纳米铁的低温热容和热力学性质

Low-temperature Heat Capacity and Thermodynamic Functions of Nano Fe

用扫描电子显微镜(SEM)测定了纳米铁试样的粒径,SEM结果表明Fe试样平均粒径d为25 nm．在84-350 K温区,用精密低温绝热量热计测定了该纳米铁试样的等压摩尔热容,拟合出其等压摩尔热容与热力学温度的函数关系式:Cp=36．831+14．772x-5．4968x2-0．7099x3-1．3188x4,其中x=(T-234)／156．根据热容与热力学函数关系,计算了以298．15 K为基准的纳米Fe(d=25 nm)热力学函数,并与文献报导的粗晶Fe及粒径87 nm Fe的热容进行了比较,从能量角度分析了不同粒径Fe热容曲线差别产生的原因．

The size of nano Fe powders was determined to be 25 nm in diameter by SEM. The isobaric molar heat capacity Cp of the nano Fe was measured with the high precision adiabatic low-temperature calorimeter in the temperature range from 84 K to 350 K. The relationship of Cp with temperature T was established as： Cp=36.831 ＋ 14.772x-5.4968x^2-0.7099x^3- 1.3188x^4, where x=（T-234）/156. The thermodynamic functions of the nano Fe, relative to the standard temperature of 298.15 K, were derived based on the heat capacity data through thermodynamic relationship. The measured Ca values were compared with those of coarse crystal powders and 87 nm Fe powders cited from literature and the difference between the Cp curves was analyzed