Exchange of Co2+ and Ni2+ for Ca2+ in xonotlite and tobermorite was investigated at 25°C. We show here for the first time that all the Ca2+ in xonotlite and tobermorite can be stoichiometrically exchanged with Co2+ or Ni2+. For example, 92.8 and 92.6% of the total Ca2+ present in zonotlite and tobermorite respectively, were exchanged by Co2+. This type of almost complete exchange of Ca2+ by Co2+ or Ni2+ did not result in the destruction of the crystal morphology of xonotlite and tobermorite which suggested a pseudomorphism. Studies of the kinetics of Co2+ exchange by xonotlite and tobermorite showed that the exchange is slow and total exchange of Ca2+ by Co2+ takes place in about 4-5 days. The Co2+ or Ni2+ exchange for Ca2+ is slow because of the necessity to break Ca-O bonds from the xonotlite and tobermorite structures. Partial Ca2+ exchange with Co2+ did not lead to a loss of all crystallinity while total exchange led to amorphization as detected by XRD.
All Science Journal Classification (ASJC) codes
- Building and Construction
- Materials Science(all)