Biodegradation and mechanical behaviour of sintered compacts of Co-Cr alloy powder doped with ZrO2 used in dentistry

Direct Metal Laser Sintering je postupak moderne tehnologije s primjenom u različitim industrijama, uključujući medicinsku industriju. Namjena ovog istraživanja bila je dobiti sinterirane kompakte Co-Cr praha dopiranog sa ZrO2 u cilju poboljšanja biološke aktivnosti implantata te ponašanja in vitro nakon uranjanja u simuliranu biološku tekućinu (SBF) tijekom 21 dana. Co-Cr prašak (ST2724G) rabljen je za izradu jednog referentnog uzorka Co-Cr i 4 kompakta Co-Cr dopirana sa ZrO2 u sljedećim postocima: a) 5 % ZrO2, b) 10 % ZrO2, c) 15 % ZrO2, d) 20 % ZrO2. Morfologija i struktura svih kompakta određena je skeniranjem elektronskim mikroskopom (SEM), EDS (kvantitativno i kvalitativno) i rendgenskom analizom difrakcije (XRD). Mikrostrukture se razlikuju u ovisnosti o koncentraciji. XRD predstavlja kvalitativnu analizu sondi Co-Cr dopiranih cirkonij-dioksidom i EDS analiza predstavlja kvalitativnu i kvantitativnu analizu kompozita kompakta, prije i nakon uranjanja u SBF tijekom 21 dana. Nakon uranjanja u SBF, može se primijetiti da su sonde Co-Cr dopirane s cirkonijem imale dobru otpornost na koroziju, a sonde Co-Cr dopirane s 20 % cirkonija nizak mehanički otpor. U ovoj analizi je utvrđeno mehaničko ponašanje Co-Cr praha proizvedenog procesom izravnog laserskog sinteriranja metala (DMLS). Stroj za sinteriranje Phenix System tipa PXS & PXM Dental koristio je Co-Cr prah (ST2724G) a za 3D ispis datoteku "stl". Ispitivanje mehaničkih svojstava (vlaka i kompresije) ostvareno je na INSTRON 8810 stroju.Direct Metal Laser Sintering process is modern technology and is used in different industries, inclusive in medicine industry. The purpose of this study was to obtain sintered compacts of Co-Cr powder doped with ZrO2 in order to improve the bioactivity of the implants and the behavior in vitro after immersion in simulated biological fluid (SBF) for 21 days. Co-Cr powders (ST2724G) were used to realize one reference sample of Co-Cr and 4 compacts of Co-Cr doped with ZrO2 in the following percents: a) 5 % ZrO2, b) 10 % ZrO2, c) 15 % ZrO2, d) 20 % ZrO2. The morphology and structure of all compacts were determined using scanning electron microscope (SEM), EDS (quantitative and qualitative) and X-ray diffraction analysis (XRD). The microstructures differ in function of concentrations. XRD presents qualitative analysis of Co-Cr probes doped with zirconia and EDS analysis presents qualitative and quantitative analysis of composites compacts, before and after immersion in SBF for 21 days. After immersion in SBF, it can be noticed that the probes of Co-Cr doped with zirconia demonstrate good corrosion resistance and that for the probe Co-Cr doped with 20 % zirconia mechanical resistance is low. In this study the mechanical behavior of Co-Cr powder manufacturing by Direct Metal Laser Sintering (DMLS) process was determined. The sintering machine Phenix Systems type PXS & PXM Dental uses the Co-Cr powder (ST2724G) and for 3D printing use "stl" file. The mechanical tests (traction and compression) was realized with an INSTRON 8810 machine

Utilization of dielectric properties assessment to evaluate the catalytic activity and rate of deactivation of heterogeneous catalysts

The use of dielectric property assessment to gauge the catalytic activity and rate of deactivation of heterogeneous catalysts is reported. Four supported catalysts containing a combination of Fe and Ni active sites and γ-Al₂O₃, ZSM-5, MCM-41, and SBA-15 supports were synthesized, characterized, and utilized to catalyze a Fischer–Tropsch process over a temperature range of 250–400 °C that was specifically directed toward the production of lower olefins. While the highest conversion was obtained from ZSM-5 and MCM-41 supports containing Fe and Ni as active sites at 350 °C, all these catalysts were observed to be deactivated by the formation of carbon on their surface. The dielectric properties of the fresh, used catalysts and supports were evaluated and correlated with their catalytic activity and structural/textural properties. It was clearly shown that the dielectric property measurement could demonstrate both the presence and magnitude of carbon deposits on the catalyst via the differences in the values of fresh and used catalysts. Furthermore, the ability to differentiate between the levels of the carbon deposition observed was shown to be independent of the morphology exhibited by the carbon deposit demonstrating that this is a method that can be generally applied

Ceramic Composite Materials Obtained by Electron-Beam Physical Vapor Deposition Used as Thermal Barriers in the Aerospace Industry

This paper is focused on the basic properties of ceramic composite materials used as thermal barrier coatings in the aerospace industry like SiC, ZrC, ZrB2 etc., and summarizes some principal properties for thermal barrier coatings. Although the aerospace industry is mainly based on metallic materials, a more attractive approach is represented by ceramic materials that are often more resistant to corrosion, oxidation and wear having at the same time suitable thermal properties. It is known that the space environment presents extreme conditions that challenge aerospace scientists, but simultaneously, presents opportunities to produce materials that behave almost ideally in this environment. Used even today, metal-matrix composites (MMCs) have been developed since the beginning of the space era due to their high specific stiffness and low thermal expansion coefficient. These types of composites possess properties such as high-temperature resistance and high strength, and those potential benefits led to the use of MMCs for supreme space system requirements in the late 1980s. Electron beam physical vapor deposition (EB-PVD) is the technology that helps to obtain the composite materials that ultimately have optimal properties for the space environment, and ceramics that broadly meet the requirements for the space industry can be silicon carbide that has been developed as a standard material very quickly, possessing many advantages. One of the most promising ceramics for ultrahigh temperature applications could be zirconium carbide (ZrC) because of its remarkable properties and the competence to form unwilling oxide scales at high temperatures, but at the same time it is known that no material can have all the ideal properties. Another promising material in coating for components used for ultra-high temperature applications as thermal protection systems is zirconium diboride (ZrB2), due to its high melting point, high thermal conductivities, and relatively low density. Some composite ceramic materials like carbon–carbon fiber reinforced SiC, SiC-SiC, ZrC-SiC, ZrB2-SiC, etc., possessing low thermal conductivities have been used as thermal barrier coating (TBC) materials to increase turbine inlet temperatures since the 1960s. With increasing engine efficiency, they can reduce metal surface temperatures and prolong the lifetime of the hot sections of aero-engines and land-based turbines

Lanthanum Ferrite Ceramic Powders: Synthesis, Characterization and Electrochemical Detection Application

The perovskite-type lanthanum ferrite, LaFeO3, has been prepared by thermal decomposition of in situ obtained lanthanum ferrioxalate compound precursor, LaFe(C2O4)3·3H2O. The oxalate precursor was synthesized through the redox reaction between 1,2-ethanediol and nitrate ion and characterized by chemical analysis, infrared spectroscopy, and thermal analysis. LaFeO3 obtained after the calcination of the precursor for at least 550–800 °C/1 h have been investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). A boron-doped diamond electrode (BDD) modified with LaFeO3 ceramic powders at 550 °C (LaFeO3/BDD) by simple immersion was characterized by cyclic voltammetry and tested for the voltammetric and amperometric detection of capecitabine (CCB), which is a cytostatic drug considered as an emerging pollutant in water. The modified electrode exhibited a complex electrochemical behaviour by several redox systems in direct relation to the electrode potential range. The results obtained by cyclic voltammetry (CV), differential-pulsed voltammetry (DPV), and multiple-pulsed amperometry proved the electrocatalytic effect to capecitabine oxidation and reduction and allowed its electrochemical detection in alkaline aqueous solution

CuBi2O4 Synthesis, Characterization, and Application in Sensitive Amperometric/Voltammetric Detection of Amoxicillin in Aqueous Solutions

CuBi2O4 synthesized by thermolysis of a new Bi(III)-Cu(II) oxalate coordination compound, namely Bi2Cu(C2O4)4·0.25H2O, was tested through its integration within carbon nanofiber paste electrode, namely CuBi/carbon nanofiber (CNF), for the electrochemical detection of amoxicillin (AMX) in the aqueous solution. Thermal analysis and IR spectroscopy were used to characterize a CuBi2O4 precursor to optimize the synthesis conditions. The copper bismuth oxide obtained after a heating treatment of the precursor at 700 °C/1 h was investigated by an X-ray diffraction and scanning electron microscopy. The electrochemical behavior of CuBi/CNF in comparison with CNF paste electrode showed the electrocatalytic activity of CuBi2O4 toward amoxicillin detection. Two potential detections, with one at the potential value of +0.540 V/saturated calomel electrode (SCE) and the other at the potential value of −1.000 V/SCE, were identified by cyclic voltammetry, which were exploited to develop the enhanced voltammetric and/or amperometric detection protocols. Better electroanalytical performance for AMX detection was achieved for CuBi/CNF using differential-pulsed and square-wave voltammetries than others reported in the literature. Very nice results obtained through anodic and cathodic currents recorded at +0.750 V/SCE and −1.000 V/SCE in the same time period using a pseudo multiple-pulsed amperometry technique showed the great potential of the CuBi/CNF paste electrode for practical applications in amoxicillin detection in aqueous solutions

Alkali Niobate Powder Synthesis Using an Emerging Microwave-Assisted Hydrothermal Method

For more than five decades, alkali niobate-based materials (KxNa1−xNbO3) have been one of the most promising lead-free piezoelectric materials researched to be used in electronics, photocatalysis, energy storage/conversion and medical applications, due to their important health and environmentally friendly nature. In this paper, our strategy was to synthetize the nearest reproductible composition to KxNa1−xNbO3 (KNN) with x = 0.5, placed at the limit of the morphotropic phase boundary (MPB) with the presence of both polymorphic phases, orthorhombic and tetragonal. The wet synthesis route was chosen to make the mix crystal powders, starting with the suspension preparation of Nb2O5 powder and KOH and NaOH alkaline solutions. Hydrothermal microwave-assisted maturation (HTMW), following the parameter variation T = 200–250 °C, p = 47–60 bar and dwelling time of 30–90 min, was performed. All powders therefore synthesized were entirely KxN1−xNbO3 solid solutions with x = 0.06–0.69, and the compositional, elemental, structural and morphological characterization highlighted polycrystalline particle assemblage with cubic and prismatic morphology, with sizes between 0.28 nm and 2.95 μm and polymorphic O-T phase coexistence, and a d33 piezoelectric constant under 1 pC/N of the compacted unsintered and unpoled discs were found

Thermally Activated Al(OH)3 Part II—Effect of Different Thermal Treatments

In this paper, the thermal decomposition of crystalline Al(OH)3 was studied over the temperature range of 260–400 °C for particles with a size between 10 and 150 µm. The weight losses and thermal effects occurring in each of the dehydration process were assessed using thermogravimetry (TG) and differential scanning calorimetry (DSC) thermal analysis. X-ray diffraction (XRD) patterns, refined by the Rietveld method, were used for mineral phase identification, phase composition analysis, and crystallinity degree determination. Moreover, the particle size distributions and their corresponding D10, D50, and D90 numeric values were determined with a laser analyzer. We observed a strong relationship between the calcination temperature, the initial gibbsite grade particle size, and the crystallinity of the resulting powders. Hence, for all endothermic effects identified by DSC, the associated temperature values significantly decreased insofar as the particle dimensions decreased. When the gibbsite was calcined at a low temperature, we identified small amounts of boehmite phase along with amorphous new phases and unconverted gibbsite, while the powders calcined at 400 °C gradually yielded a mixture of boehmite and crystalized γ-Al2O3. The crystallinity % of all phase transition products declined with the increase in particle size or temperature for all the samples

Processing of Calcium Magnesium Silicates by the Sol–Gel Route

In this work, calcium magnesium silicate ceramics were processed through the sol–gel method in order to study the crystalline and morphological properties of the resulting materials in correlation with the compositional and thermal parameters. Tetraethyl orthosilicate and calcium/magnesium nitrates were employed as sources of cations, in ratios specific to diopside, akermanite and merwinite; they were further subjected to gelation, calcination (600 °C) and thermal treatments at different temperatures (800, 1000 and 1300 °C). The properties of the intermediate and final materials were investigated by thermal analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction and Rietveld refinement. Such ceramics represent suitable candidates for tissue engineering applications that require porosity and bioactivity

High-Entropy Lead-Free Perovskite Bi_0.2K_0.2Ba_0.2Sr_0.2Ca_0.2TiO₃ Powders and Related Ceramics: Synthesis, Processing, and Electrical Properties

A novel high-entropy perovskite powder with the composition Bi0.2K0.2Ba0.2Sr0.2Ca0.2TiO3 was successfully synthesized using a modified Pechini method. The precursor powder underwent characterization through Fourier Transform Infrared Spectroscopy and thermal analysis. The resultant Bi0.2K0.2Ba0.2Sr0.2Ca0.2TiO3 powder, obtained post-calcination at 900 °C, was further examined using a variety of techniques including X-ray diffraction, Raman spectroscopy, X-ray fluorescence, scanning electron microscopy, and transmission electron microscopy. Ceramic samples were fabricated by conventional sintering at various temperatures (900, 950, and 1000 °C). The structure, microstructure, and dielectric properties of these ceramics were subsequently analyzed and discussed. The ceramics exhibited a two-phase composition comprising cubic and tetragonal perovskites. The grain size was observed to increase from 35 to 50 nm, contingent on the sintering temperature. All ceramic samples demonstrated relaxor behavior with a dielectric maximum that became more flattened and shifted towards lower temperatures as the grain size decreased