Grain refinement efficiency and mechanism of aluminium carbide in Mg-Al alloys

Detailed microscopic examination using optical and electron microscopes suggests that Al4C3, often observed in the central regions of magnesium grains on polished sections, is a potent substrate for primary Mg. Calculations of the crystallographic relationships between magnesium and Al4C3 further support the experimental observations. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Influence of the beta phase on the corrosion performance of anodised coatings on magnesium-aluminium alloys

The effect of the beta phase in Mg-Al alloys on the corrosion performance of an anodised coating was studied. It was found that the corrosion resistance of the anodised coating was closely associated with the corrosion performance of the substrate alloy. In particular, Mg alloys with a dual phase microstructure of alpha + beta with intermediate aluminium contents (namely 5%, 10% and 22% Al) after anodisation had the highest corrosion rate and the worst corrosion resistance provide by the anodised coating. The poor performance of an anodised coating was attributed partly to lower corrosion resistance of the substrate alloy and partly to the higher porosity of the anodised coating. (c) 2004 Elsevier Ltd. All rights reserved.

Comparing the concentration of calcium hydroxide in the diffuse double layer by modeling and experiment

The leaching of elements from the surface of charged fly ash particles is known to be an unsteady process. The mass transfer resistance provided by the diffuse double layer has been quantified as one of the reasons for this delayed leaching. In this work, a model based on mass transfer principles for predicting the concentration of calcium hydroxide in the diffuse double layer is presented. The significant difference between predicted calcium hydroxide concentration and the experimentally measured is explained.

XPS study of basic aluminum sulphate and basic aluminium nitrate

Basic aluminium sulphate and nitrate crystals were prepared by forced hydrolysis of aluminium salt solution followed by precipitation with a sulphate solution or by evaporation for the basic aluminium nitrate. X-ray Photoelectron Spectroscopy (XPS) confirms the chemical composition determined by ICP-AES in earlier work. High resolution XPS scans of the individual elements allow the identification of both the central (AlO4)-Al-IV group and the 12 aluminium octahedra in the [IVAlO4AlVI(OH)(24)(H2O)(12)] building unit by two Al 2p transitions with binding energies of 73.7 and 74.2 eV in both the basic aluminium sulphate and nitrate. Four different types of oxygen atoms were identified in the basic aluminium sulphate associated with the central AlO4, OH, H2O and SO4 groups in the crystal structure with transitions at 529.4, 530.1, 530.7 and 531.8 eV, respectively. (c) 2005 Elsevier B.V. All rights reserved.

Alkali hydroxide-induced gelation of pectin

The mechanism of pectin gelation depends on the degree of methoxylation. High methoxyl pectin gels due to hydrophobic interactions and hydrogen bonding between pectin molecules. Low methoxyl pectin forms gels in the presence of di- and polyvalent cations which cross link and neutralise the negative charges of the pectin molecule. Monovalent cations normally do not lead to gel formation with high methoxyl pectin solutions free of divalent cations, especially Ca. The present study found that alkali (NaOH or KOH) added to high methoxyl pectin leads to gel formation in a concentration-depended manner. It was also found that monovalent cations (Na and K) induce gelation of low methoxyl pectin and the time required for gel formation (setting time) depends on the cation concentration. The results indicate that a combined char-e neutralisation and ionic strength effect is responsible for the monovalent cation-induced gelation of pectin. (C) 2003 Elsevier Ltd. All rights reserved.

Improved corrosion resistance of AZ91D magnesium alloy by an aluminium-alloyed coating

An aluminum-alloyed coating was applied onto the surface of magnesium alloy AZ91D. The coating formed in aluminium powder at 420 degrees C is rich in the beta (Mg17Al12) phase. Polarisation curve, AC impedance, salt immersion and salt spray were carried out to investigate the corrosion behaviour and assess the corrosion performance of the coated magnesium alloy. It was found that a coated AZ91D specimen was much more corrosion resistant and harder than an uncoated one. The improved corrosion resistance was mainly ascribed to the high volume fraction of beta phase in the coating. (c) 2004 Elsevier B.V. All rights reserved.

The effect of the atmosphere and the role of pore filling on the sintering of aluminium

Alloys of Al-3.8Cu-1Mg-0.7Si, Al-4Cu-0.6Si-0.1Mg, Al-4Cu-1.2Mg and Al-1.9Mg-1.9Si were made using air atomised powder and conventional press-and-sinter powder metallurgy techniques. These were sintered under nitrogen with a controlled water content which varied from 3 to 630 ppm (a dew point of -69 to -25 degrees C), nitrogen-5%hydrogen, argon and argon-5% hydrogen, all at atmospheric pressure, or a vacuum of

The effect of aluminium content on the mechanical properties and microstructure of die cast binary magnesium-aluminium alloys

This paper investigates the relationship between mechanical properties and microstructure in high pressure die cast binary Mg-Al alloys. As-cast test bars produced using high pressure die casting have been tested in tension in order to determine the properties for castings produced using this technique. It has been shown that increasing aluminium levels results in increases in yield strength and a decrease in ductility for these alloys. Higher aluminium levels also result in a decrease in creep rate at 150 degrees C. It has also been shown that an increase in aluminium levels results in an increase in the volume fraction of eutectic Mg17Al12 in the microstructure.

Layered double hydroxide nanomaterials as potential cellular drug delivery agents

This paper briefly reviews the recent progress in using layered double hydroxide (LDH) nanomaterials as cellular delivery agents. The advantages of LDHs as cellular delivery agents are summarized, and the processes of interaction/de-intercalation of anionic drugs (genes) into/from LDH nanoparticles are discussed. Then the cellular delivery of LDH-drug (gene) nanohybrids and subsequent intracellular processes are presumably proposed. At the end, some challenges and remarks for efficient delivery of drugs (genes) via LDH nanoparticles are provided to the best of our knowledge.

Dispersion and size control of layered double hydroxide nanoparticles in aqueous solutions

We report a simple but efficient method to prepare stable homogeneous suspensions containing monodispersed MgAl layered double hydroxide (LDH) nanoparticles that have wide promising applications in cellular drug ( gene) delivery, polymer/LDH nanocomposites, and LDH thin films for catalysis, gas separation, sensing, and electrochemical materials. This new method involves a fast coprecipitation followed by controlled hydrothermal treatment under different conditions and produces stable homogeneous LDH suspensions under variable hydrothermal treatment conditions. Moreover, the relationship between the LDH particle size and the hydrothermal treatment conditions ( time, temperature, and concentration) has been systematically investigated, which indicates that the LDH particle size can be precisely controlled between 40 and 300 nm by adjusting these conditions. The reproducibility of making the identical suspensions under identical conditions has been confirmed with a number of experiments. The dispersion of agglomerated LDH aggregates into individual LDH crystallites during the hydrothermal treatment has been further discussed. This method has also been successfully applied to preparing stable homogeneous LDH suspensions containing various other metal ions such as Ni2+, Fe2+, Fe3+, Co2+, Cd2+, and Gd3+ in the hydroxide layers and many inorganic anions such as Cl-, CO32-, NO3-, and SO42-.

A novel method for the production of aluminium nitride

A method has been developed to produce thick (> 400 mu m) AlN surface layers oil aluminium plates at 540 degrees C, under nitrogen at atmospheric pressure. A critical element of the process is the use of Mg powder placed in close proximity to the Al plate surface. The Mg reduces/disrupts the natural, protective oxide film on the Al surface. The nitride layers form through two distinct modes, one growing outward from the Al plate surface and the other growing into the Al. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Eutectic grain size and strontium concentration in hypoeutectic aluminium-silicon alloys

Recently it has been shown that modification with strontium causes an increase in the size of eutectic grains. The eutectic grain size increases because there are fewer nucleation events, possibly due to the poisoning of phosphorus-based nuclei that are active in the unmodified alloy. The current paper investigates the effect of strontium concentration on the eutectic grain size. In the aluminium-10 wt.% silicon alloy used in this research, for fixed casting conditions, the eutectic grain size increases as the strontium concentration increases up to approximately 150ppm, beyond which the grain size is relatively stable. This critical strontium concentration is likely to differ depending on the composition of the base alloy, including the concentration of minor elements and impurities. It is concluded that processing and in-service properties of strontium modified aluminium-silicon castings are likely to be more stable if a minimum critical strontium concentration is exceeded. If operating below this critical strontium concentration exceptional control over composition and casting conditions is required. (c) 2005 Elsevier B.V. All rights reserved.

Fatigue crack propagation in a sintered 2xxx series aluminium alloy

Many potential applications for sintered aluminium are limited by the poor fatigue properties of the material. In order to increase understanding of the fatigue mechanisms in sintered aluminium, fatigue tests were carried out on a sintered 2xxx series aluminium alloy, AMB-2712. The alloy has a fatigue endurance strength of approximately 145 MPa (R = 0.1). Three regions were identified on the fatigue fracture surfaces. Region I contains the initiation site and transgranular crack propagation. When the size of the cyclic plastic zone ahead of the crack becomes comparable to the grain size, microstructural damage at the crack tip results in a transition to intergranular propagation. Region 2 mainly contains intergranularly fractured material, whilst the final fracture area makes up Region 3, in the form of dimple coalescence and intergranular failure. Transgranular fractographic features observed on fatigued specimens include fissure-type striations, cross-hatched grains, furrowed grains and grains containing step-like features. (c) 2006 Elsevier B.V. All rights reserved.