SH/T 0091-1991 Determination of Reserve Alkalinity of Engine Coolants and Rust Inhibitors

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Card type: Test method

1. Method number / full title / English name / replacement relationship

• Standard number: SH/T 0091-91
• Chinese title: Determination of Reserve Alkalinity of Engine Coolants and Rust Inhibitors
• English title: not provided in the available source
• Replacement relationship: not provided in the available source
• Other: approved by 1991-11-26, implemented by 1992-12-01; confirmed in the year (200) (original text as such, specific year requires confirmation against the source standard (source-text extraction))
• Reference adoption: ASTM D1121-88 "Standard Test Method for Reserve Alkalinity of Engine Coolants and Rust Inhibitors"

2. Scope of application and non-application

• Applicable to: engine coolants and concentrated coolants, concentrated rust inhibitors; may also be applicable to used engine coolants, diluted solutions of concentrated rust inhibitors, and aqueous solutions of solid rust inhibitors.
• Not applicable to: not provided in the available source.

3. Method principle

Dilute the 10 mL test sample with water to about 100 mL, then titrate with hydrochloric acid standard titration solution of concentration c(HCl)=0.1000 mol/L to a pH value of 5.5. Record the milliliters of hydrochloric acid standard titration solution consumed by the titration, to the nearest 0.1 mL. If necessary, to calculate the consumption of reserve alkalinity in performance tests, the concentration of the coolant or additive in the coolant should be recorded; the calculation method is given in Appendix A.

4. Reagents and materials (purity / preparation)

• 6.1 Unless otherwise specified, all test reagents are analytical grade reagents.
• 6.1.1 Hydrochloric acid: prepare a hydrochloric acid standard titration solution according to SH/T 0079 [c(HCl)=0.1000 mol/L].
• 6.1.2 Potassium chloride: prepare a saturated solution.
• 6.1.3 Potassium hydrogen phthalate.
• 6.1.4 Potassium dihydrogen phosphate.
• 6.1.5 Disodium hydrogen phosphate.
• 5.2 Materials: 5.2.1 filter paper; 5.2.2 degreased cotton; 5.2.3 whenever water is involved in the test, distilled water or water of equivalent purity shall be used; 25 ℃ the pH value of distilled water shall be 6.2～7.2.
• Buffer solution preparation:
  • 7.2.1 pH=4.01 (25 ℃) buffer solution: weigh potassium hydrogen phthalate 10.21 g (original text is "10.218", requires confirmation against the source standard (source-text extraction)) that has been dried at 105～110 ℃ for 1 h, weighed to 0.01 g, dissolve in freshly distilled water and dilute to 1 L.
  • 7.2.2 pH=6.86 (25 ℃) buffer solution: weigh potassium dihydrogen phosphate 3.40 g (original text is "3.408", requires confirmation against the source standard (source-text extraction)) that has been dried at 105～110 ℃ for 1 h, weighed to 0.01 g; then weigh disodium hydrogen phosphate 3.55 g (original text is "3.558", requires confirmation against the source standard (source-text extraction)) that has been dried at 105～110 ℃ for 1 h, weighed to 0.01 g; dissolve both in freshly distilled water and dilute to 1 L.
  • Note: Commercially available buffer agents or prepared buffer solutions may be used.

5. Instruments and equipment

• 5.1.1 Potentiometric titrator: any instrument with an accuracy of 0.1 pH value.
• 5.1.2 Glass electrode: type 231.
• 5.1.3 Calomel electrode: type 232.
• 5.1.4 Beaker: 150 mL.
• 5.1.5 Pipette: 10 mL.
• 5.1.6 Burette: 50 mL.

6. Recommended operating conditions

• Titration endpoint pH value: 5.5.
• Hydrochloric acid standard titration solution concentration: c(HCl)=0.1000 mol/L.
• Sample amount: 10 mL (when the reserve alkalinity is less than 2, it may be increased to 50 mL, dilute with water to about 100 mL, divide the total titration value by 5 to obtain the specified reserve alkalinity).
• Volume after dilution: about 100 mL.
• Temperature compensation: adjust the temperature compensator of the potentiometric titrator to the actual temperature of the test sample.
• Electrode calibration: calibrate with two buffer solutions whose pH value range should include the endpoint pH value of the test sample; the difference between the readings of the two buffer solutions should be within 0.05 pH value, otherwise replace the electrodes and recalibrate.
• Instrument stabilization time: after turning on the power, stabilize for 30 min (original text is "30n in", requires confirmation against the source standard (source-text extraction)).

7. Sampling and sample preparation

• 7.1.1 Sampling of concentrated liquid samples: proceed according to SH/T 0065.
• 7.1.2 Preparation of diluted liquid samples: proceed according to SH/T 0065.
• 8.1 Use a pipette to transfer 10 mL of a thoroughly mixed test sample into a 150 mL beaker; the pipette may be allowed to remain in the beaker for 1 min, then add about 90 mL of distilled water to the beaker.

8. Analytical procedure

• 8.2 Place the beaker containing the test sample on the stand of the potentiometric titrator, and completely immerse the two pre-prepared electrodes in the test sample.
• 8.3 Place the lower tip portion (fitted with a thin rubber tube) of the burette pre-filled with hydrochloric acid standard titration solution (6.1.1) into the beaker, adjust the temperature compensator of the potentiometric titrator to the actual temperature of the test sample, and record the initial pH value of the test sample.
• 8.4 Start the stirrer to make the test sample uniform.
• 8.5 Start the titration device, and observe the change in pH value; when the pH value reaches 7, adjust the titration rate so that it drips drop by drop 1 1 until the pH value reaches 5.5, then stop the titration, and record the volume of hydrochloric acid standard titration solution (6.1.1) consumed, to the nearest 0.1 mL.
• Note: If the glass electrode is covered with a film of oil, fat, or other substances, it is recommended to use a mixed solvent of toluene and ethyl acetate in a volume ratio of 1:1 to remove the film layer.
• Electrode preparation (7.3): A new glass electrode should be soaked in distilled water for 24 h before use; after the test, the electrode should be rinsed with distilled water and soaked in distilled water for later use; after continuous use for one week, if the electrode bulb surface is contaminated, the electrode bulb may be soaked in cold chromic acid cleaning solution for 30 s, then rinsed with distilled water, and soaked in distilled water for later use (Note: chromic acid cleaning solution is dangerous, easily causing severe burns, and is a strong oxidant, hygroscopic agent, and toxic substance). The saturated potassium chloride solution in the calomel electrode should be maintained at a certain height; when not in use, put on both rubber caps; after continuous use for one week, the saturated potassium chloride solution should be washed out and replaced with fresh saturated potassium chloride solution.

9. Qualitative and quantitative determination and calculation formula

• The reserve alkalinity V (mL) of the test sample is calculated according to the following formula: V = (c1 / c2) × V1 Where:
  • c1—— Actual concentration of the hydrochloric acid standard titration solution, mol/L;
  • V1—— Volume of hydrochloric acid standard titration solution consumed in the test, mL;
  • c2—— Specified concentration of the hydrochloric acid standard titration solution, i.e., 0.1000 mol/L.
• Appendix A (supplementary document) Calculation of the percentage loss of reserve alkalinity:
  • A1 Percentage loss of reserve alkalinity: refers to comparing the reserve alkalinity data obtained from a series of equivalent tests on similar coolants on an equivalent basis.
  • A2 In simulated or actual coolant use, the percentage loss of reserve alkalinity X (%) is calculated according to formula (A1): X = 100 [ (RA1/C1 − RA2/C2) / (RA1/C1) ] ……(A1) Where:
    • RA1—— Initial coolant reserve alkalinity, mL;
    • RA2—— Final coolant reserve alkalinity, mL;
    • C1—— Initial coolant or additive concentration, % (V/V);
    • C2—— Final coolant or additive concentration, % (V/V).
  • Note: When the concentration of the coolant solution is unknown, it may be determined by appropriate test methods, such as refractive index, freezing point, density, and reference to suitable tables; the water content of the coolant may be determined by the Karl Fischer method, and then its concentration calculated.
  • A3 In the case of automotive vehicle service tests, the percentage loss should be reported per some mileage unit, such as 10 000 km. Although the percentage loss of reserve alkalinity is related to the durability of the coolant and the performance and condition of the cooling system, it is only one aspect of the coolant evaluation method.

10. Precision

• 10.1 Repeatability: The difference between two results of repeated determinations by the same operator shall not exceed 0.2 mL.
• 10.2 Reproducibility: The difference between two results submitted by different laboratories shall not exceed 0.2 mL.

11. Report

Take the arithmetic mean of two results of repeated determinations, to the nearest 0.1 mL, as the reserve alkalinity of the test sample.

12. Referenced documents

• SH/T 0065 Sampling of engine coolant or rust inhibitor test samples and preparation of their aqueous solutions
• SH/T 0079 Preparation methods of reagent solutions for petroleum product testing
• ASTM D1121-88 (reference adoption)

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick Q&A