In this experiment, the process of coating TiO 2 on the surface of kaolin particles by liquid deposition method was studied, and the optimum coating process conditions were determined. The hiding power of kaolin before and after coating was tested, in order to utilize cheap kaolin. Innovative in place of expensive white powder.
1.1 Preparation of Sample 1 Sample Sample Kaolin available from a non-metallic mineral Henan, particle size -5μm64.27%, d 50 3.54μm, the true density of 2.7g / cm 3, specific surface area of 1.1386m 2 / g.
1.2 Preparation Methods Chin salt, hydrofluoric acid, boric acid as raw materials, prepared by liquid deposition coated TiO 2 film kaolin powder products, the test process: Chin salt (plus HF) → fluoride Oxygen (addition of boric acid) → homogeneous solution (addition of kaolin and water) → reaction film formation → water washing, filtration → heat treatment → product.
The kaolin products coated with TiO 2 films of different thicknesses and surface morphology were obtained by controlling the process conditions such as solution composition, reaction temperature, reaction time and heat treatment temperature.
The main device of the experiment is a super constant temperature water bath heater. A certain amount of kaolin sample, a coating homogeneous solution and water are added to the reactor, stirred to fully disperse it, and heated in a water bath to the desired modification temperature, that is, coated. Modification reaction. After the reaction is completed, the coated product is filtered, washed with water, dried, and burned to obtain a coated modified product.
1.3 Test method 1.3.1 Evaluation index of coating effect: Since the matrix kaolin and the iron oxide film are both white and the particles are fine, it is difficult to judge the coating effect. This study used opacity to evaluate the effect of kaolin before and after coating. The method of measuring the hiding power. [next]
1.3.2 Determination of the amount of dioxin coating: The filtrate after the reaction was added with H 2 O 2 to develop color. The absorbance was measured at a wavelength of 410 nm, the concentration of TiO 2 was measured on a standard curve, and the amount of TiO 2 deposited was calculated from the mass of the reaction powder. Calculated as follows:
Where: ω, the mass of kaolin, g; V, the volume of the sample solution at the time of measurement, mL; Co, C, the concentration of the salt in the solution before and after the reaction, g/mL.
2 Influence of process conditions on the coating effect The purpose of kaolin modification is to use ultra-fine kaolin as the matrix to uniformly coat the surface of the substrate with the hydrated dioxin particles formed by hydrolysis of the salt, so that the kaolin can play the role of white powder. . Therefore, it is required to control suitable reaction conditions, and the iron oxide film formed by the reaction should be uniformly and densely packed on the surface of the substrate, and at the same time, the dioxide powder can not be formed in the solution, so as to achieve the purpose of modification.
2.1 The effect of reaction time on the film formation reaction See the test reaction conditions: suspension matrix concentration 5%, pH 1.5, solution volume 100mL, fluorinated oxygen concentration 0.2mo1/L, boric acid concentration 0.3mo1/L. reaction temperature 70 °C.
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It can be seen from Fig. 1 that the growth of the film is linear at the beginning, and as the reaction time increases, the film thickness increases and eventually reaches saturation.
2.2 Effect of reaction temperature on film formation reaction Figure 2 Test reaction conditions: suspension matrix concentration 5%, pH 1.5, solution volume 100ML, ferric fluoride concentration 0.Zm ol/L boric acid concentration 0.3m o1/L, reaction Time 6h. Figure 2 shows that the higher the reaction temperature, the faster the film formation rate, indicating that the film formation reaction is an endothermic reaction. However, too high a temperature will cause evaporation of the plating solution, so the coating reaction temperature is preferably 70 ° C.
2.3 The effect of sound on the film formation reaction is shown in Figure 3. The reaction conditions were as follows: suspension concentration 5%, reaction temperature 70 ° C, solution volume 100 mL, fluorinated oxygen concentration 0.2 mo1/L, boric acid concentration 0.3 mol/L, reaction time 6 h.
As can be seen from Fig. 3, as the pH increases, the film thickness increases because the amount of TiO(OH)2 formed by the combination of OH- and TiO2 increases. However, if the pH is too high, the reaction rate will increase sharply, and TiO2 powder will be easily formed, which will affect the coating quality of the film. The pH is generally controlled to be 2 or less in the reaction.
2.4 The effect of matrix suspension concentration on the film formation reaction is shown in Figure 4. The reaction conditions were as follows: reaction temperature 70 ° C, solution volume 100 mL, fluorinated oxygen concentration 0.2 mo1/L, boric acid concentration 0.3 mol 1 /L, reaction time 6 h, pH 1.5. [next]
The particles of the kaolin matrix are fine, and in order to uniformly and efficiently coat the surface of the fine particles of the matrix, the matrix particles must be sufficiently dispersed in the plating solution. This can be achieved by adjusting the suspension concentration of the substrate. It can be seen from Fig. 4 that when the suspension concentration of the substrate is low, the matrix particles are well dispersed, and the TiO 2 film coated on the surface of the kaolin particles is thick. Therefore, the suspension concentration of the substrate during the experiment is generally controlled to be less than 5%.
2.5 The influence of stirring speed on the film formation reaction The stirring speed is not only affecting the dispersion uniformity of the kaolin matrix in the modified system, but also affecting the uniformity of the temperature distribution of the modified system. When the stirring speed is too low, the sample has a low rate of dioxide coating, indicating that the reaction rate is slow and the reaction is not uniform; when the stirring speed is increased, the reaction speed is also accelerated; but when the stirring speed is too high, the oxidation is performed. Qin's coating rate is reduced, which is due to strong mechanical forces such as shearing and impact. On the one hand, it prevents the deposition of hydrated dioxide on the surface of calcined kaolin particles, and on the other hand, it leads to the formation of hydrated dioxide. The iron film layer partially falls off and the thickness is uneven. Therefore, the stirring speed should be moderate, and the blade is generally able to cause a scum in the reaction liquid.
The experimental results show that the stirring speed is in the range of 300-800r/min, which has little effect on the modification effect and can meet the requirements of the coating.
2.6 Relationship between hiding power and heat treatment temperature The hiding power of kaolin coated with dichoxide film at different heat treatment temperatures is shown in Table 1.
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