Study of Dense Nitrogen Plasma Irradiation of Aluminum Targets by APF Plasma Focus Device

The nitridation of Al surfaces is obtained by irradiating nitrogen ions from APF device. The Vickers Micro-Hardness values are improved approximately three times for the nitrided samples comparing to the non-nitrided ones. The X-ray diffraction analysis is carried out in order to explore the phase changes in the near surface structure of the metals. The Nuclear Reaction Analysis shows the depth of the nitride composed on the metal surfaces clearly and quantitatively. The results of Scanning Electron Microscopy indicate changes in surface morphology which are the emergence of a smooth and uniform film scattered on the surface of the nitrided specimens.     

Deposition of titanium nitride on Si(1 0 0) wafers using plasma focus

Titanium nitride thin films were deposited on Si(1 0 0) substrates by using a low energy (2.3 KJ) Mather-type plasma focus device. The composition of the deposited films was characterized by X-ray diffraction (XRD). The crystallite size has strong dependence on the numbers of focus shots. The crystallinity of TiN thin films is found to increase with increasing the number of focus shots. The effect of different number of focus shots on micro structural changes of thin films was characterized by Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM). SEM results showed net-like structure for film deposited for 15 numbers of shots, which are elongated grains of Si₃N₄ in amorphous form embedded into TiN crystals. The average surface roughness was calculated from AFM images of the thin films. These results indicated that the average surface roughness increased for films deposited with increased number of focus shots. The least crystallite size and roughness are observed for film deposited with 25 focus shots.     

Structural and magnetic characterization of plasma ion nitrided layer on 316L stainless steel alloy

In this study, an FeCrNi alloy (316L stainless steel disc) was nitrided in a low-pressure R.F. plasma at 430 °C for 72 min under a gas mixture of 60% N₂–40% H₂. Structural, compositional and magnetic properties of the plasma nitrided layer was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and magnetic force microscopy (MFM). The magnetic behaviour of the nitrided layer was also investigated with a vibrating sample magnetometer (VSM). Combined X-ray diffraction, cross-sectional SEM, AFM and MFM, as well as VSM analyses provide strong evidence for the formation of the γ_N phase, [γ_N-(Fe, Cr, Ni)], with mainly ferromagnetic characteristics. The uniform nature of the γ_N layer is clearly demonstrated by the XRD, cross-sectional SEM and AFM analyses. Based on the AFM and SEM data, the thickness of the γ_N layer is found to be ～6 μm. According to the MFM and VSM analyses, ferromagnetism in the γ_N layer is revealed by the observation of stripe domain structures and the hysteresis loops. The cross-sectional MFM results demonstrate the ferromagnetic γ_N phase distributed across the plasma nitrided layer. The MFM images show variation in the size and form of the magnetic domains from one grain to another.     

Microstructure and dry-sliding wear properties of DC plasma nitrided 17-4 PH stainless steel

An attempt that the precipitation hardening steel 17-4PH was conducted by DC plasma nitriding (DCPN) is made to develop a kind of candidate material for nuclear reactor. Nitriding process performed at temperature ? 400 °C takes effect on creation of the layers composed of S-phase (expanded austenite) and (expanded martensite). Up to the temperature of 420 °C, the S-phase peaks disappear due to the transformation occurrence (S-phase → + CrN). For the samples nitrided at temperature ? 450 °C, no evidence of is found owing to a precipitation () taking place. For the 480 °C/4 h treated sample, it is the surface microhardness that plays the lead role in the wear rate reduction but the surface roughness; while for the 400 °C/4 h treated sample, it is both of the surface roughness and the S-phase formation. Dry sliding wear of the untreated 17-4PH is mainly characterized by strong adhesion, abrasion and oxidation mechanism. Samples nitrided at 400 °C which is dominated by slight abrasion and plastic deformation exhibit the best dry sliding wear resistance compared to the samples nitrided at other temperatures.     

Optimization Study of Pulsed DC Nitrogen-Hydrogen Plasma in the Presence of an Active Screen Cage

A glow discharge plasma nitriding reactor in the presence of an active screen cage is optimized in terms of current density,filling pressure and hydrogen concentrations using optical emission spectroscopy（OES）.The samples of AISI 304 are nitrided for different treatment times under optimum conditions.The treated samples were analyzed by X-ray diffraction（XRD） to explore the changes induced in the crystallographic structure.The XRD pattern confirmed the formation of iron and chromium nitrides arising from incorporation of nitrogen as an interstitial solid solution in the iron lattice.A Vickers microhardness tester was used to evaluate the surface hardness as a function of treatment time（h）.The results showed clear evidence of improved surface hardness and a substantial amount of decrease in the treatment time compared with the previous work.     

Diffraction of fast atoms under axial surface channeling conditions

For scattering of fast atoms under axial channeling conditions from surfaces diffraction effects have been observed in the distributions for scattered projectiles. Basic features concerning this recently observed new phenomenon in ion/atom surface scattering will be demonstrated for collisions of light atoms with well ordered clean and adsorbate covered surfaces of insulators and metals. We will focus our discussion on the scattering of ³He atoms with keV energies from a LiF(0 0 1) surface along low indexed axial surface channels and deduce the corrugation of the He-LiF(0 0 1) interaction potential from intensity modulations of the diffraction spots. Furthermore, we observe for the first time interference effects also for He⁺ ions which undergo charge exchange during scattering from the surface. The potential of the method for the investigation of structures of surfaces is discussed.     

Argon plasma irradiation of polypropylene

Polypropylene samples were exposed to argon plasma discharge and the changes of the PP surface properties were studied by different methods. Surface wettability was derived from contact angle measured by standard goniometry and chemical structure of the plasma modified PP was studied using X-ray photoelectron spectroscopy (XPS) and by Rutherford backscattering spectroscopy (RBS), surface morphology and roughness of samples using AFM. Zeta potential of pristine and modified PP was determined with the SurPASS. The presence of incorporated oxygen in the PP surface layer, about 60 nm thick, was observed in RBS spectra. Oxygen concentration is a decreasing function of the depth. With progressing aging time the oxygen concentration on the PP surface decreases. Plasma treatment results in a rapid decrease of the contact angle, which increases again with increasing aging time. In XPS measurement the oxygen containing structures, created by the plasma treatment, were found on the very surface of the modified PP and the zeta potential being changed too. The significant difference in zeta potential between pristine and plasma treated PP clearly indicates that the plasma treatment leads to a more hydrophilic PP surface.     

Research status and issues of tungsten plasma facing materials for ITER and beyond

This review summarizes surface morphology changes of tungsten caused by heat and particle loadings from edge plasmas, and their effects on enhanced erosion and material lifetime in ITER and beyond. Pulsed heat loadings by transients (disruption and ELM) are the largest concerns due to surface melting, cracking, and dust formation. Hydrogen induced blistering is unlikely to be an issue of ITER. Helium bombardment would cause surface morphology changes such as W fuzz, He holes, and nanometric bubble layers, which could lead to enhanced erosion (e.g. unipolar arcing of W fuzz). Particle loadings could enhance pulsed heat effects (cracking and erosion) due to surface layer embrittlement by nanometric bubbles and solute atoms. But pulsed heat loadings alleviate surfaces morphology changes in some cases (He holes by ELM-like heat pulses). Effects of extremely high fluence (∼10³⁰ m⁻²), mixed materials, and neutron irradiation are important issues to be pursued for ITER and beyond. In addition, surface refurbishment to prolong material lifetime is also an important issue.     

Cytocompatibility of Ar plasma treated and Au nanoparticle-grafted PE

Polyethylene (PE) was irradiated with inert Ar plasma, and the chemically active PE surface was grafted with Au nanoparticles. The composition and the structure of the modified PE surface were studied using X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectroscopy (RBS). Changes in the surface wettability were determined from the contact angle measured in a reflection goniometer. The changes in the surface roughness and morphology were followed by atomic force microscopy (AFM). The modified PE samples were seeded with rat vascular smooth muscle cells (VSMC) or mouse NIH 3T3 fibroblasts, and their adhesion and proliferation were studied. We found that plasma discharge and Au grafting lead to dramatic changes in the surface morphology and roughness of PE. The Au nanoparticles were found not only on the sample surface, but also in the sample interior up to the depth of about 100 nm. In addition, plasma modification of the PE surface, followed with grafting Au-nanoparticles, significantly increased the attractiveness of the PE surface for the adhesion and growth of VSMC, and particularly for mouse embryonic 3T3 fibroblasts.     

Dense plasma focus ion-based titanium nitride coating on titanium

We report the synthesis of titanium nitride coating on a titanium substrate by utilizing energetic nitrogen ions emitted from a 2.3 kJ dense plasma focus device for 30 focus shots. The number of nitrogen ions transferred to the sample by a single ion pulse of about 140 ns duration in the energy interval (40-600 keV) is about 1.09 × 10¹² with a mean energy per ion of 58 keV. The corresponding energy flux delivered to the titanium surface is estimated to be 6.17 × 10¹⁴ keV cm⁻³ ns⁻¹ leading to a transient temperature rise of the top layer of about 5400 K which helps layer growth. The coating is investigated on the basis of its morphological, compositional and hardness properties. X-ray diffraction analysis of the sample reveals the formation of a nanocrystalline titanium nitride coating having (1 1 1) and (2 0 0) plane reflections with an average crystallite size of 40 nm. The compressive residual stresses in the nitride coating have been evaluated to be 2.80 GPa and 6.81 GPa corresponding to (1 1 1) and (2 0 0) plane orientations. A complete restructuring of the manually polished titanium substrate has been observed with appearance of nano-sized multidimensional granular surface morphologies. The thickness of the nitride coating is about 1 μm, whereas the coating has a nitrogen content of 35.35 at.% and 13.78 ± 3.57 wt.% and a surface hardness of 8.19 GPa.     

Laser induced plasma plume imaging and surface morphology of silicon

Shot-to-shot variation in the characteristics of laser produced plasma plume and surface profile of N-type silicon (1 1 1) are investigated. In order to produce plasma, a Q-switched Nd: YAG laser (1064 nm, 10 mJ, 9-14 ns) is tightly focused on silicon target in air at room temperature. Target was exposed in such a way that number of laser shots was increased from point to point in ascending order starting from single shot at first point. Target was moved 2 mm after each exposure. In order to investigate shot-to-shot variation in the time integrated emission intensity regions within the plasma plume, a computer controlled CCD based image capture system was employed. Various intensity regimes were found depending strongly on the number of incident laser pulses. Plasma plume length was also found to vary with the number of pulses. The topographic analysis of the irradiated Si was performed by Scanning Electron Microscope (SEM) which shows the primary mechanisms like thermal or non-thermal ablation depend on the number of shots. Surface morphological changes were also studied in terms of ripple formation, ejection, debris and re-deposition of material caused by laser beam at sample surface. The micrographs show ripples spacing versus wavelength dependence rule [Λ ≈ λ/(1 − sin θ)]. Intensity variations with number of shots are correlated with the surface morphology of the irradiated sample.     

Investigation of biomass surface modification using non-thermal plasma treatment

The effects of non-thermal plasma (NTP) treatment on biomass in the form of pulverized palm- based empty fruit bunches (EFB) are investigated. Specifically, this study investigates the effects of NTP treatment on the surface reactivity, morphology, oxygen-to-carbon (O/C) ratio of the EFB at varying treatment times. The surface reactivity is determined by the reaction of antioxidant functional groups or reactive species with 2,2-diphenyl-1-picrylhydrazyl (DPPH). By measuring the concentration of the DPPH with a spectrophotometer, the change in the amount of antioxidant functional groups can be measured to determine the surface reactivity. The reactions of the various lignin components in the EFB with respect to the NTP treatment are discussed by qualitatively assessing the changes in the Fourier transform infrared (FTIR) spectra. The surface morphology is examined by a scanning electron microscope. To determine the amount of oxygen deposited on the EFB by the air-based NTP treatment, the oxygen and carbon contents are measured by an energy dispersive x-ray detector to determine the O/C ratio. The results show that the NTP reactor produced reactive species such as atomic oxygen and ozone, increasing the surface reactivity and chemical scavenging rate of the EFB. Consequently, the surface morphology changed, with an observed rougher surface from the images of the EFB samples. The change in the appearance of the surface is accompanied by a high O/C ratio, and is caused by reactions of certain components of lignin due to the NTP treatment. The lignin component that was modified is believed to be syringyl, as the syringyl portion in the lignin of EFBs is higher compared to the other components. Syringyl components are detected in the range of FTIR wavenumbers of 1109–1363cm ⁻¹ . With increasing NTP treatment times, the absorbance (of the peaks in the FTIR spectra) for syringyl related C−H and lignin associated C=C bonds decreases as the syringyl decomposes. The resulting release of carboxyl compounds increases the absorbance for the carbonyl C=O group. The results show that NTP treatment is able to modify the surface properties of EFB, and that the surface reactivity can be increased to improve their conversion and processing efficiencies     

辉光等离子体氮化铀表面的氢腐蚀

采用辉光等离子体氮化方法制备铀表面氮化样品。俄歇电子能谱和X射线衍射对样品的分析表明,铀表面形成了厚约250 nm、主要成分为α-U₂N_3+x的氮化层,氮化层与基体之间具有平缓的过渡层,且氮在金属铀的基体内有一定扩散。与轻微氧化样品氢腐蚀的对比实验表明,氮化处理使样品表面缺陷密度减少,改性层对氢吸附、扩散有阻挡作用,氢蚀形核较慢且其生长明显受到改性层的抑制,这表明铀表面辉光等离子体氮化可作为延缓氢腐蚀的有效手段。     

Formation and use of oxide films to impede outgassing of metals

Phenomena associated with the outgassing of metals are generally interpreted by using models based either on desorption of compounds from the surface or on diffusion of dissolved gases from the interior of the metal. It is generally recognized that surface oxide films can serve to decrease outgassing rates of metals. However, the processes associated with the outgassing of oxidized or oxide-coated metals are not well understood. Outgassing of oxidized metals is considered in light of the results of recent studies of hydrogen permeation through metals with well-characterized oxide films. The chemical stabilities of the oxides, as well as the physical imperfections of the film, are considered. A model is suggested for the expected outgassing behavior of oxidized steels at temperatures which are of interest in the design of controlled thermonuclear research experiments and reactors. The role of impurities and the usefulness of specialized oxidation treatments are discussed.     

Measurement of the Energy of Nitrogen Ions Produced in Filippov Type Plasma Focus Used for the Nitriding of Titanium

In this paper the nitrogen ion properties (maximum energy, current density and the most probable energy) are investigated by using Faraday cup in a time of flight method. These ions are produced in a Filippov type plasma focus (Sahand Facility) device and the Faraday cup was placed in a distance range of 18–24?cm from the top of the anode. Maximum and minimum most probable ion energies are 76 and 8.5?keV for the distance range of 18 and 24?cm, respectively. The displacement from 18 to 24?cm at top of the anode the ion current density varies from 4.5?×?10⁶ to 3.2?×?10⁵ (A?m^?2). For the investigation of the effect of ions bombardment of materials at different positions, at the optimum working conditions of 14?kV as a working voltage, and 0.25?Torr as a gas pressure, titanium samples are placed in a distance of 21, 22, 23 and 24?cm from the top of the anode (θ?=?0) and each sample is put under irradiation for 30 plasma shots. The structure of the nitrided surfaces and their morphologies are characterized by X-ray diffractometry and by scanning electron microscopy, respectively. The average crystallite size deduced for (200) and (222) planes of TiN deposited with 30 shots in different distances are estimate to be from ~13 to ~38?nm.     

Deposition of tungsten nitride on stainless steel substrates using plasma focus device

Tungsten nitride (WN) films were deposited on the stainless steel-304 substrate by a 2 kJ Mather-type plasma focus device. The preparation method and characterization data are presented. X-ray diffractometer (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed for the characterization of the samples obtained with different number of focus shots, respectively. The average size of crystallites (from XRD), sub-micro-structures (from SEM) and particles (from AFM images) increase when the number of shots increase from 10 to 20 then 30, then they decrease when the substrate is exposed to 40 shots.     

用于材料表面强化处理的第三代多功能PⅢ装置

第三代多功能等离子体浸没离子注入（PⅢ）装置的强流脉冲阴极弧金属等离子体源既具有强的镀膜功能，同时也具有强的金属离子注入功能；它的脉冲高压电源能输出大的电流；并可获得高的注入剂量均匀性。该装置既能执行离子注入，又能把离子注入与溅射沉积，镀膜结合在一起，形成多种综合笥表面改性工艺。本文描述了它的主要设计原则、主要部件的特性以及近期的研究工作成果。     

Deposition of zirconium carbonitride composite films using ion and electron beams emitted from plasma focus device

Nanocrystalline zirconium carbonitride (ZrCN) composite films were deposited on zirconium substrates for multiple (10, 20, 30, 40 and 50) focus shots. X-ray diffraction analysis shows diffraction peaks corresponding to nitrides (ZrN, Zr₂N and Zr₃N₄), carbide (ZrC) and carbonitride (Zr₂CN), confirming the formation of ZrCN composite films. The average crystallite size estimated for ZrN (2 0 0) and Zr₂CN (1 1 1) planes are found to vary from 10 to 20 nm. Maximum compressive stresses of ∼3.9 GPa in Zr₂N (0 0 2) plane for 30 focus shots and maximum tensile stresses of ∼6.5 GPa in ZrN (2 0 0) plane for 20 focus shots are observed. Tensile stresses observed in Zr₂CN (1 1 1) plane are transformed to compressive stresses for higher (40 and 50) focus shots. Raman analysis reveals the emergence of D and G bands related to carbide phases during the film deposition process. Scanning electron microscope analysis exhibits the nanocrystalline microstructure patterns of the composite films. Microstructure patterns showing agglomerates of 30-300 nm dimensions are also observed. Microhardness values of ZrCN composite films increases with increasing number of focus shots and is equal to 5.6 ± 0.45 GPa for 10 g imposed load, which is 4.5 times that of the virgin one.     

Coating of Titanium Nitride on Stainless Steel Targets by a 4?kJ Plasma Focus Device

Titanium nitride thin films were deposited on stainless steel (SS316L) targets by using a 4?kJ plasma focus device. The corresponding energy flux delivered to SS316L surface is estimated to be 2.69?×?10¹³?kev?cm^?3?ns^?1. X-ray diffraction analysis reveals the formation of a nanocrystalline titanium nitride coating on the surface of targets. Thickness of the elements found on the surface of treated samples which are obtained by Rutherford backscattering spectrometry analysis (RBS) were (×10¹⁵ at/cm²) .45% Ti, 50% N and 5% Fe. Scanning electron microscopy was used to indicate changes in surface morphology. Existence of grains in different size confirms the formation of TiN crystals on the surface of targets.     

The ablation characteristics of laser-assisted pulsed plasma thruster with metal propellant

In this study,a laser-assisted pulsed plasma thruster (LA-PPT) with a novel configuration is proposed as an electric propulsion thruster which separates laser ablation and electromagnetic acceleration.Owing to the unique structure of the thruster,metals can also be used as propellants,and a higher specific impulse is expected.The ablation quality,morphology,and plume distribution of various metals (aluminium alloy,red copper,and carbon steel) with different laser energies were studied experimentally.The ablation morphology and plume distribution of red copper were more uniform,as compared to those of other metals,and the ablation quality was higher,indicating its greater suitability for LA-PPT.The plume generated by nanosecond laser ablation of aluminium alloy expanded faster,which indicated that the response time of the thruster with aluminium alloy as the propellant was shorter.In addition,when the background pressure was 0.005 Pa,an obvious plume splitting phenomenon was observed in the ablation plume of the pulsed laser irradiating aluminium alloy,which may significantly reduce the utilisation rate of the propellant.