Effect of halide mineralizers on monodisperse spherical zircon powders

Abstract

Zircon has been widely applied in various traditional and emerging fields due to its distinct physiochemical advantages while monodisperse spherical zircon (MSZ) powders hitherto have not been explored for the tremendous challenges in the control of zircon crystallization and growth. Herein, systematic investigations are presented to reveal the paramount role of halide mineralizers upon the crystallization and growth of MSZ powders synthesized under highly acidic hydrothermal environments (pH <0). A formation mechanism is revealed revolving around the complexation of central Zr4+ with the Lewis basic ligand, fluorine, which forms the F‐containing species of [(OH)1–y·Ry] (R = F, Cl) to replace Zr and generates Zr‐deficient zircons as (ZrO4)1‐xSi[(OH)1‐y·Ry]4x. This finding differs much from conventional views on common fluoro‐hydroxylated hydrothermal zircons, which were generally regarded as Si‐deficient silicates from the substitution of fluoro‐hydroxyls for the [SiO4] tetrahedra. A parameter, Kr=4xy, is first proposed as an index to evaluate the stability of hydrothermal zircons. The MSZ powders demonstrate superb thermal stability at high temperature, superior photo‐reflectance, and thermal insulation over normal zircons, promising attractive prospects to extend zircon applications.

New insight into the coloration mechanism and synthesis of ultrafine Pr‐ZrSiO4 yellow pigments

“…A high-content growth inhibitor NH 4 F (the F/Zr molar ratio 2.0) and the advantageous acidic precursors have jointly promoted these advantages. Fluorine in the acidic precursors can complex with Zr 4+ more strongly than in neutral or basic solutions and even can generate the F/Zr ratios as high as 0.5−3 in final zircons (conversely, F/Zr = 0.3−0.8 in zircons synthesized at pH = 9.0); fluorine can be easily involved into the ZrSiO 4 network via the Zr species as Zr 4+ +OH − +F -→ Zr[(OH) 1-x ⋅F x ] n (4-n)+ in acidic solutions and even cannot be completely removed from the pigments after calcination at 900-1100 • C. 20,21 The fluoro-hydroxylated Zr complexes then react with the Si-OH species and the residual Zr-F terminals suppress the excessive extension of the Zr-O-Si bridging network in ZrSiO 4 , hence reducing the size of final pigments. The Finduced growth also contributes to the Zr deficiency in the pigments (Si/Zr = 1.2−1.3, Figure S4), akin to that in the hydrothermal zircon products.…”

“…The Finduced growth also contributes to the Zr deficiency in the pigments (Si/Zr = 1.2−1.3, Figure S4), akin to that in the hydrothermal zircon products. 20 In contrast, the zircons or pigments, synthesized without NH 4 F or from basic precursors (pH = ∼8.0), can only be endowed with such desirable traits (Figure S3).…”

“…It is to date still a challenge to fulfill these requirements via a facile solid-state reaction synthesis, since the robust ZrSiO 4 matrix gets crystallized only at high temperatures, typically over 1000 • C, which usually induces severely aggregated large particles with average sizes up to 3−20 μm and a wide size distribution. 2,11,[16][17][18][19] In contrast, a low-temperature hydrothermolysis can indeed realize uniform or even monodisperse zircon powders at only 150−370 • C, 20,21 but these liquid-based preferentiallygrown zircons have little encapsulation capability to any heterogenic cations or particulate chromophores (like CdS 1-x Se x and Fe 2 O 3 ); therefore, hydrothermolysis was typically applied for the precursor treatment and often followed by a high-temperature calcination. 22 Alternatively, a top-down route is generally applied to pulverize the conventional micron-sized pigments into submicron powders, 17 which consumes much energy and, however, produces the pigments with suboptimal crushed particles.…”

Formation of zircon‐type (Zr,Ti)1−x(Dy)x(SiO4)1−x(PO4)x solid solution and their optical and magnetic characteristics

“…13 Generally, ZrSiO 4 has been investigated as a potential ceramic pigment that is applied in industries for glazes, mainly due to their excellent chemical resistance displayed during dissolution phenomena. 14 Praseodymiumsubstituted ZrSiO 4 , a yellow pigment, is the most investigated material, and titanium (Ti 4+ )-, iron (Fe 3+ )-, and manganese (Mn 2+ )-substituted ZrSiO 4 have also been reported. [15][16][17][18] ZrSiO 4 formation is usually reached through a solid-state synthesis route that mainly depends on the self-stabilization mechanism by hosting impurities in its structural lattice.…”

“…Generally, ZrSiO 4 has been investigated as a potential ceramic pigment that is applied in industries for glazes, mainly due to their excellent chemical resistance displayed during dissolution phenomena 14 . Praseodymium‐substituted ZrSiO 4 , a yellow pigment, is the most investigated material, and titanium (Ti 4+ )‐, iron (Fe 3+ )‐, and manganese (Mn 2+ )‐substituted ZrSiO 4 have also been reported 15–18 .…”