NO346841B1

NO346841B1 - Heat refractive insulation material

Info

Publication number: NO346841B1
Application number: NO20210787A
Authority: NO
Inventors: Finn Erik Solvang; Knut Berg Haugen; Eivind Johannes Øvrelid
Original assignee: Ophiolite As
Priority date: 2021-06-18
Filing date: 2021-06-18
Publication date: 2023-01-30
Also published as: EP4355711A1; WO2022265520A1; WO2022265520A8; NO20210787A1

Description

Technical Field

[0001] The present invention relates to heat refractive insulation materials, the use of such materials and methods for manufacturing such materials.

Background

[0002] There is an increasing demand for insulation materials that are environmentally friendly, yet have a high strength to density ratio, a thermal heat conductivity and resistance to high-temperature operating conditions. One area where such demands are important are pipes in geothermal wells, where operating temperatures up to 600 ̊C may be encountered at depths of more than 3500 m below the earth’s surface. Other areas with such demands on insulation materials are applications concerning fire barriers and fire protection, heat conservation insulation or general thermal insulation in industrial or other settings.

[0003] Traditionally, silica-based materials have been used as insulation material for thermal insulation applications where low thermal conductivity has been needed. However, these traditional materials often do not meet the increased demands on both resistance to high-temperature conditions and a high strength to density ratio. CN 108341677 A discloses a high-strength refractory brick and a method for preparation thereof, utilizing the following raw materials: expanded perlite, diatomite tailings, alumina micro-powder, silicon carbide micro-powder, grapheme, coal gangue, high-alumina bauxite, refractory clay, inorganic fibers, a bonding agent, a water reducing agent, a foaming agent and deionized water. US 2004/157724 A1 discloses a dry refractory composition including at least matrix material, filler lightweight material, and metal fibers. CN 1072660088 B discloses a refractory cement comprising an organic binder and an inorganic binder.

[0004] Therefore, there is a clear need to provide an environmentally friendly insulation material with a high strength to density ratio, a low thermal heat conductivity and resistance to high-temperature operating conditions.

Summary of the disclosure

[0005] The present invention aims to overcome the disadvantages of the prior art, with the heat refractive insulation material of claim 1 and the method for producing a heat refractive insulation material according to claim 10.

Figures

[0006] Figure 1 shows expanded glass particles with a fraction size of 0.25 - 0.50 mm and a bulk density of 340 g/l.

[0007] Figure 2 shows silicon carbide particles with a fraction size of 0 - 2 micrometer, with D50 at 0.9 μm.

[0008] Figure 3 shows a dry mixture of expanded silica particles and SiC particles as diffractive agent.

[0009] Figure 4 shows a wet mixture.

[0010] Figure 5 shows a layer of 12 mm of wet mixture applied to a plexiglass plate.

[0011] Figure 6 shows the top surface of a sample tile of heat reflective insulating material grinded to a thickness of 10 mm after curing, according to a first exemplary embodiment.

[0012] Figure 7 shows the bottom surface of a sample tile with a thickness of 10 mm, after grinding the surface to make it even, according to a first exemplary embodiment.

[0013] Figure 8 shows the test setup to measure the thermal conductivity.

[0014] Figure 9 shows the top surface of a sample tile of a second exemplary embodiment.

[0015] Figure 10 shows the bottom surface of a sample tile of a second exemplary embodiment.

[0016] Figure 11 shows exposure of a sample tile to a propylene flame according to a third exemplary embodiment.

[0017] Figure 12 shows a sample tile after exposure to a propylene flame for 30 s and after cooling, according to a third exemplary embodiment.

Detailed description

[0018] With reference to fig. 1 - 4, the present disclosure concerns a heat refractive insulation material, comprising expanded silica particles, at least one diffractive agent and at least one liquid binder. The heat refractive insulation material comprises 20 - 94 wt% of expanded silica particles. The expanded silica particle may comprise 60 - 99.999 wt% of SiO2. The expanded silica particles preferably comprise lightweight aggregates such as expanded glass granulates, expanded glass spheres, hollow glass spheres, hollow glass microspheres, expanded perlite, crushed foam glass, or crushed pumice stones. The expanded silica particles have a particle diameter of 0.01 - 16 mm, preferably 0.1 - 2 mm, most preferably 0.25 – 1.0 mm. The expanded silica particles have a bulk density from 50 - 500 g/l, preferably 200 - 400 g/l, most preferably 250 - 350 g/l. The expanded silica particles preferably comprise recycled glass powder. Recycled glass powder may, for instance, be sourced from post-consumer recycled glass, soda lime glass, float glass, windscreens, solar panels. Advantageously, the expanded silica particles thereby form an environmentally friendly material. The expanded silica particles may comprise a residual expanding agent, such as SiC, AlN, H2O, Glycerin, Sodium Silicate, carbon black, Dolomite, CaCo3 or Al2O3 or any other suitable expanding agent.

[0019] The heat refractive insulation material further comprises 1 - 20 wt% of at least one diffractive agent. The at least one diffractive agent preferably has a refractive index above 2.4. An increased amount of the at least one diffracting agent results in an increased refraction index of the heat refractive insulation material.

Advantageously, the heat insulating properties of the material for any specific end use can thereby be achieved as desired. The at least one diffractive agent comprises silicon carbide, titanium dioxide, graphite, carbon black, or other materials with a refractive index above 2.4 and with a melting point above 1800<o>C. The at least one diffractive agent preferably comprises particles. The particles of the at least one diffractive agent may have a diameter of 0.1 - 15 μm, preferably 0.41 – 10.96 μm, most preferably 0.67 – 7.73 μm.

[0020] The particles will be selected to give maximum diffraction. Maximum diffraction for particle size/wavelength = 0.5.

[0021] For applications where the material is used for a range of temperatures , one will design the material with optimal particle size distribution for each applications.

[0022] The particle size distribution will be optimized for the gradient in the material.

[0023] For materials with large gradients, one will design multilayer materials or functionally graded materials.

[0024] To obtain maximum diffraction the particle size should preferably be 50% of the wavelength of the infrared waves for the temperature interval the heat refractive insulation material intends to operate under, see table 1.

[0025] To calculate the particle size range of the diffractive agent we have used Wiens displacement law formula that states that the spectral radiance of black-body radiations per unit wavelength, peaks at the wavelength λpeak , given by:

λpeak = b/T ,where T is the absolute temperature, b is a constant of proportionality called Wien’s displacement constant, equal to 2.897 771 955 x 10<-3 >mK. This is an inverse relationship between wavelength and temperature.

[0026] For a temperature interval from -88<o>C to 1800<o>C, equal to 185-2073 T(K) we have calculated the particle size in micrometer of a diffractive agent as percentage of wavelength in micrometer.

Table 1: Particle size in percentage of wavelength at different temperatures.

[0027] The heat refractive insulation material also comprises 5 - 60wt% of at least one inorganic binder. The at least one inorganic binder comprises 5 - 60wt% of water glass (sodium silicate), bentonite, kaolinite or cement, or any other inorganic binder or composite binder with a minimum heat resistance of 600<o>C.

[0028] The heat refractive insulation material has a density of 200 - 800 g/l, preferably 300 - 600 g/l, most preferably 350 - 450 g/l. The heat refractive insulation material has a thermal conductivity of 0.025 - 0.115 W/(mK), preferably 0.043 - 0.080 W/(mK), most preferably from 0.047 - 0.067 W/(mK). Finally, the heat refractive insulation material has a refractive index of at least 1.55. Thereby the heat refractive insulating material may refract heatwaves. Preferably, the heat refractive insulating material may refract heatwaves with a wavelength from 1.39 micrometer to 15.66 micrometer in the temperature interval from -88 to 1800<o>C (table 1). Advantageously, the heat refractive insulating material thereby achieves a low thermal conductivity and an improved ability to be utilized under high temperatures. The heat refractive insulation material may be cross-linked.

[0029] A product comprising a heat refractive insulation material according to the disclosure, comprises a thermal coating on the surface of a pipe for a geothermal well, fire barrier or a construction element such as a liquid paste or liquid mortar, a brick, a block, a plate or a half-pipe insulation component.

[0030] A method for preparing a heat refractive insulation material according to the disclosure is next described. The method comprises pre-mixing expanded silica particles and at least one diffractive agent to provide a dry mixture. The diffractive agent preferably comprises particles. The diffractive agent covers or partially covers the surface of the expanded silica particles. The method further comprises mixing at least one liquid binder into the dry mixture to provide a wet mixture. Preferably, the wet mixture is a uniform wet mixture. Preferably, the step of mixing the at least one liquid binder into the dry mixture comprises stirring until all liquids are blended in and the diffractive agent has reached a uniform distribution inside the binder. The diffractive agent may thereby form a grid in between the expanded silica particles when cured. An increased amount of liquid binder will make the wet mixture more liquid and easier to apply onto the surface uniformly or to fill a mold with a complex structure. Advantageously, a more liquid mixture is easier to apply as a coating or a liquid mortar.

[0031] The wet mixture is subsequently dried and / or cured into a solid material.

Preferably, the wet mixture is cured at a temperature of 0.1 - 200 ̊C. The curing is preferably continued until the chemical reaction between the binder and the expanded silicate particle is completed and the water in the binder has evaporated. Advantageously, after curing the heat refractive insulation material has superior fire protection capabilities, low thermal heat conductivity, high strength to density ratio, and a refraction index above traditional silica-based insulation material.

[0032] Before the step of curing the wet mixture is preferably applied as a liquid coating, a liquid mortar or a liquid fire barrier onto a surface, such as the surface of a pipe or a wall element. Alternatively, the wet mixture may be filled in a mold to form a pre-casted heat reflective insulation material. The pre-casted material may form a construction element, such as a block, a brick, a tile, a plate, or a halfpipe component. Advantageously, the casted element forms a lightweight component with improved resistance to high temperature. Further advantageously, the lightweight components may have an improved crushing resistance.

Exemplary embodiment 1

[0033] According to a first exemplary embodiment a wet mixture was prepared comprising 200 g of expanded silica particles, 20 g of a diffractive agent and 237.5 g of a binder. The expanded silica particles, shown in fig. 1, comprised recycled glass, sodium silicate and glycerin. The bulk density of the expanded silica particles was 330 g/l. The expanded silica particles comprised a particle diameter of 0.25 -0.50 mm. One example of such expanded silica particles is Poraver®, manufactured by Dennert Poraver GmbH. The diffractive agent, shown in fig. 2, comprised silicon carbide particles with a diameter up to 2 μm and with a mass median diameter D50 of 0.9 μm. One example of such a diffractive agent is produced by Fiven Norge AS. Finally, the binder comprised a sodium silicate solution with a water content > 60%.

[0034] The expanded silica particles and the diffractive agent were pre-mixed, as shown in fig.3, to form a dry mixture. The binder was then stirred into the dry mixture, to create a wet mixture, shown in fig. 4. Subsequently, the wet mixture was deposited on a plastic plate and levelled, see fig. 5. The mixture was levelled to a thickness of at 12 mm. The levelled wet mixture was then cured at 40 ̊C for 4 days, to create a solid material. The solid material was grinded to make the surface even, and cut into tiles with dimensions 10 mm x 112 mm x 94 mm. The weight of a sample tile was 57.3 g. The block density of the solid material was calculated to be 454 g/l. The thermal heat capacity of the top surface, a mid-layer and the bottom surface of the sample tile was measured yielding a top surface conductivity (in Watt per milli Kelvin) of 0.043 W/mK and a bottom surface conductivity of 0.077 W/mK. Top and bottom surface conductivity was measured at a penetration depth of 1.28 mm from the top surface and bottom surface. Midlayer conductivity was 0.058 W/mK, where the mid-layer was after grinding down the surface 5mm. It was observed that the top surface of the sample, see fig. 6, had cured more than the bottom surface of the sample, see fig. 7, at time of the test. In fig. 6 and 7 the top surface and the bottom surface were grinded to make these surfaces more even. The thermal capacity was measured using a C-Therm Thermal Conductivity Analyzer, see fig. 8.

Exemplary embodiment 2

[0035] According to a second exemplary embodiment a wet mixture was prepared comprising 200 g of expanded silica particles, 20 g of a diffractive agent and 260 g of a binder. The expanded silica particles, the refractive agent and the binder were as for the first exemplary embodiment. Next, a wet mixture was prepared, as for the first exemplary embodiment. Subsequently, the wet mixture was deposited on a plastic plate and levelled at 5 mm thickness. The levelled wet mixture was then cured at 40 ̊C for 2 days, to create a solid material. The solid material was then cut into tiles, as for the first exemplary embodiment. A thin crust of sodium silicate was observed on the bottom surface of the sample tile, see fig. 10. A corresponding crust was not observed on the top surface of the sample tile, see fig. 9. The thermal heat capacity through a sample tile was then measured, as for the first exemplary embodiment, yielding a top surface conductivity of 0.053 W/mK and a bottom surface conductivity of 0.105 W/mK. As the sample tile in the second exemplary embodiment is thinner than the sample tile in the first exemplary embodiment, and since the test is conducted at a penetration depth of 1.28mm, no mid-layer conductivity was measured for the second exemplary embodiment.

Exemplary embodiment 3

[0036] A sample tile with solid material according to the first exemplary embodiment was exposed to a propylene flame for 30 s, as shown in fig. 11. After exposure to the propylene flame the surface of the sample tile was visually examined, as shown in fig. 12. Some change in cell structure on surface was observed. No cracks originating form material tension due to heating of the sample tile were observed in the sample tile. Furthermore, no change in cell structure inside the sample tile was observed.

Claims

1. Heat refractive insulation material comprising:

20 – 94 wt% of expanded silica particles;

1 – 20 wt% of at least one diffractive agent;

5 – 60 wt% of at least one inorganic binder,

wherein the diffractive agent has a diameter of 0.1 – 15 μm.

2. Heat refractive insulation material according to claim 1, wherein the expanded silica particle comprises 60 - 99.999 wt% of SiO2.

3. Heat refractive insulation material according to any one of claims 1 - 2, wherein the expanded silica particles comprise lightweight aggregates such as expanded glass granulates, expanded glass spheres, hollow glass spheres, hollow glass microspheres, expanded perlite, crushed foam glass, or crushed pumice stones.

4. Heat refractive insulation material according to any of claims 1 - 3, wherein the expanded silica particles have a particle diameter of 0.01 - 16 mm, preferably 0.1 - 2 mm, most preferably 0.25 – 1.0 mm.

5. Heat refractive insulation material according to any of claims 1 - 4, wherein the expanded silica particles have a bulk density from 50 - 500 g/l, preferably 200 - 400 g/l, most preferably 250 - 350 g/l.

6. Heat refractive insulation material according to any of claims 1 - 5, wherein the diffractive agent comprises silicon carbide or titanium dioxide, graphite or carbon black with a refractive index above 2.4 and a melting point above 1800<o>C.

7. Heat refractive insulation material according to any of claims 1-6, wherein, the diffractive agent has a diameter of 0.41 – 10.96 μm, preferably 0.69-7.83 μm.

8. Heat refractive insulation material according to any one of claims 1-7, wherein the binder comprises at least one inorganic binder such as water glass, bentonite, kaolinite or cement, with a minimum heat resistance of 600<o>C.

9. A product comprising a heat refractive insulation material according to any of claims 1 – 8, the product comprising thermal coating on the surface a pipe for a geothermal well, a fire barrier or a construction element such as a liquid paste, a brick, a block, a plate or a half-pipe insulation component.

10. Method for producing a heat refractive insulation material according to any one of claims 1 - 8 the method comprising:

- pre-mixing expanded silica particles and the at least one diffractive agent, to form a dry mixture where the diffractive agent covers or partially covers the surface of the expanded silica particles:

- providing at least one inorganic binder;

- mixing the dry mixture and the at least one inorganic binder to form a wet mixture; - drying and / or curing the wet mixture into a solid material.

11. The method according to claim 10, wherein the wet mixture is cured at a temperature of 0.1 - 200 ̊C.

12. The method according to claims 10 or 11, further comprising, before the step of curing:

applying the wet mixture as a liquid coating or a liquid mortar onto a surface; or casting the wet mixture inside a mold to form pre-casted heat refractive insulation material.

13. The method according to claim 12, wherein the casted heat refractive insulation material comprises a block, a brick, a tile, a plate, or a half pipe component.