384
16.
VACUUM TECHNIQUE
relying on its
“
getter action
”
to assist the pumps; others use
one or two minutes for the complete evaporation.
When the pressure
is in the range from 2 to 5 >< 10“3 mm.,
run a
high voltage discharge (spark coil or small transformer)
between an electrode in the top of the bell jar and the base plate.
This tends to clean the surface and to form a coating which
adheres more strongly.
A shield may be used between coil C and P for a brief time
before permitting the metal to deposit on the plate. This avoids
an impure underlayer and hence gives a more adherent surface.
Aluminum wire may then be used in C without the nitric acid
cleaning.
For chromium deposits, put the metal in a small spiral cone (tip
down) of 4 or 5 turns of 30 mil tungsten, instead of the coil (C of
gure 16—18) and heat as rapidly as possible with, say
40 amperes.
'
If three heavy lead rods (LL of gure 16—18) are used in a triangular
form, both a cone for chromium and a spiral for aluminum can
be. used in succession without re—evacuating the apparatus.
The cone is used to keep the melted copper from running away.
A few grains of gold may be used in a coil.
A
deposit may be obtained by heating a w1re of this
material very near to its volatilization point. A trial run can
be made to determine a safe heating current. For example, an
8 mil wire of this material, 3% inches long, burned out with 7%;
amperes, and when heated with 7 amperes for one hour gave a
three—quarter coat at a distance of one centimeter.
EXPER1MENT 16—1
'
'
w
METALLIZING MIRRORS AND FIBERS
,
'
‘
_
(l) Sputœr an opaque surface of gold on a
glass.
section 16—23.) The glass must be cleaned, with
water,
(KOH) , Water, then withnitric acid (HNOs),
Water, dri‘ed and
with cotton before"
; Sputtering1ftheideposit iè to be
_
'
,
.
.<2)Alummma glass‘plàte‘b‘y tlîe“evaporation process (See
16.
VACUUM TECHNIQUE
relying on its
“
getter action
”
to assist the pumps; others use
one or two minutes for the complete evaporation.
When the pressure
is in the range from 2 to 5 >< 10“3 mm.,
run a
high voltage discharge (spark coil or small transformer)
between an electrode in the top of the bell jar and the base plate.
This tends to clean the surface and to form a coating which
adheres more strongly.
A shield may be used between coil C and P for a brief time
before permitting the metal to deposit on the plate. This avoids
an impure underlayer and hence gives a more adherent surface.
Aluminum wire may then be used in C without the nitric acid
cleaning.
For chromium deposits, put the metal in a small spiral cone (tip
down) of 4 or 5 turns of 30 mil tungsten, instead of the coil (C of
gure 16—18) and heat as rapidly as possible with, say
40 amperes.
'
If three heavy lead rods (LL of gure 16—18) are used in a triangular
form, both a cone for chromium and a spiral for aluminum can
be. used in succession without re—evacuating the apparatus.
The cone is used to keep the melted copper from running away.
A few grains of gold may be used in a coil.
A
deposit may be obtained by heating a w1re of this
material very near to its volatilization point. A trial run can
be made to determine a safe heating current. For example, an
8 mil wire of this material, 3% inches long, burned out with 7%;
amperes, and when heated with 7 amperes for one hour gave a
three—quarter coat at a distance of one centimeter.
EXPER1MENT 16—1
'
'
w
METALLIZING MIRRORS AND FIBERS
,
'
‘
_
(l) Sputœr an opaque surface of gold on a
glass.
section 16—23.) The glass must be cleaned, with
water,
(KOH) , Water, then withnitric acid (HNOs),
Water, dri‘ed and
with cotton before"
; Sputtering1ftheideposit iè to be
_
'
,
.
.<2)Alummma glass‘plàte‘b‘y tlîe“evaporation process (See