Hot-pressed Mn-Zn-Ni and Mn-Zn-Co ferrites for magnetic recordingheads

Ni²⁺ and Co²⁺ substituted Mn-Zn ferrites have been developed as high-density magnetic recording materials by hot pressing using optimum sintering parameters. Ferrite series of the composition Mn_0.6Zn_0.4-xNi_xFe₂ O₄ and Mn_0.6Zn_0.4-yCo_yFe₂O₄ were prepared by the hot-pressing technique wherein x and y varied from 0.0 to 0.4 in steps of 0.05. It yielded ferrites with improved magnetic properties having higher hardness (⩾650 Vickers units), low porosity (<0.1%), and small grain size (≈10 μm). The initial permeability increased, whereas the coercive field decreased for an Ni²⁺ concentration x or a Co ²⁺ concentration y equal to 0.05. Maximum values of saturation magnetization equal to 4850 and 5250 G were obtained for x and y equal to 0.225 and 0.275, respectively. The Curie temperature increased appreciably, whereas the DC resistivity decreased for a larger substitution of Ni²⁺ and Co²⁺ ions     

水泥熟料固化重金属Cu2+和Zn2+及水化浸出行为分析

危废处理是当前的热点问题,水泥窑协同处置作为一种有效的处理方式,逐步为社会所接受。多数的危废中包含Cu²⁺和Zn²⁺,文章研究了危废中重金属Cu²⁺和Zn²⁺在水泥熟料中的固化性能和在熟料中的分布,并探讨了重金属在水泥净浆中的浸出行为和环境安全性。通过熟料易烧性X射线衍射(XRD),矿物相分离萃取,浸出实验得出:Cu²⁺和Zn²⁺均改善了熟料易烧性;Cu²⁺促进了C₄AF的生成,同时也促进了C₃S晶粒的生长,并固溶在其中;Zn²⁺与熟料形成新的矿物相Ca₁₄Al₁₀Zn₆O₃₅。通过相对分布系数(D)和分配系数(K_f)说明Cu²⁺主要分布在硅酸盐相中,硅酸盐相固化Cu²⁺的能力强于中间相;Zn²⁺主要分布在中间相中,中间相固化Zn²⁺的能力强于硅酸盐相。掺量为2.0%的Cu²⁺和Zn²⁺在水泥净浆7 d龄期的浸出浓度最大,分别为1.724和0.387 mg·L^-1。水泥熟料固化Cu²⁺和Zn²⁺在水泥使用过程中不会对环境造成二次污染。     

Formation and magnetic properties of γ-Fe2O3particles surface modified with crystallized cobalt-ferrite

Acicular γ-Fe2O3particles were heated at 90°C in alkali solution containing Co²⁺and Fe²⁺with Co²⁺/Fe²⁺ratio of 0.5. The coercivity of resultant particles increased linearly with increasing the Co²⁺content, and the coercivity of 900 Oe was obtained for the particles with Co²⁺content of 7 wt%. The shape of the particles is acicular, and an appreciable variation of morphology by the treatment in alkali solution was not observed. Cobalt-ferrite was expected to crystallize epitaxially on the surface of γ-Fe2O3particles, and the increase of coercivity was attributed to the magnetic anisotropy of the cobalt-ferrite. A variation of coercivity by annealing at 60°C and print-through were small compared with those of the particles in which iron were homogeneously substituted by cobalt ions. Such stability was explained by considering that a very high concentration of cobalt ions exist only on the surface of γ-Fe2O3particles, and the migration of cobalt ions is extremely difficult.     

Fe2W型铁氧体BaFe2-x2+CoxFe163+O27(x=0.0~0.8)的微观结构和磁性

用固相法制备Fe₂W型铁氧体BaFe_2-x²⁺Co_xFe₁₆³⁺O₂₇(x=0.0~0.8),采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、红外光谱仪(FT-IR)和振动样品磁强计(PPMS-VSM)等手段分析其物相组成、结构和磁性并使用Reitveld拟合分析晶体结构,研究了Co²⁺部分取代Fe²⁺的Fe₂W型铁氧体的微观结构和磁性。结果表明：所有样品都是纯相铁氧体BaFe_2-x²⁺Co_xFe₁₆³⁺O₂₇。样品具有W铁氧体结构,晶粒呈良好的六角形结构且分布均匀。用 Co取代能明显提高Fe₂W型铁氧体300 K的饱和磁化强度(M_s)。     

One pot synthesis of monodispersed L-glutathione stabilized gold nanoparticles for the detection of Pb2+ ions

Direct mixture of Au³⁺ with glutathione (GSH), which act as both reduction agents and stabilizers, in aqueous solution gave rise to production of gold nanoparticles (Au NPs) with uniform sizes of around 21 nm. The GSH stabilizer Au NPs in solution show immediate aggregation after addition of 1 mol/L NaCl aqueous solution containing Pb²⁺ ions. The Pb²⁺-induced aggregation in Au NP solution is monitored by both colorimetric response and UV-vis spectroscopy. A rather broad linear range (from 0.1 to 30 μmol/L) and low detection limit (0.1 μmol/L) are explored for Au NP sensors used for detection of Pb²⁺ ions. Furthermore, the response of GSH-stabilized Au NPs toward Pb²⁺ ions is specific compared with other possible interferants (Hg²⁺, Mg²⁺, Zn²⁺, Ni²⁺, Cu²⁺, Co²⁺, Ca²⁺, Mn²⁺, Cd²⁺, and Ba²⁺).     

Magnetic properties of new manganese ferrites submicron particles

New manganese defect metastable ferrites with spinal structure were prepared by oxidation at a temperature lower than 500°C of submicron manganese substituted magnetites, Fe3-xMNxO4(0 leq x < 1). X-ray diffraction measurements and thermal analysis studies have been carried out on these systems. Low-temperature magnetic measurements have also been carried out. With these studies, it has been possible to depict the cation distribution in substituted magnetites and oxidized compounds, and to understand the complex process of oxidation. In defect spinels, vacancies are formed not only from oxidation of Fe²⁺ions, but also of Mn²⁺and Mn³⁺ions. Manganese-rich compound with x = 0.97 having high content of Mn³⁺and Mn⁴⁺ions show an important increase in coercive force, which exceeds 700 Oe at 4.2 K.     

锶磁性固体酸S2O82-/ZrO2SrFe12O19催化剂的制备和表征

以具有优异磁学特性的锶铁氧体(SrFe₁₂O₁₉)粒子为磁性基体, 负载固体酸制备锶磁性固体酸催化剂S₂O₈^2-/ZrO₂-SrFe₁₂O₁₉。利用XRD、 比表面积测试(BET)、 振动样品磁强计(VSM)、 IR等表征手段, 研究了磁性催化剂的表面性质和催化性能。结果表明: SrFe₁₂O₁₉的掺入提高了介稳的四方晶型t-ZrO₂的热稳定性; 固体酸的磁性能较好, 饱和磁化强度(M_s)在30.0 emu·g^-1左右, 矫顽力(H_c)大于3900 G, 有利于磁分离和重复使用; BET表面积为16.0 m²·g^-1, 平均孔径为8.16 nm, 属于介孔磁性材料; 以乌桕油与甲醇的酯交换为探针反应的研究表明, 该固体酸能在较短时间内有效发挥催化作用。     

Formation and magnetic properties of ultrafine spinel ferrites

Investigations of the formation and magnetic properties of MnδCo1-δFe2O4formed in alkaline aqueous solution by the coprecipitation method are covered. The lattice constant of these ferrites apparently reduced with decreasing average particle size below about 500 Å. The coercive force ratio of MnFe2O4and Co-Fe2O4is 1 to 50 and equal to that of the crystal magnetic anisotropy coefficient K1of sintered ferrites. As the average particle size became larger, the coercive force and the apparent remanence increased linearly, and superparamagnetic critical size was determined. The sizes range, for example, from 50 to 100 Å for CoFe2O4and from 150 to 200 Å. for MnFe2O4. From the correlation between the average particle size and their magnetization, the limit size of ferromagnetic critical particle was also determined. Results obtained in this experiment are approximately in accord with Néel's Version of the theory on thermal fluctuation aftereffect of magnetic fine particles.     

纳米铁钴合金/石墨复合材料的微波吸收性能研究

利用氧化石墨的吸附性能将Fe³⁺和Co²⁺吸附到氧化石墨层间制备出Fe³⁺Co²⁺/氧化石墨复合物, 再通过氢气还原制备出纳米铁钴合金/石墨复合材料, 采用XRD和SEM以及磁滞回线测试等手段对其晶体结构、微观形貌以及磁学性能进行表征, 探讨了FeCo合金含量对其微波吸收性能的影响。结果表明: 所制备的产物为石墨和纳米FeCo合金颗粒组成的二元复合材料, FeCo合金分散在石墨表面和层间, 粒径为30~150 nm。纳米铁钴合金/石墨复合材料是典型的软磁性材料, 饱和磁化强度随FeCo合金含量的减小而降低。随着FeCo合金含量的减少, 纳米FeCo/石墨复合材料的介电损耗逐渐增加, 磁损耗逐渐减小。FeCo合金含量适当时, 介电损耗和磁损耗的协同作用使复合材料具有较好的微波吸收性能。     

Investigating the Characteristics of Cobalt-Substituted MnZn Ferrites by Equivalent Electrical Elements

We investigated the electrical and magnetic properties of cobalt-substituted manganese-zinc soft ferrite by using the equivalent lumped elements acquired from the appropriate equivalent electrical circuit of polycrystalline ferrite. We applied the equivalent lumped circuit, combined with equivalent lumped resistances and capacitance, to determine the effect of microstructure on electrical and magnetic properties of cobalt-substituted manganese-zinc ferrites. Both the hysteresis loss and the eddy-current loss of soft ferrites account for a major proportion of iron loss in high-frequency switching mode power supplies. Replacing a small portion of Fe²⁺ with Co²⁺ remarkably increases the bulk resistivity of the MnZn ferrite and decreases the core loss by lowering eddy-current loss. A longer isothermal duration causes grain growth and forms a larger equivalent capacitance, which leads to a reduction in hysteresis loss. However, excess substitution of Co²⁺ for Fe²⁺ is disadvantageous to magnetic permeability and raises core loss. We measured the dc resistivity by the four-probe method on sintered disks with both sides polished and coated with a thin layer of silver paste as a good contact material. We measured the magnetic permeability by an impedance analyzer at room temperature. The total loss of Mn_0.58Zn_0.37 Co_0.01Fe_2.04O₄ ferrite core does not exceed 420 mW/cm³ at 300 kHz/70 mT.     

基于苯并噻唑类螺吡喃检测三价金属离子铁、铬、铝的比色和荧光化学传感器

合成了新型苯并噻唑类的螺吡喃化合物3-苄基-8′-甲氧基-6′-硝基-3H-螺[苯并[d]噻唑-2,2′-苯并吡喃]即SP,其可以作为比色和荧光化学传感器,用来检测溶液中的三价金属离子铁、铬和铝。由于苯并噻唑类螺吡喃化合物特殊的结构与性能,在不同的光照条件下此化合物SP可以作为重要的光响应分子。采用紫外-可见分光光度计、荧光-分光光度计、傅里叶红外光谱仪和核磁共振仪分析了化合物的性能。结果表明:此化合物具有良好的裸眼识别效果、紫外和荧光识别效果,良好的抗干扰性,较快的响应时间和较低的检测限等优点。     

Effect of substitution of divalent ions on the electrical andmagnetic properties of Ni-Zn-Me ferrites

The effect of Cu²⁺, Cd²⁺, Co²⁺, Ca²⁺, Mn²⁺, and Mg²⁺ ions on the physical properties of stoichiometric Ni_0.5Zn_0.5Fe ₂O₄ ferrite is investigated. The specimen is prepared by the conventional manufacturing method without atmosphere control. The divalent ions replace one-half the Ni²⁺ ion molar content. We found that the magnetic and electrical properties of Ni-Zn ferrite changes considerably with the substituent species. Copper ions play an important role in lowering the sintering temperature and increasing density. Manganese and cobalt ions increase electrical resistivity by about two orders of magnitude, while the Ca and Mn ions improve thermal stability of the initial permeability. We also discuss our investigation of the physical properties of the Ni-Zn-Me ferrites on the basis of site occupation of the cation species in the spinel structure     

Fe3O4/高岭土磁性复合材料对Cu2+的吸附性能

为实现高岭土（Kaolin）在Cu²⁺废水处理中的实际应用,采用球磨方法制备了剥离Kaolin,并通过氧化沉淀法制备了Fe₃O₄/Kaolin磁性复合材料。通过激光粒度分析仪、SEM、XRD对Fe₃O₄/Kaolin磁性复合材料的形貌及组成进行表征,并通过测试Fe₃O₄/Kaolin磁性复合材料对Cu²⁺的饱和吸附量和磁分离回收率,确定了当Kaolin球磨4.0 h、掺量为3.0 g时所制备的Fe₃O₄/Kaolin磁性复合材料对Cu²⁺的吸附性能最佳,平衡吸附量为17.98 mg/g。磁滞回线结果表明,Fe₃O₄/Kaolin磁性复合材料具有较好的磁响应性,饱和磁化强度约为16.19 emu/g。此外,采用Langmuir和Freundlich吸附等温式对Fe₃O₄/Kaolin磁性复合材料的吸附数据进行拟合,结果表明,Fe₃O₄/Kaolin磁性复合材料对Cu²⁺的吸附行为基本符合Langmuir吸附等温模型和Freundlich吸附等温模型,既存在单分子层吸附,也存在多分子层吸附。     

Influence of R1parameter {=Fe2O3/(Y2O3+ Sm2O3+ Lu2O3)} on magnetic bubble properties of (YSmLuCa)3(FeGe)5O12

The influence of R1{=Fe2O3/(Y2O3+Sm2O3+Lu2O3)} in the melt composition on film properties, and growth characteristics, has been investigated for (YSmLuCa)3(FeGe)5O12. The garnet phase is the primary phase when R1is kept between 10 and 60. The temperature coefficient for the bubble collapse filed changes from -0.29 to -0.19 %/°C, and the growth rate with 10°C supercooling changes from 0.60 to 0.15 μm/min, by increasing R1=10 to 60. Distribution coefficients, K^Y, K^Sm, K^Luand K^Geincrease, and K^Feand K^Cadecrease, with increasing R1.     

Zn2+掺杂诱导Eu3+激活BiOCl层状半导体的反常发光性能研究

采用固相法在500℃下成功制备Zn²⁺掺杂BiOCl:Eu³⁺层状半导体, 并研究了Zn²⁺ (0~20mol%)掺杂对Eu³⁺激活BiOCl层状半导体发光性能的影响。利用X射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电镜(SEM)、傅里叶变换红外光谱(FT-IR)、激发-发射光谱、荧光寿命衰减曲线对样品的结构和性能进行表征。研究发现, 随Zn²⁺掺杂浓度增大, BiOCl晶体结构不变, Eu³⁺荧光寿命延长, 但发光强度却出现先减后增的反常现象。综合分析表明这可能与BiOCl特殊的层状结构有关。通过XRD和XPS的表征可以推断: 当Zn²⁺掺杂浓度≤10mol%, Zn²⁺在BiOCl中掺杂方式以晶胞层间隙掺杂为主; 当Zn²⁺掺杂浓度>10mol%后, 掺杂方式逐渐向取代掺杂转变。两种掺杂机制对Eu³⁺荧光寿命的改变以及形成缺陷对基质能量传递效率的影响可能是形成上述反常现象的主要原因。研究结果有助于认识稀土掺杂层状半导体的发光性能及影响规律, 并对Eu³⁺掺杂BiOCl这类新型发光材料的开发设计具有指导意义。     

Magnetic measurements on single acicular particles of γFe2O3

Measurements of the remanent coercive force Hrhave been made upon large numbers of individual 'tape' particles of γFe2O3. The greatest range of values of Hrsound for any one sample was 300r<1100 0e, and other samples of different origins gave rather similar results. Using the data for two sets of samples, together with other known factors, the remanent loops of the corresponding tapes were synthesized. The synthesized loops resembled the experimental loops, but the remanent coercive forces were larger by 20 to 60 0e: very good agreement was obtained for one sample. The effect of a.c. demagnetization was investigated. This showed that particles of the highest Hrwere undoubtedly single, but that many of lower Hrwere multiple. Particles of similar morphologies have been observed in recording tape. A value for Hrof 1100 0e is shown to be consistent with the magnetization reversing by the buckling process.     

Accidental printing effect of magnetic recording tapes using ultrafine particles of acicular γ-Fe2O3

Five kinds of acicular γ-Fe2O3powder of which axial length varies from 0.17 to 0.80 μm with almost the same axial ratio are manufactured. The variance of coercive force and printing effect as the average axial length of the particles varies is shown. Coercive force of which particle axial length is about 0.35 μm shows maximum value. The printing effect increases according to the decrease of axial length. The printing effect increases with contacting time. The temperature dependence of coercive force and remanent magnetization are measured from 25 to 200°C. These two properties decrease as the temperature increases, but the decreasing inclination becomes steeper as the axial length is smaller. The relationship between the printing effect and the decreasing inclination of coercive force is nearly linear. From the temperature dependence of the printing effect, the activation energy of the printing effect can be calculated. The activation energy of the smallest particle is about 0.05 eV and the others are about 0.15 eV. This measured activation energy is discussed in connection with the relaxation equation.     

Magnetic and catalytic properties of Cu0.5Zn0.5Fe2O4 nanocrystallite powders

Cu0.5Zn0.5Fe2O4 nanocrystallite powders (average size 13 nm) were synthesized from Cu-Zn spent catalyst (fertilizers) industries and ferrous sulfate wastes formed during iron and steel making. Cu-Zn catalyst (22.4% Cu and 26.4% Zn) was chemically treated with sulfuric acid at temperature 80 degrees C for 1 hr for the complete dissolving of copper and zinc into sulfate solution, then the produced solution was mixed with stoichiometric ratio of ferrous sulfate and the mixture was chemically precipitated as hydroxides followed by hydrothermal processing. The parameters affecting the magnetic properties and crystallite size of the produced ferrites powder e.g., temperature, time, and pH were systemically studied. X-ray diffraction analysis was used in order to determine the average crystallite size and phase identifications of the produced powder. The magnetic properties were studied by vibrating sample magnetometry. The results showed that the average crystallite size of the powder decreased for the ferrites powder formed at 150 degrees C and then increased by increasing the temperature to 200 degrees C. Interestingly, the saturation magnetization (Bs), remanent magnetization (Br) and coercive force (Hc) were 25.03 emu/g, 0.71 emu/g, and 4.83 Oe, respectively at hydrothermal temperature 150 degrees C for 24 hr and changed to 16.38 emu/g, 0.3864 emu/g, and 5.2 Oe at 150 degrees C and 72 hr. The produced nanoferrite powders are used for studying the catalytic activity of CO conversion to CO2 at different temperatures, pH and times. The maximum conversion (82%) is obtained at temperature 150 degrees C for 24 hrs and pH 12.     

添加Ta2O5对NiCuZn铁氧体显微结构及磁性能的影响

采用固相反应法制备添加Ta₂O₅的NiCuZn铁氧体, 研究了不同Ta₂O₅含量对NiCuZn铁氧体显微结构, 静磁性能和高频损耗的影响。结果表明: Ta₂O₅具有细化NiCuZn铁氧体晶粒的作用, 可降低材料的烧结密度。随着Ta₂O₅含量的增加, 样品的饱和磁感应强度和起始磁导率单调减小, 矫顽力则逐渐增大, 截止频率逐渐升高, 而高频损耗呈先降低后增加的趋势, 其主导因素由剩余损耗逐渐过渡到磁滞损耗。当Ta₂O₅含量为0.12wt%时, 样品在3 MHz、10 mT、100℃下总损耗最小, 为139 mW/cm³, 其中磁滞损耗和剩余损耗分别为93 mW/cm³和46 mW/cm³。     

X-ray and magnetic studies of scandium substituted Ni-Zn ferrites

The approach of simultaneous substitutions by aiming at a systematic dilution of both of the sublattices to obtain the highest possible magnetization in a given system has been made use of, since this parameter is highly desirable in the fabrication of core materials for switched mode power supplies (SMPS), Ferrite series of the compositions Ni_0.65Zn_0.35Fe_2-xScO₄ , with x values ranging from 0.00 to 0.25 in steps of 0.05, and Ni _0.65-xZn_0.35+xFe_2-xSc_xO ₄, with x values ranging from 0.000-0.125 in steps of 0.025, have been prepared using optimum sintering conditions for this study. Observed variations in saturation magnetization and Curie temperature for the two series have been explained on the basis of site distributions of the Zn²⁺ and Sc³⁺ ions and the strength of the exchange interactions between magnetic ions. From the magnetization studies, conclusions have been drawn toward the cation distribution in the ferrites, Variations of lattice constant with the substituent concentration in both of the systems are also discussed