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WO2017066361A1 - Objet en céramique de phosphate de rare et son procédé de fabrication - Google Patents

Objet en céramique de phosphate de rare et son procédé de fabrication Download PDF

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Publication number
WO2017066361A1
WO2017066361A1 PCT/US2016/056706 US2016056706W WO2017066361A1 WO 2017066361 A1 WO2017066361 A1 WO 2017066361A1 US 2016056706 W US2016056706 W US 2016056706W WO 2017066361 A1 WO2017066361 A1 WO 2017066361A1
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Prior art keywords
rare earth
batch material
produce
particle size
range
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Ralph Alfred Langensiepen
Paul Maynard Schermerhorn
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Corning Inc
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Corning Inc
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    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/447—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on phosphates, e.g. hydroxyapatite
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    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • C04B35/62605—Treating the starting powders individually or as mixtures
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Definitions

  • the present disclosure is generally directed to rare earth phosphate-based ceramic articles and methods for producing rare earth or rare-earth-like materials, for example YP0 4 materials, and from which such ceramic articles can be made.
  • Refractory rare earth phosphate ceramic materials have been in use in various industries for many years. Typically, these materials are chemically derived binder phases formed by heating phosphoric acid-wetted masses of ceramic constituents, with the aqueous solution of phosphoric acid reacting with a fine ceramic powder like alumina or aluminum hydrate to form AIPO 4 .
  • rare earth phosphate ceramic material fabrication such as xenotime (YPO 4 )
  • YPO 4 xenotime
  • a wet process has traditionally been used to form fine precipitates of rare earth phosphate precursors, for example in the form of YPO 4 -2H 2 O, the mineral churchite.
  • Calcination of the dried reaction product YPO 4 -2H 2 O does result in the mineral xenotime, but the morphology of the particles is highly acicular. These fine needle-shaped particles do not process well to dense ceramics, and residual water or remnant pore channels in the crystals enhance proton conductivity in the formed ceramic. This phenomenon has been related to water weakening in the ceramic and enhanced high temperature creep, i.e., deformation. Accordingly, a dry reaction process is needed to achieve satisfactory creep properties.
  • a means to densify the reactant powder mix to compact particles in the size range desired for final ceramic processing, which particles form the YPO 4 reaction product that is sequentially sintered at temperatures higher than required for the exothermic reaction to be initiated is described.
  • granulated dense compacts of rare earth phosphates can be manufactured, for example, compacts comprising such rare earths as lanthanum oxide, cerium oxide or the rare earth-like yttrium oxide.
  • such compacts can be sized to be US Sieve size No. -50 (-48 mesh) agglomerates of greater than 50% dense Y 2 O 3 /P 2 O 5 mixed powders with a minimum of interior void space.
  • Reaction of the Y 2 O 3 and the P 2 O 5 to YPO 4 will proceed rapidly on heating the mixture to 1200°C, exhibiting a reaction volume shrinkage of at least 16%.
  • Sintering shrinkage as the temperature of the particles is further raised to 1600°C can further reduce the particle volume by up to 40% to yield No. -60 (-60 mesh) particles with greater than 90% density.
  • These particles can be reduced in size by milling, for example hammer milling, to a No. -140 /No. +325 mesh (-150 mesh/+325 mesh) size fraction that represents 55% of the desired mix for an example ceramic body formulation.
  • finer particles for the matrix can be created by dry vibratory milling to a desired 20% by weight No. -325 (-325 mesh) and 25% by weight 2 micrometer D 50 particles. Yields can be as high as 100% with milling times reduced by 50% or more over previous methods. Contamination levels may also decrease with the reduced handling of the powders.
  • compaction of dry reactants serves to eliminate excess void space between the reactant particles and to enhance the reaction rate and the crystallite size, for example in the exothermic reaction of P 2 O 5 and Y 2 O 3 to produce YPO 4 .
  • Elimination of the surface area afforded by the void space also eliminates the potential for excessive atmospheric water attachment to the P 2 O 5 particles that could affect both the reaction kinetics, morphology and phase purity of the compact so produced.
  • Mixed powders can be compacted in a suitable atmospherically protected tablet press, or an atmospherically protected iso-pressing operation. However, the resulting reactant compacts would form large dense compacts requiring extensive particle size reduction for the end product needs.
  • IBCs Intermediate bulk containers
  • IBCs Intermediate bulk containers
  • a metered flow of dry blended powder can then be directed into the sealed roll pair.
  • a dense tape of compacted powder can be formed under the action of the compactor rolls, which tape would fall into the rotating arms of a granulator device to form sieve-sized dense particles that fall either into another atmosphere protected IBC or directly into the entrance of a tumbling furnace, for example a tubular rotary furnace operating under an inert or dry air cover gas with the tube.
  • reaction to the desired xenotime mineral form may then ensue at a temperature approaching 1200°C, while sintering to dense crystalline particles suitable for subsequent rapid sizing to the desired particle size distribution would be attained at temperatures between 1500°C and 1700°C.
  • Pin mills or dry or wet ball mills may be employed to create the final size reduction from sub-millimeter particle size to the graded sub-millimeter particle size distribution necessary to produce optimal spray-dried powders for very large iso-pressing operations to form the controlled shrinkage compacts desired.
  • a ceramic body formed using a yttrium oxide precursor material other suitable precursor materials include without limitation Y2O3, SC2O3, Er 2 0 3 , Lu 2 0 3 , Tm 2 0 3 , Ho 2 0 3 , Dy 2 0 3 , Tb 2 0 3 , Gd 2 0 3 , La 2 0 3 and mixtures thereof.
  • FIG. 1 is a schematic view of an example glass making process employing a ceramic forming body
  • FIG. 2 is a perspective view, in cross section, of a ceramic block according to embodiments of the present disclosure
  • FIG. 3 is a perspective view, in cross section, of the forming body of FIG. 1 ;
  • FIG. 4 is a process flow chart outlining a method of forming a ceramic block according to the present disclosure, including the forming bodies of FIGS 1 and 3.
  • Ranges can be expressed herein as from “about” one particular value, and/or to "about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.
  • a YPC based material is a material comprising primarily YPO4, with or without an excess amount of Y2O3 or P 2 0 5 over the stoichiometry required for YPO4, and other minor components as may be found therein.
  • the term ( ⁇ 2 0 3 ) ⁇ ⁇ 2 0 5 means a yttrium phosphate material comprising Y2O3 and P 2 C"5 wherein the molar ratio of Y 2 0 3 to P 2 0 5 is x.
  • the term "sintering” refers to a thermally activated process in which solid state diffusion, driven by a reduction in surface energy, creates a solid body from a compacted mass of particles. The body thus formed is referred to as a sintered body.
  • compact refers to a compacted body formed by compression, without sintering, of a particulate material.
  • All particle size ranges are described as sieve and/or mesh sizes, for example between one mesh size and another mesh size, and are presented as US sieve sizes and expressed as No. SS, where SS denoted the sieve size, with equivalent Tyler mesh sizes included in parentheses and expressed as (TT mesh), where TT represents the Tyler mesh number.
  • a negative number e.g., -SS or -TT indicates the particles are capable of passing through the indicated screen.
  • a positive number indicates the particles are blocked by the indicated screen.
  • D 50 refers to the median diameter of the particles in a sample of particles. Thus, for a D 50 of 5 micrometers, 50% of the particles are larger than 5 micrometers and 50% of the particles are smaller than 5 micrometers.
  • the glass manufacturing apparatus 10 can comprise a glass melting furnace 12 that can include a melting vessel 14.
  • glass melting furnace 12 can optionally include one or more additional components such as heating elements (e.g., combustion burners or electrodes) configured to heat raw materials and convert the raw material into molten glass.
  • heating elements e.g., combustion burners or electrodes
  • glass melting furnace 12 may include thermal management devices (e.g., insulation components) configured to reduce heat lost from a vicinity of the melting vessel.
  • glass melting furnace 12 may include electronic devices and/or electromechanical devices configured to facilitate melting of the raw materials into a glass melt.
  • glass melting furnace 12 may include support structures (e.g., support chassis, support member, etc.) or other components.
  • Glass melting vessel 14 is typically comprised of refractory material, such as a refractory ceramic material.
  • glass melting vessel 14 may be constructed from refractory ceramic bricks, for example refractory ceramic bricks comprising alumina or zirconia.
  • the glass melting furnace may be incorporated as a component of a glass manufacturing apparatus configured to fabricate a glass ribbon.
  • the glass melting furnace of the disclosure may be incorporated as a component of a glass manufacturing apparatus comprising a slot draw apparatus, float bath apparatus, down-draw apparatus including a fusion process, up-draw apparatus, press-rolling apparatus, tube drawing apparatus or any other glass manufacturing apparatus.
  • FIG. 1 schematically illustrates glass melting furnace 12 as a component of a fusion down-draw glass manufacturing apparatus 10 for fusion drawing a glass ribbon for subsequent processing into glass sheets.
  • the glass manufacturing apparatus 10 can optionally include an upstream glass manufacturing apparatus 16 positioned upstream relative to glass melting vessel 14. In some examples, a portion of, or the entire upstream glass manufacturing apparatus 16, may be incorporated as part of the glass melting furnace 12.
  • the upstream glass manufacturing apparatus 16 can include a raw material storage bin 18, a raw material delivery device 20 and a motor 22 connected to the raw material delivery device.
  • Storage bin 18 may be configured to store a quantity of raw materials 24 that can be fed into melting vessel 14 of glass melting furnace 12, as indicated by arrow 26.
  • raw material delivery device 20 can be powered by motor 22 to deliver a predetermined amount of raw materials 24 from the storage bin 18 to melting vessel 14.
  • motor 22 can power raw materials delivery device 20 to introduce raw materials 24 at a controlled rate based on a level of molten glass sensed downstream from melting vessel 14.
  • Raw materials 24 within melting vessel 14 can thereafter be heated to form molten glass 28.
  • Glass manufacturing apparatus 10 can also optionally include a downstream glass manufacturing apparatus 30 positioned downstream of glass melting furnace 12 relative to the flow direction of molten glass.
  • a portion of the downstream glass manufacturing apparatus 30 may be incorporated as part of glass melting furnace 12.
  • first connecting conduit 32 discussed below, or other portions of the downstream glass manufacturing apparatus 30, may be incorporated as part of the glass melting furnace 12.
  • Elements of the downstream glass manufacturing apparatus, including first connecting conduit 32, may be formed from a precious metal. Suitable precious metals include platinum group metals selected from the group of metals consisting of platinum, iridium, rhodium, osmium, ruthenium and palladium, or alloys thereof.
  • downstream components of the glass manufacturing apparatus may be formed from a platinum-rhodium alloy including 70 to 90% by weight platinum and 10 to 30% by weight rhodium.
  • suitable metals can include molybdenum, palladium, rhenium, tantalum, titanium, tungsten and alloys thereof.
  • the downstream glass manufacturing apparatus 30 can include a first conditioning (i.e. processing) vessel such as fining vessel 34, located downstream from melting vessel 14 and coupled to melting vessel 14 by way of the above-referenced first connecting conduit 32.
  • molten glass 28 may be gravity fed from melting vessel 14 to fining vessel 34 by way of first connecting conduit 32.
  • gravity may cause molten glass 28 to pass through an interior pathway of first connecting conduit 32 from melting vessel 14 to fining vessel 34.
  • other conditioning vessels may be positioned downstream of melting vessel 14, for example between melting vessel 14 and fining vessel 34.
  • a cooling vessel (not shown) may be employed between the melting vessel and the fining vessel such that molten glass from the melting vessel is cooled to a temperature lower than the temperature of the molten glass in the melting vessel before entering the fining vessel.
  • Bubbles may be removed from molten glass 28 within fining vessel 34 by various techniques.
  • raw materials 24 may include multivalent compounds (i.e. fining agents) such as tin oxide that, when heated, undergo a chemical reduction reaction and release oxygen.
  • fining agents include without limitation arsenic, antimony, iron and cerium.
  • Fining vessel 34 is heated to a temperature greater than the melting vessel temperature, thereby heating the fining agent.
  • Oxygen bubbles produced by the temperature-induced chemical reduction of the fining agent(s) rise through the molten glass within the fining vessel, wherein gases in the melt produced in the melting furnace can coalesce into the oxygen bubbles produced by the fining agent.
  • the enlarged gas bubbles can then rise to a free surface of the molten glass in the fining vessel and thereafter be vented out.
  • Downstream glass manufacturing apparatus 30 can further include a second conditioning vessel such as mixing vessel 36 for mixing the molten glass that may be located downstream from fining vessel 34.
  • Mixing vessel 36 can be used to provide a homogenous glass melt composition, thereby reducing or eliminating inhomogeneity that may otherwise exist within the fined molten glass exiting the fining vessel.
  • fining vessel 34 may be coupled to mixing vessel 36 by way of a second connecting conduit 38.
  • molten glass 28 may be gravity fed from fining vessel 34 to mixing vessel 36 by way of second connecting conduit 38. For instance, gravity may cause molten glass 28 to pass through an interior pathway of second connecting conduit 38 from fining vessel 34 to mixing vessel 36.
  • mixing vessel 36 is shown downstream of fining vessel 34, mixing vessel 36 may be positioned upstream from fining vessel 34.
  • downstream glass manufacturing apparatus 30 may include multiple mixing vessels, for example a mixing vessel upstream from fining vessel 34 and a mixing vessel downstream from fining vessel 34. These multiple mixing vessels may be of the same design, or they may be of a different design from one another.
  • Downstream glass manufacturing apparatus 30 can further include another conditioning vessel such as delivery vessel 40 that may be located downstream from mixing vessel 36.
  • Delivery vessel 40 may condition molten glass 28 to be fed into a downstream forming device.
  • delivery vessel 40 can act as an accumulator and/or flow controller to adjust and provide a consistent flow of molten glass 28 to forming body 42 by way of exit conduit 44.
  • mixing vessel 36 may be coupled to delivery vessel 40 by way of third connecting conduit 46.
  • molten glass 28 may be gravity fed from mixing vessel 36 to delivery vessel 40 by way of third connecting conduit 46.
  • gravity may act to drive molten glass 28 to pass through an interior pathway of third connecting conduit 46 from mixing vessel 36 to delivery vessel 40.
  • Downstream glass manufacturing apparatus 30 can further include forming apparatus 48 comprising the above-referenced forming body 42 including inlet conduit 50.
  • Exit conduit 44 can be positioned to deliver molten glass 28 from delivery vessel 40 to inlet conduit 50 of forming apparatus 48.
  • forming body 42 can comprise a trough 52 positioned in an upper surface of the forming body and converging forming surfaces 54 that converge along a bottom edge (root) 56 of the forming body.
  • Molten glass delivered to the forming body trough via delivery vessel 40, exit conduit 44 and inlet conduit 50 overflows the walls of the trough and descends along the converging forming surfaces 54 as separate flows of molten glass.
  • the glass ribbon may subsequently be separated into individual glass sheets 60 by a glass separation apparatus (not shown).
  • the forming body for example forming body 42, is responsible for forming a viscous molten glass into a largely finished product (e.g., a glass sheet), and is therefore central to a fusion down-draw process.
  • geometric stability of the forming body is a benefit for making glass sheets with consistent thickness, and thickness variation, over a long production campaign.
  • the forming body is a long heavy object typically operating at an elevated temperature, e.g., 1200°C, for prolonged periods of time while supported only at the ends, the forming body is subjected to creeping, i.e., geometric deformation due to the weight of the forming body and the molten glass it contains, and the temperature of the forming body. Stringent requirements may therefore be imposed on the refractory materials for manufacturing the forming body.
  • a large continuous and unitary block of ceramic material 45 having substantially homogeneous composition and physical properties throughout its volume is desired to fabricate a single forming body.
  • the chemical composition of the ceramic block 45 according to embodiments disclosed herein is substantially uniform, i.e., the major components Y 2 O 3 and P 2 O 5 are distributed substantially uniformly throughout the full volume of the bulk material.
  • the material constituting the ceramic block may comprise essentially a single phase, such as the YPO 4 phase, throughout the bulk of the ceramic block in certain embodiments.
  • the material may comprise multiple phases that are all substantially uniformly distributed inside the bulk material.
  • the material constituting the ceramic block may comprise, in addition to a main YPO 4 phase, a minor Y 2 O 3 phase distributed substantially uniformly in the YPO 4 phase.
  • impurities such as A1 2 0 3 , BaO, B 2 0 3 , CaO, MgO, MnO, Zr0 2 , and the like, may be present in the bulk body at various amounts. Since these impurities are typically present at very low concentrations, the distribution thereof may exhibit an irregular pattern. For example, the concentration of sodium, [Na], may be higher in the vicinity of a surface of ceramic block 45, and lower in regions far from the surface of the block, due to the high-temperature diffusion of sodium in furnaces from the surface to the center of the block.
  • the chemical composition of the ceramic block may be represented by a formula (Y 2 0 3 ) x ⁇ 2 0 5 , where x is the molar ratio between Y 2 0 3 and ⁇ 2 0 5 , and 0.95 ⁇ x ⁇ 1.05.
  • the material may be a stoichiometric YP0 4 material, or may comprise an excess amount of either Y 2 0 3 or P 2 0 5 . Nonetheless, it is more advantageous that the Y 2 0 3 molar amount is not lower than P 2 C"5, and thus it is desired that 1.00 ⁇ x ⁇ 1.05, in certain embodiments 1.00 ⁇ x ⁇ 1.03 and in certain other embodiments 1.00 ⁇ x ⁇ 1.02. This is because excessive P 2 0 5 can lower the melting temperature of YPO 4 faster than the same amount of Y 2 0 3 .
  • the dimensions of the ceramic block can be described in terms of length L, width W and height H.
  • the block can have a large size, where L > 20 centimeters, W > 20 centimeters, and H > 20 centimeters.
  • the block can be a full solid block having a cubic, cuboidal, spherical, spheroidal, or other geometry.
  • the ceramic block 45 shown in FIG. 2 comprises a rectangular cross sectional shape.
  • the ceramic block may take a shape comprising a trough-shaped top part and a wedge-shaped bottom part connected with each other as illustrated by forming body 42 shown in FIG. 3, for example by machining.
  • the ceramic block 42, 45 can have a shape where L > 50 centimeters, W > 30 centimeters, and H > 50 centimeters.
  • the block 42, 45 may have a length L > 100 centimeters, in certain embodiments L > 200 centimeters, in certain other embodiments L > 300 centimeters.
  • ceramic block 45 shall be intended to represent a ceramic block of any shape or size, including the forming body 42, unless otherwise explicitly indicated.
  • the ceramic block of the present disclosure may comprise calcium at a concentration by weight of [Ca], where [Ca] ⁇ 100 ppm, in certain embodiments [Ca] ⁇ 80 ppm, in certain embodiments [Ca] ⁇ 50 ppm, and in certain other embodiments [Ca] ⁇ 40 ppm.
  • the ceramic block of the present disclosure may comprise zirconium at a concentration by weight of [Zr], where [Zr] ⁇ 50 ppm, in certain embodiments [Zr] ⁇ 40 ppm, in certain embodiments [Zr] ⁇ 30 ppm, in certain embodiments [Zr] ⁇ 20 ppm, and in certain other embodiments [Zr] ⁇ 10 ppm.
  • the ceramic block of the present disclosure may comprise aluminum at a concentration by weight of [Al], where [Al] ⁇ 60 ppm, in certain embodiments [Al] ⁇ 50 ppm, in certain embodiments [Al] ⁇ 40 ppm, in certain embodiments [Al] ⁇ 30 ppm, and in certain other embodiments [Al] ⁇ 20 ppm.
  • the ceramic block of the present disclosure may comprise barium at a concentration by weight of [Ba], where [Ba] ⁇ 100 ppm, in certain embodiments [Ba] ⁇ 80 ppm, in certain embodiments [Ba] ⁇ 50 ppm, and in certain embodiments [Ba] ⁇ 40 ppm.
  • the ceramic block of the present disclosure may be characterized by the sum total of [Al], [B], [Ba], [Ca], [Fe], [Hf], [K], [Li], [Mg], [Mn], [Na] and [Zr] being at most 500 ppm by weight, in certain embodiments at most 400 ppm by weight, in certain other embodiments at most 300 ppm by weight, in certain other embodiment at most 200 ppm by weight, and in certain other embodiments at most 100 ppm by weight.
  • the ceramic block of the present disclosure may further contain a low level of carbon.
  • Carbon can be entrapped in any dense material made by sintering because organic matter can be introduced into the material prior to firing, either unintentionally due to material handling issues or intentionally because organic binders may be used in processes for making them.
  • the existence of carbon can affect the mechanical properties of the ceramic block of the present disclosure, and can cause undesired outgassing during normal use thereof.
  • the ceramic block of the present disclosure can be used for handling alkali-free glass materials aimed for applications in opto-electronic devices, such as glass substrates for a liquid crystal display (LCD).
  • the ceramic block can be formed into a large-size forming body, e.g., forming body 42, used in overflow down-draw processes for making alumino silicate glass-based LCD glass substrates. It is desired that for these
  • ceramic block 45 is essentially free of alkali metal ions because such ions are particularly detrimental to semiconductor manufacturing processes conducted on the glass substrates.
  • ceramic block 45 according to the present disclosure can comprise equal to or less than 3 ppm on an elemental basis, for example equal to or less than 1 ppm, of any alkali metal.
  • the ceramic block of the present disclosure may exhibit a nominal density of at least 85%, in certain embodiments at least 87%, in certain embodiments at least 89%, in certain embodiments at least 90%, in certain embodiments at least 93%, in certain embodiments at least 95%), and in certain other embodiments at least 97%, of the theoretical density of YP0 4 under standard conditions (1 atmosphere pressure, 0°C).
  • the theoretical density of YPO 4 under standard conditions is typically considered as being 4.27 g em "3 .
  • the higher the density of the ceramic block the lower the porosity thereof.
  • ceramic block 45 comprises multiple grains, a certain level of porosity is expected to exist between the grain boundaries.
  • the porosity at the grain boundary can significantly affect the mechanical properties of the ceramic block, such as, e.g., creep rate at an elevated temperature and modulus of rupture (MOR) at both room temperature and at the elevated operating temperature.
  • MOR modulus of rupture
  • the ceramic block of the present disclosure further exhibits a low level of cracks in the crystalline grains inside the bulk material. It is believed the existence of a high level of micro- cracks in the micro-structure of ceramic block 45 can reduce the MOR and creep rate of the material under high temperature operating conditions. Such micro-cracks can propagate under load and stress, leading to material failure.
  • the ceramic block of the present disclosure is further characterized by low water content.
  • Water in ceramic block 45 can take various forms, e.g., free water present in H 2 0 form trapped at the grain boundary, or in the form of OH bonded to the surface or bulk of the material and/or the crystal grains. Without intending to be bound by a particular theory, it is believed the existence of water inside the bulk of the material can cause the formation of micro-cracks and propagation thereof under high operating temperatures.
  • the total H 2 0 content in the ceramic block in certain embodiments is maintained in a range equal to or less than 300 ppm by weight, in certain other embodiments equal to or less than 200 ppm by weight, in certain other embodiments equal to or less than 100 ppm by weight, and in still other embodiments equal to or less than 50 ppm by weight.
  • a ceramic block of the present disclosure having the composition and properties enumerated above, can be made by a carefully controlled synthesis method. Such large, high- purity, high-performance ceramic materials have not been found in nature, and therefore must be synthesized. As mentioned above, due to the high melting point of YPO 4 , a high-temperature step would be unavoidable to make the ceramic block of the present disclosure. On the other hand, also due to the high melting point of YP0 4 , directly forming such a large ceramic block 45 by melting the precursor material into a fluid, followed by cooling as is typically used in forming glass materials and some crystalline materials, would be impractical. Thus, the present disclosure describes a sintering method, i.e., heating densely packed precursor particles having the intended final composition into a densified ceramic body 45 containing multiple crystal grains.
  • the synthesizing method disclosed herein for making a large-size ceramic block 45 includes forming a precursor ceramic material using a "dry" synthesis approach, e.g., by reacting anhydrous P 2 0 5 with dry Y 2 O 3 in the desired amounts to form the precursor material with the desired end composition. Due to the highly hygroscopic nature of P 2 0 5 , the two powders are intimately mixed and reacted in a substantially closed container with a dry atmosphere cover gas or gases to prevent water absorption.
  • the dry atmosphere cover may comprise an atmosphere of any suitable dry inert gas, for example nitrogen or any of the noble gases including helium, neon, argon, krypton, xenon, radon and mixtures thereof.
  • the dry atmosphere may be continually replenished by using a continuous flow of the dry atmosphere.
  • dry what is mean is a moisture content equal to or less than 200 ppm water, for example in a range from about 100 to about 200 ppm water.
  • the raw materials of Y 2 0 3 and P 2 0 5 should be as pure as possible, and handling of both raw materials should not introduce the unwanted metals. This requires the use of clean containers made of materials substantially inert to Y 2 0 3 and P 2 0 5 , even at elevated reaction temperatures.
  • the containers may be a glass-lined container.
  • a process 100 for dry processing YPO 4 is disclosed.
  • a first step 102 dry powders of Y 2 0 3 and P 2 0 5 are obtained and stored in a manner such that the dry powders do not absorb moisture.
  • a second step 104 the dry powders of Y 2 0 3 and P 2 0 5 are mixed in a suitable intermediate bulk container (IBC).
  • IBC intermediate bulk container
  • a dry, inert cover gas is included in the IBC during step 104 to prevent water absorption, particularly by the P 2 0 5 .
  • a suitable IBC may be, for example, a Nalgene® container, available from Nalge Nunc International, a subsidiary of Thermo Fisher Scientific.
  • Y2O3 may be prepared by drying and batching the Y2O3 separately from the P2O5. Y2O3 is less absorptive of moisture than P2O5, and may, if desired, be initially processed without the need for a dry, inert cover gas.
  • P2O5 may be transferred under a dry, inert cover gas to the IBC, and upon completion of the Y2O3 processing, the Y2O3 may be transferred to the IBC. While both the Y2O3 and the P2O5 are in the IBC, the content of the IBC can be mixed, such as by tumble mixing. The contents of the IBC are maintained under a dry, inert cover gas during the mixing.
  • the content of the IBC (the Y2O3 - P2O5 mixture) is transferred, still under a dry, inert cover gas, to a roll compactor-granulator (mill).
  • the roll compactor-granulator may comprise separate devices, for example a separate roll compactor and a separate granulator, however, combination roll compactors-granulators are commercially available and may be employed if desired.
  • combined units greatly simplify the task of maintaining a dry, inert cover gas over the granular material.
  • a pharmaceutical-grade roll compactor-granulator such as, without limitation, the Chilsonator® roll compactor produced by the Fitzpatrick Company, available with an integral mill, or the Freund- Vector TFC roll compactor.
  • step 106 the roll compactor compacts the mixed Y2O3 - P2O5 content of the IBC.
  • a feed system conveys the dry powder mix to a compaction area.
  • the powder mix is compacted between counter-rotating rolls, wherein the force applied to the powder mix by the rolls compacts the powder mix to produce a compacted powder mix in ribbon form.
  • the compacted ribbon may then be broken up, for example by milling, in a granulating area, to an appropriate particle size.
  • the compacted powder mix may be granulated to a particle size in a range from about No. -40 (-40 mesh) to about No. -70 (-65 mesh), for example from about No. -45 (-42 mesh) to about No. -60 (-60 mesh).
  • a suitable particle size is No. -50 (-48 mesh).
  • the granulating is performed under a dry, inert cover gas.
  • the granulated compact is then fed in step 108 into a rotary tube furnace operating at a temperature effective to sinter the granulated compact, for example in a range from about 1550°C to about 1650°C.
  • a temperature effective to sinter the granulated compact for example in a range from about 1550°C to about 1650°C.
  • the Y2O3 and P2O5 raw materials are substantially completely reacted to form a networked material where both components are substantially evenly distributed throughout the sintered precursor material, and wherein the sintered precursor material has a mean particle size in a range from about No. -50 (-48 mesh) to about No. -80 (-80 mesh), for example No. -60 (-60 mesh).
  • the sintered precursor material may then be transferred to a series of particle sizing steps.
  • a first such particle sizing step step 110, the precursor material is milled, for example by hammer or pin milling, to a mean particle size of approximately No. -140 (-150 mesh), wherein 90% of the particles pass through a screen with an opening size of 0.104 millimeters, for example in a range from about No. -120 (-115 mesh) to about No. -170 (-170 mesh).
  • the milled precursor material can be screened to a course batch particle size in a range from about No. -140 (-150 mesh) to about No. +325 (+325 mesh).
  • step 112 may then be subjected to a first vibratory milling process in step 1 14 to a particle size in a range from about No. +270 (+270 mesh) to about No. +400 (+400 mesh), for example No. +325 (+325 mesh).
  • the product resulting from either one or both of step 112 and/or step 114 may optionally be cycled back through steps 110, 112 and 114 if desired.
  • a portion of the product resulting from step 112 may be retained as course batch material.
  • Product of step 114 may be subsequently screened during step 116 to form particulate in a range from about No. -270 (-270 mesh) to about No. -400 (-400 mesh), for example No. -325 (- 325 mesh), with a D 50 particle size of about 5 micrometers, for example in a range from about 4 micrometers to about 6 micrometers.
  • a portion of product resulting from step 116 may be retained as medium batch material.
  • the remainder of product from step 116 may then be milled in step 118, for example via a second vibratory milling process, to a D 50 particle size in a range from about 1 micrometer to about 3 micrometers, for example about 2 micrometers.
  • Product from step 118 may be designated as fine batch material.
  • a next step 120 coarse batch material, medium batch material and fine batch material are blended in a ratio suitable for the intended final product.
  • a ratio of about 50 to about 60 wt. % course batch material, about 15 to about 25 wt. % medium batch material and about 20 to about 30 wt. % fine batch material.
  • a suitable ratio may include, for example, 55 weight % course batch material, 20 weight % medium batch material and 25 weight % fine batch material.
  • the blended particulate may then be mixed at step 122, for example in a high shear mixer, then dried in spray drying step 124.
  • spray drying step 124 may include a pulse combustion spray drying step.
  • the spray dried intermediate product of step 124 can then be processed into a forming body suitable for use in a glass making process, for example a fusion down draw glass making process, although other glass making processes that employ large ceramic bodies may benefit from the ceramic bodies of the present disclosure.
  • the spray dried product of step 124 can be isostatically pressed, as represented in step 126, to form a green body.
  • the green body can then be fired at step 128 under conditions suitable to provide a fired (sintered), fully consolidated ceramic block, then optionally machined at step 130 into the final body to be used in a glass making process, although it should be understood that the sintered block may be used, for example either before or after machining, in any other apparatus or process where a large, formed ceramic body can be employed.
  • organic binders may be used with the particulate.
  • organic binder may include, for example, poly(meth)acrylates, MethocelTM, and the like.
  • the use of organic binders in the green body can result in a residual level of carbon in the final ceramic block. Residual carbon in the final ceramic block can be detrimental to the final sintering step 128 and negatively impact the resultant mechanical properties of the ceramic block.
  • the total amount of organic binders should be limited to at most 5% (i.e. in a range from about 0% to about 5%) by weight of inorganic constituents of the green body, and in certain embodiments at most 3%, in certain other embodiments at most 2%, and in still other embodiments at most 1%.
  • the nominal density of the green body affects the final nominal density of the sintered ceramic block and hence the mechanical properties thereof. Accordingly, the density of the green body is at least 60% of the theoretical density of YP0 4 crystals under standard conditions, in certain embodiments at least 63%, in certain other embodiments at least 65%, in certain other embodiments at most 67%, in certain other embodiments at least 69%, and in still other embodiments at least 70%.
  • the particles can comprise the following components: (pi) from 45% - 65% wt.% of coarse batch;
  • particles with the desired particle size distribution and amounts, and optionally the at least one organic binder material are mixed thoroughly and uniformly with each other, put into a flexible bag (e.g. urethane) that can be shaken to promote compaction, vacuumed out and then sealed for isopressing in step 126.
  • a flexible bag e.g. urethane
  • step 126 the flexible bag containing the particulate is subjected to a high pressure isopressing process to densify the particulate entered into the isopressing bag and obtain a green body with a high nominal density, and to achieve an isotropic density profile throughout the body.
  • An anisotropic density profile of the green body would be detrimental to the final properties of the final ceramic block, as an isotropic density profile of the final ceramic block would be highly desired.
  • the isopressing is typically carried out in a machine called an isopress that comprises a container and a fluid that can be pressurized to as high as 124 MPa (18000 psi).
  • the particulate in a sealed bag is then placed into the fluid, and pressurized from all directions to a pressure of at least 50 MPa, in certain embodiments at least 80 MPa, in certain other embodiments at least 100 MPa, and in still other embodiments at least 120 MPa.
  • step 128 comprises the following:
  • the green body due to the slow temperature elevation rate, the green body is subjected to a low temperature gradient from the surface to the core of the green body, and it is allowed to degas through the open pores which close slowly, reducing the entrapment of water and carbon- based contaminants as well as the chance of cracking due to thermal gradients.
  • the sintering may be carried out in an oxidizing environment, such as air, so that organic materials can be oxidized substantially completely and removed from the bulk of the green body before the full consolidation (densification) thereof.
  • the green body densifies through the elimination of the body's porosity. Such densification is manifested by the reduction of volume, i.e., shrinkage.
  • shrinkage The higher the nominal density of the green body, the lower the total shrinkage of the green body at the end of the sintering step to achieve a given final density of the resultant ceramic block 45.
  • the initial speed of shrinking is largely determined by the temperature of the green body. The higher the initial temperature, the faster the shrinking the green body will undergo. However, the higher the initial furnace temperature, the more likely a large temperature gradient from the surface to the core of the green body will result.
  • a slow temperature elevation rate is beneficial to reducing detrimental thermal gradients, and to reducing the initial shrinking speed of the green body. Therefore, the amount of shrinkage as well as the shrinking speed both can impact the final porosity, density and properties of the resultant ceramic block.
  • sintering step 1208 After the green body has been substantially completely densified, it is allowed to cool down at a low cooling rate, e.g., not over 200°C/hour from 1600°C to 200°C, in certain embodiments not over 100°C/hour, in certain other embodiments advantageously not over 50°C/hour, in still other embodiments not over 10°C/hour, so that the cooling does not result in a substantial thermal gradient inside the bulk of the ceramic block, which can cause cracking.
  • a low cooling rate e.g., not over 200°C/hour from 1600°C to 200°C, in certain embodiments not over 100°C/hour, in certain other embodiments advantageously not over 50°C/hour, in still other embodiments not over 10°C/hour, so that the cooling does not result in a substantial thermal gradient inside the bulk of the ceramic block, which can cause cracking.
  • the ceramic body may be shaped to suit the particular use to which the ceramic block will be applied, including without limitation as a forming body in a glass making process, for example forming body 42 for use in a fusion down draw process. Shaping may include machining, grinding or any other shaping process known to those skilled in the art.

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Abstract

L'invention concerne un procédé de fabrication d'un grand corps en céramique en terre rare ou en type de terre rare, par exemple un corps de formation dans un procédé de fabrication de verre et en particulier un procédé de production d'un produit particulaire sec en un nombre réduit d'étapes par rapport aux procédés traditionnels, le produit particulaire sec étant approprié pour une utilisation dans une opération d'iso-pressage utilisé pour fabriquer le corps céramique.
PCT/US2016/056706 2015-10-13 2016-10-13 Objet en céramique de phosphate de rare et son procédé de fabrication Ceased WO2017066361A1 (fr)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019195635A1 (fr) * 2018-04-06 2019-10-10 Corning Incorporated Compositions réfractaires d'aluminosilicate purifiées

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WO2006073841A1 (fr) * 2004-12-30 2006-07-13 Corning Incorporated Materiaux refractaires
US20090211299A1 (en) * 2008-02-27 2009-08-27 Cameron Wayne Tanner Modified synthetic xenotime material, article comprising same and method for making the articles
WO2011106597A1 (fr) * 2010-02-25 2011-09-01 Corning Incorporated Fabrication de xéramiquenotime xénotime par céramisation réactive
WO2012058194A1 (fr) * 2010-10-29 2012-05-03 Corning Incorporated Grand bloc en céramique à base de xénotime et son procédé de fabrication à sec

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006073841A1 (fr) * 2004-12-30 2006-07-13 Corning Incorporated Materiaux refractaires
US20090211299A1 (en) * 2008-02-27 2009-08-27 Cameron Wayne Tanner Modified synthetic xenotime material, article comprising same and method for making the articles
WO2011106597A1 (fr) * 2010-02-25 2011-09-01 Corning Incorporated Fabrication de xéramiquenotime xénotime par céramisation réactive
WO2012058194A1 (fr) * 2010-10-29 2012-05-03 Corning Incorporated Grand bloc en céramique à base de xénotime et son procédé de fabrication à sec

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019195635A1 (fr) * 2018-04-06 2019-10-10 Corning Incorporated Compositions réfractaires d'aluminosilicate purifiées

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