DE2053407B2 - A method of aluminum plating a substrate - Google Patents

Description

The invention relates to a method for »> Aluminum plating a substrate by contacting the heated substrate with one that is decomposing Alkyl aluminum compound and treatment of the plated substrate at an elevated temperature.

Here, under the phrase "an aluminum covered substrate" is one covered with aluminum Substrate to be understood in which the aluminum is produced by thermal decomposition of an alkyl aluminum compound and the decomposition by contacting the heated substrate with the alkylaluminum compound but the covered substrate has not yet been exposed to air.

It has been proposed by K. Ziegler and co-workers to coat a substrate with aluminum by bringing a heated substrate into contact with a liquid alkylaluminum compound or with the vapor of an alkylaluminum compound and thus thermally decomposing the alkylaluminum compound (see Japanese patent specification 234 069). . This method of cladding a substrate with aluminum has the following disadvantages. There are cracks and gas pores on the aluminum-covered surface, which lead to a deterioration in the corrosion resistance, the oxidation resistance at high temperature and the electrical properties of the substrate. Furthermore, the thickness of the aluminum film is not uniform, the gloss of the surface is poor, and the aluminum film tends to peel off when bent.

From the German Auslegeschrift 1 267 054 a method for aluminum plating a substrate is known in which the heated substrate is brought into contact with a decomposing alkyl aluminum compound and the plated substrate is post-treated at elevated temperature. This simple thermal aftertreatment stabilizes the aluminum precipitate and improves its acid resistance. However, the acid resistance is not yet sufficient for numerous applications.

In the older German Offenlegungsschrift 2 053 242 it was also proposed that the substrate, aluminum-plated by decomposition of an alkylaluminum compound, with oxygen, Halogen or an active hydrogen compound tapes. A thermal aftertreatment jet is not provided here.

The invention is based on the object em A method of plating a substrate with aluminum, by means of which a very acid-resistant Aluminum layer is formed, which has no cracks and pores and is firmly bonded to the substrate.

According to the invention, this object is achieved in the above-mentioned method in that the heat treatment is carried out for 10 seconds to 30 minutes at 400 to 66O ⁰ C in an inert atmosphere and the substrate before or after this heat treatment with a small amount of oxygen, halogen or a active hydrogen compound ίο brings into contact and exposes it to the air after these treatments.

The process according to the invention ensures that the aluminum film formed has no cracks or gas pores on its surface, has a uniform thickness and excellent gloss , is firmly bonded to the substrate and does not detach from it.

The alkyl aluminum compounds used according to the invention include any alkyl aluminum compounds which are capable of separating aluminum by thermal decomposition. Of these compounds, the following are preferred because they are easily thermally decomposable and economical, dialkylaluminum hydride or trialkylaluminum with n alkyl groups containing 2 to 20 carbon atoms; contain, such as triethylaluminum. Diethyl aluminum hydride. Tri-n-propyl aluminum. Tri- isopropylaluminum, tri-n-butylaluminum, di-n-butylaluminum hydride, triisobutylaluminum, diisobutylaluminum hydride, tri-n-benzylaluminum, trin-hexylaluminum, tri-n-octylaluminum, trW-ethylhexyl-aluminum, dihydride-2-aluminum. Tridecyl aluminum or mixtures thereof.

Further, the alkyl aluminum compound can be used together with a compound. which is able to form a complex compound with the alkylaluminum compound, for example with an alkali metal compound, an ether, a tertiary amine, a quaternary ammonium salt etc. which are mentioned in U.S. Patent Nos. 3,454,407 and 3,373,996 with one Aluminumbclag of high purity is also obtained one can use the alkylaluminum compound use in admixture with an inert organic solvent such as hexane. Heptane, octane, cyclopentane, Cyclohexane, Benzene, Toluene, Xylene, Petroleum, Paraffins, Alkylbenzene, Diphenyl, etc.

Substrates that can be covered include, for example, metals such as iron, steel, Aluminum, copper, brass, earthenware, glass, organic and inorganic resins, etc.

The substrate is preferably cleaned prior to the receipts.

The substrate is heated to a temperature higher than the thermal decomposition temperature of the alkylaluminum compound and brought into contact with the deposition solution or the deposition vapor. The substrate can be heated by known heating methods, for example by resistance heating or induction heating, depending on the type and shape of the substrate. Induction heating is preferred for continuous heating of particularly thin sheet metal.

As a method of making an aluminum covered substrate according to the invention, any method can be used in which a heated substrate is contacted with a liquid alkylaluminum compound or with the vapor of an alkylaluminum compound. The choice of the method in question depends on the type and shape of the substrate to be coated. The substrate can be covered with the aluminum by thermal decomposition of an alkylaluminum compound by heating once or by intermittent heating two or more times. The latter is particularly preferred. Furthermore, the latter method does not require the heat treatment of an aluminum covered substrate.

The thermal decomposition can be carried out in the presence of a compound which accelerates the thermal decomposition, such as titanium chloride, titanium bromide, vanadium chloride, ferric chloride, copper chloride, etc. mentioned in U.S. Patent 3,306,732. The addition of this compound is particularly useful in plating a substrate with poor heat stability.

It is necessary that the thermal decomposition take place in an inert atmosphere, but the pressure is under which to work is not critical.

The substrate thus covered with aluminum is then fed to the heat treatment step, or it is first brought into contact with a very small amount of a surface treatment agent, selected from compounds containing active hydrogen, oxygen and halogens is, and then fed to the heat treatment stage. The heat treatment is carried out according to the invention by placing Jas substrate on it a temperature of 400 "C to 660 ° C, preferably 450 ° C to 600 ° C, heated and maintained.

If the heat treatment temperature is lower than 400 ° C, good surface properties can be achieved can not be achieved and also a long treatment time is required for the heat treatment. For example, in the case of a substrate made of iron, a reaction between iron and aluminum takes place and the aluminum film tends to peel off.

The heat treatment can be carried out in the presence of a gas inert to aluminum or a molten one Of salt. Nitrogen, argon and helium are commonly used, but it should be noted that the invention is not limited to these substances.

The heat treatment time varies somewhat depending on the type and shape of the substrate Thickness of the aluminum film and after the heating temperature, but it is generally 10 seconds up to 30 minutes In the case of a substrate made of iron, too long a treatment time causes a reaction between the aluminum and iron, whereby the applied surface is deteriorated; therefore the substrate is preferably heat-treated for 20 seconds to 15 minutes.

After completion of the heat treatment, the substrate is exposed to the air or first brought into contact with a small amount of a surface treatment agent selected from active hydrogen-containing compounds, oxygen and halogens, and then exposed to the air.

The contact of the substrate with a surface treatment agent selected from the group consisting of active hydrogen-containing compounds, oxygen and halogens can be carried out prior to the heat treatment. As mentioned above, the contact of the substrate with a very gentle

wrestling amount of a surface treatment for boys to a better aluminum surface than if only one heat treatment is applied.

Examples of active hydrogen-containing compounds covered with that covered with aluminum

«Substrate brought into contact are: Ver connections with at least one substitutable hydrogen, such as water, ammonia, primary or secondary amine compounds, such as di-diethylamine, monobutylamine, etc .. Sulphides, for example

“5 wise hydrogen sulfide, ethylthioalcohol, dodecvhioalcohol, etc .; monohydric or polyhydric alcohols such as methanol, ethanol, isopropyl alcohol, ethylene glycol, propylene glycol, glycerin, etc .; Carboxylic acids, for example acetic acid, naphthenic acid, stearic acid, adipic acid, maleic acid. Phthalic acid, etc .; and inorganic acids such as hydrochloric acid, hydrofluoric acid, hydrobromic acid, nitric acid, etc. These active hydrogen-containing compounds

* 5 fertilizers are used as a solution, soft 10 to 10,000 parts per million, preferably 100 to 1,000 parts per million (by weight) thereof Compound in aromatic hydrocarbons such as benzene, toluene, xylene, naphthalene, alkylbenzene etc., in aliphatic hydrocarbons such as pentane, hexane, octane, decane etc. and mixtures thereof dissolved, contains, or they are used as an atmosphere of the active hydrogen-containing Compound of 0.1 to 20 mm Hg, preferably 0.1 to 10 mm Hg.

In the case of treatment with oxygen, the substrate becomes aromatic or aliphatic Hydrocarbon contacted, which is 10 to 10,000 parts per million, preferably 100 to

4 "1000 parts per million (by weight) Contains oxygen, or the oxygen is used as an oxygen atmosphere at 0.01 to 100 mg Hg, preferably 0.1 to 80 mm Hg.

Further, when halogens such as fluorine, bromine, etc. are used, they are used as a halogen atmosphere from 0.01 to 20 mm Hg, preferably 0.1 to 10 mm Hg, or as a solution with a Content of 10 to 2000 parts per million of a halogen dissolved in a suitable solvent such as paraffin. When the halogen is out of the When the vapor phase is brought into contact with the substrate, the vapor is mixed with an inert gas diluted and the treatment is carried out under normal pressure or under increased pressure.

This treatment is carried out at 0 ° C to 300 ° C, preferably 15 ° C to 200 ° C.

As mentioned above, the method of the present invention provides the following advantages over that conventional method using aluminum

6 »covered substrate discharged without any weather treatment becomes: The aluminum film on the substrate has no cracks and gas pores on its surface, exhibits uniform thickness and excellent surface gloss, and is adherent to the substrate

6s tightly bound.

The substrate covered with aluminum according to the invention has a high corrosion resistance and resistance to oxidation at high temperature

053 407

as well as excellent electrical properties. Forner can use the covered substrate of the metal removal treatment, for example the well-known sealing exercise treatment, stabilization treatment and be subjected to the old surface production. Because of these excellent properties, the value of the invention is very significant.

The following exemplary embodiments are only intended to illustrate the invention without, however Set the frame.

example 1

A 50 mm 50 mm 0.6 mm steel sheet is washed with water and then with alcohol and then dried. The steel sheet thus treated is used as a sample.

All process steps from the heat treatment of the sample to its discharge into the Air, are carried out in an argon atmosphere.

This sample is heated to 400 ° C in an argon atmosphere and then ^{immersed in 500 cm x 1 of} an alkyl aluminum solution at 20 ° C, which contains 81 percent by weight of diisobutyl aluminum hydride, 11 percent by weight of diethyl aluminum hydride, 5 percent by weight of triisobutyl aluminum and 3 percent by weight of triethyl aluminum.

After the lapse of 1 minute, the Frobe tus of the solution is withdrawn and the deposited Aikylaluminium is at 100 ° C in an argon atmosphere held and washed off. Furthermore, the same above-mentioned operation is repeated repeatedly to effect the lining with aluminum. Then you heat them up with aluminum Covered sample in the argon atmosphere to 450 ° C. After the sample has been at this temperature for 5 minutes has been held, it is cooled to room temperature in argon gas.

The v / heat-treated substrate is ^{brought into contact for 1 min with 500 cm 3 of} hexane at 20 ° C. which contains 0.01 percent by weight of water. The aluminum-covered steel sheet obtained in this way shows an excellent silver-white gloss and has very excellent surface properties.

Further, an acid resistance test is carried out by placing this coated substrate which has been covered with solid paraffin in a width of 10 mm around the substrate. immersed in 500 cm ^{3 of} a 25% by weight aqueous nitric acid solution at 20 ° C. Even after SO min has passed, no bubbles develop and no distortions are observed on the covered surface.

Reduction.

With this method, instead of water treatment, the steel sheets are treated with 500 cm «hexane, which contains 0.01 percent by weight of ethanol. furthermore with 500 cm * hexane with 0.01 weight percent

»O Oxygen, as well as with an argon atmosphere, which contains chlorine gas of 1 mm Hg, and the steel sheets are then exposed to the air. The aluminum-coated steel sheets obtained in this way show a excellent silver-white gloss and have very good surface properties.

Each steel sheet is subjected to the same acid resistance test. You raise the same Results as is the case with water treatment.

B e ί s ρ i e! 2

A substrate covered with aluminum in the same way as in Example 1 is 500 cm ^! Hexane of 20 ^c C brought into contact.

which contains 0.01 weight percent water. After that it is on for 5 min in an argon atmosphere 5 (, * i) ° C and kept at this temperature. The substrate is then cooled to room temperature in argon gas and carried out into the air obtained sheet steel coated with aluminum shows an excellent silver-white gloss and possesses extremely excellent surface properties.

This steel sheet was subjected to the same acid resistance test as in Example 1 and no bubble development was found even after 40 minutes. In this procedure, instead of being treated with water, the steel sheets are treated with: 500 cm ^{3 of} hexane containing 0.01 percent by weight of ethanol; or with 500 cm ^{3 of} He.; an with a content of 0.01 percent by weight oxygen; or with an argon atmosphere. which contains chlorine gas of 1 mm Hg. Then, as mentioned above, the sheets are heat-treated. cooled and then discharged into the air. They have excellent surface properties, as is the case with water treatment. Every sheet of steel treated in this way becomes the sow; ; Subject to resistance test as in Example 1 and the same results as with the water treatment are obtained.

Claims (1)

Claim: Method of aluminum plating a substrate by touching the heated sub strats with an thereby decomposing alkylaluminum compound and treatment of the plated substrate at elevated temperature, characterized in that the IQ see heat treatment for up to 30 minutes at «> 400 to 660 ° C in an inert atmosphere and the substrate before or after this Bringing heat treatment into contact with a small amount of oxygen, halogen or an active hydrogen compound and after »5 exposing these treatments to air.