ABSTRACT
In this paper, the kinetics and mechanism of gold nanoparticles formation during the redox reaction between AuCl4− complex and l‐ascorbic acid under different conditions were described. It ...was also shown that reagent concentration, chloride ions, and pH influence kinetics of nucleation and growth. To establish rate constants of these stages, the model of Finke and Watzky was applied. From Arrhenius and Eyring dependencies, the values of activation energy (22.5 kJ mol−1 for the nucleation step and 30.3 kJ mol−1 for the growth step), entropy (about −228 J K−1 mol−1 for the nucleation step and −128 J K−1 mol−1 for the growth step), and enthalpy (19.8 kJ mol−1 for nucleation and 27.8 kJ mol−1 for particles growth) were determined. It was also shown that the disproporationation reaction had influence on the rate of nanoparticles formation and may have impact on final particles morphology.
► NaBH
4 and H
2Asc reducers of gold precursor were used to run reaction with different rates in micromixer as a potential device to conduct AuNPs synthesis. ► Different flow rates were used to ...optimize the process. ► High flow rate makes possible to synthesize spherical AuNPs with the size of about 1
nm.
Continuous-flow process conditions for the reduction to gold nanoparticles were varied following a variation scheme aiming at impacting each of the elementary steps—mixing, reaction, polymer diffusion and polymer binding. While the last three variations are done by proper material choice (reducer; polymeric stabilizer), flow processing using a multilamination micromixer intensified the mass transfer in all these steps and particularly improved the first mixing step of the reactants. As reducers L-ascorbic acid (H
2Asc) and sodium borohydride (NaBH
4) were used and as gold particle precursor chloroauric acid (HAuCl
4). All processing runs were analysed by plasmon absorption and transmission electron microscopy to reveal size, shape and polydispersity. For the HAuCl
4–H
2Asc system, the smallest particles were 0.8–4
nm (7.5
mL/min) and 0.6–3
nm (10.0
mL/min) for the HAuCl
4–NaBH
4 system. This is at the upper edge of performance reported for batch systems in literature, i.e. among the smallest gold particles generated. While the particles made for the HAuCl
4–H
2Asc system were polydisperse and polyshaped for most process conditions (however being spherical and relatively uniform at the two largest flow rates investigated), processing with the HAuCl
4–NaBH
4 system resulted in particles sizes with small mean deviation and almost ideal spherical shape. With polyvinyl alcohol (PVA) as stabilizer, stable colloids were obtained for one week (violet coloured) up to at least 2 months (pink coloured) in case of reaction with ascorbic acid, and for at least 1 month in case of reaction with NaBH
4.
Experimental study of phase equilibria in the ternary Ag-Cu-Ga system was carried out by using DTA/DSC, isothermal equilibration and microscopic as well as x-ray analyses. DTA experiments were ...conducted for alloys, whose concentrations varied along two cross-sections determined by the ratio of mole fractions
x
Ag
/
x
Cu
= 1:1 and
x
Ag
/
x
Ga
= 1:1. Equilibration of samples was carried out at 200, 450 and 650 °C. The obtained information about phases in equilibrium was compared with the results of calculations of the phase diagram for conditions identical to our experiments. It was demonstrated that the results of calculations are compatible with the experimental data.
This work comprises results of the studies on the mechanism and kinetics of hexaamminecobalt(lli) and tetraamminepalladium(II) co-reduction in ammonia-chloride solutions at pH 9.5. Electrolyte ...stability was determined by UV-Vis absorbance measurements. Electrochemical investigations were performed by applying cyclic voltammetry (CV) combined with electrochemical quartz crystal microbalance (EQCM) as well as with spectrophotometric measurements. The results indicated that the reduction process of Co(NH(3))(6)(3+) consists of two steps. In the first step Co(NH(3))(6)(3+) is reduced to Co(NH(3))(4)(2+) and Co(NH(3))(5)(2+), and then ammonia complexes of Co(2+) are reduced to Co(0). The M/z values determined during electrogravimetric measurements indicate that the reduction process of Pd(NH(3))(4)(2+) takes place in one step due to 2-electrons irreversible reduction reaction. Deposition of Co and Pd take place only in the overpotential deposition range. It was found that the examined reactions are diffusion-controlled. In anodic part M/z values and registered CV's indicate cobalt(II) hydroxide oxidation.
Investigations of the influence of electrolysis parameters such as the concentration of metal ammonia complexes, working electrode potential and temperature on the composition, structure and ...catalytic activity of synthesized alloys for water molecule reduction reaction in 2 M NaOH (
T
= 25 °C) were conducted. The alloys were deposited under potentiostatic conditions within potential range from −0.7 to −1.1 V in electrolytes of pH 9.5, containing ammonia complexes of cobalt(III) and palladium(II), Co(NH
3
)
6
3+
and Pd(NH
3
)
4
2+
, of different concentration ratio. Structural changes in electrodeposited alloys were discussed based on results of X-ray diffraction measurements. An elemental analysis was performed using the energy-dispersive X-ray spectroscopy technique. Finally, based on results of galvanostatic measurements, the Tafel slope within the range of activation control for hydrogen evolution reaction was determined and mechanism of the process was discussed. The alloys presented low Tafel slope value, from 25.4 to 88.7 mV dec
−1
. The alloy of the highest activity for hydrogen evolution reaction contained 31.2 at.% of Pd.
ABSTRACT
In this paper, we show that using different concentrations of reagents, it is possible to produce gold nanoparticles with different morphology (size, shape). The color of obtained colloidal ...gold change from pink, violet to blue, and it corresponds to the shape change. The pink color corresponds to spherical nanoparticles and the blue one to a star shape. The mixture of those two types of nanoparticles result in a violet tone. It was also shown that kinetics of nucleation and growth process is controlled by the reaction on the gold atoms surface, i.e., comproportionation of Au(III) and Au(0) to Au(I), which can be inhibited by varying precursor and reductant concentration.
The diffusivity and activity coefficient of oxygen in liquid antimony,
bismuth and antimony-bismuth alloys were determined from coulometric
titration experiments, which were performed in the ...temperature range from
985 to 1185 K. The diffusivity in pure metals (in cm2/s) is: Dbi,O =(9.04 ? 1.82)?10-3 exp (-49115?1809/RT) DSb,O(2.87?0.22)?10-4 exp (-16720?677/RT). The standard free energy of solution of oxygen in
liquid antimony, bismuth and antimony-bismuth alloys according to the
reaction ? O2 (g) = O (infinite dilution) is calculated. The activity
coefficient of oxygen was calculated at 1085 K as a function of the alloy
composition. It was demonstrated that Wagner's model with one adjustable
parameter h gave a satisfactory description of the experimental data.
nema
Thermodynamics of Bi2O3-SiO2 system Onderka, B.; Fitzner, K.; Kopyto, M. ...
Journal of mining and metallurgy. Section B, Metallurgy,
2017, Letnik:
53, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Thermodynamic properties of the liquid Bi2O3-SiO2 solutions were determined
from the results of the electrochemical measurements by use of the solid
oxide galvanic cells with YSZ ...(Yttria-Stabilized-Zirconia) electrolyte.
Activities of Bi2O3 in the solutions were determined for 0.2, 0.3, 0.4, and
0.5 SiO2 mole fractions in the temperature range 1073-1293 K from measured
electromotive force (e.m.f) of the solid electrolyte galvanic cell: Bi,
Bi2O3-SiO2 | YSZ | air (pO2 = 0.213 bar) Additionally, heat capacity data
obtained for two solid phases 6Bi2O3?SiO2 and 2Bi2O3?3SiO2 were included into
optimization of thermodynamic properties of the system. Optimization
procedure was supported by differential thermal analysis (DTA) data obtained
in this work as well as those accepted from the literature. Using the data
obtained in this work, and the information about phase equilibria found in
the literature, binary system Bi2O3-SiO2 was assessed with the ThermoCalc
software.
nema
Corrosion resistance of pure titanium (Grade 2) and Ti-Pd alloy (Grade 7) was studied using the electrochemical techniques of potentiodynamic measurements and electrochemical impedance spectroscopy ...(EIS). Measurements were performed at the temperature of 36.6 °C in two solutions: PBS solution with pH of 7.4 simulating conditions of healthy human body, and PBS solution with pH of 5.2 and with the addition of hydrogen peroxide (0.015 mol/L) simulating the inflammatory state. It is found that, Ti Grade 7 can be a good candidate as a material for orthopedic implant application, because its corrosion resistance in the PBS solution containing H2O2 is better (lower corrosion current densities) than that of pure titanium.
EXAFS and QEXAFS experiments were carried out at Hasylab laboratory in DESY center (X1 beamline, Hamburg, Germany) to monitor the course of the hydrolysis reactions of AuCl4− complex ions as well as ...their reduction using glucose. As a result, changes in the spectra of AuCl4− ions and disappearance of absorption Au-L3 edge were registered. From the results of the experiments we have carried out, the changes in bond lengths between Au3+ central ion and Cl− ligands as well as the reduction of Au3+ to metallic form (colloidal gold was formed in the system) are evident. Good quality spectra obtained before and after the reactions gave a chance to determine the bond length characteristic of Au−Cl, Au−OH and Au−Au pairs. Additionally, the obtained results were compared with the simulated spectra of different gold (III) complex ions, possibly present in the solution. Finally, the mechanism of these reactions was suggested. Unfortunately, it was not possible to detect the changes in the structure of gold (III) complex ions within the time of reaction, because of too high rates of both processes (hydrolysis and reduction) as compared with the detection time.
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