Vacuum composite enamel ceramic and preparation process thereof

Abstract

The present application relates to the technical field of ceramics, and particularly relates to a vacuum composite glaze ceramic and a preparation process thereof. The vacuum composite glaze ceramic comprises a body, the upper part of the body is sequentially covered with an upper ground glaze and a surface glaze, and the lower part of the body is sequentially covered with a lower ground glaze and a surface glaze. The specially treated wollastonite in the surface glaze forms a directional guide structure, which promotes the directional flow of the glaze in cooperation with the vacuum environment, and realizes the differential distribution of vertical lines. The star variable material forms uniform and stable decorative points under vacuum after pretreatment, and the color is stable. The upper ground glaze inhibits the disorderly expansion of cracks with fibrous minerals, and improves the stability. The lower ground glaze forms coordinated decorative defects by matching the expansion of the body and glaze through stress regulation, and takes into account the performance and decoration. The expansion of the body is optimized and matched with the glaze layer to ensure the combination, and the vacuum degassing, zoned glazing and multi-stage vacuum firing are combined to improve the product consistency and the qualified rate, and the overall balance of the decorative effect and the performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramics, in particular to a vacuum composite glaze ceramic and a preparation process thereof. BACKGROUND

[0002] In the existing ceramic glaze decoration, there are often problems of single artistic effect and insufficient differentiation, which is difficult to form a richly layered decorative style. At the same time, the traditional glaze is prone to poor stability, and the glaze layer cracks are prone to disorderly expansion, affecting the use performance; the flow and mineral reaction of the glaze under high temperature are difficult to control, and it is difficult to balance the decoration and structural stability. In addition, the expansion coefficient of the body and the glaze layer is not reasonably matched, which is easy to cause the glaze layer to fall off or defects, further limiting the improvement of the artistic effect of the composite glaze. The glaze melting, gas escaping and reaction regulation in the vacuum environment are complex, which also restricts the development of the composite glaze ceramic. SUMMARY

[0003] An object of the present application is to solve at least the above problems by a vacuum composite glaze ceramic and a preparation process thereof.

[0004] To solve the above technical problems, the technical scheme adopted by the present application is as follows: the vacuum composite glaze ceramic comprises a body, the upper part of the body is covered with upper bottom glaze and surface glaze in sequence, and the lower part of the body is covered with lower bottom glaze and surface glaze in sequence.

[0005] The upper bottom glaze comprises the following raw materials in parts by weight: potassium feldspar 33-38 parts, quartz 14-18 parts, kaolin 11-15 parts, calcite 7-11 parts, phosphorite 2-4 parts, zinc oxide 3-5 parts, volcanic glass 2-3 parts, tourmaline 0.3-0.7 parts, barium carbonate 2-3 parts, serpentine 1-2 parts, and sepiolite 0.8-1.2 parts.

[0006] The lower bottom glaze comprises the following raw materials in parts by weight: potassium feldspar 35-40 parts, quartz 18-20 parts, kaolin 11-15 parts, calcite 7-11 parts, phosphorite 2-4 parts, zinc oxide 3-5 parts, volcanic glass 2-3 parts, tourmaline 0.3-0.7 parts, barium carbonate 2-3 parts, and star material 1.8-3.5 parts.

[0007] The surface glaze comprises the following raw materials in parts by weight: potassium feldspar 36-40 parts, quartz 16-20 parts, kaolin 9-13 parts, calcite 7-11 parts, phosphorite 1-2 parts, wollastonite 4-6 parts, zinc oxide 3-5 parts, tourmaline 0.8-1.2 parts, iron oxide 1-3 parts, manganese oxide 0.4-0.8 parts, titanium white 1-2 parts, zirconium oxide 0.5-1 parts, and spodumene 1-2 parts.

[0008] Preferably, the star material comprises the following raw materials in parts by weight: bubble-forming substance 60-70 parts, and kiln mineral 30-40 parts.

[0009] Preferably, the bubble-forming substance is at least one of dolomite and calcite; the kiln mineral is at least one of cobalt spinel and hercynite.

[0010] Preferably, the star material is pre-fired at 550℃ for 1 hour and ball-milled to D50=20-30 microns.

[0011] Preferably, the body comprises the following raw materials by weight: kaolin 23-28 parts, potassium feldspar 19-24 parts, quartz 17-21 parts, soft clay 11-17 parts, talc 5-9 parts, lepidolite 2-4 parts, spodumene 1-2 parts, glimmer 1-2 parts, zinc oxide 1-2 parts, and volcanic glass 0.5-1.5 parts.

[0012] Preferably, in the upper and lower underglazes, the phosphate rock is ball-milled to D50=30 microns, with a phosphorus pentoxide content of ≥30%; the quartz is classified by air-jet milling to D50=30 microns; and the serpentine is pulverized by air-jet milling to D50=20 microns.

[0013] The preparation process of the vacuum composite glaze ceramic comprises the following steps:

[0014] Step a, body preparation: the body raw materials are prepared by batching, crushing, magnetic separation, ball milling, aging, molding, drying, and then by bisque firing;

[0015] Step b, glaze preparation: the slurries of the underglaze and the overglaze are degassed by vacuum;

[0016] Step c, glazing: the upper underglaze, the lower underglaze, and the overglaze are applied to the body;

[0017] Step d, vacuum firing: the glazed body is fired in a vacuum furnace.

[0018] Preferably, in step c, the glazing process is as follows:

[0019] Upper underglaze application: the upper underglaze is applied to the upper part of the body, and dried at 60℃ for 30 min;

[0020] Lower underglaze application: the lower underglaze is applied to the lower part of the body, and dried at 60℃ for 30 min;

[0021] Overglaze application: the body with the upper and lower underglazes is entirely immersed in the overglaze, and the overglaze covers the entire body, and the overglaze is naturally leveled in an environment of 25-30℃ and a relative humidity of 50-60%.

[0022] Preferably, in step d, the vacuum firing comprises the following steps in sequence:

[0023] Low-temperature preheating stage: the temperature is raised from room temperature to 800℃ at a rate of 5℃ / min, and the vacuum degree is gradually increased to 100 Pa;

[0024] Mineral decomposition stage: from 800℃ to 1100℃ at a rate of 3℃ / min, continue to increase the vacuum degree to 50Pa;

[0025] High temperature melting stage: from 1100℃ to 1250℃ at a rate of 3℃ / min, maintain the vacuum degree 50Pa, keep 1250℃ for 60min;

[0026] Rapid cooling and locking stage: from 1250℃ to 1150℃ at a rate of 10℃ / min, fill in nitrogen to make the pressure in the furnace 50kPa;

[0027] Slow cooling stage: from 1150℃ to 80℃ at a rate of 3℃ / min, keep normal pressure.

[0028] Preferably, the wollastonite in the face glaze is treated by fluidized bed jet mill, the classification wheel rotation speed of the jet mill is controlled to be 800-1200r / min, and the jet mill crushing pressure is controlled to be 0.6-0.8MPa, so that the wollastonite is crushed to D50=5-7 microns.

[0029] It can be known from the above description that the vacuum composite glaze ceramic and the preparation process thereof have the following beneficial effects: the vacuum composite glaze ceramic realizes unique and hierarchical glaze surface artistic effects through differential raw material design and precise process control of the upper glaze, the lower glaze and the face glaze, the upper part and the lower part present significant decorative differences, and the ornamental property is greatly improved; the special treated wollastonite in the face glaze forms a directional guiding structure, cooperates with the vacuum environment to promote the directional flow of the glaze, realizes differential distribution of the vertical lines, and the pre-processed star variable material forms uniform and stable decorative points under the vacuum, and the color stability is good; the upper glaze improves the stability by inhibiting the disorderly expansion of cracks through fibrous minerals, and the lower glaze forms coordinated decorative defects by matching the expansion of the body glaze through stress regulation, which takes into account the glaze layer performance and decorative requirements; the body raw material design optimizes the expansion matching with the glaze layer, guarantees the body glaze combination, and the vacuum degassing, zoned glazing and multi-stage vacuum firing process improve the product consistency and the qualified rate, and the balance between the decorative effect and the performance is realized as a whole. DETAILED DESCRIPTION

[0030] The application will be further described by specific embodiments.

[0031] In order to make the technical means, creative features, purposes and effects of the application easy to understand, the application will be further described in combination with specific embodiments.

[0032] The vacuum composite glaze ceramic comprises a body, the upper part of the body is covered with an upper glaze and a face glaze in sequence, and the lower part of the body is covered with a lower glaze and a face glaze in sequence;

[0033] The upper ground glaze comprises raw materials in the following weight parts: potassium feldspar 33-38 parts, quartz 14-18 parts, kaolin 11-15 parts, calcite 7-11 parts, phosphate rock 2-4 parts, zinc oxide 3-5 parts, volcanic glass 2-3 parts, tourmaline 0.3-0.7 parts, barium carbonate 2-3 parts, serpentine 1-2 parts, sepiolite 0.8-1.2 parts;

[0034] The lower ground glaze comprises raw materials in the following weight parts: potassium feldspar 35-40 parts, quartz 18-20 parts, kaolin 11-15 parts, calcite 7-11 parts, phosphate rock 2-4 parts, zinc oxide 3-5 parts, volcanic glass 2-3 parts, tourmaline 0.3-0.7 parts, barium carbonate 2-3 parts, star material 1.8-3.5 parts; the difference between the upper ground glaze and the lower ground glaze is that the star material is added in the lower ground glaze but not in the upper ground glaze, the star material is an artificial composite mineral composed of bubble-forming substances and kiln-transformed minerals, and is used to form the kiln-transformed star point effect in the lower ground glaze area under high temperature and vacuum, because the bubble-forming substances wrap the kiln-transformed minerals and float up, the vertical lines of the lower ground glaze are more sparse than those of the upper ground glaze due to the interference of the bubble-forming substances with the directional arrangement of the vertical lines. The serpentine and sepiolite are added in the upper ground glaze but not in the lower ground glaze, the fibrous structure of the serpentine and sepiolite can inhibit the disorderly expansion of the glaze layer cracks, so the upper ground glaze is not prone to cracks, while the bubbles generated by the star material in the lower ground glaze float up to form local stress, which causes the cracks in the lower ground glaze area to be more easily formed, and the cracks in the lower ground glaze finally appear through the sparse vertical lines of the lower ground glaze.

[0035] The face glaze comprises the following raw materials by weight: potassium feldspar 36-40 parts, quartz 16-20 parts, kaolin 9-13 parts, calcite 7-11 parts, phosphate rock 1-2 parts, wollastonite 4-6 parts, zinc oxide 3-5 parts, tourmaline 0.8-1.2 parts, iron oxide 1-3 parts, manganese oxide 0.4-0.8 parts, titanium white 1-2 parts, zirconium oxide 0.5-1 part, and spodumene 1-2 parts. In the face glaze, the wollastonite is treated by air flow milling to retain a needle-shaped structure with a high length-diameter ratio (≥25:1), and the needle-shaped structure retention rate is ≥85%; in the high-temperature melting stage, the shearing force generated by the flow of the glaze drives the needle-shaped wollastonite to be oriented and arranged in a vertical downward direction, forming a "vertical guiding framework", and cooperating with the action of gravity to guide the low-viscosity liquid phase to flow preferentially in the vertical direction to form vertical lines; the phosphorus pentoxide contained in the phosphate rock cooperates with the potassium oxide in the potassium feldspar and the calcium oxide in the calcite to reduce the surface energy of the high-temperature liquid phase; the low gas content in the vacuum environment weakens the resistance of the gas to the flow of the liquid phase, further promoting the flow of the low-viscosity liquid phase in the glaze in the direction guided by the wollastonite; the zirconium oxide inhibits the conversion of iron and manganese elements to low valence states, ensuring color stability; the low-viscosity liquid phase wraps the colorant and flows downward, and when cooled, the metal oxide crystallizes and precipitates into a filamentous pattern, thereby presenting a vertical line effect on the face glaze. In the underglaze, the bubble-forming substance of the star-changing material decomposes and releases gas to form bubbles under high temperature and vacuum, the bubbles entrain the kiln-transformed minerals in the underglaze area during the floating process, float to the interface between the underglaze and the face glaze, and some penetrate into the face glaze, and after cooling, due to the stable valence state in the vacuum environment, unique kiln-transformed colors are presented, thereby forming a uniform star point effect in the lower part; the tourmaline releases trace negative ions to promote the uniform distribution of bubbles in the underglaze area; the cracks are mainly distributed in the underglaze area, the vertical lines in the lower part of the face glaze have increased spacing due to the fast flow speed of the glaze, and the bubble-forming substance destroys the formation of the vertical lines, so the cracks of the underglaze are more likely to be presented through the face glaze. The overall effect achieved by the glaze surface is: the upper part is dense vertical lines, the lower part is sparse vertical lines and densely distributed kiln-transformed star points and cracks, and has a unique artistic effect.

[0036] The star-changing material comprises the following raw materials by weight: bubble-forming substance 60-70 parts, and kiln-transformed mineral 30-40 parts. The ratio of the bubble-forming substance and the kiln-transformed mineral is matched to form kiln-transformed star points of uniform size in the underglaze area.

[0037] The bubble-forming substance is at least one of dolomite and calcite; and the kiln-transformed mineral is at least one of cobalt spinel and iron-aluminum spinel. The bubble-forming substance decomposes at high temperature to release carbon dioxide gas to form tiny bubbles, the gas is more easily escaped in a vacuum environment, the buoyancy of the bubbles is enhanced, and the kiln-transformed mineral is further entrained and floated, finally forming kiln-transformed star points at the interface between the underglaze and the face glaze and in the shallow layer of the face glaze.

[0038] The star material is pre-fired at 550°C for 1 hour, and ball milled to D50=20-30 microns. The star material is pre-treated before being added to the underglaze, and pre-firing removes crystal water and volatile impurities to avoid early decomposition of carbonates; ball milling ensures that the bubble-forming material matches the particle size of the kiln minerals, and the bubbles can effectively wrap and float the kiln minerals.

[0039] The body includes the following raw materials by weight: 23-28 parts of kaolin, 19-24 parts of potassium feldspar, 17-21 parts of quartz, 11-17 parts of soft clay, 5-9 parts of talc, 2-4 parts of lepidolite, 1-2 parts of spodumene, 1-2 parts of blue schist, 1-2 parts of zinc oxide, and 0.5-1.5 parts of volcanic glass. In the body, the lithium oxide provided by lepidolite and spodumene, in cooperation with the aluminum oxide provided by blue schist and the magnesium oxide provided by talc, forms a low-expansion phase to regulate the overall expansion characteristics of the body, the difference between the expansion coefficients of the body and the upper glaze is small, the body-glaze bonding property is good, and cracks are less likely to occur; the difference between the expansion coefficients of the body and the lower glaze is large, the body-glaze bonding property is poor, and cracks are more likely to occur.

[0040] In the upper glaze and the lower glaze, the phosphate rock is ball milled to D50=30 microns, and its content of phosphorus pentoxide is ≥30%; the quartz is classified by air jet milling to D50=30 microns; and the serpentine is crushed by air jet milling to D50=20 microns.

[0041] The preparation process of the vacuum composite glaze ceramic includes the following steps:

[0042] Step a, body preparation: the body raw materials are prepared by batching, crushing, magnetic separation, ball milling, aging, shaping, drying, and then biscuit firing;

[0043] Step b, glaze preparation: the slurries of the underglaze and the face glaze are vacuum degassed; the viscosity of the face glaze is adapted to the vertical flow requirements to improve the vertical line forming rate; vacuum degassing is used to remove bubbles in the glaze slurry to avoid pinhole defects on the glaze surface;

[0044] Step c, glazing: the upper underglaze, the lower underglaze, and the face glaze are applied to the body;

[0045] Step d, vacuum firing: the glazed body is placed in a vacuum furnace for firing.

[0046] In step c, the glazing process is as follows:

[0047] Upper underglaze is applied to the upper part of the body: the upper underglaze is applied to the upper part of the body, and dried at 60°C for 30 min; the upper part is the upper region and the lower part is the lower region, with 1 / 3 of the vertical height of the body (calculated from the bottom of the body upwards) as the boundary, and drying ensures the preliminary solidification of the upper underglaze.

[0048] Lower underglaze is applied to the lower part of the body: the lower underglaze is applied to the lower part of the body, and dried at 60°C for 30 min; the same drying is performed to ensure the preliminary solidification of the lower underglaze.

[0049] Body overall glazing: the body with upper and lower bottom glaze is overall immersed in glaze, and the surface glaze covers the whole body. The glaze paste is naturally leveled under the condition of 25-30℃ and relative humidity of 50-60%. The leveling rate of the glaze paste is stable under the temperature and humidity conditions, which improves the consistency of the initial form of the vertical lines and reduces the deviation of the vertical lines in the later firing.

[0050] In step d, the vacuum firing includes the following steps in sequence:

[0051] Low-temperature preheating stage: the temperature is raised from room temperature to 800℃ at a rate of 5℃ / min, and the vacuum degree is gradually increased to 100Pa;

[0052] Mineral decomposition stage: the temperature is raised from 800℃ to 1100℃ at a rate of 3℃ / min, and the vacuum degree is continuously increased to 50Pa; 800-1100℃ is the key interval for the decomposition of bubble-forming substances. This process promotes the decomposition of carbonates in the bubble-forming substances and releases carbon dioxide gas. The vacuum degree is reduced to 50Pa to accelerate the escape of carbon dioxide gas, which entrains the floating of kiln minerals and destroys the continuity of the surface glaze vertical lines. Local stress concentration is formed during the bubble floating process, which promotes the formation of cracks in combination with the high expansion coefficient difference between the body and the lower bottom glaze, and the cracks are visible through the sparse vertical lines; the vacuum environment inhibits the change of valence of metal oxides, so that the kiln star point color is stable and presented;

[0053] High-temperature melting stage: the temperature is raised from 1100℃ to 1250℃ at a rate of 3℃ / min, and the vacuum degree is maintained at 50Pa for 60min at 1250℃; this process promotes the overall formation of surface glaze vertical lines, the bubble floating of lower bottom glaze star change materials to the interface between lower bottom glaze and surface glaze, and the bubble floating in surface glaze;

[0054] Rapid cooling and locking lines stage: the temperature is lowered from 1250℃ to 1150℃ at a rate of 10℃ / min, and nitrogen is filled to 50kPa of pressure in the furnace;

[0055] Slow cooling stage: the temperature is lowered from 1150℃ to 80℃ at a rate of 3℃ / min, and the pressure is maintained at normal pressure.

[0056] The wollastonite in the face glaze is treated by a fluidized bed jet mill, the classification wheel rotation speed of the jet mill is controlled to be 800-1200 r / min, and the jet mill crushing pressure is controlled to be 0.6-0.8 MPa, so that the wollastonite is crushed to have a D50=5-7 microns. In the process, the jet mill of the fluidized bed forms a shearing force through a high-speed airflow, so that the wollastonite is preferentially broken along the crystal cleavage plane, and the transverse damage of the needle-shaped structure is reduced; the classification wheel generates a centrifugal force at a rotation speed of 800-1200 r / min, and screens out the needle-shaped particles with a length-diameter ratio of 25:1 or more, and the particles with a small length-diameter ratio are separated due to insufficient centrifugal force and returned to the crushing area, so that the directional retention of the high length-diameter ratio structure is realized, the problem that the needle-shaped structure is broken and the length-diameter ratio is low due to the dependence on impact crushing in the traditional ball mill is solved, and finally the retention rate of the needle-shaped structure is 85% or more; the treatment improves the strength of the "vertical guiding framework" of the wollastonite during high-temperature melting, and greatly improves the consistency of the directional arrangement of the vertical lines.

[0057] The above are only some specific embodiments of the present application, but the design concept of the present application is not limited thereto, and any non-essential modification of the present application using this concept shall be deemed to be an infringement of the protection scope of the present application.

Claims

1. A vacuum-composite, enamel-ceramic, characterized by: The body is covered with upper bottom glaze and face glaze in sequence in the upper part, and covered with lower bottom glaze and face glaze in sequence in the lower part; The upper bottom glaze comprises the following raw materials by weight: 33-38 parts of potassium feldspar, 14-18 parts of quartz, 11-15 parts of kaolin, 7-11 parts of calcite, 2-4 parts of phosphate rock, 3-5 parts of zinc oxide, 2-3 parts of volcanic glass, 0.3-0.7 parts of tourmaline, 2-3 parts of barium carbonate, 1-2 parts of serpentine, and 0.8-1.2 parts of sepiolite; The lower bottom glaze comprises the following raw materials by weight: 35-40 parts of potassium feldspar, 18-20 parts of quartz, 11-15 parts of kaolin, 7-11 parts of calcite, 2-4 parts of phosphate rock, 3-5 parts of zinc oxide, 2-3 parts of volcanic glass, 0.3-0.7 parts of tourmaline, 2-3 parts of barium carbonate, and 1.8-3.5 parts of star change material; The face glaze comprises the following raw materials by weight: 36-40 parts of potassium feldspar, 16-20 parts of quartz, 9-13 parts of kaolin, 7-11 parts of calcite, 1-2 parts of phosphate rock, 4-6 parts of wollastonite, 3-5 parts of zinc oxide, 0.8-1.2 parts of tourmaline, 1-3 parts of iron oxide, 0.4-0.8 parts of manganese oxide, 1-2 parts of titanium white, 0.5-1 part of zirconium oxide, and 1-2 parts of spodumene; The star change material comprises the following raw materials by weight: 60-70 parts of bubble-forming substance and 30-40 parts of kiln mineral; The bubble-forming substance is at least one of dolomite and calcite; and the kiln mineral is at least one of cobalt spinel and iron-aluminum spinel; The body comprises the following raw materials by weight: 23-28 parts of kaolin, 19-24 parts of potassium feldspar, 17-21 parts of quartz, 11-17 parts of soft clay, 5-9 parts of talc, 2-4 parts of lepidolite, 1-2 parts of spodumene, 1-2 parts of blue schist, 1-2 parts of zinc oxide, and 0.5-1.5 parts of volcanic glass; The wollastonite in the face glaze is treated by fluidized bed jet mill, the classification wheel rotation speed of the jet mill is controlled to be 800-1200 r / min, and the jet mill crushing pressure is controlled to be 0.6-0.8 MPa, so that the wollastonite is crushed to have a D50=5-7 microns.

2. The vacuum-composite enameled ceramic according to claim 1, characterized in that: The star change material is pre-fired at 550℃ for 1 hour, ball-milled to have a D50=20-30 microns.

3. The vacuum-composite enameled ceramic according to claim 1, characterized in that: In the upper bottom glaze and the lower bottom glaze, the phosphate rock is ball-milled to have a D50=30 microns, and the content of the phosphorus pentoxide is ≥30%; the quartz is treated by classification of the jet mill to have a D50=30 microns; and in the upper bottom glaze, the serpentine is crushed by the jet mill to have a D50=20 microns.

4. Process for the production of vacuum-composite glazed ceramic according to any one of claims 1-3, characterized in that, The method comprises the following steps: Step a, body preparation: the body raw materials are prepared by batching, crushing, magnetic separation, ball milling, aging, molding, drying, and then body firing; Step b, glaze preparation: the slurries of the upper bottom glaze, the lower bottom glaze, and the face glaze are all vacuum-deaerated; Step c, glazing: the upper bottom glaze, the lower bottom glaze, and the face glaze are applied on the body; Step d, vacuum firing: the body after glazing is placed in a vacuum furnace for firing.

5. The process for the preparation of vacuum-compounded enamel-ceramic according to claim 4, characterized in that: In the step c, the glazing process is as follows: Upper bottom glaze is applied on the upper part of the body, and the body is dried at 60℃ for 30 min; Lower bottom glaze is applied on the lower part of the body, and the body is dried at 60℃ for 30 min; Body overall glazing: the body glazed with upper and lower bottom glaze is overall immersed in glaze, and the surface glaze covers the whole body, and the body is naturally leveled at 25-30℃ and under the environment with relative humidity of 50-60%.

6. The process for the preparation of vacuum-compounded enamel-ceramic according to claim 4, characterized in that: In the step d, the vacuum firing successively includes the following steps: Low-temperature preheating stage: increasing the temperature from room temperature to 800℃ at a rate of 5℃ / min, and gradually increasing the vacuum degree to 100Pa; Mineral decomposition stage: increasing the temperature from 800℃ to 1100℃ at a rate of 3℃ / min, and continuously increasing the vacuum degree to 50Pa; High-temperature melting stage: increasing the temperature from 1100℃ to 1250℃ at a rate of 3℃ / min, maintaining the vacuum degree of 50Pa, and keeping the temperature at 1250℃ for 60min; Rapid cooling and locking stage: decreasing the temperature from 1250℃ to 1150℃ at a rate of 10℃ / min, and filling nitrogen gas to make the pressure in the furnace 50kPa; Slow cooling stage: decreasing the temperature from 1150℃ to 80℃ at a rate of 3℃ / min, and keeping normal pressure.