Preparation and electrical properties of nanostructured spinel ZnCr2O4 by combustion route

Semiconductive nanometer-sized ZnCr₂O₄ material synthesized by a solution combustion method using inorganic reagents as Zn(NO₃)₃·6H₂O, Cr(NO₃)₃·6H₂O, and glycine as a fuel. This process is a convenient, environment friendly, inexpensive and efficient for the preparation of ZnCr₂O₄ nanomaterial. The synthesized material is characterized by thermo gravimetric differential analysis, X-ray diffraction studied, energy dispersive X-ray microanalysis studies and transmission electron microscopy techniques. The increase in conductivity with increasing temperature could be attributed to negative temperature coefficient of resistance and semiconducting nature of ZnCr₂O₄.     

低温燃烧合成法制备纳米NiFe_2O_4

以九水硝酸铁、六水硝酸镍、水溶性肼类燃料为原料,添加金属离子络合剂、分散剂等为辅助剂,利用溶液燃烧合成法制备了纳米NiFe2O4粉体。利用XRD、TEM、SEM等测试方法对产物进行了表征,并研究了不同燃料、络合剂用量、分散剂用量、煅烧温度对粉体粒径和形貌的影响。实验结果表明,在以水溶性肼为燃料、络合剂2g、分散剂2g、煅烧温度800℃、煅烧时间2h时,可获得粒径均匀的纳米NiFe2O4粉体。所得产物的粒径范围为40～80nm,结构膨松,分散性良好。     

纳米增韧NiFe2O4陶瓷惰性阳极烧结行为与性能的研究

采用粉末冶金法制备NiFe₂O₄纳米粉增韧NiFe₂O₄陶瓷铝电解惰性阳极, 研究了NiFe₂O₄纳米粉添加量对NiFe₂O₄陶瓷惰性阳极烧结行为和材料性能的影响。通过线收缩和SEM对NiFe₂O₄陶瓷的烧结性能和显微结果进行分析。研究结果表明: 随着NiFe₂O₄纳米粉添加量的增加, 烧结收缩程度逐渐增大, 烧结致密化开始温度和烧结初期活化能逐渐降低, 添加量为40%时试样从900℃开始大幅度收缩, 烧结初期表观活化能下降到291.43 kJ/mol。NiFe₂O₄陶瓷惰性阳极的体积密度、抗弯强度和断裂韧性随NiFe₂O₄纳米粉添加量的增加均呈现先上升后下降的变化趋势, 气孔率和静态腐蚀率呈先下降后上升的趋势, 均在30%达到极值, 断裂韧性达到最大值3.12 MPa•m^1/2, 是未添加纳米粉试样的2.14倍。NiFe₂O₄纳米粉的添加能够明显增强晶界结合强度, 降低陶瓷材料气孔率, 从而提高断裂表面能实现增韧作用。     

Preparation of nanostructured Ti4O7

Nonstoichiometric Ti₄O₇ titanium oxide nanopowder consisting of isolated stable nanoparticles with an average size of 115 ± 30 nm has been prepared by two-step synthesis from metallic titanium and oxalic acid. The nanostructured precipitate obtained by reacting titanium and oxalic acid was reacted with flowing hydrogen at a temperature of 1170 K to give Ti₄O₇. The proposed method allows one to control the average size of titanium oxide nanoparticles.     

聚苯乙烯-SiO2/NiFe2O4磁性微球的制备与表征

以NiFe2O4纳米粒子作磁性载体、苯乙烯(ST)、正硅酸乙酯(TEOS)为原料,KH-570为交联剂,采用乳液聚合法制备了聚苯乙烯-SiO2/NiFe2O4磁性微球材料。通过VSM、FT-IR、SEM、TG-DTA、溶剂抽提等方法对磁性微球材料进行了测试。制备的NiFe2O4粒子为面心立方结构,NiFe2O4纳米颗粒及聚苯乙烯-SiO2/NiFe2O4磁性微球具有超顺磁性。聚苯乙烯-SiO2/NiFe2O4磁性微球以SiO2/NiFe2O4为核、PS为壳,通过KH-570接枝到SiO2/NiFe2O4上,核壳间以共价键相接的包覆型纳米粒子,平均直径为100nm左右,具有良好的热稳定性和耐溶剂性能。热重(TG)分析表明,磁性聚苯乙烯微球磁性物质质量分数为28.8%。     

新型共沉淀法制备铁酸镍纳米材料

以FeSO4·7H2O和NiCl2·2.5H2O为原料,采用新型化学共沉淀法制备了纳米尺寸的NiFe2O4粉体,并在不同温度下进行处理,利用XRD、TEM等手段研究了其结构特性.研究表明,350℃以上的热处理开始促进粉末的长大和晶化过程,随着温度的升高,晶化程度增强,粉末粒径增大.当热处理温度为600℃时,材料结晶较好,晶粒粒径约为24nm,粒度均匀.     

磁性纳米TiO2／NiFe2O4光催化复合材料的制备及表征

采用均匀沉淀法在磁性NiFe2O4表面包覆TiO2,制备了一种新型纳米TiO2／NiFe2O4光催化复合材料。通过改变Ti和Ni物质量之比确定了复合材料最佳钛镍比,用X射线衍射、透射电镜、UV—vis漫反射、BET、TG—DSC、磁力学测试等手段对复合材料进行了表征,以甲基橙的水溶液为模拟污染物,评价样品的光催化性能：该复合材料在光照2h后,甲基橙的脱色率可达98．5％,是一种在可见光范围内有响应、便于回收、可重复使用的高效光催化剂。     

NiFe2O4纳米晶的制备及表面效应对其比饱和磁化强度的影响

以FeSO4*7H2O和NiSO4*7H2O为原料,首先制备出颗粒细小的碱式碳酸盐前驱体,在300～700℃焙烧1h后,制备出铁酸镍纳米晶,粒径为8～54nm,粒度均匀。通过测量它的比饱和磁化强度σs与比表面积Sa,得出经验公式σs(Sa)=σs(∞)(1-aSa),运用非共线磁结构理论很好地解释了上述经验公式,并得到纳米晶的非共线表面层的厚度。,A basic carbonate precursor with very fine particles was synthesied by using FeSO4*7H2O and NiSO4*7H2O, and NiFe2O4 nanocrystallites were then obtained by calcining the precursor. The results of XRD and TEM analysis show the NiFe2O4 nanocrystallites with spherical shape are even, and their average diameters increase from 8nm to 54nm when the precursor is calcined at 300—700℃ for 1h. Their specific saturation magnetization σs and specific surface area Sa were measured. A empirical formula σs(Sa)=σs(∞)(1-aSa)was obtained which can be interpreted very well by a noncollinear magnetic structure model, and the value of the canted-layer thickness was deduced.     

空心NiFe_2O_4交联壳聚糖复合吸附剂的制备及表征

以乙二醇(EG)为溶剂,硝酸铁(Fe(NO3)3·9H2O)、硝酸镍(Ni(NO3)2·6H2O)和尿素(CO(NH2)2)为起始反应试剂,油酸(C17H33COOH)为表面修饰剂,通过简单的一步溶剂热法成功制备纯的尖晶石结构的NiFe2O4空心微球,然后经高锰酸钾氧化使其表面羧基功能化,最后在偶联活化剂1-乙基-(3-二甲基氨基丙基)碳二亚胺盐酸盐(EDC·HCl)作用下,以硫酸钠与氢氧化钠混合液为沉淀剂,在壳聚糖溶液中通过沉淀聚合法制备出一种新型的空心NiFe2O4交联壳聚糖重金属离子吸附剂。利用X射线衍射仪(XRD)、透射电子显微镜(TEM)、红外光谱仪(FT-IR)和物理特性测试仪(PPMS)表征样品的结构、形貌和磁性能,并用原子吸收分光光度计(AAS)评价吸附剂对Pb2+的吸附去除性能。结果表明,该新型吸附剂对Pb2+有较好的吸附性能,它对Pb2+的等温吸附线符合Langmuir模型,在298K、pH值为5时,吸附剂对Pb2+的饱和吸附容量为177.0mg/g。     

片状磁性纳米TiO2/SiO2/NiFe2O4制备及光催化性能

以锐钛矿磁性纳米TiO2/SiO2/NiFe2O4(TSN)为原料,采用水热法制备了片状磁性纳米TSN.利用XRD、TEM等技术对样品进行了表征.水热法处理后核壳结构的TSN部分转变为片状,催化剂磁性增强.以亚甲基兰溶液为模拟水样测试了样品的光催化性能,考察了催化剂加入量、反应时间、pH值等因素的影响.实验表明:片状磁性纳米TSN光催化性能明显优于粒状TSN.片状TSN具有良好的吸附性能,提高了光催化反应的初始速率.用于处理亚甲基兰废水时受pH值的影响较小,1小时的脱色率在90%以上.     

包覆镍铁氧体涂层的多孔陶瓷复合材料的制备与电磁性能

以多孔碳化硅陶瓷为基体,采用高分子凝胶法制备了包覆镍铁氧体涂层的多孔陶瓷复合材料。复合材料的结构、包覆涂层的表面形貌和电磁性能分别采用X射线衍射仪(XRD)、扫描电镜(SEM)和HP8510 网络分析仪进行研究。结果表明,当锻烧温度为600℃时,在多孔陶瓷表面有立方晶系尖晶石结构的镍铁氧体晶相生成。随着包覆层数的增加,多孔陶瓷表面的镍铁氧体涂层的致密度和均匀性逐渐增强。与多孔陶瓷基体相比,包覆镍铁氧体涂层的多孔陶瓷的介电损耗角正切值tanδ_ε减小,而磁损耗角正切值tanδ_μ增大,表现出较好的磁损耗特性,tanδ_μ值最大可达0.45。包覆镍铁氧体涂层的多孔陶瓷在X波段的tanδ_μ值随频率的升高呈减小趋势。     

Parametric optimization of NiFe2O4 nanoparticles synthesized by mechanical alloying

In this study, the Taguchi robust design method is used for optimizing ball milling parameters including milling time, rotation speed and ball to powder weight ratio in the planetary ball milling of nanostructured nickel ferrite powder. In fact, the current work deals with NiFe₂O₄ nanoparticles mechanochemically synthesized from NiO and Fe₂O₃ powders. The Taguchi robust design technique of system optimization with the L9 orthogonal array is performed to verify the best experimental levels and contribution percentages (% ρ) of each parameter. Particle size measurement using SEM gives the average particle size value in the range of 59–67 nm. X-ray diffraction using Cu Kα radiation is also carried out to identify the formation of NiFe₂O₄ single phase. The XRD results suggest that NiFe₂O₄ with a crystallite size of about 12 nm is present in 30 h activated specimens. Furthermore, based on the results of the Taguchi approach the greatest effect on particle size (42.10 %) is found to be due to rotation speed followed by milling time (37.08 %) while ball to powder weight ratio exhibits the least influence.     

The Magnetic Structure of NiFe2O4 Nanoparticles

Technical Physics Letters - The Mössbauer studies of the magnetic structure of nickel ferrite (NiFe2O4) nanoparticles (NPs) are presented. It is shown that the redistribution of ions over...     

Rapid Synthesis of Nanocrystalline NiFe2O4 and CoFe2O4 Powders by a Microwave-Assisted Combustion Method

A facile and rapid microwave-assisted combustion method was applied to synthesize the nanocrystalline NiFe₂O₄ and CoFe₂O₄ powders. The results suggested that application of microwave heating to synthesize the homogeneous porous NiFe₂O₄ and CoFe₂O₄ powders was achieved in a few minutes. The structure and morphology of the as-prepared nanocrystalline powders of NiFe₂O₄ and CoFe₂O₄ were investigated by means of X-ray diffraction (XRD) and tunneling electron microscopy (TEM). The XRD spectra confirmed the formation of spinel structure with a crystallite size of 30.03 nm for NiFe₂O₄ and 36.7 nm for CoFe₂O₄ nanopowders, and TEM results indicated spherical shape of the products. Magnetic measurements revealed that at room temperature while NiFe₂O₄ is superparamagnetic, CoFe₂O₄ shows ferromagnetic behavior.     

NiFe2O4/Ag复合材料的制备及其耐蚀和导电性能

以Fe2O3、NiO和Ag2O为主要原料,采用固相烧结工艺制备了NiFe2O4/Ag复合材料,用X射线衍射和扫描电子显微镜对材料的组成和微观结构进行了研究,并测量了样品在冰晶石熔盐中的静态热腐蚀速率及其高温电导率.结果表明,复合材料由NiO、NiFe2O4尖晶石和Ag三相组成.随着Ag2O含量的增多,复合材料的致密化程度先增加而后降低,当Ag2O含量为6%时,试样的致密化程度最高.Ag2O的加入在不提高试样在冰晶石熔盐中的静态热腐蚀速率的前提下,提高了试样的高温电导率.     

NiAl2O4 catalysts prepared by combustion reaction using glycine as fuel

The aim of this work is to evaluate the influence of glycine fuel used in a stoichiometric proportion and with a 10% and 20% excess of this fuel in the preparation of NiAl₂O₄ catalyst by combustion reaction. The powders were characterized by XRD, textural analysis by the BET nitrogen adsorption method, particle size distribution, and FTIR. The results show the presence of NiAl₂O₄ as a major phase and traces of NiO and Ni in all the catalysts studied here. The crystallite sizes were 22 nm in the stoichiometric composition and 18 and 9 nm, respectively, in the composition containing 10% and 20% excess glycine. The powder obtained from all the compositions presented morphological characteristics with irregular plate-shaped agglomerates. The increase in excess glycine caused the particle size in the three compositions to decrease to 59, 54 and 38 nm and the agglomerate size to increase to 7, 8 and 12 μm, respectively.     

合成和表征NiFe2O4纳米线阵列

采用真空灌注结合溶胶-凝胶和氧化铝模板法,在多孔氧化铝模板中制备了平均直径为50 nm的NiFe2O4纳米线阵列.X射线衍射结果显示所制备的纳米线是纯相的NiFe2O4纳米线,透射电镜和电子衍射的结果显示已制备的纳米线是多晶的且表面光滑,场发射扫描电镜图片显示纳米线是大面积且平行有序的、纳米线的长度和所用的氧化铝模板的厚度相当.磁测量的结果显示此纳米线阵列有形状各向异性,同块状材料相比矫顽力有所增强.对纳米线的生长机理做了简单的讨论.     

NiFe2O4纳米粒子的水热合成及表征

以Ni(NO3)2·6H2O和Fe(NO3)3·9H2O为主要原料,在聚乙二醇(PEG)存在下,采用水热法制备了磁性NiFe2O4纳米粒子,用X射线衍射仪(XRD)、透射电子显微镜(TEM)和振动样品磁场计(VSM)等分析方法对样品进行了表征.结果表明:水热法合成的NiFe2O4纳米粒子为尖晶石结构,粒度分布均匀,为方形形貌,粒子直径范围在50～60nm;比饱和磁化强度为25.83emu/g,剩磁为6.167emu/g,矫顽力达85.87Oe.