Phosphate glass is a class of optical

glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...

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 ...

s of various metals. Instead of SiO₂ in silicate glasses, 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

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 poly

silicate A silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is also used ...

s. Phosphate glasses are highly resistant to

hydrofluoric acid Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. Solutions of HF are colorless, acidic and highly corrosive. A common concentration is 49% (48–52%) but there are also stronger solutions (e.g. 70%) and pure HF has a boiling p ...

. With an addition of

iron oxide An iron oxide is a chemical compound composed of iron and oxygen. Several iron oxides are recognized. Often they are non-stoichiometric. Ferric oxyhydroxides are a related class of compounds, perhaps the best known of which is rust. Iron ...

, 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), ma ...

for immobilization of

radioactive waste Radioactive waste is a type of hazardous waste that contains radioactive material. It is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, nuclear decommissioning, rare-earth mining, and nuclear ...

Unique properties

Phosphate glasses can be advantageous over silica glasses for

optical fiber An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at ...

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 aluminium and beryllium. These heavier elements cause the g ...

and phosphate glass is fluorophosphate glass.

Silver Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...

-containing phosphate glass is used in phosphate glass dosimeters. It emits fluorescent light when irradiated by ultraviolet light, when previously exposed to

ionizing radiation Ionizing (ionising) radiation, including Radioactive decay, nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionization, ionize atoms or molecules by detaching ...

, 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