KR20130004306A - Method of making a densified body by isostatically pressing in deep sea - Google Patents

Abstract

Large block manufacturing methods include the step of isostatically pressing the green-body in the deep sea. Very large blocks can be made by this method at a relatively low cost. Deep seas can provide essentially high pressure for isopressing.

Description

Method for producing compacted body by isotropic pressure in deep sea {METHOD OF MAKING A DENSIFIED BODY BY ISOSTATICALLY PRESSING IN DEEP SEA}

This application claims the benefit of priority in US Application No. 61/307657, filed February 24, 2010.

The present invention relates to a method of forming a large block of material. In particular, the present invention relates to a method of forming a sintered large block comprising a large block of pressed particle green-body and an isostatic pressurization step. The present invention is useful for making large zircon ceramic blocks suitable for isopipes, for example, of fusion down-draw processes for glass sheet manufacture.

Large ceramic blocks are useful in the construction of many engineering structures because of their attractive mechanical properties and fire resistance. For example, large blocks of ceramics include Al ₂ O ₃ , ZrO ₂ , zircon (ZrO ₂ · SiO ₂ ), TiO ₂ , Be0, MgO, SiO ₂ , and mixtures and compounds of these components are dissolved, transported and It can be used to make components for molded metal and / or glass articles. In particular, zircon has been used to make large molded ceramic blocks (called isopipera) in the fusion down-draw process for glass sheet manufacture due to their high mechanical strength and dimensional stability at high temperatures.

It is highly desirable that structural ceramic blocks appear in a single compact shape. The ceramic block may comprise the following steps: (a) packing particulates of the ceramic material into a bag; (b) isostatically pressing the bag to an isopress at high pressure to form a green-body; And (c) sintering the green-body to obtain a dense ceramic block. The sintered ceramic block can be continuously machined to the desired dimensions and shapes.

The cost of manufacturing, installing and maintaining the isopress is very high and increases to an extremely expensive level when the ceramic block dimensions exceed about 3 meters.

Therefore, there is a need for a method of manufacturing large size ceramic blocks that is substantial and cost-effective.

The present invention satisfies this and other needs.

The present invention seeks to provide a method of forming a sintered large block comprising a large block of pressed particle green-body and an isostatic pressure step.

Several aspects of the invention are disclosed herein. It should be understood that these aspects do not overlap or overlap with each other. Thus, some of one aspect may be within the scope of the other, and vice versa.

Each aspect is described in a number of embodiments, which in turn may include one or more certain embodiments. It is to be understood that the embodiments do not overlap or overlap with each other. Accordingly, some of one embodiment or certain embodiments thereof may or may not be within the scope of other embodiments or certain embodiments, and vice versa.

The first aspect of the invention

(I) packing a plurality of particles into an airtight bag;

(II) removing gas from the interior of the bag;

(III) hermetically sealing the bag; And

(IV) forming an isostatically pressurized green-body by lowering the bag into a water tower having a depth of at least 1000 meters to a press position of at least 1000 meters below the surface of the water column. It relates to a method for producing a compact having a size of at least 1 meter.

In certain embodiments of the first aspect of the invention, in step (IV), the water tower is part of the sea on the ground surface and the pressurized position is at least 5000 meters below sea level.

In certain embodiments of the first aspect of the invention, in step (IV), the water tower is a portion of the sea on the ground surface and the pressurized position is at least 10000 meters below sea level.

In certain embodiments of the first aspect of the invention, in step (IV), the water tower is part of the sea on the ground surface and the pressurized position is at least 10500 meters below sea level.

Certain embodiments of the first aspect of the present invention provide that, in step (I), the plurality of particles comprises a ceramic, the method further comprising:

(V) sintering the green-body obtained in step (IV) at a temperature of at least 1000 ° C. to obtain a densified ceramic block:

.

In certain embodiments of the first aspect of the invention, the ceramic comprises a material selected from Be0, MgO, ZrO ₂ , ZrO ₂ .SiO ₂ , Al ₂ O _{3 ,} TiO ₂ , and mixtures and compounds thereof. do.

In certain embodiments of the first aspect of the invention,

Step (IV) is:

(IV.1) placing the hermetically sealed bag into a cage; And

(IV.2) lowering the cage from the surface of the water column to the press position.

In certain embodiments of the first aspect of the invention, in step (IV.2), the cage is attached to a cable, which cable extends and is attached to a container on the surface of the water tower.

In certain embodiments of the first aspect of the invention, the cage runs at a vertical speed of up to 10 m · s ⁻¹ .

In certain embodiments of the first aspect of the invention, the cage runs at a vertical speed of at most 1 m · s ⁻¹ .

In certain embodiments of the first aspect of the invention, a pressure sensor is installed above or near the cage, and the pressure sensor provides information of the pressure the bag receives.

In certain embodiments of the first aspect of the invention, a heating element is provided near the bag during step (IV) to maintain the desired temperature.

In certain embodiments of the first aspect of the invention, the power source of the heating element is controlled via a temperature sensor near or above the bag of the green-body.

In certain embodiments of the first aspect of the invention, the method further comprises raising the bag above the surface of the water tower after step (IV-A).

Certain embodiments of the first aspect of the invention, in step (IV-A), the bag proceeds at a vertical speed of up to 10 m · s ⁻¹ , and in some embodiments up to 5 m · s ⁻¹ , some other implementation The maximum is 1 m · s ^{−1 in the} example, the maximum 0.5 m · s ⁻¹ in some other embodiments, and the maximum 0.1 m · s ⁻¹ in some other embodiments.

In certain embodiments of the first aspect of the invention, an air pouch box capable of providing an adjustable difference between load and buoyancy is attached to the cage.

In certain embodiments of the first aspect of the invention, at the end of step (IV), the load of the air bag is reduced to provide an overall upward force on the assembly comprising the cage and the air bag.

In certain embodiments of the first aspect of the invention, the compact has a size of at least 2 meters.

In certain embodiments of the first aspect of the invention, the compact has a size of at least 3 meters.

In certain embodiments of the first aspect of the invention, the compact has a size of at least 4 meters.

In certain embodiments of the first aspect of the invention, the compact has a size of at least 5 meters.

In certain embodiments of the first aspect of the invention, the compact has a size of at least 10 meters.

In certain embodiments of the first aspect of the invention, the compacts have at least two dimensions perpendicular to one another each having a size of 2 meters.

In certain embodiments of the first aspect of the invention, the compacts have at least three dimensions perpendicular to one another each having a size of 2 meters.

In certain embodiments of the first aspect of the invention, the compact has a porosity of up to 10%, up to 8% in certain embodiments, up to 5% in certain other embodiments, up to 3% in certain other embodiments. Has porosity

One or more embodiments of the invention have one or more of the following advantages. First, considering the size of the ocean, the size of the green-body that can be isopressed in the deep ocean is substantially infinite. Secondly, the vessel for green-body transfer before and after the press may be a general purpose vessel which does not particularly represent an isostatic pressurization step, and the green body transfer cost can be distributed with the transfer of others and thus reduced. Thirdly, multiple green bodies can be pressed for a relatively short time and even at the same time without the need for an enlarged isopress. The end result is therefore to produce a large size ceramic body at low cost.

Additional features and advantages of the invention will be apparent from the following detailed description, and are in part appreciated by those skilled in the art from the detailed description and practice of the invention as indicated in the detailed description and claims, as well as the accompanying drawings.

The following general description and the following detailed description are merely embodiments of the present invention, and are intended to provide an overview or framework for understanding the nature and characteristics of the present invention as claimed.

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification.

The present invention can provide a method of forming a sintered large block comprising a large block of pressed particle green-body and an isostatic pressure step.

1 is a schematic diagram of an isopipe operation to make a glass sheet by a fusion down-draw process.
2 is a graph showing the temperature of seawater as a function of depth in a tropical region suitable for carrying out an isotropic pressure pressurization step according to one embodiment of the invention.
3 is ZrO ₂ · SiO ₂ according to an embodiment of the present invention. A flowchart showing the steps of manufacturing a ceramic block.

As mentioned above, the present invention is useful for producing any large body of any material, including isostatically pressing the green-body of a sealed bag, especially for large ceramic blocks. The body is based on oxides, phosphates or other inorganic materials. The invention is particularly useful for producing large ceramic blocks having at least one dimension, preferably having two dimensions perpendicular to each other having a size of at least 2 meters, and in some embodiments at least 2.5 meters, certain other In an embodiment it is at least 3 meters.

One particularly advantageous use of one of the present inventions is for the production of large zircons (ZrO ₂ · SiO ₂ ) based on ceramic blocks which are useful for the formation of single large ceramic components and for the molding of glass articles in the melting, conveying and conditioning of glass melts. will be. As mentioned above, high precision, high quality surface glass sheets suitable for isopipes in fusion down-draw processes, in particular for LCD substrates for glass sheet production, typically have zircon, xenotime (YPO) having high dimensional stability at the target molding temperature. ₄ ) or one part of a ceramic material, such as another refractory material. The invention will be further described below by examples of zircon-based isopipe preparation. However, it should be understood that the present invention can be used by those skilled in the art with the advantages of reading the present invention and making other articles from large blocks of material.

1 schematically shows an isopipe 100 for making glass ribbon 111 through a fusion down-draw process in operation. Isopipe 100 has a unitary zircon with a trough-shaped top 103 over a wedge shaped bottom 105. The molten glass enters the trough 103 through the inlet tube 101, flows over the two upper surfaces of the trough 103, passes over the outer side of the trough 103 and the two ribbons and wedge-shaped bottom 105. Wedge-shaped to form two converging sides of the < RTI ID = 0.0 >) < / RTI > The lower end of the part of the. The glass ribbon 111 is further cooled down and cut by size to form a rigid glass sheet and further cut from the glass ribbon for use in making LCDs. Since the two outer surfaces of the glass ribbon 111 are only exposed to ambient air and do not contact the surface of the isopipe, they are essentially scratch-free surface quality without the need for additional surface finishes such as grinding and polishing. Glass sheets made by this process tend to have very high mechanical strength due to lack of surface defects. The stability of the isopipe 100 shape during the manufacturing cycle is very important to make a precise glass sheet with the desired properties such as high thickness uniformity, low stress, high stress uniformity, and the like. Unfortunately, isopipes can be sag during manufacturing time due to their own gravity and load of molten glass, leading to shape and dimensional changes. The larger the expansion of the isopipe and the more sagging the more, the substantially constant creep rate of the material and the given operating temperature are taken into account. The porosity of zircon ceramics affects the sagging and other properties of the isopipe. Thus, in general, zircon ceramics for isopipes are preferably densified to have a porosity lower than about 10% by volume. Preferably, the pores of the zircon ceramic of the isopipe are mostly closed pores, ie they are not exposed to the ambient air surrounding the surface of the isopipe.

US Patent No. 6,974,786 and US Patent Application Publication Nos. US2008 / 0125307 A1 and US2009 / 0111679 A1 and WO09 / 054951 disclose zircon materials suitable for isopipe manufacturing in a fusion downdraw process, such materials being disclosed. Processes for manufacturing are disclosed, the contents of which are hereby incorporated by reference in their entirety.

3 shows a flow chart of an isopipe manufacturing process based on zircon ceramics in accordance with an embodiment of the present invention. In step 301, the zircon particles have the desired chemical composite, particle size and a particle size distribution. In order to achieve a high final density of zircon ceramics, the particle distribution of the powder should preferably enable high density packaging of the particles under pressure. Preferred particle size ranges from about 0.1 μm to about 100 μm, and the median particle size ranges from about 3 μm to 20 μm. The particles can be made by ball milling bulk zircon with the desired composite by using the composite method disclosed herein, such as the patent references mentioned above, followed by selection of the appropriate quadrant size. .

In step 303, the zircon powder having the desired particle size distribution is mixed into an optional binder and placed in a hermetically sealed flexible bag. The powder in the bag is compressed, for example by vibration, to enhance particle packing. The bag can be made of, for example, nylon or other waterproof flexible fiber. The bag should have a shape and volume to enclose the green-body having the desired shape and dimensions. For example, to make a final ceramic block with dimensions of 3m x 2m x 1m, the bag must be able to include such a green-body with a substantially larger size due to shrinkage of the green-body during the ignition and sintering steps. This is explained in more detail below. Metal containers, such as steel cages or boxes, can be used to wrap the bag to help support the load of the green-body and to shape the fill bag.

In step 305, the bag is vacuum sealed and then hermetically sealed. Degassing from the bag allows the particles to be pressurized deeply without having to trap the large air bag inside in a subsequent pressurization step. Steps 301,303 and 305 are advantageously performed in a plant on land, although these steps are carried out in a flotation vessel or a rig on the sea. If the green-body is transported over a long distance above the sea, it may be advantageous to perform step 305 above the sea just before step 307.

Next, in step 307, the bag, preferably wrapped in a metal cage, has an adjustable depth of at least 1000 meters (e.g., 5000 meters, 6000 meters, 7000 meters, 8000 meters, 9000 meters, 10000 meters, etc.). Is lowered into position. The lowering of the bag may be performed by an extendable cable or rig or the like that is wound around the submarine or flotation vessel. In one embodiment, the bag is placed in a stainless steel cage with multiple holes on all six sides, which are alternately wound on one end of a roll of steel cable. The cage is delivered by the vessel to the top of the Mariana Trench in the Pacific Ocean and then lowered from the vessel into seawater in an adjustable manner. Mariana Trench is known to have a maximum depth of over 10500 meters. Advantageously, the pressure sensor is installed on or near the case so that the pressure information can be transmitted to the container along the cable and by other means such as wireless transmission. Optionally, a sonar or other device can be used to monitor and place the cage during the lowering process. It is known that the pressure P output by the water tower can be calculated according to the following formula.

P = ｐ g

Where ｐ is the density of the tower, g is the acceleration of gravity, and h is the height of the tower. Thus, the deeper the sea is in the pressurized position, the higher the pressure exerted on the green-body. The pressure it receives increases as the green-body progresses from the surface of the sea to the press position. The higher the green-body pressure, the more compact the greenbody is and the better the particles are packed. In order to make a very densely sintered ceramic body, it is desirable that the pressing position be at least 8000 meters below the water surface, in some embodiments at least 9000 meters, and in other certain embodiments at least 10000 meters. At 10000 meters below sea level, the pressure is about 16 kPsi.

3 shows the temperature of seawater in the tropics. As shown in this figure, the temperature change of seawater is not critical and is from about 20 ° C. on the water surface to about 0 ° C. on the sea bottom. This is the temperature range that can be tolerated by most bag materials suitable for isopressing. When the cage is submerged by seawater, the cage has holes in all sides, so the entire bag is subject to substantially constant pressure by the water tower at the top. The green-body in the bag is therefore isostatically pressed. Gravity mixing of the cage, bag, and green-body causes the cage to descend to the sea floor unless the cage is limited by a wound cable. For example, the controlled extension of the cable via the pulley and / or the motor may limit the descent at a substantially constant vertical speed, for example up to 10 m · s ⁻¹ , and in some embodiments up to 5 m · s ^{− 1} , and in another given embodiment, at most 1 m · s ⁻¹ . The relatively slow and constant rate of descent causes the particles of the green-body to shake, move, rearrange and pack progressively, producing substantially the same overall density and porosity without large cracks and cavities therein. A rapid and sudden change in pressure on the bag is exerted so that the green body can generate an unwanted pressure gradient submerged in the green body, preferentially pressurizing at the surface area rather than the core, and packing to different degrees in the green body. Resulting in over compression, which can be detrimental to the final density, porosity and porosity distribution in the sintered ceramic block. In addition, the slow and constant rate of descent of the green body allows the temperature of the greenbody to be equal to the environment surrounding it at a sufficiently low rate to avoid any thermal shock that can be harmful to the constant packing of particles.

The cage should preferably be in contact with a sharp object such as a rock that can perforate the bag so that it does not reach the bottom of the sea to avoid contamination of the green-body by sea water. Preferably, when the cage reaches the target depth, it is held stationary at a depth for a given time so that the green-body is compressed to a stable step before the cable is rewound to recover the cage. The fixed period can range from seconds to months, preferably from hours to weeks.

The target depth is preferably at least 5000 meters below sea level, at least 8000 meters in certain embodiments, at least 9000 meters in certain other embodiments, and at least 10000 meters in certain other embodiments. The maximum depth of the ocean at a given location can be determined by using a depth meter, such as available joint data or sonar. In general, the target depth should be relatively free from high velocity flows to provide a steady and constant compression environment and relatively far from sea floor geometric erosion and volcanoes.

In step 309, the cage is raised above the sea floor, for example by rewinding the cable wound into the cage. Again, the cable rewind speed must be carefully controlled. Unlike the case extension step, the rewound cable must counteract the cage and green-body loads, the cable loads, provide the required up acceleration for the entire assembly, and are as small as the buoyancy provided by the seawater. While the cable runs upwards, pressure is applied to the green-body and the bag gradually decreases. In order to maintain the structural integrity of the pressurized green-body, sudden pressure changes must be prevented. Thus, progressive and slow cables are required. In some embodiments, the cable rewinding and at speeds of up to 10m · s ^-1, in some embodiments up to 1m · s ^-1, in some embodiments up to 0.5m · s ^-1, in certain other embodiments up to 0.1m S ^-1 . Similar to the falling phase, speed regulation in the rising phase can have a significant impact on the packing of the particles due to sudden changes in pressure and temperature that can be applied to the green-body. The slow and constantly rising vertical velocity makes the green-body parallel to the surroundings in terms of pressure and temperature, allows internal pressure to enter the green-body to gradually relax, and prevents harmful heat shock.

In another embodiment, a sealable metal box provided with a valve that allows water to enter and exit the box in an adjustable manner can be used in place of the cage to include the bag and the green-body. During the lowering process, the valve can be left open to allow seawater to flow into the box, allowing the inside and outside of the box to maintain substantially the same pressure. The box can be cubic, rectangular or spherical. During the raising process, the valve can be left open to maintain the same pressure inside and outside the box. On the other hand, it may be desirable to close the valve at a certain point during the lowering process or at a pressure point during the raising process, whereby the bag is maintained in a safe and steady environment at a constant pressure. The use of the box is advantageous in that it prevents unwanted disturbances due to ocean currents, clean or rough wildlife and the like. Optionally, while the box is at sea at some point, as in the pressurized position, it is possible for the valve to be locked and then the box to be lifted over a different position or even above sea level and where the green-body is at the same pressure in the pressurized position. Easy to receive It is also contemplated that the box with the green-body and the high-pressure water can be moved to a position on the ground, which can be fixed for a sufficient time before the pressure is released by opening the valve, and then recover the isopressed green-body. To open. In this embodiment, the box is highly required to be designed to have the same spherical shape to maximize its capacity to withstand such high pressures.

In certain embodiments, it is possible to attach an air bag to a container (cage or box) of a bag. Airbags are metal boxes that function similarly to fish or submarine airbags and may contain an adequate amount of water. Thus, during the descent phase, the pouch can be filled with water so that the entire assembly can be lowered to the target position due to gravity. During the ascending step, at least a portion of the water inside the airbag can be removed and replaced with gas, so that upward force is provided to the bags and the containers of the green-body.

In still other embodiments, heating elements may be provided in the bag and the green-body, and the temperature of the green-body may be controlled, regulated, or maintained at a higher level than seawater. Such heating elements may provide thermal energy by electricity supplied from chemical reactions stored near the vessel or bag. The temperature sensor can be provided in the green-body bag and used in the temperature control loop.

While it is desirable to wind the cage / box or other container of the green-body into a container, rig or other surface object, it is also possible to move the container and the green-body of the bag to the deep sea, after which a net, submarine or other means It is wound by the people.

Next, in step 311, the green-body is then moved to a sintering plant, even if it is first ignited to burn the binder, out of the bag, placed in a furnace, and then sintered to a temperature of at least 1000 ° C., in certain embodiments At least 1300 ° C., and in some other embodiments at least 1500 ° C., thereby forming a dense zircon block. During ignition and sintering, adjacent particles are joined together to form a strong, unitary body. Block shrinkage is typically observed and the holes in the green-body are reduced. The final densified zircon preferably has a density of at least 90% of the theoretical limit of zircon in normal environment. The sintering step can take from hours to months, preferably from hours to weeks. Upon completion of sintering, the blocks are slowly cooled to room temperature to allow annealing and prevent cracking due to thermal shock. For example, the sintering step may 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, and in certain embodiments from 20 to 80 hours In some embodiments, from 20 to 60 hours.

Finally, in step 313, the cooled large block of zircon ceramic is processed into the desired shape, i.e. has the upper trough lower wedge and has the desired size.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope and spirit of the invention. Accordingly, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and the like.

100: isopipe 101: tube
103: trough 105: lower wedge shape
109 route 111: glass ribbon

Claims (25)

(I) packing a plurality of particles into an airtight bag;
(II) removing gas from the interior of the bag;
(III) hermetically sealing the bag; And
(IV) forming an isostatically pressurized green-body by lowering the bag down the surface of the water column into a water tower having a depth of at least 1000 meters to a press position of at least 1000 meters. A dense body manufacturing method having a size of at least 1 meter. The method according to claim 1,
In step (IV), the water tower is a portion of the sea on the earth's surface and the pressurized position is at least 5000 meters below sea level. The method according to claim 1 or 2,
In step (IV), the water tower is a portion of the sea on the earth's surface and the pressurized position is at least 10000 meters below sea level. 4. The method according to any one of claims 1 to 3,
In step (IV), the water tower is a portion of the sea on the earth's surface and the pressurized position is at least 10500 meters below sea level. 5. The method according to any one of claims 1 to 4,
In step (I), the plurality of particles comprises a ceramic, the method comprising
(V) A method for producing a compact, further comprising the step of sintering the green-body obtained in step (IV) at a temperature of at least 1000 ° C. to obtain a densified ceramic block. The method according to claim 5,
Wherein said ceramic comprises a material selected from Be0, MgO, ZrO ₂ , ZrO ₂ .SiO ₂ , Al ₂ O _{3 ,} TiO ₂ , and mixtures and compounds thereof. 7. The method according to any one of claims 1 to 6,
Step (IV) is:
(IV.1) placing the hermetically sealed bag into a cage; And
(IV.2) A method for producing a compact, comprising lowering the cage from the surface of the water tower to the press position. The method of claim 7,
In step (IV.2),
And the cage is attached to the cable, and the cable extends and is attached to the container on the surface of the water tower. The method according to claim 7 or 8,
The cage in step (IV.2), wherein the cage runs at a vertical velocity of at most 10 m · s ⁻¹ . The method according to claim 9,
The cage in step (IV.2), wherein the cage runs at a vertical velocity of at most 1 m · s ⁻¹ . The method according to any one of claims 7 to 10,
A pressure sensor is installed on or near the cage, the pressure sensor provides information of the pressure received by the bag. The method according to any one of claims 1 to 11,
A heating element is provided near the bag during step (IV) to maintain the desired temperature. The method of claim 12,
The power source of the heating element is controlled via a temperature sensor near or above the bag of the green-body. The method according to any one of claims 1 to 13,
(IV-A) after the step (IV) further comprises the step of raising the bag to the upper surface of the water tower. The method according to any one of claims 1 to 14,
In step (IV-A), the bag proceeds at a vertical speed of up to 10 m · s ⁻¹ , up to 5 m · s ⁻¹ in certain embodiments, up to 1 m · s ⁻¹ in certain other embodiments, and some other implementations. example, the dense material production method, characterized in that up to 0.1m · s ^-1 at the maximum 0.5m · s ^-1, certain other embodiments. The method according to any one of claims 7 to 15,
An air bag box capable of providing an adjustable difference between load and buoyancy is attached to the cage. 18. The method of claim 16,
At the end of step (IV),
The load of the air bag is reduced to provide an overall upward force to the assembly comprising the cage and the air bag. The method according to any one of claims 1 to 17,
Wherein said compact has a size of at least 2 meters. 19. The method of claim 18,
Wherein said compact has a size of at least 3 meters. 19. The method of claim 18,
Wherein said compact has a size of at least 4 meters. 19. The method of claim 18,
Wherein said compact has a size of at least 5 meters. 19. The method of claim 18,
Wherein said compact has a size of at least 10 meters. The method according to any one of claims 1 to 22,
Wherein said compact has at least two dimensions perpendicular to each other having a size of 2 meters each. 24. The method of claim 23,
Wherein said compact has at least three dimensions perpendicular to each other having a size of 2 meters each. The method according to any one of claims 1 to 24,
The compact has a porosity of up to 10%, in certain embodiments up to 8%, in some other embodiments up to 5%, in some other embodiments up to 3% porosity manufacturing method.

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