Magnetic properties of Al, Ga, Sc, In substituted barium ferrites: A comparative analysis

CERAMICS

INTERNATIONAL,

Vol

137

11, n 4, I 985

mon ore and 35% chemically enriched ore. On substituting the common ore by the chemically enriched one the properties of the refractories were remarkably improved due to lower silicate level (about 2%) and higher chrome spinellide content. The properties of the basic refractories were correlated with their different constituent phases.

LATTICE PARAMETERS OF CUBIC SOLID SOLUTIONS IN THE SYSTEMS uR203-(1-u)MOz V.B. Glushkova,

F. Hanic and L.V. Sazonova

Short communication.

Vol. V, January/December,

1979

ELECTRICAL CONDUCTIVITY OF POLYCRYSTALLINE 3Y203*WOj AT HIGH TEMPERATURES K. Kuribayashi

and T. Sata

The electrical conductivity of polycrystalline Yh’WO12 (3Y2C3*WC3) and of polycrystalline YsWO12 doped with alkaline earth oxides or ZrOz were measured over the temperature range from 800 to 1400°C under oxygen partial pressures of 10 - 5 to 1O” atmospheres. YsW0,2 showed a ptype conductivity at higher oxygen pressures and an n-type conductivity at lower oxygen pressures. Additions of alkaline earth oxides increased the conductivity of YsWO,J in the higher oxygen pressure region. The conductivity of alkaline earth oxides-doped YhWO12 decreased monotonically with decreasing oxygen partial pressures and approached constant values at lower oxygen partial pressures. The Zr02 addition caused a decrease in the conductivity of YsWO,~ in the higher oxygen pressure region. The variations of the conductivity with oxygen pressure are discussed assuming various defects models.

MAGNETIC PROPERTIES OF Al, Ga, SC, In SUBSTITUTED BARIUM FERRITES: A COMPARATIVE ANALYSIS

THE CORROSION RESISTANCE OF STRONTIUM ZIRCONATE CERAMICS TO COAL ASH CONSTITUENTS AND POTASSIUM SEED OF MHD-GENERATORS

G. Albanese

M. Zborowska,

and A. Deriu

A comparative analysis of the magnetic properties of BaFe,z_ ,Me,0r9 (Me=Al, Ga, SC, In) ferrites is given. The influence of the substitution of iron ions on the magnetic ordering and on the magnetic properties is pointed out. The reported data indicate that the occupation by non magnetic ions of lattice sites inside the R-block leads to peculiar helical spin structures. Further confirmation of the relevant contribution of iron ions in the 12 K sublattice to the single ion uniaxial anisotropy has been obtained.

THE SOLID SOLUBILITY and Zr02 in MgO

OF Sc203, A1203, Cr203, SiO2

M. Grylicki and J. Zborowski

The resistance of dense strontium zirconate ceramics to corrosion by Al2O3, CaO, MgO, Si02 and K2CO3 as well as coal ash was investigated by the > for 2 hrs at 1700%. The corrosion process was investigated by optical polarizing microscopy, X-ray microanalysis and scanning electron microscopy. The results showed that strontium zirconate ceramics have excellent corrosion resistance against K2CO3. No corrosion effect by A1203, CaO and MgO was observed as well. Considerable corrosion occurred when silica was used which formed a baddeleite dispersed phase in a glassy matrix of a variable composition. A similar effect was observed in crucibles corroded by coal ash containing silica.

A.F. Henriksen and W.D. Kingery Scanning electron microscopy and X-ray diffraction lattice parameter measurements have been used to determine the extent of solid solubility of oxides in MgO. The solubility of Sc2O3 ranges between 0.005 and 0.044 mole fraction in the temperature interval from 1270% to 1600% with an experimental heat of solution equalling 36.8 kcallmole. Cr203 has a similar solubility range, between 0.007 and 0.038 mole fraction in the temperature interval from 1200% to 1600°C, and the heat of solution was determined to be 43.6 kcal/mole. Much smaller solubility was found for Al203, between 0.0004 and 0.007 mole fraction in the temperature interval from 1200% to 1600°C, and the heat of solution was 97.2 kcallmole. The solubility of Si02 is less than 0.00034 mole fraction at 1850% and the solubility of Zr02 is less than 0.000075 mole fraction at 1885’C.

SURFACE GLASSES

TENSION AND DENSITY OF MOLTEN IN THE SYSTEM La203-Na2Si20s

A. Passerone,

R. Sangiorgi

and G. Valbusa

Surface tension, density, and volatility of sodium disilicate, modified by additions of lo/o, 50/o, lo%, mole La203, have been evaluated at temperatures varying from 900 to 1500’%, under highly reducing conditions. These results and related data (such as activation energy of evaporation reaction; thermal expansivity; temperature coefficient of surface tension; nonideal behaviour; surface adsorption) have made possible interpretation of the role played by lanthanum in modifying the properties of the base glass.

KINETICS AND MECHANISM OF THE SOLID-STATE HIGH-TEMPERATURE TRANSFORMATION OF ANDALUSITE (A12Si05) INTO 3/S-MULLITE (3A1203-2Si02) AND SILICA (Si02) H. Schneider

and A. Majdie

The kinetics of the high-temperature transformation of andalusite (<40pm) were investigated by means of X-ray techniques. The transformation interval was determined to lie between about 1250 and 1500°C. The best fitting of the kinetic data was achieved with an exponential law of the type: 1 -(Y= exp (- kt +ct/(t + 1)). The kinetic curves are associated with a topotactic transformation mode with preservation of the aluminium-oxygen octahedral chains and diffusion of aluminium, silicon and oxygen atoms. Below 138O”C, mullite (+ Si02) formation is essentially restricted to an initial rapid period of the transformation, because nucleation and product growth occur only at energetically favored lattice sites (e.g. grain boundaries). Above 1380°C, mullite and Si02 nucleation and growth may take place throughout the volume of the low-temperature phase (andalusite) over the whole range investigated.

KINETICS AND MECHANISM OF THE REACTION BETWEEN SODIUM CARBONATE AND SILICA W. Richard Ott The kinetics and mechanism of the reaction between sodium carbonate and silica were studied using thermogravimetric analysis to monitor the percent reaction versus time. A