Single-Frequency TEA CO<Subscript>2</Subscript> Laser for Experiments on Non-Resonant Radiation Interaction with Matter

The design philosophy and output radiation parameters of single frequency TEA CO₂ laser with bleaching intracavity longitudinal modes selector (cell filled with SF₆) are described. At cavity tuning to 10P(16) line and choosing optimum SF₆ pressure in the cell the stable single frequency lasing is realized with scatter of radiation peak power in a series of “shots” less than ±7% of average value. The radiation energy density and intensity gradually tuned in the ranges 0.36–12.5 J/cm² and 2.9–100 MW/cm² correspondingly were realized in the focal plane of a lens with f = 127 mm.     

Data recording system of a dispersion interferometer based on a CO<Subscript>2</Subscript> laser

The data recording system of a multichannel double-pass dispersion interferometer based on a CO₂ laser is described. This system has been designed to record the linear density of plasmas in a real-time mode with a time discreteness of 4 μs and resolution 〈N _e L〉 ～ 0.34 × 10¹³ cm^?2 (N _e is the electron component of the plasma density, and L is the plasma size in the wave propagation direction) in the range of linear density variations of up to 10¹⁷ cm^?2. The system is built from unified recording modules that use fast ADCs to record the shape of photodetector and modulator signals and FPGA-based digital units of dataflow processing to form results of measurements. The single-channel recording module of the dispersion interferometer has been tested under actual experimental conditions of the GDL gas-dynamic trap and the TEXTOR tokamak (Julich, Germany).     

A device for measuring the content of CO<Subscript>2</Subscript> dissolved in water

The design of a simple device intended for measuring carbon dioxide content in water is described. The device is a continuous-flow chamber with a water dispersion unit built into it.     

A stabilized pulsed repetition-rate CO<Subscript>2</Subscript> laser for a laser-plasma generator of multiply charged ions

The design of a laser oscillator with a stabilized frequency composition and a stabilized intensity of output radiation is described. The oscillator’s basic component is a TEA CO₂ module pumped by a self-maintained discharge and operating in a repetition-rate mode at a frequency of up to 3 Hz. A circuit for the formation of a self-maintained homogeneous discharge in the working volume of a CO₂ + N₂ + He mixture at atmospheric pressure is the basic component of the gas-discharge module. This circuit is based on the generation of a high-voltage pulse with a special profile, which provides high-reliability excitation of a discharge and pulse-to-pulse reproducibility of the discharge characteristics. The use of a hybrid circuit in the optical oscillator allows selection of a single longitudinal mode in the output radiation spectrum, thus eliminating undesirable interference phenomena, which lead to instability of the instantaneous values of the radiation intensity. During the development of the oscillator, the optimal operating parameters of the hybrid circuit were obtained, which ensure the high quality and reproducibility of the spatiotemporal and energy parameters of laser radiation.     

Synergistic Effect of Nano-MoS<Subscript>2</Subscript> and Anatase Nano-TiO<Subscript>2</Subscript> on the Lubrication Properties of MoS<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> Nano-Clusters

A MoS₃ precursor deposited on anatase nano-TiO₂ is heated at 450 °C in an H₂ atmosphere to synthesize MoS₂/TiO₂ nano-clusters. The nano-clusters are then characterized, and their tribological properties are evaluated. MoS₂ is found to be composed of layered structures with 1–10 nm thicknesses, 10–30 nm lengths, and 0.63–0.66 nm layer distances. The MoS₂ sizes in the MoS₂/TiO₂ nano-clusters are smaller and their layer distances are larger than those of pure nano-MoS₂. The MoS₂/TiO₂ nano-clusters also present a lower average friction coefficient than pure nano-MoS₂, but the anti-wear properties of both the nano-clusters and pure nano-MoS₂ are similar. X-ray photoelectron spectroscopy indicates that nano-TiO₂ and the element Mo are transferred to the friction surface from the MoS₂/TiO₂ nano-clusters through a tribochemical reaction. This produces a lubrication film containing TiO₂, MoO₃, and other chemicals. The nano-MoS₂ changes in size and layer distance when combined with nano-TiO₂, producing a synergistic effect. This may further be explained using a micro-cooperation model between MoS₂ nano-platelets and TiO₂ solid nanoparticles.     

An experimental study on laminar CH<Subscript>4</Subscript>/O<Subscript>2</Subscript>/N<Subscript>2</Subscript> premixed flames under an electric field

This work investigates the electric field effect on gas temperature, radiative heat flux and flame speed of premixed CH₄/O₂/N₂ flames in order to gain a better insight into the mechanism of controlling the combustion process by electrophysical means. Experiments were performed on laminar Bunsen flames (Re<2200) of lean to rich mixture composition (φ =0.8–1.2) with slight oxygen enrichment (Ω=0.21-0.30). The Schlieren flame angle technique was used to determine the flame speed, and thermocouple measurements at the post flame gas were conducted. The radiative heat flux was measured by using a heat flux meter. At high field strengths, coincident with the appearance and enhancement of flame surface curvatures, an apparent change in flame speed and gas temperature was observed. However, the application of an electric field had no significant effect on flame speed and temperature when the flame geometry was unaltered. This was supported by radiative heat flux showing negligible electric field effects. The modification in flame temperature and flame speed under electric field was attributed to the field-induced flame stretch due to the body forces produced by the ionic winds. This additional flame stretch, coupled with the influence of non-unity Lewis number, accounts for such changes. This reinforces the idea that the action of an electric field on flames with a geometry that remains practically undeformed produces very minimal effect on flame speed, temperature and radiative heat flux. A possible mechanism of combustion control by the application of flame stretch using electric field was introduced.     

Turbulence generation by ultrasonically induced gaseous cavitation in the CO<Subscript>2</Subscript> saturated water flow

Emission of ultrasonic vibration to turbulent flow promotes the turbulence generation due to the resonantly oscillating pressure field and thereby induced cavitation. In addition, ultrasonic vibration is well transmitted through water and not dissipated easily so that the micro-bubbles involved in the fluid induce the gaseous cavitation if the bubbles are resonated with the ultrasonic field. In the present study, we found through LDV measurement that the gaseous cavitation induced by ultrasonic vibration to CO₂ saturated water flow in the rectangular crosssectioned straight duct enhances turbulence much more than the case of non-ultrasonic or normal ultrasonic conditions without gaseous cavitation. We also found that the fluctuating velocity component induced by emitting the ultrasonic vibration in normal direction of a rectangular channel flow can be redistributed to stream-wise component by the agitation ol gaseous cavitation.     

Tribological duality of Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript>

We report here on the friction behavior of fine- and coarse-grained Ti₃SiC₂ against steel and Si₃N₄ balls. Two successive friction regimes have been identified for both grain sizes and both counterparts. First, Type I regime is characterized by a relatively low (0.1–0.15) friction coefficient, and very little wear. Sliding occurs between a tribofilm on the ball and the Ti₃SiC₂ plane when against steel. Then, a Type II regime often follows, with increased friction coefficients (0.4–0.5) and significant wear. Compacted wear debris seems to act as a third body resulting in abrasion of the ball, even in the case of Si₃N₄. The transition between the two regimes occurs at different times, depending on various factors such as grain size, type of pin, and normal load applied. Some experiments under vacuum showed that the atmosphere plays also a major role. The reason for this evolution is not fully clear at that time, but its understanding is of major technological importance given the unusual good properties of this material.     

Mechanical properties of CO<Subscript>2</Subscript>/MIG welded structural rolled steel and stainless steel

To accomplish long-term use of specific parts of steel, welding technology is widely applied. In this study, to compare the efficiency in improving mechanical properties, rolled steel (SS400) was welded with stainless steel (STS304) by both CO₂ welding method and MIG (metal inert gas) welding method, respectively. Multi-tests were conducted on the welded specimen, such as X-ray irradiation, Vickers’ Hardness, tensile test, fatigue test and fatigue crack growth test. Based on the fatigue crack growth test performed by two different methods, the relationship of da/dN was analyzed. Although the hardness by the two methods was similar, tensile test and fatigue properties of MIG welded specimen are superior to CO₂ welded one.     

A neutron semiconductor detector based on TIInSe<Subscript>2</Subscript>

A new semiconductor detector of neutron radiation based on a TIInSe₂ crystal has been investigated. The detector is produced from a homogeneous semiconductor sample with two electric contacts and operates in an integrating mode. It is shown that, owing to its high sensitivity (～10^?13 A/(neutron cm^?2 s^?1)) and small size (the volume of the sensitive crystal element is ～7 mm³), the detector is capable of monitoring spatial, time, and intensity distributions of γ rays and neutrons in pulse research reactors.     

Tribological behaviors and mechanisms of Ti<Subscript>3</Subscript>AlC<Subscript>2</Subscript>

Tribological behaviors and the relevant mechanism of a highly pure polycrystalline bulk Ti₃AlC₂ sliding dryly against a low carbon steel disk were investigated. The tribological tests were carried out using a block-on-disk type high-speed friction tester, at the sliding speeds of 20–60 m/s under a normal pressure of 0.8 MPa. The results showed that the friction coefficient is as low as 0.1∼0.14 and the wear rate of Ti₃AlC₂ is only (2.3–2.5) × 10⁻⁶ mm³/Nm in the sliding speed range of 20–60 m/s. Such unusual friction and wear properties were confirmed to be dependant dominantly upon the presence of a frictional oxide film consisting of amorphous Ti, Al, and Fe oxides on the friction surfaces. The oxide film is in a fused state during the sliding friction at a fused temperature of 238–324 °C, so it takes a significant self-lubricating effect.     

Tribological Properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/CuCrZr Composites

Al₂O₃ particles reinforced Cu–Cr–Zr alloy matrix composite was fabricated through a powder metallurgy plus hot extrusion process by using the water atomization Cu–Cr–Zr powder as raw material. The effect of aging treatment on the tribological behavior of the composite was investigated. Experimental results show that tiny coherent precipitated phases were formed in the matrix after proper aging treatment and therefore good combination properties could be obtained. The wear rates of the Al₂O₃/CuCrZr composite and its matrix alloy were obviously influenced by the aging treatment, wherein the best wear resistance was reached at the aging temperature corresponding to the highest Vickers hardness. The major reason was that the depth of plastic deformation in the subsurface region was dramatically decreased due to the improvement of mechanical properties of the matrix, and therefore adhesion induced surface materials loss could be markedly alleviated. By comparing with the SiC20 vol%/Cu composite, it is indicated that the Al₂O₃/CuCrZr composite exhibited much better wear resistance as well as higher electrical conductivity.     

Registration of picosecond CO<Subscript>2</Subscript> laser pulses by means of two-stage parametric transformation in nonlinear crystals

A technique for registering the temporal structure of picosecond pulses of CO₂ laser radiation with an energy of 1.5–4.5 μJ at a wavelength of 10.27 μm using two-stage parametric transformation of IR radiation frequency into visible light under pumping of nonlinear crystals by Nd:YAG-laser radiation in a Q-switched mode is described. A GaSe nonlinear crystal was used at the first stage of transformation (10.27 μm + 1.064 μm → 0.964 μm). Radiation was further transformed (1.064 μm + 0.960 μm → 0.506 μm) by using the same pumping in an α-HIO₃ nonlinear crystal. For the first time, no additional optical elements were present between the stages of the frequency transformer in the proposed optical scheme. The transformed radiation was registered with a Hamamatsu Temporal Disperser C1587 streak camera in a region of the photocathode maximum spectral sensitivity of ～0.5 μm with a temporal resolution of up to 2 ps. The minimum recorded pulse duration of the CO₂ laser was ～45 ps.     

A Raman Spectroscopic Study of MoS<Subscript>2</Subscript> and MoO<Subscript>3</Subscript>: Applications to Tribological Systems

Molybdenum disulfide (MoS₂) and molybdenum trioxide are investigated using Raman spectroscopy with emphasis on the application to tribological systems. The Raman vibrational modes were investigated for excitation wavelengths at 632.8 and 488 nm using both micro-crystalline MoS₂ powder and natural MoS₂ crystals. Differences are noted in the Raman spectra for these two different wavelengths, which are attributed to resonance effects due to overlap of the 632.8 nm source with electronic absorption bands. In addition, significant laser intensity effects are found that result in laser-induced transformation of MoS₂ to MoO₃. Finally, the transformation to molybdenum trioxide is explored as a function of temperature and atmosphere, revealing an apparent transformation at 375 K in the presence of oxygen. Overall, Raman spectroscopy is an useful tool for tribological study of MoS₂ coatings, including the role of molybdenum trioxide transformations, although careful attention must be given to the laser excitation parameters (both wavelength and intensity) when interpreting Raman spectra.     

Wear Behavior of Composites Based on ZA-27 Alloy Reinforced by Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Particles Under Dry Sliding Condition

In present study, the effect of Al₂O₃ particle reinforcement on the sliding behavior of ZA-27 alloy composites was investigated. The composites with 3, 5, and 10 wt% of Al₂O₃ particles were produced by the compocasting procedure. Tribological properties of unreinforced alloy and composite were studied, using block-on-disk tribometer under unlubricated sliding conditions at different specific loads and sliding speeds. The worn surfaces of samples were examined by the scanning electron microscopy (SEM). The test results revealed that those composite specimens exhibited significantly lower wear rate than the ZA-27 matrix alloy specimens in all combinations of applied loads and sliding speeds. The difference in the wear resistance of composite with respect to the matrix alloy, increased with the increase of the applied load/sliding speed and Al₂O₃ particle content. The highest degree of improvement of the ZA-27 alloy tribological behavior corresponded with change of the Al₂O₃ particles content from 3 to 5 wt%. At low sliding speed, moderate lower wear rate of the composites over that of the matrix alloy was noticed. This has been attributed to micro cracking tendency of the composites. Significantly reduced wear rate, experienced by the composite over that of the matrix alloy at the higher sliding speeds and loads, could be explained due to enhanced compatibility of matrix alloy with dispersoid phase and greater thermal stability of the composite in view of the presence of the dispersoid. Level of wear rate of tested ZA-27/Al₂O₃ samples pointed to the process of mild wear, which was primarily controlled by the formation and destruction of mechanical mixed layers (MMLs).     

Study on the Synthesis and Tribological Property of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Based Magnetic Fluids

In this paper, Fe₃O₄ based magnetic fluids with different particle concentrations were prepared by the co-precipitation technique. The size of the Fe₃O₄ nanoparticles is about 13 nm and their shape is spherical. The tribological performances of the fluids with different concentration Fe₃O₄ nanoparticles were evaluated in a MMW-1A four-ball machine. The results show that the tribological performance of magnetic fluids with proper Fe₃O₄ nanoparticles can be improved significantly. The maximum nonseized load (P _B) has been increased by 38.4% compared with carrier liquid. The wear scar diameter has been reduced from 0.68 mm to 0.53 mm and the relative percentage in friction coefficient has decreased to 31.3%. The optimal concentration of the Fe₃O₄ nanoparticles in the carrier liquid is about 4 wt.%.     

Reducing the Energy Consumption of a Laser Photo-Acoustic SF<Subscript>6</Subscript> Gas Analyzer

Experimental studies of the operating modes of a laser photo-acoustic SF₆ gas analyzer that were aimed at reducing its energy consumption were carried out. It was shown in the experiments that an average power of CO₂ laser radiation of at least 100 mW is required for the assured detection of low SF₆ concentrations (less than 100 ppb). To reduce the energy consumption of the gas analyzer, it is proposed to decrease the repetition frequency of CO₂ laser pulses by several times and operate on subharmonics of the resonance frequency of the photo-acoustic detector. The experimental results made it possible to reduce the energy consumption of the gas analyzer to ~15 V A and use a Li-ion battery from a laptop to power it. The duration of the continuous operation of the gas analyzer on one battery charge was at least 6 h.     

Molecular beam epitaxy of BaF<Subscript>2</Subscript>/CaF<Subscript>2</Subscript> buffer layers on the Si(100) substrate for monolithic photoreceivers

This paper describes the study of the surface morphology of BaF2 epitaxial films grown by means of molecular beam epitaxy in various growth regimes on a CaF₂/Si(100) surface, which is performed by means of atomic force microscopy. The CaF₂ layers were obtained on a Si(100) substrate in a low-temperature growth regime (T _s = 500 °C). The technological regimes of growth of BaF₂ continuous films with a smooth surface on CaF₂/Si(100), suitable as buffer layers for the subsequent growth of PbSnTe layers or other semiconductors, such as A₄B₆, and solid solutions based on them.     

Dry and oil-lubricated sliding wear of Si<Subscript>3</Subscript>N<Subscript>4</Subscript> and Si<Subscript>3</Subscript>N<Subscript>4</Subscript>/BN fibrous monoliths

A high-temperature ball-on-flat tribometer was used to investigate dry and oil-lubricated friction and wear of sintered Si₃N₄ and Si₃N₄/hexagonal boron nitride (H-BN) fibrous monoliths. The friction coefficients of base Si₃N₄ flats sliding against Si₃N₄ balls were in the range of 0.6–0.8 for dry and 0.03–0.15 for lubricated sliding, and the average wear rates of Si₃N₄ were 10^–5 mm³ N^–1 m^–1 for dry sliding and 10^–10–10^–8 mm³ N ^–1m^–1 for lubricated sliding. The friction coefficients of Si₃N₄ balls against composite fibrous monoliths were 0.7 for dry sliding and 0.01–0.08 for lubricated sliding. The average specific wear rates of the pairs were of the same order as those measured for the conventional Si₃N₄ pairs. However, the fibrous monoliths, in combination with sprayed dry boron nitride, resulted in reduction in the lubricated friction coefficients of the test pairs and significant reduction in their wear rates. The most striking result of this study was that the coefficients of friction of the Si₃N₄/H-BN fibrous monolith test pair were 70–80 lower than those of either roughened or polished Si₃N₄ when tests were performed under oil-lubricated sliding conditions over long distances (up to 5000 m). The results indicated that Si₃N₄/H-BN fibrous monoliths have good wear resistance and can be used to reduce friction under lubricated sliding conditions.     

Wear Resistance of the La<Subscript>62</Subscript>Cu<Subscript>12</Subscript>Ni<Subscript>12</Subscript>Al<Subscript>14</Subscript> Bulk Metallic Glass Under Dry Friction Conditions

The wear properties of a La₆₂Cu₁₂Ni₁₂Al₁₄ bulk metallic glass (BMG) using sliding wear system under the various normal loads and the annealing conditions have been investigated. Although the La₆₂Cu₁₂Ni₁₂Al₁₄ BMG is brittle during the tensile testing, it exhibits ductile behaviors during the sliding wear process. The SEM and the EDS analyses of the wear tracks and the debris after the sliding wear processes indicate that the wear mechanism is a combination of abrasion, adhesion, and oxidation. It is found that the wear resistance is significantly affected by the normal loads. With the increases in the wear load, the wear loss and the friction coefficient decrease. In addition, it is found that the wear properties are significantly affected by the annealing conditions. Compared with the annealed BMG alloys, the as-cast BMG alloy with a low hardness exhibits good wear resistance, which is attributed to the better ductility during the wear testing.