Sintering behavior of Ni–Zn ferrite powders prepared by molten-salt synthesis

Ni_0.5Zn_0.5Fe₂O₄ powders were prepared by a novel molten-salt synthesis method. The effects of calcination processes of the powders on their sintering behaviors were investigated. Compared with the synthesis by traditional solid-state reaction, the proposed molten-salt method can significantly reduce the synthesis temperature of Ni_0.5Zn_0.5Fe₂O₄ from 800 to 550°C below, and the prepared powders have relatively high sintering activity at low temperature, which can thus decrease the sintering temperature. However, the abnormal growth of grains is easy to occur during sintering, thus resulting in uneven grain size. In particular, during the molten-salt synthesis, the holding time for calcination is a dominant factor affecting the activity and crystallization degree of the resultant powders. From the point of view of increasing the density of sintered bodies, the optimal conditions for synthesizing Ni_0.5Zn_0.5Fe₂O₄ powder by the proposed molten-salt synthesis is 400°C for 6 h. In addition, the saturate magnetization of the finally obtained ferrite ceramics has nothing to do with the preparation processes, while their coercivity depends on their densification and grain size caused by their different processing routes.     

浏阳豆豉发酵中高产酶活菌株的分离鉴定及酶活性分析

从浏阳豆豉发酵过程中分离产高酶活菌株，通过形态观察结合分子生物学技术进行鉴定，并对其产蛋白酶、脂肪酶及纤维素酶的活性进行分析。结果表明，分离得到3株菌（编号为000、5132、621）均被鉴定为溜曲霉菌（Aspergillus tamarri）。3株菌的蛋白酶、脂肪酶及纤维素酶的活性测定结果表明，菌株621蛋白酶活性最强，为（207.98±3.20）U/mL；菌株5132的纤维素酶活性最强，为（3.40±1.40）U/mL；菌株000的脂肪酶活性最高，为（90.7±0.64）U/mL。     

基于高通量测序分析不同浏阳豆豉中真菌的多样性

建立测定酱油中铅的氢化物原子荧光光谱法，同时以酱油为样本进行精密度和准确度测定，以及对酱油能力验证盲样考核样进行不确定度分析。结果表明，铅含量在0～100.00 ng/mL呈线性关系，相关系数（R）为0.999 8，该方法的检出限为0.74 μg/L，定量限为2.22 μg/L，精密度试验结果相对标准偏差（RSD）为1.16%～4.48%，回收率为93.3%～106.6%。2个盲样考核样不确定度结果分别为（0.940±0.092） mg/L和（0.460±0.035） mg/L，能力验证考核结果为满意。研究结果表明，采用水质分析质量控制工作程序对氢化物原子荧光光谱法测定酱油中铅进行分析质量控制，保证实验结果误差在可控制的范围内，获得高度可信的分析结果。     

高盐辣椒坯的品质研究

通过现有检测技术结合国家相关标准,分析6种高盐剁辣椒坯的理化和气味滋味等品质指标。结果表明:样品中氯化钠质量分数16%～29%,其脆度和亚硝酸盐的差异可能与样品原料产地和保存时间有关。采用顶空固相微萃取技术与气相色谱-质谱联用(HS-SPME-GC-MS)并结合电子鼻进行气味分析表明,6种高盐辣椒坯的主要挥发性成分数量均在20种以上,以酯类和醇类数量居多,初步判定酯类和醇类物质是高盐辣椒坯挥发性成分的主要组分。利用电子舌比较其差异,得出高盐辣椒坯的风味主要表现在涩味、苦味、鲜味和丰富性等方面。     

Ultrafine Nanoparticle‐Supported Ru Nanoclusters with Ultrahigh Catalytic Activity

The design of an ideal heterogeneous catalyst for hydrogenation reaction is to impart the catalyst with synergetic surface sites active cooperatively toward different reaction species. Herein a new strategy is presented for the creation of such a catalyst with dual active sites by decorating metal and metal oxide nanoparticles with ultrafine nanoclusters at atomic level. This strategy is exemplified by the design and synthesis of Ru nanoclusters supported on Ni/NiO nanoparticles. This Ru‐nanocluster/Ni/NiO‐nanoparticle catalyst is shown to exhibit ultrahigh catalytic activity for benzene hydrogenation reaction, which is 55 times higher than Ru–Ni alloy or Ru on Ni catalysts. The nanoclusters‐on‐nanoparticles are characterized by high‐resolution transmission electron microscope, Cs‐corrected high angle annular dark field‐scanning transmission electron microscopy, elemental mapping, high‐sensitivity low‐energy ion scattering, and X‐ray absorption spectra. The atomic‐scale nanocluster–nanoparticle structural characteristics constitute the basis for creating the catalytic synergy of the surface sites, where Ru provides hydrogen adsorption and dissociation site, Ni acts as a “bridge” for transferring H species to benzene adsorbed and activated at NiO site, which has significant implications to multifunctional nanocatalysts design for wide ranges of catalytic reactions.     

Corrosion-Fatigue Behavior of Aluminum Alloy 5083-H131 Sensitized at 448?K (175?°C)

The fatigue crack growth behavior of aluminum alloy 5083-H131 has been systematically studied as a function of degree of sensitization for aging at 448?K (175?°C). Fatigue crack growth rates were measured at load ratios of 0.1 and 0.85, in vacuum, air, and a corrosive aqueous environment containing 1?pct NaCl with dilute inhibitor. Sensitization does not affect the fatigue crack growth behavior of Al 5083-H131 significantly in vacuum or air, at low- or high-load ratio. For high-load ratio, in the 1?pct NaCl+inhibitor solution, the threshold drops by nearly 50?pct during the first 200?hours of aging, then it degrades more slowly for longer aging times up to 2000?hours. The change in aging behavior at approximately 200?hours seems to be correlated with the transition from partial coverage of the grain boundaries by ?? Al₃Mg₂ phase, to continuous full ?? coverage. ASTM G-67 mass loss levels below approximately 30?mg/cm² do not exhibit degraded corrosion-fatigue properties for R?=?0.85, but degradation of the threshold is rapid for higher mass loss levels.     

The dynamic characteristics of taper seals

Abstract

The dynamic characteristics of taper seal has been investigated. The approach is similar to Black's analysis; the stiffness and damping coefficients are derived. The results showed that the taper seals presented more stable characteristics comparing with plain seals. The practical application of this theory is increasingly used in industry.     

Strong quantum confinement effect in nanocrystalline cerium oxide

Highly uniform and well-dispersed cerium oxide quantum dots were successfully synthesized by simple precipitation method by using cerium ammonium nitrate and ammonium hydroxide as precursor materials with suitable conditions. The X-ray diffraction pattern indicates the formation of cubic phase CeO₂. The average particle size of cerium oxide from high resolution transmission electron microscopy (HRTEM) was found to be 3 nm. The X-ray photoelectron (XPS) spectrum confirms the presence of Ce³⁺ in CeO₂. Optical studies by UV–vis spectroscopy for the synthesized CeO₂ nanoparticles exhibit a blue shift (E_g = 3.78 eV) with respect to the bulk material (E_g = 3.15 eV) due to quantum confined exciton absorption.