溶液燃烧法合成Co3O4纳米粉体及热处理研究

分别以氨基乙酸、柠檬酸、葡萄糖为燃料,Co(NO_3)_2·6H_2O为氧化剂,采用溶液燃烧法合成Co_3O_4粉体,并对氨基乙酸为燃料合成的Co_3O_4粉体在500℃、600℃和700℃热处理,研究其结构、微观形貌和磁学性能。研究表明各燃料配制的前驱体溶液在300℃均可发生燃烧反应合成Co_3O_4粉体,以氨基乙酸为燃料时,合成粉体的颗粒较大,中间有气孔,分散性好,残留少量的氨基乙酸。n(氨基乙酸)∶n(硝酸钴)=1.11∶1时合成的Co_3O_4粉体600℃热处理后得到了高纯度、分散性好、平均径向尺寸80nm的Co_3O_4纳米粉体。以氨基乙酸为燃料合成的Co_3O_4产物在600℃和700℃热处理后,其矫顽力和剩磁值都比500℃热处理后的要小。     

Zn~(2+)掺杂对NiFe_2O_4纳米颗粒吸波性能的增强

采用超声活化与化学共沉淀相结合的方法制备了结晶性良好的NiFe_2O_4和Ni_(0.5)Zn_(0.5)Fe_2O_4纳米颗粒,分析了Zn~(2+)掺杂对NiFe_2O_4结构和微波吸收性能的影响。X射线衍射和SEM检测结果表明样品的形貌大多为片状结构,NiFe_2O_4粒度约在30 nm左右,Ni_(0.5)Zn_(0.5)Fe_2O_4粒度约在70 nm,随着烧结温度增加结晶性提高。振动样品磁强计分析结果表明Zn~(2+)掺杂对NiFe_2O_4的磁化性能有显著影响,其矫顽力降低,饱和磁化强度提高。矢量网络分析仪分析结果显示在NiFe_2O_4中掺杂了Zn~(2+)后,微波吸收量显著提高,有效地改善了NiFe_2O_4的吸波性能,随着烧结温度加大,NiFe_2O_4和Ni_(0.5)Zn_(0.5)Fe_2O_4吸波性能也有所增加。     

Co含量对Zn0.6CoxFe2.4-xO4结构与磁性的影响

采用溶胶-凝胶方法制备纳米尺度钴锌铁氧体Zn0.6CoxFe2.4-xO4(x=0～0.30)颗粒,利用X射线衍射仪(XRD)分析晶体结构和相变过程,利用振动样品磁强计(VSM)对其磁性进行测量和分析.实验结果表明,钴锌铁氧体Zn0.6Co0.15Fe2.25O4在800℃时生成单一尖晶石相锌钴铁氧体,在550～800℃温度区间出现R-Fe2O3过渡相.随钴含量的增加,Zn0.6CoxFe2.4-xO4的比饱和磁化强度先增后减,x=0.075～0.15比饱和磁化强度较高;Zn0.6CoxFe2.4-xO4在1300℃时x=0.075的矫顽力为47163.6A/m,x≥0.15时矫顽力在1200℃附近随温度缓慢上升,在1200～1300℃之间为平台状态,并且随钴含量的增加,矫顽力略有升高.在x=0.10附近,可同时获得较高的比饱和磁化强度和较高的矫顽力.     

共沉淀过程中镍锌添加比例对两步法制备的Ni0.5Zn0.5Fe2O4吸波性能的影响

采用共沉淀法和溶胶-凝胶法制备了纳米Ni_(0.5)Zn_(0.5)Fe_2O_4粉体。通过X射线衍射(XRD)、原子力显微镜(AFM)、矢量网络分析(VNA)等方法对4种不同添加比例的样品进行微观结构和电磁性能表征。结果表明:通过650℃煅烧,在4种添加比例下都得到了纯Ni_(0.5)Zn_(0.5)Fe_2O_4。制备的Ni_(0.5)Zn_(0.5)Fe_2O_4为球形,随着共沉淀过程中添加比例的增加,粒径先减小后增大,添加比例为60%时粒径最小,平均粒径约为44nm。在2～12.4GHz时,材料厚度越大,Ni_(0.5)Zn_(0.5)Fe_2O_4有效吸波频带越接近低频波段,且最大吸波强度达到-24.94dB。当添加比例为60%时,Ni_(0.5)Zn_(0.5)Fe_2O_4有效吸波频段为5.0～9.9GHz,有效吸波频带最宽,微波吸收性能最佳。     

两步法中煅烧温度对Ni0.5Zn0.5Fe2O4电磁性能的影响

采用两步法(共沉淀法联合溶胶-凝胶法)制备Ni_(0.5)Zn_(0.5)Fe_2O_4纳米吸波材料,探究了溶胶-凝胶法中前驱体的煅烧温度对样品微波吸收性能的影响。利用X射线衍射(XRD)、原子力显微镜(AFM)以及矢量网络分析(VNA)等方法对样品的微观结构和电磁性能进行表征。XRD分析结果表明:当煅烧温度大于650℃时,能够得到纯Ni_(0.5)Zn_(0.5)Fe_2O_4纳米粉体;AFM结果表明:随着煅烧温度的提高,样品颗粒粒径趋于细小化和均匀化;VNA结果表明:在2～12.4GHz范围内,煅烧温度为650℃时,制备的Ni_(0.5)Zn_(0.5)Fe_2O_4表现出最佳的电磁特性,具有优异的微波吸收性能。样品的有效吸波频宽为4.9GHz,最大吸波强度达到-24.94dB。     

静电纺丝法制备Sr1-xLaxFe12-xCoxO19纳米纤维及其磁性研究

采用溶胶?凝胶过程和静电纺丝技术相结合的方法,制得了PVP/Sr1-xLaxFe12-xCoxO19(x=0～0.5)复合纳米纤维,经过煅烧处理过程,获得了Sr1-xLaxFe12-xCoxO19(x=0～0.5)纳米纤维.通过SEM、TEM、XRD和VSM等技术对样品的形貌、物相、结构以及磁性能进行了表征.结果表明,800℃煅烧后的Sr1-xLaxFe12-xCoxO19(x=0.5)纳米纤维的直径主要分布在80～150 nm;这些纤维在室温下都具有硬磁特性,化学组成对铁氧体的磁性能有着显著的影响,当x≥0.3时,样品中同时出现M型的SrFe12O19、LaFeO3和CoFe2O4;在适当范围内(x≤0.1),La3+-Co2+的掺杂有利于改善锶铁氧体纤维的永磁性能,相应的矫顽力、饱和磁化强度和剩余磁化强度分别为Hc=432.02kA/m,Ms=54.7A.m2/kg,Mr=28.9A.m2/kg,与传统溶胶?凝胶法在相同条件下制得的Sr0.9La0.1Fe11.9Co0.1O19粉体样品相比,磁性能也有显著提高.     

CoFe2O4-SiO2电纺纳米纤维的对喷制备技术与磁性研究

将溶胶-凝胶法和新型双喷丝头静电纺丝技术相结合,制备了CoFe2O4-SiO2电纺纳米纤维材料。利用热分析法(TG-DTA)、X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和振动样品磁强计(VSM)等测试手段,表征了所研制纳米纤维的晶型结构、纤维形貌以及磁学性能。研究结果表明,样品中CoFe2O4为单畴结构,纤维直径在100nm左右,非晶态SiO2的存在有效抑制了CoFe2O4晶粒的生长;煅烧温度对纤维形貌和晶型结构有较大影响,随着煅烧温度的升高,饱和磁化强度(Ms)和剩余磁化强度(Mr)均增大,但矫顽力(Hc)和剩磁比(Mr/Ms)呈波动变化。     

富锂锰基正极材料Li1.2Ni0.13Co0.13Mn0.54O2的Zn2+掺杂改性

采用高温固相合成法制备富锂锰基正极材料Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54-x)Zn_xO_2(x=0,0.03,0.06,0.10),Zn~(2+)掺杂对Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_2的表面特性和电化学性能都有影响。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、拉曼光谱分析、充放电测试、倍率特性测试、循环性能测试,分析了该合成材料的晶体结构、形貌特征、微观结构和电化学性能。富锂锰基正极材料为a-NaFeO_2层状结构,R-3m空间群,结晶度高,结构稳定性好,其中Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.48)Zn_(0.06)O_2的电化学性能较好。掺杂Zn~(2+)可以提高富锂锰基正极材料的充放电比容量、倍率性能、循环性能等电化学性能。     

化学还原法制备Fe3O4纳米颗粒及其性能研究

采用化学还原法制备得到了Fe3O4纳米颗粒,并用XRD对制备条件:分散剂种类、分散剂用量、煅烧温度、煅烧时间进行了研究。研究结果表明,当选用PEG(6000)做分散剂,PEG用量为50g/L,煅烧温度为700℃,煅烧时间为120min时,制备得到的Fe3O4纳米颗粒已经具有晶型完整的反尖晶石结构。将该样品做VSM分析,分析结果表明样品饱和磁化强度可达85A.m2/kg,并且矫顽力趋近于0,呈现出良好的顺磁性。     

Bi2O3掺量对Li0.45Ni0.2Ti0.1Fe2.25O4铁氧体显微结构及磁性能的影响

采用氧化物法陶瓷工艺,在缺铁配方的基础上,制备不同Bi2O3掺量的Li0.45Ni0.2Ti0.1Fe2.25-δO4(δ=0.06)铁氧体样品。结果表明,添加Bi2O3没有在锂铁氧体中形成杂相,烧结后陶瓷样品物相组成单一,结晶状况良好;适量的Bi2O3能有效改善材料微观形貌,促进锂铁氧体的烧结致密化,有助于提高材料的饱和磁化强度4πMs和剩磁比R,降低矫顽力Hc。Bi2O3掺量为1.5%(质量分数)的样品具有较好的综合性能,表观密度d为4.72g/cm3,饱和磁化强度4πMs为2.3T,剩磁比R为0.853,矫顽力Hc为2.3×102 A/m。     

One-dimensional SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers and enhancement magnetic property

SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers of diameters about 100 nm with mass ratio 1:1 have been prepared by the electrospinning and calcination process. The SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrites are formed after calcined at 700 degrees C for 2 hours. The composite ferrite nanofibers are fabricated from nanosized Ni(0.5)Zn(0.5)Fe2O4 and SrFe12O19 ferrite grains with a uniform phase distribution. The ferrite grain size increases from about 11 to 36 nm for Ni(0.5)Zn(0.5)Fe12O4 and 24 to 56 nm for SrFe12O19 with the calcination temperature increasing from 700 to 1100 degrees C. With the ferrite grain size increasing, the coercivity (Hc) and remanence (Mr) for the SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers initially increase, reaching a maximum value of 118.4 kA/m and 31.5 Am2/kg at the grain size about 40 nm (SrFe12O19) and 24 nm (Ni(0.5)Zn(0.5)Fe2O4) respectively, and then show a reduction tendency with a further increase of the ferrite grain size. The specific saturation magnetization (Msh) of 63.2 Am2/kg for the SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers obtained at 900 degrees C for 2 hours locates between that for the single SrFe12O19 ferrite (48.5 Am2/kg) and the single Ni(0.5)Zn(0.5)Fe2O4 ferrite (69.3 Am2/kg). In particular, the Mr value 31.5 Am2/kg for the SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers is much higher than that for the individual SrFe12O19 (25.9 Am2/kg) and Ni(0.5)Zn(0.5)Fe2O4 ferrite (11.2 Am2/kg). These enhanced magnetic properties for the composite ferrite nanofibers can be attributed to the exchange-coupling interaction in the composite.     

Electrospun SrRe0.6Fe11.4O19 magnetic nanofibers: Fabrication and characterization

Substituted strontium ferrite SrRe_0.6Fe_11.4O₁₉ (Re = La, Ce) nanofibers with average diameters of 200-300 nm were manufactured by electrospinning technology combined with sol-gel method. In the process, spinnability was conferred by the addition of poly(vinyl pyrrolidone) and acetic acid, which were used as a spinning aid. Structural and morphology investigations made by X-ray diffraction, SEM and TEM revealed that SrRe_0.6Fe_11.4O₁₉ polycrystalline nanofibers were hexagonal magnetic plumbite structure. The calculation using the Scherrer's equation on the base of the X-ray diffraction spectrum indicated that the average grain size was about 30-40 nm. The magnetic properties were also investigated by the means of vibrating sample magnetometer (VSM). From the magnetization hysteresis loops, by rare earth La substitution of Fe a significant decrease in intrinsic coercivity and a slight decrease in specific saturation magnetization and specific remanent magnetization were observed as compared with SrCe_0.6Fe_11.4O₁₉ nanofibers.     

Fabrication and Magnetic Property of One-dimensional SrTiO3/SrFe12O19 Composite Nanofibers by Electrospinning

The composite nanofibers of SrTiO3/SrFe12O19 with a molar ratio of 1:1 and diameter about 120 nm were prepared by electrospinning. Effects of calcination temperature on the formation, crystallite size, morphology and magnetic property were studied by infrared spectroscopy, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The binary phase of strontium ferrite and titanate was formed after being calcined at 900℃ for 2 h and the composite nanofibers were fabricated from nanograins of SrTiO3 about 24 nm and SrFe12O19 around 33 nm. The crystallite sizes for the nanofibers increase with increasing calcination temperature and the addition of SrTiO3 has an obvious suppression effect on SrFe12O19 grain growth. The specific saturation magnetization and remanence tend to increase with the crystallite size. With increasing calcination temperature from 900 to 1050℃, the coercivity increases initially, achieving a maximum value of 520.2 kA·m-1 at 950℃, and then shows a reduction tendency.     

高致密球形LiNi0.8Co0.1Mn0.1O2颗粒的合成及性能研究

以氨水为络合剂,NaOH为沉淀剂,通过共沉淀制备了高致密、粒度均匀的球形前驱体Ni0.8Co0.1Mn0.1(OH)2.通过焙烧该前驱体和LiOH.H2O的混合物制备出球形锂离子电池正极材料LiNi0.8Co0.1Mn0.1O2.采用XRD、SEM、TEM、TGA/DSC以及恒流充放电测试对材料的结构、形貌和电化学性能进行表征.结果表明,球形前驱体是由纳米级一次颗粒团聚形成,而不是晶粒的长大,且反应时间对前驱体的形貌、粒径分布及振实密度有显著影响.750℃焙烧16 h后的正极材料,保持了完好的球形形貌,具有最佳的层状结构和电化学性能,振实密度最大(2.98 g/cm3),首次放电容量为202.4 mAh/g,倍率性能佳,在3C的放电电流下容量为174.1 mAh/g,且循环性能优良,在40次循环以后,放电容量保持率为92.3%.     

退火处理对A2B7型La0.63(Pr0.1Nd0.1Y0.6Sm0.1Gd0.1)0.2Mg0.17Ni3.1Co0.3Al0.1储氢合金相结构和电化学性能的影响

利用高频感应熔炼法制备La0.63(Pr0.1Nd0.1Y0.6Sm0.1Gd0.1)0.2Mg0.17Ni3.1Co0.3Al0.1储氢合金,对铸态合金在900℃下退火热处理24h。结构分析表明,铸态合金微观组织由CaCu5型结构、Ce5Co19型结构及Ce2Ni7型结构三相组成,而退火合金则是单相Ce2Ni7型结构。铸态和退火合金电极均具有良好的活化性能,退火合金电极放电曲线更为平坦和宽阔。两种合金电极腐蚀电位基本一致,但铸态合金电极腐蚀电流更大。合金经过退火后其电极循环稳定性(S100=83.5%)明显优于铸态合金电极(S100=69%)。在100次电化学充放电循环内,低容量充电时,退火合金电极容量不衰减,合金电极容量衰减的充电容量临界点为活化最大放电容量(Cmax)的90%。铸态和退火合金电极动力学性能差别不大,铸态合金电极高倍率放电主要由氢在其体相中扩散控制,退火合金电极高倍率放电则主要由其表面电荷转移控制。     

La0.7K0.3Ni0.9Cu0.1O3钙钛矿的制备及催化碳烟性能的研究

采用溶胶凝胶法制备了一系列La1-xKxNi1-yMyO3(M=Cu,Co,Mn)钙钛矿复合氧化物催化剂,并利用O2-TPO测试该系列催化剂催化氧化碳烟的性能。通过XRD、H2-TPR、XPS对其进行了表征,结果表明,所制备催化剂均为六方晶系钙钛矿结构。着重考察了A位K掺杂量和B位掺杂元素及其掺杂量对催化碳烟性能的影响。结果表明:当K掺杂量x=0.3时,产生更多氧空位,增加了表面吸附氧数量,同时提高了B位Ni的价态;B位Cu掺杂量y=0.1时,表面吸附氧数量增加,Ni 3+含量增大,从而提高了催化剂的活性。La0.7K0.3Ni0.9Cu0.1O3催化剂与碳烟紧密接触下,Ti、Tm分别为268.1℃和272.8℃。     

核壳结构SrFe12O19NiFe2O4复合纳米粉体的吸波性能

以Fe(NO₃)₃、 Ni(NO₃)₂和Sr(NO₃)₂为主要原料, 通过两步柠檬酸盐溶胶-凝胶法, 制备出核-壳结构SrFe₁₂O₁₉-NiFe₂O₄磁性纳米复合粉体。采用XRD、 TEM、 VSM及矢量网络分析仪对合成的粉体的结构、 形貌及吸波性能进行了分析研究。结果表明, 复合粉体的相结构与NiFe₂O₄含量有关, 当SrFe₁₂O₁₉与NiFe₂O₄的质量比为1∶2、 烧结温度为1050℃时, 复合纳米粉体的相与NiFe₂O₄接近, 核-壳结构SrFe₁₂O₁₉-NiFe₂O₄纳米复合粉体的饱和磁化强度(M_s)(51.4 emu/g)比单体SrFe₁₂O₁₉纳米粉体 (42.6 emu/g)的大; 但矫顽力(H_c) (336 Oe)比单体SrFe₁₂O₁₉纳米粉体的小, 在SrFe₁₂O₁₉ 与NiFe₂O₄的矫顽力5395～160 Oe之间。在频率为8～18 GHz范围内, 微波吸收逐渐增强, 当频率为12 GHz时, SrFe₁₂O₁₉-NiFe₂O₄纳米复合粉体的微波吸收达到最大值-9.7 dB, 是一种性能优良的吸波材料。      

Co替代对纳米晶Ni0.4CoxZn0.6-xFe2O4结构和电磁性能的影响

采用聚丙烯酰胺凝胶法制备了尖晶石型纳米晶Ni0.4CoxZn0.6-xFe2O4(x=0、0.2、0.4),同时考察了铁氧体的电磁性能.由X射线衍射(XRD)可知,随着x的增大,Ni0.4CoxZn0.6-xFe2O4的晶格常数从0.838 4 nm减小到0.835 7 nm.透射电镜(TEM)结果表明,Ni0.4Zn0.6Fe2O4铁氧体粒子的平均直径约为20 nm.Ni0.4CoxZn0.6-xFe2O4在8.2～12.4 GHz的测试频率范围内具有介电损耗和磁损耗.在频率为9.0 GHz时,Ni0.4CoxZn0.6-xFe2O4(x=0.4)复介电常数虚部的最大值达到19.6.随着X值的增加,复数磁导率虚部的共振吸收峰向高频移动.制备的复合物可以被广泛地用于抑制电磁辐射和吸收雷达波等领域.     

A novel fabrication method of magnetic Co/Ni0.4Zn0.6Fe2O4 coaxial nanocables

A highly ordered Co/Ni0.4Zn0.6Fe2O4 coaxial nanocable array has been synthesized based on porous anodized aluminum oxide template via a new approach, which combines an improved sol-gel template method and alternating current electrochemical deposition. Scanning electron microscopy and transmission electron microscopy images show the nanocables are uniform with outer diameter of about 50 nm and inner diameter of about 17 nm. X-ray diffraction patterns and energy dispersive spectrometer confirm that Co nanowires are successfully deposited into the pores of the Ni0.4Zn0.6Fe2O4 nanotubes. Normalized magnetic hysteresis loops demonstrate the coercive force and the squareness with the applied field parallel to the axis of the nanocables increase dramatically compared with that of the nanotubes.