Figure 5: Chemical parameterization of volcanic ash fusion and rheology.
From: Volcanic ash melting under conditions relevant to ash turbine interactions
(a) Net difference between the characteristic temperatures of three natural volcanic ash and that of three remelted ash from the same samples (Tnatural−remelted). (b) Chemical dependence of the characteristic temperatures using the ratio of acidic to basic major oxides (Rb/a). The data show good linearity and the best fits yield the following regressions: DT=1,282–263 Rb/a (r=−0.73; n=9); HT=1,418–517 Rb/a (r=−0.93; n=9); and FT=1,556+762 Rb/a (r=−0.80; n=9). (c) Chemical dependence of the estimated viscosity of molten volcanic ash (η), as a function of Rb/a. The data agree equally well with the geochemical composition of the ash and the best fits yield: for DT, log η=5.11–6.29 Rb/a (r=−0.81; n=9); for HT, log η=4.24–4.89 Rb/a (r=−0.81; n=9); and for FT, log η=3.58–4.59 Rb/a (r=−0.80; n=9) (d–f) Chemical composition dependence of sample geometry evolution. The data show that the average (d) shrinkage rate, (e) fusion rate and (f) wetting rate are linearly proportional to Rb/a (red line, linear fit through the data; r, correlation coefficient to indicate the accuracy of a regression). The values plotted represent the average of two independent experiments, and the s.d. of each sample is plotted.
