JPS5845138A - Window of combustion apparatus - Google Patents

Abstract

PURPOSE:To prevent a window glass from cracking and reduce the transparency, by forming a sulfuric acid-proof film of specified composition on the surface of an Li2O-Al2O3-SiO2 type transparent glass used for the window of a combustion apparatus. CONSTITUTION:A soln. of an organometallic compd., such as ethyl silicate, aluminum isopropoxide or titanium tetrabutoxide dissolved in an org. solvent, such as butyl alcohol or ethyl alcohol is coated on the surface of an Li2O- Al2O3-SiO2 type transparent crystalline glass used for the front window of various kinds of combustion apparatuses. The org. components are decomposed by heat treatment to give a transparent film consisting of SiO2, Al2O3, TiO2, and the like oxides, and having 1.55+ or -0.30 refraction coefft. and <=1.0mum thickness. This film is superior in resistance to sulfuric acid, heat, and heat shock, and prevents small cracks on the combustion side surface of the glass, and reduction of the transparency.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a front window or a viewing window of a fuel device using oil, coal, gas, etc., that is, a heating appliance, a heating furnace, a slow cooling furnace, etc.

The function of the front window in a heating appliance is to increase the heating effect by transmitting the heat rays emitted from the internal flame to the outside, and to increase the visual warmth by making the flame visible. Also, the function of the viewing window is to allow the combustion state of the flame to be observed from the outside.

These windows must withstand the high heat generated by flames and the thermal shock of ignition. Therefore, the material used for the window of the combustion device must be transparent and have excellent heat resistance and thermal shock resistance. Currently, the main materials used for the windows of heating appliances are Li2O-Al2O3-SiO2-based transparent crystallized glass, borosilicate glass, Vycor glass, etc., but borosilicate glass has sufficient heat resistance and thermal shock resistance. However, although Vycor glass has excellent thermal properties, it is expensive.

On the other hand, Li2O-Al2O3-SiO2-based transparent crystallized glass has excellent heat resistance and thermal shock resistance, and can be manufactured at a relatively low cost, making it a suitable material for windows for heating appliances. Widely used. As such Li2O-Al2O3-SiO2-based transparent crystallized glass, for example, Japanese Patent Publication No. 39-21 of 1983, invented by the present applicant,
There is 049.

As mentioned above, Li2O-Al is used in combustion devices such as heating appliances.
2O3-SiO2-based crystallized glass windows are widely used, but when this type of crystallized glass is used for a long time, delicate cracks occur on the inner surface of the window, that is, the surface on the combustion side, and the transparency deteriorates. The disadvantage is that the value is significantly reduced.

It is presumed that the occurrence of this surface crack is caused by an ion exchange reaction between Li+ and H+ in the surface layer of the crystallized glass. That is, when fuels such as petroleum, coal, city gas, and natural gas containing sulfur as impurities are burned, sulfuric acid vapor is generated, and this sulfuric acid vapor condenses on the surface of crystallized glass. Therefore, an ion exchange reaction occurs between H+ in the sulfuric acid and Li+ in the composition of the crystallized glass, and the volume of the surface layer of the crystallized glass shrinks. As a result, tensile stress is generated in the ion-exchanged surface layer relative to the interior where no ion exchange reaction occurs. It is estimated that cracks occur on the surface when the magnitude of this tensile stress exceeds the breaking stress of the crystallized glass.

It is an object of the invention to provide a combustion device window that does not develop cracks on its surface.

The present inventors have discovered that by forming a transparent film on the surface of Li2O-Al2O3-SiO2-based transparent low-expansion crystallized glass, it is possible to eliminate the drawback of cracks occurring in crystallized glass windows. .

In the present invention, the transparent film acts as a protective film to prevent sulfuric acid, which condenses on the surface of the window and causes an ion exchange reaction and causes cracks, from coming into direct contact with the surface of the crystallized glass. For this reason, the film is required to have excellent sulfuric acid resistance. Further, it is preferable that this coating has a refractive index similar to that of transparent crystallized glass.

If the refractive index of the coating is significantly different from that of crystallized glass,
In addition, strong interference colors are generated, the coating is glaring, which is unfavorable in appearance, and it also reflects heat rays generated from an internal heat source, reducing the heating effect. For example, when the refractive index of transparent crystallized glass is about 1.55, if the refractive index of the coating is 1.55±0.30, the above-mentioned problem due to the difference in refractive index will not occur. Furthermore, it is of course preferable that the coefficient of thermal expansion of the coating be close to that of crystallized glass because no stress will be applied to the coating and the adhesiveness will be good.
In the present invention, the difference in thermal expansion coefficients is not so much of a problem since a film having a very thin film thickness of 1.0 μm or less is usually sufficient to prevent cracks.

There are various methods for forming a transparent sulfuric acid-resistant film on the surface of transparent crystallized glass. For example, ethyl silicate [Si(OC2H5)4], aluminum isopropoxide [Al(OC3H7)3], titanium A solution prepared by dissolving an organometallic compound such as rhabtoxide [Ti(OC4H9)4] in an organic solvent such as butyl alcohol or ethyl alcohol is applied to the surface of crystallized glass by dip coating, spray coating, brush coating, etc. This is then heat-treated to decompose the organic components and form SiO2, Al2O3, T
It is obtained by leaving only oxide components such as iO2 on the surface of the crystallized glass.

Examples of the present invention will be described below.

Example 1 In weight %, SiO2 66.2, Al2O3 22.0
, Li2O 4.2, MgO 0.5, P2O5 1.
4, ZrO2 2.3, TiO2 1.9, Na2O0
．． 5, has a composition consisting of 0.3 K2O and 0.5 AS2O3, and has a thermal expansion coefficient of -3.0 x 10-7/℃ (30
A transparent crystallized glass plate having a temperature of 1.54 and a refractive index of 1.54 is prepared. This crystallized glass plate was immersed in a solution in which ethyl silicate was dissolved in butyl alcohol at a concentration of 1 mol SiO2/kg solution, pulled up, and then heated at 500°C for 30 minutes.
Heated for 0 minutes. As a result, an amorphous film of SiO2 having a thickness of 0.2 μm and a refractive index of 1.46 was formed on the surface of the crystallized glass plate.

Example 2 Ethyl silicate and aluminum isopropoxide were dissolved in butyl alcohol at a molar ratio of 90SiO2 and 10Al2O3, and the oxide concentration was 1 mol oxide/k.
A coating solution of g solution was prepared. The above-mentioned Example 1 was added to this coating solution.
After dipping a crystallized glass plate and pulling it up, it was heated to 3
Heated for 0 minutes. As a result, an amorphous film having a molar ratio of 90 SiO2 and 10 Al2O3 was formed on the surface of the crystallized glass plate. This coating has a thickness of 0.15μ and a refractive index of 1.4.
It was 5.

Example 3 1 mol Al2O3/k of aluminum isopropoxide
The crystallized glass plate of Example 1 described above was immersed in a solution prepared in butyl alcohol at a concentration of g solution, pulled up, and heated at 500° C. for 1 hour to form a crystalline film of Al2O3. The film thickness was 0.1μ and the refractive index was 1.62.

Example 4 Ethyl silicate and titanium tetrabutoxide in 85S
A coating solution having an oxide concentration of 1 mol oxide/kg solution was prepared by dissolving it in butyl alcohol at a ratio of iO2.15TiO2. The crystallized glass plate of Example 1 was immersed in this coating solution, pulled up, and then heated at 600° C. for 30 minutes. As a result, an amorphous film of 5SiO2 and 15TiO2 was formed on the surface of the crystallized glass plate in a molar left side view. This coating had a thickness of 0.2 μm and a refractive index of 1.54.

A crystallized glass plate having the coatings of Examples 1 to 4 above was used as a front window of a forced exhaust type kerosene stove (size 150 x 300 m).
m), and when an evaluation test was carried out using a fuel containing 10% kerosene and burning for about 1000 hours, no cracks were observed on the surface of the crystallized glass plate. On the other hand, for windows made of crystallized glass plates that do not form a coating, 50
Cracks occurred over time.

The film created on the surface of transparent crystallized glass needs to be at least transparent and resistant to sulfuric acid, but in the present invention, the material of the film is the same as in the above embodiment. Of course, it is not limited.

patent applicant Nippon Electric Glass Co., Ltd. Representative Junichi Nagasaki

Claims (4)

[Claims] (1) A window for a combustion device characterized by having a transparent sulfuric acid-resistant coating on the surface of Li2O-Al2O3-SiO2-based transparent crystallized glass. (2) The window for a fuel device according to claim 1, wherein the coating is made of oxide components of SiO2, Al2O3, and TiO2. (3) The window for a fuel device according to claim 1, wherein the coating has a refractive index of 1.55±0.30. (4) The window for a fuel device according to claim 1, wherein the thickness of the coating is 1.0 μm or less.