Oxidation behavior of molten magnesium in air/HFC-134a atmospheres

The oxidation behavior of molten magnesium in the atmosphere of air containing HFC-134a has been investigated in the temperature range of 660–760 °C. The oxidation rates and kinetics have been measured by the weight gain method and oxidation products have been characterized by XRD, SEM, EDS, XPS and AES. The results show that the oxidation kinetics is complex which cannot be described by simple equations. The rate of oxidation of molten magnesium in air/HFC-134a covering gas mixtures varies with the concentration of HFC-134a and molten temperature. Increasing the concentration of HFC-134a and decreasing the temperature can slow down the oxidation rate of molten magnesium. The film formed +on the surface of molten magnesium is mainly composed of MgF₂, MgO and C. MgF₂ is predominant product at the top layer and decreased gradually with the depth while MgO and C remain almost constant with relatively low content. The mechanisms of the oxidation of molten magnesium in air containing HFC-134a have also been discussed based on the experimental results.     

Vapor–Liquid Equilibrium of HFC-32/134a And HFC-125/134a Systems

A vapor-liquid equilibrium apparatus has been developed and used to obtain data for the binary HFC-32/134a and HFC-125/134a systems. Twenty-two equilibrium data are obtained for the HFC-32/134a system over the temperature range from 258.15 to 283.15 K at 5 K intervals and the composition range from 0.2 to 0.8 liquid mole fraction. Twenty-five equilibrium data are obtained for the HFC-125/134a system over the temperature range from 263.15 to 303.15 K at 10 K intervals and the composition range from 0.18 to 0.81 liquid mole friction. These data have been tested and found to be thermodynamically consistent. Based upon the present data, the binary interaction parameters of the Carnahan-Starling-De Santis (CSD) and Redlich–Kwong–Soave (RKS) equations of state are calculated for five isotherms for the HFC-125/134a mixture and six isotherms for the HFC-32/134a mixture. The calculated results from the CSD equation are compared with data in the open literature.     

Coloration of molten aluminium surface in various atmospheres

Various kinds of coloration were observed on a surface of metallic aluminium heated above its melting temperature under seven different atmospheres with different po₂. Similar distributions of the coloration on a diagram of temperature (600–1400 °C) and time (1–90 min) were found among these atmospheres. Yellowish colours (beige, gold, yellow, blonde, camel and sand) appeared over a fairly wide range of the diagram. From estimated thicknesses determined by weight increases and the order of appearance of the colours, it was concluded that the colour is caused by interference by the oxidized thin film produced on the smooth surface of the molten aluminium.     

Thermal Conductivity of HFC-32, HFC-125, and HFC-134a in the Solid Phase

Measurements of the thermal conductivity of HFC-32, HFC-125, and HFC-134a were carried out for the first time in both solid and liquid phases at the saturation pressure at room temperature and in the temperature ranges from 120 to 263, from 140 to 213, and from 130 to 295 K, respectively. A transient hot-wire instrument using one bare platinum wire was employed for measurements, with an uncertainty of less than ±2%. The experimental results demonstrated that the thermal conductivity of HFC-32, HFC-125, and HFC-134a in the solid phase showed a positive temperature dependence. For HFC-32 and HFC-125, there were big jumps between the solid and the liquid thermal conductivity at the melting point. But for HFC-134a, the solid and liquid thermal conductivity at the melting point is almost-continuous.     

Thermal Conductivity of Binary Refrigerant Mixtures of HFC-32/125 and HFC-32/134a in the Liquid Phase

The liquid thermal conductivity of mixtures of HFC-32/125 and HFC-32/134a was measured using the transient hot-wire apparatus in the temperature ranges from 213 to 293 K and from 193 to 313 K, respectively, in the pressure range from 2 to 30 MPa and with HFC-32 mass fractions of 0.249, 0.500, and 0.750 for each system. The uncertainty of the thermal conductivity was estimated to be ±0.7%. For practical applications, the thermal conductivity data for the two mixtures were represented by a polynomial in temperature, pressure, and mass fraction of HFC-32 with a standard deviation of 1.0%.     

制冷工质HFC-134a热力学性质计算模型

根据国外有关资料,对比分析了HFC-134a两组基于MH方程的热力学性质参数方程,优化组合出较为精确的HFC-134a热力学性质计算模型,推导了相应的焓熵计算公式,用Visual Fortran 5.0编程计算了所得模型的部分焓熵值,验证了该模型的准确性,在常见的制冷空调工程实用工作温度和压力范围内有良好的计算精度,全部计算公式均适用于工程设计应用.     

Thermal Conductivity of Ternary Refrigerant Mixtures of HFC-32/125/134a in the Liquid Phase

The liquid thermal conductivity of two ternary mixtures of HFC-32/125/134a (23.0/25.0/52.0 and 19.0/43.8/37.2 wt%) was measured using a transient hot-wire instrument in the temperature ranges from 193 to 293 K and from 213 to 293 K, respectively, and in the pressure range from 2 to 30 MPa. The thermal conductivity has an estimated uncertainty of ±0.7%. For engineering purposes, the thermal conductivity data were correlated using a polynomial in temperature and pressure for each mixture with a standard deviation of 0.6%.     

Effect of melt temperature on the oxidation behavior of AZ91D magnesium alloy in 1,1,1,2-tetrafluoroethane/air atmospheres

The oxidation behaviors of AZ91D magnesium alloy in 1,1,1,2-tetrafluoroethane/air atmospheres at temperatures between 660 °C and 760 °C have been studied. The experimental results show that with the increase of melt temperature, the oxidation rate of molten AZ91D magnesium alloy in 1,1,1,2-tetrafluoroethane/air atmospheres increased and the oxidation kinetics changed from parabolic law to linear law. On the other hand, the amount of MgF₂ in the oxide film formed on AZ91D decreased, and the amount of MgO increased. The effect of melt temperature on the oxidation behaviors is primarily related to the relative content of MgO and MgF₂ in the film, as well as the diffusion rate and the evaporation rate of magnesium through the film.     

Characterization of protective sol-gel coatings on magnesium based on phenyl-triethoxysilane precursor

Sol-gel coatings were deposited from a Phenyl-triethoxysilane precursor for corrosion protection on magnesium samples. Film porosity was measured with potentiodynamic scans and the coating's structure was characterized with secondary ion mass spectrometry and X-ray diffraction analysis. At the interface between substrate and coating a magnesium silicate layer was found which was formed by interdiffusion during the deposition process. The coated samples showed a good corrosion resistance and low porosity after heating at comparatively low temperature.     

Characterization of crystalline alumina films formed in alcohol-water solutions

Crystalline aluminum hydrous oxide [γ-AlO(OH)] thin films were prepared by hydration of a high cubicity tunnel-etched Al foil in alcohol—DI-water solutions at 95 °C for times up to 1 h. Presence of free molecular water was found to be an absolute requirement for film formation. In addition, the type of alcohol used in the hydration environment, n-propyl alcohol, ethylene glycol or glycerol, influenced the hydration kinetics, i.e. the induction time for film growth. Denser and low porosity films were suggested by field emission—scanning electron microscopy analysis. X-Ray diffraction showed the presence of only one crystalline phase identified as pseudoboehmite.     

Precise Measurements of the Vapor-Liquid Equilibria (VLE) of HFC-32/134a Mixtures Using a New Apparatus

A new apparatus for precise measurements of the vapor-liquid equilibria of mixtures by the circulation method has been developed. This apparatus has two special components: a high-stability temperature control system and a helium pressurization system. The temperature in the liquid bath surrounding the sample cell is kept constant within ±0.5mK. The helium pressurization system increases the pressure of the sampled mixture when measuring the compositions at low temperatures by gas chromatography. With these components, the uncertainty in measuring the vapor-liquid equilibria has been reduced. Using this apparatus, the vapor-liquid equilibria of HFC-32/134a mixtures were measured in a temperature range of 263.15 to 293.15K. These results are in good agreement with the calculated results from REFPROP (Ver. 6.01) with a relative pressure difference of about 2%.     

HFC-134a螺杆冷水机组中满液式蒸发器回油设计讨论

本文讨论了HFC-134a螺杆冷水机组中满液式蒸发器回油设计的三种方法直接回油、气体引射回油和手动回油.在HFC-134a满液式蒸发器中使用一种合成冷冻机油,采用三种回油组合方式是可行的,满液式蒸发器中的含油量可以控制在1%以下.     

From mine to refrigeration: a life cycle inventory analysis of the production of HFC-134a

A life cycle inventory analysis has been conducted for the production of HFC-134a (1,1,1,2-tetrafluoroethane, CH₂FCF₃)¹ through from basic raw materials (crude oil, natural gas, sulphur and fluorspar) to the pure product delivered to industrial customers. The analysis was based on real industrial operations in Japan, USA and UK. It showed that production required limestone, water and transition metal catalysts, in addition to the basic raw materials, and that the energy required to provide these raw materials in a form that can be used at the plants and to process them through intermediates into HFC-134a is the equivalent of 4.52 tonnes of CO₂ per tonne of product. Environmental releases associated with HFC-134a included waste salt brine (to the sea), mine tailings (mainly “country” rock landfilled at the mine) and small quantities of calcium sulphate and spent catalyst (both sent to landfill). In addition, greenhouse gases amounting to the equivalent of 2.1 tonnes of CO₂ per tonne of product were emitted to the atmosphere from the plants studied, an effect very much smaller than that estimated in previous studies mainly because the real release rates from current processes are very much less than those assumed in prior work. The global warming potential^{, 2} of HFC-134a is 1300, meaning that, during the first 100 years following the release of one tonne, the effect on climate change is equivalent to 1300 tonnes of carbon dioxide. Consequently, the 6.6 tonnes of carbon dioxide equivalent, emitted during production in the form of energy required and other greenhouse gases, is of relatively little importance and the key requirement to reduce environmental impact is containment during use.     

The selection of international standards for the thermodynamic properties of HFC-134a and HCFC-123

The objectives and activities of the International Energy Agency-Annex 18 are summarized. One of the goals of the Annex was to determine the formulations that best represent the thermodynamic properties of HFC-134a and HCFC-123. The formulations selected were those which accurately represented the experimental data and simultaneously exhibited thermodynamic consistency. Methods of comparison include analysis of the experimental data, statistical comparisons of values calculated from the property formulations to experimental values, and graphical analyses of the thermodynamic surface. The analytical methods used are summarized in this paper. The equations of state reviewed in these comparisons represented the most accurate formulations available in December 1992. Four equations of state were reviewed for HFC-I34a and three equations of state were considered for HCFC-123. These equations represented the work of independent researchers in Germany, Japan, and the United States. The formulations selected as international standards are presented.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Nanopatterns of ABA triblock copolymer thin films formed on water surface

Nanopatterns of hydrophobic triblock copolymer SEBS thin films formed on a water surface by using drop spreading casting and dilute solution casting methods have been studied. It is found that the surface morphologies of thin films, as well as the spreading behavior of polymer solutions on water, depend strongly on the selectivity of the solvent and the functional group which interacts with the water subphase. The resulting nanopatterns were examined in terms of the relative interaction parameter (Δχ) and the copolymer volume fraction (?) in the solution, based on the physics of solvent annealing and evaporation.     

Nitriding of titanium by NH3 RF plasma: a study of the corrosion resistance and the mechanical properties of the protective films formed at the solid surface

The exposure of a titanium sample to an NH₃ low pressure plasma leads to the formation of a nitriding layer. The products formed at the titanium surface were identified by XRD spectroscopy. The modification of the corrosion resistance characteristics of titanium due to the NH₃ plasma treatment were investigated by electrochemical tests. The recorded polarization curves of the treated titanium samples were used to determine the values of the corrosion potential E_corr. This study confirms the increasing of the corrosion resistance as a function of the time exposure and the injected electric power in the silica reactor. The plasma treatment also induces drastic changes of the titanium target in hardness.     

Characterization of the surface of bio-ceramic thin films

The biocompatibility and corrosion resistance of orthopaedic and dental implants are determined by their material composition and surface microstructural properties such as surface roughness, grain size, etc. Thin films of bio-inert materials such as oxides of Ti, Al, Zr, and bio-active materials such as hydroxy-apatite (Ca₁₀(PO₄)₆(OH)₂), compounds of calcium and phosphorous oxides are more attractive as bio-ceramic films because of their biocompatibility being higher, and toxicity being lower than those of the other materials. In this study, we mainly focused on characterization of the surface of bio-ceramics using atomic force microscopy (AFM). These films having a thickness of about 500 nm, had been processed using ion-beam sputter deposition, and ion-beam-assisted sputter deposition methods. Investigation of the surface of the films by AFM shows that irradiation with oxygen ions in the energy range of 3 keV increases the surface roughness. A detailed study of the grain size and roughness of several experimental cases of TiO₂ thin films showed that the films contained columnar grains with mean size of about 100 × 100 nm² grown in the z direction with a height of a few nanometers.     

Characterization of surface oxide films on titanium and bioactivity

Biological properties of titanium implant depend on its surface oxide film. In the present study, the surface oxide films on titanium were characterized and the relationship between the characterization and bioactivity of titanium was studied. The surface oxide films on titanium were obtained by heat-treatment in different oxidation atmospheres, such as air, oxygen and water vapor. The bioactivity of heat-treated titanium plates was investigated by immersion test in a supersaturated calcium phosphate solution. The surface roughness, energy morphology, chemical composition and crystal structure were used to characterize the titanium surfaces. The characterization was performed using profilometer, scanning electronic microscopy, ssesile drop method, X-ray photoelectron spectroscopy, common Bragg X-ray diffraction and sample tilting X-ray diffraction. Percentage of surface hydroxyl groups was determined by X-ray photoelectron spectroscopy analysis for titanium plates and density of surface hydroxyl groups was measured by chemical method for titanium powders. The results indicated that heat-treatment uniformly roughened the titanium surface and increased surface energy. After heat-treatment the surface titanium oxide was predominantly rutile TiO₂, and crystal planes in the rutile films preferentially orientated in (1 1 0) plane with the highest density of titanium ions. Heat-treatment increased the amount of surface hydroxyl groups on titanium. The different oxidation atmospheres resulted in different percentages of oxygen species in TiO₂, in physisorbed water and acidic hydroxyl groups, and in basic hydroxyl groups on the titanium surfaces. The immersion test in the supersaturated calcium phosphate solution showed that apatite spontaneously formed on to the rutile films. This revealed that rutile could be bioactivated. The analyses for the apatite coatings confirmed that the surface characterization of titanium has strong effect on bioactivity of titanium. The bioactivity of the rutile films on titanium was related not only to their surface basic hydroxyl groups, but also to acidic hydroxyl groups, and surface energy. Heat-treatment endowed titanium with bioactivity by increasing the amount of surface hydroxyl groups on titanium and its surface energy.     

R290/R134a用于家用空调器的性能匹配分析

对具有低可燃性的R290/R134a空调器样机与原R290空调器进行性能对比试验,并改变制冷剂充注量、毛细管长度、电子膨胀阀步数、换热器管径等对系统进行优化设计,使系统达到最佳匹配效果。试验结果表明：优化后的R290/R134a空调器样机的制冷能力最高达2 786 W,能效比为3.41,符合国家标准GB12021.3—2010的2级能效的要求。