Burning Rate Of Mixtures Research Articles

Regulations of the Influence of External Thermal Influences on Speed and Explosive Safe Combustion Modes of Pyrotechnic Nitrate-Metallized Mixtures with Metal Fluoride

A study was made of the regularities of the influence of the main parameters of external thermal effects (elevated heating temperatures and external pressures) on the rate and explosive modes of combustion development of compacted mixtures of magnesium, aluminum and sodium nitrate with fluoride additives metals for different values of technological parameters (excess ratio of the oxidizing agent, nature and content of the additive, dispersion of the components). The effect of technological parameters (ratio and dispersion of components, compaction coefficient, charge diameter, shell material, etc.) on the dependence of the burning rate of mixtures on elevated heating temperatures and external pressures was established; critical ranges of changes in these parameters are determined, the excess of which leads to premature explosive development of combustion of mixtures and fire hazardous destruction of products. On the basis of the research, methods were developed to prevent these destructions of products by regulating technological parameters at the stage of preparation of charge mixtures, which increases the stability of the combustion process of mixtures to external thermal influences. A database has been obtained on the burning rates of compacted mixtures of metal powders (Mg, Al), nitrate-containing oxidizer (NaNO3 ) and additives of inorganic substances (metal fluorides (LiF, NaF, BaF2 , SiF2 , SrF2 , AlF3 )) under conditions elevated heating temperatures and external pressures for various values of technological parameters, which makes it possible to determine the explosive modes of their combustion.

PREVENTION OF PREVIOUS OPERATION OF CHARGES OF PYROTECHNICAL PRODUCTS BASED ON MIXTURES OF MAGNESIUM, ALUMINUM POWDER AND METAL WASTE IN THE CONDITIONS OF EXTERNAL THERMAL ACTIONS

Mathematical models of external heating of charges of pyrotechnic products based on compacted mixtures of aluminum-magnesium alloy powders and nitrate-containing oxidizers (sodium, potassium, strontium, and barium nitrates) were refined by taking into account the temperature dependence of their thermophysical properties (volumetric heat capacity and coefficient of thermal conductivity), which allowed to more accurately determine the critical values of heat flows and durations of their influence.
 New data were obtained to determine the critical ranges of the change in the burning rate of mixtures under conditions of elevated heating temperatures and external pressures for various values of technological parameters (the coefficient of excess oxidizer α; the average particle size of metal fuel powders dм microns and oxidizer dN), exceeding the ranges of which leads to premature ignition mixtures under conditions of external thermal effects and leads to unstable explosive development of their combustion process and fire-hazardous destruction of pyrotechnic products.

Effects of nano-scale additives on the linear burning rate of nitromethane

This paper examines the effects of various nanoparticle additives on the combustion behavior of nitromethane, using a pressure-based method recently demonstrated by the authors to measure the linear burning rates of liquid monopropellants and heterogeneous mixtures with high precision. The linear burning rates of these mixtures were measured in a constant-volume system at chamber pressures ranging from 3 to 14 MPa, all without direct observation of the burning front. Nano-scale aluminum was used to increase the overall energy density of the mixture, fumed silica powder was used to increase the mixture thickness and encourage aluminum suspension, and nano-scale titania was also included based on its previous use as a burning rate modifier in solid propellants. The silica loading was varied from 1% to 3% by weight, aluminum was varied from 5% to 13.5% by weight, and titania was added at 1% by weight. The use of fumed silica yielded increased burning rates compared to those of neat nitromethane, and the pressure exponent of the burning rate curve shifted from lower to higher than the nitromethane baseline as more silica was added. This increased pressure sensitivity for mixtures containing 3% silica by weight was previously unobserved in similar studies by other groups and may be an effect of the higher specific surface area of the currently used silica. The subsequent addition of aluminum led to even faster burning rates and higher pressure exponents for all but one mixture. The addition of titania also led to elevated burning rates, with dramatically increased pressure sensitivity and rate inconsistency for chamber pressures above approximately 8 MPa but a decreased pressure sensitivity for the same mixture below 8 MPa. These changes in combustion behavior that accompanied titania were diminished by the presence of aluminum and completely negated in mixtures also containing fumed silica.

Dependence of the burning rate of transition-metal-boron systems on the component ratio

The dependence of the propagation velocity of the chemical reaction wave on the composition of the starting mixture is an important characteristic of combustion processes and is described in this article. In analyzing these dependences for group IV metal (Ti, Zr, Hf)-boron systems, the authors concluded that metastable zirconium monoboride, which was absent from the end products, may be formed in the combustion wave. Other conclusions are described. The results of comparing the calculated burning rates of mixtures of group IV metals and boron with the available experimental data are presented. A discussion of the reasons for the stage type of temperature profile in the combustion of transition metals and boron, detected in certain mixture compositions is discussed.

Effect of iron oxide on the combustion of condensed mixtures

We have invest igated the effect of-l% FezO 3 on the burning rate of model mixtures of ammonium perchlorate (AP) + polystyrene (PS) and ammonium perchlorate + po lymethyl methacry la te (PMM) when var i ous physical parameters are varied (pressure, component ra t io a, in i t im temperature T 0, presence of inert diluents--NH4C1 and AlzOa). The effect ive par t ic le sizes were approximate ly 9 p for AP ( technical), 5 g for PS (technical) , 3 g for PMM (technical) , 1 .8 g for Fe203 (ana ly t ica l grade), 12 # for NH4C1 (ana ly t ica l grade), and 8 p for AlzOs (ana ly t ica l grade). The components were mixed on t racing cIoth with a rubber stopper for one hour. From the finished mixture we pressed charges 8 mm in d iameter and 8 -10 mm ta l l with a re la t ive density 6 = P/Pmax = 0 .950.99. The exper iments were conducted in a constant-pressure bomb in nitrogen. The burning t i m e w was measured using a quartz pressure transducer. The average burning rate u = h / r was ca lcula ted . We charac ter ize the effect ol~ the Fe2Os by means of the quant i ty z = u/n0, where u and u0 are the burning rates of the mixture with and without the addit ion of FezOa.

Burning of mixtures of ammonium perchlorate and various organic substances

1. The burning rate of mixtures of ammonium perchlorate and fuels of various chemical structure has been investigated. 2. It has been established that the burning rate of the mixtures depends on the calorific value of fuels of similar structure, or, if the calorific value is the same, on the strength of the chemical bonds and the structure of the molecules.