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Combustion Performance of Model Propellant with Boron and Boron-Containing Compounds
Published in WeiQiang Pang, Luigi T. De Luca, XueZhong Fan, Oleg G. Glotov, FengQi Zhao, Boron-Based Fuel-Rich Propellant, 2019
WeiQiang Pang, Luigi T. De Luca, XueZhong Fan, Oleg G. Glotov, FengQi Zhao
The mechanism of boron particles agglomeration is largely similar to the mechanism of aluminum particles agglomeration in the combustion of composite solid propellants,147–155 but it has its own features.51 As in the case of aluminum, the boron particle agglomeration is connected with the presence of contacting particles in the condensed phase of the propellant. While passing a heat wave in the propellant, a conversion of its components (binder, oxidizer particles etc.) and simultaneous heating of the boron particles occur. In contrast with aluminum particles whose melting point is less than the temperature of the propellant burning surface, boron has a melting point above the temperature of the propellant burning surface, and even higher than the temperature of combustion products in the gas generator, and therefore boron is always present at solid state on the propellant burning surface. The boron particles, located in the propellant, are covered with a thin film of boron oxide B2O3. The boron oxide melting point (Tm B2O3 = 720 K) is commensurable with a temperature of the propellant burning surface (Ts = 700–1,000 K) and considerably less than the temperature of combustion products of the propellant in a gas generator (Tb = 1,500–2,000 K). This means that boron particles on the propellant burning surface have the liquid oxide film and contacting particles are bound by the liquid bridge of B2O3. If the contacting boron particles did not have the oxide film or it was insufficiently thick to create the liquid bridge between the particles after its melting, the sintering of the particles can occur due to their rapid heating in the propellant burning wave. Furthermore, in the vicinity of the contact of particles, various chemical compounds can be formed due to the chemical reactions of the species of the products of decomposition of solid propellant, both between themselves and with boron. In particular, the sufficiently strong boron carbide B4C and boron nitride BN can be formed. It was shown25,26,32 that for HTPB-based solid propellants, a significant increase in B4C content with increasing pressure is observed, at that at low pressures, there is a marked deviation from thermodynamic equilibrium, while at high pressures, the B4C concentration approaches equilibrium. The GAP-based propellants demonstrate the opposite behavior: for these propellants, the content of boron carbide in the combustion products decreases with increasing pressure. Thus, the boron carbide can be a predominant boron compound on the burning surface of the propellant and directly above the surface. The strong chemical compounds that are formed in the vicinity of the contact points of boron particles can create the mechanical (adhesive) bond between the particles.
Energetic aspects of elemental boron: a mini-review
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2022
Okan Icten, Birgul Zumreoglu-Karan
In contrast to the data on combustion, there is a lack of data regarding boron hydrolysis. The research started in the 1990s (Li and Williams 1991), and the possibility of hydrogen production by boron combustion in a hot steam atmosphere was first demonstrated by Rosenband, Gany, and Timnat (1998). The superheated steam generated in an autoclave at an overpressure of 0.5 bar was fed into a reactor when the temperature of the amorphous boron powder sample reached about 450°C, the melting point of boron oxide. The hydrogen yield obtained in this experiment accounts for about 60% of the theoretical amount. Vishnevetsky et al. (2008) considered the hydrolysis of boron at moderate reactor temperatures (below 600°C) in the absence of oxygen. It was confirmed that the reaction occurs only at temperatures above the melting point of boron oxide (600°C). The hydrogen yield (47–75% of the theoretical yield) depends on the steam to boron ratio and the temperature.
Effect of Purity, Surface Modification and Iron Coating on Ignition and Combustion of Boron in Air
Published in Combustion Science and Technology, 2021
Kerri-Lee Chintersingh, Mirko Schoenitz, Edward L. Dreizin
Most strategies aimed to improve boron as a fuel generally require large (typically >10 wt. %) quantities of additives to accelerate reactions. This results in a reduction in the energy density of the fuel. Most of the past research effort has focused on ignition, or reactions occurring at low temperatures and leading to full-fledged combustion. Studies have considered boron surface treatment using water (Conkling and Mocella 2010) and hydrocarbons such as methanol (Ahn et al. 2011; Kim et al. 2007; Williams and Hawn 1991) and acetonitrile (Chintersingh et al. 2016; Liu et al. 2017), that can dissolve/remove the inhibiting hydrated and un-hydrated boron oxide. Recent efforts (Chintersingh et al. 2016) and (Liu et al. 2017) showed that acetonitrile wash and subsequent surface treatment with toluene produces boron powders with little hydrated oxide, which were stable in air and exhibited reduced ignition delays. However, washing led to no discernible effect on combustion of such powders in products of a hydrocarbon flame. Since water, CO and CO2 were the primary oxidizers in that case, it is of interest to investigate whether this surface treatment plays a role in boron combustion in air, when a stronger oxidizer, oxygen is present.
Combustion Characteristics of Boron-HTPB-Based Solid Fuels for Hybrid Gas Generator in Ducted Rocket Applications
Published in Combustion Science and Technology, 2019
Syed Alay Hashim, Srinibas Karmakar, Arnab Roy
Figure 2c shows a TGA plot between temperature and weight gain of the sample. As the temperature starts to increase, TG curve drops gradually below 100% due to evaporation of moisture present in the boron particles. The weight percentage starts to increase at a temperature around 400 °C due to the reaction of oxygen with the sample. The active content of boron in the sample has been evaluated as 76.5% by calculating the percentage difference of weight gain. This investigation shows that particles are significantly covered by boron oxide (B2O3).