Spray‐dried sol‐gel glass‐ceramic powders based on the tunable thermal expansion of quartz and keatite solid solutions

Abstract

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Co2+-Stuffed Quartz Solid Solutions With Zero Thermal Expansion Synthesized by Sol-Gel Spray-Drying

“…However, powders of this composition exhibited only limited tendency towards devitrification and the undesired early formation of CoO-bearing spinel (CoAl2O4). In analogy with previous works [15][16][17], a Li2O excess was therefore added to the sample (atomic ratio Li/Si = 0.025, Li/Co = 0.1) to foster the crystallization of Qss. The composition is recalled in the following as CoQss (Li).…”

“…During the subsequent mixing of the two solutions in the desired ratio, the water of crystallization of the CoO and Al2O3 precursors favoured further hydrolysis of TEOS. Spray-drying was performed using a setup described previously [14,15]: the solution was atomized using pressurized air at 2.5 bar and channelled through a tube furnace set at 400 °C, recovering the nanobeads from a particle filter placed at the other end of the furnace.…”

“…Consequently, spray-drying is explored in this work as an alternative route to obtain zero-thermal-expansion glass-ceramic powders based on Co 2+stuffed Qss. Previous works demonstrated how this technique can be advantageously combined with conventional sol-gel processing to synthesize amorphous nanobeads of disparate compositions with only minor processing adjustments [9][10][11][12][13][14][15]. After annealing, such nanobeads can be converted into glass-ceramic powders with very promising properties, for instance TiO2based photocatalytic activity [14] or tunable thermal expansion [15].…”

“…Previous works demonstrated how this technique can be advantageously combined with conventional sol-gel processing to synthesize amorphous nanobeads of disparate compositions with only minor processing adjustments [9][10][11][12][13][14][15]. After annealing, such nanobeads can be converted into glass-ceramic powders with very promising properties, for instance TiO2based photocatalytic activity [14] or tunable thermal expansion [15]. More generally, the results of this work provide further insight into the links between composition, structure and properties of Co 2+ -stuffed Qss crystals, making way for thermally invariant materials with a lesser dependence from Li2O raw materials.…”

Towards new zero-thermal-expansion materials: Li-free quartz solid solutions stuffed with transition metal cations

“…Between 0 °C and 50 °C, commercially available materials based on Qss such as Zerodur ® can achieve a coefficient of thermal expansion (CTE) as low as (0 ± 0.007) x 10 -6 K -1 , with spatial variations that are less than 0.005 x 10 -6 K -1 over the whole volume of a telescope mirror blank with a diameter of 4 meters [13,14]. Indeed, the thermal expansion of Qss can be finely tuned, taking advantage of their variable Al/Si ratio and of the full solid solution [8,9,15,16] existing between: (i) Mgbearing Qss, exhibiting trigonal symmetry and positive thermal expansion [17][18][19][20][21]; (ii) Li-and Znbearing Qss, which were reported to be fully hexagonal (at a sufficiently high level of chemical stuffing) and to contract upon heating [8,12,[22][23][24][25][26][27].…”