Note: Descriptions are shown in the official language in which they were submitted.
~ 160409
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PREPARATION OF RAPIDLY SOLIDIFIED PARTIC,UI,ATES
TECHNICAL FIELD
This invention relates to a preparation of rapidly
solidified particulates. More particularly, the invention
concerns a method of making solid particulates through
contacting a molten stream of material with a centrifugally
disposed rotating liquid quenching fluid so as to disrupt
the molten stream into particulates and rapidly quench the
particulates, and then subsequently recovering quenched
solid particulates from the quenching fluid.
BACKGROUND
P. Duwez et al. (J. Appl. Phys. 31, p 1136-37 (1960))
teaches a propelling of a small liquid metal alloy droplet
against the target of the inside surface of a high speed
rotating cylinder at a suitable angle with centrifugal
force acting on the contacting droplet to insure good
thermal contact with the target with a large over--all
heat transfer rate and to spread the droplet into a
thinner layer of solidified material. R. Pond, Jr. et al.
(Trans. Met. Soc. AIME Vol. 245, p. 2475-2476, l~ov. 1969)
discloses casting of metallic fiber by forcing a stream
of molten alloy through an orifice onto the inside surface
of a spinning drum with the drum's radial acceleration
inducing good thermal contact and a spreading of the
contacting stream into a flat filament prior to complete
solidification.
( J. T. Gow (U.S. Pat. 2,439,772) uses a revolving
container containing a cooling or quenching liquid which
from the revolving is formed into an annular vertical
wall of revolving liquid into which are thrown globules
of molten metal at a substantially normal path thereto
to penetrate the liquid xather than glance off. In this
process Gow discharges a molten material (e.g. steel)
stream into a rotating dish-shaped receptacle to throw
3~
l 160~0~
metal from its periphery as the small globules being
thrown into the annular vertical wall of revolving
liquid. Gow in discussion of the prior art also mentions
disintegrating molten metal in the form of a stream into
droplets by means of impacting the molten metal stream
with high pressure steam or water and another method of
rapidly rotating drum or paddle wheels hitting a metal
stream to throw or bat globules therefrom. T. Yamaguchi
et al. (Appl. Phys. Lett. 33(5), 1 Sept. 1978, p. 468-470)
teaches preparation of amorphous powder by a water
atomization technique in which molten alloy is introduced
into the intersection of a pair of high velocity water
jets. B. Haak (U.S. Pat. 1,782,038) converts salts into
globular bodies through a melt being poured onto a
rotating disc which throws therefrom droplets towards the
walls of a vessel containing a rotating liquid the level
of which is higher than the rotating disc by means of
intense rotation by a stirrer.
G. R. Leghorn (U.S. Pat. 3,430,680) discloses a
casting method for selected metal shapes involving
flowing a stream of molten metal in heat-transfer contact
with one or more streams of cooling liquid mold material
flowing in the same direction. For continuous castings
the flows of liquid mold material and molten casting metal
are synchronized. For tapering and for discrete lengths
of the cast shapes there are used differential flows,
such as faster flowing mold material to create shearing
action at the interfaces of molten casting metal with the
flowing mold material. Discrete droplet or spherical
castings are shown from breakup of the introduced metal
stream by vibration means, such as illustrated by the
Fig. 17 embodiment, or by introducing uniform accurately
weighed solid particles, such as illustrated by the Fig.
18 embodiment. J. L. Engelke et al. (U.S. Pat. 3,347,959)
also teaches casting of molten metal within a continously
1 16040g
flowing stream of liquid as the mold flowing in the same
direction so as to form wire. By maintaining the velocity
of the mold stream greater than the wire-forming molten
filament, the diameter of the filament is reduced by the
action of viscous shear forces at the liquid-liquid
interface.
S. Kavesh (U.S. Pat. 3,845,805) disclo~es providing
metal filaments by a process involving rapid solification
of a molten jet in a fluid medium. This process involves
forming a free jet of the molten material in a gaseous
or evacuated environment, traversal of the free jet
through an interface into the fluid medium which is
flowing concurrently with and at essentially the same
velocity as the jet, and recovering solidified filament.
In Col. 7 in discussing factors of temperature of the
molten jet and molten jet velocity in relation to fluid
velocity in a standpipe, mention is made that "If
discontinuous filaments with tapered ends are formed, it
is an indication that jet velocity is substantially less
than the fluid velocity in the standpipe." and "pearl
necklace appearance of the filament...may be obtained
when the molten jet is superheated, e.g. about 250C.
above its melting point". In Example 7 a molten jet of
copper was disrupted and solidified as discrete spheroidal
particles in a sodium chloride brine quench fluid in
contrast to obtaining filaments in a more rapid quenching
magnesium brine quench fluid in the preceding example.
SUMMARY DISCLOSURE OF INVENTION
:
The process of the invention involves contacting a
centrifugally disposed rotating quenching fluid with an
unbroken coherent molten stream of solidifiable material,
e.g. metal, so as to disrupt the stream into particulates
and to rapidly quench the particulates to solids. The
particulate solids subsequently are recovered from the
quenching fluid.
1 1~04~9
BRIEF DESCRIPTION O~' THE DRAWINGS
-
Details of the invention are discussed in connection
with the accompanying drawings of which:
FIG. 1 is a perspective view partially in vertical
cross-section and partially illustrated diagramatically
of a simplified form of apparatus for carrying forth the
method of the invention; and
FIG. 2 is a partially vertical cross-sectional view
illustrated also in part diagramatically of an alternative
form of apparatus for carrying forth the method of the
invention.
MORE DETAILED DESCRIPTION OF THE DRAWINGS
. . . _
Referring to the drawings in which in each
illustrated drawing figure the same identifying numeral
is used to identify and refer to the same or equivalent
element and component, the FIG. 1 illustrated apparatus
is generally designated 10 and the FIG. 2 apparatus is
generally designated 30.
Apparatus 10 includes a cup-shaped element, generally
designated 11, which has a shaft 12 centrally affixed by
conventional means to a bottom section 13 of cup-shaped
element 11. Shaft 12 is rotatable at any of a variety
of chosen constant speeds by a conventional motor means
14 which means is not shown in FIG. 1 and is illustrated
diagramatically in FIG. 2. Bottom section 13 at its outer
periphery merges into an upwardly projecting cylindrical
side wall 15 which at its uppermost height turns inward
for a short distance to form a top rim 16. Located in
bottom section 13 is a small hole or opening 17 there-
through for purposes described later. In FIG. ~ theopening 17 in section 13 has been closed by a removable
threaded machine screw 17a.
In the opening encircled by top rim 16 there is
located and extends downward a vessel 18 of appropriate
inert heat-resistant material and generally cylindrical,
1 160409
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whi~h near a lowermost point has been provided with a
tip 19 containing an orifice opening 20 directed towards
side wall 15. Surrounding vessel 18 is a heating means,
such as a concentrically wound coil 21 which is connected
to a not-illustrated conventional induction power supply
which upon being activated supplies energy to melt a
material charge, e.g. metal, to a molten state or melt,
generally designated 22, which is disposed inside vessel
18.
Provision is made to provide, as required, a gas
pressure P to melt 22 and in Fig. 1 this is illustrated
diagramatically by an arrow and the letter P. For some
practices of the invention, the material melt 22 creates
an adequate static head for a molten stream flow through
orifice 20 and no pressure is applied to the melt 22.
In FIG. 2 the vessel 18 is provided with a removable top
closure 23 which is clamped, sealed, or otherwise con-
ventionally temporarily and removably used to close vessel
18. In FIG. 2 gas pressure, as illustrated diagramatically,
is provided to melt 22 by means of a gas line 24 which
extends through closure 23. Gas line 24 includes a gas
meter 25 for recording the gas pressure and a valve 26
for opening and closing to admit a gas or gases from a
supply source, not illustrated, through line 24 into
vessel 18. The vessel 18 in FIG. 2 includes a partially
diagramatically illustrated means for measuring the
temperature of melt 22 with this means including a thermo-
couple 27 which leads to a temperature gage 28 and
additional means, not illustrated, requisite for thermo-
couple temperature recording operation. Although notillustrated, instead of the temperature recording means
just described for melt 22, one could use an optical
pyrometer ~or observing melt temperature upon providing a
quar~z window or the like in top closure 23 of vessel 18.
l 1~0409
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Cup-shaped elem~nt 11, in operation of the method,
contains within a quench fluid 29, generally a liquid.
From centrifugal force created by rotation of shaft 12 and
of its attached cup-shaped element 11, the quench fluid 29
is disposed as a rotating quenching fluid forming a wall
linin~ and clinging to side wall 15 of cup-shaped element
11 .
The FIG. 2 apparatus, designated 30, in common with
the FIG. 1 apparatus 10, also includes a rotatable shaft
12 centrally affixed to a cup-shaped element 11 which
contains there within a centrifugally disposed rotating
quenching fluid 29, and also includes a vessel 18 having
a tip 19 containing an orifice 20 and having a coil 21
for induction heating a metal charge within vessel 18
to a melt 22. In contrast to the FIG. 1 apparatus,
the FIG. 2 apparatus includes for purposes explained later
a small hole or opening 17' in its side wall 15.
Additionally FIG. 2 apparatus 30 incorporates a containment
vessel, generally designated 31, which surrounds cup-shaped
element 11, and which comprises a bottom section 32,
cylindrical side wall 33, and a top closure lid 34, which
is adapted to hermetically seal containment vessel 31 by
conventional clamping means not illustrated. Also, not
illustrated and optional, but particularly useful in some
practices of the process, is a means~for providing and
controlling a gaseous environment in the interior of con-
tainment vessel 31, which gaseous environment for some
materials is an inert gas, such as;argon, helium, nitrogen,~
or the like. In the apparatus 30 of FIG. 2, the melt
vessel 18 extends upward through top closure lid 34 and by
a conventional means, not illustrated, is adapted to be
raised, lowered, and otherwise moved and located so as to
place tip 19 and orifice 20 at any of numerous locations
of various angles and distances from quench fluid 29 which
is disposed as a rotating quenching fluid forming a wall
lining and clinging to side wall 15 of cup-shaped element 11
1 16~409
-- 7 --
by centrifugal force created by rotation of shaft 12 by
motor 14. In operation, shaft 12 rotates within a sleeve
bearing 35 which extends through bottom section 32.
In apparatus 10 of FIG. 1 the hole or opening 17 in
bottom section 13 can serve as a drain opening upon
removal of screw 17a so that quench fluid 29 and formed
metal particulates, after a batch operation of apparatus 10
and cessation of rotation of shaft 12, can be drained from
and recovered from cup-shaped element 11 for subsequent
processing to separate particulates from the quench fluid
29. In apparatus 30 of FIG. 2, the hole 17' in side wall
15 functions to permit quench fluid 29 and formed
particulates to flow from cup 11 when the process is in
operation. The exiting particulates may be left to collect
in container 31 along with quench fluid 29 as a pool on top
of section 32 until their removal and recovery are desired.
Alternatively, although not illustrated, fluid 29 and
particulates exiting from the opening or hole 17' can be
directed onto or into a sieve-like container~ring for
collection of the particulates therein with quench fluid 29
then passing through and collecting as a pool on top of
bottom section 32. When particulates also collect in the
pool, the quench fluid 29 is filtered therefrom before
recirculation. Shown schematically is a fluid conduit 36,
a p~lmp 37, and a heat exchanger 38 so that quench fluid
29 can be removed from bottom section 32, cooled to a
desired temperature which is shown on gage 39 and
recirculated back inside element 11 to replenish and
maintain a desired temperature and thickness of the
quench fluid wall clinging by centrifugal force to side
wall 15. Pump 37 is of a pumping capacity along with an
appropriately sized recirculation system for fluid 29 that
an adequate supply of fluid 29 may be maintained in cup 11
during operation. The size of hole 17' also is such that
fluid 29 and particulates can pass through, but is kept
small enough that in relation to speed of rotation of C71p
l 160409
and pumping capacity of pump 37 an adequate supply of
quench fluid is maintained in cup 11.
DETAILED DISCLOSURE OF THE ~INVENTION
In general, the method of the invention involves
adding a liquid quenchant or quenching fluid (e.g. water,
oil, etc.) to the inside of the cup or drum; setting the
cup in rotation at a speed effective to cause the quench-
ant to form a parallel layer or wall along the circumfer-
ence of the c~p due to the action of centrifugal force;
and then squirting a molten unbrcken stream of the mate-
rial to be formed into particulates into this centrifu-
gually moving wall of liquid quenchant. This results in a
shearing action of the molten stream into droplets by
the high-speed moving quenchant and a quenching of these
droplets into solid particulates. The size of these
particulates and their shape and nature are controllable
by various variables or parameters in practice of the
method, including controllable parameters, such as the
employed materials, temperature of quenchant and molten
material, speed of the centrifugally disposed quenching
fluid, distance from, impact force and angle of contact
of the molten material stream with the moving wall of
quenchant, shape and size of the molten stream, and the
like. The cooling rate of the formed particulates also
is controllable by the just mentioned variables and can be
so rapid as to provide highly desirable amphorous metal
or metallic glassy particulates. Upon the molten stream
being broken into droplets by high-speed moving quenchant,
the droplets either immediately enter the quenchant and/or
travel in free flight a very short distance before reentry
into the quenchant wherein the droplets rapidly cool to
solid particulates.
In comparison t~ other known methods of preparation of
rapidly solidified particulates, this invention's method
provides numerous advantages. Substantially any liquid
1 1~0409
g
n:aterial or any material which can be placed in a liquid
state is a candidate for the quenching fluid, and
particularly appropriate quenching fluids can be selected
for different molten materials which are being made into
particulates. The employed surface speed of the
centrifugally disposed wall of the liquid quenchant can
be obtained easily and also readily changed to another
speed, if desired, with good control on this speed and thus
extremely precise control of the particle size of the
produced particulates. With laboratory apparatus,moving
quenchant speeds of from about 1400 to 8000 ft./min.
t~427 to 2439 m/min.) have been obtained easily and
successfully employed with it contemplated that speeds of
30,000 ft./min. (9144 m/min.) and greater are obtainable
and useful with appropriate apparatus. The invention's
centrifugal technique appears to be less costly than prior
art techniques involving high speed pumping or other
movement means for quenchants. Additionally the
invention's centrifugal quenchant technique can provide
more than adequate coolant capacity and temperature
control. Upon the molten stream being broken into
droplets from contacting the moving quenchant, the
molten particulates pass immediately or very quickly
enter the mass of moving liquid quenchant with extremely
high quenching rates being obtained. Heat transfer from
the molten metal particulates to cold quenched solid
particulates proceeds substantially continuously while
within the liquid quenchant. In addition a major
problem, associated with conventional water atomization
wherein an insulating steam layer prevents further cooling,
is avoided in this invention's technique because of the
rapid introduction and simultaneous movement of thick
layer of quenchant and the trapped particulates.
From extremely fine to much larger particulates can
be produced. Some of the larger spherical particulates in
~ an amorphous state are believed to be larger in size than
1 160409
-- 10 --
preparable by any known prior art method. Process control
of particulate size and/or shape is facilitated by the
invention's method. To provide extremely fine spherical
particles, e.g. finer than -325 mesh and in the amorphous
state, high quenchant speeds (e.g. 2500 rpm. and higher
or about 7500 ft./min. (2286 m./min) and higher~ are
important and preferred and are a major means of size
control. The molten stream size or shape, i.e. tip orifice
opening is apparently the next most important process
parameter towards providing desired particulates with the
molten streams of smaller cross-section favoring the
preparation of the extremely fine spherical particles.
Particularly preferred for providing those extremely fine
particles are openings of 0.010 in. (0.0254 cm.) dia. and
smaller. Higher pressures on the molten material, i.e.
higher molten stream pressures, also definitely favor the
preparation of the extremely fine spherical amorphous
particles. Particularly preferred are gas presssures on
the molten material of between 2 to 10 psi. or equivalent
differential pressures, so as to provide molten stream
velocities of preferably about 490 ft./min. (150 m/min)
and greater. To provide larger size particles and/or
particles other than in the glassy state one controls the
foregoing method parameters toward their opposing operable
extremes, such as lower quenchant speeds (e.g. about 500
rpm or about 145 ft./min. (442 m/min.)), larger size
stream, molten metal temperature much higher than the
melting point, and the like.
The employed liquid quenching fluid may be a pure
liquid, a solution, a liquified gas at higher speeds or a
solid-liquid dispersion or emulsion at lower speeds. The
quenching fluid may be inert and chemically unreactive
towards the molten material with which it is used, and
generally is so. ~.owever, the invention does not exclude
liquid quenching fluids, which may react with the
particularly employed molten material so long as such
1 160~09
reaction primarily is of a surface skin reaction-type or
of a coating of the particulates and is not significantly
deterimental to disruption and breaking up of the liquid
stream upon it contacting the rapidly moving centrifugally
disposed rotating liquid quenching fluid.
The choice of particular quenching fluid and its
temperature is made in relation to the particularly
employed molten material stream as well as other process
parameters, such as the molten stream's size and force
and angle of contact with the quenching fluid and also
as well as the depth or thickness of and movement speed
of the rapidly moving centrifugally disposed rotating
liquid quenching ~luid. Desirable qualities and
properties for the quenching fluid are that it possess a
high thermal capacity, be non toxic, be relatively non-
flammable, be of low cost, and the like. For example,
water is quite useful for streams of many molten materials
and with molten streams whose temperatures are as high as
2200F (1204C) and higher; likewise various lower
temperature aqueous salt (e.g. NaCl, MgC12, ZnCl2) brines
can be used with some molten materials; petroleum and
synthetic oils also are useful; liquified gases are
contemplated as useful; etc. Almost any liquid quenchant
or quenching fluid may be used so long as it can be placed
in the state of a rapidly moving centrifugally disposed
rotating wall-like liquid mass possessing such density and
kinetic movement force so as to disrupt and break up
the particularly employed molten stream of metal or alloy.
Particularly useful and preferred are the following Iiquid
quenchants for various molten materials: cold water or
mixture of brine and cold water for molten Fe, Ni, and
other non-reacting transition metal alloys; inert fluids
such as liquid helium for reactive materials; and oils
with varying quenching speeds for particles produced at
varying quench rates. Of course, the foregoing merely
l 160409
- 12 -
represent typical useful quenching fluids, and a variety
of alternative quench fluids also may be employed.
Although the molten stream, which is formed into
particulates, herein is described and illustrated by
specific examples with particularity as from a source
material of a metal or metal alloy through melting the
same, the invention should be and is considered operable
with any material possessing properties, in the molten
state at temperatures reasonably close to its melting
point, similar to those of molten metals. The molten
material should have, at a temperature within 25 percent
of its equilibrium melting point in K., the following
properties: a surface tension in the range of from 10 to
2,500 dynes/cm, a viscosity in the range of from 10 3 to
1 poise and reasonably discrete melting point (i.e. a
discontinuous temperature versus viscosity curve). The
present invention is deemed operable with most metals as
well as chemical compounds, and elements meeting the above
criteria. In addition, the present invention is operable
with metal alloys even where such alloys display a wide
temperature range between the first solidification of any
component within the alloy (the liquidus temperature) and
the temperature at which the lowest melting point com-
positions solidify (the solidus temperature) yielding a
completely solid material. For purposes of definition,
such an alloy would be "molten" only above the liquidus
temperature even though there is some molten material
present at a temperature between the liquidus and solidus
temperatures.
The molten stream, which is formed into particulates
by the invention's method, can be from melting by con-
ventional heating means of: a metal, for example, aluminum,
zinc, lead, tin, copper and the like; or from melting a
metal alloy, for example, a predominantly nickle alloy such
35 as Ni63Crl2Fe4B13 Sig, or Fe40Ni40P14B6~ and the like;
0~09
or from melting metastable alloy compositions, which are
known to be obtainable in the glassy or amorphous state,
for example those compositions taught in U.~. Patent No.
3,856,513 and in prior art mentioned and discussed in that
5 patent, as well as even other metastable alloy compositionG
apparently not hitherto prepared in a particulate amorphous
state, such as Mg70Zn30, Ta60Ir30Blo~ Ti60Ni3osi
Mo80~u1nP10~ etc.
As apparent from the drawings and descriptions of the
10 il~ustrated apparatus for carrying forth the method of the
invention, the molten stream traverses a limited distance
before contacting the rotating quenching fluid and thus
also has limited exposure to the atmosphere surrounding the
molten stream before breaking into particulates. Accord-
15 ingly the oxidation characteristics of many metals andalloys do not limit their operability with the present
invention. ~aterials known to be operable without the
need for complete oxidation protection include the metals
consisting essentially of iron, silver, nickel, tin, and
20 zinc. Where it is desired to provide the molten stream
with a particular atn~osphere, then this atmosphere can
be provided such as in the interior of containment vessel
31 of the FIG. 2 apparatus designated 30. The method
then can be carried out in an inert atmosphere or at
25 reduced pressure. If the molten material stream has a
significant vapor pressure, the composition and pressure
of the gas within the containment vessel can be manipulated
so as to reduce evaporation and maintain stream integrity
until the stream contacts quenchant. Also, although not
3n illustrated, in place of the illustrated melt vessel 18
disposed as illustrated in FIG. 2, one could employ other
means for heating and providing the molten material strea~
including placement within containment vessel 31 of the
melt vessel, or of a modified melt vessel (not illustrated),
35 adapted to utilize a heating means such as electron beam
heating. ~etals desirably employed with an atmosphere
l 160409
to reduce oxidation include those consisting essentially
of titanium, columbium, tantalum, zirconium, magnesium,
aluminum, and molybdenum.
For providing spherical particulates the molten stream
generally is of cylindrical cross section and issues from
a tapered tip having a tip orifice opening which is
cylindrical. Cylindrical tip orifice openings as small
as 0.005 in. (0.125mm.) diameter are useful so long as they
can be placed relatively close to the moving centrifugally
maintained moving wall of liquid quenchant. Cylindrical
tip orifice openings as large as 0.040 to 0.120 in. (1 mm.
to 3 mm.) and larger are useful for some stream com-
positions providing quenchant movement is of a high
enough velocity to break the molten stream into molten
globules or the like. Preferred are tip openings and
circular streams having a diameter between 0.005 in,
(0.125 mm.) and 0.040 in. (1 mm.). Tip orifice openings
and stream cross sections can be other than cylindrical.
Conventional m~terials are employed for construction
of useful apparatuses for practice of the invention's
method. For example, the ceramic melt vessel may be
fabricated of quartz, silica, zirconia, magnesium oxide,
beryllium oxide, boron nitride, and the like, with due
consideration to avoid reaction with the molten material
to be held therein as well as the temperature of the molten
ma~erial and pressure placed thereon to force molten
material from the tip orifice opening. The cup-shaped
element, which is rotated at high speed, generally is
fabricated of a metal, for example, stainless steel,
aluminum, molybdenum, copper, and the like. Because of
the high rotational forces to which this rotating element
is subjected, care must be used in its fabrication; its
construction material and fabrication must be selected
with regards to providing adequate strength to withstand
the forces encountered during usage; its fabrication
should include a very careful dynamic balancing so as to
~ 160~09
- 15 -
insure uniform rotation without vibration; and desirably
the employed entire apparatus is surrounded by protective
safety shields, and the like.
At the conclusion of a run and removing of the mix
of formed particulates and quenching fluid from the cup-
shaped element or drum, the quenching fluid i9 separated
by conventional means such as decanting, filtering,
centrifuging, washing, etc. from the particulates which
may be cleaned by washing, etc. and then separated by
conventional means into various shapes, sizes, and
classes of particulates. Useful for such separation are
conventional sieves, precision sieves, roll tables,
microparticle classifiers, etc.
BEST MODE OF CARRYING OUT THE INVENTION
The best mode presently known for carrying out the
invention is illustrated by the foregoing description of
the apparatuses in the drawings and their operation and
is demonstrated in the following illustrative examples.
However, since the examples are laboratory scale practices,
the full benefits and advantages to be derived upon scale
up to commercial practice and to commercial particulate
products are expected to be of much greater value.
IN THE EXAMPLES
In the illustrative examples, which follow, there
is employed a laboratory apparatus of the general
description and nature of that shown in FIG. 1. The cup-
shaped element of the employed apparatus is of aluminum,
has an internal diameter of about 13 inches (33.0 cm.), a
height of about 3-1/16 inches (7.78 cm.), and is capable
of containing liquid quenchant in amounts up to 2000 ml.
and more. The employed ceramic melt vessel is of quartz
or Vycor~ brand silica glass depending on the specific
material to be formed into particulates and is from a
tube, generally of about 1 or 2 in. (2.54 or 5.08 cm.)
~ 160409
- 16 -
diameter, which has been heat fabricated to close one end
and at its closed end to draw a tapered tip with a tip
orifice opening of the desired orifice opening size, with
a number of melt vessels being fabricated and available
for use with different tip orifice openings of from 0.005
to 0.03 in. (0.126 to 0.76 mm.). The top of this tube is
capable of being stoppered, or closed and unclosed, with
a stopper of appropriate material and through which stopper
closure there is a tube which from the melt vessel leads
to a gas pressure gauge and a tank source of supply of a
gas such as nitrogen, argon, or the like, whose pressure
is regulated by means of a valve. Melt temperature is
monitored by using a chromel-alumel thermocouple. The motor
means connected to the shaft, which centrally extends
downward from the cup, is an electrical motor of 0.5 H.P.
whose speed is variable and can be set, as desired, at a
steady speed by the electrical input thereto which
electrical input is regulated by a controller. The
induction coil heater for the ceramic melt vessel comprises
0.25 in. (0.64 cm.) copper tubing and a 30 KW induction
generator,
Procedurally the desired amount of liquid quenchant
is placed in the cup-shaped element and the element
rotated at a low speed (generally greater than 200 rpm)
adequate to immediately position the quenchant as a
centrifugally disposed ring of liquid clinging to the inner
wall of the cup-shaped element. A quantity of the
employed material (e.g. metal or alloy) to be formed into
par~iculates is placed in the silica or quartz melt vessel
which is positioned with its tip orifice opening at the
desired distance and angle from the centrifugally disposed
ring of liquid quenching fluid. A heating means, such as
an induction heater is activated to mel~ the metal or
alloy in the silica melt tube and to bring the molten
material to a desired temperature, frequently at least
about 200-300 F (93 to 149C) higher than its melting
1 ~60409
- 17 -
point. The cup-shaped element then is set in rotary
motion at the desired speed, frequently a speed of 1500 to
10,000 rpm. The desired gas pressure, e.g. 2-10 psi, is
imposed on the molten metal and molten metal flows as an
unbroken stream from the tip orifice opening to contact
the rapidly moving centrifugally disposed ring-like wall
of quenching fluid and upon such contact to be broken from
a stream into particulates some of which immediately enter
and remain in the quenchant and other particulates which
lQ within a very short distance enter the quenchant. Within
the quenchant, the particulates are subjected to extremely
rapid cooling of an order requisite to provide particulates
of a glassy or other metastable or crystalline form depend-
ing on the size of the particle which in turn depends on the
velocity of the quenching fluid and molten st~eam cross-
section.
EXAMPLE A
Greater than 99 percent pure tin powder is melted
in a melt vessel and brought to a temperature of 550F
(287.8C). Under an argon gas pressure of 5 psi the
molten tin is forced through a 0.014 in. (0.35 mm.) tip
orifice opening as a stream directed substantially
perpendicular (at 90 to the tangent, i.e. normal) to and
at a distance of between 3 to 4 in. ~7.6 to 10.2 cm.)
onto a centrifugally disposed wall of quenching fluid,
which is composed of 1000 ml. of a heavy duty automotive
vehicle petroleum oil (such as Mobil 10W40). The rapidly
moving centrifugally disposed wall of liquid oil is
maintained in its centrifugal disposition by rotation of
the cup-shaped element at 2100 rpm. After all the molten
tin in the melt vessel has been streamed into contact with
the moving oil quenchant, the run is stopped and a mixture
of particulates and oil are removed from the apparatus.
Oil is washed from the particulates with trichloroethylene
washes and the washed particulates air dried, e.g. in a
warm 150F (65.6C) oven, and then subsequently sieved
l 160409
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through a series of sieves (U.S. Sieve Series).
Particulates ~etained on the No. 50 screen are sub-
stantially all flakes with greater than 50 percenk by
weight of all particulates passing through No. 50. Those
passing through No. 50 and retained on No. 100 are a
mixture of flakes and powder, those passing through a No.
100 and retained on No. 230 are apparently all spherical
powder-like particulates, and those retained on a No. 325
are spherical powder-like particulates.
ExAMæLE B
Additional preparations are made of solid particulates
from molten tin. These preparations are made at a variety
of process parameters including: molten tin temperatures
of 900F. (482.2~C), 825F. (440.6C), and 850F (454.4C);
the molten tin under argon gas pressure of 5 psi.;tip
orifice openings of 0.014 in (0.36 mm.) and 0.015 in.
(0.38 mm.); stream distances from orifice openings to
moving centrifugally disposed wall of liquid quench fluid
of 5/8 in. (1.6 cm.) and about 1 in. (2.54 cm.); with
quench fluids of auto vehicle petroleum oil, water, and a
quench oil for metal heat treating, such as Houghton K-oil
which is of a mineral oil base containing an oxidation in-
hibitor and which meets Military Specification MIL-H-6875D;
rotating cup and quench fluid speeds of 1900, 2100, and 2500
rpm; and with molten tin streams contacting the quench fluid
in directions of substantially perpendicular to the tangent
of the moving centrifugally disposed wall of quenchant as
well as at an acute angle with the away movement of the
quenchant and at an acute angle with the approaching moving
quenchant.
In each of these runs solid particulates were prepared.
In runs at the close stream distance of 5/8 inch and also
at the molten stream acute angle with the approaching moving
quenchant, diff1culties were encountered in keeping tin
from solidifying in and clogging the tip opening so as to
be able to conduct runs of extended duration. A general
trend was noted at higher molten tin temperatures and at
1 160~0g
-- 19 --
the higher quenchant speeds of preparing greater yields
of particulates of -325 No. sieve sizes and of favoring
substantially spherical particulates being produced.
EXAMPLE C
Solid particulates are prepared from molten 2826
alloy, which consists essentially of Fe40Ni40P14B6- The
molten alloy at a temperature of about 2300F. (1260C)
is streamed from a 0.014 in. (0.356 mm.) diameter opening
for a distance of about 1 inch t2.54 cm.) at a direction
normal to and into about 2000 ml. of oil moving as a
centrifugally disposed wall of quenchant in the cup-shaped
element rotating at 2500 rpm.
EXAMPLE D
Solid particulates are prepared from molten lead of
a temperature of about 750F. (399C). The molten lead
is from a 0.015 in. (0.38 mm.) diameter orifice and is
streamed about 1 in. at an about perpendicular (i.e. normal)
direction into about 2000 ml. of water moving as a
centrifugally disposed wall of quenchant in the~cup-shaped
element rotating at about 2500 rpm. m e produced ~
particulates appear to have an oxide caating. ~ ; ;
EXAMPLE E `~
Solid particulates are prepared from a nickel-base
915 alloy, which consists essentially of Ni63Crl2Fe4B13S18. ;~
The molten alloy at a temperature of about 2200F. (1204C)
and under an argon gas pressure of 10 psi. is streamed
through a 0.`01 in. (0.25 mm.) diameter tip orifice opening
for about 1 in. (2.54 cm.) at about perpendicular direction
into about 1500 ml. of water moving as a centrifugally
disposed wall of quenchant in the cup-shaped element
rotating at about 2500 rpm. There is produced a mixture
of solid particulates of flakes, fibers, and non-spherical
to substantially spherical shape. Some fibers of about lp
.
~ 160~0g
- 20 -
diameter ar~ noted to have one enlaryed or bulbous-type
end. Some particulates are noted to be of a metallic
glassy structure and other particulates are noted to
possess crystalline structure.
EXAMPLE F
Additional preparations are made of solid particulates
from the same nickel-base alloy employed in Example E.
These preparations included the employing of 1000 ml. and
2000 ml. of water as the liquid quenchants. Other
preparations employed 2000 ml. of petroleum oil as the
liquid quenchant. With petroleum oil as the liquid
quench fluid and the molten nickel alloy stream directed
at about a 45 angle to the moving away centrifugally
disposed wall of oil quenchant, the produced particulates
were substantially all near spherical to spherical with
very little to no fiber particulates noted. With 1000 ml.
of water as the liquid quench fluid and the molten stream
from an 0.005 in. (0.127 mm.) orifice opening and 10 psi
pressure directed about perpendicular to the moving
centrifugally disposed wall of water, the size distribution
of the produced particulates is 1.6 percent by weight +50,
6.2 percent by weight -50 to +70, 16.6 percent by weight
-70 to +100, 66.7 percent by weight -100 to +230, 7.3 per-
cent by weight -23Q to +325, and 1.6 percent by weight
-325 (U.S. Sieve Series).
EXAMPLE G
Solid particulates are prepared from aluminum alloy
2024, which consists essentially in weight percent of 4.4%
Cu, 1.5% Mg, 0.6% Mn, and balance Al. The molten alloy at
a temperature of 1400F. (760C.) is streamed at about a
perpendicular direction into 2000 ml. of water moving as a
centrifugally disposed wall of quenchant in the cup-shaped
element rotating at about 2500 rpm. The produced
particulates predominantly are of irregular shape and
observed to be of very fine dendritic structure.
l 160409
- 21 -
As is apparent from the foregoing lllustrative
examples, solid particulates of flake, fiber, spherical
and irregular shapes and of various sizes can be prepared
from a diversity of materials in their molten state.
For example, water as the quenchant favors fiber and sphere
particulate formatlon, while oil as the quenchant favors
production of particulates predominantly spherical or near
spherical particulates. These shapes and sizes subse-
quently are separable and classifiable, as desired, into
various fractions of particular shape and/or range of
sizes. These particulate fractions find utility in many
applications, such as in powder metallurgical applications
wherein they can be consolidated by conventional
techniques into useful articles, or they can be used as
a feed stock powder for plasma spraying, or as elemental
or alloy powder for the prepaxation of alloys otherwise
difficult to made by conventional means, or fiber
particulates can be used in magnetic tapes, and the like.
The produced particulates and fractions thereof also
can be categorized into groups based on structure, namely
those exhibiting a crystalline state and those exhibiting
an amorphous state. The amorphous state is the non-
crystalline or glass phase and generally is obtainable by
an extremely rapid quenching technique. As is recognized
in the art, various physical and chemical properties,
which depend on atomic arrangement are uniquely different
for the crystalline and amorphous states. For many
applications the properties possessed by amorphous
particulates are desirable and useful. Generally
though one distinguishes between the two states by means
other than by their physical properties, such as their
strength and ductility and their magnetic and electrical
properties. X-ray diffraction measurements are most
often used to distinguish a crystalline from an amorphous
state. An amorphous substance reveals a diffraction
pattern with broad peaks, somewhat slmilar as observed in
l 160409
- 22 -
a liquid, while the crystalline state produces much more
sharper peaks in the diffraction pattern. Also it can be
noted that the cooling from a molten state to the amorphous
state resembles an almost continuous solidification over a
range of temperature without a discontinuous evolution of
a heat of fusion. On the other hand in proceeding to the
crystalline state, crystallization is a thermodynamic
first order transition and is associated with a heat of
~usion and a specific temperature. Thus, the metastable
amorphous state will convert to the crystalline form upon
heating to requisite sufficiently high temperature with
evolution of a heat of crystallization. In some instances
there are produced particulates which exhibit desirable
properties possessed by the amorphous state substance,
yet the substance still may be partially crystalline.
Generally the fraction or proportion of such a substance
that is partially crystalline can be estimated through
employment of X-ray or electron diffraction, electron
transmission microscopy,and thermal analysis upon
comparison of these measurements with comparable measure-
ments made of the completely crystalline and amorphous
states.
With reference to the preceding examples employing
Ni63Cr12Fe4Bl3Si8 alloy, it is known in the art that this
Ni-base alloy is a conventional brazing alloy which can be
rapidly solidified in amorphous form by a strip casting~
technique. In the preceding illustrative examples with
this alloy there were produced fibers and spherical
particulates. Mixtures of these two shapes are separated
and classified using a Bahco microparticIe classifier,
then the roll table, and then precision sieves to provide
narrow size fractions. For characterization purposes these
fractions then are subjected to optical metallaography, DSC
(Differentia: Scanning Colorimeter), and X-ray diffraction
examinations.
1 160~09
- 23 -
Etched micrographs of these Ni-alloy partlculates
of size 46-50~ are prepared and examined. In the case
of the fibers, optical metallography revealed no
structure indicating that the material is in the
amorphous form, but in the case of spherical particles,
while most are impervious to etching, a few do show
crystalline structure indicating some crystallinity.
Spherical particulates of size 88-89,u also show a
similar presence of a few particulates having crystalline
structure. It is possible that this presence of
particulates of both amorphous and crystalline structures
is explainable as resulting from an observed two different
quenching mechanisms -- one, those molten droplets which
formed from disruption of the molten stream remaining in
the moving centrifugally disposed wall of quenchant to
immediately rapidly cool and soIidify; and of two, those
molten droplets formed from the disruption of the molten
stream streaming slightly for a very short distance before
reentry into the moving centrifugally disposed wall of
quenchant to then rapidLy cool and solidify.
The just-mentioned size fractions of fiber and
spherical particulates from this Ni-base alloy also are
investigated by DSC using a Perkin Elmer DSC-2 to provide
thermograms thereof. In all instances for both fiber and
spherical particulates and for both size fractions there
was observed a distinct amorphous to crystalline trans-
formation peak, and for each namely Tx of 710K. The
46-50~ spherical particulates gave a AHx of 2.1 cal./gm.
and the 88-90~ spherical particles gave a ~Hx of 1.6
cal.~gm. ~Hx is the heat energy released during
crystallization.
An X-ray diffraction pattern is made of the spherical
particles of a 63-149~ size produced from this Ni-base
alloy. The pattern correlates with the optical metallog-
raphy observations of a mixture of amorphous with somecrystalline particulates with the pattern presenting a
l 160409
- 24 -
broad amorplous background and some sharp crystalline
peaks due to some crystalline particulates.
It is noteworthy that spherical particulates
produced from this Ni-base alloy of a size as large as
5 0.008 in. (0.12 mm.) dia. are produced in a metallic glassy
( phase.
Particulates produced in ~he preceding Exam~le
employing Al-base alloy (2024) also were examined. Under
optical metallographic techniques, the produced nearly
10 spherical particulates in an etched micrograph revealed a
very small grain size indicative of rapid quenching. The
micrograph also shows islands of dentritic structure,
indicating within the same particle that the cooling rates
had differed. The microstructure is the same as that
15 obtained by a Lebo-Grant splat quenching technique wherein
the stream of molten alloy impinges on a copper wall and
wherein they indicated attaining a cooling rate of 106K/sec.
DSC examination of 46-50~m size spherical particulates of
this Al-base alloy failed to reveal any tranformation from
20 the microcrysta~line phase to either solutionize or
precipitate when heated up to 500 C.
