β‐SiC powders were synthesized by microwave sintering at 1400‐1850°C for 60 minutes with coal minerals. Raw materials were prepared with a sol‐gel method by coating SiO2 on coal mineral particles, and microwave sintering was conducted in a microwave chamber with TE666 resonant mode. Heating rates were controlled by input microwave power and heating behavior during the microwave sintering was also investigated. XRD, SEM, Raman, TEM techniques were carried out to characterize samples. It was found that different particle size of coal mineral particles gave rise to different heating effect, leading to different growth mechanisms of SiC crystals. This might be the unique features for microwave sintering. Particular SiC crystals dominated for small coal mineral particles, which attributed to microwave plasma effect. While SiC whiskers or fibers dominated for large coal mineral particles, which corresponded to microwave coupling effect. Microwave coupling effect prevailed for low heating rate which was apt to form particular SiC crystals. Whereas, higher heating rate enhanced microwave plasma and primarily resulted in SiC whiskers or fibers.
In this study, a novel lab-scale biofortification-combination system (BCS) of Oenanthe javanica and Bacillus series was developed to improve the treatment ability of vertical subsurface flow constructed wetlands (VSFCW) at low temperatures (0–10 °C). The results showed that BCS-VSFCW overcame the adverse effects of low temperature and achieved the deep removal of nutrients. In addition, the removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) by BCS-VSFCW were 38.65%, 28.20%, 18.82%, and 14.57% higher than those of blank control, respectively. During the experiment, Oenanthe javanica and low temperature tolerant Bacillus complemented each other in terms of microbial activity and plant uptake. Therefore, VSFCW combined with Oenanthe javanica and low temperature tolerant Bacillus has a promising future in low temperature (<10 °C) areas of northern China.
Needle-like SiC whiskers were synthesised by microwave heating using graphite
sheets and tetraethoxysilane (TEOS) as raw materials. It was found that SiC
powder could be synthesised at 1000?C for 10min, lower than that of samples
made from a granular C source. Furthermore, the heating rate of the samples
made with graphite sheets was higher than that of a granular C source. The
main morphology of the SiC whiskers was needle-like, which appeared when
samples were heated at 1200?C for 10min. Size of the SiC whiskers made with
graphite sheets was more uniform than that of a granular C source, which was
attributed to the 2D thermal effect. Moreover, the size and the amount of
the SiC whiskers increased as the heating temperature increased from 1200 to
1400?C for 10min. The SiC whiskers were oxidised and decomposed into SiC
particles when heated to 1500?C for 10min and only SiC particles existed
when longer holding times were used.
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