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1.
The absorption of oxygen into aqueous alkaline suspensions of ferrous hydroxide leading to formation of extremely fine goethite and magnetite particles was performed using a bubble column with draft tube. The overall oxidation rates in both the systems were found to be promoted by the solid dissolution in the liquid film around a gas bubble even in this gas dispersed equipment, and were compared with prediction on the basis of a film-theory model incorporating the diffusion, the chemical reaction and the solid dissolution as the parallel steps. The trend of augmentation of the enhancement factor due to the solid dissolution could be represented by this modified model.  相似文献   

2.
The kinetics for oxidation of an aqueous alkaline suspension of ferrous hydroxide leading to formation of fine goethite particles was reconfirmed. The mean size of the needle-like goethite particles can be correlated well to the oxidation rate. Phenomenologically, host nuclei are generated in the early stage of the reaction, and afterwards particle growth mainly occurs through hydrolysis of ferric hydroxo-complex (intermediate species) with the number of host nuclei held almost constant. The particle size can be expected to be approximately governed by the number of host nuclei generated in the early stage of the reaction and the initial concentration of total Fe(II). By shifting the oxygen concentration in the feed stream to a lower level at a low conversion, the size distribution of the prepared particles becomes narrow.  相似文献   

3.
Acicular goethite particles were synthesized by oxidation of an alkaline suspension of ferrous hydroxide using a bubble column with draft tubes of different diameters at a constant temperature of 40°C. The oxidation rate increased with decreasing draft tube diameter. The mean size based on the major axis of acicular particle decreased with increasing oxidation rate and decreasing draft tube diameter. The major axis was found to grow preferentially compared with the minor axis. The mean size of major axis was correlated well to the modified reaction rate defined as a product of the reaction rate per unit volume of the reactor multiplied by the ratio of the column diameter to the draft tube diameter, irrespective of the draft tube diameter.  相似文献   

4.
Needle-like goethite particles were synthesized by air oxidation of an alkaline suspension of ferrous hydroxide using a standard-type bubble column of 10cm in internal diameter and 64 cm in height at a constant temperature of 40°C. Specifically, the effect of aging step by N2 stream prior to the oxidation step was investigated on both the oxidation rate and the final particle size based on the major axis of needle-like goethite particle. The time dependence of the fractional oxidation of total ferrous species with incorporated aging step exceeded that in the absence of aging step. The velocity of N2 in the aging step had negligible influence on the time dependence of the fractional oxidation. For the aging period exceeding 30min, the mean particle size was almost independent of the aging period. The mean size could be correlated considerably well with the oxidation rate, that is, decreased with increasing oxidation rate with and without incorporated aging step.  相似文献   

5.
超临界流体溶液快速膨胀法制备灰黄霉素微细颗粒   总被引:33,自引:1,他引:33       下载免费PDF全文
研究了通过超临界流体溶液快速膨胀 (RESS)技术制取灰黄霉素微细颗粒的过程 .在自行设计的实验装置上研究了RESS过程各操作变量对所制得的灰黄霉素颗粒粒度的影响 .研究结果表明 ,采用RESS方法可以制得符合粒度要求的灰黄霉素微细化产品  相似文献   

6.
单一尺寸球形氢氧化铝颗粒的形成及其机理   总被引:4,自引:0,他引:4  
用尿素均相沉淀法首次制得了单一尺寸的球形氢氧化铝颗粒。为获得单一尺寸的颗粒,需仔细控制沉淀过程:如温度、保温时间及Al~(3+)的浓度。在沉淀过程中通过对溶液pH值的测量,研究了单一尺寸颗粒的形成机制。氢氧化铝的成核极限仅达到一次,可形成单一尺寸的颗粒。相反,如溶液多次达到成核极限,则导致颗粒的多尺寸分布。另外,影响单一尺寸形成的因素尚有阴离子种类等。  相似文献   

7.
ABSTRACT

Fine particles of Tio2 were prepared from titanyl sulfate solution by the Spray pyrolysis Method( SPM) The reaction tube was divided into four zones: drying, dehydration, pyrolysis 1 and pyrolysis 2 zones. Under various reaction temperature and carrier gas flow rate, the mean size and the size distribution of particles collected at different sampling positions along the axial direction of the reactor were compared. The effects of operating conditions of drying, dehydration and subsequent pyrolysis steps on the formation mechanism of Tio2 fine particles were discussed  相似文献   

8.
分散剂在醇-水溶液加热法制备球形 ZrO2粉体过程中的作用   总被引:14,自引:4,他引:14  
李蔚  王浚  高濂 《硅酸盐学报》2000,28(6):582-584
本工作对分散剂在醇-水溶液加热法制备球形ZrO2粉体过程中的作用进行了研究。研究结果表明:在异丙醇-水溶液加热法制备球形ZrO2粉体时,聚合物分散剂起着明显的作用。当无分散剂加入时,所得ZrO2颗粒无规则且团聚严重;而当溶液中加入PEI(polyethyleneimine)时,可获得球形ZrO2颗粒,与加入PEI相比,加入NH4PAA或PEG所得ZrO2颗粒形状不够完整且团聚较多,这一区别可由聚合物分散剂在ZrO2颗粒上的吸附情况的不同得到初步解释。  相似文献   

9.
The theory of gas absorption accompanied by fast pseudo-fast order reaction which considered dependences of diffusivity, kinetic constant and Henry's law constant on absolute temperature and ionic strength was used to obtain values of effective interfacial areas and mass transfer coefficients in gas and liquid phase.

Experimental measurement of carbon dioxide absorption from mixture with air was performed in a pilot-plant column with expanded metal sheet packing irrigated with sodium hydroxide solution.

Resulting liquid and gas-side mass transfer coefficients are compared with values obtained from physical Absorption measurement of carbon dioxide into water and with measurement of gas-side mass transfer coefficient for sulphur dioxide in the same column.

The differences between determined values are discussed.  相似文献   


10.
The theory of gas absorption accompanied by fast pseudo-fast order reaction which considered dependences of diffusivity, kinetic constant and Henry's law constant on absolute temperature and ionic strength was used to obtain values of effective interfacial areas and mass transfer coefficients in gas and liquid phase.

Experimental measurement of carbon dioxide absorption from mixture with air was performed in a pilot-plant column with expanded metal sheet packing irrigated with sodium hydroxide solution.

Resulting liquid and gas-side mass transfer coefficients are compared with values obtained from physical Absorption measurement of carbon dioxide into water and with measurement of gas-side mass transfer coefficient for sulphur dioxide in the same column.

The differences between determined values are discussed.  相似文献   

11.
化学气相沉积碳化硅涂层缺陷形成的机制及控制   总被引:3,自引:2,他引:1  
利用扫描电镜对化学气相沉积碳化硅防氧化涂层的表面和断口进行观察,探讨了涂层裂纹、涂层网状缺陷和涂层面缺陷的形成机理。从涂层沉积工艺角度出发,对涂层缺陷控制进行探索,慢速沉积对上述涂层缺陷,特别是面缺陷的控制有显著效果,能获得无面缺陷的多层涂层。氧化实验结果表明:具有慢沉积多层涂层的三维C/SiC在1300℃空气中表现为缓慢的氧化质量增加。  相似文献   

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