Filtration characteristics of aluminium hydroxide mixtures (alumina hydrates)

The specific cake resistance of the alumina hydrates obtained from sodium aluminate solutions was investigated against the caustic ratio, ageing and filtration pressure using a laboratory test filter at constant pressure filtration conditions. The alumina hydrate product was produced from sodium aluminate solutions by seeding the aluminium hydroxide crystals of definite size distribution at constant solution temperature. The specific cake resistance was found to increase with the caustic ratio and filtration pressure and to decrease with the ageing of alumina hydrates in aluminate solutions.     

Mechanochemical capillary reactions in partly dehydrated gypsum and aluminium hydroxide interground powder mixtures

Authors activate gypsum and alumina (or gypsum-hemihydrate + alumina) mixtures by intensive grinding in a water-cooled planetary mill and measure water vapour adsorption, heat of solution, phase composition (by XRD) and activation energy of eliminated water (by thermal methods) of activated and non-activated samples. Thermal treatment of mechanically activated samples results in a much more intensive formation of crystalline products, thus e.g. the amount of calcium sulfoaluminate after a 2 hr/1200 °C heat treatment of the gypsum + A1(OH)₃ sample is much higher in activated samples. Based on these model experiments, authors conclude that gels are formed during mechanical activation, due to chemisorption and mechanochemical capillary reactions, which, in turn, act as crystallization nuclei, greatly affecting thermal reactions.     

Methacryloxypropyltrimethoxysilane films on aluminium: Electrochemical characteristics,adhesion and morphology

The electrochemical characteristics, adhesion and morphology of methacryloxypropyltrimethoxysilane (MAPT) films on aluminium were investigated during exposure to 3 wt.% NaCl. The MAPT films were deposited on aluminium surface from 2 to 5 vol.% methacryloxypropyltrimethoxysilane solutions, with the aim to investigate the influence of deposition parameters (silane solution concentration and curing time) on electrochemical characteristics, adhesion and morphology of MAPT films on aluminium.Using electrochemical impedance spectroscopy (EIS), potential–time measurements, adhesion measurements and optical microscopy coupled with image analysis, it was shown that films deposited from 5 vol.% solution exhibited better corrosion stability and adhesion, as well as lower porosity comparing to 2 vol.% solution and improved the corrosion protection of aluminium substrate, while the curing time had no influence on these characteristics.     

Methacryloxypropyltrimethoxysilane films on aluminium: Electrochemical characteristics, adhesion and morphology

The electrochemical characteristics, adhesion and morphology of methacryloxypropyltrimethoxysilane (MAPT) films on aluminium were investigated during exposure to 3 wt.% NaCl. The MAPT films were deposited on aluminium surface from 2 to 5 vol.% methacryloxypropyltrimethoxysilane solutions, with the aim to investigate the influence of deposition parameters (silane solution concentration and curing time) on electrochemical characteristics, adhesion and morphology of MAPT films on aluminium.Using electrochemical impedance spectroscopy (EIS), potential–time measurements, adhesion measurements and optical microscopy coupled with image analysis, it was shown that films deposited from 5 vol.% solution exhibited better corrosion stability and adhesion, as well as lower porosity comparing to 2 vol.% solution and improved the corrosion protection of aluminium substrate, while the curing time had no influence on these characteristics.     

Electrochemical production of aluminum hydroxide from kaolins

It has been shown that an electric spark discharge in saturated alkaline solution acts as a catalyst of ionization during the decomposition of kaolinite into aluminate and silicate components. The production of aluminum hydroxide from KM-1-grad kaolin (Chalgansk deposit) is 24.8–37.2% of the estimated value.     

The effect of surface modification of aluminium hydroxide on the crystallisation behaviour of aluminium hydroxide filled polypropylenes

Composites based on polypropylene (PP) (homopolymer and impact modified copolymer) and surface modified aluminium hydroxide (Al(OH)₃) have been studied using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Filler surface modifiers used included 2-dodecen-1-yl succinic anhydride (DDSA) as a dispersant and a commercial silane based coupling agent system (BA Chemicals S21). Treatment of the Al(OH)₃ with DDSA led to a considerable reduction of the capacity of the filler to nucleate crystallisation in the PP and, in some composites, promoted growth of β-PP. With the S21 treatment, however, a nucleation effect was still apparent, despite encapsulation of the filler particles with the elastomeric phase in the case of the impact modified PP. DSC and XRD studies indicated that with the untreated filler nucleation was directly associated with the filler surface. However, with the S21 treated filler this was not the case and PP nucleation was random and/or flow induced with no association with the filler surface.     

纳米Mg(OH)_2·Al(OH)_3苯甲酸乙酯包复体的制备研究

采用液相共沉淀法首先合成出纳米氢氧化镁和氢氧化铝的复合物Mg(OH)2.Al(OH)3,再制备出纳米Mg(OH)2.Al(OH)3与苯甲酸乙酯的包复体,运用TEM、XRD、TG-DTA研究复了合物及包复体的性能。结果显示复合物的平均粒径为55nm,包复体的平均粒径为75nm。包复体有较高的热稳定性,且均匀分散在有机溶剂中。     

The orientation of silver nuclei on a platinum substrate

The initial stages of silver electrocrystallization on a platinum electrode have been investigated. A pulse method was used, in which an electron pulse-generator was combined with a pulse potentiostat. A single, square potentiostatic pulse, with height and duration chosen in a way that single crystal nuclei were formed, was superposed on an initial potential at the beginning of the experiment. The crystals grew further on account of the potential initially set, and their growth was continuously followed microscopically.

The crystal orientations obtained in the various overvoltage regions, are: for the orientation axis [111], 20–50 mV; for [100], 60–100 mV; for [110], 120–170 mV; for [113], 170–200 mV; for [210], over 200 mV. The experimentally obtained orientation axes are in full agreement with those theoretically calculated for metals with a f.c.c. lattice.     

Preparation of gelatinous aluminium hydroxide from aqueous solutions of organic aluminium salts by reaction with alkali

The preparation of gelatinous aluminium hydroxide from aqueous solutions of the formate, citrate or tartrate of aluminium on addition of aqueous sodium hydroxide has been investigated under different conditions. The precipitates from aqueous solutions of aluminium formate consist of amorphous aluminium hydroxide, pseudoboehmite, bayerite, hydrargillite or their mixtures, depending on the condition of preparation. A mixed solution of aluminium citrate and sodium hydroxide yields no solid-phase product without aging on heating to enhance the hydrolysis of aluminium citrate. The resulting precipitate exists as pseudoboehmite, independent of the preparation conditions. In contrast, aluminium tartrate is not hydrolysed to precipitate aluminium hydroxide even by aging on heating.     

老化条件对氢氧化铝性质的影响

以偏铝酸钠和稀硝酸为原料,在不同温度条件下中和制备了氢氧化铝,并研究了不同老化条件对氢氧化铝粒度、晶相等的影响.实验结果表明,不同中和温度得到的氢氧化铝的粒度随老化时间变化很小,其粒度由中和温度决定,因而可以尽量缩短老化时间;经过70 ℃中和得到的氢氧化铝的粒度为28～30 μm,高于50 ℃中和条件下的17～20 μm.中和结束后不同老化温度对氢氧化铝粒度的影响一致,因此可以采用较低的老化温度;75 ℃中和的浆液中氢氧化铝随老化时间延长粒度有变大的趋势,而低温(如40 ℃)中和的浆液中氢氧化铝随老化时间延长粒度有所减小,因而要获得较大粒子,较低温度中和后一般采用老化时间为0.5 h;老化时间对氢氧化铝晶相影响较小,中和结束后,氢氧化铝晶型转化基本完成,不随老化时间增加而改变.     

氧化铝、氢氧化铝的XRD鉴定

氧化铝、氢氧化铝的晶型有多种,不同晶型的氧化铝、氢氧化铝的用途差别也很大,所以必须确定它们的晶型.X射线衍射仪在区别物质晶型方面有独特的优势.在参考前人工作的基础上,介绍了不同晶型的氧化铝、氢氧化铝的X射线衍射图及其特征衍射峰,并分析了衍射峰之间的差别,以及鉴定方法.并简单介绍了不同晶型的氧化铝、氢氧化铝的用途.     

以棒状碱式碳酸铝铵为原料制备硼酸铝晶须

在均匀设计实验法及数据挖掘技术得到的优化条件下,采用低温固相法合成棒状碱式碳酸铝铵,以棒状碱式碳酸铝铵和硼酸为原料制备硼酸铝晶须。实验结果表明,棒状碱式碳酸铝铵的Al-O骨架结构对硼酸铝晶须的合成具有诱导作用,加入助熔剂氯化钾有利于一维晶须的生长。经过X射线衍射（XRD）及扫描电镜（SEM）表征,得到的硼酸铝晶须平均直径为0.4 μm,平均长度为16 μm。     

Preparation of gelatinous aluminium hydroxide by urea from aqueous solutions containing chloride,nitrate and sulphate of aluminium

The preparation of gelatinous aluminium hydroxide from aqueous solutions containing a mixture of the chloride, nitrate or sulphate of aluminium and urea by heating at 95°C has been investigated under different conditions. The pH value of aqueous solutions, on heating for a given period of time, gradually increases, rises steeply at pH 4.0–7.5 and finally approaches a constant value. The precipitate appears at about pH 7 in the presence of chloride or nitrate ions and about pH 4 in the presence of sulphate ions. Although the gelatinous precipitates in the chloride and nitrate systems are apparently different from the granular, filterable one in the sulphate system, their compositions are not influenced by the species of aluminium salt. The fresh precipitates exist in an amorphous state, and go to pseudoboehmite by ageing. It seems that the amount of pseudoboehmite increases as the concentration of aluminium salt in aqueous solution decreases. However, the transformation from amorphous aluminium hydroxide to pseudoboehmite is reduced in the presence of sulphate ions. Furthermore, it is found that the X-ray diffraction peak for the (200) plane, as an orthorhombic structure, in the pseudoboehmite precipitated from chloride or nitrate solution is more intense than that from sulphate solution.     

Electrodeposition of aluminium and aluminium/platinum alloys from AlCl3/benzyltrimethylammonium chloride room temperature ionic liquids

This paper shows that aluminium and aluminium/platinum alloys can be deposited from room temperature ionic liquids formed from an adduct of aluminium trichloride with benzyltrimethyl ammonium chloride. The advantages of this ionic liquid over the majority of those previously investigated is that it is less water sensitive, easier to purify and form and significantly more cost effective. Voltammetry and chronoamperometry were used to investigate the deposition and stripping of aluminium on Pt, Al and Fe electrodes. Hull cell tests were performed to obtain the optimum deposition conditions and bulk electrolysis showed that uniform, adherent, crack-free aluminium deposits could be obtained from such ionic liquids. Co-electrodeposition of Al with Pt was also studied and the nucleation mechanism was found to change significantly when Pt complexes were added to the ionic solution. The platinum ligands were found to change the solubility of the complex, but had little effect on the morphology of the deposited film.     

Mullite formation from the pyrolysis of aluminium-loaded polymethylsiloxanes: The influence of aluminium powder characteristics

Polymethylsiloxane (PMS) filled with a range of aluminium powders of different size and morphology have been used to produce precursor mixtures to form mullite bodies. The size and shape of the Al powder is shown to have a strong influence on the temperature and mechanism of mullite formation, on the final microstructure and phase composition of the product. The reaction proceeds by decomposition of the PMS producing amorphous SiO₂. Al oxidation occurs both by reaction with the atmosphere and by reduction of the amorphous SiO₂ to produce α-Al₂O₃. Crystallisation of cristobalite was also observed prior to mullitisation. It is these components of the microstructure that react to produce mullite. The onset of mullite formation occurs at different temperatures, depending on the initial Al powder size and morphology. Large, flake morphology Al powders produced the greatest quantity of mullite and showed the lowest temperatures for mullite formation. XRD analysis identified 3:2 mullite in samples using large Al particles after heating to 1400 °C and at 1700 °C in samples using small Al powders.     

氢氧化铝粉体表面化学改性的研究

综述了氢氧化铝粉体在应用领域存在的主要问题，解释了氢氧化铝粉体表面化学改性的机理。详细地介绍了国内外氢氧化铝粉体的表面化学改性的方法，主要包括酯化反应法、偶联剂法、表面活性剂吸附法以及聚合物包覆法。经研究表明，氢氧化铝粉体表面化学改性后扩宽了其应用领域，具有良好的前景。     

Electrochemical microstructuring of ultra-thin passive films on aluminium

Special optical sensors require thin film devices with a layer structure of the type glass/Al/Al₂O₃ with thicknesses of oxide and metal in the range of some nm. Structures comparable with a printed circuit board were written by electrochemical potential control with a scanning droplet device. Dots, lines, or areas of different thickness ratios Al/Al₂O₃ or even with gradients can be written. Insulating lines become possible by complete oxidation of the Al metal.     

Influence of aluminium hydroxide and lime on the hydration of tricalcium silicate

Experiments by isothermal calorimetry, indicate that the hydration of 3CaO·SiO₂ (C₃S) is influenced very little by gibbsite; it is influenced by bayerite to a somewhat larger extent. In the presence of amorphous Al(OH)₃ the reaction of C₃S with water shows a very complicated course and gives four heat peaks. If CaO is added in addition to this Al(OH)₃, the third and the fourth heat peaks are more pronounced. From qualitative d.t.a., infra-red, electron-microscope and X-ray investigations, as well as from quantitative X-ray analysis, a reaction mechanism is proposed. The quantity of C₃S reacted, determined by means of quantitative X-ray analysis, is greater during the reaction of 2·00 g C₃S with 0·40 g amorphous Al(OH)₃, 0·08 g CaO and 2·00 ml water, than during the reaction of 2·00 g C₃S with 2·00 ml water.     

Electrochemical characterization of electrodeposited chromium and nickel-chromium layers on a steel substrate

Chromium was deposited on steel specimens and on electroplated steel specimens covered with a Watts nickel layer. The influence of the substrate and of the crack pattern of the electrodeposited chromium layer on the passivation and the reactivation behaviour has been studied by means of potentiodynamic polarization curve measurements and cyclic voltammetry. In the results of the above mentioned electrochemical measurements a strong influence of the substrate was found for a cracked chromium layer deposited on the steel specimen and for a cracked chromium layer deposited on a 30 m Watts nickel layer. No influence of the substrate was found in the case of a crack-free chromium layer deposited on the steel substrate or on a Watts nickel layer. It is thus possible to determine whether the chromium layer is cracked or crack free by recording a polarization curve or a cyclic voltammogram for a chromium-plated system. A mechanism is proposed for the passivation and repassivation of cracked chromium layers electrodeposited on a steel substrate or on a Watts nickel layer.