Part 1 - Nanoparticles Flashcards
What does the difference in radius between grown particles depend on?
- The time of growth. Larger time will yield a higher ∆r.
2. Initial difference in radii.
In the case of precipitation of gold by chemical reduction of aurochloric acid, why would increasing the concentration of HCl increase the induction time?
Because increasing the concentration of HCl would decrease the rate of reduction, and hence the supersaturation.
In the case of precipitation of gold by chemical reduction of aurochloric acid, what would happen to the induction time if we were to increase the concentration of aurochloric acid and ascorbic acid proportionally?
They supersaturation would increase, and the induction time would lower.
What are the two mechanisms that can account for formation of spherical crystalline particles grown from solution?
Aggregation of small particles, or growth of seed crystals.
In crude terms, describe the three different pathways of classical and non-classical crystallization, according to those who propose the mechanisms.
Nucleation clusters grow to form primary nanoparticles. These can either a) grow via classical crystallization to a single crystal, or b) aggregate via so-called oriented aggregation, which later fuses to a single-crystal. c) The last mechanism involves stabilization of the primary nanoparticles by organic compounds. These stabilized nanoparticles self-assemble into a mesocrystal, that later fuses to a single-crystal via b).
What are the two mechanisms proposed for spherulitic growth?
- Central multidirectional growth (from center and out to form spherical spherulitic particles).
- Unidirectional growth followed by low-angle branching (forms first dog-bones, then these kind of broccoli-structures before it folds around and creates spherical particles).
In the spherulitic growth of CaCO3 (vaterite), what is the effect of the initial supersaturation?
For high supersaturation (S = 7) the particles have grown by sphuerlitic mechanism no. 2, and have folded around to be spherical after 30 min. For lower supersaturation (S = 3.8), it has only formed dog-bone structures after 24 hours.
In the sperulitic growth of CaCO3 (vaterite), what is the effect of temperature? What does this imply?
For higher temperature (50 deg C) the particles fully curl around. For lower temperature (40 deg C), the resulting particles are dog-bone structures. This implies that the growth rate seems to govern the extent of curling.
