JB/T 7948.7-1999 Chemical analysis methods for molten fluxes Lead fluoride chloride-EDTA volumetric method for determination of calcium fluoride content
Some standard content:
JB/T7948.7-1999www.bzxz.net
This standard is equivalent to TOCT22978.1~~22978.10--78 "Chemical Analysis Method for Melting Flux". This standard is a revision of JB/T7948.7--95 "Chemical Analysis Method for Melting Flux - Determination of Calcium Oxide Content by Lead Fluoride-EDTA Volumetric Determination". During the revision, only editorial changes were made to the standard, and its technical content remained unchanged. This standard replaces JB/T7948.7-95 from the date of implementation. Appendix A of this standard is a prompt appendix. This standard is proposed and managed by the National Welding Standardization Technical Committee. The drafting unit of this standard: Harbin Welding Research Institute. The main drafters of this standard: Lin Kegong and Bai Shuyun. 371
1 Scope
Standard of the Machinery Industry of the People's Republic of China
Methods for chemical analysis of melted welding fluxesThe lead chblorofluoride-ED'TA volumetric methodfor determination of calcium fluoride contentJB/T 7948.7---1999
Replaces JB/T7948.7--95
This standard is applicable to the determination of calcium fluoride in melted welding fluxes. The determination range is 3.00%~~40.0%. This standard complies with GB/T1467-1978 "General Principles and General Provisions for Chemical Analysis Methods of Metallurgical Products". 2 Referenced Standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard was published, the versions shown were valid. All standards are subject to revision. Parties using this standard should explore the possibility of using the latest version of the following standards. GB/T1467-1978 General Principles and General Provisions for Chemical Analysis Methods of Metallurgical Products 3 Method Summary
This method is based on the precipitation of fluoride ions in the form of lead oxyfluoride and the titration of excess lead with EDTA solution. The percentage of calcium fluoride is converted from this.
4 Reagents
4.1 Sodium potassium carbonate.
4.2 Ammonium carbonate.
4.3 Silicon dioxide.
4.4 Glacial acetic acid.
4.5 Ethanol (99.5%).
4.6 Nitric acid (1+1).
4.7 Ammonium hydroxide (1+1).
4.8 Tartaric acid solution (5%).
4.9 Sodium chloride solution (5%).
4.10 Methyl orange solution (0.1%).
Eriochrome black T indicator: weigh 0.2g eochrome black T and 20g potassium chloride, grind evenly, and store in a bottle with a lid. Fluorine standard solution: weigh 2.210g sodium fluoride (reference reagent) dried at 105-110℃ to a constant amount, dissolve in an appropriate amount of water, transfer to a 1000mL volumetric flask, dilute to the scale with water, and mix well. This solution contains 1.0mg fluorine in 1mL. 4.13 Disodium ethylenediaminetetraacetate (C1H1N,OgNa2·H,O) (EDTA) standard solution (0.05N). 4.14
Lead acetate standard solution: Weigh 12.5g lead acetate [Pb(CH.COO)3H2O] and dissolve it in appropriate amount of water, add a few drops of glacial acetic acid (4.4), transfer it to a 500mL volumetric flask, dilute it to the mark with water, and mix it. Calibration: Transfer three portions of 25.00mL of chlorine standard solution (4.12), place them in 300mL beakers, add 10 drops of glacial acetic acid (4.4), add 20mL sodium fluoride solution (4.9) and 25.00mL lead acetate standard solution (4.14), stir, heat to 60~~70℃, stir until precipitation appears, and let it stand for 12h. Transfer the solution and precipitate into a 250mL volumetric flask, wash the beaker with water and dilute to the mark, mix with a spoon. Dry filter with medium-speed filter paper. Transfer 100.00mL of solution and follow the steps in 6.3.5. Calculate the titration degree of lead acetate standard solution (4.14) on calcium fluoride according to formula (1): mX2.055
wherein: m—the amount of fluorine equivalent to the fluorine standard solution (4.12) transferred into the calibration solution; g—the volume of lead acetate standard solution (4+14) transferred into the calibration solution, mL; Vi—the average volume of EDTA standard solution (4.13) consumed during titration (if the extreme difference exceeds 0.10mL, recalibration should be performed), mL;
the amount of calcium fluoride equivalent to 1mL of lead acetate standard solution (4.14); 2.055—the conversion factor for fluorine to calcium fluoride; K—the coefficient for converting EDTA standard solution (4.13) to lead acetate standard solution (4.14). The method is as follows: take three portions of 5.00mL of ethyl lead standard solution (4.14) and place them in 250mL conical cups respectively, add 50mL of water and 10mL of tartaric acid solution (4.8) and 10mL of ammonium hydroxide (4.7), add 0.05g of chrome black T indicator (4.11), and titrate with EDTA standard solution (4.13) until the solution changes from fragrant purple to bright blue. Calculate the coefficient of EDTA standard solution (4.13) converted to lead acetate standard solution (4.14) according to formula (2): V
Where: Vs-the volume of lead acetate standard solution (4.14) taken, mL*V4
5Sample
The average volume of EDTA standard solution (4.13) consumed during titration (if the extreme difference exceeds 0.10mL, it should be recalibrated), mL.
The sample should pass through a 200-mesh sieve. Pre-dry at 105-110℃ for 1h, place in a desiccator and cool to room temperature. 6 Analysis steps
6.1 Determination quantity
Three samples should be weighed for determination during analysis, and the average value should be taken. 6.2 Sample quantity
Weigh the sample according to Table 1:
Weighing quantity
Calcium chloride quantity
6.3 Determination
Weighing quantity
6.3.1 Place the sample (6.2) in a platinum crucible containing 4g potassium sodium carbonate (4.1), add silicon dioxide (4.3) according to Table 2, mix well, cover with 2g potassium sodium carbonate (4.1), cover the crucible, move to a high-temperature furnace at 1000℃±20℃, and melt for 20~30min. Take out and cool. 373
Silicon dioxide content in the sample
JB/T7948.7—1999
Table 2 Silica addition amount
Silica addition amount
6.3.2 Wipe the outer wall with filter paper, place in a 300mL beaker, add 50mL hot water, cover with filter paper, heat and remove the sintered block, wash with water and take out the crucible. Add 10 drops of ethanol (4.5), boil, and cool. Transfer to a 100mL volumetric flask, wash the beaker and filter paper with water and dilute to the scale, mix well. Dry filter with medium-speed filter paper. 6.3.3 Pipette 50.00mL of solution (6.3.2) into a 300mL beaker, add 1 drop of methyl orange indicator (4.10), acidify with nitric acid (4.6) until the solution turns orange-red, add 4-5g of ammonium carbonate (4.2), cover with a watch glass, and boil to remove the ammonia smell. At this time, silica condenses and precipitates. Filter with cotton into a 300mL beaker, wash the beaker with hot water and wash the precipitate 8-10 times. Discard the precipitate. 6.3.4 Acidify the solution (6.3.3) with nitric acid (4.6) until the solution changes from yellow to orange-red, add 10 drops of glacial acetic acid (4.4) and 20mL of sodium fluoride solution (4.9), add 25.00mL of lead acetate standard solution (4.14) with a burette, stir, heat to 60-70℃, stir again until a precipitate precipitates, and let stand for 12h. Transfer the solution and precipitate to a 250 mL volumetric flask, wash the beaker with water and dilute to the mark, mix. Dry filter with medium-speed filter paper.
6.3.5 Transfer 100.00 mL of solution (6.3.4) to a 250 mL conical cup, add 10 mL of tartaric acid solution (4.8) and 10 ml of ammonium hydroxide (4.7), add 0.05 g of chrome black T indicator (4.11), and titrate with EDTA standard solution (4.13) until the solution changes from lilac purple to bright blue.
Calculation of analysis results
Calculate the percentage of calcium fluoride according to formula (3): (V,-V,K)T
Wherein: V-
The volume of lead acetate standard solution (4.14) pipetted from the test solution (6.3.5), mL; The volume of EDTA standard solution (4.13) consumed during one titration, mLK-EDTA standard solution (4.14).13) Coefficient for conversion to lead acetate standard solution (4.14): T----1mL lead acetate standard solution (4.14) is equivalent to the amount of calcium fluoride, g; m
8 allowable difference
the amount of test solution (6.3.5) equivalent to the sample + g. The difference between the parallel determination results should not be greater than the allowable difference listed in Table 3. Table 3 Allowable difference
Calcium fluoride content
3. 0~5. 0
>5.0~10.0
>10.0~20. 0
≥20.040. 0
Allowable difference
JB/T 7948.7--1999
Appendix A
(Suggestive appendix)
Mechanism of adding silicon dioxide to high-fluorine low-silicon flux sample melting The high-fluorine low-silicon flux is not completely decomposed by melting the sample with potassium and sodium carbonate alone. Adding a small amount of silicon dioxide and potassium and sodium carbonate to melt together can convert calcium fluoride into soluble fluoride, so that the sample is completely decomposed. CaF,+SiO,+2NazCO=CaCO,+NazSiO,+2NaF-+CO2375
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