Core-shell type conductive titanium dioxide and preparation method thereof

Abstract

The invention discloses core-shell type conductive titanium dioxide and a preparation method thereof.The core-shell type conductive titanium dioxide comprises TiO2 and a coating layer located on the outer surface of the TiO2, the coating layer sequentially comprises a silicon coating and an ATO coating layer from inside to outside, the ATO coating layer is doped with Sb and N, the ATO coating layer is further doped with Sn, the molar ratio of N to Sn is 1: (0.1-30), the molar ratio of Sb to Sn is 1: (0.1-30), the molar ratio of Sb to Sn is 1: (0.1-30), the molar ratio of Sb to Sn is 1: (0.1-30), and the molar ratio of Sb to Sn is 1: (0.1-30). The mass of Sn is calculated by SnO2, and the mass of Sn is 10-30% of the mass of TiO2. According to the method, OH <-> is slowly released by urea, so that metal Sn and Sb oxides form a uniform coating on the surface of TiO2, a compact and uniform tin antimony oxide film layer is formed on the surface of titanium dioxide particles, and the particles are complete, so that a precipitation product is high in purity, uniform, regular and easy to filter and wash, the operation process is simple and easy to implement, and the existing defects of a coprecipitation method are effectively overcome.

Description

Technical Field

[0001] The present invention relates to the field of titanium dioxide, and particularly to a core-shell conductive titanium dioxide and a preparation method thereof. Background Art

[0002] Titanium dioxide (TiO2), known as titanium white in industry, has stable physical and chemical properties, good covering power, excellent whiteness, high scattering power, optimal brightness and gloss, etc. It is cheap and non-toxic, and can be widely used in various polymer daily chemical products such as plastics and chemical fibers. It is a versatile inorganic powder material with broad application prospects. However, under the action of external forces such as friction, impact, and tearing, these polymer products are prone to a series of electrostatic hazards due to electrostatic attraction or electrostatic discharge. The addition of conductive titanium white endows high-resistivity products with certain antistatic, conductive, or electromagnetic shielding properties. There are mainly two existing preparation technologies for conductive titanium dioxide. One is the blending method, in which a conductive material is mechanically mixed with titanium dioxide. The conductive titanium dioxide prepared by this method has uneven color and unstable conductivity. The other method is the coating method. Alkalis such as NaOH and ammonia water are added and the surface of titanium white is coated with an ATO layer by chemical coprecipitation. Instantaneous addition of a precipitant may cause a high concentration of hydroxide ions in a certain area of the system, resulting in aggregation or segregation of the final product. The conductive titanium dioxide prepared by this method has poor sintering resistance, poor dispersibility, high resistivity, and poor conductivity after later calcination.

[0003] Chinese Patent with publication number CN111040474B discloses a conductive titanium dioxide and a preparation method thereof. The conductive titanium dioxide includes a titanium dioxide substrate and a coating layer on the surface of the titanium dioxide substrate. The coating layer includes a polyaniline coating layer and an ATO coating layer in sequence from the inside to the outside. The ATO coating layer is doped with C and N in addition to Sb.

[0004] The ATO coating layer of this scheme adopts the homogeneous precipitation method. Its disadvantage is that instantaneous addition of the precipitant sodium hydroxide will cause a high concentration of hydroxide ions in a certain area of the system, resulting in the following several unfavorable phenomena: (1) The ATO film layer coated on the surface of the titanium dioxide slurry is uneven; (2) The precipitation products stannous hydroxide and antimony hydroxide aggregate and nucleate in the solution and are not coated on the surface of the titanium dioxide slurry. (3) At the same time, the impurity sodium ions introduced by the precipitant sodium hydroxide will be wrapped in the ATO coating layer, affecting its purity. Summary of the Invention

[0005] Aiming at the above deficiencies existing in the prior art, a core-shell conductive titanium dioxide and a preparation method thereof are provided, with uniform coating on the surface of titanium dioxide and good dispersibility.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: The present invention discloses a preparation method of core-shell conductive titanium dioxide. The core-shell conductive titanium dioxide comprises TiO2 and a coating layer located on the outer surface of the TiO2. The coating layer sequentially comprises a silicon coating and an ATO coating layer from the inside to the outside. The ATO coating layer is doped with Sb and N, and the ATO coating layer is also doped with Sn. The molar ratio of N / Sn is 1:0.1-30, and the molar ratio of Sb / Sn is 1:0.1-30. The mass of Sn is calculated as SnO2, and the mass of Sn is 10-30% of the mass of TiO2. The preparation method of the core-shell conductive titanium dioxide comprises the following steps: S1. Prepare titanium dioxide slurry A comprising a silicon coating; S2. Add a urea solution to the titanium dioxide slurry A, and add a dispersant and heat up to obtain slurry B; S3. Add a tin solution and an antimony solution to the slurry B, carry out a precipitation reaction and aging to obtain slurry C; S4. Filter, wash, dry and calcine the slurry C to obtain a TiO2@ATO composite powder; The preparation method of the titanium dioxide slurry A comprising a silicon coating in S1 comprises preparing a titanium dioxide slurry, adding an inorganic silicate solution, adding an acid to coat a dense layer of silicon on the surface of TiO2, and washing with water to remove impurity ions. The inorganic silicate solution is sodium silicate or potassium silicate, and its addition amount is calculated as SiO2. The mass percentage of the inorganic silicate solution is 1-3%. The acid in S1 is dilute sulfuric acid with a weight concentration of 1-10%. The dropping end point pH value of the dilute sulfuric acid is 4-6; In S3, the reaction temperature is 80-120 °C, the reaction time is 3-5 hours, and the pH at the end of the reaction is 6-8.

[0007] When the reaction time in S3 is too long, due to the low relative supersaturation of Sn 4+ , Sb 3+ in the system, the nucleation rate is much smaller than the growth rate, and the crystal has sufficient time to grow, so the particle size of the coating particles is larger. When the reaction time is too short, the relative supersaturation of metal cations in the system increases sharply, the nucleation rate is greater than its growth rate, the nucleation and growth of the coating particles are not separated independently, and finally the sizes of the ATO particles in the coating layer are different and there is an agglomeration behavior. Both of them lead to an increase in the resistivity of the composite powder. When the reaction time is appropriate, the growth of crystal nuclei in different crystal directions is more synchronous, the shape is more regular, it is in the form of uniform fine spherical particles, and the dispersion stability is good, and agglomeration can be avoided.

[0008] In S3, the end point pH is controlled at 6-8, but Sn 4+ , Sb 3+The basic precipitation is almost complete, and phosphorus can be deposited on the particle surface under this pH condition. If the pH value is too high, the resistivity value of the composite powder will increase sharply because the alkaline environment causes partial shedding and dissolution of the coating layer. If the pH value is too low, phosphorus cannot be deposited on the particle surface.

[0009] Preferably, the molar ratio of N / Sn is 1:10 - 20, the molar ratio of Sb / Sn is 1:10 - 30. The mass of Sn is calculated as SnO2, and the mass of Sn is 20 - 30% of the mass of TiO2.

[0010] The silicon layer is a dense coating layer, and the ATO coating layer includes a uniformly precipitated SnO2 oxide film layer.

[0011] Preferably, the outer layer of the coating layer further includes a phosphorus layer. In addition to doping Sb and Sn, the coating layer is also doped with P. Coating a phosphorus layer outside the ATO coating layer can avoid sintering between particles caused by high-temperature calcination and obtain titanium dioxide with excellent conductivity.

[0012] According to the embodiments of the present invention, the present invention can be further optimized. The following is the technical solution formed after optimization: The mass of the silicon coating is calculated as SiO2, and the mass of the silicon coating is 1 - 3% of the mass of TiO2.

[0013] The silicon layer of the present invention slowly releases H by dilute acid + to coat dense silicon.

[0014] In one of the preferred embodiments, the addition amount of urea in S2 is calculated as N, and the molar ratio of urea to SnO2 is 1:0.1 - 30.

[0015] Preferably, the molar ratio of N / Sn is 1:10 - 20.

[0016] The molar ratio of the addition amount of urea (calculated as N) in S2 to SnO2 is 1:10 - 20. When the total concentration of the coating agent is constant, the added urea is used to precipitate metal cations and neutralize the acid in the coating agent. The larger the molar ratio of urea to metal cations (Sn 4+ and Sb 3+ ), the higher the concentration of OH - generated. The greater the supersaturation of the system, the more conducive to the formation of uniform small-particle-size hydroxide precipitates on the surface of TiO2.

[0017] If the addition amount of urea in S2 is too little or too much, the resistivity value of the obtained product is relatively high. When the addition amount of urea is too little, the generated OH - is less, and only a small amount of new nuclei are generated in the solution, while the particles gradually grow, and the obtained coating layer is composed of oxides with larger particle sizes; when the addition amount of urea is too much, the nucleation rate is relatively fast in the early stage of the reaction. As the reaction generates OH -As the amount increases and the supersaturation increases, the precipitate is more inclined to homogenous nucleation and growth on the surface of TiO2, failing to fully play the coating role, so the resistivity of the products is relatively high.

[0018] In one preferred embodiment, the temperature is raised to 80 - 120 °C in S2.

[0019] The reaction temperature in S2 is 80 - 120 °C. If the temperature is too low, urea will not hydrolyze. At this time, the amount of OH in slurry A is extremely small, and the hydrolysis rates of Sn - and Sb 4+ are relatively slow. The amount of nuclei formed in the early stage is small, and the effective coating amount on the surface of TiO2 decreases. If the temperature is too high, the hydrolysis rate of urea accelerates, resulting in partial self-nucleation of Sn 3+ and Sb 4+ ; the particle sizes of the coating particles on the surface of TiO2 are uneven and there is a certain degree of agglomeration, leading to an increase in the resistivity of the composite powder to a certain extent. Appropriate temperature control is conducive to the full adsorption of metal ions on the TiO2 matrix and is conducive to the formation of relatively uniform particles in the coating layer, thereby improving the electrical conductivity of the coated TiO2 particles. 3+ 4+ and Sb 3+

[0020] In one preferred embodiment, in S3, the mass of Sn is calculated as SnO2, the mass of Sn is 10 - 30% of the mass of TiO2, and the Sb / Sn molar ratio is 0.1 - 30.

[0021] When the addition amount of tin oxide in S3 is 10 - 30% of the coating mass percentage and the Sb / Sn molar ratio is 0.1 - 30, the resistivity value of the composite powder reaches the lowest. At this time, the surface of TiO2 is basically completely covered by ATO nano-small particles, and the coating particles are in contact with each other to form a continuous cross-linked conductive network, with good electrical conductivity. When the coating amount is too high, although the coating layer becomes thicker on the basis of being continuous and uniform, local agglomeration and stacking phenomena occur in individual coating particles. When the coating amount is too small, the TiO2 powder cannot be completely coated, and the electrical conductivity is poor.

[0022] In one preferred embodiment, the dispersant in S2 includes one or more of inorganic dispersants and organic dispersants. The inorganic dispersant is one or more of sodium hexametaphosphate, sodium pyrophosphate, potassium tripolyphosphate, and potassium pyrophosphate. The organic dispersant is one or more of sodium polyacrylate, sodium dodecyl sulfonate, polyacrylamide, and polyethylene glycol; preferably, the weight concentration of the inorganic dispersant is 0.1 - 1%, and the weight concentration of the organic dispersant is 0.05 - 0.1%.

[0023] Dispersants can prevent solid particles in the solution from agglomerating. At the same time, inorganic dispersants of phosphorus can also be used as coating agents to coat the surface of TiO2, which is more conducive to improving the conductivity of conductive powders.

[0024] In one preferred embodiment, the dropping rate of dilute sulfuric acid in S1 is 20 to 60 minutes.

[0025] In S1, the acid is dilute sulfuric acid with a weight concentration of 1 to 10% to adjust the pH value of the slurry. The dropping rate is controlled at 20 to 60 minutes, and the acid slowly releases H + , preventing the local slurry concentration from being too high, resulting in self-nucleation of silicon and uneven coating. The end-point pH value is controlled at 4 to 6, so that all silicon is coated on the surface of TiO2 particles.

[0026] Preferably, in S1, the silicate is sodium silicate or potassium silicate, and its addition amount is 1 to 3% calculated as SiO2. Too little cannot play the role of silicon coating, and too much coating amount is likely to affect its conductivity.

[0027] Preferably, the precipitation reaction time in S3 is 3 to 5 hours, and after the reaction is completed, it is aged for 2 to 3 hours, and the pH value is 6 to 8.

[0028] Preferably, the drying temperature in S4 is 110 to 125 °C, the drying time is 6 to 8 h, and it is calcined in a non-air atmosphere. The calcination temperature is 500 to 750 °C, and the calcination time is 3 to 4 h.

[0029] Preferably, it further includes S5. Adding 0.2 to 0.5% of organosilicon by mass percentage to the TiO2@ATO composite powder to obtain core-shell conductive TiO2; preferably, the organosilicon is polysiloxane aerogel powder.

[0030] Preferably, the tin solution is tin chloride, and the antimony solution is antimony chloride solution.

[0031] Preferably, in S4, it needs to be calcined in a non-oxidizing atmosphere. Otherwise, the resistivity of the powder will be high. If the calcination temperature is too low, the conductivity of the powder is poor. If the calcination temperature is too high, the powder will sinter. If the calcination time is too short, the heating effect is not good. If the calcination time is too long, the conductive effect will not be improved.

[0032] Preferably, the addition amount of organosilicon in S5 is 0.2 to 0.5%. Organosilicon includes reactive polyether organosilicon and amino silane coupling agent.

[0033] The present invention also discloses a core-shell conductive titanium dioxide prepared according to the above preparation method.

[0034] The present invention also discloses the application of core-shell conductive TiO2 in antistatic, conductive or electromagnetic shielding products.

[0035] The beneficial effects of the present invention are as follows: (1) Using urea to slowly release OH － , enabling the formation of a uniform coating of metal Sn and Sb oxides on the surface of TiO2, ensuring the formation of a dense and uniform antimony tin oxide film layer on the surface of titanium dioxide particles, with intact particles. Therefore, the precipitation product is high-purity, uniform, regular, easy to filter and wash, and the operation process is simple and feasible, effectively improving the existing shortcomings of the co-precipitation method. (2) Using dilute acid with a relatively low concentration to slowly release H + to coat dense silicon, enabling the formation of a continuous coating on the surface of TiO2 particles, aiming to modify TiO2 to facilitate a more uniform ATO coating. (3) Using weak acid on the surface of TiO2 to slowly release H + to coat dense silicon is beneficial to the water washing efficiency of the slurry. (4) The coating of the phosphorus layer can prevent the sintering of particles caused by high-temperature calcination, further reduce the resistivity of the particles, and improve the electrical conductivity of the powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 FIG. is the XRD pattern of core-shell conductive TiO2, where a, b, c, and d respectively represent the XRD patterns of precursor TiO2, core-shell conductive TiO2 in Example 1, Example 2, and Example 3.

[0037] Figure 2 FIG. is the XRD pattern of the core-shell conductive TiO2 before and after film coating prepared in Example 1, where 1 is titanium dioxide and 2 is conductive titanium dioxide powder.

[0038] Figure 3 FIG. is the XRD pattern of TiO2@ATO, ATO, and the uncalcined precursor based on TiO2.

[0039] Figure 4 FIG. is the SEM pattern of precursor TiO2.

[0040] Figure 5 FIG. is the SEM pattern of TiO2@ATO.

[0041] Figure 6 FIG. is the electron micrograph of core-shell conductive titanium dioxide in Example 1 (i.e., homogeneous precipitation film coating).

[0042] Figure 7 For Figure 6 the electron micrograph of a single particle of core-shell conductive titanium dioxide in

[0043] Figure 8 FIG. is the electron micrograph of core-shell conductive titanium dioxide in Comparative Example 2 (i.e., homogeneous precipitation film coating).

[0044] Figure 9 For Figure 8 the electron micrograph of a single particle of core-shell conductive titanium dioxide in

[0045] Figure 10 It is the sedimentation test diagram in Example 1. Detailed implementation mode

[0046] The present invention will be described in detail below in conjunction with embodiments. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0047] The present invention provides a new method for conductive titanium dioxide, which includes the following steps.

[0048] (1) Prepare a titanium dioxide slurry, add an inorganic silicate solution, add an acid to coat a dense layer of silicon on the surface of TiO2, and wash with water to remove impurity ions to obtain slurry A.

[0049] (2) Add an appropriate amount of urea solution to slurry A, and add inorganic dispersants such as sodium hexametaphosphate, sodium pyrophosphate, potassium tripolyphosphate and potassium pyrophosphate, and organic dispersants such as sodium polyacrylate, sodium dodecyl sulfate, polyacrylamide, polyethylene glycol, etc. Then heat the material to 80-120°C to prepare a slurry, and prepare slurry B.

[0050] (3) Take appropriate amounts of tin chloride solution and antimony chloride solution respectively. Use a peristaltic pump to control the dropping speed and add them to slurry C. Control the pH value of the solution, the reaction time is 3-5 hours, and after the reaction is completed, age for 2-3 hours.

[0051] (4) After the slurry is cooled, filtered and washed, it is dried at 110-125°C for 6-8 h. Take out the dried material, grind and crush it, place it in a muffle furnace, in a non-air atmosphere, and calcine it at 500-750°C for 3-4 h to obtain the TiO2@ATO composite powder.

[0052] (5) Add 0.2-0.5% by mass of an organosilicon such as polysiloxane aerogel powder to the composite powder.

[0053] Example 1

[0054] (1) Prepare a titanium dioxide slurry, add a sodium silicate solution with a mass percentage of 1%, slowly add dilute sulfuric acid with a weight percentage concentration of 1% to the slurry until the pH value is 4.0, and wash with water to remove impurity ions.

[0055] (2) Add a urea solution, and add an inorganic dispersant of sodium hexametaphosphate with a weight concentration of 0.1% and sodium polyacrylate with a weight concentration of 0.05%. Then heat the material to 80°C. The molar ratio of urea (calculated as N) to Sn is 1:10.

[0056] (3) Add a solution of stannous chloride and antimony chloride with a mass percentage of 10% (calculated as SnO₂). Use a peristaltic pump to control the dropping rate, with a reaction time of 3 hours, control the pH value of the solution to 6.0, and age for 2 hours after the reaction. It is required that the molar ratio of the added amount of antimony chloride to stannous chloride, Sb / Sn, is 1:10.

[0057] (4) After the slurry is cooled, filtered, and washed, it is dried at 110 °C for 8 h. Take out the dried material, grind and crush it, place it in a muffle furnace, and calcine it at 650 °C for 3 h in a non-air atmosphere to obtain the core-shell type TiO₂@ATO composite powder.

[0058] (5) Add 0.3% polysiloxane to the composite powder and then air powder it.

[0059] Example 2

[0060] (1) Prepare a titanium dioxide slurry, add 3% sodium silicate solution, slowly add dilute sulfuric acid with a weight percentage concentration of 10% to the slurry until the pH value is 6.0, and wash with water to remove impurity ions.

[0061] (2) Add a urea solution, and add 1% sodium hexametaphosphate and 0.1% sodium polyacrylate as inorganic dispersants. Then heat the material to 120 °C. The molar ratio of urea (calculated as N) to Sn is 1:12.

[0062] (3) Add a solution of stannous chloride and antimony chloride with a mass percentage of 30% (calculated as SnO₂). Use a peristaltic pump to control the dropping rate, with a reaction time of 5 hours, control the pH value of the solution to 8.0, and age for 3 hours after the reaction. It is required that the molar ratio of the added amount of antimony chloride to stannous chloride, Sb / Sn, is 1:20.

[0063] (4) After the slurry is cooled, filtered, and washed, it is dried at 125 °C for 6 h. Take out the dried material, grind and crush it, place it in a muffle furnace, and calcine it at 500 °C for 4 h in a non-air atmosphere to obtain the core-shell type TiO₂@ATO composite powder.

[0064] (5) Add 0.3% polysiloxane to the composite powder and then air powder it.

[0065] Example 3

[0066] (1) Prepare a titanium dioxide slurry, add 2% sodium silicate solution, slowly add dilute sulfuric acid with a weight percentage concentration of 5% to the slurry until the pH value is 5.0, and wash with water to remove impurity ions.

[0067] (2) Add a urea solution, and add 0.8% sodium hexametaphosphate and 0.08% sodium polyacrylate as inorganic dispersants. Then heat the material to 100 °C. The molar ratio of urea (calculated as N) to Sn is 1:15.

[0068] (3) Add a stannous chloride and antimony chloride solution with a mass percentage of 20% (calculated as SnO2). Use a peristaltic pump to control the dropping rate, with a reaction time of 5 hours, control the pH value of the solution to 6.0, and age for 3 hours after the reaction. It is required that the molar ratio of the added amounts of stannous chloride and antimony chloride, Sb / Sn, is 1:15.

[0069] (4) After the slurry is cooled, filtered, and washed, it is dried at 120 °C for 8 h. The dried material is taken out, ground and pulverized, placed in a muffle furnace, and calcined at 600 °C for 4 h in a non-air atmosphere to obtain the core-shell type TiO2@ATO composite powder.

[0070] (5) Add 0.3% polysiloxane by mass percentage to the composite powder and aerate the powder.

[0071] Example 4

[0072] The difference between Example 4 and Example 3 is that in (2), a urea solution is added, and an inorganic dispersant, 0.8% sodium hexametaphosphate and 0.08% sodium polyacrylate, is added. Then the material is heated to 90 °C. Other steps are the same as those in Example 3.

[0073] Example 5

[0074] The difference between Example 5 and Example 3 is that in (2), a urea solution is added, and an inorganic dispersant, 0.8% sodium hexametaphosphate and 0.08% sodium polyacrylate, is added. Then the material is heated to 110 °C. Other steps are the same as those in Example 3.

[0075] Comparing the effects of the reaction temperature on the conductivity in Example 3, Example 4, and Example 5, in the homogeneous precipitation method, the reaction temperature is extremely crucial for the hydrolysis rate of the precipitating agent. This is because the hydrolysis rate of urea to generate OH — increases with the increase in temperature; when the temperature rises from 80 °C to 92 °C, the resistivity of the composite powder shows a downward trend and drops to the lowest at 100 °C, which is 7.5 Ω·cm. It is inferred that at this temperature, the entropy value of the mixed system is the largest and the system disorder is the best, and the precipitation particles are uniformly coated; when the reaction temperature continues to increase, the resistivity value of the composite powder increases instead. This is because at a higher system temperature, the hydrolysis rate of CO(NH2)2 is too fast, the supersaturation of the structure-forming ions increases, the particle size of the coated particles generated is too large, and part of the precipitate nucleates and grows spontaneously.

[0076] Example 6

[0077] The difference between Example 6 and Example 3 is that in (2), a urea solution is added, and an inorganic dispersant, 0.8% sodium hexametaphosphate and 0.08% sodium polyacrylate, is added. Then the material is heated to 100 °C. The molar ratio of urea (calculated as N) to Sn is 1:20. Other steps are the same as those in Example 3.

[0078] Example 7

[0079] Example 7 is different from Example 3 in that (2) urea solution is added, and 0.8% sodium hexametaphosphate and 0.08% sodium polyacrylate as inorganic dispersants are added. Then the material is heated to 100 °C. The molar ratio of urea (calculated as N) to Sn is 1:30. Other steps are the same as those in Example 3.

[0080] Comparing the effects of the addition amount of urea in Example 3, Example 6, and Example 7 on the electrical conductivity, urea is used as a precipitant. When the reaction temperature is the same, as the addition amount of the precipitant increases, the generated OH - increases. When the addition amount is relatively large, metal cations in the system are more likely to adsorb and grow on the surface of TiO2 to form nuclei, and the shell layer is uniform and dense. TiO2 has a complete coating structure, and the product has good electrical conductivity. If the addition amount of urea is too small or too large, the resistivity value of the obtained product is relatively high. When the addition amount of urea is too small, less OH- is generated, and only a small amount of new nuclei are formed in the solution, while the particles gradually grow, and the obtained coating layer is composed of oxides with larger particle sizes; when the addition amount of urea is too large, the nucleation rate is relatively fast in the early stage of the reaction. As the amount of OH - generated by the reaction increases and the supersaturation increases, the precipitate is more inclined to homogeneous nucleation and growth on the surface of TiO2, and it does not fully play a coating role. Therefore, the resistivity of the product is relatively high.

[0081] Example 8

[0082] Example 8 is different from Example 3 in that (3) a solution of tin chloride and antimony chloride with a mass percentage of 25% (calculated as SnO2) is added. The dropping rate is controlled by a peristaltic pump, the reaction time is 5 hours, the pH value of the solution is controlled at 6.0, and after the reaction is completed, it is aged for 3 hours. The addition amount of antimony chloride is required to have a molar ratio of Sb / Sn of 1:15.

[0083] Example 9

[0084] Example 9 is different from Example 3 in that (3) a solution of tin chloride and antimony chloride with a mass percentage of 30% (calculated as SnO2) is added. The dropping rate is controlled by a peristaltic pump, the reaction time is 5 hours, the pH value of the solution is controlled at 8.0, and after the reaction is completed, it is aged for 3 hours. The addition amount of antimony chloride is required to have a molar ratio of Sb / Sn of 1:15.

[0085] Example 10

[0086] Example 10 is different from Example 3 in that in (3), a solution of tin chloride and antimony chloride with a mass percentage of 20% (calculated as SnO2) is added. The dropping rate is controlled by a peristaltic pump, the reaction time is 5 hours, the pH value of the solution is controlled at 8.0, and after the reaction is completed, it is aged for 3 hours. The addition amount of antimony chloride is required to have a molar ratio of Sb / Sn of 1:20.

[0087] By comparing Comparative Example 3 with Example 9 and Example 10, the influence of the SnO2 coating amount on the electrical conductivity was obtained. When the coating amount was 15%, the resistivity value of the composite powder reached the lowest. At this time, the surface of TiO2 was basically completely covered by ATO nanoparticles, and the coated particles were in contact with each other, forming a continuous cross-linked conductive network with good electrical conductivity. When the coating amount was too small, or when the coating amount was greater than 15%, it could be seen that although the coating layer became thicker on the basis of being continuous and uniform, local agglomeration and stacking occurred in some coated particles, and the resistivity of TiO2@ATO increased slightly. This indicates that under the condition of complete coating, the choice of m(SnO2) / m(TiO2) is not the larger the better, and it should be limited to form a uniform and continuous coating layer.

[0088] Comparative Example 1 (1) Prepare a titanium dioxide slurry.

[0089] (2) Add a sodium hydroxide solution, and then heat the material to 100 °C.

[0090] (3) Add a tin chloride and antimony chloride solution with a mass percentage of 15% (calculated as SnO2). Use a peristaltic pump to control the dropping rate, with a reaction time of 5 hours, control the pH value of the solution to 8.0, and age for 3 hours after the reaction. It is required that the addition amount of antimony chloride has a molar ratio of Sb / Sn of 1:15.

[0091] (4) After the slurry is cooled, filtered, and washed, it is dried at 120 °C for 8 h. Take out the dried material, grind and crush it, place it in a muffle furnace, and calcine it at 600 °C for 4 h in a non-air atmosphere to obtain the core-shell type TiO2@ATO composite powder.

[0092] (5) Add 0.3% polysiloxane to the composite powder and aerate the powder.

[0093] Figure 3XRD patterns of TiO2@ATO, ATO and uncalcined precursors with TiO2 as the core. As can be seen from the figure, the uncalcined precursor samples have diffraction peaks at positions of 2θ = 27.4°, 36.1°, 41.2°, 54.3°, 56.3° and 68.9°, which respectively belong to the (110), (101), (111), (211), (220) and (301) crystal planes of rutile TiO2. There are no diffraction peaks of other phases, indicating that the uncalcined precursor only has the matrix rutile TiO2 phase, and the coated precipitate is amorphous. For single ATO and TiO2@ATO composites, the diffraction peaks at positions of 2θ = 26.5°, 33.8°, 37.6° and 51.7° correspond to their (110), (101), (211) and (200) crystal planes respectively. Diffraction peaks of individual antimony oxides such as Sb2O3 or Sb2O5 are not detected, indicating that no independent antimony compound phase is formed and Sb has been solid-soluted into the SnO2 lattice. According to the crystallization theory and the formation conditions of solid solutions, when the radii of two ions are close, solid solutions are easily formed, and Rs b 5+ 、Rs b 3+ and Rs n 4+ are 0.062nm, 0.092nm and 0.071nm respectively, among which Rs b 5+ is relatively close to Rs n 4+ . Therefore, first of all, Sb 5+ is solid-soluted into the SnO2 lattice in a substitutional or interstitial type, and the incorporation of impurity ions will cause lattice distortion. In addition, for TiO2@ATO after calcining the precursor, the diffraction peaks of the tetragonal SnO2 phase are increased, indicating that the coated precipitate forms a crystalline metal oxide after calcining, and the coating of ATO does not change the crystal form of the matrix.

[0094] Table 1 Comparison of Physicochemical Properties of Conductive Powders

[0095] (1) The product appearance is generally white with a slight gray color.

[0096] (2) The resistivity is measured under a pressure of 100 kg / cm 2 .

[0097] (3) The oil absorption is the minimum number of grams of refined linseed oil absorbed by 100 g of conductive powder.

[0098] (4) The moisture is determined by drying to a constant weight at 105 ± 2 °C.

[0099] (5) The specific surface area is measured by the gas adsorption BET method.

[0100] (6) The pH value of the aqueous suspension refers to the pH value when 3 g of the powder is dispersed in 27 ml of water with a pH of 7.0.

[0101] Comparative Example 2 The difference between this comparative example and the example is that urea is not added.

[0102] In this comparative example, an external precipitant sodium hydroxide is used. By adding sodium hydroxide, hydroxide ions are generated, causing tin and antimony to react with the hydroxide ions to form tin hydroxide and antimony hydroxide precipitates. Since the direct addition of sodium hydroxide will result in a locally high concentration of hydroxide ions in the solution, the following phenomena will occur: (1) Due to the locally high concentration of hydroxide ions, tin and antimony will quickly form precipitates in the solution. This quickly formed precipitate nucleus is not completely coated on the surface of the titanium dioxide particles. It may coat a point on the titanium dioxide or may not coat the surface of the titanium dioxide particles at all. (3) This leads to the inability to form a uniform tin hydroxide and antimony hydroxide film on the surface of the titanium dioxide particles. (4) The titanium dioxide particles will agglomerate, affecting the electrical conductivity of the powder.

[0103] Slurry water washing time and conductivity experiment: Take 200 ml of the slurry, filter it with a Buchner funnel, wash it with water, and finally draw the filtrate and detect its conductivity with a conductivity meter until the conductivity of the filtrate is below 50 μS / cm, indicating that the impurity ions in the slurry have been washed clean. The experimental data are as follows: Table 2 Slurry water washing time and conductivity in step (4) of the example and Comparative Example 2

[0104] In Examples 1 - 10, the coating layer of TiO2 particles adopts the homogeneous precipitation method. Urea slowly releases OH － , enabling metal Sn and Sb oxides to form a uniform coating on the surface of TiO2, ensuring the formation of a dense and uniform stannic antimonate film layer on the surface of the titanium dioxide particles, with the particles being complete. Therefore, the precipitation product is high-purity, homogeneous, regular, easy to filter and wash, and has a short water washing time.

[0105] Comparative Example 2 adopts the homogeneous precipitation method. Using an external precipitant sodium hydroxide will cause a locally high instantaneous concentration of hydroxide ions in a certain area of the system, resulting in an uneven coating of metal Sn and Sb oxides on the surface of TiO2, an irregular precipitation product, being unfavorable for washing, and a long water washing time.

[0106] Sedimentation test: The detection method of the dispersibility of titanium dioxide conductive powder is verified through a sedimentation test.

[0107] Weigh the titanium dioxide conductive powder, dissolve it with an appropriate amount of distilled water, perform ultrasonic treatment, transfer the treated sample to a graduated cylinder, let it stand, and record the sedimentation volume at the same time.

[0108] Table 3 Sedimentation time and sedimentation volume in Examples and Comparative Example 2

[0110] The slower the sedimentation rate and the smaller the sedimentation volume, the better the dispersibility of the titanium dioxide conductive powder.

[0111] In Examples 1 - 10, the coating layer of titanium dioxide particles adopts the homogeneous precipitation method. By adding urea to slowly release OH － , so that metal Sn and Sb oxides form a uniform coating on the surface of TiO2, ensuring that a dense and uniform antimony tin oxide film layer is formed on the surface of titanium dioxide particles, and the particles are complete. Therefore, the prepared conductive titanium dioxide has good dispersibility in water, slow sedimentation rate, and small sedimentation volume.

[0112] In Comparative Example 2, the homogeneous precipitation method is adopted. By adding an external precipitant sodium hydroxide, the instantaneous concentration of hydroxide ions in a certain area of the system will be too high, resulting in an uneven coating of metal Sn and Sb oxides on the surface of TiO2. The prepared titanium dioxide conductive powder is prone to agglomeration in water, with poor dispersibility, fast sedimentation rate, and large sedimentation volume.

[0113] The ATO coating layer of the present invention adopts the homogeneous precipitation method. The precipitant urea is mixed with the reaction solution at room temperature, and as the system temperature rises to a certain extent, urea slowly releases alkaline radicals. Urea can hydrolyze to generate ammonia water in an aqueous solution at a temperature above 80°C, and ammonia water further generates hydroxide ions. Thus, by controlling the temperature and material concentration, the generation rate of tin hydroxide and antimony hydroxide can be regulated, enabling tin hydroxide and antimony hydroxide to uniformly coat the surface of titanium dioxide in the slurry, and avoiding the occurrence of agglomeration phenomena.

[0114] Using urea to slowly release OH － , so that metal Sn and Sb oxides form a uniform coating on the surface of TiO2, ensuring that a dense and uniform antimony tin oxide film layer is formed on the surface of titanium dioxide particles, and the particles are complete. Therefore, the precipitation product is high-purity, uniform, regular, easy to filter and wash, the operation process is simple and feasible, effectively improving the existing disadvantages of the coprecipitation homogeneous precipitation method.

[0115] Figure 6 This is the electron microscope image of the conductive titanium dioxide powder in Example 1 (i.e., homogeneous precipitation method coating), and it can be seen that the powder particles are evenly dispersed. Figure 7 For Figure 6 the electron microscope image of a single particle of the conductive titanium dioxide powder in Figure 8 This is the electron microscope image of the conductive titanium dioxide powder in Comparative Example 2 (i.e., homogeneous precipitation coating). The powder particles show serious agglomeration and are not evenly dispersed. Figure 9 For Figure 8Electron micrograph of a single particle of the middle-conductive titanium dioxide powder, showing that the coating layer is uneven.

[0116] The content illustrated in the above embodiments should be understood that these embodiments are only used to more clearly illustrate the present invention, rather than limiting the scope of the present invention. After reading the present invention, various equivalent forms of modification of these embodiments by those skilled in the art all fall within the scope defined by the appended claims of the present invention.

Claims

1. A method for preparing core-shell conductive titanium dioxide, wherein the core-shell conductive titanium dioxide comprises TiO2 and a coating layer located on the outer surface of the TiO2, wherein the coating layer comprises a silicon coating layer and an ATO coating layer in order from the inside to the outside, wherein the ATO coating layer is doped with Sb and N, characterized in that: The ATO coating layer is also doped with Sn, the molar ratio of N / Sn is 1: 0.1-30, the molar ratio of Sb / Sn is 1: 0.1-30, the mass of Sn is calculated as SnO2, and the mass of Sn is 10-30% of the mass of TiO2; The method for preparing the core-shell conductive titanium dioxide comprises the following steps: S1, preparing titanium dioxide slurry A including silicon coating; S2, adding urea solution to titanium dioxide slurry A, and adding dispersant and heating to obtain slurry B; S3, adding tin solution and antimony solution to the slurry B, performing precipitation reaction and aging to obtain slurry C; S4, the slurry C is filtered, washed, dried and calcined to obtain TiO2@ATO composite powder; The preparation method of the silicon-coated titanium dioxide slurry A in S1 includes preparing titanium dioxide slurry, adding an inorganic silicate solution, adding an acid to coat the surface of TiO2 with a dense layer of silicon, and washing with water to remove impurity ions; the inorganic silicate solution is sodium silicate or potassium silicate, and the amount thereof added is calculated based on SiO2, and the mass percentage of the inorganic silicate solution is 1-3%, the acid in S1 is dilute sulfuric acid with a weight concentration of 1-10%, and the pH value of the end point of the dropwise addition of the dilute sulfuric acid is 4-6; In S3, the reaction temperature is 80-120° C., the reaction time is 3-5 hours, and the pH at the reaction end point is 6-8.

2. The method for preparing core-shell conductive titanium dioxide according to claim 1, characterized in that: The mass of the silicon coating is calculated as SiO2, and the mass of the silicon coating is 1-3% of the mass of TiO2.

3. The method for preparing core-shell conductive titanium dioxide according to claim 1, characterized in that: The amount of urea added in S2 is calculated as N, and the molar ratio of urea to SnO2 is 1:0.1~30.

4. The method for preparing core-shell conductive titanium dioxide according to claim 1, characterized in that: The temperature in S2 is raised to 80~120℃.

5. The method for preparing core-shell conductive titanium dioxide according to claim 1, characterized in that: The mass of Sn in S3 is calculated as SnO2, the mass of Sn is 10-30% of the mass of TiO2, and the molar ratio of Sb / Sn is 0.1-30.

6. The method for preparing core-shell conductive titanium dioxide according to claim 1, characterized in that: The dispersant in S2 includes one or more of an inorganic dispersant and an organic dispersant, the inorganic dispersant is one or more of sodium hexametaphosphate, sodium pyrophosphate, potassium tripolyphosphate and potassium pyrophosphate, and the organic dispersant is one or more of sodium polyacrylate, sodium dodecyl sulfate, polyacrylamide and polyethylene glycol; the weight concentration of the inorganic dispersant is 0.1~1%, and the weight concentration of the organic dispersant is 0.05~0.1%.

7. The method for preparing core-shell conductive titanium dioxide according to claim 1, characterized in that: The dropping rate of the dilute sulfuric acid in S1 is 20 to 60 minutes.

8. A core-shell conductive titanium dioxide prepared according to the preparation method according to any one of claims 1 to 7.

Images