JPH07309636A - Transparent glass ceramic articles and their production - Google Patents

Abstract

PURPOSE:To obtain transparent glass ceramic articles which have excellent heat resistance and impact resistance and are useful as the peep window of a combustion device using fuel contg. S-components at a high ratio by composing these articles of a prescribed compsn. and forming the articles so as to maintain specific crystal conditions. CONSTITUTION:These transparent glass ceramic articles are composed of the compsn. consisting of 55 to 68wt.% (hereafter %) SiO2, 20 to 35% Al2O3, 2 to 5% Li2O, 0.5 to 4% K2+Na2O, 1.5 to 3% TiO2, 1 to 6% ZrO2, 0.2 to 3% P2O5, 0 to 3% MgO and <=0.5 P2O5/(TiO2+ZrO2). The main crystal is constituted by precipitating a p-quartz solid soln. as the main crystal. More preferably, the degree of crystallization in the surface layer which is the part from the front surface down to at least depth of 15mum is specified to 20 to 80% of the degree of crystallization of the inside.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent glass-ceramic article and a method for producing the same, and more particularly to a transparent glass article used as a peep window of a combustion apparatus and a method for producing the same.

[0002]

2. Description of the Related Art As a viewing window for a combustion device such as a stove,
Li ₂ O-Al ₂ O ₃ -with excellent heat resistance and thermal shock resistance
SiO ₂ type transparent glass ceramics are widely used. However, since this type of glass-ceramics has low corrosion resistance, there is a problem that cracks and white turbidity are likely to occur when the glass-ceramics are used as a viewing window of a combustion device that uses a fuel containing a large amount of sulfur. This is because H ⁺ ions contained in the combustion gas replace Li ⁺ ions in the surface layer of the glass ceramic, and the volume of the precipitated crystals shrinks.

Various proposals have hitherto been made to solve such problems, for example, Japanese Patent Laid-Open No. 58-451.
No. 38 proposes to provide a corrosion-resistant protective film such as SiO _{2 on} the surface of transparent glass ceramics. Further, in JP-A-59-116150, glass ceramics having a specific composition is contacted with a molten salt containing K ⁺ ions to replace Li ⁺ ions in the surface layer, or contacted with an acid before crystallization. A method for producing a glass ceramic article having high corrosion resistance by replacing Li ⁺ ions with H ⁺ ions is disclosed.

[0004]

[Patent Document 1] Japanese Unexamined Patent Application Publication No. Sho 5
The glass-ceramic article disclosed in No. 8-45138 has a problem that the resistance to scratches is insufficient and the manufacturing cost is high because the protective film is as thin as 1 μm or less. Of the two methods disclosed in JP-A-59-116150, the method of replacing Li ⁺ ions with K ⁺ ions after crystallization is 400 to 800 ° C. for the ion exchange reaction.
High temperature and long time of about 8 hours are not practical. On the other hand, the method of replacing Li ⁺ ions with H ⁺ ions before crystallization has a drawback that the effect is insufficient.

The object of the present invention is to have sufficient corrosion resistance,
Moreover, it is an object of the present invention to provide a transparent glass-ceramic article that can be manufactured at low cost and a method for manufacturing the same.

[0006]

As a result of various studies, the inventors of the present invention have found that if a glass-rich layer is present on the surface of a glass-ceramic article, it will not be exposed to the combustion gas of a combustion device. I have found that it does not suffer from corrosion. This is because vitreous is less likely to release Li ⁺ ions than crystalline, and the volume change is less likely to occur even if Li ⁺ ions are emitted. It has also been found that such a glass-ceramic article can be produced by injecting H ⁺ ions into a Li ₂ O-Al ₂ O ₃ -SiO ₂ based glass having a specific composition and then crystallizing.

That is, the transparent glass-ceramic article of the present invention has a weight percentage of SiO ₂ 55 to 68% and Al ₂ O _{3
20~35%, Li 2 O2~5%,} K 2 O + Na 2 O
_{0.5~4%, TiO 2 1.5~3%,} ZrO 2 1~6
%, P ₂ O ₅ 0.2 to 3%, MgO 0 to 3%, P ₂ O ₅
/ (TiO ₂ + ZrO ₂ ) ≦ 0.5, β-quartz solid solution is deposited as the main crystal, and the crystallinity of the surface layer is 20 to 80% of that of the inside. To do.

The method for producing a transparent glass-ceramic article according to the present invention is such that the weight percentage of SiO _{2 is} 55-68%, A
_{l 2 O 3 20~35%, Li} 2 O2~5%, K 2 O + N
a ₂ O 0.5-4%, TiO ₂ 1.5-3%, ZrO _{2
1~6%, P 2 O 5 0.2~3} %, MgO0~3%, P
A glass molded body having a composition of ₂ O ₅ / (TiO ₂ + ZrO ₂ ) ≦ 0.5 is prepared, and an acid is brought into contact with the surface of the glass molded body, followed by heat treatment for crystallization.

[0009]

Transparent glass ceramic article of the effects of the present invention, beta-quartz solid solution having a negative thermal expansion coefficient (Li ₂ O · Al ₂
O ₃ · nSiO ₂ , where n ≧ 2) is the main crystal, and the crystallinity inside the glass-ceramic article is 60 to 85%, which is equivalent to that of the conventional glass-ceramic article used for the sight glass of a combustion apparatus. It has excellent heat resistance and thermal shock resistance.

The surface layer has a depth of at least 15 from the surface.
It refers to a portion up to μm, and is a portion where crystallization is suppressed by H ⁺ ion implantation or the like. Since this portion is richer in glass than the inside of the glass ceramic article, it is less likely to be corroded even when exposed to combustion gas, and the treated surface layer is thick and is not affected by scratches. The crystallinity of the surface layer is 20 to 80%, preferably 30 to 60% of that of the inside, and if it exceeds 80%, sufficient corrosion resistance cannot be obtained, and if it is less than 20%, the thermal expansion with the inside Cracks occur on the surface layer due to the difference in coefficient.

Next, a method for producing such a transparent glass-ceramic article will be described.

First, the weight percentage of SiO ₂ 55-68 is used.
%, Al ₂ O ₃ 20 to 35%, Li ₂ O _{2 to} 5%, K ₂
O + Na ₂ O 0.5-4%, TiO ₂ 1.5-3%, Z
rO ₂ 1-6%, P ₂ O ₅ 0.2-3%, MgO 0-3
%, P ₂ O ₅ / (TiO ₂ + ZrO ₂ ) ≦ 0.5.

The reason why the composition range of the glass molded body is limited as described above will be described below.

When H ⁺ ions are implanted into the surface of a Li ₂ O-Al ₂ O ₃ -SiO ₂ type glass molded body and then heat-treated, β-quartz solid solution precipitates inside the molded body, but β on the surface layer -Quartz solid solution is less likely to precipitate, resulting in a layer rich in glass. This is because the implantation of H ⁺ ions releases Li ⁺ ions that are a constituent of the crystal.

Incidentally, the implantation of H ⁺ ions is easier to perform as the acidity of the glass is lower. In the case of oxide glass, the acidity of the glass is determined by the type and amount of cations contained in the glass composition, and the higher the ratio of cations having a large valence and a small ionic radius, the higher the acidity of the glass. Table 1
Shows a measure of the acidity of various cation oxides reported by SUN. The larger the value, the higher the acidity. Further, the acidity of glass is obtained by summing the acidity of various ionic oxides and the molar fraction of the oxide in the glass.

[0016]

[Table 1]

Therefore, in order to effectively implant H ⁺ ions and reduce the crystallinity of the surface layer, Li
_{Among the 2} O—Al ₂ O ₃ —SiO ₂ glasses, it is necessary to select a glass having a low acidity.

TiO ₂ , which acts as a nucleating agent,
ZrO ₂ and P ₂ O ₅ are components that greatly affect the crystallinity of the surface layer. Therefore, in order to obtain crystallized glass having an appropriate crystallinity, it is necessary to consider the content and ratio of each of these components.

In the present invention, the glass composition is thus limited in consideration of the acidity and crystallinity of the glass. The reasons for limiting each component will be described below.

SiO ₂ is a main component of glass and a constituent of β-quartz solid solution, and its content is 55-55.
It is 68%, preferably 58 to 67%. SiO ₂ is 5
If it is less than 5%, the precipitation amount of the β-quartz solid solution becomes small, and sufficient heat resistance and thermal shock resistance cannot be obtained. By the way, since SiO ₂ is a component having a high acidity, it is not preferable if the amount is too large. Particularly, if it exceeds 68%, the acidity of the glass remarkably rises and it becomes difficult to implant H ⁺ ions, and it becomes difficult to improve the corrosion resistance. On the other hand, if the amount of SiO ₂ is too large, the meltability of the glass will decrease.

Al ₂ O ₃ is a constituent component of the β-quartz solid solution, and its content is 20 to 35%, preferably 21 to 3%.
It is 0%. If the Al ₂ O ₃ content is less than 20%, the workability of the glass will deteriorate, and if it exceeds 35%, the meltability will decrease.

Li ₂ O is a constituent component of the β-quartz solid solution, and its content is 2 to 5%, preferably 3 to 4.5%. If Li ₂ O is less than 2%, a sufficient crystal amount cannot be obtained, while if it is more than 5%, the crystal amount becomes too large to obtain a transparent glass ceramic article.

K ₂ O and Na ₂ O are components that lower the acidity of the glass and make it easier to melt. The total content of these is 0.5 to 4%, preferably 0.5 to 3.5. %. If the total amount of these components is less than 0.5%, the effect is not obtained, and if it is more than 4%, the thermal expansion coefficient becomes too large and the thermal shock resistance decreases.

TiO ₂ is a nucleating agent, and its content is 1.5 to 3%, preferably 1.8 to 2.5%. T
When iO ₂ is less than 1.5%, the crystallization inside the glass does not proceed sufficiently, and as a result, crystals are likely to precipitate from the glass surface having a smaller free energy, and the crystallinity of the surface layer increases, which is not preferable. On the other hand, TiO ₂ has a high acidity and a relatively small molecular weight, so that even a small amount of TiO ₂ greatly increases the acidity of glass. In particular, if it exceeds 3%, the acidity of the glass remarkably rises, H ⁺ ions cannot be sufficiently injected, and the nucleation ability becomes too strong, and the crystallinity of the entire glass article including the surface becomes too high.

ZrO ₂ is a nucleating agent, and its content is 1 to 6%, preferably 1.5 to 3%. If ZrO ₂ is less than 1%, the effect is not obtained. On the other hand, ZrO ₂ is Ti
Since it has a lower acidity than O ₂ and a large molecular weight, it can be contained in a relatively large amount, but if it exceeds 6%, the melting property is lowered, which is not preferable.

P ₂ O ₅ works effectively for nucleation and Z
It is an essential component for promoting the meltability of rO ₂ , and its content is 0.2 to 3%, preferably 0.5 to 2%. If P ₂ O ₅ is less than 0.2%, the effect is not obtained.
P ₂ O ₅ is a component having a high acidity, but since it has a large molecular weight, it can be contained up to 3%. However, if it exceeds 3%, the acidity of the glass increases, which is not preferable.

MgO is a component that improves the meltability, and its content is 0 to 3%, preferably 0 to 1%. Mg
When O is more than 3%, the crystallinity becomes too strong, and it becomes difficult to obtain a transparent glass-ceramic article.

Further, nucleating agents such as TiO ₂ and ZrO
_2, P ₂ ratio of O _{5 is, P 2 O 5 / (TiO} 2 by weight
+ ZrO ₂ ) ≦ 0.5. If this ratio exceeds 0.5, the precipitated crystals will become coarse and the transparency will decrease, and the crystallinity of the surface will become too high and the sulfuric acid resistance will deteriorate.

As long as the properties of the obtained glass ceramics are not impaired, in addition to the above components, ZnO and Ba are also included.
O can be added in a total amount of up to 4% in order to improve the meltability. Further, the total content of the above components is preferably 95% or more, and if it is less than this, a dense crystal structure cannot be obtained, so that a transparent glass-ceramic article is difficult to obtain.

Next, H ⁺ is applied to the surface of the prepared glass molded body.
Inject ions. The method of implanting H ⁺ ions is not particularly limited, but it is generated by heating sulfuric acid.
A method of contacting sulfuric acid vapor at ˜330 ° C. with the glass molded body for 0.5 to 3 hours, or ammonium sulfate of 120 to 600
A method in which a decomposition gas generated when heated at 0 ° C. is brought into contact with the glass molded body is preferable because the surface can be uniformly treated. In addition to the above, vapors of acids such as hydrochloric acid and nitric acid, and sulfur compounds that are acidic at high temperatures may be contacted. The reason for implanting H ⁺ ions before the crystallization heat treatment is that if this is performed after the crystallization heat treatment, a crack occurs on the surface due to the volume contraction of the crystals accompanying the release of Li ⁺ ions, but before the crystallization heat treatment. This is because the volume change is unlikely to occur even if Li ⁺ ions are released.

Then, the glass molded body is heated to 700 to 900 ° C.
By heat treatment for 2 to 15 hours at
It is possible to obtain a transparent glass-ceramic article which is formed by depositing a quartz solid solution and has a surface layer crystallinity of 20 to 80%, preferably 30 to 60% of that of the inside.

[0032]

EXAMPLES The present invention will be described below based on Examples and Comparative Examples.

Table 2 shows examples of the present invention (Sample Nos. 1 to 1).
4) and Table 3 shows comparative examples (Sample Nos. 5 to 7), respectively.

[0034]

[Table 2]

[0035]

[Table 3]

(Example) Each example was prepared as follows.

First, glass raw materials were prepared so that the compositions shown in Table 2 were obtained, and the glass raw materials were put into a platinum crucible and placed at 1500-16.
After melting at 00 ° C. for 15 hours, it was formed into a plate shape. Next, a glass molded body having a size of 25 × 25 × 5 mm was produced from this plate glass.

Next, this glass molded body was brought into contact with a vapor of sulfuric acid or a decomposition gas of ammonium sulfate under the conditions shown in the table.

Then, after thoroughly washing the glass molded body, the glass molded body was placed in an electric furnace and kept at 780 ° C. for 2 hours.
The temperature was raised to 840 ° C at a rate of 0 ° C / hr, and 1
After holding for a period of time, it was gradually cooled to obtain a sample. All the obtained samples were transparent.

Thin-film X-ray diffraction was performed on each of the samples thus obtained, and the main crystal and internal and surface layers (depth: 15
The X-ray diffraction main peak intensity of the crystal in the portion up to μm) was measured. Further, each sample was placed in a chamber having a volume of 1 liter, brought into contact with sulfuric acid vapor at 320 ° C. for 1.5 hours, taken out, and the surface state thereof was observed with the naked eye and an optical microscope. The results are shown in Table 2. The sulfuric acid resistance test corresponds to the case where the stove using a fuel containing a large amount of sulfur is used for about 10 years.

As a result, in each sample, the main crystal was β-quartz solid solution. Also, the main peak intensity of X-ray diffraction is 26
50-3050cps, surface layer is 850-1550cps
In each sample, the crystallinity of the surface layer is 32
It was found to be ˜51%, and the surface layer was rich in glass. Regarding the sulfuric acid resistance test, no change was observed in any sample such as cloudiness and cracks.

(Comparative Example) Sample No. 5 was prepared as follows.

First, the sample No. of the example. A glass molded body having the same composition as that of No. 1 was heat-treated under the same conditions as in Example to crystallize, and then immersed in a potassium nitrate solution at 500 ° C. for 8 hours. Then, it was sufficiently washed to obtain a transparent sample.

Next, thin film X-ray diffraction was performed on the produced sample in the same manner as in the example. The main crystal was the same β-quartz solid solution as each sample of the example, but the X-ray diffraction main peak intensity was Is 3200 cps, surface is 2700 cps
s and the crystallinity of the surface layer was found to be about 84% of that of the interior. When a sulfuric acid resistance test was conducted on this sample, it was confirmed that spot-like cracks had occurred.

Sample No. 6 and 7 were prepared as follows.

First, glass raw materials were prepared so as to have the composition shown in Table 3, which was placed in a platinum crucible and melted at 1580 ° C. for 15 hours, and then molded into a plate shape. Next, a glass molded body having a size of 25 × 25 × 5 mm was produced from this plate glass.

Next, this glass molded body was contacted with sulfuric acid vapor at 270 ° C. for 1 hour.

Subsequently, the glass molded body was washed under the same conditions as in the examples, heat-treated and then gradually cooled to obtain a transparent sample.

The sample No. manufactured in this manner was used. 6, 7
When thin film X-ray diffraction was carried out in the same manner as in Example, the main crystal was β-quartz solid solution same as each sample of Example. On the other hand, the main peak intensities of X-ray diffraction are 3100 cps and 3200 cps in the inside and 26 in the surface layer.
50 cps and 2750 cps and the surface crystallinity was found to be about 85% and 86% of that of the interior. When a sulfuric acid resistance test was conducted on this sample, all the samples were found to have network-like cracks and were clouded as a whole.

[0050]

As described above, the transparent glass-ceramic article of the present invention is excellent in heat resistance and thermal shock resistance because it precipitates β-quartz solid solution as a main crystal. Moreover, it has a thick surface layer rich in glass and has high corrosion resistance. Therefore, white turbidity and cracks are unlikely to occur, and it is suitable as a viewing window of a combustion device that uses a fuel with a high sulfur content.

Further, according to the method of the present invention, the corrosion resistance can be improved by the treatment at a low temperature for a short time, so that a transparent glass ceramic article suitable as a peep window of a combustion apparatus can be manufactured at a low cost. Is.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masayuki Ninomiya 2-7-1 Harusara, Otsu City, Shiga Prefecture Inside NEC Denki Glass Co., Ltd.

Claims (5)

[Claims] 1. SiO ₂ 55-68% by weight percentage, A
_{l 2 O 3 20~35%, Li} 2 O2~5%, K 2 O + N
a ₂ O 0.5-4%, TiO ₂ 1.5-3%, ZrO _{2
1~6%, P 2 O 5 0.2~3} %, MgO0~3%, P
₂ O ₅ / (TiO ₂ + ZrO ₂ ) ≦ 0.5, β-quartz solid solution is deposited as the main crystal, and the crystallinity of the surface layer is 20 to 80% of that inside. A transparent glass-ceramic article characterized by: 2. The surface layer has a depth of at least 15 μm from the surface.
The transparent glass-ceramic article according to claim 1, which is a portion up to m. 3. A weight percentage of SiO ₂ 55-68%, A
_{l 2 O 3 20~35%, Li} 2 O2~5%, K 2 O + N
a ₂ O 0.5-4%, TiO ₂ 1.5-3%, ZrO _{2
1~6%, P 2 O 5 0.2~3} %, MgO0~3%, P
A transparent glass characterized in that a glass molded body having a composition of ₂ O ₅ / (TiO ₂ + ZrO ₂ ) ≦ 0.5 is prepared, and then H ⁺ ions are implanted into the surface thereof, followed by heat treatment for crystallization. Method for manufacturing ceramic article. 4. The method for producing a transparent glass-ceramic article according to claim 3, wherein H ⁺ ions are injected by bringing vapor of sulfuric acid into contact with the surface of the glass molded body. 5. The method for producing a transparent glass-ceramic article according to claim 3, wherein H ⁺ ions are injected by bringing the surface of the glass molded body into contact with a pyrolysis gas of ammonium sulfate.