JP6622141B2 - Translucent ceramic sintered body and manufacturing method thereof - Google Patents

Description

  The present invention relates to a translucent ceramic sintered body that can be used for, for example, an optical dome and a lens, and has transparency such as infrared light, and a method for manufacturing the same.

  Currently, translucent ceramic sintered bodies having translucency in various wavelength ranges have been developed. Among them, magnesium fluoride sintered bodies are, for example, materials having excellent transmissivity such as infrared light, It is used for various purposes.

In particular, the magnesium fluoride polycrystals have a wide range of industrial applications such as optical domes and lenses because they can achieve both optical properties and mechanical properties.
Further, many studies have been made on this polycrystalline magnesium fluoride sintered body and its manufacturing method (for example, see Patent Documents 1 and 2).

Japanese Patent No. 1394474 Japanese Patent No. 3618048

  However, in the technique described in Patent Document 1, since the densification of the magnesium fluoride sintered body is insufficient, the overall translucency is low, and in particular, the translucency in the infrared region of 3 to 6 μm is low. There was a problem. This is presumably because more elements could not be added due to segregation due to insufficient dispersion of the added elements.

Further, in the technique described in Patent Document 2, since the additive element is 0.01% by weight or less, a general hot press of about 0.2 t / cm ² (20 MPa) despite low sinterability. Baking under conditions. Therefore, firing at a high temperature is necessary for densification, and the particle size is coarsened to 10 μm or more. As a result, the magnesium fluoride sintered body has insufficient translucency.

  This invention is made | formed in view of this background, The objective provides the translucent ceramic sintered compact which has high translucency, and its manufacturing method.

  (1) A first aspect of the present invention is a translucent ceramic sintered body comprising a magnesium fluoride sintered body containing magnesium fluoride as a main component and containing a predetermined additive element, wherein the additive element is an alkali metal element And at least one element selected from alkaline earth metal elements excluding magnesium in a range of more than 0.1% by weight and not more than 1% by weight, and a relative density of 99.5% or more of the theoretical density Has a density.

  In the first aspect, at least one or more additive elements of all the elements contained in the alkali metal element and the alkaline earth metal element (excluding magnesium) are more than 0.1 wt% and less than 1 wt%. Since it is contained in a range and the relative density is densified to 99.5% or more of the theoretical density, it has excellent light (particularly infrared light) transmission (translucency).

  That is, in this 1st aspect, since the above-mentioned additional element is included, the sinterability at the time of baking is high. Therefore, since sintering at a low temperature is possible, a fine grain structure is formed and the relative density is high. As a result, it has high translucency. In addition, since it has a sufficiently fine-grained microstructure, it has the advantage of high mechanical strength.

Thus, in this 1st aspect, since it has high translucency, there exists a remarkable effect that the performance as optical materials, such as a dome and a lens, is high.
(2) In the second aspect of the present invention, the crystals contained in the translucent ceramic sintered body have an average crystal grain size in the range of 0.15 μm to 0.85 μm.

  In the second aspect, the average particle size (that is, the average crystal particle size) of the crystals (that is, magnesium fluoride crystals) contained in the translucent ceramic sintered body is 0.15 μm to 0.85 μm. The transmittance of outside light (infrared transmittance) is further improved. In addition, this translucent ceramic sintered body has an advantage of higher mechanical strength such as bending strength.

  (3) A third aspect of the present invention is a method for producing the light-transmitting ceramic sintered body according to the first aspect or the second aspect, wherein the material of the magnesium fluoride sintered body is fired by hot pressing. In this case, the pressing pressure is in the range of 30 MPa to 100 MPa.

  In the third aspect, the translucent ceramic sintered body having the above-described characteristics can be easily manufactured by hot pressing with a pressing pressure of 30 MPa or more and 100 MPa or less. Moreover, since the pressure at the time of hot pressing is 100 MPa or less, a large transparent ceramic sintered body can be easily obtained without using a device that applies a large pressure.

  That is, there is an advantage that a translucent ceramic sintered body having high characteristics can be easily manufactured under general hot press conditions.

It is a perspective view which shows a translucent ceramic sintered compact.

[1. Embodiment]
[1-1. Constitution]
First, the translucent ceramic sintered body of the present embodiment will be described.

The translucent ceramic sintered body of the present embodiment is composed of a magnesium fluoride sintered body (MgF ₂ sintered body, which is a polycrystalline sintered body mainly composed of magnesium fluoride. Is the body.

  This translucent ceramic sintered body contains more than 0.1% by weight of at least one additive element among all elements contained in alkali metal elements and alkaline earth metal elements (excluding magmagnesium). It is contained in the range of 1% by weight or less. The translucent ceramic sintered body is densified to 99.5% or more of the theoretical density (that is, the relative density is 99.5% or more).

The theoretical density is the density (theoretical value) when the raw material is completely densified, and the relative density indicates the ratio (%) of the actual density of the sintered body to the theoretical density. .
Here, “magnesium fluoride as a main component” means that magnesium fluoride is contained in a range exceeding 50% by weight (for example, 99.0% by weight or more). A sintered body made of magnesium fluoride is preferable.

As the alkali metal element, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr) can be employed.
As alkaline earth metal elements excluding magnesium, beryllium (Be), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra) can be employed.

The translucent ceramic sintered body having the above-described configuration has excellent translucency. Therefore, the performance of optical materials such as a dome and a lens using this translucent ceramic sintered body is improved.
When the content of the additive element is 0.1% by weight or less, the above-described effects (that is, a suitable fine structure and high relative density) are difficult to obtain, and the translucency is lowered as a whole. On the other hand, when the content of the additive element exceeds 1% by weight, the translucency is lowered as a whole due to light absorption by the excessive additive element and light dispersion at the grain boundary.

  In particular, in the present embodiment, the crystal of the translucent ceramic sintered body (that is, the crystal of the magnesium fluoride sintered body) has an average crystal grain size in the range of 0.15 μm to 0.85 μm. ing.

Here, when the average crystal grain size is larger than 0.85 μm, the light transmittance in a low wavelength region near 3 μm is lowered. Further, since the crystal is coarsened, the strength of the sintered body is lowered.
On the other hand, when the average crystal grain size is smaller than 0.15 μm, it is difficult to obtain a commercially available raw material powder. Further, when pulverization is performed for atomization, impurities may be mixed, and the translucency may be lowered.

The average crystal grain size is an average grain size of each crystal (particle) in the sintered body, and in the present invention, it means a value obtained by a well-known intercept method described later.
[1-2. Production method]
Next, the manufacturing method of the translucent ceramics sintered body mentioned above is demonstrated.

  In the method for producing a light-transmitting ceramic sintered body according to the present embodiment, the material of the light-transmitting ceramic sintered body (that is, magnesium fluoride sintered body) is manufactured by hot pressing. The range of 30 MPa to 100 MPa is adopted.

  By hot pressing under this pressure condition, a translucent ceramic sintered body having the above-described characteristics can be easily produced. Moreover, since it is not necessary to apply an excessive pressure, a large (for example, about 150 mm square) translucent ceramic sintered body can be easily obtained. That is, there is an advantage that a translucent ceramic sintered body having excellent characteristics (that is, translucency and strength) can be manufactured under general hot press conditions.

  Moreover, when baking this translucent ceramic sintered compact with a hot press, the range of 580 to 800 degreeC (preferably the range of 580 to 720 degreeC or less) is employable as baking temperature.

  By hot pressing under this temperature condition, the translucent ceramic sintered body having the above-described excellent characteristics can be easily produced. That is, since firing at a high temperature is unnecessary, it is possible to suppress the crystal from becoming coarse. Therefore, a translucent ceramic sintered body having excellent translucency and strength can be easily obtained.

  As is well known, hot press is a type of pressure sintering method. For example, a raw material powder is filled in a mold made of carbon or the like and heated while being uniaxially pressed to produce a sintered body. Is the method.

Next, examples of the present invention will be described.
(Example 1)
In Example 1, samples No. 1 to No. 17 shown in Table 1 below were manufactured as samples of a translucent ceramic sintered body (that is, a magnesium fluoride sintered body) under the conditions shown below. Etc. were investigated. Sample Nos. 3 to 13 are examples of the present invention, and samples No. 1, 2, and 14 to 17 are comparative examples.

  First, as shown in Table 1 below, magnesium fluoride powder containing a predetermined amount (that is, M amount) of an additive element that is an alkali metal and / or an alkaline earth metal (excluding magnesium) was prepared as a starting material.

  As is well known, this magnesium fluoride powder was synthesized, for example, using hydrofluoric acid and a magnesium chloride solution. Since the additive element is added during this synthesis process, it is uniformly distributed in the magnesium fluoride. The amount of M was adjusted by adding in the process of synthesizing magnesium fluoride.

In addition, as an average particle diameter of this magnesium fluoride powder, the range of 0.15 micrometer-0.8 micrometer is employable, for example.
Next, the magnesium fluoride powder was filled in a carbon mold for hot pressing and fired in vacuum at 600 ° C. under a pressure of 60 MPa for 2 hours to obtain a magnesium fluoride sintered body. The additive element functions as a sintering aid during the firing and improves the sinterability.

  Then, the amount of M, the relative density, the crystal grain size (ie, average crystal grain size), and the transmittance (ie, infrared light) of the translucent ceramic sintered body (ie, magnesium fluoride sintered body) obtained by the above-described method. Transmittance). The results are shown in Table 2 below.

The M amount, relative density, crystal grain size, and transmittance were determined by the following methods, respectively.
<M amount>
The magnesium fluoride sintered body was measured by fluorescent X-ray analysis to determine the amount of M.

<Relative density>
The density of the magnesium fluoride sintered body was measured by the Archimedes method, and the relative density was determined from the ratio to the theoretical density.

<Crystal grain size>
The magnesium fluoride sintered body is broken, and an enlarged image is obtained by observing the fractured surface with a scanning electron microscope (SEM observation). From this (enlarged) SEM image, an average crystal grain size ( That is, the average crystal grain size) was determined.

<Transmissivity>
By polishing the magnesium fluoride sintered body so as to have a thickness of 3 mm and performing a well-known spectroscopic measurement on the obtained magnesium fluoride sintered body 1 for a sample (see FIG. 1). The transmittance was measured. Specifically, in the polishing, both surfaces of the sample sintered body 1 were polished using a diamond polishing disk having a particle size of 3 μm or less. In addition, the transmittance was evaluated by measuring the transmittance of infrared light (infrared rays) irradiated to the polishing surface 1a, that is, the transmittance of infrared light having wavelengths of 3 μm and 5.5 μm.

<Evaluation>
Table 2 shows the evaluation in Example 1. The evaluation in Table 2 is based on the case where the transmittance of infrared light with a wavelength of 3 μm is 80% or more (condition 1) and the transmittance of infrared light with a wavelength of 5.5 μm is 90% or more (condition 2). “○”. In addition, the case where either one of the condition 1 or the condition 2 is satisfied is defined as “Δ”. Furthermore, the case where both conditions 1 and 2 were not satisfied was set as “x”. Therefore, the order in which the evaluation is good is ◯>Δ> ×.

  As is clear from Table 2, the magnesium fluoride sintered body of Sample Nos. 3 to 13 having an M amount of more than 0.1 wt% (wt%) and 1 wt% or less has a relative density of 99.5%. As described above, the structure was sufficiently dense and the crystal grain size was a fine structure of 0.62 μm or less.

  Thereby, the transmittance | permeability of the magnesium fluoride sintered compact of sample No. 3-13 was 82% or more in the infrared light of wavelength 3 micrometers, and was 93% or more in the infrared light of wavelength 5.5 micrometers. Therefore, the evaluation was preferable as “◯”.

  On the other hand, the magnesium fluoride sintered body of sample Nos. 1 and 2 having an M amount of 0.1% by weight or less has a relative density of 98.5%, is not densified to a necessary level, and is transmitted. The rate was low for both wavelengths (ie overall low). As a result, the evaluation is not preferable as “×”.

In addition, the magnesium fluoride sintered bodies of Sample Nos. 14 to 17 in which the M amount exceeds 1% by weight are obtained by light absorption by an additive element which is a different component and light dispersion at an interface between the magnesium fluoride and the different component. The transmittance was low as a whole. As a result, the evaluation is not preferable as “×”.
(Example 2)
In Example 2, as shown in Table 1, a translucent ceramic sintered body (that is, a hook) was used in the same manner as in Example 1 using magnesium fluoride powder having an M amount of 0.4% by weight. Samples No. 18 to 25 were produced as samples of the magnesium chloride sintered body). However, the firing temperature was changed from 580 ° C. to 800 ° C., and the firing pressure was changed from 30 MPa to 100 MPa.

And the characteristic etc. were investigated like the said Example 1. FIG. The results are shown in Table 2.
As apparent from Table 2, Samples Nos. 18 to 23 fired at 720 ° C. or lower have a relative density of 100%, are sufficiently densified, and have a crystal grain size of 0.85 μm or less and fine crystals. Became an organization.

  When the transmittances of Samples Nos. 18 to 23 were examined, the transmittance was high overall (both wavelengths) as in Samples Nos. 3 to 13 of Example 1. Therefore, the evaluation was suitable as “◯”.

On the other hand, Sample Nos. 24 and 25 fired at 750 ° C. or higher were densified, but the crystal grain size was coarsened to 1 μm or more.
Therefore, the transmittance of infrared light with a wavelength of 5.5 μm was high, but the transmittance of infrared light with a low wavelength of 3 μm was low. Therefore, the evaluation is “Δ”, which is not necessarily sufficient as compared with “◯”.

[2. Other Embodiments]
In addition, this invention is not limited to the said embodiment and Example at all, and it cannot be overemphasized that it can implement with a various aspect in the range which does not deviate from this invention.

  (1) For example, as the additive element, one or more elements selected from elements other than those described in Table 1, that is, an alkali metal element and an alkaline earth metal element excluding magnesium can be used.

  (2) It should be noted that the constituent elements of the above-described embodiments can be appropriately combined.

  1 ... Magnesium fluoride sintered body (translucent ceramic sintered body)

Claims (2)

In the translucent ceramic sintered body comprising a magnesium fluoride sintered body containing magnesium fluoride as a main component and containing a predetermined additive element,
Containing at least one element selected from an alkali metal element and an alkaline earth metal element excluding magnesium as the additive element in a range of more than 0.1% by weight and less than 1% by weight;
And, have a more than 99.5% of the relative density of the theoretical density,
Furthermore, the crystal | crystallization contained in the said translucent ceramics sintered compact has the average crystal grain diameter of the range of 0.15 micrometer-0.85 micrometer, The translucent ceramics sintered compact characterized by the above-mentioned. A method for producing a translucent ceramic sintered body according to claim 1 ,
When baking the material of the said translucent ceramic sintered compact with a hot press, it is set as the calcination temperature of the range of 580 degreeC- 800 degreeC, and it is set as the press pressure of the range of 30 MPa-100 MPa. Manufacturing method of ceramic sintered body.

Images