Role Of Aluminum Research Articles

Role of dynamics of intracellular calcium in aluminium-toxicity syndrome.

This review is concentrating on the role of aluminium (Al)-calcium (Ca) interactions in Al toxicity syndrome in plants. Disruption of cytoplasmic Ca2+ homeostasis has been suggested as a primary trigger of Al toxicity. Aluminium causes an increase in cytosolic Ca2+ activity, potentially disrupting numerous biochemical and physiological processes, including those involved in the root growth. The source of Ca2+ for the increase in cytosolic Ca2+ activity under Al exposure is partly extracellular (likely to be due to the Al-resistant portion of the flux through depolarization-activated Ca2+ channels and fluxes through Ca2+ -permeable nonselective cation channels in the plasma membrane) as well as intracellular (increased cytosolic Ca2+ activity enhances the activity of Ca2+ release channels in the tonoplast and the endoplasmic reticulum membrane). The effect on increased cytosolic Ca2+ activity of possible Al-related inhibition of the plasma membrane and endo-membrane Ca2+ -ATPases and Ca2+ exchangers (CaX) that sequester Ca2+ out of the cytosol is insufficiently documented at present. The relationship between Al toxicity, cytoplasmic Ca2+ homeostasis and cytoplasmic pH needs to be elucidated. Technical improvements that would allow measurements of cytosolic Ca2+ activity within the short time after exposure to Al (seconds or shorter) are eagerly awaited. Contents I. Introduction 296 II. Symptoms of aluminium toxicity 296 III. Calcium - aluminium interactions 297 IV. The role of electrical properties of the plasma membrane in calcium-aluminium interactions 306 V. Oxidative stress 307 VI. Callose 308 VII. Cytoskeleton 308 VIII. Conclusions 309 Acknowledgements 309 References 309.

Effect of aluminum reinforcement on the dynamic fragmentation of SiC ceramics

The threat of small-to-medium caliber armor piercing projectiles requires efficient protections that can be achieved by using bilayered configurations. They consist of a front face made up of a hard material and a back face made up of a ductile material. These solutions are among the most interesting in terms of mass efficiency. To design such bilayered concepts, one needs to understand and model fragmentation of the ceramic during the first microseconds after impact. This cracking pattern may significantly reduce the multi-hit capability of the armor. A new material made of porous silicon carbide infiltrated with aluminum is considered. The presence of an aluminum skeleton may improve the residual strength after impact. The present study deals with a comparison of fragmentation properties of this new material with those of porous silicon carbide. Quasi-static experiments and edge-on-impact tests are performed. The role of aluminum is discussed. An anisotropic damage model coupled with a fragmentation study is used to analyze the experimental observations.

Role of Aluminum in Fabrication and Piezoresistive Effect of Silicon Carbide Ceramics

Role of Aluminum in Fabrication and Piezoresistive Effect of Silicon Carbide Ceramics

You can take the genome out of the organism, but can you take the organism out of the environment?

In a debate held on July 28th in Cincinnati, a new chapter in the nature versus nurture saga was initiated. The premise under discussion was whether nonfamilial, i.e. sporadic, Alzheimer disease (AD) is primarily a genetic disorder. The participants took the position that either A) genetic factors are largely responsible for the so-called sporadic cases of AD or B) environmental factors contribute to the development of sporadic AD. The argument that genetic factors result in sporadic AD was based on population based studies such as the Nun study and twin studies. The participants correctly point out the more than passing role of the APOE-e4 in the development of Alzheimer disease. In addition, a wide variety of genes and chromosomal loci have been implicated in the development of Alzheimer disease. However, although twin studies, for example, indicate a heritability of greater than 60% it is not 100%. The typical argument employed to explain this type of discrepancy is that when age corrected we get much closer since one of the siblings may die of other causes before having the “opportunity” to develop Alzheimer disease. While admitting that diet and other health related activities may influence the development of Alzheimer disease they maintain their position that non-familial Alzheimer disease is largely the result of genetics. On the other hand, the other participants argue that non-genetic factors play an important role in nonfamilial Alzheimer disease. Some of the possible factors include viruses, dietary components and metals. The unifying feature is postulated to be inflammation resulting from any of these insults. Special attention was paid to the role of aluminum, which has long been conjectured to facilitate the development of Alzheimer disease. In addition, the role of diet and especially dietary fats were discussed. With the increasing evidence of oxidative stress in the etiology of Alzheimer disease, the authors also consider the role of trace metal deposition through dietary exposure. Finally, increasing evidence in a number of chronic conditions has implicated bacterial and viral pathogens as underlying components in disease etiology. HSV-1 has been implicated as a potential underlying component in Alzheimer disease. Thus, these authors hold that environmental concerns play a large role in the development of Alzheimer disease and moreover are more tractable to intervention that are genetic predispositions. So, what can we take away from this? It is clear that genetic predisposition is important in the development of disease and that the development of disease can be modified by controlling external influences, i.e. cholesterol uptake. However, the important issue from the perspective of the prospective patient, current patient, or family members is what can we predict about the natural history of the individual. The studies listed

Possible role of aluminum in stabilizing organic matter in particle size fractions of Chernozemic and solonetizic soils

Although phyllosilicate clays, with their large surface areas, are often considered to play the leading role in stabilizing soil organic matter against microbial attack, several studies have suggested recently that oxides of Al and Fe may stabilize organic matter in some soils. The distribution of organic C and oxides in clay (< 0.2 and 0.2–2 mm) and silt fractions (2–5, 5–20, and 20–50 mm) of four Saskatchewan soils (organic C ranged from 21 to 46 g kg-1) was examined to differentiate the contributions of oxides and specific surface to organic matter retention. Carbon concentrations in the particle size fractions (separated following ultrasonic dispersion of the soils) tended to be highest in the fine silt and coarse clay fractions, not in the fine clay as would be expected if specific surface was the sole factor governing organic matter content. When data for the four soils were pooled there was a strong relationship between organic C (y) in the size fractions and Al (x) extracted by dithionite-citrate-bicarbonate [y = 33.9 x0,5 - 7.3; R2 = 0.90***], suggesting a role for A1 in determining the C storage capacity of the size fractions. The C: A1 ratio increased from an average of 12:1 in clay-sized material to 28:1 in coarse silt. Because it had less A1 per unit mass of C, organic matter in the silt separates may be more weakly bonded to mineral material than is clay-associated organic matter. This may imply that organic matter bound to silt is less stable, and thus susceptible to mineralization, than is organic matter residing in the clay fraction. Key words: Organic matter stabilization, particle size separates, extractable A1 and Fe

The role of aluminum in the crystallization of Cr–Si–Ni resistive films

The microstructure and electrical properties of both annealed Cr–Si–Ni and Cr–Si–Ni–Al films with an atomic ratio [Si]/[Cr]>2 were investigated. When sputtered amorphous Cr–Si–Ni and Cr–Si–Ni–Al films were heated up to temperature of 600 °C, they all were found to crystallize through two distinct stages. The first stage was due to the primary crystallization of nanocrystalline CrSi 2 and Si phase for Cr–Si–Ni films (or Cr(Si,Al) 2 and Si phase for Cr–Si–Ni–Al films), while the second stage was due to crystallization of the residual solute-enriched amorphous phase into CrSi 2 (or Cr(Si,Al) 2) and Si phase. The addition of Al into amorphous Cr–Si–Ni films caused the coarsening of the primary crystallization phase, resulting in a significant increase of both the electrical resistivity and the temperature coefficient of resistance (TCR) for the annealed films. Meanwhile, the subsequent crystallization of the residual solute-enriched amorphous phase was affected, resulting from the combined redistribution of Cr, Si, Al and Ni elements between the primary and parent amorphous phases.

Destabilisation of oil–water emulsions and separation by dissolved air flotation

The roles of aluminium and ferric sulphates as destabilising agents for oil–water emulsions that have been stabilised by a non-ionic surfactant (Span 20) are investigated in terms of oil removal. The effects of coagulant dose, pH, and the duration and intensity of both slow and fast mixing are considered. Electrokinetic measurements indicate that oil droplets have a negative zeta potential that is weakly dependent on pH. The chosen coagulants are shown to be effective in reducing the zeta potential of the oil droplets, and charge reversal was observed for aluminium sulphate. Oil removals up to 99.3% at pH 8 and 99.94% at pH 7 are seen for aluminium sulphate and ferric sulphate respectively. Rapid mixing times of around 120s and flocculation times ranging from 15 to 20min appear to be optimal for the DAF separation. It is concluded that relatively low average mixing speeds for coagulation and flocculation are essential for efficient operation.

On the Role of Aluminum in Finemet

The role of aluminum with respect of its influence on some intrinsic magnetic properties of the nanocrystalline Finemet, such as saturation magnetization, Curie temperature, spin-wave stiffness constant and hyperfine magnetic fields was investigated. The strengthening effect of Al on the exchange interaction was observed for the alloys with small Al content (up to 3 at.%). Higher concentration of Al (5-7 at.%) led to considerably suppressed exchange interaction.

Roles of aluminium and chromium in sulfidation and oxidation of sputter-deposited Al- and Cr-refractory metal alloys

Our recent results of the sulfidation and oxidation behavior of sputter-deposited Al- and Cr-refractory metal alloys at high temperatures are reviewed, and the roles of the aluminum and chromium in sulfidation and oxidation of these alloys are discussed in this paper. Niobium, molybdenum and tantalum are highly resistant to sulfide corrosion. Their sulfidation resistance is further enhanced by alloying with aluminum. Although Cr-refractory metal alloys also reveal high sulfidation resistance, their sulfidation rates do not become lower than those of the corresponding refractory metals. The sulfide scales formed on the Al-refractory metal and Cr-refractory metal alloys consist of two layers, comprising an outer Al 2S 3 or Cr 2S 3 layer and an inner refractory metal disulfide layer. The inner layer has a columnar structure, and the growth direction of the refractory metal disulfides is perpendicular to 0 0 1 direction. Intercalation of Al 3+ ions into NbS 2 and a decrease in the sulfur activity at the outer layer/inner layer interface by the presence of the Al 2S 3 layer are probably responsible for the improvement of the sulfidation resistance by the addition of aluminum. The oxidation resistance of niobium and tantalum is improved more effectively by the addition of chromium rather than aluminum. Although preferential oxidation of chromium does not occur, an outer protective Cr 2O 3 layer in the oxide scales is formed on Cr-rich Cr–Nb and Cr–Ta alloys due to outward diffusion of Cr 3+ ions. In contrast, continuous alumina layer cannot be formed on the Al–Nb and Al–Ta alloys, and the alloys reveal a pest phenomenon at 1073 K, and at higher temperatures rapid oxidation occurs. Concerning the oxidation of molybdenum, the addition of aluminum, which has higher activity for oxidation than chromium, is more effective in improving the oxidation resistance of molybdenum than chromium addition, since preferential oxidation of aluminum suppresses the formation of volatile molybdenum oxide.

Aluminum promotes neuronal plasticity events in a mouse neuroblastoma cell line

The effects of aluminum(III) on microtubular meshwork have been investigated using cultured murine neuroblastoma cells grown in a medium containing aluminum lactate at defined metal concentrations (10–20 μM). A role of aluminum(III) in promoting neuronal plasticity events is suggested. These events including sprouting and neurite outgrowth are associated with an increased tyrosine-tubulin (Tyr-Tub) expression, which can be due to the enhanced needs of recently formed, highly dynamic microtubules typical of neuronal plasticity. After 48 and 72 h aluminum exposure, an upregulation of Tyr-Tub expression is detected and this is concentration-dependent. A high amount of Tyr-Tub is observed also in non-treated cells, although later than in aluminum-exposed cells. Thus, it is possible that aluminum(III) accelerates neuronal plasticity events, for which Tyr-Tub is confirmed to be a useful marker.

Study of aluminum and gold as the gate electrode material on silicon nitride based MIS devices

In order to study the role of aluminum and gold as the gate electrode material, we have deposited silicon nitride films onto p-type silicon substrates via r.f. glow-discharge deposition and have fabricated metal-insulator-semiconductor (MIS) devices on these films using aluminum or gold as the top electrode material. Considerable penetration of aluminum gate material into our silicon nitride films is observed. The resulting decrease of the effective thickness of the MIS devices have led to tunneling in these films. However, no appreciable penetration of gold gate material is observed. Our study demonstrates clearly that gold is superior to aluminum as the gate electrode material in MIS devices for being suitable even when poor quality silicon nitride films are used as insulator in MIS devices.

Inhibitory effect of aluminum on dopamine β-hydroxylase from bovine adrenal gland

Aluminum is a well known neurotoxic agent that is overaccumulated in the substantia nigra of patients affected by Parkinson's disease as well as in certain cerebral areas of other neurodegenerative pathologies such as Alzheimer's disease. Although the role of aluminum in neurodegenerative diseases is yet to be clearly understood, the metal ion is known to substantially alter the activity of several key enzymes in the central nervous system. The present paper reports data on the effect of aluminum on the activity of dopamine-β-hydroxylase from bovine adrenal gland utilized as a model study. The metal ion inhibited the activity of this enzyme with a mixed type mechanism following the Michaelis-Menten equation. In the absence of Al, the enzyme exhibited a Km and Vmax of 2.56 mM of 4.12 pmol/min respectively, while in the presence of Al its Km and Vmax were 3.85 mM and 2.86 pmol/min respectively. The potential implications of aluminum in the etiopathogenesis of neurological disorders are discussed.

Improved Oxidation Resistance of Silicon Nitride by Aluminum Implantation: II, Analysis and Optimization

In the preceding paper, it was shown that aluminum ion implantation significantly improves the oxidation resistance of Si3N4 ceramics under the influence of sodium. Not only is the oxidation rate reduced by up to an order of magnitude, the phase and morphological characteristics of the oxides grown on aluminum‐implanted samples are improved as well. The role of aluminum in negating the detrimental effect of sodium on the oxidation resistance of Si3N4 ceramics can be interpreted on the basis of network modification of the oxide layers by sodium and aluminum cations. The degree of improvement in the oxidation resistance does not, however, necessarily increase with the aluminum concentration. A simple quantitative analysis is presented which correlates the optimum aluminum implant concentration and the sodium content in the gas phase for the optimization of the oxidation resistance of Si3N4 ceramics.

Aluminum: New challenges in downstream activities

During its history, aluminum’s attractive features, such as high strength-to-weight ratio, good electrical mass conductivity, and unique corrosion behavior, have led to a spectacular expansion in its use. The role of aluminum in non-aluminum-based materials is also very important; its contribution to the improvement of magnesium and titanium alloys and to highly complex packaging materials are some of the noteworthy examples. Significant cost reductions on the basic metal production level, near-to-shape fabricating methods, and the well-functioning recycling system are also major contributors to aluminum success. Imminent challenges for the industry are the need for products with very close tolerances on a mass fabricating repetitive basis and just-in-time delivery to original-equipment manufacturers and small users through distributors. A significant part of the challenges remains in the applications area, particularly automotive and aerospace.

A thermal study of optical fibres transmitting concentrated solarenergy

In this paper we develop a theoretical thermal study of optical fibres transmitting concentrated solar energy. An energy equation for simultaneous conduction and radiation of heat through optical fibres is obtained. To transmit concentrated solar energy an optical fibre tip is placed in the focus of a small paraboloidal mirror. The role of aluminium and silver as the reflective surface on the mirror that allows one to concentrate the solar energy is studied. The power supply is estimated to be 26 W at the end of a 10 m long fibre with 88% transmission efficiency. The thermal study considers a wavelength-dependent absorption coefficient of the optical fibre core in order to obtain the radiative heat flux in the fibre. The time evolution of the temperature distribution is obtained by a finite-difference method. With this result we predict that the fibre can be used 6 h.

Selective modulation of GABAA receptors by aluminum.

Aluminum has been implicated in several neurodegenerative conditions including Alzheimer's disease. Because the mammalian olfactory system has an unusual capacity for the uptake and transneuronal spread of inhaled substances such as aluminum, whole cell recording techniques were used to examine the actions of aluminum on basic membrane properties and amino acid receptors on rat olfactory bulb mitral/tufted (M/T) neurons in culture. Aluminum had little direct effects on M/T neurons. Aluminum (100 microM) did not evoke a membrane current or alter action-potential shape or duration. Aluminum also had no marked effects on the family of voltage-gated membrane currents evoked by a series of 10-mV, 50-ms depolarizing steps. However, aluminum dramatically potentiated the current evoked by 30 microM gamma-aminobutyric acid (GABA) at concentrations <100 microM. Conversely, higher concentrations of aluminum blocked the GABA-evoked current. The effects of aluminum on GABA-evoked currents were not voltage dependent. Aluminum (100 microM) equally potentiated both inward currents at -30 mV and outward currents at + 30 mV. At 300 microM, aluminum blocked both inward and outward currents to a similar extent. In some neurons, aluminum only blocked the current and potentiation was not observed. The biphasic action of aluminum on GABA-evoked currents suggests separate binding sites: a high-affinity potentiating site and a low-affinity inhibiting site. Despite its effects on GABA-evoked currents, aluminum did not alter membrane currents evoked by glutamate, N-methyl-D-aspartate, kainate, or glycine. Aluminum also did not reduce spontaneous excitatory synaptic activity, suggesting little, if any, effect on glutamate release. Although a causal role for aluminum in Alzheimer's disease and other neuropathological conditions remains controversial, it is clear that elevated aluminum concentrations in the brain are associated with a variety of cognitive impairments. The present results indicate that aluminum can alter the function of GABAA receptors and may suggest that aluminum can contribute to cognitive impairment through disruption of inhibitory circuits.

The Influence of Aluminium and Silicon on Transformation Kinetics in Low Alloy Steels

The use of aluminium to deoxidise steel is well known and has been the key to significant improvements in steel cleanness for some 100 years [1,2]. It is common practice to add more than sufficient aluminium to combine with the oxygen in the steel at the end of steel making to ensure current levels of cleanliness. Usually, therefore, steels made with current Basic Oxygen Steelmaking or electric arc practices contain excess free or soluble aluminium which can be exploited to an advantage by combining with nitrogen to form aluminium nitride, which then acts to refine grain size during subsequent processing. For most steels therefore, the aluminium additions made play several metallurgical roles; for example, the soluble aluminium to nitrogen ratio affects both the ferrite grain size and the strain ageing behaviour [3]. Many steel specifications therefore, pay particular attention to this aspect and Al/N ratio greater than 2 is normally considered to provide a fine ferrite grain size and freedom from the harmful effects of strain ageing on mechanical properties. As a direct consequence of these attributes, aluminium is usually in excess of the stoichiometric ratio of 2:1 and thus in many steels some aluminium is present in solid solution in the ferrite. Furthermore, the aluminium, invariably present in most modern steels is generally not considered to have an important or significant effect on microstructure. However, interest in the role of aluminium during microstructural evolution has been increased from work based on the formation of steel microstructures based on tough acicular ferrite in the weld heat affected zone (HAZ), thought to be nucleated by TiO compounds [4,5]. One approach which has been taken in the formation of such microstructures has been to adopt compositions which favour the formation of titanium rich inclusions, thought to be responsible for the nucleation of acicular ferrite [6]. Such steels are commonly aluminium free, or very nearly so, since a prerequisite for titanium oxide to form as inclusions is the presence of uncombined oxygen at the end of steel making. Observations made from studies into the microstructural development in weld metals appear to show aluminium having a deleterious effect on the formation of acicular ferrite, even in the presence of favourable Ti rich inclusions [7]. In weld metals, other alloying elements with marked nitride forming abilities, principally titanium, vanadium and boron, are present but there is a strong case for aluminium to be present in solid solution in ferrite. It is not obvious, as to what level the microstructure is affected, but the work by Thewlis indicates a marked change when the total aluminium content is greater than about 0.03 wt%, implying a reduction in the soluble aluminium content [8]. There have also been reports, that trace additions of aluminium less than 50ppm, can have a marked effect on the microstructure of laser welds [9]. Several other instances of a pronounced effect of aluminium on transformation behaviour have been documented, mainly in steels containing chromium and/or molybdenum additions [10-11]. No universal explanation has been offered for such effects. One interpretation suggests that partitioning of aluminium to the advancing ferrite/austenite interface reduces the boundary mobility leading to an increase in the hardenability of the steel [8,12].

Role of aluminium in structural and magnetic properties of nanocrystalline alloy FeSiBNbCu

The influence of partial substitution of Fe. Si and B elements by Al (up to 9%) is analyzed for a nanocrystalline FeSiBNbCu alloy. Structural studies show that the increment of Al deteriorates the glass forming ability of the material. Coercivity in amorphous as-quenched samples becomes lower as the Al content increases in two alloy series: while after nanocrystallization values as small as about 0,5 A/m are obtained. DSC thermograms show that addition of Al advances the nucleation of the crystalline phase. Also, a particular evolution is noticed when Si is replaced by Al: the exothermic peak characteristic of α-(Fe,Si) phase begins to split into two peaks while increasing the Al content.

Raney copper catalysts for the water-gas shift reaction: I. Preparation, activity and stability

Characterisation of partially leached Raney copper catalysts demonstrated that the chemical nature of the reactant surface could be determined by controlling the leaching process. Initial water-gas shift (WGS) activity of the Raney copper catalysts at the stated conditions compared favourably to the co-precipitated and industrial catalyst alternatives due to a similar active phase composition and high metallic copper surface areas. Raney copper catalyst deactivation in a poison-free environment was attributed to copper crystallite sintering, primarily as a result of a zinc oxide deficiency. Long term (850 h) stability of the Raney catalyst is reported for the first time. Stability improved significantly with increased ZnO loading as a result of better contact between the copper surface and ZnO crystallites. The stabilizing effect of incorporated zinc was independent of its original source. The role of aluminium was to produce Raney copper of high surface area. No beneficial effects of residual alumina in the active catalysts were observed.

Interaction of aluminum with paired helical filament tau is involved in neurofibrillary pathology of Alzheimer's disease.

Since the first reports of aluminum-induced neurofibrillary degeneration in experimental animals, extensive studies have been performed to clarify the role played by aluminum in the pathogenesis of Alzheimer's disease (AD). Additional evidence implicating aluminum in AD includes elevated levels of aluminum in the AD brain, epidemiologic data linking aluminum exposure to AD, and interactions between aluminum and protein components in the pathologic lesions of AD, i.e., neurofibrillary tangles (NFTs) and senile plaques. As most of this evidence is circumstantial and some of it is not consistent in all reports, the role of aluminum in the pathogenesis of AD has remained controversial. However, the interaction of aluminum with altered forms of tau in the paired helical filaments (PHFs) of neurofibrillary lesions is highly likely to contribute to the formation of NFTs because (1) aluminum and abnormally phosphorylated tau (known as PHF tau) are colocalized in NFTs, and (2) aluminum is known to preferentially interact with such phosphorylated proteins. Recently, it was demonstrated that aluminum binds selectively to PHF tau, induces PHF tau to aggregate, and retards the in vivo proteolysis of PHF tau. These data suggest that aluminum could serve as a cofactor in the formation of NFTs by interacting with PHF tau. This review summarizes the current understanding of how aluminum might contribute to the formation of neurofibrillary lesions from PHF tau in neurons of the AD brain.