JP2011020917A - METHOD FOR PRODUCING Ca-Gd-F-BASED TRANSLUCENT CERAMIC, Ca-Gd-F-BASED TRANSLUCENT CERAMIC, OPTICAL MEMBER, OPTICAL SYSTEM AND COMPOSITION FOR MOLDING CERAMIC - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Ca-Gd-F-based material having high Abbe number comparable with that of fluorite and having a refractive index higher than that of fluorite as a translucent ceramic. <P>SOLUTION: The translucent ceramic is produced by mixing CaF<SB>2</SB>fine particle and GdF<SB>3</SB>fine particle produced separately from the CaF<SB>2</SB>fine particle to prepare a fine particulate mixture and sintering the fine particulate mixture to make the sintered mixture transparent. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a method for producing a Ca—Gd—F based translucent ceramic made of a fluoride of calcium and gadolinium, a Ca—Gd—F based translucent ceramic, an optical member, an optical system, and a ceramic forming composition. .

Fluorite (CaF ₂ ) has a high Abbe number (νd) of 95, is excellent in refractive index dispersion characteristics, and has a small refractive index dispersion with respect to the wavelength of light. Fluorite has a high light transmittance from the ultraviolet region to the infrared region. Therefore, fluorite is known as an excellent optical material.
When a convex lens made of such an optical material is combined with a concave lens made of another material, chromatic aberration can be corrected well. Therefore, many fluorite is used in various optical systems such as a microscope objective lens (for example, Patent Document 1).

Conventionally, a fluorite single crystal has been used in an optical system. However, a method for producing fluorite ceramics as a calcium fluoride sintered body is known from Patent Document 2, for example. Patent Document 2 describes the following method for producing fluorite ceramics. A calcium compound and a fluorine compound are reacted in a solution to obtain a suspension. Next, this suspension is put in a sealed container and heated to 100 ° C. or higher and 300 ° C. or lower to produce calcium fluoride fine particles. The calcium fluoride fine particles are heated to 700 ° C. or higher and 1300 ° C. or lower and sintered to form a sintered body. Under pressure of the sintered body in an inert atmosphere 500 Kg / cm ² or more 10000 kg / cm ² or less, by heating to 800 ° C. or higher 1300 ° C. or less, the sintered body is transparent, fluorite ceramic formed Is done.

  Since the ceramics produced in this way are dense sintered bodies in which the generation of voids and the like is suppressed, excellent optical characteristics can be obtained.

JP 2004-191933 A JP 2006-206359 A

  However, in the single crystal fluorite conventionally used in optical systems, the thermal expansion strain at the time of temperature rise varies depending on the crystal orientation and is generated anisotropically. For this reason, the imaging performance of the lens is likely to deteriorate due to thermal expansion distortion caused by temperature changes. Furthermore, since cracking is likely to occur due to a rapid temperature change, there is also a problem that workability is poor.

  Moreover, although fluorite has a high Abbe number, its refractive index (nd) is very low at 1.43. Therefore, even when fluorite ceramics are used, there is a problem that the optical utilization range is easily limited.

  Although the existence of Ca—Gd—F crystals having a cubic structure is known, it is difficult to stably produce a good quality single crystal because of the large difference in specific gravity between CaF 2 and GdF 3. For this reason, it has been difficult to apply Ca-Gd-F based crystals to optical materials.

  Therefore, the present invention has a high Abbe number similar to that of fluorite, has a higher refractive index than fluorite, and has translucency that can be used as an optical material. An object is to provide ceramics and an optical member using the translucent ceramics. Also provided are a Ca-Gd-F-based translucent ceramic having a high refractive index and an Abbe number and causing isotropic thermal expansion when the temperature rises, and an optical member using the translucent ceramic. This is the issue. Furthermore, another object of the present invention is to provide an optical system using such an optical member.

Another object of the present invention is to provide a production method capable of producing a Ca—Gd—F based translucent ceramic having an Abbe as high as fluorite and having a higher refractive index than fluorite. And
Furthermore, this invention makes it another subject to provide the composition for ceramic formation which can be used conveniently for manufacturing the said Ca-Gd-F type translucent ceramics.

The Ca—Gd—F-based translucent ceramic of the present invention includes a polycrystal including a crystal of (Ca _1−X Gd _X ) F _{2 + X} (where X is a number greater than 0 and equal to or less than 0.4). And has a light-transmitting property capable of transmitting light.

  The optical member of the present invention is made of the Ca—Gd—F based translucent ceramic and is formed in a predetermined shape.

  The optical system of the present invention is an optical system including at least one pair of convex lenses and concave lenses in an optical path, and one of the convex lens or the concave lens is made of the Ca-Gd-F based translucent ceramic, and the other is It is an optical system made of a material different from the Ca—Gd—F based translucent ceramic. The optical system may further include one or more convex lenses and one or more concave lenses.

Method for manufacturing a Ca-GdF KeiToruhikari ceramic of the present invention, baked and CaF ₂ particles, by mixing the GdF ₃ particles formed separately from the CaF ₂ particles and particulate mixture, a fine particle mixture It is the manufacturing method of Ca-Gd-F type translucent ceramics which manufacture translucent ceramics by setting and making transparent.
The manufacturing method may include a manufacturing process of the CaF ₂ fine particles and / or a GdF ₃ fine particle process.
The manufacturing method may include a step of adjusting a fine particle mixture including the CaF ₂ fine particles and the GdF ₃ fine particles.

Furthermore, the ceramic forming composition of the present invention is a ceramic forming composition containing CaF ₂ fine particles and GdF ₃ fine particles prepared separately from the CaF ₂ fine particles.

The Ca—Gd—F-based translucent ceramic of the present invention is made of a polycrystal including a crystal of (Ca _1−X Gd _X ) F _{2 + X} (X is a number greater than 0 and equal to or less than 0.4). , It has translucency that can transmit light. Therefore, the Ca—Gd—F based translucent ceramic of the present invention has optical characteristics different from those of the CaF ₂ crystal and the GdF ₃ crystal. That is, according to the present invention, it is possible to provide a Ca—Gd—F based translucent ceramic having an Abbe number as high as fluorite and having a higher refractive index than fluorite. And since Ca-Gd-F type translucent ceramics are a polycrystal, it has the advantage that it is easy to produce an isotropic thermal expansion distortion at the time of a temperature rise.

  Moreover, since the optical member of this invention consists of said Ca-Gd-F type translucent ceramics, it has a high Abbe number comparable to fluorite and a higher refractive index than fluorite. Furthermore, according to the optical system of the present invention having the optical member, it is easy to realize excellent optical performance.

Further, according to the method for producing a Ca—Gd—F based translucent ceramic of the present invention, CaF ₂ fine particles and GdF ₃ fine particles prepared separately from the CaF ₂ fine particles are mixed to form a fine particle mixture. Sinter and clear the particulate mixture. Therefore, it is easy to ensure the sinterability of the fine particle mixture, and to produce a Ca-Gd-F based translucent ceramic that is a polycrystal of calcium and gadolinium fluoride and has light transmissivity. Is possible.

Furthermore, since the ceramic forming composition of the present invention contains CaF ₂ fine particles and GdF ₃ fine particles prepared separately from the CaF ₂ fine particles, the method for producing the Ca—Gd—F based translucent ceramics Can be suitably used.

FIG. 1 is a TEM photograph of CaF ₂ fine particles and GdF ₃ fine particles prepared in Example 1, wherein (a) shows CaF ₂ fine particles and (b) shows GdF ₃ fine particles. 2A is a chart showing the results of X-ray analysis of the Ca—Gd—F based translucent ceramic produced according to Example 1. FIG. FIG. 2B is a chart showing the results of powder X-ray analysis of a known CGF crystal. 4 is a graph showing the transmittance with respect to the wavelength of the Ca—Gd—F based translucent ceramics manufactured according to Example 1; In the Ca-Gd-F type translucent ceramics manufactured by Examples 1 to 3, the graph shows the refractive index change and Abbe number change when the mixing ratio of CaF ₂ fine particles and GdF ₃ fine particles is changed. is there. It is a graph which shows the correlation with an Abbe number and a partial dispersion ratio in Ca-Gd-F type translucent ceramics and various optical glasses manufactured by Example 1 thru | or 3.

  Embodiments of the present invention will be described below.

  The Ca—Gd—F based translucent ceramic of the present invention is substantially a polycrystalline body of calcium and gadolinium fluoride, and has translucency capable of transmitting light. This Ca—Gd—F-based translucent ceramic can be used as a member that transmits light inside. In particular, this translucent ceramic can be suitably used for an optical member such as a lens.

This Ca-Gd-F ceramic is a polycrystal containing calcium gadolinium fluoride (hereinafter referred to as CGF) crystals. CGF _{has (Ca 1-X Gd X)} F 2 + X (X is the number of greater than 0 and less than or equal 0.4.) The composition ratio shown (atomic ratio). The composition ratio can be accurately measured by fluorescent X-ray analysis or various chemical analysis methods.

The composition ratio of this CGF can be set to various values depending on the setting of conditions at the time of manufacture, etc., but the amount of Gd component is fixed to the amount of Gd component dissolved in the Ca component rich phase under the conditions at the time of sintering. It is preferable to adjust the composition ratio of CGF below the solubility limit. In this case, a structure in which the crystal structure of the Ca component rich phase having CaF ₂ as an end component easily functions effectively is obtained. The crystal system of CaF ₂ is cubic and GdF ₃ is orthorhombic, but CGF having a composition in the above range is cubic. A cubic crystal system is very advantageous as a condition for making ceramics transparent because it is easy to ensure crystal structure consistency at grain boundaries.

In the composition ratio of CGF represented by the above (Ca _1−X Gd _X ) F _{2 + X} , if X is larger than 0.4, the solid solution limit of Gd ions with respect to CaF ₂ is exceeded, so that a translucent ceramic is obtained. It is difficult. Therefore, the upper limit of X is set to 0.4. X is more preferably 0.1 or more and 0.4 or less. If X is less than 0.1, the difference in refractive index from fluorite cannot be made too large. In order to prevent the generation of a portion having a high Gd concentration and to obtain stable and uniform optical characteristics, X is more preferably set to 0.3 or less. Therefore, X is more preferably 0.1 or more and 0.3 or less.

The Ca—Gd—F based translucent ceramic is preferably substantially composed of CGF crystals. However, in the range where desired refractive index and Abbe number can be obtained and translucency that can be used as an optical material is obtained, one or both of CaF ₂ crystal and GdF ₃ crystal are included together with CGF crystal. It may be.
Furthermore, other unavoidable components and sintering aids may be used as long as the desired refractive index and Abbe number can be obtained and the translucency that can be used as an optical material is obtained. It may be contained in.

More preferably, the Ca—Gd—F-based translucent ceramic does not include the CaF ₂ crystal or the GdF ₃ crystal and substantially consists of a CGF crystal. The Ca—Gd—F based translucent ceramic is preferably made of a substantially homogeneous CGF crystal. For example, in a region having a volume of 1 μm × 1 μm × 1 μm, preferably the entire region, _{X in} the composition formula (Ca _1−X Gd _X ) F _{2 + X} of the CGF crystal is suppressed within a range of ± 10% with respect to the target value. It is preferable that

  Ca-Gd-F-based translucent ceramics have translucency capable of transmitting light. This translucency may be in a range according to the application of the Ca—Gd—F translucent ceramic. For example, the transmittance of light having a wavelength to be transmitted during use can be 50% or more. When the Ca-Gd-F translucent ceramic provided by the present invention is used as an optical member for correcting chromatic aberration, the wavelength used is, for example, a visible light region of 380 nm to 780 nm, and the representative wavelength is, for example, 550 nm. Further, in various optical members, a wavelength of 550 nm or less is used. Therefore, the Ca-Gd-F-based translucent ceramics may have a light transmittance of 50% or more, more preferably 50% or more of light having a wavelength of 350 nm to 550 nm. The light transmittance at the above-mentioned wavelength or wavelength range is preferably 70% or more, and more preferably 80% or more.

  This translucency is obtained by specifying a ceramic material as a fluoride of Ca and Gd. For example, even if a substance that can be a high refractive index substance is used as a fluoride such as Ce or Y instead of Gd, sufficient translucency cannot be obtained. Among other rare earths, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, and Tm can be used in place of Gd, although translucency can be obtained, but some wavelengths of visible light are absorbed, There are problems such as emitting fluorescence. However, there is a possibility that La, Eu, Tb, and Dy do not cause a problem because of relatively little absorption or low fluorescence emission intensity.

  Such a Ca—Gd—F based translucent ceramic may be used as it is, but it can also be used as an optical member having a predetermined shape. For example, Ca—Gd—F-based translucent ceramics can be processed into an optical member having various shapes such as a spherical shape, an aspherical shape, a planar shape, and a lattice shape on the light incident surface and radiation surface. Furthermore, it is also possible to use a combination of one or two or more optical members formed of similar Ca—Gd—F based translucent ceramics. Or it is also possible to use the said optical member by comprising an optical system combining the optical member formed with the other material. For example, at least one optical member formed of Ca—Gd—F based translucent ceramics is combined with at least one optical member formed of a material selected from optical glass, optical plastic, optical crystal, and the like. Can be used.

The Ca—Gd—F-based translucent ceramic as described above is a novel ceramic made of a CGF sintered body imparted with good translucency. The optical member formed by the ceramic and the ceramic have different optical properties than the optical properties of the CaF ₂ crystal and GdF ₃ crystal, a fluoride material having an Abbe number and unprecedented refractive index. Specifically, this ceramic has an Abbe number that is substantially as high as fluorite and a higher refractive index than fluorite. For example, the Ca—Gd—F based translucent ceramic has a refractive index (nd) of 1.43 to 1.55 and an Abbe number of 85 to 95. Therefore, this ceramic is easy to use for various optical systems.

  Moreover, the refractive index and the Abbe number have a linear function correlation with the abundance ratio of Ca and Gd, as shown in FIG. Therefore, it is possible to easily obtain ceramics having a desired refractive index and Abbe number by adjusting the abundance ratio of Ca and Gd.

  Furthermore, this Ca—Gd—F based translucent ceramic exhibits abnormal partial dispersion as compared with various normal glasses (general optical glasses). For example, the correlation of the partial dispersion ratio (Pg, F) with respect to the Abbe number (νd) shows a distribution that can be approximated by a straight line as shown in FIG. On the other hand, in the case of Ca-Gd-F ceramics, the partial dispersion ratio with respect to the Abbe number leaves the above straight line and shows a distribution different from that of normal glass. Specifically, the Ca—Gd—F-based translucent ceramic of the present invention can have characteristics with an Abbe number of 85 to 95 and a partial dispersion ratio of 0.53 to 0.55. For this reason, in the Ca—Gd—F based ceramics, the refractive index for a part of light such as the Fraunhofer g line can be made different from that of normal glass.

  Therefore, color correction (correction of chromatic aberration), removal of secondary spectrum, and the like can be easily performed by using the above-described abnormal partial dispersion and combining a member formed of Ca-Gd-F ceramics with another member. be able to. For example, in the case of an optical system including a convex lens and a concave lens in the optical path, a member formed of the Ca-Gd-F based translucent ceramic is used for one of the convex lens or the concave lens, and the Ca-Gd-F based transparent is used for the other. By configuring the optical system using a member formed of a material different from that of the photoceramic, it is possible to efficiently remove the secondary spectrum. For example, the optical system can be used for a telephoto lens having a long focal length.

  When producing a convex lens or a concave lens from the Ca—Gd—F based translucent ceramic according to the present invention, the surface of the Ca—Gd—F based translucent ceramic that has been roughly molded into a shape close to the target shape is formed into a predetermined shape. After processing and further optically polishing the surface, antireflection processing or the like may be performed as necessary. A known method can be appropriately used for each of these steps.

  Since this Ca-Gd-F translucent ceramic is a polycrystal, the thermal expansion strain does not show anisotropy depending on the crystal orientation when the temperature rises, and isotropic thermal expansion strain occurs. Therefore, when processing this ceramic, breakage due to distortion is unlikely to occur. Further, when light is transmitted through the ceramics, it is difficult to cause deterioration in imaging performance due to temperature changes.

Next, a method for producing such a Ca—Gd—F based translucent ceramic will be described.
To produce the Ca-GdF KeiToruhikari ceramic prepares the CaF ₂ particles, the ceramic-forming composition containing a GdF ₃ particles formed separately from the CaF ₂ particles, the ceramic they are forming It can be produced by mixing the composition for use as uniformly as possible to obtain a fine particle mixture, and sintering and transparentizing the fine particle mixture.
The manufacturing method may include a method including adjustment of the ceramic forming composition. Further, a method including production of CaF ₂ fine particles and / or GdF ₃ fine particles used in the composition may be used. In addition, it is also possible to use CaF ₂ fine particles and GdF ₃ fine particles prepared in advance, or a mixture thereof, as the ceramic forming composition. Any material can be used as long as it is a material capable of forming ceramics by performing various treatments, and contains CaF ₂ fine particles and GdF ₃ fine particles that can be sintered. The CaF ₂ fine particles and GdF ₃ fine particles contained in the composition are preferably high-purity fine particles in which the content of other components is suppressed.

The CaF ₂ fine particles and the GdF ₃ fine particles contained in the composition are manufactured separately. For example, a fine particle mixture in which CaF ₂ and GdF ₃ are simultaneously produced by adding a fluorine compound to a mixed solution containing both a calcium compound and a gadolinium compound, or a composite fine particle containing both of these components is not used in the present invention. . In such a method, it is difficult to obtain fine particles having excellent sinterability.

The CaF ₂ fine particles used in the ceramic-forming composition are desirably fine particles having a maximum particle size of 5 μm or less, preferably 3 μm or less, and more preferably 1 μm or less. The GdF ₃ fine particles are also desirably fine particles having a maximum particle size of 5 μm or less, preferably 3 μm or less, and more preferably 1 μm or less. When particles having a particle size exceeding 5 μm are contained in the composition, it is easy to generate sites where the Gd concentration is locally different in the sintered ceramic. Even if the material of the composition contains particles having a particle size exceeding the above upper limit value, it may be finely divided below the upper limit value in the process of preparing the fine particle mixture.
The fine particles include aggregates (secondary particles) in which a plurality of primary particles are aggregated. In the step of preparing the fine particle mixture, it is preferable that the secondary particles are finely divided and the proportion of the primary particles is increased to uniformly mix CaF ₂ and GdF ₃ .
The CaF ₂ fine particles preferably have a primary particle size of 200 nm or less. The GdF ₃ fine particles preferably have a primary particle size of 200 nm or less.

“Creation of CaF ₂ fine particles”
The CaF ₂ fine particles can be prepared by reacting a calcium compound and a fluorine compound in an aqueous solution, and then heating to 100 ° C. or more and 300 ° C. or less in a sealed container.

Calcium compounds used for the preparation of CaF ₂ fine particles include acetate, lactate, oxalate, ascorbate, alginate, benzoate, carbonate, citrate, gluconate, pantothenate, salicylate , Organic acid salts of calcium such as stearate, tartrate, glycerate and trifluoroacetate may be used, and inorganic salts such as calcium chloride, hydroxide, nitrate and sulfate may be used. Good. As the calcium compound, it is particularly preferable to use calcium acetate. Calcium acetate is suitable because it has a high solubility in water and impurity ions such as sulfates and chlorides hardly remain.

  As the fluorine compound, hydrofluoric acid (hydrofluoric acid) or the like can be used. If hydrofluoric acid is used as the fluorine compound, it is preferable that impurity ions hardly remain.

  Reaction of a calcium compound and a fluorine compound can be made to react by melt | dissolving each to make aqueous solution, and inject | pouring a fluorine compound aqueous solution gradually in calcium compound aqueous solution under normal temperature normal pressure.

During this reaction, it is preferable that other ions such as Gd ions are present in the reaction mixture as little as possible. When ions other than Ca ions and fluorine ions coexist in the reaction mixture, the ions are taken into the CaF ₂ fine particles to be formed, whereby the crystallinity of CaF ₂ is lowered and the particles are easily aggregated. For this reason, in the sintering described later, strongly agglomerated particles cannot be dissociated, causing problems such as voids remaining in the ceramics and lowering the density, and the sinterability tends to deteriorate. In sintering, it is often impossible to obtain a high-density sintered body even if the sintering conditions are slightly changed. Since other ions affect the sinterability sensitively and deteriorate the sinterability, it is preferable to suppress as much as possible.

Moreover, at the time of reaction, it is suitable to make the fluorine compound into an excessive amount larger than the chemical equivalent to the calcium compound (chemical equivalent when converted to CaF ₂ ). This is because the crystallinity is improved and aggregation is easily suppressed. As a result, CaF ₂ fine particles with few fluorine defects and high crystallinity are formed.

Furthermore, it is preferable to stir at the time of pouring the fluorine compound aqueous solution and to continue stirring even after the pouring is completed. This is in order to suppress aggregation of primary particles made of the generated CaF ₂ crystals. When strongly agglomerated particles are produced, the agglomerated state cannot be dissociated even when heated and pressurized during sintering and clarification, and voids remain, making it difficult to obtain dense ceramics. Therefore, it is preferable to sufficiently stir during the CaF ₂ crystal generation period.

As described above, after the calcium compound and the fluorine compound are reacted under normal temperature and normal pressure, the reaction mixture is stored in a hermetically sealed container, and a hydrothermal reaction process is performed in which heating and pressurizing processes are performed at 100 ° C. or more and 300 ° C. or less. It is preferable.
If the calcium compound and the fluorine compound are simply reacted at room temperature and normal pressure, the reaction does not proceed sufficiently, and the crystal is a fluoride with many fluorine deficiencies. Therefore, the stoichiometric ratio of crystals in the resulting reaction mixture is such that F is less than 2 with respect to Ca1, crystallinity is low, and aggregation is likely.
Therefore, it is preferable that the so-called hydrothermal reaction is further performed as described above to complete the reaction between the calcium compound and the fluorine compound. The container used for the hydrothermal reaction treatment is not particularly limited. For example, a sealed container such as an autoclave made of Teflon (registered trademark) may be used. The preferred processing temperature is 120-180 ° C. The pressure is preferably 0.2 to 1.0 MPa, which is the saturated vapor pressure of water in this temperature range.

This allows the ratio of F for Ca1 of CaF ₂ particles substantially 2 can be formed with high crystallinity CaF ₂ particles. Therefore, the surface of the CaF ₂ fine particles becomes stable, and the cohesive force between the fine particles can be easily reduced. As a result, it is possible to obtain CaF ₂ fine particles that are easy to sinter at a high density even at relatively low temperatures and have excellent sinterability.
Incidentally, according to the above method, for example, can be obtained CaF ₂ particles having an average particle diameter 100~200nm of the primary particles.

"Creation of GdF ₃ fine particles"
On the other hand, the GdF ₃ fine particles can be produced by reacting a gadolinium compound and a fluorine compound in an aqueous solution, and then heating to 100 ° C. or more and 300 ° C. or less in an airtight container in the same manner as the preparation of CaF ₂ fine particles. .

As the gadolinium compound, an organic acid salt or inorganic substance of gadolinium similar to the calcium compound can be used. Acetate, lactate, oxalate, ascorbate, alginate, benzoate, carbonate, citrate, gluconate, pantothenate, salicylate, stearate, tartrate, glyceric acid An organic acid salt of gadolinium such as a salt or trifluoroacetate salt may be used, and an inorganic salt such as a gadolinium chloride, hydroxide, nitrate or sulfate may be used. As the gadolinium compound, it is preferable to use gadolinium acetate. As the fluorine compound, hydrofluoric acid can be used.
First, similarly to the preparation of CaF ₂ , each of the gadolinium compound and the fluoride is gradually reacted as an aqueous solution under normal temperature and pressure. Here, a small amount of inorganic acid such as nitric acid may be added in order to sufficiently dissolve the gadolinium compound.

At the time of this reaction, it is preferable to reduce as much as possible other ions such as Ca ions present in the reaction mixture. Thereby, the crystallinity fall of the gadolinium fluoride formed can be suppressed and sinterability can be improved. Further, it is preferable to inject an excess amount of the fluorine compound aqueous solution with respect to the gadolinium compound aqueous solution (for example, gadolinium acetate aqueous solution) so as to exceed the chemical equivalent (chemical equivalent converted to GdF ₃ ). Thereby, the crystallinity fall of gadolinium fluoride can be suppressed and the cohesion force between fine particles can be weakened. Furthermore, it is preferable to suppress agglomeration of primary particles by continuing stirring during and after the injection of the fluorine compound aqueous solution.

And after said reaction, by carrying out the hydrothermal reaction process which accommodates and seals a reaction mixture in an airtight container, and heat-pressurizes at 100-300 degreeC, Preferably it is 120-180 degreeC, It is preferable to complete the reaction between the gadolinium compound and the fluorine compound. Thereby, fluorine deficiency can be suppressed and the crystallinity of the GdF ₃ fine particles can be increased. Therefore, the particles can be made difficult to aggregate, and GdF ₃ fine particles that can be sintered at a high density even at a relatively low temperature can be obtained.
Incidentally, according to the above method, for example, can be obtained GdF ₃ fine particles having an average particle size of 50~100nm of the primary particles.

The reaction mixture containing CaF ₂ fine particles and the reaction mixture containing GdF ₃ fine particles thus obtained are both suspensions in which fine particles of crystals are dispersed in a strongly acidic aqueous solution. Therefore, it is solid-liquid separated by a centrifuge or the like and dried at a temperature of room temperature to 200 ° C. to obtain a dry powder. Separation of a strongly acidic aqueous solution by solid-liquid separation or further drying facilitates handling during subsequent processing and storage. Furthermore, contamination of impurities in the liquid phase can be suppressed. In addition, when both the CaF ₂ fine particles and the GdF ₃ fine particles are mixed at a constant ratio, since the powder can be accurately weighed, the optical performance such as the refractive index is stabilized.

  More preferably, after the solid-liquid separation of the suspension containing the reaction mixture, one or more washing processes such as injecting a washing solvent such as water or alcohol into the reaction mixture and centrifuging to remove the supernatant liquid are performed. It is preferable to perform it once. Thereby, it is possible to more efficiently remove strongly acidic liquids and impurities. Use of an organic solvent such as alcohol is preferable because it has an effect of weakening the cohesive force between the fine particles generated during drying, and facilitates the dispersion treatment described later.

"Composition adjustment"
Then, the ceramic forming composition by mixing these dry powdery CaF ₂ particles and GdF ₃ particles. This ceramic forming composition is a material capable of forming translucent ceramics by sintering and making transparent. The ceramic forming composition only needs to contain CaF ₂ fine particles and GdF ₃ fine particles as described above in a predetermined weight ratio, and may be uniformly mixed. Moreover, it may be in a powder form, and may be dispersed or suspended in a dispersion liquid such as a slurry.

Next, after preparing the ceramic forming composition, the ceramic forming composition is mixed as a slurry or suspension by wet mixing. As a result, CaF ₂ fine particles and GdF ₃ fine particles are mixed as uniformly as possible. Mixing by wet mixing is preferable because it can be mixed more uniformly than dry mixing, and the primary particles of CaF ₂ fine particles and GdF ₃ fine particles are hardly damaged by excessive stress.
In this wet mixing, it is preferable to dissociate the aggregated state of each particle as much as possible to break it down to primary particles, and to mix them uniformly at the nano level.

The CaF ₂ fine particles and GdF ₃ fine particles used for wet mixing are, for example, secondary particles in which a plurality of primary particles are aggregated even if they are manufactured so as to easily suppress aggregation at the time of production. Further, when CaF ₂ fine particles and GdF ₃ fine particles are produced and then dried, aggregation tends to increase. For example, even if the primary particle diameter is about 150 nm for CaF ₂ and about 70 nm for GdF ₃ , the secondary particles may be about 10 μm.

When CaF ₂ particles and GdF ₃ particles are mixed in the form of large massive secondary particles and sintered, the contact area between CaF ₂ fine particles and GdF ₃ fine particles tends to be reduced during sintering. In this case, a sufficient solid phase reaction is unlikely to occur. Then, in the finally obtained Ca—Gd—F based translucent ceramic, a CaF ₂ crystal phase and a GdF ₃ crystal phase are microscopically generated, and microscopically non-uniform composition unevenness is generated. Become. If the reaction temperature is increased in order to solve this problem, this time, the release of fluorine from the fluoride occurs, causing a decrease in transmittance. Further, even in the Ca-rich phase of the CGF crystal, the composition ratio of Ca and Gd may be inhomogeneous. As a result, unevenness (non-homogeneous distribution) occurs in the refractive index, and the internal scattering in the ceramic increases with respect to the light incident on the Ca-Gd-F-based translucent ceramics. Optical characteristics such as refractive index and Abbe number cannot be obtained.
Therefore, it is preferable to dissociate the aggregated state of the particles as much as possible, destroy the aggregated particles (secondary particles), increase the proportion of primary particles, and mix the primary particles as uniformly as possible.

Effective means for dissociating the agglomerated state of the secondary particles are reduction of agglomeration force by chemical treatment and destruction of agglomerated particles by mechanical treatment.
In reducing the chemical cohesive force, when the hydrothermally treated slurry of CaF ₂ and GdF ₃ is dried, the cohesive force can be weakened by substituting and washing with higher alcohols such as propanol and then drying. Thereafter, mechanical cohesive failure is facilitated.
When preparing CaF ₂ fine particles, calcium acetate can be easily dissolved in a large amount in distilled water unlike gadolinium acetate, so nitric acid is unnecessary, but adding nitric acid is preferable because the cohesion of the finished dry powder is reduced. .

  On the other hand, as mechanical cohesive failure, mechanical cohesive failure may be performed using a stirring machine such as a stirring blade, a bead mill, a high-pressure homogenizer, a high-speed swirler, or an ultrasonic dispersing machine.

  In the case of mechanical cohesive failure, if excessive stress is applied, stress remains in the primary particles or breakage occurs, so that the ceramic is easily cracked or warped at the stage of sintering. In addition, when media type equipment such as a bead mill is used, contamination caused by wear of the beads themselves or the equipment may become a problem. Therefore, silicon nitride or silicon carbide may be used rather than partially stabilized zirconia that is generally used. The beads are preferred. More preferably, the dispersion is preferably performed using a high-pressure homogenizer that does not use a dispersion medium such as beads, that is, a medialess type apparatus.

Thereafter, the fine particle mixture in which the CaF ₂ fine particles and the GdF ₃ fine particles are uniformly mixed in the dispersion is subjected to solid-liquid separation using a centrifuge. Centrifugation may be difficult when the aggregated particles are broken and dispersed to primary particles. Therefore, when the pH of the solution is made alkaline, reaggregation occurs and the solution can be easily centrifuged. Examples of the alkali solution include inorganic alkali solutions such as sodium hydroxide and potassium hydroxide, and organic alkali solutions such as tetramethylammonium hydroxide (TMAH) and 2-hydrocarbon ethyltrimethylammonium hydroxide. If it is an organic alkali liquid, there will be no problem that impurities, such as sodium and potassium, will mix in a dispersion liquid like an inorganic alkali liquid. In addition, since the organic alkali solution is easily decomposed and detached by heating, it is difficult to remain in the Ca—Gd—F based translucent ceramics, which is preferable. When the pH is 7 or higher, centrifugal sedimentation occurs, but when the pH is 12 or higher and 13.5 or lower, a uniform sintered body is obtained, which is preferable.

In this case, reaggregation occurs after the primary particles of CaF ₂ and GdF ₃ are uniformly mixed, so that there is no problem since the uniformity of the composition of the powder as a whole is maintained. After centrifuging and discarding the supernatant, it is dried at 100 ° C. to obtain a dry powder. Alternatively, it is also possible to obtain a dry powder directly by freeze drying or spray drying without using a centrifuge.
It is desirable that 80% or more (number ratio), preferably 95% or more, of CaF ₂ fine particles and GdF ₃ fine particles are primary particles by the above-described aggregation and dissociation.
In this way, by dissociating and destroying the aggregation of the CaF ₂ fine particles and the GdF ₃ fine particles, the primary particles can be mixed more uniformly if wet mixing is performed while being dispersed almost to the primary particles. Thereby, in the sintered ceramics, the internal composition unevenness, that is, the refractive index unevenness can be reduced, and a transparent ceramic excellent in internal homogeneity can be obtained.

In the wet mixing, the mixing ratio of the CaF ₂ fine particles and the GdF ₃ fine particles can be determined based on at least one of the refractive index and the Abbe number of the desired Ca—Gd—F based translucent ceramic. This is because, as described above, the refractive index and the Abbe number have a linear function correlation corresponding to the ratio of Ca and Gd.

As described above, by performing wet mixing, a fine particle mixture in which primary particles of CaF ₂ fine particles and GdF ₃ fine particles are mixed as uniformly as possible is produced. When viewed microscopically, when the primary particles of CaF ₂ and GdF ₃ are close to each other in the fine particle mixture by wet mixing, there is an advantage that the solid-phase reaction in which CGF is generated proceeds at a lower temperature. As a result, it is preferable because fluorine escape occurring during sintering can be suppressed and the transmittance is improved.

Next, the dry powder obtained in this way is pressed by a die uniaxial press device or the like to produce a molded body. Furthermore, when it is subjected to an isostatic press, it is possible to prevent lamination (a phenomenon of peeling in layers in a direction perpendicular to the press direction) that often occurs in a uniaxial press of a mold, which is advantageous and preferable for producing a large-sized molded body. This molded body is heated to 700 ° C. or higher and 1000 ° C. or lower in the atmosphere and sintered to produce a sintered body (precursor sintered body). At this time, the aggregation of primary particles of CaF ₂ fine particles and GdF ₃ fine particles is broken, and since the crystallinity of CaF ₂ fine particles and GdF ₃ fine particles is high, it can be sintered at a high density, and a sintered body having a high relative density. It is possible to obtain
If it is less than 700 degreeC, it is difficult to sinter a dry body. On the other hand, when the sintering temperature exceeds 1000 ° C., the phenomenon that fluorine is desorbed from the crystal structure becomes remarkable, and the transparency of the ceramic is lowered. Therefore, the upper limit of the temperature was set to 1000 ° C. A preferable temperature range is 800 ° C. or higher and 900 ° C. or lower.

Thereafter, the sintered body, in an inert atmosphere such as argon or nitrogen, while pressing at 500 Kg / cm ² or more 3000 Kg / cm ² or less in pressure and heated to a temperature of 700 ° C. or higher 1300 ° C. or less (secondary It becomes transparent by sintering. This transparency can be performed using, for example, a hot isostatic press (HIP).

At this time, pores remaining inside the sintered body while being pressed are pushed out and become transparent, and the density becomes higher than the above-mentioned sintered body (precursor sintered body), resulting in a higher relative density. It is possible to make a transparent sintered body. Thereby, manufacture of Ca-Gd-F type translucent ceramics is completed.
Note that, during the formation of the precursor sintered body and during the progress of transparency, the CaF ₂ fine particles and the GdF ₃ fine particles cause a reaction (reaction sintering) accompanied by diffusion of Ca and Gd, and a large amount of CGF crystals. Crystals are formed. If the temperature during pressurization / heating is less than 700 ° C., it is difficult for CaF ₂ fine particles and GdF ₃ fine particles to react, so it is difficult to make the CGF crystal concentration distribution uniform. Therefore, the lower limit of the temperature was set to 700 ° C. On the other hand, if the temperature exceeds 1300 ° C., solid-liquid separation may occur, and it is difficult to control fluorine desorption even under pressurized conditions. Therefore, the upper limit of the temperature at the time of transparency was set to 1300 ° C. A preferable temperature range is 800 ° C. or higher and 1200 ° C. or lower, and a more preferable temperature range is 900 ° C. or higher and 1000 ° C. or lower.

The ceramic produced in the above process is a polycrystal including a CGF crystal. When coarse crystals are included in the polycrystal, the isotropic thermal expansion may be hindered. Therefore, it is desirable that the crystal grain size of the polycrystalline body constituting the ceramic is 100 μm or less.
In the above method, the fine particle mixture was sintered and transparentized in two stages, primary sintering for forming a precursor sintered body and secondary sintering for transparentization. Sintering and transparency may be performed by changing the temperature and pressure according to a predetermined history.

In the above method for producing a Ca—Gd—F based translucent ceramic, CaF ₂ fine particles and GdF ₃ fine particles produced separately from the CaF ₂ fine particles are mixed to form a fine particle mixture, and this fine particle mixture is sintered. And make it transparent. According to such a manufacturing method, it is easy to ensure the sinterability of the fine particle mixture. Therefore, it is possible to produce a Ca—Gd—F based translucent ceramic having an Abbe number as high as fluorite and having a higher refractive index than fluorite.

  In addition, a sintered body is prepared from the fine particle mixture, and the sintered body is made transparent by being heated in an inert atmosphere while being pressurized. Therefore, the sintered body is densified and Ca-Gd having high transparency is obtained. -F type translucent ceramics can be manufactured.

Furthermore, since CaF ₂ fine particles are produced by reacting calcium compounds and fluorine compounds in an aqueous solution and then heating to a predetermined temperature in a sealed container, CaF ₂ fine particles having excellent sinterability can be produced.

Further, since the GdF ₃ fine particles are produced by reacting a gadolinium compound and a fluorine compound in an aqueous solution and then heating to a predetermined temperature in a sealed container, GdF ₃ fine particles having excellent sinterability can be produced.

Further, since the CaF ₂ particles and GdF ₃ fine particles were wet-mixed to produce a particulate mixture, excessive stress hardly acts on the primary particles of CaF ₂ particles and GdF ₃ particles, cracks and warpage during sintering occurs hard.

In particular, when CaF ₂ fine particles and GdF ₃ fine particles are wet-mixed using a high-pressure homogenizer, cohesive failure can be achieved while minimizing contamination.

Furthermore, since the mixing ratio of CaF ₂ fine particles and GdF ₃ fine particles is adjusted based on at least one of the desired refractive index and Abbe number, the Ca-Gd-F system having the desired refractive index and Abbe number is used. A translucent ceramic can be easily manufactured.

Examples of the present invention will be described below.
[Example 1]
“Preparation of CaF ₂ fine particles”

  640 g of distilled water and 10 ml of nitric acid were added to 180.4 g (1 mol) of calcium acetate hydrate to completely dissolve the hydrate to prepare an aqueous calcium acetate solution.

  An aqueous hydrofluoric acid solution was prepared by adding the same weight of distilled water to 163.8 g (4 mol) of hydrofluoric acid (hydrofluoric acid) having a concentration of 50%.

  The stirring rod with blades (blade diameter 10 cm) was rotated at 300 rpm, and the aqueous hydrofluoric acid solution was slowly poured into the aqueous calcium acetate solution while stirring the aqueous calcium acetate solution. An injection port of a hydrofluoric acid aqueous solution was attached to the side of a plastic beaker (diameter 13 cm) containing a calcium acetate aqueous solution, and the hydrofluoric acid aqueous solution sucked out by a roller tube pump was injected into the calcium acetate aqueous solution over about 1 hour.

After the injection of the hydrofluoric acid aqueous solution was completed, stirring was continued for 6 hours as it was, and agglomerated particles were broken to reduce the particle size while preparing a CaF ₂ slurry.

The obtained CaF ₂ slurry was put in an autoclave made of Teflon (registered trademark), sealed, and subjected to hydrothermal reaction by heating and pressurizing at 145 ° C. for 24 hours to complete a slurry in which CaF ₂ fine particles were suspended. . The slurry was centrifuged to settle the particles. After discarding the supernatant, isopropyl alcohol was added to redisperse the particles. It was centrifuged again and the supernatant was discarded. This operation was repeated once more, and the precipitated particles were dried at 100 ° C. to obtain dry CaF ₂ powder. By repeating the alcohol substitution and the centrifugation in this manner, the CaF ₂ fine particles were thoroughly washed with isopropyl alcohol, and the cohesive force between the primary particles generated during drying was weakened as much as possible.
“Preparation of GdF ₃ fine particles”

GdF ₃ fine particles were prepared in the same manner as CaF ₂ fine particles.

  1000 g of distilled water was added to 290.4 g of gadolinium acetate hydrate, and nitric acid was further added to completely dissolve gadolinium acetate hydrate to prepare an aqueous gadolinium acetate solution.

  An aqueous hydrofluoric acid solution was prepared by adding the same weight of distilled water to 183.8 g (5 mol) of hydrofluoric acid having a concentration of 50%.

Similar to the preparation of the CaF ₂ fine particles, the aqueous hydrofluoric acid solution was slowly poured into the aqueous gadolinium acetate solution while stirring the aqueous gadolinium acetate solution. After completion of the injection, stirring was continued as it was, and agglomerated particles were broken to reduce the particle size, thereby preparing a GdF ₃ slurry. Further, the obtained GdF ₃ slurry was subjected to a hydrothermal reaction treatment in the same manner as CaF ₂ to complete a slurry in which GdF ₃ fine particles were suspended. Similar to CaF ₂ , the centrifugally precipitated particles were dried at 100 ° C. to obtain dry GdF ₃ powder.

Transmission electron microscope (TEM) photographs of the obtained CaF ₂ fine particles and GdF ₃ fine particles are shown in FIGS. 1A and 1B. The primary particle size was about 150 nm for CaF ₂ and about 70 nm for GdF ₃ . When TEM was observed at a high magnification, a lattice image was observed in the particles, and it was confirmed that both particles were well crystallized. When observed at a low magnification, both particles formed secondary particles in which a large number of primary particles were aggregated, and the maximum was about 10 μm.
"Wet mixing"

The slurry in which the finished CaF ₂ fine particles are suspended and the slurry in which the GdF ₃ fine particles are suspended are weighed and mixed so that the molar ratio is Gd / Ca = 0.3. did. Distilled water was added so that the mixed powder was 20% by weight, and the mixture was passed through an ultrasonic disperser for 20 minutes to prepare a fine particle dispersion in which aggregated particles were roughly broken. Furthermore, it is applied to a commercially available wet dispersion device (Nanomizer (registered trademark), NM2-L200, manufactured by Yoshida Kikai Kogyo Co., Ltd.), the aggregated particles are broken at a pressure of 200 MPa, and CaF2 and GdF3 fine particles are uniformly mixed in the liquid. Realized.
THAM was added to this ceramic-forming composition suspension to adjust the pH to 13 and then centrifuged. The supernatant was discarded and dried at 100 ° C. for 12 hours to obtain a mixed powder for forming ceramics.
"Sintering"

4 g of the dried powder was uniaxially press-molded using a mold having a diameter of 20 mm to form a molded body, and further, hydrostatically pressed at 50 MPa to produce a molded body. The molded body was sintered in air at 800 ° C. for 1 hour to obtain a white sintered body.
"Transparency"

Next, while applying an isostatic pressure of 1000 kg / cm ^{2 in} an argon atmosphere using a hot isostatic pressing (HIP) apparatus (Dr. HIP, manufactured by Kobe Steel, Ltd., trademark) Heated at 0 ° C. for 2 hours. By this treatment, the closed pores remaining inside the sintered body were pushed out to become transparent, and a Ca—Gd—F based translucent ceramic was obtained.
[Examples 2 and 3]

  A Ca—Gd—F based translucent ceramic was obtained in the same manner as in Example 1 except that the molar ratio of Gd / Ca in wet mixing was set to 0.1 and 0.4.

The following measurements were performed on the Ca—Gd—F based translucent ceramics obtained in Examples 1 to 3 above.
"CGF crystal"

About the Ca-Gd-F type translucent ceramics (Ca _0.7 Gd _0.3 F _2.3 ) obtained in Example 1, the results of X-ray analysis are shown in FIG. 2A and Table 1, The known data of the CGF crystal (Ca _0.88 Gd _0.12 F _2.12 ) described in JCPDS is shown in FIG.

The X diffraction pattern of the Ca—Gd—F based translucent ceramic (Ca _0.7 Gd _0.3 F _2.3 ) of Example 1 and the CGF crystal of JCPDS01-070-6178 (Ca _0.88 Gd _{0. When} compared with the X-ray diffraction pattern of ₁₂ F _2.12 . The reason why there is a slight difference in the peak position is that there is a slight difference in the lattice constant due to the difference in the Gd / Ca ratio. Therefore, a comparison of both X-ray diffraction pattern, Ca-Gd-F KeiToruhikari ceramic obtained in Example 1 are those containing one or CGF crystals consisting CGF crystal, and simply CaF ₂ particles It was confirmed that the GdF ₃ fine particles were not densely sintered.
"Transmissivity"

The transmittance of the obtained translucent ceramic (thickness 4 mm) is shown in FIG. The transmittance of light at a wavelength of 550 nm was 87.7%. When adjusting the fine particle mixture, the reduction of cohesive force due to chemical treatment and mechanical cohesive failure are used together, confirming that the light transmittance is improved in ceramics obtained by sintering and clarifying the fine particle mixture. It was done. This is considered that the unevenness of the composition inside the sintered body is reduced because the aggregated particles are dispersed to the primary particles at the stage of the fine particle mixture. Furthermore, because the primary particles of CaF ₂ and GdF ₃ are close to each other, the solid-phase reaction is promoted and the secondary sintering temperature can be made transparent at a relatively low temperature of 950 ° C. It is considered that it was able to be suppressed.
"Refractive index"

In the CGF transparent ceramics of Examples 1 to 3 manufactured by changing Gd / Ca, which is a mixing ratio of CaF ₂ fine particles and GdF ₃ fine particles, to 0.1, 0.3 and 0.4, Fraunforfer Table 2 shows the results of measuring the refractive indexes (ng, nF, ne, nd, nC) of g-line, F-line, e-line, d-line, and C-line. The refractive index was measured using a refractometer PR-2 manufactured by Carl Zeiss Jena.

"Correlation between mixing ratio of fine particles and Abbe number"

In the CGF transparent ceramics of Examples 1 to 3 manufactured by changing Gd / Ca, which is a mixing ratio of CaF ₂ fine particles and GdF ₃ fine particles, to 0.1, 0.3 and 0.4, refraction with respect to Gd / Ca The relationship between the rate (nd) and the Abbe number is shown in FIG.

The refractive index tended to increase with increasing amount of GdF ₃ fine particles, while the Abbe number tended to decrease. The refractive index increased from 1.43 for fluorite where Gd / Ca = 0 to 1.52 for Gd / Ca = 0.4. At Gd / Ca = 0.4, the Abbe number decreased to 87, but it is still in the low dispersion region. Therefore, in the range where Gd / Ca is greater than 0 and less than or equal to 0.4, an unprecedented transparent material having a high refractive index while being low dispersion has been obtained.
"Abnormal partial dispersion ratio"

    FIG. 5 shows the correlation between the Abbe number and the partial dispersion ratio, together with the correlation of various optical glasses (normal glass), based on the refractive index measured on each line. The black circles ● in the figure indicate the correlation between various optical glasses.

  The partial dispersion ratio (Pg, F) was calculated by the following equation based on the refractive indexes of Fraunhofer g line, F line, and C line. In the following formula (1), ng is the refractive index of g-line, nF is the refractive index of F-line, and nC is the refractive index of C-line.

    Pg, F = (ng−nF) / (nF−nC) (1)

  The Abbe number (νd) is calculated by the following equation (2). In the following formula, nd is the refractive index of the Fraunhofer d line, nF is the refractive index of the F line, and nC is the refractive index of the C line.

    νd = (nd−1) / (nF−nC) (2)

  In various optical glasses, the partial dispersion ratios are almost aligned. However, all three types of CGF transparent ceramics obtained in Examples 1 to 3 are far from this straight line, and are not found in various optical glasses. Partial dispersibility was confirmed.

  In particular, Gd / Ca = 0.1 is farthest, and a great effect is obtained in reducing the secondary spectrum. A telephoto lens with a long focal length has a large influence of the secondary spectrum, and thus using such a CGF transparent ceramic is effective in reducing chromatic aberration [Comparative Example 1].

A ceramic was produced in the same manner as in Example 1 except that cerium acetate was used in place of gadolinium acetate, and a transparent ceramic was not obtained.
[Comparative Example 2]

A ceramic was produced in the same manner as in Example 1 except that yttrium acetate was used in place of gadolinium acetate, and a transparent ceramic was not obtained.
[Comparative Example 3]

Instead of preparing CaF ₂ fine particles and GdF ₃ fine particles separately, a ceramic was produced in the same manner as in Example 1 except that calcium acetate and gadolinium were mixed and reacted with hydrofluoric acid to obtain fine particles. Transparent ceramics were not obtained.

  According to the present invention, it is possible to provide a Ca—Gd—F-based material having a high Abbe number comparable to that of fluorite and having a higher refractive index than fluorite as translucent ceramics. Since the above translucent ceramic exhibits abnormal partial dispersion as compared with general optical glass, an optical system having excellent optical performance can be realized by using the translucent ceramic as an optical member. Moreover, this invention can provide the composition which can be used for the manufacturing method of the said translucent ceramics, and this manufacture. Therefore, the present invention has high utility in industrial use.

Claims (21)

A method for producing a Ca-Gd-F translucent ceramic,
And CaF ₂ particles, by mixing the GdF ₃ particles formed separately from the CaF ₂ particles to adjust the particulate mixture,
A method for producing a Ca—Gd—F-based translucent ceramic, wherein the translucent ceramic is produced by sintering and transparentizing the fine particle mixture. It is a manufacturing method of the Ca-Gd-F type translucent ceramics according to claim 1,
The fine particle mixture is heated to 700 ° C. or more and 1000 ° C. or less to produce a precursor sintered body,
While pressing in the precursor sintered body 500 Kg / cm ² or more 3000 Kg / cm ² or less in pressure in an inert atmosphere, by heating to temperatures below 1300 ° C. 700 ° C. or higher, performing the transparency, Ca- A method for producing a Gd-F translucent ceramic. Furthermore, by reacting a calcium compound and a fluorine compound in an aqueous solution and then heated to 300 ° C. below 100 ° C. or higher in a closed container, comprising the step of producing the CaF ₂ particles, according to claim 1 or 2 A method for producing a Ca—Gd—F based translucent ceramic. The method further comprises a step of reacting a gadolinium compound and a fluorine compound in an aqueous solution, and then heating to 100 ° C. or more and 300 ° C. or less in a sealed container to produce the GdF ₃ fine particles. The manufacturing method of Ca-Gd-F type translucent ceramics as described in one. A method for producing a Ca-Gd-F translucent ceramic according to any one of claims 1 to 4,
5. The Ca—Gd—F-based translucent according to claim 1, wherein in preparing the fine particle mixture, the CaF ₂ fine particles and the GdF ₃ fine particles are wet-mixed to produce the fine particle mixture. Of manufacturing ceramics. Wherein in the wet mixing, and the CaF ₂ particles, the GdF ₃ manufacturing method of Ca-GdF KeiToruhikari ceramic according to claim 5, the cohesive force between the primary particles in each particle chemically reduced. The method for producing a Ca—Gd—F based translucent ceramic according to claim 6, wherein the CaF ₂ fine particles and the GdF ₃ fine particles are wet-mixed in an alkaline solution.     The method for producing a Ca—Gd—F based translucent ceramic according to claim 7, wherein the alkaline liquid is an organic alkaline liquid.       The method for producing a Ca—Gd—F based translucent ceramic according to claim 5, wherein the wet mixing is performed using a mechanical mixing unit. 10. The method according to claim 1, further comprising a mechanical cohesive failure step of mechanically destroying aggregation of primary particles in each of the CaF ₂ fine particles and the GdF ₃ fine particles in the preparation of the fine particle mixture. The manufacturing method of the Ca-Gd-F type translucent ceramics of Claim 1. 11. The mixing according to claim 1, wherein mixing is performed by adjusting a mixing ratio of the CaF ₂ fine particles and the GdF ₃ fine particles based on at least one of a desired refractive index and Abbe number. The manufacturing method of Ca-Gd-F type translucent ceramics. The translucent ceramic is a polycrystalline body containing a crystal of (Ca _1−X Gd _X ) F _{2 + X} (X is a number greater than 0 and equal to or less than 0.4). The manufacturing method of the Ca-Gd-F type translucent ceramics as described in any one of thru | or 11. _{(Ca 1-X Gd X)} F 2 + X (X is the number of greater than 0 and less than or equal 0.4.) A polycrystalline body containing crystal, Ca-Gd-with the possible translucent transmit light F-based translucent ceramics.       The Ca-Gd-F based translucent ceramic according to claim 13, wherein the transmissivity of light having a wavelength of 550 nm is 50% or more.       The Ca-Gd-F based translucent ceramic according to claim 13 or 14, wherein the refractive index is 1.43 or more and 1.55 or less, and the Abbe number is 85 or more and 95 or less.       The Ca-Gd-F based translucent ceramic according to any one of claims 13 to 15, wherein the Abbe number is 85 or more and 95 or less, and the partial dispersion ratio is 0.53 or more and 0.55 or less.   An optical member made of the Ca-Gd-F translucent ceramic according to any one of claims 13 to 16, and formed in a predetermined shape.     An optical system comprising at least one pair of convex lens and concave lens in an optical path, wherein one of the convex lens or the concave lens is made of the Ca-Gd-F based translucent ceramic according to claim 13 to 16, and the other Is an optical system made of a material different from the Ca-Gd-F translucent ceramics. And CaF ₂ particles, ceramic-forming composition characterized by containing a GdF ₃ particles formed separately from the CaF ₂ particles. The ceramic forming composition according to claim 19, wherein the CaF ₂ fine particles and the GdF ₃ fine particles are suspended or dispersed in a liquid. 21. The ceramic forming composition according to claim 19 or 20, comprising a fine particle mixture in which primary particles of CaF ₂ and primary particles of GdF ₃ are mixed.