Arc Plasma Jet Research Articles

Experimental measurements of surface damage and residual stresses in micro-engineered plasma facing materials

The thermomechanical damage and residual stresses in plasma-facing materials operating at high heat flux are experimentally investigated. Materials with micro-surfaces are found to be more resilient, when exposed to cyclic high heat flux generated by an arc-jet plasma. An experimental facility, dedicated to High Energy Flux Testing (HEFTY), is developed for testing cyclic heat flux in excess of 10 MW/m2. We show that plastic deformation and subsequent fracture of the surface can be controlled by sample cooling. We demonstrate that W surfaces with micro-pillar type surface architecture have significantly reduced residual thermal stresses after plasma exposure, as compared to those with flat surfaces. X-ray diffraction (XRD) spectra of the W-(110) peak reveal that broadening of the Full Width at Half Maximum (FWHM) for micro-engineered samples is substantially smaller than corresponding flat surfaces. Spectral shifts of XRD signals indicate that residual stresses due to plasma exposure of micro-engineered surfaces build up in the first few cycles of exposure. Subsequent cyclic plasma heat loading is shown to anneal out most of the built-up residual stresses in micro-engineered surfaces. These findings are consistent with relaxation of residual thermal stresses in surfaces with micro-engineered features. The initial residual stress state of highly polished flat W samples is compressive (≈ -1.3 GPa). After exposure to 50 plasma cycles, the surface stress relaxes to −1.0 GPa. Micro-engineered samples exposed to the same thermal cycling show that the initial residual stress state is compressive at (- 250 MPa), and remains largely unchanged after plasma exposure.

Interfacial stress evolution simulation on the graphite substrate/interlayer/diamond film during the cooling process

The addition of titanium (Ti) interlayer was verified to reduce the residual stress of diamond films. The evolution of interfacial stress during the cooling process is critical for the fabrication of large-area crack-free diamond films, so it is very worthy of further study. Variable-temperature X-ray diffraction (XRD) tests and finite element simulation were performed to evaluate the stress evolution of a diamond film. The film (with diameter of 150mm) was prepared on a graphite substrate with Ti interlayer using DC arc plasma jet. Residual compressive stress in the diamond film is gradually increased during the cooling process. Moreover, the value and growth rate of the residual stress from the XRD tests are significantly lower than the finite element simulation results. All XRD peaks of diamond, graphite, and titanium carbide (TiC) generated on both sides of the Ti interlayer shift to a larger angle. By contrast, several XRD peaks of Ti deviate to a low angle. Elastic deformation of the Ti layer may offset the lattice contraction caused by the cooling effect. Elasticity modulus of TiC is significantly greater than that of Ti, which is more inclined to release the stress of the diamond film by self-fracturing. After the variable-temperature tests, residual compressive stress of the diamond film at room temperature is 1.1GPa, whereas that before the tests is 1.4GPa. These values are significantly lower than the finite element simulation results (3.05GPa).

Intrinsic stress evolution during different growth stages of diamond film

The CVD diamond films at different growth stages were prepared on the same substrate by DC arc plasma jet CVD. The surface morphologies and residual stress of diamond films were characterized by scanning electron microscope and Raman spectroscopy. The intrinsic stress of diamond films were obtained by subtracting thermal stress from residual stress. The results showed that the intrinsic compress stress was 0.42GPa for the precoalescence stage due to the sp2 carbon inclusions in diamond islands. With the diamond islands growing up and even snapping together to form grain boundary at the coalescence stage the intrinsic compress stress was 0.06GPa. Eventually, the diamond islands coalesced into a continuous polycrystalline film, the intrinsic compress stress vanished and converted to tensile stress, the intrinsic tensile stress reached 1.41GPa due to the number of grain boundaries increasing. The evolution of intrinsic stress during diamond film initial growth was mainly attributed to the surface free energy of diamond islands changed to the free energy of grain boundaries which was consistent with the Nix-Clemens model.

Fabrication of graphene/titanium carbide nanorod arrays for chemical sensor application

Vertically stacked graphene nanosheet/titanium carbide nanorod array/titanium (graphene/TiC nanorod array) wires were fabricated using a direct current arc plasma jet chemical vapor deposition (DC arc plasma jet CVD) method. The graphene/TiC nanorod arrays were characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction spectroscopy. The TiO2 nanotube array was reduced to the TiC nanorod array, and using those TiC nanorods as nucleation sites, the vertical graphene layer was formed on the TiC nanorod surface. The multi-target response mechanisms of the graphene/TiC nanorod array were investigated for ascorbic acid (AA), dopamine (DA), uric acid (UA), and hydrochlorothiazide (HCTZ). The vertically stacked graphene sheets facilitated the electron transfer and reactant transport with a unique porous surface, high surface area, and high electron transport network of CVD graphene sheets. The TiC nanorod array facilitated the electron transfer and firmly held the graphene layer. Thus, the graphene/TiC nanorod arrays could simultaneously respond to trace biomarkers and antihypertensive drugs.

Mechanism of graphitization and optical degradation of CVD diamond films by rapid heating treatment

Polycrystalline CVD free-standing diamond films have been heat treated through a rapid heating process using a direct current (DC) arc plasma jet system within the temperature range of 1500–2000°C. The optical transmission of the diamond film decreases when the treatment temperature exceeds 1500°C. When the diamond film was annealed to 1800°C for just 1min, the infrared (IR) transmittance at λ=10.6μm of the film was significantly decreased from 60.5% to 4.0%, due to the transformation from diamond to graphite. Further increase of the temperature to 2000°C leads to complete loss of optical transmittance in only 30s, due to the detrimental occurrence of graphitization. XRD patterns indicate that graphite ultimately grows preferentially along the (0002) plane by forming disordered or turbostratic graphite as intermediate product. Raman spectra and SEM images verify that at 1500–1850°C graphitic carbon transforms from the diamond surface in the form of protruding submicron crystallites, which were still containing a number of sp3 CC bonds. In addition to graphitization on the external surface, the diamond-graphite phase transition also occurs along the grain boundaries and the calculated activation energy of the grain boundary graphitization process is 276kJ·mol−1 for the CVD diamond.

Plasmachemical Synthesis of Nanopowders in the System Ti(O,C,N) for Material Structure Modification

Refractory nanoparticles are finding broad application in manufacturing of materials with enhanced physical properties. Production of carbide, nitride, and carbonitride nanopowders in high volumes is possible in the multijet plasmachemical reactor, where temperature and velocity distributions in reaction zone can be controlled by plasma jet collision angle and mixing chamber geometry. A chemical reactor with three Direct Current (DC) arc plasma jets intersecting at one point was applied for titanium carbonitride synthesis from titanium dioxide, propane-butane mixture, and nitrogen. The influence of process operational parameters on the product chemical and phase composition was investigated. Mixing conditions in the plasma jet collision zone, particles residence time, and temperatures were evaluated with the help of Computational Fluid Dynamics (CFD) simulations. The synthesized nanoparticles have predominantly cubic shape and dimensions in the range 10–200 nm. Phase compositions were represented by oxycarbonitride phases. The amount of free (not chemically bonded) carbon in the product varied in the range 3–12% mass, depending on synthesis conditions.

Effect of carbon nanotube on processing, microstructural, mechanical and ablation behavior of ZrB2-20SiC based ultra-high temperature ceramic composites

Herein, zirconium diboride (ZrB2) is reinforced with silicon carbide (SiC) and carbon nanotube (CNT) to provide enhanced structural stability and oxidation protection against extreme thermal (>2400 °C) and oxidative environments. The ablation resistance of ZrB2-based composites was evaluated using plasma arc-jet with a heat-flux of 2.5 MW/m2 for 30 s, and the decreased oxidation-rate (from 0.77 μm/s to 0.44 μm/s) is attributed to enhanced thermal conductivity (42.3–52.3 W/mK at 1200 °C) with synergistic reinforcement of SiC and CNT. The increased onset temperature (from 679 °C to 706 °C) and decreased enthalpy of oxide formation (from 1.6 to 0.6 kJ/g), insinuates an increase in thermal stability and oxidation resistance with the synergistic addition of both SiC and CNT in ZrB2. The increase in the hardness of ZrB2 in the as-processed composites (up to 1.6 times) as well as after plasma arc jet exposure (up to 2.1 times) with synergistic reinforcement of SiC and CNT has shown to suppress crack-formation and restrict oxidation. The reduction in the analytically evaluated tensile interfacial residual stress indicates enhanced structural integrity of ZrB2-SiC-CNT composites, which is a mandatory requirement for aerospace applications.

Plasma Polymerization of 3‐Aminopropyltrietoxysilane (APTES) by Open‐Air Atmospheric Arc Plasma Jet for In‐Line Treatments

In this work, an open‐air arc plasma jet has been studied to polymerize 3‐aminopropyelthrietoxysilane (APTES), which is the most commonly used aminosilane to functionalize surfaces with amine groups. Although the discharge produced from air is highly oxidative and the gas temperature is high as compared to other atmospheric plasma sources, amine groups, as well as amide ones, were identified in the nanometers thick coatings by XPS and FTIR analysis. By comparing the results with post‐treatment and ‐grafting experiments, the partial retention of amine groups might be explained by the non‐ideal mixing of the precursor flow with the main gas stream inside the plasma jet. Beside the intrinsic plasma reactivity, hydrodynamics effects are indeed important when considering flowing atmospheric plasmas.

Interface features of the HPHT Ib substrate and homoepitaxial CVD diamond layer

This is a detailed study of the interface features of the HPHT Ib substrate and the homoepitaxial CVD diamond layer. Homoepitaxial diamond layers were prepared by a commercial type 30kWdc arc plasma Jet CVD on (100) substrates with gas mixture of Ar/H2/CH4. The internal stress and the fluorescence properties of the cross-section of the single crystal diamond bulk were characterized with polarizer optical microscopy, micro-Raman spectroscopy, and photoluminescence, as well as DiamondView luminescence imaging. A higher stress region in the homoepitaxial diamond layer near the substrate with width about 15μm was found exhibiting higher nitrogen content and presented different fluorescence properties. Studies on the surface morphology of the initial growth diamond indicated that the transformation of the surface morphology from growth hillocks to macrosteps, may play a crucial role in the interface feature.

Investigation on Plasma Jet Flow Phenomena During DC Air Arc Motion in Bridge-Type Contacts**supported by National Natural Science Foundation of China (Nos. 51307030, 51277038)

Arc plasma jet flow in the air was investigated under a bridge-type contacts in a DC 270 V resistive circuit. We characterized the arc plasma jet flow appearance at different currents by using high-speed photography, and two polished contacts were used to search for the relationship between roughness and plasma jet flow. Then, to make the nature of arc plasma jet flow phenomena clear, a simplified model based on magnetohydrodynamic (MHD) theory was established and calculated. The simulated DC arc plasma was presented with the temperature distribution and the current density distribution. Furthermore, the calculated arc flow velocity field showed that the circular vortex was an embodiment of the arc plasma jet flow progress. The combined action of volume force and contact surface was the main reason of the arc jet flow.

Cold Atmospheric Pressure Gliding arc Plasma Jet for Decontamination

A cold atmospheric pressure gliding arc plasma jet hasbeen developed and applied to disinfection. The size of the plasma output is about 6 mm in diameter and 10 mm in length. Ar gas at a flow rate of 10 slm and 25 W plasma power are used. Plasma discharge is produced between the divergent electrodes and the jet appears as an effluence of the gas flow. When a \textnormal{pseudomonas} culture is placed at 8 mm below the torch for 1minute, where the gas is at room temperature, the bacteria within a 16 mm diameter circle are almost completely killed. As the UV radiation is well below the safety regulation, the bacteria are inactivated by the total effect of UV radiation and others like the reactive species and the charged particles.

Effect of sputtered titanium interlayers on the properties of nanocrystalline diamond films

Ti interlayers with different thicknesses were sputtered on Si substrates and then ultrasonically seeded in a diamond powder suspension. Nanocrystalline diamond (NCD) films were deposited using a dc arc plasma jet chemical vapor deposition system on the seeded Ti/Si substrates. Atomic force microscopy and scanning electron microscopy tests showed that the roughness of the prepared Ti interlayer increased with increasing thickness. The effects of Ti interlayers with various thicknesses on the properties of NCD films were investigated. The results show nucleation, growth, and microstructure of the NCD films are strongly influenced by the Ti interlayers. The addition of a Ti interlayer between the Si substrate and the NCD films can significantly enhance the nucleation rate and reduce the surface roughness of the NCD. The NCD film on a 120 nm Ti interlayer possesses the fastest nucleation rate and the smoothest surface. Raman spectra of the NCD films show trans-polyacetylene relevant peaks reduce with increasing Ti interlayer thickness, which can owe to the improvement of crystalline at grain boundaries. Furthermore, nanoindentation measurement results show that the NCD film on a 120 nm Ti interlayer displays a higher hardness and elastic modulus. High resolution transmission electron microscopy images of a cross-section show that C atoms diffuse into the Ti layer and Si substrate and form TiC and SiC hard phases, which can explain the enhancement of mechanical properties of NCD.

Oxidation studies on TaC based ultra-high temperature ceramic composites under plasma arc jet exposure

An ultra-high temperature ceramic, TaC, is reinforced with SiC and carbon nanotubes (CNTs) to provide protection under extreme thermal and chemical environments. High temperature performance of spark plasma sintered TaC-based composites was evaluated through plasma arc-jet exposure under heat-flux of 2.5MW/m2 for 30s. The composite shows a significant improvement in the oxidation resistance compared to that of TaC. Complimentarily, thermogravimetric analyses (up to 1500°C) elicits shift in the onset temperature of oxide formation from 735°C in TaC to 901°C (with synergistic addition of both SiC and CNT) insinuating the enhanced thermal stability of TaC-SiC-CNT composites.

In situ measurement of the two-dimensional temperature field of a dual-jet direct-current arc plasma.

In this paper, a real time method for an in situ measurement of the two-dimensional (2-D) temperature filed of thermal plasmas is developed with the combination of the visible image processing technique and the spectroscopic line-ratio method at two specified wavelengths. After the calibration of the gray scale values of the recorded images with the CCD cameras by the emission intensity received using a spectrometer, the 2-D temperature field of the plasma arc-jet can be obtained conveniently based on the derived gray scale values of the CCD images at two specified wavelengths and the formula similar to that of spectroscopic line-ratio method. The experimental results show that the obtained temperature fields of the plasma arc-jet at different times are qualitatively reasonable and consistent with the modeling result. This newly developed method can be employed to measure the transient temperature fields of the plasmas with fluctuations during discharges effectively.

Structural evolution of Ti destroyable interlayer in large-size diamond film deposition by DC arc plasma jet

The addition of titanium (Ti) interlayer was verified to reduce the residual stress of diamond films by self-fracturing and facilitate the harvest of a crack-free free-standing diamond film prepared by direct current (DC) arc plasma jet. In this study, the evolution of the Ti interlayer between large-area diamond film and substrate was studied and modeled in detail. The evolution of the interlayer was found to be relevant to the distribution of the DC arc plasma, which can be divided into three areas (arc center, arc main, and arc edge). The formation rate of titanium carbide (TiC) in the arc main was faster than in the other two areas and resulted in the preferred generation of crack in the diamond film in the arc main during cooling. Sandwich structures were formed along with the growth of TiC until the complete transformation of the Ti interlayer. The interlayer released stress via self-fracture. Avoiding uneven fragile regions that formed locally in the interlayer and achieving cooperatively released stress are crucial for the preparation of large crack-free diamond films.

Numerical analyses of ablative behavior of C/C composite materials

Ablation experiments of C/C composite materials were conducted by using arc plasma jet. The ablated surfaces of the C/C composite material samples were monitored by using the online spectrum diagnoses during the ablation experiments. Based on energy balance, mass conservation and chemical equilibrium equations, surface ablative model was established for the C/C composite materials to study the ablation process and the thermal environment parameters. The simulation results are in good agreement with the theoretical solution and experimental results. The ablative experiment and analytical model can be recognized as the basic research method for the thermal protection materials in the aerospace applications.

Experimental setup for plasma treatment of disperse materials in the arc plasma jet

The experimental setup for the plasma treatment of particulate materials was created. Spend the processing of composite powder of chromium oxide with aluminium oxide.

Modification of MOS Devices by High-Field Electron Injection and Arc Plasma Jet Treatment

Modification of MOS Devices by High-Field Electron Injection and Arc Plasma Jet Treatment

Direct probing of anode arc root dynamics and voltage instability in a dc non-transferred arc plasma jet

The transient dynamics of the anode arc root in a dc non-transferred arc plasma torch is captured through fast photography and directly correlated with the associated voltage instability for the first time. The coexistence of multiple arc roots, the transition to a single arc root, root formation and extinction are investigated for the steady, takeover and re-strike modes of the arc. Contrary to the usual concept, the emerging plasma jet of a dc non-transferred arc plasma torch is found to carry current. An unusually long self-propelled arc plasma jet, a consequence of the phenomenon, is demonstrated.

Synthesis of a ZnO nanorod/CVD graphene composite for simultaneous sensing of dihydroxybenzene isomers

A few-layered graphene nanosheets on a Ta thin film were synthesized by a direct current (DC) arc plasma jet chemical vapor deposition (CVD) process that does not critically depend on cooling rates. The thickness of the graphene layer is about 20 μm, and the graphene sheets superimposed transversely on the outermost layer become a blooming bouquet. This structure is especially suitable as an electrode sensor. The ZnO nanorods have excellent electrochemical performance, and thus we combined ZnO nanorods and CVD graphene for a ZnO/graphene/Ta sensing electrode. The electrochemical oxidation of hydroquinone (HQ), catechol (CC), and resorcinol (RC) were investigated using cyclic voltammetry at the ZnO/graphene/Ta electrode. The results showed that it was feasible to simultaneously measure HQ, CC, and RC. The linear response ranges for HQ, CC, and RC were 0–70, 0–80, and 0–700 μmol L−1. The detection limits (S/N = 3) were 0.1, 0.2, and 1 μmol L−1, respectively. The ZnO/graphene layer shows high electrocatalytic activity toward the redox reaction of HQ, CC, and RC. This activity had high selectivity, high sensitivity and low detection limits.