Patent Application
20180044761
The present disclosure relates to a method for purifying and casting materials, and in particular, a method for purifying and casting metallic materials.
Current semiconductor fabrication processes require components made of ever increasing purity as the starting materials. These processes frequently require certain impurities in the starting materials to be at concentration levels that are lower than metrology techniques can detect. For example, many of the metals used in semiconductor fabrication must have essentially no oxygen or oxygen containing species, such as oxides, present in the metal. In some cases the starting metals must be free or essentially free of oxygen and oxygen containing species.
As greater amounts of electronic components are needed in consumer goods, the necessary volume of starting materials also increases. At the moment there is not an adequate process for producing materials at the required purity levels in large enough volumes to keep up with demand. There is thus a need for a solution that provides highly pure raw material, and in particular, highly pure raw material in large volumes.
Various inventive aspects relate to a unit or method of purifying and casting. In some embodiments, an apparatus comprises a purification chamber having a first atmosphere; a crucible positioned within the purification chamber and constructed to retain a material in a molten state; a purification supply channel constructed to provide a purification gas to within the material; a casting chamber having a second atmosphere and in fluid communication with the purification chamber; a mold positioned within the casting chamber and constructed to retain the material in a molten state; a conduit located between the purification chamber and the casting chamber, the conduit constructed to regulate flow of the material between the purification chamber and the casting chamber such that the material flows from the purification chamber to the casting chamber without exposure to a third atmosphere.
In some embodiments, a method of purifying and casting a material comprises placing a material to be purified within a crucible located within a purification chamber having a first atmosphere; providing thermal energy to the material to maintain the material in a molten state; providing a purification gas into the molten material to purify the material until a first measured condition is attained; passing the material in a fluid state from the purification chamber having a first atmosphere to a casting chamber having a second atmosphere, the purification chamber in fluid communication with the casting chamber such that the material passes from the purification chamber to the casting chamber without exposure to a third atmosphere; placing the material into a mold within the casting chamber; cooling the material within the mold to form a cast material.
In some embodiments, a system for purifying and casting comprises a first chamber having a first atmosphere; a crucible positioned within the first chamber and constructed to retain a material in a molten state; a sensor configured to measure at least a first condition within the first chamber; a purification gas supply; a purification supply channel in fluid communication with the purification gas supply and configured to deliver a purification gas to within the material; a second chamber having a second atmosphere and in fluid communication with the first chamber; a mold positioned within the second chamber; a conduit in fluid communication between the first chamber and the second chamber, the conduit configured to regulate flow of the material between the first chamber and the second chamber such that the material flows from the first chamber to the second chamber without exposure to a third atmosphere; the system configured to: maintain a material within the crucible within the first chamber in a molten state; supply purification gas through the purification supply channel into the material; determine a first measured condition has been attained within the first chamber; pass the material in a molten state from the first chamber to the second chamber such that the material passes from the first chamber to the second chamber without exposure to a third atmosphere; retain the material in the mold within the second chamber; and cool the material within the mold to form a cast material.
While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.
The current application provides a solution to the problem of providing purified and cast materials. The disclosures in the current application can potentially be applied to remove one or more impurities from a number of starting materials including metals, metal alloys, and metalloids.
The purification chamber 2 may have at top 3, bottom 5, and walls 7 extending between the top 3 and bottom 5. The purification chamber 2 may be constructed to provide an enclosed or sealed environment or atmosphere within the chamber 2. The chamber 2 may provide a controllable environment that may provide suitable characteristics for a particular use. For example, the temperature within the purification chamber 2 may be controllable to allow a user to heat, and even melt, objects placed inside the purification chamber 2. In another example, the pressure within the purification chamber 2 may be controllable to allow a user to lower or raise the pressure inside the chamber 2 in order to manipulate partial pressures of liquids or gases within the chamber 2. In some embodiments, the purification chamber 2 may be operated lower than, higher than, or at atmospheric pressure. The purification chamber 2 may be constructed to operate at positive pressure to the maximum of the device's capacity. For example, the purification chamber 2 may be constructed to operate at pressures of up to 30 psi. In another example, a gaseous environment inside the chamber 2 may be controllable to allow a user to remove or supply certain gases to the chamber 2.
In one embodiment, the purification chamber 2 may be constructed with a door 4 (which, as shown in
In one embodiment, the purification chamber 2 may be constructed with a cooling jacket 9 around the outside of the purification chamber 2. The cooling jacket 9 may be operated by providing cooling fluid to the cooling jacket 9 though cooling fluid ports 6. In one embodiment, cooling fluid ports 6 may be constructed to carry cooling fluid to the cooling jacket 9 and away from the cooling jacket 9. In one embodiment, a cooling fluid may be water. The cooling jacket 9 may be operated to maintain a suitable temperature on the outer surface of the purification chamber 2. For example, the cooling jacket 9 may maintain the outer surface of the purification chamber 2 at a temperature that allows a user to work in close proximity to the purification chamber 2 without being harmed by the purification chamber 2 temperatures.
In some embodiments, the purification chamber 2 may be constructed with a means of adding components to the interior of the chamber 2 while the chamber 2 is in use. In one embodiment, a supply channel 8 may be constructed to allow fluid communication with the interior of the chamber 2 while avoiding the need to open the purification chamber door 4. In one embodiment, the supply channel 8 may be constructed to provide a fluid, such as a gas, to the interior of the chamber 2. The supply channel 8 may be constructed with a valve 12 that may allow a user to regulate a fluid, such as a gas, entering the purification chamber 2 while the chamber 2 is in operation. The supply channel 8 may be configured to allow a user to increase a pressure within a purification chamber 2. The supply channel 8 may be operated to increase a pressure within the purification chamber 2 by adding a fluid, such as a gas, into the purification chamber 2.
In one embodiment, the supply channel 8 may provide a gas to the inside of the purification chamber 2 to purify the materials in the crucible 18. In one embodiment, a purifying gas may be supplied to the inside of the purification chamber 2 and delivered to a particular location within the material to be purified. Additionally or alternatively, a reactive gas or a reducing gas may be supplied to the inside of the purification chamber 2. In one embodiment, a delivery end 10 of the supply channel 8 may be placed within the material to be purified and a purifying gas delivered through the supply channel 8 and released into the material to be purified.
In one embodiment the delivery end 10 of the supply channel 8 may contain a distributor for dispersing purifying gas throughout the material to be purified. For example, a sparger may be connected to the delivery end 10 of the supply channel 8 to disperse purifying gas, or the delivery end 10 may include a series of axially and/or radially spaced openings for gas distribution. The purifying gas may be dispersed through the material to be purified to increase the contact area between the gas and the material to be purified. The increased contact area may allow the purifying gas to remove greater amounts of impurities in the material to be purified and may increase the efficiency of the purification. The purifying gas also may be allowed to flow over the material to be purified.
In one embodiment, the purification chamber 2 may include one or more suitable means of detecting conditions within the chamber 2 without having to open the purification chamber door 4. The purification chamber 2 may include a sensor 14 to detect conditions within the chamber 2 and allow a user to read conditions from outside the chamber 2. For example, the sensor 14 may be configured to detect temperatures within the chamber 2. The sensor 14 may be configured to detect pressures within the chamber 2. The sensor 14 may be configured to read a gas concentration level within the purification chamber 2. The sensor 14 may be configured to read an impurity concentration level within the material to be purified. The sensor 14 may be configured to read a concentration of one or more gases such as oxygen, hydrogen, nitrogen, carbon dioxide, carbon monoxide, water, argon, krypton, or xenon. The sensor 14 may also be configured to detect concentrations of one or more reducing gases such as carbon monoxide, methane, hydrocarbon-based molecules with double or triple bonds, H2SOx, NOx, or SOx, where “x” denotes the number of oxygen atoms in the molecule. In one embodiment, the sensor 14 may be configured to detect multiple conditions such as temperatures, pressures, and gas concentrations within the chamber 2 simultaneously. The sensor 14 can be positioned at any suitable location within the chamber 2.
In one embodiment, the purification chamber 2 may be constructed with a means of removing gases or other impurities from the purification chamber 2. In one embodiment, a removal line 16 may be configured to allow a user to draw material out of the purification chamber 2. The removal line 16 may allow a user to reduce the pressure within the purification chamber 2 such that the interior of the purification chamber 2 operates below atmospheric pressure. The removal line 16 may be connected to a pump that may remove gas from the purification chamber 2. The removal line 16 may additionally or alternatively remove water vapor from the purification chamber 2.
In one embodiment, a crucible 18 is located within the purification chamber 2. The crucible 18 may be constructed as substantially one piece or may contain multiple pieces. The crucible 18 may be any shape. For example, the crucible 18 may be constructed in a particular shape that has been determined to increase the efficiency of the purification process. The crucible 18 may be vertical, horizontal, or at a tilt angle. The crucible 18 may be constructed such that purified material from the crucible 18 may be transferred to the casting chamber 30.
The crucible 18 shown in
The crucible 18 may be constructed from components or materials that can withstand the purification chamber 2 operating temperatures and/or pressures. For example, the crucible 18 may be constructed to withstand high temperatures such as temperatures required to melt the material to be purified. For example, the crucible 18 may be constructed to contain a molten material, such as a metal, alkali metal, alkaline earth metal, rare earth metal, transition metal, post-transition metal, metalloid, or alloy or combination thereof. For example, the crucible may contain molten tin, chromium, copper, iron, magnesium, molybdenum, gold, silver, platinum, palladium, indium, lead, aluminum, zinc, antimony, bismuth, selenium, gallium, silicon, germanium, tellurium, thallium, and alloys and combinations thereof. The crucible 18 may be fabricated from components that do not react with the material to be purified. For example, the crucible 18 may be constructed from material that does not interact with or create impurities in the material to be purified. For example, the crucible 18 may be made of a component such as quartz or graphite, or any other material that will remain a solid at the temperatures that the purification chamber may be operating at.
The crucible 18 may be constructed to receive material already in a molten state or may be constructed to receive material in a solid or semi-solid state and subsequently heated to a molten state. A heat source may be provided to heat the material to be purified. In some embodiments, one or more heating elements may be incorporated or build into the crucible 18. Alternatively, heating elements may be incorporated into the purification chamber 2. In further embodiments, the heating element may be separate from the crucible 18 and the purification chamber 2. A suitable heating element or heat sources may include an induction heater, resistance heater, coil resistive heater, or any heat producing or generating source.
In one embodiment, the crucible 18 may contain multiple heating elements in various positions along the crucible 18 that can be individually operated. For example, multiple heating elements may be respectively spaced from one another along the axial extend of crucible 18. This configuration allows a crucible 18 to undergo zone heating wherein adjacent heating elements may be set at different temperatures. In this manner, a temperature gradient may be created in the crucible 18.
Zone heating may allow for additional purification of the product. For example, heating or maintaining the bottom 22 of the crucible 18 to a lower temperature than the top 20 may allow impurities to migrate to the top 20 due to the hotter material being less dense. Once at the top of the crucible 18, impurities within the material may be more effectively driven out of the material due to the greater surface area and/or exposure to purifying gas. As material at the top 20 of the crucible 18 cools it is replaced by material being heated at the hotter bottom 22 of the crucible 18. This circulation may be repeated throughout the purification process.
In some embodiments, the crucible 18 may be connected or joined to the purification chamber 2. In some embodiments, the crucible 18 may be removable from the purification chamber 2. For example, the crucible 18 may be removable to enable cleaning or repairing.
In one embodiment, the delivery end 10 of the supply channel 8 may be connected to delivery openings (not shown) constructed in the walls of a crucible 18. The supply channel 8 may be constructed to provide purifying gas into the purification chamber 2, carry purifying gas into the crucible 18, and deliver the purifying gas through a delivery end 10 into the material to be purified. In one embodiment, the crucible 18 may be constructed with numerous delivery openings (not shown) in the walls of the crucible 18 to allow purifying gas to be introduced to the material inside of the crucible 18 through the delivery openings.
A purifying gas may be selected from gases that react with one or more impurities in the material to be purified. In one embodiment, the purifying gas may react with the impurities and form chemical bonds with the impurities. In one embodiment, the purifying gas may be a gas that reacts with an impurity within the material to be purified, creates a chemical or physical bond with an impurity, and carries the bonded impurity out of the material. In one embodiment, purifying gases that have bonded with impurities and removed them from the material may be removed from the purification chamber 2. In one embodiment, the purifying gas may be an oxygen scavenger, and may remove oxygen, dissolved oxygen, or oxygen containing species from the material to be purified. The purifying gas may include nitrogen, hydrogen, carbon monoxide, carbon dioxide, methane, propane, hydrocarbon-based molecules with double or triple bonds, ammonia, H2S, H2SOx, NOx, or SOx, where “x” denotes the number of oxygen atoms in the molecule, and combinations thereof.
The purifying gas may include gases that are substantially nonreactive with components and/or materials within the purification chamber 2. In one embodiment, the purifying gas may include helium, argon, xenon, krypton, other noble gases, nitrogen, other inert gases, and combinations thereof. Other gases determined to be substantially unreactive with components within the purification chamber 2 may also be suitable. In one embodiment, purifying gases that have not reacted with impurities in the material to be purified may be removed from the purification chamber 2. In one embodiment, gaseous oxygen in the purification chamber 2 may be removed from the purification chamber 2.
A casting chamber 30 may be constructed in fluid communication with the purification chamber 2. The casting chamber 30 may have at top 31, bottom 33, and walls 35 extending between the top 31 and bottom 33. The casting chamber 30 may be constructed to provide an enclosed or sealed atmosphere or environment. The chamber 30 may provide a controllable environment that is the same as or different than the environment inside the purification chamber 2. For example, the temperature inside the casting chamber 30 may be controllable to allow a user to heat or cool objects inside the casting chamber 30. In another example, the pressure may be controllable to allow a user to lower or raise the pressure inside the chamber 30 in order to manipulate partial pressures of materials within the chamber 30. In some embodiments, the casting chamber 30 may be made to operate lower than, higher than, or equal to either atmospheric pressure or the pressure inside the purification chamber 2. The casting chamber 30 may be constructed to operate at positive pressure to the maximum of the device's capacity. In one embodiment, the casting chamber 30 may be constructed to operate at pressures of up to 30 psi.
In one embodiment, a casting chamber 30 may be constructed with a door 32 that opens to allow a user access to the interior of the chamber 30. In one embodiment, a casting chamber door 32 may be constructed to withstand pressure differentials inside and outside the chamber 30. In one embodiment, the casting chamber 30 may be mounted on a stand 46.
In one embodiment, a casting chamber 30 may have a purge gas supply 34 for providing purge gas to the interior of the casting chamber 30. In one embodiment, the purge gas supply 34 may be constructed outside the casting chamber 30 and have a supply line 36 to carry purge gas from the gas supply 34 into the casting chamber 30. A purge line 38 may be constructed for removing purge gas from the casting chamber 30. The purge gas supply 34 may be a tank or compressor constructed separate from the casting chamber 34. In one embodiment, a purge line 38 may connect the gas supply 34 to the casting chamber 30. The purge gas supply 34 may contain a heater to heat a purge gas before supplying the purge gas to the casting chamber 30. In one embodiment, the purge gas supply 34 may be a heated getter. The purge gas may be any gas that will drive off any water vapor, oxygen, or oxygen containing species inside the casting chamber 30. The purge gas may be a gas that will provide an oxygen free environment within the casting chamber 30. The purge gas may be a gas that will provide a water vapor free environment within the casting chamber 30. The purge gas may include a reducing gas, for example a hydrogen bearing forming gas. The purge gas may include argon, xenon, krypton, helium, other noble gases, nitrogen, other inert gases, and combinations thereof.
In one embodiment, a mold 40 may be positioned within the casting chamber 30. A casting chamber 30 may be constructed to allow a mold 40 to be added or removed from within the casting chamber 30. The mold 40 can have a suitable size, shape, and/or construction. For example, the mold 40 may be one piece or may be a multi piece construction. In one embodiment, the mold 40 may be assembled as an open cast mold with substantially one piece with an open top for receiving a molten material. In one embodiment, the mold 40 may be a two-piece mold constructed with a top and bottom. An opening may be formed in the mold 40 to allow material to enter. For example, the mold 40 may be constructed with an opening in the top. The mold opening may allow purified material to be passed into it in a molten state. The mold 40 shown in
The mold 40 may be constructed from components or materials that can withstand the casting chamber 30 operating temperatures and/or pressures. For example, the mold 40 may be constructed to withstand high temperatures such as temperatures required to melt metals, metal alloys, or organic materials. For example, the mold 40 may be constructed to contain a molten material such as a molten metal, alkali metal, alkaline earth metal, rare earth metal, transition metal, post-transition metal, metalloid, or alloy or combination thereof. For example, the mold 40 may contain molten tin, chromium, copper, iron, magnesium, molybdenum, gold, silver, platinum, palladium, indium, lead, aluminum, zinc, antimony, bismuth, selenium, gallium, silicon, germanium, tellurium, thallium, and alloys and combinations thereof. The mold 40 may be fabricated from components that do not react with the material to be cast. For example, the mold 40 may be constructed from material that does not interact with or create impurities in the material to be cast or add impurities into the casting environment. For example, the mold 40 may be made of a component such as graphite or quartz, or any other material that will remain a solid at the temperatures that the casting chamber 30 may be operating at.
The mold 40 may be selected from a suitable design depending on the method of casting used. Suitable casting methods that may be used with the disclosed purifying and casting device include but are not limited to sand or precision sand casting, permanent mold casting, semi-permanent mold casting, ingot casting, continuous casting, centrifugal casting, investment casting, low pressure die casting, high pressure die casting, vacuum die casting, squeeze casting, and composite casting.
One or more heating elements may be incorporated or built into the mold 40. Alternatively, heating elements may be incorporated into the casting chamber 30. In further embodiments, the heating element may be separate from the mold 40 and the casting chamber 30. In some embodiments, a suitable heating element may include an induction heater, resistance heater, coil resistive heater, or any heat producing or generating source.
In some embodiments, the casting chamber 30 may be constructed with a means of providing cooling to the inside of the casting chamber 30. For example, the casting chamber 30 may be constructed with a means for providing cooling to the mold 40. For example, the casting chamber 30 may have flow lines for providing cooling water to cool the mold 40.
In one embodiment, a conduit 42 may be constructed to connect the purification chamber 2 and the casting chamber 30. The conduit 42 may be constructed to allow fluid communication between the purification chamber 2 and the casting chamber 30. In one embodiment, the conduit 42 may be constructed with a means for controlling fluid communication between the purification chamber 2 and casting chamber 30. In one embodiment, the conduit 42 may be constructed with a means for controlling an environment surrounding a molten material flowing between the purification chamber 2 and casting chamber 30.
In one embodiment, the conduit 42 may contain a valve such as a gate valve 44 that may be operated by a user. The gate valve 44 may contact the bottom opening 22 of the crucible 18 positioned inside the purification chamber 2 and may allow a user to control a flow of molten material out of the crucible 18 by opening and closing the valve 44. The gate valve 44 may allow a user to control flow of molten material out of the crucible 18, through the conduit 42, and out of the purification chamber 2.
In one embodiment, the gate valve 44 may be constructed to allow molten material to flow out of the purification chamber 2 and into the casting chamber 30. The conduit 42 may provide a seal around an environment surrounding a molten material flowing from a purification chamber 2 to a casting chamber 30 such that from purification to casting, the molten material is never exposed to an environment containing impurities such as oxygen, oxygen containing species, or water vapor. Together, the purification chamber 2, the casting chamber 30, and the conduit 42 form an enclosed environment. For example, purified material flows from the purification chamber 2 to the casting chamber 30 without being exposed to a third environment containing impurities such as oxygen, oxygen containing species, or water vapor.
In one embodiment, purification step 204 includes a placement step 210. In one embodiment, material to be purified is placed in a crucible which is then placed into a purification chamber. Alternatively, material could be added to a crucible already positioned within the purification chamber. The material may be in a solid state, semisolid, or molten. The material may be melted until it is molten prior to purification.
Next, in an evacuation step 212, a first atmosphere may be created within the purification chamber. For example the purification chamber may be purged to create a first atmosphere within the purification chamber. In one embodiment, the purification chamber may undergo a vacuum cycle such that the gas within the chamber is removed. Evacuation step 212 may include a single cycle, such as a single purge or vacuum cycle. In another embodiment, the purification chamber may be subject to multiple cycles. For example, the purification chamber may be subject to cycle purging that may include alternating vacuum and purge cycles. For example, the purification chamber may first have the gas within the chamber removed to create a vacuum, followed by addition of a purge gas into the chamber. In another embodiment, the purification chamber may undergo a plurality of alternating vacuum and purge gas cycles.
In another embodiment, the purification chamber may undergo sequential purging. For example, the chamber may be purged in a first cycle with a first gas, such as a reacting gas, followed by purging in a second cycle with a second gas, such as a nonreactive gas. The first and second cycles may be repeated one or more times. Additionally or alternatively, the first atmosphere may be created by purging with three or more cycles or gases. For example, in another embodiment, a reducing gas could be used in a first purge cycle followed by a reactive gas in a second purge cycle then followed by a nonreactive gas used in a third purge cycle. The order in which each gas is used or the order in which each purge cycle is used may be varied depending on the material being cast and/or the impurity being removed. The first atmosphere may include a pressure at, below, or above atmospheric pressure. The first atmosphere may include a suitable gas composition, for example with impurities such as oxygen, oxygen containing species, or water vapor removed.
Next, in a purifying step 214, the material in the crucible is purified. During the purification step 204, the material to be purified is maintained in a molten or melted state during at least a portion of the purifying step 214 and in some embodiments, the material to be purified may be maintained in a molten state during the entire purification step 204. During the purifying step 214 the material to be purified is maintained at or above the melt temperature of the material and purifying gas is provided into the molten material to be purified. The temperature of the purification chamber can be maintained at or above the melt temperature of the material to be purified during the purifying step 214. In some embodiments, keeping the material to be purified at a temperature at or higher than the melt temperature may provide a more effective purification process. This process is continued until substantially all impurities are removed.
During the purifying step 214 a purification gas is supplied into the material to be purified. In one embodiment, a purification gas may include nitrogen, hydrogen, carbon monoxide, carbon dioxide, methane, propane, hydrocarbon-based molecules with double or triple bonds, ammonia, H2S, H2SOx, NOx, or SOx, where “x” denotes the number of oxygen atoms in the molecule, and combinations thereof. In one embodiment, a purifying gas may include gases such as helium, argon, xenon, krypton, other noble gases, nitrogen, other gases determined to be substantially unreactive with components within the purification chamber, and combinations thereof.
In one embodiment, the atmosphere within the purification chamber is monitored until a measureable condition is attained. In one embodiment, a measurable condition may be a concentration of a gas within the purification chamber. In one embodiment, a measureable condition may be a concentration of oxygen in the material to be purified. In some embodiments, the purification process may be continued until the measureable condition is achieved. In some embodiments, the purification process may continue until the material to be purified reaches a specified purity. For example, the purification process may continue until the material to be purified is at least 99.99%, at least 99.999% or at least 99.9999% pure. In one embodiment where the material to be purified is tin, the purification process may be run until the tin is at least 99.99%, at least 99.999% or at least 99.9999% pure. Additionally or alternatively, the purification process may continue until the level of one or more impurities is below a specified level. For example, the purification process may be run until one or more impurities is present at less than 5 ppm, less than 1 ppm, less than 0.1 ppm or less than 0.01 ppm. In one embodiment, the purification process may be until the oxygen concentration of the tin to be purified is less than 5 ppm, less than 1 ppm, less than 0.1 ppm or less than 0.01 ppm.
In some embodiments, multiple identical purification steps 204 may be completed. In other embodiments, the purification processes may be different. For example, a first purification step 204 may be run with a first environment within the purification chamber suitable for removing a first impurity. Following the first purification step 204, a second environment may be created within the purification chamber suitable for removing a second impurity in a second purification step 204. This process may be repeated multiple times using multiple environments each suitable for removing a particular impurity.
In one embodiment, a purified material may be removed from a purification chamber in a material transfer step 218. In one embodiment, a material transfer step 218 may involve transferring a material from the purification chamber to the casting chamber. As discussed herein, the purification chamber has a first environment, and the casting chamber has a second environment and material is not exposed to a third environment during transfer. That is, material is transferred within a closed system.
In one embodiment, a casting step 206 includes a material cast step 220. In the material cast step 220, molten material that has been purified in the purification step 204 is transferred into a mold placed within a casting chamber. Before molten material is placed in the casting chamber, the casting chamber will be purged by filling the casting chamber with a purge gas, pumping the gas within the casting chamber out, and continuing this purging process until no impurities remain in the casting chamber. In this manner, a second environment will have been created within the casting chamber before the molten material is transferred into the casting chamber in the material cast step 220. The purge step is to ensure that no oxygen, oxygen containing species, water vapor, or any other material that may add impurities into the purified material remains in the casting chamber before and during the casting step 206.
In one embodiment, the purge gas may include a reducing gas, for example a forming gas, i.e., a hydrogen bearing forming gas. In one embodiment, the purge gas includes nitrogen, argon, helium, or any combination thereof. In one embodiment, the purge gas is heated before providing it into the casting chamber. The purge gas is heated to remove any oxygen or water vapor that may be present in the purge gas or within the casting chamber.
In some embodiments, multiple casting chambers may be used in conjunction with one purification chamber. For example, the purification chamber may purify enough material to fill multiple molds. The purification chamber may be configured to allow it to connect to a first casting chamber, fill the mold positioned inside the first casting chamber, disconnect from the first casting chamber, then connect to a second casting chamber, fill a second mold positioned within the second casting chamber, and continue this process until all the purified material in the purification chamber is depleted.
In one embodiment, after the molten material has been cast it is allowed to cool in the mold in a cooling step 222. The cooling step 222 may take place at or slightly above room temperature. In one embodiment, the cast material is cooled by not providing heat to the mold and allowing the mold to cool with ambient conditions. In one embodiment, the cast material is cooled by providing cooling fluid to the outside of the mold. In one embodiment, a cooling step 222 may include providing water around the outside of the mold to remove heat from the mold. After a purified material has been cast, the mold may be removed from the casting chamber and the cast material removed from the mold.
The process described herein has been found to work successfully in producing high purity tin. It has been found that if tin is subjected to this purification process the tin can be purified until the tin is essentially free of oxygen or oxygen containing species. Casting the purified tin within a casting environment that has been purged of all or essentially all oxygen, oxygen containing species, and water vapor allows the purified tin to cool and solidify to take the shape of the mold, and this cast material has a purity level for example 99.99%, 99.999% or 99.9999% or greater. Although this process is described herein with respect to tin, this technique can also be used to form other high purity metals, metal alloys, metalloids, and organic materials.
In one embodiment, tin is subjected to the purification process to remove oxygen and/or oxygen containing species from within the tin. Molten tin may be purified in a purification chamber that has had oxygen, oxygen containing species, and water vapor evacuated from inside the chamber. Any oxygen or water vapor that is removed from the molten tin during the purification process may also be removed from the chamber. A purification gas containing oxygen scavengers can be bubbled through the molten tin with a tube inserted into the molten tin or through perforations in the vessel holding the molten tin. It has been found that by continuously supplying hydrogen gas into molten tin and removing the oxygen, oxygen containing species, and water vapor from the purification chamber, the tin can be purified to 99.99% purity or greater. The purification process may be continued until the measured concentration of oxygen in the gas inside the purification chamber is lower than current metrology techniques can detect. Using this process, molten tin can thus be produced that is essentially oxygen free. For example, using the process described herein, the purified and cast tin may have an oxygen concentration of less than 5.0 parts per million (ppm), and more particularly less than 1 ppm oxygen, less than 0.1 ppm oxygen or less than 0.01 ppm oxygen.
Once the molten tin has been purified to the desired purity, it can be cast in a mold. A casting chamber containing a mold may be connected to the purification chamber. To ensure the purified tin does not come into contact with an atmosphere that may reintroduce impurities into the purified tin, the casting chamber should be purged. One method of purging is to flush the casting chamber with an inert gas such as argon, nitrogen, or helium. Additionally or alternatively, the casting chamber may be purged with a hydrogen bearing gas. The purpose of the purging step is to drive off any impurities such as oxygen or water vapor that may be inside the casting chamber. In some embodiments, the purge gas may also be purified before being added to the casting chamber. For example, the gas purifying step may use a heated getter that will remove one or more residual impurities in the gas before it is introduced into the casting chamber. The purging process should continue while the purified tin is being cast into the mold.
The purified tin can be transferred from the purification chamber to the casting chamber through a conduit. The conduit should provide a sealed environment so the purified tin is not exposed to impurities such as oxygen, oxygen containing species, or water from the time it leaves the purification chamber till it is cast in the mold. The conduit can be opened or closed to allow molten tin to flow from the purification chamber to the casting chamber using a valve such as a gate valve.
Once the tin is poured into the mold, it may be cooled in the casting chamber while a purged environment is maintained within the casting chamber. Cooling may take place at ambient air temperatures, or a cooling fluid may be introduced around the mold to carry heat away from the mold. After the purified tin has been cast and cooled, the solid form tin may have a purity of greater than 99.99% and/or an oxygen content of less than 5 ppm.
Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the above described features.
This application claims priority to U.S. provisional application Ser. No. 62/130,985, filed Mar. 10, 2015, which is hereby incorporated herein by reference in its entirety for all purposes.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2016/019490 | 2/25/2016 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62130985 | Mar 2015 | US |
