When the enamel factory conducts chemical analysis and physical and chemical performance measurement of silica raw materials, it needs to follow certain methods. Today I will introduce the potassium fluorosilicate method. Note that in the laboratory analysis of enamel raw materials, the chemical reagents used must be of analytical purity unless otherwise specified; the addition of water and dilution with water in the text refer to distilled water; any mention of accurate weighing means the use of an analytical balance, and accurate weighing to 0.2mg.

Potassium fluorosilicate method:

Reagents and solutions: nitric acid specific gravity 1.42

Hydrochloric acid 1:1

Potassium chloride 5%

Potassium chloride solid

Potassium chloride-ethanol solution 5%

Potassium Chloride 15%

Potassium hydroxide

Sodium hydroxide standard solution 0.15N

Phenolphthalein indicator 1% ethanol solution

Analysis procedure:

Accurately weigh 0.1 g of the dried sample, place it in a nickel crucible, add 1.5 g of potassium hydroxide, melt it on a low-temperature electric furnace for 15 minutes, and then transfer it to a blowtorch to melt until the bottom of the crucible turns dark red. After cooling, soak the frit with a small amount of hot water, carefully pour it into a 300ml plastic cup, and slowly add 15ml of nitric acid to dissolve all the frit. Then wash the crucible twice with hydrochloric acid, cool to 25°C and add 3~4g of potassium chloride and stir to make the solution supersaturated. Add 10ml of 15% potassium chloride and stir with a plastic stick. At this time, there should be a small amount of potassium chloride, otherwise, it should be added until there is insoluble potassium chloride at the bottom of the cup. Let stand for 2-3 minutes, filter with fast filter paper on a waxed funnel, wash the cup wall and precipitate 3 times with 5% potassium chloride solution. Wash the filter paper once more, put the filter paper and the precipitate back into the original plastic cup, add 10ml of potassium chloride-ethanol solution, 5 drops of 1% phenolphthalein indicator, neutralize the precipitate and the residual acid on the filter paper with 0.15N sodium hydroxide, Stir while dripping, scrub the wall of the cup and crush the filter paper until the filter paper and the precipitate are reddish, immediately add 200ml of neutralized boiling water to hydrolyze the precipitate, then add 15 drops of 1% phenolphthalein indicator, and use 0.15N hydrogen Titrate the sodium oxide standard solution until the reddish color of the solution does not disappear, which is the end point.

SiO2 content % (x) is calculated according to the formula:

x=(NV×0.01502)/G×100%

In the formula, N—the equivalent concentration of sodium hydroxide standard solution

V——volume of de-sodium hydroxide standard solution for titration

G - sample weight

0.01502——Grams of 1mg equivalent SiO2

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