Note: Descriptions are shown in the official language in which they were submitted.
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~ACKGROUND OF TH~ INVENTION
Field of the Inv~ntion
This invention relates eo a re~ractory ceramic brlck, ~nd more spccific~lly, a
~~r~to"~ ceramlc hrick havin~ lovv thermal conductivity.
De8crlntion Qf th~ Prior Art
Such bricks ar~ substantially known for two ~ppllcation fields. A first
application field is for the backin~-up of rcfractory linin~s with 50-~allcd insulatin~
bricks. Thercln thr~ primary focus i~ on therm~l insulation. The~e bricks ar~ not
eYroscd to n~echanical or chemical attack of any Icind, either whcn us~ In
metallur~ical meltin~ vessels or when use~, for ex~mple, in cement oyllndrical rotary
kilns.
PE 33 26 ;270 C2 discloses such insulatln~ bricks, ~uring the production of
which are add~d combustible materials which, aftHr the firin~, tncre~se the pore
volume and th~ls the insulatin~ propertiHs of the bricks. On a simil~r prin~iple,
DE 33 02 368 A1 su~ests the us~ of li~htwei~ht expande~ clay a~re~ate to
inc:rsase the pore volume o~ htwHi~ht b~Jildinr~ brick.
A seGond application field i~ fof bricks which are ~xpased to direct thermal,
m~chanical ~nci chemi~l attack, for example in the cas~ of bricks for linlnçl cement
cylindrical rotary kilns, where a substantial criterion is also the lowest possible thermal
conductivity. The reason is primarily that cylinclriGal rotar~ kiln5 arH, as a rule,
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deliv~red as sin~le-layer kilns, which means an insulatin~ layer or backin~ is omitted.
The bri-;k~ u~Hd in thix case must consequently me~t hi~hly differin~ r~quirements~
The prlor ,~rt bricks contain approxirnately ~O to 99% by wei~ht of a metal
oxide rnatrix material.
EP O 7~3 C145 A2 discloses the use of oxidic hollow spherss, for the pro~uction
of thermally insulating formed bodies in which the hollow spheres are fixed to one
anc~the~ only ~y !bon~in~ a~ents.
BRIEF SUMNIAR'Y OF ~I~E INVENTION
The present inv~ntion is directHd to an irnproved brick for the second ~pplic~tion
field diwus~ed above, hav;n~ comparable chemical and mechanical propert;es
con~pared to the prior art brieks, bllt improved, i.e. Iower, thermal conductivity ~s
compAred to thR prior art bricks.
Thi~ can be achieved, in accordance vvith th~ prH~Hnt invention, by a brick
whir h comprises, a metal oxide matrix materi~l and a thermally stablH filler material
fabricated in the form of hollow bodies.
DETAILED DESCP~IPTION OF THE INvENTlON
Thu$, thH pr~sRnt invantion provid~s ~ refractory c~ramic brick which comprise~
gO to 9g% by wei~ht of metal oxide matrix material, and 1 to 10 % b~ wei~ht of
hollow spheres, havin~ a ~rain size less th~n 5.0 mm, o~ a thermally stabl~ flller
material, wherein ~he wei~h~ percentaE~es are based on the wei~3ht of the brick.
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Any met~l oxide m~trix material s~itable for refractory ceramic bricks oan be
employed, exarrlples of which are sintered ma~n~sia, flux ma~nesi~, alumina,
corundum, zirconium dioxide an~ spinels therefrorn.
As Indlcated above, the use of ox;de hollow spheres is known ~rorn
EP 0 723 945 A:2. 1 lovvever, in that publication, they at~ applicd for the pro~uctlon
ofthermally insulatin~ form~d bodies in which the hollow sphere~ are fixed to one
another only by bondin~ a~ents. Therefore the rstio of hollow spheres to ~ond;n~
a~ent accoJding l:o the examples in the publicatlon Is approximat~ly 10;1, even thou~h
~en~ally ~rvei~ht ratios of hollow spheres to bondin~ agent of 95:5 to 20:80 are
dlscloscd. In ~ny event, thermally irlsulatin~ formed bodies are obtained of a
c~mpletely different type than those of the pres~nt invention.
Accordin~ to a preferr~ ~mbodiment of the present invention, the wei~ht ratios
of the met~l oxldn matrix rnateriel to thH filler material is g3-g7 wt %: 3-7 wt %.
The mHtal oxi~e n~atrix meterial thus Is cl~arly the primary focu~ and Is Indlspensabl~
in l~rder to fulfil the good chemical, th~rmal and mechanical propsrties which, apart
frorn the requirecl lov~ thermal conductivity, con~inue to be dernand~d of th~ refractory
ceramic btick.
The hollow-sphere filler material can compri~Q the same material ~s the matrix
material, for exemple alumina or corundum.
Accordin~ eo another pr~fer~ed embo~iment, the filler material, to~ether with
thH metal oxide matrix rnaterial, are spinsl-formins~.
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lf, for ~xarnple, sintered ma~nesia i8 us~d as a substsntial component of the
rnatrlx rnaterlal, tlhe flller material can ~ornprlse hollow-sphere corund~m Yvhi~h, at the
correspon~ln~ firin~ temperatures is spinel-forrnin~ with the matrix rn~tnrlal, 85 wili be
~xplain~d in further detaii in the followin~.
lt h~ beeln found to be in every r~spect an optimization to 5elec:t the m~trix
materi~l and the fillr~r materi~l from components which ~rc spinel-formln~ with one
annther, wh~reby thQ stability of thH brick can addltion~lly ~e irnproved overall, and
in this way, the m~chanical, chemical and therm~l characteristics of the brick ~fr~
sirnult~nflously opti~nized.
Dependin~ on the choice of st~rtin~ material the person skilled in the art can
determine ~mpirically a suitable firin~ temperature as well as a correspondin~ firin~
time. Conventional firing temperatures ~nd tirnes are appr~priate in the present
invention .
In spite olF the hollow-sphere fluxin~ substances, throuyh the hi~h fraction of
conventional metal oxir~ matrix m~terial the pre~sure and ~brasion stren~th of the
brick, telatlve to known brick qualities, are r~tained to thH largest po~ible extent.
Thus, th~ brlck can also be used in partic~Jlar with single-lay~r llnin0s which ar~
difectly expos~cl to the p~ ular product to be treated and to the kiln atrno~phere.
i3rlcks bas~d on slntered rna~n~sie, or ma~n~si~-alumin~-spinnl are suitable for
the production ~f rotar~l kiln bricks. In this casH the flller matsrial comprises, for
ex~mplc, hollow-sphcre corundum, which should h~ve an Al~03 oontent of more than
~t7 wt %, pr~fHrably more than 99 Wt %.
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Th~ ~rain slze of thc hollow spheres ix less than 5.0 rnm, for example, 0.5 to
lesx than 5.0 mnn.
The prMsent invention will be illustratRd in more detail by reference to the
exHmples below, which are for the purpo~e of lllustration only, and ~hol~ld not be
consi~re~l to lin1lt the invention.
m~les
Reference brick ~R~ for compari~on is a brick ba~ed on sintered ma~nHsia
.5 wt ~~) with the followin~ grain ~ize distribution:
approximately 40 wt 96 in the range of 1.0 to 5.0 mm,
approxlm~3t~1y 20 wt % in thn r~nge of 0.1 to 1.0 mm, and
approximately 40 wt % in the ~ust fraction ~smaller than 0.1 n~m~.
The refer~snce brick, fired at approximately 1,700~ C, comprls~s in addltlon
5 wt % ma~ne~sia-alumina 5pin~1s of ~rain size 1 to ~ mrn as well as 2.5 wt %
corundum of ~r~3~n ~i~e 0.5 to 1.5 mm.
ComparQd to reference brick ~R) is a first brick ~A) a~cordin~ to the inventlon
comprisin~ 91 urt ~6 of th~ same sinter~ ma~nesia, S ~t ~6 of the ma~nesi~-alumina
~pinnls and ~ wt % o~ hollow-sphere corun~um with 99 wt % Al;!03 in a ~rain size of
1 to 3 mm.
A further sample ~ aec~rdin~ to the inv~ntion is 8 brick analo~ous to A which,
however, was lfirad ~or approxirnately twi~;~ the length of time as brlck /~, also at
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approxlrnat~ly 1,700~ t::, with the simultaneous spin~l fo~ mation between the hollow-
sphere corundum and th~ ma~nesitic mat~ix material.
The m~asured data for samples R, A and B are listed in ~he followin~ t~bl~.
S~rnple A B R
Bulk density (~/~cm3~ 2.83 2.80 2.85
Pnrosit~ ~%) 20.00 20.70 19.00
Cold test pressure
(Nlmm2) 42.00 35.00 50.00
Thermal conductivity (WtmK)
400~ C Z.70 2.60 4.~iO
700~ C 2,50 2.40 3.70
1100~ C 2.40 2.20 2.90
First, the expected lower bulk density of samples A and B is notable. This is
in dlrect relationship to the e~tpected higher porosity.
While the cold tHSt pr~ssure, also expect0~, decre~ses sli~htly compar~d to the
ref~rence ~ampltl, the listed values of therm~l con~u~tivity at 400, 700 and 1 100~ C
show chHracteri!itic improvements of hricks A and E~ up to ~0%.
The ~dvantages resulting thereby were verified in a ce~n~nt rotary cylindrical kiln
~t ~3n interic~ kiln t~mperE~ture of 1450~ C. The kiln shcll ~asin~ temperatures were:
- 6 -
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~pproxirnately 430~ C ~u~in~ bricks R~,
approxlrn~t~lv 390~ C ~u~ln~ bricks A~, and
approx;maeely 375~ C lusin~ bricks B~.
The~e extl3rnal kiln temparatures. which are lo~Jver by 40 to 55~ C; for the
present inventior1, reduce the heat Inss and, correspond;n~ly, the ener~y costs. In
addition, tl~--r,llal and mechanical problems of the kiln are simult~neously reduced.
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