JPS62191426A - Zirconia polycrystalline microballon and its production - Google Patents

Abstract

PURPOSE:A translucent aqueous sol in which ultramicro crystals of monoclinic ZrO2 with a specific shape are deflocculated in high dispersion is spray-dried and roasted to give the titled microballoon of very small sizes and uniform membrane thickness. CONSTITUTION:Ultrafine microcrystals of monoclinic ZrO2 of 100Angstrom or less wide rods or strips are highly deflocculated and combined with a solution or colloidal particles of at least one selected from the group consisting of rare earth metal ions such as Y<3+>, Ca<2+> and Mg<2+> to prepare a translucent aqueous sol. The sol is spray-dried form shells of porous gel on the surface of individual liquid drops and the shells are solidified by drying, then roasted over 800 deg.C, The titled microballoons which are made of ultrafine microcrystals of tetragonal or cubic ZrO2 solid solution of less than 0.5 micron in particle size and has a uniform thin film shell of 5-100 micron thickness and a diameter of 50-100 microns.

Description

[Detailed description of the invention] Pure zirconia, general zirconia containing HfO2, etc., or Y2O3°Cab,
MgO etc. were dissolved in solid solution. So-called stabilized or partially stabilized zirconia ceramics are in practical use as refractory and high-strength materials. Zirconia has the lowest thermal conductivity, so it is a hollow balloon. The present invention is extremely small,
The present invention also relates to a method for manufacturing precision rt microballoons with a thin and uniform film thickness using zirconia modules or zirconia solid solutions.

That is, the present invention consists of 8 square or cubic zirconia solid solution microcrystals with a grain size of 0.5 μm or less.

Approximately uniform thin film with a thickness of 5 to 100 μm and a diameter of 50 to 100 μm
A zirconia polycrystalline microballoon with a diameter of 0 μm and a method for producing the same.2 The method of the present invention uses rare earth metal ions such as monoclinic Y8+, Ca2+ and Mg'' (7) in the form of short rods or strips with a width of 100 Å or less as starting materials. A translucent aqueous sol is prepared containing one or more selected from the group in the form of soluble salts or colloidal particles.

This aqueous sol was spray-dried to form a shell of porous gel on the surface of each droplet, and the whole was dried and solidified.

It is characterized by being fired at a temperature of 800°C or higher.

The research that forms the basis of the present invention relates to the synthesis and properties of monoclinic zirconia ultrafine crystals in an aqueous solution conducted by the present inventor. Long-term hydrothermal treatment produces short rod-shaped monoclinic zirconia ultrafine crystals, and when the ultrafine crystal particles are sufficiently dispersed and peptized, they dry to become a translucent polycrystalline porous gel. ``Highly dispersed sol or gel of monoclinic zirconia ultrafine crystals and manufacturing method'' (January 14, 1985, application number 1981-
A patent application was filed as No. 005899. The present inventor further investigated the properties of this sol and found that the X-ray crystallite diameter was 100 Å.
The following translucent aqueous sol in which anisotropically shaped crystalline ultrafine particles are sufficiently dispersed and peptized contains 1 mol/zirconia.
It is translucent and fluid even at a concentration of about 1 liter, and when rapidly dehydrated from the surface, a porous polycrystalline thin film consisting of an aggregate of ultrafine particles is formed on the surface, and once formed, the thin film can be reused even in water. I discovered that it does not disperse. Furthermore, a sol or gel consisting of such ultrafine crystals is
If soluble salts containing metal ions that are dissolved in ZrO2 to stabilize square or cubic crystals are added to the sol and then gelled, or if the gelled product is impregnated with them, in the secondary heat treatment, 400 Monoclinic zirconia begins to form a solid solution at an extremely low temperature of 90°C and changes into a square or cubic crystal, and then at temperatures above 900°C, this becomes sintered and densified, resulting in stabilized or partially stabilized zirconia depending on the amount of added metal ions. It was discovered that polycrystalline ceramics can be obtained. The present invention includes the invention mentioned at the beginning,
This is an application of the various discoveries mentioned above.

In the present invention, the translucent aqueous sol is a highly dispersed peptized anisotropic monoclinic zirconia ultrafine crystal in the form of short rods or strips with a width of 100 Å or less.

This is essential for the formation of stable microballoons with uniform thickness and microstructure. High dispersibility is the first important factor, and translucency is the measure.

For example, even a monoclinic zirconia ultrafine particle sol with an apparent crystallite diameter of 50 Å or less that does not fully peptize and form a precipitate usually consists of aggregated particles of 500 Å or more, and even at a concentration of about 0.2 mol/l, the emulsion is low. Tall, milky and not translucent. With such a sol, it is not possible to form microballoons with a uniform thickness. The anisotropic shape of the particles is also an extremely important factor.

This is because when a sol droplet undergoes rapid dehydration, the thin film formed on the surface of the droplet must maintain its shape and have sufficient porosity to continue dehydration of the droplet.

Therefore, subsequent dehydration is performed through the porous thin film formed on the surface of the droplet, resulting in the formation of a microballoon with a uniform porous shell of ultrafine zirconia crystals. If the zirconia particles constituting the sol have an isotropic shape or a plate shape, a spherical balloon will not be formed but will be depressed or burst.

The diameter of the balloon and the thickness of the shell are determined by the IJ in the sol when spraying.
i&'l is determined by the drying and dehydration conditions such as the content m of zirconia, the size of the sprayed droplets, and the temperature.

Ultrafine particle size of 100 Å or less is essential for forming microballoons and subsequent sintering and densification.

In the method of the present invention, Y, 0. Or, if you mix a salt that becomes an oxide such as CaO.

This one in nine is transformed into square or cubic zirconia by heat treatment at a temperature of 400"C or higher, and 1300"
It becomes sintered and densified at a temperature of about ℃. In this heat treatment for densification, the ultrafine particles that make up the balloon shell sinter and form a dense structure.

Sintering within the balloon shell also occurs. However, this sintering between the balloons is much weaker than the sintering within the balloon shell, so it can be loosened relatively easily by firing at 1000'C or less. Furthermore, for firing at a higher temperature, firing in a spray state or firing with carbon interposed is desirable.

The zirconia polycrystalline microballoon that can be produced according to the present invention has a diameter of 50 to 1000 μm and a film thickness of 5 to 100 μm.
If the diameter is 10 μm or less, the ball will not become hollow by normal drying methods, but will become a solid sphere.

Stabilized zirconia has an extremely high melting point and excellent corrosion resistance and heat insulation properties, making this balloon a fire-resistant heat-insulating agent with the highest H rating. In addition, partially stabilized zirconia has the highest strength among ceramics, so such balloons have sufficient strength even with thin shells.

Gives the best lightweight filler.

Example 1 Weighed out 52f of the reagent zirconyl chloride (Zr0CI t .8H20), added about 10xt of distilled water to it, sealed the mixture in a Teflon container, heated it to 200°C in an autoclave, and kept it for 5 days. and hydrothermal treatment.
The resulting slurry mixture was diluted with distilled water to approximately 1.54 g.
The pH was increased to 5 by treatment with an ion exchange resin. The generated sol is almost completely peptized.

It was semi-transparent and the transmitted light had a reddish tinge. The apparent crystallite diameter according to X-rays is about 50 crystallites, and according to electron microscopy, it consists of monoclinic zirconia short rod-shaped ultrafine crystals with a width of about 40 crystallites and a length of about 100 crystallites, and the zirconia content in the sol. S11 is about 0.1
It was mol/4. To this sol, YCIs was added in an amount of 6 mol % based on the amount of zirconia in the sol, and after thorough mixing, the mixture was heated and concentrated in a microwave oven.

It was concentrated to a concentration of about 0.5 mol/l of zirconia. This sol is still translucent and fluid, almost like water. When this sol was sprayed into a spray dryer at about 100°C and the dried material was collected, the product had a diameter of 50 to 100°C. , μm spherical particles. When this was crushed in a mortar and observed under a scanning electron microscope, it was found that all of the shells were hollow and the thickness of the shell was about 11011. Furthermore, when this was placed in a crucible and fired at 1300℃,
A porous mass was obtained in which hollow spheres made of densified partially stabilized zirconia were loosely sintered to each other.

Claims (1)

[Scope of Claims] 1) A zirconia polycrystalline microballoon with a diameter of 50 to 1000 μm and a substantially uniform thin film of 5 to 100 μm in thickness, consisting of square or cubic zirconia solid solution ultrafine crystals with a particle size of 0.5 μm or less. 2) Short rod-shaped or strip-shaped monoclinic zirconia ultrafine crystals with a width of 100 Å or less are peptized in a highly dispersed state, and rare earth metal ions such as Y^3^+, Ca^2^+, and Mg^2 ^
A translucent aqueous sol is prepared by adding and mixing one or more selected from the group + in the form of a soluble salt or colloidal particles, and this is spray-dried to form a porous gel shell on the surface of each droplet. 1. A method for producing a zirconia polycrystalline microballoon, which comprises drying and solidifying the entire balloon at a temperature of 800°C or higher.