2. CONTENTS
INTRODUCTION
TEMPERATURE MEASUREMENT
LYOPHILIZATION PROCESS
PRINCIPLE OF FREEZE DRYING
PROBLEMS OF FREEZE DRYING
PROPOSED SYSTEM
PLASMA SPUTTERED TC
REALIZATION
CONCLUSION
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3. INTRODUCTION
Describes the realization of temperature sensor
Based on plasma sputtered thermocouple
Realized in vacuum with quite pure materials
Negligible oxidation
Accurate measurement Made inert
Thickness of few nanometers
Application in lyophilization process
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4. TEMPERATURE MEASUREMENT
Temperature is local parameter
Thermocouples for temperature measurement
Can be less invasive
Consumes negligible power
Realize in flexible and cylindric probes
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5. With these advantages, but thermocouple
Alter temperature distribution
Metalic materials react with surrounding environment
These 2 problems occur in preeze drying of
lyophilization process
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6. LYOPHILIZATION PROCESS
Process of drying a substance by sublimation
Preliminary frozen at -20⁰c
Pressure reduced to few pascals
So sublimates slowly
Leaving dried powder
Most pharmaceutical powders are made by this
method
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7. Principle of freeze drying
Drying by sublimation
Frozen liquid to gaseous state
Transfer of ice to water vapour
Function of pressure and ice temperature
Expensive
Requires specialized equipment
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8. Freeze drying consists of 3 stages
Freezing
Primary drying
Secondary drying
During freezing solution- solid
During 1⁰ drying ice removed by sublimation
2⁰ drying is for isothermal desorption
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9. Advantages of freeze drying
• Do not need refrigeration
• Can be stored at ambient temperatures
• Can be completely reconstituted with water
• Stable over 2 year life
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11. PROBLEM OF FREEZE DRYING
When pressure reduced, drying begins
Product tyemperature decreases
Sublimation is endothermic
Most of energy is by radiation
ie, quite low at low temperature too
Lead to temperature of product go down -50⁰ c to
-70 ⁰c
Turns long lyophylization times
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12. Possible solution is
To model drying process
Supply heat
But this lead to another problem
Thermal conductivity between shelf and product is
higher
ie ,sublimatiom is slower
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13. A good and easy solution is that
To monitor the temperature inside the product in
several points within the chamber
But it will alter drying proceess
And intoxicate the material
So possible solution is…..
To measure temperature near to product
Not in contact
Eg: on external wall of vial
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14. PROPOSED SYSTEM
Fig. 1. Two thermocouples deposited on the external part of a
vial tocheck the deposition effectiveness on curved surfaces.
The vial shows twocopper/copper-nickel thermocouples both
with a junction at the top of the vial, but with the other junction
at different heights. In the picture also the wires used to collect
the thermocouple voltage
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15. Extremely thin and sealed TC
Deposited via plasma sputtering
For local measurement- thin TC
Low response time
Sealed devices for specific applications
Present proposal uses a protective Siox thin film
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16. Thickness of few tens of nm
To avoid contact between metal and drying substance
This way TC can deposited on vial internal surface
Able to follow temperature changes accurately
Without altering the lyophilized material
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17. PLASMA SPUTTERED
THERMOCOUPLE
A TC can be made by 2 different materials
To form 2 junction
To measure voltage
Proportional to temperature difference
Materials are…
iron, copper, constantan, chromel, alumel, platinum,
rhodium; each couple having specific electrical and
chemical properties.
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18. Several metal couples for drying process
Choice related to
Thermoelectric power
Easiness of plasma deposition
Chemistry of TC/Siox interface
In order to ensure good adhesion
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19. •To optimize plasma process few considerations
are
Plasma pretreatment to improve adhesion
To reduce no: of defects of deposited coating
To improve barrier properties
Plasma pretreatment carried out in noble as well as
reactive gases
Such as oxygen and hydrogen
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20. •According to metal
Iron –pretreatment in oxygen plasma
Aluminum- metal surface reduction by hydrogen glow
discharge
All these require 2 step deposition
But Cu and Ni not require surface modification
So all specimens made of T type TC(Cu/CuNi)
Thermoelectric power -50 μV/◦C
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21. Thickness of active materials
Thin layer allows non invasive sensors
But high electrical resistance
Thick layer alows more invasive
Produces low resistance, but large sputtering times
So here proposed range 50nm to 500nm
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22. REALIZATION
To realize Cu/CuNi strips the active materials
deposited on glass substrate
Glass substrate is for good adhesion
Depositions done at
room temperature
100 w of input power
by argon as discharge gas
Deposition rate forCu and constantan .1nm/s
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23. Siox protective layer to coat thermocouple
Without exposing samples to air and environmental
contaminations
2 step deposition is required for deposit Siox loyer
The SiOx film can be deposited by using a
plasma which is fed with constant tetraethoxysilane
(TEOS),oxygen and argon flow rate of 1, 20 and 20
sccm respectively, at 5 Pa of pressure and 100 W of
input power.
The thickness in this case was selected to about 200
nm.
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24. Fig. 4. The first prototype of inert thermocouple (ITC). The picture shows
three strips which are sputtered on a flat glass to form two thermocouples.
The TCs are covered by a 185 nm layer of SiOx which is the responsible
for the translucent aspect
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25. Fig. 7. A FESEM image of the cross section of the constantan/SiOx
interface. The constantan thickness is of about 150 nm, while the
SiOx layer has a thickness of about 185 nm. The SiOx protecting
layer appears quite compact so that a quite good protection should
be expected.
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26. CONCLUSION
An innovative way to create non invasive temperature
sensor
Temperature mapping can be obtained
Accurate measurement
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