2.2 Chemical reactions by point contacts on solids
-Evidences on acceretion of cosmic dust-
-[ Surface oxidation of iron powder by dry ice (CO2)]
The sparse structure of the asteroid Ryugu shows that the interstellar
medium quietly touches and the adheres were composed of point of contacts
resulting in the birth of small celestial bodies. Iron powder hardly oxidize
when placed in a carbon dioxide gas (CO2).
However, if you mix fine powder iron powder (Fe) and dry ice powder (CO2) and seal it in a jar, iron powder oxidizes as shown in Fig.3. It is thought
that contact with iron (Fe) in and dry ice (CO2) makes a chemical reaction that forms ferrous oxide, and carbon was produced
due to deoxidization of CO2. Iron and dry ice make a chemical reaction. The edges of the glass container
includs dry ice are shown in Fig.4. Gray Fe, Black Fe3O4 and braown Fe2O3 is seen. The left half of Fig.5 is reduced iron fine particles and reduced
iron fine particles and dry ice. The oxidation of the surface due to mixing
is shown in the right half.
Fig.3. A glass container Fig.4. Rim of the glass container Fiｇ. 5. Oxidation of iron particles
[ Oxidation of iron fine powder on dry ice (CO2) ]
Iron fine powder becomes more reactive as it becomes a fine particle. Extremely fine iron powders oxidize when they come into contact with solid CO2 of dry ice. Iron oxalate (Fe2O3・2H2 Iron fine particles (Fe) made from dry ice (CO2 Sprinkle on the crystal. You can experiment to confirm that fine iron powder oxidizes due to cold dry ice. After sprinkling fine iron powder on dry ice for a while, Figure 6. As shown, smoke of microscopic particles is generated, and the iron particles become black to reddish in color. The reddish color is red iron oxide (Fe2O3).
Fig.6. Oxidation of ultrafine particles of iron sprinkled on dry ice solids
[Video: Oxidation of ultrafine iron powder by solid carbon dioxide]
（last modified Feb27 2023).
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