About Refractory Grade Magnesium Oxide
Refractory grade magnesium oxide is a hard-burned MgO calcined at high temperature to produce dense, well-developed periclase crystals with low surface area and low chemical reactivity. Magnesium oxide melts at about 2,800 °C, and the hard-burned form retains that thermal stability while resisting hydration far better than light-burned material.
These properties suit it to basic refractory work. MgO is the principal component of magnesia and magnesia-carbon bricks, castables, ramming and gunning mixes used to line steelmaking vessels, ladles and furnaces exposed to basic slags. Hard-burned powder is also used in magnesium phosphate cements for rapid repairs, and as a magnesium source in ceramic and glass batches. In each case the goal is a stable oxide that will not react prematurely or shrink excessively in service.
Obsidian Minerals produces this grade in Gujarat and controls MgO content together with silica, lime and iron, the impurities that most affect refractoriness and slag resistance. Particle size can be supplied as a fine powder or as graded fractions to suit a customer's mix design. Every lot is tested in an NABL-accredited laboratory, and material can be sampled before an order is confirmed, so its sizing and chemistry can be proven in your own mix and firing schedule.
Typical specifications
| Parameter | Typical Value | Test Method |
|---|---|---|
| MgO content | ≥ 90.0 % | Internal method |
| Silica as SiO₂ | ≤ 4.0 % | Internal method |
| Calcium as CaO | ≤ 3.0 % | Internal method |
| Iron as Fe₂O₃ | ≤ 1.5 % | Internal method |
| Loss on ignition (1000 °C) | ≤ 1.0 % | Internal method |
| Specific surface area (BET) | < 5 m²/g | ISO 9277 |
| Particle size | Fine powder or graded fractions, as agreed | Sieve analysis |
Typical values for guidance. Guaranteed limits are stated on the Technical Data Sheet and batch CoA. Chemistry and sizing can be agreed for specific refractory formulations.
Key features & benefits
Low reactivity, high stability
Hard-burning gives refractory grade magnesium oxide a surface area typically below 5 m²/g, so it hydrates slowly and stays dimensionally stable in castables, ramming mixes and high-temperature cements.
Controlled impurity profile
Silica, lime and iron oxide are monitored on every batch because they form low-melting phases with MgO. Keeping them within limits supports refractoriness and resistance to basic slag attack.
Graded or fine supply
Available as fine powder for matrix and binder phases, or as agreed size fractions for aggregate packing, so refractory formulators can design the particle size distribution around their placement method.
Low loss on ignition
With loss on ignition typically at or below 1.0 %, the material releases little volatile matter on heating, which limits porosity and shrinkage when refractory products are dried and fired.
Applications
Monolithic refractories
Fine and graded MgO for basic castables, ramming, gunning and spraying mixes in steel ladles, tundishes, electric arc furnaces and other vessels in contact with basic slags.
Shaped basic refractories
A magnesia source for the fine fraction of magnesia and magnesia-carbon bricks, where purity and grain density influence hot strength, slag resistance and the service life of furnace linings.
Magnesium phosphate cements
Low-reactivity MgO reacts with phosphate solutions in rapid-setting repair mortars and fire-resistant products; hard-burned material helps keep the setting reaction controllable and the working time practical on site.
Ceramic and glass batches
Introduces MgO into ceramic bodies, glazes and speciality glass compositions, where it modifies thermal expansion, firing behaviour and the chemical durability of the finished ware.
Usage & handling
- Select particle size to match the mix design: fine fractions for the matrix, coarser fractions for aggregate packing.
- For phosphate cements, test setting time at site temperature, because setting rate depends on MgO fineness and retarder level.
- Store dry and off the floor; although hard-burned MgO hydrates slowly, prolonged exposure to humidity should be avoided.
- Use dust extraction during batching and follow the SDS for personal protective equipment.
Packaging & supply
- 25 kg or 50 kg HDPE or paper bags for fine powder
- 1 MT and 1.2 MT jumbo bags for graded fractions and bulk orders
- Custom packaging and labelling on request
Frequently asked questions
How does refractory grade differ from light-burned magnesium oxide?
Refractory grade MgO is calcined at a much higher temperature, which grows dense periclase crystals and reduces surface area to typically below 5 m²/g. The result is a stable, low-reactivity oxide that resists hydration and suits high-temperature use. Light-burned MgO has a far higher surface area and is chosen when chemical reactivity is needed, as in rubber compounding.
Which impurities matter in refractory magnesium oxide?
Silica, lime and iron oxide are the most important. They react with MgO at high temperature to form lower-melting phases, which can reduce hot strength and resistance to slag. The lime-to-silica ratio also affects which phases form. Our Technical Data Sheet states guaranteed limits, and the batch Certificate of Analysis reports the tested chemistry for each lot.
Can I specify the particle size of refractory grade MgO?
Yes. The grade can be supplied as a fine powder or as graded fractions agreed with the customer, so that it fits your mix design and placement method, whether casting, ramming or gunning. Send your target size distribution or current specification, and we will confirm feasibility and arrange a sample for evaluation in your laboratory.
Is refractory grade MgO suitable for magnesium phosphate cement?
Hard-burned, low-reactivity MgO is commonly used in magnesium phosphate cements because it slows the otherwise very rapid reaction with phosphate and gives a usable working time. Setting behaviour depends on fineness, temperature and retarder dosage, so the formulation should be confirmed with laboratory trials using your own phosphate source before field use.
What documents come with refractory grade magnesium oxide?
Each consignment ships with an MSDS/SDS, a Technical Data Sheet and a batch Certificate of Analysis covering MgO content and the main impurities. Testing is carried out in an NABL-accredited laboratory under ISO 9001 certified processes. Additional test data required by your incoming inspection can be discussed when you enquire.