BLACK-WHITE INCOME INEQUALITY AND THE URBAN SYSTEM OF THE SOUTH

This article reveals the positions of 40 SMSAs in the urban system of the South in 1980, and then investigates whether SMSAs' location in this urban system has an impact on black-white income inequality. The urban sysrem analyzed here is based on Richard Wanner's two-dimensional model and ideas on how each dimension is related to racial income inequality are drawn from work by urban ecologists and radical political economists. It is hypothesized that (1) the higher an SMSA is on the “metropolitan functions” dimension, the more black-white income inequality it will have; and (2) being near the manufacturing end of the “industry structure” dimension has the effect of reducing racial income inequality. Percentage black in the SMSA and black-white educational level are also included in the analysis and the results generally support our hypotheses. The implications of these findings are discussed and the southern urban system in 1980 is compared with ealier depictions of it.     

Thermal Expansion of Orthorhombic PbO

Thermal expansion of orthorhombic PbO was investigated by high-temperature X-ray diffraction. The coefficients in the a ₀, and c ₀ directions are equal and <½ the coefficient in the b ₀ direction. The structure is described in terms of Pb–O chains extended in the a ₀ direction and bonded into layers in the b ₀ direction; appreciable Pb–Pb bonding is indicated. Coordination and bond distances observed in PbSiO₃ and lead silicate glasses, which are similar to those of massicot, and Pb _n O _n polymeric units reported in PbO vapor are interpreted as additional evidence of the importance of PbO chains as structural entities.     

Some Structural and Electrical Properties of Lithium Silicate Glasses

Dielectric measurements, analyzed in terms of the Maxwell-Wagner-Sillars theories of inhomogeneous dielectrics, have been used to investigate the phase-separation characteristics of various lithium silicate glasses. Such measurements are shown to provide evidence of the continuous or discontinuous nature of separated phases and to allow estimates of their shape factors and concentrations. The results indicate that dielectric measurements are particularly useful in following phase-separation processes in glasses from the initial to the final stages.     

Metastable Immiscibility in the B2O3–SiO2 System

Using the phase diagram and a simple solution model, a subliquidus miscibility gap was estimated for the B₂O₃-SiO₂ system. The predicted coexistence boundary, showing a consolute temperature of 520°C, was flat and symmetrical and extended across the complete binary. Gradient furnace heat treatments of selected compositions in this system resulted in phase separation which corresponded closely to the coexistence boundary initially predicted. Calculations and preliminary experimental results indicate that temperatures and compositions exist wherein metastable three-liquid immiscibility occurs in R₂0–B₂0₃-SiO₂systems.     

Control of Dielectric Constant and Loss in Alumina Ceramics

The dissipation factors and dielectric constants of alumina ceramics containing less than 100 ppm of impurities and of specimens doped with Si, Ti, Ca, Mg, Fe, and Cr ions were measured in the region 10² to 8.5 × 10⁹ cps and 25° to 875° C. Multiple regression analysis of the data at 500° C and 10⁶ cps showed a linear relation between impurity concentration and tan δ, with a correlation coefficient of 0.93. Si ions caused the greatest rise of tan δ, Mg and Ti were second, Ca third, and Cr and Fe had no significant influence. These effects diminished with rising frequency and became negligible in the microwave region. Activation energies of conduction for pure and doped alumina were estimated from measurements of δ at 10⁵ cps and 500°C. Values between 1.2 and 1.6 ev were calculated for all compositions except the one containing Mg²⁺, for which 2.0 ev was obtained. At low frequencies, the dielectric constant (k') rose exponentially with temperature, reflecting a similar rise in the number of free charge carriers contributing to interfacial polarization. At higher frequencies the temperature variation of k' fell to a shallow positive slope of about 120 ppm per °C. This coefficient was not influenced by low concentrations of impurities but could be effectively compensated without excessive loss by additions of 10 to 20% SrTi0₃.     

Systems of Na-Fe-SiO2 Glasses and Steel: I, Wetting and Adherence

Wetting behavior of molten Na₂O-Fe₂O₃-SiO₂ and Na₂O-FeO-SiO₂ glasses on very-low-carbon steel at 900°C in purified Ar was studied. The steel surface was dry-polished and cleaned by ion bombardment. Glass frit was then placed on the metal, and the system was introduced into the furnace without exposure to air. Dynamic advancing and receding contact angles were measured. Shear (push-off) tests were performed on the glass-steel composite at room temperature to determine adherence. The equilibrium contact angles were obtained from the arithmetic mean of the final advancing and receding angles. As the Fe oxide content of the glasses increased, the degree of wetting improved; Fe³⁺ was more effective than a combination of Fe³⁺ and Fe²⁺ in improving the wettability. Glasses very nearly saturated with Fe oxide exhibited high adherence values and chemically adhered to steel.