Applications In Severe Environments Research Articles

The role of precipitation in hydrogen diffusivity and mechanical properties of a high entropy alloy

In the present work, we investigate the interaction of hydrogen with the microstructure of the novel Fe38Mn25Ni24Co5Cr2Al4Ti2 high entropy alloy (HEA), under annealed and aged conditions. For this purpose, hydrogen gas permeation tests, slow strain rate tests in previously hydrogen charged specimens and thermal desorption analyzes were carried out. Under both conditions, low hydrogen diffusivity values were calculated at room temperature, comparable to that of nickel-based superalloys. Hydrogen diffusion coefficient for the alloy under annealed condition can be expressed by D=1.58x10−7m2.s−1exp(−43.7RT)kJ.mol−1 and, for the aged condition, by D=1.25x10−7m2.s−1exp(−41.9RT)kJ.mol−1. Furthermore, mechanical characterization and fracture surface analyzes demonstrate that the aging treatment improves the mechanical properties and does not impact the hydrogen embrittlement susceptibility of the alloy. Our findings contribute to the investigation of hydrogen embrittlement mechanism and provide data for the design of HEAs with suitable properties for structural applications in severe environments.

High‐performance heterocyclic para‐aramid aerogels for selective dye adsorption and thermal insulation applications

AbstractThe high‐performance polymer para‐aramid (PPTA) is discovered to gel too soon during the polymerization process, resulting in poor processing performance. In this work, a homogeneous polymer solution containing heterocyclic para‐aramid (HPPTA) was successfully synthesized by introducing 2,4‐aminophenyl‐5‐aminobenzimidazole groups into the molecular chains of PPTA, and then HPPTA aerogel was prepared using a supercritical drying technique that took advantage of the HPPTA solution's excellent property of slow gelation. When the HPPTA polymer mass fraction was 1 wt%, the aerogel had the lowest density of 0.086 g cm−3 with a BET specific surface area of 376.59 m2 g−1. The HPPTA‐2 aerogel had better adsorption performance for anionic dye methyl orange, with a maximum adsorption capacity of 319.47 mol g−1; however, its adsorption capacity for cationic dye methylene blue and neutral dye dimethyl yellow was very low, at only 19.68 and 0 mol g−1, respectively. The selective adsorption ability of HPPTA aerogel made it a simple and scalable platform for removing anionic dyes from water solutions. Furthermore, the HPPTA aerogel has outstanding thermal properties for thermal insulation applications in severe environments due to the synergistic effect of the 3D porous structure inside the aerogel and the exceptional thermal stability of the HPPTA.

Multi-functional polyethersulfone nanofibrous membranes with ultra-high adsorption capacity and ultra-fast removal rates for dyes and bacteria

The adsorption technology has been widely applied in water remediation for contamination removal of dyes and bacteria, by virtue of the advantages of adsorption technology including high efficiency, energy conservation and ease of operation. Simultaneous removal of dyes and bacteria has been realized by some reported materials, but to achieve satisfactory adsorption amounts and rates remain an unmet goal for decades. Herein, a poly(methacrylatoethyl trimethyl ammonium chloride-co-methyl methacrylate) copolymer was synthesized, and then blended with polyethersulfone for the fabrication of nanofibrous membranes via electrospinning for the use of fast and massive removal of dyes and bacteria. Owing to the introduction of abundant quaternary ammonium groups, the maximum adsorption amount for methyl orange was up to 909.8 mg g−1. In addition, the modified nanofibrous membranes showed good recyclability, broad applications in severe environments, selective adsorption ability, and excellent dynamic removal performance. Especially, thanks to the abundant functional groups, the membranes showed fast adsorption ability for bacteria through electrostatic interaction. It should be noted that the clearance ratio for Staphylococcus aureus or Escherichia coli by 6 min of static adsorption could reach 93 % or 90 % for each. Additionally, dynamic removal ratio via filtration with the nanofibrous membranes could reach 99.7 % for Staphylococcus aureus or 98.7 % for Escherichia coli in 90 s. Therefore, the proposed approach towards the quaternary ammonium modified polyethersulfone nanofibrous membranes creates a new route for ultra-high adsorption capacity and ultra-fast removal rates for dyes and bacteria in water remediation.

Structural, electronic, and mechanical properties of calcium aluminate cements: Insight from first-principles theory

Calcium aluminate cements (CACs) have attracted much attention due to their potential applications in severe environments. Up to now, their structural, electronic, and mechanical properties have not been fully determined yet. This study shed light on these properties by means of first-principles density functional theory. A total of ten phases, including C3A, C12A7, CA (CA_low, CA_A, and CA_B), CA2, CA6, C2A, C5A3 and C4A3, within the calcium aluminate (Ca-Al-O) series were investigated. The calculated lattice parameters agreed well with the experimental results. The cohesive energy was ranged between 5.90 eV/atom and 6.31 eV/atom, and the formation energy was ranged between 14.42 eV/atom and 5.51 eV/atom. The partial density of states that are important for bond formation originated mainly from O atoms, followed by Ca and Al atoms. All ten phases contained band gaps ranged between 3.74 eV and 5.30 eV. Oxygen atoms were prone to electrophilic attack while calcium atoms were prone to nucleophilic attacks. The bulk modulus, shear modulus, Young's modulus, and Poisson’s ratio for C3A, C12A7, CA_low, CA6, C2A, C4A3 were in the range of 79.37 GPa to 197.25 GPa, 42.11 GPa to 102.81 GPa, 107.33 GPa to 262.78 GPa, and 0.25 to 0.28, respectively.

Phase evolution and thermal stability of high Curie temperature BiScO3-PbTiO3-Pb(Cd1/3Nb2/3)O3 ceramics near MPB

Piezoelectric and ferroelectric ceramics with a high Curie temperature (Tc) have attracted much attention owing to their applications in severe environments. In this work, phase structure and dielectric, ferroelectric, and piezoelectric properties of (0.975 − x)BiScO3-xPbTiO3-0.025Pb(Cd1/3Nb2/3)O3 (BS-xPT-PCN) ceramics (x = 0.58–0.64) were studied. A composition-induced structural transformation occurs from the rhombohedral to tetragonal phase through an intermediate monoclinic phase with the increasing PT concentration. The relationship between the structure and electrical properties of the system was discussed. The BS-xPT-PCN system near the morphotropic phase boundary (MPB) (x = 0.62) exhibits excellent piezoelectric and ferroelectric performances with d33 = 508 pC/N, kp = 56%, and Pr = 40 μC/cm2. The high-temperature piezoelectricity of the sample with MPB (x = 0.62) was characterized by an in situ XRD. The excellent thermal stability of the crystal structure and the piezoelectric property indicate that the BS-xPT-PCN system is a promising candidate for high-temperature piezoelectric applications.

Multifunctional Ti based carbonitride coatings for applications in severe environments

In this work, the influence of NbZr and ZrSi addition to TiCN coatings are studied, aiming for their use as protective layers for parts subjected to severe corrosion and wear. The coatings with C/N ratios ranging from 0.4 to 2.5 were deposited using the cathodic arc technique in a mixture of N2 and CH4 gases, on 316 stainless steel discs and Si (111) wafers. All the coatings exhibited residual compressive stresses, with values ranging from approximately-2.4 GPa to −3.5 GPa. The addition of Si led to an increase in hardness, regardless of the C/N ratio. All coatings with high C/N ratio (~2.5) presented slightly lower stress values and superior performance in 3.5% NaCl corrosive solutions, the best performance being obtained for the TiSiZrCN coating, which exhibited the highest protective efficiency to corrosion (97.8%), due to its low corrosion current density (1.734 μA/cm2) and high polarization resistance (31.775 kΩ). The tribological tests, performed at 23 °C and 250 °C, indicated that abrasion and oxidation were the predominant wear mechanism for all coatings. At 23 °C, the friction coefficients of the coated specimens were significantly lower than those of the uncoated samples. When the collective performance across all of the experimental parameters was assessed, the coatings with C/N of about 2.5 proved to be the most suitable candidates to be used in severe service conditions.

Refractory ceramic coatings: processes, systems and wettability/adhesion

AbstractRefractory materials such as ceramics and refractory metals/alloys are widely used for structural applications in severe environments where more efficient use of energy is a prime need. Owing to properties such as high strength and refractoriness, low thermal expansion and electric conductivity these materials may be used as turbocharger rotors, valves, valve seats and turbocharger turbine wheels in gas turbine engines, tubes in industrial heat exchangers, fuel elements in nuclear reactors, fusion reactor wall material, tool materials in machining and casting and as electronic packaging. In these applications, however, these materials often experience extreme mechanical, thermal and chemical loading conditions and are expected to perform effectively beyond existing limits. The existing limits of performance for these materials can be extended only via coating technology, which presently appears to be the most suitable technical and economic approach. Thus there remains a critical need to develop a suitable and reliable refractory coating system and coating technique.In view of the above requirements, the present paper embarks on a brief review of refractory coatings. The review begins with a set of criteria required for an effective refractory coating. The criteria include general thermophysical and mechanical properties for the refractory coating only and properties of the coating–substrate as a system. The review continues with a section on methods of coating. The classification of methods of coating is based on categories such as gaseous, solution, molten/semi‐molten and solid state processes. Each category is explained with conventional and novel techniques and coatings that can be synthesized using these techniques. These categories are supplemented also with examples of applications. A major emphasis has been put on refractory materials in the following section on coating material systems. The most important materials systems have been grouped as oxides and nitrides, carbides, borides, silicides and aluminides. The general properties that make them useful as refractory coatings, along with specific materials and applications, have been reviewed. Wettability and adhesion between coating and substrate are very important for the coating–substrate system to perform effectively and reliably. The last section discusses the fundamentals of wettability and work of adhesion, based on which wetting in metal–metal, metal oxide, metal–carbon/carbide systems has been discussed. Finally, the review sets the motion of thoughts with a description on future developments. Copyright © 2001 John Wiley & Sons, Ltd.

Pultruded fiber optic ribbon sensor for applications in severe environments

A new multichannel optical sensor for monitoring large structures, consisting in an eight-optical-fiber ribbon pultruded in composite material, has been realized and completely characterized. Both strain and temperature sensitivity, and both dynamic and thermal strain response, as well as birefringence tests and mechanical characterization are reported. The experimental results confirm the capabilities of pultru- sion to realize multichannel optical sensors for large structures that are able to operate in a severe environment. The sensor can fulfill mechanical, chemical, and electrical custom requirements with quality consistency at low cost. The sensors have been used as strain sensors for an 85-m-long oil-rig riser.

Chemical reactivity in the processing and the interactions with the environment of ceramic matrix composites

C/C/SiC and SiC/C/SiC fibrous composites are non-brittle structural materials designed for applications in severe environments. Chemical reactivity plays a key role in their processing and their interactions with the atmosphere. During their processing by CVI, chemical reactions between the gaseous reactants/products and the fibers largely control the densification process of the fiber preform and the residual strength of the reinforcement. In a similar manner, chemical reactions control the evolution of the fibers, the interphase, the mechanical behavior and ultimately the lifetime, when the materials are exposed to oxidizing atmospheres.

Silicon Carbide: the Premier Paradigm for Structural and Microelectronic Device Applications in Severe Environments

ABSTRACTThe extreme thermal, mechanical, corrosion resistant and electronic properties of SiC provide multiplicative combinations of attributes which allow a variety of products for very different applications. The emphasis herein will be the consideration of both the constant stress creep properties of several types of polycrystalline SiC materials and the characteristics of different SiC-based devices having high power, high frequency and switching applications and which are operational at ≥573K. The controlling mechanism in reaction-bonded SiC within the ranges of temperature and stress of 1848K-1923K and 110–220 MPa, respectively, is glide/climb controlled by climb. The controlling creep mechanism in CVD material at T<1873K is dislocation glide controlled by the Peierls stress; above this temperature, the evidence suggests that dislocation glide/climb controlled by climb becomes an increasingly important mechanism. For sintered α-SiC within the respective temperature and stress ranges of 1670K-2073K and 138–414 MPa, the controlling creep mechanisms are grain boundary sliding accommodated by grain boundary diffusion at T<1800K and lattice diffusion at T> 1920K. By contrast, the continual development of SiC thin film deposition and the device related technologies of doping, contacts and dry etching have culminated in a host of microelectronic devices operable at high temperatures, namely, MOSFET high power devices, MESFET high frequency devices, and switches including p-n junctions and thyristors. The properties of selected devices and circuits made from them are described with an emphasis on their operation at high temperature.

Challenging ceramic matrix composites for applications in severe environments

Non-brittle ceramic matrix composites (CMCs) consisting of a ceramic matrix reinforced with continuous fibers, such as the SiC/SiC composites, exhibit outstanding mechanical properties, when properly processed. Tensile failure stress as high as 400 MPa, tensile failure strain close to 1% and energy release rate of the order of several 10 KJ.m-2 are currently achieved for 2D-SiC/PyC/SiC. The main subject of concern is probably the effect of oxidizing environment under loading. The present status of knowledge and further improvements of the materials are presented and discussed.

Ceramic-matrix composites for applications in severe environments

Ceramic-matrix composites for applications in severe environments

Properties of chemical-vapor-deposited silicon carbide for optics applications in severe environments

Important data on chemical-vapor-deposited (CVD) SiC concerning the elastic modulus, polishability, scattering measurement, thermal and cryogenic stability, and degradation owing to the effects of atomic oxygen and electron beams have been obtained with the aim of assessing the suitability of SiC as an optical substrate for severe environments. These measurements show that CVD SiC substrates exhibit excellent polishability (<0.1 nm rms) with low scatter, good retention of mechanical properties up to 1500 degrees C, superior thermal and cryogenic stability (-190 degrees to 1350 degrees C) and high resistance to atomic-oxygen and electron-beam degradation. These results suggest that CVD SiC optical substrates will perform extremely well in severe environments such as outer space, and when used in lasers, combustion, and synchrotron x rays.

Beryllium in stress-critical environments

Beryllium is a “specialty” metal whose unusual properties have been exploited in a number of energy conversion systems. Low density and high elastic modulus make it a particularly attractive material in the aerospace environment. The physical and mechanical properties of the various grades of beryllium are reviewed, along with examples of successful applications in severe environments.

On the Utilization of Ferrofluids for Transducer Applications

An assessment of the suitability of ferrofluids for acoustic transducer and receiver applications has led to the following conclusions: First, the magnetostrictive mode of operation is not efficient enough to offer an alternative to conventional solid materials in use. Second, the piston motion of the ferrofluid induced by an applied field gradient does provide a real alternative to conventional magnetostrictive transducers. For an applied static field of 4000 Oe and a field gradient of 1000 Oe/cm, it is possible to achieve an overall efficiency that is greater than that for the ferromagnetic solids. Third, ferrofluids appear to provide a desirable alternative for pressure-sensing applications in severe environments (e.g., detonations) where piezoelectric and pyroelectric materials suffer fatigue and failure. Fourth, ferrofluids offer the prospect of obtaining broadband frequency response when radiating or receiving in liquid media.