渗氮工艺的研究

利用介质阻挡放电原理，在自行研制的设备上进行了常压非平衡等离子体渗氮。研究表明，在等离子环境中，试样表面能迅速获得很深的渗层和白亮层，而电场外试样几乎无渗层。说明电场内气体电离率高，活性粒子浓度高。整个工艺过程操作简便，是一种很有发展前景的新工艺。     

Large-area and uniform surface modification of polymers by barrier discharge plasmas

A barrier discharge experimental setup for low-pressure and large-area (400 mm × 600 mm) surface modification of polymers is reported. The low-pressure barrier discharge plasma consists of pulsed and glow-like breakdowns with peak widths of several microseconds and leads to the uniform surface modification of polymers. In contrast, the filamentary discharges produced at atmospheric pressure cause surface damage and nonuniform treatment of polymers. This study indicates that barrier discharge plasmas generated in the small gas spacing at low discharge pressure result in efficient collisions between polymer surface and activated species, and an extremely low consumption of feed gas and discharge power.     

Comparison on Refinement of Iron Powder by Ball Milling Assisted by Different External Fields

The cryogenic milling and milling in conjunction with dielectric barrier discharge plasma (DBDP)have been separately set up. The combined effect of low temperature and plasma on ball milling has been investigated by examining the refinement of particle size and grain size of iron powder using scanning electron microscopy, X-ray diffraction, and small angle X-ray scattering. It was found that the mean size of iron particles could reach 104nm only after 10 hours of ball milling in conjunction with DBDP, whereas a minimum average grain size of 8.4nm was obtained by cryomilling at -20℃; however, it is difficult to refine the particle size and grain size under the same milling condition in the absence of DBDP and cryogenic temperature.     

介质阻挡低温等离子体法辅助制备钼钴基催化剂及其应用研究

对介质阻挡(DBD)低温等离子体法辅助制备催化剂的方法进行了研究。用DBD等离子体法制备了Mo/Co/K/ZSM-5催化剂。利用X射线衍射、热重分析、扫描电子显微镜等对催化剂进行表征。结果表明,等离子体法和传统焙烧处理制备的催化剂性能相近,并且利用DBD低温等离子体处理的催化剂在预处理速度,催化剂微观颗粒尺寸,分散度等方面均优于传统焙烧的处理方式。预处理后的催化剂表面活性更有利于直接通过合成气制备液体烃类燃料。     

Dielectric barrier discharge (DBD) processing of PMMA surface: Optimization of operational parameters

This paper reported the effects that the key dielectric barrier discharge (DBD) operating parameters, discharge power, processing speed, processing duration and electrode configurations, have on producing wettability changes and on uniformity in the PMMA surface region. The results obtained indicate that DBD plasma processing is an effective method for the controlled surface modification of PMMA. Relatively short exposures to the atmospheric pressure discharge produces significant wettability changes at the PMMA surface, as indicted by pronounced reductions in the water contact angle measured. It was observed that the wettability of the resultant surface shows no significant differences in respect to sites in orientation parallel (L-direction) or perpendicular (T-direction) to the electrode long axis. However, the resultant surface shown higher standard deviation (S.D.) of contact angle in T-direction than that in L-direction. Analysis of the role of each of the operating parameters concerned shows that they have a selective effectiveness with respect to resultant surface modification in terms of uniformity of modification and wettability. The number of treatment cycles and the discharge power used were found to have the most significant effects on the homogeneity of the resultant PMMA surface changes in L- and T-orientation, respectively. The number of treatment cycles was found to be the dominant factor (at significance level of 0.05) in respect of water contact angle changes at the processed PMMA surface in both orientations. The driven metal electrodes (stainless steel or aluminium) were apparently superior to the driven dielectric electrode (ceramic or quartz) configurations. The grounded electrode in each case was a silicone rubber-covered aluminium plate. The nature and scale of the surface changes that originate from the various processing conditions employed have been considered so as to determine the optimum treatment conditions in respect of processing outcomes, properties and any orientation dependence. It was revealed that higher processing speeds and longer processing durations are key for uniformity along the electrode axial orientation within the test range employed, while lower processing speeds and short exposure durations are key considerations, in the corresponding perpendicular orientation. In general, longer processing durations (low processing speeds and a high number of treatment cycles) and higher plasma powers induced greater changes in the surface wettability of the PMMA, as demonstrated by the observed water contact angles. This behaviour is taken to indicate that different combinations of DBD operating parameters and electrodes produce discharge conditions that can result in different plasma chemical processes in respect of uniformity, treatment efficiency and orientation dependence. The comparison of the processing outcomes between PMMA and PET revealed that the operating parameters have the similar selective effectiveness on both polymers, indicating the obtained results may be used as a general guidance in controllable surface processing by DBD technique.     

Plasma enhanced CVD of fluorocarbon films by low-pressure dielectric barrier discharge

Low-pressure dielectric barrier discharge (DBD) plasmas have been used to deposit polymerized fluorocarbon (FC) films on silicon substrates. The effects of discharge pressure and frequency of power supply on the film quality have been systematically investigated. The deposited films were characterized by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and static contact angle measurements. Experimental results show that FC films with a less crosslinked structure may be deposited at a relatively high pressure. Increasing the frequency of power supply leads to a significant increase in the deposition rate. All deposited FC films with a uniform microstructure show the hydrophobic property. Decreasing the frequency of power supply or increasing the deposition pressure results in the deposition of FC films with the extremely low surface roughness. The relationship between plasma parameters and the analyzed properties of deposited FC films is discussed.     

Plasma modification of polylactic acid in a medium pressure DBD

In this paper, a dielectric barrier discharge (DBD) operating in different atmospheres (air, nitrogen, helium and argon) and at medium pressure is employed to modify the surface properties of polylactic acid (PLA). Chemical and physical changes on the plasma-treated surfaces are examined using contact angle, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) measurements. Results show that the discharge gas can have a significant influence on the chemical composition of the PLA surfaces: air and argon plasmas introduce oxygen-containing groups, while nitrogen discharges add nitrogen groups to the PLA surface. Quite surprisingly, also helium plasmas incorporate a small amount of nitrogen-containing functionalities: this observation can however be explained by the fact that the helium discharge operates in the glow mode. In the near future, it will be examined whether the performed plasma treatments can enhance PLA cell attachment and proliferation, which might open the door to many interesting biomedical applications.     

Thin film deposition and surface modification with atmospheric pressure dielectric barrier discharges

This paper focuses on some of the most debated issues concerning the utilization of atmospheric pressure dielectric barrier discharges (DBDs) in surface processing of materials such as, for instance, the existence of different discharge regimes (filamentary and homogeneous) and the influence on the discharge behaviour of feed gas additives and substrate properties (chemical composition, electrical characteristics, etc.). Crucial aspects of the DBD operation which highly differentiate this approach from the well established low pressure plasma technology will be discussed.An overview of the state of the art in atmospheric pressure thin film deposition from fluorocarbon- or organosilicon-containing DBDs will be also provided. In particular the possibility of tailoring the chemical composition of the coatings, the etching-deposition competition and the influence of feed gas contaminants (i.e. air and H₂O) in the deposition of fluoropolymers will be discussed. Recent results on the deposition of SiO_xC_yH_z thin films from three different methyldisiloxanes (i.e. hexamethyldisiloxane, pentamethyldisiloxane and tetramethyldisiloxane) will allow to highlight the effect of the chemical structure of the organosilicon precursor and of the oxygen-to-methyldisiloxane feed ratio on the properties of the deposits. The results obtained through different diagnostic techniques of the plasma phase (i.e. optical emission spectroscopy and GC-MS analysis of the exhaust gas) and of the deposits (i.e. XPS, FT-IR, SEM, and WCA) allow to highlight interesting aspects of the fluorocarbon and organosilicon plasma chemistry at atmospheric pressure.     

Clarification of EDM gap phenomena using transparent electrodes

This paper describes the heat source diameter of single pulse discharge in electrical discharge machining. To observe the discharge plasma, SiC and Ga₂O₃ single crystals were used as the electrode material since they are optically transparent and electrically conductive. It was found that plasma diameter expands within a few microseconds after dielectric breakdown and the plasma diameter is much larger than the discharge crater. From the measured diameter of the crater, the heat source diameter was obtained by solving the inverse problem of heat conduction analysis, and it was found that the heat source diameter is smaller than the plasma diameter but larger than the crater diameter.     

Corrosion protection of a thin aluminium layer deposited on polyester

Organosilicon plasma polymer layers were deposited by surface dielectric barrier discharge (DBD) at atmospheric pressure, in an attempt to enhance the corrosion protection of a reflective aluminium (Al) layer applied on a polyester (PET) fabric. A number of tests were carried out to characterize the improvement of corrosion resistance - namely sodium carbonate (Na₂CO₃), water vapor and Kesternich tests - as a function of plasma treatment time, type of carrier gas, admixture of oxygen, amount of hexamethyldisiloxane (HMDSO) precursor supplied to plasma and post-plasma-treatment heating. Moreover, plasma-deposited protective films were characterized by the scanning electron microscopy (SEM), infrared spectroscopy (DRIFT FTIR), and X-ray photoelectron spectroscopy (XPS). While aluminium was consumed in the Na₂CO₃ corrosive solution within a few minutes for the untreated surface, the optimally performing plasma polymerized layers revealed an extraordinary corrosion resistance. Furthermore, the best protective organosilicon coatings showed only a 1-2% absolute reduction of reflection compared to the untreated fabric, over the complete solar spectrum (250-2500 nm).     

常压等离子体表面渗扩技术研究

分析了现有等离子体渗扩技术的研究现状,提出了常压介质阻挡强放电等离子体渗扩技术的观念,说明了这种常压等离子体渗扩技术的原理和特点,并进行了一些理论分析和计算。设计了常压介质阻挡强放电等离子渗扩技术的试验装置,在此基础上进行了初步试验研究。结果表明了常压等离子体渗扩技术渗速快,突破了现有等离子渗扩技术的真空限制,有可能成为一种有前途的金属表面渗扩技术。     

Chemical composition and bond structure of carbon-nitride films deposited by CH4/N2 dielectric barrier discharge

Carbon nitride films have been deposited by dielectric barrier discharge with a CH₄/N₂ gas mixture at different conditions. Fourier Transform Infrared (FTIR) spectroscopy, X-ray photo electron spectroscopy (XPS), Raman spectroscopy, Atomic force microscopy (AFM) and ellipsometry were used to systematically study chemical composition, bond structure and surface morphology of deposited films. Various bonds between carbon, nitrogen, hydrogen, and also oxygen were observed.     

等离子喷涂-物理气相沉积高温防护涂层研究进展

等离子喷涂-物理气相沉积（PS-PVD）是基于低压等离子喷涂发展起来的一种新型多功能薄膜及涂层制备技术。由于其独特的等离子射流特征,可实现气液固多相涂层沉积,获得非视线沉积。文中首先介绍了国内外PS-PVD技术等离子体数值模拟和在线检测技术的研究现状,其次讨论了PS-PVD羽-柱状结构热障涂层的形成机制及与传统热障涂层在热导率、抗冲蚀等性能方面的差异,阐述了PS-PVD技术制备环境障涂层的研究进展,最后对PS-PVD技术沉积高温防护涂层的优势和存在的问题进行了总结。     

甲醇对镁合金等离子体电解氧化过程的影响

以甲醇和水为混合溶剂,KOH、Na2SiO3为电解质,恒电压方式对AZ31镁合金进行等离子体电解氧化(PEO)处理,通过原子吸收分光光度计检测等离子体电解氧化处理后电解液中镁离子含量,研究甲醇对镁合金等离子体电解氧化过程的影响。结果表明,在等离子体电解氧化过程中,甲醇的加入影响镁合金PEO过程放电特性;随着甲醇浓度的增大,镁离子溶出量逐渐减少,耐点滴腐蚀、耐均匀腐蚀性能均有提高;甲醇的加入能有效降低PEO过程能耗,当溶剂中甲醇浓度为12%(体积分数)时,能耗比未加甲醇时降低42.9%。     

Dielectric barrier discharge assisted chemical vapor deposition of boron nitride phosphide films on a quartz substrate

Boron nitride phosphide films were deposited on a quartz substrate by dielectric barrier discharge assisted chemical vapor deposition. From results of X-ray photoelectron and UV-Vis absorption spectral measurements, the chemical composition of the films may be defined as BN_1 − xP_x, where the mole number (x) is variable between 0.25-0.58, through modifying the PH₃ flow rate in the film deposition process, and the corresponding optical band gap may be modulated between 4.17-3.25 eV. From measurements of X-ray diffraction and high resolution transmission electron microscopy, an amorphous matrix embedded with a hexagonal crystalline phase of BNP with a crystal lattice spacing of 0.35 nm and a textured pattern is observed. The BN_1 − xP_x films are smooth, well-adhered to the quartz substrate, and display dark resistivities on the order of 10¹¹ Ω cm and ultraviolet light photo/dark conductivity ratios higher than 10³, with negligible sensitivity in the visible region, indicating a potential application in visible/blind UV detectors.     

A new method of synthesizing ultrafine vanadium carbide by dielectric barrier discharge plasma assisted milling

A new high efficiency method of synthesis of ultrafine vanadium carbide (VC) at a low carburization temperature has been developed. Firstly, a mixture of V₂O₅ and graphite powders is milled using dielectric barrier discharge plasma assisted milling (denoted as DBDP milling) for 4 h, and then the milled powders are carburized at 1200 °C, causing the V₂O₅ to react completely with graphite to form ultrafine VC. The formation temperature of VC is much lower than that needed in the conventional milling and heating process. This is because of the greatly enhanced reaction between V₂O₅ and graphite arising from the unique lump-like morphology and large number of clean surface contacts and greater surface area induced by DBDP milling.     

Mo基体上沉积La_(1.4)Nd_(0.6)Zr_2O_7涂层的热循环失效机制

选择La1.4Nd0.6Zr2O7(LNZ)为面层材料,质量比为1∶1的Mo与LNZ复合粉末(ML)为过渡层材料,用等离子喷涂法在高温Mo合金上制备双层结构热障涂层(ML/LNZ)。研究该涂层在1200℃的热震行为,用XRD分析失效后涂层的物相组成,并借助扫描电子显微镜和能谱对热震后涂层表面不同位置进行观察比较。结果表明,涂层在1200℃下的热循环寿命非常短,涂层沿粘结层与基体的界面剥落。而高温下Mo的氧化及挥发性氧化产物(MoO3)与涂层之间的化学反应是导致ML/LNZ涂层快速失效的主要原因。与氧化钼具有良好的热化学相容性是选择Mo基体上热障涂层的首要条件。     

An investigation of ultrasonic-assisted electrical discharge machining in gas

This study focuses on using ultrasonic to improve the efficiency in electrical discharge machining (EDM) in gas medium. The new method is referred to as ultrasonic-assisted electrical discharge machining (UEDM). In the process of UEDM in gas, the tool electrode is a thin-walled pipe, the high-pressure gas medium is applied from inside, and the ultrasonic actuation is applied onto the workpiece. In our experiment, the workpiece material is AISI 1045 steel and the electrode material is copper. The experiment results indicate that (a) the Material Removal Rate (MRR) is increased with respect to the increase of the open voltage, the pulse duration, the amplitude of ultrasonic actuation, the discharge current, and the decrease of the wall thickness of electrode pipe; and (b) the surface roughness is increased with respect to the increase of the open voltage, the pulse duration, and the discharge current. Based on experimental results, a theoretical model to estimate the MRR and the surface roughness is developed.     

Machining Characteristics of EDM by Radio-frequency Plasma

An extension to the electrical discharge machining method by introduction of radio-frequency plasma is proposed. Sparking with the radio-frequency plasma can be generated in paraffin oil by simple electrical circuitry. In this paper, experimental investigations are described on the fundamental effects of the resonant frequency, type of electrode and workpiece materials on machining characteristics for high performance radio-frequency machining in paraffin oil. The results show that the removal rate and the electrode wear vary with the resonant frequency and type of electrode materials. The surface roughness can be reduced to less than 1μm Rz under suitable experimental conditions.     

玻璃掺杂量对Ca0.8Sr0.2TiO3陶瓷作为介质阻挡层等离子体放电分解CO2的影响

通过液相烧结法成功制备出不同玻璃掺杂量的Ca0.8Sr0.2TiO3陶瓷材料,并将该陶瓷材料作为介质阻挡层在圆柱型放电反应器中分解二氧化碳。研究结果发现,随玻璃掺杂量的增加,Ca0.8Sr0.2TiO3陶瓷的表面电阻增大,但在所研究的温度范围内,Ca0.8Sr0.2TiO3的介电常数并没有随玻璃掺杂量的变化而显著变化。扫描电镜结果表明,晶粒尺度和颗粒间玻璃相厚度随玻璃掺杂量增加而增大。另外,二氧化碳的转化率和转化效率随陶瓷中玻璃量的增加而提高。进一步采用Malter效应模拟放电和介电特性,根据该模型,可以解释转化特性与陶瓷样品中玻璃含量之间的关系。