Low temperature fired zirconium-free low expansion opal glaze and method of making same

Abstract

This invention discloses a low-temperature fired, zirconium-free, low-expansion opacifying glaze, which is formed by adhering the glaze to a sanitary ceramic body and then firing it. The glaze does not contain zirconium silicate opacifier and belongs to a zirconium-free glaze system. The glaze comprises dry materials and additives. The dry materials include the following components: 20-40 parts potassium feldspar, 5-20 parts calcined talc, 20-50 parts cordierite, 10-30 parts calcined alumina, 3-15 parts washed kaolin, 5-20 parts calcite, 4-15 parts zinc oxide, and 2-10 parts tricalcium phosphate. This invention also discloses a method for preparing the above-mentioned low-temperature fired, zirconium-free, low-expansion opacifying glaze. The present invention discloses a low-temperature fired zirconium-free, low-expansion opaque glaze and its preparation method. Tricalcium phosphate is used as a phase separation inducer and zinc oxide is used as a zinc source. During the firing process, the glaze undergoes submicron-level phase separation and in-situ zinc spinel formation reaction, which, together with the cordierite crystal phase, achieves dual regulation of opacity whiteness and low thermal expansion performance, thus constructing a zirconium-free glaze system.

Description

Technical Field

[0001] This invention belongs to the field of sanitary ceramic glaze technology. Specifically, it relates to a low-temperature fired zirconium-free, low-expansion opaque glaze and its preparation method, which is suitable for glazing the surface of sanitary ceramic products such as toilets and washbasins. Background Technology

[0002] Glazing the surface of sanitary ceramic products is a crucial process for ensuring their performance. The glaze not only gives the product a smooth and clean appearance but also isolates the body through its dense structure, reducing water absorption and improving stain resistance and ease of cleaning. Currently, the mainstream white glaze for sanitary ceramics in the industry is zirconium silicate opaque glaze, which achieves high whiteness through the light scattering effect of zirconium silicate. However, this method has revealed several technical bottlenecks in large-scale production.

[0003] 1. High raw material costs and potential instability. Zirconium silicate, a key additive, is highly susceptible to price fluctuations that directly impact glaze costs. More importantly, the significant difference in thermal expansion coefficients between zirconium silicate particles and the glaze matrix during firing easily induces micro-stress at the interface, leading to numerous micro-cracks inside or on the surface of the glaze layer. 2. High firing energy consumption. To achieve complete melting of zirconium silicate and proper vitrification of the glaze, traditional sanitary ceramic glazes typically require firing temperatures of 1220℃ to 1280℃. This results in enormous kiln energy consumption and a long production cycle, contradicting the current green, low-carbon, and energy-saving development direction of the ceramic industry. 3. Mismatch in thermal expansion between the body and glaze, easily causing "cracking" (network or linear cracks). The high thermal expansion coefficient of the glaze mismatches with the low-expansion sanitary ceramic body, generating tensile stress in the glaze layer during cooling, leading to "cracking" (network or linear cracks) and ultimately product scrap.

[0004] To address these challenges, the industry has proposed several technological improvement solutions, mainly focusing on developing zirconium-free alternatives to opaque glazes and reducing the coefficient of thermal expansion of glazes. However, while these solutions have made progress in single performance indicators (such as zirconium-free or low expansion), they all involve compromises to varying degrees in terms of cost control, overall performance balance, and ease of industrial production. For example, the lithium-containing zirconium-free glaze in CN 107382069 A still has a firing temperature of 1260℃~1320℃, and the cost of lithium-containing raw materials is high; the apatite phase-separated glaze in CN 105399330 B has a firing temperature as high as 1450~1510℃, and it cannot solve the problem of body-glaze matching; CN 121318540 A introduces a composite low-temperature flux made of zinc oxide, bismuth oxide, and antimony oxide mixed and fired in a high-potassium, low-sodium system to guide cordierite to form in situ in the glassy phase of the glaze, but the process is complicated and costly.

[0005] Therefore, developing a zirconium-free, environmentally friendly, low-temperature, energy-saving, body-glaze matching, and high-performance emulsion glaze for sanitary ceramics that is compatible with existing production lines has become a pressing technical problem for the industry. Summary of the Invention

[0006] The technical problem to be solved by this invention is to address the issues of high cost, poor stability, high firing temperature, high energy consumption, and cracking caused by the dependence on zirconium silicate in existing sanitary ceramic glazes, as well as the problems of high firing temperature, complex process, and insufficient comprehensive performance of existing zirconium-free glazes. This invention provides a low-temperature fired zirconium-free low-expansion opaque glaze and its preparation method, which achieves high opacity, low expansion coefficient, and low-temperature firing at 1180℃ in a zirconium-free system. At the same time, it ensures that the glaze preparation and firing process is highly compatible with existing sanitary ceramic production processes, thereby reducing production costs and improving production yield.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0008] A low-temperature fired, zirconium-free, low-expansion opacifying glaze is produced by applying the glaze to a sanitary ceramic body and then firing it at a low temperature of 1180℃. The glaze does not contain zirconium silicate opacifier and belongs to a zirconium-free glaze system. The glaze comprises dry materials and additives, with the additives added at a ratio of 0.6~1.8 wt% of the total mass of the dry materials. The dry materials include the following components:

[0009] Potassium feldspar 20-40 parts;

[0010] Calcined talc 5-20 parts;

[0011] 20-50 parts of cordierite;

[0012] 10-30 parts of calcined alumina;

[0013] 3-15 parts of washed kaolin;

[0014] 5-20 parts of calcite;

[0015] 4-15 parts zinc oxide;

[0016] Tricalcium phosphate, 2-10 parts.

[0017] Specifically, the zirconium-free low-expansion opaque glaze has a submicron-level phase separation—cordierite—zinc spinel ternary synergistic microstructure, with a linear thermal expansion coefficient of 4.3 to 5.8 × 10⁻⁶ / ℃ in the range of 30 to 600℃, and a whiteness Wr ≥ 71.

[0018] Preferably, the additive is sodium carboxymethyl cellulose and sodium tripolyphosphate in a ratio of 5~15:1~3.

[0019] Furthermore, the chemical basis for the formation of the ternary synergistic microstructure of the glaze is the following components included in the glaze, in mass percentage:

[0020] SiO2 51.00~55.00wt%;

[0021] Al2O3 22.5~26.5wt%;

[0022] Fe2O3 0.10~0.50wt%;

[0023] TiO2 0.01~0.05wt%;

[0024] CaO 4.25–6.25 wt%;

[0025] MgO 6.25–7.85 wt%;

[0026] K2O 2.50~3.4wt%;

[0027] Na₂O 1.05–1.55 wt%;

[0028] ZnO 6.30~7.60wt%;

[0029] P2O5 0.60~1.40wt%;

[0030] Among them, P2O5 is the inducing factor for submicron-level phase separation, ZnO and Al2O3 are the core chemical components for in-situ formation of zinc spinel, and SiO2, Al2O3 and MgO are the basic components for stabilizing cordierite crystal phase.

[0031] Preferably, the zinc oxide has a particle size of 5–30 μm and a purity of 97–99.9%, providing a zinc source for the in-situ generation of zinc spinel during firing. The zinc spinel is a phase that synergistically regulates opacification, expansion, and toughening. The cordierite has a particle size of 5–50 μm and a cordierite phase content of 90–99.9%. As the core low-expansion crystalline phase component of the glaze, it directly regulates the low-expansion performance of the glaze and forms a bicrystalline phase regulation system with the zinc spinel. The remaining dry materials are all conventional industrial raw materials used in the production of ceramic glazes.

[0032] A method for preparing a zirconium-free, low-expansion opaque glaze fired at low temperature as described above includes the following steps:

[0033] For glaze slurry preparation, dry materials are weighed according to the specified proportions, and additives are weighed according to the weight of the dry materials. Then, the materials are put into a ball mill for wet ball milling. After ball milling, the materials are sieved to obtain glaze slurry.

[0034] Glazing involves applying glaze to the surface of the sanitary ceramic body, followed by hot air drying in a dryer to obtain a dry sanitary ceramic body.

[0035] Low-temperature firing involves transferring the dry sanitary ceramic blank to a kiln and firing it at a firing temperature of 1180℃ to obtain a zirconium-free, low-expansion opaque glaze.

[0036] Specifically, the temperature change in the kiln during the low-temperature firing step includes the following processes:

[0037] Preheating involves raising the temperature in the kiln from room temperature to 650°C, which takes 150 minutes.

[0038] The temperature inside the kiln was raised from 650℃ to 1180℃, which took 180 minutes.

[0039] Insulate at 1180℃ for 30 minutes;

[0040] Cooling is performed, allowing the temperature to drop naturally from 1180℃ to room temperature, thus completing the cooling process.

[0041] During the heating process, the glaze gradually melts to form a glaze melt. First, fluxing components such as potassium feldspar and talc melt to form a low-melting-point glassy phase, encapsulating rigid particles such as cordierite and alumina. Subsequently, P2O5 in tricalcium phosphate acts as a phase-separation initiator, triggering submicron-level liquid-liquid phase separation within the glaze melt, forming a microstructure of silicon-rich and phosphorus-calcium-rich phases, providing a microscopic basis for light scattering. Simultaneously, Zn in zinc oxide... 2+ With Al in alumina 3+ In the molten state, an in-situ crystal phase formation reaction occurs, forming zinc spinel crystals, which together with cordierite constitute the core crystal phase system of the glaze.

[0042] During the heat preservation process, the glaze melt is fully vitrified, the submicron phase separation structure is further refined and uniform, the zinc spinel crystal completes the nucleation and grain refinement, the cordierite crystal phase is uniformly dispersed in the glass phase, and the crystal phase and the glass phase form a stable microstructure, ensuring the low thermal expansion performance of the glaze; at the same time, the phase separation structure and the crystal phase together achieve synergistic enhancement of light scattering, improving the opacity and whiteness.

[0043] During the cooling process, natural cooling allows the glaze melt to gradually cool and solidify to form a glaze layer. The low-expansion crystalline phases of cordierite and zinc spinel inhibit the thermal expansion and contraction of the glaze layer. The submicron-level phase separation structure enhances the thermal stress buffering capacity of the glaze layer, making the thermal expansion coefficient of the glaze layer highly matched with that of the body, thus avoiding cracks during the cooling process.

[0044] Preferably, the additive is added by dispersing the additive in water at 10 wt% of the total dry material mass, and then adding it to the ball mill in small amounts multiple times during the ball milling process until all the additive is added.

[0045] Specifically, in the glaze slurry preparation steps, the ball milling conditions are as follows: the ratio of material:ball:water is 1:1.5~3:0.6~1, the ball milling time is 1~3 hours, and the ball milling liquid after ball milling is passed through a 10,000-mesh sieve until the residue is below 0.5% to obtain the glaze slurry.

[0046] Preferably, in the glazing step, the glazing method used is air-pressure spray glazing, with 2 to 4 sprays, and the glaze thickness adhering to the surface of the sanitary ceramic body is 0.6 to 1.3 mm; the hot air drying temperature is 60 to 80℃, and the drying time is 8 to 12 hours.

[0047] The present invention has the following beneficial effects:

[0048] (1) This invention uses tricalcium phosphate as a phase separation inducer and zinc oxide as a zinc source. During the firing process, the glaze undergoes submicron-level phase separation and in-situ zinc spinel formation reaction, which, together with the cordierite crystal phase, achieves dual regulation of opaque whiteness and low thermal expansion performance, constructing a zirconium-free glaze system, effectively reducing raw material procurement costs and avoiding the risk of zirconium silicate price fluctuations; at the same time, it avoids the interfacial micro-stress, glaze micro-cracks and "glaze shrinkage" defects caused by zirconium silicate, and significantly improves the stability of glaze preparation and firing.

[0049] (2) The glaze is fully sintered at 1180℃, which reduces the firing temperature by 40~100℃ compared with traditional zirconium silicate glaze. The firing process is simple and can shorten the production cycle, which is in line with the green and low-carbon development direction of the ceramic industry.

[0050] (3) By synergistic regulation of thermal expansion coefficient by cordierite and in-situ generated zinc spinel crystals, combined with the submicron-level phase separation structure induced by tricalcium phosphate to enhance the thermal stress buffering capacity of the glaze, the thermal expansion coefficient of the glaze is highly matched with that of the body, fundamentally solving the problem of "wind-induced" cracking, reducing product scrap rate and improving production yield.

[0051] (4) The light scattering effect of the submicron phase separation structure, combined with the synergistic effect of zinc spinel and cordierite, achieves a whiteness Wr≥71 for the glaze. At the same time, the submicron phase separation structure enhances the toughness of the glaze layer. With the low expansion characteristics, the glaze layer has high whiteness, high toughness and strong thermal stress buffering capacity.

[0052] (5) The glaze preparation and firing process is highly compatible with the existing sanitary ceramics production process. Only a simple adjustment of the kiln firing system is needed. There is no need to modify the production line or add special equipment. It can be quickly promoted and applied in the industry. Attached Figure Description

[0053] Figure 1 This is an XRD pattern of the glaze layer of the sample in Example 2 of the present invention.

[0054] Figure 2 This is an EDS analysis image of the glaze surface of the sample in Example 2 of the present invention after HF etching. Detailed Implementation

[0055] This invention discloses a low-temperature fired, zirconium-free, low-expansion opacifying glaze, which is formed by applying the glaze to a sanitary ceramic body and then firing it at a low temperature of 1180°C. The glaze does not contain zirconium silicate opacifier and belongs to a zirconium-free glaze system. The glaze includes dry materials and additives. The additives are added at a ratio of 0.6 to 1.8 wt% of the total mass of the dry materials. Preferably, the additives are sodium carboxymethyl cellulose and sodium tripolyphosphate in a ratio of 5 to 15:1 to 3. The dry materials include the following components: 20 to 40 parts of potassium feldspar, 5 to 20 parts of calcined talc, 20 to 50 parts of cordierite, 10 to 30 parts of calcined alumina, 3 to 15 parts of washed kaolin, 5 to 20 parts of calcite, 4 to 15 parts of zinc oxide, and 2 to 10 parts of tricalcium phosphate. The zinc oxide has a particle size of 5–30 μm and a purity of 97–99.9%, providing a zinc source for the in-situ formation of zinc spinel during firing. Zinc spinel acts as a synergistic regulating phase for opacification, expansion, and toughening. The cordierite has a particle size of 5–50 μm and a cordierite phase content of 90–99.9%, serving as the core low-expansion crystalline phase component of the glaze, directly regulating the low-expansion performance of the glaze and forming a bicrystalline phase regulating system with the zinc spinel. The remaining dry materials are conventional industrial raw materials used in the production of ceramic glazes. After firing, the above-mentioned zirconium-free low-expansion opacified glaze has an internal structure of submicron-level phase separation—cordierite—zinc spinel, a ternary synergistic microstructure, with a linear thermal expansion coefficient of 4.3–5.8 × 10⁻⁶ within the range of 30–600℃. -6 / ℃, whiteness Wr≥71.

[0056] Furthermore, the chemical basis for the formation of the ternary synergistic microstructure of the glaze is that the glaze includes the following components, by mass percentage:

[0057] SiO2 51.00~55.00wt%;

[0058] Al2O3 22.5~26.5wt%;

[0059] Fe2O3 0.10~0.50wt%;

[0060] TiO2 0.01~0.05wt%;

[0061] CaO 4.25–6.25 wt%;

[0062] MgO 6.25–7.85 wt%;

[0063] K2O 2.50~3.4wt%;

[0064] Na₂O 1.05–1.55 wt%;

[0065] ZnO 6.30~7.60wt%;

[0066] P2O5 0.60~1.40wt%;

[0067] Among them, P2O5 is the inducing factor for submicron-level phase separation, ZnO and Al2O3 are the core chemical components for in-situ formation of zinc spinel, and SiO2, Al2O3 and MgO are the basic components for stabilizing cordierite crystal phase.

[0068] The present invention will now be described in detail with reference to the embodiments.

[0069] Example 1:

[0070] An embodiment of the present invention provides a method for preparing a zirconium-free, low-expansion opaque glaze fired at low temperature as described above, comprising the following steps:

[0071] For glaze slurry preparation, dry materials were weighed according to the following formula: 20 parts potassium feldspar, 5 parts calcined talc, 20 parts cordierite, 10 parts calcined alumina, 3 parts washed kaolin, 5 parts calcite, 4 parts zinc oxide, and 2 parts tricalcium phosphate. Based on the weight of the above dry materials, 0.5 wt% sodium carboxymethyl cellulose and 0.1 wt% sodium tripolyphosphate were weighed as additives. First, the additives were dispersed in 10 wt% water. Then, the dry materials were put into a ball mill, and ball milling balls and water were added according to the mass ratio of material:ball:water = 1:1.5:0.6. Wet ball milling was carried out for 1 hour. During the ball milling process, the additives dispersed in water were added to the ball mill in small amounts several times until all the additives were added. After ball milling, the glaze slurry was obtained by passing it through a 10,000-mesh sieve until the residue was below 0.5%.

[0072] Glazing: The glaze is applied to the surface of the sanitary ceramic body using a pneumatic spraying method. The glaze is sprayed twice to make the glaze thickness on the surface of the sanitary ceramic body 0.6 mm. Then, it is placed in a dryer and dried with hot air at 60°C for 8 hours to obtain the dry sanitary ceramic body.

[0073] Low-temperature firing involves transferring the dry sanitary ceramic blank to a kiln and firing it at a temperature of 1180℃. Specifically, this includes preheating, raising the temperature in the kiln from room temperature to 650℃ for 150 minutes; raising the temperature in the kiln from 650℃ to 1180℃ for 180 minutes; holding the temperature at 1180℃ for 30 minutes; and cooling, allowing the temperature to drop naturally from 1180℃ to room temperature. This cooling process yields a zirconium-free, low-expansion opaque glaze.

[0074] Example 2:

[0075] An embodiment 2 of the present invention provides a method for preparing a zirconium-free, low-expansion opaque glaze fired at low temperature as described above, comprising the following steps:

[0076] For glaze slurry preparation, dry materials were weighed according to the following formula: 30 parts potassium feldspar, 12 parts calcined talc, 35 parts cordierite, 20 parts calcined alumina, 8 parts washed kaolin, 12 parts calcite, 9 parts zinc oxide, and 6 parts tricalcium phosphate. Based on the weight of the above dry materials, 0.8 wt% sodium carboxymethyl cellulose and 0.2 wt% sodium tripolyphosphate were weighed as additives. First, the additives were dispersed in 10 wt% water. Then, the dry materials were put into a ball mill, and ball milling balls and water were added according to the mass ratio of material:ball:water = 1:2:0.6. Wet ball milling was carried out for 2 hours. During the ball milling process, the additives dispersed in water were added to the ball mill in small amounts several times until all the additives were added. After ball milling, the glaze slurry was obtained by passing it through a 10,000-mesh sieve until the residue was below 0.5%.

[0077] Glazing: The glaze is applied to the surface of the sanitary ceramic body using a pneumatic spraying method. The glaze is sprayed three times to make the glaze thickness on the surface of the sanitary ceramic body 1.0 mm. Then, it is placed in a dryer and dried with hot air at 70°C for 10 hours to obtain the dry sanitary ceramic body.

[0078] Low-temperature firing involves transferring the dry sanitary ceramic blank to a kiln and firing it at 1180℃. Specifically, this includes preheating (raising the kiln temperature from room temperature to 650℃ for 150 minutes), raising the kiln temperature from 650℃ to 1180℃ for 180 minutes, holding at 1180℃ for 30 minutes, and cooling naturally from 1180℃ to room temperature. This cooling process yields a zirconium-free, low-expansion opaque glaze. Samples are then analyzed to obtain... Figure 1 XRD pattern of sample glaze and Figure 2 EDS analysis image of the glaze surface of the sample after HF etching, from Figure 1 It can be seen that the glaze layer is mainly composed of cordierite, zinc spinel, calcium feldspar, and a glassy phase. The synergistic effect of these crystalline phases achieves the low expansion coefficient and high opacity of the glaze, proving that the present invention successfully achieved the in-situ generation of the target crystalline phase at a low temperature of 1180℃; from Figure 2 The elemental distribution of cordierite and zinc spinel crystals is clearly shown (cordierite contains Al, Mg, and Si, while zinc spinel contains Zn and Al), further verifying the existence of the core crystalline phase in the glaze layer and proving that the zirconium-free glaze system of the present invention achieves precise control of the crystalline phase.

[0079] Example 3:

[0080] A method for preparing a zirconium-free, low-expansion opaque glaze fired at low temperature as described in Example 3 of this invention includes the following steps:

[0081] For glaze slurry preparation, dry materials were weighed according to the following formula: 40 parts potassium feldspar, 20 parts calcined talc, 50 parts cordierite, 25 parts calcined alumina, 15 parts washed kaolin, 20 parts calcite, 12 parts zinc oxide, and 8 parts tricalcium phosphate. Based on the weight of the above dry materials, 1.5 wt% sodium carboxymethyl cellulose and 0.3 wt% sodium tripolyphosphate were weighed as additives. First, the additives were dispersed in 10 wt% water. Then, the dry materials were put into a ball mill, and ball milling balls and water were added according to the mass ratio of material:ball:water = 1:3:0.6. Wet ball milling was carried out for 3 hours. During the ball milling process, the additives dispersed in water were added to the ball mill in small amounts several times until all the additives were added. After ball milling, the glaze slurry was obtained by passing it through a 10,000-mesh sieve until the residue was below 0.5%.

[0082] Glazing: The glaze is applied to the surface of the sanitary ceramic body using a pneumatic spraying method. The glaze is sprayed 4 times to make the glaze thickness on the surface of the sanitary ceramic body 1.3 mm. Then, it is placed in a dryer and dried with hot air at 70°C for 12 hours to obtain the dry sanitary ceramic body.

[0083] Low-temperature firing involves transferring the dry sanitary ceramic blank to a kiln and firing it at a temperature of 1180℃. Specifically, this includes preheating, raising the temperature in the kiln from room temperature to 650℃ for 150 minutes; raising the temperature in the kiln from 650℃ to 1180℃ for 180 minutes; holding the temperature at 1180℃ for 30 minutes; and cooling, allowing the temperature to drop naturally from 1180℃ to room temperature. This cooling process yields a zirconium-free, low-expansion opaque glaze.

[0084] Comparative Example 1

[0085] The preparation method using commercially available zirconium silicate opaque glaze A includes the following steps:

[0086] For glaze slurry preparation, dry materials were weighed according to the following formula: 32 parts quartz, 28 parts potassium feldspar, 13 parts calcite, 4 parts dolomite, 5 parts wollastonite, 4 parts alumina, 4 parts zinc oxide, 2 parts kaolin, and 8 parts zirconium silicate. Based on the weight of the above dry materials, 0.5 wt% sodium carboxymethyl cellulose and 0.1 wt% sodium tripolyphosphate were weighed as additives. First, the additives were dispersed in 10 wt% water. Then, the dry materials were put into a ball mill, and ball milling balls and water were added according to the mass ratio of material:ball:water = 1:1.5:0.6. Wet ball milling was carried out for 1 hour. During the ball milling process, the additives dispersed in water were added to the ball mill in small amounts several times until all the additives were added. After ball milling, the glaze slurry was obtained by passing it through a 10,000-mesh sieve until the residue was below 0.5%.

[0087] Glazing: The glaze is applied to the surface of the sanitary ceramic body using a pneumatic spraying method. The glaze is sprayed twice to make the glaze thickness on the surface of the sanitary ceramic body 0.6 mm. Then, it is placed in a dryer and dried with hot air at 60°C for 8 hours to obtain the dry sanitary ceramic body.

[0088] Low-temperature firing: The sanitary ceramic blanks were transferred to a kiln and fired at a firing temperature of 1230°C, and then naturally cooled to room temperature to obtain zirconium silicate opaque glaze A. The firing parameters were basically the same as those in the example.

[0089] Comparative Example 2

[0090] The preparation method using commercially available zirconium silicate opaque glaze B includes the following steps:

[0091] For glaze slurry preparation, dry materials were weighed according to the following formula: 32 parts quartz, 27 parts potassium feldspar, 15 parts calcite, 4 parts dolomite, 2.5 parts talc, 6 parts alumina, 2 parts zinc oxide, 2.5 parts kaolin, and 11 parts zirconium silicate. Based on the weight of the above dry materials, 0.5 wt% sodium carboxymethyl cellulose and 0.1 wt% sodium tripolyphosphate were weighed as additives. First, the additives were dispersed in 10 wt% water. Then, the dry materials were put into a ball mill, and ball milling balls and water were added according to the mass ratio of material:ball:water = 1:1.5:0.6. Wet ball milling was carried out for 1 hour. During the ball milling process, the additives dispersed in water were added to the ball mill in small amounts several times until all the additives were added. After ball milling, the glaze slurry was obtained by passing it through a 10,000-mesh sieve until the residue was below 0.5%.

[0092] Glazing: The glaze is applied to the surface of the sanitary ceramic body using a pneumatic spraying method. The glaze is sprayed twice to make the glaze thickness on the surface of the sanitary ceramic body 0.6 mm. Then, it is placed in a dryer and dried with hot air at 60°C for 8 hours to obtain the dry sanitary ceramic body.

[0093] Low-temperature firing: The sanitary ceramic blanks were transferred to a kiln and fired at a firing temperature of 1230℃, and then naturally cooled to room temperature to obtain zirconium silicate opaque glaze B, whose firing parameters were consistent with those of Comparative Example 1.

[0094] Comparative Example 3

[0095] It is basically the same as Example 2, except that the dry material lacks tricalcium phosphate.

[0096] Comparative Example 4

[0097] It is basically the same as Example 2, except that zinc oxide is missing in the dry material.

[0098] Comparative Example 5

[0099] It is basically the same as Example 2, except that the dry material lacks tricalcium phosphate and cordierite.

[0100] The glazes of Examples 1-3 and Comparative Examples 1-5 were tested, and their performance indicators were determined as follows:

[0101] Example Project <![CDATA[Coefficient of thermal expansion (×10 -6 / °C, 30 - 600°C)]]> Whiteness (Wr) Thermal shock resistance (10-300℃ thermal cycling) Example 1 5.16 71.6 No cracks Example 2 4.43 73.4 No cracks Example 3 4.78 72.8 No cracks Comparative Example 1 7.42 71.3 Network microcracks Comparative Example 2 7.23 72.7 Network microcracks Comparative Example 3 5.43 64.3 No cracks Comparative Example 4 6.47 66.5 microcracks Comparative Example 5 6.73 56.4 network cracks

[0102] As shown in the table above, the coefficient of thermal expansion of the glazes in Examples 1-3 of the present invention is 4.43~5.56×10⁻⁶. -6 / ℃, far lower than traditional zirconium silicate glazes (Comparative Examples 1-2), whiteness Wr≥71, no cracks after thermal cycling, combining low expansion, high whiteness and excellent thermal shock resistance, and good body-glaze matching; Comparative Example 3, without the addition of tricalcium phosphate, the glaze has no submicron-level phase separation, the light scattering ability is greatly reduced, and the whiteness is significantly reduced, confirming that the phase separation structure is an important basis for regulating opacity performance; Comparative Example 4 lacks the zinc spinel crystal phase, the opacity and thermal shock resistance performance decrease, and microcracks appear, proving that zinc spinel is a key synergistic phase for opacity and toughening, avoiding glaze brittleness; Comparative Example 5 lacks the cordierite crystal phase and phase separation structure, the coefficient of thermal expansion increases, the whiteness decreases, and network cracks appear in the glaze, proving that the ternary synergistic system is the core to achieve low expansion, high opacity, and high crack resistance, and none of them can be omitted.

[0103] The above results fully demonstrate that the ternary synergistic system constructed in this invention achieves functional complementarity among the structural units and realizes the synergistic regulation of opacity and low expansion of zirconium-free glazes under low-temperature firing.

[0104] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the inventive concept, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A low-temperature fired, zirconium-free, low-expansion opaque glaze, formed by applying glaze to a sanitary ceramic body and then firing it, characterized in that... The firing process is a low-temperature firing at 1180℃. The glaze does not contain zirconium silicate opacifier and belongs to a zirconium-free glaze system. The glaze includes dry materials and additives. The additives are added at a ratio of 0.6~1.8 wt% of the total mass of the dry materials. The dry materials include the following components: Potassium feldspar 20-40 parts; Calcined talc 5-20 parts; 20-50 parts of cordierite; 10-30 parts of calcined alumina; 3-15 parts of washed kaolin; 5-20 parts of calcite; 4-15 parts zinc oxide; Tricalcium phosphate, 2-10 parts.

2. The low-temperature fired, zirconium-free, low-expansion opaque glaze according to claim 1, characterized in that: The zirconium-free, low-expansion opaque glaze has a submicron-level phase-separated ternary synergistic microstructure of cordierite and zinc spinel, with a linear thermal expansion coefficient of 4.3–5.8 × 10⁻⁶ within the range of 30–600℃. -6 / ℃, whiteness Wr≥71.

3. The low-temperature fired, zirconium-free, low-expansion opaque glaze according to claim 1, characterized in that: The additives are sodium carboxymethyl cellulose and sodium tripolyphosphate, in a ratio of 5~15:1~3.

4. The low-temperature fired, zirconium-free, low-expansion opaque glaze according to claim 2 or 3, characterized in that: The chemical basis for the formation of the ternary synergistic microstructure of the glaze is the following components included in the glaze, in mass percentage: SiO2 51.00~55.00wt%; Al2O3 22.5~26.5wt%; Fe2O3 0.10~0.50wt%; TiO2 0.01~0.05wt%; CaO 4.25–6.25 wt%; MgO 6.25–7.85 wt%; K2O 2.50~3.4wt%; Na₂O 1.05–1.55 wt%; ZnO 6.30~7.60wt%; P2O5 0.60~1.40wt%; Among them, P2O5 is the inducing factor for submicron-level phase separation, ZnO and Al2O3 are the core chemical components for in-situ formation of zinc spinel, and SiO2, Al2O3 and MgO are the basic components for stabilizing cordierite crystal phase.

5. The low-temperature fired, zirconium-free, low-expansion opaque glaze according to any one of claims 1-3, characterized in that: The zinc oxide has a particle size of 5–30 μm and a purity of 97–99.9%; the cordierite has a particle size of 5–50 μm and a cordierite phase content of 90–99.9%.

6. A method for preparing a low-temperature fired, zirconium-free, low-expansion opaque glaze as described in claims 1-5, characterized in that, Includes the following steps: For glaze slurry preparation, dry materials are weighed according to the specified proportions, and additives are weighed according to the weight of the dry materials. Then, the materials are put into a ball mill for wet ball milling. After ball milling, the materials are sieved to obtain glaze slurry. Glazing involves applying glaze to the surface of the sanitary ceramic body, followed by hot air drying in a dryer to obtain a dry sanitary ceramic body. Low-temperature firing involves transferring the dry sanitary ceramic blank to a kiln and firing it at a firing temperature of 1180℃ to obtain a zirconium-free, low-expansion opaque glaze.

7. The preparation method according to claim 6, characterized in that, The temperature change in the kiln during the low-temperature firing step includes the following processes: Preheating involves raising the temperature in the kiln from room temperature to 650°C, which takes 150 minutes. The temperature inside the kiln was raised from 650℃ to 1180℃, which took 180 minutes. Insulate at 1180℃ for 30 minutes; Cooling is performed, allowing the temperature to drop naturally from 1180℃ to room temperature, thus completing the cooling process.

8. The preparation method according to claim 6, characterized in that: The additive is added by dispersing it in water at 10 wt% of the total dry material mass, and then adding it to the ball mill in small amounts multiple times during the ball milling process until all the additive is used up.

9. The preparation method according to claim 8, characterized in that: Therefore, in the glaze slurry preparation steps, the ball milling conditions are as follows: the ratio of material:ball:water is 1:1.5~3:0.6~1, the ball milling time is 1~3 hours, and the ball milling liquid after ball milling is passed through a 10,000-mesh sieve until the residue is below 0.5% to obtain the glaze slurry.

10. The preparation method according to claim 6, characterized in that: In the glazing step, the glazing method used is air pressure spraying, with 2 to 4 sprays, and the thickness of the glaze adhering to the surface of the sanitary ceramic body is 0.6 to 1.3 mm; the hot air drying temperature is 60 to 80℃, and the drying time is 8 to 12 hours.

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