Stabilized phosphate programs

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. 

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. 

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). 

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. 

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. 

Uses Copper and steel corrosion inhibitor disperses metal oxides and silt and controls formation of min. scale and deposits under cooling water system parameters hostile to traditional stabilized phosphate programs... 

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... 

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). 

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. 

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. 

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). 

Uses Scale/deposit inhibitor and dispersant used in stabilized phosphate and zinc-based cooling water programs... 

Figure 3.13 shows the thermal stability of immobilized ODN and PNA. The signal for the Thy- and Cyt-bases obtained with temperature-programmed (TP) SIMS starts to decrease at approximately 150 °C for ODN and 200 °C for PNA. This variance is caused by the different strengths of binding between the bases and the sugar-phosphate and peptide backbones, respectively. 

Because of their high degree of hydrolytic stability and the extended abilities and effectiveness of these novel chemistries, wherever phosphate-cycle or chelant programs are employed, the circumstances generally permit all-polymer/all-organic programs to be used as technically and economically viable alternatives. 

Improved deposit control agents and phosphate/zinc stabilizers have permitted these programs to operate with high levels of calcium (up to 1200 ppm) and high pH (up to 9.0). 

The cooling system underwent a simple cleaning procedure, but the passivation and initial inhibitor dose stages were rolled into one. The plan was to maintain 250 ppm of inhibitor in the system for a 3-day period (typical inhibitor dose would be 100 to 120 ppm). However, almost no stabilizer dispersant was added and the cooling water was persistently cloudy. Thus the passivation program was of little value, and the turbidity indicated phosphate precipitation. 

Catalytic properties Phosphorus is known to have deactivation effects for some automotive catalysts and the formation of CeP04 has been identified in phosphorus contaminated catalysts (Uy et al., 2003). Nanocrystalline LaP04 would act as Lewis acid in a catalytic process, which could be determined by a temperature-programmed ammonia adsorption/desorption process (Onoda et al., 2002 Rajesh et al., 2004, 2007). In addition, the rare earth phosphate NCs could act as supports for example, Pd, Pt, or Rh supported on RPO4 show excellent catalytic reduction of NO into N2 and O2 (Tamai et al., 2000), and gold supported on RPO4 shows catalytic activity and stability for CO oxidation. 

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