稀土Gd~(3+)掺杂独居石型LaPO_4的溶胶-凝胶法制备及其热传导性能
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摘要
采用柠檬酸溶胶-凝胶法制备了稀土Gd3+掺杂的LaPO4新型热障涂层用陶瓷粉体LaPO4(x=0.0,0.1,0.2,0.3;LGPO)。通过X-ray衍射、扫描电子显微镜、TG-DSC、高温热膨胀仪和激光热导仪对样品的相组成、微观形貌、热行为、热膨胀系数和热导率进行表征。结果表明:稀土Gd3+掺杂的LGPO保持了独居石相结构;添加稀土Gd3+不仅可以降低材料的导热系数,还有利于其热膨胀系数的提高;随着稀土Gd3+掺杂量的增加,晶体中点缺陷浓度不断升高,声子平均自由程不断减小,使得稀土Gd3+掺杂的LGPO的热导率在x=0.3时达到最低值(λ=1.22W/(m·K),T=1273K),该值明显低于同温度下8YSZ的热导率。Gd3+掺杂的LaPO4体系是下一代新型热障涂层用陶瓷热门的候选材料之一。
The synthesis of Gd3+doped LaPO4(La1-xGdxPO4,x=0.0,0.1,0.2,0.3;LGPO)ceramics derived from citric acid sol-gel method using La(NO3)3·6H2O,Gd(NO3)3·6H2O and(NH4)2HPO4as precursor were investigated.The precursor,dried,and further sintered LGPO samples were characterized by X-ray diffraction,scanning electron microscopy(SEM)and differential scanning caborimetry-thermogravimetry(DSC-TG).The thermal expansion coefficients(CTE)and thermal diffusivity of these oxide materials were also evaluated by the high-temperature dilatometer and laser flash method.Those results demonstrate that all the La1-xGdxPO4 compositions are comprised of the pure monazite LaPO4 phase.Gd3+doped lanthanum orthophosphate ceramics demonstrates low thermal conductivity reduction contributed by the substaintial additional point-defect scattering with the decreasing phonon mean free path,jontly facilitate higher CTE.Thermal conductivity of the doped La1-xGdxPO4 composition was found to be lower than that of the 8wt.% yttria-stabilized zirconia(8YSZ)and showed a minimum thermal conductivity value at the composition La0.7Gd0.3PO4(λ=1.22 W/(m·K),T=1273K).Such excellent thermo-physical properties make the La1-xGdxPO4 ceramics as a promising candidate for the next generation advanced thermal barrier coatings.
The synthesis of Gd3+doped LaPO4(La1-xGdxPO4,x=0.0,0.1,0.2,0.3;LGPO)ceramics derived from citric acid sol-gel method using La(NO3)3·6H2O,Gd(NO3)3·6H2O and(NH4)2HPO4as precursor were investigated.The precursor,dried,and further sintered LGPO samples were characterized by X-ray diffraction,scanning electron microscopy(SEM)and differential scanning caborimetry-thermogravimetry(DSC-TG).The thermal expansion coefficients(CTE)and thermal diffusivity of these oxide materials were also evaluated by the high-temperature dilatometer and laser flash method.Those results demonstrate that all the La1-xGdxPO4 compositions are comprised of the pure monazite LaPO4 phase.Gd3+doped lanthanum orthophosphate ceramics demonstrates low thermal conductivity reduction contributed by the substaintial additional point-defect scattering with the decreasing phonon mean free path,jontly facilitate higher CTE.Thermal conductivity of the doped La1-xGdxPO4 composition was found to be lower than that of the 8wt.% yttria-stabilized zirconia(8YSZ)and showed a minimum thermal conductivity value at the composition La0.7Gd0.3PO4(λ=1.22 W/(m·K),T=1273K).Such excellent thermo-physical properties make the La1-xGdxPO4 ceramics as a promising candidate for the next generation advanced thermal barrier coatings.
引文
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11 Du A B,Wan C L,Qu Z X,et al.Effects of texture on the thermal conductivity of the LaPO4 monazite[J].J Am Ceram Soc,2010,93(9):2822
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14 Guo S P,You T S,Bobev S.Closely related rare-earth metal germanides RE2Li2Ge3 and RE3Li4Ge4(RE=La-Nd,Sm):Synthesis,crystal chemistry,and magnetic properties[J].Inorg Chem,2012,51(5):3119
15 Leitner J,Voňka P,Sedmidubsky D,et al.Application of neumann-kopp rule for the estimation of heat capacity of mixed oxides[J].Thermochim Acta,2010,497(1):7
16 Zeller R C,Pohl R O.Thermal conductivity and specific heat of noncrystalline solids[J].Phys Rev B,1971,4(6):2029
17 Lo Shih-Han,He Jiaqing,et al.Phonon scattering and thermal conductivity in p-type nanostructured PbTe-BaTe bulk thermoelectric materials[J].Adv Funct Mater,2012,22(24):5175
2 周宏明,易丹青,余志明,等.热障涂层的研究现状与发展方向[J].材料导报,2006,20(3):4
3 史国栋,陈贵清,梁军,等.热障涂层热导率的研究进展[J].材料导报,2006,20(10):44
4 Bansal N P,Zhu D.Effects of doping on thermal conductivity of pyrochlore oxides for advanced thermal barrier coatings[J].Mater Sci Eng A,2007,459(1):192
5 周宏明,易丹青,钟华.稀土Dy和Ce共掺杂La2Zr2O7新型热障涂层用陶瓷材料[J].无机材料学报,2008,23(3):567
6 Cao X Q,Vassen R,Stoever D.Ceramic materials for thermal barrier coatings[J].J Eur Ceram Soc,2004,24(1):1
7 刘福顺,宫声凯,徐惠彬.大功率EB-PVD陶瓷热障涂层的研究与应用[J].航空学报,2000,21(1):30
8 张玉娟,孙晓峰,金涛,等.大气等离子喷涂的YSZ纳米热障涂层的微观结构[J].金属学报,2003,39(4):395
9 胡传顺,王福会.热障涂层研究进展[J].腐蚀科学与防护技术,2000,12(3):160
10 徐惠彬,宫声凯,刘福顺.航空发动机热障涂层材料体系的研究[J].航空学报,2000,21(1):7
11 Du A B,Wan C L,Qu Z X,et al.Effects of texture on the thermal conductivity of the LaPO4 monazite[J].J Am Ceram Soc,2010,93(9):2822
12 Lehmann H,Pitzer D,Pracht G,et al.Thermal conductivity and thermal expansion coefficients of the lanthanum rareearth-element zirconate system[J].J Am Ceram Soc,2003,86(8):1338
13 Clarke D R,Levi C G.Materials design for the next generation thermal barrier coatings[J].Annual Rev Mater Res,2003,33(1):383
14 Guo S P,You T S,Bobev S.Closely related rare-earth metal germanides RE2Li2Ge3 and RE3Li4Ge4(RE=La-Nd,Sm):Synthesis,crystal chemistry,and magnetic properties[J].Inorg Chem,2012,51(5):3119
15 Leitner J,Voňka P,Sedmidubsky D,et al.Application of neumann-kopp rule for the estimation of heat capacity of mixed oxides[J].Thermochim Acta,2010,497(1):7
16 Zeller R C,Pohl R O.Thermal conductivity and specific heat of noncrystalline solids[J].Phys Rev B,1971,4(6):2029
17 Lo Shih-Han,He Jiaqing,et al.Phonon scattering and thermal conductivity in p-type nanostructured PbTe-BaTe bulk thermoelectric materials[J].Adv Funct Mater,2012,22(24):5175