Additives aluminium hydroxide

A white gelatinous precipitate of aluminium hydroxide is obtained when an alkali is added to an aqueous solution of an aluminium salt. Addition of an excess of caustic alkali causes the precipitate to redissolve, the whole process being reversed by the addition of a strong acid the actual substance present at any time depending on... 

On standing, gelatinous aluminium hydroxide, which may initially have even more water occluded than indicated above, is converted into a form insoluble in both acids and alkalis, which is probably a hydrated form of the oxide AI2O3. Both forms, however, have strong adsorptive power and will adsorb dyes, a property long used by the textile trade to dye rayon. The cloth is first impregnated with an aluminium salt (for example sulphate or acetate) when addition of a little alkali, such as sodium carbonate, causes aluminium hydroxide to deposit in the pores of the material. The presence of this aluminium hydroxide in the cloth helps the dye to bite by ad sorbing it—hence the name mordant (Latin mordere = to bite) dye process. 

Addition of ammonium hydroxide to a solution of an aluminium salt gives a white gelatinous precipitate of aluminium hydroxide, Al(OH)3, insoluble in excess. Sodium hydroxide gives the same precipitate, but in this case, it does dissolve in excess. 

In the following experiment, salicylic acid is reduced to o-hydroxybenzyl alcohol (or saligenin), which being crystalline is readily isolated the excess of hydride is destroyed by the addition of undried ether, and the aluminium hydroxide then brought into solution by the addition of sulphuric acid. 

H. 8-Hydroxyquinaldine (XI). The reactions of 8-hydroxyquinaldine are, in general, similar to 8-hydroxyquinoline described under (C) above, but unlike the latter it does not produce an insoluble complex with aluminium. In acetic acid-acetate solution precipitates are formed with bismuth, cadmium, copper, iron(II) and iron(III), chromium, manganese, nickel, silver, zinc, titanium (Ti02 + ), molybdate, tungstate, and vanadate. The same ions are precipitated in ammoniacal solution with the exception of molybdate, tungstate, and vanadate, but with the addition of lead, calcium, strontium, and magnesium aluminium is not precipitated, but tartrate must be added to prevent the separation of aluminium hydroxide. 

The carbon black generated by a fire from a rubber source increases the smoke density other products are highly toxic and often corrosive. The halogens, phosphates, borates, and their acids evolved during a fire corrode metals and electrical and electronic equipment. Hence many of the fire retardants described below cannot be used in situations where the toxic gases evolved will create their own hazards. In these cases inorganic hydroxides are used, at filler-type addition levels. Aluminium hydroxide and magnesium hydroxide are used as non-toxic fire retardant systems. 

Aluminium hydroxide is essentially non-toxic, but does require high addition levels to be effective. As a result, the physical properties of the compound usually suffer. Its fire retardancy action results from the endothermic reaction which releases water under fire conditions and produces a protective char . The endothermic reaction draws heat from the rubber/filler mass and thus reduces the thermal decomposition rate. The water release dilutes the available fuel supply, cooling the rubber surface and mass. 

Therefore, when an anhydrous aluminium salt is dissolved in water initially, the octahedral ion [A1(H20)6]3 + is formed by hydration of the Al3 ion. However, since some hydrolysis occurs, the solution will contain H30+ and be acidic. Addition of any molecule or ion which removes H30+ for example alkali, or even sodium carbonate will cause the equilibrium to be displaced to the right and hydrated aluminium hydroxide is precipitated. 

Mineral fillers and additives aluminium trihydrate (ATH), magnesium hydroxide and boron derivates are the best known but tin derivates, ammonium salts, molybdenum derivates and magnesium sulphate heptahydrate are used to varying extents and nanofillers are developing. 

The addition of sodium monohydrogen arsenate to a solution of an aluminium salt results in the precipitation of a white powder which is probably aluminium hydrogen arsenate,5 Al2(HAs04)3. The powder dissolves in acids and the solution in hydrochloric acid when boiled with ammonium sulphite yields a precipitate of aluminium hydroxide, the arsenic remaining in solution. When heated in a current of hydrogen, arsenic is volatilised.6... 

Phloroisobutyrophenone is unstable when heated in the presence of acid the addition of Rochelle salt prevents the precipitation of aluminium hydroxide when the free acid is neutralised with sodium hydroxide. If any precipitate does appear more Rochelle salt should be added the exact amount of aqueous sodium hydroxide will vary with each experimental sequence the point of neutrality is ascertained with universal indicator paper. 

Among the oxides and hydroxides which exhibit the power of acting both as acid and basic compounds are cupric hydroxide, Cu(OH)2, which dissolves in a concentrated solution of potassium hydroxide with a dark blue colour zinc and cadmium hydroxides, which dissolve in excess of alkali sodium zincate has been separated by addition of alcohol, and is precipitated in white needles of the formula Na2ZnO .8H20 and aluminium hydroxide, which dissolves in alkali, forming an aluminate, MA102 ... 

The nascent hvdrogen reduces anv nitrates or nitrites to ammonia. Atmospheric oxygen converts the ferrous salt into colloidal feme hydroxide, a reaction that is facilitated by cascade aeration. As it coagulates and settles, the ferric hydroxide punfies the water in an analogous manner to that described for aluminium hydroxide above. The process is rather expensive, however, and for this reason some American towns have added ferrous sulphate direct to their waters. This is less satisfactory as the salt is not oxidised so readily as ferrous bicarbonate m addition to this, sulphuric acid is introduced into the water. 

In 2004, Sony and Mitsubishi Plastics teamed up to develop a flame retardant PLA biodegradable resin claimed to be as strong as ABS. The new material will be used in the front panel of Sony standalone DVD players. The resin employs an aluminium hydroxide flame retardant, is rated UL94 V-2 and complies with the EU s Restrictions on Hazardous Substances (RoHS) directive. Sony says the use of additives and modifications to moulding parameters allows it to process PLA compound on conventional injection presses in commercially viable cycle times. 

The reaction is a reversible one (compare Section 1.28), and any reagent which will reduce the hydroxyl-ion concentration sufficiently should cause the reaction to proceed from right to left with the consequent precipitation of aluminium hydroxide. This may be effected with a solution of ammonium chloride (the hydroxyl-ion concentration is reduced owing to the formation of the weak base ammonia, which can be readily removed as ammonia gas by heating) or by the addition of acid in the latter case a large excess of acid causes the precipitated hydroxide to redissolve. 

Consideration is given to the influence of combinations of zinc hydroxystannate (ZHS) with hydrated fillers, on the fire properties of plasticised PVC and polychloroprene. It is shown that magnesium and aluminium hydroxides specially coated with ZHS, confer significantly increased combustion resistance and lower levels of smoke evolution to these polymers. This permits large reductions to additive loading relative to unmodified filler, without sacrificing flame retardant or smoke suppressant performance. 10 refs. 

For this reason vaccine formulation tends to follow the traditional routes innovative formulations are rare. Aluminium hydroxide, aluminium phosphate and calcium phosphate are still the only registered vaccine adjuvants for humans. Veterinary vaccines have to rely on the same components, however, a few vaccines containing a mineral oil adjuvant (Marcol) or saponin (Quil A or derivatives) have passed the registration hurdles. It remains to be seen whether and under which restrictions these adjuvants can be used in the EEC after 1996 (see also below in "Additional requirements for veterinary products"). 

The authors of [37] confirmed high efficiency of the activation of a mixture of aluminium hydroxide with silicic acid. Monophase mullite was obtained. It was free from iron impurities by treating in weak hydrochloric acid solution. In order to improve agglomeration, the powder, synthesized at 1200°C, was subjected to additional activation for 10 min. Mullite with the density of 3 g/cm was obtained. 

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