U.S. patent application number 12/389569 was filed with the patent office on 2009-06-18 for modification of alkaline earth silicate fibres.
Invention is credited to Craig John Freeman, Gary Anthony Jubb.
Application Number | 20090156386 12/389569 |
Document ID | / |
Family ID | 46124070 |
Filed Date | 2009-06-18 |
United States Patent
Application |
20090156386 |
Kind Code |
A1 |
Freeman; Craig John ; et
al. |
June 18, 2009 |
MODIFICATION OF ALKALINE EARTH SILICATE FIBRES
Abstract
A method of making refractory alkaline earth silicate fibres
from a melt, including 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.
Inventors: |
Freeman; Craig John;
(Wirral, GB) ; Jubb; Gary Anthony; (Wirral,
GB) |
Correspondence
Address: |
SMITH, GAMBRELL & RUSSELL
SUITE 3100, PROMENADE II, 1230 PEACHTREE STREET, N.E.
ATLANTA
GA
30309-3592
US
|
Family ID: |
46124070 |
Appl. No.: |
12/389569 |
Filed: |
February 20, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11263655 |
Oct 31, 2005 |
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12389569 |
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60717516 |
Sep 15, 2005 |
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Current U.S.
Class: |
501/95.1 |
Current CPC
Class: |
C03C 2213/00 20130101;
C04B 2235/3227 20130101; C04B 2235/96 20130101; C04B 2235/3201
20130101; C04B 2235/3217 20130101; C04B 2235/34 20130101; C04B
35/62665 20130101; C04B 2235/3229 20130101; C04B 35/6224 20130101;
C04B 2235/72 20130101; C04B 2235/5256 20130101; C04B 2235/3244
20130101; C04B 2235/3206 20130101; C04B 2235/3409 20130101; C03C
13/00 20130101; C04B 2235/3225 20130101; C04B 2235/3208 20130101;
C04B 2235/3224 20130101 |
Class at
Publication: |
501/95.1 |
International
Class: |
C04B 35/00 20060101
C04B035/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 1, 2004 |
GB |
GB 0424190.7 |
Feb 9, 2005 |
GB |
GB 0502701.6 |
Claims
1. A method of making refractory alkaline earth silicate fibres
comprising less than 10 wt % alumina 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.
2. A method, as claimed in claim 1, in which the amount of alkali
metal (M) expressed as the oxide M.sub.2O, is in the range 0.2 mol
% to 2.5 mol %.
3. A method, as claimed in claim 1, in which 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. A method, as claimed in claim 1, in which the composition of the
alkaline earth silicate fibre and the alkali metal content is such
that the shrinkage, as measured by the method of the description,
of a vacuum cast preform of the fibres when exposed to 850.degree.
C. for 24 hours is no greater than 3.5%.
5. A method, as claimed in claim 4, in which the composition of the
alkaline earth silicate fibre and the alkali metal content is such
that the shrinkage, as measured by the method of the description,
of a vacuum cast preform of the fibres when exposed to 1000.degree.
C. for 24 hours is no greater than 3.5%.
6. A method, as claimed as claimed in claim 5, in which the
composition of the alkaline earth silicate fibre and the alkali
metal content is such that the shrinkage, as measured by the method
of the description, of a vacuum cast preform of the fibres when
exposed to 1150.degree. C. for 24 hours is no greater than
3.5%.
7. A method, as claimed as claimed in claim 6, in which the
composition of the alkaline earth silicate fibre and the alkali
metal content is such that the shrinkage, as measured by the method
of the description, of a vacuum cast preform of the fibres when
exposed to 1250.degree. C. for 24 hours is no greater than
3.5%.
8. A method, as claimed as claimed in claim 1, in which the
composition of the alkaline earth silicate fibre and the alkali
metal content is such that the shrinkage, as measured by the method
of the description, of a vacuum cast preform of the fibres when
exposed to 1150.degree. C. for 24 hours is no greater than 2 times
the shrinkage of a fibre of the composition free of alkali
metal.
9. A method, as claimed in claim 8, in which the composition of the
alkaline earth silicate fibre and the alkali metal content is such
that the shrinkage, as measured by the method of the description,
of a vacuum cast preform of the fibres when exposed to 1150.degree.
C. for 24 hours is no greater than 1.2 times the shrinkage of a
fibre of the composition free of alkali metal.
10. A method, as claimed in claim 6, in which the composition of
the alkaline earth silicate fibre and the alkali metal content is
such that the shrinkage, as measured by the method of the
description, of a vacuum cast preform of the fibres when exposed to
1400.degree. C. for 24 hours is no greater than 3.5%.
11. A method, as claimed in claim 1, in which the inclusion as an
intended melt component of the alkali metal results in a reduction
in shot content.
12. A method, as claimed in claim 1, in which the alkali metal (M)
is present in an amount expressed as the oxide M.sub.2O less than 2
mol %.
13. A method, as claimed in claim 12, in which the alkali metal is
present in an amount less than 1.5 mol %.
14. A method, as claimed in claim 13, in which the alkali metal is
present in an amount less than 1 mol %.
15. A method, as claimed in claim 14, in which the alkali metal is
present in an amount less than 0.75 mol %.
16. A method, as claimed in claim 12, in which the alkali metal is
present in an amount greater than or equal to 0.3 mol %.
17. A method, as claimed in claim 16, in which the alkali metal is
present in an amount greater than or equal to 0.4 mol %.
18. A method, as claimed in claim 17, in which the alkali metal is
present in an amount greater than or equal to 0.5 mol %.
19. A method, as claimed in claim 18, in which the alkali metal is
present in an amount greater than or equal to 0.6 mol %.
20. A method, as claimed in claim 1, in which the alkaline earth
silicate fibre comprises <10 wt % MgO, and in which the alkali
metal M comprises predominantly sodium, potassium, or a mixture
thereof.
21. A method, as claimed in claim 20, in which at least 75 mol % of
the alkali metal is potassium.
22. A method, as claimed in claim 21, in which at least 90 mol % of
the alkali metal is potassium.
23. A method, as claimed in claim 21, in which at least 95 mol % of
the alkali metal is potassium.
24. A method, as claimed in claim 21, in which at least 99 mol % of
the alkali metal is potassium.
25. A method, as claimed in claim 1, in which the alkaline earth
silicate fibre comprises >15 wt % MgO, and in which the alkali
metal M comprises predominantly lithium.
Description
REFERENCE TO RELATED APPLICATION
[0001] The application is a divisional application and claims the
benefit of U.S. application Ser. No. 11/263,655 filed Oct. 31,
2005, which claims the benefit of priority from applicants'
provisional application 60/717,516 filed Sep. 15, 2005 now expired
and British patent applications GB 0424190.7 filed Nov. 1, 2004 and
GB 0502701.6 filed Feb. 9, 2005, all of which are relied on and
incorporated herein by reference.
INTRODUCTION AND BACKGROUND
[0002] This invention relates to alkaline earth silicate
fibres.
[0003] 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, yarns 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.
[0004] Inorganic fibrous materials can be either glassy or
crystalline. Asbestos is an inorganic fibrous material one form of
which has been strongly implicated in respiratory disease.
[0005] 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 realistic substitutes.
[0006] 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.
[0007] 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 extremely insoluble.
[0008] As intercellular fluid is saline in nature the importance of
fibre solubility in saline solution has long been recognised. If
fibres are soluble in physiological saline 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, non-metallic,
amorphous, inorganic oxide, refractory fibrous materials. The
invention particularly relates to glassy alkaline earth silicate
fibres having silica as their principal constituent.
[0009] 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. WO87/05007
stated that pure materials should be used and gave an upper limit
of 2 wt % in aggregate to the impurities that could be present. No
mention of alkali metals was made in this patent.
[0010] International Patent Application No. WO89/12032 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 Na.sub.2O in amounts ranging from 0.28 to 6.84 wt %
but gave no indication that the presence of Na.sub.2O had any
effect.
[0011] European Patent Application No. 0399320 disclosed glass
fibres having a high physiological solubility and having 10-20 mol
% Na.sub.2O and 0-5 mol % K.sub.2O. Although these fibres were
shown to be physiologically soluble their maximum use temperature
was not indicated.
[0012] Further patent specifications disclosing selection of fibres
for their saline solubility include for example European 0412878
and 0459897, French 2662687 and 2662688, PCT WO86/04807,
WO90/02713, WO92/09536, WO93/22251, WO94/15883, WO97/16386 and U.S.
Pat. No. 5,250,488.
[0013] 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.
[0014] 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.
[0015] WO93/15028 disclosed fibres comprising CaO, MgO, SiO.sub.2,
and optionally ZrO.sub.2 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 0.65 wt % were shown to be
acceptable for materials suitable for use as insulation at
1000.degree. C. WO93/15028 also required low levels of
Al.sub.2O.sub.3 (<3.97%).
[0016] WO94/15883 disclosed a number of such fibres usable as
refractory insulation at temperatures of up to 1260.degree. 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 Na.sub.2O were suspected of causing increased shrinkage in
materials for use as insulation at 1260.degree. C. The importance
of keeping the level of alumina low was stressed is stressed in
this document.
[0017] WO97/16386 disclosed fibres usable as refractory insulation
at temperatures of up to 1260.degree. C. or more. These fibres
comprised MgO, SiO.sub.2, and optionally ZrO.sub.2 as principal
constituents. These fibres are stated to require substantially no
alkali metal oxides other than as trace impurities (present at
levels of hundredths of a percent at most calculated as alkali
metal oxide). The fibres have a general composition
TABLE-US-00001 SiO.sub.2 65-86% MgO 14-35%
with the components MgO and SiO.sub.2 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.
[0018] WO2003/059835 discloses certain calcium silicate fibres
certain calcium silicate compositions for which fibres show a low
reactivity with aluminosilicate bricks, namely: [0019]
65%<SiO.sub.2<86% [0020] MgO<10% [0021] 14%<CaO<28%
[0022] Al.sub.2O.sub.3<2% [0023] ZrO.sub.2<3% [0024]
B.sub.2O.sub.3<5% [0025] P.sub.2O.sub.5<5% [0026]
72%<SiO.sub.2+ZrO.sub.2+B.sub.2O.sub.3+5*P.sub.2O.sub.5 [0027]
95%<SiO.sub.2+CaO+MgO+Al.sub.2O.sub.3+ZrO.sub.2+B.sub.2O.sub.3+-
P.sub.2O.sub.5
[0028] This patent also discloses the use of La.sub.2O.sub.3 or
other lanthanide additives to improve the 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
.about.0.5 wt % were disclosed in fibres intended for use as
insulation at up to 1260.degree. C. or more.
[0029] WO2003/060016 claims a low shrinkage, high temperature
resistant inorganic fiber having a use temperature up to at least
1330.degree. 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.
[0030] EP 1323687 claims a biosoluble ceramic fiber composition for
a high temperature insulation material comprising 75-80 wt % of
SiO.sub.2, 13-25 wt % of CaO, 1-8 wt % of MgO, 0.5-3 wt % of
ZrO.sub.2 and 0-0.5 wt % of Al.sub.2O.sub.3, wherein
(ZrO.sub.2+Al.sub.2O.sub.3) is contained 0.5-3 wt % and (CaO+MgO)
is contained 15-26 wt %.
[0031] Alkaline earth silicate fibres have received a definition in
the Chemical Abstract Service Registry [Registry Number:
436083-99-7] of: [0032] "Chemical substances manufactured in the
form of fibers. This category encompasses substances produced by
blowing or spinning a molten mixture of alkaline earth oxides,
silica and other minor/trace oxides. It melts around 1500.degree.
C. (2732.degree. F.). It consists predominantly of silica (50-82 wt
%), calcia and magnesia (18-43 wt %), alumina, titania and zirconia
(<6 wt %), and trace oxides."
[0033] This definition reflects European Health and Safety
regulations which impose special labelling requirements on silicate
fibres containing less than 18% alkaline earth oxides.
[0034] However as is clearly indicated in relation to
WO2003/059835, 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.
[0035] 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.
[0036] 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 10 wt % alumina [as indicated in WO87/05007--which first
introduced such fibres], preferably in which alumina, zirconia and
titania amount to less that 6 wt % [as indicated in the Chemical
Abstracts definition]. For regulatory reasons, preferred materials
contain more than 18% alkaline earth metal oxides.
[0037] 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.
SUMMARY OF THE INVENTION
[0038] 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.
[0039] 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.
[0040] Preferably, the amount of alkali metal (M) expressed as the
oxide M.sub.2O 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 mol
%.
[0041] 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.
[0042] 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.degree. C. for 24 hours.
[0043] 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.
[0044] The invention may be applied to all of the prior art
alkaline earth silicate compositions mentioned above.
BRIEF DESCRIPTION OF DRAWINGS
[0045] 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:
[0046] 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 Na.sub.2O content;
[0047] FIG. 2 is a graph plotting maximum, average, and minimum
values of tensile strength/density against Na.sub.2O content for
the same fibres;
[0048] FIG. 3 is a graph of experimentally determined
temperature/viscosity curves for a range of compositions;
[0049] FIG. 4 is a graph showing shot content plotted against
Na.sub.2O content for the fibres of FIG. 1
[0050] FIG. 5 is a graph of shot content against Na.sub.2O content
for a different range of alkaline earth silicate fibres
[0051] FIG. 6 is a graph of linear shrinkages for alkaline earth
silicate fibres of varying composition, compared with known
refractory ceramic fibre (RCF) fibres
[0052] FIG. 7 is a graph of the effect on blanket strength of
sodium addition to a range of alkaline earth silicate fibres
[0053] FIG. 8 contrasts micrographs showing various fibres after
exposure to a range of temperatures
[0054] FIG. 9 is a graph comparing measured thermal conductivities
for a range of fibres.
DETAILED DESCRIPTION OF INVENTION
[0055] 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).
[0056] The base melt had a nominal composition in weight
percent:
TABLE-US-00002 SiO.sub.2 73.5 CaO 25 La.sub.2O.sub.3 1.5
with other components forming minor impurities and sodium oxide
being added in specified amounts.
[0057] The melt stream temperature was monitored using a two colour
pyrometer.
[0058] Fibres produced from the spinners were passed onto a
conveyer and then needled to form blanket in a conventional
manner.
[0059] The blanket thickness, density, and tensile strength were
measured for fibres produced using a range of conditions.
[0060] 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.
[0061] 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.
[0062] 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.degree. C. and
1250.degree. C. was measured in the same manner as in
WO2003/059835.
[0063] The first thing that is noteworthy is that the blanket
strengths show a high variability. This is because the manufacture
of a blanket involves many variables, including: [0064] Composition
of the melt [0065] Temperature of the melt [0066] Melt stream
temperature [0067] Shot content (melt that has solidified in the
form of droplets rather than fibres) [0068] Fibre diameter [0069]
Fibre length [0070] Needling conditions [0071] Post-solidification
thermal history
[0072] 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.
[0073] As can be seen from FIG. 1 there appears to be relatively
little variation in 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.
[0074] However, it can be seen that with progressive increases in
Na.sub.2O 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 Na.sub.2O content. In contrast,
the shrinkage of the fibres seemed barely affected.
[0075] The fibres with nominal zero Na.sub.2O content of course had
minor trace amounts (average measured content 0.038%--maximum
0.11%). Extrapolating back to zero Na.sub.2O gives an average
tensile strength/density of 0.0675 kPa/[kg/m.sup.3]. The average
tensile strength/density for the addition of 0.3% Na.sub.2O 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.
TABLE-US-00003 TABLE 1 % linear % linear Tensile Strength Melt
Stream Blanket Blanket shrinkage shrinkage kPa (average of Tensile
Temperature thickness density 1150.degree. C./24 1250.degree. C./24
three strength/ .degree. C. (mm) (kg/m.sup.3) hours hours
measurements) density Zero nominal Na.sub.2O content 1750 7.20 118
5.67 0.048023 1750 8.18 109 8.33 0.076453 1750 16.87 161 15.33
0.095238 1750 15.12 169 15.67 0.092702 1750 15.71 134 16.00
0.119403 1750 20.51 141 13.67 0.096927 1750 19.14 138 11.33
0.082126 1750 18.58 125 9.67 0.077333 1750 18.87 141 12.00 0.085106
1750 25.92 130 14.00 0.107692 1750 24.49 140 17.00 0.121429 1750
15.88 166 13.47 0.081124 1750 17.34 144 7.33 0.050926 1750 11.00
174 16.20 0.093103 1750 22.01 124 0.52 0.88 7.91 0.06379 1760 16.60
133 18.47 0.138847 1800 8.06 129 8.67 0.067183 1800 22.04 132 12.92
0.097904 1800 21.97 139 13.62 0.09801 1850 7.75 120 9.33 0.077778
1850 18.49 133 9.31 0.069962 1850 18.12 128 8.56 0.066901 1850
17.19 123 5.33 0.043333 1850 24.49 125 5.26 0.042107 1900 21.83 114
10.57 0.092708 1910 8.50 127 12.33 0.097113 1950 8.14 115 9.33
0.081159 1950 8.92 115 10.00 0.086957 1990 19.39 123 10.67 0.086764
0.3 wt % nominal Na.sub.2O content 1800 22.82 107 19.83 0.185327
1850 17.10 149 16.91 0.113512 1900 24.40 137 17.66 0.128881 0.5 wt
% nominal Na.sub.2O content 1795 20.32 169 0.43 1.70 48.64 0.287811
1800 19.98 147 24.81 0.168913 1800 25.25 136 16.17 0.118922 1800
18.64 153 34.24 0.223769 1800 18.02 190 42.65 0.224456 1800 24.22
175 37.26 0.212895 1800 22.47 165 36.83 0.223212 1835 14.54 150
42.01 0.280067 1850 23.50 164 0.31 1.04 27.29 0.166789 1850 25.15
162 27.85 0.171681 0.7 wt % nominal Na.sub.2O content 1800 21.91
166 47.12 0.283835 1800 21.25 166 38.32 0.230863 1800 18.44 161
53.64 0.333188 1800 19.22 163 38.74 0.237669 1800 19.95 144 0.48
1.11 33.35 0.231597 1850 26.04 175 0.48 0.90 38.41 0.219467 1850
23.48 166 54.11 0.325984 1850 27.73 165 37.03 0.224404 1900 29.30
166 41.69 0.251165 1900 21.16 135 44.09 0.326617 1900 19.49 135
40.93 0.30316 1950 25.88 151 39.12 0.259073
[0076] 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.degree. C. and 1250.degree. C. were measured in the same
manner as in WO2003/059835. 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.
[0077] 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 La.sub.2O.sub.3 (as in
WO2003/059835), whereas those to the right were aimed at assessing
the effect of varying the quantity of Na.sub.2O in such a fibre.
While not conclusive, the results indicate that for these fibres
Na.sub.2O and K.sub.2O show shrinkages no worse or even better than
fibre free of Na.sub.2O, whereas Li.sub.2O appears detrimental to
shrinkage.
[0078] 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.
TABLE-US-00004 TABLE 2 Sample PAT PAT PAT Li.sub.2O PAT K.sub.2O
BG-X-04- BG-X-04- BG-X-04- STD 01 Na.sub.2O 02 03 04 0305 0277 0279
Component Na.sub.2O 0.26 0.95 0.12 0.24 0.6 0.72 1.14 MgO 0.38 0.39
0.36 0.36 0.35 0.38 0.36 Al.sub.2O.sub.3 0.6 0.64 0.56 0.62 0.38
0.02 0 SiO.sub.2 72.58 72.47 72.43 72.40 73.26 73.58 73.76 K.sub.2O
0.08 0.08 0.07 1.05 0.07 0.08 0.08 CaO 24.05 23.27 23.62 22.67
22.82 23.52 23.22 TiO.sub.2 0.1 0.10 0.11 0.15 0.1 0.1 0.1
Fe.sub.2O.sub.3 0.16 0.19 0.21 0.23 0.16 0.18 0.18 La.sub.2O.sub.3
(estimated) 1.3 1.3 1.3 1.3 1.3 1.3 1.3 Li.sub.2O 0.34* % Linear
Shrinkage 850.degree. C./24 hours 0.38 0.21 0.22 1150.degree. C./24
hours 1.05 0.88 1.58 0.63 0.47 0.36 0.59 1250.degree. C./24 hours
1.08 1.08 1.71 0.79 0.48 0.69 0.84 % Thickness shrinkage
850.degree. C./24 hours 0.42 0.71 1.31 1150.degree. C./24 hours
0.93 0.71 1.44 1250.degree. C./24 hours 0.91 0.72 6.43 Static
Solubility 24 hrs (ppm) 191 202 200 N/A
[0079] The right side of Table 2 shows firstly that only a
.about.1% higher silica content has a big effect on shrinkage,
giving a much lower shrinkage. For these fibres, linear shrinkage
at 850.degree. 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.degree. C./24hrs there is a
slight increase in both linear and through thickness shrinkage, but
at 1250.degree. 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 Na.sub.2O level
tested.
[0080] 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.
TABLE-US-00005 TABLE 3 Sample PAT Na.sub.2O PAT Na.sub.2O PAT
Na.sub.2O PAT Na.sub.2O PAT Na.sub.2O PAT Na.sub.2O 05 06 07 08 09
10 Component Na.sub.2O 0.5 0.5 0.5 0.5 0.5 1.1 MgO 0.4 0.3 0.3 0.4
0.3 0.4 Al.sub.2O.sub.3 0.6 0.5 0.6 0.8 0.6 0.8 SiO.sub.2 73.9 74.3
74.5 75.2 76.3 77.7 K.sub.2O 0.1 0.1 0.1 0.1 0.1 0.1 CaO 23.6 22.9
22.6 22.0 21.4 19.3 TiO.sub.2 0.1 0.1 0.1 0.1 0.1 0.1
Fe.sub.2O.sub.3 0.2 0.2 0.2 0.2 0.2 0.2 La.sub.2O.sub.3 1.3 1.3 1.3
1.3 1.3 1.3 % Linear Shrinkage 1150.degree. C./24 hrs 0.54 0.8 0.61
0.56 0.65 0.58 1250.degree. C./24 hrs 1.1 1.07 N/A 0.84 0.86 N/A
Static Solubility 24 hrs (ppm) 199 208 165 194 245 107
[0081] 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.
[0082] 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 addition. [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 2 wt % MgO. Also shown are shrinkages for a
conventional aluminosilicate fibre (RCF) and a magnesium silicate
fibre (MgO Silicate).
[0083] 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.degree. C. but rise thereafter. However, there is a
progressive increase in refractoriness with increasing silica
content. For the SW613 fibre containing 77 and 79% SiO.sub.2, the
shrinkage remains below that of RCF and the MgO silicate fibres up
to 1400.degree. 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.
[0084] 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
comprising:
TABLE-US-00006 SiO.sub.2 72.5-74 wt % CaO 24-26.5 wt % MgO 0.4-0.8
wt % Al.sub.2O.sub.2 <0.3 wt % La.sub.2O.sub.3 1.2-1.5 wt %
was used and varying amounts of Na.sub.2O were added. Blanket
having a density 128 kg/m.sup.3 was produced having a thickness of
.about.25 mm. The results, summarised in FIG. 7, show a dramatic
increase in blanket strength with Na.sub.2O addition.
[0085] These findings relate to compositions containing
La.sub.2O.sub.3 as a component, but similar effects of alkali metal
additions are found with alkaline earth silicate fibres not
containing La.sub.2O.sub.3 as a component.
[0086] 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.
[0087] This table shows that whereas Na.sub.2O and K.sub.2O have a
small or large respectively detrimental effect on shrinkage,
Li.sub.2O has hardly any effect on shrinkage. This does not imply
no effect at all, the inventors observed that whereas the fibres
with Na.sub.2O and K.sub.2O were similar to fibres without such
additives (coarse) the fibre with Li.sub.2O addition was
significantly finer and of better quality. At lower quantities,
Na.sub.2O and K.sub.2O may still give shrinkages that are tolerable
in most applications.
TABLE-US-00007 TABLE 4 Sample 04 MgO 01 04 MgO 02 04 MgO 03 04 MgO
04 Component Na.sub.2O 0.0 0.5 0.0 0.0 MgO 20.0 19.1 19.6 18.3
Al.sub.2O.sub.3 1.7 2.0 1.8 1.7 SiO.sub.2 77.6 77.5 77.8 78.2
K.sub.2O 0.0 0.0 0.0 1.0 CaO 0.5 0.5 0.6 0.5 TiO.sub.2 0.1 0.1 0.1
0.1 Fe.sub.2O.sub.3 0.5 0.5 0.5 0.5 Li.sub.2O 0.3 % Linear
Shrinkage 1150.degree. C./ 2.53 3.53 2.34 5.59 24 hrs 1250.degree.
C./ 2.16 3.57 2.3 9.94 24 hrs Static Solubility 24 hrs (ppm) 297
N/A 331 N/A
[0088] 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: [0089] a
high soda glass having the approximate composition in wt %:
TABLE-US-00008 [0089] SiO.sub.2 68 Na.sub.2O 13.4 CaO 7.94
B.sub.2O.sub.3 4.74 MgO 2.8 Al.sub.2O.sub.3 2.66 Fe.sub.2O.sub.3
1.17 TiO.sub.2 0.09 ZrO.sub.2 0.08 Cr.sub.2O.sub.3 0.06
[0090] an alkaline earth silicate melt comprising the approximate
composition: [0091] CaO 29 [0092] MgO 6% [0093] SiO.sub.2 64.5
[0094] + others to 100% [0095] and the same alkaline earth silicate
melt comprising respectively 1 wt % Na.sub.2O and 2 wt % Na.sub.2O
as an additive.
[0096] The viscosity/temperature graph of the high soda glass is a
smooth line rising as temperature falls.
[0097] 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).
[0098] Addition of Na.sub.2O to the melt moves this rise in
viscosity to lower temperatures.
[0099] 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.
[0100] Additionally, it is surmised that in small quantities the
alkali metal oxides serve to suppress phase separation in alkaline
earth silicate fibres.
[0101] 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.
[0102] The addition also has the effect of lowering melt stream
temperature which may assist in stability.
[0103] The effectiveness of these measures is also shown by the
amount of shot present in the finished material. In 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.
[0104] 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.
[0105] 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 .about.51% to .about.48%.
[0106] 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 WO93/15028, which were made by
spinning using a melt stream temperature of 1380-1420.degree. C.,
and with a pair of rotating spinners.
[0107] 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 % Na.sub.2O, there is a
statistical improvement in the shot content as a result of the
addition. In particular, a 3% reduction in shot for a 0.35 wt %
soda content is significant.
[0108] 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.
TABLE-US-00009 TABLE 5 Sample 04-C43-1 04C56-7 04C46-5 04C47-2
04C51-6 04C50-8 04C49-6 Component Na.sub.2O 0.11 0.35 0.66 1.01
1.47 2.03 2.46 MgO 4.78 5.90 5.18 5.47 5.71 5.76 6.20
Al.sub.2O.sub.3 1.07 0.40 0.35 0.27 0.30 0.36 0.30 SiO.sub.2 65.1
65.16 65.07 64.96 65.91 66.15 65.24 P.sub.2O.sub.5 0 0.00 0.00 0.00
0.00 0.00 0.00 K.sub.2O 0.08 0.08 0.08 0.07 0.07 0.07 0.07 CaO
28.92 27.84 28.47 28.12 26.25 25.36 24.79 TiO.sub.2 0.02 0.02 0.03
0.01 0.02 0.03 0.02 Cr.sub.2O.sub.3 0.02 0.02 0.02 0.02 0.02 0.02
0.02 Mn.sub.3O.sub.4 0.03 0.03 0.03 0.03 0.03 0.03 0.03
Fe.sub.2O.sub.3 0.2 0.19 0.19 0.18 0.18 0.18 0.18 ZnO 0 0.00 0.00
0.00 0.00 0.01 0.00 SrO 0.01 0.01 0.01 0.01 0.01 0.01 0.01
ZrO.sub.2 0 0.00 0.00 0.00 0.00 0.00 0.00 BaO 0 0.00 0.00 0.00 0.00
0.00 0.00 HfO.sub.2 0 0.00 0.00 0.00 0.00 0.00 0.00 PbO n/a n/a n/a
n/a n/a n/a n/a SnO.sub.2 n/a n/a n/a n/a n/a n/a n/a CuO n/a n/a
n/a n/a n/a n/a n/a % Linear Shrinkage 1000.degree. C./24 hours
1.42 1.33 1.54 4.18 1100.degree. C./24 hours 1.39 1.20 1.77
4.85
[0109] 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" will vary.
[0110] 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.
[0111] Although initial work was primarily related to the addition
of Na.sub.2O to alkaline earth silicate fibres, the applicants
discovered that when Na.sub.2O 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 .about.1000.degree. C. This can be seen
in FIG. 8 in which fibre a) -e) had base compositions falling in
the region:
TABLE-US-00010 SiO.sub.2 72-75 wt % CaO 22-26.5 wt % MgO 0.4-1 wt %
Al.sub.2O.sub.2 <0.3 wt % La.sub.2O.sub.3 1.2-1.5 wt %
[0112] Fibres a), b) and c) show the effect on surface appearance
of fibres after exposure to 1050.degree. C. for 24 hours on fibres
containing increasing amounts of Na.sub.2O (from .about.0 through
0.5 wt % to 1.06 wt % respectively). As can be seen, the fibre
absent Na.sub.2O has a smooth appearance indicating little
crystallisation, whereas increasing Na.sub.2O leads to an increase
in surface roughness indicative of crystallisation.
[0113] In contrast, fibres d) and e) show that at 1100.degree. C. a
fibre containing .about.0.5 wt % K2O is little different from a
fibre free of K.sub.2O, and only starts to show slight surface
roughness at 1150.degree. C.
[0114] Table 6 shows relative thermal conductivities of blankets
having approximate density of 96 kg.m.sup.-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 Na.sub.2O and K.sub.2O
seems to result in lower thermal conductivity from the blankets so
showing improved insulating ability.
TABLE-US-00011 TABLE 6 Ca Silicate Ca Silicate Ca Silicate Mg
Silicate with K.sub.2O with Na.sub.2O blanket Blanket addition
addition Na.sub.2O 0.22 0 0 1.06 MgO 0.4 19.13 0.74 0.96
Al.sub.2O.sub.3 0.79 1.58 0.15 0.13 SiO.sub.2 73.94 79.08 74.7 72.1
K.sub.2O 0.06 0 0.75 0 CaO 22.69 0.25 22.3 24.5 TiO.sub.2 0 0.06 0
0 Fe.sub.2O.sub.3 0.16 0.38 0.04 0 La.sub.2O.sub.3 2.07 NA 1.36
1.26 Temperature.degree. C. Thermal Conductivity (w m.sup.-1
K.sup.-1) 200 0.06 0.06 400 0.12 0.11 600 0.35 0.35 0.21 0.2 800
0.59 0.57 0.33 0.34 1000 0.9 0.85 0.49 0.52 1200 1.3 1.2 0.67
0.75
[0115] 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 75 mol % 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.
[0116] To test the mutual interaction of La.sub.2O.sub.3 and
K.sub.2O on the fibre properties a range of fibres were made into
blankets and tested for shrinkage at various temperatures [24 hours
at temperature].
[0117] It was found that La.sub.2O.sub.3 could be reduced and
replaced by K.sub.2O without significant harm to the shrinkage
properties of the materials, but this led to onset of
crystallisation at lower temperatures than for the La.sub.2O.sub.3
containing materials. However, replacement of La.sub.2O.sub.3 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 .about.1
.mu.m in size. The materials all had a base composition of
approximately 73.1-74.4 wt % SiO.sub.2 and 24.6-25.3 wt % CaO with
all other ingredients amounting to less than 3% in total.
TABLE-US-00012 Crystals Crystallisation Coarsen Composition Starts
@ .degree. C. ~1 mm @ .degree. C. CaO--SiO2--La2O3 (1.3%) 1100 1200
CaO--SiO2--K.sub.2O (0.75%) 1000 1100 CaO--SiO2--K.sub.2O
(0.75%)--La.sub.2O.sub.3 1050 1150 (1.3%) CaO--SiO2--K.sub.2O
(0.75%)--La.sub.2O.sub.3 1050 1150 (1.3%) CaO--SiO2--K.sub.2O
(0.8%)--La.sub.2O.sub.3 1050 1200 (0.4%) CaO--SiO2--K.sub.2O
(0.6%)--La.sub.2O.sub.3 1100 1200 (0.15%)--Al.sub.2O.sub.3
(0.94%)
[0118] Accordingly, a preferred range of compositions comprises:
[0119] 72%<SiO.sub.2<79% [0120] MgO<10% [0121]
13.8%<CaO<27.8% [0122] Al.sub.2O.sub.3<2% [0123]
ZrO.sub.2<3% [0124] B.sub.2O.sub.3<5% [0125]
P.sub.2O.sub.5<5% [0126]
95%<SiO.sub.2+CaO+MgO+Al.sub.2O.sub.3+ZrO.sub.2+B.sub.2O.sub.3+P.sub.2-
O.sub.5 [0127] M.sub.2O>0.2% and <1.5% in which M is alkali
metal of which at least 90 mol % is potassium.
[0128] More preferably SiO.sub.2 plus CaO>95%, and usefully a
preferred range of compositions comprises: [0129]
72%<SiO.sub.2<75% [0130] MgO<2.5% [0131] 24%<CaO<26%
[0132] 0.5%<Al.sub.2O.sub.3<1.5% [0133] ZrO.sub.2<1%
[0134] B.sub.2O.sub.3<1% [0135] P.sub.2O.sub.5<1% [0136]
M.sub.2O>0.2% and <1.5% in which M is alkali metal of which
at least 90 mol % is potassium.
[0137] A particularly preferred range is [0138] SiO.sub.2 74.+-.2%
[0139] MgO<1% [0140] CaO 25.+-.2% [0141] K.sub.2 O 1.+-.0.5%
[0142] Al.sub.2O.sub.3<1.5% [0143] 98%
<SiO.sub.2+CaO+MgO+Al.sub.2O.sub.3+K.sub.2O
[0144] And these preferred ranges may comprise additionally
R.sub.2O.sub.3<0.5 wt % where 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.
[0145] During further trials a second range of fibres was found
that gave good results. These fibres had the composition: [0146]
SiO.sub.2=67.8-70% [0147] CaO=27.2-29% [0148] MgO=1-1.8% [0149]
Al.sub.2O.sub.3=<0.25% [0150] La.sub.2O.sub.3=0.81-1.08% [0151]
K.sub.2O=0.47-0.63%
[0152] These fibres had a high strength (80-105 kPa for a blanket
of thickness .about.25 mm and density .about.128 kg.m.sup.3) and
and low shot content (.about.41% total shot).
[0153] The fibres may also be used in other applications where
alkaline earth silicate fibres are currently employed (e.g. as
constituents of friction materials).
* * * * *