Browsing by Author "Mohammed, Yahaya"
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Item Open Access Influence of humidity on the decomposition process of double base rocket propellant(Elsevier, 2023-09-29) Romero Jabalquinto, Alonso; Mai, Nathalie; Mohammed, Yahaya; Gill, Philip P.The decomposition mechanisms of the polymer cellulose nitrate (NC) which is used in double base (DB) rocket propellants, have been extensively studied, and the influence of storage temperature on the lifetime of these energetic formulations is well known. However, the impact of humidity and water on the polymer decomposition process is poorly understood. This paper studies the influence of humidity on the decomposition chemistry of NC and its impact on shelf life. Stabiliser consumption was first analysed by ageing the propellant in sealed vials at different humidity levels for 7 days at an isothermal temperature of 90 °C. Samples were also analysed using heat flow calorimetry (HFC) at isothermal temperatures of 80 °C, 90 °C, and 100 °C. The results indicates that stabiliser depletion increases with increasing water content. Life assessment calculations (AOP 48 ed2) show that increasing the absolute humidity from 6 to 22 g m-3 will decrease the propellant life from 11 to 6 years (25 °C equivalents). The HFC results follow the same trend as the stabiliser depletion where greater absolute humidity increases the heat flow by up to 400 %. Unlike the pass/fail criteria for stabiliser depletion, the HFC samples passed the 10-year (25 °C equivalent) life criteria (STANAG 4582). A multi-temperature (80, 90, 100 °C) kinetic analysis of the initial heat flow showed that the heat flow rate increased with increasing humidity, but the activation energy for all humidity levels remained at 131 (± 3) kJ mol−1.Item Open Access 'Taking the heat' - developing propellants for high-temperature applications(Cranfield University, 2016-12-06 16:15) Mohammed, Yahaya3MT (three minute thesis) presented at the 2016 Defence and Security Doctoral Symposium. Since the early 1800s, nitrocellulose (NC) based propellants have gained popularity due to their low cost, ease of manufacture, and good ballistics. Vehicle airbags, small arms ammunition, aircraft ejection seat, tactical missiles and short to medium range rockets are some of the areas where NC propellants have been applied. Typical homogenous NC-based propellants depending on the energetic constituents are classified as single, double or triple base. Sometimes these propellants are further modified using high explosive additives depending on the performance requirements. The problem with NC, like other nitrate esters, is its poor thermal stability due to the weak RO-NO2 bonds especially, when exposed to high temperature and high humidity conditions as found in sub-Saharan Africa. Similarly, in deep-lying oil wells, NC propellants are problematic due to the high likelihood of ‘cook off'. Several accelerated ageing studies involving the exposure of propellants to high temperatures for the purpose of determining their failure mechanism and stability over time have been conducted. However, few of these studies were focused on the behaviours of NC propellants in tropical, sub-Saharan African climate. This research is aimed at understanding the degradation mechanism of NC propellants (double base) in a typical West African climate. The thesis will be focused on formulating alternative propellant compositions with better performance and thermal resilience. On the completion of the research, it is expected that a new surveillance technique suitable for sub-Saharan African climate will be developed. The first phase of the research will cover the thermal and mechanical analysis of NC propellants in high-temperature environments leading to the design of a bespoke propellant surveillance method for this climate. While the second the phase will cover formulation, characterization and testing of new binder and filler compositions as possible substitutes to NC-based propellants.Item Open Access Yahaya Mohammed PhD(Cranfield University, 2018-09-13 09:13) Gill, Philip; Mohammed, Yahaya; Mai, NathalieThe Effect of Moisture on High Temperature Ageing of Extruded Double Base Propellant Nitrocellulose (NC) based propellants are commonly used in military munitions and cartridge/propellant actuated devices (CAD/PAD). These propellants are generally classified as nitrate esters and are known for their tendency to chemically degrade over time. This chemical instability has been attributed to the relatively weak O-N bond has been shown to be responsible for this instability responsible for this bond on is the primary reason for this chemical instability. There are two possible reaction pathways for nitrate ester decomposition and these are hydrolysis and thermolysis. Thermolysis involves a thermally induced cleavage of the -O-NO2 bonds or with the release of NOx radicals. Hydrolysis on the other hand, involves the reaction of NOx with water to form acids and hydroxyl radicals. While thermolysis is thought to dominate at higher temperatures, hydrolysis has been described as the dominant mechanism at lower temperatures. The free radicals generated due to hydrolysis or thermolysis are highly reactive and will attack the nitrocellulose polymer, producing more radicals and eventually leading to a highly exothermic autocatalytic reaction. Although chemical stabilizers are added to nitrate ester propellants during manufacture to mop-up the NOx radicals, the stabilizers are eventually consumed. In determination of the stability of propellants, several techniques are used, depending on what mechanism is investigated. In most cases, a combination of techniques is required. In this paper, the influence of moisture on high temperature (80 – 100 °C) ageing of an extruded double base (EDB) propellant was examined using heat flow calorimetry (HFC). Propellant samples were preconditioned at relative humidity values of 0, 25, 50, 75, and 95% relative humidity (RH) before ageing in the HFC. The result showed that a direct correlation between humidity levels and heat flow, and it showed that moisture affects the heat flow values and shape of the HFC curve especially at early conversion and at the onset of autocatalysis. This is significant because it gives an indication that moisture influences the decomposition of NC propellants even at higher temperatures.