Two Determination Methods of Silicon Content in High Carbon Silicon

High carbon-silicon, also called a silicon-carbon alloy, is a new type of alloy that can replace the ferrosilicon, silicon carbide, and carbon raiser to reduce the amount of deoxidizer.

Background of High Carbon Silicon

The high carbon silicon can improve the quality of the molten steel, improve the quality of the finished product, reduce the adding amount of alloy, and reduce the production cost of steelmaking.

High Carbon Silicon
High Carbon Silicon

There is neither a national standard of silicon content in high carbon silicon nor a standard sample of high carbon silicon. Therefore, it is necessary to study the determination methods of silicon content in high carbon silicon. By studying various test methods, this article finds out the best analysis method for silicon content in high-carbon silicon, formulates the analysis operation process, provides an accurate high carbon silicon content detection and analysis, and provides accurate product information for steel mills.

Determination Methods of Silicon Content in High Carbon Silicon

Since there is no standard sample for high carbon-silicon, and with the high silicon content. We take the ferro silicon as a standard sample, with which silicon content is 75.13%, 76.74%, and 76.42%. At present, the chemical analysis methods of silicon content are the gravimetric method and titration method.

Gravimetric Method for Silicon Content Determination – Sodium Hydroxide, Sodium Peroxide

Reagent and Equipment

  • Nickel crucible 50ml
  • White porcelain crucible 50ml
  • Beaker 300ml
  • Triangular flask 250ml
  • Sodium hydroxide AR
  • Sodium peroxide AR
  • Concentrated hydrochloric acid AR
  • Ammonium chloride saturated solution
  • Gelatin: 1%
Reagent and Equipment
Reagent and Equipment

The Process of Gravimetric Method for Silicon Content Determination for High Carbon Silicon

  1. Take 0.3g of sample into the nickel crucible, add 4g of sodium hydroxide, and 1g of sodium peroxide, stir well and cover the crucible. Put the crucible on the electric furnace at low temperature for 5-10 minutes, then, with 750℃ high temperature for 10 minutes. Remove the crucible and rotate the crucible to disperse the melt on the crucible walls.
  2. After the melt is cooled, put it in the beaker (add 75ml of water, and 5ml of concentrated hydrochloric acid), and add 20ml of concentrated hydrochloric acid, and low-temperature heating to dissolve the melt.
  3. Put the substance in a clean crucible, cover the crucible with a watch glass, and evaporate to near dryness on the low-temperature electric furnace. Take the crucible from the electric furnace, cool down for a while, add 25ml of ammonium chloride saturated solution and 20ml of gelatin, stir well and keep warm for 10 minutes.
  4. Filter with quantitative filter paper put the filtrate in the triangular flask, and wash the beaker with distilled water. Put the filter paper into the weighed white porcelain crucible.
  5. Put the white porcelain crucible on the electric furnace, after the ashing process, burn the crucible at 900℃ for 30 minutes, and weigh the crucible at last.


The gravimetric method is a traditional way of silicon content determination, which is suit for ferrosilicon, silicon manganese, calcium silicon, etc. The reagents used in the test are commonly used in laboratories.


  • The operation is complicated and takes a long time.
  • The test result has a large error, and the detected silicon content is low because the strong alkali treatment reagent is easy to splash.
  • High temperatures can easily cause crucible damage.

Acid-base Titration – Potassium Fluorosilicate Precipitation

Reagent and Equipment

  • Hydrofluoric acid
  • Potassium nitrate saturated solution
  • Potassium nitrate lotion
  • Neutral water
  • Bromothymol blue indicator
  • Sodium hydroxide standard solution concentration
Acid-base titration
Acid-base titration

The Process of Acid-base Titration for Silicon Content Determination for High Carbon Silicon

  1. Take 0.1000g of sample into the plastic cup, add 10ml of hydrogen nitrate, and slowly add 10ml of hydrofluoric acid dropwise until the sample is completely dissolved.
  2. A period of time later, add 20ml of potassium nitrate saturated solution, shake up, and place it in the cold water for 10 minutes, complete precipitation of potassium fluorosilicate.
  3.  Filter the solution with quantitative filter paper, wash the beaker three times with potassium nitrate washing solution, and wash the precipitate 4-5 times.
  4. Put the precipitate and filter paper in the plastic cup, stir and break the filter paper into pieces with a plastic stick, then add 10ml of potassium nitrate- ethanol solution.
  5. Add 5-6 drops of bromothymol blue indicator, add sodium hydroxide standard solution dropwise to titrate blue, add neutral boiling water, and then use sodium hydroxide standard solution to titrate blue.


An acid-base titration is a common method. The operation is easy and quick. The reagents used in the test are commonly used in laboratories.


Too many times of precipitation and washing, and a small amount of potassium fluoride silicate dissolves, resulting in low results.

Through the study, the best determination method of silicon content in high carbon silicon has been found. The acid-base titration is easy to operate, easy to promote, and the results are fed back to the steel mill customers so that they can control the quality of high carbon silicon in the shortest time, so as to better control the quality of steelmaking products

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