Aluminas hydroxides

Alumina gel(s), 2 422, 427-428 drying of, 23 66-67, 78 Alumina hydrates, 2 421, 428 crystalline, 2 422-426 economic aspects, 2 432 gelatinous, 2 426-427 health and safety factors, 2 432 manufacture, 2 428-431 properties of normal coarse grade, 2 429t shipping and analysis, 2 431-432 uses of, 2 432 Alumina hydroxides economic aspects, 2 432 health and safety factors, 2 432 physical data, 2 423t uses of, 2 432... 

See also Alumina hydroxides classification, 2 422 Aluminum particle size, 10 22-23 Aluminum perchlorate, 18 278 Aluminum phosphide, 2 284 19 58 Aluminum-polyphenylenevinylene-ITO, in photovoltaic devices, 22 221 Aluminum production, 9 639-640 Aluminum recycling, 2 305 21 371-372 economic aspects of, 21 402 remelting, 2 333-334 Aluminum reduction, of ferrovanadium, 25 518... 

Fine-mesh screen printing, 9 221 Fine ore drums, 15 453 Fine particles, suspensions of, 22 54 Fine particulate matter (PM2.s), 1 799 Fine-pore wick structure, 13 232 Fine precipitated alumina hydroxides, 2 430 properties of commercial, 2 429t Fine quicklime, 15 27 Fines removal, in crystallization, 8 124 Fine structural properties, of polyester fibers, 20 5... 

In drop-coagulation to form beads of alumina hydroxide, the top of a column holding oil and 100°C is fed with a blend of a sol of aluminium oxychloride and hcxamcthylcnc tctraminc. Under the influence of the temperature, the amine is decomposed to liberate ammonia, which neutralizes the chloride ions. The product is then ripened, dried, calcined and can be used as a support for reforming catalysts or hydrodesulfurization catalysts [2], In the same way. a silica sol feeding the bottom of a column of trichloroethylene at around 75 °C permits obtaining silica beads at the top. 

With the exception of alumina hydroxides, fire-retardant phosphorus compounds are now used in greater quantities than any of the other main types of retardants, that is, antimony oxide, borates or halogenated hydrocarbons. Advantages claimed for organophosphorus-based fire retardants are relatively low toxicity and minimum harmful volatiles under burning conditions [37]. 

Aluminum oxide, hydrated n. Al(OH)3. Crystalline powder, balls, or granules. Used as a pigment or a base for organic lakes and as an extender for inks. Density, 2.4g/cm (19.8-20.2lb/gal) O.A., 41-53lb/ 100 lb. Particle size, 0.38-8.5 pm. Syn alumina hydroxide, alumina trrhydrate, alumina hydrate, hydrated alumina, gibb-site and transparent white. 

Figure 6.5 The effect of filler particle size on the ignition times (UL 94 configuration) of PMMA filled with alumina hydroxide...

Boron trioxide is not particularly soluble in water but it slowly dissolves to form both dioxo(HB02)(meta) and trioxo(H3B03) (ortho) boric acids. It is a dimorphous oxide and exists as either a glassy or a crystalline solid. Boron trioxide is an acidic oxide and combines with metal oxides and hydroxides to form borates, some of which have characteristic colours—a fact utilised in analysis as the "borax bead test , cf alumina p. 150. Boric acid. H3BO3. properly called trioxoboric acid, may be prepared by adding excess hydrochloric or sulphuric acid to a hot saturated solution of borax, sodium heptaoxotetraborate, Na2B407, when the only moderately soluble boric acid separates as white flaky crystals on cooling. Boric acid is a very weak monobasic acid it is, in fact, a Lewis acid since its acidity is due to an initial acceptance of a lone pair of electrons from water rather than direct proton donation as in the case of Lowry-Bronsted acids, i.e. 

Aluminium oxide. The commercial material, activated alumina, is made from aluminium hydroxide it will absorb 15-20 per cent, of its weight of water, can be re-activated by heating at 175° for about seven hours, and does not appreciably deteriorate with repeated use. Its main application is as a drying agent for desiccators. 

ALUMDIUMCOMPOUNDS - ALUMINIUMOXIDE(ALUMINA) - HYDRATED] (Vol 2) b-aluminumoxide hydroxide)... 

Tetrahydrofurfuryl alcohol reacts with ammonia to give a variety of nitrogen containing compounds depending on the conditions employed. Over a barium hydroxide-promoted skeletal nickel—aluminum catalyst, 2-tetrahydrofurfur5iarnine [4795-29-3] is produced (113—115). With paHadium on alumina catalyst in the vapor phase (250—300°C), pyridine [110-86-1] is the principal product (116—117) pyridine also is formed using Zn and Cr based catalysts (118,119). At low pressure and 200°C over a reduced nickel catalyst, piperidine is obtained in good yield (120,121). 

Aqueous solutions of caustic soda aie highly alkaline. Hence caustic soda is ptimatily used in neutralization reactions to form sodium salts (79). Sodium hydroxide reacts with amphotoric metals (Al, Zn, Sn) and their oxides to form complex anions such as AlO, ZnO. SnO ", and (or H2O with oxides). Reaction of AI2O2 with NaOH is the primary step during the extraction of alumina from bauxite (see Aluminum compounds) ... 

Magnesium Hydroxide. Magnesium hydroxide [1309-42-8] is another metal hydrate that decomposes endothermically, accompanied by the formation of water. It decomposes at 330°C, which is 100°C higher than alumina trihydtate, and can therefore be used in polymers that ate processed at higher temperatures. 

Starch is a polysaccharide found in many plant species. Com and potatoes are two common sources of industrial starch. The composition of starch varies somewhat in terms of the amount of branching of the polymer chains (11). Its principal use as a flocculant is in the Bayer process for extracting aluminum from bauxite ore. The digestion of bauxite in sodium hydroxide solution produces a suspension of finely divided iron minerals and siUcates, called red mud, in a highly alkaline Hquor. Starch is used to settle the red mud so that relatively pure alumina can be produced from the clarified Hquor. It has been largely replaced by acryHc acid and acrylamide-based (11,12) polymers, although a number of plants stiH add some starch in addition to synthetic polymers to reduce the level of residual suspended soHds in the Hquor. Starch [9005-25-8] can be modified with various reagents to produce semisynthetic polymers. The principal one of these is cationic starch, which is used as a retention aid in paper production as a component of a dual system (13,14) or a microparticle system (15). 

There are several processes available for the manufacture of cryoHte. The choice is mainly dictated by the cost and quaUty of the available sources of soda, alumina, and fluoriae. Starting materials iaclude sodium aluminate from Bayer s alumina process hydrogen fluoride from kiln gases or aqueous hydrofluoric acid sodium fluoride ammonium bifluoride, fluorosiUcic acid, fluoroboric acid, sodium fluosiUcate, and aluminum fluorosiUcate aluminum oxide, aluminum sulfate, aluminum chloride, alumina hydrate and sodium hydroxide, sodium carbonate, sodium chloride, and sodium aluminate. 

Most A1F. and cryoHte producers have their own HF production faciUties. HF vapor is reacted with alumina trihydrate to form A1F. in a fluid-bed reactor. HF is reacted with sodium hydroxide to form sodium fluoride, which is then used to produce cryoHte. Producers who manufacture these products solely for use in the aluminum industry do not generally install Hquid HF storage and handling faciHties, and do not participate in the merchant HF market. 

The magnesia and alumina suspension is prepared by treatment of an aqueous solution, containing aluminum and magnesium salt in the desired proportion, with sodium hydroxide. The coprecipitated aluminum and magnesium hydroxides are collected by filtration, washed free of soluble salts, and stabilized by the addition of a suitable hexatol. 

A.lkaline Solutions. The most important example of alkaline leach is the digestion of hydrated alumina from bauxite by a sodium hydroxide solution at 160-170°C, ie, the Bayer process (see Aluminumand aluminum alloys). 

Aluminum. All primary aluminum as of 1995 is produced by molten salt electrolysis, which requires a feed of high purity alumina to the reduction cell. The Bayer process is a chemical purification of the bauxite ore by selective leaching of aluminum according to equation 35. Other oxide constituents of the ore, namely siUca, iron oxide, and titanium oxide remain in the residue, known as red mud. No solution purification is required and pure aluminum hydroxide is obtained by precipitation after reversing reaction 35 through a change in temperature or hydroxide concentration the precipitate is calcined to yield pure alumina. 

Aluminum compounds, particularly the hydroxides and oxides are very versatile. Properties range from a hardness iadicative of sapphire and comndum to a softness similar to that of talc [14807-96-6] and from iuertness to marked reactivity. Aluminas that flow and filter like sand may be used for chromatography (qv) others are viscous, thick, unfilterable, and even thixotropic (1). 

Eigure 1 illustrates the Bayer process as it is practiced in the 1990s. The primary purpose of a Bayer plant is to process bauxite to provide pure alumina for the production of aluminum. World production of Al(OH)2 totaled ca 55 x 10 t in 1988. Practically all of the hydroxide was obtained by Bayer processing and 90% of it was calcined to metallurgical grade alumina (AI2O2). However, about 10% of the bauxite processed serves as feedstock to the growing aluminum chemicals industry. 

The aluminum containing compound having the largest worldwide market, estimated to be over 30 x 10 t in 1990, is metal grade alumina. Second, is aluminum hydroxide. In 1990 the market for Al(OH)2 should approach or exceed 3.5 million metric tons which is equivalent to 2.3 million tons on an alumina basis. The spHt between additive and feedstock appHcations for Al(OH)2 (16) is roughly 50 50. Additive appHcations include those as flame retardants (qv) in products such as carpets, and to enhance the properties of paper (qv), plastic, polymer, and mbber products. Significant quantities are also used in pharmaceuticals (qv), cosmetics (qv), adhesives (qv), poHshes (qv), dentifrices (qv), and glass (qv). 

Aluminum sulfate has largely replaced alums for the major appHcations as a sizing agent in the paper industry and as a coagulant to clarify municipal and industrial water suppHes. In terms of worldwide production, it ranks third behind alumina and aluminum hydroxide, with markets in excess of 3 x 10 t/yr (19). 

The activated aluminas comprise a senes of nonequilibrium forms of partially hydroxylated aluminum oxide [1344-28-1], AI2O2. The chemical composition can be represented by Al20 2 ranges from about 0 to 0.8. They are porous soHds made by thermal treatment of aluminum hydroxide... 

The large majority of activated alumina products are derived from activation of aluminum hydroxide, rehydrated alumina, or pseudoboehmite gel. Other commerical methods to produce specialty activated aluminas are roasting of aluminum chloride [7446-70-0], AIQ calcination of precursors such as ammonium alum [7784-25-0], AlH2NOgS2. Processing is tailored to optimize one or more of the product properties such as surface area, purity, pore size distribution, particle size, shape, or strength. 

Rehydration Bonded Alumina. Rehydration bonded aluminas are agglomerates of activated alumina, which derive their strength from the rehydration bonding mechanism. Because more processing steps are involved in the manufacture, they are generally more expensive than activated aluminum hydroxides. On the other hand, rehydration bonded aluminas can be produced in a wider range of particle shape, surface area, and pore size distribution. 

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