|Title of Invention||
"MODIFICATION OF ALKALINE EARTH SILICATE FIBRES"
|Abstract||A method of making refractory alkaline earth silicate fibres from a melt, comprises the use as an intended component of alkali metal to improve the mechanical properties of the fibre in comparison with a fibre free of alkali metal.|
|Full Text||MODIFICATION OF ALKALINE EARTH SILICATE FIBRES
This invention relates to alkaline earth silicate fibres.
Inorganic fibrous materials are well known and widely used for many purposes (e.g. as
thermal or acoustic insulation in bulk, mat, or blanket form, as vacuum formed shapes, as
vacuum formed boards and papers, and as ropes, yams or textiles; as a reinforcing fibre for
building materials; as a constituent of brake blocks for vehicles). In most of these
applications the properties for which inorganic fibrous materials are used require resistance to
heat, and often resistance to aggressive chemical environments.
Inorganic fibrous materials can be cither glassy or crystalline. Asbestos is an inorganic
fibrous material one form of which has been strongly implicated in respiratory disease.
It is still not clear what the causative mechanism is that relates some asbestos with disease but
some researchers believe that the mechanism is mechanical and size related. Asbestos of a
critical size can pierce cells in the body and so, through long and repeated cell injury, have a
bad effect on health. Whether this mechanism is true or not regulatory agencies have
indicated a desire to categorise any inorganic fibre product that has a respiratory fraction as
hazardous, regardless of whether there is any evidence to support such categorisation.
Unfortunately for many of the applications for which inorganic fibres are used, there are no
Accordingly there is a demand for inorganic fibres that will pose as little risk as possible (if
any) and for which there are objective grounds to believe them safe.
A Line of study has proposed that if inorganic fibres were made that were sufficiently soluble
in physiological fluids that their residence time in the human body was short; then'damage
would not occur or at least be minimised. As the risk of asbestos linked disease appears to
depend very much on the length of exposure this idea appears reasonable. Asbestos is
As intercellular fluid is saline in nature the importance of fibre solubility in saline solution
has long been recognised. If fibres are soluble io physiological sahne solution then, provided
the dissolved components are not toxic, the fibres should be safer than fibres which are not so
soluble. Alkaline earth silicate fibres have been proposed for use as saline soluble, nonmetallic,
amorphous, inorganic oxide, refractory fibrous materials. The invention particularly
relates to glassy alkaline earth silicate fibres having silica as their principal constituent.
International Patent Application No. WO87/05007 disclosed that fibres comprising magnesia,
silica, calcia and less than 10 wt% alumina are soluble in saline solution. The solubilities of
the fibres disclosed were in terms of parts per million of silicon (extracted from the silica
containing material of the fibre) present in a saline solution after 5 hours of exposure.
W087/05007 stated that pure materials should be used and gave an upper limit of 2wt% in
aggregate to the impurities that could be present No mention of alkali metals was made in
International Patent Application No. W089/12032 disclosed additional fibres soluble in
saline solution and discusses some of the constituents that may be present in such fibres. This
disclosed the addition of NajO in amounts ranging from 0.28 to 6.84wt% but gave no
indication that the presence of NaiO had any effect.
European Patent Application No. 0399320 disclosed glass fibres having a high physiological
solubility and having 10-20mol% NaiO and 0-5mol% KjO. Although these fibres were
shown to be physiologically soluble their maximum use temperature was not indicated.
Further patent specifications disclosing selection of fibres for their saline solubility include
for example European 0412878 and 0459897, French 2662687 and 2662688, PCT
W086/04S07, WO90/02713, W092/09536, WO93/22251, W094/15883,-W097/16386 and
United States 5250488.
The refractoriness of the fibres disclosed in these various prior art documents varies
considerably and for these alkaline earth silicate materials the properties are critically
dependent upon composition.
As a generality, it is relatively easy to produce alkaline earth silicate fibres that perform well
at low temperatures, since for low temperature use one can provide additives such as boron
oxide to ensure good fiberisation and vary the amounts of the components to suit desired
material properties. However, as one seeks to raise the refractoriness of alkaline earth silicate
fibres, one is forced to reduce the use of additives since in general (albeit with exceptions) the
more components are present, the lower the refractoriness.
W093/15028 disclosed fibres comprising CaO, MgO, SiOj, and optionally ZrO? as principal
constituents. Such fibres are frequently known as CMS (calcium magnesium silicate) or
CMZS ((calcium magnesium zirconium silicate) fibres. WO93/15028 required that the
compositions used should be essentially free of alkali metal oxides. Amounts of up to
0.65wt% were shown to be acceptable for materials suitable for use as insulation at 1000°C.
WO93/15028 also required low levels of A12O3 ( W094/15883 disclosed a number of such fibres usable as refractory insulation at
temperatures of up to 1260°C or more. As with WO93/15028, this patent required that the
alkali metal oxide content should be kept low, but indicated that some alkaline earth silicate
fibres could tolerate higher levels of alkali metal oxide than others. However, levels of 0.3%
and 0.4% by weight NaaO were suspected of causing increased shrinkage in materials for use
as insulation at 1260°C. The importance of keeping the level of alumina low was stressed is
stressed in this document.
W097/16386 disclosed fibres usable as refractory insulation at temperatures of up to 1260°C
or more. These fibres comprised MgO, SiO?, and optionally ZrCh as principal constituents.
These fibres are stated to require substantially no alkali metal oxides other than as trace
impurites (present at levels of hundredths of a percent at most calculated as alkali metal
oxide). The fibres have a general composition
with the components MgO and SiOa comprising at least 82.5% by weight of the fibre, the
balance being named constituents and viscosity modifiers. Such magnesium silicate fibres
may comprise low quantities of other alkaline earths. The importance of keeping the level of
alumina low was stressed is stressed in this document.
WO2003/059835 discloses certain calcium silicate fibres certain calcium silicate
compositions for which fibres show a low reactivity with aluminosilicate bricks, namely:
strength of the fibres and blanket made from the fibres. This patent application does not
mention alkali metal oxide levels, but amounts in the region of ~0.5wt% were disclosed in
fibres intended for use as insulation at up to 1260°C or more.
WO2003/060016 claims a low shrinkage, high temperature resistant inorganic fiber having a
use temperature up to at least 1330 C, which maintains mechanical integrity after exposure to
the use temperature and which is non-durable in physiological fluids, comprising the
fiberization product of greater than 71.25 to about 85 weight percent silica, 0 to about 20
weight percent magnesia, about 5 to about 28.75 weight percent calcia, and 0 to about 5
weight percent zirconia, and optionally a viscosity modifier in an amount effective to render
the product fiberizable.
EP 1323687 claims a biosoluble ceramic fiber composition for a high temperature insulation
material comprising 75-80 wt% of SiO2, 13-25 wt% of CaO, 1-8 wt% of MgO, 0.5-3 wt% of
ZrO2 and 0-0.5 wt% of A12O3, wherein (Zr02 + A1203) is contained 0.5-3 wt% and (CaO
MgO) is contained 15-26 wt%.
Alkaline earth silicate fibres have received a definition in the Chemical Abstract Service
Registry [Registry Number: 436083-99-7] of:-
"Chemical substances manufactured in the form of fibers. This category encompasses
substances produced by blowing or spinning a molten mixture ofalfcaline earth
oxides, silica and other minor/trace oxides. It melts around 1500°C (2732°F). It
consists predominantly of silica (50-82 wt%). calcia and magnesia (18-43 wt%),
alumina, titania and zirconia ( This definition reflects European Health and Safety regulations which impose special
labelling requirements on silicate fibres containing less than 18% alkaline earth oxides.
However as is clearly indicated in relation to W02003/059835, WO2003/060016 and EP
1323687, the silica content of alkaline earth silicate fibres is increasing with the demand for
higher use temperatures and this is leading to lower alkaline earth contents.
The present invention is applicable not only to alkaline earth silicate fibres in this narrow
definition reflected in the Chemical Abstracts definition, but also to alkaline earth silicate
fibres having lower levels of alkaline earth oxides.
Accordingly, in the present specification alkaline earth silicate fibres should be considered to
be materials comprising predominantly of silica and alkaline earth oxides and comprising less
than 10wt% alumina [as indicated in W087/05007 - which first introduced such fibres],
preferably in which alumina, zirconia and titania amount to less that 6wt% [as indicated in
the Chemical Abstracts definition]. For regulatory reasons, preferred materials contain more
than 18% alkaline earth metal oxides.
The prior art shows that for refractory alkaline earth silicate fibres, alkali metals have been
considered as impurities that can be tolerated at low levels but which have detrimental affects
on refractoriness at higher levels.
The applicant has found that, contrary to received wisdom in the field of refractory alkaline
earth silicate fibres, the addition of minor quantities of alkali metals within a certain narrow
range improves the mechanical quality of fibres produced (in particular fibre strength)
without appreciably damaging the refractoriness of the fibres.
Accordingly, the present invention provides a method of making refractory alkaline earth
silicate fibres from a melt, comprising the inclusion as an intended melt component of alkali
metal to improve the mechanical and/or thermal properties of the fibre in comparison with a
fibre free of alkali metal.
Preferably, the amount of alkali metal (M) expressed as the oxide IV^O is greater than 0.2
mol% and preferably in the range 0.2 mol% to 2.5 mol%, more preferably 0.25 mol% to 2
By "a fibre free of alkali metal" is meant a fibre in which all other components are present in
the same proportions but which lacks alkali metal.
The alkali metal is preferably present in an amount sufficient to increase the tensile strength
of a blanket made using the fibre by >50% over the tensile strength of a blanket free of alkali
metal, and less than an amount that will result in a shrinkage as measured by the method
described below of greater than 3.5% in a vacuum cast preform of the fibre when exposed to
1250°C for 24 hours.
It will be apparent that the alkali metal may be provided either as an additive to the melt
(preferably in the form of an oxide), or by using as ingredients of the melt appropriate
amounts of materials containing alkali metal as a component or impurity, or both as an
additive and as a component or impurity. The invention lies in ensuring that the melt has the
desired quantity of alkali metal to achieve the beneficial effects of the invention.
The invention may be applied to all of the prior art alkaline earth silicate compositions
The scope and further features of the invention will become apparent from the claims in the
light of the following illustrative description and with reference to the drawings in which:-
Fig. 1 is a graph showing tensile strength/density plotted against melt stream temperatures as
determined in a production trial for a number of fibres of differing Na2O content;
Fig. 2 is a graph plotting maximum, average, and minimum values of tensile strength/density
against NaaO content for the same fibres;
Fig. 3 is a graph of experimentally determined temperature/viscosity curves for a range of
Fig. 4 is a graph showing shot content plotted against Na2O content for the fibres of Fig. 1
Fig. 5 is a graph of shot content against Na20 content for a different range of alkaline earth
Fig. 6 is a graph of linear shrinkages for alkaline earth silicate fibres of varying composition,
compared with known refractory ceramic fibre (RCF) fibres
Fig. 7 is a graph of the effect on blanket strength of sodium addition to a range of alkaline
earth silicate fibres
Fig 8 contrasts micrographs showing various fibres after exposure to a range of temperatures
Fig. 9 is a graph comparing measured thermal conductivities for a range of fibres.
The inventors produced fibre blanket using a production trial line at their factory in
Bromborough, England. Fibre was produced by forming a melt and allowing the melt to fall
onto a pair of spinners (as is conventionally known).
The base melt had a nominal composition in weight percent:-
with other components forming minor impurities and sodium oxide being added in specified
The melt stream temperature was monitored using a two colour pyrometer.
Fibres produced from the spinners were passed onto a conveyer and then needled to form
blanket in a conventional manner.
The blanket thickness, density, and tensile strength were measured for fibres produced using
a range of conditions.
The blanket was produced with a view to determining the effect on fibre quality of melt
stream temperature, since it was believed that this had an effect on fibre quality.
The inventors also decided to add alkali metal oxides with the view of flattening the
viscosity-temperature curve of the melt as this was thought a relevant factor in fibre
production as explained further below.
The results of these tests are set out in Table 1 and illustrated graphically in Figs. 1 and 2. In
Table 1, the melt stream temperature, blanket thickness, blanket density, tensile strength and
tensile strength divided by density is shown for all compositions. [The tensile strength
divided by density is calculated to counteract the variation attributable to different amounts of
material being in the blanket]. Also for selected compositions the shrinkage of a preform at
1150°C and 1250°C was measured in the same manner as in WO2003/059S35.
The first thing that is noteworthy is that the blanket strengths show a high variability. This is
because the manufacture ofa blanket involves many variables, including:-
• Composition of the melt
• Temperature of the melt
• Melt stream temperature
• Shot content (melt that has solidified in the form of droplets rather than fibres)
• Fibre diameter
• Fibre length
• Needling conditions
• Post-solidification thermal history
By producing a range of fibres on a single line and significantly varying only melt stream
temperature and composition (each of which will have an affect on shot content, fibre
diameter and fibre length) it was hoped to reduce such variability. However because a blanket
is an aggregated body of individual fibres, there is inevitably a statistical variation in such
aggregate properties as tensile strength.
As can be seen from Fig. 1 there appears to be relatively little variation hi strength with melt
stream temperature, but since the range of melt stream temperatures chosen was selected to
encompass ranges previously found to be effective, this is not surprising.
However, it can be seen that with progressive increases in NaiO content, the strength tends to
increase. Fig. 2 shows the maximum, minimum, and average strengths found for a range of
compositions and it can be seen that blanket strength shows a strong positive correlation with
content. In contrast, the shrinkage of the fibres seemed barely affected.
The fibres with nominal zero Na2O content of course had minor trace amounts (average
measured content 0.038% - maximum 0.1 1%). Extrapolating back to zero NaiO gives an
average tensile strength/density of 0.0675 kPa/[kg/m ]. The average tensile strength/density
for the addition of 0.3% Na2O is 0.1426. The increase in blanket strength is over 100% and
smaller additions (e.g. 0.25 mol%) would be expected to exceed a 50% improvement.
Encouraged by this, and with a view to determining the upper limit of alkali metal oxide that
was appropriate, the inventors produced a range of further alkaline earth silicate fibres using
an experimental rig in which a melt was formed of appropriate composition, tapped through a
8-16 mm orifice, and blown to produce fibre in a known manner. (The size of the tap hole
was varied to cater for the viscosity of the melt - this is an adjustment that must be
determined experimentally according to the apparatus and composition used). Shrinkage of
preforms of the fibre at 1150°C and 1250°C were measured in the same manner as in
W02003/059835. Total solubility in ppm of the major glass components after a 24 hour static
test in a physiological saline solution were also measured for some of the examples.
The results of these studies are shown in Table 2. The fibres in the left of the table were
aimed at assessing the effect of adding approximately equimolar amounts of alkali metal
addition to calcium silicate fibre containing L^Oa (as in W02003/059S35), whereas those to
the right were aimed at assessing the effect of varying the quantity of NaaO in such a fibre.
While not conclusive, the results indicate that for these fibres Na20 and K^O show shrinkages
no worse or even better than fibre free of Na2O, whereas LiaO appears detrimental to
However, this latter conclusion is thought unsafe since it was determined that the lithium had
been added in the form of lithium tetraborate, and the boron addition may have had a
significant effect. Until proven otherwise, the applicants are assuming that all alkali metals
can be used in the invention, but that the absolute amount of alkali metal may vary from
metal to metal and fibre to fibre. The solubility figures show that total solubility is slightly
increased by the addition of alkali metal oxide.
The right side of Table 2 shows firstly that only a ~1% higher silica content has a big effect
on shrinkage, giving a much lower shrinkage. For these fibres, linear shrinkage at
850°C/24hrs seemed unaffected by all soda additions tested, however the same is not true for
thickness shrinkage, although it is still low. At 1150°C/24hrs there is a slight increase in both
linear and through thickness shrinkage, but at 1250°C/24hrs through thickness whilst still
acceptable grows more significantly for the highest soda addition. All of these figures are
acceptable for some applications whereas other applications could not tolerate the highest
NajO level tested.
The improvement in shrinkage with higher silica levels led the inventors to look to materials
containing still higher silica levels and the results are set out in Table 3 below.
These results show low shrinkage and a reasonably high solubility across the range. It
appears that addition of alkali metal oxide may increase the amount of silica that can be
added to produce a workable alkaline earth silicate fibre, and perhaps with an acceptable
solubility. This is of great significance since, in general, increasing silica content permits
higher use temperatures for alkaline earth silicate fibres.
Fig. 6 shows the shrinkage at various temperatures of preforms of a range of alkaline earth
silicate fibres. The reference SW613 refers to lanthanum containing materials of composition
similar to those set out in Table 3 with varying silica contents as indicated but absent any
alkali metal additioa. [Silica and calcia comprising most of the material with lanthanum oxide
being present in about 1.3%]. One of these fibres also has an addition of 2wt% MgO. Also
shown are shrinkages for a conventional aluminosilicate fibre (RCF) and a magnesium
silicate fibre (MgO Silicate).
It can be seen that all of the SW613 fibres have a shrinkage lower than that of RCF and the
MgO silicate fibres up to 1350°C but rise thereafter. However, there is a progressive increase
in refractoriness with increasing silica content. For the SW613 fibre containing 77 and 79%
Si02, the shrinkage remains below that of RCF and the MgO silicate fibres up to 1400°C and
better could be expected for higher silica contents. In contrast, it can be seen also that
addition of 2% MgO to the SW613 compositions is detrimental to shrinkage. High silica
alkaline earth silicate fibres are difficult to make and addition of alkali metals to such
compositions should improve the quality of such fibres and ease manufacture.
Having shown such effects the applicants conducted a trial to make blanket on a production
line, to see whether the initial results on shrinkage were confirmed. A base composition
SiO2 72.5 - 74wt%
CaO 24 - 26.5wt%
A1202 La2O3 1.2-1.5wt%
was used and varying amounts of Na2O were added. Blanket having a density 128kg/m3 was
produced having a thickness of ~25mrn. The results, summarised in Fig. 7, show a dramatic
increase in blanket strength with Na20 addition.
These findings relate to compositions containing LaaO} as a component, but similar effects of
alkali rnetal additions are found with alkaline earth silicate fibres not containing La2O3 as a
The inventors also tested other alkaline earth silicate fibres comprising predominantly
magnesium as the alkaline earth component (magnesium silicate fibres) and the results are set
out in Table 4.
This table shows that whereas Na20 and KiO have a small or large respectively detrimental
effect on shrinkage, Li2O has hardly any effect on shrinkage. This does not imply no effect at
all, the inventors observed that whereas the fibres with Na^O and KiO were similar to fibres
without such additives (coarse) the fibre with Li2O addition was significantly finer and of
better quality. At lower quantities, NaaO and KiO may still give shrinkages that are tolerable
in most applications.
The purpose of adding alkali metal is to try to alter the viscosity temperature curve for
alkaline earth silicates so as to provide a more useful working range for the silicates. Fig. 3
shows a graph experimental viscosity/temperature curves for:-
• a high soda glass having the approximate composition in wt%:-
• an alkaline earth silicate melt comprising the approximate composition:-
+ others to 100%
• and the same alkaline earth silicate melt comprising respectively 1 wt% Na20 and 2 wt%
Na2O as an additive.
The viscosity/temperature graph of the high soda glass is a smooth line rising as temperature
For the known alkaline earth silicate melt (SW) the viscosity is lower and then rises steeply at
a critical temperature value (this is shown as a slope in the graph but that is an artefact of the
graphing process - it actually represents a much steeper change).
Addition of Na'2O to the melt moves this rise in viscosity to lower temperatures.
This extends the working range of the melt so that it becomes less dependent upon
temperature so increasing the tolerance of the melt to fibre forming conditions. Although the
melt stream temperature is important, the melt cools rapidly during the fibre forming process
and so a longer range of workability for the composition improves fibre formation. The
addition of the alkali metal oxides may also serve to stabilise the melt stream so that for a
given set of conditions there is an amount that reduces shot.
Additionally, it is surmised that in small quantities the alkali metal oxides serve to suppress
phase separation in alkaline earth silicate fibres.
Since the alkaline earth silicate systems have a two liquid region in their phase diagrams, the
applicants suspect that addition of alkali metal oxides may move the melts out of a two-liquid
region into a single phase region.
The addition also has the effect of lowering melt stream temperature which may assist in
The effectiveness of these measures is also shown by the amount of shot present in the
finished material, hi the fibre forming process, droplets of melt are rapidly accelerated (by
being flung off a spinning wheel or being blasted by a jet of gas) and form long tails which
become the fibres.
However that part of the droplets that does not form fibre remains in the finished material in
the form of particles known in the industry as "shot". Shot is generally detrimental to the
thermal properties of insulation formed from the fibres, and so it is a general aim in the
industry to reduce the quantity of shot.
The applicants have found that addition of minor amounts of alkali metal to the melt has the
effect of reducing the amount of shot, and this is shown in Fig. 4 for the lanthanum
containing materials of Table 1, where it can be seen that the shot content was reduced from
Similar effects apply to lanthanum free materials. Table 5 shows the analysed compositions
of a range of alkaline earth silicate fibres (having a lower maximum use temperature) made in
accordance with the compositions of W093/1502S , which were made by spinning using a
melt stream temperature of 1380-142G°C, and with a pair of rotating spinners.
Fig. 5 shows experimentally determined shot contents with error bars indicating one standard
deviation about mean. It can be seen that in the range 0.35 to 1.5 wt% NaaO, there is a
statistical improvement in the shot content as a result of the addition. In particular, a 3 %
reduction in shot for a 0.35wt% soda content is significant.
Since there seems no detrimental effect on shrinkage at such levels (and indeed a slight
improvement) it can be seen that addition of alkali metal oxides is beneficial for the
production of such materials.
Addition of the alkali metal should be at levels that do not excessively detrimentally affect
other properties of the fibre (e.g. shrinkage), but for different applications what is "excessive"
The fibres can be used in thermal insulation and may form either a constituent of the
insulation (e.g. with other fibres and/or fillers and/or binders) or may form the whole of the
insulation. The fibres may be formed into blanket form insulation.
Although initial work was primarily related to the addition of NaaO to alkaline earth silicate
fibres, the applicants discovered that when Na2O was used as the additive to high calcium -
low magnesium fibres it had a tendency to promote crystallisation (and hence powderiness of
the fibres) after exposure to temperatures of ~1000°C. This can be seen in Fig. 8 in which
fibre a) -e) had base compositions falling in the region:-
Fibres a), b) and c) show the effect on surface appearance of fibres after exposure to 1050°C
for 24 hours on fibres containing increasing amounts of Na20 (from ~0 through 0.5wr% to
1.06wt% respectively). As can be seen, the fibre absent Na2O has a smooth appearance
indicating little crystallisation, whereas increasing Na2O leads to an increase in surface
roughness indicative of crystallisation.
In contrast, fibres d) and e) show that at 1100°C a fibre containing ~0.5wt% K20 is little
different from a fibre free of KjO, and only starts to show slight surface roughness at 1150°C.
Table 6 shows relative thermal conductivities of blankets having approximate density of
96kg.m"3 formed from fibres having the principal ingredients shown. It also shows thermal
conductivities of these blankets and these figures are shown in Fig. 9. It can be seen that
addition of Na20 and K2O seems to result in lower thermal conductivity from the blankets so
showing improved insulating ability.
The applicants have therefore identified further advantages of the use of alkali metal oxides
as additives to alkaline earth silicate blanket materials, and particular advantage to the use of
potassium. In particular, to avoid promotion of crystallisation by sodium, preferably at least
75mol% of the alkali metal is potassium. More preferably at least 90%, still more preferably
at least 95% and yet still more preferably at least 99% of the alkali metal is potassium.
To test the mutual interaction of LaaOa and KjO on the fibre properties a range of fibres were
made into blankets and tested for shrinkage at various temperatures [24 hours at temperature].
It was found that La^Ch could be reduced and replaced by KjO without significant harm to
the shrinkage properties of the materials, but this led to onset of crystallisation at lower
temperatures than for the La2O3 containing materials. However, replacement of La2O3 in part
by alumina cured this problem. Table 7 indicates a range of materials tested, the temperature
at which crystallisation commenced, and temperature at which the crystals reached ~1 um in
size. The materials all had a base composition of approximately 73.1-74.4wt% SiC>2 and 24.6-
25.3 wt% CaO with all other ingredients amounting to less than 3% in total.
CaO-SiO2-K2O (0.75%) -La2O3 (1.3%)
CaO-Si02-K2O (0.75%) -La2O3 (1.3%)
CaO-Si02-K20 (0.8%) -La203 (0.4%)
CaO-Si02-K20 (0.6%) -La2O3 (0.15%)-A1203 (0.94%)
Starts @. °C
Accordingly, a preferred range of compositions comprises:-
72% MgO 13.8%
More preferably SiO2 plus CaO > 95%, and usefully a preferred range of compositions
72% MgO 24% 0.5%
A particularly preferred range is
During further trials a second range of fibres was found that gave good results. These fibres
had the composition:-
SiO2 = 67.8-70%
CaO = 27.2-29%
A1203 = La2O3 = 0.81-1.08%
K2O = 0.47-0.63%
These fibres had a high strength (80 - 1 OSkPa for a blanket of thickness ~25mm and density
~128kg.m3) and and low shot content (-41% total shot).
The fibres may also be used in other applications where alkaline earth silicate fibres are
currently employed (e.g. as constituents of friction materials).
1. A method of making refractory alkaline earth silicate fibres comprising
predominantly silica and alkaline earth oxides and which comprise less than
lOwt% alumina and which are soluble in physiological saline solution and
non-toxic, wherein the fibres are formed from a melt, and the method
comprises the step of adding alkali metal, wherein at least 75mol% of the
alkali metal is potassium, as an intended melt component during manufacture
of the fibres to improve the mechanical andlor thermal properties of the fibre.
2. The method as claimed in Claim 1, wherein the amount of alkali metal (M)
expressed as the oxide MzO, is in the range 0.2 mol% to 2.5 mol%, preferably
0.25 to 2 mol%.
3. The method as claimed in claim 1, wherein the alkali metal is included in an
amount sufficient to increase the tensile strength of a blanket made using the
fibre by >50% over the tensile strength of a blanket free of alkali metal, and
less than an amount that will result in an excessive shrinkage at the intended
maximum use temperature.
4. The method as claimed in any one of claims 1 to 1 1, wherein the alkali metal
(M) is present in an amount expressed as the oxide MzO less than 2 mol%.
5. The method as claimed in claim 4, wherein the alkali metal is present in an
amount less than 1.5 mol%.
6. The method as claimed in Claim 5, wherein the alkali metal is present in an
amount less than 1 mol%.
7. The method as claimed in claim 6, wherein the alkali metal is present in an
amount less than 0.75 mol%.
8. The method as claimed in any one of claims 1 to 7, wherein the alkali metal is
present in an amount greater than or equal to 0.3 mol%.
9. The method as claimed in claim 8, wherein the alkali metal is present in an
amount greater than or equal to 0.4 mol%
10. The method as claimed in claim 9, wherein the alkali metal is present in an
amount greater than or equal to 0.5 mol%.
11. The method as claimed in claim 10, wherein the alkali metal is present in an
amount greater than or equal to 0.6 mol%.
12. The method as claimed in any one of claims 1 to 11, wherein the alkaline earth
silicate fibre comprises
13. The method as claimed in claim 11, wherein at least 90mol% of the alkali
metal is potassium.
14. The method as claimed in Claim 11, wherein at least 95mol% of the alkali
metal is potassium.
15. The method as claimed in Claim 1 lT wherein at least 99mol% of the alkali
metal is potassium.
16. Refractory alkaline earth silicate fibres comprising predominantly silica and
alkaline earth oxides and which comprise less than 10wt% alumina, which are
soluble in physiological saline solution and non-toxic, and which comprise
alkali metal characterized in that
at least 75mol% of the alkali metal is potassium; and,
composition in weight percent
65% MgO 13.5% AI20-j ZrO2 B203 Pz05 72% 95% M20 > 0.5%
wherein M is alkali metal.
18. The refractory alkaline earth silicate fibres as claimed in claim 17, wherein
19. The refractory alkaline earth silicate fibres as claimed in claim 18, wherein:-
0.5wt% 20. The refractory alkaline earth silicate fibres as claimed in Claim 16 having the
composition in weight percent
75% MgO 13.8% A1203 Zr02 B203 P205 75%
M20 > 0.2%
wherein M is alkali metal.
2 1. The refractory alkaline earth silicate fibres as claimed in claim 20, wherein:-
0.2 wt% 22. The refractory alkaline earth silicate fibres as claimed in any one of claims 17
to 2 l5 wherein:-
97.5wt % 23. The refractory alkaline earth silicate fibres as claimed in any one of claims 17
to 22, comprising additionally
0. lwt% wherein R is selected from the group Sc, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy,
Ho, Er, Tm, Yb, Lu, Y or mixtures thereof
24. The refractory alkaline earth silicate fibres as claimed in any one of claims
17to 23, wherein M comprises predominantly & potassium, or a mixture
thereof with sodium.
25. The refractory alkaline earth silicate fibres as claimed in claim 24, wherein at
least 90 mol% of the alkali metal is potassium.
26. The refractory alkaline earth silicate fibres as claimed in claim 24, wherein at
least 95mol% of the alkali metal is potassium.
27. The refractory alkaline earth silicate fibres as claimed in claim 24, wherein at
least 99mol% of the alkali metal is potassium.
28. The refractory alkaline earth silicate fibres as claimed in any one of claims 17
to 27, wherein M20 is present in an amount less than 2.5 mol%.
29. The refractory alkaline earth silicate fibres as claimed in claims 28, wherein
M20 is present in an amount less than 2 mol%.
30. The refractory alkaline earth silicate fibres as claimed in claims 29, wherein
M20 is present in an amount less than 1.5 mol%.
3 1. The refractory alkaline earth silicate fibres as claimed in claims 30, wherein
M20 is present in an amount less than 1 mol%.
32. The refractory alkaline earth silicate fibres as claimed in claims 3 1, wherein
M20 is present in an amount less than 0.75 mol%.
33. The refractory alkaline earth silicate fibres as claimed in any of claims 17 to
32, wherein the alkali metal is present in an amount greater than or equal to
34. The refractory alkaline earth silicate fibres as claimed in claims 33, wherein
the alkali metal is present in an amount greater than or equal to 0.4 mol%.
35. The refractory alkaline earth silicate fibres as claimed in claims 34, wherein
the alkali metal is present in an amount greater than or equal to 0.5 mol%.
36. The refractory alkaline earth silicate fibres as claimed in claims 35, wherein
the alkali metal is present in an amount greater than or equal to 0.6 mol%.
37. The refractory alkaline earth silicate fibres as claimed in any one of claims 17
to 36, wherein the amount of MgO is less than 2 wt%.
38. The refractory alkaline earth silicate fibresas claimed in claim 16 having the
composition in weight percent
72% MgO 13.8% A1203 Zr02 B2O3 P205 95% SiO2 + CaO + MgO + A1203 + ZrO2 + B203 + P205
M20 > 0.2% and 4.5%
wherein M is alkali metal of which at least 90mol% is potassium.
39. The refractory alkaline earth silicate fibres as claimed in claim 38wherein
Si02 plus CaO >95%
40. The refractory alkaline earth silicate fibres as claimed in claim 39, having the
composition in weight percent
72% MgO 24% 0.5% Zr02 B203 P205 M20 > 0.2% and 4.5%
in which M is alkali metal of which at least 90mol% is potassium.
41. The refractory alkaline earth silicate fibres as claimed in claim 38 or claim 39:
having the composition in weight percent:-
Si02 MgO CaO 25+2%
to 4 1, comprising additionally
R2O3 wherein R is selected from the group Sc, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy,
Ho, Er, Tm, Yb, Lu, Y or mixtures thereof
43. The refractory alkaline earth silicate fibres as claimed in Claim 16 having the
composition in wt%:-
SiOz = 67.8-70%
CaO = 27.2-29%
MgO = 1-1.8%
A1203 = La203 = 0.81-1.08%
K20 = 0.47-0.63%
44. Thermal insulation comprising fibres as claimed in any of claims 17-to 43 or
made by the method of any one of Claims 1 to 1 1.
45. The thermal insulation as claimed in claim 44 is in the form of a blanket.
|Indian Patent Application Number||2552/DELNP/2007|
|PG Journal Number||43/2013|
|Date of Filing||04-Apr-2007|
|Name of Patentee||THE MORGAN CRUCIBLE COMPANY PLC|
|Applicant Address||QUADRANT, 55-57 HIGH STREET, WINDSOR, BERKSHIRE SL4 1LP, GREAT BRITAIN|
|PCT International Classification Number||C03C 13/00|
|PCT International Application Number||PCT/GB2005/004149|
|PCT International Filing date||2005-10-26|