Research On Thermal Stability Of Typical Guanidine Compounds

Guanidine compounds refer to materials with guanidine functionality group and their derivatives.They,well known for their poor thermal stability,are widely applied in numerous fields.Four representative materials,Aminoguanidine nitrate(AGN),Guanidine nitrate(GN),1-Methyl-3-nitroguanidine(MNQ)and nitroguanidine(NQ),are selected as the objects for research on the thermal stability of guanidine compounds.Firstly,Rapid Screening Calorimeter(RSC)was used to preliminarily screen the thermal stability of the four Guanidine compounds.The results showed that there are strong thermal decomposition reactions during the scan temperature range with a large amount of gas generated.The order of the onset decomposition temperature of the four selected guanidine compounds is as below:To(MNQ)<To(NQ)<To(AGN)<To(GN).while the order of gas output is as:V(MNQ)<V(GN)<V(AGN)<V(NQ).Secondly,Differential Scanning Calorimeter(DSC)was used to study their thermal decomposition behavior under dynamic mode.The results indicated a "coupling phenomenon" in NQ’s heatflow peaks,referring to the part overlap of the endothermal melting peak and exothermal decomposition peak.In order to separate the overlapped peaks,NQ solution in water was investigated as well.And for GN and AGN,the DSC results showed the combination of multiple decomposition peaks,indicating a complicated decomposition mechanism.As expected,the order of the decomposition temperature obtained by DSC is the same as that by RSC.which indicates MNQ possesses the poorest stability.Then,isothermal DSC experiments for these samples were conducted.The heatflow curves of NQ,NQ solution and MNQ showed a "bell shaped" peak,demonstrating the self-catalytic properties,while the isothermal decomposition of GN can be clearly taken as a combination of 3 exothermal peaks.The aqueous solution of NQ was proved to be described by a sing-step decomposition mechanism,while waves of activation energy curves confirmed that the decomposition of the four guanidine compounds themselves were much more complicated.After that,the model function equation of NQ solution were obtained via model fitting method.The decomposition peaks of GN under both dynamic and isothermal mode were all of "coupling phenomenon of multiple peaks",thus AKTS was used to decouple the isothermal curve,and three separated peaks(one decelerating model peak and two sigmoidal model peaks)were obtained.The N-th model was chosen as the mechanism of the first decomposition step and the autocatalytic model was chosen to describe the second and third reaction.Based on these,kinetic parameters of each step were calculated by nonlinear fitting.Finally,accelerating rate calorimeter(ARC)was used to investigate their thermal decomposition character under adiabatic mode.The experimental results showed that,NQ,GN and MNQ all were dominated by one strong exothermal stage whereas three weak exothermal stages were detected for AGN.The gas output calculated based on ARC data demonstrated that a lot of non-condensable gas was produced during the decomposition for all the four chemicals,and the order of the gas output is the same as RSC results.The values of TMKad and TD24 were aslo obtained,The order of TD24 of the four compounds is as below:TD24(MNQ)<TD24(NQ)<TD24(AGN)<TD24(GN),which is the same as that obtain by To.demonstrated that MNQ was of the poorest stability compared with the others.