WO2002076719A1 - Method for coating ceramic on quartz surface - Google Patents

Method for coating ceramic on quartz surface Download PDF

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Publication number
WO2002076719A1
WO2002076719A1 PCT/KR2001/001726 KR0101726W WO02076719A1 WO 2002076719 A1 WO2002076719 A1 WO 2002076719A1 KR 0101726 W KR0101726 W KR 0101726W WO 02076719 A1 WO02076719 A1 WO 02076719A1
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WO
WIPO (PCT)
Prior art keywords
quartz
ceramic
coating
quartz tube
ceramic powder
Prior art date
Application number
PCT/KR2001/001726
Other languages
French (fr)
Inventor
Cheol-Hwan Cho
Original Assignee
Cheol-Hwan Cho
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Publication date
Application filed by Cheol-Hwan Cho filed Critical Cheol-Hwan Cho
Publication of WO2002076719A1 publication Critical patent/WO2002076719A1/en

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    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C17/00—Surface treatment of glass, not in the form of fibres or filaments, by coating
    • C03C17/22—Surface treatment of glass, not in the form of fibres or filaments, by coating with other inorganic material
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C17/00—Surface treatment of glass, not in the form of fibres or filaments, by coating
    • C03C17/22—Surface treatment of glass, not in the form of fibres or filaments, by coating with other inorganic material
    • C03C17/23—Oxides
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2218/00—Methods for coating glass
    • C03C2218/30—Aspects of methods for coating glass not covered above
    • C03C2218/31—Pre-treatment

Definitions

  • the present invention relates to a method for coating ceramic on a quartz surface, and more particularly to a method for coating ceramic on the surface of a quartz tube used in a semiconductor manufacturing process or in a variety of heating devices, or on surfaces of diverse quartz plates to efficiently restrict energy from being outwardly discharged from the associated quartz tube or quartz plates, thereby being capable of obtaining a maximum thermal efficiency.
  • quartz exhibits a low thermal expansion coefficient and a low thermal contraction coefficient, so that it has a reduced possibility of being damaged due to heat of high temperature.
  • quartz has mainly been applied to semiconductor manufacturing processes requiring heat of high temperature and diverse heating devices.
  • quartz is particularly used in the form of a quartz tube.
  • a coil is wound around the quartz tube in order to maintain the interior of the quartz tube at a high temperature.
  • a silicon wafer is placed into the heated quartz tube so that it is subjected to a wafer treating process.
  • the wafer treating process which is the most important processing step in a semiconductor manufacturing process, is an impurity diffusion process for doping an impurity in a silicon wafer. That is, the silicon wafer is placed into the quartz tube which is, in turn, placed in an electric furnace.
  • a gas, liquid or solid impurity, for example, P0C1 3 is injected into the quartz tube under the condition in which the quartz tube is heated to a desired high temperature by the electric furnace, so that it is diffused in the silicon wafer.
  • the quartz tube used in the above mentioned process has a drawback in that it exhibits great heat loss . That is, a large part of energy supplied to the quartz tube during the wafer treating process is outwardly discharged, in the form of visible rays, from the quartz tube. Furthermore, heat rays, that is, infrared rays, are transmitted through the quartz tube, thereby degrading the energy efficiency of the quartz tube. For this reason, a large amount of electric power is required to maintain the interior of the quartz tube at a high temperature. In particular, it is difficult to control the quartz tube to have a uniform internal temperature. As a result, there may be a deviation in treating temperature, thereby resulting in an increase in the rate of defective products. Furthermore, the heat loss caused by the outward discharge of heat from the quartz tube increases the temperature of the working room. As a result, there is a problem in that a degradation in the working environment occurs .
  • a technique has been proposed in which a ceramic coating is formed on a quartz tube applied to a heater in order to reduce the amount of visible rays outwardly discharged from the quartz tube while increasing the amount of infrared rays radiated from the quartz tube in accordance with the characteristics of ceramic of absorbing long wavelength radiation such as infrared rays, thereby achieving an increase in energy conservation, so that the heater has an increased thermal efficiency.
  • the ceramic paint coated on the quartz tube is subjected to a high temperature during the heating process, its paint components may be carbonized. Also, the quartz tube may be oxidized at its surface. As a result, the paint coated on the quartz tube may be peeled off. In this case, the quartz tube cannot gain a desired effect of the ceramic coating.
  • an object of the invention is to provide a method for coating ceramic on a quartz surface, which is capable of providing a superior fusibility of ceramic to the quartz surface while restricting an outward discharge of energy from the quartz surface as much as possible, thereby achieving a maximization in energy efficiency.
  • this object is accomplished by providing a method for coating ceramic on a quartz surface, comprising the steps of: heating the quartz surface; and injecting ceramic powder onto the quartz surface at the point of time when the quartz surface is melted, thereby forming a ceramic coating on the quartz surface.
  • Fig. 1 is a view schematically illustrating a heating device used to perform a procedure of forming a ceramic coating on the surface of a quartz tube in accordance with an embodiment of the present invention
  • Fig. 2 is a photograph showing the coated state of a ceramic coating formed under the condition in which oxygen and hydrogen mixed together in a ratio of 1:3.5 based on discharge pressure (kg/cm 2 ) are used
  • Fig. 3 is a photograph showing the coated state of a ceramic coating formed under the condition in which oxygen and hydrogen mixed together in a ratio of 1:1.5 based on discharge pressure (kg/cm 2 ) are used;
  • Fig. 4 is a photograph showing the coated state of a ceramic coating formed under the condition in which oxygen and hydrogen mixed together in a ratio of 1:5 based on discharge pressure (kg/cm 2 ) are used.
  • the present invention provides a method for coating ceramic on a quartz surface, involving the steps of heating the quartz surface, and injecting ceramic powder onto the quartz surface at the point of time when the quartz surface melts, thereby forming a ceramic coating on the quartz surface .
  • the quartz surface As the quartz surface is heated, its color is changed to scarlet. When the quartz surface is further heated, it becomes light red and begins to melt. When ceramic powder is injected onto the quartz surface at this time, a coating is formed on the quartz surface. Where the injection of ceramic powder onto the quartz surface is conducted prior to the point of time when the quartz surface melts, the ceramic powder cannot be effectively fused onto the quartz surface. That is, the ceramic powder may be separated from the quartz surface.
  • Various methods may be used as means for heating the quartz surface in order to melt the quartz surface.
  • flames formed using a mixture of hydrogen (H 2 ) and oxygen (0 2 ) are preferably used.
  • the mixture is prepared by mixing hydrogen and oxygen in a ratio of 1:3.0 to 1:4.0 based on discharge pressure (kg/cm 2 ).
  • the quartz surface is heated using flames formed by hydrogen and oxygen mixed in a ratio of less than 1:3.0 or more than 1:4.0, it cannot reach its melting point. In this case, there is a problem in that no coating is formed.
  • the formation of a flame by a mixture of oxygen and hydrogen may be achieved using a general heating device. It is desirable to supply ceramic powder into the interior of the heating device when the quartz surface is melted by the flame, thereby allowing the ceramic powder to be injected along with the flame in a state in which the ceramic powder is entrained in the flame. That is, the ceramic powder is injected onto the quartz surface while being entrained in the oxygen/hydrogen flame at the point of time when the quartz surface is melted. Accordingly, it is possible to easily form a desired ceramic coating.
  • Fig. 1 is a view schematically illustrating a heating device used to perform the procedure of forming a ceramic coating on the surface of a quartz tube in accordance with an embodiment of the present invention.
  • the heating device includes a device body 10 provided with a hydrogen gas supply passage 11 and an oxygen gas supply passage 12.
  • hydrogen gas supplied through the hydrogen gas supply passage 11 is mixed with oxygen gas supplied through the oxygen gas supply passage 12.
  • the heating device also includes a torch 16 for forming a flame from the mixed gas outwardly discharged from the device body 10.
  • the mixing ratio of oxygen gas and hydrogen gas may be controlled by control valves 13 and 14 respectively installed at the hydrogen gas supply passage 11 and oxygen gas supply passage 12.
  • a separate ceramic powder supply vessel 20 is mounted to the device body 10 so as to supply ceramic powder into the interior of the device body 10.
  • a ceramic powder supply valve 21 is also provided to control the supply of ceramic powder.
  • the supplied ceramic powder is mixed with hydrogen and oxygen gas during the process of forming a mixture of the hydrogen and oxygen gas, and then fed to the torch 16 along with the hydrogen/oxygen mixture.
  • the supply of the ceramic powder is controlled by the ceramic powder supply valve 21 so that the ceramic powder is injected only when its injection is desired.
  • a non-treated straight quartz tube 30 to be coated with ceramic is held by rotatable chucks included in a lathe (not shown), and is rotated 360° by the chucks.
  • the torch 16 of the heating device is positioned at a portion of the quartz tube 30 to be heated.
  • oxygen and hydrogen are supplied to the heating device, thereby forming a flame at the torch 16.
  • the quartz tube 30 is heated by the flame.
  • the quartz tube 30 increases in temperature, its surface is gradually changed to scarlet.
  • the quartz surface becomes light red and begins to melt.
  • the ceramic powder contained in the ceramic powder supply vessel 20 is supplied into the device body 10 under the control of the ceramic powder supply valve 21. As a result, the ceramic powder is entrained in the flame, so that it is injected onto the melted quartz surface, thereby forming a ceramic coating on the quartz surface.
  • ceramic powder baked at a desired temperature is used.
  • the ceramic coating is formed using a non-baked ceramic material, this ceramic material is melted due to a high temperature when it is entrained in the flame.
  • a vitreous layer is formed on the quartz tube 30.
  • the vitreous layer exhibits a severe thermal expansion at a high temperature, thereby causing the quartz tube 30 to be damaged.
  • a variety of ceramic matrices baked at a high temperature of 1,200 to 1,800 °C may be used.
  • the grain size of the ceramic powder may be appropriately adjusted in accordance with the working conditions. However, it is preferred that the ceramic powder have a grain size of 20 to 100 ⁇ m. This grain size is determined, taking into consideration the maximum grain size allowing the ceramic powder to pass through the torch and the thickness of the coating.
  • the coating formed using the ceramic powder has a thickness of 100 to 300 ⁇ m.
  • the ceramic coating has a thickness of more than 300 ⁇ m, a degradation in the energy efficiency of the quartz tube 30 may occur. Also, there is a problem in that the quartz tube 30 may easily be damaged. Where the thickness of the ceramic coating is less than 100 ⁇ m, the energy efficiency of the quartz tube 30 is degraded. Accordingly, it is preferred that the thickness of the ceramic coating be within the above mentioned range.
  • a non-treated straight quartz tube which is denoted by the reference numeral 30 in Fig. 1, was held by rotatable chucks included in a lathe, and was rotated 360° by the chucks.
  • the torch 16 of the heating device was positioned at a portion of the quartz tube 30 to be heated.
  • oxygen and hydrogen were supplied to the heating device in a ratio of 1:3.5 based on discharge pressure (kg/cm 2 ) , thereby forming a flame at the torch 16.
  • the quartz tube 30 was heated by the flame. As the quartz tube 30 increased in temperature, its surface was gradually changed to scarlet. When the quartz surface was further heated, it became light red.
  • the ceramic powder supply valve 21 installed in the device body 10 of the heating device was manipulated to entrain ceramic powder in the flame, so that the ceramic powder was injected onto the quartz surface, thereby forming a ceramic coating having a thickness of 200 ⁇ 10 ⁇ m.
  • the coated state of the ceramic coating formed in the above mentioned fashion is shown in a photograph of Fig. 2. Referring to Fig. 2, it can be seen that the ceramic coating has a good quality.
  • a non-treated straight quartz tube which is denoted by the reference numeral 30 in Fig. 1, was held by the rotatable chucks of the lathe, and was rotated 360° by the chucks.
  • the torch 16 of the heating device was positioned at a portion of the quartz tube 30 to be heated. Thereafter, oxygen and hydrogen were supplied to the heating device in a ratio of 1:1.5 based on discharge pressure t w» « —
  • the quartz tube 30 was heated by the flame. As the quartz tube 30 increased in temperature, its surface was gradually changed to scarlet. Although the quartz surface was further heated, there was no change in the color of the quartz surface. Then, the ceramic powder supply valve 21 installed in the device body 10 of the heating device was manipulated to entrain ceramic powder in the flame, so that the ceramic powder was injected onto the quartz surface, thereby forming a ceramic coating having a thickness of 200 ⁇ 10 ⁇ m.
  • the coated state of the ceramic coating formed in the above mentioned fashion is shown in a photograph of Fig. 3. Referring to Fig. 3, it can be seen that the ceramic coating is separated from the surface of the quartz tube 30.
  • a non-treated straight quartz tube which is denoted by the reference numeral 30 in Fig. 1, was held by the rotatable chucks of the lathe, and was rotated 360° by the chucks.
  • the torch 16 of the heating device was positioned at a portion of the quartz tube 30 to be heated.
  • oxygen and hydrogen were supplied to the heating device in a ratio of 1:5 based on discharge pressure (kg/cm 2 ), thereby forming a flame at the torch 16.
  • the quartz tube 30 was heated by the flame. As the quartz tube 30 increased in temperature, its surface was gradually changed to scarlet. Although the quartz surface was further heated, there was no change in the color of the quartz surface.
  • the ceramic powder supply valve 21 installed in the device body 10 of the heating device was manipulated to entrain ceramic powder in the flame, so that the ceramic powder was injected onto the quartz surface, thereby forming a ceramic coating having a thickness of 200 ⁇ 10 ⁇ m.
  • the coated state of the ceramic coating formed in the above mentioned fashion is shown in a photograph of Fig. 4. Referring to Fig. 4, it can be seen that the ceramic coating is separated from the surface of the quartz tube 30.
  • Examples 4 to 7 Ceramic coatings were formed using the same method as Example 1, except that they had respective thicknesses of 50 ⁇ 10 ⁇ m, 100 ⁇ 10 ⁇ m, 300 ⁇ 10 ⁇ m, and 400 ⁇ 10 ⁇ m.
  • Experiment 1 An experiment was carried out using the quartz tubes respectively formed with the ceramic coatings formed in Example 1 and Examples 4 to 6 along with a quartz tube not coated with ceramic in order to identify respective thermal efficiencies of those quartz tubes.
  • the quartz tubes were heated by coils installed in respective quartz tubes under the same condition.
  • the maximum temperature of each quartz tube heated in the above mentioned fashion was measured using an infrared temperature measuring device (Model TVS-620 manufactured by AVIO Company, Ltd., Japan) .
  • the results of the measurement are described in the following Table 1.
  • Example 4 50 ⁇ 10 ⁇ m 589 °C
  • Example 7 400 ⁇ 10 ⁇ m 547 °C Non-coated - 512 °C
  • the quartz tubes of Examples 1, 5 and 6 each having a coating thickness within the thickness range of the present invention exhibit maximum temperatures higher than that of the non-coated quartz tube by 100 °C or more, respectively.
  • the quartz tube of Example 4 having a coating thickness less than the thickness range of the present invention and the quartz tube of Example 7 having a coating thickness more than the thickness range of the present invention exhibit maximum temperatures higher than that of the non-coated quartz tube, but lower than those of Examples 1, 5 and 6 each having a coating thickness within the thickness range of the present invention, respectively.
  • the method of the present invention in which a ceramic coating is formed on a quartz surface, has been described in conjunction with the embodiment applied to a quartz tube, it may be applied to a quartz surface having a planar shape or quartz surfaces having diverse structures.
  • the present invention provides a method for coating ceramic on a quartz surface, which is capable of efficiently preventing an outward discharge of energy from the quartz surface, thereby achieving a maximization in energy efficiency.

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Abstract

Disclosed is a method for coating ceramic on a quartz surface, for example, the surface of a quartz tube used in a semiconductor manufacturing process or in a variety of heating devices, or surfaces of diverse quartz plates, to efficiently prevent energy from being outwardly discharged from the associated quartz tube or quartz plates, thereby being capable of obtaining a maximum thermal efficiency. The method involves the steps of heating a quartz surface, and injecting ceramic powder onto the quartz surface at a point of time when the quartz surface is melted, thereby forming a ceramic coating on the quartz surface.

Description

METHOD FOR COATING CERAMIC ON QUARTZ SURFACE
Field of the Invention
The present invention relates to a method for coating ceramic on a quartz surface, and more particularly to a method for coating ceramic on the surface of a quartz tube used in a semiconductor manufacturing process or in a variety of heating devices, or on surfaces of diverse quartz plates to efficiently restrict energy from being outwardly discharged from the associated quartz tube or quartz plates, thereby being capable of obtaining a maximum thermal efficiency.
Description of the Related Art
Generally, quartz exhibits a low thermal expansion coefficient and a low thermal contraction coefficient, so that it has a reduced possibility of being damaged due to heat of high temperature. By virtue of such characteristics, quartz has mainly been applied to semiconductor manufacturing processes requiring heat of high temperature and diverse heating devices.
In semiconductor manufacturing processes, quartz is particularly used in the form of a quartz tube. A coil is wound around the quartz tube in order to maintain the interior of the quartz tube at a high temperature. A silicon wafer is placed into the heated quartz tube so that it is subjected to a wafer treating process. The wafer treating process, which is the most important processing step in a semiconductor manufacturing process, is an impurity diffusion process for doping an impurity in a silicon wafer. That is, the silicon wafer is placed into the quartz tube which is, in turn, placed in an electric furnace. A gas, liquid or solid impurity, for example, P0C13, is injected into the quartz tube under the condition in which the quartz tube is heated to a desired high temperature by the electric furnace, so that it is diffused in the silicon wafer.
However, the quartz tube used in the above mentioned process has a drawback in that it exhibits great heat loss . That is, a large part of energy supplied to the quartz tube during the wafer treating process is outwardly discharged, in the form of visible rays, from the quartz tube. Furthermore, heat rays, that is, infrared rays, are transmitted through the quartz tube, thereby degrading the energy efficiency of the quartz tube. For this reason, a large amount of electric power is required to maintain the interior of the quartz tube at a high temperature. In particular, it is difficult to control the quartz tube to have a uniform internal temperature. As a result, there may be a deviation in treating temperature, thereby resulting in an increase in the rate of defective products. Furthermore, the heat loss caused by the outward discharge of heat from the quartz tube increases the temperature of the working room. As a result, there is a problem in that a degradation in the working environment occurs .
In order to solve the problems involved with the quartz tube, a number of research efforts to minimize heat loss have been made. By virtue of such research efforts, various effective methods have been proposed.
In particular, a technique has been proposed in which a ceramic coating is formed on a quartz tube applied to a heater in order to reduce the amount of visible rays outwardly discharged from the quartz tube while increasing the amount of infrared rays radiated from the quartz tube in accordance with the characteristics of ceramic of absorbing long wavelength radiation such as infrared rays, thereby achieving an increase in energy conservation, so that the heater has an increased thermal efficiency.
An example of such a technique is disclosed in Korean Utility Model Application No. 88-10897 entitled "Quartz Tube for Heater Formed with Far-infrared Ceramic Paint Coating" . In accordance with this technique, a desired amount of far- infrared ceramic paint is coated on the outer surface of a quartz tube, and heated at an appropriate temperature for an appropriate time, so that it is cured, thereby forming a ceramic coating. In use, this ceramic-coated quartz tube increases the amount of infrared rays radiated from the quartz tube in accordance with the characteristics of ceramic of absorbing long wavelength radiation, that is, infrared rays, thereby achieving an increase in energy conservation. Accordingly, where the quartz tube is applied to a heater, the thermal efficiency of the heater can be increased.
However, since the ceramic paint coated on the quartz tube is subjected to a high temperature during the heating process, its paint components may be carbonized. Also, the quartz tube may be oxidized at its surface. As a result, the paint coated on the quartz tube may be peeled off. In this case, the quartz tube cannot gain a desired effect of the ceramic coating.
SUMMARY OF THE INVENTION
Therefore, the present invention has been made to solve the above mentioned problems, and an object of the invention is to provide a method for coating ceramic on a quartz surface, which is capable of providing a superior fusibility of ceramic to the quartz surface while restricting an outward discharge of energy from the quartz surface as much as possible, thereby achieving a maximization in energy efficiency.
In accordance with the present invention, this object is accomplished by providing a method for coating ceramic on a quartz surface, comprising the steps of: heating the quartz surface; and injecting ceramic powder onto the quartz surface at the point of time when the quartz surface is melted, thereby forming a ceramic coating on the quartz surface.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the drawings, in which:
Fig. 1 is a view schematically illustrating a heating device used to perform a procedure of forming a ceramic coating on the surface of a quartz tube in accordance with an embodiment of the present invention;
Fig. 2 is a photograph showing the coated state of a ceramic coating formed under the condition in which oxygen and hydrogen mixed together in a ratio of 1:3.5 based on discharge pressure (kg/cm2) are used; Fig. 3 is a photograph showing the coated state of a ceramic coating formed under the condition in which oxygen and hydrogen mixed together in a ratio of 1:1.5 based on discharge pressure (kg/cm2) are used; and
Fig. 4 is a photograph showing the coated state of a ceramic coating formed under the condition in which oxygen and hydrogen mixed together in a ratio of 1:5 based on discharge pressure (kg/cm2) are used.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides a method for coating ceramic on a quartz surface, involving the steps of heating the quartz surface, and injecting ceramic powder onto the quartz surface at the point of time when the quartz surface melts, thereby forming a ceramic coating on the quartz surface .
As the quartz surface is heated, its color is changed to scarlet. When the quartz surface is further heated, it becomes light red and begins to melt. When ceramic powder is injected onto the quartz surface at this time, a coating is formed on the quartz surface. Where the injection of ceramic powder onto the quartz surface is conducted prior to the point of time when the quartz surface melts, the ceramic powder cannot be effectively fused onto the quartz surface. That is, the ceramic powder may be separated from the quartz surface.
Various methods may be used as means for heating the quartz surface in order to melt the quartz surface. In accordance with the present invention, flames formed using a mixture of hydrogen (H2) and oxygen (02) are preferably used. The mixture is prepared by mixing hydrogen and oxygen in a ratio of 1:3.0 to 1:4.0 based on discharge pressure (kg/cm2). Where the quartz surface is heated using flames formed by hydrogen and oxygen mixed in a ratio of less than 1:3.0 or more than 1:4.0, it cannot reach its melting point. In this case, there is a problem in that no coating is formed.
Flame formed by a mixture of oxygen and propane gas or a mixture of oxygen and ethylene gas cannot heat the quartz surface to a temperature sufficient to make the quartz surface melt. In this case, an incomplete ceramic coating is formed. As a result, there may be a phenomenon in which the ceramic powder of the ceramic coating is separated from the quartz surface without being fused onto the quartz surface.
The formation of a flame by a mixture of oxygen and hydrogen may be achieved using a general heating device. It is desirable to supply ceramic powder into the interior of the heating device when the quartz surface is melted by the flame, thereby allowing the ceramic powder to be injected along with the flame in a state in which the ceramic powder is entrained in the flame. That is, the ceramic powder is injected onto the quartz surface while being entrained in the oxygen/hydrogen flame at the point of time when the quartz surface is melted. Accordingly, it is possible to easily form a desired ceramic coating.
Now, the procedure of forming a ceramic coating on a quartz surface in accordance with the present invention will be described in detail, with reference to the annexed drawings .
Fig. 1 is a view schematically illustrating a heating device used to perform the procedure of forming a ceramic coating on the surface of a quartz tube in accordance with an embodiment of the present invention. As shown in Fig. 1, the heating device includes a device body 10 provided with a hydrogen gas supply passage 11 and an oxygen gas supply passage 12. In the device body 10, hydrogen gas supplied through the hydrogen gas supply passage 11 is mixed with oxygen gas supplied through the oxygen gas supply passage 12. The heating device also includes a torch 16 for forming a flame from the mixed gas outwardly discharged from the device body 10. The mixing ratio of oxygen gas and hydrogen gas may be controlled by control valves 13 and 14 respectively installed at the hydrogen gas supply passage 11 and oxygen gas supply passage 12. In accordance with the present invention, a separate ceramic powder supply vessel 20 is mounted to the device body 10 so as to supply ceramic powder into the interior of the device body 10. A ceramic powder supply valve 21 is also provided to control the supply of ceramic powder. In accordance with such a configuration, the supplied ceramic powder is mixed with hydrogen and oxygen gas during the process of forming a mixture of the hydrogen and oxygen gas, and then fed to the torch 16 along with the hydrogen/oxygen mixture. The supply of the ceramic powder is controlled by the ceramic powder supply valve 21 so that the ceramic powder is injected only when its injection is desired.
Now, the method of the present invention for forming a ceramic coating on a quartz surface using the heating device having the above mentioned configuration will be described.
First, a non-treated straight quartz tube 30 to be coated with ceramic is held by rotatable chucks included in a lathe (not shown), and is rotated 360° by the chucks. In this state, the torch 16 of the heating device is positioned at a portion of the quartz tube 30 to be heated. Thereafter, oxygen and hydrogen are supplied to the heating device, thereby forming a flame at the torch 16. The quartz tube 30 is heated by the flame. As the quartz tube 30 increases in temperature, its surface is gradually changed to scarlet. When the quartz surface is further heated, it becomes light red and begins to melt. At this time, the ceramic powder contained in the ceramic powder supply vessel 20 is supplied into the device body 10 under the control of the ceramic powder supply valve 21. As a result, the ceramic powder is entrained in the flame, so that it is injected onto the melted quartz surface, thereby forming a ceramic coating on the quartz surface.
For the ceramic powder, ceramic powder baked at a desired temperature is used. Where the ceramic coating is formed using a non-baked ceramic material, this ceramic material is melted due to a high temperature when it is entrained in the flame. As a result, a vitreous layer is formed on the quartz tube 30. The vitreous layer exhibits a severe thermal expansion at a high temperature, thereby causing the quartz tube 30 to be damaged. Furthermore, it is impossible to form a ceramic coating having a uniform thickness. Accordingly, it is desirable to use ceramic powder baked at a desired temperature . In accordance with the present invention, a variety of ceramic matrices baked at a high temperature of 1,200 to 1,800 °C may be used.
The grain size of the ceramic powder may be appropriately adjusted in accordance with the working conditions. However, it is preferred that the ceramic powder have a grain size of 20 to 100 μm. This grain size is determined, taking into consideration the maximum grain size allowing the ceramic powder to pass through the torch and the thickness of the coating.
Preferably, the coating formed using the ceramic powder has a thickness of 100 to 300 μm. Where the ceramic coating has a thickness of more than 300 μm, a degradation in the energy efficiency of the quartz tube 30 may occur. Also, there is a problem in that the quartz tube 30 may easily be damaged. Where the thickness of the ceramic coating is less than 100 μm, the energy efficiency of the quartz tube 30 is degraded. Accordingly, it is preferred that the thickness of the ceramic coating be within the above mentioned range.
Where ceramic powder previously heat-treated to be baked is used to form the ceramic coating on the outer surface of the quartz tube 30 in the above mentioned fashion, various advantages are obtained. That is, it is possible to reduce the thermal expansion of the ceramic coating while maximizing the energy efficiency of the quartz tube 30 by virtue of far- infrared rays emitted from the ceramic coating. In particular, the ceramic coating efficiently restricts energy from being outwardly discharged from the quartz tube, thereby reducing loss of energy. As a result, there is reduced waste of electric power.
Hereinafter, the present invention will be described in detail, in conjunction with various examples. These examples are provided only for illustrative purposes, and the present invention is not to be construed as being limited to those examples.
Example 1
A non-treated straight quartz tube, which is denoted by the reference numeral 30 in Fig. 1, was held by rotatable chucks included in a lathe, and was rotated 360° by the chucks. In this state, as shown in Fig. 1, the torch 16 of the heating device was positioned at a portion of the quartz tube 30 to be heated. Thereafter, oxygen and hydrogen were supplied to the heating device in a ratio of 1:3.5 based on discharge pressure (kg/cm2) , thereby forming a flame at the torch 16. The quartz tube 30 was heated by the flame. As the quartz tube 30 increased in temperature, its surface was gradually changed to scarlet. When the quartz surface was further heated, it became light red. At this time, the ceramic powder supply valve 21 installed in the device body 10 of the heating device was manipulated to entrain ceramic powder in the flame, so that the ceramic powder was injected onto the quartz surface, thereby forming a ceramic coating having a thickness of 200 ± 10 μm.
The coated state of the ceramic coating formed in the above mentioned fashion is shown in a photograph of Fig. 2. Referring to Fig. 2, it can be seen that the ceramic coating has a good quality.
Example 2
A non-treated straight quartz tube, which is denoted by the reference numeral 30 in Fig. 1, was held by the rotatable chucks of the lathe, and was rotated 360° by the chucks. In this state, as shown in Fig. 1, the torch 16 of the heating device was positioned at a portion of the quartz tube 30 to be heated. Thereafter, oxygen and hydrogen were supplied to the heating device in a ratio of 1:1.5 based on discharge pressure t w» « —
(kg/cm2), thereby forming a flame at the torch 16. The quartz tube 30 was heated by the flame. As the quartz tube 30 increased in temperature, its surface was gradually changed to scarlet. Although the quartz surface was further heated, there was no change in the color of the quartz surface. Then, the ceramic powder supply valve 21 installed in the device body 10 of the heating device was manipulated to entrain ceramic powder in the flame, so that the ceramic powder was injected onto the quartz surface, thereby forming a ceramic coating having a thickness of 200 ± 10 μm.
The coated state of the ceramic coating formed in the above mentioned fashion is shown in a photograph of Fig. 3. Referring to Fig. 3, it can be seen that the ceramic coating is separated from the surface of the quartz tube 30.
Example 3
A non-treated straight quartz tube, which is denoted by the reference numeral 30 in Fig. 1, was held by the rotatable chucks of the lathe, and was rotated 360° by the chucks. In this state, as shown in Fig. 1, the torch 16 of the heating device was positioned at a portion of the quartz tube 30 to be heated. Thereafter, oxygen and hydrogen were supplied to the heating device in a ratio of 1:5 based on discharge pressure (kg/cm2), thereby forming a flame at the torch 16. The quartz tube 30 was heated by the flame. As the quartz tube 30 increased in temperature, its surface was gradually changed to scarlet. Although the quartz surface was further heated, there was no change in the color of the quartz surface. Then, the ceramic powder supply valve 21 installed in the device body 10 of the heating device was manipulated to entrain ceramic powder in the flame, so that the ceramic powder was injected onto the quartz surface, thereby forming a ceramic coating having a thickness of 200 ± 10 μm.
The coated state of the ceramic coating formed in the above mentioned fashion is shown in a photograph of Fig. 4. Referring to Fig. 4, it can be seen that the ceramic coating is separated from the surface of the quartz tube 30.
Referring to Examples 1 to 3 , it can be understood that when hydrogen and oxygen are mixed together in a ratio less than or more than the ratio range of the present invention, the surface of the quartz tube cannot reach its melting point, so that the ceramic coating formed on the quartz surface is incompletely bonded, to be separated from the quartz surface, whereas when hydrogen and oxygen are mixed together in a ratio within the ratio range of the present invention, a completely bonded ceramic coating is formed on the quartz surface.
Examples 4 to 7 Ceramic coatings were formed using the same method as Example 1, except that they had respective thicknesses of 50 ± 10 μm, 100 ± 10 μm, 300 ± 10 μm, and 400 ± 10 μm.
Experiment 1 An experiment was carried out using the quartz tubes respectively formed with the ceramic coatings formed in Example 1 and Examples 4 to 6 along with a quartz tube not coated with ceramic in order to identify respective thermal efficiencies of those quartz tubes. In the experiment, the quartz tubes were heated by coils installed in respective quartz tubes under the same condition. The maximum temperature of each quartz tube heated in the above mentioned fashion was measured using an infrared temperature measuring device (Model TVS-620 manufactured by AVIO Company, Ltd., Japan) . The results of the measurement are described in the following Table 1.
Table 1
Quartz Tubes Thickness of Coating Maximum Temperature Example 1 200 ± 10 μm 688 °C
Example 4 50 ± 10 μm 589 °C
Example 5 100 ± 10 μm 667 °C
Example 6 300 ± 10 μm 654 °C
Example 7 400 ± 10 μm 547 °C Non-coated - 512 °C
Referring to Table 1, it can be seen that the quartz tubes of Examples 1, 5 and 6 each having a coating thickness within the thickness range of the present invention exhibit maximum temperatures higher than that of the non-coated quartz tube by 100 °C or more, respectively. On the other hand, the quartz tube of Example 4 having a coating thickness less than the thickness range of the present invention and the quartz tube of Example 7 having a coating thickness more than the thickness range of the present invention exhibit maximum temperatures higher than that of the non-coated quartz tube, but lower than those of Examples 1, 5 and 6 each having a coating thickness within the thickness range of the present invention, respectively. Although the method of the present invention, in which a ceramic coating is formed on a quartz surface, has been described in conjunction with the embodiment applied to a quartz tube, it may be applied to a quartz surface having a planar shape or quartz surfaces having diverse structures. As apparent from the above description, the present invention provides a method for coating ceramic on a quartz surface, which is capable of efficiently preventing an outward discharge of energy from the quartz surface, thereby achieving a maximization in energy efficiency. Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

WHAT IS CLAIMED IS:
1. A method for coating ceramic on a quartz surface, comprising the steps of : heating the quartz surface by a flame; and injecting ceramic powder onto the quartz surface at a point of time when the quartz surface is melted, thereby forming a ceramic coating on the quartz surface.
2. The method according to claim 1, wherein the flame is formed by a mixture of hydrogen (H2) and oxygen (02) .
3. The method according to claim 2, wherein the injection of the ceramic powder is carried out by entraining the ceramic powder in the flame at the point of time when the quartz surface is melted.
4. The method according to any one of claims 1 to 3 , wherein the flame is formed by hydrogen (H2) and oxygen (02) mixed in a ratio of 1:3.0 to 1:4.0 based on discharge pressure (kg/cm2) .
5. The method according to any one of claims 1 to 3 , wherein the ceramic powder has a grain size of 20 to 100 μm.
6. The method according to claim 4, wherein the ceramic powder has a grain size of 20 to 100 μm.
7. The method according to claim 5, wherein the ceramic powder comprises ceramic matrices baked at a high temperature of 1,200 to 1,800 °C.
8. The method according to claim 6, wherein the ceramic powder comprises ceramic matrices baked at a high temperature of 1,200 to 1,800 °C.
9. The method according to claim 5, wherein the ceramic coating has a thickness of 100 to 300 μm.
10. The method according to claim 6, wherein the ceramic coating has a thickness of 100 to 300 μm.
11. The method according to claim 8, wherein the ceramic coating has a thickness of 100 to 300 μm.
PCT/KR2001/001726 2001-03-24 2001-10-12 Method for coating ceramic on quartz surface WO2002076719A1 (en)

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