TABLE 1.
Physico-chemical characteristics of the crystalline silica polymorphs.
| Sample | SSA (m2/g) | Sample compositionc (oxide wt% ± SD) | Particle size (µm) ± SD in medium (.01 M PBS) | ς-Potentialf (mV, pH 7.4) | •OH radical generationg | |||
|---|---|---|---|---|---|---|---|---|
| CE average diam.d | D90d | D50d | Z-average (PdI)e | |||||
| Quartz | 5.0a | SiO2: 98.8 ± 0.7 | 1.9 ± 0.9 | 3.1 ± 0.2 | 1.6 ± 0.1 | — | −27 ± 2.0 | absent |
| Al2O3: 1.2 ± 0.7 | ||||||||
| Cristobalite | 2.3a | SiO2: 99.9 ± 0.2 | 1.4 ± 1.3 | 2.0 ± 0.1 | 1.1 ± 0.1 | — | −26 ± 1.4 | absent |
| Al2O3: .1 ± 0.2 | ||||||||
| Tridymite | 5.2b, h | SiO2: 100 ± 0.2 | 1.3 ± 0.6 | 1.8 ± .03 | 1.1 ± .02 | — | −24 ± 1.1 | absent |
| Coesite | 18b | SiO2: 100 ± 0.3 | — | — | — | .70 ± .12 (.23) | −22 ± 1.4 | absent |
| Stishovite | 20b | SiO2: 93.4 ± .7i | 3.0 ± 2.6 | 6.5 ± 0.2 | 2.0 ± 0.1 | .66 ± .22 (.59) | −19 ± 1.2 | absent |
| Al2O3: 4.1 ± 0.6 | ||||||||
| TiO2: 2.5 ± 0.6 | ||||||||
a, b Evaluated by BET method, Kra or N2 b adsorption.
cEvaluated by SEM-EDS analysis.
dAssessed by Flow Particle Image Analysis (FPIA), CE diameter, the diameter of the circle having the same projected area as the particle; D50 and D90, the values at which the cumulative frequency reaches 50 or 90%.
eMeasured by Dynamic Light Scattering (DLS), the polydispersity index (PdI) is reported in brackets.
fMeasured by Electrophoretic Light Scattering (ELS) in .01M PBS (pH 7.4).
gMeasured by Electron Paramagnetic Resonance (EPR) coupled with spin trapping probe (i.e., DMPO).
hFrom (Daniel et al., 1993).
iChlorine contamination due to the mineral extraction procedure (Fahey, 1964; Bohn and Stöber, 1966) was detected (1.41 ± 2.29 wt. %).