HiBarSens: Tunable diode laser spectroscopy for ultra barrier measurement

Transcription

1 HiBarSens: Tunable diode laser sectroscoy for ultra barrier measurement AIMCAL Web Coating & Handling Conference 2012 October 23, 2012 Myrtle Beach / USA Harald Beese, Fraunhofer IWS Dresden, Germany Fraunhofer

2 Outline High sensitive ermeation measurement system for WVTR <10-3 g m -2 d -1 based on TDLAS sensors Comarison of isostatic and quasi-isostatic ermeation measurement modes in one setu Contribution to understand water vaor ermeation measurement rocesses at ultra low rates Presentation of a new ultra sensitive diffusion controlled WVTR measurement mode Fraunhofer

3 Why measurements of WVTRs? Demands on barrier roerties Food industry Pharmaceutical industry Anorganic solar cells Organic solar cells Water transmission Permeationsrate rate WVTR g[h 2 O]m g[h -2 d -1 2 O] m -2 d ,1 0,01 1E currently measurable by standard methods 1E-4 Vacuum isolation aneele Organic LED 1E-5 1E ? Fraunhofer 3

4 WVTR of 10 x g m -2 d -1 is equivalent to: Water with the a weight of: Industry standard WVTR Ameba Head of a in er day and square meter samle! Fraunhofer 4

5 General asects of ermeation measurements Categorization of ermeation measurement setus absolute ressure mode quasi isostatic mode (accumulation) isostatic mode (carrier gas) ,2 konstant 1,2 0 1,2 = 0... total ressure 1 ermeate comartment 2 feed gas comartment Pressure difference Closed Volumes similar ressures Closed volumes No ressure difference Gas exchange to atmoshere ossible Fraunhofer 5

6 High sensitive WVTR measurement technologies Coulometric Ca-Test Isostatic setu P 2 O 5 Sensor Signal caused by electro-chemical reaction of water LOD(WVTR): 5x10-4 g m -2 d -1 Prearation of thin Ca-coating Signal caused by change of transarency resulting from reaction of Ca + 2H 2 O Ca(OH) 2 + H 2 LOD(WVTR) 1x 10-7 g m -2 d -1 Others Tritium: LOD(WVTR) 2,4 x 10-8 g m -2 d -1 (Radioactive!) GC: LOD(WVTR) 1x 10-7 g m -2 d -1 (Accumulation!) Pressure: LOD(WVTR) 2x10-4 g m -2 d -1 (Accumulation!) Dunkel, (2005): A new method for measuring ultra-low water-vaor ermeation for OLED dislays. In: J. Soc. Inf. Dislay 13 (7), S Nisato, G (2008): Evaluating High Performance Diffusion Barriers: the Calcium Test ICEPT-HDP. Piscataway, NJ: IEEE Nörenberg, H. (Hg.) (2007): Permeation Measurements at g/m2/day and below for Alications in Flexible Electronics. ro flex 2007, Fraunhofer 6 Schmidt, M.M (Hg.) (2011): Accumulating gas-chromatograhic ermeation test (ACP) for the measurement of ultra-low water vaor transmission rates. LOPE-C Frankfurt, M.

7 What determines the sensitivity of a WVTR measurement? N 2 + H 2 O Lower limit of detection of the Sensor Adsortion / desortion of moisture H 2 O N 2 Sealing of the test cell Fraunhofer 7

8 temerature q / C VH3 The exerimental setu gas inlet max. 3bar VH1 urifier VH2 mass flow controller To measurement modes in one setu Active samle sealing Two ressure H 2 O generator High temerature stability by external thermostat measurement cell laser feed gas comartment exhaust gas VH4 laser temerature stability +/- 0,05K :00 36:00 72:00 108:00 144:00 180:00 time t / hh:mm VH3 VH4 ermeate comartment Fraunhofer 8

9 Transmission Tunable Diode Laser Absortion Sectroscoy (TDLAS) Princile of TDLAS Concentration measurement by absortion sectroscoy according Beer Lambert law Tunable light source (l = µm) with narrow emission frequency range Enhanced sensitivity by wavelength modulation sectroscoy (WMS) Fraunhofer 9

10 rel. error err / % water vaor volume fraction by TDLAS / m Tuning the sensitivity by otical ath length White tye multi ath setu with 20 reflections for otical ath length of 2 m within 121 cm³ cell volume LOD = 150 b V (3s) Measurement under tyical alication conditions (ressure, temerature) water vaor volume fraction by CSFG / m Calibration of concentration at national metrology institute (PTB) No sensor drift or damage caused by saturation or over-drying Minimal maintenance Fraunhofer 10

11 Isostatic ermeation measurement mode water vaor transmission rate WVTR / g m -2 d -1 c H2O (adosrbed) Reuther, 38 C / 90 RH% transient isot herm Desortion Adsort Adsortion Desort Isot herm steady state (at moshere) steady state ( V 1 ) :00 12:00 24:00 36:00 48:00 60:00 72:00 time t / hh:mm c H2O (gashase) 1. System urge with a re-dried inert gas 2. Concentration gradient inside the samle is formed 3. Calculation of WVTR is only valid for steady-state concentrations! WVTR iso V M H (1 ) A R T 2 O Fraunhofer 11

12 Water vaor transmission rate WVTR / g m -2 d -1 c H2O (adosrbed) Examle of ultra barrier measurement in isostatic mode POLO barrier film Adjusting the gas 38 C/ 90 % RH WVTR = 3 x 10-4 g m -2 d -1 Desortion transiente cell isotherme Adsortion steady state ( V 1 ) Isotherme steady state (atmoshere) 10-4 urge flow V 2 > urge flow V :00 24:00 48:00 72:00 96:00 120:00 144:00 Time t / hh:mm steady state ( V 2 ) c H2O (gashase) Lower LOD WVTR by reduction of carrier gas flow (30 sccm => 5 68 h) New equilibrium concentration is achieved from below Lower LOD in isostatic mode: 10-5 g m -2 d -1 Fraunhofer 12

13 water vaor volume fraction / m Quasi isostatic ermeation measurement mode system urge measurement of the blank value WVTR= 5x10-6 g m -2 d -1 quasi-isostatic measurement WVTR= 3x10-4 g m -2 d x x x x10-4 water vaor transmission rate WDD / g m -2 d x :00 24:00 48:00 72:00 96:00 120:00 time t / hh:mm 1. System urge with a re-dried inert gas 2. Measurement of blank value 5 x 10-6 g m -2 d -1 (lower values after longer urge eriods ossible) 3. increasing concentration after adding of water - break through 4. Calculation of water vaor transmission rate in steady state mode: WVTR q iso V t' PC M A R T H2O Fraunhofer 13

14 water vaor volume fraction / m Isostatic measurement vs. quasi isostatic measurement: Subsequent measurements 150 0,05 WVTR iso WVTR iso WVTR iso WVTR iso 125 0,04 measured concentration and calculated WVTR in isostatic and q-isostatic mode WVTR q-iso WVTR q-iso WVTR q-iso 0,03 0, ,01 water vaor transmission rate WVTR / g m -2 d :00 24:00 48:00 72:00 96:00 120:00 144:00 time t / hh:mm 0,00 1. Isostatic measurement until steady state conditions concentration gradient over the samle is fully alied 2. Quasi isostatic measurement u to 100 m shows a factor 4 5 lower WVTR, WVTR changes with concentration 3. Reeated measurements confirm that result Fraunhofer 14

15 quotient Isostatic measurement vs. quasi isostatic measurement: Comarison for different samles comarison of isostatic and q-isostatic mode #1 #2 * #3 quotient m out / m gas quotient WVTR iso / max. WVTR q-iso increasing WVTR #4 samle number #5 #6 The underestimation of WVTR q-iso is caused by absortion of water A mass balance of outgassed and gas hase water confirms these results The underestimation factor deends on the material and concentration The relationshi can be described by adsortion isotherms Adsortion isotherms are no a riori knowledge Fraunhofer 15

16 Isocanic measurements Gas hase measurements (ressure sensors, GC, MS, TDLAS ) of condensable gases like water vaor need a constant artial ressure at the ermeate comartment! This condition is called isocanic non isoconic isocanic 1 2 t t 1 2 t t Low well defined removal caacity of the ermeate is required H2O = H2O,0 + a t = constant H2O H2O... water vaor artial ressure 1 ermeate com artm ent 2 feed gas c omartment Fraunhofer 16

17 Princile of diffusion controlled ermeate removal A samle Dx D A caillary Dx Constant water vaor concentration = isocanic condition High level of water vaor concentration Level of water vaor concentration can be tuned by the length and inner diameter of caillary WVTR D x A caillary A samle Fraunhofer 17

18 Results of diffusion controlled ermeate removal a) WVTRiso b) 85 RH% -4 = 2.2 x gm d -4 = 3 x gm d = 4.2 x gm d 50 d) WVTRiso = x gm d ,5-7,0 diffusion controlled setu membrane diffusion controlled setu isostatic results 1 isostatic results RH% -2-1 ln (WVTR / g m d ) Calculated WVTRs of ultra-barrier substrates as a function of the samle temerature (Arrhenius Plot) sulemented by readings of isostatic carrier gas measurements water volume fraction / m Measured water vaor volume fraction using isostatic and isocanic conditions as a function of temerature 60 c) WVTRdiff temerature / C 25-7,5-8,0 1,4 x 10-4 g m-2 d-1-8,5-9,0-9,5 0, WDD (T ) g m d 0,38 e kj mol R T 0,39-1 0,40 0, / (RT / J mol ) Fraunhofer 18

19 Conclusion Water vaor ermeation measurement instrument with a TDLAS Sensor Adsortion leads to a significant underestimation of the WVTR in the quasi isostatic measurement mode (accumulation in gas hase) Reliable WVTR measurements based on gas concentration measurements need isocanic conditions (constant artial ressure at ermeate comartment) Isostatic and isocanic carrier gas measurements down to 10-5 g m -2 d -1 Presentation of a new isostatic and isocanic measurement mode using diffusion based ermeate removal with otential LOD of 10-6 g m -2 d -1 Fraunhofer 19

20 Many thanks for your attention! Fraunhofer 20