热处理温度对锌铁氧体纳米结构及磁化性能的影响

采用化学共沉淀法制备尖晶石型ZnFe2O4纳米颗粒,将所得产物在450～900℃焙烧4h,使用FT-IR、XRD、TG-DTG、HRTEM及VSM研究烧结温度对化学成分、微结构及磁化性能的影响。研究结果表明:随着烧结温度升高,ZnFe2O4纳米颗粒尺寸从14nm增大到了50nm,而磁化强度从3.374emu/g降低到了2.168emu/g。     

纳米MgAl_2O_4颗粒的制备

在干法室温常压状态下,利用滚压振动磨大批量制备尺度在50~80 nm的铝纳米颗粒。以研磨后的铝粉和商业镁粉为原料,Na_2CO_3、NaOH的不同配比为沉淀剂或NaHCO_3为沉淀剂,在超声波作用下发生水解反应、经干燥、焙烧后制备出具有纳米结构的MgAl_2O_4颗粒。采用X射线衍射仪(XRD)和场发射扫描电子显微镜(SEM)对纳米MgAl_2O_4颗粒样品进行表征。结果表明,经500℃焙烧处理后,几乎全部转变成粒径为100 nm左右的MgAl_2O_4尖晶石超细粉末,并且颗粒分散性较好。比传统制备镁铝尖晶石粉末的温度低几百摄氏度。     

共沉淀法合成ZnFe_2O_4纳米颗粒及其电磁性能研究

采用共沉淀法制备出尖晶石型ZnFe2O4纳米颗粒,通过透射电子显微镜(TEM)、X射线衍射仪(XRD)、振动样品磁强计(VSM)和矢量网络分析仪分析样品的表面形貌、晶体结构、化学成分、磁化性能和电磁性能。研究结果表明,前驱体混合物的焙烧温度为500℃时得到ZnFe2O4纳米颗粒,尺寸在14~17nm范围内,粒度分布均匀,为单晶立方结构;当焙烧温度为500~800℃时,样品表现出亚铁磁性,随着焙烧温度升高,颗粒尺寸增大,离子的倒反系数减小,饱和磁化强度降低;所选样品在2~18GHz频率范围内多次出现损耗峰,介质在松弛极化和色散过程中,将电场能转化为热能而耗散掉,从而获得良好的电磁性能。所用方法工艺简单,设备成本低。     

超声波化学法制备纳米铁酸锌粉末的影响因素

超声辐射Fe(NO3)3·9H2O、不同锌盐和脲的混合水溶液得到前驱体,再经过高温焙烧得到纳米ZnFe2O4粉末.得到的纳米ZnFe2O4粉末用X射线衍射(XRD),傅立叶转换红外光谱(FT-IR)表征得到确认.系统研究了超声波化学法制备纳米铁酸锌粉末工艺中不同锌盐、超声波辐射时间、焙烧温度和焙烧时间等影响因素,结果表明:Fe(NO3)3·9H2O与Zn(NO3)2·6H2O为原料,超声波辐射为4h,焙烧温度为950q℃,焙烧时间为14h可制备结晶良好、分散性好、粒度小于100nm的尖晶石型铁酸锌粉末.     

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。     

化学共沉淀法制备油溶性Fe_3O_4纳米颗粒

采用化学共沉淀法制备粒径小于10 nm的油溶性Fe3O4纳米颗粒,对其结构和性能进行表征,并讨论氨水加入方式对Fe3O4纳米颗粒形貌和产率的影响。结果表明:油酸成功包覆在反尖晶石型Fe3O4纳米颗粒的表面,并使其在多种油性溶剂中具有良好的分散性能;磁滞回线显示制得的Fe3O4纳米颗粒具有良好的超顺磁性;氨水加入方式的改变对Fe3O4纳米颗粒的生长具有明显的影响,进而影响Fe3O4纳米颗粒的产率。     

合成条件对纳米锌铁氧体形貌与性能的影响

采用多元醇法制备ZnFe_2O_4纳米颗粒,研究回流时间、升温速率和回流温度对产物尺寸、形貌和磁性能的影响。通过X射线衍射仪(XRD),透射电子显微镜(TEM),傅里叶红外光谱和振动样品磁强计对样品的结构、形貌和磁性能进行表征。结果表明:制备的ZnFe_2O_4纳米颗粒分散性较好,尺寸较均一。随着回流时间的延长和回流温度的升高,ZnFe_2O_4颗粒粒径增大。回流温度为270℃时,制备的ZnFe_2O_4饱和磁化强度为35.09A·m~2/kg,剩磁较小,矫顽力为4.2kA/m,表现出亚铁磁性。     

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。     

ZnAl_2O_4和La_2O_3对Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷介电性能的影响

通过传统的固相反应合成掺杂ZnAl_2O_4和La~(3+)(来自La_2O_3)的Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷粉体,干压成型后在空气气氛下常压烧结制备ZnAl_2O_4和La~(3+)掺杂Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷样品。分别研究了La~(3+)和ZnAl_2O_4的掺杂量对复合陶瓷样品的微观形貌、相组成和介电性能的影响。结果表明:ZnAl_2O_4具有细化晶粒的作用;Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷样品的致密度随La~(3+)和ZnAl_2O_4含量的增加而增加;介电常数和谐振频率温度系数随ZnAl_2O_4含量的增加而减小,随La_2O_3添加量变化不大;品质因数值随ZnAl_2O_4含量的增加先增加后减小。制备出的ZnAl_2O_4和La~(3+)掺杂Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷致密度达到94%以上,介电常数在40~50之间,谐振频率温度系数小于40×10~(-6)℃~(-1),品质因数大于38 000GHz,可以用于通信技术领域。     

静电纺丝法制备尖晶石型LiMn_2O_4纳米纤维锂离子电池正极材料

通过静电纺丝法成功制备出尖晶石型LiMn_2O_4纳米纤维前驱丝,进一步在600~800℃之间对纳米纤维前驱丝进行煅烧,在700℃得到表面光滑且结晶度良好的LiMn_2O_4纳米纤维材料。通过X射线衍射可知LiMn_2O_4的结构为尖晶石型;通过扫描电镜发现LiMn_2O_4的直径约为350nm;再将LiMn_2O_4正极材料组装成扣式电池,通过测试其充放电性能,可知LiMn_2O_4正极材料在0.1C倍率下的首次充放电比容量分别为114.1和112mAh/g,在1C、2C、5C和10C倍率下的放电比容量分别为109.1、101.9、91.3和80.6mAh/g,而且在1C倍率下循环100次之后,容量保持率为92.7%;循环伏安曲线表明其两对氧化还原峰为3.92/4.10V和4.05/4.22V,是典型的尖晶石型LiMn_2O_4材料,且循环性能良好;由交流阻抗图谱可知LiMn_2O_4样品的电荷转移阻抗约为622.21Ω。     

An investigation on the properties of SnO2 nanoparticles synthesized using two different methods

Tin oxide SnO₂ nanoparticles have been synthesized using chemical co-precipitation and solvothermal methods. The structures and morphologies of SnO₂ prepared using both routes were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), fourier infrared absorption spectroscopy (FT-IR), UV–Vis Spectroscopy and BET specific surface area. The XRD patterns showed the presence of the tetragonal structure in the nanometric range and both crystallinity as well as crystal size increased with the increasing in temperature. The size of the produced tin dioxide nanoparticles was from 6.2 to 10.6 nm by solvothermal route while it was from 9.3 to 16.2 nm for nanoparticles by co-precipitation pathway. Furthermore, TEM results showed that the sizes of SnO₂ particles in all powders were tetragonal like structure and the grain size was increased with temperature. FT-IR spectra revealed that intensity of the transverse optical mode of Sn–O stretching vibration was increased with the sintering temperature while the bending vibration of O–Sn–O showed a blue shift. The optical band gap was shifted to a lower energy with increasing temperature due to the improvement of the crystallinity and the value was varied from 2.9 to 4.25 eV. The specific surface area of the as-made SnO₂ in comparison with such calcined samples decreased with increasing the calcination temperature due to the changes in the sample particle size and in the sample crystal phases.     

Salt-assisted Low Temperature Solid State Synthesis of High Surface Area CoFe2O4 Nanoparticles

A novel salt-assisted low temperature solid state method using CoCl2·6H2O, FeCl3·6H2O and NaOH as pre-cursor and using NaCl as a dispersant to synthesize high surface area CoFe2O4 nanoparticles, has been investigated. The effects of the molar ratio of added salt and calcination temperature on the characteristics of the products were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and Brunauer, Emmett and Teller (BET) surface area analysis. Results showed that the introduction of leachable inert inorganic salt as a hard agglomeration inhibitor in the mixture precursorled to the formation of high dispersive CoFe2O4 nanoparticles; and the increase in specific surface area from 28.28 to 73.97 m2/g, and the saturation magnetization is 84.6 emu/g.     

Mn-doped zinc aluminate nanoparticles: hydrothermal synthesis, characterization, and photoluminescence properties

A two-step synthesis method was developed to fabricate Mn-doped zinc aluminate (ZnAl2O4) nanoparticles, including the first step of ageing, and the second step of crystallization. The effects of preparation conditions, such as ageing temperature, crystallization time, and the pH on the Mn-doped ZnAl2O4 nanoparticles were systematically investigated. The photoluminescence (PL) properties of green phosphor Mn-doped ZnAl2O4 nanoparticles were also discussed. Compared with the bulk sample, the PL spectrum of Mn-doped ZnAl2O4 nanoparticles has distinct blue shift. This procedure provides a facile way for the synthesis of well-crystallized ZnAl2O4:Mn at low temperature.     

Synthesis, characterization and photocatalytic H2 generation over ternary indium titanate nanoparticles

A low temperature surfactant-free solution-phase method has been successfully developed for the synthesis of ternary In2TiO5, nanoparticles using a solvothermal route. The mechanistic aspects of synthesis of In2TiO5 nanoparticles from precursors, In(acac)3 and Ti(IV) isopropoxide in benzyl alcohol at 220 degrees C under solvothermal conditions, were investigated by GC-MS and 13C{1H} NMR analysis. The N2-BET surface area of the 5-8 nm sized In2TiO5 nanoparticles was found to be 60 m2 g(-1), which decreased with increase in calcination temperature; 38 m2 g(-1) at 800 degrees C; 5 m2 g(-1) at 1200 degrees C. The High resolution transmission electron microscopy (HR-TEM) shows well-developed lattice fringes of the crystalline nanoparticles, and selected area electron diffraction (SAED), pattern was indexed to be orthorhombic In2TiO5. The nanoparticles show better photocatalytic hydrogen generation from water-methanol mixtures over bulk In2TiO5, anatase TiO2 nanoparticles prepared by identical route and commercial TiO2 photocatalyst (Degussa, P25) under UV-visible irradiation (16% UV + 84% visible). Photocatalytic properties as a function of crystallinity and surface area of indium titanate nanoparticles have also been investigated. The high photoactivity obtained is correlated with the electronic and crystal structure of In2TiO5.     

Salt-assisted Low Temperature Solid State Synthesis of High Surface Area CoFe2O4 Nanoparticles

A novel salt-assisted low temperature solid state method using CoCl₂?6H₂O, FeCl₃?6H₂O and NaOH as pre- cursor and using NaCl as a dispersant to synthesize high surface area CoFe₂O₄ nanoparticles, has been investigated. The effects of the molar ratio of added salt and calcination temperature on the characteristics of the products were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and Brunauer, Emmett and Teller (BET) surface area analysis. Results showed that the introduction of leachable inert inorganic salt as a hard agglomeration inhibitor in the mixture precursor led to the formation of high dispersive CoFe₂O₄ nanoparticles; and the increase in specific surface area from 28.28 to 73.97 m²/g, and the saturation magnetization is 84.6 emu/g.     

Photocatalytic degradation of gaseous toluene over ZnAl2O4 prepared by different methods: a comparative study

The development of a "green" treatment process for typical indoor pollutants such as toluene is greatly desirable. In this study, ZnAl(2)O(4) nanoparticles were prepared via three different routes, i.e., solvothermal, citrate precursor and hydrothermal methods. Their structural properties were systematically investigated by X-ray powder diffraction (XRD), scanning electronic microscopy (SEM), energy-dispersive X-ray spectra (EDX), Brunauer-Emmett-Teller (BET), UV-vis diffuse reflectance spectroscopy (DRS), and Fourier transform infrared spectroscopy (FT-IR) techniques. The photo-induced charge separation in the samples was demonstrated by surface photovoltage (SPV) measurement. The photocatalytic performances of the ZnAl(2)O(4) samples and nanostructured TiO(2) samples were comparatively studied by the degradation of gaseous toluene under UV lamp irradiation in in situ FTIR reactor. The results indicated that the sample synthesized by facile solvothermal method exhibited about 90% photocatalytic efficiency of toluene. The toluene was mineralized into carbon dioxide and water as the major species. The photocatalytic oxidation of gaseous pollutant over UV-illuminated ZnAl(2)O(4) is a promising technique for air purification.     

Photoluminescence and raman study of CdS-Al2O3 nanocomposite films prepared by sol-gel techniques

The optical and microstructural properties of CdS-Al2O3 nanocomposite (CdS-Al2O3 = 20:80 to 50:50) thin films synthesized by sol-gel techniques were studied. Optical transmission spectra indicated a marked blue shift of the absorption edge due to quantum confinement. Band gaps of CdS-Al2O3 nanocomposites were found to vary in the range 3.69-2.61 eV. The sizes of the nanocrystals, estimated from the blue shift (0.2-1.2 eV) of the absorption edges and transmission electron microscopy, were found to vary in the range 2.8-7.0 nm. X-ray diffraction studies showed reflections from (111), (200), (220), and (311) planes of CdS in the cubic phase. Microstructural characterization by high-resolution transmission electron microscope (HRTEM) indicated well crystallinity of the nanoparticles and lattice fringes supported the cubic phase of CdS. Raman spectroscopy was carried out for CdS-Al2O3 nanocomposites, which indicated a prominent peak at approximately 299 cm(-1). Significant changes in the peak position and intensity of the Raman peak were observed with varying the annealing temperature (373-573 K). Photoluminescence measurements indicated a prominent broad peak at approximately 1.81 eV due to the surface defects in the CdS nanocrystallites. The present study revealed Al2O3 to be a good capping material for CdS nanoparticles.     

Preparation and characterization of ATO nanoparticles by various coprecipitation

A series of Sb doped SnO₂ (ATO) nanoparticles, with Sb doping levels 0–20 at.% has been prepared by two different coprecipitation routes. Effect of preparation process, Sb doping concentration and calcination temperature on the crystallinity and morphology of ATO nanoparticles were investigated and analyzed. The prepared nanoparticles were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, selective area electron diffraction, X-ray diffraction and energy dispersive X-ray spectroscopy. Results indicated that the prepared ATO nanoparticles were tetragonal, and isostructural with rutile lattice structure as known from bulk SnO₂. The ATO nanoparticles prepared via process I (homogeneous coprecipitation) presented obviously weaker crystallinity, smaller average crystallite size and harder agglomeration than that prepared via process II (heterogeneous coprecipitation). The crystallinity and average crystallite size of ATO nanoparticles prepared via process II increased with increasing calcination temperatures and reducing Sb doping concentrations, respectively. The increased crystallinity, dispersibility and average crystallite size for ATO nanoparticles prepared via process II may be due to the formation of ATO crystal nuclei, leading to an improved formation dynamics of ATO nanoparticles.     

Rapid synthesis and characterization of maghemite nanoparticles

Fe2O3-SiO2 nanocomposites were prepared by a sol-gel method using various evaporation surface to volume (S/V) ratios ranging from 0.03 to 0.2. The Fe2O3-SiO2 sols were gelated at various temperatures ranging from 50 degrees C to 70 degrees C, and subsequently they were calcined in air at 400 degrees C for 4 hours. The structure and the magnetic properties of the prepared Fe203-SiO2 nanocomposites were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA), and vibrating sample magnetometer (VSM) measurements. The gelation temperature of the Fe2O3-SiO2 sols influenced strongly the particle size and crystallinity of the maghemite nanoparticles. It was observed that the particle size of maghemite nanoparticles increased with the increasing of the gelation temperature of the sols, which may be due to the agglomeration of the maghemite particles at elevated temperatures inside the microporosity of the silica matrix during the gelation process, and the subsequent calcination of these gels at 400 degrees C resulted in the formation of large size iron oxide particles. Magnetization studies at temperatures of 10, 195, and 300 K showed superparamagnetic behavior for all the nanocomposites prepared using the evaporation surface to volume ratio (S/V) of 0.1, 0.2, 0.09, and 0.08. The saturation magnetization, Ms, values measured at 10 K were 5.5, 8.5, and 9.5 emu/g, for the samples gelated at 50, 60, and 70 degrees C, respectively. At the gelation temperature of 70 degrees C, gamma-Fe2O3 crystalline superparamagnetic nanoparticles with the particle size of 9 +/- 2 nm were formed in 12 hours for the samples prepared at the S/V ratio of 0.2.