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[求助] 三氧化二铁α、β、γ、σ这4种形式，每一种都有什么特性，什么性状

三氧化二铁α、β、γ、σ这4种形式，都哪个有磁性，哪个没有磁性，他们之间如何转变等信息，越详细越好，

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1楼 2013-07-15 08:49:07

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大毛毛虫: 金币+5, ★★★很有帮助, 非常感谢要是在详细点就好了 2013-07-17 09:22:59

这是我以前查到的资料，可以参考一下
Fe2O3的几种相态：
ferric oxide has Different forms: Alpha phase,Beta phase,Gamma phase,Epsilon phase, and amorphous phase.

Alpha phaseα-Fe2O3 has the rhombohedral, corundum (α-Al2O3) structure and is the most common form. It occurs naturally as the mineral hematite which is mined as the main ore of iron. It is antiferromagnetic（反铁磁性的） below ~260 K (Morin transition temperature), and weak ferromagnetic between 260 K and 950 K (Neel temperature).[1] It is easy to prepare using both thermal decomposition and precipitation in the liquid phase. Its magnetic properties are dependent on many factors, e.g. pressure, particle size, and magnetic field intensity.

Beta phaseCubic face centered, metastable, at temperatures above 500 °C converts to alpha phase. It can be prepared by reduction of hematite by carbon, pyrolysis of iron(III) chloride solution, or thermal decomposition of iron(III) sulfate.

Gamma phaseCubic, metastable, converts to the alpha phase at high temperatures. Occurs naturally as the mineral maghemite. Ferrimagnetic. Ultrafine particles smaller than 10 nanometers are superparamagnetic. Can be prepared by thermal dehydratation of gamma iron(III) oxide-hydroxide, careful oxidation of iron(II,III) oxide. The ultrafine particles can be prepared by thermal decomposition of iron(III) oxalate.

Epsilon phaseRhombic, shows properties intermediate between alpha and gamma. So far has not been prepared in pure form; it is always mixed with the alpha phase or gamma phases. Material with a high proportion of epsilon phase can be prepared by thermal transformation of the gamma phase. The epsilon phase is metastable, transforming to the alpha phase at between 500 and 750 °C. Can also be prepared by oxidation of iron in an electric arc or by sol-gel precipitation from iron(III) nitrate.