Sn含量对轧制Mg-6Bi-Sn合金组织演变和腐蚀性能的影响

研究了轧制态Mg-6Bi-xSn (x=0,1,2,3,%,质量分数) 4种合金的组织演变和腐蚀性能。结果表明：研究合金均表现出等轴晶组织和少量的孪晶组织,随着Sn含量的增加,平均晶粒尺寸分别为 (15.63±1.37),(13.71±1.15),(10.86±1.39) 和 (12.29±1.15) μm;第二相体积分数分别为 (3.56±0.06)%,(3.67±0.09)%,(3.76±0.36)%和 (9.58±0.69)%。另外,随着Sn含量的增加,腐蚀速率先减小再增大,这是因为晶粒细化和第二相颗粒增加竞争机制的结果,Mg-6Bi-2Sn合金由于其均匀的微观组织而表现出最佳的耐腐蚀性能。     

Larger pore volume tetraphenyladamantane-based hybrid porous polymers: Facile Friedel–Crafts preparation,CO2 capture,and Rhodamine B removal properties

Synthesis of covalently linked porous polymers with high surface area and larger pore volume for two or more task-specific functionalities is always a big challenge. In this article, the facile Friedel–Crafts reaction is employed to construct the hierarchical hybrid porous polymers (HPPs) from tetraphenyladamantane and octavinylsilsesquioxane. The resulting polymers, HPP-1 to HPP-3, possessed the surface areas from 1356 to 1511 m² g⁻¹, and the pore volumes from 2.05 to 2.67 cm³ g⁻¹. All these polymers feature micropores, mesopores, and macropores in nature. The resultant polymers exhibit high CO₂ adsorption capacity up to 2.0 mmol g⁻¹ (8.82 wt %), at 273 K, 1.0 bar, and the maximum Rhodamine B (RB) sorption capacity of 653.6 mg g⁻¹. To illustrate the adsorption process, the effects of factors, contact time, initial concentration, temperature, and pH value on the adsorption capacity of RB were studied. The adsorption equilibrium data displayed a better fitting to the Langmuir isotherm model than the Freundlich model and the adsorption kinetics fitted well with the pseudo-second-order kinetic model. The recycle experiments displayed that the capacity recovery was still higher than 95% after four cycles. Theses polymers are promising to be the adsorbents for capturing CO₂ and removing RB. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 136, 48572.     

Balling behavior of stainless steel and nickel powder during selective laser melting process

Balling phenomenon, as a typical selective laser melting (SLM) defect, is detrimental to the forming quality. In this work, a detailed investigation into the balling behavior of selective laser melting of stainless steel and pure nickel powder was conducted. It was found that the SLM balling phenomenon can be divided into two types generally: the ellipsoidal balls with dimension of about 500?μm and the spherical balls with dimension of about 10?μm. The former is caused by worsened wetting ability and detrimental to SLM quality; the latter has no obvious detriment to SLM quality. The oxygen content plays an important role in determining the balling initiation, which can be considerably lessened by decreasing the oxygen content of atmosphere to 0.1%. A high laser line energy density, which can be obtained by applying high laser power and low scan speed, could enable a well-wetting characteristic. The effect of scan interval on balling initiation is not obvious as long as the scan track is continuous. The surface remelting procedure can also alleviate the balling effect in a certain extent, due to the melting and wetting of metal balls. Moreover, the balling phenomenon of pure nickel was also studied, and the results implied that the balling discipline had a universality.     

Effects of particle size and dispersion methods of In2O3‐SnO2 mixed powders on the sintering properties of indium tin oxide ceramics

Three group samples were used to investigate the effects of particle size and dispersion methods of In₂O₃‐SnO₂ mixed powders on the sintering properties of ITO ceramics by BET, SEM, XRD, and EPMA, etc. High‐density (99.8% of TD) ITO ceramics, with dimensions of 350 × 250 × 8 mm³ for the industrial application, were obtained by the mixed powders of In₂O₃ calcined at 1000°C and SnO₂ with BET 6.0 ± 0.5 m²/g and collocation use of ball mill for 300 minutes, stirred mill for 60 minutes, and sand mill for 3 minutes. The results indicate that: (i) the larger the SnO₂/In₂O₃ particle size ratio, the higher the density of ITO ceramics, (ii) the dispersion of mechanical ball‐mill methods for nanosized In₂O₃ and SnO₂ powders is beneficial to the densification and structural homogeneity, and (iii) the smaller the relative grain size, the more uniform the distribution of grain size.     

S2O82-/ZrO2-SiO2催化合成柠檬酸三丁酯

以S2O82- /ZrO2-SiO2固体酸为催化剂,以柠檬酸、正丁醇为原料合成柠檬酸三丁酯,考察了影响反应酯化率的各种因素,确定了反应的最佳条件。实验表明:当n(Zr):n(Si)=1:13时,催化剂用量为0.75g,醇酸比为1∶4,反应温度140℃,反应时间3.5h,柠檬酸的转化率可达98.3%。     

Densification mechanisms and microstructural evolution during spark plasma sintering of boron carbide powders

Micron-sized boron carbide (B₄C) powders were subjected to spark plasma sintering (SPS) under temperature ranging from 1700 °C to 2100 °C for a soaking time of 5, 10 and 20 min and their densification kinetics was determined using a creep deformation model. The densification mechanism was interpreted on the basis of the stress exponent n and the apparent activation energy Q_d from Harrenius plots. Results showed that within the temperature range 1700–2000 °C, creep deformation which was controlled by grain-boundary sliding or by interface reaction contributed to the densification mechanism at low effective stress regime (n = 2,Q_d = 459.36 kJ/mol). While at temperature higher than 2000 °C or at high stress regime, the dominant mechanism appears to be the dislocation climb (n = 6.11).     

深基坑地下连续墙的无扰动综合施工技术

结合工程实践,从施工信息化、降水模拟分析、既有建筑保护、无扰动切除钢绞线、施工监测等方面,总结出深基坑地下连续墙无扰动综合施工技术.该综合施工技术应用后,周边监测点的不均匀沉降及变形均控制在2 mm内,为邻近既有地铁的城市新建工程提供了一定的参考价值.     

316L Stainless Steel with Gradient Porosity Fabricated by Selective Laser Melting

To fabricate 316L stainless steel part with a pore gradient structure, the method using selective laser melting (SLM) technique is exploited. Scan tracks feature, densification, and tensile property of SLM-produced samples prepared via different scan speeds were investigated. The results show that the porosity is strongly influenced by scan speed. On this basis, a gradient changed scan speed was applied in every SLM layer for the purpose of producing a gradient porosity metal. The results indicate that the structure exhibits a gradually increased porosity and a reduced molten pool size along the gradient direction of scan speed variation. The forming mechanisms for the gradient porosity were also addressed.     

硬脂酸钠原位改性碳酸钙的研究

采用原位法制备改性碳酸钙,即在改性剂存在条件下,由氢氧化钙经过碳酸化制备改性碳酸钙.研究了改性剂种类、改性剂加入时间、改性剂用量对改性效果的影响.结果显示:硬脂酸钠的改性效果相对较好;产品活化度显示改性碳酸钙是憎水性的;当在消化时加入3%的硬脂酸钠(以碳酸钙质量计)时,改性碳酸钙的活化度可达97.1%.FT-IR,DTA分析表明:其憎水性是由于硬脂酸钠以离子键的形式结合到碳酸钙表面形成难溶硬脂酸钙结果所致.     

Microstructure and Mechanical Properties of TiC-Reinforced Al-Mg-Sc-Zr Composites Additively Manufactured by Laser Direct Energy Deposition

In order to refine the microstructure and improve the performance of direct energy deposited (DED) additively manufactured Al-Mg-Sc-Zr alloy, TiC-modified Al-Mg-Sc-Zr composites were prepared by DED and the effect of TiC content on the microstructure and performance was studied. In the absence of TiC particle, the microstructure of Al-Mg-Sc-Zr alloy prepared by DED consisted of fine grains with average size of 8.36 μm, and well-dispersed nano-Al₃(Sc,Zr) particles inside the grains and Mg₂Si phase along the grain boundaries. With the addition of 1 wt% TiC, the microstructure of TiC/Al-Mg-Sc-Zr prepared by DED became finer apparently compared with that without TiC; while the further increase of TiC content to 3 wt%, the microstructure of TiC/Al-Mg-Sc-Zr prepared by DED became coarser with appearance of a new kind of needle-like (Ti,Zr)₅Si₃ phase. Also, the addition of TiC decreased the porosity of Al-Mg-Sc-Zr prepared by DED. Simultaneously, after the addition of TiC, the tensile strength increased from 283.25 MPa to 344.98-361.51 MPa, and the elongation increased from 3.61% to 9.58-14.10%. The potential mechanism of the microstructure evolution and strength improvement was discussed. This research will provide new insights into the available metal matrix composites by laser additive manufacturing (LAM).