About High Activity Magnesium Oxide
High activity magnesium oxide is a light-burned MgO with a specific surface area above 100 m²/g, produced for compounders of chloroprene (CR) and fluorocarbon (FKM) rubber. Its fine crystallite structure gives a large reactive surface, so it captures acidic species quickly and takes an active part in the cure.
In chloroprene compounds, MgO works alongside zinc oxide. It moderates the onset of cure, giving useful scorch safety during mixing and processing, and absorbs the hydrogen chloride released as the polymer crosslinks. In FKM, a high activity grade acts as an acid acceptor for the hydrogen fluoride generated during bisphenol or diamine cures, helping to protect both compound and tooling. A higher surface area generally means more acid-accepting capacity per kilogram, which can allow a lower dosage or a more consistent cure at the same loading.
Activity is only useful if it survives transport and storage. Light-burned MgO reacts slowly with atmospheric moisture and carbon dioxide, so Obsidian Minerals tests surface area and loss on ignition on every batch, reports them on the Certificate of Analysis, and packs this grade in moisture-resistant HDPE bags. Samples are available for rheometer and scorch trials before a full order is placed, and our team can share typical results for each lot.
Typical specifications
| Parameter | Typical Value | Test Method |
|---|---|---|
| MgO content (ignited basis) | ≥ 95.0 % | Internal method (complexometric titration) |
| Specific surface area (BET) | > 100 m²/g | ISO 9277 |
| Loss on ignition (1000 °C) | ≤ 8.0 % | Internal method |
| Calcium as CaO | ≤ 1.5 % | Internal method |
| Iron as Fe₂O₃ | ≤ 0.10 % | Internal method |
| Residue on 45 µm sieve | ≤ 0.5 % | Internal method |
| Bulk density (loose) | 0.20–0.45 g/cm³ | Internal method |
| Appearance | White, fine powder | Visual |
Typical values for guidance only. Guaranteed limits are stated on the Technical Data Sheet and batch CoA. Surface area can decline if the product is exposed to humid air.
Key features & benefits
Surface area above 100 m²/g
This high activity magnesium oxide offers a large reactive surface that captures hydrogen chloride and hydrogen fluoride quickly, giving compounders more acid-accepting capacity per kilogram than lower surface area grades.
Scorch control in chloroprene
Used with zinc oxide in CR compounds, the grade delays the onset of cure during mixing, milling and extrusion, widening the processing window before the compound begins to set up in the barrel or mould.
Low coarse residue
Residue on a 45 µm sieve is typically below 0.5 %, which supports fast, uniform dispersion in internal mixers and reduces the risk of undispersed specks in thin-walled mouldings, sheet and extruded profiles.
Batch-reported activity
Every lot is tested for surface area, MgO content and loss on ignition in an NABL-accredited laboratory, and the results appear on the batch Certificate of Analysis so incoming QC can verify activity before use.
Moisture-resistant packing
Packed in HDPE bags, or in jumbo bags with a liner on request, to limit the moisture and carbon dioxide uptake that would otherwise reduce reactivity during transit and warehousing.
Applications
Chloroprene (CR) compounds
Hoses, belts, wire and cable jackets, gaskets and moulded seals use high activity MgO as an activator and acid acceptor, balancing scorch safety with a consistent state of cure in the finished part.
Fluoroelastomer (FKM) seals
In bisphenol-cured FKM O-rings, shaft seals and gaskets, the grade neutralises hydrogen fluoride liberated during cure and post-cure, helping to protect mould surfaces and support stable vulcanisate properties.
CSM and other halogenated polymers
Chlorosulphonated polyethylene and other halogen-containing elastomers rely on an efficient acid acceptor to stabilise the compound against acidic by-products released during processing, vulcanisation and service at elevated temperature.
Polychloroprene contact adhesives
Solvent-borne polychloroprene adhesives use reactive MgO to scavenge acid and, together with tert-butyl phenolic resins, to form the resinate that builds heat resistance in the bond line.
Usage & handling
- Typical CR recipes use around 4 phr MgO with about 5 phr zinc oxide; FKM recipes commonly specify 3–15 phr depending on the cure system. Confirm the dosage in your own trials.
- Add MgO early in the mixing cycle with the polymer so it disperses fully; in CR compounds, add zinc oxide late or on the mill to preserve scorch safety.
- Keep bags closed in a cool, dry store and reseal part-used bags immediately to protect surface activity.
- Use within the shelf life stated on the Technical Data Sheet and rotate stock first-in, first-out.
- Avoid generating dust; use local exhaust ventilation and the PPE described in the SDS.
Packaging & supply
- 25 kg HDPE bags for moisture protection; paper bags on request
- 1 MT and 1.2 MT jumbo (FIBC) bags, with liner on request
- Custom and private-label packaging on request
- MSDS/SDS, TDS and batch CoA with every shipment
Frequently asked questions
What surface area does high activity magnesium oxide have?
This grade has a typical specific surface area above 100 m²/g, measured by the BET method. Surface area is the main indicator of MgO activity: the higher it is, the faster the oxide reacts with acids released during cure. The value for each lot is reported on the batch Certificate of Analysis, and the guaranteed limit is stated on the Technical Data Sheet.
Why does high activity MgO lose activity in storage?
Light-burned magnesium oxide slowly reacts with moisture and carbon dioxide in air, forming magnesium hydroxide and carbonate on the particle surface. This reduces the reactive area available in the compound and can shorten scorch time or change cure rate. Keep bags closed, store them dry and use the oldest stock first to keep performance consistent.
Can this grade replace a lower activity MgO at the same dosage?
Not always. A higher activity grade reacts faster, so a direct swap can change scorch time, cure rate and final properties. Most compounders run rheometer and Mooney scorch tests at the current dosage and at a reduced level before switching. We supply samples so you can complete those trials on your own formulation and equipment.
Is high activity MgO suitable for FKM compounds?
Yes. It is used as an acid acceptor in fluoroelastomer compounds, typically alongside calcium hydroxide in bisphenol cure systems, to neutralise hydrogen fluoride formed during cure and post-cure. Customers should confirm suitability, dosage and any specific purity requirements against the polymer supplier's recommendations and their own test results before adopting it in production.
How do I order high activity magnesium oxide?
Send our sales team your required quantity, packaging preference and destination country. We will confirm availability and share the Technical Data Sheet, along with a sample if you need one for qualification. Each shipment is supplied with an MSDS/SDS, Technical Data Sheet and batch Certificate of Analysis, and custom packaging can be discussed on request.