JPH0561228B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to chromium nitride-zirconia-based dense sintered ceramics and a method for producing the same.

[Prior Art and Problems] Hitherto, chromium nitride-zirconia-based sintered bodies have hardly been developed. It is known that a sintered body of chromium nitride alone can be obtained by sintering a Cr metal powder compact in a nitrogen gas atmosphere. However, in this case, since reaction sintering is used, dense sintering cannot be achieved, and a porosity of 30 to 40% remains. Therefore, the reality is that we have not even reached the point of considering the development of its uses.

On the other hand, sintered bodies of zirconia alone have recently been significantly developed, and it is well known that partially stabilized zirconia provides excellent ceramics.

However, zirconia has problems such as relatively low thermal conductivity and lack of thermal shock resistance.

[Means for Solving the Problems] In view of the above problems, the present inventor was researching chromium nitride sintered bodies, and discovered that he mixed zirconia powder with Cr powder and heated the mixed powder compact with nitrogen. It was discovered that when fired in a gas atmosphere, reaction sintering occurred and a dense sintered body consisting of chromium nitride and zirconia was formed, eliminating the drawbacks of each, and the present invention was completed.

That is, in the present invention, chromium nitride and zirconia are sintered and mixed, the total porosity is 10% or less,
Another object of the present invention is to provide chromium nitride-zirconia ceramics having a bulk density of 5.5 g/cm ³ or more.

Furthermore, the present invention is made of chromium metal powder and zirconia powder, and the mixing ratio of zirconia powder is 20.
The present invention provides a method for producing chromium nitride-zirconia ceramics, which comprises firing a compacted powder mixture containing up to 80% by weight in a nitrogen gas atmosphere to nitride chromium metal powder.

[Function] In the ceramics according to the present invention, chromium nitride mainly has a composition of Cr ₂ N,
This compound is a non-stoichiometric compound, and Cr ₂ N _1-x (0≦x<0.24) with a smaller nitrogen ratio than this also exists,
The composition of chromium nitride changes depending on the firing temperature.
Therefore, the chromium nitride used in the present invention is Cr ₂ N _1-x
(0≦x<0.24).

On the other hand, zirconia naturally includes pure zirconia, but also zirconia stabilized with Y ₂ O ₃ , CaO, MgO, etc., or partially stabilized zirconia.

As mentioned above, the ceramic according to the present invention is a sintered body of chromium nitride and zirconia, but since both are uniformly mixed and sintered, it has an even better quality that is different from a single sintered body of each. Indicates physical properties. In other words, compared to a base made of only chromium nitride,
By mixing zirconia, densification becomes easier, and at the same time, by mixing ZrO ₂ , which has a high melting point, the fire resistance can be further increased. Furthermore, as seen in the zirconia-dispersed alumina base, for example, the ceramics of the present invention constitute a dense sintered body that can also be considered as a zirconia-dispersed chromium nitride base, making it excellent in toughness and strength. It can be.

On the other hand, compared to the base material made of zirconium alone,
The presence of chromium nitride, which has higher thermal conductivity than zirconia, also improves thermal shock resistance, making it suitable for use as a high-temperature material in cases where temperature fluctuations are large.

Figures 1 and 2 are attached to clarify the characteristics of the chromium-zirconia ceramics of the present invention.

1 and 2 are graphs showing the physical properties of chromium nitride-zirconia ceramics in the embodiments of the present invention described later, and FIG. 1 shows the properties of each sample obtained in Example 1 described later. Fig. 1a is a graph showing the relationship between the raw material mixing ratio and relative X-ray diffraction intensity, and Fig. 1b is a graph showing the relationship between the raw material mixing ratio and the total porosity. FIG. 1b is a graph diagram showing the relationship between
is a graph diagram showing the relationship between raw material mixing ratio and density. Furthermore, Figure 2 is a graph showing the characteristics of each sample obtained in Example 2 at each firing temperature, and Figure 2a shows the relationship between firing temperature and relative X-ray diffraction intensity. FIG. 2b is a graph showing the relationship between firing temperature and total porosity, and FIG. 2c is a graph showing the relationship between firing temperature and density. Note that the relative X-ray intensities in FIGS. 1a and 2a are expressed using the strongest line among the diffraction lines of the structure obtained by X-ray diffraction of the sample. 1st
The results shown in Figures a and 2a indicate that the chromium nitride-zirconia ceramic of the present invention is a sintered body composed of chromium nitride (Cr ₂ N _1-x ) and zirconia. The results shown in Figures b and 2b show that the sintered body can be a dense sintered body with a total porosity of 5% or less. This becomes clear from the results of the relationship between the degree of vacuum and the bulk density shown in FIGS. 1c and 2c.

The chromium nitride-zirconium ceramics of the present invention can be produced industrially advantageously by firing a mixed powder compact made of chromium metal powder and zirconia powder in a nitrogen gas atmosphere to nitride the chromium metal powder. can.

In the method for producing chromium nitride-zirconia ceramics of the present invention, a sintered body with characteristics can be obtained depending on the mixing ratio of zirconia in the mixed powder compact made of chromium metal powder and zirconia powder. Therefore, although there is no need to specifically limit the amount, in many cases, a range of 30 to 80% by weight is suitable.

The reason for this is that the porosity of the sintered body decreases as the zirconia mixing ratio increases, and in a sintered body with a zirconia mixing ratio of 30 to 80% by weight, densification sintering with a porosity of about 5% is performed. This is because it can be done.
Therefore, at such a composition ratio, a dense sintered body substantially free of pores can be obtained by adjusting the particle size structure of the starting materials.

Of course, pure metal chromium and zirconia can be used as raw materials, but impurities that are inevitably mixed in during their preparation pose no problem.

As for zirconia, as mentioned above,
Zirconia stabilized with Y ₂ O ₃ , CaO or MgO or the like may also be suitable raw materials.

Moreover, there is no reason to particularly limit the properties and molding method of the molded product of the raw material mixture, and it can be prepared using many known desired means.

Therefore, the above-mentioned molded body is characterized by being fired in a nitrogen gas atmosphere, but the nitriding reaction occurs only in metallic chromium and not in zirconia.

Therefore, when firing the molded body, it is necessary to perform the firing at a temperature at least at which the metal chromium in the mixture is nitrided.

The nitriding reaction of metallic chromium powder itself in a nitrogen gas atmosphere occurs even at temperatures below 1000°C, but in most cases a temperature of 1200°C or higher is appropriate in order to cause sufficient reaction and sintering with zirconia. can be,
A temperature range of 1300-1600°C is preferred.

The metal chromium nitriding reaction is of course dependent on temperature, but it generally proceeds quickly, and for the same reason as above, the firing time at the maximum temperature is 0.5 to 3 hours.
The preferred time is 1 to 2 hours.

The ceramics thus obtained are made of chromium nitride.
It becomes a zirconia-based dense sintered body, and because of its characteristic physical properties, it can be advantageously used industrially. For example, the melting point of chromium nitride is over 1800℃,
Since the melting point of zirconia is as high as 2700°C, and the two do not react with each other, it is highly conceivable that the ceramics of the present invention can be used as high-temperature structural materials according to their respective characteristics.

[Example] The present invention will be further explained below with reference to Examples.

Example 1 Cr metal powder [particle size is 74 μm (200 mesh) or less] and ZrO ₂ powder were mixed in various proportions, and this mixed powder was molded into a square plate shape of 20 × 20 × (10 to 15) mm. It was molded into. This was placed in an alumina crucible and placed in an electric furnace. Next, while flowing nitrogen gas at a flow rate of 1/min, the temperature was raised to 1500°C at a rate of 600°C/hour, and after maintaining the temperature at 1500°C for 1 hour,
It was cooled at a rate of °C/hour. For each of the sintered bodies thus obtained, the true density and bulk density were measured, and the total porosity was also determined. The composition was also examined by X-ray analysis. These results are shown in FIG. As is clear from FIG. 1a, the constituents were chromium nitride and zirconia. Figure 1c
As is clear from the above, the true density changes linearly in proportion to the mixing ratio. On the other hand, the bulk density of the mixed sintered body was higher than that of either single substance. In addition, the total porosity of chromium nitride-zirconia ceramics is less than 10% in sintered bodies obtained from mixtures containing 20 to 80% Cr, and especially when Cr is
In the case of 20 to 60% by weight, a dense sintered body with a total porosity of about 5% was obtained.

Almost the same results were obtained when zirconia partially stabilized with Y ₂ O ₃ and CaO and stabilized zirconia were used as the zirconia.

In FIG. 1a, the relative X-ray diffraction intensity is expressed by the intensity of the highest line among the X-ray diffraction lines of the structure obtained by X-ray diffraction of the sample.

In addition, 78 wt% Cr + 22 wt% obtained in this example
When the microstructures of the fractured surfaces of the sintered body A made of ZrO ₂ and the sintered body B made of 57% Cr + 43% ZrO ₂ were observed with a scanning electron microscope, electrons were observed as shown in attached Figure 3 A and B. A micrograph was obtained. In addition, 19mm in electron micrographs Figure 3 A and B is 20μ.
Corresponds to m.

Example 2 A mixed powder compact containing 47% by weight of Cr and 53% by weight of ZrO ₂ was molded in the same manner as in Example 1, heated in a nitrogen gas atmosphere at various temperatures of 1000 to 1500°C for 1 hour,
The same items as in Example 1 were measured for each sintered body. At calcination temperatures below 1100℃, CrN formation is observed, but at calcination temperatures above 1200℃, CrN formation is observed.
CrN disappeared and became Cr ₂ N _1-x and ZrO ₂ . At the same time, densification progresses, and the porosity becomes approximately 20% at 1200℃, and as the temperature further increases, the porosity decreases, and by firing at 1500℃, a dense chromium nitride-zirconia based sintered body with a density of approximately 5% is obtained. It became. The results obtained are shown in FIG.

[Effects of the Invention] The chromium nitride-zirconia ceramic sintered body according to the present invention is a dense sintered body with a total porosity of 10% or less, and has better thermal conductivity than zirconia.

Therefore, since the thermal shock resistance of zirconia ceramics can be improved, the ceramics according to the present invention can be advantageously substituted in fields where zirconia ceramics are used.

Further, according to the manufacturing method according to the present invention, the above-mentioned ceramics can be industrially advantageously manufactured and provided.

[Brief explanation of drawings]

Figure 1 shows each sample obtained in Example 1.
Fig. 1a is a graph showing the relationship between the raw material mixing ratio and relative X-ray diffraction intensity, and Fig. 1b is a graph showing the relationship between the raw material mixing ratio and the total porosity. FIG. 1c is a graph showing the relationship between raw material mixing ratio and density, and FIG. 2 is a graph showing the characteristics of each sample obtained in Example 2. FIG. 2A is a graph showing the relationship between firing temperature and relative X-ray diffraction intensity, and FIG. 2B is a graph showing the relationship between firing temperature and total porosity. FIG. 2c is a graph showing the relationship between firing temperature and density, and FIGS. 3A and 3B are scanning type graphs showing the microstructure of the fractured surface of the sintered body obtained in Example 1. This is an electron micrograph.

Claims (1)

[Claims] 1. Chromium nitride and zirconia are sintered and mixed, the total porosity is 10% or less, and the bulk density is
Chromium nitride-zirconia ceramics characterized by having a weight of 5.5 g/cm ³ or more. 2. Chromium nitride, which is characterized by nitriding the chromium metal powder by firing a mixed powder compact consisting of chromium metal powder and zirconia powder in which the zirconia powder has a mixing ratio of 20 to 80% by weight in a nitrogen gas atmosphere. - A method for producing zirconia ceramics. 3. The method for producing chromium nitride-zirconia ceramics according to claim 2, wherein the firing in a nitrogen gas atmosphere is performed at a temperature of 1200°C or higher.