Srdjan Petrović

RESPONSE SURFACE OPTIMIZATION FOR ACTIVATION OF BENTONITE USING MICROWAVE IRRADIATION

Microwave irradiation as a means for heating bentonites during acid activation has been investigated in the past but it has never been optimized for industrial applications. The purpose of this study was to apply a factorial 23 experimental design to a Serbian bentonite in order to determine the influence of microwave heating on the acid-activation process. The effect of acid activation under microwave irradiation on the textural and structural properties of bentonite was studied as a model reaction. A mathematical, second-order response surface model (RSM) was developed with a central composite design that incorporated the relationships among various process parameters (time, acid concentration, and microwave heating power) and the selected process response of specific surface area of the bentonite. The ranges of values for the process parameters chosen were: time, 5–21 min; acid concentration, 2–7 M; and microwave heating power, 63–172 W. The effect of individual variables and their interaction effects on the textural and structural properties of the bentonite were determined. Statistical analysis showed that the duration of microwave irradiation was less significant than the other two factors. The model showed that increasing the time and acid concentration improved the textural properties of bentonites, resulting in increased specific surface area. This model is useful for setting an optimum value of the activation parameters for achieving the maximum specific surface area. An optimum specific surface area of 142 m2g−1 was achieved with an acid concentration of 5.2 M, activation time of 7.4 min, and microwave power of 117 W.

Angular distributions of relativistic ions channeled in the bent Si crystals

Abstract The angular distributions of relativistic protons channeled in the bent 〈1 0 0〉 Si crystals are considered. The ion energy is 7 TeV, the radius of curvature of the crystal is 49.8 m and the crystal thickness is varied from 0.1 to 0.5 cm (before bending), corresponding to the bending angle range from 0.02 to 0.1 mrad. The crystal thickness range under consideration corresponds to the reduced crystal thickness range from 2.1 to 10.35. The angular distributions of transmitted protons were generated by the computer simulation method using the numerical solution of the ion equations of motion, with the Lindhards expression for the continuum interaction potential of the ion and the crystal. The results of the analysis show that the angular distribution has a periodic behavior for the reduced crystal thickness, Λ, smaller than about 5. For variable Λ larger than 5 the angular distribution is “frozen”, i.e. its shape does not change, and this is accompanied by a slow decrease of the number of transmitted ions as Λ increases.

β-Carotene removal from soybean oil with smectite clay using central composite design

In this study removal of β-carotene from soybean oil by adsorption on acid activated smectite clay from Serbia was investigated and a factorial 23 experimental design was applied. The effects of relevant factors, such as temperature, solid-to-liquid ratio and time, on removal of β-carotene were investigated. In order to check these factors and their effect on the removal of β-carotene, we have established a model of this technique following a methodological strategy using experiments design. The mathematical model is established using a central composite design. The model describes the changes of the measured responses of β-carotene removal efficiency according to the temperature, solid-to-liquid ratio and time. The graphical representation of this model in the space of the variables enabled us to define the optimum conditions of these parameters. The optimum conditions to obtain the maximum removal of β-carotene from soybean oil were a temperature of 80°C, a solid-to-liquid ratio of 1: 25 and a time of 1255 s. Under these optimal conditions, the experimental values agreed with the predicted values, using analysis of variance, indicating a high goodness of fit of the model used and the success of response surface methodology for optimizing adsorption β-carotene of acid activated smectite clay from soybean oil.

Rainbows with Positrons and Carbon Nanotubes

This chapter is devoted to the rainbows occurring in channeling of positrons of incident kinetic energy of E0 = 1 MeV in (11, 9) chiral single-wall carbon nanotubes. As it has been said and explained in Subsect. 2.3.1, the process will be treated using quantum mechanics. In this case, the mass of the projectiles is sufficiently small and their incident kinetic energy sufficiently low that they clearly exhibit their wave properties. As it has been demonstrated in Chap. 1, in such a case, each rainbow is composed of a principal rainbow and one or more supernumerary rainbows. The principal rainbow is the primary, secondary, or a higher order rainbow.

Rainbows in Proton Channeling in Silicon Crystals

In this chapter, some of the high-resolution proton channeling measurements with a very thin (100) Si crystal conducted by the Singapore group [45–48] will be thoroughly analyzed. Those extraordinary measurements have proven to be crucial for verification of the theory of crystal rainbows as the proper theory of ion channeling in crystals. We shall present the results of three experimental and theoretical studies that were induced by those measurements and performed jointly by us and the Singapore group. The first study leads to the very accurate ion-atom interaction potentials [133]. As a continuation, we shall additionally explore the process that is inverse to the transmission process under consideration, and, thus, fully answer the question of its multiplicity, which is directly connected to the essence of the crystal rainbow effect, being the ion focusing along a line reflecting the symmetry of the illuminated crystal. The second study is devoted to the effect of superfocusing of channeled ions, which is the effect of spatial focusing occurring in the middle of each rainbow cycle [134]. The third study contains the proof that the doughnut effect in ion channeling, occurring with tilted crystals, which has been seen and measured many times, is in fact a crystal rainbow effect [130]. Before presenting the results of the second and third studies, we shall describe in detail the superfocusing and doughnut effects, respectively.

Rainbows with Protons and Carbon Nanotubes

Carbon nanotubes were discovered by Iijima in 1991 (Iijima Nature 354:56, 1991). They can be described as sheets of carbon atoms rolled up into cylinders with the atoms lying on the hexagonal lattice sites. The diameters of nanotubes are of the order of a few nanometers, and their lengths can be above a hundred micrometers. Nanotubes can be single-walled and multiwalled ones, depending on the number of cylinders they include. A nanotube is achiral or chiral. If it is achiral, the nanotube includes the atomic strings parallel to its axis. If it is chiral, the nanotube contains the atomic strings that spiral around its axis. Nanotubes have remarkable geometrical and physical properties (Saito R, Dresselhaus G, Dresselhaus MS (2001) Physical Properties of Carbon Nanotubes. Imperial College Press, London). As a result, they have begun to play an important role in the field of nanotechnologies (R.H. Baughman, A.A. Zakhidov, W.A. de Heer, Carbon nanotubes – The route toward applications. Science 297, 787 (2002)).