U.S. patent number 3,655,360 [Application Number 04/879,610] was granted by the patent office on 1972-04-11 for metals and metal alloys and preparation thereof.
This patent grant is currently assigned to Chevron Research Company. Invention is credited to Robert H. Lindquist.
United States Patent |
3,655,360 |
Lindquist |
* April 11, 1972 |
METALS AND METAL ALLOYS AND PREPARATION THEREOF
Abstract
Process for preparing dispersion-hardened metals and metal
alloys, comprising forming a solution comprising metal halide
precursors, selected from fluorides, bromides and iodides, of the
continuous and dispersed phases of the final product, adding an
epoxy compound to said solutions whereby a gel comprising metal
hydroxides is formed, converting said metal hydroxides to oxides,
and reducing the oxide precursors of the continuous phase of the
final product, and products so prepared.
Inventors: |
Lindquist; Robert H. (Berkeley,
CA) |
Assignee: |
Chevron Research Company (San
Francisco, CA)
|
[*] Notice: |
The portion of the term of this patent
subsequent to July 29, 1986 has been disclaimed. |
Family
ID: |
25374497 |
Appl.
No.: |
04/879,610 |
Filed: |
November 24, 1969 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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796222 |
Feb 3, 1969 |
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582238 |
Sep 27, 1966 |
3458306 |
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Current U.S.
Class: |
419/19; 75/363;
75/956 |
Current CPC
Class: |
C22C
1/1026 (20130101); Y10S 75/956 (20130101) |
Current International
Class: |
C22C
1/10 (20060101); B22f 009/00 () |
Field of
Search: |
;75/.5AC |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rutledge; L. Dewayne
Assistant Examiner: Stallard; W. W.
Parent Case Text
RELATED APPLICATIONS
This application is a continuation-in-part of Robert H. Lindquist
application Ser. No. 796,222 for "Preparation of Metals and Metal
Alloys," filed Feb. 3, 1969, which in turn is a
continuation-in-part of Robert H. Lindquist application Ser. No.
582,238 for "Preparation of Metals and Metal Alloys," filed Sept.
27, 1966, now U.S. Pat. No. 3,458,306.
Claims
What is claimed is:
1. A process for preparing a material comprising a continuous phase
selected from metals and metal alloys surrounding a dispersed phase
of refractory metal oxide particles, which comprises:
A. forming a solution comprising:
a. at least one metal halide selected from the halides of metals
which in the oxide form are reducible to the metal form in hydrogen
at a temperature in the range 600.degree. to 1,800.degree. F., and
halides being further selected from metal fluorides, bromides and
iodides,
b. at least one metal halide selected from the halides of metals
the oxides of which are not reducible in hydrogen at a temperature
in the range 600.degree. to 1,800.degree. F., said halides being
further selected from metal fluorides, bromides and iodides,
and
c. a lower alkanol;
B. adding to said solution an epoxy compound, whereby the
components of said solution and said epoxy compound react to form a
mixture comprising halohydrins and a gel containing metal
hydroxides;
C. separating said gel from said halohydrins;
D. converting said metal hydroxides in said gel to metal
oxides;
E. subjecting the resulting metal oxide-containing material to a
reducing treatment whereby at least one of said metal oxides is
reduced to metal without reduction of at least one other of said
metal oxides;
F. compacting the resulting metal-containing material.
2. A process for preparing a material comprising a continuous phase
selected from metals and metal alloys surrounding a dispersed phase
of refractory metal oxide particles, which comprises:
A. forming a solution comprising:
a. at least one metal halide selected from the halides of metals
which in the oxide form are reducible to the metal form in hydrogen
at a temperature in the range 600.degree. to 1,800.degree. F., the
metal cation of said metal halide being present in said solution in
an amount of at least 45 weight percent of the total metal cations
in said solution, said halide being further selected from metal
fluorides, bromides and iodides,
b. at least one metal halide selected from the halides of metals
the oxides of which are not reducible in hydrogen at a temperature
in the range 600.degree. to 1,800.degree. F., the metal cation of
said metal halide being present in said solution in an amount of
less than 55 weight percent of the total metal cations in said
solution, said halide being further selected from metal fluorides,
bromides and iodides, and
c. a lower alkanol;
B. adding to said solution an epoxy compound selected from the
group consisting of lower alkylene oxides and epihalohydrins,
whereby a gel comprising metal hydroxides is formed;
C. converting said metal hydroxides to oxides, including oxides
reducible in hydrogen at 600.degree. to 1,800.degree. F., and metal
oxides not so reducible;
D. subjecting the resulting metal oxide-containing material to a
reducing treatment at a temperature in the range 600.degree. to
1,800.degree. F.
3. In a process for producing a composition comprising a continuous
phase comprising a material selected from the group consisting of
iron, cobalt, nickel and alloys of at least two of these metals
with each other, said composition further comprising a dispersed
phase comprising particles of a refractory metal oxide, the
improvement which comprises:
A. forming a solution comprising:
a. at least one metal halide selected from the group consisting of
halides of iron, cobalt, and nickel, said halides being further
selected from fluorides, bromides and iodides, the metal cation of
said metal halide being present in said solution in an amount of at
least 45 weight percent of the total metal cations in said
solution, and
b. at least one metal halide selected from the halides of Y, Ca,
La, Be, Th, Mg, U, Hf, Ce, Al, Zr, Ba, Ti, Si, Ta, V, Nb and Cr,
said halides being further selected from fluorides, bromides and
iodides, the metal cation of said metal halide being present in
said solution in an amount of less than 55 weight percent of the
total metal cations in said solution; and
c. a lower alkanol;
B. adding to said solution an epoxy compound selected from the
group consisting of lower alkylene oxides and epihalohydrins,
whereby the components of said solution and said epoxy compound
react to form a mixture comprising halohydrins and a gel containing
at least one metal hydroxide;
C. subjecting said gel to a calcination treatment, whereby said
metal hydroxides are converted to metal oxides;
D. subjecting the resulting metal oxide-containing material to a
reducing treatment, whereby all iron, cobalt and nickel oxides
present are reduced to the corresponding metals, without reduction
of at least one other oxide present.
Description
INTRODUCTION
This invention relates to production of metals and metal alloys,
more particularly to production of materials selected from the
group consisting of iron, cobalt, nickel, alloys of at least two of
these metals with each other, and alloys of at least one of these
metals with at least one of certain other metals. In preferred
embodiments of the invention, the metals and alloys are produced
containing particles of a refractory oxide of a dissimilar material
imparting improved characteristics, particularly in
high-temperature service, to the metals and alloys.
PRIOR ART
Various methods are known for producing metals and metal alloys in
which particles of a refractory oxide of a different metal are
incorporated to improve various characteristics of the metals and
metal alloys. The incorporation of the refractory oxide particles
is known as dispersion strengthening, the metal or metal alloy is
referred to as the continuous phase, and the refractory oxide
particles are referred to as the dispersed phase or filler.
The dispersed phase generally is incorporated in the continuous
phase by: (a) selecting as the dispersed phase particles of a metal
oxide material that has a high free energy of formation, .DELTA.T,
and therefore that is resistant to reduction to the metal in
hydrogen; (b) forming around the dispersed phase a continuous phase
of one or more metal compounds easily reducible to metal in
hydrogen, (c) subjecting the resulting mass to a reducing treatment
in hydrogen, whereby the continuous phase is converted to metal
form without concurrent reduction to the metal of the dispersed
oxide phase, and (d) pressing the resulting powdery mass under high
pressure into a dense, coherent "compact," which can be further
worked, for example rolled, extruded or machined.
Various theories and models, sometimes conflicting, have been
proposed to predict and/or explain the improvement in strength and
other characteristics of metals and alloys that results from the
presence therein of a dispersed phase of refractory oxide
particles. It is not a present purpose to present any such theories
or models, because whatever the correct theory or model may be,
there is no dispute that the dispersed phase results in improved
characteristics of metals and metal alloys, particularly improved
strength characteristics, especially in high-temperature service.
Prior art theories and models, and methods of preparation of
dispersion-strengthened metals and metal alloys, are well set forth
in many publications, including the following articles and papers
and U.S. patents:
A. articles and Papers
1. "A theory of Dispersion Strengthening," paper by F. V. Lenel and
G. S. Ansell, presented at 1960 International Powder Metallurgy
Conference, pp. 267-306.
2. "New Design Data on TD Nickel," Robert E. Stuart, Materials in
Design Engineering, August 1963, pp. 81-85.
3. "Dispersion Strengthening Models," G. S. Ansell and J. S.
Hirschhorn, ACTA Metallurgica, Vol. 13, 1965, pp. 572-576.
4. "Creep of Thoriated Nickel above and below 0.5 T.sub.m," B. A.
Wilcox and A. H. Clauer, Transactions of the Metallurgical Society
of AIME, Vol. 236, April 1966, pp. 570-580.
5. "The Structure of Nickel electrodeposited with Alumina
Particles," E. Gillam, K. M. McVie and M. Phillips, Journal of the
Institute of Metals, Vol. 94, pp. 228-229.
B. u.s. pats.
1. Alexander et al. No. 2,972,529
2. Alexander et al. No. 3,019,103
3. Grant et al. No. 3,069,759
4. Grant et al. No. 3,176,386
DISADVANTAGES OF VARIOUS PRIOR ART METHODS OF PRODUCING DISPERSION
STRENGTHENED METALS AND METAL ALLOYS
Prior art methods of producing dispersion strengthened metals and
metal alloys involve numerous disadvantages. In a typical prior art
method of producing thoria dispersed nickel, particles of thoria
are mixed in an aqueous solution of nickel nitrate, and the nickel
nitrate is precipitated with sodium hydroxide during vigorous
agitation, thus depositing nickel hydroxide around the thoria
particles. The resulting precipitate must be filtered and washed to
remove sodium nitrate. The precipitate is then dried to convert the
nickel hydroxide to nickel oxide. The nickel oxide is then reduced
to nickel metal. The nickel metal is in the form of a powder
containing dispersed thoria particles. The powder may be
fabricated, as by hot pressing, extrusion, etc. In such a process,
these disadvantages exist:
a. No control exists over the size of the dispersed oxide particles
during conduct of the process.
b. Particles size must be selected in advance, from a range of
sizes that is limited to sizes producible by available
technology.
c. Selective precipitation and selective crystallization,
particularly in the case of metal alloy preparation, are caused by
non-homogeneity of original mixture, and are serious problems that
can be controlled only in part by vigorous agitation. Final product
quality is drastically affected by minor deviations from uniformity
of dispersion of the oxide particles in the original mixture.
d. Soluble salts such as sodium nitrate must be essentially
completely removed by washing, because such contaminants adversely
affect final product quality. It is known that such complete
removal is extremely difficult.
OBJECTS
In view of the foregoing, it is an object of the present invention
to provide a process for producing metals and metal alloys from
metal salts, and particularly for producing metals and metal alloys
in a continuous phase containing a dispersed phase of refractory
metal oxide particles, that avoids the aforesaid disadvantages.
It is a further object of the present invention to provide, in such
a process for producing dispersion strengthened metals and metal
alloys, means for controlling, during conduct of the process,
particle size of the continuous phase metal or alloy, as well as
dispersed oxide particle size.
STATEMENT OF INVENTION
In accordance with a first embodiment of the present invention,
there is provided a process for producing metals and metal alloys
which comprises:
A. Forming a solution comprising:
a. at least one metal halide selected from the halides of metals
which in the oxide form are reducible to the metal form in hydrogen
at a temperature in the range 600.degree. to 1,800.degree. F., said
halides being further selected from metal fluorides, bromides and
iodides,
b. at least one metal halide selected from the halides of metals
the oxides of which are not reducible in hydrogen at a temperature
in the range 600.degree. to 1,800.degree. F., said halides being
further selected from metal fluorides, bromides and iodides,
and
c. a lower alkanol;
B. Adding to said solution an epoxy compound, whereby the
components of said solution and said epoxy compound react to form a
mixture comprising halohydrins and a gel containing at least one
metal hydroxide;
C. Separating said gel from said halohydrins;
D. Converting said metal hydroxide in said gel to a metal
oxide;
E. Reducing said metal oxide to metal; and
F. Compacting said metal, preferably to a density at least 90
percent of the theoretical density.
In accordance with a second embodiment of the present invention,
there is provided a process for preparing a material comprising a
continuous phase selected from metals and metal alloys surrounding
a dispersed phase of refractory metal oxide particles, which
comprises:
A. Forming a solution comprising:
a. at least one metal halide selected from the halides of metals
which in the oxide form are reducible to the metal form in hydrogen
at a temperature in the range 600.degree. to 1,800.degree. F., the
metal cation of said metal halide being present in said solution in
an amount of at least 45, preferably at least 70, weight percent of
the total metal cations in said solution, said halide being further
selected from metal fluorides, bromides and iodides,
b. at least one metal halide selected from the halides of metals
the oxides of which are not reducible in hydrogen at a temperature
in the range 600.degree. to 1,800.degree. F., the metal cation of
said metal halide being present in said solution in an amount of
less than 55, preferably less than 30, weight percent of the total
metal cations in said solution, said halide being further selected
from metal fluorides, bromides and iodides, and
c. a lower alkanol;
B. Adding to said solution an epoxy compound selected from the
group consisting of lower alkylene oxides and epihalohydrins,
whereby a gel comprising metal hydroxides is formed;
C. Converting said metal hydroxides to oxides, including metal
oxides reducible in hydrogen at 600.degree. to 1,800.degree. F.,
and metal oxides not so reducible; and
D. Subjecting the resulting metal oxide-containing material to a
reducing treatment, preferably in hydrogen, at a temperature in the
range 600.degree. to 1,800.degree. F.
The metals which in the oxide form are reducible to the metal form
in hydrogen at a temperature in the range 600.degree. to
1,800.degree. F. include Ni, Co, Fe, Cu, Cd, Tl, Ge, Sn, Pb, Bi,
Mo, W, Re and In.
The metals the oxides of which are not reducible in hydrogen at a
temperature in the range 600.degree. to 1,800.degree. F. include Y,
Ca, La, Be, Th, Mg, U, Hf, Ce, Al, Zr, Ba, Ti, Si, Ta, V, Nb and
Cr.
In accordance with a third, and preferred, embodiment of the
present invention, there is provided, in a process for producing a
composition comprising a continuous phase comprising a material
selected from the group consisting of iron, cobalt, nickel and
alloys of at least two of these metals with each other, said
composition further comprising a dispersed phase comprising
particles of a refractory metal oxide, the improvement which
comprises:
A. Forming a solution comprising:
a. at least one metal halide selected from the group consisting of
halides of iron, cobalt, and nickel, said halides being further
selected from fluorides, bromides and iodides, the metal cation of
said metal halide present in said solution in an amount of at least
45, preferably at least 70, weight percent of the total metal
cations in said solution, and
b. at least one metal halide selected from the halides of Y, Ca,
La, Be, Th, Mg, U, Hf, Ce, Al, Zr, Ba, Ti, Si, Ta, V, Nb and Cr,
said halides being further selected from fluorides, bromides and
iodides, the metal cation of said metal halide being present in
said solution in an amount of less than 55, preferably less than
30, weight percent of the total metal cations in said solution;
and
c. a lower alkanol;
B. Adding to said solution an epoxy compound selected from the
group consisting of lower alkylene oxides and epihalohydrins,
whereby the components of said solution and said epoxy compound
react to form a mixture comprising halohydrins and a gel containing
at least one metal hydroxide;
C. Subjecting said gel to a calcination treatment, whereby said
metal hydroxides are converted to metal oxides;
D. Subjecting the resulting metal oxide-containing material to a
reducing treatment, whereby all iron, cobalt and nickel oxides
present are reduced to the corresponding metals, without reduction
of at least one other oxide present.
In accordance with a fourth embodiment of the present invention,
there is provided a material comprising a continuous phase selected
from metals and metal alloys surrounding a dispersed phase of
refractory metal oxide particles, said particles being 0.005 to 1.0
micron in diameter and having an interparticle spacing of 0.01 to
1.0 micron, said material being prepared by any of the first three
embodiments above.
In accordance with a fifth embodiment of the present invention
there is provided a composition comprising a continuous phase
selected from metals and metal alloys surrounding a dispersed phase
of refractory metal oxide particles, said particles being 0.005 to
1.0 micron in diameter and having an interparticle spacing of 0.01
to 1.0 micron, said material being prepared by any of the first
three embodiments above.
The epoxy compound used in the process of the present invention may
be any epoxy compound that will react at a reasonable rate with the
anion of the metal salt or metal salts present. The epoxy compound
preferably is a lower alkylene oxide or an epihalohydrin. Said
lower alkylene oxide may be, for example, ethylene oxide, propylene
oxide or butylene oxide.
The lower alkanol used in the process of the present invention may
be any lower alkanol, including methanol, ethanol, 1-propanol,
2-propanol, 1-butanol, 2-butanol, 2-methyl-2-propanol, and
2-methyl-1-propanol.
In the process of the present invention a mixture, comprising
halohydrins and a metal hydroxide-containing gel, results from the
addition of an epoxy compound to the starting solution. Upon
drying, this mixture conveniently releases the halohydrins, which
vaporize off easily. Accordingly, no washing or other contaminant
removal procedures are required.
EXAMPLES
The following examples, although using metal chlorides, illustrate
how the process of the present invention may be carried out using
fluorides, bromides and iodides, which halides produce similar
results.
Example 1
a solution of the following composition was prepared:
1,270 g. NiCl.sub.2.sup. . 6H.sub.2 0 6.4 g. AlCl.sub.3.sup. .
6H.sub.2 0 2 liters MeOH
a 1,500 cc. quantity of propylene oxide was added to the solution
at room temperature. In 40 minutes the resulting mixture had set up
into a gel.
Approximately 95 weight percent of said gel was subjected to a
calcination treatment in an oxygen-containing atmosphere, as
follows:
a. 4 hours in air at 800.degree. F., then
b. 4 hours in 0.sub.2 at 1,000.degree. F.
The material resulting from the calcination treatment was a crumbly
or powdery mass. It was subjected to a reducing treatment in an
ebullating bed reactor, to reduce the nickel oxide portion thereof
to nickel metal, as follows:
a. 1 hour in H.sub.2 at 600.degree. F., then
b. 2 hours in H.sub.2 at 800.degree. F., then
c. 2 hours in H.sub.2 at 1,000.degree. F., then
d. 2 hours in H.sub.2 at 1,450.degree. F.
The ebullating bed reactor consisted of an upright quartz tube
containing at the base a fritted quartz disc through which the
hydrogen passed and caused the powder to bubble up or ebullate into
the space above the disc, thereby preventing appreciable powder
sintering during the reduction reaction, which would otherwise
occur, particularly at temperatures above about 1000.degree. F.
The material resulting from the reducing treatment was a powder,
which was found to weigh 320 grams, and to consist essentially of
98 weight percent nickel metal and 2 weight percent Al.sub.2
0.sub.3.
A portion of the nickel-Al.sub.2 0.sub.3 powder was hot pressed to
a cylindrically shaped compact having a diameter of 11/2 inches and
a thickness of one-fourth inch, in a graphite die under a low
pressure of hydrogen for one-half hour at a temperature of
1,100.degree. C. and a pressure of 3,500 psig. The resulting
cylindrical compact was rolled to lower its thickness 10 percent,
and was then annealed in hydrogen at 1,100.degree. C. The
so-annealed compact could be cold rolled to a thickness of 0.050
inch without further annealing, and this was done. From the
resulting 0.050-inch-thick material, two elongated tensile strength
specimens were machined.
Said two tensile strength specimens were tested for tensile
strength at elevated temperature, in a 10,000-pound capacity
tensile test machine, at a cross-head speed of 0.020 inches per
minute, after the specimens had been heated to a stable temperature
of 2,200.degree. F. in a wire wound furnace for about 5 hours.
Tension was applied by the machine pull rods to each specimen via
dispersion hardened nickel pins inserted in holes near each end of
the specimen.
The results of said tensile strength tests were:
First Second specimen specimen Percent elongation of 1-in. gage
length of specimen 1.0 - Ultimate tensile strength, p.s.i. 5,270
4,000
Example 2
A solution of the following composition was prepared:
1,270 g. NiCl.sub.2.sup. . 6H.sub.2 0 12.8 g. AlCl.sub.3.sup. .
6H.sub.2 0 2 liters MeOH
a 1,500 cc. quantity of propylene oxide was added to the solution
at room temperature. In 40 minutes the resulting mixture had set up
into a gel.
Approximately 95 weight percent of said gel was subjected to the
same calcination treatment as in Example 1. The material resulting
from the calcination treatment was subjected to the same reducing
treatment as in Example 1.
The material resulting from the reducing treatment was a powder,
which was found to weigh 320 grams, and to consist essentially of
96 weight percent nickel metal and 4 weight percent Al.sub.2
0.sub.3.
A portion of the nickel-Al.sub.2 0.sub.3 powder was hot pressed,
rolled, annealed, further rolled, and machined to produce an
elongated tensile strength specimen, all exactly according to the
procedure recited in Example 1.
Said tensile strength specimen was tested for tensile strength at
elevated temperature, exactly according to the procedure used in
Example 1.
The results of said tensile strength test were:
Percent elongation of 1-in. gage length of specimen 1.6 Ultimate
tensile strength, p.s.i. 2510
Example 3
A solution of the following composition was prepared:
1,200 g. NiCl.sub.2.sup. . 6H.sub.2 O 1,875 liters MeOH
An 1,100 cc. quantity of propylene oxide was added to the solution
at room temperature. The resulting mixture set up into a gel, which
was dried 48 hours at room temperature, then 72 hours at
150.degree. F.
Approximately 95 weight percent of said gel was subjected to the
same calcination treatment as in Example 1. The material resulting
from the calcination treatment was subjected to the same reducing
treatment as in Example 1.
The material resulting from the reducing treatment was a powder,
which was found to weigh 300 grams, and to consist essentially of
nickel metal.
A portion of the nickel metal powder was hot pressed, rolled,
annealed, further rolled, and machined to produce two elongated
tensile strength specimens, all exactly according to the procedure
recited in Example 1.
Said two tensile strength specimens were tested for tensile
strength at elevated temperature, exactly according to the
procedure used in Example 1.
The results of said tensile strength tests were:
First Second specimen specimen Percent elongation of 1-in. gage
length of specimen 4.6 11.0 Ultimate tensile strength, p.s.i. 1,480
2,500
Example 4
A solution of the following composition was prepared:
2,540 g. NiCl.sub.2.sup. . 6H.sub.2 0 10.0 g. ThCl.sub.2 4 liters
MeOH
A 1,060 ml. quantity of propylene oxide was added to the solution
at room temperature. The resulting mixture set up into a gel within
1 hour.
Approximately 95 weight percent of said gel was subjected to a
calcination treatment in air for 6 hours at 1,100.degree. F.
The material resulting from the calcination treatment was subjected
to the same reducing treatment as in Example 1.
The material resulting from the reducing treatment was a powder,
which was found to weigh 600 grams, and to consist essentially of
98 weight percent nickel metal and 2 weight percent Th0.sub.2.
The Th0.sub.2 in said material was determined by electron
microscope examination to be in the form of particles having an
average diameter of 200 Angstroms.
A portion of the nickel-Th0.sub.2 powder was hot pressed, rolled,
annealed, further rolled, and machined to produce an elongated
tensile strength specimen, all exactly according to the procedure
recited in Example 1.
Said tensile strength specimen was tested for tensile strength at
elevated temperature, exactly according to the procedure used in
Example 1.
The results of said tensile strength tests were:
Percent elongation of 1-in. gage length of specimen 2.5 Ultimate
tensile strength, p.s.i. 3800
Example 5
In a manner similar to that set forth in Examples 1-4, these
further metal-dispersed oxide specimens were prepared: ##SPC1##
Example 6
In a manner similar to that set forth in Examples 1-4, these
further metal alloy-dispersed oxide compositions were prepared:
##SPC2##
PROCESS CONDITIONS AND PARTICLE SIZES
The gel formation step of the present process may be conducted at
ambient to slightly elevated temperatures.
The desired particle size for the dispersed refractory metal oxide
component in the final product, when dispersion hardened metals or
metal alloys are produced by the present process, is 0.005 to 0.1
micron in diameter. Contrary to prior art processes, this particle
size varies as a function of process conditions, thereby providing
great flexibility to the process. The size of the dispersed
refractory metal oxide particles is a function of the temperature
during the calcination step, and the length of time the step is
conducted. The temperature is in the general range 800.degree. to
2,400.degree. F., with smaller particles resulting from the use of
lower temperatures and shorter periods. Temperatures should be
chosen with regard to the particle size desired and the melting
points of the materials used. When operating within the ranges set
forth herein for proportions of ingredients, calcination
temperatures, etc., the dispersed oxide particles in the final
product will be extremely uniformly dispersed, and will have an
interparticle spacing of 0.01 to 1.0 micron.
The grain size of the metal and metal alloy continuous phases of
the products produced by the process of the present invention is a
function of the temperature during the reduction step, and the
length of time the step is conducted. The temperature is in the
general range 600.degree. to 1,800.degree. F., with smaller grain
sizes resulting from the use of lower temperatures and shorter
periods. A preferred temperature-time combination is 600.degree. to
1,600.degree. F. for not substantially longer than necessary for
reduction reactions to be completed. A gradual increase in
temperature from a temperature in the range of about 600.degree. to
800.degree. F. to a higher temperature will provide these
advantages: (a) much of the reduction will occur at lower
temperatures, which contribute to a fine-grained final product; (b)
the subsequent higher temperatures will shorten the time necessary
for completion of the reduction reactions, and a minimal time at a
given temperature also contributes to a fine-grained final product;
and (c) the length of time the reduction step is conducted at
temperatures above 1,000.degree. F., where care must be taken to
avoid powder sintering, can be minimized.
Exceptionally fine-grained metal and metal alloy continuous phases
can be obtained in the products produced by the process of the
present invention. Further, it is well known that a grain growth
phenomenon occurs in conventional dispersion hardened metal and
metal alloy shaped materials during stressing of the materials,
particularly at elevated temperatures. Dispersion hardened metal
and metal alloy shaped materials made from products of the present
process show a markedly reduced grain growth, compared with the
conventional materials, probably due in large part to the excellent
and uniform dispersion of the dispersed oxide phase. Grain
diameters for the continuous metal phase of shaped materials made
from products of the present process have been found to be 10-20
microns after tensile strength tests, compared with grain diameters
of 300 to 500 microns for conventional dispersion hardened shapes
of the same composition after the same tensile strength tests.
Recrystallization of conventional shaped dispersion strengthened
materials after extensive cold rolling, resulting in coarse grain
size, is a known problem. The shaped materials made from products
of the present process have demonstrated superior resistance to
this recrystallization phenomenon, compared with similar prior art
materials.
PROPORTIONS OF INGREDIENTS
The present process will be found to be most highly effective for
producing high-quality metals and alloys when: (1) total weight of
the metal halide starting materials is 15 to 40 percent, preferably
20 to 30 percent, of the weight of the lower alkanol; and (2) the
mols of epoxy compound used per mol of halide ion is 1.1 to 2.0,
preferably 1.4 to 1.8.
It is highly desirable that water be present in the starting
solution in the present process, either in the form of free water
or water of hydration. Most desirably, 2 to 6 mols of water will be
present per mol of halide ion.
When producing dispersion hardened metals or metal alloys, the
final product after the reduction step preferably will consist of
80 to 99.5 weight percent metal or metal alloy and 20 to 0.5 weight
percent dispersed refractory metal oxide. Those skilled in the art
upon reading the present specification will be able to produce
products of this or any desired weight ratio of metal or metal
alloy to dispersed metal oxide that is obtainable by observing the
requirement that the metal cation of the metal halide precursor of
the metal or metal alloy of the continuous phase is present in the
starting solution in an amount of at least 45, preferably at least
70, weight percent of the total metal cations present in that
solution. If more than 30 weight percent of the metal cations in
the starting solution were metal cations of the metal halide
precursor of the metal oxide dispersed phase of the final product,
that product would have inadequate ductility compared with the
products of the present process. However, for applications in which
a somewhat lower ductility can be tolerated, other advantages may
be achieved when up to about 55 weight percent of the metal cations
in the starting solution are metal cations of the metal halide
precursor of the metal oxide dispersed phase of the final product.
A final product comprising alumina dispersed in copper is a useful
example.
The proportions of the various ingredients are varied within the
foregoing ranges as necessary to produce the best product with the
particular ingredients used. The best product will be obtained when
a clear gel is produced in the gelation step, without accompanying
precipitation. With this guide, and with the foregoing ranges as
guides, those skilled in the art may determine optimum proportions
for the particular ingredients being used.
REDUCTION STEP
The temperatures used in the step of reducing the oxide of the
continuous phase material have been set forth above. The reduction
step may be carried out in a stream of hydrogen, with care being
taken to prevent problems that can be caused by localized
overheating, leading to temperature runaways and liquid metal
formation, and also to prevent sintering of the metal oxide
particles of the dispersed phase. Such problems can be prevented by
use of the ebullating bed technique previously described and by
taking care to maintain temperatures below the sintering
temperature of the metal oxide particles. Further aids in achieving
this protection include addition of hydrogen no faster than
necessary to maintain an ebullating bed, when an ebullating bed is
used, and dilution of the hydrogen with an inert gas such as
nitrogen, as described in connection with the reduction step in
U.S. Pat. No. 3,019,103. The extent of reduction necessary has been
discussed previously, and in this connection the oxygen content of
the product set forth in connection with the reduction step in U.S.
Pat. No. 3,019,103 is applicable.
SINTERING THE REDUCED PRODUCT
Although not in all events necessary, particularly in small-scale
operations, the reduced product may be sintered as described in
U.S. Pat. No. 3,019,103.
COMPACTING AND WORKING THE PRODUCT
The product of the present process, in the form of a powder, may be
readily compacted, and the discussion in this connection in U.S.
Pat. No. 3,019,103 is applicable. The powder product of the present
process preferably is used by compacting it, preferably to a
density at least 90 percent, and more preferably at least 95
percent, of the theoretical density. The resulting compact
preferably is thermomechanically worked and shaped into a desired
material of construction.
It is well known that further working of compacted metallic
powders, particularly those containing a dispersed metal oxide
phase, greatly enhances tensile strength and other desirable
properties of the final shaped products. Those skilled in the art
have available a number of combinations of conventional steps of
thermomechanical working that are applicable to improvement of
properties of compacts prepared from powders produced by the
process of the present invention. Such further thermomechanical
working treatments would greatly increase the tensile strengths of
the materials given in the examples in the present application, as
well as further enhancing other properties such as creep
resistance. The further thermomechanical working treatments
probably effectively develop an optimum and complex dislocation
stopping network comprising dispersed oxide particles, grain
boundaries and sub-boundaries, and dislocation tangles.
SUMMARY OF ADVANTAGES
From the foregoing, it may be seen that the advantages of the
process of the present invention, over prior art processes for
producing metals and metal alloys, particularly dispersion
strengthened metals and metal alloys, include:
a. Control may be exercised over grain size of the continuous phase
metal or metal alloy.
b. Control may be exercised over particle size of the dispersed
phase metal oxide.
c. Higher quality materials, particularly metal alloys, are more
easily produced, because all components are homogeneously dispersed
in the original solution, and therefore in the subsequent gel.
d. A volatile organic material -- an epoxy compound -- is used to
cause a gel to form, rather than causing precipitation by using a
metal hydroxide or other basic hydroxide that leaves an impurity
that must be removed by washing after the precipitation is
completed. The undesired components of the epoxy compound vaporize
off as halohydrins, leaving no contaminant removal problem.
e. No washing facilities are required.
f. Metal halide starting materials are available at low cost
compared with many prior art starting materials.
It may also be seen that the process of the present invention
produces materials, particularly dispersion hardened metals and
metal alloys, which may be formed into shapes having at least the
following advantages, particularly under stress at elevated
temperatures:
a. Superior resistance to creep, occurring over relatively short
periods.
b. Superior resistance to fatigue, occurring over relatively long
periods.
c. Superior resistance to grain growth in the continuous phase.
d. Superior resistance to recrystallization.
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