美国TA仪器——微量热技术在火炸药研究之应用

Thermal Runaway Process
• Temperature acceleration “the Arrhenius effect” depends on
several factors such as:
– – – – Total energy content of the substance Thermal decomposition properties Thermal conductivity Heat capacity
25.2
25.0
Method: Insert empty ampoule in sample side (A) Change the thermostat temperature by typically 1°C (accuracy 0.01°C) -- blue curve Restore the original temperature Fill ampoule with a known amount of sample and seal it Repeat the temperature change with the same limits -- turquoise curve Calculate Cp from the energy difference between the curves and the sample weight For best accuracy also include a calibration substance with known Cp
3 – samples 1 – reference Sample Flexibility ≤ 1 mL sample Vol. Temp Range: -40 to 150°C
1-48 – samples Sample Flexibility 1-20 mL sample Vol. Temp Range: 15 – 150°C
• Non-specific – anything going on in the sample will be
detected, expected response will not have to be defined
• Sampary • Not dependent on physical state of the sample
Std Vol & Low Vol
SolCal
TAM Air
Scanning Microcalorimetry
Sensitive
mW
Discovery DSC
µW
MC DSC Nano DSC
nW
More Sensitive
Diffusion-bonded Sensor 50-Sample Autosampler Sample Size: up to 20 mg Scan Rate: 0.1 – 100°C/min
tons.
• During transportation the material can be temporarily exposed to elevated
temperatures and in some cases also to elevated relative humidity.
• This might increase the rate of decomposition and thus the rate of heat
Heat loss (conduction, convection, radiation)
Simple model for self-heating
4500 4000 3500
Heat loss d
Heat production
Heatflow (µW)
3000 2500 2000 1500 1000 500 0 0
75
Effect of reduced heat loss
Heat Flow
25
50 Temperature, °C
75
Effect of unstable propellant
Heat Flow
25
50 Temperature, °C
75
General Equation for self-heating substances
• Non-destructive
• Direct • Continuous
Introduction
• Unstable substances
– Percarbonates – Propellants – Peroxides Degradation of energetic materials could result in self-heating and subsequent explosion It is important to secure safety in manufacturing, storing and transportation
(ex. 1 order → Q proportional to P with rate const., k, as proportionality constant)
Heatflow (琺 /g)
Energy (J/g)
Arrhenius plot
5 4,5 4 3,5 3
ln P
2,5 2 1,5 1 0,5 0 0,003
Self-heating and runaway reactions
• If the rate of heat production exceeds the rate of heat loss to
•
the surroundings the temperature of the sample will increase. As a result the decomposition rate will increase and ultimately result in a thermal runaway reaction with a risk for explosion and personal injury.
Energy (J/g)
Time (d)
Heat flow vs. Energy
18000 16000
Heat flow (µW/g)
14000 12000 10000 8000 6000 4000 2000 0 0 5000 10000 Energy (J/g) 15000 20000
“Shows how the reaction rate varies with the extent of reaction”
• •
Transportation and Storage
• Fine chemicals such as explosives, organic peroxides and sodium
percarbonate may under go self-heating under certain conditions.
Pcrit
Heat production P(T)
Heat loss Safe range
Tamb
Tcrit
100 120 140
Tamb
20 40 60 80
Temp (°C)
Effect of increased storage temperature
Heat Flow
25
50 Temperature, °C
1 – sample Max Sensitivity 1 mL or 190 µL cells Temp Range: 2 – 80°C
Introuduction
• Universal – if something is happening in the sample it will
be detected
Microcalorimetry
• Direct measurement of the critical parameter – Heat
• • •
Production rate Reaction parameter α Activation energy by measurement at different temperatures Heat capacity
TAM III - a Modular and Flexible Multichannel Microcalorimetric System
Heat flow vs. Time
18000 16000
flow (µW/g) Heat Heatflow (琺/g)
14000 12000 10000 8000 6000 4000 2000 0 0 1 2 Time (d) Time (d) 3 4
EA 1 1 P(T , a ) P(T0 , a ) exp R T T 0
Direct measurement on new sample
Q(t ) a (t ) H
Arrhenius plots, measurements at several T
• Self heating is associated with a heat balance between heat production
caused by decomposition reactions and heat transfer to the surroundings.
• Transportation is usually performed in large bulk quantities, e.g. several
f(t, P, Q)
Shows how the reaction rate varies with time.