BS 6200-3 8 2-1991 Sampling and analysis of iron steel and other ferrous metals - Methods of analysis - Determination of carbon - Steel and cast iron non-aqueous titrimetric method.pdf

1、BRITISH STANDARD BS 6200-3.8.2: 1991 Sampling and analysis of iron, steel and other ferrous metals Part 3: Methods of analysis Section 3.8 Determination of carbon Subsection 3.8.2 Steel and cast iron: non-aqueous titrimetric method after combustionBS6200-3.8.2:1991 This British Standard, having been

2、 prepared under the directionof the Iron and SteelStandards Policy Committee, was published underthe authority of the Standards Board and comes intoeffect on 29November1991 BSI 09-1999 The following BSI references relate to the work on this standard: Committee reference ISM/18 Draft for comment 91/3

3、5212 DC ISBN 0 580 19948 7 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Iron and Steel Standards Policy Committee (ISM/-) to Technical Committee ISM/18, upon which the following bodies were represented: BCIRA British Steel Industry De

4、partment of Trade and Industry (Laboratory of the Government Chemist) Ferro Alloys and Metals Producers Association Ministry of Defence Amendments issued since publication Amd. No. Date CommentsBS6200-3.8.2:1991 BSI 09-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scop

5、e 1 2 Principle 1 3 Reagents 1 4 Apparatus 1 5 Sampling 4 6 Procedure 4 7 Calculation and expression of results 7 8 Test report 8 Figure 1 Apparatus for the determination of carbon: non-aqueous titration 2 Figure 2 Detail of tuyre for rapid insertion of the sample 3 Figure 3 Detail of heat-resisting

6、 glass prolong for manganese dioxide 3 Figure 4 Standardization using carbon dioxide injection 6 Table 1 Mass of test portion and titrant concentration 4 Table 2 Precision data 8 Table 3 Predicted valves of r and R 8 Publications(s) referred to Inside back coverBS6200-3.8.2:1991 ii BSI 09-1999 Forew

7、ord This Subsection of BS6200 has been prepared under the direction of the Iron and Steel Standards Policy Committee and supersedes method4 for the determination of carbon in BSI Handbook No.19, to which it is technically equivalent. BS6200 is a multipart British Standard covering all aspects of the

8、 sampling and analysis of iron, steel and other ferrous metals. A list of contents, together with general information, is given in Part1. Other methods for the determination of carbon in ferrous metals have been published in BS6200-3.8.3 and in BSEN10036. A method for the determination of non-combin

9、ed carbon (graphite) has been published as Subsection3.8.5 for use in conjunction with BSEN10036. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard do

10、es not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 8, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. T

11、his will be indicated in the amendment table on the inside front cover.BS6200-3.8.2:1991 BSI 09-1999 1 1 Scope This Subsection of BS6200 describes a non-aqueous titrimetric method for the determination of carbon in steel and cast iron. The method covers the range of carbon contents found in all type

12、s of steel, pig and cast iron and commercially pure iron. NOTEThe titles of the publications referred to in this Subsection of BS6200 are listed on the inside back cover. 2 Principle The test portion is burnt in pure oxygen at a high temperature (up to1350 C) in the presence of a flux. Oxides of sul

13、fur are removed with manganese dioxide and carbon dioxide is absorbed in a mixture of dimethylformamide-ethanolamine. It is then titrated with tetra-n-butylammonium hydroxide. 3 Reagents During analysis use only reagents of recognized analytical grade. 3.1 Benzoic acid, standard solution,0.1mol/L, i

14、n toluene, equivalent to 1.2mg carbon per millilitre. Dissolve1.221g of high-purity benzoic acid C 6 H 5 COOH, in toluene which has been neutralized previously with tetra-n-butylammonium hydroxide (3.14) to the change point of thymolphthalein(3.15). Transfer to a100mL volumetric flask, dilute to the

15、 mark with neutralized toluene and mix. 3.2 Benzoic acid, standard solution,0.02mol/L, in toluene. Transfer by means of a safety pipette, calibrated for delivery of toluene,20mL of benzoic acid solution(3.1) to a100mL volumetric flask, dilute to the mark with neutralized toluene and mix. 3.3 Carbon

16、dioxide absorbent. Replacement for soda asbestos manufactured from synthetic silicates; granular, particle size from0.71mm to1.18mm,(14mesh to22 mesh). 3.4 Carbon dioxide, gas, not less than99.8% purity. 3.5 Charcoal, activated for gas absorption; granular, particle size from0.85mm to1.70mm, (10mesh

17、 to18mesh). 3.6 Dimethylformamide absorption solution. Add2mL of thymolphthalein(3.15) and5mL of monoethanolamine to150mL of dimethylformamide and mix. WARNING. Suitable safety precautions should be taken when making and using this solution. Dimethylformamide is toxic if inhaled, ingested or absorbe

18、d through the skin. 3.7 Fluxes. Tin powder, low in carbon, or alternatively use freshly calcined carbon-free trilead tetraoxide instead of tin powder. When trilead tetraoxide is used keep it in a hot muffle furnace, at450 C to480 C. Pure iron of known carbon content less than0.005% (m/m) and in a si

19、milar state of division to the test sample may be required as a supplementary flux for highly alloyed steels. 3.8 Magnesium perchlorate, anhydrous, Mg(ClO 4 ) 2 ; granular, particle size from0.71mm to1.18mm, (14 mesh to22mesh). 3.9 Manganese dioxide, chemically-reactive precipitated grade; granular,

20、 particle size from0.50mm to1.70mm, (10 mesh to30mesh). 3.10 Oxygen, at least99.5% purity. 3.11 Platinized ceramic fibre, 5% platinum. 3.12 Synthetic ceramic fibre. 3.13 Tetra-n-butylammonium hydroxide, 0.1mol/L, (0.1N) approximately, in toluene/methanol. NOTEThis reagent is best obtained from comme

21、rcial suppliers. 3.14 Tetra-n-butylammonium hydroxide, 0.02mol/L, (0.02N), approximately. Transfer200mL of tetra-n-butylammonium hydroxide(3.13) to a1L volumetric flask, dilute to the mark with toluene and mix. Allow to stand for24h before standardization and use. NOTEIf this reagent is stored in a

22、cold room two phases may separate. To avoid this it is recommended that the titrant is stored at a room temperature of20 C or above. If separation still occurs it can be overcome by making small additions of anhydrous methanol and shaking until the solution is clear. 3.15 Thymolphthalein, 1g/L. Diss

23、olve0.1g of thymolphthalein in100mL anhydrous methanol. 4 Apparatus 4.1 Ordinary laboratory apparatus 4.2 Volumetric glassware, in accordance with classA of BS846, BS1583 or BS1792, as appropriate. 4.3 Apparatus for carbon determination NOTEThe apparatus for the determination of carbon by combustion

24、 and non-aqueous titration is shown diagramatically in Figure 1.BS 6200-3.8.2:1991 2 BSI 09-1999 Figure 1 Apparatus for the determination of carbon: non-aqueous titrationBS6200-3.8.2:1991 BSI 09-1999 3 4.3.1 General. Make all delivery tubes of glass, using either polyethylene or heat-shrinkable poly

25、olefine tubing as the connecting sleeving. Under no circumstances use polyvinylchloride for this purpose. Where necessary, use guard tubes containing carbon dioxide absorbent(3.3) to prevent ingress of carbon dioxide from the atmosphere. Place the reservoir for the dimethylformamide absorption solut

26、ion(3.6) at bench level and pressurize it with a small bulb hand-bellows fitted with a guard tube. 4.3.2 Oxygen supply. Pass a supply of oxygen (3.10) through a silica tube containing5% platinized synthetic ceramic fibre (3.11) maintained at a temperature of625 C to oxidize any carbonaceous impuriti

27、es to carbon dioxide. Remove carbon dioxide and water vapour by subsequent absorption in carbon dioxide absorbent (3.3) and magnesium perchlorate (3.8). NOTEBlank values obtained from oxygen purified in this manner are extremely low, of the order of0.00015% carbon on the basis of a1g sample. 4.3.3 C

28、ombustion unit. Use an electric furnace capable of operating up to a temperature of1350 C. Position the highly refractory combustion tube, e.g.aluminous porcelain or mullite, of internal diameter660mm 22mm, in the furnace so that it is heated over250mm of the centre portion of its length. Draw purif

29、ied oxygen for the combustion of the sample into the furnace via the open-ended tuyre (see Figure 2) fitted to the combustion tube, and through the system by means of a small variable-speed pump. Allow excess oxygen to escape to atmosphere via the open end of the tuyre to prevent ingress of air duri

30、ng introduction of the sample and throughout the combustion cycle. After combustion pass the gases through a synthetic ceramic fibre filter (3.12) to remove solid particles before leaving the tube. Pass the exit gases through precipitated manganese dioxide (3.9) (see Figure 3) to remove sulfur dioxi

31、de before entering the absorption/titration cell. Check the efficient operation of the manganese dioxide at regular intervals by analysing a high-sulfur free-cutting steel of known and, preferably, low carbon content. 4.3.4 Absorption and titration system. Collect the carbon dioxide in the absorptio

32、n/titration cell by absorption in dimethylformamide absorption solution (3.6). Set the end of the gas bubbler at least50mm below the surface of the absorption solution. Use a burette having a tap made of polytetrafluoroethylene. NOTEA piston burette with certified precision has also been found to be

33、 satisfactory. Figure 2 Detail of tuyre for rapid insertion of the sample Figure 3 Detail of heat-resisting glass prolong for manganese dioxideBS6200-3.8.2:1991 4 BSI 09-1999 After absorption of carbon dioxide, pump the gas stream through activated charcoal (3.5) to remove toxic vapours before exit

34、to the atmosphere outside the laboratory. 4.4 Combustion boats. Keep boats for the combustion of test portions in a hot muffle furnace at approximately1000 C and remove them individually for immediate transfer to the combustion tube when required in6.3. 4.5 Gas injection device, required only if sta

35、ndardization method A (see6.5.2), is used. NOTECommercial gas injection devices of the piston-action type have a nominal volume of5mL. The actual calibrated volume is specified by the manufacturer. When a piston injection device is used ensure that the piston remains in the carbon dioxide stream for

36、 at least60s between each injection. 5 Sampling Carry out sampling in accordance with BS1837. NOTEBS6200-2, which will supersede BS1837, is currently in preparation. On its publication, this Subsection will be amended to include sampling in accordance with BS6200-2. 6 Procedure 6.1 Test portion Weig

37、h, to the nearest0.001g, a test portion in the form of fine drillings or millings, previously washed with diethyl ether and dried, in accordance with the expected carbon content as shown in Table 1. Select the test portion and titrant so that the volume of titrant does not exceed12mL irrespective of

38、 its strength. (See6.3, 6.4 and6.5.) Table 1 Mass of test portion and titrant concentration 6.2 Blank test Determine the blank value of the apparatus, boat and flux, but without a test portion, using conditions exactly as detailed in6.3 and make the appropriate correction. 6.3 Determination With the

39、 furnace at working temperature (see6.4) introduce20mL of the dimethylformamide absorption solution (3.6) into the absorption/titration cell. Select the titrant concentration in accordance with Table 1. If the addition of titrant already made and the addition likely for the next test portion will to

40、gether total more than12mL, renew the absorption solution (3.6). Regulate the flow of oxygen from the supply line to register2L/min to3L/min on the input flowmeter then, by means of the variable-speed pump, draw oxygen through the system at450mL/min as registered on the output flowmeter. Transfer an

41、 empty boat to the combustion furnace and pass oxygen at the regulated rate for2min to3min to ensure complete oxidation of carbonaceous matter. Remove and allow to cool while the test portion is weighed. Titrate the absorption solution with tetra-n-butylammonium hydroxide (3.13 or3.14) to a blue end

42、 point. Transfer the test portion (6.1) to the pre-ignited combustion boat without delay. Cover the test portion with1g of tin flux (3.7) and push the boat into the hot zone of the furnace. NOTEIf trilead tetraoxide is used as flux it is recommended that it is not weighed but transferred directly to

43、 the combustion boat by means of a calibrated scoop holding approximately2g, thus preventing pick-up of carbon during cooling and weighing. Continue the titration with tetra-n-butylammonium hydroxide solution (3.13 or3.14) as the absorption solution becomes decolourized during the combustion period

44、until a stable blue colour marks the end point. Record the volume of titrant used during the period following the introduction of the boat, flux and test portion. Remove the boat and if combustion is incomplete reject the result. WARNING. After use keep all waste solutions in containers sealed with

45、guard tubes containing activated charcoal and dispose of them safely. 6.4 Alternative combustion conditions For carbon and low-alloy steels use the hot zone having a temperature in the range1050 C to1100 C as measured on the inside of the combustion tube. For highly alloyed steels and3% silicon stee

46、ls use temperatures up to1350 C, depending upon the type of steel, to ensure complete combustion. Some types of high chromium nickel steels require a supplementary aid to the combustion in addition to tin powder or trilead tetraoxide. In these cases mix the test portion with an equal mass of iron of

47、 known low carbon content less than0.005% (m/m) in a similar state of division to the test portion. Add the same amount of iron to the blank test so that it is an inclusive correction for the carbon content of boat, flux and iron. Carbon Test portion Titrant % (m/m) g mol/L 0.010 to 0.20 1 0.02 (see

48、 3.14) 0.20 to 1.00 1 0.10 (see 3.13) 1.00 to 4.00 0.25 0.10 (see 3.13) 4.00 0.2 or less, as necessary 0.10 (see 3.13)BS6200-3.8.2:1991 BSI 09-1999 5 6.5 Standardization 6.5.1 General Standardize the tetra-n-butylammonium hydroxide (3.13 or3.14) using one of the methods described in6.5.2 or6.5.3. Ca

49、lculate the strength of the titrant using the appropriate equations in6.5.4. Repeat the standardization at frequent intervals if there are wide variations of temperature in the laboratory. 6.5.2 Method A: carbon dioxide injection Position the gas injection device (see Figure 4) between the combustion furnace and the absorption/titration cell. Connect to a supply of carbon dioxide(3.4). Pass the carbon dioxide through a delay coil to allow the gas to reach ambient temperature, then through the injection valve and on to the atmosphere