Fluorosilicic acid

  • Hydrosilicofluoric acid
  • Fluosilicic acid
  • Silicofluoric acid
  • Hydrogen hexafluorosilicate
Formula
H2SiF6Si
Structure
Description
Colorless to straw yellow liquid with a slightly acrid odor.
Uses
Agent in water fluoridation, in preliminary treatment of hides & skins, & to reduce reflectivity in glass surfaces, disinfectant for copper and brass vessels, impregnating ingredient to preserve wood & to harden masonary, chemical intermediate for aluminum trifluoride, cryolite, & fluorsilicates, electroplating agent for chromium.

Registry Numbers and Inventories.
CAS
16961-83-4
EC (EINECS/ELINCS)
241-034-8
EC Index Number
009-011-00-5
EC Class
Corrosive
S 26 27 45
RTECS
VV8225000
RTECS class
Other
UN (DOT)
1778
Merck
13,4209
Beilstein/Gmelin
16181 (G)
EPA OPP
75305
Swiss Giftliste 1
G-2326
Canada DSL/NDSL
DSL
US TSCA
Listed
Austrailia AICS
Listed
New Zealand
Listed
Japan ENCS (MITI)
Listed
Korea ECL
Listed

Properties.
Formula
F6H2Si
Formula mass
144.09
Melting point, °C
-20.0
Density
1.27 g/cm3
Solubility in water
Soluble

Hazards and Protection.
Storage
The more concnsolution (but not anhydrous liq) can be stored in glass, although some etching will take place around the surface. Usually stored in iron containers.
Handling
All chemicals should be considered hazardous. Avoid direct physical contact. Use appropriate, approved safety equipment. Untrained individuals should not handle this chemical or its container. Handling should occur in a chemical fume hood.
Protection
Workers handling dangerous substances should be supplied with eye and face protection, resp protective equipment, protective clothing and foot and leg protection. Additional protection may be provided by use of lanolin as barrier cream.
Respirators
Wear positive pressure self-contained breathing apparatus (SCBA).
Small spills/leaks
Neutralizing Agents for Acids and Caustics: Lime.
Stability
Fumes in air dihydrate fumes in air 60.97% Solution.
Incompatibilities
Can react with strong acids (such as sulfuric acid) to release fumes of toxic hydrogen fluoride Attacks glass and materials containing silica Reacts exothermically with chemical bases (examples: amines, amides, inorganic hydroxides) Reacts with active metals, including iron and aluminum to dissolve the metal and liberate hydrogen and/or toxic gases Reacts with cyanide salts and compounds to release gaseous hydrogen cyanide.
Decomposition
Dangerous when heated to decomposition, emits highly toxic and corrosive fumes of fluorides.

Fire.
Fire fighting
Fire Extinguishing Agents Not to Be Used: Avoid direct contact between water and acid.Fire Extinguishing Agents: Use dry chemical, carbon dioxide or water spray on adjacent fires.
Fire potential
Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive and/or toxic fumes.
Hazards
Contact with metals may evolve flammable hydrogen gas.
Combustion products
Irritating fumes of hydrogen fluoride may form in fire.

Health.
Exposure limit(s)
TLV (as F): ppm; 2.5 mg/m3 (as TWA) (ACGIH 1995-1996).
Poison_Class
2
Exposure effects
Hyperactive reflexes, painful muscle spasms, weakness and tetanic contractures may be noted due to fluoride induced hypocalcemia. Prenatal fluoride supplementation (2.2 mg NaF or 1 mg fluoride daily) during the last two trimesters of pregnancy has been reported to be safe.
   Ingestion
Epigastric pain, nausea, dysphagia, salivation, hematemesis, and diarrhea may be noted. These effects may be delayed for several hours following exposure. Gi symptoms are noted when 3 to 5 mg/kg of fluoride are ingested.
   Inhalation
Respirations are first stimulated then depressed. Death is usually from respiratory paralysis. Following inhalation, coughing and choking may be noted.
   Skin
Urticaria and pruritus have been reported following exposure to fluoride.
   Eyes
See Inhalation.

First aid
 
   Ingestion
Give large amounts of water; do NOT induce vomiting.
   Inhalation
Remove to fresh air. If breathing is difficult, give oxygen.
   Skin
Remove contaminated clothing and shoes. Flush with water.
   Eyes
Immediately wash with water for 15 min.; call a physician.

Transport.
UN number
1778
Response guide
Hazard class
8
Packing Group
II
 
USCG CHRIS Code
HFS
 
1 Non-oxidizing mineral acids
Std. Transport #
4930026
 
IMO Pollution Category
C
IMO Hazard code
S/P