Study of the Structural Changes and Internal Activator Transport Behavior after Activation of Aluminum-Based Flameless Ration Heaters: Experimental and Molecular Dynamics Simulations

K Si and CX Liu and DQ Zhang and JJ Fang and H Yin and CJ Zhang, ACS OMEGA (2023).

DOI: 10.1021/acsomega.3c02057

Aluminum-based flameless ration heaters (AFRHs) are heatingelementsin food packaging. Water is used to activate AFRHs. The material propertiesof each region of AFRHs were determined by X-ray diffraction, scanningelectron microscopy, and hydrogen and heat generation. The resultsshow that the internal cross-section shows stratification with hydrogenand heat production capacities of 105.2 & PLUSMN; 9.7 mL/g and 1435.0 & PLUSMN; 30.3 J/g for the outer layer, 27.1 & PLUSMN; 4.4 mL/g and 80.4 & PLUSMN; 3.1 J/g for the inner layer, and 1.1 & PLUSMN; 0.01 mL/g and 1.2 & PLUSMN; 0.05 J/g for the middle layer, respectively. According to thecorrespondence between aluminum and hydrogen in the aluminum-waterreaction relationship, the reaction efficiency of the outer layerand the inner layer is as low as 64 and 80%, which is an indicationof low reaction efficiency. To analyze the reasons for low reactionefficiency, a pore channel model of 3.5 nm tricalcium aluminate (C(3)A) was developed using molecular dynamics (MD) to reveal theadsorption behavior of the activator in the pore channel. The resultsshow that the activator is subject to solid surface adsorption inthe pore channel with a low diffusion coefficient. Oxygen atoms onthe surface adsorb hydrogen atoms to form hydrogen bonds and sodiumions to form ionic bonds with calcium ions. This increases the retentiontime of the activator on the surface. The MD results explain the lowreaction efficiency of AFRHs at the microscopic scale. Moreover, itprovides ideas and a basis for the optimization of AFRHs.

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