ASTM D2448-85(2012)
(Test Method)Standard Test Method for Water-Soluble Salts in Pigments by Measuring the Specific Resistance of the Leachate of the Pigment
Standard Test Method for Water-Soluble Salts in Pigments by Measuring the Specific Resistance of the Leachate of the Pigment
SIGNIFICANCE AND USE
4.1 This test method provides a reliable means for the determination of the relative amounts of these salts when comparing different lots of the same pigment grade. Water-soluble salts also affect the water resistance and blister resistance of coatings, especially primers for steel. Conductivity measurements, however, cannot be used as the only method to determine and compare the amount of water soluble salts of pigments with the same chemical composition but produced by different manufacturing processes.
SCOPE
1.1 This test method covers the determination of the specific resistance of the aqueous leachate from a pigment as an index of water-soluble salt content. This test method is applicable to white pigments and colored pigments (organic and inorganic). The water-soluble salts content is a function of the specific resistance of the solution formed by extracting the pigment with water.
1.2 This test method is based on a water to pigment ratio of 9+1. The leachate yield (minimum 160 mL) sufficient for rinsing the cylinder dip cell and thermometer plus the minimum 80 mL required for the measurement to determine the quantity of pigment to be used.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D2448 −85 (Reapproved 2012)
Standard Test Method for
Water-Soluble Salts in Pigments by Measuring the Specific
Resistance of the Leachate of the Pigment
This standard is issued under the fixed designation D2448; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 4. Significance and Use
1.1 Thistestmethodcoversthedeterminationofthespecific 4.1 This test method provides a reliable means for the
resistance of the aqueous leachate from a pigment as an index determination of the relative amounts of these salts when
of water-soluble salt content. This test method is applicable to comparing different lots of the same pigment grade. Water-
white pigments and colored pigments (organic and inorganic). soluble salts also affect the water resistance and blister resis-
The water-soluble salts content is a function of the specific tance of coatings, especially primers for steel. Conductivity
resistance of the solution formed by extracting the pigment measurements, however, cannot be used as the only method to
with water. determine and compare the amount of water soluble salts of
pigments with the same chemical composition but produced by
1.2 This test method is based on a water to pigment ratio of
different manufacturing processes.
9+1. The leachate yield (minimum 160 mL) sufficient for
rinsing the cylinder dip cell and thermometer plus the mini-
5. Apparatus
mum 80 mL required for the measurement to determine the
5.1 Centrifuge (optional), having a 500-mL capacity per
quantity of pigment to be used.
cup.
1.3 The values stated in SI units are to be regarded as
5.2 Filter Paper (Note 1)—For high reliability avoid use of
standard. No other units of measurement are included in this
filter paper containing soluble material. Each filter should be
standard.
washed with reagent water in the funnel until resistance of the
1.4 This standard does not purport to address all of the
filtrate is greater than 200 000Ω · cm.
safety concerns, if any, associated with its use. It is the
NOTE 1—The size of the filter paper will be determined by how
responsibility of the user of this standard to establish appro-
voluminous the pigment is. Some organic pigments require at least a
priate safety and health practices and determine the applica-
185-mm paper for proper filtering.
bility of regulatory limitations prior to use.
5.3 Filter Aid (optional)—The use of a filter aid may be
desirable with some pigments to improve filtration. However,
2. Referenced Documents
the filter aid must be treated to meet the same specifications for
2.1 ASTM Standards:
filter paper as given in 5.2.
D1193 Specification for Reagent Water
5.4 Ungraduated Cylinders, approximately 35 mm wide by
3. Summary of Test Method
125 mm deep.
3.1 A weighed quantity of pigment is added to water and 5.5 Thermometer, graduated in 0.2°C intervals.
boiled. For hydrophobic pigments methyl alcohol is used to 3
5.6 Conductivity Bridge.
facilitate wetting. After filtration, the specific resistance of the
5.7 Conductivity Cell, having a cell constant, K,of1.The
filtrate is determined using a conductivity bridge.
cell constant recommended for various ranges of electrolytes is
as follows:
5.7.1 For specific resistances of less than 250Ω · cm, use a
This test method is under the jurisdiction of ASTM Committee D01 on Paint
cell with a constant of 10 or more.
and Related Coatings, Materials, andApplications and is the direct responsibility of
Subcommittee D01.31 on Pigment Specifications.
5.7.2 For specific resistances from 250 to 200 000Ω · cm,
Current edition approved Nov. 1, 2012. Published November 2012. Originally
use a cell with a constant of 1. This covers the range for most
approved in 1966. Last previous edition approved in 2007 as D2448 – 85 (2007).
pigments.
DOI: 10.1520/D2448-85R12.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Any commercially produced conductivity bridge and conductivity cell is
the ASTM website. satisfactory.
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D2448−85 (2012)
FIG. 1Specific Resistance of Potassium Chloride at 25°C
5.7.3 For specific resistances of reagent water or of over 7.2 Calculate the cell constant, K, as follows:
200 000Ω · cm, use a cell with a constant of 0.1.
K 5 R /R
~ !
25 m s
6. Reagents
where:
R = specific resistance at 25°C (see 8.2.2), and
6.1 Purity of Reagents—Reagent grade chemicals shall be
m
R = specific resistance in ohm centimetres of an 0.002 N
used in all tests. Unless otherwise indicated, it is intended that
s
KCl solution at 25°C (Table 1) = 3427Ω · cm.
all reagents shall conform to the specifications of the Commit-
tee onAnalytical Reagents of theAmerican Chemical Society,
NOTE 2—In general the “cell constant” is not greatly affected by
where such specifications are available. Other grades may be
variations in the strength of the KCl solution, but for greatest accuracy,
used, provided it is first ascertained that the reagent is of measurements should be made at or near the specific resistance of the
solution to be measured and at values that utilize the medium range of the
sufficiently high purity to permit its use without lessening the
scale of the conductivity bridge, using the same multiplier tap.
accuracy of the determination.
7.3 The specific resistances of KCl solutions are shown for
6.2 Purity of Water—Unless otherwise indicated, references
concentrations from 0.001 N to 0.073 N at 25 C in Fig. 1. This
to water shall be understood to mean reagent grade water as
curve, almost a straight line, was made from pub
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