Thermal behavior of α-(Cu–Al–Ag) alloys, i.e. alloys
with composition less than about 8.5 mass% Al, was studied using differential
scanning calorimetry (DSC), differential thermal analysis (DTA), scanning
electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray
diffractometry (XRD). The results indicated that the presence of silver introduces
new thermal events ascribed to the formation of a silver-rich phase and, after
addition higher amounts than 8 mass% Ag to the Cu–8 mass% Al alloy it
is possible to observe the formation of the γ1
phase (Al4Cu9), which is only
observed in alloys containing minimum of 9 mass% Al. These results may be
attributed to some Ag characteristics and its interaction with Cu and Al.
Authors:Magdalena Troć, A. Skoczowski, and Małgorzata Barańska
The extracts from sunflower and mustard leaves were separated using SPE-Columns. The mustard seeds were germinated on water
(24 h) and subsequently on crude extracts or separate fractions. The heat production rate was measured by isothermal calorimetry
at 21°C and changes in seed cotyledons by FT-Raman spectroscopy. Crude extracts strongly inhibited seed germination. The water
and ‘methanol’ fractions of mustard and sunflower extracts have a similar influence on the pattern of heat efflux. FT-Raman
spectroscopy showed that extracts caused changes in cotyledons mainly in the content of fatty acids, carotenoids and flavonoids.
Isothermal calorimetry and Raman spectroscopy are useful for the study of allelopathic interactions.
Authors:A. Magdalena, A. Adorno, R. Silva, and T. Carvalho
In this work the effect of Ag concentration on the thermal behavior of the Cu-10 mass% Al and Cu-11 mass% Al alloys with additions
of 4, 6, 8 and 10 mass% Ag was studied using differential scanning calorimetry (DSC), in situ X-ray diffractometry (XRD) and
scanning electron microscopy (SEM). The results showed that for the Cu-10 mass% Al alloy Ag addition induce the β′1 phase formation and for the Cu-11 mass% Al alloy these additions increase the amount of martensite formed on quenching and
decrease the stability range of this phase on heating.
Authors:T. Carvalho, R. Silva, A. Adorno, and A. Magdalena
The Ag-rich phase precipitation in the Cu-9 mass% Al was studied using differential scanning calorimetry (DSC), X-ray diffractometry
(XRD) and scanning electron microscopy (SEM). The results indicated that Ag additions did not interfere on the metastable
transitions sequence of the Cu-mass% Al alloy but Ag precipitation disturbs the β phase formation reaction and the martensitic
phase decomposition reaction.
Authors:A. G. Magdalena, A. T. Adorno, T. M. Carvalho, and R. A. G. Silva
In the Cu–Al system, due to the sluggishness of the β ↔ (α + γ1) eutectoid reaction, the β phase can be retained metastably. During quenching, metastable β alloys undergo a martensitic transformation to a β′ phase at Al low content. The ordering reaction β ↔ β1 precedes the martensitic transformation. The influence of Ag additions on the reactions containing the β phase in the Cu–11mass%Al alloy was studied using differential scanning calorimetry and in situ X-ray diffractometry. The results indicated that, on cooling, two reactions are occurring in the same temperature range, the β → (α + γ1) decomposition reaction and the β → β1 reaction, with different reaction mechanisms (diffusive for the former and ordering for the latter) and, consequently, with different reaction rates. For lower cooling rates, the dominant is the decomposition reaction and for higher cooling rates the ordering reaction prevails. On heating, the (α + γ1) → β reverse eutectoid reaction occurs with a resulting β phase saturated with α. The increase of Ag concentration retards the β → (α + γ1) decomposition reaction and the β → β1 ordering reaction, which occurs in the same temperature range, becomes the predominant process.
Authors:R. A. G. Silva, E. S. Machado, A. T. Adorno, A. G. Magdalena, and T. M. Carvalho
The completeness of β-phase decomposition reaction in the Cu–11wt%Al–xwt%Ag alloys (x = 0, 1, 2, and 3) was studied using differential scanning calorimetry (DSC), X-ray diffractometry (XRD), and optical microscopy (OM). The results indicated that β-phase transformations are highly dependent on cooling rate and on the presence of Ag. On slow cooling, the silver presence prevents the β- and β1-phase decomposition; thus, inducing the martensitic phase formation. After rapid cooling, a new thermal event is observed and the reverse martensitic transformation is shifted to lower temperatures.
Authors:T. M. Carvalho, A. T. Adorno, A. G. Magdalena, and R. A. G. Silva
The eutectoid transformation may be defined as a solid-state diffusion-controlled decomposition process of a high-temperature phase into a two-phase lamellar aggregate behind a migrating boundary on cooling below the eutectoid temperature. In substitutional solid solutions, the eutectoid reaction involves diffusion of the solute atoms either through the matrix or along the boundaries or ledges. The effect of Ag on the non-isothermal kinetics of the reverse eutectoid reaction in the Cu–9 mass%Al, Cu–10 mass%Al, and Cu–11 mass%Al alloys were studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The activation energy for this reaction was obtained using the Kissinger and Ozawa methods. The results indicated that Ag additions to Cu–Al alloys interfere on the reverse eutectoid reaction, increasing the activation energy values for the Cu–9 mass%Al and Cu–10 mass%Al alloys and decreasing these values for the Cu–11 mass%Al alloy for additions up to 6 mass%Ag. The changes in the activation energy were attributed to changes in the reaction solute and in Ag solubility due to the increase in Al content.
Authors:R. A. G. Silva, A. T. Adorno, A. G. Magdalena, T. M. Carvalho, M. Stipcich, A. Cuniberti, and M. L. Castro
In this study the effect of Ag additions on the thermal behavior of the Cu–22.55 at.%Al alloy was studied using electrical resistivity measurements, in situ X-ray diffractometry, differential scanning calorimetry, and optical microscopy. The results indicated that Ag additions do not change the phase transformations sequence in the studied alloys, but modify its critical temperatures due to a change on entropy of system. It was verified that at the cooling rate of 10 K/min the decomposition of β phase into (α + γ1) is incomplete, but for lower cooling rates than 1.0 K/min this reaction is completed.
Authors:A. Waśko, Monika Kordowska-Wiater, M. Podleśny, Magdalena Polak-Berecka, Z. Targoński, and Agnieszka Kubik-Komar
The central composite design was developed to search for an optimal medium for the growth of
OXY. The effect of various media components, such as carbon sources, simple and complex nitrogen sources, mineral agents, and growth factors (vitamins B, amino acids) was examined. The first-order model based on Plackett-Burman design showed that glucose, sodium pyruvate, meat extract and mineral salts significantly influenced the growth of the examined bacteria. The second-order polynomial regression confirmed that maximum biomass production could be achieved by the combination of glucose (12.38 g/l), sodium pyruvate (3.15 g/l), meat extract (4.08 g/l), potassium phosphate (1.46 g/l), sodium acetate (3.65 g/l) and ammonium citrate (1.46 g/l).The validation of the predicted model carried out in bioreactor conditions confirmed the usefulness of the new medium for the culture of
OXY in large scale. The optimal medium makes the culture of the probiotic bacterium
OXY more cost effective.