Sodium Metasilicate Pentahydrate vs Anhydrous — Which Grade to Buy
Anhydrous and pentahydrate are different specifications. Anhydrous dry matter is 95.0–98.5%. Pentahydrate dry matter is 56–60%. Shelf life on each approved TDS is 12 months from the date of manufacture when stored in the original, unopened packaging under the recommended storage conditions.
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Short answer
Buy pentahydrate if you dissolve the product in water at ambient temperature and the 56–60% dry-matter band suits the formula. Buy anhydrous if you dry-blend it into a powder or want the 95.0–98.5% dry-matter band. Anhydrous (Na₂SiO₃, CAS 6834-92-0) is specified at SiO₂ 45.0–48.0% and Na₂O 50.0–51.5%. Pentahydrate (Na₂SiO₃·5H₂O, CAS 10213-79-3) is specified at Na₂O 28–30% and SiO₂ 28–30%.
Key Specification Differences
The decisive difference is the published dry matter. Anhydrous sodium metasilicate is specified at SiO₂ 45.0–48.0%, Na₂O 50.0–51.5% and dry matter 95.0–98.5%. Pentahydrate is specified at Na₂O 28–30%, SiO₂ 28–30% and dry matter 56–60%. Dry matter is Na₂O plus SiO₂.
Iron is typical ≤100 ppm on anhydrous forms and typical ≤80 ppm on pentahydrate. It is not a specification. Compare the published Na₂O, SiO₂ and dry-matter bands.
Dry matter is the published comparison
Pentahydrate dry matter is 56–60% (Na₂O+SiO₂). Anhydrous dry matter is 95.0–98.5%. Freight is paid on the tonnes shipped.
Ask for both forms on one RFQ if the plant can trial either. The quotation states the form you name.
Handling, Dissolution and Hot-Climate Storage
Anhydrous sodium metasilicate is specified with dry matter 95.0–98.5% and is supplied as white powder or white granules. It is the form for dry-blend systems. Shelf life is 12 months from the date of manufacture when stored in the original, unopened packaging under the recommended storage conditions.
Pentahydrate appearance is typical white granules or white powder. Melting point is typical 72–73°C. Shelf life is the same 12 months from the date of manufacture when stored in the original, unopened packaging under the recommended storage conditions. Storage is: keep tightly closed in a cool, dry, ventilated warehouse; protect from moisture and keep away from acids.
How to Choose Between Them
Choose pentahydrate when you dissolve it in water at room temperature and want it in solution within minutes; when your formulation is a liquid — degreaser, floor cleaner, bottle wash, boiler treatment; when your warehouse stays below normal summer temperatures and turns stock over within months; and when freight is a small part of your landed cost.
Choose anhydrous when you dry-blend it into a powder or tablet, where added water would cake the mix; when the goods will pass through a hot port or warehouse; when you pay freight on a long route and want to move fewer tonnes of water; and when your dosing system feeds granules or beads by weight and needs free-flowing material.
Switching From One Grade to the Other
Confirm any change of form in your own trial.
Both forms ship in a 25 kg PP woven bag with PE liner or a 1,000 kg FIBC. Without pallets, 25 kg bags load at 27 mt per 20-foot container. On pallets, anhydrous 25 kg bags load at 24 mt and pentahydrate 25 kg bags load at 22 mt. 1,000 kg bags load at 20 mt. When sending an RFQ, state the form, CAS number, packing, and destination port.
FAQ
How do I compare anhydrous and pentahydrate?
Compare the published bands. Anhydrous is Na₂O 50.0–51.5%, SiO₂ 45.0–48.0% and dry matter 95.0–98.5%. Pentahydrate is Na₂O 28–30%, SiO₂ 28–30% and dry matter 56–60%.
Can I substitute one grade for the other?
Only after a trial in your own process. Anhydrous dry matter is 95.0–98.5%. Pentahydrate dry matter is 56–60%.
Which grade ships more efficiently?
Anhydrous dry matter is 95.0–98.5%. Pentahydrate dry matter is 56–60%. Loading without pallets is 27 mt of 25 kg bags per 20-foot container for both. On pallets, anhydrous 25 kg bags load at 24 mt and pentahydrate 25 kg bags load at 22 mt.
Why did my pentahydrate arrive caked?
Pentahydrate melting point is typical 72–73°C. Storage on the TDS is: keep tightly closed in a cool, dry, ventilated warehouse; protect from moisture and keep away from acids. Shelf life is 12 months from the date of manufacture when stored in the original, unopened packaging under the recommended storage conditions.
Do the two grades have the same CAS number?
No. Pentahydrate is CAS 10213-79-3; anhydrous is CAS 6834-92-0. Put the CAS on your RFQ and your import documents so the quotation and the customs entry refer to the same product.
Ready to RFQ
A quotation is easier to price with application, monthly quantity (MT), packing, destination port and buyer type. Grade is optional. The form can be sent with an email or a WhatsApp number. Approved TDS, SDS and stamped COA samples are on Downloads; a shipment COA is issued per order. No prices are shown on the form.
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