Structural and electrical properties of MgO-doped Mn1.4Ni1.2Co0.4−xMgxO4 (0 ≤ x ≤ 0.25) NTC thermistors

We have prepared polycrystalline Mn_1.4Ni_1.2Co_0.4−xMg_xO₄ (0 ≤ x ≤ 0.25) samples using a solid-state reaction process and investigated the MgO doping effect on the microstructure and the electrical properties. It was found that, as the amount of Mg content in the Mn_1.4Ni_1.2Co_0.4−xMg_xO₄ samples increased, both the grain size and density decreased. The as-sintered Mn_1.4Ni_1.2Co_0.4−xMg_xO₄ samples contained Mn- and Ni-rich phases with cubic spinel structure. The MgO-doped Mn_1.4Ni_1.2Co_0.4−xMg_xO₄ negative temperature coefficient (NTC) thermistors provided various electrical properties, depending on Mg content. The electrical resistivity, B_25/85 constant, and activation energy of the Mn_1.4Ni_1.2Co_0.4−xMg_xO₄ NTC thermistors increased with increasing Mg content. The values of ρ₂₅, B_25/85 constant, and activation energy of the NTC thermistors were 11,185–20,016 Ω cm, 3635–4032 K, and 0.313–0.348 eV, respectively.     

密胺餐具中甲醛、重金属的迁移量研究及风险分析

目的 研究餐具的使用和清洗方法对餐具中甲醛、重金属迁移量的影响,降低消费者的使用风险。方法 通过研究密胺餐具经过极端不当条件使用后甲醛迁移量的变化和有、无图案印刷密胺餐具的重金属迁移量,对各种条件下密胺餐具的使用方式进行风险评估。结果 经过微波炉使用（中火）、钢丝球擦洗（10次）、模拟蒸煮温度使用（100 ℃）后,密胺餐具的甲醛迁移量均显著增高。食品接触面有图案印刷和无图案印刷密胺餐具中的重金属（As,Pb,Cd）迁移量变化不大,均低于国家标准要求。结论 不正确的使用密胺餐具,如微波炉使用、反复利器擦洗、蒸煮使用后,甲醛迁移量均会明显增大,甚至超过标准限量值,造成极大的安全隐患,存在极高风险。     

电感耦合等离子体质谱法在食品中重金属检测中的应用

重金属元素是食品安全领域重要的检测项目,目前,用于检测重金属的仪器主要有原子吸收光谱仪、原子荧光光谱仪、电感耦合等离子体发射光谱仪、电感耦合等离子体质谱仪(inductively coupled plasma mass spectrometer,ICP-MS)等。ICP-MS具有线性范围宽、灵敏度高、精密度好、检出限低、可同时分析多种元素等优点,广泛应用于医学、生物学、食品安全等多种领域。本文综述了近年来电感耦合等离子质谱法在食用油、面制品、乳及乳制品、水产品、果蔬及其他食品检测中的应用,并对该领域的发展前景进行了展望,以期为ICP-MS技术测定食品中重金属的检测发展提供一定的参考价值。     

Review of the structural characterization,quality evaluation,and industrial application of Lycium barbarum polysaccharides

BackgroundLycium barbarum polysaccharides (LBPs) are considered to be the major bioactive components in L. barbarum. Due to the considerable health benefits of LBPs, and the significant research interest in LBPs, quality evaluation of LBPs and their related products is imperative for ensuring their efficacy and safety. The bioactivities of polysaccharides are closely associated with their physicochemical properties, which can be easily monitored via chemical techniques. Therefore, analysis of physicochemical properties is a more straightforward and viable approach for the quality control of polysaccharides.Scope and approachIn this review, special techniques for the structural characterization of LBPs are summarized and discussed. In addition, quality evaluation approaches of LBPs that have never been emphasized are highlighted herein. Furthermore, industrial applications of LBPs are reviewed and discussed.Key findings and conclusionsHigh-performance anion-exchange chromatography coupled with pulsed amperometric detection is one of the most effective techniques for analysis of both acidic and neutral LBPs. Size-exclusion chromatography coupled with multi-angle laser light scattering and refractive index detection is able to determine absolute molecular weights, chain conformations, and contents of LBPs. Fingerprinting analysis and saccharide mapping analysis are effective approaches for quality evaluation of LBPs. However, the lack of appropriate quality evaluation approaches indicates an unreliable regulation of LBPs and their related products. This reveals the deficiency in the quality control of commercial products. Thus, the development of reliable approaches for pharmacological activity-based quality control of LBPs and their related products must be extensively investigated.     

三标度模糊层次评判模型在食品安全风险 评估中的应用

目的采用国家食品标准与三标度层次分析法(TAHP)对新疆小麦粉和食用植物油进行风险评估。方法层次构建中采用三标度(0,1,2)定量确定各个有害物的危害程度,并建立相应的比较和判断矩阵。通过矩阵运算获得各个危害物的权重并进行一致性检验。结果采用TAHP在MATLAB软件的辅助下计算各有害物的权重并检验其一致性。一致性检验结果为小麦粉为0.089,4种植物油为0.085,均低于0.1。利用各危害物权重因子构建的风险模型分别运用于新疆小麦粉和食用植物油2010、2014和2015年的风险评估,结果与实际情况较为吻合。结论该风险模型不仅可应用于上述食品质量风险评估,而且还可推广应用于其他食品的安全评价模型的构建,以及对食品质量安全的调查、评估和监督提供参考。     

琥珀及其主要仿制品的红外光谱鉴定

通过常规宝石学和红外光谱测试方法对琥珀及其仿制品共26件实验样品进行观察和测试,并对实验结果进行分析和对比,得出除常规宝石学检测手段外,红外光谱方法是目前检验琥珀及其仿制品较为有效的方法。     

干切牛肉冻干产品的复水品质研究

将干切牛肉冻干产品复水,观察它们的形状、色泽、微观结构等变化。实验表明：复水冻干产品的形状、色泽与及微观结构与新鲜产品相比,无显著改变。气质串联色谱(GC-MS)分析表明：干切牛肉冻干复水后风味物质种类、含量变化较小;感官实验表明：冻干复水干切牛肉的口感与新鲜制品极为相似。     

采用复合锌基钎料钎焊铜铝焊接接头的微观组织及力学性能

在Zn-27Al钎料表面电镀Ni制备复合锌基钎料,在氮气保护的电阻炉中用复合锌基钎料和Zn-27Al钎料对Cu与Al进行钎焊试验,运用金相显微镜、电子探针、X射线衍射仪分析了接头的微观组织,通过拉伸试验评定了接头的力学性能.结果表明:与未电镀镍层的Zn-27Al钎料钎缝相比,复合锌基钎料钎缝中没有组织偏聚,组织分布更均...     

微波爆聚法快速合成MgAl-硬脂酸根-LDH／PMMA纳米复合材料的研究

采用微波爆聚法,将镁铝摩尔比为3的硬脂酸根插层水滑石与甲基丙烯酸甲酯（MMA）单体快速聚合,借助红外光谱、X射线衍射、热分析和高分辨透射电镜等表征手段对其进行了表征。结果表明,制备得到的MgAl-硬脂酸根-LDH／聚甲基丙烯酸甲酯（PMMA）纳米复合材料快速实现了剥离的纳米水滑石片层均匀分散于PMMA基体中,与PMMA基体相容性较好,界面效应减弱,而且该材料热稳定性较纯PMMA有较大提高。