SODIUM METASILICATE
International Programme on Chemical Safety
Poisons Information Monograph 500
Chemical
1. NAME
1.1 Substance
Sodium Metasilicate
1.2 Group
Silicon oxide, sodium compound
1.3 Synonyms
Disodium Metasilicate; Sodium Silicate;
Sodium Metasilicate, 9-hydrate;
Sodium Metasilicate, anhydrous Soluble Glass;
Waterglass
1.4 Identification numbers
1.4.1 CAS number
6834-92-0 (anhydrous)
1.4.2 Other numbers
10213-79-3 (pentahydrate)
13517-24-3 (nonahydrate)
RTECS Number VV9275000 (sodium metasilicate)
(IPCS/CEC,1993).
1.5 Brand names, Trade names
To be completed by each Centre using the monograph.
1.6 Manufacturers, Importers
To be completed by each Centre using the monograph.
2. SUMMARY
2.1 Main risks and target organs
Sodium metasilicate is strongly irritating to the skin,
eyes and respiratory tract. Acute exposures involving the
inhalation of dusts may result in irritation of the
respiratory tract and corrosive damage may result from
contact with mucous membranes. Prolonged exposures can lead
to inflammatory changes and ulcerative problems in the mouth.
Possible bronchial and gastrointestinal problems can occur,
depending upon concentration and duration of exposure.
2.2 Summary of clinical effects
Initial clinical manifestations of acute ingestion can
include dysphagia, drooling, pain and haematemesis. Oral,
oesophageal, and gastric burns may be present. Extensive
mucosal damage leads to fever, tachypnoea, tachycardia,
hypertension, and shock. Acute complications include
aspiration pneumonia, burns of the epiglottis and vocal
cords, and laryngeal obstruction. Acute perforation of the
oesophagus or stomach with mediastinal or peritoneal abscess,
sepsis, and death may occur. Possible longterm sequelae of
acute exposure include oesophageal stricture, squamous cell
oesophageal cancer, vocal cord paralysis, and pyloric
stenosis.
2.3 Diagnosis
Diagnosis is based on a history of exposure to this
corrosive agent and characteristic findings of skin, eye, or
mucosal irritation or redness and the presence of injury to
the gastrointestinal tract. Victims with oral or oesophageal
injury nearly always have drooling or pain on swallowing.
2.4 First-aid measures and management principles
Inhalation: Remove from exposure; give supplemental
oxygen if required. Skin and eyes: Remove all affected
clothing and wash skin and irrigate eyes with copious water
or saline.
Ingestion: Immediately give water or milk to drink if the
patient is able to swallow. The volume administered should
not be so excessive as to cause gastric distension and induce
vomiting. Do not induce emesis or give pH-neutralising
solutions such as dilute vinegar or bicarbonate. If
oesophageal or gastric perforation is suspected, obtain
immediate surgical or endoscopic consultation.
3. PHYSICO-CHEMICAL PROPERTIES
3.1 Origin of the substance
Fusing silica (sand) with sodium carbonate at 1400°C
produces sodium metasilicate. The various hydrates of sodium
metasilicate, range from the anhydrous to the nonahydrate,
with the anhydrous and the penta- and nonahydrates being the
most common forms (Clayton & Clayton, 1993).
3.2 Chemical structure
Chemical formula: Na2SiO3.nH2O
Relative molecular mass 122.07 anhydrous
212.15 pentahydrate
284.21 nonahydrate
(Clayton & Clayton, 1993).
3.3 Physical properties
3.3.1 Colour
Colourless to white or grayish white
3.3.2 State/Form
Solid-crystals
3.3.3 Description
The anhydrous and the pentahydrate are produced
as amorphous beads, whereas the nonahydrate appears as
efflorescent sticky crystals.
Melting point 1089°C anhydrous
72°C pentahydrate
47.8°C nonahydrate (Clayton & Clayton,
1993).
pH of a 1% aqueous solution is about 13 (Clayton &
Clayton, 1993).
Solubility: The metasilicates are highly water soluble
(Clayton & Clayton, 1993).
Insoluble in alcohol, acid and salt solutions
(Budavari, 1989).
Flammability: Not combustible (IPCS/CEC, 1993).
Stability: Solutions of sodium metasilicate, when
heated or acidified, are hydrolysed to free sodium
ions and silicic acid (Clayton & Clayton, 1993).
3.4 Hazardous characteristics
Corrosiveness: In moist air it is corrosive to metals
like zinc, aluminium, tin and lead, forming hydrogen gas
(IPCS/CEC, 1993).
Reactivity: The substance is a strong base, it reacts
violently with acid (IPCS/CEC, 1993).
4. USES/CIRCUMSTANCES OF POISONING
4.1 Uses
4.1.1 Uses
Soap; detergent; bath/washing product
4.1.2 Description
A major use is as a builder (a material that
enhances or maintains the cleaning efficiency of the
surfactant, principally by inactivating water
hardness) in soaps and detergents. It is also used
extensively as an anti-corrosion agent in boiler-water
feed (Clayton & Clayton, 1993).
4.2 High risk circumstance of poisoning
Unintentional ingestion by children of a dishwashing
detergent directly from the container or of the residue from
an automatic dishwasher soap compartment. Intentional
ingestion.
4.3 Occupationally exposed populations
Factory workers involved in formulation and packaging of
sodium metasilicate or metasilicate containing products.
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