Embodiments of the present disclosure generally relate to methods for processing fumed metallic oxides. More specifically, embodiments of the present disclosure relate to methods for processing fumed metallic oxides that exhibit a dominantly branched morphology into metallic oxide agglomerations that exhibit a dominantly globular morphology.
The present applicant has recognized that fumed metallic oxides, such as “fumed silica” (fumed silicon dioxide, SiO2) and “fumed alumina” (fumed aluminum oxide, Al2O3), can be used in a wide variety of applications, including use as adhesives, pharmaceutical and food additives, beauty and skin care products, ink toners, and coatings. Fumed metallic oxides are, in some embodiments, fine white powders with high surface area that become colorless when dispersed in a liquid or polymer. They can be very versatile, exhibit a high degree of purity, and may provide added benefits to compositions, including, but not limited to, thickening properties, anti-sagging reinforcement, scratch and abrasion resistance, corrosion resistance, anti-caking properties, increased flowability, and increased adsorption. However, the present applicant has also recognized that fumed metallic oxides may, in some embodiments, exhibit a very high fractal dimension and a dominantly branched morphology, which can create difficulties in handling, dispensing, storing, and conveying the fumed oxide. Additionally, fumed metallic oxides may pose serious inhalation risks due to their propensity to become airborne and potentially break apart into nanoscale primary particles. Accordingly, the present applicant has recognized an ongoing need to reduce the inhalation risks and handling difficulties of fumed metallic oxides without sacrificing the high surface area and other desirable properties.
In accordance with one embodiment of the present disclosure, a method for processing fumed silica into silica agglomerations is provided. The method may include providing fumed silica particles, combining the particles with a liquid carrier to form a solution of suspended fumed silica particles, atomizing the solution, and subjecting the atomized droplets to a temperature range to remove the liquid carrier and produce the silica agglomerations. The provided fumed silica may have a Brunauer Emmett Teller surface area of greater than about 50 meters squared per gram (m2/g), a dominant branched morphology comprising from 5 nanometer (nm) to 50 nm primary particles, and an average bulk density of less than 64 kilograms per cubic meter (kg/m3). The solution of suspended fumed silica particles may comprise from about 2 weight percent (wt %) to about 8 wt % of the fumed silica particles. Similarly, at least a majority of the silica-containing droplets may have a droplet diameter of about 250 nm to about 100 micrometers (μm) and a fumed silica particle weight percentage of from about 2 wt % to about 8 wt %. The droplets may be subjected to a temperature of from about 50° C. to about 1500° C. for a period of time of at least about 0.5 seconds to produce silica agglomerations. Substantially all of the produced silica agglomerations may exhibit a second BET surface area that is at least about 75% of the BET surface area of the fumed silica particles and may have a dominant globular morphology characterized by an average bulk density of greater than 64 kg/m3.
In accordance with another embodiment of the present disclosure, a method for processing fumed metallic oxides into metallic oxide agglomerations is provided. The method may include providing fumed metallic oxide particles, combining the particles with a liquid carrier to form a solution of suspended fumed metallic oxide particles, atomizing the solution, and subjecting the atomized droplets to a temperature range to remove the liquid carrier and produce the metallic oxide agglomerations. The provided fumed metallic oxide particles may have a Brunauer Emmett Teller surface area of greater than about 50 m2/g and a dominant branched morphology comprising from 5 nm to 50 nm primary particles. The solution of suspended fumed metallic oxide particles may comprise from about 2 wt % to about 8 wt % of the fumed metallic oxide particles. Similarly, at least a majority of the metallic oxide-containing droplets may have a droplet diameter of about 250 nm to about 100 micrometers (μm) and a fumed metallic oxide particle weight percentage of from about 2 wt % to about 8 wt %. The droplets may be subjected to a temperature of from about 50° C. to about 1500° C. for a period of time of at least about 0.5 seconds to produce metallic oxide agglomerations. Substantially all of the produced metallic oxide agglomerations may exhibit a second BET surface area that is at least about 75% of the BET surface area of the fumed metallic oxide particles, and may have a dominant globular morphology.
Although the concepts of the present disclosure are described herein with primary reference to some specific processing assembly configurations, it is contemplated that a wide variety of processing assembly configurations will be suitable for the processing methodology disclosed herein.
The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:
The following description of the embodiments is exemplary and illustrative in nature and is in no way intended to be limiting it its application or use. Reference will now be made in detail to embodiments and methods for producing metallic oxide agglomerations, examples of which are illustrated in the accompanying drawings. As mentioned above, whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. Specific embodiments will now be described with references to the figures.
The fumed metallic oxide particles 110 may have a Brunauer Emmett Teller (BET) surface area of greater than about 50 meters squared per gram (m2/g). As used herein, “BET surface area” refers to the average surface area of the metallic oxide particles as measured by the BET (Brunauer Emmett Teller) nitrogen absorption method according to ASTM D-6556. In some embodiments, the fumed metallic oxide particles 110 may have a BET surface area of greater than about 100 m2/g, or greater than about 150 m2/g, or 200 m2/g, or 250 m2/g. For instance, the fumed metallic oxide particles 110 may have a BET surface area of from about 50 m2/g to about 650 m2/g, or from about 200 m2/g to about 600 m2/g, or from about 250 m2/g to about 650 m2/g, or from about 350 m2/g to about 650 m2/g. In some embodiments, the fumed metallic oxide particles 110 may have a BET surface area of from about 50 m2/g to about 600 m2/g, or from about 50 m2/g to about 500 m2/g, or from about 50 m2/g to about 400 m2/g. The fumed metallic oxide particles 110 may, in some embodiments, have a BET surface area of from about 150 m2/g to about 450 m2/g, or from about 250 m2/g to about 450 m2/g, or from about 200 m2/g to about 500 m2/g, or from about 350 m2/g to about 600 m2/g, or from about 300 m2/g to about 500 m2/g. Having a high BET surface area may be commercially desired. Further, fumed metallic oxide particles 110 having a high BET surface area may allow the produced metallic oxide agglomerations 410 to retain the high surface area of the fumed metallic oxide particles 110.
In one or more embodiments, the fumed metallic oxide particles 110 may be characterized by a dominant branched morphology comprising from about 5 nanometer (nm) to about 50 nm primary particles. As used herein, “dominant branched morphology” refers to a particle in which branched, subdivided portions of the particle make up a majority of the dimensional surface extremities of the particle. In some embodiments, the fumed metallic oxide particles 110 may have primary particles from about 10 nm to about 50 nm, or from about 15 nm to about 50 nm, or from about 25 nm to about 50 nm, or from about 35 nm to about 50 nm, or from about 10 nm to about 40 nm, or from about 10 nm to about 30 nm, or from about 10 nm to about 20 nm, or from about 25 nm to about 45 nm. The size of the primary particles may be important to allow the fumed metallic oxide particles 110 to be sufficiently branched so as to exhibit a high BET surface area. The average primary particle size should be high enough to allow for increased BET surface area (such as above about 5 nm) but should not be too high (such as above about 50 nm) to where the fumed metallic oxide particles 110 exhibit more of a straight chain morphology rather than branched.
Referring still to
The liquid carrier 130 may be any liquid suitable to combine with the fumed metallic oxide particles 110 to support a suspension. In some embodiments, the liquid carrier 130 may be an organic or inorganic solvent. For instance, the liquid carrier 130 may comprise H2O, and, in some embodiments, the liquid carrier 130 may be water. Alternatively, the liquid carrier 130 may comprise supercritical carbon dioxide (“scCO2”) or an alcohol. It should be understood that while the solvent is termed a “liquid” carrier 130, the solvent may, in some embodiments, comprise a supercritical fluid, which does not have a distinct liquid or gas phase. As used herein, “supercritical” refers to a substance at a pressure and a temperature above that of its critical point, such that distinct phases do not exist and the substance may exhibit the diffusion of a gas while dissolving materials like a liquid. In some embodiments, organic solvents may not be as desirable as a liquid carrier 130 due to potential formation of volatile organic compounds (VOCs), which can be a health hazard. In some embodiments, ultrapure water, including but not limited to distilled or deionized water, may be used as the liquid carrier 130 to produce resulting metallic oxide agglomerations 410 with a substantially unchanged chemical composition. The ultrapure water may not react with the fumed metallic oxide particles 110 and may evaporate without leaving a residue on the produced metallic oxide agglomerations 410. The liquid carrier 130 may be selected such that the produced metallic oxide agglomerations 410 exhibit a high purity, such that they have substantially the same chemical composition as the provided fumed metallic oxide particles 110. In some embodiments, the produced metallic oxide agglomerations 410 may be comprised of less than about 2 wt % of impurities. In other embodiments, the metallic oxide agglomerations 410 may be comprised of less than 5 wt % impurities, or less than 3 wt % impurities, or less than 1 wt % impurities, or less than 0.5 wt % impurities.
In some embodiments, the method may comprise doping the solution of suspended fumed metallic oxide particles 120 such that the produced metallic oxide agglomerations 410 do not have substantially the same chemical composition as the provided fumed metallic oxide particles 110. In some embodiments, the doping step may comprise selecting the liquid carrier 130 such that the produced metallic oxide agglomerations 410 do not have substantially the same chemical composition as the provided fumed metallic oxide particles 110 but rather are altered by the introduction or one or more substances. For instance, the solution of suspended fumed metallic oxide particles 120 may be doped with a doping agent. As used herein, “doping agent” refers to an element or molecule inserted into or onto a substance to alter the chemical, electrical, or optical properties of the substance. In some embodiments, the doping may result in that the produced metallic oxide agglomerations 410 may not have substantially the same chemical composition as the provided fumed metallic oxide particles 110. In some embodiments, the doping agent may comprise a trace impurity inserted in very low quantities to alter the chemical, electrical, or optical properties of the produced metallic oxide agglomerations 410. The liquid carrier 130 may comprise one or more doping agents, such as two or more or three or more doping agents. In some embodiments, the doping step may comprise introducing a carrier gas to the solution of suspended fumed metallic oxide particles 120 such that the produced metallic oxide agglomerations 410 do not have substantially the same chemical composition as the provided fumed metallic oxide particles 110. In some embodiments, one or more carrier gases may be introduced to the solution of suspended fumed metallic oxide particles 120 to dope the produced metallic oxide agglomerations 410. The gases could include, but are not limited to, nitrogen, silane, phosgene, or combinations thereof. Solid doping agents could include, for example, semiconducting quantum dots or other colloidal nanoparticles. Liquid doping agents could include dissolved metal salts, such as AgNO3, NaCl, or Al(NO3)3.
Still referring to
The solution of suspended fumed metallic oxide particles 120 may comprise from about 2 wt % to about 8 wt % fumed metallic oxide particles 110. In some embodiments, the solution of suspended fumed metallic oxide particles 120 may comprise from about 4 wt % to about 8 wt %, or from about 3 wt % to about 8 wt %, or from about 2 wt % to about 7 wt %, or from about 3 wt % to about 6 wt %, or from about 4 wt % to about 7 wt %, or from about 5 wt % to about 7 wt % fumed metallic oxide particles 110 suspended in the liquid carrier 130. The solution of suspended fumed metallic oxide particles 120 may comprise about 6 wt % fumed metallic oxide particles 110, or may comprise about 1.5 wt %, or about 2 wt %, or about 3 wt %, or about 5 wt %, or about 7 wt %, or about 10 wt %, or about 12 wt % fumed metallic oxide particles 110.
As shown in
In some embodiments, the atomized metallic oxide-containing droplets 220 may be characterized by a droplet diameter of from about 250 nm to about 100 micrometers (μm). In other embodiments, the metallic oxide-containing droplets 220 may have a droplet diameter of from about 250 nm to about 50 μm, or from about 250 nm to about 10 μm, or from about 250 nm to about 1 μm, or from about 250 nm to about 500 nm. In one or more embodiments, the metallic oxide-containing droplets 220 may have a droplet diameter of from about 300 nm to about 50 μm, or from about 500 nm to about 50 μm, or from about 1 μm to about 50 μm, or from about 5 μm to about 50 μm, or from about 15 μm to about 50 μm. The metallic oxide-containing droplets 220 may have a droplet diameter of from about 300 nm to about 5 μm, or from about 500 nm to about 5 μm, or from about 1 μm to about 25 μm, or from about 250 nm to about 500 nm, or from about 250 nm to about 750 nm. The droplet size may be central to the rearrangement of the fumed metallic oxide particles 110. The metallic oxide-containing droplets 220 may need to be large enough to permit the fumed metallic oxide particles 110 to rearrange, but cannot be too large such that the fumed metallic oxide particles 110 are spaced too far apart from one another, which may require large amounts energy to move or rearrange the fumed metallic oxide particles 110.
In some embodiments, the metallic oxide-containing droplets 220 may be characterized by a fumed metallic oxide particle 110 weight percentage of from about 2 wt % to about 8 wt %. The fumed metallic oxide particles 110 may alternatively comprise from about 4 wt % to about 8 wt %, or from about 3 wt % to about 8 wt %, or from about 2 wt % to about 7 wt %, or from about 3 wt % to about 7 wt %, or from about 4 wt % to about 7 wt %, or from about 5 wt % to about 7 wt % fumed metallic oxide particles 110. For example the metallic oxide-containing droplets 220 may comprise about 6 wt % fumed metallic oxide particles 110, or may comprise about 2 wt %, or about 3 wt %, or about 6 wt %, or about 7 wt %, or about 10 wt %, or about 12 wt % fumed metallic oxide particles 110. The amount of fumed metallic oxide particles 110 in the metallic oxide-containing droplets 220 may be important to producing the metallic oxide agglomerations 410, as too many fumed metallic oxide particles 110 may not properly rearrange into a globular morphology due to the increased amount of energy required to rearrange the fumed metallic oxide particles 110. Likewise, too few fumed metallic oxide particles 110 may not be sufficient to rearrange into a globular morphology and therefore may remain branched and substantially unchanged from the starting fumed metallic oxide particles 110.
Referring again to
Without being bound by theory, in some embodiments, the metallic oxide-containing droplets 220 may comprise fumed metallic oxide particles 110, which may rearrange inside of the metallic oxide-containing droplets 220 when subjected to the previously-mentioned temperature range. Upon drying the liquid carrier 130, metallic oxide agglomerations 410 may form, which may be dominantly globular in morphology. As used herein, “dominant globular morphology” refers to a particle that is free of branched portions greater than about 5 nm and which exhibits a rounded shape at the majority of the dimensional surface extremities of the particle.
In some embodiments, substantially all of the produced metallic oxide agglomerations 410 may exhibit a dominant globular morphology and a BET surface area that is at least about 75% of the BET surface area of the BET surface area of the fumed metallic oxide particles 110. In some embodiments, the metallic oxide agglomerations 410 may exhibit a BET surface area that is at least about 80% of the BET surface are of the fumed metallic oxide particles 110, or at least about 85%, or at least about 90%, or at least about 95%. Due to their dominantly globular morphology, the produced metallic oxide agglomerations 410 may have a reduced propensity to aerosolize when compared to the fumed metallic oxide particles 110. The metallic oxide agglomerations 410 may not pose a serious inhalation risk and may be easier to handle and process without incurring additional health risks. The metallic oxide agglomerations 410 may retain the amorphous chemistry of the fumed metallic oxide particles 110 such that the chemical composition and purity and the properties of the fumed metallic oxide particles 110 are substantially maintained in the produced metallic oxide agglomerations 410.
In some embodiments, the method may further comprise a collecting step 405 in which the metallic oxide agglomerations 410, or at least a majority of the produced metallic oxide agglomerations 410, are collected by filtration, condensation, or other means. It should be understood that the collecting step 405 may not be necessary in one or more embodiments. In some embodiments, the metallic oxide agglomerations 410 may be collected with a filter 420. The filter 420 may comprise a bag filter, a vacuum filter, a sieve, a membrane, or any other means of separating and collecting the metallic oxide agglomerations 410. While the filter 420 is depicted as conical in nature, which may be representative of a Büchner or Hirsch funnel, it should be understood that the filter 420 may comprise any size or shape known to those skilled in art. Alternatively or additionally, the metallic oxide agglomerations 410 may be collected via condensation, such as through a condensation collector, through impaction, or through a cyclone separator.
In one or more embodiments, the processing method may be substantially reversible, such that the metallic oxide agglomerations 410 may be reverted back into a solution of suspended fumed metallic oxide particles 120. In some embodiments, the method may comprise redispersing the metallic oxide agglomerations 410 in the liquid carrier 130 to form a solution of suspended fumed metallic oxide particles 120. The liquid carrier 130 may, in some embodiments, comprise water, solvent, or a mixture of multiple liquids. As discussed above, the liquid carrier 130 may be an organic or inorganic solvent.
Referring now to
In one or more embodiments, immediately following the atomization step 205, the fumed metallic oxide particles 110 may be dispersed in the liquid carrier 130. Following atomization, the fumed metallic oxide particles 110 may begin to undergo a first rearranging step 315. In some embodiments, the first rearranging step 315 may begin upon subjecting the metallic oxide-containing droplets 220 to a temperature of from about 50° C. to about 1500° C., as discussed above. Without being bound by theory, in the first rearranging step 315, the fumed metallic oxide particles 110 may begin to rearrange and densify. Through the passage of time, the increase in temperature, or both, the metallic oxide-containing droplets 220 may undergo a second rearranging step 325 and even may undergo a final rearranging step 335 to further rearrange before undergoing a densifying step 345 into a globular morphology. In some embodiments the liquid carrier 130 may be substantially removed during the densifying step 345, or after the densifying step 345. In some embodiments, the liquid carrier 130 may be removed from the metallic oxide-containing droplets 220 through evaporation, which may include applying heat 308 to the metallic oxide-containing droplets 220. In other embodiments, the metallic oxide-containing droplets 220 may be vaporized, chemically or physically separated from the produced metallic oxide agglomerations 410, or, in some embodiments, may be further reacted to form gaseous species. The removal of the liquid carrier 130 is represented in
Referring now to
In some embodiments, a carrier 235 may be used to propel the metallic oxide-containing droplets 220 through the drier 318, the heater 328, or both. The carrier 235 may be a carrier gas, as discussed above, which may comprise nitrogen, helium, hydrogen, argon, air, combinations thereof, inert gas, or a reactive gas. The carrier 235 may be injected into the solution of suspended fumed metallic oxide particles 120, the metallic oxide-containing droplets 220, or both. In some embodiments, the injection of a carrier 235 may aid in the movement of the particles throughout the processing components. In one or more embodiments, a vacuum 437 may alternatively or additionally be applied to propel the metallic oxide-containing droplets 220 through the drier 318, the heater 328, or to a filter 420, which may collect the metallic oxide agglomerations 410. As mentioned above, in some embodiments, the metallic oxide agglomerations 410 may not be filtered but may be collected through other means.
Referring now to
In
In contrast,
Again referring to
It will be apparent to those skilled in the art that various modifications and variations may be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.
In order that the embodiments may be more easily understood, reference is made to the following examples, which are intended to illustrate embodiments disclosed and described herein. The examples are in no ways limiting in scope.
Fumed silica (silicon oxide, SiO2) was processed according to embodiments shown and described herein to produce silica agglomerates with a globular morphology. As depicted in Table 1, below, fumed silica commercially available from Evonik and Strem Chemicals was mixed with deionized water to form a solution of suspended fumed silica particles. The solution was atomized using an ultrasonic transducer. The droplet size was varied to produce the desired % wt of solid fumed silica particles present in the droplets. The droplets were dried to remove the deionized water at varying residence times and flow rates by flowing the liquid aerosol through a tube furnace for the time and temperatures listed below.
The BET surface area of Evonik and Strem fumed silica is listed as being around 200 m2/g, however the BET of the starting fumed silica particles were measured to be between 207 and 214 m2/g. For the BET surface area retention percentages depicted in Table 3, the highest measured value of 214 m2/g was used to ensure accuracy. All of the resulting silica agglomerations were characterized as amorphous by x-ray diffraction analysis. Notably, as shown below in Table 3, the resulting silica agglomerates all retained extraordinarily high BET surface areas, with some samples within over 90% BET surface area retention. As shown in Comparative Example 3, if the percent weight of solids in the atomized droplets is too low, such as below 2 wt %, as discussed above, the BET surface area of the produced agglomerate may not retain 75% of the BET surface area of the starting fumed oxide.
1Strem Chemicals Fumed Silica, 0.012 micron, 200 BET Surface Area (m2/g)
Similarly, fumed alumina was also processed according to embodiments of the methods shown and described herein. Fumed alumina, commercially available from Evonik Chemicals was mixed with deionized water to form a solution of suspended fumed alumina particles. The solution was atomized using an ultrasonic transducer. The droplet size was varied to produce the desired % wt of solid fumed alumina particles present in the droplets. The droplets were dried to remove the deionized water at varying residence times and flow rates by flowing the liquid aerosol through a tube furnace for the time and temperatures listed below. All of the resulting alumina agglomerations were characterized as amorphous by x-ray diffraction analysis. Notably, as shown below in Table 3, the resulting alumina agglomerates all retained extraordinarily high BET surface areas, with some samples within over 90% BET surface area retention.
2Evonik Aeroxide Alu 130, 110-150 BET Surface Area (m2/g)
Finally, a mixture of fumed metallic oxides was also processed according to embodiments of the methods shown and described herein. Fumed alumina, commercially available from Evonik Chemicals, and fumed silica, commercially available from Sigma Aldrich and Evokik Chemicals, was mixed with deionized water to form a solution of suspended fumed oxide particles. The solution was atomized using an ultrasonic transducer. The droplet size was varied to produce the desired % wt of solid fumed mixed oxide particles present in the droplets. The droplets were dried to remove the deionized water at varying residence times and flow rates by flowing the liquid aerosol through a tube furnace for the time and temperatures listed below. All of the resulting mixed oxide agglomerations were characterized as amorphous by x-ray diffraction analysis. Notably, as shown below in Table 3, the resulting mixed oxide agglomerates all retained extraordinarily high BET surface areas, with some samples within over 80% BET surface area retention.
3Sigma-Aldrich Fumed Silica, 0.007 microns, 395 ± 25 BET Surface Area (m2/g)
4Evonik Aeroxide Alu 130, 110-150 BET Surface Area (m2/g)
5Evonik Aerosil Fumed Silica, 350-410 BET Surface Area (m2/g)
As shown in Table 4, the methods of the present disclosure may allow for the production of metallic oxide agglomerations that exhibit a dominantly globular morphology to reduce the inhalation risks presented by fumed metallic oxide particles, but retain the desired properties of their fumed counterparts, such as a high BET surface area. As shown above, the produced metallic oxide agglomerates may have a BET surface area retention of at least about 75%, at least about 80%, at least about 85%, at least about 90%, or even at least about 95%.
Having described the subject matter of the present disclosure in detail and by reference to specific embodiments thereof, it is noted that the various details disclosed herein should not be taken to imply that these details relate to elements that are essential components of the various embodiments described herein, even in cases where a particular element is illustrated in each of the drawings that accompany the present description. Further, it will be apparent that modifications and variations are possible without departing from the scope of the present disclosure, including, but not limited to, embodiments defined in the appended claims. More specifically, although some aspects of the present disclosure are identified herein as preferred or particularly advantageous, it is contemplated that the present disclosure is not necessarily limited to these aspects.
It should be noted that one or more of the following claims utilize the term “wherein” as a transitional phrase. For the purposes of defining the present invention, it is noted that this term is introduced in the claims as an open-ended transitional phrase that is used to introduce a recitation of a series of characteristics of the structure and should be interpreted in like manner as the more commonly used open-ended preamble term “comprising.”
This application is a continuation of U.S. patent application Ser. No. 15/146,037 filed May 4, 2016.
Number | Date | Country | |
---|---|---|---|
Parent | 15146037 | May 2016 | US |
Child | 15949726 | US |