DRYING OF Y-Ba-Cu-O COMPLEX OXIDE SUSPENSION BY SUPERCRITICAL CARBON DIOXIDE

Abstract

Fine and homogeneous powders of Y-Ba-Cu complex oxides are necessary to improve the quality of YBCO bulk high temperature superconductors. The powders which contain BaCO₃ must be sintered for producing YBCO super-conductors at temperature above 850 °C. Therefore, complex oxide is desired. In order to prepare fine complex oxides powders, suspension was synthesized by simultaneous hydrolization of 2-propanol solution of metal isopropoxides. However, the suspension was not dried by a hot air drying method, because aggregation occurs due to cohesion of particle along with evaporation. Also, the suspension could not be freeze-dried, because the freezing point of 2-propanol is ?88.5°C. So, supercritical fluid drying method using supercritical carbon dioxide was applied. The results from these experiments suggest that this method is useful for drying of the suspension prepared by the alkoxide route.     

DRYING OF Y-Ba-Cu-O COMPLEX OXIDE SUSPENSION BY SUPERCRITICAL CARBON DIOXIDE

Fine and homogeneous powders of Y-Ba-Cu complex oxides are necessary to improve the quality of YBCO bulk high temperature superconductors. The powders which contain BaCO₃ must be sintered for producing YBCO super-conductors at temperature above 850 °C. Therefore, complex oxide is desired. In order to prepare fine complex oxides powders, suspension was synthesized by simultaneous hydrolization of 2-propanol solution of metal isopropoxides. However, the suspension was not dried by a hot air drying method, because aggregation occurs due to cohesion of particle along with evaporation. Also, the suspension could not be freeze-dried, because the freezing point of 2-propanol is -88.5°C. So, supercritical fluid drying method using supercritical carbon dioxide was applied. The results from these experiments suggest that this method is useful for drying of the suspension prepared by the alkoxide route.     

乙醇超临界干燥制备二氧化锰超细粉体

以MnCl2和NaOH为原料,利用超临界流体干燥技术(SCFD)制备了MnO2超细粉 体,采用X-射线衍射、粒度分析和扫描电镜确定了粒子的形貌和粒径,结果表明,采用超临界流 体干燥技术可以制备出颗粒细、大小均匀的纳米粒子。     

超临界流体干燥二氧化锰超细粉体的研制与表征

以MnCl2和NaOH为原料,利用超临界流体干燥技术(SCFD)制备了MnO2超细粉体,研究和讨论了反应温度、反应物浓度、反应时间等对实验结果的影响,确定了最佳反应条件.XRD物相分析,产物为γ-MnO2,透射电镜和粒度分析仪观察,粒子基本为球形,平均粒径60nm,没有明显的团聚现象.     

Convective Drying Kinetics of Single Droplets of Aqueous Glucose

The convective drying kinetics of single droplets of aqueous glucose was measured using a single droplet drying rig. The effects of air temperature and velocity were evaluated. It was found that the droplet of aqueous glucose shrank uniformly, retaining a nearly spherical shape during drying. The normalized volume (d/d₀)³ of the droplet decreased linearly with its moisture content. A constant-drying-rate-like period occurred when the moisture content of the droplet was higher than an amount of about 1.0 kg kg^?1 dry solid. The diameter of the droplet decreased sharply due to the evaporation of water, while its temperature remained at a wet-bulb-like temperature in this period. When the moisture content of the droplet was lower than the above-mentioned value, the drying transferred to a falling-drying-rate-period, during which the temperature of the droplet rose quickly and approached the air temperature as drying continued. The effect of air temperature on the drying of single droplets of aqueous glucose was more pronounced when compared with that of air velocity.     

Spouted Beds of Inert Particles for Drying Suspension

A brief review of Brazilian research on drying process in spouted beds shows its relevance and evolution trends. Needs for applying this technique to dry pasty materials are discussed, focusing on a new model approach in order to overcome operational problems with particle agglomeration and with thermal efficiency. Based on this approach, two cases, drying of black liquor in a conical spouted bed of inert polypropylene particles under intermittent operation and drying of egg emulsion in a conical spouted bed of inert glass beads under continuous operation, are presented and analyzed.     

Spouted Beds of Inert Particles for Drying Suspension

ABSTRACT

A brief review of Brazilian research on drying process in spouted beds shows its relevance and evolution trends. Needs for applying this technique to dry pasty materials are discussed, focusing on a new model approach in order to overcome operational problems with particle agglomeration and with thermal efficiency. Based on this approach, two cases, drying of black liquor in a conical spouted bed of inert polypropylene particles under intermittent operation and drying of egg emulsion in a conical spouted bed of inert glass beads under continuous operation, are presented and analyzed.     

陶瓷粉体常用的干燥方法

详细叙述了陶瓷粉体采用的热风干燥、红外线干燥、喷雾干燥、冰冻干燥等干燥方法,分析了各种干燥方法的优缺点。在实际应用中,可根据不同的陶瓷粉体选择相适应的干燥方法,以便能获得理想的干燥效果。     

超临界流体干燥技术制备纳米二氧化锰

采用溶胶法和超临界流体干燥技术，在533K，7．6MPa的条件下，用超临界乙醇作为干燥剂制备纳米级二氧化锰，采用X射线衍射，透射电镜确定了二氧化锰粒子的行貌和粒径，结果表明，用超临界流体干燥技术可以得到颗粒细，大小均匀，抗团聚非常好的纳米粒子。     

Final Drying of Whole Milk Powder in Vibrated-Fluidized Beds

Abstract

Vibro-fluidized beds are widely used in drying sticky powders and agglomerated materials as milk powder. Using a vibro-fluidized laboratory scale dryer, this work is aiming at analyzing preliminarily the effect of its operational variables on the drying kinetics and characteristics of whole milk powder. The full-factorial design technique with three replications at the central point has been employed to generate data and correlations to quantify the effect of inlet air temperature, air flow rate, and vibration bed amplitude on the drying curves and the milk powder properties related to its faster reconstitution in water (as tapped density, Hausner cohesion ratio, agglomerate size distribution, and internal pore concentration). Results obtained are analyzed and discussed to identify the adequate operation condition for final drying whole milk powder in vibro-fluidized beds, assuring a high product quality.     

Final Drying of Whole Milk Powder in Vibrated-Fluidized Beds

Vibro-fluidized beds are widely used in drying sticky powders and agglomerated materials as milk powder. Using a vibro-fluidized laboratory scale dryer, this work is aiming at analyzing preliminarily the effect of its operational variables on the drying kinetics and characteristics of whole milk powder. The full-factorial design technique with three replications at the central point has been employed to generate data and correlations to quantify the effect of inlet air temperature, air flow rate, and vibration bed amplitude on the drying curves and the milk powder properties related to its faster reconstitution in water (as tapped density, Hausner cohesion ratio, agglomerate size distribution, and internal pore concentration). Results obtained are analyzed and discussed to identify the adequate operation condition for final drying whole milk powder in vibro-fluidized beds, assuring a high product quality.     

超临界流体制备超微粉体的研究进展

超临界流体制备超微粉体是一项新技术，利用超临界流体较好的溶解、扩散和传输能力，能制备出高质量的超微粉体，根据其工艺原理可分为：超临界流体快速膨胀法（RESS），超临界流体脱溶剂法（GAS）和超临界流体微乳法，本文对RESS，GAS和超临界流体微乳法制备超微粉体的原理进行了总结，并对这3种方法在食品、医药、化工材料等领域中的研究现状进行了介绍。     

Supercritical Fluid Extraction of Ethylene Oxide from Its Aqueous Solution

The mutual solubility of ethylene oxide and supercritical carbon dioxide was studied at T = 308 K in the pressure range P = 4.2–20 MPa, and the phase distribution of ethylene oxide in the water–ethylene oxide–supercritical carbon dioxide system was investigated at T = 308 and 323 K and P = 7.3–20.0 MPa.     

聚丙烯粉料干燥效果差的原因与措施

介绍了环管法聚丙烯装置干燥单元的工艺流程和原理。对造成粉料干燥效果差的因素,如洗涤后的氮气温度、汽蒸罐中粉料的湿含量、干燥停留时间、干燥氮气流量和温度、干燥器故障,作了详细的分析。并针对车间产品干燥中出现过的一些问题,提出了干燥系统优良运行的操作措施。     

Storage stability and mechanism of polyvinyl pyrrolidone based alkoxide composite electrospun fibres

Abstract

Polyvinyl pyrrolidone (PVP) based titanium n-butoxide (TNBT) and zirconium n-propoxide (ZNP) composite fibres were prepared by electrospinning, and the corresponding fibres with the addition of acetic acid (HAc) were also prepared for comparison. The storage stabilities of four alkoxide composite fibres and PVP electrospun fibres under standard laboratory conditions (20°C, 65% relative humidity) were investigated. Some unexpected but interesting phenomena were discovered. Electrospun PVP fibres lose their fibrous shapes after they have been stored for only 24 h. The TNBT, ZNP and ZNP(HAc) composite fibres still remain their morphologies even though they have been stored for 15 days, exhibiting excellent chemical and morphological stability in the air, because the hydrolysis and condensation of alkoxide have completed during the electrospinning process, while TBNT(HAc) composite fibres hydrolyse and condense during the storage period. This investigation provides useful knowledge for preparing ceramic electrospun fibres, especially for large scale production or electrospinning over extended time.     

银杏叶提取物的超临界流体干燥实验研究

银杏叶提取物是一种天然保健产品。传统的冷冻干燥或者喷雾干燥对于保健品品质均有不同程度的破坏。通过L25 5^5正交试验设计,研究银杏叶提取物超临界流体干燥中超临界流体的压力、温度、流量以及干燥时间和提取物初始固含量等参数对于产品中残留溶剂的影响;根据正交试验结果分析得出了优化的工艺参数,并根据优化参数的校核试验验证了所得的相关结论。     

超临界流体干燥法制备纳米掺锑氧化锡粉体

以SnCl4.5H2O和SbCl3乙醇溶液为原料制备前驱体掺锑氢氧化锡胶体沉淀,采用乙醇超临界流体干燥法干燥前驱体;用TG-DTA、XRD、TEM、BET等方法对粉体的结构、物相、形貌进行表征。结果表明,采用乙醇超临界流体干燥法可得到高比表面积的掺锑氧化锡纳米粉体。     

纳米二氧化硅水性浆料的研制

通过分散剂表面改性的方法．应用高速机械搅拌，高剪切砂磨和超声波分散等多种分散手段．制备了亲水型和疏水型两种类型纳米SiO2的水性浆料，通过常温沉降实验、Zeta电位测试以及透射电镜观察．研究了分散剂类型，用量、润湿剂类型．pH值、水性树脂和分散手段等多种因素对纳米SiO2水性浆料分散稳定性的影响。在最佳分散剂．润湿剂、pH值和加入水性树脂的条件下．通过砂磨和超声波分散相结合的手段．制得了分散稳定性良好的纳米SiO2水性浆料。     

Effects of Wood Drying Schedules on Fluid Flow in Paulownia Wood

Effects of three drying schedules on fluid flow were studied in the sapwood and heartwood of Paulownia wood (Paulownia fortunei). Boards with a commercial thickness of 5 cm were randomly dried to a final moisture content of 8 ± 2% using a mild (T₆E₃), a moderate (T₆E₄), and a severe (T₇E₄) drying schedule. Permeability measurement was carried out when specimens reached the final moisture content. Results showed a significant difference in the specific gas permeability as well as liquid permeability of the boards dried under the three drying schedules. Furthermore, a significant difference was observed in the gas permeability of sapwood and heartwood, dried under the different schedules, but not much significant difference was seen in the liquid permeability between sapwood and heartwood. T₆E₃ had the highest liquid permeability; furthermore, it was reported to have resulted in the lowest warping and most homogeneous moisture profile. This mild schedule is therefore recommended for commercial drying of Paulownia wood when further preservation and impregnation processes are planned for the dried boards. In the meantime, it is concluded that the age and drying schedule have significant effects on the formation of tyloses, significantly affecting gas and liquid permeability in Paulownia wood.     

氧化铝粉体在水悬浮液中的分散特性研究

采用Zeta电位表征Al_2O_3粉在悬浮液中的分散特性,研究了超声波分散时间、不同粒度Al_2O_3粉以及分散剂六偏磷酸钠的浓度和Al_2O_3粉体悬浮液pH值对Al_2O_3粉体Zeta电位的影响.研究结果表明:Zeta电位绝对值随超声波作用时间发生明显变化,在一定条件下存在一个最佳分散时间为4～6 min;悬浮液中Al_2O_3粉体颗粒的粒度对悬浮液的Zeta电位有重要影响;在Al_2O_3粉体悬浮液中添加分散剂六偏磷酸钠,Zeta电位随其浓度发生变化,存在一个最佳浓度0.5%;在不同pH值下,Al_2O_3粉体悬浮液的Zeta电位不同,在碱性条件下,粉体的分散性较好,且碱性越强,分散性越好.