Ivan B. Cutler

Electrical and mechanical relaxation in CaF2 doped with NaF

Abstract A loss peak caused by addition of NaF to CaF2 was studied by dielectric loss and internal friction methods. The observed relaxation times of the sodium ion-fluorine vacancy dipole in electrical and mechanical fields are given by equations (1) and (2). T elec. = 7.25 × 10 −15 exp 0·53 kT (1) Tx mech. = 3.29 × 10 −15 exp 0·53 kT (2) It is proposed that the dipole relaxation occurs by fluorine vacancy jumps in the 〈100〉 direction of the first coordination shell of the sodium impurity. A possible explanation of the observed peak broadening as a function of dipole concentration is offered.

Absorption of water in waste glass as a precursor for foam formation

Abstract The objective of this research is to describe the formation of foam glass from waste glass using water as a gasifying agent similar to natural perlite. Artificial perlite with up to 10% water content may be made from waste soda-lime glass by subjecting the glass to water vapor under moderate pressures (less than 250°C). The maximum rate of absorption requires a minimum amount of liquid water to be in contact with the glass. Excess liquid water dilutes the corrosion action of alkali formed. Rate of water absorption as a function of water content and 1N NaOH solution content were examined on rods of glass as well as glass powder. Water adsorption was obtained by heating glass compositions in saturated steam in an autoclave. In general, the absorption of water was related to particle size, liquid water content, hydroxide ion concentration and glass composition.

Diffusion in polycrystalline magnesiowüstite determined by reduction kinetics

Abstract Polycrystalline magnesiowustite samples (5 wt% Fe 2 O 3 doped) were reduced (or oxidized) at various temperatures in CO 2 CO gas mixtures and N 2 O 2 gas mixtures. The reaction was followed continuously with a Cahn microbalance. The kinetics in the high oxygen partial pressure region (0.18−9.6 × 10 −6 atm) were controlled by cation vacancy diffusion. The chemical diffusion coefficient of iron in magnesiowustite was found to increase linearly with the concentration of cation vacancies. The activation energy for diffusion was found to be 45 kcal/mol. The pseudochemical diffusion coefficient of iron in magnesiowustite evaluated from the kinetics of reduction and oxidation in low oxygen partial pressure atmospheres (10 −7 –10 −10 atm) was found to decrease as the concentration of cation vacancies increased. The reduction kinetics could be interpreted best by assuming an initial desorption of oxygen on the surface of the solid solution, and the migration of oxygen away from the grain boundaries of the sample followed by an associated solid state diffusion process.

Carbothermal Reduction of Silica

Silicon carbide, silicon nitride or silicon monoxide may be produced by carbothermal reduction of silica depending on conditions. The mechanism for the reduction of silica involves a chain reaction, gas-solid scheme. Both silica and carbon surfaces are involved. An explanation for the role of iron as a catalyst is given.

Determination of an Effective Viscosity of Powders as a Function of Temperature

A method is described for determining the effective viscosity of powder compacts during densification as a function of temperature. The method utilizes constant rate of heating and is easily adapted to determining the sintering temperature of a powder compact as well as measuring the effective viscosity. The method can be used for crystalline as well as glassy (amorphous) systems. Values of the coefficient of viscosity or diffusion can be determined for powders of simple particle geometry and known particle size distribution. For practical applications, an effective viscosity is proposed as a better measure of densification characteristics. Illustration of the method is made by examining shrinkage characteristics of various ceramic powder compacts at constant rates of heating.

Microstructural Control During Sintering of β″-Alumina Compositions Through Ceramic Processing Modification

The exaggerated grain growth during high temperature (1585° – 1600°C) sintering of Li2O-stabilized β″-alumina compositions is essentially a process or very rapid growth of stabilized 3″ nuclei to large dimensions (>100 µm) while the matrix remains extremely fine-grained (< 3 µm). The final grain size is therefore inversely proportional to the cube root of the volume fraction originally occupied by these nuclei~1 Such a relationship was reported by Cutler in the case of seeded alpha alumina powders and more recently by Lacour and Paulus3 in the case of barrium-hexaferrite. The occurrence of an exaggerated grain growth during sintering of ceramics has been shown to depend on the flux-growth mechanism wherein a film or channel of liquid phase surrounds the growing nuclei. The growth of nuclei to large dimensions takes place by the solution of surrounding fine grains in the liquid and their precipitation on the growing crystal surface. While Cooy4 and Stuijts5 reported accidental impurities as the cause of liquid phase formation, Lacour and Paulus3 showed that local inhomogenities can also give rise to a liquid phase responsible for the flux growth.

Activated Sintering of Alumina by Quenching Point Defects

Aluminum oxide powders containing iron oxide were passed through a reducing oxygen acetylene flame. The resulting spherical particles of alumina coming out of the flame were quenched in water. The above process resulted in reduction of iron oxide dissolved in alumina and formation of large numbers of point defects. Quenching of the alumina spheres led to the quenching of large numbers of nonequilibrium point defects. The number of these quenched-in defects over the equilibrium concentration were estimated by using the sintering techniques. Activated sintering of alumina was observed in the case of aluminum oxide spheres containing quenched-in defects.

Extrusion of soft solids through a tube

Abstract The flow, without plug action, of soft solids through a cylindrical tube is analyzed using the Eyring plasticity equation. Experiments were conducted with lead and wax flowing at various rates at several temperatures. A satisfactory correlation is obtained with the theoretical expression and the experimental data.

Flocculation of Mineral Suspensions With Coprecipitated Polyelectrolytes

Coprecipitation of anionic and cationic polyelectrolytes has been applied to flocculation of several mineral systems. Results obtained in a study of the flocculation of kaolinite and hematite suspensions of polycationic and polyanionic electrolytes are presented. Greatly increased settling rates were observed following precipitation of positive and negative polyelectrolytes on the surface of finely divided minerals in aqueous suspension. The ratios of polycationic to polyanionic electrolytes required to produce maximum sedimentation have been shown to correspond closely with the equivalence points obtained by light scattering studies of systems containing the positive and negative polyelectrolytes by themselves.

The Effect of Impurities on the Properties of Ceramic Materials

The effects of impurities on structural properties, such as diffusion, sintering, grain growth, and crystal growth, and mechanical properties, such as plastic deformation, creep, brittle fracture and internal friction, and electrical and optical properties of ceramic materials are discussed. It was concluded that ceramic materials differ markedly from metals in that impurities promote the formation of vacancies that are stable at low temperatures, and impurities form donor and acceptor levels in the energy gap between the conductions and valence band. (P.C.H.)