This review explores strategies for stabilizing the polymorphic phases of ammonium nitrate (AN), a promising chlorine-free oxidizer for green propellant systems. Despite its eco-friendly decomposition products, AN’s widespread use is limited by phase transitions near ambient temperature, which cause volumetric expansion, reduced density, and mechanical instability. To address these issues, researchers have investigated various additives such as potassium salts, metal oxides, organic compounds, polymers, and metal-organic frameworks (MOFs and ZIFs). These materials inhibit AN’s undesirable transitions and improve thermal performance. Recent innovations include hybrid systems and nanostructured additives that combine stability with enhanced energetic output.
Efficient cooling of proton exchange membrane fuel cells (PEMFCs) is vital for their safe operation and also attaining longer life and higher power. The narrow range of operating temperature and high manufacturing costs, have introduced major challenges in fuel cell designs. Recently, one of the main goals of the researchers has been laid upon solving these problems in order to commercialize the fuel cell. The manufacturing and machining of graphite plates is about 60% of the total stack cost. Due to the high flexibility, metal plates can be extruded easily by stamping therefore their manufacturing is more economical compared to graphite plates. By stamping a metal plate into the desired form, the reacting and cooling flow fields are shaped simultaneously and hence reduce the time of manufacturing compared to graphite plates. In this study, an innovative numerical design of fuel cell's cooling flow field with metallic bipolar plates is presented. In this design, it has been attempted to let the fluid pass through the cooling flow field using the spacer plate. The main design criterion is the uniform distribution of temperature. To evaluate the uniformity of temperature, the temperature contour and index of uniform temperature (IUT) have been taken into consideration. Moreover, at each step of the design procedure, the generated hot spots have been identified by the temperature contour and tried to be avoided for the next step. In the 1st design, the maximum temperature and IUT are 378 K and 2.09, respectively, which have been reduced to 351.20 K and 1.45, by step by step improvement of the 1st design. After achieving the desired design, the performance of the cooling design is investigated in various Reynolds numbers and finally, the Reynolds number 2500 is proposed as the suitable Reynolds number for the operation of this cooling design. (c) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
In this paper, the impact of the inlet flow rate, operating pressure, stack configuration and inlet manifold width on the oxygen distribution among the channels of a fuel cell stack is studied. The standard deviation is used to calculate the severity of oxygen maldistribution. The oxygen flow in the U configuration is more uniformly distributed than in the Z configuration. The most even oxygen distribution is obtained for the UZ configuration. The standard deviation for the U, Z and UZ configurations at an inlet flow rate of 80 SLPM is calculated as 0.023, 0.038 and 0.009. The oxygen distribution for the U configuration is independent of the inlet flow rate. The standard deviation for the Z and UZ configurations reduces to 0.030 and 0.007 at an inlet flow rate of 40 SLPM. In addition, the operating pressure does not affect the oxygen distribution in three configurations. The standard deviation for the Z and UZ configurations increases from 0.38 and 0.009 to 0.4 and 0.012 as the inlet manifold width decreased from 15 mm to 12.2 mm. In contrast, the flow distribution in the U configuration stack improves and the standard deviation decreases from 0.023 to 0.019.
Imatinib (IMA), a commonly used tyrosine kinase inhibitor, has become an increasing concern as a pharmaceutical contaminant because of its persistence in aquatic environments and possible mutagenic effects. This study introduces a rationally engineered MgV2O4@Cu2V2O7 (MVO@CVO) Z-scheme heterostructure, synthesized through an easy one-step hydrothermal process, for visible-light-driven photocatalytic degradation of IMA. The optimized MVO@CVO composite degraded over 90 % of IMA within 35 min under visible light, with an apparent rate constant roughly 8 times higher than pristine MVO and 3 times higher than CVO. UV-Vis DRS and Tauc analysis showed a bandgap reduction from 3.25 eV in MVO and 2.25 eV in CVO to 1.85 eV in the composite. Radical quenching experiments identified superoxide anions and surface-bound hydroxyl radicals as the primary reactive species. DFT calculations confirmed a bandgap around 2.0 eV, with a minimal interfacial lattice mismatch below 3.5 %, and strong electronic coupling at the interface, enabled by Cu-O-V linkages that facilitate charge transfer. The reconstructed Z-scheme mechanism enhances spatial charge separation, enabling CB electrons in MVO (-0.005 eV vs NHE) to reduce O-2 to center dot O-2(-) , and VB holes in CVO (+2.90 eV) to oxidize H2O/OH- to center dot OHads. This synergistic charge routing overcomes thermodynamic constraints usually seen in type-II systems. The composite maintained more than 90 % of its activity after five cycles, showing excellent reusability. These results position MVO@CVO as a promising, scalable, and durable photocatalyst for removing pharmaceutical pollutants in water purification.
Molecular explosives such as RDX (1,3,5-Trinitroperhydro-1,3,5-triazine) and HMX (1,3,5,7-Tetranitro-1,3,5,7-tetrazocane) have seen increasingly widespread use in various applications for decades since their discovery and synthesis. These explosives are used either in pure form or in various mixtures, including composite explosives, polymer-bonded explosives (PBXs), and cocrystals. Therefore, studying the thermal behavior and responses to temperature changes for explosives RDX and HMX is remains of significant interest to producers, consumers, and researchers. Common methods of thermal analysis, such as thermogravimetry (TG), differential thermal analysis (DTA), and differential scanning calorimetry (DSC) in both isothermal and non-isothermal procedures are used to investigate thermal behavior. In this review, the results of thermal behavior studies of RDX and HMX in their pure form, and in composites, PBXs, cocrystals, also, in the presence of additives have been presented and analyzed. Kinetic parameters and the mechanism of thermal decomposition reactions are evaluated and discussed.
