JPH0416552A - Transparent spinel sintered body and production thereof - Google Patents

Abstract

PURPOSE:To improve characteristics such as light transmissivity and linear transmissivity and to obtain a complex arbitrary shape by rendering a specified compsn. having an increased molar ratio of Al2O3 to MgO. CONSTITUTION:This transparent spinel sintered body is a spinel sintered body having a compsn. represented by a formula MgO.nAl2O3 (where 1<n<5) and a dense structure and is produced as follows: a powdery mixture giving the above-mentioned compsn. is preformed as starting material and heated to >=1,300 deg.C to obtain a primary sintered body having a spinel single phase or a spinel-alumina mixed phase and this sintered body is subjected to secondary sintering at >=1,400 deg.C under >=10kgf/cm<2> compressive pressure.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a translucent dense sintered body of spinel having the compositional formula M o O-n AL Os (where n is 1 < n × 5). and its manufacturing method.

[Conventional technology]

Translucent ceramics include AjltQs and BeO.

M (I O, Zn O, PLZT (composite oxide of lead, lan'in, zirconium, titanium), Yes
, Mu ALα and many other oxide sintered bodies are known.

Among these, the translucent spinel sintered body (tvlaALo) has excellent heat resistance, a relatively small coefficient of thermal expansion, excellent corrosion resistance against basic vapors such as sodium, and a wide wavelength range from ultraviolet to infrared. It has characteristics such as being transparent over a wide range, and is being developed for use as a heat-resistant and corrosion-resistant light-transmitting material.In particular, heat-resistant IM@ Although it has a high corrosion resistance, it is expected to compensate for its insufficient corrosion resistance against sodium vapor. Roughly translucent spinel sintered body has excellent mechanical properties such as hardness 1 strength as well as the above properties, so it can be used for bearings and other JS construction materials such as precision machines where single crystals have traditionally been used, and R light bodies. It is also being considered for use in fields such as functional base materials and decorative materials.

The method for manufacturing the translucent sintered body of spinel<MaALα is to use magnesia (M!70) fine powder and alumina (A
ll, O,) A mixture of fine powders is used as a starting material, and when sintering this, the conditions such as purity 9 particle size and particle size distribution of the raw material powder! A sintered body manufacturing method that involves knotting and long-term high-temperature treatment [R, T, Bratton, Ceramic
Bulletin, 48,759-762.10
69-1075 (1969) ], *t7less method [J, D, Daw & P, S, N1chol
son, Journal of 7he Amer
ican Ceramic 5ociety-V
arshneya, 58 225-230 (19
77)] and Ca0-ri as a sintering agent.
- Added sintering method (R, J, 8ratton, J
our own of the aseric
an Cerai+ic 3ociety,
57°238-286 (1974>) etc. have already been disclosed.

(Problems to be Solved by the Invention) The above-mentioned known method for manufacturing translucent spinel is to obtain equimolar spinel of magnesia and alumina (to MQ0/△L), but the solid phase diffusion during the sintering process is solid. Since it does not involve a dissolution reaction, the densification reaction conditions require high temperatures and long periods of time, and the abnormal growth of crystal grains often creates pores between the particles, which improves the mechanical strength, translucency, linear transmittance, etc. of the sintered body. It had the disadvantage that its characteristics were insufficient.

Moreover, regarding the shape of the sintered body, it was not possible to obtain any shape other than a simple shape, and the practical requirements could not be met.

[Means to solve the problem]

The present invention eliminates the drawbacks of the conventional spinel sintered body and its manufacturing method by increasing the molar ratio of ALα component to MgO as a spinel composition, and in particular, transmits a transparent material having extremely excellent light transmittance and linear transmittance. We succeeded in obtaining a photosensitive spinel sintered body.

That is, the translucent spinel sintered body of the present invention has MQO
-n A Log (where n is 1<1<5, particularly preferably n=1.2 to 4.0), and is characterized by having a dense spinel structure,
The manufacturing method includes preforming a starting raw material of a mixed powder conforming to the above-mentioned compositional formula, heating it at a temperature of 1300° C. or higher to form a primary sintered body of a spinel medium phase or a mixed phase of spinel and alumina, Furthermore, it is characterized by performing a step of secondary sintering this at a heating temperature of 1400° C. or higher and a compression pressure of 1 okgf/d or higher.

In the above manufacturing method, conditions such as the purity and grain size of the raw materials and their mixing state need to be sufficiently adjusted as in the conventional method, but the secondary sintering under pressure at the final stage of firing is necessary. In addition to grain boundary movement due to solid-phase diffusion during the reaction, an increase in the amount of reaction occurs due to the increase in the molar ratio of ALO to MoO, and dynamic reaction-diffusion occurs as the volume increases during the formation of a spinel solid solution. The existence of this process is considered to be one of the conditions for favorable coalescence.

In this way, for example, as the first step of the sintering process, a primary sintered body of a mixed phase of spinel solid solution and α-AL is created by sintering under normal pressure atmosphere, and as the second step, hot isostatic pressing at a higher temperature ( M
It is possible to produce a dense translucent sintered body consisting only of spinel solid solution phases of aO-nALo, composition, and composition.

A major advantage of the manufacturing method of the present invention is that when preforming the starting material mixed with raw material powder, pressure forming and casting can be used as the forming means.

Injection molding, extrusion molding, doctor blade molding.

A known forming method such as roll forming is used to form a preform into an arbitrary shape, and this is sintered under normal pressure to obtain a primary sintered body with relatively no open bores. The body does not require an airtight coating (it can be made into a highly translucent spinel sintered body in any shape by pressure sintering using HIP as it is).

[Effect]

The basic reaction process in the production method of the present invention is Ml)0+
nALOs −” MQ O・(n*) ALOa+mA1Os
(1) 1<n<5 0≦m・gu
Forming a primary sintered body consisting of a mixed phase of spinel and α-AL through the n-1 reaction, and pressing this primary sintered body under pressure, M! J O・<n W )AL(1+mALO
s → MQO-nALOs (2) Spinel solid solution (MgO・nAJl,o,) with solid-phase reaction-diffusion
A translucent sintered body is manufactured by carrying out a secondary sintering reaction that produces .

In the above reaction, the density to α-AL is > the density of the spinel solid solution, so (
When y>Q in equation 2), the reaction is accompanied by volumetric expansion, and effective pressure sintering promotes the production of a dense sintered body with excellent translucency.

In addition, in the above equations (1) and (2), when Vt=O, the composition of the primary sintered body becomes Mg0-nAjl, a spinel intermediate phase, but this primary sintered body is formed under the following pressure sintering conditions. If the internal pressure is transmitted evenly and effectively, a dense translucent sintered body can be obtained by high-pressure secondary sintering.

Spinel (MgA) was used instead of magnesia (Mob).
The desired sintered body can also be obtained by a similar sintering reaction using LQ as a raw material, and the basic reaction is M(l ALQ, + (n-1) ALOs → Mg
0-(n-p)ALO,+pALO,<3)Q<n<5
．． Q≦1) <Fl-1M(IO-(n-p)
ALO*+p ALOi -)M Q O-n A
A translucent sintered body is obtained by L Os (4) in the same manner as above.

In the case of p-0 in the above, a dense translucent sintered body can be obtained in the same manner as the above-mentioned p-o.

Note that the value of n in the above formula is preferably 1.2 to 4 in order to maintain stable translucency.

Reaction of equation (1) in which spinel is produced from magnesia and alumina, and alumina is dissolved in spinel (2) (3>
The reaction in equation (4) is a reaction accompanied by b volumetric expansion,
Sintering performed using these reaction formulas is a type of reaction sintering.

The preferable sintering temperature in formula (1) or formula (3) is a temperature at which fine, suitable unreacted α-A LOn remains without abnormal growth of sintered grains as the structure of the sintered body. The temperature is usually 1300°C or higher, which is determined by the value of (lightning or p becomes smaller), the effect of pressure sintering is enhanced, and only the surface layer may become translucent. The sintered fill of formula (2) or (4) is equivalent to or higher than the above-mentioned secondary sintering 1i[, and is usually suitably at 1400° C. or higher.

The reaction of formula (1) or formula (3) may be carried out in an atmospheric atmosphere at normal pressure or under pressure such as, for example, a hot press. Sintering in a hydrogen stream, which is carried out in the production of translucent alumina sintered bodies, is also effective in improving translucency because it can eliminate the entrapment of the gas phase into the sintered bodies. I think that the.

The raw materials can be mixed after mixing each oxide powder to the desired composition ratio, or precipitated by a method such as hydrolysis from a mixed solution of inorganic salts of each metal or organic compounds such as flukoxide to produce mixed powder. You may do so.

The reaction of formula (2) or (4) is the reaction of formula (1) or (3)
The sintering reaction may be carried out continuously after the sintering reaction, or the sintered body may be taken out of the oven, cooled, and then pressurized to 1 m again, thereby producing a translucent sintered body. For example, hot pressing can be carried out continuously, and HfPtR sintering can be performed by making a primary sintered body of a mixed phase of spinel and α-AL, then taking it out of the furnace and placing it in a HIPI place for secondary sintering. A translucent sintered body.

Pressure sintering is effective in suppressing grain growth, and for this purpose it requires at least 10klJf/m, preferably 100klJf/m.
It is appropriate to apply a compressive force of gf/a/.

If the primary sintered body of spinel and α-Aiα mixed phase is made into a sintered body with dense closed pores, it will be possible to
This is advantageous because it can be directly sintered by HIP.

When HIP sintering is performed, for example, in an argon gas atmosphere in a furnace using a carbon heating element, the transparent sintered body is colored dark brown due to the reducing atmosphere. In this case, 1000 again
It has been found that annealing for several hours or more at an appropriate temperature of 0.degree. C. or higher makes the material colorless and transparent.

〔Example〕

Purity 99.9 as spinel (tvloALO,) raw material
A powder with a purity of 9999% or more and a central grain size of 0.5μ was used as an alumina (Ajl, O,) raw material.

The weight of each raw material powder shown in Table 1 was determined and wet mixing was performed for 2 to 7 days using ethyl alcohol as a dispersion medium.

After drying the wet-mixed powder and molding by -axial pressure,
The mixture was subjected to cold isostatic pressing (hereinafter referred to as CIP) at 1500 klJ/cj and fired in the atmosphere at 1500°C for 12 hours to obtain 8 types of primary sintered bodies shown in Table 1.

The bulk density measurement results of this primary sintered body by the Fulchimedes method are shown as pre-HIP density in Table 1.

Note that the sintered bodies of NO, 1, 2, and 3 were all porous bodies that exhibited water absorption properties, and were unsuitable for HIP treatment as they were, so density measurements were not performed.

The air-sintered sintered bodies No. 4 to 8 were heated at a heating rate of 2 using a HIP device using argon gas as a pressure body.
00℃/hour, held at 1800℃ for 1 hour, cooling rate 200
Pressure sintering was carried out under a temperature program of 1800° C./hour at a pressure of 1500 k (lf, 'en/).

The HIP-sintered sintered bodies No. 4 to 8 were transparent and colored dark brown. The bulk density of the sintered body is shown in Table 1 as HIPI density.

When the crystal phase was identified using powder X-ray diffraction method,
The diffraction intensity of the raw material powder, which is a mixture of spinel and α-ALO (corundum), was approximately proportional to the mixing ratio.

On the other hand, regarding the primary sintered body, NO, 1, 2, and 3 were spinel single phase, indicating that alumina was completely dissolved in spinel after sintering at 1500° C. for 12 hours.

In Nos. 014 to 8, alumina could not be completely dissolved and remained partially as α-ALα, and the sintered body with a high alumina mixing ratio showed the tendency that the most amount of residual alumina remained.

) It was revealed from the Xs diffraction pattern that all the secondary sintered bodies formed by HIP had a single spinel phase.

The three-point bending strength of the above NOs, 4, 6, and 8 was measured at 221 and 242.239 MPa, respectively, which is equivalent to or higher than the conventional spinel sintered bodies with MgAfl and α compositions. Ta.

As a result of annealing the translucent secondary sintered body in the air at 1300°C or 1400°C for 7 hours, it was No. 4.
~8 All samples became cloudy. Powder x 1m diffraction result, α-
Since the presence of the ALO phase was observed, it is considered that the phase was separated and crystallized into α-AL.

1200℃, N when performing 7:-r between 12@.

In samples 4 to 1, a thin α-AI) and white phase powder was observed on the surface layer, but it was found that when the surface was polished, it became a colorless and transparent spinel single phase. In No. 8, there were also speckled white cloudy parts inside, and it was observed that α-ALα was precipitated as a solid solution, but at 1100°C.

Under the conditions of 12 hours and 1150°C for 24 hours, there was almost no solid solution precipitation, and the sintered body was colorless and transparent and had a homogeneous structure.

Under the annealing conditions of 1000°C and 12 hours, α-ALα
There was no precipitation, and the dark brown color approached colorless and transparent.

From the above experimental results, the optimal conditions for 7-neel are m-11
It is clear that the temperature is 00 to 1200°C for more than 12 hours.

The temperature at which solid solution precipitation occurs is higher when the value of n is smaller, and lower when the value of n is larger.

Example 2 A powder with a purity of 99.99% or more and an average particle diameter of 031 μm was used as a magnesia raw material, and a powder with a purity of 99.9% was used as an alumina raw material.
Powders with a purity of 999% or more and a median particle size of 0.5 μm (Alumina 1, used in Example 1) and a purity of 9999% or more and an average particle size of 0.15 μm (Alumina 2) were used.

The basis weight of each raw material powder shown in Table 2 was weighed, wet mixing was performed using ethyl alcohol as a dispersion medium in the same manner as in Example 1, dry bonding, -axis pressure molding, and carbonization at 1500 kQf/ai.
IP molding was performed to obtain a preform.

This was heated in the atmosphere at 1300℃ for 6 hours, and then at 1400℃ for 6 hours.
time.

1500℃, 6 hours 1.1550℃ 16 hours, 1600
It was sintered at ℃ for 6 hours to obtain a primary sintered body.

Next, each primary sintered body sintered in the atmosphere was heated in a HIP furnace filled with argon gas at a weighing speed of 00°C/'hours for 17 hours.
Hold at 50°C for 1 hour, cool down rate at 300°C for 77 hours, 115
The pressure when held at 0°C is 1500k (l f / ai,
and heating rate 200°C/hour, 1100°C 18i? li
Secondary sintering was performed under the conditions of J holding, temperature decreasing rate of 300°C/hour, and pressure of 1500k (If/sr) when holding 1100°C.

In the primary sintered bodies where n was 1.0 and 15, the atmospheric sintered bodies treated at both temperatures had open pores and were water-absorbing sintered bodies. Further, the secondary sintered body obtained by directly performing HIP treatment did not exhibit translucency.

An atmospheric sintered body with n of 2.0 and a temperature of 1400° C. or less showed water absorption, and although this was directly sintered by HIP, it did not become translucent. However, the primary sintered body at 1,500° C. or higher was a dense sintered body with only closed pores, and after the secondary sintering, it became a dense sintered body that exhibited translucency.

When the value of n was 25 and 30, a dense primary sintered body was obtained by primary sintering at 1400° C. or higher, and all exhibited excellent translucency after secondary sintering.

When n is 4.0 and 5.0, all primary sintered bodies of 1400°C or higher become dense sintered bodies close to the theoretical density, and secondary sintered bodies are translucent, but these sintered bodies are The linear transmittance is much lower and slightly translucent than when n is 2.0, 2.5, or 3.0.

When the crystal phase of the HIP sintered body that showed translucency was identified by powder xm diffraction droplets, n was 2, 0.2.5.
．． 3.0, it was found that the secondary sintered body at 1700°C and 1750°C was a single phase of spinel. On the other hand, when n is 4.0 or more, it is spinel and α-ALO.

The existence of both phases was revealed. Known spinel alumina phase parallel diagram (Della M, Roy, Ru5
tcv Ray, and E, F, 0sbori
, J.A.I., Ceras, SQC,,36,
149 (1953)), a high temperature is required for alumina to completely form a solid solution in spinel. The reason why the translucency decreases when n is 4.0 or more is
The coexistence of alumina was pointed out, and under higher temperature conditions,
It is thought that since the sintered body has a spinel phase, a sintered body exhibiting excellent translucency can be obtained.

An annealing experiment was conducted on the secondary sintered body in the same manner as in Example 1 in an atmospheric furnace. The unity is n is 2.0, 2.5
．． 30 is the same as Example 1, and when n is 4.0 or more, it becomes translucent even under the low temperature conditions of I 000° C. for 6 hours.

Air sintering at 1550℃ for 6 hours, argon atmosphere H1P
Sintering at 1750℃ and 1500℃! If, ・cd, 1 hour, for a flat material with n = 2.0 annealed in the atmosphere at 1150°C for 12 hours, the surface was mirror-polished to a thickness of 2.301 m, and then exposed to light. Transmittance to 19
I! from 0 to 7000ns! The results measured in the circle are shown in 1a! It was shown to.

As shown in the graph of Figure 1, the light transmittance of the product of the present invention is
50% or more in the wavelength range of 300 to 5600 n-,
It is almost equivalent to the conventional MgALα type translucent spinel sintered body, but the transmittance of 80% or more is 2200-53 for the conventional product.
00n-, whereas in the product of the present invention it is 900-5
It has a wide wavelength range of 100ns, and while the conventional product had a peak at 4600n* and had a transmittance of 85%, the product of the present invention has a transmittance of 900 to 4SOOn.
It showed a flat transmittance of 90-92% in the annular range. Furthermore, the in-line light transmittance of the product of the present invention was far superior to that of the conventional product.

Such a remarkable improvement in light transmittance is something that could never be achieved using conventional techniques, and can be called truly surprising.

We compared and examined two types of alumina raw materials, but within the scope of this example, there was almost no difference in whether or not they formed into a primary sintered body with dense closed pores under atmospheric conditions. There was also no difference in whether the secondary sintered body produced by HIP had translucency.

Example 3 This example was conducted using a combination of magnesia and alumina, using the powder used in Example 2 as the magnesia raw material and the same powder as Alumina 2 of Example 2 as the alumina raw material.

In an argon gas atmosphere, the HIP pressure was set to 1500k (lf
/d1 When the holding time was kept constant at 1 hour and the HIPg degree was changed, it was investigated how the translucency of the secondary sintered body changes. The results are shown in Table 3.

In this example, the HIP increasing rate was the same as in Example 1.2, but the temperature decreasing rate was 400° C. for 77 hours.

Whether or not the secondary sintered body produced by HIP becomes translucent depends on the primary sintering conditions under atmospheric pressure in the previous step.

Therefore, Table 3 shows the atmospheric sintering conditions for the primary sintered body and whether the secondary sintered body by HIP exhibited translucency.
It is divided into three stages: opaque, semi-transparent, and transparent. "Non-transparent" means that no light passes through, "semi-transparent" means that it is opaque even if it is translucent, and [transparent] means that light passes through with a high one-line transmittance so that the perspective image is clear without distortion. shows.

According to this, in the range of this example, a translucent sintered body is obtained when n is 1.80 or more, and the primary sintered body is dense, has closed pores, and has H
If IP processing IfT is possible, HIP temperature 1100
It can be seen that all the materials become transparent primary sintered bodies at temperatures above ℃.

Similarly, when n was 2.00, all transparent light transmittance was exhibited at HIP 1 degree of 1650° C. or higher.

The presence of both spinel and α-ALα phases was identified in the semi-transparent sintered body described in Table 3 by powder XJ11 diffraction. However, even if the pores are removed, α-AL has optical anisotropy and is completely transparent because refraction and scattering occur at the crystal grain interface where the refractive index increases. It is thought that this will not happen.

Example 4 How does the translucency of the secondary sintered body change when the HIP temperature is kept constant at 1750°C and the holding time is 1 hour in an argon gas atmosphere and the l-11P pressure is changed? The results of the investigation are shown in Table 4. The temperature increase/decrease rate of HIP is the same as in Example 3.

As in Example 3, a mixed powder of magnesia-alumina was used as the starting material, and the same raw material oxides as in Example 13 were also used.

According to this result, 2
Translucent and transparent cases were observed even at pressures of 00 kgf, 'en/.

The results in Table 4 show that the higher the gas pressure in HIP sintering, the shorter the reaction time to form a single spinel phase.

〔effect〕

As explained above, the translucent spinel sintered body of the present invention has a dense composition of M2O・nALα, and its light transmittance and linear transmittance are significantly higher than that of the conventional MoALO. It has excellent properties, and its manufacturing method allows for easy manufacturing with any product shape selected, making it a great contribution to the field of heat-resistant and translucent materials.

[Brief explanation of the drawing]

FIG. 1 is a graph of the measurement results of the light transmission band from 190 to 7000n+++ of the translucent spinel sintered body shown in Example 2 of the present invention.

Claims (1)

[Claims] 1). Compositional formula MgO・nAl_2O_3 (where n is 1<
A translucent spinel sintered body having a dense structure with n<5. 2). A mixture of fine magnesia powder and fine alumina powder is used as a starting material, and the preformed body is heated to a temperature of 1,300°C or higher to form a primary sintered body of a spinel single phase or a mixed phase of spinel and α-alumina, and then the primary sintering process is performed. The body is 140
The sintering reaction is carried out at a heating temperature of 0°C or higher and a compressive force of 10 kgf/cm^2 or higher, resulting in the composition formula MgO・nAl_
2. A method for producing a translucent spinel sintered body, characterized in that the secondary sintered body has a dense structure of O_3 (where n is 1<n<5). 3). Spinel (MgAl_2O_4) as starting material
3. The method for producing a translucent spinel sintered body according to claim 2, wherein a mixture of fine powder and fine alumina powder is used. 4). 4. The method for producing a translucent spinel sintered body according to claim 2 or 3, wherein the secondary sintered body is annealed at a temperature of 1000° C. for 12 hours or more, and then subjected to surface polishing if desired.