Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
  • C23G1/025—Cleaning or pickling metallic material with solutions or molten salts with acid solutions acidic pickling pastes

Definitions

• the present invention relates to the treatment of metal surfaces. More particularly, the present invention relates to a process and composition for treating the surface of steel articles, e.g. in the form of plates, to provide for improved adherence of paint to the surface of the article to protect the same from the effects of corrosion.
• mill scale formed on steel in the course of rolling, forging or stamping under heat, constitutes an extremely harmful layer preventing good adherence of paint or other protective coating on the metal of the base, thus risking exposure of the metal base to destruction by corrosion.
• the addition to the acid bath of agents for inhibiting the corrosion of the metal serves the purpose of limiting the speed of attack of the steel which might be too extensive and produce a deterioration of the objects, either by a substantial diminishing of the material, or as the result of the so-called hydrogen embrittlement which is imparted to the piece, and which is manifested by a substantial reduction of the elastic properties of the metal.
• Another object of the present invention is to provide a de-mill scaling material which can be applied on all steel or cast iron objects and which can effectively and rapidly remove the mill scale layer therefrom without an appreciable attack on the metal of the base.
• the invention concerns the provision of a paste material having a viscosity suflicient to enable the paste to be applied with a brush or with a spray gun (with the aid of a vessel under pressure) on vertical members or on a ceiling, the paste preferably having a thickness of between 0.01 and several millimeters without running ofi, that is, such as to remain at the same thickness as long as it is not removed.
• the paste in accordance with the invention, has a suificiently strong action to provide for the de-mill scaling operation in a relatively short period of time, and of such composition to keep the sheet metal protected against all attack and irregular corrosion of the canker type, as well as all corrosion in the interstices between two plates which are riveted, welded or bolted.
• the product provided in accordance with the invention is a paste material which comprises as essential components one or more oxidizing anions and an inert pulverized mineral charge (incapable of being attacked, particularly by acids) such as silicates.
• the mineral charge in accordance with the invention is preferably composed of an insoluble silicate or of silica itself, such as clay or kaolin (aluminum silicate), talc (magnesium silicate), bentonite or ground shells (silica and calcium silicate).
• the mineral charge should be finely ground and moistened with water, in order to obtain a greasy paste so that it can be spread out in the manner of an oil paint.
• Ground quartz or silica which is entirely dehydrated is not suitable, since a paste made therefrom has the tendency to form lumps.
• the function of the mineral charge utilized in the paste formed in accordance with the invention is not that of a thickening agent for the acid solution, but that of a porous vehicle or vessel, that is, to serve as a support for osmotic phenomena.
• the function of the silicates contained in the charge conforming to the invention can be compared to that of a porous vessel in which a plant is grown.
• the porous vessel serves for the exchange of humidity and air between the roots of the plant (and the surrounding earth) and the surrounding atmosphere resulting from the osmotic pressure which is established through the vessel.
• the inventor has been able to show that the swelling colloidal charges capable 4a of forming a true gel with water, such as bentonite, are preferable to others due to their particular capability of serving as a porous vessel, that is, to absorb either the water provided by the atmospheric humidity, or other moistening agent, in swelling, according to the expression used in mineral chemistry, and the present invention preferably utilizes such charges.
• Another property of such swelling colloidal charges is the possibility of obtaining the same viscosity of the paste with ditferent proportions of the liquid-solid components, according to the pH of the medium from which the first gel has been formed.
• the bentonite has been added to a sulfuric a cid solution in order to obtain a given viscosityfit willbe necessary to have 35% of bentonite and 65% of acid solution.
• a gel 0 entontte is formed with water and the sulfuric acid is then added in order to obtain the same viscosity of the paste, and the same final proportion of the sulfuric acid with respect to the water, it will be necessary to have 25% of bentonite and 75% of acid solution (water and acid).
• a primary condition is the obtaining of such a viscosity that the paste can be applied on a ceiling or on a vertical wall without running, in a layer having a thickness of the order of 1 mm., but the proportions of the active ingredients are not critical, having effect only on the speed of action of the paste material.
• the rH-value is the logarithm, to the base 10, of the reciprocal of the hydrogen pressure which would produce the same electrode potential as that of a given oxidation-reduction system, in a solution of the same pH-value.
• the pH of the paste can be whatever at the moment its rH or r0 satisfies the condition described above. It can clearly be located between 0 and 10.
• oxidizing agents such as hypochlorites or periodates, produce upon reduction salts which are good conductors and which enable the paste to continue its action, but certain others such as KMnO, produce insoluble products which make the iron passive and interrupt the action of the paste.
• the invention provides for the addition to the paste of a salt or an acid soluble in a liguid which is a good conductor which avoids this passive action and has, besides, the advantage of aiding the formation of electrolytic piles of the type described below, in the case where the mill scale has a certain porosity.
• These salts or acids preferably have the following properties:
• They can be sulfates, acetates, pyrophosphates, of metals, preferably alkaline metals, for example,
• the first solution is practically destroyed at the end of a day or two, the third has a duration of more than three months. Therefore, it is preferable to avoid the prolonged presence of strong acid ions.
• the proportions of the components can be varied within very great limits. According to the concentration of the oxidizing agent, the paste is more or less active, but its action remains the same and therefore the proportions are not critical.
• the paste is more or less fluid, and more or less adapted to various types of de-mill scaling operations.
• the conditions of employment themselves being quite varied, and the layers of mill scale being very different in composition and thickness, the specifying of proportions of the components does not have very im portant significance.
• the proportion of water of aqueous solution in the paste will be regulated as a function of the viscosity sought, which depends on the instruments used for applying the paste. This can be determined by one skilled in the art, and according to the instrument employed, i.e. a spray gun, a brush, painter knife, it will be necessary to adopt a certain viscosity from which the necessary proportion of the liquid can be determined. Besides, the user can always increase the fluidity at the time of use by the simple addition of water.
• the proportion of the oxidizing agent this can vary between 1% and 20% with respect to the total weight of the paste, according to the oxidizing agent adopted and the activity of the paste sought.
• the electrolyte can be employed in the proportion of 1% to 30% according to its conductivity and its eventual particular activity in the electrolytic pile. But it is to be noted that these proportions are not critical.
• the acid utilized can be any mineral acid having a pH less than 2.5, with the exception of an acid capable of reducing the oxidizing anion present in the paste (such as HBr, H SO H PO H PO etc.).
• an acid capable of reducing the oxidizing anion present in the paste such as HBr, H SO H PO H PO etc.
• the acid which seems to be of the greatest interest, at least from the point of view of economy is sulfuric acid, at a concentration varying between 5% to 50% .with re spect to the water contained in the paste.
• the oxidizing anion can be of any type, so long as it is reduced by nascent hydrogen at ordinary temperature and can oxidize the ferrous sulfate formed by the action of H on the iron and eventually the layer of FeO, as for example the anions CrO Cr O' MnO N0 N0 C10 1 C105, etc.
• Those anions are preferable which aresiisceptible of changing color when they pass from the oxidized state to the reduced state, such as the anion CI'gO-f' which is orange yellow and which, by reduction, is transformed to the blue green cation Cr+++, or the anion MnOywhich is dark brown and which by reduction is transformed into the pale rose cation Mn++.
• the paste which in the absence of these oxidizing anions, is white or colorless, is strongly colored in the presence thereof, either to an orange yellow in the case of the presence of Cr O- ions, or to dark brown in the case of the presence of MnO and when it is applied on the mill scaled metal it shows the same colorations.
• the acid penetrates through the pores of the mill scale, it attacks the ferrous oxide and the underlying iron, which it transforms into R250, and liberates hydrogen.
• These two products act as reducers of the oxidizing anion which they reduce to the state of a reduced cation, with clear change of color of the paste at that point.
• the change in color of the entire surface does not mean that the acid has penetrated everywhere (because the change of coloration can also be produced by the diffusion of the hydrogen ion through the paste and the local reduction of the oxidizing anion), it nevertheless indicates that the acid has penetrated through a great number of the pores of the mill scale and that it continues to carry out its action of dissolution on the FeO and Fe under the mill scale between two or more pores. It is then preferable to wait a few days after the change of color of the entire surface before proceeding to remove the paste by washing and to expose the thus Washed sheet metal to atmospheric agents for the purpose of forming rust.
• the preferred proportions are of the order of 0.5 to 5% in weight with respect to the paste, but these limits may be exceeded without difiiculty.
• the ferrous hydroxide thus formed is more easily transformed to rust by the oxygen of the air or the oxidizing agent contained in the paste (than the ferrous sulfate which requires for its transformation to rust both oxygen and water) according to the reaction:
• the invention provides, in the case of the two types of oxidizing agents described, for leaving the above paste applied at least one week, washing it off, allowing the action of the atmospheric agents to continue for some time until the piece is completely covered by rust, and then removing the rust by any appropriate means.
• Example 1 A solution is first prepared containing:
• the gel thus formed is applied to the surface to be demill scaled, either with the aid of a spray gun, or with a brush.
• the process in accordance with the invention is preferably carried out as follows:
• the paste is applied on the mill scaled surface and it is allowed to react for a few days.
• the minimum period which the paste is left on the sheet metal should be 48 hours, but it can be left on for several months without having any accelerating or retarding elfect on the de-mill scaling process.
• the paste when the paste is applied on marine sheet metal in the course of storing the same in the storage depot, it will be left on until the sheets are drawn out for use.
• the paste When the paste is applied on the bottom of a ship already built, for example, it will be left on 5 to 6 days. At the end of 8 days it dries.
• the layer of mill scale being thicker, requires a greater pressure of hydrogen than a thin layer in order to be raised up. It is for these two conjugate reasons that when a thick layer of mill scale is met with, it is not detached from its iron base together with the paste.
• the mill scale is then fissured and its adherence to the metal is considerably diminished.
• the ferrosoferric salts formed by the action of the oxidizing and ionizing agents on the iron and the ferrous oxide do not .occupy a volume sutficient to exert an adequate pressure on the mill scale for the purpose of entirely detaching it.
• the oxygen of the air no longer finds an obstacle to its passage through the pores of the mill scale to the ferrosoferric salts, which is oxidizes to ferric salts which themselves, under the action of the humidity, hydrolyze to rust Fe O xH O.
• the period of exposure of the sheet metal to atmospheric agents after removal of the paste is from 1 to 3 weeks, generally 15 days, and in all cases a period necessary so "that the entire surface is covered by powdered rust, which can be removed by simple brushing with a metallic brush.
• Example 2 There is first prepared a solution containing:
• 'Ihis paste acts by the formation both of an electronic pile and an electrolytic pile.
• the electronic pile reduces KMnO to Mn0 as in Example l.
• the electrolytic pile when the products penetrate through the pores of the mill scale, reduces the red KMnO, to white manganese acetate.
• Example 2 The application is carried out as in Example 1, and the period of reaction varies also from 15 days to 1 month, including the time of exposure to the air for rushing.
• Example 3 There is prepared a solution composed of:
• the paste of straw yellow passes then to a white color.
• the mode of application and the action of this paste are the same as those indicated in Examples 1 and 2.
• Example 4 There is prepared at first a solution containing:
• the pH of the paste is taken immediately after the entire surface has been colored blue green, it will be found that it is still less than 2, that is, that all the acid has not reacted by penetration through the pores of the mill scale. If the sheet covered by the paste which has turned green is left exposed for three to four days (three to four days after the complete change of coloration), and if the pH of the paste is taken, it will be found that it has gone up to about 4 in a practically uniform manner, that is, that all of the acid has already reacted, and that it can be removed by washing without risk of having the wash water remaining acid.
• Example 5 A very thick gel is first prepared starting with:
• the change of color of the paste is manifested by its turning from dark violet to rose or very clear brown, when the acid succeeds in infiltrating through the pores of the calamine to the metal and produces the liberation of hydrogen and the formation of ferrous sulfate, both oxidized by the potassium permanganate.
• a method of removing mill scale from an iron body containing the same on the surface thereof comprising the steps of applying to said surface a composition consisting essentially of a paste of an aqueous solution of a non-reducing acid electrolyte having in said solution in said paste a degree of ionization greater than 0.01 ion grams per liter, said solution containing at least one oxidizing anion having in solution in said paste an rH value greater than 27, the pH value of said solution in in said paste being numerically less than 2.5 at rH values between 27 and 41 and being numerically up to 10 at rI-I values greater than 41, said solution being free of any acid capable of reducing the oxidizing anions in the paste, and of at least one finely divided mineral substance inert to said solution and being distributed therethrough and dispersed therein in an amount sufiicient to form said paste with said solution, said finely divided mineral substance acting as a porous vehicle for said solution so as to cause controlled oxidation of ferrous ions to ferric ions and the
• a method of removing mill scale from an iron body containing the same on the surface thereof comprising the steps of applying to said surface a composition consisting essentially of a paste of an aqueous solution of a non-reducing acid electrolyte having in said solution in said paste a degree of ionization greater than 0.01 ion grams per liter, said solution containing at least one oxidizing anion having in solution in said paste an rH value between 27 and 41, the pH value of said solution in said paste being numerically less than 2.5, said solution being free of any acid capable of reducing the oxidizing anions in the paste, and of at least one finely divided mineral substance inert to said solution and being distributed therethrough and dispersed therein in an amount sufiicient to form said paste with said solution, said finely divided mineral substance acting as a porous vehicle for said solution so as to cause controlled oxidation of ferrous ions to ferric ions and the formation of goethite which results in the loosening of the mill scale; maintaining said composition on said surface
• a method of removing mill scale from an iron body containing the same on the surface thereof comprising the steps of applying to said surface a composition consisting essentially of a paste of an aqueous solution of a non-reducing acid electrolyte having in said solution in said paste a degree of ionization greater than 0.01 ion grams per liter, said solution containing at least one oxidizing anion having in solution in said paste an rH value greater than 27, the pH value of said solution in said paste being numerically less than 2.5 at rH values between 27 and 41 and being numerically up to at rH values greater than 41, said solution being free of any acid capable of reducing the oxidizing anions in the paste, and of at least one finely divided mineral substance inert to said solution and being distributed therethrough and dispersed therein in an amount sufiicient to form said paste with said solution, said finely divided mineral substance acting as a porous vehicle for said solution so as to cause controlled oxidation of ferrous ions to ferric ions and the formation of goe
• a method of removing mill scale from an iron body containing the same on the surface thereof comprising the steps of coating said surface with a composition consisting essentially of a paste of an aqueous solution of a non-reducing acid electrolyte having in said solution in said paste a degree of ionization greater than 0.01 ion grams per liter, said solution containing at least one oxidizing anion having in solution in said paste an rH value greater than 27, the pH value of said solution in said paste being numerically less than 2.5 at rH values between 27 and 41 and being numerically up to 10 at rH values greater than 41, said solution being free of any acid capable of reducing the oxidizing anions in the paste, and of at least one finely divided mineral substance inert to said solution and being distributed therethrough and dispersed therein in an amount suflicient to form said paste with said solution, said finely divided mineral substance acting as a porous vehicle for said solution so as to cause controlled oxidation of ferrous ions to ferric ions and the formation of goe
• a method of removing mill scale from an iron body containing the same on the surface thereof comprising the steps of applying to said surface a composition consisting essentially of a paste of an aqueous solution of a non-reducing acid electrolyte having in said solution in said paste a degree of ionization greater than 0.01 ion grams per liter, said solution containing at least one oxidizing anion having in solution in said paste an rH value greater than 41, the pH value of said solution in said paste being between 0 and 10, said solution being free of any acid capable of reducing the oxidizing anions in the paste, and of at least one finely divided mineral substance inert to said solution and being distributed therethrough and dispersed therein in an amount sufficient to form said paste with said solution, said finely divided mineral substance acting as a porous vehicle for said solution, said finely divided mineral substance acting as a porous vehicle for said solution so as to cause controlled oxidation of ferrous ions to ferric ions and the formation of goethite which results in the loosening
• a method of removing mill scale from an iron body containing the same on the surface thereof comprising the steps of applying to said surface a composition consisting essentially of a paste of an aqueous solution of a non-reducing acid electrolyte having in said solution in said paste a degree of ionization greater than 0.01 ion grams per liter, said solution containing at least one oxidizing anion having in solution in said paste an rH value greater than 27 and being selected from the group consisting of Crop Cr O MnO N0 N0 1 ClO C10 1 MnOp, C10, and- IO the pH value of said solution in said paste being numerically less than 2.5 at rH values between 27 and 41 and being numerically up to 10 at rH values greater than 41, said solutions being free of any acid capable of reducing the oxidizing anions in the paste, and of at least one finely divided mineral substance inert to said solution and being distributed therethrough and dispersed therein in an amount sufiicient to form said paste with said solution, said

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• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
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• 1953
  • 1953-03-05 FR FR1075489D patent/FR1075489A/fr not_active Expired
  • 1953-04-29 FR FR63845D patent/FR63845E/fr not_active Expired
  • 1953-06-24 FR FR1085422D patent/FR1085422A/fr not_active Expired
• 1954
  • 1954-02-23 BE BE526720D patent/BE526720A/xx unknown
  • 1954-03-01 US US413450A patent/US3073726A/en not_active Expired - Lifetime
  • 1954-03-01 CH CH320340D patent/CH320340A/fr unknown
  • 1954-03-03 GB GB6277/54A patent/GB787841A/en not_active Expired
  • 1954-03-03 DE DEF14078A patent/DE1191657B/de active Pending

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