High-efficiency simultaneous extraction of rare earth elements and iron from NdFeB waste by oxalic acid leaching

Iron can not be recovered at high value because only rare earth elements are effectively recovered from NdFeB waste via oxidation roasting-hydrochloric acid leaching process.In this study,a new method for leaching NdFeB waste with oxalic acid was developed.The high-efficiency,simultaneous and high-value recovery of rare earth elements and iron was realized to simplify the process and improve the economic benefit.Results of the oxalic acid leaching experiments show that under the optimum leaching conditions at 90℃ for 6 h in the aqueous solution of oxalic acid(2 mol/L) with a liquid-solid ratio of60 mL/g,the iron leaching efficiency and precipitation rate of rare earth oxalate reach 93.89% and 93.17%,respectively.Rare earth oxalate and Fe(C₂O₄)3^3- were left in the residue and the leaching solution,respectively.The leaching mechanism was further analyzed by characterising the leach residues obtained through X-ray powder diffraction(XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy(SEM-EDS).Results of the leaching kinetics study indicate that the process of oxalic acid leaching follows the shrinking nucleus model,and the leaching kinetics model is controlled by the mixed factors of diffusion and chemical reaction.The leaching residue was calcined at 850℃ for 3 h and then decomposed into rare earth oxide,which can be directly used to prepare rare earth alloy via molten salt electrolysis.For the leaching solution,ferric oxalate solution was reduced using Fe powder to prepare the ferrous oxalate(FeC₂O₄-2H₂O).     

采用超声波特性参量研究PBX炸药的热处理

对压制成型Φ20mm×10mm高聚物粘结炸药PBX03试样进行了50℃条件下累积9天的热处理试验,采用超声波特性参量检测了热处理试样,获得了PBX03试样热处理作用及机理的新认识:PBX03试样的超声波增益和声速值在热处理过程中均呈现出趋同的特征;适当的热处理有助于改善PBX03压制件内部质量的一致性;PBX03中TATB的不可逆长大可能是前述结果的主要致因。     

胶接接头界面理论及其表面处理技术研究进展

胶接是用胶粘剂将被粘物表面连接在一起,形成可承受外载的胶接接头的过程,是涉及材料粘附、高分子材料老化机理、表面技术、力学性能测试等多个学科领域的边缘学科.介绍了与胶接接头界面紧密相关的弱界面层理论和润湿理论等领域的研究进展,总结了胶接接头表面处理方面的主要方法.     

A study of the influence of lanthanum fluoride on the tribological properties of bonded solid film lubricants and its mechanism of function

The influence of lanthanum fluoride (LaF₃) on the characteristics of phenolepoxy-bonded MoS₂ dry films was investigated. The functional mechanism was specifically studied using several analytical means. The results showed that the wear life of dry films containing a certain amount of LaF₃ was considerably increased over that of the films without LaF₃. However, the effect of LaF₃ on the friction coefficient of the dry films was shown to be negligible. It was found that the addition of LaF₃ is effective in reducing the oxidation tendency of MoS₂ in the films during the friction process. The reason for this is investigated by the authors.     

Fabrication of novel AlN-SiC-C refractories by nitrogen gas-pressure sintering of Al4SiC4

Novel AlN-SiC-C refractories were fabricated by nitrogen gas-pressure sintering using single Al₄SiC₄ as raw-material. The high nitrogen pressure is essential and effective for the nitridation because it contributes to the diffusion of the nitrogen atoms into the interior matrix of Al₄SiC₄ specimen. Different from traditional carbon-containing refractories and ceramic bonded carbon materials (CBCs), the resulted products possess a honeycomb microstructure consisting of interlocked structure of worm-like SiC and C particles with a AlN ceramic boundary. AlN-SiC nanoparticles and aluminum carbonitride particles (Al-C-Ns) were formed at the interface between AlN-rich and C/SiC-rich area, which acted as transition phases that make these two areas combined tightly. The as-prepared AlN-SiC-C refractories at 1700 ℃ by a 20 atm pressure showed a relative density of 75.8%, combining a bulk density of 2.20 g/cm³ with a flexural strength of 120.9 MPa. Furthermore, the potential reaction mechanism responsible for fabrication of AlN-SiC-C refractories was revealed.     

埋地管线用重防腐涂料的技术发展

介绍了埋地管线用重防腐涂料的主要发展历程,对几种常用埋地管线用防腐材料进行了评价和对比,从中得出熔结环氧粉末涂料应用于埋地管线中的优势。     

莫来石结合碳化硅高温吸热陶瓷抗氧化性能的研究

以碳化硅及合成莫来石微粉为主要原料,制备了用于非真空太阳能吸热管的莫来石结合碳化硅高温陶瓷涂层。针对碳化硅基材料高温氧化问题,测定了样品的烧成增重率及亮度并结合XRD、SEM研究了莫来石结合碳化硅陶瓷的抗氧化性能。结果表明,莫来石添加量为20%,经1 380℃烧成样品的抗氧化性最好,其增重率为7.49%,亮度值为46.61。XRD分析烧结体主晶相为碳化硅(α-SiC)和莫来石(3Al2O3.2SiO2),并含有少量的方石英(SiO2),莫来石作为结合相在碳化硅晶粒周围形成"骨架",与SiO2玻璃相形成三围的网状保护层包裹在碳化硅表面,阻止碳化硅氧化。     

热处理对原位烧结(Ti,V)C钢结硬质合金组织及耐磨性的影响

利用粉末冶金技术,原位烧结合成了(Ti,V)C钢结硬质合金,并用扫描电镜、X射线衍射仪等研究了热处理对原位烧结(Ti,V)C钢结硬质合金组织和耐磨性的影响。结果表明:烧结态(Ti,V)C钢结硬质合金基体组织为细珠光体组织;1 000℃淬火后的组织转变为片状马氏体+(Ti,V)C硬质相颗粒+少量未溶碳化物;回火过程中合金具有较高的抗回火稳定性,在500℃左右回火时存在二次硬化现象;该合金在1 000℃淬火、经250,500℃回火后具有较好的耐磨性。     

高聚物粘结炸药及涂层表面抗变形与回弹性研究

采用纳米压痕技术测试并比较研究了两种高聚物粘结炸药(P1、P2)及其两种涂层(C1、C2)在"加载-卸载-恢复"过程中各阶段的表面变形情况及回弹性能.结果表明,这四种材料表面抗变形能力从大到小的顺序是: P1>P2>C1>C2,而回弹性从大到小的顺序则是: C2>C1>P2>P1,其中C1与P1、P2力学性能差异较小,而C2与P1、P2具有显著差异.并采用Boltzmann非线性回归函数对这四种材料表面变形及回弹曲线进行拟合,拟合曲线与试验数据吻合较好,相关系数均大于0.99.     

Preform impregnation to optimize the properties and microstructure of RB-SiC prepared with laser sintering and reactive melt infiltration

Indirect selective laser sintering (SLS) was combined with reactive melt infiltration (RMI) to fabricate RB-SiC, and the effects of preform impregnation with different carbon source on the carbonized sample and final RB-SiC were investigated. Results show that the impregnation treatment led to increased bulk density and mechanical strength of samples at all stages. The pore size dwindled and the porosity decreased significantly for the carbonized sample, and the content of Si reduced for the final RB-SiC. The impregnation with PF resin containing 30 % nano carbon black (PFnanoC) seems more promising for the comprehensive properties improvement, the final RB-SiC had a relatively fewer amount of residual pore and carbon and showed superior mechanical properties compared with those of sample impregnated with only PF resin. Kinetics analysis indicates a slower pore-clogging rate under the PFnanoC impregnation condition, which avoided or hindered a too-early infiltration cease during the RMI process.