Properties - Walter Schottky Institut

Gases
Dr. Ralf Meyer
Walter Schottky Institut
Technische Universität München
The danger is real !
Fire damage due to Silane
Burnt out scrubber after silan was admitted too quickly
Walter Schottky Institut
Technische Universität München
Risk categories due to gases
Can be toxic
Flammable / Explosive
Arsine
AsH3
Hydrogen
H2
Phosphine
PH3
Silane
SiH4
Methane
CH4
Chemical weapons !
Oxygen
O2
Can be irritant
Can cause suffocation
Chlorine
Cl2
Nitrogen
N2, LN2
Helium
He
Boron trichloride BCl3
Carbon dioxide CO2
Silicon
tetrachloride
Tetraflouromethane
SiCl4
Irritant when combined
with moisture
(Mucous membranes)
CF4
Dichlorodifluoromethane
CCl2F2
Sulfur
hexafluoride
SF6
Gases from all categories are used in the WSI !
Walter Schottky Institut
Technische Universität München
Properties of toxic gases
Arsine (AsH3)
Employed in the first world war as a chemical weapon (Grünkreuz)
Properties:
-
Gaseous under NTP, colourless
Smell: Garlic-like
Used as liquified gas (15 bar at 20°C)
Explosive (Vol.% in air: 4 - 78)
Relative density cf. air: 2.7
Toxicity:
-
Lethale dose: 20 ppm over 50 min (very poisonous)
Poisonous: 3 - 10 ppm after several hours
Smell threshold: ca. 1 ppm
MAK-value: 0.05 ppm ( = Alarm threshold)
Effects:
Damage to the red blood cells and the central
nervous system (delayed response)
Walter Schottky Institut
Technische Universität München
Properties of toxic gases
Phosphine (PH3)
Used as a poison for vermin
Properties:
-
Toxicity:
- Lethale dose: 20 ppm over 50 min (very poisonous)
- Smell threshold: ca. 1 ppm
- MAK-value: 0.1 ppm ( = Alarm threshold)
Effects:
Irritates the eyes, skin and respiratory system;
Damages the central nervous system;
Delayed pulmonary odema possible
Walter Schottky Institut
Gaseous under NTP, colourless
Smells of rotten fish
Used as liquified gas (35 bar at 20°C)
Spontaneously flammable (Vol.% in air: 1 - 100)
Relative density cf. air: 1.2
Technische Universität München
Properties of irritant gases
Chlorine (Cl2, poisonous)
Chemical weapon using in 1st world war (Chlorine gas)
Properties:
- Yellow - green gas (under normal conditions)
- Pungent smell
- Inflammable, but very, very reactive
- Relative density cf. air: 2.5
Toxicity:
- Lethal dose: 5000 ppm ( = 0.5%, poisonous)
- Smell threshold: ca. 0.1 … 10 ppm
- MAK-value: 0.5 ppm ( = Alarm value)
Effects:
Poisonous upon inhalation, deadly in large amounts;
strong irritant when combined with moisture
 Extreme irritant to respiratory system, eyes, skin
and digestive system.
Walter Schottky Institut
Technische Universität München
Properties of irritant gases
Silicon tetrachloride (SiCl4)
Properties:
-
Colourless, volatile liquid
Suffocating smell
Formation of HCl (!) when combined with moisture
Relative density cf. air: 5.9
Boron trichloride (BCl3)
Properties:
- Colourless gas
- Suffocating smell
- Formation of hydrochloric and boric acid,
when combined with moisture
- Used as liquified gas (1,3 bar at 20°C)
- Relative density cf. air: 4.1
Walter Schottky Institut
Technische Universität München
Eigenschaften der ätzenden Gase
Adverse health effects due to formation of the acids
HCl
Properties:
- strongly corrosive
- Relative density cf. air: 1.3
Toxicity:
- Smell threshold: ca. 10 ppm
- Alarm threshold: 10 ppm
Effects:
irritant when combined with moisture
 Irritation of mucous membranes
(eyes and respiratory passages)
Walter Schottky Institut
Technische Universität München
Metallorganic compounds
Precursors for gas phase epitaxy (MOVPE)
Composition:
metal + organic rest
e.g.: Tri Methyl Indium = TMIn, In(CH3)3
Compounds used in WSI: TMGa, TEGa, TMIn, TMSb, DMZn
Properties:
- coulorless, oily liquids (TMIn solid)
- vapour pressure < 100 mbar
- Spontaneously flammable, when exposed to air
Effects:
Formation of toxic metallic dusts due to combustion
 pulmonic harms
Extinguish fire with sand, powder or CO2 !
(not with water or halon!)
Walter Schottky Institut
Technische Universität München
Gaslager im Untergeschoss
AsH3, PH3
Chlorines
SiH4, CH4, H2
…
Aisle for maintenance purposes (KEEP FREE!)
Walter Schottky Institut
Gas storage
Technische Universität München
Critical labs
Upper floor
P H3 / SiH4
B2H6 / SiH4
H2
D2
N2 04
RIE
Clean room
Cl2
BCl3
SF6
RIE
Cl2
SiCl4
SiH4
…
MOVPE
AsH3
PH3
MO‘s
H2
Seminar room
Ground floor
Walter Schottky Institut
Technische Universität München
Critical labs ZNN
WSI
Seminarraum
Gaslager H2, N2
Standort
Cl
/ SF6
2 / BCl3Gasflaschen
RIE
Reinraum
0.018
Walter Schottky Institut
Technische Universität München
Safety installations
Passive
- Separate room with fire resistant gas storage cabinets (F90)
- Helium leak checked, partly doublewalled tubes
- „normally closed“ valves
- Flow delimiter in connectors of gas cylinders
Active
- Permanent monitoring of recirculating and exhaust air with
automatic shutdown of all systems, closing of all gas cylinders
and alarm of the fire brigade
- Powerful ventilation
- Usage of waste gas cleaning systems
(passive dry bed chemisorber)
Walter Schottky Institut
Technische Universität München
Life-safety system
Walter Schottky Institut
Technische Universität München
Life-safety system (e.g. MOVPE)
Walter Schottky Institut
Technische Universität München
Behaviour in case of an emergency

Only one acoustic alarm, no distinction between gas or fire alarm
Fire department receives separate signals
1
Bring system or experiment in safe state !
2
Take care of guests, students, service engineers, …
3
Leave the building uninterrupted (1 min)

Meeting point:
- Good weather:
between WSI and department of physics, LMU
- Bad weather:
entrance area Physik II
Walter Schottky Institut
Technische Universität München