Materials

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14 pages, 9256 KiB

Open AccessArticle

Investigations Regarding the Addition of ZnO and Li₂O-TiO₂ to Phosphate-Tellurite Glasses: Structural, Chemical, and Mechanical Properties

by Mihail Elisa, Stefan-Marian Iordache, Ana-Maria Iordache, Constantina Raluca Stefan, Ileana Cristina Vasiliu, Daniel Cristea, Doru Ursutiu, Cornel Samoila, Bogdan Alexandru Sava, Lucica Boroica, Marius Catalin Dinca, Ana Violeta Filip, Mihai Eftimie and Monica Enculescu

Materials 2022, 15(5), 1644; https://doi.org/10.3390/ma15051644 - 22 Feb 2022

Viewed by 1616

Abstract

Phosphate and tellurite glasses can be used in optics, optoelectronics, magneto-optics, and nuclear and medical fields. Two series of phosphate-tellurite glasses, (50-x)ZnO-10Al₂O₃-40P₂O₅-xTeO₂ and (40-x)Li₂O-10Al₂O [...] Read more.

Phosphate and tellurite glasses can be used in optics, optoelectronics, magneto-optics, and nuclear and medical fields. Two series of phosphate-tellurite glasses, (50-x)ZnO-10Al₂O₃-40P₂O₅-xTeO₂ and (40-x)Li₂O-10Al₂O₃-5TiO₂-45P₂O₅-xTeO₂ (x = 5, 10), were synthesized by a non-conventional wet-route, and the mechanical properties as key performance measures for their application in optoelectronics were investigated. X-ray Diffraction (XRD) measurements revealed the vitreous nature of the investigated materials. Instrumented indentation tests allowed the calculation of hardness (H) and Young’s modulus (E) using the Oliver and Pharr model. The influence of increasing the TeO₂ content, as well as the substitution of ZnO by Li₂O-TiO₂, on the variation of hardness, Young’s modulus, penetration depth (PD), and fracture toughness (FT) was evaluated in both series. As a general trend, there is a decrease in the hardness and Young’s modulus with increasing penetration depth. The addition of Li₂O and TiO₂ instead of ZnO leads to improved hardness and elastic modulus values. Regarding the H/E ratio, it was found that the samples with lower TeO₂ content should be significantly more crack-resistant compared to the higher TeO₂ content samples. The H³/E² ratio, being lower than 0.01, revealed a poor resistance of these glasses to plastic deformation. At the same time, a decrease of the fracture toughness with increasing TeO₂ content was noticed for each glass series. Based on dilatometry measurements, the thermal expansion coefficient as well as the characteristic temperatures of the glasses were measured. Field Emission Scanning Electron Microscopy-Energy Dispersive X-ray analysis (FESEM-EDX) revealed a uniform distribution of the elements in the bulk samples. The mechanical properties of these vitreous materials are important in relation to their application as magneto-optical Faraday rotators in laser cavities. Full article

(This article belongs to the Special Issue Collection of Papers in Material Science from Romania)

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15 pages, 6191 KiB

Open AccessCommunication

Some Theoretical and Experimental Extensions Based on the Properties of the Intrinsic Transfer Matrix

by Nicolae Cretu, Mihail-Ioan Pop and Hank Steve Andia Prado

Materials 2022, 15(2), 519; https://doi.org/10.3390/ma15020519 - 10 Jan 2022

Cited by 2 | Viewed by 1226

Abstract

The work approaches new theoretical and experimental studies in the elastic characterization of materials, based on the properties of the intrinsic transfer matrix. The term ‘intrinsic transfer matrix’ was firstly introduced by us in order to characterize the system in standing wave case, [...] Read more.

The work approaches new theoretical and experimental studies in the elastic characterization of materials, based on the properties of the intrinsic transfer matrix. The term ‘intrinsic transfer matrix’ was firstly introduced by us in order to characterize the system in standing wave case, when the stationary wave is confined inside the sample. An important property of the intrinsic transfer matrix is that at resonance, and in absence of attenuation, the eigenvalues are real. This property underlies a numerical method which permits to find the phase velocity for the longitudinal wave in a sample. This modal approach is a numerical method which takes into account the eigenvalues, which are analytically estimated for simple elastic systems. Such elastic systems are characterized by a simple distribution of eigenmodes, which may be easily highlighted by experiment. The paper generalizes the intrinsic transfer matrix method by including the attenuation and a study of the influence of inhomogeneity. The condition for real eigenvalues in that case shows that the frequencies of eigenmodes are not affected by attenuation. For the influence of inhomogeneity, we consider a case when the sound speed is varying along the layer’s length in the medium of interest, with an accompanying dispersion. The paper also studies the accuracy of the method in estimating the wave velocity and determines an optimal experimental setup in order to reduce the influence of frequency errors. Full article

(This article belongs to the Special Issue Collection of Papers in Material Science from Romania)

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9 pages, 1855 KiB

Open AccessArticle

Nanocrystallized Ge-Rich SiGe-HfO₂ Highly Photosensitive in Short-Wave Infrared

by Catalin Palade, Ana-Maria Lepadatu, Adrian Slav, Valentin Serban Teodorescu, Toma Stoica, Magdalena Lidia Ciurea, Doru Ursutiu and Cornel Samoila

Materials 2021, 14(22), 7040; https://doi.org/10.3390/ma14227040 - 20 Nov 2021

Cited by 7 | Viewed by 1762

Abstract

Group IV nanocrystals (NCs), in particular from the Si–Ge system, are of high interest for Si photonics applications. Ge-rich SiGe NCs embedded in nanocrystallized HfO₂ were obtained by magnetron sputtering deposition followed by rapid thermal annealing at 600 °C for nanostructuring. The [...] Read more.

Group IV nanocrystals (NCs), in particular from the Si–Ge system, are of high interest for Si photonics applications. Ge-rich SiGe NCs embedded in nanocrystallized HfO₂ were obtained by magnetron sputtering deposition followed by rapid thermal annealing at 600 °C for nanostructuring. The complex characterization of morphology and crystalline structure by X-ray diffraction, μ-Raman spectroscopy, and cross-section transmission electron microscopy evidenced the formation of Ge-rich SiGe NCs (3–7 nm diameter) in a matrix of nanocrystallized HfO₂. For avoiding the fast diffusion of Ge, the layer containing SiGe NCs was cladded by very thin top and bottom pure HfO₂ layers. Nanocrystallized HfO₂ with tetragonal/orthorhombic structure was revealed beside the monoclinic phase in both buffer HfO₂ and SiGe NCs–HfO₂ layers. In the top part, the film is mainly crystallized in the monoclinic phase. High efficiency of the photocurrent was obtained in a broad spectral range of curves of 600–2000 nm at low temperatures. The high-quality SiGe NC/HfO₂ matrix interface together with the strain induced in SiGe NCs by nanocrystallization of both HfO₂ matrix and SiGe nanoparticles explain the unexpectedly extended photoelectric sensitivity in short-wave infrared up to about 2000 nm that is more than the sensitivity limit for Ge, in spite of the increase of bandgap by well-known quantum confinement effect in SiGe NCs. Full article

(This article belongs to the Special Issue Collection of Papers in Material Science from Romania)

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10 pages, 1420 KiB

Open AccessArticle

Stainless Steel Surface Nitriding in Open Atmosphere Cold Plasma: Improved Mechanical, Corrosion and Wear Resistance Properties

by Alice O. Mateescu, Gheorghe Mateescu, Adriana Balan, Catalin Ceaus, Ioan Stamatin, Daniel Cristea, Cornel Samoila and Doru Ursutiu

Materials 2021, 14(17), 4836; https://doi.org/10.3390/ma14174836 - 26 Aug 2021

Cited by 6 | Viewed by 1836

Abstract

This work presents preliminary results regarding improving the mechanical, wear and protective properties (hardness, coefficient of friction, corrosion resistance) of AISI 304 stainless steel surfaces by open atmosphere cold plasma surface treatment method. Comparative evaluations of the morphological, corrosion resistance, mechanical and tribological [...] Read more.

This work presents preliminary results regarding improving the mechanical, wear and protective properties (hardness, coefficient of friction, corrosion resistance) of AISI 304 stainless steel surfaces by open atmosphere cold plasma surface treatment method. Comparative evaluations of the morphological, corrosion resistance, mechanical and tribological properties for different periods of treatment (using N₂ gas for cold plasma generation in an open atmosphere) were performed. AFM surface analyses have shown significant surface morphology modifications (average roughness, FWHM, surface skewness and kurtosis coefficient) of the treated samples. An improved corrosion resistance of the N₂ treated surfaces in open atmosphere cold plasma could be observed using electrochemical corrosion tests. The mechanical tests have shown that the surface hardness (obtained by instrumented indentation) is higher for the 304 stainless steel samples than it is for the un-treated surface, and it decreases gradually for higher penetration depths. The kinetic coefficient of friction (obtained by ball-on-disk wear tests) is significantly lower for the treated samples and increases gradually to the value of the un-treated surface. The low friction regime length is dependent on the surface treatment period, with a longer cold plasma nitriding process leading to a significantly better wear behavior. Full article

(This article belongs to the Special Issue Collection of Papers in Material Science from Romania)

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22 pages, 11835 KiB

Open AccessArticle

Using the Stochastic Gradient Descent Optimization Algorithm on Estimating of Reactivity Ratios

by Iosif Sorin Fazakas-Anca, Arina Modrea and Sorin Vlase

Materials 2021, 14(16), 4764; https://doi.org/10.3390/ma14164764 - 23 Aug 2021

Cited by 2 | Viewed by 2198

Abstract

This paper describes an improved method of calculating reactivity ratios by applying the neuronal networks optimization algorithm, named gradient descent. The presented method is integral and has been compared to the following existing methods: Fineman–Ross, Tidwell–Mortimer, Kelen–Tüdös, extended Kelen–Tüdös and Error in Variable [...] Read more.

This paper describes an improved method of calculating reactivity ratios by applying the neuronal networks optimization algorithm, named gradient descent. The presented method is integral and has been compared to the following existing methods: Fineman–Ross, Tidwell–Mortimer, Kelen–Tüdös, extended Kelen–Tüdös and Error in Variable Methods. A comparison of the reactivity ratios that obtained different levels of conversions was made based on the Fisher criterion. The new calculation method for reactivity ratios shows better results than these other methods. Full article

(This article belongs to the Special Issue Collection of Papers in Material Science from Romania)

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8 pages, 3805 KiB

Open AccessArticle

Structure and Heat Transfer in Zircaloy-4 Treated at High Temperatures

by Mărioara Abrudeanu, Maria Magdalena Dicu and Maria Minodora Pasăre

Materials 2021, 14(16), 4494; https://doi.org/10.3390/ma14164494 - 10 Aug 2021

Viewed by 1346

Abstract

Zircaloy-4 has an important role in the construction of generation III nuclear reactors. An important application is the fuel element sheath, which must have excellent corrosion resistance in the working environment, adequate mechanical characteristics and very good heat transfer properties from the combustible [...] Read more.

Zircaloy-4 has an important role in the construction of generation III nuclear reactors. An important application is the fuel element sheath, which must have excellent corrosion resistance in the working environment, adequate mechanical characteristics and very good heat transfer properties from the combustible element to the coolant. The corrosion processes at high temperatures, the accidents that lead to significant increases in temperature and the structural transformations associated with them affect the heat transfer process. The paper presents research on the influence of high temperatures on the microstructure and thermal diffusivity of the zy-4 alloy. The samples were treated in air, at temperatures between 850 and 1050 °C for 60 min. The corrosion layers were characterized microstructurally and chemically. Furthermore, the transformations produced in the base material under the corrosion layer were analyzed. The values of thermal diffusivity were determined and correlated with the structural transformations. Considering the state of research on the materials appropriate to be used for new generation reactors, the current importance of third-generation reactors for energy systems and the fact that they will operate in the coming years, we consider that the study offers useful outcomes in the field of nuclear energy. Full article

(This article belongs to the Special Issue Collection of Papers in Material Science from Romania)

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11 pages, 4324 KiB

Open AccessArticle

Characterization of Archaeological Artefacts Using Methods Specific to Materials Science: The Case Study of Dacian Ceramics from 2nd c. BC to 1st c. AD

by Laura Teodorescu, Ayed Ben Amara, Nadia Cantin, Rémy Chapoulie, Cătălin Ducu, Sorin Ciucă, Claudiu Tulugea, Carol Terteci and Mărioara Abrudeanu

Materials 2021, 14(14), 3908; https://doi.org/10.3390/ma14143908 - 13 Jul 2021

Cited by 3 | Viewed by 1867

Abstract

Combined analysis methods such as optical microscopy (OM), cathodoluminescence (CL) microscopy, X-ray diffraction (XRD), and scanning electron microscopy–energy dispersive X-ray spectrometry (SEM–EDX) have made it possible to obtain the first physico-chemical data of Dacian potsherds, exhumed at the archeological site of Ocnița-Buridava, Romania; [...] Read more.

Combined analysis methods such as optical microscopy (OM), cathodoluminescence (CL) microscopy, X-ray diffraction (XRD), and scanning electron microscopy–energy dispersive X-ray spectrometry (SEM–EDX) have made it possible to obtain the first physico-chemical data of Dacian potsherds, exhumed at the archeological site of Ocnița-Buridava, Romania; the samples were provided by the “Aurelian Sacerdoțeanu” County Museum Vâlcea, dating from the 2nd century BC to the 1st century AD. The mineralogical and petrographic analyses revealed two types of ceramic pastes, taking into account the granulometry of the inclusions and highlighting the choice of the potter for fabricating the ceramic either by wheel or by hand. All samples showed an abundance in quartz, mica (muscovite and biotite), and feldspars. These observations were confirmed by cathodoluminescence imagery, revealing heterogeneous pastes with varied granulometric distributions. The XRD patterns indicated the presence of the mineral phases, indicating a firing temperature below 900 °C. The wheel-made ceramics have a fine, compact matrix with very fine inclusions (<40 µm). On the other hand, the hand-made ceramics present a coarse matrix, with inclusions whose granulometry reaches approximately 2 mm. The difference between these two types of ceramics is also confirmed by the mineralogical and chemical analysis. The wheel-made potsherds are more abundant in MgO, Al₂O₃, and CaO contents. Full article

(This article belongs to the Special Issue Collection of Papers in Material Science from Romania)

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18 pages, 16951 KiB

Open AccessArticle

The Effects of Modifying the Activity of Nitriding Media by Diluting Ammonia with Nitrogen

by Mihai Ovidiu Cojocaru, Mihai Branzei, Andrei Mihai Ghinea and Leontin Nicolae Druga

Materials 2021, 14(9), 2432; https://doi.org/10.3390/ma14092432 - 07 May 2021

Cited by 1 | Viewed by 1549

Abstract

This paper discusses the issue of the effects of modifying the activity of nitriding media by diluting ammonia with nitrogen and the concomitant variation in the degree of ammonia dissociation on the layer’s growth kinetics and their phase composition. To understand and quantify [...] Read more.

This paper discusses the issue of the effects of modifying the activity of nitriding media by diluting ammonia with nitrogen and the concomitant variation in the degree of ammonia dissociation on the layer’s growth kinetics and their phase composition. To understand and quantify the effects of the variation in the main parameters that influence the layer growth kinetics, the experimental programming method was used and mathematical models of interactions between influence and kinetics parameters were obtained for two metallic materials: Fe-ARMCO and 34CrAlMo5 nitralloy steel. It was concluded that the nitriding operating temperature and the degree of nitrogen dilution of the ammonia have statistically significant influences on the kinetics of the nitrided layer. In the same context, it was analytically proved and experimentally confirmed that the ammonia degree dissociation from the gaseous ammonia-nitrogen mixture, along with the dilution degree of the medium with nitrogen, significantly influences the nitrogen potential of the gaseous mixture used for nitriding and thus the concentration of nitrogen in balance at the medium thermochemically processed metal product interface. Full article

(This article belongs to the Special Issue Collection of Papers in Material Science from Romania)

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