Magnesium Oxide

Magnesium oxide (MgO, CAS 1309-48-4), also called magnesia or calcined magnesite, is supplied by Global Chemicals LLC from Muscat stock in two grades that behave very differently. Light-burned (caustic-calcined) MgO is calcined at lower temperature, keeps a high surface area and reacts readily with water to form magnesium hydroxide. Dead-burned MgO is fired close to 2,000°C into periclase, is almost unreactive, and is the material of refractory linings. Assay runs 85–98% MgO depending on grade and source.

In oil-well cementing. Light-burned MgO is the classic expanding additive. Dosed at 0.5–3% by weight of cement, it hydrates slowly after the slurry has set, and the volume increase compensates for shrinkage and improves the bond between cement, casing and formation. The reactivity grade is matched to bottom-hole temperature so that expansion happens after placement, not before; this is the specification point that matters most when ordering.

In drilling fluids. A slurry of MgO reads about pH 10.3–10.5 and buffers rather than spikes, so it is used as a sustained alkalinity source in high-temperature water-based muds and in some completion brines where sodium hydroxide would be too aggressive.

Other uses. Refractory bricks and ramming mixes (dead-burned), wastewater neutralisation where a slow, self-limiting pH rise is wanted, magnesium chemical manufacture, and animal feed.

Properties and handling. White to off-white powder, insoluble in water, mildly alkaline. Light-burned grades absorb moisture and carbon dioxide from the air and lose reactivity, so keep bags sealed and use opened bags promptly. Dust control and a particle mask are the normal precautions.

What to specify when you order. Grade (light-burned or dead-burned), MgO assay, reactivity or citric-acid activity for cementing grades, particle size, and pack: 25 kg bags or bulk bags. Certificates of analysis accompany each lot and the SDS is available on request.