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1 April 26, 2004 by Ricky Magee Columbian Chemicals Company STSA – Life without CTAB.

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Presentation on theme: "1 April 26, 2004 by Ricky Magee Columbian Chemicals Company STSA – Life without CTAB."— Presentation transcript:

1 1 April 26, 2004 by Ricky Magee Columbian Chemicals Company STSA – Life without CTAB

2 2 Outline Introduction Theory Results Comparison with CTAB surface area Surface Chemistry Effects New Developments Conclusions

3 3 Introduction Importance of Surface Area Traditional Surface Area Techniques Timeline of STSA at ASTM

4 4 Importance of Surface Area Surface area is one of the most important characteristics of the carbon black. Surface area of carbon black is a function of particle size, degree of aggregation and porosity. Therefore, surface area alone is not a reliable measure of particle size. In the absence of porosity, surface area values are an indication of a carbon blacks particle size (fundamental property). According to IUPAC convention, micropores are characterized by diameters less than 20 Å or 2 nm.

5 5 80 m 2 /g 100 m 2 /g 400 m 2 /g Effect of Aggregation and Porosity on Surface Area

6 6 Traditional Surface Area Tests AttributeCTABIodineNSA Surface Type MeasuredExternalTotal Affect of OxidationUnknownSevereMinimal PrecisionPoorGood DifficultyHighLow Set-up CostsMediumLowHigh

7 7 Timeline of STSA at ASTM D5816 – STSA approved as ASTM standard in D1765 (CB Classification System)– In 1997, STSA was added as a typical value in Table 1, with corresponding CTAB values deleted. D6556 – Combined NSA (D4820) and STSA (D5816) into a single standard in The NSA section was modernized and data interpretation simplified. D3765 – In 2003, estimated CTAB values of SRB-6 carbon blacks was added to CTAB method.

8 8 Theory Nitrogen Adsorption Saturated Vapor Pressure de Boer t-values and V a -t plots Pore filling model Application of CB t Equation

9 9 Nitrogen Adsorption The concentration of nitrogen is expressed as relative pressure (P/P o ). A relative pressure of 0.0 is measured at absolute vacuum, while a value of 1.0 is measured at nitrogens saturated vapor pressure (P o ). The typical range for measuring NSA (BET) is P/P o = 0.05 to 0.30.

10 10 Saturated Vapor Pressure Saturated vapor pressure is the pressure at which nitrogen gas condenses. It is based on atmospheric pressure and the temperature of the liquid nitrogen in the dewar. It is usually mm Hg above ambient pressure due to impurities. Critical for measuring accurate STSA values.

11 11 Saturated Vapor Pressure Elevation Sea Level 900 m Atm. Pressure Sat. Vapor Press P/P o Value = P/P o Value = P/P o Value = All values in mm Hg

12 12 Thickness Model

13 13 Thickness Equations de Boer t = log P/P o CB t = 0.88 (P/P o ) (P/P o ) Carbon Black t curve based on N762

14 14 V a –t Plot m /g 2 60 m /g 2 90 m /g 2 Thickness ( Å ) Vol. Ads. (cc/g)

15 15 Pore Filling Model P/P o = 0.0P/P o = 0.05 P/P o = 0.2 P/P o > 0.2

16 16 Adsorption Isotherms N110 N326 N660 N472 Vol. Adsorbed (cc/g) Relative Pressure

17 17 V a –t Plot for Standard Carbon Blacks based on CB t equation P/P o = 0.2 N472 N110 N326 N660 P/P o = 0.5 Thickness ( Å ) Vol. Adsorbed (cc/g)

18 18 Results STSA versus CTAB Surface Chemistry Precision Statements

19 19 Tread Carbon Blacks NSA STSA CTAB N N N N N N All values in m 2 /g

20 20 Carcass Carbon Blacks NSA STSA CTAB N N N N N N All values in m 2 /g

21 21 CTAB versus STSA STSA (m 2 /g) CTAB (m 2 /g) R 2 =

22 22 Effect of Surface Oxidation on CTAB Measurements Sample # 1 # 2 # 3 Oxygen (%) STSA (m 2 /g) CTAB (m 2 /g) Difference

23 23 Sample Sample # 1 # 2 # 3 # 1 # 2 # 3 STSA (m 2 /g) Initial Value Initial Value CTAB (m 2 /g) Initial Value Initial Value Difference Effect of Surface Oxidation on CTAB Measurements

24 24 Effect of Heat Treatment on ASTM SRB NSA Iodine N683 N660N762N220N135 N330 %Change

25 25 Effect of Heat Treatment on ASTM SRB N683 N660N762N220 N135N330 %Change STSA CTAB

26 26 Precision N121 Control Chart Run # CTAB STSA Diff. From Mean (m 2 /g)

27 27 Effect of Solution Aging on CTAB Solutions Run # CTAB (m 2 /g)

28 28 Surface Area Precision Study from Original STSA Paper

29 29 Potential Errors in NSA/STSA Measurements Improper degassing time/temperature. Improper sample weight. Inaccurate or changing P o value.

30 30 NSA/STSA Control Chart using ASTM B-6 (N220) Mean = ± 1.1 (ASTM = ± 1.6) Mean = ± 2.1 (ASTM = ± 2.9) Data collected over a 4 month period

31 31 NSA/STSA Control Chart with P o Outliers Removed ( P >20mm Hg) Mean = ± 1.1 (Previous = ± 1.1) Mean = ± 1.5 (Previous = ± 2.1)

32 32 Effect of Dewar Stability A single sample of ASTM B-6 (N220) degassed at 300°C then run multiple times, measuring the P o after each run using the standard Gemini (600 ml) and a large volume (2 L) dewars.

33 33 Modified Gemini

34 34 Effect of Dewar Stability – 1 Hr. Equilibration Time NSA (m 2 /g)STSA (m 2 /g) 1 Hour Equil.Mean 3 3 Dewar #1 - Std (600 ml) Dewar #2 - Std (600 ml) Dewar #3 - Large (2 L)* Dewar #3 - Large (+15 mm)* * = Filled and covered overnight before analysis

35 35 Effect of Dewar Stability – 2 Hr. Equilibration Time NSA (m 2 /g)STSA (m 2 /g) 1 Hour Equil.Mean 3 3 Dewar #1 - Std (600 ml) Dewar #2 - Std (600 ml) Dewar #3 - Large (2 L)* Dewar #3 - Large (+15 mm)* * = Filled and covered overnight before analysis

36 36 P o Summary A minimum 2 hour dewar equilibration is required (longer is better). Large volume dewars allow improved precision. Other P o options exist for newer, higher-end instruments. Changes to D6556 are required based on this study.

37 37 Analysis Time Standard Value Standard Method (D6556) Modified Method (3 pt.) Sample IDNSASTSANSASTSANSASTSA (m 2 /g) A-6 (N134) B-6 (N220) C-6 (N326) D-6 (N762) E-6 (N660) F-6 (N683) Mean Values

38 38 Analysis Time Standard Method (D6556)Modified Method (3 pt.) Sample IDAnalysis Degassing TotalAnalysis Degassing Total Time (min.) A-6 (N134) B-6 (N220) C-6 (N326) D-6 (N762) E-6 (N660) F-6 (N683) Mean Values

39 39 Conclusions STSA provides the following advantages over CTAB: over CTAB: l Improved precision and accuracy, provided proper attention to P o l Less affected by surface oxidation l Less operator time l Measured simultaneously with NSA l No reagent preparation


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