CN1139705A - Blackening agent for iron and steel surface at normal temp. - Google Patents

Abstract

The present invention belongs to the field of metal surface treatment technology, and specially relates to a blackening agent for protecting metal surface and refining treatment. Said blackening agent is mainly comprised of phosphoric acid, monophosphoric acid, dihydropotassium, cupric sulfate, selenium dioxide, EDTA, sodium citrate and polyvinyl alcohol. Said invention uses CuSO4-H2SeO2 system, and under the condition of a certain acidity makes the complex oxidation-reduction reaction and continuous precipitation reaction on the steel and iron surface so as to implement blackening process.

Description

Normal temperature steel blackening agent

The invention belongs to the field of metal surface treatment, and relates to a normal-temperature steel blackening agent for protecting ferrous metal surfaces and performing finishing treatment.

At present, the surface protection of ferrous metal is generally carried out by adopting an alkaline bluing process which utilizes NaOH-NaNO₂High-temperature oxidation system, long production period, low efficiency, large energy consumption, high cost, and environmental pollution (NaNO) caused by waste gas, waste liquid and waste residue₂Is carcinogen), has poor labor conditions and risks of electric shock and scald, has selectivity on steel types in actual production, is difficult to ensure bluing quality especially on cast steel, nodular cast iron and high alloy steel, has poor corrosion resistance and moisture resistance of bluing films on seawater and marine climate, and cannot meet the production requirements in coastal areas and the corrosion resistance and moisture resistance requirements of marine transportation and marine operation. In recent years, although some units in China are engaged in the development of the normal-temperature steel blackening agent, the technical process is neither mature nor perfect, and the normal-temperature steel blackening agent is not generally applied to industrial production, and has the main problems that: (1) the blackening film is loose, the matrix is not firmly combined, and the defect of normal-temperature blackening is overcome. (2) More precipitates are generated in the blackening process and must be filtered and removed in time, otherwise, the blackening liquid is invalid due to autocatalysis, even if double-groove alternative deslagging and alternative use are adopted in actual production, inconvenience must be brought to production, the production process is complicated, the blackening quality is influenced, and the discharged slag often pollutes the environment. (3) Too short blackening timeThe blackening film is rough and loose and can be immediately removed by touch, and meanwhile, the time required for finishing each blackening operation according to the process requirement is longer than the specified blackening time, so that even an automatic production line is difficult to apply to actual production, and mass production is not referred. (4) The blackening agent has poor stability and short storage period, and if the blackening agent is used for more than two months, the blackening agent is deteriorated and ineffective for five months, so that the requirements of users cannot be met. Since the links of purchasing, transporting, accepting, warehousing, using and the like are performed from the production of the product to the use of the user, a long time is needed, and if the storage period is too short, the product is not used up and is invalid, which is certainly a waste for producers or actors. The Shanxi province scientific and technical Committee organizes related experts to identify the hairThe method overcomes the defects of the alkaline blackening process and the defects of the similar products. The product has advanced formula and reasonable process, also solves the problem of product stability, does not deteriorate and lose efficacy in at least one year of storage period, has the advantages of energy saving, high efficiency, continuous use, no precipitation, zero emission, no pollution, simple operation, safe use, proper blackening time, high economic benefit, no selection on steel types, fine and compact blackening film, firm combination with a substrate, no bottom exposure after being wiped for 20 times by standard qualitative filter paper, and better corrosion resistance and humidity resistance than alkaline bluing and similar products.

The invention aims to provide a method for realizing continuous use without sediment in actual production, zero emission and no pollution; the invention also aims to provide a method for solving the problem of solution stability and achieving stable chemical performance in long-term storage; the invention further aims to provide a method for making the blackening film layer uniform, fine, compact and consistent in color and luster, firmly combined with the substrate, and incapable of exposing the substrate after being rubbed for 20 times by using standard qualitative filter paper.

The purpose of the invention can be realized by the following scheme: the normal temperature steel blackening agent consists of phosphoric acid, potassium dihydrogen, copper sulfate, selenium dioxide, ETDA, citric acid, polyethylene acid and CuSO₄-H₂SeO₃The system performs complex oxidation-reduction reaction on the surface of steel under a certain acidity conditionSlow and continuous precipitation reaction to form uniform, compact, black and bright colored film, which mainly comprises the following reaction steps: $\left(1\right)3\mathrm{Fe}+{\mathrm{SeO}}_3^{2-}+6H^{+}=3{\mathrm{Fe}}^{2+}+{\mathrm{Se}}^{2-}+3H_{2}O\↓$ (2) (3) $\left(4\right)3{\mathrm{Zn}}^{2+}+2{\mathrm{PO}}_4^{3-}={\mathrm{Zn}}_3{\left({\mathrm{PO}}_4\right)}_2\↓$ $\left(5\right)2{\mathrm{Zn}}^{2+}+{\mathrm{Fe}}^{2+}+2{\mathrm{PO}}_4^{3-}={\mathrm{Zn}}_2\mathrm{Fe}{\left({\mathrm{PO}}_4\right)}_2\↓$

the above-mentioned film-forming reaction must be carried out under a certain acidity condition, and in the course of blackening process, the acidity of the solution tends to decrease,the invention adopts H₃PO₄--KH₂PO₄The buffering system controls the change of the acidity of the solution by controlling the proper buffering capacity, so that the blackening film-forming reaction is carried out within a certain PH range, thereby not only ensuring the quality of the blackening film, but also increasing the number of blackening heads and fully utilizing the blackening liquid, which is one of the technical characteristics of the invention. The invention adopts the addition of EDTA complexing agent and polyvinyl alcohol high molecular compound. EDTA capable of reacting with Cu in solution²⁺Complex reaction occurs to generate complex ions which have relative stability under a certain acidity condition, thereby controlling Cu in the solution²⁺The concentration of the organic acid can control the film forming reaction speed. In order to ensure that the blackening film is fine, uniform and compact and is firmly combined with the matrix,the proper film forming assistant is selected, namely, a proper amount of sodium citrate is added, so that the crystal boundary of the steel surface can be fully exposed, effective nucleation active points are increased, and a fine, uniform and compact colored film with fine crystals can be formed. In addition, the addition of the additives such as sodium citrate, EDTA, polyvinyl alcohol and the like does not have the unique function of the additives, and can also play a comprehensive effect, and the additives can assist in film formation, enhance the stability of the solution, prolong the storage period and overcome the defect that similar products generate precipitates in the use process although the additives are not directly formed into films.

Due to the adoption of the scheme, the effect of the invention can be concluded from the following aspects: compared with the prior art, the alkaline bluing process of the invention has the advantages of fast time (4-10min), slow operation temperature (1-2h), normal temperature (140 ℃) and suitability for wide (non-selective) narrow (selective) steel type at 150 ℃, simple and complicated saponification procedures, no toxicity, no large environmental pollution, no labor condition, and poor qualityThe invention has pure color uniformity, black, uniform black or brownish red, good uniform corrosion resistance, better firmness, better deoiling requirement, higher energy consumption, low energy consumption (electricity saving of 100 percent), low cost (1/3-1/2 of alkaline bluing), high production efficiency (6 times of alkaline bluing), and the like: comparative items the present inventionThe process time of similar products is 4-10min, 2-4min, the solution stability is stable (stored for 12-18 months), the solution is unstable (stored for 3-5 months), the industrial three wastes discharge zero discharge is discharged, the color fastness of the black film is firm and not firm, the pH value is 1.72-2.232-2.6, the process is simple, the aging speed of complex solutions is low (durable), the color of the black film is fast (not durable), and the black amount of per kilogram of solution is not less than 5m²Not less than 4m²

By combining the technical scheme of the invention, the embodiment is as follows:

the invention is a complex liquid substance formed by dissolving and mixing various component chemicals in water, all the components are interdependent and restricted with each other, and the blackening agent can produce excellent blackening effect only when the contents of all the components are mixed according to a certain proportion in a certain range, and experimental results prove that the optimal proportion is as follows when the working temperature is 20-25 ℃: polyvinyl alcohol with phosphoric acid-copper sulfate diselenide ETDA sodium citrate as component

The content of the potassium dihydrogen oxide selenium oxide is 21.6g/l, 7g/l, 6.8g/l, 11g/l, 16.6g/l, 15g/l, and if the temperature is lower than 10 ℃, the mixture ratio is as follows: polyvinyl alcohol with phosphoric acid-copper sulfate diselenide ETDA sodium citrate as component

The content of potassium dihydrogen phosphate selenium oxide is 26g/l 14g/l 8g/l 7.8g/l 10.8g/l 19g/l

In addition, when the blackening is carried out, because the components and the tissues of the raw materials are different, the pretreatment for blackening and the blackening time are not completely the same, and the following list shows: low carbon steel in hydrochloric acid for blackening before component and tissue treatmentAdding 10% sulfuric acid to remove rust for medium carbon steel 4-5min, removingrust with hydrochloric acid 1: 1 for medium carbon steel 6-7min, removing rust with concentrated hydrochloric acid for high carbon steel 6-8min manganese steel 6-9min, removing rust with concentrated HCl 9-12min for chromium steel 6-9min, treating pearlite for 4-6min with nodular cast iron 1: 1HCl for 6-8min, and processing and hardening at 180-250 g H ion-bearing iron per liter for 4-6min₂SO₄4-6min tempering Marek's state is the same as above for 4-6min

Claims (3)

1. A blackening agent for steel and iron at ordinary temp is prepared from phosphoric acid, potassium dihydrogen, copper sulfate, selenium dioxide, EDTA, sodium citrate, polyvinyl alcohol and CuSO₄-H₂SeO₃The system carries out complex oxidation-reduction reaction and slow continuous precipitation reaction on the surface of steel under a certain acidity condition, and the reaction formula is as follows: $3\mathrm{Fe}+{\mathrm{SeO}}_3^{2-}+6H=3{\mathrm{Fe}}^{2+}+3H_{2}O\↓$ $3{\mathrm{Zn}}^{2+}+2{\mathrm{PO}}_4^{3-}={\mathrm{Zn}}_3\left({\mathrm{PO}}_4\right)\↓$ $2{\mathrm{Zn}}^{2+}+{\mathrm{Fe}}^{2+}+2{\mathrm{PO}}_4^{3-}=\mathrm{ZnFe}{\left({\mathrm{PO}}_4\right)}_2\↓$ the method is characterized in that: the acidity of the blackening film-forming reaction is 3H₃PO₄-KH₂PO₄A buffer system, which enables the blackening film-forming reaction to be carried out in a certain pH range.

2. An ambient blackening agent according to claim 1, wherein: EDTA complexing agent and polyvinyl alcohol are added in the blackening film.

3. An ambient blackening agent according to claim 1, wherein: adding a film-forming additive, namely sodium citrate, into the blackening film.