JB/T 7948.12-1999 This standard is equivalent to ΓOCT 2978.1~.10-78 "Methods for chemical analysis of melting flux". This standard is a revision of JB/7948.12-95 "Methods for chemical analysis of melting flux - EDTA volumetric method for determination of calcium oxide and magnesium oxide". During the revision, only editorial changes were made according to relevant regulations, and its technical content has not changed. This standard is applicable to the determination of calcium oxide and magnesium oxide in melting flux, with a determination range of 1.00%~20.0%. This standard was first issued in 1985 as GB 5292.12-85 and adjusted to JB/T 7948.12-95 in April 1996. JB/T 7948.12-1999 Chemical analysis method for melting flux EDTA volumetric method for determination of calcium oxide and magnesium oxide content JB/T7948.12-1999 standard download decompression password: www.bzxz.net

JB/T7948.12—1999
This standard is equivalent to IOCT22978.1~22978.10—78 "Chemical Analysis Method for Melting Flux". This standard is a revision of JB/T7948.12--95 "Chemical Analysis Method for Melting Flux - EDTA Volumetric Method for Determination of Calcium Oxide and Magnesium Oxide". During the revision, only editorial changes were made to the standard, and its technical content remained unchanged. This standard replaces JB/T7948.12—95 from the date of implementation. 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. 393
1 Scope
Standard of the Machinery Industry of the People's Republic of China
Methods for chemical analysis of melted welding fluxes
EDTA volumetric method for determination of calcium oxide and magnesium oxide contentJB/T 7948.12—1999
Replaces JB/T7948.12-95
This standard is applicable to the determination of calcium oxide and magnesium oxide in melted welding fluxes. The determination range is 1.00%~20.0%. 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 all 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 JB/T7948.2-1999 Chemical Analysis Methods for Fusion Welding Flux Potentiometric Titration Method for Determination of Manganese Oxide Content JB/T7948.4-1999 Chemical Analysis Methods for Melting Flux EDTA Volumetric Method for Determination of Aluminum Oxide Content JB/T7948.6-1999 Chemical Analysis Methods for Melting Flux Pyrolysis Method for Determination of Calcium Fluoride Content 3 Method Summary
This method is based on the titration of calcium with EDTA solution in an alkaline medium with a pH of 12, using a fluorescent yellow complexing agent (or calcein) as an indicator. At the equivalence point, the green fluorescence of the complex formed by calcium and the fluorescent yellow complexing agent turns into the orange color of the free indicator. The amount of calcium oxide converted from calcium fluoride is deducted from the total calcium content measured to calculate the percentage of calcium oxide. In an ammonia medium with a pH of 10, use chrome black T as an indicator to titrate the total amount of calcium and magnesium with EDTA solution. At the equivalence point, the red-purple color of the complex formed by calcium, magnesium and chrome black T changes to the bright blue color of the free indicator. Calculate the percentage of magnesium oxide based on the difference in volume between the EDTA solution consumed in titrating the total amount of calcium and magnesium and the EDTA solution consumed in titrating the amount of calcium. 4 Reagents
4.1 Ammonium hydroxide (specific gravity 0.88).
4.2 Hydrochloric acid (1+1).
4.3 Potassium hydroxide solution (30%).
4.4 Sodium diethyldithiocarbamate solution L(C,H,)2N+CS2Na·3HzO](copper reagent) (10%). 4.5 Ammonium hydroxide-ammonium chloride buffer solution: Weigh 67.5g of ammonium hydroxide and dissolve it in an appropriate amount of water, add 570mL of ammonium hydroxide (4.1), and dilute to 1000mL with water.
4.6 Mixed indicator: weigh 0.2g fluorescent yellow complexing agent or calcein and 0.05g thymolphthalein, grind in an agate mortar, then add 20g potassium chloride and grind. Store in a bottle with a lid. Approved by the State Bureau of Machinery Industry on 1999-06-24.894
Implemented on 2000-01-01
4.7 Malachite green solution (1%).
JB/T7948.12—1999
4.8 Chrome black T indicator: weigh 0.2g Chrome black T and 20g potassium chloride and grind. Store in a bottle with a lid. 4.9 Calcium oxide standard solution: Weigh 0.8923g of calcium carbonate (reference reagent) previously dried at 110℃ to constant weight, place in a 300mL beaker, add a small amount of water to moisten, cover with a watch glass, add 10mL of hydrochloric acid (4.2), and heat until completely dissolved. Cool, transfer to a 1000mL volumetric flask, dilute to scale with water, and mix. This solution contains 0.0005g of calcium oxide in 1ml. 4.10 Magnesium oxide standard solution: Weigh 0.3015g of metallic magnesium (99.999%), place in a 300mL beaker. Add a small amount of water, cover with a watch glass, and slowly add 25mL of hydrochloric acid (4.2) (the effect is intense, place in a cold water bath). Then place on an electric stove and heat to boil for several minutes. Cool, transfer to a 1000mL volumetric flask, dilute to scale with water, and mix. This solution contains 0.0005g of magnesium oxide in 1ml. 4.11 Disodium ethylenediaminetetraacetate (C1oH14N2O.Naz·H2O) (EDTA) standard solution (0.025N). Calibration:
4.11.1 Take three portions of 10.00mL calcium oxide standard solution (4.9) and place them in 250mL L-shaped cups respectively. Add 100mL water and 2-3 drops of malachite green solution (4.7). Add potassium hydroxide solution (4.3) slowly under vigorous stirring until the solution fades. Add 0.05g mixed indicator (4.6). Titrate with EDTA standard solution (4.11) until the solution changes from green fluorescence to rose red. Calculate the titration degree of EDTA standard solution (4.11) on calcium oxide according to formula (1): T,=V
Where: ml—the amount of calcium oxide contained in the calcium oxide standard solution (4.9) transferred, g; (1)
V,—the average volume of EDTA standard solution (4.11) consumed during titration (if the extreme difference exceeds 0.10mL, it should be recalibrated) mL;
Ti—the amount of calcium oxide equivalent to 1mL EDTA standard solution (4.11), g. 4.11.2 Transfer three portions of 10.00mL of magnesium oxide standard solution (4.10) and place them in 250mL conical cups respectively, add 100mL of water and 10mL of ammonium hydroxide-magnesium chloride buffer solution (4.5), add 0.05g of chrome black T indicator (4.8), and titrate with EDTA standard solution (4.11) until the solution changes from lilac purple to bright blue.
Calculate the titer of EDTA standard solution (4.11) on magnesium oxide according to formula (2): T.
Where: mz-
The amount of magnesium oxide contained in the magnesium oxide standard solution (4.10) is transferred, g; (2)
The average volume of EDTA standard solution (4.11) consumed during titration (if the extreme difference exceeds 0.10ml., it should be recalibrated) mL:
5 samplewww.bzxz.net
1mLEDTA standard solution (4.11) is equivalent to the amount of magnesium oxide, g. The sample should pass through a 200 mesh sieve. Pre-dry at 105110℃ 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 volume
Weigh 0.5000g of sample and follow the steps 7.3.1 to 7.3.5 of JB/T7948.2-1999 to transfer 50.00mL of test solution. 6.3 Determination
6.3.1 Treat the test solution (6.2) according to the steps 6.3.1 to 6.3.2 of JB/T7948.4-1999, combine the two filtrates and transfer them to a 500mL volumetric flask, and add the copper reagent solution (4.4) according to Table 1. 395
Amount of manganese oxide
10.0~20.0
>20, 0~40. 0
740. 0-50. 0
JB/T7948.12-1999
Table 1 Amount of copper reagent added
Amount of copper reagent added
Close the bottle cap, shake vigorously for 4~5min, dilute with water to the scale, and mix well. Let stand for 1h, and filter with two medium-speed filter papers. 6.3.2 Determination of calcium oxide
Pipette 100.00mL solution (6.3.1) into a 500mL conical cup, add 2~3 drops of peacock edge solution (4.7), and slowly add potassium hydroxide solution (4.3) under vigorous stirring until the solution fades. Add 0.05g of mixed indicator (4.6) and titrate with EDTA standard solution (4.11) until the solution changes from green fluorescence to rose red. 6.3.3 Determination of magnesium oxide
Pipette 100.00mL of solution (6.3.1) into a 500mL conical cup, add 50mL of water, and titrate with ammonium hydroxide (4.1) Neutralize to a pH of about 10 (test with pH paper). Add 10 mL of ammonium hydroxide-ammonium fluoride buffer solution (4.5), add 0.05 g of chrome black T indicator (4.8), and titrate with EDTA standard solution (4.11) until the solution changes from lilac purple to bright blue (this is the total amount of calcium and magnesium). 7 Calculation of analysis results
7.1 Calculate the percentage of total calcium oxide according to formula (3): Total CaO
Wherein: V, volume of EDTA standard solution (4.11) consumed in titrating the total calcium content (6.3.2), mL; Ti——1 mLEDTA standard solution (4.11) equivalent to the amount of calcium oxide + g, ml
-the amount of test solution (6.3.2) equivalent to the sample*8. 7.2 Calculate the percentage of calcium oxide according to formula (4): CaO = Total Ca0-CaF, X 0.718.
Wherein: CaFz
The amount of calcium oxide calculated according to JB/T7948.6, the conversion factor for converting calcium fluoride into calcium oxide. 7.3 Calculate the percentage of magnesium oxide according to formula (5): Mg0-Y×100%
Wherein, V,-
The volume of EDTA standard solution (4.11) consumed by titrating the total amount of calcium and magnesium (6.3.3), mL; The volume of EDTA standard solution (4.11) consumed by titrating the total amount of calcium (6.3.2), mLT2-1mL. The amount of magnesium oxide equivalent to EDTA standard solution (4.11)?g1m2
8Allowed whole
The amount of test solution (6.3.3) equivalent to the sample, g. The difference between the parallel determination results should not be greater than the allowable difference listed in Table 2. ：396
Calcium oxide or oxidation modulus
0.50~-1.00
>1.00~～2.00
>2.00～4.00
>4.00~10.0
≥10.0~20.0
JB/T 7948.12-1999
Allowable difference
Allowable difference
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