关于如何对低硫灰口铸铁进行孕育处理的探讨

研究了低硫情况下电炉熔炼如何改进孕育效果的方法．研究表明，对含硫较低铸铁的孕育方法的改进，不一定非要通过补硫或改善孕育剂的方法来实现；通过增加原有孕育剂的数量、改进孕育方法同样能改善孕育效果．     

A Universal Laser-Pulse Apparatus for Thermophysical Measurements in Refractory Materials at Very High Temperatures

This paper presents a new experimental technique enabling thermophysical measurements to be carried out at very high temperatures in a very simple and small pressurized vessel in which the sample is heated by a continuous wave laser, and subsequently subjected to a short temperature pulse. The adopted method is essentially an extension of the laser-flash technique, widely used for thermal diffusivity measurements, whereby, in addition, the heat capacity and, hence, the thermal conductivity, , are simultaneously evaluated from the pulse analysis. Results are presented for the thermal diffusivity and heat capacity of graphite, zirconia, and uranium dioxide up to temperatures above 3000 K.     

Caffeine in Coffee: Its Removal. Why and How?

The popularity of coffee as a beverage is ever increasing despite the fact that there are reports antagonized to its consumption. Of the several factors cited, the alkaloid caffeine present in coffee can cause addiction and stimulate the central nervous system. It has an effect on the cardiovascular system with a slight increase in blood pressure and heart output. It undergoes biotransformation in the human body to form methylated derivatives of uric acid. In recent times, much effort has gone into the research on the removal of caffeine in coffee, resulting in a specialty product called decaffeinated coffee. Decaffeination methods mainly employ organic solvents or water or supercritical carbon dioxide. These methods with their attendant advantages and disadvantages are reviewed in this article.     

Electrodeposition of PbO2 and Bi–PbO2 on Ebonex

Electrodeposition of PbO2 and Bi–PbO2 on Ebonex was carried out under various conditions, and the surfaces and coating/substrate interfaces examined by SEM, XPS and SIMS. Excellent adhesion to Ebonex was obtained with both crystalline and amorphous surfaces. Low plating temperatures resulted in dark grey, bright PbO2 and black, mirror-like Bi–PbO2 surfaces. Extrapolation of electrode lifetime test data indicated corrosion rates of 716 m yr–1 for PbO2 and 158 m yr–1 for Bi–PbO2.     

Tribological investigation of cast iron air-conditioning compressor surfaces in CO2 refrigerant

Tribological investigations of air-conditioning compressors have been a topic of great interest in recent years and gray cast iron has been a commonly used material by various compressor manufacturers. The scope of this paper is to determine the role of oxygen and in particular carbon dioxide refrigerant (R744) in cast iron samples tribologically tested using an Ultra High Pressure Tribometer that is suitable for tribological testing of compressor contact interfaces that operate with carbon dioxide refrigerant. A series of experiments was performed in environments of air, nitrogen (N₂), oxygen (O₂) and carbon dioxide (CO₂). While it was found that the presence of oxygen is beneficial, CO₂ has a more positive effect on the surfaces than in the case of pure O₂ suggesting that the use of CO₂ promotes a different wear mechanism. Also, it was found that CO₂ has better tribological performance over a range of pressures between 100 psi (0.69 MPa) to 600 psi (4.1 MPa), compared to lower pressures. Furthermore, CO₂ was compared with tetrafluorethane (R134a), a common hydrofluorocarbon refrigerant and found to have superior tribological performance. Two surface chemical analysis techniques were utilized to examine the surfaces after tribological testing. Auger electron spectroscopy (AES) was used to track changes in the elemental composition while X-ray photoelectron spectroscopy (XPS) was utilized to detect the different chemical states resulting from compound formation on the tribologically tested surfaces. It was found that CO₂ leads to better tribological performance of the interface due to the formation of carbonates on the surface, which reduce friction and prevent wear.     

The distribution of sulfur compounds in hydrotreated jet fuels: Implications for obtaining low-sulfur petroleum fractions

The mechanism by which jet fuels are hydrotreated to reduce sulfur levels has some important implications in terms of the species and distribution of sulfur compounds remaining in the fuel. The species of sulfur that are most difficult to remove by hydrotreating, such as benzothiophenes and methyl- and dimethyl-benzothiophenes, are concentrated in the higher-boiling fraction of the fuel. Consequently, the lower-boiling fractions of the fuel contain much less sulfur. It may be possible, therefore, to obtain petroleum fractions that contain low levels of sulfur simply by distillation of the jet fuel into low-boiling and high-boiling fractions. A multi-element simulated distillation procedure according to ASTM D-2887, standard test method for boiling range distribution of petroleum fractions by gas chromatography, was coupled with atomic emission detection (GC-AED) and was used to estimate the sulfur concentration in various fractions of jet fuel, namely 20, 50, and 60%. The estimations of sulfur concentration were verified by comparing them to analyzed sulfur concentrations in several fractions of physical distillations of the jet fuels according to a modified ASTM D-86, standard test method for distillation of petroleum products at atmospheric pressure. Sulfur analyses showed that for all fuels analyzed, the initial 20% boiling fraction of the fuel contained no more than approximately 5% of the total sulfur concentration. The initial 50% boiling fraction of the fuel contained no more than 25% of the total sulfur concentration, and in most cases contained significantly less (8-16%). The total concentration of sulfur in the jet fuels tested ranged from 260 to 1380 μg/g, and there did not appear to be a direct relationship between total sulfur concentration and percentage of sulfur in each jet fuel boiling fraction.     

Theoretical investigation of catalytic HCO3 hydrogenation in aqueous solutions

Density functional theory along with a dielectric continuum solvation model has been applied to identify possible reaction intermediates for the catalytic hydrogenation of HCO₃⁻ anion into HCO₂⁻ that occurs in aqueous solutions in the presence of water-soluble ruthenium complexes. Bicarbonate ion is shown to coordinate to a Ru-dihydride species, which then undergoes a protonation process that yields a CO₂ complex. The CH bond formation is found to take place via CO₂ insertion into a RuH bond and the direct elimination of the formate product is shown to be an energetically favored step, which is assisted by the water medium. We find that water is directly involved in the reaction as a protonating/deprotonating agent and also acts as a coordinating ligand.     

Radiation absorption and rate constants for carbaryl photocatalytic degradation in a solar collector

We discuss an analytical model for the evaluation of radiation absorption in a tubular photocatalytic reactor. The model has no adjustable parameters and takes into account scattering in all directions. We compare the results of this model with those of Monte Carlo (MC) simulations and of a Lambert–Beer (LB) approximation, for a reactor illuminated by a parabolic solar concentrator. A good correspondence is found with the MC simulations. In particular, the model displays the correct saturation behavior of absorption for large catalyst particle concentrations, which is not obtained with the LB approximation. We have carried out experiments for the degradation of carbaryl in a solar parabolic collector (PC). The model is used to calculate the rate constant for this degradation from the experimental data. The theoretical model predictions reproduce well, the trends observed in the experiments.     

Polymer synthesis and characterization in liquid / supercritical carbon dioxide

The use of carbon dioxide as an inert solvent has emerged recently as an important development in polymer chemistry. The past year has seen major advances in the synthesis of a variety of polymeric materials in carbon dioxide. At the same time complementary studies have successfully elucidated the physical behavior of a range of polymers in carbon dioxide solution. Herein we review both synthetic and physical studies that are defining the scope of this approach.     

Quantification of aroma vapours sorbed in polyethene films using supercritical carbon dioxide

Extraction with supercritical carbon dioxide was used to quantity the amounts of seven different aroma vapours sorbed in polyethene films. The method was found to completely extract all aroma compounds from the films. The solution of aroma compounds in the polymer films decreased with increasing polymer density. Monoterpenes were always completely sorbed in the films, whereas aldehydes and ketones had a much lower affinity for the films. The sulphur-containing compound, thiophene, was difficult to analyse due to its adsorption on metal surfaces.