Raman Spectral Investigations on the Phase Transition Behaviors of MgSO4·7H2O Crystals in Different Efflorescence Processes
WANG Feng1,2, ZHANG Yun-hong2
1. Chemistry Department, School of Physics and Chemistry, Henan Polytechnic University, Jiaozuo 454000，China 2. Institute for Chemical Physics, Beijing Institute of Technology, Beijing 100081, China
Abstract：In the present paper, the in situ confocal Raman spectra of MgSO4·7H2O crystal in different efflorescence processes were obtained through changing relative humidities in differernt ways. Thus, detailed investigation of phase transition of MgSO4·7H2O crystal was achieved. At 3% RH, the phase transition of MgSO4 crystal from MgSO4·7H2O to MgSO4·3H2O both occurred in the fast-efflorescence and slow-efflorescence processes. However, in the deliquescence process, distinct phase transition behaviors were found between the MgSO4·3H2O crystals which formed in different efflorescence processes. the MgSO4·3H2O crystals formed in fast-efflorescence process transformed to MgSO4·6H2O crystals at 70% RH in the deliquescence process. On the contrary, the MgSO4·3H2O crystals formed in slow-efflorescence process deliquesced to supersaturated MgSO4 droplet. The studies indicated that there is a correlation between the phase transition behaviors and ways of changing RH for the different MgSO4 crystal hydrates.
Key words：MgSO4·7H2O;Phase transition;Raman spectra;Efflorescence process
[1] Vaniman D T, Bish D L, Chipera S J, et al. Nature, 2004, 431: 663. [2] Vaniman D T, Chipera S J, Bish D L, et al. XXXXVI Lunars and Planetary Science Conference, Abstract No.1486. [3] Wang A, Freeman J J, Jolliff B L, et al. Geochimica et Cosmochimica Acta, 2006, 70: 6118. [4] Gendrin A, Mangold N, Bibring J P, et al. Sicence, 2006, 307: 1587. [5] Tosca N S, Mclennan S M, Lindsley D, et al. Journal of Geophysical Research, 2004, 109: E05003. [6] Golden D C, Ming D W, Morris R V, et al. Journal of Geophysical Research, 2005, 110: E12S07. [7] Emons H H, Ziegenbalg G, Naumann R, et al. Journal of Thermal Analysis, 1990, 36: 1265. [8] Chou I M, Seal II R R, Hemingway B S. American Mineralogist, 2002, 87: 108. [9] Encarnacion R A, Daniel J M R, Carlos R N. Journal of Physical Chemistry B, 2007, 111: 41. [10] Sattar A J, Christine S, Joachim U. Journal of Crystal Growth, 2002, 236: 400. [11] Pasupathi G, Philominathan P. Materials Letters, 2008, 62: 4386. [12] Genceli F E, Pascual M R, Kjelstrup S, et al. Crystal Growth & Design, 2009, 9: 1318. [13] Wang F, Zhang Y H, Li S H, et al. Analytical Chemistry, 2005, 77: 7148. [14] Wang F, Shou J J, Zhang Y H. Chinese Science Bulletin, 2008, 53(15): 2414. [15] Speight J G. Lange’s Chemistry Handbook，16th Edition. McGraw-Hill Professional, 2004.
