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30
Jul
2023
0

Alumina – The Most Common Form of Aluminium Oxide

A white odorless crystalline powder that is water insoluble. It is the most commonly produced form of aluminium oxide (Al2O3)....

A white odorless crystalline powder that is water insoluble. It is the most commonly produced form of aluminium oxide (Al2O3). It may be prepared by various methods, and the properties vary according to the method used.

The alumina produced is of such high quality that it is used in electrical and chemical applications, aerospace parts, abrasives and for wear resistance in the manufacture of refractories. It is extremely hard and has excellent dielectric strength, high melting point, and resistance to corrosion by air, water vapor, and sulfurous atmospheres. It is also a good thermal and electrical insulator. It is the basis of the alumina ceramics that are used to protect coal fired power plant flue gas ducting and pulverized fuel lines, as well as for other applications that require a tough, wear resistant material.

Inhalation studies using tagged gamma aluminium oxide have shown that inhaled alumina behaves as an insoluble dust. The lungs clear a substantial percentage of the inhaled aluminium from the lungs. A small percentage of the remaining inhaled alumina, however, is sequestered and retained in the lungs. This is a result of alumina’s ability to act as an inert carrier and its capacity to form adsorption sites for a variety of substances including volatile organic compounds.

Alumina may contain contaminating materials such as sodium, iron(III) oxide, and calcium. It also contains small amounts of gallium, and this is the major impurity in Bayer process solutions (it is a catalyst for polymerization of ethylene oxide). Activated alumina has an improved adsorption profile than molecular sieves but requires lower regeneration temperature and less heat duty than other adsorbents.


28
Jul
2023
0

Limiting the Aluminium Oxidation Reaction

Aluminium oxide is used as a catalyst support in many industrial processes such as hydrodesulfurization and some Ziegler-Natta polymerizations. However,...

Aluminium oxide is used as a catalyst support in many industrial processes such as hydrodesulfurization and some Ziegler-Natta polymerizations. However, aluminium oxidation is also an important contaminant in the production of alumina. Hence, it is essential to develop methods for limiting the oxidation reaction during processing and in the final product.

The oxidation reaction of aluminium is a spontaneous process that can lead to the formation of the low-melting, brittle aluminium oxide, corundum. The reaction is driven by the strong electrostatic interaction between aluminium ions and oxygen molecules. This strong interaction can also be influenced by the presence of other ions such as chloride or sulphide.

For example, exposing aluminium to chlorine gas leads to the formation of the soluble compound aluminium chloride (AlCl2). The reaction with sulphur dioxide leads to the formation of the brittle aluminium sulfate anhydride, Al2SiO4. This is known as the galvanic corrosion reaction. The corrosion is slow, but it eventually eats through the aluminium oxide skin and exposes bare metal. This is called the corrosive attack.

Alumina is a white, brittle material that has good heat and electrical conductivity. It is made by leaching the ore bauxite with caustic soda, precipitating the resulting hydrated aluminium oxide, washing and filtering it to obtain the alumina hydrate, and finally calcining to remove water to produce anhydrous aluminium oxide. The alumina is the raw material for making many common products, such as pots and pans, foil, mirrors, and other household items.


26
Jul
2023
0

Aluminium Oxide As a High-K Dielectric Material

Aluminium oxide, commonly referred to as alumina, is one of the most common and widely used oxide engineering ceramics. It...

Aluminium oxide, commonly referred to as alumina, is one of the most common and widely used oxide engineering ceramics. It has a wide band gap, high breakdown field and high dielectric constant making it an excellent choice for gate insulator and surface passivation layers in electronic devices. Alumina is available in several crystalline phases but all revert to the most stable hexagonal alpha phase at elevated temperatures. Alpha phase alumina is the strongest, stiffest and hardest of all oxide ceramic materials with excellent refractoriness, thermal properties and electrical characteristics.

In order to explore the potential of monolayer alumina as a high-k dielectric material, we have investigated its insulating properties using current-voltage and capacitance-voltage measurements. For Al2O3 ALD films deposited on n-type Si(1 0 0) and Mo-coated Si(1 0 0), we have found that they exhibit excellent insulating properties with low leakage currents and Fowler-Nordheim tunneling up to a dielectric constant of k7.6. The measured insulating properties are consistent with the presence of a thin interfacial oxide layer with an average thickness of 11 A.

In addition, we have also carried out ab initio molecular dynamics simulations of the Al2O3 monolayer on graphene. We find that the monolayer remains atomically stabilized over a temperature range of 300 K and a time period of 10 ps. Moreover, the variation of the monolayer Al-O bond length is within 0.1 A, which is smaller than that of bulk alumina and comparable to that of Y2O3 monolayer on graphene34.


19
Jul
2023
0

Electrolysis of Aluminium Oxide and Sodium Chloride

The electrolysis of aluminium oxide and sodium chloride is an important industrial process. It is a way of extracting the...

The electrolysis of aluminium oxide and sodium chloride is an important industrial process. It is a way of extracting the element aluminium from its principal commercial source, the bauxite ore.

Aluminium is the most abundant metallic element on Earth, but it occurs in nature only in very complex forms and is hard to isolate in its pure metal form. The Hall-Heroult process of producing aluminum by electrolysis was developed in 1886 by Charles M. Hall, then a 21-year-old student at Oberlin College in Ohio. It was the first large-scale application of electrolysis — a process that uses electrical energy to drive unfavorable chemical reactions to completion. Electrolysis is used to isolate the reactive metals such as sodium, potassium and aluminum from their natural compounds.

Unlike other aluminium refining processes that use water-based solutions, the Hall process electrolyses a molten salt solution. This is because it would be expensive to melt the highly insoluble aluminium oxide (Al2O3), whose melting point is 2072 degC. Instead, it is dissolved in a molten cryolite electrolyte that lowers the melting point to 950 degC.

A direct electric current passes through the ionic solution in an electrolytic cell and chemical oxidation and reduction reactions take place. At the cathode, ions of aluminium are reduced to produce liquid aluminium (Al3+ - Al0). At the anode, chloride ions discharge to form chlorine gas. Because aluminium is denser than the electrolyte, the liquid aluminium sinks to the bottom of the cell and is collected as the pure molten metal. The aluminium is then alloyed with copper (and smaller amounts of magnesium, silicon and iron) to make a stronger, lighter and better corrosion-resistant material called 'Duralumin' that is used in car components, greenhouses and window frames and the steel strands that hold overhead power lines.


19
Jul
2023
0

Aluminium Oxide Capacitors With a Low Dielectric Constant

dielectric constant aluminium oxide al2o3

Aluminium oxide, commonly referred to as alumina, is one of the most desirable engineering materials due to its superior strength, stiffness and dielectric properties. It exists in a variety of crystalline phases which all revert to the most stable hexagonal alpha phase at elevated temperatures making it suitable for structural applications.

Alumina is also a very good dielectric material, with an extremely low permittivity and tangent loss. Combined with its high quality factor, dielectric breakdown can be achieved at very low electric fields, making it a very effective capacitor material. The ability to store electrical energy in the form of charges is a key requirement for many electronic devices, and is the primary reason that the capacity of a capacitor is inversely proportional to its thickness.

This article reports on the synthesis and characterization of hydrothermally as-grown g-phase alumina by atomic layer deposition (ALD). The as-prepared material was confirmed to be of crystalline structure through X-ray diffraction spectroscopy, with a bending vibration in the Al-O-Al band in the FTIR spectra confirming that the as-prepared material was g-Al2O3.

The electrical characteristics were determined using complex impedance measurements and spectroscopic ellipsometry. It was found that the capacitance increased with increasing film thickness, and this was attributed to Fowler-Nordheim tunneling via a thin interfacial oxide layer at the Si substrate. Leakage currents measured at high electric fields were also consistent with this interpretation. ALD films grown at 80, 100, 150 and 250 degC showed a significantly higher dielectric breakdown strength than those grown at lower temperatures. This was attributed to the decrease in carbon impurity levels and oxygen defects, as confirmed by X-ray photoelectron spectroscopy.


19
Jul
2023
0

The Mechanism of Aluminum Oxide Layer Growth

Aluminum is able to form a self-healing, oxide layer on its surface which reliably insulates and protects it from the...

Aluminum is able to form a self-healing, oxide layer on its surface which reliably insulates and protects it from the ambient environment. This ability is the basis of its widespread use in many applications. However, the mechanism of the oxide layer formation is largely unknown. Although the early stages of oxygen molecule absorption have been effectively elucidated with surface science techniques (scanning tunneling microscopy /l/, work function measurements /l/, and X-ray photoemission spectroscopy /l/), the overall kinetics of oxide layer growth remains poorly understood.

In nature, a passive oxide layer of about a monolayer covers the aluminium surface and stops oxidation by the action of an electric field generated by charge separation between aluminum ions at the oxide-gas interface and oxygen ions at the metal-oxide interface. The net reaction rate is zero, indicating that the formation of the passive oxide layer is an equilibrium process.

When anodic polarization is applied to a single-crystal aluminium substrate with (100), (110) and (111) faces, the oxide layer begins to grow quickly in dry oxygen at 25 degrees C and 760 mm Hg pressure. After a few days of exposure the aluminium oxide layer grows to an 'effective limit' of approximately 30 angstroms, measured by three different methods (anodic polarization, electron diffraction and capacity).

As the oxide layer thickness increases the atomic structure of the metal becomes more ordered with a reduction in lattice spacing. The increased crystalline order also leads to an increase in the electrostriction stress that develops between adjacent atoms of the forming oxide. This additional tensile component of the electrostriction stress causes each oxide flake to exert lateral forces against its nearest neighbor, with each flake constraining its neighbor in a hexagonal arrangement.


18
Jul
2023
0

Aluminium Reacts With Oxygen to Produce Aluminium Oxide

aluminium reacts with oxygen to produce aluminium oxide, which is a white powder. The chemical formula for aluminium oxide is...

aluminium reacts with oxygen to produce aluminium oxide, which is a white powder. The chemical formula for aluminium oxide is Al2O3. This compound is amphoteric, meaning that it can ionise in water and react with acids as well as bases. The ions form a crystal structure that is similar to corundum. It is also commonly used as abrasive in the manufacture of sandpaper and grinding wheels. It is also the main ingredient in some sodium vapor lamps.

Metallic aluminium does not normally react with water in air, but it can react to produce aluminium oxide if the surface is corroded. A layer of aluminium oxide, known as passivation, forms on the surface of aluminium to prevent it from reacting with oxygen in the air. The thickness of the passivation layer can be increased by a process called anodising. This is often done on aluminium alloys to increase their corrosion resistance, as well as for decorative effects.

When aluminium is exposed to acid, a layer of aluminium oxide forms on the surface of the metal. This protects the aluminium from the acid, but if it is damaged the acid will react with the exposed aluminium to produce toxic hydrogen gas.

Aluminium oxide can be produced by reacting elemental aluminium with diatomic oxygen (O2) in the air. This is a combination reaction because the reactants are different and both have a positive electrical charge. The molecular formula for the product is Al2O3, which has the same chemical properties as the pure elemental aluminium. The aluminium ions in the compound are closely packed together, but they have an uneven distribution of positive and negative charges so that the compound is electrically neutral.


18
Jul
2023
0

Aluminium Tertiary Butoxide Catalyzes the Oxidation of Secondary Alcohols to Ketones

The aluminium tertiary butoxide (AlOBut) is one of numerous organo-metallic compounds available from American Elements for uses requiring non-aqueous solubility....

The aluminium tertiary butoxide (AlOBut) is one of numerous organo-metallic compounds available from American Elements for uses requiring non-aqueous solubility. It has been shown to catalyze the oxidation of secondary alcohols to ketones in an efficient and selective manner without other sensitive functional groups such as amines and sulfides being oxidized or reduced. This process is termed an Oppenauer oxidation or Meerwein-Pondorff-Verley reduction.

The classic Oppenauer oxidation utilizes an alkoxide-catalysed hydrogen transfer between alcohol and an excess of ketone hydride acceptor in acetone solvent to generate the corresponding ketone in high yields. However, this reaction suffers from the competition of aldol condensation reactions with the product aldehyde and Tishchenko reactions leading to esters. Additionally, this oxidation requires high temperatures and the generation of water as by-product which hydrolyzes and consumes the catalyst at stoichiometric conditions.

In the present study, the ketal epoxides 2a-i and 2b-i of 4-phenyl-3-buten-2-ol were converted to the corresponding benzaldehyde and benzaldehyde under milder conditions by treatment with AlOBut. These treatments resulted in the formation of the sterically restrained, bridged ring system (6) while maintaining all methyl groups in pseudoequatorial positions and preserving the C-6 stereochemistry of the benzaldehyde. The benzaldehyde was further converted to the chiral ether 8 by treating with a small amount of iodine in a mixture of acetone and water, to form the corresponding benzaldionone in stoichiometric yield.

The use of aluminium tertiary butoxide for the oxidation of alcohols to ketones is a simple, low-cost alternative to the classical Oppenauer synthesis and also allows access to the aldol condensation of the resulting -ketal products to give polyols such as citral.


18
Jul
2023
0

What Is Aluminum Oxide Hydroxide Cas?

Aluminum oxide hydroxide cas is a compound that has a wide variety of scientific research applications. It can be used...

Aluminum oxide hydroxide cas is a compound that has a wide variety of scientific research applications. It can be used to study the effects of aluminum on cellular proteins and DNA, as well as its potential therapeutic and toxic properties. In addition, this chemical can be used to develop new materials for use in a wide range of industrial applications.

Aluminium oxide hydroxide is an amphoteric material that can be easily dissolved in water and various acids. It can also form a hydrated layer on the surface of other materials, making it an ideal material for a number of laboratory experiments. It is also non-toxic and safe to handle in a lab setting, which makes it an excellent research tool.

The synthesis of aluminum oxide hydroxide is relatively simple, and it can be produced using several different methods. Some of the most common methods include hydrothermal synthesis, sol-gel synthesis, and precipitation methods. Each method has its own unique advantages and disadvantages, but all of them can be used to produce high-quality aluminum oxide hydroxide.

The most common way to produce aluminum oxide hydroxide is to dissolve aluminum chloride in water and then add sodium hydroxide to the solution. This will cause the aluminum chloride to precipitate out of the water as a white powder, which is aluminum hydroxide. The powder can then be filtered and dried to obtain the final product. This is the same process that is used to produce alumina, the material that is commonly found in electrical resistance heating elements.


18
Jul
2023
0

Alcohol and Aluminium Oxide

alcohol and aluminium oxideThe dehydration of alcohols produces alkenes – for example when ethanol is heated over an aluminium oxide...

alcohol and aluminium oxide

The dehydration of alcohols produces alkenes - for example when ethanol is heated over an aluminium oxide catalyst it gives ethene. Aluminium oxide is also used in the production of alumina – an aluminium product used for making glass, ceramics and other industrial products.

Corundum is a naturally occurring mineral containing aluminium oxide and is found in nature as the gemstone ruby and sapphire. It is also an important industrial material – for example as a support for some industrial catalytic reactions such as hydrodesulfurization and some Ziegler-Natta polymerisations.

Sodium aluminate, the most common source of commercially available aluminium hydroxide, is an inorganic chemical that is often referred to simply as NaAlO2 (anhydrous) or NaAl(OH)4 (hydrated). Molecular dynamics simulations using the ReaxFF force field show that the oxidation of alumina on itself is a complex process involving both surface hydroxyl groups and the aluminium atoms within the crystalline structure. The evolution of the density and stoichiometry over the course of the oxidation simulation is shown in Fig. 3. The changes in the calculated density reflect the changing oxygen stoichiometry and atomic distribution of the aluminium and oxygen atoms on the surface.

The stoichiometry is influenced by the method of oxidation as well as the structural properties of the resulting oxide and junction layer. Fritz et al have reported stoichiometries of 1.1-1.3 for oxide regions resulting from thermal oxidation with and without UV illumination, plasma oxidation and physical vapour deposition by heating the Al2O3 pellets.