Formation Mechanism of Combined Crystals and Applications to Development of New Functional Materials

2001 Fiscal Year Final Research Report Summary

• Project/Area Number: 12450316
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 反応・分離工学
• Research Institution: Tokyo University of Agriculture and Technology
• Principal Investigator: MATSUOKA Masakuni Tokyo University of Agriculture and Technology, Faculty of Technology, Professor, 工学部, 教授 (40016671)
• Co-Investigator(Kenkyū-buntansha): UCHIDA Hirohisa Tokyo University of Agriculture and Technology, Faculty of Technology, Assistant Professor, 工学部, 助手 (70313294) ; TAKIYAMA Hiroshi Tokyo University of Agriculture and Technology, Faculty of Technology, Lecture, 工学部, 講師 (40251582)
• Project Period (FY): 2000 – 2001
• Keywords: Combined Crystal / Ternary System / Nucleation / Crystal Growth / Solid-solid Interface / Solid-liquid Interface / Phase Equilibria / Functional Material

Research Abstract

We, in the previous studies, observed the formation of combined crystals by the spontaneous nucleation of potassium chloride crystals on the surfaces of sodium chloride contacted with supersaturated NaCl - KC1 - H_2Oernary solutions. The present study aims to elucidate the mechanism of formation of the combined crystals and to investigate their possibilities of applications to new functional materials. For the NaCl - KC1 -H_2Oternary system, spontaneous nucleation of potassium chloride was induced during the steady growth of NaCl substrate. Deposition of potassium chloride crystals on the sodium chloride substrate crystals was clearly observed and the crystals deposited were found to be in the same orientation. From the observation of dissolving surfaces of sodium chloride substrate crystals placed in aqueous solutions that contained potassium chloride and were undersaturated with respect to sodium chloride, nucleation of potassium chloride was observed. The nucleation was caused by th e local high supersaturation created by the dissolution of sodium chloride into the mother liquor. The solution structures near the solid-liquid interface between sodium chloride crystals and NaCl - KQ - H_2Oternary solutions were studied by molecular dynamics simulations to elucidate the mechanism of formation of the combined crystals. The solution structures and the local compositions near the solid-liquid interfaces were completely different from those of the mother liquors. The formation of shallow grooves at the interface between sodium chloride substrate and potassium chloride deposit was observed, and the width and depth of the grooves were larger and the shape changed with time. This would be because the structure of the grooves was unstable and was therefore affected by moisture. The formation of combined crystals were also observed for the NaNO_ 3-KNO_3 -H_2O and NaCl - KNO_3 - H_2O ternary systems, and this result will be useful for the applications of the combined crystals to the new functional materials.