Determination of oxidation states of uranium dioxide pellets by two-step flow-coulometry

Abstract

1601identified with pH(S) in the operational definition of pH. Nevertheless, too little is yet known concerning the residual liquid-junction potential in these solvents at low temperatures to permit one to assess the internal consistency of the pH scale defined by these reference points. Measurements of pH under these extreme conditions are rendered difficult by the extraordinarily high resistance of the usual glass electrodes. In addition, modified reference electrodes will doubtless prove a necessity. LITERATURE CITED(1) M. Sankar, J. B. Macaskill, and R. G. Bates, J . Solution Chem., 8, 887 (1979) 0 Spivey and Shedlovsky 0 Present work 47T 0 10 2 0 30 wt X EIOH Figure 3. pK(molality scale) for acetic acid in ethanol/water mixtures at 0 and 25 OC as a function of the composition of the solvent. Data in water are from Ref. 6 and 7of pH measurements in ethanol/water media at temperatures below 0 "C. The values of PQH for the acetate and phosphate buffers given in Table I11 may fill this need. When used as reference solutions, the PQH of these buffer solutions is \ --I A chemical method for analysis of distribution of oxidation states of metals in solids has been developed as a reference to other methods based on physical measurements. A solid is dissolved with a continuous flow of strong phosphoric acid from surface to bulk, and oxidation states of the dissolved ions are determined consecutively by two-step flow-coulometry. Strong phosphoric acid dissolves such solids as uranium or iron oxides to Ions whose oxidation states are the same as those in solids. The oxidized surface of about 20 A on a UOz pellet which had stood for about 10 years at room temperature in alr was estimated to be U02.05, and the O/U ratio decreased toward the bulk until 0.1 pm. After the pellet was heated for 10 h at 300 or 430 O C in air, the oxidized surface layer increased to about 8 pm (400 8, of powdered U308 + UO,+,, 0.66 > x > 0.01) or about 820 pm (370 prn of powdered U308 -t 3 prn of U,08 + 450 pm of UOZ+,, 0.66 > x > 0.01), respectively.Analysis of oxidation states of metals in solids based on physical measurements gives abundant information on ma-terial science. These physical methods can be classified broadly into methods (1) for analysis of very thin layers at the surface such as by X-ray photoemission spectrometry (XPS) or Auger electron spectrometry (AES) and methods ( 2 ) which give overall information on a solid such as measurements of conductivity or electromotive force (EMF). There are many difficulties still remaining with these methods. In the former, for example, pretreatment of the surface and composition of the matrix greatly affect the result of analysis, and, in the latter, interaction between sample and electrode and the presence of impurities often give serious trouble. Therefore, calibration by reference materials and careful evaluation of data obtained are required. Obviously, data obtained by chemical analyses offer many suggestions for the interpretation of results obtained by physical methods.Although ...

Development of an electrochemistry apparatus for the heaviest elements

“…The electrochemistry apparatus developed is based on the flow electrolytic cell [13][14][15]. A cross sectional view of the apparatus is illustrated in Fig.…”

“…The apparatus is based on a flow electrolytic cell [13][14][15] equipped with a chemically modified electrode [16][17][18][19] that is quite suitable for rapid and efficient chemical experiments of the heaviest elements. A chemically modified method was applied to separate ions of interest in different oxidation states on the electrode.…”

Transformation and reactions of porphyrin iron(III) derivatives in an organic solution at the aqueous|organic solution interface

“…(28) indicates that Eðc ½FeðOEPÞ 2 O;DCE ¼ c ½FeðOEPÞ 2 OH þ ;DCE Þ shifts 0.059 V to more positive with the increase of pH by 1. Regarding the calculation of Eðc ½FeðOEPÞ 2 O;DCE ¼ c ½FeðOEPÞ 2 OH þ ;DCE Þ, E 00 H þ used was 0.18 V versus TPhBE (which corresponds to DG 0 tr ¼ 53 kJ mol À1 ) reported previously [27,43].…”

Selective Ion Transfer Accompanied by a Respiration Mimetic Reaction at an Aqueous/Organic Solutions Interface

“…The peak was identical with that of the one-electron-oxidation product of DMFC, DMFC + , which had been prepared using a column electrode. 10,11 Therefore, it may be reasonable to estimate the electrolysis product to be DMFC + . The DMFC + produced by electrolysis for 5 h was estimated to be 3.08×10 -5 mol.…”