Stability phosphates

NOTE However, there exist many cooling system operators and (unfortunately) small water treatment service companies who fail to understand that simple polyacrylate dispersants are generally unsatisfactory for use in stabilizing phosphate. 

This development was further accelerated when, in the late 1970s and early 1980s, chromates began to fall out of favor (for both environmental and occupational health reasons), and thus the need arose to find suitable (organic) alternatives for use as effective corrosion inhibitors. Various stabilized phosphate and zinc/organic programs were developed at this time... 

Many modifications of stabilized phosphate technology now exist (for example, zinc is often included) and new, further improved calcium phosphate stabilizers have emerged. 

Sulfonated styrene, maleic anhydride (SS/MA) has proved to be a popular inhibitor for calcium phosphate control in stabilized phosphate and other polyphosphate programs. As such, it competes with other calcium phosphate control technologies, such as acrylic acid, hydroxypropyl acrylate copolymer (AA/HPA) and acrylic acid, 2-acrylimido-2-methylpropanesulfonic acid (AA/AMPS, or sometimes known as AA/SA), and acrylic acid, sodium 3-allyloxy-2-hydroxypropane sulfonate copolymer (AA/COPS). 

In essence, stabilized phosphate programs involve the treatment of controlled amounts and ratios of O-PO4 and P-PO4, and other inhibitors, combined with a suitable stabilizing polymer, usually added separately. Today a blend of halogen-stable, stabilizing polymers are usually provided. Under prescribed operating conditions, this program can often provide excellent corrosion inhibition. Optimum results, however, usually require careful, almost knife-edge, analytical control. 

A formulation for an updated, stabilized phosphate, 2 drum product, used perhaps in a steelwork or fertilizer plant, is shown next. 

The success of stabilized phosphate programs, but mixed with growing concerns over phosphate levels in the environment, has resulted in the development of many programs with lower PO4 content but blended with various combinations of zinc, phosphonate, and polymers. 

Typically, these low PO4 programs have been designed to operate at higher pH levels than stabilized phosphate programs, which reduces the risk of pH upsets and iron phosphate deposition. 

Alkaline phosphate programs These programs use the reverse ratios of phosphate compared with stabilized phosphate. Typically, the 0 P ratio is 1 2, with approx. 5 ppm PO4 in the cooling water, at 100 ppm alkalinity, down to 2 ppm PO4 at 300 ppm alkalinity. 

The chemical treatment employed is a combination/derivation of an Alkaline Zinc Polymer Program and a Stabilized Phosphate Program. It operates at an alkaline pH and uses zinc to synergize with phosphate to enhance corrosion protection and reduce the amount of PO4 required (this is Chemical 1). It requires a PO4 stabilizer polymer (Chemical 2). 

Any proposal for a future chemical inhibitor program needs to employ an alkaline zinc/stabilized phosphate base, similar to that currently used, as required by the customer. However, as noted previously, the inhibitor needs improved deposit control agent (DCA) performance. This is especially important, as a new program would not start with a properly cleaned cooling system (an on-line clean will be recommended, but is likely to have only limited effect). Thus the inhibitor would include better/more polymers. 

Adding some acid to reduce and maintain the circulating water pH to approximately 7.6 to 7.8, which benefits biocidal and stabilized phosphate control. 

The development and testing of a suitable inhibitor program of alkaline zinc/stabilized phosphate combination was undertaken in the United States. The conditions for the trial unfortunately required the product to be similar to the existing vendor s program (a me-too" product). In addition, the formulation had to be fairly simple, as the raw material blending was to take place within the region by relatively inexperienced people (which saved on the cost of effectively importing water). 

Sometimes they are two-pack programs, as with most Stabilized Phosphate Programs. Or they may be designed to control a more limited set of circumstances, with additional, specific adjunct products being employed, as and when necessary. 

As with individual treatment components, all inhibitor treatments within any inhibitor category (such as stabilized phosphate or zinc polymer phosphonate), from different vendors, cannot be considered to be the same Certainly there are similarities, but for each category, each particular vendor makes use of slightly different specialty raw materials and adjusts the formulation to meet particular market needs, performance demands, or pricing policies. Therefore care is required when trying to compare proposals ( apples with apples ). 

Table 8.4 Stabilized Phosphate Program Selection Notes...

If significant phosphate is present, it is possible that a stabilized phosphate program has been used and the O-P ratios have not been maintained correctly, or the total phosphate reserve has been too high (check the makeup for phosphate content), or the reserve phosphate specific dispersant has been maintained at too low a level in relation to the calcium hardness. 

It is well known that the addition of soluble calcium salts reduces the heat stability of milk, whereas the addition of calcium complexing agents with the appropriate control of pH improves heat stability. Phosphates and citrates have often been used to increase the heat stability of concentrated milks (Augustin and Clarke, 1990 Pouliot and Boulet, 1991 Sweetsur and Muir, 1982a). A reduction in activity by the addition of these salts contributes to the improved heat stability of concentrated milks, but the effects of salts on the equilibrium of caseins between the serum and micellar phases of milk also affect heat stability. 

FIGURE 15.6 Loss of a resonance-stabilized phosphate ion in production of ATP. 

When ADP is phosphorylated to ATP, there is a loss of the resonance-stabilized phosphate ion, resulting in a decrease in entropy. (8" denotes a partial negative charge.)... 

Ortho-phosphate when dosed for corrosion control (i) at the water treatment plant to check process control, and (ii) through the distribution network to check variation caused by mixing of source waters and to check water stability (phosphate attenuation should not normally exceed 10%) - random daytime sampling from consumers taps will provide the most representative check of variation across the water supply system. 

The typical features of chemical modifiers used in graphite furnace AAS are exemplified by the use of hydrofluoric acid as a modifier in the determination of Cu and Mn in seawater [328], and by the use of CaCl2 and ZrOQ2 as modifiers in the determination of B [329]. Tsalev et al. [330] determined Cd and Pb with stabilized phosphate deposited on permanently modified platforms, while Pereira-Filho et al. [331] used Zr and Pd + Mg as modifiers in the determination of Al, Cd, and Pb in biological slurry samples dispensed on Lvov platforms. They studied the elemental distributions of P, S, Ca, Ti, Fe, Zr, Hf, and Pd on these platforms by micro synchrotron radiation X-ray fluorescence and the morphology of the platforms by scanning electron microscopy. 

Georgieva R., Chakarova K. K. and Petrov Jr. 1.1. (2002) Electrothermal atomic absorption spectrometric determination of cadmiiun and lead with stabilized phosphate deposited on permanently modified platforms,... 

Use steps 1, 2, 3, 10 and 11 in Section 6.16.4 only, under the procedure for the Stabilized Phosphate-Fluoride Method in Section 6.16.2. The results, however, give poorer durability than with that method. 

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