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

1

April 26, 2004

byRicky 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 black’s particle size (fundamental property).

• According to IUPAC convention, micropores are characterized by diameters less than 20 Å or 2 nm.

5

80 m2/g 100 m2/g 400 m2/g

Effect of Aggregation and Porosityon Surface Area

6

Traditional Surface Area Tests

Attribute CTAB Iodine NSASurface Type

Measured External Total Total

Affect of Oxidation Unknown Severe Minimal

Precision Poor Good Good

Difficulty High Low Low

Set-up Costs Medium Low High

7

Timeline of STSA at ASTM

• D5816 – STSA approved as ASTM standard in 1995.

• 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 2000. 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 Va-t plots

• Pore filling model

• Application of CB t Equation

9

Nitrogen Adsorption

• The concentration of nitrogen is expressed as

relative pressure (P/Po).

• A relative pressure of “0.0” is measured at

absolute vacuum, while a value of “1.0” is

measured at nitrogen’s saturated vapor

pressure (Po).

• The typical range for measuring NSA (BET) is

P/Po = 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 10 - 20 mm Hg above ambient

pressure due to impurities.

• Critical for measuring accurate STSA values.

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Saturated Vapor Pressure

Elevation

Sea Level 900 m

• Atm. Pressure 760 685

• Sat. Vapor Press. 775 700

• P/Po Value = 0.1 78 70

• P/Po Value = 0.2 155 140

• P/Po Value = 0.3 233 210

All values in mm Hg

12

Thickness Model

Small Particles Large Particle

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Thickness Equations

13.99

de Boer t = 0.034 - log P/Po

CB t = 0.88 (P/Po)2 + 6.45 (P/Po) + 2.98

Carbon Black t curve based on N762

14

Va–t Plot

0 1 2 3 4 5 6 7 8 9

0

10

20

30

40

50

60

30 m /g 2

60 m /g 2

90 m /g 2

Thickness (Å)

Vol

. Ads

. (cc

/g)

15

Pore Filling Model

P/Po = 0.0 P/Po = 0.05

P/Po = 0.2 P/Po > 0.2

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Adsorption Isotherms

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

20

40

60

80

100

120

140

N110

N326

N660

N472

Vol

. Ads

orbe

d (c

c/g)

Relative Pressure

17

Va–t Plot for Standard Carbon Blacksbased on CB t equation

0 1 2 3 4 5 6 7 8 9 10 11 12

0

20

40

60

80

100

120P/P o = 0.2

N472

N110

N326

N660

P/P o = 0.5

Thickness (Å)

Vol

. Ads

orbe

d (c

c/g)

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Results

• STSA versus CTAB

• Surface Chemistry

• Precision Statements

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Tread Carbon Blacks

NSA STSA CTAB

N110 135.3 119.7 123.6

N121 122.8 116.5 120.4

N220 116.0 107.7 109.5

N234 117.2 111.2 115.6

N330 76.6 74.7 80.0

N339 91.0 88.5 94.8

All values in m2/g

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Carcass Carbon Blacks

NSA STSA CTAB

N539 38.4 37.7 41.0

N550 38.1 38.2 38.6

N650 36.4 35.3 38.9

N660 33.0 33.1 34.9

N762 25.7 25.7 26.9

N787 29.7 29.6 31.0

All values in m2/g

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CTAB versus STSA

0 20 40 60 80 100 120 1400

20

40

60

80

100

120

140

STSA (m2/g)

CT

AB

(m

2 /g)

R2 = 0.9985

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Effect of Surface Oxidation on CTAB Measurements

Sample # 1 # 1 # 2 # 2 # 3 # 3

Oxygen (%) 2.0 1.9 1.5

STSA (m2/g) 86.4 85.7 90.8

CTAB (m2/g) 100.1 97.5 97.7

Difference -13.7 -11.8 -6.9Difference -13.7 -11.8 -6.9

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Sample Sample # 1 # 1 # 2 # 2 # 3 # 3

STSA (mSTSA (m22/g) 86.3 86.3 90.0/g) 86.3 86.3 90.0 Initial Value 86.4 85.7 90.8Initial Value 86.4 85.7 90.8

CTAB (mCTAB (m22/g) 87.3 85.9 89.2/g) 87.3 85.9 89.2 Initial Value 100.1 97.5 97.7Initial Value 100.1 97.5 97.7

Difference -1.0 0.4 0.8Difference -1.0 0.4 0.8

Effect of Surface Oxidation on CTAB Measurements

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Effect of Heat Treatment on ASTM SRB-5

00

55

1010

1515

2020

2525NSANSA

IodineIodine

N683N683N660N660N762N762N220N220N135N135 N330N330

%C

han

ge%

Ch

ange

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Effect of Heat Treatment on ASTM SRB-5

--10.010.0

-7.5-7.5

-5.0-5.0

-2.5-2.5

0.00.0

2.52.5

5.05.0

N683N683N660N660N762N762N220N220N135N135 N330N330

%C

han

ge%

Ch

ange

STSASTSA

CTABCTAB

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PrecisionN121 Control Chart

Run #

1 5 9 12 16 20

-2.5

-1.5

-0.5

0.5

1.5

2.5

CTAB

STSA

Dif

f. F

rom

Mea

n (m

2 /g)

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Effect of Solution Agingon CTAB Solutions

0 10 20 30 40 50 60

Run #Run #

115

116

117

118

119

120

121

122

CT

AB

(m

2 /g)

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Surface Area Precision Studyfrom Original STSA Paper

NSANSA STSASTSA CTABCTAB00

11

22

33

44

55

66 Between LabBetween Lab

WithinWithin LabLab

Per

cen

tP

erce

nt

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Potential Errors in NSA/STSA Measurements

• Improper degassing time/temperature.

• Improper sample weight.

• Inaccurate or changing Po value.

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NSA/STSA Control Chartusing ASTM B-6 (N220)

101.5

102.0

102.5

103.0

103.5

104.0

104.5

105.0

105.5

106.0

106.5

107.0

107.5

108.0

108.5

109.0

109.5

110.0

110.5

111.0

111.5

112.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Surf

ace

Are

a (m

2/g)

Mean = 109.6 ± 1.1

(ASTM = 110.0 ± 1.6)

Mean = 105.4 ± 2.1

(ASTM = 105.4 ± 2.9)

Data collected over a 4 month period

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NSA/STSA Control Chart with Po Outliers Removed (P >20mm Hg)

101.5

102.0

102.5

103.0

103.5

104.0

104.5

105.0

105.5

106.0

106.5

107.0

107.5

108.0

108.5

109.0

109.5

110.0

110.5

111.0

111.5

112.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Surf

ace

Are

a (m

2/g)

Mean = 109.5 ± 1.1

(Previous = 109.6 ± 1.1)

Mean = 105.4 ± 1.5 (Previous = 105.4 ± 2.1)

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Effect of Dewar Stability

• A single sample of ASTM B-6 (N220) degassed at

300°C then run multiple times, measuring the Po after

each run using the standard Gemini (600 ml) and a

large volume (2 L) dewars.

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Modified Gemini

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Effect of Dewar Stability – 1 Hr. Equilibration Time

  NSA (m2/g) STSA (m2/g)

1 Hour Equil. Mean 3 Mean 3

Dewar #1 - Std (600 ml) 110.0 1.83 104.7 4.86

Dewar #2 - Std (600 ml) 110.0 1.23 104.3 2.16

Dewar #3 - Large (2 L)* 109.9 0.18 105.4 0.57

Dewar #3 - Large (+15 mm)* 109.9 0.15 105.3 0.33

* = Filled and covered overnight before analysis

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Effect of Dewar Stability – 2 Hr. Equilibration Time

  NSA (m2/g) STSA (m2/g)

1 Hour Equil. Mean 3 Mean 3

Dewar #1 - Std (600 ml) 110.2 0.60 105.2 0.87

Dewar #2 - Std (600 ml) 109.9 0.99 104.2 1.95

Dewar #3 - Large (2 L)* 109.9 0.15 105.3 0.33

Dewar #3 - Large (+15 mm)* 109.9 0.15 105.3 0.33

* = Filled and covered overnight before analysis

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Po Summary

• A minimum 2 hour dewar equilibration is required

(longer is better).

• Large volume dewars allow improved precision.

• Other Po options exist for newer, higher-end

instruments.

• Changes to D6556 are required based on this study.

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Analysis Time

  Standard ValueStandard Method

(D6556)Modified Method

(3 pt.)

Sample ID NSA STSA NSA STSA NSA STSA

  (m2/g) (m2/g) (m2/g) (m2/g) (m2/g) (m2/g)

A-6 (N134) 143.9 135.7 142.1 133.7 142.7 133.7

B-6 (N220) 110.0 105.4 109.4 104.6 108.8 105.3

C-6 (N326) 78.3 79.2 78.3 79.1 77.6 79.8

D-6 (N762) 30.6 29.6 30.4 29.0 30.7 29.2

E-6 (N660) 36.0 35.1 35.5 34.7 35.1 33.8

F-6 (N683) 35.3 34.1 34.7 33.2 34.6 32.8

Mean Values 72.4 69.9 71.7 69.1 71.6 69.1

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Analysis Time

  Standard Method (D6556) Modified Method (3 pt.)

Sample ID Analysis Degassing Total Analysis Degassing Total

 Time (min.)

Time (min.)

Time (min.)

Time (min.)

Time (min.)

Time (min.)

A-6 (N134) 33 30 63 20 10 30

B-6 (N220) 30 30 60 17 10 27

C-6 (N326) 23 30 53 17 10 27

D-6 (N762) 20 30 50 15 5 20

E-6 (N660) 19 30 49 15 5 20

F-6 (N683) 20 30 50 14 5 19

Mean Values 24.2 30.0 54.2 16.3 7.5 23.8

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Conclusions

STSA provides the following advantages STSA provides the following advantages

over CTAB:over CTAB: Improved precision and accuracy, provided

proper attention to Po

Less affected by surface oxidation

Less operator time

Measured simultaneously with NSA

No reagent preparation