A lithium-free low-temperature sintering aid, its preparation method and its application

Abstract

This invention provides a lithium-free low-temperature sintering aid, its preparation method, and its application, belonging to the field of ceramic production technology. First, sodium tetraborate decahydrate, sodium metaborate tetrahydrate, and rare earth oxides are mixed and sintered to prepare a first sintering aid. Then, the first aid is mixed and sintered with raw materials such as quartz to obtain a lithium-free low-temperature sintering aid. The lithium-free low-temperature sintering aid prepared by this invention is used to prepare low-temperature sintered ceramic green bodies. It can promote the reaction, thereby lowering the sintering temperature of the ceramic; simultaneously, it promotes the crystallization of the ceramic, resulting in smaller and more uniform crystal sizes, thus improving the mechanical properties of the ceramic; and it promotes the particle dispersion of the ceramic, resulting in higher sintering density of the ceramic material.

Description

Technical Field

[0001] This invention relates to the field of ceramic production technology, and in particular to a lithium-free low-temperature sintering aid, its preparation method, and its application. Background Technology

[0002] Ceramics are a common inorganic non-metallic material. Due to their excellent properties and wide range of applications, they have become an indispensable material in modern industry and daily life. Traditional ceramic preparation typically employs high-temperature sintering, where raw materials undergo chemical reactions at high temperatures to form a dense ceramic structure. However, traditional high-temperature sintering requires high temperatures and long sintering cycles, resulting in high energy consumption and potentially leading to grain growth and deformation, thus reducing material performance. To address these problems in traditional ceramic preparation, low-temperature sintering technology has been researched. Low-temperature sintering technology refers to sintering at lower temperatures to prepare high-quality ceramic materials. This method offers several advantages over traditional high-temperature sintering methods:

[0003] First, low-temperature sintering ceramic technology is energy-saving and environmentally friendly. Traditional high-temperature sintering requires equipment such as high-temperature furnaces, consuming a large amount of energy and generating a significant amount of pollutants. In contrast, low-temperature sintering ceramic technology can complete the sintering process at a lower temperature, reducing energy consumption and environmental pollution.

[0004] Secondly, low-temperature sintering ceramic technology can improve material properties. Low-temperature sintering allows ceramic materials to complete sintering in a shorter time, thereby reducing grain growth time and improving properties such as density and hardness.

[0005] Furthermore, low-temperature sintering ceramics technology is highly adaptable. This technology can be applied to the preparation of various ceramic materials, such as oxide ceramics, non-oxide ceramics, and glass ceramics.

[0006] Therefore, low-temperature sintering technology has significant advantages over traditional high-temperature sintering technology, such as lower energy consumption, less environmental pollution, and shorter preparation cycles. Various ceramic materials, such as oxide ceramics, non-oxide ceramics, and glass ceramics, can be prepared using low-temperature sintering technology. Furthermore, this technology can also prepare ceramic materials with complex shapes, improve production efficiency, reduce production costs, and achieve directional preparation. These characteristics make low-temperature sintering technology a promising field for ceramic material preparation. The research and development of low-temperature sintering ceramic technology is one of the trends in modern ceramic technology development.

[0007] From the perspective of the entire ceramic production process, sintering accounts for more than 50% of both energy consumption and CO2 emissions. Therefore, reducing the sintering temperature is the most direct and effective way to reduce energy consumption and CO2 emissions during sintering. Literature research shows that reducing the temperature by 100°C can reduce energy consumption and emissions by at least 10%. Furthermore, lowering the sintering temperature can shorten sintering time and improve ceramic production efficiency. Reaching such high temperatures requires a large amount of energy and generates significant CO2 emissions. Therefore, in the ceramic manufacturing field, how to reduce the sintering temperature required for ceramic sintering is one of the current focuses of attention. Research has found that the addition of low-temperature sintering aids can effectively reduce the sintering temperature of raw ceramic powder, and thus it is widely used in the current ceramic manufacturing field. However, traditional low-temperature sintering aids generally contain lithium oxide. This is because lithium has a relatively small atomic mass and strong chemical activity, which can promote the crystal phase transformation of ceramic materials, thereby reducing the sintering temperature and thus reducing energy consumption. In recent years, lithium resources have been widely used as an important raw material in some industries, leading to a continuous rise in the price of lithium resources in the domestic market. This has also significantly increased the cost of traditional lithium-containing low-temperature sintering aids, which has an extremely adverse impact on the low-temperature ceramics industry.

[0008] Currently, almost all fluxes added to low-temperature sintered ceramics are alkali metal oxides such as Na, K, and Li, which are used for melting and strengthening, and also achieve a cooling effect. However, Li oxides, which have the best melting effect, are not very competitive in practical production applications due to their high price.

[0009] Rare earth elements are known as "industrial gold" because of their excellent photoelectric and electromagnetic properties. They can be combined with other materials to form a wide variety of new materials with different properties. Their most significant function is to greatly improve the quality and performance of other products. Summary of the Invention

[0010] In view of this, the present invention provides a method for preparing a lithium-free low-temperature sintering aid, comprising the following steps:

[0011] (1) Sodium tetraborate decahydrate and sodium metaborate tetrahydrate were mixed at a mass ratio of 65-70:30-35 to obtain mixture A; then mixture A was mixed with rare earth oxides to obtain mixture B;

[0012] (2) The mixture B is placed in a muffle furnace for sintering. After sintering, it is taken out and quickly quenched in water to obtain a transparent glassy product. The transparent glassy product is ground into fine powder to obtain the first sintering aid.

[0013] (3) Mix quartz, Al2O3, CaO, MgO, K2O, Na2O, B2O3 and the first sintering aid evenly to obtain mixture C. Place mixture C in a muffle furnace for sintering to obtain lithium-free low-temperature sintering aid.

[0014] Preferably, the mass ratio of mixture A to rare earth oxide in step (1) is 50:1-2; the rare earth oxide is any one of Eu2O3, CeO2, (PrNd)xOy, and Dy2O3.

[0015] Preferably, the specific steps of sintering in step (2) are as follows: raise the temperature to 600℃ at a heating rate of 3-3.5℃ / min and hold for 30-40min; continue to raise the temperature to 900-950℃ at a heating rate of 3-3.5℃ / min and hold for 100min; then raise the temperature to 1100-1150℃ at a heating rate of 1.5℃ / min and hold for 120min;

[0016] The sintering step in step (3) is the same as in step (2).

[0017] Preferably, the mixture C in step (3) consists of the following raw materials in the following mass percentages: quartz 61%, Al2O3 8-10%, CaO 0.1-3%, MgO 0.1-2%, K2O 1-4%, Na2O 4-9%, B2O3 10-15%, and primary sintering aid 5%.

[0018] Another object of the present invention is to provide a lithium-free low-temperature sintering aid prepared by the above method.

[0019] The application of the lithium-free low-temperature sintering aid prepared in this invention, used to prepare low-temperature sintered ceramic green bodies, includes the following steps:

[0020] S1. Add the lithium-free low-temperature sintering aid to the ceramic body powder at a mass ratio of 1%-5% and mix evenly. Add water at a mass ratio of 40-45% of the ceramic body powder and ball mill for 2 hours to form a uniform slurry. Then pour it into a gypsum mold to form a ceramic green body after solidification.

[0021] S2 After drying the ceramic green body, it is placed in a muffle furnace for sintering. The sintered ceramic green body is then cooled to room temperature with the furnace and taken out to obtain a low-temperature sintered ceramic green body.

[0022] The specific steps of the sintering are as follows: raise the temperature to 600℃ at a heating rate of 3-3.5℃ / min and hold for 30min; continue to raise the temperature to 900-950℃ at a heating rate of 3-3.5℃ / min and hold for 30min; then raise the temperature to 1100-1150℃ at a heating rate of 1.5℃ / min and hold for 120min.

[0023] Preferably, the ceramic body powder in step S1 is composed of the following raw materials in the following mass percentages: SiO2 67.02wt%, Al2O3 26.94wt%, Fe2O3 1.25wt%, MgO 0.39wt%, CaO 1.06wt%, Na2O 0.61wt%, K2O 2.35wt%, TiO2 0.38wt%.

[0024] Preferably, the drying temperature in the oven in step S2 is 80-85℃, and the drying time is 20-24h.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention provides a lithium-free low-temperature sintering aid, its preparation method, and its application. The lithium-free low-temperature sintering aid, prepared using rare earth oxides and other raw materials, promotes the reaction during the ceramic sintering process, thereby lowering the sintering temperature. Compared to common porcelain, whose firing temperatures are mostly above 1200℃, and some even reach around 1400℃, the ceramic produced by this invention can be fired at 1100℃.

[0027] Lithium-free low-temperature sintering aids containing rare earth oxides can promote the crystallization of ceramics, resulting in smaller and more uniform crystal sizes, thereby improving the mechanical properties of ceramics. At the same time, they can help form solid solutions, prevent crystal transformation, inhibit grain growth, generate molten liquid phases, and reduce the cost of low-temperature sintering aids.

[0028] Lithium-free low-temperature sintering aids containing rare earth oxides can promote the dispersion of ceramic particles, resulting in higher sintering density of ceramic materials, thereby improving the quality and service life of ceramics, increasing the sintering strength of ceramics by 250%, and reducing water absorption by 1000%. Detailed Implementation

[0029] The present invention will be further described below with reference to the embodiments.

[0030] Example 1

[0031] A method for preparing a lithium-free low-temperature sintering aid, comprising the following steps:

[0032] (1) Sodium tetraborate decahydrate and sodium metaborate tetrahydrate were mixed at a mass ratio of 67:33 to obtain mixture A; then mixture A was mixed with Eu2O3 at a mass ratio of 50:1 to obtain mixture B;

[0033] (2) The mixture B is placed in a muffle furnace for sintering. After sintering, it is taken out and quickly quenched in water to obtain a transparent glassy product. The transparent glassy product is ground into fine powder to obtain the first sintering aid.

[0034] The specific steps of the sintering are as follows: the temperature is raised to 600℃ at a heating rate of 3.2℃ / min and held for 30min; the temperature is then raised to 920℃ at a heating rate of 3.2℃ / min and held for 100min; and the temperature is then raised to 1100℃ at a heating rate of 1.5℃ / min and held for 120min.

[0035] (3) Mix 60% quartz, 10% Al2O3, 3% CaO, 2% MgO, 4% K2O, 6% Na2O and 10% B2O3 and 5% primary sintering aid by mass to obtain mixture C. Place mixture C in a muffle furnace for sintering to obtain lithium-free low-temperature sintering aid. The sintering step in step (3) is the same as in step (2).

[0036] The steps for preparing low-temperature sintered ceramic green bodies using the aforementioned lithium-free low-temperature sintering aid are as follows:

[0037] S1. Add the lithium-free low-temperature sintering aid to the ceramic green body powder at a mass ratio of 3% and mix evenly. Add water at a mass ratio of 40-45% of the ceramic green body powder and ball mill for 2 hours to form a uniform slurry. Then pour it into a gypsum mold to form it. After solidification, the ceramic green body is obtained.

[0038] The ceramic green body powder is composed of the following raw materials in the following mass percentages: SiO2 67.02wt%, Al2O3 26.94wt%, Fe2O3 1.25wt%, MgO 0.39wt%, CaO 1.06wt%, Na2O 0.61wt%, K2O 2.35wt%, TiO2 0.38wt%.

[0039] S2. The ceramic green body is placed in an oven at 80°C and dried for 24 hours. Then it is placed in a muffle furnace for sintering. After the sintered ceramic green body is cooled to room temperature, it is taken out to obtain a low-temperature sintered ceramic body.

[0040] The specific steps of the sintering are as follows: the temperature is raised to 600℃ at a heating rate of 3.2℃ / min and held for 30min; the temperature is then raised to 920℃ at a heating rate of 3.2℃ / min and held for 30min; and then the temperature is raised to 1100℃ at a heating rate of 1.5℃ / min and held for 120min.

[0041] Example 2

[0042] A method for preparing a lithium-free low-temperature sintering aid, the steps of which are as described in Example 1:

[0043] The difference is that in step S1 of Example 2, the lithium-free low-temperature sintering aid is added to the ceramic green body powder at a mass ratio of 3% and mixed evenly.

[0044] Example 3

[0045] A method for preparing a lithium-free low-temperature sintering aid, the steps of which are as described in Example 1:

[0046] The difference is that in step (1) of Example 3, the rare earth oxide is CeO2;

[0047] In S1, the lithium-free low-temperature sintering aid is added to the ceramic green body powder at a mass ratio of 5% and mixed evenly.

[0048] Example 4

[0049] A method for preparing a lithium-free low-temperature sintering aid, the steps of which are as described in Example 1:

[0050] The difference is that in step (1) of Example 4, the rare earth oxide is Pr-Nd;

[0051] In S1, the lithium-free low-temperature sintering aid is added to the ceramic green body powder at a mass ratio of 5% and mixed evenly.

[0052] Example 5

[0053] A method for preparing a lithium-free low-temperature sintering aid, the steps of which are as described in Example 1:

[0054] The difference is that in step (1) of Example 5, the rare earth oxide is Dy2O3;

[0055] In S1, the lithium-free low-temperature sintering aid is added to the ceramic green body powder at a mass ratio of 4% and mixed evenly.

[0056] Comparative Example 1

[0057] A ceramic green body powder consisting of 67.02 wt% SiO2, 26.94 wt% Al2O3, 1.25 wt% Fe2O3, 0.39 wt% MgO, 1.06 wt% CaO, 0.61 wt% Na2O, 2.35 wt% K2O, and 0.38 wt% TiO2, along with 40-45% water by weight, was placed in a 10 L ball mill jar. After ball milling for 2 hours, the mixture was poured into a plaster mold. After solidification, the mold was removed, and the ceramic sample strip was dried in an oven for 24 hours. The dried sample strip was then placed in a muffle furnace and sintered according to the lithium-free low-temperature sintering aid process described above. The sintered ceramic sample strip was then removed and tested for compressive strength, water absorption, bending strength, and shrinkage.

[0058] The low-temperature sintered ceramic green bodies prepared in Examples 1-5 and Comparative Example 1 were tested for compressive strength, water absorption, bending and shrinkage. For each example, 3-5 samples were tested and the average value was taken.

[0059] Flexural strength test method: After measuring the sample dimensions and determining the span, use a universal tensile testing machine to test and record the maximum force at break. The three-point flexural strength formula is: P = 3 × F × L / 2 × a × b 2 (P - Strength (MPa); F - Maximum Force (N); L - Span (mm); a - Width (mm); b - Thickness (mm)). Reference Standard: GB / T 6569-2006

[0060] Water absorption test method: The dry weight of the test sample is recorded as M1. It is boiled in distilled water for 2 hours and then soaked for 20 hours. The weight after absorption is recorded as M2. The absorption rate is calculated using the formula: W = (BG) / G × 100% (W - absorption rate; G - dry weight (g); B - saturated weight (g)). Reference standard: ASTM C373-88 (2006) standard.

[0061] Standard thickness deformation test method: A refractory frame is placed inside a muffle furnace. A 25cm sample strip is fired on the refractory frame in the muffle furnace at 1100℃, and the sample bends naturally under gravity. The thickness at different locations is measured and the average value is recorded as S. At the same time, the vertical distance L between the bend vertex and the horizontal lines at both ends is measured on graph paper and recorded as h between the two ends of the refractory frame. Wq = L × S² / 100 (Wq - standard thickness deformation; L - vertical distance between the bend vertex and the horizontal lines at both ends in cm; S - thickness in mm). Reference standard: bending 14-20 mm. The deformation coefficient P is calculated as: P = 4LS 2 / 3h 4 .

[0062] Shrinkage test method: A 10 cm long straight scratch is etched on the surface of the unsintered ceramic sample strip. The length of the straight scratch on the surface of the sintered ceramic sample is measured. The shrinkage test formula is: Ws = (10 – I) × 100% (Ws – shrinkage rate; I – length after sintering in cm). Reference standard: shrinkage rate < 9%.

[0063] The test results are shown in Table 1:

[0064] Table 1

[0065]

[0066] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. The application of a lithium-free low-temperature sintering aid, characterized in that, It is added to ceramic green body powder for the preparation of low-temperature sintered ceramic green bodies; The ceramic green body powder is composed of the following raw materials in the indicated mass percentages: SiO2 67.02wt%, Al2O3 26.94wt%, Fe2O3 1.25wt%, MgO 0.39wt%, CaO 1.06wt%, Na2O 0.61wt%, K2O 2.35wt%, TiO2 0.38wt%. The preparation method of the lithium-free low-temperature sintering aid includes the following steps: (1) Sodium tetraborate decahydrate and sodium metaborate tetrahydrate were mixed at a mass ratio of 65-70:30-35 to obtain mixture A; then mixture A was mixed with rare earth oxides to obtain mixture B; (2) The mixture B is placed in a muffle furnace for sintering. After sintering, it is taken out and quickly quenched in water to obtain a transparent glassy product. The transparent glassy product is ground into fine powder to obtain the first sintering aid. (3) Mix quartz, Al2O3, CaO, MgO, K2O, Na2O, B2O3 and the first sintering aid evenly to obtain mixture C. Place mixture C in a muffle furnace for sintering to obtain a lithium-free low-temperature sintering aid. In step (1), the mass ratio of mixture A to rare earth oxides is 50:1-2; the rare earth oxides are Eu2O3, CeO2, and (PrNd). x O y Any one of Dy2O3; The mixture C in step (3) consists of the following raw materials in the following mass percentages: quartz 61%, Al2O3 8-10%, CaO 0.1-3%, MgO 0.1-2%, K2O 1-4%, Na2O 4-9%, B2O3 10-15%, and first sintering aid 5%.

2. The application of the lithium-free low-temperature sintering aid according to claim 1, characterized in that, The specific steps of sintering in step (2) are as follows: raise the temperature to 600℃ at a heating rate of 3-3.5℃ / min and hold for 30-40min; continue to raise the temperature to 900-950℃ at a heating rate of 3-3.5℃ / min and hold for 100min; then raise the temperature to 1100-1150℃ at a heating rate of 1.5℃ / min and hold for 120min. The sintering step in step (3) is the same as in step (2).

3. The application of the lithium-free low-temperature sintering aid according to claim 1, characterized in that, Includes the following steps: S1. Add the lithium-free low-temperature sintering aid to the ceramic body powder at a mass ratio of 1%-5% and mix evenly. Add water at a mass ratio of 40-45% of the ceramic body powder and ball mill for 2 hours to form a uniform slurry. Then pour it into a gypsum mold to form a ceramic green body after solidification. S2 After drying the ceramic green body, it is placed in a muffle furnace for sintering. The sintered ceramic green body is then cooled to room temperature with the furnace and taken out to obtain a low-temperature sintered ceramic green body. The specific steps of the sintering are as follows: raise the temperature to 600℃ at a heating rate of 3-3.5℃ / min and hold for 30min; continue to raise the temperature to 900-950℃ at a heating rate of 3-3.5℃ / min and hold for 30min; then raise the temperature to 1100-1150℃ at a heating rate of 1.5℃ / min and hold for 120min.

4. The application of the lithium-free low-temperature sintering aid according to claim 3, characterized in that, The drying temperature in step S2 is 80-85℃, and the drying time is 20-24h.

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