Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》
Abstract： A solution for electro-spinning of fibers was prepared via non-hydrolytic sol-gel method with ethanol and dimethyl formamide (DMF) as solvent, MgCl2 and AlCl3 as raw material and polyvinylpyrrolidone (PVP) as additive. With the above solution, precursor fibers of magnesia- alumina spinel were prepared by electrospinning technology, which then were calcined at 900℃ to finally produce fibers of magnesia-alumina spinel. The effect of gelation temperature, the content of gel and PVP on the phase composition and microstructure of magnesia-alumina spinel fibers was studied by XRD, FTIR, SEM and TEM. The result shows that magnesia-alumina spinel fibers could be produced with the fiber precursor prepared with the fresh solution which was not subjected to sol-gel treatment, but such fibers were crosslinked seriously and on which there existed significant amount of moniliform particles; For those made of the fiber precursor prepared with the solution after gelation at 120℃, such fibers were apt to fracture and the diameter of which increased with the increasing dosage of gel and PVP; For those made of the fiber precursor prepared with the solution after gelation at 100℃ with a dosage of 0.068 mol/L gel and 0.045 g/mL PVP, the fibers were smooth, continuous and homogeneous with an average diameter 121 nm, and furthermore, these fibers still showed good a morphology even after calcined at 1600℃.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》
Abstract： The reaction products of a system of geopolymer could be great different due to the variation of the chemical composition of raw materials and the activated conditions. In the system of geopolymer containing calcium, the reaction mechanism, composition of products, and their structures could be more complex. Metakaolin (MK)-based geopolymer was prepared from metakaolin with different amount of five kinds of crystal calcium resources and two kinds of non-crystal calcium sources. The effect of calcium resource on the performance and reaction mechanism of the geopolymer was then systematically studied. The result showed that the dissolution of Si and Al related to the structure of the calcium resources and had a strong positive correlation, but no clear relationship with Ca. The compressive strength of MK- based geopolymer could decrease by addition of calcium resources. The compressive strength of geopolymer with non- crystal calcium resource was higher than that with crystal one. The dessolved amount of calcium from the calcium resource had a negative connection with the compressive strength. It provided the theoretical and experimental base for broadening the raw material resources of geopolymer system, and for utilization of industrial solid wastes containing calcium.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Amorphous alloy is a new type of material that exhibits exceptional properties or combinations of properties that are often not achievable in conventional crystalline materials. Fe-based amorphous alloys has attracted significant attention over the last few decades because of their low cost and enhanced mechanical performance. However, they are more suitable for the industrial application of coatings due to the fatal disadvantages of poor toughness. High velocity oxygen-fuel (HVOF) spraying is a good way to make amorphous alloy coatings (AMCs), for the individual droplets are cooled at a rate of around 107 K/s which is much higher than the critical cooling rate of the amorphous alloys during the thermal spraying. Fe-based AMCs obtained by using the HVOF spray method are important materials for industrial applications because of high glass- forming ability and exceptional performances, such as excellent corrosion resistance, high hardness, and superior wear resistance. In this work, Fe-CrMoMnWBCSi AMCs were prepared by HVOF thermal spray. The microstructure and amorphous characteristics of AMCs were characterized by SEM and XRD. Electrochemical corrosion behavior of AMCs was investigated in different concentration of NaCl and H2SO4 solutions compared with that of 304 stainless steel and ND steel. The surface film of materials after immersed in two solutions was analysed by XPS. The results indicated that HVOF thermal spraying Fe-based AMCs presented dense layered structure, high amorphous phase content and low porosity. The composite structure of AMCs was formed with some nanocrystallite phases embedded in the amorphous matrix. AMCs exhibited better resistance to pitting corrosion and relatively low uniform corrosion resistance due to the porosity, while the pitting potential of 304 stainless steel was sensitive to NaCl concentration. XPS results revealed that the presence of Cr, Mo and W oxides in the passive film of AMCs may result in the better corrosion resistance. The enrichment of Mo4+ oxides on the surface favored the formation of a more stable and protective layer which could be assumed to be responsible for the observed high stability of passive film. The diminishing or avording pores may be beneficial to further improve the pitting corrosion resistance of AMCs in NaCl solution. In all cases, AMCs showed better resistance to H2SO4 solutions corrosion due to the high stability of passive film. 304 stainless steel and ND steel presented stable passivation behavior only in high concentration of H2SO4 solution. In the lower concentration solution of H2SO4, the amorphous structure of the thinner coatings could facilitate the formation of thicker passivation film and lead to the higher corrosion resistance. The corrosion resistance of AMCs in H2SO4 solution could be enhanced significantly by formation of high amorphous phase.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Nano melamine phosphate (NMP) flame retardant was synthesized using melamine and phosphoric acid as reagents by means of a solvothermal method. The prepared NMP was then characterized by means of Fourier transform infra-red spectroscopy, X-ray diffraction, and transmission electron microscopy. Effect of solvents, different kinds of surfactants (i.e. SDS, CTAB and NP), reaction temperature and time on the morphology of reaction product was investigated. It is found that the NMP can only be obtained by using benzene as a solvent. If distilled water and anhydrous ethanol were used as solvent, the particle size of the product is in micro scale. As reaction temperature or reaction time increases, the morphology of the products changes greatly. Moreover, types of surfactants have a great influence on the morphology of the products. Moreover, The polyethylene glycol toughened phenolic foam with addition of NMP exhibits a flexural strength 39% higher than that with addition of micro MP.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：通过等离子喷焊NiCrBSi+Ti混合粉末制备TiC硬质增强镍基复合耐磨层, 利用OM, SEM, XRD及EDS, 研究了喷焊层微观组织、物相及元素组成特征, 并利用显微硬度仪及耐磨料磨损试验机对喷焊层显微硬度及耐磨料磨损性能进行测试. 结果表明, NiCrBSi+Ti混合粉末喷焊层主要包括由保留有共晶组织形态的（γ-Ni+?1-Ni3Si）与过共析组织（?-Fe+FeNi3）组成的基体相; 以及镶嵌于基体中的M7C3和M23C6等硬质相; CrB弥散分布于喷焊层中; 原位生成的TiC一部分作为M7C3和M23C6等后析出相的形核核心; 一部分以细小颗粒（＜1 μm）弥散于基体中; 部分甚至偏聚为大尺寸TiC（＞1 μm）块体. Ti的加入, 显著细化了喷焊层组织; Ti添加量为6%时, 喷焊层性能最好, 显微硬度可达800 HV0.5, 磨损质量约为14.5 mg, 耐磨性约为纯NiCrBSi喷焊层的2倍以上.
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