铁对双气氛法测定粉煤灰中碳含量的影响

Effect of iron on the determination of carbon content in fly ash by dual atmosphere TG method

铁的氧化物作为粉煤灰的常见组分,在双气氛热重法测定粉煤灰碳含量的过程会发生物相变化。为了研究铁氧化物的存在对双气氛法测定粉煤灰碳含量的影响,分别用XRD和TG-MS研究了氧化铁的影响机理及不同形式氧化铁的还原过程,使用TG进一步定量研究铁含量对双气氛热重法碳含量测定的影响。结果表明,铁氧化物会在惰性段、565℃以上与碳发生还原反应,铁氧化物被未燃尽单质碳还原生成单质铁,在氧化段,经过空气气氛阶段后单质铁部分重新转化为铁氧化物,造成碳含量的测定结果偏低;所有形式的氧化铁都与碳发生分步还原反应,Fe_(2)O_(3)更易被碳还原,950℃还原最大失重量为4.5%;粉煤灰中氧化铁含量小于8.53%时,双气氛热重法测定碳含量可以得到较可靠的测量结果,适用于我国大部分的粉煤灰测定。

As a common component of fly ash,the phase change of iron oxide will occur in the process of dual-atmosphere thermogravimetric determination of fly ash carbon content.In order to study the influence of the presence of iron oxides on the determination of the carbon content of fly ash by the dual atmosphere TG method,XRD and TG-MS were applied to study the influence mechanism of iron oxide and the reduction process of different forms of iron oxide.The results show that the presence of iron oxides will undergo a reduction reaction with carbon in the inert atmosphere above 565℃,the iron oxides are reduced by unburned carbon to form elemental iron and in the oxidation atmosphere,the elemental iron is partially oxidized through the air atmosphere,which results in a lower measurement result of carbon content.All forms of iron oxide undergo a stepwise reduction reaction with carbon,and ferric oxide is easier to be reduced by carbon.The maximum reduction weight loss at 950℃is 4.5%.When the iron oxide content in the fly ash is less than 8.53%,the dual-atmosphere thermogravimetric method has a reliable measurement result for the determination of carbon content,which is suitable for the determination of most fly ash in China.