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1、INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXAYHAPOCHAH OPTAHM3AMFl IlO CTAHAAPTM3AMM Petroleum products and lubricants - Neutralization number - Potentiometric titration method Produits p4 troliers et lubrifian ts - lndice de
2、neutralisa tion - Mb thode par titrage po ten tiomk trique IS0 6619 First edition 1988-12-01 Reference number IS0 6619: 1988 (E) Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/23/2007 2
3、2:15:55 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 6619 : 1988 (E) Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normall
4、y carried out through IS0 technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison with ISO, also take part in th
5、e work. IS0 collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International St
6、andards by the IS0 Council. They are approved in accordance with IS0 procedures requiring at least 75 % approval by the member bodies voting. International Standard IS0 6619 was prepared by Technical Committee ISO/TC 28, Petroleum products and lubricants. Annex A of this International Standard is fo
7、r information only. 0 International Organization for Standardization, 1988 Printed in Switzerland Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/23/2007 22:15:55 MDTNo reproduction or n
8、etworking permitted without license from IHS -,-,- INTERNATIONAL STANDARD IS0 6619: 1988 (E) Petroleum products and lubricants - Neutralization number - Potentiometric titration method 1 Scope 1.1 This International Standard specifies a method for the determination of acidic constituents in petroleu
9、m products and lubricants soluble or nearly soluble in mixtures of toluene and propan-2-01. It is applicable for the determination of acids whose dissociation constants in water are larger than 10Wg; ex- tremely weak acids whose dissociation constants are smaller than 10mg do not interfere. Salts re
10、act if their hydrolysis con- stants are larger than 10Bg. NOTE - In new and used oils, the constituents that may be considered to have acidic characteristics include organic and inorganic acids, esters, phenolic compounds, lactones, resins, salts of heavy metals, salts of ammonia and other weak base
11、 constituents, acid salts of polybasic acids, and additives such as inhibitors and detergents. 1.2 This method may be used to indicate relative changes that occur in an oil during use under oxidizing conditions regardless of the colour or other properties of the resulting oil. Although the titration
12、 is made under definite equilibrium condi- tions, the method does not measure an absolute acidic or basic property that can be used to predict performance of an oil under service conditions. No general relationship between bearing corrosion and acid or base number is known. NOTE - A colour-indicator
13、 titration method is also available in IS0 6618 (see bibliography in annex AL The acid numbers obtained by the potentiometric method may or may not be numerically the same as those obtained by IS0 6618, but they are generally of the same order of magnitude. 1.3 New and used petroleum products may co
14、ntain acidic constituents that are present as additives or as degradation products formed during service, such as oxidation products. The relative amounts of these materials can be determined by titrating with bases. The acid number is a measure of this amount of acidic substances in the oil under t
15、he conditions of the test. The acid number is used as a guide in the quality con- trol of lubricating oil formulations. It is also sometimes used as a measure of lubricant degradation in service. Any condemning limits must be empirically established. As a variety of oxidation products contribute to
16、the acid number and the organic acids vary widely in corrosion proper- ties, the test cannot be used to predict corrosiveness of an oil under service conditions. No general correlation is known be- tween acid number and the corrosive tendency of oils toward metals. Compounded engine oils can, and us
17、ually do, have an acid number in this test. 2 Definitions For the purposes of this International Standard, the following definitions 2.1 acid milligrams quired to t apply rn number: The quantity of base, expressed in of potassium hydroxide per gram of sample, re- trate potentiometrically a test port
18、ion in a specified solvent from its initial meter reading to a meter reading cor- responding to that obtained with a freshly prepared basic non- aqueous buffer solution or a well defined inflection point as specified in the standard. 2.2 strong acid number: The quantity of base, expressed in milligr
19、ams of potassium hydroxide per gram of sample, re- quired to titrate potentiometrically a test portion in a specified solvent from its initial meter reading to a meter reading cor- responding to that obtained with a freshly prepared acidic non- aqueous buffer solution or a well defined inflection po
20、int as specified in the standard. I Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/23/2007 22:15:55 MDTNo reproduction or networking permitted without license from IHS -,-,- is0 6619: 1
21、988 E) 3 Principle The test portion is dissolved in a mixture of toluene and propan-2-01 containing a small amount of water and titrated potentiometrically with alcoholic potassium hydroxide using a glass indicating electrode and a calomel reference electrode. The meter readings are plotted manually
22、 or automatically against the respective volumes of titrating solution and the end points are taken only at well defined inflections in the resulting curve. When no definite inflections are obtained, end points are taken at meter readings corresponding to those found for non- aqueous acidic and basi
23、c buffer solutions. 4 Reagents During the analysis, use only reagents of recognized analytical grade, and only distilled water or water of equivalen t purity. 4.1 Non-aqueous acidic buffer solution Add 10 ml of buffer stock solution A (4.5) to 100 ml of titration solvent. Use within 1 h. 4.2 Non-aqu
24、eous basic buffer solution Add 10 ml of buffer stock solvent. Use within 1 h. solution B (4.6) to 100 ml of titration 4.3 2,4,6-Trimethylpyridine (y-Collidine) (A the dates of sampling and testing shall be noted. 6.2 Heat the laboratory sample of used oil to 60 + 5 OC in the original container with
25、agitation until all of the sediment is homogeneously suspended in the oil. If the original container is a can, or if it is glass and more than three-fourths full, transfer the entire sample to a clear glass bottle having a capacity at least one-third greater than the volume of the sample. Transfer a
26、ll traces of sediment from the original container to the bottle by violent agitation of portions of the sample in the original container. 5.1.5 Burette (E in figure l), 10 ml capacity, graduated in 0,05 ml divisions, and calibrated with an accuracy of + 0,02 ml. The burette shall have a glass stopco
27、ck and shall have a tip that extends 100 to 130 mm beyond the stopcock. The burette for KOH shall have a guard tube containing soda lime or other CO*-absorbing substance. NOTE - When laboratory samples are visibly free from sediment, the heating procedures described may be omitted. 6.3 After complet
28、e suspension of all sediment, strain the test sample or a convenient aliquot through a loo-mesh screen to remove large contaminating particles. 4 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Res
29、ale, 04/23/2007 22:15:55 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 6619: 1988 E) 7 Preparation of electrode system 7.1 Maintenance of electrodes 7.1.1 Clean the glass electrode (5.1.2) at frequent intervals (not less than once every week during continual use) by i
30、mmer- sing in cold chromic acid cleaning solution. A suitable detergent instead of the chromic acid cleaning solution can also be used. NOTE - In order to prevent damage to the electrode, do not leave it immersed in the chromic acid for more than a few minutes. 7.1.2 Drain the calomel reference elec
31、trode (5.1.3) at least once each week and refill with fresh KCI electrolyte (4.10). Ascertain that crystallized KCI is present. Maintain the elec- trolyte level in the calomel electrode above that of the liquid in the titration beaker at all times. 7.1.3 When the electrodes are not in use, immerse t
32、he lower halves in water. Do not allow them to remain immersed in titra- tion solvent for any appreciable period of time between titra- tions. Although the electrodes are not particularly fragile, handle them carefully at all times. 7.2 Preparation of electrodes 7.2.1 Before and after use, wipe the
33、glass electrode thoroughly with a clean cloth or a soft absorbent tissue, and rinse with water. Wipe the calomel reference electrode with a cloth or tissue, carefully remove the ground-glass sleeve and thoroughly wipe both ground surfaces. 7.2.2 Replace the sleeve loosely and allow a few drops of el
34、ectrolyte to drain through to flush the ground-glass joint. Wet the ground surfaces thoroughly with electrolyte, set the sleeve firmly in place, and rinse the electrode with water. 7.2.3 Prior to each titration, soak the prepared electrodes in water for at least 5 min immediately before use, and tou
35、ch the tips of the electrodes with a dry cloth or tissue to remove the excess water. 7.3 Testing of electrodes 7.3.1 Test the meter/electrode combination when first put into use, or when new electrodes are installed, and retest at intervals thereafter by dipping the electrodes into a well stirred mi
36、xture of 100 ml of the titration solvent and 1,0 to 1,5 ml of 0,l mol/l alcoholic KOH solution (4.11). 7.3.2 The meter/electrode combination is suitable for use when the potential changes more than 480 mV from the poten- tial between the same electrodes when dipped into the acidic non-aqueous buffer
37、 solution (4.1). NOTE - Cleaning the electrodes thoroughly, keeping the ground-glass joint free of foreign materials, and regular testing of the electrodes are very important in obtaining reproducible potentials, since contamina- tion may introduce uncertain, erratic and undetectable liquid-contact
38、potentials. While this is of secondary importance when end points are chosen from inflection points in the titration cu rve, it may be quite serious when end points are c hosen at arbitrarily fixed cell potentials. 8 Standardization of apparatus 8.1 Determination of meter readings for the non-aqueou
39、s buffer solutions corresponding to acid end points To ensure comparable selection of end points when definite in- flection points are not obtained in the titration curve, determine daily, for each electrode pair, the meter readings obtained with the acidic (4.1) and basic (4.2) non-aqueous buffer s
40、olutions. 8.2 Prepare the electrodes as described in 7.2, immerse them in the non-aqueous buffer solution and stir for 5 min, maintain- ing the buffer solution at a temperature within 2 OC of that at which the titrations are to be made. Read the cell voltage. The readings so obtained are taken as th
41、e end points in titration curves having no inflection points. 9 Procedure for total acid number and strong acid number 9.1 Into the 250 ml titration beaker (5.1.6), introduce a weighed quantity of test sample, as prescribed in table 1, and 125 ml of titration solvent (4.13). Prepare the electrodes a
42、s directed in 7.2. Place the beaker on the titration stand (5.1.7) and adjust its position so that the electrodes are about half-immersed. Start the stirrer (5.1.4), and stir throughout the determination at a rate sufficient to produce vigorous agitation without spattering and without stirring air i
43、nto the solution. Table 1 - Size of test portion I Acid number Mass of Accuracy of test portion, g weighing, g 0,05 to I,0 20,o III 2,0 0,lO I,0 to 5,0 5,0 * 0,5 0,02 5 to 20 I,0 zk 0,l 0,005 20 to loo 0,25 zk 0,02 0,001 100 to 250 0,l f 0,Ol 0,ooo 5 the beaker. Record the intitial burette and meter
44、 (cell potential) readings. 9.3 Manual titration method 9.3.1 Add suitable small portions of 0,l mol/l alcoholic KOH solution and, after waiting until a constant potential has been established, record the burette and meter readings. NOTE - Consider the cell potential to be constant when it changes l
45、ess than 5 mV per minute. This may mean waiting approximately 1 to Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/23/2007 22:15:55 MDTNo reproduction or networking permitted without lic
46、ense from IHS -,-,- IS0 6619:1988 (E) 2 min per 100 mV change in potential when adding crements; 0,l ml increments may require 3 to 5 min. 0,05 ml in- 9.3.2 At the start of the titration and in any subsequent regions (inflections) where 0,l ml of 0,l mol/l KOH solution consistently produces a total
47、change of more than 30 mV in the cell potential, add 0,05 ml portions. 9.3.3 In the intermediate regions (plateaux) where 0,l ml of 0,l mol/l alcoholic KOH solution changes the cell potential less than 30 mV, add larger portions sufficient to produce a total potential change approximately equal to,
48、but not greater than, 30 mV. 9.3.4 Titrate in this manner until the potential changes less than 5 mV per 0,l ml of KOH solution added and the cell potential indicates that the solution is more basic than the non- aqueous basic buffer. 9.3.5 Remove the titrated solution and rinse the electrodes and b
49、urette tip with the titration solvent, then with propan-2-01 and finally with distilled water. Immerse the electrodes in distil- led water for at least 5 minutes before another titration to restore the aqueous gel layer of the glass electrode. Store elec- trodes in distilled water when not in use. If electrodes are found to be dirty and contaminated, proceed as in clause 7. 9.4 Automatic titration method 9