Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
131~2~
This invention relates to a process for the m~lufacture of carbon-bound
shayed parts which contain mineral fibres.
The invention concerns a process for the manufacture of shaped parts
which contain r~fractory or fireproof mineral fibres, in which process
the mineral fibres are embeddea in ~ carbonaceous matrjx. The invention
also conce ms sllaped parts which are carbon-bound and which contain
mineral fibres m~lufactured accordin~ to this process.
Carbon-bo~l~ shaped parts containing mineral ibres are kno~. Thus, a
moulde~ body composed of a heat-insulating material and a process for
its manufacture are described in DE 30 09 182 C2. According to this
m~lufacturillg process, carbonaceous substances, e.g. solid resins,
either are mixed with the mineral fibres which form 15 to 60% by mass of
the material of the moulded bod~, or the fibres are immersed in liqui~
carbonaceous substances. Synthetic resins, bituminous mineral oil or
tar may be used as the carbonaceous substances. The pyrolysis, or
cracking, of the carbonaceous substances tllen take place after shaping.
In addition, a refractory, heat-insulating material which is composed of
aluminium silicate fibres and a binding agent, and which con~ains
particulate, refractory fillers, is know~l from DE-~S 19 47 904. A
furtller plate material whlch contains ceramic fibres, and a process for
its productioll~ are described in EP 00 77 444 Al. The manufacture of
this~ plate material also takes ~lace from an aqueous slurry of the
flbres. Such a slurry contains inorganic, refractory fillers. A
flocculation agent or a precipitation agent is used in the form of a
cationic polyacryl ~nide. A process for the manufacture of light-weigll
',
.: ,
~, " ,,, ~ , . . .
. --3--
13~926
shaped bodies composed of ceramic fibres, finely divided refractory
matter, inorganic binding a~ents and conventional additives, is known
from ~ 34 36 781, wherein, a two-stage flocculent-precipitation yrocess
and a mixing of the two ~locculated dispersions takes place. Accordillg
to thi.s state of the art, using a di.spersion of the fibres for shaping,
with or without 1Occulatioll, however, no shaped bodies which have a
carbon bond are manufactured.
;
The present illvention provides a process for the manufacture of shaped
parts ~hich contain refractory or fireproo~ milleral ~ibres, in w}lich
process the mineral fibres are embedded in a carbonaceous matrix,
wherein finely particled pitch, tar or resol or novolak resins are
flocculated from an aqueous suspension onto the mineral fibres present
in the aqueous suspension, a green shaped part is produced from the
suspension, and the green shaped part is dried and subjected to
pyrolysis at temperatures of from 350~C to 1300~C. The parts produced
have a carbon bond and carbonaceous phase. The process is simple in its
execution and facilitates the manufacture of such shaped parts, ~he bulk
density of whi.ch can be widely adjusted. In particular a low bulk
densi.ty can be ac!lieved.
;
Accolding to a preferred embodiment, finely particled refractory or
fireproof substances and/or inorganic binding agents and~or
hydraulically setting refractory cements are also flocculated onto the
minelal fibres in the suspension.
, .. .
.
-4--
13~26
As a result hereof, it is possible to re~ulate the properties of the
resulting refractory shaped parts and, also, to control their bulk
density. ~loreover, the advantage arises, when usin~ inor~anic binding
agents, that a relatively great strength can be achieved in ~l
intermediate temperature range of 40U to 800C and, when using
hydraulically setting refractory cements. A further advanta~D is that,
after drying, a high green stren~t}l of the shaped body is already
achieve~.
Jn a furtller preferred elllbodim~nt, a cationic s~arch is used as
flocculation agent.
In the process according to the invention, the mineral fibres may be
added in a quantity of from 5 to 90% by mass, the pitch, the tar or the
resol or novolak resin in a quantity of from 10 to 30, preferably 15 to
25~ by mass, the finely particled refractory or fireproof substances in
a quantity of from 5 to 70~ by mass, the inorganic bindi.ng agents in a
quantity of from 5 to Z5% by nlass, and the hydraulically setting
refractory cements in a quantity of Erom S to 20% by mass, these
speclfications relating to the dried shaped part which has not yet been
subjected to pyrolysis.
lhe refrnctory or f~reproof mlneral fibres used in the process according
to ~he invention can be any milleral fibres, preferably fibres of silicon
dioxi.de, of aluminium oxide, the A12O3 con~ent of which is preferably at
least 72%, or of an alumi.nium silicate material, in parti.cular having at
least 40 to 60% of Al~03 and 6U to 40% of SiO2.
~.;
::,
~'
, .. ~ . ...
131~92~
i`he diameter of these mineral fibres is preferably smaller than 15 l~n,
i.e. so small that breaking of the fibres when tlley are processed need
not be feared. Jn view o the conditions under which such fibres are
produce~, their di~neter is usually greater than 1 ~m.
Tlle length of these fibres conveniently should exceed 3 mm, so that the
fibres can fulfill their funstion as mechanical reinforcillg Wit}lill the
shaped body. lhere is no critical maxim~n value for the length of the
fibres, with the exception of the critical len~th determjned by the
m~mler of manufacture of tlle fibres.
In the process according to the invelltion, a finely particled pitch, tar
or resol or novolak resin is used. These are con~nercially known
substances. The maxim~n grain size o these ~inely particled
carbonaceous substances is, preferably, 0,09 nnn The finely particled
curbonaceous substances cause the developmei~t of the strength of the
shaped parts durin~ drying at temperatures exceeding 30C. The fi3lely
particled carbonaceous substances in addition fonn a carbonaceous phase,
i.e. accwnulations and coatings fo~n Oll the mineral fibres and, in the
case of a large component of carbonaceous substances, a continuous
carbonaceous matrix is achieved. Ater pyrolysis by heat treatmellt of
the shaped part, the carbonaceous phase results in the improved
resistance to abrasion and resistance to corrosion.
~; Flocculatioll agents are used in the process. These are anionic or
cationlc substances, cationic starcbes being preferTed. The cationic
polyacrylamide flocculation agellls used in ~P 00 77 4~ can, however,
~,
, .. . ~ ,., . ~ . .
also be elllployed, as can other cationic flocculatioll agents, kno~m
yer se, in the form of polyelectrolytes, e.g. methacrylate. These
cationic flocculatjon agents are usually prepared in the fonn of a
solution having a concelltratioll of 0,5 to 1% by mass, and are further
diluted before use to solutions of OJOS to 0,1% by mass; a similar
situation arises in respect of aniol]ic agents, such as anionic
polyeletrolytes based on acrylic amide.
According to a further preferred embodimeJlt, finely particled,
refractory or fireproof substances are flocculated OlltO the mineral
fibres in the aqueous suspension, together with the pitch, tar or resol
or novolak resin. Such finely particled or finely divided refractory
matter having a grain size of~ 0,09 nm can be convelltional refractory
matter, e.g. fireclay, bauxite, alumina, carundum, zirconiu~ dioxide,
zircon mineral, magnesium oxide, cordierite, carbon, i.e. graphite,
coke, silicon carbide and/or chrolni~ oxide. Such finely particled
refractoly matter can be used si~lgly or in the form of mixtures.
In addition, in the process according to the invention, an inorganic
bindiJlg a~ell-t can also be flocculated together Wit]l the pitCll, tar or
resol or novolak resin. Such inorganic binding agents may be colloi~al
SiOz or colloidal A12O3. The strength of the shaped parts is further
improved by means of these inorganic binding agellts.
Ill the same way, hydraulically setting refractory cemen~s, e.g.
alwninous cement or rapid-hardening cements having a high A12O3 conten~
can be flocculated together with the pitch, tar or resol or novolak
. ,~ ., .,, ~.. . . .. . .
131~92~
resin. The shaped part obtains its strength as a result of the setting
of the refractory cemeIlt. The finely particled refractory matter,
iIlorganic binding agents and hydraulically setting refractory cemeIlts
can, in each case, be used individually or in any desired mixture or
combination.
In the process according to the invention, mineral fibres in the
suspension are pre$erably used in a cluwltity of from 5 to 15~ by mass or
6~ to 70% by mass. Shaped parts having a low mineral-fibre component
are distinguished by a relatively low speci~ic gravity an~ a low theImal
conductlvity, while manifesting good strength ~Id resistance to wear.
In the case of a lar~er mineral-fibre component, there is, at ~irst,
only~a slight reduction in the specific gravity. At the same tin~e, the
strength is gre~tly reduced, with the result that such compositioIls of
the suspensioIl should not be regarded as be~ng particularly suitable.
It is only when there is a predomin~lt co~nponent of mineral fibr~s from
about 6~% by mass, that shape~ parts are obtained in advantageous manner
which have a very low thennal conductivity, low specific gravity and
relatively high strength.
.
In order to protect the carbon~ceous phase in the shaped parts against
.
corrosion by way of oxidation, elementary silicon or metallic aluminium
in the folm of a powder having a grain size below 0,09 nm can be
illtroduced into the susyension as antioxida~lt agents during the
mallufacture of the shaped paTts~ In the~course ~f the pyrolysis of the
shaped~parts by means of heat treatment, the ~ltioxidant agent partially
.
~ ;; reacts~wlth the carbon to form carbides.
; ~
::
::
,~.,,,~- : ~ ... .
. ~ ,
13~926
In the process according to the invention, as a first step, an aqueous
suspension of the mineral fibres is prepared. Such a suspension usually
has u consistellcy of 0,5 to 3% by mass. Subsequent to the preparation
of this a~lueous suspension of the milleral fibres, the finely par~icled
pitch, tar or resol or novolak resin is scattered into this suspension
and mi~ed well therewith. In like manner, finely particled refractory
matter, inor~anic binding agents and hydraulically setting refractory
cemellts are, optionally, added In this stage. Subse~uently, the
solution of tlle flocculation agent described above is added, usually in
a qu~tity of 5 g o~ the flocculation agent, calculated as solid matter,
per 100 kg of the suspension.
Subsequently, the green shaped body is moulded from the dispersion which
colltaills the flocculated suspension, in the usual manner. The
dispersion is fillecl into a mould which has a perforated bottom. The
dispersioll is dewatered by means of the draining of the liquid through
the perforated bottom, this process possibly being assisted by
establishing a vacuwn, and possibly by additional pressing power, ancl
the shaped body is formed.
Ihe shaped bodies are usually dried at temperatures of from 110 to
180C. After dryin~, the shaped parts are treated at temperatures of
between 350C up to temperatures of~ 1300C. A partial or com~lete
pyrolys~s, or cokin~, of the pitch, tar or resol or novolak resins,
takes place. This results in the fonnation or intensification of tlle
carbon-binding of t}le mineral fibres and the furtller development of the
carbonaceous phase. In the case of a high component of the carbonaceous
::
. ,~ .. .
9 ~ ~ -
yhase, the milleral fibres can be en~.bedded in it, as in a carbonaceous
matri~. The temperature of the heat treatnlent in each case depends on
the finely particled pitch, tar or resol or novolak resin used, and
furthemlore whether a shayed part is required which has already been
subjected to pyrolysis up to 10~%, or whether a subsequent pyrolysis of
the shaped part is possible or desired when in use by the end-user.
The heat treatment for the pyrolysis, or coking, of the pitch, tar,
resol or novolak resin is undertakell in the maluler kno~l per se in
llOII-OXi.diZillg a~mosphere, i.e. in an inert gas, such as nitrogen, car~on
monoxide or carbon dioxide.
The invention will be described in more detail with reference to the
ollowing non-limitin~ E~amples.
~xan~le ]
63 parts by mass of mineral fibres having an A1203 content of 47% by
mass, remainder SiO2, were reduced to a 1% suspension with water with
the assist~lce of a powerful stirring apparatus. To this were added 7,5
parts by mass colloidal sllica, 23 yarts by mass of a finely particled
solid novolak resin having an average grain size of 2 to 3 ~, and 6,5
parts by mass o~ finely particled alumina~(A1~03~ having a grain size of
~10 ~m, and were also well stirred in the suspensioll. Subsequently, a
0,5% solution of a cationic starch was added, causing the flocculation
of the novolak resin arid the finely particled refractory matter and of
the inorganic binding agent. The solution was dewatered on a screen
,
-10 -
~31~
mould with the creation of a vacuum to fonn plates, and these plates
were subsequently dried at lZ0 to 150C. These plates were then
heat-treate~ in a non-oxi~izi-l~ atmosphere at 1200C, resulting in the
coking of the novolak resin.
The bulk density of the plates thus pro~uced amounted to 0,41 ~/cm3.
Their cold-bending strength lay at 2,2 N/mm2.
Example Z
The procedure of Example 1 was repeated, but using 70 parts by mass of
the mineral fibres used in Example 1, 24 parts by mass of resol resin
~and 6,0 parts by mass of the silica used in Ex~mple l. Flocculation was
again carrie~ out by means of a cationic starch, the latter being added,
calculate~ on solid content, in a quantity of 0,lZ5 parts by mass.
Tlle further processing was carried out in accordance with the proced~lre
under ~alnple 1. Plates havin~ a bulk density of about 0,4 ~ 3 were
obtaine~. -
ample 3
' 85 palts by mass of the mineral fibres used in Exan~le 1 ~Id 15 parts by
mass of the novolak resin used in xample 1 were added to a 0,5% by Inass
suspensioll ;in ~ater (consistency = ~,5%). Agaill, there was
precipitation o the novolak resin Oll the ceramic ~ibres, usin~ the
cationic starch used in ~xample ]. Subsequently, plates were again
:
.,.,.. ~, :,
1 3 ~ 6
manufactured whi ch were heat-treated at 380C. lhis resulted in a
partial pyrolysis of the novolak resin.
The bulk density of the plates amounted to 0,4 g/cm3.
A suspensioll was preyared with l.5~ by mass of mineral fibres ~Id 30% by
mass of novolak resin accordiIlg to Example l, with the additional
components ~uartz pow~er below 0,09 mm at 33% by mass and colloi.dal
silicic acid at 12% by mass. Metalli.c aluminium powder having a ~rain
size of less than 0,09 mln at 8% by mass was also added as antioxidant
agellt. The flocculation of the suspension was achieved with a total of
2~ by mass of starch. The plates obtai.ned from the flocculated
suspensiorl accordin~ to the screen mould process, and after dryin~ and
coking at 800C, had a bulk density of 0,62 g/all3 and a cold-bendin~
strength of 3,2 N/n~n2.
Example 5
A suspenslon, having the same components~as in Example 4j was prepared,1.5% by mass of rapid-hardenin~ cement ~70% by mass Al2O3 contellt) was
aiso added~in ad~i.tion to 5% by mass of mineral fibres, 48% by mass of
quartz powder, 25% by mass of novolak resin, 2% by mass of colloidal
sil~clc~acid and 5% by mass of elementary aluminium powder. After the
vacuum-scleenin~ process, a plate having a bulk densi.ty of 0,95 g/cm3
.
13~92~
was obtained. The cold-bending strengtll amo~ted to ~,2 N/mm~ ater
coking at 800C.
Exall le 6
further suspension was prey~red using the same componenfs as in
Ex~nple 4, the quartz powder however being replaced by finely ground
sintered alwnina, having a grain size of less than 0,09 nun. ~dded to
the suspension were: 20% by mass of mineral ibres, ~5% by m~ss of fine
alwnina, lO~o by mass of novolak resin, ]5% by n~ass of colloidal silicic
acid, and 8% by mass of elementary silicon. In ad~ition, a portion o~
2% by mass of starch was used. After flocculation and Wit]l the aid of a
screen mould, plates were produced from the dispersion, the plates were
subse~uently dried and heat-treated at 800C.
The bulk density of the ~lates amounted to 0,7 g/cm3.
:
,...
.
