Reasons for the anomalous dependence of the specific impulse of rocket propellants on the content of borohydride

We investigate the cause of the appearance of two maxima in the curve of the specific impulse of a high-energy composition with increasing content of the borohydride component in it. It is shown that such anomalies can occur for some values of the enthalpy of formation of the oxidizer, for a certain hydrogen content in the boron-containing fuel, etc. As the content of borohydride in the composition is increased, a time comes when oxygen is not sufficient for the formation of B$_2$O$_3$ and excess boron begins to be oxidized by nitrogen to condensed boron nitride. Under certain conditions, this can lead to a second local maximum of the specific impulse.