Acta Phys. -Chim. Sin. ›› 2010, Vol. 26 ›› Issue (09): 2323-2330.doi: 10.3866/PKU.WHXB20100903

• THERMODYNAMICS,THERMOCHEMISTRY AND SOLUTION CHEMISTRY • Previous Articles     Next Articles

Structure of Supersaturated Aqueous SodiumPentaborate Solution

ZHOU Yong-Quan1,2, FANG Chun-Hui1, FANG Yan1   

  1. 1. CAS Key Laboratory of Salt Lake Resources and Chemistry, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, P. R. China;
    2. Graduate School of Chinese Academy of Sciences, Beijing 100049, P. R. China
  • Received:2010-01-20 Revised:2010-06-01 Published:2010-09-02
  • Contact: FANG Chun-Hui, FANG Yan E-mail:fangch@isl.ac.cn, fangy8@isl.ac.cn
  • Supported by:

    The project was supported by the Major State Basic Research Development Programof China (973) General Program(2008CB617612) and National Natural Science Foundation of China (20873172).

Abstract:

We determined the time-averaged and space-averaged structures of supersaturated aqueous sodiumpentaborate solutions by rapid liquid X-ray diffractometry at 298 and 323 K. Difference radial distribution functions (DRDF) and their theoretical partial radial distribution functions for B-B, B-O, O-O, Na-O and Na-B atom pairs were obtained from accurate diffraction data. The effects of concentration and temperature on the structure of the solutions were also discussed. Three main species (B3O3(OH)- 4, B5O6(OH)- 4 and B(OH)3) were found to exist in supersaturated aqueous sodium pentaborate solutions and their hydrated structures were determined by model design and quantitative calculations. Higher temperature and higher concentration result in higher polyborates. As the concentration decreases, interaction distances and the average coordination number of the octahedral hexahydrated Na+ ion hardly changes while the hydration number of the polyborate increases. In concentrated solutions, the terminal-oxygen of the polyborates connects with the hydrated Na+ in a monodentate formto produce a contact ion pair with a characteristic distance of 0.328 nm.

Key words: Solution structure, X-ray diffraction, Sodiumpentaborate, Supersaturated aqueous solution, Radial distribution function, Polyborate anion

MSC2000: 

  • O645