This description relates to a micro-scale vehicle having a propulsion device.
Various techniques have been used to create micro-scale vehicles and propulsion devices thereof. However many of these micro-scale vehicles do not have the capability to maneuver in a desirable fashion because of the types of propulsion devices that have been developed and used in these vehicles. Thus, a need exists for systems, methods, and apparatus to address the shortfalls of present technology and to provide other new and innovative features.
In one general aspect, an apparatus can include a controller and a fuel container. The apparatus can include a propulsion device including a carbon nanotube structure including a parallel array of micro-channels configured to receive the fuel. Each of the micro-channels included in the array of micro-channels can achieve a length:width aspect ratio greater than 40:1 and can include a catalyst.
The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.
In some implementations, the propulsion device 110 can function as a propulsion device for the vehicle 100. In some implementations, the propulsion device 110 can be configured to provide propulsion in one or more directions. In some implementations, the propulsion device 110 can be used for positioning and or thrust. In some implementations, the propulsion device 110 can provide propulsion in addition to other propulsion devices such as a propeller. In some implementations, the propulsion device 110 can be used in conjunction with one or more steering mechanisms.
In some implementations, the propulsion device 110 can include, or can be, a carbon nanotube (CNT) structure. In some implementations, the propulsion device 110, or a portion thereof, can be referred to as a microfilter. In some implementations, the propulsion device 110 can be a CNT structure that includes, or can be, a multi-walled carbon nanotube microarray membrane (CNT-MM). In some implementations, the propulsion device 110 can include a two-dimensional array of micro-channels (which can be lumens therethrough). The micro-channels can be aligned in parallel with one another within the propulsion device 110. A direction of thrust or propulsion from the micro-channels can be aligned along a lumen defined by the micro-channels.
In some implementations, one or more of the micro-channels of a CNT structure included in the propulsion device 110 can have a length (or micro-channel):width (across the lumen defined by the micro-channel) aspect ratio greater than 10:1 (e.g., 40:1, 50:1, 100:1, 200:1). In some implementations, one or more micro-channels of the propulsion device 110 can have a different aspect ratio. For example, a first micro-channel of the propulsion device 110 can have a first aspect ratio and a second micro-channel the propulsion device 110 can have a second aspect ratio. As another example, a first micro-channel of a first CNT structure of the propulsion device 110 can have a first aspect ratio and a second micro-channel of a second CNT structure of the propulsion device 110 can have a second aspect ratio. An example of a CNT structure 300 with a high aspect ratio is illustrated in at least
In some implementations, the propulsion device 110 can include multiple CNT structures that are aligned (e.g., stacked) in series or aligned laterally. In a series configuration, a microchannel (e.g., a lumen of the microchannel) associated with a first CNT structure can be aligned along the same line (or substantially along the same line) as a microchannel associated with a second CNT structure. In other words, microchannel associated with the first CNT structure can be axially aligned with microchannel of the second CNT structure. Said differently, the CNT structures may be stacked along a direction that is aligned with a propulsion direction. In a lateral configuration, a microchannel associated with a first CNT structure can be aligned parallel to (and lateral to) a microchannel associated with a second CNT structure. In some implementations, a lateral configuration can be referred to as a vertical configuration because the CNT structures may be vertically stacked one above the other, which is orthogonal to a horizontal propulsion direction. In other words, the CNT structures may be stacked along a direction that is orthogonal to a propulsion direction. In some implementations, the propulsion device 110 can include multiple CNT structures that are aligned nonparallel to one another such that a first CNT structure has a microchannel aligned in a first direction and a second CNT structure is aligned in a second direction nonparallel to (e.g., orthogonal to) the first direction.
As shown in
As shown in
In some implementations, the control mechanism 130 can include a processor such as a microcontroller. In some implementations, the control mechanism 130 can include one or more wireless devices configured to transmit and/or send wireless communications. In some implementations, the control mechanism 130 can include an electronic storage component such as a memory.
Although not shown in
As shown in
In some implementations, the vehicle 100 can include a variety of payloads. For example, the vehicle 100 can include a payload for delivery to a location.
In some implementations, the utility of the vehicle 100, which can be an unmanned MUV, can be important for exploring confined spaces. In some implementations, the vehicle 100 can have a desirable spatial agility when maneuvers require, for example, burst-propulsion.
In this implementation, the vehicle 200 includes a propulsion device 210 and a fuel container 220. The propulsion device 210 is included in a housing 214. Although illustrated in this implementation as being outside of the housing 214, in some implementations, the fuel container 220 can also be included within the housing 214. As shown in
Referring back to
In some implementations, the vehicle 100 can be configured for exploration of confined spaces such as shipwrecks, submerged oil pipelines, and various military purposes. In some implementations, the vehicle 100 can be configured to perform tight radius turns, burst-driven docking maneuvers, and low-speed course corrections, in contrast to some propeller-based systems that can be limited in such abilities and can be often used for long-endurance missions. These relatively complex motions often require energy-dense fuels, which can be quickly and efficiently utilized to provide sudden bursts of propulsion. Such energy-dense fuels/reagents include hydrogen peroxide (H2O2), methanol, hydrocarbons, and/or so forth and can be contained in the fuel container 120.
As a specific example, the decomposition of H2O2 as a fuel in the fuel container 120 used for locomotion in micro-scale applications can be of particular interest because of its scalability, as well as possessing a relatively large power density (up to 45 times that of Ni—Cd batteries in MUVs). In addition, H2O2 can be an environmentally friendly fuel, expending only green by-products (i.e., oxygen, O2, and water) during decomposition. In some implementations, when exposed to a metal catalyst such as platinum (Pt), H2O2 can be broken down in an exothermic reaction into O2 (and water) which provides thrust through the significant volumetric change relative to the liquid fuel within the propulsion device 110.
The propulsion device 110 of the vehicle 100 can have a structure that relies on transport-enhancing mechanisms to decompose a fuel such as a H2O2 fuel. The propulsion device 110 can have a catalytic structure that employs transport-enhancement, but that can be fabricated for burst-propulsion of MUVs and their associated payloads. Thrust required for these applications is provided by the fabrication of scalable catalytic structures which offer the high surface area to fuel volume ratios required for burst-propulsion, while maintaining a small volumetric profile.
Carbon nanotube (CNT)-templated microfabrication, which can be included in the propulsion device 110, is a new approach to constructing high aspect ratio structures that capitalizes on the very large length to diameter ratios present for carbon nanotubes. For modest growth lengths of, for example, 1 mm and a nominal spacing of, for example, 100 nm between carbon nanotubes, aspect ratios of, for example, 10-10,000 are achievable for vertically aligned growth. When combined with lithographically defined growth, almost any aspect ratio in this range can be realized. This range is significantly better than typical etching techniques for high aspect ratio structures such as Deep Reactive Ion Etching (DRIE) and offers distinct advantages over Lithography, Electroplating, and Molding (LIGA) in cost, time, and scalability. Using patterned CNTs as a scaffold, additional materials can be coated on or infiltrated into the forest, making these structures rigid and reinforced. The conditions and duration of an infiltration procedure can be controlled to result in highly dense or highly porous regions. Therefore two-tier, porous materials can be constructed with CNT-templated microfabrication; larger (micron-scale) spacings controlled by lithography and smaller (nanometer-scale) spacings controlled by carbon nanotube forest density and subsequent infiltration. Multi-walled carbon nanotube microarray membranes (CNT-MMs) fabricated by this method thereby provide a versatile microstructure for reagent-based burst-propulsion. Thus, this distinct CNT-templated microfabrication process enables the growth of aligned, high aspect ratio CNT micro-channel membranes—a three-dimensional microstructure that cannot be formed from conventional, stand-alone CNT fabrication techniques such as screen-printing, electrospraying, alcohol catalytic chemical vapor deposition, plasma-enhanced chemical vapor deposition, self-assembled monolayer linking, and thermal crosslinking.
CNT-MM structures, which can be included in the propulsion device 110, can be functionalized using electroless deposition of a catalyst such as Pt onto CNTs to provide highly catalytic microstructures for burst-propulsion applications. For example, deposition by the reduction of chloroplatinic acid can be one-step process offering several advantages. Most notably is that the morphology and density of, for example, Pt nanoparticles on carbon structures is controllable. Similar depositions can be performed on highly ordered 3D graphene. This technique can provide effective electrocatalytic functionalization for scalable substructures. Furthermore, Pt deposited in this fashion on nanocellulose is highly durable during MUV propulsion tests using, for example, 30% w/w H2O2. Based on this, electroless deposition of Pt nanoparticles by the reduction of chloroplatinic acid can provide a controllable, scalable, and mechanically robust catalytic structure for the aggressive decomposition of H2O2 fuel at relatively high concentrations (e.g., 50% w/w).
Following deposition, CAT-CNT-MMs, which can be included in the propulsion device 110, can be inspected and characterized using both scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In some implementations, for example, Pt-CNT-MMs can have continuous coverage of Pt on the CNT micro-channels. These catalytic structures can have hydrophobicity (from water contact angle analysis), electroactive specific surface area (from cyclic voltammetry (CV) experiments), surface area calculated (from Brunauer-Emmett-Teller (BET) analysis on nitrogen adsorption experiments), as well as effective activation energy (from H2O2 decomposition profiles).
As noted above, an example of the vehicle 100 can have an average thrust (e.g., a maximum average thrust) of 0.209±0.049 N using, for example, eight, inline Pt-CNT-MMs exposed to 50% w/w H2O2 in a manually driven high burst flow. This generated thrust falls within the milli-Newton thrust range typically required for MUV propulsion, while leaving the possibility for thrust generation improvement through the inclusion of additional Pt-CNT-MMs in the reaction chamber. Accordingly, the vehicle 100 can be a union of CNT-templated microfabricated structures with electroless chemical deposition of catalytic Pt nanoparticles for thrust generation by the decomposition of H2O2 for MUVs.
At least some aspects of the propulsion device 110 can be fabricated using CNT-templated microfabrication. Aspects of the microfabrication process are illustrated in at least
The microfabrication process can include exploiting lithographically defined metal (e.g., iron (Fe)) catalyst regions, whereon vertically aligned CNT forests can be, for example, grown in a quartz tube furnace with, for example, ethylene gas (C2H4 at 750° C.) acting as the carbon feedstock gas (shown in at least
In summary,
In some implementations, the CNT-MMs included in the propulsion device 110 can be patterned using a close-packed, diamond-shaped channel mask. In some implementations, the CNT-MMs can have a different profile shape or pattern (e.g., a circular pattern, a hexagonal pattern, a square or rectangular pattern, an irregular or regular pattern of different shapes or profiles) (when viewed along a direction of the microchannels). In some implementations, a hydraulic diameter of greater than a few microns, or less than a few microns can be defined within the CNT-MMs. In some implementations, CNT-MMs with a wall thickness (e.g., minimum wall thickness) of a few microns or less can be defined (e.g., ˜2.0 μm). In some implementations, additional CNT-templated microfabrication parameters can be used to define CNT-MMs with a variety of dimensions (e.g., approximately 600 μm thick with channel aspect ratios of 150:1).
In some implementations, reactive ion etching (ME) can be used to remove the carbon floor layer formed at the base of the CNT-MM against the substrate during the CVD infiltration process. In some implementations, the ME process can also function to enhance subsequent metallic deposition, therefore, the face opposite the carbon floor layer can also be etched.
In some implementations, nanostructured morphologies of a catalyst (e.g., Pt catalyst) can be tuned and subsequently exploited to enhance electrocatalytic performance of the propulsion device 110. Specifically, needle-like or urchin-like structures display favorable electrocatalytic activity because of their large surface area and desirable geometry (corners, edges, etc.). As a specific example, this morphology is desirable for H2O2 decomposition, and can be achieved by chemically depositing Pt under conditions of relatively low solution pH (≦2.5) and relatively high Pt loading concentration (≧20% w/w Pt—C) resulting in growth of relatively dense Pt nanowires (approx. 10-30 nm in length and 3-4 nm in diameter) on non-porous, singular carbon spheres, carbon nanotubes, and cellulose paper as well as three-dimensional graphene.
Specifically, highly catalytic urchin-like Pt can be deposited as nanoparticles onto the CNT-MMs. In some implementations, the Pt can be deposited deep within the CNT microchannels. Electroless deposition can be performed on a per-mass basis and can involve CNT-MM submersion in a static solution of relatively low pH (<1.5) and high Pt molarity (H2PtCl6.(H2O)6 at ˜10 mM) for each deposition. Dense coverage of urchin-like Pt nanoparticles is produced as the reduction time of the Pt precursor is increased. This is realized when there is an abundance of H+ ions in solution (i.e., low pH). Given that no base additives may employed in some implementations, solution pH can be inversely related to Pt molarity. Thus, for a given volume of solution, the desired Pt nanoparticle morphology and density can be obtained by increasing the Pt—C loading of the solution (25-30% w/w Pt—C) and maintaining a low solution pH (<1.5).
Due to their high surface energy and micro/nanoscale surface roughness, CNT structures that can be included in a propulsion device 110 such as shown in
In some implementations, hydrophobic disposition of CNT substrates can be altered by ultraviolet assisted ozone treatment, ME, chemical oxidation and subsequent functionalization, chemical etching, and by patterning the CNTs to form hydrophobic topologies. In some implementations, O2 ME can be used because it allows for a controllable means of modifying the CNT surfaces to be hydrophilic. Accordingly, in some implementations, each CNT-MM included in the propulsion device 110 can be exposed to a brief O2 etch after growth to improve the penetration of aqueous solution into the CNT-MM pores during Pt deposition.
In some implementations, the hydrophobic nature of the CNT-MMs can be observed during each stage of the fabrication process.
In some implementations, ultrapure water droplets (10 μL) can be dispersed onto separate regions across the surface of a CNT-MM propulsion device before O2 etching. In some implementations, the water droplets may not appear to wet the CNT-MM channels at any appreciable rate indicating that the surface appeared to be hydrophobic as shown in
Specifically,
In some implementations, post O2 etched CNT-MM propulsion devices can have hydrophilic behavior as water can spread along the top surface of the membrane and then wick through to the bottom surface of the membrane as shown in
In some implementations, current-voltage analysis can be employed to quantify the electroactive surface area for CNT-MMs fabricated under prescribed conditions. In some implementations, CV tests can be conducted for CNT-MM propulsion devices acting as the working electrode, a Ag/AgCl electrode acting as the reference electrode and a coiled Pt wire as the counter electrode. In some implementations, initial tests can be ere performed using a ferricyanide solution acting as mediator.
In some implementations, electroactive surface areas (EASAs) can be calculated using the Randles-Sevcik Equation (Equation 1), where ip is the peak redox current A, n is the number of electrons transferred per redox reaction, A is the EASA cm2, D is the mediator diffusion coefficient (6.7×10−6 cm2 s−1 for a ferricyanide solution of 4 mM Fe(CN)63− and 1 M KNO3), c is the solution concentration mol cm−3, and v is the potential scan rate V s−1.6 CVs obtained with a potential scan that can be cycled between −0.2 and 0.6 V versus the Ag/AgCl reference electrode with a scan rate of 10 mV s−1 (See
i
p=2.686×105n3/2AcD1/2v1/2 (1)
In some implementations, to allow for comparison between CNT-MMs of any dimension as well as account for variations in growth across the CNT-MM surface, CV data can be normalized according to propulsion device mass. Hence, EASA calculations can be used to determine the electroactive specific surface area (SSA, EASA per unit mass) for each propulsion device. In some implementations, CNT-MM can have an average SSA of 293±28 cm2 g−1.
In some implementations, a linear relationship can exist between the magnitude of the normalized anodic peak current and the square root of the scan rate for the CNT-MM propulsion device within the ferricyanide mediator solution as shown in
CNT-MM propulsion devices can exhibit a type II nitrogen adsorption isotherm indicative of a macroporous material, with an average calculated BET surface area of, for example, 61 m2 g−1 and a pore volume of 0.118 cm3 g−1. Table 1 shows the average calculated BET surface area for CNT-MM propulsion devices with comparison to similar structures. Most notably, the BET surface area for the CNT-MMs is approximately half that of pristine CNTs. This is likely attributable to the carbon-infiltration step of the CNT-MM fabrication process, which not only contributes additional mass throughout the structure, but may also cause a reduction in surface area by joining adjacent CNTs. However, the infiltration procedure allows for controllable porosity (mass/surface area) and improved structural integrity.
The effectiveness and durability of catalysts for H2O2 decomposition within the propulsion device 110, for example, can be dependent upon multiple factors including material composition, surface area, and reaction temperature. Namely, catalytic performance can be an ability to reduce the activation energy required for a given chemical reaction. A variety of catalysts can be used for lowering the activation energy associated with H2O2 decomposition including metal catalysts (e.g., Pt, Pd, Au and Ag) as well as metal oxide catalysts (e.g., MnO2, Fe2O3, K2Cr2O7). In some implementations, although highly effective at lowering the activation energy of H2O2 decomposition, metal oxide catalysts are consumed during H2O2 decomposition and therefore would not be able to provide recurring thrust for MUV propulsion. Accordingly, in some implementations, metal catalysts can be used in the propulsion device 110. In some implementations, the effectiveness of metal catalysts for H2O2 decomposition can be proportional to the exposed catalyst surface area. In some implementations, in the case of Pt catalysts, more exposed metal correlates to more free catalytic sites available for Pt—(OH) and Pt—(H) binding—two reactions that are involved in the eight kinetic steps in H2O2 decomposition with Pt metal catalysts. Furthermore, in some implementations, the reaction rate for the decomposition of H2O2 can tend to dramatically increase as the temperature of the exothermic reaction increases. In some implementations, this phenomenon can be due to the auto decomposition of H2O2 at elevated temperatures and to the fact that oxygen solubility remains low even at higher temperatures. Hence the reaction rates of H2O2 decomposition can tend to increase due to the conflation of both increased surface area and reaction temperature in some implementations.
In some implementations, transport processes may also alter the performance of the Pt-CNT-MM catalysts within the propulsion device 110, including the following: transport of reactants from the main fuel stream to the Pt-CNT-MM surface; transport of reactants within the CNT microchannels to the Pt metal surface; adsorption/desorption of reactants/products at the Pt metal surface; transport of desorbed products from the Pt metal through the CNT microchannels; and transport of desorbed products from within the CNT microchannels to the main stream of fluid. Consequently, the activation energy can change according to the rate of flow introduced into the reaction chamber. Therefore, an effective activation energy of the Pt-CNT-MM as measured within a convective fuel flow field can mimic, in part, the convective flow field that would be experienced in an actual MUV reaction chamber. In some implementations, the impact of convection on activation energy may not be considered and often the conditions of fluid stirring are not provided. In some implementations, the activation energy under flowing conditions can be equivalent to the effective activation energy, though specific to the conditions of the flow field.
In some implementations, the effective activation energy (Ea) for H2O2 decomposition by the micro/nanostructured Pt-CNT-MMs can be empirically determined. In some implementations, H2O2 decomposition testing can be performed on replicate Pt-CNT-MM propulsion devices (referred to as Propulsion devices A, B, and C). Each propulsion device can be exposed to 1% w/w H2O2 solution at three different temperatures (0° C., 17.5° C. and 35° C.) in a test flask while the differential pressure, resulting from O2 generation during decomposition of H2O2, can be monitored (Equation 2).
2H2O2→2H2O(l)+O2(g) (2)
The measured differential pressure generated by the reaction products (taken as the average of two or more test runs per propulsion device) can be plotted for comparison against two distinct control propulsion devices, both tested at 35° C. (shown in
Differential pressure data shown in
where [H2O2] is the quantity of hydrogen peroxide remaining in solution at time t, [H2O2]o is the initial quantity of H2O2 in solution, and kobs is the reaction rate constant s−1 over time.
The natural log of the Arrhenius Equation (Equation 4) with the calculated observed reaction rate constants are used to calculate the effective activation energy.
Here, Ea is the effective activation energy of the catalyst J mol−1, and A is the pre-exponential factor s−1. By plotting the natural log of the observed reaction rate constant for each test run as a function of inverse temperature for Propulsion device A, the effective activation energy (26.96 kJ mol−1) can be acquired from the slope of the linear fit of the data (shown in
Table 2, provides an overview of the calculated decomposition kinetics for a Pt-CNT-MM (Propulsion device A), including the entropy of activation, ΔS (J mol−1 1; where ΔS=R·ln(A)). This effective activation energy of 26.96 kJ mol−1 can improve upon similar nanostructured surfaces such as those comprised of graphene (28.8 kJ mol−1) and Pt/palladium nanoparticles on Nafion (34.0-36.3 kJ mol−1). Furthermore, the effective activation energy is lower than a Pt-paper catalyst (29.5 kJ mol−1) where similar Pt nano-urchins can be deposited on cellulose sheets—such improvement can be due to the higher surface area achieved by the three dimensional architecture created by the CNT microchannels of the CNT-MM as opposed to the planar structure of the cellulose sheets.
Specifically,
The MUV submersible 800 illustrates the ability of Pt-CNT-MMs to produce thrust via H2O2 decomposition. The MUV submersible 800 can be fabricated via, for example, a 3D printer. As shown in
In some implementations, heterogeneous catalytic reactions can be heavily dependent on the mass transfer of reactant (fuel) to the catalytic surface. Thrust generated via decomposition of H2O2 fuel can therefore be dependent on the introduction rate of the fuel to the Pt-CNT-MM surface. This introduction rate can be modified in at least three ways—by changing the fuel concentration, changing the fuel flowrate, and/or by changing the available catalytic surface area. Accordingly, propulsion can be performed using a variety of H2O2 concentrations (e.g., 20, 35, and 50% w/w) at a variety of average flowrates (e.g., 10 mL s−1) for a variety of combinations of CNT structures (e.g., one, two, four, six, or eight Pt-CNT-MMs). Also, propulsion can be manually driven flowrate (e.g., high burst flowrate) using a variety of conditions such as, for example, 50% w/w H2O2 for one, four, or eight Pt-CNT-MMs.
In
Comparison of corresponding 20 and 50% w/w H2O2 cases demonstrates that an increase in fuel concentration lends to greater generated thrust. Initially, with an increased quantity of Pt-CNT-MMs (increased catalytic surface area), there is a notable increase in measured thrust. For 20 and 35% w/w H2O2 runs, no appreciable thrust is observed by having greater than six Pt-CNT-MMs. This may be due to the H2O2 fuel approaching total decomposition within the reaction chamber of the MUV submersible 800 for these conditions.
Thrust produced at a fixed fuel concentration (50% w/w H2O2) for varying flowrates is presented in
In some implementations, an increase in H2O2 fuel concentration, catalytic surface area, and flowrate can, alone, or in various combinations, contribute to additional thrust. In some implementations, thrust generated by catalysis can be dependent on the introduction rate of H2O2 fuel to the Pt-CNT-MM structure. In some implementations, the fuel can approach complete decomposition for a given fuel concentration and flowrate by addition of Pt-CNT-MMs.
As noted above, in some implementations, CNT-templated microfabrication techniques can be used to fabricate carbon-infiltrated multi-walled CNT scaffolds composed of highly ordered and aligned microchannels with desired geometry. Furthermore, urchin-like Pt nanoparticles can then be deposited onto, and throughout, the entirety of the CNT-MMs to provide a high aspect ratio catalytic microstructure for the enhanced propulsion of MUVs. In some implementations, Pt nanoparticle can be deposited onto carbon-infiltrated MWCNTs. In some implementations, a propulsion device (e.g., the propulsion device 110 shown in
In some implementations, post O2 etched CNT-MM and Pt-CNT-MM propulsion devices can demonstrate hydrophilic behavior, which can be suited for aqueous-based characterization and propulsion methods and can be a significant shift from the hydrophobic nature of non-etched CNT-MMs. In some implementations, CNT-MM propulsion devices can achieve an average electroactive surface area of, for example, 293±28 cm2 g−1 (in some implementations, greater or lesser values can also be achieved) within a ferricyanide based CV solution. Additionally, effective activation energy testing of Pt-CNT-MM propulsion devices revealed a favorable performance of, for example, 26.96 kJ mol−1 (in some implementations, greater or lesser values can also be achieved).
In some implementations, Pt-CNT-MMs as propulsion devices can be functionalized in 25-30% w/w Pt—C solution, for the propulsion of MUVs. In some implementations, multiple (e.g., 2, 4, 8, 10, 20) inline Pt-CNT-MMs included in a propulsion device can be exposed to manually driven high burst flows of 50% w/w H2O2, producing a maximum average thrust of, for example, 209±49 mN (in some implementations, greater or lesser values can be achieved). This propulsive bursting thrust can fall within the milli-newton thrust for MUV propulsion, and can be at least 6.5 times greater than that produced by biomimetic propulsion designs. The vehicles described herein minimize (or reduce) component exposure to the environment and includes a simple, static architecture relative to other micro-propulsion systems. Furthermore, additional thrust can be attained within the vehicles described herein by enhancing the introductory rate of the H2O2 fuel to the Pt-CNT-MMs, which would effectively increase the locomotive capability of this propulsion system.
As discussed above, a propulsion device can be formed using CNT-MM Fabrication. In some implementations, a silicon wafer can be coated with a relatively thin aluminum oxide film (Al2O3, >30 nm) using e-beam evaporation primarily to act as a barrier to subsequent reactions between the iron layer and the underlying silicon substrate. In some implementations, AZ nLOF2020 photoresist can be applied (e.g., can be spun on at 2750 rpm for 60 seconds) and soft baked (e.g., soft baked at 110° C. for 60 seconds). In some implementations, CNT-MM pore geometry and dimensions (diamond shape with nominal diagonal dimensions (e.g., dimensions of 4.5×9.0 μm) can be defined on the wafer by photolithography, and hard baked (e.g., hard baked at 110° C. for 60 seconds). In some implementations, the photoresist can be developed (e.g., developed in a lightly agitated, AZ300MIF solution). In some implementations, a relatively thin iron film (Fe, ˜7 nm) can be thermally evaporated onto the wafer surface as a catalyst for CNT growth. In some implementations, the wafer can be sonicated in solvent (e.g., insolvent for >10 minutes), rinsed (e.g., with Isopropyl Alcohol (IPA)), and dried (e.g., with compressed air to remove the entire photoresist layer and portions of the Fe layer in a lift-off process). In some implementations, to protect the wafer during propulsion device dicing, a relatively thin photoresist layer (e.g., AZ 3330) can be applied to (e.g., can be spun on) the wafer and soft baked. In some implementations, propulsion devices can be diced into (e.g., diced into 16.93×16.93 mm) squares or other shapes using a dicing saw. In some implementations, preparatory to CNT growth, diced propulsion devices with patterned Fe can be solvent cleaned to remove the protective photoresist layer.
In some implementations, CNT-MMA propulsion devices can be grown, released, and cleaned. After a quality inspection check with an optical microscope, diced propulsion devices can be placed on a quartz boat (e.g., in a Lindberg/Blue M Tube Furnace) for CNT growth. In some in some implementations, CNTs can be grown (e.g., for 26 minutes in flowing hydrogen (H2, ˜216 sccm) and ethylene (C2H4, ˜280 sccm) at 750° C.). In some implementations, this can result in a relatively substantial height of the CNT-MM (e.g., height of approximately 600 μm). In some implementations, CNT-MMs can then be coated with carbon in a subsequent infiltration step (e.g., at 900° C. for 20 minutes) with similar gases and flowrates as those used during CNT growth (H2 at ˜200 sccm and C2H4 at ˜280 sccm). In some implementations, this can result in carbon-infiltrated CNTs with diameters of a lesser measurement than the height (e.g., approximately 290 nm). In some implementations, during carbon infiltration, the CNT-MM structure can self-release from the wafer substrate. In some implementations, CNT-MMs can be exposed to a brief (e.g., 7 minute O2) plasma etching (e.g., at 300 W using an Anelva Reactive Ion Etcher (ME), DEM-451) to remove the carbon floor (additional carbon blocking the base of the CNT-MM channels) and enhance hydrophilicity to improve subsequent deposition of Pt catalyst (e.g., 5 minutes for removal of the carbon floor layer; 2 minutes for opposite face).
In some implementations, urchin-like Pt nanoparticle can be deposited within a propulsion device (e.g., propulsion device 110 shown in
In some implementations, electrodes can be attached for cyclic voltammetry testing of a propulsion device. In some implementations, a silver epoxy can be used to attach Nichrome wire to each propulsion device used for CV testing. After the silver epoxy is cured (e.g., approximately 24 hrs), a chemically inert lacquer coating can be applied to the silver joint. In some implementations, CV tests can be conducted using a three-electrode cell with the CNT-MM propulsion devices acting as the working electrode, a Ag/AgCl electrode acting as the reference electrode and a coiled Pt wire as the counter electrode. In some implementations, tests can be performed using a ferricyanide solution acting as mediator. In some implementations, multiple cycles (e.g., 3 cycles, 5 cycles, 10 cycles, 100 cycles) can be run per propulsion device test through a potential range (e.g., of −0.2-0.6 V) at a scan rate (e.g., of 10 mV s−1). In some implementations, the peak redox current for each propulsion device can be taken as the average of both anodic/cathodic peak currents of the latter two CV cycles. In some implementations, runs can be performed at room temperature.
In some implementations, nitrogen gas adsorption testing of a propulsion device can be performed. In some implementations, Nitrogen adsorption analysis can be performed at a temperature such as 77 K. In some implementations, portion devices can be degassed (e.g., at 100° C.) prior to analysis. In some implementations, surface area can be calculated by the Brunauer-Emmett-Telller (BET) method, pore size can be measured by the Barrett-Joyner-Halenda (BJH) method using the adsorption branch of the isotherm, and total pore volume can be determined by the single point method at relative pressure (P/PO) 0.97.
In some implementations, effective activation energy tests, by H2O2 decomposition, can be conducted using Pt-CNT-MM propulsion devices fabricated following one or more of the procedures described above. Each propulsion device can be tested two or more times, after which the pressure data can be averaged per propulsion device. The test apparatus can include flasks (e.g., two, 125 mL, round-bottom flasks). In some implementations, one flask can be used for the Pt-CNT-MM test environment and the other as a reference environment. In some implementations, magnetic stir bars can be placed inside each flask and rotated (e.g., at 250 rpm) to increase the amount of H2O2 contacting the catalytic Pt-CNT-MM propulsion devices and mimic, in part, the convective flow environment experienced through injection of H2O2 fuel into a MUV. In some implementations, to ensure the flasks are airtight, rubber septums with a rim seal can be positioned on each flask. In some implementations, the flasks can be placed inside ice or water baths on top of a hot plate stirrer to maintain isothermal conditions during each of the two or more runs per propulsion device (0° C., 17.5° C. and 35° C.). In some implementations, to ensure that steam may not be produced during testing, such that all generated pressure can be due to the release of O2, a relatively low concentration H2O2 solution (1% w/w H2O2, diluted from 30% w/w H2O2) can be used for all tests. In some implementations, the H2O2 solution stock can be placed within a container (e.g., a 50 mL container) and immersed in the respective ice/water baths in order to achieve thermal equilibrium prior to testing. After achieving thermal equilibration, each flask can be vented by temporary insertion of an unattached needle and allowed to equilibrate with atmospheric pressure. In some implementations, the amount of O2 generated during each test can be measured as a pressure differential between the testing and reference environments. In some implementations, to measure the pressure differential, an differential pressure manometer (e.g., measuring up to ±5 psi/34.5 kPa) can be connected to each flask via two high strength silicone tubes (e.g., diameter 0.375 in/9.525 mm). In some implementations, the tubing can be connected to the manometer and syringe needles using barbed fittings. In some implementations, the two syringe needles connected to the pressure manometer can be inserted into the test and control flasks, respectively, by piercing through the diaphragm of each septa. In some implementations, the differential pressure between the test and control flasks can be zeroed before recording data and then measured as a function of time with a computer via a connection (e.g., a universal serial bus (USB) connection). In some implementations, H2O2 solution (e.g., 10 mL of the H2O2 solution) can be simultaneously injected into each flask while a stir bar (e.g., the magnetic stir bars) stirred the solution (e.g., at 200 rpm). In some implementations, resultant differential pressure vs. time data can be used to determine catalyst performance and effective activation energy with the Arrhenius Equation.
In some implementations, an MUV test submersible can be configured with computer aided design software and printed with a 3D printer, for example, with a PMMA like resin. The test submersible can be fitted to a rigid arm (e.g., a 30.5 in. (0.77 m) rigid arm through screw thread fastening and submerged into a water tank (350 gal)). In some implementations, the opposite end of the arm can be secured to a torque transducer (Interface model 5350-50:50 oz-in sensor) mounted above the water tank. The transducer can be used to measure torque measurements with 0.001 N-m precision along the parallel axis of the test submersible via a CPU connection. Force (thrust) measurements can be calculated via software on the CPU. H2O2 can be pumped into a reaction chamber via a 50 mL syringe connected to the test submersible's reaction chamber via high strength silicone tube (dia.: 0.375 in./9.525 mm) that fits over, for example, a plastic barbed fitting.
It will also be understood that when an element, such as a layer, a region, or a substrate, is referred to as being on, connected to, electrically connected to, coupled to, or electrically coupled to another element, it may be directly on, connected or coupled to the other element, or one or more intervening elements may be present. In contrast, when an element is referred to as being directly on, directly connected to or directly coupled to another element or layer, there are no intervening elements or layers present. Although the terms directly on, directly connected to, or directly coupled to may not be used throughout the detailed description, elements that are shown as being directly on, directly connected or directly coupled can be referred to as such. The claims of the application may be amended to recite exemplary relationships described in the specification or shown in the figures.
As used in this specification, a singular form may, unless definitely indicating a particular case in terms of the context, include a plural form. Spatially relative terms (e.g., over, above, upper, under, beneath, below, lower, and so forth) are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. In some implementations, the relative terms above and below can, respectively, include vertically above and vertically below. In some implementations, the term adjacent can include laterally adjacent to or horizontally adjacent to.
While certain features of the described implementations have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the scope of the implementations. It should be understood that they have been presented by way of example only, not limitation, and various changes in form and details may be made. Any portion of the apparatus and/or methods described herein may be combined in any combination, except mutually exclusive combinations. The implementations described herein can include various combinations and/or sub-combinations of the functions, components and/or features of the different implementations described.
This application claims priority to and the benefit of U.S. Provisional Patent Application No. 62/071,974, filed Oct. 7, 2014 and U.S. Provisional Patent Application No. 62/081,330, filed Nov. 18, 2014, both of which are incorporated herein by reference in their entireties.
This application was made with government support under Navy Contract No. N00173-11-1-G002. The government has certain rights in this application.
Number | Date | Country | |
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62071974 | Oct 2014 | US | |
62081330 | Nov 2014 | US |