Aluminium zinc phosphate

Fig. 7. Absorption spectrum of trivalent chromium in an aluminium zinc phosphate glass...

Cleaners containing silicate can cause problems. They should not be used prior to an alkaline process on aluminium, owing to the formation on the surface of alkali-insoluble aluminium silicate. Silicated cleaners can also cause problems before some surface-sensitive zinc phosphating solutions, especially the more modern low-zinc type. 

Conversion coating Conversion coatings are chemical solutions which react with the metal surface to create a corrosion-resistant layer onto which the coating can bond. For mild steel iron phosphate is used to attain good adhesion, but it does not give the underfilm corrosion resistance which can be obtained using zinc phosphate. Zinc coatings can be treated with either zinc phosphate or chromate. Aluminium is usually treated with chromate... 

The actions of zinc and aluminium differ. In general, metal ions such as zinc merely serve to neutralize the acid and are present in solution as simple ions (Holroyd Salmon, 1956 O Neill et al., 1982). But aluminium has a special effect in contrast to zinc, it prevents the formation of crystallites during the cement-forming reaction in zinc phosphate cements. 

It is interesting that this cement has been known for over 100 years and yet certain features of its chemistry remain obscure. The exact nature of the matrix is still a matter for conjecture. It is known that the principal phase is amorphous, as a result of the presence of aluminium in the liquid. It is also known that after a lapse of time, crystallites sometimes form on the surface of the cement. A cement gel may be likened to a glass and this process of crystallization could be likened to the devitrification of a glass. Therefore, it is reasonable to suppose that the gel matrix is a zinc aluminophosphate and that entry of aluminium into the zinc phosphate matrix causes disorder and prevents crystallization. It is not so easy to accept the alternative explanation that there are two amorphous phases, one of aluminium phosphate and the other of zinc phosphate. This is because it is difficult to see how aluminium could act in this case to prevent zinc phosphate from crystallizing. 

As we have seen in Section 6.2, there is some evidence for supposing that zinc phosphate cements contain an amorphous aluminium phosphate or zinc aluminophosphate phase. Also, as we shall see in Section 6.5, amorphous aluminium phosphate is the binding matrix of dental silicate cement. 

Williams, J. I., Gates, G. L., Hembree, J. H. MacKnight, J. P. (1979). The frozen-aluminium-slab mixing technique its effect on zinc phosphate cements. Jourrml of Dentistry for Children, 46, 398-403. 

The mitigation of corrosion can be achieved economically by the use of corrosion inhibitors. Chromate has been extensively used in an aqueous environment for the protection of aluminium, zinc and steel. Although chromates are cheap and effective, they are not acceptable because of their toxicity. Alternate inhibitors such as molybdates, organic inhibitors such as phosphonates, mixtures of phosphates, borates and silicates and surfactants like sulfonates have been used in place of chromates. Chromates are anodic inhibitors and help to form passive oxide on the metal surface. 

Ammonium orthophosphates.—Evaporation of a solution of phosphoric acid neutralized with excess of ammonia yields the trihydrate of tjae normal phosphate, (NH4)3P04,8HS0, in the form of transparent prisms.5 A pentahydrate has also been described.6 When the ammoniaeal solution is heated with aluminium, the phosphate of this metal is formed zinc liberates hydrogen.7... 

The rated indicators, on the other hand, include the content of dissolved oxygen, active chlorine, ammonia and ammonia ions, iron, manganese, aluminium, zinc, magnesium, calcium, phosphates, nitrites, nitrates, chlorides, sulphates, humin substances, all dissolved constituents, anions of tensides, copper, hydrogen carbonates and pH value. This category also includes radioactivity characterized by total volume alpha-activity, and in surface waters also by total volume beta-activity. 

The zinc phosphate cement dates back to at least 1879, when Rollins reported a formulation based on syrupy orthophosphoric acid [13]. The first really satisfactory cement of this type was reported by Fleck in 1902 [14], His report described a paper based on zinc oxide that had been deactivated by heating, together with a solution of phosphoric acid modified by the inclusion of aluminium and zinc. These two approaches to moderating the reaction led to a setting process that took place at a sufficiently slow speed that a smooth paste could be prepared from the components, and there was time to apply it before hardening took place. 

Many pure inorganic compounds have been useful as ion-exchangers tin(II) hexacyanoferrate(II) extracts nickel(II) (424) aluminium and zinc phosphate extract Cr(III) (425) cerium(IV) phosphate sorbs Pb(II), Ag(I), and T1(I)... 

A buildup of Al + in the zinc phosphating baths will restrict the amount of coating formed unless these ions are ranoved by addition of fluoride or borate. An advantage of zinc phosphating, however, is that it avoids the use of toxic hexavalent chromium compounds. Some simple bath compositions for zinc and manganese phosphating of aluminium are... 

The aluminium alloy Ac-120 samples of 50 X 200 mm gauge were produced with a EDT (electron discharge texturing) surface finish by Alusuisse Sierre AG, Sierre, Switzerland [40j. The surface topography was evaluated following each of four fabrication steps (a) AR, (b) pretreated in a film-forming zinc phosphate process (PP), (c) after cataphoretic lacquer BC and (d) after application of the TC lacquer. 

Ceramics. Mixed calcium phosphates, calcium sulfates, zinc calcium phosphates, aluminium calcium phosphates, metacalcium phosphates, sodium metacalcium phosphate, calcium carbonate, magnesium calcium carbonate and magnesium carbonate. 

In this section, the pigments discussed in more detail include the zinc phosphates and one type of nonzinc phosphate, aluminium triphosphates. 

Another group of second-generation phosphate pigments includes salts formed between phosphoric acid and different metafile cations, for example, hydrated modified aluminium-zinc hydroxyphosphate and hydrated zinc hydroxymolybdate phosphate. Trials using these salts in alkyd binders indicate that pigments of this type can provide corrosion protection comparable to that of zinc yellow [67-69]. 

Oxides with group 13-15 elements (B, Al, Sn, As) cobalt aluminium oxide cobalt boron oxide (cobalt borate) cobalt tin oxide (cobalt stannate) cobalt arsenic oxide (cobalt arsenate) eobalt arsenic oxide hydrate and erythrite (Co3(As04)2.8H20) cobalt ammonium arsenic oxide smaltite ((Co,Ni)As3 n). Phosphates cobalt phosphate (Co3(P04)2) cobalt phosphate tetrahydrate Co3(P04)3.4H20 cobalt phosphate octahydrate Co3(P04)2.8H20 cobalt aluminium phosphate cobalt ammonium phosphate (C0NH4PO4.H2O) cobalt magnesium phosphate cobalt zinc phosphate. 

Cobalt group Cobalt aluminium phosphate Cobalt ammonium phosphate Cobalt magnesium phosphate Cobalt zinc phosphate Cobalt violet Bersch (1901) 232 Church (1901) 210-211 Co/oar dex(1971) 77360-2 Corbeil et al. (2002) Gentele (1860) 79 Heaton (1928) 163 Jannicke (1893) Rozenberg (1997)... 

Filiform corrosion is characterised by the formation of a network of threadlike filaments of corrosion products on the surface of a metal coated with a transparent lacquer or a paint him, as a result of exposure to a humid atmosphere. This phenomenon first attracted attention because of its formation on lacquered steel, and for this reason it is sometimes referred to as underfilm corrosion, but although it is most readily observed under a transparent lacquer it can also occur under an opaque paint film or on a bare metal surface. Filiform corrosion has been observed on steel, zinc, magnesium and aluminium coated with lacquers and paints, and with aluminium foil coated with paper. Surface treatment of the metal by phosphating or chromating lessens the tendency for filiform corrosion to occur, but it is not completely... 

Phosphate solutions containing fluorides are used for processing steel, zinc and aluminium when assembled together, but chromate solutions are generally preferred when aluminium is treated alone. The increasing use of cathodic electrophoretic painting on steel, however, has led to a reassessment of the basic processes and formulations that might be most effective. 

Discussion. This method is based upon the precipitation of lead chlorofluoride, in which the chlorine is determined by Volhard s method, and from this result the fluorine content can be calculated. The advantages of the method are, the precipitate is granular, settles readily, and is easily filtered the factor for conversion to fluorine is low the procedure is carried out at pH 3.6-5.6, so that substances which might be co-predpitated, such as phosphates, sulphates, chromates, and carbonates, do not interfere. Aluminium must be entirely absent, since even very small quantities cause low results a similar effect is produced by boron ( >0.05 g), ammonium (>0.5 g), and sodium or potassium ( > 10g) in the presence of about 0.1 g of fluoride. Iron must be removed, but zinc is without effect. Silica does not vitiate the method, but causes difficulties in filtration. 

Determination of titanium with tannic acid and phenazone Discussion. This method affords a separation from iron, aluminium, chromium, manganese, nickel, cobalt, and zinc, and is applicable in the presence of phosphates and silicates. Small quantities of titanium (2-50 mg) may be readily determined. 

Determination of uranium with cupferron Discussion. Cupferron does not react with uranium(VI), but uranium(IV) is quantitatively precipitated. These facts are utilised in the separation of iron, vanadium, titanium, and zirconium from uranium(VI). After precipitation of these elements in acid solution with cupferron, the uranium in the filtrate is reduced to uranium(IV) by means of a Jones reductor and then precipitated with cupferron (thus separating it from aluminium, chromium, manganese, zinc, and phosphate). Ignition of the uranium(IV) cupferron complex affords U308. 

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