Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B25/00—Phosphorus; Compounds thereof
  • C01B25/16—Oxyacids of phosphorus; Salts thereof
  • C01B25/26—Phosphates
  • C01B25/37—Phosphates of heavy metals
  • C01B25/375—Phosphates of heavy metals of iron

Definitions

• This invention relates to a process for the preparation of white iron phosphate. More particularly, it relates to a preparation of a white iron phosphate which is suitable as an agent for inhibiting corrosion in primer paints.
• the herein disclosed process for preparing white iron phosphate, FePO .2H O comprises commingling in water phosphoric acid, a ferrous salt selected from the group consisting of ferrous sulfate, ferrous chloride and ferrous nitrate and an oxidizing agent selected from the class con sisting of the alkali metal chlorates, ammonium chlorate and hydrogen peroxide, each of said acid and said oxidizing agent being added in sufiicient amount to provide at least one equivalent per equivalent of said ferrous salt, heating for at least A hour at a temperature of from 50 C. to about 95 C., adjusting the pH to a value of about 2 to about 6, and recovering White, insoluble iron phosphate which precipitates.
• Another advantageous feature of the process of the instant invention concerns the recovery or precipitation step.
• the basic material for example, sodium hydroxide
• the reaction mixture remains as a clear, homogeneous solution.
• precipitation of white iron phosphate commences as the pH of the system attains a value of from 2 to about 6.
• This method of mixing and heating reactants insures complete oxidation of ferrous iron and thus prohibits precipitation of undesired ferrous compound prior to the addition of alkali. Consequently, with complete oxidation, homogeneity of reaction is obtained and the ultimate precipitate is uniformly of the desired higher valence state of 3.
• complete neutralization may be effected, it is undesirable to do so in view of the fact that the color of the final product is adversely affected.
• the above molecular stoichiometry can be converted to an equivalent basis if the ferrous salt is chosen arbitrarily as a constant having a value of one equivalent.
• an equivalent amount of phosphoric acid is an equimolar amount
• an equivalent amount of a chlorate oxiding agent is a molar amount and of a peroxide is a /2 molar amount
• an equivalent amount of basic material is a two molar amount.
• the oxidation step consists of simultaneously adding at least an equivalent amount of oxidizing agent, and heating the resulting mixture for at least hour at a temperature of from about 50 C. to about 95 C. In this regard, even at the lower temperature limits, there will be no need to continue heating for more than a period of 2-3 hours.
• the time factor will depend on the temperature and the mole ratios of reagents wherein, in general, the higher the temperature, the shorter the oxidation period. Similarly, molar excesses of any one reagent or several reagents will enhance the rate of reaction. Most particularly preferred are temperatures in the range of from C. to about C.
• oxidizing agent it is preferred to use at least an equivalent amount per equivalent of ferrous salt, however, an excess will not cause any adverse effects. Although it is possible to use as much as a 2 equivalent excess, it is most preferred to use only an excess of about .1 to .5 equivalent.
• the recovery or precipitation step consists of adding to the heated, oxidized solution while stirring, an aqueous solution of a basic material such as sodium hydroxide or sodium carbonate in a sufficient amount to provide at least one equivalent per equivalent of ferrous salt and recovering the precipitated white iron phosphate which forms. It is possible to add a slight excess of base, however, no advantage results from so doing. Depending on the amount of base used, the pH of the mixture at the 3. point where precipitation of iron phosphate is virtually complete will vary from a value of about 2 to about 6.
• the yield of white iron phosphate is almost quantitative.
• the collection process consists of filtering, washing and drying utilizing conventional methods.
• the white iron phosphate, FePO .2H O, which is isolated analyzes approximately 42% Fe O 39% P and the balance free and combined water.
• Iron phosphate prepared by the process of this invention has been found to be an effective corrosion-inhibitor in primer paints.
• the method of evaluating iron phosphate for anti-corrosion properties is demonstrated by the following series of tests:
• A Salt Fog Resistance Test
• B Water Immersion Resistance Test
• C Humidity Resistance Test Standard automotive alkyd and epoxy primer surfacers were selected as test mediums. Controls were pigmented with an iron oxide-barium sulfate combination, a known corrosion inhibitive pigment combination, whereas the test samples were pigmented with iron phosphate. Paints were prepared of 18-gauge bonderized steel with each paint applied by spray at uniform dry film thicknesses of .91.0 mil. The panels obtained in this manner were subjected to tests B and C above.
• each panel was coated with the test primer surfacer and cured whereupon the lower half of each test panel was top-coated with a black automotive type enamel and cured.
• Test panels were then scored in the form of an X and subjected to the Salt Fog Resistance test. After exposure of 1000 hours duration, the test panels were removed and the lower half of each was stripped of paint laying bare the steel substrate which revealed the degree of protection the primer surfacers and the top coated primer surfacer afforded the steel substrate.
• iron phosphate In addition to its use as an anti-corrosion agent in primer paints, iron phosphate is prepared herein, may also find utility, due to its chemical purity, as a food grade additive in foods, vitamin preparations and in feeds. Further, due to its chemical composition, it may have utility as a plant nutrient ingredient or fertilizer stabilizer.
• Example I With stirring, FeSO (2280 g., M) in 12.5 1. of solution is added to a 16 1. volume of water, followed by the addition of 85% H PO (1715 ml., 25 M). To this mixture is added 500 ml. of an aqueous solution containing 275 g., 2.6 M of NaClO whereupon the resulting mixture is stirred and heated to 85 C. for /2 hour. Precipitation of the white iron phosphate product is accomplished by gradually adding 16 l. of basic solution containing NaOH (1275 g., 32 M). During the addition of base, stirring and heating are continued and when precipitation is complete, the product is filtered, Washed and dried to give virtually a quantitative yield of white iron phosphate, FPO42H20.
• Example II The procedure of Example I is repeated wherein a stoichiometric equivalent amount of ferrous chloride is used in place of ferrous sulfate with comparable results.
• Example III The procedure of Example I is repeated wherein a stoichiometric equivalent amount of ferrous nitrate is used in place of ferrous sulfate with comparable results.
• Example IV The procedure of Example I is repeated wherein the following equivalents of phosphoric acid per equivalent of ferrous sulfate are used:
• Example V The procedure of Example I is repeated wherein the oxidation step is carried out using the following FeSO /NaClO equivalent ratios and reaction conditions:
• Example VI The procedure of Example I is repeated wherein the following equivalent amounts of sodium hydroxideper equivalent of ferrous sulfate are used:
• Example VII With stirring, 284 ml. of an aqueous ferrous sulfate solution containing 70.5 g. of FeSO is combined with 500 m1. of water, and then with 52 ml. of an 85.3% phosphoric acid solution. Subsequently, 8.35 g., of NaClO in 50 ml. of water is added and the entire mixture diluted to a 2500 ml. volume with water, stirred and heated to temperature of 70 C. for a period of one hour. While maintaining said temperature and stirring, 500 ml. of an aqueous solution containing 51.2 g. of Na CO is added. Upon complete precipitation, the product is filtered, washed and dried to give virtually a quantitative yield of white iron phosphate, FePO -2H 0.
• Example VIII The procedure of Example VII is repeated wherein a stoichiometric equivalent amount of ammonium hydroxide is used in place of Na CO with comparable results.
• Example IX The procedures of Examples I, II, III, IV, V, VI, VII and VIII are repeated wherein a stoichiometric equivalent amount of potassium chlorate is used in lieu of sodium chlorate and satisfactory results are obtained.
• Example X The procedures of Examples I, II, III, IV, V, VII and VIII are repeated wherein a stoichiometric equivalent amount of lithium chlorate is used in lieu of sodium chlorate and substantially the same results are obtained.
• Example XI The procedures of Examples I, II, III, IV, V, VI, VII, and VIII are repeated wherein a stoichiometric equivalent amount of ammonium chlorate is used in lieu of sodium chlorate and substantially the same results are obtained.
• Example XII The procedures of Examples I, II, III, IV, V, VI, VII and VIII are repeated wherein a stoichiometric equivalent amount of hydrogen peroxide is used in place of sodium chlorate and satisfactory results are obtained.
• Example XIII The corrosion resistance of iron phosphate obtained by any of the synthetic methods outlined in Examples I to XII was measured in automotive primer sur-facers and a comparison made to a standard corrosion inhibitive pigment combination consisting of iron oxide and barium sulfate. These measurement studies consisted of three studies:
• Salt fog study Each panel, prepared of 18-gauge bonderized steel, was coated with the primer surfacer (either control or test pigmentation) and cured. The lower half of each panel was top coated with a black automotive type enamel and cured. The panels were then scored by making 2 diagonal marks in the form of an X and Subjected to salt fog conditions. Following exposure of 1000 hrs. duration, the panels were removed and the lower half of each panel was stripped of paint laying bare the steel substrate, revealing the degree of protection the primer surfacers and the top coated primer surfacer afforded the steel substrate.
• a process for the preparation of white iron phosphate of the formula FePO -2H O which comprises commingling in water phosphoric acid, a ferrous salt selected from the group consisting of ferrous sulfate, ferrous chloride and ferrous nitrate and an oxidizing agent selected from the class consisting of the alkali metal chlorates, ammonium chlorate and hydrogen peroxide, each of said acid and said oxidizing agent being added in sufficient amount to provide at least one equivalent per equivalent of said ferrous salt, heating for at least hour at a temperature of from C. to about 95 C., adjusting the pH to a value of about 2 to about 6, and recovering white, insoluble iron phosphate which precipitates.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Paints Or Removers (AREA)
• Chemical Treatment Of Metals (AREA)

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Citations (3)

• 1965
  • 1965-06-16 US US464572A patent/US3407034A/en not_active Expired - Lifetime
• 1966
  • 1966-01-07 GB GB948/66A patent/GB1135552A/en not_active Expired
  • 1966-06-09 BE BE682329D patent/BE682329A/xx not_active IP Right Cessation
  • 1966-06-10 DE DE1966P0039657 patent/DE1567769B1/de active Pending

Patent Citations (3)

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