Examination of techniques for synthesizing highly efficiency thermoelectric material NaCo2O4.

研究了高效热电材料NaCo2O4的合成工艺。尝试了常用的烧结法、热压法、等离子烧结法、空气压制法、熔体凝固法。在球磨机中加入适量的Na_2CO_3和Co_2O_3粉末，用甲醇研磨。混合粉末干燥后，在880℃下烧结12h或24 h，再将前驱体在球磨机中研磨成粉。然后通过各种工艺对粉末进行烧结。一种是在不同的温度下热压不同的退火时间。其中一个在冲压模具中成形为5 mm x 6 mm x 20 mm大小。在880~1000℃的温度范围内，对样品进行了不同时间的烧结。将部分试件在10kgf/cm^2以下的空气气氛中压制，制成多孔试件和精密试件。部分粉末在等离子烧结机中进行5min~15min的烧结，烧结温度范围为70 0~85 0℃。一些…为5 mm x 6 mm x 20 mm的试件更多的n尺寸被加热到1100℃，然后熔化并缓慢冷却到950℃。研究了高效热电材料NaCo2O4的合成工艺。尝试了常用的烧结法、热压法、等离子烧结法、空气压制法、熔体凝固法。在球磨机中加入适量的Na_2CO_3和Co_2O_3粉末，用甲醇研磨。混合粉末干燥后，在880℃下烧结12h或24 h，再将前驱体在球磨机中研磨成粉。然后通过各种工艺对粉末进行烧结。一种是在不同的温度下热压不同的退火时间。其中一个在冲压模具中成形为5 mm x 6 mm x 20 mm大小。在880~1000℃的温度范围内，对样品进行了不同时间的烧结。将部分试件在10kgf/cm^2以下的空气气氛中压制，制成多孔试件和精密试件。部分粉末在等离子烧结机中进行5min~15min的烧结，烧结温度范围为70 0~85 0℃。将尺寸为5 mm×6 mm×20 mm的样品加热到1100℃，然后熔化并缓慢冷却到950℃。除了在空气中压制外，其他方法如热压法、等离子烧结法和熔凝法都不能将多孔样品制成精密样品。然而，这些精密样品的热电性能并不比通常的烧结方法好很多。它们只比通常的烧结法好20%。原因可能是样品中蒸发的Na原子或从Na2CO3粉末中吸收了多余的Na原子，放置在样品周围以防止Na原子的蒸发。因此，如何将钠的浓度控制在最佳状态是最重要的问题。较少

Synthesizing techniques for highly efficiency thermoelectric material NaCo2O4 have been examined. Usual sintering method, hot press method, plasma-sintering method, pressing method at air, melt solidification method were tried. Appropriate amount of Na2Co3 and Co oxide powder were mixed and grind in a boll mill by using methanol. The mixed powder was dried and sintered at 880℃ for 12h or 24 h. The precursor was again grind in the boll mill to make powder. Then the powder was sintered by various techniques. One is hot pressed at various temperatures for various anneal times. One is shaped to 5 mm x 6mm x 20mm size in a pressed mold. The specimens were sintered in a temperature range from 880〜1000℃ for various anneal times. Some of the specimens were pressed in an air atmosphere under 10kgf/cm^2 to make porous specimen to precise specimen. Some of powder is sintered in a plasma sintering machine in the temperature range 700〜850℃ for 5 min〜15min. Some of specimens with 5 mm x 6mm x 20mm i … More n size were heated up to 1100℃ and they were melted and slowly cooled to 950℃.Synthesizing techniques for highly efficiency thermoelectric material NaCo2O4 have been examined. Usual sintering method, hot press method, plasma-sintering method, pressing method at air, melt solidification method were tried. Appropriate amount of Na2Co3 and Co oxide powder were mixed and grind in a boll mill by using methanol. The mixed powder was dried and sintered at 880℃ for 12h or 24 h. The precursor was again grind in the boll mill to make powder. Then the powder was sintered by various techniques. One is hot pressed at various temperatures for various anneal times. One is shaped to 5 mm x 6mm x 20mm size in a pressed mold. The specimens were sintered in a temperature range from 880〜1000℃ for various anneal times. Some of the specimens were pressed in an air atmosphere under 10kgf/cm^2 to make porous specimen to precise specimen. Some of powder is sintered in a plasma sintering machine in the temperature range 700〜850℃ for 5 min〜15min. Some of specimens with 5 mm x 6mm x 20mm in size were heated up to 1100℃ and they were melted and slowly cooled to 950℃.We could not make porous specimen to precise specimen by any other method such as hot press method, plasma sintering method and melt and solidification method excepting by pressing them at air atmosphere. However, thermoelectric properties of these precise specimens are not so much better than that made from by usual sintering method. They are only 20% better than the usual sintering method. The reasons were expected that Na atoms evaporated from specimens or excess Na atoms were absorbed from Na2Co3 powder, which were put around the specimen to prevent the evaporation of Na atoms. Consequently, the most important problem is how to control the Na concentration at the best condition. Less