Heat transfer compositions, apparatuses and processes of preparation

Abstract

A geopolymer composition can include a geopolymer matrix together with a density-reducing material and a thermally conductive material. Advantageously, the density-reducing material can have a bulk density less than the density of geopolymer matrix without the density-reducing material. The composition can include, based on a total weight of the composition, the density-reducing material in an amount of 5 wt% to 50 wt% and / or the thermally conductive material in an amount of 3 wt% to 30 wt%. Such geopolymer compositions can be applied as one or more geopolymer layer on a thermally conductive substrate. The geopolymer compositions and layers can withstand relatively high temperatures and transfer heat relatively rapidly, which can be useful for a variety of apparatuses.

Description

41384.04063HEAT TRANSFER COMPOSITIONS, APPARATUSES AND PROCESSES OF PREPARATIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and all benefit of U.S. Provisional Patent Application No. 63 / 689,709, filed on August 31, 2024, the entire disclosure of which is fully incorporated herein by reference.TECHNICAL FIELD

[0002] The present disclosure relates to geopolymer compositions and apparatuses including such geopolymer compositions.BACKGROUND

[0003] Generally, heat transfer may be broadly classified as active (e.g., heat exchangers) or passive (e.g., heat sinks). Heat (e.g., thermal) transfer is controlled by three pathways including conduction, convection and radiation. Heat transfer is also controlled by specific material properties including but not limited to thermal conductance, heat capacity, thermal inertia, surface area, surface color, and finish.

[0004] Efficient movement of heat from one location to another may be critical to optimum operation of equipment and instruments. Often times the goal of heat transfer is to remove heat from the system and relocate it to an external environment. In certain instances, heat removed from a system may actively be used for a subsequent use, such as for example, in waste heat recovery units or counter flow heat exchangers. In other instances, system efficiency may be derived from creating a new equilibrium. In other words, heat energy at higher temperatures is eliminated from the system at near the same rate it is input.

[0005] In addition, many systems routinely operate for long time periods in oxidative atmospheres, e.g., air, at temperatures at or above 150 - 200 °C, which can degrade certain materials used for heat transfer.

[0006] Accordingly, a need exists for improved heat transfer compositions and apparatuses effectuating rapid movement of heat from a hotter area to a cooler area.41384.04063SUMMARY

[0007] The present disclosure is directed to a geopolymer composition and apparatus including such geopolymer compositions which allow rapid movement of heat from an area having a relatively higher temperature to an area having a relatively lower temperature.

[0008] In one implementation, a geopolymer composition comprises a geopolymer matrix, and a thermally conductive material. Such thermally conductive materials can facilitate thermal transport through the geopolymer composition and can include one or more of a thermally conductive carbon, carbon fiber, carbon nanomaterial, silver, copper, aluminum, thermally conductive ceramic, or a combination thereof. The geopolymer composition further can comprise a density-reducing material in the geopolymer matrix to reduce the density of the geopolymer matrix relative to the geopolymer matrix without the density -educing material. Such density-reducing materials advantageously can improve thermal characteristics of the geopolymer composition. The density-reducing material advantageously can have a bulk density less than the density of the geopolymer matrix without the density-reducing material. In some aspects, the density -reducing material can include a porous aggregate, hollow beads, e.g., hollow glass beads, hollow ceramic beads, or a combination thereof. In some aspects, the density-reducing material can act as the thermally conductive material, e.g., thermally conductive hollow beads can act as both a thermally conductive material and as a densityreducing material. In other aspects, the density-reducing material can comprise a thermally nonconductive inorganic material. Further, geopolymer compositions of the present disclosure can be in the form of a geopolymer layer.

[0009] Advantageously, the geopolymer composition includes the thermally conductive material and / or the density-reducing material dispersed through the geopolymer matrix. Geopolymer compositions and layers of the present disclosure further advantageously can withstand relatively high temperatures and can facilitate heat transfer by the thermally conductive material through an otherwise insulating geopolymer matrix.

[0010] In some aspects, the density-reducing material, e.g., thermally nonconductive inorganic material, can be included in the geopolymer composition from 5 wt% to 50 wt%, based on a total weight of the geopolymer composition. In addition, or other aspects, the thermally conductive material can be included in the geopolymer composition from 3 wt% to 30 wt%, based on a total weight of the geopolymer composition.41384.04063

[0011] Processes of preparing the composition are also described in accordance with one or more implementations.

[0012] In another implementation, the present disclosure is directed to an apparatus having a geopolymer composition thereon. Such an apparatus can include a substrate with a geopolymer layer disposed thereon. The geopolymer layer can comprise a geopolymer matrix having: (i) a thermally nonconductive inorganic material, and (ii) a thermally conductive material. Advantageously, the geopolymer matrix can have the thermally nonconductive inorganic material and the thermally conductive material dispersed through the geopolymer matrix. In some aspects, the thermally nonconductive inorganic material can be included in the geopolymer layer from 5 wt% to 50 wt%, based on a total weight of the geopolymer layer. In addition, or other aspects, the thermally conductive material can be included in the geopolymer layer from 3 wt% to 30 wt%, based on a total weight of the geopolymer layer.

[0013] Processes of preparing the apparatus are also described in accordance with one or more implementations. For example, the geopolymer layer can be applied to a surface of a substrate of the apparatus by spraying, rolling, brushing, spin coating, and / or dip coating a mixture onto the surface. The mixture can comprise geopolymer matrix forming components of: (1) a metal silicate; (2) a metal oxide; (3) a water-soluble caustic agent; and (4) water. The mixture further comprises (5) a density-reducing material that has a bulk density which is less than a density of a geopolymer matrix formed from the geopolymer matrix forming components; and (6) a thermally conductive material. The mixture can be applied on a surface of a substrate and cured to form the geopolymer layer on the surface of the substrate.

[0014] Additional advantages of the present disclosure will become readily apparent to those skilled in this art from the following detailed description, wherein only certain aspects are shown and described, simply by way of illustration of carrying out certain subject matter. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In the drawings, which are not necessarily drawn to scale, like numerals can describe similar components in different views. Like numerals having different letter suffixes can represent41384.04063 different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various aspects discussed in the present document.

[0016] FIG. 1 illustrates an apparatus including a geopolymer layer on a substrate layer in accordance with an aspect of the present disclosure.

[0017] FIG. 2 illustrates a flowchart of a process of preparing a geopolymer composition in accordance with an aspect of the present disclosure.

[0018] The figure(s) depicts various examples only for purposes of illustration. One skilled in the art will readily recognize from the following discussion that alternative examples of the structures and methods illustrated herein can be employed without departing from the principles described herein.DETAILED DESCRIPTION

[0019] The present disclosure may be understood more readily by reference to the following detailed description and examples included therein.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

[0021] The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0022] As used in the specification and in the claims, the term “comprising” can include the embodiments “consisting of’ and “consisting essentially of.” The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open- ended transitional phrases, terms, or words that require the presence of the named ingredients / steps and permit the presence of other ingredients / steps. However, such description should be construed as also describing compositions or processes as “consisting of’ and “consisting essentially of’ the41384.04063 enumerated ingredients / steps, which allows the presence of only the named ingredients / steps, along with any impurities that might result therefrom, and excludes other ingredients / steps.

[0023] As used herein, the terms “about” and “at or about” mean that the amount or value in question can be the value designated some other value approximately or about the same. It is generally understood, as used herein, that it is the nominal value indicated ±10% variation unless otherwise indicated or inferred. The term is intended to convey that similar values promote equivalent results or effects recited in the claims. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but can be approximate and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. In general, an amount, size, formulation, parameter or other quantity or characteristic is “about” or “approximate” whether or not expressly stated to be such. It is understood that where “about” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

[0024] Unless indicated to the contrary, the numerical values should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value.

[0025] All ranges disclosed herein are inclusive of the recited endpoint and independently of the endpoints. The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value; they are sufficiently imprecise to include values approximating these ranges and / or values.

[0026] As used herein, approximating language can be applied to modify any quantitative representation that can vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially,” may not be limited to the precise value specified, in some cases. In at least some instances, the approximating language can correspond to the precision of an instrument for measuring the value. The modifier “about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression “from about 2 to about 4” also discloses the range “from 2 to 4.” The term “about” can refer to plus or minus 10% of the indicated number. For example,41384.04063“about 10%” can indicate a range of 9% to 11%, and “about 1” can mean from 0.9-1.1. Other meanings of “about” can be apparent from the context, such as rounding off, so, for example “about 1” can also mean from 0.5 to 1.4. Further, the term “comprising” should be understood as having its open-ended meaning of “including,” but the term also includes the closed meaning of the term “consisting.” For example, a composition that comprises components A and B can be a composition that includes A, B, and other components, but can also be a composition made of A and B only. Any documents cited herein are incorporated by reference in their entireties for any and all purposes.

[0027] The term “average diameter,” as used herein with respect to the thermally non-conductive hollow beads, refers to an average of the diameters of each bead of the thermally non-conductive hollow beads.

[0028] The term “average length,” as used herein, refers to an average of the lengths of the thermally conductive material.

[0029] The term “average geometrical dimension,” as used herein, refers to an average of the largest dimensions of the thermally conductive material.

[0030] The term “ambient temperature,” as used herein, refers to about 20 °C.

[0031] The term “thermal inertia,” as used herein, refers to the property of a material that expresses the degree of slowness with which its temperature reaches that of the environment. A relatively lower thermal inertia indicates a faster return to equilibrium with the environment. A relatively higher thermal inertia indicates a greater resistance of a material to return to ambient temperature. Thermal inertia is calculated as the square root of the product of volumetric heat capacity and thermal conductivity (i.e., thermal inertia = ^(volumetric heat capacity x thermal conductivity)).

[0032] The term “thermal conductivity,” as used herein, refers to a measure of a material’s ability to conduct heat. The defining equation for thermal conductivity is q = -kAT, where q is the heat flux, k is the thermal conductivity, and AT is the temperature gradient. An alternative is thermal conductivity calculated by multiplying heat capacity by density and by thermal diffusivity (i.e., thermal conductivity = (heat capacity x density) x thermal diffusivity).

[0033] The term “thermal diffusivity,” as used herein, refers to the rate of heat transfer through a medium.41384.04063

[0034] The term “heat capacity,” as used herein, refers to the number of heat units needed to raise the temperature of the material by one degree.

[0035] The term “volumetric heat capacity,” as used herein, refers to the heat capacity of a material divided by the volume of the material.

[0036] The term “density” as used herein, refers to a material’s mass per unit of volume.

[0037] The term “bulk density” or “apparent density” as used herein, refers to the mass of the combination of particles in a material divided by the bulk volume of the material, where the bulk volume is the total volume occupied by the material including any particles included with or contained within or around the bulk material. The bulk volume includes void volume between the particles and any internal volume within any particles within the bulk material that have an internal volume, including for example hollow beads.

[0038] According to an implementation of the present disclosure, geopolymer compositions can include a geopolymer matrix and a thermally conductive material. In addition, the geopolymer composition can include a density-reducing material which has a bulk density less than a density of the geopolymer matrix. That is, the density-reducing material has a bulk density that is less than the density of the geopolymer matrix formed from geopolymer forming components and without the density-reducing material.

[0039] Such geopolymer compositions can be formed as a geopolymer layer such as a geopolymer layer on a thermally conductive substrate, e.g., a metallic substrate. Such geopolymer compositions can exhibit advantageous thermal properties. It is believed such geopolymer compositions and layers behave analogously to a micro-channel heat exchanger which allows heat transfer by convective flow of fluids through micro-channels. In the case of the geopolymer compositions and layers of the present disclosure, heat is transferred very rapidly and efficiently by the thermally conductive material through an otherwise insulating geopolymer matrix. Such heat removal can be more effective when the thermally conductive material extends between adjacent and opposite surfaces of a geopolymer layer.

[0040] Advantageously, the geopolymer compositions and layers of the present disclosure are thermally stable due to the generally inorganic nature of the compositions and layers. In one aspect, the geopolymer compositions and layers of the present disclosure are stable at temperatures exceeding 150° Celsius, such as exceeding 200° Celsius, or 250° Celsius, or 300° Celsius, or 350°41384.04063Celsius, or higher. That is, the geopolymer compositions and layers of the present disclosure do not degrade, e.g., lose weight, when exposed to such temperatures in air for at least 4 hours. Such thermal stability can be determined by ASTM E2550-17, or an equivalent test.

[0041] The amounts of density-reducing material and the thermally conductive material in the geopolymer matrix can be selected to improve heat transfer. For example, in some aspects, the density-reducing material can be included in the geopolymer composition from 5 wt% to 50 wt%, based on a total weight of the geopolymer composition. In addition, or other aspects, the thermally conductive material can be included in the geopolymer composition from 3 wt% to 30 wt%, based on a total weight of the geopolymer layer.Geopolymer Matrix

[0042] In certain aspects, the geopolymer matrix of the geopolymer composition or geopolymer layer can be prepared from an aqueous formulation including geopolymer matrix forming components of: (1) a metal silicate; (2) a metal oxide; (3) a water-soluble caustic agent; and (4) water. Such geopolymer forming components can form a geopolymer matrix, for example, a metallosilicate polymer network with metal atoms linking silicate groups. Further, the aqueous formulation of the present disclosure advantageously can have all of the components that react to form the geopolymer matrix (e.g., metal silicate, metal oxide, water-soluble caustic agent, and other reactive components) dissolved or substantially dissolved in the formulation to allow formation of thin coating layers from such a formulation.

[0043] In other implementations, the aqueous formulation of the present disclosure can include optional components such as: one or more catalysts or activators, e.g., carbonates or bicarbonates, phosphate acids and partial acids, or organic carboxylic acids to modify time of cure and / or reactivity of the formulation components; one or more rheology modifiers; one or more ceramic particles such as ceramic spheres, Zeeospheres, Carborundum (SiC), AI2O3, etc.; one or more fibers such as those composed of cellulose or cellulose derivatives, jute, coir, a polyamide, polyethylene terephthalate, acrylic, modacrylic, polyacrylonitrile, polyvinylalcohol, basalt, glass, quartz, carbon, etc.; one or more surfactants; or any combination thereof. Certain of these components may or may not be soluble in the formulation and may be solid components of the aqueous formulation.

[0044] The amounts of the components used to form the aqueous formulation can be adjusted for ease of application of the formulation to a surface of the cylindrical layer and the desired41384.04063 characteristics of the formed coating. For example, the aqueous formulation for forming a geopolymer layer can have a weight ratio of the metal silicate to metal oxide ranging from about 5: 1 to 1 :5, e.g., from about 4.5: 1, 4: 1, 3.5: 1, 3: 1, 2.5: 1, 2:1, 1.5: 1, 1 : 1 to 1 : 1, 1 : 1.5, 1 :2, 1 :2.5, 1 :3, 1 :3.5, 1 :4, 1 :4.5, and any value thereof or therebetween. The aqueous formulation can have a weight ratio of the metal silicate to metal oxide ranging from about 1 : 1 to about 1 :3 for rapid curing formulations and from about 3 : 1 to about 1.5 : 1 to form very thin coatings. In some implementations the aqueous formulation includes, based on the total weight of the aqueous formulation, 10 wt% to 45 wt% of the metal silicate, 5 wt% to 65 wt% of the metal oxide, and 5 wt% to 30 wt% of the water soluble caustic agent. In addition, the aqueous formulation can include, based on the total weight of the aqueous formulation, 25 wt% to 80 wt% of the water. For example, when used for dip-coating, the geopolymer layer can be formed from, on a weight basis, 10 wt% to 30 wt% of the metal silicate, 30 wt% to 40 wt% of the metal oxide, 5 wt% to 10 wt% of the water soluble caustic agent, and 20 wt% to 50 wt% of the water, based on the total weight of the formulation. When applied with an atomized spray application, the aqueous formulation can be prepared from, on a weight basis, 15 wt% to 35 wt% of the metal silicate, 5 wt% to 30 wt% of the metal oxide, 10 wt% to 25 wt% of the water soluble caustic agent, and 35 wt% to 70 wt% of the water, based on a total weight of the formulation. Although, the metal silicate and the metal oxide components are listed separately in the present disclosure, these components can be included in the aqueous formulation from a source that has both of these components together, such a kaolin, etc. and forming the aqueous formulation is not limited to using the metal silicate and the metal oxide as separate components.

[0045] Useful metal silicates that can be used to form the aqueous formulations of the present disclosure include one or more of: an alkali metal silicate, an alkaline earth metal silicate, sodium silicate, lithium silicate, potassium silicate, neosilicates, sorosilicates, cyclosilicates, inosilicates, phyllosilicates, tectosilcates, mullite, kaolinite, muscovite, etc. or one or more combinations thereof. The alkali metal silicate can include a sodium silicate, e.g., sodium metasilicate, Na2.vSi.O2. A or (Na2O)v (Si O2)., such as sodium metasilicate (Na2SiOs), sodium orthosilicate (Na4SiO4), sodium pyrosilicate (Na6Si2O?), etc. These sodium silicate compounds are generally colorless transparent solids or white powders, and soluble in water in various concentrations. In some aspects of the present disclosure, the formulations comprise sodium metasilicate as the majority of the metal silicate, e.g., the metal silicate comprises at least 50 wt% sodium metasilicate such as at least 60 wt% of sodium metasilicate. The alkaline earth metal silicate can include a calcium silicate (Ca2SiO4), 2CaO SiCh, larnite (3CaO SiCh), alite (2CaO 2SiO2), 2CaO 2SiO2, wollastonite (CaSiCh), a magnesium silicate, etc.41384.04063

[0046] Metal oxides that can be used to form the aqueous formulations of the present disclosure include one or more of: aluminum trihydrate (ATH), zinc oxide (ZnO), iron oxide, titanium dioxide (TiCh), copper oxide, tin oxide, zirconium oxide, manganese oxide, nickel oxide, silver oxide, vanadium oxide, bismuth oxide or one or more combinations thereof. Further, it is understood that metal oxides in aqueous solutions can convert to their equivalent hydroxide, and thus the use of metal hydroxide is equivalent to use of the metal oxide (e.g., ZnO is equivalent to Zn(OH)2). Hence, a metal oxide in the present disclosure is understood to include or be substituted for its metal hydroxide. In some aspects of the present disclosure, the aqueous formulations are formed from aluminum trihydrate as the metal oxide in percent of the metal oxide of at least 20 wt % of the total metal oxide, e.g., 20 wt% to 100 wt%; 10 wt% to 50 wt%; or 75 wt% to 100 wt% of the total metal oxide. In some aspects of the present disclosure, the formulations are formed from zinc oxide as the metal oxide in percent of the metal oxide of at least 20 wt % of the total metal oxide, e.g., 20 wt% to 100 wt%; 10 wt% to 50 wt%; or 75 wt% to 100 wt% of the total metal oxide.

[0047] The water-soluble caustic agent of the aqueous formulation is designed to facilitate dissolution of the alkali metal silicate and metal oxide in water and any other component that can react with the alkali metal silicate and metal oxide in water. Examples of water-soluble caustic agents useful for the present disclosure include, without limitation one or more of: an alkali metal hydroxide (such as NaOH, KOH), alkali metal carbonates (such as Na2COs, K2CO3), alkali metal phosphates (such as NasPO4, K3PO4), Na2O(SiO2), ammonium hydroxide, or one or more combinations thereof. Sufficient amount of water-soluble caustic agent is combined with the alkali metal silicate and metal oxide to form an aqueous formulation with the desired level of solids and will increase the pH of the formulation to generate a pH of no less than 8, such as a pH no less than 8.5, 9, 9.5, 10, 10.5, 11, 12, 12.5, 13, 13.5, 14, etc. Increasing the pH tends to increase the amount of alkali metal silicate and metal oxide dissolved in the formulation.

[0048] In some aspects, the aqueous formulations of the present disclosure has at least 95 wt% of the alkali silicate content as silicate ions in solution. This state can be determined, for example, when the solution can be passed through a 0.5 pm filter with no remaining visible particulate residue.

[0049] To facilitate spray application of the aqueous formulations of the present disclosure, the aqueous formulation can have a viscosity ranging from about 25 cP to about 1,000 cP as determined by cup and bob viscosity measurement at a temperature of 85 °F (29.4 °C), e.g., a viscosity ranging from about 20 cP to about 200 cP for very thin, uniform coating layers and about 140 cP to about41384.04063700 cP for thicker, rougher coating layers. Viscosity of the system measured by rotational viscometry (cup and bob viscosity measurement) is performed as per ASTM D2196, D2556, D7867.

[0050] The aqueous formulations of the present disclosure can be prepared by combining geopolymer matrix forming components of a metal silicate, a metal oxide, a water-soluble caustic agent, and water to form the formulation. The metal silicate and the metal oxide can be from the same source material or separate source materials or a combination thereof. The aqueous formulations can further include combining other components that can react with the metal silicate and the metal oxide in the formulation to form the geopolymer matrix.

[0051] In addition to the geopolymer matrix forming components, the aqueous formulation can further comprise, as a mixture, (i) a density-reducing material that has a bulk density which is less than a density of a geopolymer matrix formed from the geopolymer matrix forming components; and / or (ii) a thermally conductive material.Second Material

[0052] The geopolymer compositions and layers of the present disclosure further can include a density-reducing material. Such a density-reducing material should have a bulk density that is less than a density of the geopolymer matrix without the density-reducing material. This can be determined by determining the bulk density of the density-reducing material and comparing that bulk density to the density of the geopolymer matrix form from geopolymer matrix forming materials and without the density-reducing material.

[0053] For example, the density-reducing material can comprise a porous aggregate and / or hollow beads, which can be dispersed in the geopolymer matrix. The porous aggregate can include natural or artificial bulk stone material of porous structure with a density of not more than 1,200 kg / m3(1.2 g / cm3). There are many materials of this type available with a bulk density ranging from about 50 kg / m3to 1000 kg / m3(about 0.05 g / cm3- 1 g / cm3), including vermiculite, perlite, diatomaceous earth, and expanded clay aggregate. The hollow beads can include hollow glass beads, hollow ceramic beads, or one or more combinations thereof. The hollow beads can include thermally non- conductive hollow beads. The hollow beads can include thermally non-conductive hollow beads, which act as thermally non-conductive density-reducing material. The hollow beads can also be a thermally conductive material, e.g., thermally conductive hollow beads that can act as a thermally conductive material and as a density -reducing material.41384.04063

[0054] The density-reducing material, e.g., thermally non-conductive inorganic material, can be present in a range of about 5 wt% to 50 wt% of the geopolymer composition or geopolymer layer. In some aspects, the density-reducing material is dispersed through the geopolymer matrix.

[0055] Porous aggregate and / or hollow spheres advantageously can provide certain structure (e.g., compression strength) and reduced weight to the geopolymer compositions and layers of the present disclosure. In an aspect, the hollow beads can be spherical. Useful hollow beads are thermally non- conductive and can include hollow glass beads, hollow ceramic beads, or one or more combinations thereof. As the average diameter of the thermally non-conductive hollow beads increases (e.g., from 5 microns to 500 microns), the beads generally become lighter, thereby providing lower density and relatively lower thermal inertia to the geopolymer compositions and layers of the present disclosure. The thermally non-conductive hollow beads can exhibit insulative characteristics, such as ceramic or glass, such that heat will not move through the beads. The non-conductive hollow beads help to channel heat through the thermally conductive material in the geopolymer compositions and layers of the present disclosure.

[0056] In an aspect, where the thermally non-conductive hollow beads are hollow glass beads, the hollow glass beads can comprise at least 75 wt% glass, at least 80 wt%, at least 85 wt%, at least 90 wt%, at least 95 wt%, or at least 99 wt% glass based on the total weight of the hollow glass beads. In embodiments, the hollow glass beads can consist of glass. In embodiments, where the thermally non-conductive hollow beads are hollow ceramic beads, the hollow ceramic beads can comprise at least 75 wt%, at least 80 wt%, at least 85 wt%, at least 90 wt%, at least 95 wt%, or at least 99 wt% ceramic based on the total weight of the hollow ceramic beads. In embodiments, the hollow ceramic beads can consist of ceramic.

[0057] In another aspect, the thermally non-conductive hollow beads can be electrically non- conductive. In these or other aspects, the thermally non-conductive hollow beads can lack a coating or other components that would impart or increase the electrical conductivity of the thermally non- conductive hollow beads.

[0058] In yet another aspect, the thermally non-conductive hollow beads can have a minimum average diameter (e.g., greater than or equal to 5 microns) to ensure a desired density is achieved. For example, the thermally non-conductive hollow beads can comprise an average diameter from 5 microns to 1000 microns. In embodiments, the thermally non-conductive hollow beads can comprise an average diameter greater than or equal to 5 microns, greater than or equal to 10 microns, or even41384.04063 greater than or equal to 25 microns. In embodiments, the thermally non-conductive hollow beads can comprise an average diameter less than or equal to 1000 microns, less than or equal to 750 microns, less than or equal to 500 microns, less than or equal to 400 microns, less than or equal to 300 microns, less than or equal to 200 microns, less than or equal to 100 microns, or even less than or equal to 50 microns. In embodiments, the thermally non-conductive hollow beads can comprise an average diameter from 5 microns to 1000 microns, from 5 microns to 750 microns, from 5 microns to 500 microns, from 5 microns to 400 microns, from 5 microns to 300 microns, from 5 microns to 200 microns, from 5 microns to 100 microns, from 5 microns to 50 microns, from 10 microns to 1000 microns, from 10 microns to 750 microns, from 10 microns to 500 microns, from 10 microns to 400 microns, from 10 microns to 300 microns, from 10 microns to 200 microns, from 10 microns to 100 microns, from 10 microns to 50 microns, from 25 microns to 1000 microns, from 25 microns to 750 microns, from 25 microns to 500 microns, from 25 microns to 400 microns, from 25 microns to 300 microns, from 25 microns to 200 microns, from 25 microns to 100 microns, or even from 25 microns to 50 microns, or any and all subranges formed from any of these endpoints. In embodiments, the thermally non-conductive hollow beads can comprise a graded aggregate as to average diameter to optimize the filling ratio.

[0059] Certain thermally non-conductive hollow beads that can be used in the present disclosure are commercially available such as from Zeeospheres Ceramics, LLC, such as ceramic microspheres grades N-200, N-600, and N-800; or under the brand name EXTENDOSPHERES® from Sphere One Inc.; or under the brand name E-SPHERES® from Envirospheres Pty Ltd.Thermally Conductive Material

[0060] The geopolymer compositions and layers of the present disclosure include a thermally conductive material. As an example, the thermally conductive material can be present in a range of about 3 wt% to 30 wt%, based on a total weight of the geopolymer composition or geopolymer layer. In some aspects, the thermally conductive material is dispersed through the geopolymer matrix.

[0061] Advantageously, the thermally conductive material can act as a conduit to transfer heat out of geopolymer compositions and layers of the present disclosure and, when present with densityreducing material, e.g., thermally non-conductive hollow beads, the thermally conductive material can channel heat through and around the thermally non-conductive material and ultimately out of geopolymer compositions and layers of the present disclosure. In so doing, the geopolymer compositions and layers can exhibit low thermal inertia.41384.04063

[0062] The thermally conductive material can include a thermally conductive carbon, carbon fiber, carbon nanomaterial, silver, copper, aluminum, a thermally conductive ceramic blend, or one or more combinations thereof. The thermally conductive material can include milled carbon fiber, graphene, carbon black, diamond dust, or a combination thereof. Thermally conductive ceramic blends can include any one or more of boron nitride, beryllium oxide, aluminum beryllium oxide, silicon carbide, copper aluminum oxide, or aluminum nitride.

[0063] The thermally conductive material can have a regular shape, an irregular shape, or a combination thereof. The shapes can include plates, particles, acicular, fibrous, filamentous, tubular, or a combination thereof. The shapes can be of micron size, nano size, or a combination thereof.

[0064] The thermally conductive material can have an average length from 5 microns to 500 microns. In embodiments, the thermally conductive material can comprise an average length greater than 10 microns, greater than or equal to 25 microns, greater than or equal to 50 microns, greater than or equal to 75 microns, or even greater than or equal to 100 microns. In embodiments, the thermally conductive material can comprise an average length less than or equal to 500 microns, less than or equal to 400 microns, less than or equal to 300 microns, or even less than or equal to 200 microns. In embodiments, the thermally conductive material can comprise an average length from 10 microns to 500 microns, from 10 microns to 400 microns, from 10 microns to 300 microns, from 10 microns to 200 microns, from 25 microns to 500 microns, from 25 microns to 400 microns, from 25 microns to 300 microns, from 25 microns to 200 microns, from 50 microns to 500 microns, from 50 microns to 400 microns, from 50 microns to 300 microns, from 50 microns to 200 microns, from 75 microns to 500 microns, from 75 microns to 400 microns, from 75 microns to 300 microns, from 75 microns to 200 microns, from 100 microns to 500 microns, from 100 microns to 400 microns, from 100 microns to 300 microns, or even from 100 microns to 200 microns, or any and all subranges formed from any of these endpoints.

[0065] In embodiments, the thermally conductive material can comprise an average geometrical dimension from 1 nm to 800 nm. In embodiments, the thermally conductive material can comprise an average geometrical dimension greater than or equal to 1 nm, greater than or equal to 10 nm, or even greater than or equal to 20 nm. In embodiments, the thermally conductive material can comprise an average geometrical dimension less than or equal to 800 nm, less than or equal to 500 nm, or even less than or equal to 400 nm. In embodiments, the thermally conductive material can comprise an average geometrical dimension from 1 nm to 800 nm, from 1 nm to 500 nm, from 1 nm to 400 nm, from 10 nm to 800 nm, from 10 nm to 500 nm, from 10 nm to 400 nm, from 20 nm to41384.04063800 nm, from 20 nm to 500 nm, or even from 20 nm to 400 nm, or any and all subranges formed from any of these endpoints.

[0066] In another implementation of the present disclosure, an apparatus can be formed by applying a mixture onto a substrate of the apparatus to form a geopolymer layer. One or more methods of applying the mixture can be employed. For example, the mixture can be applied by spraying, rolling, brushing, spin coating, and / or dip coating the mixture to form the geopolymer layer onto a surface of the substrate. The mixture can include an aqueous formulation including geopolymer matrix forming components together with (i) a density -reducing material that has a bulk density which is less than a density of a geopolymer matrix formed from the geopolymer matrix forming components; and (ii) a thermally conductive material.

[0067] In some aspects, the apparatus can be formed into a variety of useful shapes. For example, the apparatus can be in the shape of plates, rods, tubes (pipes) by well-known fabrication processes, or used to form an active geopolymer layer that rapidly releases heat from underlying thermally conductive structures, e.g., metallic structures, with these shapes. The ease of producing a variety of shapes, or metallic parts with these shapes, including a geopolymer layer according to the present disclosure that rapidly releases stored heat, can provide (sub)components that are easily assembled into larger or more complex systems producing lower cost more efficient heat exchangers and heat sinks, for example.Geopolymer Composition and Apparatus

[0068] FIG. 1 illustrates an exemplary apparatus according to an aspect of the present disclosure. The apparatus 100 comprises geopolymer layer 104 located on a substrate 102. The apparatus 100 can comprise an article of manufacture such as an engine, semiconductor chip, such as a microprocessor chip, electronic device, electric motor, heat sink system, radiator, etc. The apparatus can be employed in many systems, such as for example, heating-ventilation-air conditioning (HVAC) systems, industrial processes, refrigeration and cooling systems, the systems for the food and beverage industry, renewable energy systems, automobiles, waste heat recovery systems, power plants, chemical processing and marine applications, for example.Substrate Layer

[0069] Referring again to FIG. 1, the apparatus 100 can include a substrate layer 102. In aspects, the substrate layer 102 can comprise a thermally conductive material. For example, substrate layer41384.04063102 can comprise a metal. Additionally, substrate layer 102 can comprise steel, aluminum, copper, brass, bronze, titanium, nickel, glass, ceramic, or a combination thereof.

[0070] In certain aspects, the substrate layer 102 can have a thickness appropriate for the substrate in the apparatus. For example, substrate layer 102 can have a thickness from 0.25 mm to 15 mm, from 1 mm to 10 mm, from 5 mm to 15 mm, or even from 5 mm to 10 mm, or any and all subranges formed from any of these endpoints.Geopolymer Layer

[0071] In some aspects, geopolymer layer 104 can be directly on the surface of the substrate without a separate adhesion layer between the geopolymer layer 104 and substrate 102. For this example, the geopolymer layer includes a geopolymer matrix having dispersed therein: (i) a densityreducing material with a bulk density less than a density of the geopolymer matrix; and (ii) a thermally conductive material. The density-reducing material can comprise a thermally nonconductive inorganic material such as a porous aggregate and / or hollow beads, for example, and the thermally conductive material can include a thermally conductive carbon, carbon fiber, carbon nanomaterial, silver, copper, aluminum, or one or more combinations thereof, for example.

[0072] Advantageously, geopolymer layer 104 can exhibit relatively low thermal inertia (e.g., less than or equal to about 2,500 J / m2K s1 / 2, or from about 420 J / m2K s1 / 2to about 2,500 J / m2K s1 / 2). Such a low thermal inertia can facilitate the geopolymer layer returning to a low temperature, e.g., ambient temperature after being exposed to a higher temperature at a desired cooling rate. In some embodiments, the relatively low thermal inertia of the geopolymer layer 104 can reduce the maximum temperature of the apparatus.

[0073] Thermal conductivity of a material may be used to understand the heat transferability of a material. The greater the thermal conductivity, the greater the degree of accepting heat from the environment. However, as mentioned hereinabove, thermal conductivity is calculated by multiplying heat capacity by density and by thermal diffusivity. Thus, focusing on thermal conductivity may provide an advantage to high density and high heat capacity material and may not appreciate the potential effectiveness of lightweight materials on improved thermal characteristics. Thermal conductivity does not take into account the ability of a material to release heat from a volume. Accordingly, when considering materials for use in heat-exchange or heat-release applications, thermal conductivity may not give the user an advantage over alternative materials. As such, thermal41384.04063 inertia may be more prudent to evaluate for these applications. In certain, geopolymer layer 104 can have a thermal inertia from 420 J / m2K s1 / 2to 2,500 J / m2K s1 / 2.

[0074] In addition to low thermal inertia, the geopolymer layer 104 can have a relatively low heat capacity (e.g., less than or equal to 1.75 J / gK) such that the apparatus 100 exhibits an overall reduced heat capacity.

[0075] In some implementations, the geopolymer layer 104 can have a geopolymer matrix with a density from about 1.8 g / cm3to about 2.9 g / cm3. The density of the geopolymer matrix will depend on the composition of the components used to form the matrix. In addition, the density of the geopolymer composition or layer (as opposed to the geopolymer matrix) will depend on the composition of geopolymer matrix forming components and any added density -reducing material. In some implementations, the density of the geopolymer composition or layer can be inversely proportional to the amount of density-reducing material, e.g., porous aggregate and / or hollow beads, added to form the geopolymer composition or layer. In some implementations, the density of the geopolymer layer 104 is less than 1.8 g / cm3, such as less than 1.6 g / cm3, 1.4 g / cm3, 1.2 g / cm3, etc.

[0076] The geopolymer layer 104 can include a volumetric heat capacity in the range of from about 1.2 J / K-cm3to about 2.0 J / K cm3.

[0077] In embodiments, the polymeric layer 104 can have a thickness greater than or equal to 0.1 mm, greater than or equal to 0.5 mm, greater than or equal to 1 mm, greater than or equal to 3 mm, or even greater than or equal to 5 mm. In embodiments, the polymeric layer 104 can have a thickness less than or equal to 15 mm, less than or equal to 13 mm, or even less than or equal to 10 mm. In embodiments, the polymeric layer 104 can comprise a thickness from 0.1 mm to 15 mm, from 0.1 mm to 13 mm, from 0.1 mm to 10 mm, from 0.5 mm to 15 mm, from 0.5 mm to 13 mm, from 0.5 mm to 10 mm, from 1 mm to 15 mm, from 1 mm to 13 mm, from 1 mm to 10 mm, from 3 mm to 15 mm, from 3 mm to 13 mm, from 3 mm to 10 mm, from 5 mm to 15 mm, from 5 mm to 13 mm, or even from 5 mm to 10 mm, or any and all subranges formed from any of these endpoints.

[0078] In aspects, the apparatus can include more than one geopolymer layer 104. The multilayered structure can include, for example, one or more thick geopolymer layers (e.g., from greater than 1 mm to 15 mm), and / or one or more thin geopolymer layers (e.g., from 0.1 mm to 1 mm), or a combination thereof.41384.04063

[0079] In one aspect, geopolymer layer includes thermally non-conductive hollow beads as a density-reducing material. Because such beads are hollow, they allow for the geopolymer layer 104 to be lightweight, thereby providing lower density and relatively lower thermal inertia to the geopolymer layer 104. The thermally non-conductive hollow beads, such as ceramic or glass hollow beads, can exhibit insulative characteristics that resist heat flow through the beads. Such non- conductive hollow beads help to channel heat through the thermally conductive material.

[0080] According to even another aspect of the present disclosure, the geopolymer layer 104 can be formed directly on a surface of substrate 102 by applying, e.g., spraying, rolling, brushing, spin coating, and / or dip coating, a mixture thereon. The mixture can comprise a metal silicate, a metal oxide, a water soluble caustic agent, water, a density-reducing material (a thermally nonconductive inorganic material), and a thermally conductive material. Such a mixture can further include optional components such as one or more catalysts and / or activators.Process of Preparing the Geopolymer Composition and Apparatus

[0081] According to a further implementation of the present disclosure, processes are described for preparing the above-mentioned geopolymer compositions and apparatuses.

[0082] In an aspect, FIG. 2 depicts a flowchart of an example process 200. In some implementations, one or more process blocks of FIG. 2 can be performed by a device. Process 200 can include a step 202 of curing a mixture having an aqueous formulation including geopolymer matrix forming components together with (i) a density-reducing material that has a bulk density which is less than a density of a geopolymer matrix formed from the geopolymer matrix forming components; and (ii) a thermally conductive material. The aqueous formulation that comprises geopolymer matrix forming components include a metal silicate, a metal oxide, a water-soluble caustic agent, and water.

[0083] In some aspects, a further step 204 can include forming the geopolymer layer on a surface of a substrate by applying the mixture on a surface of a substrate prior to or after curing the mixture. The mixture can be applied in variety of ways including spraying, brushing, rolling, dip coating, electrodeposition, etc. In one aspect, the mixture is applied to the surface of the substrate by spraying the mixture onto the substrate as an aerosol, e.g., a suspension of fine liquid droplets in air or another gas. Aerosol sprays can be generated from aerosol spray dispensers, atomizers, etc. Further still, in some aspects, the thermally conductive geopolymer matrix can be applied to a carrier such as a41384.04063 paper, woven textile, or nonwoven fabric and then cured partially or completely prior to being applied and bonded to the surface of the substrate. If residual curing is required it can be done after being bonded to the substrate. Further, more than one geopolymer layer can be applied to the substrate with each layer having the same or different thicknesses and each layer having the same or different compositions.

[0084] Concurrent with or after applying one or more mixtures to the substrate, the mixture dries or is dried. Drying the mixture causes it to cure and bond to the surface of the substrate. Upon drying, the geopolymer forming components form long-range, covalently bonded, non-crystalline (amorphous) networks such as a geopolymeric matrix.

[0085] Drying, i.e., curing, can be carried out conveniently in air at ambient conditions. For example, the aqueous formulation can be dried in air from a temperature range of about 5 °C to about 50 °C. Drying can also be carried out by heating at a temperature of from about 50 °C to about 500 °C in air or another gas, such as heating from 50 °C to about 500 °C, 50 °C to about 200 °C, 50 °C to about 150 °C. Exposing an applied mixture of the present disclosure to heat can increase the hardness of the formed geopolymer layer.

[0086] In some aspects, more than one geopolymer layer can be formed on the substrate. Each layer can independently have a thickness in the range of from about 0.25 mm to about 10 mm.

[0087] Only certain features and aspects of the present disclosure and examples of their versatility are shown and described in the present disclosure. It is to be understood that the technology disclosed herein is capable of use in various other combinations and environments and is capable of changes or modifications. Thus, for example, those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific substances, procedures and arrangements described herein. Such equivalents are considered to be within the scope of the invention and are covered by the following claims.

Claims

1. 41384.04063WHAT IS CLAIMED IS:

1. A geopolymer composition comprising: a geopolymer matrix;5 wt% to 50 wt% of a density-reducing material that has a bulk density less than the density of the geopolymer matrix without the density-reducing material; and3 wt% to 30 wt% of a thermally conductive material.

2. The geopolymer composition of claim 1, wherein the density-reducing material comprises any one or more of glass beads, or ceramic beads.

3. The geopolymer composition of claim 1, wherein the density-reducing material is in the form of hollow spheres.

4. The geopolymer composition of claim 1, wherein the density-reducing material comprises a porous aggregate.

5. The geopolymer composition of claim 1, wherein the thermally conductive material is about 5 to 500 microns in diameter.

6. The geopolymer composition of claim 1, wherein the thermally conductive material comprises any one or more of a thermally conductive carbon, carbon fiber, carbon nanomaterial, silver, copper, aluminum, thermally conductive ceramic, or a ceramic blend.

7. The geopolymer composition of claim 6, wherein the carbon fiber includes milled carbon fiber.

8. The geopolymer composition of claim 1, wherein the thermally conductive material comprises any one or more of graphene, carbon black, or diamond dust.

9. The geopolymer composition of claim 1, wherein the thermally conductive material comprises a ceramic blend of any one or more of boron nitride, aluminum beryllium oxide, silicon carbide, copper aluminum oxide, or aluminum nitride.

10. The geopolymer composition of any one of claims 1-9, wherein the geopolymer matrix comprises a metallosilicate polymer network.41384.0406311. The geopolymer composition of any one of the preceding claims, wherein the densityreducing material comprises hollow glass beads, hollow ceramic beads, or a combination thereof.

12. The geopolymer composition of any one of the preceding claims, wherein the geopolymer matrix is formed from an aqueous formulation that comprises geopolymer matrix forming components of: (1) a metal silicate; (2) a metal oxide; (3) a water-soluble caustic agent; and (4) water.

13. The geopolymer composition of claim 12, wherein the aqueous formulation further includes the density-reducing material that has a bulk density which is less than a density of a geopolymer matrix formed from the geopolymer matrix forming components; and the thermally conductive material.

14. The geopolymer composition of claim 12, wherein a ratio of metal silicate to metal oxide ranges from about 5: 1 to about 1 :5.

15. The geopolymer composition of claim 12, wherein the metal silicate comprises at least 50 wt% sodium metasilicate.

16. The geopolymer composition of claim 12, wherein the aqueous formulation comprises, based on a total weight of the aqueous formulation, 10 wt% to 45 wt% of the metal silicate; 5 wt% to 65 wt% of the metal oxide; and 5 wt% to 25 wt% of the water soluble caustic agent.

17. The geopolymer composition of claim 12, wherein the aqueous formulation comprises, based on the total weight of the aqueous formulation, 25 wt% to 80 wt% of the water.

18. The geopolymer composition of claim 12, wherein the aqueous formulation has a pH of no less than 9.

19. The geopolymer composition of claim 12, wherein the metal silicate comprises any one or more of an alkali metal silicate, or alkaline earth silicate.

20. The geopolymer composition of claim 12, wherein the metal silicate comprises any one or more of alkaline earth silicate, sodium silicate, lithium silicate, or potassium silicate.41384.0406321. The geopolymer composition of claim 12, wherein the metal silicate comprises any one or more of neosilicates, sorosilicates, cyclosilicates, inosilicates, phyllosilicates, tectosilcates, Mullite, Kaolinite, or Muscovite.

22. The geopolymer composition of claim 12, wherein the metal oxide comprises one or more of: aluminum trihydrate (ATH), zinc oxide (ZnO), iron oxide, titanium dioxide (TiCh), copper oxide, tin oxide, zirconium oxide, manganese oxide, nickel oxide, silver oxide, vanadium oxide, bismuth oxide, or any combination thereof.

22. The geopolymer composition of claim 12, wherein the water-soluble caustic agent comprises one or more of: an alkali metal hydroxide, Na2O(SiO2), Li2O(SiO2), K2O(SiCh), or ammonium hydroxide.

23. The geopolymer composition of claim 12, wherein the metal silicate comprises one or more of an alkali metal or alkaline earth silicate; the metal oxide comprises one or more of aluminum trihydrate (ATH), zinc oxide (ZnO), iron oxide, titanium dioxide (TiO2), copper oxide, zirconium oxide, manganese oxide, nickel oxide, silver oxide, vanadium oxide, bismuth oxide; and the water-soluble caustic agent comprises one or more of: NaOH, KOH, or Na2O(SiO2),Li2O(SiO2), K2O(SiO2), or ammonium hydroxide.

24. The geopolymer composition of claim 12, wherein the aqueous formulation further comprises any one or more catalysts, activators, or rheology modifiers.

25. The geopolymer composition of any one of the preceding claims, wherein the composition is formed as any one or more of a plate, rod, or tube.

26. A process of preparing the geopolymer composition as in any one of the preceding claims comprising: curing a mixture comprising: (1) a metal silicate; (2) a metal oxide; (3) a water soluble caustic agent; (4) water; (5) the density-reducing material; and (6) the thermally conductive material to form the geopolymer composition.

27. The process of claim 26, wherein curing occurs at a temperature from about 5 °C to about 500 °C.

28. An apparatus comprising: a substrate; and41384.04063 a geopolymer layer disposed on a surface of the substrate, wherein the geopolymer layer comprises a geopolymer matrix having dispersed therein (i) 5 wt% to 50 wt%, based on a total weight of the geopolymer layer, of a thermally nonconductive inorganic material, and (ii) a thermally conductive material.

29. The apparatus of claim 28, wherein the thermally conductive material extends between adjacent or opposite surfaces of the geopolymer layer.

30. The apparatus of claim 28, wherein the thermally conductive material is present in amount of 3 wt% to 30 wt% of the geopolymer layer.

31. The apparatus of claim 28, wherein the surface of the substrate is thermally conductive.

32. The apparatus of claim 28, wherein the surface of the substrate is metal.

33. The apparatus of claim 28, wherein the substrate comprises any one or more of steel, aluminum, copper, brass, bronze, titanium, nickel, semiconductor, or ceramic.

34. The apparatus of claim 28, wherein the geopolymer layer is stable at temperatures exceeding 150° Celsius.

35. The apparatus of any one of claims 28-34, wherein the apparatus is a heat exchanger.

37. A process of making the apparatus of any one of claims 28-34 comprising: disposing the geopolymer layer on the surface of the substrate.

38. The process of claim 36, wherein disposing the geopolymer layer on the surface of the substrate comprises: spraying, rolling, brushing, spin coating, and / or dipping a mixture comprising: (1) a metal silicate, (2) a metal oxide, (3) a water soluble caustic agent, (4) water, (5) the thermally nonconductive inorganic material, and (6) the thermally conductive material; and curing the mixture.

37. The process of claim 36, wherein more than one layer of the geopolymer layer is disposed on the surface of the substrate.

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