Geoscience Reference
In-Depth Information
pertaining to the synthesis of quartz by Schafhaul during 1845
[20]
. The best known
source of natural quartz, even today, is Brazil, which has large occurrences of high-
quality electronic grade quartz. As a matter of fact, Brazil was the only supplier of
large crystals of high-quality natural quartz for electronic applications until World
War II. Shortages in the United States and Europe caused by German submarine
activity prompted efforts to synthesize large crystals of quartz, in the laboratory,
using seeds. Spezia (1900
1909) was the first to attempt the seeded growth of
quartz crystals and to carry out a systematic study of the solubility. However, the
growth rate was poor. It was only during World War II that Nacken could achieve
higher growth rates for quartz by the hydrothermal technique. The pilot scale
production of quartz began during mid-1950s in the United States and erstwhile
USSR. Several countries attempted the artificial growth of large size single crystals
of quartz. Especially, after the publication of the works of Nacken in 1950
[21]
and
the captured German reports
[22,23]
, several laboratories began studying quartz
crystal growth almost simultaneously and the hydrothermal technique became a
very popular tool for developing many complex inorganic compounds. Industrial
scale production occurred essentially during 1960s and 1970s, with a peak develop-
ment between 1968 and 1976, especially in the United States, Japan, and Europe.
In the growth of
α
-quartz by the conventional method, the autoclaves used by
most of the workers were modified Bridgman-type autoclaves. The design and con-
struction of the modified Bridgman autoclave is described in Chapter 3. The typical
laboratory size autoclave is 1
v
diameter
3
1
0
length. The pressure autoclave used in
Europe and the United States is 13
10
0
length with 350 l internal
volume, which gives some 150 kg of quartz per cycle. But an evolution concerning
vessel's dimensions has to be noted, especially in Japan, where autoclaves with
1000
v
diameter and
.
2000 kg of quartz
per cycle. The evolution of the autoclaves, the sealing involved, and the volume
are discussed in Chapter 3. These larger internal volume autoclaves are provided
with Grey-Loc type of sealing. Parallel to the increase in output, electronic compo-
nents manufacturers have been looking, for the past 2
1
5000 l of internal volume are in operation producing 500
2
decades, for a material with
steadily increasing performances for professional applications in the telecommuni-
cations field, civilian as well as military.
In the growth of
α
-quartz, available nutrient material such as small particle size
α
-quartz, silica glass, high-quality silica sand, or silica gel is placed in a liner made
up of iron or silver with a suitable baffle and a frame to hold the seed plates.
A mineralizer solution with a definite molarity is poured into the liner to make the
required percent fill (% fill). The increased solubility in the presence of mineralizer
increases the supersaturation without spontaneous nucleation and consequently
allows more rapid growth rates on the seeds. Figure 3.3 shows the cross section of
the modified Bridgman autoclave used in the growth of quartz crystals. The com-
mercial autoclaves used have 10
inner diameter and are 10 feet long unlined.
These autoclaves can work at conditions up to 30,000 psi and 400
C. Most of these
experiments are carried out for 25
v
90 days to obtain full size crystals, 4 cm in the
Z-direction and 12.5
15 cm in the Y-direction. Temperature gradient is varied
according to the nutrient used. 1N NaOH (1 M) or Na
2
CO
3
(1 M) are the most
