含成形剂的纳米微晶ZrO2粉末压形规律的研究

本文对管道反应制备的纳米微晶ＺｒＯ２粉末的模压数据进行处理。结果表明,该ＺｒＯ２粉末压形规律黄培云压形方程。     

含成形剂的纳米微晶ZrO2粉末压形规律的研究

本文对管道反应制备的纳米微晶ZrO₂（Y₂O₃3mol％）粉末的模压数据进行处理．结果表明,该ZrO₂粉末压形规律遵循黄培云压形方程．根据黄培云压形方程计算出纳米微晶ZrO₂陶瓷粉体的压制模量为11．9～12．7MPa,压制过程的非线性指数为7．15．成形剂量的增加将降低粉末体的压制模量,而其非线性指数却保持不变．结合ZrO₂压坯的孔隙、孔径测定,分析得出纳米微晶ZrO₂粉末理想的成形压力范围应在40-140MPa;这为纳米微晶ZrO₂粉末压形提供了理论基础．     

The effect of contact torques on porosity of cohesive powders

The porosity of uniaxially compacted cohesive powders depends on the applied stress (including gravity). The case, where these stresses are weak, is considered. The compaction results in a porosity which is a function of sliding, rolling and torsion friction. By contact dynamics simulations it is shown that the influences of contact torques (static rolling and torsion friction) on the porosity are significant and approximately additive. The relevance for nano-powder pressure sintering is discussed.     

退火处理对非晶态Ni-P合金超细粉结构及磁性能的影响

采用液相脉冲放电技术,在NiSO4溶液中用NaH2PO2为还原剂,制备出了Ni-P合金超细粉体材料。将Ni-P合金粉在200～450℃下退火处理,并通过X射线衍射(XRD)、透射电镜(TEM)和场发射扫描电镜(FESEM)对退火前后Ni-P合金粉的结构、形貌进行了分析。用振动样品磁强计(VSM)对Ni-P合金粉进行了磁性能分析。结果表明所制备的超细Ni-P合金粉为非晶结构,颗粒直径在300～500nm之间,颗粒之间紧密结合成链枝状形貌。Ni-P合金粉在250～280℃退火后具有良好的软磁性能,250℃退火后矫顽力降低至0.437×10-4T。     

Effect of mechanical milling and heat treatment on the structure and magnetic properties of gas atomized Mn-Al alloy powders

Ferromagnetic Mn-Al alloy powders were fabricated by mechanical milling and heat treatment with gas-atomized powders. Different processes, i.e., heat treatment before ball milling and ball milling before heat treatment, result in different microstructures and magnetic properties of the powders. It was found that H_c increased and M_r decreased with the size reduction regardless of the sequence of heat treatment and ball milling. However, tendency of the change in H_c and M_r depended on the sequence. Further annealing of the powders ball-milled after heat treatment resulted in slight decrease of H_c and large increase of M_r. The magnetic properties, M_r = 41.2 emu/g, H_c = 3.1 kOe, were obtained from the powders ball-milled for 5 h after heat treatment at 650 °C for 20 min, and subsequent annealing at 280 °C for 20 min.     

铜导电胶电性能的研究

以改性树脂和混合树脂为粘料，铜粉为导电性填料，并配以适当添加剂、固化剂制备铜导电胶。该胶具有电阻率较低，性能稳定，粘接力强等优点。     

粉末冶金高速压制技术的研究进展

主要介绍了高速压制技术的特点和研究进展.高速压制技术是一项低成本、高效率成型高密度粉末冶金零件的新技术,由于具有良好的性价比而备受关注.其压制速度快,可使材料性能更加优良、生产更加经济化,具备用中小型设备生产超大零件的能力,具有广阔的应用潜力.     

Tooling Design and Compaction Analysis on P/M Copper Bushes

The successful production of P/M (powder metallurgy) components depends to a large extent on the tooling used for powder compaction. While designing the tool, the complexities arise from the interaction of the parameters such as powder characteristics, expected green density, the size and geometry of the product, and to whom the properties of the tool materials during compaction should be addressed. Floating type of compaction tooling set (die, punches, and core rod) was designed and fabricated. Pure electrolytic copper powder was compacted in the above-mentioned tool to obtain P/M copper bushes. Compaction pressure-density relationship and their influence on green strength are analyzed.     

Research on the powder classification and the key parameters affecting tablet qualities for direct compaction based on powder functional properties

Direct compaction (DC) is the ideal method for tablet production. However, DC requires the highest quality powder functional properties, such as good flowability, compressibility, compactibility, and appropriate elasticity. In the present study, 24 types of natural plant product (NPP) powders, prepared using three commonly used methods, and 18 types of fillers were evaluated for their fundamental and functional properties. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used to classify the powders and analyze the characteristics of each category of powder, based on functional properties. Partial least squares (PLS) regression models were established to predict the tensile strength (TS), ejection force (EF), disintegration time (DT), and solid fraction (SF) based on the powder’s functional properties. The results show that: (i) Except for the direct pulverization powder, the fundamental properties among the NPP powders were similar; however, the functional properties were quite different; (ii) The powders could be classified well based on their functional parameters (w, a, k_G, y₀, k_a, k_b, b, k_FES, k_E3). The order of powders suitable for DC is Group 4 > Group 5 > Group 2 > Group 3 > Group 1; (iii) The compressibility and compactibility of the powder are beneficial to the TS and EF of the tablet. The compressibility of the powders correlated negatively with DT; nevertheless, the compactibility correlated positively with DT and SF. The true density (ρ_true), median particle size (D_0.5) of the powders correlated negatively with SF. Overall, this study systematically evaluated the properties of commonly used NPP powders and fillers and found the key properties that affect the quality of tablets.     

截断式脉冲水射流冲蚀煤岩特性数值模拟

基于光滑粒子动力学和有限元法(smoothed particle hydrodynamics-finite element method,SPH-FEM)耦合算法,建立了截断式脉冲水射流冲蚀煤岩的数值计算模型.通过对比数值模拟结果与相同工况下的实验结果,验证了该模型的有效性.在此基础上,探究了在截断式脉冲水射流冲击作用...     

Variability of pulse wave velocity and mortality in chronic hemodialysis patients

We have already demonstrated that in chronic hemodialysis (HD) patients, the cyclic variations in both hydration status and blood pressure are responsible for changes in pulse wave velocity (PWV). The aim of this study is to verify whether the cyclic variation of PWV influences mortality in dialysis patients. We studied 167 oligoanuric (urinary output <500 mL/day) patients on chronic standard bicarbonate HD for at least 6 months. They performed 3 HD sessions of 4 hours per week. Patients were classified into 3 groups: normal PWV before and after dialysis (LL); high PWV before and normal PWV after dialysis (HL); and high PWV before and after dialysis (HH). The carotid-femoral PWV was measured with an automated system using the foot-to-foot method. Analysis of variance was used to compare the different groups. The outcome event studied was all-cause mortality and cardiovascular mortality. The PWV values observed were LL in 44 patients (26.3%); HL in 53 patients (31.8%); and HH in 70 patients (41.9%). The 3 groups of patients are homogenous for sex, age, and blood pressure. The HH group had a higher prevalence of (P<0.001) ASCVD. It is interesting that the distribution of patients in the 3 groups is correlated with the basal value of PWV. In fact, when the basal measure of PWV is elevated, there is a higher probability that an HD session cannot reduce PWV (<12 ms). A total of 53 patients (31.7%) died during the follow-up of 2 years: 5 patients in the LL group (11.4%); 16 in the HL group (30.2%); and 32 in the HH group (50.7%) (LL vs. HL, P=0.047; LL vs. HH, P<0.00001; HL vs. HH, P=0.034). We evidence for the first time that different behaviors of PWV in dialysis subjects determine differences in mortality.     

Constitutive modeling for the dynamic recrystallization evolution of AZ80 magnesium alloy based on stress-strain data

In order to improve the understanding of the dynamic recrystallization (DRX) behaviors of as-cast AZ80 magnesium alloy, a series of isothermal upsetting experiments with height reduction 60% were performed at the temperatures of 523 K, 573 K, 623 K and 673 K, and the strain rates of 0.01 s⁻¹, 0.1 s⁻¹, 1 s⁻¹ and 10 s⁻¹ on a Gleeble 1500 thermo-mechanical simulator. Dependence of the flow stress on temperature and strain rate is described by means of the conventional hyperbolic sine equation. By regression analysis, the activation energy of DRX in the whole range of deformation temperature was determined to be Q = 215.82 kJ mol⁻¹. Based on dσ/d? versus σ curves and their processing results, the ?ow stress curves for AZ80 magnesium alloy were evaluated that they have some characteristic points including the critical strain for DRX initiation (?_c), the strain for peak stress (?_p), and the strain for maximum softening rate (?*), which means that the evolution of DRX can be expressed by the process variables. In order to characterize the evolution of DRX volume fraction, the modified Avrami type equation including ?_c and ?* as a function of the dimensionless parameter controlling the stored energy, Z/A, was evaluated and the effect of deformation conditions was described in detail. Finally, the theoretical prediction on the relationships between the DRX volume fractions and the deformation conditions were validated by the microstructure graphs.     

Fe/C复合纳米炭粉的制备及其磁学性能研究

以高温煤焦油沥青为原料,以体积比7∶3的浓硫酸和浓硝酸混合酸为氧化剂,制备水性中间相沥青;采用溶胶-凝胶法先形成碳基溶胶,加入FeCl3后进一步形成复合Fe/C凝胶;凝胶经醇水交换、常温干燥和900℃炭化制备出Fe/C复合磁性纳米炭粉。利用FT-IR、XRD、TG和TEM等对水性中间相沥青、磁性纳米炭原粉以及磁性纳米炭粉进行表征。结果表明:采用溶胶-凝胶和常温干燥的方法可以制备出粒度均匀、形状近似于椭圆形的Fe/C复合磁性纳米炭;其磁性纳米炭粉的平均粒径约5 nm,以聚集成粒度为20 nm～30 nm的团聚体形式存在。磁性纳米炭粉中的碳以无定型结构的形式存在,Fe元素以α-Fe、Fe2O3和Fe3C的形式存在,Fe/C复合磁性纳米炭粉具有软磁性和较高的磁响应性。     

Electromagnetic shielding effectiveness of amorphous metallic spheroidal-and flake-based magnetodielectric composites

Flexible,lightweight,conductive materials,having both high rf losses and high permeability,are extremely desirable for applications as electromagnetic(EM)shielding.Gas atomized spherical FeSi-based ferromagnetic metallic particles,having a mean diameter of 14.6 μm with a standard deviation of 7.3 μm,were measured to have a room temperature saturation magnetic flux density of 1.49 T with a coercivity of 160 A/m.Ball milling of the amorphous particles led to aspect ratios from 1:1(spherical)to＞100:1(flake-like).Flake-like particles,suspended in paraffin,were found to not only increase the surface area of fillers enhancing the polarization mechanism but also increase the complex permeability and complex permittivity,and thus provide broadband shielding effectiveness.A loading factor of 40 vol.％of the～15 μm diameter powders provided the largest △WRL=-20dB of 9.49 GHz(i.e.,6.55＜f＜16.04 GHz)at a coating thickness of 2 mm.Overall,powder composites show a wide absorption potential above 18 GHz for＜1.5 mm thicknesses.The optimized flake-based composites exhibit strong EM wave absorption with an SE of-40 dB and SE＜-10 dB of 17.57 GHz at 40 vol.％filler at a thickness of 1.6 mm.     

Densification behavior of aluminum alloy powder mixed with zirconia powder inclusion under cold compaction

Densification behavior of composite powders was investigated under cold compaction. Experimental data were obtained for aluminum alloy powder mixed with zirconia powder inclusion under triaxial compression. The Cap model with constraint factors was implemented into a finite element program (ABAQUS) to simulate compaction responses of composite powders during cold compaction. Finite element results were compared with experimental data for densification behavior of composite powders under cold isostatic pressing and die compaction. The agreement between experimental data and finite element calculations from the Cap model with the constraint factors was good for composite powders with low volume fractions of inclusions.     

油墨特性与残余波动对墨滴成形的影响分析

为得到期望的喷射墨滴,分别针对油墨特性中3个具有代表性的参数:韦伯数、雷诺数及奥内佐格数进行了分析,给出了适用于新技术领域的油墨特性范围,同时针对标准脉冲在喷墨头上应用所存在的残余波动问题,通过建立离散时间模型的方法设计出了一种优化脉冲,然后根据墨滴喷射时弯液面速度的变化情况,将标准脉冲和优化脉冲下墨腔中残余波动的影响进行了实验对比分析,发现在优化脉冲驱动下喷射出的墨滴更符合实际需求。