Effect of boron, phosphorus and fluorine on shear stress relaxation in haplogranite melts

The strain rate-T dependence of shear viscosity and modulus of haplogranite melts differs from that of single relaxation time viscoelastic behaviour. The viscoelastic behaviour of haplogranite melt follows stretched exponent relaxation with beta = 0.5 with an Arrhenian T dependence of the shear viscosity indicating 'strong' liquid behaviour. The addition of B (sub 2) O (sub 3) , P (sub 2) O (sub 5) or F (sub 2) O (sub -1) into the haplogranite melt results in increased stretched exponential relaxation with beta < 0.5 and in broadening of the stress relaxation spectrum over 6-7 decades of log (sub 10) time units in comparison to the approx 5 log (sub 10) time units width observed for haplogranite melt. The addition of these components weakens the structure of the melts, making their structure more compressible and less rigid.