JP2004502530A - Multi-stage size reduction, blending and drying systems and methods. - Google Patents

Abstract

A system and method for milling, blending and processing material particles and additives using a high pressure liquid energy mill (104). The mill discharges a slurry composed of the materials, additives and particles of the energy transfer liquid. This slurry is introduced into a hydrocyclone (310) to separate the particles by size. This slurry is introduced into a spray dryer (108). The spray dryer atomizes the slurry, and the slurry evaporates and drops through a heating zone. The collector (112) captures the dried particles that have fallen.

Description

[0001]
(Background of the Invention)
(Field of the Invention)
The present invention relates to systems and methods for multi-stage processing of materials. More specifically, the present invention relates to systems and methods for treating particles of a material in a liquid energy mill using additives and a spray dryer. More specifically, the invention relates to a system and method for subjecting material particles and additives to a liquid energy mill for grinding and blending the particles, and a spray dryer for drying the particles.
[0002]
(Related fields)
Conventional milling machines use mechanical crushing, or crushing and attrition, to break down mineral particles into smaller particles. Conventional milling machines have low efficiency due to frequent application of stress in the absence of particles. As a result, most of the energy input is wasted, for example, in non-productive contacts between the crusher or between the crusher and the mill wall, both of which reduce the overall energy efficiency of the process . A more efficient way to induce simple tensile failure uses a high pressure liquid jet or a different liquid jet in the grinding process.
[0003]
Size reduction involves breaking chemical bonds in a material to create a new surface. Thus, the chemical process associated with the rupture significantly affects the energy required to induce this rupture. This effect extends beyond the bond itself to include the surrounding environment. For example, the presence of liquid at the tip of a crack reduces the force required to propagate the crack and improves efficiency. One explanation for this effect is that the liquid penetrates into the microcracks that precede the main crack, thereby participating in highly reactive events that occur during fracture. Capillary flow of these liquids into the material prior to the primary liquid surface travels at the rate of crack propagation and thus provides a means to more easily transfer energy within the crack tip zone. Accordingly, liquid energy mills that provide liquid for capillary flow are commonly used in grinding materials.
[0004]
Liquid energy mills discharge a slurry of liquid and particles. Usually, these particles must be dried before further processing, as is the case for ceramic powders. Due to the fine size of the powder (ie, large surface area to volume), drying can be a lengthy and cumbersome process. In addition, if the slurry contains a multi-component mixture of particles, separation of the materials can occur during drying, which results in undesirable non-uniformities. Further, the powder may agglomerate during the drying process, requiring further processing for deagglomeration.
[0005]
Spray dryers have been developed to dry powder particles while they are suspended in the air. Spray drying involves atomizing a slurry of particles and liquid into droplets and evaporating the liquid from the droplets using warm air. The dry particles are then separated from the liquid vapor. Spray drying is used in industries such as the chemical, dairy, and food industries.
[0006]
Particles obtained from a liquid energy mill are commonly used for powder processing. This process is important in the ceramic, structural ceramic, and electrical industries. In one example, the milled powder is used to make a ceramic component for the ceramic industry. A binder, acting like an adhesive, is spread over this powder, resulting in a powder-binder mixture. The mixture is injection molded or precision cast to give a solid formed from a compact of the mixture. The formed compact is sintered at an elevated temperature, at which temperature the binder evaporates or decomposes in a "burn out" process to yield a finished monolithic product.
[0007]
Standard known requirements in selecting an appropriate binder include:
-Clean burning without residual residues;
Non-reactive with the powder so as not to change the surface properties;
Thermal decoupling in a relatively short time;
-Appropriate liquid properties, such as low viscosity to aid mixing;
-Proper wetting properties for proper adhesion to the powder surface.
[0008]
Ideally, the binder covers almost all individual granules of the ceramic powder. The coating thickness is controlled by the viscosity and wetting properties of the binder. Unless the viscosity is very low, achieving thin coatings is difficult. However, low viscosity binders typically require the addition of solvents or elevated temperatures during mixing of the binder material with the powder. Both of these are undesirable. Because the solvent needs to be removed before further processing of the powder, and the high temperature during mixing requires precise temperature control within the bulk of the mixture, requiring special equipment and additional costs Because you do. In addition, high amounts of binder are undesirable. This is because large voids may remain in the ceramic as the binder evaporates and is removed from the ceramic. Such voids impair the integrity and mechanical properties of any finished product.
[0009]
Before the binder is introduced into the powder, the powder must be thoroughly treated. Processing of the powder often involves drying the powder if it is wet. Particles from the spray dryer typically require further processing (eg, adding a binder for the ceramic, as described above) before becoming useful.
[0010]
What is needed is a method and apparatus for introducing additives, such as solid materials or liquid binders, during the grinding stage of powder processing, where during grinding and drying, The additives blend well, and the binder coats the solid blend, where a thin coating of the binder on the particles can be achieved.
[0011]
(Summary of the Invention)
The present invention relates to systems and methods for grinding and treating solid particles of one or more materials. The method includes introducing the material into a liquid energy mill to break the material into particles. The liquid energy mill discharges a slurry consisting of particles and an energy transfer liquid. This slurry is introduced into a spray dryer. The spray dryer atomizes the slurry and the mist falls through a heating zone to evaporate the liquid. A collector captures the dried, falling particles.
[0012]
In another embodiment, a liquid energy mill discharges the slurry and introduces the slurry into a hydrocyclone, which is then introduced into a spray dryer. The hydrocyclone sorts the milled particles by size and returns oversized particles to the liquid energy mill.
[0013]
In another embodiment, the liquid energy mill discharges the slurry, introduces the slurry into a spray dryer, and introduces the dried particles into a cyclone. In the cyclone, the particles are sorted by size. Any oversized particles are returned to the liquid energy mill.
[0014]
In another embodiment, an additive is introduced into a liquid energy mill and processed with the material. The additive can be either a solid substance or a liquid (eg, a binder or a solvent). The slurry discharged from the mill contains additives, material particles, and energy transfer liquid. This slurry is introduced into a hydrocyclone and a spray dryer. The hydrocyclone sorts the particles according to size, and the spray dryer atomizes the slurry, which falls through a heating zone and evaporates the liquid. A collector captures the dry, falling particles that are coated with and / or blended with and / or dissolved with the additive.
[0015]
The above and other features and advantages of the present invention will become apparent from the following more detailed description of preferred embodiments of the invention, as illustrated in the accompanying drawings.
[0016]
(Detailed description of preferred embodiments)
A preferred embodiment of the present invention will now be described with reference to the figures. In these figures, like reference numbers indicate identical or functionally similar elements. Also in the figures, the left-most digit of each reference number corresponds to the figure in which the reference number is first used. While specific configurations and arrangements are discussed, it should be understood that this is done for illustrative purposes only. One skilled in the art will recognize that other configurations and arrangements may be used without departing from the spirit and scope of the invention.
[0017]
FIG. 1 illustrates an embodiment of a system 100 for grinding, blending, and processing materials into particles. The system 100 includes a high pressure pump 102 connected to a liquid energy mill 104. Mill 104 is equipped with a feed pump 106 for introducing particles into spray dryer 108. A condenser 110 and a collector 112 are connected to the spray dryer 108. A recirculation circuit 114 connects the condenser 110 to the high pressure pump 102. However, it will be apparent to one skilled in the art that various configurations of these elements may be used to implement the system 100 of the present invention.
[0018]
The liquid energy mill 104 can be any standard liquid energy mill that can grind the material, as will be apparent to those skilled in the art, and for introducing solid materials, additives, and / or binders into the mill. May be provided. In one embodiment, the liquid energy mill is disclosed in pending, co-pending US patent application Ser. No. 09 / 413,489, filed Oct. 6, 1999, which is incorporated herein in its entirety. Which is incorporated herein by reference.
[0019]
System 100 is useful for grinding and processing several materials. For example, additives can be introduced into the system 100 and blended with the particles in a mill 104 for powder processing. The additive may be a solid material, added to the mill in combination with the primary material, or the additive may be a liquid, such as a liquid binder or solvent for powder processing.
[0020]
In one embodiment, the mill 104 is designed to achieve ultrafine particles with a composite size of less than 15 microns (also referred to as product size). Preferably, the ultrafine particles have a product size in the range of 1-5 microns. Even more preferably, the product size of the ultrafine particles obtained from use of the mill 104 is less than 1 micron.
[0021]
It will be apparent to those skilled in the art that the mill 104 can be used to process various other materials (both organic and inorganic) having various feed sizes. For example, the mill 104 may be used to treat any of the following: ceramic materials, such as ceramics for electronic applications (eg, barium and strontium titanate, lead zirconate, and others). Titanates and zirconates, and high temperature ceramic superconductors); ceramics for structural applications (eg, alumina, zirconia, magnesia, and other oxide systems); non-oxidizing ceramics (eg, toughness applications and Nitrides, borides, silicides, and carbides used for abrasive applications); carbon and carbon by-products (including coke and coke by-products); minerals (eg, anthracite, magnetite, alumina, mica) , Silica, and zircon, metals used for sintering, alloying and other applications of powdered metals (eg, , Chromium, nickel, zinc, copper and brass), other oxides used for polishing and cutting applications (eg, garnet and rare earth oxides), and any others that need to be finely ground In addition, the mill 104 can be used to process various organic materials, including, for example, wood, food and products for use as pharmaceuticals.
[0022]
Typically, the average size of the material added to mill 104 for milling is less than 1/2 inch in diameter, and preferably less than 1/4 inch, but as will be apparent to those skilled in the art. , Larger particles may be introduced into the mill 104. However, larger particles can take more time to grind to very small particle sizes. Prior to introducing the particles into the mill 104, larger particles may be reduced to a smaller size using a grinder or crusher.
[0023]
In one embodiment, the particles to be ground in the mill 104 are dry as they are fed to the mill. In another embodiment, these particles may be supplied to mill 104 as part of a slurry (eg, a mixture of material particles and a liquid). The liquid can be aqueous or non-aqueous (eg, water or organic liquids such as alcohols and oils).
[0024]
Introducing the solid additive into the liquid energy mill 104 produces a mixture of the material to be milled and the additive. This material and the additives are ground at the same time and help each other break. The additives can be introduced at different stages of the mill to achieve different grinding ratios. As such, the resulting mixture may include particles of the additive that are larger than the particles of the material, ie, not as ground as the particles of the material. For example, if the additives are introduced with the materials at the beginning of the mill, the additives and materials may have approximately the same size grinding ratio. This is because both the material and the additive are subjected to the same milling process. Similarly, if the additive is introduced at an intermediate stage of the mill or near a later stage, the additive will not undergo much grinding and may therefore have different size grinding ratios. This ratio also depends, of course, on the initial size of the material, the material properties, and the type of grinding stage used in the mill, as will be apparent to those skilled in the art.
[0025]
Simultaneous grinding of the materials and additives in a liquid energy mill provides intimate and vigorous mixing. As the material particles impact and come into contact with the additive particles, they are ground into a homogeneously blended mixture of the material and additive particles.
[0026]
Each of the additives and materials can be fed to the mill at the desired rate to achieve the desired properties and produce the appropriate proportions of the mixture. Such mixing eliminates the need for further mixing or addition of the material after the milling process to obtain the desired proportions.
[0027]
As noted, the additive can also be a liquid, such as a solvent or a binder. If the additive is a liquid, the additive may be introduced into the liquid energy mill as a secondary stream in addition to the energy transfer liquid stream. The additive may be introduced as a liquid stream at the front end of the liquid energy mill (eg, high pressure pump 102) or may be introduced further along mill 104 in one of the subsequent chambers. If such an additive is introduced with the material into the main chamber of the high pressure liquid energy mill, the liquid additive will coat the surface of the broken material equally as it forms.
[0028]
In manufacturing processes that require a binder, it is important that nearly all individual granules of the particles are coated in order for the resulting product formed from the particles and the binder to exhibit consistent material properties. is there. For ceramics, it is advantageous to compress the coated particles into a compact compact having a density close to the theoretical density of solid ceramics. The compact is sintered, resulting in a finished ceramic that is virtually free of holes and voids. Therefore, it is important that the coating on the particles is thin. This is because the thick coating, i.e., excess binder, leaves voids and holes in the resulting product if the binder is removed from the product during sintering.
[0029]
In order to obtain a thin coating of the binder, the binder must spread evenly over the individual solid particles, with the smallest possible thickness. This is achieved either by lowering the viscosity of the binder, or by forcing it to penetrate and spread uniformly across the particles under pressure. However, the lower viscosity range of the binder is limited. Above the lower end of this range, the binder dissociates from the particles, drips from the product, and causes degradation of its lubricating properties (required during subsequent powder compaction). It is advantageous to use as little binder as possible, while obtaining sufficient coating on each particle. This reduces the occurrence of voids and voids when the binder is removed during sintering.
[0030]
In a liquid energy mill, the binder material is subjected to all the pressure and energy of the energy transfer liquid. Two binders suitable for use in a liquid energy mill for grinding alumina powder are methyl methacrylate ("MMA") and cyanoacrylate. These binders are not water-soluble and therefore are not subject to dissolution when the energy transfer liquid used in the mill is water. In addition, these binders exhibit the desired property of having rapid polymerization in a controllable reaction. MMA polymerizes under standard atmospheric conditions. Therefore, there is no need to add an inhibitor. For example, adding an inhibitor such as Topanol or hydroquinone to the MMA solution to 0.1% inhibits polymerization at atmospheric pressure.
[0031]
It is generally preferred that the binder material not be dissolved by the liquid used for energy transfer in the mill. However, dissolution of the binder material is acceptable if the binder has a vapor pressure lower than the vapor pressure of the liquid used for energy transfer in the mill. This allows the liquid to evaporate in the spray dryer and leave the binder material to form a thin coating over the dried solid particles. Examples of binders that can be used in the present invention include, but are not limited to: CARBOWAX® polyethylene glycol (manufactured by Union Carbide Chemicals and Plastics Co., Inc., Danbury, CT). ) And Methocelcellulose ether (manufactured by DOW Chemical, Midland, MI). Polyvinyl alcohol can also be used. Examples of polyvinyl alcohols that may be used in the present invention include: Elvanol 75-15 (manufactured by EI du Pont de Nemours & Co., Inc., Williamton, DE); and Airvol 205 (Manufactured by Air Products and Chemicals, Inc., Allentown, PA). The energy transfer liquid can be, for example, water or a suitable alcohol (eg, isopropanol), which has a higher vapor pressure than the binder and evaporates readily in the spray dryer, leaving a mixture of dry powders. It will be apparent to those skilled in the art that various liquids can be used as the energy transfer liquid in the mill.
[0032]
In many cases, no changes in chemical reactions or surface properties should take place in the mill or spray dryer. For example, in the case of barium titanate or strontium titanate, water can alter the surface properties of the particles by introducing hydroxide ions, which translates into high-performance particles made from these materials. In electronic components (eg, miniaturized multilayer capacitors, and various converters), this is undesirable. To avoid chemical changes, isopropanol alcohol is used according to the invention as an energy transfer liquid. This alcohol is completely inert to the solid. An alcohol-soluble binder (eg, CARBOWAX®) can be added to the mill during milling. The above process can also be used for lead zirconate, which is also sensitive to water. Lead zirconate is widely used in the manufacture of active electronic devices (eg, solid state pressure sensors).
[0033]
In some cases, altering chemical reactions and surface properties is desirable. In these cases, a solvent may be used as an additive, rather than as a binder, to initiate the reaction of the material in a liquid energy mill. This solvent is preferably miscible with the liquid that can be used for energy transfer. In addition, this solvent can be used as an energy transfer liquid if a high concentration of solvent is required to complete the dissolution.
[0034]
It is advantageous to initiate the reaction in a liquid energy mill with the exhaustive blend achieved in the mill. Furthermore, as the particles are crushed, they have a larger surface area / volume ratio, increasing the reaction rate.
[0035]
One example of such a reaction produces coal tar pitch. Coal tar pitch is used to produce a number of carbon products, such as graphite electrodes for the metal industry, specifically graphite and refractories for the nuclear industry, and graphite fibers for high performance composites. Used for The solvent N-methylpyrrolidone ("NMP") forms coal tar pitch from anthracite. The rate of reaction between NMP and anthracite coal particles is dramatically increased by subjecting the liquid energy mill to high pressure and mechanical shock. The carbon extracted in the resulting coal tar pitch is used to make many carbon products, including those described above. In this case, a spray dryer can be used to regenerate the unused solvent and energy transfer liquid by evaporation, concentration and recirculation.
[0036]
As shown in FIG. 1, the system 100 includes a spray dryer 108 that is attached directly to the outlet of the liquid energy mill 104 via an optional feed pump 106. The liquid energy mill 104 discharges a slurry containing the comminuted material particles and the energy transfer liquid. If the additive is introduced into a liquid energy mill, this output contains the comminuted material, the energy transfer liquid, and the additive. As will be apparent to those skilled in the art, the materials and additives can consist of more than one material or additive.
[0037]
As shown in FIG. 2, spray dryer 108 is attached to feed pump 106 and consists of atomizing components (eg, nozzle 204 and heating chamber 206). Typically, a spray dryer mixes the droplets with a drying medium (eg, air) to efficiently separate the particles from the liquid as the particles fall through the air.
[0038]
There are four general stages in spray drying: atomization, mixing, drying, and separation. First, the feed or slurry is atomized into droplets. This is accomplished by introducing the slurry to a feed pump 106, which passes the slurry through an atomizing nozzle 204. The energy required to overcome the pressure drop across the nozzle opening is provided by feed pump 106.
[0039]
Second, the droplets are mixed with a drying medium (eg, air). The air may be added through a blower via nozzle 204, may be added via an additional nozzle, or may simply be present in chamber 206. Other drying media can be introduced to the spray dryer 108, as will be apparent to those skilled in the art. For example, if the liquid, additive, or material is sensitive to oxygen, an inert gas (eg, nitrogen) can be introduced as a drying medium. If the gas is added through a blower, the gas may be injected into chamber 206 simultaneously with the atomized slurry. The conventional method of introducing gas and slurry simultaneously uses coaxial nozzles, where one nozzle introduces gas and the other nozzle introduces slurry.
[0040]
Third, the droplets are dried. Drying occurs when an atomizing atomizer is provided to a heating zone of chamber 206 or when a hot gas (eg, air or an inert gas as described above) is injected into chamber 206. Flash drying quickly evaporates the liquid from the slurry, leaving only dry particles. Small size droplets allow for rapid drying and require a residence time in the heating zone ranging from 1 to 60 seconds, depending on the application. This short residence time allows drying of the solid material without pyrolysis.
[0041]
Fourth, the product is separated from the gas. As the particles continue to fall, they exit the chamber 206 and accumulate in the particle collector 112 located at the bottom of the chamber 206. The now evaporated liquid is exhausted or collected in condenser 110. Spray dryer by-products are evaporated liquid and dried particles.
[0042]
The use of a spray dryer in connection with a liquid energy mill offers several advantages over conventional drying techniques. For example, spray drying produces a very uniform product from a multi-component solid / slurry. Spray dryers can evaporate the energy transfer liquid from the slurry, leaving additives and materials. If the additive is a liquid, the drying temperature is kept below the decomposition temperature of the binder. As the energy transfer liquid evaporates, a very thin binder coating polymerizes on each particle. After drying in a spray drier, the particles are sufficiently coated to be compact for sintering. No further process is required.
[0043]
Furthermore, the resulting collected particles are fine, dry and fluffy soft. The prior art (e.g., boiling the vapor from the particles) leaves agglomerates of the particles and consequently does not completely blend the additives. Spray dryers also dry particles much faster than prior art drying. Spray dryers dry the product quickly because the particulates expose all sides of the particles to the heat of drying. The particles are subjected to flash drying and can be dried for anywhere from 3 to 40 seconds, depending on the application. Thus, heat sensitive particles can be dried quickly without overheating of the particles. When drying begins, evaporated liquid forms around the particles. This "protective envelope" maintains the solid particles at the boiling temperature of the liquid being evaporated or at a lower temperature. As long as the evaporation process occurs, the temperature of the solid does not approach the dryer temperature, even if the dryer temperature is higher than the liquid evaporation temperature.
[0044]
A further advantage is that the spray dryer can operate as part of a continuous process where particles are collected and dry particles are provided at the same time, rather than having to collect the particles and then dry them. is there. This also allows for fast turnaround times and product changes. This is because there is no product hold-up in the dryer.
[0045]
The acceptable volume of the chamber 206 may be determined by the formula: (dwell time) x (volume flow) = volume of the chamber, where the volume flow is the throughput. Furthermore, due to the larger surface area per unit mass, fine particles typically require a longer dry residence time than larger particles. Thus, the residence time can be longer for finer materials. Also, materials having hydroscopic properties require longer residence times in the chamber 206. Increased temperatures can also be used to facilitate drying of such materials.
[0046]
Spray dryers are used to dry any slurry, whether the slurry is composed of particles of material, additives and an energy transfer liquid, or only of particles of the material and an energy transfer liquid. obtain. Further, the spray dryer may be a standard spray dryer known in the art of spray drying. Spray dryer manufacturers and suppliers include U.S. Pat. S. Dryer Ltd. of Migdal Ha'emek, Israel, Niro, Inc. of Columbia, MD, APV of Rosemont IL, and Spray Drying Systems, Inc. companies such as Randallstown, MD.
[0047]
Conventional spray dryers may be equipped with a condenser 110. Since all drying occurs in the enclosed chamber 206, vapor capture and condensation is easily achieved. The condenser 110 collects the evaporated liquid from the chamber 206 and allows the used liquid to be recovered. Thus, spray drying provides a simple way to include vapors from the evaporated liquid. As shown in FIG. 1, a liquid recirculation circuit 114 may connect the condenser 110 to the high pressure pump 102 located in the first chamber of the liquid energy mill. This allows the condensed liquid to be recycled by returning the used liquid from the spray dryer to the liquid energy mill. This reduces waste and includes liquids, which are particularly important when the liquid is a regulated product, such as isopropanol. Isopropanol can be used as a liquid in a liquid energy mill, introduced into an evaporating spray dryer, recondensed in a condenser, and returned to the liquid energy mill for reuse. In this manner, liquid vapors are included without the danger of releasing harmful vapors into the atmosphere.
[0048]
If the liquid is water, the water may be released from the spray dryer as steam and may be condensed for disposal or may be recycled through a liquid recirculation circuit. It will be apparent to those skilled in the art that various liquids can be used as the energy transfer liquid in the mill.
[0049]
In another embodiment, the slurry is introduced directly from a liquid energy mill into a spray dryer. This embodiment does not use a feed pump connected to a nozzle for atomization. Instead, a high pressure is maintained in the mill 104 using a liquid restrictor at the outlet port of the energy mill. The slurry bypasses the feed pump 106 and is injected into the spray dryer 108 directly from the outlet of the mill 104. To achieve proper separation of particles and liquid in the spray dryer 108, the liquid pressure at the outlet of the mill 104 must be high enough to achieve complete atomization of the slurry. By eliminating the need for a feed pump to introduce the slurry into the spray dryer, the system operates more economically.
[0050]
FIG. 3 illustrates another embodiment of a system 100 for grinding, blending, and processing material into particles. This embodiment includes a hydrocyclone 310 located between the mill 104 and the feed pump 106. The hydrocyclone 310 can be located either before or after the feed pump 106, but is preferably located before the feed pump 106. A second feed pump (not shown) can be used to introduce the slurry from the mill 104 to the hydrocyclone 310, or, as shown in FIG. Can be introduced.
[0051]
The hydrocyclone 310 helps classify solid particles emitted from the liquid energy mill 104 by separating very fine particles from coarser particles. The coarser particles are returned to high pressure pump 102 through recirculation line 312 for further grinding and processing and are reintroduced to mill 104. Alternatively, recirculation line 312 may return particles directly to mill 104 or may remove particles completely from system 100. As the particles are still under pressure from hydrocyclone 310, recirculation line 312 is a tube or enclosed circuit that moves the particles to mill 104 or high pressure tube 102.
[0052]
The slurry from the mill 104 enters the hydrocyclone at high speed through the inlet opening and flows into the conical separation chamber. As the slurry swirls down in this chamber, its speed increases. Larger particles are forced against the wall, fall to the bottom, and are discharged through a restricted discharge nozzle into the recirculation line 312. This rotation forms an internal vortex which lifts the finer particles from the bottom of the hydrocyclone 310 before exiting the discharge nozzle and passes them through the front outlet to feed pump 106 Or directly to the spray dryer 108.
[0053]
In another embodiment, hydrocyclone 310 is a dry cyclone located behind spray dryer 108. In this embodiment, the particles are dried in spray dryer 108 and collected in collector 112. These dry particles are introduced from the collector 112 into the cyclone 310, where they are classified according to size. The cyclone 310 operates substantially similar to the hydrocyclone described above, using gas as a fluid instead of a liquid. In addition, oversized particles are reintroduced to liquid energy mill 104 or high pressure pump 102 via recirculation line 312. Dry separation usually results in a more precise and accurate size distribution, since gases usually have a lower surface tension than liquids.
[0054]
The hydrocyclone 310 can be a commercially available hydrocyclone used for particle sorting, cleaning, countercurrent washing, concentration, and the like. Examples of hydrocyclones and manufacturers of cyclones are Warman International, Inc. of Madison, WI (CAVEX (R) Hydrocyclone Technology), Polytech Filtration Systems, Inc. , Of Sudbury, MA (POLYCLON (R) Hydrocycle Technology), and Dorr-Oliver, Inc. , Of Milford, CT (DORRCLONE® HYDROCLONES).
[0055]
Hydrocyclone 310 recirculates a larger or coarser material fraction to mill 104 for further size reduction. As such, hydrocyclone 310 helps to achieve a narrow size distribution of the final particles. In addition, hydrocyclone 310 provides a more intimate mixture of particles and additives. The residence time in the hydrocyclone 310 is typically short and is a function of the processing speed and equipment size (volume). Therefore: residence time = device volume / treatment time (volume / hour). Typically, this residence time in the hydrocyclone 310 is less than 60 seconds, and is preferably between 2 and 50 seconds. Thus, the use of hydrocyclone 310 does not limit the achievable processing speed in mill 104 and subsequent spray dryer 108.
[0056]
Depending on the size and performance of the hydrocyclone, the residence time is varied for a given processing speed. Therefore, properly sized hydrocyclones must be used to effectively mill, blend and treat the particles. An improperly sized hydrocyclone may limit the residence time of other components of the system 100.
[0057]
The following example using system 100 will further aid in understanding the present invention.
[0058]
(Example 1)
Using system 100, strontium titanate (SrTiO.sub.2) having a final particle size in the range of 0.5 to 2 microns is useful for waveguides, delay lines, filters, and other radar applications. ₃ ), Magnesium oxide (MgO) and barium titanate (BaTiO) ₃ ) May be obtained. The apparent composition is 60 v / o MgO, 40 v / o (0.55 BaO-0.45 SrTiO). ₃ Where the latter material is 55 mol% BaTiO ₃ , 45 mol% SrTiO ₃ It is. BSTO has a density of about 5.62 to 5.63 g / cc.
[0059]
It is preferred if the MgO particle size is somewhat smaller than the other phases. Thus, MgO is supplied as an initial feed to the first stage of the liquid energy mill 104 and is added to the second stage of the mill 104 (a mixture of barium titanate and strontium titanate, preferably as a clinker clinker). I do. As a result of the grinding of the MgO in the first stage, the particle size of the MgO is smaller than the particle size of the titanate mixture introduced in the second stage. These materials use isopropanol as the liquid energy medium because they are very reactive to both water and carbon dioxide. A suitable binding additive (eg, CARBOWAX®) may be added to either the first or second stage of the mill. CARBOWAX® is soluble in isopropanol and provides an intimate mixture with the slurry. Depending on the outlet pressure of the mill 104, the slurry may be introduced directly from the mill 104 into the hydrocyclone 310 or may be sent to a feed pump located between the mill 104 and the hydrocyclone 310.
[0060]
Hydrocyclone 310 removes particles from a slurry mixture having a diameter greater than about 2 microns. The effectiveness of removing particles that are too large in hydrocyclone 310 may be increased by adjusting the inlet pressure to the hydrocyclone for a desired size fraction of the slurry less than 2 microns. Particles that are too large are returned to high pressure pump 102 or reintroduced directly to mill 104 through recirculation line 312.
[0061]
At the product outlet of the hydrocyclone, a feed pump 106 can be used to send the slurry to the spray dryer 108. Hot nitrogen gas at about 200-600 ° C is used as a drying medium for flash evaporation of isopropanol. The dried powder mixture, coated with a binder deposited on the particle surface, is collected in a collector 112 at the bottom of the spray dryer for further processing (eg, compression and shaping, etc.).
[0062]
The steam and gas obtained in the spray dryer 108 are directed to a condenser 110. Condenser 110 condenses isopropanol by pressure changes, temperature changes, or both, as will be apparent to those skilled in the art. The condensed isopropanol is returned to the high-pressure pump 102 through the recirculation circuit 114 and recirculated. Nitrogen is removed from condenser 110 and reintroduced to spray dryer 108 for discharge or further drying.
[0063]
(Example 2)
The system 100 may also be used to obtain an intimate powder mixture composed of lead-zirconium and barium titanate useful for high voltage and high voltage capacitors for power filters. The targeted apparent composition was unexpected PZT, PbO: 0.51 Zr: 0.49 TiO. ₃ (A typical starting composition for PZT materials) and barium titanate (BaTiO ₃ )). The resulting product has a narrow particle distribution of about 1-2 microns, well mixed without large aggregates.
[0064]
Since there is no requirement for size distinction between the two materials, PZT and BaTiO ₃ May be introduced into the first stage of the mill 104. Furthermore, PZT and BaTiO ₃ Are both water sensitive, so isopropanol is used. A suitable binder (eg, CARBOWAX®) is used in the mill in the same manner as described with reference to Example 1. A system 100 using a hydrocyclone 310, a spray dryer 108 and a condenser 110 is used as described with reference to Example 1. The final product is a mixture without agglomeration, high homogeneity and a narrow particle size distribution.
[0065]
While the invention has been shown and described in detail with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail can be made without departing from the spirit and scope of the invention. Understood by.
[Brief description of the drawings]
FIG.
FIG. 1 shows a first embodiment of the system of the invention for the grinding and processing of solid particles of material.
FIG. 2
FIG. 2 shows an embodiment of a spray dryer with a collector and a condenser.
FIG. 3
FIG. 3 shows another embodiment of FIG. 1 with a hydrocyclone and a recirculation line.

Claims (57)

A method for grinding and treating solid particles of a material, the method comprising:
(A) introducing the material into a liquid energy mill;
(B) milling the material in the liquid energy mill, wherein at least a portion of the material is divided into particles, and the liquid energy mill discharges a liquid and a slurry of the particles. , Process; and
(C) introducing the slurry into a spray dryer, wherein the spray dryer comprises a collector for collecting and separating a portion of the material from the liquid;
A method comprising: The method of claim 1, further comprising introducing the slurry into a hydrocyclone to remove any of the particles that are too large. 3. The method of claim 2, wherein the slurry is introduced into the hydrocyclone using a feed pump. 3. The method of claim 2, wherein any particles that are too large are reintroduced into the liquid energy mill. 2. The method according to claim 1, wherein:
(D) introducing particles into a drying cyclone after exiting the spray dryer to remove any particles that are too large;
The method further comprising: The method of claim 1, wherein the slurry is introduced into the spray dryer using a feed pump. The method of claim 1, wherein the spray dryer further comprises a steam condenser. The method of claim 7, wherein the liquid is recycled from the vapor condenser and reused in the liquid energy mill. The method of claim 1, wherein the particles have an average size of less than 15 microns. The method of claim 1, wherein the material is selected from the group consisting of solid organic materials and solid inorganic materials. The method of claim 1 wherein the material comprises: a mineral comprising: a carbon-containing mineral such as anthracite; an oxide such as alumina, silica, rare earth oxide, zircon, mica and magnetite; Oxidized ceramics such as alumina, zirconia, magnesia, titanate, zirconate, garnet; non-oxidized ceramics such as nitrides, borides, silicides and carbides; and metals such as chromium, copper, nickel and zinc A method selected from the group consisting of: Ultrafine particles of a material having a product size of less than 5 microns, made by the method of claim 1. 13. The ultrafine particle of claim 12, wherein the material is selected from the group consisting of: a solid organic material and a solid inorganic material. 14. The ultrafine particle of claim 13, wherein the material comprises the following: carbon-containing minerals such as anthracite, oxides such as alumina, silica, rare earth oxides, zircon, mica and magnetite. Minerals; ceramic oxides such as alumina, zirconia, magnesia, titanates, zirconates, garnets; non-oxidizing ceramics such as nitrides, borides, silicides and carbides; and chromium, copper, nickel and zinc. Ultrafine particles selected from the group consisting of such metals. A method for grinding and treating solid particles of a material, the method comprising:
(A) introducing the material into a liquid energy mill;
(B) introducing an additive into the liquid energy mill;
(C) milling the material in the liquid energy mill, wherein at least a portion of the material is divided into particles, and the liquid energy mill separates the liquid, the additive, and the particles. Discharging the slurry, the process,
A method comprising: Less than:
(D) introducing the slurry into a spray dryer;
16. The method of claim 15, further comprising: Less than:
(E) introducing the slurry into a dry cyclone;
17. The method of claim 16, further comprising: 17. The method of claim 16, wherein the slurry is introduced into the spray dryer using a feed pump. 17. The method of claim 16, wherein said spray dryer further comprises a steam condenser. 20. The method of claim 19, wherein said liquid is recycled from said vapor condenser and recycled in said liquid energy mill. Less than:
(D) introducing the slurry into a hydrocyclone;
16. The method of claim 15, further comprising: 22. The method of claim 21, wherein the slurry is introduced into the hydrocyclone using a feed pump. 22. The method of claim 21, wherein any of the particles that are too large are reintroduced into the liquid energy mill. Less than:
(E) introducing the slurry into a spray dryer;
22. The method of claim 21, further comprising: The method according to claim 15, wherein the additive comprises a thermoplastic liquid. The method of claim 15, wherein the material comprises alumina powder. 27. The method of claim 26, wherein said additive is soluble in said liquid. 28. The method of claim 27, wherein the additive is a binder selected from at least one of the following: methyl methacrylate and cyanoacrylate. 16. The method of claim 15, wherein said particles have a size of less than 15 microns. 16. The method of claim 15, wherein each of the material and the additive has a feed size of less than 0.5 inches in diameter. 16. The method of claim 15, wherein the material is selected from the group consisting of: a solid organic material and a solid inorganic material. 32. The method of claim 31, wherein the material comprises: a carbon-containing mineral such as anthracite, an oxide such as alumina, silica, rare earth oxides, zircon, mica, and magnetite. Ceramic oxides such as alumina, zirconia, magnesia, titanate, zirconate, garnet; non-oxidizing ceramics such as nitrides, borides, silicides and carbides; and chromium, copper, nickel and zinc A metal selected from the group consisting of: 16. Ultrafine particles of a material having a product size of less than 5 microns made by the method of claim 15. 34. The ultrafine particle of claim 33, wherein the material is selected from the group consisting of: a solid organic material and a solid inorganic material. 35. The ultrafine particle of claim 34, wherein the material comprises: a carbon-containing mineral such as anthracite, an oxide such as alumina, silica, rare earth oxides, zircon, mica and magnetite. Ceramic oxides such as alumina, zirconia, magnesia, titanate, zirconate, garnet; non-oxidizing ceramics such as nitrides, borides, silicides and carbides; and such as chromium, copper, nickel and zinc Ultrafine particles selected from the group consisting of natural metals. A system for grinding and treating solid particles of a material, the system comprising:
A liquid energy mill wherein at least a portion of the material is divided into particles;
A spray dryer that receives the particles and a slurry of the liquid from the liquid energy mill;
A system comprising: 37. The system of claim 36, wherein the spray dryer comprises a collector for collecting and separating the particles of the material from the liquid.
Use as described in. 37. The system of claim 36, wherein the slurry is introduced into the spray dryer using a feed pump. 37. The system of claim 36, wherein said spray dryer further comprises a steam condenser. 40. The system of claim 39, wherein the liquid is recycled from the vapor condenser and recycled in the liquid energy mill. 37. The system of claim 36, further comprising a drying cyclone. 37. The system of claim 36, further comprising a hydrocyclone. 43. The system of claim 42, wherein the slurry is introduced into the hydrocyclone using a feed pump. 43. The system of claim 42, wherein any of the particles that are too large are reintroduced into the liquid energy mill. A system for grinding and treating solid particles of a material, the system comprising:
A liquid energy mill, wherein an additive is introduced and at least a portion of the material is divided into particles;
A spray drier receiving a slurry of the particles, the additives and the liquid from the liquid energy mill, comprising a collector for separating the liquid from the particles of the material;
A system comprising: 46. The system of claim 45, wherein the slurry is introduced into the spray dryer using a feed pump. 46. The system of claim 45, wherein the spray dryer further comprises a steam condenser. 48. The system of claim 47, wherein said liquid is recycled from said vapor condenser and recycled in said liquid energy mill. 46. The system of claim 45, further comprising a hydrocyclone, wherein the hydrocyclone receives a slurry of the particles, the additive and the liquid from the liquid energy mill and discharges the slurry to the spray dryer. 50. The system of claim 49, wherein the slurry is introduced into the hydrocyclone using a feed pump. 50. The system of claim 49, wherein any of the particles that are too large are reintroduced into the liquid energy mill. 46. The system of claim 45, further comprising a drying cyclone receiving dry particles from the spray dryer. 53. The system of claim 52, wherein any of the particles that are too large are reintroduced into the liquid energy mill. 28. The method according to claim 27, wherein said additive is a solvent. The method according to claim 1, wherein the liquid is an energy transfer liquid, and the energy transfer liquid is a solvent capable of dissolving solid particles. 16. The method of claim 15, wherein the liquid is an energy transfer liquid, and the energy transfer liquid is a solvent that can dissolve solid particles. 16. The method of claim 15, wherein the liquid energy reduces the size of the particles while simultaneously blending the particles with the additive.