Pushed by human activities, the atmospheric CO₂ concentration has reached levels which have made extreme weather events more likely, and which threaten permanent climate changes for the world. In order to combat this, CO₂ emissions must be reduced significantly. Electricity production and industry are two sectors which contribute greatly to the production of CO₂, thus a reduction in the amount of CO₂ produced by thermal power plants and factories could make a significant contribution to combatting climate change. The electrochemical reduction of CO₂ in those sources is considered very likely to be a solution to the problem. In this study, the activity of a Pt oxide electrode in the electrochemical reduction of CO₂ was investigated in a sulfuric acid solution. Pt oxide electrodes have shown superior activity for the methanol oxidation reaction, which is the reverse reaction of CO₂ electrochemical reduction. Cyclic voltammetry of the Pt oxide electrode in a CO₂-saturated H₂SO₄ solution showed a definite anodic peak at 0.6-0.8 V vs. SHE, which was not observed in an Ar-deaerated electrolyte. Thus, it was determined that the anodic peak could be related to the re-oxidation of the reduction product of CO₂ during cathodic polarization. The activity of the Pt oxide electrode for CO₂ reduction was much higher than that of the Pt electrode. It was concluded that the residual oxygen, which was hardly detected in the Pt electrode, improved the activity for CO₂ electrochemical reduction on the Pt oxide electrode. Gas chromatography-mass spectrometry of the electrolytic solution after CO₂ reduction revealed that the reduction product was mainly CH₃OH. These results should be very useful for developing a new electrochemical reduction system for converting CO₂ into CH₃OH.

The rheological properties of cement slurries (including fresh concrete and high concentration paste for filling etc.) are complicated, therefore they are approximated by the Bingham plastic model. In recent years, the application of Herschel-Bulkley model is recommended for drilling mud. The rheological coefficients of these models are obtained by using measurement results of the rotational viscometer or experimental results of the flow in a circular pipe, and the pressure loss in pipe flows is obtained from these rheological coefficients. Therefor it is essential to properly select the model in order to design the slurry transportation. In the field of well drilling, the flow in a concentric annulus with a relatively large pipe diameter ratio is approximated by the flow in a parallelplate, so it is also necessary to consider the flow in a parallel-plate. In this study, first, a method to determine the rheological coefficients by the least squares method from measurement results of the rotational viscometer using the function provided in a spreadsheet is shown and a method to quantitatively select the rheological model using Akaike's information criterion is also shown. Next, after the exact solutions of flows in a circular pipe and in a parallel-plate is summarized, an approximate expression of wall shear stress is derived and the error analysis is performed, and its effectiveness is confirmed by using past experimental data. In addition, a method of calculating the rheological coefficients by the least squares method from measurement results of flows in a circular pipe and in a parallel-plate using spreadsheet is shown and this method is practiced by using the experimental data of the flow in pipes.