776MAGNESITE, DEAD-BURNED
upon heating at some temperature below 1450C so Hazard: (Solid metal) Combustible at 650C. (Pow-
that some carbon dioxide is retained (2–10%) and der, flakes, etc.) Flammable, dangerous fire hazard.
the magnesium oxide displays adsorptive capacity Use dry sand or talc to extinguish.
or activity.
Use: Aluminum alloys for structural parts, die-cast
Grade: Technical, chemical, synthetic rubber, USP
auto parts, missiles, space vehicles; powder for py-
(light, medium light, heavy).
rotechnics and flash photography, production of
Use: Magnesium oxychloride and oxysulfate ce-
iron, nickel, zinc, titanium, zirconium; antiknock
ments, 85% magnesia insulation, rubber (reinforc-
gasoline additives; magnesium compounds and Gri-
ing agent, accelerator), uranium processing, chemi-
gnard syntheses; cathodic protection; reducing
cal processing, rayon, refractories, paper pulp, acid-
agent; desulfurizing iron in steel manufacture; pre-
neutralizing fertilizers, welding-rod coatings,
cision instruments; optical mirrors; dry and wet bat-
fillers, glass constituents, abrasives.
teries.
See magnesium oxide.
magnesium acetate.
magnesite, dead-burned.
(burnt magnesia;
CAS: 142-72-3. (1) Mg(OOCCH
3
)
2
or (2)
dead-burned magnesia; refractory magnesia;
Mg(OOCCH
3
)
2
•4H
2
O.
burnt magnesite; magnesium oxide). MgO. The
Properties: Colorless, crystalline aggregate or mo-
granular product obtained by burning (firing) mag-
noclinic crystals; acetic acid odor. (1) Mp 323C, d
nesite or other substances convertible to magnesia
1.42; (2) mp 80C, d 1.45. Soluble in water and dilute
upon heating above 1450C long enough to form
alcohol.
granules suitable for use as a refractory (ASTM).
Derivation: Interaction of magnesium carbonate and
Synthetic magnesium hydroxide or chloride is
acetic acid.
sometimes used instead of magnesite as a source.
Use: Dye fixative in textile printing, deodorant, disin-
Grade: 85–87% (from magnesite ores); 97–99%
fectant, and antiseptic.
(from seawater and brines).
Use: Refractories, as grains or basic brick, the latter
magnesium acetylacetonate. Mg(C
5
H
7
O
2
)
2
.
especially in open hearth furnaces for steel, furnaces
Crystalline powder, slightly soluble in water, resis-
for nonferrous metal smelting, and in cement and
tant to hydrolysis, a chelating nonionizing com-
other kilns.
pound.
See magnesium oxide.
magnesium amide. Mg(NH
2
)
2
.
magnesite, synthetic. Magnesium oxide,
Properties: Whitish to gray crystals. D 1.40. Decom-
MgO, as obtained from seawater, seawater bitterns,
poses when heated.
or well brines. The preliminary product is usually
Derivation: Reaction of magnesium with ammonia
magnesium hydroxide or chloride, which is then
under elevated pressure.
heated, or sometimes treated with steam and heated
Hazard: A pyrophoric material igniting in air at
in the case of the chloride, to obtain the oxide.
room temperature. Evolves ammonia on vigorous
Synthetic magnesite constitutes the purer grades of
reaction with water.
dead-burned magnesite.
Use: Catalyst for polymerization.
magnesium.
magnesium ammonium arsenate dihydrate.
CAS: 7439-95-4. Mg. Metallic element of atomic
CAS: 14644-70-3. mf: AsO
4
•H
3
N•Mg•2H
2
O.
number 12, group IIA of the periodic table, aw
Hazard: A poison by ingestion and skin contact.
24.305, valence
=
2; 3 isotopes. Magnesium is the
central element of the chlorophyll molecule; it is
magnesium ammonium orthophosphate.
also an important component of red blood cor-
See magnesium ammonium phosphate.
puscles.
Properties: Silvery, moderately hard, alkaline-earth
magnesium ammonium phosphate. (mag-
metal; readily fabricated by all standard methods.
nesium ammonium orthophosphate).
Lightest of the structural metals; strong reducing
MgNH
4
PO
4
•6H
2
O.
agent; electrical conductivity similar to aluminum.
Properties: White powder. D 1.71, mp (decomposes
D 1.74, mp 650C, bp 1107C. Soluble in acids; insol-
to magnesium pyrophosphate, Mg
2
P
2
O
7
). Soluble in
uble in water.
acids; insoluble in alcohol and water.
Source: Magnesite and dolomite; seawater and
Derivation: By the interaction of solutions of a mag-
brines.
nesium salt and ammonium phosphate.
Derivation: (1) Electrolysis of fused magnesium
Use: Fire retardant for fabrics, fertilizer.
chloride (Dow seawater process); (2) reduction of
magnesium oxide with ferrosilicon (Pidgeon
process).
magnesium arsenate. (arsenic acid, magne-
Available forms: Ingots, bars, fine powder (up to sium salt).
99.6% pure), sheet and plate, rods, tubing, ribbon, CAS: 10103-50-1. Mg
3
(AsO
4
)
2
•xH
2
O.
flakes. Properties: White powder. When pure it is insoluble