The Earth’s interior is a real high pressure and high temperature world. Because the Earth’s deep interior cannot be directly observed, experimental investigations at high pressures and high temperatures have been playing an important role. Geophysical observations have revealed that the interior of the Earth is divided into several layers by the discontinuities of seismic wave velocity and density. The development of the high pressure technique has been made it possible to understand the nature of such seismic wave discontinuities. This article outlines the structure of the Earth and explains how high pressure experiments have contributed to the study of the Earth’s interior.

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Methods to synthesize diamond under high pressure and temperature conditions are summarized, and characteristics of the synthetic diamonds are also presented. There are two ways to synthesize diamonds. One is to grow large crystals in mm size, and the other is to grow grit size up to 1 mm. Typical morphology and optical properties are demonstrated.

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Various physical phenomena which can be easily observed in diamond anvil are reviewed. The phenomena include crystal growth and phase transformation in H₂O ice, growth and the formation of negative crystal in CCl₄ ice, index matching of MnF₂ crystal and alcohol under pressure, and the color change in AgI associated with the phase transformations. All these phenomena can be observed easily below 2 GPa and can be used as a good example to teach physics.

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To investigate molecular and cellular biology of deep-sea multicellular organisms, the author has developed a novel piezo-stat aquarium system (Deep Aquarium System). Using this system, the author succeeded in maintaining a variety of deep-sea multicellular organisms under pressure and under atmospheric conditions after gradual and slow decompression. Furthermore, the author successfully cultivated pectoral fin cells of a living deep-sea fish that decompressed to atmospheric pressure. The deep-sea fish cells passaged more than 20 times and were succeeded in freeze storage under atmospheric condition. The deep-sea fish cells have greater pressure tolerance abilities than conger eel and mouse cells.

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Until recently, the factor that has played a predominant role in food processing was not “ pressure” but “ heat” , although both factors are independently responsible for transforming the state of a substance. Food processing can be achieved without any cleavage of covalent bond contained in the ingredients of food. Moreover, high-pressure treatments are considered to be very promising for food processing of the future. This is because decomposition of nutrients and production of stench can be minimized more effectively and energy consumption can be reduced more efficiently when compared with heat treatment. Further, when a food product in a container is subjected to high-pressure treatment, uniform processing throughout the food can be guaranteed.

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The quality of cutting of diamond anvils from the stone crystal has a decisive influence on high-pressure generation using a diamond anvil cell (DAC). Recently, we have established a high-precision processing technology for the cutting. The development enabled to design a simple and convenient DAC without any adjustment mechanism to parallelize culet-faces of opposite anvils. The current situation in the manufacturing floor is also reported on.

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These days, science education in senior high schools is one of the hot issues. Interest in natural science for high-school students, as well as people, has seemed to fade away. Therefore, in high school science lessons, teachers are required to improve the quality of science awareness. It is very important to foster scientific interest and romance so as to create scientist in the future. This paper describes a trial of teaching high pressure science in a high school by making and using a high-pressure cell of simple form.

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In this article, novel techniques on chemical conversion of cellulosic biomass and waste polymers with sub- and supercritical fluids are introduced. The phenomenon that highly-crystallized cellulose particles can dissolve into water near the critical point of water is described. It is also introduced that product distributions are tunable by manipulating typical operating parameters such as temperature and pressure on hydrothermal treatment of biomass and its related compounds. As for waste polymers, reaction pathways and kinetics on solvolysis of polyesters and polyamides in sub- and supercritical fluids are elucidated. Furthermore, new researches, hydrothermal electrolysis and supercritical plasma techniques, are finally introduced.

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In this article, we propose a novel hydrogen storage system which has both lightness and compactness a combination of a lightweight high pressure vessel and hydrogen storage alloy. The system is expected as a promising formation to improve the properties of hydrogen storage techniques in weight and volume other than the conventional techniques using compressed hydrogen or hydrogen storage alloy individually. The novel system requires a hydrogen storage alloy with higher volumetric hydrogen density as well as higher gravimetric density, and with higher equilibrium dissociation pressure than the hydrogen storage alloys which have ever been used for hydrogen storage systems.

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Among metal hydrides, magnesium hydride (MgH₂) would be a promising candidate for hydrogen storage materials because of its high hydrogen-storage capacity (7.6 mass%). However, the dehydrogenation temperature is too high for wide practical applications. Novel magnesium-based hydrides with better dehydrogenation properties than MgH₂ can be prepared under hydrogen pressure of gigapascal (GPa). For instance, Mg₇TiH₁₆ (6.9 mass%) would release hydrogen at a lower temperature by 130 K than MgH₂. The Mg-H ionic bonding distance in Mg₇TiH₁₆ is longer than that in MgH₂. The observed lower dehydrogenation temperature seems to be consistent with the structure.

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