JP2012218974A - Method for producing translucent ceramic and optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing translucent ceramics having optical characteristics as a high refractive index and low dispersion and an optical element made of the translucent ceramics obtained by the method for producing the same.SOLUTION: The method for producing the translucent ceramics has a step for sintering a molded body of a crystal grain comprising LaAlO(x represents 0.75≤x≤0.80) at 1,650°C to 1,800°C. The optical element is made of the translucent ceramics obtained by the producing method. It is preferable that the refractive index of the translucent ceramics is 2.00 or more and Abbe number is 35 or more.

Description

  The present invention relates to a method for producing translucent ceramics and an optical element, and particularly to a high-precision optical element used for a lens or the like.

In recent years, the production amount of cameras such as digital cameras has increased, and higher performance optical lenses have been demanded. In particular, optical materials having a high refractive index and low dispersion have been required. LaAlO ₃ crystal has a high refractive index and low dispersion performance not found in conventional optical glass, but there has been no practical application as an optical lens so far.

  Two structural features are conceivable for fabricating an optical lens using a crystalline material. One is a single crystal, and the other is a polycrystalline body (hereinafter referred to as ceramics) obtained by sintering fine crystal grains.

The single crystal has a high transmittance, but for the production of the single crystal, a special apparatus having a heat resistance of not less than the melting point, for example, 2000 ° C. or more in the case of LaAlO ₃ is required. In addition, the number of devices that can be taken from one apparatus is small, and it takes time for crystal growth, resulting in high manufacturing costs.

  On the other hand, with ceramics, the transmittance decreases due to pores, grain boundaries, and impurities, or when the lens is processed into a lens shape, defects occur on the lens surface, resulting in a good optical lens. There was a problem that it was difficult.

As translucent ceramics as an optical component material, Ln _x Al _y O _{[x + y] × 1.5} system described in Patent Document 1 (Ln is a rare earth element, x is 1 ≦ x ≦ 10, y is 1 ≦ y ≦ 5) is known.

JP 2010-85736 A

In order to produce a translucent ceramic, it is necessary to sufficiently eliminate pores that cause scattering and bring the powder filling rate close to 100%. However, ceramics composed of LaAlO ₃ crystals having a rhombohedral structure have a large amount of scattering because pores and grain boundaries tend to remain during sintering, and it has been difficult to obtain a ceramic with high transmittance.

  This invention is made | formed in view of such a background art, and provides the manufacturing method of translucent ceramics which has an optical characteristic of a high refractive index low dispersion.

  Moreover, this invention is providing the optical element which consists of translucent ceramics obtained by said manufacturing method.

A method for producing a light-transmitting ceramic that solves the above-described problem is obtained by using a molded body of crystal particles made of La _x Al _(2-x) O ₃ (x represents 0.75 ≦ x ≦ 0.80) 1650. It has the process of sintering at 1 degreeC or more and 1 degreeC or less.

  Moreover, this invention is an optical element characterized by consisting of translucent ceramics obtained by said manufacturing method.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of translucent ceramics which has an optical characteristic of a high refractive index and low dispersion can be provided.

  Moreover, according to this invention, the optical element which consists of translucent ceramics obtained by said manufacturing method can be provided.

  Hereinafter, the present invention will be described in detail.

In the method for producing a translucent ceramic according to the present invention, a molded body of crystal particles made of La _x Al _(2-x) O ₃ (x represents 0.75 ≦ x ≦ 0.80) is 1650 ° C. or higher. It has the process of sintering at 1800 degrees C or less, It is characterized by the above-mentioned. The translucent ceramic obtained by the production method of the present invention has high refractive index and low dispersion optical characteristics.

  In addition, the present invention is characterized by providing an optical element having optical characteristics of high refractive index and low dispersion, made of translucent ceramics obtained by the above-described manufacturing method.

  Examples of the optical element of the present invention include lenses and prisms used in optical systems.

  A method for producing a translucent ceramic according to the present invention will be described.

First, spherical La _x Al _(2-x) O ₃ (x is 0.75 ≦ x ≦ 0.80 ₎ having an average particle size of 10 μm or less by a method such as plasma melting using an optical grade oxide powder. Crystal grains are produced.

For the oxide powder, oxides of La ₂ O ₃ and Al ₂ O ₃ are preferably used. In La _x Al _(2-x) O ₃ , x satisfies 0.75 ≦ x ≦ 0.80.

_{La x Al (2-x)} O 3 in the present invention is a composition containing a large amount of Al than LaAlO _3. The reason why the composition contains a large amount of Al is to prevent the phase transition from cubic to rhombohedral in the cooling process by bringing the crystal structure close to cubic. Grain boundaries are reduced by suppressing structural changes.

  Next, a step of sintering the compact of crystal grains at 1650 ° C. or higher and 1800 ° C. or lower is performed. Specifically, spherical crystal particles are sintered at 1650 ° C. or higher and 1800 ° C. or lower while being pressed by a discharge plasma sintering method. In addition, it is preferable to fill the mold with crystal particles and perform sintering at 1650 ° C. or higher and 1800 ° C. or lower under pressure.

  After the sintered body obtained by sintering is annealed at a temperature of 900 ° C. or higher and 1300 ° C. or lower, a light-transmitting ceramic is obtained through grinding and polishing processes. The translucent ceramic is an optical element such as an optical lens.

  The sintering temperature by the discharge plasma sintering method or the like is 1650 ° C. or higher and 1800 ° C. or lower, preferably 1700 ° C. or higher and 1750 ° C. or lower. When the temperature is lower than 1650 ° C., the grain growth does not proceed, so that the translucency cannot be obtained. When the temperature is higher than 1800 ° C., most of the material is volatilized or fused to the sintered mold and damaged.

  The translucent ceramic has a refractive index of 2.00 or more and an Abbe number of 35 or more. The translucency of the translucent ceramics can be confirmed by the transmittance measured with a spectrophotometer CARY4G manufactured by Varian.

  Hereinafter, the present invention will be specifically described with reference to examples of a method for producing a translucent ceramic. Table 1 shows manufacturing conditions and manufactured ceramics.

<Measurement method>
(1) Refractive index A refractive index shows the value (nd) calculated | required and measured by wavelength 587nm using the ellipsometer (brand name "M-2000", JA Woollam Japan Co., Ltd.).
(2) Abbe number The Abbe number is obtained by using an ellipsometer to obtain refractive indexes nd, nF, and nC at wavelengths of 587 nm, 486 nm, and 656 nm, and the Abbe number νd is represented by νd = (nd−1) / (nF− The value calculated | required by the type | formula of nC) is shown.

Example 1
An oxide raw material of La ₂ O ₃ and Al ₂ O ₃ having a purity of 99.9% or more is prepared, and the raw materials are adjusted and mixed so as to have a ratio of La _0.75 Al _1.25 O ₃ . In order to make this mixed raw material react, after processing at 1500 degreeC for 4 hours, it grind | pulverizes with a ball mill. The pulverized powder is introduced into thermal plasma, heated, melted and then cooled to be processed into spherical particles having an average particle diameter of 2 μm.

  The spherical particles are filled in a mold made of graphite and sintered at a maximum temperature of 1750 ° C. and a pressure of 1 MPa or higher in a vacuum or nitrogen atmosphere. At this time, the rate of temperature increase until reaching the maximum temperature was 40 ° C./min or more, and the holding time at the maximum temperature was 30 minutes. The holding time at the maximum temperature is preferably 3 minutes or more and 60 minutes or less. Any sintering means may be used as long as it can be sintered under the above-mentioned conditions, but in this experiment, discharge plasma sintering was used.

  The obtained translucent sintered body was annealed at 900 ° C. for 1 hour or longer, then ground and polished to obtain an optical element having a thickness of 1 mm. The refractive index and Abbe number of the optical element were 2.04 and 35, respectively. Moreover, the translucency of the optical element was confirmed by the transmittance measured with a spectrophotometer CARY4G manufactured by Varian.

Example 2
In the same manner as in Example 1, spherical particles of La _0.80 Al _1.20 O ₃ are produced. The spherical particles were filled in a mold and sintered at a maximum temperature of 1750 ° C. and a pressure of 1 MPa or more in a vacuum or nitrogen atmosphere.

  The obtained translucent sintered body was annealed at 900 ° C. for 1 hour or longer, then ground and polished to obtain an optical element having a thickness of 1 mm. The refractive index and Abbe number of the obtained optical element were 2.04 and 36, respectively. Moreover, the translucency of the optical element was confirmed by the transmittance measured with a spectrophotometer CARY4G manufactured by Varian.

Comparative Example 1
In the same manner as in Example 1, spherical particles of La _0.88 Al _1.12 O ₃ are produced. The spherical particles were filled in a mold and sintered at a maximum temperature of 1750 ° C. and a pressure of 1 MPa or more in a vacuum or nitrogen atmosphere.

  The obtained translucent sintered body was annealed at 900 ° C. for 1 hour or longer, then ground and polished to obtain an optical element having a thickness of 1 mm. The obtained optical element was unsuitable for use as an optical element because pores remained.

Comparative Example 2
LaAlO ₃ spherical particles are produced in the same manner as in Example 1. The spherical particles were filled in a mold and sintered at a maximum temperature of 1200 ° C. or 1750 ° C. under a pressure of 1 MPa or higher in a vacuum or nitrogen atmosphere.

  The obtained translucent sintered body was annealed at 900 ° C. for 1 hour or longer, then ground and polished to obtain an optical element having a thickness of 1 mm. The obtained optical element was unsuitable for use as an optical element because pores remained.

Example 3
In the same manner as in Example 1, spherical particles of La _0.75 Al _1.25 O ₃ are produced. The spherical particles were filled in a mold and sintered at a maximum temperature of 1650 ° C. and a pressure of 1 MPa or higher in a vacuum or nitrogen atmosphere.

  The obtained translucent sintered body was annealed at 900 ° C. for 1 hour or longer, then ground and polished to obtain an optical element having a thickness of 1 mm. The refractive index and Abbe number of the obtained optical element were the same as those in Example 1. Moreover, the translucency of the optical element was confirmed by the transmittance measured with a spectrophotometer CARY4G manufactured by Varian.

Example 4
In the same manner as in Example 1, spherical particles of La _0.75 Al _1.25 O ₃ are produced.
The spherical particles were filled in a mold and sintered at a maximum temperature of 1800 ° C. and a pressure of 1 MPa or higher in a vacuum or nitrogen atmosphere.

  The obtained translucent sintered body was annealed at 900 ° C. for 1 hour or longer, then ground and polished to obtain an optical element having a thickness of 1 mm. The refractive index and Abbe number of the obtained optical element were the same as those in Example 1. Moreover, the translucency of the optical element was confirmed by the transmittance measured with a spectrophotometer CARY4G manufactured by Varian.

Comparative Example 3
In the same manner as in Example 1, spherical particles of La _0.75 Al _1.25 O ₃ are produced. The spherical particles were filled in a mold and sintered at a maximum temperature of 1250 ° C. or 1600 ° C. and a pressure of 1 MPa or higher in a vacuum or nitrogen atmosphere.

  Since the obtained sintered body had a low sintering temperature, a large number of pores remained, which was inappropriate for use as an optical element.

Comparative Example 4
In the same manner as in Example 1, spherical particles of La _0.75 Al _1.25 O ₃ are produced. The spherical particles were filled in a mold and sintered at a maximum temperature of 1850 ° C. and a pressure of 1 MPa or higher in a vacuum or nitrogen atmosphere.

  Since the obtained sintered body has a high sintering temperature, it is fused to the mold and damaged, and is inappropriate for use as an optical element.

  Since the translucent ceramic obtained by the production method of the present invention has high refractive index and low dispersion optical characteristics, it can be used for optical elements such as lenses and prisms used in optical systems.

Claims (4)

_{La x Al (2-x)} O 3 (x represents. A 0.75 ≦ x ≦ 0.80), comprising a step of sintering at 1650 ° C. or higher 1800 ° C. or less compact of crystal particles made of A method for producing translucent ceramics.   The method for producing a translucent ceramic according to claim 1, wherein the crystal particles are filled in a mold and sintered at 1650 ° C or higher and 1800 ° C or lower under pressure.   The method for producing a translucent ceramic according to claim 1 or 2, wherein the translucent ceramic has a refractive index of 2.00 or more and an Abbe number of 35 or more.   An optical element comprising a translucent ceramic obtained by the manufacturing method according to claim 1.