Formation of microcrystals, micropuddles, and other spatial inhomogenieties in surface reactions under ambient conditions: an atomic force microscopy study of water and nitric acid adsorption on MgO(100) and CaCO3(104).
In this study, atomic force microscopy (AFM) is used to image freshly cleaved MgO(100) and CaCO3(104) as these surfaces undergo reaction with water and nitric acid under ambient conditions of temperature, pressure, and relative humidity. The reaction of water and nitric acid results in the formation of hydroxylated and nitrated surfaces, respectively. It is clear from the AFM images that there are spatial inhomogenieties and surface features that form on micrometer and nanometer length scales as these reactions proceed. These features, which include hillocks, patches, microcrystallites, and micropuddles, are due to surface and phase segregation as a result of facile ion mobility in the presence of adsorbed water. In addition, instabilities and oscillations in the AFM images provide an indication of liquid formation and the deliquescence (i.e., a solid to liquid-phase transition) of nitrate salts as a function of relative humidity.
Krueger
Brenda J
BJ
Department of Chemistry and the Central Microscopy Research Facility, The University of Iowa, Iowa City, Iowa 52242.
Ross
Jean L
JL
Grassian
Vicki H
VH
D000327:Adsorption; D002119:Calcium Carbonate / Q000737:chemistry*; D017610:Calcium Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D003460:Crystallization; D006900:Hydroxylation; D017616:Magnesium Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D008277:Magnesium Oxide / Q000737:chemistry*; D018625:Microscopy, Atomic Force / Q000379:methods*; D009566:Nitrates / Q000138:chemical synthesis* / Q000737:chemistry; D017942:Nitric Acid / Q000737:chemistry*; D010316:Particle Size; D012680:Sensitivity and Specificity; D013499:Surface Properties; D014867:Water / Q000737:chemistry
D017610:Calcium Compounds; D017616:Magnesium Compounds; D009566:Nitrates; D014867:Water; D008277:Magnesium Oxide; D017942:Nitric Acid; C018330:magnesium nitrate; D002119:Calcium Carbonate; C059948:calcium nitrate