DE463778C - Process for preparing or regenerating a phosphate-containing rust protection bath - Google Patents

Description

Process for preparing or regenerating a phosphate-containing rust protection bath The invention relates to a method for preparing or regenerating a phosphate Rust protection bath and consists in the fact that one preferably strongly acidic soluble phosphates, des Iron in ferroform or orthophosphates of manganese, zinc or cadmium alone for itself or as a mixture in solid, i.e. granular, crystalline or powdery Form in the solvent bz «-. Bad enters.

In particular, the invention consists in the fact that a primary phosphate one or more metals of the electrochemical series from manganese to Iron including dissolving in water.

The use of a primary iron (II) Phosphates (primary ferrophosphates).

There have already been various procedures for preparing or suggested for the regeneration of phosphate-containing rust protection baths. All of these However, it is common that one does not have finished, especially primary phosphates of the brought suitable metals into the solution, but rather only their components, such as iron in the appropriate form and phosphoric acid or phosphoric acid alone. Some of the necessary phosphates were thus created in the bath itself with the shared use of components that are damaged by the bathroom's attack on the with the Rust thrust material to be covered object itself emerged. With a special one Proposal; who wants to create manganese phosphates in the bath is the formation of the Manganese phosphates without dissolving iron from the object to be covered at all not possible.

It was also proposed in general, acidic phosphates of iron. "Zinc and manganese, apparently in solid form, for the production of a Anti-rust paint (but not from anti-rust baths). The through the Invention, the first choice among these phosphates was there not available, rather only the use of ferric phosphates is recommended, - in such a way that this entered into an approximately ro percent phosphoric acid solution will .will. But it is a fact that ferric phosphates in such a phosphoric acid solution are insoluble, also in water. I would therefore use a rust protection bath in the Following this well-known proposal, if it were to be prepared, it would be ineffective. The ferric phosphate in the approximately 10% phosphoric acid solution would with the too protective iron object can never react, but only represent a useless ballast of this phosphoric acid solution, which otherwise alone would attack the iron object and therefore corrode it.

Finally, solid metaphosphates of all kinds was suggested Metals to be used. Besides that a number the proposed Metals do not form any phosphates at all, are those mentioned there, although they can be produced Metaphosphates of iron and manganese insoluble in water and dilute phosphoric acid, as is known from the literature and confirmed by extensive experiments by the inventor became. Above all, metaphosphates are also only used generally in this proposal spoken, positive however only suggested to form ferric metaphosphates that are ineffective.

In contrast, the invention has the advantages that for the first time for the production of an effective and non-corrosive iron object to be protected Corrosion protection baths suitable, specific phosphates are selected and made available that can even be entered directly into water and you thereby the ready-to-use immediately after previous heating or boiling, of course Anti-rust bath receives: An expert control is also not required here like checking the bathroom. The ibzw for the production. Regeneration of the anti-rust bath Rather, the required chemical compound is in turn based on an expert Paths made; it is - because it is dry - easy and cheap to transport. About that in addition; it can be stored in a minimum of space, while on the other hand it is effective, economical and safe to use, as it is sufficient after: added Regulations a certain amount of the ready-delivered salt of a certain Amount of solvent, e.g. B. water to be incorporated. To this comes: the other Advantage that even a deviation from this prescribed ratio in further Borders are without disadvantage insofar as the workpiece to be covered is still not attacked by the anti-rust bath, i.e. noticeably in its shape or weight is changed.

The invention is based on the following fundamental findings and Considerations: Iron and other metals make a number of phosphates, one of which some.solve - I, but others are insoluble. With appropriate treatment, iron can be covered with a shell of insoluble phosphate. There are big ones Number of different iron phosphates that arise under different conditions. These phosphates range from the strongly acidic to the basic phosphates. Will an object made of iron or containing iron in a pure phosphoric acid solution is used, no rust protection skin forms on this object as long as it is used insoluble phosphates, as long as there is no iron from the object itself in the bath went into solution and formed iron phosphates.

The inventor has examined the physico-chemical processes of the formation of a rust protection skin on iron-containing objects in detail and has come to the following knowledge: B. the following equation: Fe + - H3 PO, = Fe (H, POJ = + H_. When an aqueous solution of the pure primary phosphate is boiled, a reaction occurs which leads to a state of equilibrium, expressed by the following equation: Fe (H. , PO,) 2 + Aq. - FeHPO, _ -I- H:; PO, -I- Aq. This equilibrium is largely independent of the concentration of the solution.

Such a solution of primary iron phosphate that boiled for some time - has been distinguished - for the production of an anti-rust coating proven. In this solution there is no corrosion of the iron object to be covered instead, but only separation of insoluble phosphates by interaction Mix the surface of the object to be protected and the dissolved primary Phosphate is formed. For the latter, the following equation applies Fe (H_PO,) = -f- Fe - z FeHPO, -) - H .. or a FeHPO, + Fe - Fei (PO.,) _ + H ,. The anti-rust coating consequently, as the quantitative analysis has also shown, consists of an insoluble one Mixture of secondary and tertiary iron (II) phosphate.

The advantage of this method is therefore that the one to be protected Iron object does not result in a loss of weight, but in certain circumstances on the contrary a small increase in weight, basically no significant change in weight, undergoes corrosion and weight loss in most of the earlier processes entered. if not by chance this corresponds to the mentioned equilibrium Concentration had been achieved. A sure way to always and without special Care has been taken to achieve such a balance in the rust protection bath to this day has not yet been proposed anywhere and is indicated for the first time by the invention. if it was said earlier that there is an interaction between the iron of the to protective object and the - here only mentioned as an example - primary iron phosphates occurs, this is to be understood as meaning that from the surface of the iron the dissolved primary phosphate is absorbed with the formation of the insoluble phosphates is.

When the baths are made by the freezing process, these are used by metallic iron and phosphoric acid emanated as components to be combined in the bath, An expert management and constant control of the acidity of the bath was necessary. This is because the bath contains more acid than the degree of equilibrium recognized by the invention corresponds, an attack on the object to be protected must take place. while in the case of a lower concentration of acid, insoluble phosphates are found in the bath separate, which form a worthless sludge and come off as a loss.

Once a bath according to the invention has been completed, it can be unlimited Time can be used if care is taken that what is used up from time to time Salt is simply added back in solid form.

In the following some examples of implementation of the invention are now described. First and foremost, it is the purpose of the invention to create an as pure as easy to use ferrodihydrogen orthophosphate (primary iron (II) phosphate) or to produce similar phosphates of other metals. The production of ferrophosphate shall be described first. To represent it, "-ground iron filings or small pieces of metallic iron in a strong solution of phosphoric acid introduced. The degree of concentration of the acid can vary considerably among different Conditions; but for the reasons to be explained later, a concentration of 6o to 75 percent preferred.

It is advisable to heat the acid to around 100 ° C or to get the acid solution between that temperature and its boiling point, whichever the latter is around 115 ° C for a 65 percent solution. The iron filings are introduced slowly to prevent excessive foaming, and the The solution is kept in motion until all iron filings are dissolved are. The time within which the dissolution of the iron takes place depends on the Concentration of the acid, the condition of the iron, the temperature and the volume of the container in relation to its filling with the acid. With the mentioned Concentrations and temperatures can contain a sufficient amount of iron in the acid about an hour if there is enough space in the container a foam forms in it, the volume of which is about five times as large as that of the original volume of liquid. With greater space utilization of the container a correspondingly longer time is required for the dissolution, which is then to be conducted more slowly.

As the iron dissolves in the acid, hydrogen is released. At the same time, a certain amount of water vapor is also evolved. This Hydrogen and water vapor cause the air to not interfere with the air to any significant extent Solution can come into contact. This effect can be increased by covers the container and only leaves one opening free through which the developed hydrogen and escaping water vapor can escape, so that the The surface of the solution is covered with these gases and air is sealed off. It it is undesirable for air to have free access to the solution, since ferrodihydrogen phosphate Has a tendency to oayclation and thereby assumes a less soluble form. the The amount of iron that is dissolved in a given amount of acid can vary widely Limits can be changed according to the circumstances. However, there is a ratio of 1 part by weight of iron to 10 parts by weight of a 65 percent phosphoric acid solution satisfying results. After preparing the solution in the described The next step is suitable filtration. The purpose of this Filtration is that of removing all insoluble impurities from the solution, such as B. Coal, which is usually brought in with your iron, and also leftovers undissolved iron. Unpolluted iron in the rust preventive continues its effectiveness quite considerably, since the rust protection bath acts on this iron and thereby wears out in the same way as if it were on the workpiece to be protected against rust would act, so that ultimately the strength of the rust preventive bath is reduced and with a given amount of admixtures of metallic iron, a much smaller one Antirust effect results as a rust preventive bath without such impurities.

After filtration, the solution is transferred to a crystallization tank brought in. By this container coiled pipes can be passed through the either steam or cold water flows through it. Ferrophosphate is more soluble in a six percent Solution of phosphoric acid than in a solution higher concentration. There is so much in one process stage of crystallization as possible Ferrodihydrogenphosph_hat should be crystallized out of the solution, it is desirable to have a fairly concentrated salt solution in this crystallization tank to obtain. If the solution coming out of the filter is weaker than expected, then water can be expelled from it by heating steam through the coiled pipe in the container and thereby heats the solution until it has the necessary Has reached a level of concentration. But the manufacturing process is common so directed that the solution has approximately the desired concentration level, when it enters the crystallization tank. .

To speed up the crystallization, cold water is passed through passed the coiled pipes. It is preferred that the crystallization take place a little slowly to be carried out, since larger crystals are obtained in this way, the specific Have advantages, as will be discussed later. The crystals will be then separated from the mother liquor by centrifugation, the latter in the dissolution container can be returned. The crystals thus obtained can, if necessary continue to be dried, with oxidation options as far as practical only have to be switched off, since moist crystals in the presence of air oxidize and become insoluble to a considerable extent. There should therefore be no water in the crystallized product may be present with the exception of that which has entered the crystals Crystal water. The crystals retain their water of crystallization when they are at high temperatures should not be dried above 60 ° C. Crystals dried in the manner described do not absorb moisture from the air and are therefore once they have been thoroughly dried, relatively stable when exposed to outside air will. Nevertheless, there is always a certain risk of oxidation from moisture and air exist, and for these reasons, large crystals are preferable because they have a relatively smaller surface area with a larger volume, the could oxidize. During the drying process, the crystals can be heated to such an extent that that the water of crystallization is expelled from them if desired. The anhydrous The product is more slowly oxidized than the one containing water of crystallization. Although the anhydrous Product has certain advantages, it is still used for normal use water of crystallization should be preferred to the more easily soluble and cheaper. As discussed earlier, 60 to 75 percent acid is preferably used. Assuming such a concentration and the volume of the solution up to Maintained at the beginning of crystallization, the result is: the best yield achieved. If a 5% acid is assumed and here, too, the volume is maintained essentially constant until crystallization begins, then a poor yield of unsightly crystals obtained, in part because the ferrodih3-drug phosphate to a greater extent in a weaker acid than in a more concentrated one Acid is soluble. If the host uses 85 percent acid, it is again difficult to to obtain a satisfactory crystallization. The solution can be based on appropriate Concentration at the time when the crystallization takes place, if the acid used first does not have the appropriate concentration. It but it is preferred to use acid in such a concentration that no or only minor corrections to the acid concentration are necessary to get the correct one Ausl: ristallisation achieved.

1v. Aitgandilly drug phosphate can be used in essentially the same way produced like the similar ferrous salt. The main modifications exist in that it takes a little more manganese than iron to reach the same level of saturation to achieve the solution, and that precautions against oxyclation of the manganese phosphate are unnecessary.

It is sometimes desirable to use manganese and herrosalt together, and for this purpose ferromanganese, an alloy of manganese and iron, be used as a suitable starting product, both the iron and the Manganese in ferromanganese is converted into the corresponding phosphates in the same process will.

Zinc dihydrogen phosphate (primary zinc phosphate) can be used in the same Are represented in the same way as the similar salts of manganese and iron with the exception that a considerably greater amount of zinc than iron. is necessary to the same To achieve the saturation level of the solution, and that further greater concern is necessary is to prevent overheating during drying because the crystals are under 6o ° C above, 2its melt.

Ferrodiltvdrogeitortltophospliate (primary iron (II-1 phosphate), now directly dissolved in water, results in without the addition of any other Reagents a good postal protective bath that approximately before use i Hour to heat or boil accordingly.

The salt can be used in various proportions. So a good rust protection bath has been achieved by adding approximately 3,170 g of the Salt introduced into about 55o l of water as the lowest measure, or, as approx highest level, about 32 kg of salt introduced into the same amount of water. at completely pure iron gave the best results about 6,800 grams of the salt in 55o 1 water; but it has been found that a larger amount of salt produces quicker results results from incompletely purified iron, and it was therefore considered to be average The strength of the bath was found to be about 153/4 kg of salt in 55o 1 of water. The concentration of the solution in the anti-rust bath drops; when the workpiece with insoluble phosphates is covered. As discussed earlier, the result is boiling an aqueous solution of the primary iron (II) phosphate the formation of a certain Amount of secondary iron (II) phosphate and free acid. The acidity of the Baths can therefore be used as a good indicator of the strength of the solution for anti-rust purposes and it is therefore a reliable means of determining the Amount of salt added at a given time - must be used in order to achieve the normal strength of the Solution. The acidity of the bath can be expressed in digits, which indicates the number of cubic centimeters 1 - /. 10 = normal alkali that is required is to neutralize 10 cc of the anti-rust solution, with phenolphthalein as Indicator is used.

It has now been found that the addition of 4:53 g of the salt to water is about 5501 a unit supplies to the acid content of the solution; If the test is carried out in the manner outlined above and 1,53 / 4 kg of the salt are added to 550 liters of water when the anti-rust bath is being prepared, then the solution will have about 35 units of acid content. Additional amounts of salt can be added at any time to bring the solution to its normal strength. In ordinary work, in which the anti-rust bath is used continuously the same day, it is most convenient to add the amount of salt at night which is indicated as necessary by the acidity of the bath. If, for example, the bath has 28 units of acid content at the end of a day's operation, 3 170 g of salt will have to be added to the 5'o 1 of water in the solution. The heat supply to the bath is turned off during the night so that it stays warm but does not boil. This method of adding the necessary amounts of salt at DegDe- # i1111 der -Nacht in such a way that the salt remains in the warm but not boiling solution for a number of hours has proven to be particularly effective until the desired strength of the solution is restored. If the anti-rust bath is used continuously for 24 hours, it can be regenerated at any time.

Manganese dihydrogen phosphate and zinc diluent drug phosphate can be either alone or in various proportions with one another or with ferrodihydrogen phosphate can be used in essentially the same way as earlier used for ferrous salt alone .has been described. The application of the mixture of ferrous and manganese salts changes does not significantly increase the amount of salt required to produce a desired acid content of the bath is necessary, but in such a bath it becomes a considerably larger one Amount of workpieces can be covered with the anti-rust agent until its acidity drops to a certain value as if ferrous salt is used alone, and further the anti-rust layer is a bit smoother and more resistant to rust.

The number of metals - those used to make a rust preventive can be used is limited by a number of factors; she must produce phosphates that are similar in nature and solubility to ferrophosphates are. and they must not be under iron in the electrochemical series.

Metals meet these requirements in the electrochemical Voltage series from manganese to iron including sequence. Cadmium is too expensive to be used as the main component of a rust preventive, although cadmium is often found in commercial zinc and therefore to some extent also in the commercial salt can be included.

The invention is of course not limited to the illustrated procedures restricted, i but can be modified in various ways.

Claims (3)

PAT E NTANSPRÜCF1E: i. Process for preparing or regenerating a phosphate-containing rust protection bath, characterized in that phosphates, with advantage strongly acidic soluble phosphates of iron in ferrous form or orthophosphates of manganese, zinc or cadmium alone or in a mixture in solid, i.e. granular, crystalline or powdery form enters the solvent or bath. 2. The method according to claim i, characterized in that: that one a primary phosphate of one or more metals of the electrochemical series from manganese to iron and including dissolves in water. 3. Method of manufacture one for the preparation or regeneration of a rust protection bath according to claim i or 2 suitable manganese phosphates or a mixture of manganese and ferro phosphate, characterized in that an iron-manganese alloy is used to represent it (e.g. ferromanganese) goes out. q .. method of making a for preparation or Regeneration of a rust protection bath according to claim i or a suitable compound, characterized in that the compound from a 6o- to 75 percent solution the phosphoric acid can precipitate or crystallize out. 5. Method of preparation or regeneration of a rust protection bath, characterized in that one; according to Claim i or 2 obtained solution in a manner known per se for some time to suitable , Heated to temperature (boils), making it ready for use as a rust protection soon. _