Zirconia has excellent mechanical, thermal, optical and electrical properties and is widely used in high-temperature structural materials, high-temperature optical elements, thermal sensors and fuel cells. There are many preparation methods of zirconia, including mechanical chemical ball mill method, tube ion technology sol-gel method, co-precipitation method, hydrothermal method and microwave hydrothermal method, etc., among which sol-gel method is favored for its simple process, room temperature operation, high product purity, good particle uniformity and other advantages.
1 experimental part
1.1 reagents and instruments
Zirconium oxychloride (ZrOCl2·8H2O, analytically pure), ammonia water (NH3·H2O, 25%), anhydrous ethanol (analytically pure).
202a-3 electric drying oven, phs-25 acidity meter, AW220 electronic analytical balance, hh-22 digital thermostatic water bath, 3-0 box resistance furnace, dds-11a type conductivity meter.
1.2 experimental steps
1.2.1 sink lake
The aqueous solution of ZrOCl2 prepared was added to the precipitant by dropping ammonia water under the condition of continuous stirring. Meanwhile, the pH of the solution was controlled to be about 10. After dropping, the solution was further stirred, and then aging was allowed.
1.2.2 wash polyester
Deionized water was added to the precipitated filter cake, which was thoroughly stirred, drained and repeatedly washed for 4-5 times. The specific conductivity of the washing solution was measured to be less than 10-5s ·m-1. It can be considered that the obtained Zr(OH)4 gel was basically free of chloride ions, and the Zr(OH)4 hydrogel was further washed with anhydrous ethanol to obtain alcohol gel.
The drying/roasting process adopts two methods: ordinary drying and nitrogen drying under normal pressure. Ordinary drying is to dry Zr(OH)4 hydrogel or alcohol gel in the oven, and the dried sample in the form of hydroxide, and then roasting in muffle furnace to get oxide. Nitrogen drying under normal pressure is to put Zr(OH)4 hydrogel or alcohol gel into quartz tube, and then pass nitrogen, roasting at set temperature to get ZrO2 powder.
Results and discussion
2.1 effect of roasting temperature on properties of zirconia
2.1.1 influence of roasting temperature on crystal shape and purity of the product
Figure 1 shows the sol-gel method of X-ray diffraction (XRD) analysis of nanometer zirconium dioxide, Z1 ~ Z5 ZrO2 – AP – 350 ℃ respectively, ZrO2 – AP – 600 ℃, ZrO2 – AP – 800 ℃, ZrO2 – CP – 400 ℃, ZrO2 – CP – 600 ℃ the X ray diffraction analysis graph of the sample. According to the position and shape of the main diffraction peak, the peak shape of Z3 is sharp and the crystallinity is higher. Compared with Z5, Z4 has sharp peak shape, high crystallinity and severe lattice defects. Z5 and Z3 are similar in structure and morphology, and tend to be amorphous. Their peak shape is wider and lower, and their particle size should be the smallest, while their specific surface area should be the largest. It can be seen from the above analysis that the crystallinity of the product increases with the increase of roasting temperature.
2.1.2 influence of roasting temperature on particle size of products
Figure 2, figure 3 and figure 4 for ZrO2 – AP – 350 ℃, ZrO2 – AP – 600 ℃ and ZrO2 – AP – 800 ℃ the TEM results of the sample. Can be seen from the figure when the calcination temperature is 350 ℃, the samples of even distribution, particle size is smaller; When burning temperature is 600 ℃, particles, uneven distribution of formation of spherical particles; When roasting temperature rise to 800 ℃, the reunion between particles is very obvious, particle size increases obviously, formation of irregular particles. As can be seen from the above analysis, with the increase of roasting temperature, the particle size of the product increases, and the agglomeration phenomenon is more serious.
2.1.3 influence of roasting temperature on specific surface area of products
With the increase of roasting temperature, the pore diameter moves towards the direction of large hole, because the increase of temperature is conducive to the growth of grain, and the specific surface area of the product is reduced.
2.2 influence of gel form on properties of zirconia
2.2.1 influence of gel form on product crystal shape
In figure 1 Z1, Z5 ZrO2 respectively – AP – 600 ℃ and ZrO2 – CP – 600 ℃ the X ray diffraction analysis graph of the sample. It can be seen from the figure that the positions of the main diffraction peaks obtained are basically the same, but the main diffraction peaks are not single. Therefore, in addition to ZrO2, the products obtained also contain ZrO1.99. The main crystal shape of Z1 is ZrO2, which also contains a certain amount of ZrO1.99. Z5 has tended to be amorphous, with a wide peak shape and a low peak shape. Its particle size should be the smallest and specific surface area the largest. It can be seen that at the same roasting temperature, the purity of ZrO2 with hydrogel as the precursor is lower than that of ZrO2 with hydrogel as the precursor, and the crystal shape of products with hydrogel as the precursor is generally better than that of ZrO2 with alcohol gel as the precursor, that is, the particle size of alcohol gel is smaller.
2.2.2 influence of gel form on particle size of products
Figure 5 for ZrO2 – CP – 600 ℃ the TEM results of the sample. Compared with figure 3, you can see that ZrO2 – CP after 600 ℃ temperature roasting, form a relatively even distribution of spherical particles; And ZrO2 – AP – 600 ℃ of the reunion between particles is very obvious, particle size increases obviously, forming irregular particles; It can be seen from the above results that the particle size of the sample with alcohol gel as the precursor is smaller than that of the sample with hydrogel as the precursor.
2.3 effect of drying method on properties of zirconia
2.3.1 influence of drying method on particle size of products
Figure 6 for ZrO2 – CN – 600 ℃ TEM picture of product. And figure 5 ZrO2 – CP – 600 ℃, ZrO2 – CP – 600 ℃ the product particle size small, ZrO2 – CN – 600 ℃ the product particle size is larger, reunion phenomenon is more serious. It can be seen that the particle size of the product dried in the flowing nitrogen atmosphere under atmospheric pressure is smaller than that of the product dried in the static air under atmospheric pressure.
2.3.2 influence of drying method on specific surface area and pore diameter of products
ZrO2 – CN after 600 ℃ treatment samples than surface than ZrO2 – CP after 600 ℃ treatment the smaller than the surface of the sample. It can be seen that the specific surface area of samples obtained by flowing nitrogen atmosphere drying is generally larger than that obtained by static air drying.
Nanometer zirconia was prepared by sol-gel method with cheap inorganic salt zirconium chloride as raw material and ammonia as precipitant. The following conclusions were drawn:
(1) with the increase of roasting temperature, the particle size of the product increases and agglomeration becomes more serious.
(2) ZrO2 prepared with alcohol gel as the precursor has small particle size and large specific surface area.
(3) ZrO2 dried under atmospheric flow nitrogen has smaller particle size and larger specific surface area.