Ultrafast high-temperature sintering setup with controlled ambient gas environment

Abstract

The present disclosure provides an ultrafast high-temperature sintering device comprising an environmental chamber with walls defining an internal volume, a sealable opening for access, and ports coupled to the internal volume. The device includes a heater portion configured to sandwich a target sample between two resistive heating coil elements, with alloy shields on either side to reduce radiation heat loss. The environmental chamber enables controlled ambient gas environments from oxidizing to inert to vacuum conditions. The heating elements comprise Fe-Al-Cr alloy coils in substantially planar snaking patterns, providing oxidation resistance at high temperatures. The device enables densification of ceramic materials including AI2O3, ZrO2, TiO2. LiZr2(PO4)3, and Li7La3Zr2O12 within minutes while maintaining precise environmental control.

Description

[0001] Princeton - 105276

[0002] ULTRAFAST HIGH-TEMPERATURE SINTERING SETUP WITH CONTROLLED

[0003] AMBIENT GAS ENVIRONMENT

[0004] CROSS-REFERENCE TO RELATED APPLICATIONS

[0005] This application claims priority' to U.S. Provisional Application No. 63 / 723,854, titled Ultrafast high-temperature sintering setup with controlled ambient gas environment, filed November 22, 2024, which is hereby incorporated by reference in its entirety.

[0006] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0007] This invention was made with government support under Grant No. N00014-23-1-2047 awarded by the Office of Naval Research. The government has certain rights in the invention.

[0008] FIELD OF INVENTION

[0009] The present disclosure relates to high-temperature ceramic processing equipment, and more particularly to an ultrafast high-temperature sintering setup with controlled ambient gas environment for rapid densification of ceramic materials.

[0010] BACKGROUND

[0011] Ceramic materials are widely used in various industrial applications due to their desirable properties such as high temperature resistance, chemical stability, and mechanical strength. The densification of ceramic materials typically requires high-temperature sintering processes to achieve the desired material properties and structural integrity. Conventional sintering methods involve heating ceramic powders or green bodies at elevated temperatures for extended periods, often ranging from several hours to days, to promote particle bonding and eliminate porosity.

[0012] Traditional sintering approaches face several challenges that limit their efficiency and applicability. The extended processing times result in high energy consumption and reduced manufacturing throughput. Additionally, prolonged exposure to high temperatures can lead to undesirable effects such as grain grow th, compositional changes, and volatilization of certain elements, particularly in lithium-containing ceramics where lithium loss can significantly impact material performance.

[0013] The ambient environment during sintering plays a crucial role in determining the final properties of ceramic materials. Different atmospheric conditions, including oxidizing, Princeton - 105276 reducing, inert, or vacuum environments, can influence phase formation, stoichiometry, and defect chemistry. However, many existing rapid sintering techniques are limited in their ability to operate under various controlled atmospheres, restricting their versatility for processing different types of ceramic materials.

[0014] Recent developments in rapid sintering technologies have show n promise for reducing processing times while maintaining or improving material quality. These methods include flash sintering, spark plasma sintering, microwave sintering, and ultrafast high-temperature sintering. While these techniques can achieve densification in significantly shorter timeframes compared to conventional methods, many suffer from limitations such as restricted operating environments, complex control systems, or compatibility issues with certain material compositions.

[0015] The development of sintering systems that can operate under controlled ambient gas environments while maintaining rapid heating capabilities would expand the range of ceramic materials that can be processed efficiently . Such systems would be particularly beneficial for materials that are sensitive to atmospheric conditions or require specific gas environments to achieve optimal properties.

[0016] SUMMARY

[0017] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0018] According to an aspect of the present disclosure, an ultrafast high-temperature sintering device is provided. The device comprises an environmental chamber having one or more walls defining an internal volume of space and a sealable opening configured to allow access to the internal volume of space, and a plurality of ports operably coupled to the internal volume of space through at least one of the one or more walls. The device comprises a heater portion configured to sandwich a target sample between two heating elements, each heating element being a resistive heating coil, the heater portion including one or more alloy shields disposed on either side of the two heating elements, each alloy shield configured to reduce radiation heat loss.

[0019] According to other aspects of the present disclosure, the ultrafast high-temperature sintering device may include one or more of the following features. The environmental chamber may comprise a cylindrical stainless-steel vacuum chamber. The sealable opening Princeton - 105276 may comprise a door with a transparent viewport configured to enable real-time temperature monitoring. Each resistive heating coil may be configured in a substantially planar snaking pattern. Each heating element may be composed of a Fe-Al-Cr alloy. The Fe-Al-Cr alloy may exhibit oxidation resistance at high temperatures enabling operation in oxidative environments. The heater portion may include two connector components, each connector component comprising a ceramic portion at least partially surrounded by a metal portion, each connector component operably coupled to a different end of the two heating elements. Each connector component may be configured to receive DC current from a DC power supply. The device may further comprise an insulative layer surrounding the heater portion within the environmental chamber. The plurality of ports may comprise at least one electrical feedthrough, at least one gas inlet valve, at least one gas outlet valve, and at least one pressure gauge port. The device may further comprise a pressure gauge operably coupled to the pressure gauge port. The device may further comprise one or more service lines, each service line coupled to one of the plurality of ports. The one or more service lines may comprise an inlet gas line configured to connect to a target gas cylinder and an outlet gas line configured to connect to a vacuum pump. The target sample may comprise ceramic materials, such as AI2O3, ZrCh, T1O2. LiZr2(PO4)3, and / or Li?La3Zr20i2.

[0020] According to another aspect of the present disclosure, a sintering system is provided. The system comprises the ultrafast high-temperature sintering device and a DC power supply operably coupled to the heating elements within the environmental chamber of the ultrafast high-temperature sintering device.

[0021] According to other aspects of the present disclosure, the sintering system may include one or more of the following features. The system may further comprise a thermal camera configured to monitor temperature of the target sample through the transparent viewport of the environmental chamber. The thermal camera may be configured to provide real-time temperature monitoring during ultrafast heating and cooling cycles.

[0022] According to another aspect of the present disclosure, a method for high-temperature sample densification is provided. The method comprises sandwiching a target sample between two resistive coil heating elements, and within an environmental chamber, such that the target sample and the two resistive coil heating elements are disposed between two alloy shields, each alloy shield configured to reduce radiation heat loss. The method comprises sealing the environmental chamber. The method comprises realizing fast high-temperature densification by passing DC current through the two resistive coil heating elements and transferring heat to the target sample. Princeton - 105276

[0023] According to other aspects of the present disclosure, the method may include one or more of the following features. The method may further comprise a step of controlling an ambient gas environment within the environmental chamber by introducing a selected gas through a gas inlet valve and removing gases through a gas outlet valve. The ambient gas environment may be selected from the group consisting of oxidizing environments, inert environments, and vacuum environments.

[0024] The foregoing general description of the illustrative embodiments and the following detailed description thereof are merely exemplary aspects of the teachings of this disclosure and are not restrictive.

[0025] BRIEF DESCRIPTION OF FIGURES

[0026] Non-limiting and non-exhaustive examples are described with reference to the following figures.

[0027] FIG. 1 illustrates an ultrafast high-temperature sintering device, according to aspects of the present disclosure.

[0028] FIG. 2 depicts an exploded view of a heating portion of a device around a target sample, according to an embodiment.

[0029] FIG. 3 illustrates a view of a heating portion of a device around a target sample, without shields, according to aspects of the present disclosure.

[0030] DETAILED DESCRIPTION

[0031] The following description sets forth exemplar}' aspects of the present disclosure. It should be recognized, however, that such description is not intended as a limitation on the scope of the present disclosure. Rather, the description also encompasses combinations and modifications to those exemplary aspects described herein.

[0032] The field of ceramic processing has long been constrained by conventional sintering methods that require extended processing times and substantial energy consumption. Traditional ceramic densification typically involves high-temperature sintering for periods ranging from tens of hours to several days, creating manufacturing bottlenecks and increasing production costs. These lengthy processing cycles present challenges for industrial scalability and contribute to elevated energy' consumption per unit mass of processed materials. The conventional approach may also lead to compositional changes in temperature-sensitive materials, particularly those containing volatile components such as lithium-based ceramics used in energy storage applications. Princeton - 105276

[0033] Ultrafast high-temperature sintering represents an emerging approach to ceramic processing that addresses these manufacturing limitations. This technology enables the densification of various ceramic materials within minutes rather than hours, potentially reducing processing time by factors exceeding 100. The approach utilizes rapid heating mechanisms to achieve sintering temperatures while maintaining controlled environmental conditions. Such rapid processing may help preserve material stoichiometry by minimizing the time available for volatile component loss during high-temperature exposure.

[0034] The development of ultrafast sintering methods has particular relevance for advanced ceramic applications including solid-state electrolytes, structural ceramics, and functional materials. In some cases, these materials exhibit complex phase relationships and polymorphic behavior that may be influenced by processing conditions. The abi 1 i ty to control heating rates, dwelling times, and ambient atmospheres during sintering provides opportunities to tailor material properties and microstructures. Additionally, the reduced processing times associated with ultrafast sintering may enable new manufacturing approaches for ceramic components where conventional methods prove impractical.

[0035] Environmental control during ceramic processing presents another consideration for advanced sintering applications. Many ceramic materials require specific atmospheric conditions to achieve desired properties or prevent degradation. Traditional ultrafast sintering approaches have been limited in their ability to operate under diverse environmental conditions, particularly oxidizing atmospheres. The expansion of ultrafast sintering capabilities to include controlled ambient gas environments opens new possibilities for processing a broader range of ceramic materials while maintaining the benefits of rapid densification.

[0036] Referring to FIG. 1, an ultrafast high-temperature sintering device 100 provides a comprehensive solution for rapid ceramic processing under controlled environmental conditions. The ultrafast high-temperature sintering device 100 represents a departure from conventional sintering approaches by enabling ceramic densification within minutes rather than the tens of hours typically associated with traditional methods. In some cases, the ultrafast high- temperature sintering device 100 may achieve complete densification of ceramic materials in timeframes ranging from approximately two to five minutes, depending on material composition and desired properties. The device configuration allows for processing under various controlled environments, including oxidizing, inert, and vacuum conditions, through the implementation of specialized heating elements that maintain stability across diverse atmospheric compositions. Princeton - 105276

[0037] The ultrafast high-temperature sintering device 100 incorporates multiple integrated components that work in coordination to achieve rapid heating and controlled processing conditions. The device structure enables precise control over heating rates, dwelling temperatures, and cooling cycles while maintaining environmental isolation from external atmospheric conditions. In some cases, the ultrafast high-temperature sintering device 100 may accommodate various sample sizes and geometries, providing flexibility for different ceramic processing applications. The system design facilitates real-time monitoring and control of processing parameters, allowing operators to adjust conditions during sintering operations based on observed material behavior.

[0038] As shown in FIG. 1, the ultrafast high-temperature sintering device 100 demonstrates a configuration that addresses limitations associated with earlier ultrafast sintering approaches. Traditional ultrafast sintering methods utilizing carbon-based heating elements may be restricted to inert or vacuum environments due to carbon degradation in oxidizing atmospheres. The ultrafast high-temperature sintering device 100 overcomes these environmental limitations through the incorporation of oxidation-resistant heating elements that maintain performance across diverse atmospheric conditions. This capability expansion enables processing of ceramic materials that may benefit from or require exposure to oxidizing environments during sintering operations.

[0039] The ultrafast high- temperature sintering device 100 may provide processing capabilities that extend beyond basic ceramic densification to include applications in solid-state synthesis, heterostructure manufacturing, and coating formation. In some cases, the rapid heating and cooling cycles achievable with the ultrafast high-temperature sintering device 100 may enable control over material phase transformations and microstructural development. The device configuration supports various ceramic compositions, including oxide ceramics, composite materials, and specialized compositions for energy storage applications. The environmental control capabilities of the ultrafast high-temperature sintering device 100 may allow for processing of materials that exhibit sensitivity to atmospheric composition during high- temperature exposure.

[0040] The ultrafast high-temperature sintering device 100 includes a main body 102 that forms the primary structural component of an environmental chamber. The main body 102 incorporates a sidewall 104 (or more than one sidewall, if the chamber is not cylindrical) that defines an internal volume of space 106 within the environmental chamber.

[0041] In some cases, the main body 102 may be constructed from, e.g.. stainless steel materials that provide structural integrity' and chemical resistance during high-temperature Princeton - 105276 processing operations. However, the chamber may be constructed from any suitable material capable of withstanding high temperatures and providing structural integrity’ during processing operations, including but not limited to stainless steel, ceramic materials, refractory metals such as tungsten or molybdenum, or heat-resistant alloys. Such materials may ensure structural integrity7and operational reliability’ under elevated temperature conditions while maintaining compatibility with various atmospheric environments.

[0042] The sidewall 104 extends around the perimeter of the main body 102 to create a sealed enclosure that isolates the internal volume of space 106 from external atmospheric conditions. The environmental chamber configuration enables precise control over atmospheric composition within the internal volume of space 106 during ceramic processing operations.

[0043] As shown in FIG. 1. the environmental chamber may be configured as a cylindrical stainless-steel vacuum chamber that provides structural stability and corrosion resistance under diverse processing conditions. The cylindrical configuration of the main body 102 distributes mechanical stresses uniformly around the sidewall 104, enabling the environmental chamber to withstand vacuum conditions and elevated pressures during processing operations. In some cases, the stainless steel construction of the main body 102 may provide compatibility with oxidizing, inert, and vacuum environments while maintaining structural integrity at elevated temperatures. The cylindrical geometry’ of the environmental chamber facilitates uniform heat distribution within the internal volume of space 106 and provides efficient space utilization for processing equipment and sample materials.

[0044] The environmental chamber incorporates a sealable opening 134 that provides access to the internal volume of space 106 for sample loading and equipment maintenance operations. A cover 112 (or door, if attached to the main body 102 with at least one hinge) may be disposed over the sealable opening 134 and may be positioned at one end of the main body 102 to enable easy opening and closing of the environmental chamber. The cover 112 may include a transparent port 114 that allow s visual monitoring of processing operations within the internal volume of space 106. In some cases, the transparent port 114 may comprise a glass viewport that enables real-time temperature monitoring through optical measurement techniques. The transparent port 114 may provides optical access for thermal imaging equipment while maintaining the sealed environment within the internal volume of space 106 during processing operations.

[0045] With continued reference to FIG. 1, the environmental chamber includes a plurality' of ports 116, 118, 120, 122 that provide various functional connections between the internal volume of space 106 and external systems. The plurality of ports may be operably coupled to Princeton - 105276 the internal volume of space 106 through the sidewall 104 or other walls of the environmental chamber. A port 116 may provide a port for connecting a pressure gauge, for monitoring pressure conditions within the environmental chamber during processing operations. The pressure gauge 124 enables operators to monitor vacuum levels, atmospheric pressures, and pressure changes during heating and cooling cycles. In some cases, the pressure gauge 124 may provide feedback for automated control systems that maintain desired pressure conditions throughout processing operations. The pressure gauge 124 may be calibrated to measure pressure ranges appropriate for various processing environments, including vacuum conditions and elevated pressures associated with gas introduction operations.

[0046] A port 118 may provide electrical feedthrough capabilities for power delivery' to heating elements within the internal volume of space 106. One or more electrical lines 128 operably coupled to a power supply 126 may pass through port 118. A port 120, 122 may be coupled to a service line 132, and may function as a gas inlet and / or outlet for controlling the atmospheric compositions within the environmental chamber. Port 120, 122 may be operably coupled to a valve 130. Service line connections may enable fluid and / or gas management during processing operations. In some cases, a service line 132 may comprise an inlet gas line configured to connect to a target gas cylinder (not shown) for introducing specific atmospheric compositions into the internal volume of space 106. The service line may alternatively comprise an outlet gas line configured to connect to a vacuum pump (not shown) for removing gases and achieving vacuum conditions within the environmental chamber. The valves may provide flow control capabilities that enable precise regulation of gas introduction and removal rates during processing operations. Multiple sendee lines may be connected to different ports to enable simultaneous control of gas inlet and outlet operations.

[0047] As further show n in FIG. 1, the main body 102 includes mounting holes 136 positioned around the perimeter of the environmental chamber to facilitate secure installation and positioning during operation. The mounting holes 136 may accommodate fastening hardware that secures the ultrafast high-temperature sintering device 100 to support structures or work surfaces. In some cases, the mounting holes 136 may be threaded to accept bolts or screws of specific sizes and configurations. The positioning of the mounting holes 136 around the main body 102 provides multiple attachment points that distribute mechanical loads and prevent movement during processing operations. The mounting holes 136 may be sized and positioned to accommodate various mounting configurations depending on installation requirements and available support structures. The mounting holes may allow the cover 112 to be coupled to the main body. Princeton - 105276

[0048] The environmental chamber configuration enables operation under specific electrical parameters that support rapid heating operations within the internal volume of space 106. In some cases, the system may operate at electrical parameters including 25V and 12A DC current, with approximately 6A current passing through each heating coil during processing operations. The electrical feedthrough capabilities provided by the plurality7of ports enable safe delivery of electrical power to heating elements while maintaining environmental isolation within the internal volume of space 106. The electrical connections may incorporate sealing mechanisms that prevent atmospheric contamination while allowing electrical current flow to heating elements positioned within the environmental chamber.

[0049] Referring to FIG. 2, the ultrafast high-temperature sintering device 100 incorporates an insulative layer 108 positioned within the internal volume of space 106 to provide thermal management during processing operations. The insulative layer 108 may comprise ceramic fiber support material that surrounds and supports processing components while minimizing heat transfer to the sidewall 104 of the main body 102. In some cases, the insulative layer 108 may be constructed from high-temperature ceramic fibers, refractory materials, or other thermally insulating compositions that maintain structural integrity at elevated temperatures. The insulative layer 108 provides thermal isolation that protects the environmental chamber structure from excessive heat exposure while maintaining processing temperatures within the internal volume of space 106. The positioning of the insulative layer 108 within the environmental chamber enables efficient heat retention during rapid heating cycles while preventing thermal damage to external components and systems.

[0050] As shown in FIG. 2, a heater portion 110 may be positioned within the internal volume of space 106 and surrounded by the insulative layer 108 to provide controlled heating capabilities for ceramic processing operations. The heater portion 110 may be configured to sandwich a target sample 212 between two heating elements 204, 206 during processing operations. The target sample 212 may comprise various ceramic materials that undergo densification through rapid heating and controlled atmospheric exposure. In some cases, the target sample 212 may comprise ceramic materials selected from compositions including AI2O3, ZrO2, TiO2, LiZr2(PC>4)3, and LnLasZnOn. among other ceramic compositions suitable for energy storage applications, structural applications, or functional material applications. The heater portion 110 enables precise positioning of the target sample 212 relative to heating elements to achieve uniform temperature distribution and controlled heating rates during processing operations. Princeton - 105276

[0051] The heater portion 110 includes heating elements 204, 206 that function as resistive heating coils to generate thermal energy through electrical resistance heating. Each heating element 204, 206 may be configured as a resistive heating coil that converts electrical energy into thermal energy through Joule heating mechanisms. The heating elements 204, 206 may be positioned in substantially parallel arrangements that enable uniform heat distribution to the target sample 212 positioned between the heating elements. In some cases, each resistive heating coil may be configured in a substantially planar snaking pattern that maximizes surface area contact with the target sample 212 while providing uniform heat distribution across the sample geometry'. The snaking pattern configuration of the heating elements 204, 206 may comprise dense serpentine arrangements that optimize heat transfer efficiency and enable rapid temperature increases during processing operations.

[0052] With continued reference to FIG. 2, each heating element 204, 206 may be composed of a Fe-Al-Cr alloy that provides oxidation resistance and thermal stability at elevated temperatures. The Fe-Al-Cr alloy composition may comprise kanthal alloy materials that exhibit exceptional resistivity’ to oxidation at high temperatures, enabling operation in oxidative environments without degradation of heating element performance. In some cases, the Fe-Al- Cr alloy exhibits oxidation resistance at high temperatures enabling operation in oxidative environments, inert atmospheres, and vacuum conditions without compromising heating element integrity or performance characteristics. The kanthal alloy composition of the heating elements 204, 206 represents a departure from carbon-based heating elements that may degrade in oxidizing atmospheres, thereby expanding the range of atmospheric conditions suitable for ultrafast sintering operations. The alloy composition enables the heating elements 204, 206 to achieve temperatures up to 1200°C within 30 seconds while maintaining structural stability and electrical conductivity throughout heating and cooling cycles.

[0053] The heating elements 204, 206 may be configured to achieve ultrafast heating rates greater than 1000°C per minute during processing operations. The rapid heating capabilities of the heating elements 204, 206 enable ceramic densification within timeframes ranging from approximately two to five minutes, depending on material composition and processing requirements. In some cases, the heating elements 204, 206 may reach temperatures up to 1200°C within 30 seconds of electrical power application, providing rapid thermal energy delivery' to the target sample 212. The heating rate capabilities of the heating elements 204, 206 may be controlled through electrical current regulation and power supply management to achieve desired temperature profiles during processing operations. The rapid heating and Princeton - 105276 cooling cycles achievable with the heating elements 204, 206 may enable control over material phase transformations and microstructural development in processed ceramic materials.

[0054] As further shown in FIG. 2, the heater portion 110 includes a first alloy shield 202 and a second alloy shield 214 disposed on either side of the heating elements 204, 206. The first alloy shield 202 may be positioned above the heating elements 204, 206, while the second alloy shield 214 may be positioned below the heating elements 204, 206 to provide thermal management during processing operations. Each alloy shield 202, 214 may be configured to reduce radiation heat loss from the heating elements 204, 206 and target sample 212 during high-temperature processing operations. The alloy shields 202, 214 may be constructed from high-temperature alloy materials that maintain structural integrity and reflective properties at elevated temperatures. In some cases, the alloy shields 202, 214 may comprise refractory metal compositions, high-temperature steel alloys, or specialized heat-resistant materials that provide thermal reflection and heat retention capabilities. The positioning of the alloy shields 202, 214 creates a thermal enclosure around the heating elements 204, 206 and target sample 212 that minimizes heat loss to surrounding components and maximizes heating efficiency during processing operations.

[0055] Referring to FIG. 3, the heating elements 204, 206 may include first ends 208 and second ends 210 that provide electrical connection points for power del i x cry during processing operations. The first ends 208 and second ends 210 of the heating elements 204, 206 may extend outward from the main body portions of the heating elements to facilitate electrical connections with external power supply systems. In some cases, the first ends 208 and second ends 210 may be configured to accommodate various electrical connection methods including clamping mechanisms, threaded connections, or welded joints depending on system requirements and installation configurations. The positioning of the first ends 208 and second ends 210 enables electrical cunent flow through the heating elements 204, 206 while maintaining proper spacing and alignment for target sample 212 positioning between the heating elements.

[0056] As shown in FIG. 3, the heater portion 110 may include connector components 300 that provide electrical interface capabilities between the heating elements 204, 206 and external power supply systems. Each connector component 300 may comprise a ceramic portion 304 that provides electrical insulation and thermal stability during high-temperature operations. The ceramic portion 304 may be at least partially surrounded by a metal portion 306 that provides electrical conductivity and mechanical support for electrical connections. In some cases, the ceramic portion 304 may comprise high-temperature ceramic materials including alumina, Princeton - 105276 zirconia, or other refractory' ceramic compositions that maintain electrical insulation properties at elevated temperatures. The metal portion 306 may comprise aluminum pieces, copper alloys, or other electrically conductive materials that provide low-resistance electrical pathways for current delivery to the heating elements 204, 206.

[0057] With continued reference to FIG. 3, each connector component 300 may be operably coupled to a different end of the heating elements 204, 206 to provide electrical power distribution during processing operations. The connector components 300 may be configured to receive DC current from the power supply 126 through the electrical lines 128 that pass through the port 118 of the environmental chamber. In some cases, each connector component 300 may be configured to receive DC current from a DC power supply that provides controlled electrical power delivery to the heating elements 204. 206. The metal portion 306 of each connector component 300 may extend from a first end 308 to a second end 310 to provide electrical connection points and mechanical attachment capabilities. The first end 308 of the metal portion 306 may provide connection to the heating elements 204, 206, while the second end 310 of the metal portion 306 may provide connection to external electrical lines 128 from the power supply 126. The connector components 300 may include aluminum pieces mounted onto ceramic screws with washers and nuts for electrical connection, providing secure mechanical attachment and reliable electrical contact during processing operations.

[0058] The power supply 126 provides controlled electrical energy delivery to the heating elements 204, 206 through a DC power configuration that enables precise current regulation during processing operations. The power supply 126 may be positioned external to the environmental chamber to prevent thermal exposure while maintaining electrical connectivity7to the heater portion 110 through specialized feedthrough mechanisms. In some cases, the power supply 126 may comprise a DC power supply that delivers electrical current at specific parameters optimized for rapid heating operations. The power supply 126 may incorporate current regulation capabilities that enable operators to adjust electrical power delivery based on material requirements and desired heating profiles during ceramic processing operations. The positioning of the power supply 126 external to the main body 102 provides thermal protection while enabling electrical control over heating element operations within the internal volume of space 106.

[0059] The power supply 126 may operate at electrical parameters including 25V and 12A DC current during typical processing operations. The electrical current distribution through the heating elements 204. 206 may result in approximately 6A current passing through each heating element during simultaneous operation. The electrical parameters of the power supply Princeton - 105276

[0060] 126 enable rapid heating rates while maintaining controlled current flow through the heating elements 204, 206. In some cases, the 25V operating voltage of the power supply 126 provides adequate electrical potential to drive current through the resistance of the heating elements 204, 206 while maintaining safe operating conditions. The 12A total current capacity of the power supply 126 enables simultaneous operation of both heating elements 204, 206 with balanced current distribution for uniform heating performance. The current distribution of approximately 6A through each heating element may provide balanced thermal energy generation that promotes uniform temperature distribution across the target sample 212 during processing operations.

[0061] An electrical line 128 provides electrical connectivity between the power supply 126 and the heating elements 204, 206 within the environmental chamber. The electrical line 128 may comprise insulated conductors that carry electrical current from the power supply 126 to the connector components 300 positioned within the internal volume of space 106. In some cases, the electrical line 128 may incorporate multiple conductors to enable independent current delivery to each heating element 204, 206 during processing operations. The electrical line 128 may be constructed from copper conductors, aluminum conductors, or other electrically conductive materials that provide low-resistance current pathways while maintaining flexibility for installation and maintenance operations. The insulation of the electrical line 128 may comprise high-temperature materials that maintain electrical isolation and safety during elevated temperature processing conditions.

[0062] The electrical line 128 passes through the port 1 18 of the environmental chamber to establish electrical connectivity between external power supply systems and internal heating components. The port 118 may incorporate electrical feedthrough mechanisms that maintain environmental isolation while enabling electrical current flow to the heating elements 204, 206. In some cases, the electrical feedthrough configuration of the port 118 may include sealing mechanisms that prevent atmospheric contamination of the internal volume of space 106 during electrical power delivery' operations. The feedthrough mechanisms may comprise hermetic seals, gasket systems, or other sealing technologies that maintain vacuum integrity and atmospheric control while accommodating electrical conductor passage. The electrical feedthrough capabilities provided by the port 118 enable safe delivery of electrical power to the heater portion 110 while preserving the controlled environmental conditions within the environmental chamber.

[0063] The electrical connections between the electrical line 128 and the connector components 300 may incorporate various connection methods to ensure reliable cunent Princeton - 105276 deliver^' during processing operations. The metal portion 306 of each connector component 300 may provide electrical interface points for the electrical line 128 through mechanical connections, welded joints, or threaded attachment mechanisms. In some cases, the electrical connections may incorporate contact surfaces that maintain low electrical resistance while accommodating thermal expansion and contraction during heating and cooling cycles. The connection methods may include clamping mechanisms that provide secure mechanical attachment and reliable electrical contact between the electrical line 128 and the connector components 300. The electrical connections may be designed to withstand mechanical stresses associated with thermal cycling while maintaining electrical continuity throughout processing operations.

[0064] The electrical power delivery system enables precise control over heating element operation through current regulation and power management capabilities. The power supply 126 may incorporate control systems that enable operators to adjust electrical current flow to the heating elements 204, 206 based on processing requirements and material characteristics. In some cases, the power delivery system may include feedback mechanisms that monitor electrical parameters and adjust current flow to maintain desired heating profdes during processing operations. The electrical control capabilities may enable programmable heating cycles that incorporate specific temperature ramp rates, dwelling periods, and cooling profiles for different ceramic materials and processing applications. The power delivery system may provide real-time monitoring of electrical parameters including voltage, current, and power consumption to enable process optimization and quality control during ceramic processing operations.

[0065] A sintering system may incorporate the ultrafast high-temperature sintering device along with additional components that provide comprehensive processing capabilities for ceramic materials. The sintering system configuration enables integrated operation of heating, monitoring, and control functions through coordinated component interactions. In some cases, the sintering system may provide enhanced processing control through the incorporation of specialized monitoring equipment and power delivery’ systems that work in conjunction with the environmental chamber and heater portion. The system integration approach enables operators to achieve precise control over processing parameters while maintaining real-time visibility' into material behavior during rapid heating and cooling operations. The sintering system may accommodate various ceramic compositions and processing requirements through configurable component arrangements and adjustable operating parameters. Princeton - 105276

[0066] The sintering system includes a DC power supply that may be operably coupled to the heating elements within the environmental chamber of the ultrafast high-temperature sintering device. The DC power supply provides controlled electrical energy delivery that enables rapid heating operations while maintaining precise current regulation throughout processing cycles. In some cases, the DC power supply may incorporate programmable control capabilities that allow operators to establish specific heating profiles based on material requirements and desired processing outcomes. The DC power supply configuration enables consistent electrical power deliver}^ to the heating elements while providing protection against electrical faults and overcurrent conditions. The coupling between the DC power supply and heating elements may be achieved through electrical feedthrough mechanisms that maintain environmental isolation within the chamber while enabling reliable power transmission.

[0067] The DC power supply may provide electrical current regulation capabilities that enable precise control over heating element operation during ceramic processing operations. The power supply configuration may incorporate current monitoring systems that provide feedback regarding electrical parameters during heating cycles. In some cases, the DC power supply may include voltage regulation features that maintain consistent electrical potential across varying load conditions and temperature changes within the heating elements. The power supply may incorporate safety features including current limiting, thermal protection, and fault detection systems that protect both the heating elements and the processed materials from electrical anomalies. The DC power supply configuration enables repeatable processing conditions through consistent electrical parameter delivery across multiple processing cycles.

[0068] The sintering system may incorporate a thermal camera that provides optical temperature monitoring capabilities for processed materials within the environmental chamber. The thermal camera may be configured to monitor temperature of the target sample through a transparent viewport of the environmental chamber (such as a transparent viewport in a door of the environmental chamber, the door being located at one end of the chamber) during processing operations. In some cases, the thermal camera may utilize infrared detection technologies that enable non-contact temperature measurement of ceramic materials at elevated temperatures. The thermal camera positioning relative to the transparent viewport enables direct optical access to the target sample without compromising the sealed environment within the chamber. The thermal monitoring capabilities provided by the thermal camera may enable operators to observe temperature distribution patterns across the target sample during rapid heating and cooling cycles. Princeton - 105276

[0069] The thermal camera may be configured to provide real-time temperature monitoring during ultrafast heating and cooling cycles that characterize the sintering system operation. The real-time monitonng capabilities enable operators to observe temperature changes as heating elements deliver thermal energy to the target sample during processing operations. In some cases, the thermal camera may provide continuous temperature data that enables process optimization and quality control during ceramic densification operations. The real-time temperature monitoring may enable detection of temperature variations, hot spots, or cooling patterns that influence material properties and processing outcomes. The thermal camera configuration may incorporate data logging capabilities that record temperature profiles throughout processing cycles for analysis and process development purposes.

[0070] The thermal camera integration with the sintering system may provide temperature measurement capabilities across temperature ranges appropriate for ceramic processing applications. The camera configuration may enable temperature monitoring from ambient conditions through elevated temperatures exceeding 1200°C during rapid heating operations. In some cases, the thermal camera may incorporate calibration features that ensure measurement accuracy across the operating temperature range of the sintering system. The thermal monitoring system may provide temperature resolution capabilities that enable detection of small temperature variations during processing operations. The thermal camera may incorporate focusing mechanisms that enable precise temperature measurement of specific regions within the target sample during processing cycles.

[0071] The sintering system configuration enables coordinated operation of the DC power supply and thermal camera to provide comprehensive process control and monitoring capabilities. The system integration may enable automated control functions that adjust electrical power delivery based on observed temperature conditions during processing operations. In some cases, the sintering system may incorporate feedback control mechanisms that utilize thermal camera data to regulate DC power supply output for maintaining desired temperature profiles. The coordinated operation of system components may enable programmable processing cycles that incorporate specific heating rates, dwelling temperatures, and cooling profiles based on material requirements. The sintering system may provide data acquisition capabilities that record both electrical parameters from the DC power supply and temperature data from the thermal camera for process analysis and optimization purposes.

[0072] A method for high-temperature sample densification provides a systematic approach to ceramic processing that utilizes rapid heating mechanisms and controlled environmental conditions to achieve material densification within minutes rather than the extended timeframes Princeton - 105276 associated with conventional sintering approaches. The method incorporates specific procedural steps that enable precise control over heating rates, atmospheric compositions, and thermal management during ceramic processing operations. In some cases, the method may accommodate various ceramic compositions and material geometries through configurable processing parameters and adjustable environmental conditions. The method enables operators to achieve consistent processing outcomes through standardized procedural sequences while maintaining flexibility for material-specific requirements and processing objectives.

[0073] The method begins with sandw iching a target sample betw een two resistive coil heating elements within an environmental chamber, such that the target sample and the two resistive coil heating elements are disposed between two alloy shields. The sandwiching configuration positions the target sample in direct thermal contact with both heating elements to enable uniform heat distribution during processing operations. Each alloy shield may be configured to reduce radiation heat loss from the heating elements and target sample during elevated temperature processing conditions. The positioning of the alloy shields above and below the heating elements creates a thermal enclosure that minimizes heat transfer to surrounding components while maximizing thermal energy retention within the processing zone. In some cases, the alloy shields may comprise high-temperature materials that maintain reflective properties and structural integrity7throughout heating and cooling cycles.

[0074] The target sample positioning between the resistive coil heating elements enables direct thermal energy transfer through conductive and radiative heat transfer mechanisms during processing operations. The resistive coil heating elements may be configured in substantially planar arrangements that maximize surface area contact with the target sample while providing uniform temperature distribution across the sample geometry. In some cases, the heating elements may incorporate serpentine or snaking patterns that optimize heat transfer efficiency and enable rapid temperature increases during processing cycles. The spacing between the heating elements may be adjusted to accommodate various target sample thicknesses and geometries while maintaining optimal thermal contact for efficient heat transfer operations.

[0075] Following target sample positioning, the method proceeds with sealing the environmental chamber to establish controlled atmospheric conditions for processing operations. The sealing process isolates the internal processing environment from external atmospheric conditions, enabling precise control over gas compositions, pressure levels, and contamination prevention during ceramic processing cycles. The environmental chamber sealing may be achieved through mechanical closure mechanisms that provide hermetic sealing capabilities while maintaining access for monitoring and control functions. In some cases, the Princeton - 105276 sealing process may incorporate gasket systems, O-ring seals, or other sealing technologies that maintain vacuum integrity and atmospheric isolation throughout processing operations. The sealed environment enables operators to establish specific atmospheric compositions that may influence material properties and processing outcomes during ceramic densification operations.

[0076] The method incorporates a step of controlling an ambient gas environment within the environmental chamber by introducing a selected gas through a gas inlet valve and removing gases through a gas outlet valve. The gas control capabilities enable operators to establish specific atmospheric compositions that may be beneficial or necessary for particular ceramic materials during processing operations. The gas inlet valve provides controlled introduction of selected gases into the sealed environmental chamber, while the gas outlet valve enables removal of unwanted gases or achievement of vacuum conditions. In some cases, the gas control system may enable simultaneous gas introduction and removal operations to maintain desired atmospheric compositions while preventing pressure buildup within the environmental chamber. The valve control mechanisms may provide precise flow regulation that enables gradual atmospheric transitions or rapid gas exchange operations depending on processing requirements.

[0077] The ambient gas environment may be selected from oxidizing environments, inert environments, and vacuum environments depending on material requirements and processing objectives. Oxidizing environments may be established through the introduction of oxygencontaining gases that promote specific chemical reactions or prevent reduction reactions during high-temperature processing operations. Inert environments may be created through the introduction of noble gases or nitrogen that prevent oxidation reactions while maintaining atmospheric pressure within the environmental chamber. Vacuum environments may be achieved through gas removal operations that eliminate atmospheric interference with processing operations while enabling specific material behaviors under reduced pressure conditions. In some cases, the environmental control capabilities may enable sequential atmospheric changes during processing cycles to accommodate materials that benefit from different atmospheric conditions at various processing stages.

[0078] The method proceeds with realizing fast high-temperature densification by passing DC current through the two resistive coil heating elements and transferring heat to the target sample. The DC current application generates thermal energy through electrical resistance heating mechanisms within the heating elements, creating rapid temperature increases that enable ceramic densification within minutes of processing time. The cunent flow through the resistive coil heating elements may be controlled through power supply regulation to achieve Princeton - 105276 specific heating rates and temperature profiles during processing operations. In some cases, the DC current application may result in heating rates exceeding 1000°C per minute, enabling target samples to reach processing temperatures within seconds of current application. The heat transfer from the heating elements to the target sample occurs through conductive contact and radiative heat transfer mechanisms that provide uniform temperature distribution across the sample geometry.

[0079] The fast high-temperature densification process enables ceramic materials to achieve structural consolidation and property development within processing timeframes ranging from approximately two to five minutes depending on material composition and desired characteristics. The rapid heating approach may minimize volatile component loss in temperature-sensitive materials while achieving adequate thermal energy for densification reactions and microstructural development. In some cases, the fast densification process may enable control over material phase transformations and grain growth behaviors through precise temperature control and rapid thermal cycling capabilities. The densification process mayresult in ceramic materials with enhanced density, improved mechanical properties, and tailored microstructural characteristics compared to materials processed through conventional extended-time sintering approaches.

[0080] The method may incorporate rapid cooling capabilities that enable target samples to return to ambient temperatures within controlled timeframes following completion of high- temperature processing operations. Natural cooling processes may enable target samples to reach room temperature within approximately one minute following termination of electrical current flow to the heating elements. In some cases, accelerated cooling may be achieved through compressed air assistance that reduces cooling times to approximately ten seconds through enhanced convective heat transfer mechanisms. The rapid cooling capabilities may enable preservation of high-temperature material phases or microstructural features that might otherwise transform during extended cooling periods. The cooling rate control may provide additional processing variables that influence final material properties and characteristics in processed ceramic components.

[0081] The environmental control capabilities of the method enable processing of ceramic materials that may be sensitive to atmospheric composition during high-temperature exposure operations. The transition from carbon-based heating elements to kanthal heating elements enables processing under oxidizing conditions without degradation of heating element performance or contamination of processed materials. In some cases, the oxidation-resistant heating elements may maintain structural integrity and electrical conductivity throughout Princeton - 105276 processing cycles in oxygen-containing atmospheres that would cause degradation in carbonbased heating systems. The environmental flexibility provided by the method enables processing of ceramic compositions that require specific atmospheric conditions for optimal property development or prevention of unwanted chemical reactions during high-temperature processing operations.

[0082] The method configuration enables processing of various ceramic materials including oxide ceramics, composite materials, and specialized compositions for energy storage applications through adjustable processing parameters and environmental conditions. The procedural flexibility accommodates materials with different thermal expansion characteristics, densification behaviors, and atmospheric sensitivity requirements through configurable heating profiles and environmental control options. In some cases, the method may be applied to processing of ceramic materials for battery applications, structural components, or functional materials that require specific property combinations achievable through rapid thermal processing approaches. The method provides a systematic approach to ceramic processing that combines rapid heating capabilities with environmental control functions to achieve material densification and property development within significantly reduced processing timeframes compared to conventional ceramic processing methods.

[0083] The ultrafast high-temperature sintering device operates through coordinated interactions between multiple system components that enable rapid ceramic densification under controlled environmental conditions. The heat generation process begins when DC current flows through the resistive heating coils, creating thermal energy through Joule heating mechanisms that convert electrical energy into heat at rates sufficient to achieve temperatures exceeding 1000°C within seconds. The electrical resistance of the Fe-Al-Cr alloy heating elements generates controlled thermal output that may be regulated through current adjustment and power supply management during processing operations. The positioning of heating elements in substantially parallel arrangements enables uniform heat distribution to ceramic materials positioned between the coils, while the serpentine coil configurations maximize surface area contact for efficient thermal energy transfer to target samples.

[0084] The heat transfer mechanisms within the system operate through multiple pathways that ensure uniform temperature distribution across processed ceramic materials during rapid heating cycles. Conductive heat transfer occurs through direct contact between the heating elements and target samples, providing immediate thermal energy delivery to ceramic surfaces during current application. Radiative heat transfer contributes additional thermal energy through electromagnetic radiation emitted by the heated coil surfaces, creating secondary Princeton - 105276 heating effects that penetrate into ceramic materials during processing operations. The alloy shields positioned above and below the heating zone create a thermal enclosure that reflects radiated heat back toward the target sample while minimizing heat loss to surrounding chamber components. The thermal management system enables rapid temperature increases while maintaining controlled heat distribution patterns that promote uniform densification across ceramic sample geometries.

[0085] Environmental control functions operate through integrated gas management systems that enable precise atmospheric composition control during ceramic processing operations. The sealed chamber configuration isolates the processing environment from external atmospheric conditions, while the port-based gas introduction and removal systems enable operators to establish specific atmospheric compositions based on material requirements. Gas inlet valves provide controlled introduction of selected atmospheric gases including oxygen for oxidizing environments, nitrogen or noble gases for inert conditions, or vacuum pumps for reduced pressure processing. The environmental control capabilities enable processing of ceramic materials that may require specific atmospheric conditions for optimal property development or prevention of unwanted chemical reactions during high-temperature exposure. The transition from carbon-based to kanthal heating elements enables operation under oxidizing conditions without heating element degradation, expanding the range of atmospheric environments suitable for ultrafast sintering applications.

[0086] The rapid densification process occurs through accelerated sintering mechanisms that achieve ceramic consolidation within minutes rather than the extended timeframes associated with conventional processing methods. The ultrafast heating rates enable ceramic particles to reach sintering temperatures rapidly, promoting particle bonding and pore elimination through enhanced diffusion processes at elevated temperatures. The controlled heating profiles enable operators to achieve specific temperature ramp rates and dwelling periods that optimize densification while minimizing grain growth or volatile component loss in temperaturesensitive materials. The rapid cooling capabilities of the system enable preservation of high- temperature phases or microstructural features through controlled thermal cycling that may influence final material properties. The densification mechanisms may result in ceramic materials with enhanced density characteristics, improved mechanical properties, and tailored microstructural features compared to materials processed through conventional extended-time sintering approaches.

[0087] The insulative layer comprising ceramic fiber support material provides thermal management functions that enable efficient heat retention while protecting chamber Princeton - 105276 components from excessive temperature exposure during processing operations. The ceramic fiber composition maintains structural integrity at elevated temperatures while providing thermal isolation between the heating zone and chamber walls. The insulative layer positioning within the chamber creates a thermal barrier that minimizes heat transfer to external components while maintaining processing temperatures within the heating zone. The support functions of the insulative layer enable proper positioning and alignment of heating elements and target samples during processing operations. The ceramic fiber material selection provides compatibility with various atmospheric environments while maintaining insulative properties throughout heating and cooling cycles.

[0088] Scalability of the ultrafast sintering technology may be achieved through systematic expansion of system components and processing capabilities to accommodate larger sample sizes and increased production volumes. The scaling approach may involve expanding the overall system dimensions to accommodate larger ceramic components or multiple samples during simultaneous processing operations. Additional heating element units may be incorporated into scaled systems to maintain uniform temperature distribution across expanded processing zones while preserving rapid heating capabilities. Computational modeling techniques may be employed to optimize heating element arrangements and power distribution patterns that achieve efficient heating performance across larger processing areas. The modeling approaches may enable prediction of temperature distribution patterns, identification of optimal heating element spacing, and determination of power requirements for scaled processing operations. The scalability considerations may include mechanical support systems, electrical power distribution networks, and environmental control capabilities that maintain processing performance across expanded system configurations.

[0089] The application areas enabled by ultrafast high-temperature sintering technology extend beyond conventional ceramic densification to include specialized manufacturing processes that benefit from rapid thermal cycling and controlled environmental conditions. Ultrafast high- temperature solid state synthesis of complex materials may be achieved through rapid heating and cooling cycles that enable formation of specific phases or compounds that may be difficult to achieve through conventional processing methods. The controlled atmospheric environments and rapid thermal processing capabilities enable synthesis of materials with tailored compositions and properties for specialized applications. Manufacturing of diffusion- free heterostructures may be accomplished through rapid processing that minimizes interdiffusion between different material layers while achieving adequate bonding and Princeton - 105276 structural integrity. The rapid heating and cooling cycles may preserve sharp interfaces between dissimilar materials while enabling structural consolidation of multilayer components.

[0090] Rapid formation of coating layers on nanoparticles represents another application area where ultrafast sintering technology provides processing advantages through controlled thermal exposure and environmental management. The rapid heating capabilities enable surface modification of nanoparticle materials through controlled thermal treatment that may alter surface chemistry or create protective coating layers. The environmental control functions enable processing under specific atmospheric conditions that promote desired surface reactions while preventing unwanted oxidation or contamination during coating formation processes. The rapid cooling capabilities may enable preservation of coating layer properties or prevention of coating degradation through controlled thermal cycling. The processing flexibility provided by the ultrafast sintering approach enables optimization of coating formation parameters including heating rates, dwelling temperatures, and atmospheric compositions based on specific nanoparticle materials and desired coating characteristics. The application versatility of the technology enables processing of various material systems including energy storage materials, structural ceramics, and functional materials that benefit from rapid thermal processing under controlled environmental conditions.

[0091] Example

[0092] Conventional ultra-high temperature sintering (UHS) utilizes carbon or graphite-based materials as heating elements. Using carbon electrical contacts enables exceedingly high temperatures (e.g. > 2000°C ) and high voltages. However, carbon can chemically react with the solid electrolyte and oxygen at elevated temperatures. This can lead to contamination of the solid electrolyte unless it is processed in an inert environment. This makes large-scale integration challenging. Replacing carbon heating elements with alloy materials (e.g.. Fe — Cr — Al alloy) can enable fast sintering in air Processing in air can enable scalable processing at low costs. In addition, sintering in air can suppress oxygen vacancies and deleterious side reactions with carbon.

[0093] In practice, powders synthesized via conventional solid-state synthesis techniques are ty pically subjected to uniaxial pressure to form green body pellets. The pellets are then sandwiched between two coils, and a DC voltage is applied on both ends of the coils to enable rapid Joule heating bringing the pellet to about 1200°C within 30 seconds as seen with a thermal camera. This allows sintering and rapid densification of solid electrolyte materials within minutes ( > 90%relative densities). The modified air-compatible UHS method enables Princeton - 105276 high temperature ramping rates and is flexible to different environments. Fast ramp rates reduce the total energy’ cost when compared to spark-plasma sintering and conventional sintering.

[0094] Microstructure-driven polymorphism

[0095] NASICON-type LiZn(PO4)3 (LZP) is one type of solid electrolyte that demonstrates a relatively high bulk ionic conductivity. LZP demonstrates exceptional air and moisture stabilitysimilar to other NASICON-type Li-ion conductors such as Lii+xAlxTi2-x(PO4)3 (LATP) and Lii+xAlxGe2-x(PO4)3 (LAGP), and demonstrates greater chemical compatibility with lithium metal than LATP and LAGP. However, microstructural heterogeneity- due to the grain size, grain boundaries, and polymorphism can drive a range of degradation mechanisms. Polymorphism or the presence of multiple phases of ion conducting materials can result in regions that are highly conducting and regions that have limited conductivity.

[0096] It has been reported that LZP can exhibit four different polymorphic phases: (1) a- rhombohedral, (2) a'-triclinic, (3) / ?-monoclinic, and (4) ?' -tetragonal phases. The / ?- monoclinic and / ?' -tetragonal phases are less common in solid electrolytes processed at high temperatures relevant for high density components. Instead, most reports studying LZP for battery applications report the a rhombohedral or a'-tri cl inic phase. The processing route, precursors selection, dopant, particle size, and processing time and temperature can all influence the ratio of polymorphic phases in the final sintered solid electrolyte. Fast sintering approaches enable a rapid way to examine material transformation pathways and observe how polymorphism can be controlled.

[0097] The cry stal structures of a -rhombohedral and a '-triclinic phases are very similar, making Rietveld refinement on X-ray diffraction (XRD) necessary- for quantifying two phases. The a-rhombohedral phase has a higher symmetry and lithium ions are more equally distributed. The a '-triclinic phase has a slightly distorted Zr — P — 0 network which causes lithium ions to selectively occupy two distinct sites in the crystal. The ionic conductivity' of the a -rhombohedral phase is 2 to 3 orders of magnitude greater than the n'-triclinic phase. Nevertheless, the a'-lriclinic phase is thermodynamically more stable at room temperatures than the a: -rhombohedral phase. Phase transformation between the ct '-tri cl i ni c phase and a rhombohedral phase occurs between 20 °C and 60 °C.

[0098] Thus, high-temperature processing steps will induce a phase transformation between the rhombohedral and triclinic phases and ultimately lead to a heterogeneous material system with a mixture of phases. Control and stabilization of the highly conducting a-rhombohedral phase at room temperature via dynamic processing conditions is of interest. One approach to Princeton - 105276 obtaining higher concentrations of the rhombohedral phase is to sinter the sample for a longer time. Sintering LZP using conventional high temperature furnaces ( 18 h / 1200°C ) results in solid electrolytes with approximately 75% to 85% rhombohedral phases. Nevertheless, lithium is highly volatile at elevated temperatures, which possibly results in the loss of lithium during long sintering conditions.

[0099] The phase homogeneity within the sample was also considered, and it was observed that the rhombohedral phase distribution is homogeneous when the depth to the sample surface is greater than 0.2 mm.

[0100] Table 1 Effect of particle size and the distribution of powders. The initial phase of the green bodies was kept to be triclinic (i.e., no preheating step), and no sintering aid was used.

[0101] The rhombohedral phase has a higher density (3.15 g cm'2) than the triclinic phase (3.11 g cm'2). Therefore, there will be a volume expansion within the pellet when the solid electrolyte transforms from the predominantly high-temperature stable phase (e.g. rhombohedral) to the predominantly low-temperature stable phase (e.g. triclinic). It has been hypothesized that the rhombohedral phase is likely stabilized at room temperature in a stressed form instead of distorting to the thermodynamically stable triclinic phase. Increasing the packing density (e.g. low porosity) of the green powders can lead to compressive stresses during densification and suppress the rhombohedral-to-triclinic volume expansion phase transformation pathway. To systematically explore the role porosity plays in this phase transformation three types of powders were prepared: (1) coarse (10 pm). (2) fine (0.5 pm), and (3) mixed. The mixed sample was composed of particles between 0.5 and 5 pm in diameter. Powder XRD confirmed that the predominant phase for all these powders is triclinic. Sintering pellets at 1200 °C for 2 min results in dense solid electrolytes. A greater concentration of rhombohedral phase is achieved with pellets processed from fine powders (e.g. dense electrolytes) when compared with the coarse powders (see Table 1). Princeton - 105276

[0102] The pellet sintered from the mixed powders produces solid electrolytes with the lowest rhombohedral phase ratio. The corresponding sample shrinkage (indicated by the diameter of sintered pellets) and relative density follow a similar trend (Table 1). The fine-powder pellets give the smallest diameter (highest shrinkage) and highest relative density, while the mixed- powder yields the highest diameter (lowest shrinkage) and lowest density, suggesting a stress- driven stabilization of the rhombohedral phase. Compared to the case of coarse powders, the green body pressed from fine powders likely achieves higher initial packing density as well as a higher sintering activity thanks to the much larger surface area. For the case of mixed powders with a wide particle size distribution, as previously demonstrated, densification is likely prevented during sintering because of the increased contact area between particles which overcompensates the enhancement from particle rearrangement.

[0103] Implications of powders in the green body

[0104] In addition to stress-driven impacts on phase transformations, the initial polymorphic phase composition in the green body can also significantly affect densification mechanisms and the polymorphism of the sintered pellets. Green body LZP pellets pressed with powders synthesized via a conventional solid state reaction route demonstrate nearly a pure triclinic phase at room temperature. When the green body pellet is heated to over 60°C, it transforms to an almost pure rhombohedral phase. This trend agrees with previous literature findings.

[0105] Therefore, the initial polymorphic phase ratio of the green body pellets can be controlled through simple preheating strategies. Preheating the green body to a temperature above which it is known to exist in an almost pure (e.g., at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% pure) singular form may be advantageous. Here, preheating the green body to, e.g., 80 °C for 15 minutes can result in a green body which is almost purely rhombohedral prior to sintering. Green bodies, subjected to the preheating step resulting in an initial concentration of rhombohedral phase, result in a greater shrinkage and higher density (95%) solid electrolyte (Table 2) after 5 min high-temperature sintering. A higher packing density likely assists in the stabilization of the rhombohedral phase. A rhombohedral phase ratio approaching 81% was achieved with green pellets sintered with a preheating stage. The absence of a preheating stage resulted in a lower rhombohedral phase ratio (72%)

[0106] Table 2. Effect of starting polymorphism of the green body. The particle size of the green bodies was kept to be fine, and no sintering aid was used. Princeton - 105276

[0107] Ultra-fast high temperature sintering results in materials which experience ultrahigh heating rates ( > 103°C min-1). The LZP particles with a triclinic phase in the pressed green body experiencing such high heating rate will likely not have sufficient time to be converted to a rhombohedral phase. High heating rates can lead to incomplete or non-uniform phase transformation throughout the thickness of the pellet, resulting in a mixture of rhombohedral and triclinic phases during the initial sintering step. Powders with non-uniform and uniform phase concentrations due to preheating experience different grain growth properties and microstructural transformations during densification, which are observed directly with scanning electron microscopy. Samples with mixed polymorphic phases show clear neck growth and coarsening between particles upon sintering. Upon further sintering the mixed phase, the green body shows more significant grain growth, grain size heterogeneity, and coarsening which all lead to an increase in the porosity of the ceramic. Pow ders with purely rhombohedral starting powders demonstrate more controlled grain growth processes and densification. The densification mechanism and phase transformation pathway for a pellet initially comprised of a high concentration of a-rhombohedral are very different from a pellet comprised of a mixture of cr'-triclinic and a -rhombohedral phases.

[0108] The material transformation pathways experienced by the triclinic and rhombohedral phases during sintering differ drastically. From the SEM images on different sintering stages, it is plausible that the triclinic particles experience more significant grain coarsening and mass transportation. This may be attributed to several factors. The slightly low er density of the triclinic phase may result in residual porosity when a triclinic grain undergoes a phase transformation between the triclinic phase and the rhombohedral phase during high- temperature sintering. Moreover, there may be a surface energy difference between the two polymorphs, similar to what was previously observed in Y2O3 polymorphic systems. A phase with a higher surface energy7can initiate greater surface diffusion than the lower surface-energy7phase and result in neck growth. Neck growth induces more significant grain growth and prevents densification in the mixed-phase sample by forming a vermicular-shaped grain network. Additionally, the pore redistribution during nucleation and growth of the Princeton - 105276 rhombohedral phase from the triclinic phase might also create interconnected pore networks that are detrimental to densification. All these factors can contribute to the lower porosity and lower rhombohedral phase ratio observed in the sample without the preheating stage. Given the unique high heating rate during ultrafast sintering, extra consideration on polymorphism of starting and final materials is needed to understand and control the sintering behaviors and materials performance.

[0109] Implications of liquid sintering aid on polymorphism

[0110] The transport and electrochemical properties of a solid electrolyte are greatly influenced by the electrolyte density, microstructure (grain size, grain boundary, etc.) and the stoichiometry of lithium. Lithium tends to occupy interstitial sites in LZP, and it has been suggested that higher lithium concentration in the interstitial sites aids in the stabilization of the rhombohedral phase. High temperature sintering can lead to lithium evaporation which can reduce the concentration of the rhombohedral phase in the solid electrolyte and decrease transport properties. To explore the impact of lithium stoichiometry on the phase transformation pathway we combined the LLP powders with 10% molar ratio excess Li(Li2COs). The excess mass ratio was around 0.78% (Li2CO? to LZP). Solid electrolytes sintered with excess lithium achieved 85% rhombohedral phase after 5 minutes fast sintering, while solid electrolytes without the excess lithium only achieved 72% rhombohedral phase (Table 3). The solid electrolyte sintered with excess lithium also demonstrated greater shrinkage and a higher density (Table 3).

[0111] This shows similarities in terms of relative density, rhombohedral phase ratio, and ionic conductivity (see below) compared to the previously discussed samples with additional preheating. On the other hand, introduction of Li2CO3 rules out the need of having a pure rhombohedral green body. Ex situ imaging of the grain growth process during fast sintering sheds light onto the role the L12CO3 plays in densification and grain growth during fast sintering. A solid electrolyte with excess lithium was heated to 1200 °Cand then immediately cooled down to room temperature (within 10 seconds) and imaged using scanning electron microscopy to understand the microstructural properties at the initial sintering stage. The solid electrolyte with additional Li2COs at this stage has very small grains with limited neck growth between adjacent grains, similar to the preheated sample described in the previous section.

[0112] When the same solid electrolyte is held at 1200 °C for only 30 seconds significant changes were observed to the microstructure. Very large grains on the order of 1 pm - 5 pm are present after only 30 seconds of sintering. Li2CO3 can act as a liquid sintering aid and decompose to the Li2O liquid and coat LZP particles. The liquid coating likely resists the Princeton - 105276 microstructural evolution associated with the triclinic particles and limits surface diffusion and neck growth.

[0113] Table 3 Effect of Li2CO3 as a sintering aid. The particle size in the green bodies was kept to be fine, and no preheating step was added.

[0114] Control over polymorphic phases in LZP can be achieved via microstructural control (e.g. particle size), initial polymorphism control and the use of a sintering aid. All of these have been shown to be effective strategies for controlling the ratio of rhombohedral to triclinic polymorph in a LZP solid electrolyte. The ionic conductivity is directly correlated with the rhombohedral phase ratio in the solid electrolyte. This confirms previous reports which show that the rhombohedral phase is at least two orders of magnitude more conductive than the triclinic phase. The room temperature ionic conductivity of the 85% rhombohedral solid electrolyte is 1.3 x 10’5S cm1which agrees with values reported by previous studies with room temperature rhombohedral phase stabilization. The subtracted activation energy is about 0.40 eV for most of the ultrafast-sintered samples with a high rhombohedral phase ratio, whereas the pellets densified from coarse powders demonstrate a lower activation energy' of 0.30 eV. Meanwhile, the least ionic conductive sample is the one sintered from mixed powders, showing only 4.1 x 10‘8S cm’1room temperature ionic conductivity, agreeing well with its very low rhombohedral phase ratio (44%). The cycling stability7testing results of Li|LZP|Li symmetric cells suggest that for LZP solid electrolytes with a rhombohedral phase ratio more than 75% (and associated high density), the cell voltage stability' is relatively good with small voltage increase over time.

[0115] A number of implementations have been described. Nevertheless, it w ill be understood that various modifications may be made w ithout departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the follow ing claims.

Claims

Princeton - 105276CLAIMS1 . An ultrafast high-temperature sintering device, comprising: an environmental chamber having one or more walls defining an internal volume of space and a sealable opening configured to allow access to the internal volume of space, and a plurality of ports operably coupled to the internal volume of space through at least one of the one or more walls; and a heater portion configured to sandwich a target sample between two heating elements, each heating element being a resistive heating coil, the heater portion including one or more alloy shields disposed on either side of the two heating elements, each alloy shield configured to reduce radiation heat loss.

2. The ultrafast high-temperature sintering device of claim 1, wherein the environmental chamber comprises a cylindrical stainless-steel vacuum chamber.

3. The ultrafast high- temperature sintering device of claim 1, wherein the sealable opening comprises a cover or door with a transparent viewport configured to enable real-time temperature monitoring.

4. The ultrafast high-temperature sintering device of claim 1, wherein each resistive heating coil is configured in a substantially planar snaking pattern.

5. The ultrafast high- temperature sintering device of claim 1, wherein each heating element is composed of a Fe-Al-Cr alloy.

6. The ultrafast high-temperature sintering device of claim 5, wherein the Fe-Al-Cr alloy exhibits oxidation resistance at high temperatures enabling operation in oxidative environments.

7. The ultrafast high-temperature sintering device of claim 1, wherein the heater portion includes two connector components, each connector component comprising a ceramic portion at least partially surrounded by a metal portion, each connector component operably coupled to a different end of the two heating elements.Princeton - 1052768. The ultrafast high- temperature sintering device of claim 7, wherein each connector component is configured to receive DC current from a DC power supply.

9. The ultrafast high-temperature sintering device of claim 1, further comprising an insulative layer surrounding the heater portion within the environmental chamber.

10. The ultrafast high-temperature sintering device of claim 1, wherein the plurality of ports comprises at least one electrical feedthrough, at least one gas inlet valve, at least one gas outlet valve, and at least one pressure gauge port.

11. The ultrafast high-temperature sintering device of claim 10. further comprising a pressure gauge operably coupled to the at least one pressure gauge port.

12. The ultrafast high-temperature sintering device of claim 10, further comprising one or more service lines, each service line coupled to one of the plurality of ports.

13. The ultrafast high-temperature sintering device of claim 12, wherein the one or more service lines comprise an inlet gas line configured to connect to a target gas cylinder and an outlet gas line configured to connect to a vacuum pump.

14. The ultrafast high-temperature sintering device of claim 1 , wherein the target sample comprises one or more ceramic materials.

15. A sintering system, comprising: the ultrafast high-temperature sintering device of claim 1; and a DC power supply operably coupled to the two heating elements within the environmental chamber of the ultrafast high-temperature sintering device.

16. The sintering system of claim 15, further comprising a thermal camera configured to monitor temperature of the target sample through a transparent viewport of the environmental chamber.

17. The sintering system of claim 16, wherein the thermal camera is configured to provide real-time temperature monitoring during ultrafast heating and cooling cycles.Princeton - 10527618. A method for high-temperature sample densification, comprising: sandwiching a target sample between two resistive coil heating elements, and within an environmental chamber, such that the target sample and the two resistive coil heating elements are disposed between two alloy shields, each alloy shield configured to reduce radiation heat loss; sealing the environmental chamber; and realizing fast high-temperature densification by passing DC current through the two resistive coil heating elements and transferring heat to the target sample.

19. The method of claim 18. further comprising a step of controlling an ambient gas environment within the environmental chamber by introducing a selected gas through a gas inlet valve and removing gases through a gas outlet valve.

20. The method of claim 19, wherein the ambient gas environment is an oxidizing environment, an inert environment, or a vacuum environment.

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