Note: Descriptions are shown in the official language in which they were submitted.
1140947
The invention relates to a material for hot or plasma
spraying especially non-metallic refractory material suitable
for the formation of resistant coating sand to a process of
the production of such a material as well.
At present miscellaneous metallic and non-metallic
materials are known and for the produciton of protective
coatings are used; composition of the materials is varied
according to required properties of the coating regarding as
chemical composition of starting materials as their physical
properties. It deals with materials exhibiting required
properties especially refractoriness, abrasive wear resistance,
minimum porosity, good holding on subjacent material and
resistance to mechanical and thermal impacts as well as chem-
ical resistance to the influence of surrounding medium, the
problem still remains in reaching complexity of these proper-
ties in one spraying.
For example metallic especially noble deficient materials
as chromium, titanium, nickel and similar, even refined with
another additives or alloy additions, if necessary, are used
with these materials, as it follows from properties of their
starting components, very good mechanical properties of the
resulting coating are achieved but heat resistance or chemical
resistance of coatiny thus made is usually substantially worse.
Another large group of spraying materials are non-
metallic materials especially those based on oxide ceramics
where spraying material is made up either from one oxide or
from a mixture of several oxides in proper ratio. Typical
representatives of these materials are materials on the basis
of aluminium oxide A12O3 whose characteristic feature is com-
position of the coating from a mixture of gamma and alphaA12O3 modification. At temperatures above 1180C irreversible
1:14~47
modification transformation of the A12O3 gamma modification
to the alpha modification takes place at the same time what
is accompanied with permanent contraction and increase of
volume weight. Coatings on the basis A12O3, the so-called
corundum coatings are characterized by extraordinary abrasive
wear resistance, high adhesion to subjacent material and by
very good electric properties, their corrosion resistance is
however lower as a result of open porosity, which amonts 6 to
8 ~ and after transformation to alpha modification it increases
to 9 to 10 %. Coatings on the basis of zirconium oxide ZrO2
have especially excellent heat insulating properties, layers
made from chromium oside Cr2O are very hard and abrasive wear
resistant, coatings of titanium oxide Tio2 are compact and
well machinable and there are very hard for example layers of
hafnium oxide HfO2; common disadvantage of these one-component
~praying materials is however relatively high porosity and
from it resulting smaller resistance ~o influences of aggres-
sive media.
This disadvantage is partially overcome by coatings on the
basis of silicium oxide SiO2 which forms compact coating with
very small coefficient of thermal expansion and with zero
porosity. This coating is considerably resistant to corrosion
and sudden temperature changes, on the other hand its resis-
tance to mechanical impacts is however entirely insufficient.
The problem of improving properties of plasma coatings
was lately solved by formation of mixture of several oxides
exhibiting in proper ratio more convenient properties than
the properties of basic components are. It is for example
zirconium silicate ZrSiO4 at which in coating composition
ZrO2 prevails in volume stable tetragonal modification in
homogenous mixture with SiO2 in glass form. At temperatures
-- 2
- 1140~47
above 1150C zircon is reversely synthetized. The coating has
excellent resistance to temperature changes, a good heat
insulating power and it very well resists to corrosion by
melted glass materials, slags and by colored metals due to
poor wetting of zircon by the above-ment-ioned melts. The
general corrosion resistance is however negatively influenced
by that open porosity of coating is 15 to 25 % in spite oE
presence of glass form of SiO2.
From further multicomponent spraying materials for example
magnesia spinel MgA1204 can be presented; it has low porosity,
high electrical resistance and excellent adhesion to subjacent
material but its corrosion resistance is already substantially
lower. There are also very spread multicomponent spraying
materials on the basis of A1203 with additives of TiO2 or
Cr203 where TiO2 addition increases especially compactness of
th0 coating at simultaneous improvement of resistance to tem-
perature changes and Cr203 addition ensures better abrasive
wear resistance however other disadvantages are not in1uenced.
Finally it is known also the use of A1203 with addition of
SiO2. This spraying material retains very good mechanical
properties of corundum coatings the presence of SiO2 enhallcing
also corrosion resistance. With regard to the mechanism oE
transfGrmation of gamma and alpha A1203 modifications however
not even here as a result of the negative influencing of
resulting coating porosity can be reached corrosion resistance
comparable with protective SiO2 layers what is at simultaneous
achieving oE hiyh reEractorincss, abrasivc wear and suddcn
temperature chan~es resistance the main object of this inven-
tion.
Further possible way how to lower porosity of the per-
formed coating and thus increase corrosion resistance is a
-~ 114~)947
choice of proper granulation of starting spraying material or
use of amorphous additive as for example æinc by what hardness
` and heat resistance of the coating becomes however again
worse. Known two~component coatings with amorphous additive
besides it do not make possible sufficient adaptation of the
resistance to corrosion medium of given composition.
With respect to a process of the production of spraying
material for hot or plasma spraying there are use altogether
traditional ways of the treatment by melting of starting
materials or their mixtures in arc furnaces and by subsequent
treatment on granularity and the shape proper for the applica-
tion by plasma burner. These processes are considerably
uneconomical with respect to relatively s~lall treated amounts
of material especially with respect to high melting temperatures
of usual spraying materials. Besides it at the treatment of
materials alloyed with small amounts of additives to very small
grains of the size usual at the spraying by plasma stream
there are already revealed the heterogeneities in the structure
of material negatively influencing the quality of the per-
formed coatings.
It is known as well a substanitally power-consuming
alloying of spraying materials by diffusion of corresponding
additives under high temperatures or granulation of the mix-
ture of grains of individual components proper only or the
production of spraying materials consisting of two or more
fundamental components contained in the mixture in relatively
high weight ratio. It is known a process as well where the
relatively large grains of one or more components are enve-
loped by very fine additives with the grain size smaller than
0.3 micrometer. However not even these processes comply with
the requirement of high homogenity of spraying material.
-- 4 --
114V947
The above drawbacks of prior art spraying materials
for hot or plasma spraying are overcome by a spraying material f
consisting of several metal oxides of which at least one
oxide is a glass-forming oxide, said spraying material being
characterized in thàt it is formed of at least two fundamental
oxides in the amount 50 to 99~ by weight, and by at least
one glass-forming oxide with the melting point lower about
50 to 1100C than the melting points of said fundamental
oxides in the amount 1 to 50~ by weight.
In particular the present invention provides a
spraying material suitable for hot or plasma spraying consisting
essentially of a plurality o~ metal oxides of which at least
one oxide is a glass-formint oxide, characterized by being
formed of
(a) two or more fundamental oxides selected from
the group consisting o A12O3, MgO, CaO, BaO,
Cr2o3, TiO2 and ~rO2 in an amount of 50 to 99%
by weight
and (b) one or more glass forming oxides having a melt-
ing point 50C to 1100C lower than the melting
points of said fundamental oxides, in an amount
of 1% to 50% by weight,
said fundamental oxides having a particle size of 0.01 to 0.2 mm,
said glass forming oxides having a particle size of 0.0002 to
0.04 mm.
The glass forming oxide may, for example, be SiO2.
Spraying material can preferably contain agglomerates
50 to 80~ by weight CaO, 1 to 5~ by welght MgO, and 18 to 45~
by weight SiO2, or 50 to 90% by weight MgO, 1 to 5% by weight
CaO, and 5 to 45% by weight SiO2, or 90 to 95% by weight
Cr2o3, 2 to 8% by weight TiO2, and 1 to 3% by weight SiO2, or
65 to 75% by weight Cr2O3, 20 to 30% by weight MgO, and 2 to
ll~V947
10% by weight SiO2, or 30 to 40% by weight Al2O3, 15 to 25%
by weight CaO, and 35 to 50% by weight SiO2, or 25 to 30% by
weight A12O3, 40 to 45~ by weight BaO, and 25 to 35~ by weight
SiO2, or 46 to 51~ by weight A12O3, 33 to 41% by weight ZrO2,
and 8 to 21% by weight SiO2, or 25 to 30~ by weight A12O3,
25 to 30% by weight Cr2o3, 25 to 30% by weight ZrO2, and 10
to 25% by weight SiO2.
The above mentioned drawbacks of prior art processes
of the production of spraying materials for hot or plasma
spraying consisting of several metal oxides from which at
least one oxide is a glass-forming oxide are overcome by the
process according to the invention characterized in that
fundamental oxides and said glass-forming oxide or oxides are
brought separately or in a previously prepared mixture into
a suitably stabllized plasma stream with a concentration
of charged partlcles between 2.00 x 1024 and 0.3 x 1023,
for example into a water stabillzed plasma stream,they are
partially melted or melted-down and the resulting agglomerates
are captured or recove~ed for example by water or air screen.
The fundamental oxidescan have a particle size of 0.01 to 0.2
mm and the glass oxide or oxides can have a particle size
of 0.0002 to 0.04 mm.
The process according to the invention can be
preferably carried out so that into the plasma stream is
brought a mixture of fundamental oxides with particle size
0.01 to 0.2 mm and glass-forming oxide or oxides with particle
size 0.0002 to 0,04 mm, particles of fundamental oxides being
surface melted and particles of glass-forming oxide or oxides
being melted-down or so that fundamental oxides and glass-
forming oxide or oxides are brought separately or in advance
prepared mixture into the plasma stream with concentration
of charged particles between 2.00 x 1024 and 0.3 x 1023,
-- 6 --
114~)947
especially into water stabilized plasma, they are partially
melted or melted-down ànd partially melted or melted-down
are put directly on the surface which is to be protected by
the coating.
The subject matter of the invention is further
elucidated in several examples of concrete embodiment.
Example 1
Into the plasma stream of water stabilized plasma
burner adapted for spraying of powdered materials is brought
a mixture of 65% by weight of powdered CaO with particle size
0.04 to 0.06 mm, 3% by weight of MgO with the same size, and
32% by weight of SiO2 with particle size 0.0005 to 0.0008 mm,
individual particles are exposed to temperature between 15 000
and 60 000C and after relevant reactions took place they are
captured by water screen. Resulting agglomerates are formed
predominantly by dlcalciumsllicate accompanied wlth small
amount of montlcelllte as a bindlng phase and with smaller
amount of glass phase~
~14~)947
Example 2
Into the plasma stream are brought 70 % by weight of MgO
and 2 % by weight of CaO in a mixture with 28 % by weight of
SiO2 under conditions analogous as in the preceding example.
Materials are put on the surface o preheated constructional
component and they are let to cool slowly. Resulting material
of the coating will be formed by forsterite accompanied with
small àmount of periclase, monticellite and of glass phase.
Example 3
For spraying carried out under condiditons analogous to
the preceding example 95 % by weight of Cr2O3, 3 % by weight
of TiO2, and 2 % by weight of SiO2 are used. Resulting mate-
rial will be formed mostly by eskolaite and by small amount
of glass phase.
Example 4
70 % by weight of Cr2O3, 25 % by weight of MgO, and 5 %
by weight of SiO2 are used. Resulting material will be mostly
formed by chrompicotite accompanied with small amount of for-
sterite and of glass phase.
Example 5
36 % by weight of A12O3, 20 % by weight of CaO, and 44
by weight of SiO2 are used. Substantial part of resulting
material will be forrned by anorthite accompanied with glass
phase.
Example 6
27 % by weight of A12O3, 41 '~ by weight of ~aO, and 32 %
by weight of SiO2 are used. Resulting material will be mostly
formed by celsian accompanied with glass phase.
Example 7
46 to 51 % by weight of A12O3, 33 to 41 % by weight oE
ZrO2, and 12 to 16 % by weight of SiO2 are used. ~esulting
114~947
material will be mostl~ formed by corundum accompanied with
baddeleyite, mullite and glass phase.
~xample 8
2~ % by weight of A12O3, 28 % by weight of Cr2O3, 28 % by
weight of ZrO2, and 16 % by weight of SiO2 are used. Resulting
material will consist of approximately equal parts of baddele-
yite, ruby and eskolaite accompanied with smaller amount of
glass phase.
The materials prepared according to the above-described
examples give security o~ high refractoriness, resistance to
corrosion by metallic or non-metallic melts, abrasive wear
resistance and of sudden changes of temperature. It deals with
new materials of proper composition and properties containing
always definite amount o glass phase of SiO2 which substan-
tially increases corrosion resistance of coating. Besides
this glass phase there is always present also crystalline phase
physical and chemical properties of which are co-decisive Eor
maximum resistance of coating to corrosive medium of given
composition and which is formed at least by two fundamental
oxides with respect to necessity o suficiently fine choice
of its properties.
~ ligh homogeneity of performed coating even at relatively
small amounts o~ some additives is achieved by the capture oE
resulting agglomerates by water or air screen and by their new
application using plasma burner. With very good results all
mentioned spraying materials can be put directly on the sur-
face which is to be protected by the coating, practically non-
porous coating being obtained at conservation of very good
mechanical properties by the choice o~ proper percentual con-
tent and size of SiO2 particles.
_ ~ _
