Search Results (32)

The slurry aluminizing process is widely employed to enhance the oxidation and corrosion resistance of nickel-based superalloys used in high-temperature environments such as gas turbines and aerospace engines. This study investigates the effects of the concentration of Al vapors in the reactor chamber and the initial slurry layer thickness on the microstructure, chemical composition, and phase composition of aluminide coatings. Coatings were manufactured on Ni-based superalloy substrates using CrAl powders as an aluminum source and chloride- and fluoride-based activator salts. The effect of the initial thickness of the slurry layer was studied by varying the amount of deposited slurry in terms of mg_slurry/cm²_sample (with constant mg_slurry/cm³_chamber). The microstructure and phase composition of the produced aluminide coatings were evaluated by SEM, EDS, and XRD analysis. Slurry thickness can affect concentration gradients during diffusion, and the best results were obtained with an initial slurry amount of 100 mg_slurry/cm²_sample. The effect of the Al vapor phase in the reaction chamber was then investigated by varying the mg_slurry/cm³_chamber ratio while keeping the slurry layer thickness constant at 100 mg_slurry/cm²_sample. This parameter influences the amount of Al at the substrate surface before the onset of solid-state diffusion, and the best results were obtained for a 6.50 mg_slurry/cm³_chamber ratio with the formation of 80 µm coatings (excluding the interdiffusion zone) with a β-NiAl phase throughout the thickness. To validate process flexibility, the same parameters were successfully applied to produce platinum-modified aluminides with a bi-phasic ζ-PtAl2 and β-(Ni,Pt)Al microstructure. Full article

This study investigates the thermally induced phase transformation of Ni-exchanged LTA zeolite as a dual-purpose method for nickel immobilization and the synthesis of stable ceramic pigments. The process describes a cost-effective and sustainable alternative to conventional pigment production, aligning with circular economy principles. Upon thermal treatment at temperatures ranging between 900 °C and 1300 °C, Ni-exchanged LTA zeolite undergoes a transformation to NiAl₂O₄ spinel, confirmed by XRPD, FTIR, and thermal analysis. Initially, NiO is formed, but as the temperature increases, it dissolves and transforms into NiAl₂O₄. Colorimetric studies revealed intensified blue pigmentation with increasing temperature, correlating with crystallite growth and structural evolution. SEM analysis showed morphological changes from cubic particles to sintered agglomerates, enhancing pigment stability and hardness. The Ni-LTA sample calcined at 1300 °C showed the highest hue angle, which was consistent with the formation of over 99 wt.% of the nickel aluminate crystalline phase at this temperature. The results demonstrate that Ni-LTA zeolite can be effectively transformed into durable greenish-blue pigments suitable for application in porcelain. This transformation is especially evident at 1300 °C, where a spinel phase (NiAlSi₂O₄) forms, with colorimetric values: L = 58.94, a* = –16.08, and b* = –15.90. Full article

Aluminide coatings on nickel-based superalloys were synthesized via a high-temperature “clean” low-activity vapor-phase process. This process is environmentally friendly and meets manufacturers’ environmental protection requirements. Hence, it fulfils the Industry 4.0 requirements, where the reduction of environmental impact in the industrial sector is a key issue. Surface morphology, cross-section microstructure, and phase composition of the coatings were studied and compared by using an optical microscope and a scanning electron microscope (SEM) equipped with an energy dispersive spectroscope (EDS) and X-ray diffraction (XRD). Bare and coated superalloys’ lifetime was evaluated and compared via air exposure at 1100 °C. High-temperature low-activity aluminizing of the IN713, IN625, and CMSX4 superalloys enabled the obtainment of the desirable β-NiAl phase. The highest nickel content in the chemical composition of the IN713 superalloy among the investigated superalloys resulted in the highest aluminide coatings’ thickness. Moreover, the higher refractory elements concentration in the IN625 and CMSX4 superalloys than that in the IN713 superalloy may contribute to a thinner aluminide coatings’ thickness. Refractory elements diffused to the surface of the superalloy and formed carbides or intermetallic phases, which impeded outward nickel diffusion from the substrate to the surface and thereby inhibited coating growth. The obtained coatings fulfilled the requirements of ASTM B 875. Despite the fact that the coating formed on IN713 was thicker than that formed on IN625, the lifetime of both coated superalloys was comparable. Oxidation resistance of the aluminide coatings formed on the IN713 and IN625 superalloys makes them the favored choice for gas turbine applications. Full article

This critical review evaluates chemical looping combustion using a syngas derived from gasified biomass (BMD Syngas). It is anticipated that establishing such a process will open new opportunities for CO₂ sequestration and the use of highly concentrated CO₂ in the manufacturing and synthesis of fuels from entirely renewable feedstocks. This review focuses on the process conducted through using two interconnected fluidized bed units: a nickel oxide reduction unit (an endothermic Fuel Reactor) and a nickel oxidation unit (an exothermic Air Reactor). In this respect, a high-performance OC (HPOC) with Ni on a γ-Al₂O₃ fluidizable support (20wt% Ni, 1wt% Co, 5wt% La/γ-Al₂O₃) was developed at the CREC (Chemical Reactor Engineering Centre) of the University of Western Ontario, Canada. The HPOC was studied in a CREC Riser Simulator. The benefits of this mini-fluidized unit are that it can be operated at 2–40 s reaction times, 550–650 °C temperatures, 1.3–2.5 H₂/CO ratios, and 0.5–1 biomass/syngas stoichiometric ratios, mimicking the conditions of industrial-scale CLC units. When using a syngas derived from biomass and the HPOC under these operating conditions, 90% CO, 92% H₂, and 88% CH4 conversions, together with a 91% CO₂ yield, were obtained. These results allowed the prediction of a 1.84–3.0 wt% ($g_{O_2}/g_{{OC}_{}}$) oxygen transport capacity, with a 40–70% nickel oxide conversion. The experimental data acquired with the CREC Riser Simulator permitted the development of realistic kinetic models. The resulting kinetics were used in combination with Computational Particle Fluid Dynamics (CPFD) to demonstrate the operability of a large-scale industrial syngas CLC process in a downer fuel unit. In addition, these CPFD simulations were employed to corroborate that high CO₂ yields are achievable in 12–15 m length downer fuel units. Full article

Rising greenhouse gas concentrations are causing climatic change that threatens ecosystem sustainability. This study investigated the impact of silica incorporation into alumina-supported nickel catalysts for the partial oxidation of methane (POM), a crucial process for syngas production. The investigation also focuses on the impact of using different calcination temperatures. The catalysts were synthesized using the impregnation method and structurally characterized with BET, TPR, FTIR, UV, XRD, TGA, Raman, and TEM analysis techniques. These characterization techniques revealed that increasing the silica content reduced the surface area and weakened the interaction between nickel and the support. The calcination temperature significantly influenced catalyst properties, affecting pore structure, nickel reducibility, and the formation of nickel aluminates and silicates. Activity tests of synthesized catalysts were performed in a packed-bed reactor at 600 °C with a 24 mL/min gas flow rate. The catalyst composition of 5Ni/10Si + 90Al demonstrated the highest activity, achieving optimal performance at lower calcination temperatures. This catalyst generates a greater concentration of active sites, primarily due to nickel oxide (NiO), which creates these sites through both mild and strong interactions. The degree of graphitization is notably lowest for the 5Ni/10Si + 90Al composition. This catalyst achieved an impressive hydrogen yield of approximately 54%, with an H₂/CO ratio of 3.4 over a streaming period of up to 240 min. When the silica loading exceeds 10 wt.%, the interaction between the metal and the support weakens, resulting in a significant decrease in surface area and, subsequently, lower catalytic activity. The 5Ni/10Si + 90Al catalyst, which was prepared with calcination temperatures above 500 °C, has very few active sites during the Partial Oxidation of Methane (POM) reaction at a reaction temperature of 600 °C. This catalyst also exhibits a high degree of crystallinity, which leads to reduced exposure of the active sites. As a result, incorporating higher weight percentages of silica into the 5Ni/xSi + (100 − x) Al catalysts results in decreased activity. When the silica loading exceeds 10 wt.%, the interaction between the metal and the support weakens, resulting in a significant decrease in surface area and, subsequently, lower catalytic activity. The 5Ni/10Si + 90Al catalyst, which was prepared with calcination temperatures above 500 °C, has very few active sites during the POM reaction at a reaction temperature of 600 °C. This catalyst also exhibits a high degree of crystallinity, which leads to reduced exposure of the active sites. As a result, incorporating higher wt.% of silica into the 5Ni/xSi + (100 − x) Al catalysts results in decreased activity. These findings highlight the complex interplay between silica content, calcination temperature, and catalyst properties, significantly influencing catalytic performance in POM. Full article

Aircraft engine turbine blades are covered with protective coatings. These coatings should have the best thermophysical convergence with the blade’s parent material. The aim is to create heat-resistant covering for aircraft engine turbine blades made of nickel superalloy. The results of tests on coatings are presented; the inner layer is an adhesive layer of the MeCrAlY type, applied to the blade by means of supersonic thermal spraying, and the outer layer is diffusion-aluminized in the first case using the Vapor Phase Aluminizing method, and in the second using the suspension method. The inner layer of the coating protects the blade material against high-temperature corrosion, and the outer layer against high-temperature fuel combustion product stream. The protective coatings applied to aircraft engine turbine blades were subjected to an engine test in test bench conditions and then to material tests. A protective coating with an internal layer of MeCrAlY type applied to the blade by supersonic spraying and an external layer aluminized by the Vapor Phase Aluminizing method protects the nickel superalloy against high-temperature diffusion changes, protects it against oxidation and provides it thermal insulation. Full article

The wastewater generated by the pharmaceutical industry poses a risk to the environment due to undesirable characteristics such as low biodegradability, high levels of contaminants, and the presence of suspended solids, in addition to the high load of organic matter due to the presence of drugs and other emerging products in the effluent. This study aims to reduce the impact of wastewater pollution by removing amoxicillin (AMO) antibiotics as an organic pollutant. In this concept, two synthesized catalysts, NiAl₂O₄ and ZnO, are sensitive oxides to light energy. The prepared materials were then characterized using X-ray diffraction, UV–vis solid reflectance diffuse, Raman spectroscopy, scanning electron microscopy, BET, and ATR-FTIR spectroscopy. The effects of principal operating parameters under sunlight, namely, the percentage of the mixture of NiAl₂O₄ and ZnO, the pH of the medium, and the initial concentration of the antibiotic were studied experimentally to determine the optimal conditions for achieving a high degradation rate. The results showed that photodegradation is higher at a pH of 6, with a weight percentage of the mixture of 50% for both catalysts in 1 g/L of the total catalyst dose. Then, the effect of the initial concentration of AMO on the photodegradation reaction showed an important influence on the photodegradation process; as the degradation rate decreases, the initial AMO concentration increases. A high degradation rate of 92% was obtained for an initial AMO concentration of 10 mg/L and a pH of 6. The kinetic study of degradation established that the first-order model and the Langmuir–Hinshelwood (LH) mechanism fit the experimental data perfectly. The study showed the success of using heterosystem photocatalysts and sustainable energy for effective pharmaceutical removal, which can be extended to treat wastewater with other organic emerging pollutants. On the other hand, modeling was introduced using Gaussian process regression (GPR) to predict the degradation rate of AMO under sunlight in the presence of heterogeneous ZnO and NiAl₂O₄ systems. The model evaluation criteria of GPR in terms of statistical coefficients and errors show very interesting results and the performance of the model used. Where statistical coefficients were close to one (R = 0.9981), statistical errors were very small (RMSE = 0.1943 and MAE = 0.0518). The results suggest that the model has a strong predictive power and can be used to optimize the process of AMO removal from wastewater. Full article

Slags from the Silesia–Cracow Upland (Poland), including ten historical slags (deposited in waste dumps) and four contemporary slags (from current production), were examined to compare their chemical and mineralogical properties as well as to assess their potential for the recovery of selected metals and critical raw materials. The historical slags associated with the smelting of polymetallic ores originating from Mississippi Valley-type (MVT) deposits consisted primarily of gypsum. The contemporary slags, obtained from industrial waste rich in zinc and lead, were predominantly spinels (magnesium-aluminate and ferric) that exhibited higher iron content (up to 46.6 wt% of Fe₂O₃) compared to the historical slags (up to 26.1 wt% of Fe₂O₃). The zinc content was similar for both the slag types (3.5 wt% Zn). The average titanium and arsenic contents in the old and contemporary slags were at the same level as well, with 0.21 wt% (Ti) and 0.13 wt% (As), respectively. The contemporary slags contained higher levels of critical raw materials, such as cobalt, nickel, copper, and manganese, compared to the historical slags. Rare earth elements (REEs) were also more abundant in the contemporary slags, with an average content of 212 ppm, while the historical slags averaged 124 ppm. These findings underscore the potential for recovering valuable metals and critical raw materials from such slags, presenting opportunities for resource optimisation and environmental management. Full article

Thermal barrier coatings (TBCs) are widely used to improve the oxidation resistance and high-temperature performance of nickel-based superalloys operating in aggressive environments. Among the TBCs, aluminide coatings (ACs) are commonly utilized to protect the structural parts of jet engines against high-temperature oxidation and corrosion. They can be deposited by different techniques, including pack cementation (PC), slurry aluminizing or chemical vapor deposition (CVD). Although the mentioned deposition techniques have been known for years, the constant developments in materials sciences and processing stimulates progress in terms of ACs. Therefore, this review paper aims to summarize recent advances in the AC field that have been reported between 2019 and 2023. The review focuses on recent advances involving improved corrosion resistance in salty environments as well as against high temperatures ranging between 1000 °C and 1200 °C under both continuous isothermal high-temperature exposure for up to 1000 h and cyclic oxidation resulting from AC application. Additionally, the beneficial effects of enhanced mechanical properties, including hardness, fatigue performance and wear, are discussed. Full article

Platinum plays a crucial role in the superior high-temperature oxidation resistance of Pt-modified nickel aluminide (PtAl) coatings. However, PtAl coatings usually serve in thermo-mechanical coupling environments. To investigate whether Pt contributes to the high-temperature mechanical properties of PtAl coating, stress rupture tests under 1100 °C/100 MPa were performed on PtAl coatings with varying Pt contents. The different coatings were obtained by changing the thickness of the electroplated Pt layer, followed by a diffusion heat treatment and the aluminizing process in the present work. The results of the stress rupture tests indicated that an increasing Pt content resulted in a significant decrease in the stress rupture life of PtAl-coated superalloys under 1100 °C/100 MPa. Theoretical calculations and microstructural analysis suggested that an increased coating thickness due to the Pt content is not the main reason for this decline. It was found that the cracks generated close to the substrate in high-Pt-coated superalloys accelerated the fracture failure. Full article

A series including single and mixed Ni-Co aluminates was obtained using the precursor method, with malic acid as a ligand. The malate precursors (polynuclear coordination compounds) were isolated and characterized by Fourier Transform Infrared (FTIR), Ultraviolet/Visible/Near Infrared (UV–Vis–NIR) spectroscopy, and thermal analysis. The UV–Vis–NIR spectra of the synthesized complex compounds highlighted the presence of Co²⁺ and Ni²⁺ in an octahedral environment. The thermal decomposition of these precursors led to Co_1−xNi_xAl₂O₄ (x = 0, 0.1, 0.25, 0.5, 0.75, 0.9, and 1) spinels. The effect of Ni²⁺ substitution on the structure, morphology, and optical properties of the obtained oxides was studied with the help of different characterization tools. XRD, FTIR, and Raman spectra evidenced the formation of the spinel phase. The size of the crystallites and the agglomeration degree of the particles decrease when the nickel content increases. The band gap (BG) value is not significantly influenced by the Ni substitution. The fluorescence spectra recorded for all samples show a similar pattern, but different intensities of the emission bands. Full article

In this study, we examined the effects of an aluminization process on the microstructure and texture of Haynes 282 nickel samples fabricated using the direct metal laser sintering technique. The aluminization process involved the use of chemical vapor deposition with AlCl₃ vapors in a hydrogen atmosphere at a temperature of 1040 °C for 8 h. Following the 3D printing and aluminization steps, we analyzed the microstructure of the Haynes 282 nickel alloy samples using light microscopy and scanning electron microscopy. Additionally, we investigated the texture using X-ray diffractometry. A texture analysis revealed that after the process of direct laser sintering of metals, the texture of the Haynes 282 nickel alloy samples developed a texture typical of cast materials. Then, in the aluminization process, the texture was transformed—from foundry-type components to a texture characteristic of recrystallization. Full article

Catalytic gas-phase hydrogenation of CO₂ into CH₄ was tested under three different nickel/aluminate catalysts obtained from precursors of hexaaluminate composition (MAl₁₆O₁₉, M = Mg, Ca, Ba). These catalysts were prepared using a carbon template method, where carbon is self-generated from a sol-gel that contains an excess of citric acid and the Al and M salts (Ba²⁺, Ca²⁺, Mg²⁺) by two-step calcination in an inert/oxidizing atmosphere. This procedure yielded Ni particles decorating the surface of a porous high surface area matrix, which presents a typical XRD pattern of aluminate structure. Ni particles are obtained with a homogeneous distribution over the surface and an average diameter of ca 25–30 nm. Obtained materials exhibit a high conversion of CO₂ below 500 °C, yielding CH₄ as a final product with selectivity >95%. The observed trend with the alkaline earth cation follows the order NiBaAlO-PRx > NiCaAlO-PRx > NiMgAlO-PRx. We propose that the high performance of the NiBaAlO sample is derived from both an appropriate distribution of Ni particle size and the presence of BaCO₃, acting as a CO₂ buffer in the process. Full article

In this study, we investigate the effect of a hierarchically ordered macroporous structure of alumina support on the steam reforming of 1-methyl naphthalene with mesoporous alumina-supported nickel and potassium (xK/Ni–MeAl), and macroporous alumina-supported nickel and potassium (xK/Ni–MaAl) catalysts. Hierarchically ordered macroporosity in Al₂O₃ supports plays an important role in maintaining the high Ni dispersion through multiple interactions in Ni–K over AlO₄ tetrahedra in alumina. This, in turn, improves the catalytic performance of steam reforming, including high gas yields, turnover frequency for hydrogen production, and 1-methyl naphthalene conversion. At high K content, the Ni active sites over xK/Ni–MeAl catalysts significantly decrease, resulting in almost zero steam reforming rate in the reaction test. Conversely, the potassium–alumina interaction in xK/Ni–MaAl catalysts not only diminishes the formation of the inactive nickel aluminate phase but also maintains the highly dispersed Ni active sites, resulting in a high steam reforming rate. Full article

To obtain highly homogeneous cobalt–nickel aluminate spinels with small crystallite sizes, CoNiAl alloy thin films were primarily deposited using Laser-induced Thermionic Vacuum Arc (LTVA) as a versatile method for performing processing of multiple materials, such as alloy/composite thin films, at a nanometric scale. Following thermal annealing in air, the CoNiAl metallic thin films were transformed into ceramic oxidic (Co,Ni)Al₂O₄ with controlled composition and crystallinity suitable for thermal stability and chemical resistance devices. Structural analysis revealed the formation of (Co,Ni)Al₂O₄ from the amorphous CoNiAl alloys. The mean crystallite size of the spinels was around 15 nm. Thermal annealing induces a densification process, increasing the film thickness together with the migration process of the aluminum toward the surface of the samples. The sheet resistance changed drastically from 200–240 Ω/sq to more than 10⁶ Ω/sq, revealing a step-by-step conversion of the metallic character of the thin film to a dielectric oxidic structure. These cermet materials can be used as inert anodes for the solid oxide fuel cells (SOFCs), which require not only high stability with respect to oxidizing gases such as oxygen, but also good electrical conductivity. These combination metal–ceramics are known as bi-layer anodes. By controlling the crystallite size and the interplay between the oxide/metal composite, a balance between stability and electrical conductivity can be achieved. Full article