EXPERIMENTAL STUDY OF BORON CARBIDE FORMATION IN COMBUSTION OF BORON-CONTAINING SOLID PROPELLANTS

Using model aluminum dodecaboride (AlB)/binder mixtures imitating the matrix of boron-containing solid propellants, the process of formation of boron carbide in combustion of such propellants has been experimentally studied. To characterize the samples under study, thermogravimetric analysis and differential thermal analysis were used, which made it possible to determine the initial stage of decomposition of samples with different contents of AlB. Experiments on the rapid thermal decomposition of samples were carried out on the original URAN-1 installation, which makes it possible to create heat flows to the sample surface in the range of 70 to 300 W/cm. It has been shown that the condensed residue formed during the pyrolysis of the binder consists mainly of carbon, which, upon interaction with boron, forms boron carbide. The dependence of the mass of the carbonaceous residue on the boron content in the propellant matrix (mixture of binder and powdered boron-containing fuel) has been determined. The mass rate of matrix pyrolysis has been studied as a function of the incident energy flux density and the content of powdered boron-containing fuel in the matrix. It is shown that during high-speed heating of the matrix, the amount of boron carbide formed strongly depends on the rate of energy supply. The dependence of the relative mass of the resulting boron carbide on the temperature in the pyrolysis zone was determined, which can be conditionally divided into four areas: (1) up to a temperature of 1400°C, boron carbide is practically not formed; (2) in the temperature range from 1400°C to about 1700°C, the amount of boron carbide formed increases sharply with increasing temperature from zero to about 10–15%; (3) in the temperature range from 1700°C to about 2500°C, the amount of boron carbide formed is slightly dependent on temperature; (4) for temperatures above 2500°C, the amount of boron carbide formed in the condensed products of the studied samples sharply increases with temperature, and at T ≈ 2600°C reaches 50% of the mass of the entire sample residue. A theoretical analysis of the investigated process has been carried out.