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Basic data
| Standard ID | GB/T 20975.18-2020 (GB/T20975.18-2020) |
| Description (Translated English) | Methods for chemical analysis of aluminium and aluminium alloys - Part 18: Determination of chromium content |
| Sector / Industry | National Standard (Recommended) |
| Classification of Chinese Standard | H12 |
| Classification of International Standard | 77.120.10 |
| Word Count Estimation | 14,149 |
| Date of Issue | 2020-06-02 |
| Date of Implementation | 2021-04-01 |
| Older Standard (superseded by this standard) | GB/T 20975.18-2008 |
| Quoted Standard | GB/T 8005.2; GB/T 8170-2008 |
| Issuing agency(ies) | State Administration for Market Regulation, China National Standardization Administration |
| Summary | This standard specifies the extraction and separation-diphenylcarbazide spectrophotometry, flame atomic absorption spectrometry, ammonium persulfate oxidation-ferrous ammonium sulfate titration method for the determination of chromium content in aluminum and aluminum alloys, water leaching-diphenyl Determination of hexavalent chromium content in aluminum and aluminum alloys by spectrophotometric method with carbonyl dihydrazide. This standard applies to the arbitration determination of chromium content in aluminum and aluminum alloys and hexavalent chromium content in aluminum and aluminum alloys. Extraction and separation - diphenylcarbazide spectrophotometric determination of chromium determination range: 0.000 1% ~ 0.60%; flame atomic absorption spectrometry determination of chromium determination range: 0.010% ~ 0.60%; persulfuric acid by oxidation - ferrous ammonium sulfate Determination of chromium by titration Determination range |
GB/T 20975.18-2020: Methods for chemical analysis of aluminium and aluminium alloys - Part 18: Determination of chromium content
---This is a DRAFT version for illustration, not a final translation. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.) will be manually/carefully translated upon your order.
Methods for chemical analysis of aluminium and aluminium alloys--Part 18.Determination of chromium content
ICS 77.120.10
H12
National Standards of People's Republic of China
Replace GB/T 20975.18-2008
Chemical analysis methods of aluminum and aluminum alloys
Part 18.Determination of Chromium Content
2020-06-02 released
Implementation on 2021-04-01
State Administration for Market Regulation
Issued by the National Standardization Management Committee
Foreword
GB/T 20975 "Methods for Chemical Analysis of Aluminum and Aluminum Alloys" is divided into 37 parts.
---Part 1.Determination of mercury content;
---Part 2.Determination of arsenic content;
---Part 3.Determination of copper content;
---Part 4.Determination of iron content;
---Part 5.Determination of silicon content;
---Part 6.Determination of cadmium content;
---Part 7.Determination of manganese content;
---Part 8.Determination of zinc content;
---Part 9.Determination of lithium content by flame atomic absorption spectrometry;
---Part 10.Determination of tin content;
---Part 11.Determination of lead content;
---Part 12.Determination of titanium content;
---Part 13.Determination of vanadium content;
---Part 14.Determination of nickel content;
---Part 15.Determination of boron content;
---Part 16.Determination of magnesium content;
---Part 17.Determination of strontium content;
---Part 18.Determination of chromium content;
---Part 19.Determination of Zirconium Content;
---Part 20.Determination of Gallium Content Butyl Rhodamine B Spectrophotometry;
---Part 21.Determination of calcium content;
---Part 22.Determination of beryllium content;
---Part 23.Determination of antimony content;
---Part 24.Determination of total rare earth content;
---Part 25.Determination of element content by inductively coupled plasma atomic emission spectrometry;
---Part 26.Determination of carbon content by infrared absorption method;
---Part 27.Determination of cerium, lanthanum and scandium content by inductively coupled plasma atomic emission spectrometry;
---Part 28.Determination of cobalt content by flame atomic absorption spectrometry;
---Part 29.Determination of molybdenum content thiocyanate spectrophotometric method;
---Part 30.Determination of hydrogen content by heating extraction thermal conductivity method;
---Part 31.Determination of phosphorus content molybdenum blue spectrophotometric method;
---Part 32.Determination of Bismuth Content;
---Part 33.Determination of potassium content by flame atomic absorption spectrometry;
---Part 34.Determination of sodium content by flame atomic absorption spectrometry;
---Part 35.Determination of Tungsten Content Thiocyanate Spectrophotometric Method;
---Part 36.Determination of silver content by flame atomic absorption spectrometry;
--- Part 37.Determination of Niobium Content.
This part is Part 18 of GB/T 20975.
This section was drafted in accordance with the rules given in GB/T 1.1-2009.
This part replaces GB/T 20975.18-2008 "Methods for Chemical Analysis of Aluminum and Aluminum Alloy Part 18.Determination of Chromium Content". versus
Compared with GB/T 20975.18-2008, the main technical changes except for editorial changes are as follows.
--- Added standard use safety warnings;
--- Added "Normative Reference Documents" (see Chapter 2);
--- Added "Terms and Definitions" (see Chapter 3);
---Added requirements for reagents and water used in analysis (see 4.2, 5.2, 6.2, 7.2);
---Modified the reagents of "Extraction Separation-Diphenylcarbazide Spectrophotometry", deleted and stored in the refrigerator (see 4.2.6 and 4.2.7,
3.6 and 3.7 of the.2008 edition);
---Modified the reagent of "Extraction Separation-Diphenylcarbazide Spectrophotometry", "4-methyl-pentanone-2" was changed to "4-methyl-2-pentane
Ketone", delete the purification and cooling use (see 4.2.8, 3.10 of the.2008 edition);
---Modified the reagents of "Extraction Separation-Diphenylcarbazide Spectrophotometry", and revised "Diphenylcarbazide Acetone Solution" to
"Diphenylcarbazide ethanol solution" (see 4.2.12, 3.11 of the.2008 edition);
---Modified the reagents of "Extraction Separation-Diphenylcarbazide Spectrophotometry", deleted the aluminum matrix solution (see.2008 edition
3.13);
--- Modified the reagents of "Extraction Separation-Diphenylcarbazide Spectrophotometry" and deleted the purification when preparing chromium standard storage solution
Process (see 4.2.13, 3.14 of the.2008 edition);
---Modified the determination of "extraction separation-diphenylcarbazide spectrophotometric method", by "and first cooling with running water, and then placed in an ice bath
"To the temperature is 5℃~10℃" is revised to "cool to room temperature", and the corresponding content in the note is deleted (see 4.6.2,.2008 edition
6.4.2);
---Modified the precision of "Extraction Separation-Diphenylcarbazide Spectrophotometry" and "Flame Atomic Absorption Spectroscopy", which is allowed by
Change "Poor" to "Reproducibility" (see 4.9.2 and 5.9.2, 8.2 and 17.2 of the.2008 edition);
---Added ammonium persulfate oxidation-ferrous ammonium sulfate titration method (see Chapter 6);
---Added the water extraction-diphenylcarbazide spectrophotometric method for the determination of hexavalent chromium in aluminum and aluminum alloys (see Chapter 7);
--- Deleted "Quality Assurance and Control" (see Chapter 9 and Chapter 18 of the.2018 edition);
--- Added "Test Report" (see Chapter 8).
This part was proposed by China Nonferrous Metals Industry Association.
This part is under the jurisdiction of the National Nonferrous Metals Standardization Technical Committee (SAC/TC243).
Drafting organizations of this section. Guangdong Industrial Analysis and Testing Center, Chinalco Zhengzhou Nonferrous Metals Research Institute Co., Ltd., Nonferrous Metals Technology
Economic Research Institute, Northeast Light Alloy Co., Ltd., Changsha Research Institute of Mining and Metallurgy Co., Ltd., Guizhou Research Institute of Analysis and Testing, Kunming Metallurgy
Research Institute, Beikuang Testing Technology Co., Ltd., Hebei Stone New Metal Materials Co., Ltd., Shandong Yankuang Light Alloy Co., Ltd., National
Recycled non-ferrous metal rubber and plastic materials quality supervision and inspection center, Chinalco Mining Co., Ltd., China Aluminum Materials Application Research Institute Co., Ltd., Beijing
Institute of Nonferrous Metals and Rare Earth Applications.
The main drafters of this section. Zhang Yongjin, Xie Hui, Zhang Yuanke, Xu Siting, Xi Huan, Xiong Xiaoyan, Shi Lei, Zhou Bing, Wang Fang, Zhang Tianjiao, Ma Yanhong,
Xu Bin, Long Anlu, Liu Weili, Yi Jia, Luo Haixia, Xue Ning, Wei Yanqin, Han Zhengqian, Liu Beibei, Hao Yuepeng, Zhang Juan, Liu Fei, Zhang Jin'e, Wang Xue.
The previous versions of the standards replaced by this part are as follows.
---GB/T 6987.18-1986, GB/T 6987.18-2001;
---GB/T 6987.30-2001;
---GB/T 20975.18-2008.
Chemical analysis methods of aluminum and aluminum alloys
Part 18.Determination of Chromium Content
Warning---Personnel using this section should have practical experience in formal laboratory work. This section does not point out all possible safety issues
question. The user is responsible for taking appropriate safety and health measures and ensuring compliance with the conditions stipulated by relevant national laws and regulations.
1 Scope
This part of GB/T 20975 specifies extraction separation-diphenylcarbazide spectrophotometry, flame atomic absorption spectrometry, persulfuric acid
Determination of chromium content in aluminum and aluminum alloy by ammonium oxidation-ferrous ammonium sulfate titration method, water leaching-diphenylcarbazide spectrophotometric method for determination of aluminum and aluminum
The content of hexavalent chromium in the alloy.
This section applies to the arbitration determination of chromium content in aluminum and aluminum alloys and hexavalent chromium content in aluminum and aluminum alloys. Extraction separation-diphenyl carbon
Determination of chromium by hydrazide spectrophotometry. 0.0001%~0.60%; Determination of chromium by flame atomic absorption spectrometry.
0.010%~0.60%; ammonium persulfate oxidation-ferrous ammonium sulfate titration method to determine chromium determination range. 2.00%~23.00%; water leaching-diphenyl
The determination range of hexavalent chromium by carbohydrazide spectrophotometry. 0.0001%~0.10%.
Note. When the mass fraction of chromium is 0.010%~0.60%, the extraction separation-diphenylcarbazide spectrophotometry is the arbitration method.
2 Normative references
The following documents are indispensable for the application of this document. For dated reference documents, only the dated version applies to this article
Pieces. For undated references, the latest version (including all amendments) applies to this document.
GB/T 8005.2 Terminology of Aluminum and Aluminum Alloy Part 2.Chemical Analysis
GB/T 8170-2008 Numerical rounding rules and the expression and determination of limit values
3 Terms and definitions
The terms and definitions defined in GB/T 8005.2 apply to this document.
4 Extraction separation-diphenylcarbazide spectrophotometric determination of chromium
4.1 Method summary
The sample was dissolved in a mixed acid of hydrochloric acid, nitric acid and sulfuric acid, and the chromium in the residue was recovered by filtration. Oxidize trivalent chromium ion to hexavalent chromium with cerium ammonium nitrate
Ion, extract the hexavalent chromium ion with 4-methyl-2-pentanone, and back-extract it into the water phase to form a colored complex with diphenylcarbazide.
The absorbance is measured at the wavelength of 545nm with a spectrophotometer to determine the chromium content.
4.2 Reagents
Unless otherwise stated, only reagents and laboratory secondary water confirmed to be analytically pure are used in the analysis.
4.2.1 Nitric acid (ρ=1.42g/mL).
4.2.2 Sulfuric acid (ρ=1.84g/mL).
4.2.3 Hydrochloric acid (ρ=1.19g/mL).
4.2.4 Hydrofluoric acid (ρ=1.14g/mL).
4.2.5 Sulfuric acid (2 7).
4.2.6 Hydrochloric acid (1 1).
4.2.7 Hydrochloric acid (1 24).
4.2.8 4-Methyl-2-pentanone.
4.2.9 Mixed acid. Mix.200mL hydrochloric acid (4.2.3),.200mL nitric acid (4.2.1) and 400mL water in a suitable container. In the cold
With constant stirring, carefully add 120mL sulfuric acid (4.2.2). After cooling, dilute with water to 1000mL. Stored in dark colored glass
In a glass container.
4.2.10 Ammonium cerium nitrate solution (22g/L). Weigh 2.2g ammonium cerium nitrate [(NH4)2Ce(NO3)6] and dissolve it in a small amount of water and add
25mL sulfuric acid (4.2.5), dilute with water to 100mL, and mix.
4.2.11 Nickel chloride solution (200g/L). Weigh 20g of nickel chloride hexahydrate and dissolve it in a small amount of water, add 60mL hydrochloric acid (4.2.3), and use
Dilute with water to 100mL and mix well.
4.2.12 Diphenylcarbazide ethanol solution (10g/L). Weigh 0.50g of diphenylcarbazide and dissolve it in 50mL of absolute ethanol.
Equipped when used.
4.2.13 Chromium standard storage solution. Weigh 0.5658g of potassium dichromate that has been pre-dried at 140℃ for 2h and cooled in a desiccator (reference
Reagents), dissolve with an appropriate amount of water and transfer to a 1000mL volumetric flask, dilute to the mark with water, and mix. This solution 1mL contains.200μg chromium.
4.2.14 Chromium standard solution A. Pipette 50.00mL chromium standard stock solution (4.2.13) into a 500mL volumetric flask, dilute to the mark with water,
Mix well. This solution 1mL contains 20μg chromium.
4.2.15 Chromium standard solution B. Pipette 5.00mL chromium standard stock solution (4.2.13) into a 1000mL volumetric flask, dilute with water to
Degree, mix well. This solution 1mL contains 1μg chromium.
4.3 Apparatus
Spectrophotometer.
4.4 Sample
Process the sample into chips with a thickness of not more than 1mm.
4.5 Analysis steps
4.5.1 Sample
According to Table 1, weigh the sample (4.4) of mass (m0) to the nearest 0.0001g.
Table 1
Chromium mass fraction wCr/% sample mass m0/g pipette test solution volume V1/mL
0.0001~0.050 1.00 20.00
>0.050~0.10 0.40 10.00
>0.10~0.60 0.10 10.00
4.5.2 Parallel test
Do two tests in parallel and take the average value.
4.5.3 Blank test
Do a blank test with the sample.
4.6 Determination
4.6.1 Place the sample (4.5.1) in a 250mL beaker, cover with a watch glass, and add 50mL of mixed acid (4.2.9) in batches.
When it is pure aluminum (wAl≥99.99%), add a few drops of nickel chloride solution (4.2.11) before adding the mixed acid (4.2.9), and wait until the sample is completely dissolved
After that, use a small amount of water to wash the wall of the cup and the tableware, heat the test solution until thick white smoke is emitted, remove it to cool, blow the wall of the cup with water, and dissolve it with 40mL~60mL water
Decompose and heat the solution until the salts are completely dissolved. Transfer to a 100mL volumetric flask, dilute to the mark with water, and mix. If silicon is precipitated, use slow speed
Filter paper, wash the residue with warm water, collect the filtrate and washing liquid in a 100mL volumetric flask. Place the residue and filter paper in a platinum crucible
In the middle, carefully dry, ash, and then burn at 1000 ℃ for 20 minutes. After cooling, add 2 drops of sulfuric acid (4.2.2), 1mL of nitric acid (4.2.1) and
A few milliliters of hydrofluoric acid (4.2.4) are placed in the crucible and carefully heated until thick white smoke is emitted. Continue heating until the white smoke of the crucible is exhausted, cool, and use a little water to make the residue
The residue is completely dissolved (heating if necessary), and this solution is combined in the main filtrate. After cooling, dilute to the mark with water and mix well.
4.6.2 Pipette the test solution into a 50mL colorimetric tube with a scale according to Table 1, add 2.0mL cerium ammonium nitrate solution (4.2.10), and dilute with water
To 30mL, mix well. Immerse the colorimetric tube in a boiling water bath for 25min, remove the colorimetric tube, and cool to room temperature.
4.6.3 Transfer the solution into a 100mL separatory funnel A marked with a graduation. Wash the colorimetric tube with a small amount of water, and merge the lotion into the separatory funnel.
The control volume is 45mL. Add 4.5mL hydrochloric acid (4.2.6) and mix well. Add 25mL 4-methyl-2-pentanone (4.2.8) and shake for 1 min.
Let stand for layering, remove the water phase and place it in another separator B of the same. Then add 25mL 4-methyl-2-pentanone to separatory funnel B
(4.2.8) and shake for 1 min. Set aside for layering, discard the water phase, combine the organic phase into the separatory funnel A, let the clear solution stand, and discard the water phase.
Add 25 mL of hydrochloric acid (4.2.7) to the organic phase, shake for 5 seconds, stand still for layering, and discard the aqueous phase.
4.6.4 According to the mass fraction of chromium in the sample, the following treatments are performed.
a) When the mass fraction of chromium is 0.0001%~0.0050%, the organic phase is back-extracted once with 10 mL of water, and the second and third times are added respectively.
Re-extract with 5mL water, shake for 30s each time, and collect the released water phase in a 25mL volumetric flask. Add 0.6mL sulfuric acid
(4.2.5) Mix well in a 25mL volumetric flask, add 0.5mL diphenylcarbazide ethanol solution (4.2.12), dilute with water to
Scale and mix well.
b) When the chromium mass fraction is >0.0050%~0.60%, the organic phase is back-extracted three times with water, each time with 25mL of water and shaken
Swing for 30s, the released water phase was collected in a 100mL volumetric flask. Add 2.5mL sulfuric acid (4.2.5) to a 100mL volumetric flask,
Mix well, add 2.0mL diphenylcarbazide ethanol solution (4.2.12), dilute to the mark with water, and mix.
4.6.5 After standing for 10 minutes, discard a little upper layer solution, transfer part of the test solution to the corresponding absorption cell, and set it at the wavelength of the spectrophotometer.
At 545nm, use water as the reference, measure the absorbance, subtract the absorbance of the blank test solution, and check the corresponding chromium content from the working curve
(m1).
4.7 Drawing of working curve
4.7.1 According to the chromium quality score, the working curve drawing is divided into the following two types.
a) When the chromium mass fraction is 0.0001%~0.0050%. in 6 50mL colorimetric tubes with graduations, move 0mL,
0.50mL, 1.00mL, 2.50mL, 5.00mL, 10.00mL chromium standard solution B (4.2.15), add 2.0mL cerium nitrate
Ammonium solution (4.2.10), wash the wall of the tube with water and dilute to 30mL, and mix. The following is carried out according to 4.6.2~4.6.5.
b) When the mass fraction of chromium is >0.0050%~0.60%. transfer 0mL, 0mL, and 0mL into 7 50mL colorimetric tubes with graduations.
4.00mL, 10.00mL, 20.00mL chromium standard solution B (4.2.15) and 2.00mL, 4.00mL, 6.00mL chromium standard solution
Solution A (4.2.14), add 2.0mL cerium ammonium nitrate solution (4.2.10), wash the tube wall with water and dilute to 30mL, and mix. the following
Proceed according to 4.6.2~4.6.5.
4.7.2 After standing for 10 minutes, discard a little upper layer solution, pipette part of the series of standard solutions into the corresponding absorption cell, and apply the spectrophotometer wave
At 545nm, use water as the reference to measure the absorbance, subtract the absorbance of the "zero" concentration solution in the series of standard solutions, and use the amount of chromium as the horizontal
Mark, absorb absorbance as ordinate, draw working curve.
4.8 Test data processing
The chromium content is calculated as the chromium mass fraction wCr, calculated according to formula (1).
wCr=
m1V0×10-6
m0V1 ×
100% (1)
Where.
m1---The amount of chromium found from the working curve, in micrograms (μg);
V0---Total volume of test solution, in milliliters (mL);
m0---the mass of the sample, in grams (g);
V1---The volume of the test solution taken, in milliliters (mL).
When the chromium mass fraction is greater than or equal to 0.0010%, the calculation result retains two significant digits; when the chromium mass fraction is less than 0.0010%, the calculation result is retained
A valid number. The rounding of values shall be implemented in 3.2 and 3.3 of GB/T 8170-2008.
4.9 Precision
4.9.1 Repeatability
The measured value of two independent test results obtained under repeatability conditions, within the average range given below, these two test results
The absolute difference does not exceed the repeatability limit r, and the repeatability limit r does not exceed 5%. The repeatability limit r is within the linear range according to the data in Table 2.
Obtained by interpolation or extension method.
Table 2
wCr/% 0.0003 0.0044 0.081 0.37 0.57
r/% 0.0001 0.0005 0.006 0.02 0.03
4.9.2 Reproducibility
The measured values of two independent test results obtained under reproducibility conditions are within the average range given below. These two test results
The absolute difference does not exceed the reproducibility limit R, and the reproducibility limit R does not exceed 5%. The reproducibility limit R is linear according to the data in Table 3.
Obtained by interpolation or extension.
table 3
wCr/% 0.0003 0.0044 0.081 0.37 0.57
R/% 0.0001 0.0007 0.008 0.03 0.04
5 Determination of chromium by flame atomic absorption spectrometry
5.1 Method summary
The sample is dissolved in hydrochloric acid and hydrogen peroxide, and the wavelength of the atomic absorption spectrometer is 357.9nm, and the air-acetylene (or nitrous oxide-ethane
(Acetylene) flammable flame measures the absorbance of chromium to determine the chromium content.
5.2 Reagents
Unless otherwise stated, only reagents and laboratory secondary water confirmed to be analytically pure are used in the analysis.
5.2.1 Pure aluminum (wAl≥99.99%, wCr< 0.0005%).
5.2.2 Nitric acid (ρ=1.42g/mL).
5.2.3 Hydrofluoric acid (ρ=1.14g/mL).
5.2.4 Hydrogen peroxide (ρ=1.10g/mL).
5.2.5 Hydrochloric acid (ρ=1.19g/mL).
5.2.6 Hydrochloric acid (11).
5.2.7 Sulfuric acid (1 1).
5.2.8 Aluminum matrix solution (20g/L). Weigh 20.00g pure aluminum (5.2.1), place it in a 1000mL beaker, and cover with a watch glass. Add to the total
600mL of hydrochloric acid (5.2.6), after the violent reaction stops, slowly heat to complete dissolution, and then add a few drops of hydrogen peroxide (5.2.4),
Boil for a few minutes to decompose excess hydrogen peroxide and cool. Transfer the solution into a 1000mL volumetric flask, dilute to the mark with water, and mix.
5.2.9 Lanthanum chloride solution (100g/L). Weigh 100g of lanthanum oxide, place it in a 500mL beaker, add.200mL of hydrochloric acid (5.2.5) to dissolve.
Transfer to a 1000mL volumetric flask, dilute to the mark with water, and mix.
5.2.10 Chromium (Ⅲ) standard stock solution. weigh 1.414g of reference dichromic acid which has been dried at 140℃ for 2h and cooled in a desiccator
Potassium, placed in a 400mL beaker, covered with a watch glass. Dissolve with 20mL water and 10mL hydrochloric acid (5.2.6). Add 10mL hydrogen peroxide dropwise
(5.2.4), let it stand for 12h~24h until the yellow color of the solution disappears completely, warm (do not boil) to decompose excess hydrogen peroxide, and cool. Transfer the solution
Put it into a 1000mL volumetric flask, dilute to the mark with water, and mix well. This solution 1mL contains 500μg chromium.
5.2.11 Chromium (Ⅲ) standard solution. Pipette 25.00mL chromium (Ⅲ) standard stock solution (5.2.10) into a 500mL volumetric flask and dilute with water
To the mark, mix well. 1mL of this solution contains 25μg of chromium.
5.3 Apparatus
Atomic absorption spectrometer with chromium hollow cathode lamp. The instrument should meet the following conditions.
---Characteristic concentration. In a solution consistent with the measurement sample solution matrix, the characteristic concentration of chromium should not be greater than 0.1μg/mL.
---Precision. Use the highest concentration of standard solution to measure absorbance 10 times, and its standard deviation should not exceed the average value of absorbance
1.0%, use the lowest concentration standard solution (not the "zero" concentration solution) to measure the absorbance 10 times, the standard deviation should not exceed the minimum
The average absorbance of the high concentration standard solution is 0.5%.
---Linear working curve. Divide the working curve into five equal sections according to the concentration, the difference between the absorbance difference of the highest section and the absorbance difference of the lowest section
The ratio should not be less than 0.70.
5.4 Sample
Process the sample into chips with a thickness of not more than 1mm.
5.5 Analysis steps
5.5.1 Sample
Weigh a sample (5.4) with a mass (m2) of 1.00g, accurate to 0.0001g.
5.5.2 Parallel test
Do two tests in parallel and take the average value.
5.5.3 Blank test
Weigh 1.00g pure aluminum (5.2.1) instead of the sample (5.5.1), and do a blank test with the sample.
5.6 Determination
5.6.1 Place the sample (5.5.1) in a 250mL beaker, cover with a watch glass, add 30mL-40mL of water, and add 30mL in batches
Hydrochloric acid (5.2.6), after the violent reaction stops, slowly heat until the sample is dissolved, add an appropriate amount of hydrogen peroxide (5.2.4) dropwise, and boil for a few minutes
Decompose excess hydrogen peroxide and cool.
5.6.2 If there is insoluble matter, filter and wash. Place the residue together with filter paper in a platinum crucible, ash, burn at about 550 ℃, and cool. Join
2mL sulfuric acid (5.2.7) and 5mL hydrofluoric acid (5.2.3), and nitric acid (5.2.2) was added dropwise until the solution was clear. Heat to evaporate to dryness, burn at 700℃
Boil for a few minutes and let cool. Use as little hydrochloric acid (5.2.6) as possible to dissolve the residue. Combine this test solution with the original filtrate.
5.6.3 According to the mass fraction of chromium in the sample, the following treatments are performed.
a) When the mass fraction of chromium is 0.010%~0.20%, transfer the test solution (5.6.1) or the combined test solution after treating the insoluble matter into a 100mL volume.
Add 5mL lanthanum chloride solution (5.2.9) to the measuring flask (V2) [if determined by air-acetylene flame and deemed necessary], dilute with water
Release to the mark and mix well.
b) When the chromium mass fraction is >0.20%~0.60%, transfer the test solution (5.6.1) or the combined test solution after treating insoluble matter into 100mL
In the vol...
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