feldspar and sodium-oxide

Low- and non-leucite-containing commercial porcelains with low firing temperatures have become popular. However, improving the strength of glass porcelains is difficult. The purpose of this study was to determine if dispersed glass particles could be used as a reinforcing agent for an all-glass porcelain. We produced 3 feldspathic glasses (high-fusing, medium-fusing, low-fusing) by melting powders consisting of potassium-feldspar and 0, 5, or 20 mass% Na2O, respectively. For high-fusing, medium-fusing, and low-fusing feldspathic glasses, the deformation temperatures were 945 degrees C, 647 degrees C, and 518 degrees C, and the thermal expansion coefficient values were 8.6 x 10(-6)/degrees C, 10.3 x 10(-6)/degrees C, and 13.4 x 10(-6)/degrees C between 25 degrees C and the glass-transition temperature, respectively. The high-fusing-glass (or medium-fusing-glass) powders were mixed with low-fusing-glass powders before being fired into test specimens. The mean flexural strength and fracture toughness (K1C) of 3 single-glass porcelains ranged from 57 to 63 MPa and from 0.68 to 0.73 MPa m(1/2), respectively, presenting no significant differences in one-way ANOVA. However, the flexural strength of 50% high-fusing-glass + 50% low-fusing-glass porcelain was 114 MPa (p < 0.05) and K1C was 1.2 MPa m(1/2) (p < 0.05). Microcracks were observed with a back-scattered scanning electron microscope and were associated with the high- (or medium-) fusing glass particles, suggesting residual stress in the low-fusing-glass matrix due to a coefficient of thermal expansion mismatch between the dispersed glass particles and the matrix glass. The dispersing glass particles appeared to act as a reinforcing agent for strengthening a glassy porcelain.

Topics: Aluminum Silicates; Analysis of Variance; Dental Porcelain; Glass; Hot Temperature; Humans; Materials Testing; Microscopy, Electron, Scanning; Oxides; Pliability; Potassium; Potassium Compounds; Powders; Sodium Compounds; Stress, Mechanical; Surface Properties; Thermodynamics

The desirable thermal properties of matrix glass to the strength of feldspar porcelain with leucite crystal were investigated. Five kinds of feldspar glasses, each with different a content of Na2O, were prepared for the matrix glasses of the leucite-containing porcelains. The specimens were arranged by mixing each glass powder with high-purity natural leucite crystals (0, 20 and 40%) followed by firing. The thermal properties of the glass and the transformation temperature of the leucite were measured. A three-point bending test was performed to measure the flexural strength of the porcelains. The glass transition temperature and deformation temperature of the glass-only porcelains were decreased as the Na2O content increased. The Na2O-modified glasses were substantially strengthened by the leucite dispersion. However, the strength of the porcelains was affected by the relation between the transformation temperature of the leucite and the thermal properties of the glass matrix. It was concluded that control of the residual stress in the composite porcelain is an important factor in developing high strength porcelain containing leucite.

Topics: Aluminum Silicates; Dental Porcelain; Differential Thermal Analysis; Glass; Microscopy, Electron, Scanning; Oxides; Potassium Compounds; Sodium Compounds; Surface Properties; Temperature; Tensile Strength; X-Ray Diffraction