Phosphate glass

Phosphate glass is a class of optical glasses composed of metaphosphates of various metals. Instead of SiO2 in silicate glasses, the glass forming substrate is P2O5.

Physical properties

P2O5 crystallizes in at least four forms. The most familiar polymorph (see figure) comprises molecules of P4O10. The other polymorphs are polymeric, but in each case the phosphorus atoms are bound by a tetrahedron of oxygen atoms, one of which forms a terminal P=O bond. The O-form adopts a layered structure consisting of interconnected P6O6 rings, not unlike the structure adopted by certain polysilicates.[1]

The P4O10 cagelike structure which provides the basic building block for phosphate glass formers.

Phosphate glasses are highly resistant to hydrofluoric acid. Within addition of iron oxide, they act as efficient heat absorbers.

Iron phosphate and lead iron phosphate glass are alternatives to borosilicate glass for immobilization of radioactive waste.[2]

Unique properties

Phosphate glasses can be advantageous over silica glasses for optical fibers with high concentration of doping rare earth ions.[3][4]

A mix of fluoride glass and phosphate glass is fluorophosphate glass.

Silver-containing phosphate glass is used in phosphate glass dosimeters. It emits fluorescent light when irradiated by ultraviolet light, when previously exposed to ionizing radiation, in an amount proportional to the dose.[5]

Some phosphate glasses are bio-compatible and water-soluble and are suited for use as degradable tissue and bone scaffolds within the human body.[6]

References

  1. ↑ Karabulut M, Melnik E, Stefan R, Marasinghe GK, Ray CS, Kurkjian CR, Day DE (2001). "Mechanical and structural properties of phosphate glasses". Journal of Non-Crystalline Solids 288 (1–3): 8–17. doi:10.1016/S0022-3093(01)00615-9.
  2. ↑ "Iron Phosphate Glass as an Alternative Waste-Form for Hanford LAW". Pacific Northwest National Laboratory. February 2003. Retrieved 22 March 2010.
  3. ↑ Dr. Rüdiger Paschotta. "Silica Fibers". Encyclopedia of Laser Physics and Technology. RP Photonics Consulting GmbH. Retrieved 22 March 2010.
  4. ↑ Karabulut M, Melnik E, Stefan R, Marasinghe GK, Ray CS, Kurkjian CR, Day DE (2001). "Mechanical and structural properties of phosphate glasses". Journal of Non-Crystalline Solids 288 (1–3): 8–17. doi:10.1016/S0022-3093(01)00615-9.
  5. ↑ "Phosphate glass dosimeter". European Nuclear Society. Retrieved 22 March 2010.
  6. ↑ Bitar M, C Knowles J, Lewis MP, Salih V (December 2005). "Soluble phosphate glass fibres for repair of bone-ligament interface". Journal of Materials Science: Materials in Medicine 16 (12): 1131–6. doi:10.1007/s10856-005-4718-3. PMID 16362212.