Metastable phases and ‘metastable’ phase diagrams
Metastable phases and ‘metastable’ phase diagrams
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DOI：
10.1088/0953-8984/18/42/010
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发表时间：
2006-04
期刊：
影响因子：
--
通讯作者：
V. Brazhkin
中科院分区：
文献类型：
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作者：
V. Brazhkin
这项工作讨论了物质的亚稳态相变的定性性质。凝聚介质物理学的研究对象主要是具有亚稳相的物质的平衡态，而在化学中，研究的绝大多数有机物质都是亚稳的。事实证明，在常压下，许多基于轻元素的简单分子化合物（包括：大多数碳氢化合物;氮氧化物，水合物和碳化物;一氧化碳（CO）;醇类，甘油）也是亚稳态物质，即它们不匹配给定原子化学组成的吉布斯自由能最小值。在中等温度和压力下，特定亚稳相的相变在整个实验可获得的时间段内是可逆的，并遵守平衡热力学定律。在足够高的压力（1-10 GPa）下，大多数分子相不可逆地转化为能量效率更高的聚合相。这些转变与转变前后的吉布斯自由能相等不一致，即它们不是“经典”意义上的相变。在常压下得到的聚合物相可以在高于初始亚稳分子相的熔融温度下存在。这种聚合物的突出例子是聚乙烯和CO的聚合改性。许多能量中间聚合物相显然可以在常压下通过“经典”化学技术合成。在较高的压力（10-100 GPa）下，聚合改性转化为简单稳定相的混合物。
The work discusses the qualitative nature of phase transitions for metastable states of substances. The objects of the physics of condensed media are primarily the equilibrium states of substances with metastable phases viewed as an exception, while in chemistry the overwhelming majority of organic substances under investigation are metastable. It turns out that at normal pressure many simple molecular compounds based on light elements (these include: most hydrocarbons; nitrogen oxides, hydrates, and carbides; carbon oxide (CO); alcohols, glycerin) are metastable substances too, i.e. they do not match the Gibbs free energy minimum for a given atomic chemical composition. At moderate temperatures and pressures, the phase transitions for particular metastable phases are reversible throughout the entire experimentally accessible time period with the equilibrium thermodynamics laws obeyed. At sufficiently high pressures (1–10 GPa), most molecular phases irreversibly transform to more energy efficient polymerized phases. These transformations are not consistent with the equality of the Gibbs free energies between the phases before and after transition, i.e. they are not phase transitions in the ‘classical’ meaning. The resulting polymeric phases at normal pressure can exist at temperatures above the melting one for an initial metastable molecular phase. Striking examples of such polymers are polyethylene and a polymerized modification of CO. Many energy-intermediate polymeric phases can apparently be synthesized by the ‘classical’ chemistry techniques at normal pressure. At higher pressures (10–100 GPa) polymerized modifications transform to a mixture of simple stable phases.