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 gasses. The phosphorus vapor condenses and solidifies 2 P₂(v) → P₄(s) and the other gasses escape. Often the gasses 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. He requires lead (or silver) chloride, producing potentially toxic byproducts.

1. Add lead chloride to urine
2. Mix thoroughly for some time
3. A precipitate of lead phosphate will form

   PbCl(aq) + XPO₄(aq) → XCl(aq) + Pb₃(PO₄)₂(s)

4. Gather the precipitate and make a cake of it
5. Add an excess of carbon, charcoal
6. Perform a dry distillation on the phosphate cake yielding solid lead (II) oxide, carbon dioxide gas, and phosphorus vapor

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 (avoiding aluminum oxide as much as possible)
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