A low temperature preparation method of conductive rutile titanium dioxide based on pre-crystallized intermediate

Abstract

This invention discloses a low-temperature preparation method for conductive rutile titanium dioxide based on a pre-crystallized intermediate, belonging to the field of advanced functional powder material preparation technology. The method includes the following steps: S1, hydrothermal pre-crystallization to prepare an active intermediate; S11, slurry preparation and accelerator addition; S12, hydrothermal crystallization reaction; S13, washing and drying; S2, controlled co-precipitation loading of a tin-antimony conductive layer; S21, matrix redispersion; S22, precursor solution preparation; S23, co-current co-precipitation reaction; S24, aging and post-treatment; S3, low-temperature simultaneous calcination; S31, calcination procedure; S32, simultaneous conversion mechanism; S321, matrix crystal transformation; S322, conductive layer crystallization; S33, post-calcination treatment. Through a single low-temperature calcination step, the rutile phase crystal transformation of the titanium dioxide matrix and the crystallization of the antimony-doped tin dioxide conductive layer on the surface can be completed simultaneously, greatly reducing energy consumption and production cycle.

Description

Technical Field

[0001] This invention relates to the field of advanced functional powder material preparation technology, and in particular to a low-temperature preparation method for conductive rutile titanium dioxide based on pre-crystallized intermediates. Background Technology

[0002] With the rapid development of emerging industries such as new energy, electronic information, and high-end manufacturing, and the increasing demand for material functionality in fields such as specialty coatings, electronic components, and antistatic plastics, traditional titanium dioxide, while possessing excellent pigment properties such as high whiteness and high hiding power, struggles to meet special application requirements such as antistatic and electromagnetic shielding due to its lack of conductivity. Against this backdrop, conductive titanium dioxide has emerged. Using titanium dioxide as a matrix, it undergoes special processing such as nanotechnology, surface coating, or semiconductor doping to fully retain the original excellent pigment properties of titanium dioxide while endowing it with good conductivity or antistatic functions. This makes it a new type of electronically conductive functional semiconductor pigment, effectively filling the functional gap of traditional titanium dioxide.

[0003] However, existing technologies for achieving conductivity in titanium dioxide primarily rely on bulk doping modification and surface coating composite methods. Both methods require a two-step calcination process. These two independent calcination processes not only extend the production cycle but also double energy consumption, directly leading to high production costs. Furthermore, because the secondary coating is performed on rutile particles that have already been sintered at high temperatures and have significantly reduced surface activity, the bond between the conductive layer and the titanium dioxide matrix is ​​mostly physical adhesion or weak chemical interaction, resulting in poor stability. Under harsh operating environments, the conductive layer is prone to peeling off, affecting the product's lifespan and conductivity stability.

[0004] There are already relevant invention patents concerning the preparation of conductive titanium dioxide, as detailed below:

[0005] Chinese Patent Application No. CN201911220294.8, entitled "A Conductive Titanium Dioxide and its Preparation Method," discloses a conductive titanium dioxide and its preparation method. The conductive titanium dioxide comprises a titanium dioxide substrate and a coating layer on the surface of the titanium dioxide substrate. The coating layer, from the inside out, includes a polyaniline coating layer and an ATO coating layer. The ATO coating layer, in addition to Sb doping, also does not contain C or N. The conductive titanium dioxide provided by this invention possesses the advantages of PANI, ATO, and TiO2, and achieves a significant improvement in conductivity, exhibiting superconducting properties. This invention also provides a method for preparing conductive titanium dioxide. Before polyaniline coating, the titanium dioxide is first polymer-modified. After coating with the polyaniline film and ATO, subsequent calcination and organic surface agent treatment provide better wettability and dispersibility for later use of the titanium dioxide. The titanium dioxide prepared by this method has fine and uniform particles, high dispersibility, high weather resistance, and good formulation applicability.

[0006] While the aforementioned existing patents can produce titanium dioxide with fine and uniform particles, high dispersibility, high weather resistance, and formulation applicability, the production cost during the conductivity conversion process remains high. The complex process steps not only increase raw material consumption and labor costs, but the calcination stage still relies on traditional methods. This failure to effectively reduce energy consumption ultimately makes it difficult to lower product production costs, failing to meet the cost control requirements of large-scale industrial production. Furthermore, multiple coating and processing steps may increase the production cycle, further impacting production efficiency. Summary of the Invention

[0007] The purpose of this application is to provide a low-temperature preparation method for conductive rutile titanium dioxide based on precrystallized intermediates, in order to solve the problem of high production costs in the existing preparation of conductive titanium dioxide.

[0008] This invention provides a novel low-temperature integrated preparation method based on a pre-crystallized active intermediate. This method completely abandons the traditional two-step calcination mode. By performing hydrothermal pre-crystallization treatment on metatitanic acid, a special precursor with high reactivity is constructed. This precursor can simultaneously complete the complete transformation of the titanium dioxide matrix to the rutile phase and the crystallization and firm bonding of the antimony-doped tin dioxide conductive layer on the surface in a single medium-temperature calcination step that coincides with the optimal phase formation temperature of ATO.

[0009] A low-temperature preparation method for conductive rutile titanium dioxide based on precrystallized intermediates, specifically including the following steps:

[0010] S1, Hydrothermal precrystallization to prepare active intermediates: The original metatitanic acid, whose main component is hydrated titanium dioxide, is converted into a special precursor that can be rapidly transformed into rutile phase at a lower temperature thereafter. The surface of the rutile phase is rich in active sites such as hydroxyl groups.

[0011] S11, Slurry preparation and accelerator addition: Take industrial metatitanic acid filter cake, add deionized water, and prepare a uniform titanium dioxide slurry in a high-speed shear disperser.

[0012] S12, hydrothermal crystallization reaction: The mixed slurry is transferred to a corrosion-resistant high-pressure hydrothermal reactor, sealed, and then placed in a homogeneous reactor;

[0013] S13, Washing and Drying: After the reaction is completed, the product is cooled naturally, vacuum filtered, and washed to completely remove free chloride ions and other impurities. The washed filter cake is dried and then coarsely crushed to obtain a loose pre-crystallized active intermediate powder.

[0014] S2, Controllable co-precipitation loading of tin-antimony conductive layer: On the surface of precrystallized active intermediate powder particles, tin-antimony compounds are attached in a highly uniform and compact manner to form an amorphous hydroxide precursor layer;

[0015] S21, Matrix redispersion: The precrystallized active intermediate powder is redispersed in deionized water. After ultrasonic pretreatment for 10 minutes, it is transferred to a reactor with a constant temperature jacket and strong stirring to preheat and maintain the slurry temperature.

[0016] S22, Preparation of precursor solution: This involves the preparation of tin-antimony salt mixture and precipitant. Tin tetrachloride and antimony trichloride are weighed according to the molar ratio of Sn to Sb in the tin-antimony salt mixture. Tin tetrachloride and antimony trichloride are dissolved together in hydrochloric acid solution and stirred until completely clear and transparent. The precipitant is prepared as a 10%-15% ammonium bicarbonate aqueous solution.

[0017] S23, Co-precipitation reaction: A dual-channel precision metering pump is used to simultaneously and slowly add the tin-antimony salt mixture and the precipitant to the pre-crystallized active intermediate powder slurry, which is under vigorous stirring, at a constant and matched flow rate.

[0018] S24, Aging and Post-treatment: After the addition is complete, continue to maintain the system temperature at about 60℃ and stir at a constant speed for aging for 2.0-3.0 hours to ensure complete deposition reaction and stable aging of the precursor. Then, cool and filter the slurry and wash it with a large amount of deionized water until there is no white precipitate in the filtrate after testing with 0.1mol / L silver nitrate solution to completely remove chloride ions and obtain filter cake. Dry the filter cake obtained after removing chloride ions to obtain composite precursor powder loaded with uniform amorphous tin antimony hydroxide.

[0019] S3, Low-temperature synchronous calcination: Achieve dual transformation in a single heat treatment process by placing the composite precursor powder obtained in step S2 into a programmable temperature controlled muffle furnace or rotary kiln and calcining it in static air or low-flow oxygen atmosphere.

[0020] S31, calcination program: heat up to the target temperature of 580℃-620℃ at a heating rate of 2-3℃ / min, and calcine at this temperature for 1.5-2.5 hours.

[0021] S32, simultaneous conversion mechanism: two solid-state reactions occur simultaneously during the medium-temperature calcination process;

[0022] S321, matrix crystal transformation: a precrystallized intermediate powder with high activity and internal storage of phase change driving energy is activated at a relatively low temperature of 0~600℃ and rapidly and completely transforms into a well-crystallized rutile titanium dioxide matrix.

[0023] S322, conductive layer crystallization: the amorphous tin-antimony hydroxide uniformly coated on the surface of the composite precursor powder is dehydrated and oxidized, and crystallized into an antimony-doped tin dioxide nanocrystalline layer with excellent conductivity. Since the matrix and the conductive layer precursor undergo phase transformation and growth simultaneously during calcination, a strong chemical bonding interface is formed between the two.

[0024] S33, Post-calcination treatment: After calcination, the material is cooled naturally in the furnace or cooled to room temperature under the protection of flowing nitrogen. Finally, it is deagglomerated and refined by an air jet mill, and then sieved and graded as needed to obtain highly conductive rutile titanium dioxide.

[0025] As a further improvement of the present invention, in step S11, the moisture content of the metatitanic acid filter cake is controlled at 40%-60%, the concentration of the titanium dioxide homogeneous slurry is 150-250 g / L, and a rutile phase change promoter is added to the homogeneous slurry. The amount of the rutile phase change promoter added is 1.0%-3.0% of the mass of titanium dioxide in the homogeneous slurry. The rutile phase change promoter is tin tetrachloride, which is used to provide Sn in a hydrothermal environment. 4+ ions, the Sn 4+ Ions are adsorbed onto the surface of titanium dioxide crystals, effectively catalyzing and reducing the activation energy of the anatase-to-rutile phase transition. By controlling the metatitanic acid filter cake, both uniform slurry dispersion and meeting the reaction conditions for subsequent hydrothermal precrystallization can be ensured, while the Sn provided by tin tetrachloride can also be utilized. 4+ Ions adsorbed on the surface of the titanium dioxide lattice effectively catalyze the phase transition process and reduce the activation energy of the transformation from anatase to rutile.

[0026] As a further improvement of the present invention, in step S12, the filling degree of the mixed slurry in the reactor is 60%-75%, and the mixed slurry needs to be reacted in a homogeneous reactor at a temperature of 180℃-220℃ for 4-6 hours. The metatitanic acid will undergo a dissolution-recrystallization process in the homogeneous reactor. This dissolution-recrystallization is used to induce the formation of a slurry product mainly composed of anatase microcrystals and rich in active hydroxyl groups on the surface. This allows the metatitanic acid to fully complete the dissolution-recrystallization process, ensuring both the stability and sufficiency of the hydrothermal reaction, and inducing the formation of a slurry product mainly composed of anatase microcrystals and rich in active hydroxyl groups on the surface. This lays a crucial precursor foundation for subsequent low-temperature crystal form transformation and uniform loading of the conductive layer.

[0027] As a further improvement of the present invention, in step S13, the washing is performed using hot deionized water at 60-80℃, and the hot deionization is repeated until the conductivity of the filtrate is lower than 50 μS / cm. The filter cake drying is carried out at 100℃-120℃ for 10-15 hours. XRD analysis of the pre-crystallized active intermediate powder shows that its main component is anatase phase with trace amounts of rutile phase. Deionized water can efficiently and thoroughly remove impurities such as free chloride ions, avoiding interference from impurities with subsequent crystal transformation and conductive layer loading, and allows the filter cake to dry fully without damaging the precursor structure.

[0028] As a further improvement of the present invention, in step S21, the precrystallized active intermediate powder is dispersed at a titanium dioxide solid content of 10%-15%, and the slurry temperature is maintained between 55°C and 65°C.

[0029] As a further improvement of the present invention, in step S22, the molar ratio of Sn to Sb is 10:1-12:1, the concentration of the hydrochloric acid solution is 1.5-2.0 mol / L, and the total concentration of metal ions in the hydrochloric acid solution is controlled at 0.8-1.2 mol / L.

[0030] As a further improvement of the present invention, in step S23, the process of adding the tin-antimony salt mixture and the precipitant is monitored and adjusted in real time by a pH meter. The real-time monitoring and feedback are used to ensure that the pH value of the reaction system is strictly stable within the range of 3.8-4.2.

[0031] As a further improvement of the present invention, in step S23, the dropping time is 2.5-3.5 hours, and the pH range and slow dropping method are used to ensure that the hydrolysis precipitation reaction of tin-antimony ions and the adsorption process of the active sites on the surface of the pre-crystallized active intermediate powder particles are carried out synchronously and uniformly.

[0032] As a further improvement of the present invention, in step S24, the drying operation is carried out at 90°C-110°C for 12-18 hours.

[0033] Compared with the prior art, the beneficial effects of this invention are as follows:

[0034] 1. Abandoning the traditional two-step high-temperature calcination method for preparing conductive titanium dioxide, this method achieves simultaneous rutile phase transformation of the titanium dioxide matrix and crystallization of the antimony-doped tin dioxide conductive layer through a single low-temperature calcination step at 580℃-620℃. Compared to the traditional two independent calcination processes requiring temperatures above 750℃, this significantly reduces energy consumption and production cycle, solving the problem of high production costs in existing technologies from the core of the process, and better meeting the cost control requirements of large-scale industrial production.

[0035] 2. Through a low-temperature hydrothermal reaction at 180℃-220℃, combined with tin tetrachloride and rutile phase transformation promoter, the original metatitanic acid is converted into a pre-crystallized intermediate mainly composed of anatase with abundant hydroxyl active sites on its surface. This intermediate can rapidly and completely transform into the rutile phase at low temperatures of 300℃-600℃. This method reduces the temperature and energy consumption of crystal transformation and provides sufficient active sites for the uniform loading of the subsequent conductive layer.

[0036] 3. Using dual-channel co-precipitation technology, the molar ratio of Sn to Sb is precisely controlled at 10:1-12:1, the reaction pH is stabilized at 3.8-4.2, and the Sn is slowly added at a constant temperature of 60℃ for 2.5-3.5 hours to complete aging. Combined with ultrasonic pretreatment, the matrix is ​​fully dispersed, and a uniform, non-agglomerated amorphous tin-antimony hydroxide layer can be formed on the surface of the intermediate.

[0037] 4. The transformation of the titanium dioxide matrix crystal form and the crystallization of the conductive layer occur simultaneously and grow synergistically during the same calcination process, forming a strong chemical bonding interface between the two, which can effectively improve the conductivity stability and service life of the product.

[0038] 5. The intermediate is repeatedly washed with hot deionized water at 60℃-80℃ until the conductivity of the filtrate is below 50μS / cm. After co-precipitation, it is tested with silver nitrate solution to ensure no chloride ion residue remains, thus thoroughly removing free impurities. This refined impurity removal process ensures the high purity and excellent performance of the final product. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a flowchart of the steps of the present invention.

[0041] Figure 2 This is a graph showing the resistivity of C1 versus pressure in this invention.

[0042] Figure 3 This is a graph showing the resistivity of C2 versus pressure in this invention.

[0043] Figure 4 This is a graph showing the resistivity of C3 versus pressure in this invention.

[0044] Figure 5 This is a graph showing the resistivity of D1 versus pressure in this invention. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] A low-temperature preparation method for conductive rutile titanium dioxide based on precrystallized intermediates, such as... Figure 1 As shown, it includes the following steps:

[0047] S1, Hydrothermal Precrystallization Preparation of Active Intermediates: The core of this step is to transform the original metatitanic acid, whose main component is hydrated titanium dioxide, into a special precursor that can be rapidly transformed into the rutile phase at a lower temperature thereafter, and whose surface is rich in active sites such as hydroxyl groups. The specific operation is as follows:

[0048] S11, Slurry Preparation and Accelerator Addition: Take industrial metatitanic acid filter cake with a moisture content controlled at 50%, add an appropriate amount of deionized water, and fully disperse in a high-speed shear disperser to prepare a homogeneous slurry with a titanium dioxide concentration of 200 g / L. Add rutile phase transformation accelerator tin tetrachloride to this homogeneous slurry at a dosage of 2.0% of the titanium dioxide mass in the homogeneous slurry. Tin tetrachloride accelerator can provide Sn in a hydrothermal environment. 4+ Ion, Sn 4+ Ions can be adsorbed on the surface of titanium dioxide crystal lattice, effectively catalyzing and reducing the activation energy of the anatase to rutile phase transition, laying the foundation for subsequent low-temperature crystal form transformation.

[0049] S12, Hydrothermal Crystallization Reaction: The prepared slurry is transferred to a corrosion-resistant high-pressure hydrothermal reactor. The filling degree of the slurry in the reactor is controlled at 70%. After sealing the reactor, it is placed in a homogeneous reactor. The reaction temperature of the homogeneous reactor is set at 200℃ and maintained at this temperature for 5 hours. During this process, metatitanic acid undergoes a complete process from dissolution to recrystallization. This process can induce the formation of a slurry product mainly composed of anatase microcrystals and rich in active hydroxyl groups on the surface, providing sufficient active sites for the uniform loading of the subsequent conductive layer.

[0050] S13, Washing and Drying: After the hydrothermal reaction, the reactor was naturally cooled to room temperature. The product inside the reactor was then vacuum filtered to obtain a filter cake. The filter cake was repeatedly washed with hot deionized water at 70℃ until the conductivity of the filtrate was below 50 μS / cm, thoroughly removing free chloride ions and other impurities. The cleaned filter cake was placed in a drying oven at 110℃ and dried for 12 hours. After drying, it was coarsely crushed to obtain a loose precrystallized active intermediate powder. XRD analysis showed that the main component of the precrystallized active intermediate powder was anatase phase, with trace amounts of rutile phase, which meets the requirements for subsequent low-temperature crystal transformation.

[0051] Using step S1 as a comparison with the corresponding steps in the existing two-step calcination method, the advantages of the present invention compared to the prior art are analyzed in detail. The specific comparison table is as follows:

[0052] Table 1. Comparison of Step S1 and Corresponding Steps in the Two-Step Calcination Method

[0053]

[0054] Based on Table 1 above, it can be concluded that, by comparing step S1 of this method with the corresponding steps of the existing two-step calcination method, the S1 step of this method features a dedicated hydrothermal pre-crystallization process. This process uses a low-to-medium temperature hydrothermal reaction at 200℃ combined with a 2.0% tin tetrachloride phase transformation promoter to treat metatitanic acid. After hot washing at 70℃ until the filtrate conductivity is <50μS / cm, impurities are thoroughly removed, ultimately yielding a loose, pre-crystallized active intermediate dominated by anatase and rich in hydroxyl groups. This method exhibits low overall energy consumption and high product activity. In contrast, the existing two-step calcination method lacks a pre-crystallization step, directly calcining the original metatitanic acid at 750-850℃ without the addition of a promoter, resulting in incomplete impurity removal and a product with low surface activity (rutile phase), leading to significantly higher energy consumption. Compared to the corresponding steps of the existing two-step calcination method, step S1 of this method has significant advantages in energy consumption control, product performance, and compatibility with subsequent processes.

[0055] S2, Controllable Co-precipitation Loading of Tin-Antimony Conductive Layer: The core of this step is to achieve highly uniform and compact adhesion of tin-antimony compounds on the surface of pre-crystallized active intermediate powder particles, forming an amorphous hydroxide precursor layer. The specific operation is as follows:

[0056] S21, Matrix redispersibility: Take the pre-crystallized active intermediate powder prepared above and redisperse it in deionized water at a titanium dioxide solid content ratio of 12%. Place the dispersion system in an ultrasonic device for pretreatment for 10 minutes to ensure uniform powder dispersion and no agglomeration. Then, transfer the dispersed slurry to a reactor equipped with a constant temperature jacket and strong stirring, preheat and maintain the slurry temperature at 60°C to provide a stable temperature environment for the subsequent coprecipitation reaction.

[0057] S22, Preparation of precursor solution: Prepare tin-antimony salt mixed solution and precipitant separately:

[0058] Tin-antimony salt mixture: Weigh appropriate amounts of tin tetrachloride and antimony trichloride according to the molar ratio of Sn to Sb of 11:1, and dissolve them together in a 1.8 mol / L hydrochloric acid solution. Stir continuously until the solution is completely clear and transparent, and control the total concentration of metal ions in the hydrochloric acid solution to 1.0 mol / L.

[0059] Precipitant: Prepare a 12% ammonium bicarbonate aqueous solution and stir until the ammonium bicarbonate is completely dissolved.

[0060] S23, Co-precipitation Reaction: Using a dual-channel precision metering pump, the prepared tin-antimony salt mixture and ammonium bicarbonate precipitant are simultaneously and slowly added dropwise at a constant and matched flow rate to the pre-crystallized active intermediate powder slurry, which is under vigorous stirring. During the addition process, a pH meter is used for real-time monitoring and feedback adjustment to ensure that the pH value of the reaction system is strictly stable at 4.0, and the total addition time is controlled to 3.0 hours. This pH range and slow addition method allow the hydrolysis and precipitation reaction of tin-antimony ions and the adsorption process of the active sites on the surface of the pre-crystallized active intermediate powder particles to proceed synchronously and uniformly, ensuring the uniformity and compactness of the conductive layer load.

[0061] S24, Aging and Post-treatment: After the tin-antimony salt mixture and precipitant were added dropwise, the system temperature in the reactor was maintained at approximately 60°C, and the mixture was stirred at a constant speed for 2.5 hours to ensure the deposition reaction was complete and the amorphous tin-antimony hydroxide precursor was stabilized. The slurry was then cooled to room temperature and filtered. The filter cake was washed with a large amount of deionized water until no white precipitate was found in the filtrate when tested with 0.1 mol / L silver nitrate solution, thus completely removing chloride ions from the system. The chloride-free filter cake was placed in a drying oven at 100°C and dried for 15 hours to obtain a composite precursor powder loaded with uniform amorphous tin-antimony hydroxide.

[0062] Using step S2 as a comparison with the corresponding step in the existing two-step calcination method, the advantages of the present invention compared with the prior art are analyzed in detail. The specific comparison table is as follows:

[0063] Table 2. Comparison of S2 steps and corresponding stages in the two-step calcination method.

[0064]

[0065] Based on Table 2 above, it can be concluded that, by comparing the corresponding steps of the conductive layer loading in step S2 of this method with those in the existing two-step calcination method, the S2 step of this method precisely controls the matrix dispersion, precursor preparation, and co-precipitation process. The matrix is ​​dispersed with a 12% solid content, pretreated with ultrasound, and kept at a constant temperature of 60℃. The precursor solution is prepared with a precise Sn:Sb molar ratio of 11:1, using a dual-channel dropwise addition method with strict pH control at 4.0 for 3 hours, followed by 2.5 hours of constant temperature aging at 60℃ and silver nitrate testing to ensure no chloride ion residue, ultimately achieving uniform loading of tin-antimony hydroxide. In contrast, the existing two-step calcination method lacks ultrasonic dispersion and constant temperature control, has no fixed Sn:Sb ratio, lacks strict pH control in co-precipitation, lacks a dedicated aging step, and has inaccurate impurity removal, easily leading to uneven conductive layer loading and agglomeration.

[0066] S3, Low-Temperature Synchronous Calcination: The core of this step is to achieve dual transformations during a single heat treatment process, namely, the transformation of the matrix crystal form and the crystallization of the conductive layer occur simultaneously. The specific operation is as follows:

[0067] S31, Calcination Procedure: The composite precursor powder obtained in step S2 is placed in a temperature-controlled muffle furnace and calcined under a static air atmosphere. The calcination program is set as follows: the temperature is increased to the target temperature of 600℃ at a heating rate of 2.5℃ / min, and then calcined at this temperature for 2.0 hours to ensure the complete completion of the dual conversion reaction.

[0068] S32, Simultaneous Conversion Mechanism: During the above-mentioned medium-temperature calcination process, two solid-state reactions occur simultaneously, achieving simultaneous conversion:

[0069] Matrix crystal transformation: The precrystallized intermediate powder with high activity and internal storage of phase change driving energy is activated at a relatively low temperature of 300℃ and rapidly and completely transforms into a well-crystallized rutile titanium dioxide matrix.

[0070] Conductive layer crystallization: The amorphous tin-antimony hydroxide uniformly coated on the surface of the composite precursor powder undergoes a dehydration and oxidation reaction, simultaneously crystallizing into an antimony-doped tin dioxide nanocrystalline layer with excellent conductivity. Because the substrate and the conductive layer precursor undergo phase transformation and growth simultaneously during calcination, a strong chemical bonding interface is formed between them, effectively improving the adhesion between the conductive layer and the substrate and preventing the conductive layer from detaching.

[0071] S33, Post-calcination treatment: After calcination, the material in the muffle furnace is naturally cooled to room temperature. The cooled material is then fed into an air jet mill for deagglomeration and refinement to remove agglomerated particles. Finally, according to actual application requirements, the refined powder is sieved and classified to obtain a highly conductive rutile titanium dioxide product.

[0072] Using step S3 as a comparison with the corresponding step in the existing two-step calcination method, the advantages of the present invention compared with the prior art are analyzed in detail. The specific comparison table is as follows:

[0073] Table 3. Comparison of S3 steps and corresponding steps in the two-step calcination method.

[0074]

[0075] Based on Table 3 above, it can be concluded that, by comparing step S3 of this method with the corresponding calcination and post-treatment steps of the existing two-step calcination method, the S3 step of this method uses a single low-temperature synchronous calcination at 600℃, with a programmed heating rate of 2.5℃ / min and constant temperature calcination for 2.0 hours, simultaneously achieving matrix crystal transformation and conductive layer crystallization, forming a strong chemical bonding interface. Subsequent airflow pulverization for depolymerization and sieving ensures product quality. In contrast, the existing two-step calcination method requires two separate calcinations, resulting in a higher overall temperature and faster heating rate. Crystal transformation and conductive layer crystallization occur separately, resulting in only physical adhesion and weak bonding. Furthermore, the post-treatment involves only simple crushing without standardized depolymerization and grading.

[0076] Example 1

[0077] 1. Hydrothermal Precrystallization: Weigh 400g of industrial metatitanic acid filter cake with a TiO2 content of 50%, add deionized water, and prepare a slurry of 200 g / L in a disperser. Add 6.0g of tin tetrachloride (2.0% by mass of TiO2) as a promoter to the slurry and stir for 30 minutes to mix evenly. Transfer the mixed slurry into a 2L polytetrafluoroethylene-lined hydrothermal reactor, filling it to approximately 70%. After sealing, place it in a forced-air drying oven and react at 200℃ for 5 hours. After the reaction, cool, filter the product, wash it with 70℃ hot water until the conductivity of the filtrate is <50 μS / cm, dry the filter cake in a 110℃ oven for 12 hours, and grind it to obtain the precrystallized active intermediate.

[0078] 2. Co-precipitation loading: Weigh 100g of the above pre-crystallized active intermediate powder, disperse it in 700ml of deionized water, sonicate for 10 minutes, and then transfer it to a jacketed 2L glass reactor. Heat and maintain the internal temperature at 60℃, stirring at high speed. Dissolve 75.0g of SnCl4·5H2O and 2.8g of SbCl3 in 100ml of 2.0 mol / L hydrochloric acid to prepare a tin-antimony salt mixture. Prepare a 12% ammonium bicarbonate aqueous solution as a precipitant. Under automatic pH control, add the tin-antimony salt mixture and precipitant to the M1 slurry dropwise at a matched flow rate using two peristaltic pumps, with a total dropwise addition time of 3 hours. After the addition is complete, continue aging at 60℃ for 2.5 hours. Then cool, filter, wash with deionized water until no chloride ions are present, and dry the filter cake at 100℃ for 15 hours to obtain the composite precursor.

[0079] 3. Low-temperature synchronous calcination: The composite precursor powder is evenly spread in an alumina crucible and placed in a muffle furnace. Under air atmosphere, the temperature is programmed to rise to 600℃ at a rate of 2.5℃ / min, and then calcined at this temperature for 2.0 hours. After calcination, the furnace is cooled to room temperature. The material is then removed, pulverized by an air jet mill, and passed through a 400-mesh sieve to obtain the final conductive titanium dioxide product, denoted as C1.

[0080] Example 2

[0081] 1. Hydrothermal precrystallization: The steps are the same as in Example 1, but the accelerator is replaced with zinc chloride, and the amount added is 2.0% of the mass of TiO2 based on ZnO.

[0082] 2. Coprecipitation loading: The steps are the same as in Example 1, but the amounts of SnCl4·5H2O and SbCl3 are adjusted so that the Sn:Sb molar ratio is 10:1 and the target ATO loading is 12% of the TiO2 mass.

[0083] 3. Low-temperature synchronous calcination: The steps are the same as in Example 1, but the final calcination temperature is set to 590℃. The resulting product is denoted as C2.

[0084] Example 3

[0085] 1. Hydrothermal precrystallization: The steps are the same as in Example 1.

[0086] 2. Co-precipitation loading: The steps are the same as in Example 1, but the target ATO loading is adjusted to 18%.

[0087] 3. Low-temperature synchronous calcination: The steps are the same as in Example 1, but the final calcination temperature is set to 620℃.

[0088] The resulting product is denoted as C3.

[0089] Compared with the traditional two-step calcination method

[0090] 1. First step calcination: Take the same batch of metatitanic acid filter cake as in Example 1, and without any hydrothermal treatment, calcine it directly in a muffle furnace at 900°C for 2 hours to obtain a common rutile titanium dioxide matrix, denoted as R1.

[0091] 2. Second step of coating and calcination: Take 100g of R1 powder, load the ATO precursor on its surface using the same co-precipitation loading process as in Example 1, and dry it to obtain the precursor powder.

[0092] 3. Second step calcination: Place the loaded precursor powder in a muffle furnace and calcine at 600°C for 2 hours. The resulting product is designated as D1.

[0093] Analysis of the above embodiments and comparative examples leads to the conclusion that, under the same ATO loading and final calcination temperature, the resistivity of product C1 obtained by the method of the present invention is nearly two orders of magnitude lower than that of product D1 obtained by the traditional two-step method. This directly proves that the present invention, by constructing an active intermediate to achieve low-temperature simultaneous conversion, can greatly optimize the crystal quality and conductive network of the ATO conductive layer. Furthermore, through C2 and C3, it can be shown that adjusting the loading or calcination temperature can achieve a good balance between conductivity and whiteness, meeting the needs of different application scenarios.

[0094] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-temperature preparation method for conductive rutile titanium dioxide based on a pre-crystallized intermediate, characterized in that, Specifically, the steps include the following: S1, Hydrothermal precrystallization to prepare active intermediates: The original metatitanic acid, whose main component is hydrated titanium dioxide, is converted into a special precursor that can be rapidly transformed into rutile phase at a lower temperature thereafter. The surface of the rutile phase is rich in active sites such as hydroxyl groups. S11, Slurry preparation and accelerator addition: Take industrial metatitanic acid filter cake, add deionized water, and prepare a uniform titanium dioxide slurry in a high-speed shear disperser. S12, hydrothermal crystallization reaction: The mixed slurry is transferred to a corrosion-resistant high-pressure hydrothermal reactor, sealed, and then placed in a homogeneous reactor; S13, Washing and Drying: After the reaction is completed, the product is cooled naturally, vacuum filtered, and washed to completely remove free chloride ions and other impurities. The washed filter cake is dried and then coarsely crushed to obtain a loose pre-crystallized active intermediate powder. S2, Controllable co-precipitation loading of tin-antimony conductive layer: On the surface of precrystallized active intermediate powder particles, tin-antimony compounds are attached in a highly uniform and compact manner to form an amorphous hydroxide precursor layer; S21, Matrix redispersion: The precrystallized active intermediate powder is redispersed in deionized water. After ultrasonic pretreatment for 10 minutes, it is transferred to a reactor with a constant temperature jacket and strong stirring to preheat and maintain the slurry temperature. S22, Preparation of precursor solution: This involves the preparation of tin-antimony salt mixture and precipitant. Tin tetrachloride and antimony trichloride are weighed according to the molar ratio of Sn to Sb in the tin-antimony salt mixture. Tin tetrachloride and antimony trichloride are dissolved together in hydrochloric acid solution and stirred until completely clear and transparent. The precipitant is prepared as a 10%-15% ammonium bicarbonate aqueous solution. S23, Co-precipitation reaction: A dual-channel precision metering pump is used to simultaneously and slowly add the tin-antimony salt mixture and the precipitant to the pre-crystallized active intermediate powder slurry, which is under vigorous stirring, at a constant and matched flow rate. S24, Aging and Post-treatment: After the addition is complete, continue to maintain the system temperature at about 60℃ and stir at a constant speed for aging for 2.0-3.0 hours to ensure complete deposition reaction and stable aging of the precursor. Then, cool and filter the slurry and wash it with a large amount of deionized water until there is no white precipitate in the filtrate after testing with 0.1mol / L silver nitrate solution to completely remove chloride ions and obtain filter cake. Dry the filter cake obtained after removing chloride ions to obtain composite precursor powder loaded with uniform amorphous tin antimony hydroxide. S3, Low-temperature synchronous calcination: Achieve dual transformation in a single heat treatment process by placing the composite precursor powder obtained in step S2 into a programmable temperature controlled muffle furnace or rotary kiln and calcining it in static air or low-flow oxygen atmosphere. S31, calcination program: heat up to the target temperature of 580℃-620℃ at a heating rate of 2-3℃ / min, and calcine at this temperature for 1.5-2.5 hours. S32, simultaneous conversion mechanism: two solid-state reactions occur simultaneously during the medium-temperature calcination process; S321, matrix crystal transformation: a precrystallized intermediate powder with high activity and internal storage of phase change driving energy is activated at a relatively low temperature of 0~600℃ and rapidly and completely transforms into a well-crystallized rutile titanium dioxide matrix. S322, conductive layer crystallization: the amorphous tin-antimony hydroxide uniformly coated on the surface of the composite precursor powder is dehydrated and oxidized, and crystallized into an antimony-doped tin dioxide nanocrystalline layer with excellent conductivity. Since the matrix and the conductive layer precursor undergo phase transformation and growth simultaneously during calcination, a strong chemical bonding interface is formed between the two. S33, Post-calcination treatment: After calcination, the material is cooled naturally in the furnace or cooled to room temperature under the protection of flowing nitrogen. Finally, it is deagglomerated and refined by an air jet mill, and then sieved and graded as needed to obtain highly conductive rutile titanium dioxide.

2. The low-temperature preparation method of conductive rutile titanium dioxide based on pre-crystallized intermediate as described in claim 1, characterized in that: In step S11, the moisture content of the metatitanic acid filter cake is controlled at 40%-60%, the concentration of the titanium dioxide homogeneous slurry is 150-250 g / L, and a rutile phase change promoter is added to the homogeneous slurry. The amount of rutile phase change promoter added is 1.0%-3.0% of the mass of titanium dioxide in the homogeneous slurry. The rutile phase change promoter is tin tetrachloride, which is used to provide Sn in the hydrothermal environment. 4+ ions, the Sn 4+ Ions are adsorbed onto the lattice surface of titanium dioxide, thereby effectively catalyzing and reducing the activation energy of the anatase to rutile phase transition.

3. The low-temperature preparation method of conductive rutile titanium dioxide based on pre-crystallized intermediate as described in claim 1, characterized in that: In step S12, the filling degree of the mixed slurry in the reactor is 60%-75%. The mixed slurry needs to be reacted in a homogeneous reactor at a temperature of 180℃-220℃ for 4-6 hours. The metatitanic acid will undergo a process of dissolution to recrystallization in the homogeneous reactor. The dissolution to recrystallization is used to induce the generation of a slurry product with anatase microcrystals as the main component and active hydroxyl groups on the surface.

4. The low-temperature preparation method of conductive rutile titanium dioxide based on pre-crystallized intermediate as described in claim 1, characterized in that: In step S13, the washing is performed using hot deionized water at 60-80℃. The hot deionization is repeated until the conductivity of the filtrate is below 50 μS / cm. The filter cake is dried at 100℃-120℃ for 10-15 hours. XRD analysis of the pre-crystallized active intermediate powder shows that its main component is anatase phase with trace amounts of rutile phase.

5. The low-temperature preparation method of conductive rutile titanium dioxide based on pre-crystallized intermediate as described in claim 1, characterized in that: In step S21, the precrystallized active intermediate powder is dispersed at a titanium dioxide solid content of 10%-15%, and the slurry temperature is maintained between 55℃ and 65℃.

6. The low-temperature preparation method of conductive rutile titanium dioxide based on pre-crystallized intermediate as described in claim 1, characterized in that: In step S22, the molar ratio of Sn to Sb is 10:1-12:1, the concentration of the hydrochloric acid solution is 1.5-2.0 mol / L, and the total concentration of metal ions in the hydrochloric acid solution is controlled at 0.8-1.2 mol / L.

7. The low-temperature preparation method of conductive rutile titanium dioxide based on pre-crystallized intermediate as described in claim 1, characterized in that: In step S23, the process of adding the tin-antimony salt mixture and precipitant is monitored and adjusted in real time using a pH meter. The real-time monitoring and feedback are used to ensure that the pH value of the reaction system is strictly stable within the range of 3.8-4.

2.

8. The low-temperature preparation method of conductive rutile titanium dioxide based on pre-crystallized intermediate as described in claim 7, characterized in that: In step S23, the dropping time is 2.5-3.5 hours, and the pH range and slow dropping method are used to ensure that the hydrolysis and precipitation reaction of tin-antimony ions and the adsorption process of the active sites on the surface of the pre-crystallized active intermediate powder particles are carried out synchronously and uniformly.

9. The low-temperature preparation method of conductive rutile titanium dioxide based on pre-crystallized intermediate as described in claim 1, characterized in that: In step S24, the drying operation is carried out at 90°C-110°C for 12-18 hours.

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