喷雾热解法制备球形YAG:Ce3+荧光粉研究

采用喷雾热解法制备了无团聚的球形YAGCe3+荧光粉. 考察了前驱体溶液浓度、载气流速、热解温度对实验结果的影响. 当溶液浓度从0.05 mol·L-1增加至0.8 mol·L-1时, 所制备的前驱体粒子的平均粒径也从0.60增加至1.50 μm, 前驱体产量随着前驱体溶液的浓度增加呈现先上升后下降的趋势. 提高载气流速可以增加前驱体的产量. 当热解温度大于800 ℃时, 得到的粒子呈现实心球体. 通过比较喷雾热解法与固相煅烧法所制备的荧光粉, 喷雾热解法制备的荧光粉具有发光强度高、形貌好、粒径分布窄等优点.     

喷雾热解法制备球形YAG∶Ce~(3+)荧光粉研究

采用喷雾热解法制备了无团聚的球形YAG∶Ce3+荧光粉。考察了前驱体溶液浓度、载气流速、热解温度对实验结果的影响。当溶液浓度从0.05 mol.L-1增加至0.8 mol.L-1时,所制备的前驱体粒子的平均粒径也从0.60增加至1.50μm,前驱体产量随着前驱体溶液的浓度增加呈现先上升后下降的趋势。提高载气流速可以增加前驱体的产量。当热解温度大于800℃时,得到的粒子呈现实心球体。通过比较喷雾热解法与固相煅烧法所制备的荧光粉,喷雾热解法制备的荧光粉具有发光强度高、形貌好、粒径分布窄等优点。     

静电喷雾法制备聚膦腈微球

用静电喷雾法制备了粒径窄分布的甘氨酸乙酯-苯丙氨酸乙酯取代聚膦腈的微球.主要探讨了溶剂、溶液浓度、流速、喷射电压及接收距离对微球形貌和粒径的影响.微球的表面形貌与溶剂性质和聚合物溶液浓度密切相关,微球粒径受聚合物溶液流速的影响比较显著,随流速增大粒径呈单调上升趋势.结果显示对于[η]=0.1 dL/g的(甘氨酸乙酯)0.3(苯丙氨酸乙酯)0.7取代聚膦腈,以0.25 g/mL的四氢呋喃溶液进行静电喷雾,可获得粒径分布窄(1~2μm)且近球形的微粒,其工艺条件可进一步用于载药聚膦腈微球的制备和控制释放研究.     

Triton X-100六角液晶相中制备镁铝层状双金属氢氧化物纳米片及其药物载体应用

以Triton X-100 六角相溶致液晶作微反应器, 采用共沉淀法制备了镁铝层状双金属氢氧化物(LDHs)纳米薄片(L-LDHs). 以双氯芬酸钠(DS)为药物模型分子, 采用离子交换法制备了DS插层LDHs (DS/L-LDHs)纳米杂化物, 在37.0 ℃、pH=7.2的缓冲溶液中, 考察了纳米杂化物的药物释放性能, 并与传统溶液共沉淀法制备的镁铝LDHs (S-LDHs)纳米片状颗粒进行了对比. 采用粉末X射线衍射(XRD)、傅里叶变换红外(FT-IR)光谱、场发射扫描电镜(FE-SEM)、透射电镜(TEM)和N₂吸附-脱附等技术对所制备的LDHs和DS/LDHs 样品的晶体结构、比表面积、形貌特征等进行了表征. 结果表明, L-LDHs比S-LDHs具有更低的片厚度, 更高的比表面积和药物负载量, 所形成的DS/L-LDHs纳米杂化物药物释放速率也明显低于DS/S-LSHs, 即L-LDHs更适于作药物载体. DS/L-LDHs纳米杂化物的药物释放过程符合准二级动力学方程, 受颗粒内部扩散过程控制. 溶致液晶模板法可实现LDHs的形貌可控制备, 为LDHs基功能材料的研发提供了新途径.     

草酸共沉淀法制备YBCO粉体的热力学分析

采用草酸共沉淀法制备YBCO粉末,计算了不同pH值下草酸盐共沉淀粉末的沉淀率,并对制取YBCO前驱体粉末过程中的Ba(NO3)2-Y(NO3)3-Cu(NO3)2-H2C2O4-H2O体系进行热力学分析,采用XRD对制备的YBCO进行了分析计算。结果表明:溶液中不同草酸根离子浓度下各离子沉淀完全的最佳pH范围不同,当草酸浓度为0.1 mol·L-1,pH为2~6时,溶液中离子的沉淀率达到99%以上。随着草酸根离子浓度增大,完全沉淀时,共沉淀液中各金属离子所需的pH值范围增大。热力学计算与试验结果吻合。草酸共沉淀法制备的YBCO粉末物相纯度高,杂质少,颗粒细小,平均粒径为35.4 nm。     

微乳液和均匀沉淀耦合法制备CeO2纳米粒子

用W/O微乳液和草酸二甲酯均匀沉淀耦合法制备出单分散性好并具有较窄粒度分布的CeO2纳米粒子,测试了其形貌、粒径及粒径分布和晶体结构等特征.实验结果表明,表面活性剂的种类和反应物的相对初始浓度对产物平均粒径具有规律性的影响;随着焙烧温度升高,产物的平均粒径明显增大.     

YxTi2On(1.7≤x≤2.1)系固态电解质的共沉淀法合成及电导率研究

以TiCl3、YCl3溶液和氧化钛、氧化钇为原料,通过共沉淀法和固相法制备了YxTi2On(1.7≤x≤2.1,x=1.7,1.8,1.9,2.0,2.1)系烧绿石型固态电解质样品。粉体经700℃处理后在透射电镜下可见其粒径小于100 nm的晶粒。用共沉淀法制得的样品通过1500℃/5 h烧结后的相对密度近94%,且比用固相法经1550℃/5 h烧结所获相同组成样品的相对密度明显要高。X衍射表明样品A(x=1.7)的主晶相为烧绿石和二氧化钛,而样品D(x=2.0)和E(x=2.1)都为烧绿石。从扫描电镜照片可见,样品E的晶界随着烧结温度的提高变得更清晰,晶体生长也更充分。随着Y2O3含量的增加,YxTi2On(1.7≤x≤2.1)系电解质的电导率随之增加。用共沉淀法所得样品的电导率明显高于相应固相法所得样品。随烧结温度和测量温度的提高,样品E的电导率增加。     

新方法合成规则六角片状层状双金属氢氧化物

探索了一种合成规则的层状双金属氢氧化物(简称LDHs)六角纳米片的新方法,该方法基于传统的共沉淀法,并借鉴了尿素法的优点。 系统研究了沉淀剂、反应溶剂、反应时间和沉淀剂滴加速率对最终得到的粒子结晶度和形貌的影响。 研究结果表明,采用NH4OH为沉淀剂,以乙醇/水混合溶液为溶剂得到的LDHs纳米粒子结晶度高,晶型发育完美,呈现规则的六角片状,单分散性良好,粒径介于100~250 nm之间。 乙醇的加入一方面减慢了NH4OH电离出OH-的速率,降低了溶液过饱和度;另一方面,乙醇分子包裹在LDHs粒子周围,其表面的羟基起到了空间位阻作用,阻止粒子之间的团聚。 最佳反应时间既要保证LDHs晶粒的充分发育和成长,又要防止粒子之间的团聚。反应时间较短(1 h)时,晶粒发育不完全,粒子呈现不规则的六角片形;反应时间较长(4 h)时,LDHs粒子出现了六角片状重叠现象;只有当反应时间适中(3 h),LDHs粒子因晶胞生长充分而粒径分布均匀,并呈现规则六角片状。 沉淀剂滴加速率的不同会改变体系的过饱和度,从而影响LDHs粒子的形貌,滴加速率较低(0.025 mL/s)时,得到的粒子形貌规则、单分散性良好,且随着滴加速率的降低,粒子粒径逐渐增大。     

锂电池正极材料LiV3O8制备及电化学性能影响因素

采用溶胶-凝胶法制备锂离子电池正极材料LiV3O8,研究了LiOH溶液的浓度对LiV3O8的结构、粒径、电导率和电化学性能的影响。实验发现,LiV3O8衍射峰的强度、粒径与电导率可以通过改变LiOH溶液浓度来控制。测试了LiV3O8材料的结构、粒径分布和电化学性能。结果表明,随着LiOH溶液浓度的增加,样品的结晶度降低,晶粒的择优取向(100)晶面的衍射峰强度明显减弱;当LiOH溶液浓度为0.030 mol/L时,可以得到较为理想的粒径分布和较高的电导率为9.06×10-2s/cm;LiV3O8材料的容量及循环性能均与LiOH溶液浓度有关,选择0.030 mol/L的LiOH溶液时,样品的比容量最大为310 mA.h/g;循环15次后,容量衰减最少为4%。     

反相微乳液法制备LaMnAl11O19-α甲烷燃烧催化剂

 在反相微乳液中以碳酸铵共沉淀法制备了LaMnAl11O19-α 甲烷燃烧催化剂,比较了反相微乳液法与普通碳酸铵共沉淀法对催化剂相结构、比表面积、孔结构及其催化甲烷燃烧性能的影响. 结果表明,反相微乳液法制备的催化剂前驱体平均粒径为2.3 nm,而普通碳酸铵共沉淀法得到的催化剂前驱体平均粒径为30.1 nm. 在乙醇超临界干燥阶段,反相微乳液法制备的催化剂前驱体较容易发生铝羟基分子间脱水,形成较为丰富的孔,保持了各组分分布的均匀性,从而促进了六铝酸盐的形成,所得样品具有较大的比表面积和较高的催化甲烷燃烧的活性.     

络合法制备纳米硫酸钡及其影响因素的分析

以Na2SO4和BaCl2为原料,EDTA为络合剂,水为反应介质,采用络合法制备纳米BaSO4。并研究了反应物浓度、体系pH、反应温度、滴加速度和干燥方式等因素对产物粒径大小和粒径分布的影响。通过考察和分析,初步得出纳米BaSO4最佳制备条件为:反应温度为35℃,pH为6,3种反应物EDTA、BaCl2、Na2SO4的反应浓度均为0.5 mol/L。     

Sol-Gel and Ultrafine Particle Formation via Dielectric Tuning of Inorganic Salt-Alcohol-Water Solutions

Under some conditions, inorganic salts can be as good precursors for sol-gel-type processing as those obtained from expensive metalloorganic precursors such as alkoxides. In this work, the formation of monodispersed hydrous zirconia microsphere particles (particularly nanosized) and gels was achieved in solutions of zirconyl chloride dissolved in alcohol-water mixed solvents. The dielectric property of the mixed alcohol-water solvent directly affects the nucleation and growth of zirconia clusters/particles in homogeneous solutions. A lower dielectric constant of mixed solvent corresponds to a lower solubility of inorganic solute and, thus, a shorter induction period for nucleation as well as higher solid particle growth kinetics. Dynamic light scattering (DLS) was used to monitor the homogeneous nucleation and growth processes, while final particles and gels were studied by scanning electron microscopy (SEM) and high-temperature X-ray diffraction (HTXRD). The sol-gel processes in the mixed solvent system can be adjusted using the processing parameters, including the initial inorganic salt concentration (C), alcohol/aqueous medium volume ratio of the mixed solution (RH), incubation temperature (T), incubation time (t), concentration of hydroxypropyl cellulose (HPC), and ammonia neutralization. Monodispersed submicron and nanoscale (<100 nm) zirconia microspheres/powders were successfully synthesized under conditions of high RH (5) and using HPC (molecular weight of 100,000, 2.0x10(-3) g/cm(3)) and ammonia neutralization. Initial salt concentration affects the particle size significantly. Gel materials were obtained under conditions of low RH (1.0). Microstructure and transparency of gels changed significantly from low (0.05 M) to high (0.2 M) concentration of the metal salt. We have also demonstrated that monodispersed particle production can be achieved not only at low temperatures (<100 degrees C) but also at room temperature using an inorganic salt precursor. Copyright 2000 Academic Press.     

双羟基复合金属氧化物的晶面生长选择性及晶粒尺寸控制

采用成核／晶化隔离法合成镁铝双羟基复合金属氧化物（LDH）,考察了晶化温度及晶化时间对晶体结构,晶面生长选择性及晶粒尺寸的影响规律。结果发现晶化温度相同时,随晶化时间延长,LDH的晶体结构趋于完整,晶粒尺寸增大;晶化时间相同时,随晶化温度升高,晶体结构趋于完整,晶粒尺寸显著增大,实验条件下得到的LDH,其沿a轴方向的尺寸均大于沿c轴方向的尺寸,即共沿a轴方向的生长速率比沿c轴方向的生长速度快,亦即[110]晶面的生长速率比[003]晶面的生长速率快。根据LDH晶粒尺寸随晶化时间及晶化温度的变化规律,选择合适的晶化条件,制备得到了粒径分布窄的纳米LDH。     

Preparation of titania particles utilizing the insoluble phase interface in a microchannel reactor

A stable interface between two insoluble currents in a microchannel reactor has been obtained by selecting the solvents and adjusting the flow rate; titania particles with a size of less than 10 nm could be prepared continuously on this interface; this new method shows great advantage for the control and measurement of particle sizes.     

Kinetic study of heterogeneous reaction of deliquesced NaCl particles with gaseous HNO3 using particle-on-substrate stagnation flow reactor approach

Heterogeneous reaction kinetics of gaseous nitric acid with deliquesced sodium chloride particles NaCl(aq) + HNO3(g) --> NaNO3(aq) + HCl(g) were investigated with a novel particle-on-substrate stagnation flow reactor (PS-SFR) approach under conditions, including particle size, relative humidity, and reaction time, directly relevant to the atmospheric chemistry of sea salt particles. Particles deposited onto an electron microscopy grid substrate were exposed to the reacting gas at atmospheric pressure and room temperature by impingement via a stagnation flow inside the reactor. The reactor design and choice of flow parameters were guided by computational fluid dynamics to ensure uniformity of the diffusion flux to all particles undergoing reaction. The reaction kinetics was followed by observing chloride depletion in the particles by computer-controlled scanning electron microscopy with energy-dispersive X-ray analysis (CCSEM/EDX). The validity of the current approach was examined first by conducting experiments with median dry particle diameter D(p) = 0.82 microm, 80% relative humidity, particle loading densities 4 x 10(4) 相似文献   

Influence of Operating Conditions on BaSO4 Crystal Size and Morphology in a Continuous Couette Precipitator

Precipitation of a sparingly soluble salt in the annular gap of a continuous Couette reactor with two unpremixed feeds has been experimentally investigated. Barium chloride and sodium sulphate in stoichiometric ratio are fed at different flow rate in the lower part of the reactor; different feeding modes have been considered. The dependence of precipitation yield, mean crystal size and particle size distribution on rotation speed, axial flow rate and initial supersaturation ratio has been studied. Depending on the operating conditions crystals with different morphologies have been obtained, varying from dentritic tabular crystals to complex pyramidal ones and from single crystals to aggregates. This revised version was published online in August 2006 with corrections to the Cover Date.     

Studies on fluoride adsorption capacities of amorphous Fe/Al mixed hydroxides from aqueous solutions

This study evaluated the effectiveness of amorphous iron and aluminum mixed hydroxides in removing fluoride from aqueous solutions. A series of mixed Fe/Al samples were prepared at room temperature by co-precipitating Fe and Al mixed salt solutions at pH 7.5. The compositions (Fe:Al molar ratio) of the oxides were varied as 1:0, 3:1, 2:1, 1:1 and 0:1 and the samples were characterized by XRD, BET surface area and pH_ZPC. The XRD studies indicated the amorphous nature of the samples and Al(III) incorporation on Fe(III) hydroxides. Batch adsorption studies for fluoride removal on these materials showed that the adsorption capacities of the materials were highly influenced by solution pH, temperature and initial fluoride concentration. The rate of adsorption was fast and equilibrium was attained within 2 h. The adsorption followed first-order kinetics with intraparticle diffusion as the rate determining step for all the samples. The experimental data fitted well to both Langmuir and Freundlich adsorption isotherms. All samples exhibited very high Langmuir adsorption capacities; the sample with molar ratio 1 has shown maximum adsorption capacity of 91.7 mg/g. The thermodynamic parameters were determined to study the feasibility of the adsorption process.     

水热法合成高功率锂离子二次电池用球形Li4Ti5O12负极材料

以球形TiO2和LiOH溶液为反应物,通过水热法合成了尖晶石型Li4Ti5O12,并使用X射线衍射(XRD)、傅里叶变换红外(FTIR)光谱、扫描电镜(SEM)和激光粒度分布(PSD)对其结构、形貌和电化学性能进行了表征.结果表明:通过该法得到的产品颗粒大小均匀,粒度分布狭窄,结构与标准Li4Ti5O12谱图一致.实验选定温度下所得的Li4Ti5O12均表现出良好的电化学性能.其中,800°C热处理所得样品的电化学性能最好,室温下,以35mA·g-1的电流密度进行充放电,其可逆容量达到162mAh·g-1,同时这种材料也表现出良好的倍率性能,即使在720mA·g-1的电流密度条件下进行充放电,其可逆容量仍可达到124mAh·g-1.     

Emulsion polymerization of styrene in a single continuous stirred-tank reactor

The effects of mean residence time, initiation rate, and emulsifier concentration on particle formation, particle growth, and polymerization rate are examined for the emulsion polymerization of styrene in a completely mixed continuous stirred-tank reactor. Experimental measurements of number of particles, particle size distribution, polymerization rate, and molecular weights are compared with theoretical predictions. A theoretical model which incorporates Stockmayer's modification of the Smith-Ewart theory into the particle growth equation allows reasonably accurate prediction of polymerization rate, particle formation rate, and particle size distribution. Agreement between experimental measurements of number-average and weight-average molecular weights and a theory based on Smith-Ewart case 2 kinetics is also reasonable.