阅读说明：本技术 多晶yag烧结体及其制造方法 (Polycrystalline YAG sintered body and method for producing same ) 是由 三上充 山崎芳树 于 2018-10-29 设计创作，主要内容包括：一种多晶YAG烧结体,其特征在于,在将包围YAG烧结体的最小的长方体的尺寸设为Amm×Bmm×Cmm时,最大值(A,B,C)小于等于150mm,最小值(A,B,C)大于20mm且小于等于40mm,并且在使波长300nm～1500nm(但是,不包括存在由添加元素引起的吸收的波长)的光透过时的光损耗系数为0.002cm<Sup>-1</Sup>以下。另外,一种多晶YAG烧结体,其特征在于,在将包围YAG烧结体的最小的长方体的尺寸设为Amm×Bmm×Cmm时,最大值(A,B,C)大于150mm且小于等于300mm,最小值(A,B,C)大于5mm且小于等于40mm,并且在使波长300nm～1500nm(但是,不包括存在由添加元素引起的吸收的波长)的光透过时的光损耗系数为0.002cm<Sup>-1</Sup>以下。本发明的实施方式的课题在于提供一种大型且透明的多晶YAG烧结体及其制造方法。(A polycrystalline YAG sintered body, characterized in that, when the size of a smallest rectangular parallelepiped surrounding the YAG sintered body is Amm x Bmm x Cmm, the maximum value (A, B, C) is 150mm or less, the minimum value (A, B, C) is 20mm to 40mm or less, and the optical loss coefficient when light having a wavelength of 300nm to 1500nm (excluding the wavelength having absorption by an additive element) is transmitted is 0.002cm ‑1 The following. Further, a polycrystalline YAG sintered body characterized in that the surrounding isWhen the smallest rectangular parallelepiped size of the YAG sintered body is Amm X Bmm X Cmm, the maximum value (A, B, C) is more than 150mm and not more than 300mm, the minimum value (A, B, C) is more than 5mm and not more than 40mm, and the optical loss coefficient when light having a wavelength of 300nm to 1500nm (excluding the wavelength having absorption by an additive element) is transmitted is 0.002cm ‑1 The following. An object of an embodiment of the present invention is to provide a large transparent polycrystalline YAG sintered body and a method for producing the same.)

1. A polycrystalline YAG sintered body, characterized in that, when the size of a smallest rectangular parallelepiped surrounding the YAG sintered body is Amm x Bmm x Cmm, the maximum value (A, B, C) is 150mm or less, the minimum value (A, B, C) is 20mm to 40mm or less, and the optical loss coefficient when light having a wavelength of 300nm to 1500nm (excluding the wavelength having absorption by an additive element) is transmitted is 0.002cm^-1The following.

2. A polycrystalline YAG sintered body, characterized in that, when the size of a smallest rectangular parallelepiped surrounding the YAG sintered body is Amm x Bmm x Cmm, the maximum value (A, B, C) is more than 150mm and not more than 300mm, the minimum value (A, B, C) is more than 5mm and not more than 40mm, and the optical loss coefficient when light having a wavelength of 300nm to 1500nm (excluding the wavelength having absorption by an additive element) is transmitted is 0.002cm^-1The following.

3. A method for producing a polycrystalline YAG sintered body according to claim 1 or 2, wherein Y is contained₂O₃Powder and Al₂O₃Mixing powder, molding to obtain a molded body with a relative density of 60% or more, and sintering the molded body while maintaining a vacuum degree of 1 × 10 in a temperature raising step and a maintaining step^-2Sintering at 1600-1900 ℃ while keeping Pa or less, and after sintering, setting the cooling rate to 100 ℃/h or less to 1100 ℃.

4. The method of producing a polycrystalline YAG sintered body as claimed in claim 3, wherein the cooled sintered body is subjected to HIP treatment at 1600 to 1800 ℃ and 100 to 200 MPa.

5. The method of producing a polycrystalline YAG sintered body as claimed in claim 4, wherein after the HIP treatment, the annealing treatment is carried out in the atmosphere at 1300 to 1500 ℃.

Technical Field

The present invention relates to a polycrystalline YAG (yttrium aluminum garnet) sintered body and a method for producing the same.

Background

YAG (yttrium aluminum garnet) is a composite oxide (Y) comprising yttrium and aluminum₃Al₅O₁₂) A crystal of garnet structure of (1). From the past, it has been known that: 1) the Y element constituting the YAG is subjected to substitution solid solution by adding an element from Ce having an atomic number of 57 to Yb having an atomic number of 70 among the rare earth elements; or 2) an element of Ti having an atomic number of 22 to Ni having an atomic number of 28 among transition metals is added to make Al element constituting YAG undergo substitution solid solution, whereby the element after substitution becomes an emission center and has strong fluorescence, and a phosphor, a laser medium, or the like is produced using the element. Further, since YAG itself, to which no element is added, is transparent and hard in the visible light region (hardness 8.5), it can be used as a material for a window (window) that can be used under severe environments (plasma and the like).

Heretofore, such YAG ceramics have been used by embedding a powder shape which is easy to produce in a resin or by growing a single crystal. However, although powder is easy to produce, light emission is easily scattered, and light emission efficiency is not high. On the other hand, although scattering of a single crystal is small and thus luminous efficiency is high, since the single crystal is grown from a melt of an oxide at a high temperature close to 2000 ℃ at the time of growing the single crystal, it is necessary to use extremely expensive iridium having oxidation resistance at a high temperature, and the growth rate must be set to about 1 mm/hour which is extremely slow, otherwise a large number of defects are generated, and transmittance is deteriorated and the strength of the crystal itself is also deteriorated. Further, the grown single crystal has a large number of micro-cracks, and there is a problem that unexpected breakage occurs when the single crystal is processed into a desired shape.

In recent years, it has been realized to produce polycrystalline YAG that suppresses as much as possible the pores (voids) present at grain boundaries by using the same method of shape sintering as in producing ordinary ceramics, and it is known that the polycrystalline YAG exhibits excellent transmission characteristics, although slightly inferior to single crystals. Further, since the phosphor is produced by sintering the same powder as the ceramic, there is no segregation phenomenon of the additive element observed in the melt growth of the single crystal (a phenomenon in which a gradient is observed in the concentration of the additive element in the ingot grown), and the solid solution limit of the additive element is also higher than that in the single crystal growth, so that a bright phosphor which cancels the inferior transmission characteristic to the single crystal and a laser medium having high emission intensity can be produced. Examples of inventions relating to a polycrystalline YAG sintered body include patent documents 1 and 2.

Since laser light can generate a high light intensity, a very strong local electromagnetic field can be applied to a substance, and in recent years, many studies have been made on the application of laser light. For example, cutting (laser processing) of metal or the like; forming plasma by irradiating droplets of molten tin or the like with laser light, and applying the plasma to a light source for ultra-fine lithography by generating extreme ultraviolet light using the plasma; the laser beam is used to effectively accelerate the heavy particles, and the accelerated heavy particles are irradiated to the affected part, thereby being beneficial to cancer treatment; and the like. Lasers used in such fields are called high power lasers, and are lasers having particularly high light intensity among lasers, and since large-sized products can be produced relatively easily, glass to which neodymium or ytterbium is added has been used as a laser medium for high power lasers.

However, glass or the like to which neodymium or the like is added has a weak mechanical strength and a poor thermal conductivity, and therefore, when it is oscillated, it takes several hours to cool, which is problematic in continuous use. In this respect, the YAG is particularly suitable as a laser medium for a high-power laser because it has high mechanical strength and good thermal conductivity. Further, as the laser medium is larger, a laser with higher output power can be constructed, and since the laser medium is produced by powder sintering, it is easy to increase the size, and therefore, polycrystalline YAG (sintered body) which is comparable to single crystal in quality is considered to be an optimum laser medium. On the other hand, laser-oscillated polycrystalline YAG has been made for 20 years or more since 1995 for the first time, but the largest size has been about Φ 100mm so far.

Disclosure of Invention

Problems to be solved by the invention

The invention provides a large transparent polycrystalline YAG sintered body and a method for producing the same.

Means for solving the problems

An embodiment of the present invention is a polycrystalline YAG sintered body, wherein when a size of a smallest rectangular parallelepiped surrounding the YAG sintered body is Amm × Bmm × cm, a maximum value of A, B, C is 150mm or less, a minimum value of A, B, C is more than 20mm and 40mm or less, and an optical loss coefficient when light having a wavelength of 300nm to 1500nm (excluding a wavelength where absorption by an additive element is present) is transmitted is 0.002cm^-1The following.

Further, an embodiment of the present invention is a polycrystalline YAG sintered body in which a maximum value of A, B, C is greater than 150mm and 300mm or less, a minimum value of A, B, C is greater than 5mm and 40mm or less, and an optical loss coefficient when light having a wavelength of 300 to 1500nm (excluding a wavelength where absorption by an additive element is present) is transmitted is 0.002cm^-1The following.

In addition, an embodiment of the present invention is a method for producing a polycrystalline YAG sintered body, the method comprising adding Y₂O₃Powder and Al₂O₃Molding a mixed powder of the powders to produce a molded article having a relative density of 60% or more,when the molded body was sintered, the degree of vacuum was maintained at 1X 10 in the temperature raising step and the maintaining step^-2Sintering at 1600-1900 ℃ while keeping Pa or less, and after sintering, setting the cooling rate to 100 ℃/h or less to 1100 ℃.

Effects of the invention

According to the embodiment of the present invention, a large transparent polycrystalline YAG sintered body can be stably produced.

Drawings

Fig. 1 is a schematic view of a scattered light measurement system according to an embodiment of the present invention.

Detailed Description

In recent years, application of laser light to material processing and the like has been studied, and a laser having higher output power has been demanded. Conventionally, YAG ceramics to which Nd, Yb, or the like is added have been used as laser media, but if YAG ceramics larger than ever can be produced, more excitation light can be emitted, and therefore lasers with high output power can be produced.

Since polycrystalline YAG is produced by powder sintering, it can be produced in any shape. However, as the sintered body gradually becomes larger, sintering unevenness remains in the center portion, and the sintered body becomes opaque as a whole. For example, in the prior art, when one side (or diameter) of the sintered body is as large as 100mm, the other side (or thickness) is preferably about 10mm, and 20mm is a limit. In addition, when one side (or diameter) of the sintered body is larger than 150mm, it becomes very difficult to manufacture a sintered body having the other side (or thickness) larger than 5 mm.

As a result of intensive studies on the sintering process of a large YAG sintered body, it has been found that a residual hole (uneven sintering) tends to remain in the central portion since sintering starts from the outer peripheral portion, and this becomes remarkable as the size increases. On the other hand, it was found that: instead of preparing polycrystalline YAG by preparing a powder having a YAG composition in advance and sintering the powder as shown in patent document 1, a powder prepared by mixing Y is used₂O₃、Al₂O₃Or the like, and heating the molded bodyThe reaction sintering for preparing polycrystalline YAG while reacting is beneficial to large-scale production.

Based on these findings, the YAG sintered body according to the embodiment of the present invention is characterized in that when the size of a smallest rectangular parallelepiped surrounding the YAG sintered body is Amm × Bmm × cm, the maximum value of A, B, C is 150mm or less, and the minimum value of A, B, C is 20mm to 40mm or less; or A, B, C has a maximum value of 150nm to 300mm inclusive, A, B, C has a minimum value of 5mm to 40mm inclusive, and the optical loss coefficient when light having a wavelength of 300 to 1500nm (excluding wavelengths where absorption by an additive element is present) is transmitted is 0.002cm^-1The following. If the optical loss coefficient is 0.002cm^-1Hereinafter, it can be said that the laser medium has excellent transmission characteristics, a bright phosphor, and high emission intensity. Such a large transparent polycrystalline YAG sintered body can be said to be a novel sintered body which has not been present so far.

The YAG sintered body is a sintered body produced by a powder sintering method, contains a polycrystal, and has a composite oxide (Y) containing yttrium and aluminum₃Al₅O₁₂) A crystal of garnet structure of (1). The Y element constituting the YAG can be substitutionally solid-dissolved by adding an element of Ce having an atomic number of 57 to Yb having an atomic number of 70 among rare earth elements; the Al element constituting YAG may be substituted and solid-dissolved by adding an element from Ti having an atomic number of 22 to Ni having an atomic number of 28 to the transition metal. In the present disclosure, these elements are referred to as "added elements". The substituted element becomes a luminescence center and can have strong fluorescence. Of course, the YAG sintered body according to the embodiment of the present invention may be YAG itself to which no element is added.

The YAG sintered body according to the embodiment of the present invention has a maximum value of A, B, C, that is, a maximum value of A, B, C of 150mm or less, where Amm × Bmm × cm is a smallest rectangular parallelepiped (virtual) size surrounding the sintered body; A. b, C, A, B, C, is greater than 20mm and not greater than 40 mm. More preferably 30mm or more. Alternatively, the maximum value of A, B, C, i.e., the maximum value of A, B, C, is greater than 150mm and 300mm or less; A. b, C, A, B, C, is greater than 5mm and not greater than 40 mm. More preferably 10mm or more. In the present application, a sintered body having such a size is referred to as a "large-sized" or "large-sized" sintered body. The size of the sintered body is the size after sintering (immediately after the end of sintering), but the sintered body whose size is reduced by cutting or the like is also included within a range not departing from the gist of the present invention. The sintered body may have a disk-like shape or a rectangular parallelepiped shape.

A laser medium of polycrystalline YAG known so far has a diameter of about 100mm and a thickness of about 10mm, and when it is desired to increase the size of the laser medium, it is difficult to perform a uniform sintering reaction because a sintered body contains a plurality of raw materials (components) and the physical properties of the sintered body are different from each other. Further, since high transparency is required over the entire surface like a laser medium, it is extremely difficult to increase the size of the YAG sintered body compared to other applications. However, in the present invention, the sintered body having a significantly increased size and a small optical loss coefficient is first realized by the method described later. Therefore, by using such a large laser medium, a laser with high output power can be constructed.

The optical loss coefficient in the embodiment of the present invention is an optical loss coefficient in the case of transmitting light of a wavelength at which absorption by an additive element is not caused. The optical loss coefficient in the wavelength range of 300nm to 1500nm is measured, for example, without introducing any additive element. In addition, for example, when Nd is added, since light is absorbed in a wavelength range of 300nm to 1000nm, an optical loss coefficient at a wavelength other than the above range, for example, at a wavelength of 1064nm is measured. When the sintered body becomes opaque due to sintering unevenness or the like, the optical loss coefficient decreases over the entire measurement wavelength range (300nm to 1500nm), and therefore, even if the optical loss coefficient in the wavelength range in which light is absorbed by the additive element is removed as described above, no particular problem occurs. For example, by preparing a YAG single crystal into which an additive element is introduced and measuring the absorption, the absorption wavelength of light due to the additive element can be grasped in advance.

In the embodiment of the present invention, the optical loss coefficient is measured as follows.

A schematic diagram of a scattered light measurement system is shown in fig. 1. Light from a light source 1 (halogen lamp) is converted into monochromatic light of a selected specific wavelength by a beam splitter 2 and emitted. The light is collimated by 2 lenses 3 and 4 and is incident on an integrating sphere 6. A photodetector (photomultiplier tube) 9 is provided at a position passing through the integrating sphere 6, and the intensity of transmitted light is observed. Its signal 14 is input into the lock-in amplifier 10.

On the other hand, another photodetector (photomultiplier tube) 8 is provided at a position 90 degrees to the traveling direction of the transmitted light in the integrating sphere via a baffle 7. The photodetector 8 observes the intensity of the scattered light. On the other hand, the baffle 7 is inserted to eliminate intensity variations due to direct entry of scattered light and directional dependence of scattered light of the measurement object. The signal 13 from the photodetector 8 is also input to the lock-in amplifier 10. A chopper 5 is interposed between the lenses 3 and 4, and light is turned on/off at a constant cycle (frequency f), and a signal 12 thereof is inputted to a lock-in amplifier 10 as a reference signal.

Thus, the measurement signal is input in a state modulated at the frequency f, and the modulation component is removed by the lock-in amplifier 10, thereby obtaining the signal intensity to be obtained. In general, a noise component called 1/f fluctuation is included in nature, and the smaller the frequency f, the larger the noise, and the larger the frequency f, the smaller the noise. Such a configuration is adopted in order to reduce the influence of noise from the outside and to enable more accurate measurement by performing measurement at a large frequency f by modulation using a chopper.

Although a sample 11 to be measured was set at the center of the integrating sphere, the transmitted light intensity i (t)0 and the background scattered light intensity i(s)0 were first measured without placing the sample. Next, a plurality of samples 11 (thickness Ln (n is 1,2 …)) having different thicknesses and having cylindrical surfaces with entire surfaces polished were set at the center of the integrating sphere so that transmitted light was perpendicular to the bottom surface of the cylindrical surface, and the transmitted light intensity i (t) n and the scattered light intensity i(s) n were measured. Then, surface scattering coefficients r (t), r(s), and optical loss coefficients a (t), a(s) are obtained by fitting the following equations by the least square method.

Then, of the obtained A (T) and A (S), the larger value is used as the value of the optical loss coefficient.

[ mathematical formula 1]

[ mathematical formula 2]

Next, a method for producing a polycrystalline YAG sintered body according to an embodiment of the present invention will be described.

(regarding the raw material powder)

Preparation of Y₂O₃Powder, Al₂O₃The powder is used as a raw material. Further, an oxide powder (for example, Nd) containing the above-mentioned additive element is prepared as necessary₂O₃Powder). The raw material powder preferably has an average particle diameter of 0.3 to 10 μm. The purity of the raw material powder is preferably 4N or more, but when the addition ratio of the additive element is small, the purity may be reduced depending on the amount of the additive element. For example, in the case of substituting Nd for 1% of Y, even in the case of Nd₂O₃The raw material powder contains 1% of impurities in the powder₂O₃、Al₂O₃In the case of incorporation, Nd₂O₃The impurity amount of (2) was 0.01% of the total, which corresponds to 4N.

In addition, oxides (CaO, MgO, SiO) containing Ca, Mg, Si, Zr, La were prepared₂、ZrO₂、La₂O₃) Fluoride (CaF)₂Etc.), carbonates (CaCO₃) Composite oxide (MgAl)₂O₄Etc.) as a sintering aid.

(about mixing)

Adding the above-mentioned Y₂O₃Powder, Al₂O₃The powder, an oxide powder containing an additive element as needed, and a sintering aid are put into a mixing and pulverizing machine such as a ball mill, and wet-mixed for 4 to 20 hours by a ball mill using water as a solvent and alumina as a medium. In this case, in order to suppress the mixing unevenness caused by the aggregation of the raw material powder, it is preferable to add an appropriate amount of the dispersant. The mixing time is determined from the above range according to the particle diameter of the raw material powder used, the ratio of the solvent and the medium to the raw material, and the diameter of the medium.

After the mixing, a liquid sintering aid may be further added to the slurry taken out of the mixing and pulverizing machine. For example, a metal salt (Ca (C)) dissolved in water may be added₃H₅O₃)₂、CaCl₂Calcium lactate aqueous solution), and the like. Polyvinyl alcohol, acrylic binder, and alkaline aluminum chloride (Al) may be added to the slurry in an amount of 0.005 to 0.01 wt% based on the amount of the powder contained in the slurry₂(OH)_nCl_6-n)_m(n is more than 0 and less than 6, m is less than or equal to 10) and aluminum lactate is used as a binder.

(granulation and Molding)

Subsequently, the mixed slurry is dried, and then forcibly sieved with a sieve or spray-dried to produce granulated powder. The sintering aid may be added at this point. For example, an organometallic compound Si (OC)₂H₅)₄) Metal salt (Ca (C)) dissolved in water₃H₅O₃)₂、CaCl₂Calcium lactate aqueous solution), and the like. Polyvinyl alcohol, acrylic adhesive, and alkaline aluminum chloride (Al) may be added to the powder in an amount of 0.005 to 0.01 wt%₂(OH)_nCl_6-n)_m(n is more than 0 and less than 6, m is less than or equal to 10) and aluminum lactate is used as a binder.

The resulting material is placed in a mold (e.g., 150 mm. times.40 mm) and cold-pressed, and then CIP molding is carried out at 150MPa to 200 MPa. In the case of producing a molded article, the above-mentioned polyvinyl alcohol or acrylic binder may be used as a binder, but these organic components disappear during sintering, and a part thereof becomes a gap to deteriorate the sinterability. On the other hand, alkaline aluminum chloride and aluminum lactate gel during drying to bond surrounding powder, and become alumina components after firing to remain so as to reduce gaps, and by using alkaline aluminum chloride and aluminum lactate alone or in combination with polyvinyl alcohol and an acrylic binder, the improvement of relative density at the time before firing described later can be significantly facilitated, and the sinterability can be improved.

(for preheating)

Next, the molded article is heated at 100 to 300 ℃ for 4 to 6 hours in the air to remove water. Then, the molded article is heated at 800 to 1000 ℃ for 1 to 3 hours to remove organic components and the like contained in the sintering aid, the binder and the like, thereby making the relative density of the molded article 60% or more. Although heating is performed to remove the excess components as described above, when heating is performed at a high temperature (heating at 800 to 1000 ℃) rapidly, the molded article may be broken due to rapid expansion of moisture, and therefore, heating in two stages as described above is preferable. It is important to achieve a relative density of the molded body of 60% or more at the time before sintering in this manner.

(for sintering, HIP)

In the temperature raising step and the holding step, the degree of vacuum is preferably maintained at 1 × 10 in the sintering of the molded article^{- 2}Pa or less. The largest cause of the decrease in the degree of vacuum in the temperature increasing step and the holding step is considered to be residual moisture. Y used as main raw material of polycrystalline YAG₂O₃Has absorption property, and further, Al₂O₃Although not having the image Y₂O₃The same degree of absorbency, but also absorbency. The reason is considered to be that moisture in the air is absorbed at the time of production of the molded article or at the time of filling of the heating device. Particularly in the case of a large-sized molded article, water is not uniformly absorbed at every site, and there is a local difference. This causes heating unevenness at the time of reaction sintering, and as a result, warpage and opaque regions due to density unevenness and thermal strain after sintering occur. Therefore, in order to perform uniform sintering, it is important to adjust the degree of vacuum in such a manner.

Specifically, the molded article is charged into a vacuum heating furnace and then heated at 200 to 300 ℃ for about half a day while operating a rotary pump. After several hours, the degree of vacuum was rapidly deteriorated, and sometimes exceeded 100Pa, but gradually stabilized and reached 1Pa or less. After heat treatment at 200-300 ℃, cooling to normal temperature, and sintering after confirming that the vacuum degree is not deteriorated. The sintering is carried out at 1700 to 1900 ℃ for 10 to 20 hours. In this case, when sintering is performed in an atmosphere containing nitrogen, nitrogen remains in the sintered body to reduce the density, and therefore, sintering is preferably performed in a vacuum, a reducing atmosphere, or an oxygen atmosphere not containing nitrogen.

When heating is performed at a high temperature of 1700 to 1900 ℃, the cooling rate after the heater is turned off is high, and particularly the cooling rate of the portion near the furnace side surface is remarkably high, and particularly when the size is increased, the heat distribution in the sintered body becomes large, and the sintered body is cracked due to the thermal strain generated therein. Therefore, the cooling rate at the time of temperature reduction is preferably kept at 100 ℃/hr or less up to 1100 ℃.

Then, HIP (hot isostatic pressing) is performed for 1 to 4 hours at 1600 to 1800 ℃ and 100 to 200MPa in an inert atmosphere such as Ar.

(for annealing)

Then, the sintered body obtained above is heated at 1300 to 1500 ℃ for 5 to 15 hours in the air. This makes it possible to relax the internal stress remaining in the sintered body after HIP and to compensate for insufficient oxygen because oxygen deficiency occurs when vacuum heating is performed.

This makes it possible to obtain a large transparent polycrystalline YAG sintered body.