▎ 摘　　要

NOVELTY - Generation of microbubbles involve obtaining water by heating and pressurizing water and gas in a subcritical state, cooling or depressurizing the gas-liquid mixed fluid in which the gas is in supercritical state to bring the temperature or pressure of the gas-liquid mixed fluid below the critical temperature or pressure of the gas to generate microbubbles in the gas-liquid mixed fluid, and heating or pressurizing the gas-liquid mixed fluid so that the temperature or pressure of the gas-liquid mixed fluid is equal to or higher than the critical temperature or pressure of the gas to dissolve the microbubbles in the gas-liquid mixed fluid. By repeatedly performing the microbubble dissolution step and microbubble generation step, the generation and disappearance of the microbubbles are repeated in the gas-liquid mixed fluid. USE - Generation of microbubbles e.g. microbubble and nanobubble for refining sample e.g. cellulose, expanded graphite and layered titanium oxide for producing cellulose nanofiber and graphene (all claimed). ADVANTAGE - The method generates microbubbles and utilizes both the characteristics of the microbubbles and the ability to hydrolyze subcritical water. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following: (1) microbubble generation apparatus (1), which comprises an accommodating portion for accommodating the gas-liquid mixed fluid in which the water is in subcritical state and the gas is in supercritical state, and a control unit (11) for controlling the temperature or pressure of the gas-liquid mixed fluid in the accommodating portion. The control unit cools or depressurizes the gas-liquid mixed fluid in the accommodating unit to bring the temperature or pressure of the gas-liquid mixed fluid below the critical temperature or pressure of the gas; (2) sample refinement, which involves mixing a sample with the gas-liquid mixed fluid, and peforming the microbubble dissolution step and microbubble generation step repeatedly. The sample is refined by the generated microbubbles; and (3) sample refinement apparatus, which contains a mixing unit for mixing the sample with the gas-liquid mixed fluid, accommodating portion for accommodating the gas-liquid mixed fluid after mixing, and control unit for controlling the temperature or pressure of the gas-liquid mixed fluid in the accommodating portion. DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of microbubble generation apparatus. (Drawing includes non-English language text) Microbubble generation apparatus (1) Control unit (11) Cooling unit (12) Heating unit (13) Fluid production apparatus (20)