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National Standard of the People's Republic of China
Method for chemical analysis of graphite
Method for chemical analysis of graphite1 Subject content and scope of application
This standard specifies the reagents, instruments, analysis steps, result calculation and tolerance for chemical analysis of graphite. GB/T 3521--95
Replaces GB3521-83
This standard applies to the analysis of moisture, volatile matter, ash, fixed carbon, sulfur and acid-soluble iron in natural graphite products. 2 Reference standards
GB/T3518 Phosphorus flake graphite
GB/T3519 Microcrystalline graphite
3 General provisions
3.1 The samples for chemical analysis obtained by the sampling methods specified in GB/T3518 and GB/T3519 should be placed in plastic bags or ground-mouth bottles, and the sample volume should not be less than 50g.
3.2Except for the sample for moisture determination, all other analysis items shall be analyzed after drying at 105-110℃ to constant weight. 3.3The weighing of high, medium and low carbon samples shall be accurate to 0.1mg, and when constant weight is required, the difference between two weighings shall not exceed 0.3mg. The weighing of high purity graphite samples shall be accurate to 0.02mg, and the constant weight shall be the difference between two weighings shall not exceed 0.05mg. 3.4All analysis items must be measured in parallel. The analysis of sulfur shall be carried out with a blank test, and the titration analysis of iron shall be carried out with a control test, and the measured results shall be corrected.
3.5The calculation results of high purity graphite shall be expressed to three decimal places, and the calculation results of other items shall be expressed to two decimal places. 4 Moisture determination method
4.1 Summary of method
Dry the sample at 105-110℃ to volatilize the attached water, and calculate the percentage of moisture based on the volatilization amount. 4.2 Instruments
4.2.1 Oven or other instruments with equivalent performance: working temperature is 105～110℃; 4.2.2 Balance: sensitivity 0.1mg.
4.3 Analysis steps
Weigh 1～2g of undried sample, put it into a ground-mouth weighing bottle that has been dried to constant weight, and place it in an oven at 105～110℃. Open the lid, bake for 1～2h, take out the weighing bottle, cover it, place it in a desiccator to cool to room temperature, and weigh it. Put it in the oven and bake for 30min, take it out, cool it, and weigh it. Repeat this process until constant weight is achieved. The last data is used as the basis for calculation. 4.4 Calculation of results
The moisture content is calculated according to formula (1):
= mo= ㎡ × 100
Approved by the State Administration of Technical Supervision on February 7, 1995 (1)
Implemented on October 1, 1995
Where: 1-moisture content, %;
The mass of the sample before drying, g;
m——The mass of the sample after drying, g.
5 Determination of volatile matter
5.1 Nitrogen protection method (arbitration method)
5.1.1 Summary of the method
GB/T 3521---95
The sample is placed in a nitrogen flow and ignited at high temperature to decompose and release the volatile substances therein. The ignition loss is the volatile matter. 5.1.2 Instruments and materials
5.1.2.1 Balance: Sensitivity 0.1mg.
5.1.2.2 Pyrolysis furnace: Square tube furnace with gas path system (see Figure 1), working temperature 950±20℃. 2
Figure 1 Flow chart of pyrolysis furnace system
1—Gas flow fine-tuning valve: 2—Flowmeter; 3—Square quartz tube: 4—Pyrolysis furnace, 5—Sample guide 6—Quartz boat and tray, 7—Furnace mouth baffle 5.1.2.3 Quartz boat: Sample loading capacity is 0.5~1g. 5.1.2.4 Nitrogen: High-purity nitrogen (99.995%) can be used directly; pure nitrogen (99.9%) needs to be purified before use. 5.1.3 Analysis steps
Weigh 0.5~1g of sample into a constant-weight quartz boat, place the quartz boat in a tray, put it into the mouth of a pyrolysis furnace that has been heated to 950℃ and has a stable nitrogen flow (about 200mL/min), close the furnace door, preheat for 1~2min, push the tray into the high-temperature zone, and start timing. After 7min of scorching, move the tray to the furnace mouth, cool for about 2min, take it out, place it in a desiccator and cool it to room temperature, and weigh it. 5.2 Box-type high-temperature furnace method
5.2.1 Summary of the method
The sample is scorched at high temperature to decompose and release the volatile substances in it. The ignition loss is the volatile matter. 5.2.2 Instruments and materials
5.2.2.1 Balance: sensitivity 0.1mg.
5.2.2.2 Box-type high-temperature furnace: the maximum temperature is not less than 1000℃. 5.2.2.3 Double-covered porcelain crucible.
5.2.2.4 Crucible stand: Made of stainless steel plate or stainless steel wire mesh. 5.2.3 Analysis steps
Accurately weigh 1g of sample and evenly spread it on the bottom of the double-covered porcelain crucible with constant weight. Place the crucible on the crucible stand, cover it with double covers, place it in a box-type high-temperature furnace, and close the furnace door. For samples with a fixed carbon content of not less than 98%, burn at 400±20℃ for 1h. For samples with a fixed carbon content of less than 98%, burn at 950±20℃ for 7min. Start timing from the time the sample is placed in the furnace. The furnace temperature should rise to 950±20℃ within 3min after the sample is placed in the furnace, otherwise the result will be invalid. After burning, quickly take out the crucible and cool it for 1~2min, then move it to a desiccator to cool it to room temperature and weigh it. 278
5.3 Calculation of results
The percentage of volatile matter is calculated according to formula 2):
Wherein: α2——Percentage of volatile matter, %; m——Mass of dry sample before calcination, g; ml——Mass of sample after calcination, g.
6 Ash determination method
6.1 Summary of method
GB/T 3521—95
ml×100
The residue obtained after the sample is calcined at high temperature to completely release graphite and volatiles is the ash content. 6.2 Instruments and materials
6.2.1 Balance: Sensitivity is 0.1mg and 0.01mg; 6.2.2 Pyrolysis furnace: square tube furnace with gas path system (see Figure 1) or box-type high-temperature furnace. 6.2.3 Sample boat: Quartz boat is used for square tube furnace; square porcelain boat is used for box-type high temperature furnace; sample loading is 0.5～3g. 6.3 Analysis steps
Weigh 0.3～1g (1～2g for high purity graphite) of sample and place it in a constant weight sample boat, place the sample boat in a pyrolysis furnace heated to 900～1000℃, preheat for 1min, push it into the high temperature zone, introduce oxygen flow or air flow, burn until there are no black spots, take it out and cool it slightly, place it in a desiccator, cool it to room temperature, and weigh it. Put it in the furnace and burn it for 30min (burn it for 10min when oxygen flow is introduced), take it out, cool it, and weigh it. Repeat this process until constant weight.
6.4 Calculation of results
The ash content is calculated according to formula (3):
Wherein: 3--ash content, %,
m--mass of the dry sample before calcination, g,
m2--mass of the residue after calcination, g. 7 Fixed carbon determination method 1
7.1 Summary of method
--Indirect carbon determination method
m2×100
(3)
The indirect carbon determination method is also called the combustion method, that is, after measuring the volatile matter and ash of the sample, they are subtracted from the total amount, and the difference is the fixed carbon content. This method is applicable to graphite products with a carbon content greater than 50%. 7.2 Calculation of results
7.2.1 The fixed carbon percentage of high, medium and low carbon graphite is calculated according to formula (4): Where: a4 -
fixed carbon percentage, %;
volatile matter percentage, %;
ash percentage, %.
100% - z -~ x3
7.2.2 The fixed carbon percentage of high purity graphite is calculated according to formula (5): Where: 5 -
fixed carbon percentage, %,
zs = 100% - xg
(4)
(5)
rs - ash percentage, %.
8 Determination of sulfur
8.1 Summary of the method
GB/T 3521-95
The sample is burned in an oxidizing atmosphere at 1200-1250°C, so that sulfur, sulfide and sulfate in the form of sulfur dioxide escape. And introduced into potassium iodide starch absorption liquid, titrated with potassium iodate. The reaction formula is: KIO: + 5KI + 6HCI = 312 + 6KCl + 3H,0SO2 + I2+ 2H,OH,SO + 2HI
8.2 Reagents
8.2.1 Hydrochloric acid solution [1.5% (V/V)]: Dilute 15ml hydrochloric acid (HCl, density 1.19) to 1L with water. 8.2.2 Potassium iodate standard solution: 0.0888 g/L. Accurately weigh 0.0888 g potassium iodate (KIOs) standard reagent and dissolve it in water, transfer it into a 1000 mL volumetric flask, and dilute to the mark. Store in a brown bottle. 1 mL of this solution is equivalent to 0.04 mg of sulfur. 8.2.3 Starch-potassium iodide solution: weigh 2 g of soluble starch and add it to 50 mL of water to make it into a paste. Add the paste to 150 mL of boiling water while stirring, boil for 1 to 2 minutes, and add 6 g of potassium iodide (KI) after cooling. 8.2.4 Sulfur standard: coke with persulfur content determined by the axcala method. 8.3 Instrument: See Figure 2 for the sulfur determination device.
100~150
Furnace temperature 1200~1250℃
Figure 2 Sulfur determination device
100~150
1-Safety bottle; 2-Chromic acid washing bottle; 3-Alkaline potassium permanganate washing bottle; 4-Anhydrous calcium fluoride drying tower; 5-High temperature porcelain tube (1300℃); 6-Tube electric furnace (1300℃); 7-Porcelain boat; 8-Burette, 9, 10-Sulfur determination cup 8.4 Analysis steps
8.4.1 Tightness check of the device: Rapidly increase the furnace temperature to 1200~1250℃, pass oxygen or air, adjust the flow rate to 0.7~～0.8L/min, check that there is no leakage in the device before conducting the test. 8.4.2 Sample determination: Add 2/3 volume of hydrochloric acid solution to the sulfur cup, add 10mL of starch-potassium iodide solution, and drop potassium iodate standard solution until the solution in the sulfur cup turns light blue. Prepare a reference solution in the same way to determine the end point. Ventilate for 4 to 5 minutes. If the blue color of the solution in the sulfur cup disappears, drop potassium iodate standard solution until the blue color does not disappear. Weigh 0.2 to 1g of sample (depending on the sulfur content), put it into the burned porcelain boat, and quickly push the porcelain boat into the combustion tube with a sulfur-free metal hook. Immediately block the tube mouth and perform ventilation combustion at 1200 to 1250℃. The ventilation speed should be 80 to 100 bubbles per minute. When the gas enters the lower part of the sulfur cup and the blue color disappears, immediately drop potassium iodate standard solution. The dropping speed should be limited to keep the solution in the absorber at the original blank light blue color, until the light blue color of the solution remains unchanged for 1 to 2 minutes as the end point. 8.4.3 Determination of correction factor: Accurately weigh 1g of sulfur standard sample into a calcined porcelain boat, and proceed as in 8.4.2. 8.5 Calculation of results
8.5.1 The correction factor is calculated according to formula (6):
GB/T 3521-95
Wherein: F--correction factor, i.e., the mass of sulfur equivalent to 1.00mL potassium iodate solution, ug/mL; -mass of sulfur standard sample, g,
A--sulfur content of sulfur standard sample, μg/g;
V. ~volume of potassium iodate standard solution consumed, mL. 8.5.2 The percentage of sulfur is calculated according to formula (7): r
Wherein: I. —Sulfur content in the sample, %, VF × 10-6
V——Volume of potassium iodate standard solution consumed by the sample, mL, F——Correction factor, μg/mL,
Mass of dry sample,.
9 Determination of acid-soluble iron (in terms of Fe%) 9.1 Sulfosalicylic acid colorimetric method (arbitration method) 9.1.1 Summary of the method
· (6)
(7)
In an ammonia solution with a pH of 8~~10.5, trivalent iron and sulfosalicylic acid form a stable yellow complex with a maximum absorption at 420nm, which is used for iron colorimetry.
9.1.2 Reagents
9.1.2.1 Hydrochloric acid: density 1.19, 1+1.
9.1.2.2 Ammonia water: 1+1. Mix 1 volume of ammonia water with the same volume of water. 9.1.2.3 Iron standard solution
a Preparation: Accurately weigh 1.4297g of high-purity (or spectrally pure) ferric oxide, add 50mL of hydrochloric acid (1+1), dissolve and transfer to a 1000mL volumetric flask, dilute to scale with water, and shake well. This solution contains 1mg of iron per milliliter (1mgFe/mL), which is solution A. Accurately pipette 10.0mL of solution A, place in a 250mL volumetric flask, dilute to scale with water, and shake well. This solution contains 0.04mg of iron per milliliter (0.04mgFe/mL), which is solution B. .b. To draw the working curve, accurately measure 0.0, 1.03.0, 5.0, 7.0, 10.0, 15.0, 20.0 mL of iron standard solution B (equivalent to 0.00, 0.04, 0.12, 0.20, 0.28, 0.40, 0.60, 0.80 mg of iron), respectively, and put them into 100 mL volumetric flasks, add 2 mL of sulfosalicylic acid solution, and shake well. Add ammonia water to make the solution color change from purple to yellow and add 4 mL in excess, dilute with water to the scale, and shake well. Let it stand for 10 minutes. Use 1 cm colorimetric blood to measure the absorbance of the solution at a wavelength of 420 nm. Draw the working curve with iron content as the horizontal axis and absorbance as the vertical axis. 9.1.2.4 Sulfosalicylic acid solution: 200 g/L. 9.1.2.5 Ammonium thiocyanate solution: 100 g/L. 9.1.3 Instrument: Spectrophotometer or other instruments with equivalent performance. 9.1.4 Analysis steps
Weigh 0.5g (1~3g when the iron content is less than 0.5%) of the sample and place it in a 150mL beaker. Wet the sample with a small amount of water, add 25mL of hydrochloric acid (density 1.19), stir, and immerse the sample completely in the acid. Cover with table III, place on the electric hot plate, keep it slightly boiling for 20 minutes, remove it, wash the surface blood and the wall of the cup with water, cool it slightly, filter it with medium-speed qualitative filter paper into a 250mL volumetric flask, wash it with hot water until there is no iron ion (check with ammonium thiocyanate solution, no red), cool it, dilute it to the scale, and shake it well. This is the sample solution. Use a pipette to draw 10mL of the sample solution into a 100mL volumetric flask, add 2mL of sulfosalicylic acid solution, and shake it well. The following steps are the same as 9.1.2.3.b.
9.1.5 Calculation of results
The percentage of acid-soluble iron is calculated according to formula (8): GB/T 3521--95
m×1000×100
Wherein: 7—the percentage of acid-soluble iron in the sample, %; —the iron content in 100mL of colorimetric solution obtained from the working curve, mg; —the ratio of the total volume of the sample solution to the volume of the sample solution taken; n
m---the mass of the sample, g.
9.2 Sodium thiosulfate volumetric method
9.2.1 Method summary
(8)
Add potassium iodide to a slightly acidic solution (pH=1.5~～~2.0) to reduce trivalent iron to divalent iron. The generated free iodine is measured by adding sodium thiosulfate solution until the blue color disappears, using starch solution as an indicator. The reaction equation is as follows: 2Fe3++21-=3Fe2++I2
2S20-+12-S,0-+21
9.2.2 Reagents
9.2.2.1 Potassium iodide;
9.2.2.2 Hydrochloric acid: density 1.19.1+1.9.2.2.3 Saturated sodium carbonate solution.
9.2.2.4 Standard sodium thiosulfate solution: c(Na2S,O)=0.05mol/L. a.
Set aside.
Preparation: Weigh 13g sodium thiosulfate (Na2S,O) and dissolve it in 1L water, slowly boil for 10min, cool, and filter after standing for two weeks. b. Calibration: Weigh 0.075g of standard potassium dichromate dried to constant weight at 120℃, weigh to 0.0001g, put it in an iodine volumetric flask, dissolve it in 25mL water, add 2g potassium iodide and 20mL sulfuric acid solution (20%), spread evenly, add a stopper, stand in a dark place for 10min, add 150mL water, titrate with the prepared sodium thiosulfate solution until it turns light yellow, add 2mL starch indicator solution, continue titrating until the solution changes from blue to bright green, and perform a blank test at the same time.
The concentration of sodium thiosulfate standard solution is calculated according to formula (9): c(Na,S,O,) = (V,- V) X 0. 049 03m
Wherein: c(Na?S,O,)——the molar concentration of sodium thiosulfate standard solution, mol/L; m——the mass of potassium dichromate, g;
V,——the volume of sodium thiosulfate standard solution consumed, mL; V2——the volume of sodium thiosulfate standard solution consumed in the blank test, mL; (9)
0.04903——the mass of potassium dichromate in grams equivalent to 1.00mL sodium thiosulfate standard solution (c(NazS,O:)=1.000mol/L).
9.2.2.5 Sulfuric acid solution: 20%.
Slowly inject 20mL of concentrated sulfuric acid into 100mL of water, cool and shake well. 9.2.2.6 Starch indicator solution: 10 g/L.
Weigh 1.0g soluble starch in 5mL water to make it into a paste. Add the paste to 90mL boiling water under stirring, boil slightly for 1~2min, cool, dilute to 100mL, and use for two weeks. 9.2.3 Analysis stepswww.bzxz.net
Weigh 1~3g (depending on the iron content) of the sample, place it in a 200mL tall beaker, moisten it with a little water, add 25mL hydrochloric acid (density 1.19) and stir, so that the sample is completely immersed in the acid, cover it with blood, boil slightly on the hot plate for 20min, remove it, wash the blood and the cup wall with water, filter it with medium-speed qualitative filter paper into a 250mL iodine volume flask, and wash it with hot water until there is no iron ion (check with ammonium thiocarbamide solution, no red). Discard the residue and filter paper. If the volume exceeds 100mL, it should be evaporated and concentrated. 282
GB/T3521—95
Adjust the test solution to slightly acidic (pH=1.5-2) with saturated sodium carbonate solution and (1+1) hydrochloric acid solution, add 2g potassium iodide, shake the hook, add a stopper, place in a dark place for 10 min, add 2mL starch indicator solution, titrate with sodium thiosulfate solution until the blue color disappears completely, and perform a blank test at the same time.
9.2.4 Calculation of results
The percentage of acid-soluble iron is calculated according to formula (10): xgm
Wherein:
c(NaS,O,)
c(Na,S,O,) X (V- V,) X 55. 852×100
m × 1 000
The percentage of acid-soluble iron in the sample, %;
The molar concentration of sodium thiosulfate standard solution, mol/L; V,——the volume of sodium thiosulfate standard solution consumed, mLV
10Tolerance difference
The volume of sodium thiosulfate standard solution consumed in the blank test, mL: (10 )
With 1.00 mol sodium thiosulfate standard solution (c(NazS,O,)=1.000 mol/L), the mass of iron in grams;
the mass of the sample, g.
The allowable difference between the two parallel determination results shall comply with the provisions of the following table. The arithmetic mean of the two parallel determination results that do not exceed the tolerance shall be taken as the final result. Otherwise, the determination shall be repeated. %
Analysis items
Volatile matter
Acid-soluble iron
(in Fe%)
0.20~~0.50
0.50~1.00
1.00~～2.00
2.00~10.00
10.00~30.00
1.00~2.50
Same laboratory
Allowance difference
Different laboratories
Additional remarks:
This standard is proposed by the State Administration of Building Materials Industry. This standard is under the jurisdiction of Shandong Nanshu Graphite Mine.
GB/T3521--95
This standard is drafted by Weiyang Nonmetallic Mineral Research Institute of State Administration of Building Materials Industry and Shandong Nanshu Graphite Mine. The main drafters of this standard are Liu Youhong and Jiang Keping.
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