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pH value of an aqueous suspension
slurry form, the pH value is determined after dilution to a concentration of 100 g per kilogram of suspension.
This SCAN-test Method specifies a method for determining the pH value of an aqueous suspension of a filler or pigment used in the production of paper. The
Method is applicable to all kinds of fillers and pigments,
Distilled or deionised water
, freshly boiled and
The sampling procedure is not covered by this
, of known pH values close to 4
− Suitable buffer solutions are commercially
Fillers and pigments − Dry matter content
available. They can also be prepared in the laboratory as follows:
Buffer solution, pH 4,01
: In a 1000 ml volumetric
For the purpose of this Method, the following definition
to the mark. There is normally no need to dry the
− the value determined on the slurry
salt. The solution is stable for 2 months.
when the dry filler or pigment is dispersed at about
Buffer solution, pH 9,18
: In a 1000 ml volumetric flask, dissolve 3,80
decahydrate (borax), Na2B4O7 ⋅ 10 H2O, in distilled water from which carbon dioxide has been expelled
A slurry of 10 g of pigment in 90 ml of water is
by boiling. Dilute to the mark. The solution is
prepared. The pH of the slurry is measured at room
stable for 6 weeks. The solution will absorb carbon
temperature. For fillers or pigments delivered in the
dioxide when in contact with ambient air. Therefore, keep the solution in a stoppered bottle
and do not leave the bottle open more than is
− The solid particles in the suspension affect
the performance of the glass electrode and may cause large errors. Therefore stirring of the suspension should be stopped in good time before
the measurement. The 30 min period stated above
pH measuring device,
consisting of a glass
electrode, a reference electrode and a suitable potentiometer, calibrated against buffer solutions of
Express the pH to the nearest 0,1 unit as the mean of the
duplicate determinations. The individual results should not differ by more than 0,2 units; if they do, repeat the determination on two additional suspensions.
Preparation of sample
The test report should include reference to this
Keep samples in water-vapour-tight vessels, such as
glass or plastic jars with a tightly fitting lid. Determine
the dry matter content in accordance with SCAN-P 39.
Before taking a portion for analysis, make sure that
(b) identification of the material tested;
(c) the result; (d) any departure from the procedure described in this
SCAN-test Method or any other circumstances that
Carry out the procedure in duplicate. Weigh a portion of the sample containing (10,0 ± 0,5) g of dry filler or
pigment into a 250 ml beaker. Add 90 ml of distilled water (5.1) and a magnetic rod.
Many pigments contain small amounts of water-soluble
If the sample is a slurry, weigh a sample of about
salts. Suspensions made from such pigments have a low
20 g and calculate the volume of water required to obtain
buffer capacity and their pH value is therefore poorly
a slurry containing (10,0 ± 0,5) g of solid material per
defined. This may lead to poor reproducibility since the
90 ml of water. Prepare the dilute slurry in a beaker.
measured pH value can depend on the time allowed for
Place the beaker on the stirring device (6.1) and start
stirring and settling. If the time allotted is shorter than
the stirrer. Adjust it to produce a vortex and let it run for
here specified, for example in routine control, the
30 min. Stop the stirring and allow the suspension to
Calibrate the pH meter (6.2) with the two buffer
solutions (5.2). Rinse the electrodes several times with pure water. Immerse the electrodes in the supernatant liquid above the filler or pigment and measure the pH value after 2 min.
SCAN-test Methods are issued and recommended by
KCL, PFI and STFI-Packforsk for the pulp, paper and
board industries in Finland, Norway and Sweden.
Distribution: Secretariat, Scandinavian Pulp, Paper
and Board Testing Committee, Box 5604,
SE-114 86 Stockholm, Sweden.
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