High Purity Metal Silicon Powder: Grades, Mesh Sizes and Chemical Composition

What Metal Silicon Powder Is

Metal silicon powder, also called industrial silicon powder or crystalline silicon powder, is a finely ground powder produced from industrial silicon. Industrial silicon itself is the metallurgical grade of the element, made by reducing quartz in an electric furnace, and the powder is obtained by grinding that material to a defined mesh band. The main component of the powder is silicon, so its behaviour follows that of the element: it is hard, chemically stable at room temperature, and it shares the semiconductor character that makes silicon the base material of the electronics industry.

Industrial silicon is used mainly as an additive for non ferrous alloys. It also serves as a strict alloying agent for silicon steel and as a deoxidiser for special steel grades and non ferrous alloy melts. After further process treatment the same base material can be pulled into single crystal silicon for electronic use, which is why the impurity levels of the powder are controlled so tightly in the first place.

Metal silicon powder is graded by the content of the three main impurities, iron, aluminium and calcium. A lower impurity total means a lower silicon loss in the melt, less slag, and predictable recovery of the silicon addition, which is what a steel or aluminium plant is buying when it specifies a grade instead of simply ordering silicon.

Grades and Chemical Composition

The table gives the analysis series used for metal silicon powder. Each grade is quoted as a minimum silicon content with maximum iron, aluminium and calcium, and the values are expressed in weight per cent of the powder as delivered.

Grade, Si minimum	Si, per cent min	Fe, per cent max	Al, per cent max	Ca, per cent max
Si 99.6	99.6	0.2	0.15	0.05
Si 99.2	99.2	0.4	0.2	0.1
Si 99.0	99.0	0.4	0.4	0.2
Si 98.5	98.5	0.5	0.5	0.3
Si 98.0	98.0	0.6	0.5	0.3
Low grade	95 to 97	total impurity content 3.0 per cent maximum

The silicon figure is a minimum and the impurity figures are maximums, so a batch that analyses at 99.7 per cent silicon with iron, aluminium and calcium below the limits of the ordered grade is acceptable material rather than a different grade. Assay is carried out per lot and reported on the certificate of analysis, which is the document used to release the powder into production.

Mesh Sizes and Particle Distribution

Particle size is quoted in mesh and is chosen to suit the way the powder is fed into the process. Coarser fractions flow freely and are easy to weigh, while finer fractions disperse faster and are used where a high surface area is needed. Chemical silicon powder is available in the following mesh bands:

Si 20-100 mesh

Si 30-120 mesh

Si 40-160 mesh

Si 100-200 mesh

Si 45-325 mesh

Si 50-500 mesh

Refractory silicon powder is supplied in finer cuts, from 150 mesh down to 600 mesh, and uses the same analysis series as the table above. Low grade powder is offered at 200 mesh and 325 mesh with a silicon content between 95 and 97 per cent. A mesh band describes the screening window and not a single particle size, so the particle size distribution of a delivered lot should be read from the screening report rather than inferred from the mesh number alone.

Applications in Steelmaking, Aluminium and the Electronics Industry

As a deoxidiser, silicon combines with dissolved oxygen in the steel bath and the reaction product leaves the melt with the slag, which lowers the oxygen content and improves cleanliness. As an alloying agent it raises strength and electrical resistivity in silicon steel, the flat product used for transformer and motor laminations, where the silicon content is controlled within a narrow band.

In non ferrous metallurgy, aluminium silicon alloys take the powder as a silicon source, and the fine powder dissolves quickly in the aluminium melt. The same material is used in refractory mixes, where fine silicon powder improves the packing density of the lining and takes part in the high temperature reactions that protect the brick surface.

The purity grades matter in the electronics route, where the base material is refined and then pulled into single crystal silicon for wafers. That route consumes material of closely defined chemistry, but it makes the general point that silicon purity is a specification with real process consequences rather than a marketing label.

Packing, Storage and Quality Control

Metal silicon powder is packed in moisture resistant bags or drums so that the material stays dry in transit, since damp powder can generate gas when it is charged to a hot bath and can also form lumps that no longer feed evenly. Storage under cover, away from standing water and with bags kept off the floor, protects the mesh band as much as the chemistry, because the fine fraction is the part that reacts with moisture first.

Quality control is based on lot chemical analysis for silicon, iron, aluminium and calcium, together with screening to confirm the mesh band. Because the grades differ only in the level of the same three impurities, a batch check that ignores one of them can release material that behaves quite differently in the melt, so all three are reported on the certificate.

FAQ: Metal Silicon Powder Grades and Uses

Q: Is metal silicon powder the same as industrial silicon powder?
Yes. Industrial silicon powder, metal silicon powder and crystalline silicon powder refer to the same product, ground from industrial silicon and graded by the content of iron, aluminium and calcium.

Q: How are the grades defined?
Each grade sets a minimum silicon content with maximum iron, aluminium and calcium, from Si 99.6 at the top of the range down to the low grade of 95 to 97 per cent silicon with a total impurity content of 3.0 per cent maximum.

Q: Which mesh sizes are available?
Chemical silicon powder is offered in bands from 20-100 mesh to 50-500 mesh, refractory silicon powder runs from 150 mesh to 600 mesh, and low grade powder is supplied at 200 mesh and 325 mesh.

Q: What is the main use of the powder in steelmaking?
It acts as a deoxidiser for special steel grades and non ferrous melts, and as an alloying agent for silicon steel, where the silicon addition raises strength and electrical resistivity.

Q: Does the powder have semiconductor properties?
Silicon is a semiconductor element and the powder shares the behaviour of the base element, but electronic grade material requires much tighter chemistry and is produced by a separate refining route.

Q: How is a delivered lot checked?
Against the lot certificate of analysis for silicon, iron, aluminium and calcium plus a screening report for the mesh band, with the packing inspected for moisture damage.