JP2006240951A - Li2O-Al2O3-SiO2-BASED CRYSTALLINE GLASS AND Li2O-Al2O3-SiO2-BASED TRANSPARENT CRYSTALLIZED GLASS FORMED BY HEAT-TREATING THE SAME - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide Li<SB>2</SB>O-Al<SB>2</SB>O<SB>3</SB>-SiO<SB>2</SB>-based transparent crystallized glass hardly causing crack even in being exposed in a combustion atmosphere for a long time and Li<SB>2</SB>O-Al<SB>2</SB>O<SB>3</SB>-SiO<SB>2</SB>-based crystalline glass used for producing the same. <P>SOLUTION: The Li<SB>2</SB>O-Al<SB>2</SB>O<SB>3</SB>-SiO<SB>2</SB>-based crystalline glass has ≥0.20/mm β-OH and ≤100 pieces /cm<SP>2</SP>of crystals present on the surface and having ≥0.05 μm particle diameter and the Li<SB>2</SB>O-Al<SB>2</SB>O<SB>3</SB>-SiO<SB>2</SB>-based transparent crystallized glass is formed by heat-treating the Li<SB>2</SB>O-Al<SB>2</SB>O<SB>3</SB>-SiO<SB>2</SB>-based crystalline glass having ≥0.20/mm β-OH and ≤100 pieces/cm<SP>2</SP>of crystals present on the surface and having ≥0.05 μm particle diameter. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a Li ₂ O—Al ₂ O ₃ —SiO ₂ transparent crystallized glass used for a front window or a viewing window of a combustion apparatus using petroleum, gas, coal, wood, or the like as a fuel, and the crystallized glass. The present invention relates to a Li ₂ O—Al ₂ O ₃ —SiO ₂ based crystalline glass used for production.

  The function of the front window in the heating appliance is to enhance the heating effect by transmitting heat rays emitted from the burning flame to the outside, and visually add warmth so that the flame can be seen.

  The observation window is used for observing the inside of the combustion device and the combustion state from the outside.

  Therefore, the front window and viewing window used in the combustion device must be transparent so that they will not be damaged even if they are exposed to high temperatures due to combustion heat or subjected to thermal shock during ignition, etc., and the inside can be observed. Is required.

Until now, as a window material of a combustion apparatus, borosilicate glass, quartz glass, or Li ₂ O—Al ₂ O ₃ —SiO ₂ transparent crystallized glass in which β-eucryptite or β-quartz solid solution is deposited as a main crystal is used. However, borosilicate glass has poor heat resistance and thermal shock resistance compared to other glasses, and quartz glass has the disadvantage that it is a very expensive material although it has excellent heat resistance and thermal shock resistance. .

On the other hand, the above-described Li ₂ O—Al ₂ O ₃ —SiO ₂ transparent crystallized glass has a low coefficient of thermal expansion and high mechanical strength, so it has excellent heat resistance and thermal shock resistance, and is relatively inexpensive. It is widely used as a window material for combustion devices.

However, when the Li ₂ O—Al ₂ O ₃ —SiO ₂ transparent crystallized glass is exposed to a combustion atmosphere using petroleum, gas, coal, wood, etc. as a fuel, the inner surface of the window material, that is, the combustion side There is a problem that the surface is chemically corroded, fine cracks are generated, and transparency and strength are impaired.

  The mechanism for generating fine cracks is as follows.

First, generation petroleum, coal, gas, SO _x is generated in the fuel and sulfur combustion contained combustion atmosphere such as wood, the H ₂ SO ₄ SO _x is reacts with H ₂ O in the combustion atmosphere To do.

Next, hydrogen ions generated from H ₂ SO ₄ and lithium ions in the crystal of the Li ₂ O—Al ₂ O ₃ —SiO ₂ based transparent crystallized glass undergo ion exchange.

  Since hydrogen ions are smaller than lithium ions, the crystals shrink and cracks occur on the surface of the crystallized glass.

In order to solve the above problem, a method of providing a film such as SiO _{2 on} the surface of the Li ₂ O—Al ₂ O ₃ —SiO ₂ transparent crystallized glass has been implemented, but it is preferable because the manufacturing cost increases. Absent.

In addition, the lithium ion content in the Li ₂ O—Al ₂ O ₃ —SiO ₂ transparent crystallized glass is lowered to suppress the ion exchange reaction with hydrogen ions, but the transparency Have a problem that the thermal expansion coefficient is not sufficiently reduced and heat resistance and thermal shock resistance are hardly obtained.

Therefore, the amount of β-OH contained in the Li ₂ O—Al ₂ O ₃ —SiO ₂ crystalline glass is set to 0.35 / mm or more, so that the crystal component is formed on the glass surface after crystallization by heat treatment. A method has been proposed in which a layer (glass-rich layer) having a low concentration is formed, and the glass-rich layer serves as a barrier to suppress ion exchange and suppress generation of cracks (for example, Patent Documents 1 and 2). reference.).
JP 2000-10295 A JP 2000-149426 A

However, although the Li ₂ O—Al ₂ O ₃ —SiO ₂ based transparent crystallized glass described in Patent Documents 1 and 2 has improved acid resistance as compared with the conventional transparent crystallized glass, In other words, the acid resistance is not easily maintained, and cracks may occur.

An object of the present invention is to provide a Li ₂ O—Al ₂ O ₃ —SiO ₂ transparent crystallized glass that is less likely to crack even when exposed to a combustion atmosphere for a long time, and Li ₂ O used for producing the same. and to provide a -Al ₂ O ₃ -SiO ₂ based crystallized glass.

The present inventors are acid resistant in Li ₂ O—Al ₂ O ₃ —SiO ₂ based transparent crystallized glass in which a glass rich layer having a low concentration of crystal components is formed on the glass surface by the action of moisture contained in the glass. Various investigations were conducted to find out the cause of the decline.

As a result, the Li ₂ O—Al ₂ O ₃ —SiO ₂ -based transparent crystallized glass where cracks are likely to occur is the Li ₂ O—Al ₂ O ₃ —SiO ₂ -based crystallinity before crystallization by heat treatment. It was found that there were particularly many crystals on the surface of the glass. Thus, it has been found that the acid resistance of the crystallized glass can be improved by reducing the number of crystals precipitated on the surface of the crystalline glass.

That is, the Li ₂ O—Al ₂ O ₃ —SiO ₂ crystalline glass of the present invention has a β-OH amount of 0.20 / mm or more and the number of crystals having a particle size of 0.05 μm or more present on the surface. Is 100 pieces / cm ² or less.

In addition, the Li ₂ O—Al ₂ O ₃ —SiO ₂ transparent crystallized glass of the present invention has a β-OH amount of 0.20 / mm or more and a crystal having a particle size of 0.05 μm or more present on the surface. Is formed by heat-treating Li ₂ O—Al ₂ O ₃ —SiO ₂ crystalline glass having a number of 100 / cm ² or less.

Since the Li ₂ O—Al ₂ O ₃ —SiO ₂ crystalline glass of the present invention has a β-OH amount of 0.20 / mm or more, a glass-rich layer is formed on the surface of the heat-treated crystallized glass. Easy and sufficient acid resistance is obtained. Further, since the number of crystals having a particle size of 0.05 μm or more present on the surface is as small as 100 / cm ² or less everywhere, even if the crystalline glass is crystallized, Li ₂ O—Al ₂ O ₃ —SiO ₂ The number of crystals present on the surface of the system crystallized glass is reduced. Therefore, the crystallized glass is excellent in acid resistance that is hard to crack on the surface for a long period of time even when exposed to a combustion atmosphere using petroleum, coal, gas, wood, etc. Will not be damaged.

  A preferable β-OH amount is 0.23 / mm or more, more preferably 0.25 / mm or more. In addition, the amount of β-OH is calculated by measuring the infrared absorption spectrum of the crystalline glass using an infrared spectrometer and using the following equation.

β-OH amount (/ mm) = {log (T ₃₈₅₀ / T ₃₅₀₀ )} / t
T ₃₈₅₀ : transmittance around ₃₈₅₀ cm ⁻¹
T ₃₅₀₀ : Minimum transmittance of absorption band near ₃₅₀₀ cm ^-1
t: Thickness (mm) of crystalline glass at the time of spectrum measurement
In order to increase the amount of β-OH, a glass raw material having a high water content (for example, aluminum hydroxide) is selected, the amount of water contained in the combustion gas when the glass is melted, A method such as bubbling water vapor is used alone or in combination.

  When the crystal grain size present on the surface of the crystalline glass is 0.05 μm or more, the crystal acts as a crystal growth nucleus when crystallizing the glass, so that the crystal is exposed on the surface of the crystallized glass. It tends to be easy. Therefore, it is difficult to obtain sufficient acid resistance and cracks are likely to occur. If the crystal grain size is smaller than 0.05 μm, the effect of acting as a crystal growth nucleus is small and it is difficult to cause a reduction in acid resistance.

If the number of crystals is more than 100 / cm ² , the long-term acid resistance tends to be lowered. Preferably, it is 70 pieces / cm ² or less. The number of crystals is the same as the number of crystals larger than 25 μm in the 5 mm square (0.25 cm ² ) measured using an optical microscope with a magnification of 200 times, and the 5 mm square measured using an electron microscope. The number of crystals having a particle size of 0.05 to 25 μm was added to calculate the number of crystals existing per 1 cm ² , and the value with the largest number of crystals among the 10 measured points was calculated. To adapt.

  Since it exists on the surface of the crystalline glass, the surface of the crystalline glass may be polished. However, unpolished is preferable because an increase in the number of steps and costs associated therewith can be eliminated. By the way, since there was no knowledge about the crystals present on the surface, it was not polished.

In the Li ₂ O—Al ₂ O ₃ —SiO ₂ crystalline glass, the crystals present on the surface are precipitated by being held in a temperature range in which crystals are likely to precipitate in the molding step and annealing step. _It contains one or more components selected from the group consisting of ₂ O, Al ₂ O ₃ , SiO ₂ , ZrO ₂ and TiO ₂ . Note that Li ₂ O, Al ₂ O ₃ and SiO ₂ are components constituting the crystallized glass crystal, and ZrO ₂ and TiO ₂ are added so that the crystal precipitates uniformly, and serve as crystal growth nuclei. It is a working ingredient.

The Li ₂ O—Al ₂ O ₃ —SiO ₂ crystalline glass of the present invention has a mass ratio, and the value of Li ₂ O / (Al ₂ O ₃ + SiO ₂ ) is 0.03 to 0.06. ,preferable. If it is less than 0.03, it is difficult to increase the degree of crystallinity, so that the thermal expansion coefficient cannot be sufficiently reduced, and heat resistance and thermal shock resistance tend to be difficult to obtain. On the other hand, if it exceeds 0.06, the degree of crystallinity becomes high when crystallized by heat treatment, so that a glass-rich layer is hardly formed on the glass surface, and acid resistance tends to be difficult to obtain.

In the Li ₂ O—Al ₂ O ₃ —SiO ₂ crystalline glass of the present invention, the total amount of ZrO ₂ , TiO ₂ and P ₂ O ₅ is preferably 2 to 10% in terms of mass%. If the total amount of ZrO ₂ , TiO _2, and P ₂ O ₅ acting as a nucleating agent is less than 2%, the deposited crystal particles become large and the visible light is scattered and hardly transmitted, so that transparency is impaired. Cheap. In addition, inhomogeneous crystallization occurs and a difference occurs in the coefficient of thermal expansion partially, so that there is a risk of damage due to thermal shock or the like. On the other hand, if the total amount of the nucleating agent is more than 10%, the formation of crystal growth nuclei occurs too frequently, so that the crystal is likely to precipitate on the surface of the crystalline glass by heat treatment such as annealing, and crystallized by heat treatment. Even if it performs, there exists a tendency for a glass rich layer to be hard to be formed on the surface and to obtain acid resistance easily. A glass-rich layer is hardly formed on the glass surface, and acid resistance tends to be hardly obtained.

_{Incidentally, Li 2 O-Al 2 O} 3 -SiO 2 system suitable composition range of the crystalline glass of the present invention, as represented by mass _{percentage, SiO 2 50~75%, Al 2} O 3 15~30%, Li 2 O 2-5%, Na ₂ O 0-7%, K ₂ O 0-7%, MgO 0-8%, ZnO 0-8%, BaO 0-8%, TiO ₂ 0.5-10%, ZrO _{2 0~7%, P 2 O 5} 0~7%, as 2 O 3 0~2.5%, Sb 2 O 3 0~2.5%, a SnO ₂ 0 to 2.5%.

Next, the Li ₂ O—Al ₂ O ₃ —SiO ₂ crystalline glass of the present invention is produced.

In the method for producing crystalline glass, the Li ₂ O—Al ₂ O ₃ —SiO ₂ based crystalline glass is maintained in a temperature range of 1200 ° C. to 1300 ° C. including local heating in the molding step and the annealing step. It is to suppress the time to 1 minute or less. When Li ₂ O—Al ₂ O ₃ —SiO ₂ crystalline glass is kept in a temperature range of 1200 to 1300 ° C., crystals are most likely to precipitate. Therefore, if the temperature is maintained for more than 1 minute in this temperature range, a large number of crystals are precipitated on the surface of the crystalline glass, making it difficult to obtain sufficient acid resistance.

  Also, in the molding process, the diameter of the stretching roller is increased to 10 cm or more so as not to be held in the temperature range of 1200 ° C. to 1300 ° C. for more than 1 minute, and heat is easily released from the roller, or the roller is cooled with water. It is preferable to cool the crystalline glass quickly.

In the annealing step, it is preferable to use a burner or an electric heating device of 11000 kcal / m ² or less. When a burner or an electric heating device of 11000 kcal / m ² or less is used, the crystalline glass is not easily heated locally, and the glass is not easily kept at a temperature higher than the assumed temperature range for a long time locally. It becomes difficult. As a result, sufficient acid resistance is easily obtained and cracks are unlikely to occur. In general, electric heating is more difficult than glass to heat the glass uniformly and it is difficult to keep crystals in a temperature range where crystals are likely to precipitate locally for a long time. Is advantageous.

  In addition, it is necessary to consider that the burner flame contains a high concentration of water vapor. When the burner flame directly touches the surface of the crystalline glass, water vapor generated from the burner flame may diffuse into the glass from the surface of the crystalline glass. Since the water vapor diffused in the glass has an action of promoting the precipitation of crystals, the crystals are likely to be deposited on the surface of the crystalline glass when combined with the heat from the burner flame.

  In addition, in the forming step and the annealing step, the crystalline glass is manufactured in a state in which the change in wind speed is 4 m / s or less. When the amount of change in the wind speed is 4 m / s or less, deviation from the temperature profile in production design is unlikely to occur, and a difference in temperature profile for each crystalline glass produced continuously is unlikely to occur. The quality of the water becomes stable, and acid cracks are less likely to occur. In this case, the amount of change in the wind speed can be 4 m / s or less by completely covering the molding process and the annealing process. In addition, by laying out near the molding device and annealing furnace so that there are no doors or windows leading to the outside air, for example, within 3 m, the influence from the outside air is reduced, and the amount of change in the wind speed can be reduced to 4 m / s or less. . Note that the amount of change in wind speed is the difference between the maximum value and the minimum value of the wind speed measured in any one hour. By the way, in order to reduce the temperature difference of crystalline glass, or to shorten the holding time in the temperature range where crystals are likely to precipitate, it can be used without any problem if this condition is satisfied even if controlled air is passed. .

Hereinafter, the Li ₂ O—Al ₂ O ₃ —SiO ₂ crystalline glass and the Li ₂ O—Al ₂ O ₃ —SiO ₂ transparent crystallized glass of the present invention will be described in detail using examples.

  Examples 1 to 11 are shown in Tables 1 and 2, and Comparative Examples 1 to 3 are shown in Table 3. Table 4 shows Samples A and B.

  Examples 1 to 11 and Comparative Examples 1 to 3 were produced as follows.

  First, glass raw materials were mixed so as to have the composition shown in the table, put into a platinum crucible, and melted at 1550 ° C. for 8 hours using an electric furnace. In addition, the amount of β-OH was adjusted by using a hydroxide instead of an oxide as a glass raw material.

  Next, the molten glass is poured out on a carbon surface plate, formed into a thickness of 5 mm using a stainless roller, and then cooled to room temperature using an annealing furnace set at 700 ° C. to obtain a plate-like crystalline glass. Produced.

  Subsequently, in order to completely remove crystals precipitated in the forming step and the annealing step, the surface of the crystalline glass was ground by 50 μm, and then optical polishing was performed.

  Next, the surface of the crystalline glass is heated using a burner capable of locally heating the polished crystalline glass, and the precipitated crystals are measured under the above conditions using an optical microscope and an electron microscope, and are present on the surface. The number of crystals having a particle size of 0.05 μm or more was calculated. Examples 1 to 11 and Comparative Example 3 were heated with a burner for 30 seconds, and Comparative Examples 1 and 2 were heated with a burner for 90 seconds.

Finally, crystallized glass was obtained by holding the crystalline glass at 780 ° C. for 3 hours using an electric furnace and then holding at 870 ° C. for 1 hour. In any crystallized glass, the main crystal was β-quartz solid solution, and the average linear thermal expansion coefficient was in the range of −10 to 10 × 10 ⁻⁷ / ° C.

  Sample A shown in Table 4 was prepared by molding and annealing the molten glass having the composition of Example 1 so that it was not held for 1 minute or longer in the temperature range of 1200 to 1300 ° C. (about 30 seconds). B was prepared in the same manner as Sample A except that it was held for 1 minute or longer (about 90 seconds) in a temperature range of 1200 to 1300 ° C. Incidentally, the samples A and B are not surface-polished.

  The acid resistance was evaluated by two methods, an acceleration test and a mounting test.

  In the accelerated test, acid resistance was evaluated as follows.

  20 mL of a 6 vol% sulfuric acid aqueous solution was injected into a 1 L beaker. Next, a net was placed in a beaker, a sample processed to 25 × 25 × 5 mm was placed thereon, covered with a glass plate, and held at 380 ° C. for 60 minutes. Subsequently, the sample was taken out and the appearance was visually observed.

  In the mounting test, acid resistance was evaluated as follows.

  A sample processed to 50 × 200 × 5 mm was placed on the front of a stove using light oil as fuel, and combustion was continued for 40 days under normal combustion conditions. The sample was removed from the stove and the appearance was visually observed. The acid resistance was evaluated as “◎” when no crack was observed, “◯” when a slight crack was observed, and “X” when a crack was significantly recognized.

  As is clear from Tables 1 and 2, Examples 1 to 11 were excellent in transparency and acid resistance.

  On the other hand, as is clear from Table 3, Comparative Examples 1 to 3 had poor acid resistance although there was no problem with transparency.

Further, as apparent from Table 4, sample A has a holding time at 1200 to 1300 ° C. of 1 minute or less, and therefore the number of crystals can be 100 / cm ² or less, and the acid resistance is high. It was. On the other hand, Sample B had low acid resistance.

The Li ₂ O—Al ₂ O ₃ —SiO ₂ transparent crystallized glass obtained by heat-treating the Li ₂ O—Al ₂ O ₃ —SiO ₂ crystalline glass of the present invention is a petroleum stove, wood stove, boiler, etc. Not only can it be used as a front plate or a viewing window for combustion equipment, but also high-tech product substrates such as color filters and image sensor substrates, setters for firing electronic components, shelf plates for microwave ovens, top plates for cooking appliances, fire protection window glass, etc. Can also be used.

Claims (5)

Li ₂ O—Al ₂ O, characterized in that the amount of β-OH is 0.20 / mm or more and the number of crystals having a particle size of 0.05 μm or more present on the surface is 100 / cm ² or less. ₃ —SiO ₂ crystalline glass. The Li ₂ O—Al ₂ O ₃ —SiO ₂ based crystalline glass according to claim 1, wherein the surface is not polished. The value of Li ₂ O / (Al ₂ O ₃ + SiO ₂ ) in terms of mass ratio is 0.03 to 0.06, Li ₂ O—Al ₂ O ₃ — according to claim 1 or 2 SiO ₂ crystalline glass. The total amount of ZrO ₂ , TiO ₂ and P ₂ O ₅ is 2 to 10% in terms of mass%, and Li ₂ O—Al ₂ O ₃ — according to any one of claims 1 to ₃ SiO ₂ crystalline glass. A Li ₂ O—Al ₂ O ₃ —SiO ₂ transparent crystal obtained by heat-treating the Li ₂ O—Al ₂ O ₃ —SiO ₂ crystalline glass according to claim 1. Glass.