JP4677743B2 - Li2O-Al2O3-SiO2 transparent crystallized glass for combustion device window - Google Patents

Description

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

  The function of the front window in a combustion apparatus such as a heating appliance is to increase the visual warmth by making the flame visible while increasing the heating effect by transmitting heat rays emitted from the internal flame to the outside. .

  The function of the viewing window of the combustion device is to allow observation of the combustion state of the flame from the outside.

  Therefore, these windows used in the combustion apparatus are required to be transparent so that the inside can be observed, and to be excellent in heat resistance and thermal shock resistance so as not to be damaged even when exposed to high temperatures. .

Currently, borosilicate glass, quartz glass, Li ₂ O—Al ₂ O ₃ —SiO ₂ based transparent crystallized glass (hereinafter referred to as crystallized glass) and the like are used as window materials for combustion devices (for example, (See Patent Documents 1 and 2.) However, borosilicate glass does not have sufficient heat resistance and thermal shock resistance, and quartz glass satisfies the required characteristics but is very expensive.

On the other hand, crystallized glass is transparent and excellent in heat resistance and thermal shock resistance, and can be manufactured at a relatively low cost. Therefore, it is widely used as a window material for combustion devices.
Japanese Utility Model Publication No. 6-24650 JP 2001-48582 A JP 2000-44282 A

  However, when crystallized glass is exposed to a combustion atmosphere, fine cracks are generated on the surface, and the transparency of the effective surface of the window material tends to be impaired, and the mechanical strength tends to be impaired. is doing.

  The reason why the above problem occurs is as follows.

In the combustion atmosphere of a combustion apparatus that uses petroleum, coal, gas, wood, or the like as fuel, SOx produced by combustion of sulfur contained in the fuel exists, and H ₂ O produced by combustion reacts with SOx. As a result, sulfuric acid is produced. When an ion exchange reaction between Li ⁺ in the crystal and H ^{+ of} sulfuric acid occurs on the surface of the crystallized glass, the crystal volume shrinks and fine cracks are generated on the surface of the crystallized glass.

  In order to solve such a problem, a method of forming a film of silica or the like on the surface of crystallized glass has been proposed, but this method has a problem that the manufacturing cost increases.

Attempts have also been made to reduce the Li ⁺ content in the crystallized glass and make it difficult for ion exchange reaction with H ⁺ to occur, but the transparency is impaired and the thermal expansion coefficient is increased, resulting in a thermal shock. Sexuality may be impaired.

Further, by heat-treating Li ₂ O—Al ₂ O ₃ —SiO ₂ based crystalline glass (hereinafter referred to as crystalline glass) having an amount of β-OH of 0.35 / mm or more, the surface of the crystallized glass is incorporated inside. A method for suppressing ion exchange between Li ⁺ and H ^{+ in} a crystal by forming a layer having a lower crystallinity than that has been proposed (see Patent Document 3).

  However, even if this method is used, it is difficult to obtain sufficient acid resistance over a long period of time.

An object of the present invention is to provide an inexpensive combustion apparatus window that is less likely to generate fine cracks on its surface even when exposed to a combustion atmosphere containing sulfuric acid generated by burning fuel such as petroleum, coal, gas, and wood for a long time. to provide a use _{Li 2 O-Al 2 O 3} -SiO 2 based transparent crystallized glass.

  As a result of various studies, the present inventors have found that the cause of the insufficient acid resistance of the crystallized glass having a large amount of β-OH is a fine scratch existing on the surface of the crystallized glass (specifically, Depends on the number of lengths of 1 μm or more), that is, if there are surface scratches in the crystallized glass (hereinafter referred to as scratches), the glass rich layer penetrates and the portion with high crystallinity is exposed, It is found that the acid resistance is lowered and is proposed as the present invention.

It was also found that in order to obtain sufficient acid resistance over a long period of time, the number of surface scratches having a length of 1 μm or more must be an average of 70 pieces / cm ² or less. In the conventional production, there was an average of 90 to 200 scratches / cm ² as described above.

That is, the Li ₂ O—Al ₂ O ₃ —SiO ₂ transparent crystallized glass for a combustion apparatus window of the present invention has an average crystallinity of 65 % by mass or more and a glass rich layer of 0.2 μm or more from the surface. It has a thickness, and surface scratches having a length of 1 μm or more are 70 / cm ² or less on the effective surface.

The Li ₂ O—Al ₂ O ₃ —SiO ₂ transparent crystallized glass for a combustion apparatus window of the present invention has a long time in a combustion atmosphere containing sulfuric acid generated by burning fuel such as petroleum, coal, gas, and wood. Even when exposed, fine cracks are unlikely to occur on the effective surface. Therefore, transparency and mechanical strength do not decrease. The effective surface refers to a surface that needs transparency as a front window or a viewing window and is exposed to a combustion atmosphere.

In other words, a glass-rich layer with a lower degree of crystallinity than the inside is formed on the surface of the crystallized glass, and there are few scratches that penetrate this layer, so that ion exchange between Li ⁺ and H ⁺ in the crystal is performed. By suppressing it, sufficient acid resistance can be obtained over a long period of time. Therefore, since it is not necessary to coat the surface of crystallized glass with silica or the like, it can be manufactured at low cost.

  Note that the flaw that is a problem in the present invention is a flaw that occurs after crystallization and is distinguished from a flaw that occurs before crystallization. Scratches attached before crystallization are sharp, whereas scratches attached after crystallization have a complicated shape such as being branched into branches or having many irregularities.

  If the average crystallinity is lower than 65% by mass, sufficient mechanical strength cannot be obtained, and the thermal expansion coefficient increases, resulting in poor heat resistance and thermal shock resistance.

  The average crystallinity is determined by using an X-ray diffractometer (RINT2100, manufactured by Rigaku) and measuring the scattering intensity area of the crystalline glass before crystallization measured in the range of the diffraction angle 2θ of 10 to 60 ° and the crystallized glass. The crystal peak area was determined from the value calculated using the multiple peak separation method.

The glass-rich layer is a layer having a crystallinity of 60% by mass or less of the average crystallinity. When this layer is thinner than 0.2 μm, ion exchange between Li ⁺ and H ⁺ in the crystal is suppressed. Therefore, sufficient acid resistance cannot be obtained.

  In addition, the thickness of the glass rich layer was measured using an atomic force microscope (AFM) on the fractured surface of the crystallized glass.

  When the length of the scratch is longer than 1 μm, the depth of the scratch tends to penetrate the glass rich layer. Therefore, if the length of the scratch is shorter than 1 μm, the scratch is difficult to penetrate the glass-rich layer, so that the portion having a high degree of crystallinity is not easily exposed and the acid resistance is not impaired. The scratch length was calculated by observing the surface with an electron microscope.

When the number of scratches having a length of 1 μm or more is more than 70 / cm ^{2, the} acid resistance is impaired because the number of places where Li ⁺ and H ⁺ in the crystal can exchange ions increases. Note that the number of scratches was calculated by observing the surface of 10 cm ² at an arbitrary 10 locations in units of 1 cm ² with an electron microscope.

Combustion apparatus for windows _{Li 2 O-Al 2 O 3} -SiO 2 based transparent crystallized glass of the present invention, beta-OH amount is less than 0.20 / mm, than 0.2μm is glass-rich layer Since it tends to be thin, it is not preferable.

β-OH amount (/ mm) = [log (T ₃₈₅₀ / T ₃₅₀₀ )] / t
T _3850: 3850cm ^-1 vicinity of the transmittance T _3500: 3500 cm transmittance near ^-1 t: thickness of the crystalline glass during spectrum measurement (mm)
In order to increase the amount of β-OH, a raw material with a high water content (for example, aluminum hydroxide) is selected, the amount of moisture in the combustion gas when melting the glass is increased, or the amount of water vapor in the molten glass is increased. Techniques such as bubbling are used alone or in combination.

The Li ₂ O—Al ₂ O ₃ —SiO ₂ transparent crystallized glass for a combustion apparatus window of the present invention has a thermal shock resistance when the average thermal expansion coefficient at 30 to 750 ° C. is −10 to 10 × 10 ⁻⁷ / ° C. It is preferable because of its excellent properties.

Preferred composition range of _{Li 2 O-Al 2 O 3} -SiO 2 based transparent crystallized glass for a combustion apparatus windows of the present invention, in _{mass%, 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%, 0~8% MgO, 0~8% ZnO, 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%, SnO ₂ 0-2. 5%.

The following describes how to create a combustion apparatus for windows _{Li 2 O-Al 2 O 3} -SiO 2 based transparent crystallized glass of the present invention.

  First, a glass raw material is prepared so as to have a predetermined composition and melted at 1550 to 1750 ° C. for 4 to 20 hours. In order to increase the amount of β-OH, it is preferable to use a glass material having a high water content or to bubble water vapor into the molten glass.

Next, the molten glass is formed into a shape such as a flat plate, a curved plate, a cylinder using various forming methods such as a roll forming method, a press forming method, a dunner method, and a down draw method, and Li ₂ O—Al ₂ O _3. After obtaining a molded body of —SiO ₂ crystalline glass, annealing is performed at 500 to 700 ° C.

Subsequently, the crystalline glass molded body was held at 700 to 800 ° C. for 1 to 4 hours to perform nucleation, and subjected to heat treatment at 800 to 950 ° C. for 0.5 to 3 hours to precipitate β-quartz solid solution. A molded body of Li ₂ O—Al ₂ O ₃ —SiO ₂ -based crystallized glass is produced.

  So far, measures to prevent scratches that can be visually confirmed from sticking to the surface of the crystallized glass have been studied, but as described above, fine scratches in units of μm to mm that have not been focused on are problematic. Therefore, it is necessary to take measures to reduce fine scratches entering the surface of the crystallized glass while the crystallized glass is moved and conveyed from the crystallization process to the packing process.

  There are the following four methods for reducing scratches on the surface of crystallized glass.

  The first is the movement / conveyance and packing from the crystallization process to the packing process in an atmosphere with little dust.

  Even if the surface of the crystallized glass is scratched by dust smaller than 0.5 μm, the scratch is fine, so there is almost no effect on the acid resistance of the crystallized glass obtained by heat treatment. .

Even if the size of dust present in the air is 0.5 μm or more, if it is less than 2 mg / m ³ , the number of scratches on the surface of the crystallized glass tends to be 70 pieces / cm ² or less. .

Incidentally, when the size in the dust is Knoop hardness 0.5μm or contains 500 kg / mm ² or more particles, so easily especially scratch the surface of the crystallized glass, 1 mg / m ³ below Should. The particles having a Knoop hardness of 500 kg / mm ² or more include Li ₂ O—Al ₂ O ₃ —SiO ₂ crystalline glass, Li ₂ O—Al ₂ O ₃ —SiO ₂ crystalline glass, and SiO ₂ as main components. glass _{and, SiO 2, Al 2 O 3} , ZrO 2, Zr 2 SiO 4 and the like.

  In the packing process, in order to prevent the other crystallized glass from being scratched by the edge part of the crystallized glass, the edge part of the crystallized glass is covered so as to cover the edge part of the crystallized glass. Pack with slip-out paper that protrudes 2 cm or more. The interleaving paper may be made of paper, but is preferably made of foamed polyethylene because it can easily absorb impacts and can suppress generation of scratches.

  As the second method, there is a method in which the crystallized glass is washed in the moving / conveying step and the packing step after the crystallization step and the attached dust is removed. Cleaning can be performed with water, an organic solvent, an air jet, or the like.

As a third method, a material having a Knoop hardness of less than 500 kg / mm ² is applied to a portion where the setter or roller used for movement / transport from the crystallization process to the packing process and the crystallized glass can come into contact (specifically, Specifically, the use of metals such as stainless steel) may be mentioned. This can prevent the surface of the crystallized glass from being scratched because the hardness is low even if a setter or a roller comes into contact with the surface of the crystallized glass due to vibration or the like during movement or conveyance.

In addition, when a piece of Knoop hardness larger than 500 kg / mm ² adheres to a portion that can come into contact with the crystallized glass, particularly when the size is 1 mm or more, the surface of the crystallized glass is likely to be scratched. , Up to 100 pieces or less should be removed.

  As the fourth method, in particular, in the case of plate-like crystallized glass, the crystallized glass is stood with a jig or the like, and moved and conveyed from the crystallization process to the packing process.

  In other words, if dust or glass pieces adhere to the setter or roller, moving and transporting the plate-shaped crystallized glass while it is laid will scratch the effective surface, but if it is stood diagonally, the crystallized glass Will contact the setter or roller only at the edge, so there will be no scratches on the effective surface.

  The contact angle between the setter or roller and the crystallized glass is preferably 60 to 120 °.

By taking one or more measures as described above, the number of scratches having a length of 1 μm or more can be reduced to 70 / cm ² or less.

  Hereinafter, the present invention will be described in detail based on examples.

  Table 1 shows Samples 1 to 5 as Examples and Sample 6 as a Comparative Example, and Table 2 shows Samples 7 to 9.

  Samples 1 to 6 were prepared as follows.

By mass%, SiO ₂ 65.8%, Al ₂ O ₃ 21.5%, Li ₂ O 4.0%, TiO ₂ 2.0%, ZrO ₂ 2.3%, P ₂ O ₅ 1.5% , Na ₂ O 0.5%, K ₂ O 0.3%, BaO 1.5%, As ₂ O ₃ 0.5%, Sb ₂ O ₃ 0.1% Was put in a platinum crucible and melted at 1550 ° C. for 8 hours. In order to increase the amount of β-OH, steam bubbling was performed at the beginning of melting.

  Next, the molten glass is poured onto a carbon surface plate, formed into a thickness of 5 mm using a stainless roller, and then cooled to room temperature using a slow cooling furnace set at 700 ° C. to produce a plate-like crystalline glass. did.

  Subsequently, in order to completely remove scratches on the surface of the crystalline glass, the surface was ground and then mirror-polished.

Furthermore, nucleation was performed by holding at 780 ° C. for 3 hours using an electric furnace, and heat treatment was performed at 870 ° C. for 1 hour to precipitate a β-quartz solid solution to obtain crystallized glass. All samples were transparent with no cloudiness observed, and the average linear thermal expansion coefficient at 30 to 750 ° C. was in the range of −10 to 10 × 10 ⁻⁷ / ° C.

  Finally, the surface of the crystallized glass was scratched by the number shown in the table, using a scratching device equipped with a diamond indenter that shows the exact amount of displacement.

  The crystal seeds were evaluated using an X-ray diffractometer (Rigaku, RINT2100).

  For the thermal expansion coefficient, the sample was processed into a solid bar of 50 mm × 5 mmφ, and the average linear thermal expansion coefficient in a temperature range of 30 to 750 ° C. was measured.

  The average crystallinity is determined by multiple peak separation of the scattering intensity area of the crystalline glass before crystallization and the crystal peak area of the crystallized glass measured using an X-ray diffractometer with a diffraction angle 2θ of 10 to 60 °. It calculated | required from the value calculated using the method.

  The thickness of the glass rich layer was measured using an atomic force microscope (NanoScope manufactured by Digital Instruments).

  The amount of β-OH was measured using an infrared spectroscope (SpeckinGX manufactured by PerkinElmer) and calculated from the above formula.

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

  The acceleration test was evaluated as follows.

  First, 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, lightly covered with a glass plate, and held at 380 ° C. for 60 minutes. Then, the sample was taken out and the external appearance was evaluated visually. A sample in which no crack was observed was indicated by “◎”, a sample in which a slight crack was observed was indicated by “◯”, and a sample in which a crack was markedly recognized was indicated by “X”.

  The mounting test was evaluated as follows.

  First, a sample processed to 50 × 200 × 5 mm was disposed on the front surface 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 evaluated. A sample in which no crack was observed was indicated by “◯”, and a sample in which a crack was significantly recognized was indicated by “x”.

Next, the mirror-polished crystalline glass (50 × 200 × 5 mm) prepared in Sample 1 was crystallized and packed in an environment where dust was 1.5 mg / m ³ , and the crystallized glass was used as Sample 7. .

  In addition, a nucleation is performed by holding at 780 ° C. for 3 hours using an electric furnace, and heat treatment is performed at 870 ° C. for 1 hour to produce crystallized glass on which β-quartz solid solution is deposited, and then a sheet made of polyethylene foam (150 × 300 × 1 mm) and packed in a flat manner so as to protrude 2 cm or more from each edge of the crystallized glass.

Sample 8 was crystallized and packed in an environment where the dust was 5 mg / m ³ . However, it was produced in the same manner as Sample 7 except that it was washed with distilled water after crystallization and before packing.

Sample 9 was prepared in the same manner as Sample 7 except that it was crystallized and packed in an environment where the dust was 5 mg / m ³ .

The number of scratches having a length of 1 μm or more on the surfaces of Samples 7 to 9 was measured using an electron microscope, and the number per 1 cm ² was calculated.

  Moreover, acid resistance was evaluated by said method.

  As is clear from Table 1, in samples 1 to 5 as examples, acid resistance was good both in the acceleration test and in the mounting test.

  On the other hand, in Sample 6 as a comparative example, fine cracks were generated both in the acceleration test and in the mounting test, and the acid resistance was not sufficient.

Further, as apparent from Table 2, Samples 7 and 8 had scratches having a length of 1 μm or more and 40 pieces / cm ² or less, and the acid resistance was good in both the acceleration test and the mounting test. . On the other hand, Sample 9 had 100 scratches / cm ² of scratches with a length of 1 μm or more. Fine cracks were generated both in the acceleration test and in the mounting test, and the acid resistance was not sufficient.

Claims (2)

The average crystallinity is 65% by mass or more, the glass-rich layer has a thickness of 0.2 μm or more from the surface, and surface scratches of 1 μm or more in length are 70 / cm ² or less on the effective surface. combustion device window and _{Li 2 O-Al 2 O 3} -SiO 2 based transparent crystallized glass. The Li ₂ O—Al ₂ O ₃ —SiO ₂ based transparent crystallized glass for a combustion apparatus window according to claim 1, wherein the β-OH amount is 0.20 / mm or more.