In order to develop new dental restorative materials, it is imperative to evaluate and understand the structure–property relationships of the human tooth. Three major structural parts of human tooth i.e. enamel, dentin and dentin–enamel junction have been characterized in the present work in terms of microstructure, phase analysis and compositional gradient. It has been observed that microindentation hardness varies from enamel to dentin with the highest hardness observed for enamel at the outermost surface (around 3.5 GPa). Hardness values monotonically decrease with depth to less than 1 GPa, measured at the interior dentin. Furthermore, the measured hardness variation is found to have a noticeable correlation with the compositional variation.
In order to evaluate the tribological properties of the human tooth, fretting wear tests were carried out against sintered alumina under a load of 1 N for 2000 to 10,000 cycles. A variation in coefficient of friction (ranging from 0.12 to 0.55) was measured in our experiments. The wear mechanism is dominated by fretting fatigue and adhesive wear, involving the formation of oxidized calcium phosphate based compounds and its subsequent transfer from tooth to alumina surface. The experimental results also reveal that the human tooth is more susceptible to adhesion wear than abrasion or attrition at fretting contacts. 相似文献
Compost samples from two composting facilities, the Urbana (Illinois) Landscape Recycling Center (ULRC) and Illinois State University (ISU), were selected to examine the effect of compost age on atrazine removal from solution. The ULRC samples were made from yard waste without an additional nitrogen source. The ISU samples were made from yard waste or sawdust with the addition of manure. The 6-month-old ULRC compost had the greater capacity to remove atrazine from solution, which we attributed to its greater organic carbon content. The addition of nitrate into ULRC compost could influence the extent of atrazine removal, but did not have a significant impact on atrazine removal when applied to ISU compost, probably because manure was added to the yard waste to produce the compost. For both ULRC and ISU samples, the presence of sodium azide inhibited atrazine removal, suggesting that microbial activity contributed to the atrazine removal. Metabolic analysis demonstrated that hydroxyatrazine was the major identified metabolite that accumulated in solution before significant ring mineralization could occur. When compared with the ISU compost, the ULRC compost sample had a greater capacity to remove atrazine from solution during the 120 days of study because of the larger humic acid content. The experimental results suggested that less-mature compost may be better suited for environmental applications such as removing atrazine from tile-drainage waters. 相似文献
The present study investigates the oxidation of dimethyl sulfoxide (DMSO) by conventional ozonation and the advanced oxidation processes (AOPs). The major degradation products identified were methanesulfinate, methanesulfonate, formaldehyde, and formic acid in ozonation process. The subsequent degradation of intermediates shows that methanesulfonate is more resistance to ozonation, which reduces the mineralization rate of DMSO. The effect of t-butanol addition and ozone gas flow dosage on the degradation rate was evaluated. The rate constant of the reaction of ozone (k(D)) with DMSO was found to be 0.4162 M(-1)S(-1). In the second part of this study, DMSO degradation and TOC mineralization were investigated using O(3)/UV, O(3)/H(2)O(2) and UV/H(2)O(2) processes. In all theses processes the degradation of target organics is more pronounced than TOC removal. The efficiencies of these processes were evaluated and discussed. The formation of sulfate ion in all AOPs have been identified and compared with other processes. Overall it can be concluded that ozonation and ozone-based AOPs are promising processes for an efficient removal of DMSO in wastewater. 相似文献
To improve the dewetting characteristic and reducing the clay adhesion of molds, a series of “morphological” and “functional” biomimetic roughness units was fabricated on 45# steel mold surfaces by laser and machining methods. The anti-adhesion and wettability behaviors of samples with different roughness units were investigated. The results indicated that the adhesion forces of samples with different roughness units were lower than that of the smooth one and decreased with increasing the area ratio of roughness units. Contact angle measurements of water on biomimetic roughness surfaces showed that the apparent contact angle increased from 76.9° to 97.5° with the increase of area ratio of biomimetic units. The anti-adhesion mechanism of biomimetic mold was the dual roughness structure of biomimetic units that could decrease the wettability of mold surfaces and reduce the adhesion of clay. 相似文献
The issues of reducing CO2 emissions, sustainably utilizing natural mineral resources, and dealing with industrial waste offer challenges for sustainable development in energy and the environment. We propose an efficient methodology via the co-reaction of K-feldspar and phosphogypsum for the extraction of soluble potassium salts and recovery of SO2 with reduced CO2 emission and energy consumption. The results of characterization and reactivity evaluation indicated that the partial melting of K-feldspar and phosphogypsum in the high-temperature co-reaction significantly facilitated the reduction of phosphogypsum to SO2 and the exchange of K+(K-feldspar) with Ca2+(CaSO4 in phosphogypsum). The reaction parameters were systematical y investigat-ed with the highest sulfur recovery ratio of~60%and K extraction ratio of~87.7%. This novel methodology possesses an energy consumption reduction of~28%and CO2 emission reduction of~55%comparing with the present typical commercial technologies for utilization of K-feldspar and the treatment of phosphogypsum. 相似文献