New technology for production of spherical alumina supports for fluidized bed combustion

Fluidized bed catalytic combustion has proved to be very promising for industrial application. The milestone problem is the development of support and catalyst with a high mechanical and thermal stability. We have developed a new technology for production of alumina supports with desired spherical shape, texture and structure. In this paper several pathways to produce aluminum hydroxide of a pseudoboehmite structure including conventional and new technologies are discussed. Properties of spherical granules depend on the method of granulation and most attention has been paid to development and optimization of hydrocarbon–ammonia molding to produce uniform alumina spheres. Several methods to estimate mechanical strength of spherical aluminas are applied to evaluate mechanical durability of prepared catalysts in a fluidized bed. Optimization of high quality spheres production focused on study of the effect of initial hydroxide properties and molding conditions on properties of the final product. Modification of spherical alumina with oxides of Mg, Ce, La and Si proved to be effective to substantially improve the mechanical and thermal stability. This effect is most pronounced when pairs of these dopes are introduced simultaneously.     

多孔球形莫来石基浇注料的制备及性能研究

为制备保温性能及机械性能均较优异的高温窑炉用隔热耐火材料,以多孔球形莫来石、矾土细粉、α-Al₂O₃微粉、硅微粉和Secar71水泥为主要原料,制备了多孔球形莫来石基浇注料,研究了矾土细粉掺量对多孔球形莫来石基浇注料机械性能、导热系数、抗侵蚀性能及热震稳定性的影响。结果表明,改变矾土细粉的掺量,可使多孔球形莫来石基浇注料在保持较高机械性能的基础上提高保温性、热震稳定性和抗侵蚀性能。随着矾土细粉掺量的增加,多孔球形莫来石基浇注料的机械性能变化不大,但导热系数小幅降低,抗侵蚀性能出现较大差异,热震稳定性先提高后降低。当矾土细粉掺量为28%(质量分数)时,多孔球形莫来石基浇注料的机械性能、热震稳定性及抗侵蚀性能良好,在1 000 ℃时导热系数为0.905 W·m^-1·K^-1。多孔球形莫来石基浇注料的导热系数低于中间包和钢包永久层用高铝浇注料,可替代中间包、钢包永久层用高铝浇注料以减少热损失。     

A novel approach to fabricate porous alumina ceramics with excellent properties via pore-forming agent combined with sol impregnation technique

An innovative approach for fabricating porous alumina ceramics (PACs) with improved mechanical and thermal properties using walnut shell powders as pore-forming agent combined with alumina sol impregnation is reported in the present work. It is demonstrated that uniform distribution of spherical pores can be observed in as-prepared PACs by using above technical route. The decrease of walnut shell powder sizes significantly promotes the enhancement of crushing strength and reduction of thermal conductivity of the PACs. Meanwhile, the impregnated alumina sol is favoring for the formation of spherical micro-pores, then further improves their mechanical and thermal insulation performances. The lowest thermal conductivity and highest crushing strength of resulting sample reach 0.16?W/m?K and 29.2?MPa, respectively. This novel method offers new possibilities to fabricate high-quality PACs.     

Sintering behavior and mechanical properties of alumina/zirconia multilayers composite via nano-powder processing

The present research has been focused on the development of functionally graded alumina–zirconia composites, which particularly have high mechanical and thermal properties. In this study, different components of alumina–zirconia layers were enhanced between two layers of pure alumina and alumina with 20 mol% zirconia. The effect of this enhancement on consolidation, sintering condition, hardness and toughness values of the multilayer samples was evaluated. The results showed that the cracks were distributed in the co-sintering multi-layered structure. The cracks were formed due to the residual stress caused by differences in thermal expansion and sintering between successive layers. The final shape and mechanical properties of the gradual samples were found to be improved.     

大孔容活性氧化铝的生产

活性氧化铝在多个工业领域有重要用途。孔容是产品的重要技术指标之一。如何生产大孔容活性氧化铝,已成为研究、生产的重要课题。报道了以氢氧化铝为原料,应用快脱法,生产高质量活性氧化铝的工业生产结果,其产品具有大孔容、低松装密度、高强度、大比表面积的特点。多年的工业实践证明,快脱法是生产大孔容活性氧化铝的有效途径。实验研究了生产过程中固相的物相组成。实验已证明,拟薄水铝石可作为生产活性氧化铝的扩孔剂,在快脱法作业程序中,掺加适量的大孔容拟薄水铝石,可使球状氧化铝的孔容提高到0.76 mL/g。     

Fabrication and characterisation of cellular alumina articles produced via radiation curable dispersions

A general and versatile method for the production of cellular materials from radiation curable solvent-free colloidal ceramic dispersions containing pore formers has been developed. By this technique cellular ceramic articles with a precisely controlled porosity, cell size and shape are obtained for compositions containing solid pore formers. Monolithic bulk samples are obtained by thermal curing, whereas thin films and multi-layered articles are advantageously produced by UV curing. In this work the influence of three different spherical pore former types, PE, PS and PMMA, on the processing and final properties of the porous materials using alumina as model material is studied. The effect of pore former type and concentration on rheology, curing behaviour, debinding and sintering steps as well as thermal conductivity and mechanical strength of the sintered cellular materials is presented. It is also shown that the choice of pore former type modifies the sintering behaviour and resulting properties.     

Influence of thermal treatment and aging time on the stability and swelling properties of nano/micron-sized polymeric spheres for improved oil recovery application

Understanding the knowledge of swelling and stability properties of polymeric spheres are essential for improved oil recovery; these properties will allow guaranteeing an efficient block of high permeability channels and large pore throats. These properties of nano/micron-sized polymeric spheres commercially available for improved oil recovery applications were investigated. The polymeric spheres emulsion was characterized by scanning electron microscopy (SEM). Data analysis reveals uniform and spherical structures with an average diameter of 47 ± 4.8 nm. After hydration, polymeric spheres can swell due to water absorption reaching an average particle diameter of 3.3 ± 0.2 μm. The effect of aging time, thermal treatment, the removal of the oil phase, and the dispersing stabilizer on the swelling and stability was studied. It has been found that polymeric spheres structure suffers deterioration with the progressive aging time, temperature increase, and with the removal of the oil phase and dispersing stabilizer. As a result, crosslinked polymer aggregates are formed which subsequently acquiring fibrillar morphologies. Further, this study provides an understanding of the stability and swelling behavior of polymeric microspheres using polydimethylsiloxane microdevices. The results evidenced that the behavior of the polymeric spheres can be beneficial to improve oil recovery. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48030.     

球形氧化铝制备过程中影响因素的研究

介绍了球形氧化铝的各种制备工艺及成形方法，并以油柱成形法制备球形氧化铝。利用低温液氮吸附仪、压汞仪以及智能强度测定仪对其物化性质进行了测定，重点考察了不同铝源合成的水合氧化铝、加料方式、扩孔剂和胶溶剂用量对球形氧化铝性质的影响。实验结果表明，制备水合氧化铝的铝源是影响球形氧化铝的重要因素；并流加料方式能制得大孔容、低表观密度、高强度的球形氧化铝；球形氧化铝的制备过程中，要制得适合于油柱成形的铝溶胶，胶溶剂加入量有最佳的用量范围，胶溶剂用量愈大，球性氧化铝的强度、比表面、孔容愈大，而孔径却随之变小；活性炭粉能有效地提高球形氧化铝的压汞孔容。     

高频热等离子体制备特种粉体研究进展

高频感应热等离子体具有能量密度大、温度高和冷却速率快等特点,是制备特种粉体的重要手段之一. 本工作介绍了过程所在高频热等离子体制备特种粉体方面的研究进展. 利用热等离子体的高温和快速冷却过程,粗颗粒经等离子体弧高温气化,通过控制冷却速率能得到纳米粉体,利用该方法制备了纳米球形硅、铁、钴和镍等粉体,纳米硅粉可用于锂离子电池负极材料. 具有固定熔点的不规则颗粒在等离子体弧中经熔融形成球形液滴,快速冷却能获得规则致密的球形颗粒,通过等离子体球化制备了高熔点的钨、钼、铌、铬等规则致密的球形粉体. 利用活性氢的瞬时强化还原反应,采用化学气相沉积能制备超细钨、钼、镍和铜等球形金属超细粉体. 活性氧有助于调控颗粒的氧化生长过程,采用金属等的氧化反应可获得多种特殊形貌的氧化物.     

Effect of hollow spheres on the properties of lightweight periclase-magnesium aluminate spinel refractories

This study presents new lightweight periclase-magnesium alumina spinel refractories for the working lining of cement rotary kilns in which magnesium alumina spinel hollow spheres are used to replace conventional dense fused magnesia-aluminate spinel aggregates. The effects of adding spinel hollow spheres on the physical properties, mechanical strength, thermal conductivity, and slag resistance of the samples were explored. The results showed that compared with the sample prepared with dense aggregates, the sample prepared with hollow spheres had a 10.3% higher cold compressive strength, 44.1% higher modulus of rupture (MOR), and lower bulk density. Additionally, with increasing hollow spheres content, the thermal conductivity decreased from 3.79 W/(m·K) to 2.53 W/(m·K), and the high-temperature MOR increased from 2.82 to 4.09 MPa. The highest residual strength ratio was 90.73% (15 wt.% hollow spheres), which is 1.17 times that of the sample prepared without hollow spheres. Moreover, microstructure and energy dispersive spectroscopy of crucible specimens after corrosion by cement clinker showed that specimens with 15 wt.% hollow sphere additions had a better slag resistance. Introducing hollow spheres reduced the thermal conductivity of the refractories, providing a new strategy for improving the heat insulation performance of kiln linings.     

Polymer membranes for high temperature proton exchange membrane fuel cell: Recent advances and challenges

Proton-exchange membrane fuel cells (PEMFCs) are considered to be a promising technology for efficient power generation in the 21st century. Currently, high temperature proton exchange membrane fuel cells (HT-PEMFC) offer several advantages, such as high proton conductivity, low permeability to fuel, low electro-osmotic drag coefficient, good chemical/thermal stability, good mechanical properties and low cost. Owing to the aforementioned features, high temperature proton exchange membrane fuel cells have been utilized more widely compared to low temperature proton exchange membrane fuel cells, which contain certain limitations, such as carbon monoxide poisoning, heat management, water leaching, etc. This review examines the inspiration for HT-PEMFC development, the technological constraints, and recent advances. Various classes of polymers, such as sulfonated hydrocarbon polymers, acid-base polymers and blend polymers, have been analyzed to fulfill the key requirements of high temperature operation of proton exchange membrane fuel cells (PEMFC). The effect of inorganic additives on the performance of HT-PEMFC has been scrutinized. A detailed discussion of the synthesis of polymer, membrane fabrication and physicochemical characterizations is provided. The proton conductivity and cell performance of the polymeric membranes can be improved by high temperature treatment. The mechanical and water retention properties have shown significant improvement., However, there is scope for further research from the perspective of achieving improvements in certain areas, such as optimizing the thermal and chemical stability of the polymer, acid management, and the integral interface between the electrode and membrane.     

Effects of spherical silica on the properties of an epoxy resin system

The spherical silica powders were prepared by using an oxygen–acetylene flame method. After spheroidization, a scanning electron microscope investigation revealed that the spheroidization efficiency of the powder was nearly 100%, XRD patterns indicated that the raw crystal silica became amorphous silica. In this study, composites of spherical silica and an epoxy resin were prepared with a homogenizer, followed by a stepwise thermal curing process. The thermal stability and thermal degradation behavior of the composites were studied by a thermogravimetric analyzer. Meanwhile, the effects of spherical silica powder on dynamic mechanical, coefficient of thermal expansion, and mechanical properties of epoxy/silica composites were also investigated. The initial decomposition temperature and mechanical properties increased significantly after adding the spherical silica into the composite. The maximum properties of thermal stability and mechanical properties were observed when spherical silica accounted for 30% of the system. The thermal expansion had been significantly reduced by the addition of silica. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

填料对电机用轻量化导热灌封胶性能的影响

以端乙烯基硅油、含氢硅油为原料,添加填料、催化剂等制得有机硅灌封胶,探讨了α-氧化铝、球形氧化铝、氮化硼、有机蒙脱土对灌封胶性能的影响.结果表明,单纯采用α-氧化铝作填料时,灌封胶的流动性较差、排泡时间过长;采用相同粒径的球形氧化铝替代α-氧化铝能降低灌封胶的黏度,提高流动性和排泡速度,但会降低热导率,且胶料密度过高;...     

The effect of alumina particulate morphology on the properties of reinforced poly(propylene) and poly(ethylene-co-vinyl acetate) composites

The effect of alumina particulates on a thermoplastic matrix is investigated, in particular the effect altering the alumina particle size and morphology has on the mechanical properties. Different grades of alumina are used and two thermoplastic matrices; namely poly(propylene) and poly(ethylene-co-vinyl acetate). Investigations showed that optimum properties were achieved with the alumina of smallest particle size and lowest aspect ratio. Preliminary work has also been performed on the use of silane coupling agents and they have proved effective in increasing the tensile properties of the composites.     

Gas permeation and thermomechanical properties for macroporous alumina focused on necking size at grain boundaries

The gas permeation and thermomechanical properties of macroporous alumina used as a support substrate for microporous ceramic permselective membranes were investigated. The porosity, pore size, and apparent necking size between grains of macroporous alumina were systematically varied, and the relationships between the porous microstructure and material properties were examined. The grain necking size at alumina grain boundaries was evaluated by microstructural observations. The nitrogen gas permeance of the porous alumina increased with increasing pore size. All the measured thermal and mechanical properties decreased with increasing porosity. The properties of porous alumina samples with extensive grain necking showed higher values even in samples with the largest pore size. The high thermal conductivity of porous alumina with extensive grain necking was due to the low interfacial thermal resistance at grain boundaries. Porous alumina with extensive grain necking had high thermal shock strength due to the higher thermal conductivity. It was demonstrated that a porous structure combining high gas permeability and excellent fracture resistance could be successfully achieved.     

氧化铝及碳纤维对EPDM/MVQ共混胶性能的影响

选用EPDM/MVQ共混胶为基体,研究了氧化铝、碳纤维/氧化铝对EPDM/MVQ共混胶力学性能、导热性能及导电性能的影响。结果表明,随着氧化铝用量的增加,共混胶的力学性能下降,导热性能增加,电阻变化不大;当氧化铝用量为200份时,复合材料的拉伸强度达到4.5MPa,导热系数达到1.1W/(m·k),选用氧化铝/碳纤维混合填料体系,当氧化铝和碳纤维的用量分别为100份和15份时,复合材料的拉伸强度达到4.8MPa,导热系数达到0.66 W/(m·k)。     

Effect of powder,binder and process parameters on anisotropic shrinkage in tape cast ceramic products

The effect of powder, binder and process parameters on the properties of cast alumina tapes and their anisotropic shrinkage were investigated. Three alumina powders with different particle shapes (platelets, spherical, standard) and three PVB binders with different chain lengths were used. In addition, casting velocity and blade gap height were varied. The orientation of the particles in the tape was detected quantitatively by image analysis of micrographs. The shrinkage anisotropy is more than 12% for the platelet shaped powder and 8% for the standard powder, whereas the spherical particles lead to almost isotropic shrinkage. The influence of the organic binder chain length proved to be minor compared to the influence of the particle morphology. The variation of casting speed and blade gap height has no effect on anisotropic shrinkage in the investigated parameter range. This is explained by theoretical considerations of particle rotation in a sheared fluid.     

Thermal properties of homogenous lanthanum hexaaluminate/alumina composite ceramics

Lanthanum hexaaluminate has the potential to be applied in thermal barrier coatings due to its relative low thermal conductivity and low sinterability at temperatures higher than 1100 °C. One of the main problems in developing this material as a thermal barrier coating is difficulty in controlling the microstructure in order to combine the low thermal conductivity with high structural reliability.The idea behind this study was to take advantage simultaneously of the low thermal conductivity of lanthanum hexaaluminate and of the high mechanical properties of alumina by developing alumina-rich and lanthanum hexaaluminate-rich alumina/lanthanum hexaaluminate ceramic composites. The thermal properties of the alumina/hexaaluminate ceramic composites were compared as a function of temperature and lanthanum hexaaluminate content (20–80 vol.%). The results showed that the alumina/lanthanum hexaaluminate ceramic composites have sufficient low thermal conductivity to be used in thermal barrier coatings.     

Greener adhesives based on UF/soy protein reinforced with montmorillonite clay for wood particleboard

There is a global concern about the types of adhesives used for the binding of wood particles, most of which include formaldehyde in their formulation. The aim of this work is to study the effect of raw montmorillonite (Mt) particles on blended urea formaldehyde (UF)/soy protein (SP) adhesives for the manufacture of wood particleboards to reduce the use of this carcinogenic component. Rheology showed that Mt does not alter the viscosity of adhesives at high shear rates, so they can be applied by spray. Thermogravimetric analysis/derivative thermogravimetry (TGA/DTG) analysis revealed an enhancement of their thermal stability due to the presence of clay particles. Polymer–Mt interaction was studied by small amplitude X-ray scattering and scanning electron microscopy. According to these results, the exfoliated structure of the clay particles was achieved. Wood particleboards were manufactured with UF/SP/Mt adhesives in order to study their mechanical properties. The three-point bending test showed that Mt particles improved the modulus of both rupture and elasticity. UF/SP/Mt resins proved to be a prominent product for the development of environmentally friendlier particleboards with desirable mechanical properties.     

Effect of varying hydrolysis time on extraction of spherical bacterial cellulose nanocrystals as a reinforcing agent for poly(vinyl alcohol) composites

Bacterial cellulose nanocrystal (BCNC) was prepared from bacterial cellulose (BC) using acid hydrolysis for 12, 24 and 72 h. The effect of the BCNC was estimated as a means of reinforcing the poly(vinyl alcohol) (PVA) matrix in terms of mechanical and thermal properties. The effect of the hydrolysis time on BCNC extraction was evaluated by considering morphology, changes in chemical functional groups, crystallinity and thermal stability. Atomic force microscopy (AFM) images revealed the diameters of spherical cellulosic particles were in the range 16–35 nm with the smaller ones resulting from a longer hydrolysis treatment time. Fourier transform infrared (FTIR) spectroscopy showed no changes in the functional groups between BC and BCNC samples for all hydrolysis extraction times. However, X-ray diffraction (XRD) proved that the crystallinity of the BCNC increased up to 87% in comparison with the BC. The thermal stability of nanocellulose decreased over a longer hydrolysis period. Furthermore, the BCNC showed an improved effect on the PVA matrix in both tensile and thermal analysis. Therefore, BCNC obtained by acid hydrolysis for 24 h could be used as a reinforcing agent for material industries.