Soaking and formation of tetrabasic lead sulfate

Soaking and formation (first charge) stages of the Faure process were studied as separate stages from various 4PbO·PbSO4 (4BS) precursors (pure tetrabasic lead sulfate or industrial tetrabasic positive active material). The evolution during soaking and formation of the various well-defined 4BS precursors was followed by means of scanning electron microscopy, X-ray diffraction and wet chemical analysis. The following results arise from this approach. The sulfation stage results in the formation of PbSO4 crystals with two completely different morphologies. The first type of PbSO4 crystals nucleate at the 4BS needle surface and this leads rapidly to large polyhedral particles of 2 μm in diameter. The second type of PbSO4 crystals consist of very small interconnected grains (0.2 μm) that result from the slow transformation of the 4BS needle into PbSO4 via a metasomatic process. Since the 2 μm PbSO4 polyhedral particles resulting from the first sulfation process are more difficult to convert into PbO2, the PbO2 crystal growth mainly takes place on the second type of PbSO4 small 0.2 μm interconnected crystals. It can be concluded that the 4BS formation route mainly proceeds via the double metasomatic process 4BS → PbSO4 → PbO2 leading to the textural relationship between PbO2 and its precursor 4BS. The double metasomatic process gives rise to the same type of macrotexture at 20 and 55°C with a rigid skeleton and a high porosity. On the other hand, the thickness of the individual PbO2 grains (i.e. the microtexture) depends on temperature. Very thin interconnected PbO2 crystals are obtained at 20°C while thicker grains are observed at 55°C. These textural observations are confirmed by C/20 discharge capacity measurements on tetrabasic-based plates and batteries. The influence of soaking duration is outlined

Individual exposure level following indoor and outdoor air pollution exposure in Dakar (Senegal)

International audienceThe consequences of indoor and outdoor air pollution on human health are of great concern nowadays. In this study, we firstly evaluated indoor and outdoor air pollution levels (CO, CO2, NO, NO2, PM10) at an urban site in Dakar city center and at a rural site. Then, the individual exposure levels to selected pollutants and the variations in the levels of biomarkers of exposure were investigated in different groups of persons (bus drivers, traders working along the main roads and housemaids). Benzene exposure levels were higher for housemaids than for bus drivers and traders. High indoor exposure to benzene is probably due to cooking habits (cooking with charcoal), local practices (burning of incense), the use of cleaning products or solvent products which are important emitters of this compound. These results are confirmed by the values of S-PMA, which were higher in housemaids group compared to the others. Urinary 1-HOP levels were significantly higher for urban site housemaids compared to semirural district ones. Moreover, urinary levels of DNA oxidative stress damage (8-OHdG) and inflammatory (interleukin-6 and -8) biomarkers were higher in urban subjects in comparison to rural ones. The air quality measurement campaign showed that the bus interior was more polluted with PM10, CO, CO2 and NO than the market and urban or rural households. However, the interior of households showed higher concentration of VOCs than outdoor sites confirming previous observations of higher indoor individual exposure level to specific classes of pollutants

Social factors and non-native attitudes towards varieties of spoken English: a Japanese case study

This paper, through the employment of a verbal-guise study and techniques incorporated from perceptual dialectology, investigated the attitudes of 558 Japanese university students towards six varieties of English speech. Although the results suggest a particularly favourable attitude towards standard and non-standard varieties of UK and US English in terms of 'status', informants expressed greater 'solidarity' with a Japanese speaker of heavily-accented English. Differences in the students' gender, self-perceived proficiency in English, exposure to English and evaluations of varieties of Japanese all had significant effects on the informants' attitudes. The findings are discussed in relation to the pedagogical and language planning implications in English language teaching inside and outside Japan