About Standard Activity Magnesium Oxide
Standard activity magnesium oxide is a general-purpose, light-burned MgO with a moderate specific surface area, typically 30–70 m²/g. It sits between our high activity rubber grade and the hard-burned refractory grade, and is chosen where some chemical reactivity is needed but a very fast reaction would be difficult to control.
Its uses are broad. Compounders use it as an acid acceptor and stabiliser in less demanding rubber and PVC formulations, and as a thickening agent in unsaturated polyester sheet and bulk moulding compounds, where MgO reacts with acid end-groups to raise viscosity in a controlled way. In construction, moderately reactive MgO is a component of magnesium-based boards, flooring and binders. It is also used as a neutralising agent and pH buffer in chemical processing and effluent treatment.
Because the reaction rate is slower than that of high activity material, this grade tends to be less sensitive to small changes in mixing time or temperature, which can make day-to-day processing more forgiving. Obsidian Minerals supplies it from Gujarat with batch-level test data for MgO content, surface area and loss on ignition. Particle size can be adjusted to a customer's requirement, and samples are provided for trials so the grade can be checked against your current material before switching.
Typical specifications
| Parameter | Typical Value | Test Method |
|---|---|---|
| MgO content (ignited basis) | ≥ 94.0 % | Internal method |
| Specific surface area (BET) | 30–70 m²/g | ISO 9277 |
| Loss on ignition (1000 °C) | ≤ 6.0 % | Internal method |
| Calcium as CaO | ≤ 2.0 % | Internal method |
| Iron as Fe₂O₃ | ≤ 0.20 % | Internal method |
| Residue on 45 µm sieve | ≤ 1.0 % | Internal method |
| Appearance | White to off-white powder | Visual |
Typical values for guidance. Guaranteed limits are stated on the Technical Data Sheet and batch CoA. Surface area and particle size can be adjusted by agreement.
Key features & benefits
Moderate, controllable reactivity
A surface area of typically 30–70 m²/g gives standard activity magnesium oxide enough reactivity to accept acids and neutralise, without the very rapid reaction that can shorten processing time in sensitive formulations.
Thickening agent for polyester resins
In SMC and BMC formulations the grade reacts with the carboxyl end-groups of unsaturated polyester resin, building viscosity over a predictable maturation period so the compound can be handled and moulded.
One grade, several industries
The same material serves rubber, PVC, resins, magnesium-based building products and neutralisation duties, which helps buyers simplify qualification and purchasing across several production lines and sites.
Particle size to order
Standard material is milled to a low 45 µm residue for good dispersion. Finer or coarser cuts can be developed with customers where a specific flow, dusting or reaction profile is required.
Documented quality
MgO content, surface area and loss on ignition are recorded for each batch under ISO 9001 certified processes and supplied on the Certificate of Analysis together with the Technical Data Sheet.
Applications
General rubber goods
Acid acceptor and mild activator in chloroprene blends and other halogenated compounds for industrial mouldings, rollers and extruded profiles where a moderate cure rate is acceptable to the compounder.
SMC and BMC thickening
Chemical thickener in unsaturated polyester sheet and bulk moulding compounds for electrical enclosures, automotive panels and sanitary parts, typically dispersed in a carrier paste before addition to the resin.
Magnesium-based building materials
Reactive component in magnesium oxychloride and magnesium oxysulphate binders for fire-resistant boards, industrial flooring and decorative panels, where reactivity influences setting time and strength development.
Neutralisation and pH control
Mild alkali for neutralising acidic process streams and effluents, offering a buffered pH response that is easier to control than strong alkalis such as caustic soda or hydrated lime.
Usage & handling
- Typical loading in halogenated rubber compounds is 2–6 phr; in SMC and BMC, thickener levels of around 0.5–2 % on resin are common. Optimise in your own formulation.
- For resin systems, pre-disperse MgO in a carrier paste or part of the resin to avoid agglomerates and uneven thickening.
- For magnesium binders, verify setting time with your own brine or salt solution, as reactivity depends on solution strength and temperature.
- Keep bags sealed and dry; light-burned MgO gradually absorbs moisture and carbon dioxide from air.
- Handle with dust control and wear the PPE listed in the SDS.
Packaging & supply
- 25 kg or 50 kg HDPE or paper bags
- 1 MT or 1.2 MT FIBC jumbo bags for bulk users
- Custom and private-label packing on request
Frequently asked questions
What is standard activity magnesium oxide?
It is a light-burned MgO with a moderate surface area, typically 30–70 m²/g. It reacts more slowly than high activity grades, which suits applications such as resin thickening, general rubber compounding, magnesium binders and neutralisation, where a steady reaction is easier to manage than a very fast one. Guaranteed limits are given on the Technical Data Sheet.
Can standard activity MgO be used to thicken SMC and BMC?
Yes. It is used as a thickening agent in unsaturated polyester moulding compounds. The thickening rate depends on resin acid value, moisture, temperature and how well the MgO is dispersed, so dosage and carrier system should be validated in your own maturation trials. Samples are available for this purpose, along with the Technical Data Sheet.
How is it different from the high activity grade?
The main difference is surface area. The high activity grade exceeds 100 m²/g and is designed for fast acid acceptance in CR and FKM. The standard grade has a lower surface area and a slower reaction, which makes it better suited to general-purpose uses and less critical compounds where a very fast reaction is not needed.
Is standard activity MgO suitable for magnesium oxychloride boards?
It is used in magnesium-based binders, but board manufacturers often need a specific reactivity window to balance working time against early strength. Share your current formulation and test method with us; we can supply a sample and, where needed, discuss adjusting particle size or reactivity to suit your process and raw materials.
What packaging is available for standard activity magnesium oxide?
Standard activity magnesium oxide is packed in 25 kg or 50 kg HDPE or paper bags, or in 1 MT and 1.2 MT jumbo bags for bulk handling. Custom and private-label packaging can be arranged on request. Each shipment is accompanied by an MSDS/SDS, Technical Data Sheet and batch Certificate of Analysis.