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The extreme state of high friction, severe wear, and oxidation invariably occur in mechanical contacts during high temperature steel processing. The application of lubricant to mitigate the aforementioned hindrances can enhance the process performance effectively. Melt lubricants are regarded as a highly promising class due to their good thermal stability and unique physical chemistry. The present study evaluates tribological responses of an alkaline metal borate on steel tribo-pair at 800 °C by ball-on-disk testing. It has been found that the borate melt significantly reduces the friction coefficient and the wear loss in accompany with providing excellent oxidation resistance. On the disk, the formation of a bilayered tribofilm dominates synergistic functionalities while the emergence of an ultrafine-grained layer considerably reinforces the interface integrity of the opposing ball. Cross-sectional examinations of the contact interfaces were carried out on both steel counterparts by FIB/STEM. STEM/HAADF-EDS reveal the formation of a boundary film featuring high concentration of B and significant depletion of O superimposed on a Na-rich film on the rubbing disk. On the opposing surface, a chemically complex film consisting of Na, Fe, O, amorphous C and [3] B which resides on nanograins of iron oxide is evidenced by STEM/EELS-EDS.

Biochar may serve as a tool to sustainably mitigate climate change via carbon sequestration and by improving soil fertility. Biochar has shown to retain nitrate in its pores, which increases with an organic coating of the inner surfaces and residence time in soil ("aging"). Here we investigated the plant accessibility of the captured nitrate in field-aged biochar, as a prerequisite for developing carbon-based N fertilization techniques with environmental benefits. Based on previous results, we hypothesized that part of the biochar-captured nitrate would remain unavailable for plants. A twofactorial greenhouse experiment was designed, where the N was applied either as Ca(NO 3) 2 or as n captured in field-aged biochar at five increasing N doses to quinoa and perennial ryegrass in pots. Interestingly, the biochar-captured N was as plant available as the mineral nitrate, except for the highest dosage. Refuting our hypothesis, no significant amounts of N were extractable at the end of the study from the biochar-soil mixtures with repeated-extraction protocols. Thus, N captured by biochar may improve the N use efficiency in agriculture. Further research should evaluate the role of biochar particle size, root morphology, mycorrhization, and soil moisture (variations) for nitrate retrieval from biochar particles by plants because the captured biochar N was less available in the field as under present controlled conditions. Abbreviations BC Biochar BC-aged Field-aged biochar Since preindustrial times (ca. 1,750), anthropogenic CO 2 emissions have increased atmospheric CO 2 mixing ratios by approximately 150% to more than 410 ppm to date, at an unprecedented rate of increase of currently 2.24 ppm per year 1. In December 2015, the COP21 stated in the Paris Agreement that humanity intends 'to keep atmospheric temperature rise to well below the 1.5 °C by 2050'. To achieve this goal, it is not only necessary to curb anthropogenic CO 2 emissions drastically within the next 30 years but also to additionally remove about 300 Gt of carbon from the atmosphere until 2,100 (using negative emission technologies, NETs, e.g. 2,3 ; see also www.4per1 000.org). Among various NETs, natural climate solutions (NCS) such as afforestation/reforestation, combustion/pyrolysis 4,5 and soil C sequestration (SOC stock increase; biochar) offer multiple co-benefits, supporting the UN's sustainable development goals (SDGs 3). NCS involving soil management strategies play an important role among the available spectrum of NETs. It is estimated that if the full potential of carbon sequestration in the biosphere (vegetation and soil 155 and 178 Pg respectively