Morphological Signatures of Salt Crystals under Controlled Humidity Using Advanced Image Analysis

We designed, fabricated, and utilized a humidity control chamber to investigate how controlled relative humidity (RH) affects crystallization patterns of two different salts; sodium chloride (NaCl) and ammonium chloride (NH₄Cl) on glass slides. We also performed high-resolution imaging and MATLAB-based analysis to extract morphological and textural features of dried salt deposits, which were then assessed using Principal Component Analysis (PCA) technique. Results showed that humidity significantly impacted drying times and crystal morphologies. NH₄Cl formed dendritic structures that grew more complex with higher humidity, while NaCl produced cubic/hopper crystals, whose size and aggregation varied with humidity. PCA analysis showed humidity-specific patterns, with NH₄Cl displaying greater sensitivity. Our results demonstrate that the controlled humidity systematically alters salt crystallization dynamics, and advanced image analysis can precisely quantify these morphological signatures. Deep learning neural network models predict the correct salts from their image morphologies with over 97% accuracy.