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The present study investigated oxidation reactivity and hot lubricity of a sodium silicate melt at different Na 2 O/SiO 2 ratios under elevated temperature stimulation. Static oxidation prevention was achieved at 920 °C when the Na 2 O/SiO 2 ratio reached 1:3 (trisilicate) and 1:2 (disilicate), but it started to deteriorate in the case of 1:1 (metasilicate). At a high concentration of sodium (metasilicate), a severe corrosion reaction between the melt and oxide took place that resulted in a composite coating on the steel substrate. This high-temperature reaction accelerated the formation of ionic charges from the steel base and promoted oxidation. However, friction and wear reduction is proportional to an increase in the sodium oxide fraction. Metasilicate (1:1) exhibited excellent lubricity under the hot frictional test at 920 °C compared to other lubricants. It was due to the formation of the sodium-saturated surfaces and an amorphous silica layer, which was associated with the high-temperature reactivity of sodium toward the oxide surface. In addition, the NaFeO 2 −Fe 2 O 3 composite film, as the reaction product of individual sodium charge and oxide, plays a significant role in maintaining the tribofilm stability for metasilicate, which was not present for disilicate. This study advances the understanding of how sodium-containing compounds perform oxidation prevention and generate lubricity at hot rubbed surfaces.

Abstract:The study aims to assess the urban heat island (UHI) effects in the city under the present land use conditions as well as those conditions proposed by the Hanoi Master Plan 2030 through numerical simulation, using Weather Research and Forecasting (WRF). Furthermore, this paper assesses additional land use scenarios with different spatial and green space configurations. The results show that the implementation of the master plan does not significantly affect the peak air temperature in the built-up areas (approximately 1 °C higher at the maximum). However, high temperature areas, with temperature of 40-41 °C, would expand widely over the new built-up areas. On the other hand, the nocturnal air temperature would increase by up to 2-3 °C over the newly expanded built-up areas. The number of hotspots increased further when the strategic green spaces in the master plan were not taken into account. However, the cooling effect of the strategic green spaces did not OPEN ACCESSBuildings 2015, 5 934 reach the existing city center sufficiently because the green spaces are located far from the city center. The large and centralized green spaces proposed in the master plan were seen to be insufficient to mitigate UHIs compared to the equally distributed green spaces. Moreover, the greater reduction of hotspot areas by up to 56.5% was seen when the mixed forest is employed as the land cover in the green spaces.

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