Patent Description:
3D printing, also known as additive manufacturing, is a technology of building three dimensional (3D) solid objects by depositing layers of materials in a design defined by a computer software using many of the commonly available CAD (computer aided design) packages. This technology can create highly customized complex parts and products that are difficult or impossible to manufacture using traditional technologies.

There are several major 3D printing technologies differing mainly in the way layers are built to create the final 3D object. Some methods use melting or softening materials to produce the layers. For example, Selective Laser Sintering (SLS) and Selective Laser Melting (SLM) work by respectively sintering or melting metal, plastic, ceramic, or glass powders using irradiative heating. The heating is done by various light sources emitting electromagnetic radiation in ultraviolet (UV), visible, or infrared (IR) range that is absorbed by the powder, and the radiation energy is converted to heat. Typically, the light source is a lamp or a laser. For example, metal powders are typically heated by fiber lasers emitting IR radiation. For example, the popular M <NUM> SLS 3D printer manufactured by EOS (Germany) uses a Yb-fiber laser rated at about <NUM> kilowatt power operating at about <NUM>,<NUM> nanometer wavelength. The second group of methods, exemplified by Fused Deposition Modeling (FDM), works by extruding melted plastic filaments or metal wires through an extrusion nozzle. The third group of methods such as stereolithography (SLA) and Digital Light Processing (DLP) are based on curing (solidifying) liquid materials (such as photopolymer resins) with electromagnetic radiation in UV, visible, or IR ranges. Typically, SLA lasers require much less power compared to SLS lasers. For example, the popular Form1+ 3D printer manufactured by Formlabs (Somerville, MA) uses a <NUM> watt laser operating at about <NUM> nanometer wavelength.

Current challenges include improving the available 3D printing materials to impart advanced properties and versatility needed for industrial applications, as well as enabling faster 3D printing processes.

For further disclosures related to the nanocarbon 3D printing materials (including nanocarbon oxides), for example, see the following publications: <NPL>); <NPL>); <NPL>); <NPL>); <NPL>); <NPL>); <NPL>); <NPL>).

A variety of CNT materials (i.e., single-wall, double-wall, and multi-wall CNTs) are commercially available as dry powders and/or suspensions. These CNT materials may be synthesized by variety of CNT synthesis methods. Some examples of the CNT synthesis methods are arc-discharge methods, laser-vaporization methods, and chemical vapor deposition method (CVD). See, for example, following publications: <NPL>); <NPL>); <NPL>, <CIT>.

The arc-discharge method employs evaporation of metal-catalyzed graphite electrodes in electric arcs that involve very high (about <NUM>,<NUM>) temperatures. The laser-vaporization method employs evaporation of graphite target by lasers in conjunction with high-temperature furnaces. These two methods operate in a batch mode and may therefore be poorly suited to high- volume, low cost production. The CVD method is based on decomposition of carbon-containing gases on supported catalyst and may offer the more efficient, low-cost, and scalable method of producing CNTs. Currently, most commercial CNT materials are manufactured by the CVD method.

For examples of 3D printers and 3D printing techniques, see:<CIT>; <CIT>; <CIT>; <CIT>;<CIT>; and <CIT>. From the international patent application publication <CIT> and the United States patent application publications <CIT>, <CIT>, <CIT> and <CIT> a feedstock comprising a composite material formed of a first material and a coating material coating said first material is known. This known coating material may enhance electromagnetic absorption, such as a coating comprising carbon, such as graphite. Further, from the United States patent application publication <CIT>, a <NUM>-step mixing is known for creating a coating material. It is an object of the invention to create a feedstock having high electrical and thermal conductivity. This and other objects are achieved by the combination of features claimed in the independent claims. Advantageous embodiments are claimed in the dependent claims.

The drawings are of illustrative embodiments. They do not illustrate all embodiments. Other embodiments may be used in addition or instead. Details that may be apparent or unnecessary may be omitted to save space or for more effective illustration. Some embodiments may be practiced with additional components or steps and/or without all of the components or steps that are illustrated. When the same numeral appears in different drawings, it refers to the same or like components or steps.

Illustrative embodiments are now described. Other embodiments may be used in addition or instead. Details that may be apparent or unnecessary may be omitted to save space or for a more effective presentation. Some embodiments may be practiced with additional components or steps and/or without all of the components or steps that are described.

In this disclosure, the word "form" may mean "deposit", "coat", "dispose", "laminate", "apply", "place", "provide", "position", "manufacture" or the like. In this disclosure, the phrase "any combination thereof or "a combination thereof may mean "a mixture thereof, "a composite thereof", "an alloy thereof, or the like. In this disclosure, the indefinite article "a" and phrases "one or more" and "at least one" are synonymous and mean "at least one".

Addition of carbon nanotubes (CNT), and their mixtures, to metal, may lead to formation of nanocarbon composites with increased electrical conductivity, increased thermal conductivity, increased mechanical strength, and other improvements in properties.

Addition of nanocarbons in the form of carbon nanotubes also may lead to increased absorption of incident light in wide frequency range (e.g., UV, visible, IR) thereby improving the efficiency of irradiative heating of the feedstock and photochemical reactions. This may lead to higher rates and increased throughput of 3D printing processes, thereby making 3D printed parts more competitive on the market.

A major challenge in these tasks is ensuring a high degree of dispersion of carbon in the carbon composite materials since only well-dispersed carbons impart useful properties. Typically, carbon agglomeration results in underutilized potential of the composite material and degraded properties of product.

Another challenge is preventing structural or other damage to carbons in the process of fabrication of nanocarbon composites. Damaged carbons may exhibit inferior properties when incorporated in composite materials.

The feedstock of the instant disclosure may provide several advantages to the 3D printing of objects. For example, three dimensional objects may be printed at higher throughputs by using the feedstocks of the instant disclosure. The production costs of such articles may thereby be decreased while production rates are increased. The use of these feedstocks may also decrease the power requirements of the 3D printers, thereby decreasing the prices of such printers.

The feedstocks of the instant disclosure may also provide materials with improved properties for 3D printing technologies. These improvements may include (but not limited to) higher electrical and thermal conductivity, better mechanical and thermal properties.

According to an embodiment, the feedstock may be used in a 3D printer that may have a configuration that dispenses a feedstock; deposits a layer of the feedstock on a surface; delivers an electromagnetic radiation to selected areas of the feedstock layer; and prepares a three-dimensional object. The coating may absorb the delivered electromagnetic radiation at a selected area of the feedstock layer, convert the absorbed electromagnetic radiation to heat, and transfer the heat to the metal thereby heating the selected area of the feedstock layer, and causing the feedstock to bond to each other, and thereby forming a bonded feedstock layer.

The deposition of the first layer may happen on any surface. For example, this surface may be a surface of another object.

The 3D printer may further have a configuration that deposits a layer of feedstock on a surface of the bonded feedstock layer formed before; and forms another bonded feedstock layer. Thus, the 3D printer of the instant disclosure may prepare an object layer by layer.

According to the invention, this disclosure also relates to a feedstock. The feedstock according to the invention comprises metal particles and a coating formed on a surface of the metal particles.

According to the invention, the coating comprises a nanocarbon in form of carbon nanotubes (CNTs), which may be a single-wall carbon nanotube, a double-wall carbon nanotube, a multi-wall carbon nanotube, or a combination thereof.

The metal particles may be of any metal. The examples of the metal may be titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, ruthenium, rhodium, palladium, aluminum, indium, gallium, tin, silver, gold, platinum, lead, bismuth, steel, bronze, brass, or a combination thereof.

The coating may absorb the delivered electromagnetic radiation at a selected area of the feedstock layer, may convert the absorbed electromagnetic radiation to heat, and may then transfer the heat to the metal thereby heating the selected area of the feedstock layer, and causing the feedstock to bond to each other, and thereby forming a bonded feedstock layer.

The coating has an absorbance of the electromagnetic radiation. The absorbance of the coating may be higher than absorbance of the metal. For example, the absorbance of the coating may be at least <NUM> percent, at least <NUM> percent, at least <NUM> percent, or at least <NUM> percent higher than the absorbance of the metal.

Because the coating has an absorbance of the electromagnetic radiation higher than that of the metal, heating rate of the feedstock comprising the metal and the coating may be higher than that of a feedstock without the coating. For example, the heating rate of the feedstock comprising the metal and the coating may be at least <NUM> percent, at least <NUM> percent, at least <NUM> percent, or at least <NUM> percent higher than that of a feedstock without the coating.

The coating may be sufficiently thick to substantially absorb electromagnetic radiation, but not too thick to cause defects in the composite object and thereby negatively impact properties of the composite object. For example, the coating thickness may be in the range of <NUM> nanometers to <NUM> micrometers, in the range of <NUM> nanometers to <NUM> micrometers, or in the range of <NUM> micrometer to <NUM> micrometers.

For example, a 3D printer may emit the electromagnetic radiation at any power suitable to form a bonded feedstock layer. Lowest emission power that forms a bonded feedstock layer may be preferred since manufacturing cost of the 3D printers and/or operating costs of such printers may thereby be decreased. For example, the 3D printer may emit the electromagnetic radiation with power less than or equivalent to <NUM>,<NUM> watts, with power less than or equivalent to <NUM>,<NUM> watts; with power less than or equivalent to <NUM> watts; or with power less than or equivalent to <NUM> watts.

Any three-dimensional object prepared by any of the 3D printers disclosed above may be within scope of this instant disclosure.

This disclosure also relates to a feedstock as disclosed above. This feedstock may be used in preparation of 3D objects by any equipment or method. For example, this feedstock may be used in preparation of 3D objects by any of the 3D printers disclosed above.

According to the invention, the nanocarbon is a non-agglomerated nanocarbon in form of a carbon nanotube (CNT), which may be a single-wall carbon nanotube, a double-wall carbon nanotube, a multi-wall carbon nanotube, or a combination thereof.

The metal particles may comprise any metal. The examples of the metal may comprise titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, ruthenium, rhodium, palladium, aluminum, indium, gallium, tin, silver, gold, platinum, lead, bismuth, steel, bronze, brass, or a combination thereof.

The coating may have an absorbance of the electromagnetic radiation. The absorbance of the coating may be higher than absorbance of the metal. For example, the absorbance of the coating may be at least <NUM> percent, at least <NUM> percent, at least <NUM> percent, or at least <NUM> percent higher than the absorbance of the metal.

Any three-dimensional object prepared by using any of the feedstocks disclosed above may be within scope of this instant disclosure.

The instant disclosure also relates to a method of preparation ("preparation method"). For example, the preparation method may be preparation of a suspension of a carbon in a solvent ("method of preparation of a carbon suspension"). For example, the method may comprise processing a conditioned mixture at a high shear rate and thereby preparing a carbon suspension. In this preparation method, the conditioned mixture may be prepared by a method comprising processing a solution at a low shear rate. The low shear rate may be lower than <NUM>,<NUM>-<NUM>. The high shear rate may be equivalent to or higher than <NUM>,<NUM>-<NUM>.

In this method, first, the conditioned mixture may be prepared. The conditioned mixture may be prepared by processing a solution at a shear rate lower than <NUM>,<NUM>-<NUM>. The low shear rate processing of the solution may be achieved by using any low shear mixing equipment. Such mixing equipment is disclosed, for example, in a publication by <NPL>.

In this method, second, a carbon suspension is prepared by processing the conditioned mixture at a shear rate higher than <NUM>,<NUM>-<NUM>. Examples of the high shear rate equipment may be rotor-stators, colloid mills, homogenizers and microfluidizers, as disclosed in Deutsch publication. Microfluidizer high shear fluid processors manufactured by Microfluidics Corporation (Westwood, MA) may be suitable for high shear processing of the conditioned mixture. Such microfluidizers may process the conditioned mixture at a shear rate higher than <NUM>,<NUM>,<NUM>-<NUM>. After this high shear processing, a carbon suspension comprising substantially non-agglomerated carbons may be obtained.

The solution may comprise a carbon and a solvent. The solution may be substantially free of any dispersing agent. The carbon may be substantially free of functional groups that can facilitate dispersion of the carbon nanotubes in the solution.

Embodiments of the carbon nanotube may be a single-wall carbon nanotube, a double-wall carbon nanotube, a multi-wall carbon nanotube, or a combination thereof.

In this method, the solvent may be any solvent. For example, the solvent may comprise water, an acid, a base, an aromatic solvent, an alcohol, an aromatic solvent, benzene, halogenated benzene, xylene, toluene, a dichlorobenzene, dimethylformamide, formamide and its derivatives, N-methylpyrrolidinone, dichloroethane, dibromoethane, carbon disulfide, pyridine, or a combination thereof.

In this method, the conditioned mixture may substantially be free of any dispersing agent.

The preparation method may further comprise depositing the carbon nanotubes suspension on a surface of metal particles.

The metal particles may comprise any metal. For example, the metal particles may comprise titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, ruthenium, rhodium, palladium, aluminum, indium, gallium, tin, silver, gold, platinum, lead, bismuth, steel, bronze, brass, or a combination thereof.

According to the invention, the preparation method may further comprise removing the solvent; thereby forming a coating on a surface of the metal particles; and thereby preparing a feedstock. According to the invention, the solvent may be removed until the feedstock is substantially free of solvent. The solvent may be removed by any technique. For example, the solvent may be removed by evaporation, centrifugation, using drying agents (e.g. absorbents or adsorbents), or a combination thereof.

The coating has a thickness. The coating thickness may be in the range of <NUM> nanometers to <NUM> micrometers; the range of <NUM> nanometers to <NUM> micrometers; or in the range of <NUM> micrometer to <NUM> micrometers.

After the removal of the solvent, the coating may essentially comprise the carbon nanotubes.

Any three-dimensional composite object prepared by using the carbon suspension prepared by the method disclosed above may be within the scope of the instant disclosure.

As disclosed above, the CNT materials may be synthesized by variety of CNT synthesis methods. The CNT formation and growth may stop during the synthesis. The CNT formation and growth may stop due to decreased catalyst activity when the catalyst's surface is covered with an amorphous carbon layer. Or, the CNT formation and growth may be stopped after a pre-determined period of synthesis. At this process stage, the CNTs are "as-synthesized CNTs".

The as-synthesized CNTs may be processed before they are used. For example, the as-synthesized CNTs may be incorporated into a liquid or mixed with a liquid. This incorporation may be done, for example, to dissolve impurities (e.g. non-CNT material), to provide a CNT suspension, or a combination thereof. Examples of impurities may be non-CNT carbons (e.g., amorphous carbon), inorganic catalysts, catalyst supports, or a combination thereof.

The liquid mixture at this process stage may comprise a liquid and an as-synthesized nanotubes nanocarbon ("the nanocarbon slurry"). The liquid may comprise any liquid. For example, the liquid may comprise water, or mixtures thereof. The solvent may comprise any solvent. For example, the solvent may comprise a hydrocarbon solvent such as alcohol, ketone, ester, ether, alkane, alkene, aromatic hydrocarbons (such as benzene and various derivatives), or mixtures thereof. The nanocarbon slurry may further comprise an acid, a base, a suspension agent, or a combination thereof.

In one example, the CVD process may involve passing a hydrocarbon vapor through a reactor at a sufficiently high temperature, varying in the range of <NUM> to <NUM>, and in presence of a catalyst to decompose the hydrocarbon. In one example, the catalyst may comprise metals and/or metal oxides (e.g., Fe, Co, Ni, Mo, their oxides, and a combination thereof). The catalyst may be nanoparticles of such metals and/or metal oxides. In one example, support material may comprise alumina, silica, magnesium oxide, and a combination thereof. The CNTs may form and grow on catalyst particles in the reactor and may be collected upon cooling the system to a room temperature. These CNTs collected directly from the reactor and not yet treated in any way are the as- synthesized CNTs. The as-synthesized CNTs may comprise at least <NUM> wt% inorganic impurities including the catalyst and the support material, which may need to be removed to produce a material comprising CNTs with desired properties.

In one example, the as-synthesized CNTs may be purified by being immersed in acids (such as H<NUM>SO<NUM>, HNO<NUM>, HCI, and a combination thereof) and refluxed for a period varying in the range of <NUM> hour to <NUM> hours resulting in significantly decreased amount of impurities (down to a few wt% of impurities). The purified CNT material may be thoroughly washed to remove any residual acid and then dried in a convection oven at a temperature varying in the range of <NUM> to <NUM> for a period varying in the range of <NUM> hour to <NUM> hours.

The as-synthesized and purified CNTs may easily be dispersed in the liquid since they may not be substantially agglomerated. However, upon being wetted and subsequently dried, the CNT material may be converted into an agglomerated and tangled mat comprising irregular clusters of individual CNTs, as shown in <FIG>. This post-drying transition may occur due to high amount of the CNTs' atomically smooth surface and attendant large surface energy. This condition may make the conformation of straight individual CNTs energetically unstable and susceptible to deformation and agglomeration.

The instability may greatly be enhanced by introducing a liquid between individual CNTs and then evaporating the liquid. In other words, wetting and then drying CNTs may induce severe agglomeration due to attraction forces exerted by liquids in intimate contact with the CNT surface. Upon drying, CNTs may coalesce into large bundles (including tens to hundreds of CNTs in cross section), which then form a highly tangled structure, as shown in <FIG> by way of example. These agglomerated structures may not exhibit many of the remarkable properties expected of individual, well-dispersed and/or isolated CNTs.

Commercially available CNT materials are typically those of the purified and dried grade, marketed either as a powder obtained after drying, or as a CNT suspension produced by re-dispersing the dry purified powder in either an aqueous or organic solvent. The commercially available purified grades of the CNT materials ("the commercial CNTs") may undergo at least one wetting and drying cycle before they are supplied to a user. The commercial CNTs may thereby have agglomerated structures.

It may then be difficult to disperse this agglomerated structure down to the level of individual CNTs that may be required for many applications. To accomplish this task, commercially available grades of CNT materials may have to be subjected to vigorous harsh treatments that may consume a lot of energy and inflict considerable collateral damage upon the CNT material (e.g., by destroying some CNTs, creating defects in CNT walls, and/or cutting CNTs into shorter segments) resulting in degraded nanocarbon material properties.

In one example, this disclosure relates to a method comprising using the as-synthesized CNTs, the non-agglomerated and/or non-damaged CNTs, the CNT slurry, or the combination thereof in preparation of the nanocarbon composites. The drying-induced agglomeration and entanglement, as well as damage during processing of agglomerated CNT may thereby be avoided. For example, the purified CNTs may be kept in a suspension or, at least, as the nanocarbon slurry (the "purified CNT slurry"). In other words, the as-synthesized CNT materials may be purified by refluxing in acids but then never be allowed to dry before reaching the customer, instead being kept as the purified CNT slurry. The customer may either use the purified CNT slurry or, if necessary, exchange the liquid with another liquid and process the CNT slurry as desired, allowing it to dry only at the final step of their process. This arrangement would significantly facilitate dispersion and prevent damaging of CNT materials resulting in improvement of product properties and performance.

The process of dispersing the purified CNT slurry material down to the level of individual CNTs may be accomplished through any of mixing, sonicating, or homogenizing techniques, or a combination thereof. As compared to the current commercial CNT materials, the dispersion of the purified CNT slurry material may require much less effort and inflict much less damage to CNTs in the process of achieving the desired degree of dispersion. The same considerations may apply to other types of nanocarbon materials. Higher degree of dispersion and reduced damage to nanocarbon structure may result in improved properties. The dispersion process may be carried out in either aqueous or organic solvents. Examples of aqueous or organic solvents may comprise water, toluene, alcohol, carbon disulfide, dichlorobenzene, other benzene derivatives, aromatic solvents, dimethylformamide, N-methylpyrrolidinone, pyridine, and mixtures thereof.

The purified CNT slurry may comprise a liquid and a CNT. The CNT may comprise less than <NUM> wt%, less than <NUM> wt%, or less than <NUM> wt% of the CNT slurry. Presence of sufficient number of liquid molecules in intimate contact with CNTs stabilizes the system and prevents CNT agglomeration.

A convenient method to evaluate the degree of agglomeration of CNTs incorporated into composite materials may be through examination of scanning electron microscopy (SEM) and/or transmission electron microscopy (TEM) images. The CNT agglomerates are readily visible in SEM and/or TEM images at magnifications <NUM>,<NUM> or <NUM>,<NUM> times and less, depending on agglomerate size. The non-agglomerated CNTs are much smaller in size and may be seen in SEM and/or TEM images at magnifications <NUM>,<NUM> or <NUM>,<NUM> times and higher.

The damage to CNTs caused by a harsh dispersion process may be evaluated by measuring Raman spectroscopy, in particular, using the intensity ratio of the so-called G-band and D-band. The G-bands that are typically detected at about <NUM>,<NUM>-<NUM> (within ±<NUM>-<NUM>) are due to the non-defective graphitic CNT structure of, while the D-bands (at about <NUM>,<NUM>-<NUM> within ±<NUM>-<NUM>) are predominantly due to structural defects, as disclosed by <NPL>).

The intensity ratio of the G-band to the D-band (i.e., the G/D ratio) may be used as a measure of relative concentration of CNT defects. Similar evaluation process based on G/D ratio maybe used for graphene materials, as disclosed by <NPL>).

To evaluate the damage inflicted on CNT wall structure in the process of dispersing the CNT material, the G/D ratio may be measured and compared before and after the dispersion process. The comparison may be done using the same measurement conditions. The as-synthesized and/or the purified CNT slurry may have the same or higher G/D ratio after the dispersion, while the agglomerated CNTs (e.g., dry powder) may have decreased G/D ratio after the dispersion due to the damage inflicted on CNT material during the dispersion process. The G/D ratio of a nanocarbon incorporated in a nanocarbon composite being <NUM>% lower than, <NUM>% lower than, <NUM>% lower than, <NUM>% lower than that of the as-synthesized nanocarbon may indicate a non-damaged nanocarbon. Also, the G/D ratio of a nanocarbon incorporated in a composite being at least <NUM>% higher than, at least <NUM>% higher than, at least <NUM>% higher than, at least <NUM>% higher than, or at least equal to that of the as-synthesized nanocarbon may indicate a non-damaged nanocarbon.

The disclosure is illustrated further by the following additional examples that are not to be construed as limiting the disclosure in scope to the specific procedures or products described in them.

As-synthesized multi-wall CNT material (comprising about <NUM> wt% inorganic impurities) was refluxed in excess amount of about <NUM> HCl for about <NUM> hours, and then filtered to remove the main volume of the acid while keeping the CNT material wet. The purified product (comprising about <NUM> wt% inorganic impurities) was washed two times with de-ionized water to remove the residual acid, and then separated into three parts for the experiments described in other Examples. The first part was dried in a convection oven at about <NUM> for about <NUM> hours. The second part was kept wet and refluxed in water (at CNT concentration of about <NUM>/L) for about <NUM> hours to loosen up the CNTs. The third part was washed with copious amounts of toluene three times thereby substantially replacing the water with toluene as a solvent and bringing the CNT concentration to about <NUM>/L. Then, the CNT-toluene suspension was refluxed for about <NUM> hours. Finally, both these CNT suspensions (one in water and one in toluene) were separately passed <NUM> times through a Microfluidizer high shear fluid processor (LM-<NUM>, Microfluidics Corporation, Newton, MA) at <NUM>,<NUM> psi pressure yielding two suspensions of non-agglomerated and/or non-damaged CNTs. These suspensions were stable over the period of <NUM> weeks. The G/D ratio as measured with about <NUM> laser excitation varied in the range of <NUM> to <NUM>, both before and after dispersion indicating that the concentration of structural defects did not change. All the above treatment steps are scalable and highly reproducible.

Dried powder of purified multi-wall CNT material prepared in Example <NUM> as the first part was dispersed following exactly the same process as the other two parts. To produce a stable CNT suspension, the dry powder was first refluxed in water at CNT concentration of about <NUM>/L for about <NUM> hours, then passed <NUM> times through the Microfluidizer. The G/D ratio for the multi-wall CNT dry powder material as measured with about <NUM> laser excitation may vary in the range of <NUM> to <NUM>. After dispersing, the G/D ratio decreased to a level varying in the range of <NUM> to <NUM> indicating increased concentration of CNT defects.

The multi-wall CNT material may be provided, for example, by Thomas Swan & Co Ltd (UK), Nanocyl (Belgium), or many other suppliers. The step of Microfluidizer treatment may be combined or substituted with any high shear mixing, sonication, wet ball milling, another similar treatment, or a combination thereof. Similar simple and efficient process may be designed to produce the as-synthesized or the purified non-agglomerated and/or non-damaged CNT slurries.

A highly dispersed and stable suspension of non-agglomerated and/or non-damaged CNT material ("the well-dispersed CNT suspension") in either water or organic solvents is thereby obtained. The well-dispersed CNT suspension may be used in preparation of composites suitable for the 3D printing.

In the case of SLS technologies that use metal powder as feedstock, there is a technical challenge of mixing nanocarbons with metal powders in a way that prevents nanocarbons from becoming airborne, and also affords achieving the desired proportions. Dry nanocarbon is comprised of particles that may be small (~mm or less in length, width, thickness, and/or specific dimension) and have relatively low density (varying in the range of <NUM>/cc to <NUM>/cc). These lightweight nanocarbon particles may easily get airborne thereby presenting potential health hazard and affecting the nominal nanocarbon-to-metal ratio.

This problem is solved by devising a process to physically attach the lightweight nanocarbon particles to surfaces of metal particles which may be denser and easier to feed. This step is carried out prior to feeding the particles into the 3D printer, so that the feedstock may comprise a metal core coated with a nanocarbon shell, as shown in <FIG>.

On practical level, nanocarbon particles may be coated and attached to metal particles through a variety of coating techniques using a suspension of a nanocarbon in an either aqueous or organic solvent, such as spray coating, dip coating, spin coating, wet ball milling, etc. Process parameters are determined by type of a nanocarbon, type of a metal, shape and size of the particles, conditions of the surfaces (such as terminating functional group). The strength of adhesion may need to be just sufficient to allow the metal particles to be processed up to the sintering or melting step without causing detachment of the coated nanocarbons.

After the sintering or melting step, the coated nanocarbons may be captured and incorporated within the metal matrix leading to improved properties. Incorporation of the non-agglomerated and/or non-damaged CNT into metal structure may result in a CNT composite with improved electrical, thermal, mechanical, and other properties that may be suitable for 3D-printed products.

Exemplary procedures to produce CNT-coated metal particles are described in Examples <NUM>-<NUM>.

Iron powder granules (average diameter about <NUM> micrometers) were immersed into the aqueous CNT suspension of Example <NUM>, agitated for about <NUM> hours with a magnetic stirrer at <NUM>,<NUM> rpm, then allowed to dry in a convection oven at about <NUM> for about <NUM> hours. Weight uptake by the granules yielded the amount of attached CNT of about <NUM> wt%. Examination under microscope has shown the average CNT coating thickness of <NUM> micrometers. The CNT-coated iron granules may be used as a feedstock for SLS, SLM, and related type 3D printers.

Iron granules (average diameter about <NUM> micrometers) were immersed into the toluene suspension of non-agglomerated and/or non-damaged CNT of Example <NUM> and subjected to a modified wet ball milling process. In particular, the wet iron/CNT mixture was agitated for about <NUM> minutes in a ball milling apparatus either with the standard balls (batch <NUM>), or with the standard balls removed (batch <NUM>). Due to the repeated impacts with iron granules or the standard balls, CNTs get attached to the metal surface. The mixture was dried in a convection oven at about <NUM> for about <NUM> hours. Alternatively, the solvent may be removed by other methods, such as centrifuging. The amount of attached CNT was about <NUM> wt% and about <NUM> wt% in batches <NUM> and <NUM>, respectively. The average coating thickness was <NUM> and <NUM> micrometers in batches <NUM> and <NUM>, respectively. The CNT-coated iron granules may be used as a feedstock for SLS, SLM, and related type 3D printers.

Other type CNTs, may also be employed in this application either alone or in various combinations. The described process may also be used for other metals, such as titanium, vanadium, chromium, manganese, cobalt, nickel, copper, zinc, ruthenium, rhodium, palladium, aluminum, indium, gallium, tin, silver, gold, platinum, lead, bismuth, and alloys, such as steel, bronze, brass, and a combination thereof. These nanocarbons, metals, and/or alloys may be commercially available from many suppliers.

Aluminum granules (average diameter about <NUM> micrometers) were immersed into the toluene suspension of non-agglomerated and/or non-damaged CNT prepared in Example <NUM> and agitated for about <NUM> minutes in a ball milling apparatus either with the standard balls (batch <NUM>), or with the standard balls removed (batch <NUM>). The mixture was dried in a convection oven at about <NUM> for about <NUM> hours. The CNT-coated granules appear black and non-reflective (<FIG>), while pure aluminum granules appear white and shiny (<FIG>). The amount of attached CNT was about <NUM> wt% in batch <NUM> and about <NUM> wt% in batch <NUM>. The average CNT coating thickness was about <NUM> micrometer and about <NUM> micrometers in batches <NUM> and <NUM>, respectively. The CNT-coated aluminum granules may be used as a feedstock for SLS, SLM, and related type 3D printers.

The batch <NUM> CNT-coated aluminum granules of Example <NUM> were used to produce aluminum-CNT composite objects and evaluate their properties. The composite objects were fabricated by melting the CNT-coated aluminum granules under argon atmosphere at about <NUM> for about <NUM> hour while stirring to homogenize the melt, then casting the melt into a cylinder-shaped die (<NUM> in diameter and <NUM> in height) and cooling down to <NUM> (<FIG>). Under optical microscope, no defects could be observed on surfaces of batch <NUM> samples (<FIG>), while multiple defects were observed on batch <NUM> samples (shown by the arrow in <FIG>). Examination with SEM at high magnification showed that these defects were due to CNT agglomerates (<FIG>). Pure aluminum samples were prepared as reference following exactly the same procedure but from uncoated aluminum granules. Electrical resistivity, tensile strength, and elongation were evaluated at about <NUM> for both CNT-containing and pure aluminum cast samples without any further treatment of the samples. The electrical resistivity was measured using four probe technique, and the tensile properties were evaluated with an Instron (Norwood, MA) Testing System. For the reference pure aluminum sample, the electrical resistivity was about <NUM> microOhms. cm, tensile strength was about <NUM> MPa, and elongation was about <NUM>%. For the CNT-containing aluminum sample (batch <NUM>), the electrical resistivity was about <NUM> microOhms. cm, tensile strength was about <NUM> MPa, and elongation was about <NUM>%. To summarize, in the aluminum-CNT composite (batch <NUM>), electrical resistivity was decreased by about <NUM>%, tensile strength was increased by about <NUM>%, and elongation was increased by about <NUM>%, compared to the pure aluminum. Hence, the properties of the aluminum-CNT composite were improved if there was no agglomeration of CNT.

The batch <NUM> CNT-coated aluminum granules of Example <NUM> were used to produce aluminum-CNT composite objects according to the procedures of Example 6and evaluate their properties. For the aluminum-CNT composite of batch <NUM>, the electrical resistivity was about <NUM> microOhms. cm, tensile strength was about <NUM> MPa, and elongation was about <NUM>%. To summarize, in the aluminum-CNT composite (batch <NUM>), electrical resistivity was increased by about <NUM>%, tensile strength was decreased by about <NUM>%, and elongation was decreased by about <NUM>%, compared to the reference pure aluminum sample. The partial degradation of properties in the aluminum-CNT composite of batch <NUM> may be attributed to the agglomeration of CNT (<FIG>) captured within structure of the composite object.

In this specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise.

Unless otherwise stated, all measurements, values, ratings, positions, magnitudes, sizes, and other specifications that are set forth in this specification, including in the exemplary features that follow, are approximate, not exact.

The scope of protection is limited solely by the claims that now follow. That scope is intended and should be interpreted to be as broad as is consistent with the ordinary meaning of the language that is used in the claims when interpreted in light of this specification, except where specific meanings have been set forth.

Claim 1:
A feedstock for selective laser sintering or melting comprising:
metal particles; and
a coating formed on a surface of the metal particles; wherein
the coating comprises non-agglomerated carbon nanotubes;
the coating is substantially free of any dispersing agent;
the coating has a coating thickness; and wherein the coating thickness is in the range of <NUM> nanometers to <NUM> micrometers.