某微细粒嵌布磁铁矿选矿工艺研究

针对某微细粒磁铁矿进行了全磁选流程和磁选-反浮选流程对比试验研究。结果表明,在最终磨矿细度相当的情况下,2种工艺流程都获得了产率48%左右、TFe品位66%左右、回收率80%左右的铁精矿指标,而采用磁选-反浮选流程的第三段磨矿量比全磁选流程减少了2/3。磁选-反浮选流程具有显著的节能降耗优势。     

天然气水合物储层泥质细粉砂挡砂介质堵塞规律与微观挡砂机制

中国南海海域部分天然气水合物储层中地层砂为高泥质含量细粉砂，开采防控砂难度较大。针对高泥质细粉砂挡砂机制问题，使用粒度中值为10.13 μm的泥质细粉砂样品，模拟单向气液携砂流动条件，使用绕丝筛板、金属烧结网、金属纤维、预充填陶粒4类挡砂介质在20~80 μm挡砂精度下进行挡砂模拟实验，采用显微成像系统观察挡砂介质内部及表面砂粒沉积与堵塞动态，分析介质流通性能和挡砂性能变化，总结堵塞规律、微观挡砂机制与形态及其控制因素。研究结果表明，不同类型和精度的挡砂介质对泥质细粉砂的堵塞总体呈现堵塞开始、堵塞加剧和堵塞平衡3个阶段。随着驱替进行，挡砂介质渗透率逐渐降低，幅度会高达90%以上；同时过砂速度减缓，最终过砂率为5%~10%。根据堵塞规律和微观图像分析，提出了粗组分分选桥架、局部砂团适度挡砂、整体砂桥阻挡等挡砂介质对泥质细粉砂的3种微观挡砂机制。以粗组分分选桥架挡砂机制为主的挡砂工况下，挡砂介质堵塞渗透率较高，但过砂率超过15%，挡砂效果较差；以整体砂桥挡砂机制为主时，过砂率在10%以下，挡砂性能较好，但各类挡砂介质的堵塞渗透率不足1 D，流通性能较差。局部砂团适度挡砂机制为主时介质挡砂性能及流通性能介于两者之间。挡砂介质对天然气水合物储层泥质细粉砂的微观挡砂机制和形态受挡砂介质类型、精度、地层砂特征以及流动条件等因素控制，其规律对于水合物泥质细粉砂防控砂优化有指导意义。     

Predictive process mapping for laser powder bed fusion: A review of existing analytical solutions

One of the main challenges in the laser powder bed fusion (LPBF) process is making dense and defect-free components. These porosity defects are dependent upon the melt pool geometry and the processing conditions. Power-velocity (PV) processing maps can aid in visualizing the effects of LPBF processing variables and mapping different defect regimes such as lack-of-fusion, under-melting, balling, and keyholing. This work presents an assessment of existing analytical equations and models that provide an estimate of the melt pool geometry as a function of material properties. The melt pool equations are then combined with defect criteria to provide a quick approximation of the PV processing maps for a variety of materials. Finally, the predictions of these processing maps are compared with experimental data from the literature. The predictive processing maps can be computed quickly and can be coupled with dimensionless numbers and high-throughput (HT) experiments for validation. The present work provides a boundary framework for designing the optimal processing parameters for new metals and alloys based on existing analytical solutions.     

Designing amorphous formulations of polyphenols with naringin by spray-drying for enhanced solubility and permeability

Naringin (NAR), a major flavanone (FVA) glycoside, is a component of food mainly obtained from grapefruit. We used NAR as a food additive to improve the solubility and permeability of hydrophobic polyphenols used as supplements in the food industry. The spray-dried particles (SDPs) of NAR alone show an amorphous state with a glass transition temperature (T_g) at 93.2 °C. SDPs of hydrophobic polyphenols, such as flavone (FVO), quercetin (QCT), naringenin (NRG), and resveratrol (RVT) were prepared by adding varying amounts of NAR. All SDPs of hydrophobic polyphenols with added NAR were in an amorphous state with a single T_g, but SDPs of hydrophobic polyphenols without added NAR showed diffraction peaks derived from each crystal. The SDPs with NAR could keep an amorphous state after storage at a high humidity condition for one month, except for SDPs of RVT/NAR. SDPs with NAR enhanced the solubility of hydrophobic polyphenols, especially NRG solubility, which was enhanced more than 9 times compared to NRG crystal. The enhanced solubility resulted in the increased membrane permeability of NRG. The antioxidant effect of the hydrophobic NRG was also enhanced by the synergetic effect of NAR. The findings demonstrated that NAR could be used as a food additive to enhance the solubility and membrane permeability of hydrophobic polyphenols.     

The influence of FeNi nanoparticles on the microstructures and soft magnetic properties of FeSi soft magnetic composites

In this work, a new type of FeSi/FeNi soft magnetic powder core (SMPC) was successfully fabricated by coating FeNi nanoparticles on the surface of FeSi micrometer powder. The effects of different contents of FeNi nanoparticles on the micromorphology, internal structures, and soft magnetic properties of SMPCs were studied. The results show that FeNi nanoparticles adhere to the surface of FeSi powder, which can effectively fill the air gap between FeSi powder and is beneficial to the compaction of the powder cores during the pressing process. Thus, the density of the SMPCs is increased. Compared to FeSi SMPCs, the comprehensive soft magnetic properties of FeSi/FeNi SMPCs have been greatly improved. When adding 15 wt% FeNi nanoparticles, the SMPCs exhibit excellent magnetic properties with high effective permeability (increased by 43.8 %) and low core loss (decreased by 22.1 %). The high performance FeSi/FeNi SMPCs prepared in this work are expected to be widely used in power choke coils, uninterruptible power supplies, and boosts and inverter inductors.     

Rapid synthesis of Y3Al5O12 powders via plasma electrolysis

Yttrium aluminum garnet (Y₃Al₅O₁₂, YAG) is an important functional material. However, the strict and complicated preparation has limited its wide application. This study aimed to rapidly synthesize Y₃Al₅O₁₂ by plasma electrolysis for the first time. The prepared powder was studied from topography, structure and elements by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The powder had a good crystal form with a spherical shape. The single kind of diffraction peak of Y₃Al₅O₁₂ in XRD revealed the high purity of the synthesized powders. The study of the relationship between the applied voltage and the synthesized powder revealed a threshold voltage of 210 V under the present condition. The higher voltage led to the damage of the electrode due to excessive heat. The synthesis of the YAG powder had a melt-quench process. The two processes were carried out at the same time.     

Evolution of precursor powders prepared by oxalate freeze drying towards high performance Bi-2212 wires

Bi₂Sr₂CaCu₂O_x (Bi-2212) precursor powders were synthesized by the oxalate freeze drying (OFD) method. In comparison with the traditional method, the novel method could shorten the processing steps and thus improve the fabrication efficiency of precursor powder. The phase, microstructure and superconducting properties of Bi-2212 precursor powders and wires were characterized by X-ray diffraction, scanning electron microscopy and four-probe method, respectively. The thermal behavior, surface area and particle size of powders were also discussed. The results indicated that large surface area and small particle size might improve the reactivity and uniformity of powders. These properties were beneficial for the rapid and homogeneous formation of Bi-2212. High-purity crystallized Bi-2212 powders without Bi-2201 and alkaline-earth cuprates phases could be achieved. Furthermore, multi-filamentary Bi-2212 wires with OFD powders showed good microstructures without noticeable pores and large secondary particles. Therefore, high engineering critical current densities (J_e) of 1619 A/mm² and critical current densities (J_c) of 7039 A/mm² were obtained in Bi-2212 wires at 4.2K, self field. It indicated that the oxalate freeze drying method would be a potential candidate for the mass production of high performance Bi-2212 wires.