JPH0672016B2 - Thin plate zirconia-based crystallites - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Zirconia (ZrO ₂ and its solid solution are collectively referred to herein as zirconia) is a highly refractory oxide and has various applications as fine ceramics. In particular, solid solutions of Y ₂ O _{3 and} others are in the spotlight as oxygen sensors and high-strength engineering ceramics, and are also used in large quantities as raw materials for piezoelectric ceramics. Generally, fine particle zirconia is used as a raw material for these fine ceramics, and most of the fine spherical particles are used as a ground product or a fine powder having a similar shape because of its excellent packing and sinterability. . However, since there is no conventional industrial manufacturing method for thin plate-shaped zirconia particles, it is the current situation that even a description of the trial of its application cannot be seen at all.

The inventor noticed that the thin plate-shaped zirconia has a special application possibility, and repeated various experiments. Successful synthesis of microcrystals. According to chemical analysis, these microcrystals are compounds with a layered structure containing Zr as the main metal component and SO ₄ ²⁻ ions whose atomic number is approximately 2/5. The thickness is 500 Å or less, and the direction parallel to the layers. Can be crystallized into a hexagonal plate-shaped or disk-shaped thin plate having a size 5 times or more that of the above.

According to electron diffraction, this thin plate crystal has hexagonal or trigonal symmetry crystal axes perpendicular to the plane of the layer, and its powder X-ray diffraction pattern shows that the major peak is square or cubic zirconia, as shown in FIG. It has a crystal structure in almost the same position as that of. SO ₄ ²⁻ is relatively less than Zr, and the spatial arrangement of Zr and O is similar to that of tetragonal or cubic zirconia.
The fact that the spatial concentration of Zr is close to that of ZrO ₂ is extremely important. As shown in Fig. 1, the water contained up to 200 ° C is lost by heating, but the crystal structure is maintained almost unchanged, and the air itself does not change. It is stable up to 600 ℃, and if it is heat-treated at a higher temperature, it decomposes and desulfurizes to form zirconia thin slab particles with relatively strong strength.

This thin plate zirconia-based crystallite containing SO ₄ ^2- is 0.1 to 1.5 g ・ atom / l containing soluble zirconia salt as Zr, and SO ₄ ^2- ion is 0.3 to 3.0 g ・ ion / l containing PH 1.0 or less. 1 acidic solution
It can be produced and crystallized in the liquid by heat treatment at 10 to 300 ° C. In the region where the Zr concentration in the aqueous solution is 0.1 atom / l or less or the SO ₄ ^2- ion concentration is 0.3 g · ion / l or less, the precipitate has poor crystallinity and loses the thin plate-like characteristics, and is monoclinic. Zr
O ₂ will be mixed. Also, Zr is 1.5g ・ atom / l or more,
Alternatively, in the region where SO ₄ ^2- is 3.0 g · ion / l or more, high temperature and long time are required for precipitation, which is not practical. In order to obtain good results, Zr is 0.2--1.0 g ・ atom and SO ₄ ²⁻ ion is 0.4--1.5 g ・ i.
It is desirable that it is on / l and the molar ratio of SO ₄ ^2- / Zr is 1.0 or more.

The microcrystals obtained by the method of the present invention coagulate and settle at a pH of about 3 or more, and peptize at a pH of about 5 to 6 to form a sol. Further, if water is replaced with an organic solvent and then dried or freeze-dried, individual particles without aggregation can be obtained.

The thin plate-like crystallites containing SO ₄ ²⁻ contain water, but they are released at about 200 ° C. or below, and the crystal structure, especially the mutual relation between Zr and O, hardly changes. This crystal structure is maintained up to about 600 ℃, and is desulfurized and decomposed at 600-700 ℃ to form zirconia.
This zirconia becomes a thin plate shape, leaving the shape of microcrystals before decomposition, but some agglomeration occurs between the zirconia particles depending on the decomposition conditions. However, most of this agglomeration occurs between the layers, and the thin plate-like characteristics are not lost. It is also possible to obtain individual thin plate-shaped zirconia fine particles without agglomeration by interposing a carbonaceous substance between thin plate-like microcrystals for thermal decomposition and then burning and removing carbon at a low temperature. If Y ₂ O ₃ , CaO, etc. are allowed to coexist during thermal decomposition, they form solid solution and become thin plate-like particles of stabilized or partially stabilized zirconia. These desulfurized thin plate zirconia fine particles have a hexagonal plate shape or a disk shape depending on the shape of the original particles, and are dense or porous depending on the desulfurization conditions, but all have sufficient shape maintaining strength. These fine particle powders can be dispersed again in water to form a sol.

As described above, the thin plate-like fine particles of the present invention are extremely close to ZrO ₂ before desulfurization as well as desulfurization, and are stable up to 600 ° C. or more themselves, and they retain their original shape by heat desulfurization to become thin plate zirconia. Both have similar functions and effects and have almost the same uses as ceramic raw materials. Both
It is suitable as a main raw material or auxiliary raw material for thin plate or sheet ceramics. Both of them are easy to arrange in the plane direction at the time of molding, and give molding strength even to an extremely thin film.
In addition, the shrinkage in the area direction during firing is reduced to prevent the occurrence of cracks or warpage. In addition, both have a unique effect as a raw material for piezoelectric ceramics such as PZT, and the piezoelectric crystals formed by reacting with zirconia are oriented by the thinness of zirconia and enhance its performance. In addition, the sol or sludge in which these fine particles are suspended is oriented in the surface direction when applied to a solid surface, so in addition to surface treatment of ceramics,
In general, it is also extremely valuable as a coating material, paint filler, cosmetics, rust preventive paint, oxidation resistant heat resistant paint, etc.

Example 1 A zirconia sulfate aqueous solution was prepared by dissolving the reagent zirconia carbonate in sulfuric acid. The solution concentration is about 1.0 mol / l as Zr, H ₂ SO ₄
Was about 1.5 mol / l and PH was less than 1. This was sealed in a Teflon container and heat-treated at 200 ° C. for 4 days in an autoclave to obtain a white precipitate. This is composed of hexagonal plate-like crystallites with a side of about 1000 Å or more and a thickness of about 70 Å when observed with a transmission electron microscope after washing with water and drying.
Met.

The chemical composition of this crystallite is approximately Zr ₅ O according to chemical analysis.
Corresponding to ₈ (SO ₄ ) ₂ · nH ₂ O, its weight change due to heating is as shown in Fig. 1. Water is removed up to about 200 ° C and decomposed and desulfurized near 650 ° C. Powder X-ray diffraction pattern (CuKα) of this crystallite
As shown in Fig. 2 (a), most of the major peaks are almost the same as those of the tetragonal ZrO ₂ particles (Fig. 2 (e)), except for the peak showing a layered structure with 2θ close to 8 °. In the position. These crystallites are thermally stable, and even after calcination at 600 ° C for 2 hours, the peak around 8 ° only shifts to a slightly higher angle, as shown in Fig. 2 (b), and the other peaks. The position and the intensity of are almost unchanged. The calcined product at 700 ° C. becomes monoclinic zirconia as shown in FIG. 2 (c), but the monoclinic zirconia particles completely leave a thin plate-like skeleton according to a transmission electron microscope.

Example 2 Ammonia was added to the reagent zirconyl chloride to form a precipitate of zirconium hydroxide, which was thoroughly washed with water and then concentrated sulfuric acid was added to obtain a transparent aqueous solution. From this, the Zr concentration was changed to 0.5 mol / l, H ₂
Aqueous solution with SO ₄ concentration of 1.0 mol / l and Zr concentration
An aqueous solution containing 0.25 mol / l and H ₂ SO ₄ concentration of 0.5 mol / l was prepared, and each was sealed in a Teflon container and treated at 200 ° C for 3 days in an autoclave. Obtained. According to chemical analysis, electron microscope observation, and powder X-ray diffraction, the former is almost the same as that obtained in Example 1 in chemical composition, crystallinity, particle shape, and the latter is shown in FIG. As shown in d), the crystallinity is somewhat poor, but they have the same crystal structure and are disk-shaped.
The chemical composition is plate-like microcrystals with almost the same chemical composition, and zirconia calcined at 900 ℃ completely retains the plate-like shape.

[Brief description of drawings]

FIG. 1 shows the results of thermogravimetric analysis of the powder of thin plate zirconia-based microcrystals containing SO ₄ ^{2− according} to the present invention. Fig. 2 shows the powder X-ray diffraction pattern (CuKα) of the sample.
Is a thin plate-like zirconia-based microcrystal containing SO ₄ ^2- of the present invention, which has high crystallinity, (b) is a powder obtained by calcining (a) to 600 ° C., (c) is (a) 700 ° C. Powder calcined into
(D) is somewhat less crystalline than (a), (e)
Is a tetragonal ZrO ₂ microcrystal obtained by calcining a hydroxide at low temperature.

Claims (1)

[Claims] 1. A soluble zirconium salt having a Zr of 0.1 to 1.5.
PH containing g ・ atm / l, SO ₄ ^2- ion 0.3 to 3.0 g ・ ion / l
A thin plate zirconia-based crystallite having a chemical composition substantially equivalent to Zr ₅ O ₈ (SO ₄ ) ₂ · nH ₂ O, obtained by heat-treating an acidic aqueous solution of 1.0 or less at 110 to 350 ° C .; Main metal ion and SO _{4 which} is almost 2/5 of the number of atoms
A compound with a layered structure containing ^2- ions, which has a hexagonal or trigonal symmetry crystal axis perpendicular to the layer plane, and the mutual position of Zr and O resembles that of ZrO ₂ crystals, and the main peaks of its powder X-ray analysis pattern Some of the crystals are in the same position as tetragonal or cubic ZrO ₂ , and are thin plate zirconia-based microcrystals characterized by spreading in the direction parallel to the layer plane and having a thickness of 500 Å or less.