Phosphate glass is a class of optical glass

Glass

Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

es composed of metaphosphate

Metaphosphate

A metaphosphate ion is an oxyanion that has the empirical formula PO3−. The structure of a metaphosphate ion can be described as being made up of PO4 structural units in which each unit shares two corners with another unit...

s of various metals. Instead of SiO₂

Silicon dioxide

The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...

 in silicate glasses, the glass forming substrate is P₂O₅

Phosphorus pentoxide

Phosphorus pentoxide is a chemical compound with molecular formula P4O10 . This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desiccant.-Structure:...

.

P₂O₅ crystallizes in at least four forms. The most familiar polymorph

Polymorphism (materials science)

Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...

 (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 polysilicate

Silicate

A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...

s.
Phosphate glasses are highly resistant to hydrofluoric acid

Hydrofluoric acid

Hydrofluoric acid is a solution of hydrogen fluoride in water. It is a valued source of fluorine and is the precursor to numerous pharmaceuticals such as fluoxetine and diverse materials such as PTFE ....

. With addition of iron oxide

Iron oxide

Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...

, they act as efficient heat absorbers.

Iron phosphate and lead iron phosphate glass are alternatives to borosilicate glass

Borosilicate glass

Borosilicate glass is a type of glass with the main glass-forming constituents silica and boron oxide. Borosilicate glasses are known for having very low coefficients of thermal expansion , making them resistant to thermal shock, more so than any other common glass...

 for immobilization of radioactive waste

Radioactive waste

Radioactive wastes are wastes that contain radioactive material. Radioactive wastes are usually by-products of nuclear power generation and other applications of nuclear fission or nuclear technology, such as research and medicine...

.

Phosphate glasses can be advantageous over silica glasses for optical fiber

Optical fiber

An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...

s with high concentration of doping rare earth ions.

A mix of fluoride glass

Fluoride glass

Fluoride glass is a class of non-oxide optical glasses composed of fluorides of various metals. Due to their low viscosity, it is very difficult to completely avoid the occurrence of any crystallization while processing it through the glass transition...

 and phosphate glass is fluorophosphate glass

Fluorophosphate glass

Fluorophosphate glass is a class of optical glasses composed of metaphosphates and fluorides of various metals. It is a variant of phosphate glasses.Some fluorophosphate glasses are used as low dispersion glasses. Some show anomalous partial dispersion...

.

Silver

Silver

Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity 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 radiation

Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...

, 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.