The Fabrication of ZrO2–ZrC Microspheres by Internal Gelation and Carbothermal Reduction Process

ZrO₂–ZrC (ZrCO) ceramic microspheres were fabricated by combination of internal gelation and carbothermal reduction process. The internal gelation broth containing carbon powders was prepared and stored at room temperature of 25°C to form a precursor of microspheres. By dropping droplets of the broth into hot silicone, the gel microspheres would solidify within a few seconds by decomposition of hexamethylenetetramine (HMTA). The dispersability of the carbon powders in the broth is the key factor to producing ZrCO microspheres with uniform density distribution, as zirconium carbides are generated by the direct reduction of ZrO₂ with carbon. The ZrCO ceramic microspheres fabricated with various mass ratio of ZrO₂ and ZrC have good sphericity and no cracks through optimizing washing and heat treatment process.     

Heterogeneous styrene–divinylbenzene copolymers in collapsed and reexpanded states

The pore structure of styrene–divinylbenzene (DVB) copolymers formed by phase separation before or after gelation was compared using apparent densities and mercury porosimetry. The copolymers were prepared with di-2-ethylhexyl phthalate (DOP) as diluent. The pore structure of copolymers formed in homogeneous gelation can collapse upon drying in the rubbery state. The collapsed pores have a mean diameter of about 100–200 Å corresponding to the interstices between the microspheres. The collapsed microspheres reexpand again during the sulfonation or chloromethylation reactions, or during the solvent exchange. The pore structure of styrene–DVB networks formed in heterogeneous gelation do not collapse on drying in the swollen state, this being a stable and permanent porosity. The critical crosslink density for transition from homogeneous to the heterogeneous gelation represents a borderline between stable and unstable porosity. The drastical change of swelling and porosity values at the critical crosslink density is due to the collapse of unstable pores.     

An improvement of microfluidic-assisted internal gelation in the preparation of millimeter-sized ceramic microspheres

The microspheres prepared by the microfluidic-assisted internal gelation process are still challenging to reach the millimeter size due to the large gravity. The gravity would affect the sphericity and size uniformity of microspheres. The improved microfluidic-assisted internal gelation process is designed and optimized to produce large-sized monodisperse ceramic microspheres with good sphericity. The movement mechanism of millimeter-sized sol droplets and gel microspheres in the microchannel is summarized and the state of the dispersed phase entering the measuring cylinder is controlled. The friction between the gel microspheres and the tubing wall is reduced as much as possible, and ZrO₂ ceramic microspheres of 500 ± 5 μm with good sphericity are prepared with the broth at room temperature. The mechanism of sol droplets entering the oil surface is explored to demonstrate the superiority of the improved microfluidic-assisted internal gelation process. The improved microfluidic-assisted internal gelation process could be directly extended to preparing other millimeter-sized monodisperse ceramic microspheres.     

An Improved Internal Gelation Process for Preparing ZrO2 Ceramic Microspheres Without Cooling the Precursor Solution

ZrO₂ microspheres were prepared with an improved internal gelation process without cooling the precursor solution. The stability of the broth for internal gelation process has been systematically investigated, and the results show that the preparation and storage temperature, the concentration of NO₃^? and the urea in the broth have important effects on the stability of the broth. Through optimizing the broth formulation the broth prepared can be stable for 14 h at 25°C. The prepared ZrO₂ ceramic microspheres have uniform size and good sphericity, with a density of 5.87 g/cm³.     

微通道内双重孔结构SiO2微球的制备

利用微流控技术制备双重孔结构SiO₂微球具有微观结构和宏观形貌可控的优点。在同轴环管微通道中,通过pH和温度变化引发快速凝胶过程制备得到了具有双重孔结构的SiO₂微球,考察了有机相溶剂性质、有机相流速以及凝胶温度等因素对微球宏观形貌以及微观结构的影响规律。实验结果表明,制备得到的SiO₂微球粒径在300～600 μm可调,比表面积可以达到1000 m²·g^-1,介孔孔径在4～10 nm之间,大孔孔径在400～1500 nm之间。实验发现有机相流速的增大会导致微球粒径的减小,提高三辛胺对盐酸的萃取速率,加快二氧化硅溶胶粒子的凝胶过程,更易生成松散的网状大孔结构。较高的凝胶温度会增大SiO₂微球介孔的孔容和孔径。     

Sol-gel derived silica membranes with tailored microporous structures

The template effect of amphiphilic systems on the porous structure of silica gel layers has been studied. Membranes with a tailor-made microporosity and pore diameters of between 1 and 2 nm were obtained from these gels. Two different preparation methods have been used and their influence on the sol-to-gel transition of silicon alkoxide sols has been investigated. The first method entails the incorporation of non-ionic surfactants which modify the porous structure of gels. In this case, specific surface area, pore size and porous volume can be varied in the final material as a function of chain length and concentration of the surfactant. In the second method, self-assembled systems made of cationic surfactants develop during the gelation process and lead to an ordered gel structure. After elimination of the organic mesophase by heating, the membrane material exhibits an ordered microporosity with pore size directly related to the size of the surfactant molecules.     

Precisely Controlling Preparation of Ceria‐Stabilized Zirconia Microspheres of ~100 μm by External Gelation

Ceria‐stabilized zirconia (CSZ) microspheres of ~100 μm were prepared by external gelation process. The inner diameter of nozzle was 0.2 mm. The key process parameters including broth pH value, Zr concentration, flow rate, and vibration frequency were optimized for precise control of the diameter. The optimum parameters were found to be flow rate of 11.08 mL/min, Zr concentration of 0.72 mol/L, and vibration frequency of 2650 Hz. CSZ microspheres with an average diameter of 103.1 μm and standard deviation of 4.4 were prepared under these conditions. CSZ microspheres showed good monodispersity, good sphericity, and high density.     

The effect of washing process on the cracking of ZrO2 microspheres by internal gelation

ZrO₂ microspheres are widely used as a simulant of UO₂ in the development of nuclear fuel. However, the cracking of ZrO₂ microspheres prepared by internal gelation is still a challenge during drying and sintering processes. To address this issue, we designed and optimized the washing process for obtaining crack-free ZrO₂ microspheres. Through thermogravimetric, infrared, Raman, BET, and SEM analysis, it is shown that the cracking of the microspheres is mainly related to the pores in microspheres. The washing solvent with low surface tension is used to reduce the effect of capillary force on pore shrinkage. Therefore, the optimal washing process was designed as trichloroethylene (TCE)—0.5 M NH₃.H₂O—Propylene glycol methyl ether (PM) and gel microspheres with a high specific surface area of 315.3 m²/g and pore volume of 0.4125 cm³/g were obtained. The characterizations also further showed that when the microspheres were dried and sintered, the water vapor and the decomposition gas of organic matter were completely released from the pores in the microspheres. Our new washing process could be directly extended for preparing crack-free ceramic microspheres by internal gelation.     

超大孔聚(苯乙烯-甲基丙烯酸缩水甘油酯)共聚微球的制备及孔结构的调控

使用表面活性剂反胶团法制备超大孔聚(苯乙烯-甲基丙烯酸缩水甘油酯)[P(ST-GMA)]共聚微球,考察了功能单体GMA含量、油溶性表面活性剂、稀释剂、交联剂对微球孔径的影响. 结果表明,随GMA含量增加,微球孔径显著增大;表面活性剂用量从1.6 g增加到2.0 g时,微球孔径由100 nm增加到720 nm;随稀释剂疏水性增强,微球孔径增大;交联剂用量由1.0 g增加到2.0 g,微球孔径由550 nm变为100 nm左右. 在此基础上,通过条件优化合成了具有特定孔径的不同功能单体GMA含量的超大孔P(ST-GMA)共聚微球,可连接不同配基,用于色谱分离介质及酶的固定化.     

The preparation of ZrO2–ZrC ceramic microspheres by internal gelation process with sucrose as a carbon source

ZrO₂–ZrC (ZrCO) ceramic microspheres were fabricated by internal gelation and carbothermal reduction. The effect of various carbon sources on the stability of the broth was investigated, the carbon sources which have little effect on the stability of the broth were chosen as the carbon sources for carbothermal reduction, and the component distribution and microstructure of the sintered ZrCO microspheres were analyzed. The results indicate that the broth was stable at room temperature when sucrose was used as the carbon source, and crack-free ZrC–ZrO₂ ceramic microspheres with good sphericity and uniform distribution of ZrC and ZrO₂ could be successfully prepared. Moreover, the ZrC–ZrO₂ ceramic microspheres fabricated have no obvious pores and free carbon.     

Preparation of CeO2 microspheres by internal gelation process with copolymerization using acrylic acid

Cerium dioxide microspheres were successfully prepared by internal gelation process with copolymerization using acrylic acid. The effects of acrylic acid (AA)/hexamethylenetetramine (HMTA) molar ratio and concentration of solution containing urea and HMTA on the stability of precursor solution and on the prepared microspheres were investigated. The results indicated that acrylic acid could modify the urea resin and slow down the decomposition of urea resin. The stability of precursor solutions was improved with the increase of AA/HMTA molar ratio, but the surfaces of gelled microspheres became rough and cracked when the ratio was greater than 1. The solution containing urea and HMTA had a significant effect on the stability of precursor solution and on the surface morphology, specific surface area, pore volume and average pore diameter of the microspheres. The porous CeO₂ microspheres were obtained by heat treatment at 600?°C for 2?h.     

Synthesis of macroporous poly(styrene-divinyl benzene) microspheres by surfactant reverse micelles swelling method

Macroporous poly(styrene-divinyl benzene) microspheres with pore size of about 500 nm were prepared by a new method, surfactant reverse micelles swelling method. The macroporous microspheres were prepared by convenient suspension polymerization. The difference from conventional suspension polymerization was that a higher concentration of surfactant was added in the oil phase. The effects of the amount and type of surfactants on the morphology of microspheres were investigated, and the formation mechanism was also discussed. Macropores were formed when the concentration of surfactant was much higher than critical micelle concentration (cmc). It was proposed that a large amount of reverse micelles formed by adding a large amount of surfactant in the oil droplet phase, and the reverse micelles could absorb water from the external aqueous phase. The water in the oil phase formed macropores after polymerization. The method developed in this study was convenient to prepare microspheres with larger pore size than the conventional method such as agglomeration method of nanoparticles.     

Monosodium Titanate in Hydrous Titanium Oxide Spheres for the Removal of Strontium and Key Actinides from Salt Solutions at the Savannah River Site

Abstract

Fine powders of monosodium titanate effectively remove strontium and plutonium from alkaline salt supernatant. At the Savannah River Site, larger, porous particles with monosodium titanate were desired for continuous column operations. The internal gelation process was used to make hydrous titanium oxide microspheres with 32 and 50 wt% monosodium titanate. With actual supernatant, the microspheres with 50 wt% monosodium titanate produced average batch distribution coefficients of 35,000 mL/g for plutonium and 99,000 mL/g for strontium. These microspheres were tested using a simulant and a flow rate of 5.3 bed volumes per hour. The plutonium removal dropped from 99% to 94% while the strontium removal remained nearly 100%. The microspheres exhibited good flow performance and no particle degradation.     

乳液法结合溶胶-凝胶法制备多孔TiO2微球

为了进一步提高二氧化钛（ TiO₂）的反射率,采用乳液法结合溶胶 -凝胶法,以聚乙二醇（PEG）为相分离诱导剂,制备了内部具有不连续多孔结构的 TiO₂微球。考察了 PEG的添加量对 TiO₂微球内部孔径大小的影响。研究结果表明： TiO₂微球内部的孔径随 PEG的用量增加而增大。基于溶胶-凝胶转变和相分离过程,详细介绍了多孔 TiO₂微球的形成机理。当 PEG的添加量为 9.0%时,所制备的多孔 TiO₂微球在近红外区的积分平均反射率为 84.9%,比常见钛白粉提高了 5.4%。     

中孔碳孔径及有序性影响因素

以表面活性剂F127为模板剂制备了有序中孔碳材料,研究了影响中孔碳孔径分布及有序性的各工艺参数,采用XRD, SEM, TEM和N2吸/脱附等手段对有序中孔碳进行了表征. 结果表明,F127用量、反应温度、搅拌时间、碳化温度和碳化升温速率等因素直接影响中孔碳结构的有序性及孔径分布. F127用量为40%、反应温度40℃、搅拌时间30 min、碳化温度800℃、升温速率1℃/min时,所得中孔碳有序性好且孔径分布比较集中.     

无机盐诱导凝胶法制备纤维素气凝胶

在纤维素-7% NaOH-12%尿素水溶液体系中加入少量无机盐诱导和促进体系形成凝胶,研究了不同种类和用量的无机盐对凝胶形成过程的促进作用,促进能力依次为：阴离子相同时,钾盐>钠盐>锂盐;阳离子相同时,氯盐>溴盐>硝酸盐. 无机盐浓度越高对凝胶形成的促进作用越明显. 在此基础上结合溶剂置换和超临界CO2干燥技术,提出了无机盐诱导凝胶法制备纤维素气凝胶的新工艺,用SEM、氮吸附仪和压汞仪对所制气凝胶材料进行了结构表征,材料具有介孔到大孔范围的多孔结构,介孔的比表面积为284 m2/g,孔体积为2.0 cm3/g,平均孔径为20.5 nm;大孔的孔体积为13.95 cm3/g,平均孔径为0.732 μm,孔隙率达91%.     

Mesoporous characteristics of crystalline indium-titania synthesized by the sol-gel route

Mesoporous nanocrystalline titanium dioxide with narrow pore size distribution was prepared by the sol-gel technique. During synthesis, the gels were doped with indium salt incorporation in the early gelation stage. The presence of indium had an evident influence on the phase transition of TiO₂ and the nucleation process. Crystal sizes were estimated by X-ray diffraction (XRD). Mesoporous structures in indium-doped titania were maintained after heat treatment at 400 and 600 °C for 4 h, exhibiting significant thermal stability. The brookite phase was observed in samples that underwent phase transition. In this paper, we have studied the relationship between textural properties and phase transition, discussing the possible role of average crystal size.     

可降解聚乳酸多孔微球的制备探究

以聚乳酸为壁材,碳酸氢铵为致孔剂,采用双乳液溶剂挥发法,制备出具有孔状的聚乳酸微球,探讨制备条件对聚乳酸微球的影响.结果表明,在内外水相体积比1∶7.5,初乳化搅拌速度1 000 r/min下制得的PLA多孔微球的球形和孔结构较好.     

DETERMINATION OF THE OPTIMUM PREPARATION CONDITION OF THE SOL-GEL SiO2 USING THE RESPONSE SURFAC METHODOLOGY

A typical sol - gel process consists of the liquid reaction, the solution gelation, and followed by the dehydration. The surface properties of silica gel such as surface area, pore volumes, and the pore diameter were affected by the manufacturing variables including pH values, gelation and dehydration temperatures. The objective of this study is to determine the optimum preparation conditions to maximize a response of surface area, or minimize its pore diameter. In addition, interactions between process variables were studied and their significance to the surface properties was also weighted. It was found that the surface area of silica gels increased with an increasing amount of NH₄OH to a maximum value and then decreased. As a drying temperature kept constant, the surface area and the pore volume increased with an increasing gelation temperature. However, the pore diameter was not influenced by this factor and the pore size was almost uniform at a low NH₄OH concentration. For a higher NH₄OH concentration, the pore volume and the pore diameter became larger but the surface area became smaller as the gelation temperature increased. By means of the response surface methodology analysis, the optimum processing condition was found to be 0.0155 mole of NH₄OH, 80,3°C for gelation temperature, and 63.2°C for the dehydration. As a result the maximum surface area corresponding to the optimum preparation conditions was 818.9 (m²/g) as expected.     

DETERMINATION OF THE OPTIMUM PREPARATION CONDITION OF THE SOL-GEL SiO2 USING THE RESPONSE SURFAC METHODOLOGY

A typical sol - gel process consists of the liquid reaction, the solution gelation, and followed by the dehydration. The surface properties of silica gel such as surface area, pore volumes, and the pore diameter were affected by the manufacturing variables including pH values, gelation and dehydration temperatures. The objective of this study is to determine the optimum preparation conditions to maximize a response of surface area, or minimize its pore diameter. In addition, interactions between process variables were studied and their significance to the surface properties was also weighted. It was found that the surface area of silica gels increased with an increasing amount of NH₄OH to a maximum value and then decreased. As a drying temperature kept constant, the surface area and the pore volume increased with an increasing gelation temperature. However, the pore diameter was not influenced by this factor and the pore size was almost uniform at a low NH₄OH concentration. For a higher NH₄OH concentration, the pore volume and the pore diameter became larger but the surface area became smaller as the gelation temperature increased. By means of the response surface methodology analysis, the optimum processing condition was found to be 0.0155 mole of NH₄OH, 80,3°C for gelation temperature, and 63.2°C for the dehydration. As a result the maximum surface area corresponding to the optimum preparation conditions was 818.9 (m²/g) as expected.