Ceramic powder, method for producing ceramic powder, and method for producing ceramic structures using ceramic powder

Abstract

To provide a ceramic powder for obtaining a high-definition ceramic structure in a short time in the production of a ceramic structure using an additive manufacturing method in which modeling is performed by irradiating a raw material powder with laser light.SOLUTION: A ceramic powder used in an additive manufacturing method in which modeling is performed by irradiating a raw material powder with laser light, including a first particle group which consists of particles of a first inorganic compound, and whose average particle size is 10 μm or greater and 100 μm or less and a second particle group which consists of a second inorganic compound having an absorption band at the wavelength of the laser beam and having an average particle size smaller than the first particle group, and the particle included in the second particle group is disposed on a surface of the particle included in the first particle group.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a raw material powder used in manufacturing ceramic molded objects by three-dimensional molding utilizing the melting and solidification (including sintering of the raw material powder) of the raw material powder by irradiation with laser light, and to a ceramic molding method using the same. [Background technology]

[0002] In recent years, additive manufacturing (also known as three-dimensional fabrication technology) using laser light has developed significantly, and its technological level has risen. Particularly in the metal field, selective laser sintering (SLS) or selective laser melting (SLM), a type of powder bed fusion bonding (powder bed deposition), has enabled the production of intricate and diverse objects. These methods involve using laser lithography to melt and bond or sinter metal powders into desired shapes. For lithography, small, high-power, and low-cost lasers in the near-infrared region, such as YAG lasers and fiber lasers, are predominantly used.

[0003] SLS and SLM are, in principle, applicable to ceramic powders. However, most common insulating ceramics are highly transparent to light in the visible to infrared region. That is, the ceramic particles used as raw materials absorb very little laser light in this wavelength range. Therefore, when additive manufacturing of ceramics using SLS or SLM equipment, it is necessary to irradiate the material with a laser beam of excessive power compared to the thermal energy required to melt the material in the processed area. In that case, most of the irradiated laser light is transmitted and diffused through the ceramic particles, so an area larger than the beam diameter of the laser light melts, making it difficult to form a clear boundary. For this reason, it has been difficult to fabricate high-resolution ceramics using SLS or SLM in the past.

[0004] To address these problems, for example, Non-Patent Document 1 proposes additive manufacturing of eutectic oxide ceramics by laser irradiation. Specifically, by using an Al2O3-ZrO2 eutectic system, the melting point of the powder used for molding is lowered, thereby reducing the laser power required for melting. This method also has the advantage that, due to the formation of a microstructure unique to eutectic systems during solidification, ceramic structures with high mechanical strength can be fabricated. While this method has shown some improvement in detail, the fabrication accuracy is still insufficient, with numerous surface protrusions still occurring. In addition, fabricating ceramic structures with laser light is time-consuming compared to metals due to the slower heat transfer and reaction rates. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Physics Procedia 5 (2010) 587-594 [Overview of the project] [Problems that the invention aims to solve]

[0006] This invention solves these problems and provides a ceramic raw material powder for obtaining high-resolution ceramic structures in a short time in additive manufacturing of ceramic structures using SLS and SLM equipment. It also provides a method for producing such a raw material powder and a method for obtaining high-resolution ceramic structures using such a raw material powder. [Means for solving the problem]

[0007] According to a first aspect of the present invention, a ceramic powder is provided for use in additive manufacturing, which involves irradiating a raw material powder with laser light to form a ceramic powder, comprising: a first particle group consisting of particles of a first inorganic compound with an average particle diameter of 10 μm or more and 100 μm or less; and a second particle group consisting of particles of a second inorganic compound having an absorption band at the wavelength of the laser light and having an average particle diameter smaller than that of the first particle group, wherein the particles in the second particle group are arranged on the surface of the particles in the first particle group.

[0008] A second aspect of the present invention provides a method for producing ceramic powder as described above, comprising at least the steps of: covering the surface of particles in the first particle group with a metal component-containing liquid that serves as a precursor for the second particle group; and heating the particles in the first particle group covered with the metal component-containing liquid to arrange the particles in the second particle group on the surface of the particles.

[0009] According to a third aspect of the present invention, a method for manufacturing a ceramic structure using an additive manufacturing method in which a laser beam is irradiated onto a raw material powder to form the structure is provided, comprising the steps of (i) placing the ceramic powder described above into a laser irradiation section, and (ii) selectively irradiating the ceramic powder placed into the laser irradiation section with laser light to melt and then solidify the portion of the ceramic powder irradiated with the laser light, and repeating steps (i) and (ii) to manufacture the ceramic structure. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view showing an example of an apparatus for irradiating ceramic powder with laser light according to the present invention. [Figure 2] This is a schematic cross-sectional view showing an example of a device for irradiating ceramic powder with laser light, different from the one shown in Figure 1. [Figure 3]Figure 3(a) shows a magnified schematic diagram of a part of the present invention and a comparative ceramic powder, where Figure 3(b) shows the case where the second particle group is relatively small, and Figure 3(b) shows the case where the second particle group is relatively large. [Figure 4] This is a photograph showing an electron microscope image of a magnified portion (one grain) of an example of the ceramic powder of the present invention. [Modes for carrying out the invention]

[0011] The following describes embodiments for carrying out the present invention. This invention relates to a ceramic powder suitably used as a raw material powder for obtaining ceramic structures (formed objects) by additive manufacturing technology using laser light. The ceramic powder of this invention comprises a first particle group consisting of particles of a first inorganic compound that serve as aggregate for the ceramic structure, and a second particle group consisting of particles of a second inorganic compound that act as a laser light absorber, with an average particle diameter smaller than that of the first particle group. The particles in the second particle group are arranged (usually in multiples) on the surface of the particles in the first particle group. Such a ceramic powder can absorb laser light with the second particle group, causing it to heat up, and efficiently transfer that heat to the first particle group. As a result, it becomes possible to scan the laser light at high speed and melt the material, which in turn increases the molding speed.

[0012] The ceramic powder of the present invention has the following characteristics. (1) Melting and solidification occur upon irradiation with laser light. This allows for the formation of ceramic structures. (2) It contains a first group of particles consisting of particles of the first inorganic compound, with an average particle diameter of 10 μm or more and 100 μm or less. (3) It contains a second group of particles consisting of a second inorganic compound, the average particle size of which is smaller than that of the first group of particles. (4) The particles in the second group of particles are arranged on the surface of the particles in the first group of particles, and the second inorganic compound is an absorber that has an absorption band at the wavelength of the laser light. The following will describe each feature in detail.

[0013] (Feature 1) The ceramic powder of the present invention is a raw material for obtaining a ceramic structure and contains ceramics as a main component. Further, when irradiated with laser light, the powder at the irradiated site melts, and when the irradiation of the laser light is stopped, it has the property of solidifying. In the present invention, the case of "melting and solidifying" includes not only the case of completely becoming a liquid (viscous fluid) state and then solidifying, but also the case where each particle (surface) constituting the powder softens and binds to each other (so-called sintering). This property is preferably exhibited by the powder having the following Feature 2, Feature 3, and Feature 4.

[0014] There is no limitation on the type of laser to be used, and the lasers used in metal three-dimensional modeling devices can be used as they are. For example, solid lasers such as fiber lasers and YAG lasers, which are small, high-power, and relatively inexpensive, used in SLS devices and SLM devices can be used. The oscillation wavelength of a general solid laser is from 800 nm to 1200 nm, which is included in the so-called near-infrared region (0.75 to 2.5 μm). The oscillation mode of the laser may be continuous oscillation or pulse oscillation.

[0015] When attempting to obtain a high-definition ceramic structure (modeled object), the irradiation diameter of the laser light is preferably 10 μm or more and 200 μm or less. On the other hand, when emphasizing the modeling speed and attempting to obtain a large modeled object in a short time, the irradiation diameter of the laser light is preferably 200 μm or more and 2000 μm or less.

[0016] FIG. 1 is a schematic cross-sectional view showing an example of an apparatus for irradiating a ceramic powder of the present invention with a laser beam. FIG. 1 shows the apparatus configuration in the case of the selective laser sintering method (SLS), which is a kind of powder bed fusion method. This method is also called a powder bed direct shaping method. The apparatus of FIG. 1 is composed of a powder hopper 11, a shaping stage section 12, a recoater section 13, a scanner section 14, and a laser 15. The powder hopper 11 is filled with the ceramic powder of the present invention. The powder hopper 11 and the shaping stage section 12 have a mechanism for moving in the vertical direction, and the ceramic powder can be transferred from the powder hopper 11 to the shaping stage section 12 by the recoater section 13. In the shaping stage section 12, the ceramic powder is spread over an area wider than the maximum horizontal cross-section of the target ceramic shaped object.

[0017] Subsequently, the laser 15 and the scanner section 14 irradiate the laser beam on the portion to be solidified among the ceramic powder (the uppermost layer) in the shaping stage section 12 for drawing. The ceramic powder in the portion irradiated with the laser beam absorbs the laser beam by the second particle group and converts the energy into heat. The second particle group melts, and the heat is transmitted to melt the first particle group. When the irradiation portion of the laser beam moves to another location, the melted portion is cooled and solidified. By this process, a one-layer shaped object is obtained. The ceramic powder that has not melted remains in the same layer. A new layer of ceramic powder is spread over this layer and irradiated with the laser beam, and the powder at an arbitrary location is melted and solidified to form a shaped object integrated with the previously shaped object. By repeating such steps, a ceramic structure (shaped object) having an arbitrary three-dimensional shape can be manufactured.

[0018] Figure 2 is a schematic cross-sectional view showing an example of another type of apparatus for irradiating the ceramic powder of the present invention with laser light. Figure 2 is a diagram illustrating a fabrication method called directed energy deposition, or cladding method. The cladding nozzle 21 has a plurality of powder supply holes 22 and has the function of ejecting the ceramic powder of the present invention from these powder supply holes 22 at a desired flow rate. By irradiating the region where the beam of this ejected ceramic powder is focused with a laser 23, a ceramic fabricated object can be additionally provided at a desired location on the substrate 20. In other words, in this case, the ceramic powder is ejected (placed) from the cladding nozzle 21 to the laser irradiation area and selectively receives laser light irradiation in the above (focused) region. Unlike powder bed deposition, this method has the advantage of being able to fabricate on curved surfaces.

[0019] (Feature 2) The ceramic powder of the present invention contains a first group of particles having an average particle diameter of 10 μm or more and 100 μm or less. By setting the average size of the first group of particles, which serve as aggregate for ceramic molded objects, to 10 μm or more and 100 μm or less, the fluidity required for powder transfer by the recoater section and cladding nozzle during molding (e.g., 40 seconds / 50g or less) can be satisfied, and the molded object can be given sufficient strength. From the same viewpoint, a more preferable average particle diameter for the first group of particles is 15 μm or more and 40 μm or less. Each particle included in the first group of particles is preferably spherical from the viewpoint of fluidity, but may also be irregular in shape, or have anisotropic shapes such as plate-like or needle-like. The average particle diameter can be calculated as the equivalent circle diameter of the projection image from a micrograph of the powder. For example, the average particle diameter can be obtained by randomly selecting particles included in the first group of 100 or more particles constituting the powder, excluding the particles included in the second group of particles placed on the surface, and averaging the values ​​of the equivalent circle diameters for each particle. If there is variation in the size of each particle, a combination of microscope images at different magnifications may be used. However, it is more preferable that the dispersion of the equivalent circle diameter of each first particle is small, and that the particle diameter (equivalent circle diameter) of 99% or more of the particles is between 10 μm and 100 μm.

[0020] In this invention, "powder" refers to an aggregate of particles that can be recognized as isolated particles. "Particle group" refers to an aggregate of particles that satisfy predetermined conditions. The first particle group does not have to consist of particles of a single composition, as long as it has the predetermined average particle diameter; it may be a mixture of multiple types of particles with different compositions.

[0021] In this invention, an inorganic compound refers to an oxide, nitride, oxynitride, carbide, or boride containing one or more elements from the group of elements that includes antimony and bismuth, in addition to the elements from Groups 1 to 14 of the periodic table excluding hydrogen. Furthermore, the particles made of the inorganic compound may be composed of one type of inorganic compound, or they may be a composite of two or more types of inorganic compounds. By using inorganic compound particles as the main component of the molding powder, the result of the melting and solidification reaction when irradiated with laser light can be made into a ceramic-like material.

[0022] The particles of the first inorganic compound included in the first particle group preferably consist mainly of metal oxides. By making the ceramic powder mainly of metal oxides, high-strength molded objects can be obtained. Here, metal oxide refers to an oxide containing one or more elements from the element group excluding boron, carbon, silicon, germanium, and the elements of Group 13 (nitrogen group) and Group 14 (oxygen group) from the above element group. Among metal oxides, it is preferable that the particles included in the first particle group consist mainly of aluminum oxide, silicon dioxide, or zirconium oxide. When aluminum oxide, silicon dioxide, or zirconium oxide are the main components and aggregates of the molded object, it is possible to produce molded objects with excellent mechanical strength, heat resistance, electrical insulation, and environmental compatibility.

[0023] The particles in the first particle group may consist of a single type of metal oxide, but combining them with other materials may reveal new functions and become even more desirable. For example, a combination of aluminum oxide and zirconium oxide, or a combination of aluminum oxide and rare earth metal oxides such as gadolinium oxide or yttrium oxide, are examples. When the particles in the first particle group consist of these combinations of metal oxides, a eutectic is formed during heating, resulting in a lower melting temperature compared to when they consist of only one type of metal oxide, and making the melting and solidification reactions by laser irradiation relatively easier. Moreover, a eutectic structure appears in the fabricated object after melting and solidification, which may result in higher mechanical strength than when they consist of only one type of metal oxide. From this perspective, it is desirable that the particles in the first particle group contain aluminum oxide and gadolinium oxide. Furthermore, the particles in the first particle group may also contain the above metal oxides with aluminum nitride or boron nitride, and by combining these compositions and using them as the first particle group, it may be possible to achieve lighter weight and higher strength than when using oxides alone.

[0024] (Feature 3) The ceramic powder of the present invention includes a first particle group consisting of particles of a first inorganic compound, and a second particle group consisting of particles of a second inorganic compound, with an average particle diameter smaller than that of the first particle group. The second inorganic compound has light-absorbing ability to laser light of a wavelength used in additive manufacturing. The particles in the second particle group are arranged on the surface of the particles in the first particle group. In other words, although the first particle group consisting of the first inorganic compound and the second particle group consisting of the second inorganic compound have different chemical compositions, both are the main components of the ceramic powder of the present invention.

[0025] The surface of a particle in the first particle group typically contains multiple particles from a second particle group, each having a smaller average particle diameter than the first particle group. Figures 3(a) and 3(b) are schematic diagrams showing a magnified view of a single particle 1 from the first particle group and multiple particles 2 or 3 from the second particle group arranged on its surface, which constitute the ceramic powder of the present invention. The ceramic powder of the present invention is an aggregate of many particles having the morphology shown in Figures 3(a) and 3(b).

[0026] In Figures 3(a) and 3(b), particle 1 is approximately spherical, but the shape is not particularly limited for obtaining the effects of the present invention. Numerous particles 2 or 3 are present on the surface of particle 1, and these particles 2 and 3 are particles included in the second particle group. The particle diameter of the particles included in the second particle group, which is strongly involved in the manifestation of the effects of the present invention, is smaller than that of the particles included in the first particle group in terms of average particle diameter, but it is acceptable for a small amount of particles included in the second particle group to be equal to or greater than the particles included in the first particle group to be mixed in the ceramic powder. In that case, a small amount of composite particles will be included in the ceramic powder in which particles included in the second particle group are not necessarily arranged on the surface of particles included in the first particle group, but this is not a problem as long as it does not hinder the manifestation of the effects of the present invention. The particle diameter can be calculated from a micrograph of the powder as the equivalent diameter of the circle of the projected image. As will be explained in detail in Feature 4 below, the second particle group has the function of absorbing laser light and generating heat. It is more preferable if the average particle diameter of the second particle group is between 0.05 μm and 2 μm, because this further increases the heat transfer rate to particle 1.

[0027] Figure 3(a) shows the configuration when particles 2, with an average particle diameter of 0.05 μm or more and 2 μm or less, are arranged on the surface of particle 1. When the average particle diameter of particle 2 is 0.05 μm or more, the energy absorption efficiency by particle 2 when irradiated with laser light increases. On the other hand, when the average particle diameter of particle 2 is 2 μm or less, the contact area between particle 1 and particle 2 increases, and the heat transfer rate from particle 2 to particle 1 increases. A more preferable average particle diameter of particle 2 is 0.05 μm or more and less than 1 μm.

[0028] Figure 3(b) is a schematic diagram showing one particle 1 included in the first particle group constituting the ceramic powder of the present invention, and particles 3 included in a plurality of second particle groups arranged on its surface. Particle 3 is relatively larger than particle 2 in Figure 3(a), and particle 3 has a particle diameter greater than 2 μm (but less than 10 μm). In Figure 3(a) and Figure 3(b), only the particle diameter of particles 2 and 3 differs; the chemical composition and crystal structure are assumed to be the same. Furthermore, the same particle 1 is used, and the amount of particle 2 or particle 3 attached to particle 1 is also assumed to be the same mass. In this case, when laser light is irradiated onto the ceramic powders in Figure 3(a) and Figure 3(b) under the same conditions, the amount of heat generated by particle 2 and particle 3 in each ceramic powder is approximately the same.

[0029] However, in the ceramic powder shown in Figure 3(a), the total contact area between particle 2 and particle 1 is large, so the heat generated by particle 2 is quickly transferred to particle 1, and the melting of particle 1 begins quickly and efficiently. On the other hand, in the ceramic powder shown in Figure 3(b), the contact area between particle 3 and particle 1 is relatively small, so the heat transfer rate is slow, and a lot of heat is lost by diffusion into the surrounding environment. As a result, melting is slower, and the molding speed is slower compared to the case in Figure 3(a).

[0030] However, the comparison of heat transfer rates using Figure 3(a) and Figure 3(b) is a comparison within the range of the molding powder of the present invention, and even with the configuration in Figure 3(b), molding is possible in a shorter time than with conventional molding powders.

[0031] The effects of the present invention can be obtained as long as particles 2 and 3 are in contact with the surface of particle 1, so the strength and method of adsorption are not relevant. Furthermore, particles 2 or 3 may partially penetrate into the interior of particle 1 by chemical bonding between particle 1 and particle 2 or particle 3.

[0032] When these particles 2 and 3 are placed on the surface of particle 1, it is desirable to adhere them to particle 1 with the highest possible coverage. For example, when particle 1 is observed two-dimensionally under a microscope, it is desirable that the coverage of particle 2 or particle 3 be 10 area percent or more. The ideal coverage is 100 area percent.

[0033] On the surface of particle 1, not only particles 2 with an average particle diameter of 0.05 μm or more and 2 μm or less may be arranged, but particles 3 with an average particle diameter exceeding 2 μm may also be arranged together with particles 2. However, it is preferable that the area covered by particles 2 exceeds the area covered by particles 3.

[0034] The mass ratio of the first particle group to the second particle group contained in the ceramic powder is not limited, but for example, it is preferable that the mass of the second particle group is between 2% and 20% of the mass of the first particle group, as this results in good molding speed, molding accuracy, and the strength of the molded object. Hereafter, particle 2 and particle 3 will be referred to collectively as particle 2 without distinction.

[0035] Furthermore, the ceramic powder of the present invention may contain particle groups other than the first and second particle groups for the purpose of improving the properties of the ceramic powder itself or the ceramic structure formed therefrom. However, in order to fully obtain the effects of the present invention, it is desirable that the combined proportion of the first and second particle groups in the ceramic powder of the present invention be 80% by mass or more, more preferably 90% by mass or more. In addition, it is desirable that the proportion of the first particle group alone in the ceramic powder of the present invention be 70% by mass or more.

[0036] (Feature 4) The second particle group consists of particles of a second inorganic compound that acts as an absorber, having an absorption band at the wavelength of the laser light. An absorber suitable for the second particle group efficiently absorbs the laser light, causing it to heat up, which then propagates to surrounding non-absorbent compositions, resulting in a temperature increase. This enables localized heating within the laser light irradiation area, forming an interface between the irradiated and unirradiated areas, and allowing for high-precision fabrication.

[0037] Preferably, the particles of the second inorganic compound included in the second particle group undergo a compositional change upon laser irradiation, and have the characteristic that their laser light absorption rate in the solidified object is lower than before laser irradiation. If the laser light absorption rate is low in the region after the laser irradiation and the fabrication process is completed, it is possible to suppress the alteration of the ceramics in the fabricated region when the adjacent region is subsequently irradiated with laser light.

[0038] Preferably, the particles of the second inorganic compound included in the second particle group consist of metal oxides, and the change in laser light absorption rate is due to a change in the valence state of the metal element. When the laser light absorption rate changes due to a change in valence state, there is no change in volume. In contrast, when the absorption rate changes due to the release of volatile substances from the absorber particles, the effect of volume change is significant. Examples of metal oxides whose valence state changes upon irradiation with laser light, resulting in a decrease or disappearance of laser light absorption rate, include oxides of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Hf, Ta, W, In, Sn, Bi, Ce, Pr, Sm, Eu, Tb, and Yb. Multiple types of particles made of these metal oxides may be combined and used as the second particle group.

[0039] For use in ceramic fabrication, lasers with wavelengths around 1000 nm, such as Nd:YAG lasers and Yb fiber lasers, are preferred due to their availability and controllability of irradiation energy. Materials that exhibit high absorption of laser light within this wavelength range, and that cause a decrease in absorption, include terbium oxide containing tetravalent terbium (Tb4O7) or praseodymium oxide containing tetravalent praseodymium (Pr6O7). 11 ) is preferably used. When the second group of particles of the present invention mainly consists of terbium oxide containing tetravalent terbium, or praseodymium oxide containing tetravalent praseodymium, it is effectively heated by laser light absorption and then loses its absorbent ability due to a decrease in valence.

[0040] Terbium oxide and praseodymium oxide exhibit diverse valency states in the metallic part. Taking terbium oxide as an example, there are typically two states: Tb4O7 and Tb2O3. The former state is represented by the molecular formula Tb4O7, but the ratio of metal to oxygen is not strictly defined, encompassing compositions close to 4:7. In the former state, the metallic part of Tb4O7 is Tb 4+ and Tb 3+ While the latter state consists of roughly equal amounts of each, the metallic part of Tb2O3 is Tb 3+ It consists only of that.

[0041] Tb4O7 has a high infrared absorption rate around 1000 nm wavelength, and its absorption rate can exceed 60% and reach 70%. On the other hand, Tb 4+ As the fraction of decreases, the absorption rate decreases, and Tb 3+ In Tb2O3, which is composed solely of terbium, the absorption rate is approximately 7%. Therefore, terbium oxide (Tb4O7), in which the absorber contains tetravalent terbium, is suitable as the main component of inorganic compound particle B that realizes the present invention. Similarly, praseodymium oxide (Pr6O), in which the absorber contains tetravalent praseodymium 11 ) is also suitable as the main component of inorganic compound particles B that realize the present invention.

[0042] X-ray absorption fine structure analysis (XAFS) can be applied as a method to evaluate the valence. By utilizing the characteristic that the rise energy of the absorption edge differs for each valence, the valence can be evaluated from the profile.

[0043] (Manufacturing method) The method for producing the ceramic powder having the above characteristics is not particularly limited, but a preferred method is described below. The method for producing the ceramic powder of the present invention has the following characteristics. (5) The process includes a step of covering the surface of the particles in the first particle group with a metal component-containing liquid that serves as a precursor for the particles in the second particle group. (6) The process includes heating the particles in the first particle group that have been covered with the metal component-containing liquid in the above step, thereby arranging the particles in the second particle group on the surface of the particles in the first particle group.

[0044] (Feature 5) A suitable manufacturing method for producing the ceramic powder of the present invention includes a step of covering the surface of particle 1, which is included in the first particle group, with a metal component-containing liquid that serves as a precursor for particle 2, which is included in the second particle group.

[0045] Suitable materials for particle 1 are as described above, and commercially available metal oxide particles can also be used, for example. Surface modification of particle 1 may be performed to improve the wettability and adhesion of the surface of particle 1. Methods of surface modification include irradiation with energy rays, such as ultraviolet rays, and application or immersion treatment of surface modifiers such as silane coupling agents or phosphonic acid derivatives.

[0046] The metal oxide-containing liquid that serves as a precursor to particle 2 is a solution or dispersion of a composition that can be converted into particle 2 by heating. Examples of the composition include hydrolyzable or thermally decomposable organometallic compounds. More specifically, metal complexes such as metal alkoxides, organic acid salts, and β-diketone complexes of the above metals can be used. Another example of a metal complex is an amine complex. Examples of β-diketones include acetylacetone (=2,4-pentanedione), heptafluorobutanoylpivaloylmethane, dipivaloylmethane, trifluoroacetylacetone, and benzoylacetone. β-diketone complexes can be considered a form of metal alkoxide because they are coordinated to the metal by an oxygen element.

[0047] For example, when the main component of particle 2 is terbium oxide, one method is to include a terbium alkoxide in the metal component-containing solution of the precursor. Examples of terbium alkoxides include terbium-n-butoxide, terbium-t-butoxide, terbium-methoxypropoxide, terbium-2,4-pentanedione, terbium-methoxyethoxide, terbium-2,4-pentanedione, and terbium-2,2,6,6-tetramethyl-3,5-heptanedione.

[0048] Examples of praseodymium alkoxides include praseodymium-n-butoxide, praseodymium-t-butoxide, praseodymium-methoxypropoxide, praseodymium-hexafluoropentanedione, praseodymium-2,4-pentanedione, praseodymium-2,2,6,6-tetramethyl-3,5-heptanedione, and praseodymium(III)-6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate. Alkoxides of other metal species are similar.

[0049] The metal alkoxide and its solution may be commercially available, or it may be synthesized by the method described in the claims and section

[0003] of Japanese Patent Publication No. 9-157272. The composition containing each component metal can be prepared as a metal component-containing liquid by dissolving or dispersing it in a suitable solvent. The solvent is appropriately selected from various known solvents considering dispersibility and applicability.

[0050] Solvents used in preparing metal component-containing solutions include alcohol-based solvents such as methanol, ethanol, n-butanol, n-propanol, and isopropanol; ether-based solvents such as tetrahydrofuran and 1,4-dioxane; cellosolve-based solvents such as methyl cellosolve and ethyl cellosolve; amide-based solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; and nitrile-based solvents such as acetonitrile. When using metal alkoxides as the metal component, it is preferable to use alcohol-based solvents.

[0051] The amount of solvent used in preparing the metal component-containing liquid is not particularly limited, but adjusting the amount of solvent so that the metal solid content concentration is approximately 5% to 20% by mass is suitable for coating the surface of particle 1.

[0052] The method for covering the surface of particle 1 with the metal component-containing liquid is not particularly limited, but includes methods such as immersing particle 1 in the liquid, adding the liquid to particle 1, or spraying the liquid onto particle 1.

[0053] (Feature 6) After the above step, a step is performed to form particle 2 on the surface of particle 1 by simultaneously heating particle 1 and the metal component-containing liquid attached to its surface.

[0054] This heating causes the solvent in the metal component-containing liquid to volatilize, and the metal component is further oxidized and atomized, resulting in particle 2 precipitating on the surface of particle 1. If the precursor composition is hydrolyzable, the hydrolysis reaction proceeds and a bond between metal and oxygen is formed, resulting in the formation of fine metal oxide particles with a particle size of less than 1 μm. Furthermore, since particle 2 is formed by a chemical reaction, the bond with the base particle 1 is strong, and the contact area is large. Therefore, the heat transfer rate from particle 2 to particle 1 increases when irradiated with laser light.

[0055] The optimal heating temperature is selected depending on the type of material, but it is preferable to perform stepwise heating, for example, by heating to around 150°C to 300°C to volatilize the solvent, and then heating to around 550°C to 750°C to form particles.

[0056] The heating method is not limited, and a dryer, hot plate, electric furnace, atmosphere furnace, etc., can be used. After heating, the obtained powder may be further crushed to make it finer, or the powder may be sieved to standardize the particle size.

[0057] (How to use) The method for manufacturing ceramic structures (formed objects) using the ceramic molding powder of the present invention as a raw material and irradiating it with a laser has the following characteristics. (7) The present invention comprises the step (i) of placing the ceramic molding powder of the present invention into a laser irradiation section. (8) The process includes (ii) selectively irradiating the ceramic molding powder placed in the laser irradiation section with laser light to sinter or melt the ceramic molding powder and then solidify it (including the case of sintering). (9) The process includes step (iii) of manufacturing a ceramic structure (form) by repeating steps (i) and (ii).

[0058] (Feature 7) The method for placing the ceramic molding powder of the present invention in the laser irradiation section is as described in Feature 1. For example, in the apparatus shown in Figure 1, the ceramic molding powder of the present invention, filled in the powder container 11, can be placed in the molding stage section 12 by the recoater section 13. Furthermore, as explained in Feature 1 using Figure 2, by ejecting the ceramic molding powder to a predetermined location and irradiating that location with laser light, it is possible to form a molded object on a curved base.

[0059] (Feature 8) The method for selecting the laser beam to solidify the ceramic molding powder after melting is as described in Feature 1. As mentioned above, in the present invention, sintering is also considered a form of operation in which the material is solidified after melting. Strictly speaking, sintering refers to a reaction in which the powder is bound together in a solid phase (without melting) to promote grain growth, while melting refers to a reaction in which the powder becomes a liquid phase, but this also includes an intermediate state in which solid and liquid phases are mixed. Prior to step (ii), it is preferable to spread the ceramic molding powder placed in the laser irradiation section and then irradiate it with laser light, as this allows for the production of a denser molded product.

[0060] (Feature 9) Performing steps (i) and (ii) once each yields a patterned single-layer ceramic object. By spreading new ceramic molding powder on top of this and repeating steps (i) and (ii) with different patterns, a ceramic object with a desired three-dimensional shape can be manufactured.

[0061] After molding, heat treatment may be performed to increase the density and strength of the molded object, or to re-oxidize it. At that time, it is also possible to apply or impregnate the object with organic or inorganic compounds as a glaze. There are no restrictions on the heating method; resistance heating, induction heating, infrared lamp heating, laser heating, electron beam heating, etc., can be used depending on the purpose.

[0062] [Examples] The ceramic powder of the present invention, its manufacturing method, and its usage method will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0063] (Example 1) The ceramic powder of the present invention was manufactured by the following procedure. For the first particle group, we used a mixture of commercially available industrial products: Al2O3 powder (purity 99% or higher, average particle size 20 μm) and Gd2O3 powder (purity 99% or higher, average particle size 20 μm), mixed in a mass ratio of 1:1.

[0064] As a metal component-containing solution that serves as a precursor for the particles constituting the second group of particles, a metal alkoxide solution of terbium, a hydrolyzable organometallic compound, was prepared. Specifically, terbium-2,4-pentanedione, which is commercially available as a general reagent, was dissolved in 1-methoxy-2-propanol as a solvent to prepare a solution with a converted concentration of metal oxide (Tb4O7) of 10% by mass.

[0065] 97g of the first group of particles was measured and placed in a high-purity alumina container, and 25g of the metal component-containing liquid was added and thoroughly stirred.

[0066] The container was placed in an electric furnace under an atmospheric environment and subjected to heat treatment by running a program that maintained a maximum temperature of 600°C for 3 hours. After the electric furnace cooled to room temperature, the contents were removed from the alumina container and crushed to obtain the ceramic powder of the present invention.

[0067] Figure 4 shows an image of a portion of the manufactured powder observed under an electron microscope. Figure 4 is an image observed at 5000x magnification to show a typical structure of the ceramic powder of Example 1, but other particles constituting the powder had a similar structure. The spherical particles with a diameter of approximately 20 μm that occupy most of the observation field in Figure 4 were found to be aluminum oxide according to SEM-EDX analysis and X-ray diffraction measurement, and were identified as particle 1, which is included in the first particle group. The group of fine particles adhering to the surface of particle 1 were found to be terbium oxide (Tb4O7) according to SEM-EDX analysis and X-ray diffraction measurement, and were identified as the second particle group. The average particle diameter of the second particle group, obtained by image processing of the observed image, was estimated to be at most 0.3 μm. Since the second particle group also includes particles too fine to be recognized by image processing, the actual flat particle diameter is thought to be even smaller. The coverage rate of particle 1 by particle 2, which is included in the second particle group, calculated from the observed image was approximately 14 area %. Furthermore, although not visible in the observation image in Figure 4, there was also an aggregate of gadolinium oxide (particle 1) in the vicinity of this particle, with similarly fine particles (particle 2) attached to it.

[0068] When the ceramic powder of Example 1 was heated and dissolved in dilute sulfuric acid, and its composition was analyzed by ICP emission spectrometry, the mass proportions of Al2O3, Gd2O3, and Tb4O7 were 46.6, 50.3, and 2.46, respectively. The content of other components was less than 0.1% by mass relative to the ceramic powder. Al2O3 and Gd2O3 constituted the first particle group, accounting for a total of 96.9% by mass.

[0069] (Examples 2 and 3) The ceramic powder of the present invention was manufactured in the same manner as in Example 1, except that the raw material types and mixing ratios were changed according to Table 1. As the zirconium oxide which is the first particle group, ZrO2 powder (purity 99% or more, average particle diameter 15 μm) commercially available as an industrial product was used. As the metal alkoxide of praseodymium, praseodymium-2,4-pentanedionate commercially available as a general reagent was used. The addition amount of the metal component-containing liquid which becomes the precursor of the second particle group with respect to the first particle group was appropriately changed.

[0070] (Example 4 and Example 5) The ceramic powder of the present invention was produced in the same manner as in Examples 1 to 3, except that the raw material species and the blending ratio were changed according to Table 1. However, instead of using the one derived from the metal alkoxide solution for the second particle group, commercially available Tb4O7 powder (average particle diameter: 3 μm) and Pr6O 11 powder (average particle diameter: 4 μm) were used.

[0071] (Comparative Examples 1 to 3) According to the blending ratio shown in Table 1, a comparative ceramic powder was produced in the same manner as in Example 1. However, in Comparative Example 1, the ceramic powder was composed of only the first particle group without adding the second particle group. In Comparative Example 2, without using the metal component-containing liquid which becomes the precursor of the second particle group, the powder having an average particle diameter of 40 μm created by calcining commercially available Tb4O7 powder in an electric furnace at 700 ° C and Pr6O 11 powder (average particle diameter: 50 μm) were mixed to constitute a powder for ceramic shaping.

[0072] Table 1 TIFF0007830405000001.tif45170

[0073] (Use of the powder for ceramic shaping) To clarify the differences in the molding speed of the ceramic powders in each example and comparative example, each powder was spread to a thickness of approximately 50 μm on a flat alumina substrate with a sufficient surface area, and then the surface was irradiated with a laser. The laser focal size was set to 100 μm and the output power to 30 W. The laser beam was scanned over a length of 4.5 mm, drawing two lines at a pitch of 50 μm. The scanning speed was performed at 100 mm / sec, 250 mm / sec, 500 mm / sec, and 1000 mm / sec, and the melting state was compared. Table 2 shows the results of microscopic observations to determine whether the powder in the laser irradiation area solidified and formed into a ceramic-like structure after laser irradiation.

[0074] When the ceramic powders of Examples 1, 2, and 3 were irradiated with laser light, ceramic-like objects could be obtained at any scanning speed. In particular, at scanning speeds of 250 to 1000 mm / second, the width of the boundary between the laser-irradiated and unirradiated areas was 15 μm or less, resulting in high fabrication accuracy. When ceramic objects with excellent fabrication accuracy were obtained in this way, "a" was recorded in Table 2. On the other hand, at a scanning speed of 100 mm / second, there was fluctuation in the boundary line of the ceramic object, and its width was somewhat large at about 40 μm. In this way, although the conditions were sufficient to obtain ceramic objects, there were some shortcomings in fabrication accuracy, so "b" was recorded in Table 2.

[0075] Thus, the ceramic molding powder that satisfies the requirements of the present invention enables ceramic molding even at high scanning speeds, and can reduce the time required to obtain the desired molded object by more than double.

[0076] When the ceramic powder of Comparative Example 1 was irradiated with laser light, a ceramic object was obtained at a scanning speed of 100 mm / second, but its boundaries were irregular in shape, and there were some areas where melting had not progressed. Furthermore, when the scanning speed was 250 mm / second or higher, melting did not progress, and no conversion from powder to object was observed. In cases where a ceramic object could not be obtained with sufficient accuracy, "c" was recorded in Table 2.

[0077] When laser light was irradiated onto the ceramic powders of Comparative Examples 2 and 3, highly accurate molded objects were obtained at scanning speeds of 100-250 mm / second. However, at a scanning speed of 500 mm / second, the molded objects contained a small amount of powder, and at 1000 mm / second, melting did not progress, and no conversion from powder to molded object was observed.

[0078] [Table 1]

[0079] (Example 4) The ceramic fabrication powders from Examples 1 to 3 were fed into the SLS apparatus shown in Figure 1, and the additive manufacturing process was repeated multiple times with a laser scanning speed of 1000 mm / second to obtain three-dimensional ceramic fabricated objects of the desired shape. (Industrial applicability)

[0080] By using the ceramic molding powder of the present invention, finely detailed ceramic objects can be obtained through three-dimensional molding, making it applicable in the field of ceramic parts requiring complex shapes. [Explanation of symbols]

[0081] 1. Particles included in the first group of particles 2, 3 Particles included in the second group of particles 11 powder powder 12. Modeling Stage Section 13. Recoater Section 14. Scanner section 15 Lasers 20 Base 21 Cladding Nozzle 22 Powder supply hole 23 Lasers

Claims

1. The process of arranging ceramic powder, The process involves irradiating the ceramic powder with laser light, A method for manufacturing ceramic structures, which involves repeating the process to form a molded object, The ceramic powder comprises composite particles consisting of first particles containing a first inorganic compound and second particles containing a second inorganic compound, which have a smaller particle size than the first particles and are attached to the surface of the first particles. A manufacturing method characterized in that, upon irradiation, the second particle absorbs the laser light and generates heat, thereby causing the portion of the powder irradiated with the laser light to become liquid, and further, a solidification reaction occurs in the liquid, resulting in the molded object having the result of the solidification reaction.

2. The first inorganic compound is an oxide, nitride, oxynitride, carbide, or boride. The second inorganic compound is an oxide, nitride, oxynitride, or boride. The manufacturing method according to claim 1, characterized in that it

3. The first inorganic compound is aluminum oxide. The manufacturing method according to claim 2, characterized in that it

4. The first inorganic compound is silicon dioxide or zirconium oxide. The manufacturing method according to claim 1 or 2, characterized in that it is a method of production according to claim 1 or 2.

5. The first inorganic compound is a nitride, oxynitride, carbide, or boride. The second inorganic compound is an oxide, nitride, oxynitride, carbide, or boride. The manufacturing method according to claim 1, characterized in that it

6. The result of the aforementioned coagulation reaction is a eutectic structure. The manufacturing method according to any one of claims 1 to 5, characterized by the above.

7. Upon irradiation, the second inorganic compound undergoes a compositional change, causing the absorption rate of the laser light to decrease. The manufacturing method according to any one of claims 1 to 6, characterized by the above.

8. The second inorganic compound is an oxide, The decrease in absorption rate is due to a change in the valence of elements other than oxygen that constitute the second inorganic compound. The manufacturing method according to claim 7, characterized in that it

9. The second inorganic compound is an oxide of a metal element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Hf, Ta, W, In, Sn, Bi, Ce, Pr, Sm, Eu, Tb, and Yb. The manufacturing method according to any one of claims 1 to 8, characterized by the above.

10. The first particle contains two or more composite inorganic compounds. The manufacturing method according to any one of claims 1 to 9.

11. The first particle contains a first type of metal oxide and a second type of metal oxide. The manufacturing method according to any one of claims 1 to 10, characterized by the above.

12. The second type of metal oxide is a rare earth metal oxide. The manufacturing method according to claim 11, characterized in that it

13. In the ceramic powder, the mass of the second inorganic compound is 2% or more and 20% or less relative to the mass of the first inorganic compound. The manufacturing method according to any one of claims 1 to 10, characterized by the above.

14. In the ceramic powder, the sum of the mass of the first inorganic compound and the mass of the second inorganic compound is 80% or more of the mass of the ceramic powder. The manufacturing method according to any one of claims 1 to 13, characterized by the above.

15. In the ceramic powder, the mass of the first inorganic compound is 70% or more of the mass of the ceramic powder. The manufacturing method according to any one of claims 1 to 14.

16. In the ceramic powder, the average particle diameter of the first particle group consisting of particles containing the first inorganic compound is 10 μm or more and 100 μm or less. The manufacturing method according to any one of claims 1 to 15, characterized by the above.

17. In the ceramic powder, the average particle diameter of the second particle group, which consists of particles containing the second inorganic compound, is 0.05 μm or more and less than 10 μm. The manufacturing method according to any one of claims 1 to 16, characterized by the above.

18. The laser light is an Nd:YAG laser or a Yb fiber laser. The manufacturing method according to any one of claims 1 to 17, characterized by the above.

19. The aforementioned molded object is formed by powder bed deposition. The manufacturing method according to any one of claims 1 to 18, characterized by the above.

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