Controllable formation of Er–Yb codoped Al2O3 films by the non-aqueous sol–gel method

1 mol%Er³⁺–10 mol%Yb³⁺ codoped Al₂O₃ thin films have been prepared on thermally oxidized SiO₂/Si(110) substrates by a dip-coating process in the non-aqueous sol–gel method from the hydrolysis of aluminum isopropoxide [Al(OC₃H₇)₃] under isopropanol environment. Addition of N,N-dimethylformamide (DMF) as a drying control chemical additive (DCCA) into the sol suppresses formation of the cracks in the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films when the rare-earth ion is doped with a high doping concentration. Homogeneous, smooth and crack-free Er³⁺–Yb³⁺ codoped Al₂O₃ thin films form at the conditions by a molar ratio of 1:1 for DMF:Al(OC₃H₇)₃. A strong photoluminescence spectrum with a broadband extending from 1.400 to 1.700 µm centered at 1.533 µm is obtained for the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films, which is unrelated to the addition of DMF. Controllable formation of the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films may be explained by the fact that the DMF assisted the deprotonation process of Al–OH at the surfaces of gel particles, resulting in enhancement of the degree of polymerization of sols and improvement of the mechanical properties of gel thin films.     

INCORPORATED C70 IN SOL AND GEL

C₇₀ is incorporated in gel by a sol-gel process with using 3-amino-propyltriethoxysilane (NH₂(CH₂)₃Si(OC₂H₅)₃, APTS) and 3-glycidoxypropltrimethoxysilane (CH₂OCHCH₂O(CH₂)₃Si(OCH₃)₃, GPTMS) as precursors. C₇₀ is firstly mixed with APTS to form C₇₀-NH₂(CH₂)₃Si(OC₂H₅)₃ compound by the reaction between C₇₀ and amino-group of APTS, and then the compound is hybridized with GPTMS to form solid gel. The linkage of C₇₀ and APTS is estimated and confirmed with FT-IR spectra, and the UV/Visible spectra of the sol and gel are measured.     

三效催化剂涂层制备与性能研究

薄水锅石作为γ-Al₂O₃的前驱体,加入CeO₂-ZrO₂-La₂O₃和扩孔剂等助剂制备蜂窝陶瓷载体涂层,研究了涂层料液的表观粘度、因含量与载体负载量的关系,粘度对料液中粒径分布和涂层性能的影响,利用SEM、BET表面积、超声波震荡和热冲击等方法研究了涂层的性能.结果表明,涂层料液中适宜的固含量为30％～40％;一次浸量>二次浸量>三次浸量,适宜的负载量为8％～15％;低粘度料液以小颗粒为主,颗粒分布均匀,制备的涂层有较好的抗震动和抗热冲击性能;高粘度涂层料液的颗粒较大和粒径分布较宽,有利于提高载体的负载量,但涂层的性能明显下降.堇青石蜂窝陶瓷载体经一步法负载涂层后,可获得约 50 m²/g的表面积.     

Al2O3-SiO2复合气凝胶的制备及改性剂对其结构与隔热性能的影响

以AlCl₃·6H₂O为前驱体,采用离子交换工艺和溶胶-凝胶法,在正硅酸四乙酯（TEOS）乙醇溶液中浸泡实现Al₂O₃和SiO₂的复合,经表面改性和常温常压干燥制备出低成本、无杂质离子、低热导率的Al₂O₃-SiO₂复合气凝胶。探索了不同有机硅烷改性剂对Al₂O₃-SiO₂复合气凝胶结构和隔热性能的影响。结果表明,在改性剂为三甲氧基甲基硅烷（MTMS）,改性环境为中性（pH为7）时,Al₂O₃-SiO₂复合气凝胶表现出最均匀的微观结构,SiO₂和Al₂O₃主要以无定形形式存在。MTMS可有效减少Al₂O₃-SiO₂湿凝胶表面的-OH基团,形成Si-O-Si和Al-O-Si基团。Al₂O₃-SiO₂气凝胶比表面积和孔体积分别达到574 m2/g和2.3 cm3/g,热导率低至0.029 W（m·K）-1。以上研究为促进气凝胶材料在隔热领域的应用提供了支持。      

Dielectric and piezoelectric properties of sol–gel derived Ca doped PbTiO3

Synthesis of Ca doped PbTiO₃ powder by a chemically derived sol–gel process is described. Crystallization characteristics of different compositions Pb_1−xCa_xTiO₃ (PCT) with varying calcium (Ca) content in the range x = 0–0.45 has been investigated by DTA/TGA, X-ray diffraction and scanning electron microscopy. The crystallization temperature is found to decrease with increasing calcium content. X-ray diffraction reveals a tetragonal structure for PCT compositions with x ≤ 0.35, and a cubic structure for x = 0.45. Dielectric properties on sintered ceramics prepared with fine sol–gel derived powders have been measured. The dielectric constant is found to increase with increasing Ca content, and the dielectric loss decreases continuously. Sol–gel derived Pb_1−xCa_xTiO₃ ceramics with x = 0.45 after poling exhibit infinite electromechanical anisotropy (k_t/k_p) with a high d₃₃ = 80 pC/N, ′ = 298 and low dielectric loss (tan δ = 0.0041).     

Evolution of ettringite in presence of carbonate, and silicate ions

The main objective of this work was to study the evolution of ettringite when in contact with a solution containing carbonate and silicate ions.

Ettringite was synthesised and put in contact with three types of saturated solutions: (a) CaCO₃ and silica gel saturated solution; (b) MgCO₃ and silica gel saturated solution and (c) C–S–H gel plus portlandite and CaCO₃ saturated solution. The temperature of the experiment was 4 ± 2 °C. At different ages the samples were studied by: FTIR, XRD, NMR, and SEM/EDX.

Ettringite evolves with time, reacting with carbonates and silicates and decomposing to poorly crystallised products when it is in contact with solutions (a) and (b). Ettringite decomposition rate is much higher when it is in contact with saturated magnesium carbonate solution (b) than when in contact with the solution (a). After 90 days of exposure in solution (b) ettringite decomposition starts, followed by reorganization of the atoms giving place to a semi-stable poorly crystallised compound. However 130 days are necessary for ettringite decomposition in solution (a). Ettringite in contact with solution (c) evolves more slowly and it almost remains unchanged after 380 days of treatment. Ca(OH)₂ formed in the C₃S and C₂S hydration retards ettringite decomposition.     

Mechanical properties and microstructure of bioactive ORMOSILs containing silica particles

We synthesized organically modified silicate (ORMOSILs) gels with colloidal silica (CS) (AEROSIL®) starting from polydimethylsiloxane (PDMS), tetraethoxysilane (TEOS) and calcium nitrate (Ca(NO₃)₂·4H₂O) through sol–gel processing. Dynamic mechanical analysis indicated that relative height of the tanδ peak at about −100 °C increased with an increase in the relative content of the inorganic components. This peak growth was accounted for by the relative increase in PDMS–colloidal silica particle interactions. The colloidal silica could control the mechanical behavior of the hybrids. The gel of a specific composition could deposit apatite within 3 days of soaking in the simulated body fluid (SBF), since it included many calcium ions on the surface.     

Thermal nonlinear refraction in the dye-doped sol–gel xTiO2 · (100 − x)SiO2 system

The build-up time of the thermal lens effect induced by a Gaussian beam in the DO3-doped sol–gel system xTiO₂ · (100 − x)SiO₂ at different compositions, both in the liquid and gel phases has been measured in a Z-scan geometry. While the pure titania samples show a minimum of the thermal diffusivity, a maximum is found for x ≈ 30. The sol to gel transformation leads to an increase of the build-up times at all compositions.     

Preparation, patterning and luminescent properties of nanocrystalline Gd2O3:A (A=Eu, Dy, Sm, Er) phosphor films via Pechini sol–gel soft lithography

Nanocrystalline Gd₂O₃:A (A=Eu³⁺, Dy³⁺, Sm³⁺, Er³⁺) phosphor films and their patterning were fabricated by a Pechini sol–gel process combined with a soft lithography. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical microscopy, UV/vis transmission and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 500 °C and that the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free non-patterned phosphor films were obtained by optimizing the composition of the coating sol, which mainly consisted of grains with an average size of 70 nm and a thickness of 550 nm. Using micro-molding in capillaries technique, we obtained homogeneous and defects-free patterned gel and crystalline phosphor films with different stripe widths (5, 10, 20 and 50 μm). Significant shrinkage (50%) was observed in the patterned films during the heat treatment process. The doped rare earth ions (A) showed their characteristic emission in crystalline Gd₂O₃ phosphor films due to an efficient energy transfer from Gd₂O₃ host to them. Both the lifetimes and PL intensity of the rare earth ions increased with increasing the annealing temperature from 500 to 900 °C, and the optimum concentrations for Eu³⁺, Dy³⁺, Sm³⁺, Er³⁺ were determined to be 5, 0.25, 1 and 1.5 mol% of Gd³⁺ in Gd₂O₃ films, respectively.     

溶胶-凝胶法制备Al3+、Yb3+掺杂石英光纤纤芯的研究

以正硅酸乙酯、氯化铝和氯化镱为前驱体, 用溶胶-凝胶法制备了Al³⁺、Yb³⁺掺杂石英光纤纤芯。采用ICP-AES分析发现: 碱催化的掺杂硅凝胶上下层组分存在较大差异, 酸催化条件能够消除组分差异。将酸催化溶胶经凝胶化、热处理、玻璃化、光学加工, 获得了φ2.5 mm×50 mm的芯棒。测试2 mm厚芯棒玻璃的光谱和荧光寿命, 1020 nm的荧光寿命为896 μs, 羟基含量为0.4×10^-6, 并通过显微拉曼光谱分析玻璃结构。采用管棒法制备预制棒, 2000℃高温拉制了Al³⁺、Yb³⁺掺杂单包层石英光纤。用光纤折射率分布测试仪测得纤芯折射率波动Δn小于2×10^-4, 表明纤芯具有良好的光学均匀性。本研究结果提供了一种大模场掺镱石英光纤纤芯材料的制备方法, 并为溶胶-凝胶法制备均匀多组分材料的研究提供了理论参考。     

Influence of processing conditions on the luminescence of YVO4:Eu nanoparticles

Single-phase YVO₄:Eu³⁺ nanopowders were synthesized by sol–gel combustion method using citric acid as a chelating agent and reducer. The microstructures and photoluminescence (PL) properties of the as-prepared YVO₄:Eu³⁺ nanopowders were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and PL spectroscopy. The luminescence intensities of the YVO₄ nanoparticles doped with 5 mol% Eu³⁺ ions strongly depended on the calcination temperature, the molar ratio of citric acid to nitrates and the amounts of the Li⁺ additive.     

EDTA络合溶胶-凝胶法制备Y2O3:Eu纳米晶

以金属硝酸盐和EDTA为原料,用EDTA络合溶胶-凝胶法制备出Y₂O₃:Eu纳米晶,并对合成条件进行了优化.分别用TG-DTA、FTIR、XRD、SEM、荧光分光光度计等手段对凝胶的热分解机理,Y₂O₃:Eu的形成过程以及纳米晶的性质进行了研究.结果表明:硝酸根离子可以加速EDTA凝胶的热分解,仅在600℃焙烧即可得到颗粒细小、组分均匀,纯立方相的’Y₂O₃:Eu纳米晶,颗粒基本呈球形,粒径随温度升高逐渐长大,600℃时,约为20nm,1000℃时,约为70nm.     

磁性复合凝胶球对Pb(Ⅱ)的吸附特性与机制

以海藻酸钠(SA)作为基体前驱材料,通过离子交联法包埋固化L-甲硫氨酸(L-met)和纳米Fe₃O₄形成磁性复合凝胶球SA@Fe₃O₄/L-met。实验探究了SA@Fe₃O₄/L-met在不同pH、投加量和初始离子浓度条件下对Pb(Ⅱ)吸附能力的影响。结果表明,在pH=5、投加量为0.5 g·L?1、初始浓度为20 mg·L?1时,SA@Fe₃O₄/L-met对Pb(Ⅱ)能达到较好的吸附效率,最大吸附量可达到328.02 mg·g?1,远大于Fe₃O₄@SA与SA的吸附量142.5 mg·g?1和152.8 mg·g?1。吸附动力学和热力学研究表明该吸附过程分别对准二级动力学方程和Langmuir方程的拟合程度更大,且反应过程是一个熵增吸热的过程。最后采用SEM、XPS、VSM等对SA@Fe₃O₄/L-met的结构与性能进行表征分析,发现SA@Fe₃O₄/L-met中的氨基和羧基通过配位反应与Pb(Ⅱ)结合,同时还存在着离子交换作用。经过5次解吸后SA@Fe₃O₄/L-met的吸附量仍能达到210.5 mg·g?1,是一种较理想的环保吸附剂。      

Correlation of sol–gel processing parameters with microstructure and properties of a ceramic product

A very high purity MgAl₂O₄ spinel precursor can be prepared via a low temperature process called “Oxide One Pot Synthesis (OOPS)”. Sol–gel processing of such precursors offers the opportunity to prepare spinels with controlled microstructures, which is key to optimizing their properties for application as humidity sensors. Sol–gel processing of a double alkoxide precursor was carried out in buffer solutions in the pH range 8–12, to investigate the effect on the physical properties of the calcined ceramic products. The structure and morphology of the latter were characterized using FTIR, XRD, SEM and BET surface area measurements. Sol–gel processing results in a calcined product with a narrow pore size distribution, which contains a spinel phase of high crystallinity. At higher pH values, increasing amounts of an -Al₂O₃ phase are formed. At all pH values, the calcined product exhibits high water adsorption, up to 0.312 g H₂O/g sample.     

Optical properties of rare earth ion (Nd, Er and Tb)-doped alumina films prepared by the sol–gel method

Rare earth ion (Nd³⁺, Er³⁺ and Tb³⁺)-doped alumina films were prepared by the sol–gel method using aqueous alumina sol. The effects of dopant concentration and treatment temperature on the optical properties, absorption and emission were examined for the doped films. Alumina films prepared by this method gave a high dopant concentration (0–15 mol% per alumina). Significant concentration quenching did not occur in this concentration range. The emissions from ⁵D₃ and ⁵D₄ of Tb³⁺-doped film reflected sensitively a matrix environment around Tb³⁺ ions. Er³⁺- and Nd³⁺-doped alumina films resonantly excited by cw Ti–sapphire laser (800 nm) showed upconversion emission at room temperature. The former gave 548 nm (⁴S_3/2→⁴I_15/2) and 640 nm (⁴F_9/2→⁴I_11/2) signals, and the latter 640 nm (⁴G_7/2→⁴I_11/2), which were dependent on alumina.     

Synthesis and characterization of polyvinylpyrrolidine assisted tantalum pentoxide films

Micron thick tantalum pentoxide (Ta₂O₅) films have been proposed as thermal insulating layers in microchemical systems, but so far it has been difficult to deposit thick enough films over complex substrates. So far sol–gel films cracked upon heating whenever the film thicknesses were above 350 nm. A 350 nm thick film is too thin for effective insulation. Other techniques are not suitable for coating the complex structures associated with microchemical systems. In this paper we report sol–gel synthesis of 1.6 μm thick tantalum pentoxide (Ta₂O₅) films. The films are almost crack free, and adhere to silicon surfaces even upon flashing to 900 °C. The key to the synthesis is the addition of Polyvinylpyrrolidine (PVP) to the sol. Films grown in the absence of PVP all show cracks upon calcination to 900 °C while few cracks are seen with PVP. X-ray diffraction and Fourier transform infra red analysis show that orthorhombic Ta₂O₅ is formed in all cases. X-ray photoelectron spectroscopy shows the O:Ta ratio to be 2.8:1. This shows that sol–gel is a viable process for making the micron thick films of Ta₂O₅ needed as insulators for microchemical systems.     

Sol–gel synthesis and luminescence of unexpected microrod crystalline Ca5La5(SiO4)3(PO4)3O2:Dy phosphors employing different silicate sources

Ca₅La₅(SiO₄)₃(PO₄)₃O₂ doped with Dy³⁺ were synthesized by sol–gel technology with hybrid precursor employed four different silicate sources, 3-aminopropyl-trimethoxysilane (APMS), 3-aminopropyl-triethoxysilane (APES), 3-aminopropyl-methyl-diethoxysilane (APMES) and tetraethoxysilane (TEOS), respectively. The SEM diagraphs show that there exist some novel unexpected morphological structures of microrod owing to the crosslinking reagents than TEOS as silicate source for their amphipathy template effect. X-ray pictures confirm that Ca₅La₅(SiO₄)₃(PO₄)₃O₂:Dy³⁺ compound is formed by a pure apatitic phase. The Dy³⁺ ions could emit white light in Ca₅La₅(SiO₄)₃(PO₄)₃O₂ compound, and the ratio of Y/B is 1.1, when the Dy³⁺ doped concentration is 1.0 mol%.     

纳米BaTiO3的制备及其负载Ni基催化剂的应用研究

采用溶胶-凝胶法制备了纳米BaTiO₃,用纳米BaTiO₃粉体作载体通过浸渍法制备出Ni/BaTiO₃催化剂,并将其用于CO₂重整CH₄制合成气反应,纳米BaTiO₃粉体粒径为25～60nm,颗粒外貌近似球形,其最佳制备条件为:水解用水量10mL,混合溶液pH=4～5,凝胶化温度343K,973K下煅烧处理,在反应温度为1073K,空速12000mL/(h·g·cat)下,Ni/BaTiO₃催化剂可使重整反应的CH₄和CO₂转化率分别达到94.4％和93.3％。     

Systematics of Chromatographic Separations of Fullerenes in Silica-Gel Activated Charcoal Mixtures

C₆₀-C₇₀ separations using several compositions of silica gel-activated charcoal mixtures are described. High yields and fast separations are obtained for silica gel-activated charcoal ratio of 3:1 and silica gel particle size of 200 μ.     

Low temperature synthesis and structural characterization of nanocrystalline YAG prepared by a modified sol–gel method

Nanocrystalline yttrium aluminum garnet, Y₃Al₅O₁₂ or YAG, was synthesized by means of a modified glycolate or sol–gel method that consists of a mixture of salts in an aqueous media. The monophasic nanocrystalline YAG was obtained at 800 °C, which is much lower than others prepared by wet-chemical methods and little higher than alkoxide sol–gel process. The structural evolution features of the nanocrystalline powder were studied by XRD, FT-IR, ²⁷Al MAS NMR, AFM, SEM and TEM. The crystallite sizes range from 26 to 95 nm for 800 and 1150 °C, respectively, suggesting the possibility to be controlled by the annealing temperature. The experimental results indicate the existence of oxygen defects and Al atoms with distorted or incomplete coordination sphere. The feasibility of the modified glycolate method for the preparation of nanocrystalline YAG is discussed.