Nominal Composition Research Articles

Extreme rejuvenation of a bulk metallic glass at the nanoscale by swift heavy ion irradiation

Swift heavy ions can be used as a tool to tune material properties by generating high aspect ratio, nanometric trails of defects, or new disordered phases. This work explores different aspects of using this tool for rejuvenating and enhancing plasticity in bulk metallic glasses. An amorphous alloy with a nominal composition of Pd40Ni40P20 was irradiated with GeV-accelerated Au ions. Irradiation-induced out-of-plane swelling steps up to approximately 100 nm in height are measured at the boundary between irradiated and non-irradiated areas. Changes of the relaxation enthalpy have been investigated using differential scanning calorimetry. Low-temperature heat capacity measurements substantiate an irradiation-induced increase of the boson peak height with increasing fluences. Accompanying transport measurements using radioactive Ag atoms as tracer also revealed increased diffusion rates in the irradiated samples dependent on the total fluence. Nano-indentation measurements show enhanced plasticity in the ion-irradiated glass which can be correlated with an increased heterogeneity as indicated by variable resolution fluctuation electron microscopy. The whole volume of the derived data substantiates a prominent enhancement of the excess volume in the solidified ion tracks and the irradiation-induced modifications are discussed and analyzed in the framework of strong glass rejuvenation within the nanometric ion tracks.

Modulating microwave attributes of Ba1−xSrxTiO3 nanoparticles: Insights into strontium concentration, structural intricacies and electromagnetic dynamics

In this pioneering investigation, we meticulously synthesized Ba1−xSrxTiO3 nanoparticles, with Sr concentrations varying between 0.0 and 0.4 at intervals of 0.1, via a refined chemical approach. The crux of our study lies in establishing the intricate correlations between the chemical constitution (primarily Sr concentration), salient structural attributes (encompassing lattice and microstructural parameters), electrical dynamics and consequential microwave characteristics. X-ray diffraction (XRD) analyses reinforced the unity between the average ionic radii of the Ba/Sr ions and the lattice constants. Scanning electron spectroscopy (SEM) furnished insights into the microstructural intricacies, while the nominal chemical composition was ascertained via energy-dispersive X-ray (EDX) spectroscopy. A deep dive into the electrical realm revealed the temperature and field-dependent behaviors of permittivity, tangent losses and polarization. The electromagnetic traits of Ba1−xSrxTiO3 (where 0.0 < x < 0.4) were meticulously delineated by analyzing the experimentally determined S-parameters across a frequency spectrum of 6 to 18 GHz. Our findings elucidate that the predominant losses of electromagnetic wave energy are attributable to aggregated electrical losses, predominantly steered by polarization processes. Our findings demonstrate a significant attenuation in the reflected wave energy, with values spanning from − 14.3 to − 17.1 dB, highlighting the potential of these nanoparticles for cutting-edge applications in electromagnetic interference mitigation.

Inhibition of Ti-rich precipitates and improvement of the irradiation resistance in V-4Cr-4Ti by adding La element

Four kinds of V-4Cr-4Ti-xLa (nominal composition x = 0, 0.1, 0.5, 1.0 wt.%) alloys with different La contents were prepared by vacuum arc melting. Three of them (x = 0, 0.1, 1.0 wt.%) were selected for single He+ (2000 appm for peak concentration) irradiation and sequential He+/V2+ (10 dpa for peak damage) irradiation at 550 °C. The results showed that the addition of La element could refine the grains by forming the second phase La2O3 particles. Moreover, the addition of La element reduced the sum of impurity elements concentration in the alloy, which inhibited the formation of Ti-rich precipitates and affected the vacancy concentration, thus affecting the evolution of He bubbles under different irradiation types. In addition, the V-4Cr-4Ti-1.0La alloy had a lower irradiation hardening after sequential He+/V2+ irradiation, which might be related to the removal of impurity elements. This work provided a reference for the performance optimization of vanadium alloy for fusion reactors.

Enhancement of strength-plasticity synergy in a graphene metallic glass composite

Metallic glass (MG) shows great potential for a wide range of functional and structural applications. However, it remains a challenge to enhance the ductility of metallic glasses without compromising their strength during development. A composite of bulk metallic glass/graphene (BMG/C(n)) was prepared using the suction casting method in argon atmosphere, with a nominal composition of (Zr60Ni20Al20)100-x(C(n))x (x = 5,10,15). The results indicate that the graphene well dispersed in the BMG matrix without any other intermetallic compounds present. Mechanical property testing reveals a significant increase in both plasticity and hardness with increasing graphene content, while maintaining high fracture strength of the BMG matrix.

Corrosion Behavior of Nickel–Titanium Continuous-Casted Alloys

Variations in the corrosion behavior of biomedical NiTi alloys in Cl− containing and acidic environments present a problem with their biological implantation. The objective of this research was to evaluate the synergy of the microstructure, the corrosion behavior, and the biocompatibility of novel continuous-cast NiTi alloys and to compare them with commercial NiTi alloys. The two alloys have a practically identical nominal chemical composition, but they differ in production technology. The continuous casting technology involved vacuum induction melting of the basic components and vertical continuous casting, while the commercial NiTi alloy was produced through a process of casting, hot rolling, and forming into square shapes. The microstructure was revealed to determine the surface area and size of grains. The corrosion of a commercial nickel–titanium alloy and one prepared by a novel continuous casting method in acidic and chloride-containing solutions was studied via analytical and electrochemical tests. Localized corrosion characteristics related to oxide properties, when exposed to 9 g L−1 NaCl solution, were examined with focused ion beam analysis and subsequent microchemical analysis of the formed corrosive products. Corrosion potential over time and the oxide film resistance were analyzed using linear polarization measurements. To obtain a preliminary estimate of biocompatibility, human fibroblast cells were used in indirect contact, i.e., alloy conditioning medium. The continuous casting method resulted in a reduction in the average grain size in comparison to the commercial sample and better corrosion stability of the sample in an acidic environment. Also, in a solution of 9 g L−1 NaCl the commercial sample showed high values for the corrosion current density (jcorr = 6 μA cm−2), which indicated low corrosion resistance, while the continuous casting sample possessed much better corrosion stability and lower values for the corrosion current density (jcorr = 0.2 μA cm−2). In line with that, elemental analysis of the corroded surfaces showed higher Cl− ion deposition over the surface layer of the commercial sample, suggesting local oxide breakdown. Moreover, NiTicc reached a value three times higher for polarization resistance (Rp = 270 kΩ cm2) over time in comparison to the commercial sample (Rp~100 kΩ cm2). Biocompatibility evaluation showed that human fibroblast cells exhibited altered metabolic activity. An MTT assay showed that cells’ mitochondrial activity dropped below that of control cells in the presence of both materials’ supernatants.

Improvement in electrical properties of Bi-2212 superconducting materials substituted with large-scale nano-sized tin

In the current work, the effect of nano-sized Sn (50 nm)/Sr partial replacement on the superconducting properties such as crystal structure, quality of intra- and intergrain boundary coupling, dc electrical resistivity, and dc magnetization in the Bi-2212 ceramic superconductors were investigated. Ceramic superconductors with nominal composition of Bi2Sr2-x(Sn)xCa1Cu1.75Na0.25Oy where x = 0.25, 0.30, 0.35 and 0.40 were prepared by solid-state reaction method and characterized by powder X-ray diffraction (XRD), dc electrical resistivity, scanning electron microscopy (SEM) and magnetic hysteresis (M–H) measurements. Phase examination of by XRD indicated that the doping of x = 0.25 ratio nano-sized SnO2 to the strontium sites improved the formation of the Bi-2212 high-temperature superconducting phase. SEM micrographs showed that the morphological structure of all samples consisted of plate-like grains, which were separated from each other by grain boundaries, indicating the Bi-2212 superconducting phase. The highest superconductivity transition temperature among the samples was measured as the Tconset = 86 K at x = 0.25 in Bi2Sr2-x(Sn)xCa1Cu1.75Na0.25Oy. M–H loops of the Bi2Sr2-x(Sn)xCa1Cu1.75Na0.25Oy sample at x = 0.25 ratio is larger compared to other examples, indicating improvement intergrain connectivity as well as enhanced flux pinning centers. In addition, the critical current (Jc) values of the samples were calculated from M–H measurement using Bean’s critical current model. The best Jc values were obtained as 570 A/cm2 at 15 K, which is a relatively high value for BSCCO superconductors with polycrystalline structure.

Growth and characterization of novel piezo-/ferroelectric single crystals from the PSN-BS-PT ternary system

Bismuth-based single crystals with the nominal composition of 0.1Pb(Sc1/2Nb1/2)O3-0.315BiScO3-0.585PbTiO3 (0.1PSN-0.315BS-0.585PT) ternary complex perovskite system were successfully grown using a high-temperature solution growth (HTSG) method. A mixture of PbO and Bi2O3 in a molar ratio of 73:27 was used as flux, and the flux to charge ratio was optimized to be 70:30 (wt%). The grown crystals, with dimensions up to 3 mm, exhibit a pseudo-cubic morphology. The XRD patterns of the ground powder and naturally formed pseudo-cubic facets confirm that the grown single crystals crystallize in the perovskite structure with the rhombohedral symmetry as the major phase, and the naturally grown pseudo-cubic facets are parallel to {100}C. The domain structures in the (001)-oriented single crystals examined by polarized light microscopy (PLM) and optical crystallography reveal the coexistence of rhombohedral and monoclinic phases in majority, with the presence of a minor tetragonal phase likely grown at the late stage of the growth, demonstrating the morphotropic phase boundary (MPB) characteristics for the grown crystals. Upon heating, phase transition from the major rhombohedral and monoclinic to the cubic phase take place at TC = 370 °C. The ferroelectric properties are displayed by polarization-electric field (P-E) hysteresis loops with a remanent polarization of 17 µC/cm2 and a high coercive field of 68 kV/cm. The piezoelectric coefficient (d33) is found to be 478 pC/N. The high Curie temperature and decent piezo- and ferroelectric performance of the PSN-BS-PT crystals make this ternary complex perovskite system a promising candidate for potential applications in high-temperature and high-power electromechanical transduction.

Sintering and crystallization kinetics of bioactive glass 13–93

This study investigates the sintering and crystallization behavior and kinetic of the bioactive glass (BG) 13–93 with nominal composition (in mol%): 54.6 SiO2 - 1.7 P2O3 - 22.1 CaO - 6.0 Na2O - 7.9 K2O - 7.7 MgO. Sintering and crystallization were investigated non-isothermally for various particle size fractions smaller than 315 µm as well as for bulk samples. Densification was not hindered by the presence of crystalline phases across all particle size fractions. Afterwards, wollastonite was found as the dominant crystal phase at higher temperature which resorb primary surface precipitation-like quartz crystallites. The growth direction shifts into volume when the sample surface is nearly covered. The crystal growth rate of wollastonite was calculated from the crystalline surface layer thickness measured during heating. The findings of this study are relevant for the high temperature processing of BG 13–93.

Nanostructured Cu12+xSb4S13 tetrahedrites prepared by solvothermal synthesis in 1-(2-aminoethyl)piperazine for efficient thermal energy harvesting

Intrinsically low lattice thermal conductivity and the earth-abundant nature of elements make tetrahedrites very promising sulfur-based materials for thermoelectric applications. Although the thermoelectric performance of lightweight sulfides is usually restricted due to high lattice thermal conductivity, nanoengineering may effectively enhance the energy conversion performance of tetrahedrites by disturbing phonon transport. In this work, we modified our unique solvothermal synthesis method with 1-(2-aminoethyl)piperazine as a solvent and pure elements as reagents to obtain both copper-rich and copper-poor tetrahedrites with nanometric grain sizes ranging from 40 to 300 nm. The powders obtained were densified by the PECS method at T = 573 K and p = 40 MPa. The structural and thermal properties of the fabricated materials were systematically investigated as a function of temperature to revisit the phase evolution of the Cu-Sb-S system in the vicinity of the tetrahedrite compounds. The Seebeck coefficient of the investigated materials changes from 150 µVK−1 up to 400 µVK−1 at 300 K due to the effective tuning of the carrier concentration. In turn, the nanocrystalline nature of the prepared tetrahedrites, which influences the strong phonon scattering at grain boundaries, results in an ultralow lattice thermal conductivity of around 0.25 Wm−1K−1 at 300 K. As a result of the tuned electronic transport and ultralow lattice thermal conductivity, the highest ZT parameter of 0.9 at 596 K was achieved for the nominal composition Cu13Sb4S13. This is one of the best values reported to date for low-cost and environmentally friendly tetrahedrites at this temperature. The resultant nanomaterials can be used as components in novel inorganic and organic-inorganic composites for direct conversion of heat to electricity.

The Microstructural Evolution and Corrosion Behavior of Zn-Mg Alloys and Hybrids Processed Using High-Pressure Torsion.

Zinc (Zn) alloys, particularly those incorporating magnesium (Mg), have been explored as potential bioabsorbable metals. However, there is a continued need to enhance the corrosion characteristics of Zn-Mg alloys to fulfill the requirements for biodegradable implants. This work involves a corrosion behavior comparison between severe-plastic-deformation (SPD) processed cast Zn-Mg alloys and their hybrid counterparts, having equivalent nominal compositions. The SPD processing technique used was high-pressure torsion (HPT), and the corrosion behavior was studied as a function of the number of turns (1, 5, 15) for the Zn-3Mg (wt.%) alloy and hybrid and as a function of composition (Mg contents of 3, 10, 30 wt.%) for the hybrid after 15 turns. The results indicated that HPT led to multimodal grain size distributions of ultrafine Mg-rich grains containing MgZn2 and Mg2Zn11 nanoscale intermetallics in a matrix of coarser dislocation-free Zn-rich grains. A greater number of turns resulted in greater corrosion resistance because of the formation of the intermetallic phases. The HPT hybrid was more corrosion resistant than its alloy counterpart because it tended to form the intermetallics more readily than the alloy due to the inhomogeneous conditions of the materials before the HPT processing as well as the non-equilibrium conditions imposed during the HPT processing. The HPT hybrids with greater Mg contents were less corrosion resistant because the addition of Mg led to less noble behavior.

Structural and electrical conduction properties of Y3+ ions substituted Li-Zn-Ti ferrites

Rare earth yttrium substituted lithium ferrites Li0.5Zn0.1Ti0.1Y x Fe2.3– x O4 with nominal composition x = 0.00 to 0.10 in steps of 0.02 was prepared by the conventional ceramic method. The samples were sintered at 1050 °C for 6 h using resistive conventional heating. X-ray diffraction (XRD) patterns confirmed the formation of a single phase with a spinel structure. FTIR studies also confirmed the tetrahedral and octahedral metal-oxygen bonding of the spinel structure. Structural parameters like density, lattice constant, and crystallite size, site distances, bond length distances were measured from XRD data. The crystallite size reduces while the density increased with the progressive substitution of Y3+ ions. The Fe3+ ions at the A and the B sites mainly contributes to the electromagnetic properties of ferrites. Y3+ ions preferably entering the B sites can significantly interfere with the conduction mechanism of lithium ferrites. The objective of the present work is to find out the effect of Y3+ substitution on the structural and electrical conduction response Li-Zn-Ti ferrites. The DC resistivity initially is found to increase for concentration x = 0.04 and then decrease with further substitution. The study of the temperature dependence of DC resistivity depicts two types of conduction mechanisms in the range studied. The results obtained are analyzed and presented in the paper.

Phase Relationship and Ni Solubility in Nanoparticles of Ce0.9Zr0.1O2

AbstractThe phase relationship, defect formation, and incorporation of Ni in Ce0.9Zr0.1O2 have been investigated in samples of nominal composition (Ce0.9Zr0.1)1‐xNixO2‐δ with x=0.03, 0.05 and 0.1, synthesized by a cation complexation route and heat treated at 600, 800 and 1000 °C. Several structural (XRD, XAS, HRTEM) and spectroscopic (XPS, Raman) techniques have been used. Our data show the lattice parameters determined from XRD do not significantly vary with the Ni content or annealing temperature. The increasing defect concentration with increasing Ni content revealed by Raman spectra was associated to the formation of oxygen vacancies in the bulk due to coexistence of NiO and Ce0.9Zr0.1O2. On the other hand, no variation in the oxygen vacancies concentration was detected at the surface with increasing the Ni content by XPS data. In those samples with the lowest Ni concentrations (3 and 5 %) and heat treated at 600 °C, the analysis of the EXAFS zone of the K‐edge of Ni indicates that local order around Ni cations is not long‐range, suggesting the presence of a noncrystalline phase. When the Ni content is higher (10 %) and/or the temperature of the thermal treatment is increased, the crystallization of NiO is clearly detected by XRD, EXAFS and HRTEM.

Observation and enhancement through alkali metal doping of p-type conductivity in the layered oxyselenides Sr2ZnO2Cu2Se2 and Ba2Zn1-x O2-x Cu2Se2.

The optoelectronic properties of two layered copper oxyselenide compounds, with nominal composition Sr2ZnO2Cu2Se2 and Ba2ZnO2Cu2Se2, have been investigated to determine their suitability as p-type conductors. The structure, band gaps and electrical conductivity of pristine and alkali-metal-doped samples have been determined. We find that the strontium-containing compound, Sr2ZnO2Cu2Se2, adopts the expected tetragonal Sr 2 Mn 3 SbO 2 structure with I4/mmm symmetry, and has a band gap of 2.16 eV, and a room temperature conductivity of 4.8 × 10-1 S cm-1. The conductivity of the compound could be increased to 4.2 S cm-1 when sodium doped to a nominal composition of Na0.1Sr1.9ZnO2Cu2Se2. In contrast, the barium containing material was found to have a small zinc oxide deficiency, with a sample dependent compositional range of Ba2Zn1-x O2-x Cu2Se2 where 0.01 < x < 0.06, as determined by single crystal X-ray diffraction and powder neutron diffraction. The barium-containing structure could also be modelled using the tetragonal I4/mmm structure, but significant elongation of the oxygen displacement ellipsoid along the Zn-O bonds in the average structure was observed. This indicated that the oxide ion position was better modelled as a disordered split site with a displacement to change the local zinc coordination from square planar to linear. Electron diffraction data confirmed that the oxide site in Ba2Zn1-x O2-x Cu2Se2 does not adopt a long range ordered arrangement, but also that the idealised I4/mmm structure with an unsplit oxide site was not consistent with the extra reflections observed in the electron diffractograms. The band gap and conductivity of Ba2Zn1-x O2-x Cu2Se2 were determined to be 2.22 eV and 2.0 × 10-3 S cm-1 respectively. The conductivity could be increased to 1.5 × 10-1 S cm-1 with potassium doping in K0.1Ba1.9Zn1-x O2-x Cu2Se2. Hall measurements confirmed that both materials were p-type conductors with holes as the dominant charge carriers.

Thermoelectric properties of Gd and Se double substituted tetrahedrite.

The compound Cu12Sb4S13, known as tetrahedrite, is an eco-friendly p-type thermoelectric material with earth-abundant, low-cost, and less toxic constituents. This contemporary work studied the thermoelectric properties of Gd and Se double-substituted tetrahedrites. The samples with nominal composition Cu11.95Gd0.05Sb4S13-xSex (where x = 0, 0.2, 0.4, 0.6, and 0.8) were prepared using the solid-state synthesis and sintered using high vacuum hot pressing. The structural analysis using X-ray diffraction revealed a successful tetrahedrite phase formation, and the systematic increase of lattice parameters with the selenium content (x) indicated successful Se substitution. The electron probe microanalysis revealed the presence of secondary phases Cu3SbS4, CuSbS2, and CuGdS2. The Raman spectroscopy showed a weakening Sb-S/Se bond with increased Se content in the samples. The +3 and -2 oxidation states of Gd and Se, respectively, were confirmed from the XPS study. Gd3+, a higher valence substituent at the Cu+/Cu2+ tetrahedral site, helped reduce the carrier concentration. On the other hand, the isoelectronic substitution of Se2- for S2- enhanced the thermopower and power factor by introducing resonant energy states near the Fermi level. Consequently, a maximum power factor of ∼1.35 (±0.08) mW m-1 K-2 at ∼729 K was obtained for the sample x = 0.4. The sample x = 0.4 also exhibited the lowest thermal conductivity ∼ 1.18 (±0.04) W m-1 K-1 at 729 K. The Callaway model indicates that the lowering in the lattice thermal part of conductivity of this sample is due to the combined effect of point defect and Umklapp scattering. The simultaneous improvement of carrier concentration and thermal conductivity resulted in a relatively high zT of ∼0.83 (±0.09) in the x = 0.4 sample.

Proton conductivity of fluorite based rare earth titanates (LnxTi1-x)4O8-2x (Ln = Yb, Er, Ho, 0.667 ≤ x ≤ 0.765).

Solid solutions of rare earth titanates with high contents of rare earth oxides of up to 50-62% have been synthesized by the co-precipitation method and their structure, microstructure and conductivity in dry and wet air have been studied. Proton conductors have been found for the first time in solid solutions of rare earth titanates with a high content of Ln2O3 (>50%) with a nominal formula composition of (LnxTi1-x)4O8-2x (Ln = Yb, Er, Ho, 0.667 ≤ x ≤ 0.765). Among (LnxTi1-x)4O8-2x (Ln = Yb, Er, Ho, x = 0.684), (HoxTi1-x)4O8-2x (x = 0.684) showed the maximum conductivity in wet air. In this context, four additional compositions (HoxTi1-x)4O8-2x (x = 0.718, 0.734, 0.75, and 0.765) were synthesized in the holmium series. An increase in the holmium content leads to an increase in the proton transfer coefficients; at the same time, a more complex nature of the dependence of the conductivity under dry and wet atmospheres is observed. For the fluorite-like solid solution (HoxTi1-x)4O8-2x (0.701 ≤ x ≤ 0.765), the proton transfer coefficients were found to be ∼0.9 in the range of 200-450 °C. As the temperature continues to rise, the proton conductivity decreases quite sharply and the transfer coefficient becomes as low as 0.3 at 700 °C. The increase in proton conductivity in the Yb-Er-Ho series is associated with an increase in the hydrophilic properties of rare earth cations. In the (HoxTi1-x)4O8-2x (x = 0.667 ≤ x ≤ 0.765) series, the conductivity in wet air was ∼1 × 10-6 S cm-1 at 450 °C for most compositions. The conductivity of ceramics with x = 0.701 and 0.75 is about 2 times higher, which may be due to the optimal size of pyrochlore nanodomains in the fluorite matrix for x = 0.701 and the formation of pure fluorite for x = 0.75, respectively.

Evaluation of fracture resistance behavior of Alloy 690 material upto 1000°C

Alloy 690 is a nickel-based alloy with a nominal composition of 30% Cr and 10% Fe (wt%). It is denoted as Ni-30Cr-10Fe. This alloy is currently being investigated by various researchers for its use in nuclear industry as a possible replacement of alloy 600 steam generator tubes because of its excellent resistance to inter-granular stress corrosion cracking in water reactor environment. Alloy 690 is mainly used in vitrification melters for immobilization of high level waste in nuclear recycle plant. The temperature of water reactor environment is considerably lower compared to that of vitrification application, where temperature can reach an order of 1000 to 1100˚C. The mechanical and fracture properties of alloy 690 at the elevated temperature is important from the point of view of design and safety analysis of vitrification melter components and it is not available in literature. For this purpose, single edged notched tensile specimens have been fabricated from alloy 690 plates of 10 mm thickness. The fracture specimens have been tested in the temperature range of 25˚C to 1000˚C, which is the operating range of vitrification melters. The crack initiation toughness was obtained using modified blunting line equation in order to account for material strain hardening effect at a given temperature. From the fracture test results, it was observed that the initiation toughness is lowest at 700˚C. To understand this behavior, scanning electron microscopy was carried out on the fracture surface of the tested specimens. The fracture surface of the specimen tested at 700˚C showed presence of brittle phases in the microstructure, which are responsible for lower value of fracture toughness at this condition. The results of this work shall be useful for design and analysis of vitrification melter components.

Innovative pathways to high-performance glass ceramics: Harnessing nature's treasures with chromium and zirconium nucleation catalysts

This study explores the novel production of high-performance glass ceramics (GCs) by harnessing readily available and cost-effective raw materials schist, dolomite, and magnesite for the first time. The nominal composition for the base glass, G(30), was designed based on the eutectic composition of the diopside-anorthite ratio with 30% enstatite content within the quaternary CaO-MgO-Al2O3-SiO2 system. To enhance nucleation, chromium (Cr2O3) and zirconium (ZrO2) oxide were separately introduced into the base glass batch in two ratios (0.5% and 1%), producing four additional batches-Cr(0.5), Cr(1), Zr(0.5), and Zr(1), orderly. All these batches were melted at temperatures ranging from 1450 °C to 1550 °C then cast into glass discs and rods. Double-stage heat treatment schedule, 750 °C /2 h followed by 950 °C and 1050 °C/1 h separately, was employed to induce the transformation of prepared glass into GCs. X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques were applied to orderly investigate the developed crystalline phases and the prevailing micro-structures of the prepared GCs. The glass ceramic with the highest Cr2O3 ratio, Cy(1) which was treated at 1050 °C/1 h, displayed the most adequate microstructure and minimal pore formation in comparison with other GCs. As well, the favorable physicochemical properties, Vickers microhardness (6.43 GPa), low thermal expansion coefficient (0.171 ×10 −6 °C−1) at 29–100 °C, and the exceptional resistance for acid and alkali corrosion (95%), nominate such GS sample, Cy(1), for several architectural applications.

Fabrication and characterization of novel ZnO-loaded mesoporous bioactive glass nanospheres with enhanced physiochemical properties and biocompatibility for bone tissue engineering

Novel ZnO-modified mesoporous bioactive glass nanospheres (MBNs) were developed by a modified sol-gel method and their physiochemical behavior and cytocompatibility were systematically evaluated. Compared to previous researches, an offered synthesis method resulted in much less compositional deviation between the nominal and real compositions, while retaining spherical shape and dispersion of the nanoparticles. The MBNs exhibited a higher specific surface area (280–343 m2/g) and a larger pore volume than various ZnO-loaded bioactive glasses prepared before. In contrast to most mesoporous bioceramics doped with ZnO, the current nanoparticles revealed an excellent bioactivity within 14 days immersion in simulated body fluid (SBF). Furthermore, an optimum ZnO content for enhanced viability of bone marrow mesenchymal stem cells cultured with ionic extracts of the nanoparticles is 0.5%. Thanks to a high particle dispersion, good textural properties, bioactivity, and high cytocompatibility, the prepared nanoparticles can be recommended as promising filler materials dental/bone tissue engineering.

Formulation development of metakaolin geopolymer with good workability for strength improvement and shrinkage reduction

This study aims to optimize formulation and preparation of metakaolin based geopolymer for good workability, high compressive strength, and reduced drying shrinkage by considering alkaline activator composition, liquid to solid mass ratio, curing condition, and admixtures. The optimized geopolymer paste was further modified by granulated blast furnace steel slag (GBFS) and ordinary Portland cement (OPC) as calcium sources and carbon fibers as reinforcing additive for further strength improvement and shrinkage alleviation, in which the improvement mechanisms were manifested through mechanical strengths and microstructure observations. An optimized combination of modifiers and curing condition was obtained by Orthogonal Array Testing method. Experimental results indicate that sodium silicate is essential in the synthesis of alkali activator with nominal composition of Na2O·1.3SiO2·10.8H2O for strength development and cracking prevention. Good workability and high compressive strength of paste specimens could be attained by liquid to solid mass ratio of 1.21 between alkaline activator and metakaolin with ambient curing. The modified geopolymer pastes presented further improved compressive strength and reduced drying shrinkage. The microstructure images showed that the formation of cement hydration products, ettringite crystals, and more condensed matrix structure by using OPC as additive in geopolymer. The optimized geopolymer paste was made with 2% carbon fiber, 33% Portland cement and 10% GBFS and cured at ambient temperature achieved ultimate compressive strength of 73 MPa with reduced drying shrinkage. This ultimate compressive strength was 55% and 65% higher than non-modified geopolymer and ordinary Portland cement pastes, respectively, and was higher than 80% values in related studies.

Powder production, FAST processing and properties of a Nb-silicide based alloy for high temperature aerospace applications

A Nb-silicide based alloy with nominal composition Nb–18Ti–22Si–6Mo-1.5Cr–2Sn-1Hf (at. %), designed for high temperature aerospace applications, was produced via a powder metallurgy (PM) route. The raw elements were arc melted, crushed, and milled to powder, then consolidated using Field Assisted Sintering Technology (FAST). The compressive creep of the alloy was evaluated using electro-thermal mechanical testing (ETMT). The study demonstrated the production of larger 60 mm diameter samples, with potential for further scale up. The microstructure of the FAST alloy, which is comprised of bcc Nbss and tetragonal αNb5Si3 was more homogenous compared with the cast alloy, with some interstitial contamination that occurred during powder production. The FAST alloy had lower density than state of the art Ni-based superalloys and refractory metal complex concentrated alloys (RCCAs) and high entropy alloys (RHEAs), and its yield strength and specific yield strength was higher than those of the latter metallic Ultra high temperature materials (UHTMs) and comparable to those of Nb-silicide based alloys with B addition. The stress exponent n in compressive creep was in the range 1.7–2.6, similar to that of binary Nb–10Si and Nb–16Si alloys and its creep rate at 1200 °C and 100 MPa was similar to that of the MASC alloy (Nb–25Ti–16Si-8Hf-2Al–2Cr (at.%)). Like the latter, the creep of the FAST alloy did not meet the creep goal.