【作者】 张中建；

【导师】 金应荣；

【作者基本信息】 西华大学 ， 材料加工， 2008， 硕士

【摘要】 Ca-Co-O系材料中，Ca₃Co₄O₉、Ca₂Co₂O₅和Ca₃Co₂O₆都具有热电性能，因而受到了广泛的关注和研究。这些研究大多集中在理论计算、掺杂改性以及组织形态控制三方面，对材料加热和冷却过程中的组织转变没有进行细致研究，考虑到Ca₃Co₄O₉和Ca₃Co₂O₆在高温下都会分解，在制备材料时大都将烧结温度控制在分解温度以下，这可能是没有制备出具有实用价值的热电材料的原因之一。本文尝试突破分解温度的限制，寻找制备Ca-Co-O系材料的新方法。本文以CaCO₃和Co₂O₃为原料，按名义组成Ca₃Co₄O₉、Ca₂Co₂O₅和Ca₃Co₂O₆配料，经过预烧结、电弧熔炼以及退火处理制各样品，观察了三种样品凝固后和不同温度退火后的组织形态，为探索Ca-Co-O系材料的制备新方法奠定了基础。实验结果表明，熔炼后的样品除了芯部有疏松和缩孔外，其余部位都比较致密。样品都由含钴氧化钙（以下称α相）和含钙氧化钴（以下称β相）组成，凝固组织中有粗大的树枝晶。名义组成为Ca₃Co₄O₉的样品在880℃经36h退火后，出现了Ca₃Co₄O₉和Ca₃Co₂O₆两个新相，经96h退火后，Ca₃Co₂O₆相消失，样品呈现单一的Ca₃Co₄O₉相。名义组成为Ca₃Co₂O₆的样品在880℃经100h退火后，主相为Ca₃Co₂O₆，伴有少量的Ca₃Co₄O₉相和β相，名义组成为Ca₂Co₂O₅的样品在880℃经100h退火后，主相为Ca₃Co₂O₆和Ca₃Co₄O₉，没有出现期望的Ca₂Co₂O₅相。样品经1000℃×9h和1050℃×9h退火后，组织变得比较均匀。样品经1200℃×9h退火后，名义组成为Ca₃Co₂O₆和Ca₂Co₂O₅的样品组织均匀，由α相和β相组成，名义组成为Ca₃Co₄O₉的样品虽然也由α相和β相组成，但β相呈球形，α相分布在球形β相之间的间隙处，且有分解的迹象。经880℃×5h进一步退火，α相的分解表现得更加明显。α相分解时产生细条状β相，β相呈束状分布，束与束之间可能有一定的位向关系。分析认为，束状β相可能仅在一定得温度范围和成分范围内出现，以有序的束状β相为基础，有可能制备出具有一定取向的Ca₃Co₄O₉热电材料。更多还原

【Abstract】 In Ca-Co-O series materials, Ca₃Co₄O₉, Ca₂Co₂O₅ and Ca₃Co₂O₆ all have thermoelectric properties and thus been investigated widely, most of these studies focus on theoretical calculations, doping and controlling of microstructure, a little on the microstructure transformation in heating and cooling process, considering the decomposition of Ca₃Co₄O₉ and Ca₃Co₂O₆, the sintering temperature were mostly controlled below the decomposition temperature, that may be one of the reason for valuable thermoelectric materials prepared unsuccessfully. This paper attempts to explore a new preparing method of Ca-Co-O materials above the decomposition temperature.With CaCO₃ and Co₂O₃ as starting materials, samples with nominal composition of Ca₃Co₄O₉, Ca₂Co₂O₅ and Ca₃Co₂O₆ have been prepared by pre-sintering, arc-melting and annealing at different temperature in this paper, and the microstructure of samples investigated respectively. All of these are the foundation for exploring new preparing method of Ca-Co-O materials.It is shown that the melted samples are compact except needle holes and shrinkage caves in centre, consist of two solid solutions, calcium oxide containing divalent cobalt oxide （a phase） and divalent cobalt oxide containing calcium oxide （βphase）, with large dendrite in microstructure.In the samples with nominal composition of Ca₃Co₄O₉ annealed at 880℃, Ca₃Co₄O₉ and Ca₃Co₂O₆ were observed when annealed for 36h, but Ca₃Co₂O₆ disappeared when annealed for 96h, so the samples with unique Ca₃Co₄O₉ can be obtained. In the samples with nominal composition of Ca₃Co₂O₆ annealed at 880℃for 100h, Ca₃Co₂O₆ are the main phase with a few of Ca₃Co₄O₉ and a phase. In the samples with nominal composition of Ca₂Co₂O₅ annealed at 880℃for 100h, Ca₃Co₂O₆ and Ca₃Co₄O₉ are the main phase, with no expected Ca₂Co₂O₅.In the samples annealed at 1000℃and 1050℃for 9h, homogenized microstructure can be observed.Samples with nominal composition of Ca₂Co₂O₅ and Ca₃Co₂O₆ annealed at 1200℃for 9h consist of a andβ. Samples with nominal composition of Ca₃Co₄O₉ annealed at 1200℃for 9h consist of a andβ, too, butβphase is spherical, a with signs of decomposition locates at the gap between sphericalβ. After being further annealed at 880℃for 5h, the decomposition of a is even more obvious, andβarrays obtained between which there may be certain orientation relationship.Based onβarrays, which perhaps appear only in a certain range of temperature and composition, there is the possibility of preparing Ca₃Co₄O₉ thermoelectric materials with a certain orientation.更多还原