Magnesium hydroxide forms in the presence of water (MgO + H2O → Mg(OH)2), but it can be reversed by heating it to remove moisture.

[12] Pure MgO is not conductive and has a high resistance to electric current at room temperature.

The latter is obtained by the treatment of magnesium chloride MgCl2 solutions, typically seawater, with limewater or milk of lime.

High temperatures 1500 – 2000 °C diminish the available surface area and produces dead-burned (often called dead burnt) magnesia, an unreactive form used as a refractory.

[citation needed] MgO is prized as a refractory material, i.e. a solid that is physically and chemically stable at high temperatures.

According to a 2006 reference book:[14] By far the largest consumer of magnesia worldwide is the refractory industry, which consumed about 56% of the magnesia in the United States in 2004, the remaining 44% being used in agricultural, chemical, construction, environmental, and other industrial applications.MgO is used as a refractory material for crucibles.

Many heavy metals species, such as lead and cadmium, are least soluble in water at mildly basic conditions (pH in the range 8–11).

[33] It helps dissipate heat from friction surfaces, preventing overheating, while minimizing wear on metal components.

[34] Its stability under high temperatures ensures reliable and durable braking performance in automotive and industrial applications.

[36] Optimized IGZO/MgO TFTs demonstrated an electron mobility of 1.63 cm²/Vs, an on/off current ratio of 10⁶, and a subthreshold swing of 0.50 V/decade at −0.11 V.[37] These TFTs are integral to low-power applications, wearable devices, and radiation-hardened electronics, contributing to enhanced efficiency and durability across diverse domains.