超软X射线流气式正比计数管

介绍了一种用于测量183～933eV超软X射线的圆柱形、侧窗式、流气式正比计数管,工作气体是0.11MPa的P-10气体或氦气-丙烷混合气体。计数管内径为φ25mm,直径为φ0.3mm的入射窗是由厚度80～90μgcm~2聚乙烯甲醛制成的。该计数管的特点:(1)薄窗,对软X射线透过率高。(2)流气式,工作寿命长。(3)能量分辨率好。(4)计数率高(1×10~(14)个/s)。(5)可测能区宽(0.183～10keV)。(6)可以方便更换窗膜材料、厚度及窗口直径。近几年来该计数管已经为高强度低能X光源提供较好监测。     

The effect of Pb and other elements found in recycled polypropylene on the manufacturing of lead-acid battery cases

Polypropylene (PP) is one of the most common plastics used in the manufacturing of lead-acid battery cases, where the recycling of the material has become common practice, being both economically viable and environmentally friendly. During the recycling process, the various components of the spent battery are separated, where the crushed battery case is washed in order to remove any excess acid and lead-containing particles. The plastic components are subsequently melted and extruded into pellets that are then blended with virgin material to injection mold new battery cases and lids. This study showed that a significant amount of lead-containing particles in the form of lead dioxide and lead sulfate remain in the recycled plastic, and are evenly distributed throughout the polymer matrix. TEM studies showed that the particles are less than 1 μm in size and X-ray diffraction analysis of ashed recycled PP samples showed the presence, amongst others, of talc, calcium carbonate, rutile and iron oxide. These compounds come from a range of fillers, flame-retardants, colorants and impurities that originated from the various original battery cases that were recycled. The study showed that modern X-ray fluorescence (XRF) analysis is a quick and reliable method to quantify the amount of the elements found in the plastic and that the concentration of Pb in the plastic can be used as a type of “tracer” to determine the amount of recycled PP used in the manufacturing of a particular battery case. The study also showed that there is possible environmental contamination, in particular with Pb and Br contained in recycled PP during the injection molding process and the burning of the plastic. The Pb- and Br-containing particles are small enough to become air-borne during the burning process of the plastic, resulting in them being part of the soot and other hydrocarbon oils that are emitted. No Pb was observed in the gases emitted during simulated low-temperature injection molding conditions; however, a significant amount of Br was detected in the gases at the lower temperatures. Clear environmental waste classification of the battery case plastic should be done before its final incineration where the amount of trace metals present and its possible contamination to the environment should be considered. Care should also be taken for machine operators who work with the recycled plastic, that no excessive exposure to the halogenated compounds is experienced.     

A correlation between the variable melt flow index and the molecular mass distribution of virgin and recycled polypropylene used in the manufacturing of battery cases

This study looked at establishing a correlation between the variable melt flow index (VMFI) values of molten polypropylene (PP) with different piston-load masses using a standard MFI analyser. The study was done using virgin PP and recycled PP obtained from recycling Pb-acid batteries. The study showed that the results would fit a suitable power function equation where the size of the exponent reflects the increase in flow characteristics of the polymer with increased piston-load mass. The established correlation was then compared to the average molecular weight distribution of virgin PP determined by gel permeation chromatography (GPC). Good agreement was obtained for the range of grades of virgin PP samples that correlated well with the Mark-Houwink power law where the inverse of the MFI (1/MFI) would be proportional to the average molecular weight to the power of 3.4 (Mw^3.4). GPC analysis cannot be effectively used to study recycled PP, where a number of factors can influence the melt flow properties such as fillers, impurities and the presence of polyethylene in the polymer matrix. Instead, a comparative understanding of the flow behaviour of recycled PP to that of virgin PP was done by using the VMFI method to possibly show the dissimilar polymer melt flow behaviour of using virgin and recycled PP material in injection moulding of new battery cases and lids, or when attempting to seal the lid to the battery case during manufacturing.     

Instability of highly concentrated emulsions with oversaturated dispersed phase. Role of a surfactant

Instability of highly concentrated emulsions of the water-in-oil type which were investigated in this work is related to the existence of the internal phase as an oversaturated salt solution in water. The principal features of crystallization of these systems were studied by as earlier. This study is devoted to the development of this investigation and based on involving different surfactants and various concentrations of surfactants. It was shown that the originally proposed mechanism of crystallization, which suggested that growing crystals break through interfacial layers, was valid for all highly concentrated emulsions under investigation. Moreover, the Kholmogorov-Avrami kinetic equation with an unusually high exponent value equal to 6 is also applicable to different systems. It was proven that the general relationship between the growth of the yield stress and the degree of crystallization can be formulated for all surfactants studied in the work. The role of a surfactant consists in varying the characteristic time constant for the rate of crystallization. This time constant is much lower for a low-molecular-weight surfactant compared to oligomeric surfactants. This constant noticeably increases with an increase of concentration and the decrease of the average droplet size.     

PALLADIUM CATALYZED REACTION OF 3-TRIMETHYLSILYLPROPARGYLIC CARBONATES WITH DINUCLEOPHILES

Methyl 3-trimethylsilylpropargyl carbonate reacted with dinucleophiles under the catalysis of palladium(0) complex to give the corresponding desilylated annulation products.     

Potential facile separation strategy for mixtures of 3- and 4-methylpyridine by employing N,N′-bis(9-phenyl-9-xanthenyl)ethylenediamine as an alternative host compound

In the present work, a plausible host candidate is provided for the separation of 3-methylpyridine (3MP) from 4-methylpyridine (4MP), isomers that are extremely difficult to separate by conventional means. Host compound N,N′-bis(9-phenyl-9-xanthenyl)ethylenediamine (H2), when recrystallized from an equimolar mixture of 3MP and 4MP, contained 91.6% 3MP, a significantly improved outcome compared with the alternate host compound N,N′-bis(9-phenyl-9-thioxanthenyl)ethylenediamine (H1) which only enclathrated 70% of this isomer in the same experimental conditions. Single crystal diffraction and thermoanalytical experiments were conducted in order to investigate this preference for 3MP by considering both host?guest interactions and relative complex stabilities. Many of the guest components in 3(H2)·5(3MP)·0.268(O) experienced at least one other short contact measuring less than the sum of the van der Waals radii of the involved atoms, an observation that may explain the selectivity of H2 for this guest since this was not the case in complexes containing PYR and 4MP. Results from the thermal analyses were less informative.

     

Influence of surface modification of zinc oxide–based nanomaterials on the photocatalytic reduction of carbon dioxide

ZnO (Z-1), Co-doped ZnO (Z-2), and Co-doped ZnO/rGO (Z-3) nanocomposites are successfully synthesized using a solvothermal method and investigated toward the photoreduction of CO₂ to CH₃OH. The as-prepared ZnO (Z-1), Co-doped ZnO (Z-2), and Co-doped ZnO/rGO (Z-3) nanomaterials are characterized by a range of spectroscopic, imaging, and thermal techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray analysis, thermogravimetry analysis-differential thermal calorimetry, UV–Vis diffuse reflectance spectroscopy, scanning electron microscopy, and transmission electron micrograph. It was found that Z-3 presented a higher CH₃OH rate of 30.1 μmol/g compared with Z-2 (27.3 μmol/g) and Z-1 (7.5 μmol/g). Enhanced catalytic activity of Z-3 over other samples was because of the combined effect of the amount of Co, reduced graphene (rGO), and surface area (10.62 m²/g). Theoretical calculation revealed that photocatalytic activity has some relationship with the E_LUMO = ?2.922 eV (doped ZnO). The results can not only provide an important indication about the influence of Co and rGO on the activity of CO₂ photoreduction over ZnO but also demonstrate a strategy for tuning the CO₂ photoreduction performance. Our work may lay the groundwork for directing the future design of efficient metal-modified ZnO photocatalysts for CO₂ reduction.