Method of passivation of contact surface of refractory reservoir made from mullite and slip used for realization of this method

FIELD: production of metal alloys by casting.

SUBSTANCE: proposed method includes application of slip on contact surface; slip contains 50-70 mass-% of aluminum oxide powder Al₂O₃ and 30-50 mass-% of binder which contains 50-60 mass-% of aluminum chloride AlCl₃ dissolved in 40-50 mass-% of water. Then reservoir is dried and roasted in oxidizing atmosphere at temperature of 1450-15500°C for at least 20 min. In some cases, use is made of slip containing water-soluble organic dye. Used as organic dye is methylene blue at total content of 0.1-0.5 mass-%. Specification gives description of slip used for passivation of contact surface of refractory reservoir. Proposed method makes it possible to form absolutely inert coat on contact surfaces of ceramic reservoirs relative to alloys of titanium coat.

EFFECT: enhanced efficiency and reliability.

8 cl

EFFECT:

The technical field

The invention relates to the production of metal alloys molding and, in particular, to a method and products of the passivation of the contact surface of the ceramic tanks on the basis of mullite, such as crucibles and moulds.

The terms "on the basis of mullite or mainly of mullite," you see the tanks of pure mullite or tanks, the main mass component of which is mullite.

The state of the art and problem statement

Mullite, i.e., aluminum silicate with the chemical formula 2SiO₂·3Al₂About₃is a cheap material to make fire-resistant tanks with excellent resistance to temperature fluctuations caused by the casting of metals and alloys during casting. In particular, the crucibles of pure mullite and from a material mainly containing mullite, can be found on sale at low prices. Mullite is also used for the manufacture of molds, such as molds.

Titanium alloys are widely used in the aviation industry, but they have the disadvantage that at high temperature, they react chemically with the greater part of the materials of which make crucibles and molds, in particular with pure silicon dioxide SiO₂or forming part of mullite. The criminal code of the related reactions lead to inclusions in cast products undesirable components, the potential to degrade the quality of the products.

To eliminate this drawback, the prior art cover contact surface of the tank with a layer of inert material (see, for example, SU 881079), such as aluminum oxide. To get this aqueous suspension, called the "slip"of filler in the form of flour alumina Al₂O₃and a product called "binder", this itself is specified binder is a mixture of water with colloidal silicon dioxide SiO₂; cause the composition to the contact surface; dry the tank and put the tank firing at a high temperature, typically at a temperature of 1200°within hours, with the specified firing causes the crystallization of the components and the formation of strong and resistant contact layer.

It is believed that silicon dioxide binder chemically reacts with the titanium. It should be noted that the reservoir, consisting only of aluminum oxide, is completely chemically inert to titanium, but it will be too fragile to resist the temperature fluctuations during the pouring of the metal during melting.

The first problem is the formation of the contact surface of ceramic vessels, mainly made of mullite or even pure mullite, coatings, absolutely inert the CSOs in relation to titanium alloys during melting.

The second problem is obtaining such coatings with low cost.

Disclosure of inventions

In order to solve the above problems, the invention proposes a method of passivating the contact surface of the refractory vessel, mainly of mullite, characterized in that the contact surface applied slurry containing 50-70 wt.% flour alumina Al₂O₃and 30-50 wt.% binder containing 50-60 wt.% aluminum chloride AlCl₃dissolved in 40-50 wt.% water, followed by drying and firing of the tank in an oxidizing atmosphere at a temperature of 1450-1550°C for at least 20 minutes

In the present invention a slurry for use in the passivation of the contact surface of the refractory vessel, mainly of mullite, characterized in that it contains 50-70 wt.% flour alumina Al₂O₃and 30-50 wt.% binder containing 50-60 wt.% aluminum chloride AlCl₃dissolved in 40-50 wt.% water.

The authors found that a solution of aluminium chloride has a binding capacity comparable to the classical suspension of colloidal silicon dioxide. During the oxidative roasting of aluminum in the binder is converted into aluminum oxide which crystallizes together with the loaded alumina, while svoboden the th chlorine appears in the form of gas. So get perfectly clean contact layer of aluminum oxide, able to communicate with titanium melting, without joining with him in a chemical reaction; we thus solve first the problem set.

The method is economical, because

- used ingredients are cheap;

although the firing is carried out at higher temperatures, it is short-term;

the coating slurry may be applied by spray or brush, depending on the relative content of the filler and the binder selected.

Thus, solved the second problem.

Detailed description

The invention and its proposed benefits will be more obvious due to the described example of embodiment of the invention.

The method which is the object of the present invention, includes the following operations.

1) obtaining a slurry formed of the filler in the form of flour alumina Al₂O₃binding and very little additives methylene blue.

Aluminum oxide called flour, since we are talking about the fine powder, the particles of which have a size of about 40 microns. Flour alumina Al₂O₃forms filler slurry and ranges from 50% to 70% of the total mass of the slip.

Thus, the binder constitutes from 30% to 50% of the total mass of the slip is. The specified binder is a solution of aluminum chloride AlCl₃in the water. While aluminum chloride AlCl₃ranges from 50% to 60% by weight of the total binder, and water, thus, ranges from 40% to 50% by weight of the total binder.

2) the Application of the slip at the contact surface of the tank, but such application may be made by known methods.

When loading flour alumina Al₂O₃in the amount of from 50 to 55 wt.% and a binder in an amount of from 45 to 50 wt.% the resulting slurry is relatively liquid and can be applied by spray.

When loading flour alumina Al₂O₃in the amount of from 55 to 70 wt.% and a binder in an amount of from 30 to 45 wt.% the resulting slurry is more dense, and it is mainly applied by brush.

When loading flour alumina Al₂O₃more than 70 wt.% and a binder in a quantity of less than 30 wt.% the slip becomes very thick and difficult to apply thin layers.

On the contrary, when loading flour alumina Al₂O₃fewer than 50 wt.% and spanning more than 50 wt.% the slip is very liquid and has the disadvantage that it gives a strong shrinkage and cracking during drying.

Preferably the slurry additionally contains an organic dye soluble in the ode.

As mullite, alumina and aluminium chloride are white staining slip methylene blue allows you to visually control the thickness and uniformity of application. In practice, the number of methylene blue is from 0.1% to 0.5% of the total mass of the slip. It is obvious that methylene blue can be replaced with any subjected to pyrolysis of the organic dye, that is, dye, collapsing at high temperature, but has a sufficiently strong coloring power, so that it can be used in very small quantities and not worsen the floor.

3) Drying the coating by known methods, for example by placing the tank in the oven for one hour at a temperature of 120°C.

4) Baking the coating in a furnace in an oxidizing atmosphere at a temperature in the range from 1450°C to 1550°for from 20 minutes to one hour, usually at a temperature of 1500°C for 30 minutes, the speed of increasing and decreasing temperature must be at least 300°With an hour to limit the effects of thermal expansion.

The oxidizing atmosphere can be simply atmospheric air. During oxidative roasting of aluminum from aluminum chloride is converted to aluminum oxide and fills the volume originally occupied by the binder, while chlorine is released and excreted in the form of gas is.

1. Method of passivating the contact surface of the refractory vessel, mainly of mullite, characterized in that the contact surface applied slurry containing 50-70 wt.% flour alumina Al₂About₃and 30-50 wt.% binder containing 50-60 wt.% aluminum chloride AlCl₃dissolved in 40-50 wt.% water, followed by drying and firing of the tank in an oxidizing atmosphere at a temperature of 1450-1550°C for at least 20 minutes

2. The method according to claim 1, characterized in that the use of slurry, optionally containing an organic dye soluble in water.

3. The method according to claim 2, characterized in that the dye used methylene blue, with a total content of 0.1-0.5 wt.%.

4. The method according to any one of claims 1 to 3, characterized in that the slurry contains 50-55 wt.% flour alumina Al₂O₃and 45-50 wt.% binder, the coating is applied by spray.

5. The method according to any one of claims 1 to 3, characterized in that the slurry contains from 55 to 70 wt.% flour alumina Al₂About₃and 30-45 wt.% binder, the coating is applied by brush.

6. The slip for use in the passivation of the contact surface of the refractory vessel, mainly of mullite, characterized in that it contains 50-70 wt.% flour alumina Al₂About₃and 30-50 wt.% binder containing 5-60 wt.% aluminum chloride AlCl ₃dissolved in 40-50 wt.% water.

7. The slip according to claim 6, characterized in that it contains 50-55 wt.% flour alumina Al₂About₃and 45-50 wt.% the binder.

8. The slip according to claim 6, characterized in that it contains 55-70 wt.% flour alumina Al₂About₃and 30-45 wt.% the binder.