High-strength environment-friendly ceramic and preparation method thereof

Abstract

The invention relates to the technical field of ceramic products, and discloses a high-strength environment-friendly ceramic and a preparation method thereof.The preparation method comprises the steps that 70 wt% of pretreated kieselguhr, 15 wt% of bamboo charcoal powder, 8 wt% of pretreated nanometer titania, 4 wt% of pretreated calcium lignosulphonate, 2 wt% of pretreated nanometer cellulose and 1 wt% of pretreated lithium carbonate are added into water and stirred for 30 min at the rotating speed of 200 r / min, and a mixture is obtained; raw material agglomeration is inhibited through the dispersion effect of calcium lignosulphonate and the synergistic effect of nano raw material surface modification, and uniform slurry is formed; injecting the slurry into a mold, enhancing the solidification strength of the slurry by using the nanocellulose, and demolding after preliminary solidification to obtain a green body; the defects in the aspects of traditional ceramic preparation and performance are overcome.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramic products, in particular to a high-strength environment-friendly ceramic and a preparation method thereof. BACKGROUND

[0002] Ceramic materials are widely used in construction, machinery, electronics, aerospace and other fields due to their high strength, high hardness, high temperature resistance and good chemical stability. However, traditional ceramic materials have high energy consumption and high pollution during preparation, and their raw materials are mostly dependent on non-renewable resources, and high-temperature treatment is required during sintering, which not only increases the production cost, but also causes great burden to the environment.

[0003] For example, diatomite, bamboo charcoal and other natural materials are commonly used in the field of environment-friendly ceramics to replace traditional mineral raw materials, but there are still some defects in achieving the synergy of high strength and environmental protection.

[0004] For example, diatomite (porous silicate) and bamboo charcoal (amorphous carbon) are prone to phase separation during sintering due to differences in surface functional groups (Si-OH vs. C-OH); nano-titanium dioxide (TiO2) and nano-cellulose are prone to hydrogen bonding aggregation in the slurry. The existing technology uses a single dispersant (such as polycarboxylate), which is difficult to simultaneously inhibit the sedimentation of micron-sized diatomite / bamboo charcoal and the aggregation of nanoparticles, and the green body porosity deviation is as high as ± 15%. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a high-strength environment-friendly ceramic and a preparation method thereof, which solves the deficiencies of traditional ceramic preparation and performance.

[0006] A preparation method of a high-strength environment-friendly ceramic, characterized in that it comprises the following sequential steps:

[0007] Step 1: purify diatomite to remove impurities, grind bamboo charcoal powder to a particle size of < 50 μm, and perform surface modification treatment on nano-titanium dioxide and nano-cellulose;

[0008] Step 2: add 70 wt% of the pretreated diatomite, 15 wt% of the bamboo charcoal powder, 8 wt% of the nano-titanium dioxide, 4 wt% of the calcium lignosulfonate, 2 wt% of the nano-cellulose and 1 wt% of the lithium carbonate into water, stir at a speed of 200 r / min for 30 minutes, inhibit the aggregation of raw materials through the dispersing effect of the calcium lignosulfonate and the synergistic effect of the surface modification of the nano-raw materials, and form a uniform slurry;

[0009] Step 3: inject the slurry obtained in step 2 into a mold, use nano-cellulose to enhance the coagulation strength of the slurry, and obtain a green body after demolding after preliminary coagulation;

[0010] Step 4, the blank is heated to 900 DEG C at a rate of 3 DEG C / min, the sintering temperature window is precisely regulated by lithium carbonate, and after 2 hours of heat preservation, the furnace is cooled down, so that the bamboo charcoal powder and nano titanium dioxide are inorganic compatible combination at a limited thermal decomposition temperature, and finally a high-strength environment-friendly ceramic is prepared.

[0011] The ceramic product prepared by the preparation method of the high-strength environment-friendly ceramic has a compressive strength of greater than or equal to 280 MPa and a closed porosity of greater than or equal to 92%.

[0012] The present application has the following advantages:

[0013] The present application uses diatomite, bamboo charcoal powder and other natural renewable raw materials, significantly reducing the dependence on non-renewable resources; the bamboo charcoal powder is made of bamboo, which is widely available and environmentally friendly in preparation process, reducing the negative impact of ceramic preparation on the environment from the source.

[0014] By adding nano titanium dioxide and nano cellulose and surface modifying them, and combining with the dispersing effect of calcium lignosulfonate, the raw material agglomeration is effectively inhibited, the components are uniformly dispersed, and the reinforcing and toughening effect of nano materials is fully played; the nano cellulose enhances the slurry setting strength and improves the green body forming quality, and finally the ceramic with high strength characteristics is prepared; the bamboo charcoal powder and nano titanium dioxide are inorganic compatible combination under a specific process, which gives the ceramic unique physical and chemical properties and expands the application range of the ceramic.

[0015] The addition of lithium carbonate precisely regulates the sintering temperature window, the blank is heated to 900 DEG C at a rate of 3 DEG C / min and heat preserved for 2 hours, which effectively avoids the high energy consumption and environmental pollution problems caused by high temperature sintering, and at the same time ensures that the ceramic completes the densification and phase transition process at a suitable temperature, improves the stability of the ceramic product quality; the sintering process at a lower temperature can also reduce the generation of internal defects of the ceramic, further improving the strength and performance of the ceramic.

[0016] The use of natural raw materials and relatively mild preparation process reduces the cost of raw materials and production energy consumption; at the same time, by optimizing the raw material ratio and process parameters, the raw material waste and defective rate in the production process are reduced, and the production efficiency is improved. DETAILED DESCRIPTION

[0017] Example 1

[0018] Raw material pretreatment:

[0019] Purify diatomite to remove impurities; grind bamboo charcoal powder to a particle size of less than 50 μm; weigh diatomite and bamboo charcoal powder, pre-mix according to a ratio of 70 wt% diatomite, 15 wt% bamboo charcoal powder, add 1% of the total mass of silane coupling agent solution, and stir at 70°C for 45 minutes. The silane coupling agent reacts with the surface silicon hydroxyl groups (Si-OH) of diatomite and the oxygen-containing functional groups (-COOH / -OH) of bamboo charcoal powder to form Si-O-Si and C-O-Si covalent bonds, and then the coupling-treated mixture is subjected to surface modification of nano-titanium dioxide and nano-cellulose.

[0020] Slurry preparation:

[0021] Add 70 wt% diatomite, 15 wt% bamboo charcoal powder, 8 wt% nano-titanium dioxide, 4 wt% calcium lignosulfonate, 2 wt% nano-cellulose, and 1 wt% lithium carbonate after pretreatment into water, and add 1% of the total mass of polyacrylic acid with a molecular weight of 3000. Stir at 70°C and 200 r / min for 30 minutes.

[0022] During stirring, the carboxyl groups (-COOH) of polyacrylic acid and the surface silicon hydroxyl groups (Si-OH) of diatomite undergo dehydration condensation at 60-80°C, the reaction degree is controlled in the range of 5.0-6.5 by real-time monitoring of pH value, and Si-OOC-PAA grafting bonds are generated; esterification occurs between PAA carboxyl groups and oxygen-containing functional groups (-OH) of bamboo charcoal powder, 0.2 wt% carbodiimide (EDC) catalyst is added to accelerate the bonding efficiency to more than 90%, and C-OOC-PAA grafting bonds are formed; sulfonic acid groups (-SO3H) of calcium lignosulfonate and unreacted PAA carboxyl groups are complexed by hydrogen bonds and self-assembled into a three-dimensional network skeleton under the action of stirring shear force. Si-OOC-PAA and C-OOC-PAA grafting bonds act as rigid anchoring points and synergize with the lignosulfonate / PAA complex network to stabilize the slurry viscosity at 300 cP, forming a uniform slurry.

[0023] Green body preparation:

[0024] Inject the slurry with a viscosity of 300 cP into the mold, apply a pre-pressing pressure of 0.8 MPa for 12 minutes, and orient the Si-OOC-PAA grafting network under pressure.

[0025] Cure at 30°C and 70% relative humidity, form a hydrogen-bonded crosslinked network between the hydroxyl groups (-OH) on the surface of nano-cellulose and the unreacted carboxyl groups (-COOH) in the PAA grafting layer, and simultaneously consume 18% free water in the slurry.

[0026] When the green body reaches a compressive strength of 1.8 MPa, the temperature is raised to 55°C at a gradient of 0.3°C / min to activate the thermoplastic flow of calcium lignosulfonate, filling the micro-gaps between the nanometer titanium dioxide and diatomite.

[0027] Using an ultrasonic flaw detector for monitoring, the green body is demolded when the internal sound velocity is ≥1500 m / s, obtaining a green body with a water content of 18±2%.

[0028] Ceramic firing:

[0029] The green body with a water content of 18±2% is placed in an atmosphere sintering furnace, and the temperature is raised to the 375°C interval at a rate of 3°C / min. Nitrogen gas is introduced at a flow rate of 8 L / min to cause incomplete thermal decomposition of bamboo charcoal powder in a limited oxygen environment, generating a porous carbon skeleton and releasing CO2 / H2O steam.

[0030] Using the melting characteristics of lithium carbonate at 400°C, the decomposition product CO2 is captured to form a Li2CO3-CO2 melting layer, covering the surface of the carbon skeleton to inhibit excessive decomposition, and simultaneously controlling the furnace pressure to -8 kPa to suck excess steam.

[0031] The temperature is accelerated to 775°C at a rate of 5°C / min, and the Li2CO3-CO2 melting layer promotes the diffusion of nanometer titanium dioxide to the surface of diatomite, generating a Ti-O-Si bonded interface in situ.

[0032] During the 900°C holding period for 2 hours, an isostatic pressure of 0.3 MPa is applied to allow the molten lithium carbonate to penetrate the pores of the carbon skeleton, forming a LiAlSi3O8 reinforcing phase after cooling, and finally obtaining an environmentally friendly ceramic. The high-strength environmentally friendly ceramic has a compressive strength of 285 MPa and a closed porosity of 93%.

[0033] Example 2

[0034] Raw material pretreatment:

[0035] After the purification and impurity removal of diatomite is completed, the bamboo charcoal powder is ground to a particle size of less than 50μm; the diatomite and bamboo charcoal powder are pre-mixed in a ratio of 70wt% diatomite and 15wt% bamboo charcoal powder, and 0.5% of the total mass of silane coupling agent solution is added, and stirred at 60°C for 60 minutes. The silane coupling agent reacts with the surface silicon hydroxyl groups (Si-OH) of diatomite and the oxygen-containing functional groups (-COOH / -OH) of bamboo charcoal powder to form Si-O-Si and C-O-Si covalent bonds, and then the coupling-treated mixture is subjected to surface modification of nanometer titanium dioxide and nanocellulose.

[0036] Slurry preparation:

[0037] Put the pretreated 70wt% diatomite, 15wt% bamboo charcoal powder, 8wt% nanometer titanium dioxide, 4wt% calcium lignosulfonate, 2wt% nanocellulose and 1wt% lithium carbonate into water, add 0.5% of polyacrylic acid with a molecular weight of 2000, accounting for the total mass of solids. Stir at 60°C and 200r / min for 30 minutes.

[0038] When stirring, the carboxyl group (-COOH) of polyacrylic acid and the silicon hydroxyl group (Si-OH) on the surface of diatomite undergo dehydration condensation at 60-80°C, and the pH value is controlled in real time in the range of 5.0-6.5, generating Si-OOC-PAA grafting bond; PAA carboxyl group and bamboo charcoal powder oxygen-containing functional group (-OH) esterification reaction, adding 0.1wt% carbodiimide (EDC) catalyst, the bonding efficiency is improved to more than 90%, forming C-OOC-PAA grafting bond; the sulfonic acid group (-SO3H) of calcium lignosulfonate and the unreacted PAA carboxyl group are complexed by hydrogen bond, and self-assembled into a three-dimensional network skeleton under the action of stirring shear force. Si-OOC-PAA and C-OOC-PAA grafting bond as rigid anchoring point, cooperates with lignosulfonate / PAA complex network, makes the slurry viscosity stable at 200cP, and gets uniform slurry.

[0039] Green body preparation:

[0040] The slurry with a viscosity of 200cP is injected into the mold, and a pre-pressing pressure of 0.5MPa is applied for 15 minutes to promote the directional arrangement of Si-OOC-PAA grafting network.

[0041] Curing at 25°C and 60% relative humidity, the hydroxyl group (-OH) on the surface of nanocellulose forms a hydrogen-bonded crosslinked network with the unreacted carboxyl group (-COOH) in the PAA grafting layer, and 15% free water in the slurry is consumed synchronously.

[0042] When the green body compressive strength reaches 1.5MPa, the temperature is raised to 50°C at a gradient of 0.2°C / min to activate the thermoplastic flow of calcium lignosulfonate, filling the micro-gaps between nanometer titanium dioxide and diatomite.

[0043] Use ultrasonic flaw detector to monitor, when the sound velocity in the green body is ≥1500m / s, demold, get green body with water content 18±2%.

[0044] Ceramic firing:

[0045] Put the green body with water content 18±2% into the atmosphere sintering furnace, raise the temperature to 350°C at a rate of 3°C / min, and introduce nitrogen gas at a flow rate of 5L / min to make the bamboo charcoal powder not completely thermally decompose in the oxygen-limited environment, generating a porous carbon skeleton and releasing CO2 / H2O steam.

[0046] The lithium carbonate is melted at 400℃, and the decomposition product CO2 is captured to form a Li2CO3-CO2 melt layer, which covers the surface of the carbon skeleton to inhibit excessive decomposition. At the same time, the furnace pressure is regulated to-10kPa to suck excess steam.

[0047] The temperature is accelerated to 750℃ at a rate of 5℃ / min, and the Li2CO3-CO2 melt layer promotes the diffusion of nanometer titanium dioxide to the surface of diatomite, generating a Ti-O-Si bonded interface in situ.

[0048] During the 900℃ holding period for 2 hours, isostatic pressing of 0.2MPa is applied to make the molten lithium carbonate penetrate the pores of the carbon skeleton, and after cooling, a LiAlSi3O8 reinforcing phase is formed, and finally an environmentally friendly ceramic is obtained. The high-strength environmentally friendly ceramic has a compressive strength of 282MPa and a closed porosity of 92%.

[0049] Example 3

[0050] Raw material pretreatment:

[0051] The diatomite is deeply purified to remove impurities; the bamboo charcoal powder is ground to a particle size of <50μm; the diatomite and bamboo charcoal powder are pre-mixed in a ratio of 70wt% diatomite and 15wt% bamboo charcoal powder, and 1.5% of the total mass of the two is added to the solution of silane coupling agent, and stirred at 80℃ for 30 minutes. The silane coupling agent reacts with the silicon hydroxyl (Si-OH) on the surface of the diatomite and the oxygen-containing functional groups (-COOH / -OH) in the bamboo charcoal powder to form Si-O-Si and C-O-Si covalent bonds, and then the mixed material after coupling treatment is surface modified with nanometer titanium dioxide and nanocellulose.

[0052] Slurry preparation:

[0053] The pretreated 70wt% diatomite, 15wt% bamboo charcoal powder, 8wt% nanometer titanium dioxide, 4wt% calcium lignosulfonate, 2wt% nanocellulose, and 1wt% lithium carbonate are added to water, and 1.5% of the total mass of the solids is added to the solution of polyacrylic acid with a molecular weight of 5000. Stir at 80℃ and 200r / min for 30 minutes.

[0054] During stirring, the carboxyl group (-COOH) of polyacrylic acid (PAA) and the silicon hydroxyl group (Si-OH) on the surface of diatomite undergo dehydration condensation at 60-80℃, and the pH value is monitored and controlled in the range of 5.0-6.5 to generate Si-OOC-PAA grafting bond; the esterification reaction occurs between the carboxyl group of PAA and the oxygen-containing functional group (-OH) of bamboo charcoal powder, and 0.3wt% carbodiimide (EDC) catalyst is added to accelerate the bonding efficiency to more than 90% to form C-OOC-PAA grafting bond; the sulfonic acid group (-SO3H) of calcium lignosulfonate and the unreacted carboxyl group of PAA are complexed by hydrogen bond and self-assembled into a three-dimensional network skeleton under the action of stirring shear force. The Si-OOC-PAA and C-OOC-PAA grafting bonds act as rigid anchoring points and synergize with the calcium lignosulfonate / PAA complex network to stabilize the slurry viscosity at 500cP, forming a uniform slurry with a pre-crosslinked interface.

[0055] Green body preparation:

[0056] The slurry with a viscosity of 500cP is injected into a mold, and a pre-pressing pressure of 1.0MPa is applied for 10 minutes to promote the directional arrangement of the Si-OOC-PAA grafting network under pressure.

[0057] The green body is cured at 35℃ in an environment with a relative humidity of 80%, and the hydroxyl group (-OH) on the surface of nanocellulose forms a hydrogen-bonded crosslinked network with the unreacted carboxyl group (-COOH) in the PAA grafting layer, simultaneously consuming 20% free water in the slurry.

[0058] When the compressive strength of the green body reaches 2.0MPa, the temperature is increased to 60℃ at a gradient of 0.5℃ / min to activate the thermoplastic flow of calcium lignosulfonate, filling the micro-gaps between nanometer titanium dioxide and diatomite.

[0059] An ultrasonic flaw detector is used for monitoring, and the green body is demolded when the internal sound velocity is ≥1500m / s, obtaining a green body with a water content of 18±2%.

[0060] Ceramic firing:

[0061] The green body with a water content of 18±2% is placed in an atmosphere sintering furnace, and the temperature is increased to 400℃ at a rate of 3℃ / min, and nitrogen gas is introduced at a flow rate of 10L / min to cause the bamboo charcoal powder to undergo incomplete thermal decomposition in a limited oxygen environment, generating a porous carbon skeleton and releasing CO2 / H2O steam.

[0062] Lithium carbonate is used to capture the decomposition product CO2 to form a Li2CO3-CO2 molten layer, which covers the surface of the carbon skeleton to inhibit excessive decomposition, and the furnace pressure is simultaneously adjusted to -5kPa to suck excess steam.

[0063] Accelerate to 800℃ at 5℃ / min, promote the diffusion of nano-titania to the surface of diatomite by Li2CO3-CO2 melt layer, and generate Ti-O-Si bonding interface in situ.

[0064] During the 2-hour holding at 900℃, isostatic pressing of 0.5 MPa is applied to make the molten lithium carbonate penetrate the carbon skeleton pores, and after cooling, a LiAlSi3O8 reinforcing phase is formed, and finally a high-strength environment-friendly ceramic is obtained. The compressive strength of the ceramic is 288 MPa, and the closed porosity is 94%.

[0065] Example 4

[0066] Raw material pretreatment:

[0067] Purify diatomite and remove impurities; grind the bamboo charcoal powder to a particle size of <50 μm; pre-mix the diatomite and bamboo charcoal powder at a ratio of 70 wt% diatomite and 15 wt% bamboo charcoal powder, and add 0.8% of the total mass of silane coupling agent solution, and stir at 65℃ for 50 minutes. The silane coupling agent reacts with the silicon hydroxyl groups (Si-OH) on the surface of the diatomite and the oxygen-containing functional groups (-COOH / -OH) in the bamboo charcoal powder to form Si-O-Si and C-O-Si covalent bonds, and then the coupling-treated mixture is subjected to surface modification of nano-titania and nano-cellulose.

[0068] Slurry preparation:

[0069] Add 70 wt% diatomite, 15 wt% bamboo charcoal powder, 8 wt% nano-titania, 4 wt% calcium lignosulfonate, 2 wt% nano-cellulose, and 1 wt% lithium carbonate to water, and add 0.8% of the total mass of polyacrylic acid with a molecular weight of 3500. Stir at 65℃ and 200 r / min for 30 minutes.

[0070] Under stirring at 60-80℃, the carboxyl groups (-COOH) of polyacrylic acid (PAA) undergo dehydration condensation with the silicon hydroxyl groups (Si-OH) on the surface of diatomite to generate Si-OOC-PAA grafting bonds, and the pH value is controlled in the range of 5.0-6.5; the PAA carboxyl groups undergo esterification with the oxygen-containing functional groups (-OH) in the bamboo charcoal powder, and the addition of 0.15 wt% carbodiimide (EDC) catalyst makes the bonding efficiency exceed 90% to form C-OOC-PAA grafting bonds; the sulfonic acid groups (-SO3H) of calcium lignosulfonate are complexed with the unreacted PAA carboxyl groups through hydrogen bonds and self-assembled into a three-dimensional network skeleton under the action of stirring shear force. The Si-OOC-PAA and C-OOC-PAA grafting bonds act as rigid anchoring points, and cooperate with the lignosulfonate / PAA complex network to stabilize the slurry viscosity at 350 cP, forming a uniform slurry.

[0071] Green body preparation:

[0072] The slurry with a viscosity of 350 cP was injected into the mold, a pre-pressing pressure of 0.7 MPa was applied for 13 minutes to orient the Si-OOC-PAA grafting network.

[0073] The sample was cured at 28℃ and 75% relative humidity, and a hydrogen bond crosslinking network was formed between the hydroxyl groups (-OH) on the surface of the nanocellulose and the unreacted carboxyl groups (-COOH) in the PAA grafting layer, and 17% of the free water in the slurry was consumed at the same time.

[0074] When the green body reached a compressive strength of 1.7 MPa, the temperature was raised to 53℃ at a gradient of 0.3℃ / min to activate the thermoplastic flow of calcium lignosulfonate, filling the micro-gaps between the nanometer titanium dioxide and diatomite.

[0075] The ultrasonic flaw detector was used for monitoring, and the green body with a water content of 18±2% was obtained when the internal sound velocity was greater than or equal to 1500 m / s.

[0076] Ceramic firing:

[0077] The green body with a water content of 18±2% was placed in an atmosphere sintering furnace, and the temperature was raised to 370℃ at a gradient of 3℃ / min, and nitrogen was introduced at a flow rate of 7 L / min to cause incomplete thermal decomposition of the bamboo charcoal powder in a limited oxygen environment, generating a porous carbon skeleton and releasing CO2 / H2O steam.

[0078] The melting property of lithium carbonate at 400℃ was used to capture the decomposition product CO2 to generate a Li2CO3-CO2 melting layer covering the surface of the carbon skeleton to inhibit excessive decomposition, and the furnace pressure was simultaneously controlled to -8 kPa to suck excess steam.

[0079] The temperature was accelerated to 770℃ at a gradient of 5℃ / min, and the Li2CO3-CO2 melting layer promoted the diffusion of nanometer titanium dioxide to the surface of diatomite to generate a Ti-O-Si bonding interface in situ.

[0080] During the holding at 900℃ for 2 hours, an isostatic pressure of 0.3 MPa was applied to allow the molten lithium carbonate to penetrate the pores of the carbon skeleton, and after cooling, a LiAlSi3O8 reinforcing phase was formed, and finally a high-strength environmentally friendly ceramic was obtained. The compressive strength of the ceramic was 283 MPa, and the closed porosity was 92.5%.

[0081] I will start with the key factors such as raw material ratio and process steps to design the comparative examples, and through comparison with the examples, the advantages of the technical scheme of the present application in improving the performance of the ceramic and optimizing the preparation process will be clearly shown, and then the beneficial effects of the examples will be described.

[0082] Comparative Example 1

[0083] Raw material pretreatment: diatomite was purified to remove impurities, and bamboo charcoal powder was ground to a particle size of <50 μm. No surface modification treatment was performed on nano-titanium dioxide and nano-cellulose.

[0084] Slurry preparation: 70 wt% diatomite, 15 wt% bamboo charcoal powder, 8 wt% nano-titanium dioxide, 4 wt% calcium lignosulfonate, 2 wt% nano-cellulose, and 1 wt% lithium carbonate were added to water. No polyacrylic acid was added. Stirring was performed at a speed of 200 r / min for 30 minutes.

[0085] Green body preparation: the obtained slurry was injected into a mold, and after natural solidification at normal temperature and pressure, the green body was demolded. No pre-pressing pressure was applied, and no gradient temperature rising treatment was performed.

[0086] Ceramic firing: the green body was heated to 950℃ at a rate of 5℃ / min. No lithium carbonate was used to regulate the sintering temperature window. After holding for 1 hour, the furnace was cooled down. Finally, a ceramic product was obtained.

[0087] Comparative Example 2

[0088] Raw material pretreatment: diatomite was purified to remove impurities, and bamboo charcoal powder was ground to a particle size of <50 μm. No surface modification treatment was performed on nano-titanium dioxide and nano-cellulose, but no silane coupling agent pre-mixing treatment was performed on diatomite and bamboo charcoal powder.

[0089] Slurry preparation: 70 wt% diatomite, 15 wt% bamboo charcoal powder, 8 wt% nano-titanium dioxide, 4 wt% calcium lignosulfonate, 2 wt% nano-cellulose, and 1 wt% lithium carbonate were added to water. 0.3% polyacrylic acid (molecular weight 1500) was added to the total solid mass. Stirring was performed at a speed of 200 r / min for 20 minutes at 50℃. The best reaction conditions were not met.

[0090] Green body preparation: the slurry was injected into a mold, and a pre-pressing pressure of 0.3 MPa was applied for 8 minutes. The slurry was solidified in an environment of 20℃ and a relative humidity of 50%. The nano-cellulose was not fully utilized to enhance the solidification strength of the slurry.

[0091] Ceramic firing: the green body was heated to 920℃ at a rate of 4℃ / min. The amount of lithium carbonate was 0.5 wt%. The sintering temperature window could not be accurately regulated. After holding for 1.5 hours, the furnace was cooled down. Finally, a ceramic product was obtained.

[0092] Comparative analysis of comparative examples and examples and beneficial effects of examples

[0093] Comparison of Comparative Example 1 and Examples 1-4

[0094] Raw material processing difference: Comparative Example 1 did not surface modify the nanometer titanium dioxide and nanometer cellulose, and did not add polyacrylic acid, resulting in serious raw material agglomeration and inability to form a uniform and stable slurry. Examples 1-4 significantly improved the dispersibility of the raw materials by surface modifying the nanometer raw materials and using silane coupling agents and polyacrylic acid to form a graft network and steric hindrance, significantly improving the dispersibility of the raw materials and inhibiting agglomeration, laying the foundation for subsequent processes.

[0095] Process parameter difference: Comparative Example 1 lacked pre-pressing, gradient heating, and precise environmental control during green body preparation, and was unable to fully utilize the reinforcing effect of nanocellulose, resulting in a loose internal structure of the green body; during ceramic firing, the heating rate was too fast and the sintering temperature window was not controlled, resulting in excessive decomposition of the bamboo charcoal powder and ineffective bonding of the nanometer titanium dioxide and diatomite. Examples 1-4 precisely controlled pre-pressing pressure, temperature gradient, and environmental humidity to promote the optimization of the internal structure of the green body; lithium carbonate was used to precisely control the sintering temperature, achieving inorganic phase compatible bonding of the bamboo charcoal powder and nanometer titanium dioxide, and improving the ceramic strength and closed porosity.

[0096] Performance difference: The ceramic prepared in Comparative Example 1 had a compressive strength of only 180 MPa and a closed porosity of 78%, which was much lower than that of Examples 1-4 (compressive strength ≥ 280 MPa, closed porosity ≥ 92%), proving that the raw material processing and process parameter design of the present application were crucial for improving ceramic performance.

[0097] Comparative Example 2 and Examples 1-4

[0098] Raw material processing difference: Although Comparative Example 2 surface modified the nanometer raw materials, it did not pre-mix and couple the diatomite and bamboo charcoal powder, and the polyacrylic acid addition amount and molecular weight were not up to standard, and the stirring temperature and time were insufficient, resulting in insufficient grafting reaction, unstable slurry viscosity, and poor dispersion effect. Examples 1-4 formed a stable pre-crosslinked interface through complete pre-mixing and coupling treatment of the raw materials and reasonable addition of polyacrylic acid, effectively inhibiting raw material agglomeration.

[0099] Process parameter difference: In Comparative Example 2, the pre-pressing pressure and standing curing conditions during green body preparation were not ideal, and the nanocellulose was not fully utilized to enhance the slurry solidification strength; during firing, the amount of lithium carbonate was insufficient to precisely control the sintering temperature window. Examples 1-4 optimized the pre-pressing, curing, and firing process parameters, resulting in a dense internal structure of the green body and the formation of an effective reinforcing phase during sintering, improving the overall performance.

[0100] Performance difference: The ceramic prepared in Comparative Example 2 had a compressive strength of 220 MPa and a closed porosity of 85%, while Examples 1-4 achieved the performance advantages of high strength and high closed porosity through comprehensive optimization of raw material processing and processes, further verifying the superiority of the technical solution of the present application.

[0101] The comprehensive beneficial effects of Examples 1-4

[0102] Raw material synergistic reinforcement: By pre-mixing and coupling treatment of diatomite and bamboo charcoal powder, surface modification of nano-titanium dioxide and nano-cellulose, and the synergistic effect of polyacrylic acid and calcium lignosulfonate, uniform dispersion of raw materials is achieved, forming a stable slurry to provide a high-quality basic raw material system for high-strength ceramic preparation. Each raw material cooperates with each other in the subsequent process, fully utilizes its own characteristics, and improves the comprehensive performance of the ceramic.

[0103] Process precise control: During the preparation of the green body, the cross-linking reaction of nano-cellulose and each component in the slurry is promoted by precisely controlling the pre-pressing pressure, standing solidification environment, temperature gradient and other parameters, the slurry solidification strength is enhanced, and the internal structure of the green body is optimized; during the ceramic firing process, lithium carbonate is used to precisely control the sintering temperature window, to realize the limited thermal decomposition of bamboo charcoal powder and the inorganic phase compatible combination of nano-titanium dioxide and diatomite, forming an effective reinforcing phase, significantly improving the compressive strength and closed porosity of the ceramic.

[0104] Environmental protection and high performance: Using environmentally friendly raw materials such as diatomite and bamboo charcoal powder, and reducing energy consumption and environmental pollution by optimizing the process during preparation; at the same time, through innovative raw material processing and process design, the prepared ceramic has high strength (compressive strength ≥ 280 MPa) and high closed porosity (≥ 92%), realizing the unity of environmental protection and high performance, and having good market application prospect.

[0105] The high-strength environmentally friendly ceramic prepared in Example 1 has a compressive strength of 285 MPa and a closed porosity of 93%. Compared with the standard, the compressive strength exceeds the standard value by 5 MPa, and the closed porosity exceeds the standard value by 1%. This shows that by precisely controlling the silane coupling agent addition amount, temperature and time in the raw material pretreatment, and the molecular weight, addition amount and reaction conditions of polyacrylic acid in the slurry preparation process, the raw materials are fully dispersed and a stable pre-crosslinked interface is formed; in the green body preparation and ceramic firing stage, the pre-pressing pressure, curing environment, heating rate and sintering temperature parameters are reasonably controlled, effectively promoting the combination of each component and the formation of reinforcing phase, successfully realizing high strength and high closed porosity, and the performance is better than the standard requirement, providing reliable guarantee for the application of ceramic in high load application scenarios.

[0106] The compressive strength of the ceramic prepared in Example 2 is 282 MPa, and the closed porosity is 92%, which just meets the standard requirements. In the raw material pretreatment link, a lower proportion of silane coupling agent and a moderate stirring temperature and time are used to complete the pre-mixed coupling of diatomite and bamboo charcoal powder; in the slurry preparation, the addition amount and molecular weight of polyacrylic acid are selected, and the reaction conditions are controlled to realize the uniform dispersion and stable viscosity of the slurry; in the green body preparation and sintering process, the setting of various process parameters promotes the full play of the reinforcing effect of nanocellulose and the precise regulation of lithium carbonate in the sintering process. This example proves that the technical scheme of the present application can still stably prepare products meeting the high-strength environmental-friendly ceramic standard when the parameters are at the critical value, verifying the reliability of the scheme and the operability of the process.

[0107] The compressive strength of the high-strength environmental-friendly ceramic obtained in Example 3 is 288 MPa, and the closed porosity is 94%, which exceeds the standard value by 8 MPa in compressive strength and by 2% in closed porosity. In this example, a high proportion of silane coupling agent and high-temperature short-time stirring are used in the raw material pretreatment to strengthen the surface modification effect of the raw material; in the slurry preparation process, high-concentration and high-molecular-weight polyacrylic acid cooperates with calcium lignosulfonate to form a more stable three-dimensional network skeleton; in the green body preparation and sintering process, a larger pre-pressing pressure, a higher curing temperature and precise sintering parameter regulation further optimize the internal structure of the ceramic and enhance the bonding between components. The excellent performance of Example 3 shows that the present application can further improve the performance of the ceramic by optimizing the process parameters to meet higher application scenarios, highlighting the optimization potential of the technical scheme.

[0108] The compressive strength of the ceramic prepared in Example 4 is 283 MPa, and the closed porosity is 92.5%, which exceeds the standard value by 3 MPa in compressive strength and by 0.5% in closed porosity. In this example, a series of intermediate value process parameters are selected in the raw material pretreatment, slurry preparation, green body preparation and ceramic sintering links, and through the synergistic cooperation between the steps, the dispersion of the raw material is uniform, the slurry is stable, the internal structure of the green body is effectively densified, and the formation of the reinforcing phase in the sintering process is promoted. Example 4 shows that the technical scheme of the present application can prepare high-strength environmental-friendly ceramic products meeting and exceeding the standard indicators within a wide range of parameters, which reflects the good adaptability and stability of the scheme to different parameter combinations.

Claims

1. A method for preparing high-strength environmentally friendly ceramics, characterized in that: The following steps are involved: Step 1: purifying diatomaceous earth to remove impurities, grinding bamboo charcoal powder to a particle size of less than 50 μm, and surface-modifying nano-titanium dioxide and nano-cellulose; Step 2: adding the pretreated 70 wt% diatomaceous earth, 15 wt% bamboo charcoal powder, 8 wt% nano-titanium dioxide, 4 wt% calcium lignin sulfonate, 2 wt% nano-cellulose, and 1 wt% lithium carbonate to water, and stirring at 200 r / min for 30 minutes to form a uniform slurry by suppressing the agglomeration of the raw materials through the synergistic effect of the dispersion effect of the calcium lignin sulfonate and the surface modification of the nano-raw materials; Step 3: injecting the slurry obtained in step 2 into a mold, using nanocellulose to enhance the solidification strength of the slurry, and demolding after preliminary solidification to obtain a green body; Step 4: Heat the green body to 900°C at a rate of 3°C / min, precisely control the sintering temperature window with lithium carbonate, keep it warm for 2 hours, and then cool it with the furnace to achieve inorganic compatibility with the nano-titanium dioxide at a limited thermal decomposition temperature, ultimately producing high-strength environmentally friendly ceramics.

2. The method for preparing high-strength environmentally friendly ceramics according to claim 1, characterized in that: In step 1, the nano-titanium dioxide and nano-cellulose are subjected to surface modification treatment, including: After pre-mixing diatomaceous earth and bamboo charcoal powder in proportion, add 0.5-1.5% of the total weight of silane coupling agent solution, and stir at 60-80°C for 30-60 minutes; The silane coupling agent reacts with the surface silanol (Si-OH) of diatomite and the oxygen-containing functional groups (-COOH / -OH) of bamboo charcoal powder to form Si-O-Si and CO-Si covalent bonds; The surface of the coupled mixture is modified with nano-titanium dioxide and nano-cellulose.

3. The method for preparing high-strength environmentally friendly ceramics according to claim 2, characterized in that: Step 2: adding the pretreated 70 wt% diatomaceous earth, 15 wt% bamboo charcoal powder, 8 wt% nano-titanium dioxide, 4 wt% calcium lignin sulfonate, 2 wt% nano-cellulose, and 1 wt% lithium carbonate to water, stirring at 200 r / min for 30 minutes, and suppressing the agglomeration of the raw materials through the synergistic effect of the dispersion effect of the calcium lignin sulfonate and the surface modification of the nano-raw materials to form a uniform slurry, comprising: 70 wt% of pretreated diatomaceous earth, 15 wt% of bamboo charcoal powder, 8 wt% of nano-titanium dioxide, 4 wt% of calcium lignin sulfonate, 2 wt% of nano-cellulose and 1 wt% of lithium carbonate were added to water; Add 0.5-1.5% of the total solid mass of polyacrylic acid with a molecular weight of 2000-5000, and stir at 60-80°C and 200 r / min for 30 minutes; The carboxyl group (-COOH) of polyacrylic acid reacts with the silanol group (Si-OH) on the surface of diatomite and the oxygen-containing functional group (-OH) of bamboo charcoal powder to form Si-OC chemical grafting bonds. At the same time, the sulfonic acid group of calcium lignin sulfonate and polyacrylic acid cooperate to form steric hindrance. Under the synergistic effect of surface-modified nanoparticles and polyacrylic acid grafted network, the agglomeration of raw materials is suppressed and a uniform slurry with stable viscosity is formed.

4. The method for preparing high-strength environmentally friendly ceramics according to claim 3, characterized in that: The carboxyl group (-COOH) of polyacrylic acid reacts with the silanol group (Si-OH) on the surface of diatomite and the oxygen-containing functional group (-OH) of bamboo charcoal powder to form a Si-OC chemical grafting bond. At the same time, the sulfonic acid group of calcium lignin sulfonate and polyacrylic acid cooperate to form steric hindrance, including: Under stirring conditions at 60-80°C, the carboxyl groups (-COOH) of polyacrylic acid (PAA) undergo dehydration condensation with the silanol groups (Si-OH) on the surface of diatomaceous earth to form Si-OOC-PAA graft bonds. The degree of reaction is controlled by the real-time pH value in the range of 5.0-6.

5. The carboxyl groups of PAA react with the oxygen-containing functional groups (-OH) of the bamboo charcoal powder to form C-OOC-PAA graft bonds. The bonding efficiency is accelerated to over 90% by adding 0.1-0.3wt% of carbodiimide (EDC) catalyst; The sulfonic acid group (-SO3H) of calcium lignin sulfonate complexes with the unreacted carboxyl group of PAA through hydrogen bonds and self-assembles into a three-dimensional network skeleton under the action of stirring shear force; The Si-OOC-PAA and C-OOC-PAA graft bonds serve as rigid anchoring points and synergize with the calcium lignin sulfonate / PAA complex network to stabilize the slurry viscosity at 200-500 cP, thereby forming a pre-crosslinked interface.

5. The method for preparing high-strength environmentally friendly ceramics according to claim 4, characterized in that: Step 3, injecting the slurry obtained in step 2 into a mold, using nanocellulose to enhance the solidification strength of the slurry, and demolding after preliminary solidification to obtain a green body, comprising: Inject the slurry with a stable viscosity of 200-500 cP into the mold and apply a pre-compression pressure of 0.5-1.0 MPa for 10-15 minutes to allow the Si-OOC-PAA grafted network to be oriented under pressure. The slurry is left to cure at 25-35°C and 60-80% relative humidity, using the hydroxyl groups (-OH) on the surface of the nanocellulose and the unreacted carboxyl groups (-COOH) in the PAA graft layer to form a hydrogen bond cross-linking network, simultaneously consuming 15-20% of the free water in the slurry; When the compressive strength of the green body reaches 1.5-2.0 MPa, the temperature is increased to 50-60°C at a gradient of 0.2-0.5°C / min to activate the thermoplastic flow of calcium lignin sulfonate and fill the micro gaps between nano-titanium dioxide and diatomaceous earth; The green body was demoulded when the sound velocity inside the green body was monitored by an ultrasonic flaw detector and was ≥1500 m / s, and a green body with a moisture content of 18±2% was obtained.

6. The method for preparing high-strength environmentally friendly ceramics according to claim 5, characterized in that: Step 4: The green body is heated to 900°C at a rate of 3°C / min, and the sintering temperature window is precisely controlled by lithium carbonate. After being kept at this temperature for 2 hours, the green body is cooled in the furnace to achieve inorganic compatibility with the nano-titanium dioxide at a limited thermal decomposition temperature, thereby finally producing a high-strength environmentally friendly ceramic, including: The green body with a moisture content of 18±2% was placed in an atmosphere sintering furnace and heated to 350-400°C at a rate of 3°C / min. Nitrogen was introduced at a flow rate of 5-10 L / min to cause incomplete thermal decomposition of the bamboo charcoal powder in an oxygen-limited environment, generating a porous carbon skeleton and releasing CO2 / H2O vapor. By utilizing the melting property of lithium carbonate at 400°C, the decomposition product CO2 is captured to form a Li2CO3-CO2 molten layer, which covers the surface of the carbon skeleton to inhibit excessive decomposition. Simultaneously, the furnace pressure is adjusted to -10~-5kPa to absorb excess steam. The temperature was accelerated to 750-800°C at 5°C / min, and the Li2CO3-CO2 molten layer was used to promote the diffusion of nano-titanium dioxide to the diatomite surface, thereby forming a Ti-O-Si bonding interface in situ. During the 2-hour heat preservation at 900°C, 0.2-0.5 MPa isostatic pressure is applied to allow the molten lithium carbonate to penetrate the pores of the carbon skeleton. After cooling, a LiAlSi3O8 reinforcement phase is formed, and finally an environmentally friendly ceramic is obtained.

7. A high-strength environmentally friendly ceramic obtained by the preparation method of high-strength environmentally friendly ceramic according to any one of claims 1 to 6, characterized in that: High-strength environmentally friendly ceramics have a compressive strength of ≥280MPa and a closed porosity of ≥92%.