【作者】 魏德生；

【导师】 魏雨；

【作者基本信息】 河北师范大学 ， 物理化学， 2009， 硕士

【摘要】 铁氧化物用途非常广泛,也是种重要的化工原料。有关铁氧化物的研究中,以Ferrihydrite转化过程的研究较为引人注目。本研究室一直从事铁氧化物的研究,前期的研究表明了微量Fe(Ⅱ)对Ferrihydrite的相转化具有明显的催化作用。本实验室前期有关Ferrihydrite相转化行为的研究,都是在常规加热的方式下进行的,前期研究表明温度及升温速率对Ferrihydrite的催化相转化行为有很大影响。探讨不同加热方式对Ferrihydrite催化相转化过程的影响,全面了解在各种条件和环境中Ferrihydrite的催化相转化规律,对控制反应过程、为工业生产纳米铁红提供指导,是我们要达到的目标之一。本文旨在近中性条件下,采用微波加热的方式,研究Fe(Ⅱ)离子存在时Ferrihydrite的相转化规律,实现由Ferrihydrite快速、低能耗地制备出超细、均一、各种形貌的α-Fe2O3粒子。,因此该研究结果一方面对于全面了解Ferrihydrite的催化相转化机理具有重要的理论意义;另一方面,该研究结果对指导各种形貌α-Fe2O3的控制合成具有实际指导价值。本论文主要研究内容及结果如下:(1)系统研究了以氢氧化钠为沉淀剂、氯化铁为原料制备的Ferrihydrite在微波加热下的催化相转化过程。考察了初始pH、Ferrihydrite的微结构、Fe(Ⅱ)离子和Fe(Ⅲ)离子浓度等因素对相转化过程的影响。结果表明:在微波加热下Ferrihydrite的相转化产物为α-Fe2O3。(2)通过对Ferrihydrite在两种加热方式下催化相转化行为的比较发现:微波加热与常规加热下Ferrihydrite催化相转化的行为大致相同,产物的物相及形貌相同,但粒径大小及相转化时间有差异。微波加热制备出的α-Fe2O3粒子,粒径更小、相转化时间更短、能耗低。(3)分析Ferrihydrite在两种加热方式下相转化行为的异同得出: Ferrihydrite在微波加热下比在常规加热下,经历固相转化机制的比重增大,形成α-Fe2O3粒子过程中α-Fe2O3晶核的生长过程为速控过程。(4)在研究中发现Fe(Ⅱ)加入量(β= nFe(Ⅱ)/nFe(Ⅲ))对制得的α-Fe2O3微粒的形貌有影响。当pH=7时随β值的变化(由0.02-0.07),α-Fe2O3粒子的形貌由球形变为纺锤形。pH=9时随β值的变化(由0.02-0.07),α-Fe2O3粒子的形貌由球形变为准立方体形。Ferrihydrite在pH近中性环境下,形成非球形的α-Fe2O3粒子的机理是由于加入的Fe(Ⅱ)离子在α-Fe2O3晶核上发生配位吸附,导致了α-Fe2O3晶的非等轴生长,从而形成了非球形的(如纺锤体、准立方体等)α-Fe2O3粒子。更多还原

【Abstract】 The use of iron oxides is very broad and iron oxides are also important industrial chemicals. Much attention has been paid to the transformation of ferrihydrite in the study on iron oxides. Our group has been engaged in the study on iron oxides, and we found that the presence of trace Fe(II) has obvious catalytic role in the phase transformation of ferrihydrite. Our pre-research on the phase transformatiom behaviour of ferrihydrite was carried out under the conditions of the conventional heating manner. Preliminary study discovered that the temperature and heating rate have a great effect on the phase transformation behaviour of ferrihydrite.One of our goals is to investigate the effects of the different heating methods on the catalytic phase transformation of ferrihydrite and comprehensive understand the laws of the transformation under different conditions and environment. So that we can control the transformation from ferrihydrite to the goal product and provide guidance for the industrial production of nano-iron oxide red.The present work aims at understanding the nature of the transformation of ferrihydrite induced by microwave in the presence of trace Fe(II). We try to reach the goal to fastly and low power prepare ultra-fine, homogeneous, various morphologies ofα-Fe2O3 particles from ferrihydrite. Not only is this study of academic importance but also of practical value. The main research aspects are summarized as follows.(1) The phase transformation of ferrihydrite, prepared by using ferric chloride and sodium hydroxide as raw materials, was studied in the presence of trace Fe(II) in detail. The effect of various factors such as the initial pH, the conditions of ferrihydrite formation as well as the concentrations of Fe(II) and Fe(III) ions was discussed. The results show that the poducts obtained are hematite.(2)Comparing ferrihydrite phase transformation by microwave heating with by conventional heating, it was found that their mechanisms are same. Theα-Fe2O3 particles prepared in microwave heating are smaller size, shorter time to phase transformation and lower energy consumption than in conventional heating.(3)Analysising the difference of phase transformation behaviors by the two heating methods, it shows that the proportion of the solid state transformation from ferrihydrite to hematite is more enlarged in microwave heating than in conventional heating. The growth process ofα-Fe2O3 nuclei is the rate-determining process in the formation processes ofα-Fe2O3 particles.(4) The results showed that Fe (II) addition amount (β= nFe(Ⅱ)/nFe(Ⅲ)) influences the morphology ofα-Fe2O3 particles. When pH=7 along withβvalue variety (by 0.02-0.07), the morphology ofα-Fe2O3 particle varies from sphere to spindle. When pH=9 along withβvalue variety(by 0.02-0.07), the morphology ofα-Fe2O3 particles varies from sphere to quasi-cube. The formation of non-spherical-shapedα-Fe2O3 particles from ferrihydrite is due to Fe2+ cation ligand adsorption on the surface ofα-Fe2O3 nuclei, which results inα-Fe2O3 crystalline non-equiaxed growth, thus the formation of a non-spherical (eg, spindle, quasi-cube, etc.)α-Fe2O3 particles.更多还原