Development of 'Ultra-High-Pressure SPS Device' Stably Generating Over 10 GPa — Space Seed Holdings and Okayama University of Science Jointly Achieve Low-Temperature Synthesis of Materials

Space Seed Holdings Co., Ltd. (Headquarters: Minato-ku, Tokyo; Representative Director: Kengo Suzuki; hereinafter 'SS-HD'), in joint research with Professor Yoshihisa Mori of Okayama University of Science, has developed a new type of spark plasma sintering (SPS) device capable of stably generating ultra-high pressures exceeding 10 GPa. The results were presented at the 2026 Spring Meeting of the Japan Society of Powder and Powder Metallurgy (late May 2026, Osaka).

This device overcomes two major challenges of conventional ultra-high-pressure SPS: 'extremely small sample size' and 'non-uniform pressure and temperature distribution,' demonstrating the ability to sinter millimeter-scale samples under uniform pressure.

Presentation Overview

Title (Japanese)
Development of an Ultra-High-Pressure SPS Device Incorporating a Clamp-Type High-Pressure Generator

Title (English)
Development of an Ultra-High-Pressure SPS System Incorporating a Clamp-Type High-Pressure Generator

Presenters
Yoshihisa Mori¹, Kanji Kameyama¹, Kengo Suzuki² (1. Okayama University of Science / 2. Space Seed Holdings)

Venue
Japan Society of Powder and Powder Metallurgy 2026 Spring Meeting (late May 2026, Osaka), Presentation No. 3-9A

Device Photo: Clamp-type ultra-high-pressure SPS (UHP-SPS) device installed inside an SPS chamber

Background: The desire to increase pressure, but measurement becomes difficult with higher pressure

Spark Plasma Sintering (SPS) is a technique that allows sintering and densification of uniaxially pressed powder in a short time and at low temperatures by applying pulsed electric current. Commercially available SPS devices typically apply pressures of several tens to hundreds of MPa. The research group had previously developed an ultra-high-pressure SPS device combining a piston-cylinder type high-pressure cell and reported that applying pressure significantly lowers the vitrification temperature of SiO₂. Pressure is a crucial parameter that can not only densify materials but also alter their state.

However, the conventional piston-cylinder type had fundamental limitations. The sample size was on the sub-millimeter order, and the non-uniformity of pressure and temperature distribution inside the cell was significant, making it difficult to quantitatively evaluate 'what happened at what pressure and temperature.' The higher the pressure, the more difficult it became to precisely interpret the obtained results.

Content of the Presentation: Achieving 'Uniformity and Large Volume' with a Multi-Anvil Method

The research group developed a new clamp-type high-pressure generator based on the 'palm cubic' type high-pressure generator, which has a proven track record in physical property measurements from low to high pressures. The palm cubic has a multi-anvil press structure that isotropically pressurizes the sample with six anvils. Compared to the uniaxial pressurization of the piston-cylinder type, it offers advantages of more uniform pressure distribution and significantly larger sample volume. By installing this within the chamber of an existing SPS device, they constructed an ultra-high-pressure SPS system. The achievable pressure exceeds 10 GPa, far surpassing the uniaxial pressurization type.

For pressure calibration of the device, the electrical resistance change (phase transition) of bismuth (Bi) was used as a pressure fixed point. When a load of 30 tons was applied by the press and the four clamp screws were torque-controlled, the phase transition point Bi II–III (2.70 GPa) was confirmed at a torque of 100 N·m, and Bi I–II (2.55 GPa) was confirmed at a torque of 50 N·m. This allows estimation of clamp pressures of approximately 2.6–2.7 GPa and 2.5 GPa, respectively (estimates at room temperature; pressure release occurs during heating, so pressure identification under heated conditions will be further advanced).

Regarding heating, by adding a new thermal insulation layer mechanism, heating up to near 1273 K became possible with a current of approximately 100 A. Under a 70 A heating condition, the high-temperature zone was localized only near the sample, and the temperature rise on the anvil side and the clamp body was suppressed, confirming that the thermal insulation structure functions effectively.

As a verification experiment, SPS sintering of SiO₂ powder was performed. The recovered sample was millimeter-scale, approximately 2 mm in diameter and 1 mm in height, significantly larger than samples from the conventional piston-cylinder type. The sample changed from powder to ceramic and further to a transparent glassy state, with transparency confirmed under the low-temperature condition of a clamp torque of 75 N·m and 873 K. This result is comparable to the condition of approximately 2 GPa and 873 K in the conventional piston-cylinder type.

Technical Highlights

- Stable generation of over 10 GPa: Applied the multi-anvil (palm cubic) structure with six anvils to a clamp type, stably achieving ultra-high pressure far exceeding the uniaxial pressurization type.
- Uniform pressure distribution and large sample volume: Isotropic pressurization suppresses non-uniform pressure distribution, expanding the recovered sample to a millimeter scale of approximately 2 mm diameter and 1 mm height, overcoming the challenge of conventional sub-millimeter samples.
- Pressure calibration using bismuth phase transitions: Used Bi II–III (2.70 GPa) / Bi I–II (2.55 GPa) as pressure fixed points to correlate clamp torque with generated pressure.
- Thermal insulation structure enabling localized heating: Added a thermal insulation layer, enabling heating up to near 1273 K with approximately 100 A current. At 70 A, the high temperature is localized near the sample, suppressing temperature rise in the device body.
- Confirmed transparent vitrification under low temperature and pressure conditions: SiO₂ was made transparent at a torque of 75 N·m and 873 K, demonstrating that pressure is not just a densification factor but a design parameter for controlling material state.

Expected Applications

The ability to achieve both uniform ultra-high pressure and precise temperature control with easy-to-handle millimeter-scale samples significantly advances the quantitative evaluation of material synthesis conditions. Specifically, applications are expected in a wide range of material processes, including low-temperature synthesis of new materials, control of non-equilibrium states not normally obtainable, and exploration of high-pressure synthesized materials such as diamond and c-BN (cubic boron nitride). By enabling precise handling of pressure as a design variable, this technology moves material development closer to a stage where conditions can be predicted and designed, rather than relying on trial and error.

Future Developments

The research group will further advance pressure identification under heated conditions to improve calibration accuracy across both pressure and temperature axes. SS-HD will continue its joint research with Professor Yoshihisa Mori of Okayama University of Science, accumulating material synthesis data using this device and expanding its application to the company's own material and process development, including the space utilization research project 'SPACE LAB.' Based on the already completed patent applications for next-generation high-pressure SPS technology, SS-HD will leverage the knowledge gained from prototype development for both intellectual property and commercialization.

Comment from Kengo Suzuki, Representative Director of SS-HD

'Pressure is not just a force to shrink and solidify things. We want to treat pressure as a 'pen for the blueprint that rewrites the state of the material itself.' With the device development we have advanced with Professor Mori, we can now obtain ultra-high-pressure sintered materials, which were difficult to measure accurately under uniform pressure, as millimeter-sized samples. I feel great significance in having reached the entrance of a stage where we can design materials while foreseeing the conditions.

SS-HD's long-term goal is to assemble the technologies necessary for humanity to live in space by 2040. In space, where the materials that can be transported from Earth are limited, technology to create necessary materials from local resources with low energy is essential. I am confident that this ultra-high-pressure SPS technology will become one of the foundational technologies for material manufacturing in space.'