Heat-absorbing materials

Abstract

A thermally insulating apparatus comprises a first material (10) configured to at least partially enclose an article (30), such as a flight data recorder and / or cockpit voice recorder or a part thereof, the first material (10) comprising or consisting of a metal fluoride hydrate; and a second material (20) configured to at least partially enclose the first material (10), the second material (20) comprising or consisting of an inorganic scrubbing agent.

Description

[0001] Heat-absorbing materials

[0002] Field of the Invention

[0003] The present invention relates to thermochemical materials (TCMs). In particular, but not exclusively, the invention relates to thermochemical materials (TCMs) and compositions for use in the thermal protection of objects such as electronic components, for example in flight data recorders and / or cockpit voice recorders

[0004] Certain electronic components require to be protected from heat in case of an emergency, such as a fire. An example of this type of electronic component is flight data recorders. Other non-limiting examples include memory circuits and cockpit voice recorders.

[0005] Previous approaches that have been identified for the protection of electronic components from the effects of heat include the use of phase-change materials (PCMs) that absorb heat on melting, e.g. waxes and paraffins; and thermochemical materials (TCMs) that decompose via one or more endothermic reactions on heating. Examples of TCMs include: salt hydrates, (e.g. hydrates of lithium and sodium acetate, hydrates of magnesium sulfate and sodium sulfate); metal carbonates and bicarbonates; metal hydroxides; boric acid; aldehydes; carbohydrates.

[0006] However, many of these materials are associated with a number of disadvantages including: containment of molten liquids; flammability of materials; longterm stability; corrosion; toxicity; and / or requirement for gas release.

[0007] An example of a conventional TCM is copper sulfate pentahydrate [CUSO4.5H2O]. However, this material has limited energy absorption properties.

[0008] There is a need in the art for a material that may exhibit one or more of the following properties:

[0009] The material should reach a peak temperature of less than 160°C (solder melting point for lead-containing solders) when placed in an oven at 260°C for ten hours as defined by ED-112B section 2-4.2.6 of Statement of Requirement (‘SoR’);

[0010] The thermal design of the CPMM should maintain the electronic components within the Crash Protected Memory Module (‘CPMM’) below 85°C when 100 mW of power is dissipated within those components and the ambient external temperature is 70°C; The volume of candidate material should be less than or equal to the design detailed in section 8 of SoR (i.e. a 104.5 cm3hollow cylinder) and therefore the material should have energy density.

[0011] Endothermic materials are known in the art, as disclosed for example in WO1999011455A1 (Hayes) and US6652770B2 (Hayes). However, the components disclosed therein suffer from a number of disadvantages. Either their heat absorption characteristics are not satisfactory, or they are associated with undesirable toxicity. This is true of, for example, fluoride-based compounds.

[0012] It is an object of the invention to address and / or mitigate one or more problems associated with the prior art.

[0013] According to a first aspect, there is provided a thermally insulating apparatus, the apparatus comprising: a first material configured to at least partially enclose an article, the first material comprising or consisting of a metal fluoride hydrate; and a second material configured to at least partially enclose the first material, the second material comprising or consisting of an inorganic scrubbing agent.

[0014] Preferably, the first material may be in dry and / or solid form.

[0015] Preferably, the second material may be in dry and / or solid form.

[0016] The article may be selected from the list consisting of: an electronic device such as a battery or battery pack; a recording device such as a data, image or sound recorder, e.g. a flight data recorder, a cockpit voice recorder, a ship voyage recorder, or a part thereof, e.g. a memory unit of such recording device; an electronic component, such as a memory chip, a circuit board, or the like; a flammable solid object such as paper-based documents; an object containing a flammable fluid such as a gas cylinder, a gas canister, or the like; an explosive material such as chemical explosives, propellants or pyrotechnics.

[0017] The article may be a recording device such as a data, image or sound recorder, e.g. a flight data recorder, a cockpit voice recorder, or a ship voyage recorder, or a part thereof, e.g. a memory unit of such recording device. The first material, e.g. metal fluoride hydrate, may comprise or may consist of one or more compounds selected from the list consisting of aluminium fluoride trihydrate (AIF3.3H2O), copper fluoride dihydrate (CUF2.2H2O), iron fluoride trihydrate (FeFs.SFW), and chromium fluoride hydrate ([Cr(H2O)e]F3 or [Cr(H2O)e]F3.3H2O).

[0018] In an embodiment, the first material, e.g. metal fluoride hydrate, may comprise or may be aluminium fluoride trihydrate (AIF3.3H2O). The second material, e.g. inorganic scrubbing agent, may comprise or may consist of any metal salt hydroxide, metal salt oxide, metal salt carbonate, or metal salt hydrogencarbonate. The second material, e.g. inorganic scrubbing agent, may comprise or may consist of one or more compounds selected from the list consisting of silica (SiC>2), magnesium oxide (MgO), calcium carbonate (CaCOs), sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH). In an embodiment, the second material, e.g. inorganic scrubbing agent, may comprise or may consist of silica.

[0019] The first material and / or the second material may comprise one or more additives. In an embodiment, the first material and / or the second material may comprise a lubricant, e.g. graphite. The provision of a lubricant such as graphite may help with shaping, e.g. compression and / or packing, of first material and / or the second material.

[0020] Advantageously, the provision of a metal fluoride hydrate allows heat absorption by the first material through dehydration below the hydrolysis temperature (e.g. below about 380°C), thereby avoiding release of undesirable compounds such as hydrogen fluoride. Further, above the hydrolysis temperature (e.g. above about 380°C), the first material may undergo hydrolysis, further absorbing heat.

[0021] Advantageously, also, the provision of scrubbing agent may allow the capture of undesirable compounds such as hydrogen fluoride upon hydrolysis of the first material above its hydrolysis temperature, e.g. above about 380°C.

[0022] Further advantageously, the inventors have discovered that certain scrubbing agents are capable of acting as heat absorbers / high temperature insulators and / or thermochemical materials, thereby providing a dual function as both thermochemical materials and scrubbing agents.

[0023] The first material may partially enclose the article.

[0024] Advantageously, the first material may fully enclose the article. This may provide optimum heat protection.

[0025] At least part of the first material may be in contact with the article.

[0026] At least part of the article may be separated from the first material by a packing material, or by a first gap or space. For example, when the article is separated from the first material by a packing material, the packing material may comprise a glass material such as spheriglass®.

[0027] The whole article, e.g. the entire outer surface of the article, may be in contact with the first material. In such instance, there may be no gap or space or packing material between the article and the first material.

[0028] The second material may partially enclose the first material.

[0029] Advantageously, the second material may fully enclose the first material. This may provide optimum heat protection and / or scrubbing functionality.

[0030] At least part of the second material may be in contact with the first material.

[0031] At least part of the first material may be separated from the second material by a second gap or space or liner.

[0032] The whole first material, e.g. the entire outer surface of the first material, may be in contact with the second material. In such instance, there may be no gap or space between the first material and the second material.

[0033] The thickness, e.g. average thickness, of the first material, may be approximately 1-100mm, e.g. about 5-20 mm.

[0034] The thickness, e.g. average thickness, of the second material, may be approximately 1-100 mm, e.g. about 5-20 mm.

[0035] However, it will be appreciated that the thickness of the first material and / or of the second material may vary, for example depending on the particular application, i.e. on the type of article to be protected.

[0036] According to a second aspect, there is provided an insulated article, wherein the insulated article comprises: an article; and an insulating apparatus at least partially enclosing the article, wherein the insulating apparatus comprises: a first material comprising or consisting of a metal fluoride hydrate and at least partially enclosing the article; and a second material configured to at least partially enclose the first material, the second material comprising or consisting of an inorganic scrubbing agent.

[0037] The article may be selected from the list consisting of: an electronic device such as a battery or battery pack; a recording device such as a data, image or sound recorder, e.g. a flight data recorder, a cockpit voice recorder or a ship voyage recorder; an electronic component, such as a memory chip, a circuit board, or the like; a flammable solid object such as paper-based documents; an object containing a flammable fluid such as a gas cylinder, a gas canister, or the like; an explosive material such as chemical explosives, propellants or pyrotechnics.

[0038] The article may comprise or may be a recording device such as a data, image or sound recorder, e.g. a flight data recorder or a cockpit voice recorder or a part thereof, e.g. a memory unit of such recording device.

[0039] The features described in relation to the first aspect may equally apply to the second aspect and, merely for brevity, are not repeated here.

[0040] According to a third aspect, there is provided a method for providing heat protection to an article, the method comprising at least partially enclosing an article in a first material, the first material comprising or consisting of a metal fluoride hydrate; and at least partially enclosing the first material in a second material, the second material comprising or consisting of an inorganic scrubbing agent.

[0041] The method may comprise partially enclosing the article with the first material.

[0042] The method may comprise fully enclosing the article with the first material. This may provide optimum heat protection.

[0043] The method may comprise contacting the article with the first material.

[0044] The method may comprise contacting the at least part of the article with the first material. In such instance, part of the article may be separated from the first material by a first gap or space or by a packing material.

[0045] The method may comprise contacting the whole article, e.g. the entire outer surface of the article, with the first material. In such instance, there may be no gap or space or packing material between the article and the first material.

[0046] The method may comprise partially enclosing the first material with the second material.

[0047] The method may comprise fully enclosing the first material with the second material. This may provide optimum heat protection and / or scrubbing functionality.

[0048] The method may comprise contacting the first material with the second material. The method may comprise contacting at least part of the first material with the second material. In such instance, part of the first material may be separated from the second material by a second gap or space.

[0049] The method may comprise contacting the whole first material, e.g. the entire outer surface of the first material, with the second material. In such instance, there may be no gap or space between the first material and the second material.

[0050] The features described in relation to any aspect of the invention may equally apply to any other aspect and, merely for brevity, are not repeated. For example, features described in relation to compositions or apparatus can apply in relation to methods, and vice versa.

[0051] Brief Description of Drawings

[0052] Embodiments of the invention are described with reference to the accompanying drawings, in which:

[0053] Figure 1 shows a thermally insulated article according to a first embodiment;

[0054] Figure 2 shows a thermally insulated article according to a second embodiment;

[0055] Figure 3 shows DSC / TG measurements of AIF3.3H2O under flowing dry air at a heating rate of 1 °C / min;

[0056] Figure 4 shows a comparison of XRPD patterns of bulk heating tests of AIF3.3H2O at temperatures up to 260 °C;

[0057] Figure 5 shows a comparison of XRPD patterns of bulk heating tests of AIF3.3H2O at temperatures up to 160 °C;

[0058] Figure 6 shows a comparison of theoretical and experimental XRPD patterns of AIF3.3H2O;

[0059] Figure 7 shows a comparison of theoretical and experimental XRPD patterns of sample from Ni tube-furnace heating of AIF3.3H2O;

[0060] Figure 8 shows an XRPD pattern of a Microtherm® silica material;

[0061] Figure 9 shows a comparison of XRPD data for mixture of AIF3.3H2O and Microtherm®;

[0062] Figure 10 shows a comparison of DSC data between pure AIF3.3H2O and that of a mixture of AIF3.3H2O and Microtherm®;

[0063] Figure 11 shows a comparison of XRPD patterns of sample from 1000°C heating with theoretical patterns of AI2O3 and AIF3; Figure 12 shows a comparison of XRPD patterns of sample from controlled 1000°C heating, with simulated patterns of AI2O3 and AIF3.

[0064] Detailed Description

[0065] In the present disclosure, reference is made to a number of terms, which have the meanings provided below, unless a context indicates to the contrary. The nomenclature used herein for defining compounds, in particular the compounds according to the invention, is in general based on the rules of the IIIPAC organisation for chemical compounds, specifically the “IIIPAC Compendium of Chemical Terminology (Gold Book)”. For the avoidance of doubt, if a rule of the IIIPAC organisation is in conflict with a definition provided herein, the definition herein is to prevail. Furthermore, if a compound structure is in conflict with the name provided for the structure, the structure is to prevail.

[0066] The term “comprising” or variants thereof is to be understood herein to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0067] The term “consisting” or variants thereof is to be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, and the exclusion of any other element, integer or step or group of elements, integers or steps.

[0068] The term “about” herein, when qualifying a number or value, is used to refer to values that lie within ± 5% of the value specified. For example, if a temperature is specified to be about 5 to about 13 °C, temperatures of 4.75 to 13.65 °C are included.

[0069] Reference to physical states of matter (such as liquid or solid) refer to the matter’s state at 25 °C and atmospheric pressure unless the context dictates otherwise.

[0070] Figure 1 shows a thermally insulated article 5 according to a first embodiment.

[0071] The article 5 comprises an element of a flight data recorder 30, in particular a memory unit thereof, as typically found in an aircraft.

[0072] The flight data recorder 30 is enclosed in a first material 10 which is made of a metal fluoride hydrate, in this embodiment aluminium fluoride trihydrate. The first material 10 acts as a thermochemical material which decomposes upon exposure to heat, first by dehydration, and then by hydrolysis, depending on the temperature and duration of exposure to heat. The first material 10 is enclosed in a second material 20 which is made of an inorganic scrubbing material, in this embodiment silica (Microtherm®). Advantageously, the provision of scrubbing agent as the second material 20 surrounding the first material 10 allows the capture of undesirable compounds such as hydrogen fluoride upon hydrolysis of the first material 10 above its hydrolysis temperature. Advantageously also, the inventors have discovered that certain scrubbing agents, including silica, are capable of acting as heat absorbers / insulators and / or thermochemical materials, thereby providing a dual function as both thermochemical materials and scrubbing agents.

[0073] Figure 2 a thermally insulated article 105 according to a second embodiment. The insulated article 105 of Figure 2 is generally similar to the insulated article 5 of figure 1 , like parts denoted by like numerals, but incremented by ‘100’.

[0074] In this embodiment, rather being completely enclosed, the article 130 is only partially enclosed by the first material 110 around an upper surface and sides thereof. Similarly, the first material 110 is only partially enclosed by the second material 120 around an upper surface and sides thereof. This may be useful when the first and / or second materials are configured to rest or lay on a surface or support to enclose the article 130.

[0075] In addition, in Figure 2, rather than the first material 10 being in contact with the article 30, the second material being in contact with the first material 10, the article 130 is separated from the first material 110 by a first gap or space 140, and the first material 110 is separated from the second material 120 by a second gap or space 150.

[0076] It will be understood that the present embodiments are provided by way of example only, and that various modifications can be made to the present embodiments without departing from the scope of the invention.

[0077] Examples

[0078] Example 1 : Investigation of aluminium fluoride trihydrate

[0079] Aluminium fluoride trihydrate (AIF3.3H2O) sample was purchased from Fisher Scientific UK Ltd (97% purity). All tests were conducted without further purification. Thermal analysis

[0080] Thermal capacity was investigated for AIF3.3H2O using Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC).

[0081] Initial thermal analysis was conducted using a NETZSCH Proteus DSC / TG instrument in the School of Chemistry. 8.085 mg powder sample of AIF3.3H2O was loaded into the DSC pan without further treatments. DSC / TG measurements were performed under a flow of dry air over the temperature range of 30-350 °C at a heating rate of 1 °C / min. DSC / TG results are shown in Figure 3.

[0082] As can be seen in Figure 3, the DSC / TG data suggest that the thermal decomposition of AIF3.3H2O begins at approximately 90 °C. One major thermal decomposition step of AIF3.3H2O was observed in the temperature range up to about 350 °C. TG data show a dramatic mass loss of 34.70 %, corresponding to the loss of 2.5 water molecules upon the first dehydration step in the temperature range of 90 to 160 °C. The thermal storage capacity of AIF3.3H2O in this temperature range is about 1001 J / g, corresponding to a volumetric energy storage density of 2900 J / cm3. This is followed by a slow mass loss and endothermic process upon heating to 350 °C, likely associated with the second dehydration event that leads to the formation of anhydrous AIF3.

[0083] Bulk Decomposition Tests

[0084] AIF3.3H2O is believed to undergo different thermal decomposition pathways at different temperature conditions. In the lower temperature range up to ca 380°C, AIF3.3H2O undergoes 2 steps of dehydration to form anhydrous AIF3. Above 380°C and with rapid heating, AIF3.3H2O hydrolyses to form AI2O3 and HF gas. The latter is acidic and extremely toxic.

[0085] Bulk decomposition tests were performed to assess the nature of gaseous products of AIF3.3H2O under a range of heating conditions.

[0086] The initial test was conducted using both glass vials and an aluminium container. Approximately 5g of AIF3.3H2O was loaded into each container with a thermocouple placed in the centre of the sample. Lids were loosely placed on both containers, which were wrapped with aluminium foil for heat insulation. A hot plate was used to control the temperature. Samples were heated up to 260°C at a heating rate of 1 °C / min. pH indicator paper was used to test the acidity of any released vapours An initial pH test was conducted with a solution of AIF3.3H2O in deionised water. The pH indicator paper remained yellow when it was placing in the sample solution, indicating no hydrolysis of AIF3.3H2O occurs under ambient conditions.

[0087] The hot plate was set to heat up to 260°C at a heating rate of 1 °C / min. When the sample in the aluminium container reached 260°C, a pH indicator paper dampened by deionised water, was placed over the sample to test vapours. The indicator turned red immediately, suggesting that acidic gas (HF) was released from AIF3.3H2O sample at 260°C. It was worth noting that, due to the differences of thermal conductivity of aluminium and glass, the sample in the glass vial was at 179°C.

[0088] About 1g of sample was removed for X-ray powder diffraction. The remaining sample was kept at 260°C for about 10h. Vapours from both sample containers were tested using dampened pH indicator paper. Both indicators gradually turned red after a few seconds, suggesting AIF3.3H2O was still releasing HF on holding at 260°C for about 10h.

[0089] Samples were then removed from the heat and cooled to room temperature (approximately 23°C). The sample in the aluminium container had turned brown after being kept at 260°C for 10h, while the majority of the sample in the glass vial remained white with a faint brown colouration after having been held at 179°C for 10h. The origin of the brown colouration was not known - it was suggested that it is potentially from decomposition of a transition-metal containing impurity in the sample, e.g. FeF3.xH2O.

[0090] XRPD was used to identify decomposition products of AIF3.3H2O under different temperature conditions, using aBruker D2 X-ray diffractometer. The XRPD pattern of anhydrous AIF3 was simulated using the published crystal structure of AIF3. As is clearly shown in Figure 4, after being heated up to 260°C, AIF3.3H2O fully converted to a poorly crystalline sample of anhydrous AIF3. No additional decomposition products were observed, even after being kept at 260°C for 10h. In addition, AIF3.3H2O fully dehydrated after being held at 179°C for 10h. No difference in XRPD patterns were observed between samples from the aluminium container and glass vial, despite the colour difference.

[0091] The bulk heating tests were repeated over a lower temperature range up to 160°C. Approximately 5 g of AIF3.3H2O was loaded into the aluminium container and a glass vial, respectively. The hotplate was heated to 160°C at a heating rate of 1°C / min, together with an empty glass vial. Due to the limitation of thermal conductivity of glass, the highest temperature of the sample in glass vials were about 109°C . When samples reached the target temperature, a pH indicator paper damped with deionised water was used to test vapours of samples, by placing it above sample for about 30s. The empty glass vial, heated up to 109°C, was tested first. No colour changes of the pH indicator ensured that following test results were affected by sample containers.

[0092] Nevertheless, vapours from both samples of AIF3.3H2O induced the colour changes of the pH indicators, suggesting sample started to release some HF at 109 °C. The darker colour of the indicator shown when placed in the aluminium container compared to the glass vial, suggests that higher temperature conditions induced higher amount of HF released from the AIF3.3H2O sample.

[0093] Approximately 1g of sample was removed from the aluminium container for XRPD measurement, whilst the remainder of the sample was maintained at the same temperature conditions for about 30h.

[0094] A pH test of vapours of the sample in the Al container was conducted again after being kept at 160°C for 30h. After being placed above the sample for about 30s, the indicator changed to a light-red colour, suggesting that an acidic gas (HF) was still being produced from the sample, but at much lower concentration.

[0095] Samples were then cooled to room temperature. No colour changes of samples were observed. XRPD measurements were conducted for phase identification, as shown in Figure 5.

[0096] Figure 5 shows that upon heating to 160°C, a certain amount of AIF3.3H2O dehydrated, leading to a formation of a poorly crystalline material of anhydrous AIF3. After being kept at 160°C for 30h, AIF3.3H2O fully dehydrated. Moreover, the hydration of AIF3.3H2O was much slower at 109°C. After being maintained for 30h, it partially dehydrated to form AIF3, with a significantly amount of sample remained as AIF3.3H2O. No additional decomposition products were observed in the XRPD patterns.

[0097] It has been reported that the hydrolysis reaction of AIF3.3H2O may only occur at temperatures above around 370°C, and that at temperatures below 370°C, pure dehydration reaction of AIF3.3H2O occurs. However, the bulk heating tests discussed above clearly show that small traces of HF were generated at much lower temperature conditions, highlighting the risks of metal halide fluoride hydrates, such as AIF3.3H2O, as TMCs.

[0098] Purity T ests

[0099] In order to determine the origin of HF, purity tests were carried out on samples of AIF3.3H2O. XRPD test

[0100] The initial test of impurities of starting material of AIF3.3H2O was conducted using a Bruker D2 X-ray powder diffractometer. The XRPD patter was simulated from the published crystal structure of AIF3.3H2O (P-form).

[0101] Close inspection of the XRPD data (Figure 6) showed a few mismatched peaks with very weak intensities in the range 20= 40° to 50°, indicating that there may indeed be a small amount of impurities present in the sample of AIF3.3H2O.

[0102] Potassium thiocyanate test

[0103] According to the bulk heating tests, transition metal fluoride hydrates (e.g. FeFs.xFW) were suspected as part of the impurity. In order to confirm, a potassium thiocyanate test was conducted. Potassium thiocyanate is a chemical compound with the molecular formula of KSCN. The thiocyanate anion (colourless) is known to react instantly with iron(lll) ions to form an intense red colour.

[0104] Approximately 1g of AIF3.3H2O was dissolved in deionised water (5 ml), approximately 0.5g of KSCN was then added to the solution. The sample remained colourless, indicating that the AIF3.3H2O sample does not contain any iron compounds.

[0105] Inductively Coupled Plasma-Optical Emission Spectrometry

[0106] In order to identify other possible metal impurities, Inductively Coupled Plasma- Optical Emission Spectrometry (ICP-OES) was employed to further determine the detailed elemental contents of the AIF3.3H2O sample.

[0107] ICP-OES is a sensitive technique in which the identity and quantity of elements in aqueous samples can be determined using plasma and a spectrometer. The solution for analysis is transferred by a peristaltic pump though a nebulizer into a spray chamber. The produced aerosol is lead into an argon-ion plasma. In the ICP-OES the plasma is generated at the end of a quartz torch by a cooled induction coil through which a high frequency alternate current flows. As a consequence, an alternating magnetic field is induced which accelerates electrons in a circular trajectory. Due to collisions between the argon atom and the electrons, ionisation occurs, giving rise to a stable plasma that reaches temperatures of 6000-7000 K. Atomisation and ionisation of the sample occurs. Due to the thermal energy taken up by the electrons, they reach a higher "excited" state. When the electrons drop back to their ground state, energy is liberated as light (photons). Each element has its own characteristic emission spectrum that is measured with a spectrometer. The test results of ICP-OES suggested that the sample is predominantly AIF3.3H2O with trace amounts of B (222 ppm), Na (227 ppm), and K (152 ppm). This further confirmed that there are no transition metals present in the sample. Therefore, the origin of HF evolution is intrinsic to decomposition of AIF3.3H2O, and is also believed to be dependent on sample processing and heating rates.

[0108] Quantitative measurements of HF

[0109] Quantitative measurements of HF were conducted using an aluminium tube furnace. An inlet stainless steel tube was connected to the Al tube for nitrogen gas flow via a flow meter. A stainless steel exit tube was immersed in deionised water contained in a polythene beaker.

[0110] 10.017 g of loosely packed AIF3.3H2O powder was loaded in an Al sample boat, and placed in the centre of the Al tube contained within a tube-furnace. It was then heated to 260 °C at a heating rate of 10 °C / min, under a flowing nitrogen gas stream at a flow rate of ca 0.3 L / min. The sample was maintained at 260 °C for a period of 1 hour and the gas stream was bubbled through 10 mL deionised water contained in the polythene beaker. The resulting solution was titrated with 0.001 M NaOH solution to determine concentration of HF in solution using phenolphthalein indicator to show the end point. Under this conditions, approximately 0.1 mg HF was released, corresponding to 0.001 wt% evolution of HF based on the mass of AIF3.3H2O.

[0111] 10.008 g of AIF3.3H2O in pellets form were also tested using the same experimental setup. 0.064 mg of HF was released, corresponding to 0.00064 wt% evolution of HF based on the mass of AIF3.3H2O. Pellets remained intact after heating.

[0112] 9.9671 g of pellets of AIF3.3H2O were loaded in a Ni sample boat, and placed in the centre of the Ni tube contained within a tube furnace. It was then heated to 260C at a heating rate of 10 °C / min, under a nitrogen gas stream at a flow rate of ca 0.1 L / min. The sample was maintained at 260 °C for a period of 4 hours and the gas stream was bubbled through 10 mL deionised water contained in the polythene beaker. The resulting solution was titrated with 0.05 M NaOH solution to determine concentration of HF in solution using phenolphthalein indicator to show the end point. Under these conditions, 42.2 mg HF was released, corresponding to 0.43 wt% evolution of HF based on the mass of AIF3.3H2O. Moreover, sample experienced 38.9 wt% weight loss during heating. 6.09 g of sample remained after heating, which is close to the theoretical weight loss corresponding to complete dehydration (39 wt%). After cooling to room temperature, solid residues were analysed using XRPD for phase identification, as shown in Figure 7. As can be seen from figure 7, the experimental XRPD pattern of sample matches well with the reference pattern (simulated) for AIF3, confirming that AIF3.3H2O fully dehydrated to form AIF3. No aluminium oxide was detected. Overall, test results highlight very low levels of HF produced under these heating conditions.

[0113] HF Scrubbing

[0114] As explained above, the inventors have discovered a system which may provide superior heat protection by using thermochemical materials, whilst reducing the potential exposure to undesirable compounds such as hydrogen fluoride by using a scrubbing agent. In particular, the inventors have discovered that thermal protection may be improved by selecting scrubbing agents capable of acting as heat absorbers and / or thermochemical materials.

[0115] Tests were carried out using Silica (Microtherm®).

[0116] The initial test was performed on a Microtherm® plug material using XRPD to identify its chemical composition. A small amount of material was ground into powder and an XRPD pattern was collected using a Bruker D2 diffractometer, as shown in Figure 8.

[0117] The XRPD data of Figure 8 suggest that the Microtherm® plug is a mixture of amorphous and crystalline material. The crystalline phase is a mixture of two polytypes of silicon carbide, while the amorphous phase is likely to be fumed silica (based on the material specification).

[0118] The Microtherm® plug was then tested as a scrubbing material for HF by heating together with AIF3.3H2O using a tube furnace. 7.092 of AIF3.3H2O was loaded into a Ni boat, covered by a layer of 0.5078 g of Microtherm® (7.2 wt%). The sample was then maintained in the tube furnace at -260 °C for 4h under flowing nitrogen gas. 19.61 mg of HF was evolved, corresponding to 0.28 wt% evolution of HF based on mass of AIF3.3H2O. Hence, the thin layer of Microtherm® reduced the amount of HF released by 34.7 %.

[0119] After heating, XRPD was performed on the sample for phase identification. As is shown clearly in Figure 9, the XRPD pattern of the sample from the above HF scrubbing test matches that of a mixture of Microtherm® plug and the product from heating of pure AIF3.3H2O for 4h, indicating that there is no direct chemical reaction between the Microtherm® plug and AIF3.3H2O upon heating. AIF3.3H2O was fully dehydrated to form AIF3.

[0120] DSC measurements were performed on a mixture of the Microtherm® plug and AIF3.3H2O (1 :1 by volume ; approximately 33 wt%). The mixture was intimately ground to give a fine powder. DSC data were collected over the temperature range 30 - 350°C, at a heating rate of 1 °C / min. No significant changes were observed between DSC data of the mixture and that of pure AIF3.3H2O over the same temperature conditions, as shown in Figure 10. This confirmed that no direct reaction between AIF3.3H2O and Microtherm® occurred and that the materials are compatible over this temperature range.

[0121] These experiments confirmed that silica was likely to be a potentially suitable material for scrubbing HF produced through thermal decomposition of AIF3.3H2O. Moreover, it does not appear to alter the thermal or chemical behaviour of AIF3.3H2O in the temperature range up to 350 °C.

[0122] Although initial experiments were carried out using silica as a scrubbing agent, it will be appreciated that other types of scrubbing agents may be used, including metal salt hydroxides, metal salt oxides, metal salt carbonates, or metal salt hydrogencarbonates.

[0123] High-temperature heating

[0124] In the context of a flight data recorder, in the event of a severe crash incident, the flight data recorder may experience high-temperature conditions up to 1100°C. Experiments were therefore conducted to explore the behaviour of AIF3.3H2O at these elevated temperatures. High-temperature heating experiments were conducted using a high-temperature furnace in a fume hood. Due to instrumental constraints, the highest temperature of the oven used was around 1000°C.

[0125] 0.2997 g powder of AIF3.3H2O was loaded into an alumina container and heated at 1000°C for 1 h in the furnace.

[0126] 0.1278 g sample remained in the container after heating. XRPD was conducted for phase identification. Theoretical XRPD patterns were simulated from published crystal structures of AI2O3 and AIF3.

[0127] Figure 11 shows that the residue comprised a mixture of AI2O3 and AIF3 in the ratio 66:34 wt% based on Rietveld analysis of the powder pattern.

[0128] Further tests were conducted with controlled heating conditions using the same oven. AIF3.3H2O was loaded into an alumina container and heated to 1000°C at a heating rate of about 2°C per min. It was maintained at 1000°C for 1 h in the furnace. XRPD data were collected after the sample had cooled back to room temperature.

[0129] As is shown clearly in Figure 12, the XRPD pattern of treated sample matches that of a mixture of AI2O3 and AIF3, suggesting that sample went through both dehydration and hydrolysis upon heating up to 1000°C. The product is a mixture of 38 wt% of AI2O3 and 62 wt% of AIF3, indicating that approximately 50% of sample undergoes dehydration and 50% undergoes hydrolysis.

[0130] Compared to the faster heating regime, the amount of HF was significantly reduced at the lower heating rate. Heating of 200 g of AIF3.3H2O to 1000°C at this rate would release approximately 44 g HF. Assuming the following reaction:

[0131] 4HF + SiO2SiF4+ 2H2O,

[0132] Around 33g silica would be required to scrub all of the HF (assuming complete reaction), but substantially more could be required -perhaps as much as 66 g if all AIF3 is converted to alumina. However, at elevated temperatures HF will be exceptionally reactive and will react with most materials to produce much less reactive fluorides, e.g. metal fluorides, fluorocarbons. Therefore, it is believed that any HF formed under these high-temperature conditions will be consumed.

Claims

CLAIMS:

1. A thermally insulating apparatus, the apparatus comprising: a first material configured to at least partially enclose an article, the first material comprising or consisting of a metal fluoride hydrate; and a second material configured to at least partially enclose the first material, the second material comprising or consisting of an inorganic scrubbing agent.

2. An apparatus according to claim 1, wherein the first material is dry and / or is in solid form.

3. An apparatus according to claim 1 or claim 2, wherein the second material is dry and / or is in solid form.

4. An apparatus according to any preceding claim, wherein the article is an aircraft electronic device or part thereof.

5. An apparatus according to claim 4, wherein the article comprises or consists of a memory unit of an aircraft recording device.

6. An apparatus according to claim 5, wherein the recording device is a flight data recorder or a cockpit voice recorder.

7. An apparatus according to any preceding claim, wherein the metal fluoride hydrate consists of one or more compounds selected from the list consisting of aluminium fluoride trihydrate (AIF3.3H2O), copper fluoride dihydrate (CUF2.2H2O), iron fluoride trihydrate (FeFs.SFW), and chromium fluoride hydrate ([Cr(H2O)e]F3 or [Cr(H2O)6]F3.3H2O).

8. An apparatus according to claim 7, wherein the metal fluoride hydrate consists of aluminium fluoride trihydrate (AIF3.3H2O).

9. An apparatus according to any preceding claim, wherein the inorganic scrubbing agent comprises or consists of a metal salt hydroxide, a metal salt oxide, a metal salt carbonate, or a metal salt hydrogencarbonate.

10. An apparatus according to claim 9, wherein the inorganic scrubbing agent comprises or consists of one or more compounds selected from the list consisting of silica (SiC>2), magnesium oxide (MgO), calcium carbonate (CaCCh), sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH).

11. An apparatus according to claim 10, wherein the inorganic scrubbing agent consists of silica.

12. An apparatus according to any preceding claim, wherein the first material fully encloses the article.

13. An apparatus according to any preceding claim, wherein the second material fully encloses the first material.

14. An insulated article, wherein the insulated article comprises: an article; and an insulating apparatus at least partially enclosing the article, wherein the insulating apparatus comprises: a first material comprising or consisting of a metal fluoride hydrate and at least partially enclosing the article; and a second material configured to at least partially enclose the first material, the second material comprising or consisting of an inorganic scrubbing agent.

15. An insulated article according to claim 14, wherein the article comprises a memory unit of a flight data recorder or a cockpit voice recorder.

16. A method for providing heat protection to an article, the method comprising at least partially enclosing an article in a first material, the first material comprising or consisting of a metal fluoride hydrate; and at least partially enclosing the first material in a second material, the second material comprising or consisting of an inorganic scrubbing agent.

17. A method according to claim 16, wherein the article comprises a memory unit of a flight data recorder or a cockpit voice recorder.

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