Phosphate glass is a class of optical
glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...
es composed of
metaphosphate
A metaphosphate ion is an oxyanion that has the empirical formula . It was first postulated in 1955 but was not observed until 1979, when it was detected by mass spectrometry. Metaphosphate is an intermediate in the hydrolysis of phosphate esters b ...
s of various metals. Instead of
SiO2 in
silicate glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...
es, the glass forming substrate is
P2O5.
Discovery
Dr. Alexis G. Pincus of the American Optical Company supplied aluminium phosphate glass samples for Manhattan Project-era Oak Ridge researchers, and was anecdotally called the inventor in 1945 in a Columbia University researcher's note by Aristid V. Grosse.
Physical properties
P
2O
5 crystallizes in at least four forms. The most familiar
polymorph (see figure) comprises molecules of P
4O
10. 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 P
6O
6 rings, not unlike the structure adopted by certain poly
silicates.
Phosphate glasses are highly resistant to
hydrofluoric acid. With an addition of
iron oxide, they act as efficient heat absorbers.
Iron phosphate and lead iron phosphate glass are alternatives to
borosilicate glass
Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficients of thermal expansion (≈3 × 10−6 K−1 at 20 °C), m ...
for immobilization of
radioactive waste
Radioactive waste is a type of hazardous waste that contains radioactive material. Radioactive waste is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, rare-earth mining, and nuclear weapons r ...
.
Unique properties
Phosphate glasses can be advantageous over silica glasses for
optical fiber
An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass ( silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a mea ...
s with high concentration of doping rare earth ions.
A mix of
fluoride glass
Fluoride glass is a class of non-oxide optical glasses composed of fluorides of various metals. They can contain heavy metals such as zirconium, or be combined with lighter elements like aluminum and beryllium. These heavier elements cause the g ...
and phosphate glass is
fluorophosphate glass.
Silver
Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
-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.
Some phosphate glasses are bio-compatible and water-soluble and are suited for use as degradable tissue and bone scaffolds within the human body.
References
{{Glass forming
Glass compositions
Phosphates