Search

Refractory materials are used worldwide in process equipment. However, gaseous and liquid process products penetrate the surface layer and deep into the volume of refractories, destroying rather expensive constructions that are complicated to repair. To address this challenge, there is a need to develop protective coatings for refractory materials that can limit the penetration of working media and extend their operational lifespan. In this work, the application of gas-dynamic cold spraying (CGDS) to produce a coating on the refractory materials using fine titanium dioxide (TiO2) particles is explored. These particles are accelerated within a nitrogen flow, passing through a Laval nozzle, and then sprayed onto a fireclay surface. The mechanisms of particle deposition and layer formation on porous surfaces through experiments and numerical simulations were investigated. The geometry of a typical refractory pore was determined, which was then incorporated into computational fluid dynamics (CFD) simulations to model the cold spraying process of porous substrates. As a result, the influence of the particle size on its velocity and angle of penetration into pores was established. Experimental findings demonstrate the effective closure of pores and the formation of a particle layer on the refractory surface. Furthermore, the nanoindentation tests for the refractory samples showcase capabilities for checking coating thickness for porous materials. [ABSTRACT FROM AUTHOR]

Molten salt has a wide electrochemical window and excellent ion conductivity, which makes it possible to electrodeposit refractory metals in molten salt to obtain coatings. Meanwhile, the electroplating rate will be faster as a result of the high temperature in the molten salt. However, due to the complex chemical/electrochemical reaction of refractory metal ions with multiple valence states in molten salt, the precise control of electroplating is difficult. In this paper, the electrode reaction process, grain nucleation and growth model, and regulation mechanism of coatings are discussed. Subsequently, the research progress of various refractory metal coatings is reviewed, and the effects of technical parameters on the morphology and properties of the coatings are discussed. The challenges faced by refractory metal molten salt electroplating are summarized and potential future research directions are also proposed. [ABSTRACT FROM AUTHOR]

Milti-principal cation oxide ceramics with excellent mechanical properties for potential applications in coating materials. A Multi-principal cation mullite (MPCM) ceramic is synthesized with MgO, TiO 2 , Cr 2 O 3 , ZrCl 2 O·8H 2 O and Al 2 O 3 , SiO 2 via solid state reaction at 1600 °C. It is determined that 96.9 % of the sample composition is mullite. MPCM ceramic exhibits higher compressive strength (981 ± 19 MPa) and fracture toughness (3.37 ± 0.05 MPa∙m1/2), the compressive strength has raised by 453 MPa, and the added value of solution strengthening (452 MPa) is gained by using solid-solution strengthening theory. The improvement of compressive strength is mainly due to the solution strengthening effect of the four oxides(Mg, Ti, Zr, Cr), and the improvement of fracture toughness is caused by the grain hindrance during crack propagation. Moreover, its application at the high-temperature resistant coating is verified through experimentation. The interfacial binding force, as an important mechanical property index for ceramics, is researched. In this study, pure mullite powder and MPCM powder are coated onto the refractory TaWNbV alloy matrix by slurry coating method, and the interfacial toughness of the two coatings mingled with the matrix is calculated to be 72.9 and 62.6 J·m−2, respectively. The "shrinking cylinder" model is introduced to interpret the oxidative weight gain mechanism of the two coatings. [ABSTRACT FROM AUTHOR]

This work uses the direct current magnetron sputtering (DCMS) of equi-atomic (AlTiZrHfTa) and Si targets in dynamic sweep mode to deposit nano-layered (AlTiZrHfTa)Nx/SiNx refractory high-entropy coatings (RHECs). Transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) are used to investigate the effect of Si addition on the oxidation behavior of the nano-layered coatings. The Si-free nitride coating exhibits FCC structure and columnar morphology, while the Si-doped nitride coatings present a FCC (AlTiZrHfTa)N/amorphous-SiNx nano-layered architecture. The hardness decreases from 24.3 ± 1.0 GPa to 17.5 ± 1.0 GPa because of the nano-layered architecture, whilst Young's modulus reduces from 188.0 ± 1.0 GPa to roughly 162.4 ± 1.0 GPa. By increasing the thickness of the SiNx nano-layer, kp values decrease significantly from 3.36 × 10−8 g2 cm−4 h−1 to 6.06 × 10−9 g2 cm−4 h−1. The activation energy increases from 90.8 kJ·mol−1 for (AlTiZrHfTa)Nx nitride coating to 126.52 kJ·mol−1 for the (AlTiZrHfTa)Nx/SiNx nano-layered coating. The formation of a FCC (AlTiZrHfTa)-Nx/a-SiNx nano-layered architecture results in the improvement of the resistance to oxidation at high temperature. [ABSTRACT FROM AUTHOR]

An oxygen‐resistant refractory high‐entropy alloy is synthesized in microlattice or bulk form by 3D ink‐extrusion printing, interdiffusion, and silicide coating. Additive manufacturing of equiatomic HfNbTaTiZr is implemented by extruding inks containing hydride powders, de‐binding under H2, and sintering under vacuum. The sequential decomposition of hydride powders (HfH2+NbH+TaH0.5+TiH2+ZrH2) is followed by in situ X‐ray diffraction. Upon sintering at 1400 °C for 18 h, a nearly fully densified, equiatomic HfNbTaTiZr alloy is synthesized; on slow cooling, both α‐HCP and β‐BCC phases are formed, but on quenching, a metastable single β‐BCC phase is obtained. Printed and sintered HfNbTaTiZr alloys with ≈1 wt.% O shows excellent mechanical properties at high temperatures. Oxidation resistance is achieved by silicide coating via pack cementation. A small‐size lattice‐core sandwich is fabricated and tested with high‐temperature flames to demonstrate the versatility of this sequential approach (printing, sintering, and siliconizing) for high‐temperature, high‐stress applications of refractory high‐entropy alloys. [ABSTRACT FROM AUTHOR]

To improve the oxidation resistance of alumina–carbon refractories, SiO 2 –B 4 C-glass composite coating was prepared by slurry brushing method on the surface of refractories. Effect of SiO 2 content on the oxidation resistance of the coating was studied. Oxidation resistance mechanism and failure reason of the SiO 2 –B 4 C-glass coating were discussed. Results showed that introducing SiO 2 could increase viscosity activation energy and elevate the glass layer's viscosity at high temperature. With the increase of SiO 2 content, the glass viscosity at high temperature gradually increased. When SiO 2 content was too low, the glass exhibited smaller viscosity and larger fluidity, so the glass layer was easy to be washed away. When SiO 2 content was too high, the glass phase with high viscosity and low fluidity could not uniformly cover on the surface of alumina–carbon refractories. The composite coating with SiO 2 content of 55 wt% exhibited excellent oxidation resistance, which could effectively protect alumina–carbon refractories at 800 °C for 100 h with weight loss of only −1.721%. Excellent oxidation resistance of the coating mainly depended on the glass layer with good self-healing ability. With the extension of oxidation time, the coating thickness decreased, leading to the relatively poor self-healing ability and reduced weight gain rate of the coating. [ABSTRACT FROM AUTHOR]

Nanomaterials are widely used in modern technologies due to their unique properties. Developing methods for their production is one of the most important scientific problems. In this review, the advantages of electrochemical methods for synthesis in molten salts of nanostructured coatings and nanomaterials for different applications were discussed. It was determined that the nanostructured Mo2C coatings on a molybdenum substrate obtained by galvanostatic electrolysis have a superior catalytic activity for the water-gas shift reaction. The corrosion-resistant and wear-resistant coatings of refractory metal carbides on steels were synthesized by the method of currentless transfer. This method also was used for the production of composite carbon fiber/refractory metal carbide materials, which are efficient electrocatalysts for the decomposition of hydrogen peroxide. The possibility to synthesize GdB6 nanorods and Si and TaO nanoneedles by potentiostatic electrolysis was shown. [ABSTRACT FROM AUTHOR]

Switching the properties of the Ag contact groups of an electromagnetic relay with the electrodeposited Ni-W and Co-W alloy coatings was studied. It is shown that these coatings are able to stabilize the spread of contact resistance within the entire test interval and to increase the service life of Ag contact groups from 2.3 × 106 to 4.5 × 106 commutation cycles. According to our research, the service life of coated contact groups is mainly determined by a change in the surface morphology caused by the electrical erosive transfer of the contact materials and to a lesser extent by the formation of poorly conductive adsorbed hydrocarbon films. [ABSTRACT FROM AUTHOR]

In the ANSYS Fluent program, a computer simulation was performed for the production of ingots from aluminum alloy 5052 at a semi-continuous casting plant (SCCP). This method analyzed the nature of the melt temperature distribution in the metal path with two types of refractory coatings and estimated the heat loss during the melt passage from the mixer to the mold of the casting machine. The findings reveal that during the experimental verification of the casting of ingots, the results of the direct temperature measurements differed by no more than 2%–3% from the temperatures obtained by modeling, and the replacement of metal path cartridges made of refractory concrete with a density of 2090 kg/m3 for concrete with a density of 1300 kg/m3 reduced heat losses during the casting of ingots on the SCCP and reduced the temperature of the start of casting of alloy 5052 by 45°C, decreasing the hydrogen concentration in castings from 0.18–0.19 to 0.15 cm3/100 g. [ABSTRACT FROM AUTHOR]

The present paper concerns the examination of four types of alcohol-based refractory coatings with one and the same viscosity with graphite particle sizes of 60 µm, 80 µm, 100 µm and 120 µm and with the same viscosity. Different particle sizes are obtained by grinding and the coating is applied by immersion in the suspension of sand matrix samples. Results about microhardness and roughness of the coatings are obtained. They show that as the size of the graphite particles decreases, the microhardness increases and the roughness decreases. The dependency of the microhardness on the particle size has an almost linear character, and the roughness is an increasing exponential function. [ABSTRACT FROM AUTHOR]

TaC and HfC are recognized as potential ultra-high temperature ceramics for application in refractories and coating materials. However, the test of mechanical property under high temperature is difficult. In this paper, the mechanical properties of TaC and HfC at high temperature are systematically investigated by density functional theory. The results revealed that their elastic constants, elastic moduli and elastic anisotropy all display a monotonic decreasing trend with increasing temperature, and the anisotropy of TaC is stronger than that of HfC at a given temperature. TaC and HfC both have eight possible dislocations. As the applied shear stress increases, the activation energies and critical resolved shear stress (CRSS) of all dislocations are decreased. As the temperature increases, the CRSS is decreased. Moreover, the yield strength and hardness of TaC and HfC both decreased with the increase of temperature. The hardness decrease from 0 to 400 K is mainly due to the proportion change of the two major dislocations ( 1 / 2 1 1 ¯ 0 0° perfect dislocations and 1 / 6 1 2 ¯ 1 30° partial dislocations). Then the hardness sharply decreases at 400 K, which is attributed to the activation of 1 / 6 11 2 ¯ 90° partial dislocations. The hardness decrease from 500 K is attributed to the CRSS change of 1 / 6 11 2 ¯ 90° partial dislocations and 1 / 6 1 2 ¯ 1 30° partial dislocations. In addition, the influence of strain rate and dislocation density are revealed, which shows that their hardness are both increased with increasing strain rate, while decreased with increasing dislocation density. [ABSTRACT FROM AUTHOR]

Bilayer alumina/mullite and mullite/alumina coatings were sprayed on conventional silico-aluminous refractory bricks by atmospheric plasma spraying. The wear behaviour of these coatings were assessed under sliding contact conditions up to 1000 °C through a ball-on-disk test. Afterwards, a set of physical and mechanical properties were evaluated before and after the wear tests, with the aim of correlating these properties with the wear behaviour. The results of the wear tests indicate that when alumina is applied as the top coating, the wear mechanism operating on its surface at 25 and 1000 °C is ductile deformation, whereas brittle deformation occurs at 500 and 750 °C. When mullite was used as the top coating, brittle deformation was observed at all temperatures evaluated. However, both coatings possess higher wear resistances than the silico-aluminous brick used as substrate, and thus, these coatings potentially offer enhanced protection from the abrasive wearing of non-structural refractories normally used in furnaces for glass and cement production. [ABSTRACT FROM AUTHOR]

In order to improve the high-temperature oxidation resistance of refractory high-entropy alloys (RHEAs), we used micro-arc oxidation (MAO) technology to prepare ceramic coatings on AlTiCrVZr alloy, and the effects of voltage on the microstructure and high-temperature oxidation resistance of the coatings were studied. In this paper, the MAO voltage was adjusted to 360 V, 390 V, 420 V, and 450 V. The microstructure, elements distribution, chemical composition, and surface roughness of the coatings were studied by scanning electron microscopy (SEM), energy dispersive (EDS), X-ray photoelectron spectroscopy (XPS), and white-light interferometry. The matrix alloy and MAO-coated samples were oxidized at 800 °C for 5 h and 20 h to study their high-temperature oxidation resistance. The results showed that as the voltage increased, the MAO coating gradually became smooth and dense, the surface roughness decreased, and the coating thickness increased. The substrate elements and solute ions in the electrolyte participated in the coating formation reaction, and the coating composition was dominated by Al2O3, TiO2, Cr2O3, V2O5, ZrO2, and SiO2. Compared with the substrate alloy, the high-temperature oxidation resistance of the MAO-coated samples prepared at different voltages was improved after oxidation at 800 °C, and the coating prepared at 420 V showed the best high-temperature oxidation resistance after oxidation for 20 h. In short, MAO coatings can prevent the diffusion of O elements into the substrate and the volatilization of V2O5, which improves the high-temperature oxidation resistance of AlTiCrVZr RHEAs. [ABSTRACT FROM AUTHOR]

Opportunities are described for developing coatings for refractory alloys beyond the current state-of-the-art silicide coatings, which are inadequate for long-term application in combustion environments due to silica volatility. It is proposed that multicomponent rare earth oxides provide an ideal material system to tailor all necessary properties for environmental/thermal barrier coatings in a single layer, differing from current trends to adopt multi-layer systems that are prone to thermochemical-mechanical interface failure mechanisms. The article discusses opportunities, proof-of-concept, and challenges to accomplish these single-layer rare earth oxide coatings. Properties of interest include isotropic phase stability, processability, thermal expansion, thermal conductivity, ability to perform as a radiation barrier, stability in combustion environments, CMAS resistance, and ability to act as an oxygen diffusion barrier. Both experimental and computational approaches for property optimization are described. [ABSTRACT FROM AUTHOR]

In this study, TaMoCrTiAl refractory high-entropy alloy coating without defects was successfully prepared on the Ti6Al4V substrate by laser metal deposited. Microstructure and properties were investigated systematically by multiple characterization methods. The results of phase and morphology experiments indicate that the coating comprised a BCC phase and a partial Laves phase. The coating, with an average thickness of 990 μm, exhibits good metallurgical bonding with the substrate. Further observation reveals that the cladding region consists of irregular bulk crystals. The heat-affected zone has a fine grain size, whereas the substrate has coarse and uneven grains. The high-temperature oxidation test shows that the formation of an Al2O3 oxide layer enhances the coating's high-temperature oxidation resistance. According to the results of microhardness tests, the average microhardness in the coating is about 570.98 HV (1.87 times that of the substrate) due to the formation of the leave phase particles and the fine-grain strengthening. The presence of Titanium, chromium and molybdenum elements in the coating facilitates the formation of a passivation film, thereby enhancing its corrosion resistance. Furthermore, the coating exhibits the smallest grinding force (43.637 N) and the lowest roughness (0.506 μm) at an experimental temperature of 100 °C, which demonstrates that appropriately elevating the experimental temperature can decrease the grinding force and enhance the flatness of the grinding surface. • TaMoCrTiAl refractory high-entropy alloy coating was prepared on the Ti6Al4V substrate by laser metal deposited. • The essential reason for the microhardness difference between the substrate and cladding layer was discussed. • The microstructure, corrosion resistance, oxidation resistance, and grinding performance of the coating were investigated. [ABSTRACT FROM AUTHOR]

The present paper concerns casting properties (gas permeability and friability) of samples applied with refractory coatings with dimensions of the refractory filler - 60 µm, 80 µm, 100 µm and 120 µm respectively. The investigated coatings are designed to prevent the formation of sintering effect during the production of iron alloy castings (steel and cast iron). The base, on which those paints are applied represents standard test samples for determining the casting properties of moulding and core mixtures made of corning sand. The obtained results show that the increase of the size of the graphite particles leads to an increase in gas permeability and it almost does not affect friability. [ABSTRACT FROM AUTHOR]

Developing materials that do not ablate, which are thermally insulating and strong at temperatures above 1650 °C, is of prime importance for the thermal protection of aerospace vehicles, but remains a great challenge. Carbon aerogels (CAs) are attractive candidates for thermal protection due to their excellent thermostability and thermal insulation. However, their poor anti‐oxidative performance and difficulty in producing an anti‐oxidative refractory coating, as well as brittleness and low mechanical strength severely limit their practical use, especially in oxidizing environments. Here, an unusual carbon fiber‐reinforced carbon–ceramic composite with gradual changes in composition and pore size is reported. On the top is a carbon fiber‐reinforced SiCC modified by mullite‐Al2O3 and at the bottom is a carbon fiber‐reinforced analogous CA. The resulting material shows excellent ablation resistance, outstanding thermal insulation, extremely high thermostability, and strong load‐carrying capacity. Compared with conventional porous non‐ablative and thermal insulating materials with a working temperature of 1600 °C and a specific strength of 10 MPa g–1 cm–3, its respective values are increased to 1900 °C and 119 MPa g–1 cm–3. This work provides a new way to improve the ablation resistance property of nano‐porous carbon monoliths, and the carbon‐ceramic composite developed has great promise for ultra‐high temperature thermal protection in aerospace. [ABSTRACT FROM AUTHOR]

YPO4 qualifies as a strongly effective environmental barrier coating material against highly aggressive corrosive environments like molten uranium due to its remarkable phase stability, physical and chemical compatibility, high melting point, inertness to reactive metals, low thermal conductivity and closely matching thermal expansion coefficient. Non-availability of a suitable synthesis route and rare commercial availability of phase pure spray grade YPO4 powder restricted development of relevant atmospheric plasma spray (APS) coating. The study addresses the problem first by establishing an effective synthesis route for spray grade granulated YPO4, followed by the development of APS coating, its detailed characterization and testing compatibility of the coating with molten Uranium. Yttrium nitrate is reacted with ortho-phosphoric acid under appropriate PH control to obtain spray grade granules through powder compaction, sintering, crushing, and sieving. Chemical and phase purity are established through XRD, FTIR and Raman spectroscopy. Development of thick thermal spray coating of YPO4 on graphite and molybdenum substrates and a thorough characterization of the developed coatings in terms of XRD, Raman spectroscopy, FTIR, SEM, EDX, adhesion strength, thermal expansion coefficient, and interface microstructure have been reported. Physical and chemical compatibility between YPO4 and graphite and that between the coating and molten uranium have been explored. [ABSTRACT FROM AUTHOR]

This paper introduces a thorough approach for classifying refractory coatings used on chemically bonded sand according to their thickness, which is essential for monitoring mold and core coatings in foundries. The method combines feature extraction through vectorized principal component analysis (VPCA) with classification modeling using a machine learning algorithm. The study examines five different scenarios, which involve the utilization of raw axial, radial, and temperature data, as well as the use of scalar properties. Additionally, the study involves extracting features from the first two approaches and training on the complete dataset. An assessment of performance is carried out, showcasing the strong ability to classify accurately across all levels of coating thickness. In addition, Hotelling's T-squared statistics are used to identify changes in the process, offering valuable information about the structure and distinctiveness of the data classes. This study demonstrates the efficacy of feature extraction methods and machine learning algorithms in accurately categorizing coating thicknesses, providing practical solutions for applications in the foundry industry. This systematic methodology not only improves the comprehensibility and effectiveness of classification models but also offers vital understanding into process monitoring and identification of abnormalities within intricate datasets. [ABSTRACT FROM AUTHOR]

Absorbing materials have gained great applications for the capability of electromagnetic (EM) reflection reduction. So far, it is still very challenging to simultaneously achieve high-temperature resistance and broad working band in one design. This work reports a composite coating to realize this goal by using refractory Al 2 O 3 coating and high-temperature conductive FeCrAl by atmospheric plasma spraying (APS). The reflection reduction mechanism is the phase cancellation instead of absorption. By spraying the FeCrAl structure on the surface of Al 2 O 3 coating, it can behave as resonators to produce a phase difference. Here, with a thin thickness of 1.7 mm, the composite coating shows stable wideband EM reflection reduction from room temperature up to 700 °C, which originates from the excellent conductivity of FeCrAl and the steady dielectric property of Al 2 O 3. In addition, a protective layer is employed to isolate the contact between the structural layer and the outside high-temperature environment, which prevents the conductive structure from corrosion and greatly enhances the practicability and feasibility for daily maintaining. Sample characterizations show that these layers are prepared of low porosity and closely bonded to form the composite coating. The EDX mapping scan results and microstructure analysis demonstrate that the composite coating can exhibit excellent stability at high temperatures. Meanwhile, XRD results at different temperatures indicate the phase structure of Al 2 O 3 coating is not damaged. This study provides a route to achieve temperature insensitive EM reflection reduction over a wide frequency range and enlighten a promising future of this material system. [ABSTRACT FROM AUTHOR]

Refractory high entropy alloys have broad application prospects due to their excellent comprehensive properties in high temperature environments, and they have been widely implemented in many complex working conditions. According to the latest research reports, the preparation technology of bulk and coating refractory high entropy alloys are summarized, and the advantages and disadvantages of each preparation technology are analyzed. In addition, the properties of refractory high entropy alloys, such as mechanical properties, wear resistance, corrosion resistance, oxidation resistance, and radiation resistance are reviewed. The existing scientific problems of refractory high entropy alloys, at present, are put forward, which provide reference for the development and application of refractory high entropy alloys in the future, especially for plasma-facing materials in nuclear fusion reactors. [ABSTRACT FROM AUTHOR]

Chemically bonded sand systems are an important part of foundry technology and their interactions at the mold-steel interface are of great interest. With today's emphasis on near-net-shape steel castings and more stringent dimensional requirements, there is a need to characterize as-cast surface quality. Part I of this two-part paper focused on surface quality at uncoated as-cast steel/chemically bonded sand interfaces. The results of Part I suggest that refractory coating (wash) technologies may be required. Therefore, Part II focuses on studying the effects of refractory coating, metal, and chemically bonded sand system on as-cast surface quality. Refractory coatings, designed for steel castings, were applied to disk-shaped specimens by four industrial partners using normal production techniques. A small and practical casting trial, using disk-shaped specimen cores, was developed at Western Michigan University. This trial allows several core specimens to be wetted simultaneously from a known head pressure, temperature, and steel alloy. The casting trials were conducted at Saginaw Valley State University. The results show that various combinations of refractory coatings and chemically bonded sand systems provide different as-cast surface quality. Also, a new refractory coating technology (sol–gel) may provide a superior as-cast surface quality with silica and ceramic sands in a steel casting. Traditional refractory coatings, while still better than no coating, performed worse. Finally, the refractory coatings can affect the shakeout/collapsibility of a chemically bonded sand system. Overall, this indicates that more engineering of these coatings may be required for steel. [ABSTRACT FROM AUTHOR]

This paper is focused on the preparation procedures, using a talc-based filler, to improve the rheologic properties of the lost foam refractory coatings. Talc, with grain size of 40 μm, was mechanically activated in a vibration mill over the following times: 10, 20 and 30 min. Depending on the time required for the mechanical activation, the change in the filler grain size and shape was analysed along their effects on the talc-filled lost foam coating dispersion ability and stability. In order to characterize the filler, the following methods were used: X-ray diffraction, scanning electron microscopy and optic microscopy. The coating composition was tuned by choosing the suitable grain size and shape factor of the activated filler. In addition, different coating components (additives, solvent) were applied to alter the coating generation procedure. It was shown that the application of this type of the lost foam refractory coatings - water-based coatings - have a positive influence on quality of the aluminium alloy castings, which contributes to reducing the cost of cleaning and processing of the castings. Also, alcohol-based refractory coatings with talc-based activated fillers were tested and used to have the castings produced in the sand moulds. [ABSTRACT FROM AUTHOR]

The paper reports the development of RF sputtered boron carbide coatings as refractory and UV-shielder for high-temperature goggles and spacecraft applications. The advancement in the design and fabrication of machinery and UV optics necessitates the development of low-cost, eco-friendly preparation of wear-resistant refractory coatings with strong absorption in the UV region. Boron carbide coatings have proven their potential as abrasives besides their electronic applications. In the present work, boron carbide coatings are prepared by RF sputtering technique using the target prepared by low-temperature hydrothermal synthesis using cotton as carbon precursor. The sample synthesized and the film prepared are subjected to structure, morphological, and optical characterizations. The X-ray diffraction, Fourier transform infrared, micro-Raman and X-ray photoelectron studies confirm the formation of boron-rich boron carbide with the thermal stability of 87% at 800 °C, revealed through the thermogravimetric analysis. The Tauc plot analysis gives the bandgap energy of the boron carbide target and film as 2.66 eV and 2.70 eV, respectively. The UV–Vis spectroscopic study also reveals the potential of the sample and the film in blocking UVB and UVC. The CIE plot from the photoluminescence study suggests the sample to be a blue light emitter. [ABSTRACT FROM AUTHOR]

Results of studying effective use of nanostructured filler and single- and (or) two-layer application of flame retardant on wood are presented. It is established that sodium water glass is the most effective binder in the production of refractory protective coatings for building structures. The fire-resistant composition of sodium water glass and higher silicon oxide proposed may be attributed to group I of fire-retardant efficiency. [ABSTRACT FROM AUTHOR]

The aim of this study was to develop an efficient method for producing refractory metal coatings. To that end, tantalum coatings were deposited on Ti6Al4V substrates using a self-designed wire electrical explosion spraying technique. A uniform, dense coating was obtained for an energy density of 88.4 J/mm3 and a spraying distance of 5mm. The surface roughness of the tantalum coatings increased with the spraying distance as the latter affected the size distribution, velocity, and temperature of the explosive products, and so the flattening degree of splats. In addition, the microstructure of coating was also affected by the spraying distance. The adhesive strength of the tantalum coatings was 76 N at an energy density of 88.4 J/mm3 and spraying distance of 5 mm. The α-Ta phase and a metallurgy layer near the interface ensured that the adhesive strength of the tantalum coatings deposited by wire electrical explosion spraying was higher than those generated using other techniques. [ABSTRACT FROM AUTHOR]

Pulsed electric current is used to inhibit the erosion of rare earth-bearing molten steel to refractory by interfering with its interface reaction. The refractory samples are eroded by molten steel for 5–30 min, and the average thickness of the erosion layer increases by 397% from 160 μm to 795 μm. However, the average thickness of the erosion layer only increases by 40% from 150 to 210 μm under the action of pulsed electric current. The desiliconization and oxidation of Ce/La at interface lead to a loose and porous erosion layer and the formation of initial deposits CeAlO3/LaAlO3 and CeAl11O18/LaAl11O18. The adhesion of inclusions to the deposits leads to an increase in the thickness of the erosion layer. However, the pulsed electric current inhibits the desiliconization and oxidation of RE, thereby forming a Si-rich amorphous phase, which coats on refractory surface and acts as a protective film to reduce further erosion of the refractory by the molten steel. As a result, the refractory material forms a dense erosion layer and a smooth surface under the action of pulsed electric current. [ABSTRACT FROM AUTHOR]

In this article, homogeneous multi-functional materials and artificially design method are proposed to design ultra-thin metasurfaces, which broaden the application over a wide range of temperatures due to their excellent mechanically-thermally stable structure and electromagnetic functional performance. Ideal environmental barrier coating material of ytterbium monosilicate (Yb 2 SiO 5) possesses stable dielectric property over a wide temperature and frequency range. As a thermal corrosion resistant coating, NiCrAlY possesses excellent conductivity at high temperatures. These two materials are selected as substrate and conductive units to composite temperature insensitive ultra-thin refractory metasurface coating (RMC) for wideband radar cross section (RCS) reduction. Three types of RMC patterns are discussed, namely chessboard, staggered, and random. The prototype of staggered pattern was prepared using atmospheric plasma spraying (APS) technique. Both the simulated and experimental results indicated that RCS is reduced remarkably in a wideband frequency, as well as demonstrated stable reduction performance over a broad range of temperatures. Along with a protective layer of Yb 2 SiO 5 , only a thickness of 1.4 mm is required. The protective layer is employed to isolate the contact between the structural layer and the outside environment, which can significantly increase the service life of the metasurface. This work brings bright prospects for various kind of metasurfaces in practical high temperature applications and significantly enriches the research of metasurfaces. [ABSTRACT FROM AUTHOR]

Polymer nanostructures have drawn tremendous attention due to their wide applications in nanotechnology. However, the morphology of the polymer nanostructures is fragile under harsh conditions such as high-power irradiation and organic-solution environments during the fabrication or the measurement processes, significantly limiting their potential applications. In this work, we propose and demonstrate a simple approach to improve the stability of polymer nanostructures by coating a conformal ultrathin oxide film via atomic-layer deposition. Due to the refractory and dense coating of the oxide layer, the stability of polymer structures is enhanced by the prohibition of deformation occurrences from thermally induced reflow and organic solution. As a proof of concept, poly(methyl methacrylate) (PMMA) nanostructures coated with a sub-10-nm TiO2 layer are demonstrated, and the structures exhibit high temperature stability at 180 °C and good resistance to soluble damage from organic solutions. Subsequently, the mechanism of the improved thermal stability is analyzed via mechanical simulations. Such an effective approach is proposed to significantly broaden the application of polymer nanostructures as functional elements for optical structures/devices that require excellent thermal and chemical stability. [ABSTRACT FROM AUTHOR]

Micro arc oxidation (MAO) coatings were in situ prefabricated on refractory high entropy alloys (RHEAs). We systematically studied the evolution of the surface and cross-sectional morphologies and composition of the MAO ceramic coatings on AlTiCrVZr substrate with oxidation time. It was found that the surface elements in AlTiCrVZr exhibit competitive oxidation behavior during the MAO process. The inner layer of the MAO ceramic coating was mainly composed of ceramic oxides of the substrate elements, and the outer layer primarily consisted of ceramic oxides formed by the solute ions. Finally, we propose a growth model of the ceramic oxide coatings based on the formation mechanism of the MAO ceramic coating and the physical and chemical properties of the ceramic oxides formed by the principal elements in the RHEAs. • Formation process of micro arc oxidation coatings on RHEAs was analyzed. • Competitive oxidation mechanism of elements in RHEAs during MAO process has been revealed. • Growth model of MAO coating on RHEAs was established. [ABSTRACT FROM AUTHOR]

Refractory materials hold great promise to develop functional multilayer coating for extreme environments and temperature applications but require high temperature and complex synthesis to overcome their strong atomic bonding and form a multilayer structure. Here, a spontaneous reaction producing sophisticated multilayer refractory carbide coatings on carbon fiber (CF) is reported. This approach utilizes a relatively low-temperature (950 °C) moltensalt process for forming refractory carbides. The reaction of titanium (Ti), chromium (Cr), and CF yields a complex, high-quality multilayer carbide coating composed of 1) Cr carbide (Cr3C2), 2) Ti carbide, and 3) Cr3C2 layers. The layered sequence arises from a difference in metal dissolutions, reactions, and diffusion rates in the salt media. The multilayer-coated CFs act as a permeable oxidation barrier with no crystalline degradation of the CFs after extreme temperature (1,200 °C) and environment (oxyacetylene flame) exposure. The synthesis of high-quality multilayer refractory coating in a fast, efficient, easy, and clean manner may answer the need for industrial applications that develop cheap and reliable extreme environment protection barriers. [ABSTRACT FROM AUTHOR]

Crystalline phases are promising materials (matrices) for isolating nuclear waste with long-lived radionuclides, actinides first of all. Melting in an induction-heated cold crucible was used to produce a potential matrix with the following nominal composition: 50 wt % TiO2, 10 wt % MnO, 10 wt % CaO, 5 wt % Al2O3, 5 wt % Fe2O3, 10 wt % ZrO2, and 10 wt % CeO2 (actinide simulator). The target murataite phase is the predominant phase in the sample; crichtonite and glass are present as well. The emergence of glass is due to contamination of the melt by the refractory coating of the crucible. As in other samples produced by melting, murataite is represented by zonal crystals, the center of which is enriched in heavy elements (Zr and Ce). Murataite accounts for up to 80% of simulated radioactive waste. Irradiation with a dose of 22 million Gray resulted in partial amorphization of crichtonite. According to the results of a dynamic test (single pass flow test, SPFT), the rate of Ce leaching (powder, water, 70°C) is 10–4–10–5 g/(m2 day). [ABSTRACT FROM AUTHOR]

TiB 2 , ZrB 2 , and SiC powders with particles measuring several micrometers were first agglomerated and then deposited onto the substrate of a porous carbon block as a barrier to molten cryolite-based salt. Scanning electron microscopy, X-ray diffraction, and transmission electron microscopy were conducted to investigate the fine microstructure of the obtained ceramic coating and to elucidate the evolution of agglomerated powder from sprayed particles in plasma jet to splats on a substrate. Results indicated that a highly dense ceramic coating consisting of a solid solution (Ti x Zr 1-x)B 2 , residual TiB 2 , and ZrB 2 was obtained. The compactness of the coating and the formation of a solid solution phase was mainly caused by a SiC-rich liquid phase, as determined from a boride and silicon carbide pseudodiagram. After being submerged in molten cryolite-based salt for 8 h, the ceramic coating was firmly bonded to a carbon block. No molten slat permeated the ceramic coating. [ABSTRACT FROM AUTHOR]

The paper presents the results obtained for the distribution of heat flux incident upon a refractory plate of a hypersonic flight vehicle moving at space velocities at various distances from the Earth's surface. The paper also provides the results of studying phase transitions in the near-wall boundary layer occurring during the hypersonic flow over the ablating surface. The effect of the catalytic wall on heat flux is analyzed. The emphasis is on the analysis of mass loss from the surface of high-velocity flight vehicles based on detailed consideration of the mechanism of heterogeneous catalytic reactions taking place under the surface mass transfer conditions. A temperature distribution is provided across the thickness of the boundary layer at the stagnation point of a blunt-nosed body with a refractory coating for a specific section of the flight path. The mass loss from the surface of crystalline refractory bodies is determined. [ABSTRACT FROM AUTHOR]

The results of tests performed under laboratory and production conditions on refractory coatings developed for the protection of expensive nichrome alloys based on technogenic raw material are presented. The results for the cost-effectiveness of fire-resistant sitall coatings developed using secondary raw material and the performance of the coatings at high temperatures are presented. [ABSTRACT FROM AUTHOR]

High emissivity coatings which aim to help the cement industry reduce heat loss in its production process have been developed with different CeO2 and AlH6O12P3 ratios (1:3, 1:5, and 1:12 by volume). The coating slurries were shear thinning and after heat treatment in air at 1300°C, 1°C/min, dwell 3 hours, XRD revealed that CePO4 forms more easily as the Ce/P ratio decreases. The composition with a 1:5 ratio of CeO2:AlH6O12P3 was gun sprayed on basic refractory bricks, then heat treated under the same conditions as the slurries. SEM, (S)TEM and EDX were used to study thickness, microstructure, and chemical composition of the coatings which revealed that the coating was composed of pores, CeO2 grains, CePO4 grains, and M‐P‐O glass. SEM images show that CePO4 was nucleated from a reaction between CeO2 and AlH6O12P3. Consequently, CePO4 grains (~2 µm diameter) were smaller than CeO2 (~10 µm diameter). The emissivities of un‐coated and coated basic refractory bricks were measured at 1100 and 1300°C over the wave number range of 700‐12 000 cm−1. At both temperatures, the emissivity of the coated bricks was higher than the uncoated bricks and the emissivity was measured to be higher at a higher temperature for both samples. The coated bricks gave the highest emissivity of 0.81 from 1050 to 11 000 cm−1 which is about twice the un‐coated bricks for the same conditions. This demonstrates that the developed high emissivity coating has potential to be used with basic refractory brick. [ABSTRACT FROM AUTHOR]

W+ irradiation of TiAlN is used to demonstrate growth of dense, hard, and stress-free refractory nitride coatings with no external heating during reactive magnetron sputtering. Ti0.40Al0.27W0.33N nanocomposite films are deposited on Si(001) substrates using hybrid high-power impulse and dc magnetron cosputtering (HiPIMS and DCMS) in an industrial sputtering system employing substrate rotation during film growth from six cathodes. Two W targets powered by HiPIMS serve as a pulsed source of energetic W+ ions with incident fluxes analyzed by in situ time- and energy-resolved mass spectroscopy, while the remaining four targets (two elemental Ti targets and two Ti plates with Al plugs) are operated in the DCMS mode (W-HiPIMS/TiAl-DCMS) to provide a continuous flux of metal atoms and sustain a high deposition rate. A negative substrate bias Vs is applied only in synchronous with the W+-ion-rich portion of each HiPIMS pulse in order to provide film densification by heavy-ion irradiation of the TiAlN layers deposited between W+-ion exposures. W is selected for densification due to its high mass and relatively low reactivity with N2, thus minimizing target poisoning while enhancing gas rarefaction. Dense Ti0.40Al0.27W0.33N alloy films, grown with no external substrate heating (substrate temperature Ts lower than 150 °C due to heat load from the plasma) and Vs = 500 V, exhibit a nanoindentation hardness of H = 23.1 GPa and an elastic modulus of E = 378 GPa, which are, respectively, 210% and 40% higher than for reference underdense DCMS Ti0.58Al0.42N films grown under the same conditions, but without W+ irradiation. The W ion bombardment does not affect the film stress state, which is compressive and low at 1.2 GPa. [ABSTRACT FROM AUTHOR]

To create blades of gas-turbine engines of new generation made of materials based on alloys of the Nb–Si system, we study the surface layer formed on niobium by its silicides with additionally introduced titanium elements. It is shown that the heat resistance of these specimens does not depend on the method of formation of the surface layer and depends only on its thickness. The addition of titanium increases the heat resistance of the specimens at 1350°C depending on its content. We also performed the thermodynamic analysis of the possibility of simultaneous saturation of the surface of niobium with titanium and boron under the action of vapors of the NaCl activator. [ABSTRACT FROM AUTHOR]

Copyright of Materials & Technologies / Materiali in Tehnologije is the property of Institute of Metals & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Results of scientific researches show the trend of active using nitrides and borides of transition metals and their combination in developing protective materials. While single elements nitrides have been well studied, their multilayer modifications and combinations require more detailed study. Physical-mechanical properties and structural-phase state of multilayer coating according to the deposition conditions is an important task for the study. It will be the analysis of physical-mechanical and electrical properties of coatings based on refractory metals nitrides, their structure and phase composition and surface morphology depending on the parameters of condensation. It was established the structure and behavior of nano scale coatings based on refractory metals nitrides (Ti, Zr) depending on the size of nano grains, texture, stress occurring in coatings. [ABSTRACT FROM AUTHOR]