CS256414B1 - A method for determining barium concentration in liquid and solid lubricants - Google Patents

Abstract

The purpose of the solution is a simple and low-tech method for determining the concentration of barium in lubricants, which will enable obtaining information on the content of effective barium additives in laboratory and operational conditions. The stated purpose is achieved by decomposing a lubricant sample with concentrated hydrochloric acid at elevated temperature, extracting soluble barium salts into the aqueous phase, adjusting the ionic strength and pH of the aqueous phase, and determining barium by direct potentiometry using a barium ion-selective electrode in combination with a suitable reference electrode.

Description

The invention relates to a method of determining the concentration of barium in liquid and solid lubricants potentiometrically, using an ion-selective electrode.

Organic barium compounds, e.g. of the bis/alkylphenol/- disulfide type, bis/alkylphenol/- condensation salt of alkylphenol with formaldehyde, barium petrosulfonate, are used as additives with which lubricants are modified to improve their performance characteristics. Determining the barium concentration is one of the parameters for evaluating the quality of lubricants during production and during their operational use. So far, the barium concentration in lubricants has been determined by the gravimetric method and the atomic absorption spectrophotometry method. The disadvantage of the gravimetric method is the high time required and, due to the number of necessary work operations, the possibility of errors affecting the final result of the determination. The direct atomic absorption spectrophotometry method using oil-soluble organometallic standard solutions is fast and accurate, but requires the use of expensive instrumentation. The basic shortcoming of both methods used so far is that the measurement result is the total barium concentration, which expresses the concentration of barium in the form of the still active, original additive and the concentration of barium formed by the decomposition of these additives, due to operating conditions and bound in the form of insoluble and undesirable inorganic compounds in lubricants, such as barium sulfate in the case of using lubricants for diesel engine lubrication. The result of measuring the barium concentration by the methods used so far does not express the extent to which the additives contained in the lubricant have been depleted due to operating conditions.

The above-mentioned shortcomings are eliminated by the method of determining the barium concentration according to the invention, the essence of which is

-2236 414 decomposition of effective barium additives in the lubricant with concentrated hydrochloric acid at a temperature of 363 K / 90 °C /, extraction of barium salts into the aqueous phase, in which ee after adjusting the ionic strength and pH using tris-/hydroxymethyl/-aminomethane or other substances, e.g. monoethanolamine, diethanolamine or triethanolamine, at pH 8.1 to 9.9 determines the barium concentration potentiometrically, with a barium ion-selective electrode with low selectivity coefficients towards interferents present in the solution, for example an electrode with a plastic membrane, formed by a film of plasticized polyvinyl chloride with a composition of 30 to 31 wt. % high molecular weight polyvinyl chloride, 68 to 69 wt. % 2,4-dinitrophenyl-n-octyl ether as a plasticizer and 1 to 2 wt. % complex salts with a neutral carrier of the composition L ₂ ^Ba /ϊϊ©/^» fcde I» is a neutral carrier, N,N''-diphenyl~N,N'-di-/2-ethoxycarbonylphenyl/ 3,6,9-trioxaundecandioic acid diamide, Ba is a barium cation and TPB is a tetraphenylborate anion. The concentration of barium in the ionic form is determined by direct potentiometry, an ion-selective electrode with a membrane of the above composition in combination with a reference saturated calomel or other electrode.

The method of preparing a lubricant sample and determining the barium concentration according to the invention is time-saving, requires simple tools for sample preparation and for the actual measurement, commonly available measuring equipment, e.g. a pH meter, which allows measuring the electromotive force with an accuracy of - 1 mV. The method is simple and can be applied in every laboratory and operation with basic laboratory equipment. For a lubricant sample weighing 1 g, a volume of 5 ml of concentrated hydrochloric acid is sufficient for decomposition at elevated temperature and a total volume of 50 ml of the native phase for extraction.

For the actual measurement, 10 ml of the aqueous phase after extraction is measured, and the ionic strength and pH are adjusted. This procedure allows the determination of the barium concentration in the range of 68/Ug to 680 mg per 1 g of the material, which in aqueous extracts corresponds to a barium concentration of 10*^ mol.l“ ¹ to 10“ ¹ mol.I* ¹ . The results of the measurement of the barium concentration are not affected by the presence of ions up to a concentration of Fe^ ⁺ - 200/Ug.g \ Al^ - 200 /Ug.g” ¹ , Cu ²⁺ - 200/Ug.g” ¹ , Pb ²⁺ - 200/Ug.g“ ¹ , Zn ²⁺ - 200/Ug.g“ ¹ .

-3256 414

Lubricants containing barium-based additives may also contain calcium additives, such as calcium dialkyldithiophosphoric acid, calcium petrosulfonate. As is evident from Fig. 1, which shows the course of barium concentration measurement in model samples containing equimolar concentration of calcium ions, and from Fig. 2, which shows the course of barium concentration measurement in Sunday samples containing calcium ions in concentrations of 10 ¹ mol.l” ¹ 1 , 10 ² mol.l” ¹ 2 and 10' ³ mol.l” ¹ , the results of barium concentration measurement in the range of concentrations from 10 mol.l to 10” ¹ mol.l ¹ are not influenced by up to a hundred-fold excess of calcium ions.

Claims (1)

Method for determining the barium concentration in liquid and solid lubricants by potentiometry, characterized in that the lubricant sample is decomposed with concentrated hydrochloric acid at a temperature of 343 to 363 K (70 to 90 ° C), the soluble barium salts are extracted into an aqueous phase from which by adjusting the ionic strength and pH by one of the substances selected from the group of tris- (hydroxymethyl) -aminomethane, monoethanolamine, diethanolamine or triethanolamine, the barium concentration is determined by direct potentiometry of a barium ion-selective electrode having a membrane of 30-31 wt. high molecular weight polyvinyl chloride, 68 to 69 wt. % Of 2,4-dinitrophenyl-n-octyl ether as plasticizer and 1-2 wt. complex salts with a neutral carrier of the composition Lg Ba / TFB / g, wherein L is a neutral carrier, N, N'-diphenyl-N, N'-di- (2-ethoxycarbonylphenyl) diamide 3,6,9-trioxaundecanedioic acid, Ba is a barium cation and TPB is a tetrafenylborate anion, in combination with a reference electrode.