Migration Mechanisms of Al3+/Li+ Lattice Impurities during Phase Transition from α-Quartz to β-Quartz: An Implication for Purification of High-Purity Quartz

Abstract

The quality of high-purity quartz (HPQ) that used in strategic industries is normally limited due to lattice impurities. In order to reveal the migration pathway of lattice impurities in quartz particles during phase transition from α-quartz to β-quartz, α-quartz and Al3+/Li+-substituted α-quartz (S-α-quartz) was investigated under 846.15 K and 101.325 kPa based on density functional theory. Results showed that β-quartz exhibited more interstitial volume, dominating the migration of lattice impurities. This further indicates that the phase transition process was beneficial for the migration of lattice impurity from a structural point of view. Moreover, Al3+ and Li+ mainly migrated from the intracell to lattice surface along the c axis. In addition, Li+ migrated more easily than Al3+ due to higher mean square displacement values. From a thermodynamic point of view, the lower energy barrier in the case of the Al3+ and Li+ lattice suggested that the presence of lattice impurities promoted phase transition. This study therefore provides an excellent theoretical basis for the removal of lattice impurities of HPQ from an atomic perspective, for the first time.

New insight into the plastic deformation mechanisms during the SiO2 phase transition process

“…, four Si–O bonds), and each O atom was boned with two surrounding Si atoms to connect silica tetrahedron. 16,29,30 However, the specific Si–O bond length and Si–O–Si angle were different for these typical SiO 2 phases, i.e. , the Si–O bond length were 1.619/1.625 Å, 1.614 Å, 1.608 Å and 1.615/1.619 Å in α-quartz, β-quartz, β-cristobalite and α-cristobalite, while the Si–O–Si angle were 153.19 ° , 144.47 ° , 180.00 ° and 153.27 ° , respectively ( Table 1 ), resulting in different crystal systems for these typical SiO 2 phases, i.e.…”

“…Similar to our previous research, 16 the generalized gradient approximation (GGA) with PW91 correlation potential was considered to perform the DFT calculation through Materials Studio in CASTEP package. 25 A kinetic energy cutoff of 360 eV was chosen for the geometric optimization calculation, and the Monkhorst–Pack scheme k -point meshes were 3 × 3 × 4, 2 × 2 × 3, 1 × 2 × 2 and 1 × 1 × 2 for α-quartz, β-quartz, β-cristobalite and α-cristobalite.…”

“…The interstitial volume was calculated through the methods in our previous research. 16 And the lattice stress was calculated via eqn (1) : 26,27 S L = − B × (Δ V / V ) where S L , B and V were the lattice stress, bulk modulus and bulk volume of SiO 2 phases, Δ V was the bulk volume changes between SiO 2 phases. The formation energy was calculated via eqn (2) : 28 E f = E tol − aE Si − bE O − cE Ti − dE Al − eE Li − fE H where E f was the formation energy, E tol was the total energy of SiO 2 phase, a , b , c , d , e and f were the numbers of Si, O, Ti, Al, Li and H atoms in SiO 2 phase, respectively.…”

“… 10,14–16 Within which, the leaching process can only remove the surface impurities, 10 while the lattice impurities can migrate from the intracell to surface during high-temperature roasting process. For instance, Wei et al 16 investigated the migration mechanisms during phase transition from α-quartz to β-quartz, suggesting that the lattice impurity of Al 3+ and Li + migrated from intracell to quartz sand surface via the c axis. Wu et al 17 indicated that the lattice impurities of Al 3+ , Fe 3+ , K + and Ti 4+ migrated from intracell to surface during the NH 4 Cl roasting process.…”

“… 19–23 However, the plastic deformation mechanisms during these phase transitions were still unclear, which significantly affected the properties of SiO 2 lattice and the removement of lattice impurities. For instance, Wei et al 16 indicated that the interstitial volume was increased during the phase transition from α-quartz to β-quartz, beneficial to the migration of lattice interstitial impurities, such as Li + . Blankenburg et al 24 found that the defects or twinning formed during the phase transition from α-quartz to β-quartz influenced the distribution of lattice impurities.…”