Crystallization and matrix formation - Structure stability and evolution

4 important questions on Crystallization and matrix formation - Structure stability and evolution

What is the difference between the stability of a glassy or crystalline product?

The stability of a glass is indefinite. The crystal structure evolves in time, as a product is generally not 100% crystalline, but are a mixture of different crystalline, liquid or rubbery phases.

To make ice cream, a scarped surface heat exchange is used. Why can this lead to uncontrolled recrystallisation? And what can be done to solve this?

The scraping, makes the tiny flakes of ice in the ice cream of highly irregular shape. The irregular shaped flakes want to recrystallise into a more stable shape that is closer to spherical (reduce surface area).

The ice cream can be stored at -18 C for some time. This enables the irregular crystals to smoothen their surfaces and come more regular.

How can sintering or accretion take place?

In a very concentrated suspension, the crystals may touch each other. This smoothens out the irregularities on single crystals, but also induces a migration of the crystalline molecules to the contact point between the two touching crystals. This leads to the formation of a neck between the two crystals. If this happens everywhere in the suspension, a network of crystals is created, the product becomes solid.
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What is the difference in appearance between a monocrystal and a polycrystalline matrix?

Monocrystal is transparent, the polycrystalline matrix (dense) is opaque.

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