Electrothermic compositions

Abstract

According to the invention there is provided an electrothermic composition comprising: a carbon component; a graphite component having a crystallinity of 99.9% and wherein the graphite is heat treated at a temperature of 2500° C. to 3000° C., and a binder, whereby the composition has a thermal coefficient of electrical resistance (TCR) of ±0.0001 to 0.0010 per ° C. over a temperature range of from about 20° C. to 60° C. in an airborne environment, wherein the ratio of the first conductive component and the second resistor component is selected between 10:1 to 1:10.

Claims

1. An electrothermic composition comprising: a first conductive carbon component selected from the group consisting of: conventional thermal blacks, furnace blacks, lamp blacks, channel blacks, surface-modified carbon blacks, surface functionalised carbon blacks, and heat-treated carbons; a second resistor component which is graphite having a crystallinity of 99.9% and wherein the graphite is heat treated at a temperature of 2500° C. to 3000° C.; and a binder; whereby the composition has a thermal coefficient of electrical resistance (TCR) of ±0.0001 to 0.0010 per ° C. over a temperature range of from about 20° C. to 60° C. in an airborne environment, wherein the ratio of the first conductive component and the second resistor component is selected between 10:1 to 1:10.

2. A composition according to claim 1 wherein the binder has a Tg below 0° C.

3. A composition according to claim 1 wherein the first conductive carbon component is produced by a process at a temperature of least 1000° C.

4. A composition according to claim 1 wherein the first conductive carbon component has a shape selected from the group consisting of flake-like, spherical-like, needle-like, plate-like, wire-like, tube-like, whisker-like, ball-like, single-wall, double-wall, multi-wall carbon nano tubes, buckyballs, quantum dots, and combinations thereof.

5. A composition according to claim 1 wherein the average particle size of the first conductive carbon component is in the range of between about 10 nm to 50 nm.

6. A composition according to claim 1 wherein the first conductive carbon component is included in the composition in a concentration of between 1 and 40% wt of the total weight of the composition.

7. A composition according to claim 1 wherein the first conductive carbon component has a surface area of between 200 and 2000 m.sup.2/g.

8. A composition according to claim 1 wherein the graphite has a particle size in the range of between about 250 nm to 500 μm.

9. A composition according to claim 1 wherein the graphite is present in the composition in a concentration of between 1 and 40% wt of the total weight of the composition.

10. A composition according to claim 1 wherein the graphite has a surface area of from about 25 to about 500 m.sup.2/g.

11. A composition according to claim 1 wherein the graphite is selected from the group consisting of: calcined petroleum coke, crystalline flake graphite, flake graphite, expandable graphite, purified flake graphite, purified crystalline flake graphite, purified petroleum coke, purified synthetic graphite, purified-vein graphite, synthetic graphite, and vein graphite.

12. A composition according to claim 1 wherein the graphite has a shape selected from the group consisting of flake-like, spherical-like, needle-like, plate-like, wire-like, tube-like, whisker-like, ball-like, nano graphites, tubes, wires, and combinations thereof.

13. A composition according to claim 1 wherein the graphite has a particle size between 1-40 micron.

14. A composition according to claim 1 wherein the thermal conductivity in the horizontal direction of the graphite is between 100 to 2000 W/m.Math.K, or wherein the thermal conductivity in the vertical direction of the graphite is between 1 to 100 W/m.Math.K.

15. A composition according to claim 1 wherein the surface area of the graphite is 1% to 80% less than the surface area of the first conductive carbon component.

16. A composition according to claim 1 wherein the binder is a resinous binder, comprising 1 to 90% by volume or weight of the composition and is selected from the group consisting of: organic, inorganic, natural, synthetic, animal, vegetable, or mineral, aqueous, solvent, thermoplastic, thermosetting, rigid, flexible binder systems and combinations thereof.

17. A composition according to claim 16 wherein the binder is selected from the group consisting of acrylics, alkyds, carbon fibre, cellulosics, epoxies, fluoro-plastics, ionomers, natural rubber, nylons, phenolics, polyamides, polybutadienes, polyesters, polyamides, polypropylenes, polyurethanes, silicone resins, and silicone rubbers, styrene-butadiene, nitrile rubbers, polysulphide rubbers, vinyl-ethyelene, and polyvinyl acetates.

18. A composition according to claim 1 wherein the composition is devoid of metal or metal oxide.

19. A method for generating heat on a floor, wall, or calling, the method comprising the steps of: (a) providing a composition according to claim 1; (b) attaching electrodes to said composition or a material formed from the composition; (c) connecting said electrodes to a source of electricity; and (d) energizing said source of electricity, thereby generating heat at a temperature of between 10 and 60° C. from said composition or a material formed from the composition.

20. The method of claim 19, wherein the electricity has a voltage of less than 50 V.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

(2) FIGS. 1a and 1b are images of the carbon black VULCAN® XC72 in a glass glaze after heating at 400° C. and 650° C., respectively;

(3) FIG. 2 is same carbon black component before exposure to heat and not incorporated into a vehicle; and

(4) FIG. 3 is graph of resistance for various graphite materials dispersed in various ratios in a glaze.

(5) FIG. 4 shows the manufacturing process of glass fibre.

(6) FIG. 5 shows carbon and graphite being added into precursors for carbon fibres, such as polyacryonitrile (PAN), rayon and pitch.

DEFINITIONS

(7) In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention only and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one having ordinary skill in the art to which the invention pertains.

(8) Unless the context clearly requires otherwise, throughout the description and the claims, the words ‘comprise’, ‘comprising’, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of ‘including, but not limited to’.

(9) As used herein, the phrase “consisting of” excludes any element, step, or ingredient not specified in the claim. When the phrase “consists of” (or variations thereof) appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole. As used herein, the phrase “consisting essentially of” limits the scope of a claim to the specified elements or method steps, plus those that do not materially affect the basis and novel characteristic(s) of the claimed subject matter.

(10) With respect to the terms “comprising”, “consisting of”, and “consisting essentially of”, where one of these three terms is used herein, the presently disclosed and claimed subject matter may include the use of either of the other two terms. Thus, in some embodiments not otherwise explicitly recited, any instance of “comprising” may be replaced by “consisting of” or, alternatively, by “consisting essentially of”.

(11) To provide a more concise description, some of the quantitative expressions given herein are not qualified with the term ‘about’. It is understood that whether the term ‘about’ is used explicitly or not, every quantity given herein is meant to refer to the actual given value, and it is also meant to refer to the approximation to such given value that would reasonably be inferred based on the ordinary skill in the art, including approximations due to the experimental and/or measurement conditions for such given value. In what follows, or where otherwise indicated, ‘%’ will mean ‘weight %’, ‘ratio’ will mean ‘weight ratio’ and ‘parts’ will mean ‘weight parts’. The examples are not intended to limit the scope of the invention.

(12) The recitation of a numerical range using endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

(13) The terms ‘preferred’ and ‘preferably’ refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Example 1—Preparation and Application of Coatings

(14) In this example, coatings are made by initially forming a pigment grind and then letting down the grind in additional solvent with the incorporation of additives as is necessary, desirable, or convenient. Basic compositions are described in the following examples.

(15) Mixture A: 10 g Hi-Black 40B2 carbon pigment (Evonik HIBLACK® 40B2; DBP absorption 130, surface area 153 m.sup.2/g) was ground to 500 microns using a high-speed cyclone mill. 20 g natural graphite (from AMP metals Australia) was added (92% purity flake graphite). A final mesh size of 325 micron was established for Mixture A.

(16) Mixture B: 10 g Hi-Black 40B2 pigment was ground to 550 microns using a high-speed cyclone mill. 40 g of natural graphite (from AMP metals Australia) was added. These powders were added to 350 mls of glaze, placed in two one litre plastic containers under a high-speed disperser and dispersed at 8000 rpm for 5 minutes. The mixture was allowed to cool. Both mixtures were quite viscous, and mixture B required an additional 20 mls of water.

(17) Mixtures A and B were made up and sprayed out on 46×30 cm (18″×12″) panels. The panels were then allowed to dry and the voltage and current were recorded at room temperature of 20° C. Copper electrode tape (from 3M) was applied to both sides of a pair of 48 cm long×30 cm wide (18 inch long×12 inch wide) enamel coated metal oven trays, at 30 cm (12 inch) spacing. Mixture A was applied to one plate, while Mixture B was applied to the other by spray gun at 6.2×10.sup.5 Pa to 9.7×10.sup.5 Pa (90 to 140 psi), and the glaze mixtures were allowed to air dry.

(18) AC current at 240V was applied to plate with Mixture A (20 g graphite). The panel was brought up to temperature 193° C. The current drawn was measured at 1.9 amps and it remained constant at this value for 24 months. The plate was allowed cool to room temperature (20° C.), and current was applied again and the amps drawn were measured at 1.9 amps where it remained, with a resistance of 110 ohms.

(19) AC current at 240V was applied to Mixture B (40 g graphite). The panel was brought up to a temperature of 183° C. The current drawn was measured at 1.8 amps, with a resistance of 125 ohms and it remained constant at this value for 24 months. The plate was allowed to cool to room temperature (20° C.) and the resistance increased to 197 ohms. Current was reapplied and current drawn was found to drop to 1.1 amps at room temperature. On reheating, the current increased to 1.8 amps and the resistance decreased to 125 ohms where it remained stable.

(20) These examples demonstrate that for the Mixture A, the TCR value is zero over the range of temperatures measured, since the current drawn remains constant at 1.8 amps. In Mixture B the temperature recorded was 183° C. the current drawn was 1.8 amps and the resistance was 125 ohms. The sample remained at this value and then was allowed to cool to room temperature of 20° C. The resistance increased to 197 ohms, and then current was applied again. The current dropped to 1.1 amps at room temperature. The current was then increased to 1.8 amps and the resistance decreased to 125 ohms where it remained stable. This is a demonstration of the stability of the compositions, which display a TCR of zero.

(21) Since mixture A does not change its resistance or the amount of current drawn when cooled to room temperature and when reheated, it shows a constant TCR value of substantially zero. However, the second panel shows increase in resistance and lowering of the current drawn when cooled to room temperature, which shows that the carbon particle has a constant TCR value at a given ratio of graphite.

(22) In Mixture B, where higher amounts of graphite are used, the carbon black component does not appear to have the ability to stabilise the TCR at zero. This indicates that the proportions of carbon black and graphite in the compositions of the invention are important in stabilizing the TCR values and, accordingly, affect the physical properties of the coatings, glazes, and compositions of the invention.

Example 2

(23) Composition A: Copper tape was placed 25 cm (10 inches) apart on porcelain coated 30×30 cm (12×12″) plates, 10 g of Hi-Black 40B2 carbon and 300 mls glaze were mixed in a high-speed disperser until the particle size of the carbon in the glaze reached 500 nm. An evaporation type ink drawdown gauge was used to measure the particle sizes. A further 50 mls of glaze was added, followed by 30 g of natural vein graphite with a particle size of 325 microns. The mixture was allowed to mix for a further minute. 150 mls of Composition A was sprayed onto one of the 30×30 cm (12×12″) porcelain panels at a spray pressure of about 9.0×10.sup.5 Pa (130 psi). The panel was air dried and resistance and current drawn were measured. At an applied voltage of 240V, current drawn was 1.87 amps, while the resistance was 114 ohms, and the temperature produced by the panel was 296° C.

(24) Composition B: Copper tape was placed 25 cm (10 inches) apart on porcelain coated 30×30 cm (12×12″) plates. 10 g of Hi-Black 40B2 carbon and 300 mis glaze were in a high-speed disperser until particle size of the carbon in the glaze reached 500 nm (evaporation type ink drawdown gauge was used to measured the particle sizes). A further 50 mls of glaze was added, followed by 30 g of 2935 Thermo pure flake graphite with a particle size of 325 microns. The mixture was allowed to mix for a further minute. 150 mls of Composition B were sprayed onto one of the 30×30 cm (12×12″) porcelain panels at a spray pressure of about 7.6×10.sup.5 Pa (110 psi). The panel was air dried and resistance and current drawn were measured. At an applied voltage of 240V, the current drawn was 1.91 amps, while the resistance was 111 ohms, and the temperature produced by the panel was 193° C.

(25) It can be seen from these examples that varying the graphite source alone caused a difference in temperature of 103° C. Accordingly, without wishing to be bound by theory, the graphite seems to controls the heat generation. Whilst carbon has been found to be the main contributor to the neutral TCR values of these formulations, graphite is useful in the present compositions as a controller of heat generation. The graphite seems to control the amount of heat, meaning that it is a resistor, and that the concentration of it in the material will to some extent control the amount of heat being generated, but a certain amount of carbon is required in order to provide a TCR of approx 0 so that it is stable over time.

Example 3

(26) Test 1: 10 g of the graphite component or the carbon black component (VULCAN® XC72) is placed into a crucible made of a refractory grade ceramic and placed in an electric kin at 400° C. for five minutes. The crucible is withdrawn and allowed to cool and the weight is recorded. If there is no loss recorded in weight after heating, a high magnification visual inspection is carried out to examine for any visual heat stress or damage to the composition, such as burning, weight loss or significant changes in colour. If no visual damage is apparent and the conductive properties remain the same compared to before heating, the material is considered suitable for use in the compositions of the invention. This procedure can also be used to determine the minimal temperature required for cross-linking or fusing the components of the composition into glazes, glass frit porcelains, enamels, and powder coats, etc.

(27) An example of a visual examination is shown in FIGS. 1a and 1b, in which the FIG. 1a image is a sample of the carbon black VULCAN® XC72 in a glass glaze. After heating at 400° C., the image shows there is no visible damage to the carbon black or glass glaze. FIG. 1b shows the results for heating VULCAN® XC72 in a glass glaze at temperatures of 650° C. which is above the melting point of this carbon black. The damage caused by melting is clearly evident. It is believed that the ash part of the carbon black is the first part of the structure to degrade, particularly when electrical current and high temperatures are applied. It is believed that the smaller ash particles get hotter when electrical current is applied compared to the larger carbon particles. For example, the darker ash particles in FIG. 1a are observed to be very stable throughout the coating but FIG. 1b the smaller darker ash particles have enlarged and melted causing craters indicating visual damage and carbon black particle failure.

(28) FIG. 2 illustrates the same carbon black component before exposure to heat and not incorporated into a vehicle. The smaller darker particles are the ash content. It should be noted that small losses in weight will occur at 950° C. for most carbon blacks. This loss is generally 1.5% to 25% and depends on the structure, the type of carbon black, its manufacturing process, and the length of time the carbon is exposed to those temperatures.

(29) Test 2: In this test, the temperature is elevated slowly to between 600° C. and 1100° C. to investigate the melting points of the carbon black conductive particles or their weight loss. Since the time required to complete this aspect of testing can extend over hours to days, their structure and conductivity and their ability to maintain their electrical connection with each other in these glasses and glazes can be simultaneously tested. This provides an opportunity to match the carbon black with an appropriate glass frit for ease of application and formulation and formula modification. Also, acquiring the right glass frit and firing temperatures of these conductive glazes and matching of these glazes to the conductive particles, the connector, and the substrate on which they are applied is important. In other words, matching the coefficient of thermal expansion with the conductive graphite, conductive carbon, the connector, and the glaze, and also the substrate must be considered. Preferably the melting point of the glaze or glass is below that of the conductor, the resistor, and the connector. While temperatures of up to 1100° C. have been utilised herein, it is envisaged that temperatures of as high as 3425° C. (6917° F.) can be utilised when used as conductors in arc furnaces. However, since both carbon and graphite mixtures above 950° C. in an airborne environment are hard to maintain because of carbon evaporation, high temperature pigments, such as thermally purified processed graphites and carbons, with high structure to extremely high structures will have to be included in the compositions. Some graphites can be used to temperatures of around 3600° C. and some pure carbons can also achieve these temperatures.

(30) Test 3: The third test relates to procedures for introduction of the composition of the invention into glazes, glasses, frits, days, porcelains, enamels, and powder coats. Preferably the carbon and graphite particles go through the following tests and the final weights recorded to test for final loss of weight at a set temperature. Their electrical resistance is preferably tested against a dry non-fired sample to investigate their electrical properties, mechanical properties and physical properties for degradation. In most cases this can be done by using an oil absorption process, for example, dibutylphthalate absorption (DBPA or DBP). Thus, comparative testing between treated and original absorption factors indicates changes in properties (D1510-12, Standard Test Method for Carbon Black). The carbon black samples tested were a.) DERUSSOL® NA 9 Carbon Black Component: carbon electrical resistivity in PP 8 wt. % carbon black: 43 Ω.Math.cm; iodine absorption between 1075 and 1125 mg/g; DBP-absorption between 380 and 420 ml/100 g; ash content %≤1.0≤2.0; sulfur content %≤0.4≤0.8; fleetingness at 105° C.≤1.0≤1.0; pH-value 7-8; and b.) carbon black from Jiangxi Eastern Dragon Charcoal Industry Co. Ltd: iodine value: 1100 mg/g, specific surface area: 1350 m.sup.2/g, Iron content: 200 ppm, ash content 3%, pH Value: 3-5, moisture content 10%, chloride: ≤0.05%, mesh size: 200 mesh or 325 mesh. After testing, carbon sample (a) had a weight loss of 3 to 5%; and carbon sample (b) had a weight loss of 14%. 20 g of each material was placed in to 1200° C. ceramic dish and then placed into a Kiln at 400° C. for five minutes. They were then allowed to cool and removed from the kiln. They were re-weighed and this was repeated at 500, 600 and 700° C. in an airborne environment. At 400° C. carbon a.) had no weight loss, and carbon b.) had a 3% weight loss. At 500° C. carbon a.) had 2% weight loss and carbon b.) had a 6% weight loss. At 600° C. carbon a.) had a weight loss of 4% and carbon b.) had a 9% weight loss. At 700° C. carbon a.) had a weight loss of 5% and carbon b.) had a weight loss of almost 14%. Preferred carbons to be used in these glazes have a 1 to 5% loss at these temperatures.

(31) Test 4: TCR testing of glaze comprising a graphite and carbon combination according to the invention. The compositions of the invention to be tested are sprayed onto a metal panel having a dielectric enamel coating applied thereto. The panel is then air dried and the current and resistance at certain applied voltages is recorded. The panels are then placed in the kiln and fired at the appropriate temperatures. The panels are withdrawn from the kiln and allowed to cool and their current and resistance at certain applied voltages are recorded, again at room temperature. The coated panels are then placed into a deep freezer at −23° C. and left for approximately 24 hours at which time they were removed and their amps, ohms, volts recorded again after which the panels are allowed to warm to room temperature. The coated panels are then placed into an oven and bought up to temperature of around 250° C. and they are removed from the oven hot and their amps, ohms, volts are recorded again. If the coatings have the same constant resistant values at room temperature and in a deep freezer and in the oven then their TCR values are zero or at substantially zero. Ground coat was applied to both sides of steel metal panels measuring 22×20 cm (8½″×8″). The ground coat was used as a dielectric surface between metal and the coatings/glazes of the invention. In this case the firing temperature was 990° C. After firing at 450° C., the panel was allowed to cool to room temperature. The resistance was recorded at 320 ohms, and then 150V AC was applied. The current drawn was 1.1 amps and the panel reached 190° C. The panel was allowed to cool and the resistance was recorded again at 320 ohms. The panel was then placed into a refrigerator and taken down to −23° C. and the resistance was measured at 334 ohms. The panel was placed back into the oven and reheated to 250° C. and the resistance measured at 322 ohms. Therefore, the TCR is zero.

(32) TCR Investigations of Glaze Material Before Firing

(33) Formulation and application procedures for unfired conductive glazes, elements, coatings, enamels, porcelains, and coatings before firing will be now described. The glazes can be applied by brush or roller, but are preferably sprayed onto the surface to be coated. The components of the compositions were ground in the following order using a high-speed cyclone mill: 10 g High black 40B2, ground to 550 microns, then 20 g graphite 2935K from superior graphite was added. It was left at a larger mesh size of 325 microns. The powders were then added to 350 mls of glaze and placed in a 1 L plastic container under a high-speed disperser and the mixture was operated at 8000 rpm for 5 minutes. The mixture was then allowed to cool. The resulting mixture was quite viscous.

(34) Copper electrode tape from 3M was applied to a second 46×30 cm (18×12″) coated enamel metal oven tray and glaze mixture was applied by spray gun and allowed to air dry. AC current at 240V was applied and the panel was brought up to temperature. The temperature recorded was 200° C., and the current drawn was 1.9 amps. It has remained at this level for two years and four months and is still maintaining the same resistance of 110 ohms at the time of writing. This particular sample is unfired.

(35) A second formulation was prepared. Components in the following order were ground using a high-speed cyclone mill. 10 g DERUSSOL Carbon NA 9 carbon black (Degussa) was ground to 550 microns. 30 g graphite 2939 K from Superior Graphite's USA was then added and was left at a larger mesh size of 325 microns. The mixture of powders was then added to 450 mls of glaze and placed in a 1 L plastic container under a high-speed disperser and the mixture was operated at 8000 rpm for 5 minutes. The mixture was then allowed to cool the mixture was found to be quite viscous. The TCR values are in the following paragraph.

(36) Copper electrode tape (3M) was applied to both sides (30 cm; 12 inches apart) of an 46×30 cm (18×12″) plate (900° C.) coated enamel metal oven tray. The glaze mixture was applied by spray gun at around 6.2×10.sup.5 Pa to 9.0×10.sup.5 Pa (90 to 130 psi) and allowed to air dry. Current at 240 V was applied to bring the panel up to temperature (310° C.). The current drawn was 1.8 amps. It remained at this temperature and resistance (90 ohms) for 2 years and four months. This particular sample is unfired.

(37) These results demonstrate that the compositions of the invention have a TCR of zero and hold temperature for long periods of time without degradation. In other examples, the carbon and graphite compositions of the invention (or the carbon/carbon compositions of the invention) can be incorporated into aluminium oxide powder and pressed into a solid brick or pressed into a solid rod to, for example, make a heating element. These compositions have a TCR of approximately 0 and can remain at elevated temperatures in an airborne environment for extended periods of time. In other examples, the carbon and graphite compositions of the invention (or the carbon/carbon compositions of the invention) can be incorporated into refractory materials. In one example, the compositions of the invention are incorporated into Thermobond. Thermo bond is a two part system (dry powder formulation and liquid activator) added together to form a uniquely bonded refractory material The Liquid activator is acid based in the bonded system. An example formulation below thermobond powder 1 kg carbon DERUSSOL Carbon NA 9 carbon black (Degussa) 20 g and graphite 20 g (from AMP metals Australia) was added (92% purity flake graphite), liquid activator 900 mils mixed together uniformly which created a thick slurry. 200 g of the mixture was applied to a fire brick at 0.5 mm thickness. The brick was exposed to microwaves for 20 seconds and the temperature of the mixture increased from room temperature (20° C.) to 110° C. The brick was allowed to cool and removed from the microwave. The thermobond was completely cured. The brick was exposed to microwaves again for 10 seconds and the top surface rose to 220° C. This particular sample was left for three weeks, and then microwaved for 10 seconds. The surface of the brick rose to 218° C., which is a good demonstration of retained electrical values of these particles when exposed to microwaves. The second brick with Copper electrodes were applied to the brick and on the application of 240 V at 1 amp a temperature of 240° C. was achieved. The temperature of this brick rose 3° C. in eight weeks and the current and resistance stayed the same.

(38) TCR Investigations of Glaze Material after Firing

(39) Firing temperatures of glazes and matching of the properties of the glazes to the substrate which they are applied can be quite important. Some of the firing temperatures used in these tests are as follows. Cross-linking/fusion temperatures and firing temperatures are preferably in the range of 150° C. to 1200° C. Higher cross-linking/fusion temperatures are used from 1200° C. through to 2100° C. in special applications, while lower firing temperatures between 200° C. and 550° C. are used in other applications. The fusion/melting temperature can be chosen depending on the glass frit used and the melting point of the conductor, resistor, connector and in some cases the substrate. These conductive glazes, glass frits, porcelains, and powder coats have the ability to be recoated and refired to add additional conductivity to the first coating. These coatings can also be laminated between each other to be a multiple layer heating device or system. These discoveries can be utilised in many different applications other than heating. Multilayer material or glazes, or coatings with specific mechanical physical and electrical properties can be used electronic electrical memory storage or other multilayer devices.

(40) All enamelling processes described herein involve the mixture and preparation of frit (the unfired enamel mixture); preparation of the substrate; the application of the coating, firing of the coating; and then finishing processes. Most applications involve two layers of enamel: a ground-coat to bond to the substrate and a cover-coat to provide the desired external properties. The ground coat in the present examples are glazes which are fired at or below these temperatures, but in some special applications firing temperature can go up beyond 1400° C. For example, ground coat was applied to both sides of steel metal panels measuring 20×20 cm (8″×8″). The ground coat was used as a dielectric surface between the metal and the coatings/glazes of the invention. In this case the firing temperature was 990° C. Two copper electrode tapes were applied to the surface 20 cm (8 inches) apart on the plate (copper tape by 3M with a high temperature adhesive). Glaze mixtures were applied by spray gun at 6.2×10.sup.5 Pa to 9.0×10.sup.5 Pa (90 to 130 psi) and the panels were air dried. The coated glaze appeared to be about 1 mm in thickness when wet and 0.5 mm when dry. An electric kin is then brought up to temperature of 450° C. The panel was then placed inside the oven for approximately 1 minute after which it was removed and allowed to cool, and the resistance was recorded as 320 ohms. Using a varaic transformer, 150V of AC was applied and temperatures of 190° C. at 1.1 amps from the panel was recorded for 5 months. This shows the ability of these particles to cross-link into a glass and maintain their electrical connectivity.

(41) The resistance of the dry panel before firing was 100 ohms and increased to 320 ohms on firing. An increase of 220 ohms in resistance must be taken into consideration when formulating, such as by decreasing the amount of clay or glass frit in the formulation of the glaze and by the addition of other materials to lower the firing temperature and increase melt flow rate of the glazes. The dramatic increase in resistance on firing is thought to be due to the cross-linking of the glaze reducing the connection between the conductive particles. Also, inclusion of the glass glaze coating and the copper tape connections is thought to increase the resistance. It has been found that the increase in resistance varies from 10% to 220% depending on the nature of the conductive carbon and graphite in the compositions of the invention used and the nature of the glaze.

(42) An example of a formulation of the microwave curing embodiment is given below: Resin composition: 68% solids siloxane (TempTech 32800 clear with 32% xylol) sourced from Pittsburgh's paint and glass (500 mL). Carbon black: 5 grams carbon black E90 Specific surface area 1250 m2/g. Ash content 1%; pH Value 7, mesh size=200 mesh. graphite 99% pure spherical; average density 1.65 gm/cm; 10 grams and average particle size 100 μm both carbon and graphite supplied by Jiangxi Eastern Dragon Co. Ltd China

(43) Both carbon and graphite (supplied by Jiangxi Eastern Dragon Co. Ltd China) were mixed together. The mixture was placed into laboratory disperser and blended at 5000 rpm for one minute. The mixture was then removed from the disperser and 100 ml placed into a microwaveable Pyrex dish, which was placed into a microwave oven. The microwave oven was set on defrost mode for 20 seconds, and the temperature of the mixture went from 20° C. to 90° C. in 20 seconds. The mixture was allowed to cool and then tested for curing. The mixture was approximately 85% cured. The mixture was then placed back into the microwave for another 15 seconds. The temperature of the mixture went from 20° C. to 70° C. The mixture was allowed to cool and the test indicated that the composition or mixture was 98% cured. The mixture was then placed back into the microwave for a third time for another 10 seconds. The microwave was set on defrost mode and the temperature rose from 20° C. to 90° C. The mixture was then allowed cool to room temperature.

(44) A true RMS Fluke multimeter (model number 681) was used to test the dry resin mixture. The resistance recorded was 530 ohms at 20° C. The mixture was then placed back into the microwave for another 10 seconds. The temperature of the mixture went from 20° C. to 93° C. The mixture was allowed to cool to 2° C. and then the resistance was recorded again at 529 ohms. The dry resin mixture in the Pyrex dish was then placed into a refrigerator and taken down to −18° C. The resistance was again measured at 535 ohms. The microwave oven used in this experiment is a Samsung 1100 series 240 V at 50 Hz 1500 W running at 2450 MHz at 1000 W output.

(45) Table 1 below illustrates Examples of the present invention using a first carbon component and a second carbon component. These mixtures were tested and displayed a TCR of about zero or were substantially stable within the parameters defined. It was also found that the TCR was about zero or remained substantially stable both when the composition was unfired or when it had been fired.

(46) TABLE-US-00002 TABLE 1 Carbon and Carbon Examples Composition mix units Example 1 surface area BP2000 30 grams of 1440 m2/g surface area HIBLACK ® 600L 10 grams of 270 m2/g Duncan pure translucent glaze 1000 ml TEGO ® Disper 750 W 60 GRAMS Example 2 surface area HIBLACK ® 600L 25 grams of 270 m2/g surface area HIBLACK ® 420B 10 grams of 150 m2/g Duncan pure translucent glaze 800 ml TEGO ® Disper 750 W 20 GRAMS Example 3 surface area carbon black E90 25 grams 1250 m2/g surface area Vulcan XC 72 15 grams 770 m2/g Duncan pure translucent glaze 1100 ml TEGO ® Disper 750 W 70 grams Example 4 surface area carbon black E90 25 grams 1250 m2/g surface area HIBLACK ® 30L 20 grams 138 m2/g Duncan pure translucent glaze 850 ml TEGO ® Disper 750 W 60 grams

(47) Table 2 below illustrates Examples of the present invention using a carbon component and a graphite component. These mixtures were tested and displayed a TCR of about zero or were substantially stable within the parameters defined. It was also found that the TCR was about zero or remained substantially stable both when the composition was unfired and when it had been fired.

(48) TABLE-US-00003 TABLE 2 Carbon and Graphite Examples Composition mix units Example 1 surface area of 1440 m2/g BP2000 30 grams (99% purity flake graphite 5500 Synthetic Graphite 10 grams Duncan pure translucent 800 ml glaze TEGO ® Disper 750 W 40 GRAMS Example 2 surface area of 270 m2/g HIBLACK ® 600L 25 grams (92% purity flake graphite Graphite AMP 10 grams Duncan pure translucent 600 ml glaze Example 3 surface area 1250 m2/g carbon black E90 25 grams (92% purity flake graphite Graphite AMP 15 grams Duncan pure translucent 800 ml glaze TEGO ® Disper 750 W 20 grams Example 4 surface area 1250 m2/g carbon black E90 25 grams (99% purity flake graphite) 5500 Synthetic Graphite 20 grams Duncan pure translucent 850 ml glaze TEGO ® Disper 750 W 20 grams Example 5 surface area 270 m2/g PRINTEX U 15 grams (92% purity flake graphite Graphite AMP 30 grams Duncan pure translucent 600 ml glaze Example 6 surface area 1050 m2/g Raven 7000 25 grams (92% purity flake graphite Graphite AMP 15 grams Duncan pure translucent 800 ml glaze TEGO ® Disper 750 W 30 grams

(49) Table 3 below illustrates Examples of the present invention using a carbon component, a graphite component and a sioxane binder. These mixtures were tested and displayed a TCR of about zero or were substantially stable within the parameters defined. It was also found that the TCR was about zero or remained substantially stable when the composition was unfired or when they had been fired.

(50) TABLE-US-00004 TABLE 3 Carbon, Graphite and Binder Examples Composition mix units Example 1 surface area of 1440 m2/g BP2000 30 grams (99% purity flake graphite 5500 Synthetic Graphite 10 grams 68% solids siloxane TempTech 32800 PPG 200 ml % pigment Solvent, xylene 100 ml 16.7% % pigment to binders 20.00% Example 2 surface area of 1440 m2/g BP2000 25 grams (92% purity flake graphite Graphite AMP 10 grams 68% solids siloxane TempTech 32800 PPG 220 ml % pigment Solvent, xylene 110 ml 13.7% % pigment to binders 15.91% Example 3 surface area 1250 m2/g carbon black E90 25 grams (92% purity flake graphite Graphite AMP 15 grams 68% solids siloxane TempTech 32800 PPG 400 ml % pigment Solvent, xylene 70 ml 7.8% % pigment to binders 10.00% Example 4 surface area 1250 m2/g carbon black E90 25 grams (99% purity flake graphite 5500 Synthetic Graphite 20 grams 68% solids siloxane TempTech 32800 PPG 270 ml % pigment Solvent, xylene 60 ml 12.0% % pigment to binders 16.67% Example 5 surface area m2/g PRINTEX U 15 grams (92% purity flake graphite Graphite AMP 30 grams 68% solids siloxane TempTech 32800 PPG 200 ml % pigment Solvent, xylene 100 ml 13.0% % pigment to binders 22.50% Example 6 surface area 1050 m2/g Raven 7000 25 grams (92% purity flake graphite Graphite AMP 15 grams 68% solids siloxane TempTech 32800 PPG 400 ml % pigment Solvent, xylene 70 ml 7.8% % pigment to binders 10.00%

(51) Testing was conducted on various graphites in an opaque glaze to determine their resistance at various ratios in the glaze. The following graphites were tested: a.) TIMREX® Primary Synthetic Graphite b.) TIMREX® Natural Flake Graphite c.) TIMREX® Coke d.) Lectromet (sourced from ESPI Metals) e.) Electro (sourced from ESPI Metals) f.) Aeromet (sourced from ESPI Metals) g.) ESPI Super Conductive (sourced from ESPI Metals) h.) Thermo pure (sourced from Superior graphite company) i.) Graphite (sourced from Ashbury)

(52) The specific supplier information on these graphites can be seen in the tables below.

(53) TABLE-US-00005 TIMREX ® TIMREX ® Primary Natural Synthetic Flake TIMREX ® Material units Graphite Graphite Coke Thickness Mm 0.1 0.2 0.2 Specific Gravity g/cm.sup.3 1.5 0.9 to 2.0 1.5 to 1.8 Volume Resistivity Ω/CM 3.0 * 10.sup.13 3.0 * 10.sup.13 3.0 * 10.sup.13 Conductivity w/m-k 20 15 5 (vertical direction) Conductivity w/m-k 300 to 500 300 to 500 300 to 500 (horizontal direction)

(54) TABLE-US-00006 GRADE: ESPI Super Lectromet Electro Aeromet Conductive Average Apparent 1.65 1.74 1.80 1.82 Density gm/cm.sup.3 Coefficient Thermal 7.7 (4.3) 8.3 (4.6) 8.5 (4.7) 8.5 (4.7) Expansion 10.sup.−6 ° C. (° F.) Electrical Resistivity 1.9 × 1.6 × 1.5 × 1.8 × 21° C. (70° F.) 10.sup.−5 (750) 10.sup.−5 (630) 10.sup.−5 (580) 10.sup.−5 (690) ohm .Math. m (uohm-in) Porosity (um) 0.6 0.7 0.8 0.8

(55) Various ratios of graphite to glaze were tested to determine the overall resistance. The results can be seen in FIG. 3. From this data it can be seen that the amount of graphite can affect the overall resistance in carrier, and judicious selection of the amount of graphite in conjunction with the carbon can enable formulation of compositions of the invention.

Example 4

(56) Preparation/Method

(57) Three plywood boards were painted with one coat of Sample 4A, 4B or 4C as described in the following table, each applied at the same thickness using t32 mesh over a rectangular area measuring 190 mm×210 mm. Copper electrodes were applied to each side of the rectangular area in the same position for each sample.

(58) Results

(59) The following resistances were measured across the rectangular sample areas for each of Samples 4A, 4B and 4C. The resin used in each case was an HOPE resin:

(60) TABLE-US-00007 Sample 4A 4B 4C Resin RV 15 RV 15 RV 15 HDPE WB HDPE WB HDPE WB Resin mass (g) 80 80 80 Carbon black NG 100% NG 100% NG 100% Liquid Liquid Liquid conductive conductive conductive black black black Carbon black 10 10 10 mass (g) Graphite 3775-99.9% AF99-99% 325A-85.9% crystallinity; crystallinity crystallinity heat treated to 2500-3000° C. Graphite mass (g) 10 10 10 Resistance measured 14.8 142.8 1416.0 across panel (Ω) at 20° C. Resistance measured 14.8 140 1377.0 across panel (Ω) at 40° C. Resistance measured 14.7 135 1330.0 across panel (Ω) at 60° C. TCR* over range −0.00017 −0.0014 −0.0015 20-60° C. (/° C.) *TCR.sub.20-60° C. = [R.sub.60° C./R.sub.20° C. − 1]/(60° C. − 20° C.)

(61) The crystallinity and heat treatment of graphite in Sample 4A contributes to the thermal stability of the coating and is 10× more conductive than that of the AF99 and 100× more conductive than that of the 325A graphites in Samples 4B and 4C. respectively. This is despite the operating temperature of 20-60° C.

(62) Furthermore, the TCR of Sample 4A is an order of magnitude lower (0.1Ω drop across 20-60° C.) than that of Sample 4B (8.0Ω drop across 20-60° C.) and Sample 4C (47Ω drop across 20-60° C.), an effect also attributed to the crystallinity and heat treatment of graphite in Sample 4A. The substantially lower TCR of Sample 4A is beneficial for applications such as underfloor heating as the resistance of the composition hardly changes with variations in operating temperatures of 20-60° C., resulting in electrical stability over extended time periods and the tendency to avoid thermal “run away”. Furthermore, heat output of coatings with TCRs closer to zero are easier to control and show minimal variation in their day-to-day electrical conductivity and heat generation, which is particularly useful in domestic settings where coatings are likely to be repeatedly heated and cooled and/or used over an extended period of time. Even small efficiencies in electrical stability are important as the cost savings are cumulative over time, and especially for heating applications that are run for days, weeks, months, and even years at a time. The coatings of the invention provide such efficiencies and are a significant improvement over the prior art.

(63) While the invention has been described with reference to preferred embodiments, those skilled in the art will understand that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Also, all citations referred herein are expressly incorporated herein by reference. The following examples show how the present invention can be practiced. They should be construed as illustrative of the invention and not a limitation of it.