Science and Technology of Energetic Materials

Vol.63, No.6 (2002)

Research paper

Reactivity and burning rate of manganese-barium chromate-lead chromate delay composition
Toshihiro Okitsu, Takeshi Yabuki, and Michinori Takizuka


As for a Mn - BaCrO4 - PbCrO4 system delay, the combustion characteristics and the lifetime vary depending on the surface condition and particle size of Mn used.
   The Mn delay as well as tungsten delay is important for the defense industry from flexibility to control the burning rate widely. The Mn delay does not generate gaseous products during burnlng fundamentally, but tungsten delay does. Therefore, the Mn delay is useful for the delay in closed burnlng system or in a sealed container.
   Generally, the metallic Mn is oxidized in air gradually, and the oxidized surface has Mn oxides such as MnO and Mn2O3. The oxidized surface remarkably reduces the reactivity of Mn remarkably. So a heating deterioration and an accelerated againg test for Mn were carried out to examine the progress of oxidation on the surface of Mn powders. We have confirmed that Mn increased in weight in this deterioration test.
   Finally, we knew that the Mn used in the delay composition has to satisfy the following conditions from this new finding :
(1) The oxidizer of the Mn - BaCrO2 - PbCrO4 delay composition is PbCrO4, while BaCrO4 acts as a burning rate modifier.
(2)Burning rate becomes slower as the particle size of Mn is increased. On the other hand, burning rate increased as the one decreased. However, the particle is too fine, the combustion reaction is interrupted, since the thickness of preheating area becomes extremely narrow.
(3)Mn powders after grinding should be treated to prevent the surface from oxidation.

Moreover, we had found out the following facts.
(1)The delay composition does not become to react at last, as the surface of Mn in the composition is gradually oxidized with aging.
(2)Grinding of Mn must be carried out in an inert atmosphere.
(3)The delay composition must be designed to increase the heat of combustion especially for the delay composition with low burning rates.
(4)The coefficient of the variation which is the percentage of value divided standard deviation by average burning rate must have the value less than 5 % for the delay composition for low burning rate types.

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