Characteristics of the Weathered Surfaces of Phosphate Glasses Brad Tischendorf* & Richard Brow University of Missouri-Rolla USA XX International Congress on Glass Oct. 1, 2004 Kyoto, Japan

Oct. 1, 2004XX ICG : Kyoto, Japan2 Phosphate glasses are prone to weathering degradation Scattered light due to weathering Example of a badly weathered glass surface

Oct. 1, 2004XX ICG : Kyoto, Japan3 Surface corrosion is due to precipitation of hydrated orthophosphate crystals

Oct. 1, 2004XX ICG : Kyoto, Japan4 Weathering depends on the interactions between water and the glass surface Diffusion of water and hydration of chains and modifiers Glass Dissolution with chain and cation removal into solution Weathering reactions with surface hydrolysis and crystallization Aqueous Humid

Oct. 1, 2004XX ICG : Kyoto, Japan5 Glass compositions These glass compositions have been chosen to act as models for commercial phosphate glass amplifiers such as those used at the National Ignition Facility K2OK2OMgOBaOCaOAl 2 O 3 P2O5P2O5 O/P Ratio (KCAP) (KBAP) (KMAP) LG LHG

Oct. 1, 2004XX ICG : Kyoto, Japan6 Techniques used to measure the different reaction mechanisms Diffusion and Hydration –Weight gain of samples during weathering –Elastic Recoil Detection (ERD) for H depth profiles Surface Hydrolysis –MAS NMR –High Pressure Liquid Chromatography (HPLC) Surface Crystallization –Thin Film X-ray Diffraction (TF-XRD)

Oct. 1, 2004XX ICG : Kyoto, Japan7 This slide won’t be included, it’s to add commentary for you The first step was to measure how much water is getting into the glass surfaces. Initially we simply measured the gain in weight as a function of weathering time. This was then followed by measurement on H depth profiles with ERD The two results seem to qualitatively agree with the systems we have looked at.

Oct. 1, 2004XX ICG : Kyoto, Japan8 Following the weight gain at 50ºC/80%RH shows MgO containing glasses reacting faster

Oct. 1, 2004XX ICG : Kyoto, Japan9 The same effect is observed at 40ºC/80% RH

Oct. 1, 2004XX ICG : Kyoto, Japan10 At 25ºC/80%RH there is no measurable weight gain until after 14 days

Oct. 1, 2004XX ICG : Kyoto, Japan11 ERD shows equal amounts of water present on the KMAP and KBAP surfaces after 7 days

Oct. 1, 2004XX ICG : Kyoto, Japan12 This data agrees with the weight gain data: after 7 days, KMAP and KBAP are near the same

Oct. 1, 2004XX ICG : Kyoto, Japan13 NMR indicates compositional differences in the rates of reactivity of the glasses 7 days 50 o C 80%RH

Oct. 1, 2004XX ICG : Kyoto, Japan14 This slide won’t be included, it’s to add commentary for you Now that we know how much water was getting in we wanted to measure the structural changes occurring due to this water. WE began with NMR which shows a rate of reactivity where KAP>KMAP>KBAP. Downside is that NMR probes entire sample and must be a powdered sample,not necessarily representative of a real system. So we looked into HPLC where we could take a polished piece of glass and dissolve the surface away to measure its structure.

Oct. 1, 2004XX ICG : Kyoto, Japan15 HPLC provides a method to probe the structure of phosphate glass surfaces A solution containing the phosphate glass is loaded into the injection valve. Once injected, the gradient pump ramps the solution from 0.05 to 0.5M NaCl. After separation, the phosphate species are reacted at 170ºC in 1.8M H 2 SO 4 with ammonium molybdate The resultant “blue” species concentration is measured with the UV-VIS

Oct. 1, 2004XX ICG : Kyoto, Japan16 HPLC experimental procedure Glass plates were polished to 1  m finish Plates were measured and weighed then placed into a controlled humidity temperature environment Samples periodically removed and weighed for weight gain, then surface removed in a solution of EDTA Weight loss was measured Solution was run through HPLC system Prior to and after runs, all solutions were refrigerated for storage Nomenclature: –P 1 = PO 4 –P 3m = P 3 O 9 ring species

Oct. 1, 2004XX ICG : Kyoto, Japan17 Standard solutions of known phosphate species are used to calibrate species and concentrations P 1 – 26% P 2 – 26% P 3 – 25% P 3m – 23%

Oct. 1, 2004XX ICG : Kyoto, Japan18 Runs of stored samples show they are stable for at least 3 weeks when refrigerated This plot shows LHG-8 weathered for 4 days at 25ºC and 80%RH immediately after surface removal, and after sitting for three weeks

Oct. 1, 2004XX ICG : Kyoto, Japan19 HPLC shows that KAP reacts rapidly at 50ºC and 80%RH P 1 – 62% P 2 – 32% P 3 – 4%

Oct. 1, 2004XX ICG : Kyoto, Japan20 Increased production of PO4 and P2O7 is seen in the MgO containing glass at 50ºC/80%RH

Oct. 1, 2004XX ICG : Kyoto, Japan21 As is seen in the weight gain data, this trend continues at lower temperatures of 40 and 25ºC

Oct. 1, 2004XX ICG : Kyoto, Japan22 The ratio’s of P 1 +P 2 show the same dependence with MgO glasses more reactive

Oct. 1, 2004XX ICG : Kyoto, Japan23 Weathered surface removal from LG-770 trends with either absolute or relative humidity Not sure, may dump this section

Oct. 1, 2004XX ICG : Kyoto, Japan24 Activation Energies for water diffusion and chain hydration/hydrolysis Rough calculations from both ERD profiles and weight gain data show that KMAP exhibits a diffusion activation energy of ~1 kJ/mole –Problem is that these were two point fits Calculations of the activation energy of chain hydration/hydrolysis gives numbers near 100 kJ/mole whether weight loss is measured directly by surface removal or by the results of HPLC concentration conversions

Oct. 1, 2004XX ICG : Kyoto, Japan25 Ongoing work Adding additional humidity's to the study Compare the rates of reactivity of poly and pyro- phosphate glasses to the meta-phosphate species already studied What is the effect of surface preparation on the weathering rate?

Oct. 1, 2004XX ICG : Kyoto, Japan26 The type of sample studied may affect the results of the chromatography experiment

Oct. 1, 2004XX ICG : Kyoto, Japan27 Conclusions The rates of penetration of water into glass surfaces has been measured The effect of this water on the structure of the glass surface was studied The dependence of these reactions on glass composition was studied.

Oct. 1, 2004XX ICG : Kyoto, Japan28 Acknowledgements This work is funded by Lawrence Livermore National Laboratory. Work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. Special Thanks to: Joe Hayden of Schott Glass Technologies for Glass Cullet used to produce weathering samples Barney Doyle of Sandia National Laboratories for running the ERD spectra used in this study Todd Alam and Brian Cherry also of Sandia National Laboratories for their aid in performing the NMR experiments Fred Stover of Asteris for HPLC advice and providing phosphate standards

Oct. 1, 2004XX ICG : Kyoto, Japan29 If anyone asks, will have this on hand to show reproducibility of past work A binary glass 55ZnO*45P 2 O 5 was run to verify the system was working and calibrations were correct