Taizo Utsunomiya

The thermal stability of binary alkali metal nitrates

Abstract The thermal stability of binary alkali metal nitrates has been investigated by DSC and the simultaneous measurement of TG, DTA, DTG and EGA. The solid solutions containing sodium nitrate are thermally unstable and cluster readily to each component species. The decomposition temperature of nitrates does not decrease by the coexistence of other nitrates, while the melting temperature does not decrease. The behaviour of the thermal decomposition is reasonably interpreted by thermodynamic considerations.

An X-ray diffraction study of anharmonic thermal vibrations in the ionic conductor, barium chloride fluoride (BaClF)

Abstract Integrated intensities of X-ray reflections from a barium chloride fluoride single crystal were measured at 24, 180, 289, 402, 467 and 610°C. The intensities were used for the determination of the anharmonic potential parameters up to the third order. Harmonic potential parameters for each ion were obtained from the temperature dependence of thermal parameters, and anharmonic potential parameters were determined by the least-squares procedures, utilizing the temperature factor formalism based on the cumulant expansion. As a result, it has been found that the Ba2+ and Cl− ions show an anharmonicity, while no significant anharmonic effect was detected for the F− ion. From the potential calculated around the Cl− and F− ions, it was found that both Cl− and F− ions diffuse more easily within the (001) plane than along the c axis.

Acid—base and redox reactions in fused sodium nitrite

Abstract Acid—base and redox reactions in binary systems of sodium nitrite and several oxides with different acidity and oxidizing ability have been investigated. Kinetic parameters have been obtained by analyzing thermogravimetric data under a constant heating rate. Sodium peroxide is the main basic species in the nitrite melt. Peroxide ion is disproportionated into oxide ion and oxygen atom in the melt. The activation energy of the formation of peroxide is constant, irrespective of the acidity of oxides, while that of the disproportionation increases with increase in acidity. On the other hand, the species which possess oxidizing ability are sodium nitrite, nitrate and peroxide. The nitrate and peroxide are formed intermediately during the course of the reaction. Below 600°C, the oxidizing ability decreases in the order; peroxide, nitrite, nitrate.

The thermal stability of alkali and alkaline-earth metal hydroxide—nitrate systems

Abstract The thermal stability of alkali and alkaline-earth metal hydroxide—nitrate systems has been investigated by thermal analysis, voltammetry and observation with a high-temperature microscope. The melts of alkali metal hydroxide—nitrate systems are thermally stable to at least 300°C above the melting temperatures. The melts have a strong oxidizing ability caused by the strong chemical interaction between hydroxide and nitrate ions. The thermal stability of strontium and barium hydroxide—nitrate systems increases at some peculiar compositions. Although nitrates of strontium and barium decompose in the solid state, the thermal decomposition of the mixtures of these hydroxide—nitrate systems is initiated via the liquid state as a result of the increase in the thermal stability of liquids.

THE REACTION OF TERNARY MIXTURES OF SODIUM NITRATE, DIBORON TRIOXIDE AND SILICA

The reaction and the thermal changes of the ternary system NaNO3-B2O3-SiO2 have been investigated by means of high-temperature thermogravimetry, derivative thermo-gravimetry, microscopy, differential thermal analysis, gas chromatography, X-ray diffractometry and IR spectrometry. The combination of these techniques provides information on the reaction process. The major reactions which take place in this system are as follows: several sodium borates are preferentially formed in a liquid-phase reaction after NaNO3 and B2O3 melt, with the generation of O2, NO and N2. SiO2 does not take part in the reaction below 550‡. Sodium borates with B/Na=9 to 1 are formed successively with the generation of O2 and NO as the temperature increases. The reaction products around 700‡ are mixtures of borates and silicates. Borosilicates are formed above 750‡.ZusammenfassungDie Reaktionen und die thermische VerÄnderung des ternÄren Systems NaNO3-B2O3-SiO2 wurde mittels Hochtemperatur-Mikroskopie, TG, DTG, DTA, Gaschromatographie, Röntgendiffraktometrie und IR-Spektrometrie untersucht. Die Kombination dieser Methoden liefert Informationen über den Reaktionsprozess. Verschiedene Natriumborate werden vorzugsweise durch Flüssigphasenreaktion von NaNO3/B2O3-Schmelzen unter Freisetzung von O2, NO und N2 gebildet. Siliciumdioxid nimmt unterhalb 550‡ an der Reaktion nicht teil, bildet jedoch mit geschmolzenem Natriumnitrat Silikate bei Temperaturen über 550‡. Natriumborate mit B/Na-VerhÄltnissen von 9–1 werden mit steigender Temperatur unter Entwicklung von O2 und NO gebildet. Bei Temperaturen um 700‡ werden Mischungen von Boraten und Silikaten als Reaktionsprodukte erhalten. Borsilikate werden über 750‡ gebildet.РЕжУМЕс пОМОЩьУ ВысОкОтЕМп ЕРАтУРНОИ МИкРОскОп ИИ, тг, Дтг, ДтА, гАжОВОИ хРО МАтОгРАФИИ, РЕНтгЕНОВскОИ ДИФФР АктОМЕтРИИ И Ик спЕкт РОскОпИИ БылИ ИсслЕДОВАНы РЕАкцИИ И тЕРМИЧЕскИ Е ИжМЕНЕНИь тРОИНОИ с ИстЕМы NaNO3-B2O3-SiO2. ЁтИ кОМБИНИРОВА ННыЕ МЕтОДы пОжВОлИлИ пОл УЧИть ИНФОРМАцИУ О РЕ АкцИОННых пРОцЕссАх. пОслЕ плАВлЕНИь НИтРАтА НА тРИь И ОкИсИ БОРА, Иж жИ ДкОФАжНОИ РЕАкцИИ пРЕДпОЧтИтЕ льНО ОБРАжУУтсь НЕскОлькО БОРАтОВ НА тРИь с ВыДЕлЕНИЕМ кИс лОРОДА, АжОтА И ОкИсИ АжОтА. кР ЕМНИИ НИжЕ 550‡ В РЕАкцИУ НЕ Вс тУпАЕт. ВышЕ 550‡ oН ВстУп АЕт В РЕАкцИУ с РАсплАВлЕН НыМ НИтРАтОМ НАтРИь, ОБРА жУь сИлИкАты. пОслЕДО ВАтЕльНО ОБРАжУУтсь БОРАты НА тРИь с ОтНОшЕНИЕМ В: Na=9−1 с ВыДЕлЕНИЕМ кИсл ОРОДА И ОкИсИ АжОтА пО МЕРЕ УВЕлИЧЕНИь тЕМпЕРАт УРы. пРИ тЕМпЕРАтУРЕ ОкОл О 700‡ пРОДУктАМИ РЕАкцИ И ьВльЕтсь сМЕсь БОРАтОВ И сИлИк АтОВ. Б ОРОсИлИкАты ОБРАжУ Утсь ВышЕ 750‡.

Uniformity of the composition of spinel ferrite particles prepared by air oxidation of hydroxide precursors in suspension

Abstract Co and Mn ferrites were prepared by air oxidation of their hydroxide precursors in suspensions. The distributions of Co or Mn within the particles were evaluated by dissolving the particles in a HCl solution, and determining the amount of Co or Mn released from the particles at different times. The evaluation revealed that a considerably high Mn concentration was found near the surface of the Mn ferrite particles, and that the Co concentration was uniform throughout the Co ferrite particles.