JP7323880B2 - Cerium oxide fine particle dispersion and method for producing cerium oxide fine particles - Google Patents
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この発明は、シングルナノサイズの酸化セリウム微粒子分散液及び酸化セリウム微粒子の製造方法に関する。 TECHNICAL FIELD The present invention relates to a dispersion of single nano-sized cerium oxide fine particles and a method for producing cerium oxide fine particles.
従来から、磁気記録媒体用基板、半導体ウエハ、光学レンズ、プリズム、ミラー等の製造において、ガラス、カーボン及びセラミックス等の材料の表面を研磨する研磨材として、酸化セリウム粒子が使用されており、ガラス、カーボン及びセラミックス等の材料表面に傷を付けることがないように、シングルナノサイズで粒度の揃った酸化セリウム微粒子が求められている。 Conventionally, cerium oxide particles have been used as an abrasive for polishing the surfaces of materials such as glass, carbon, and ceramics in the manufacture of substrates for magnetic recording media, semiconductor wafers, optical lenses, prisms, mirrors, and the like. In order not to damage the surface of materials such as carbon and ceramics, there is a demand for cerium oxide fine particles having a single nano-size and a uniform particle size.
また、酸化セリウム粒子は、ガソリン車・ディーゼル車の排出ガス中の３種類の有害成分（炭化水素 (ＨＣ) 、一酸化炭素 (ＣＯ) 、窒素酸化物（ＮＯＸ））を酸化・還元によって同時に浄化する三元触媒の助触媒としても使用されており、その酸素貯蔵放出能力により、排出ガス中の酸素濃度を一定にすることで、主触媒による排出ガスの浄化効率を向上させる役割を果たしている。特に、酸化セリウム粒子を微細化することにより、排出ガスとの比界面積が増加し、酸素の貯蔵・放出の応答性がよくなり、これに伴って、主触媒による排出ガスの浄化効率がさらに向上すると考えられるので、酸化セリウム粒子を微細化することが期待されている。 In addition, cerium oxide particles simultaneously oxidize and reduce three types of harmful components (hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides ( NOx )) in exhaust gas from gasoline and diesel vehicles. It is also used as a co-catalyst for a purifying three-way catalyst, and its oxygen storage and release capacity keeps the oxygen concentration in the exhaust gas constant, thereby improving the exhaust gas purification efficiency of the main catalyst. . In particular, by miniaturizing the cerium oxide particles, the specific interfacial area with the exhaust gas increases, improving the responsiveness of oxygen storage and release, and along with this, the purification efficiency of the exhaust gas by the main catalyst is further improved. Therefore, it is expected to refine the cerium oxide particles.
酸化セリウム微粒子の製造方法は、例えば、特許文献１に開示されている。この製造方法では、硫酸セリウム水溶液または塩化セリウム水溶液と水酸化ナトリウム水溶液とを、酸化セリウム（ＣｅＯ２）換算のモル数に対する水酸化ナトリウムのモル数の割合（ＮａＯＨ／ＣｅＯ２）が１～１０となる範囲で混合し、５０～９８℃に加温した状態で、３～２４時間熟成した後、冷却することにより沈殿物を生成するようになっており、これを乾燥することで結晶子径５～５０ｎｍの酸化セリウム微粒子得ることができる。 A method for producing cerium oxide microparticles is disclosed in Patent Document 1, for example. In this production method, an aqueous solution of cerium sulfate or an aqueous solution of cerium chloride and an aqueous solution of sodium hydroxide are mixed so that the ratio of the number of moles of sodium hydroxide to the number of moles of cerium oxide (CeO 2 ) (NaOH/CeO 2 ) is 1 to 10. After mixing in a range of 50 to 98 ° C., aging for 3 to 24 hours, and cooling to form a precipitate, which is dried to have a crystallite diameter of 5. Cerium oxide microparticles of ~50 nm can be obtained.
しかしながら、上述した製造方法では、５０～９８℃に加温した状態で、３～２４時間熟成する必要があるので、生産効率が悪いといった問題がある。 However, in the production method described above, since it is necessary to heat the product to 50 to 98° C. for 3 to 24 hours, there is a problem that the production efficiency is low.
そこで、この発明の課題は、シングルナノサイズの酸化セリウム微粒子が分散された酸化セリウム微粒子分散液及びシングルナノサイズの酸化セリウム微粒子を低コストで簡単に製造することにある。 Accordingly, an object of the present invention is to easily produce a cerium oxide fine particle dispersion in which single nano-sized cerium oxide fine particles are dispersed and single nano-sized cerium oxide fine particles at low cost.
上記の課題を解決するため、請求項１に係る発明は、比表面積相当直径が１０ｎｍ未満の酸化セリウム微粒子分散液の製造方法であって、セリウムイオン含有水溶液と塩基性水溶液とを混合してｐＨ＜８に調整した後、この混合液に対して酸素ガスの通気を開始し、この混合液が透明になった時点またはそれ以降の時点で酸素ガスの通気を停止した後に、酸性水溶液を加えてｐＨ≦１に調整することを特徴としている。
また、請求項２に係る発明は、比表面積相当直径が１０ｎｍ未満の酸化セリウム微粒子分散液の製造方法であって、セリウムイオン含有水溶液と塩基性水溶液とを混合してｐＨ＜８に調整した後、この混合液に対して酸素ガスの通気を開始し、この混合液が透明になった時点で、酸素ガスの通気を停止すると共に酸性水溶液を加えてｐＨ≦１に調整することを特徴としている。
In order to solve the above problems, the invention according to claim 1 is a method for producing a cerium oxide fine particle dispersion having a specific surface area equivalent diameter of less than 10 nm, wherein a cerium ion-containing aqueous solution and a basic aqueous solution are mixed to obtain a pH After adjusting to <8, oxygen gas bubbling is started through the mixture, and oxygen gas bubbling is stopped when the mixture becomes clear or later, and then an acidic aqueous solution is added. It is characterized by adjusting to pH≦1 .
Further, the invention according to claim 2 is a method for producing a cerium oxide fine particle dispersion liquid having a specific surface area equivalent diameter of less than 10 nm, wherein the cerium ion-containing aqueous solution and the basic aqueous solution are mixed to adjust the pH to <8. Aeration of oxygen gas is started to the mixed liquid, and when the mixed liquid becomes transparent, the aeration of oxygen gas is stopped and an acidic aqueous solution is added to adjust the pH to ≤ 1. .
前記セリウムイオン含有水溶液としては、塩化セリウム水溶液、硝酸セリウム水溶液等が挙げられる。 Examples of the cerium ion-containing aqueous solution include an aqueous cerium chloride solution and an aqueous cerium nitrate solution.
前記塩基性水溶液としては、水酸化カリウム水溶液、水酸化ナトリウム水溶液、水酸化リチウム水溶液、水酸化セシウム水溶液、アンモニア水等を使用することができる。 As the basic aqueous solution, an aqueous potassium hydroxide solution, an aqueous sodium hydroxide solution, an aqueous lithium hydroxide solution, an aqueous cesium hydroxide solution, an aqueous ammonia solution, or the like can be used.
また、酸素ガスの通気量は、１Ｌ／ｍｉｎ／１００ｍＬ以上１０Ｌ／ｍｉｎ／１００ｍＬ以下であることが好ましく、２Ｌ／ｍｉｎ／１００ｍＬ以上５Ｌ／ｍｉｎ／１００ｍＬ以下であることがより好ましい。 The oxygen gas flow rate is preferably 1 L/min/100 mL or more and 10 L/min/100 mL or less, and more preferably 2 L/min/100 mL or more and 5 L/min/100 mL or less.
前記酸性水溶液としては、塩酸、希硝酸、希硫酸等を使用することができる。 Hydrochloric acid, dilute nitric acid, dilute sulfuric acid, or the like can be used as the acidic aqueous solution.
また、請求項３に係る発明は、比表面積相当直径が１０ｎｍ未満の酸化セリウム微粒子の製造方法であって、請求項１または２に記載の製造方法により得られた酸化セリウム微粒子分散液から酸化セリウム微粒子を分離、回収することを特徴としている。 Further, the invention according to claim 3 is a method for producing cerium oxide fine particles having a specific surface area equivalent diameter of less than 10 nm, wherein the cerium oxide fine particle dispersion liquid obtained by the production method according to claim 1 or 2 is converted to cerium oxide fine particles. It is characterized by separating and collecting fine particles.
請求項１に係る発明の酸化セリウム微粒子分散液の製造方法では、セリウムイオン含有水溶液と塩基性水溶液とを混合してｐＨ＜８に調整した後、この混合液に対して酸素ガスの通気を開始し、この混合液が透明になった時点またはそれ以降の時点で酸素ガスの通気を停止することで、混合液中に粒子径が１０ｎｍ未満の酸化セリウム微粒子が生成されるので、粒子径が１０ｎｍ未満の酸化セリウム微粒子が分散された酸化セリウム微粒子分散液を製造することができる。 In the method for producing a cerium oxide fine particle dispersion according to the first aspect of the invention, the cerium ion-containing aqueous solution and the basic aqueous solution are mixed to adjust the pH to <8, and then oxygen gas is introduced into the mixed solution. However, by stopping the oxygen gas flow at the time when the mixture becomes transparent or at a time after that, cerium oxide microparticles having a particle diameter of less than 10 nm are generated in the mixture. It is possible to produce a cerium oxide fine particle dispersion in which less than cerium oxide fine particles are dispersed.
また、この酸化セリウム微粒子分散液の製造方法によれば、セリウムイオン含有水溶液を出発原料とし、塩基性水溶液の添加及び酸素ガスの通気という簡易な工程によって、加熱・熟成することなく、３０℃以下で短時間に粒子径が１０ｎｍ未満の酸化セリウム微粒子分散液を低コストで効率よく製造することができる。 Further, according to this method for producing a cerium oxide fine particle dispersion liquid, a cerium ion-containing aqueous solution is used as a starting material, and the cerium ion-containing aqueous solution is used as a starting material. , a cerium oxide fine particle dispersion having a particle diameter of less than 10 nm can be efficiently produced at low cost in a short period of time.
また、この酸化セリウム微粒子分散液の製造方法では、酸素ガスの通気を停止した後に、酸性水溶液を加えてｐＨ≦１に調整することで、生成された酸化セリウム微粒子の凝集が抑制され、分散性に優れた酸化セリウム微粒子分散液を得ることができる。 In addition, in this method for producing a cerium oxide fine particle dispersion, after stopping the oxygen gas flow, an acidic aqueous solution is added to adjust the pH to ≤ 1, thereby suppressing aggregation of the produced cerium oxide fine particles and dispersing them. A cerium oxide fine particle dispersion having excellent properties can be obtained.
特に、請求項２に係る発明の酸化セリウム微粒子分散液の製造方法では、混合液が透明になった時点で酸素ガスの通気を停止すると共に酸性水溶液を加えてｐＨ≦１に調整することで、生成された酸化セリウム微粒子の凝集だけでなく、粒成長も同時に抑制されるので、粒子径がより小さく、分散性に優れた酸化セリウム微粒子分散液を得ることができる。 In particular, in the method for producing a cerium oxide fine particle dispersion liquid according to the second aspect of the invention, when the mixed liquid becomes transparent, oxygen gas ventilation is stopped and an acidic aqueous solution is added to adjust the pH to ≤ 1. Since not only the aggregation of the generated cerium oxide fine particles but also grain growth is suppressed at the same time, it is possible to obtain a fine cerium oxide fine particle dispersion having a smaller particle size and excellent dispersibility.
また、請求項３に係る発明の酸化セリウム微粒子の製造方法のように、請求項１または２に記載の製造方法により得られた酸化セリウム微粒子分散液から酸化セリウム微粒子を分離、回収することで、粒子径が１０ｎｍ未満の酸化セリウム微粒子を得ることができる。 Further, as in the method for producing cerium oxide fine particles of the invention according to claim 3 , by separating and recovering the cerium oxide fine particles from the cerium oxide fine particle dispersion liquid obtained by the production method according to claim 1 or 2 , Cerium oxide microparticles having a particle diameter of less than 10 nm can be obtained.
特に、透明で分散性のよい酸化セリウム微粒子分散液については、アルコールを添加することによって酸化セリウム微粒子を凝集させ、これを分離回収すればよい。前記アルコールとしては、メチルアルコール、エチルアルコール、ｎ－プロピルアルコール、イソプロピルアルコール等の低脂肪族アルコールを使用することができる。 In particular, for a transparent cerium oxide fine particle dispersion liquid with good dispersibility, the cerium oxide fine particles are aggregated by adding alcohol, and then separated and recovered. As the alcohol, low-fat alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol and isopropyl alcohol can be used.
以下、本発明の実施例について図面を参照して説明するが、本発明の酸化セリウム微粒子分散液及び酸化セリウム微粒子の製造方法は実施例に限定されるものではない。 EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings, but the cerium oxide fine particle dispersion and the method for producing cerium oxide fine particles of the present invention are not limited to the examples.
（実施例１）
表１及び表２に示すように、塩化セリウム７水和物［ＣｅＣｌ３・７Ｈ２Ｏ］（分子量３７２．５８）を用いて調整した０．１ｍｏｌ／Ｌの塩化セリウム水溶液５０ｍＬと、０．２ｍｏｌ／Ｌに調整した水酸化ナトリウム水溶液２５ｍＬとを混合した後、酸素ガスを２Ｌ／ｍｉｎの流量で１時間通気した。なお、塩化セリウム水溶液と水酸化ナトリウム水溶液とを混合した時点（酸素ガスの通気前）のｐＨは５．１９であった。塩化セリウム水溶液と水酸化ナトリウム水溶液との混合液は、初期時点で不透明なピンク色を呈するが、酸素ガスの通気を開始して１０分程度経過すると透明な褐色となり、酸素ガスの通気を停止した時点（酸素ガスの通気を開始して１時間経過した時点）で不透明な淡黄白色の粒子分散液が得られた。このようにして得られた粒子分散液を遠心分離（１００００ｒｐｍ、５分）することによって淡黄白色の粒子を回収し、１７０℃のオーブンで一晩乾燥を行った。
(Example 1)
As shown in Tables 1 and 2, 50 mL of a 0.1 mol/L cerium chloride aqueous solution prepared using cerium chloride heptahydrate [CeCl 3.7H 2 O] (molecular weight 372.58) and 0.2 mol After mixing with 25 mL of an aqueous sodium hydroxide solution adjusted to /L, oxygen gas was passed through at a flow rate of 2 L/min for 1 hour. The pH was 5.19 when the cerium chloride aqueous solution and the sodium hydroxide aqueous solution were mixed (before oxygen gas was introduced). The mixed liquid of the cerium chloride aqueous solution and the sodium hydroxide aqueous solution exhibited an opaque pink color at the initial stage, but turned transparent brown after about 10 minutes from the start of the oxygen gas ventilation, and the oxygen gas ventilation was stopped. An opaque pale yellowish white particle dispersion was obtained at the time point (one hour after the oxygen gas was introduced). The thus-obtained particle dispersion was centrifuged (10000 rpm, 5 minutes) to collect pale yellowish white particles, which were dried in an oven at 170° C. overnight.
（実施例２）
表１及び表２に示すように、０．１ｍｏｌ／Ｌの塩化セリウム水溶液５０ｍＬと、０．２ｍｏｌ／Ｌの水酸化ナトリウム水溶液５０ｍＬとを混合した点を除き、実施例１と同様の方法により、粒子分散液及び粒子を生成した。なお、塩化セリウム水溶液と水酸化ナトリウム水溶液とを混合した時点（酸素ガスの通気前）のｐＨは７．３４であった。塩化セリウム水溶液と水酸化ナトリウム水溶液との混合液は、実施例１と同様に、初期時点で不透明なピンク色を呈するが、酸素ガスの通気を開始して１０分程度経過すると透明な褐色となり、酸素ガスの通気を停止した時点（酸素ガスの通気を開始して１時間経過した時点）で得られた粒子分散液は不透明な淡黄白色を呈していた。
(Example 2)
As shown in Tables 1 and 2, in the same manner as in Example 1, except that 50 mL of 0.1 mol/L cerium chloride aqueous solution and 50 mL of 0.2 mol/L sodium hydroxide aqueous solution were mixed. A particle dispersion and particles were produced. The pH was 7.34 when the cerium chloride aqueous solution and the sodium hydroxide aqueous solution were mixed (before oxygen gas was introduced). The mixed liquid of the cerium chloride aqueous solution and the sodium hydroxide aqueous solution was initially opaque pink in the same manner as in Example 1, but turned transparent brown after about 10 minutes from the start of oxygen gas ventilation. The particle dispersion obtained at the time when the oxygen gas ventilation was stopped (one hour after the oxygen gas ventilation was started) had an opaque pale yellowish white color.
（実施例３）
表１及び表２に示すように、塩化セリウム水溶液と水酸化ナトリウム水溶液との混合液が透明になった時点（酸素ガスの通気を開始して１０分程度経過した時点）で酸素ガスの通気を停止した点を除き、実施例２と同様の方法により、粒子分散液及び粒子を生成した。なお、得られた粒子分散液は、酸素ガスの通気を開始して１時間経過した時点で不透明な淡黄白色を呈していた。
(Example 3)
As shown in Tables 1 and 2, when the mixture of the cerium chloride aqueous solution and the sodium hydroxide aqueous solution became transparent (about 10 minutes after the start of the oxygen gas ventilation), the oxygen gas ventilation was stopped. A particle dispersion and particles were produced in the same manner as in Example 2, except that it was stopped. The obtained particle dispersion exhibited an opaque pale yellowish white color 1 hour after the oxygen gas was introduced.
（実施例４）
表１及び表２に示すように、塩化セリウム水溶液と水酸化ナトリウム水溶液との混合液が透明になった時点（酸素ガスの通気を開始して１０分程度経過した時点）で酸素ガスの通気を停止すると共に液中の溶存酸素を追い出すためにアルゴンガスを流量２．０Ｌ／ｍｉｎで３０分間通気した点を除き、実施例２と同様の方法により、粒子分散液及び粒子を生成した。なお、得られた粒子分散液は、酸素ガスの通気を開始して１時間経過した時点で不透明な淡黄白色を呈していた。
(Example 4)
As shown in Tables 1 and 2, when the mixture of the cerium chloride aqueous solution and the sodium hydroxide aqueous solution became transparent (about 10 minutes after the start of the oxygen gas ventilation), the oxygen gas ventilation was stopped. A particle dispersion liquid and particles were produced in the same manner as in Example 2, except that the process was stopped and argon gas was passed for 30 minutes at a flow rate of 2.0 L/min to expel dissolved oxygen in the liquid. The obtained particle dispersion exhibited an opaque pale yellowish white color 1 hour after the oxygen gas was introduced.
（実施例５）
表１及び表２に示すように、塩化セリウム水溶液と水酸化ナトリウム水溶液との混合液が透明になった時点（酸素ガスの通気を開始して１０分程度経過した時点）で酸素ガスの通気を停止すると共に粒子分散液のｐＨが１になるように１ｍｏｌ／Ｌの塩酸を加えた点を除き、実施例２と同様の方法により、粒子分散液を生成した。なお、得られた粒子分散液は、酸素ガスの通気を開始して１時間経過した時点で透明な淡黄色を呈しており、２－プロパノールを添加することによって粒子を凝集させた後、遠心分離（１００００ｒｐｍ、５分）することによって淡黄白色の粒子を回収し、１７０℃のオーブンで一晩乾燥を行った。
(Example 5)
As shown in Tables 1 and 2, when the mixture of the cerium chloride aqueous solution and the sodium hydroxide aqueous solution became transparent (about 10 minutes after the start of the oxygen gas ventilation), the oxygen gas ventilation was stopped. A particle dispersion was produced in the same manner as in Example 2, except that 1 mol/L of hydrochloric acid was added so that the pH of the particle dispersion became 1 while stopping. The obtained particle dispersion exhibited a transparent pale yellow color one hour after the start of oxygen gas aeration, and the particles were aggregated by adding 2-propanol and then centrifuged. (10000 rpm, 5 minutes) to collect pale yellow-white particles and dry them in an oven at 170° C. overnight.
（比較例１）
表１及び表２に示すように、０．１ｍｏｌ／Ｌの塩化セリウム水溶液５０ｍＬと、０．２ｍｏｌ／Ｌに調整した水酸化ナトリウム水溶液７５ｍＬとを混合した点を除き、実施例１と同様の方法により、粒子分散液及び粒子を生成した。なお、塩化セリウム水溶液と水酸化ナトリウム水溶液とを混合した時点（酸素ガスの通気前）のｐＨは１３．５であった。塩化セリウム水溶液と水酸化ナトリウム水溶液との混合液は、初期時点で不透明なピンク色を呈するが、酸素ガスの通気に伴い不透明な褐色となり、酸素ガスの通気を停止した時点（酸素ガスの通気を開始して１時間経過した時点）で得られた粒子分散液は不透明な淡黄色を呈していた。
(Comparative example 1)
As shown in Tables 1 and 2, the same method as in Example 1 except that 50 mL of a 0.1 mol/L cerium chloride aqueous solution and 75 mL of a 0.2 mol/L sodium hydroxide aqueous solution were mixed. produced a particle dispersion and particles. The pH was 13.5 when the cerium chloride aqueous solution and the sodium hydroxide aqueous solution were mixed (before oxygen gas was introduced). The mixture of the cerium chloride aqueous solution and the sodium hydroxide aqueous solution exhibits an opaque pink color at the initial stage, but it turns opaque brown as the oxygen gas is introduced, and when the oxygen gas is stopped 1 hour after the start), the obtained particle dispersion had an opaque pale yellow color.
（比較例２）
表１及び表２に示すように、０．１ｍｏｌ／Ｌの塩化セリウム水溶液５０ｍＬと、０．２ｍｏｌ／Ｌに調整した水酸化ナトリウム水溶液１００ｍＬとを混合した点を除き、実施例１と同様の方法により、粒子分散液及び粒子を生成した。なお、塩化セリウム水溶液と水酸化ナトリウム水溶液とを混合した時点（酸素ガスの通気前）のｐＨは１３．６であった。塩化セリウム水溶液と水酸化ナトリウム水溶液との混合液は、比較例１と同様に、初期時点で不透明なピンク色を呈するが、酸素ガスの通気に伴い不透明な褐色となり、酸素ガスの通気を停止した時点（酸素ガスの通気を開始して１時間経過した時点）で得られた粒子分散液は不透明な淡黄色を呈していた。
(Comparative example 2)
As shown in Tables 1 and 2, the same method as in Example 1 except that 50 mL of 0.1 mol/L cerium chloride aqueous solution and 100 mL of sodium hydroxide aqueous solution adjusted to 0.2 mol/L were mixed. produced a particle dispersion and particles. The pH was 13.6 when the cerium chloride aqueous solution and the sodium hydroxide aqueous solution were mixed (before oxygen gas was introduced). As in Comparative Example 1, the mixture of the cerium chloride aqueous solution and the sodium hydroxide aqueous solution exhibited an opaque pink color at the initial stage, but turned opaque brown as the oxygen gas was introduced, and the oxygen gas introduction was stopped. The particle dispersion obtained at this time (one hour after the oxygen gas was started to pass) had an opaque pale yellow color.
（比較例３）
表１及び表２に示すように、０．１ｍｏｌ／Ｌの塩化セリウム水溶液５０ｍＬと、０．２ｍｏｌ／Ｌに調整した水酸化ナトリウム水溶液１２５ｍＬとを混合した点を除き、実施例１と同様の方法により、粒子分散液及び粒子を生成した。なお、塩化セリウム水溶液と水酸化ナトリウム水溶液とを混合した時点（酸素ガスの通気前）のｐＨは１３．８であった。塩化セリウム水溶液と水酸化ナトリウム水溶液との混合液は、比較例１と同様に、初期時点で不透明なピンク色を呈するが、酸素ガスの通気に伴い不透明な褐色となり、酸素ガスの通気を停止した時点（酸素ガスの通気を開始して１時間経過した時点）で得られた粒子分散液は不透明な淡黄色を呈していた。
(Comparative Example 3)
As shown in Tables 1 and 2, the same method as in Example 1 except that 50 mL of 0.1 mol/L cerium chloride aqueous solution and 125 mL of sodium hydroxide aqueous solution adjusted to 0.2 mol/L were mixed. produced a particle dispersion and particles. The pH was 13.8 when the cerium chloride aqueous solution and the sodium hydroxide aqueous solution were mixed (before oxygen gas was introduced). As in Comparative Example 1, the mixture of the cerium chloride aqueous solution and the sodium hydroxide aqueous solution exhibited an opaque pink color at the initial stage, but turned opaque brown as the oxygen gas was introduced, and the oxygen gas introduction was stopped. The particle dispersion obtained at this time (one hour after the oxygen gas was started to pass) had an opaque pale yellow color.
実施例１～５及び比較例１～３で得られた淡黄白色または淡黄色の粒子を、Ｘ線回折装置（ＭｉｎｉＦｌｅｘII型 Ｒｉｇａｋｕ社製）を用いてＸ線結晶構造解析を行ったところ、図１～８に示すＸ線回折チャートが得られた。これらのＸ線回折チャートには、酸化セリウム［ＣｅＯ２］について、データベース化された入射角に対する回折強度がそれぞれプロットされており、上記淡黄白色粒子または淡黄色粒子のＸ線回折チャートのピークが、プロットされた酸化セリウムのデータベースと略一致していることから、それぞれの各粒子分散液中に存在している粒子は単相の酸化セリウムであることは明らかである。 The pale yellowish white or pale yellow particles obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were subjected to X-ray crystal structure analysis using an X-ray diffractometer (MiniFlex II type, manufactured by Rigaku). The X-ray diffraction charts shown in 1-8 were obtained. In these X-ray diffraction charts, the diffraction intensity for cerium oxide [CeO 2 ] is plotted against the incident angle in the database, and the peak of the X-ray diffraction chart of the pale yellowish white particles or pale yellow particles is , approximately agrees with the plotted cerium oxide database, it is clear that the particles present in each particle dispersion are single-phase cerium oxide.
また、実施例１～５及び比較例１～３で得られた粒子については、窒素吸着式比表面積測定装置（ＢＥＬＳＯＲＰｍｉｎ 日本ベル社製）を用いてＢＥＴ法により比表面積を測定し、比表面積Ｓｗと粒子径ｘならびに粒子の真密度ρの関係式［Ｓｗ＝６／（ρｘ）］及び酸化セリウムの真密度７２２０ｋｇ／ｍ３を用いて算出した粒子径（比表面積相当直径）ｘを、比表面積Ｓｗと共に表３に示す。 Further, for the particles obtained in Examples 1 to 5 and Comparative Examples 1 to 3, the specific surface area was measured by the BET method using a nitrogen adsorption type specific surface area measuring device (BELSORPmin manufactured by Bell Japan), and the specific surface area Sw and the particle diameter x and the relational expression of the true density ρ of the particles [Sw = 6 / (ρx)] and the particle diameter (diameter equivalent to the specific surface area) calculated using the true density of cerium oxide 7220 kg / m 3 , the specific surface area It is shown in Table 3 together with Sw.
また、実施例５で得られた粒子については、透過電子顕微鏡（ＴＥＭ）で観察したところ、図９に示すＴＥＭ画像が得られた。同図に示すＴＥＭ画像からは、粒子径が約３ｎｍの粒子が合成できたことを確認することができた。 Further, when the particles obtained in Example 5 were observed with a transmission electron microscope (TEM), the TEM image shown in FIG. 9 was obtained. From the TEM image shown in the figure, it was confirmed that particles with a particle diameter of about 3 nm were synthesized.
表１及び表３から分かるように、セリウムイオンを含有する塩化セリウム水溶液と、塩基性水溶液である水酸化ナトリウム水溶液とを混合した混合液のｐＨが８を下回っている実施例１～５で得られた酸化セリウム微粒子は、その粒子径（比表面積相当直径）が１０ｎｍを下回っているのに対して、混合液のｐＨが８以上である比較例１～３で得られた酸化セリウム微粒子は、その粒子径（比表面積相当直径）が１０ｎｍを上回っており、シングルナノサイズの酸化セリウム微粒子を生成するには、混合液のｐＨが８を下回るように、塩化セリウム水溶液と水酸化ナトリウム水溶液とを混合する必要がある。 As can be seen from Tables 1 and 3, the pH of the mixture obtained by mixing the cerium ion-containing cerium chloride aqueous solution and the sodium hydroxide aqueous solution, which is a basic aqueous solution, is below 8. The cerium oxide microparticles thus obtained have a particle diameter (diameter equivalent to a specific surface area) of less than 10 nm, whereas the cerium oxide microparticles obtained in Comparative Examples 1 to 3, in which the mixed solution has a pH of 8 or higher, The particle diameter (specific surface equivalent diameter) exceeds 10 nm, and in order to generate single nano-sized cerium oxide fine particles, an aqueous cerium chloride solution and an aqueous sodium hydroxide solution are mixed so that the pH of the mixed solution is below 8. Must be mixed.
特に、酸素ガスを通気する前の混合液のｐＨが中性域に調整された実施例２～５で得られた酸化セリウム微粒子は、混合液のｐＨが弱酸性域に調整された実施例１で得られた酸化セリウム微粒子よりも、粒子径が小さくなっており、生成される酸化セリウム微粒子の粒子径をより小さくするには、混合液のｐＨを中性域に調整しておくことが望ましい。 In particular, the cerium oxide microparticles obtained in Examples 2 to 5, in which the pH of the mixed liquid was adjusted to a neutral range before passing oxygen gas, were used in Example 1, in which the pH of the mixed liquid was adjusted to a weakly acidic range. The particle diameter is smaller than that of the cerium oxide microparticles obtained in (1), and in order to further reduce the particle diameter of the cerium oxide microparticles produced, it is desirable to adjust the pH of the mixed liquid to a neutral range. .
また、表２及び表３から分かるように、混合液が透明になった後も酸素ガスを通気し続けた実施例１～２及び比較例１～３、混合液が透明になった時点で酸素ガスの通気を停止した実施例３、混合液が透明になった時点で酸素ガスの通気を停止し、その後３０分間アルゴンガスを通気した実施例４は、いずれも一旦透明になった粒子分散液が、酸素ガスの通気を開始して１時間経過した時点では、粒子分散液中の酸化セリウム微粒子が凝集することにより不透明な状態に変化したのに対して、混合液が透明になった時点で酸素ガスの通気を停止すると共に粒子分散液のｐＨが１になるように塩酸を加えた実施例５は、生成された粒子分散液が、酸素ガスの通気を開始して１時間経過した時点でも、粒子分散液中の酸化セリウム微粒子が凝集して不透明な状態に変化することなく、透明な状態を維持し続けた。従って、分散性に優れた酸化セリウム微粒子分散液を生成するためには、酸素ガスの通気を停止した後に塩酸等の酸性水溶液を加えてｐＨを１以下に調整することが望ましい。 Further, as can be seen from Tables 2 and 3, Examples 1 to 2 and Comparative Examples 1 to 3 continued to pass oxygen gas even after the mixed liquid became transparent, and oxygen gas was added when the mixed liquid became transparent. Example 3, in which gas ventilation was stopped, and Example 4, in which oxygen gas ventilation was stopped when the liquid mixture became transparent, and then argon gas was introduced for 30 minutes, were both particle dispersion liquids that had once become transparent. However, one hour after the start of oxygen gas ventilation, the cerium oxide fine particles in the particle dispersion aggregated and changed to an opaque state. In Example 5, in which the ventilation of oxygen gas was stopped and hydrochloric acid was added so that the pH of the particle dispersion became 1, the generated particle dispersion was not even 1 hour after the initiation of oxygen gas ventilation. , the cerium oxide microparticles in the particle dispersion did not aggregate and changed to an opaque state, and the transparent state was maintained. Therefore, in order to produce a cerium oxide fine particle dispersion with excellent dispersibility, it is desirable to adjust the pH to 1 or less by adding an acidic aqueous solution such as hydrochloric acid after stopping the oxygen gas flow.
特に、混合液が透明になった時点で酸素ガスの通気を停止し、直ちに粒子分散液のｐＨが１になるように塩酸を加えた実施例５で得られた酸化セリウム微粒子は、その粒子径が４．２６ｎｍと最も小さく、生成された酸化セリウム微粒子の凝集だけでなく、粒成長も同時に抑制されているものと考えられる。従って、粒子径がより小さく、分散性に優れた酸化セリウム微粒子分散液を得るためには、混合液が透明になった時点で酸素ガスの通気を停止し、直ちに塩酸等の酸性水溶液を加えることで粒子分散液のｐＨを１以下に調整することが望ましい。 In particular, the cerium oxide fine particles obtained in Example 5, in which oxygen gas was stopped when the mixed liquid became transparent, and hydrochloric acid was immediately added so that the pH of the particle dispersion liquid became 1, had a particle diameter of is the smallest at 4.26 nm, and it is considered that not only the aggregation of the generated cerium oxide fine particles but also grain growth are suppressed at the same time. Therefore, in order to obtain a cerium oxide fine particle dispersion having a smaller particle size and excellent dispersibility, oxygen gas flow should be stopped when the mixture becomes transparent, and an acidic aqueous solution such as hydrochloric acid should be immediately added. It is desirable to adjust the pH of the particle dispersion to 1 or less.
以上のように、実施例１～５の酸化セリウム微粒子の製造方法では、塩化セリウム水溶液を出発原料とし、水酸化ナトリウム水溶液の添加及び酸素ガスの通気という簡易な工程によって、加熱・熟成することなく、３０℃以下で短時間に比表面積相当直径が１０ｎｍ未満の酸化セリウム微粒子を低コストで効率よく製造することができる。 As described above, in the methods for producing cerium oxide microparticles of Examples 1 to 5, an aqueous cerium chloride solution is used as a starting material, and the simple steps of adding an aqueous sodium hydroxide solution and ventilating with oxygen gas are performed without heating or aging. , cerium oxide microparticles having a specific surface area equivalent diameter of less than 10 nm can be produced efficiently at low cost in a short time at 30°C or lower.
また、上述した各実施例では、セリウムイオン含有水溶液として塩化セリウム水溶液を使用しているが、これに限定されるものではなく、例えば、硝酸セリウム水溶液等の種々の水溶性セリウム塩の水溶液を使用することができる。 In each of the above-described examples, an aqueous cerium chloride solution is used as the cerium ion-containing aqueous solution, but the present invention is not limited to this. can do.
また、上述した各実施例では、アルカリ水溶液として水酸化ナトリウム水溶液を使用しているが、これに限定されるものではなく、水酸化カリウム水溶液、水酸化リチウム水溶液、水酸化セシウム水溶液等の水溶性のアルカリ金属水酸化物、アンモニア等を使用することができる。 In each of the above-described examples, an aqueous sodium hydroxide solution is used as the alkaline aqueous solution, but the present invention is not limited to this. alkali metal hydroxide, ammonia, etc. can be used.
本発明は、シングルナノオーダーの酸化セリウム微粒子分散液及びシングルナノオーダーの酸化セリウム微粒子を製造する際に利用することができる。 INDUSTRIAL APPLICABILITY The present invention can be used when producing a single nano-order cerium oxide fine particle dispersion and a single nano-order cerium oxide fine particle.
Claims (3)
セリウムイオン含有水溶液と塩基性水溶液とを混合してｐＨ＜８に調整した後、この混合液に対して酸素ガスの通気を開始し、この混合液が透明になった時点またはそれ以降の時点で酸素ガスの通気を停止した後に、酸性水溶液を加えてｐＨ≦１に調整することを特徴とする酸化セリウム微粒子分散液の製造方法。 A method for producing a cerium oxide fine particle dispersion having a diameter equivalent to a specific surface area of less than 10 nm, comprising:
After mixing the cerium ion-containing aqueous solution and the basic aqueous solution to adjust the pH to <8, oxygen gas is started to flow through the mixed solution, and when the mixed solution becomes transparent or after that, 1. A method for producing a cerium oxide fine particle dispersion, characterized by adding an acidic aqueous solution to adjust the pH to ≤ 1 after stopping oxygen gas flow.
セリウムイオン含有水溶液と塩基性水溶液とを混合してｐＨ＜８に調整した後、この混合液に対して酸素ガスの通気を開始し、この混合液が透明になった時点で、酸素ガスの通気を停止すると共に酸性水溶液を加えてｐＨ≦１に調整することを特徴とする酸化セリウム微粒子分散液の製造方法。 A method for producing a cerium oxide fine particle dispersion having a diameter equivalent to a specific surface area of less than 10 nm, comprising:
After the cerium ion-containing aqueous solution and the basic aqueous solution are mixed to adjust the pH to <8, oxygen gas is introduced into the mixed solution, and when the mixed solution becomes transparent, the oxygen gas is introduced. is stopped and an acidic aqueous solution is added to adjust the pH to ≤1.
請求項１または２に記載の製造方法により得られた酸化セリウム微粒子分散液から酸化セリウム微粒子を分離、回収することを特徴とする酸化セリウム微粒子の製造方法。 A method for producing cerium oxide fine particles having a specific surface area equivalent diameter of less than 10 nm, comprising:
3. A method for producing cerium oxide fine particles, which comprises separating and recovering cerium oxide fine particles from the cerium oxide fine particle dispersion liquid obtained by the production method according to claim 1 or 2 .
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