The method of measuring zinc oxide content is discussed

0 Introduction
zinc oxide, also known as zinc white. As a white pigment, zinc oxide coloring and covering force is not as good as zinc palladium and titanium white powder, but in the price of goldstone-type titanium white powder has a greater advantage, and not easy to powder, with good light resistance, heat resistance and weather resistance, suitable for exterior coatings. Its use has increased year by year and replaced part of the trend of titanium dioxide
china
. Recently, there has been adulterated zinc oxide, suspected of mixing calcium carbonate into zinc oxide for profit. The true zinc oxide content of adulterated zinc oxide was not effectively measured by GB/T 3185-1992. Therefore, combined with X-ray fluorescence spectroscopy, the problems of the old method are analyzed and the new method is re-established, and the feasibility of the new method is verified by a large number of experiments.
1 Problem analysis of the old method
take adulterated zinc oxide, according to GB/T 3185-1992 assay method and X-ray fluorescence spectroscopy test, the results are seen in Table 1.
can be seen from Table 1: the ZnO content measured by GB/T 3185-1992 contains CaCO3 content, resulting in a serious deviation in the measurement results. Analysis of GB/T 3185-1992 assay method, the principle of which is in the solution pH-10, chromium black T as an indicator, with EDTA (acetylacetylatedi-sodium) for process titration. The relevant parameters for chromium black T can be found in Table 2.
can be seen by Table 2: chromium black T and Zn2, Ca2 plus can occur in the case of chromium black T as an indicator when the solution pH is 10. Therefore, under this condition, EDTA can not only titrate Zn2 plus, but also titration Ca2 plus, so it can be judged that GB/T 3185-1992 measurement method titration zinc oxide has limitations, can not remove calcium impurities interference, resulting in a large deviation in the measurement results, need to replace the new method to determine zinc oxide content.
2 New method establishes
2.1 Basic Principles
Solution pH s 5.5 to 6, and under the condition that methanol orange is used as an indicator, zinc oxide is titration directly with EDTA standard solution.
2.2 Reagent preparation and calibration
hydrochloric acid: analysis pure (1 to 1);
2.3 Instruments and equipment
balance: accurate to 0.1 mg; conical burners: 250 mL; electric furnace.
2.4 Test step
says to take samples from 0.13 to 0.15 g (accurate to 0.1 mg) that were dried at 105 degrees C, placed in a 250 mL conical canty, moistened with a small amount of water, and added hydrochloric acid (1 1) 3 mL, after heating dissolved water 100 mL, plus 3 to 4 drops of methylphenol orange indicator, and then add 2 g he6 medehyteamine, fully shake, with EDTA standard titration solution titration, solution from fuchsia to bright yellow, that is, the end point.
2.5 Calculation
Pressed Zinc Oxide Content (X):
: X -Zinc Oxide Content, % as a Percentage of Mass;
C-EDTA Standard Titration Solution Concentration, mol/L;
V - Consumption of EDTA Standard Solution Volume, mL;
m - mass of the sample, g;
0.081 39 - the mass of zinc oxide in grams equivalent to the 1.0 mL EDTA standard titration solution ( C (EDTA) - 1.000 mol/L.
the average of the results of the 2 measurements, the results are accurate to 0.1%.
3 Verification Test
3.1 New method test pure zinc oxide (content 99.99%)
The results of the new method test pure zinc oxide are found in Table 3.
the t-value distribution table, the confidence probability is 95%, the t-table is 3.18, 2.67 < 3.18.
results are not significantly different from the standard values, so the new method can accurately determine pure zinc oxide.
3.2 New method tests zinc oxide with calcium-containing impurities
A sample is made of pure zinc oxide and analysis of pure calcium carbonate by 1:1 (m/m), B sample by pure zinc oxide and analysis of pure calcium carbonate by 2:1 (m/m). The results of the new method of testing doping zinc oxide can be found in Table 4.
the t-value distribution table, the confidence probability is 95%, the t-table is 3.18, 3.00< 3.18.
the above results and standard values are not significantly different, so the new method for calcium-containing impurities zinc oxide can also be accurately measured.
4 Conclusion
Through the above demonstration test, the analysis of GB/T 3185-1992 to determine the zinc oxide content has limitations, can not remove calcium impurities interference, resulting in a large deviation in the measurement results. The new method established to determine the zinc oxide content is accurate and feasible, and can effectively shield the interference of calcium impurities, the results are true and reliable. Therefore, the new method has great practical value, which makes up for the deficiency of GB/T 3185-1992 measurement method, and helps to improve the accuracy of zinc oxide content determination.