Examination of techniques for synthesizing highly efficiency thermoelectric material NaCo2O4.

研究了高效热电材料NaCo2O4的合成技术。试验了常规烧结法、热压法、等离子烧结法、空气加压法、熔体凝固法。将适量的Na2Co3和Co氧化物粉混合，在棉铃机中以甲醇为原料进行研磨。将混合粉料在880℃下干燥烧结12h或24h，将前驱体再次入球磨粉碎制粉。然后用各种工艺对粉末进行烧结。一种是在不同温度下进行不同时间的热压。一个是在压模中形成5毫米x 6毫米x 20毫米的尺寸。试样在880 ~ 1000℃的温度范围内进行不同退火次数的烧结。部分试样在10kgf/cm^2的空气压力下受压，制成多孔试样到精密试样。部分粉末在等离子烧结机中，在700 ~ 850℃的温度范围内烧结5min ~ 15min。将尺寸为5mm × 6mm × 20mm的试样加热至1100℃，熔化后缓慢冷却至950℃。研究了高效热电材料NaCo2O4的合成技术。试验了常规烧结法、热压法、等离子烧结法、空气加压法、熔体凝固法。将适量的Na2Co3和Co氧化物粉混合，在棉铃机中以甲醇为原料进行研磨。将混合粉料在880℃下干燥烧结12h或24h，将前驱体再次入球磨粉碎制粉。然后用各种工艺对粉末进行烧结。一种是在不同温度下进行不同时间的热压。一个是在压模中形成5毫米x 6毫米x 20毫米的尺寸。试样在880 ~ 1000℃的温度范围内进行不同退火次数的烧结。部分试样在10kgf/cm^2的空气压力下受压，制成多孔试样到精密试样。部分粉末在等离子烧结机中，在700 ~ 850℃的温度范围内烧结5min ~ 15min。将尺寸为5mm x 6mm x 20mm的部分试样加热至1100℃，熔化后缓慢冷却至950℃。除了在空气中加压外，其他任何方法如热压法、等离子烧结法、熔融凝固法都不能将多孔试样制成精密试样。然而，这些精密样品的热电性能并不比通常的烧结方法好多少。它们只比通常的烧结方法好20%。原因可能是Na原子从试样中蒸发了，或者是Na2Co3粉末吸收了多余的Na原子，在试样周围放置Na2Co3粉末以防止Na原子蒸发。因此，如何将钠离子浓度控制在最佳状态是最重要的问题。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