Note: Descriptions are shown in the official language in which they were submitted.
-` ~284418
A Process for Manufacturing a Product Suitable
for Producing Pure Quartz Glass as well as a Process
for Producing Pure Quartz Glass from this Pro-
duct and Use of this Product for Growing Piezo-
electric Crystals
The present invention is concerned with the manufacture
of pure quartz glass and relates in particular to the
production of a product suitable for producing such pure
quartz glass, from types of quartz which have been con-
sidered unsuitable for producing pure quartz glass up tonow. The invention further relates to the use of
the product obtained from such types of quartz
according to the invention, for growing piezoelectric
crystals.
1 0
Ever since quartz was first industrially processed into
quartz glass (flint glass) around the turn of the cen-
tury, crude quartz has been used for this purpose, which
was selected frorn the various deposits according solely
to the criterion that it be more or less clear as water
but at least transparent.
The quartz glass melted from this raw material was more
or less clear as water or at least transparent, also de-
pending on the particular way the method is carried out.
- By improving the melting and processing techniques, the
transparency and optical behavior of quartz glass melted
from crude quartz which was not quite clear as water but
only transparent, could be adapted to the properties of
quartz glass melted from crude quartz which was clear
as water, for example by minimizing the bubble content,
homogenization, etc.
Ithas beoome increasingly necessary to search for an im-
provement in the process techniques because the reserves
of crude quartz which is clear as water do not suffice
128~4~8
-- 2 --
to meet the growing demand.
In the known methods for melting quartz glass, the
at least transparent crude quartz obtained is broken
into pieces of up to approx. 100 g, heated above the
alpha-beta transformation point of the quartz of 573C
and then quenched in soft, demineralized or deionized
water.
The extremely pure product thus obtained is then ground
down to a grain of less than approx. 1 mm in an agate
mill or by means of grinding tools with similarly un-
problematic abrasion, sifted, fractionated and possibly
subjected to mechanical and/or chemical final cleaning
in order to eliminate certain superficial contamination
which has come into the product during the reducing pro-
cess. This product can be melted, for example, in a
crucible. A shaped body may be removed from the melt.
But the product may also be ground ~further to an even
smaller grain size and then introduced into a gas or
plasma burner from which, contained in the flame, it
hits a catching body on which a quartz glass body builds up.
There is also a known method (IMC-Spruce-Pine, North
Carolina) in which pegmatite, because of the feldspar,
is processed to a floatable grain < 300 ~m using custom-
ary crushing and grinding tools and the quartz contained
in the pegmatite is processed using a combination of
mechanical and chemical means to form a raw material
which is suitable for customary, but not for higher-
quality, quartz glass products. For the extremely
pure raw material is contaminated in an undesirable
fashion in this method both by flotation residue and
by the abrasion of the reducing tools, so that it can-
not be used for a large number of applications, inparticular for use in optics, in semiconductor tech-
- ~ 2a44:18
-- 3
nology, in communication engineering (optical fibers) and in the
lamp industry.
The demand for quartz glass which has greatly increased in the
last ten years or so for a growing number of applications such as
the lighting industry, the semiconductor industry, communication
engineering, smelting plants, chemical engineering and optics,
confronts the suppliers of crude quartz with problems which are
diffucult to solve. It is to be expected that the reserves of
crude quartz whch is clear as water or transparent will shortly no
longer meet the constantly increasing demand of the producers of
quartz glass. The large reserves of quartz which is not
transparent (milky quartz) which do exist have not been exploited
for the processing of quartz glass up to now because most of this
non-transparent quartz is so contaiminated by nature that quartz
glass obtained therefrom cannot be used for any subsequent
application.
The invention provides a process making it possible to produce
from non-tranparent quartz (milky quartz) a product which is
marketable as such and can be used by the producer of quartz glass
to produce pure quartz glass if he keeps to certain procedural
conditions resulting from a development of the invention when
melting this product.
In accordance with the present invention there is provided a
process for manufacturing a product from natural non-transparent
quartz (milky quartz), this product being suitable for producing
pure quartz glass, characterized by the following procedural steps:
a)reducing the milky quartz obtained from the deposit
into pieces of a size in whcih the pieces are homogeneous in
themselves
b) washing the pieces obtained in an acid bath and then
rinsing them with soft, demineralized or deionized water
1284~8
- 3a -
c) sorting out the pieces still located in the rinsing bath
according to their degree of translucency as it appears to the
observer, eliminating contaminated and/or intergrown pieces, and
combining pieces having the same degree of translucency into groups
d) separating drying the resulting groups of pieces
having the same degree of translucency of grinding them wet or
after drying into a granulated material.--
Also in accordance with the present invention there is
provided a process for manufacturing a product from natural
non-transparent quartz (milky-quartz), the product being suitable
for producing pure quartz glass, characterized by the steps of:
a) reducing the natural non-transparent quartz into
pieces which are homogeneous in themselves;
b) washing said homogenuous pieces in a strong acid bath
for a time sufficient to remove their excess sodium and potassium
content;
c) rinsing said homogeneous pieces in a purified water
solution;
d) measuring the translucency of said homogeneous pieces
in said purified water solution to identify contaminated and
intergrown pieces and groups of pieces having the same degree of
translucency
e) separating said groups of pieces identified as having
said same degree of translucency, one from the other, and from
said contaminated and intergrown pieces to form at least one group
of pieces in which all of the individual pieces within said group
have the same degree of translucency; and
f) granulating.said at least one group of pieces to form
30 said product.
Further in accordance with the present invention there is
provided a process for producing a shaped body of pure quartz
glass from natural non-transparent quartz characterized by the
35 steps of:
-`` 1284418
- 3b -
a) reducing natural non-transparent quartz into pieces which are
homogeneous in themselves;
b) washing said homogeneous pieces in a strong acid bath
for a time sufficient to remove their excess sodium and potassium
content;
c) rinsing said homogeneous pieces in a pure water
solution;
d) removing all contaminated pieces from among said
homogeneous pieces
e) measuring the translucency of said homogeneous pieces
in said pure water solution to identify at least one group of
homogeneous pieces having the same degree of translucency;
f) separating said groups of pieces identified as having
said same degree of translucency, one from the other, to form at
least one group in which all of the pieces within said group have
the same degree of translucency;
g) granulating said at least one group of homogeneous
pieces having the same degree of translucency to produce a
granulated product;
h) washing said granulated product in an acid bath
i) rinsing said washed granulated product in deionized
water,
j) drying said rinsed granulated product; and
~ k) heating said dried granulated product in a degased
: 25 crucible to a temperature higher than 1850C in a high-vacuum to
melt said granulated product and produce a shaped body of pure
quartz glass.
- Further in accordance with the present invention there is
30 provided a process for producing a shaped body of pure quartz
crystal glass from natural non-transparent quartz comprising the
steps of:
~: a) reducing the natural non-transparent quartz into
; pieces which are homogeneous in themselves;
b) washing said homogeneous pieces in a strong acid bath
for a time sufficient to remove their excess sodium and potassium
content;
~1~ F
,
~ ' ' .
'' . , ' :~.,
~2844i8
- 3c -
c) rinsing said homogeneous pieces in a pure water solution;
d) measuring the translucency of said homogeneous pieces
to identify contaminated and intergrown pieces and groups of
pieces having the same degree of translucency
e) separating the groups of pieces having the same degree
of translucency, one from the other, and from said contaminated
and intergrown pieces to form at least one group of pieces in
which all of the individual pieces within said group have the same
degree of translucency;
f) granulating said at least one group of homogeneous
pieces having the same degree of translucency to produce a
granulated product having a grain size ranging from 90 micrometers
to 300 micrometers;
g) heating said granulated product from 30 to 20 minutes
15 in a reactive atmosphere at a temperature between 1050C and
1300C then cooling to room temperature; and
h) flame-spraying said cooled granulated product on a
catching body to produce said shaped body of pure quartz crystal
glass.
Thus the problem i8 solved according to the invention by processes
which include the following basic procedural steps:
a) grinding the milky quartz obtained from the deposit into
; 2S pieces of a size in whcih the pieces are homogeneous in themselves;
b) washing the pieces obtained in an acid bath and then
rinsing them with deionized water;
`~'~
, .. . . . . ... .... .... . ... .. . . ....... .
-" ~L28~ L8
c) sorting out the pieces still located in the rinsing
bath accord$ng to their degree of translucency,
eliminating contaminated and/or intergrown pieces,
and combining pieces having the same degree of
translucency into groups; and
d) separately drying the resulting groups of pieces
having the same degree of translucency or grinding
them wet or after drying into a granulated material.
The crude milky quartz used consists 99.8% of SiO2.
Such crude quartz is found, for example, in Arkansas,
U.S.A., in particular in Blocker Lead Mine No. 4.
The content of water of crystallization of this crude
milky quartz is approx. 0.2~, the total contamination
less than 65 ppm.
The following comparison of analyses of quartz which
ranges from clear as water to transparent,with milky
20 quartz -
Chemical Analvsis
transp.milky quartz
Al 15 15 in ppm
25 Fe 3 3
Ca
Mg
Na 2 15-20
K 2 7
30 Li
Ti
~others) kl 10 kl 20
LOI (~) kl 0.001kl 0.2
(analyses: most modern measurement with AAS (ICP
':'.~'~
~2844~8
5500 by Perkin Elmer)) -
shows that, in addition to the considerably higher OH
content, in particular the Na and K content of the
milky quartz varies up to a considerable degree from
the corresponding values of transparent quartz. The
Na content is higher by a factor of approx. 10 and the
K content by a factor of approx. 3 to 5.
This increased content of Na and K is essentially what
gives non-transparent quartz its milky appearance, mak-
ing it unsuitable for conventional processing to
quartz glass.
/
The product obtained according to the present invention can be
usec to produce a shaped body according to a process in
which quartz ~s melted in the conventional manner in a
crucible made of refractory metal or graphite under low
pressure with a temperature increase fro~ 8 to 10C/per
minute up to a temperature higher than 1735C and re-
moved as a shaped body from the crucible after a resi-
dence time of 10 to 30 minutes and possibly after in-
crezsing the pressure, when, in a development of the
invention, the inventive quartz is cleaned in an acid
batr. before being fed into the crucible, then rinsed
with deionized water and subsequently dried, whereupon
the product treated in this manner is melted in a high
vacuum in the degassed crucible by heating it at a tem-
perature higher than 1850C.
The acid bath preferably consists of hydrofluoric acid.
The melting in a high vacuum as was termed essential
above takes place advantageously with a vacuum of 10
torr.
1`' ' ~ " ''
~Z84~8
-- 6 --
Depending on the degree of milkiness of the product
obtained according to the inventive process, it may
be necessary to include a residence period of 10 to
30 minutes at a temperature of the material slightly
hig~er than 600C while heating this product, the shorter
residence time applying to quartz which is less milky
and the longer residence time to quartz which is rela-
tively milky.
It ~ay be expedient in the case of particularly milky
initial products to include, in a further development
of the invention, a second residence period of up to
30 ~inutes at a temperature of the material slightly
higher than 1050C. These measures insure that prac-
tically all contamination remaining in the milky quartz,in particular the Na and K, is either expelled directly
or at least d$ssolved from the union of the quartz crys-
tal to the extent that it is completely eliminated dur-
ing subsequent heating.
It ~ay be particularly expedient to support this clean-
ing process by keeping the melt at a temperature between
1800C and 1850C for a period of 30 to 10 minutes before
removing the shaped body from the crucible.
The result of the inventive process is quartz glass
which no longer differs from quartz glass which has been
procuced from initial quartz which is completely clear
as ~-ater.
The ground end product can also be used to produce a
shaped body from pure quartz glass, by melting ground
quartz in a gas or plasma burner and directing the
flare containing the molten quartz towards a catching
; 35 body on which the quartz glass shaped body builds up,
~ wher. one starts with granulated material produced
*, ~
. .
~Z844~8
-- 7 --
according to the invention, reduces it further to a grain
size of 90 ~m to 300 ~m, heats the resulting reduced
granulated material to approx. 1050 to approx. 1300C
for approx. 30 to 20 minutes in an oxygen and/or chlo-
rine atmosphere, cools it down to room temperature againand finally pours it off into the storage vessel of the
burner, from which this granulated material is intro-
duced into the burner itself.
The proposed heat treatment of 30 to 20 minutes at approx.
1050 to approx. 1300C in an oxygen and/or chlorine at-
mosphere not only reliably expels the water of crystal-
lization and any gas pockets but also reduces the alkali
content, in particular the sodium and potassium content
which may be present in the starting material for the
inventive product up to ten or fifteen times what is
present in quartz which is clear as water.
The burnin~ dcwn of the ground product in the gas or
plasma burner takes place in the conventional manner
so that it need not be dealt with in more detail.
