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US2171981A - Cleaning of metallic surfaces - Google Patents

Cleaning of metallic surfaces Download PDF

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Publication number
US2171981A
US2171981A US175623A US17562337A US2171981A US 2171981 A US2171981 A US 2171981A US 175623 A US175623 A US 175623A US 17562337 A US17562337 A US 17562337A US 2171981 A US2171981 A US 2171981A
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solution
sheet
pickling
precipitate
sample
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US175623A
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Heimberger Walter
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    • 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
    • C23G1/08—Iron or steel

Definitions

  • the present invention relates to the cleaning of metallic surfaces by pickling-and more especially to the pickling of iron. It is concerned with the treatment of metals such as iron preparatory to the coating of the metal surface with enamel or paint or another metal. It is an object of my invention to render the pickling process simpler and cheaper and less dangerous for the operator and to improve the quality of the pickled product.
  • Iron in the form of sheet or other roller products is not as a rule resistant against the action of the atmosphere or of acids.
  • the surface of the metal In order to produce stability, the surface of the metal must be efllclently protected'by painting or enameling or metallizing or like? measures. An efllcient protection is however'obtained only, if the protective coating is applied'to the clean metal.
  • pickling baths consist as a rule of sulfuric acid orhyd'rochloric acid with a concentration of some per cent, for instance 10%.
  • the acid strength must be very low, go much lower than hitherto used for the pickling operation.
  • the acid strength must be low enough to allow the formation of basic ferric salts by hydrolytic action. I have found that for this purpose the concentration of the acid 5 during the operation proper must not exceed 0.1%, since insoluble iron compounds 'do not occur before the concentration of the acid has dropped to or below this value.
  • the acid concentration must be the lower. the lower the tema0 perature of the pickling bath. I have further found that the content of the pickling bath at the beginning of the operation should not exceed about 1% sulfuric acid.
  • insoluble ferric hydroxide or 45 other insoluble basic ferricsalts in the form of colloids as attained under these conditions-of concentration and temperature does not yet secure any particular advantage.
  • An electrolyte may generally be considered suitable for this purpose, if its anion differs from that of the pickling acid and its kation is less noble, in the sense of the electromotive series, than the metal to be pickled.
  • An oxidant must be present in the pickling bath for converting the ferrous .ions into ferric ions.
  • the electrolyte which serves to coagulate or precipitate the colloidal iron compounds may be'identical with the oxidant and may for instance be an alkali metal nitrate.
  • Fig. l is a diagram showing the pH values of a sulfuric acid solution of different acid concentrations.
  • Fig. 2 shows diagrammatically the concentration of sulfuric acid at which, at different temperatures, basic iron salts start precipitating so that the solution will become turbid
  • Figs. 3 to 10 show diagrammatically curves obtained by titrating baths with caustic soda solution, as will be explained more in detail farther 40 below.
  • a pickling bath i. e., a bath containing a suitable electrolyte, an oxidizing agent and a mineral acid of a strength not exceeding about 1%, this bath being heated to at least 50 0., part of the acid is consumed in the formation of iron salts.
  • colloidal ferric hydroxide When according to my invention colloidal ferric hydroxide is formed and coagulated or some other insoluble basic ferric compound is produced by hydrolysis, the anion of the dissolved, tri-valent iron salt is completely 'or partly set free, as may be guessed from the above equations, and it is capable of again participating, in the form of acid, in pickling reactions. A fresh portion of iron may therefore be dissolved. Since part of the colloidal ferric hydroxide is continuousl'y precipitated as insoluble matter under the action of the electrolyte present, shortly after the begining of the pickling process, i. e., after the blank has ben placed in the bath, a chemical equilibrium is established which shows the peculiarity that the concentration of the dissolved iron is kept very low and practically constant.
  • the state of the pickling solutions may be ascertained by establishing titrating curves which fairly accurately show the quantities of bi-valent and tri-valent iron compounds present in the solution.
  • titrating curves are established in the following manner: the starting point of the curve is represented by the pH value of the solution itself, the further values of the curve are obtained by gradually adding to ccrns. of the solution small quantities of a solution of caustic soda, determining the pH value after every such addition and plotting the values thus obtained as points of the curve.
  • ferric hydroxide precipitates, while at the pH value of about 6.3 fer.- rous hydroxide is precipitated.
  • the length of the horizontally extending part of the curve which follows these values allows to guess the quantity of iron ionsof the corresponding valence present; the horizontal part of the curve is the longer, the more iron of the corresponding valence is dissolved.
  • the solutions were mixed in cold state.
  • the pH value of the starting solution was drawn from the curve of Fig. 1.
  • Test No. 1 the influence of an aqueous solution containing 0.1% H2SO4+2% NaNOs on black plate was investigated at 20 C.
  • This solution was rendered turbid by the formation of insoluble ferric compounds only when ferric ions could form and when the soluton was neutralized to such an extent that Fe( H): could form.
  • the titrating curves showed that this state is attained at a pH value of 2.9 to 3.1, corresponding to about Both the pickling effect of the cold solution on scale and the oxidimng efiect of the sodium nitrate added were very small and a clean ironsurface could not be attained with certainty.
  • the titrations show that only very small quantities of iron compounds were formed.
  • the solution contained 0.3% H:SO4+2% NaNOa.
  • the color of the solution was brown olive.
  • the solution wascontinuously heated.
  • the sheet was wiped, nearly the half of the scale was found to be removed.
  • the color of the solution was greyish-brown.
  • the sample-precipitate was dark brown.
  • the pickling bath was in good condition.
  • the sheet was wiped and showed only some stripes of scale.
  • the sheet was again placed in the solution. A strong covering formed.
  • the sheet was wiped.
  • The. scale showed to be still further dissolved.
  • the sheet was again introduced in the solution and a strong covering formed.
  • Test No. 4 The results of Test No. 4 may be summarized as follows:
  • the pickling velocity was greater than in Test No. 2, but it was considerably reduced by a further addition of sodium nitrate.
  • the pickling effeet of the solution is good and secures clean surfaces.
  • the slight brown color of the solution in the second part of the test cannot be attributed to theformation of colloids. since the increased content of sodium nitrate prevents the formation of colloids.
  • the brown color may indicate the formation of Fe(NO1):. 1
  • Test No. 5 was carried through with the same starting concentrations as Test No. 4, but at 80 C.
  • the clean-pickling eifect of the solution is satisfactory.
  • the pickling velocity is increased due to the higher temperature, but a further std--v dit.on of sodium nitrate proved again to reduce the pickling velocity.
  • An addition to the pick ling bath of 4% NaNOa may thus be considered as the highest quantity admissible at a pickling temperature of 80 C.
  • the specific consumption of acid, calculated on the surface of the pickled sheet only amounts to about one half of that found in Test No. 4.
  • the eifect of the presencein the solution of ferric ions may be illustrated by two further tests. numbered No. 8 and No. 9, in both of which the pickling bath contained 0.7% HaSO4+2% NaNOa, giving a starting pH value of 1.02, while the temperaturewas C.
  • the solution was allowed to stand, while maintained at 65 C.. until the sample-precipitate became brown. 5:50 p.m. The sample-precipitate was dark brown. I 6:00 p.m. The sample-precipitate was brown. The solution was left standing over night and allowed to cool down.
  • Test No. 8and 9 The results of Test No. 8and 9 may be summarized as follows:
  • Test No. 13 The influence of too high an acid strength at the start is shown by Test No. 13, which may therefore also be detailed.
  • a solution containing 2% HzSO4+2% NaNOa was used and the pickling operation was carried out at 65 C.; the pH value at the beginning was thus 0.7.
  • the solution must be warmer than 50 C.
  • the starting concentration of sulfuric acid must not exceed 1 per cent.
  • the oxidizing agent present in the solution must sumce to prevent the presence of any substantial quantity of ferrous compounds in .the soiution,'since otherwise the content in dissolved iron compounds cannot be prevented from increasing.
  • the content of sodium nitrate must be less than 5 per cent.
  • the starting acid strength of the solution should not be too low, since theoxldizing effect of the sodium nitrate decreases with decreasing starting acid concentration.
  • the bath is not enriched with metal salts.
  • the solution may thereforebe used almost infinitely without spoiling the product, and needs to be replenished only from time to time by an addition of acid or salt.
  • a solution 'of nitric acid and ma nesium may for instance be replaced, without an undue increase in magnesium ions, by an addition to the bath of sulfuric acid; or an addition of alkali nitrate may be used to strengthen the oxidizing effect of the bath without increasing its acidcontent. always be taken that the admissible concentration of acid is not exceeded.
  • the starting acid concentration is not distinguished from the acid concentration maintained in the course of the pickling operation. This difference is however important according to my invention, since the desired result is only obtained by a very small acid concentration during the pickling operation, while the starting acid concentration is preferably rendered high enough to secure that the required quantity of ferric ions is formed in the bath.
  • the iron which is dissolved by the pickling action may be recovered in the form of basic iron compounds and may be utilized as pigment.
  • the pickling time is rather long, if my process is directly applied to strongly s'caled or rusted blanks.
  • the method of pickling iron which comprises acting on the metal with an aqueous solution, heated to at-least 50 C., which contains free mineral acid in an amount sufliciently low to permitthe metal salts formed to be precipitated by hydrolytic action, an oxidant, and up to about 5 per cent of a salt, the anion of which difiers from that of the acid and the kation of which is less noble, in the sense of the electromoti've series, than the metal to be treated.
  • the method of pickling iron which comprises acting on .the metal with an aqueous so- I lution, heated to atleast 50 0., which contains free mineral acid in a concentration of not more than 1 per cent, an oxidant in an amount sumcient to oxidize substantially all the dissolved ions of the metal under treatment, and a salt, the anion of which differs from that of the acid and the 'kation of which is less noble, in the sense of the electromotive series, than the metal under treatment, allowing the acid concentration of said solution, while it is in contact with the metal under treatment, to drop below 0.1per cent and maintaining it below 0.1 per cent during the pickling treatment.
  • the method of pickling iron which comprises acting on an iron surface with an aqueous solution, heated to at least C., which contains up to 1 per cent sulfuric acid and up to about 5 per cent of an alkali metal nitrate, allowing the acid concentration of said solution to drop during its action on the metal under treatment, below 0.1 per cent and maintaining it below 0.1 per cent for clean-pickling said metal.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
US175623A 1934-10-23 1937-11-20 Cleaning of metallic surfaces Expired - Lifetime US2171981A (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
DE2171981X 1934-10-23
DE786191X 1934-10-23
DE453704X 1934-10-23
DEH141603D DE618614C (de) 1934-10-23 1934-10-24 Verfahren zum Blankbeizen von Metallen

Publications (1)

Publication Number Publication Date
US2171981A true US2171981A (en) 1939-09-05

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US175623A Expired - Lifetime US2171981A (en) 1934-10-23 1937-11-20 Cleaning of metallic surfaces

Country Status (6)

Country Link
US (1) US2171981A (fr)
BE (1) BE408376A (fr)
DE (1) DE618614C (fr)
ES (1) ES137426A1 (fr)
FR (1) FR786191A (fr)
GB (1) GB453704A (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2511988A (en) * 1945-05-09 1950-06-20 Columbia Steel Company Pickling process
US3074823A (en) * 1959-05-01 1963-01-22 Kaiser Aluminium Chem Corp Method for removing complex sodium aluminum silicate scale
US3189450A (en) * 1958-01-22 1965-06-15 Kocsuta Michael Pretreatment of iron containing base plates and their use in photoengraving

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1813441B2 (fr) † 2006-01-25 2012-11-21 KUM Limited Article de bureau ou cosmétique en matériau de magnesium

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2511988A (en) * 1945-05-09 1950-06-20 Columbia Steel Company Pickling process
US3189450A (en) * 1958-01-22 1965-06-15 Kocsuta Michael Pretreatment of iron containing base plates and their use in photoengraving
US3074823A (en) * 1959-05-01 1963-01-22 Kaiser Aluminium Chem Corp Method for removing complex sodium aluminum silicate scale

Also Published As

Publication number Publication date
FR786191A (fr) 1935-08-28
BE408376A (fr) 1935-04-30
DE618614C (de) 1935-09-12
ES137426A1 (es) 1935-06-16
GB453704A (en) 1936-09-14

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