A method for preparing a cobalt-free black glaze for heat-resistant pots and its decorative products.
Cobalt-free black glaze was prepared by using the Cu2O-Al2O3-SiO2 system, which solved the problems of cobalt resource dependence and compatibility, and achieved a low-cost, stable color and high-strength heat-resistant glaze suitable for spodumene ceramic bodies.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JINGDEZHEN CERAMIC UNIV
- Filing Date
- 2026-04-23
- Publication Date
- 2026-05-26
AI Technical Summary
Existing black glazes for heat-resistant pots rely on cobalt resources, resulting in high costs and significant environmental risks. Furthermore, cobalt-free alternatives have poor compatibility with lithium-based glazes, leading to unstable color development and making large-scale application difficult.
Using the Cu2O-Al2O3-SiO2 system, with cuprous oxide as the copper source, and melting under a neutral or weakly reducing atmosphere, a cobalt-free black glaze is prepared by forming the synergistic effect of Cu+, Cu2+, Fe2+, Fe3+, Mn2+, and Mn3+ ions, ensuring that the thermal expansion matches the spodumene-based body and that the color is stable.
It achieves low cost and low environmental risk of cobalt-free black glaze, matching thermal expansion coefficient, and the compressive stress between the glaze and the body improves product strength, has stable color, strong process compatibility, and is suitable for large-scale production.
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Figure CN122079488A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of ceramic glaze technology, and in particular to a method for preparing a cobalt-free black glaze for heat-resistant pots and its decorative products. Background Technology
[0002] Heat-resistant cookware has become widely used in kitchens in recent years, and its core performance requirement is the ability to withstand drastic temperature changes without cracking. To achieve this, both the body and glaze of the heat-resistant cookware must possess low thermal expansion characteristics. Currently, the mainstream technical solution in the industry is to introduce lithium-based raw materials (such as spodumene and petalite) into the body and glaze, utilizing lithium ions to form low-expansion crystals such as β-spodumene at high temperatures, thereby reducing the coefficient of thermal expansion of the ceramic to 2.5 × 10⁻⁶. -6 Below / ℃, it meets the requirements for use in cases of rapid heat change.
[0003] In terms of glazes, traditional black heat-resistant pots often employ a multiphase system of "lithium-based low-expansion glaze + cobalt-containing spinel colorant." The lithium-based glaze provides the low-expansion matrix, while the cobalt-containing colorant (mainly Co-Al, Co-Cr, and Co-Fe spinels) provides the black color. While this system meets basic heat resistance and decorative requirements, it has several significant drawbacks. First, there is the issue of cobalt resource dependence and cost. Cobalt is a scarce strategic resource with highly concentrated global reserves, resulting in persistently high and volatile prices. Cobalt-based colorants, represented by cobalt oxide, account for over 60% of the raw material cost of black glazes, leading to high production costs and challenges to supply chain security. Second, there are environmental and health risks associated with cobalt. Although most cobalt and its compounds are fixed in the glaze layer during firing, trace amounts still leach out over long-term use. With increasingly stringent environmental regulations on heavy metal leaching limits for ceramic products, cobalt-containing glazes face increasing compliance pressure. Third, there is the compatibility challenge between cobalt-free alternatives and lithium-based glazes. To address these issues, the industry has attempted to develop various cobalt-free black pigments, primarily including Fe-Cr-Mn-Ni spinel-type pigments and encapsulated carbon black-type pigments. However, these cobalt-free pigments generally exhibit severe color instability when applied to lithium-based low-expansion glazes. Research and analysis by the inventors have revealed that the root cause lies in the fact that the highly active lithium ions in the lithium-based glaze react with the crystal structure of the spinel-type pigment during high-temperature firing, displacing or destroying the occupancy of color-producing ions in the pigment lattice, leading to fading of black, reddening, browning, or uneven coloring. Simultaneously, the reaction of lithium ions with pigment components generates new low-expansion crystals, further diluting the coloring effect. This compatibility challenge makes it difficult to achieve large-scale application of spinel-type and encapsulated cobalt-free pigments in the field of heat-resistant cookware using lithium-based glazes. Non-lithium-based glazes, due to their mismatch in thermal expansion, are also difficult to apply in the heat-resistant cookware industry. Therefore, the industry must continue to rely on cobalt-containing lithium-based glaze solutions.
[0004] Currently, there is no technical solution for a heat-resistant black glaze for pots that can simultaneously meet the requirements of being free of cobalt and other heavy metal colorants, having a coefficient of thermal expansion that matches that of spodumene-based green bodies, exhibiting stable color in lithium-based glaze systems, and having a preparation process compatible with existing ceramic production equipment. Therefore, developing a new type of black glaze that can fundamentally solve the above problems has significant industrial value and application prospects. Summary of the Invention
[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a cobalt-free black glaze for heat-resistant pots that is simple in process, low in cost, and can be mass-produced, as well as the decorative products thereof.
[0006] This invention is achieved through the following technical solution: a method for preparing a cobalt-free black glaze for heat-resistant pots, characterized by comprising the following steps: Step 1: Melting of the frit: Weigh the raw materials according to the following mass percentages: cuprous oxide 21-39%, aluminum oxide 13-29%, silicon dioxide 32-65%, iron oxide 0.6-3.0%, manganese oxide 0.3-2.0%. Mix them evenly and place them in a corundum crucible. Heat the mixture at a rate of 5-10℃ / min to a temperature of 1510-1630℃ and melt it. Hold the mixture at this temperature for 1-6 hours. During the melting process, control the atmosphere to be neutral or weakly reducing. After the glass melt is uniformly melted, quench it with water to obtain a black glass frit. Step 2: Crushing and sieving: Dry and crush the black glass frit obtained in Step 1, and pass it through a 150-320 mesh sieve to obtain black glass powder; Step 3: Glaze preparation: Mix the obtained black glass powder with water at a mass percentage of 100:50 to 100:65, add 3 to 9% kaolin and 0 to 0.3% suspending agent or dispersant, ball mill until uniform, and prepare glaze.
[0007] In step one, the aluminum oxide and silicon dioxide are derived from pure oxides or natural minerals.
[0008] In step one, a neutral or weakly reducing atmosphere is achieved by adding reducing carbon powder, using a sealed crucible with a lid, or controlling the oxygen concentration in the kiln.
[0009] The suspending agent in step three is sodium carboxymethyl cellulose, and the dispersant is sodium tripolyphosphate.
[0010] A product decorated with a cobalt-free black glaze for a heat-resistant pot is characterized in that the glaze obtained in step three of claim 1 is applied to the surface of a bisque-fired spodumene heat-resistant pot body, dried, and then fired at 1210-1260°C for 0.5-3 hours to obtain a black glaze layer.
[0011] The specific gravity of the glaze is 1.65–1.80 g / cm³. 3 The glazing method is spraying, dipping, or pouring glaze, and the glaze thickness is 0.3–0.7 mm.
[0012] The black glaze is a copper-aluminum-silicon system black glass.
[0013] The average coefficient of thermal expansion of the black glass from room temperature to 600°C is 1.26 × 10⁻⁶. -6 ~1.63×10 -6 / ℃.
[0014] The black glass's color is determined by Cu. + Cu 2+ Fe 2+ Fe 3+ Mn 2+ Mn 3+ Formed through the synergistic effect of ions.
[0015] The gloss of the black glass is 82-88. According to the QB / T 2580-2018 6.5 standard, the thermal shock resistance test is carried out. After being dry-fired at 450℃ and then rapidly cooled in water at 20℃, no cracks are found after 1 to 3 consecutive tests.
[0016] This invention uses the Cu2O-Al2O3-SiO2 system as the frit glaze and cuprous oxide as the copper source. Since the copper in this raw material is monovalent, its ionic radius is approximately 77 pm, which is basically consistent with the lithium ion radius (76 pm) in low-thermal-expansion spodumene. Furthermore, monovalent copper ions exist as a network exosome in the glass structure and cannot connect to the network structural units [SiO4] or [AlO4]. Therefore, the Cu2O-Al2O3-SiO2 system and Li2O-Al2O3-SiO2 glass not only have highly similar network structures but also both have very low coefficients of thermal expansion. Thus, the Cu2O-Al2O3-SiO2 system glass frit can theoretically be used as a ceramic glaze with a low coefficient of thermal expansion. Even if the glaze precipitates crystals similar to spodumene structure when the body is reheated, the low thermal expansion characteristics of the glaze will not change. The radius of divalent copper ions is approximately 73 pm, which is not significantly different from that of lithium ions. However, divalent copper ions can connect two network structural units [SiO4] or [AlO4] in the glass structure, resulting in a more compact network structure. This leads to a network structure characteristic completely different from that of Li2O-Al2O3-SiO2 glass, and also causes it to lose the low thermal expansion properties of Li2O-Al2O3-SiO2 glass. Therefore, to achieve the preparation of low thermal expansion glazes, cuprous oxide must be used as the copper source instead of copper oxide, and melting must be carried out in a neutral or weakly reducing atmosphere.
[0017] In the Cu2O-Al2O3-SiO2 system, monovalent copper ions are unstable at high temperatures and readily form zero-valent metallic copper colloids under reducing or neutral atmospheres, thus exhibiting a red or pale yellow color. However, monovalent copper ions on the surface of glass or glaze in this system are easily oxidized to divalent copper ions upon contact with oxygen, resulting in a blue-green or even emerald green color. This color is also observed in Fe... 2+ Fe 3+ Mn 2+ Mn 3+ The final appearance is black due to the synergistic effect of color-developing ions, thus achieving an appearance similar to adding cobalt black pigment or black spinel pigment.
[0018] Compared with the prior art, the present invention has the following beneficial effects.
[0019] 1. Achieve cobalt-free black coloring, reducing costs and environmental risks.
[0020] This invention abandons traditional cobalt-containing colorants and utilizes Cu in a copper-aluminum-silicon glass system. + Cu 2+ Fe 2+ Fe 3+ Mn 2+ Mn 3+ The synergistic effect of multiple ions forms a stable black color under a neutral to weakly reducing atmosphere. It contains no cobalt or other heavy metal colorants, which significantly reduces raw material costs and avoids dependence on cobalt resources and its potential environmental and health risks.
[0021] 2. The coefficient of thermal expansion is perfectly matched with the blank, improving product performance.
[0022] The black glass powder obtained by this invention has an average coefficient of thermal expansion of 1.26 × 10⁻⁶ from room temperature to 600°C. -6 ~1.63×10 -6 The temperature is / ℃, slightly lower than the coefficient of thermal expansion of spodumene-based low-thermal-expansion ceramic bodies. After firing, a beneficial compressive stress state is formed between the glaze layer and the body, effectively improving the overall strength and thermal shock resistance of the heat-resistant pot, and extending the product's service life.
[0023] 3. Fundamentally solve the problem of reaction between lithium glaze and pigment.
[0024] Traditional cobalt-free colorants are difficult to stably color in lithium-based glazes due to the high reactivity of lithium ions. This invention employs a non-lithium frit glaze solution, uniformly dissolving coloring ions in a glass network structure. The glaze contains no lithium elements or spinel-structured coloring crystals, and lithium ions in the body do not affect the glaze's color. This fundamentally avoids the problem of colorant particles being eroded by lithium ions, ensuring the stability of the black color and the reliability of the glaze layer performance.
[0025] 4. It has strong process compatibility and is suitable for industrial production.
[0026] The raw materials used in this invention are all bulk industrial raw materials with wide availability; the process steps such as frit melting, crushing, glazing, and firing are highly compatible with existing ceramic production equipment, requiring no additional special equipment, making it easy to achieve large-scale production and having good industrialization prospects. Attached Figure Description
[0027] Figure 1 The graph shows the thermal expansion coefficient curve of the glaze layer prepared in Example 3. Detailed Implementation
[0028] To further illustrate the present invention, the technical means and effects adopted to achieve the intended purpose of the invention, the present invention will be described in detail below with reference to preferred embodiments.
[0029] Example 1 A method for preparing a cobalt-free black glaze for heat-resistant pots includes the following steps: The raw materials were weighed according to the following mass percentages: cuprous oxide 21%, aluminum oxide 18.4%, silicon dioxide 58%, iron oxide 0.6%, and manganese oxide 2%. All raw materials were pure oxides. After being mixed evenly, the mixture was placed in a corundum crucible and heated to 1510℃ at a rate of 5℃ / min. The temperature was maintained for 6 hours. During the melting process, the melting atmosphere was controlled to be neutral by sealing the crucible. After the glass melt was uniformly melted, it was quenched with water to obtain a black glass frit. The obtained black glass frit is dried, ball-milled and pulverized, and passed through a 150-mesh sieve to obtain black glass powder. The black glass powder obtained in step two is mixed with water at a mass ratio of 100:60, and kaolin at a mass of 6% of the black glass powder is added. The mixture is ball-milled for 30 minutes to make a glaze.
[0030] The specific gravity of the obtained glaze is 1.65 g / cm³. 3 The glaze was applied to the surface of the bisque-fired spodumene heat-resistant pot body by dipping, with a glaze thickness of 0.3 mm. After drying for 24 hours, the pot was fired at 1210℃ for 3 hours to obtain a black glaze.
[0031] The black glaze is a copper-aluminum-silicon system black glass, with an average coefficient of thermal expansion of 1.26 × 10⁻⁶ from room temperature to 600°C. -6 / ℃, coloring is due to Cu + Cu 2+ Fe 2+ Fe 3+ Mn 2+ Mn 3+The synergistic effect of ions resulted in a gloss level of 85 for the black glass. Thermal shock resistance was tested according to QB / T 2580-2018 6.5 standard, involving dry burning at 450℃ followed by rapid cooling in 20℃ water; no cracks were observed after three consecutive cycles. Example 2
[0032] A method for preparing a cobalt-free black glaze for heat-resistant pots includes the following steps: The raw materials were weighed according to the following mass percentages: cuprous oxide 22.8%, alumina 29%, silicon dioxide 46.4%, iron oxide 0.6%, and manganese oxide 1.2%. The alumina and some of the silicon dioxide were derived from kaolin, while the rest were pure oxides. After thorough mixing, the mixture was placed in a corundum crucible and melted at 1580℃ at a rate of 10℃ / min for 3.5 hours. A weak reducing atmosphere was maintained during the melting process by adding reducing carbon powder to the furnace. After the glass melt was homogeneous, it was water-quenched to obtain a black glass frit.
[0033] The obtained black glass frit is dried, pulverized by air jet mill, and passed through a 250-mesh sieve. The black glass powder obtained in step two is mixed with water at a mass ratio of 100:50. Kaolin and sodium carboxymethyl cellulose (0.3% by mass) of the black glass powder are added as suspending agents. The mixture is ball-milled for 45 minutes to make a glaze.
[0034] The specific gravity of the obtained glaze is 1.80 g / cm³. 3 The glaze was applied to the surface of the bisque-fired spodumene heat-resistant pot body by dipping, with a glaze thickness of 0.4 mm. After drying for 24 hours, the pot was fired at 1230℃ for 1.5 hours to obtain a black glaze.
[0035] The black glaze is a copper-aluminum-silicon system black glass, with an average coefficient of thermal expansion of 1.63 × 10⁻⁶ from room temperature to 600°C. -6 / ℃, the color of the black glass is determined by Cu + Cu 2+ Fe 2+ Fe 3+ Mn 2+ Mn 3+ The synergistic effect of ions results in a gloss level of 88 for the black glass. Thermal shock resistance was tested according to QB / T 2580-2018 6.5 standard, involving dry burning at 450℃ followed by rapid cooling in 20℃ water; no cracks were observed after two consecutive tests. Example 3
[0036] A method for preparing a cobalt-free black glaze for heat-resistant pots includes the following steps: The raw materials were weighed according to the following mass percentages: cuprous oxide 37%, alumina 26.4%, silicon dioxide 32%, iron oxide 3.0%, and manganese oxide 1.6%. All alumina was replaced with kaolin. The silicon dioxide was derived from pure oxides and silicon dioxide, and the other raw materials were pure oxides. After thorough mixing, the mixture was placed in a corundum crucible and heated to 1630℃ at a rate of 6℃ / min for melting. The temperature was maintained for 1 hour. During melting, the oxygen concentration in the furnace was controlled below 0.5% to achieve a weakly reducing atmosphere. After the glass melt was homogeneous, it was water-quenched to obtain a black glass frit.
[0037] The black glass frit was dried, pulverized using an air jet mill, and passed through a 320-mesh sieve to obtain black glass powder. The black glass powder obtained in step two was mixed with water at a mass ratio of 100:65. Kaolin (9% by mass of the black glass powder) and sodium tripolyphosphate (0.1% by mass) were added as dispersants. The mixture was ball-milled for 60 minutes to prepare a glaze.
[0038] The specific gravity of the obtained glaze is 1.70 g / cm³. 3 The glaze was applied to the surface of a bisque-fired spodumene heat-resistant pot body using a glazing method, with a glaze layer thickness of 0.7 mm. After drying for 24 hours, it was fired at 1260℃ for 0.5 hours to obtain a black glaze layer. The black glaze is a copper-aluminum-silicon system black glass, and the average coefficient of thermal expansion of the glaze glass from room temperature to 600℃ is 1.39 × 10⁻⁶. -6 / ℃, the color of the black glass is determined by Cu + Cu 2+ Fe 2+ Fe 3+ Mn 2+ Mn 3+ The synergistic effect of ions results in a gloss level of 82 for the black glass. Thermal shock resistance was tested according to QB / T 2580-2018 6.5 standard, involving dry burning at 450℃ followed by rapid cooling in 20℃ water; no cracks were observed after three consecutive cycles. Example 4
[0039] A method for preparing a cobalt-free black glaze for heat-resistant pots includes the following steps: The raw materials were weighed according to the following mass percentages: cuprous oxide 39%, aluminum oxide 16%, silicon dioxide 41.6%, iron oxide 2.1%, and manganese oxide 1.3%. All raw materials used were pure oxides. After being mixed evenly, the mixture was placed in a corundum crucible and heated to 1560°C at a rate of 8°C / min. The temperature was maintained for 4 hours. During the melting process, the melting atmosphere was controlled to be neutral by sealing the crucible. After the glass melt was uniformly melted, it was quenched with water to obtain a black glass frit.
[0040] The obtained black glass frit was dried, rapidly pulverized by a high-speed mill, and then ball-milled and passed through a 150-mesh sieve to obtain black glass powder. The obtained black glass powder was mixed with water at a mass ratio of 100:58, and 6% kaolin and 0.2% sodium carboxymethyl cellulose were added as suspending agents. The mixture was ball-milled for 40 minutes to prepare a glaze.
[0041] The specific gravity of the obtained glaze is 1.72 g / cm³. 3 A glaze layer with a thickness of 0.5 mm is formed on the surface of the bisque-fired spodumene heat-resistant pot body by glazing. After drying for 15 hours, the pot body is fired at 1220℃ for 2.5 hours to obtain a black glaze layer.
[0042] The black glaze is a copper-aluminum-silicon system black glass, with an average coefficient of thermal expansion of 1.56 × 10⁻⁶ from room temperature to 600°C. -6 / ℃, coloring is due to Cu + Cu 2+ Fe 2+ Fe 3+ Mn 2+ Mn 3+ The synergistic effect of ions resulted in a gloss level of 84 for the black glass. Thermal shock resistance was tested according to QB / T 2580-2018 6.5 standard; after being dry-fired at 450℃ and then rapidly cooled once in 20℃ water, no cracks were observed. Example 5
[0043] A method for preparing a cobalt-free black glaze for heat-resistant pots includes the following steps: The raw materials were weighed according to the following mass percentages: cuprous oxide 21.1%, alumina 13%, silicon dioxide 65%, iron oxide 0.6%, and manganese oxide 0.3%. All the alumina and some of the silicon dioxide were derived from kaolin, while the rest were pure oxides. All raw materials were mixed thoroughly and placed in a corundum crucible. The temperature was increased to 1600℃ at a rate of 7℃ / min, and the melting time was 2 hours. During the melting process, the oxygen concentration in the furnace was controlled below 0.5% to achieve a weakly reducing atmosphere. After the glass melt was homogeneous, it was water-quenched to obtain a black glass frit.
[0044] The obtained black glass frit was dried, pulverized by air jet mill, and passed through a 320-mesh sieve. The black glass powder was mixed with water at a mass ratio of 100:62. Kaolin (4% by mass of black glass powder) and sodium carboxymethyl cellulose (0.1% by mass) were added as suspending agents. The mixture was ball-milled for 30 minutes to prepare a glaze slurry.
[0045] The specific gravity of the obtained glaze slurry was 1.76 g / cm³. 3A black glaze layer was obtained by applying a glaze to the surface of a bisque-fired cordierite heat-resistant pot body using a glazing method. The glaze layer was 0.6 mm thick. After drying for 20 hours, it was fired at 1250℃ for 1 hour to obtain a black glaze layer. The black glaze is a copper-aluminum-silicon system black glass, and the average coefficient of thermal expansion of the glaze glass from room temperature to 600℃ is 1.49 × 10⁻⁶. -6 / ℃, the color of the black glass is determined by Cu + Cu 2+ Fe 2+ Fe 3+ Mn 2+ Mn 3+ The synergistic effect of ions results in a gloss level of 86 for the black glass. Thermal shock resistance was tested according to QB / T 2580-2018 6.5 standard; after being dry-fired at 450℃ and then rapidly cooled twice in 20℃ water, no cracks were observed.
[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the principles and spirit of the present invention are included within the protection scope of the present invention.
[0047] Comparative Example 1 A method for preparing a cobalt-free black glaze using copper oxide as the copper source includes the following steps: Raw materials were weighed according to the following mass percentages: 21.1% copper oxide, 13% aluminum oxide, 65% silicon dioxide, 0.6% iron oxide, and 0.3% manganese oxide. All aluminum oxide and some silicon dioxide were derived from kaolin, while the rest were pure oxides. All raw materials were mixed thoroughly and placed in a corundum crucible. The temperature was increased to 1600℃ at a rate of 7℃ / min, and the melting time was 2 hours. A weakly reducing atmosphere was maintained during the melting process. After the glass melt was homogeneous, it was cast into a mold. The average coefficient of thermal expansion of the prepared frit sample from room temperature to 600℃ was measured to be 4.69 × 10⁻⁶. -6 / ℃. Because the frit uses divalent copper oxide as a raw material, it changes the structure of the glass frit, and its coefficient of thermal expansion is much greater than that of the ceramic body. It is no longer a low thermal expansion material and cannot be used as a glaze in heat-resistant pots.
Claims
1. A method for preparing a cobalt-free black glaze for heat-resistant pots, characterized in that... Includes the following steps: Step 1: Melting of the frit: Weigh the raw materials according to the following mass percentages: cuprous oxide 21-39%, aluminum oxide 13-29%, silicon dioxide 32-65%, iron oxide 0.6-3.0%, manganese oxide 0.3-2.0%. Mix them evenly and place them in a corundum crucible. Heat the mixture at a rate of 5-10℃ / min to a temperature of 1510-1630℃ and melt it. Hold the mixture at this temperature for 1-6 hours. During the melting process, control the atmosphere to be neutral or weakly reducing. After the glass melt is uniformly melted, quench it with water to obtain a black glass frit. Step 2: Crushing and sieving: Dry and crush the black glass frit obtained in Step 1, and pass it through a 150-320 mesh sieve to obtain black glass powder; Step 3: Glaze preparation: Mix the obtained black glass powder with water at a mass percentage of 100:50 to 100:65, add 3 to 9% kaolin and 0 to 0.3% suspending agent or dispersant, ball mill until uniform, and prepare glaze.
2. The preparation method according to claim 1, characterized in that, In step one, the aluminum oxide and silicon dioxide are derived from pure oxides or natural minerals.
3. The preparation method according to claim 1, characterized in that, In step one, a neutral or weakly reducing atmosphere is achieved by adding reducing carbon powder, using a sealed crucible with a lid, or controlling the oxygen concentration in the kiln.
4. The preparation method according to claim 1, characterized in that, The suspending agent in step three is sodium carboxymethyl cellulose, and the dispersant is sodium tripolyphosphate.
5. A product decorated with a cobalt-free black glaze for heat-resistant pots, characterized in that, The glaze obtained in step three of claim 1 is applied to the surface of the bisque-fired spodumene heat-resistant pot body, dried, and then fired at 1210-1260°C for 0.5-3 hours to obtain a black glaze layer.
6. The product according to claim 5, characterized in that, The specific gravity of the glaze is 1.65–1.80 g / cm³. 3 The glazing method is spraying, dipping, or pouring glaze, and the glaze thickness is 0.3–0.7 mm.
7. The product according to claim 5, characterized in that, The black glaze is a copper-aluminum-silicon system black glass.
8. The product according to claim 5, characterized in that, The average coefficient of thermal expansion of the black glass from room temperature to 600°C is 1.26 × 10⁻⁶. -6 ~1.63×10 -6 / ℃.
9. The product according to claim 5, characterized in that, The black glass's color is determined by Cu. + Cu 2+ Fe 2+ Fe 3+ Formed through the synergistic effect of ions.
10. The product according to claim 5, characterized in that, The gloss of the black glass is 82-88. According to the QB / T 2580-2018 6.5 standard, the thermal shock resistance test is carried out. After being dry-fired at 450℃ and then rapidly cooled in water at 20℃, no cracks are found after 2 or 3 consecutive tests.