Crystals can grow at an astonishing rate if the right conditions are present. For instance, large industrial quartz crystals can be grown in laboratories in a matter of days under controlled conditions. Ice crystals can also form quickly in lakes or puddles overnight. And, the giant crystals in pegmatites can also grow rapidly.
Crystals tend to grow faster in warmer temperatures due to the quicker evaporation of the liquid containing the dissolved material. Additionally, a slow crystallization process encourages the growth of larger crystals. Figure 3.17 shows the crystallization of acetanilide from water with two different velocities. The crystals that grew in Figure 3.17a formed much faster and are smaller than the larger and slower growing crystals in Figure 3.17b.
For crystals to have enough time to grow, the evaporation rate must be slow. The evaporation rate of beakers, crystallization plates, Petri dishes and watch crystals can be regulated by covering the plate with aluminum foil and drilling holes in the foil. The foil delays evaporation compared to an open container, while the holes allow some solvent vapor to escape, preventing a completely closed system. The number of holes in the sheet can be increased for less volatile solvents, or fewer holes can be made to slow the evaporation of a highly volatile solvent. Nucleation occurs relatively slowly since the initial crystalline components must collide with each other in the correct orientation and location for them to adhere and form the crystal.
Crystal growth is an important stage in a crystallization process and consists of the addition of new atoms, ions or polymer chains in the characteristic arrangement of the crystal lattice. This will stimulate crystals to grow on the side of the vial, as there is more solvent in contact with the side and the angle prevents the newly formed crystals from falling directly to the bottom of the vial. Therefore, the magnitude of the force of attraction in a 25 mm crystal that captures ions from its immediate vicinity will be 10 thousand times greater than in a 2500 mm crystal that has exhausted its immediate environment and has to attract ions at much greater distances. In general, it is believed that mechanical and other properties of a crystal are also relevant to its growth rate, and that its morphology provides a link between growth kinetics and physical properties. Similarly, crystallization can be considered as a crystal lattice that collects solutes from a solution.
It took more than three years, an excursion to collect crystal samples from a pegmatite mine in Southern California, hundreds of laboratory measurements to accurately map out their chemical composition, and a deep dive into some materials science articles from 50 years ago to create a model Mathematician who could transform chemical profiles into crystal growth rates. Recrystallizations for purification purposes are a well-known and widely applied technique, but cultivating crystals suitable for single-crystal X-ray diffraction (XRD) is less well known and is more of an art than a science. The electrostatic force that attracts ions to growing crystalline faces weakens with the square of the distance to the crystal. We observed that time scales of crystal growth in pegmatitic systems can approximate those of slow sliding and seismic fluence, raising questions about whether crystal growth may be important during failure or fault healing. Very small holes reduce maximum resolution at which glass diffracts, larger holes destroy it. If after two weeks no crystals have formed in a sample, it may be time to reconsider your culture technique with solvents or crystals and try another method. According to the old Garbage In = Garbage Out rule, a crystal structure is only as good as its glass used for data collection.
Because favorable conditions for crystal growth are likely fleeting, it is logical to assume that crystal growth should occur over a relatively short period of time.
