The Characterization of Novel
Carboxysilane Depositions on
Stainless Steel Substrates for
Inertness, Wear Resistance,
and Corrosion Resistance
Applications
Gary Barone, Marty Higgins, David Smith
SilcoTek Corporation
Overview
• Use of Coatings
• Selecting Coatings
– Coating Materials/Properties
– Durability
– Corrosion Testing
– Moisture Resistance
– Chemical Inertness
• Conclusion
Using Coatings
• Most analytical pathways are stainless steel
– Great structurally
– Good corrosion resistance
– Poor chemical properties for analytical chemists
• Coatings used to improve material properties.
• Industries are demanding harsher services for
silicon coatings (like SilcoNert
®
2000 (Sulfinert).
• Carboxysilane coatings (Dursan
®
) more robust.
Factors Contributing to Poor
Sampling Reliability
• Durability/Wear
• Corrosion
• Moisture
• Design
– Chemical & Material Compatibility/Inertness
– Instrument Compatibility
– Installation
Selecting Coatings
• Fluoropolymers
– Very inert
– Very corrosion
resistant
– Broad pH applicability
– Poor adhesion
– Poor wear resistance
– Good to 260°C
• Silicon (SilcoNert
®
2000)
– Very inert
– Great adhesion
– No carryover
– Good corrosion
resistance
– Limited pH range
– Susceptible to steam
cleaning
– Poor wear resistance
– Good to 450°C
New Coating
• Carboxysilane (Dursan
®
)
– Good inertness
– Great adhesion
– No carryover
– Good corrosion resistance
– Broad pH applicability
– Steam cleaning, no problem
– Good wear resistance
– Tested to 450°C
– Still accumulating application data
Coating/Material Properties
Property Silicon
(SilcoNert 2000)
Carboxysilane
Dursan
PTFE,
PFA
Max Temperature 450ºC 450ºC 260ºC
Min Temperature -196ºC -100ºC -240ºC
Low pH limit 0 0 0
High pH limit 7 14 14
Thickness 0.12um to 0.5um 0.5um to 1.0um 25um
Adhesion Very Good Very Good Poor
Wear resistance 90% of Stainless 2 times
316 Stainless
10% of SS
(est.)
Moisture contact 72-90° 104-140° 125°
Inertness vs. SS Excellent Good Excellent
Improving wear resistance
& Durability
• Equipment and sample conditions can
damage surfaces and increase activity.
• Valve cycling/purging cause delamination
• Particulate in sample streams
• Abrasive cleaning
• Existing coatings
• Prone to wear
• Easily damaged
• Result: Adsorption & loss of sample
Wear and Friction Data
Load 2.0 N
Duration 20 min
Speed 80 rpm
Radius 3mm
Revolutions 1,554
Ball Diameter 6mm
Ball Material SS 440
• Pin on Disc: ASTM G133
• Base substrate is mirror-finish SS 316
Courtesy of Nanovea Inc.
Avg. Coeff. Friction
Wear Rate
(x10
-5
mm
3
/Nm)
Uncoated SS 0.589 13.810
Carboxysilane (
Dursan) 0.378 6.129
Silicon
(SilcoNert 2000) 0.7 14.00
Pull Strength Measurements
• Paints delaminated from the stainless steel
Pull Strength Measurements
• Dursan more “slippery” difficult to bond adhesive.
Adhesive bond failed before coating. Demonstrating
reduced friction characteristics.
Challenge of Corrosion
• Samples can contain corrosives that quickly attack
stainless
– Hydrochloric acid (HCl)
– Sulfuric acid (H
2
SO
4
)
– Saltwater
• Physical loss of equipment due to corrosion
– Maintenance
– Replacement cycles
• Corrosion increases surface activity and particulates
• Silicon coatings susceptible to caustics
Acid Corrosion Resistance
• ASTM G31 Guidelines: 6M HCl; 24hr; 23ºC
316L SS Silicon
Carboxysilane
MPY 181.98 4.32 0.44
Improvement Factor over
316L stainless
--- 42 411
Photo after 19hr
exposure
Dursan coated
Silcolloy coated
Acid Corrosion Resistance
ASTM G31
5% HF 70% Nitric 85% Phosphoric 25% Sulfuric
MPY
rate
factor MPY rate factor MPY rate factor MPY rate factor
316
SS 120.00 - 0.78 - 0.62 - 54.64 -
Carboxysilane
80.38 1.49 0.10 7.50 0.08 8.00 5.36 10.19
Silicon
44.26 2.71 0.36 2.14 0.28 2.18 23.62 2.31
Exposure to Caustic Base
• 1M KOH; 24hr; 22ºC
ASTM G31 316L SS Silicon Carboxysilane
MPY 0 3.40 0.01
Improvement Factor
Over Silicon
Infinite Dissolution 261
Challenges of Moisture
• Benefits of coating that help release water
faster
– Components less susceptible to corrosion
– Faster cycle times
– Increased accuracy
– Eliminate moisture/sample interaction
Impact of Moisture
60
70
80
90
100
110
Dry H2S Sample (%) H2S with Moisture (%)
Day 1
Day 14
Presence of moisture in sampling system
reduced H
2
S response by 22%: 50ppm sample
Measuring Hydrophobicity
DI Water 304 SS SilcoNert
2000
Dursan PTFE
Advancing 36.0 87.3 105.5 125.4
Receding 5.3 51.5 85.3 84
Kruss K100
Tensiometer
Testing on
304 SS
¼” OD tubing
DI Water Contact Angle Illustrations (advancing) on flat surfaces:
304 SS SilcoNert 2000 Dursan
Chemical Inertness
• Stainless Steel:
– Adsorbs sulfur compounds
– Causes loss of mercury
– Demonstrates poor transportability (tailing) of
polar organics such as alcohols
– Adsorbs ammonia
• Need coating that is chemically inert for
analytical systems
Total Sulfur Recovery
36ppb & 25ppm, 300cc cylinder
50
55
60
65
70
75
80
85
90
95
100
0 2 4 6 8 10 12
% Recovery
Day
Dursan: 25ppm 97% Recovery
SS 80% loss in 1 day
SilcoNert: 36ppb 99%+
recovery
21
Mercury 50 Day Stability
Average Mercury Response Comparison of Stainless
Steel vs. Silicon Functionalized Surfaces
0
1
2
3
4
5
6
7
0 10 20 30 40 50 60
Days after fill
Average Mercury
Concentration (ug/m
3
)
Untreated cylinders (n=2) Functionalized cylinders (n=2)
Courtesy of Spectra Gases Inc.
Ammonia Adsorption
100PPV, 500sccm, 1.8m tubing, min
• Measured PTR-MS signals of ammonia (m17). At t=10min the gas stream was switched in a way
• that it passed additionally the different 1.8m long lines. The PFA line seems to be best for Ammonia, while
• the steel line completely adsorbs the 100ppbv of Ammonia in the sample gas for hours. All lines were 1.8 m,
• not heated (30°C), sample gas flow was 500 sccm (std. ml/min) of 100 ppb of ammonia in N2. Courtesy of IONIMED Analytik
Selecting Coatings
Factor
Fluoropolymers
Weight
Silicon
(SilcoNert )
Weight
Carboxysilane
(Dursan)
Weight
Durability Poor wear
resistance
Fair wear resistance Good wear
resistance
Corrosion Excellent Good Good
Moisture Excellent Good Excellent
Inertness Excellent Excellent/ no carryover Good
Chemical /
Material
Compatibility
Poor adhesion/
Broad pH range
Excellent adhesion Excellent
Instrument
Compatibility
Good Good Excellent
Installation 260c max 450c max 450c max
Conclusion
• Analytical and Process industries demanding
increased performance from coating
• Coating selection dictated by application
– Corrosion resistance
– Moisture resistance
– Inertness
– Wear
• Broad spectrum environments and applications
may involve a tradeoff in performance.
– In field applications, carboxysilane coatings (Dursan)
may be the best overall performer.
