Microencapsulation of materials using cenospheres
1. A composition, comprising:
- a perforated cenosphere and a core material, wherein the core material is encapsulated inside the perforated cenosphere, wherein the core material comprises a phase change material, wherein the phase change material is 20% or more by weight of the composition, and wherein the phase change material is paraffin wax.
Disclosed are methods for incorporating core materials such as phase change materials or admixtures into building materials like concrete. The methods use cenospheres, which are then etched and loaded with the core material. The composition can also be coated with a thin film. Compositions containing cenospheres loaded with the various core materials are disclosed, as are building materials containing such compositions.
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- 1. A composition, comprising:
- a perforated cenosphere and a core material, wherein the core material is encapsulated inside the perforated cenosphere, wherein the core material comprises a phase change material, wherein the phase change material is 20% or more by weight of the composition, and wherein the phase change material is paraffin wax.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
- 11. A method of encapsulating a core material inside a perforated cenosphere, comprising:
contacting a cenosphere with an acid solution, thereby providing the perforated cenosphere; and contacting the perforated cenosphere with the core material, thereby encapsulating the core material in the perforated cenosphere and forming a composition comprising the core material encapsulated inside the perforated cenosphere; wherein the core material comprises a phase change material; wherein the phase change material is 20% or more by weight of the composition, and wherein the phase change material is paraffin wax.
- View Dependent Claims (12, 13, 14, 15, 16, 17)
This application claims the benefit of priority to U.S. Provisional Application No. 62/198,997, filed Jul. 30, 2015, which is hereby incorporated herein by reference in its entirety.
This invention was made with government support under Grant No. 23006 awarded by the National Science Foundation. The government has certain rights in the invention.
The buildings sector of the United States accounts for approximately 40% of the U.S. primary energy consumption and 39% of the U.S. carbon dioxide emissions. To cope with this challenging situation, efforts are needed to improve energy efficiency of U.S. buildings, which will not only save money for both homeowners and business owners, but also reduce the environmental impacts of energy use.
One approach to address these issues has been to incorporate phase change materials (PCMs) into construction materials to enhance the building'"'"'s energy efficiency through Thermal Energy Storage (TES) and thermal regulation. PCMs change their phase from solid to liquid and vice versa at their phase change temperatures with large amount of energy absorbed or released. Thermal inertia (mass) of the building can be significantly increased by integrating PCMs into construction materials. PCMs have been considered as a promising method of TES in terms of narrowing the gap between the peak and off-peak loads of energy/electricity demand, reducing diurnal temperature fluctuations, and utilizing the free cooling at night for day peak cooling load shaving.
Two primary methods have been used to incorporate PCMs into construction materials: (1) microencapsulation of PCMs and (2) form-stable PCMs composites. In the first method, PCMs are encapsulated within a protective polymer shell. The produced microencapsulated PCMs can preserve PCMs as long as possible through the heating/cooling cycles. This microencapsulation method increases the heat transfer area, decreases the reactivity of the PCMs, limits the interaction with the construction materials, enhances the low heat conductivity, and facilitates the handling of the PCMs. However, it also suffers a few drawbacks preventing practical applications of the PCMs in construction materials. For example, the protection shell is made of polymers that usually have low mechanical stiffness and strength. As a result, the mechanical stiffness and strength of the construction materials can be reduced significantly by adding the microcapsules. The microcapsules can also been easily broken during the mixing of concrete, leading to leaking of the PCMs. The polymeric shell also has low chemical and thermal stability. It can be deteriorated by UV light, oxidation, and other aggressive chemicals. It can also lose its stability when temperature exceeds its glass transition temperature. The polymer shells can also be flammable, and therefore cannot be adopted by the building industry. Further, the thermal conductivity of the polymer shells is often very low, making thermal exchange between the PCMs inside the shell and the outside environment much more difficult.
In the second method, PCMs are first absorbed into porous materials such as light weight aggregates and diatomite particles to form stable composites, which are then added into the construction materials. When using porous particles to absorb PCM there are no protective layers on the surface of the composites. As a result, PCMs can still leak from the porous material once the temperature exceeds the phase change materials, leading to reduction or loss of the claimed thermal storage capacity.
Similar approaches have been tried when introducing materials other than PCMs into construction materials. This is especially prevalent when introducing admixtures into concrete. Incompatibility between the admixtures and hydration of cement is a major problem in the manufacture of concrete when the admixture is directly added into the mix. For example, water reducers, the most commonly used admixtures in concrete can have undesirable side effects such as rapid loss of workability, excessive quickening/retardation of setting, reduced rates of strength gain, and changes in long term behavior. Similarly, shrinkage reducing admixtures, which are used to reduce drying and autogenous shrinkage in concrete elements, can also cause side effects in concrete as they reduce the rate of cement hydration and strength development in concrete.
As a major ingredient of concrete, water is also used as an admixture in high strength concrete (HSC) to reduce autogenous shrinkage of the concrete through internal curing. Autogenous shrinkage is mainly caused by the capillary tension in the pore fluid caused by self-shrinkage. In the case of HSC with a water to cement ratio (W/C) below 0.3, the autogenous shrinkage can account for more than 50% of the total contraction deformation. Serious cracking can be induced in early-age concrete by autogenous shrinkage. These cracking problems cannot be mitigated through conventional full water curing because of HSC'"'"'s compact pore structure and very low permeability. To minimize or eliminate autogenous shrinkage, additional moisture has to be provided within the concrete when it is needed. This additional moisture is essentially used as an admixture in concrete. However, it cannot be added directly into concrete during mixing because the compressive strength of HSC can be significantly reduced.
Undesirable interaction with cement hydration can prevent applications of some other admixtures in concrete. For example, bioactive agents have been shown to prevent corrosion of stainless steel and aluminum. They provide an eco-friendly method to prevent the corrosion in concrete. However, when these bioactive agents are simply mixed in with concrete, the 28-day compressive strength of the concrete was reduced by more than 60%. This is because the bioactive agents can cover the surface of cement particles and therefore prevent the cement particle from reacting with water, resulting in less CSH produced and much lower compressive strength.
As with PCMs, polymer based microcapsules or porous composites have been tried as a way incorporate admixtures into concrete without imparting undesirable effects caused by interactions with the admixture and concrete. For example, compositions that modify viscosity, impart antimicrobial properties, improve corrosion or fire resistance, or modify the water needed have been microencapsulated or adsorbed into porous composites and then mixed with concrete. As noted, however, these methods can have drawbacks such as breakage of the microcapsule, high manufacturing cost, leakage of the admixture, poor delivery of the admixture, or simply poor performance.
What are thus needed are new compositions and methods that can be used to incorporate PCMs and other admixtures into building materials such as concrete. The compositions and methods disclosed herein seek to address these and other needs.
In accordance with the purposes of the disclosed materials, compounds, compositions, articles, devices, and methods, as embodied and broadly described herein, the disclosed subject matter, in one aspect, relates to compositions and methods for preparing and using the disclosed compositions. In a further aspect, disclosed herein are compositions comprising cenospheres and core materials, wherein the core material is encapsulated inside the cenosphere. In specific examples, the core material is a phase change material. This in a specific aspect, disclosed herein are compositions comprising cenospheres and PCMs, wherein the PCMs are encapsulated within the cenospheres. In further examples, the core material is an admixture, such as viscosity modifiers, antimicrobial agents, corrosion inhibitors, fire retardants, water, air, and the like. Thus in a further aspect, disclosed are compositions comprising cenospheres and any of such admixtures, where the admixtures are encapsulated inside the cenosphere. Methods of using cenospheres to encapsulate core materials like PCMs and other admixtures are also disclosed. Also, methods of adding the disclosed compositions to building materials such as concrete, and the materials produced thereby, are disclosed.
Additional advantages of the disclosed subject matter will be set forth in part in the description that follows, and in part will be obvious from the description, or can be learned by practice of the aspects described below. The advantages described below will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive.
The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several aspects of the disclosure and together with the description, serve to explain the principles of the disclosure.
The materials, compounds, compositions, articles, and methods described herein may be understood more readily by reference to the following detailed description of specific aspects of the disclosed subject matter and the Examples and Figures included therein.
Before the present materials, compounds, compositions, and methods are disclosed and described, it is to be understood that the aspects described below are not limited to specific synthetic methods or specific reagents, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.
Also, throughout this specification, various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which the disclosed matter pertains. The references disclosed are also individually and specifically incorporated by reference herein for the material contained in them that is discussed in the sentence in which the reference is relied upon.
In this specification and in the claims that follow, reference will be made to a number of terms, which shall be defined to have the following meanings:
Throughout the description and claims of this specification the word “comprise” and other forms of the word, such as “comprising” and “comprises,” means including but not limited to, and is not intended to exclude, for example, other additives, components, integers, or steps.
As used in the description and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a composition” includes mixtures of two or more such compositions, reference to “the compound” includes mixtures of two or more such compounds, reference to “an agent” includes mixture of two or more such agents, and the like.
“Optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.
A weight percent (wt. %) of a component, unless specifically stated to the contrary, is based on the total weight of the formulation or composition in which the component is included.
Reference will now be made in detail to specific aspects of the disclosed materials, compounds, compositions, articles, and methods, examples of which are illustrated in the accompanying Examples and Figures.
Disclosed herein are compositions that comprise a core material encapsulated within cenospheres.
Cenospheres are hollow inorganic particles generated in coal burning power plants with size ranging from a few micrometers to hundreds of micrometers, as shown in
In the disclosed compositions, the cenosphere can have an average diameter of from about 1 μm to about 2,000 μm, from about 20 μm to about 1,000 μm, or from about 30 μm to about 80 μm. In further examples, the average diameter of the cenosphere can be about 1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, or 2000 μm, where any of the stated values can form an upper or lower endpoint when appropriate.
The payloads of the core material inside the cenospheres can be from about 20% to about 90%, about 50% to about 70% by weight, or about 60% by weight of the composition (core material plus cenosphere). In other examples, the disclosed compositions can contain about 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or 90% core material by weight of the composition, where any of the stated values can form an upper or lower endpoint when appropriate.
The disclosed compositions can also comprise a majority of intact, loaded, cenospheres. That is, before preparing the disclosed compositions the cenosphere based starting material can be filtered to remove the broken cenospheres. This can be done via water filling under vacuum followed by gravity separation. Thus, intact cenospheres are isolated and used. In certain examples, this means the final cenosphere composition, after loading, can comprise at least about 50, 60, 70, 80, or 90% by weight intact cenospheres.
The disclosed compositions can also comprise an outer coating on the cenosphere. Suitable outer coatings include silica, alumina, or titania.
In one aspect, the disclosed compositions comprise a PCM as the core material that is inside a cenosphere. These are denoted herein as “CenoPCMs.”
A PCM is a composition with high latent heat that undergoes a phase change at a desired temperature. For example, when a PCM freezes, changing from liquid to solid, it releases large amounts of energy in the form of latent heat of fusion. When the material melts, an equal amount of energy is absorbed from the environment as it changes from solid to liquid. Likewise, when a PCM condenses from gas to liquid it releases large amounts of energy in the form of latent heat of vaporization, absorbing an equal amount of energy from the environment as it boils, changing from liquid to gas.
In specific examples, a suitable PCM for the disclosed CenoPCMs can comprise water, a salt-water solution, a sugar alcohol, a paraffin, a fatty acid, a salt hydrate, a nitrate, a hydroxide, a hygroscopic material, or combinations thereof. More specifically, the PCM can be urea; ureidopyrimidone; N,N-dialkylpiperidinum; N,N-dialkylpyrrolidinium; LiF and BeF2; NaF and BeF2; LiF and NaF and KF; NaF and ZrF4; KNO3 and KCl; KNO3 and K2CO3; LiBr and KBr; KNO3 and KBr; KNO3 and LiOH; FeCl2 and KCl; KCl and LiCl; K2CO3 and KOH; K2SO4 and KOH; FeCl2 and NaCl; KCl and MnCl2; LiBr and LiI; KCl—MgCl2; MnCl2 and NaCl; LiCO3 and LiOH; LiBr and LiF; NaCl and MgCl2; K2CO3 and MgCO3; KF and KBF4; Na2SO4 and ZnSO4; CaCl2 and LiCl; LiCl and Li2SO4; KF and LiF; K2CO3 and Li2CO3; Li2CO3 and Na2CO3; LiCl and LiF; CaCl2 and NaCl; KVO3 and BaTiO3; KCl and LiBr and NaBr; KBr and LiCl and NaCl; LiBr and NaBr and KBr; NaOH and NaCl and Na2CO3; KCl and LiCl and Li2SO4; MgCl2 and KCl and NaCl; NaCl and KCl and FeCl2; KCl and LiCl and CaF2; CaCl2 and KCl and LiCl; NaCl and KCl and LiCl; KF and AlF3 and ZrF4; MnCl2 and KCl and NaCl; Na2SO4 and K2SO4 and ZnSO4; Na2CO3 and K2CO3 and ZnSO4; Na2CO3 and K2CO3 and LiCO3; KCl and NaCl and LiF; LiCl and NaCl and Li2SO4; LiCl and KCl and CaCl2 and CaF2; KCl and NaCl and LiCl and Li2SO4; NaNO3; KNO3; KNO3 and KCl; KNO3 and K2CO3; KNO3 and KBr; FeCl2 and KCl; KCl and LiCl; K2CO3 and KOH; K2SO4 and KOH; FeCl2 and NaCl; LiBr and KBr; NaOH and NaCl and Na2CO3; MgCl2 and KCl and NaCl; NaCl and KCl and FeCl2; CaCl2 and KCl and LiCl; MgCl2 and KCl and NaCl; MgCl2 and KCl and NaCl; NaOH and NaCl and Na2CO3; MnCl2 and KCl and NaCl; Na2CO2 and K2CO3 and Li2CO3; LiF and LiCl and LiVO3 and Li2SO4 and Li2MoO4; LiF and LiCl and Li2SO4 and Li2MoO4; LiF and KF and KCO4 and KCl; LiF and LiOH; LiF and BaF2 and KF and NaF; LiF and KF and NaF and KCl; LiF and NaF and KF and MgF2; LiF and NaF and KF; LiF and KF and NaF; LiF and NaF and KF; LiF and LiCl; KF and LiCl; KF and LiCl; LiF and KF; LiF and LiVO3 and Li2MoO4; LiCl and KCl and LiCO3 and LiF; LiCl and KCl; KCl and MnCl2 and NaCl; LiClLiVO3 and Li2MoO4 and Li2SO4 and LiF; NaCl and KCl and MgCl2; KCl and MgCl2 and NaCl; NaCl and MgCl2; KCl and ZnCl2; KCl and MgCl2; NaCl═MgCl2; LiCl and Li2SO4 and Li2MoO4; KCl and MnCl2; LiCl and Li2SO4 and LiVO3; KCl and MnCl2; NaCl and MgCl2; CaCl2 and KCl and NaCl and NaF; CaCl2 and KCl and MgCl2 and NaCl; CaCl2 and KCl and NaCl; KCl and MgCl2; LiCl and LiF and MgF2; CaCl2 and CaF2 and NaF; CaCl2 and NaCl; NaOH and NaCl and Na2CO3; LiOH and LiF; Li2CO3 and K2CO3 and Na2CO3; Li2CO3 and K2CO3; Li2CO3 and K2CO3; Zn and Mg; Al and Mg and Zn; Mg and Cu and Zn; Mg and Cu and Ca; Mg and Al; formic acid; caprilic acid; glycerin; D-Lactic acid; methyl palmitate; camphenilone; docasyl bromide; caprylone; phenol; heptadecanone; 1-cyclohexylooctadecane; 4-heptadacanone; p-joluidine; cyanamide; methyl eicosanate; 3-heptadecanone; 2-heptadecanone; hydrocinnamic acid; cetyl alcohol; α-nepthylamine; camphene; O-nitroaniline; 9-heptadecanone; thymol; sodium acetate; trimethylolethane; methylbehenate; diphenyl amine; p-dichlorobenzene; oxalate; hypophosphoric acid; O-xylene dichloride; β-chloroacetic acid; nitro naphthalene; trimyristin; heptaudecanoic acid; α-chloroacetic acid; bee wax; bees wax; glycolic acid; glyolic acid; p-bromophenol; azobenzene; acrylic acid; dinto toluent; phenylacetic acid; thiosinamine; bromcamphor; durene; benzylamine; methyl bromobenzoate; alpha napthol; glautaric acid; p-xylene dichloride; catechol; quinine; acetanilide; succinic anhydride; benzoic acid; stibene; benzamide; acetic acid; polyethylene glycol; capric acid; eladic acid; lauric acid; pentadecanoic acid; trustearin; myristic acid; palmatic acid; stearic acid; acetamide; methyl fumarate; K2HPO4.6H2O; FeBr3.6H2O; Mn(NO3)2.6H2O; FeBr3.6H2O; CaCl2.12H2O; LiNO3.2H2O; LiNO3.3H2O; Na2CO3.10H2O; Na2SO4.10H2O; KFe(SO4)2.12H2O; CaBr2.6H2O; LiBr2.2H2O; Zn(NO3)2.6H2O; FeCl3.6H2O; Mn(NO3)2.4H2O; Na2HPO4.12H2O; COSO4.7H2O; KF.2H2O; MgI2.8H2O; CaI2.6H2O; K2HPO4.7H2O; Zn(NO3)2.4H2O; Mg(NO3).4H2O; Ca(NO3).4H2O; Fe(NO3)3.9H2O; Na2SiO3.4H2O; K2HPO4.3H2O; Na2S2O3.5H2O; MgSO4.7H2O; Ca(NO3)2.3H2O; Zn(NO3)2.2H2O; FeCl3.2H2O; Ni(NO3)2.6H2O; MnCl2.4H2O; MgCl2.4H2O; CH3COONa.3H2O; Fe(NO3)2.6H2O; NaAl(SO4)2.10H2O; NaOH.H2O; Na3PO4.12H2O; LiCH3COO2H2O; Al(NO3)2.9H2O; Ba(OH)2.8H2O; Mg(NO3)2.6H2O; KAl (SO4)2.12H2O; MgCl2.6H2O; gallium-gallium antimony eutectic; gallium; cerrolow eutectic; Bi—Cd—In eutectic; cerrobend eutectic; Bi—Pb—In eutectic; Bi—In eutectic; Bi—Pb-tin eutectic; Bi—Pb eutectic; CaCl2.6H2O and CaBr2.6H2O; Triethylolethane and water and urea; C14H28O2 and C10H20O2; CaCl2 and MgCl2.6H2O; CH3CONH2 and NH2CONH2; Triethylolethane and urea; Ca(NO3).4H2O and Mg(NO3)3.6H2O; CH3COONa.3H2O and NH2CONH2; NH2CONH2 and NH4NO3; Mg(NO3)3.6H2O and NH4NO3; Mg(NO3)3.6H2O and MgCl2.6H2O; Mg(NO3)3.6H2O and MgCl2.6H2O; Mg(NO3)3.6H2O and Al(NO3)2.9H2O; CH3CONH2 and C17H35COOH; Mg(NO3)2.6H2O and MgBr2.6H2O; Napthalene and benzoic acid; NH2CONH2 and NH4Br; LiNO3 and NH4NO3 and NaNO3; LiNO3 and NH4NO3 and KNO3; LiNO3 and NH4NO3 and NH4Cl; or combinations thereof.
In some examples, the melting temperature of the PCM can be at least about −100° C. (e.g., at least about −50° C., at least about 0° C., at least about 50° C., at least about 100° C., at least about 150° C., at least about 200° C., at least about 250° C., at least about 300° C., at least about 350° C. or at least about 400° C.). In some embodiments, the melting temperature of the PCM can be about 400° C. or less (e.g., about 350° C. or less, about 300° C. or less, about 250° C. or less, about 200° C. or less, about 150° C. or less, about 100° C. or less, about 50° C. or less, about 0° C. or less, or about −50° C. or less). The melting temperature of the PCM can range from any of the minimum temperatures described above to any of the maximum temperatures described above. For example, the melting temperature of the PCM can range from about −100° C. to about 400° C. (e.g., from about 0° C. to about 300° C., or from about 100° C. to about 200° C.)
In certain embodiments, the PCM comprises a salt water solution, and has a melting temperature of from about −100° C. to about 0° C. In some embodiments, the PCM comprises a paraffin, and has a melting temperature of from about 0° C. to about 150° C. In some embodiments, the phase change material is a salt hydrate with a melting temperature of 50° C. to 100° C. In some embodiments, the phase change material comprises a sugar alcohol, and has a melting temperature of from about 50° C. to about 225° C. In some embodiments, the phase change material comprises a nitrate, and has a melting temperature of from about 150° C. to about 300° C. In some embodiments, the phase change material comprises a hydroxide, and has a melting temperature of from about 200° C. to about 400° C.
In some embodiments, the melting enthalpy of the PCM can be at least about 100 MJ/m3 (e.g., at least about 150 MJ/m3, at least about 200 MJ/m3, at least about 250 MJ/m3, at least about 300 MJ/m3, at least about 350 MJ/m3, at least about 400 MJ/m3, at least about 450 MJ/m3, at least about 500 MJ/m3, at least about 550 MJ/m3, at least about 600 MJ/m3, or at least about 650 MJ/m3). In some embodiments, the melting enthalpy of the PCM can be about 100 MJ/m3 or less (e.g., about 650 MJ/m3 or less, about 600 MJ/m3 or less, about 550 MJ/m3 or less, about 500 MJ/m3 or less, about 450 MJ/m3 or less, about 400 MJ/m3 or less, about 350 MJ/m3 or less, about 300 MJ/m3 or less, about 250 MJ/m3 or less, about 200 MJ/m3 or less, or about 150 MJ/m3 or less). The melting enthalpy of the PCM can range from any of the minimum values described above to any of the maximum values described above. For example, the melting enthalpy of the PCM can range from about 100 MJ/m3 to about 100 MJ/m3 (e.g., from about 200-400 MJ/m3).
In some embodiments, the phase change material comprises a salt water solution, and has a melting enthalpy of from about 150 MJ/m3 to about 300 MJ/m3. In some embodiments, the phase change material comprises a paraffin, and has a melting enthalpy of from about 150 MJ/m3 to about 200 MJ/m3. In some embodiments, the phase change material comprises a salt hydrate, and has a melting enthalpy of from about 200 MJ/m3 to about 600 MJ/m3. In some embodiments, the phase change material comprises a sugar alcohol, and has a melting enthalpy of from about 200 MJ/m3 to about 400 MJ/m3. In some embodiments, the phase change material comprises a nitrate, and has a melting enthalpy of from about 200 MJ/m3 to about 600 MJ/m3. In some embodiments, the phase change material comprises a hydroxide, and has a melting enthalpy of from about 450 MJ/m3 to about 700 MJ/m3.
As a result the CenoPCMs have several beneficial properties that make them useful for building materials. For examples, the disclosed CenoPCMs can have high stiffness/strength. The cenosphere shell of a CenoPCM has much higher stiffness/strength than a polymeric shell used in existing microencapsulated PCMs. As a result, CenoPCM can endure strong mixing during the manufacturing of the materials, and will not significantly reduce stiffness/strength of the produced materials.
The disclosed CenoPCMs can also have high chemical and thermal stability. Since cenospheres are hollow fly ash particles, they have the same chemical and thermal stability as fly ash. When used in concrete, they can react slowly with the hydration product of Portland cement. This reaction will generate calcium silicate hydrate gel (CSH gel), which can make the CenoPCM shell even stronger.
The disclosed CenoPCMs can also have low flammability. Cenospheres are nonflammable and therefore can reduce the flammability of the PCM core, so that the disclosed CenoPCMs can be accepted by US building industry.
The disclosed CenoPCMs can also have high thermal conductivity. Since cenospheres are inorganic, their thermal conductivity is much higher than the organic polymeric shells used in existing microencapsulated PCMs, making thermal exchange between PCMs inside the shell and outside environment much easier and faster.
With all these advantages, CenoPCM can eliminate major barriers preventing application of PCMs in traditional building materials. For example, CenoPCM can be integrated into construction and building materials to improve energy efficiency of buildings.
Also, disclosed are various building materials that comprise the disclosed CenoPCMs. For example, disclosed herein is a composition comprising cement and the disclosed CenoPCMs. Also, disclosed herein is a composition comprising an insulating material and the disclosed CenoPCMs. Still further, disclosed herein is a composition comprising a roofing material and the disclosed CenoPCMs. In a further example, disclosed herein is a flooring material (e.g., tile, porcelain, linoleum, engineered hardwood) that comprises the disclosed CenoPCMs. In still a further example, disclosed herein is a wall material (e.g., gypsum, drywall, plaster, stucco, PVC) that comprises the disclosed CenoPCMs.
In another aspect, the disclosed compositions comprise an admixture as the core material that is inside a cenosphere. One type of admixture that can be included is an antimicrobial agent. Any antimicrobial agent that can prevent or reduce microbial growth in the disclosed compositions can be used. Examples of suitable antimicrobial materials include metals such as copper, zinc, or silver and/or salts thereof. Further examples of suitable antimicrobial agents include natural and synthetic organic compositions such as β-lactam antibiotics like penicillin or cephalosporin, and protein synthesis inhibitors like neomycin. Antimicrobial agents such as lactic acid, acetic acid, or citric acid can also be used. In some other examples, an antimicrobial agent can comprise a quarternary ammonium compound such as benzalkonium chloride, benzethonium chloride, methylbenzethonium chloride, cetylalkonium chloride, cetylpyridinium chloride, cetrimonium, cetrimide, dofanium chloride, tetraethylammonium bromide, didecyldimethylammonium chloride, and domiphen bromide. The antimicrobials can be used in effective amounts, e.g., an amount that will prevent or reduce microbial growth. Thus disclosed herein are compositions comprising a cenosphere and an antimicrobial agent, wherein the antimicrobial agent is encapsulated inside the cenosphere.
Another suitable admixture that can be used in the disclosed compositions is a fire retardant. Suitable fire retardants can comprise an organic composition or an inorganic composition. In some examples, a suitable fire retardant such as tris(2-chloro-1-(chloromethyl)ethyl)phosphate, aluminum hydroxide, magnesium hydroxide. In some embodiments, a fire retardant can comprise a zeolite. The fire retardants can be used in effective amounts, e.g., an amount that will prevent or reduce combustion. Thus disclosed herein are compositions comprising a cenosphere and a fire retardant, wherein the fire retardant is encapsulated inside the cenosphere.
Still further, another suitable admixture that can be used in the disclosed compositions is a corrosion inhibitor such as sodium sulfite, chromates, and polyphosphates. Thus disclosed herein are compositions comprising a cenosphere and a corrosion inhibitor, wherein the corrosion inhibitor is encapsulated inside the cenosphere.
In yet another example, the disclosed compositions can comprise water as an admixture. This composition can be used to promote self curing properties into concrete. Thus disclosed herein are compositions comprising a cenosphere and water, wherein the water is encapsulated inside the cenosphere.
In still another example, the disclosed compositions can comprise a water reducer as an admixture. Thus disclosed herein are compositions comprising a cenosphere and a water reducer, wherein the water reducer is encapsulated inside the cenosphere. Examples of water reducers are lignosulphonates, hydroxycarboxylic acids, carbohydrates, and other specific organic compounds, for example glycerol, polyvinyl alcohol, sodium alumino-methyl-siliconate, sulfanilic acid and casein as described in the Concrete Admixtures Handbook, Properties Science and Technology, V. S. Ramachandran, Noyes Publications, 1984.
In yet another example, the disclosed compositions can comprise a viscosity modifier as an admixture. Cellulose, PEG-Glycol derivative, Natural Gums, amorphous silica, and the like. Thus disclosed herein are compositions comprising a cenosphere and a viscosity modifier, wherein the viscosity modifier is encapsulated inside the cenosphere.
In yet another example, the admixture can be a superplasticizer, such as a polyacrylate aqueous solution. Thus disclosed herein are compositions comprising a cenosphere and a superplasticizer, wherein the superplasticizer is encapsulated inside the cenosphere.
In yet another example, the admixture can be air. Thus disclosed herein are compositions comprising an empty perforated cenosphere, wherein air is encapsulated inside the cenosphere.
Other examples of admixtures that can be incorporated into cenospheres are listed below.
The disclosed compositions can be prepared by a method generally illustrated in
The acid solution can contain be a hydrofluoric acid based solution. For example, solutions of hydrofluoric acid and ammonium hydroxide (e.g., comprising ammonium fluoride, HF, water) can be used. Other hydrofluoric acid solutions can be used as well, e.g., those comprising hydrofluoric acid and hydrochloric acid, to produce perforated cenospheres.
Next, liquid PCMs are loaded into the perforated cenospheres (
A thin layer of silica can be coated on the PCM loaded cenospheres to prevent the possible leaking of the liquid PCM, as shown in
The sol-gel method can also be used to prepare the silica nanoparticle solution. Tetraethoxysilane (TEOS) can be used as the precursor for sol-gel synthesis since it reacts readily with water with either a basic or acidic catalyst. This reaction is called hydrolysis, because a hydroxyl ion becomes attached to the silicon atom. The process comprises a series of hydrolysis and condensation reactions of the TEOS, as shown in
Alternatively, a thin layer of TiO2 can also be coated on censpheres to add a self-cleaning function to the concrete. This thin layer of nanoparticle coating can be applied before or after the loading of the admixture, depending on the nature of the intended application.
In addition, a thin layer of polymer can also be coated on the cenosphere to seal the perforated cenosphere shell. Any polymer which sufficiently adheres to the cenosphere shell can be used for coating.
The disclosed methods can also comprise the step of adding the disclosed compositions into a building material, such as concrete, mortar, cement, asphalt, tar, tile, brick, ceramics, gypsum, plaster, stucco, porcelain, linoleum, engineered hardwoods, PVC, insulation, roofing and flooring materials, and the like. A recent Oak Ridge National Laboratory (ORNL) study indicated that PCM integrated wallboard can result in up to 22% electricity savings from wall-generated cooling loads (Biswas et al., 2014. Applied Energy, 131, 517-529). Another study showed both cooling and heating energy savings are achievable with distributed PCM mixed with cellulose insulation in wall cavities (Biswas et al., 2014 Energy Conversion and Management, 88, 1020-1031).
In one specific example, the disclosed methods comprise adding the disclosed compositions to concrete. Portland cement-based concrete (PCC) is the most widely used construction material in our civil infrastructure system, accounting for 70% of all building and construction materials. Manufacturing of PCC not only consumes large amounts of natural resources, but also produces considerable greenhouse gases. Cement production in the U.S. accounts for up to 7% of the nation'"'"'s total CO2 emissions. PCC is also susceptible to deterioration when exposed to harsh environments. Low tensile strength, high brittleness, and low volume stability make PCC vulnerable to cracking. PCC'"'"'s higher permeability, porous microstructure, and thermodynamically unstable chemical compounds such as calcium silicate hydrate (CSH) make it susceptible to acid and sulfate attack. Deterioration of PCC has emerged as one of the largest challenges in maintaining and protecting the U.S. civil infrastructure system.
To this end, the disclosed compositions can be a versatile low cost tool for concrete manufacturing that minimizes or avoids undesired interactions between the admixtures and hydration of cement through the controlled release of admixture or through sealing the admixtures in concrete. The disclosed compositions can load and then release or seal the admixtures within concrete as needed. As a result, optimal effects of the admixture can be reached and/or new desirable functions can be added to concrete.
The following examples are set forth below to illustrate the methods and results according to the disclosed subject matter. These examples are not intended to be inclusive of all aspects of the subject matter disclosed herein, but rather to illustrate representative methods and results. These examples are not intended to exclude equivalents and variations of the present invention which are apparent to one skilled in the art.
Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, pH, etc.) but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in ° C. or is at ambient temperature, and pressure is at or near atmospheric. There are numerous variations and combinations of conditions, e.g., component concentrations, temperatures, pressures, and other reaction ranges and conditions that can be used to optimize the product purity and yield obtained from the described process. Only reasonable and routine experimentation will be required to optimize such process conditions.
A commercially obtained cenosphere (
The same procedure as Example 1 was followed except that paraffin waxes were used as the core material.
The compositions produced in Example 2 were combined into concrete. These cenospheres were compared with commercially available microencapsulated PCMs.
Table 2 shows the effect of adding 5% CenoPCM on the strength of concrete. It can be seen that 15% of strength reduction can be induced by CenoPCM. This is mainly caused by the PCM absorbed on the surface of the CenoPCM, which absorbs some mixing water in concrete and therefore reduces the workability of concrete. If we wash the CenoPCM better, this strength reduction will become insignificant. As comparison, after adding 0.5 wt %, 1 wt %, 3 wt % and 5 wt % CIBA'"'"'s phase change materials microcapsules, the percentage reduction in strength is approximately 25%, 45%, 70% and 80% for addition, respectively.
A mesoporous thin film can be coated on the surface of the loaded, perforated cenosphere. This can reduce the permeability of the cenosphere wall for applications requiring very slow release or sealing of the admixture, and enhance the mechanical performance of concrete. The thin film can be silica, alumina, or titania, which can provide a self-cleaning function to the concrete. This thin layer coating can be applied before or after the loading of the admixture, depending on the nature of the intended application.
The sol-gel method can be used to prepare a silica nanoparticle solution because of its low cost and ease of implementation. Tetraethoxysilane (TEOS) can be the precursor for sol-gel synthesis since it reacts readily with water with either a basic or acidic catalyst. The process comprise a series of hydrolysis and condensation reactions of the TEOS (
In a specific method, silica sol can be first prepared through hydrolysis of TEOS with ammonium hydroxide or a nitric acid solution as catalyst. Then a simple dip coating method can be used to apply the silica sol on the surface of cenospheres to form a porous thin film of nanosilica. The permeability of this thin film can be determined by the packing properties of the nanosilica, which can be controlled by the concentration of the precursor and the pH value of the sol. In other words, the loading/releasing properties of the nanosilica coated cenosphere can be further modified by adjusting the concentration of TEOS and pH value of the sol.
Nanosilica particles can not only have pozzolanic reaction with calcium hydroxide, but also can serve as nucleating sites for the hydration reaction of cement to promote the production of CSH. As a result, a very dense interface transition zone between the cenosphere and cement paste can be produced. This dense interface can significantly increase the strength of the concrete. In addition, the produce dense interface transition zone can provide extra measure to prevent leaking of some admixture (e.g., PCM).
Coating the cenospheres with nanosilica thin films can also eliminate a drawback of traditional addition of nanoparticles as a dry powder additive to concrete-poor dispersion of the nanoparticle. Due to strong van der Waals forces between nanoparticles, nanoparticles tend to conglomerate. To achieve good dispersion of nanoparticles in concrete, strong physical blending using ultrasonic waves or chemical functionalization are commonly used. With the disclosed compositions, silica nanoparticles are directly grown on the surface of cenospheres. After homogeneously mixing these cenospheres into cement mixture, the silica nanoparticles are self-dispersed into the cement matrix. In this way, the time-consuming and difficult task of dispersing nanoparticles is eliminated.
Also, there is less risk of silica inhalation when the silica nanoparticles are coated on the cenosphere.
Organic polymers can be coated on the perforated cenospheres though spray drying, fluidized bed, or other known techniques.
Internal curing is a relatively new manufacturing method for high performance concrete. In this method, saturated LWAs or SAPs are typically used as water reservoirs to continuously supply water to replenish the empty pore volume that is created by self-desiccation. This will reduce autogenous shrinkage and also improve the curing of concrete at the early age. Thus, internal curing can be used to produce a dense crack-free microstructure, which is the desire of using a low water-to-cement ratio (w/c). Benefits of internal curing have also been shown to include reduced shrinkage of sealed concrete, increased compressive strength and flexural strength (especially at later ages), reduced potential for cracking and increased durability.
When used in internal curing for concrete, water loaded within cenospheres has to be readily available to be released to the surrounding cementitious matrix in order to optimize internal curing of concrete. An ideal internal curing agent should release most of its absorbed water at high relative humidity within an appropriate time. In this example, the water release from the cenospheres at two different relative humidity levels: 50% and 95%, was performed. The results are shown in
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.