Phosphate treatment

Many methods have been developed since 1945. They are better known by their trademark 

These solutions comprise phosphates, fluorides and chromates [9]. 

Conversion treatments based on phosphates of trivalent chromium, which yield a deep emerald green layer. The baths comprise chromium anhydride, phosphoric acid and hydrofluoric acid. This type of conversion is widely used for products that are lacquered by the coil-coating process and used in the building industry. The weight of the layer ranges from 400 to 800 mg-m , and its thickness is roughly 400 nm for a deposition of 1 g-m . These layers combine good corrosion resistance with excellent adherence for lacquer. 

Alloy series Typical treatment Properties of the anodic coating Typical application 

---

Parkerizing A trade name for a process for phosphate treatment of steel. See phosphate coatings. 

Chromium Phosphate. Chromium phosphate treatment baths are strongly acidic and comprise sources of hexavalent chromium, phosphate, and fluoride ions. Conversion coating on aluminum precedes by the foUowing reactions (24) ... 

In dmm boilers sodium hydroxide (caustic), sodium phosphate, or both may be added for pH and scale control. Sodium hydroxide is used more in Europe than in the United States, where sodium phosphate treatment is usually preferred. In boilers operating above 4 MPa (580 psia), caustic concentrations must be carefully controlled to prevent highly corrosive deposits from forming. In the lowest pressure boilers, phosphate treatment may be used to compensate for lower purity feedwater. As the boiler pressure increases, the allowable phosphate concentration decreases, and at 16.5 MPa (2400 psia) or above, equiUbrium phosphate treatment may be used. In this treatment, caustic is added to a low phosphate concentration in the boiler to maintain the proper pH (20). 

Steam and calcium hydroxide is formed. If the cooling water tends to form acid ia the boiler, either caustic or phosphate may be added to counteract the effect. When the cooling water tends to form base, only phosphate treatment is appropriate. Many dmm boilers that are operated on AVT have provision for phosphate or caustic treatment duriag condenser leaks because the amines used ia AVT have neither significant bufferiag capacity nor precipitate conditioning properties ia the boiler. 

Another approach is the use of polyphosphate-based blends including proprietary chemicals. The exact mechanism of the observed effect is not completely understood. In the polyphosphate mode of operation, the polyphosphate is dosed ia quantities of 2—5 ppm periodically, sludge resulting from phosphate treatments is removed by acid cleaning (see Dispersants). 

Phospha.te Treatment. Calcium phosphate is virtually insoluble in boiler water. Even small levels of phosphate can be maintained to ensure the precipitation of calcium phosphate in the bulk boiler water, away from heating surfaces. Therefore, the introduction of phosphate treatment eliminates the formation of calcium carbonate scale on tube surfaces. When calcium phosphate is formed in boiler water of sufficient alkalinity, a particle with a relatively nonadherent surface charge is produced. This does not prevent the development of deposit accumulations over time, but the deposits can be controlled reasonably well by blowdown. 

Phosphate—Polymer Control. Phosphate treatment results are improved by organic supplements. Naturally occurring organics such as lignins, tannins, and starches were the first supplements used. The organics were added to promote the formation of a fluid sludge that would settle in the mud dmm. Bottom blowdown from the mud dmm removed the sludge. 

Phosphate—Chelant—Polymer Combinations. Combinations of polymer, phosphate, and chelant are commonly used to produce results comparable to chelant—polymer treatment in boilers operating at 4137 x 10 Pa or less. Boiler cleanliness is improved over phosphate treatment, and the presence of phosphate provides an easy means of testing to confirm the presence of treatment in the boiler water. 

In certain cases rinsing may be dispensed with after non-accelerated phosphate treatment, but blistering of paint due to local concentration of solution in seams and crevices may occur. Rinsing is generally applied, regardless of the type of phosphate process employed... 

Phosphate Treatment of Iron and Steel for Protection aganst Corrosion, BS 3189 1973, British Standards Institution, London... 

The best protection is given by paint. An etch-primed paint scheme can be applied directly to the metal for other paints an inorganic treatment must be given to ensure good adhesion. Of the two classes of inorganic treatment, phosphate treatment has little protective value in itself, but chromate passivation gives appreciable protection and in mildly corrosive surroundings may be sufficient in itself. 

Water treatment for utility power boilers must be first class and generally necessitates extremely sophisticated pre- and post-boiler treatment processes. Internal water chemistry usually rellies on the use of caustic-free, phosphate treatment or all-volatile treatment (AVT) programs. 

Coordinated phosphate programs These programs are formulated to avoid the formation of hydroxyl alkalinity (free caustic). They tend to be employed in higher pressure WT boilers and require very careful control. Variants include congruent control and equilibrium phosphate treatment. 

Equilibrium Phosphate Treatment general area to prevent P04 hideout... 

Phosphate need not be used in boilers where hardness can be eliminated from the FW at all times. Its use is not recommended for boilers that may exhibit severe hideout (see the section on coordinated phosphate treatment). In these circumstances, sodium hydroxide is the preferred alkalizing agent and should be dosed to a maximum of 1.5x the sodium chloride content. 

Dooley, R.B. Paul, L.D. Phosphate Treatment and Corrosion Fatigue. Ultrapure Water, Tall Oaks Publishing, Inc., USA, February 1997. 

Hydroxy groups on benzene rings can be replaced by NH2 groups if they are first converted to aryl diethyl phosphates. Treatment of these with KNH2 and potassium... 

Ives JA, Carr JA, Mendel DB, Tai CY, Lambkin R, Kelly L, Oxford JS, Hayden FG, Roberts NA (2002) The H274Y mutation in the influenza A/HINI neuraminidase active site following oseltamivir phosphate treatment leave virus severely compromised both in vitro and in vivo. Antiviral Res 55 307-317... 

Phosphate treatment, in industrial water treatment, 26 132 Phosphatic limestone, 15 28 Phosphating, metal surface, 16 214-218 Phosphazenes, 19 55-57... 

Due to environmental concerns, research efforts have been directed toward the replacement of chromate-based post-treatments. This paper focuses on a new unique chromium free post-treatment based on "Mannich derivatives" of po1y-viny1pheno 1 which have demonstrated excellent performance on both zinc and iron phosphate treatments. 

Stanforth, R. Qiu, J. 2001. Effect of phosphate treatment on the solubility of lead in contaminated soil. Environmental Geology, 41, 1-10. 

Uchida, T., Itoh, I. Harada, K. 1996. Immobilization of heavy metals contained in incinerator fly ash by application of soluble phosphate - treatment and disposal cost reduction by combined use of high specific surface area lime . Waste Management, 16, 475-481. 

Shackney S, Hasson J. Precipitious fall in serum calcium hypotension and acute renal failure after IY phosphate treatment of hypercalcemia. Arch Intern Med 1968 122 150. 

Fig. 10. Recommended phosphate content of boiler water for drum boilers, using coordinated phosphate treatment...

Combined Threshold Effect and Corrosion Inhibition/Phosphate Treatment Program... 

Makitie O, Kooh SW, Sochett E. Prolonged high-dose phosphate treatment a risk factor for tertiary hyperparathyroidism in X-linked hypophosphatemic rickets. Clin Endocrinol 2003 58 163-8. 

---