二元炭质-二氧化硅干凝胶和气凝胶制备碳化硅晶须

以炭质水性中间相和正硅酸乙酯(TEOS)为原料,由溶胶-凝胶法分别制得二元干凝胶和气凝胶前驱体.在氩气气氛中,通过碳热还原分别合成了直径在纳米级的SiC晶须.利用红外光谱,X-射线衍射和透射电子显微镜对合成的β-SiC晶须进行了表征,结果表明,SiC晶须的生长过程为"VS"机理,合成温度和前驱体制备工艺对SiC晶须的性质有较大的影响.     

应用超临界流体干燥技术制备纳米锑掺杂氧化锡的研究

以无机盐SnCl4·5H2O,SbCl3为起始原料,以乙醇为溶剂,采用溶胶-凝胶法制备纳米锑掺杂氧化锡(ATO)粒子.在洗涤除去醇凝胶中的NH+和Cl-后,尝试将超临界流体干燥(Supercritical Fluid Drying,SCFD)技术应用于醇凝胶的干燥.醇凝胶干粉经过高温烧结后,制得了疏松结构的纳米ATO粉体.采用XRD、TG/DSC、FESEM、TEM等分析方法对制得的前驱体干粉、纳米ATO粒子进行表征.XRD结果表明,采用溶胶.凝胶法结合超临界流体干燥技术制得了疏松的、四方型金红石结构的纳米ATO粉体,纳米ATO晶化程度高,并随着烧结温度的升高而升高.TG/DSC分析显示,600℃时前驱体分解完全,得到约78.2%的ATO粒子.从FESEM及TEM照片可以看出,疏松的纳米ATO粒子轻微地贴在一起,粒子的粒径在25 nm左右.经过对超临界CO2干燥技术(SCFD)消除前驱体粒子团聚的机理进行分析,揭示了采用超临界CO2流体干燥醇凝胶能够使前驱体粒子保持松敝的结构.因此采用溶胶-凝胶法结合超临界流体技术制得疏松的前驱体干粉,对最终获得粒径小、低团聚、分散性好的纳米ATO粉体的至关重要.     

聚丙烯酰胺在炭黑粒子表面的功能修饰及其在传感领域的应用

考察了不同结构的醇羟基和不同反应条件对丙烯酰胺在炭黑表面接枝聚合反应的影响;在聚丙烯酰胺接枝炭黑（PAAm-g-CB）存在下,通过异丙醇铝（AIP）的溶胶-凝胶化反应,制得了一种新颖的具有智能响应性的PAAm-g-CB/Al2O3凝胶杂合材料,研究了其气敏性能.结果发现,随反应时间和反应温度提高,单体转化率和接枝率提高;不同醇羟基结构对引入到炭黑表面的醇羟基含量有一定影响,并按（CH3）2CH-OH＞CH3-OH＞CH3CH2-OH＞CH3（CH2）6CH2-OH＞CH3（CH2）3CH2-OH顺序递增.由PAAm-g-CB/Al2O3凝胶杂合材料可制得对丙酮蒸气响应能力强的负蒸气系数传感材料,该传感材料具有良好的响应重复性及对丙酮等强极性溶剂良好的选择性.     

疏水性二氧化硅气凝胶的合成及表征

本文以正硅酸乙酯为原料,经溶胶-凝胶过程制备二氧化硅醇凝胶,再利用二甲基二氯硅烷对醇凝胶进行化学表面修饰,最后用超临界干燥方法制备了疏水性二氧化硅气凝胶.运用红外光谱、BET、扫描电镜、X射线衍射等测试方法对制得样品的结构、形貌及化学组成进行了分析.结果表明该样品是表面存在疏水基团-CH3 的疏水性SiO2 气凝胶,是呈连续网络结构的球状纳米粒子,孔径分布主要集中在2～10 nm,是热稳定性较高的非晶、多孔、轻质介孔材料.     

溶胶-凝胶法制备ZnO多孔薄膜

以聚乙二醇(polyethyleneglycol,PEG2000)为模板剂,醋酸锌(Zn(CH3COO)2·2H2O)为前驱体,乙醇为溶剂,二乙醇胺[NH(C2H4OH)2]为络合剂,通过溶胶凝胶法在玻璃基片上制备了ZnO多孔薄膜。利用红外光谱,热重差热分析及扫描电镜等测试方法对薄膜的结构和特性进行了分析。探讨了样品在溶胶凝胶及煅烧过程中的物理化学变化。研究了前驱体浓度、PEG2000加入量及不同水浴温度对薄膜结构和性能的影响。结果表明:当m[Zn(CH3COO)2]/m[PEG2000]=9.43∶1(质量比),将溶胶在70℃水浴下处理1h,最终可制得具有一定多孔结构的ZnO薄膜。     

常压制备疏水性二氧化硅气凝胶及表面结构表征

用咪唑盐离子液体[C6Mim][BF4]作溶剂和催化剂,经由溶剂置换、常压分级干燥,制备出大块SiO2气凝胶。气凝胶表面结构决定了气凝胶是否具有疏水性,我们用不同比例的甲基三甲氧基硅烷(MTMS)和正硅酸乙脂(TEOS)前驱体来改变气凝胶孔表面Si—OH、Si—O—CH3、Si—CH3组成,网络表面结构用1HNMR核磁共振和傅里叶红外衍射表征。结果表明疏水基团和亲水基团共同组成了气凝胶材料的表面,疏水试验也表明样品具有很好的疏水性。     

凝胶结合Al_2O_3-ZrO_2复相陶瓷性能研究

研究了凝胶结合剂对Al2O3-ZrO2二元复相陶瓷性能的影响。实验以ZrOCl2.8H2O和AlCl3.6H2O为原料,通过一定的工艺分别制得Zr(OH)4和Al(OH)3溶胶,将两种溶胶强制搅拌混合、静置水洗得到凝胶,凝胶经醇水交换、干燥、研磨和煅烧制得Al2O3-ZrO2复合粉。将凝胶按照一定的比例加入到Al2O3-ZrO2复合粉中混合后半干压成型,分别在1630℃、1650℃、1780℃、1800℃下保温3小时烧成并测定其性能。结果表明:当凝胶结合剂的添加量为15%时,烧成温度大幅度降低至1650℃,此时试样有最佳力学性能和抗热震性能,试样的显气孔率为3.7%,体积密度为4.53g/cm3,耐压强度达到488Mpa,抗热震次数4次。     

溶胶-凝胶旋涂法制备ZnO∶Cd薄膜

溶胶-凝胶法是一种有效制膜技术,以二水合醋酸锌Zn(CH3COO)2·2H2O为前驱体,以乙二醇甲醚CH3OCH2CH2OH为主要溶剂,以乙醇胺C2H7NO作为稳定剂制备溶胶溶液.将滴有此溶胶溶液的基片放入旋转涂覆机旋转,再在表面滴入氯化镉( CdCl2·2.5H2O)溶液,然后对基片进行热处理.经X-射线衍射测量,发...     

溶胶-凝胶法制备超细氧化镁陶瓷纤维

以碱式碳酸镁和柠檬酸为原料,采用溶胶- 凝胶法成功制得超细氧化镁陶瓷纤维,并应用红外光 谱仪(FTIR)分析了胶体的形成;应用DSC分析了凝 胶前驱体的热处理过程;通过XRD、SEM分析和观察 了凝胶前驱体纤维及其于450℃热处理后所得到的 超细氧化镁陶瓷纤维的形貌和结构。结果表明:凝胶 的可纺性主要受合成反应溶液中柠檬酸与镁离子物 质的量比、溶液的pH值及搅拌时间的影响,在柠檬 酸与镁离子的物质的量比为2,溶液的pH值在4.0 ～5.0,搅拌时间为16～18h的条件下,制得的凝胶 具有较好的可纺性;凝胶的热分解经历脱水、分解及 氧化镁的形成3个阶段,前驱体凝胶纤维经450℃保 温0.5h处理后,可得到直径均匀,表面光滑、致密的 超细氧化镁陶瓷纤维,其直径可在1μm以下。     

碳气凝胶的常压干燥制备及结构控制

研究了碳气凝胶在常压条件下的制备过程和干燥方法. 用扫描电镜、比表面测量仪及孔径分布仪对其结构进行了表征与测试. 通过改变催化剂和溶剂的用量,可以实现碳气凝胶的颗粒直径及孔洞由纳米到微米级的连续调节. 通过降低催化剂浓度并以丙酮进行溶剂替换,成功实现了碳气凝胶的常压干燥. 常压干燥样品具有250~650 kg/m3的低密度和250~550 m2/g的高比表面积. 分析了其溶胶-凝胶反应机理,围绕毛细压力和材料强度等方面探讨了其常压干燥的实现途径.     

Ce_(0.7)Zr_(0.3)/γ-Al_2O_3纳米固溶体的制备及其结构

以氯氧化锆、硝酸铈、硝酸铝为原料,按n(Ce)∶n(Zr)=0.7∶0.3的比例,采用化学共沉淀法与有机物共沸蒸馏法,将CeO2、ZrO2分散到γ-Al2O3表面上使其形成Ce0.7Zr0.3O2/γ-Al23固溶体。用XRD考察纳米固溶体在不同温度下焙烧后的相结构。结果表明:Ce0.7Zr0.3O2/γ-Al2O3纳米固溶体为立方晶型,且随着焙烧温度的升高,样品的衍射峰依次变强,峰宽变窄。     

Sulfated zirconia grafted on a mesoporous silica aerogel: Influence of the preparation parameters on textural, structural and catalytic properties

Silica supported sulfated zirconia catalysts were synthesized via a new method by grafting sulfated zirconia on the surface of a silica aerogel previously prepared. The main parameters studied in this work were the S/Zr, Zr/Si molar ratios and the support nature. The synthesized solids were characterized using XRD, N₂ physisorption at 77 K, TG-DTA/SM, sulfur chemical analysis and adsorption–desorption of pyridine followed by infrared spectroscopy. These solids were tested in the n-hexane isomerization reaction. Two types of mesopores were observed on the silica aerogel. This mesoporosity was affected depending on the preparation parameters.

The increase of the Zr/Si molar ratio induces the decrease of the size of zirconia particles deposed on the support. In this case, appreciable amounts of sulfur are retained with the presence of a relatively strong Brönsted and Lewis acid sites on the catalyst surface. A high density of Brönsted sites seems to be interesting in the n-hexane isomerization reaction.     

Effects of Extra Al powder Additions on Properties of ZrN-based Composites Prepared by Aluminothermic Reduction and Nitridation Process

ZrN-based composites were synthesized from zirconia via aluminothermic reduction and nitridation proces with Al powders and Mg O as the reductant and sintering aids,respectively. ZrN-based composites are promising for application in the refractory materials or other high temperature industry fields. The effects of extra Al powder on physical properties,phase transformation and microstructures were investigated. Products with differen phase composition and morphologies were obtained with different Al powders additions. The products were composed of Zr N,ZrO_2,MgAl_2O_4,and Zr Al_3O_3 N by aluminothermal reduction and nitridation of zirconia with 0% extra Al powders addition. The diffraction peaks o Zr N were the strongest while peaks of ZrO_2 vanished with 6% extra Al addition. The thermodynamic calculation indicated that introducing Mg O into the system could promote the reaction process.     

The Role of Acetic Acid and Glycerol in the Synthesis of Amorphous MgO Aerogels

Although sol–gel-derived magnesium-oxide (MgO) aerogels have a wide variety of applications, mostly thin films and powders of brucite, i.e. Mg(OH)₂ aerogels, have been reported. Typically, the brucite structure is converted to the periclase form of MgO upon heat-treatment. We report the role of acetic acid (HAc) and glycerol in the synthesis of amorphous MgO aerogel monoliths through the alkoxide sol–gel method. The two ligands work in concert to retard the nucleophilic substitution with water and decrease the rate of gelation, allowing for Mg–O bond formation while reducing the number of hydroxyl bonds. The amorphous material crystallizes to the periclase (MgO) phase at 400°C without going through the brucite transition, resulting in a novel amorphous MgO aerogel. Specifically, we discuss the modification of the Pechini process to an Mg-alkoxide sol–gel process. The roles of the ligands are investigated in the MgO gelation process through Fourier transform infrared spectroscopy, X-ray diffractometry, and thermogravimetric analysis/DSC. The physical properties of the aerogels are also reported.     

Low-Temperature Hydrothermal Synthesis of Yttrium-Doped Zirconia Powders

The feasibility of low-temperature synthesis of yttrium-doped zirconia (Y-ZrO₂) crystalline powders in aqueous solutions at lessthan equal to100°C has been evaluated, and the hydrothermal crystallization mechanism for Y-ZrO₂ powders also has been investigated. Coprecipitated (Y,Zr) hydroxide gel, mechanical mixtures of Y(OH)₃ and Zr(OH)₄ gel, and Y(OH)₃ gel have been reacted in boiling alkaline solutions. Coprecipitated (Y,Zr) hydroxide gel crystallized to cubic or tetragonal Y-ZrO₂ at pH 13.9. The yttrium content in the powder synthesized from coprecipitated (Y,Zr) hydroxide is consistent with the initial precursor solution composition, as expected from the similarity in solubility of Zr(OH)^-₅ and Y(OH)^-₄. A diffusionless mechanism for the transformation of the (Y,Zr) hydroxide gel to Y-ZrO₂ is proposed, and the phase stability in aqueous solution is discussed in terms of an in situ crystallization model. It is also demonstrated through thermodynamic arguments with experimental verification that the stable form of the Y-ZrO₂ at 25°C is the anhydrous phase, not the metal hydroxide as previously thought.     

Synthesis of nano-phase ZrC by carbothermal reduction using a ZrO2–carbon nano-composite

Carbothermal reduction of Zr-sucrose gels powders into nano-phase ZrC, or ZrC-Zr(C,O) core-shell powders, via a composite of 2–4 nm sized ZrO₂ and amorphous carbon, is described. Samples with 1.7–20 sucrose-carbon:Zr ratio gels heated to 1495 °C at 10 °Cmin^?1, with 3 and 30 min hold time were studied in detail using; TG, XRD, SEM, TEM, STEM-EDX, and XPS with Ar⁺-ion etching. After 1495 °C, 3 min, the samples with 12-20C:Zr ratios yielded weakly agglomerated 30 to 40 nm sized ZrC particles, surrounded by a dense 5 nm thick shell of Zr(C,O). With 5C:Zr significant amounts of ZrO₂ was present after heating at 1495 °C for 3 min, while after 30 min annealing, ZrC particles without residual amorphous carbon was obtained. Minor amounts of zirconia was found in most samples, which in similarity with the 5 nm Zr(C,O) shell, is believed to stem from post synthesis oxidation.     

微乳法制备纳米氧化锆及其结构分析

以四水合硫酸锆为原料,通过油酸/正丁醇/氨水体系制备纳米ZrO2。运用热重-差热分析、红外光谱分析、X射线衍射、激光粒度分布、透射电子显微镜等手段对产物的结构和形态进行了表征。实验结果表明,所合成的ZrO2为四方晶型,产物的形状为球形,粒径在20 nm左右。红外光谱测试结果表明,随着煅烧温度的升高,Zr─O─Zr键的吸收频率产生红移;随着微乳体系中氨水浓度的增大,所制备样品的Zr─O─Zr键的吸收频率产生红移,ZrO2的粒径增大。     

Evolution of the Phase Content of Zirconia Powders Prepared by Sol-Gel Acid Hydrolysis

The evolution of the phase content in zirconia powders that have been prepared by sol—;gel acid hydrolysis has been investigated using the perturbed-angular-correlation (PAC) technique and X-ray diffractometry. As a consequence of performing annealing treatments at increasing temperatures between room temperature and 1000°C, the amorphous starting material transforms to the tetragonal form and then to the monoclinic form. The metastable tetragonal phase exhibits two hyperfine components, one of which describes very defective zirconium surroundings. The evolution of PAC relative fractions is in agreement with the diffraction results. The durability of the samples in sodium hydroxide seems to increase as the relative amount of the most-defective zirconium surroundings of the tetragonal form increases.     

溶胶-凝胶法制备氧化铝-氧化锆复合粉体

以A1C13·6H2O和ZrOCl2·8H2O为起始原料、NH3·H2O为沉淀剂,采用溶胶一凝胶法制备A12O3含量为51．74％（质量分数,下同）、ZrO2含量为44．95％的A12O3-ZrO2复合粉体。借助X射线荧光分析仪、X射线衍射仪、高温热重仪、激光粒度分析仪和扫描电子显微镜对复合粉体的化学成分、物相组成和粒径分布等进行了表征。结果表明：A12O3-ZrO2复合粉体化学成分均匀性好,粒径较细,粒径小于0．5μm的约为5％,在0．5～5．0μm的约为55％,大于5．0μm的约为40％;随热处理温度升高,复合粉体析晶程度逐渐提高,800℃热处理时t-ZrO2相析出量较少;12O0℃热处理时则析出大量的t-ZrO2相、少量刚玉相和微量c-ZrO2相;1350℃后,刚玉相和c-ZrO2相数量明显增多。     

Preparation of silica aerogel from oil shale ash by fluidized bed drying

The silica aerogel with high specific surface area and large pore volume was successfully synthesized using oil shale ash (OSA) via ambient pressure drying. The oil shale ash was burned and leached by sulfuric acid solution, and then was extracted using sodium hydroxide solution to produce a sodium silicate solution. The solution was neutralized with sulfuric acid solution to form a silica gel. After washing with water, the solvent exchange with n-hexane, and the surface modification with hexamethyldisilazane (HMDZ), the aged gel was dried by fluidization technique and also using a furnace to yield silica aerogels. The physical and textural properties of the resultant silica aerogels were investigated and discussed. The results have been compared with silica aerogel powders dried in a furnace. From the results, it is clear that the properties of silica powders obtained in fluidized bed are superior to that of powders dried in the furnace. Using fluidization technique, it could produce silica aerogel powders with low tapping density of 0.0775 g/cm³, high specific surface area (789 m²/g) and cumulative pore volume of 2.77 cm³/g.