Wyniki wyszukiwania - Biblioteka Nauki

1

Polymer electrolytes based on POE and Na-TFS salt for all-solid-state batteries

100%

Martinez-Cisneros C. S. , Sanchez J. Y. , Levenfeld B. , Varez A.

Journal of Achievements in Materials and Manufacturing Engineering

|

2015

|

tom Vol. 73, nr 2

72--79

EN

Purpose: Currently, electrochemical energy storage systems mostly focus on lithiumion batteries; especially in the field of portable electronics and electric transportation. Nevertheless, it is expected that the exponential growth of these markets and limited lithium resources will increase the price of lithium-based energy storage systems. To meet growing demands in terms of green and sustainable electric power storage, alternative electrochemical technologies towards post lithium-ion batteries are required. Design/methodology/approach: In the present study, polymer electrolytes based on poly(oxyethylene) (POE) and Na-TFS (NaCF3SO3) were developed to be used in solventfree batteries. Electrolytes were prepared using two methodologies: (i) a green-chemistry approach based on lyophilization combined with hot-pressing and (ii) the film-casting method. Findings: Advantages and limitations of both approaches were investigated by several characterization techniques (morphology, thermal and conductivity studies). Using lyophilization/hot-pressing, waste and chemical derivatives production is prevented (Green Chemistry approach) and uniform and porous-free films with controllable thickness and improved mechanical properties are achievable. Research limitations/implications: Further work regarding the development and application of novel polymer backbones is necessary to reach performances comparable to lithium-based polymer electrolytes in terms of electrical properties (conductivity). Originality/value: This work is in total agreement with the current need of developing alternative materials towards sustainable and environmental friendly post lithium-ion batteries. This global aspiration is supported by the recent re-emerging focus on sodium-ion batteries.

2

Synthesis and characterization of anion-exchange membranes with various functional groups

100%

Perez-Prior M. T. , Garcia-Garcia T. , Varez A. , Levenfeld B.

Archives of Materials Science and Engineering

|

2015

|

tom Vol. 72, nr 1

16--25

EN

Purpose: In the current study anion-exchange membranes comprised of different functional groups were prepared to be used as electrolyte in fuel cells. Design/methodology/approach: Polysulfone was firstly chloromethylated followed by nucleophilic substitution reaction with the corresponding N-compound, trimethylamine and 1-methylbenzimidazole to obtain the resulting quaternary ammonium and benzimidazolium functionalized membranes, respectively. The membranes thus prepared as well as the starting polymers were characterized by 1H-NMR and FTIR analysis. Findings: The thermal stability of the membranes was lower than the original polymers. However, both membranes exhibited high thermal stability for typical fuel cell operation temperatures below 100°C. The capacity of these materials to absorb water was more favored when benzimidazolium groups were inserted to the polymer instead of quaternary ammonium ones. The ionic conductivity of the membranes in dilute aqueous solution of potassium hydroxide was studied by means of impedance spectroscopy. The results show a clear correlation between the membrane’s electrochemical behaviour with the electrolyte solution embedded in the membrane. In addition, the nature of the functional group modifies the membrane ionic conductivity. So, the membrane ionic conductivity was more than twice as high when the quaternary ammonium groups were replaced by the benzimidazolium ones. Research limitations/implications: The nature of the functional group as well as the number of exchangeable groups plays an important role on the ionic transport through the membrane. Therefore, the membrane ionic conductivity could be significantly improved by modifying the chemical structure of the polymer. Originality/value: The current study describes the main properties of benzimidazolium functionalized membranes. The electrochemical characteristics of this material as well as the thermal stability have been compared to the most commonly used comprising quaternary ammonium groups.

3

Wpływ metody formowania na strukturę i własności spiekanych stali szybkotnących

88%

Dobrzański L. A. , Matula G. , Levenfeld B. , Varez A. , Torralba J. M.

Inżynieria Materiałowa

|

2003

|

tom R. XXIV, nr 6

597-600

PL

W pracy wykazano, że stale doświadczalne typu HS6-5-2 i HS12-1-5-5 wytwarzane metodą formowania gęstwy polimerowo-proszkowej (PIM) cechują się niższą temperaturą spiekania w stosunku do tych samych gatunków stali wytwarzanych przez prasowanie i spiekanie (PM). Stwierdzono, że wyższą gęstość, bardziej jednorodną strukturę z drobnymi wydzieleniami faz węglikowych otrzymuje się podczas spiekania stali formowanych z gęstwy w atmosferze mieszanki gazów ochronnych.

EN

In that paper it has been demonstrated that experimental steels of the HS6-5-2 and HS12-1-5-5 type made by the polymer-powder slurry forming (PIM) characterised by a lower sintering temperature, in relation to the same steel grades manufactured by compaction and sintering (PM). It has been found out that higher density, more homogeneous structure with fine precipitations of carbide phases are obtained during sintering of steels formed out of the slurry in the atmosphere of inert gases.

4

Surface modification of a duplex stainless steel for plastic-metal hybrid parts

88%

Sotomayor M. E. , Sanz J. , Cervera A. , Levenfeld B. , Varez A.

Archives of Materials Science and Engineering

|

2015

|

tom Vol. 72, nr 2

86--93

EN

Purpose: Of this paper is the evaluation of three different surface treatments on a duplex stainless steel, in order to improve its adhesive properties on a thermoplastic like polysulfone. Design/methodology/approach: In order to improve the adhesion between stainless steel and polysulfone, shot-peening, acid (aqua regia) etching and atmospheric pressure plasma jet have been used. The topography and surface activation effects have been evaluated by means of SEM and contact angle measurements. Additionally, aging studies have been performed to evaluate the effect of storage time of parts on atmospheric plasma torch surface treatment. Finally, to test the effectiveness of the treatments, it has been carried out successfully shear strength tests by tension of adhesive assemblies previously modified with the treatments. It has been also examined rupture failures that have occurred in these assemblies. Findings: Aqua regia and plasma torch treatments have reached the optimal surface modification condition under wettability criteria. Shear strength tests demonstrated that the improved surface adhesion provided on this substrate and the polysulfone is achieved by shot-peening and acid etching treatments. Research limitations/implications: A deeper analysis varying several conditions like humidity could be suggested in order to evaluate the effectiveness of surface treatment. Originality/value: Up to now there is no any study in the literature about the comparison of different surface treatment on duplex stainless steels and the subsequent evaluation of the adhesion of a polymer like polysulfone.