GB/T 35069-2018 in English

Background and significance of the standard

This standard is under the jurisdiction of the Coking Chemistry Sub-Technical Committee of the National Coal Chemical Industry Standardization Technical Committee, proposed by the China Iron and Steel Association, and supported by many leading companies in the industry. The formulation of the standard fills the gap in the determination method of phosphorus content in coke in China and provides a scientific basis for industries such as metallurgy and casting.

Technical principle and analysis steps

This standard adopts the reduced phosphomolybdate spectrophotometry and completes the determination through the following steps:

1. Sample decomposition:After ashing, it is dissolved in acid, emitting perchloric acid fumes, so that all phosphorus is oxidized to orthophosphoric acid.
2. Color reaction: In the presence of bismuth salt, add ammonium molybdate to generate bismuth-phosphorus molybdenum ternary heteropoly acid, use ethanol as a stabilizer, and use ascorbic acid to reduce it to bismuth-phosphorus molybdenum blue.
3. Absorbance measurement: Use a spectrophotometer to measure the absorbance of the color solution at a wavelength of 700 nm, and find the corresponding phosphorus amount on the calibration curve.

Precision and result processing

The standard specifies the calculation method of repeatability limit r and reproducibility limit R to ensure the reliability of the measurement results. The analysis results must be rounded according to GB/T8170, with the following specific requirements:

• When the phosphorus content is less than 0.010%, round it to 4 decimal places.
• When the phosphorus content is greater than or equal to 0.010%, round it to 3 decimal places.

Implementation Suggestions

To ensure the effective implementation of the standard, the following suggestions are made:

1. Laboratory conditions:Equipped with a spectrophotometer that meets the requirements of GB/T7729, and ensure the safety control of the acid-base environment.
2. Staff training:Analysts need to receive professional training and be familiar with standard operating procedures and safety regulations.
3. Quality control:Regularly calibrate the instrument and use standard solutions for curve correction to ensure the accuracy of the measurement results.