Which process involves using a heating unit to create a synthetic crystal from a rotating solid rod of chemicals?

The process referred to in the question is known as "Pulling." This technique involves the growth of a crystal from a solid feed rod, utilizing controlled temperature and rotation to create high-quality synthetic crystals.

In pulling, the solid rod, made of the necessary chemical components, is heated at one end to induce melting. As the rod is pulled upward and rotated, the molten material solidifies into a crystal that forms from the tip of the rod. This method is particularly effective for creating large, single crystals with fewer defects, making it widely used in the production of synthetic gemstones and in semiconductor applications.

In contrast, flame fusion creates crystals by melting powders of materials in a flame, which leads to rapid formation of crystals but typically results in more inclusions and defects. Floating zone employs a different technique of heating and melting a small liquid zone within a solid material, which is also distinct from the pulling process. Lastly, hydrothermal growth involves synthesizing crystals in a water solution under high pressure and temperature conditions, which is not related to the use of a solid rod.

This understanding of the pulling method highlights its importance in producing high-quality synthetic gems and contributes to knowledge of different crystallization methods used in gemology and materials science.