ナトリウム化合物(NaO,NaO,およびNaOH)の擬3元系状態図の研究

Pseudo-ternary phase diagram in the NaO-NaO-NaOH system

斉藤 淳一  ; 青砥 紀身 ; 天藤 雅之*

Saito, Junichi; Aoto, Kazumi; not registered

一般に状態図はある温度での化合物の存在状態(固体、液体および固体+液体)を知るのによく使われている。主要なナトリウム化合物(Na2O, Na2O2 およびNaOH)による高速増殖炉(FBR)用構造材料の腐食挙動を理解するために、これら化合物の状態図を把握することはたいへん重要である。しかし、本研究で対象としている系では、これまでNa2O-NaOH系状態図が調べられているが、それ以外の擬2元系および擬3元系状態図の研究はない。 本研究ではそれらナトリウム化合物の存在状態を明らかにするために、擬2元系および擬3元系状態図の作成を試みた。示差走査熱量計(DSC)を用いて2成分および3成分系の一連の熱分析を行った。その結果、状態図を作成するのに有効な情報である液相線温度および3元共晶点が得られた。これらDSC測定結果に基づき、熱力学計算ソフトThermo-Calcの相互作用パラメータを最適化することにより正確な擬2元系および擬3元系Na2O-Na2O2 -NaOH状態図を提示できた。

Generally, the phase diagrams are always used to understand the present state of compounds at certain temperature. In order to understand the corrosion behavior of structural material for FBR by main sodium compounds (NaO, NaO and NaOH), it is very important to comprehend the phase diagrams of their compounds. However, only NaO-NaOH pseudo-binary phase diagram had been investigated previously in this system. There is no study of other pseudo-binary or ternary phase diagrams in the NaO-NaO-NaOH system. In this study, in order to clarify the present states of their compounds at certain temperatures, the pseudo-binary and ternary phase diagrams in the NaO-NaO-NaOH system were prepared. A series of thermal analyses with binary and ternary component system has been carried out using the differential scanning calorimetry (DSC). The liquidus temperature and ternary eutectic temperatures were confirmed by these measurements. The beneficial indications for constructing phase diagrams were obtained from these experiments. On the basis of these results, the interaction parameters between compounds which were utilized for the Thermo-Calc calculation were optimized. Thermo-Calc is one of thermodynamic calculation software. Consequently the accurate pseudo-binary and ternary phase diagrams were indicated using the optimized parameters.