US 8,945,934 B2 · Potentiometric titration method for measuring concentration of acid mixture of aluminum etchant

Abstract

The present invention provides a potentiometric titration method for measuring concentration of acid mixture of aluminum etchant, which prepares identified potassium hydroxide-ethanol solution or sodium hydroxide-ethanol solution as a titrant and uses a monohydric alcohol and a diol as an anhydrous medium for the acid mixture of aluminum etchant to carry out titration of the acid mixture of aluminum etchant so as to realize measurement of concentration of each acid contained in the acid mixture of aluminum etchant through a one-stage process of potentiometric titration thereby reducing the complication of operation of inspection and uncertainty of inspection result and achieving the purposes of carrying out inspections with high precision and high performance. The method can efficiently and accurately measure the concentrations of nitric acid, phosphoric acid, and acetic acid contained in the acid mixture of aluminum etchant.

A potentiometric titration method for measuring concentration of acid mixture of aluminum etchant, comprising the following steps:

(1) preparing an alkali-ethanol solution having a concentration of 0.8-1.2 mol/L with alkali as solute and anhydrous ethanol as solvent;
(2) setting the alkali-ethanol solution so prepared still and precipitated for 20-30 days and afterwards, extracting upper clear liquid in the alkali-ethanol solution;
(3) diluting the upper clear liquid with anhydrous ethanol to a concentration of 0.1-0.2 mol/L and performing a vacuum-filtrating process to obtain a titrative alkali-ethanol solution;
(4) baking potassium hydrogen phthalate in an oven at 105° C. for 10-12 hours and then placing the potassium hydrogen phthalate in a dryer for cooling for at least 1 hour;
(5) with the potassium hydrogen phthalate obtained above as solute and distilled water as solvent, preparing a potassium hydrogen phthalate solution in an automatic potentiometric-titrator by weighing an appropriate amount of the potassium hydrogen phthalate obtained above and added with the distilled water, the result of weighing the potassium hydrogen phthalate being as precise as 0.1 mg;
(6) dripping the titrative alkali-ethanol solution in the potassium hydrogen phthalate solution by using the automatic potentiometric-titrator to achieve a first end point, and computing concentration of the titrative alkali-ethanol solution;
(7) repeating Step (6) twice and computing an average of the concentrations of the titrative alkali-ethanol solution for the three titrations in order to determine an actual concentration of the titrative alkali-ethanol solution;
(8) providing an acid mixture of aluminum etchant, which includes an acid mixture sample comprising nitric acid, phosphoric acid, and acetic acid and adding a first solvent and a second solvent in the acid mixture sample and uniformly stirring to obtain an acid mixture solution of aluminum etchant, the first solvent being monohydric alcohol and the second solvent being diol;
(9) dripping the titrative alkali-ethanol solution in the acid mixture of aluminum etchant by using the automatic potentiometric-titrator to achieve a first, a second and a third equivalence points and computing concentrations of nitric acid, phosphoric acid, and acetic acid contained in the acid mixture of aluminum etchant according to amounts of consumption of the titrative alkali-ethanol solution when the first, second, and third equivalence points occur by applying the following formulas:
mHNO3%=VEP1×C×MHNO3/m;
mH3PO4%=V(EP2-EP1)×C×MH3PO4/m;
and
mHAC%=V(EP3-EP2)×C×MHAC/m;
wherein C is concentration of the alkali-ethanol solution;
VEP1 is the volume of the alkali-ethanol solution consumed at the first equivalence point;
V(EP2-EP1) is difference between volumes of the alkali-ethanol solution consumed at the second and the first equivalence points;
V(EP3-EP2) is difference between volumes of the alkali-ethanol solution consumed at the third and the second equivalence points;
m represents the mass of the acid mixture of aluminum etchant used;
and M is molar mass of each one of the acids;
and
(10) repeating Step (9) twice and computing averages of the concentrations of nitric acid, phosphoric acid, and acetic acid contained in the acid mixture of aluminum etchant for the three measurements to determine actual concentrations of nitric acid, phosphoric acid, and acetic acid.

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Potentiometric titration method for measuring concentration of acid mixture of aluminum etchant

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Potentiometric titration method for measuring concentration of acid mixture of aluminum etchant

Life of this patent

Abstract

Claims11