Changes in the sorption properties of dispersed copper containing ammonium compounds in the surface layer resulting from interaction with water vapours

Abstract

Purpose. The change in sorption properties of stabilized dispersed copper with layered ammonium compounds resulting from long-term (up to 200 hours) interaction with saturated water vapours was studied.

Methods and methodology. The stabilized copper powder, PMS-1, with an average particle size of about 84 microns and a moisture content of less than 0.05 %, was used as the initial dispersed metal. Particle size measurements and the calculation of the specific surface area of the samples were performed using laser diffraction data (Malvern Mastersizer 3000). Modification of the surface of copper powders was carried out in a gas environment by vapours of alkamon and/or triamon based on quaternary ammonium compounds and by vapours of hydrophobic silicon-organic liquid HSL based on ethylhydridesiloxane. The composition of triamon in vapours corresponds to the chemical formula with low molecular (C₁-C₂) organic radicals in the nitrogen atom. The cationic part of alkamon contains a larger hydrocarbon radical - C₁₇. The following copper-based samples were obtained by means of consecutive and mixed treatment with the vapours of the above mentioned reagents: Cu/(A+T), Cu/A, Cu/T, Cu/T/A, Cu/A/T, Cu/A/HSL, Cu/T/HSL.

The water vapour sorption and adsorption isotherms of the samples were measured gravimetrically, using the exicator method, with a vapor pressure of P_H2O/P_S ranging from 0.45 to 1.00 (where P_s is the saturation pressure). The adsorption of water vapour was additionally evaluated by the presence of the O1s peak with the binding energy of 532.5 eV (VG Escalab 220iXL).

Results. The analysis of adsorption isotherms of surface-modified copper samples shows a weak adsorbate-adsorbent interaction. The isotherms are most typical for non-porous solids. The highest level of water adsorption within the first 100 hours of interaction (P_H2O/P_s = 0.98 ± 0.02) was demonstrated by the initial copper powder (PMS-1). The sorption level for the Cu/A/HSL sample is more than twice lower. Samples Cu/HSL and Cu/(A+T) have the lowest level of water vapour adsorption. Within the time interval from 130 to 216 hours it remains constant (0.0063 and 0.0049 g/g, respectively). The obtained results are important for the creation of chemically stable and water-repellent metallic fillers and additives, as well as components of materials used in electronics.

Conclusion. It was determined that during long-term (24-216 hours) interactions of saturated water vapour with surface-modified copper-based powders, the magnitude of water sorption (a, g/g) changes according to a complex function, similar to the one describing damped oscillations. A mathematical description of the process based on the linear and the Gauss function was proposed. It allows to approximate the experimental data (relative error 5-7 %) of the time dependences a = f(t) and 1/a = F(t) . The suggested description is relatively simple, physically meaningful and allows for quantitative description of nonlinear effects in the studied systems.

It was shown that among the synthesized copper-based samples with adsorbed reagents based on quaternary ammonium compounds (triamon-T and alkamon-A) and organohydridesiloxane adsorbed from the vapours of HSL, the most hydrophobic are samples of Cu/A/HSL and Cu/T/A with consequently applied layers of structurally similar substances, such as ammonium compounds with molecules of different size (Cu/T/A).

CONFLICT OF INTEREST

The authors declare the absence of obvious and potential conflicts of interest related to the publication of this article.

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