Note: Descriptions are shown in the official language in which they were submitted.
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~ SP~CIFICATION
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The presen~ invention relates to transparent articles
having improved abrasion resistance and to a method of prod-
ucing such articles.
The architectural trend toward using more glass in
commercial buildings has been enhanced by the availability of
special coated and tinted glasses which not only ~erve an
aesthetic purpose but also are functional. The most signi-
ficant advantages of the special glasses are in the area of
air conditioning. Since it generally costs from three to six
times more to cool a building one degree than to heat it by
the same amount (depending on the amount of glass used), the
use of an exterior glass which will reduce the amount of solar
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radiation entering a building can provide substantial 5aving~
since less air conditioning equipment i~ required and its
operation is less costly The special glasses are al~o used
in other areas where low heat transmittance is required,
i,e~, automobile wlndows and oven windows.
Over the past decade the market for colored and
reflective glass has grown significantly~ The colored glass
involYed is basically of two types -- tinted and coated.
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Tinted glass i5 generally made by adding selective metals such
as iron, cobalt, and nickel to the molten glass during product-
ion. This method of producing colored glass is time consuming
and wasteful in that when a different color of glass is des-
ired, a four or five-day run of glass must be discarded while
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the change is made and the new batch ~tabilized. Also, large
qua~tities of different colors and types of glass must be
inventoried. In addition, although tinted glass does reduce
glare, it also absorbs heat (including ~olar radiation) and
the absorbed heat is re-radiated from both sides of the glass.
Therefore, a ~reater amount of heat is allowed to pass through
the glass than with coated glass.
Coated or reflective glass is provided with a thin
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film of a reflective substance on one of its surfaces. The
thin film reflects the solar radiation much more effectively
~ than tinted glass since the glass does not absorb the radiat-
; ion. Among the materials presently employed for this purpose
chromium which can be deposited on glass sheets either by
thermal deposition or by the sputter-coating technique.
However, it has been found that pure chromium coatings, while
: used with considerable success, are not wholly satisfactory
~n all case~ in that they are susceptible to being marred or
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damaged when exposed over a period of time to varying atmos-
pheric conditions, or when subjec~ed ~o repeated cleaning or
rough handling, Efforts have been made to overcome this
condition by overlaying the cbromium ~ilm with a protective
coating of a siliceous material, such as Pyrex glass, but
thi~ has not proven entirely successful.
It is thererore the primary objective of this invent-
ion to 1mprove the abrasion resistance of sputtered coatings
on ~lass sheets,
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- More particularly, it is the purpose of this invent-
ion to provide a transparent coating for glass sheets or plates,
deposited thereon by sputter-coating, and which possesse9
greater resistance to surface abrasion than relatively pure
chromium coatings,
A typic~l article according to the present invention
comprises a body of transparent glassy siliceous material
having a smooth continuous surface, and a continuous abrasion
reslstant transparent reflective film of chromium silicide
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adhered to said smooth continuous surface, said chromium
silicide film consisting essentially of chromium and silicon.
The chromiu~ silicide film is preferably of a thickness of
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from about 200 to 1,000 A.
m e transparent bodies ~f primary concern are archit-
ectural glass, although other uses are possible, such as
vehicle windows and oven wlndows. The glassy siliceous
material is preferably conventional silicate glass, including
window glass, plate glass and float glass, although any ofthe
conventional or special purpose glasses may be employed as long
as they are transparent.
In preparing glass products according to this invent-
s ion, t~e bod~ of transparent glassy siliceous material is first
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cleaned by a conventional washing operation and then placedin a deposition chamber containing an inert gas~ The gas in
the chamber is preferably maintained at a pressure of from 5
to 50 microns, At pre3sures below 5 microns the rate of
deposition during coating is insu~fic~ent for most purpose
and there is increased danger of surface con~aminatîon, At
pressures above 50 microns the efficiency of the process is
significantly reduced. me glass body is preferably heated
to a temperature of about 250C, prior to processing.
- The smooth continuous surface is usually ion bomb-
arded within the chamber to finally clean and prepare the
surface for receiving the coating~ This is generally done by
the off-sputtering or reverse sputtering technique which is
commonly known, Typically, the sputter-coating time is about
twenty minutes at a power density of 0.1 to 1,0-watt/cm2~
~ith certain types of substrates and certain washing or clean-
ing processes (prior to insertion in the chamber), the
sputter-cleaning step may be unnecessary,
The clean, smooth sur~ace i9 then sputter-coated with
a continuous film of chromium silicide until a uniform coating -
of the desired thickness i9 obtained, Typical sputtering con-
ditions are 5,000 volts potential on the target (coating mater-
ial) and a resulting current density of 0,5 to 1,0 ma/cm2 for a
time period of 0,2 to several minutes depending on the thick-
ness of coating desired,
The target usually consists of a relatively thin
rectangular metal plate having a layer of the coating material
to be sputtered applied to one surface thereof, The metal
plate ordinarily constitutes the bottom wall of a hollow
cathode which is formed with a chamber through which a cooling
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medium, such as w~ter, is circulated, The cathode is posit-
ioned in the deposltion chamber clo5ely adjacent the top
thereof, with the glass ~heet to be coated supported horizont-
ally therebeneath to receive the chromium silicide upon the
upper surface thereof,
As is well known, chromium forms several silicides,
including Cr3 Sil Cr2 Si, Cr Si and Cr Si2. Also that silicon
forms a solid solution of silicon in chromium and can dissolve
up to seven and one-half per cent of the silicon, The compos-
ition of the silicides are as follows:
Silicide wt/o Silicon
Cr3 Si 15
Cr2 ~i 21
r Si 35
Cr Si2 52
The silicided-chromium material used for forming the
sputtered films of this invention is preferably in the lower
part of the range of composition i,e, about six to fifteen
wt!o silicon, This is preferred in order ~o retain properties,
~uch as reflectance and absorbance substantially si~ilar to
that of pure chnomium, while still providing a hard abrasion
. resistant coating, The corrosion resistance in a normal atmos-
phere is similar for both the chromium silicide and the relat-
ively pure chromium currently being used,
For the preparation of sputtered silicide chromium
films on glass according to the present invention, a sputter-
ing target was prepared by reacting silicon with electrolytic
¢hromium, This was accomplished as outlined below;
~ I. A 12 x 12 x 1/~ inch sheet of mild 3teel was
: electroplated with chromium on one surface
as usual to form a chromium sputtering
target,
II, Silicon powder (-325 mesh~ was sprinkled on
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the electroplated surface to a depth o~ -
about 1/~ inch,
III. The target wi~h the silicon powder was heated
in a pure argon atmosphere at 1400F, for
12 hoursO Thiq caused some of the silicon
to dissolve in the chromlum to form some
- chromium silicide.
IV, The excess residual unreacted silicon powder
was brushed from the silicide chromium target.
The above method will result in a target consisting
of a solid solution of silicon in chromium along with some
chromium silicide (Cr3 Si).
The target was then used for the deposition of
silicided chromium films onto 10 x 10 x 1/~ inch sheets of
float (soda-lime-silica) glass by the sputtering process above
described, As shown by the data given in the following
Table I, the silicided chromium films have abrasion resistance
significantly superior to those of unsilicided chromium. The
abrasion resistance of the sputtered films was measured with
a Tabor Abraser with 1000-g wei~hts and a CS-lOF wheel.
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The data given in Table I above is correlated with
the graph shown in the accompanying drawing wherein line 10
represents the commercial sputtered coatings of substantially
pure chromium and line 11 the sputtered chromium silicide
coatings of this invention~ As will be seen, the chromium
silicide coatings possessed substantially greater resistance
to abrasion than the sputtered unsilicided chromium coatings
of equal thickness. Also that the superiority of the chrom-
ium silicide coatings over the unsilicided chromium coatings
increased with increased coating thickness. For example, it
required 975 abrasion cycles to remove a silicided chromium
coating of a thickness of 615 ~ as against 300 cycles for an
unsilicided chromium coating of the same thickness. On the
other hand, it required 1300 cycles to remove a chromium
silicide coating of a thickness of 9~0 A as against 450 cycles
for an unsilicided chromium coating of equal thickness.
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