engineering

Magnesium oxide

Magnesium oxide is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Magnesium oxide rather than just read about it. In short: Magnesium oxide (MgO), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ions held together by ionic bonding.

Key takeaways

Magnesium oxide belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Magnesium oxide to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Magnesium oxide from memory before moving on to harder problems.

Reference excerpt

Magnesium oxide (MgO), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ions held together by ionic bonding. Magnesium hydroxide forms in the presence of water (MgO + H2O → Mg(OH)2), but it can be reversed by heating it to remove moisture. Magnesium oxide was historically known as magnesia alba (literally, the white mineral from Magnesia), to differentiate it from magnesia nigra, a black mineral containing what is now known as manganese.

Related oxides While "magnesium oxide" normally refers to MgO, the compound magnesium peroxide MgO2 is also known. According to evolutionary crystal structure prediction, MgO2 is thermodynamically stable at pressures above 116 GPa (gigapascals), and a semiconducting suboxide Mg3O2 is thermodynamically stable above 500 GPa. Because of its stability, MgO is used as a model system for investigating vibrational properties of crystals.

Electric properties Pure MgO is not conductive and has a high resistance to electric current at room temperature. The pure powder of MgO has a relative permittivity in between 3.2 and 9.9 k {\displaystyle k} with an approximate dielectric loss of tan(δ) > 2.16×103 at 1kHz.

Production Magnesium oxide is produced by the calcination of magnesium carbonate or magnesium hydroxide. The latter is obtained by the treatment of magnesium chloride MgCl2 solutions, typically seawater, with limewater or milk of lime.

Mg2+ + Ca(OH)2 → Mg(OH)2 + Ca2+ Calcining at different temperatures produces magnesium oxide of different reactivity. 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. Calcining temperatures 1000 – 1500 °C produce hard-burned magnesia, which has limited reactivity and calcining at lower temperature, (700–1000 °C) produces light-burned magnesia, a reactive form, also known as caustic calcined magnesia. Although some decomposition of the carbonate to oxide occurs at temperatures below 700 °C, the resulting materials appear to reabsorb carbon dioxide from the air.

Applications

Refractory insulator MgO is prized as a refractory material, i.e. a solid that is physically and chemically stable at high temperatures. It has the useful attributes of high thermal conductivity and low electrical conductivity. According to a 2006 reference book:

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. It is also used as an insulator in heat-resistant electrical cable.

Biomedical Among metal oxide nanoparticles, magnesium oxide nanoparticles (MgO NPs) have distinct physicochemical and biological properties, including biocompatibility, biodegradability, high bioactivity, significant antibacterial properties, and good mechanical properties, which make it a good choice as a reinforcement in composites.

Heating elements It is used extensively as an electrical insulator in tubular construction heating elements as in electric stove and cooktop heating elements. There are several mesh sizes available and most commonly used ones are 40 and 80 mesh per the American Foundry Society. The extensive use is due to its high dielectric strength and average thermal conductivity. MgO is usually crushed and compacted with minimal airgaps or voids.

Cement MgO is one of the components in Portland cement in dry-process plants. Sorel cement uses MgO as the main component in combination with MgCl2 and water.

Fertilizer MgO has an important place as a commercial plant fertilizer and as animal feed.

Fireproofing It is a principal fireproofing ingredient in construction materials. As a construction material, magnesium oxide wallboards have several attractive characteristics: fire resistance, termite resistance, moisture resistance, mold and mildew resistance, and strength, but also a severe downside as it attracts moisture and can cause moisture damage to surrounding materials.

Medical Magnesium oxide is used for relief of heartburn and indigestion, as an antacid, magnesium supplement, and as a short-term laxative. It is also used to improve symptoms of indigestion. Side effects of magnesium oxide may include nausea and cramping. In quantities sufficient to obtain a laxative effect, side effects of long-term use may rarely cause enteroliths to form, resulting in bowel obstruction.

Waste treatment Magnesium oxide is used extensively in the soil and groundwater remediation, wastewater treatment, drinking water treatment, air emissions treatment, and waste treatment industries for its acid buffering capacity and related effectiveness in stabilizing dissolved heavy metal species. Many heavy metals species, such as lead and cadmium, are least soluble in water at mildly basic conditions (pH in the range 8–11). Solubility of metals increases their undesired bioavailability and mobility in soil and groundwater. Granular MgO is often blended into metals-contaminating soil or waste material, which is also commonly of a low pH (acidic), in order to drive the pH into the 8–10 range. Metal-hydroxide complexes tend to precipitate out of aqueous solution in the pH range of 8–10. MgO is packed in bags around transuranic waste in the disposal cells (panels) at the Waste Isolation Pilot Plant, as a CO2 getter to minimize the complexation of uranium and other actinides by carbonate ions and so to limit the solubility of radionuclides. The use of MgO is preferred over CaO since the resulting hydration product (Mg(OH)2) is less soluble and releases less hydration heat. Another advantage is to impose a lower pH value (about 10.5) in case of accidental water ingress into the dry salt layers, in contrast to the more soluble Ca(OH)2 which would create a higher pH of 12.5 (strongly alkaline conditions). The Mg2+ cation being the second most abundant cation in seawater and in rocksalt, the potential release of magnesium ions dissolving in brines intruding the deep geological repository is also expected to minimize the geochemical disruption.

Niche uses

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Magnesium oxide

Start with the simplest possible case. Write down what Magnesium oxide claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Magnesium oxide before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Magnesium oxide ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Magnesium oxide

In research: Magnesium oxide appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Magnesium oxide in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Magnesium oxide is common in secondary-school and first-year university syllabi. It links to neighbouring topics Antacids, Ceramic materials, E-number additives, so understanding it makes those chapters shorter.
In everyday life: Look for Magnesium oxide outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Magnesium oxide in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Magnesium oxide means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Magnesium oxide out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Magnesium oxide in simple terms?

Why does Magnesium oxide matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Magnesium oxide?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Magnesium oxide.