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  • B30—PRESSES
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  • B28—WORKING CEMENT, CLAY, OR STONE
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  • B30—PRESSES
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  • B30B11/00—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses
  • B30B11/001—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses using a flexible element, e.g. diaphragm, urged by fluid pressure; Isostatic presses
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  • C03B17/00—Forming molten glass by flowing-out, pushing-out, extruding or drawing downwardly or laterally from forming slits or by overflowing over lips
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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
  • C04B35/10—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 aluminium oxide
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  • C04B35/48—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 zirconium or hafnium oxides, zirconates, zircon or hafnates
  • C04B35/481—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 zirconium or hafnium oxides, zirconates, zircon or hafnates containing silicon, e.g. zircon
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  • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
  • C04B2235/3231—Refractory metal oxides, their mixed metal oxides, or oxide-forming salts thereof
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Definitions

• the present invention relates to methods of forming large blocks of materials.
• the present invention relates to methods of forming large blocks of compressed particle green-bodies and sintered large blocks involving a step of isostatic pressing.
• the present invention is useful, for example, in making large zircon ceramic blocks suitable for an isopipe of a fusion down-draw process for making glass sheets.
• Large ceramic blocks are useful in construction of many engineering structures due to their attractive mechanic properties and refractoriness.
• large blocks of ceramics comprising AI2O3, Zr0 2 , zircon (Zr0 2 Si0 2 ), Ti0 2 , BeO, MgO, Si0 2 , and mixtures and combinations thereof can be used in making components for melting, delivering and forming metal and/or glass articles.
• zircon has been used in making the large forming ceramic block (called isopipe) in fusion down-draw processes for making glass sheets due to high mechanical strength and dimensional stability at high temperatures.
• Ceramic blocks have been made by a process comprising the following steps: (a) packing particles of the ceramic material into a bag; (b) isostatically pressing the bag to form a green-body inside an isopress at a high pressure; and (c) sintering the green-body to obtain a densified ceramic block.
• the sintered ceramic block can be subsequently machined into desired dimensions and shapes.
• each aspect is illustrated by a number of embodiments, which, in turn, can include one or more specific embodiments. It is to be understood that the embodiments may or may not overlap with each other. Thus, part of one embodiment, or specific embodiments thereof, may or may not fall within the ambit of another embodiment, or specific embodiments thereof, and vice versa.
• a first aspect of the present invention is directed to a method for making a densified body having a dimension of at least 1 meter, comprising the following steps:
• the green-body water column is part of the sea on the planet earth, and the pressing location is at least 5000 meters below the surface of the sea.
• the green-body water column is part of the sea on the planet earth, and the pressing location is at least 10000 meters below the surface of the sea.
• step (IV) the water column is part of the sea on the planet earth, and the pressing location is at least 10500 meters below the surface of the sea.
• step (I) the plurality of particles comprise a ceramic, and the method further comprises a step (V) as follows:
• the ceramic comprises a material selected from BeO, MgO, Zr0 2 , Zr0 2 Si0 2 , A1 2 0 3 , Ti0 2 , and mixtures and combinations thereof.
• step (IV) comprises:
• step (IV.2) the cage is attached to a cable, and the cable is extendably attached to a vessel on the surface of the water column.
• the cage travels at a vertical speed of at most 10 ms -1 .
• the cage travels at a vertical speed of at most 1 ms "1 .
• a pressure sensor is installed on or near the cage, which provides information of the pressure the bag is subjected to.
• a heating element is provided surrounding the bag during step (IV) to maintain a desired temperature thereof.
• the power of the heating element is controlled via a temperature sensor near or on the bag of the green-body.
• the method further comprises the following step (IV-A):
• the bag in step (IV-A), travels at a vertical speed of at most 10 m-s-1 , in certain embodiments at most 5 m-s-1 , in certain other embodiments at most 1 m-s-1, in certain other embodiments at most 0.5 m-s-1, in certain other embodiments at most 0.1 m-s-1.
• a bladder box capable of providing adjustable difference between weight and buoyancy thereof is attached to the cage.
• step (IV) at the end of step (IV), the weight of the bladder is reduced to provide an overall upward force for the assembly comprising the cage and the bladder.
• the densified body has a dimension of at least 2 meters.
• the densified body has a dimension of at least 3 meters.
• the densified body has a dimension of at least 4 meters.
• the densified body has a dimension of at least 5 meters.
• the densified body has a dimension of at least 10 meters.
• the densified body has at least two dimensions perpendicular to each other each of at least 2 meters.
• the densified body has three dimensions perpendicular to each other each of at least 2 meters.
• the densified body has a porosity of at most 10% by volume, in certain embodiments at most 8%, in certain other embodiments at most 5%, in certain other embodiments at most 3%.
• One or more embodiments of the preset invention have one or more of the following advantages.
• the vessel for transporting the green-body before and after the pressing can be a general purpose vessel not specifically dedicated to the isostatic pressing step, the cost of transportation for the green bodies can be shared with the transportation of other goods, and therefore reduced.
• FIG. 1 is a schematic illustration of an isopipe operating to make a glass sheet by a fusion down-draw process.
• FIG. 2 is a diagram showing the temperature of sea water as a function of depth thereof in a tropical area that is suitable for carrying out the isostatic pressing step according to one embodiment of the present invention.
• FIG. 3 is a flow chart showing the steps of making a Zr0 2 Si0 2 ceramic block according to one embodiment of the present invention.
• the present invention may be utilized for making any large bodies of any material involving a step of isostatically pressing a green-body in a sealed bag, especially a green-body for a large ceramic block based on oxides, phosphates or other inorganic materials.
• the present invention is especially useful for making large ceramic blocks having at least one dimension, desirably at least two dimensions perpendicular to each other, of at least 2 meter in size, in certain embodiments at least 2.5 meters, in certain other embodiments at least 3 meters.
• One particularly advantageous use of the present invention is for the fabrication of large zircon (Zr0 2 Si0 2 ) based ceramic blocks useful for making large-size unitary ceramic components in the melting, delivery and conditioning of glass melt and forming of glass articles.
• the isopipe of a fusion down-draw process for making glass sheets, especially high-precision, high surface quality glass sheets suitable as LCD substrates is typically made of a unitary piece of ceramic material such as zircon, xenotime (YP0 4 ) or other refractory materials having high dimensional stability at the target forming temperature.
• the present invention will be further illustrated by the embodiment of making a zircon-based isopipe below. However, it should be understood that, upon reading the present disclosure and with the benefit of the teachings herein, the present invention can be used by one having ordinary skill in the art in making other articles from large blocks of materials, mutatis mutandis.
• FIG. 1 schematically illustrates an isopipe 100 in operation to make a glass ribbon 111 via a fusion down-draw process.
• the isopipe 100 comprises a unitary piece of zircon comprising a trough-shaped upper part 103 over a wedge-shaped lower part 105.
• Molten glass enters into trough 103 through an inlet tube 101, overflows both the top surfaces of the trough 103, forms two ribbons over the external side surfaces of the trough 103 and the two converging side surfaces of the wedge-shaped lower part 105, and fuse at the root 109, which is the lower tip of the wedge-shaped part, to form a single glass ribbon 111 which is drawn downward in the direction 113.
• the glass ribbon 111 is further cooled down downstream (not shown) to form a rigid glass sheet, which is further severed from the glass ribbon, cut to size and used for making LCDs. Because both external surfaces of the glass ribbon 111 were exposed only to ambient air and never came into contact with the surfaces of the isopipe, they are of pristine surface quality essentially free of scratches without the need of further surface finishing such as grinding and polishing.
• the glass sheets made by this process tend to have very high mechanical strength due to the lack of surface flaws.
• the stability of the shape of the isopipe 100 during the production cycle is very important.
• the isopipe can sag overtime due to the gravity of itself and the load of molten glass, leading to shape and dimension shift.
• the porosity of the zircon ceramic affects the sagging and other properties of the isopipe. Therefore, in general, the zircon ceramic for an isopipe is desirably densified to having a porosity of lower than about 10% by volume.
• the pores in the zircon ceramic of an isopipe are mostly closed pores, i.e., they are not exposed to the ambient air surrounding the surface of the isopipe.
• United States Patent No. 6,974,786 and United States Patent Application Publication Nos. US2008/0125307 Al and US2009/0111679 Al and WO09/054951 disclose zircon materials suitable for making isopipes in fusion down-draw processes and processes for making such materials, the contents of which are incorporated herein by reference in their entirety.
• FIG. 3 shows the flow chart of the process of making an isopipe based on zircon ceramics according to one embodiment of the present invention.
• step 301 a powder of zircon having desired chemical composition, particle size and particle size distribution is made.
• particle distribution of the powder should desirably enable a dense packing of the particles under pressure.
• An exemplary particle size range is from about 0.1 ⁇ to about 100 ⁇ , with a median particle size in the range from 3 ⁇ to 20 ⁇ .
• the particles can be made by ball- milling bulk zircon having the desired composition such as those disclosed in the above- mentioned patent references by using the synthesis methods disclosed therein, followed by selection at the proper sieve size.
• the zircon powder having the desired particle size distribution are mixed with optional binders and placed into a hermetically sealable, flexible bag.
• the powder inside the bag is compacted by, e.g., vibration, to improve particle packing.
• the bag can be made of, e.g., nylon or other water-proof flexible fabric.
• the bag should have the shape and volume to house a green-body having the desired shape and dimension.
• the bag should be able to contain such a green-body having a size significantly larger due to the shrinkage of the green-body during the firing and sintering step, described in greater detail infra.
• a metal container such as steel cage or box may be used to house the bag.
• step 305 the bag is vacuumed and then hermetically sealed. The removal of gas from the bag allows the particles to be pressed intimately without trapping large air pockets inside in the subsequent pressing step. Steps 301, 303 and 305 are
• step 305 on the sea immediately before step 307.
• the bag desirably housed inside a metal cage, is lowered into the sea at a location where the depth is at least 1000 meters (e.g., 5000 meters, 6000 meters, 7000 meters, 8000 meters, 9000 meters, 10000 meters, and the like) in a controllable manner.
• the lowering of the bag can be carried out by using a submarine or a extendable cable tethered to a floating vessel or a rig or the like.
• the bag is placed inside a stainless steel cage having a plurality of holes on all six sides, which, in turn, is tethered to one end of a roll of steel cable.
• the cage is brought to above the Mariana Trench in the Pacific Ocean by a vessel, and then lowered into sea water from the vessel in a controllable manner.
• the sea at the Mariana Trench is known to have a maximal depth of more than 10500 meters.
• a pressure sensor is installed on or near the cage, so pressure information can be transmitted to the vessel along the cable or by other means such as wireless transmission.
• a sonar or other device may be used to monitor and locate the cage during the lowering process. It is known that the pressure P exerted by a water column can be calculated according to the following equation:
• the pressing location is at least 8000 meters below sea level, in certain embodiments at least 9000 meters, in certain other embodiments at least 10000 meters. At 10000 meters below sea level, the pressure is about 16 kPsi.
• FIG. 3 shows the temperature of sea water in a tropical area.
• the temperature variation of sea water is not significant, from about 20°C from the surface to about 0°C on the sea floor. This is a temperature range that can be tolerated by most bag material suitable for isopressing.
• the cage has holes on all sides, once it is submerged by sea water, the whole bag is subjected to a substantially even pressure exerted by the water column above it. Hence the green-body inside the bag is pressed isostatically. The combination of the gravity of the cage, the bag and the green-body would allow the cage to descend to the sea floor if the cage is not restricted by the tethered cable.
• the controlled extension of the cable via, e.g., a pulley and/or a motor, can limit the descending to a substantially constant vertical speed, e.g., of at most 10 meters per second (m-s 1 ), in certain embodiments at most 5 ms "1 , in certain other embodiments at most 1 ms "1 .
• a substantially constant vertical speed e.g., of at most 10 meters per second (m-s 1 )
• m-s 1 meters per second
• a relatively slow and constant descending speed allows the particles in the green-body to shuffle, shift, rearrange and pack gradually, resulting in a substantially even overall density and porosity without large cracks and cavity trapped inside.
• the green body can result in unwanted pressure gradient locked inside the green-body, preferential pressing in the surface region than in the core, leading to different levels of packing and compaction in the green-body, which can be detrimental for the final density, porosity and porosity distribution in the sintered ceramic block.
• the slow and steady denscending speed of the green body allows the temperature of the green body to equilibrate with the environment surrounding it at a sufficiently slow speed to avoid any thermal shock which could be detrimental for a uniform packing of the particles.
• the cage should not be allowed to reach the sea floor to avoid contact with sharp objects such as rock which could puncture the bag, causing contamination of the green-body by sea water.
• the cage is held statationery at the depth for a given period of time so that the green-body is compressed to a stable stage before the cable is retracted to retrieve the cage.
• the holding period can range from several minutes to several months, desirably from several hours to several weeks.
• the target depth is desirably at least 5000 meters below sea level, in certain embodiments at least 8000 meters, in certain other embodiments at least 9000 meters, in certain other embodiments at least 10000 meters.
• the maximal depth of the sea at a given location can be determined according to available public data, or by using a depth meter such as a sonar. In general, the target depth should be relatively free from highspeed current and relatively far from geothermal eruptions and volcanos on the sea floor to provide a steady and even compaction environment.
• step 309 the cage is raised to above the sea surface by, e.g., retracting the cable tethered to the cage. Again, the cable retraction speed should be carefully controlled. Unlike the cable extension step, the retracting cable has to counter the weight of the cage and green-body, the weight of the cable, and provide the upward acceleration needed for the whole assembly, minus the buoyancy provided by sea water. While the cage travels upward, the pressure exerted on the green-body and the bag decreases gradually. To maintain the structural integrity of the compressed green-body, sudden pressure change should be avoided. Thus, a gradual, slow cable retraction speed is desired.
• the cable is retracted at a speed of at most 10 ms "1 , in certain embodiments at most 1 ms "1 , in certain embodiments at most 0.5 ms "1 , in certain other embodiments at most 0.1 ms "1 .
• speed control in the ascending step can have significant impact on the packing of the particles due to abrupt changes of pressures and temperature can impose on the green-body.
• a slow and constant ascending vertical speed allows the green-body to equilibrate with the surrounding environment both in terms of pressure and temperature, allows the internal pressure inside the green-body to release gradually, and avoids detrimental thermal shock.
• a sealable metal box equipped with a valve that allows controllable ingress and egress of water into the box may be used in lieu of the cage to contain the bag and the green-body.
• the valve can be kept open to allow sea water to flow into the box and maintain sutantially the same pressure in and outside of the box.
• the box can be cubic, oblong or spherical.
• the valve can be kept open to maintain a pressure equilibrium in and outside of the box.
• a box is advantageous in that it prevents unwanted disturbance due to current, innocent or malicious wild life in the sea, and the like.
• the valve is closed, and then the box is raised to a differing location or even above sea level, where the green- body is subjected to the same pressure at the pressing location.
• the box with the green-body and high-pressure water can be shipped to a location on land, where it may be held for a sufficient period of time before the pressure is relieved by opening the valve, and then opened to retrieve the isopressed green-body.
• the box is designed to have a shape such as a spherical shape to maximize its ability to withstand such high pressure.
• a bladder to the container (cage or box) of the bag.
• the bladder is a metal box with function similar to that of a fish or a submarine, which can contain adjustable amount of water.
• the bladder can be filled with water such that the whole assembly can be lowered down to the target location due to gravity.
• the ascending step at least part of the water inside the bladder can be removed and replaced with gas, so that an upward force is provided to the container of the bag and green-body.
• a heating element can be provided to the bag and the green-body, so that the temperature of the green-body can be controlled and adjusted or maintained at a higher level than the water in the sea.
• Such heating element can provide the termal energy by electricity supplied from the vessel, or from reactions of chemicals stocked around the bag.
• a temperature sensor can be provided to the bag of the green-body and used in a temperature control loop.
• step 311 the green-body is then shipped to a sintering facility, where it is taken out of the bag, placed into a furnace, first fired to burn out the binder, if any, and then sintered to a temperature of at least 1000°C, in certain embodiments at least
• the sintering step can take from several hours to several months, desirably from several hours to several weeks. Upon completion of the sintering, the block is slowly cooled down to room temperature to allow annealing and prevent cracking due to thermal shock. For example, the sintering step can take from 1 hour to 150 days, in certain embodiments from 2 hours to 100 days, in certain embodiments from 10 hours to 90 days, in certain embodiments from 20 hours to 80 days, in certain embodiments from 20 hours to 60 days.
• step 313 the cooled large block of zircon ceramics is machined to the desired shape, i.e., having an upper trough and a lower wedge, having desired sizes.

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