Natural aluminum oxide

CAS 1344-28-1. A Oj. The mineral corundum is natural aluminum oxide, and emery, ruby, and sapphire are impure crystalline varieties. The mixed mineral bauxite is a hydrated aluminum oxide. 

PZCs/IEPs of natural aluminum oxides are presented in Table 3.180. 

SYNONYMS aluminum oxide, aluminum trioxide, corundum, impure corundum, natural aluminum oxide. 

OTHER COMMENTS Emery is an impure variety of aluminum oxide (AI2O3), sometimes with small amounts of iron, magnesium, and silica. Corundum is natural aluminum oxide (AI2O3), which is a different and hard crystalline form of aluminum oxide. This material may be used in various polishing and abrasive operations may also be utilized during grinding and milling operations. 

Natural aluminum oxide [Note Emery is an impure variety of AI2O3 which may contain small impurities of iron, magnesium silica Corundum is natural AI2O3.] ... 

For most samples, which are soluble in organic solvents and of low molecular weight, adsorption chromatography (also called liquid-solid chromatography, LSC) on silica gel, aluminum oxide, or other inorganic oxides is suitable. Separation is based on specific interaction of the functional groups on the surface of the adsorbent with those of the sample. Silica gel is by far the most widely used adsorbent, available in consistent quality and at comparatively low cost. Due to its ionic nature aluminum oxide offers additional selectivity however, it is more difficult to obtain products with consistent separation properties. Therefore, separations on aluminum... 

Corundum k3- r9n-d9m [Tamil kuruntam akin to Sanskrit kuruvinda ruby] (1804) n. Natural aluminum oxide (including many gemstones), extremely hard, used as a filler in plastics to impart hardness, heat resistance, and abrasion resistance. 

Chrome baths always contain a source of hexavalent chromium ion (e.g., chromate, dichromate, or chromic acid) and an acid to produce a low pH which usually is in the range of 0-3. A source of fluoride ions is also usually present. These fluoride ions will attack the original (natural) aluminum oxide film, exposing the base metal substrate to the bath solution. Fluoride also prevents the aluminum ions (which are released by the dissolution of the oxide layer) from precipitating by forming complex ions. The fluoride concenfration is critical. If the concentration is too low, a conversion layer will not form because of the failure of the fluoride to attack the natural oxide layer, while too high a concentfa-tion results in poor adherence of the coating due to reaction of the fluoride with the aluminum metal substrate. 

The compounds of greatest importance are aluminum oxide, the sulfate, and the soluble sulfate with potassium (alum). The oxide, alumina, occurs naturally as ruby, sapphire, corundum, and emery, and is used in glassmaking and refractories. Synthetic ruby and sapphire are used in lasers for producing coherent light. 

Corundum. Comndum [1302-75-5] (see Aluminum compounds) is a naturally occurring massive crystalline mineral composed of aluminum oxide. It is an impure form of the gems mby and sapphke. Prior to 1900 comndum was an important abrasive for the production of grinding wheels. Today it is mainly employed as a loose abrasive for grinding and polishing optical lenses. Almost all the world s supply of comndum now comes from Africa, primarily from Zimbabwe. 

Except for siUca and natural abrasives containing free siUca, the abrasive materials used today are classified by NIOSH as nuisance dust materials and have relatively high permissable dust levels (55). The OSHA TWA allowable total dust level for aluminum oxide, siUcon carbide, boron carbide, ceria, and other nuisance dusts is 10 mg/m. SiUca, in contrast, is quite toxic as a respkable dust for cristobaUte [14464-46-1] and tridymite [15468-32-3] the allowable TWA level drops to 0.05 mg/m and the TWA for quartz [14808-60-7] is set at 0.1 mg/m. Any abrasive that contains free siUca in excess of 1% should be treated as a potential health hazard if it is in the form of respkable dust. Dust masks are requked for those exposed to such materials (see Industrial hygene). 

Aluminum Oxide. Emery [57407-26-8] is a natural oxide of aluminum with various impurities. One of these impurities, iron oxide, also acts as an abrasive. Pure aluminum oxide is made from bauxite [1318-16-7] and has partially replaced emery. 

In 1885, Charles Martin Hall invented his aluminum process and Hamilton Young Castner in 1890 developed the mercury-type alkali-chlorine cell, which produced caustic (sodium hydroxide) in its purest form. Edward G. Acheson in 1891, while attempting to make diamonds in an electric furnace, produced silicon carbide, the first synthetic abrasive, second to diamond in hardness. Four years later, Jacobs melted aluminum oxide to make a superior emeiy cloth. Within two decades, these two abrasives had displaced most natural cutting materials, including naturally occurring mixtures of aluminum and iron oxides. 

He became intimately familiar with a wide range of catalytic materials—including aluminum oxide, silica, and clay, as well as nickel, platinum, zinc, and copper—and their role individually and as mixtures 111 effecting chemical transformation. One of Ipatieffs most important lines of research was his breakthrough work on the nature and mechanisms of catalytic promoters on organic reactions. 

Aluminum (third most abundant element) is found as the Al+ ion in oxides and as the complex ion AlFImportant minerals are bauxite, which is best described as a hydrated aluminum oxide, Al203-.xH20, and cryolite, NaaAlFs. The element is readily oxidized and is not found in an uncombined state in nature. 

Aluminum Oxide (Alumina, oAlumina, Corundum, Alandum). A1203, mw 101.96, v hard white cryst powd, mp 2045°, bp 2980°, d 3.965g/cc. Insol in w, v si sol in aq alkaline solns. Found in nature as a mineral such as bauxite. Lab prepn is by heating aluminum hydroxide to above 1100°. 

Conventional ceramics are made from natural raw materials such as clay or silica advanced ceramics require extremely pure manmade starting materials such as silicon carbide, silicon nitride, zirconium oxide, or aluminum oxide and may also incorporate sophisticated additives to produce specific microstractures. 

Another way to protect a metal uses an impervious metal oxide layer. This process is known as passivation, hi some cases, passivation is a natural process. Aluminum oxidizes readily in air, but the result of oxidation is a thin protective layer of AI2 O3 through which O2 cannot readily penetrate. Aluminum oxide adheres to the surface of unoxidized aluminum, protecting the metal from further reaction with O2. Passivation is not effective for iron, because iron oxide is porous and does not adhere well to the metal. Rust continually flakes off the surface of the metal, exposing fresh iron to the atmosphere. Alloying iron with nickel or chromium, whose oxides adhere well to metal surfaces, can be used to prevent corrosion. For example, stainless steel contains as much as 17% chromium and 10% nickel, whose oxides adhere to the metal surface and prevent corrosion. 

Alumina— Siliceous Aluminum Oxides of Forms of Naturally Chemically Metals Sundry refract- tories... 

The Nature of Space Charge in Anodic Aluminum Oxides... 

In conclusion, the particles from the extruder breaker plate were identified as being polyetherimide. The particles in the polymeric matrix, however, appear to be inorganic in nature, containing aluminum and oxygen, as aluminum oxide, with traces of copper. 

We begin with the structure of a noble metal catalyst. The emphasis is on the preparation of rhodium on aluminum oxide and the nature of the metal-support interaction. Next we focus on a promoted surface in a review of potassium on noble metals. This section illustrates how single crystal techniques have been applied to investigate to what extent promoters perturb the surface of a catalyst. The third study deals with the sulfidic cobalt-molybdenum catalysts used in hydrotreating reactions. Here we are concerned with the composition and structure of the catalytically active... 

In natural waters CaC03 (calcite) nucleation occurs primarily heterogeneously. Many surfaces such as algae, biomass, aluminum silicates, aluminum oxides serve... 

Pure metallic aluminum is not found in nature. It is found as a part of compounds, especially compounded with oxygen as in aluminum oxide (Al O ). In its purified form, aluminum is a bluish-white metal that has excellent qualities of malleability and ductility. Pure aluminum is much too soft for construction or other purposes. However, adding as little as 1% each of silicon and iron will make aluminum harder and give it strength. 

Aluminum reacts with acids and strong alkali solutions. Once aluminum is cut, the fresh surface begins to oxidize and form a thin outer coating of aluminum oxide that protects the metal from further corrosion. This is one reason aluminum cans should not be discarded in the environment. Aluminum cans last for many centuries (though not forever) because atmospheric gases and soil acids and alkalis react slowly with it. This is also the reason aluminum is not found as a metal in its natural state. 

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