Elsevier

Chemical Physics

Volume 313, Issues 1–3, 27 June 2005, Pages 101-106
Chemical Physics

Effects of the electrolytes in a closed unstirred Belousov–Zhabotinsky medium

https://doi.org/10.1016/j.chemphys.2005.01.003Get rights and content

Abstract

Complex periodic and aperiodic behaviors are reported in an unstirred Belousov–Zhabotinsky reaction at different concentrations of added electrolytes. A route to chaos following a Ruelle–Takens–Newhouse (RTN) scenario is identified. A 3-fold torus was also found in phase space. In this paper, we prove that the concentration of inert added electrolytes is a bifurcation parameter for the sequence period-1  period-2  period-3  chaos.

Introduction

The Belousov–Zhabotinsky (BZ) reaction is the most famous oscillatory chemical reaction in a homogeneous liquid phase for studying temporal, spatial and spatiotemporal nonlinear dynamics in nonequilibrium systems [1], [2], [3]. Significant research has been undertaken to understand chemical chaos that have been usually observed in a continuously flow stirred tank reactor (CSTR) [1], [3], [4]. It has been also reported that transient chaotic oscillations are observed in the BZ oscillating chemical reaction in a stirred batch reactor experimentally and numerically [5], [6], [7], [8].

Recently, we have observed aperiodic oscillations during the chemical evolution of a closed unstirred cerium catalyzed BZ system [9]. These aperiodic oscillations are an example of transient chaos because they are sensitive to the initial conditions, the major distinctive features of chaos [9], [10]. The chaotic regime is bounded by two periodic zones. The onset of chaos spontaneously starts by a Ruelle–Takens–Newhouse (RTN) scenario [11], [12] as soon as convection motion couples to diffusion and local kinetics. The chaotic motion continues for about 2 h and ends by an inverse RTN scenario [13]. Differently from the first transition (RTN scenario), the last seems related to the consumptions of the reactants [12], [13]. In previous papers, we studied the effect of different experimental conditions on the system dynamics. We showed that viscosity, temperature and reactor geometry are important control parameters for the transition to chaos [14], [15], [16], [17]. They play an important role in the coupling of chemical kinetics, diffusion and convection allowing or preventing the onset of chaos. A common feature of these systems is that the transition to chaos always takes place through an RTN scenario.

In this paper, we will show that the added electrolyte concentration is another bifurcation parameter responsible for the transition chaos to periodicity of a closed unstirred BZ reaction.

Section snippets

Experimental

All experiments were performed isothermically at ∼20 °C in a batch reactor (spectrophotometer cuvette, 1 × 1 × 4 cm3). The dynamics were monitored by the solution absorbance at 320 nm using quartz UV grade spectrophotometer cuvettes. A double beam spectrophotometer (Varian, series 634) was used. All chemicals were of analytical quality and were used without further purification. The following concentrations of reactants stock solutions were used: Ce(SO4)2 0.004 M, malonic acid 0.30 M, KBrO3 0.09 M; each

Results

In this section, we will illustrate in detail the results obtained adding Na2SO4 to the BZ solution; we obtained analogous results for the others electrolytes. Fig. 1(a) shows the typical spectrophotometric recording in absence of stirring. Two transitions: periodic  aperiodic  periodic can be observed. The Fourier transform of a significant interval of the aperiodic region (Fig. 1(b)), shows a broad band spectrum (Fig. 1(c)); it is a common feature of all aperiodic time series. Our previous

Discussion and concluding remarks

Recently, it has been showed that the BZ reaction in a closed reactor presents a lot of complex behaviors which depend sensibly on the experimental conditions. Many clues led us to claim that the route to chaos following an RTN scenario is due to a coupling between nonlinear chemical kinetics and transport phenomena (diffusion and convection). Unfortunately, we are not able to completely decouple these three phenomena and to tune independently one of them. On the other hand, we can choose

Acknowledgement

This work was supported by MIUR (Italy).

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