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Патент USA US3027342

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March 27, 1962
K- H- J- MEDIN
3,027,332
HEAT RESISTING MATERIALS AND METHODS FOR THEIR MANUFACTURE
Filed Nov. 8, 1960
I0 Log
specific resistance
in units of nmmZ/m
To infinity and non-conducting
0 lb 20 5'0 4'0 50 60 7'0 250 96 I00 wi "/0 SiOz
I00 90 so 70 so so 40 30 20 IO
0
wt "4, MoSiz
INVENTOR.
KARL HERBERT JOACHIM MEDIN
ATTORNEYS.
United States Patent 0
1
3,027,332
Patented Mar. 27, 1962
2
and/or oxides or other rare earth metals.
3 027,332
HEAT RESISTING MATERIALS AND METHODS
FOR THEIR MANUFACTURE
The oxide
component may also contain small quantities of oxides
of the metal atoms included in the silicide component.
Karl Herbert Joachim Merlin, Lidingo, Sweden, assignor
to Aktieholaget Kanthal, Hallstahammar, Sweden, a
The silicide component consists of one or more silicides
of the average formula MSix in which M is one or more
which are silicides and oxides, and it further concerns
The metals W and Nb are less advantageous and more
corporation of Sweden
Filed Nov. 8, 1960, Ser. No. 67,988
Claims priority, application Sweden June 10, 1953
of the metal atoms Mo, Cr, V, Ti, Zr and Ta and at
being from 0.6 to 2. The three remaining metals of the so
called transition metals in groups IV, V and VI of the
Claims. (Cl. 252-520)
10 periodic system, i.e. W, Nb and Hf, afford great similari—
ties with Mo, Ta and Zr respectively in that the properties
This application is a continuation-in-part of the applica
of the material will not be considerably affected if they
tion Serial No. 657,058, ?led on May 6, 1957, and being
are included amongst the other metal atoms. However,
a continuation-in-part of the application Serial No. 388,—
the metal Hf is very expensive and di?icult to obtain so
444, ?led on October 26, 1953, now abandoned, and re
that it would scarcely be a practical proposition to use it.
lates to heat resisting materials the chief constituents of
powder metallurgical processes for manufacturing such
expensive than Mo and Ta respectively. However, unless
materials.
stated to the contrary, whenever Mo, Ta and Zr are
Such materials must have a high degree of resistance
mentioned, also W, Nb and Hf respectively may be in
to oxidation which necessitates a relatively low porosity. 20 cluded. In the oxide component the silica content may
The materials must have sufficient mechanical strength and
be from 1 to 60% by weight of the material and, if
not be unduly brittle in order to permit normal handling
' there is any other oxide or oxides, this or these respec
at room temperature and in order to withstand conven~
tively may constitute totally 0 to 60% by weight of the
tional service conditions. As will be hereinafter de
material.
scribed, the foregoing characteristics of the materials will 25
It is a known fact that certain metal ions, particularly
vary with the compositions thereof.
_ those of Mo and W, reduce the surface tension of certain
Some of the materials made according to the present
ceramic masses considerably. Certain other metal ions,
invention are particularly suitable as electrical resistances
such as those of vanadium, have a similar in?uence al
to be used at high temperatures. For such materials it
is important that they possess suitable electrical resistance 30 though much Weaker. In sintering of objects contain
ing molybdenum silicide a small portion of the silicide
characteristics.
In a material consisting of a conductor, such as a sili
will be oxidized, molybdenum ions then being formed
which are solved in the-silica formed at the same time in
cide, and ceramic constituents such as SiOg, the conduc
tivity of the material will decrease with increasing per
the oxidation process. A similar solution of molybdenum
centages of the ceramic constituents. At contents of 35 ions is assumed to take place in sintering cerametallic
70% to 80% by weight of the ceramic constituents, the
compositions of molybdenum silicide and an oxide com—
material will no longer be conductive since direct electri
ponent containing silica. An essential feature in our
cal contact between silicide granules is substantially com
patent application Ser. No. 388,444 is that the sintering
pletely interrupted by the presence of the non-conductive
is facilitated by the silica being present in the powder
40
ceramic granules.
metallurgical manufacture of heat resistant materials con
At low temperatures, the conductivity appears to de
_taining
a silicide component and an oxide component.
pend substantially entirely on the electrically conducting
silicide component. The condition becomes diiferent at
high temperatures, i.e., above 800 to 1000° C. At such
temperatures most ceramic materials have a certain de
gree of conductivity which increases rapidly with increas
ing temperature in these ranges.
These conditions result in the fact that the conductivity
of materials composed essentially of silicide and ceramic
materials have pronounced maximum values at certain
temperatures and pronounced minimum values at other
temperatures. This results in considerable di?iculty in the
utilization of such materials and gives rise to the necessity
of providing material of de?nite composition ranges for
It is mentioned also in our said application that an addi
tion of such substances which lower the melting point or
reduce the surface tension of silica, will facilitate this
sintering-promoting function of the silica to a high de
. gree.
To the silica, molybdenum ions may be supplied
in two principally different ways, i.e. the one consisting
in oxidizing the silicide component and the other in
50 adding, to the oxide component, before starting the
powder metallurgical manufacture, molybdenum oxide or
other suitable molybdenum compound. Molybdenum is,
however, a weakly positive metal and it is thus self-evi
dent that in oxidizing a silicide component, containing in
use in speci?c applications as will be hereinafter more 55 addition to molybdenum also a more positive metal, such
fully described.
According to this invention, the improved heat resistant
as titanium, the appearance of molybdenum ions in the
oxide components will be more or less suppressed. Be
material is composed esentially of a silicide component
fore all, this will occur when the more positive silicide
constituting from 35 to 99% by Weight of the material
and an oxide component, constituting 1 to 65% by weight 60 component is solvable in silica, such as in the case of
TiOg. On the other hand, chromium oxide is not soluble
of the material and consisting of silica and, if desired,
in silica and the presence of chromium in the oxide com
of one or more of the oxides A1203, BeO, ZrOZ, Y2O3
3
3,027,332
4
ponent does thus not disturb, to any appreciable degree,
the oxidation of the molybdenum silicide into molyb
denum ions and silica (compare Example 7 given below).
tion between the oxides included. Both zirconium oxide
and zirconium silicate have good heat resistivity but less
favorable resistivity against temperature changes so that
It has now been found in practice that if the silicide
component includes a quantity of molybdenum being es
products having high contents of these oxides, such as ac
sentially less than from 50 to 60% by weight of the
silicide component the concentration of molybdenum ions
where intense ?uctuations of temperature occur. Alumi
cording to Example 6, should thus not be applied in cases
nium oxide, such as corundum, has good mechanical
strength and also a very high degree of hardness and is
will be reduced in the oxide component and the action
of these ions to lower the surface tension for the silica
suitable as grinding means.
correspondingly weakened whereby the sintering of the
heat resistant material will no more be sufficiently facili
tated. In such a case it will be necessary to supply molyb
denum oxide to the silica in the raw material, preferably in
a preparatory step of melting or sintering. In Example 10
cited below there is included as a silicide component 8% 15
Ti, 56% Mo and 36% Si. In the oxidation during
the ?nal sintering there are formed about ten parts SiOz
which constitute the oxide component of the material
together with ?ve parts Al2O3+25 parts SiO2 containing
Oxide components consisting of a preponderant portion
of silica glass, such as according to the Examples 10 and
11, obtain a good resistivity .against temperature ?uctua
tions due to the low thermal expansion coe?icient of the
silica.
The silicide component may include silicides having
371K2—662/3 atomic percent Si which may also be written
M5Si3 to MSiZ in which M is a transition metal. The di
silicides have the advantage of having a high resistivity
against oxidation attacks whereas the silicides M5Si3 have
traces of M003 originally added. The silica formed in 20 a higher thermodynamic stability which appears, inter alia,
the oxidation of the silicide component will also include
therein that they do not react quite as easy with, for in
traces of oxides of Ti which, due to its stronger positive
stance, oxides as the disilicides do. In its special class
character, will suppress those Mo ions which otherwise
MoSi2 has the highest resistivity against oxidation attacks
would have appeared in the silica layer around the silicide
whereas TaSi2, due to its high melting point of 2400° C.
grains. For this reason it will be necessary in Example .10 25 and a certain plastic workability imparts toughnesss and
to introduce a surplus of Mo ions in the oxide component
high mechanical strength to products having a high con
already from the beginning in order to obtain such a re
tent of tantalum silicide, such as in Examples 11 and 12
duction in the surface tension of SiO2 that will favor the
below.
sintering process. Further, the sintering may be facili
The size of grain for material according to the inven
tated in another way, for instance, by producing a liquid
tion should be small, preferably less than about 10 mi
phase in the sintering process. In the systems Ti~Si and
crons. Before all this relates to the silicide component
Zr-Si it is known that there are low melting eutectics.
In the system Ti4i there are two such eutectics corre
which could not be made to sinter to a low porosity if the
grains are too coarse. Generally it is advantageous to
sponding to 8.5 and 78% by weight of Si both having
make also the ceramic component with a grain size being
a melting point of 1330” C. The presence of such an 35 less than 20 microns. In this connection the statement
easily fusible silicide component may, to a certain de
gree, form a substitute for the molybdenum ions which
that the size should be less than 10 microns means that
90% by weight of the material has a grain size less
would otherwise assist the function of the silica by their
than 10 microns.
reduction of the surface tension.
As regards the porosity of the ?nal product it is ad
In the Example 8 below there is a molybdenum silicide 40 vantageous to have a porosity as low as possible. The
poor in Si combined with a low melting titanium silicide
present invention is not restricted to the porosity being
rich in Si so that the composition of the silicide com
below 10% by volume. It is, however, self-evident that
ponent corresponds to a mixture of disilicides
both mechanical strength and resistivity against oxida
tion attacks will suffer if the porosity becomes too high,
(Ti0.27Mo'0.'73 ) Sis
As stated above, also vanadium ions have a similar in
45
particularly if the portion of throughgoing pores becomes
high.
Products according to the invention may ?nd many
practical applications. As structural parts (compare Ex
?uence on the surface tension of the silica and it will
be possible, as seen from the Example 5 below, to sinter 50 amples 11 and 12) in apparatus and machines in which
a high resistivity against oxidation attacks in combination
a material containing solely vanadium silicide and silica
with a high heat resistance are desirable such materials
into dense products without any particular addition of
may be used particularly for the temperature range of
molybdenum ions.
1.000~1.400° C.
In Example 11 below there is also included vanadium
As electric resistance elements for the generation of
silicide but due to the higher oxide content a further 55
oxide must be added in the form of M003 for the pur
pose of reducing the surface tension.
Oxide components in products according to the inven
high temperatures up to 1700° C. those materials are
particularly suitable in which the silicide component sub
stantially contains Mo, Ti, V or W, such as in Examples
7 and 10. It is particularly advantageous for the resist~
tion may, as above stated, contain in addition to silica one
ance element to use materials the silicide component of
or more of the oxides BeO, A1203, ZrO2 and rare earths. 60
which consists of MoSiz and the oxide component of
Said oxides may be combined in a way well known for a
which consists of SiO; and A1203. Such compositions
man skilled in the art of ceramics and it is possible to
manufacture oxide components having particularly advan
tageous properties. Due to its very good resistance
against temperature ?uctuations and its low speci?c weight
beryllium oxide is used in certain ceramic combinations
known before. In Example 4 below there is included,
in addition to a small quantity of pure silica favoring the
afford a good resistivity to heat and have satisfactory elec
trical properties. They will be treated in another con
nection. Through the addition of such oxides which are
electrically insulating also at high temperatures, such as
SiO2, A1203 and BeO the speci?c resistance may be in
creased at will and by the addition of certain other di
silicides, such as those of Cr, Ti and Ta, also the temper
sintering, a ceramic component which is well known as a
ature coef?cient of the resistance may be varied from a
70
heat resisting material under the commercial designation
positive to a negative value which may be very useful for
“4811 C.” The composition hereof corresponds to the
special purposes.
formula 48BeO—2Al2O3—ZrO2 together ‘with a small.
It is also possible to use material according to the in
quantity of CaO. This ceramic component is preferably.
vention for cold resistances, for instance, in case only an
manufactured in advance. in, known manner through reac 75 ohmic resistance without the generation of heat is desired.
3,027,332
5
6
Further, the material may be used in cathodes and in
many other applied ?elds of electrotechnics.
Such materials which have hard oxide components, for
and oxide particles before sintering must have a grain
size less than 10 microns if a product of suitable high
density and low pore volume is to be obtained. The
instance, of corundum are suitable as abrasives, compare
relative pore volume should not exceed 10% if the re
Example 13, and they can further be applied as protect
ing tubes for thermo-elements (Example 10) and in cer
tain cases also as such elements proper and further, in the
chemical industry, as containers of different kinds, such
sulting product is to have good mechanical strength and
as crucibles, muf?es (Example 5) and tubes (Example 9)
higher contents of oxide material are employed, for ex
su?icient resistance to oxidation. In the sintering process
there is always a certain amount of grain growth, par
ticularly if the quantity of oxide material is small. If
and'nozzles which all must be resistant to corrosion and 10 ample over 20%, the grain growth will be insigni?cant in
heat fluctuations.
sintering, and after long periods of use of the ?nal product
As stated above some of the materials according to
at high temperatures the grain growth will not exceed
this invention are applicable in electrical resistor adapted
20 to 50%. In the present invention involving ?nely
for very high temperatures. In respect of such materials
divided particles the silica assists the sintering, i.e., it
the silicide component consists substantially entirely of
renders a “wetting” action between the silicide grains and
MoSiz. However, the addition of small quantities of
the oxide grains.
TaSiz and TiSi-Z, i.e., up to 10% by weight of the silicide
As previously noted, it has been found. that the com
component, have been found to improve the mechanical
position of the oxide component and its percentage in the
strength of the material and to have a favorable in?uence
heat resistant material are interdependent to a certain
on the electrical properties of the material as will be 20 degree. It has been found that substantially four dif
hereinafter described.
ferent types of heat resistant materials may be manu
The oxide component is composed of SiO;, with or
factured having oxide components in percentages by
without the addition of A1203 in quantities hereinafter
weight as follows:
set forth.
Materials having silicide and oxide components have 25
Type I.--Oxide component 1 to 4% of the material, com
posed of 1 to 4% of SiOz and 0 to %% A1203.
Type II.—Oxide component 4 to 20% of the material,
1400° C. to 1700° C. It will be evident that such ma
composed of 4 to 20% SiOz and 0 to 3% A1203.
terials must have extremely high resistance to oxidation
attacks. MoSi2 is the most resistant of the silicides and 30 Type 1Il.-—Oxide component 25 to 35% of the material,
the addition of any substantial quantity of other silicides
. composed of l to 10% SiOz and 15 to 34% A1203.
reduces the oxidation resistance of the material. How
Type IV.—Oxide component 35 to 65% of the material,
ever, as previously noted, small additions of TaSi2 and‘
composed of 20 to 60% Si02 and 5 to 20% A1203.
TiSig improve the mechanical strength of the material
and the temperature coe?‘icient of electrical resistance of 35
In the materials of types I-IV listed above, the maxi
the material. For pure MoSiz the speci?c electrical re
mum allowable operating temperature is reduced from
sistance is
1700° C. for material type I, via 1600" C. for material of
type II, to 1400° C. to 1500’ C. for materials of types III
0.4 ohm mmF/m. at 20° C.,
40 and IV. The reduction in allowable operating temper
1.9 ohm mm.2/m. at 800° C., and
atures appearing between types I and IV is a result of
3.0 ohm mm.2/m. at 1600” C.,
the increasing oxide contents between types I and IV.
been found to be particularly suitable for use as electrical
resistance materials at temperatures ranging between
whereas the corresponding values for MoSi2+l0% TiSiz
are 1.1, 2.2, and 3.0 ohm mmF/m. respectively. If higher
contents, i.e., above 10%, of such other silicides are in
cluded in addition to MoSi2 the ability to endure violent
temperature changes is substantially reduced.
‘As previously noted, most ceramic materials become
’ Material I is subject to a considerable grain growth and
Will therefore be brittle, whereas, material II is subject
only to an insigni?cant grain growth and maintains a good
mechanical strength also after a very long time of use.
i The materials III and IV have, due to their high oxide
content, a considerably higher resistance than the ma
terials I and II which compensates somewhat for the
conductive at elevated temperatures, and MoSi2 at tem 50
lower operating temperature.
peratures between 1500” C. and 1700° C. has only a small
positive temperature coefficient of electrical resistance,
Materials of type IV have
high speci?c electrical resistance. The upper limit of
the oxide component is 65%“due to the fact that the
i.e., at 1500° C. 2.9 and at 1700° C. 3.1 ohm mm.2/m.
material must have a practical degree of electrical con
It is, therefore, important that any oxide added does not
ductivity.
,
have a pronounced negative coe?icient of electrical re
sistance since the resulting temperature coe?icient of the
: While, as previously described, materials I-IV having
material may be negative. Materials having such nega
speci?c compositions of oxide component as set forth,
tive characteristics at operating temperatures are not
are desirably employed, the invention relates generally to
suitable as electrical resistance materials and the present
materials including from 1 to 65% oxide component of
invention is thus concerned only with oxides having low 60 which A1203 may be from 0 to 34% and SiO2 from 1 to
electrical conductivity even at high temperatures. Thus,
65%. Materials with high oxide contents are dif?cult
only Si02 and A1203, which do not have a pronounced
to manufacture with low porosity and, with respect to
negative coe?icient of electrical resistance, are employed
materials of type IV, it is necessary to add substances such
for the production of electric resistance materials. Fur
thermore, both of these oxides have exceedingly low 65 as alkaline silicate or boric acid which reduces the melt
ing point of the silica. ‘The quantity of alkaline silicate
conductivity even in these elevated temperatures.
may be from 1/2 to 5% by weight of the material (counted
In addition to the foregoing, SiOz has a further desir
as
pure SiO2 in the water glass). At the high sintering
able etfect of facilitating the sintering of the grains of
temperatures these silicates are decomposed and leave
material forming the silicide and oxide components as
will be hereinafter described. The A1203 is additionally 70 only pure silica which will be included in the oxide com
ponent.
desirably employed for the reason that it has a coefficient
Also other substances reducing the melting point of
of linear thermal expansion which agrees exactly with
silica or the oxide component respectively may be used
the coe?icient of expansion of MoSiZ at temperatures be
tween 20 and 1500*‘ C.
in producing said materials having a high oxide content.
It has been found that at least 90% of all of the silicide 75 As additional substances reducing the melting point of
3,027,332
7
Silica may be counted also such impurities, for instance,
CaQ, MgO, TiO2, Fe2O3, Na2O et cetera, which normally
a rather considerable oxidation takes place appearing
partly in the formation ‘of layers of Si02 which further
occur in natural and synthetical materials rich in silica.
Products employing'the material according to the pres
ent’ invention may be manufactured according to usual
powder metallurgical methods by forming a powder mix
ture and sintering it.
the sintering between the silicide grains and, as a case
may be, also between the oxide and silicide grains and
partly as free silica in larger grains. The above material
of type II is preferably manufactured in such a way that
molybdenum disilicide to which is added silica and, if
In exceptional cases so called pressures sintering in
desired, tantalum disilicide, titanium disilicide and/or
graphite forms may be used advantageously. The type
alumina, is mixed with a few percent of silica or, if
of atmosphere of sintering has a critical influence on the 10 desired, aluminium silicate and is pressed to a suitable
result. If a powder of pure MoSi2 is sintered in an inert
shape and is sintered in a protective gas having about
gas or in hydrogen which only includes traces of oxidizing
1/2% oxygen at a temperature rising to 1300" C. and then
gases, for instance, less than 0.1% by volume of oxygen,
further sintered in air up to a temperature of 1600° C.
there is no provable oxidation of the molybdenum disili 15 Products of the types I and III should be sintered at such
cide and in any case there is formed less Si02 than 1%
a high temperature as possible, i.e. about 1700” C., and
by weight of the material and the material obtained will
in a pure atmosphere containing in addition to inert gases
fall outside the scope of the present invention. If the
sintering of the silicide takes place in an atmosphere which
only at most 1% by volume of oxygen. In producing
the product of type I the silica formed is su?icient to
includes higher content of an oxidizing gas, such as water 20 facilitate sintering, whereas as regards the product III
vapor, there will occur a de?nite oxidation the degree of
the high percentage of alumina prevents an ef?cient sinter
which is determined by temperature and time and the
composition of the gas and also of the shape and size of
ing and thus a higher temperature is required.
Heat resistant products employing the materials may
the grains et cetera of the bodies to be sintered. For
be formed in several different ways, i.e., by cold pressing
25
instance, it has been found that a protecting atmosphere
of rods, by extrusion of rods or tubes and by pressure
having 99% by volume of hydrogen and 1% by volume
sintering, preferably in graphite forms, of rods or in the
of water vapor is capable of oxidizing at 1600° C. a body
shape of other objects having small dimensions. In the
consisting of pure MoSi2 and having a maximum grain
extrusion a temporary binding means, such as wax or
size of 8 microns to an extent which gives a ?nal product
para?in, may be added which makes the mass supple.
having the composition 98% MoSi2 and 2% SiO2. The
Such plastifying additions may be advantageously used
which contain Si and which, upon oxidation and/or heat
ing, remain in the heat resistant material as SiO2. Such
an addition is alkaline silicate which, upon heating, is
sintering time is in this case. 5 minutes and inasmuch as
the sintered bodies already after this time were without
any provable porosity there did not occur any further
provable oxidation after a further sintering for a long 35 transformed to SiO2. Another is organic silicate, such
time. If the sintering is made instead at 1500° C. it
as ethyl silicate, which upon hydrolysis, affords a ?nely
takes a longer time to close the pores and the degree of
oxidation after 20 minutes in said gas is seen from a
divided or colloidal hydrate of SiOz having a favorable
influence on the progress of the sintering in which it is
composition of 4% by weight of SiO,, and the balance.
transformed into SiO2. Also other ?nely divided binding
MoSiz. However, it is not suitable to sinter too long in 40 means containing silica may be used. Extruded heating
hydrogembecause then certain undesirable reactions may
take place. Similar results may be obtained with other
protective atmospheres consisting of 99% inert gas such
as argon and 1% Water vapor or oxygen.
A micro
scopic examination has revealed that the silica formed
elements are preferably formed with an incandescent zone
of small cross section and adjacent terminal zones of
larger dimensions. Elements being cold pressed and pres
45 sure sintered may be brought into the desired shape by
extends substantially along narrow paths between the
mechanical working and may be provided with cold ter-'
minal zones having larger cross sectional dimensions.
‘
silicide crystals and appears to a very small extent in the
Materials of type I ?nd their application in small
form of discrete silica grains. The wetting action between
furnaces and apparatus in which the operating tempera
silica and silicides has been proved to be very good and 50 ture is very high. The considerable growth of the grain
the silica has a clear function of preventing the grain
size of the material and its small mechanical strength
growth. In the molybdenum disilicide which was sin
con?nes, however, the application of this material to very
tered in the pure inert atmosphere and in which the silica
special cases.
content was less than 1% in the ?nal products, the quan 55
Materials of type II may be extruded to ‘very long
strings and be shaped to almost any type of element,
such as loops, meanders, spirals etc. The material has
a good mechanical strength and a small growth of grain
and may thus be used also in average sized and large
furnace plants. The moderate content of oxides in the
tity of this silica is insuf?cient to form thin layers between
the silicide grains and there will be almost no effect of
assisting sintering. If the original powder mixture in
addition to MoSi2, also includes TaSiZ or TiSiz or an
oxide such as A1203 or aluminium silicate or silica the
result obtained in sintering in a protecting atmosphere
which is not entirely pure will be as above stated.
On
types I and II has but an insigni?cant in?uence on the
speci?c electrical resistance which at 1600° C. amounts
the other hand, if the sintering is made in an atmosphere
to 3 to 5 ohms mmF/m. in ‘both cases. The speci?c re
including higher contents of water vapor or oxygen the
sistance
at ordinary room temperature varies between
oxidation will be correspondingly more intense ‘which 65 0.3 and 1.0 ohm and is higher in case the silicide coin
may be ascertained thereby that individual silica grains
occur in the ?nal product. The sintering may then also
be carried out in two steps, for instance, a ?rst sintering
step within the temperature range from ordinary room
ponent includes TiSiz or TaSiZ.
- Material of the type III is of particular advantage when
ever there are high demands on a good resistivity against
temperature shocks.
temperature up to 1300° C. performed in a very pure 70
protective atmosphere, an intermediate product being then
obtained having about 20% by volume of pores. This
intermediate product is then sintered in the second sinter
The coef?cients of thermal expan
sion in respect of the two substances A1203 and MoSiz
are practically identical and due thereto the resistivity of
the product against ?uctuations in temperature will be
good. Material of type III is manufactured only in very
ing step which may be performed in ordinary air so that 75 small dimensions which has connection with the limited
3,027,332
10
9
C. a resistance of 2 ohms which, at a terminal voltage of
possibilities of the pressure sintering method from a prac
12 volts, corresponds to a developed heat power of 72
tical and economical point of view.
watts.
Material of type IV having substantially SiO2 as its
Whereas in respect of Example 3 the speci?c electrical
oxide component has a good resistivity against tempera
ture shocks, because silica is present in the form of glass 5 resistance at room temperature is 200 ohms mmP/m.
as stated above said resistance will be as much as 8000
having a very low coe?icient of thermal expansion. Ma~
ohms in respect of Example 4. Considering the fact that
terials of this type may be extruded to strings of great
the oxide component in Example 3 is 43% and, in the
length. Due to its high oxide content the mechanical
Example
4, 48% by weight of the material it is clearly
strength of this material is small and it will substantially 10 understood that in this range the material rapidly goes
be used in bodies of small dimensions, in which the high
over from being a conductor to being an electrical in
resistance may be utilized.
sulator. The upper limit for the oxide component vof
Following are listed four different practical examples
65% is thus also the limit for a material having any ap
of producing different materials falling within the types
preciable electrical conductivity as stated .in conjunction
I to IV.
15 with Table A.
Table A
Example No _ _ -
1
2
3
4
Maximum
Powder mixture
size of
Percent by weight
grain, a
MOSlz, smelted 1 ............................. ._
_ 9
48
Mosiz, sintered 2 ______________ __
-
5
50
Smcltcd corundum (99% A1201)
_
10
8-A12O3 (from A12SO4) ...... -.
_
<1
%
Caleined chamotte 3. . _.
Smelted mullite 41.---
_
.
6
8
.......... -.
Silica-?ller (98% S102) ________________________ _-
<1
1%
Kind of forming
_________________________________ -
85
60
55
1U
10
_________ -_
15
______________________ ._
_________ -_
30
001d‘
pressing
6000
kgJcm.2
Seebelow.
String
pressing
binding
medium.5
H2+0.2%
See below. __________ __
35
COld
casting
binding
medium.a
Pre-sintering:
Atmosphere
by vol. 02.
Maximum temperature, ° C __________________________ -_
1,200
Corresponding time, in minutes ______________________ -_
30
See below. __________ __
See below_
Final sintering:
Atmosphere
H2+0.5%
Pressure
H1+0.5%
by vol. 02. sintering
in graph
H1+0.5%
byvol. O2. byvol. 0a.
ite form
150 kg./
em.2
Maximum temperature, °_C __________________________ ._
1, 650
1, 500
1, 450
1, 450
Corresponding time, in minutes ...................... .-
5
2
20
20
57
9
34
52
9
39
Percent by weight
Sintered-product:
Mo?h
A1203"
SiO»
96
%
3%
78
10
12
Percent by volume
Porosity
Type of materiaL.
5
I
7
6
IV
9
IV
1 Produced by smelting in electric arc furnace and in argon.
2Produced by reaction in hydrogen gas at 1,100u C. on a
mixture of Mo-powder and Sipowder, the latter consisting of
‘97% Si and 2% Fe.
_ 3 Consisting of 35% A1203, 60% SiO-z and the remainder of
rmpuri y.
4- Consisting of 70% A1203, 25% SiOz and the remainder of
impurity.
5Besides temporary softening means, to 100 grams powder
mixture are added 3 grams SiOa in form of hydrated silica
and water to suitable consistency.
6To 100 grams powder mixture is added 4 grams S102 in
form of hydrated silica.
Water added to casting consistency.
The material according to the above Example 3 has 70 On the attached drawing-there is plotted a logarithmic
a speci?c electrical resistance of 200 ohms at ordinary
curve the ordinate indicating the 10log or" the speci?c re
room temperature and 1000 ohms at 1000” C. and may
sistance as a function of the oxide component content
be used, for example, for cigar lighters in motor cars.
being represented by the abscissa.
A small plate having the dimensions 5 by 10 by 1 milli
Below a Table B follows indicating nine further ex
metres and thicker terminals has, for instance, at 1000° 75 amples of the invention.
3,027,332
TABLE ~B
I
a
- "
Example >No """
“" """> "’ """
,
a
Powder mixture, percent
by Welght
Example 10
5
6
7
V
Powder mixture
8
-
.
fb
Maximum
Percen
of grain '
weight y size
microns
.
mal
grain
gllgégif‘gg’ybsg? """""""""""""""" "
MoSi~(l2% Si .1111.
size, #
A1203 (A1280; 700° C.)_
5
25
SiOQ-glass plus 5% M003."
Ti.-Si,78
S1 ____________ __
4
TiSi'z, 54;: Si.
8
Ti-Si; 8% Si__
10
.
"
.
7 I
Silicide component __________________________ __
Ti
30—50
<1
Mo
Si
60
8
56
34
BeO .............. __
.r
10
Oxide
ZrOr“
__
10
Thereof A1203
gargaiu
-_
1%
Thereof SiOa
SiOz-glass+5% M003"...
8
__
v
Duration of maximum temperature, 3 minutes.
Final product, percent by Weight:
5
10
2-g aSS _________ __
V
Maximum temperature, 1,600° C.
6
a
8
'
extrusion.
8
A1203 (smelted corundum)_
A1203 (AlzSO4 700° C.)---_
'
Final sintering:
Atmosphere, air.
10
'
'
Presintering: At 1,200‘a C. in H2 plus 0.2% by volume of O2.
6
8
%
'
<1
Kind of forming: Addition of wax plus Na water glass and
8 ~
'
'
2
10
5
component
n, ____ __T___,_ _____ _, _______ __
5
‘
35
Example 1'1 '5
7
Kind of forming __________________ -_ Cold pressing at 4,000 kg./cm.2
40
* ~
*
Percent
Maximum
weightby size
ofegén,
Powder mixture
m or
Presinterlng _____________________ __ At v1,000 to l 2005 (>3. in pure protcc-
_
‘
_
tive gas (Hz or Argon+0.2% by 25 VS12_(52% Si)_.v ............................... ..
volume 02). Mechanical work’I‘.aS12(24% S1)__
2o
25
6
8
ing if desired.
20
8
30
8
SgOz-glass. _ ._v________ __
-
SiOz-glass plus 5% M003 .................... __
Emiltmosp
smtet?ngz
H2+0 ' 87a Air---- H2+0 ' 217O b y
ere ------------------ -by‘g’lume
‘
Kind of forming and ?nal sintering :
Volume 0’
30
Maximal temperature "0 .... __
1, 600
1, 500
Duration
minutes ____________________
of maximal temp.,__
5
15
10
1,550
15
Final product..
Maximum temperature, 1,550° Cr
Duration of maximum temperature, 4-. minutes.
Finals533110133;ggggjgyjffflf; __________________ __
gd
Si
35
Silicidecomponent,percentby
weight _____________________ __
Composition of silicidet com
96
72
_
Pressure sintering'in graphite form 150 kgs/cm?.
2
7
1,650
V
87
,
50
Thereof S10”
50
57
Example 12
‘ I
Ti
‘
Percent by Maximum
Powder mixture
.50
4°
Egan‘); parts 558%
erco p ats
r
5
weight
size of grain,
microns
TaSia (24% so _______________________________ __
15
s
Terms (9% Si)____
10
10
_
wsiiom so“. --
5
5
47g
10
10 45 m2
_____________________________
__
'
_'
‘
'
'
'
5
10
33
4
8
138 ...... 43
--
jfgereogpartrs
peg
91‘80 par S
2
3 ------ --
50
38
.
Oxide component
____________________________ __'
ponent, percent by weight‘
nent,
Thereof
percent
parts
byA1203
weight._______________________
__
4
28._
v
Mail
B80
812566256‘)
‘ """"""""""
_
_
_"
8102 glass plus 5% Mo va ---------------- --
2 _______ __
Kind of forming and ?nal sintering:
Pressure sintering in graphite form 150 kgsJcm?.
Maximum temperature, 1,500“ C.
50 Final product, percent by weight:
‘ Duration of maximum temperature, 4 minutes.
Example 9
,
Silicide
a
V
Powder mixture
r
.
i
,
.Maxlmum
Percent by size ofgraln, 55
welght
TaSi; (24% Si).
MoSu (37% S1) _______ __
20
64
8
8‘
s
5
5
.
Thereof 'ZI‘O2
5
30
Y203 and other rare earths_ _
SiOr glass plus 5% M003 ................ -.
23
Si .
Thereof
55
______________r __>__.;_'_.‘_;._'___
r
_. ,
Oxlde component ____________________________ __
Thereof A1208
Thereof B90
microns
'
Tier, (54% Si) _____________________________ -_._
component
r
Mo
-
S102
~
"
'
'
<
~
>
'
5'
'
5
47
5
"
4
Example 1'3
I
5
‘
10
8 60
Percent by
Maximum
weight
size of grain,
microns
Powder mixture
Ergo (gélz, go.
‘
I
£283
corundgm).
8
I"
1g
_
55
30-50
.
23'
2
Presmtermg.
At 1,200"i C. in H2 plus 0.2% by volume of 0a. 65 sioTglass
plus4700D
5% M .___
003 ____________________ ___
5
<1
extruswn-
Nfoféfuga, 3131""
2o
18
Kind of forming: Addition of wax plus Na water glass and
5
8
Final sintering:
Atmosphere H2+ 0.8 by volume of O2.
_
Maximum temperature 1,500° C.
Pressure sintermg in graphite form 150 kgsjcm},
ataxirnum tjemperuture, t1,4:00" C.
Final product, percent by weight:
0
Ta
2
Mo
20
‘
'
Oxide component _~.'_‘__‘..__.'.__'__; _ _ _ _ _ _
_ __V_____
Thereof YaOs and other rare earths__~_;__;_____'.___
SiOn
‘
70 Final #3535, gerlcrgi?lglylgeigllrntgemtum' 4 minutes
.
Elicide component __;. _________ __'.__>__; _______ .._
Si
_
Kind of forming and'?nal sintering:
Duration of maximum temperature, 10 minutes.
.
ilicide component __________________________ __
35
i
26
V r
11
Mo
'
_
-
25
3g
65
Thereof A1208
‘60
Thereof SiO:
_
'
'
5
‘
'
Si
Oxide component ____________________________ __
10 75
'
r
48
15
'
'
*
r
r
5
3,027,332
13
Example 14
100 parts of molybdenum disilicide powder having
grain sizes ?ner than 10 microns are mixed with silica
hydrate corresponding to 5 parts of silica, 5 parts of
paraffin and water added to suitable workability. The
plastic mixture is worked 48 hours under vacuum and
extruded. The extruded rods, 7 and 14 mm. respec
tively, are dried and pre-sintered under pure hydrogen
14
been hydrolyzed and sintered from a powder mixture
thereof having an average particle size less than about
10 microns, containing silica in the form of an organic
silicate, said sintering having been carried out in an at
mosphere selected from a group consisting of the noble
gases, hydrogen and such gases containing small amounts
of an oxygen-containing gas, said silicate producing a
?ne dispersion of silica particles upon heating during said
sintering, the amount of said silicide and of said silica
up to 1000" C. The rods are then pushed through a
being such as to facilitate the sintering of the powder
furnace under pure hydrogen at 1300-1400“ C. and after
without rendering the sintered powder electrically non
that treatment they have strength enough to be handled.
conductive, said silicide component constituting 99‘ to
The porosity is now about 20% by volume and the tech
35 % by weight of the material and said silica constitut
nical composition corresponds to the raw materials used.
ing 1 to 65% by weight of the material, said material
The rods are now sintered a few minutes in air at
being resistant to prolonged temperatures in the range
1600° C. by means of direct current heating. Because
1500—l700° C. in air and having a porosity not greater
of the silica addition the material can be formed by hand
than 10%.
at 1600" C. into any desired shape. The heating in air
3. The process of claim 1 in which the organic silicate
gives a product with 0-5% porosity and a fair strength.
is ethyl silicate.
The material is however oxidized to an extent,‘ which cor
4. A process for making sintered refractory metal
responds to the formation of about 6% by weight SiOZ, 20 silicide material, said process comprising mixing silica
which is formed from the silicide. The sintered product
with at least one of the refractory metal silicides of the
therefore contains 2 different phases: MoSi2 and quartz
metals of the group consisting of Ti, V, Mo and W,
glass.
After a few hours at 1500~1600° C. some re
and alkali metal ions in an amount sufficient to lower
action takes place. The practical result of this reaction 25 the melting temperature of said silica, said silicide ma
is that the material cannot be formed any more and thus
retains its shape.
‘One of the most important properties of these ele
ments is that they are completely surrounded by a very
thin layer of quartz glass, which is formed when the
rods are sintered in air above 1200° C. It is therefore
very important that the cooler ends are also heated in
oxidizing atmospheres before the welding operation.
As seen above the material of the elements contains
a ceramic phase corresponding to about 10% by weight
of the material. This ceramic phase is very important
as it effectively stops the grain growth of the silicide.
terial having an average particle size less than about
10 microns, and sintering the resultant mixed material, said
sintering being carried out in an atmosphere selected from
a group consisting of the noble gases, hydrogen and such
gases containing small amounts of an oxygen-containing
gas, the amount of said silicide and of said silica being
such as to facilitate the sintering of the powder without
rendering the sintered powder electrically non-conductive,
said silicide component constituting 99 to 35 % by weight
of the material and said silica constituting l to 65% by
weight of the material, said material being resistant to
prolonged temperatures in the range 1500-1700" C. in
air and having a porosity not greater than 10%.
SiO2, A1203 or combinations thereof in ?ne particle size
5. A sintered refractory metal silicide material, said
and in certain proportions to manufacture a material 40 material consisting essentially of silica and at least one
adapted to be used at elevated temperatures by sintering
of the refractory metal silicides of the metals of the group
in a certain type of atmosphere, and the use of certain
consisting of Ti, V, Mo and W, said material having
materials and techniques in the manufacture of such
been sintered from a powder mixture thereof having an
product, disclosed but not claimed in the present appli
average particle size less than about 10 microns con
cation, are disclosed and claimed in the copending ap
taining alkali metal ions in an amount suf?cient to lower
The use of molybdenum disilicide in admixture with
plication Serial No. 657,058, ?led May 6, 1957, of Nils
Gustav Schrewelius and Karl Herbert Joachim Medin,
said Medin being the sole inventor of the present ap
the melting temperature of said silica, said sintering hav
‘1. A process for making sintered refractory metal sili
cide material, said process comprising mixing an organic
rendering the sintered powder electrically non-conduc
ing been carried out in an atmosphere selected from the
group consisting of the noble gases, hydrogen and such
plication and said copending application being owned by
gases containing small amounts of an oxygen-containing
the same assignee as the present application.
50 gas, the amount of said silicide and of said silica being
What I claim is:
such as to facilitate the sintering of the powder without
tive, said silicide component constituting 99 to 35 % by
silicate with at least one of the refractory metal silicides
weight of the material and said silica constituting 1 to
of the metals of the ‘group consisting of Ti, V, Mo and 55 65 % by weight of the material, said material being re
W, said silicide material having an average particle size
sistant to prolonged temperatures in the range 1500
less than about 10 microns, and hydrolyzing and sinter
1700° C. in air and having a porosity not greater than
ing the resultant mixed material, said sintering being
10%.
carried out in an atmosphere selected from a group con
6. A process for making sintered refractory metal
sisting of the noble gases, hydrogen and such gases con
silicide material, said process comprising mixing silica
taining small amounts of an oxygen-containing gas, said
with at least one of the refractory metal. silicides of the
silicate producing a ?ne dispersion of silica particles upon
metals of the group consisting of Ti, V, Mo and W,
heating during said sintering, the amount of said silicide
and boric acid in an amount su?icient to lower the melt
and of said silica being such as to facilitate the sintering
ing temperature of said silica, said silicide material having
of the powder without rendering the sintered powder
an average particle size less than about 10 microns, and
electrically non-conductive, said silicide component con
sintering the resultant mixed material, said sintering be
stituting 99 to 35% by weight of the material and said
ing carried out in an atmosphere selected from a group
silica constituting 1 to 65% by weight of the material,
consisting of the noble gases, hydrogen and such gases
said material being resistant to prolonged temperatures
containing small amounts of an oxygen~containing gas,
in the range 15004700" C. in air and having a 70 the amount of said silicide and of said silica being such
porosity not greater than 10% .
2. A sintered refractory metal silicide material, said
material consisting essentially of silica and at least one
of the refractory metal silicides of the metals of the group
as to facilitate the sintering of the powder without render
ing the sintered powder electrically non-conductive, said
silicide component constituting 99 to 35% by weight of
the material and said silica constituting l to 65% by
consisting of Ti, V, Mo and W, said material having 75 weight of the material, said material being resistant to
15
3,027,332
16
prolonged temperatures in the range 1500-1700” C; in air
‘and having a porosity not greater than 10%.
7. A sintered refractory metal silicide material, said
material consisting essentially of silica and at least one of
the refractory metal silicides of the metals of the group
consisting of Ti, V, Mo and W, said material having been
range 1500-1700° C. in air and having a porosity not
sintered from a powder mixture thereof having an aver
greater than 10%.
of the powder without rendering the sintered powder,
electrically non-conductive, said silicide component consti~
tuting 99 to 35% by weight of the material and said silica
constituting 1 to 65% by weight of the, material, said
material being resistant to prolonged temperatures in the
age particle size less than about 10 microns containing
boric acid in an amount su?icient to lower the melting
silicide material, said process comprising mixing silica
temperature of said silica, said sintering having been
with at least one of the refractory metal silicides of the
carried out in an atmosphere selected from the group
metals of the group consisting of Ti, V, Mo and W, and
at least one ion of the group consisting of Mo, W and V
consisting of the noble gases, hydrogen and such gases
containing small amounts of an oxygen-containing gas;
the amount of said silicide and of said silica being such
as to facilitate the sintering of the powder without render
in an amount su?icient to lower the surface tension of
said silica, said silicide material having an average particle
size less than about 10 microns, and sintering the resultant
mixed material, said sintering being carried out in an
atmosphere selected from a group consisting of the noble
gases, hydrogen and such gases containing small amounts
ing the sintered powder electrically non-conductive, said
silicide component constituting 99 to 35% by weight
of the material and said silica constituting 1 to 65% by
Weight of the material, said material being resistant to
of an oxygen-containing gas, the amount of said silicide
and of said silica being such as to facilitate the sintering
prolonged temperatures in the range 1500~1700° C. in
air and having a porosity not greater than 10%.
of the powder without rendering the sintered powder
electrically non-conductive, saidrsilicide component con
stituting99 to 35% by weight of thepmaterial and said
silica constituting 1 to 65% by weight of the‘ material,
said material being resistant to prolonged temperatures
8. A sintered refractory metal silicide material, said
material consisting essentially of silica and at least one
of the refractory metal silicidesmof the metals of the group
consisting of Ti, V, Mo and W, and at least one ion of
the group consisting of Mo, W and V in an amount suf
?cient to lower the surface tension of said silica, said
material having been sintered from a powder mixture
thereof having an average particle size less than about vl0
microns, said sintering having been carried out in an
atmosphere selected from a group consisting of the noble
gases, hydrogen and such gases containing small amounts
of an oxygen-containing gas, the amount of said silicide
and of said silica being such as to facilitate the sintering
t
9. A process for making sintered refractory metal
in the range 1500-1700° C. in air and having a porosity
not greater than 10%.
References Cited in the ?le of this patent
3D
UNITED STATES PATENTS
2,747,260
Carlton et a1. ________ __ May 29, 1956
FOREIGN PATENTS
674,137
Great Britain ________ .... June 18, 1952
UNITED STATES PATENT OFFICE
CERTIFICATE OF CORRECTION
Patent No.’ 3,027,332.
March 27, 1962
Karl Herbert Joachim Medin
are in the above numbered pat
Patent should read as
It is hereby ce rtified that error appe
tion and that the said Letters
ent requiring correc
corrected below.
d —- 10 microns ——-‘
Column 4, line 35‘z for "-20 microns" rea
Signed and sealed this 10th day of July 1962.
(SEAL)
Attc?t:
ERNEST w. SWIDER
DAVID L- LADD
.
Att-esting Officer
_
Commissioner of Patents
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