The Chinese Journal of Process Engineering

Identification of Anamorph Yeast of Tremella aurantialba and Optimization of Medium Composition for Production of Exopolysaccharides

LIU Chun-hui YANG Xiu-wei YU Jian-guo MA Wei-xin QU Wei-jing BAO Yan-jie WU Wen-bin ZHUANG Xiu-yuan

. 2012, 12(6): 0-0.

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A yeast-like fungus strain B1 isolated from wild fungus Tremella aurantialba was identified and initially characterized. Two phylogenetic trees were generated based on the sequences of large subunit ribosomal RNA gene D1/D2 regions and internal transcribed spacer (ITS) regions of related fungi, respectively. The analysis of D1/D2 regions and ITS sequences showed that fungus B1 was clustered together with T. aurantialba, T. aurantia and T. microspore in the phylogenetic trees. Both the morphological characteristic and phylogenetic analysis established that fungus B1 was one of the anamorph strains of T. aurantialba and belongs to Tremella genus. A fermentation medium for exopolysaccharides (EPS) production by T. aurantialba B1. Plackett-Burmen design was used to evaluate the effects of different components in the culture medium. Glucose and yeast extract have significant influence on the EPS production. The concentrations of two factors were optimized subsequently using central composite design and response surface analysis. The results showed that 49.2 g/L glucose and 10.4 g/L yeast extract could lead to the maximum production of EPS (4.99 g/L). The optimized medium led to a 1.5-fold enhancement of the production of EPS by T. aurantialba B1, as compared with that without optimization.

Multi-objective Optimization of Burner Arrangement in a Regenerative Aluminum Melting Furnace Based on Non-dominated Sorting Genetic Algorithm-II

WANG Ji-min; YAN Hong-jie ZHOU Jie-min LI Shi-xuan; GUI Guang-chen;

. 2012, 12(6): 901-908.

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Based on the features of melting process of regenerative aluminum melting furnaces, a mathematical model with user-developed burner reversing and burning capacity model and melting model, was established. Based on validating results by heat balance test for an aluminum melting furnace, CFD software FLUENT was used to simulate the coupling field between aluminum bath and combustion space. Considering influence analysis of burner arrangement on the performance of regenerative aluminum melting furnace, the relationship between burner arrangement and evaluation criteria was built using non-linear regression. Non-dominated sorting genetic algorithm-II was used to deal with multi-objective optimization for burner arrangement. The results show that the minimum RSD (relative standard deviation) of aluminum temperature (2.65%), dimensionless melting time (0.82) and RSD of furnace temperature (14.03%) could be obtained under the optimum conditions of vertical angle of burner 23.56o, height of burner 1471.81 mm, and horizontal angle between burners 62.05o.

Experimental Study on the Flow Field in Cryogenic Taylor Bubble Wake in an Inclined Pipe

LIU Yi-peng ZHAO Xian-lin WANG Ping-yang LIN Shuai-nan DU Zhao-hui

. 2012, 12(6): 909-916.

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In order to investigate the complex characteristics in the wake of Taylor bubble in cryogenic liquid tube flow, the flow field in the wake was measured using particle image velocimetry (PIV) technique. The PIV measurement results were further analyzed by snapshot proper orthogonal decomposition (POD). The criterion for determining the wake structure using inverse viscosity number Nf is applicable for liquid nitrogen if surface tension effect can be neglected in a vertical tube, but not applicable for the tube at the inclination of 60o to the horizontal. The Nf number of present experiment is much larger than the critical value for the occurrence of an open wake. However, a closed wake was observed both in instantaneous and average flow field as q being above 60o. The axial size of vortex in the wake (Lwake) increases with the increase of Taylor bubble length (LTB) in an exponential function of Lwake= 51.3-123.5exp(-LTB/2.9). POD analysis shows that the first several POD modes can effectively capture the main features in Taylor bubble wake. The first 4 modes occupy the 15.6%, 6.4%, 5.6% and 3.8% of total energy. The vortexes distribution coincides with the maximum velocity fluctuation. The present study explores the scope of the theory for normal atmospheric temperature liquid.

Statistical Characteristics of Taylor Bubbles in Cryogenic Gas-Liquid Slug Flow?I. Taylor Bubble Length

LIU Yi-peng ZHAO Xian-lin WANG Ping-yang LIN Shuai-nan DU Zhao-hui

. 2012, 12(6): 917-924.

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The effects of inclination angle (q) and tube inner diameter on the Taylor bubble length in cryogenic gas-liquid slug flow were experimentally studied using high speed digital camera within four different test tubes under six different inclination angles. The results show that the length distribution of cryogenic Taylor bubbles fits to lognormal function. The standard deviation of Taylor bubble length is influenced by the jet from liquid film. It increases first and then decreases with the decrease of q. The mean value of dimensionless Taylor bubble length linearly increases with the increase of the tube axial position, and gradually decreases with the increase of tube inner diameter. The linear and exponential functions give satisfactory fitting results. Overall the dimensionless Taylor bubble length increases with q, and its minimum value occurs in the region of 70o≤q≤90o.

Numerical Simulation of Flow Field in a Slab Continuous Casting Mold

LI Ji-yong ZHANG Li-feng WANG Qiang-qiang

. 2012, 12(6): 925-932.

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A three-dimensional steady-state fluid flow in a 1300 mm×230 mm continuous casting slab mold was simulated using FLUENT to evaluate the performance of a submerged entry nozzle (SEN) and the effects of casting speed and SEN submergence depth on the fluid flow in the mold. The surface velocity and jet impingement depth were calculated and compared. The results show that under the action of nozzle A, the flow field in the mold has a higher surface velocity, smaller jet impingement depth and bigger level fluctuation, slag entrapment happens more easily. And this effect will be enhanced with increasing of casting speed. With increasing of casting speed, the maximum surface velocity in the mold gradually increases at 0.06 m/s, the jet impingement depth tends to be smaller. Under three different submergence depths of 150, 170 and 190 mm, the maximum surface velocity is 0.599, 0.518 and 0.465 m/s, and the impingement depth of the jet 385, 410 and 420 mm, respectively. With increasing of the submergence depth of SEN, the surface velocity becomes lower, the jet impingement depth bigger. In the actual production process, a lower casting speed and bigger submergence depth are recommended for nozzle A. For the persuit of high casting speed, a parallel nozzle is needed rather than nozzle A.

Performance of Rotary Valve Used in a Pulsed Extraction Column

LI Shao-wei LIU Ji-lian JING Shan

. 2012, 12(6): 933-939.

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The pulse generation process of the rotary valve pulse generator used in pulsed extraction column was theoretically analyzed and studied. The theoretical model including the inflating and deflating through the rotary valve and the location variation of liquid surface due to the effect of pulsed gas in the pulse leg was derived. The experimental results of single phase flow, which is produced by the large-scale rotary valve pulse generator used in the no-plate extraction column with the inertial diameter of 0.3 m and height of 5.6 m, are in good agreement with those calculated by the theoretical model.

Numerical Simulation of Transient Molten Steel Flow Phenomena during Casting Start Period in a Compact Strip Production Funnel-type Mould

XU Mian-guang LIU He-ping QIU Sheng-tao

. 2012, 12(6): 940-945.

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A three-dimensional mathematical model was built to study the transient molten steel flow phenomena during the casting start period in the compact strip production (CSP) process. An algorithm of volume of fluid (VOF) was used to simulate the air-steel interface. The obtained numerical results were validated by those available in the literature. The results show that at the beginning of filling process, the droplets separated from the jet of molten steel and sputtering by the jet impacting on the free surface of molten steel may contact with the mould copper plate. At the beginning of movement of the dummy bar, there exists serious fluctuation in the meniscus and the maximum wave height is about 25 mm. During the casting start process, the stabilization of free surface may need 80.0 s after moving of the dummy bar and when the meniscus is stable, there still exists flow deviation of molten steel in the funnel-type mould. When the molten steel surface is stable, the dummy bar is 3 m or so far away from the meniscus.

Numerical Simulation of Three-phase Fluid Flow in a Bottom-blown Steelmaking Ladle

ZHANG Jiang-shan LI Jing-she YANG Jing-bo LIU Hong-wei TONG Zh-xin

. 2012, 12(6): 946-951.

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Multiphase volume of fluid (VOF) method was used to simulate argon-steel-slag three-phase flow in a bottom-blown steelmaking ladle. Transient multiphase flow features in the ladle were described and compared with steady simulation. Slag eye diameter and droplet dispersion height were quantified under different gas flow rates, showing that as gas flow rate rose, slag eye diameter and slag droplet dispersion height increased and jumped at 600 L/min, so critical gas flow rate was 600 L/min. Slag eye diameter dropped sharply from 455 to 110 mm, and the possibility of slag entrapment increased, when the slag layer height rose from 150 to 300 mm at the gas flow rate of 300 L/min.

Effect of Electromagnetic Field Intensity on Laminar Flame and NO Generation Characteristics

CHEN Wei-peng ZHU Bing-shen SHI Qing-xiang ZHAO Zeng-wu LI Bao-wei WU Wen-fei

. 2012, 12(6): 952-956.

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The electromagnetic field was placed on both sides of the laminar flame from combustion of liquefied gas and air, and the magnetic-field intensity measured. The laminar free jet flame temperature was detected with rhodium-doubled thermocouple and the NO concentration measured. The laminar free jet flame and NO generation characteristics under different intensity electromagnetic field were analyzed. The results show that the electromagnetic field makes the flame length shorten and the bottom diameter of flame increase. With the increase of electromagnetic field intensity, the temperature of flame bottom rises. Moreover, the electromagnetic field can change the probability of collision among ions or ion groups, such as N, HCN and CN, and oxygen, which results in the decrease of NO concentration. The electromagnetic field makes the maximum NO concentration reduce 4.26 mg/m3 and 78.60%.

Reaction Characteristics of Removal of Tin from Tin-bearing Iron Concentrate by Sulfidation Roasting

QIU Zai-jun LI Lei WANG Hua WEI Yong-gang LIAO Bin

. 2012, 12(6): 957-961.

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The reaction characteristic of tin removal from tin-bearing iron concentrate by sulfidation roasting was studied. The sulfidation roasting process includes two parts: reduction and sulphuration volatilization. The reaction system should be controlled at weak reductive atmosphere for promoting tin volatilization. The TG-DSC analysis results of pyrite show that a liquid phase is generated in the bulk with increasing of temperature to 1150℃, and the roasting temperature should be kept at around 1150℃ to promote the sulphuration volatilization of tin. XRD analysis results show that the original iron phases of Fe3O4 and Fe2O3 are transformed into FeO and metallic iron after the sulfidation roasting of pyrite, tin-bearing iron concentrate and coal. When the temperature is increased, FeO and metallic iron contents are increased significantly, and the process realizes the iron prereduction of concentrate. The kinetic analysis results show that the apparent activation energy of tin removal reaction is 13.96 kJ/mol, and the reaction limiting step the mass transfer of reactants.

Simulation of Efficient Low NOx Combustion-supporting Technology by Local Oxygen Enrichment in a Pulverized Coal Boiler

XIANG Yu-hua ZHANG Jia-yuan ZHANG Xiao-hui

. 2012, 12(6): 962-967.

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To solve the problems such as low thermal efficiency, high NOx emission and slag bonding in a 150 t/h pulverized coal boiler, A new idea was proposed to use enriched-oxygen air as the over flame air and welted edge air. Using k-e- -g turbulence combustion model for computation of the gas phase and two competing reactions for coal devolatilization, the flow and temperature fields and NOx emission in the boiler were simulated. After the oxygen-enriched combustion technology was used, the boiler combustion efficiency was above 96% and the efficiency over 91.40%, the NOx emission was 625~763 mg/m3, the slagging phenomenon did not occur on the furnace water-cooled wall and superheater.

Preparation of Mn-containing Electrolysis Solution from the Manganese Oxide Ore with High Content Phosphorus and Iron by Sulfation Roasting and Aqueous Leaching

YUAN Ming-liang SONG Cong

. 2012, 12(6): 968-972.

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In order to overcome the shortcomings of traditional methods, the method of sulfation roasting and leaching of manganese oxide ore was used to prepare manganese-containing electrolysis solution, wherein the ore and pyrite were roasted at high temperature, making the tetravalent manganese become water-soluble divalent manganese. Meanwhile, the sulfation process was completed in the roasting process, so the roasted clinker could be directly leached by water, abandoning the traditional process of acid leaching. Through the experiments, the molar ratio of S to Mn at 3, roasting temperature 600℃, and roasting time 270 min were set as the optimum conditions. The leaching rate of Mn reached 85.6% under the conditions, indicating that the present method is entirely feasible.

Preparation and Characterization of Toltrazuil-Hydroxypropyl-β-cyclodextrin Inclusion Complex

LU Chao-cheng YANG Jing ZHANG Wei HU Jun ZHOU Tao JIN Chao FU Hua-lin

. 2012, 12(6): 982-988.

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The complexation of Toltrazuril (Tol) with hydroxypropyl-b-cyclodextrin (HP-b-CD) was studied. Solution-stirring method was selected to prepare the Toltrazuil-hydroxypropyl-b-cyclodextrin inclusion complex (Tol-HP-b-CD). The effects of concentration of acetonitrile, temperature, inclusion molar ratio of HP-b-CD to Tol, and pH value on its yield, inclusion ratio and drug loading ratio were studied. The complex was evaluated by thin layer chromatography, phase solubility technique and microscope. The results showed that the complex prepared under the optimized conditions had the average yield, inclusion ratio and drug loading ratio of 86.45%, 60.44% and 7.00%, respectively. Solubility of Tol was increased up to 9.90 mg/mL by complexation with HP-b-CD, compared with the unprocessed Tol. It is evident from the results that complexation with HP-b-CD is a feasible way to prepare a rapidly dissolved Tol oral product.

Fermentative Production of Optically Pure D-Lactic Acid by Genetically Engineered Escherichia coli

ZHAO Xiao TIAN Tian ZHAO Jin-fang WANG Yong-ze WANG Jin-hua

. 2012, 12(6): 989-995.

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By genetic engineering, the competing fermentative pathway genes (adhE, frdBC, pta, pflB, aldA) and the repressor gene (cscR) of the sucrose operon were deleted from Escherichia coli W, a sucrose positive strain. The constructed strain, WD 206, efficiently utilized 100 g/L sucrose for production of 88.15 g/L lactic acid in 72 h in the media of mineral salts, with extreme low levels of by-products. The product yield of lactic acid was 84% and D-lactic acid optical purity 99%. These results demonstrate that the strain has great potential for production of D-lactic acid with high optical purity by using inexpensive substrates such as sugar cane and/or beet molasses, which are primarily composed of sucrose.

Coupled-feeding Strategy Based on the Cell Growth and Metabolism during 1,3-Propanediol Fermentation

SONG Zhi-yuan TENG Hu XIU Zhi-long

. 2012, 12(6): 996-1001.

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A substrate feeding strategy was studied in the fed-batch fermentation of 1,3-propanediol by Klebsiella pneumoniae, which was distinctively coupled with cell growth and metabolism using glycerol as substrate. The functional relationship between substrate consumption, biomass and alkaline consumption was established by analysis of the cell growth kinetics during logarithmic growth and stationary phase, respectively. The fed-batch on-line experimental results showed that the glycerol concentration was controlled at 20±2 g/L, and the final 1,3-propanediol concentration reached 80.3 and 78.8 g/L, which increased 25.0 and 23.5 g/L compared with that of manual feeding-back strategy.

Cloning and Transcriptional Expression Analysis of ARE Gene in Rhodosporidium toruloides

ZHANG Guo-ling OURA Takahiro DU Wei LIU De-hua KAJIWARA Susum

. 2012, 12(6): 1002-1007.

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The ARE gene of Rhodosporidium toruloides was cloned and its transcriptional expression level analyzed. 2624 bp DNA sequence of ARE gene with 6 introns was clarified. The open reading frame was 2028 bp coding 675 amino acids. The transcriptional expression of ARE gene in the cells cultivated in nitrogen-limited medium increased with culture time. It was supposed that the transcriptional expression of ARE gene was related to lipid accumulation in R. toruloides.

Screening and Identification of 2-Keto-D-gluconic Acid-producing Strain

NIU Pan-qing YANG Ai-hua YANG Song-xin LI Zhen CHEN Jian;

. 2012, 12(6): 1008-1013.

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A 2-keto-D-gluconic acid (2-KGA) producing strain Serratia sp. FMME043 was isolated from the soil by the method of flat discolor circle with (NH4)2SO4 as nitrogen source. The optimal conditions, glucose 180 g/L, (NH4)2SO4 2.0 g/L and KH2PO4 1 g/L, were obtained through one-factor experimental design. Furthermore, the highest 2-KGA concentration 169.5 g/L and yield 0.87 mol/mol were achieved under the optimum conditions with initial pH 7.0, liquid volume 75 mL in a 750 mL flask, culture temperature 30℃, and shaker rotating speed 200 r/min. These results were also confirmed in a 7 L fermentor.

Preparation and Adsorption Properties of Magnetic Rhizopus oryzae Biosorbent for Congo Red

ZHANG Ya-dan WAN Yong-jun CHEN Li-yan LI pei-bei FU Yong-qian

. 2012, 12(6): 1014-1019.

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A magnetic biosorbent was synthesized with Rhizopus oryzae powder, FeSO4 and Fe3O4. With the anionic azo dye Congo Red (CR) solution as the target pollutant, the effects of m-RBps dosage, pH value and initial CR concentration were studied, and the adsorption kinetics and thermodynamics discussed. The results indicated that the decolorization rate of CR increased with rising of the adsorbent dosage, and the effect of initial CR concentration on its adsorption capacity was remarkable. When the pH value, CR concentration and m-RBps dosage were 7.0, 20 mg/L and 1.0 g/L, respectively, the effect of adsorbent was the best, and over 98.68% of CR was removed. The adsorption of CR on m-RBps followed the Langmuir isotherm model. The adsorption procedure met pseudo-second-order kinetic equation, and the intra-particle diffusion was the rate-controlling step. Furthermore, the magnetic biosorbent could be easily recycled with an external magnetic field, thus simplifying the further processing of adsorption of anionic azo dye.

Kinetic Model of Biomass Pyrolysis Based on Three-component Independent Parallel First-order Reactions

WANG Xin-yun WAN Xin-jun CHEN Ming-qiang WANG Jun

. 2012, 12(6): 1020-1024.

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The pyrolysis behavior of two kinds of typical biomass (pine wood and cotton stalk) was studied in nitrogen atmosphere at various heating rates by thermogravimetric analysis (TGA). The pyrolysis process can be divided into three stages: evolution of moisture (<200℃), devolatilization (200~400℃) and carbonization (>400℃). The comparison of DTG curves of two biomass materials show that the higher the hemicellulose content of biomass, the more evident the shoulder peak of DTG curve. The weight loss process of two materials was simulated by the kinetic model assuming cellulose, hemicellulose and lignin pyrolyzing independently and in parallel, obeying first-order reactions. The pyrolysis kinetic parameters corresponding to the three components were estimated by the nonlinear least square algorithm. The results show that their fitting curves are in good agreement with the experimental data. Their activation energy values for pine wood and cotton stalk are in the range of 188~215, 90~102, 29~49 and 187~214, 95~101, 30~38 kJ/mol, respectively. The corresponding pre-exponential factors are in the range of 1.8′1015~2.0′1016, 1.6′107~7.1′108, 9.3′101~1.5′103 and 1.2′1015~6.7′1017, 1.2′108~1.4′109, 1.4′102~4.6′102 min-1, respectively. In addition, the activation energy of cellulose and lignin increased and their contributions to volatile tended to fall, whereas the activation energy of hemicellulose decreased and its contribution to volatile tended to rise with increasing of heating rate.

Study on the Cleanliness of 55SiMnMo Steel Produced by Consteel-LF-VD-CC Process

AN Li-na LI Jing-she SUN Li-yuan XIONG Jia-ze WANG Zhu-sheng XIA hui-hua

. 2012, 12(6): 1025-1031.

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In order to study the fracture problem of drill rod caused by its hard inclusions which were found in the 55SiMnMo hollow steel billet produced by Consteel-LF-VD-CC process, the cleanliness of 55SiMnMo steel during the whole production process was analyzed by the methods of systematic sampling and comprehensive analysis of gas content and inclusions in it. The influential factors on the steel cleanliness were discussed and some measures to improve steel cleanliness were proposed. It was found that the reason for the fracture of drill rod was pure big Al2O3 inclusion with sharp corners and irregularly shaped MgO-CaO-SiO2 inclusion. Three process problems were found: air absorption happened during later refining; calcium treatment was not perfect to change inclusions; obvious air absorption and slag entrapment happened at the beginning of molten steel pouring. The T[O] content of billet was 9×10-6, and the main micro-inclusions were MnS and Al-Mn composite inclusions and SiO2-Al2O3-MnO-CaO for the macro-inclusions.

Synthesis and Photoelectrochemical Properties of Pt Nanoparticles Modified TiO2 Nanotube Arrays

HUANG Qing-ming XU Guang-qing FENG Chun-xiao LU Jun WU Yu-cheng

. 2012, 12(6): 1032-1037.

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Well aligned TiO2 nanotube arrays were prepared by anodic oxidation method in a glycol solution containing 0.4 mol/L HF, and Pt nanoparticles were deposited on anatase TiO2 nanotube arrays by hydrothermal reduction method in the solution containing chloroplatinic acid and citric acid. The structure, morphology and composition of modified TiO2 nanotubes were analyzed, and electrochemical and photoelectrochemical properties measured by an electrochemical workstation combined with a 5 W LED light (365 nm wavelength). TiO2 nanotubes are vertically aligned with a diameter of 150 nm, wall thickness of 20 nm and length of 20 mm. The electrodeposited Pt nanoparticles were in an ordered assembly with a uniform distribution on the inner wall of nanotubes with a particle size of about 10 nm. Comparison of cyclic voltammograms of TiO2 and TiO2(Pt) nanotube arrays in the darkness and under UV illumination shows that Pt nanoparticles modification enhances the electrochemical activities of TiO2 nanotubes and photocurrent response. The highest photocurrent was achieved to be 289.84 mA when Pt deposition temperature was 100℃.

Study on Synthesis, Characterization and Antibacterial Activity of Rare Earth Complexes with Water-soluble Chitosan

WU Jin-xiu LI Mei LIU Zhao-gang HU Yan-hong WANG Mi-tang

. 2012, 12(6): 1038-1042.

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Rare earth-chitosan complexes (CS-La, CS-Nd, CS-Sm, CS-Eu and CS-Dy) were prepared by natural water-soluble chitosan (CS) and rare earth ions (La3+, Nd3+, Sm3+, Eu3+ and Dy3+) in aqueous solution at pH value from 4 to 5 under room temperature, and characterized by FT-IR, UV and TG-DTA. The antibacterial activity of rare earth-chitosan complexes, water-soluble chitosan and rare earth nitrate were also examined. The result of antibacterial activity test showed that the five complexes all had selective antibacterial property, and good bacteriostatic effect to Escherichia coli and Staphylococcus aureus. The minimal inhibitory concentration (MIC) of the five bacteria (Escherichia coli, Staphylococcus aureus, Proteus species, Candida albicans, and Pseudomonas aeruginosa) ranged from 120 to 500 μg/mL, less than 800 μg/mL. The antibacterial activity of complexes was superior to that of water-soluble chitosan and rare earth nitrate. The antibacterial property of CS-Sm to Echerichia coli was the best, its MIC 125 μ g/mL. While, that of CS-Nd and CS-Sm to Staphylococcus aureus was the best, and both of the MIC were 120 μg/mL.

Effect of CuO Additive on Sintering and Microwave Dielectric Properties of Ca(Sm0.5Nb0.5)O3 Ceramics

LI Jia-mao QIU Tai FAN Chuan-gang;

. 2012, 12(6): 1043-1047.

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Ca(Sm0.5Nb0.5)O3 microwave dielectric ceramics with different contents of CuO sintering additive were prepared by conventional high-temperature solid state method, and the effects of CuO additive on the sintering, structure and microwave dielectric properties of Ca(Sm0.5Nb0.5)O3 ceramics were studied. The results show that the densification of Ca(Sm0.5Nb0.5)O3 grains could be improved and a reduction of sintering temperature (about 200℃) obtained by adding CuO into Ca(Sm0.5Nb0.5)O3 ceramics. At 1350℃ for 4 h, Ca(Sm0.5Nb0.5)O3 ceramics with 1.5%(w) CuO addition possess good microwave dielectric properties, relative dielectric constant er=23.98, product quality and frequency Q×f=27754.5 GHz and temperature coefficient of resonant frequency tf=-2.7×10-6 ℃-1.

Effect of Pyrocarbon Matrix Micro-structure on Mechanical Properties of C-C Composites

WANG Xiang-hui WENG Li YU Shou-quan

. 2012, 12(6): 1048-1052.

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The carbon-carbon (C-C) composites with different pyrocarbon matrix micro-structure were obtained using PAN based carbon fiber felts infiltrated by isothermal chemical vapor infiltration (CVI) under the conditions of 1000℃ and 5.0~20.0 kPa, and the effect of pyrocarbon micro-structure on the composites mechanical properties was studied. It was found that the C-C composite with monolayer lower texture prepared under 8.0 kPa displays higher breaking strength and obvious brittle fracture behavior for the stronger interface force between pyrocarbon and carbon fiber, which lead to the breaking simultaneously as loading. While the C-C composite with medium texture-high texture-medium texture prepared under 10.0~20.0 kPa shows good mechanical properties and the pseudo-plastic failure behavior, which is related to multiple crack deflections caused by the interfacial sliding between different pyrocarbon layers with a varying texture degree and the delamination micro-cracking within the highly textured pyrocarbon layer. The breaking strength of the materials reaches to 86±3 and 82±4 MPa, respectively.

Size Distribution and Yield of Printed Circuit Board by Cryogenic Grinding

ZHOU Cui-hong PAN Yong-tai CHANG Jun-ying KONG Hui

. 2012, 12(6): 1053-1057.

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Adpoting liquid nitrogen as refrigerating medium, a cryogenic grinding system was set up to cool the printed circuit board material to its embitterment temperature. The effects of freezing temperature and processing time and setting conditions on the particle size distribution were examined. Orthogonal experiments were carried out to determine the optimal working conditions. The results show that the fractal dimension of product is 1.94 with regular particle size, and the yield of 0.5~1.4 mm particles is 43.8% when the cooling temperature is -30℃. There is no evident change of fractal dimension for different processing times. When the processing time is longer, cutter gap lower and frequency bigger, the yield is higher. The best working condition will be achieved when the crushing time is 10 min and discharge size of crusher is not less than 3 mm.

Electroacoustic Measurement of Zeta Potential in Aqueous Colloids

GONG Zhi-fang SU Ming-xu CAI Xiao-shu

. 2012, 12(6): 1058-1061.

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An electroacoustic probe was developed for measuring acoustic impedance and Zeta potential in colloids simultaneously. Meanwhile, a set of experimental device was established and its stability verified to be good after repeated experiments. Measured acoustic impedance by multiple echo method was incorporated into a theoretical model to calculate Zeta potential. The measurements of Zeta potential in the colloids of nano-loess and nano-titanium dioxide were -52.69 and -16.09 mV, respectively. Zeta potential trend of 5%~30% volume concentration colloids of silica sol was measured and analyzed, showing that the method can be used for high concentration plastic body measurement. The comparison with the results of Malvern Zeta potential measurement instrument yielded a small and accepted deviation. This method is expected to achieve on-line measurement.

Advances in Research of Porous Silicon-based Anode Composites for Li-ion Batteries

ZHU Xiao-yi WANG Yan-hong CHEN Han XIA Lin-hua SU Fa-bing

. 2012, 12(6): 1062-1072.

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Research progress in porous silicon-based anode materials for Li-ion batteries was reviewed, focusing on the effects of their morphology and compound on the electrochemical properties. The reasons of poor cycling performance are analyzed. It is pointed out that to control the huge volume change and SEI growth during the cycling is an effective way for improvement of the performance. Outlook for the future development of porous silicon composite anode materials and further research of designing porous structure based silicon nanocomposites for the application of silicon anodes are finally outlined.

Research Progress in Modeling of Slurry Bed Reactors for Fischer-Tropsch Synthesis Technology

YANG Tao TANG Xiao-jin ZHANG Zhan-zhu

. 2012, 12(6): 1073-1080.

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Based on the thermal state research results in the literature, the research progress in mathematical modeling of slurry bed reactors for Fischer-Tropsch synthesis is reviewed, and the modeling is summarized from four aspects of ideality of flow, type of bubble, research dimension and method. By classification and analysis, it is found that the modeling is becoming much more complicated and closer to the reality. With the development of CFD technology, the models with multi-dimension, multi-bubble classes and non-ideal flow characteristics will be the trend of this field. The algorithms for vapor-liquid equilibrium of synthesis gas and the distribution of products between the gas and liquid phases are analyzed systematically. The Henry's law is suitable for the calculation of synthesis gas solubility, and the equations of state are well used to obtain the vapor-liquid equilibrium of products.

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