A practical guide to barium sulfate, why particle size governs performance in an inert filler, how barite differs from blanc fixe, and how it is supplied, from a US-based distributor.
Barium sulfate (BaSO4, CAS 7727-43-7) is a white, chemically inert, high-density mineral filler used as an extender in coatings, plastics, and rubber, and as a weighting agent in drilling fluids and shielding concrete. Because it is inert, its performance is governed by particle size rather than chemistry. Stratus Chemical supplies industrial and micronized grades in bags and supersacks across the United States.
| Property | Value |
|---|---|
| Chemical name | Barium sulfate |
| Synonyms | Blanc fixe (precipitated), barite, barytes, heavy spar (natural), barium sulphate |
| CAS number | 7727-43-7 |
| Molecular formula | BaSO4 |
| Molecular weight | 233.39 g/mol |
| EC / EINECS | 231-784-4 |
| Colour index | C.I. Pigment White 21 |
| Appearance | White powder |
| Water solubility | Practically insoluble |
| Grades supplied | Industrial, micronized |
| Packaging | Bags, supersacks |
| Documentation | COA & SDS provided on request |
The figures below are representative of a micronized grade. They are indicative rather than guaranteed: distributions vary by grade, source, and lot, and the certificate of analysis for your material governs.
| Parameter | Typical value |
|---|---|
| Mean particle size, D50 | 1.4 µm |
| Top size, D98 | 7 µm |
| Top size, D100 | 12 µm |
| Retained on 325 mesh (45 µm) | 0.0 wt. % |
| Retained on 200 mesh (75 µm) | 0.0 wt. % |
Nothing retained on 325 mesh with a top size of 12 µm places this firmly in the fine filler and extender range rather than the coarse weighting grades used in drilling. Tell us the distribution your formulation needs and we will confirm what is available.
Barium sulfate is the barium salt of sulfuric acid, occurring naturally as the mineral barite and also produced synthetically by precipitation. Two properties define its commercial usefulness, and both are physical rather than chemical.
The first is inertness. Barium sulfate is one of the least reactive materials in common industrial use: insoluble in water, unaffected by acids and alkalis, stable to heat and light, and non-reactive toward the resins, polymers, and solvents it is compounded into. It goes into a system and does nothing except occupy space and add mass.
The second is density. At roughly 4.5 g/cm³ it is far heavier than the other common mineral fillers, which is precisely why it is chosen where weight, sound damping, or radiation attenuation is the objective.
Both names describe barium sulfate, but they are different products and the choice has real consequences.
Natural barite is mined and ground. It is substantially cheaper, and it carries the mineral impurities that come with an ore, which cap its brightness and give a broader particle size distribution with a longer coarse tail. For filler and weighting duties where appearance does not matter, it is the economical answer.
Precipitated barium sulfate, traditionally called blanc fixe, is made by chemical reaction rather than grinding. That yields much finer particles, a narrow and controllable distribution, higher purity, and higher brightness. Coatings and plastics that depend on gloss, colour consistency, and smooth surface finish generally specify it, and pay for it.
When you request a quote, say which you need. A specification that reads only "barium sulfate, 98% min" can be answered with either, and the two will not behave the same in a coating.
With a reactive material, assay tells you most of what you need to know. With an inert one it tells you very little, because the product is not participating in any chemistry. Everything barium sulfate does in a formulation is a physical effect, and particle size distribution controls nearly all of it.
In a coating, fine particles fill between the pigment particles and give a smooth surface that reflects light evenly, so gloss depends directly on the distribution and especially on the coarse tail. A small percentage of oversize particles produces visible defects in a high-gloss finish that no amount of purity compensates for.
In plastics, particle size governs how well the filler disperses and therefore whether it reinforces the polymer or creates stress concentrations that reduce impact strength. In any system, it also sets the maximum loading achievable before viscosity rises beyond what the process can handle.
This is why a barium sulfate specification lists D50, D98, and top size, and why those lines deserve more attention than the assay above them.
The largest use for fine grades. Barium sulfate extends titanium dioxide, which is the expensive component of a white coating, without dulling it; improves gloss and surface hardness; and adds chemical resistance. Automotive primers and industrial coatings rely on it heavily.
Used as a functional filler where density is wanted: sound damping in automotive parts, weight and feel in moulded goods, and improved dimensional stability. Its inertness means it does not interfere with cure systems or degrade at processing temperature.
Coarser barite grades are the standard weighting agent in oil and gas drilling mud, raising fluid density to control formation pressure. This duty uses a different grade from the fine material described above, specified by specific gravity and to industry standards rather than by fine particle distribution.
High-density barium sulfate is incorporated into concrete and plaster for X-ray room shielding, where the barium attenuates radiation and allows a thinner wall than ordinary concrete would need.
Barium sulfate is used in paper coating, in battery plate expanders, as the base for lithopone pigment, and as a white reflectance standard for instrument calibration.
| Filler | Where it wins | Trade-off |
|---|---|---|
| Barium sulfate | High density, complete chemical inertness, good gloss, radiopaque | Considerably more expensive than carbonate fillers and heavy to freight |
| Calcium carbonate | Cheapest common extender, widely available, easy to handle | Reacts with acids and gases off, lower density, less suited to aggressive systems |
| Talc | Platy structure improves barrier properties and stiffness in plastics | Lower density and can reduce gloss; anisotropic behaviour complicates formulation |
| Kaolin clay | Good opacity contribution and low cost, useful in paper and coatings | Lower density and brightness than precipitated barium sulfate, more abrasive on equipment |
How to choose: start by asking whether an inert extender is really all you need. If it is, calcium carbonate is cheaper and usually adequate. Barium sulfate earns its premium in three situations: acidic or chemically aggressive systems where a carbonate would react, applications where density itself is the objective, and high-gloss coatings where the fine, narrow distribution of precipitated material delivers a finish carbonate cannot. Outside those, the cost difference is hard to justify.
Store barium sulfate dry in closed original packaging, off damp floors. The material is chemically stable and does not degrade in storage; the practical problems are moisture pickup causing caking, and fine powder bridging in hoppers.
Barium sulfate itself is essentially non-hazardous because it does not dissolve, but the dust is a nuisance and respirable particulate irritating to the respiratory tract, so use the ventilation and respiratory protection specified in the Safety Data Sheet and avoid dry sweeping of spills.
Keep it away from strong reducing agents and finely divided metals, and check the Safety Data Sheet for the incompatibilities listed for your specific grade before storing it alongside other materials.
One point worth raising with any supplier: soluble barium content. Insolubility is the entire reason barium sulfate is benign, and contamination with soluble barium compounds undoes that. Request the soluble barium figure on the certificate of analysis rather than assuming it was tested.
Barium sulfate is used chiefly as a chemically inert functional filler and extender in coatings, primers, plastics, and rubber, where it adds density, hardness, gloss, and chemical resistance without reacting with the system. Coarser grades are used as a weighting agent in oil well drilling fluids and in radiation shielding concrete. Stratus Chemical supplies industrial and micronized grades across the United States.
The CAS number for barium sulfate is 7727-43-7. Its molecular formula is BaSO4 and its molecular weight is 233.39 g/mol. Its EC number is 231-784-4 and its colour index designation is C.I. Pigment White 21. It is also known as blanc fixe in its precipitated form and as barite, barytes, or heavy spar as the natural mineral.
Both are barium sulfate, but they are made differently and behave differently. Barite is the mined natural mineral, ground to size; it costs less and carries mineral impurities that limit brightness and give a broader particle size distribution. Blanc fixe is chemically precipitated, which produces a much finer, more uniform, and brighter product at higher cost. Coatings and plastics that depend on gloss and colour consistency generally specify precipitated material; cost-driven filler and weighting applications generally use natural.
Because barium sulfate is chemically inert, it does not participate in the system it is added to. Its value comes from physical behaviour, and particle size controls almost all of that: gloss and surface smoothness in a coating, dispersion and mechanical properties in a plastic, settling behaviour in a suspension, and how much can be loaded before viscosity becomes unworkable. Two products at the same purity will perform completely differently at different particle sizes, so read the distribution rather than only the assay.
Barium sulfate is essentially insoluble in water and body fluids, which is why it is the one barium compound considered benign, and why it is used as a radiocontrast agent in medical imaging. Soluble barium compounds are a different matter and are toxic. The practical consequence for a buyer is that soluble barium content is a real specification parameter for barium sulfate, since contamination with soluble barium salts removes the reason the product is safe. Request the soluble barium figure on the certificate of analysis.
Calcium carbonate is far cheaper and is the default filler where cost per unit volume governs. Barium sulfate is chosen where its specific properties are needed: chemical inertness in acidic or aggressive systems where carbonate would react and gas off, high density for sound damping or weighting, better gloss retention in coatings, and radiopacity. If a plain extender will do, calcium carbonate usually wins on cost; if the system is acidic or the density and inertness are the point, barium sulfate is not really substitutable.
Stratus Chemical supplies barium sulfate in bags and supersacks, in industrial and micronized grades, with a certificate of analysis provided for each shipment. Tell us the grade, particle size distribution, brightness requirement, and volume and we will confirm pricing and availability within one business day.
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