Hydrothermal Synthesis of Porous Al2O3/Al Metal Ceramics: II. Mechanism of Formation of a Porous Al(OH)3/Al Composite

The formation of a porous layer of aluminum hydroxide on the surface of aluminum particles and the aggregation of Al(OH)₃/Al composite particles were analyzed theoretically. It was found that the diffusion mass transfer of the hydroxo complexes of aluminum through the porous structure of a growing layer of aluminum hydroxide to the outer surface is a rate-limiting step in the synthesis of the porous composite. A model mechanism of formation of the porous composite was developed, and rate equations were derived for describing the growth of an aluminum hydroxide layer on the surface of an aluminum particle and changes in the degree of aluminum conversion and the contact radius between composite particles. Based on the developed mathematical model and experimental data, the diffusion coefficient of the hydroxo complexes of aluminum in the porous structure of aluminum hydroxide was calculated.     

Hydrothermal Synthesis of Porous Al2O3/Al Metal Ceramics: III. Effect of the Thermal Dehydration of Bayerite on the Formation of a Porous Al2O3/Al Composite

It was found that the diffusion permeability of a porous cover on aluminum particles increased as a result of the structural transformations of bayerite into active aluminum oxide on the thermal treatment of a porous Al(OH)₃/Al composite. The cyclic treatment (each cycle included a treatment with water at 100°C and a thermal treatment at 550°C) eliminated diffusion limitations and resulted in the formation of porous Al₂O₃/Al metal ceramics with a required set of adsorption–structure and mechanical properties. The following two competing processes were found to affect the formation of the mechanical properties of the synthesized material: the formation of new contacts in the course of the precipitation of aluminum hydroxide and the degradation of old contacts under the action of mechanical stresses that appear in the course of synthesis.     

Porous Al2O3/Al Metal Ceramics Prepared by the Oxidation of Aluminum Powder under Hydrothermal Conditions Followed by Thermal Dehydration: I. Composition and Macrocharacteristics of Composites

The macrotexture and mechanical properties of porous Al₂O₃/Al metal ceramics prepared by the hydrothermal treatment of aluminum powder in a closed space are studied using gravimetry, pycnometry, mercury porosimetry, and scanning electron microscopy. Analytical expressions that relate the porosity, density, and mechanical strength of parent materials and final products to the composite synthesis conditions are derived.     

Physicochemical Principles of the Synthesis of Porous Composite Materials through the Hydrothermal Oxidation of Aluminum Powder

The main versions of the synthesis of a new class of porous cermet materials such as Al₂O₃/Al, MO_x/Al₂O₃/Al, and M¹/MO_x/Al₂O₃/Al and ceramic composites on their basis were analyzed. These ceramic composites were prepared through the stage of the hydrothermal oxidation of aluminum powder and were designed for catalytic and adsorption processes. Equations that express the dependence of the apparent density of the resulting composite on the density of the initial powder mixture, on the concentration of the powdered active component, and on the conversion of aluminum are given. It was found that the formal kinetics of aluminum oxidation with water at 100°C can be described by the Kolmogorov-Erofeev equation. The results were compared with data obtained in an autoclave at higher temperatures and steam pressures. The synthesis parameters that affect the total pore volume and the specific surface area of aluminum oxide obtained from aluminum powder were determined. For the case of the transfer of soluble components from an autoclave to a press mold, the molar coefficients of this process were calculated. The texture peculiarities of composites were analyzed. The texture exhibited a polymodal character with developed micropore, mesopore, and ultramacropore structures, which are responsible for the high permeability of granulated composites. Factors affecting the mechanical properties of metal ceramics were studied. The catalysts and products of composite materials were exemplified.     

Porous Al2O3/Al Metal Ceramics Prepared by the Oxidation of Aluminum Powder under Hydrothermal Conditions Followed by Thermal Dehydration: II. Composition and Microtexture of the Composites

The microtexture of Al₂O₃/Al composites with different oxide contents formed in the hydrothermal treatment of aluminum followed by thermal decomposition of boehmite is examined by a set of adsorption and structural analysis techniques. Two main types of alumina microtexture are found: relatively loose agglomerates of amorphous particles and highly ordered aggregates of well-crystallized primary blocks of a larger size, the fraction of which increases with the oxide content of the composite leads to an increase in the fraction of micropores and a decrease in the fraction of mesopores. The mechanism of thermal decomposition of boehmite prepared by the hydrothermal oxidation of aluminum is refined.     

有机相化学镀铝法制备Al/石墨烯复合材料粉末

采用有机相化学镀法制备了Al/石墨烯复合材料粉末。使用傅里叶红外光谱仪、拉曼光谱仪、ASAP2020全自动快速比表面与孔隙度分析仪和配备EDS能谱的扫描电子显微镜表征样品。结果表明,镀铝后,石墨烯表面的含氧基团基本消失,发生空间弯曲折叠形成包覆结构,导致中孔和大孔的形成,石墨烯层间距变大。此外,氮气吸附-脱附结果显示,Al/石墨烯复合材料粉末的孔道以微孔和中孔为主,Brunauer-Emmett-Teller比表面积为91 m~2·g~(-1);通过Barret-Joyner-Halenda解吸模型计算得到的平均孔径为8.77 nm,孔体积为0.45 cm~3·g~(-1)。X射线衍射分析并没有发现Al_4C_3晶体结构的出现,表明镀铝过程并未或生成很少(小于检测下限)脆相Al_4C_3。最后,微观表面分析表明,当加入的NaH量略大于理论值时,实验结果与理想体系基本吻合,镀铝效果最佳。     

Simultaneous Al2O3 Doping and Sulfation in Hierarchically Porous ZrO2 Solid Acids by an One‐pot Synthesis for Enhanced Recycling Catalytic Performances

Alumina doping and sulfation in hierarchically porous zirconia solid acids have been achieved simultaneously via one‐pot and bi‐surfactant‐assisted self‐assembly process, using aluminum sulfate as both Al and SO₄^2? sources. The prepared composite solid acids showed much enhanced acidity and recycling catalytic activity for an esterification reaction compared with sulfated zirconia without alumina doping and Al‐doped sulfated zirconia without hierarchically porous structure.     

铝含量对含铝碳化硅陶瓷先驱体结构和性能的影响

采用不同比例的乙酰丙酮铝[Al(AcAc)3]与聚硅碳硅烷(PSCS)反应制备含铝碳化硅陶瓷的先驱体聚铝碳硅烷(PACS). 采用气相凝胶色谱(GPC)、化学分析和红外等手段对不同铝含量的PACS组成和结构进行了表征, 研究了铝含量对PACS结构和性能的影响. 结果表明, 随着铝含量的增加, PACS的氧含量增加, 分子量分布变宽, 主要活性基团Si—H键的含量降低, PACS的可纺性降低. 当Al(AcAc)3/PSCS(质量比)大于20%以后, PACS不可纺. 热重-差热分析(TG-DTA)的研究表明: 当制备PACS的Al(AcAc)3/PSCS(质量比)大于4%, PACS在N2中400～560 ℃之间的失重明显降低. 铝含量在0.4～0.7 wt%的PACS, 制备的Si-Al-C-O纤维抗张强度最高. Al(AcAc)3/PSCS＝6 wt%时制备的PACS, 烧结的SiC(Al)纤维最致密.     

Porous Al2O3/Al Metal Ceramics Prepared by the Oxidation of Aluminum Powder under Hydrothermal Conditions Followed by Thermal Dehydration: IV. Effect of Oxide Additives on the Composition and Texture Characteristics of MO x /Al2O3/Al Composites

The synthesis, structure, and texture of metal ceramics based on Al₂O₃/Al with powdered oxide additives (CaO, MgO, Al₂O₃, La₂O₃, and TiO₂) were studied. Analytic expressions were derived to relate the main macroscopic characteristics of the composites.     

AlMCM-41介孔分子筛的合成及表征

以拟薄水铝石为铝源、水玻璃为硅源、十六烷基三甲基溴化铵为模板剂,在110℃时水热晶化合成了含Al的MCM-41介孔分子筛.采用X射线衍射(XRD)、N2吸附-脱附、固体29Si、27Al魔角旋转核磁共振技术(MASNMR)、扫描电镜(SEM)及吡啶吸附傅里叶变换红外(FTIR)光谱技术对AlMCM-41分子筛进行了表征.结果表明:AlMCM-41分子筛具有六方排列的孔道结构,同时具有很高的相对结晶度、比表面积和孔容,且孔分布单一;AlMCM-41分子筛中Si原子在骨架内键合的程度更高,使AlMCM-41分子筛具有更好的骨架晶化程度;同时具有四配位骨架铝,使AlMCM-41介孔分子筛具有适当的酸性.     

A study of the alumina-silica gel adsorbent for the removal of silicic acid from geothermal water: increase in adsorption capacity of the adsorbent due to formation of amorphous aluminosilicate by adsorption of silicic acid

Two kinds of adsorbents (Si adsorbent and Al adsorbent) for the removal of silicic acid from geothermal water to retard the formation of silica scales were prepared using silicic acid contained in geothermal water. The Si adsorbent was prepared by evaporating geothermal water, and the Al adsorbent was prepared by evaporating geothermal water after the addition of aluminum chloride. The specific surface area of the Si adsorbent was small and it's adsorption capacity of silicic acid was low. Although the specific surface area of the Al adsorbent was also small, it was significantly increased by the adsorption of silicic acid and it's adsorption capacity was high. Based on the change in the local structure of aluminum ion by the adsorption of silicic acid, the Al adsorbent was considered to be silica particles covered with crystalline aluminum hydroxide. Moreover, it was concluded that the increase in the specific surface area of the Al adsorbent and the decrease in the zeta potential were due to the formation of an amorphous aluminosilicate with a large surface area and a negative charge (one 4-coordinated Al) by the reaction between aluminum ions and silicic acids.     

Hydrothermal Synthesis of Porous Al2O3/Al Metal Ceramics: I. Oxidation of Aluminum Powder and Structure Formation of Porous Al(OH)3/Al Composite

The properties of ASD-1 aluminum powder and its oxidation with water at 100°C were studied. It was found that the microstructure of a surface oxide film and the conditions of oxidation significantly affected the dynamics of changes in the pH of the solution and in the degree of aluminum conversion into the hydroxide. Experimental data on the oxidation in combination with electron-microscopic measurements and the determination of adsorption and texture characteristics resulted in the conclusion that colloid-chemical processes, which include the dissolution of aluminum and the formation and precipitation of the hydroxo complexes of aluminum, are fundamental for the synthesis of porous metal ceramics.     

Structure of mechanically activated high-energy Al + polytetrafluoroethylene nanocomposites

The structure of high-energy Al/polytetrafluoroethylene nanocomposites prepared by mechanochemical synthesis is studied by X-ray diffraction analysis, scanning electron microscopy, atomic force microscopy, and chemical analysis. It is revealed that the composite consists of aluminum particles with sizes of 100–150 nm separated by the polymer layers. The formation of nanocomposite is accompanied by the accumulation of dislocations with the density ρ = (4 ± 1.5) × 10¹⁰ cm⁻². Upon the shock-wave initiation of activated samples, Al + (-C₂ F₄-) → AlF₃ + C reaction propagates in detonation-similar regime at supersonic speed. The velocity of detonation is the highest at the stoichiometric component ratio.     

Bimetallic Al(III) Compounds as Catalysts for the Synthesis of Biodegradable Polyesters and Polycarbonates

Ethylenediamine bridged benzoxazine proligands were synthesized by a modified Mannich condensation reaction. The reaction of the proligands with two equivalents of AlMe₃ resulted in the formation of dinuclear Al(III) compounds in high yield and purity. When the ligand binds to the Al(III) center, it forms two separate six-membered N,O-chelates with the two Al atoms that resembles the N-alkylated salan moiety. Each aluminum atom adopts a distorted tetrahedral geometry as revealed from the single-crystal X-ray diffraction studies of 1 . The catalytic activity of these aluminum compounds was investigated towards the ROP of rac-LA and ROCOP of epoxides (PO, CHO, tBuGE) and phthalic anhydride and ROCOP of CHO with CO₂. These aluminum compounds showed notable catalytic activity towards the ROP and ROCOP reactions in the absence of cocatalyst.     

A Molecular Hexacoordinated Triorganoaluminum Compound with Trifold Si–H···Al Coordination

The synthesis of a hexacoordinate triorganoaluminum compound Al(NapSiH)₃ ( 6 ) (NapSiH = 8‐dimethylsilylnaphthyl) is reported. Three additional Si–H ··· Al contacts complete the coordination sphere around the central aluminum atom. Structural and spectroscopic evidence is provided for an activation of the Si–H bond by the aluminum Lewis acid. This activation is however small when compared to other recently described aluminum / silane complexes. These findings are supported by the results of quantum mechanical calculations, which indicate the presence of three Si–H ··· Al three center intractions in complex 6 .     

Adsorption of nitrogen on aluminum, Al2O3, and AlN powders at 78 K

The adsorption of nitrogen on aluminum powders of ASD-4 and UDA grades, aluminum oxide (α-Al₂O₃), and aluminum nitride is studied at 78 K in the adsorbate relative pressure range (P _a /P ₀) of 0 to 1. It is shown that the nature of the chemical bonds and the structure and state of the adsorbent determine the share of the adsorption isotherms and their attribution to a particular type of isotherms. With an increase in the fraction of metal bonds in an adsorbent, the isotherms become more convex, indicating enhancement of the effect of lateral interactions. The specific surfaces of samples are calculated.     

Synthesis and formation mechanism of TiO2/Al2O3 nanobelts by electrospinning

Poly(vinyl pyrrolidone) (PVP)/[Ti(SO₄)₂ + Al(NO₃)₃] composite nanobelts were prepared via electrospinning technology, and TiO₂/Al₂O₃ nanobelts were fabricated by calcination of the prepared composite nanobelts. The samples were characterized by thermogravimetric-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). XRD results show that the composite nanobelts were amorphous in structure, and pure phase TiO₂/Al₂O₃ nanobelts were obtained by calcination of the relevant composite nanobelts at 950°C for 8 h. SEM analysis indicates that the surface of as-prepared composite nanobelts was smooth, the widths of the composite fibers were in narrow range, and the mean width was ca. 8.9 ± 2.1 μm, thickness was about 255 nm, and there is no cross-linking among nanobelts. The width of TiO₂/Al₂O₃ nanobelts was ca. 1.3 ± 0.1 μm and the thickness was about 105 nm. TG-DTA analysis reveals that the N,N-dimethylformamide (DMF), organic compounds and inorganic salts in the composite nanobelts were decomposed and volatilized totally, and the weight of the sample kept constant when sintering temperature was above 900°C, and the total weight loss percentage was 81%. FTIR analysis manifests that crystalline TiO₂/Al₂O₃ nanobelts were formed at 950°C. The possible formation mechanism of the TiO₂/Al₂O₃ nanobelts was preliminarily discussed.     

Synthesis and performance of electroless Ni–P–TiCN composite coatings on Al substrate

Electroless Ni–P and Ni–P–TiCN composite coatings have been deposited successfully on Al substrates. Scanning electron microscopy (SEM) and energy dispersive X‐ray (EDX) techniques were applied to study the surface morphology and the chemical composition of the deposited films. Moreover, X‐ray diffraction (XRD) proved that Ni–P and Ni–P–TiCN deposits have amorphous structures. The properties of Ni–P–TiCN/Al composite films such as hardness, corrosion resistance and electrocatalytic activity were examined and compared with that of Ni–P/Al film. The results of hardness measurements reveal that the presence of TiCN particles with Ni–P matrix improves its hardness. Additionally, the performance against corrosion was examined using Tafel lines and electrochemical impedance spectroscopy techniques in both of 0.6 M NaCl and a mixture of 0.5 M H₂SO₄ with 2 ppm HF solutions. The results indicate that the incorporation of high dispersed TiCN particles into Ni–P matrix led to a positive shift of the corrosion potential and an increase in the corrosion resistance for all aluminum substrates after their coating with Ni–P–TiCN. In addition, Ni–P–TiCN/Al electrodes showed a higher electrochemical catalytic activity and stability toward methanol oxidation in 0.5 M NaOH solution compared with that of Ni–P/Al. Copyright © 2014 John Wiley & Sons, Ltd.     

生物模板法制备木材陶瓷*

生物模板法是一种制备具有生物形貌特点的结构和功能材料的新方法。由于木材组织结构方面的独特性,制备其多级孔结构的木材生态陶瓷在探索特殊微观结构和性能之间的关系方面有着重大的意义。本文总结了生物模板法制备陶瓷材料技术的发展现状,并且指出了各种工艺的优缺点,着重介绍了木材陶瓷的发展历史、制备方法、机理和性能,概述了木材陶瓷在骨移植材料和催化材料方面的应用和发展前景。     

Synthesis of Aluminum N,N-Dialkylcarbamates by Insertion of CO2 into Al−N Bonds

Despite decades of research on various carbamates and their important applications, only one aluminum N,N-dialkylcarbamate (ADC) with an aluminum:carbamate ratio of 1 : 3 has been structurally described and comprehensively studied so far, namely tris(diisopropyl)carbamate. The reasons for this situation include problems with the used synthetic routes. The process of CO₂ insertion into Al−N bonds of tris(dialkylamido)alanes resolved these difficulties. Using this advantageous synthetic route, the dimethyl and diethyl, as well as the pyrrolidino, piperidino, and N-methylpiperazino derivatives were now successfully prepared. These ADCs were investigated by solid-state NMR spectroscopy, where line-shape analyses of the ²⁷Al NMR spectra allowed conclusions with respect to the determination of the quadrupole coupling parameters. Furthermore, data of an intermediate during the CO₂ insertion into tris(diisopropylamido)alane were obtained by in-situ IR spectroscopy, which were complemented by NMR measurements of samples periodically taken during the reaction. Partial hydrolysis of tris(pyrrolidino)carbamate revealed a complex Al₃(μ₃-O) cluster structure, which was elucidated by single crystal X-ray diffraction.