A simple model for the interaction of a low-current vacuum arc with a copper cathode

Experimental and theoretical studies of the arc-cathode region have been made for several decades, but the task is not yet complete, despite many efforts and much progress. In this work, a numerical model describing the arc-cathode region is developed. The arc is treated as a steady-state phenomenon. The model is then applied to a vacuum arc discharge interacting with a Cu cathode at low current of 4–50 A. The model yields the temperature and electric field strength at the cathode surface, density of the current of the electrons emitted, total current density, cathode spot radius, different kinds of power densities in heating and cooling the cathode, and the plasma electron density. The comparison with experimental results shows good agreement. Published in Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 6, pp. 63–72, November–December, 2007.     

Photocatalytic pretreatment of oily wastewater from the restaurant by a vacuum ultraviolet/TiO2 system

The present study aims at investigating the performance of a vacuum ultraviolet (VUV, 185 nm) and TiO(2) oxidation system for the pretreatment of oily wastewater from restaurant. The influence of irradiation time, pH, dissolved oxygen (DO), the dosage of TiO(2) and the initial chemical oxygen demand (COD) concentration on COD removal efficiency was ascertained and optimum process conditions for stable and effective operation were determined. Under the optimum conditions of irradiation 10 min, initial COD 3981 mg/L, TiO(2) 150 mg/L, pH 7.0 and flow rate of air 40 L/h, the process of VUV and TiO(2)/VUV achieved removal efficiencies of COD, BOD(5) and oil as 50±3%, 37±2%, 86±3%, and 63±3%, 43±2%, 70±3%, respectively. The biodegradability factor f(B) of the wastewater was determined as 1.56 which indicated that the VUV/TiO(2) process improved the biodegradability of the oily wastewater significantly. Results clearly indicate that VUV/TiO(2) photolysis tends to destruct parts of COD, BOD(5), and ammonia, as well as enhances the biodegradability of the oily wastewater simultaneously. Thus, this technique could be used as a pretreatment step for conventional biological treatment of oily wastewater.     

Experimental study of the transition to high-current regime of discharge with a hollow self-heated titanium cathode in nitrogen

It is established that rapid formation of a nitride layer on the surface of a self-heated hollow titanium cathode in arc discharge in nitrogen leads to an increase in the thermal stability and emissive properties of the cathode. Optimum regimes of cathode training that ensures rapid Ti → TiN transition over the entire cathode wall thickness in the active zone are determined, which allows the operation temperature to be increased above 2200 K at a discharge current of up to 50 A for the cathode with an inner diameter of 8 mm and a wall thickness of 1 mm. Results of measurements of the current-voltage characteristics of discharge, thermal regimes of operation, and chemical composition of the cathode are presented. The rates of erosion of the cathode operating in nitrogen and argon have been determined.     

Development and study of a radiance measurement system based on a CCD array in the vacuum and near ultraviolet region

We describe methods and instrumentation that we have developed for measuring the radiance distribution over the emitting region of plasma emitters in the extreme vacuum ultraviolet region. The radiance comparator for vacuum and near ultraviolet radiation includes a reflecting telescope based on highly reflective nanostructures, a set of filters to eliminate the effect of scattered light and higher orders of diffraction, and a cooled CCD array.     

Improving the conductance of ZnO thin film doping with Ti by using a cathodic vacuum arc deposition process

The Ti-doped ZnO films compared to un-doped ZnO films were deposited onto Corning XG glass substrates by using a cathodic vacuum arc deposition process in a mixture of oxygen and argon gases. The structural, electrical and optical properties of un-doped and Ti-doped ZnO films have been investigated. When the Ti target power is about 750 W, the incorporation of titanium atoms into zinc oxide films is obviously effective. Additionally, the resistivity of un-doped ZnO films is high and reduces to a value of 3.48 × 10⁻³ Ω-cm when Ti is incorporated. The Ti doped in the ZnO films gave rise to the improvement of the conductivity of the films obviously. The Ti-doped ZnO films have > 85% transmittance in a range of 400-700 nm.     

Estimation of safe exposure time from an ophthalmic operating microscope with regard to ultraviolet radiation and blue-light hazards to the eye

Hazards from the optical radiation of an operating microscope that cause damage at the corneal, lenticular, and retinal levels were investigated; we considered, in particular, ultraviolet radiation (UVR) and blue light. The spectral irradiance from a Zeiss operation microscope OPMI VISU 200 was measured in the corneal plane between 300 and 1100 nm. Effective irradiance and radiance were calculated with relative spectral effectiveness data from the American Conference for Governmental and Industrial Hygienists. Safe exposure time to avoid UVR injury to the lens and cornea was found to be 2 h without a filter, 4 h with a UVR filter, 200 a yellow filter, and 400 h with a filter combination. Safe exposure time to avoid retinal photochemical injury was found to be 3 min without a filter and with a UVR filter, 10 min with a yellow filter, and 49 min with a filter combination. The effective radiance limit for retinal thermal injury was not exceeded. The hazard due to the UVR component from the operating microscope is not critical, and operation time can be safely prolonged with the use of appropriate filters. The retinal photochemical hazard appears critical without appropriate filters, permitting only some minutes of safe exposure time. The calculated safe exposure times are for worst-case conditions and maximal light output and include a safety factor.     

Direct-Sun column ozone retrieval by the ultraviolet multifilter rotating shadow-band radiometer and comparison with those from Brewer and Dobson spectrophotometers

A methodology for direct-Sun ozone retrieval using the ultraviolet multifilter rotating shadow-band radiometer (UV-MFRSR) is presented. Total vertical column ozone was retrieved in three stations: Mauna Loa, Hawaii, in the U.S., and Regina, Saskatchewan, and Toronto, Ontario, in Canada, from direct solar irradiances of the UV-MFRSR at 325-, 305-, 332-, and 311-nm channels (2-nm FWHM). The total uncertainty of ozone retrievals in this study is +/-2.0%. For Mauna Loa the mean ratios of the UV-MFRSR column ozone retrievals to the collocated Dobson and Brewer were 0.998 and 0.986 between May and September of 1999. The mean ratio of UV-MFRSR retrievals to the collocated Brewer retrievals was 1.012 in Toronto between April and August of 1999, and the mean ratio of retrievals of the UV-MFRSR to the collocated Brewer was 0.988 in Regina between June and September of 1999. Total vertical column ozone values for solar zenith angles of >70 degrees were not considered, because of the signal-to-noise ratio and the angular response of the instruments, and were not used in the evaluation. The advantages of total vertical column ozone retrieval using UV-MFRSR include relatively low cost, computer-controlled operation, automated calibration stability checks, and minimal maintenance. It allows for the real-time measurement of total vertical column ozone. The UV-MFRSR is being used at 28 sites across the United States and 2 sites in Canada that form the U.S. Department of Agriculture UV-B Radiation Monitoring and Research Program. This constitutes a unique network of total vertical colunm ozone measurement.     

The influence of deposition rate on the stress and microstructure of AlN films deposited from a filtered cathodic vacuum arc

Aluminium nitride (AlN) thin films have been reactively deposited using a filtered cathodic vacuum arc system. A pulsed substrate bias was applied in order to increase the average energy of the depositing species. The stress and microstructure of the films were determined as a function of the deposition rate and pulse bias amplitude/frequency. The stress generated in films grown with high voltage pulsed bias depended on the deposition rate and a transition from tensile stress to compressive stress occurred as the deposition rate increased. This trend was accompanied by progressive changes in the microstructure. In order of increasing deposition rate, the films exhibited: a porous structure with tensile stress; a dense AlN film with compressive stress; and a dense AlN film showing evidence of a thermally induced reduction in stress.     

Structural and optical properties of Ti-doped ZnO thin films prepared by the cathodic vacuum arc technique with different annealing processes

Highly transparent Ti-doped ZnO thin films were prepared on glass substrates at a deposition rate of approximately 33 nm/min using the cathodic vacuum arc technique with a Zn target power of 550 W and a Ti target power of 750 W, respectively. X-ray diffraction measurements have shown that the Ti-doped ZnO thin film with a vacuum post-annealing condition is c-axis oriented but an amorphous phase at the other post-annealing atmosphere and as-deposited condition. Transmittance measurements show that the best optical quality of the Ti-doped ZnO thin films occurred at a post-annealing atmosphere of N₂/H₂ mixed gases. Additionally, the optical transmittance of all films has been found more than 85% in a range of 500-700 nm. The lowest electrical resistivity was 3.48 × 10⁻³ Ω cm, obtained on as-deposited films. However, the post-annealing condition greatly increased the resistivity.     

Calibration of ultrahigh vacuum gauge from 10 Pa to 10 Pa by the two-stage flow-dividing system

A new two-stage flow-dividing system has been developed for the calibration of ultrahigh vacuum gauges from 10⁻⁹ Pa to 10⁻⁵ Pa for N₂, Ar, and H₂. This system is designed based on the techniques for our previously developed calibration system in the range from 10⁻⁷ Pa to 10⁻² Pa. Three modifications were performed to extend the calibration pressure to a lower range. The relative standard uncertainty of the generated pressure (k = 1) is in the range from 2.3% to 2.6%, from 10⁻⁹ Pa to 10⁻⁵ Pa. The characteristics of ultrahigh vacuum gauges were also examined by using this system. The stabilities of the pressure reading, the linearity, the temperature dependence, and the long-term stability were examined. These results show that the calibration of ultrahigh vacuum gauges is possible in the range from 10⁻⁹ Pa to 10⁻⁵ Pa for N₂, Ar, and H₂ with the uncertainty of about 6.0% (k = 2) by this new system.     

Effects of spray parameters on the microstructure and property of Al2O3 coatings sprayed by a low power plasma torch with a novel hollow cathode

Al₂O₃ coating is deposited using a low power plasma torch with a novel hollow cathode through axial powder injection under a plasma power up to several kilowatts. The effects of the main processing parameters including plasma arc power, operating gas flow and spray distance on particle velocity during spraying, and the microstructure and property of the coating are investigated. The microstructure of the Al₂O₃ coating is examined using optical microscopy and X-ray diffraction analysis. The property of the coating is characterized by dry rubber wheel abrasive wear test. The velocity of in-flight particle is measured using a velocity/temperature measurement system for spray particle based on thermal radiation from the particle. The dependency of the microstructure and property of the coating on spray particle conditions are examined by comparing the particle velocity, and microstructure and abrasive wear weight loss of subsequent coating deposited by low power plasma spray with those of the coating by conventional plasma spray at a power one order higher. X-ray diffraction analysis of the coating revealed that Al₂O₃ particles during low power plasma spraying reach to sufficiently melting state prior to impact on the substrate with a velocity comparable to that in conventional plasma spraying. The experiment results have shown that processing parameters have significant influence on the particle conditions and performance of deposited Al₂O₃ coating. The coating of comparable microstructure and properties to that deposited by conventional plasma spray can be produced under a power one order lower. From the present study, it can be suggested that a comparable coating can be produced despite plasma power level if the comparable particle velocity and molten state are achieved.     

A method for the measurement of thin film optical constants with a spectral photometer from 230 nm to 850 nm and its application to plasma silicon (oxy) nitride

A technique to measure the complex index of refraction of thin solid films in the visible and near-UV range with a spectral photometer using polarized light is introduced. The complex index of refraction of amorphous silicon (oxy)nitride films deposited in a glow discharge with different gas flow ratios of NH₃:SiH₄ and N₂O:SiH₄ at 270°C was measured as a function of wavelength. The real part of the index of refraction at 632.8 nm of the films investigated varies from 1.5 to 2.5. The results could be confirmed by scanning ellipsometry.     

Structures and light emission properties of nanocrystalline FeSi2/Si formed by ion beam synthesis with a metal vapor vacuum arc ion source

Thin layers of nanocrystalline FeSi₂ embedded in Si structures have been formed by Fe implantation using a metal vapor vacuum arc (MEVVA) ion source under various implantation and thermal annealing conditions. The microstructures were studied in details and correlated with the photoluminescence (PL) properties. It is found that higher lattice coherence between the FeSi₂ nanocrystals and the Si matrix is associated with better light emission efficiency. Multiple-cycle implantation schemes were introduced and it is shown that with appropriate process design the dose quenching effect can be suppressed to achieve light emission enhancement in higher dose samples. De-convolution of the PL spectra into two or three peaks was performed and their temperature and excitation power dependence were analyzed. The analysis results indicate that the 1.55-μm emission really originated from FeSi₂ and that the emission peaks are likely donor- or accepted-level-related. MOS structures with the incorporation of implanted nanocrystalline FeSi₂ were fabricated. Electroluminescence (EL) spectra from these devices showed two peak features of which one peak corresponds to FeSi₂ emission and the other corresponds to enhanced Si band-edge emission. Clear room-temperature EL signals from these device structures were observed. A model is proposed to qualitatively understand the temperature dependence of the EL spectra.     

Computer simulation comparison of efficiencies of the time-interval and digital methods of detecting radiation described by a normal distribution

A comparative analysis of the time-interval and digital methods of detecting radiation described by a normal distribution is carried out by computer simulation. An algorithm is developed for simulating these methods and calculating their performance curves. A conclusion is drawn as to their suitability for practical application. Translated from Izmeritel'naya Tekhnika, No. 3, pp. 39–40, March, 1999.     

Comparison of the characteristics of a plasma generated by a d.c. arc plasmatron and a high-voltage a.c. plasmatron with rail-shaped electrodes (gliding arc) as applied to the synthesis of carbon nanomaterials

Comparative results of investigating the parameters of plasmas generated by atmospheric-pressure electric-arc plasmatrons of two types operating in the regime of simultaneous partial oxidation of hydrocarbons and their pyrolysis, have been given. It has been established by spectral and thermophysical measurements that the component composition of the plasma and its thermal characteristics at exit from a d.c. plasmatron significantly differ from the parameters of a plasmatron of the second type — an a.c. plasmatron with rail-shaped electrodes of the gliding-arc type. The temperature nonequilibrium and the presence of the carbon dimers C₂ in the plasma (in the absence of the monomer C) generated by the rail-shaped-electrode plasmatron point to the fact that realization of the synthesis of fullerene-containing particles and, probably, particles containing nanotubes is, in principle, possible in reactors based on it, just as in more energy-intensive reactors with low-voltage d.c. arc plasmatrons. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 4, pp. 3–11, July–August, 2006.     

Mean and variance of energy reflected from a diffuse object illuminated by radiation with partial temporal coherence

Closed-form integral expressions are developed for the mean and variance of power and energy received from a diffusely reflective object upon illumination by laser radiation with partial temporal coherence. Expressions are presented in dimensionless form and analytic approximations to the integrals are given for signal variations at a receiver caused by fully developed laser speckle. Results are presented in terms of three parameters: the mutual Fresnel number of the receiver and object, the number of longitudinal modes of the illuminating source, and the dimensionless mode spacing of the illuminating source. The calculations assume high light levels and free-space geometry.     

Mathematical simulation of the transformation of radiation formed by a plane resonator and an optical system in a paraxial approximation

A mathematical model of the transformation of radiation produced by a flat optical resonator, single lens, and a two-lens optical system with the use of the Kirchhoff scalar theory of diffraction is constructed and investigated. __________ Translated from Izmeritel’naya Tekhnika, No. 11, pp. 20–23, November, 2007.     

How to search the experimental conditions that improve a Partial Least Squares calibration model: Application to a flow system with electrochemical detection for the determination of sulfonamides in milk

This paper deals with the selection of experimental conditions and how the signals obtained in these conditions influence the fitted Partial Least Squares calibration model. The multivariate signals come from a flow analysis system with amperometric detection when determining sulfadiazine, sulfamerazine and sulfamethazine in milk.The solution (carrier plus analyte) was pumped through the system to provide a continuous supply of analyte to the cell. The detector was programmed for a scan mode operation being the multivariate signal the hydrodynamic voltammogram. To obtain an analytical signal of enough analytical quality, the Net Analyte Signal and its standard deviation have been optimised by using an experimental design. The conflicting behaviour of the two responses has been solved by estimating the Pareto-optimal front.The multivariate signals recorded in the optimal conditions found have been calibrated by Partial Least Squares regression and their figures of merit validated according to the criteria established in European Decision 2002/657/EC.In relation to the permitted limit, 100 µg l^− 1 in milk, for the total content of sulfonamides established in the Commission Regulation EC no. 281/96 the proposed method has a decision limit of 109.1 µg l^− 1 and the capability of detection is 117.9 µg l^− 1 for both probability of false non-compliance and of false compliance equal to 5%. A recovery of 86.5% ± 2.4% (n = 5) has been obtained.     

Prediction of ethylene content in melt-state random and block polypropylene by near-infrared spectroscopy and chemometrics: comparison of a new calibration transfer method with a slope/bias correction method

This paper reports the prediction of the ethylene content (C2 content) in random polypropylene (RPP) and block polypropylene (BPP) in the melt state by near-infrared (NIR) spectroscopy and chemometrics. NIR spectra of RPP and BPP in the melt states were measured by a Fourier transform near-infrared (FT-NIR) on-line monitoring system. The NIR spectra of RPP and BPP were compared. Partial least-squares (PLS) regression calibration models predicting the ethylene (C2) content that were developed by using each RPP or BPP spectra set separately yielded good results (SECV (standard error of cross validation): RPP, 0.16%; BPP, 0.31%; correlation coefficient: RPP, 0.998; BPP, 0.996). We also built a common PLS calibration model by using both the RPP and the BPP spectra set. The results showed that the common calibration model has larger SECV values than the models based on the RPP or the BPP spectra sets individually and is not practical for the prediction of the C2 content. We further investigated whether a calibration model developed by using the BPP spectra set can predict the C2 contents in the RPP sample set. If this is possible, it can save a significant amount of work and cost. The results showed that the use of the BPP model for the RPP sample set is difficult, and vice versa, because there are some differences in the molar absorption coefficients between the RPP and BPP spectra. To solve this problem, a transfer method from one sample spectra (BPP) set to the other spectra (RPP) set was studied. A difference spectrum between an RPP spectrum and a BPP spectrum was used to transfer from the BPP calibration set to the RPP calibration set. The prediction result (SEP (standard error of prediction), 0.23%, correlation coefficient, 0.994) of RPP samples by the transferred calibration set and model showed that it is possible to transfer from the BPP calibration set to the RPP calibration set. We also studied the transfer from the RPP calibration set (the range of C2 content: 0-4.3%) to the BPP calibration set. The prediction result of C2 content (the range of C2 contents: 0-7.7%) in BPP by use of the calibration model based on the transferred BPP spectra from the RPP spectra showed that the transfer method is only effective for the interpolation of the C2 content range by the nonlinear change in the peak intensities with the C2 content.