5-1
·  The autoclave is filled to some predetermined factor with water plus mineralizer (NaOH or Na2CO3).
·
·  The baffle localizes the temperature gradient so that each zone is nearly isothermal.
·
·  The seeds are thin slices of (usually)
Z-cut single crystals.
·
·  The nutrient consists of small (~2½ to 4 cm) pieces of single-crystal quartz (“lascas”).
·
·  The temperatures and pressures are typically about 3500C and 800 to 2,000 atmospheres; T2 - T1 is typically 40C to 100C. 
·
·  The nutrient dissolves slowly (30 to 260 days per run), diffuses to the growth zone, and deposits onto the seeds.
Cover
Closure
area
Autoclave
Seeds
Baffle
Solute-
nutrient
Nutrient
dissolving zone, T2
T2 > T1
Growth
zone, T1
Nutrient
Hydrothermal Growth of Quartz
   Prior to ~1956, the material used for quartz resonators was natural quartz, i.e., mined quartz.  Today, it is “cultured quartz,” i.e., quartz grown in factories.  Although this quartz is often referred to as “synthetic quartz,” nobody has yet found a way to synthesize single crystal quartz directly from silicon and oxygen. Large quartz bars (typically ~15 cm long) of uniform size and shape are grown from small, irregularly shaped pieces of quartz (called “lascas” by the culturing process described above.  So, strictly speaking, the quartz is “cultured quartz”.
   Quartz is a common material in the earth’s crust (e.g., sand is mostly quartz), however, the high purity crystals needed for quartz growing are not so common.  Most of the nutrient materials used by quartz growers are mined in Brazil and the USA (near Jessieville, Arkansas).
   The autoclave is a long, thick-walled ~25 to 100 cm inner diameter steel tube that can withstand the high temperatures and pressures of the growth process.
   The anisotropy of quartz is discussed on the next page, and in chapter 3, where it is pointed out that the highest etching rate direction is the Z-direction.  Similarly, during quartz growing, the Z-direction is the fastest direction of growth.


R. A. Laudise and R. L. Barns, “Perfection of Quartz and Its Connection to Crystal Growth,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 35, No. 3, pp. 277-287, May 1988, IEEE Catalog 88CH2588-2.