High pressure synthesis of new super hard materials in the boron suboxide system and their functional evaluation

在低压烧结条件下，在二十面体硼原子团簇的菱面体晶胞空腔中加入氧原子或轻金属，制备了新型硼氧化物超硬材料与其它超硬材料的复合材料。这些复合材料的机械性能进行了研究沿着与他们的化学和电气性能。本课题的主要研究成果和结论如下：1.低氧化硼（B_6O）及其与金刚石复合材料的高压烧结是一种化学稳定性高的超硬材料，也是近年来发展起来的热电转换靶材。然而，这种材料非常脆，难以烧结，因此延迟了其作为工业材料的实际应用。本研究以B_2O_3和无定形硼为原料合成B_6O粉末，采用高压烧结法制备了B_6O烧结体，并对B_6O单相烧结体的力学性能和热性能进行了研究。为了在不降低压坯硬度的前提下提高压坯的断裂韧性，研究了B_6O与金刚石二元复合体系。在使用细粒度金刚石粉末的情况下，制备了具有增加的断裂韧性的超硬复合材料，其室温电导率高达10^<-3>S/cm. 2的数量级。AlMgB_2<14>及其与其它超硬材料复合材料的高压烧结AlMgB_2<14>也是一种具有类似B_6O晶体结构的超硬材料，有望表现出更高的机械强度。利用<14>自制的AlMgB_2粉末在高压下制备了单相烧结体。压坯的硬度与B_6O相当，但断裂韧性较低。AlMgB_2与B_6O或TiB_2复合体系的出现<14>，使合金的硬度提高，但断裂韧性降低。

New super-hard materials in the boron suboxide system, which contains oxygen atom or light mmetals in the cavity of the rhombohedral unit cell of icosahedral boron clusters, were sintered in composite with other super-hard material under high pressure. The mechanical properties of these composites were investigated along with their chemical and electrical properties. The main results and conclusions in the project term were summarized as follows.1. High pressure sintering of boron suboxide (B_6O) and its composite with diamondB_6O is known as a super-hard material with high chemical stability and also a target material for thermoelectric conversion recently. However, this material is so brittle and difficult to sinter that its actual application as an industrial material is delayed. In the present study, we prepared the sintered compact of B_6O by high pressure sintering of B_6O powder synthesized from B_2O_3 and amorphous boron, and elucidated the mechanical and thermal properties of B_6O single phase sintered compact. In order to enhance the fracture toughness of the compact without decreasing its hardness, the binary composite system of B_6O and diamond was investigated. In case of using fine-grained diamond powder, a superl-hard composite with an increased fracture toughness was prepared and its electrical conductivity at room temperature was as high as the magnitude of 10^<-3> S/cm.2. High pressure sintering of AlMgB_<14> and its composite with other super-hard materialAlMgB_<14> is also a super-hard material with analogous crystal structure to B_6O and expected to exhibit higher mechanical strength. Single phase sintered compact of AlMgB_<14> was prepared originally under high pressure using the powder synthesized in our laboratory. This compact showed the hardness as high as B_6O, though the fracture toughness was similarly low. Presentation of the composite systems of AlMgB_<14> with B_6O or TiB_2 resulted in higher hardness, hut lower fracture toughness.