Nickel oxide (NiO) powder is prepared by decomposition of basic nickel carbonate (mNiCO3.nNi(OH)2.xH2O) (BNC) in microwave field with silicon carbide (SiC) as an indirect heating medium. The decomposition proceeds sta...Nickel oxide (NiO) powder is prepared by decomposition of basic nickel carbonate (mNiCO3.nNi(OH)2.xH2O) (BNC) in microwave field with silicon carbide (SiC) as an indirect heating medium. The decomposition proceeds stage by stage: firstly BNC removes its crystal water with the heat provided by BNC itself and SiC which absorb microwave energy,then removes CO2 and H2O from the anhydride (mNiCO3 .nNi(OH)2) and begins to produce NiO with the heat provided by SiC, and finally decomposes into NiO powder completely with the heat provided by the produced NiO which absorbs microwave energy strongly. In the microwave irradiation process, the decomposition of BNC can be accelerated by increasing the amount of BNC, the amount of SiC and the microwave field power. The size of the NiO granule is about 18ourn when the size of BNC used is about 15ourn.展开更多
A self-crosslinkable liquid highly branched polycarbosilane（LHBPCS） with 5.07% vinyl group and a C/Si ratio of 1.33 was used as the precursor to prepare Si C ceramic material. Microwave heating technique and convent...A self-crosslinkable liquid highly branched polycarbosilane（LHBPCS） with 5.07% vinyl group and a C/Si ratio of 1.33 was used as the precursor to prepare Si C ceramic material. Microwave heating technique and conventional heating method were applied for the heating treatment process. It was found that, compared with conventional heating method, microwave heating technique could enhance the crystallinity of Si C ceramic material with small grain size at much lower curing temperature and within shorter time. In addition, the SiO_2 additive could lead to less α-Si C and excess carbon, but worsen the crystallinity of β-Si C in the final samples.展开更多
Electromagnetic absorption(EMA)materials with light weight and harsh environmental robustness are highly desired and crucially important in the stealth of high-speed vehicles.However,meeting these two requirements is ...Electromagnetic absorption(EMA)materials with light weight and harsh environmental robustness are highly desired and crucially important in the stealth of high-speed vehicles.However,meeting these two requirements is always a great challenge,which excluded the most attractive lightweight candidates,such as carbon-based materials.In this study,SiC_(nw)-reinfbrced SiCNO(SiC_(nw)/SiCNO)composite aerogels were fabricated through the in-situ growth of SiC_(nw) in polymer-derived SiCNO ceramic aerogels by using catalyst-assisted microwave heating at ultra-low temperature and in short time.The phase composition,microstructure,and EMA property of the SiC_(nw)/SiCNO composite aerogels were systematically investigated.The results indicated that the morphology and phase composition of SiC_(nw)/SiCNO composite aerogels can be regulated easily by varying the microwave treatment temperature.The composite aerogels show excellent EMA property with minimum reflection loss of -23.9 dB@13.8 GHz,-26.5 dB@10.9 GHz,and -20.4 dB@14.5 GHz and the corresponding effective bandwidth of 5.2 GHz,3.2 GHz,and 4.8 GHz at 2.0 mm thickness for microwave treatment at 600℃,800℃,and 1000℃,respectively,which is much better than that of SiCN ceramic aerogels.The superior EMA performance is mainly attributed to the improved impedance matching,multireflection,multi-interfacial polarization,and micro current caused by migration of hopping electrons.展开更多
This paper presents a simple and cost-effective method for the production of micro-sized silicon carbide whiskers at high yield and the effect on heat transfer enhancement for the whisker laden fluids. For SiC whisker...This paper presents a simple and cost-effective method for the production of micro-sized silicon carbide whiskers at high yield and the effect on heat transfer enhancement for the whisker laden fluids. For SiC whisker synthesis, the starting powder mix- ture is obtained by milling short carbon fibers with the white ashes of rice hulls. Calcina：ion in argon, together with the subse- quent purification process, results in a high yield of SiC whiskers, which possess a diameter of 200-400 nm and a length of several tens of microns. The formation of the whiskers is discussed according to VS growth mechanism. Convective heat transfer performance in small channel tubes is then studied for fluid systems mixed with those micro-sized SiC whiskers at different concentrations. The heat transfer coefficient of SiC containing fluid can be significantly improved in comparison to the base fluid.展开更多
文摘Nickel oxide (NiO) powder is prepared by decomposition of basic nickel carbonate (mNiCO3.nNi(OH)2.xH2O) (BNC) in microwave field with silicon carbide (SiC) as an indirect heating medium. The decomposition proceeds stage by stage: firstly BNC removes its crystal water with the heat provided by BNC itself and SiC which absorb microwave energy,then removes CO2 and H2O from the anhydride (mNiCO3 .nNi(OH)2) and begins to produce NiO with the heat provided by SiC, and finally decomposes into NiO powder completely with the heat provided by the produced NiO which absorbs microwave energy strongly. In the microwave irradiation process, the decomposition of BNC can be accelerated by increasing the amount of BNC, the amount of SiC and the microwave field power. The size of the NiO granule is about 18ourn when the size of BNC used is about 15ourn.
基金Funded by the National Natural Science Foundation of China(Nos.91226202 and 91426304)
文摘A self-crosslinkable liquid highly branched polycarbosilane（LHBPCS） with 5.07% vinyl group and a C/Si ratio of 1.33 was used as the precursor to prepare Si C ceramic material. Microwave heating technique and conventional heating method were applied for the heating treatment process. It was found that, compared with conventional heating method, microwave heating technique could enhance the crystallinity of Si C ceramic material with small grain size at much lower curing temperature and within shorter time. In addition, the SiO_2 additive could lead to less α-Si C and excess carbon, but worsen the crystallinity of β-Si C in the final samples.
基金the financial support from the National Natural Science Foundation of China(Nos.U1904180 and 52072344)Excellent Young Scientists Fund of Henan Province(No.202300410369)+1 种基金Henan Province University Innovation Talents Support Program(No.21HASTIT001)China Postdoctoral Science Foundation(No.2021M692897).
文摘Electromagnetic absorption(EMA)materials with light weight and harsh environmental robustness are highly desired and crucially important in the stealth of high-speed vehicles.However,meeting these two requirements is always a great challenge,which excluded the most attractive lightweight candidates,such as carbon-based materials.In this study,SiC_(nw)-reinfbrced SiCNO(SiC_(nw)/SiCNO)composite aerogels were fabricated through the in-situ growth of SiC_(nw) in polymer-derived SiCNO ceramic aerogels by using catalyst-assisted microwave heating at ultra-low temperature and in short time.The phase composition,microstructure,and EMA property of the SiC_(nw)/SiCNO composite aerogels were systematically investigated.The results indicated that the morphology and phase composition of SiC_(nw)/SiCNO composite aerogels can be regulated easily by varying the microwave treatment temperature.The composite aerogels show excellent EMA property with minimum reflection loss of -23.9 dB@13.8 GHz,-26.5 dB@10.9 GHz,and -20.4 dB@14.5 GHz and the corresponding effective bandwidth of 5.2 GHz,3.2 GHz,and 4.8 GHz at 2.0 mm thickness for microwave treatment at 600℃,800℃,and 1000℃,respectively,which is much better than that of SiCN ceramic aerogels.The superior EMA performance is mainly attributed to the improved impedance matching,multireflection,multi-interfacial polarization,and micro current caused by migration of hopping electrons.
基金supported by Louisiana Board of Regents ITRS Program(Grant Nos.LEQSF(2007-10)-RD-B-02 and CFAW-Ceramics LLC)
文摘This paper presents a simple and cost-effective method for the production of micro-sized silicon carbide whiskers at high yield and the effect on heat transfer enhancement for the whisker laden fluids. For SiC whisker synthesis, the starting powder mix- ture is obtained by milling short carbon fibers with the white ashes of rice hulls. Calcina：ion in argon, together with the subse- quent purification process, results in a high yield of SiC whiskers, which possess a diameter of 200-400 nm and a length of several tens of microns. The formation of the whiskers is discussed according to VS growth mechanism. Convective heat transfer performance in small channel tubes is then studied for fluid systems mixed with those micro-sized SiC whiskers at different concentrations. The heat transfer coefficient of SiC containing fluid can be significantly improved in comparison to the base fluid.
