Carbon nanotube hybrid materials for concrete applications

Abstract

To provide hybrid materials in which carbon nanotubes are dispersed in construction materials in a commercially viable, practical, safe, economical, and effective manner. [Solution] A carbon nanotube (CNT) hybrid material comprising a blend of a catalyst supported on at least one of a metal support, a metalloid support, a metal oxide support, or a carbon support, and at least one material selected from the group consisting of cementitious materials, materials used in the production of cementitious materials, and materials used to reinforce cementitious materials, and CNTs on the blend.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims priority to U.S. Provisional Patent Application No. 63 / 255,067, filed October 13, 2021, the entire disclosure of which is incorporated herein by reference for all purposes.

[0002] Background This disclosure relates to carbon nanotube hybrid materials.

Background Art

[0003] The concrete industry, like other sectors of the construction industry, is currently facing significant technical challenges due to environmental pressure to substantially reduce CO2 emissions generated during the production process and, more strongly, economic pressure to improve the performance efficiency and durability of construction materials in order to manufacture stronger, thinner, and lighter structural members at low cost. These technical, environmental, and economic requirements have a major impact on its manufacturing cost and, as a result, its price in the market. The world production of concrete in 2020 was approximately 4.1 billion tons, which corresponds to approximately 8.0% of the world's CO2 emissions (a total of approximately 36.4 billion metric tons) considering the CO2 emissions generated during the cement manufacturing process (1.56 billion metric tons), fuel and power consumption (1.16 billion metric tons), and transportation (0.17 metric tons). Due to the accelerating economic and population growth in some regions of the world (e.g., Asia and the Middle East), the future world concrete production capacity is predicted to increase by 5 billion metric tons by 2030, and currently, China is the leading global concrete producer (about 53% of the global production volume).

[0004] Various strategies have been employed to improve the sustainability of concrete and, furthermore, to develop environmentally friendly or environmentally sustainable concrete. These strategies include incorporating recycled materials and waste (industrial, agricultural, and household) into concrete, optimizing its mix design, reducing CO2 emissions by reducing the Portland cement content, partially replacing Portland cement with cement-based materials and binders (e.g., nanoalumina particles, fly ash, silica fume, blast furnace slag), improving the durability and extending the lifespan of concrete using reinforcing materials (e.g., carbon fiber (CF), carbon nanotubes (CNT), steel fibers), reducing long-term resource consumption, and selecting environmentally conscious construction methods. It has been observed that nano-Al2O3 particles may be effective in increasing the modulus of elasticity of cement mortar. With 5 wt.% nano-Al2O3 (particle size ~150 nm), the modulus of elasticity increased by 143% over a 28-day curing period. During cement hydration, nanoalumina particles were utilized to fill pores at the sand-paste interface, forming a dense, low-porosity interface transition zone (ITZ). The effective densification of the ITZ contributed to a significant increase in the elastic modulus of the mortar.

[0005] Reinforcing cementitious matrices with carbon nanomaterials can provide a viable alternative to achieving the above objectives. Carbon nanotubes (CNTs) have attracted attention as reinforcing materials for cementitious matrices due to their mechanical properties (Young's modulus of 1 TPa, tensile strength of individual tubes >60 GPa, and fracture deformation exceeding 12%), low density, unique physical and chemical properties, thermal and electrical conductivity, and piezoelectric response. These properties have made CNTs a suitable candidate for reinforcement in cement-based smart materials.

[0006] The ability of CNTs to reinforce nanocomposite materials (i.e., CNT-reinforced cement-based materials) depends on many factors, in particular, the intrinsic structure and surface properties of the CNTs, whether they are single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (FWCNTs), or multi-walled carbon nanotubes (MWCNTs), their final aspect ratio (e.g., whether the nanotubes were shortened as a result of decomposition treatment), the quality of CNT dispersion in the matrix, the CNT content level, the composition and structure of the matrix, and the interfacial bonding state between the CNTs and the matrix. The effects of MWCNT length (short and long), the fracture properties of nanocomposite materials when the weight ratio of surfactant to MWCNTs is constant, and the effect of surfactant concentration on the fracture properties of nanocomposite materials reinforced with 0.08 wt.% long MWCNTs have been studied. Fracture mechanics test results show that the flexural strength and Young's modulus of the cement matrix significantly increased through the use of small amounts of MWCNTs (0.048 wt.% and 0.08 wt.%) compared to similar materials without CNTs, indicating that the nanocomposite materials exhibit an increase in Young's modulus of at least 15% and up to approximately 55%, and an increase in flexural strength of at least 8% and up to approximately 40%. An increase of over 45% in 28-day flexural strength is achieved with the addition of 0.08 wt.% MWCNTs compared to the unmodified control. In particular, high concentrations of short MWCNTs are required to achieve effective strengthening, while low amounts of long MWCNTs are needed to achieve the same level of mechanical performance.

[0007] Nanocomposite materials with various concentrations of MWCNTs and surfactants in various concentrations and combinations have also been studied. These studies have shown that nanocomposite materials with 0.5 wt.% MWCNTs can be strengthened by 175% and 55% respectively in fracture toughness and critical opening displacement compared to plain cement paste. Furthermore, researchers prepared CNT-reinforced fly ash cement paste by adding 0.5% and 1 wt% CNTs to a cement-fly ash system (20 wt% of cement) and found that the use of CNTs results in nanocomposite materials with higher compressive strength. The highest strength obtained was 54.7 MPa at 28 days with 1 wt.% CNT (a nearly 100% increase in relative strength compared to Portland cement paste). The use of 0.5% carboxyl-functionalized MWCNTs resulted in 149% and 35% strengthening of fracture toughness and critical opening displacement, respectively, compared to plain cement paste. A comparison of the mechanical properties of carbon fiber (CF) reinforced cement and carbon nanotube (CNT) reinforced cement materials demonstrated that the flexural and compressive strengths of CNT reinforced cement materials were 30% and 100% higher, respectively, than those of CF reinforced cement materials (Table 1).

[0008] CNTs have been shown to have at least twice the thermal conductivity of diamond. The negative coefficient of thermal expansion of CNTs results in higher thermal stability. Therefore, CNTs are expected to improve the thermal stability of cement-based materials. In a comparison of the thermal performance of CF-reinforced cement-based materials and CNT-reinforced cement-based materials, it was observed that the thermal conductivity of CNT-reinforced cement-based materials was at least 35% and 85% greater (typically 0.5–0.8 W / mK) than that of carbon fiber (CF)-reinforced cement-based materials and unreinforced cement-based materials, respectively (Table 1).

[0009] [Table 1]

[0010] Cement / CNT hybrids and fly ash / CNT hybrids were prepared using iron ions naturally present in cement or fly ash as a CNT / CF catalyst. These hybrids have been used to produce CNT / CF-reinforced cement paste. The material has shown a twofold increase in compressive strength compared to plain cement paste. A 34% increase in tensile strength was achieved using a cement / CNT hybrid containing 0.3 wt.% CNTs.

[0011] Cement-based materials may have defects and microcracks both within the material and at its interfaces, even before external loads are applied. These defects and microcracks arise from excess water, bleeding, plastic settlement, thermal and shrinkage strains, and stress concentrations imposed by external constraints. Under applied loads, the distributed microcracks propagate, coalesce, and align to form macrocracks, sometimes leading to sudden and catastrophic failure of concrete structures. Under fatigue loads, cement-based materials crack easily, and these cracks provide easy access routes for harmful substances.

[0012] There is a growing need to monitor crack structures, prevent further crack propagation, and ensure timely repair, safety, and long-term durability of critical structures. Non-destructive assessment, such as the attachment or embedding of external sensors (e.g., resistance strain gauges, optical sensors, piezoelectric ceramics, shape memory alloys, and fiber-reinforced polymer bars) into or on the structure, has been used in many ways to meet this need. However, these sensors have several drawbacks, including low durability, low sensitivity, high cost, low survival rate, and / or undesirable compatibility with the structure (i.e., loss of the structure's mechanical properties). There is a need for structural materials themselves to have sensing capabilities (i.e., structural materials to be multifunctional or high-performance).

[0013] Self-detecting (piezoresistive) cement-based materials, enhanced with conductive fillers, increase their ability to detect stress, strain, or cracks on their own while maintaining good mechanical properties. Conductive fillers can be classified as fibrous fillers and particulate fillers. Suitable fibrous fillers include short carbon fibers (CF), surface-modified CF, steel fibers, and carbon-coated nylon fibers, while effective particulate fillers include carbon black, steel fibers, and nickel powder. As piezoresistive cement-based materials deform or are subjected to stress, the contact state between the filler and the matrix changes, affecting the electrical resistance of the cement-based material. Therefore, strain, stress, cracks, and damage can be detected by measuring electrical resistance. Self-detecting cement-based materials have potential not only in the field of structural integrity monitoring and evaluation of the condition of concrete structures, but can also be used for road traffic control, border security, structural vibration control, etc. Charged concrete with heating capabilities also enables more effective radiant floor heating and prevents freezing of roads and sidewalks.

[0014] Dispersing carbon nanotubes in construction materials in a commercially viable, practical, safe, economical, and effective manner is currently a major technological challenge. Due to their high hydrophobicity, carbon nanotubes tend to form bundles or ropes in aqueous and organic dispersions, meaning the material cannot efficiently disperse and integrate into the cementitious matrix material. Cement consists of particles with a broad particle size distribution, ranging from approximately 1 to 30 μm. Some studies in the scientific literature have employed combinations of chemical and mechanical dispersion techniques for CNTs. Surfactants combined with sonication have been successfully employed to enhance the dispersion of CNTs and water-reducing additives, thereby altering the fluidity of CNT-cement mixtures. However, sonication and high-shear mixing techniques are not commercially scalable and can cause excessive damage to the CNT structure, reducing their efficiency in improving mechanical strength, electrical and thermal conductivity, and piezoelectric response. A high CNT aspect ratio is required to reach the penetration limit at very low CNT filling levels in the concrete matrix. Handling CNT powder may pose potential health and safety risks. The manufacturing cost of CNTs is very high, making their application impractical in cost-sensitive markets such as construction. This also represents a significant limitation on the industrial use of CNTs in construction materials.

[0015] prior art CNT hybrid materials (CNT-carbon, CNT-metal, and CNT-metal oxides) today correspond to third-generation carbon nanotubes. CNT / CF-cement hybrid materials have been synthesized from Portland cement by growing CNT / CF from naturally occurring iron catalyst particles in cement (4 wt.% Fe2O3). CNT / CF were grown using a modified chemical vapor deposition (CVD) method, which included the addition of a screw feeder to continuously move the cement through the reactor. This enabled the continuous production of CNT-cement hybrid materials. Reaction temperatures ranged from 500 to 700°C, and acetylene, CO, and CO2 gas mixtures were used as carbon sources. Performance test results showed that the addition of 0.4 wt.% CNT / CF-cement hybrid material to cement paste increased compressive strength and electrical conductivity by 2-3 times and 40 times, respectively. However, this method of synthesizing hybrid CNT-CF-cement materials is impractical for at least the following reasons, despite not requiring the dispersion of CNT / CF in the matrix: 1) Only particles containing iron oxide react to produce CNTs and CFs. 2) CNT / CF has a low aspect ratio value (L / D < 100), 3) Since the iron oxide content and particle size vary depending on the type of cement, differences arise in the carbon yield and morphological properties of CNT / CF. 4) Contact between cement particles under a high-temperature reducing atmosphere during hybrid material synthesis can also cause undesirable structural changes in the cement particle components and lead to the formation of other types of amorphous carbon compounds, 5) Unreactable ethylene and carbon monoxide must be burned, which generates CO2 emissions. [Overview of the project]

[0016] Each embodiment and example is directed to a carbon nanotube (CNT) hybrid material comprising a blend of a catalyst supported on at least one of a metal support, a metalloid support, a metal oxide support, or a carbon support, and at least one material selected from the group consisting of cementitious materials, materials used in the production of cementitious materials, and materials used to reinforce cementitious materials, and CNTs on the blend.

[0017] To ensure uniform distribution, there is a need to develop a new generation of carbon nanomaterials that exhibit high dispersion and can be easily integrated into cementitious matrices using conventional mixing equipment. These novel carbon nanomaterials preferably do not require the use of surfactants or water-reducing agents. This is achievable if the material has an optimized hydrophilic / hydrophobic balance. In some embodiments, the hydrophilic portion of the material is alumina and the hydrophobic portion is carbon nanotubes (CNTs). This is why this material disperses better than CNTs alone. These novel carbon nanomaterials should significantly improve one or more of the mechanical, electrical, and thermal properties of advanced construction materials and exhibit piezoelectric response. They should also be safe materials and have lower production costs.

[0018] In some embodiments, this disclosure describes carbon hybrid nanomaterials based on carbon nanotubes and nanoalumina particles (e.g., particle size of several hundred nanometers) exhibiting a high aspect ratio (e.g., L / D > 1000). In some embodiments, these hybrid materials are used in advanced construction materials, including but not limited to cementitious materials such as cement, foamed cement, and other compatible materials, as well as fly ash.

[0019] In some examples, CNT-alumina hybrid materials are synthesized using catalysts that combine a transition metal supported on alumina particles (e.g., particle size <70 microns). This alumina has a high specific surface area (>300 m²). 2It has a concentration of ( / g). The amount of active metal supported on the alumina support is less than 1 wt.%, which is about 3 to 5 times less than conventional catalysts used in prior art for carbon nanotube synthesis. This results in a high degree of dispersion of the active metal on the surface of the support, enabling the synthesis of long, straight, smaller diameter (e.g., ≤15 nm) CNT tubes (e.g., ≥10 microns). This hybrid CNT-nanoalumina material exhibits balanced hydrophobic / hydrophilic properties depending on the carbon compound of the material, which varies between 5 and 70 wt.%. The aspect ratio of the CNTs is also a function of the carbon yield. Alumina particles can be added to the reactor along with the catalyst, either alternatively or additionally.

[0020] In some embodiments, the synthesis of the hybrid material CNT-Al2O3 is carried out by CCVD using a rotary tube catalytic reactor or a fluidized bed reactor, typically at temperatures between 600 and 700°C and atmospheric pressure. An example of such a reactor system is shown in Figure 1 and described below. In some embodiments, ethylene is used as the carbon source, but other types of carbon sources, such as methane, ethane, acetylene, and / or CO, are available. The residence time of the material in the reaction zone depends on the carbon yield required for the specific application, but typically varies between 5 and 20 minutes.

[0021] Dispersion of CNT-Al2O3 hybrids in aqueous solutions is highly useful for distributing carbon nanomaterials within cement matrices, which can be easily done using known mixing methods for conventional cement-based materials. Hybrid materials can be integrated with cement particles using various techniques, for example, by mechanical mixing of powders, or by two consecutive preparation steps: 1) preparing a suspension of the CNT-Al2O3 hybrid in an aqueous solution, and 2) adding the suspension of the CNT-Al2O3 hybrid to the cement matrix.

[0022] There are several differences between the known hybrid CNT-cement materials and those of the present disclosure. In the prior art, the iron contained in the cement acts as a catalyst for the formation of CNT / CF. Since the iron content in the cement is variable, a constant carbon yield cannot be obtained. Also, a low CNT aspect ratio (L / D < 100) does not provide the benefit of a significant increase in the mechanical, electrical, and thermal conductivity properties of the concrete. Furthermore, contacting concrete particles under highly reducing conditions at high reaction temperatures can result in structural changes in the components of the cementitious material. Additionally, the known synthesis methods are not scalable to the extent required for real-world concrete production.

[0023] This CNT-Al2O3 hybrid material offers competitive advantages over the prior art. These advantages include, but are not limited to, the following: 1) This material has high aspect ratio carbon nanotubes (at least about 1000 in some embodiments) and alumina nanoparticles (100 - 800 nm particle size), which are additives used for the mechanical reinforcement of concrete. 2) Its dispersion is easier than that of individual carbon nanotubes using industrial mixing techniques. 3) The carbon nanotubes exhibit a narrow and uniform diameter distribution of about 10 ± 3 nm, which results in high conductivity of the material. 4) This hybrid material is synthesized continuously using a commercial rotary tube reactor. 5) The content of the active metal in the catalyst is less than 1 wt.%, which enables better control of the growth rate of the tubes (straight and long tubes). 6) This material is safe, easy to use in practice, and has low production costs. 7) When incorporated into concrete, this material exhibits excellent performance compared to pristine CNTs in terms of mechanical reinforcement, electrical conductivity, and piezoelectric response. 8) Small amounts of CNT-Al2O3 hybrid materials can enable the production of environmentally friendly smart concrete and reduce cement consumption by allowing the incorporation of larger amounts of other additives, such as fly ash, into the concrete mixture. As a result, the lower cement consumption contributes to the reduction of CO2 emissions, which are a cause of global warming.

[0024] The present disclosure contemplates catalyst supports other than alumina particles. By way of example, but not limited to, other metal oxides, carbon materials, and potentially semimetals are contemplated. Non-limiting examples of metal oxide supports include alumina, magnesia, and fly ash. Examples of carbon-based catalyst supports include graphite, graphene, carbon black, activated carbon, carbon nanofibers, vapor-grown carbon nanofibers, carbon fibers, carbon nanotubes, and the like. U.S. Patent Application Publication No. 2022 / 0048772 discloses carbon-CNT hybrid materials. U.S. Patent Application Publication No. 2022 / 0250912 discloses CNT hybrid materials using metal and metal oxide supported catalysts. The disclosures of both of these prior applications and their publications are incorporated herein by reference for all purposes.

[0025] This disclosure is not limited to compositions comprising supported catalyst particles blended with other particles considered to be cementitious materials. This disclosure also includes compositions in which the other particles may not be considered by some to be cementitious materials, even if cementitious materials may be one of the basic components used in the production of ordinary Portland cement. For example, in some embodiments, alumina constitutes the "other" particles. Alumina may also, or additionally, be used as a catalyst support. Thus, this disclosure considers, together with cementitious materials, other particles containing other components used in the production of cementitious materials or used to reinforce cementitious materials, including but not limited to alumina. Furthermore, the "other" particles may include, but not limited to, carbon nanofibers, carbon fibers, graphene, nanoclay, and other reinforcing materials used in or available in cementing agents.

[0026] All embodiments and features described below can be combined in any technically feasible way.

[0027] In one embodiment, the carbon nanotube (CNT) hybrid material comprises a blend comprising a catalyst supported on at least one of a metal, metalloid, metal oxide or carbon support, a cementitious material and / or a material used or usable for the production or reinforcement of cement / cementitic materials, and CNTs on the blend.

[0028] Some embodiments include one or any combination thereof of the features described above and / or below. In the embodiments, the cementitious material includes hydraulic cement. In the embodiments, the hydraulic cement includes Portland cement. In the embodiments, the cementitious material includes auxiliary cementitious material (SCM). In the embodiments, the SCM includes fly ash. In the embodiments, the catalyst is supported on nanoalumina particles.

[0029] Some embodiments include one or any combination thereof of the features described above and / or below. In an embodiment, CNTs are grown on at least a portion of the blend in a rotary kiln reactor. In an embodiment, a supported catalyst and cementitious material or other material are blended and then fed into a reactor where CNTs are grown on this blend. In an embodiment, a supported catalyst is fed into a reactor where CNTs are grown on the supported catalyst to produce a hybrid material, which is then blended with cementitious material or other material. In an embodiment, the hybrid material is blended with cementitious material or other material by mechanical mixing of the two in powder form. In an embodiment, the hybrid material is blended with cementitious material or other material by preparing a suspension of the hybrid material in an aqueous solution and then mixing the suspension with cementitious material or other material. In an embodiment, the material includes a powder.

[0030] In another embodiment, the carbon nanotube (CNT) hybrid material comprises a fly ash material containing iron oxide and other metal oxides, and CNTs on the fly ash. In the example, the CNTs are grown on the fly ash in a rotary kiln reactor. In the example, the material comprises a powder.

[0031] In another embodiment, the carbon nanotube (CNT) hybrid material comprises a catalyst supported on alumina and CNTs grown on the catalytic site on the alumina, wherein the CNTs have an L / D aspect ratio of more than about 1000, or more than about 400, or more than about 700.

[0032] Some embodiments include one or any combination thereof of the above and / or below features. In the embodiments, prior to CNT growth, the alumina contains aggregates of basic alumina particles with a particle size of less than approximately 1 micron. In the embodiments, the CNTs induce deaggregation of the basic alumina particles within the CNT hybrid material. In the embodiments, the catalyst contains a transition metal. In the embodiments, the nanoalumina particles have a diameter of less than 70 microns. In the embodiments, the catalytically active metal supported on the alumina is less than 1% by weight. In the embodiments, the CNTs are grown on the alumina particles in a rotary kiln reactor.

[0033] Some embodiments include one or any combination thereof of the features described above and / or below. In an embodiment, a supported catalyst is supplied into a reactor where CNTs are grown on the supported catalyst to produce a hybrid material, which is then blended with a cementitious material or other material. In an embodiment, the hybrid material is blended with a cementitious material or other material by mechanical mixing of these two materials in powder form. In an embodiment, the hybrid material is blended with a cementitious material or other material by preparing a dispersion of the hybrid material in an aqueous solution, which is then mixed with the cementitious material or other material. In an embodiment, the material includes a powder.

[0034] Some embodiments include one of the above and / or below features, or any combination thereof. In embodiments, the material further comprises carbon black. In embodiments, the carbon black is mixed with the supported catalyst before the CNTs grow. In embodiments, the carbon black is present at a level of about 10% to about 50% by weight of the supported catalyst. In embodiments, the material comprises an aqueous dispersion of the hybrid material and carbon black. In embodiments, the aqueous dispersion is mixed with a cementitious material or other material. [Brief explanation of the drawing]

[0035] Various aspects of at least one embodiment are described below with reference to the accompanying drawings, which are not intended to be drawn to scale. The drawings include providing a description and further understanding of the various aspects and embodiments, are incorporated herein and constitute part of the invention, but do not define the limitations of the invention. In the drawings, identical or substantially identical components shown in different drawings may be represented by the same reference numerals. For clarity, not all components are shown in all drawings.

[0036] [Figure 1] This shows a rotary kiln catalytic reactor for the continuous production of CNT-Al2O3 hybrid materials. [Figure 2] For sample 2, the change in mechanical properties is shown as a function of the curing period. [Figure 3] Figures 3A to 3C show TGA analysis of Portland cement and Sample 1 before and after the reaction, respectively. [Figure 4] Includes SEM images taken at low magnification (25KX) and high magnification (100KX) corresponding to samples 1 and 2. [Figure 5] This is a cartoon representation of CNT-Al2O3 nanohybrid material and Portland cement containing CNT-Al2O3 nanohybrid. [Figure 6] Figures 6A–6C include SEM images of CNTs / CFs grown on fly ash particles. [Figure 7] This includes TGA analysis of CNTs / CFs grown on fly ash particles. [Figure 8] For sample 4, the change in mechanical properties is shown as a function of the curing period. [Figure 9] This shows the conductive properties of various CNT-Al2O3-cement samples. [Figure 10] Figures 10A and 10B show the piezoresistive response characteristics corresponding to samples 4 and 5, respectively. [Figure 11]Figures 11A and 11B include SEM images taken at 10KX and 50KX magnification, respectively, showing MWCNTs with a high aspect ratio. [Figure 12] The conductive properties of CNT-Al2O3-cement samples and CNT compositions prepared using various mixing methods are shown. [Figure 13] Figures 13A and 13B show the piezoresistive responses of CNT-Al2O3-cement samples and CNT compositions prepared using various mixing methods. [Figure 14] This shows the piezoresistive response of a CNT-Al2O3-carbon black cement sample. [Figure 15] This shows the piezoresistive response of a 60wt.%CNT-Al2O3-cement hybrid material. [Figure 16] Figures 16A to 16C contain SEM images taken at 5KX, 10KX, and 25KX magnification, respectively, of several different CNT-Al2O3 hybrid materials. [Modes for carrying out the invention]

[0037] The embodiments of the systems, methods, and apparatus discussed herein are not limited in application to the details of the configuration and arrangement of components described below or illustrated in the accompanying drawings. The systems, methods, and apparatus can be implemented in other embodiments and can be carried out in a variety of ways. Specific embodiments are provided herein for illustrative purposes only and are not intended to be limiting. In particular, functions, components, elements, and features discussed in relation to any one or more embodiments are not intended to preclude similar roles in other embodiments.

[0038] The examples disclosed herein can be combined with other examples in any way consistent with at least one of the principles disclosed herein, and references to “examples,” “several examples,” “alternative examples,” “various examples,” “one example,” etc., are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or property described may be included in at least one example. The appearance of such terms herein does not necessarily refer to the same example.

[0039] Furthermore, the expressions and terminology used herein are for illustrative purposes only and should not be considered limiting. Any singular reference herein to an embodiment, component, element, act, or function of a computer program product, system, or method may include plural embodiments, and any plural reference herein to an embodiment, component, element, act, or function may include singular examples only. Accordingly, singular or plural references are not intended to limit the systems or methods, their components, acts, or elements, that are currently disclosed. The use herein of “includes,” “contains,” “has,” “contains,” “involves,” and variations thereof means that the following items and their equivalents and additional items are included. References to “or” may be interpreted as comprehensive, so that the terms used with “or” can refer to a single term, multiple terms, or all of the terms described.

[0040] Figure 1 is a schematic diagram of an exemplary rotary tube reactor system 10 configured for use in achieving the hybrid material production process of the present disclosure. The following description illustrates certain aspects of the present disclosure but does not limit its scope.

[0041] The catalyst supply system 16 can operate as follows: Catalyst particles in powder form are supplied to the catalyst supply storage container 1. Subsequently, air is removed from the catalyst supply storage container 1 using an inert gas flow. The inert gas is preheated to a temperature between 60 and 150°C to allow for the removal of moisture from the catalyst during the purging process. The catalyst particles are then transferred to a second catalyst supply storage container 2 via a screw feeder. This device controls the amount of catalyst supplied to the reactor 12. The catalyst and reaction gas supply system 14 can operate as follows: Catalyst particles contained in the second catalyst supply storage container are supplied to the rotary tube reactor via a metal tube coupled to a vibrating catalyst particle supply system. The supply system is maintained in an inert gas atmosphere to suppress unwanted reactions. When other materials are added along with the catalyst to produce CNT hybrid materials, these other materials may be supplied together with the catalyst, or a separate parallel supply system may exist for the other materials. The second supply system (not shown) may be the same as the catalyst supply system, or it may be configured to supply these materials to the reactor after they have reached the reaction temperature. In some embodiments, the catalyst and other materials are pre-blended together before being supplied to the reactor in the manner described above for catalyst supply.

[0042] The tubes supplying the catalyst / other materials to the reactor are long enough so that their ends are located inside the rotating tube in the furnace's preheating zone. In some embodiments, the length of the inner tube is about 1 / 3 to 1 / 6 the length of the rotating tube in the furnace's high-temperature (reaction) zone. In some embodiments, the diameter of the inner tube is 1 / 3 to 1 / 2 the diameter of the rotating tube. In some embodiments, there are multiple heating zones in the reactor. In some embodiments, the reactor is heated by gas or electricity.

[0043] This configuration results in catalyst particles that reach the desired reaction temperature before contact with the reaction gas. The inner tube is made of special corrosion-resistant steel such as Inconel or titanium. The length and diameter of the inner tube relative to the rotating tube are selected to ensure efficient heat transfer during the catalytic process.

[0044] The temperature at the point of close contact between the process gas and catalyst particles is measured by a thermocouple introduced into a thermowell, indicated by a solid black line, at the reactor inlet block. Depending on the type of material being synthesized, a flyer or other mass distribution structure (schematically shown in Figure 1) can be placed in the rotating tube to improve mass and heat transfer between the solid particles and the reaction gas. Flyers can also improve the flow of material within the rotating tube. The residence time of the catalyst in the reactor is controlled by the rotation speed of the tube and its inclination angle.

[0045] The resulting product is separated from the gas at the outlet of the reactor, for example, using a gas / solid separator 22. A valve system discharges the product into a container (e.g., a purge container 28) that has an inert gas injection to remove ethylene and hydrogen and cool the material before packaging (e.g., in a storage drum 30).

[0046] The liquid condenser 24 is used to remove undesirable reaction by-products before hydrogen separation and recycling of the reaction gases.

[0047] Unreacted ethylene (or other carbon source reaction gases) and hydrogen are subsequently separated using an H2 membrane separator 26, which may contain organic polymers, nanoporous inorganic materials (ceramics, oxides, porous bicore glass, etc.), concentrated metals (Pd, and metal alloys), and carbon and carbon nanotube-based membranes.

[0048] The unreacted carbon source is then recycled by the recycling system 20, and the hydrogen can be used for other catalytic industrial processes, or for power or heat generation, or for transport. The recycled gas can contain ethylene and hydrogen, which facilitates the production reactions of carbon nanotubes and hybrid materials through improved heat transfer and catalytic activation. The amount of unused ethylene to be supplied to the reactor depends on the level of ethylene conversion in the production of carbon nanotubes / hybrid materials.

[0049] The gas composition can be detected at several points shown in Figure 1 using a mass spectrometer or other instrument. The composition data can be used for process control and for other purposes, such as recording gas components and quality. The gas composition data (and other variables) are input to a controller (not shown in Figure 1), which controls valves, heaters, particle feeders, and other process equipment (all not shown in Figure 1) used to maintain desired process conditions.

[0050] Further details of the reactor and its use are disclosed in U.S. Patent Application No. 17 / 954,899, filed on 28 September 2022, the entirety of which disclosure is incorporated herein by reference for all purposes.

[0051] The following detailed description of the examples illustrates, but is not limited to, the scope of this disclosure.

[0052] Example 1: Preparation of CNT-cement hybrid material

[0053] In this example, two CNT-Al2O3 hybrid materials were prepared as follows.

[0054] For the first material (Sample 1), fine powder of a CoMoFe / MgO-Al2O3-based MWCNT catalyst (described in U.S. Patent No. 9855551) was mechanically blended with Portland cement in a composition ratio of 20 / 80 wt.%. Then, CNT synthesis was carried out on this blend in a rotating tube reactor at 600°C in the presence of an ethylene stream of 80% V in hydrogen for a reaction time of 10 minutes. The second material (Sample 2) was prepared by mechanically blending Portland cement powder with a pre-synthesized hybrid MWCNT-Al2O3 material in a composition ratio of 20 / 80 wt.%. The compositions of both CNT-Al2O3-cement materials are shown in Table 2. In both cases, the alumina content was practically the same, and the MWCNT content was 5 wt.% for Samples 1 and 3, and 3 wt.% for Sample 2. The results of the mechanical performance tests are shown in Table 3.

[0055] [Table 2]

[0056] [Table 3]

[0057] Figure 2 shows the changes in mechanical properties of sample 2 as a function of curing time. Both flexural strength and modulus gradually increase with curing time, while compressive strength decreases during the first 7 days but remains constant thereafter. After a 28-day curing period, sample 2 has a flexural strength of +65%, a modulus of 45%, and a compressive strength of 20% higher than the standard cement mortar. The values ​​observed for sample 1 were 53%, 24%, and 15%, respectively.

[0058] Figures 3A and 3B show the results of thermogravimetric analysis (TGA) of Portland cement before and after treatment under reaction conditions of 675°C with a residence time of 10 minutes in the presence of an ethylene + H2 gas mixture. As shown in the figures, significant structural and compositional changes occur in the cement after the reaction. These structural changes can have a significant impact on the mechanical, electrical, and thermal conductivity properties of the concrete. This explains the results obtained for sample 1, which had a higher MWCNT content than sample 2, but showed less improvement in the mechanical properties of the cementitious material. Figure 3C shows the TGA analysis of sample 1, where the signal at 565°C may be attributable to MWCNTs.

[0059] Figure 4 includes four SEM images taken at low magnification (25KX) and high magnification (100KX) corresponding to samples 1 and 2, with the top row showing images of sample 1 and the bottom row showing images of sample 2. In sample 1, the formation of short MWCNTs (<200nm) with a diameter of approximately 25-45nm can be clearly confirmed. It can be observed that some cement particles are not in contact with the nanotubes. In contrast, in sample 2, it can be confirmed that a mesh of long MWCNTs with a diameter of 10-15nm surrounds and fills the spaces between cement particles.

[0060] Figure 5 is a simplified diagram of the preparation of a CNT-Al2O3 hybrid material and a Portland cement additive using a CNT-Al2O3 nanoparticle hybrid material. The catalyst contains primary or basic nanoalumina particles smaller than 1 micron, which typically aggregate to form particles with a particle size <100 microns. During catalyst preparation, the active metal deposits not only within the pores but also on the outer surface of the basic particles. During synthesis, the active metal catalyzes the decomposition reaction of the carbon source to CNT + H2. The growth of CNTs in all directions causes deaggregation of the basic alumina particles. The hybrid CNT-Al2O3 material is formed. Integration of the CNT-Al2O3 nanohybrid into Portland cement is achieved by deaggregation of the nanohybrid particles during aqueous dispersion preparation.

[0061] The same concept applies to other types of catalysts. For example, silica fume consists of nanometer-sized elemental SiO2 particles. When 10% nanoSiO2 was added along with a dispersant, a 26% increase in compressive strength after 28 days of curing was observed. The combined addition of nanoSiO2, large amounts of fly ash, and silica fume proved to be a very efficient method for achieving good mechanical performance and an economical method using both additives.

[0062] Example 2: Growth of CNTs on fly ash particles Figures 6A to 6C are SEM images corresponding to the synthesis of CNTs and CFs on fly ash particles. Fly ash is a coal combustion product consisting mainly of fine metal oxide particles, discharged with the exhaust gas from coal-fired boilers. SiO2 (both amorphous and crystalline forms), Al2O3, Fe2O3, and CaO are the main chemical components present in fly ash. Fly ash can replace some or most of Portland cement in concrete production, resulting in higher porosity in the initial stages and improved mechanical strength, chemical resistance, and durability.

[0063] CNT synthesis was carried out in a rotating tube reactor at 650°C in the presence of an ethylene stream with 80% V in hydrogen for a reaction time of 10 minutes. Iron oxide particles contained in the fly ash acted as a catalyst.

[0064] As shown in Figure 6A, not all particles exhibit CNT / CF growth. Fly ash particles with CNT / CF are clearly shown in Figure 6B. Images taken at the highest magnification (Figure 6C, 25KX) show the formation of braids of CNTs and CFs on the surface of the fly ash particles, with a length of approximately 1–1.5 microns and a diameter of several hundred nanometers. The CNT / CF content on the fly ash particles is approximately 9 wt.%, as determined by TGA analysis (Figure 7).

[0065] Example 3: Influence of CNT aspect ratio on mechanical properties, electrical properties, and piezoelectric response

[0066] In this example, three CNT-Al2O3 hybrid materials (Samples 3, 4, and 5) with different CNT content (15, 20, and 25 wt.%) relative to the weight of alumina, as shown in Table 4 below) were synthesized following the procedure described in Example 1. The amount of carbon deposited on the Al2O3 nanoparticles varied between 3 and 10 minutes, depending on the reaction time.

[0067] CNT-Al2O3 hybrid material powders were mechanically blended with Portland cement in proportions such that the MWCNT content in each sample was the same (0.15 wt.%). Table 4 shows the weight composition and aspect ratio characteristics of each sample. As the carbon yield increased, the length of the tubes gradually increased, but the diameter remained unchanged (10 ± 3 nm). As a result, the CNT aspect ratio increased as a function of the increase in carbon yield during the synthesis of the CNT-Al2O3 hybrid material.

[0068] [Table 4]

[0069] Mechanical performance tests (flexural strength, modulus of elasticity, and compressive strength) were performed on samples 3, 4, and 5. The results are shown in Table 5. The mechanical properties of the cement significantly improved as the aspect ratio (L / D) increased.

[0070] Figure 8 shows the change in mechanical properties of sample 4 as a function of the curing period.

[0071] As the curing period increases, the rate of increase in flexural strength and modulus of elasticity becomes larger compared to the mortar standard. In the case of compressive strength, the rate tends to decrease from 36% to 19% in the first 7 days, and then tends to stabilize. After a 28-day curing period, the flexural strength, modulus of elasticity, and compressive strength values ​​were 81%, 50%, and 22%, respectively. These results show an improvement in flexural strength and modulus of elasticity compared to the sample prepared in Example 1, where the MWCNT content in the cement of Samples 1 and 2 was 5 wt.% and 3 wt.% respectively, compared to 0.15 wt.% for Samples 3 and 4.

[0072] [Table 5]

[0073] Figure 9 shows the electrical conductivity characteristics of samples 3, 4, and 5 under various curing periods. The most conductive material was sample 5, which had the highest CNT aspect ratio (730).

[0074] The results of the piezoresistive response tests corresponding to samples 4 and 5 are shown in Figures 10A and 10B, respectively. Sample 5 shows the change in resistivity (Δρ / ρ) when the sample is subjected to various stress levels. o This indicates that ) is the largest.

[0075] Example 4: Influence of CNT-Al2O3 cement preparation method

[0076] In this example, a MWCNT-Al2O3 hybrid material with 35 wt.% MWCNTs and an L / D ratio > 1000 was used. Figures 11A and 11B are EM images of the MWCNT-Al2O3 hybrid material taken at various magnifications (10KX and 50KX, respectively). Long MWCNTs exceeding 10 microns in length and alumina nanoparticles with a diameter of approximately 500 nm were observed.

[0077] Aqueous suspensions were prepared by mixing 0.10 or 0.15 wt.% of the MWCNT-Al2O3 hybrid material with 0.4% of the cement's superplasticizer using 350 ml of H2O. Dispersions were prepared using sonication or an intensive mixer. In the intensive mixer, the dry form of the MWCNT-Al2O3 hybrid material and the mixed water were placed in a bowl and mixed at a speed of 285 rpm for 10 minutes. Dry materials (cement and sand) were added to the mixture for the preparation of mortar specimens.

[0078] Figure 12 shows the change in electrical conductivity as a function of curing time for samples prepared according to various mixing techniques and CNT content in cement. Increasing the CNT content in cement from 0.10 wt.% to 0.15 wt.% reduces the resistivity of the material by approximately 39%. For samples containing 0.15% CNTs in cement, no significant difference in electrical conductivity was observed when using ultrasonic treatment or an intensive mixer. No significant difference in piezoelectric response was observed among samples prepared using various mixing devices. See Figures 13A and 13B (sonic treatment and intensive mixing, respectively). These results clearly demonstrate that CNT-Al2O3 materials can be easily dispersed using conventional mixing devices.

[0079] Example 5: CNT-Al2O3-Carbon Black Hybrid Material for Smart Concrete

[0080] As described above, carbon black (CB) has been used as an additive to enhance electrical conductivity and piezoelectric response in the production of smart concrete. In this example (sample 6), catalyst powder was mixed with carbon black in a fixed ratio (40% by weight of the catalyst), and CNT synthesis was carried out in a rotary tube reactor under the reaction conditions described in Example 1. Subsequently, an aqueous dispersion was prepared using the hybrid material CNT-Al2O3-CB, and then mixed with cement powder according to the same procedure as used in Example 4.

[0081] Table 6 shows the weight composition of the hybrid material CNT-Al2O3-CB and the cement mixture. The total conductive carbon composition is 0.13 wt.% (MWCNT = 0.08 wt.% and CB: 0.05 wt.%), which is consistent with the MWCNT content of samples 3-5 (cement). Note that the MWCNT composition is lower than that of samples 3-5.

[0082] [Table 6]

[0083] [Table 7]

[0084] Table 7 shows the electrical and mechanical conductivity characteristics of the hybrid material (CNT-Al2O3-carbon black) of sample 6 in cement as a function of curing time. Compared with the results obtained for sample 5, an improvement in the conductivity characteristics of the cement is observed. The piezoelectric response of sample 6 (Figure 14) also increased significantly (from 3.9% to 7.82%).

[0085] Table 7 also shows the improvement in mechanical properties (in percentage) compared to the mortar standard. Flexural strength and elastic modulus properties also showed significant improvements of approximately 74% and 55%, respectively, compared to the mortar standard after a 28-day curing period. Compressive strength increased by 4%.

[0086] Example 6

[0087] In this example, a MWCNT-Al2O3 hybrid material containing 60 wt.% MWCNTs was prepared and a series of experiments were conducted in combination with Portland cement, the CNT hybrid material, and 30 wt.% fly ash. Table 8 shows the changes in mechanical properties (compared to the Portland cement standard) of various prepared samples obtained after a 28-day curing period. Table 8 also shows the improvement (in %) of mechanical properties compared to the mortar standard. Mechanical strength properties increased slightly after adding 30% fly ash to the mortar. Adding 0.1 wt.% of the CNT-Al2O3 hybrid material to the mortar increased flexural strength, elastic modulus, and compressive strength by approximately 88%, 82%, and 11%, respectively. This material also showed the highest piezoelectric response value (Figure 15). Addition of 30 wt.% fly ash and the CNT-Al2O3 hybrid material to the mortar resulted in an improvement of approximately 11% in compressive strength properties and an increase of approximately 28% and 25% in flexural strength and elastic modulus values, respectively.

[0088] [Table 8]

[0089] Comparing the results obtained using MWCNT-Al2O3-CB (Example 5) and CNT-Al2O3 (Example 6), it is clear that despite the difference in total carbon content in the cement (0.13% for MWCNT-Al2O3-CB and 0.08 wt.%) for the CNT-Al2O3 hybrid material, superior performance benefits in mechanical strengthening, electrical conductivity, and piezoelectric properties are obtained.

[0090] Example 7

[0091] In this example, CNT-Al2O3 hybrid materials having various CNT compositions were synthesized by mechanically blending alumina powder with the CoMoFe / MgO-Al2O3 catalyst powder used in Example 1. The composition of alumina powder in the blend varied from 0 to 95 wt.%. The particle sizes of both materials varied between 1 and 10 microns in diameter (average = 3 to 4 μm) as determined by laser scattering techniques. CNT synthesis was carried out in a rotating tube reactor at a temperature of 650°C in the presence of a gas stream containing 80% V ethylene and 20% V hydrogen for a reaction time of 10 minutes.

[0092] Table 9 shows the synthesis results of CNT-Al2O3 hybrid materials obtained from various catalyst-alumina blends. The results clearly show that diluting the catalyst particles with alumina powder by 20% maintains a CNT yield of 80 wt.% or higher. As the alumina composition in the blend increases, the CNT yield tends to gradually decrease until the CNT composition in the hybrid material reaches 27% for a 95% Al2O3 and 5 wt.% catalyst blend.

[0093] [Table 9]

[0094] SEM images of the CNT-Al2O3 hybrid materials in Table 9, taken at various magnifications (5K, 10K, and 25K), are shown in Figures 16A to 16C, respectively, for alumina compositions in the blend ranging from 0% to 90 wt.% (0%, 20%, 40%, 60%, 80%, and 90%). When alumina is not blended with catalyst particles, the formation of a compact mesh of highly entangled CNTs is observed. When alumina powder is gradually blended with catalyst particles, the formation of rod-shaped CNT structures is observed. These CNT rods separate from each other as the alumina content in the blend increases. The diameter of the CNTs remains constant for all analyzed samples (8–13 nm), but they become longer. Alumina and catalyst particles with a particle size of approximately 0.5–2 microns were observed at a higher rate in samples containing more than 80 wt.% alumina. Figure 16C shows clear evidence of open mesh formation of CNTs when the alumina content in the blend exceeds 20 wt.%. These tubes are easily unraveled and require less energy for dispersion. Compared to prior art, this material can be readily integrated into suspensions, powders, or granular cement particles.

[0095] While several aspects of at least one embodiment have been described above, it should be understood that various changes, modifications, and improvements are readily apparent to those skilled in the art. Such changes, modifications, and improvements are intended to be part of this disclosure and within the scope of the invention. Accordingly, the foregoing description and drawings are illustrative only, and the scope of the invention should be determined by the proper interpretation of the appended claims and their equivalents.

Claims

1. A carbon nanotube (CNT) hybrid material, A blend comprising a catalyst supported on at least one of a metal support, a metalloid support, a metal oxide support, or a carbon support, and at least one material selected from the group consisting of cementitious materials, materials used in the production of cementitious materials, and materials used to reinforce cementitious materials, A carbon nanotube (CNT) hybrid material containing CNTs in a blend.

2. The cementitious material is the material according to claim 1, wherein the cementitious material includes hydraulic cement.

3. The material according to claim 2, wherein the hydraulic cement includes Portland cement.

4. The cementitious material is the material according to claim 1, wherein the cementitious material includes an auxiliary cementitious material (SCM).

5. The material according to claim 4, wherein SCM includes fly ash.

6. The catalyst is supported on nanoalumina particles, as described in claim 1.

7. The material according to claim 1, wherein the CNTs are grown on at least a portion of the blend in a rotary kiln reactor.

8. The material according to claim 7, wherein a supported catalyst and a cementitious material are blended and then supplied into a reactor where CNTs are grown on the blend.

9. The material according to claim 7, wherein a supported catalyst is supplied into a reactor, where CNTs are grown on the supported catalyst to create a hybrid material, and the hybrid material is then blended with a cementitious material.

10. The hybrid material is a blend of a cementitious material and the material according to claim 9, which is a blend of the two in powder form by mechanical mixing.

11. The material according to claim 9, wherein the hybrid material is blended with a cementitious material by preparing a dispersion of the hybrid material in an aqueous solution and then mixing the dispersion with the cementitious material.

12. A carbon nanotube (CNT) hybrid material, A fly ash material containing iron oxide and other metal oxides, A carbon nanotube (CNT) hybrid material containing CNTs on fly ash.

13. The material according to claim 12, wherein the CNTs are grown on fly ash in a rotary kiln reactor.

14. A carbon nanotube (CNT) hybrid material, A catalyst supported on alumina, A carbon nanotube (CNT) hybrid material comprising CNTs grown on a catalytic site on alumina, wherein the CNTs have an aspect ratio of over 1000.

15. The material according to claim 14, wherein, prior to CNT growth, the alumina comprises aggregates of basic alumina particles having a particle size of less than approximately 1 micron.

16. The material according to claim 15, wherein the CNTs cause deaggregation of the basic alumina particles within the CNT hybrid material.

17. The material according to claim 14, wherein the nanoalumina particles have a diameter of less than 70 microns.

18. The material according to claim 14, wherein the catalytically active metal supported on the alumina is less than 1% by weight.

19. The material according to claim 14, wherein the CNTs are grown on alumina particles in a rotary kiln reactor.

20. The material according to claim 19, wherein a supported catalyst is supplied into a reactor, where CNTs are grown on the supported catalyst to create a hybrid material, and the hybrid material is then blended with a second material selected from the group of materials consisting of cementitious materials, materials used in the production of cementitious materials, and materials used to strengthen cementitious materials.

21. The material according to claim 20, wherein the hybrid material is blended with a second material by mechanical mixing of the two in powder form.

22. The material according to claim 20, wherein the hybrid material is blended with a second material by preparing a dispersion of the hybrid material in an aqueous solution and then mixing the dispersion with the second material.

23. The material according to claim 14, further comprising carbon black.

24. The material according to claim 23, wherein carbon black is mixed with a supported catalyst before the CNTs grow.

25. The material according to claim 24, wherein carbon black is present at a level of about 10% to about 50% by weight of the supported catalyst.

26. The material according to claim 24, comprising an aqueous dispersion of a hybrid material and carbon black.

27. The material according to claim 26, wherein the aqueous dispersion is mixed with the cementitious material.

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