Obtaining, Characterization and Applications of Advanced Materials

1. Introduction

This special issue focused on scientific works in the field of obtaining, characterization and recent applications of advanced materials, protective films, nanomaterials with multiple uses, including medical, heritage artefact conservation science and civil and industrial engineering.

Attention has been focused on materials used in environmental engineering, health care, dentistry and civil engineering, as well as the methods used in the handling and processing of these materials.

Materials ranging from nano to macro, including others, ceramics, composites, biomaterials, polymers, and more have been obtained through fine syntheses, and others have been investigated to gain new knowledge about the processing and practical applications of new materials.

2. The Published Articles

The first article [1] focuses on a catalyst based on molybdenum oxide supported on mesoporous silica with a cerium (Ce) modifier, which was prepared by in situ synthesis and used in a hydrogen peroxide desulfurization system (H₂O₂) of dibenzothiophene (DBT), benzothiophene (BT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT) from fuel oils. Freshly, after synthesis, its catalytic performance was studied involving Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Brunner-Emmet-Teller (BET) and X-ray Photoelectron Spectroscopy (XPS).

The second article [2] focuses on polycrystalline diamond (PCD) coated mechanical sealing rings, which were prepared by hot filament chemical vapor deposition (HFCVD) on graphite loaded silicon carbide (GSiC) substrates using incandescent filament.

The polycrystalline diamond deposition process has, in the initial phase, a nucleation, then a growth of the layer through a dense coating with a grain size of 4 µm and a thickness of 12.3 µm. The evolution of the crystalline phase and their morphologies on the substrate was investigated during the growth process of diamond crystallites. The well-developed PCD coating, as confirmed by Raman spectroscopy and X-ray diffractometry, significantly improves the applied mechanical sealing limit under harsh operating conditions at the pressure-velocity combination, regardless of whether the combination is for a hard-to-soft mating or a mating combination difficult to very difficult.

The samples obtained were evaluated using the same friction and wear testing machine, with adjustable rotation speed and load, which allowed to compare GSiC with sintered silicon carbide (SSiC) with the combination (GSiC/SSiC), taking the GSiC variants by the combination based on graphite (GSiC/graphite), PCD with a combination of graphite (PCD/graphite) and PCD with a combination of SSiC (PCD/SSiC). The highest pressure velocity (PV) limit of 42.31 MPa·m/s with 4 kN load at a rotation speed of 4500 rpm was found. For them, an extremely low but stable coefficient of friction and super mechanical properties were obtained in harsh working conditions. These can be accepted as a source of PCD coverage as the high PV limit.

Another article [3] with a topic on a close field of advanced materials, focuses on the study of implants based on iron (Fe) alloys, which has attracted attention in recent years due to its biodegradability, biocompatibility and superior mechanical properties. However, too slow degradation in a physiological environment limits its further clinical application. The paper studied the alloy of Fe with mesoporous carbon (MC), manufactured by means of a laser additive, which was used as a bone implant.

In particular, MC possesses a noble standard corrosion potential and excellent electrical conductivity, thus acting as an effective cathode and activating micro-galvanic corrosion in the Fe matrix. More importantly, its large specific surface area improved the cathode-to-anode surface ratio, which further improved the galvanic corrosion effect. As a consequence, the corrosion rate was improved from 0.09 to 0.24 mm/year based on immersion tests. In addition, the Fe/MC composite exhibited good cytocompatibility as well as excellent mechanical properties.

Another study [4] aims to evaluate the corrosion resistance of carbon steel, used for manufacturing carabiners, coated with three different types of phosphate layer. These have been obtained by phosphate conversion coating with three different types of phosphate solutions: zinc-based phosphate solution, zinc-iron-based phosphate solution and manganese-based phosphate solution. In addition, the test to evaluate the lubricant capacity was performed by comparing zinc phosphate samples with those coated (impregnated) with molybdenum disulfide dispersions in oil and respectively zinc phosphate covered with an elastomer-based paint layer. Considering the areas where carabiners are used (civil constructions, navigation, oil industry, rescue operations, etc.), the corrosive environments studied were rainwater, Black Sea water and fire extinguishing solution. The structure of the deposited layers was studied by scanning electron microscopy, while the structure of the interface between the alloy and the corrosive medium was analyzed by electrochemical impedance spectroscopy. According to this study, the corrosion resistance of zinc-based phosphate-coated and zinc/iron-based phosphate-coated samples is higher than that of the studied carbon steel samples despite the corrosion environment.

The fifth article [5] studies the effect of using TiO₂ nanoparticles in the production of cement composites, already known worldwide, as having high self-cleaning capacity, antimicrobial, antibacterial, antifungal properties and contributing to the reduction of environmental pollution. The paper aims to analyze the influence that TiO₂ nanoparticles have on the cementation matrix in terms of hydrophilicity, this being one of the two main parameters of the self-cleaning mechanism. Experimental tests, carried out using the indirect method of measuring surface water absorption, indicated that an addition of 3–6% (compared to the amount of cement) of TiO₂ nanoparticles is effective in increasing the surface hydrophilicity of cement composites. An excess of TiO₂ nanoparticles in the composite matrix of 10% TiO₂ nanoparticles (relative to the amount of cement) not only does not improve the performance of the surface in terms of hydrophilicity, but also visibly reduces it.

The sixth article [6] presents the expertise of the authentication of a painting by Nicolae Grigorescu by involving multi-analytical techniques, in order to identify and evaluate some archeometric and chemometric characteristics of the pictorial materials and the support, used in determining the age. The painting is made with oil colors on pressed cardboard, with preparation based on chalk dust and animal glue. The painting shows two elements as fakes, which have attracted suspicion, namely the author’s signature (showing a semi-transparent covering veil), and, on the reverse, a writing of the date, made by a very controversial art historian. According to the authors’ previous experiments, the investigation was carried out by direct analysis with magnification devices, in reflected UV (ultraviolet), VIS (visible) and NIR (near infrared) light, and by optical microscopy (OM), scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDX) and µ-FTIR. The results showed that the painting is authentic and belongs to Nicolae Grigorescu, and the dating previously established by Amelia Pavel through the writing on the back is certain.

Another article [7] focuses on new materials and ecological processes for cleaning old paintings that require special attention to the selection of processes and systems compatible with the chemical nature and adhesion of dirt deposits, in order not to affect the polychrome layer or the state of preservation of Vbechi paintings. The study was carried out on a 19th century icon made in fat tempera, on a thin layer of preparation, showing oxidatively fouled dirt. The cleaning was done using extracts obtained from sage, St. John’s wort and, respectively, licorice root teas obtained through different extraction processes: microwave oven, ultrasound, boiling and, respectively, room temperature.

The last article [8] looks at vernacular buildings, which are usually built using materials at hand, including wood, natural stone and bricks (either clay or mud bricks). All these materials being exposed to a series of environmental factors, their structure and integrity are affected. According to the previous experiments of the authors, the specialized literature was reviewed from 2010–2019, using different scientometric databases and keywords, such as: historical material, cultural heritage and terms regarding the effects of deterioration and degradation. The evaluation of the results was carried out by manual inspection (reading the entire document) and the selection of papers to be inserted in the current review was done by evaluating the contribution in the field. This review summarizes various aspects related to the restoration and preservation interventions of the wooden and masonry elements of traditional buildings, including the materials used for biocidal interventions, protection against abiotic factors, cleaning agents and consolidation. Finally, a critical discussion was carried out regarding the current limitations and future perspectives in the review of these activities, which consider the role of material science specialists in the context of cultural heritage conservation.

3. Conclusions

In conclusion, this special issue managed to collect high-quality works on the obtaining, characterization and practical applications of new advanced materials, obtained through special syntheses and we hope, based on the previous experiences of the authors’ collective, by citing the most representative published works of these in recent years, to provide a solid state-of-the-art reference in this research field.