JP6478223B2 - Yttrium-containing oxyapatite-type lanthanum / germanate ceramics - Google Patents
Yttrium-containing oxyapatite-type lanthanum / germanate ceramics Download PDFInfo
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- 229910052746 lanthanum Inorganic materials 0.000 title claims description 44
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 title claims description 44
- 239000000919 ceramic Substances 0.000 title claims description 37
- 229910052727 yttrium Inorganic materials 0.000 title claims description 31
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 title claims description 31
- 229910052760 oxygen Inorganic materials 0.000 claims description 32
- 239000001301 oxygen Substances 0.000 claims description 32
- -1 oxygen ion Chemical class 0.000 claims description 28
- 238000000034 method Methods 0.000 claims description 13
- 238000010438 heat treatment Methods 0.000 claims description 9
- 239000007787 solid Substances 0.000 claims description 8
- 239000007864 aqueous solution Substances 0.000 claims description 7
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 6
- 239000000446 fuel Substances 0.000 claims description 6
- 229910052732 germanium Inorganic materials 0.000 claims description 6
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 claims description 6
- 150000007524 organic acids Chemical class 0.000 claims description 6
- SVVNWZBZUCIAMR-UHFFFAOYSA-N [GeH](=O)[O-].[La+3].[GeH](=O)[O-].[GeH](=O)[O-] Chemical compound [GeH](=O)[O-].[La+3].[GeH](=O)[O-].[GeH](=O)[O-] SVVNWZBZUCIAMR-UHFFFAOYSA-N 0.000 claims description 4
- 239000007784 solid electrolyte Substances 0.000 claims description 4
- 239000013078 crystal Substances 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 claims description 2
- 238000005245 sintering Methods 0.000 claims description 2
- 229910052586 apatite Inorganic materials 0.000 claims 1
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 description 9
- 238000005259 measurement Methods 0.000 description 7
- 238000000634 powder X-ray diffraction Methods 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- 238000006116 polymerization reaction Methods 0.000 description 5
- 238000003746 solid phase reaction Methods 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- 238000002441 X-ray diffraction Methods 0.000 description 4
- YBMRDBCBODYGJE-UHFFFAOYSA-N germanium dioxide Chemical compound O=[Ge]=O YBMRDBCBODYGJE-UHFFFAOYSA-N 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 239000012071 phase Substances 0.000 description 4
- 239000000843 powder Substances 0.000 description 4
- 239000000047 product Substances 0.000 description 4
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 3
- 235000011114 ammonium hydroxide Nutrition 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Natural products N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 239000012153 distilled water Substances 0.000 description 2
- 229940119177 germanium dioxide Drugs 0.000 description 2
- 238000002847 impedance measurement Methods 0.000 description 2
- GJKFIJKSBFYMQK-UHFFFAOYSA-N lanthanum(3+);trinitrate;hexahydrate Chemical compound O.O.O.O.O.O.[La+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O GJKFIJKSBFYMQK-UHFFFAOYSA-N 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 239000002243 precursor Substances 0.000 description 2
- 229910001233 yttria-stabilized zirconia Inorganic materials 0.000 description 2
- QBAZWXKSCUESGU-UHFFFAOYSA-N yttrium(3+);trinitrate;hexahydrate Chemical compound O.O.O.O.O.O.[Y+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O QBAZWXKSCUESGU-UHFFFAOYSA-N 0.000 description 2
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonium chloride Substances [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 1
- 238000007088 Archimedes method Methods 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000003637 basic solution Substances 0.000 description 1
- 244000309464 bull Species 0.000 description 1
- 239000012700 ceramic precursor Substances 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 238000003980 solgel method Methods 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229910021642 ultra pure water Inorganic materials 0.000 description 1
- 239000012498 ultrapure water Substances 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Description
本発明は、オキシアパタイト型ランタン・ゲルマネートセラミックスに関し、詳細には、イットリウムを含み、比較的低温においても高い酸素イオン伝導性を示す、オキシアパタイト型ランタン・ゲルマネートセラミックスに関する。 The present invention relates to an oxyapatite type lanthanum / germanate ceramic, and more particularly to an oxyapatite type lanthanum / germanate ceramic that contains yttrium and exhibits high oxygen ion conductivity even at a relatively low temperature.
オキシアパタイト型ランタン・ゲルマネートは、式Ｌａ９．３３＋ｘ’ （ＧｅＯ４）６Ｏ２＋３ｘ’／２（０．４８＞ｘ’＞０．０７）で表される。この物質は高い酸素イオン伝導性を有することから、その焼結体（セラミックス）には固体酸化物燃料電池、及び酸素濃度検出センサー等への応用が期待されている。
The oxyapatite- type lanthanum germanate is represented by the formula La 9.33 + x ′ ( GeO 4 ) 6 O 2 + 3 x ′ / 2 (0.48> x ′> 0.07). Since this substance has high oxygen ion conductivity, its sintered body (ceramics) is expected to be applied to solid oxide fuel cells, oxygen concentration detection sensors, and the like.
しかし、該酸素イオン伝導性は、図１の破線で示すように８００℃〜７００℃の温度で急激に低下することが報告されている（非特許文献１）。これはランタン・ゲルマネートが上記温度範囲において、六方晶型から三斜晶型へと相変化するためである。 However, it has been reported that the oxygen ion conductivity rapidly decreases at a temperature of 800 ° C. to 700 ° C. as shown by the broken line in FIG. 1 (Non-patent Document 1). This is because lanthanum germanate undergoes a phase change from the hexagonal type to the triclinic type in the above temperature range.
ランタンの一部を、ランタンと等原子価のイットリウムで置換することによって、該相変化が抑制されて酸素イオン伝導性が高くなることが報告されている（非特許文献２）。同報告においてランタン・ゲルマネートは固相反応により、１１００℃で24時間加熱して調製される。その後、約１時間粉砕され、８０００ｋｇ／ｃｍ２の圧力でプレスされた後、１３００℃で２時間焼結されてランタン・ゲルマネートセラミックスが得られる。 It has been reported that by replacing part of lanthanum with lanthanum and valence yttrium, the phase change is suppressed and oxygen ion conductivity is increased (Non-patent Document 2). In the same report, lanthanum germanate is prepared by heating at 1100 ° C. for 24 hours by solid phase reaction. Thereafter, it is pulverized for about 1 hour, pressed at a pressure of 8000 kg / cm 2 , and then sintered at 1300 ° C. for 2 hours to obtain a lanthanum / germanate ceramic.
ところで、本発明者らはランタン・ゲルマネートの製造方法として、水溶液を用いた錯体重合法（又はゾル‐ゲル法）を開発した（特許文献１）。該方法は固相反応に比べて、簡易であるのみならず、７００℃程度の低温で行うことができるという利点を有する。 By the way, the present inventors have developed a complex polymerization method (or sol-gel method) using an aqueous solution as a method for producing lanthanum germanate (Patent Document 1). This method has an advantage that it can be carried out at a low temperature of about 700 ° C. as well as simpler than solid phase reaction.
上記ランタンの一部をイットリウムで置換したランタン・ゲルマネートも、より低温で調製することができれば、産業上好ましい。 A lanthanum germanate obtained by substituting a part of the lanthanum with yttrium is industrially preferable if it can be prepared at a lower temperature.
そこで本発明者らは、上記錯体重合法を応用したところ、驚くことに、非特許文献２で報告されているものよりも顕著に高い酸素イオン伝導性が達成されることを見出した。即ち、本発明は、下記式（１）：
ＬａｘＹｙ（ＧｅＯ４）６Ｏｚ （１）
（式（１）において、７．５≦ｘ＜８．８、１≦ｙ≦２、２．２≦ｚ≦２．７である）で表され、６００℃における酸素イオン伝導度が２．３×１０−３[Ｓ／ｃｍ] 以上である、イットリウム含有オキシアパタイト型ランタン・ゲルマネートセラミックスである。
また、本発明は上記イットリウム含有オキシアパタイト型ランタン・ゲルマネートセラミックスを含む固体酸化物燃料電池用の固体電解質及び酸素センサーである。
Therefore, the present inventors have found that, when the complex polymerization method is applied, oxygen ion conductivity significantly higher than that reported in Non-Patent Document 2 is achieved. That is, the present invention provides the following formula (1):
La x Y y (GeO 4 ) 6 O z (1)
(In formula (1), 7.5 ≦ x <8.8, 1 ≦ y ≦ 2, 2.2 ≦ z ≦ 2.7), and the oxygen ion conductivity at 600 ° C. is 2.3. It is an yttrium-containing oxyapatite-type lanthanum / germanate ceramic that is at least 10 −3 [S / cm].
The present invention also provides a solid electrolyte and an oxygen sensor for a solid oxide fuel cell comprising the yttrium-containing oxyapatite-type lanthanum germanate ceramics.
本発明のイットリウム含有ランタン・ゲルマネートセラミックスは、非特許文献２記載のほぼ同等の組成のセラミックスに比べて高い酸素イオン伝導性を示す。この理由は、但し本発明を限定する趣旨ではないが、上記錯体重合法により、固相反応に比べてより均一で微細なセラミックス前駆体が得られ、９０％以上の高い相対密度を有するセラミックスがもたらされるからであると考えられる。 The yttrium-containing lanthanum / germanate ceramics of the present invention exhibit higher oxygen ion conductivity than ceramics having substantially the same composition as described in Non-Patent Document 2. This reason is not intended to limit the present invention, but the above complex polymerization method provides a more uniform and fine ceramic precursor than solid phase reaction, and a ceramic having a high relative density of 90% or more is obtained. It is thought that it is brought about.
本発明のイットリウム含有オキシアパタイト型ランタン・ゲルマネートセラミックス（以下、「セラミックス」と略する場合がある）は、下記式（１）で表される。
ＬａｘＹｙ（ＧｅＯ４）６Ｏｚ （１）
式（１）において、７．５≦ｘ＜８．８、１≦ｙ≦２、２．２≦ｚ≦２．７であり、好ましくは７．７≦ｘ≦８．７、１≦ｙ≦２、２．３≦ｚ≦２．７である。各パラメータが上記範囲内のセラミックスは、Ｙを含まないランタン・ゲルマネートに見られる、８００℃〜７００℃における急激な酸素イオン伝導度の低下が見られず、且つ、６００℃において、既知の酸素イオン伝導度のうち最も高い値である２．２×１０−３[Ｓ／ｃｍ]より高い酸素イオン伝導度を有する。
The yttrium-containing oxyapatite-type lanthanum-germanate ceramics of the present invention (hereinafter sometimes abbreviated as “ceramics”) is represented by the following formula (1).
La x Y y (GeO 4 ) 6 O z (1)
In formula (1), 7.5 ≦ x <8.8, 1 ≦ y ≦ 2, 2.2 ≦ z ≦ 2.7, preferably 7.7 ≦ x ≦ 8.7, 1 ≦ y ≦ 2, 2.3 ≦ z ≦ 2.7. Ceramics in which each parameter is within the above range does not show a sudden decrease in oxygen ion conductivity at 800 ° C. to 700 ° C., which is found in lanthanum germanate not containing Y, and is known oxygen at 600 ° C. It has an oxygen ion conductivity higher than 2.2 × 10 −3 [S / cm], which is the highest value among the ion conductivities.
図１は、後述する実施例で調製した本発明のセラミックス（○：実施例４、□：実施例２）、非特許文献１記載のＬａ10（ＧｅＯ4）Ｏ3（破線）、及び非特許文献２記載のＬａ7.8Ｙ2（ＧｅＯ4）Ｏ2.8（一点破線）の、７７３Ｋ（実施例４については６７３Ｋ）〜１２７３Ｋにおける酸素イオン伝導度を比較して示すグラフである。同図において、縦軸は酸素イオン伝導度（σ［Ｓ／ｃｍ］と温度（Ｋ）の積の対数、上側横軸は温度（Ｋ）、下側横軸は温度の逆数［１０−３／Ｋ］である。非特許文献２記載のＬａ7.8Ｙ2（ＧｅＯ4）Ｏ2.8の６００℃における酸素イオン伝導度は２．２×１０−３[Ｓ／ｃｍ]である。これに対して、本発明のＬａ8.7Ｙ1（ＧｅＯ4）Ｏ2.6及びＬａ7.8Ｙ2（ＧｅＯ4）Ｏ2.7は、夫々、６．１×１０−３、４．９×１０−３[Ｓ／ｃｍ]であり、顕著に高い。 FIG. 1 shows ceramics of the present invention prepared in the examples described later (◯: Example 4, □: Example 2), La 10 (GeO 4 ) O 3 (broken line) described in Non-Patent Document 1, and non-patents. of Reference 2 of La 7.8 Y 2 (GeO 4) O 2.8 ( dashed line), (for example 4 673 K) 773 K is a graph comparing the oxygen ion conductivity at ～1273K. In the figure, the vertical axis represents the logarithm of the product of oxygen ion conductivity (σ [S / cm] and temperature (K), the upper horizontal axis represents temperature (K), and the lower horizontal axis represents the reciprocal of temperature [10 −3 / The oxygen ion conductivity of La 7.8 Y 2 (GeO 4 ) O 2.8 described in Non-Patent Document 2 at 600 ° C. is 2.2 × 10 −3 [S / cm]. La 8.7 Y 1 (GeO 4 ) O 2.6 and La 7.8 Y 2 (GeO 4 ) O 2.7 of the present invention are 6.1 × 10 −3 and 4.9 × 10 −3 [S / cm], respectively. Remarkably high.
好ましくは、本発明のセラミックスは６００℃において４．５×１０−３ [Ｓ／ｃｍ]以上の酸素イオン伝導度を示す。酸素イオン伝導度の上限値については、特に制限はないが、実際上６．５×１０−３[Ｓ／ｃｍ]程度であると概算される。該酸素イオン伝導度の測定方法の詳細は後述する。 Preferably, the ceramic of the present invention exhibits an oxygen ion conductivity of 4.5 × 10 −3 [S / cm] or more at 600 ° C. Although there is no restriction | limiting in particular about the upper limit of oxygen ion conductivity, It is estimated that it is about 6.5 * 10 < -3 > [S / cm] actually. Details of the method for measuring the oxygen ion conductivity will be described later.
上記高い酸素イオン伝導度は、結晶構造に基づく。図２は、特許文献１記載の方法で合成した粉末を１３５０℃で焼結した、Ｙを含まないランタン・ゲルマネート（第１、２段）、後述する参考例２のセラミックス（第３段）、及び実施例１、２、４のセラミックス（第６〜４段）の室温における粉末Ｘ線回折を、Ｌａが多い順に比較して示すものである。なお、縦軸は任意スケールの強度である。同図、第５及び６段は、六方晶型ランタン・ゲルマネート及び三斜晶型のランタン・ゲルマネートの粉末Ｘ線回折をデジタルパターンで示したものである。三斜晶型は、六方晶型に比べてピークが多く、ピーク自体がブロードになる。図２において、Ｙを含まないランタン・ゲルマネートは、第６段に示す三斜晶型の回折パターンと一致する。これに対して、実施例１、２及び４の回折は第５段に示す六方晶型の回折パターンと良い一致を示し、高い酸素イオン伝導度につながっている。 The high oxygen ion conductivity is based on the crystal structure. FIG. 2 shows a powder synthesized by the method described in Patent Document 1, sintered at 1350 ° C., lanthanum germanate containing no Y (first and second stages), and ceramics of Reference Example 2 described later (third stage). And X-ray powder diffraction at room temperature of the ceramics of Examples 1, 2, and 4 (6th to 4th stages) are compared in the order of increasing La. The vertical axis represents the intensity of an arbitrary scale. In FIG. 5, the fifth and sixth stages show the digital X-ray diffraction patterns of hexagonal lanthanum germanate and triclinic lanthanum germanate. The triclinic type has more peaks than the hexagonal type, and the peaks themselves are broad. In FIG. 2, lanthanum germanate containing no Y matches the triclinic diffraction pattern shown in the sixth stage. On the other hand, the diffraction in Examples 1, 2, and 4 is in good agreement with the hexagonal diffraction pattern shown in the fifth stage, leading to high oxygen ion conductivity.
図４は、六方晶型と三斜晶型のＸ線回折における差をより明確に示すために、図２の第１段目のＬａ9.8（ＧｅＯ4）6Ｏ2.7と、同図第４段の実施例４のセラミックスのＸ線回折を抜き出したものである。矢印で示す２θ（度）において、両者に差があることが分かる。 FIG. 4 shows La 9.8 (GeO 4 ) 6 O 2.7 in the first stage in FIG. 2 and the fourth stage in the figure in order to more clearly show the difference in X-ray diffraction between the hexagonal type and the triclinic type. The X-ray diffraction of the ceramic of Example 4 is extracted. It can be seen that there is a difference between the two at 2θ (degrees) indicated by the arrow.
本発明のＹ含有ランタン・ゲルマネートセラミックスは、以下の工程（１）〜（４）を含む錯体重合法で作ることができる。
（１）ランタン源、イットリウム源、ゲルマニウム源を夫々含む水溶液を調製する工程、
（２）工程（１）で得られる３つの水溶液を所定の比で混合してｐＨを調整することによって、粘性ゲルを生成する工程、
（３）工程（２）で得られる粘性ゲルを加熱して、粉体状ゲルを得る工程、
（４）工程（３）で得られる粉体状ゲルを焼結する工程。
The Y-containing lanthanum / germanate ceramics of the present invention can be produced by a complex polymerization method including the following steps (1) to (4).
(1) preparing an aqueous solution containing a lanthanum source, an yttrium source, and a germanium source,
(2) A step of producing a viscous gel by mixing the three aqueous solutions obtained in step (1) at a predetermined ratio and adjusting the pH,
(3) A step of heating the viscous gel obtained in step (2) to obtain a powdery gel,
(4) A step of sintering the powdered gel obtained in step (3).
工程（１）において、ランタン源としては例えば硝酸ランタン６水和物を用い、これを０．１〜２モル％、好ましくは１〜２モル％の濃度で水に溶解する。イットリウム源としては例えば硝酸イットリウム６水和物を用い、これを０．１〜２モル％、好ましくは１〜２モル％の濃度で水に溶解する。ゲルマニウム源としては例えば二酸化ゲルマニウムを用い、これを０．００５〜０．５モル％、好ましくは０．０１〜０．１モル％の濃度で、ｐＨ９〜１０の希アンモニア水等の塩基性溶液に溶解する。水としては、蒸留水、脱イオン水、超純水等を用いることができる。 In step (1), for example, lanthanum nitrate hexahydrate is used as the lanthanum source, and this is dissolved in water at a concentration of 0.1 to 2 mol%, preferably 1 to 2 mol%. As the yttrium source, for example, yttrium nitrate hexahydrate is used and dissolved in water at a concentration of 0.1 to 2 mol%, preferably 1 to 2 mol%. For example, germanium dioxide is used as a germanium source, and this is added to a basic solution such as dilute ammonia water having a pH of 9 to 10 at a concentration of 0.005 to 0.5 mol%, preferably 0.01 to 0.1 mol%. Dissolve. As water, distilled water, deionized water, ultrapure water, or the like can be used.
工程（２）において、工程（１）で得られた各水溶液を、目的とする組成に応じた量比で混合する。混合の順番は任意でよい。次いで、混合液のｐＨを１〜１．８、好ましくは１．３〜１．８に調整する。調整に用いる酸としてはクエン酸等の有機酸が好ましく、より好ましくは該有機酸当量：（ゲルマニウム、イットリウム及びランタンの合計当量又は価数）が１：１〜１：２、好ましくは１：１．５〜１：１．７である。本工程において、粘性ゲルが得られる。 In step (2), each aqueous solution obtained in step (1) is mixed in a quantitative ratio according to the target composition. The order of mixing may be arbitrary. Next, the pH of the mixed solution is adjusted to 1 to 1.8, preferably 1.3 to 1.8. The acid used for the adjustment is preferably an organic acid such as citric acid, more preferably the organic acid equivalent: (the total equivalent or valence of germanium, yttrium and lanthanum) is 1: 1 to 1: 2, preferably 1: 1. .5 to 1: 1.7. In this step, a viscous gel is obtained.
工程（３）において、上記ゲルを、加熱マントルを用いて３００〜６００℃、好ましくは３００〜５００℃で加熱する。１〜３時間程度の加熱で、灰状の生成物が得られる。該生成物を粉砕し、好ましくは残留炭素を除去するために７００〜８００℃で加熱する。このように、固相反応に比べて顕著に低い温度の加熱によって、本発明のセラミックスの前駆体であるＹ含有ランタン・ゲルマネートを粉体状ゲルの形態で得ることができる。 In the step (3), the gel is heated at 300 to 600 ° C., preferably 300 to 500 ° C., using a heating mantle. An ash-like product is obtained by heating for about 1 to 3 hours. The product is ground and preferably heated at 700-800 ° C. to remove residual carbon. Thus, Y-containing lanthanum germanate, which is a precursor of the ceramic of the present invention, can be obtained in the form of a powdered gel by heating at a temperature significantly lower than that of the solid phase reaction.
工程（４）において、得られた粉体状ゲルを、空気下で１３３０〜１４００℃で５〜７時間焼結することによって、本発明のセラミックスを得ることができる。 In the step (4), the obtained powdered gel is sintered under air at 1330 to 1400 ° C. for 5 to 7 hours to obtain the ceramic of the present invention.
得られたセラミックスは、上述のとおり６００℃程度の低温においても、優れた酸素イオン伝導度を示し、酸素センサーとして有用であるだけでなく、固体酸化物燃料電池用の固体電解質としても好適である。現在のところ、固体酸化物燃料電池には、イットリア安定化ジルコニア（YSZ）等の固体酸化物電解質が用いられ、７００〜１，０００℃の高温で運転される。本発明のセラミックスを用いれば電池の運転温度を６００℃程度に低下することができるので、エネルギー効率を顕著に向上することができる。 The obtained ceramic exhibits excellent oxygen ion conductivity even at a low temperature of about 600 ° C. as described above, and is not only useful as an oxygen sensor but also suitable as a solid electrolyte for a solid oxide fuel cell. . Currently, solid oxide fuel cells use a solid oxide electrolyte such as yttria stabilized zirconia (YSZ) and operate at a high temperature of 700-1,000 ° C. If the ceramic of the present invention is used, the operating temperature of the battery can be lowered to about 600 ° C., so that the energy efficiency can be remarkably improved.
以下、本発明を実施例により説明するが、本発明はこれらに限定されるものではない。
＜実施例１〜４、参考例１、２＞
下記手順により、表１に示す組成のランタン・ゲルマネートセラミックスを調製した。
（１）硝酸ランタン６水和物を１．９モル％の濃度で、硝酸イットリウム６水和物を１．０モル％の濃度で、夫々、蒸留水に溶解した。二酸化ゲルマニウムをｐＨ９．５の希アンモニア水溶液に０．０１モル％の濃度で溶解した。
（２）上記３つの水溶液を、表１に示す各組成になるような量で混合したところ、白色の沈殿が生じた。該沈殿を、硝酸を加えることによって溶解し、得られた反応液に、クエン酸と希アンモニア水を、ｐＨが約１．８になるように添加した。クエン酸当量：（ゲルマニウム、イットリウム及びランタンの合計当量）は約１：１であった。
（３）生成された粘性ゲルを、加熱マントルを用いて６７３Ｋ（４００℃）で加熱した。得られた灰状の生成物を粉砕し、残留炭素を除去するために１００３Ｋ（７３０℃）で加熱した。
（４）得られた粉体を、空気下で、１６２３Ｋ（１３５０℃）で６時間焼結した。得られたセラミックスの相安定性は、８７３Ｋで１２時間加熱することにより確認した。
EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these.
<Examples 1-4, Reference Examples 1 and 2>
Lanthanum germanate ceramics having the composition shown in Table 1 were prepared by the following procedure.
(1) Lanthanum nitrate hexahydrate was dissolved in distilled water at a concentration of 1.9 mol% and yttrium nitrate hexahydrate at a concentration of 1.0 mol%, respectively. Germanium dioxide was dissolved in a dilute aqueous ammonia solution at pH 9.5 at a concentration of 0.01 mol%.
(2) When the three aqueous solutions were mixed in such amounts as to have the respective compositions shown in Table 1, a white precipitate was formed. The precipitate was dissolved by adding nitric acid, and citric acid and dilute aqueous ammonia were added to the resulting reaction solution so that the pH was about 1.8. Citric acid equivalent: (total equivalent of germanium, yttrium and lanthanum) was about 1: 1.
(3) The produced viscous gel was heated at 673 K (400 ° C.) using a heating mantle. The resulting ash-like product was ground and heated at 1003 K (730 ° C.) to remove residual carbon.
(4) The obtained powder was sintered at 1623 K (1350 ° C.) for 6 hours under air. The phase stability of the obtained ceramic was confirmed by heating at 873 K for 12 hours.
＜比較例１＞
比較例１として、非特許文献１記載のＬａ10（ＧｅＯ4）6Ｏ3のデータを示す。
<Comparative Example 1>
As Comparative Example 1, data of La 10 (GeO 4 ) 6 O 3 described in Non-Patent Document 1 is shown.
＜比較例２＞
比較例２として、非特許文献２記載のＬａ7.8Ｙ2（ＧｅＯ4）6Ｏ2.8のデータを示す。
<Comparative example 2>
As Comparative Example 2, data of La 7.8 Y 2 (GeO 4 ) 6 O 2.8 described in Non-Patent Document 2 is shown.
＜粉末Ｘ線測定＞
上記工程（３）で得られた粉体について、室温でリガク社製RINT-2500装置を用い（測定条件：ＣｕＫα線、１２ｋＷ（管球電圧４０ｋＶ、管球３００ｍＡ））、粉末Ｘ線測定を行った。
<Powder X-ray measurement>
The powder obtained in the above step (3) was measured at room temperature using a RINT-2500 device manufactured by Rigaku Corporation (measurement conditions: CuKα ray, 12 kW (tube voltage 40 kV, tube 300 mA)). It was.
＜酸素イオン伝導度測定＞
実施例２〜４、参考例２について、下記手順で酸素イオン伝導度を測定した。
直径約１６ｍｍ、厚み約１ｍｍになるよう１６２３Ｋで６時間焼結した試料の両面に白金ペーストを用いて電極を取り付けた。イオン伝導度はプリンストンアプライドリサーチ社製VersaStat 3により交流インピーダンス法で測定した。試料を測定セルに取り付けた後、電気炉温度を１０００℃まで１分間に１０℃の速度で昇温した。測定温度に達した後、３０分から１時間該温度で保持した後にインピーダンス測定を開始した。インピーダンス測定後、５０℃おきに降温、温度保持したのちに測定する操作を４０００℃まで繰り返した。結果を表１に示す。
<Oxygen ion conductivity measurement>
For Examples 2 to 4 and Reference Example 2, oxygen ion conductivity was measured by the following procedure.
Electrodes were attached to both surfaces of a sample sintered at 1623K for 6 hours to have a diameter of about 16 mm and a thickness of about 1 mm using platinum paste. The ionic conductivity was measured by the AC impedance method using VersaStat 3 manufactured by Princeton Applied Research. After attaching the sample to the measurement cell, the electric furnace temperature was raised to 1000 ° C. at a rate of 10 ° C. per minute. After reaching the measurement temperature, the impedance measurement was started after the temperature was maintained for 30 minutes to 1 hour. After the impedance measurement, the temperature was lowered every 50 ° C. and the temperature was kept, and the measurement was repeated up to 4000 ° C. The results are shown in Table 1.
＜セラミックスの相対密度＞
実施例２、３、４、参考例２のセラミックスの相対密度をアルキメデス法によって測定した。結果を表１に示す。
<Relative density of ceramics>
The relative densities of the ceramics of Examples 2, 3, 4 and Reference Example 2 were measured by the Archimedes method. The results are shown in Table 1.
図２及び４に関して上述したとおり、実施例１〜４の粉末Ｘ線回折は、六方晶型を有し、酸素イオン伝導度が高く、相対密度も９０％以上である。比較例２の相対密度に関し、非特許文献２には「理論密度に対する相対密度＞８５％」とあるのみで、実測値は示されていないが、その酸素イオン伝導度から考えると本発明の実施例には及ばない。参考例１は（図３、第４段）、Ｘ線回折においてＬａ２Ｇｅ２Ｏ７のピークが検出され（図中●で示す）、２相含まれていることが分かった。また、参考例２（図３、第１段）は三斜晶型となっていた。 As described above with reference to FIGS. 2 and 4, the powder X-ray diffraction of Examples 1-4 has a hexagonal type, high oxygen ion conductivity, and a relative density of 90% or more. Regarding the relative density of Comparative Example 2, Non-Patent Document 2 only states that “relative density with respect to theoretical density> 85%”, and the actual measurement value is not shown, but considering the oxygen ion conductivity, the implementation of the present invention. There is no example. In Reference Example 1 (FIG. 3, 4th stage), a peak of La 2 Ge 2 O 7 was detected by X-ray diffraction (indicated by ● in the figure), and it was found that two phases were contained. Reference Example 2 (FIG. 3, first stage) was a triclinic crystal type.
本発明のイットリウム含有ランタン・ゲルマネートセラミックスは６００℃程度の低い温度においても酸素イオン伝導性が高い。また、同セラミックスの前駆体は、有機酸を用いた錯体重合法により、固相反応に比べてより低い温度で調製することができる。該イットリウム含有ランタン・ゲルマネートセラミックスは酸素センサー、固体酸化物燃料電池用の固体電解質用途に好適である。 The yttrium-containing lanthanum germanate ceramic of the present invention has high oxygen ion conductivity even at a low temperature of about 600 ° C. Moreover, the precursor of the ceramic can be prepared at a lower temperature than a solid phase reaction by a complex polymerization method using an organic acid. The yttrium-containing lanthanum / germanate ceramics are suitable for solid electrolyte applications for oxygen sensors and solid oxide fuel cells.
Claims (9)
ＬａｘＹｙ（ＧｅＯ４）６Ｏｚ （１）
（式（１）において、９．４＜ｘ＋ｙ＜９．８１、７．７≦ｘ≦８．７、１≦ｙ≦２、２．３≦ｚ≦２．７である）で表され、六方晶型の結晶構造を有する焼結体であり、
前記焼結体は、９０％以上の相対密度を有し、
６００℃における酸素イオン伝導度が２．３×１０−３［Ｓ／ｃｍ］以上である、イットリウム含有オキシアパタイト型ランタン・ゲルマネートセラミックス。 Following formula (1):
La x Y y (GeO 4 ) 6 O z (1)
Is represented by (formula (1), which is 9.4 <x + y <9.81,7.7 ≦ x ≦ 8.7,1 ≦ y ≦ 2,2.3 ≦ z ≦ 2.7), A sintered body having a hexagonal crystal structure,
The sintered body has a relative density of 90% or more,
Yttrium-containing oxyapatite-type lanthanum / germanate ceramics having an oxygen ion conductivity at 600 ° C. of 2.3 × 10 −3 [S / cm] or more.
前記水溶液を混合し、有機酸を用いてｐＨを調整することによって、粘性ゲルを生成する工程であって、前記有機酸は、前記有機酸の当量：ゲルマニウム、イットリウム及びランタンの合計当量が１：１〜１：２を満たし、前記ｐＨは１〜１．８を満たす、生成する工程と、A step of producing a viscous gel by mixing the aqueous solution and adjusting the pH using an organic acid, wherein the organic acid has an equivalent of the organic acid: a total equivalent of germanium, yttrium and lanthanum is 1: A step of satisfying 1-1: 2 and the pH satisfying 1-1.8,
前記粘性ゲルを３００℃〜６００℃で加熱して、粉体状ゲルを得る工程と、Heating the viscous gel at 300 ° C. to 600 ° C. to obtain a powdered gel;
前記粉体状ゲルを１３３０℃〜１４００℃で５〜７時間焼結する工程とSintering the powdered gel at 1330 ° C. to 1400 ° C. for 5 to 7 hours;
を包含する、請求項１〜４のいずれか１項に記載のイットリウム含有オキシアパタイト型ランタン・ゲルマネートセラミックスを製造する方法。A method for producing an yttrium-containing oxyapatite-type lanthanum-germanate ceramic according to any one of claims 1 to 4.
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