pable of *luminescence (including
phosphorescence). Phosphors that release their energy after a short delay
of between 10
–10 and 10
–4 second are
sometimes called scintillators.
phosphor bronze An alloy of copper containing 4% to 10% of tin and
0.05% to 1% of phosphorus as a deoxidizing agent. It is used particularly
for marine purposes and where it is
exposed to heavy wear, as in gear
wheels. See also bronze.
phosphorescence See luminescence.
phosphoric(V) acid (orthophosphoric acid) A white rhombic solid,
H 3 PO 4 ; r.d. 1.834; m.p. 42.35°C; loses
water at 213°C; very soluble in water
and soluble in ethanol. Phosphoric(V)
acid is very deliquescent and is generally supplied as a concentrated
aqueous solution. It is the most commercially important derivative of
phosphorus, accounting for over 90%
of the phosphate rock mined. It is
manufactured by two methods; the
wet process, in which the product
contains some of the impurities originally present in the rock and applications are largely in the fertilizer
industry, and the thermal process,
which produces a much purer product suitable for the foodstuffs and detergent industries. In the wet process
the phosphate rock, Ca 3 (PO 4 ) 2 , is
treated with sulphuric acid and the
calcium sulphate removed either as
gypsum or the hemihydrate. In the
thermal process, molten phosphorus
is sprayed and burned in a mixture
of air and steam. Phosphoric(V) acid
is a weak tribasic acid, which is best
visualized as (HO) 3 PO. Its full systematic name is tetraoxo-phosphoric(V)
acid. It gives rise to three series of
salts containing phosphate(V) ions
based on the anions [(HO) 2 PO 2 ]
– ,
[(HO)PO 3 ]
2– , and PO 4
3– . These salts are
acidic, neutral, and alkaline in character respectively and phosphate ions
often feature in buffer systems.
There is also a wide range of higher
acids and acid anions in which there
is some P–O–P chain formation. The
simplest of these is pyrophosphoric
acid (technically heptaoxodiphosphoric(V) acid), H 4 P 2 O 7 , produced by
heating phosphoric(V) acid (solid) and
phosphorus(III) chloride oxide.
Metaphosphoric acid is a glassy polymeric solid (HPO 2 ) x .
phosphorous acid See phosphonic
acid.
phosphorus Symbol P. A nonmetallic element belonging to
*group 15 (formerly VB) of the periodic table; a.n. 15; r.a.m. 30.9738; r.d.
1.82 (white), 2.34 (red); m.p. 44.1°C
(α-white); b.p. 280°C (α-white). It occurs in various phosphate rocks,
from which it is extracted by heating
with carbon (coke) and silicon(IV)
oxide in an electric furnace (1500°C).
Calcium silicate and carbon monoxide are also produced. Phosphorus
has a number of allotropic forms.
The α-white form consists of P 4 tetrahedra (there is also a β-white form
stable below –77°C). If α-white phosphorus is dissolved in lead and
heated at 500°C a violet form is obtained. Red phosphorus, which is a
combination of violet and white
phosphorus, is obtained by heating
α-white phosphorus at 250°C with air
excluded. There is also a black allotrope, which has a graphite-like
structure, made by heating white
phosphorus at 300°C with a mercury
catalyst. The element is highly reactive. It forms metal *phosphides and
covalently bonded phosphorus(III)
and phosphorus(V) compounds. Phosphorus is an *essential element for
living organisms. It is an important
constituent of tissues (especially
bones and teeth) and of cells, being
required for the formation of nucleic
phosphor bronze
412
p
www.AzShimi.ir www.AzShimi.com
phosphorescence). Phosphors that release their energy after a short delay
of between 10
–10 and 10
–4 second are
sometimes called scintillators.
phosphor bronze An alloy of copper containing 4% to 10% of tin and
0.05% to 1% of phosphorus as a deoxidizing agent. It is used particularly
for marine purposes and where it is
exposed to heavy wear, as in gear
wheels. See also bronze.
phosphorescence See luminescence.
phosphoric(V) acid (orthophosphoric acid) A white rhombic solid,
H 3 PO 4 ; r.d. 1.834; m.p. 42.35°C; loses
water at 213°C; very soluble in water
and soluble in ethanol. Phosphoric(V)
acid is very deliquescent and is generally supplied as a concentrated
aqueous solution. It is the most commercially important derivative of
phosphorus, accounting for over 90%
of the phosphate rock mined. It is
manufactured by two methods; the
wet process, in which the product
contains some of the impurities originally present in the rock and applications are largely in the fertilizer
industry, and the thermal process,
which produces a much purer product suitable for the foodstuffs and detergent industries. In the wet process
the phosphate rock, Ca 3 (PO 4 ) 2 , is
treated with sulphuric acid and the
calcium sulphate removed either as
gypsum or the hemihydrate. In the
thermal process, molten phosphorus
is sprayed and burned in a mixture
of air and steam. Phosphoric(V) acid
is a weak tribasic acid, which is best
visualized as (HO) 3 PO. Its full systematic name is tetraoxo-phosphoric(V)
acid. It gives rise to three series of
salts containing phosphate(V) ions
based on the anions [(HO) 2 PO 2 ]
– ,
[(HO)PO 3 ]
2– , and PO 4
3– . These salts are
acidic, neutral, and alkaline in character respectively and phosphate ions
often feature in buffer systems.
There is also a wide range of higher
acids and acid anions in which there
is some P–O–P chain formation. The
simplest of these is pyrophosphoric
acid (technically heptaoxodiphosphoric(V) acid), H 4 P 2 O 7 , produced by
heating phosphoric(V) acid (solid) and
phosphorus(III) chloride oxide.
Metaphosphoric acid is a glassy polymeric solid (HPO 2 ) x .
phosphorous acid See phosphonic
acid.
phosphorus Symbol P. A nonmetallic element belonging to
*group 15 (formerly VB) of the periodic table; a.n. 15; r.a.m. 30.9738; r.d.
1.82 (white), 2.34 (red); m.p. 44.1°C
(α-white); b.p. 280°C (α-white). It occurs in various phosphate rocks,
from which it is extracted by heating
with carbon (coke) and silicon(IV)
oxide in an electric furnace (1500°C).
Calcium silicate and carbon monoxide are also produced. Phosphorus
has a number of allotropic forms.
The α-white form consists of P 4 tetrahedra (there is also a β-white form
stable below –77°C). If α-white phosphorus is dissolved in lead and
heated at 500°C a violet form is obtained. Red phosphorus, which is a
combination of violet and white
phosphorus, is obtained by heating
α-white phosphorus at 250°C with air
excluded. There is also a black allotrope, which has a graphite-like
structure, made by heating white
phosphorus at 300°C with a mercury
catalyst. The element is highly reactive. It forms metal *phosphides and
covalently bonded phosphorus(III)
and phosphorus(V) compounds. Phosphorus is an *essential element for
living organisms. It is an important
constituent of tissues (especially
bones and teeth) and of cells, being
required for the formation of nucleic
phosphor bronze
412
p
www.AzShimi.ir www.AzShimi.com