Development and research of a laser photo-acoustic SF<Subscript>6</Subscript> gas analyzer

An analysis of various optical schemes for the development of a laser SF₆ gas analyzer based on a CO₂ laser operating in free-running mode and a resonant photo-acoustic detector (PAD) is presented. The use of a sealed gas-filled cell to normalize PAD signals on the absorbed power in the cell is suggested. Compensation for the influence of the tuning of the CO₂ laser wavelength near 10.6 μm on measured SF₆ concentration is possible. The results of experimental studies of a laser photo-acoustic SF₆ gas analyzer at various concentrations, including in the air flow, are presented. It is shown experimentally that the relative measurement error of the SF₆ concentration due to the instability of the laser radiation wavelength does not exceed 5% in the range from ~80 ppb to 40 ppm. The limit of the sensitivity of the developed gas analyzer was ~1 ppb SF₆.     

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.     

Surface and sub-micron sub-surface evolution of Al390-T6 undergoing tribological testing under submerged lubrication conditions in the presence of CO<Subscript>2</Subscript> refrigerant

Carbon dioxide (CO₂) with its environmental benefits is considered a good replacement for commonly used synthetic refrigerants. In this study, the surface and sub-surface changes in simulated CO₂ environment during the initial or transient stages of a sliding contacting interface were investigated. Pin-on-disk configurations involving Al390-T6 disks in contact with 52100 steel pins were used in controlled tribological experiments using a High Pressure Tribometer. In order to evaluate the effectiveness of CO₂ refrigerant, comparative tribological experiments involving a conventional refrigerant and different commonly used lubricants were initially performed in a step-increasing load manner under submerged lubricated conditions. Subsequent detailed experiments for investigating the surface and sub-surface changes were performed in the presence of CO₂ refrigerant and the best performing lubricant, polyalkyline glycol. Burnishing was observed on the surfaces during the transient (evolutionary) stage, which indicated asperity contacts due to the breaking of the elasto-hydrodynamic lubrication film. In order to quantify the surface and sub-micron sub-surface changes that occurred during this transient stage of tribological operation, several analytical tasks were performed, which involved the measurements of nanomechanical properties, chemical compositions of the topmost 200 nm surface layer, and surface roughness. Such studies of detailed evolutionary changes that occurred during the transient stage of a tribopair shed light on the complex interactions between surface and sub-surface changes that determine whether successful tribological conditions will eventually be achieved. Based on the analyses presented in this work, it is concluded that CO₂ is a viable refrigerant from a tribology point of view.     

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.     

Determining the coefficient of transverse turbulent diffusion in a flow of the active medium of a CO<Subscript>2</Subscript> laser with fast axial gas circulation

A method for determining the coefficient of transverse turbulent diffusion in a flow of the active medium of a CO₂ laser with fast axial gas circulation is described. The method is based on the phase conjugation during degenerate intracavity four-wave mixing.__________Translated from Pribory i Tekhnika Eksperimenta, No. 2, 2005, pp. 114–119.Original Russian Text Copyright © 2005 by Buyarov, Galushkin, Dubrov, Zavalov.     

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.     

Tribological Property of Ni<Subscript>3</Subscript>Al Matrix Composites with Addition of BaMoO<Subscript>4</Subscript>

The Ni₃Al matrix composites with addition of 10, 15, and 20 wt% BaMoO₄ were fabricated by powder metallurgy technique, and the tribological behaviors were studied from room temperature to 800 °C. It was found that BaAl₂O₄ formed during the fabrication process. The Ni₃Al composites showed poor tribological property below 400 °C, with high friction coefficients (above 0.6) and wear rates (above 10⁻⁴ mm³/Nm). However, the composites exhibited excellent self-lubricating and anti-wear properties at higher temperatures, and the composite with addition of 15 wt% BaMoO₄ had the lowest wear rate (1.10 × 10⁻⁵ mm³/Nm) and friction coefficient (0.26). In addition, the results also indicated that BaAl₂O₄ for the Ni₃Al composites did not exhibit lubricating property from room temperature to 800 °C.     

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.     

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.     

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.     

A Dispersion Interferometer Based on a CO<Subscript>2</Subscript> Laser

A double-pass dispersion interferometer based on a 9.6-μm CO₂ laser with a sensitivity of 〈 n _e l〉_min ∼ 1 × 10¹³ cm⁻² and a temporal resolution of ∼50 μ s, designed to measure linear plasma density, is described. A ZnGeP₂ nonlinear crystal is used as the frequency doubler. The main advantages of the interferometer are its compactness and a low sensitivity to vibrations of optical elements. The interferometer requires no special vibration isolation. Its main components are arranged compactly on an optical bench outside the apparatus, except for a window for radiation injection and a retroreflector; these are mounted on the wall of the experimental facility's vacuum chamber. The advantages of the dispersion interferometer have been demonstrated in an experiment with a gas-dynamic trap. __________ Translated from Pribory i Tekhnika Eksperimenta, No. 5, 2005, pp. 96–106. Original Russian Text Copyright ? 2005 by Solomakhin, Bagryanskii, Voskoboinikov, Zubarev, Kvashnin, Lizunov, Maksimov, Khil'chenko.     

Flow measurement challenges for carbon capture,utilisation and storage

Carbon Capture, Utilisation and Storage (CCUS) is a key element in the United Kingdom Government strategy for reducing carbon dioxide (CO₂) emissions. The UK aims to capture and store 10 million tonnes of CO₂ each year by 2030.At each stage in the CCUS infrastructure, accurate measurement of the CO₂ flow rate is required, over a range of temperatures, pressures, flow rates and fluid phases, where the flow measurement must be validated through a credible traceability chain. The traceability chain provides the underpinning confidence required to verify meter performance, financial and fiscal transactions, and environmental compliance. The UK equivalent of the EU Emissions Trading System (EU ETS) specifies a maximum uncertainty value for CO₂ flow measurement. Accordingly, the provision of accurate and traceable flow measurement of CO₂ is a prerequisite for an operational CCUS scheme.However, there are currently no CO₂ flow measurement facilities, nationally or internationally, providing traceable flow calibrations of gas phase, liquid/dense phase and supercritical phase CO₂ that replicate real-world CCUS conditions. This lack of traceable CO₂ gas and liquid flow measurement facilities and associated flow measurement standards is a significant barrier to the successful implementation of CCUS projects worldwide.This paper presents an overview of the traceability chain required for CO₂ flow measurement in the UK and globally. Current challenges are described along with potential solutions and opportunities for the flow measurement community.     

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).     

Microstructure and Lubrication Properties of Lamellar Liquid Crystal in Brij30/[Bmim]PF<Subscript>6</Subscript>/H<Subscript>2</Subscript>O System

The microstructure of lamellar liquid crystal composed by nonionic surfactant polyoxyethylene laurylether (Brij30), room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF₆) and water is investigated by deuterium nuclear magnetic resonance (²H NMR) and rheological techniques. And the lubrication properties of the lamellar mesophase are determined to illustrate their relationship with the microstructure. The results show that the structure strength of the lamellar phase is enhanced with increasing amount of Brij30, so the anti-wear capacity of the lamellar phase is improved. But, both of the structure strength and lubrication properties are impaired with increasing water content in the system due to the increased interlayer space and the penetration of water into the amphiphile bilayer. However, though the structure of the lamellar phase is disturbed by [Bmim]PF₆, the lubrication properties are still improved due to the inherent lubrication properties of [Bmim]PF₆.     

A facility for studying the spatial and temporal characteristics of a plume produced by interaction of high-power CO<Subscript>2</Subscript> laser pulses with a solid-state target in various gas environments

An experimental facility for studying the kinetics of molecular association formation from atoms produced by evaporation of the target material by powerful CO₂ laser pulses is described. First experimental results are presented for the spectral and spatial-temporal characteristics of the spread of Al atoms produced in interactions of laser radiation with aluminum oxide Al₂O₃, followed by AlO formation in various low-pressure (0.1–0.3 Torr) atmospheres. Images of structurally similar forms condensed on a glass surface have been observed with an atomic-force microscope.     

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.     

The Effect of Morphology on the Tribological Properties of MoS<Subscript>2</Subscript> in Liquid Paraffin

The tribological properties of liquid paraffin (LP) containing molybdenum disulfide (MoS₂) additives, including nano-balls, nano-slices, and bulk 2H-MoS₂, are evaluated using a four-ball tribometer. Results show that all MoS₂ additives used can improve the tribological properties of LP, and that nanosized MoS₂ particles function as lubrication additives in LP better than micro-MoS₂ particles do. The LP with nano-balls presents the best antifriction and antiwear properties at the MoS₂ content of 1.5 wt%. This is ascribed to the chemical stability of the layer-closed spherical structure of nano-balls. The Stribeck curves confirm that the rotation speed of 1,450 rpm used is located at the mixed lubrication region under 300 N. MoS₂ nano-slices have small sizes and easily enter into the interface of the friction pair with a roughness of 0.032 μm, functioning as a lubricant in LP better than nano-balls do at the MoS₂ content of 1.0 wt%. The Stribeck curves also show that the differences between the two nano samples were magnified at high rotation speeds in hydrodynamic lubrication region. The application of nano-slices in high sliding speeds will be more advantageous. This work furthers the understanding of the relationship between the tribological properties and morphology of MoS₂.     

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.     

Synthesis and Tribological Properties of Stearic Acid-Modified Anatase (TiO<Subscript>2</Subscript>) Nanoparticles

Anatase (TiO₂) nanoparticles with an average diameter of 10 nm were synthesized by solvothermal method followed by surface modification with stearic acid (SA). As-prepared, the nanoparticles (SA-TiO₂) were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetry (TGA) and differential scanning calorimetry (DSC). The tribological properties of SA-TiO₂ as an additive of liquid paraffin (LP) were evaluated by a four-ball tester. The results show that LP with SA-TiO₂ exhibited good anti-wear and friction-reduction properties under the all applied loads. Comparing LP with LP-containing SA, LP-containing TiO₂, and LP-containing SA-TiO₂, the LP-containing SA-TiO₂ had the best load-carrying capacity. It was deduced that the boundary lubricating film was mainly composed of TiO₂ deposits and an adsorbing film of SA which contribute to the excellent lubricating effect of SA-TiO₂ in LP.     

Comparison of the efficiency of modification of SHMPE by nanofibers (C,Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) and nanoparticles (Cu,SiO<Subscript>2</Subscript>) when obtaining antifriction composites

The effect of various nanofillers (nanofibers of Al₂O₃ and carbon, nanopowders of copper and SiO₂) on the physico-mechanical and tribotechnical properties of superhigh-molecular polyethylene is investigated. It is determined that the modification of superhigh-molecular polyethylene by nanofibers and nanoparticles within the limits of 0.1–05 wt % results in a substantial rise in its deformation-strength characteristics and a multifold increase in its tribotechnical characteristics. By the methods of X-ray structure analysis, infrared spectroscopy, and electron microscopy, it is shown that modification of the polymer by the mentioned nanofillers results in the formation of an ordered (lamellar) permolecular structure. It is revealed that nanofibers form a stable film of friction transfer more quickly in comparison with nanoparticles. The optimum compositions of nanofillers, which determine the high wear resistance and the low constant of friction for polymer, are determined. The mechanical activation of the binder and filler powders provides a uniform distribution of the nanopowder within the binder and additionally enhances the physico-mechanical and tribotechnical properties of the composite.