PDF(Pubmed)
Abstract：
There are still many unsolved mysteries in the thermal decomposition process of urea. This paper studied the thermal decomposition process of urea at constant temperatures by the thermal gravimetric-mass spectrometry analysis method. The results show that there are three obvious stages of mass loss during the thermal decomposition process of urea, which is closely related to the temperature. When the temperature was below 160 °C, urea decomposition almost did not occur, and molten urea evaporated slowly. When the temperature was between 180 and 200 °C, the content of biuret, one of the by-products in the thermal decomposition of urea, reached a maximum. When the temperature was higher than 200 °C, the first stage of mass loss was completed quickly, and urea and biuret rapidly broke down. When the temperature was about 240 °C, there were rarely urea and biuret in residual substance; however, the content of cyanuric acid was still rising. When the temperature was higher than 280°C, there was a second stage of mass loss. In the second stage of mass loss, when the temperature was higher than 330 °C, mass decreased rapidly, which was mainly due to the decomposition of cyanuric acid. When the temperature was higher than 380 °C, the third stage of mass loss occurred. However, when the temperature was higher than 400 °C, and after continuous heating was applied for a sufficiently long time, the residual mass was reduced to almost zero eventually.
摘要：
尿素的热分解过程仍有许多未解之谜。本文采用热重-质谱分析方法研究了尿素在恒温下的热分解过程。结果表明,尿素热分解过程中存在明显的质量损失,这与温度密切相关。当温度低于160℃时，尿素分解几乎没有发生，熔化的尿素慢慢蒸发。当温度在180到200℃之间时，缩二脲的含量，尿素热分解的副产物之一,达到了最大值。当温度高于200℃时，质量损失的第一阶段很快完成，尿素和缩二脲迅速分解。当温度约为240℃时，残留物质中很少有尿素和缩二脲；然而，三聚氰酸的含量仍在上升。当温度高于280℃时，有第二阶段的质量损失。在质量损失的第二阶段，当温度高于330°C时，质量迅速下降，这主要是由于三聚氰酸的分解。当温度高于380℃时，发生了质量损失的第三阶段。然而,当温度高于400°C时，在连续加热足够长的时间后，残余质量最终减少到几乎为零。
