High-hardness acid-and-alkali-resistant lead-free bone china secondary sintered block and preparation method thereof

Abstract

This invention relates to the field of ceramic frit glaze technology, and in particular to a high-hardness, acid and alkali resistant, lead-free bone china secondary firing frit. By weight percentage, its chemical composition includes SiO2: 55-62%, Al2O3: 10-14%, ZrO2: 4-8%, B2O3: 5-7%, Li2O: 0.8-1.5%, SrO: 2-4%, ZnO: 3-5%, CaO: 2-3%, BaO: 1-2%, P2O5: 2-3%, MgO: ≤1%, Na2O+K2O: 3-5%, rare earth oxides: 0-2.5%, Fe2O3+TiO2: ≤0.3%. The frit does not contain PbO or CdO, and is a lead-free and cadmium-free environmentally friendly frit. This high-hardness, acid and alkali resistant, lead-free bone china secondary firing fused block and its preparation method adopt a lead- and cadmium-free environmentally friendly formula system. The content of PbO and CdO is 0, eliminating the risk of heavy metal leaching. It fully complies with the safety standards of EU, US and Chinese GB 4806.4 for food contact materials. At the same time, it controls Fe2O3+TiO2≤0.3%, resulting in high glaze whiteness, no impurities, and no yellowing defects. It is green, environmentally friendly and safe, and can be widely used in the production of high-end daily-use bone china tableware and teaware.

Description

Technical Field

[0001] This invention relates to the field of ceramic frit glaze technology, specifically to a high-hardness, acid and alkali resistant, lead-free bone china secondary firing frit and its preparation method. Background Technology

[0002] Bone china, internationally recognized as a high-end fine porcelain for daily use, is widely used in high-end tableware, teaware, and art porcelain products due to its delicate texture, high whiteness, good transparency, and warm luster. The industry generally employs a two-stage firing process: high-temperature bisque firing followed by low-temperature glaze firing. The glaze firing temperature is mostly concentrated between 1080-1140℃, and the glaze material is mainly frit glaze to ensure the smoothness, gloss, and compatibility of the glaze with the body. For a long time, traditional bone china frit glazes, in pursuit of low melting points, high fluidity, and a wide firing range, have mostly introduced heavy metal oxides such as PbO and CdO as fluxing components. While this achieves good glaze effects, it poses a serious risk of heavy metal leaching, failing to meet food contact safety and environmental protection requirements, and has become a key bottleneck restricting the high-quality development of the industry.

[0003] With the continuous upgrading of safety standards for daily-use ceramics both domestically and internationally, regulations such as those of the European Union, the United States, and my country's GB 4806.4 impose strict limits on the leaching of lead and cadmium. Lead-free and cadmium-free production has become a mandatory development direction for bone china glazes. Against this backdrop, the industry has successively launched several lead-free frit glazes, mostly using alkali metals, alkaline earth metals, and boron compounds to replace lead flux, which has solved the heavy metal problem to some extent. However, several technical shortcomings remain that are difficult to address simultaneously. First, the glaze's hardness and wear resistance are insufficient. Existing lead-free frit glazes generally have a Mohs hardness below 5H and a microhardness mostly below 500HV, resulting in poor scratch and abrasion resistance. They cannot withstand the high-frequency washing of dishwashers, and scratches, loss of gloss, and burrs appear after short-term use, severely impacting service life and appearance quality. Second, their resistance to acid and alkali corrosion is weak. Most formulas introduce excessive amounts of alkali metal components such as Na2O and K2O to lower the firing temperature, leading to a loose glaze network structure. Immersion in common acid and alkali media such as 4% HCl and 5% NaOH easily causes corrosion, loss of gloss, and darkening, making it difficult to meet the long-term needs of catering applications. Third, the body and glaze have poor compatibility, making secondary firing prone to defects. Bone china bodies are rich in calcium phosphate (P2O5), with unique thermal expansion characteristics. The expansion coefficient of conventional lead-free frit is not precisely matched, easily causing problems such as glaze chipping, shrinkage, peeling, pinholes, and bubbles during secondary glazing, resulting in a low yield. Fourth, the firing range is narrow, leading to poor industrial stability. Most lead-free frits rely on a single flux system, and temperature fluctuations of ±20℃ can lead to glaze crystallization, opacity, or incomplete melting, making them unsuitable for large-scale continuous production. Fifth, high hardness, high gloss, and high translucency are mutually restrictive. Increasing hardness can easily lead to a dull glaze and reduced transparency; pursuing high gloss and high translucency often sacrifices hardness and corrosion resistance, making it difficult to simultaneously meet the aesthetic and durability requirements of high-end bone china.

[0004] Several existing technologies and patents have been published regarding lead-free frit glazes for bone china, attempting to address the aforementioned issues, but significant limitations remain. Reference document CN101585717A (High Acid and Alkali Resistance Lead-Cadmium Frit Glaze for Bone China) discloses a lead-cadmium frit glaze whose chemical composition is primarily SiO2 and Al2O3, combined with alkali metals and alkaline earth metals as fluxes, achieving lead-free properties and improving acid and alkali resistance. However, this comparative document has significant shortcomings: First, it does not introduce a synergistic hardening mechanism between ZrO2 and rare earth elements, resulting in limited improvement in glaze hardness, with the Mohs hardness still below 5.5H and insufficient wear resistance. Second, the fluxing system is a conventional composite flux without a gradient fluxing design, leading to a narrow firing temperature window and large fluctuations in batch production. Third, it does not precisely match the expansion coefficient for the high-calcium, high-phosphorus body of bone china, leaving the risk of glaze chipping and shrinkage during secondary firing. Fourth, it fails to resolve the contradiction between high hardness and high gloss and high transparency, resulting in insufficient jade-like texture and transparency of the glaze, making it difficult to meet the quality requirements of high-end bone china.

[0005] Another existing technology enhances glaze strength by increasing SiO2 and Al2O3 content, but this often leads to higher melting temperatures and decreased fluidity, resulting in pinholes and orange peel texture on the glaze. This necessitates increasing the amount of alkali metals, which further reduces corrosion resistance and thermal stability. Some solutions attempt to add ZrO2 to improve hardness, but due to the lack of effective means to stabilize t-ZrO2, the glaze tends to become opaque, lose its gloss, and suffer from reduced whiteness and transparency, deviating from the core quality characteristics of bone china. Furthermore, most lead-free frit glazes lack a closed-loop acid and alkali resistance control system, resulting in high total alkali metal content. Long-term use still poses a risk of corrosion and cannot meet the stringent requirements of dishwashers and acidic / alkaline environments in restaurants.

[0006] In summary, the current field of lead-free frit glaze for secondary firing of bone china faces a common industry challenge: achieving lead-free status while simultaneously achieving high hardness, high corrosion resistance, wide firing range, body-glaze compatibility, and high gloss and transparency. Existing technologies and patents have failed to simultaneously achieve: lead- and cadmium-free environmental friendliness, Mohs hardness of 6-7H, microhardness of 800-900HV, resistance to corrosion from 4% HCl / 5% NaOH for 24 hours, and a coefficient of thermal expansion of 6.5-7.2×10⁻⁶. -6 The material exhibits comprehensive properties such as high hardness, acid and alkali resistance, lead and cadmium-free properties, a wide firing range, excellent body-glaze compatibility, and high gloss and transparency during secondary firing. Therefore, developing a high-hardness, acid and alkali-resistant, lead and cadmium-free, wide-range firing range, excellent body-glaze compatibility, and high gloss and transparency secondary-fired bone china ingot and its preparation method is of significant practical importance and engineering application value for breaking through international technical barriers, enhancing the core competitiveness of my country's high-end daily-use ceramics, and meeting the demands for green safety and durability. Summary of the Invention

[0007] The purpose of this invention is to provide a high-hardness, acid and alkali resistant, lead-free bone china secondary firing fused block and its preparation method, so as to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a high-hardness, acid and alkali resistant, lead-free bone china secondary firing block, the chemical composition of which, by weight percentage, includes: SiO2: 55-62%, Al2O3: 10-14%, ZrO2: 4-8%, B2O3: 5-7%, Li2O: 0.8-1.5%, SrO: 2-4%, ZnO: 3-5%, CaO: 2-3%, BaO: 1-2%, P2O5: 2-3%, MgO: ≤1%, Na2O+K2O: 3-5%, rare earth oxides: 0-2.5%, Fe2O3+TiO2: ≤0.3%; The frit is free of PbO and CdO, making it a lead-free and cadmium-free environmentally friendly frit. It is suitable for the secondary firing process of bone china, with a glaze firing temperature of 1060-1140℃ and a coefficient of thermal expansion of 6.5-7.2×10⁻⁶. -6 / ℃.

[0009] Preferably, the rare earth oxide is one or a combination of CeO2, Y2O3, and La2O3; The CeO2 content is 0.5-1.2%, the Y2O3 content is 0.3-0.8%, and the La2O3 content is 0.2-0.5%. The rare earth oxides are used to stabilize the tetragonal phase t-ZrO2, refine the glaze grains, and improve the hardness and thermal stability of the glaze surface.

[0010] Preferably, the ZrO2 is introduced from zircon sand and exists in the frit structure as tetragonal t-ZrO2, forming a phase transformation toughening structure, so that the microhardness of the glaze reaches 800-900 HV and the Mohs hardness reaches 6-7H.

[0011] Preferably, the frit adopts a gradient composite fluxing system, which is composed of B2O3 low-temperature fluxing, Li2O expansion regulation, SrO / ZnO medium-temperature flow stabilization, and CaO / BaO high-temperature remelting, so that the viscosity of the frit is stable in the range of 1060-1140℃, the firing temperature window is ≥80℃, and the glaze surface is free of pinholes, glaze flow, crystallization and loss of gloss.

[0012] Preferably, the difference in the coefficient of thermal expansion between the frit and the bone china body is ≤0.5×10⁻⁶. -6 / ℃, achieving a high degree of matching between the body and glaze, preventing glaze from chipping, shrinking, peeling, or cracking during the second firing process.

[0013] Preferably, the frit is constructed by strictly controlling Na2O+K2O≤5% and increasing the CaO / SrO / ZnO ratio to build an acid and alkali resistant silicate network, which can withstand immersion in 4% HCl and 5% NaOH at room temperature for 24 hours, and the glaze surface is free from corrosion, loss of gloss and glaze peeling.

[0014] Preferably, the P2O5 is derived from the bone ash component of the bone china body and is used to enhance the interfacial bonding force between the glaze layer and the body, thereby improving the bonding strength between the glaze and the body and the thermal shock stability.

[0015] A method for preparing a high-hardness, acid- and alkali-resistant, lead-free bone china secondary firing ingot includes the following steps: S1: Raw material pretreatment: Quartz and zircon sand are crushed to below 200 mesh, kaolin is dried to a moisture content of <1%, and the Fe2O3 content in quartz is controlled to be <0.1%; S2: Dry mixing of ingredients: Weigh the raw materials according to the proportions described in any one of claims 1-7, place them in a ball mill and dry mix for 30-40 minutes, with a material-to-ball ratio of 1:1.5, so that the raw materials are mixed evenly; S3: High-temperature melting: The mixed raw materials are kept at 1350-1400℃ for 2-3 hours until the melt is clear, free of particles, and completely melted; S4: Water quenching granulation: The molten liquid is quickly poured into cold water for rapid water quenching to obtain loose and easily grindable frit particles; S5: Fine grinding: The frit particles are ball-milled until the residue on a 325-mesh sieve is <0.1%, to obtain a frit glaze slurry that can be directly applied to the glaze. S6: Glaze firing and shaping: Apply glaze slurry to the surface of bone china body, and carry out a second glaze firing in an oxidizing atmosphere. The glaze firing temperature is 1060-1140℃, and the temperature is held for 30-60 minutes. After natural cooling, it is removed from the kiln.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This high-hardness, acid and alkali resistant, lead-free bone china secondary firing fused block and its preparation method adopt a lead- and cadmium-free environmentally friendly formula system. The content of PbO and CdO is 0, eliminating the risk of heavy metal leaching. It fully complies with the safety standards of EU, US and Chinese GB 4806.4 for food contact materials. At the same time, it strictly controls Fe2O3+TiO2≤0.3%, resulting in high glaze whiteness, no impurities, and no yellowing defects. It is green, environmentally friendly and safe, and can be widely used in the production of high-end daily-use bone china tableware and teaware.

[0017] 2. This high-hardness, acid and alkali resistant, lead-free bone china secondary firing fused block and its preparation method utilize a SiO2-Al2O3 network framework, tetragonal t-ZrO2 phase transformation toughening, and rare earth oxide synergistic modification to achieve a Mohs hardness of 6-7H and a microhardness of 800-900HV on the glaze surface. This enhances scratch resistance and wear resistance, making it suitable for long-term use in dishwashers with high-frequency cleaning. Furthermore, by strictly controlling the total amount of alkali metals and optimizing the alkaline earth metal ratio to construct a dense, corrosion-resistant network, it exhibits no corrosion, no loss of gloss, and no glaze peeling under 24-hour immersion in 4% HCl and 5% NaOH at room temperature, thus improving product lifespan and applicable scenarios.

[0018] 3. This high-hardness, acid and alkali resistant, lead-free bone china secondary firing ingot and its preparation method, taking into account the high calcium and high phosphorus characteristics of bone china green bodies, precisely control the coefficient of thermal expansion within 6.5-7.2×10. -6 / ℃, the difference in the coefficient of thermal expansion between the body and the glaze is ≤0.5×10 -6 / ℃, without glaze chipping, shrinkage, peeling, or cracking during secondary glazing; adopting a four-stage gradient composite fluxing system of B2O3-Li2O-SrO / ZnO-CaO / BaO, the firing temperature window is ≥80℃, the glaze surface is bright and smooth, without pinholes, bubbles, or crystallization loss of gloss, it has strong adaptability to kiln temperature fluctuations, high yield, and is suitable for large-scale continuous production. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of the preparation method of the present invention; Figure 2 This is a cross-sectional view of the lead-free bone china secondary firing block in Embodiment 1 of the present invention; Figure 3 This is a cross-sectional view of the lead-free bone china secondary firing block in Embodiment 2 of the present invention; Figure 4 This is a cross-sectional view of the lead-free bone china secondary firing block in Embodiment 3 of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Please see Figures 1-4 This invention provides a technical solution: a high-hardness, acid and alkali resistant, lead-free bone china secondary firing block, the chemical composition of which, by weight percentage, includes: SiO2: 55-62%, Al2O3: 10-14%, ZrO2: 4-8%, B2O3: 5-7%, Li2O: 0.8-1.5%, SrO: 2-4%, ZnO: 3-5%, CaO: 2-3%, BaO: 1-2%, P2O5: 2-3%, MgO: ≤1%, Na2O+K2O: 3-5%, rare earth oxides: 0-2.5%, Fe2O3+TiO2: ≤0.3%; The frit is free of PbO and CdO, making it a lead-free and cadmium-free environmentally friendly frit. It is suitable for the secondary firing process of bone china, with a glaze firing temperature of 1060-1140℃ and a coefficient of thermal expansion of 6.5-7.2×10⁻⁶. -6 / ℃.

[0023] Rare earth oxides are one or more combinations of CeO2, Y2O3, and La2O3; The CeO2 content is 0.5-1.2%, the Y2O3 content is 0.3-0.8%, and the La2O3 content is 0.2-0.5%. The rare earth oxides are used to stabilize the tetragonal phase t-ZrO2, refine the glaze grains, and improve the hardness and thermal stability of the glaze surface.

[0024] ZrO2 is introduced from zircon sand and exists in the frit structure as tetragonal t-ZrO2, forming a phase transformation toughening structure, which makes the microhardness of the glaze reach 800-900HV and the Mohs hardness reach 6-7H.

[0025] The frit adopts a gradient composite fluxing system, which is composed of B2O3 low-temperature fluxing, Li2O expansion regulation, SrO / ZnO medium-temperature flow stabilization, and CaO / BaO high-temperature replenishment. This makes the frit viscosity stable in the range of 1060-1140℃, with a firing temperature window of ≥80℃, and the glaze surface free of pinholes, glaze flow, crystallization and loss of gloss.

[0026] The difference in the coefficients of thermal expansion between the frit and the bone china body is ≤0.5×10. -6 / ℃, achieving a high degree of matching between the body and glaze, preventing glaze from chipping, shrinking, peeling, or cracking during the second firing process.

[0027] The frit is constructed by strictly controlling Na2O+K2O≤5% and increasing the CaO / SrO / ZnO ratio to build an acid and alkali resistant silicate network. It can withstand immersion in 4% HCl and 5% NaOH at room temperature for 24 hours without corrosion, loss of gloss, or glaze peeling.

[0028] P2O5 is derived from the bone ash component of bone china body and is used to enhance the interfacial bonding between the glaze and the body, improve the bonding strength between the glaze and the body, and enhance thermal shock stability.

[0029] Example 1 1. Chemical composition of the frit (weight percentage %) SiO2: 58 Al2O3: 12 ZrO2: 6 B2O3: 6 Li2O: 1.0 SrO:3 ZnO: 4 CaO: 2.5 BaO: 1.5 P2O5:2 Na₂O + K₂O: 4.3 CeO2: 0.7 MgO: 0.5 Fe2O3+TiO2: 0.2 PbO: 0 CdO: 0 2. Preparation steps (1) Raw material pretreatment: Quartz and zircon sand are crushed to below 200 mesh, kaolin is dried to a moisture content of 0.8%, and quartz has an Fe2O3 content of 0.08%; (2) Dry mixing of ingredients: Weigh according to the above proportions, dry mix in a ball mill for 35 minutes, with a material-to-ball ratio of 1:1.5; (3) High-temperature melting: Melt at 1380℃ for 2.5h, the melt is clear and free of particles; (4) Water quenching: The molten liquid is quickly poured into cold water for quenching to obtain loose molten clinker particles; (5) Fine grinding: ball mill until 0.08% residue remains on a 325-mesh sieve; (6) Glazing: The bone china body is glazed, oxidizing atmosphere, held at 1100℃ for 45 minutes, and then cooled naturally.

[0030] 3. Performance test results Glazing temperature: 1100℃ Coefficient of thermal expansion: 6.8 × 10⁻⁶ -6 / ℃ Body-glaze expansion difference: 0.3×10 -6 / ℃ Mohs hardness: 6.5H Microhardness: 850 HV Acid resistance: Immersion in 4% HCl at room temperature for 24 hours showed no corrosion or loss of gloss. Alkali resistance: After soaking in 5% NaOH at room temperature for 24 hours, there is no corrosion or loss of gloss. Firing temperature window: 90℃ Glaze condition: glossy and smooth, free of pinholes, glaze runs, and crystallization. Glaze-body bonding: no glaze chipping, no glaze shrinkage, no glaze peeling Heavy metals: Pb and Cd were not detected. Example 2:

[0031] 1. Chemical composition of the frit (weight percentage %) SiO2: 56 Al2O3: 11 ZrO2:5 B2O3: 5.5 Li2O: 1.2 SrO: 3.5 ZnO: 3.5 CaO: 2.2 BaO: 1.8 P2O5: 2.2 Na₂O + K₂O: 3.8 Y2O3: 0.5 MgO: 0.6 Fe2O3+TiO2: 0.25 PbO: 0 CdO: 0 2. Preparation steps (1) Raw material pretreatment: Quartz and zircon sand are crushed to below 200 mesh, and kaolin is dried to a moisture content of 0.7%; (2) Dry mixing of ingredients: Weigh according to the proportion, dry mix in a ball mill for 30 minutes, with a material-to-ball ratio of 1:1.5; (3) High-temperature melting: Melt at 1360℃ for 2.5h; (4) Water quenching: rapid water quenching to form granules; (5) Fine grinding: ball mill until 0.07% residue remains on a 325-mesh sieve; (6) Glaze firing: Oxidizing atmosphere, 1080℃ for 40 min.

[0032] 3. Performance test results Glazing temperature: 1080℃ Coefficient of thermal expansion: 6.6 × 10⁻⁶ -6 / ℃ Body-glaze expansion difference: 0.2×10 -6 / ℃ Mohs hardness: 6H Microhardness: 820 HV Acid resistance: No abnormalities were observed after soaking in 4% HCl for 24 hours. Alkali resistance: No abnormalities were observed after soaking in 5% NaOH for 24 hours. Firing temperature window: 85℃ Glaze condition: glossy, free of pinholes and bubbles Glaze-body bonding: no glaze chipping, no glaze shrinkage Heavy metals: Pb and Cd were not detected. Example 3:

[0033] 1. Chemical composition of the frit (weight percentage %) SiO2: 60 Al2O3: 13 ZrO2: 7 B2O3: 6.5 Li2O: 1.1 SrO: 2.5 ZnO: 4.5 CaO: 2.8 BaO: 1.2 P2O5: 2.5 Na₂O + K₂O: 4.0 La2O3: 0.3 MgO: 0.4 Fe2O3+TiO2: 0.18 PbO: 0 CdO: 0 2. Preparation steps (1) Raw material pretreatment: Quartz and zircon sand are crushed to below 200 mesh, and kaolin is dried to a moisture content of 0.6%; (2) Dry mixing of ingredients: Weigh according to the ratio, dry mix in a ball mill for 40 minutes, with a material-to-ball ratio of 1:1.5; (3) High-temperature melting: Melt at 1400℃ for 2 hours; (4) Water quenching: rapid water quenching; (5) Fine grinding: ball mill until 0.05% residue remains on a 325-mesh sieve; (6) Glaze firing: Oxidizing atmosphere, 1120℃ for 50 min.

[0034] 3. Performance test results Glazing temperature: 1120℃ Coefficient of thermal expansion: 7.0 × 10⁻⁶ -6 / ℃ Body-glaze expansion difference: 0.4×10 -6 / ℃ Mohs hardness: 7H Microhardness: 900 HV Acid resistance: No abnormalities were observed after soaking in 4% HCl for 24 hours. Alkali resistance: No abnormalities were observed after soaking in 5% NaOH for 24 hours. Firing temperature window: 95℃ Glaze condition: High gloss, strong jade-like texture, no crystallization Glaze-body bonding: no glaze chipping, no cracking, and a dense bond. Heavy metals: Pb and Cd were not detected. Example 4 (Comparative example: lead-containing frit of traditional bone china) 1. Chemical composition of the frit (weight percentage %) SiO2: 52 Al2O3:8 ZrO2: 1 B2O3:4 PbO:5 Na₂O + K₂O: 8 CaO: 3 MgO: 2 ZnO:2 Fe2O3+TiO2: 0.5 CdO: 0.1 2. Preparation steps The traditional process is as follows: ingredient preparation → mixing → melting at 1250℃ → water quenching → ball milling → glaze firing at 1120℃.

[0035] 3. Performance test results Mohs hardness: 4H Microhardness: 450 HV Acid resistance: Slight loss of gloss and slight corrosion after soaking in 4% HCl for 24 hours. Alkali resistance: After soaking in 5% NaOH for 24 hours, the glaze loses its gloss and becomes dull. Coefficient of thermal expansion: 8.5 × 10⁻⁶ -6 / ℃ Body and glaze compatibility: poor; prone to glaze chipping and shrinkage. Firing temperature window: 30℃ Glaze condition: Prone to pinholes and bubbles Heavy metals: Pb leaching exceeded the standard, failing to meet food contact standards. Comparison table of experimental data from Examples 1 to 4: Glazing firing temperature (°C) 1100 1080 1120 1120 <![CDATA[Coefficient of thermal expansion (×10⁻ 6 / °C)]]> 6.8 6.6 7.0 8.5 <![CDATA[Difference in expansion coefficients of body and glaze (×10⁻ 6 / °C)]]> 0.3 0.2 0.4 >1.2 Mohs hardness (H) 6.5 6 7 4 Microhardness (HV) 850 820 900 450 4% HCl 24h acid resistance No corrosion, no loss of gloss No corrosion, no loss of gloss No corrosion, no loss of gloss Slight corrosion, slight loss of gloss Alkali resistance of 5% NaOH for 24 hours No corrosion, no loss of gloss No corrosion, no loss of gloss No corrosion, no loss of gloss Obvious loss of gloss, dull glaze Firing temperature window (°C) 90 85 95 30 Glaze condition Glossy and smooth, free of pinholes, glaze runs, and crystallization. Glossy, free of pinholes and bubbles High gloss, strong jade-like texture, no crystallization Pinholes and bubbles are easily produced. Body and glaze bonding No glaze chipping, no glaze shrinkage, no glaze peeling No glaze chipping or shrinkage No glaze chipping, no cracking, and dense bonding. Easily chipped glaze, shrinkage glaze, poor compatibility Pb and Cd precipitation Not detected Not detected Not detected Pb exceeded the standard and did not meet food standards. Adapted scenarios Suitable for high-end tableware and dishwashers Low-temperature rapid firing, daily-use porcelain High-hardness, high-transparency, high-grade bone china Ordinary low-end, non-food contact It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0036] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-hardness, acid and alkali resistant, lead-free bone china secondary firing block, the chemical composition of which, by weight percentage, includes: SiO2: 55-62%, Al2O3: 10-14%, ZrO2: 4-8%, B2O3: 5-7%, Li2O: 0.8-1.5%, SrO: 2-4%, ZnO: 3-5%, CaO: 2-3%, BaO: 1-2%, P2O5: 2-3%, MgO: ≤1%, Na2O+K2O: 3-5%, rare earth oxides: 0-2.5%, Fe2O3+TiO2: ≤0.3%; The frit does not contain PbO or CdO, and is a lead-free and cadmium-free environmentally friendly frit. The frit is suitable for the secondary firing process of bone china, with a glaze firing temperature of 1060-1140℃ and a coefficient of thermal expansion of 6.5-7.2×10⁻⁶. -6 / ℃.

2. The high-hardness, acid and alkali resistant, lead-free bone china secondary firing block according to claim 1, characterized in that: The rare earth oxide is one or more combinations of CeO2, Y2O3, and La2O3; The CeO2 content is 0.5-1.2%, the Y2O3 content is 0.3-0.8%, and the La2O3 content is 0.2-0.5%. The rare earth oxides are used to stabilize the tetragonal phase t-ZrO2, refine the glaze grains, and improve the hardness and thermal stability of the glaze surface.

3. The high-hardness, acid and alkali resistant, lead-free bone china secondary firing block according to claim 1, characterized in that: The ZrO2 is introduced from zircon sand and exists in the frit structure as tetragonal t-ZrO2, forming a phase transformation toughening structure, which makes the microhardness of the glaze reach 800-900HV and the Mohs hardness reach 6-7H.

4. The high-hardness, acid and alkali resistant, lead-free bone china secondary firing block according to claim 1, characterized in that: The frit adopts a gradient composite fluxing system, which is composed of B2O3 low-temperature fluxing, Li2O expansion regulation, SrO / ZnO medium-temperature flow stabilization, and CaO / BaO high-temperature replenishment. This makes the frit viscosity stable in the range of 1060-1140℃, with a firing temperature window of ≥80℃, and the glaze surface free of pinholes, glaze flow, crystallization and loss of gloss.

5. The high-hardness, acid and alkali resistant, lead-free bone china secondary firing block according to claim 1, characterized in that: The difference in the coefficient of thermal expansion between the frit and the bone china body is ≤0.5×10. -6 / ℃, achieving a high degree of matching between the body and glaze, preventing glaze from chipping, shrinking, peeling, or cracking during the second firing process.

6. The high-hardness, acid and alkali resistant, lead-free bone china secondary firing block according to claim 1, characterized in that: The frit is constructed by strictly controlling Na2O+K2O≤5% and increasing the CaO / SrO / ZnO ratio to build an acid and alkali resistant silicate network, which can withstand immersion in 4% HCl and 5% NaOH at room temperature for 24 hours without corrosion, loss of gloss, or glaze peeling.

7. The high-hardness, acid and alkali resistant, lead-free bone china secondary firing block according to claim 1, characterized in that: The P2O5 is derived from the bone ash component of the bone china body and is used to enhance the interfacial bonding force between the glaze layer and the body, improve the bonding strength between the glaze and the body, and enhance thermal shock stability.

8. A method for preparing a high-hardness, acid- and alkali-resistant, lead-free bone china secondary firing block according to any one of claims 1-7, characterized in that, Includes the following steps: S1: Raw material pretreatment: Quartz and zircon sand are crushed to below 200 mesh, kaolin is dried to a moisture content of <1%, and the Fe2O3 content in quartz is controlled to be <0.1%; S2: Dry mixing of ingredients: Weigh the raw materials according to the proportions described in any one of claims 1-7, place them in a ball mill and dry mix for 30-40 minutes, with a material-to-ball ratio of 1:1.5, so that the raw materials are mixed evenly; S3: High-temperature melting: The mixed raw materials are kept at 1350-1400℃ for 2-3 hours until the melt is clear, free of particles, and completely melted; S4: Water quenching granulation: The molten liquid is quickly poured into cold water for rapid water quenching to obtain loose and easily grindable frit particles; S5: Fine grinding: The frit particles are ball-milled until the residue on a 325-mesh sieve is <0.1%, to obtain a frit glaze slurry that can be directly applied to the glaze. S6: Glaze firing and shaping: Apply glaze slurry to the surface of bone china body, and carry out a second glaze firing in an oxidizing atmosphere. The glaze firing temperature is 1060-1140℃, and the temperature is held for 30-60 minutes. After natural cooling, it is removed from the kiln.

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