Favorable vibrated fluidization conditions for cohesive fine particles

The present study was performed to clarify the operational range for vibro-fluidization of fine cohesive particles (glass beads, d_p = 6 μm). Decreasing and increasing gas velocity methods were examined to clarify the favorable vibro-fluidization region. The upper limit of the gas velocity for intermittent channel breakage was higher in the case of the increasing gas velocity method than the decreasing gas velocity method. This was because the changes in the bed flow pattern from a favorable (intermittent channel breakage) to an unfavorable fluidization state (stable channels) were moderate in the case of the increasing gas velocity method. In the increasing gas velocity method, two kinds of cross-points were obtained from the relationship between the gas velocity and the bed pressure drop. At one of the gas velocities at these cross-points, the bed void fraction reached its maximum. In the present study, the above-mentioned gas velocity was defined as the upper limit of gas velocity for favorable vibro-fluidization, u_chu. A favorable vibro-fluidization region was determined by combining u_chu with u_chl, which is the lower limit of gas velocity for intermittent channel breakage obtained in a previous study. The value of u_chu was found to have a maximum corresponding to a certain vibration strength.     

Synthesis and characterization of mesoporous materials: Silica–zirconia and silica–titania

An experimental strategy was developed to obtain mesoporous SiO₂–ZrO₂ and SiO₂–TiO₂ mixed oxides by a sol–gel method, treating the gels hydrothermally. The solids were characterized by nitrogen physisorption, pyridine thermodesorption, ²⁹Si nuclear magnetic resonance, SEM and X-ray diffraction. The effects of ZrO₂ content, the generated pressure in the synthesis vessel and further modification of this type of procedure on the solids properties were studied. It was found that SiO₂–ZrO₂ and SiO₂–TiO₂ mixed oxides dried at atmospheric pressure developed type I isotherms. On the other hand, for the SiO₂–ZrO₂ and SiO₂–TiO₂ mixed oxides that were treated under pressure in the autoclave (at high SiO₂ content) the porosity was improved and mesoporous materials exhibiting type IV adsorption isotherms. Specific surface area and pore size distribution were a function of ZrO₂ and TiO₂ content. The materials exhibited narrow pore size distributions with pore diameters in the region of mesopores at about 4 nm and high surface areas, the highest being 481 m²/g for the 10 wt% ZrO₂ Si–Zr material. Differences in acidity as determined by pyridine thermodesorption were observed to depend on the synthesis parameters and ZrO₂ and TiO₂ concentration.     

Electrophoretic deposition of nanostructured TiO2/alginate and TiO2-bioactive glass/alginate composite coatings on stainless steel

Abstract

Two alginate (Alg) based composite coatings on stainless steel AISI 316L substrates, one containing titania nanoparticles (n-TiO₂) and another one a mixture (50/50 wt-%) of n-TiO₂ and bioactive glass (BG), intended for biomedical applications, were developed by electrophoretic deposition (EPD) from ethanol/water suspensions. Different n-TiO₂ (2–10 g L^?1) and BG (1–5 g L^?1) contents were studied for a fixed alginate concentration (2 g L^?1), and the properties of the electrophoretically obtained coatings were characterised. Coatings with high ceramic content (up to 67 vol.-%) were obtained. The presence of BG particles improves the mechanical properties of the coatings by increasing the adhesion to the substrate and also accelerates the formation of hydroxyapatite after immersion of the coatings in simulated body fluid. The electrochemical behaviour of the coated substrates, evaluated by polarisation curves in Dulbecco’s modified eagle medium at 37°C, confirmed the corrosion protection function of the novel EPD coatings. The present polymer–ceramic composite coatings belong to an emerging family of bioactive, compliant coatings that are promising for a range of biomedical applications.     

TiO2/粉煤灰的制备及其光催化性能研究

以钛酸丁酯、乙醇和硝酸为原料,制备出混合溶液（A）将其包覆于粉煤灰表面,高温煅烧即得到负载型二氧化钛光催化剂。用X射线衍射（XRD）和扫描电镜（SEM）对粉煤灰的结构和成分进行了表征,以甲基橙的降解为模型反应,分析了煅烧温度、保温时间、负载型二氧化钛催化剂的投入量和混合溶液A的投入量对光催化性能的影响。结果表明,以粉煤灰为载体,采用适宜的制备方法和光催化降解工艺,负载型二氧化钛催化剂能够获得较高的光催化活性。     

Microwave-assisted hydrothermal synthesis of Eu2O3-coated spherical Y2O3 ceramic particles

This paper reports on the synthesis of uncoated and Eu₂O₃-coated spherical Y₂O₃ ceramic particles using optimized hydrothermal (HM) and microwave-assisted hydrothermal (MWHM) routes. The integration of microwave and hydrothermal processes was shown to enhance the reaction kinetics during the synthesis of uncoated Y₂O₃. Spherical particles of pure Y₂O₃ phase with an average particle size of 600 nm and uniform size distribution were obtained via the MWHM process at 180 °C following reaction duration of only 1 h. Y₂O₃ spherical particles were coated with Eu₂O₃ via a hydrolysis method at room temperature. The band gap of the resulting phosphors was estimated at 5.7 eV. Eu₂O₃-coated Y₂O₃ particles synthesized via the HM and MWHM present bright red PL emission under UV excitations; however, Y₂O₃ particles obtained via the MWHM method are more efficient than those yielded via the HM technique. Eu₂O₃-coated Y₂O₃ particles derived using the optimized MWHM technique present efficient emissions of red light with color purity and down conversion efficiency of approximately 85% and 80%, respectively. The present study demonstrates the suitability of employing coated phosphors in optical display technologies.     

Growth mechanism of monodispersed TiO2 fine particles by the hydrolysis of Ti(OC2H5)4

In order to investigate the growth mechanism of TiO₂, the monodispersed TiO₂ fine particles were prepared by hydrolysis of Ti(OC₂H₅)₄ using the seed preparation method. Although it was impossible to grow TiO₂ particles to more than 1 μm with conventional liquid phase reaction method, we obtained monodispersed T1O₂ fine particles of up to 2.5 urn. Nielsen’s chronomal analysis and Overbeek’s theory were applied to clarify the particle growth mechanism. The particle growth mechanism was found out as a first-order polynuclear layer growth mechanism and the growth rate constant, k_P was about 6.45X10^-6 cm/s.     

Synthesis and characterization of Au/TiO2 core-shell structure nanoparticles

Au/TiO₂ core-shell structure nanoparticles were synthesized by sol-gel process, and the morphology and crystallinity of TiO₂ shell were investigated by TEM and UV-vis absorption spectrometer. Au/TiO₂ core-shell structure nanoparticles could be prepared by the hydrolysis of TOAA (titanium oxide acethylacetonate) in gold sol ethanol solution with water. The thickness of TiO₂ shell on the surface of gold particles was about 1 nm. To investigate the crystallinity of TiO, shell, UV light with 254 nm and radioactive ray of⁶⁰Co were irradiated on the TiO₂-coated gold sol ethanol solution. The surface plasmon band of gold nanoparticles appeared only when the radioactive ray was irradiated on the TiO₂-coated gold sol ethanol solution. From these results, it was found that the TiO, shell was amorphous and the MUA (mercaptoundecanoic acid) layer on the Au particle for its dispersion in ethanol did not act as an obstacle to disturb the movement of electrons onto the surface of Au particles.     

Dispersion behaviour of fine collophane particles in the presence of different dispersants and metal ions

ABSTRACT

Recent, studies have shown that selective flocculation flotation is an effective method for enhancing the flotation of a fine mineral. Fine-grained collophane is difficult to disperse naturally, thereby affecting its subsequent flotation separation. Therefore, it is important to study the dispersion behaviour and mechanism of fine-grained cellophane to choose an appropriate method to improve the dispersion effect of the flotation system. The influences of different types of poly-anionic dispersants, such as (sodium silicate (ZSS); sodium carbonate (ZSC); sodium hexametaphosphate, ZSP) and metallic cations with different valences (Al³⁺, Ca²⁺, Na⁺) on the dispersion behaviour effect of fine-grained collophane were investigated in this work using the sedimentation balance method. The zeta potential measurements and the extended-DLVO (Derain-Landau-Verwey-Overbake) theory were used to explain the distinction of dispersion behaviour. In the presence of dispersants, the dispersion of collophane was in the order of ZSP>ZSS>ZSC. Zeta potential analysis indicated that the absolute value of the surface potential followed the order of ZSP>ZSS>ZSC. That is, the collophane particles in the ZSP system had stronger electrostatic repulsion, resulting in a better dispersion zeta potential effect zeta potential. ZSP was adopted as dispersant to study the effects of metal ions on dispersion. In the ZSP dispersant system, metal ions can suppress the dispersion behaviour of fine-grained collophane. The suppression effect followed the order of Al³⁺>Ca²⁺>Na⁺, because of the greater charge and better neutralization ability of trivalent ions for the same concentration. The results of the extended-DLVO calculations showed that the dispersion stability was attributed to the electrostatic repulsion and hydration repulsion, and hydration repulsion had a greater influence on the stability than electrostatic repulsion. This paper provides reference information for adjusting the dispersion behaviour effect of fine-grained collophane, thereby guiding the actual flotation separation.     

Uniform coating of TiO2 nanoparticles using biotemplates for photocatalytic wastewater treatment

Immobilization of TiO₂ particles over substrates like glass can facilitate the separation after photocatalytic runs. Photocatalytic activity of TiO₂ coatings is related to its morphology, crystallography, optical properties and adherence of the coating. Biotemplates, including animal-based and herbal-based templates are inexpensive, biocompatible and abundant and can control the quality of TiO₂ coating. In this study the effects of biotemplates such as agar, gelatin, and starch on the physiochemical properties of TiO₂ coatings were investigated. Synthesized coatings were characterized by XRD, BET, FESEM, TEM, FTIR, EDX, and UV-Vis DRS analyses. The results showed that using biotemplates reduces the TiO₂ crystallite size. Template-free TiO₂ had 30 nm crystallite size, but using templates like agar decreased the size to 18 nm. Moreover, the addition of biotemplates decreased the thickness of TiO₂ coatings compared to template free coating. And the use of biotemplates also limits the pore size distribution and increases BET surface area. According to EDX, TiO₂ coating with agar indicated a uniform Ti distribution and crack-free homogenous morphology. TEM analysis of agar-templated TiO₂ film showed a uniform morphology of TiO₂ particles with average particle size of 20 nm. The UV-Vis DRS also confirmed a reduction in the band gap of TiO₂ after the introduction of biotemplates. The study of the photocatalytic performance of samples showed that agar-templated TiO₂ coating was able to remove 62.4% of methylene blue, while the coatings synthesized with gelatin and starch were just able to remove 42.77% and 35%, respectively. The TiO₂ coating with agar was studied at different pH values and different initial methylene blue concentrations as well. The stability test of agar-templated TiO₂ coating after four runs indicated just 5% of activity lost.     

Characterization of zirconia modified porous stainless steel supports for Pd membranes

A thin well-bonded zirconia film was formed on a porous stainless steel support by a sol-gel dip-coating method followed by firing in hydrogen atmosphere. The zirconia layer has a cubic phase structure. The surface composition of the film was analyzed by X-ray photoelectron spectroscopy. A comparison between H₂-fired and air-fired samples indicated that the surface/interface composition of the sample fired in air was rich in Fe₂O₃, whereas that of the fired in H₂ contained more metastable cubic zirconia phase and spinel type iron chromate. Binding energy shifts of Zr and Fe in the mixed oxides, together with the presence of iron and chromium oxides suggests that interfacial reaction between the coating and the substrate occurred, which is favorable for a good adhesion of the layers. The average pore size of the support modified by multilayer zirconia coatings declined drastically from original 2 μm to the coated top-layer 0.4 μm. The ZrO₂ film showed a hydrogen selectivity of 2.7 for H₂/N₂, and a hydrogen flux of 1.159 × 10⁻³ mol/m².s at room temperature and with a pressure difference of 101 kPa across the film.     

The preparation and surface characterization of zirconia polymorphs

Zirconium hydroxides were obtained by precipitation of zirconium chloride with aqueous ammonia at constant pH followed by hydrothermal treatment The effect of thermal activation of the zirconium hydroxide on physical properties, and the effect of crystalline phase on the surface properties of zirconia were studied. The pressure during the hydrothermal treatment of zirconium hydroxide affected the surface area, particle growth, and phase transformation of the zirconia product. Hydrothermally treated zirconia under atmospheric pressure (LP) shows higher surface area than that under high pressure (HP) and untreated (UT). HP zirconia shows a mixture of tetragonal and monoclinic phase after hydrothermal treatment due to the higher solubility and reprecipitation rate, whereas LP sample shows a tetragonal crystal structure from 600 to 1,050 ℴC. Monoclinic phase zirconia shows greater CO₂ and NH₃ surface adsorption than amorphous and tetragonal phase zirconia. This suggests that the crystal structure of zirconia strongly affects the amount and strength of the surface adsorption site.     

The characteristic and osteogenic effect of a nanoporous coating of zirconia implant

Zirconia ceramics have become increasingly used as dental implant material which is mainly due to their “tooth-like” color, superior biocompatibility, and excellent mechanical properties. However, the bio-inertness of the zirconia surface limits its use for a wider range of clinical applications. To enhance the surface bioactivity, a combination of magnetron sputtering, and anodization has in the present study been used to deposit a homogeneous nano-porous coating (ZrNP) on the zirconia surface (forming ZrO₂/ZrNP with a ZrNP pore diameter of 20–30 nm, and a ZrNP layer thickness of ～2 μm). EDS and XRD analysis showed that the distribution of the surface chemical components, as well as the crystalline structure of the zirconia (ZrO₂), remained unchanged. On the other hand, the hydrophilicity of the ZrO₂/ZrNP surface became significantly improved (as compared with a control group). In addition, the bond strength of the coating was decreased as a result of the anodization treatment. Moreover, both the Zr and ZrNP nanolayers exhibited improved proliferation and osteogenic properties in the in vitro cell experiment. Also, the ZrNP nanolayer was found to promote the biocompatibility and osteogenic ability to the largest extent. The ZrNP nanolayer did also provide numerous adhesion sites for MC3T3-E1 whereby the cell morphology could be enhanced. Additionally, the nano porous ZrNP layer improved the new bone formation around the zirconia implant and did robustly enhance the push out bond strength, thereby indicating the best osteointegration ability. In conclusion, a nano porous zirconium layer has been found to be very promising for the improvement of the bioactivity of the zirconia implant material.     

金红石型纳米二氧化钛表面包覆的若干研究

对金红石型纳米TiO2进行表面处理是钛白粉工业化生产中必不可少的关键步骤,处理的方法和包覆的程度直接影响到产品的应用范围。介绍了金红石型纳米TiO2表面包覆的机理、包覆的方式以及对包覆效果进行表征的一些常用方法。     

Ag+修饰改性TiO2薄膜的制备、表征及日光催化性能研究

采用溶胶-凝胶法,制备了Ag^＋/TiO2薄膜.利用XRD、SEM等测试手段进行了样品的表征分析,以降解罗丹明B为反应模型,研究了薄膜的日光催化活性和薄膜的重复使用效果.结果表明,Ag掺杂以后可以明显地提高TiO2薄膜的催化活性,薄膜的使用次数可达到5次以上,且仍有明显的降解效果.     

单分散球形二氧化钛的制备

以钛酸丁酯为原料．采用溶胶-凝胶法合成了单分散球形二氧化钛。研究了TBT的加入量,NaCl溶液加入量,NaCl溶液加入的先后顺序,煅烧温度,煅烧时间对单分散球形二氧化钛的影响。采用XRD、TEM、粒度分析仪等对其结构和形貌进行了表征。     

Two-step alcohothermal synthesis and characterization of enhanced visible-light-active WO3-coated TiO2 heterostructure

A new kind of WO₃-coated TiO₂ heterostructure with higher photocatalytic activity was prepared via a novel two-step alcohothermal synthesis process. The effects of the WO₃ addition on the TiO₂/WO₃ products were systematically studied, including analysis of the phases, observation of the morphologies and calculation of the band gaps. Under illumination, the conduction band electrons of TiO₂ are excited and accompanied by the generation of positive holes. In this heterostructure, the conduction band electrons of WO₃ occupy the nearest valence band of TiO₂ and then combine with the internal holes, inhibiting the flow of the electrons transferred from the conduction band of TiO₂. Compared with anatase TiO₂, the WO₃-coated TiO₂ heterostructure (weight ratio of WO₃:TiO₂ = 1:2) with a finer grain size exhibits excellent photocatalytic performance.     

Electrostatic dispersion of fine particles in the air

The paper studied the method of keeping fine particles from aggregating in the air by electrostatic dispersion. The effects of electrode voltage, diameter, humidity and rest time, as well as van der Waals forces, electrostatic forces and liquid bridge forces between particles on electrostatic dispersion of powder were discussed. It was shown that optimal electrostatic dispersion effect of calcium carbonate and talcum particles can be achieved with corona voltage of 29 kV, particle size of 2–25 μm, and proper rest time of 48 h. Criteria for electrostatic dispersion were put forward on the basis of experimental results. Theoretical calculation indicated that the criteria for electrostatic dispersion were in good agreement with experimental results.     

Preparation and characterization of Al3+-doped TiO2 tight ultrafiltration membrane for efficient dye removal

Al³⁺-doped TiO₂ (AT) tight ultrafiltration membrane with stable anatase phase was prepared by a modified sol-gel process using butyl titanate and aluminum chloride as the precursor and aluminum source respectively. The removal of Alizarin red-S was investigated by filtration experiment. A dip-coating process on homemade flat Al₂O₃ intermediate layer by TiO₂ sol followed by heat treatment was adopted to obtain the desired AT membrane. The addition of Al³⁺ inhibits the phase transformation of nanosized TiO₂ from anatase to rutile and restrains the growth of crystallite, resulting in the pore size of the separation layer reducing to 3.5 nm. The prepared AT1-500 membrane exhibits enhanced hydrophilicity with no cracks or pinholes, and shows a water permeability of 9.6 L m^-2 h⁻¹ bar⁻¹ and cut-off molecular weight (MWCO) of 4650 Da. The membrane demonstrated a retention rate of 96.9% for Alizarin Red-S (250 ppm) and maintained almost constant under repeated using.     

Flotation behaviour of fine particles with respect to contact angle

The flotation behaviour of methylated quartz particles of different size, but within the size range from 0.2 to 50 μm, and varying contact angle, was probed in a mechanical flotation cell. Results suggest that particles of a given size need to possess a minimum critical contact angle (θ_crit) for flotation to occur. This behaviour is shown not to be solely dependent on fine particles having lower collision efficiency with bubbles, but rather due to a combination of low collision efficiency and particles not having enough kinetic energy at collision with bubbles to form the three phase line of contact and initiate the attachment process. In the particle size range investigated, the critical contact angle increases with a decrease in particle size.     

电除尘器飞灰粒径表征及细颗粒降温团聚

基于50000m³/h实烧烟气中试系统,采用Mastersizer 2000E激光粒度分析仪和电子低压冲击仪（ELPI）,首次对电除尘器飞灰几何粒径和空气动力学粒径进行全面表征。结果表明,电除尘器入口及各电场的飞灰几何粒度分布均呈双峰分布特征,各电场峰值依次右移,但末级旋转电极电场≤ 1μm的颗粒占比略有升高,电除尘器入口及第1～5电场飞灰几何中位径分别为6.607μm、17.378μm、2.884μm、2.577μm、2.460μm、2.480μm;温度降低,电除尘器入口飞灰几何粒度分布的双峰均右移,颗粒团聚现象明显,80℃、90℃、110℃、130℃、150℃时电除尘器入口飞灰几何中位径分别为13.183μm、10.500μm、10.171μm、6.607μm、7.586μm,从130℃降至90℃,电除尘器入口几何粒径≤ 1μm、≤ 2.5μm、≤ 10μm的飞灰占比分别减少了19.8%、19.2%、12.6%;不同温度时,电除尘器对空气动力学粒径0.03～10μm段颗粒的个数浓度、质量浓度均有较高脱除效率,均在75%以上,最高可达99.9%;温度降低,电除尘器进出口空气动力学粒径不同粒径段颗粒个数浓度和质量浓度均有不同程度降低,从130℃降至90℃、80℃,对应电除尘器入口PM_2.5团聚效率分别为46.76%、60.08%,对应电除尘器出口PM₁₀减排分别为59.80%、91.08%,PM_2.5减排分别为45.94%、76.22%,PM1减排分别为40.40%、62.12%。