Search

The present work had evaluated the effect of cryogenic treatment (233 K) on the degradation of polymeric biomaterial using a numerical model. The study on effect of cryogenic temperature on mechanical properties of cell-seeded biomaterials is very limited. However, no study had reported material degradation evaluation. Different structures of silk-fibroin-poly-electrolyte complex (SFPEC) scaffolds had been designed by varying hole distance and hole diameter, with reference to existing literature. The size of scaffolds were maintained at 5 × 5 mm2. Current study evaluates the effect of cryogenic temperature on mechanical properties (corelated to degradation) of scaffold. Six parameters related to scaffold degradation: heat transfer, deformation gradient, stress, strain, strain tensor, and displacement gradient were analyzed for three different cooling rates (− 5 K/min, − 2 K/min, and − 1 K/min). Scaffold degradation had been evaluated in the presence of water and four different concentrations of cryoprotectant solution. Heat distribution at various points (points_base, point_wall and point_core) on the region of interest (ROI) was found similar for different cooling rates of the system. Thermal stress was found developing proportional to cooling rate, which leads to minimal variation in thermal stress over time. Strain tensor was found gradually decreasing due to attenuating response of deformation gradient. In addition to that, dipping down of cryogenic temperature had prohibited the movement of molecules in the crystalline structure which had restricting the displacement gradient. It was found that uniform distribution of desired heat at different cooling rates has the ability to minimize the responses of other scaffold degradation parameters. It was found that the rates of change in stress, strain, and strain tensor were minimal at different concentrations of cryoprotectant. The present study had predicted the degradation behavior of PEC scaffold under cryogenic temperature on the basis of explicit mechanical properties. [ABSTRACT FROM AUTHOR]

Under conventional temperature regimes, optical fiber sensors (OFS) have been extensively utilized for real-time monitoring of strain and temperature responses in transportation, energy, and civil engineering structures. However, in low-temperature environments, OFS applications confront challenges such as poor adhesion, diminished sensitivity, weak signal transmission, and complex compensation requirements. Therefore, it is crucial to conduct in-depth research on the high-precision calibration characteristics of strain and temperature in cryogenic conditions. In this study, we propose an enhanced calibration technique for fiber Bragg grating (FBG) strain/temperature sensitivity, covering a low-temperature range of 77–296 K. Employing a custom-designed low-temperature testing apparatus, we calibrated the thermo-optic coefficients, temperature, and strain sensitivity coefficients. Subsequently, this improved method was applied to measure the coefficient of thermal expansion of various materials. The results confirm the accuracy of the proposed method and present the strain/temperature measurement properties of FBG. This research provides guidance for the precise use of FBG in low-temperature environments. [ABSTRACT FROM AUTHOR]

As the maritime industry's emphasis on sustainable fuels has increased, liquid hydrogen (LH2) has emerged as a promising alternative due to its high energy density and zero-emission characteristics. While the experience of using natural gas in ships can serve as a basis for the introduction of hydrogen, the different risks associated with the two fuels must also be considered. This review article provides a methodology for selecting suitable metal materials for shipboard LH2 storage and piping systems based on operational requirements. The effects of both liquid and gaseous hydrogen environments on metal materials are first comprehensively reviewed. The minimum requirements for metal materials in liquefied natural gas (LNG) storage systems, as stipulated in the IGC and IGF codes, were used as a baseline to establish minimum requirements for liquid hydrogen. The applicability of austenitic stainless steel, a representative metal material for cryogenic use, to a liquid hydrogen environment according to nickel content was examined. In order to apply liquid hydrogen to the marine environment, the minimum requirements for liquid hydrogen were organized based on the minimum requirements for metal materials in the LNG storage system covered by the IGC and IGF codes. Finally, to expand the material selection criteria for low-temperature cargo and fuel storage facilities at sea, slow strain tensile testing, fatigue life, and fracture toughness considering the hydrogen environment and cryogenic temperature were derived as evaluation items. [ABSTRACT FROM AUTHOR]

To solve the cryogenic temperature problems faced by all-concrete liquefied natural gas (ACLNG) storage tanks during servicing, a low temperature resistant and high strength concrete (LHC) was designed from the perspectives of reducing water-binder ratio, removing coarse aggregates, optimizing composite mineral admixture and utilizing steel fibers. The variation laws of compressive and tensile strength, elastic modulus and Poisson's ratio for C60 concrete and LHC were compared and analyzed under the temperatures from 10 to −165 °C through uniaxial compression and tensile tests. The rapid freezing method was adopted to analyze the evolution process of mass and relative dynamic elastic modulus loss rates for C60 and LHC in 0–300 freeze-thaw cycles. The gas permeability test was carried out, and the laws of gas permeability coefficient varied with temperature and cryogenic freeze-thaw cycles were obtained. Then, the grey dynamic model GM (1,1) was used to predict the variation laws of physical and mechanical parameters on the basis of the test data. The test results demonstrate that the compressive strength, elastic modulus and Poisson's ratio for both C60 and LHC increase significantly from 10 to −165 °C, but the specific variation laws are different, and there is a phenomenon that some parameters decrease after reaching a critical temperature range for C60. The uniaxial tensile strength increases first and then decreases as temperature decreases, and finally increases slightly at −165 °C for both C60 and LHC. The mass and relative dynamic elastic modulus loss rates of LHC are much lower than that of C60 under different freeze-thaw cycles. The gas permeability coefficient of C60 declines gradually with the drop of temperature, and increases gradually with the number of freeze-thaw cycles while the gas permeability coefficient of LHC basically remains stable and is much lower than that of C60. Therefore, such a conclusion can be drawn that LHC has better properties at cryogenic temperature. On the premise of providing consistent functional mode, GM (1,1) can predict the test data with high accuracy, which well reflects the variation laws of relevant parameters. [ABSTRACT FROM AUTHOR]

As the urgency for carbon-neutral fuels grows in response to global warming and environmental pollution, liquid hydrogen, with its high energy density, emerges as a promising candidate. Stored at temperatures below 20 K, liquid hydrogen's containment system requires materials resilient to such cryogenic temperatures. Austenitic stainless steel, including 304L grade, has been widely used due to its favorable properties. However, designing pressure vessels for these systems necessitates a deep understanding of fracture mechanics and accurate assessments of the material's fracture toughness at cryogenic temperatures. The mechanical behavior at these temperatures differs significantly from that at room temperature, making testing at 20 K a complex procedure that requires stringent facilities. This study examines the tensile behavior and fracture toughness of 304L stainless steel at cryogenic temperatures, comparing and analyzing the characteristics observed at 20 K with those at room temperature. The phenomenon of discontinuous yield, with abrupt stress drops and stepwise deformation at low temperatures, has been identified, resulting in more complex stress–strain curves. Limitations were found in the calculation of the crack length during the assessment of fracture toughness in stainless steel under extremely low-temperature environments through the J-integral compliance method. To address these constraints, a comparative analysis was carried out to determine potential corrective measures. [ABSTRACT FROM AUTHOR]

The current study confirms that modified carbon fiber reinforced polymer (CFRP) composites have higher fracture toughness than unmodified CFRP composites achieved by exploiting the synergistic effect of a polycarbonate (PC)/acrylonitrile butadiene styrene (ABS) blend in toughening the diglycidyl ether of bisphenol A (DGEBA) epoxy resin. The CFRP composite specimens are tested at near cryogenic temperatures using TMA, DMA, and microcrack analysis to determine the best‐suited concentration of ABS in the PC/ABS blend. TMA and DMA results, as well as microcrack analysis at cryogenic temperatures (CT), confirm that the blend 90/10 is effective in reducing the brittle nature of DGEBA resin and increasing bond strength, resulting in the fracture toughness enhancement of CFRP specimens at CT. Further investigation of 90/10 modified CFRP (90/10 m‐CFRP) and unmodified CFRP specimens using Mode II fracture using ENF test and SEM analysis reveal significant reduction in brittle characteristics of matrix with increase in elongation at failure and fracture surface morphologies confirm nano web‐like structures bridging the CF layers, proving to improve fiber/matrix bond strength. This study concludes the effectiveness of hybrid PC/ABS blend in synergistically‐modifying DGEBA resin for improved fracture toughness of CFRP laminates across a wide temperature range (−150°C to 150°C). [ABSTRACT FROM AUTHOR]

The mechanical properties of a fine-grained (FG) Ti-6Al-4V extra-low interstitial (ELI) alloy were investigated by tensile tests at 298 K and 77 K. The experimental results indicated that, at 77 K, the alloy exhibits a small uniform elongation of 2.65%, but has a fracture elongation of 19.2%, showing superior post-necking elongation. At 298 K, the alloy displays a single dislocation slipping, β→α″ phase transformation occurred, and 6.35% uniform elongation was obtained, whereas the coupling of dislocation slipping and twinning deformation behaviors dominated at 77 K. The limited uniform elongation is attributed to the absence of martensite phase transformation at 77 K, whereas the decent fracture elongation is ascribed to the resistance offered by twinning against plastic instability.

Quasi-static tensile deformation behaviors at room temperature (RT) and 77 K of the CT20 alloy with a //ND texture were investigated. The CT20 alloy with equiaxed microstructure exhibits excellent mechanical properties with simultaneous increase in strength and elongation at cryogenic temperature. In current study, the initial //ND texture promotes basal slip actuation effectively and continuously increases Schmid factor (SF) of other slip systems to promote multiple slip. Cryogenic temperature weakens the deformation texture due to the promotion of multiple slip. Since the decrease of the stacking fault energy (SFE), more twins in number and variety nucleate at 77 K and promote multiple slip. It causes strong cryogenic twinning-induced plasticity (TWIP) effect. Grain refinement induces strong cryogenic dynamic Hall-Petch effect resulting in high strain-hardening rate (SHR) and strength. The yield strength (YS, ∼1052.67 MPa), ultimate tensile strength (UTS, ∼1102.51 MPa) and elongation (EL, ∼21.1 %) of the 77 K specimen are about 84.1 %, 69.1 % and 38.8 % higher than its counterpart at RT, respectively. In addition, cryogenic temperature changes the initiation location of cracks and promotes cracks initiation at grain boundaries homogeneously.

Ejectors have emerged as a viable solution for handling Boil-Off-Gas (BOG) generated by cryogenic storage tanks. The efficiency of ejector-based systems plays is highly dependent on the ejector's performance which is influenced by various factors including the geometry of the ejector and the boundary conditions. In this study, an axisymmetric supersonic ejector was designed, optimized, and evaluated for BOG removal. The baseline geometric dimensions design of the ejector was obtained via theoretical analysis. Subsequently, computational fluid dynamics (CFD) simulations were employed to optimize the boundary conditions and geometrical parameters. Experimental investigations were conducted to validate the design and evaluate the ejector's performance. The results highlighted the significant influence of two key parameters, namely, the mixing chamber diameter (Dm) and the nozzle exit position (NXP), on the ejector's performance. Optimized Dm showed an increase of about 12.5% compared with the baseline geometry. By operating the ejector within its on-design geometric and boundary conditions, the maximum entrainment ratio (ER) was achieved. The CFD models successfully identified and validated various flow phenomena, including double choke, single choke, and backflow, which were consistent with the experimental observations. Both the numerical models and experimental findings demonstrated that the modified ejector achieved an entrainment ratio of 1.06 under its design condition showing a 33.66% increase compared with that obtained using the baseline geometry. These results indicate the potential of the supersonic ejector as an alternative solution for BOG applications, emphasizing its efficacy in handling this industrial challenge.

ABSTRACT: Investigation into the structural and magnetic properties of organic molecules at cryogenic temperature is beneficial for reducing molecular vibration and stabilizing magnetization, and is of great importance for constructing novel spintronics devices of better performance and scaling the device size down to nanoscale. In order to explore the possibility of fabricating molecule-based memory chips of ultrahigh density, two-dimensional close-packed molecular arrays with carboxylic acid molecules were constructed in the current work and the magnetic properties in a low-temperature scanning tunneling microscope were also investigated. The results demonstrated that each nonmagnetic molecule can be controllably and independently switched into a stable spin-carrying state at 4 K by applying a voltage pulse with atomic resolution. Benefiting from the small size of a single molecule as the basic storage bit, the two-dimensional molecular arrays allowing controllable electrical manipulations on each molecule can behave as a platform of memory chip with an ultrahigh storage density of ∼320 terabytes (Tb) (or ∼2500 terabits) per square inch. This work highlights the potential and advantage of employing organic molecules in developing future cryogenic information storage techniques and devices at nanoscale.

Exploring metallic microfibers with an excellent combination of high strength and ductility is a challenge for structural applications under extreme conditions. In this work, a heterogeneous gradient structure was introduced into CoCrFeNi high-entropy alloy (HEA) microfibers via thermomechanical processing. The annealed CoCrFeNi microfiber displays an ultrahigh yield strength of ∼ 1 GPa, an ultimate tensile strength of 1.45 GPa, and an outstanding uniform elongation of 75% at 150 K. These excellent properties originate from the ultrafine grains and heterogeneous gradient structure, as well as the activation of multiple deformation mechanisms including deformation twins, dense dislocations, stacking faults, Lomer-Cottrell locks, phase transformation and 9R phase. Our work not only suggests that HEA microfibers have great potential for structural applications in cryogenic environments, but also sheds light on the design of advanced multi-component metallic microfibers with superior mechanical properties.

This study investigated the gas tungsten arc (GTA) weldability of a base metal (BM) Fe60Co15Ni15Cr10 medium-entropy alloy (MEA) by applying CoCrFeMnNi and CrFeMnNiCu fillers. Sound welds without macro defects, such as internal pores or cracks, were obtained. The CoCrFeMnNi-based weld consisted of a face-centered cubic (FCC) structure, whereas the CrFeMnNiCu-based weld comprised (Co, Cr, Fe)-rich phase of FCC1 and a Cu-rich phase of FCC2 with the same FCC structure formed by phase separation. In the CrFeMnNiCu-based weld with a Cu-rich phase, the weld metal (WM) was stronger than that in the CoCrFeMnNi-based weld. The tensile fracture of all specimens occurred in the coarse-grained heat-affected zone (CGHAZ) at 298 K, while the tensile properties of the CrFeMnNiCu-based weld were improved compared to those of the CoCrFeMnNi-based weld, probably because the Cu-rich phase present in WM blocks the movement of dislocations. The WM of all tensile specimens at 77 K exhibited deformation twins, and deformation-induced martensitic transformation occurred in the BM and CGHAZ, showing improved strength and ductility compared to those at 298 K. [ABSTRACT FROM AUTHOR]

As a carbon-free fuel, hydrogen has received significant attention recently since it can help enable low-carbon-economy. Hydrogen has very broad flammability range and very low minimum ignition energy, and thereby there are severe safety concerns for hydrogen transportation and utilization. Cryo-compressed hydrogen is popularly used in practice. Therefore, it is necessary to investigate the combustion properties of hydrogen at extremely low or cryogenic temperatures. This study aims to assess and interpret the effects of cryogenic temperature on premixed hydrogen/air flame propagation and acceleration in a thin closed channel. Different initial temperatures ranging from normal temperature (T 0 = 300 K) to cryogenic temperature (T 0 = 100 K) are considered. Both one- and two-dimensional hydrogen/air flames are investigated through transient simulations considering detailed chemistry and transport. It is found that when the initial temperature decreases from T 0 = 300 K to T 0 = 100 K, the expansion ratio and equilibrium pressure both increase substantially while the laminar flame speeds relative to unburned and burned gasses decrease moderately. The one-dimensional flame propagation is determined by laminar flame speed and thereby the combustion duration increases as the initial temperature decreases. However, the opposite trend is found to happen to two-dimensional flame propagation, which is mainly controlled by the flame surface area increase due to the no-slip side wall constraint and flame instability. Based on the change in flame surface area, three stages including the initial acceleration, steady burning and rapid acceleration are identified and investigated. It is demonstrated that the large expansion ratio and high pressure rise at cryogenic temperatures can significantly increase the flame surface area in early stage and promote both Darrieus-Landau instability (hydrodynamic instability) and Rayleigh-Taylor instability in later stage. These two instabilities can substantially increase the flame surface area and thereby accelerate flame propagation in hydrogen/air mixtures at cryogenic temperatures. The present study provides useful insights into the fundamental physics of hydrogen flames at extremely low temperatures, and is closely related to hydrogen safety. [ABSTRACT FROM AUTHOR]

A series of experiments were carried out in a closed tube at cryogenic temperature (77 K) for hydrogen-oxygen mixtures. Flame propagation speed and overpressure were measured by optical fibers and pressure sensors, respectively. The first and second shock waves were captured in the cryogenic experiments, although the shock waves always precede the flames in all cases indicating the absence of stable detonation. However, strong flame acceleration was observed for all situations, which is consistent with the prediction by expansion ratio and Zeldovich number. Besides, the tube diameter and length are also critical for flame acceleration to supersonic. All the flames in this work accelerate drastically reaching the C-J deflagration state. But at 0.4 atm, only fast flame is formed, while at higher initial pressures, the flame further accelerates to a galloping mode manifesting a near-limit detonation, which could be indicated by the stability parameter χ. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department 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.)

This study investigates the origin of low-frequency (LF) 1/ $f$ noise in Si n-channel metal-oxide-semiconductor field-effect transistors (n-MOSFETs) under cryogenic operation. The fluctuation of the drain current increased with decreasing temperature, exhibiting LF 1/ $f$ noise of more than two orders of magnitude higher at 2.5 K compared with that at 300 K. As revealed by the temperature dependence of the normalized current spectral density, the LF 1/ $f$ noise at 2.5 K is primarily governed by carrier number fluctuations. To obtain insight into the carrier trapping centers under cryogenic operation, we investigate the effect of oxide/Si interface states on the LF 1/ $f$ noise by utilizing Si n-MOSFETs with different surface orientations, i.e., different interface trap densities ( $\text{D}_{\mathrm {it}}$ ). The LF 1/ $f$ noise is comparable between the surface orientations at 300 K, whereas excess noise was observed at 2.5 K for the surface orientation with higher $\text{D}_{\mathrm {it}}$ in the order of (100)< (120) $\le $ (110)-orientations. This indicates that the LF 1/ $f$ noise at cryogenic temperatures originates from oxide/Si interface defects and disorders, that is, the interface states and band tail states. These states are localized at the conduction-band edge, which contributes to noise generation as the Fermi level approaches the conduction-band edge at cryogenic temperatures. This study demonstrates the significance of the oxide/Si interface quality in suppressing the LF 1/ ${f}$ noise in Si MOS devices operated at cryogenic temperatures.

AISI 316H stainless steel, which is a type of cryogenic temperature steel, has excellent potential in the cryogenic engineering field. However, its performance at cryogenic temperatures, especially its mechanical properties, has not been adequately investigated. This study investigates the quasi-static mechanical behavior and strengthening mechanism of 316H at cryogenic temperatures using uniaxial tensile testing. The dynamic mechanical behavior and strengthening mechanism were initially investigated at different temperatures and strain rates using the Split-Hopkinson pressure bar (SHPB) test. During quasi-static deformation at decreasing temperatures, the yield strength and tensile strength increased significantly and the elongation decreased. Additionally, martensitic transformation was observed at temperatures below −120 °C, which is the main cryogenic temperature strengthening mechanism. During the SHPB test, the flow stress increased as the temperature and strain rate decreased and increased, respectively. The strain rate and temperature sensitivity factors were negatively correlated with temperature, and the cryogenic temperature had a significant strengthening effect. A modified Johnson-Cook constitutive model, which considers the effect of cryogenic temperatures, was established to describe the mechanical properties of 316H over a wide range of temperatures and strain rates.

In this paper, micro harmonic vibration was applied to the typical titanium alloys to clarify their damping performance at cryogenic temperatures. The effects of vibration modulus at different frequencies were elaborately analyzed, and the crack propagation mechanism was discussed. The increase of internal dislocations improves the damping performance and eventually leads to interface cracking, which is positively correlated with frequency. More importantly, dislocations of β phase aggregated at the interface, leading to interface cracks and transgranular fractures by stress concentration. Whereas, dislocations in the α phase are first activated and then glide toward the boundary to cause cracking, resulting in intergranular fracture. During harmonic vibration at 0∼−60 °C with 200 Hz, the crack propagation of α phase always has a hysteresis behavior compared with that of β phase. When ΔK = 0.137 MPa m1/2 (−60 °C, 200 Hz), the second crack tip of β phase is deflected in different directions, leading to higher harmonic vibration energy is consumption. As a result, the crack growth rate slows down and the damping performance reaches its peak. This contribution is expected to provide experimental data and theoretical support for the vibration damping behavior of typical titanium alloys at cryogenic temperature.

In this study, the CrCoNi medium-entropy alloys (MEA) were processed by asymmetric rolling (298 K) and asymmetric cryorolling (ACR) (173 K and 83 K), respectively. During the rolling process, as the strain increased (from 50% to 80% reduction), the dislocation distribution inhomogeneity intensified. Meanwhile, the variation of twinning in different systems was more prominent. The cryogenic temperature promoted the inhomogeneity of the structure in the CrCoNi MEA, allowing dislocation cells and dislocation tangling zones to generate at lower strains. And the twinning susceptibility to temperature was more notable than that to strain. Secondary twins, and high-density stacking faults were found in the 173 K ACR CrCoNi MEA at low strain. And tertiary twins were found in the 83 K ACR CrCoNi MEA. It can be found from the experimental results that the improvement effect of the cryogenic environment during rolling on the mechanical properties of the CrCoNi MEA was greater than that of the increase in reduction (50%–80%). Asymmetric cryorolling shows a more efficient strengthening influence on CrCoNi MEA subjected to smaller deformation.

Photodetectors that can operate over a wide range of temperatures, from cryogenic to elevated temperatures, are crucial for a variety of modern scientific fields, including aerospace, high-energy science, and astro-particle science. In this study, we investigate the temperature-dependent photodetection properties of titanium trisulfide (TiS3)- in order to develop high-performance photodetectors that can operate across a wide range of temperatures (77 K–543 K). We fabricate a solid-state photodetector using the dielectrophoresis technique, which demonstrates a quick response (response/recovery time ~0.093 s) and high performance over a wide range of temperatures. Specifically, the photodetector exhibits a very high photocurrent (6.95 × 10−5 A), photoresponsivity (1.624 × 108 A/W), quantum efficiency (3.3 × 108 A/W·nm), and detectivity (4.328 × 1015 Jones) for a 617 nm wavelength of light with a very weak intensity (~1.0 × 10−5 W/cm2). The developed photodetector also shows a very high device ON/OFF ratio (~32). Prior to fabrication, the TiS3 nanoribbons were synthesized using the chemical vapor technique and characterized according to their morphology, structure, stability, and electronic and optoelectronic properties; this was performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and a UV–Visible–NIR spectrophotometer. We anticipate that this novel solid-state photodetector will have broad applications in modern optoelectronic devices. [ABSTRACT FROM AUTHOR]

The magnetic spectrometer AMS-100, which includes a superconducting coil, is designed to measure cosmic rays and detect cosmic antimatter in space. This extreme environment requires a suitable sensing solution to monitor critical changes in the structure such as the beginning of a quench in the superconducting coil. Rayleigh-scattering-based distributed optical fibre sensors (DOFS) fulfil the high requirements for these extreme conditions but require precise calibration of the temperature and strain coefficients of the optical fibre. Therefore, the fibre-dependent strain and temperature coefficients K T and K ϵ for the temperature range from 77 K to 353 K were investigated in this study. The fibre was integrated into an aluminium tensile test sample with well-calibrated strain gauges to determine the fibre's K ϵ independently of its Young's modulus. Simulations were used to validate that the strain caused by changes in temperature or mechanical conditions was the same in the optical fibre as in the aluminium test sample. The results indicated a linear temperature dependence of K ϵ and a non-linear temperature dependence of K T . With the parameters presented in this work, it was possible to accurately determine the strain or temperature of an aluminium structure over the entire temperature range from 77 K to 353 K using the DOFS. [ABSTRACT FROM AUTHOR]

A Tm,Ho:YAP laser at cryogenic temperature is demonstrated for the first time with simultaneous emission at 2000 nm and 2119 nm. The feasibility of switching wavelength and achieving balanced output powers at two widely separated wavelengths has been confirmed by investigating the temperature dependence of the laser spectra. The optimal temperature for balanced output evidently diminishes as the pump power density increases, thereby manifesting a rate of change quantified at 1.19 K/W. At the optimal temperature of 43.1 K, the optical-to-optical conversion efficiency of the Tm,Ho:YAP simultaneous dual-wavelength laser (SDWL) with a pump power of 11.8 W is 12.7%, corresponding to a slope efficiency of 15.8%. [ABSTRACT FROM AUTHOR]

The quest for widespread applications especially in extreme environments accentuates the necessity to design materials with robust mechanical and thermodynamic stabilities. Almost all existing materials yield temperature-variant mechanical properties, essentially determined by their different atomic bonding regimes. In general, weak non-covalent interactions are considered to diminish the structural anti-destabilization of covalent crystals despite the toughening effect. Whereas, starting from multiscale theoretical modeling, we herein reveal an anomalous stabilizing effect in cellulose nanocrystals (CNCs) by the cooperation between the non-covalent hydrogen bonds and covalent glucosidic skeleton, namely molecular levers (MLs). It is surprising to find that the hydrogen bonds in MLs behave like covalent bindings under cryogenic conditions, which provide anomalously enhanced strength and toughness for CNCs. Thermodynamic analyses demonstrate that the unique dynamical mechanical behaviors from ambient to deep cryogenic temperatures are synergetic results of the intrinsic temperature dependence veiled in MLs and the overall thermo-induced CNC destabilization/amorphization. As the consequence, the variation trend of mechanical strength exhibits a bilinear temperature dependence with ∼ 77 K as the turning point. Our underlying investigations not only establish the bottom—up interrelations from the hydrogen bonding thermodynamics to the crystal-scale mechanical properties, but also facilitate the potential application of cellulose-based materials at extremely low temperatures such as those in outer space. [ABSTRACT FROM AUTHOR]

The 2195 aluminum alloy is widely used in cryogenic storage tanks for space vehicles, where it can reach a temperature of 20 K. In order to explore the reasons for the increased strength of 2195 aluminum alloys at cryogenic temperatures, uniaxial tensile tests were conducted in the range of 20 K–298 K. Tensile fracture was observed. In addition, the microstructures under different temperatures were observed using EBSD (electron back-scattered diffraction) and TEM (transmission electron microscopy) techniques, and the dislocation density of the material was quantitatively characterized using the modified Williamsone–Hall method based on XRD (X-ray diffraction) analysis. The results indicated that the ultimate strength increased at an increasing rate with the temperature decrease, while the elongation increase was insignificant. The fracture's surface exhibited that dimple characteristics seemed to be unapparent while the quantity of tearing ridges was enhanced by the temperature decrease. Meanwhile, the fracture mode changed from ductile to brittle fracture. The microdeformation degree revealed by KAM images showed an aggravating trend, and the deformation tended to be more uniform. The increasingly enhanced dislocation density quantitatively revealed by the modified Williamsone–Hall method also proved this and that the increase in dislocations had a similar trend to that of tensile strength, which was furtherly revealed by TEM images. This indicated that the more regions are involved in deformation, the more dislocations are generated in the material during deformation, resulting in an increase in strength at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

In deep space exploration the exploration equipment will inevitably experience the harsh environment of cryogenic temperature. Solder joints belong to the most vulnerable parts of electronic equipment, and the harsh environment of extreme cryogenic temperature will seriously threaten the reliability of solder joints. In this paper, Sn3.0Ag0.5Cu/Cu solder joints were prepared and stored at cryogenic temperatures (−50 °C, −100 °C, and −196 °C) for up to 960 h, whilst studying the microstructural evolution and deterioration of shear properties. The results showed that the influence of cryogenic temperature on microstructure deterioration was greater than that of storage time. With the decrease of storage temperature and the extension of storage time, the Ag3Sn intermetallic compounds (IMCs) were uniformly dispersed in the β-Sn matrix; the size decreased and the number increased. After being stored at −196 °C for 960 h, some microcracks appeared at the interface of the solder joints. Meanwhile, the shear force of the solder joints was reduced by 19.02%, and the fracture mode changed from ductile fracture to ductile–brittle mixed fracture. Therefore, it is of great scientific significance to reveal the microstructural evolution and deterioration of shear properties of the solder joints under long-term storage at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

We propose coating side-polished optical fiber (SPF) with epoxy polymer to form a fiber-optic sensor for cryogenic temperature measuring applications. The thermo-optic effect of the epoxy polymer coating layer enhances the interaction between the SPF evanescent field and surrounding medium, considerably improving the temperature sensitivity and robustness of the sensor head in a very low-temperature environment. In tests, due to the evanescent field–polymer coating interlinkage, transmitted optical intensity variation of 5 dB and an average sensitivity of − 0.024 dB/K were obtained in the 90–298 K range. [ABSTRACT FROM AUTHOR]

Non‐contact ratiometric luminescence thermometry continues to gain popularity over decades due to its fascinating features of high accuracy, fast response, and simplicity. In this regard, rational design of optical thermometers with ultrahigh relative sensitivity and low temperature resolution has become a cutting‐edge topic. Herein, a luminescence intensity ratio thermometric method depending on the emission line at 698 nm (peak 1) and the emission bands at 713 and 721 nm (peaks 2 and 3) of Li1.97Zn1.0292Ge3O8:0.08%Cr3+ is proposed. As temperature elevates from 50 to 300 K, the 698 nm emission line undergoes an 84‐fold increase while the 713 and 721 nm emission bands show the opposite decline trend. This fascinating feature enables high relative sensitivity of 13.09% K−1 and low temperature resolution of 0.032 K, which are superior to most of the reported optical thermometers. This work is expected to provide more insights for designing excellent and reliable optical thermometers by employing Cr3+ activated luminescent materials. [ABSTRACT FROM AUTHOR]

Developing novel optical thermometry with ultrahigh relative sensitivity and temperature resolution has become a cutting-edge topic. For this purpose, under obeying Boltzmann distribution, a series of Li 2 Zn 0.9992-x A x Ge 3-y B y O 8 :0.08% Cr3+ (B= Sc3+, In3+, A = Si4+) phosphors were studied, which the luminescence intensity ratio between the transition of 4T 2g →4A 2g emission and the R line based on thermally coupled energy levels constitutes a temperature sensing work with a relative sensitivity of 9.46% K−1, 9.73% K−1, and 10.38% K−1, respectively. It is worth mentioning that the luminescence intensity of the R line (peak 1) increases significantly with the increase of temperature, while the transition of 4T 2g →4A 2g (peak 2) with high intensity at low temperature gradually quenching, and this opposite trend is an important advantage for the design of excellent thermometers. Compared the best relative sensitivity of Li 2 Zn 0.9992-x A x Ge 3-y B y O 8 :0.08%Cr3+ (B= Sc3+, In3+, A = Si4+) with the crystal field Dq /B, it can be concluded that relative sensitivity increasing gradually with decreasing the intensity of crystal field. Finally, by testing the stability of the sample at 50 K, a thermal resolution of 0.082 K, 0.080 K and 0.077 K was obtained, respectively, which is one of the best thermal resolutions so far, while the repeatability of the sample stability at 50 K and 300 K cycles was higher than 99%. Our work is expected to provide guiding insights for optimizing the sensitivity of Cr3+-based luminescence intensity ratio thermometers. [Display omitted] [ABSTRACT FROM AUTHOR]

The rising demand for liquefied natural gas (LNG)-fueled ships requires the LNG bunkering facility that partially uses a ship-to-ship operation. The bunkering process of LNG fuel may have a greater risk due to LNG volatility. The cryogenic temperature of LNG poses a threat to the personnel and structural embrittlement to ships. Therefore, cryogenic spill protection optimization was introduced concerning the structural strength analysis using finite element (FE) by utilizing cryogenic temperature loads provided by the computational fluid dynamics (CFD) model of an LNG release. This study aims to build a platform for transferring the temperature load profile from CFD to FE software accurately. The CFD model usually uses a structured Cartesian grid, and the FE method adopts an unstructured tetrahedral or hexahedral mesh. As a result, both configurations store results at different positions, and it is not preferred for the load profile to be transferred directly. The error will be greater due to the variance of positions. Random Forest, a machine learning method, has been employed that uses a regression technique to deal with a continuous variable. An accurate load profile for the FE model can be obtained by adopting decision tree learning in Random Forest. The procedure for determining the temperature load profile is presented in this article.

Thermal, thermo-mechanical and mechanical properties of four different commercially available polyetheretherketones (PEEK) based materials were investigated. PEEK matrix was either modified and/or reinforced with carbon fibres, graphite and/or PTFE. Impact strength was measured at three different temperatures: 25 °C, −100 °C, and −195 °C. At 25 °C, thermal stability and mechanical properties, including the elastic modulus, compression, and impact strength, were enhanced with the addition of carbon fibres. Matrix modification had a minor impact on thermal stability, while the mechanical properties decreased, except for impact strength. At −100 °C, the mechanical properties of the neat polymers were improved, including increased impact strength by 20% compared to values at 25 °C. Addition of fillers hindered the rise of impact strength due to complex mechanisms caused by different coefficients of thermal expansion of reinforcements and matrix. At −195 °C, the significant increase of impact strength was revealed for unmodified PEEK reaching 30 times higher values than at 25 °C, while matrix modification suppressed the rise of impact strength. The scratch test indicated the superior behaviour of unfilled PEEK during the tested load range (up to 15 N), while the effect of the fillers was observed at much lower load threshold of 7 N.

The influence of Laser shock peening without coating at a cryogenic temperature (CLPwC) on SS 304 alloy was investigated. Three different laser energies, such as 150 mJ, 300 mJ, and 450 mJ were chosen to investigate the effects of CLPwC in SS 304 steel. The impact of CLPwC on the residual stress, surface roughness, hardness, phase transformation and microstructural changes was studied. The XRD studies show the peak broadening and strain-induced martensite (γ→α′) of 36.3% after CLPwC at 9 GW cm−2. The work-hardening effect was observed up to 300–400 μm depth from the peened surface. The microhardness could effectively increase to 309.43 HV at 9 GW cm−2 when it compared to unpeened hardness (192.1 HV). Relaxation of compressive residual stress at cryogenic temperature was distinguished, and the maximum compressive stress of −138 MPa was obtained at 50 μm from the surface. Microstructural studies were carried out by different techniques such as EBSD and TEM. An increase in low angle grain boundary fraction (43%) and grain size reduction was observed using EBSD after CLPwC. The TEM investigations revealed deformation twins (width of 6–70 nm), shear bands, stacking faults, and martensitic phase. Strain induced martensitic phase is witnessed in XRD, EBSD, TEM studies.

In this study, ZnTe crystal was applied to provide precise thermal sensing for cryogenic temperatures. Multiple techniques, namely Raman and photoluminescence spectroscopies, were used to broaden the operating temperature range and improve the reliability of the proposed thermometers. Raman-based temperature sensing could be applied in the range of 20–100 K, while luminescence-based thermometry could be utilized in a narrower range of 20–70 K. However, the latter strategy provides better relative thermal sensitivity and temperature resolution. The best thermal performances based on a single temperature-dependent parameter attain Sr = 3.82% K−1 and ΔT = 0.12 K at T = 50 K. The synergy between multiple linear regression and multiparametric thermal sensing demonstrated for Raman-based thermometry results in a ten-fold improvement of Sr and a two-fold enhancement of ΔT. All studies performed testify that the ZnTe crystal is a promising multimode contactless optical sensor for cryogenic thermometry. [ABSTRACT FROM AUTHOR]

In this paper, the detailed photophysical properties of two phosphorescent salts, [Ir(ptpy)2(4,4′-Cl2bpy)]PF6, 1, and [Ir(4-Clppy)2(4,4′-Cl2bpy)]PF6, 2, where ptpy = 2-(p-tolyl) pyridinato; 4,4′-Cl2bpy = 4,4′-dichloro-2,2′-bipyridine, and 4-Clppy = 4-chloro-2-phenylpyridinato) have been studied in CH2Cl2 and PS (polystyrene) film at 77–300 K and in PMMA (polymethyl methacrylate) film in the temperature range of 1.5–300 K. The decay curves are monoexponential in the whole range. Temperature versus the decay time plots in PMMA for complexes display two distinct ranges, one at low temperature (T ≤ 77 K) with ФPL ≈ 100% that corresponds to thermal distribution between the triplet substates, and the other at higher temperatures (T > 77 K) in which the decay time reaches a plateau and the ФPL starts to decrease and amounts to ФPL = 35% and 60% for complexes 1 and 2, respectively, at room temperature. Applying the three-level equation in the first part gives the values of τ(I) = 110 μs, τ(II) = 10.5 μs, τ(III) = 342 ns for complex 1 and τ(I) = 142 μs, τ(II) = 11 μs, τ(III) = 353 ns for complex 2. Obtained zero-field splitting of 105 and 110 cm−1 of T1 state of complexes 1 and 2, respectively, can be assigned to be largely of 3MLCT character of this state. For the second part (T > 77 K) with the contribution of the thermally activated decay processes, we add two additional terms in Eq. (1) to get the decay rate k(Q) = 7.2 × 106 s−1, ∆E(Q-I) = 304 cm−1 for 1 and k(Q) = 4.3 × 106 s−1 and ∆E(Q-I) = 638 cm−1 for 2 which proposed the active role of metal-centered (3MC) triplet excited states in the non-radiative deactivation pathways. [ABSTRACT FROM AUTHOR]

Basing our findings on our previous pulsed laser testing results, we have experimentally demonstrated that there is an inflection point of a single event transient (SET) in the silicon-germanium heterojunction bipolar transistors (SiGe HBTs) with a decreasing temperature from +20 °C to −180 °C. Additionally, the changes in the parasitic resistivity of the carrier collection pathway due to incomplete ionization could play a key role. In this paper, we found that the incident-heavy ion's parameters could also have an important impact on the SET inflection point by introducing the ion track structures generated by Geant4 simulation to the TCAD transient simulation. Heavy ion with a low linear energy transfer (LET) will not trigger the ion shunt effect of SiGe HBT and the inflection point will not occur until −200 °C. For high LET ions' incidence, the high-density electron-hole pairs (EHPs) could significantly affect the parasitic resistivity on the pathway and lead to an earlier inflection point. The present results and methods could provide a new reference for the effective evaluation of single-event effects in bipolar transistors and circuits at cryogenic temperatures and provide new evidence of the SiGe technology's potential for applications in extreme cryogenic environments. [ABSTRACT FROM AUTHOR]

Graphene-based micro/nanoscale materials have not been used much for thermal sensing while they have great potential advantages over current sensors for micro/nanoscale measurement. This work reports on the discovery of ultra thermal sensing capability, especially at cryogenic temperatures for graphene microfibers (GMFs). From 295 K down to 11 K, the electrical resistance of GMF increases by around five orders of magnitude (105-fold). GMF's extreme thermal sensitivity is explored by using it for dynamically measuring its thermophysical properties. At 25 K, a temperature change as small as 0.027 K can be sensed with high confidence. Moreover, the fibers still have extreme sensitivity after current annealing. When the annealing temperature becomes higher, the microstructure of the material improves considerably, thereby ensuring application robustness in thermally hostile environment. GMF presents a novel ultra-sensitive material for temperature measurement at the micro/nanoscale, especially at cryogenic temperatures while its temporal response can reach a level of ms. This work reports on the discovery of ultra thermal sensing capability of GMFs, especially at cryogenic temperatures. From 295 K down to 11 K, the electrical resistance of GMF increases by around five orders of magnitude. At 25 K, a temperature change of 0.027 K can be sensed with high confidence. The GMFs still have extreme sensitivity after current annealing. [Display omitted] • Discovery of ultra thermal sensing capability of graphene microfibers (GMFs). • Around five orders of magnitude resistance change for GMFs from 295 K to 11 K. • A temperature change of 0.027 K can be sensed with high confidence at 25 K. • GMFs still retain extreme thermal sensitivity after current annealing. [ABSTRACT FROM AUTHOR]

Composite components' fabrication generates vast amounts of fiber wastes. This research suggests using short carbon fibers (SCFs) as secondary reinforcement in glass fiber reinforced polymer (GFRP) composite for cryogenic application. The SCFs (0.1, 0.3, and 0.5 wt%) were embedded in GFRP composites. Flexural test was performed to assess the integrity and durability of composites at in‐situ cryogenic temperature (CT), and after ex‐situ cryo‐aging in liquid nitrogen for various time intervals (0.25, 0.5, 1, 2, 4, 8, and 16 h). The composite with 0.1 wt% of SCFs showed the highest enhancement in flexural performance in all testing conditions, ∼16% at Room Temperature (RT), ∼12% at Cryogenic Temperature (CT, and between 13% and 39% after cryo‐aging. Composites with SCFs retained their strength at CT and after cryo‐aging, suggesting that the waste fibers could be economically reused and preferred over other expensive nanofillers as secondary reinforcements in GFRP composites for cryogenic applications. [ABSTRACT FROM AUTHOR]

Understanding the deformation-induced transformation-induced plasticity (TRIP) in high-entropy alloys (HEAs) is critical for obtaining desired mechanical properties. In this study, the deformation-induced phase transformation behavior of Fe55Co17.5Ni10Cr12.5Mo5 HEA was investigated by microstructural characterization using scanning electron microscopy-based techniques. The results showed the initiation of body-centered cubic (BCC) variants at the intersections of hexagonal close-packed (HCP) variants. The growth of BCC variants occurred through the HCP phase with a Burgers orientation relationship. Heterogeneous strain distributions at the phase boundaries also induced additional BCC variants with unusual crystallographic characteristics, although the growth of these BCC variants was inhibited. The TRIP behavior during a cryogenic-temperature tensile test of the Fe55Co17.5Ni10Cr12.5Mo5 alloy provided an extra strain-hardening rate by absorbing plastic deformation energy to initiate BCC and HCP variants and additional strain-hardening capability of the transformed BCC phase. Because of the extra strain-hardening rate, the Fe55Co17.5Ni10Cr12.5Mo5 alloy achieved an outstanding tensile strength (1.2 GPa) and ductility (0.81) combination at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

The performed investigations concerned the influence of degree and temperature of deformation on the microstructure and mechanical properties of metastable austenite in 304 stainless steel after its strain-induced martensitic transformation. Samples of steel strip were cold-rolled within the degree of deformation from 20% to 70% and stretched at room and cryogenic temperature. The microstructure was observed by means of a scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It has been found that in samples stretched at a temperature of -100 ℃ and -196 ℃ microstructure of the matrix displayed a considerable density of dislocations with lath areas of the martensite α' and precipitations of carbides M23C6. Fractographic examinations permitted to determine the influence of the deformation temperature on the character of the fracture of investigated steel obtained during the decohesion of samples in a tensile test at room and cryogenic temperature. After cold rolling and tensile test at room temperature the samples have transcrystalline ductile fracture. However, after the plastic deformation at cryogenic temperature, ductile facture with characteristic smooth areas with traces of plastic deformation of the surface and numerous craters were observed. [ABSTRACT FROM AUTHOR]

In this paper, we present an empirical model for the bulk electron mobility in Si as a function of doping and temperature, down to the cryogenic range. With regard to lattice scattering, we have proposed an empirical model for the lattice dilation energy as a function of doping, using the data extracted from experimental results of bulk electron mobility at higher temperatures and low doping levels. We have also developed a new model for the ionized impurity scattering time using a novel approach of combining the scattering cross-section and the carrier velocity into a single variable. Finally, the Matthiessen's rule was applied in order to obtain the net mobility. The results showed an excellent match with the experimental data reported in the literature over a wide range of temperature (20–400 K). Also, when compared to the results of some other classic models, with respect to the same set of experimental data, our results showed a much superior match, particularly in the cryogenic range. Finally, this model can be integrated easily to any of the empirical surface carrier mobility models for MOSFETs. [ABSTRACT FROM AUTHOR]

This study aims to investigate the low-velocity impact response of boron nitride nanoparticles (BNNPs) added carbon fiber reinforced pipes (CFRPs) at various temperature values. Carbon fiber/epoxy composite specimens with (±55°)3 winding angles were manufactured with the filament winding method. Low-velocity impact tests were performed with a 15 J energy level at five different temperatures between −196°C and 23°C ranges to understand the cryogenic environment effect on BNNP added carbon fiber reinforced tubes and neat carbon fiber reinforced tubes. The force-displacement and contact force-time graphs were attained in consequence of low-velocity impact tests. The damage areas, their size and characteristics were scrutinized both visually and with the aid of a Microscope. The test results showed that when ambiance temperatures decreased, the damage areas considerably increased both filled with BNNP and without BNNP filament wound carbon fiber reinforced tubes. [ABSTRACT FROM AUTHOR]

In this work, the numerical simulation of a SiGe heterojunction bipolar transistor (HBT) for DC and AC performance operating at cryogenic temperature with a hydrodynamic carrier transport model is analyzed. A new modified temperature-dependent Si1−xGex energy bandgap model was used. Using a simplified 2D TCAD design structure, the device characteristics on 55 nm SiGe HBT technology and the mobility model are calibrated with experimental data. Base current reversal due to induced impact-ionization at the collector-base junction is analyzed, where the estimated collector-emitter breakdown voltage with the base open (BVCEO) is 1.48 V at 300 K. This reveals good voltage handling ability. At cryogenic temperatures, dopant incomplete ionization in the lightly doped collector region shows a 28% decrease in ionized dopant concentration at 50 K; this affects the base-collector depletion capacitance. The emitter electron barrier tunneling leakage on collector current is studied using a non-local e-barrier tunneling model at different temperatures that shows an improvement in peak DC gain at lower temperatures. Using the small-signal ac analysis, the cut-off frequency and the maximum oscillation frequency are extracted for high-frequency application, and the base widening effect is discussed. A comparison of this work with measured data on 90 nm SiGe HBT is also discussed in brief, which shows improvements in the simulated structure. [ABSTRACT FROM AUTHOR]

In this study, the tribological properties of drawn PTFE were tested on a CSM tribometer at room temperature and cryogenic temperature. The orientation degree and worn surface morphology of drawn PTFE were studied and correlated with the friction and wear behaviors. It was found that the sample with low friction coefficient corresponded to high orientation degree in the parallel direction at room temperature, while the friction coefficient barely changed with increasing draw ratio in the perpendicular direction. The friction coefficient of drawn PTFE at liquid nitrogen temperature is higher than that at room temperature in the perpendicular direction, while the two values are almost undistinguishable within error range in the parallel direction. The wear volume of drawn PTFE at liquid nitrogen temperature is lower than that at room temperature in both perpendicular and parallel directions due to the mitigation of adhesive wear of drawn PTFE under liquid nitrogen temperature. [ABSTRACT FROM AUTHOR]

Ultrasonic velocity and attenuation measurements of a commercially available Ni-rich polycrystalline Ni–Ti alloy were simultaneously obtained upon cooling from room temperature (RT) down to 130 K. The anelastic spectra show multiple anomalies in both velocity and attenuation curves, which evidence a complex nature of structural rearrangements exhibited by Ni–Ti alloy, associated with relaxations and phase transformations. In particular, some evident anomalies at 285 and 180 K, not previously exploited using ultrasonic measurements on Ni-rich polycrystalline Ni–Ti alloy, were associated with austenite to pre-martensitic (B2 → R) and pre-martensitic to martensitic (R → B19’) phase transitions, respectively. The peculiar temperature separation between these transformations was interpreted based on chemical composition and the Ni–Ti alloy microstructure evolution. X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were also used to add complementary results about phase transformations and thermal events exhibited by Ni–Ti alloy at low temperatures. XRD, Rietveld refinement, SEM and transmission electron microscopy (TEM) analyses confirm the coexistence of the austenite B2, martensite B19’, and Ni4Ti3 phases at RT. DSC measurements indicated reversible two-stage martensitic transitions involving B2 ↔ R ↔ B19’ phase transformations at similar temperatures than the observed from ultrasonic anomalies. Besides that, several anelastic relaxation events identified around the phase transitions reveal the occurrence of complex physical mechanisms, such as accommodation of the twinned R-phase and martensite domain walls, twinning boundaries mobility, and the coupling between stress-induced dislocation motion and interstitial diffusion, not reported simultaneously in the literature. The ferroelastic nature of martensite and pre-martensite phase transformations was confirmed for a commercially available Ni-rich polycrystalline Ni–Ti alloy studied in this work.

Green composite cementitious materials based on low carbon requirements have broad application potential in the field of cryogenic engineering and construction. In this study, the stability of various composite cementitious materials at cryogenic temperatures (-165°C) was evaluated. The macromechanical behavior of the relative compressive strength of four hardened slurries with different deterioration degrees caused by cryogenic treatment was investigated. X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and 29Si magic-angle spinning nuclear magnetic resonance (29Si MAS NMR) spectroscopy were used to analyze the structural stability of the hydration products after the cryogenic treatment. Results indicate the compressive strength of the hardened paste at −165°C decreased to varying degrees compared to the peak strength, even under drying conditions, and the magnitude of the strength reduction decreased as the amount of supplemental cementitious materials (SCMs) increased. The hydration products of the hardened cement paste with a large dose of SCMs exhibited excellent stability at −165°C, and the increase in Ca2+ and bound water in the hydration products was positively correlated with the Ca/Si ratio after cryogenic treatment, as determined by quantitative XRD and TGA analyses and also substantiated by FTIR. Via the experimental and deconvolution results of 29Si MAS NMR, the mean chain lengths (MCLs) gradually decreased with increasing Ca/Si ratios at ambient temperature. Furthermore, after exposure to cryogenic temperatures, the low-Ca/Si silicate chains slightly aggregate owing to cryogenic treatment, and cryogenic temperatures can increase the susceptibility to disaggregation of low-Al or Al-free silicate chain structures. When Ca/Si >1.5, Q2 (1Al) was more easily fractured, and the fracture of the silicate chain was likely the essential reason for the Ca2+ spillover at cryogenic temperatures. Al incorporation effectively inhibited the decalcification of the hydration products, and its incorporation was related to the SCMs dosage. Therefore, the use of a large admixture of SCMs as concrete materials for AC-LNG tanks is likely preferable. • the stability of various composite cementitious materials at −165°C was evaluated. • Ca2+ increased after cryogenic treatment and were positively correlated with Ca/Si. • the low-Ca/Si system of slurries had excellent stability at cryogenic temperatures. • Al could decrease the disaggregation of silicate chain after cryogenic treatment. • a large dose of SCMs in concrete provides an improved option for AC-LNG tanks. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of 35Co-34Cr-24Ni-7Mo medium entropy alloy, known as MP35N, were investigated at different cryogenic temperatures (77 K and 195 K) and compared with those at room temperature (295 K). The microstructural features at the mentioned three distinct temperatures were characterized by X-Ray diffraction, electron back skater diffraction analysis and transmission electron microscopy. It was found that, compared to room temperature, cryogenic temperatures significantly increased the yield strength and tensile strength from 330 MPa and 1300 MPa at 295 K to 711 MPa and 1890 MPa at 77 K, respectively, without a noticeable change in elongation. Microstructural investigation revealed that lower deformation temperatures resulted in higher dislocation density, higher stacking fault probability, more mechanical twins, and a more homogeneous dislocation structure. Up to a strain of 0.4, no sign of fcc to hcp phase transformation was observed in EBSD, TEM images, or SAED patterns, even at 77 K. The higher work hardening due to mechanical twinning, increased dislocation density, and lower stacking fault energy, in addition to a more homogeneous dislocation structure, postponed the formation of geometric instabilities and maintained a ductile fracture mechanism at cryogenic temperatures. • Remarkable strength, toughness, and homogenous plasticity at cryogenic temperatures. • Higher dislocation density with more uniformly distribution at cryogenic temperatures. • The pronounced role of twinning as the second deformation mechanism at cryogenic temperatures. • No hcp phase generated from the strain-induced transformation of fcc at cryogenic temperatures. [ABSTRACT FROM AUTHOR]