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环境中氮的过剩和短缺问题及其解决途径
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作者 胡金润 杨丹 《葛洲坝集团科技》 2019年第2期78-80,共3页
氮是人和自然环境中重要的元素,人类活动对全球氮循环造成了及大地干扰。氮素利用极度不均匀,过量的氮在发达国家引起了各种问题,但是在其他国家,缺氮的土壤却威胁着粮食安全,氮的过剩和短缺已经成为全球主要环境问题。人类必须提高认... 氮是人和自然环境中重要的元素,人类活动对全球氮循环造成了及大地干扰。氮素利用极度不均匀,过量的氮在发达国家引起了各种问题,但是在其他国家,缺氮的土壤却威胁着粮食安全,氮的过剩和短缺已经成为全球主要环境问题。人类必须提高认识、改变行为和加强监管,减少氮排放,增加氮的有效利用,共同应对这一全球性问题。 展开更多
关键词 氮循环 氮的利用 氮的污染 过剩 短缺
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Single-source-precursor synthesis and air-plasma ablation behavior of(Ti,Zr,Hf)C/SiC ceramic nanocomposites at 2200℃
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作者 Li Lu Qingbo Wen +5 位作者 jinrun hu Tianxing Jiang Xiangchao Ren Yalei Wang Yi Zeng Xiang Xiong 《Journal of Advanced Ceramics》 SCIE EI CAS CSCD 2024年第7期1043-1059,共17页
Dense monolithic(Ti,Zr,Hf)C/SiC ceramic nanocomposites with four different molar ratios of metallic elements in the(Ti,Zr,Hf)C phase(i.e.,Ti:Zr:Hf=1:1:1,2:3:5,2:3:3,and 1:2:1)were prepared upon pyrolysis of novel(Ti,Z... Dense monolithic(Ti,Zr,Hf)C/SiC ceramic nanocomposites with four different molar ratios of metallic elements in the(Ti,Zr,Hf)C phase(i.e.,Ti:Zr:Hf=1:1:1,2:3:5,2:3:3,and 1:2:1)were prepared upon pyrolysis of novel(Ti,Zr,Hf)-containing single-source precursors(SSPs),followed by spark plasma sintering(SPS).A thorough characterization was conducted to elucidate the synthesis of the SSPs,polymer-to-ceramic transformation,chemical/phase compositions,and microstructure of the SiTiZrHfC-based ceramics.The results revealed the feasibility of synthesizing nanocomposites with high(Ti,Zr,Hf)C contents using the SSP method.These nanocomposites were characterized by a unique microstructure with in situ generated(Ti,Zr,Hf)C@C core-shell nanoparticles homogeneously mixed withβ-SiC.The ablation behavior of the nanocomposites was evaluated on an air-plasma device for 60 s.Impressively,the nanocomposites exhibited excellent ablation resistance,and the lowest linear ablation rate reached−0.58μm/s at 2200°C.Notably,the ablation resistance can be dramatically improved by precisely tailoring the atomic ratios of metal elements within the(Ti,Zr,Hf)C phase via the molecular design of the SSPs.The formation of a multiple-oxide layer with both a high-meltingpoint phase((Ti,Zr,Hf)O_(2))and low-melting-point phases((Zr,Hf)TiO_(4))and glassy SiO_(2),as well as their structure,played a critical role in the enhanced ablation resistance.The uniform distribution of the high-melting-point(Ti,Zr,Hf)O_(2)nano/microparticles throughout the glassy SiO_(2)matrix significantly enhanced the viscosity and stability of the oxide layer by the pinning effect,offering superior protection against the ingress of oxygen atoms and excellent resistance to mechanical erosion. 展开更多
关键词 ultrahigh-temperature ceramics(UHTCs) multicomponent carbide NANOCOMPOSITES ablation behavior multiple oxides
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