ASTM D1121-98(2003)
(Test Method)Standard Test Method for Reserve Alkalinity of Engine Coolants and Antirusts
Standard Test Method for Reserve Alkalinity of Engine Coolants and Antirusts
SCOPE
1.1 This test method covers the determination of the reserve alkalinity of new, unused engine coolants, and liquid antirusts as received, of used or unused aqueous dilutions of the concentrated materials, and of aqueous dilutions of solid antirusts.
1.2 The values stated in SI units are to be regarded as the standard.
1.3 This standard does not purport to address all of the safety problems, 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:D1121–98 (Reapproved 2003)
Standard Test Method for
Reserve Alkalinity of Engine Coolants and Antirusts
This standard is issued under the fixed designation D 1121; 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 (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope products, is diluted to about 100 mL with water and titrated
potentiometrically with 0.100 N hydrochloric acid to a pH of
1.1 This test method covers the determination of the reserve
5.5. The volume of acid used is reported to the nearest 0.1 mL.
alkalinity of new, unused engine coolants, and liquid antirusts
The concentration of coolant or additive in the coolant solution
as received, of used or unused aqueous dilutions of the
shall be recorded if required, for calculation of depletion of the
concentrated materials, and of aqueous dilutions of solid
reserve alkalinity during performance tests.
antirusts.
1.2 The values stated in SI units are to be regarded as the
5. Significance and Use
standard.
5.1 Reserve alkalinity is the number of millilitres, to the
1.3 This standard does not purport to address all of the
nearest 0.1 mLof 0.100 N hydrochloric acid (HCl) required for
safety problems, if any, associated with its use. It is the
the titration to a pH of 5.5 of a 10-mL sample of an undiluted,
responsibility of the user of this standard to establish appro-
unused coolant, antirust, or coolant additive, and unused or
priate safety and health practices and determine the applica-
used solutions thereof.
bility of regulatory limitations prior to use.
5.2 Reserve alkalinity is a term applied to engine coolants
2. Referenced Documents and antirusts to indicate the amount of alkaline components
present in the product. It is frequently used for quality control
2.1 ASTM Standards:
during production, and values are often listed in specifications.
D 1123 Test Method for Water in Engine Coolant Concen-
When applied to used solutions, reserve alkalinity gives an
trate by the Karl Fischer Reagent Method
approximate indication of the amount of remaining alkaline
D 1176 Standard Practice for Sampling and Preparing
components. Unfortunately, the term is sometimes misused in
Aqueous Solutions of Engine Coolants or Antirusts for
that its numerical value is said to be directly related to coolant
Testing Purposes
quality, the higher the number, the better the coolant. ASTM
D 1287 Test Method for pH of Engine Coolants and Anti-
CommitteeD-15onEngineCoolantsbelievesthereisaneedto
rusts
correct some misconceptions and place the term in its proper
3. Terminology
perspective.
5.3 Reserve alkalinity (R.A.) as defined in Section 3 of this
3.1 Definition:
method is the number of millilitres of 0.1-N hydrochloric acid
3.1.1 reserve alkalinity—the number of millilitres, to the
requiredtotitrate10mLofconcentratedcoolanttoapHof5.5.
nearest 0.1 mL, of 0.100 N hydrochloric acid required for the
The term is not a completely accurate description of the
titration to a pH of 5.5 of a 10-mL sample of an undiluted
property being measured because “alkalinity” usually refers to
unused coolant, antirust, or coolant additive, and unused or
the pH range above 7.0.
used solutions thereof.
5.4 A review of the origin of the term may be helpful in
4. Summary of Test Method
attempting to understand its proper use. When ethylene glycol
was first used as an engine coolant, it was uninhibited. The
4.1 A 10-mL sample of concentrated coolant, antirust,
need for inhibition soon became apparent and triethanolamine
coolantadditive,oranaqueousenginecoolantcontainingthese
was incorporated. When solutions of this inhibited glycol were
titrated with dilute hydrochloric acid, it was found that the
This test method is under the jurisdiction ofASTM Committee D15 on Engine
steepest part of the neutralization curve occurred at a pH of
Coolants and is the direct responsibility of Subcommittee D15.04 on Chemical
about 5.0. Following the introduction of triethanolamine, other
Properties.
buffers, such as borates and phosphates, have been used.
Current edition approved Oct. 10, 1998. Published December 1998. Originally
published as D 1121 – 50 T. Last previous edition D 1121 – 93.
Annual Book of ASTM Standards, Vol 15.05.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D1121–98 (2003)
Titrationto5.5wasemployedwiththesebufferswhichhavean protected with a soda-lime tube or the equivalent while cooling
end point close to 5.5. and in storage. The pH of the water shall be between 6.2 and
5.5 Generally, most metals in an automotive cooling system 7.2 at 25°C. Take precautions to prevent contamination of the
corrode less in solutions which are mildly alkaline. The distilled water with traces of the material used for protection
commonly used alkaline buffers, borates and phosphates, help against carbon dioxide.
to maintain this desirable alkalinity and a stable pH for 7.3 Standard Buffer Solution —The buffer solutions for
substantial additions of acid. A well inhibited coolant contains checking pH assemblies and glass electrodes shall be stored in
smaller amounts of other inhibitors (in addition to the buffers), bottles of chemically resistant glass or polyethylene and shall
to give broad range corrosion protection for all of the metals be prepared from salts sold specifically for use, either singly or
found in the cooling system. These additional inhibitors may in combination, as pH standards. The salts shall be dried for 1
contribute very little to the titration, but they can provide h at 110°C before use.
excellent corrosion protection. 7.4 Hydrochloric Acid (0.100 N)—Prepare and standardize
5.6 The alkaline inhibitors provide buffering action and 0.100 N hydrochloric acid (HCl).
neutralize acids introduced into the coolant by exhaust gas 7.5 Phthalate Buffer Solution (0.05 M, pH = 4.01 at
leakage, by residual acid cleaner, or by the oxidation of 25°C)—Dissolve 10.21 g of potassium hydrogen phthalate in
ethylene glycol and propylene glycol. Some inhibitors which distilled water and dilute to 1 L.
contribute little or no reserve alkalinity may give excellent 7.6 Phosphate Buffer Solution (0.025 M with respect to
corrosion protection to certain metals but have little capacity to each phosphate salt, pH = 6.86 at 25°C)—Dissolve 3.40 g of
combat acid contamination. In view of this, the magnitude of potassium dihydrogen phosphate (KH PO ) and 3.55 g of
2 4
the R. A. in a coolant is not always a good criterion in anhydrous disodium hydrogen phosphate (Na HPO ) in dis-
2 4
determining its potential protective properties. tilled water and dilute to 1 L.
5.7 Insummary,theprecautionagainstthemisuseofreserve 7.7 Potassium Chloride Electrolyte—Prepare a saturated
alkalinity is that the reserve alkalinity of an engine coolant solution of potassium chloride (KCl) in water.
solution is not a dependable measure of its ability to prevent
8. Sampling
corrosion, nor can it satisfactorily indicate the additional life of
the solution. 8.1 Sample the material in accordance with Standard Prac-
tice D 1176.
6. Apparatus
9. Preparation of Electrode System
6.1 The pH meter, glass electrode, and calomel electrode,
9.1 Maintenance of Electrodes—Clean the glass electrodes
shall be as specified in the section onApparatus (Section 5) of
Test Method D 1287. at frequent intervals (not less than once every week during
continual use) in accordance with the manufacturer’s instruc-
6.2 It is recognized that many laboratories use a combina-
tion electrode system for measuring the reserve alkalinity of tions. Drain the calomel electrodes at least once each week and
fill with KCl electrolyte. Keep the electrolyte level in the
engine coolants. It should be noted that results obtained from
calomelelectrodeabovethatoftheliquidinthetitrationbeaker
using a combination electrode system have been found to be
at all times. When not in use, immerse the lower half of the
statistically different from resu
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