阅读说明：本技术 一种铝前驱体包覆钛白粉及其制备方法和制备铝包覆钛白粉的方法 (Aluminum precursor coated titanium dioxide, preparation method thereof and method for preparing aluminum coated titanium dioxide ) 是由 邹丽霞 黄前 曹小红 刘若妍 于 2021-09-15 设计创作，主要内容包括：本发明公开了一种铝前驱体包覆钛白粉,钛白粉表面包覆氧化铝前驱体。本发明还公开了铝前驱体包覆钛白粉的制备方法和制备铝包覆钛白粉的方法。本发明的包覆过程区别于通常铝包覆方法的直接形成水合氧化铝包覆到钛白粉上。本发明先生成铝前驱体,并包覆在钛白粉表面,而铝前驱体分子链式结构,前驱体更容易包覆在钛白粉表面；而且溶液中氧化铝前驱体表面有大量羟基,使其颗粒间排斥作用较大,自相成核难度大,有利于异相成核,从而完美包覆钛白粉,之后干燥脱出水分,相邻胶粒的非架桥羟基自发转变为架桥羟基；同时,凝胶部分结构配位水排除,包膜颗粒间也形成架桥羟基,从而使钛白粉表面包覆层均匀致密,使钛白粉的耐候性能优于传统铝包覆方法。(The invention discloses aluminum precursor coated titanium dioxide, wherein the surface of the titanium dioxide is coated with an aluminum oxide precursor. The invention also discloses a preparation method of the aluminum precursor coated titanium dioxide and a method for preparing the aluminum coated titanium dioxide. The coating process of the invention is different from the conventional aluminum coating method which directly forms hydrated alumina to coat the titanium dioxide. According to the invention, an aluminum precursor is generated and coated on the surface of the titanium dioxide, and the aluminum precursor has a molecular chain structure, so that the precursor is easier to coat on the surface of the titanium dioxide; in addition, a large number of hydroxyl groups are arranged on the surface of the alumina precursor in the solution, so that the repulsion action among particles is large, the difficulty of self-phase nucleation is large, and heterogeneous nucleation is facilitated, so that titanium dioxide is perfectly coated, then the titanium dioxide is dried to remove water, and non-bridging hydroxyl groups of adjacent colloidal particles are spontaneously converted into bridging hydroxyl groups; meanwhile, the coordination water in the gel part structure is removed, and bridging hydroxyl groups are formed among the coating particles, so that the surface coating layer of the titanium dioxide is uniform and compact, and the weather resistance of the titanium dioxide is superior to that of the traditional aluminum coating method.)

1. A novel aluminum precursor coated titanium dioxide is characterized in that the surface of the titanium dioxide is coated with an aluminum oxide precursor.

2. The novel aluminum precursor-coated titanium dioxide of claim 1, wherein the aluminum oxide precursor is aluminum ammonium hydroxycarbonate.

3. The process for preparing the novel aluminum precursor-coated titanium dioxide according to any one of claims 1-2, which comprises the steps of,

(1) preparing titanium dioxide slurry with the mass fraction of 40-200g/L, adding sodium hexametaphosphate which accounts for 1-5% of the mass fraction of the titanium dioxide as a dispersing agent, and performing ultrasonic dispersion for 30-120 min;

(2) adding soluble aluminum salt accounting for 0.5-10% of the mass fraction of the titanium dioxide, wherein the concentration of the soluble aluminum salt solution is 0.1-3mol/L, and stirring for 0.5-3 h;

(3) adding soluble ammonium salt accounting for 50-200% of the mass fraction of the soluble aluminum salt used in the step (2), wherein the concentration of the soluble ammonium salt solution is 0.1-3mol/L, and uniformly stirring;

(4) dropwise adding basic ammonium salt accounting for 50-300% of the mass fraction of the soluble aluminum salt used in the step (2) through a constant-pressure funnel at a constant speed, wherein the concentration of the basic ammonium salt solution is 1-10mol/L, and reacting for 0.5-8 h;

(5) controlling the reaction temperature to be 30-100 ℃, stirring at the speed of 100-500r/min, dropwise adding 1mol/L alkali liquor to adjust the pH value in the coating process to 7-11, and then continuing to react for 0.5-4 h;

(6) and (3) sealing the solution obtained in the step (5) by using a preservative film, standing and aging at 20-90 ℃ for 1-48h, and filtering to obtain the aluminum precursor coated titanium dioxide.

4. The method for preparing the novel aluminum precursor-coated titanium dioxide according to claim 3, wherein the soluble aluminum salt in the step (2) includes but is not limited to aluminum sulfate, aluminum nitrate, and aluminum chloride.

5. The method for preparing the novel aluminum precursor-coated titanium dioxide according to claim 3, wherein the soluble ammonium salt in step (3) includes but is not limited to ammonium sulfate, ammonium nitrate, ammonium chloride, soluble metal ammonium salts.

6. The method for preparing the novel aluminum precursor-coated titanium dioxide according to claim 3, wherein the soluble metal ammonium salt includes but is not limited to aluminum ammonium sulfate and aluminum ammonium alum.

7. The method for preparing the novel aluminum precursor-coated titanium dioxide according to claim 3, wherein the basic ammonium salt in step (4) includes, but is not limited to, ammonium bicarbonate and ammonium carbonate.

8. The method for preparing the novel aluminum precursor-coated titanium dioxide according to claim 3, wherein the alkali solution in the step (5) includes but is not limited to sodium silicate solution, sodium hydroxide solution, and ammonia solution.

9. The method for preparing aluminum-coated titanium dioxide powder according to any one of claims 1-2, which comprises the steps of,

drying the aluminum precursor coated titanium dioxide at the temperature of 30-200 ℃ for 0.5-24 h to obtain the aluminum coated titanium dioxide.

Technical Field

The invention belongs to the technical field of titanium dioxide coating, and particularly relates to a preparation method of aluminum-coated titanium dioxide.

Background

Titanium dioxide (TiO)₂) Is an important inorganic chemical pigment, and especially has important application in the industries of coating, printing ink, papermaking, plastic rubber, chemical fiber, ceramic and the like under the condition of modified coating. Titanium dioxide (English name: titanium dioxide) as the main component₂) The white pigment of (2) is a polycrystalline compound having a lattice structure in which dots are arranged regularly. At present, the main modification coating methods of titanium dioxide comprise metal oxide single coating, silicon-aluminum binary coating, organic coating and the like.

The method mainly comprises the steps of coating metal oxide by using aluminum oxide, coating zirconium oxide, coating silicon oxide and the like, wherein main reagents are silicon, aluminum and zirconium oxide, and silicon and aluminum unit coatings have the characteristics of low cost, low consumption and low pollution₂The coating agent mainly comprises zirconium sulfate, zirconium tetrachloride, zirconium oxychloride and zirconium nitrate, but the substances are expensive, so that the price of the coated titanium dioxide is high. In addition, a cerium oxide coating is also adopted, and a typical cerium oxide coating experiment uses tetrabutyl titanate as a precursor, absolute ethyl alcohol as a solvent, and a sol-gel method is adopted to prepare titanium dioxide gel with different ion doping amounts. Different masses of Ce (NO)₃Dissolving the solution into absolute ethyl alcohol according to a certain molar ratio, dripping the solution into tetrabutyl titanate solution, violently stirring the solution, and finally dripping acetic acid with a certain concentration to obtain dibutyl phthalateAnd (3) gelling the titanium oxide, and drying the gel to obtain the cerium-coated titanium dioxide. The metal oxide single-coated product is mostly produced by adopting an acid-base neutralization method, the neutralization speed is high, and a loose spongy coating can be formed; the neutralization speed is slow, a compact film is generated, but the particle growth speed is fast, the process control is difficult, and the self-phase nucleation of silicon or aluminum in the coating agent is serious, so the coating layer on the surface of the titanium dioxide is easy to be uneven, the product stability is poor, the adaptability is poor, and the like.

The silicon-aluminum binary coating mainly comprises 1) a silicon-aluminum oxide composite coating mode, 2) a silicon-aluminum oxide binary single-drop coating mode and 3) a binary double-drop coating mode. In the inorganic treatment, only one metal hydrated emulsion or hydroxide is generally used as a coating agent for TiO₂The improvement of chalking resistance and gloss retention is limited. Therefore, the processing agent of two or more oxides of silicon, aluminum and the like, namely a composite coating and a double coating, is always applied in the production process.

The organic coating mainly comprises chemical adsorption and physical adsorption, has the functions of improving the rheological property, dispersion and wetting of the titanium dioxide in an organic medium, and has the mechanism of changing the surface property of titanium dioxide particles. The organic surface coating is modified by inorganic surface coating. The addition method comprises two methods: one is wet adding, that is, adding water to the filter cake twice to make prize material before washing and drying. The method is suitable for titanium dioxide with large silicon oxide coating amount, and adopts a spray drying process. The other method is dry adding, the titanium dioxide is added during jet milling, and the aqueous solution of the organic dispersant can be sprayed from a feed inlet of a jet mill during operation.

In the existing titanium dioxide coating technology, the problem of uneven coating is very common, for example, in common silicon coating, aluminum coating, zirconium coating, silicon-aluminum binary coating and aluminum-zirconium binary coating, because self-phase nucleation and heterogeneous nucleation in the coating process are difficult to control, the formed coating layer is not compact enough, and the coating thickness in some places is thick, and some places are thin or even none. In a common inorganic coating method, no matter unit coating or multi-component coating, self-phase nucleation of a coating agent exists in the coating process, and if heterogeneous nucleation among the coating agents exists in the multi-component coating method during simultaneous coating, the conditions can cause different thicknesses of the coating layers on the surface of the titanium dioxide, even the coating defects exist, so that the weather resistance of the coated titanium dioxide is not obviously increased, and the application of the titanium dioxide is limited. Particularly, the situation is more prominent in the current aluminum-clad film process. Aluminum is a relatively inexpensive element and has its value in applications. Therefore, how to obtain the aluminum-coated aluminum alloy with simple process and uniform and compact coating layer is the problem which is solved by the invention.

Disclosure of Invention

The technical problem to be solved by the invention is to provide the aluminum precursor coated titanium dioxide with more easily heterogeneous nucleation than self-phase nucleation, so that the prepared aluminum coated titanium dioxide film layer is more uniform and compact.

The invention solves the technical problems through the following technical scheme:

the aluminum precursor coated titanium dioxide is characterized in that the surface of the titanium dioxide is coated with an aluminum oxide precursor with heterogeneous nucleation which is easier than self-phase nucleation.

In order to obtain better technical effect, the alumina precursor is basic ammonium aluminum carbonate.

The invention aims to solve another technical problem of providing a process for preparing the aluminum precursor coated titanium dioxide, and providing a titanium dioxide coating technology which has the advantages of simple and stable coating process, easy operation and control, uniform and compact coating layer and cheap coating agent.

A preparation method of aluminum precursor coated titanium dioxide comprises the steps of,

(1) preparing titanium dioxide slurry with the mass fraction of 40-200g/L, adding sodium hexametaphosphate which accounts for 1-5% of the mass fraction of the titanium dioxide as a dispersing agent, and performing ultrasonic dispersion for 30-120 min;

(2) adding soluble aluminum salt accounting for 0.5-10% of the mass fraction of the titanium dioxide, wherein the concentration of the soluble aluminum salt solution is 0.1-3mol/L, and stirring for 0.5-3 h;

(3) adding soluble ammonium salt accounting for 50-200% of the mass fraction of the soluble aluminum salt used in the step (2), wherein the concentration of the soluble ammonium salt solution is 0.1-3mol/L, and uniformly stirring;

(4) dropwise adding basic ammonium salt accounting for 50-300% of the mass fraction of the soluble aluminum salt used in the step (2) through a constant-pressure funnel at a constant speed, wherein the concentration of the basic ammonium salt solution is 1-10mol/L, and reacting for 0.5-8 h;

(5) controlling the reaction temperature to be 30-100 ℃, stirring at the speed of 100-500r/min, dropwise adding 1mol/L alkali liquor to adjust the pH value in the coating process to 7-11, and then continuing to react for 0.5-4 h;

(6) and (3) sealing the solution obtained in the step (5) by using a preservative film, standing and aging at 20-90 ℃ for 1-48h, and filtering to obtain the aluminum precursor coated titanium dioxide.

For better technical effect, the soluble aluminum salt in step (2) includes but is not limited to aluminum sulfate, aluminum nitrate, aluminum chloride;

for better technical effect, the soluble ammonium salt in step (3) includes but is not limited to ammonium sulfate, ammonium nitrate, ammonium chloride, soluble metal ammonium salt;

for better technical results, the soluble metal ammonium salts include, but are not limited to, aluminum ammonium sulfate, aluminum ammonium alum;

for better technical effect, the basic ammonium salt in step (4) includes, but is not limited to, ammonium bicarbonate and ammonium carbonate.

For better technical effect, the alkali solution in step (5) includes but is not limited to sodium silicate solution, sodium hydroxide solution, and ammonia solution.

A method for preparing aluminum-coated titanium dioxide by coating titanium dioxide with aluminum precursor comprises the following steps,

and (4) drying the aluminum precursor coated titanium dioxide obtained in the step (6) for 0.5-24 h at the temperature of 30-200 ℃ through a drying oven to obtain the aluminum coated titanium dioxide.

The key point of the invention is the process method of partially or completely converting the alumina precursor into the hydrated alumina coated titanium dioxide by coating the prepared aluminum precursor with the titanium dioxide and then drying. Compared with the prior art for coating titanium dioxide with aluminum, the technology has the main advantages that: the coating process is different from the conventional aluminum coating method, and the hydrated alumina is directly coated on the titanium dioxide. The technology forms an aluminum precursor to be coated on the surface of the titanium dioxide, the molecular volume of the aluminum precursor is larger than that of hydrated alumina, and the aluminum precursor is in a chain structure, so that compared with the direct coating of the hydrated alumina, the precursor is easier to coat on the surface of the titanium dioxide; and the surface of the alumina precursor in the solution has a large amount of hydroxyl groups, so that the rejection among particles is large, the difficulty of self-phase nucleation is large, and heterogeneous nucleation is facilitated, so that the precursor can nucleate on the surface of the titanium dioxide more easily, and the titanium dioxide is coated. The coating reaction is single, and the problem of poor coating effect caused by self-phase nucleation of the coating agent in the common aluminum coating method can be effectively avoided. Then drying, wherein non-bridging hydroxyl groups of adjacent colloidal particles are spontaneously converted into bridging hydroxyl groups along with the removal of water; meanwhile, the coordination water of the gel part structure is removed, and bridging hydroxyl groups are formed among the coating particles. The drying temperature and time are controlled, and the coating precursor can be partially or completely converted into hydrated alumina, so that the surface coating layer of the titanium dioxide is uniform and compact, and the weather resistance of the titanium dioxide is superior to that of the traditional aluminum coating method.

Drawings

FIG. 1 is a TEM image of uncoated titanium dioxide in a comparative example of the present invention;

FIG. 2 is a TEM picture of aluminum-coated titanium dioxide according to the conventional process of the present invention;

FIG. 3 is a TEM image of the titanium dioxide coated by the aluminum precursor method in the embodiment of the present invention.

Detailed Description

The invention is explained in further detail below with reference to the figures and examples.

Example 1

An aluminum precursor coated titanium dioxide, the surface of the titanium dioxide is coated with an aluminum oxide precursor.

In this embodiment, the alumina precursor is basic ammonium aluminum carbonate.

Example 2

An aluminum-coated titanium dioxide is characterized in that an aluminum precursor coated with the titanium dioxide is dried and converted into a hydrated alumina film, and the hydrated alumina film is coated on the surface of the titanium dioxide.

Example 3

A preparation method of aluminum precursor coated titanium dioxide comprises the steps of,

(1) mixing laboratory-prepared titanium dioxide or titanium white slurry or commercially available titanium dioxide or titanium white slurry with water to prepare titanium dioxide slurry with the concentration of 40-200g/L, adding sodium hexametaphosphate accounting for 1-5% of the mass fraction of the titanium dioxide into the titanium dioxide slurry as a dispersing agent, and performing ultrasonic dispersion;

(2) adding soluble aluminum salt accounting for 0.5-10% of the mass fraction of the titanium dioxide, wherein the concentration of the soluble aluminum salt solution is 0.1-3mol/L, and stirring for 0.5-3 h; soluble aluminum salts include, but are not limited to, aluminum sulfate, aluminum nitrate, aluminum chloride;

(3) adding soluble ammonium salt accounting for 50-200% of the mass fraction of the soluble aluminum salt used in the step (2), wherein the concentration of the soluble ammonium salt solution is 0.1-3mol/L, and uniformly stirring; the soluble ammonium salts include, but are not limited to, ammonium sulfate, ammonium nitrate, ammonium chloride, soluble metal ammonium salts including, but not limited to, aluminum ammonium sulfate, aluminum ammonium alum;

(4) dropwise adding basic ammonium salt accounting for 50-300% of the mass fraction of the soluble aluminum salt used in the step (2) through a constant-pressure funnel at a constant speed, wherein the concentration of the basic ammonium salt solution is 1-10mol/L, and reacting for 0.5-8 h; the basic ammonium salts include, but are not limited to, ammonium bicarbonate, ammonium carbonate;

(5) controlling the reaction temperature to be 30-100 ℃, stirring at the speed of 100-500r/min, and dropwise adding 1mol/L alkali liquor to adjust the pH value of the coating process to 7-11, wherein the alkali liquor comprises but is not limited to sodium silicate solution, sodium hydroxide solution and ammonia water solution; then continuously reacting for 0.5-4h, and coating a layer of uniform and compact aluminum precursor on the surface of the titanium dioxide;

(6) and (3) sealing the solution obtained in the step (5) by using a preservative film, standing and aging at 20-90 ℃ for 1-48h, and filtering to obtain the aluminum precursor coated titanium dioxide.

Example 4

A method for preparing aluminum-coated titanium dioxide by coating titanium dioxide with aluminum precursor comprises the following steps,

drying the aluminum precursor coated titanium dioxide obtained in the embodiment 3 at 30-200 ℃ for 0.5-24 h by a drying oven to convert the aluminum precursor into a hydrated alumina film, wherein the hydrated alumina film is coated on the surface of the titanium dioxide, so that the effect of coating a layer of uniform and compact hydrated alumina film on the surface of the titanium dioxide is achieved, the radiation of ultraviolet rays to the titanium dioxide is blocked, the photocatalytic activity of the titanium dioxide is reduced, the weather resistance of the titanium dioxide is improved, and the aluminum coated titanium dioxide is obtained.

Example 5

A preparation method of aluminum precursor coated titanium dioxide comprises the following steps:

(1) adding water into commercially available titanium dioxide, stirring to prepare titanium dioxide slurry with the mass fraction of 40g/L, taking 1L of titanium dioxide slurry, and adding sodium hexametaphosphate accounting for 1% of the mass fraction of the titanium dioxide as a dispersing agent; weighing 0.4g of sodium hexametaphosphate, dissolving with water, adding into the titanium dioxide slurry, and performing ultrasonic dispersion;

(2) adding soluble aluminum salt accounting for 10% of the mass fraction of the titanium dioxide, weighing 0.04g of the soluble aluminum salt, preparing a solution with the concentration of the soluble aluminum salt solution being 0.1mol/L, and stirring for 3 hours; the soluble aluminum salt is one or a combination of aluminum sulfate, aluminum nitrate and aluminum chloride;

(3) adding soluble ammonium salt accounting for 50% of the mass fraction of the soluble aluminum salt used in the step (2), weighing 0.2g of the soluble ammonium salt, preparing a solution, wherein the concentration of the soluble ammonium salt solution is 0.1mol/L, and uniformly stirring; the soluble ammonium salt is one or a combination of more of ammonium sulfate, ammonium nitrate, ammonium chloride and soluble metal ammonium salt, and the soluble metal ammonium salt is one or a combination of two of aluminum ammonium sulfate and aluminum ammonium alum;

(4) dropwise adding basic ammonium salt accounting for 50% of the mass fraction of the soluble aluminum salt used in the step (2) through a constant-pressure funnel at a constant speed, weighing 0.2g of ammonium bicarbonate and/or ammonium carbonate, preparing a solution, wherein the concentration of the basic ammonium salt solution is 1mol/L, and reacting for 4 hours;

(5) controlling the reaction temperature to be 30 ℃, stirring at the speed of 500r/min, dropwise adding 1mol/L alkali liquor to adjust the pH value in the coating process to 9, continuing to react for 4 hours, and coating a layer of uniform and compact aluminum precursor on the surface of the titanium dioxide; the alkali liquor is one or a combination of more of sodium silicate solution, sodium hydroxide solution and ammonia water solution;

(6) and (4) sealing the solution obtained in the step (5) by using a preservative film, standing and aging at 50 ℃ for 48h, and filtering to obtain the aluminum precursor coated titanium dioxide.

Example 6

A method for preparing aluminum-coated titanium dioxide by using aluminum precursor-coated titanium dioxide comprises the step of drying the aluminum precursor-coated titanium dioxide obtained in the embodiment 5 at 100 ℃ for 4 hours by using a drying oven to obtain the aluminum-coated titanium dioxide.

Comparative example

Non-coated titanium dioxide: the sample was designated as A and the commercially available titanium dioxide used in step (1) of example 5 was taken, as shown in FIG. 1.

Traditional process aluminum coated titanium dioxide: marking as a sample B, preparing a titanium dioxide solution with the mass fraction of 120g/L, adding sodium hexametaphosphate accounting for 3% of the mass fraction of the titanium dioxide as a dispersing agent, stirring and dispersing for 1h, then adding aluminum sulfate accounting for 3% of the mass fraction of the titanium dioxide, adjusting the pH to 9 through 1mol/L sodium hydroxide solution, filtering and drying to obtain the aluminum-coated titanium dioxide in the traditional process, wherein the formula is shown in figure 2.

Certain aluminum-coated titanium dioxide in China: titanium dioxide coated with certain aluminum in China¹The test sample is marked as a C sample, is selected from Vancylron and Difuxing, and is a process research for improving the weather resistance of titanium dioxide; titanium dioxide coated with certain aluminum in China²Marked as sample D, selected from Maringhua, Shicheng, Jiangjian, Jindongzhou, xuhongying, Muhongxin, quick characterization of titanium pigment weather resistance modern coatings and paintings, 2011, 14(10), 18-19+ 37.

The aluminum coated titanium dioxide prepared in example 6, identified as sample E, is shown in fig. 3.

The A, B, C/D and E samples were compared as follows.

Comparative study of SEM pictures

Fig. 1 is an SEM picture of a sample a, fig. 2 is an SEM picture of a sample B, and fig. 3 is an SEM picture of an E sample, all of which are 20nm in scale.

As can be seen from the figure, the surface of the titanium dioxide of the sample A is smooth, and no coating substance is seen;

the surface of the titanium dioxide of the sample B is uneven, the titanium dioxide is unevenly coated with a plurality of aluminum oxides, the whole titanium dioxide sample is locally thicker and thinner, and even some parts are not covered with the aluminum oxides;

the surface of the titanium dioxide of the sample E is uniformly coated with the alumina, the thickness is uniform, and the high coating range is realized, which indicates that a compact alumina protective layer is formed on the surface of the titanium dioxide.

(II) comparative study on degradation Rate

Table 1 shows the degradation condition of different titanium dioxide products on rhodamine, and the specific experimental method is as follows:

(1) preparing 1g/L titanium dioxide solution, respectively mixing 50mL of titanium dioxide solution with 8mg/L rhodamine B solution with the same volume, and uniformly stirring to obtain a mixed solution;

(2) centrifuging the mixed solution prepared in the step (1) at the rotating speed of 10000r/min for 10min, taking supernate and measuring the absorbance A by using an ultraviolet spectrophotometer₀；

(3) Taking 5mL of the mixed solution prepared in the step (1) by using a graduated test tube, sealing, placing on a fixed shaker, and irradiating under ultraviolet light; irradiating for n hours (n is 1h, 2h, 3h, 4h, 5h), taking out the solution, centrifuging at 10000r/min for 10min, collecting supernatant, measuring absorbance with ultraviolet spectrophotometer, and recording as A_n。

By the formula R ═ A₀-A_n)/A₀X 100%, the degradation rate at each illumination time was calculated.

TABLE 1 degradation rate of different titanium dioxide products on rhodamine (%)

As can be seen from Table 1, the degradation rates of different products for rhodamine B at the same time are ranked from large to small: uncoated titanium dioxide > certain brand of aluminum-coated titanium dioxide in China > traditional process aluminum-coated titanium dioxide > example 4 prepares aluminum-coated titanium dioxide.

Therefore, the shielding of the photocatalytic capability by the prepared aluminum-coated titanium dioxide is superior to the aluminum-coated products and the aluminum-coated experimental products in the traditional process in the market.

(III) comparison of whiteness

Table 2 shows the whiteness values of uncoated titanium dioxide, conventional aluminum-coated titanium dioxide, certain aluminum-coated titanium dioxide in China and aluminum-coated titanium dioxide prepared in example 4, which were measured by a WSB-2 whiteness meter of Shanghai Pinxuan science and technology Co., Ltd.

TABLE 2 whiteness of different products

It can be seen from table 2 that the whiteness values of different titanium dioxide products are in descending order: the aluminum-coated titanium dioxide prepared in example 4 > certain aluminum-coated titanium dioxide in China > non-coated titanium dioxide > aluminum-coated titanium dioxide in the conventional process.

Therefore, the whiteness of the aluminum-coated titanium dioxide obtained by the technology is superior to that of aluminum-coated products and experimental products of aluminum-coated products in the market in the traditional process.

(IV) comparison of light loss ratios

The conventional process, a certain amount of the titanium dioxide coated with aluminum and the titanium dioxide coated with aluminum prepared in example 4 were respectively prepared into paint films (resin: acrylic acid), the paint films were aged in an artificial aging oven for 2 months, the aging results were expressed by the light loss ratio and the yellow variation (yellow variation is the value of yellow phase after aging-the value of yellow phase before aging), and the comparison results are shown in tables 3 to 4.

TABLE 3 comparison of gloss loss of artificially aged coating films

TABLE 4 comparison of the film yellowness after Artificial ageing

As can be seen from the results in tables 3-4, after the aluminum-coated titanium dioxide prepared by the invention is artificially aged, the light loss rate and the yellow variation are both smaller than those of the aluminum-coated titanium dioxide prepared by the traditional process and certain aluminum-coated titanium dioxide prepared by the traditional process in China, so that the weather resistance of the aluminum-coated titanium dioxide prepared by the technology is superior to that of the aluminum-coated products and the aluminum-coated experimental products prepared by the traditional process in the market.

The process for coating titanium dioxide with the aluminum precursor has single nucleation, is uniform and is easy to control. In the process of drying the precursor, non-bridging hydroxyl groups of adjacent colloidal particles are spontaneously converted into bridging hydroxyl groups along with the removal of water; meanwhile, the coordination water of the gel part structure is removed, and bridging hydroxyl groups are formed among the coating particles, so that the surface coating layer of the titanium dioxide is uniform and compact, and the weather resistance of the titanium dioxide is improved more obviously.