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RISS 인기검색어
- 검색키워드
- 저자 : Mysen, Bjorn O. (검색결과 1 건)
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Lee, Sung Keun,Yi, Yoo Soo,Cody, George D.,Mibe, Kenji,Fei, Yingwei,Mysen, Bjorn O. American Chemical Society 2012 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.116 No.3
<P>Probing the pressure-induced structural changes and the extent of disorder in aluminosilicate glasses and melts at high pressure remains a challenge in modern physical and chemical sciences. With an aim of establishing a systematic relationship between pressure, composition, and glass structures, we report <SUP>27</SUP>Al and <SUP>17</SUP>O 3QMAS NMR spectra for sodium aluminosilicate glasses [Na<SUB>2</SUB>O:Al<SUB>2</SUB>O<SUB>3</SUB>:SiO<SUB>2</SUB> = 1.5:0.5:2<I>n</I> with <I>n</I> = 1 (NAS150520, <I>X</I><SUB>SiO2</SUB> = 0.5), 2 (NAS150540, <I>X</I><SUB>SiO2</SUB> = 0.67), and 3 (NAS150560, <I>X</I><SUB>SiO2</SUB> = 0.75)], quenched from melts at pressures up to 8 GPa. We also explore the stability of the <SUP>[4]</SUP>Al–O–<SUP>[4]</SUP>Al cluster in the highly depolymerized, NAS150520, glass at high pressure. For given glass composition, the <SUP>[5,6]</SUP>Al peak intensity increases with increasing pressure. The population of <SUP>[5,6]</SUP>Al increases linearly with <I>X</I><SUB>SiO2</SUB> from NAS150520 (<I>X</I><SUB>SiO2</SUB> = 0.5) to NAS150560 glass (<I>X</I><SUB>SiO2</SUB> = 0.75) at both 6 and 8 GPa. The <SUP>[5,6]</SUP>Al/<I>X</I><SUB>SiO2</SUB> ratio also tends to increase with pressure, indicating a possible relationship between <SUP>[5,6]</SUP>Al fraction and <I>X</I><SUB>SiO2</SUB> that depends on pressure. The effect of pressure on the network connectivity in the sodium aluminosilicate glasses is manifested in the increase in <SUP>[4]</SUP>Si–O–<SUP>[5,6]</SUP>Al peak intensity and the decrease in the nonbridging oxygen (NBO) fraction with increasing pressure. The fraction of <SUP>[4]</SUP>Si–O–<SUP>[5,6]</SUP>Al in NAS150520 is smaller than in NAS150560. Taking into consideration the pressure-induced Al coordination transformation in the fully polymerized glass (albite, Na<SUB>2</SUB>O:Al<SUB>2</SUB>O<SUB>3</SUB>:SiO<SUB>2</SUB>= 1:1:6, NBO/T = 0), the fraction of <SUP>[5,6]</SUP>Al at a given pressure varies <I>nonlinearly</I> with variations of NBO/T. <SUP>[5,6]</SUP>Al fraction at 8 GPa increases with decreasing degree of melt polymerization from ∼8% for fully polymerized albite melt (NBO/T = 0) to ∼37% for partially depolymerized melt (NAS150560, at NBO/T = 0.29). Then it gradually decreases to ∼15% for NAS150520 with further increase in NBO/T of 0.67. This observed trend in the densification behavior at a given pressure indicates competing densification mechanisms involving steric hindrance vs changes of NBO fraction in the silicate melts. The NMR results also suggest that both NBO and BO, particularly <SUP>[4]</SUP>Si–O–<SUP>[4]</SUP>Si, interact with Na<SUP>+</SUP>, and thus the Na<SUP>+</SUP> distribution is likely to be homogeneous around both NBO and BO at high pressure without spatial segregation of silica-rich and alkali-rich domains for the glass compositions studied here. The presence of the <SUP>[4]</SUP>Al–O–<SUP>[4]</SUP>Al cluster is distinct in the NMR spectrum for NAS150520 glass at both 6 and 8 GPa. A new scheme of pressure-induced structural transitions in silicate melts involving <SUP>[4]</SUP>Al–O–<SUP>[4]</SUP>Al includes the formation of <SUP>[4]</SUP>Al–O–<SUP>[5]</SUP>Al.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2012/jpccck.2012.116.issue-3/jp206765s/production/images/medium/jp-2011-06765s_0008.gif'></P>
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