silicon and orthoclase

A detailed analysis was undertaken of the X-ray photoelectron spectra obtained from microcline, orthoclase and several samples of plagioclase with varying Na/Ca ratio. Comparison of the spectra was made based on the chemical bonding and structural differences in the Al- and Si-coordination within each specimen. The spectra for Si 2p and Al 2p vary with the change in symmetry between microcline and orthoclase, while in plagioclase an increase in Al-O-Si linkages results in a small but observable decrease in binding energy. The overall shapes of the O 1s peaks observed in all spectra are similar and show shifts similar to those observed for Si 2p and Al 2p. The lower-VB spectra for microcline and orthoclase are similar intermediate between α-SiO2 and α-Al2O3 in terms of binding energies. In the plagioclase series increasing coupled substitution of Na and Si for Ca and Al results in a change of the overall shape of the spectra, showing a distinct broadening associated with the presence of two separate but overlapping bands similar to the 21 eV band observed for quartz and the 23 eV band observed for corundum. The bonding character for microcline and orthoclase is more covalent than that of α-Al2O3, but less than that of α-SiO2. In contrast, the plagioclase samples show two distinct bonding characters that are comparable with those of α-SiO2 and α-Al2O3.

Topics: Aluminum Compounds; Aluminum Oxide; Calcium; Carbon; Cations; Minerals; Models, Chemical; Molecular Conformation; Oxygen; Potassium; Potassium Compounds; Silicates; Silicon; Silicon Dioxide; Sodium; Spectrum Analysis; X-Ray Diffraction

To identify the strength limiting flaws in in vitro test specimens of a fine-grained feldspathic dental porcelain.. Four-point flexural strengths were measured for 26 test specimens. The fracture origin site of every test specimen was studied using stereoptical and scanning electron microscopy. A fractographically labeled Weibull strength distribution graph was prepared.. The complex microstructure of the feldspathic dental porcelain included a variety of feldspars, tridymite, and a feldspathoid as well as pores/bubbles and residual glass. The relatively high flexural strength is due in part to the fine grain size. Fractography revealed five flaw types that controlled strength: baseline microstructural flaws, pores/bubbles, side wall grinding damage, corner machining damage, and inclusions. The baseline microstructural flaws probably were clusters of particular crystalline phases.. Each flaw type probably has a different severity and size distribution, and hence has a different strength distribution. The Weibull strength distribution graph blended the strength distributions of the five flaw types and the apparent good fit of the combined data to a unimodal strength distribution was misleading. Polishing failed to eliminate deeper transverse grinding cracks and corner damage from earlier preparation steps in many of the test pieces. Bend bars should be prepared carefully with longitudinal surface grinding whenever possible and edge chamfers should be carefully applied. If the grinding and preparation flaws were eliminated, the Weibull modulus for this feldspathic porcelain would be greater than 30. Pores/bubbles sometimes controlled strength, but only if they touched each other or an exposed surface. Isolated interior bubble/pores were harmless.

Topics: Aluminum; Aluminum Compounds; Aluminum Silicates; Crystallization; Dental Polishing; Dental Porcelain; Dental Stress Analysis; Glass; Humans; Materials Testing; Microscopy, Electron, Scanning; Particle Size; Pliability; Porosity; Potassium; Potassium Compounds; Silicates; Silicon; Silicon Dioxide; Sodium; Sodium Compounds; Spectrometry, X-Ray Emission; Stress, Mechanical; Surface Properties; X-Ray Diffraction

Topics: Air Pollutants; Air Pollutants, Occupational; Aluminum Compounds; Aluminum Oxide; Aluminum Silicates; Dust; Kaolin; Potassium Compounds; Quartz; Silicates; Silicon; Spain; Spectrophotometry, Infrared