Sol-gel法制备纳米晶镍锌钴铁氧体/二氧化硅复合颗粒的研究

开发了用溶胶-凝胶法制备纳米晶镍锌钴复合铁氧体颗粒的技术,并对溶胶-凝胶工艺的影响因素进行了研究探讨.用扫描电镜(SEM)、电子探针(EPMA)和X射线衍射(XRD)对样品进行了表征,得到球状分布的纳米晶镍锌钴铁氧体/二氧化硅复合颗粒,并优化了制备工艺.     

模板渗透法制备氧化锌纳米管阵列

采用溶胶-凝胶法,以醋酸锌和氢氧化锂为主要原料制备了纳米氧化锌溶胶;再以其为构造单元在阳极氧化铝模板(AAO)中通过减压渗透法制备了氧化锌纳米管阵列.同时利用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线衍射(XRD)和能谱(EDS)对所得的氧化锌纳米颗粒、纳米管进行了分析.结果表明,所得的氧化锌纳米颗粒,粒径为2～5nm,分布较窄,属于纤锌矿型六方晶系;所得氧化锌纳米管,阵列结构规整,外径约为300nm,壁厚约为50nm,长度可以达到5μm以上.     

由多聚硅氧烷制备二氧化硅气凝胶

SiO2 气凝胶是一种新型轻质纳米多孔材料。本工作以多聚硅氧烷 (E -4 0 )为硅源 ,用溶胶 -凝胶法制备出了SiO2气凝胶。研究了催化剂、温度、水等因素对其溶胶 -凝胶过程的影响 ;讨论了F离子以及水对E -4 0水解 -缩聚反应的作用机理 ;并用孔径分布测定仪、TEM等方法对其微结构进行了研究。结果表明 :由E -4 0为硅源制备的SiO2 气凝胶骨架颗粒为十几nm ;孔径分布较广 ,其峰值在 3 0nm附近 ,此外 ,还存在几nm的微孔。     

纳米SiO_2材料的制备及其发光性能研究

采用溶胶-凝胶法制备了纳米SiO2,样品在800℃下煅烧2h。X-射线衍射(XRD)及扫描电子显微镜(SEM)测试结果表明,该材料具有非晶态结构,颗粒尺寸为90~100nm。该样品在紫外灯照射下发出强烈的黄绿色可见光;对样品进行荧光光谱分析表明,该材料可以发射出较强的490nm的蓝绿光和弱的520nm的绿光。     

超分子水凝胶模板法制备项链状TiO2纳米颗粒

以钛酸四丁酯为钛源,以一种水性凝胶剂,3-{[(2S)-2-(十八酰胺基)-3-苯丙基]酰胺基}丁羧酸四乙胺盐(简记为TC18PheBu)在水溶液中自组装形成的聚集体为模板,经溶胶-凝胶缩聚,煅烧得到一种项链状TiO2纳米颗粒.FE-SEM分析表明所制得的项链状TiO2纳米颗粒直径约为200～400nm.采用FT-IR技术探讨了TiO2纳米颗粒形成机理.即在钛酸四丁酯水解形成的带负电的低聚物与TC18PheBu中季铵盐正离子之间,通过静电相互作用自组装形成纳米颗粒.XRD图谱表明TiO2纳米颗粒为锐钛矿晶型二氧化钛.     

溶胶-凝胶法制备Fe-18Cr-9W纳米复合粉末

以硝酸铁、硝酸铬、钨酸、柠檬酸、异丙醇、氨水为原料,通过两步合成方法制备了Fe-18Cr-9W合金复合粉末。采用溶胶一凝胶法制得混合盐的络合凝胶,将凝胶在450℃和550℃煅烧,获得均匀分散的氧化物纳米粉末。通过SEM对氧化物颗粒形貌进行观察,发现所得氧化物颗粒粒径为30～80nm;采用H2-CO共还原法,调节并控制反应气氛和保护气氛（H2：CO=1：4）,对氧化物颗粒在700℃进行保护气氛下还原2h,得到了粒径约50～80nm的Fe-18Cr-9W纳米复合粉末。前驱体中加入柠檬酸分散剂起了改善氧化物粉末的形态与降低了粉粒团聚程度的作用;还原温度的选择对还原后合金颗粒粒径有重要影响。     

块状纳米孔超级绝热材料的制备与表征

以正硅酸乙酯为硅源,采用两步溶胶-凝胶法结合超临界干燥技术制备出了块状无裂纹SiO_2气凝胶,体积密度在50kg·m~(-3)和300kg·m~(-3)之间,样品尺寸约为300mm×300mm×50mm。热学测试表明,常温常压下体积密度大约为100kg·m~(-3)的样品导热系数为0．020 W/m·K,并采用XRD、SAXS、BJH和SEM等其他方法对典型样品(100kh·m~(-3))进行了测试。测试结果表明,SiO_2气凝胶是非晶态的,并且具有纳米多孔结构(骨架颗粒平均粒径为6．8nm,孔径主要集中在10～20nm范围内,而且所有孔径都在70nm以内)。因而可作为具有一定潜在应用价值的块状纳米孔超级绝热材料。     

纳米TiO2粉体的制备及其表征

采用溶胶-凝胶技术制备了纳米TiO2粉体,并对其热性能、相结构、颗粒大小和分布进行了表征,结果表明,TiO2干凝胶粉经300℃煅烧后已有锐钛矿相出现,经550℃煅烧后有金红石相出现,完全相转变的温度约为600℃,纳米TiO2粉体的颗粒尺寸随煅烧温度的升高而增大,采用溶胶,凝胶技术制备的干凝胶粉经400℃煅烧后可获得团聚轻、颗粒大小分布比较均匀、颗粒尺寸约为15nm的球状TiO2粉体,     

BaTiO3纳米粉体的制备和性能

采用溶胶-凝胶和溶胶-沉淀的方法合成了立方相纳米BaTiO3粉体．溶胶-凝胶法制备的粉体平均粒径为19nm，颗粒分布均匀、含少量BaCO3．溶胶-沉淀法得到了纯BaTiO3粉，平均粒径为42nm，存在部分团聚．两种方法相比，溶胶-凝胶法的粉体烧结密度较高，介电性能较好．讨论了两种合成方法的晶粒形成机理及对材料微观结构和介电性能的影响．     

pH值对溶胶凝胶-燃烧合成纳米晶LaMnO_3粉末的影响

以硝酸镧、硝酸锰和柠檬酸为原料,采用溶胶凝胶燃烧合成技术制备了超细LaMnO3粉末。借助XRD、DTA、SEM、FT-IR等分析仪器研究了溶胶凝胶-燃烧合成技术合成超细LaMnO3粉末的过程,着重讨论了前驱体溶液不同pH值对溶胶凝胶燃烧合成过程及合成产物的影响。结果发现,采用溶胶凝胶燃烧合成技术能合成纳米晶的LaMnO3粉末,随前驱体溶液pH值增加,燃烧反应速率增加,合成粉体的平均晶粒尺寸随pH值增加而减小。通过控制前驱体溶液pH值能一步合成超细LaMnO3颗粒(粒径200nm)。     

Metal nanoparticle doped coloured coatings on glasses and plastics through tuning of surface plasmon band position

Several noble metal nanoparticles doped sol-gel derived thin coloured films have been synthesized and characterized. These are pure (Ag, Au, Cu and Pt), mixed/alloy (Ag-Cu, Au-Cu, Au-Ag and Au-Pt) nanoparticles in SiO₂, Au in mixed SiO₂-TiO₂ and SiO₂-ZrO₂, Au and Ag nanoparticles in inorganic-organic hybrid film matrices etc. This investigation leads to the development of tailor-made coloured coatings by tuning the surface plasmon resonance (SPR) band positions originating from the embedded nanometals by controlling mainly (i) refractive index of the film matrices and (ii) nanoalloy composition. In the later case a new layer-by-layer (two-layer) synthetic protocol has been developed to prepare binary nanoalloy particles with controlled atomic ratios.     

A facile synthesis of MPd (M = Co, Cu) nanoparticles and their catalysis for formic acid oxidation

Monodisperse CoPd nanoparticles (NPs) were synthesized and studied for catalytic formic acid (HCOOH) oxidation (FAO). The NPs were prepared by coreduction of Co(acac)(2) (acac = acetylacetonate) and PdBr(2) at 260 °C in oleylamine and trioctylphosphine, and their sizes (5-12 nm) and compositions (Co(10)Pd(90) to Co(60)Pd(40)) were controlled by heating ramp rate, metal salt concentration, or metal molar ratios. The 8 nm CoPd NPs were activated for HCOOH oxidation by a simple ethanol wash. In 0.1 M HClO(4) and 2 M HCOOH solution, their catalytic activities followed the trend of Co(50)Pd(50) > Co(60)Pd(40) > Co(10)Pd(90) > Pd. The Co(50)Pd(50) NPs had an oxidation peak at 0.4 V with a peak current density of 774 A/g(Pd). As a comparison, commercial Pd catalysts showed an oxidation peak at 0.75 V with peak current density of only 254 A/g(Pd). The synthesis procedure could also be extended to prepare CuPd NPs when Co(acac)(2) was replaced by Cu(ac)(2) (ac = acetate) in an otherwise identical condition. The CuPd NPs were less active catalysts than CoPd or even Pd for FAO in HClO(4) solution. The synthesis provides a general approach to Pd-based bimetallic NPs and will enable further investigation of Pd-based alloy NPs for electro-oxidation and other catalytic reactions.     

Superparamagnetic bimetallic iron-palladium nanoalloy: synthesis and characterization

Iron-palladium nanoalloy in the particle size range of 15-30?nm is synthesized by the relatively low temperature thermal decomposition of coprecipitated [Fe(Bipy)(3)]Cl(2) and [Pd(Bipy)(3)]Cl(2) in an inert ambient of dry argon gas. The silvery black Fe-Pd alloy nanoparticles are air-stable and have been characterized by EDX-RF, XRD, AFM, TEM, magnetometry, (57)Fe M?ssbauer and impedance spectroscopy. This Fe-Pd nanoalloy is in single phase and contains iron sites having up to 11 nearest-neighboring atoms. It is superparamagnetic in nature with high magnetic susceptibility, low coercivity and hyperfine field.     

Synthesis of lead-free (K, Na)(Nb, Ta)O3 nanopowders using a sol-gel process

Lead-free (K0.5Na0.5)(Nb0.7Ta0.3)O3 piezoelectric material was successfully synthesized via a sol-gel process. Crystalline (K0.5Na0.5)(Nb0.7Ta0.3)O3 nanopowders were obtained after heat treatment at 700 degrees C. The particle size was estimated to be 87nm +/- 23 nm. The transmission electron microscopy images showed that individual nanoparticles were single crystalline and had a pseudo-cubic structure with a lattice parameter of -3.96 angstroms. Both X-ray diffraction and scanning electron microscopy studies consistently showed that the crystallization of the (K0.5Na0.5)(Nb0.7Ta0.3)O3 occurred slightly above 500 degrees C. The samples have an appropriate stoichiometry as found via energy dispersive X-ray spectroscopy. The demonstration of the synthesis of (K0.5Na0.5)(Nb0.7Ta0.3)O3 via a sol-gel process as presented in this paper can provide an important foundation for the development of a synthetic route towards (K0.5Na0.5)(Nb0.7Ta0.3)O3 doped with various other elements for high performance piezoelectric devices.     

Effects of MgO and MgO/Pd seed-layers on perpendicular magnetic anisotropy of CoPd thin films

We studied the effects of MgO and MgO/Pd seed-layers on perpendicular magnetic anisotropy in co-sputtered CoPd films. CoPd films with the MgO seed-layer showed perpendicular magnetic properties that were superior to those with another after annealing. The loop squareness was unity, indicating strong perpendicular magnetic anisotropy, when the MgO seed-layer was thicker than 2 nm. We observed that the out-of-plane CoPd (111) texture was strongly developed, as well as the in-plane tensile stress in the CoPd films. The magnetoelastic anisotropy coming from a negative magnetostriction λ₁₁₁ under the in-plane tensile stress dominating over other anisotropies is likely responsible for creating such strong perpendicular magnetic anisotropy. In the case of the MgO/Pd seed-layer, the CoPd films showed mixed anisotropy having both in-plane and out-of-plane magnetic anisotropy components after annealing. The appearance of the strong (100) texture of the CoPd films with the MgO/Pd seed-layer is believed to have caused the decrease in the perpendicular magnetic anisotropy that originated from the magnetoelastic anisotropy due to the additional contribution from the positive magnetostriction λ₁₀₀ but less contribution from the negative magnetostriction λ₁₁₁ when the CoPd films are under in-plane tensile stress.     

Grain size control of calcined SnO2 nanocrystals: Raman study and room temperature ethanol sensing properties

SnO2 nanoparticles were prepared via a sol-gel method by heating the mixture of hydrous SnO2 nanoparticles and SiO2 nanospheres at 600 degrees C. The average particle size of the obtained SnO2 nanoparticles is 3.3 nm, smaller than that of the SnO2 nanoparticles ( 6.4 nm) prepared by calcining the pure hydrous SnO2 at 600 degrees C. The restricting effect of SiO2 on the growth of SnO2 nanoparticles was discussed by Raman spectra. A blue shift of A1g ) and B2g Raman modes in SnO2/SiO2 composite was observed, and it was considered to be a compressive stress effect. The obtained SnO2 nanoparticles with a size of about 3.3 nm exhibit enhanced ethanol response at room temperature, and their recovery time is much shorter than that of the SnO2 nanocrystals with a size of about 6.4 nm.     

Preparation and characterization of the transparent hybrids of silicone epoxy resin and titanium dioxide nanoparticles via sol-gel reactions

In order to prepare transparent hybrid films of high refractive index, nanoparticles of TiO2 were prepared and dispersed in a silicone epoxy (SE) resin synthesized from diphenyl silane diol and [2-(3,4-epoxycyclohexyl)ethyl] trimethoxysilane by sol-gel reactions. It was found that amorphous TiO2 nanoparticles of about 5 nm modified with hexahydro-4-methyl phthalic anhydride [HMPA] were dispersed in the SE resin without agglomerations. The refractive index of the hybrids increased linearly with increasing the TiO2 contents. The hybrid containing 30 wt% of the TiO2 particles showed light transmittance of 94% at 450 nm and refractive index of 1.63. The fine dispersion of the TiO2 nanoparticles was attributable to the sol-gel reactions between the SE resin and TiO2 nanoparticles and the modification of the TiO2 particles with HMPA.     

Template-assisted CoPd nanowire arrays: magnetic properties and FORC analysis

Highly hexagonally ordered CoPd alloy nanowire arrays were synthesized through electrochemical deposition techniques into the nanopores of anodic alumina membranes used as templates. Two different electrolytes were used for this purpose, one with pH = 4.1 and the other with pH = 7. Under applying different electrodeposition parameters and by adjusting both, the current density and the electrolyte composition, it could be possible make to vary the composition of CoPd alloy nanowires in a wide range. Their composition and morphology were investigated by SEM and EDX. The magnetic properties of the nanowires array have been measured with a VSM as a function of the temperature, ranging from RT down to 50 K, for different CoPd alloy nanowires composition. Also, the temperature influence on the reversible-irreversible magnetization processes related with the magnetization reversal of the CoPd nanowires array has been analyzed by first order reversal curve (FORC) method.     

Preparation, characterization, and magnetic studies of Bi0.5X0.5(X = Ca, Sr)MnO nanoparticles

Nanoparticles (dia. approximately 5-7 nm) of Bi0.5X0.5(X = Ca, Sr)MnO3 are prepared by polymer assisted sol-gel method and characterized by various physico-chemical techniques. X-ray diffraction gives evidence for single phasic nature of the materials as well as their structures. Mono-dispersed to a large extent, isolated nanoparticles are seen in the transmission electron micrographs. High resolution electron microscopy shows the crystalline nature of the nanoparticles. Superconducting quantum interferometer based magnetic measurements from 10 K to 300 K show that these nanomanganites retain the charge ordering nature unlike Pr and Nd based nanomanganites. The CO in Bi based manganites is thus found to be very robust consistent with the observation that magnetic fields of the order of 130 T are necessary to melt the CO in these compounds. These results are supported by electron magnetic resonance measurements.     

嵌有纳米碳颗粒凝胶玻璃的制备及其发光特性

以磷酸三乙酯、硝酸铝和正硅酸乙酯为原料,通过它们的水解制备了ｘＡｌ_２Ｏ_３·ｘＰ_２Ｏ₅·１００ＳｉＯ_２（ｘ＝０．２５～３）凝胶．在６００℃对凝胶进行热处理,使其中的有机基团炭化,从而制备出了镶嵌有碳纳米颗粒的ｘＡｌ_２Ｏ_３·ｘＰ_２Ｏ_５·１００ＳｉＯ_２（ｘ＝０．２５,０．５）凝胶玻璃．在室温下以５３２ｎｍ激光（Ｎｄ：ＹＡＧ）激发,在 ６３０ｎｍ处有一强的发光峰,该发光现象是由镶嵌在凝胶玻璃中的纳米碳颗粒产生的．