GB2534410A

GB2534410A - Inorganic fibre compositions

Info

Publication number: GB2534410A
Application number: GB1501164.6A
Authority: GB
Inventors: Freeman Craig; Thomas David; English Thomas
Original assignee: Morgan Advanced Mat PLC
Current assignee: Morgan Advanced Mat PLC
Priority date: 2015-01-23
Filing date: 2015-01-23
Publication date: 2016-07-27
Also published as: WO2016116763A1; GB201501164D0

Abstract

Inorganic fibres are formed by a sol-gel process as a glass having the composition - 66.5 < Al203 < 73.5 wt%; 11.5 < Si02 < 15.5 wt%; 4 < Ca0 < 13.5 wt%; 4 < Sr0 < 13.5 wt%; and having an alkaline earth metal oxide content of between 12 wt% and 20 wt% and having an Al203+ SiO2 content of between 80 wt% and 87 wt%. Methods of manufacture comprise formation of a sol comprising precursors of aluminium oxide, silicon oxide, calcium oxide and strontium oxide, forming fibres from the sol and firing the resultant fibres at a temperature in excess of 900 degrees C to produce the said fibres. Applications thereof include thermal insulation, mastics, composite materials, papers, support structures for catalysts, friction materials, catalyst bodies, fibre blends and automobile components.

Description

INORGANIC FIBRE COMPOSITIONS

Field of the Invention

This invention relates to inorganic fibre compositions, and in particular to alkaline earth aluminosilicate fibres. The invention is also concerned with sol-gel processes for producing such fibres, and the use of such fibres in support structures for catalyst bodies in pollution control devices such as automotive exhaust system catalytic converters and diesel particulate filters.

Background

Fibrous materials are well known for their use as thermal and/or acoustic insulating materials and are also known for their use as strengthening constituents in composite materials such as, for example, fibre reinforced cements, fibre reinforced plastics, and as a component of metal matrix composites. Such fibres may be used in support structures for catalyst bodies in pollution control devices such as automotive exhaust system catalytic converters and diesel particulate filters and may be used in the catalyst bodies themselves. Such fibres may be used as a constituent of friction materials [e.g. for automotive brakes]. The fibres of the present invention have a range of properties and may be usable in any or all of these applications depending on the properties shown.

WO 2007/054697 discloses inorganic fibres having a composition comprising a refractory base composition comprising silica and alumina and an additional component selected from alkaline earth metal oxides, alkali metal oxides, and mixtures thereof The fibres disclosed therein exhibit a low shrinkage at elevated temperature, and a high resilience at temperature, and also have the virtue of having a degree of solubility in body fluids which is significantly higher than the solubility of pure mullite fibres. As described in said document, there is a trade-off in these requirements, with the invention disclosed therein permitting the production of highly refractory-slightly soluble materials at one extreme to very soluble-reasonably refractory materials at the other with a range of characteristics in between.

Due to public health concerns surrounding inhaled fibres, governments and regulators are adopting measures to discourage or even ban the use of fibres below a certain level of biosolubility. Consequently, there is a pressing need to find fibres with improved mechanical properties and improved biosolubility so that high-resilience materials can be utilised without falling foul of regulatory restrictions.

Summary of the Invention

The applicants have discovered a particular range of sol-gel fibres which may yield both improved biosolubility and mechanical strength for applications taking place at 650°C, which conveniently is a temperature useful for certain automotive applications of inorganic fibres.

Accordingly, in a first aspect, the present invention provides alkaline earth aluminosilicate fibres having a composition comprising: 66.5 < A1203 < 73.5 wt%; 11.5 < Si02 < 15.5 wt%; 4 <CaO < 13.5 wt%; 4 < Sr° < 13.5 wt%; and having an alkaline earth metal oxide content of between 12 wt% and 20 wt% and having an A1203 + SiO2 content of between 80 wt% and 87 wt%.

The scope of the claimed invention is as set out in the claims, and the scope thereof is incorporated into this description by reference.

Further features of the invention are as set out in the appended claims and exemplified in the

following description.

For the avoidance of doubt it should be noted that in the present specification the term "comprise" in relation to a composition is taken to have the meaning of include, contain, or embrace, and to permit other ingredients to be present. The terms "comprises" and "comprising" are to be understood in like manner. It should also be noted that no claim is made to any composition in which the sum of the components exceeds 100%.

Where a patent or other document is referred to herein, its content is incorporated herein by reference to the extent permissible under national law.

Further it should be understood that usage in compositions of the names of oxides [e.g. alumina, silica, quicklime, calcia, strontia] does not imply that these materials are supplied as such, but refers to the composition of the final fibre expressing the relevant elements as oxides. The materials concerned may be provided in whole or in part as mixed oxides, compounded with fugitive components [e.g. supplied as carbonates] or indeed as non-oxide components [e.g. as halides].

To prove the concept of the invention, a number of compositions were made by forming various aluminosilicate compositions comprising alkaline earth oxide additives. Except for such differences as highlighted below, the manufacturing method was similar to that of the fibres disclosed in PCT application no. WO 2007/054697. The precursors used were composed of a base sol to which was added precursors for the desired alkaline earth. An aluminium chlorohydrate was used as the source of alumina. A mixture of siloxane and colloidal silica sol acted as a source of silica. The precursors used for the preparation of the base sol for the production of the fibre in the present invention can be accomplished by other conventional methods known in the art. These include the use of inorganic oxy compounds, alkoxides, and chlorides.

The invention is not limited to any particular method of forming the fibres from the sol, and other methods [e.g. rotary or centrifugal formation of fibres; drawing; air jet attenuation] may be used. The compositions described herein and other alkaline earth aluminosilicate fibres may also be made by melt methods, and such fibres may avoid problems that flow from formation by a sol-gel route.

Alkaline earth oxides or alkali metal oxides used to alter the properties of the sol-gel formed fibres according to the present invention were included by adding soluble salts in the sol precursor. These include salts such as chlorides or nitrates [e.g calcium nitrate tetrahydrate, strontium nitrate, magnesium nitrate hexahydrate, potassium chloride].

The process used experimentally involved feeding a liquid sol onto a rapidly spinning shallow cup having inclined sides. Fiberisation has been demonstrated from 3,000rpm up to 15,000rpm. Alternative methods successfully used include: * Sol is extruded through 300 x 0.2 mm holes spaced evenly around the periphery of a disc rotating at 2600 r.p.m. Air at 15°C and 45% relative humidity is blown through an annular orifice past the disc to attenuate the sol streams. Hot air at 160 -200°C is blown through a further annular orifice outside the fiberising air annular orifice to dry the sol streams into green fibre.

* A spinning disc of a closed cup design with rows of holes around the circumference (typically -0.5mm diameter), the sol being fed to the spinner through the shaft.

* A fibre blowing system where sol is forced through small orifices (typically -0.3mm) using pressure generated using compressed or pressurised air. Surrounding each orifice is a shroud of air to dry and draw the fibres.

The applicant previously used a method in which sol was ejected from the lip of the cup by centrifugal force, forming thin streams of material. As the ejected material left the cup it passed through a stream of hot air which dried and gelled the sol to form an unfired fibre. The temperature of this air was measured using a thermocouple positioned in the hot air flow just above the spinning cup. The air temperature used for the majority of examples was -60°C. Some sols were fiberised using drying air up to -80°C. The air temperature needs to be selected to meet the viscosity and drying characteristics of the sol and the additives present. Typically temperatures of 30°C to 150°C may be used as appropriate. Any other suitable means for drying the fibre may be employed, for example, by circulating dehumidified air or gas around the fibre.

The applicant presently uses a process in which sol is extruded through 0.4 mm diameter holes with a spacing of 3 mm using compressed air to provide back pressure. The liquid streams are then attenuated by airstreams either side of the sol streams and broadly parallel with them. The air streams are at a distance of 1 mm from the sol streams. The air pressure used is 0.1 bar and the resultant air velocity about 120 m/s. The air is humidified and cooled to maintain 25-35°C and a relative humidity of between 45 and 65%. The chamber into which the sol streams are attenuated is kept at a temperature of between 90 and 100°C measured at a distance 500 mm from the fiberi sing heads.

It has been discovered that the process of drying the fibres can have a significant effect on their subsequent physical properties. In the event fibres are not properly dried on emergence, "kinks" can appear in the fibres produced and mechanical resilience suffers accordingly. Beneficially, it has been discovered that the spacing of the fibre streams involved has an effect on drying; a 3mm spacing between nozzles/holes/orifices/points of origin for fibre streams can ensure that sufficient airflow exists to allow for proper drying.

The fibres were collected in alumina kiln trays and heat treated by placing the tray in a kiln and firing. Superior results were obtained when the fibres were fired at 900°C for an hour, allowed to cool, and subsequently fired at 1050-1150°C (usually 1100°C) for an hour (with a 100°C/hr ramp rate). This has the beneficial effect of controlling the level of crystallisation in the fibres, and in particular the ratio of y-alumina crystals to amorphous material in the fibres. Limiting crystallisation helps to ensure improved biosolubility of the fibres produced.

Comparative fibre As well as producing fibres as outlined above, comparative fibres were obtained from various sources. Two known fibres were obtained from commercial sources. The first of these were Maftec Autowrap fibres (comprising 72.3% alumina, 27.5% silica by weight). The second of these were Saffil LD Mat fibres, found to comprise 96% alumina and 4% silica by weight. These provided examples of aluminosilicate fibres with excellent mechanical properties but extremely poor levels of solubility. They are referred to henceforth as the "Maftec" and "Saffil" fibres respectively.

A third comparative fibre, comprising 70% alumina, 19% alumina, and 11% calcia by weight, was produced based on the methods of fibre production disclosed in disclosed in PCT application no. WO 2007/054697. This will be referred to subsequently as the "PCT" fibre.

Example fibres

The applicants have investigated a range of fibres to determine the effect of calcia, strontia, and total amount of silica and alumina on properties. Table 1 summarises a range of example fibres of the present invention and the comparative fibres, providing their compositions as well as shot content. Higher shot content appears to correlate with diminished mechanical resilience. Shot content can be less than 6wt%, or less than 2 wt%, or even less than 1.5 wt%.

To balance the requirements of biosolubility and mechanical resilience for fibres intended for applications at around 650°C, a typical compositional range might be:- 66.5 < A1203 < 73.5 wt%; 11.5 < Si02 < 15.5 wt%; 4 < CaO < 13.5 wt%; 4 < Sr0 < 13.5 wt%; with an alkaline earth metal oxide content of between 12 wt% and 20 wt% and an A1203 + SiO2 content of between 80 wt% and 87 wt%.

It can be that the proportion of A1203 is at least 69.5 wt%. It can be that the proportion of A1203is at most 72 wt%. It can be that the proportion of A1205 is at most 70 wt%. It can be that the proportion of A1203 is 69.7+0.1 wt%.

Sample A1203 (wt%) Si02 (wt%) CaO (wt%) SrO (wt%) Shot Content 226 68.7 12.8 10.6 7.6 0.5 237 66.8 15.4 10.2 7.3 5.89 242 68.7 13 10.6 7.5 0.5 248 69.7 13.1 9.9 7.1 1.1 255 71.9 11.5 9.9 7.2 3.5 270 69.2 13.2 10.1 7.2 2.1 272 71.9 12 8.8 6.9 1.0 275 73.2 13.6 5.9 7 3.4 278 67.8 14 9.7 8 4.8 281 68.8 13.2 13.5 4.2 4.89 283 68.6 13.6 4.1 13.4 5 285 66.7 13.5 9.6 9.9 1.5 287 69.2 13.1 10.1 7.3 2.85 Maftec 72.3 27.5 0 0 0.3 (comparative) Saffil 96.0 4.0 0 0 0.6 (comparative) (comparative) Table 1: Samples, comparative examples, and compositional data It can be that the proportion of Si02 is at least 12 wt%. It can be that the proportion of Si02 is at least 12.8 wt%. It can be that the proportion of Si02 is at most 14 wt%. It can be that the proportion of Si02 is at most 13.25 wt%. It can be that the proportion of Si02 is 13 1+0 1 wt%.

It can be that the proportion of Ca0 is at least 5.9 wt%. It can be that the proportion of Ca0 is at least 8.8 wt%. It can be that the proportion of CaO is at least 9.75 wt%. It can be that the proportion of CaO is at most 10.6 wt%. It can be that the proportion of CaO is at most 10 wt%. It can be that the proportion of Ca0 is 9.9+0.1 wt%.

It can be that the proportion of SrO is at least 7 wt%. It can be that the proportion of SrO is at most 10 wt%. It can be that the proportion of SrO is at most 7.25 wt%. It can be that the proportion of SrO is 7.1+0.1 wt%.

In the case of most of the fibres the source of silica in the sol gel consisted of a 50:50 mixture by mass of siloxane and colloidal silica, the colloidal silica in question being marketed under the brand name "Ludox CL" (30 wt% suspension of silica in water, pH 4.5). In two samples, nos. 270 and 287, the colloidal silica in question was that marketed under the brand name "Levasil 200S" in a 50:50 mixture of Levasil to siloxane. The resultant fibres had inferior properties compared with sample no. 248. Consequently it is considered preferable to use Ludox CL instead of Levasil 2005 as a source of colloidal silica. Levasil 200S has a comparable silica concentration and pH to Ludox CL, but whereas Levasil 200S provides silica with an average particle size of 15nm and provides aluminium salts as a counter ion, Ludox CL provides silica with an average particle size of 12nm and has provides chloride as a counter ion. These factors may be related to the difference in performance.

Comparative fibres and fibres according to the present invention were assessed on mechanical resilience through a hot cyclic compression test, in which the materials were subjected to cyclic compression between two different pressures at 650°C and the retained force measured; the more force retained, the more resilient the material. Static solubility (normalised and otherwise) and flow through solubility measurements were also made in accordance with the procedure set out in W02008/065363, save that the test proceeded for 24 hours instead of 5 hours due to the lower solubility of the fibres involved. The results are given below in Table 2.

Sample Retained pressure force Static solubility (ppm) Normalised static Flow through solubility (ng/cm2hr) (kPa) on 5000th cycle (open gap) solubility 226 49 104 133 N/A 237 13 98 286 N/A 242 40 101 120 N/A 248 47 106 245 245 255 28 N/A N/A N/A 270 14 94 185 N/A 272 32 110 253 205 275 34 86 165 107 278 29 118 373 N/A 281 25 87 226 N/A 283 25 80 217 N/A 285 39 100 234 N/A 287 17 93 193 N/A Maftec 67 3.2 N/A 1 (comparative) Saffil 63 3.5 N/A N/A (comparative) (comparative) Table 2: Samples, comparative examples, and performance on tests of mechanical resilience and static solubility It will be noted that whilst the Maftec and Saffil comparative fibres enjoy a high level of mechanical resilience, their solubility is negligible. The PCT comparative fibre based on the criteria of WO 2007/054697 can attain a level of mechanical resilience which is still somewhat impressive, and is about 15-20 times as soluble (depending on what measure of solubility you consult) as the Maftec and Saffil fibres.

The fibres according to the present invention can provide an even greater level of solubility -some have a flow through solubility over 200 times greater than the Maftec fibre, for instance. Even more significantly and unexpectedly, fibres according to preferred modes of the present invention, such as sample no. 248, actually present a heightened level of solubility with no appreciable drop in mechanical resilience compared with the PCT comparative fibre.

Variants The present invention does not preclude the presence of other components, for example:- * alkaline earth metals other than calcium and strontium may be present * alkali metals may be present * transition metals and lanthanide elements may be present and although the claims are expressed in terms of oxides, halide components may also be present.

Potential uses The fibres of the present invention can be used, subject to meeting relevant performance criteria, for any purpose for which fibrous inorganic materials, and particularly alkaline earth silicate and aluminosilicate materials, have been used heretofore; and may be used in future applications where the fibre properties are appropriate. In the following reference is made to a number of patent documents relating to applications in which the fibres may be used, subject to meeting relevant performance criteria for the application. The fibres of the present invention can be used in place of the fibres specified in any of these applications subject to meeting relevant performance criteria.

For example, the fibres may be used as:- * bulk materials; * deshotted materials [W02013/094113]; * in a mastic or mouldable composition [W02013/080455, W02013/080456] or as part of a wet article [W02012/132271]; * as a constituent in needled or otherwise entangled [W02010/077360, W02011/084487] assemblies of materials, for example in the form of blanket, folded blanket modules, or high density fibre blocks [W02013/046052], * as a constituent of non-needled assemblies of materials, for example felts, vacuum formed shapes [W02012/132469], or papers [W02008/136875, W02011/040968, W02012/132329, W02012/132327]; * as a constituent (with fillers and/or binders) of boards, blocks, and more complex shapes [W02007/143067, W02012/049858, W02011/083695, W02011/083696], * as strengthening constituents in composite materials such as, for example, fibre reinforced cements, fibre reinforced plastics, and as a component of metal matrix composites; * in support structures for catalyst bodies in pollution control devices such as automotive exhaust system catalytic converters and diesel particulate filters [W02013/015083], including support structures comprising: o edge protectants [W02010/024920, W02012/021270]; o microporous materials [W02009/032147, W02011019394, W02011/019396]; o organic binders and antioxidants [W02009/032191], o intumescent material [W02009/032191]; o nanofib rill ated fibres [W02012/021817]; o microspheres [W02011/084558]; o colloidal materials [W02006/004974, W02011/037617] o oriented fibre layers [W02011/084475]; o portions having different basis weight [W02011/019377]; o layers comprising different fibres [W02012065052]; o coated fibres [W02010122337], o mats cut at specified angles [W02011067598]; [NB all of the above features may be used in applications other than support structures for catalytic bodies] o in the form of an end cone [e.g. US6726884, US8182751] * as a constituent of catalyst bodies [W02010/074711]; * as a constituent of friction materials [e.g. for automotive brakes [JP56-16578]]; * for fire protection [W0201 V060421, W02011/060259, W02012/068427, W02012/148468, W02012/148469, W02013074968], and optionally in combination with one or more intumescent materials, endothermic materials, or both intumescent and endothermic materials * as insulation, for example; o as insulation for ethylene crackers [W02009/126593], hydrogen reforming apparatus [US4690690]; o as insulation in furnaces for the heat treatment of metals including iron and steel [US4504957], o as insulation in apparatus for ceramics manufacturing.

The fibres may also be used in combination with other materials. For example the fibres may be used in combination with polycrystalline (sol-gel) fibres [W02012/065052] or with other biosoluble fibres [W02011/037634].

Bodies comprising the fibres may also be used in combination with bodies formed of other materials. For example, in insulation applications, a layer of material according to the present invention [for example a blanket or board] may be secured to a layer of insulation having a lower maximum continuous use temperature [for example a blanket or board of alkaline earth silicate fibres] [W02010/120380, W02011133778]. Securing of the layers together may be by any known mechanism, for example blanket anchors secured within the blankets [US4578918], or ceramic screws passing through the blankets [see for example DE3427918-A1].

Treatment of the.fibres In formation of the fibres or afterwards they may be treated by applying materials to the fibres.

For example:-

* lubricants may be applied to the fibres to assist needling or other processing of the fibres; * coatings may be applied to the fibres to act as binders; * coatings may be applied to the fibres to provide a strengthening or other effect, for example phosphates [W02007/005836] metal oxides [W02011159914] and colloidal materials such as alumina, silica and zirconia [W02006/004974]; * binders may be applied to the fibres to bind the fibres subsequent to incorporation in a body comprising such fibres.

Many variants, product forms, uses, and applications of the fibres of the present invention will be apparent to the person skilled in the art and are intended to be encompassed by this invention.

By providing biosoluble fibres having improved mechanical properties and solubility over the fibres of W02007054697, the present invention extends the range of applications for which biosoluble fibres may be used. This reduces the present need, for many applications, to use fibres that are not biosoluble.

Claims

CLAIMSInorganic fibres having a composition comprising:-66.5 < A1203 < 73.5 wt%; 11.5 < Si02< 15.5 wt%; 4 < CaO < 13.5 wt%; 4 < Sr() < 13.5 wi%; and having an alkaline earth metal oxide content of between 12 wt% and 20 wt% and having an A1203 + SiO, content of between 80 wt% and 87 wt%.
2. Inorganic fibres, as claimed in Claim 1 in which 69.5 wt% < A1,03
3. Inorganic fibres, as claimed in any preceding Claim in which A1203 < 72 wt%.
4. Inorganic fibres, as claimed in any preceding Claim in which A1203 <70 wt%.
5. Inorganic fibres, as claimed in any preceding Claim in which A1203 = 69.7±0.1 wt%.
6. Inorganic fibres, as claimed in any preceding Claim, in which 12 wt% < SiO2.
7. Inorganic fibres, as claimed in any preceding Claim, in which 12.8 wt% < SiO2.
8. Inorganic fibres, as claimed in any preceding Claim, in which SiO2 < 14 wt%.
9. Inorganic fibres, as claimed in any preceding Claim, in which SiO2 < 13.25 wt%.
10. Inorganic fibres, as claimed in any preceding Claim, in which Si°, = 13.1+0.1 wt%.
11. Inorganic fibres, as claimed in any preceding Claim, in which 5.9 wt% < CaO.
12. Inorganic fibres, as claimed in any preceding Claim, in which 8.8 wt% < CaO.
13. Inorganic fibres, as claimed in any preceding Claim, in which 9.75 vvt% < Ca0.
14. Inorganic fibres, as claimed in any preceding Claim, in which CaO < 10.6 wt%.
15. Inorganic fibres, as claimed in any preceding Claim, in which CaO < 10 wt%.
16. Inorganic fibres, as claimed in any preceding Claim, in which CaO = 9.9+0.1 wt%
17. Inorganic fibres, as claimed in any preceding Claim, in which 7 wt% < SrO.
18. Inorganic fibres, as claimed in any preceding Claim, in which SrO < 10 wt%.
19. Inorganic fibres, as claimed in any preceding Claim, in which SrO < 7.25 wt%.
20. Inorganic fibres, as claimed in any preceding Claim, in which SrO = 7.1+0.1 wt%.
21. Inorganic fibres, as claimed in any preceding claim, having a composition comprising:- 69.5 < A1203 < 70 wt%; 12.8 < Si02 < 13 25 wt%; 9.75 < Ca0 < 10 wt%; 7 < SrO < 7.25 wt%
22. Inorganic fibres, as claimed in any preceding claim, having a composition comprising:-A1203 = 69.7+0.1 wt%; SiO2 = 13.1+0.1 wt%; CaO = 9.9+0.1 wt%; SrO = 7.1+0.1 wt%.
23. Inorganic fibres, as claimed in any preceding Claim, in which the fibres have a shot content of less than 6wt%.
24. Inorganic fibres, as claimed in any preceding Claim, in which the fibres have a shot content of less than 2w1%.
25. Inorganic fibres, as claimed in any preceding Claim, in which the fibres have a shot content of less than 1.5wt%.
26. A method of producing sol-gel fibres as claimed in any preceding claim comprising:-the formation of a sol comprising precursors for aluminium oxide, silicon oxide, calcium oxide and strontium oxide forming fibres from the sol firing the resultant fibres at a temperature in excess of 900°C to produce fibres as claimed in any preceding claim.
27. A method as claimed in Claim 26, in which fibres are fired at about 1100°C.
28. A method as claimed in Claim 27, in which fibres are fired first at about 900°C, allowed to cool, and subsequently fired at 1050-1150°C
29. A method as claimed in Claim 28, in which fibres are fired first at about 900°C, allowed to cool, and subsequently fired at 1050-1150°C
30. A method as claimed in Claim any of claims 26-29, in which the precursor for silicon oxide is a mixture of siloxane and a colloidal silica.
31. A method as claimed in Claim 30, in which the mixture consists of 50% siloxane and 50% of colloidal silica by mass.
32. Thermal insulation comprising inorganic fibres as claimed in any one of Claims 1 to 25 00 Thermal insulation, as claimed in Claim 31, in which the insulation is in the form of a blanket of needled or otherwise entangled fibres.34. Mastics comprising inorganic fibres as claimed in any one of Claims 1 to 25.35. Composite materials comprising inorganic fibres as claimed in any one of Claims 1 to 25.36. Papers comprising inorganic fibres as claimed in any one of Claims 1 to 25.37. Support structures for catalyst bodies, the structures comprising inorganic fibres as claimed in any one of Claims 1 to 25.38. Friction materials comprising inorganic fibres as claimed in any one of Claims 1 to 25.39. Catalyst bodies comprising inorganic fibres as claimed in any one of Claims 1 to 25.40. Fibre blends comprising inorganic fibres as claimed in any one of Claims 1 to 25.41. Fibre blends as claimed in Claim 39, in which the other fibres are or include polycrystalline fibres.42. Automobiles and components for automobiles or automotive applications comprising inorganic fibres as claimed in any one of Claims 1 to 25.