JPH0557166A - Production of coated fine particle - Google Patents

Abstract

PURPOSE:To obtain coated fine particles by dissolving a 1st and 2nd solutes separately into corresponding 1st and 2nd solvents to form the 1st and 2nd supercritical systems respectively, forming fine particles of the 1st solute by the adiabatic expansion of the 1st system, pressurizing the expanded system to mix with the 2nd system, depositing the 2nd solute on the surface of fine particles of the 1st solute by the adiabatic expansion of the mixed system. CONSTITUTION:A 1st solute (e.g. SiO2) and a 2nd solute (e.g. La2O3) are dissolved separately into a 1st solvent (e.g. water and a 2nd solvent (e.g. water) contained in corresponding vessels 1, 3 to form 1st and 2nd systems in supercritical or subcritical state, respectively. The 1st system is introduced into a vessel 1 by adiabatic expansion to form fine particles of SiO2 through an oversaturated state. This system, after being pressurized again to the same pressure with the 2nd system, is mixed with the 2nd system; the mixed system is then introduced into the vessel 2 by adiabatic expansion to deposit La2O3 on the surface of of SiO2 fine particles through an oversaturated state to prepare coated fine particles. In result, the solute can be deposited from the solvent in a supercritical or subcritical state with good reproducibility to grow to fine particles.

Description

【発明の詳細な説明】Detailed Description of the Invention

【０００１】[0001]

【産業上の利用分野】本発明は、被覆微粒子の製造方法
に関し、殊に超臨界状態または亜臨界状態にある溶媒が
高い溶解能力を示すことを利用し、該溶媒中に溶解され
ている溶質を、圧力制御により被覆微粒子として析出さ
せる方法に関するものである。被覆微粒子は、触媒、フ
ァインセラミックス成形材料、磁性材料、感光材料、セ
ンサ材料等に応用される。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing coated fine particles, and in particular, the fact that a solvent in a supercritical state or a subcritical state exhibits a high dissolving ability, and a solute dissolved in the solvent is utilized. The present invention relates to a method of depositing as fine particles by pressure control. The coated fine particles are applied to catalysts, fine ceramics molding materials, magnetic materials, photosensitive materials, sensor materials and the like.

【０００２】[0002]

【従来の技術】微粒子は体積当りの表面積が著しく大き
く、その表面エネルギーも著しく大きくなることから、
焼結、吸着、触媒等の各種技術分野において重要な役割
を果たしている。また微粒子がアモルファス状固体であ
れば、結晶状のものに比べて微粒子自体のエネルギーも
更に高くなり、表面の活性は非常に高いものとなる。こ
うしたことから微粒子の製造方法については様々な手段
が研究されており、夫々の技術分野で多様な効果を発揮
している。2. Description of the Related Art Fine particles have a remarkably large surface area per volume, and their surface energy also remarkably increases.
It plays an important role in various technical fields such as sintering, adsorption, and catalysts. Further, when the fine particles are amorphous solid, the energy of the fine particles themselves becomes higher than that of the crystalline particles, and the surface activity becomes very high. For these reasons, various means have been studied for producing fine particles, and various effects have been exhibited in each technical field.

【０００３】近年、数百気圧以上の高圧下に形成した超
臨界流体内に溶質を溶解し、これを大気圧または減圧下
の雰囲気に向けてオリフィスから基板上に噴射し、噴流
中での瞬時の減圧過程における過飽和状態の発生を利用
して、基板上に固体皮膜や超微粒子を形成する技術がス
ミス・リチャード・ディーらによって提案されている
（公表特許昭６１−５００２１０号）。彼らによれば、
オリフィスからの『噴射プロセスは膨張中の溶剤クラス
ターの形成、および溶液の自由ジェットまたは超音波膨
張から生じるマッハディスク（ Mach Disk）における溶
剤クラスター「崩壊（freak up）」現象の影響を受け
る』ことが指摘されている（前記公表特許公報第４頁右
上欄）。つまりマッハディスクによる衝撃によって溶媒
の凝集核を一度に破壊して溶質の超微粒子からなる固体
析出物を形成し、これを基体上に膜状に堆積させるもの
である。従ってこの技術は、膜製造分野にはひとつの指
針を与えるものであると言える。また超臨界流体では溶
解度が著しく高くなることが一般的に知られており、こ
の性質を利用して水晶の単結晶育成や混合物からの特定
の溶質の抽出等に応用されているが、上記技術は超臨界
流体から固体皮膜や超微粒子を形成しようとする発想か
らくるものであると位置付けることができる。In recent years, a solute is dissolved in a supercritical fluid formed under a high pressure of several hundreds of atmospheres or more, and the solute is jetted from an orifice onto a substrate toward an atmosphere under atmospheric pressure or reduced pressure, and instantaneously in a jet stream. A technique for forming a solid film or ultrafine particles on a substrate by utilizing the occurrence of a supersaturated state in the depressurizing process has been proposed by Smith Richard D. et al. (Published patent No. 61-500210). According to them
"The injection process is subject to the formation of solvent clusters during expansion and the phenomenon of solvent cluster" freak up "in Mach Disks resulting from free jet or ultrasonic expansion of the solution" from the orifice. It has been pointed out (the above-mentioned published patent publication, page 4, upper right column). That is, the agglomeration nuclei of the solvent are destroyed at once by the impact of the Mach disk to form a solid precipitate composed of solute ultrafine particles, which is deposited in a film form on the substrate. Therefore, it can be said that this technique provides one guide in the field of membrane production. It is generally known that the solubility of supercritical fluids becomes extremely high, and this property has been applied to the growth of single crystals of quartz and the extraction of specific solutes from a mixture. Can be considered to come from the idea of forming a solid film or ultrafine particles from a supercritical fluid.

【０００４】微粒子への酸化物のコーティング（被覆）
技術としては、気相法ではＣＶＤ法、液相法ではアルコ
キシド法等が知られている。ＣＶＤ法はコーティング材
質によっては強い毒性と可燃性を兼ね備えたガスを取扱
うため、複雑で大形のガス設備が必須となり、製造コス
トが高くなる。また高温で処理する場合は製品に熱ひず
みが残る。アルコキシド法は、アルコキシド自体が非常
に高価なものであるため、同様に製造コストが高くな
る。更にいずれの方法も大規模なスケールで生産するに
は技術的に困難な問題が多い等の欠点を有すると言われ
ており、実用化されているものは少ない。Oxide coating on fine particles
As a technique, a CVD method is known as a vapor phase method, and an alkoxide method is known as a liquid phase method. Since the CVD method handles a gas that has both strong toxicity and flammability depending on the coating material, a complicated and large-scale gas facility is indispensable and the manufacturing cost becomes high. When processed at high temperature, thermal strain remains in the product. Since the alkoxide method itself is very expensive, the alkoxide method also raises the manufacturing cost. Furthermore, it is said that each of these methods has drawbacks such as many technically difficult problems in producing them on a large scale, and few of them have been put into practical use.

【０００５】[0005]

【発明が解決しようとする課題】本発明者らはかねてよ
り超臨界状態の応用という観点から様々な研究を進めて
おり（例えば化学工学第５４年会，１９８９年）、上記
従来技術についてもその効果の確認を行った。しかしな
がら本発明者らの実験によれば、噴流中で超微粒子を形
成する方法では次のような幾つかの問題があることが判
明した。 音速の領域で製造される固体は、その性状（微粒子の
形成数、大きさ、形状等）の再現性が劣る。 噴流中の溶質の全てが、目的とする薄膜または微粒子
のどちらか一方になるとは限らず、回収されないまま大
気中へ飛散するものもあり、従って歩留りが悪くなる。 ノズルを安定的に同一孔径・同一形状に製作すること
は困難であり、少しの違いによっても噴流が変化するた
め、製造条件の再現性及び生成微粒子の回収が均一性に
劣る。 固化した微粒子の回収が困難である。The present inventors have been conducting various researches from the viewpoint of application of the supercritical state for some time (for example, Chemical Engineering 54th Annual Meeting, 1989), and the above-mentioned conventional techniques are also The effect was confirmed. However, according to the experiments by the present inventors, it was found that the method of forming ultrafine particles in a jet has some problems as follows. Solids produced in the sonic region have poor reproducibility of their properties (number of fine particles formed, size, shape, etc.). Not all of the solutes in the jet flow are the target thin film or fine particles, and there are some that scatter into the atmosphere without being collected, and thus the yield becomes poor. It is difficult to stably manufacture the nozzle with the same hole diameter and the same shape, and the jet flow changes even with a slight difference, so that the reproducibility of the manufacturing conditions and the recovery of the produced fine particles are poor. It is difficult to collect the solidified particles.

【０００６】本発明は上記事情に着目してなされたもの
であって、その目的は超臨界状態または亜臨界状態にあ
る溶媒中から、溶質を再現性良く析出・成長させて微粒
子を製造することができ、また回収も容易で、操作が簡
単で、更に装置の大形化が可能な単純な装置構成で、安
価な被覆微粒子を製造することができる方法を提供しよ
うとするものである。The present invention has been made in view of the above circumstances, and its purpose is to produce fine particles by reproducibly depositing and growing a solute from a solvent in a supercritical state or a subcritical state. It is an object of the present invention to provide a method capable of producing inexpensive coated fine particles with a simple device configuration that can be obtained, is easy to collect, is easy to operate, and can be made large in size.

【０００７】[0007]

【課題を解決するための手段】上記目的を達成した本発
明とは、第１溶質と第２溶質を夫々対応する第１溶媒と
第２溶媒に別々に溶解して夫々を超臨界状態または 亜
臨界状態の第１系と第２系とした後、第１系を断熱膨張
させ過飽和状態を経て第１溶質の微粒子を生成し、これ
を再び第２系と同一の圧力まで昇圧してから第２系と混
合し、その後該混合系を断熱膨張させ過飽和状態を経て
上記第１溶質の微粒子表面に第２溶質を析出せしめて被
覆微粒子を形成することを要旨とするものである。Means for Solving the Problems The present invention, which has achieved the above-mentioned object, means that the first solute and the second solute are separately dissolved in the corresponding first solvent and second solvent, respectively, and each of them is brought into a supercritical state or a sub-solvent. After making the first system and the second system in the critical state, the first system is adiabatically expanded to generate fine particles of the first solute through the supersaturated state, and this is boosted again to the same pressure as the second system before The gist of the present invention is to form a coated fine particle by mixing the second solute with the second system and then adiabatically expanding the mixed system to cause a supersaturated state to deposit the second solute on the surface of the fine particles of the first solute.

【０００８】[0008]

【作用】以下、図面に基づいて本発明の原理及び作用・
効果について説明する。図１は高温高圧水中へのＳｉＯ
₂ の溶解度の変化を示すグラフ（G.C.Kennedy,1950）で
ある。図１から明らかなように、臨界温度以上では、温
度および／または圧力が上るにつれてＳｉＯ₂ の溶解度
が上がる。The principle and operation of the present invention will now be described with reference to the drawings.
The effect will be described. Figure 1 shows SiO in high temperature and high pressure water.
_It is a graph (GC Kennedy, 1950) which shows the change of the solubility of ₂ . As is clear from FIG. 1, above the critical temperature, the solubility of SiO ₂ increases with increasing temperature and / or pressure.

【０００９】例えば、図１の点Ａ（550 ℃，750 Bars）
でＳｉＯ₂ を飽和溶解した超臨界水を、オリフィスを経
て大気圧下へ断熱的に膨張させる場合では、熱力学的計
算によればラインＬ₁ の如き経過を辿って超臨界水の温
度および圧力が下降し、従ってＳｉＯ₂ の溶解度も下降
する。但し、溶解度が下降しても溶質固体は直ちに析出
することはなく、過飽和状態が形成された後で析出す
る。For example, point A in FIG. 1 (550 ° C., 750 Bars)
In the case of adiabatically expanding supercritical water in which SiO ₂ is saturated and dissolved under an atmospheric pressure through an orifice, according to thermodynamic calculation, the temperature and pressure of the supercritical water follow the course as shown by line L _1. Decreases, and therefore the solubility of SiO ₂ also decreases. However, even if the solubility decreases, the solute solid does not immediately precipitate, but it precipitates after the supersaturated state is formed.

【００１０】今、初期条件の溶解度をＸｏ，降圧中の任
意の瞬間圧力に対応する溶解度をＸｐとすると、過飽和
度Ｃは下記(I) 式のように表される。Now, assuming that the solubility under the initial conditions is Xo and the solubility corresponding to an arbitrary instantaneous pressure during depressurization is Xp, the supersaturation degree C is expressed by the following equation (I).

【００１１】[0011]

【数１】 [Equation 1]

【００１２】図１から明らかなように、大気圧下におけ
るＳｉＯ₂ の溶解度はほとんど０であり、従ってオリフ
ィスから噴射するとき（即ち瞬時に断熱膨張するとき）
の過飽和度は無限大となる。As is apparent from FIG. 1, the solubility of SiO ₂ under atmospheric pressure is almost zero, and therefore when jetted from the orifice (that is, when adiabatic expansion occurs instantaneously).
The degree of supersaturation of is infinite.

【００１３】一般に、過飽和度が小さいと溶質は析出せ
ず、ある過飽和度（臨界過飽和度）を超えると核が発生
する確率が実質的に現れ始め、更にそれより大きくなる
と核発生の確率が高くなっていく。従って圧力が低下し
て過飽和度が無限大に近くなると、超微細核が無数に発
生し、それらが噴射流の下流側の固体表面上に堆積すれ
ば薄膜を形成することになる。このことから、薄膜では
なく微粒子状に形成したい場合においては、過飽和度を
ある程度までに抑えて核発生数もある程度の範囲内と
し、発生核を微粒子にまで成長させる必要がある。Generally, if the degree of supersaturation is small, the solute does not precipitate, and if the degree of supersaturation exceeds a certain degree (critical supersaturation degree), the probability of nucleation begins to appear, and if the degree of supersaturation is further higher, the probability of nucleation increases. It will become. Therefore, when the pressure decreases and the degree of supersaturation approaches infinity, an infinite number of ultrafine nuclei are generated, and when they are deposited on the solid surface on the downstream side of the jet flow, a thin film is formed. From this, when it is desired to form fine particles instead of a thin film, it is necessary to suppress the degree of supersaturation to a certain degree and keep the number of nuclei generated within a certain range to grow the generated nuclei into fine particles.

【００１４】上述の様な過飽和度と核発生の確率との関
係は、実際の工業界でも多くの例が認められるが、これ
を統計力学の手法に基づいてマクドナルド（McDonald）
が計算した例を下記表１に示す（黒田登志雄著，結晶は
生きている，株式会社サイエンス社発行）。この表１は
０℃の水蒸気の蒸気圧（4.58Torr）をＰｅとし、取扱う
環境の蒸気圧をＰとしたときの、種々の過飽和度比Ｐ／
Ｐｅに対する核発生頻度Ｊｓ，臨界核の半径ｒ^* ，臨界
核中に含まれる分子数ｉ^* を夫々示している。Many examples of the relationship between the degree of supersaturation and the probability of nucleation as described above are recognized in the actual industry, but this is based on the method of statistical mechanics, McDonald (McDonald)
An example of the calculation is shown in Table 1 below (by Toshio Kuroda, Crystals are alive, published by Science Co., Ltd.). This Table 1 shows various supersaturation ratios P /, where Pe is the vapor pressure (4.58 Torr) of water vapor at 0 ° C and P is the vapor pressure of the environment to be handled.
The nuclear generation frequency Js for Pe, the radius r ^{* of} the critical nucleus, and the number of molecules i ^* contained in the critical nucleus are shown.

【００１５】[0015]

【表１】 [Table 1]

【００１６】表１から次のように考察できる。Ｐ／Ｐｅ
が３以下では実質的に核は発生しないと考えてもよい。
Ｐ／Ｐｅが４のときは、毎秒当りの核発生確率が５個／
cm³・sec となり、Ｐ／Ｐｅがそれより多くなると実用上
核が発生し得る条件となる。但し、Ｐ／Ｐｅが８にもな
ると、核発生頻度Ｊｓが４×10¹⁵個／cm³・sec にもな
り、実際上は無数と表現される状態となる。From Table 1, the following can be considered. P / Pe
It may be considered that when n is 3 or less, nuclei are not substantially generated.
When P / Pe is 4, the probability of nuclear generation per second is 5 /
It becomes cm ³ · sec, and when P / Pe is larger than that, it is a condition in which a nucleus can be practically generated. However, when P / Pe is increased to 8, the nuclear generation frequency Js is also increased to 4 × 10 ¹⁵ pieces / cm ³ · sec, which is actually expressed as an infinite number.

【００１７】こうして発生した核のまわりには気体分子
が凝集し、先に発生した核から順次大きくなり気体分子
の数が少なくなっていく。それが閉じられた系内で行わ
れるならば、Ｐ／Ｐｅは結果的に減少し、核発生の頻度
は低下する。この傾向は、意図的にＰ／Ｐｅを小さくし
た場合においても同様であり、例えばＰ／Ｐｅが３以下
に下った場合には、新たな核の発生の確率は実質上０と
なり、それまでに発生した核に基づく粒が成長して気体
分子を消費しつつ、Ｐ／Ｐｅが更に下って遂には１に達
する。しかし表１から明らかなように、臨界核の半径ｒ
^* は10Å以下のものであって、そのままでは微粒子とし
て使用できず、エネルギー的にも不安定であり、大きな
ものに成長しようとする傾向があり、本発明はこのよう
な点に着目して研究を行った。The gas molecules are aggregated around the thus-generated nuclei, and the nuclei that have been previously generated become larger in size and the number of gas molecules decreases. If it is done in a closed system, P / Pe will eventually decrease and the frequency of nucleation will decrease. This tendency is the same when P / Pe is intentionally reduced, and for example, when P / Pe is 3 or less, the probability of new nuclei is virtually zero, and by that time Grains based on the generated nuclei grow and consume gas molecules, while P / Pe further decreases and finally reaches 1. However, as is clear from Table 1, the radius r of the critical nucleus is
^* Is 10 Å or less, cannot be used as fine particles as it is, is unstable in energy, and tends to grow into large ones. I went.

【００１８】前記表１は純成分（水）の０℃における蒸
気（水蒸気）についての計算の一例であり、蒸気から液
滴発生に係るものである。しかしながらこのような傾向
は、気・固転移や液・固転移の場合についても成立す
る。また一方が溶質で他方が溶媒の成分系についても成
立するものである。但し、この場合は過飽和度として
（Ｐ−Ｐｅ）／Ｐｅの代わりに、前記(I) 式に示したＣ
が用いられることが多い。Table 1 above is an example of calculation of steam (steam) at 0 ° C. of pure component (water), and relates to generation of droplets from steam. However, this tendency also holds in the case of gas-solid transition and liquid-solid transition. Further, it is also true for a component system in which one is a solute and the other is a solvent. However, in this case, as the degree of supersaturation, instead of (P-Pe) / Pe, C shown in the above formula (I) is used.
Is often used.

【００１９】以上のような事情を考慮しつつ、スミスら
の技術を検討すると、下記のような知見が得られた。オ
リフィスから噴射された直後の大気圧下におけるＳｉＯ
₂ の溶解度Ｘｐはほとんど０に近く、従って過飽和度Ｃ
は無限大であり、このとき核は無数に発生し、それに伴
って過飽和度Ｃが瞬時に０に近づくので発生した無数の
核の成長はほとんど起こらない。これが前記技術におけ
る薄膜、超微粒子の形成の基本原理となっている。しか
も上記技術では、オリフィスからの噴射に当り、マッハ
ディスクにおける衝撃によって、クラスター（核の基に
なる分子の集団）を粉砕することになり、より一層の微
細化が図られている。尚スミスらによる研究では、Ｓｉ
Ｏ₂ 以外に有機物の代表としてポリスチレンの例も示さ
れているが、ここにおいては大気圧から更に減圧雰囲気
に噴射しており、これは前記(I)式における平衡濃度Ｘ
ｐを更に小さくして、過飽和度Ｃを大きくするものであ
り、上記傾向に拍車をかける結果となっている。When the technique of Smith et al. Was examined in consideration of the above circumstances, the following findings were obtained. SiO under atmospheric pressure immediately after being injected from the orifice
Solubility Xp of ₂ is almost 0, and therefore supersaturation C
Is infinite, and at this time, innumerable nuclei are generated, and the supersaturation degree C instantly approaches 0 with it, so that the innumerable nuclei generated hardly occur. This is the basic principle of forming a thin film and ultrafine particles in the above technique. Moreover, in the above technique, when jetted from the orifice, the cluster (a group of molecules serving as the core of the nucleus) is crushed by the impact on the Mach disk, and further miniaturization is achieved. In addition, in the research by Smith et al.
O ₂ is also shown an example of polystyrene as a representative of organic matter in addition to, but has been further injected to a reduced pressure atmosphere from atmospheric pressure wherein this equilibrium concentration X in the formula (I)
The value of p is further reduced to increase the degree of supersaturation C, which results in accelerating the above tendency.

【００２０】一方本発明においては、ある程度成長した
微粒子を製造することを目的としており、ここにその原
理を説明する。例えば前記表１において、Ｐ／Ｐｅが４
になる状態で10秒間保持させると、５個×10＝50個の核
が形成されるが、これらの核は表１のｉ^* に示す如く少
なくとも87個の分子の集合体となっている。そこでこの
分子集合体を核として次々に分子を取り込んで核は成長
するが、695 個以上の集合体に成長した段階でＰ／Ｐｅ
＝２に変化させるならば、その核は695 個以上の分子集
合体であるという理由によって分解消滅することなく引
続き成長を続けていくことが可能になる。即ち50個の粒
子はそのまま成長を続けることになる。50個の粒子が分
子数695 個以上に成長する間に、さらに生成・増加して
くる新たな核は、それらの分子数が臨界核の分子数ｉ
^* ，695 個に満たないという理由で、Ｐ／Ｐｅを４から
２にした時点で再び分解気化して消失する。結局、粒径
が比較的大きな粒子のみが粒子成長を達成することがで
き、最終的に粒径の揃った微粒子となる。尚Ｐ／Ｐｅを
４から３→２→１と変化させると、粒子の近傍における
過飽和状態にはかなり大きな差が生じる。試算によれ
ば、蒸気圧Ｐが１，２，３，４のとき、１cm³ 中にある
蒸気分子の数は夫々、1.6 ，3.2 ，4.8 ，6.4 （×1
0¹⁷）であり、このような差は成長の立場から見ると形
態上重大な差異が生じる原因になるものと考えられる。On the other hand, the present invention aims to produce fine particles that have grown to some extent, and the principle thereof will be described here. For example, in Table 1 above, P / Pe is 4
In this state, 5 × 10 = 50 nuclei are formed, and these nuclei are aggregates of at least 87 molecules as shown by i ^* in Table 1. Therefore, the nuclei grow by taking in molecules one after another by using this molecular aggregate as a nucleus, but when P / Pe grows into an aggregate of more than 695 aggregates.
If it is changed to = 2, the nucleus can continue to grow without being decomposed and disappeared because it is a molecular aggregate of 695 or more. That is, 50 particles will continue to grow as they are. The new nuclei that are further generated and increased while the number of 50 particles grows to more than 695 molecules is that the number of molecules is i
^{* Because} it is less than 695, when P / Pe is changed from 4 to 2, it decomposes and vaporizes again and disappears. Eventually, only particles having a relatively large particle size can achieve particle growth, and finally become fine particles having a uniform particle size. When P / Pe is changed from 4 to 3 → 2 → 1, a considerably large difference occurs in the supersaturated state in the vicinity of the particles. According to the calculation, when the vapor pressure P is 1, 2, 3, 4, the number of vapor molecules in 1 cm ³ is 1.6, 3.2, 4.8, 6.4 (× 1), respectively.
0 ^17), and this difference is considered to cause the watch and form a serious difference from the standpoint of growth occurs.

【００２１】例えば前記図１における点Ａ（750 気圧）
から断熱膨張させて点Ａ′（500 気圧）に達したとする
と、超臨界流体中のＳｉＯ₂ 溶解度はＸ₇₅₀ ＝0.165 か
らＸ₅₀₀ ＝0.07に変化し、このときのＸ₇₅₀ ／Ｘ₅₀₀
（以下溶解度比と言うことがある）は2.2 となる。ここ
で有限個のＳｉＯ₂ 凝集核が発生・成長し始めたと仮定
すると、溶解度Ｘの値は低下し、新たな核は発生しなく
なる。そこで500 気圧から例えば300 気圧まで徐々に圧
力を下げると、そのときの溶解度比（Ｘ／Ｘ₃₀₀)は再び
増加するが、上記溶解度比2.2 を超えない限りにおいて
は、新たな核発生はなく、既存の粒子が成長するだけで
ある。以下同様の原理で、新たな核が発生しない程度の
速度で蒸気圧を大気圧まで下げることによって、粒径の
揃った微粒子が得られる。そして大気圧近傍において
は、溶解度がほとんど０に近くなり、圧力・温度を急激
に下げても粒子の性状に大きく影響を与えることはほと
んどない。しかしながら、残存圧力を急激に解放する前
の溶解度が無視できない程度に実質的な数値を示す場合
は、溶解度の絶対値が低くてもその条件における溶解度
比が核発生条件を満たし、臨界核が発生することによ
り、既にいくらか成長してきた大きな粒子の表面に微細
粒子が付着或は独立に成長することなどもあり得る。For example, point A in FIG. 1 (750 atm)
If it reaches a point A '(500 atm) after adiabatic expansion from, the solubility of SiO ₂ in the supercritical fluid changes from X ₇₅₀ = 0.165 to X ₅₀₀ = 0.07, at which time X ₇₅₀ / X ₅₀₀
(Hereinafter sometimes referred to as the solubility ratio) is 2.2. Assuming that a finite number of SiO ₂ agglomerated nuclei have started to be generated and grown, the value of the solubility X decreases and new nuclei do not occur. Therefore, when the pressure is gradually reduced from 500 atm to 300 atm, the solubility ratio (X / X ₃₀₀ ) at that time increases again, but no new nucleation occurs unless the solubility ratio above 2.2 is exceeded. Only existing particles grow. Thereafter, according to the same principle, the vapor pressure is reduced to the atmospheric pressure at a speed at which new nuclei are not generated, whereby fine particles having a uniform particle size can be obtained. In the vicinity of atmospheric pressure, the solubility is almost zero, and even if the pressure and temperature are drastically reduced, the properties of the particles are hardly affected. However, if the solubility before the sudden release of the residual pressure shows a substantial value that cannot be ignored, even if the absolute value of the solubility is low, the solubility ratio in that condition satisfies the nucleation condition and a critical nucleus is generated. By doing so, fine particles may adhere to or grow independently on the surface of large particles that have already grown to some extent.

【００２２】これまでの説明では臨界核発生の過飽和度
比Ｘ／Ｘｐを2.2 と仮定して便宜的に述べたが、現在の
技術ではこの値を容易に測定することができない。仮に
測定できたとしても、温度、圧力、溶解度等の全ての操
作条件、溶質や溶媒の種類、更には微量添加される酸ま
たはアルカリ或はいわゆるエントレーナ等の影響を受け
るであろうから、特定の条件を明らかにしても一般的な
意味はない。また操業条件に関しても減圧をどの程度の
速度で行うか、或は途中で一旦中断して段階的に減圧し
ていくかといったことなども、個々の対象物質、条件、
目的粒子の性状をもとにして適応条件が定められる。し
かしながら本発明は高圧容器の閉じられた系内で行うも
のであるので、比較的余裕のある条件範囲で再現し得る
ものであって工業的操作に困惑を来たすほど厳密な条件
設定が求められるものではない。In the above description, the supersaturation ratio X / Xp for critical nucleation was assumed to be 2.2 for convenience, but this value cannot be easily measured with the current technology. Even if it could be measured, it would be affected by all operating conditions such as temperature, pressure, solubility, type of solute and solvent, and acid or alkali added in a trace amount, or so-called entrainer. Clarifying the conditions has no general meaning. Regarding the operating conditions, how much decompression should be performed, or whether it should be interrupted once in the middle and gradually reduced in pressure, etc.
Adaptive conditions are determined based on the properties of the target particles. However, since the present invention is carried out in a closed system of a high-pressure container, it can be reproduced in a relatively wide range of conditions, and strict condition setting is required so as to cause confusion in industrial operation. is not.

【００２３】また上記の説明においては、出発条件とし
て図１の点Ａからの断熱膨張の例で説明してきたが、こ
の条件では臨界点以下の圧力を通って気液共存線に入っ
て、液滴が発生しはじめる。この時点において、なお相
当量の溶解度が残留していれば、液滴として凝集する水
分自体が表１に示した傾向を有し、かつ水分子とＳｉＯ
₂ 分子が混合または水素会合したクラスター、更には臨
界核を構成することもあり得る。そして上記水滴は、数
を増し、または成長する。そして最終に水分が除去され
た場合には固体が得られる。この過程を図２の水蒸気圧
の温度−比エントロピ線図上で示せば、気液共存領域を
示す境界線の頂点（臨界点ｃ）より右側を点Ａから直下
に下降することを意味する。In the above description, the example of adiabatic expansion from the point A in FIG. 1 has been described as the starting condition, but under this condition, the liquid enters the gas-liquid coexistence line through the pressure below the critical point, Drops start to form. At this point, if a considerable amount of solubility still remains, the water itself which aggregates as droplets has the tendency shown in Table 1, and water molecules and SiO 2
_{It is possible that two} molecules form a mixed or hydrogen-associated cluster or even a critical nucleus. Then, the water droplets increase in number or grow. Then, when water is finally removed, a solid is obtained. If this process is shown on the temperature-specific entropy diagram of the water vapor pressure in FIG. 2, it means that the point on the right side of the apex (critical point c) of the boundary line showing the gas-liquid coexistence region descends directly from the point A.

【００２４】これに対して図１および図２の点Ｂは超臨
界状態から、亜臨界状態（臨界温度よりも低い液相域）
を経て、或は点Ｂ′は亜臨界状態から出発して減圧し臨
界点ｃの液側（左側）を通って気液共存域に入る。On the other hand, point B in FIGS. 1 and 2 is changed from the supercritical state to the subcritical state (liquid phase region lower than the critical temperature).
Or at the point B'starting from the subcritical state, the pressure is reduced and passes through the liquid side (left side) of the critical point c into the gas-liquid coexisting region.

【００２５】亜臨界状態における臨界核発生について
も、数値は表１の場合と異なるが、臨界核半径、核発生
頻度と過飽和度比の関係はやはり同じ傾向を示す。また
亜臨界域から気液共存域に入る場合においては、前記点
Ａを出発点とする場合と異なり、水蒸気の割合が増加す
る方向に状態変化が進みながら飽和溶解度が下降するこ
とになる。Regarding the critical nucleus generation in the subcritical state, although the numerical values are different from those in Table 1, the relationship between the critical nucleus radius, the nuclear generation frequency and the supersaturation ratio shows the same tendency. In addition, when entering the gas-liquid coexistence region from the subcritical region, unlike the case where the point A is used as a starting point, the saturated solubility decreases while the state change progresses in the direction in which the proportion of water vapor increases.

【００２６】亜臨界からまたは亜臨界を通過して減圧
し、微粒子を作る場合においても、圧力下降速度を制御
することによって様々な形態の微粒子が得られる。さら
に亜臨界の液体から気液共存域に入ることによって気化
の進行に伴う凝集メカニズムの変化も利用し、一層多様
な形状、粒度分布が期待できる。Even when the fine particles are produced by depressurizing from or through the subcritical state, various forms of fine particles can be obtained by controlling the pressure lowering rate. Furthermore, by entering the gas-liquid coexistence region from the subcritical liquid, the change in the agglomeration mechanism accompanying the progress of vaporization is also utilized, and more diverse shapes and particle size distributions can be expected.

【００２７】以上述べてきた核は、主として分子レベル
の凝集であるが、これが成長したときの粒子は、超微細
粒子の凝集体であることを必ずしも意味するものではな
い。成長した粒子は、アモルファス状の固体であり、ま
たそれが成長の過程や取出しまでの温度経過等により、
一部または全部が結晶構造になることもあり得るし、ま
たそれらが凝集することもあり得る。The nuclei described above are mainly agglomerates at the molecular level, but the particles when they grow do not necessarily mean that they are agglomerates of ultrafine particles. The grown particles are amorphous solids, and depending on the growth process and the temperature elapse until extraction,
Some or all of them may have a crystalline structure, and they may aggregate.

【００２８】本発明によって得られる微粒子がその形態
において広範な多様性を有していることを以下説明す
る。まず比較的穏やかな過飽和条件下で製造すると、分
子または極めて小さな（一般に臨界核半径以下の半径
の）粒子も大きな粒子の表面に付着するように成長す
る。またＸ／Ｘｐを小さくして成長した後新たに核発生
をし得る条件が与えられた場合には、新たに生成した核
が大きくなりかけた状態で、先に存在する大きな微粒子
に付着することもある。更に新たな核発生はしないが、
過飽和度が相当に高いような条件で製造すると球状微粒
子表面にひげ状体が急成長する。尚ひげ状体が成長する
微粒子については、表１における臨界半径が示すとお
り、過飽和度比が小さくなるとある程度以上の大きさの
ひげでなければ、エネルギー的にＸ／Ｘｐ＝１の条件で
は存在が許容されず、急激にＸ／Ｘｐ＝１になる時はす
でに発生していたひげが消失することもあり得る。It will be explained below that the fine particles obtained by the present invention have a wide variety of morphology. When first prepared under relatively mild supersaturated conditions, molecules or very small particles (generally below the critical core radius) also grow to adhere to the surface of large particles. Further, when the condition that new nucleation is possible after growth with a small X / Xp is given, the newly generated nuclei should be attached to the large particles that are present before the nuclei become large. There is also. No further nucleation,
When produced under conditions where the degree of supersaturation is considerably high, whiskers grow rapidly on the surface of the spherical fine particles. As shown in the critical radius in Table 1, if the whisker-like particles grow, if the whiskers have a whisker of a certain size or more when the supersaturation ratio becomes small, they will exist under the condition of X / Xp = 1 in terms of energy. It is not allowed, and when X / Xp = 1 suddenly, the whiskers that have already occurred may disappear.

【００２９】上記の説明では凝集する物質は、溶質であ
るとの前提で述べたが、溶質と溶媒が会合し、吸着する
などした状態のクラスターや凝集体が発生することも当
然あり得る。このような場合には、高圧力下で凝集した
粒子は、減圧過程で溶媒が再び気化消失して粒子が多孔
質になったり、条件によっては「空気の抜けたボール」
のように変形した後固い粒子として取出されることもあ
る。In the above description, the substance to be aggregated is described as a solute. However, it is naturally possible that a solute and a solvent associate with each other to generate a cluster or aggregate in a state of being adsorbed. In such a case, the particles agglomerated under high pressure, the solvent is vaporized again in the depressurization process and the particles become porous, or "air deflated balls" depending on the conditions.
After being deformed as described above, it may be extracted as hard particles.

【００３０】本発明は降圧にともなう過飽和の発生を駆
動力とするものであるから、できれば溶質は、降圧開始
条件における飽和溶解度に近く溶解しておくことが、圧
力の効率的利用の立場からは好ましいが、目的によって
は未飽和の状態から減圧し飽和を経て過飽和に至ること
もあり得る。Since the present invention uses the driving force to generate supersaturation due to the pressure drop, it is preferable from the standpoint of efficient use of pressure that the solute is dissolved close to the saturation solubility under the pressure drop start condition, if possible. It is preferable, but depending on the purpose, it is possible that the unsaturated state is reduced to depressurize and then saturated to reach supersaturation.

【００３１】また本発明は気体分子運動論などの統計力
学に基礎をおく臨界核発生理論を考察することによって
得られたもので、極めて一般性が高い。従ってＳｉＯ₂
／超臨界水の例に留まらず、高温高圧力下で溶解度を増
す全ての系に適用され、水を溶媒とするものでは種々の
酸化物、一部の水酸化物、或は一部の硫酸塩や燐酸塩な
どの種々の化合物の微粒子が得られる。このとき用いる
水は適量の酸またはアルカリやハロゲンを添加するなど
溶解度を増すように調整したものであってもよい。また
溶媒を二酸化炭素、メタン、プロパン、メタノールをは
じめ近年超臨界抽出に使われているような溶媒とするこ
とによって有機物などの微粒子も得られる。２種以上の
溶質を超臨界流体に適正なモル比で溶解し、反応させて
微粒子を得ることも可能である。The present invention was obtained by considering the theory of critical nucleus generation based on statistical mechanics such as gas molecule kinetic theory, and is extremely general. Therefore SiO ₂
Not limited to supercritical water, it is applicable to all systems that increase solubility under high temperature and high pressure, and when water is used as a solvent, various oxides, some hydroxides, or some sulfuric acid are used. Fine particles of various compounds such as salts and phosphates are obtained. The water used at this time may be adjusted to increase the solubility by adding an appropriate amount of acid, alkali or halogen. Fine particles such as organic substances can also be obtained by using a solvent such as carbon dioxide, methane, propane, and methanol which has been used in recent years for supercritical extraction. It is also possible to dissolve two or more solutes in a supercritical fluid at an appropriate molar ratio and react them to obtain fine particles.

【００３２】本発明における微粒子生成の駆動力は断熱
膨張である。これによって高圧容器内を非常に広い膨張
速度範囲で均一に制御できる。ここでいう断熱膨張は高
圧容器の閉じられた系内で行われるから、断熱膨張時の
流体の温度下降はさけられず、従って膨張開始温度に保
持された容器から流体への熱の流入はさけられない。比
較的低温に保持した他の高圧容器に流体を移しかえて断
熱膨張させる場合には逆に熱の流出をともなう。しかし
これらは操作上必要な伝熱であって凝集、析出の駆動力
が圧力変化に伴う断熱膨張であることに変りはない。The driving force for producing fine particles in the present invention is adiabatic expansion. As a result, the inside of the high-pressure container can be uniformly controlled within a very wide expansion velocity range. Since the adiabatic expansion here is performed in the closed system of the high-pressure container, the temperature drop of the fluid during adiabatic expansion is unavoidable, and therefore the inflow of heat into the fluid from the container held at the expansion start temperature is avoided. I can't. On the contrary, when the fluid is transferred to another high-pressure container kept at a relatively low temperature to be adiabatically expanded, heat is conversely discharged. However, these are heat transfer necessary for operation, and the driving force for aggregation and precipitation is adiabatic expansion accompanying pressure change.

【００３３】本発明の微粒子を被覆する方法は、基本的
には上述の超臨界流体を利用した微粒子の作製方法を応
用するものであり、２種類の溶質を夫々別々に超臨界流
体あるいは亜臨界流体に溶解した後、第１の溶媒を温
度、圧力を低下させて溶質の微粒子を作製し、次に第２
の溶媒と混合し、その後圧力及び温度を低下させて、第
１の微粒子表面に第２の溶質を析出させ、被覆微粒子を
作製するものである。この方法における重要点は、 第１の微粒子生成後、残留した溶液には新たな核発生
や既に生成した粒子を成長させるだけの溶質濃度が無い
こと、 第２の溶媒と混合した際第１の微粒子が溶解しないこ
と又は溶解するとしても極く微量であること、 混合時に第２の溶質が核を発生して第１の溶質に対し
て独立した粒子を成長させることがないこと、 の３点である。The method of coating fine particles of the present invention basically applies the above-described method of producing fine particles using a supercritical fluid, and the two solutes are separately supercritical fluid or subcritical fluid. After being dissolved in the fluid, the temperature and pressure of the first solvent are lowered to prepare solute fine particles, and then the second solvent is added.
The solvent and the solvent are mixed together, and then the pressure and temperature are lowered to precipitate the second solute on the surface of the first fine particles to prepare coated fine particles. The important point in this method is that after the formation of the first fine particles, the remaining solution does not have a solute concentration enough to generate new nuclei or grow the already formed particles. The three points are that the fine particles do not dissolve, or that there is a very small amount even if they dissolve, and that the second solute does not generate nuclei and grow independent particles with respect to the first solute during mixing. Is.

【００３４】重要点，の達成のためには第１の溶質
の微粒子作製をできるだけ低温、低圧で行なう。例えば
図１において、温度、圧力を下げると溶解度は下る。十
分に温度を下げ、圧力を０にすれば溶解度が下り生成し
た微粒子の周囲の溶媒には新たな核を発生あるいは成長
させる能力は無い。次に、この状態で第２溶媒と同じ圧
力まで加圧する。温度によってはこの時溶解能力が増加
するが、温度が十分低い状態でかつ短時間であればこの
心配は無く、既生成の微粒子が溶解消滅することはな
い。次にこの同圧状態で第２溶媒と混合すると混合直後
には、第１溶媒と第２溶媒の中間的な温度になる。即ち
第１溶媒の温度は上昇することになる。この時溶解度が
増えると問題であるが、実際には図１の600Bars までの
データで見るように圧力一定では溶解度は温度変化に対
して極大値をとることがわかる。この傾向は温度上昇に
よる溶媒能の上昇と密度の低下（密度と溶解度がほぼ比
例）のためと言われており、いずれの溶媒、溶質でも成
り立つものである。図３に酸化ランタンの水への溶解度
を示す。従って溶質微粒子を含む第１溶媒が第２溶媒と
同圧下で温度上昇があっても第１溶媒の溶解能力はむし
ろ下ることになり、微粒子が溶解消滅することはない。In order to achieve the important point, the fine particles of the first solute are prepared at the lowest possible temperature and low pressure. For example, in FIG. 1, the solubility decreases as the temperature and pressure are lowered. If the temperature is sufficiently lowered and the pressure is set to 0, the solubility decreases and the solvent around the generated fine particles has no ability to generate or grow new nuclei. Next, in this state, the pressure is increased to the same pressure as the second solvent. Depending on the temperature, the dissolution capacity increases at this time, but if the temperature is sufficiently low and the time is short, this concern does not occur, and the generated fine particles do not dissolve and disappear. Next, when the second solvent is mixed in the same pressure state, the temperature becomes an intermediate temperature between the first solvent and the second solvent immediately after mixing. That is, the temperature of the first solvent will rise. At this time, there is a problem when the solubility increases, but in reality it can be seen that the solubility takes a maximum value with respect to temperature changes at a constant pressure, as can be seen from the data up to 600 Bars in FIG. It is said that this tendency is due to an increase in solvent ability and a decrease in density due to temperature increase (the density and the solubility are almost proportional to each other), and is valid for any solvent and solute. Figure 3 shows the solubility of lanthanum oxide in water. Therefore, even if the temperature of the first solvent containing the solute particles is increased under the same pressure as that of the second solvent, the dissolving ability of the first solvent is rather decreased, and the particles are not dissolved and disappeared.

【００３５】の重要点について述べると、第２溶媒は
混合前に高温に保たれ第２溶質を飽和溶解しており、第
１溶媒に混合直後温度が低下する為、上記の溶解度の極
大値の高温側から該極大値に向って溶解度が変化するの
で溶媒の溶解能力は増加し、従って混合時に第２溶質が
析出することはない。第１溶媒と第２溶媒の混合状態で
は、第１溶媒で若干薄められた第２溶媒の中に、第２溶
質が完全に溶け込んでおり、その中に第１溶質の微粒子
が浮遊している状態が生じる。次にこの混合流体を減圧
膨張させ、第２溶媒への第２溶質の溶解度の過飽和を起
させると、第１溶質の微粒子は種の役目を果し、第２溶
質がこの微粒子の表面に析出し成長する。この工程では
第１溶質はほとんど溶けていないので溶液から新たに核
発生することはない。また過飽和度の制御すなわち圧力
温度コントロールにより、第２溶質の新たな核も発生せ
ず、第１溶質微粒子に第２溶質を被覆することができ
る。As to the important point of the above, since the second solvent is kept at a high temperature before the mixing and the second solute is saturated and dissolved, and the temperature immediately after the mixing is lowered in the first solvent, the maximum value of the above-mentioned solubility is obtained. Since the solubility changes from the high temperature side toward the maximum value, the solvent dissolution capacity increases, and therefore the second solute does not precipitate during mixing. In the mixed state of the first solvent and the second solvent, the second solute is completely dissolved in the second solvent slightly diluted with the first solvent, and the fine particles of the first solute are suspended in the second solvent. A condition arises. Next, when the mixed fluid is expanded under reduced pressure to cause supersaturation of the solubility of the second solute in the second solvent, the fine particles of the first solute serve as a seed, and the second solute is deposited on the surface of the fine particles. And grow. In this step, the first solute is hardly dissolved, so that no new nucleation occurs from the solution. Further, by controlling the degree of supersaturation, that is, controlling the pressure and temperature, new nuclei of the second solute are not generated, and the first solute fine particles can be coated with the second solute.

【００３６】以上のように、溶解度の温度依存性の特徴
（極大値を持つこと）を利用し、夫々の物質の溶解度の
極大値の両側で夫々別個に溶解した後、混合して被覆微
粒子を作製する。As described above, the characteristics of the temperature dependence of the solubility (having the maximum value) are utilized, and the particles are separately dissolved on both sides of the maximum value of the solubility of each substance, and then mixed to form the coated fine particles. Create.

【００３７】上記製造方法を実現する装置構成を図４に
示す。夫々ピストン棒が挿入された第１、第２、第３高
圧高温容器三筒が図のようにバルブを介して連通してい
る。第１容器、第２容器、第３容器は夫々温度が異なっ
ている。第１容器には第１溶質が溶解し、第３容器には
第２溶質が溶解している。第２容器は空の状態で、ピス
トン棒は上端側にあり、温度は低い。第１バルブを開
き、第１容器内の溶媒を第２容器内のピストン棒を引下
げることにより膨張させ第１容器のピストン棒で送り出
す。第２容器内では温度、圧力が下がり微粒子が析出す
る。次に第１バルブを閉じ、第２容器を第３容器と同圧
まで加圧する。第２バルブを開き、第２容器のピストン
棒で第２容器内溶媒を第３容器内へ圧力一定で移送す
る。（又は第３容器から第２容器へ移送してもよい。）
その後第３容器のピストン棒を後退させて減圧膨張さ
せ、第２容器から送り込んだ微粒子の表面に第３容器内
の第２溶質を析出させて、コーティング（被覆）する。
その後第３バルブを開き、第３容器のピストン棒を前進
させて被覆微粒子を回収する。FIG. 4 shows an apparatus configuration for realizing the above manufacturing method. The first, second, and third high-pressure high-temperature container three cylinders into which the piston rods are inserted respectively communicate with each other via valves as shown in the figure. The first container, the second container, and the third container have different temperatures. The first solute is dissolved in the first container and the second solute is dissolved in the third container. The second container is empty, the piston rod is on the upper end side, and the temperature is low. The first valve is opened, the solvent in the first container is expanded by pulling down the piston rod in the second container, and the solvent is delivered by the piston rod in the first container. In the second container, the temperature and pressure are lowered and fine particles are deposited. Next, the first valve is closed and the second container is pressurized to the same pressure as the third container. The second valve is opened, and the solvent in the second container is transferred into the third container with a constant pressure by the piston rod of the second container. (Or you may transfer from a 3rd container to a 2nd container.)
After that, the piston rod of the third container is retracted and expanded under reduced pressure, and the second solute in the third container is deposited on the surface of the fine particles sent from the second container and coated.
After that, the third valve is opened and the piston rod of the third container is advanced to collect the coated fine particles.

【００３８】本発明によって得られた微粒子はその表面
積の大きさ、活性の高さ、そしてその他微粒子の形態的
特徴等を有効に利用することにより、多用な用途が考え
られる。微粒子の工業的利用技術の開発は今後多くの先
端技術分野に進展し得るものと考えられるから、本発明
で得られる微粒子の応用範囲は今後更に拡大していくも
のと期待される。The fine particles obtained by the present invention can be used for various purposes by making effective use of the surface area size, high activity, and other morphological characteristics of the fine particles. Since it is considered that the development of industrial use technology of fine particles can progress to many advanced technical fields in the future, the application range of the fine particles obtained by the present invention is expected to be further expanded in the future.

【００３９】以下本発明を実施例によって、更に具体的
に説明するが、下記実施例は本発明を限定する性質のも
のではなく、前・後記の趣旨に徴して設計変更すること
は、いずれも本発明の技術的範囲に含まれるものであ
る。The present invention will be described in more detail with reference to the following examples. However, the following examples are not intended to limit the present invention, and any design changes may be made in view of the spirit of the preceding and the following. It is included in the technical scope of the present invention.

【００４０】[0040]

【実施例】図４に本発明を実施する為に構成される装置
構成例の概略説明図を示す。シリカ（ＳｉＯ₂ ）微粒子
に酸化ランタン（Ｌａ₂ Ｏ₃ ）を以下に記すようにコー
ティングした。DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 4 is a schematic explanatory view of an example of the configuration of an apparatus configured to carry out the present invention. Fine particles of silica (SiO ₂ ) were coated with lanthanum oxide (La ₂ O ₃ ) as described below.

【００４１】内容積140ml の外熱式第１高圧容器１に水
晶（シリカ単結晶，ＳｉＯ₂ ）の粒（約２〜３mm米粒
大）約20g をステンレス製の網に包んで挿入し、施蓋密
閉後550 ℃に昇温した。その後該第１容器１に連通した
ポンプにより第１容器１内へ水を供給し600kgf/cm²に加
圧した後供給側のバルブを閉め５時間保持した。次に別
に200 ℃に保持した内容積140ml の空の外熱式高圧容器
２との連絡バルブ４を開き、シリカを溶解した第１容器
１のピストンを進め、空の第２容器２のピストンを後退
させて空の第２容器２内へ減圧膨張させた。この時の第
２容器２内の温度は（ＣＡ熱電対により測定）は約300
℃であった。圧力が０であることを確認した後、別途酸
化ランタン（Ｌａ₂ Ｏ₃ ）のパウダ（−80メッシュ）を
シリカの場合と同様に外熱式第３容器３内で水に溶解
し、550 ℃，600kgf/cm²で５時間保持した。第３容器３
との連絡バルブ５を開き、シリカの入っている第２容器
２のピストンで圧力を一定に保持しながら酸化ランタン
の入っている第３容器３のピストンを押し進め、内部流
体全量を移動した。移動後の第２容器２内温度は約400
℃であった。次に第２容器２のピストンを後退させて容
器内を圧力０まで徐々に減圧した。その後開放バルブ６
を開けて第２容器のピストンを前進させ、内部の流体を
排出、捕集し、メンブレンフィルタで濾過し、メンブレ
ンフィルタ上に残留した微粒子を電子顕微鏡（ＳＥＭ）
で観察し、同時にＥＰＭＡによる元素分析を行った結
果、微粒子を確認でき、Ｓｉ及びＬａ元素が検出され
た。Approximately 20 g of crystal (silica single crystal, SiO ₂ ) particles (about 2-3 mm rice grain size) are wrapped in a stainless steel net and inserted into the externally heated first high-pressure container 1 having an internal volume of 140 ml, and the lid is closed. After sealing, the temperature was raised to 550 ° C. After that, water was supplied into the first container 1 by a pump communicating with the first container 1 to pressurize it to 600 kgf / cm ² , and then the valve on the supply side was closed and kept for 5 hours. Next, open the communication valve 4 for the empty externally heated high-pressure vessel 2 with an internal volume of 140 ml that was kept at 200 ° C, advance the piston of the first vessel 1 in which silica was dissolved, and move the piston of the empty second vessel 2 It was retracted and expanded under reduced pressure into the empty second container 2. At this time, the temperature in the second container 2 (measured by CA thermocouple) is about 300.
It was ℃. After confirming that the pressure was 0, a powder (-80 mesh) of lanthanum oxide (La ₂ O ₃ ) was separately dissolved in water in the external heating type third container 3 in the same manner as in the case of silica, and 550 ° C. , 600 kgf / cm ² for 5 hours. Third container 3
The communication valve 5 was opened, and the piston of the third container 3 containing lanthanum oxide was pushed forward while the pressure of the piston of the second container 2 containing silica was kept constant to move the entire internal fluid. The temperature inside the second container 2 after transfer is about 400.
It was ℃. Next, the piston of the second container 2 was retracted to gradually reduce the pressure inside the container to zero. Then open valve 6
Open the piston and move the piston of the second container forward, discharge and collect the fluid inside, filter with a membrane filter, and remove the fine particles remaining on the membrane filter with an electron microscope (SEM).
As a result of the elemental analysis by EPMA at the same time, fine particles were confirmed and Si and La elements were detected.

【００４２】[0042]

【発明の効果】本発明は以上のように構成されているの
で、超臨界状態または亜臨界状態にある溶媒中から、溶
質を再現性良く析出・成長させて微粒子を製造すること
ができ、また回収も容易で、操作が簡単で、さらに装置
の大形化が可能な単純な装置構成で、安価な被覆微粒子
を製造することができる方法が提供できることとなっ
た。EFFECT OF THE INVENTION Since the present invention is constituted as described above, fine particles can be produced by reproducibly depositing and growing a solute from a solvent in a supercritical state or a subcritical state. Thus, it is possible to provide a method capable of producing inexpensive coated fine particles with a simple device configuration that is easy to recover, easy to operate, and can be upsized.

【図面の簡単な説明】[Brief description of drawings]

【図１】高温高圧水中へのＳｉＯ₂ の溶解度の変化を示
すグラフである。FIG. 1 is a graph showing changes in the solubility of SiO _{2 in} high temperature and high pressure water.

【図２】水蒸気圧の温度−エントロピ線図である。FIG. 2 is a temperature-entropy diagram of water vapor pressure.

【図３】高温高圧水中へのＬａ₂ Ｏ₃ の溶解度の変化を
示すグラフである。FIG. 3 is a graph showing changes in the solubility of La ₂ O _{3 in} high temperature and high pressure water.

【図４】本発明を実施するための各種装置構成例を示す
概略説明図である。FIG. 4 is a schematic explanatory diagram showing a configuration example of various devices for carrying out the present invention.

Claims (2)

【特許請求の範囲】[Claims] 【請求項１】 第１溶質と第２溶質を夫々対応する第１
溶媒と第２溶媒に別々に溶解して夫々を超臨界状態また
は亜臨界状態の第１系と第２系とした後、第１系を断熱
膨張させ過飽和状態を経て第１溶質の微粒子を生成し、
これを再び第２系と同一の圧力まで昇圧してから第２系
と混合し、その後該混合系を断熱膨張させ過飽和状態を
経て上記第１溶質の微粒子表面に第２溶質を析出せしめ
て被覆微粒子を形成することを特徴とする被覆微粒子の
製造方法。1. A first solute corresponding to each of the first solute and the second solute.
Dissolve in a solvent and a second solvent separately to form a first system and a second system in a supercritical state or a subcritical state respectively, and then adiabatically expand the first system to generate fine particles of a first solute through a supersaturated state. Then
This is again pressurized to the same pressure as the second system, mixed with the second system, and then the mixed system is subjected to adiabatic expansion to cause a supersaturated state and then the second solute is deposited on the surface of the fine particles of the first solute and coated. A method for producing coated fine particles, which comprises forming fine particles. 【請求項２】 請求項１の方法で被覆微粒子を形成した
後、更に第ｎ（ｎは３以上の自然数）溶質と第ｎ溶媒か
らなる第ｎ系との間に請求項１と同様の操作を行い（ｎ
−１）層の被覆層で被覆微粒子を形成することを特徴と
する被覆微粒子の製造方法。2. The same operation as in claim 1 after forming coated fine particles by the method of claim 1 and further between the n-th (n is a natural number of 3 or more) solute and the n-th system consisting of the n-th solvent. (N
-1) A method for producing coated fine particles, which comprises forming coated fine particles with a coating layer of layer 1.