JP2017178691A - Production method of alumina sintered body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method by which there can be obtained an alumina sintered body having sufficient smoothness even without grinding and polishing.SOLUTION: The method for producing an alumina sintered body of the present invention provides an aluminum sintered body in a second sintered state by sintering an alumina compact via an aluminum intermediate in a first sintered state. In this production method, surroundings of the alumina intermediate is converted to an atmosphere containing Al at least in the step where an alumina intermediate is converted to an alumina sintered body. According to this production method, an alumina sintered body having sufficient smoothness can be obtained even without grinding and polishing. The reason for this is not clear but it is presumed that, during the course of conversion from the alumina intermediate to the alumina sintered body, in-plane surface smoothness of the sintered particles is imoproved and, moreover, the Al-containing atmosphere effectively prevents generation of a step in the grain boundary present between the sintered particles.SELECTED DRAWING: None

Description

本発明は、アルミナ焼結体の製法に関する。   The present invention relates to a method for producing an alumina sintered body.

従来より、アルミナ成形体を焼成してアルミナ焼結体を製造する方法がいくつも報告されている。例えば、特許文献１には、アルミニウム粉末とアルミナ粉末との原料混合粉を成形し、得られた成形体を酸化性雰囲気中において反応焼結することによりアルミナ焼結体を得る方法が開示されている。この方法によれば、成形体からの寸法変化率が小さく、また割れや変形の発生が少なく、表面粗さが良好なアルミナ焼結体が得られると説明されている。特許文献２には、アルミナ粉末と、高分子結合剤であるポリビニルアルコールと、高分子潤滑剤であるステアリン酸とを含むスラリー状の懸濁液を噴霧乾燥して顆粒を生成し、その顆粒を乾式加圧成形した後に、脱脂、焼成してアルミナ焼結体を得る方法が開示されている。この方法によれば、平坦度（同一面内の任意の３点の高低差）が３０〜５０μｍ程度のアルミナ焼結体が得られるため、研削加工や研磨加工が不要であると説明されている。   Conventionally, a number of methods for producing an alumina sintered body by firing an alumina molded body have been reported. For example, Patent Document 1 discloses a method of obtaining an alumina sintered body by forming a raw material mixed powder of aluminum powder and alumina powder and subjecting the obtained molded body to reaction sintering in an oxidizing atmosphere. Yes. According to this method, it is described that an alumina sintered body having a small surface deformation ratio with a small dimensional change rate from the molded body and less cracking and deformation can be obtained. In Patent Document 2, a slurry-like suspension containing alumina powder, polyvinyl alcohol as a polymer binder, and stearic acid as a polymer lubricant is spray-dried to produce granules. A method of obtaining an alumina sintered body by degreasing and firing after dry pressure molding is disclosed. According to this method, it is described that an alumina sintered body having a flatness (a height difference of three arbitrary points in the same plane) of about 30 to 50 μm can be obtained, so that grinding and polishing are unnecessary. .

特開平９−２５５４１２号公報Japanese Patent Laid-Open No. 9-255412 特許第５１８１１９８号公報Japanese Patent No. 5181198

しかしながら、上述した２つの特許文献に開示されたアルミナ焼結体よりも平滑性の高いアルミナ焼結体を研削・研磨加工を施すことなく得られる製法の開発が望まれている。   However, development of a manufacturing method that can obtain an alumina sintered body having higher smoothness than the alumina sintered bodies disclosed in the two patent documents described above without grinding and polishing is desired.

本発明はこのような課題を解決するためになされたものであり、研削・研磨加工を施さなくても十分平滑性の高いアルミナ焼結体が得られる製法を提供することを主目的とする。   The present invention has been made to solve such problems, and has as its main object to provide a production method capable of obtaining an alumina sintered body having sufficiently high smoothness without being subjected to grinding / polishing.

本発明のアルミナ焼結体の製法は、
アルミナ成形体を焼成して第１の焼結状態のアルミナ中間体を経て第２の焼結状態のアルミナ焼結体を得るアルミナ焼結体の製法であって、
少なくとも前記アルミナ中間体から前記アルミナ焼結体に変化する段階では、前記アルミナ中間体の周りをＡｌ含有雰囲気にする
ものである。 The method for producing the alumina sintered body of the present invention is as follows.
A method for producing an alumina sintered body by firing an alumina molded body to obtain an alumina sintered body in a second sintered state through an alumina intermediate in a first sintered state,
At least in the stage of changing from the alumina intermediate to the alumina sintered body, an atmosphere containing Al is formed around the alumina intermediate.

本発明の製法によれば、研削・研磨加工を施さなくても十分平滑性の高いアルミナ焼結体を得ることができる。その理由は定かではないが、アルミナ中間体からアルミナ焼結体に至る途中で、焼結粒子の面内での平坦性を改善するだけでなく、焼結粒子同士の間に存在する粒界に段差が発生するのをＡｌ含有雰囲気が有効に抑制したのではないかと推察される。   According to the production method of the present invention, an alumina sintered body having sufficiently high smoothness can be obtained without grinding or polishing. The reason for this is not clear, but on the way from the alumina intermediate to the alumina sintered body, not only improves the flatness of the sintered particles in the plane, but also the grain boundaries existing between the sintered particles. It is speculated that the Al-containing atmosphere effectively suppresses the generation of the step.

板状アルミナ粒子の模式図で、（ａ）は平面図、（ｂ）は正面図。It is a schematic diagram of plate-like alumina particles, (a) is a plan view, (b) is a front view.

以下に、本発明の一実施形態について説明する。本実施形態のアルミナ焼結体の製法は、アルミナ成形体を焼成して第１の焼結状態のアルミナ中間体を経て第２の焼結状態のアルミナ焼結体を得る製法であって、少なくとも前記アルミナ中間体から前記アルミナ焼結体に変化する段階では、前記アルミナ中間体の周りをＡｌ含有雰囲気にするものである。   Hereinafter, an embodiment of the present invention will be described. The method for producing an alumina sintered body of the present embodiment is a production method for obtaining an alumina sintered body in a second sintered state by firing an alumina molded body through an alumina intermediate in a first sintered state, In the stage of changing from the alumina intermediate to the alumina sintered body, an atmosphere containing Al is formed around the alumina intermediate.

まず、アルミナ成形体を作製する。具体的には、アルミナを主成分とする原料粉末を所定の形状に成形してアルミナ成形体を得る。成型方法としては、特に限定されるものではなく、例えばテープ成形、押出成形、鋳込み成形、射出成形、一軸プレス成形、ゲルキャストなどが挙げられる。原料粉末としては、１種類のアルミナ粉末を用いてもよいし、平均粒径の異なる２種以上のアルミナ粉末の混合物を用いてもよいし、形状の異なる２種以上のアルミナ粉末の混合物を用いてもよい。配向性の良好なアルミナ焼結体を得るには、板状アルミナ粉末と微細アルミナ粉末との混合物を原料粉末として用いるのが好ましい。原料粉末には、アルミナ粉末以外にＭｇＯ等の焼結助剤粉末を添加してもよいし、バインダーや可塑剤、分散剤、分散媒などを適宜添加してもよい。アルミナ成形体は、原料粉末に有機物を添加した場合にはその有機物が分解・蒸発する温度で脱脂を行ったあと次工程で用いるのが好ましい。   First, an alumina molded body is produced. Specifically, a raw material powder mainly composed of alumina is formed into a predetermined shape to obtain an alumina molded body. The molding method is not particularly limited, and examples thereof include tape molding, extrusion molding, casting molding, injection molding, uniaxial press molding, and gel casting. As the raw material powder, one kind of alumina powder may be used, a mixture of two or more kinds of alumina powders having different average particle diameters may be used, or a mixture of two or more kinds of alumina powders having different shapes may be used. May be. In order to obtain an alumina sintered body with good orientation, it is preferable to use a mixture of plate-like alumina powder and fine alumina powder as a raw material powder. In addition to the alumina powder, a sintering aid powder such as MgO may be added to the raw material powder, or a binder, a plasticizer, a dispersant, a dispersion medium, or the like may be added as appropriate. When an organic substance is added to the raw material powder, the alumina molded body is preferably used in the next step after degreasing at a temperature at which the organic substance decomposes and evaporates.

次に、アルミナ成形体を焼成して第１の焼結状態のアルミナ中間体を経て第２の焼結状態のアルミナ焼結体を得る。その際、少なくともアルミナ中間体からアルミナ焼結体に変化する段階では、アルミナ中間体の周りをＡｌ含有雰囲気にする。こうすることにより、研削・研磨加工を施さなくても十分平滑性の高いアルミナ焼結体を得ることができる。Ａｌ含有雰囲気とは、アルミナ中間体を戴置する空間内に、アルミナ中間体とは別にＡｌを含む化合物を共存させた状態をいう。Ａｌ化合物としては、Ａｌを含む限り化合物の材質には特に限定はないが、アルミナ、スピネル（ＭｇＡｌ₂Ｏ₄）、窒化アルミニウムが好ましく、このうちアルミナが特に好ましい。また、化合物の形態には特に限定はないが、固体が好ましく、特に粉末が好ましい。 Next, the alumina compact is fired to obtain an alumina sintered body in the second sintered state through the alumina intermediate in the first sintered state. At that time, at least at the stage of changing from the alumina intermediate to the alumina sintered body, an atmosphere containing Al is formed around the alumina intermediate. By doing so, an alumina sintered body having sufficiently high smoothness can be obtained without performing grinding and polishing. The Al-containing atmosphere refers to a state in which a compound containing Al is allowed to coexist in addition to the alumina intermediate in the space where the alumina intermediate is placed. As the Al compound, the material of the compound is not particularly limited as long as Al is contained, but alumina, spinel (MgAl ₂ O ₄ ), and aluminum nitride are preferable, and among these, alumina is particularly preferable. The form of the compound is not particularly limited, but a solid is preferable, and a powder is particularly preferable.

第２の焼結状態は、第１の焼結状態と比べて焼結が進んだ状態であり、例えば開気孔率及び閉気孔率の少なくとも一方が第１の焼結状態より低くなっている状態や相対密度（焼結体密度の理論密度に対する比）が第１の焼結状態より高い状態などをいう。第１の焼結状態は、開気孔率や閉気孔率が小さい方が好ましく、特に開気孔率が小さいほうが好ましい。開気孔率は３％以下が好ましく、２％以下がより好ましく、１％以下が更に好ましく、実質ゼロであるのが特に好ましい。第２の焼結状態は、開気孔率や閉気孔率が第１の焼結状態より小さくなっていることが好ましく、実質ゼロであることが特に好ましい。なお、開気孔率が実質ゼロとは、開気孔率がゼロの場合のほか、開気孔の測定条件下において開気孔が発見されなかった場合も含む意である。   The second sintered state is a state in which the sintering is advanced as compared with the first sintered state, for example, a state in which at least one of the open porosity and the closed porosity is lower than the first sintered state. Or the relative density (ratio of the sintered body density to the theoretical density) is higher than the first sintered state. In the first sintered state, it is preferable that the open porosity and the closed porosity are small, and it is particularly preferable that the open porosity is small. The open porosity is preferably 3% or less, more preferably 2% or less, still more preferably 1% or less, and particularly preferably substantially zero. In the second sintered state, the open porosity and closed porosity are preferably smaller than those in the first sintered state, and particularly preferably substantially zero. In addition, the meaning that the open porosity is substantially zero includes not only the case where the open porosity is zero, but also the case where no open pore is found under the measurement conditions of the open pore.

アルミナ成形体を焼成してアルミナ中間体とする工程（前段階）では、所定の温度で焼成を行う。このときの圧力は常圧でも常圧を超える圧力でもよい。ここで、所定の温度とは、アルミナ成形体のアルミナ粒子同士の少なくとも一部が焼結する温度をいい、１０００〜１６５０℃の範囲で設定された温度が好ましい。焼成雰囲気は、Ａｌ含有雰囲気であってもよいが、特にこれに限定されず、大気雰囲気であっても不活性ガス雰囲気であっても真空雰囲気であってもよい。なお、アルミナ成形体は炉内に直接配置してもよいが、炉内の汚染やハンドリングの観点から、容器に入れた状態で炉内に配置するのが好ましい。その場合、容器の材質は特に限定されないが、焼成中に揮発する成分を含まず、アルミナと反応しないものが好ましい。   In the step (previous stage) of firing the alumina molded body to obtain an alumina intermediate, firing is performed at a predetermined temperature. The pressure at this time may be a normal pressure or a pressure exceeding the normal pressure. Here, the predetermined temperature means a temperature at which at least a part of the alumina particles of the alumina molded body is sintered, and a temperature set in a range of 1000 to 1650 ° C. is preferable. The firing atmosphere may be an Al-containing atmosphere, but is not particularly limited thereto, and may be an air atmosphere, an inert gas atmosphere, or a vacuum atmosphere. The alumina molded body may be disposed directly in the furnace, but it is preferably disposed in the furnace in a state of being put in a container from the viewpoint of contamination in the furnace and handling. In that case, although the material of a container is not specifically limited, The thing which does not contain the component volatilized during baking and does not react with an alumina is preferable.

また、アルミナ中間体を焼成してアルミナ焼結体とする工程（後段階）では、Ａｌ含有雰囲気下、前段階の焼成温度（所定の温度）を超える温度で焼成するのが好ましい。このときの圧力は、常圧でも常圧を超える圧力でもよいが、常圧を超える圧力が好ましい。後段階の温度は、１７００〜２０５０℃（好ましくは１７５０〜２０００℃）の範囲で設定された温度としてもよい。後段階では、Ａｌ含有雰囲気下、熱間等方圧加圧法（ＨＩＰ）で焼成してアルミナ焼結体を得るようにするのが好ましい。ＨＩＰ焼成は、Ａｌ含有雰囲気下でアルミナ中間体を焼成するのに適しているからである。ＨＩＰ焼成の場合の圧力は、緻密化の観点では、２０ＭＰａ以上が好ましく、５０ＭＰａ以上がより好ましく、１００ＭＰａ以上が更に好ましく、１５０ＭＰａ以上が最も好ましく、特に上限はない。但し、装置コストの観点では、圧力が低い方がよく、２００ＭＰａ以下が現実的である。したがって、１５０ＭＰａ以上、２００ＭＰａ以下が特に好ましい。アルミナ中間体をＡｌ含有雰囲気下でＨＩＰ焼成するにあたり、アルミナ中間体を非気密な容器に入れたあと該容器をアルミナ粉末で覆うか該容器内にアルミナ粉末を共存させた状態で、不活性ガス中でＨＩＰ焼成するのが好ましい。こうすれば、ＨＩＰ焼成時、非気密な容器に収容されたアルミナ中間体の周りの雰囲気は、その容器を覆うアルミナ粉末又はその容器内に共存するアルミナ粉末によってアルミナ雰囲気（アルミナを含有する不活性ガス雰囲気）になる。不活性ガスとは、例えば窒素ガスやアルゴンガス、ヘリウムガス、ネオンガスなどが挙げられる。容器の材質は特に限定されないが、焼成中に揮発する成分を含まず、アルミナと反応しないものが好ましい。   Further, in the step (post-stage) of firing the alumina intermediate to form an alumina sintered body, firing is preferably performed at a temperature exceeding the firing temperature (predetermined temperature) in the previous stage in an Al-containing atmosphere. The pressure at this time may be a normal pressure or a pressure exceeding the normal pressure, but a pressure exceeding the normal pressure is preferable. The post-stage temperature may be a temperature set in the range of 1700 to 2050 ° C. (preferably 1750 to 2000 ° C.). In a later stage, it is preferable to obtain an alumina sintered body by firing by hot isostatic pressing (HIP) in an Al-containing atmosphere. This is because HIP firing is suitable for firing an alumina intermediate in an Al-containing atmosphere. The pressure in the case of HIP firing is preferably 20 MPa or more, more preferably 50 MPa or more, still more preferably 100 MPa or more, most preferably 150 MPa or more, and there is no particular upper limit in terms of densification. However, from the viewpoint of apparatus cost, it is better that the pressure is low, and 200 MPa or less is realistic. Therefore, 150 MPa or more and 200 MPa or less is particularly preferable. In HIP firing of an alumina intermediate in an Al-containing atmosphere, the alumina intermediate is placed in a non-airtight container and then the container is covered with alumina powder or the alumina powder is allowed to coexist in the container. Of these, HIP firing is preferred. In this way, during the HIP firing, the atmosphere around the alumina intermediate housed in the non-airtight container is changed to an alumina atmosphere (inactive containing alumina) by the alumina powder covering the container or the alumina powder coexisting in the container. Gas atmosphere). Examples of the inert gas include nitrogen gas, argon gas, helium gas, neon gas, and the like. The material of the container is not particularly limited, but preferably does not contain a component that volatilizes during firing and does not react with alumina.

前段階と後段階は、２回に分けて別々に行ってもよいし、１つの炉内で連続して行ってもよい。前段階と後段階を２回に分けて別々に行う場合、前段階のアルミナ中間体を一旦炉から取り出し、後段階でそのアルミナ中間体を同じ炉又は別の炉に入れて焼成するのが好ましい。その場合、少なくとも後段階の工程の焼成雰囲気はＡｌ含有雰囲気とする必要がある。一方、前段階と後段階を１つの炉内で連続して行う場合、焼成雰囲気は当初からＡｌ含有雰囲気とする必要がある。   The pre-stage and the post-stage may be performed separately in two steps, or may be performed continuously in one furnace. In the case where the former stage and the latter stage are performed separately in two steps, it is preferable that the alumina intermediate in the former stage is once taken out from the furnace, and the alumina intermediate is fired in the same furnace or another furnace in the latter stage. . In that case, the firing atmosphere in at least the subsequent step needs to be an Al-containing atmosphere. On the other hand, when the pre-stage and the post-stage are continuously performed in one furnace, the firing atmosphere needs to be an Al-containing atmosphere from the beginning.

なお、本発明は上述した実施形態に何ら限定されることはなく、本発明の技術的範囲に属する限り種々の態様で実施し得ることはいうまでもない。   It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

以下に、本発明の実施例について説明する。なお、以下の実施例は本発明を何ら限定するものではない。   Examples of the present invention will be described below. The following examples do not limit the present invention.

［実験例１］
１．アルミナ焼結体の作製
（１）板状アルミナ粉末の作製
高純度γ−アルミナ粉末（ＴＭ−３００Ｄ、大明化学製）９６質量部と、高純度ＡｌＦ₃粉末（関東化学製、鹿特級）４質量部と、種結晶として高純度α−アルミナ粉末（ＴＭ−ＤＡＲ、大明化学製、Ｄ５０＝１μｍ）０．１７質量部とを、溶媒をＩＰＡ（イソプロピルアルコール）としてφ２ｍｍのアルミナボールを用いて５時間ポットミルで混合した。ポットミル混合した後、ＩＰＡをエバポレータにて乾燥し、混合粉末を得た。得られた混合粉末３００ｇを純度９９．５質量％の高純度アルミナ製のさや（容積７５０ｃｍ³）に入れ、純度９９．５質量％の高純度アルミナ製の蓋をして電気炉内でエアフロー中、９００℃、３時間熱処理した。エアーの流量は２５０００ｃｃ／ｍｉｎとした。熱処理後の粉末を大気中、１１５０℃で４２．５時間アニール処理した後、φ２ｍｍのアルミナボールを用いて４時間粉砕して平均粒径２μｍ、厚み０．３μｍ、アスペクト比約７の板状アルミナ粉末を得た。粒子の平均粒径、平均厚み、アスペクト比は、走査型電子顕微鏡（ＳＥＭ）で板状アルミナ粉末中の任意の粒子１００個を観察して決定した。平均粒径は、粒子板面の長軸長の平均値、平均厚みは、粒子の短軸長（厚み）の平均値、アスペクト比は、平均粒径／平均厚みである。図１は、板状アルミナ粒子の模式図であり、（ａ）は平面図、（ｂ）は正面図である。板状アルミナ粒子は、平面視したときの形状が略六角形状であり、その粒径は図１（ａ）に示したとおりであり、厚みは図１（ｂ）に示したとおりである。 [Experimental Example 1]
1. Production of sintered alumina (1) Production of plate-like alumina powder 96 parts by mass of high-purity γ-alumina powder (TM-300D, manufactured by Daimei Chemical Co., Ltd.) and 4 masses of high-purity AlF ₃ powder (manufactured by Kanto Chemical Co., Inc.) 5 parts by using 0.17 parts by mass of high-purity α-alumina powder (TM-DAR, manufactured by Daimei Chemical Co., D50 = 1 μm) as a seed crystal and a φ2 mm alumina ball with IPA (isopropyl alcohol) as a solvent. Mix in pot mill. After pot mill mixing, IPA was dried with an evaporator to obtain a mixed powder. 300 g of the obtained mixed powder was put in a sheath made of high-purity alumina having a purity of 99.5% by mass (volume: 750 cm ³ ), covered with a lid made of high-purity alumina having a purity of 99.5% by mass, and airflowing in an electric furnace. , 900 ° C. for 3 hours. The air flow rate was 25000 cc / min. The heat-treated powder is annealed in the atmosphere at 1150 ° C. for 42.5 hours, and then pulverized for 4 hours using φ2 mm alumina balls to obtain a plate-like alumina having an average particle diameter of 2 μm, a thickness of 0.3 μm, and an aspect ratio of about 7. A powder was obtained. The average particle diameter, average thickness, and aspect ratio of the particles were determined by observing 100 arbitrary particles in the plate-like alumina powder with a scanning electron microscope (SEM). The average particle size is the average value of the major axis length of the particle plate surface, the average thickness is the average value of the minor axis length (thickness) of the particle, and the aspect ratio is the average particle size / average thickness. FIG. 1 is a schematic view of plate-like alumina particles, where (a) is a plan view and (b) is a front view. The plate-like alumina particles have a substantially hexagonal shape when viewed in plan, the particle size is as shown in FIG. 1 (a), and the thickness is as shown in FIG. 1 (b).

（２）テープ成形
上記（１）で作製した板状アルミナ粉末２．０質量部と、平均粒径がこの板状アルミナ粉末の厚みより小さい微細アルミナ粉末（ＴＭ−ＤＡＲ、平均粒径０．１μｍ、大明化学製、以下「市販品１」という）９８．０質量部とを混合した。この混合アルミナ粉末１００質量部に対し、酸化マグネシウム（５００Ａ、宇部マテリアルズ製）０．０３５質量部と、バインダーとしてポリビニルブチラール（品番ＢＭ−２、積水化学工業製）７．８質量部と、可塑剤としてジ（２−エチルヘキシル）フタレート（黒金化成製）３．９質量部と、分散剤としてトリオレイン酸ソルビタン（レオドールＳＰ−Ｏ３０、花王製）２質量部と、分散媒として２−エチルヘキサノールとを加えて混合した。分散媒の量は、スラリー粘度が２００００ｃＰとなるように調整した。このようにして調製されたスラリーを、ドクターブレード法によってＰＥＴフィルムの上に乾燥後の厚さが４０μｍとなるようにシート状に成形した。得られたテープを３０ｍｍ四方の正方形に切断した後これらを３０枚積層し、厚さ１０ｍｍのＡｌ板の上に載置した後、パッケージに入れて内部を真空にすることで真空パックとした。この真空パックを８５℃の温水中で２００ｋｇｆ／ｃｍ²の圧力にて静水圧プレスを行い、アルミナ成形体を得た。なお、混合アルミナ粉末の組成とＭｇＯ添加量を表１に示す。 (2) Tape molding 2.0 parts by mass of the plate-like alumina powder prepared in the above (1) and fine alumina powder (TM-DAR, average particle size of 0.1 μm) whose average particle size is smaller than the thickness of this plate-like alumina powder , Manufactured by Daimei Chemical Co., Ltd., hereinafter referred to as “commercially available product 1”). With respect to 100 parts by mass of this mixed alumina powder, 0.035 parts by mass of magnesium oxide (500A, manufactured by Ube Materials), 7.8 parts by mass of polyvinyl butyral (product number BM-2, manufactured by Sekisui Chemical Co., Ltd.) as a binder, and plastic 3.9 parts by mass of di (2-ethylhexyl) phthalate (manufactured by Kurokin Kasei) as an agent, 2 parts by mass of sorbitan trioleate (Leodol SP-O30, manufactured by Kao) as a dispersant, and 2-ethylhexanol as a dispersion medium And mixed. The amount of the dispersion medium was adjusted so that the slurry viscosity was 20000 cP. The slurry thus prepared was formed into a sheet shape on a PET film by a doctor blade method so that the thickness after drying was 40 μm. The obtained tape was cut into 30 mm squares, and 30 of them were stacked, placed on an Al plate having a thickness of 10 mm, and then put into a package to make the inside vacuum, thereby obtaining a vacuum pack. This vacuum pack was hydrostatically pressed at a pressure of 200 kgf / cm ² in 85 ° C. warm water to obtain an alumina molded body. Table 1 shows the composition of the mixed alumina powder and the amount of MgO added.

（３）焼成
得られたアルミナ成形体を脱脂炉中に配置し、６００℃で１０時間の条件で脱脂を行った。脱脂後のアルミナ成形体を９０ｍｍ角のアルミナ製の鞘に入れ、大気中、１２５０℃で４時間の条件で常圧焼成し、アルミナ中間体を得た。得られたアルミナ中間体を内径５０ｍｍ、高さ４０ｍｍの蓋付きのアルミナ製の小坩堝に入れ、更にその小坩堝を内径７４ｍｍ、高さ６０ｍｍの蓋付きのアルミナ製の大坩堝に入れた。その大坩堝を、８００℃で４時間熱処理した高純度α−アルミナ粉末（ＡＫＰ−２０、住友化学製）６０ｇを用いて埋設し、ＨＩＰ焼成をＡｒガス、圧力１８５ＭＰａ、１９００℃で２時間の条件で行い、アルミナ焼結体を得た。 (3) Firing The obtained alumina molded body was placed in a degreasing furnace and degreased at 600 ° C. for 10 hours. The degreased alumina molded body was placed in a 90 mm square alumina sheath and fired at 1250 ° C. for 4 hours under atmospheric pressure to obtain an alumina intermediate. The obtained alumina intermediate was placed in a small alumina crucible with a lid having an inner diameter of 50 mm and a height of 40 mm, and the small crucible was further placed in a large alumina crucible with a lid having an inner diameter of 74 mm and a height of 60 mm. The large crucible was embedded using 60 g of high-purity α-alumina powder (AKP-20, manufactured by Sumitomo Chemical Co., Ltd.) heat-treated at 800 ° C. for 4 hours, and HIP firing was performed under conditions of Ar gas, pressure 185 MPa, 1900 ° C. for 2 hours. To obtain an alumina sintered body.

２．アルミナ焼結体の評価
得られたアルミナ焼結体に対して以下に示す評価を行った。これらの結果を表１に示す。
（１）凹凸の山と谷の最大値（ＰＶ）測定
得られたアルミナ焼結体の表面（戴置した際に坩堝に触れていない側）を光学計測機器（Zygo社製NewView7300）を用いて、０．１００ｍｍ×０．１４０ｍｍの範囲にて測定した。
（２）表面粗さ（Ｒａ）測定
得られたアルミナ焼結体の表面（戴置した際に坩堝に触れていない側）を前出の光学計測機器を用いて、０．１００ｍｍ×０．１４０ｍｍの範囲にて測定した。
（３）開気孔率、密度測定
ＪＩＳＲ１６３４に準拠してアルキメデス法にて開気孔率、嵩密度を測定した。 2. Evaluation of Alumina Sintered Body The obtained alumina sintered body was evaluated as follows. These results are shown in Table 1.
(1) Maximum value of uneven peaks and troughs (PV) measurement The surface of the obtained alumina sintered body (the side not touching the crucible when placed) was measured using an optical measuring instrument (NewView7300 manufactured by Zygo). , Measured in the range of 0.100 mm × 0.140 mm.
(2) Surface Roughness (Ra) Measurement The surface of the obtained alumina sintered body (the side not touching the crucible when placed) is 0.100 mm × 0.140 mm using the optical measuring instrument described above. It measured in the range.
(3) Open porosity and density measurement Based on JISR1634, the open porosity and bulk density were measured by the Archimedes method.

［実験例２］
アルミナ焼結体を作製するにあたり、上記１．（２）のテープ成形において板状アルミナ粉末を用いず微細アルミナ粉末のみ使用したこと、酸化マグネシウムを添加しないこと、上記１．（３）の焼成においてＨＩＰ焼成を１８５０℃で行ったこと以外は、実験例１と同様にしてアルミナ焼結体を作製し、そのＰＶ及びＲａを測定した。また、アルミナ中間体及びアルミナ焼結体の開気孔率、嵩密度も測定した。結果を表１に示す。 [Experiment 2]
In producing the alumina sintered body, the above 1. In the tape molding of (2), only the fine alumina powder is used without using the plate-like alumina powder, no magnesium oxide is added, An alumina sintered body was produced in the same manner as in Experimental Example 1 except that HIP firing was performed at 1850 ° C. in the firing of (3), and the PV and Ra thereof were measured. Moreover, the open porosity and bulk density of the alumina intermediate and the alumina sintered body were also measured. The results are shown in Table 1.

［実験例３］
アルミナ焼結体を作製するにあたり、上記１．（２）のテープ成形において微細アルミナ粉末として、高純度α−アルミナ粉末（ＡＫＰ−２０、住友化学製、以下「市販品２」という）を使用したこと、上記１．（３）の焼成において脱脂体を１５５０℃で常圧焼成したこと、ＨＩＰ焼成をＮ₂ガス、１９５０℃で行ったこと以外は、実験例１と同様にしてアルミナ焼結体を作製し、そのＰＶ及びＲａを測定した。また、アルミナ中間体及びアルミナ焼結体の開気孔率、嵩密度も測定した。結果を表１に示す。 [Experiment 3]
In producing the alumina sintered body, the above 1. In the tape molding of (2), high-purity α-alumina powder (AKP-20, manufactured by Sumitomo Chemical Co., Ltd., hereinafter referred to as “commercial product 2”) was used as the fine alumina powder. In the firing of (3), an alumina sintered body was produced in the same manner as in Experimental Example 1, except that the degreased body was fired at 1550 ° C. under normal pressure, and HIP firing was performed at 1950 ° C. with N ₂ gas. PV and Ra were measured. Moreover, the open porosity and bulk density of the alumina intermediate and the alumina sintered body were also measured. The results are shown in Table 1.

［実験例４］
アルミナ焼結体を作製するにあたり、埋設用の高純度α−アルミナ粉末を３０ｇとしたこと以外は、実験例２と同様にしてアルミナ焼結体を作製し、そのＰＶ及びＲａを測定した。また、アルミナ中間体及びアルミナ焼結体の開気孔率、嵩密度も測定した。結果を表１に示す。 [Experimental Example 4]
In producing the alumina sintered body, an alumina sintered body was produced in the same manner as in Experimental Example 2 except that 30 g of the high-purity α-alumina powder for embedding was used, and PV and Ra thereof were measured. Moreover, the open porosity and bulk density of the alumina intermediate and the alumina sintered body were also measured. The results are shown in Table 1.

［実験例５］
上記１．（３）の焼成においてＨＩＰ焼成を行う際に、埋設しないこと以外は、実験例１と同様にしてアルミナ焼結体を作製し、そのＰＶ及びＲａを測定した。また、アルミナ中間体及びアルミナ焼結体の開気孔率、嵩密度も測定した。結果を表１に示す。 [Experimental Example 5]
Above 1. When performing HIP firing in firing of (3), an alumina sintered body was produced in the same manner as in Experimental Example 1 except that it was not embedded, and its PV and Ra were measured. Moreover, the open porosity and bulk density of the alumina intermediate and the alumina sintered body were also measured. The results are shown in Table 1.

［実験例６］
上記１．（３）の焼成においてＨＩＰ焼成を行う際に、埋設しないこと以外は、実験例２と同様にしてアルミナ焼結体を作製し、そのＰＶ及びＲａを測定した。また、アルミナ中間体及びアルミナ焼結体の開気孔率、嵩密度も測定した。結果を表１に示す。 [Experimental Example 6]
Above 1. When performing the HIP firing in the firing of (3), an alumina sintered body was produced in the same manner as in Experimental Example 2 except that it was not embedded, and its PV and Ra were measured. Moreover, the open porosity and bulk density of the alumina intermediate and the alumina sintered body were also measured. The results are shown in Table 1.

［実験例７］
上記１．（３）の焼成においてＨＩＰ焼成を行う際に、埋設しないこと以外は、実験例３と同様にしてアルミナ焼結体を作製し、そのＰＶ及びＲａを測定した。また、アルミナ中間体及びアルミナ焼結体の開気孔率、嵩密度も測定した。結果を表１に示す。 [Experimental Example 7]
Above 1. When performing HIP firing in firing of (3), an alumina sintered body was produced in the same manner as in Experimental Example 3 except that it was not embedded, and its PV and Ra were measured. Moreover, the open porosity and bulk density of the alumina intermediate and the alumina sintered body were also measured. The results are shown in Table 1.

［評価結果］
表１を参照しながら各実験例の表面状態について説明する。実験例１と実験例５とを比べると、両者は同じ原料粉末を用いてアルミナ成形体を作製し、そのアルミナ成形体を同じ常圧焼成条件で焼成してアルミナ中間体を作製し、そのアルミナ中間体を焼成雰囲気以外は同じＨＩＰ焼成条件で焼成してアルミナ焼結体を得た。ＨＩＰ焼成時の雰囲気は、実験例１ではアルミナ含有雰囲気、実験例５ではアルミナ非含有雰囲気とした。その結果、アルミナ焼結体の表面状態を示すＰＶとＲａは、実験例１の方が実験例５に比べて格段に小さい値であった。実験例１では、アルミナ中間体を焼成してアルミナ焼結体を得る段階でアルミナ含有雰囲気を採用したため、アルミナ焼結体の最表面を構成するアルミナ粒子の面内での平坦性が改善し、粒子間の段差の発生が抑制され、表面の平滑性が十分高まり、その結果ＰＶ及びＲａが良好な値になったと考えられる。これに対して、実験例５では、アルミナ中間体を焼成してアルミナ焼結体を得る段階でアルミナを含有しない雰囲気を採用したため、アルミナ焼結体の最表面を構成するアルミナ粒子の面内での凹凸や粒子間の段差が大きくなり、ＰＶ及びＲａが良好な値にならなかったと考えられる。 [Evaluation results]
The surface state of each experimental example will be described with reference to Table 1. Comparing Experimental Example 1 and Experimental Example 5, both produced an alumina molded body using the same raw material powder, and the alumina molded body was fired under the same atmospheric pressure firing conditions to produce an alumina intermediate. The intermediate was fired under the same HIP firing conditions except for the firing atmosphere to obtain an alumina sintered body. The atmosphere during HIP firing was an alumina-containing atmosphere in Experimental Example 1 and an alumina-free atmosphere in Experimental Example 5. As a result, PV and Ra indicating the surface state of the alumina sintered body were much smaller in Experimental Example 1 than in Experimental Example 5. In Experimental Example 1, since the alumina-containing atmosphere was adopted at the stage of firing the alumina intermediate to obtain the alumina sintered body, the flatness in the plane of the alumina particles constituting the outermost surface of the alumina sintered body was improved, It is considered that the occurrence of a step between the particles is suppressed and the smoothness of the surface is sufficiently increased, and as a result, PV and Ra have good values. On the other hand, in Experimental Example 5, since an atmosphere not containing alumina was adopted at the stage of firing the alumina intermediate to obtain the alumina sintered body, the surface of the alumina particles constituting the outermost surface of the alumina sintered body was used. It is considered that the unevenness and the level difference between the particles became large, and PV and Ra did not become good values.

実験例２と実験例６との関係や実験例３と実験例７との関係は、実験例１と実験例５との関係と同じである。つまり、実験例２，３ではアルミナ中間体を焼成してアルミナ焼結体を得る段階でアルミナ含有雰囲気を採用したのに対し、実験例６，７ではその段階でアルミナ非含有雰囲気を採用した以外は実験例２，３とそれぞれ同じ条件で焼成した。その結果、実験例２，３では、それぞれ実験例６，７と比べてＰＶ及びＲａが良好な値のアルミナ焼結体が得られた。実験例４では、埋設用のアルミナ粉末を実験例２と比べて半分にした以外は、実験例２と同じ条件で焼成したが、その場合でもＰＶ及びＲａが良好な値のアルミナ焼結体が得られた。   The relationship between Experimental Example 2 and Experimental Example 6 and the relationship between Experimental Example 3 and Experimental Example 7 are the same as the relationship between Experimental Example 1 and Experimental Example 5. That is, in Experimental Examples 2 and 3, an alumina-containing atmosphere was adopted at the stage where the alumina intermediate was fired to obtain an alumina sintered body, whereas in Experimental Examples 6 and 7, an alumina-free atmosphere was adopted at that stage. Were fired under the same conditions as in Experimental Examples 2 and 3, respectively. As a result, in Experimental Examples 2 and 3, an alumina sintered body having good values of PV and Ra as compared with Experimental Examples 6 and 7, respectively, was obtained. In Experimental Example 4, firing was performed under the same conditions as in Experimental Example 2 except that the alumina powder for embedding was halved compared to Experimental Example 2, but even in that case, an alumina sintered body with good values of PV and Ra was obtained. Obtained.

なお、上述した実験例１〜７のうち、実験例１〜４が本発明の実施例に相当し、実験例５〜７が比較例に相当する。   Of the experimental examples 1 to 7 described above, experimental examples 1 to 4 correspond to examples of the present invention, and experimental examples 5 to 7 correspond to comparative examples.

Claims (5)

アルミナ成形体を焼成して第１の焼結状態のアルミナ中間体を経て第２の焼結状態のアルミナ焼結体を得るアルミナ焼結体の製法であって、
少なくとも前記アルミナ中間体から前記アルミナ焼結体に変化する段階では、前記アルミナ中間体の周りをＡｌ含有雰囲気にする、
アルミナ焼結体の製法。 A method for producing an alumina sintered body by firing an alumina molded body to obtain an alumina sintered body in a second sintered state through an alumina intermediate in a first sintered state,
At least at the stage of changing from the alumina intermediate to the alumina sintered body, an atmosphere containing Al is formed around the alumina intermediate.
A method for producing an alumina sintered body. 前記Ａｌ含有雰囲気は、アルミナを含有する雰囲気である、
請求項１に記載のアルミナ焼結体の製法。 The Al-containing atmosphere is an atmosphere containing alumina.
The manufacturing method of the alumina sintered compact of Claim 1. アルミナ成形体を所定の温度で焼成して前記アルミナ中間体を作製し、その後、前記アルミナ中間体を前記所定の温度を超える温度で前記Ａｌ含有雰囲気下で焼成して前記アルミナ焼結体を得る、
請求項１又は２に記載のアルミナ焼結体の製法。 The alumina molded body is fired at a predetermined temperature to produce the alumina intermediate, and then the alumina intermediate is fired at a temperature exceeding the predetermined temperature in the Al-containing atmosphere to obtain the alumina sintered body. ,
The manufacturing method of the alumina sintered compact of Claim 1 or 2. 前記アルミナ中間体を焼成するにあたり、前記アルミナ中間体をＨＩＰ焼成する、
請求項３に記載のアルミナ焼結体の製法。 In firing the alumina intermediate, HIP firing the alumina intermediate,
The manufacturing method of the alumina sintered compact of Claim 3. 前記アルミナ中間体を焼成するにあたり、前記アルミナ中間体を非気密な容器に入れたあと該容器の周囲をアルミナ粉末で覆うか該容器内にアルミナ粉末を共存させた状態で、不活性雰囲気でＨＩＰ焼成する、
請求項３又は４に記載のアルミナ焼結体の製法。 In firing the alumina intermediate, the alumina intermediate is placed in a non-airtight container, and then the periphery of the container is covered with alumina powder or the alumina powder coexists in the container, and the HIP is heated in an inert atmosphere. Bake,
The manufacturing method of the alumina sintered compact of Claim 3 or 4.

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