JPH013050A - Manufacturing method of superconducting ceramics - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing superconducting ceramics, and more specifically, to a method for manufacturing superconducting ceramics that can achieve mixing of elements constituting the superconducting ceramics at the atomic level. Regarding manufacturing methods.

[Prior Art] Superconducting ceramics have conventionally been made using compounds as raw materials, such as Y t O3, La5hs, Cub, and SrCO3.
, [3a] After mixing COs etc., drying and pulverizing, the raw material powder is pressed, then pre-sintered, pulverized and pressed again, and finally sintered, which is the so-called dry mixing method. There is.

[Problems to be Solved by the Invention] When mixing and sintering in such a solid state, reactions between raw material compounds proceed in very small areas such as contact points or contact surfaces between powder particles. Therefore, interdiffusion of molecules and/or atoms within the particle is required for the atoms inside the particle to react. However, the diffusion rate of molecules and atoms in solids is extremely low, and the reaction efficiency cannot be said to be high. Therefore, it is difficult to achieve a reaction close to 100% by heating at a high temperature for a long time.

In order to encourage interdiffusion of molecules or atoms, it is conceivable to pulverize the compound to reduce the particle size and increase the surface area, but pulverizing the powder not only requires a large amount of energy and time, but also requires a large amount of energy and time. There are limits to miniaturization, and at best only micron-order particles can be obtained.

SUMMARY OF THE INVENTION Therefore, the present invention aims to provide a manufacturing method that mixes the constituent elements of superconducting ceramics at the atomic level and efficiently obtains homogeneous and high-quality superconducting ceramics.

[Means for solving the problems] According to the present invention, the above problems are solved. Compounds containing at least the constituent elements of superconducting ceramics (hereinafter simply referred to as raw material compounds) are mixed in a liquid state, heated to dryness,
This problem is solved by a method for manufacturing superconducting ceramics that is characterized by subsequent sintering. The liquid state of one starting compound can be realized by a solution or a molten state of the compound.

An acid, an alkali, or water can be used as a solvent for preparing a solution of the raw material compound. The solvent may be selected depending on the type of compound. If the raw material compound is a water-soluble salt (eg, nitrate), water can be used as a solvent. If the raw material compound is a water-insoluble compound (for example, an oxide), it is preferable to use an acid or an alkali as a solvent. Examples of acids include nitric acid, hydrochloric acid, hydrofluoric acid, or mixtures thereof, and hydrogen peroxide. Aqueous ammonia is preferred as the alkali.

When the raw material compound is dissolved in acid, elements that are the main components of superconducting ceramics, such as La, Sr, Cu5Y, B
Complex salts such as a are formed. Depending on the type of acid, the salt may contain water of crystallization or free water, so it is necessary to remove water by drying in vacuum at a constant temperature in advance to prevent bumping during sintering. Therefore,
It is preferred to select acids that do not form salts with low boiling points or low decomposition temperatures. Further, it is preferable to use an acid in which only oxygen atoms remain as constituent elements of the ceramic in the sintering process, other than impurity elements. For example, when nitric acid is used, nitrate radicals remain during drying, but during high-temperature heating or sintering, the nitrate radicals are removed and only the oxide remains.

The solution is made by dissolving all the raw material compounds in a solvent at once.
Alternatively, solutions of each raw material compound may be prepared in advance and then mixed.

Another method of achieving a liquid flow state is to melt the raw material compound by heating it to a temperature above its melting point. In this case, it is preferable to use a compound with a relatively low melting point, and nitrates are particularly preferable.

For example, the melting point of yttrium nitrate is +50°C, the melting point of barium nitrate is 592°C, and the melting point of cupric nitrate is 114°C.
The temperature is 5°C. However, the melting point of the mixture is lower than that of the individual compounds due to freezing point depression. For example, if each nitrate is mixed with a composition such that Y:Ba:Cu=I:2.3 after sintering, the melting point of the mixture will be 230-240.
The temperature drops to ℃. It is generally preferred to melt at a temperature not exceeding 300°C. Although it is possible to carry out melting at a temperature of 300-500°C, the melting time may be short and homogeneous mixing may not be achieved.

The compounds mixed in a solution or molten state as described above are then heated to dryness and sintered to form superconducting ceramics.

Heating to dryness is the temperature at which water evaporates, for example 100 to 1
It is carried out at a temperature of 50 DEG C., preferably from 100 to 130 DEG C., under atmospheric pressure or reduced pressure.

Sintering is carried out under the same conditions as in the conventional dry mixing method of powder mixing. For example, YIBa.

CL130? In the system, the sintering temperature is 800~100℃
, preferably 950 to 1000°C, and the sintering time is
The time is 30 minutes to 5 hours, preferably 1 to 2 hours. The atmosphere is usually atmospheric.

By the way, since the sintering process is performed at a high temperature of 800° C. or higher, the released nitrate radicals become nitrite gas, causing bumping, and a part of the product may be lost. In addition, nitrite gas corrodes the inside of the sintering furnace.

Therefore, in the present invention, after heating to dryness or drying at constant temperature in vacuum, the raw material compound mixture is heated to dryness in an air atmosphere for 300 min.
It is heated at a temperature of ~900°C to sufficiently release nitrite gas, and then subjected to sintering.

Heating is carried out by gradually raising the temperature from 300°C to a temperature of 850 to 9008°C, and at that high temperature for a certain period of time, for example, 0.5 to 9008°C.
It may be held for 1 hour.

In a preferred embodiment, the temperature is first heated at 300 to 500°C in an air atmosphere.
The remaining moisture is removed and some of the nitrous gas is released. Residual moisture includes moisture that cannot be sufficiently removed by drying or subsequent constant temperature vacuum drying, and moisture that is absorbed by the compound mixture due to its high deliquescent property when left in the atmosphere. Then, 850
Heated at a temperature of ~900°C and heated to 300°C in an atmospheric atmosphere.
Nitrate radicals that cannot be removed by heating at 00°C are completely released as nitrite gas. It also converts some of the nitrates into oxides.

When heated at a temperature of 300 to 500°C in an air atmosphere,
It is difficult to produce a complete composite nitrate or composite oxide of the constituent elements of superconducting ceramics, and only partially uniform compounds are produced. Therefore, in the atmospheric atmosphere, 850~
If this is sufficiently pulverized and mixed in a mortar or the like before heating at a temperature of 900°C, a uniform intermediate product can be efficiently obtained by heating at a temperature of 850 to 900°C in an air atmosphere. Although it is an intermediate product, depending on the system, it may already have the same structure as superconducting ceramics in terms of crystal structure analysis at this stage.

The raw material compounds that can be used in the present invention are not particularly limited, but include, for example, the following compounds: 5ctO3, S c (N 03) 3 ・Xtl 20,
S c (OtT) ・C03” xHtO,5C2(
S 04) 3” xll, o: Y2O3, Y(NO
s)s HXI[20,Y2(S 04)3 ・xll
to,yt(co,)・xl(to;LatO3,L
a(NO3)3”x)-12o, L a2(S
O4)3・xHtOlLay(CO3)・xi-Its
;BedSBe(NOa)y ・xHto, BeSO4
・xlltI'i4gCOs' xHto, (MgC
O3)4・Mg(OH)t・xHtOlMg(No 3
)t ・XHto, Mg;Ca(NOa)t''XI(
20; S r(N O3)t, SrCO3: B a(N O3)t, I3 a CO3; Cu, Cu
b, CuzOlCu(N 03)?・xHp O;t
lo(NOs)3 xHtOlHo(CI-(sCOO
)3 ・Xl-1,0,Ho(C0,3)3'XH
tO;DY(NO3)s”xllto,Dy(CtO
+), xH2O.

However, it is not limited to these.

A compound containing a constituent element corresponding to the sintering aid may be added to the solution or melt together with the raw material compound.

[Effects of the Invention] In the present invention, since the raw material compounds are mixed in a liquid state, the constituent elements of the superconducting ceramic are mixed at the atomic level. Therefore, since the superconducting ceramic production reaction occurs efficiently during sintering, the sintering time is shortened and the product composition is made uniform.

In addition, the nitrate radicals should be sufficiently removed before sintering (by
Bumping during sintering and corrosion of the sintering furnace can be prevented.

[Example] Next, examples will be shown to explain the present invention in more detail.

Example 1 LazO311,4g, 5rCO30,83g and C
3.00 g of uO was placed in a quartz beaker, and 60 mC of diluted nitric acid (1 volume of special grade nitric acid: 1 volume of water) was added to dissolve the raw material compound. A blue clear solution resulted.

The obtained solution was heated to 200° C. on a hot plate, and when it became syrupy, it was transferred onto a water bath to avoid bumping, and heated at 100° C. to dryness.

The syrup-like mixture is applied as is to the surface of a substrate (e.g., sapphire substrate, alumina substrate), and further coated for 10 minutes.
It can be heated to dryness at 0°C.

In this way, a superconducting ceramic layer can be formed on the surface of the substrate.

The dried mixture was heated at 130°C for 3 hours at 10″-1~1
It was dried at a constant temperature of Torr to evaporate most of the excess moisture.

The dry mixture was then sintered at 1100° C. in air.

During sintering, the rate at which nitrates are decomposed and nitrite gas is generated can be adjusted by adjusting the rate of temperature rise.

It is also possible to control porosity by adjusting void generation. This allows the production rate of the final product to be increased. If you are simply producing raw material powder for superconducting ceramics, you can raise the temperature to increase the porosity, increase the reaction rate, and increase the production speed.

When the crystal structure of the ceramic obtained by sintering was analyzed by powder X-ray diffraction, it was found to be a NiF-type crystal structure, which is a typical crystal structure of high-temperature superconducting ceramics.

The sintered material can be further pulverized and used as a raw material for producing a superconducting ceramic molded article having a desired shape. Therefore, the above sintered material was pulverized, and 1
00 kg/cm2 pressure, diameter 8111 thickness 2Wm
Pressure molded into a disk shape, and then heated again at 1100℃ in the atmosphere.
Sintered for hours.

On the other hand, a syrup-like liquid obtained by heating a nitric acid solution of the raw material compound was applied to the surface of the sapphire substrate, heated to dryness at 100°C, further dried under reduced pressure at 130°C for 3 hours, and then heated at +100°C in the atmosphere. It was sintered for 1 hour. When the crystal structure of this coated ceramic was analyzed by X-ray diffraction, it was found to have a KzNiF4 type crystal structure, similar to the disk-shaped sample.

When the critical temperature (zero resistance temperature) of the disc-shaped sample and the coated sample was measured, they were both 30 to 40.

Example 2 Production of Y1Ba2CusO7-X-based superconducting ceramics Cu0 in 40 m12 of diluted nitric acid (1 volume of special grade nitric acid, 1 volume of water)
3.58 g of YtO3 and 1.69 g of YtO were dissolved, and a solution of 7.859 g of barium nitrate in 5011f2 of water was added thereto with stirring. The obtained solution was heated to evaporate water to become a syrup, and then the water was further evaporated while stirring, and when it began to solidify, it was ignited at 300° C. for 1 hour to dry up. During ignition, nitrous gas was released. The dry matter was taken out and thoroughly ground in a mortar. 9 pieces of crushed material
By heating in an air atmosphere at 00° C. for 1 hour, nitrite gas was sufficiently released. After that, this was crushed again in a mortar and press-molded under the conditions of 300 kg/cm' x 2 minutes, and from 19 samples, 3 mm x 311 m x 30 m
A block of m shape was obtained. The molded product was sintered by heating at 950° C. for 1 hour in an air atmosphere. No bumping was observed during sintering. Furthermore, almost no nitrite gas was released during sintering, and no corrosion deterioration of the sintering furnace was observed. When the electrical properties of the fired crystal were measured, it stably showed the properties of 'I' c - about 85KS Jc - about j50A/cy'. As a result of elemental analysis of the fired crystal, the elemental composition is Y:B
a:Cu=1:2+3, and in X-ray diffraction, Y
No peaks other than +BatCu307-x were detected at all, and no foreign phases other than bores were observed in scanning electron microscopy, confirming that a very homogeneous superconducting ceramic was obtained.

Incidentally, FIG. 1 shows a chart obtained by the above-mentioned X-ray diffraction.

Comparative example CuO powder, BaCO5 powder, Y, 03 powder 237:394
After mixing at a weight ratio of 113 and thoroughly pulverizing in a mortar, 90
The mixture was heated at 0° C. for 1 hour and ground again in a mortar. The pulverized product was press-molded and sintered in the same manner as in Example 2.

The X-ray diffraction diagram of the obtained fired crystal is shown in Figure 2.4-0 In the X-ray diffraction diagram of the fired crystal of Example 2 shown in Figure 1, Y+Bat
Only the peak of Cu307-X is observed, but in Fig. 2, in addition to the peak of Y1BayCu30t-x, Cu
It contains peaks of O and BaCO3, and the sintered product contains C.
It is clear that uO and I3 a CO3 are considerably present4'. Moreover, the fired crystal obtained in the comparative example did not exhibit superconducting properties.

Example 3 Production of Y+Ba2Cu*07-x-based superconducting ceramics Y (N OJt ・6 tl 20, Ba (N O
3)! , Cu(NOl), 3HtO at 5.8 near, 9
- They were mixed at a weight ratio of 1096, heated and melted at 250°C, thoroughly mixed, and dried.

This was ignited at 300°C for 1 hour. During this time, nitrite scum was released. Next, thoroughly grind in a mortar and further heat to 900°C.
The nitrite gas was sufficiently released by heating in an atmospheric atmosphere for 1 hour.

Thereafter, this was crushed in a mortar, press-molded and sintered in the same manner as in Example 2 to obtain sintered crystals. No bumping was observed during sintering, and almost no nitrite gas was released during sintering. The obtained sintered crystals exhibited superconductivity. The composition ratio of the fired crystal was Y:Ba:Cu=I:2:3, and no diffraction peaks other than Y, Ba, and Cu307-x groups were detected in X-ray diffraction, and a homogeneous superconducting ceramic was obtained. was confirmed.

[Brief explanation of drawings]

Figure 1 shows the X-ray diffraction diagram of the sintered crystal obtained in Example 1, and FIG. 2 is an X-ray diffraction diagram of the baked crystal obtained in the comparative example.

Claims (16)

[Claims] 1. A method for producing superconducting ceramics, which comprises mixing compounds containing at least constituent elements of superconducting ceramics in a liquid state, heating to dryness, and then sintering. 2. 2. The method for producing superconducting ceramics according to claim 1, wherein the liquid state of the compound containing the constituent elements of superconducting ceramics is an acid solution, an alkaline solution, or an aqueous solution of the compound. 3. 3. The method for producing superconducting ceramics according to claim 2, wherein the solution is a nitric acid solution of the compound. 4. 4. The method for producing a superconducting lamix according to claim 3, wherein deoxidizing radical heating is performed between the heating drying process and the sintering process. 5. Deoxidizing root heating at a temperature of 300 to 900°C,
A method for producing superconducting ceramics according to claim 4, which is carried out in an air atmosphere. 6. Deoxidized root heating is performed at 300-500℃ and 850℃.
The method for producing superconducting ceramics according to claim 5, which is carried out in at least two stages of heating at ~900°C. 7. Deoxidizing root heating is continued from 300℃ to 850~90℃.
The method for producing superconducting ceramics according to claim 5, wherein the temperature is raised to 0°C and then maintained at a temperature of 850 to 900°C for a certain period of time. 8. The method for producing superconducting ceramics according to claim 6, wherein after the first heating step at 300-500°C, the mixture is pulverized and a second heating step at 850-900°C is performed. 9. 2. The method for producing superconducting ceramics according to claim 1, wherein the liquid state of the compound containing the constituent elements of superconducting ceramics is a molten product of the compound. 10. 10. The method for producing superconducting ceramics according to claim 9, wherein the compound is a salt containing constituent elements of superconducting ceramics. 11. 11. The method for producing superconducting ceramics according to claim 10, wherein the salt is a nitrate. 12. 12. The method for producing a superconducting laminate according to claim 10 or 11, wherein heating is performed between the heating drying step and the sintering step in order to remove acid radicals constituting the salt. 13. 13. The method for producing superconducting ceramics according to claim 12, wherein the deoxidizing radical heating is performed in an air atmosphere at a temperature of 300 to 900°C. 14. Deoxidized root heating is performed at 300-500℃ and 85℃.
14. The method for producing superconducting ceramics according to claim 13, which is carried out in at least two stages of heating at 0 to 900°C. 15. Deoxidizing root heating is continued from 300℃ to 850~9
14. The method for producing superconducting ceramics according to claim 13, which is carried out by raising the temperature to 00°C and then maintaining the temperature at 850 to 900°C for a certain period of time. 16. The method for producing superconducting ceramics according to claim 14, wherein after the first heating step at 300-500°C, the mixture is pulverized and a second heating step at 850-900°C is performed.