Thermal Insulation

Abstract

The present invention relates to inorganic fibres having a composition comprising: 61.0 to 70.8 wt % SiO.sub.2; 28.0 to 39.0 wt % CaO; 0.10 to 0.85 wt % MgO other components, if any, providing the balance up to 100 wt %,

The sum of SiO.sub.2 and CaO is greater than or equal to 98.8 wt % and the other components comprise less than 0.70 wt % Al.sub.2O.sub.3, if any.

Claims

1. Inorganic fibres having a composition comprising: 61.0 to 70.8 wt % SiO.sub.2; 28.0 to 39.0 wt % CaO; 0.10 to 0.85 wt % MgO other components, if any, providing the balance up to 100 wt %, wherein the sum of SiO.sub.2 and CaO is greater than or equal to 98.8 wt % and the other components comprise less than 0.70 wt % Al.sub.2O.sub.3, if any.

2. The inorganic fibres of claim 1, comprising 0.01 to less than 0.65 wt % Al.sub.2O.sub.3.

3. The inorganic fibres according to claim 1, which after heat treatment at 1100° C. for 24 hours comprise surface crystal grains with an average crystallite size of 0.90 μm or less.

4. The inorganic fibres of claim 1, wherein the other components account for at least 0.3 wt % of the composition of the inorganic fibres.

5. The inorganic fibres of claim 1, wherein the sum of SiO.sub.2+CaO+MgO is greater than or equal to 99.3 wt % of the fibre composition.

6. The inorganic fibres of claim 1, wherein the sum of SiO.sub.2+CaO+MgO+Al.sub.2O.sub.3 is greater than or equal to 99.5 wt % of the fibre composition.

7. The inorganic fibres of claim 1, wherein the fibre composition comprises less than 0.80 wt % MgO.

8. The inorganic fibres according to claim 1, wherein the amount of Al.sub.2O.sub.3 is less than 0.35 wt %.

9. The inorganic fibres of claim 1, wherein the sum of SiO.sub.2 and CaO is greater than or equal to 99.0 wt %.

10. The inorganic fibres of claim 1, wherein the sum of SiO.sub.2 and CaO is greater than or equal to 99.1 wt %.

11. The inorganic fibres of claim 1, wherein the sum of SiO.sub.2 and CaO is greater than or equal to 99.2 wt %.

12. The inorganic fibres of claim 1, wherein the composition comprises less than 70.0 wt % SiO.sub.2.

13. The inorganic fibres according to claim 1, wherein then composition comprises greater than 64.5 wt % SiO.sub.2.

14. The inorganic fibres according to claim 1, wherein the composition comprises 65.7 wt % or greater SiO.sub.2.

15. The inorganic fibres according to claim 1, wherein the sum of the other components is in the range 0.05 to 1.0 wt % of the fibre composition, said other components comprising one or more oxides or fluorides of lanthanides, Li, Na, K, Sr, Ba, Cr, Fe, Zn, Y, Zr, Hf; Ca, B, P or combinations thereof.

16. The inorganic fibres according to claim 15, wherein the sum of the other components comprise one or more oxides or fluorides of lanthanides, Sr, Ba, Cr, Zr or combinations thereof.

17. The inorganic fibres according to claim 15, wherein the sum of the other components is in the range 0.1 to 0.8 wt %.

18. The inorganic fibres according to claim 1, wherein the composition comprises: 65.7 to 69.0 wt % SiO.sub.2; 30.0 to 34.2 wt % CaO; 0.10 to 0.60 wt % MgO; 0 to 0.50 wt % Al.sub.2O.sub.3; and the sum of SiO.sub.2 and CaO is greater or equal to 99.0 wt %.

19. The inorganic fibres according to claim 1, wherein the composition comprises: 65.7 to 69.0 wt % SiO.sub.2; 30.0 to 34.2 wt % CaO; 0.10 to 0.45 wt % MgO; 0 to 0.40 wt % Al.sub.2O.sub.3; and the sum of SiO.sub.2 and CaO is greater or equal to 99.2 wt %.

20. The inorganic fibres according to claim 1, wherein the other components comprise 0 to 0.25 wt % alkali metal oxides.

21. The inorganic fibres according to claim 1, wherein the other components comprise 0 to 0.20 wt % alkali metal oxides.

22. The inorganic fibres according to claim 1, wherein the arithmetic mean fibre diameter is less than 6.0 μm.

23. A thermal insulation comprising inorganic fibres as claimed in claim 1.

24. The thermal insulation according to claim 23 in the form of a blanket of the inorganic fibres.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0104] FIG. 1 is a SEM image of fibre sample C-24

[0105] FIG. 2 is a SEM image of a fibre produced accordingly to the prior art (sample C-23)

[0106] FIG. 3 is a SEM image of a fibre sample 19

[0107] FIG. 4 is a SEM image of a fibre sample 31

[0108] FIG. 5 is a SEM image of a fibre sample 22

[0109] FIG. 6 is a SEM image of a fibre sample 20

[0110] FIG. 7 is a SEM image of a fibre sample C-36

[0111] FIG. 8 is a SEM image of sample 8

[0112] FIG. 9 is a SEM image of sample 26

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0113] Fibres according to the invention and comparative fibres described herein have been produced at either the French production facilities in Saint Marcellin, France by spinning [made from the melt by forming a molten stream and converting the stream into fibre by permitting the stream to contact one or more spinning wheels]; or at the applicant's research facilities in Bromborough, England by spinning or alternatively by blowing [fibres made from the melt by forming a molten stream and converting the stream into fibre by using an air blast directed at the stream]. The invention is not limited to any particular method of forming the fibres from a melt, and other methods [e.g. rotary or centrifugal formation of fibres; drawing; air jet attenuation] may be used. The resultant fibres were then fed onto a conveyor belt and entangled by needling methods, as known in the art.

[0114] The raw materials used to produce the inorganic fibres of a preferred embodiment of the present invention are lime and silica sand. The chemical analysis (normalised) of the lime used is provided in Table 1 below. The incidental impurities (100−CaO−SiO.sub.2) in the lime is typically less than 2.0 wt %. The silica sand purity may be 98.5 wt % of 99.0 wt % or higher. Typically, the silica sand had a purity of greater than 99.5 wt % silica and less than 200 ppm Fe.sub.2O.sub.3; less than 1000 ppm Al.sub.2O.sub.3; less than 200 ppm TiO.sub.2, less than 100 ppm CaO and less than 100 ppm K.sub.2O.

TABLE-US-00001 TABLE 1 Lime Un-normalised bag CaO Al.sub.2O.sub.3 Fe.sub.2O.sub.3 K.sub.2O MgO SiO.sub.2 ZrO.sub.2 XRF total B1 97.97 0.28 0.21 0.04 0.41 1.09 0.01 98.39 B2 98.12 0.30 0.21 0.04 0.38 0.93 0.00 99.17 B3 97.79 0.30 0.21 0.04 0.37 1.26 0.02 99.39 B4 97.56 0.35 0.21 0.04 0.38 1.43 0.01 99.00 B5 97.64 0.54 0.21 0.04 0.38 1.15 0.01 99.94 B6 97.61 0.49 0.22 0.04 0.41 1.15 0.04 99.92 B7 97.97 0.33 0.20 0.04 0.40 1.01 0.01 98.93 B8 95.15 0.34 0.20 0.04 0.40 3.85 0.00 99.94

[0115] The fibres/blankets made therefrom were then evaluated using the test methodology as described:

Test Methodology

[0116] The EN 1094-1-2008 standard was used for the shrinkage, tensile strength and resiliency tests.

Shot Content

[0117] Shot content was determined by a jet sieve method as detailed in WO2017/121770, incorporated herein by reference.

Thermal Stability (Shrinkage)

[0118] The method for determination of dimensional stability of refractory materials, including the refractory glass fibre insulation materials, is based on the EN ISO 10635. This method is a shrinkage test that measures the change of a flat specimen's linear dimensions after a heat treatment.

[0119] The shrinkage test requires a relatively rigid specimen's so that the linear dimensions could be accurately determined before and after the heat treatment. In cases where a needled fibre blanket specimen were not available, starch bonded vacuum formed boards were prepared from the glass fibre samples.

[0120] To prepare the vacuum formed boards, the as made fibre material were chopped using a small-scale industrial granulator through a #6 mesh (.sup.˜3 mm opening). Chopped fibre samples were lightly cleaned using a sieve to remove any debris and large glass residues. 40 g of chopped clean fibre was mixed in 500 ml of 5 wt % concentration potato starch in water solution to create a slurry. Subsequently a vacuum former was used to produce 75×75 mm boards with a thickness of 10-15 mm. The vacuum former consists of a sealed acrylic mould with a 100 μm mesh bottom, a vacuum pump was used to remove the water from the slurry while manually compressing the shape using a flat plate. Vacuum formed boards were dried at 120° C.

[0121] To measure permanent linear shrinkage, the linear dimensions of specimen were measured to an accuracy of ±5 μm using a travelling microscope. The specimens were subsequently placed in a furnace and ramped to a temperature 50° C. below the test temperature (e.g. 1300° C.) at a rate of 300° C./hour and then ramped at 120° C./hour for the last 50° C. to test temperature and held for 24 hours. Specimens were allowed to cool down naturally to room temperature at the end of this heat treatment. After heat treatment, the specimen's linear dimensions were measured again using the same apparatus to calculate the change in dimensions. Shrinkage values are given as an average of 4 measurements.

Reactivity with Mullite

[0122] Needled fibre blanket specimens with approximate dimensions of 50 mm×100 mm were used for this test. Blanket specimens were placed on a fresh mullite Insulating Fire Brick (JM 28 IFB). The specimen, along with the IFB substrate, was heated treated at 1200° C. for 24 hours to confirm the reactivity after the heat treatment. The specimen and IFB were inspected for any sign of melting or reaction. The sample which did not react with the IFB at all were evaluated as good (0). The sample which reacted with the IFB (the sample was adhered to IFB or sign of melting was observed) were evaluated as poor (X).

Bio-Solubility

[0123] The biological solubility of fibrous materials can be estimated in a system in which the material is exposed to a simulated body fluid in a flow-through apparatus (i.e., in vitro). This measurement of solubility is defined as the rate of decrease of mass per unit surface area (Kdis). Although several attempts have been made to standardize this measurement, there is currently no international standard. Major protocol differences among laboratories include different simulated body fluid chemistries (and, most significantly, different buffering and organic components), flow rates, mass and/or surface area of samples, determination methods for specific surface area, and determination of mass loss. Consequently, Kdis values should be regarded as relative estimates of chemical reactivity with the simulated body fluid under the specific parameters of the test, not as measures of absolute solubility of fibrous particles in the human lung. The flow through solubility test method used in this study is a 3-week long solubility test in pH 7.4 saline. Two channels of each unique specimen are simultaneously tested. Samples of saline solution flowing over the fibre specimens are taken after 1, 4, 7, 11, 14, 19 and 21 days. The saline samples are analysed using the ICP method to measure the oxide dissolution levels in ppm level. To validate the flow test results and calculate the final dissolution rates for each specimen, the square root of remaining fibre mass against sampling times are plotted. Deviation from a linear trend could suggest an issue with the results. A good linear regression fit was observed in the flow test results conducted in this study. Based on the historical data collected by authors, a minimum of 150 ng/cm.sup.2 hr dissolution rate is required for a fibre to have exoneration potential. In the static solubility test method, fibre specimens are agitated in saline solution at 37° C. to replicate conditions within the lungs. The test monitors fibre dissolution after 5 or 24 hours using the ICP method.

Resiliency

[0124] The resiliency test (EN1094-1-2008) demonstrates the ability of fibre insulation products to spring back after being compressed to 50% of their initial thickness. Samples for resiliency testing in this document were in needled blanket form. As made or heat treated blanket specimens were cut to 100 mm×100 mm squares and dried at 110° C.±5° C. for 12 hours to remove any absorbed moisture. Specimens were subsequently allowed to cool to room temperature and then test immediately. The initial thickness of blanket specimens were measured using the pin and disk method prior to resiliency testing. An Instron® universal mechanical test frame, equipped with 150 mm diameter flat compression platens was used for the resiliency tests. During the test, the specimens were compressed to 50% of their original thickness at a rate of 2 mm/min, the specimens were then held under compression for 5 minutes. Subsequently the specimens were allowed to spring back by lifting the compression platen until 725 Pa (for specimens 96 kg/m.sup.3 bulk density) or 350 Pa (for specimens <96 kg/m.sup.3 bulk density) was registered on the load cell and then held for a further 5 minutes. Following this test, the resiliency values were calculated using the formula below:

[00001]$R=\frac{d_f}{d_0}⨯100R=\mathrm{Resiliency}{d}_f=\mathrm{Thickness}\mathrm{after}\mathrm{testing}{d}_0=\mathrm{Initial}\mathrm{Thickness}$

Tensile Strength

[0125] The parting strength of a blanket is determined by causing rupture of test pieces at room temperature. Samples are cut using a template (230±5 mm×75±2 mm). The samples are dried at 110° C. to a constant mass, cooled to room temperature and then measured and tested immediately.

[0126] The width is measured using a steel rule to a 1 mm accuracy across the middle of the piece and the thickness of the sample is measured on each sample (at both ends of the sample) using the EN1094-1 needle method. A minimum of 4 samples for each test are taken along the direction of manufacture.

[0127] The samples are clamped at each end by clamps comprising a pair of jaws having at least 40 mm×75 mm in clamping area with serrated clamping surfaces to prevent slippage during the test. These dimensions give an unclamped span of 150±5 mm to be tested. The clamps are closed to 50% of the sample thickness (measured using a Vernier caliper or ruler).

[0128] The clamps are mounted in a tensile testing machine [e.g. Instron® 5582, 3365 using a 1 kN load cell, or a machine of at least the equivalent functionality for testing tensile strength]

[0129] The crosshead speed of the tensile testing machine is a constant 100 mm/min throughout the test.

[0130] Any measurement with the sample breaking nearer to the clamp jaw than to the centre of the sample is rejected.

[0131] The maximum load during the test is recorded to allow strength to be calculated.

[0132] Tensile strength is given by the formula:

[00002]$R\left(m\right)=\frac{F}{W⨯t}\mathrm{Where}:R\left(m\right)=\mathrm{Tensile}\mathrm{Strength}\left(\mathrm{kPa}\right)F=\mathrm{Maximum}\mathrm{Parting}\mathrm{Force}\left(N\right)W=\mathrm{Initial}\mathrm{Width}\mathrm{of}\mathrm{the}\mathrm{active}\mathrm{part}\mathrm{of}\mathrm{the}\mathrm{test}\mathrm{piece}\left(\mathrm{mm}\right)T=\mathrm{Initial}\mathrm{Thickness}\mathrm{of}\mathrm{test}\mathrm{piece}\left(\mathrm{mm}\right)$

[0133] The test result is expressed as the mean of these tensile strength measurements together with the bulk density of the product.

Fibre Diameter

[0134] Fibre diameter measurements were carried out using the Scanning Electron Microscope (SEM). SEM is a micro-analytical technique used to conduct high magnification observation of materials' microscopic details. SEM uses a tungsten filament to generate an electron beam, the electron beam is then rastered over a selected area of the specimen and the signal produced by the specimen is recorded by a detector and processed into an image display on a computer. A variety of detectors can be used to record the signal produced by the sample including secondary electrons and backscattered electrons detectors.

[0135] The particular SEM equipment used operates under vacuum and on electrically conductive specimens. Therefore, all glass/ceramic fibre specimens need to be coated with gold or carbon prior to SEM analysis. Coating was applied using an automated sputter coater at approximately 20 nm. In order to prepare the fibrous specimens for diameter measurements, fibre specimens were crushed using a pneumatic press at 400 psi. The aim of crushing is to ensure the sample is crushed enough to be dispersed without compromising the fibre length, crushing results in fibres with aspect ratios >3:1. The crushed fibre specimens is then cone and quartered to ensure representative sampling. Crushed and quartered fibres are dispersed in IPA. Typically, 50 μg of fibres are placed in a 50 mL centrifuge tube and 25 mL IPA is added. A SEM stub is then placed at centre of a petri dish, then the centrifuge tube is vigorously shaken and emptied into the petri dish containing the SEM stub. The petri dish is left in fume cupboard for 1 hour for the fibres to settle on the SEM stub. The SEM stub is then carefully coated with gold in preparation for SEM imaging.

[0136] Following this sample preparation step, an automated software on the SEM equipment is utilised to collect 350 unique secondary electron images at 1500× magnification from the SEM stub. Following the image collection step, the images are processed by the Scandium® system available from Olympus Soft Imaging Solutions GmbH, to measure the diameter of fibres. The process involves manual inspection of measured fibres in every image to ensure only the fibres particles with aspect ratios greater than 3:1 are measured. The final fibre diameter distribution is reposted in a graph as well as numerical average/arithmetic mean diameter.

Crystal Grain Size

[0137] Crystal grain size measurements on heat treated fibre materials were carried out using the Scanning Electron Microscope (SEM). SEM is a micro-analytical technique used to conduct high magnification observation of materials' microscopic details. SEM uses a tungsten filament to generate an electron beam, the electron beam is then rastered over a selected area of the specimen and the signal produced by the specimen is recorded by a detector and processed into an image display on a computer. A variety of detectors can be used to record the signal produced by the sample including secondary electrons and backscattered electrons detectors.

[0138] The particular SEM equipment used operates under vacuum and on electrically conductive specimens. Therefore, all glass/ceramic fibre specimens need to be coated with gold or carbon prior to SEM analysis. Coating was applied using a automated sputter coater at approximately 20 nm. In order to prepare the fibrous specimens for grain size measurements, fibre specimens were cone and quartered to ensure representative sampling. A SEM stub is prepared with a small representative sample of the specimen and carefully coated with gold in preparation for SEM imaging.

[0139] Following this sample preparation step, the SEM equipment is utilised to collect several unique secondary electron images at suitable magnification based on morphology (typically in 5000-10000× magnification range) from the SEM stub. Following the image collection step, the images are processed by a computer software program (Olympus Scandium®) to measure the grain size by drawing circles around the visible grain boundaries in several SEM images. The process involves manual inspection of fibres in every image to ensure only the fibres are in focus. The final grain size is reported as numerical average of all measurements (minimum of 10 measurements of representative crystals). Due to limitation in magnification and resolution of SEM images, the minimum measurable grain size was about 0.4 μm. Samples with lower crystal grain sizes were reported as having a mean grain size value <0.4 μm.

Melting Temperature

[0140] The melting temperature of the fibres was determined by DSC (10k/min temperature increase from 30° C. to 1500° C.). Sample 26b (50 mg of fine powder ground from fibre) had a melting temperature of

Fibre Composition

[0141] Fibre composition was determined using standard XRF methodology. Results were normalised after analysis performed on SiO.sub.2, CaO, K.sub.2O, Al.sub.2O.sub.3, MgO and oxide components listed in Table 5. Un-normalised results were discarded if the total weight of the composition fell outside the range 98.0 wt % to 102.0 wt %.

Results

[0142] Referring to Table 2 & 3, there is shown the composition of inorganic fibres as % weight of the total composition according to Examples 1 to 26 and Comparative Examples C1 to C4.

TABLE-US-00002 TABLE 2 CaO + Sample SiO.sub.2 CaO Al.sub.2O.sub.3 K.sub.2O MgO SiO.sub.2 C-1 72.8 24.9 1.1 0.6 0.6 97.7 C-2 71.2 28.1 0.33 0.06 0.17 99.3  1 70.7 28.8 0.26 0.03 0.13 99.5  2 70.6 28.9 0.28 0.04 0.16 99.5  3 70.6 28.5 0.55 0.12 0.19 99.1  4 70.5 28.4 0.69 0.18 0.23 98.9  5 70.3 29.1 0.36 0.05 0.17 99.4  6 69.5 30.0 0.27 0.04 0.15 99.5  7 69.4 30.1 0.32 0.03 0.15 99.5  8 67.7 31.9 0.25 0.03 0.15 99.6  9 67.1 32.4 0.28 0.02 0.15 99.5 10 66.0 33.1 0.60 0.04 0.18 99.1 11 65.7 33.8 0.22 0.03 0.15 99.5 12 65.6 34.0 0.27 0.02 0.15 99.6 13 65.3 34.2 0.23 0.03 0.16 99.5 14 65.0 34.5 0.35 0.02 0.17 99.5 15 64.5 35.1 0.19 0.06 0.16 99.6 16 63.3 36.1 0.22 0.10 0.29 99.4 17 62.8 36.7 0.23 0.07 0.16 99.5 18 61.5 38.0 0.21 0.09 0.16 99.5 19 67.2 32.3 0.07 0.02 0.23 99.5 20 69.0 30.2 0.49 0.03 0.23 99.2 21 66.0 33.5 0.18 0.02 0.32 99.5 22 66.3 33.2 0.19 0.01 0.26 99.5 C-23 66.3 33.2 — 0.004 0.03 99.5 C-24 65.8 34.2 0.02 0.0 0.0 100.0 25 63.3 36.1 0.22 0.10 0.29 99.4 26 68.0 31.3 0.18 0.27 0.21 99.3 26b 67.1 32.4 0.23 0.10 0.15 99.5 C-3 60.7 38.9 0.26 0.07 0.17 99.6 C-4 64.9 29.8 0.15 0.01 5.2 94.7 C-5 60.7 38.8 0.23 0.12 0.17 99.5 Examples with the prefix “C” are comparative examples

[0143] As illustrated in Table 3, inorganic fibre compositions with silica levels less than 65.7 wt % were found to be not compatible with mullite based bricks, adhering to the bricks after being in contact at 1200° C. for 24 hrs. Inorganic fibre compositions with higher silica levels had generally higher shot content and higher fibre diameter.

TABLE-US-00003 TABLE 3 Shrinkage Mullite at Shot Mean Fibre Reactivity @ 1300° C. content diameter Sample 1200° C. (24 hrs) % wt (μm) C-1 ◯ 2.0 — 6.9  C-2 ◯ 1.4 59.3 — 1 — 0.9 51.9 5.7  2 ◯ 1.4 52.0 — 3 ◯ 2.2 54.5 — 4 ◯ 2.7 53.4 2.67 5 ◯ 1.1 50.6 — 6 ◯ — 49.5 — 7 ◯ 1.2 47.8 — 8 ◯ 2.0 34.6 — 9 ◯ 1.4 47.3 — 10 ◯ 1.2 36.6 3.02 11 ◯ 0.8 37.7 — 12 X 1.3 37.4 3.33 13 X 2.0 39.7 — 14 X — 38.2 2.87 15 — 2.2 — — 16 — 1.7 — — 17 — 2.6 — — 18 — 3.3 — — 19 — 2.1 — — 20 — 1.7 — — 21 — 1.6 — 2.65 22 — 1.1 — 2.37 25 1.7 26 2.0 C-3 — 8.6 — — C-4 X 14.5  — — C-5 — 5.6 — —

Effects of Impurities

[0144] To assess the effects of the incidental impurities in the raw materials, an ultra pure sample (24) was produced using a silica (SiO2: 99.951 wt %, Al.sub.2O.sub.3: 0.038 wt % Fe.sub.2O.sub.3: 0.012 wt %) and calcia (CaO: 99.935 wt %, SiO.sub.2: 0.011 wt %, Al.sub.2O.sub.3: 0.012 wt % Fe.sub.2O.sub.3: 0.011 wt %, SrO: 0.031 wt %). The remaining components were less than the XRF detection limit (<0.01 wt %).

[0145] To assess the effect of impurities, additional amounts of Al.sub.2O.sub.3, MgO and ZrO.sub.2 were added to the existing incidental impurities. With reference to Table 4a, increasing amounts of MgO and Al.sub.2O.sub.3 results in reduced thermal stability at 1300° C. (24 hrs), as measured by the % shrinkage. Example C-34 is a repetition of sample E-174 from U.S. Pat. No. 5,332,699.

Shrinkage @ 1300° C. for 24 Hours

[0146] The lowest shrinkage (best high temperature performance) was observed in samples 32 & 33. Sample 33 was a control sample with no additives, whereas Sample F has a slightly elevated MgO level, although in both samples, the sum of SiO.sub.2 and CaO is greater than 99.0 wt %. Sample 32 appears to be an anomaly in the correlation between shrinkage and MgO content of Samples C-30 to 33. Likewise, Example 37 is also considered a suspect result, with the shrinkage result expected to be below 4%. The results indicate that, in general, a higher CaO+SiO.sub.2 level corresponds to fibre compositions with improved high temperature stability as measured by the shrinkage test.

TABLE-US-00004 TABLE 4a Static CaO + Solubility Shrinkage at # SiO.sub.2 CaO Al.sub.2O.sub.3 K.sub.2O MgO ZrO.sub.2 SiO.sub.2 (pH 7.4) ppm 1300° C. C-27 59.9 35.2 0.34 0.10 4.31 0.00 95.1 380 24.1 C-28 62.4 35.4 0.24 0.13 1.66 0.00 97.8 265 6.1 C-29 62.6 35.7 0.23 0.06 1.35 0.00 98.3 375 11.3 C-30 65.7 33.1 0.19 0.09 0.97 0.00 98.8 294 7.0 31 65.4 33.4 0.20 0.08 0.82 0.00 98.8 270 3.4 32 66.1 33.0 0.19 0.10 0.56 0.00 99.1 289 1.7 33 66.1 33.4 0.18 0.05 0.25 0.00 99.5 548 2.6 C-34 63.4 34.9 0.84 0.08 0.47 0.32 98.3 301 5.7 C-35 65.5 32.6 1.48 0.13 0.21 0.00 98.1 167 6.6 C-36 65.5 33.1 1.04 0.18 0.20 0.00 98.6 208 4.1 37 65.5 33.6 0.56 0.14 0.26 0.00 99.1 249 5.0 Examples with the prefix “C” are comparative examples

Surface Crystal Size

[0147] The ultra-pure raw materials were difficult to form fibres and when fibres were formed, yield was low and fibre diameter was large (e.g. >500 μm). As illustrated in FIG. 1, The surface of the fibres contain a mean crystal grain size approaching 5 μm, with cracking also observed. The prevalence of surface crystals was also noted on the high purity sample of the prior art (FIG. 2), with a mean crystal grain size of about 1 μm.

[0148] As indicated in Table 4a, higher totals of CaO+SiO.sub.2 tend to correspond to higher high temperature performance and bio-solubility. Table 4b further discloses the correlation between high temperature performance and the MgO content.

TABLE-US-00005 TABLE 4b Shrinkage # SiO.sub.2 CaO Al.sub.2O.sub.3 K.sub.2O MgO ZrO.sub.2 CaO + SiO.sub.2 at 1300° C. 38 65.36 33.72 0.17 0.02 0.76 0.00 99.09 3.8 39 65.20 34.05 0.16 0.01 0.58 0.00 99.25 2.7 40 65.23 34.12 0.15 0.01 0.51 0.00 99.35 2.2 41 65.50 33.65 0.16 0.01 0.66 0.00 99.15 3.2 42 65.44 33.77 0.14 0.01 0.58 0.01 99.21 2.9 43 65.43 33.88 0.14 0.01 0.52 0.01 99.31 2.2 44 65.46 33.87 0.15 0.01 0.47 0.01 99.33 3.1 45 65.56 33.75 0.24 0.02 0.41 0.02 99.31 2.2 46 65.51 33.90 0.14 0.01 0.37 0.01 99.41 2.1 47 65.72 33.68 0.18 0.01 0.36 0.01 99.40 1.8 48 65.87 33.59 0.17 0.02 0.32 0.01 99.45 1.8 49 65.93 33.48 0.15 0.01 0.39 0.01 99.41 1.9 50 65.98 33.46 0.18 0.02 0.32 0.01 99.43 1.6 51 66.16 33.36 0.15 0.01 0.29 0.01 99.52 1.4 52 66.33 33.25 0.14 0.01 0.27 0.01 99.58 1.2 53 66.25 33.30 0.15 0.01 0.26 0.01 99.55 1.4 54 65.56 33.84 0.14 0.01 0.41 0.01 99.40 1.3 55 66.26 33.22 0.19 0.01 0.26 0.01 99.48 1.1

[0149] The effect of the additional of MgO is illustrated in FIGS. 3 & 4, with sample 19 (FIG. 3) and sample E (FIG. 4) representing a composition with MgO being the predominant minor oxide component. The results indicate that MgO levels of up to at least 1 wt % are able to suppress crystal grow at 1100° C. The effect of the additional of increased levels of Al.sub.2O.sub.3 are illustrated in FIGS. 5, 6 & 7, with a mean crystal size of almost 1 μm obtained with an Al.sub.2O.sub.3 content of 1.04 wt %, with CaO+SiO.sub.2 wt % of 98.6 wt %. The effect of K.sub.2O content is illustrated in FIGS. 8 (sample 8) and 9 (sample 26), with the increase in K.sub.2O content from 0.03 wt % (sample 8) to 0.27 wt % (sample C-26) corresponding to an increase in crystal size from below the detection limit (<0.4 μm) to 0.54 μm.

[0150] The results confirm that either too little or too much minor components within the composition may lead to elevated crystal size, which is related to a deterioration in high temperature mechanical performance. In particular, MgO has been shown to supress crystal growth, whilst Al.sub.2O.sub.3 has been demonstrated to promote crystal growth, particularly at elevated levels (e.g. greater than 0.80 wt % Al.sub.2O.sub.3). Apart from the main incidental impurities of Al.sub.2O.sub.3, MgO and K.sub.2O, the XRF analysis measured the metal oxides listed in Table 6. The maximum and minimum incidental impurity level of each of the metal oxides is provided. Typically, these minor incidental impurities are less than 0.3 wt % or less than 0.25 wt % or less than 0.20 wt %; and typically at least 0.10 wt %.

TABLE-US-00006 TABLE 5 Shrinkage Grain size % wt of at (μm) @ largest 1300° C. 1100° C. minor Example (24 hrs) (24 hrs) component  4 2.7 0.47 0.69 Al.sub.2O.sub.3  7 1.2 <0.4 0.32 Al.sub.2O.sub.3  8 0.8 <0.4 0.25 Al.sub.2O.sub.3 11 1.4 <0.4 0.22 Al.sub.2O.sub.3 19 2.1 <0.4 0.23 MgO.sup.  20 1.7 0.48 0.49 Al.sub.2O.sub.3 21 1.6 <0.4 0.32 Al.sub.2O.sub.3 22 1.1 <0.4 0.26 Al.sub.2O.sub.3 C-23 — 0.94 0.03 MgO.sup.  C-24 — 4.93 0.02 Al.sub.2O.sub.3 25 1.7 0.48 0.29 MgO.sup.  26 2.0 0.54 0.27 K.sub.2O .sup.  C-27 24.1  — 4.31 MgO.sup.  C-28 6.1 — 1.66 MgO.sup.  C-29 11.3  — 1.35 MgO.sup.  C-30 7.0 <0.4 0.97 MgO.sup.  31 3.4 <0.4 0.82 MgO.sup.  32 1.7 <0.4 0.56 MgO.sup.  33 2.6 — 0.2 MgO .sup.  C-34 5.7 0.94 0.84 Al.sub.2O.sub.3 C-35 6.6 — 1.48 Al.sub.2O.sub.3 C-36 4.1 0.90 1.04 Al.sub.2O.sub.3 37 5.0 <0.4 0.56 Al.sub.2O.sub.3

TABLE-US-00007 TABLE 6 Max level Min level Incidental impurities (% wt) (% wt) BaO 0.01 0.00 Cr.sub.2O.sub.3 0.02 0.00 Fe.sub.2O.sub.3 0.13 0.08 HfO.sub.2 0.00 0.00 La.sub.2O.sub.3 0.07 0.00 Mn.sub.3O.sub.4 0.00 0.00 Na.sub.2O 0.03 0.00 P.sub.2O.sub.5 0.00 0.00 SrO 0.03 0.00 TiO.sub.2 0.03 0.00 V.sub.2O.sub.5 0.01 0.00 SnO.sub.2 0.01 0.00 ZnO 0.00 0.00 ZrO.sub.2 0.02 0.00

Thermal Conductivity of Bodies of Inorganic Fibres

[0151] Thermal conductivity of a body of melt formed fibres (e.g. a blanket or other product form) is determined by a number of factors including in particular:— [0152] Diameter of the fibres; and [0153] “Shot” (unfiberised material) content
Fine diameter fibres provide low thermal conductivity to a body of fibres by reducing the scope for conduction through the solid and permitting finer inter-fibre porosity increasing the number of radiate-absorb steps for heat to pass by radiation from one side of the body to the other.

[0154] The presence of shot in a blanket increases thermal conductivity of the blanket by increasing the scope for conduction through the solid. Shot also increases the density of a blanket. The lower the shot content, the lower the thermal conductivity and density. For two bodies of identical fibre content and chemistry, the body with the lower shot content will have both the lower density and lower thermal conductivity.

[0155] In reference to Table 7, inorganic fibres were produced with a fibre diameter between approximately 2.6 to 3.0 μm and a shot content between 33 and 41 wt %. From the dataset provided in Tables 7 & 8, there is no clear correlation between fibre characteristics and thermal conductivity, although a larger data set should provide this expected relationship.

TABLE-US-00008 TABLE 7 Shot SEM Fibre (>45 μm) diameter SAMPLE % wt (μm) 10 36.6 3.02 12 32.5 2.65 13 40.6 — 14 38.3 2.70 15 38.7 2.76 P61-0488 32.1 3.01

TABLE-US-00009 TABLE 8 Conductivity (W/m .Math. K) 400° 600° 800° 1000° 1100° 1200° Density Strength Density SAMPLE C. C. C. C. C. C. Kg/m.sup.3 kPa Kg/m.sup.3 10 0.08 0.13 0.22 0.33 0.40 0.47 88 35 91 12 0.07 0.12 0.21 0.32 0.39 0.46 96 50 95 13 0.08 0.13 0.20 0.28 0.33 0.39 111 50 121 14 0.07 0.11 0.18 0.27 0.33 0.39 105 48 115 15 0.07 0.12 0.19 0.29 0.35 0.41 105 56 123 P61-0488 0.07 0.11 0.17 0.24 0.28 0.32 128 60 132

Bio-Solubility

[0156] Referring now to Table 9, there is shown data for bio-solubility testing.

[0157] A 21 day static and long flow through solubility test in saline pH 7.4 was conducted on the compositions shown in Table 9. Two samples of each fibre composition were simultaneously tested, with the average results reported. The saline samples were analysed using the ICP method to measure the oxide dissolution levels in ppm level. The results confirm that the fibres have low biopersistence. A low biopersistence fibre composition is taken to be a fibre composition which has a dissolution rate, in the flow solubility test, of at least 150 ng/cm.sup.2 hr or at least 170 ng/cm.sup.2 hr or at least 200 ng/cm.sup.2 hr.

[0158] The inorganic fibres under the present invention have comparable or improved bio-solubility in comparison with prior art fibre compositions C1 and C2. As indicated by the specific surface area measurements, fine fibre dimensions promote increased bio-solubility.

Summary of Results

[0159] The above results highlight that the fibre composition of the present disclosure is able to produce a refractory fibre with great utility without the need for the deliberate additional of significant amounts of additives to enhance one or more fibre properties. This unexpected result also enables refractory fibres to be produced with a lower carbon footprint due to the reduced number of raw materials required for its production.

TABLE-US-00010 TABLE 9 Static Flow through Specific Solubility Dissolution Rate Surface Sample (pH 7.4 saline) (pH 7.4 saline) Area Description (total ppm) (ng/cm.sup.2 hr) (m.sup.2/g) C-1 230 125 0.1652 C-2 313 379 0.2526 11 378 348 0.2887 16 295 326 0.3375 17 370 — — 18 208 — — 19 333 — — 20 292 — — 26 473 — —

Potential Uses

[0160] 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.

[0161] For example, the fibres may be used as:— [0162] bulk materials; [0163] deshotted materials [WO2013/094113]; [0164] in a mastic or mouldable composition [WO2013/080455, WO2013/080456] or as part of a wet article [WO2012/132271]; [0165] as a constituent in needled or otherwise entangled [WO2010/077360, WO2011/084487] assemblies of materials, for example in the form of blanket, folded blanket modules, or high density fibre blocks [WO2013/046052]; [0166] as a constituent of non-needled assemblies of materials, for example felts, vacuum formed shapes [WO2012/132469], or papers [WO2008/136875, WO2011/040968, WO2012/132329, WO2012/132327]; [0167] as a constituent (with fillers and/or binders) of boards, blocks, and more complex shapes [WO2007/143067, WO2012/049858, WO2011/083695, WO2011/083696]; [0168] as strengthening constituents in composite materials such as, for example, fibre reinforced cements, fibre reinforced plastics, and as a component of metal matrix composites; [0169] in support structures for catalyst bodies in pollution control devices such as automotive exhaust system catalytic converters and diesel particulate filters [WO2013/015083], including support structures comprising: [0170] edge protectants [WO2010/024920, WO2012/021270]; [0171] microporous materials [WO2009/032147, WO2011019394, WO2011/019396]; [0172] organic binders and antioxidants [WO2009/032191]; [0173] intumescent material [WO2009/032191]; [0174] nanofibrillated fibres [WO2012/021817]; [0175] microspheres [WO2011/084558]; [0176] colloidal materials [WO2006/004974, WO2011/037617] [0177] oriented fibre layers [WO2011/084475]; [0178] portions having different basis weight [WO2011/019377]; [0179] layers comprising different fibres [WO2012065052]; [0180] coated fibres [WO2010122337]; [0181] mats cut at specified angles [WO2011067598]; [0182] [NB all of the above features may be used in applications other than support structures for catalytic bodies] [0183] as a constituent of catalyst bodies [WO2010/074711]; [0184] as a constituent of friction materials [e.g. for automotive brakes [JP56-16578]]; [0185] for fire protection [WO2011/060421, WO2011/060259, WO2012/068427, WO2012/148468, WO2012/148469, WO2013074968]; [0186] as insulation, for example; [0187] as insulation for ethylene crackers [WO2009/126593], hydrogen reforming apparatus [U.S. Pat. No. 4,690,690]; [0188] as insulation in furnaces for the heat treatment of metals including iron and steel [U.S. Pat. No. 4,504,957]; [0189] as insulation in apparatus for ceramics manufacturing.

[0190] 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 [WO2012/065052] or with other biosoluble fibres [WO2011/037634].

[0191] 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] [WO2010/120380, WO2011133778]. Securing of the layers together may be by any known mechanism, for example blanket anchors secured within the blankets [U.S. Pat. No. 4,578,918], or ceramic screws passing through the blankets [see for example DE3427918-A1].

Treatment of the Fibres

[0192] In formation of the fibres or afterwards they may be treated by applying materials to the fibres.

[0193] For example:— [0194] lubricants may be applied to the fibres to assist needling or other processing of the fibres; [0195] coatings may be applied to the fibres to act as binders; [0196] coatings may be applied to the fibres to provide a strengthening or other effect, for example phosphates [WO2007/005836] metal oxides [WO2011159914] and colloidal materials such as alumina, silica and zirconia [WO2006/004974]; [0197] binders may be applied to the fibres to bind the fibres subsequent to incorporation in a body comprising such fibres.

[0198] 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.

[0199] By providing biosoluble fibres having maximum continuous use temperature higher than alkaline earth silicate fibres, 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.