Small Amounts Of Aluminum Research Articles

Studies on wetting behavior of hot‐dip galvanizing process by use of model specimens with tailored surface oxides

The hot‐dip galvanizing process is widely used in steel production for automotive applications. The wetting behavior of molten zinc containing a small amount of aluminum and a steel surface is one of the most important issues concerning this process. Especially, studies on the degradation of wettability caused by surface oxides of steels have been focused on in recent years. This present work focused on the wetting of MnO which is a typical oxide appearing on steel surfaces. The reaction between the aluminum in the molten zinc and the MnO has been expected to improve wettability in the galvanizing process. However, no direct evidence has been reported on this, likely due to the difficulty of observation during the process. For this observation, a simple MnO layer was prepared, and wetting experiments by the sessile drop method were conducted in a laboratory‐made apparatus. The apparatus included a unique spin‐off technique that allowed us to stop a reaction during wetting and make an interface analysis at an early stage of the wetting. It was revealed that aluminum precipitated at the interface during wetting, which is assumed to be due to the aluminothermic reaction. However, the contact angle of the wetting was large and did not change during the wetting. The decrement of the MnO by the reaction was estimated as small as a few nanometers in 7 seconds. This indicated that the effect of the reaction on wettability in the real process condition can be seen to be minor. Copyright © 2012 John Wiley & Sons, Ltd.

Impacts of silica on the sustainable productivity of reverse osmosis membranes treating low-salinity brackish groundwater

Brackish water desalination is increasingly being considered as an alternative drinking water treatment processes. The impacts of high silica (63 mg/L) on the performance of brackish water reverse osmosis (BWRO) while treating a brackish groundwater (1315 mg/L of TDS) were investigated. This study demonstrated the importance of pilot-scale testing in understanding the long-term impacts of silica fouling in order to maintain the sustainable flux and recovery of new generation BWRO membranes. Two commercial membranes, selected from bench-scale coupon testing, were evaluated at pilot scale. The results suggested that due to the presence of high silica, operational flux and recovery were limited to 16.9 Lm − 2 h − 1 and 75%, respectively, for both RO membranes. The silica fouling predominantly occurred in the second stage of the RO systems, and membrane autopsy revealed that the foulant layer was primarily comprised of inorganic elements (10% organic, 90% inorganic) including silicon and a small amount of aluminium. The antiscalant and chemical cleaning were essential to minimize silica scaling and to restore flux; however, the flux decline rates were faster in the subsequent cycles indicating the detrimental effects of silica deposition. The annual chemical cost could be significantly high due to the increased frequency of chemical cleaning.

Phase-transformation and grain-growth kinetics in yttria-stabilized tetragonal zirconia polycrystal doped with a small amount of alumina

Microstructure development during sintering in 3 mol% Y 2O 3-stabilized tetragonal zirconia polycrystal doped with a small amount of Al 2O 3 was investigated in the isothermal sintering conditions of 1300–1500 °C. At the low sintering temperature at 1300 °C, although the density was relatively high, the grain-growth rate was much slow. In the specimen sintered at 1300 °C for 50 h, Y 3+ and Al 3+ ions segregated along grain boundaries within the widths of about 10 and 6 nm, respectively. In grain interiors, the cubic-phase regions were formed by not only a grain-boundary segregation-induced phase-transformation mechanism but also by spinodal decomposition. The grain-growth behavior was kinetically analyzed using the grain-size data in 1300–1500 °C, which indicated that the grain-growth rate was enhanced by Al 2O 3-doping. These phase-transformation and grain-growth behaviors are reasonably explained by the diffusion-enhanced effect of Al 2O 3-doping.

Formation of acid sites in amorphous silica-alumina

A suite of amorphous silica-aluminas (ASAs) was prepared by homogeneous deposition–precipitation (HDP) of aluminium on a silica surface followed by calcination. The HDP process was investigated in detail by 27Al NMR spectroscopy of solid and liquid aliquots of the synthesis mixture. Deposition occurs predominantly via a hydrolytic adsorption of aluminium onto the hydroxyl groups of the silica surface. Precipitation becomes more significant at higher aluminium concentration. Depending on the aluminium loading, the surface contains four- and six-coordinated aluminium as well as patches of aluminium hydroxides. Calcination results in two competing process, that is the diffusion of aluminium into the silica network and sintering of aluminium into separate patches of a phase which mainly consists of octahedral Al. These ASAs exhibit Brønsted acidity similar to industrial amorphous silica-aluminas prepared by the grafting of aluminium on very reactive silica gels. Their acidity does not vary systematically with the aluminium concentration, except below 5 wt% Al 2O 3. The acidity increases with the calcination temperature. The active sites form due to the diffusion of aluminium into the silica network at high temperatures, leading to Al substitutions of Si atoms. This is expected as the acidity does not correlate with anything else, viz., the amount of four-coordinated aluminium nor the presence of segregated Al or five-coordinated aluminium at the interface of these domains and the mixed silica-alumina phase. The surface of an amorphous silica-alumina consists of isolated aluminium grafted onto the silica surface (pure silica-alumina phase) with a very small amount of aluminium in the silica network, which brings about the Brønsted acidity, and small patches of aluminium oxides.

Work-function engineering of carbon nanotube transparent conductive films

We developed a method that allows control of the work function of carbon nanotube (CNT) transparent conductive films on a flexible sheet of plastic. The approach involves the deposition of small amount of metals, such as aluminum, on CNT transparent conductive films followed by a measure of the work function of the films using in situ ultraviolet photoelectron spectroscopy. Core-level spectra of the films were collected in order to investigate the chemical reaction when a small amount of aluminum was deposited on their surface in a stepwise manner. The measurements revealed that deposition of less than 0.5 nm of aluminum was enough to control the work function of CNT transparent conductive films.

Effects of Preparation Conditions on Surface and Catalytic Properties of Copper and Zinc Mixed Oxides System

Copper-zinc mixed oxides treated with small amounts of alumina and having the formula 0.5 CuO: 0.5ZnO: 0.05 Al2O3 were prepared by coprecipitation of their mixed hydroxides from their mixed nitrates solutions using 1 M NaOH solution. The precipitation was carried out at different pH values varying between 7 to 9.5 and at 50 and 70 o C. The results revealed that the bulk of various solids consisted of CuO and ZnO having ratios varying between 0.91 and 1.20. While the surface Cu/Zn ratio was bigger than those present in the bulk and varied between 1.16 to 1.64 depending on the pH value and calcination temperature. The mixed oxide solids existed as nanocrystalline CuO and ZnO phases. The surface characteristics are strongly dependent on both the pH value and calcination temperature. The computed SBET val- ues varied between 21and 108 m 2 /g and all adsorbents are mesoporous solids. The prepared solids showed a good cata- lytic activity in CO oxidation by O2 which proceeds via first order kinetics in all cases. The activation energy of the cata- lyzed reaction was determined for various solids and the computed values were very small indicating the big catalytic ac- tivity of the investigated solids.

Gemischte Erdalkalimetall‐Aluminide “AIIAl2”

AbstractMixed Alkaline Earth Aluminides “AIIAl2”Mixed alkaline earth aluminides near the composition A1IIxA2II1–xAl2 (AII = Ca, Sr, Ba) were synthesized from stoichiometric ratios of the elements in tantalum crucibles; their crystal structures were determined using single‐crystal X‐ray data. Starting from the binary cubic Laves phase CaAl2 (|:ABC:| stacking of aluminium Kagomé nets) up to 73 % of calcium can be replaced by strontium (Ca0.27Sr0.73Al2, cubic, space group , a = 821.2(2) pm; Z = 8, R1 = 0.0083). The new ternary compound Ca1.1Sr5.9Al13 (trigonal, space group , a = 582.35(3), c = 1655.2(2) pm, Z = 1, R1 = 0.0387) forms the structure type originally reported for ‘Ba7Al13’, which exhibits blocks of three Kagomé nets ABC as a section of the MgCu2 structure. Blocks of two connected Kagomé nets (Sr5Al9 structure type: trigonal, space group , Z = 3) are stable from a Sr proportion of approx. 90 % (Ca0.5Sr4.5Al9: a = 582.61(5), c = 3549.0(6) pm, R1 = 0.0512) through the binary Sr phase up to the barium substituted compound Sr3.9Ba1.1Al9 (a = 590.88(2), c = 3585.2(2) pm, R1 = 0.0212). This structure type is also observed on the Ca–Ba section i.e. at a comparable merged cation radius, between Ca3.3Ba1.7Al9 (a = 578.91(14), c = 3537.7(13) pm, R1 = 0.0462) and Ca2.6Ba2.4Al9 (a = 582.23(6), c = 3570.2(7) pm, R1 = 0.0309). Starting from the binary Ba compound Ba21Al40 (trigonal, space group P31m, Z = 1), only a small Ca (Ca1.9Ba19.1Al40: a = 1048.5(2), c = 1718.3(4) pm, R1 = 0.0624) and Sr substitution (Sr4.3Ba16.7Al40 (a = 1048.64(11), c = 1713.1(2) pm, R1 = 0.0242) is possible without a structure change. Also only a small amount of aluminium can be substituted by Ge (Ba21Al39.2Ge0.8: a = 1053.10(13), c = 1718.4(2) pm, R1 = 0.0576) or In (Ba21Al35.3In4.7: a = 1061.10(9), c = 1738.1(2) pm, R1 = 0.0569) in the latter structure. In this series of compounds near the composition AAl2, the radii of the cations appears to be the decisive element, that governs structure and to some extent even the composition. The available tolerances and the individual site distributions are discussed. For an electronic comparison, FP‐LAPW band structure calculations are performed for binary aluminides of all observed structure types and the results are compared to those of the simple electron counting methods.

The aluminium effect on the structure of silico-phosphate glasses studied by NMR and FTIR

Silico-phosphate glasses of NaCaPO 4-SiO 2 and NaCaPO 4-AlPO 4-SiO 2 system have been the subject of the presented investigations. Glasses of these systems are the basis for the preparation of glassy-crystalline biomaterials [R.D. Rawlings, Clin. Mater. 14 (1993) 155]. Detailed knowledge of the precursor glass structure is necessary for proper design of the glassy-crystalline biomaterials preparation procedure. Since there is no long-range ordering in glasses, spectroscopic methods which make it possible to study the short range ordering should be applied. MIR studies carried out in the work have allowed to establish that the glasses of the systems studied show domain composition [L.L. Hench, R.J. Splinter, T.K. Greenlee, W.C. Allen, J. Biol. Res. Symp. 2 (1971) 117; L.L. Hench, R.J. Splinter, W.C. Allen, T.K. Greenlee, J. Biol. Res. 5 (1972) 117]. Domain structure is close to that of the corresponding crystalline phases. It has been shown that even small amount of aluminium in the glass (5 mol.% of AlPO 4) significantly influences both, its texture (microscopic and EDX studies) and its structure (spectroscopic studies). 27Al NMR investigations have made it possible to establish unequivocally that aluminium occurs exclusively in tetrahedral coordination, i.e. it is involved in the formation of glass framework. Presence of aluminium results in significant changes in the [SiO 4] 4− and [PO 4] 3− tetrahedra environment which is reflected in 23Na, 31P and 29Si NMR spectra. Changes in the shapes and positions of the bands in the NMR spectra of glasses belonging to the NaCaPO 4-AlPO 4-SiO 2 system confirm great influence of aluminium on silico-phosphate glasses structure.

Thermal solid–solid interactions and physicochemical properties of Co 3O 4/MoO 3 system treated with Al 2O 3

The thermal solid–solid interactions between Co 3O 4 and MoO 3 and their physicochemical properties in the presence and absence of Al 2O 3 have been investigated using thermal analysis (TG–DTG–DTA), X-ray diffraction (XRD) techniques, electron spin resonance (ESR) and catalytic decomposition of H 2O 2 at 30, 40 and 50 °C. The pure and variously doped mixed solids were subjected to heat treatment at 350, 550, 750 and 1000 °C. The amounts of dopant were 1.23, 2.44, 4.76 and 9.09 mol% Al 2O 3. The results revealed that only Co 3O 4 phase was detected for the pure mixed solids calcined at 350, 550 and 750 °C. Doping of the system under investigation with alumina enhanced the formation of crystalline cobalt molybdate phase starting from 350 °C. The degree of crystallinity of CoMoO 4 phase increased with increasing calcination temperature and amount of dopant. Crystalline Al 2(MoO 4) 3 and CoAl 2O 4 phases detected for the solids heavily doped with alumina and calcined at 750 and 1000 °C, respectively as a result of solid–solid interactions between the reacted oxides. CoO phase was detected only for the pure mixed solids and that doped with small amount of alumina and calcined at 1000 °C. The catalytic activity of mixed oxides was higher than that of single oxides obtained at the same temperature. The catalytic activity of Co 3O 4/MoO 3 system progressively decreased with increasing the amount of alumina dopant and with increasing calcination temperature.

Continuous Si–C–O–Al fiber derived from aluminum-containing polycarbosilane precursor

Abstract By modifying polymer precursor polycarbosilane (PCS) with a metallic alkoxide, SiC fibers containing heteroatoms (such as Ti, Zr and Al) could be prepared. Continuous Si–C–O–Al fibers were fabricated by the melt-spinning of aluminum-containing polycarbosilane (Al-PCS) precursor, air-curing and pyrolizing at 1350 °C. These fibers contained small amount of aluminum and 7 wt.% oxygen. The fibers were characterized by chemical analysis, tensile strength test, X-ray diffraction (XRD), Auger electron spectroscopy (AES), scanning electron microscopy (SEM), atomic force microscopy (AFM), high resolution transmission electron microscopy (HRTEM). The tensile strength, Young’s modulus and diameter of the Si–C–O–Al fibers are 2.6 GPa, 210 GPa, 12∼14 μm, respectively.

The corrosion of Fe 3Al alloy in liquid zinc

A systematic study of the isothermal corrosion testing and microscopic examination of Fe 3Al alloy in liquid zinc containing small amounts of aluminum (less than 0.2 wt.%) at 450 °C was carried out in this work. The results showed the corrosion of Fe 3Al alloy in molten zinc was controlled by the dissolution mechanism. The alloy exhibited a regular corrosion layer, constituted of small metallic particles (diameter: 2–5 μm) separated by channels filled with liquid zinc, which represented a porosity of about 29%. The XRD result of the corrosion layer formed at the interface confirmed the presence of Zn and FeZn 6.67. The corrosion rate of Fe 3Al alloy in molten zinc was calculated to be approximately 1.5 × 10 −7 g cm −2 s −1. Three steps could occur in the whole process: the superficial dissolution of metallic Cr in the corrosion layer, the new phase formation of FeZn 6.67 and the diffusion of the dissolved species in the channels of the corrosion layer.

Preparation of MCM-48 materials with enhanced hydrothermal stability

A supercritical fluid method has been developed to prepare hydrothermally stable, high quality mesoporous MCM-48 materials. Pure silica MCM-48 materials were post-treated by supercritical carbon dioxide containing a small amount of aluminum tri-sec-butoxide (sc-CO2/Al). The hydrothermal stability of these treated MCM-48 materials in boiling water was studied by powder X-ray diffraction, nitrogen absorption analysis, transmission electron microscopy, and 29Si and 27Al MAS NMR. 27Al MAS NMR studies suggest that incorporation of the tetrahedral Al atoms into the framework of MCM-48 plays an essential role in enhancing the hydrothermal stability of these materials. For comparison, precursors containing other atoms, including Zr and Ti were also tested but most of these were found to have little influence on the hydrothermal stability of MCM-48.

Laser Weldability of Aluminum Alloy and Steel

With the intention of improving butt or lap joint of dissimilar materials, specially devised weld beads together with lap and butt-joints were produced between A5052 and SPCC, where A5052 butt-joint was melted by heat-conduction of SPCC weld bead in addition to the formation of a limited weld fusion zone at the lap part in A5052 alloy. The thickness of intermetallic compounds at the butt-joint interface was approximately 2 μm and free of cracks. It was also revealed that crack-free lap weld metals were formed between aluminum alloy and steel when the penetration was controlled to be of less than 0.3 mm in depth at small heat input. It was moreover found that the majority of a laser weld fusion zone solidified as alpha(bcc)-iron phase containing small amount of aluminum, and cracks were absent in the case of hard intermetallic (AlxFey type) layer of less than 10μm zone. It was confirmed that a weld with lap and butt joints possessed high strength (leading to the load 3500 N to 4,380 N for 40 mm width specimen). In addition, SPCC and A1100 or A5052 were subjected to lap welding with a cw YAG laser, where one to three passes were performed to produce wider bonded areas. Dissimilar steel and aluminum joints with good mechanical properties were obtained, since the fracture occurred in the aluminum alloy base metal in the tensile test. It is concluded that welded joints of high strength can be produced between aluminum alloy and steel with proper devices.

New material for flashlamp cathodes

It has recently been shown that porous tungsten can be sintered at much lower temperatures (T<1200°C) than those employed in conventional sintering techniques (T>2000°C). This was achieved by the addition of a small amount of aluminium to tungsten at the powder preparation stage. As a result, homogeneous microstructures with uniform porosity distributions were obtained. This short article presents some of the results from the tests conducted, using the reactive sintered compacts as cathodes in flashlamps. The results were found to be encouraging. However, the blackening of the quartz lamp was observed after a certain amount of time (3–20 h) suggesting sputtering, with some grey deposits accumulating on the surface of the cathode. Further improvements are anticipated by focusing on the optimisation of the structure/performance relationship.

Theoretical model of the interfacial reactions between solid iron and liquid zinc-aluminium alloy

Steel strip is often coated with a layer of zinc in order to protect it against corrosion. One of the most commonly used coating processes is continuous hot dip galvanizing. In this process, the steel strip is immersed in a molten zinc bath containing small amounts of aluminium (less than 1 wt%).

Modelling of the galvanizing reactions

In continuous hot dip galvanizing, steel strip is immersed in a molten zinc bath containing small amounts of aluminium. A model has been developed describing the kinetics, of the galvanizing reactions that occur at the steel/liquid zinc interface (dissolution of iron, heterogeneous nucleation and growth of the intermetallic phase Fe2Al5Znx). The model has been validated using experimental data available in the literature for a three-second galvanizing treatment.

Sintering Aids in the Consolidation of Boron Carbide (B4C) by the Plasma Pressure Compaction (P2C) Method

Boron carbide (B4C) powder has been densified by a novel method of powder consolidation known as Plasma Pressure Compaction (P2C). The P2C technique allows for rapid consolidation of powder by Joule heating of the powder bed. Powder is placed in graphite dies, and uniaxial pressure and low-voltage, high-amperage (10 V, 5000 amps maximum) direct current are applied to achieve densification. Pure B4C powder was consolidated at lower temperature and hold time to densities equal to those achieved by conventional hot pressing. With the addition of a small amount of alumina (Al2O3) as a sintering aid, densities as high as 97% theoretical were attained.

Characterization of Wall-Type Nickel Catalysts for Methanol Decomposition, Prepared on an Aluminum Plate by Electroless Plating

Various wall-type nickel catalysts were prepared on aluminum plates by electroless plating under changing conditions for displacement plating of zinc and chemical reduction plating of nickel, and their physicochemical properties were investigated. Correlation between these physicochemical properties and the decomposition properties of methanol over these plated catalysts was examined. The results show that the decomposition performance of the plated catalysts does not correlate with the surface areas of the plated layer but depends on the ratio of the crystallite size of nickel particles, as determined by XRD, to that of aluminum particles. This finding suggests the involvement in catalytic activity of aluminum that dissolves from the substrate in the plated layer as well as nickel, which is considered as the active site.Elemental component analysis and elemental state analysis in the plated layer indicate that the use of sodium hypophosphite monohydrate as a reducing agent results in the incorporation of phosphorus in the plated layer, and the plated catalyst with high selectivity of carbon monoxide and hydrogen for methanol decomposition contains large amounts of zinc and phosphorus, and a small amount of aluminum, with nickel in the bulk layer of this catalyst being in a metallic-state. The finding in which granular Ni3P and Ni/ZnO catalysts, with high selectivity for methanol decomposition, had metallic-state nickel suggests that some incorporation of phosphorus and zinc oxide, that increased the metallic-state of nickel, and the small amount of aluminum in the plated layer produce the high selectivity for methanol decomposition.

Aging mechanisms of lithium cathode materials

Batteries for stationary and automotive applications are required to provide extended cycle life and calendar life. Lithium–manganese oxides (LiMn2O4) with spinel structure and lithium–nickel–cobalt mixed oxides (LiNiCoO2) with layered structures have been extensively studied in the last few years for usage in high energy and high power batteries in order to replace lithium–cobalt oxide (LiCoO2) as cathode material in terms of cost, abundance and performance. In this paper, we summarize some basic mechanisms responsible for capacity fading under cycling and different storage conditions for both types of cathode materials. Lithium–nickel–cobalt mixed oxides show excellent storage stability in the discharged state and low metal solubility in the electrolyte. The cycling stability is mainly influenced by structural changes in the delithiated state and thermal instability arises from oxygen release at elevated temperatures in the charged state. Small amounts of aluminum and magnesium dopants stabilize the layered structure and increase cycling stability of lithium–nickel–cobalt oxide. Different mechanisms of capacity fading especially at higher temperatures are discussed for lithium–manganese oxide spinels. Capacity fading is highly dependent on cycling and storage conditions and caused by structural changes as well as by side reactions with electrolyte catalyzed by decomposition products of LiPF6 conducting salt and H2O impurities in the electrolyte.

A New Aluminum Coordination Site in Si‐C‐Al‐N‐(O) Ceramics

A variety of Si‐C‐Al‐N‐(O) ceramics with different AlN and SiC contents were prepared by pyrolysis of Si‐Al‐C‐O precursors at 1700°C in nitrogen. In those ceramics containing small amounts of aluminum, a new 27Al MAS NMR peak at 134.3 ppm was found. The existence of this peak is discussed in relation to recent findings in aluminum‐containing complex ceramic systems.