纳米钡铁氧体的制备与磁性研究

采用溶胶凝胶法在不同pH值和煅烧温度条件下制备了M型纳米钡铁氧体样品,利用X射线衍射、场发射扫描电镜以及振动样品磁强计研究了溶液pH值和煅烧温度对纳米钡铁氧体的微结构和磁性能的影响.实验结果表明:溶液pH值及煅烧温度对钡铁氧体的相结构和磁性能都有很大影响.当溶液pH值在3以上时,有利于BaFe12O19相的形成,纳米钡铁氧体的晶粒尺寸约50 nm,饱和磁化强度Ms和矫顽力Hc在pH=7时达到最高.对于pH=7的样品,在700℃左右开始有BaFe12O19相形成,同时伴有较多量的α-Fe2O3和少量的BaFe2O4与BaCO3杂相.随着温度的升高,BaFe12O19主相不断形成积累,杂相逐渐减少,当煅烧温度为800℃时,样品基本上为纯BaFe12O19相,经900℃热处理后样品磁性能最佳:饱和磁化强度达到Ms=61.6(A·m2)/kg,矫顽力为Hc=4.56×105A/m.     

湿法制备锰锌铁氧体粉体的研究

以硫酸亚铁、硫酸锌和硫酸锰为原料,分别采用化学共沉淀法和溶胶-凝胶法制备锰锌铁氧体粉体.结果表明,溶液pH值是影响MnZn铁氧体合成的主要因素:草酸铵作为沉淀剂,溶液pH=4,柠檬酸作为络合剂,溶胶pH=5,在800℃均能获得高活性的锰锌铁氧体粉体.以溶胶-凝胶法制得粉体在1200℃煅烧获得单相、细晶、致密的MnZn铁氧体,材料矫顽力Hc=4.529×79.6 A/m.以共沉淀制备的粉体需较高温度(1250℃)烧结,晶粒尺寸较大,但粒径分布较均匀,铁氧体的饱和磁感应强度较大(Bs=57.62(A·m2)/kg.     

溶胶-凝胶法制备热敏锰锌铁氧体及其磁性研究

采用以硫酸锰、硫酸锌、硫酸亚铁以及柠檬酸为原料的溶胶-凝胶方法制备热敏锰锌铁氧体.在900℃煅烧,得到锰锌铁氧体的粉体.将粉体压成环形样品,在平衡气氛下,1350℃烧结.采用扫描电镜(SEM)分析锰锌铁氧体烧结体的显微结构;用HP4192,测量从室温到150℃的烧结体的磁导率.结果表明在800℃热处理,得到尖晶石结构的锰锌铁氧体粉体.在平衡气氛下,1300℃烧结2 h,得到尖晶石结构的锰锌铁氧体烧结体.扫描电镜(SEM)图谱显示烧结体显微结构致密,晶粒平均尺寸大约在5-10μm锰锌热敏铁氧体的磁导率μi在居里温度附近发生突变,说明锰锌热敏铁氧体的磁性由铁磁相转变为顺磁相在铁离子含量不变的条件下,随着锌离子含量(Zn2 )的增加,锰离子含量(Mn2 )的减少,锰锌热敏铁氧体的居里温度降低;锰锌热敏铁氧体的磁导率μi,随着锌离子含量(Zn2 )的增加而降低.     

软磁锰锌铁氧体的晶粒生长动力学实验分析

用共沉淀相转化法合成出的纳米锰锌铁氧体粉体经柠檬酸进行表面处理,压制成环型后经两步烧结得到烧结样品.用XRD、SEM以及VSM等方法对烧结样品进行了表征,并用球模型烧结方程探讨了烧结过程中的晶粒生长机制,结果表明锰锌铁氧体的晶粒生长指数,n≈2,表观生长激活能Q=71.14 kJ/mol,由此可知锰锌铁氧体在烧结过程中的晶粒生长主要受晶界迁移机制控制.当烧结温度为1000℃时,锰锌铁氧体样品已达到理论密度的94%,其磁性能较好.     

电沉积微纳米镍的组织结构与力学性能

在氨基磺酸镍体系的镀液中通过直流、脉冲电沉积分别制备了不同晶粒尺寸的块体镍.通过室温单向拉伸实验比较了这些镍的力学性能. 结果表明:拓宽电沉积纳米镍的晶粒尺寸分布可显著提高其塑性,同时,保留较高的强度.所制备的具有宽晶粒尺寸分布(5～120 nm)的平均晶粒尺寸为27.2 nm的纳米镍,抗拉强度为1162～1211 MPa,断裂伸长率为10.4%～11.4%.与平均晶粒尺寸为22.4nm的窄晶粒尺寸分布(5～60 nm)的纳米镍相比,抗拉强度降低约200 MPa,但断裂伸长率提高了3.4%.通过对纳米镍微观组织的TEM观察,揭示了宽晶粒尺寸分布纳米镍中塑性的显著提高源于塑性变形中大晶粒(100 nm以上)内存在类似传统粗晶材料中的晶内位错滑移.     

电沉积宽晶粒度分布纳米镍的组织结构与力学性能研究

通过直流与脉冲电沉积分别制备平均晶粒度为20～30 nm,宽晶粒度分布(5～120 nm)的纳米镍.在室温静拉伸应变速率范围内,直流电沉积制备的纳米镍的平均抗拉强度和平均断裂延伸率分别为1176 MPa与10.6%.而由脉冲电沉积技术制备的纳米镍抗拉强度可达1500 MPa之上,最高断裂延伸率可达13.3%.与电沉积获得的普通窄晶粒度分布的纳米镍相比,宽晶粒度分布的纳米镍的塑性要高出100%以上.其原因是大型晶粒内部允许位错的存在,且理论计算表明,晶内位错可通过Frank-Read源机制进行增殖.     

高能球磨法制备纳米晶Ni粉的研究

采用高能球磨法制备出了纳米晶镍粉,并利用X射线衍射仪（XRD）、扫描电镜（SEM）、透射电镜（TEM）等分析检测手段,研究了该纳米晶镍粉末的结构、形貌和相的变化。结果表明,镍粉末平均粒度和晶粒度随球磨时间增加不断减小,而应变随球磨时间增加不断增大;当高能球磨54h后,球磨产物为FCC结构的鳞片状多晶体,晶粒度为17nm左右,应变为0.48%,颗粒尺寸为150～200nm;球磨时间增加至98h,产物中出现非晶相,但仍以多晶为主,晶粒尺寸为7nm,应变为1.24%,粉末团聚严重。     

Preparation and Characterization of Nickel-Zinc Ferrites by a Solvothermal Method

用溶剂热法合成了镍锌铁氧体,并用XRD,SEM,VSM对其进行了性能表征。系统地研究了溶剂热合成条件如镍锌元素比、溶剂热温度、溶剂热时间对样品形貌以及性能的影响。结果表明,当温度为160 ℃时,并未形成镍锌铁氧体,镍锌铁氧体的形成温度为180 ℃;随着溶剂热时间的延长,镍锌铁氧体颗粒变得更加均匀且粒径变大,饱和磁化强度增加;镍锌铁氧体中镍元素的增加不会显著地改变镍锌铁氧体的形貌,却可以使镍锌铁氧体的饱和磁化强度增加。当Ni离子的浓度x=0.30时,饱和磁化强度最高;当Ni离子浓度x=0.20时,饱和磁化强度最低。     

镍铁氧体/聚苯胺复合材料的制备及其性能

采用超声场下原位聚合法制备镍铁氧体/聚苯胺复合材料,并采用x射线衍射仪(XRD)和HP8510网络分析仪研究其结构和电磁性能.结果表明:十二烷基苯磺酸(DBSA)掺杂后的聚苯胺是部分结晶的,镍铁氧体与聚苯胺分子链之间存在某些相瓦作用;与聚苯胺相比,镍铁氧体/聚苯胺复合材料的介电损耗角正切值tanδ<,ε>与磁损耗角正切值tanδ<,m>都增大;镍铁氧体含量为5%和15%(质量分数)的复合材料分别具有最大的tanδ<,ε>暝值和最大tanδ<,m>值;镍铁氧体含量为15%的试样在8～18 GHz范围内综合吸波性能最好,具有最大衰减-23.4 dB,-8 dB带宽为5.73 GHz.     

超声波搅拌-脉冲电沉积法制备纳米镍

在脉冲电沉积过程中,采用超声波搅拌制备了厚度约为90 μm的金属镍镀层.XRD和TEM对不同超声波强度下制备的镀层的分析表明,镍镀层的晶粒尺寸随着超声波强度的变化而变化.在固定脉冲电解参数导通时间(ton)和关断时间(toff)分别为0.2和0.8 ms、平均电流密度为10 A/dm2、镀液pH值为4.0、温度为50 ℃的条件下,当施加的超声波强度由0 W增至50 W时,镀层平均晶粒尺寸从45 nm减至24 nm;但当超声波强度增至70 W时,镀层的平均晶粒尺寸增至38 nm.显微硬度测试结果表明,平均粒径为24 nm的镍镀层的HV高达760.     

Effects on direct synthesis of large scale mono-disperse Ni0.5Zn0.5Fe2O4 nanosized particles

Mono-disperse Ni_0.5Zn_0.5Fe₂O₄ spinel ferrite particles have been synthesized directly via the hydrothermal method using sodium dodecyl sulfate (SDS) as surfactant. Particle size could be varied from 6 to 19 nm by changing the experiment parameters. X-ray diffraction, high resolution TEM images confirmed the high crystallinity of ferrite nanocrystals. The effects of precursor suspension pH value, reaction temperature and surfactant (SDS) concentration on phase purity, particle size and dispersed property were discussed. The results indicated that mono-disperse Ni_0.5Zn_0.5Fe₂O₄ spinel ferrite nanoparticle had been obtained at pH value range (8–9), reaction temperature (90 °C) and moderate SDS concentration (>0.2 mM). The magnetic measurement shows that as prepared Ni_0.5Zn_0.5Fe₂O₄ nanoparticle possesses good super-paramagnetic behavior. We also put forward a primary experimental model to shed light on the controllability of the monodispersity of the nanosized particles.     

Effect of Annealing on Microstructure and Hardness of Hot and Cold Rolled Zr705

主要研究了热轧和冷轧后Zr705合金在200～850℃温度范围内的退火行为.与冷轧后Zr705相比,热轧Zr705试样在较高的温度获得峰值硬度,且峰值硬度值较低.通过微观组织观察发现,热轧后Zr705试样中的β相向ω相的转变速率低于冷轧Zr705试样.经500℃退火后冷轧和热轧试样中均可观察到部分再结晶晶粒,但在热轧Zr705试样中的再结晶晶粒更多.热轧和冷轧Zr705试样在700℃保温1h后均再结晶完全.     

Preparation of Nano-SnO2 Abrasives and Their Application in Chemical Mechanical Polish of Ruthenium

利用固相反应法制备纳米二氧化锡磨料并研究了制备条件对平均粒径的影响.结果表明,在500 ℃/4 h条件下制得的纳米二氧化锡粉体在水中有良好的分散性和稳定性.利用自制的抛光液对高纯钌片进行化学机械抛光,与二氧化硅磨料抛光液比较,材料去除速率和表面粗糙度都降低.当抛光液中含1％(质量分数,下同)二氧化锡、1％过硫酸铵、1％酒石酸和3 mmol/L咪唑,pH=8.0,抛光压力为17.24 kPa时,材料去除速率(MRR)和表面粗糙度(Ra)分别为6.8 nm/min和4.8 nm.     

Synthesis, structural and magnetic characterization of nanocrystalline nickel ferrite—NiFe2O4 obtained by reactive milling

Nanocrystalline nickel ferrite (NiFe₂O₄) has been synthesized from a stoichiometric mixture of oxides NiO and α-Fe₂O₃ in a high energy planetary mill. An annealing at 350 °C, after milling, was used to improve the solid state reaction. The obtained powders were investigated by X-ray diffraction, magnetic measurements, scanning electron microscopy, X-ray microanalysis and differential scanning calorimetry. The particles size distribution was analyzed using a laser particle size analyser. The nickel ferrite begins to form after 4 h of milling and continuously form up to 16 h of milling. The obtained nickel ferrite has many inhomogeneities and a distorted spinel structure. The mean crystallites size at the final time of milling is 9 ± 2 nm and the lattice parameter increases with increase the milling time. DSC measurements revealed a large exothermic peak associated with cations reordering in the crystalline structure. The magnetization of the obtained powder depends on the milling time and annealing. After the complete reaction between the starting oxides the milling reduces the magnetization of the samples. The magnetization increases after annealing, due to the reorganization of the cations into the spinel structure.     

Structural,Dielectric,and Magnetic Studies on Electrospun Magnesium Ferrite-Polyvinylidene Fluoride Core–Shell Composite Fibers

The sub-micron(of the order of 150 nm) thick core–shell composite fibers of magnesium ferrite-polyvinylidene fluoride are prepared by electrospinning.The loading of magnesium ferrite is varied from 1 to 10 wt%.The study results by X-ray diffraction,scanning electron microscope,and infra-red spectroscopy indicate the formation of core–shell structure and an enhancement in the amount of b-phase compared to a-phase in the polyvinylidene fluoride.The particle size of the magnesium ferrite in the fiber is evaluated to be 30 nm.The low frequency dielectric studies indicate that the addition of the magnesium ferrite increases the polarization resulting in the increase in the dielectric constant but decreases the dielectric loss.The magnetization measurements indicate an increased value of coercivity compared to bulk due to the nano-size of the magnesium ferrite.The microwave absorption at the ferromagnetic resonance increases with the increase in the concentration of magnesium ferrite.The resonance field is found to vary with the loading of MFO.     

外场作用下由工业TiOSO4液合成介孔二氧化钛

以工业硫酸氧钛为钛源,采用复合模板合成路线,分别于超声,微波和水热外场作用下合成了介孔二氧化钛前驱体.通过调节反应体系的pH值来控制TiOSO4液的水解和缩聚速率.煅烧脱除模板后得到锐钛型的介孔二氧化钛.产物采用XRD,氮等温吸附脱附,粒度分布,SEM,TEM,SAD和X射线能谱分析(XPS)等技术进行了表征.结果表明具有强极化作用和温和水热环境的外场利于制备结构更佳的介孔二氧化钛;超声振动利于介观结构的形成.在微波辐照下,所制得介孔二氧化钛的比表面积为146.6 m2/g,平均孔径2.57 nm,晶粒尺寸13.65 nm.超声、微波和水热较常规合成方法更利于形成和稳定介孔结构.     

Direct synthesis of zirconium powder by magnesium reduction

The direct synthesis of zirconium powder has been conducted through an analysis of the chemical reaction between evaporated ZrCl₄ and molten magnesium over a range of reduction temperatures, concentration of hydrochloric acid, and stirring time. The observed results indicated that the purity of zirconium powder increased with increased stirring time, and Mg and MgCl₂ were removed by 10 wt% of hydrochloric acid solution. The pure zirconium powder was obtained by stirring again for 5 h using 5 wt% of hydrochloric acid solution. It was noted that the mean particle size increased when the reaction temperature was increased, and the size of the powder at 1,123 K and 1,173 K was found to be 10 μm and 15 μm, respectively. In addition, the purity of the powder was also improved with temperature, and its purity finally reached up to 99.5% at 1,250 K. Overall, pure zirconium powder was obtained after a stirring stage for 5 hours using 5 wt% of hydrochloric acid solution.     

Preparation of Mn−Zn ferrite from spent zinc-carbon batteries by alkali leaching,acid leaching and Co-precipitation

The treatment of spent zinc-carbon batteries for the recovery of valuable metals followed by conversion to Mn−Zn ferrite has been conducted employing two-stage alkali and acid leaching and co-precipitation method. In the first stage, leaching process was carried out with 4 M NaOH, which resulted in a recovery of 63.4 %Zn and 0.1% Mn. Electrowinning of alkali leaching solution containing 12.75 g/L Zn at a current density of 0.2 A/cm² produced Zn metal of 15 nm to 30 nm size and 99.9% purity. The second stage leaching of residue with 3 M H₂SO₄ and 6 vol.% H₂O₂ at a solid/liquid ratio of 1∶10 indicated the leaching efficiency of 98.0% Zn, 97.9% Mn and 55.2% Fe. The obtained leaching solution was finally adjusted to suitable mole ratios of Mn∶Zn∶Fe (1∶1∶4) by the addition of Zn and Fe sulfate salts followed by pH control to produce Mn−Zn ferrite powder. The characterization of the ferrite powder showed uniform nano-crystalline particles of about 20 nm size with spinel structure.     

水热合成钨前驱体-碳热还原-碳化制备超细纳米级碳化钨

提出了一种以水热合成的PbWO₄为原料,然后通过碳热还原-碳化获得超细WC的方法。以PbWO₄为钨中间产品,避免了氨氮试剂的引入;采用碳还原的方式可避免水蒸气的产生,抑制了钨粉的长大。结果表明：在初始pH为7.0、反应温度为160 ℃,反应时间为4.5 h的条件下,Na₂WO₄溶液中99.9%（质量分数）以上的W以PbWO₄的形式回收。然后采用低温碳还原PbWO₄,在C:W摩尔比为5、950 ℃的条件下还原3 h,获得了W和C的混合物,该混合物中预加富余的C有助于抑制钨粉的团聚。然后将W和C混合物高温碳化,在1200 ℃下反应6 h,获得了粒径约为60 nm的WC粉末。     

水热法制备稳定氧化锆纳米粉体

目的制备分散性好、粒径分布窄的稳定氧化锆纳米粉体。方法采用水热法制备氧化锆纳米粉体,考察水热时间、p H值、温度和有机添加剂丙三醇,对氧化锆粉体颗粒粒径、结晶度及稳定性的影响。通过XRD和SEM分析技术对不同条件下制备的样品进行表征。结果结晶度随着水热反应温度的升高而提高,形核速率在250℃时快速增加,粒径在150~250℃出现先长大后减小的规律。反应溶液的p H值影响样品的结晶度,通过调节溶液p H值可以减小粉体颗粒之间的团聚,改善粉体的分散性。水热反应进程越充分,样品的平均粒径越大。加丙三醇后,在反应条件为200℃、p H=10、t=12 h时制备钇掺杂量3%的氧化锆粉体,于1000℃煅烧12 h,得到分散性好、粒径分布窄的单立方相纳米氧化锆粉体颗粒。结论通过设定水热法反应温度、p H值、时间,可以制备粒径可控的稳定氧化锆纳米粉体,且钇掺杂可有效提高氧化锆的稳定性。加入丙三醇可以有效地改善粉体的分散性和稳定性,煅烧稳定氧化锆纳米粉体可以有效减小粉体粒径分布和提高粉体的结晶度。