Ultrafine particles prepared by evaporating pure Fe in CH4 atmosphere using arc-dischargeheating method, were found to consist of Fe-C solid solution, γ-Fe and Fe3C phases. EfFect of annealing temperature on phase tr...Ultrafine particles prepared by evaporating pure Fe in CH4 atmosphere using arc-dischargeheating method, were found to consist of Fe-C solid solution, γ-Fe and Fe3C phases. EfFect of annealing temperature on phase transformation and hyperfine interactions has been investigated by Mossbauer spectroscopy, X-ray diffraction (XRD), differential thermal analysis and thermogravimetry (DTA-TG), transmission electron microscopy (TEM), oxygen determination and vibrating sample magnetometer (VSM) measurements. It was observed that phase transformation of γ-Fe to α-Fe occurs during annealing in vacuum. The mechanism causing the change of hyperfine interactions with annealing temperature differs for Fe-C solution and interstitial compounds. DifFerence of hyperfine interactions of Fe-C solid solution in the starting sample and its annealed samples is ascribed to the improvement of activation of interstitial carbon atoms. Stress-relieving in structure of annealed Fe3C particle can result in a weak influence on hyperfine interactions. Parameters fitted to the Mossbauer spectra show the existence of superparamagnetism in all the samples. Absorbed and combined oxygen on particle surface of the starting sample were determined.展开更多
In the paper, dicalcium silicate (C2S) was modified to obtain higher performance, and the solutionizing pattern of BaSO4 in cement clinker was analyzed theoretically. According to experimental results, solutionizing o...In the paper, dicalcium silicate (C2S) was modified to obtain higher performance, and the solutionizing pattern of BaSO4 in cement clinker was analyzed theoretically. According to experimental results, solutionizing of BaSO4in cement clinker improved crystal plane distance of C2S as well as the relations of coordination. The performance tests show that the strength of C2S modified by BaSO4 changes and the reactivity of C2S increases significantly.展开更多
In the present work,mechanical alloying of a powder mixture of nickel and graphite(up to 15wt%)was carried out in an attrition mill under a nitrogen atmosphere.The as-milled powders were characterized by scanning elec...In the present work,mechanical alloying of a powder mixture of nickel and graphite(up to 15wt%)was carried out in an attrition mill under a nitrogen atmosphere.The as-milled powders were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),and transmission electron microscopy(TEM).The 15wt%graphite dissolved into the nickel(exceeding the negligible solid solubility in the nickel–carbon system),thereby forming a supersaturated solid solution of graphite in a nickel matrix.The dissolved graphite occupied interstitial positions along the dislocation edges and at the grain-boundary regions.A three-step graphite dissolution mechanism has been proposed.The associated changes in the nickel lattice,such as changes in the crystallite size(62 to 43 nm),lattice strain(0.12%to 0.3%),and lattice parameter(0.3533 to 0.3586 nm),which led to the formation of the supersaturated solid solution,were also evaluated and discussed.展开更多
Ultra-high-temperature ceramic nanowires have shown increasing potential for use as thermal structural components.Herein,novel single-crystal Hf_(0.5)Ta_(0.5)C solid solution nanowires were synthesized and incorporate...Ultra-high-temperature ceramic nanowires have shown increasing potential for use as thermal structural components.Herein,novel single-crystal Hf_(0.5)Ta_(0.5)C solid solution nanowires were synthesized and incorporated with a HfC coating to construct a robust structure with Hf_(0.5)Ta_(0.5)C solid solution nanowires uniformly distributed and interconnected within the coating.The novel Hf_(0.5)Ta_(0.5)C solid solution nanowires could effectively hinder crack propagation through crack tip pinning and crack deflection.This mechanism substantially enhanced the elastic modulus and fracture toughness of the HfC coating by 53.29%and 59.67%,respectively.The toughened HfC coating displayed superior fracture toughness and good interfacial binding strength with the substrate to resist severe oxidation and scouring.Additionally,the high thermal conductivity of the toughened HfC coating promoted heat transmission.Thus,in comparison to the pure HfC coating,the toughened HfC coating displayed smaller mass and linear ablation rates of−0.35 mg·s^(−1)and−0.46μm·s^(−1),which decreased by 39.66%and 36.98%,respectively.Our work not only simultaneously enhances the mechanical properties and ablation resistance of HfC-coated carbon/carbon(C/C)composites but also provides novel prospects for advanced ultrahigh-temperature ceramic nanowires under extreme conditions.展开更多
文摘Ultrafine particles prepared by evaporating pure Fe in CH4 atmosphere using arc-dischargeheating method, were found to consist of Fe-C solid solution, γ-Fe and Fe3C phases. EfFect of annealing temperature on phase transformation and hyperfine interactions has been investigated by Mossbauer spectroscopy, X-ray diffraction (XRD), differential thermal analysis and thermogravimetry (DTA-TG), transmission electron microscopy (TEM), oxygen determination and vibrating sample magnetometer (VSM) measurements. It was observed that phase transformation of γ-Fe to α-Fe occurs during annealing in vacuum. The mechanism causing the change of hyperfine interactions with annealing temperature differs for Fe-C solution and interstitial compounds. DifFerence of hyperfine interactions of Fe-C solid solution in the starting sample and its annealed samples is ascribed to the improvement of activation of interstitial carbon atoms. Stress-relieving in structure of annealed Fe3C particle can result in a weak influence on hyperfine interactions. Parameters fitted to the Mossbauer spectra show the existence of superparamagnetism in all the samples. Absorbed and combined oxygen on particle surface of the starting sample were determined.
文摘In the paper, dicalcium silicate (C2S) was modified to obtain higher performance, and the solutionizing pattern of BaSO4 in cement clinker was analyzed theoretically. According to experimental results, solutionizing of BaSO4in cement clinker improved crystal plane distance of C2S as well as the relations of coordination. The performance tests show that the strength of C2S modified by BaSO4 changes and the reactivity of C2S increases significantly.
文摘In the present work,mechanical alloying of a powder mixture of nickel and graphite(up to 15wt%)was carried out in an attrition mill under a nitrogen atmosphere.The as-milled powders were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),and transmission electron microscopy(TEM).The 15wt%graphite dissolved into the nickel(exceeding the negligible solid solubility in the nickel–carbon system),thereby forming a supersaturated solid solution of graphite in a nickel matrix.The dissolved graphite occupied interstitial positions along the dislocation edges and at the grain-boundary regions.A three-step graphite dissolution mechanism has been proposed.The associated changes in the nickel lattice,such as changes in the crystallite size(62 to 43 nm),lattice strain(0.12%to 0.3%),and lattice parameter(0.3533 to 0.3586 nm),which led to the formation of the supersaturated solid solution,were also evaluated and discussed.
基金the National Key R&D Program of China(No.2021YFA0715803)the National Natural Science Foundation of China(Nos.52293373 and 52130205)+1 种基金the Joint Fund of Henan Province Science and Technology R&D Program(No.225200810002)the Fundamental Research Funds of Henan Academy of Sciences(No.240621040).
文摘Ultra-high-temperature ceramic nanowires have shown increasing potential for use as thermal structural components.Herein,novel single-crystal Hf_(0.5)Ta_(0.5)C solid solution nanowires were synthesized and incorporated with a HfC coating to construct a robust structure with Hf_(0.5)Ta_(0.5)C solid solution nanowires uniformly distributed and interconnected within the coating.The novel Hf_(0.5)Ta_(0.5)C solid solution nanowires could effectively hinder crack propagation through crack tip pinning and crack deflection.This mechanism substantially enhanced the elastic modulus and fracture toughness of the HfC coating by 53.29%and 59.67%,respectively.The toughened HfC coating displayed superior fracture toughness and good interfacial binding strength with the substrate to resist severe oxidation and scouring.Additionally,the high thermal conductivity of the toughened HfC coating promoted heat transmission.Thus,in comparison to the pure HfC coating,the toughened HfC coating displayed smaller mass and linear ablation rates of−0.35 mg·s^(−1)and−0.46μm·s^(−1),which decreased by 39.66%and 36.98%,respectively.Our work not only simultaneously enhances the mechanical properties and ablation resistance of HfC-coated carbon/carbon(C/C)composites but also provides novel prospects for advanced ultrahigh-temperature ceramic nanowires under extreme conditions.
