Presentation on theme: "1 April 26, 2004 by Ricky Magee Columbian Chemicals Company STSA – Life without CTAB."— Presentation transcript:
1 April 26, 2004 by Ricky Magee Columbian Chemicals Company STSA – Life without CTAB
2 Outline Introduction Theory Results Comparison with CTAB surface area Surface Chemistry Effects New Developments Conclusions
3 Introduction Importance of Surface Area Traditional Surface Area Techniques Timeline of STSA at ASTM
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 80 m 2 /g 100 m 2 /g 400 m 2 /g Effect of Aggregation and Porosity on Surface Area
6 Traditional Surface Area Tests AttributeCTABIodineNSA Surface Type MeasuredExternalTotal Affect of OxidationUnknownSevereMinimal PrecisionPoorGood DifficultyHighLow Set-up CostsMediumLowHigh
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 Theory Nitrogen Adsorption Saturated Vapor Pressure de Boer t-values and V a -t plots Pore filling model Application of CB t Equation
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 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 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 Thickness Model
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 V a –t Plot m /g 2 60 m /g 2 90 m /g 2 Thickness ( Å ) Vol. Ads. (cc/g)
15 Pore Filling Model P/P o = 0.0P/P o = 0.05 P/P o = 0.2 P/P o > 0.2
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 Effect of Heat Treatment on ASTM SRB NSA Iodine N683 N660N762N220N135 N330 %Change
25 Effect of Heat Treatment on ASTM SRB N683 N660N762N220 N135N330 %Change STSA CTAB
26 Precision N121 Control Chart Run # CTAB STSA Diff. From Mean (m 2 /g)
27 Effect of Solution Aging on CTAB Solutions Run # CTAB (m 2 /g)
28 Surface Area Precision Study from Original STSA Paper
29 Potential Errors in NSA/STSA Measurements Improper degassing time/temperature. Improper sample weight. Inaccurate or changing P o value.
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 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 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 Modified Gemini
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 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 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 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 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 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