Phosphorus

 

Phosphorus

Chemical formula	P
Atomic Number	15
OTP appearance	grey white solid
Molar Mass(g/mol)	30.97
Density(g/cc)	1.82
Melting Point(°C)	44.2
Boiling Point(°C)	280.5
NFPA 704	4 4 2

Uses

Primary

• Matches (red allotrope)
• Dopant for silicon semiconductors

Other

• Feedstock for phosphoric acid
• Fertilizer
• Detergents
• Pesticides

Natural Occurrence

• Elemental phosphorus does not occur naturally
• Phosphorus occurs naturally in bone, urine and the mineral apatite

Hazards

• Some allotropes of phosphorus ignite spontaneously in air.
• Metallic phosphorus is very toxic

Character

Allotropes

Elemental phosphorus has several relevant allotropes with widely differing properties.

White

Phosphorus freshly condensed from a gaseous state is white (sometimes called yellow) phosphorus. It will autoignite if exposed to air.

Red

Heating white phosphorus over 250°C will convert it to red phosphorus. Red phosphorus will not autoignite in air unless heated to around 300°C.

Violet

Heating red phosphorus over 550°C for 8-24 hours will convert it to violet phosphorus.

Black

High temperatures and high pressures required to produce, but completely stable thereafter.

Production

Extraction

Production of elemental phosphorus is usually accomplished by dry distillation of a solid mixture which contains phosphate, producing phosphorus vapor P₂(v) along with other gases. The phosphorus vapor condenses and solidifies 2 P₂(v) → P₄(s) and the other gases escape. Often the gases are cooled by bubbling them through a water bath, which has several added advantages, including preventing the phosphorus from coming into direct contact with external oxygen and also a hard-stop for the phosphorus vapor, allowing the rest of the system to operate at high enough temperatures to prevent phosphorus deposition before the water bath.

From excretia

Expected yield from human urine is between 0.20 and 0.45 ml of solid phosphorus per liter.

Brand

Brand originally produced phosphorus by boiling urine to produce a cake of solids which was then air-dried and then dry distilled

1. Boil urine, yielding solids
2. Air dry solids into a cake containing phosphates
3. Perform a dry distillation on the phosphate cake yielding phosphorus vapor

Boyle

Boyle improved on the system lowering the activation energy and lowering contamination levels

1. Evaporate urine at low temperature yielding solids
2. Air dry solids into a cake containing phosphates
3. Add silicon dioxide to the cake
4. Perform a dry distillation on the phosphate cake yielding phosphorus vapor

Marggraf

Andreas Sigismund Marggraf improved it further by removing the need to boil urine, a noxious process.

From bone black

1. Combine bone black with excess carbon and silicon dioxide (avoiding aluminum oxide as much as possible)
2. Mix intimately
3. Perform a dry distillation on the result yielding phosphorus vapor

   Ca₃(PO₄)₂(s) + 5 C(s) + 3 SiO₂(s) → 3 CaSiO₃ + 5 CO(g) + P₂(v)

From apatite minerals

1. Combine apatite with excess carbon and silicon dioxide
2. Mix intimately
3. Perform a dry distillation on the result yielding phosphorus vapor

   4 Ca₅(PO₄)₃X + 18 SiO₂ + 30 C → 3 P₄ + 30 CO + 18 CaSiO₃ + 2 CaX₂

4. Optionally, if fluorapatite is present treat the CaX₂ fraction with sulfuric acid, producing calcium sulfate and hydrofluoric acid

   CaF₂ + 2 H₂SO₄ → Ca(SO₄)₂ + 2 HF

Synthesis

via aluminum

Aluminum for the preparation of Phosphorus

The applications of aluminum in the arts multiply with much the same rapidity as do those of electricity The Berichte describes a new method of preparing phosphorus by its use as a reducing agent The process is so simple that it can easily be illustrated on the lecture table. Hydrogen ammonium sodium phosphate is fused in a porcelain crucible until it is changed into sodium metaphosphate aluminum turnings are then dropped into the liquid and the freed phosphorus bursts into flame Now if the experiment is tried with a glass tube instead of a crucible a slow current of dry hydrogen being passed over the mixture of the salt and aluminum the phosphorus distills into the cooler part of the tube without the formation of any phosphureted hydrogen The residue consists of alumina sodium aluminate and a phosphide of alumina AlP

By these steps in the process only 30 per cent of the phosphorus in the mineral used can be obtained but the phosphide is decomposed entirely by heating with silica and this may be added at the beginning of the experiment and the reaction proceeds without difficulty and without loss

It is advised that for the lecture table a combustion tube a yard long be used; two and a half parts of aluminum six parts of sodium metaphosphate (obtained from heating previously the hydrogen ammonium sodium phosphate) and two parts of finely pulverized silica are placed in the tube a slow current of hydrogen is passed through and heat is applied until the reaction begins This is shown by sudden incandescence and phosphorus is seen to condense in globules on the cooler part of the tube at the end where the hydrogen escapes.

Instead of this phosphate any ordinary phosphate may be used but experimenters are warned not to use the superphosphates containing calcium sulphate mixed with them such as are used for fertilizing purposes because the sulphate is suddenly decomposed by the aluminum with an explosion when a certain temperature is reached

See Also

References