Results for “Al2(SO4)3” | Engineering Papers

DOE OSTI2020

Materials Data on Al2(SO4)3 by Materials Project

Al2(SO4)3 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. there are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six equivalent SO4 tetrahedra. All Al–O bond lengths are 1.89 Å. In the second Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six equivalent SO4 tetrahedra. All Al–O bond lengths are 1.90 Å. S6+ is bonded to four O2- atoms to form SO4 tetrahedra that share corners with four AlO6 octahedra. The corner-sharing octahedra tilt angles range from 26–37°. There is one shorter (1.47 Å) and three longer (1.48 Å) S–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one S6+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one S6+ atom. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one S6+ atom. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one S6+ atom.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Sapphire advanced mitigation process: wet etch to expose sub-surface damage and increase laser damage resistance and mechanical strength

In this study, a novel, to the best of our knowledge, method of wet chemical etching of sapphire workpieces (such as optics, wafers, windows, and cones), called the sapphire advanced mitigation process (or sapphire AMP), has been developed that exposes sub-surface mechanical damage created during the optical fabrication process and significantly enhances the surface laser damage resistance (> 2×) and mechanical strength (up to ~ 2.6×). Sapphire AMP involves first treating the workpiece with a mixture of sulfuric and phosphoric acid ([H 2 SO 4 ]:[H 3 PO 4 ]= 1 : 3) at 220°C, followed with phosphoric acid at 160°C, then with sodium hydroxide base (NaOH) and surfactant at 40°C, and finally with a high-pressure deionized water spray rinse. Sapphire AMP has been demonstrated on both A- and C-plane sapphire workpieces. The mechanism of this etch process involves the reaction of the sapphire (Al 2 O 3 ) surface with sulfuric acid (H 2 SO 4 ) forming aluminum sulfate [Al2(SO4)3], which has low solubility. The high phosphoric acid content in the first and second steps of sapphire AMP results in the efficient conversion of Al 2 (SO 4 ) 3 to aluminum phosphate (AlPO 4 ), which is very soluble, greatly reducing reaction product redeposition on the workpiece surface. Sapphire AMP is shown to expose sub-surface mechanical damage on the sapphire surface created during the grinding and polishing processes, whose etched morphology has either isotropic or anisotropic evolution depending on the nature of the initial surface damage. Sapphire AMP was also designed to remove the key known surface, laser absorbing precursors (namely, foreign chemical impurities, the fracture surface layer of preexisting sub-surface damage, and reaction product or foreign species redeposition or precipitation). Static and sliding indention induced surface microfractures on sapphire are shown after sapphire AMP to have a significant decrease in the fast photoluminescence intensity (a known metric for measuring the degree of laser damaging absorbing precursors). In addition, the onset of laser damage (at 351 nm 3 ns) on sapphire AMP treated workpieces was shown to increase in fluence from ~ 4 to >9.5J/cm 2 . Finally, biaxial ball-on-ring mechanical tests on sapphire disks showed an increase in the failure stress from 340 MPa (with pre-existing 28 µm flaws) to ~ 900MPa after sapphire AMP, which is attributed to the blunting of the surface microfractures.

36 MATERIALS SCIENCE↗