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| HS Code | 476468 |
| Chemical Formula | Na2SiO3·5H2O |
| Molecular Weight | 212.14 g/mol |
| Cas Number | 10213-79-3 |
| Appearance | White crystalline powder or granules |
| Odor | Odorless |
| Ph 1 Percent Solution | 12.4 |
| Melting Point | 72 °C |
| Specific Gravity | 1.75 |
| Solubility In Water | Readily soluble |
| Vapor Pressure | Negligible |
| Decomposition Temperature | >72 °C |
As an accredited Sodium Metasilicate Pentahydrate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 25 kg net in multi-layer kraft bags with PE liner, securely sealed, labeled with product name and safety information. |
| Container Loading (20′ FCL) | 20′ FCL: palletized 25kg bags, polyethylene-lined, shrink-wrapped, stowed in dry container, secured to prevent moisture and cargo shift. |
| Shipping | Shipping description: **UN 3262, Corrosive Solid, Basic, Inorganic, N.O.S. (sodium metasilicate pentahydrate), Class 8, Packing Group III.** Use UN-approved, leak-tight, moisture-resistant packaging. Keep dry and segregate from acids, food, and incompatible metals. Label as corrosive, and include emergency response documentation for all transport modes. |
| Storage | Store Sodium Metasilicate Pentahydrate in a cool, dry, well-ventilated area inside a tightly sealed, corrosion-resistant container. Protect from moisture and humidity, as it may cake or degrade. Keep away from acids, reactive metals, and incompatible chemicals. Label clearly, and ensure access to an eyewash station for safe handling. |
| Shelf Life | Sodium metasilicate pentahydrate has a shelf life of two years when stored tightly sealed in a cool, dry place. |
Na2SiO3·5H2O (CAS 10213-79-3) enters institutional warewash powder production as a post-tower dry-admix rather than as a slurry component, because the pentahydrate water releases at 72°C and can cause granule bridging in spray-dried base powder. The anhydrous equivalent contains 29.0–29.5 wt% Na2O and 28.0–28.5 wt% SiO2; a 1 wt% aqueous solution at 25°C has pH 12.4–12.8. In phosphate-free automatic dishwashing powders, the addition ratio is controlled at 5–15 wt% of finished powder, while liquid machine dishwashing concentrates carry 1–5 wt% metasilicate pentahydrate after pH adjustment to 11.8–12.4. Total alkalinity expressed as Na2O is held within ±0.3 wt% by mid-batch sampling and acid-base titration, and the ingredient declaration is aligned with EC No 648/2004 Annex VII and the AISE/IKW professional warewash framework. Downstream production uses a ploughshare mixer or ribbon blender in which nonionic surfactant is sprayed at 60–70°C onto the moving powder bed; metasilicate pentahydrate is post-added only after the granulate has cooled below 40°C to prevent hydrate bridging. Compact tablet production is run on a rotary tablet press at 18–30 kN compression force with radial crush hardness at 90–150 N. Terminal product types include automatic dishwashing powders, all-in-one tablets, institutional single-dose sachets, and low-foam machine detergents for flight catering and hospital warewash. The filling line boundary is 60% RH; above that, dehumidified air or 0.5–1.0 wt% hydrophobic silica flow aid is required to maintain flowability.
Alkaline immersion cleaning of cold-rolled steel stampings before zinc phosphating is run with sodium metasilicate pentahydrate at 20–40 g/L of working bath; the powder concentrate is formulated at 15–25 wt% metasilicate pentahydrate, 10–20 wt% sodium carbonate, 5–10 wt% tetrasodium EDTA, and the balance low-foam nonionic surfactant. The working pH is maintained between 11.5 and 12.5 by conductivity-based replenishment, with the soak stage held at 70–85°C for 5–15 min. The preplate cleaning sequence is referenced to ASTM B322-99 and ISO 2080:2008 for surface preparation terminology. The immersion tunnel comprises alkaline soak, warm rinse at 40–50°C, deionized water rinse with conductivity below 10 µS/cm, and hot air drying at 95–110°C. Terminal products include automotive body panels, fasteners, drawn wire, and electroplated brass or zinc-nickel components. The process incompatibility is mixed-metal loading: above 5 wt% zinc die-cast surface area in the load, bath attack becomes measurable as a mass loss exceeding 0.05 mg/cm²·min, requiring a lower-pH metasilicate/borate blend or a segregated line.
| Parameter | Control range | Analytical or equipment method | Outside-range failure mode |
|---|---|---|---|
| Bath temperature | 70–85°C | Immersion thermocouple | Below 65°C: emulsified oil removal drops below 80%; above 90°C: heater scaling |
| Working pH | 11.5–12.5 | Automatic pH electrode with KCl gel electrolyte | Below 11.0: steel discoloration; above 12.8: zinc die-cast attack |
| Sodium metasilicate pentahydrate in working bath | 20–40 g/L | Silicate titration with ammonium molybdate | Below 15 g/L: low alkaline reserve; above 50 g/L: rinse drag-out and silicate scale |
| Oil loading | <2 g/L | Hexane extraction gravimetric | Above 2 g/L: pH decay and soil redeposition |
When cotton knit preparation moves from batch exhaust bleaching to continuous pad-steam processing, the sodium metasilicate pentahydrate dose in the pad liquor is adjusted to 0.8–2.0 g/L, alongside 1.5–3.0 g/L of 35% hydrogen peroxide and 0.5–1.2 g/L caustic soda. The metasilicate acts as a buffered alkali reserve and peroxide stabilizer; decomposition is measured by AATCC TM102 titration, and baths are accepted when residual peroxide after 60 min at 98°C remains above 85% of initial concentration. Color fastness to peroxide bleaching is evaluated according to ISO 105-N02:1993. The pad-steam range is operated at 70–80% wet pickup, steaming at 100–102°C for 20–30 min, followed by hot wash at 85–95°C with 1–2 g/L of a reducing agent to eliminate residual peroxide. Terminal products include bleached cotton jersey, terry toweling, denim preparation, surgical gauze, and cotton/polyester blends. The operational limit is silica scale: above 3.0 g/L metasilicate pentahydrate, calcium and magnesium hardness in process water above 50 mg/L as CaCO₃ precipitates silicate scale on guide rollers and J-box internals, requiring inhibited acid descaling at pH 2.0–3.0.
Pressure casting of vitreous china sanitaryware uses sodium metasilicate pentahydrate at 0.05–0.30 wt% on dry body solids, introduced into the ball mill after the clay has been blunged with water and recycled scrap. The addition is controlled against soluble sulfate interference: process water containing sulfate above 300 mg/L suppresses deflocculation and requires barium carbonate precipitation before electrolyte adjustment. Slip viscosity is measured by rotational viscometer at 20°C and 100 s−1, with acceptable values between 300 and 500 mPa·s at 62–65 wt% solids. Rheology measurement is performed according to ISO 3219-1:2021; fired sanitaryware is assessed under EN 997:2012, and ceramic tile definitions follow ISO 13006:2018. Downstream production includes wet grinding in a porcelain-lined ball mill with alumina media to a residue below 0.5% on a 45 µm sieve, deaeration, pressure casting at 1.2–1.8 MPa, demolding after 20–40 min, and drying to 0.5% moisture. Terminal products include sanitaryware, tableware, ceramic basins, and high-voltage porcelain insulators. The critical threshold is over-deflocculation: above 0.40 wt% metasilicate pentahydrate on dry solids, the slip becomes dilatant and casting rate falls while green strength measured by three-point bending drops below 2.0 MPa, producing handling cracks.
Mixed office waste flotation deinking lines add sodium metasilicate pentahydrate directly in the high-consistency pulper at 0.5–2.0 wt% based on oven-dry fiber, together with 1.0–2.5 wt% hydrogen peroxide, 0.5–1.2 wt% sodium hydroxide, and 0.2–0.5 wt% DTPA. The silicate source stabilizes peroxide, buffers pH between 9.8 and 10.8, and contributes to ink detachment; brightness development is evaluated by ISO 2470-1:2016 diffuse blue reflectance. Downstream production is a two-loop deinking system: pulping at 12–15% consistency and 45–55°C for 20–30 min; pre-flotation in a primary cell bank at 1.0–1.2% consistency; then dispersion through a disc refiner at 40–55 kWh/t specific energy; then post-flotation and washing. Terminal products include recycled newsprint, tissue, and printing/writing paper containing 70–100% recovered fiber. The operational boundary is calcium-induced silicate scaling: process water hardness above 200 mg/L as CaCO₃ and metasilicate addition above 2.5 wt% produce adherent scale on flotation cell rotors and accept lines, requiring acid descaling and reducing ink removal efficiency. Published mill data for this specific configuration are limited; furnish and water chemistry dictate whether the upper addition limit is constrained by brightness gain or by scaling.
Sodium metasilicate pentahydrate is fed as a 1–10 wt% aqueous solution into boiler feedwater or municipal distribution lines at 5–25 mg/L as SiO₂ after softening and before the feedwater pump. The silicate forms a protective film on carbon steel by anodic passivation; film formation is monitored by linear polarization resistance probes with corrosion rate targets below 0.05 mm/year. Compliance for potable water applications is referenced to NSF/ANSI/CAN 60 and for boiler water additives to FDA 21 CFR 173.310. Downstream production in a steam boiler system includes injection through a chemical metering pump with stroke length controlled by feedwater flow, a static mixer downstream of the injection quill, and periodic blowdown to maintain total dissolved solids below 2,000 mg/L. Terminal products are closed-loop cooling water, low-pressure steam boilers, potable water distribution pipelines, and hot water district heating networks. The process boundary is magnesium hardness: above 20 mg/L as CaCO₃ magnesium in feedwater, metasilicate can precipitate as magnesium silicate on boiler tubes; pre-softening to below 10 mg/L total hardness is required. In closed loops, the dosage is reduced to 5–10 mg/L as SiO₂ when the circulating water contains glycol, because glycol degradation products can consume alkaline reserve and destabilize the silicate film.
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Sodium metasilicate pentahydrate is an inorganic alkali compound with the molecular formula Na₂SiO₃·5H₂O, CAS registry number 10213-79-3, EINECS number 229-912-9, and relative molecular mass 212.14 g/mol. The product is supplied as white, free-flowing, spherical granules or coarse crystalline powder with a loose bulk density between 0.85 and 1.05 g/cm³ and an aqueous solubility of approximately 610 g/L at 20 °C. The anhydrous salt fraction contains 29.0–30.0% sodium oxide and 27.8–28.5% silicon dioxide, yielding a molar SiO₂:Na₂O ratio close to 1.0:1.0 and placing the compound in the stoichiometric metasilicate class rather than the higher-ratio silicate glasses. A 1 wt% aqueous solution measured at 25 °C exhibits a pH of 12.3–12.8 per ISO 4316:1977. Thermal dehydration initiates near 50 °C, and the pentahydrate melts in its own water of crystallization at 72.2 °C, a property that distinguishes it from anhydrous forms during storage and make-down. In aqueous systems, the solid dissolves to yield monomeric orthosilicate and oligomeric silicate anions responsible for both alkalinity contribution and surface-modifying reactivity in end-use applications.
Commercial production of sodium metasilicate pentahydrate proceeds by high-temperature fusion of silica sand with sodium carbonate at 1400–1500 °C in regenerative cross-fired furnaces, followed by dissolution of the resulting glass in demineralized water and continuous crystallization from supersaturated mother liquor in scraped-surface crystallizers. The crystallized mass is screened, fluid-bed dried at 40–50 °C, and packed into moisture-barrier multiwall paper bags. The specification parameters in Table 1 represent consensus values for industrial detergent and water-treatment grades across major producing sites. Batch-to-batch variation in Na₂O content is typically maintained within ±0.3 wt% through continuous online refractometry of the liquor feed. Analytical verification relies on acid-base titration and gravimetric silica determination as specified in ASTM D501-03, while pH is determined potentiometrically according to ISO 4316:1977. Granulometry is controlled by sieve analysis per ISO 2591-1:1988, with maximum retention on an 850 µm sieve of 5 wt% and a fines fraction below 150 µm limited to 10 wt% to reduce dust generation during transfer.
| Parameter | Typical Range | Analytical Reference |
|---|---|---|
| Na₂O content | 29.0–30.0 wt% | ASTM D501-03, acid-base titration |
| SiO₂ content | 27.8–28.5 wt% | ASTM D501-03, gravimetric dehydration |
| Water of crystallization | 42.0–44.0 wt% | Loss on ignition at 550 °C to constant mass |
| pH, 1 wt% aqueous, 25 °C | 12.3–12.8 | ISO 4316:1977, potentiometric |
| Water-insoluble matter | ≤ 0.1 wt% | Filtration through Whatman Grade 40, drying at 105 °C |
| Iron | ≤ 50 mg/kg | ICP-OES |
| Loose bulk density | 0.85–1.05 g/cm³ | Gravity-fed 1 L graduated cylinder, no tapping |
| Sieve retention, 850 µm | ≤ 5.0 wt% | ISO 2591-1:1988 |
In large-format powder detergent plants operating horizontal ribbon blenders with working capacities between 1.5 and 2.0 m³, sodium metasilicate pentahydrate is introduced as a dry-blended builder at inclusion levels of 2–12 wt% depending on soil load classification. The compound contributes an Na₂O alkalinity reserve of 29.2% by mass, which maintains wash liquor pH above 11.2 at 0.5 wt% total detergent dosing even after acidic fatty soils from proteinaceous food residues are neutralized during the first 10–15 minutes of the wash cycle. Silicate anions released during dissolution sequester calcium and magnesium hardness by forming colloidal silicometallic complexes, reducing anionic surfactant precipitation in process water at 250–400 mg/L CaCO₃ equivalent hardness. On aluminum food-contact surfaces, sodium metasilicate pentahydrate passivates the oxide layer at dissolved silicate concentrations between 50 and 500 mg/L SiO₂; below this threshold, the alkaline environment can promote localized pit initiation in chloride-bearing washwaters. Formulators employing proteolytic enzymes must cap metasilicate loading so that liquor pH does not exceed 10.5, above which subtilisin-type protease activity declines rapidly, with published half-life data for commercial stabilized proteases remaining formulation-dependent. Liquid slurry make-down in agitated tanks of 5–15 m³ demonstrates a moderate exotherm of 8–12 °C per 10 wt% addition, which is substantially lower than the exotherm measured with anhydrous material.
The differentiation among sodium metasilicate hydration states is determined by water of crystallization content and its consequences for dry blending, dissolution exotherm, and storage stability. Anhydrous sodium metasilicate (Na₂SiO₃, CAS 6834-92-0) contains no structural water, provides 50.8 kg Na₂O per 100 kg product, but releases a dissolution exotherm that can raise local liquor temperature by 15–25 °C during slurry make-down. Pentahydrate carries 42.4% water of crystallization, delivering 29.2 kg Na₂O per 100 kg product while moderating the exotherm and permitting faster dissolution in ambient water without external cooling. Nonahydrate (CAS 13517-24-3) contains 57.0% water, delivers 21.8 kg Na₂O per 100 kg, and dissolves with minimal exotherm but is markedly more prone to caking in storage atmospheres exceeding 60% relative humidity. Compared with liquid sodium silicate solutions, sodium metasilicate pentahydrate maintains a fixed 1:1 SiO₂:Na₂O ratio and a higher pH per unit Na₂O, which is advantageous where a compact solid alkalinity source is required. Sodium orthosilicate, with an Na₂O:SiO₂ ratio of 4:1, is significantly more aggressive toward aluminum and skin and is reserved for heavy-duty degreasing operations where high causticity is the primary requirement.
| Property | Anhydrous Na₂SiO₃ | Pentahydrate Na₂SiO₃·5H₂O | Nonahydrate Na₂SiO₃·9H₂O |
|---|---|---|---|
| CAS registry number | 6834-92-0 | 10213-79-3 | 13517-24-3 |
| Water of crystallization | 0 wt% | 42.4 wt% | 57.0 wt% |
| Relative molecular mass | 122.06 g/mol | 212.14 g/mol | 284.20 g/mol |
| Na₂O delivery per 100 kg product | 50.8 kg | 29.2 kg | 21.8 kg |
| Caking tendency at 65% relative humidity | Low | Low to moderate | High |
After horizontal concrete surfaces are mechanically ground to a 200-grit resin-bond diamond finish, a diluted aqueous solution of sodium metasilicate pentahydrate at 30–40% solids is applied by low-pressure sprayer at a rate of 0.15–0.30 L/m². The silicate anion reacts with free portlandite in the cement paste pore network to generate additional calcium silicate hydrate gel, densifying the upper 2–6 mm of the slab. Field measurements on concrete finishing lines indicate that surface hardness, assessed with a Type N rebound hammer, typically increases by 8–15% after 7 days of cure at 20 °C and 50% relative humidity, although published controlled-study data for this specific formulation configuration is limited. Compared with lithium silicate densifiers, sodium metasilicate pentahydrate exhibits slower penetration because of larger silicate oligomers in solution but carries substantially lower raw material cost per square metre. Over-application or failure to remove residual liquid after 20–30 minutes of reaction produces a white sodium carbonate surface bloom that must be mechanically abraded rather than water-rinsed. Production-floor observations indicate that a Na₂O content fluctuation of ±0.3 wt% between supplier lots alters open time sufficiently to require 5–10% adjustment of dilution water to stabilize the gelation front.
When boiler feedwater with low total alkalinity is conditioned for corrosion control in mild steel steam-raising systems, sodium metasilicate pentahydrate is fed as a 0.5–2.0% aqueous stock solution through positive-displacement metering pumps into the deaerator storage section or directly into the feedwater line upstream of the economizer. Residual silicate is maintained between 2 and 20 mg/L as SiO₂ in the boiler drum. Under 21 CFR 173.310, sodium metasilicate is recognized as a boiler water additive for steam contacting food, provided treatment follows current good manufacturing practice. The compound is evaluated under NSF/ANSI/CAN 60 for drinking water treatment chemicals at site-specific maximum feed rates. The protective film formed on carbon steel consists of an iron-silicate complex that suppresses oxygen pitting in the temperature range 120–180 °C. Operational boundary: total silica in boiler water must remain below 50 mg/L at drum pressures exceeding 60 bar to prevent silica volatilization and deposition on superheater tubes and turbine blades.
In hydrogen peroxide brightening of thermomechanical pulp, sodium metasilicate pentahydrate is supplied to stock preparation at 0.5–3.0% on oven-dry pulp as a stabilizer and alkalinity source for peroxide systems operating at pH 10.5–11.2. Silicate anions complex transition metal ions, particularly iron and manganese, which would otherwise catalyze wasteful peroxide decomposition; for a furnish containing 50 mg/kg extractable manganese, process-scale bleaching trials with metasilicate at 2.0% on pulp demonstrate reduced peroxide consumption relative to unstabilized controls, with the magnitude depending on transition metal loading and liquor carryover. In textile desizing, the compound is applied in kier boiling at 5–10 g/L to saponify waxes and swell cellulosic fibres prior to oxidative bleaching. Handling of the dry product requires moisture exclusion: prolonged storage above 65% relative humidity initiates surface dissolution and interparticle fusion, producing hard agglomerates that resist pneumatic conveying and rotary valve feeding. The compound is incompatible with concentrated acids, which precipitate gelatinous silicic acid and can block metering pumps and spray nozzles. Ammonia-liberating nitrogen compounds must not be combined with metasilicate in closed mixing vessels, as amine vapour evolution creates pressure hazards.
