Improvement in coercivity,thermal stability,and corrosion resistance of sintered Nd-Fe-B magnets with Dy_(80)Ga_(20) intergranular addition

To investigate the coercivity,corrosion resistance,and thermal stability of Nd-Fe-B magnets,their properties were investigated at room and high temperature before and after doping with Dy_(80)Ga_(20)(at.%) powder.The coercivity of the magnets increased from the undoped value of 12.72 kOe to a doped value of 21.44 kOe.A micro-structural analysis indicates that a well-developed core-shell structure forms in the magnets doped with Dy_(80)Ga_(20) powder.The improvement in magnetic properties is believed to be related to the refined and uniform matrix grains,continuous grain boundaries,and a hardened(Nd,Dy)_2Fe_(14)B shell surrounding the matrix grains.Additionally,the doped magnets exhibit an obvious improvement in thermal stability.For the magnets with added Dy_(80)Ga_(20) powder,the temperature coefficients of remanence(α) and coercivity(β) increased to-0.106%℃~(-1) and-0.60%℃~(-1) over the range 20-100 ℃,compared to temperature coefficients of-0.117%℃~(-1)(α) and-0.74%℃~(-1)(β) in the regular magnets without Dy_(80)Ga_(20) powder.The irreversible loss of magnetic flux(Hirr) was investigated at different temperatures.After being exposed to 150 ℃ for 2 h,the Hirr of magnets with 4 wt.%Dy_(80)Ga_(20) decreased by ~95%compared to that of the undoped magnets.The enhanced temperature coefficients and Hirr indicate improved thermal stability in the doped Nd-Fe-B magnets.The intergranular addition of Dy_(80)Ga_(20) also improved the corrosion resistance of the magnets because of the enhanced intergranular phase.In a corrosive atmosphere for 96 h,the mass loss of the sintered magnets with 4 wt.%Dy_(80)Ga_(20) was 2.68 mg/cm~2,less than 10%of that suffered by the undoped magnets(28.1 mg/cm~2).     

引言

2022年是《分析测试学报》创刊40周年.值此不惑之年,《学报》开展了40周年刊庆系列专辑组稿活动. 生物医学分析是通过运用生物学、医学及分析化学的手段,从微观到宏观研究生命系统的状态变化,采用诸如生物质谱进行蛋白质组学、代谢组学等生物大分子、小分子物质分析,生物成像研究细胞器的正常及病理形态的超微结构分析.     

一维链状配合物{[Fe(SO_4)(DPPZ)_2]·H_2O}_n的水热合成及其晶体结构

以FeSO_4和二吡啶[3,2-a: 2',3'-c]并吩嗪(DPPZ)为原料,采用水热法合成了一维链状配位聚合物{[Fe(SO_4)(DPPZ)_2]·H_2O}_n,利用元素分析、红外光谱、X射线单晶衍射和热重分析对其结构进行了表征.该配合物属于单斜晶系,P2_1/m空间群,a=1.3569(3) nm,b=0.6519(13) nm, c=1.7250(3) nm, α=90°,β=111.29(3)°,γ=90°,V=1.4217(5) nm~3,Z=2,d_c=1.713 g/cm~3,μ=0.671 mm~(-1),F(000)=750, R_1=0.0491, wR_2=0.1250.     

高效体积排阻色谱法测定改性柑橘果胶的分子质量

改性柑橘果胶(MCP)是一种具有抗肿瘤细胞生长、侵袭和转移活性的多糖。由于多糖的分子质量对其活性有很大的影响,因而需要测定其分子质量。选择的色谱条件为：TSK G3000PWXL色谱柱,以50 mmol/L醋酸铵缓冲液为流动相,流速为0.5 mL/min,柱温为40 ℃,样品质量浓度为10 g/L,进样体积为20 μL,示差折光检测器检测。采用Pullulan糖标准品,经校正获得回归方程,通过回归方程计算得到的MCP平均相对分子质量为:Mn为21000,Mp为46000,Mw为43000,Mz为66000。MCP的多分散性指数(PD)为2。该方法具有良好的重现性,而且简便、快速,为MCP的生产工艺、质量控制和组效关系等的研究提供了实用的分析检测手段。     

油-微乳-盐水三相体系中间相微乳液的电子显微研究

利用液态乳液样品的冷冻溶蚀制样技术,对油-微乳-盐水三相体系中间相微乳作了电子显微镜观察,从形态学的角度对这一类型的微乳液的微观形态进行了分析,并结合胶体与界面化学的理论,对中间相微乳液的微组织结构作了一些探讨。     

拟连续Domain的拟基及其权

在定向完备偏序集(即dcpo)上引入了拟基的概念,给出了拟基的若干刻画并在此基础上定义了拟连续Domain的权。探讨了拟连续Domain的权与该拟连续Domain上赋予内蕴拓扑时的拓扑空间的权之间的关系。     

关于自然偏序集的自然连续性

在自然偏序集中引入自然way-below关系,定义自然偏序集的自然连续性.证明在自然连续的自然偏序集上,自然way-below关系具有插入性,自然Scott开集格是完全分配格.利用(&)*收敛刻画了自然偏序集上的自然way-below关系,自然Scott拓扑和自然连续性.     

紫外光谱净信号法测定酸性环境下复方磺胺甲噁唑片两个有效组分

被分析组分的光谱净信号将正交于其它药物组分和辅料光谱所张成的光谱子空间,从而消除其它组分对被分析组分的光谱干扰,此净信号将与被分析组分的浓度成正比,据此建立了药物制剂分析的净信号方法。本文利用该方法研究了在酸性条件下紫外光谱测定复方磺胺甲噁唑片的两种有效成分磺胺甲噁唑(SMZ)和甲氧苄啶(TMP)。SMZ和TMP的线性范围分别为0.48~7.84μg/mL(r=0.9981)和0.12~1.5μg/mL(r=0.9986),平均回收率分别为99.5%和101.0%,RSD分别为1.87%和3.60%。本法简便、快速和准确,可用于酸性条件下复方磺胺甲噁唑片中SMZ和TMP含量的快速、同时准确测定。     

Decline of nucleation in the heating process with a high heating rate

The effect of the heating rate on the nucleation of metallic glass in a rapid heating process starting from the glass transition temperature is investigated. The critical nucleus radius increases with the increase of the temperature of the undercooling liquid. If the increment rate of the critical nucleus radius, owing to the heating process, is higher than the growth rate of the nuclei, the nuclei generated at the low temperature will become the embryos at the high temperature. This means that the high heating rate can make no nucleation happen in the heating process. In consideration of the interfacial energy, the growth rate of the nuclei increases with the increase of their size and the growth rate of the critical nucleus is zero. Thus, the lower heating rate can also make the nuclei decline partially. Finally, this theory is used to analyze the nucleation process during laser remelting metallic glass.     

基于WSGGM模型修正的对冲火焰燃烧分区特性研究

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