Moisture in Materials work at NPL - the first steps Presentation to TMAN meeting at NPL

Transcription

1 Moisture in Materials work at NPL - the first steps Presentation to TMAN meeting at NPL Paul Carroll 4 th February 2009

2 Overview : Study completed : findings / recommendations Gaining expertise develop a NMS initial capability to make moisture measurements Measurement principles and applicability of new instrumentation Initial results certified reference materials / comparison Support for several current projects across NPL Planned future work Potential for collaboration

3 Study Methodology - Needs for NMS support for measurement of moisture in materials Consultation process to understand current measurement requirements Literature study technical developments, published standards, trade association guidelines Survey of industry, academia, NPL colleagues, end users and instrument manufacturers Wood Agricultural produce Powders Pharmaceuticals Foodstuffs Construction materials / Building design Polymeric and Composite materials

4 Areas of NPL surveyed Materials metals, plastics, composites, adhesives, powders Biotechnology Building materials evaluation Structural health monitoring RF and microwave dielectric measurement Terahertz measurements Nuclear waste storage Moisture diffusion modelling

5 Measurement principles Absolute (direct) : Loss on drying Karl Fischer titration Thermogravimetric analysis Inferential (indirect) : comparisons made against absolute techniques - Capacitance - Resistance - Near infrared reflectance (NIR) - Microwave dielectric spectroscopy - Time domain reflectometry - Nuclear Magnetic Resonance (NMR)

6 Scope of measurements Different types of moisture measurements identified : Bulk ( total ) moisture content Surface (or near-surface) moisture Moisture profile (at varying depths) Moisture transport Moisture at interfaces Increasing difficulty

7 Measurement Issues Range / Cost Accuracy required - claimed uncertainty Inferential (indirect) versus absolute (direct) Online (real-time) versus laboratory analysis Contact versus non-contact (destructive) Surface, capillary or bound water content Moisture content - water or other volatiles? Sample preparation homogeneity of batch Industry regulations - trade Interpretation of procedural standards

8 Study Recommendations Good practice guidance through publications, events and consultancies. Knowledge transfer of best practice across sectors. Measurement services such as calibration of instruments or proficiency tests with certified reference materials. Promote an emphasis towards outcome-based verification (calibration, checks against reference materials, proficiency testing) not reliance on procedural standards. NPL to develop initial measurement capability in support of internal projects which could provide traceable calibration to some instrument types and consultancy opportunities in the future.

9 NPL Moisture Measurement Instrumentation Analytical Balance Microwave Resonance Moisture Analyser Evolved vapour analysis Images: Sartorius

10 Loss on drying measurement Thermogravimetric principle Option 1 - Analytical balance and drying oven Balance range 1 mg to 230g Balance resolution 10μg Moisture content (%) = m w m w m d 100% Balance can also be used to determine moisture diffusion coefficients gain on wetting

11 Loss on drying measurement Option 2 - Moisture Analyser Incorporates heating element Sample range 0.100g to 150g Balance resolution 1 mg Temperature range 40 to 220 C Portable Both Balances : Traceable measurements to NPL mass standards Mass loss water or other volatiles?

12 Evolved vapour coulometric analyser Sample mass 2 to 2000mg Oven temp. up to 400 C, programmable heating profile Detects water content in the range 15% down to ppm range Measurement technique combines thermal analysis and coulometry

13 Measurement theory : Dry Gas Nitrogen + H 2 O Dry gas H 2 + O 2 P 2 O 5 +3H 2 O 2H 3 PO 4 Oven - up to 400 C P 2 O 5 and H 2 O Electrolytic Cell Sample inserted into oven Water vapour evolved - saturates gas stream Reaction with P 2 O 5 Cell - water molecules dissociate into hydrogen and oxygen. Each electrolysed water molecule contributes 2 electrons to electronic charge Faraday s Law electrolytic current a measure of water molecules detected.

14 Example results P.E.T granules:

15 Microwave Microwave resonance technology Water in sample interferes with resonance of microwave Non-destructive Fast measurement < 1s Range 0.1 to 85% moisture content 0.01% moisture content resolution Accuracy dependent on calibration by L.O.D and sample type ~ ±0.05% moisture content Not compatible with metallic powders

16 Microwave measurement principle Presence of water causes shift of resonant frequency peak position and half-height width. Parameters influenced by moisture and density of material. Transmission Filled Applicator Empty Applicator 2 3 Frequency (GHz) With correct calibration, measurements become density independent

17 Initial Results Use of evolved vapour analysis to determine water content of certified reference materials supplied by LGC Making comparison measurements across instrumentation of flour conditioned to different moisture contents Measuring moisture content of coatings conditioned to different moisture contents

18 Certified reference materials Standard Water Content (%) Unc. (%) water content Temp. to evolve H 2 O ( C) WDS 400 mean result (% water content) St. Deviation (% water content) Hydranal water standard 0.01% Potassium Citrate Sodium tartrate

19 Comparison measurements Condition bulk samples of Plain Flour MC % 10 5 Desiccated (~5%RH) Ambient (~30%RH) NaCl (75% RH) 0 KNO3 (95% RH) 1/19/09 1/20/09 1/21/09 1/22/09 1/23/09 1/24/09 1/25/09 1/26/09 1/27/09 1/28/09 1/29/09 Date

20 Comparison measurements All measurements made at 110 C %RH Flour conditioned Loss on Drying Moisture analyser Evolved vapour analysis 5% % % %

21 Support for NPL Projects Surface Acoustic Wave investigation into whether SAW principle can be used to detect changes in moisture content of coatings Hygroscopic coatings identified, Si substrate Coatings too thick / soft to get meaningful SAW measurements at present.

22 Future Work Develop experience / expertise with new instrumentation Comparison measurements using more certified reference materials Make measurements following ISO 62:1999 Plastics Determination of water absorption to provide repeatability data for revision of standard. Potential for measurement of moisture content in powders on-site at production lines or on samples sent to NPL for analysis. Develop calibration service for indirect measurement instruments where requirement exists

23 Potential for collaboration Instruments available in our facility for use applicable to a wide range of projects Continue supporting NPL projects Verification of instrumentation and reference materials Support for uncertainty estimation Proficiency test equivalence analysis

24 Summary Report findings, current requirements, recommendations New capability at NPL equipment, technologies, different applications Initial results obtained Support for NPL projects Potential for collaboration / consultation using new facility at NPL

25 Report : Needs for NMS support for measurement of moisture in materials P Carroll, S A Bell Available as free download at : Questions? paul.carroll@npl.co.uk Tel :