2020-04-05 19:37:09

MPa glass activated Of setting

责任者: NICHOLSON, JW 单位: LAB GOVT CHEMIST,TEDDINGTON TW11 0LY,MIDDX,ENGLAND. 来源出处: JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, v 6, JUL 1995, p 404- 408 摘要: Water-activated versions of zinc polycarboxylate and glass-polyalkenoate dental cements have been used in a study of the effect of electrolytes on setting behaviour and properties. In addition to pure water, 1 M solutions of NaCl, NaF, Na2SO4 and NaNO3 have been used to activate setting. The setting reaction of the zinc polycarboxylate was found to be profoundly affected by the presence of such electrolytes, with the working time generally being shorter, a nd the overall set sharper. The setting reaction of the glass-polyalkenoate was less affected: there was generally no change in the working time, though the set was slightly less sharp. After 24 h at 37 degrees C most of the zinc polycarboxylates had compressive strengths of about 90 MPa, with differences between the different specimens not being statistically significant. The exception was the cement made with aqueous sodium sulphate, which had a compressive strength of 56.8 MPa. By contrast, the strengths of the various glass-polyalkenoates fell into three groups: water- and NaF-activated at 80-85 MPa, Na2SO4- and NaNO3-activated, at 65 MPa, and NaCl-activated, at 53 MPa. These differences were significant at least the 99% confidence level. They are discussed in terms of the effect of the electrolytes on the conformation adopted by the reacting poly(acrylic acid) molecules in solution. It is concluded that the differences in response to the presence of sodium salts between the zinc polycarboxylate and the glass-polyalkenoate confirm the view that these cements set to give substantially different microstructures. 关键词: CHRYSOTILE ASBESTOS; QUANTUM WIRES; ABSORPTION SPECTRA; CONDUCTIVITY; NEUTRALIZED POLY(ACRYLIC ACID); IONOMER CEMENTS