High cerium content(Nd-Pr-Ce)_(2)Fe_(14)B melt-spun ribbons with high coercivity

The effects of wheel speeds on the magnetic properties and microstructures of[(Nd,Pr)_(1-x)Ce_(x)]-Fe-B meltspun ribbons were investigated.Compared to melt-spun ribbons with low cerium(Ce)content(x=0.2),amorphous formation can be suppressed at high wheel speed in the ribbons with a relatively high Ce content(x=0.8),and with the increase of the wheel speed,the magnetic properties of the ribbons with high Ce content raise continuously.At high wheel speed,the coercivity mechanism of melt-spun ribbons is mainly pinning field,and the high wheel speed introduces a large number of defects into the matrix as pinning sites.Furthermore,ribbons with high Ce content form a fine and uniform grain structure,so the grain boundary area enlarges,which further hinders the movement of domain walls.The combined effects of the above factors enable ribbons with high Ce content to have excellent magnetic properties(Hcj=0.977 T,Mr=64 m^(2) A/kg)at the wheel speed of 35 m/s.

染发剂中6种强还原性染料的稳定同位素标记液质联用分析方法

建立了染发剂中6种染料的稳定同位素标记液质联用分析方法,选用丹磺酰氯和丹磺酰氯-D6为衍生化试剂,合理设计衍生化反应过程并优化衍生化反应条件,建立衍生化产物的多反应监测(MRM)方法,以丹磺酰氯-D6衍生化产物作为同位素内标对染料定性、定量分析。得到较佳衍生化反应条件:反应时间为50 min,反应温度为30℃和衍生化溶剂中三乙胺的添加量为20μL。质谱分析采用电喷雾离子源正离子(ESI+)模式下多反应监测(MRM)方式。结果显示,6种染料衍生化产物的质量浓度范围为0.45~4.3μg/mL,平均回收率为83.7%~114.3%,相对标准偏差(RSD)为2.3%~8.9%。结果表明该方法不仅提高了染料的稳定性,染料衍生化产物在4℃条件下,10天内化学性质稳定,还可排除强基质效应对染料准确定量分析,为禁限用染料的定性、定量分析提供新思路。

Coercivity enhancement of nanocrystalline hot-deformed Nd-Fe-B magnets by low-melting eutectic MM-Cu(MM=La,Ce,Pr,Nd) alloys addition

MM85Cu15(MM = La,Ce,Pr,Nd) eutectic alloys were added into the hot-deformed Nd-Fe-B magnets to enhance the coercivity.It is found that three endothermic peaks occur on the differential scanning calorimetry curve of the MM-Cu melt-spun ribbons at 432.2,451.1 and 516.5℃.The peaks substantially correspond to three types of MM-Cu low-melting eutectic phase.The coercivity of magnets increases when the MM-Cu content is lower than 4 wt%,and then keeps almost no change with the content further increasing to 5 wt%.The coercivity of the hot-deformed magnets with 4 wt% and without MM-Cu addition is 948 and 683 kA/m,respectively.Nearly all the platelet-shaped grains are isolated by the thickened intergranular phase after MM-Cu addition.Moreover,the average grain size of the magnets with MM-Cu addition decreases compared with that of the magnet without MM-Cu addition.Scanning electron microscopy images show that the areal fraction of the RE-rich grain boundary phase increases from 8.6% to 15.1% after MM-Cu addition.The La,Ce together with Cu and Ga aggregate at the grain boundary regions separating neighboring grains and smoothing the grain boundaries.Therefore,both the thickened grain boundary and decreased mean grain size result in the enhancement of coercivity after MM-Cu eutectic alloy addition.

Spatial heterogeneity and source apportionment of soil metal(loid)s in an abandoned lead/zinc smelter

Metal smelting have brought severe metal(loid)s contamination to the soil.Spatial distribution and pollution source analysis for soil metal(loid)s in an abandoned lead/zinc smelter were studied.The results showed that soil was contaminated heavily withmetal(loid)s.The mean of lead(Pb),arsenic(As),cadmium(Cd),mercury(Hg)and antimony(Sb)content in topsoil is 9.7,8.2,5.0,2.3,and 1.2 times higher than the risk screening value for soil contamination of development land of China(GB36600-2018),respectively.Cd ismainly enriched in the 0–6mdepth of site soil while As and Pbmainly deposited in the 0–4mlayer.The spatial distribution of soil metal(loid)s is significantly correlated with the pollution source in the different functional areas of smelter.As,Hg,Sb,Pb and copper(Cu)were mainly distributed in pyrometallurgical area,while Cd,thallium(Tl)and zinc(Zn)was mainly existed in both hydrometallurgical area and raw material storage area.Soil metal(loid)s pollution sources in the abandoned smelter are mainly contributed to the anthropogenic sources,accounting for 84.5%.Specifically,Pb,Tl,As,Hg,Sb and Cumainly from atmospheric deposition(55.9%),Cd and Zn mainly from surface runoff(28.6%),While nickel(Ni)mainly comes from parent material(15.5%).The results clarified the spatial distribution and their sources in different functional areas of the smelter,providing a new thought for the risk prevention and control of metal(loid)s in polluted site soil.

Combined amendment reduces soil Cd availability and rice Cd accumulation in three consecutive rice planting seasons

The scientific application of stabilized materials has been considered an effective method for the in situ remediation of Cd-contaminated soil.This study aimed to investigate the persistence of the effect of a combined amendment of limestone and sepiolite(LS)on soil Cd availability and accumulation in rice grown in a mildly Cd-contaminated paddy field(0.45 mg/kg of Cd)over three consecutive rice seasons.1125–4500 kg/ha of LS was applied to the soil before the first rice planting season and 562.5–2250 kg/ha of LS was supplemented before the third rice planting season.The application of LS(1125–4500 kg/ha)increased the soil p H by 0.44–1.09,0.18–0.53,and 0.42–0.68 in the first,second,and third season,respectively,and decreased the soil acid-extractable Cd content by 18.2–36.4%,17.7–33.5%,and9.6–17.6%.LS application significantly decreased the Cd contents in the rice tissues.The application of 4500 kg/ha of LS decreased the Cd content in brown rice to below the National Food Limit Standard of 0.2 mg/kg(GB 2762-2017)in the three consecutive rice seasons.However,the effect of LS on the soil-rice system was significantly weakened in the third season.The supplementary application of 562.5–2250 kg/ha of LS further decreased the Cd content in brown rice by 26.1–56.5%and decreased the health risk index by 23.7–43.8%.Therefore,it was recommended to apply 4500 kg/ha of LS in the first season and to supplement2250 kg/ha of LS in the third season to effectively guarantee the clean production of rice in three consecutive rice seasons.

基于服务贸易统计制度的跨境服务增值税政策研究

从服务贸易统计制度来看,服务进出口统计遵循"属人"原则,而增值税的消费地属性决定了其"属地"原则。因此,服务的出口和进口并不必然对应增值税退税和征税。本文基于《国际服务贸易统计手册》等服务贸易统计制度的视角,重新评析增值税消费地原则在服务贸易进出口中的适用范围。建议根据服务贸易进出口的具体模式,分别明确B2B、B2C服务贸易的增值税政策,在此基础上合理界定跨境服务出口零税率范围,并逐步加强跨境服务进口税收征管。