a compendium of tech stuff

Jan 27, 2013

On 3:35 PM by Lalith Varun   No comments
     A Catalyst is a substance that is used in small amounts relative to the reactants that modifies the rate of reaction without it being consumed in the reaction and this process is called Catalysis. Catalysts that accelerate the reaction are called positive catalysts while the ones that slow down are called inhibitors. Catalysts react with one or more reactants to form intermediate compounds, which on further reaction gives the final products and regenerating the catalyst during this process.

The action of catalysts have been proposed by G. S. Pearson in 4 models.
1) by accelerating fuel decomposition
2) by accelerating HCLO4 decomposition
3) by accelerating the solid-fuel / HCLO4 reaction on fuel surface
4) by accelerating gaseous fuel reactions in gas phase
In addition catalysts may also enhance AP decomposition.

Catalysts for HCLO4 decomposition can be divided into 3 groups,
1) Highly effective oxides (Cr2O3, NiO, Al2O3, Fe2O3 and CuO)
2) Less reactive oxides (TiO2 and Cu2O)
3) Inactive oxides (CdO, MgO and CaO)
Copper Chromite accelerates the decomposition of HCLO4 but doesn't affect the binder degradation. The relative effectiveness of various catalysts in the ignition process depends on the surface area, particle size and quantity of catalyst used.

     Ignition of propellants is an enormously complex process and a single rate determining step cannot explain it. One or more types of mechanism models such as gas-phase, condensed-phase and catalytic reactions contribute to the ignition process. A single reaction will depend on many factors such as pressure, local temperature, chemical and physical structure, local concentration, etc.