An experimental study of cross polarization from1H to27Al in crystalline and amorphous materials

The conditions for successful¹H?²⁷Al cross polarization experiments have been investigated. It was found that boehmite was a good material for setting up the Hartmann-Hahn match condition, and both tetrahedral and octahedral aluminium was observed in a variety of environments. The contact time dependence of the CP signal was studied for several samples and simulations showed thatT _IS could be estimated and hence information on mean¹H?²⁷Al distances in glasses deduced. CP signals could be obtained even ifT _1? ^Al is much less thanT _IS, contrary to some previous suggestions. MAS reduces both the size of the CP signal and the optimum contact time and to maintain signal strength spinning should be as slow as possible.