DE1914046A1 - Aluminium film deposition on metallic and - non-metallic surfaces - Google Patents

Abstract

Alkyl aluminium (1) which decomposes under heat liberating aluminium is suspended in an organic liquid whose boiling point is below the decomposition temp. of (1) and which does not react with (1). The substrate to be plated is heated to above the decomposition temp. of (1) and brought into contact with the solution of (1). Spec., (1) is dissolved in the organic solvent.

Description

Method of coating surfaces with aluminum The present The invention relates to a method for coating surfaces with aluminum. she particularly relates to a method of depositing an adherent aluminum film by means of an organic aluminum dissolved in a low-boiling solvent Connection on one surface.

Various systems have heretofore been used to accomplish different metallic and non-metallic surfaces or substrates with an aluminum surface to provide. Plating methods have been used in which an aluminum foil with the desired surface by extensive surface treatment of the object and a subsequent combination of heat and pressure has been associated. There are high operating pressures are required, which limits the type of objects that can be coated.

There are also serious corrosion and operational problems.

The various known vacuum methods produce very thin films and are subject to a low production scale, batch manufacturing and strong Size restrictions.

The heat destruction one of aluminum compounds is in the literature besclorieben. Aluminum hydride has broken down into aluminum and hydrogen (Ber.75B, pp.20003-12, 1942). However, the usefulness of this compound is as economical source of aluminum for plating due to its exosive nature questionable. In U.S. Patents 2,599,978 and 2,824,828, the decomposition of Aluminum compounds described in the gas phase. Gas phase decomposition and plating was also described by Powell (Vapor Plating). In gas phase plating a number of practical problems arise. I) the system must be against atmospheric Contamination must be tightly sealed, constant pressure conditions must be maintained and the gas flow rates must be regulated within narrow limits. In addition, there are many problems with vaporizing decomposable materials and In almost all cases, carrier gases must be provided to prevent the flow of the decomposable To give direction to gas. All additives to the gas stream, for example modifiers, must also be volatile at the working temperature and the rate of addition must be carefully regulated.

The object to be plated must be heated in the closed system and be prepared, which entails expensive process equipment.

In U.S. Patent 3,041,197 the aluminum plating is through Describe solution plating. This system uses a heat-decomposable aluminum compound in a liquid or solid solution or dispersion, the liquid or solid Solution has a boiling point above the decomposition temperature of the aluminum compound owns, with a heated pad brought into contact, whereby the formation of aluminum on the substrate is caused. Other means can be for example reducing agents or. Anti-oxidants, be present. The underlay can be made of any desired material as long as it is at a temperature above the decomposition temperature of the aluminum compound can be heated, In the said U.S. patent also states that the solvent is the decomposition temperature influenced and generally degraded. The deposited aluminum film is grained by means of conventional plet bottom can be anodized.

However, that described in US Pat. No. 3,04,197 has proven itself Procedure certain disadvantages. Example has the alkyl decomposition in the high-boiling Solvents cause the bath to gradually turn black. There are also kicking Difficulty in achieving uniform plating based on the alkyl content of the bath must be protected against oxidation and hydrolysis, the bath tends during of immersion for smoking and spraying, and the like.

The aim of the present invention is therefore to provide an improved one Method of cladding a surface with aluminum. Another goal of the The present invention is to provide a method of achieving uniform: 1 Aluminum coating on a base. More goals, items, and benefits of the invention will be apparent from the following description.

The foregoing and other objects of the invention are achieved by the substrate with a solution of the heat-decomposable aluminum compound in a liquid solvent for the aluminum compound plated, the solvent has a boiling point which is not higher than the decomposition temperature of the Aluminum compound.

According to one embodiment of the present invention, the hot pad immersed in a 13ad of aluminum allryl solution. According to a Another embodiment is a solution of the aluminum alkyl compound on the hot Sprayed underlay.

In the context of the present invention, everyone is liquid, not reactive hydrocarbon suitable, which has a boiling point that does not is higher than the heat set temperature of the aluminum compound in which the aluminum compound can be dissolved or suspended and which does not react with the aluminum compound. In practice, the plating bath temperature is determined by the hot pad that is immersed in it is influenced and the properties of the coated surface are affected by the Affects the temperature of the bath. Suitable coatings are obtained when the bath or spray a temperature of at least 50 ° C and preferably above 100 ° C having. In general, a bath temperature in the range of 100 to 150 ° C is used and therefore the boiling point of the solvent is above the bath temperature, but is not higher than the decomposition temperature of the aluminum compound.

Suitable solvents include liquid organic solvents with a boiling point in the desired range.

Examples of such solvents include toluene, ethylbenzene, Xylene, kerosene, and the like. Any of them can be used in the practice of the present invention Organic compound containing aluminum, which is released under heat decomposed by aluminum and dissolved or suspended in a solvent medium can be used to produce an aluminum film on a base will. In practice, due to price, availability, security and the Temperature to which the documents are heated can be, the aluminum alkyls, such as aluminum trimethyl, aluminum triethyl, aluminum diethyl hydride, aluminum triisopropyl and aluminum triisobutyl compounds preferred for use. Other suitable Compounds include diisopropyl aluminum hydride, dibutyl aluminum hydride, and diisobutyl hydride. According to the above US Pat. No. 3,041,197, aluminum triisobityl is particularly preferred, while according to the invention with aluminum triethyl, that according to the said USA patent least preferred compound, excellent results are obtained. According to the invention, aluminum diethyl hydride is preferred. The higher members of the alkyl series are generally just as suitable as those of the lower alkyl series, with in particular the links are suitable, their thermal decomposition points or areas in general Range from 170 to 500 ° C, preferably from 300 to 500 ° C. For examples such compounds include aluminum triisopentyl, aluminum triisooctyl, aluminum tridodecyl and the like Substituted aluminum alkyls, preferably those in which the substituting Radical is a saturated aliphatic radical are usually suitable. Substituents, which tend to react with the freshly deposited aluminum coatings or films, are usually avoided. Aluminum mono- and dialkyls can also be used for example, ethyl aluminum dihydride and diethyl aluminum hydride Find application.

In general, the aluminum alkyl in the solvent can be from 10 to 90 wt.% Aluminum compound vary, but it is preferably used in a 30th grade Up to 70% by weight solution or dispersion is used.

As mentioned earlier, various smaller components can be included in the the solvent medium can be used, if desired, the physical and modify chemical properties of the deposited film. It can for example wetting agents to promote adhesion, oxidizing and reducing Connections are used.

The surface to be coated should be completely clean and free from be any oxides. This cleaning can be done mechanically, for example by driving off with steel wool, sandblasting, by rubbing with sandpaper and The cleaning can also be done mixed, for example with ammoniacal Citric acid solution, dilute HCl or dilute phosphoric acid and the like. The chemical Detergents can be cleaned by washing with water and drying with a drying agent Agents such as acetone or methanol can be removed.

As from the USA patent application Ser.No. 444 392 from March 31, 1965 emerges, the documents, in particular metal bases, are advantageous before heating covered with an oil or wax. This treatment apparently prevents too very little oxidation of the metal to be plated.

Plating can be done by any suitable method. That Plating bath (aluminum compound in solvent) is at a temperature below the boiling point of the solvent iind generally above room temperature held. The temperature used is determined in large measure by the nature of the solvent 5, the aluminum compound and the desired aluminum surface are determined. as As a general rule, a temperature in the range from 100 to 150 ° C is used. It however, any temperature up to the boiling point of the solvent can be used. i) The zit plating substrate is brought to a temperature above the decomposition temperature the aluminum compound heated. The mat can be immersed in the bath or the bath can be sprayed onto the hot surface. Because the bathroom is cooler as the support, the support must be at a temperature above the decomposition temperature of the aluminum connection. This excess temperature does not need to be great his and depends to some extent on the temperature of the bath or the plating solution. In general, a temperature in the range of 350 to 1000 ° C can be used, with 350 to 700 ° C being preferred.

In the case of the liquid phase plating of aluminum on substrates it would have been expected that a solvent would be required, dos a higher boiling point possesses as the decomposition temperature of the aluminum alkyl. It was to be assumed that such a solvent removes the plating at the highest possible temperature Without boiling the solvent and thus minimal splashing was also allowed zti expects that. by plating at such a temperature, a lower one Underlay temperature is enabled. It would still have been expected that a higher boiling solvent provides greater protection against atmospheric oxidation and hydrolysis provides. The teaching of the invention shows that surprisingly iron the opposite is true in each case.

There was little, if any, difference in the case an aluminum plating, which was measured with a bath temperature of 50 (: resp. of 150 0C has been produced. On the other hand, aluminum claddings show a pronounced difference that results from a solution of the aluminum compound in low boiling solvents such as lierosin and xylene are or are made from the aluminum compound in a high-boiling solvent, such as Slinera101 or petroleum wax. The lower boiling one Solvent produces a more uniform l> lattiening and is allowed by that Working with a much higher concentration of aluminum compound. The lower Boiling solvents have a higher vapor pressure at a given temperature as higher-boiling solvents they therefore supply a larger amount of solvent molecules in the vapor phase directly above the surface of the aluminum compound, whereby the Oxidation possibilities are reduced.

Another unexpected advantage of the system according to the invention is that the spraying of the solvent / aluminum compound solution upon contacting with bases with high temperature compared with the higher boiling solutions is greatly reduced. It would have been expected that the higher-boiling solutions have less tendency to splash, surprisingly, however, the opposite has been found found. This can be attributed to the lower viscosity of the solvent A very important one that lets the vapor bubbles escape with less interference The advantage of using the lower-boiling solvents is a more effective one Aluminum utilization. It has been found that with the higher boiling solvents, like mineral oil, in connection with aluminum alkyl compounds the bath during the Plating process turns gray to black through suspended aluminum. In the This difficulty is caused by the use of the low-boiling solvent according to the invention did not occur, rather the bath remains water-clear during the plating process.

The following examples are intended to further illustrate the invention. but not limit. Aluminum compounds that contribute to the release of the Aluminum is decomposed, as well as solvents that are below the decomposition temperature of the aluminum compound boil, can be used as long as the aluminum compound is effectively dispersed in the solvent.

Example 1 The plating is inside a nitrogen purge Drying chamber carried out. A 3.8 internal diameter container holds 38 grams filled with a 50% solution of triethylaluminum in colorless mineral oil. The solution is heated to 150 ° C with an oil bath. A row of mild steel or soft iron sections with a size of 2.54 cm x 7.62 cm x 1.5 mm in a muffle furnace, which is also located in the drying chamber, to 600 ° C heated.

When the sections have reached the temperature of 600 C, will the lid removed from the aluminum alkyl solution and immersed in the solution. I) The section is quickly plated with aluminum. After 3 minutes the section will removed from the solution. The temperature of the solution t increases to 174 ° C.

The aluminum alkyl solution smokes during the plating process If this is the case, the lid is removed from the container in each case.

Another section is removed from the furnace and placed in the aluminum alkyl / mineral oil solution immersed. In this attempt, the drying chamber fills with smoke in such a way that the bathroom can no longer be seen, which is why the attempt is interrupted. The plating solution got dark.

Example 2 The experiment of Example 1 is repeated with the exception that the solution consists of 20% diethyl aluminum in the mineral oil. Also in this In this case, the experiment must be interrupted due to excessive smoke formation.

Example 3 The experiment is repeated, 79 g of mineral oil with 10% Triethylaluminum can be used. At this concentration the smoke formation is true not excessive and the aluminum coating appears to be even, however will after plating some of the aluminum washed off the section, What shows that decomposition to aluminum does not completely lead to plating Has.

The plating solution is cloudy.

Example 4 The experiment is repeated with the exception that one 10% solution of diethyl aluminum hydride in xylene used as plating bath will. All five sections are immersed one at a time. The solution does not audit and the plating is smoother than in the previous experiments. It won't Aluminum is washed off the platings and the solution remains clear as water.

Example 5 In this experiment the oven temperature is for heating of the sections 400 ° C. The plating solution consists of 83 grams of a 47.5% solution of diethyl aluminum hydride in xylene.

The solution will not smoke during the plating process no aluminum washed off the sections and the solution is after plating all five sections still clear as water. The solution splatters during plating not.

Claims (9)

1> t e 11 t a n 5 p p r ii c h e 1 .. Method of cladding a substrate with aluminum, thereby characterized, de «ß one an aluminum alkyl, which is released in the warmth fully decomposes aluminum, in an organic liquid that has a boiling point below the temperature required for the decomposition of the aluminum alkyl, the is not reactive with the aluminum alkyl, suspended, the to be plated Pad to a temperature above that required for the decomposition of the aluminum alkyl Temperature and the heated surface contacted with the aluminum alkyl solution, 2. A method for plating a surface with aluminum, characterized in that that one is an aluminum alkyl, which is in the heat with the deposition of aluminum decomposed, brings into an organic solvent for the aluminum alkyl, wherein the solvent is not reactive with the aluminum alkyl and one Has a boiling point which is lower than the decomposition temperature of the aluminum alkyl, the surface to be plated to a temperature above the decomposition temperature of the aluminum alkyl is heated and the surface with the mixture of aluminum alkyl and organic solvent contacted. 3, method according to claim 2, characterized in that the aluminum alkyl is dissolved in the organic solvent. 4. The method according to claim 3, characterized in that the plating is carried out in a bath, the bath temperature in the range from 50 to 150 ° C is held. 5. A method of plating a surface with aluminum, thereby characterized in that one is a solution of an aluminum alkylyer bond through Heat decomposes to release aluminum in an organic solvent for the aluminum alkyl compound, the solvent being at the solution temperature is stable and has a boiling point below the decomposition temperature of the aluminum alkyl compound and wherein the solution has 10 to 90% by weight of the aluminum compound in the solvent contains that one keeps the solution in the temperature range of 50 to 150 C, the Surface to a temperature above the decomposition temperature of the aluminum alkyl compound heated and the surface contacted with the solution. 6. The method according to claim 5, characterized in that the solvent is a saturated hydrocarbon. 7. The method according to claim 6, characterized in that the surface is heated to a temperature in the range of 350 to 1000 ° C. 8. The method according to claim 7, characterized gek ennzeiciiiict that the Contacting is done by immersion. 9. The method according to claim 7, characterized in that the contacting happens by spraying.