BS EN ISO 9455‑3:2020 pdf – Soft soldering fluxes — Test methods Part 3: Determination of acid value, potentiometric and visual titration methods

BS EN ISO 9455‑3:2020 pdf – Soft soldering fluxes — Test methods Part 3: Determination of acid value, potentiometric and visual titration methods.
1 Scope This document specifies two methods for the determination of the acid value of a flux of types 1 and 2 only, as defined in ISO 9454-1. Method A is a potentiometric titration method and is to be considered as the reference method. Method B is an alternative, visual end-point, titration method. 2 Normative references There are no normative references in this document. 3 Terms and definitions No terms and definitions are listed in this document. ISO and IEC maintain terminological databases for use in standardization at the following addresses: — ISO Online browsing platform: available at https: //www .iso .org/obp — IEC Electropedia: available at http: //www .electropedia .org/ 4 Method A: Potentiometric titration method 4.1 Principle A prepared, weighed sample of the flux is dissolved in a suitable solvent. The resulting solution is titrated with standard tetrabutyl ammonium hydroxide solution, using a glass electrode, the pH or mV readings being recorded simultaneously. From the graph of volume of titrant against pH or mV readings, the point of inflexion is determined, from which the acid value is calculated. As fluxes of classes 1131 and 1231 (see ISO 9454-1) can lose some acidity during the determination of non-volatile matter, the non-volatile matter obtained from carrying out the procedure of ISO 9455-1 or ISO 9455-2 on these classes of flux should not be used for this determination. 4.2 Reagents Use only reagents of recognized analytical quality and only distilled, or deionized, water. 4.2.1 Tetrabutyl ammonium hydroxide [(CH 3 CH 2 CH 2 CH 2 ) 4 N(OH)] 0,1 M (0,1 mol/l).
4.2.2 Propan-2-ol [(CH 3 ) 2 CHOH], neutralized with tetrabutyl ammonium hydroxide solution (4.2.1) to a faint pink colour, using phenolphthalein as indicator. 4.2.3 Ethanol (C 2 H 5 OH), anhydrous, neutralized with tetrabutyl ammonium hydroxide solution (4.2.1) to a faint pink colour using phenolphthalein as indicator. 4.2.4 Toluene (C 6 H 5 CH 3 ), neutralized with tetrabutyl ammonium hydroxide solution (4.2.1) to a faint pink colour using phenolphthalein as indicator. 4.2.5 Ethanol/toluene mixture, made by mixing equal volumes of the anhydrous ethanol (4.2.3) and toluene (4.2.4). 4.3 Apparatus Usual laboratory apparatus and, in particular, the following. 4.3.1 Millivoltmeter or pH meter. 4.3.2 Glass electrode. 4.3.3 Saturated calomel, or silver chloride/silver, electrode. 4.3.4 Magnetic, or mechanical, stirrer, with variable speed drive. 4.3.5 Automated titration system with evaluating processor unit. 4.4 Procedure 4.4.1 General By preliminary experiments, determine whether the sample is soluble in propan-2-ol, anhydrous ethanol, toluene or the ethanol/toluene mixture. If it is not completely soluble in any of these solvents, select the one in which it appears to be the most soluble. If it is equally soluble in all four solvents, then use propan-2-ol. Carry out the following procedure, in triplicate, on the flux example. Weigh, to the nearest 0,001 g, approximately 0,5 g of the solid flux sample, or 2,0 g of the liquid flux sample taking steps to prevent loss of volatile matter during the weighing. Transfer the weighed sample to a 250 ml low form beaker. Add 100 ml propan-2-ol (4.2.2) or the selected solvent (4.2.3 to 4.2.5), according to the solubility characteristics of the flux. Cover with a watch glass and dissolve the flux by gentle agitation.
5.2 Reagents Use only reagents of recognized analytical quality and only distilled, or deionized, water. 5.2.1 Ethanol, anhydrous, neutralized with potassium hydroxide, 0,1 mol/l in alcohol (5.2.5), to a faint pink colour using phenolphthalein as indicator. 5.2.2 Toluene, neutralized with potassium hydroxide, 0,1 mol/l in alcohol (5.2.5), to a faint pink colour using phenolphthalein as indicator. 5.2.3 Ethanol/toluene mixture, made by mixing equal volumes of the anhydrous ethanol (5.2.1) and toluene (5.2.2). 5.2.4 Propan-2-ol, neutralized with potassium hydroxide, 0,1 mol/l in alcohol (5.2.5), to a faint pink colour using phenolphthalein as indicator. 5.2.5 Potassium hydroxide solution, 0,1 mol/l in alcohol. Use a commercially available standard solution or one prepared from a commercially available concentrated standard solution by dilution with ethanol (5.2.1). Alternatively, prepare a 0,1 mol/l potassium hydroxide solution by dissolving 3 g ± 0,1 g potassium hydroxide (KOH) in 500 ml of ethanol (5.2.1) and standardize this solution against an accurately weighed amount of benzoic acid (about 0,5 g) dissolved in ethanol (5.2.1). 5.2.6 Phenolphthalein indicator solution. Add 1 g of phenolphthalein to approximately 50 ml methanol and mix. When dissolved, dilute to 100 ml with methanol and mix. 5.3 Apparatus Ordinary laboratory apparatus is required. 5.4 Procedure By preliminary experiments, determine whether the sample is soluble in propan-2-ol, anhydrous ethanol, toluene or the ethanol/toluene mixture. If it is not completely soluble in any of these solvents, select the one in which it appears to be the most soluble. If it is equally soluble in all four solvents, then use ethanol as the selected solvent. Carry out the following procedure in triplicate on the flux sample.