High rising speed discharge current pulse for EDM generated by inductive boosting voltage circuit

This paper introduces a newly developed EDM pulse generator whose high open voltage for discharge is generated by induced electromotive force using a power supply of only 5 V. The pulse generator can generate short duration and high discharge current pulses. The rising time of discharge current pulses to 5 A can be made shorter than 50 ns with a pulse duration of 200 ns or shorter. The results proved that such discharge current pulse shapes increase material removal volume per discharge and that the higher boosting open voltage facilitates the machining of high resistivity materials.     

脉冲电场下制备AZ91D镁合金部分重熔过程的组织演变

研究利用低压脉冲电场技术制备的AZ91D镁合金在部分重熔过程中的组织演变,考察加热温度和保温时间对不同脉冲电压制备的AZ91D合金初生相形态和尺寸的影响。结果表明:经低压脉冲电场处理后,将AZ91D镁合金进行部分重熔可得到非枝晶的半固态合金,随坯料制备的脉冲电压增加,重熔时初生相变得圆整且尺寸减小,但制备坯料的脉冲电压过高,重熔时初生相尺寸有所增加;脉冲电场处理后的AZ91D镁合金坯料经适当的部分重熔处理可获得具备触变过程所需要的组织状态。     

Apatite/polypyrrole composite prepared by a biomimetic process

Apatite coatings were fabricated on polypyrrole (PPy) substrate by a biomimetic process using simulated body fluid (SBF). PPy was chemically synthesized with heparin sodium salt and toluene-4-sulfonic acid (P-TSA) as dopants. But apatite coatings were not induced when PPy was prepared without dopants, which suggests that heparin sodium salt and P-TSA play an important role in the formation of the apatite coatings. The possible mechanism responsible for the formation of apatite coatings was discussed. It is expected that this apatite/polypyrrole composite can be used as bioactive coatings on metal implants and tissue engineering scaffolds.     

液相脉冲放电制备Cr-C涂层的性能

以铬/石墨半烧结体电极为工具电极,利用液相脉冲放电涂层（EDC）技术,在普通中碳钢表面制备出以Cr₇C₃为主相的耐磨涂层。对涂层的硬度、结合力、摩擦性能进行了检测与分析,并考察了峰值电流、脉冲宽度对涂层性能的影响。结果表明,涂层与基体呈冶金结合,结合力达83.5 N。涂层厚度随峰值电流及脉冲宽度的增加而增加。当峰值电流小于10 A时,涂层硬度逐渐增加,而当脉冲宽度大于8 μs时,涂层硬度逐渐减小。硬度从涂层表面至基体呈逐渐减小的梯度分布,涂层表面硬度最高达1820 HV0.2。与H13热作模具钢相比,在相同的载荷下,涂层的摩擦因数较小,仅为0.12左右,展现出良好的减摩耐磨特性。     

Metal/polymer nanocomposite thin films prepared by plasma polymerization and high pressure magnetron sputtering

Recently, there is much interest in nanocomposites consisting of metal nanoparticles dispersed in a dielectric matrix due to their novel functional properties. In many cases the formation of metal clusters is affected by chemical reactions of the metal with the host matrix material during deposition. The integration of a magnetron cluster source into a plasma deposition process allows the pre-formation of clusters in the gas phase and subsequent co-deposition with the matrix material. We chose plasma polymerization of HMDSO as deposition method for the matrix in this case. Here we focus on the composition of the nanocomposites generated by high pressure magnetron sputtering combined with a plasma polymer. The influence of magnetron power, total and HMDSO partial gas pressure on the cluster formation as well as nanocomposite film properties were investigated by ex situ X-ray photoelectron spectroscopy. Furthermore optical und morphological properties of the prepared nanocomposites have been characterized.     

Thermoeffusion of hydrogen in a-C : H films prepared by glow discharge

The structure and properties of hydrogen-doped amorphous carbon (a-C : H) films are determined by the hydrogen content and the structure of the hydrogen bonding with the lattice.

Study of the thermal effusion of hydrogen (TEH) provides information concerning both the thermal stability of the films and the chemical bonding of hydrogen.

Wild and Koidl [1] measured the TEH in a-C : H films as a function of the bias potential V_b. They found that as V_b was increased from 50 to 500 V, the TEH threshold temperature increased from 300 to 600 °C. In a study of the thermal stability of a-C : H films prepared by glow discharge, Watanabe and Okumura [2] observed that on heating to 350 °C the thickness and optical gap of the films decreased and at still higher temperatures the films decomposed. Nadler et al. [3] investigated the thermal annealing effect in films prepared by the decomposition of hydrocarbons. On annealing at 500 °C, they observed hydrogen effusion from sp³ states and formation of C=C bonds, accompanied by a decreased transparency of the films.

In an investigation of a-C : H films prepared by r.f. glow discharge, we observed changes in the structure of the amorphous network and of the hydrogen bonding with the lattice as well as in the electronic properties of such films [4]. The data obtained suggest that TEH occurs differently in a-C : H films of different structures. Therefore it would be of interest to experiment on the TEH in a-C : H films.     

Electrocatalytic properties of polypyrrole films prepared with platinate(II) counter-ions

Polypyrrole/PtCl₄²⁻ composites were studied with respect to their possible use as a hydrogen electrode, e.g. for fuel cell applications. The impact of composite conditioning on its electrochemical activity for the hydrogen oxidation reaction (HOR) was studied. The cathodic polarization of samples containing a high amount of PtCl₄²⁻ ions after synthesis leads to the formation of polypyrrole/Pt composites active for HOR. Their behavior is, however, different from that of bulk Pt and strongly depends on the potential at which the reduction proceeds. Both electrochemical and IR measurements displayed the self-degradation of composites exposed to cathodic potentials exceeding a certain level. The presence of metallic Pt is proved by means of X-ray photoelectron spectroscopy (XPS) and the extent of platinate ions reduction/motion is discussed. Subsequently the possibility of tuning composite activity by changing the thickness or using a competing counter-ion during synthesis was tested.     

Surface discharge characteristics of MgO thin films prepared by RF reactive magnetron sputtering

This paper describes the surface glow-discharge effect of MgO thin films prepared by reactive radio-frequency planar magnetron sputtering on the dielectric layer of an alternating-current plasma display panel. By introducing an MgO coating on the dielectric the discharge voltage decreases sharply, although the thickness is only a few tens of Ångstroms. The lowest discharge voltage is obtained for the sample prepared at a 30% O₂ content in an O₂+Ar gas mixture and at a sputtering gas pressure of about 5 mTorr. Moreover, high transparency (95%) is also obtained under the same experimental conditions. The samples prepared show more sputter-resistant properties than samples prepared by the electron-beam method and no cracks are observed on the surface after post-deposition annealing.     

High dielectric constant polyaniline/poly(acrylic acid) composites prepared by in situ polymerization

An ultra-high dielectric constant composite of polyaniline, PANI–DBSA/PAA, was synthesized using in situ polymerization of aniline in an aqueous dispersion of poly-acrylic acid (PAA) in the presence of dodecylbenzene sulfonate (DBSA). The water-soluble PAA served as a polymeric stabilizer, protecting the PANI particles from macroscopic aggregation. A very high dielectric constant of ca. 2.0 × 10⁵ (at 1 kHz) was obtained for the composite containing 30% PANI by weight. The influence of the PANI content on the morphological, dielectric and electrical properties of the composites was investigated. The frequency dependence of dielectric permittivity, dielectric loss, loss tangent and electric modulus were analyzed in the frequency range from 0.5 kHz to 10 MHz. SEM micrograph revealed that composites with high PANI content (i.e., 20 wt%) consisted of numerous nano-scale PANI particles that were evenly distributed within the PAA matrix. The high dielectric constants of these composites were attributed to the sum of the small capacitors of the PANI particles.     

Improvement in the quality of polypyrrole films prepared electrochemically on a mercury anode

The synthesis and some properties of polypyrrole formed on a mercury anode are described. Conductivity values in the range 40 – 90 S/cm compare favourably with those of films produced on other electrodes. Use of the p-toluenesulphonate anion at a concentration of 0.3 M, pH of 4.8, and a temperature of 0 °C led to the best conductivity observed in free-standing films produced on a mercury anode. A maximum thickness of about 280 μm was achieved under optimum conditions.     

Reflection and absorption studies on polypyrrole films electrochemically prepared with different electrolyte types

Free standing polypyrrole (PPY) films, electrochemically prepared with different types of electrolytes (sodium toluenesulfonate (NaTSO), p-toluenesulfonic acid (ATSO) and lithium perchlorate (LiClO₄)) were investigated by two different spectroscopic methods. Specular reflectance measurements were performed by Fourier transform infrared (FTIR) spectroscopy in the range 200–6000 cm⁻¹. The optical constants for PPY films were calculated from the reflectance spectra with Kramers–Kronig technique. The reflection spectra are sensitive to the nature of the electrolyte and to the d.c. conductivity values. The absorption spectra of PPY films were obtained in the range 2500–25 000 cm⁻¹ by photopyroelectric (PPE) spectroscopy. Besides the bipolaronic absorption bands, this method reveals the characteristic vibrational bands of NH and N⁺H. The observed changes of the intensity of these bands after the electrochemical reduction and subsequent treatment with HCl are due to the deprotonation and protonation processes in the PPY samples.     

脉冲放电强度对磁控溅射Cr薄膜微观结构的影响

在脉冲非平衡磁控溅射环境中,通过提高脉冲靶电压(分别为600、700及800 V)使工作气体Ar获得3种不同强度的异常辉光放电状态(单脉冲峰值靶功率密度分别为10、30及70 W/cm2),并分别制备Cr薄膜.利用SEM、AFM、XRD及TEM等方法研究、比较了非平衡磁控溅射Cr薄膜的微观结构在不同Ar气脉冲异常辉光放电强度条件下的差异.结果表明,随Ar气脉冲异常辉光放电强度的增强:Cr薄膜沉积速率显著提高,薄膜表面粗糙度略有增大,但表面颗粒未出现长大现象,且尺寸均匀、细小,择优生长的Cr(110)晶面的衍射峰强度明显降低,结晶效果逐渐降低.不同异常辉光放电强度条件下制备的Cr薄膜均以柱状方式生长,微观组织呈现出纳米级尺度的晶粒(直径5 ～ 10 nm)镶嵌式分布的形态.     

High purity boron nitride thin films prepared by the PDCs route

Hexagonal boron nitride (h-BN) thin films (< 10 μm) were successfully obtained on various substrates (graphite-standard and HOPG, quartz and SiC) using the preceramic polymer route. Thin films were formed using precursor solutions of poly(2,4,6-trimethylamino)borazine (polyMAB) as a source of BN. Various preparation conditions were used (i.e. solvent, precursor nature and concentration, substrate and deposition method) and their impact on final BN film quality measured. Surface morphology was observed by Scanning Electronic Microscopy (SEM) and Atomic Force Microscopy (AFM). Presence of BN material was confirmed by infrared and Raman spectroscopies and the structure observed by High Resolution Transmission Electronic Microscopy (HRTEM). The chemical composition of samples analyzed by X-ray Photoelectron Spectroscopy (XPS) gives a B/N ratio close to 1. Boron nitride films were also prepared using borazine (B₃N₃H₆) as precursor. Initial results are presented and compared with those obtained from polyMAB solutions.     

High photocatalytic activity of Cu_2O/TiO_2/Pt composite films prepared by magnetron sputtering

Cu_2O/TiO_2/Pt three-layer films were deposited on glass substrates using magnetron sputtering method.The surface morphology and the optical properties of the composite film were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), ultravioletvisible spectroscopy(UV-Vis) and photoluminescence spectroscopy(PL). The photocatalytic activity of the samples was evaluated by the photocatalytic degradation of methyl orange(MO) aqueous solution under visible light irradiation. The results indicate that the Cu_2O/TiO_2/Pt composite films are made up of three layers which are Pt layer,anatase-TiO_2 layer and Cu_2O layer from bottom to top. The surface of the films is even and composed of regular-shaped spherical particles. The photocatalytic activity of the Cu_2O/TiO_2/Pt three-layer film is much higher than that of the Cu_2O/TiO_2 double-layer film. Such enhancement is ascribed to the presence of Pt layer, which further inhibits the photogenerated electron-hole recombination, prolongs the lifetime of the photogenerated carriers, increases the quantum efficiency and hence improves the photocatalytic activity of the film effectively.     

Synthesis and characterization of polypyrrole/TiO2 composite by in situ polymerization method

Polypyrrole/TiO₂ composite is prepared by in situ polymerization of pyrrole on the TiO₂ template. The TiO₂ microbelts are prepared by sol–gel method using the absorbent cotton template for the first time. Then the TiO₂ microbelts are used as template for the preparation of polypyrrole/TiO₂ composites. The structure, morphology and properties of the composites are characterized with scanning electron microscope (SEM), IR and Network Analyzer. A possible formation mechanism of TiO₂ microbelts and polypyrrole/TiO₂ composites has been proposed. The effect of the molar ratio of pyrrole/TiO₂ on the photocatalysis properties and microwave loss properties of the composites is investigated.     

脉冲放电对焊接接头的强化分析

对含有裂纹的16Mn焊接接头脉冲放电后的拉伸过程进行了数值模拟,分析了脉冲放电强化对裂纹前缘应力状态的影响.数值分析表明,经脉冲放电强化后,焊接接头受拉时裂纹前缘处的应力集中降低,抗拉性能得到了提高;对含有裂纹的16Mn焊接接头试件进行脉冲放电和拉伸性能试验.结果表明,通过脉冲放电强化,裂纹前缘钝化并产生了硬而韧的白亮层组织,试件的断口变得均匀、拉伸性能平均提高了17.8%.数值模拟和试验证实了电磁热止裂技术对降低焊接接头应力集中、提高其抗拉性能的有效性.     

Reticulated vitreous carbon/polypyrrole composites as electrodes for lithium batteries: Preparation,electrochemical characterization and charge–discharge performance

Polypyrrole (PPy) composites were prepared via electrochemical deposition onto reticulated vitreous carbon (RVC) – a tridimensional material – and tested as cathodes in lithium batteries. Different RVC/polypyrrole electrodes were prepared and characterized: PPy doped with ClO₄^? (RVC/PPy) as an anion-exchanger film; PPy doped with a large anion – poly(styrenesulphonate) – (RVC/PPyPSS) as a cation-exchanger film; and a bi-layer polymeric film formed by an inner layer of the former and an outer layer of the latter (RVC/PPy/PPyPSS). Photomicrographies, voltammetric profiles and electrochemical impedance spectroscopy data have shown different morphological and electrochemical characteristics for polypyrrole doped with small or large anions, and a peculiar behavior for the bi-layer electrodes. Charge/discharge results indicated that the RVC/PPy electrode can attain specific capacities as high as 95 mAh g^?1. PSS-doped polypyrrole electrodes also presented high specific-capacity values when the bi-layer configuration (RVC/PPy/PPyPSS) and lower charge–discharge currents were used. Impedance data indicated that the counter-ion diffusion within the bi-layer is hindered, which explains the slower activation of this composite when compared to that of RVC/PPy.     

Study on polypyrrole film by electrochemical polymerization in aqueous solution

Electroactive polypyrrole (PPy) film was prepared by electrochemical polymerization in aqueous solution. E.s.r. analysis of the film showed that the peak-to-peak linewidth is related with heat treatment, standing time and environmental atmosphere of the film. Oxygen and water molecules participate in electrochemical polymerization of pyrrole (Py) from aqueous solution and introduce

and OH groups into the structure of PPy film, as has been verified by XPS and FT-i.r. spectroscopy. The conductivity of the film measured by the four-probe method is less than that of the films prepared in organic solvent. The mechanism of electrochemical polymerization to form PPy in aqueous solution has been proposed.     

Two-phase nanostructured carbon nitride films prepared by direct current magnetron sputtering and thermal annealing

Two-phase nanocrystalline/amorphous carbon nitride films have been successfully prepared by direct current magnetron sputtering and the following thermal annealing at 1000 K. The analysis of Raman spectra supports the existence of sp³-hybridized C-N bonds in the films. The results obtained from X-ray photoelectron spectroscopy (XPS) indicate that the fractional concentration of the tetrahedral bonded crystalline phase in the carbon nitride films is 40%, and the ratio of N:C in the tetrahedral bonded crystalline phase is 1.12:1. Transmission electron microscopy (TEM) investigations indicate that the films contain a very dense and homogenous distribution of nanocrystalline grains, and the lattice parameters of these crystalline phases are in good agreement with the theoretically predicted β-C₃N₄ lattice constant. The films deposited on Si substrates have a high hardness of 40 GPa, and the correlations between the microstructure of the films and their mechanical properties are discussed.