Smaller Cell Volume Research Articles

An efficient low cost means of biophysical gene transfection in primary cells

Efficient, facile gene modification of cells has become an indispensable part of modern molecular biology. For the majority of cell lines and several primary populations, such modifications can be readily performed through a variety of methods. However, many primary cell lines such as stem cells frequently suffer from poor transfection efficiency. Though several physical approaches have been introduced to circumvent these issues, they often require expensive/specialized equipment and/or consumables, utilize substantial cell numbers and often still suffer from poor efficiency. Viral methods are capable of transducing difficult cellular populations, however such methods can be time consuming for large arrays of gene targets, present biohazard concerns, and result in expression of viral proteins; issues of concern for certain experimental approaches. We report here a widely applicable, low-cost (< $100 CAD) method of electroporation, applicable to small (1–10 μl) cell volumes and composed of equipment readily available to the average investigator. Using this system we observe a sixfold increase in transfection efficiency in embryonic stem cell lines compared to commercial devices. Due to efficiency gains and reductions in volume and applied voltage, this process improves the survival of sensitive stem cell populations while reducing reagent requirements for protocols such as Cas9/gRNAs transfections.

Electrophysiology of fluoride channels in the yeasts Saccharomyces cerevisiae and Candida albicans.

Tight regulation of molecules moving through the cell membrane is particularly important for free-living microorganisms because of their small cell volumes and frequent changes in the chemical composition of the extracellular environment. This is true for nutrients, but even more so for toxic molecules. Traditionally, the transport of these diverse molecules in microorganisms has been studied on cell populations rather than on single cells, mainly because of technical difficulties. The goal of this chapter is to make available a detailed method to prepare yeast spheroplasts to study the movement of fluoride ions across the plasma membrane of single cells by the patch-clamp technique. In this procedure, three steps are critical to achieve high resistance (GΩ) seals between the membrane and the glass electrode: (1) appropriate removal of the cell wall by enzymatic treatment; (2) balance between the osmotic strength of sealing solutions and cell membrane turgor; and (3) meticulous morphological inspection of spheroplasts suitable for gigaseal formation. We show now that this method, originally developed for Saccharomyces cerevisiae, can also be applied to Candida albicans, an opportunistic human pathogen.

A-site deficient perovskite lithium praseodymium titanate as a high-rate anode for lithium-ion batteries

On account of the low operating potential and slow electrochemical kinetics, graphite anode suffers from poor rate performance and severe safety problems in lithium-ion batteries (LIBs). Therefore, it’s urgent to find alternatives. Due to the abundant intrinsic vacancies and ion migration channels, A-site deficient perovskites could be used as not only solid state electrolytes (SSEs), but also anodes for LIBs. Here, Li0.38Pr0.54TiO3 is firstly demonstrated as a high-rate anode material without any additional modification. With an average operating potential of 0.76 V vs. Li+/Li, the Li0.38Pr0.54TiO3 anode possesses a high specific capacity of 217 mAh g−1 at 0.1C (1C = 200 mA g−1), impressive rate capability (124 mAh g−1 at 40C), and excellent cycling performance (96.75 % capacity retention over 2100 cycles at 10C). Through in-situ analysis and theoretical computations, we confirm the outstanding performance originates from small cell volume change (5.98 %), low band gap (2.57 eV), and low diffusion energy barrier (0.11 eV). The LiFePO4//Li0.38Pr0.54TiO3 full cell shows superior cycling stability (79.78 % capacity retention over 1000 cycles at 5C). Moreover, the relationship between A-site structure and electrochemical properties is discussed from the perspective of vacancy concentration. Our finding also provides a novel perspective for the discovery of high-performance oxide perovskite anodes.

Structural, in-situ Raman spectroscopy and XPS studies on ZrW2-xMoxO8 ceramics with tunable negative thermal expansion properties

This study presents an analysis of the characterization and crystal structure of a series of materials, namely ZrW2-xMoxO8 (0 ≦ x ≦ 1). The isotropic coefficient of thermal expansion of these materials exhibited a systematic and progressive approach from negative values to zero thermal expansion, which is dependent on the increasing value of x. The range of the linear coefficient of thermal expansion, αl, for the entire series was observed to be between −8.44 × 10−6/°C and approximately −4.0 × 10−6/°C. In-situ X-ray diffraction and In-situ Raman spectroscopy were used to study the different structures of ZrW2-xMoxO8 (0 ≦ x ≦ 1), elucidating the changing rule of the thermal expansion coefficient and the mechanism of the ordered-disordered phase transition. According to Rietveld refinement results, Mo doping causes a decrease in the lattice parameters of the entire system and slows down the transverse motion of the bridge oxygen atoms in the small cell volume, which reduces the negative thermal expansion. As the interaction between W (Mo) and a single coordination oxygen atom weakened, the phase transition temperature decreased. This is because the W(Mo)1O4 and W(Mo)2O4 polyhedron can be flipped more easily via the "ratchet" process due to the lower electronegativity of the Mo atom (2.16 Pauling) compared to that of the W atom (2.36 Pauling). Furthermore, the impact of Mo substitution for W sites on the electronic structure was initially reported through X-ray photoelectron spectroscopy.

An Image-Based Identification of Aggressive Breast Cancer Circulating Tumor Cell Subtypes.

Using previously established CTC lines from breast cancer patients, we identified different morphometric subgroups of CTCs with one of them having the highest tumorigenic potential in vivo despite the slowest cell proliferation in vitro. This subgroup represents 32% of all cells and contains cells with small cell volume, large nucleus to cell, dense nuclear areas to the nucleus, mitochondria to cell volume ratios and rough texture of cell membrane and termed "Small cell, Large mitochondria, Rough membrane" (SLR). RNA-seq analyses showed that the SLR group is enriched in pathways and cellular processes related to DNA replication, DNA repair and metabolism. SLR upregulated genes are associated with poor survival in patients with ER+ breast cancer based on the KM Plotter database. The high tumorigenic potential, slow proliferation, and enriched DNA replication/repair pathways suggest that the SLR subtype is associated with stemness properties. Our new findings provide a simple image-based identification of CTC subpopulations with elevated aggressiveness, which is expected to provide a more accurate prediction of patient survival and therapy response than total CTC numbers. The detection of morphometric and transcriptomic profiles related to the SLR subgroup of CTCs also opens opportunities for potential targeted cancer treatment.

O3-Type Na0.95Ni0.40Fe0.15Mn0.3Ti0.15O2 Cathode Materials with Enhanced Storage Stability for High-Energy Na-Ion Batteries.

O3-type layered oxides with high initial sodium content are promising cathode candidates for Na-ion batteries. However, affected by the undesired transition metal slab sliding and reaction with H2O/CO2, their further application is typically hindered by unsatisfactory cycling stability upon charging to high voltage and poor storage stability under humid air. Herein, we demonstrate a Fe/Ti cosubstitution strategy to simultaneously enhance the electrochemical performance and storage stability of pristine O3-NaNi0.5Mn0.5O2 cathode material, via employing high redox potential and inactive stabilized dopants. The resultant Fe/Ti cosubstituted Na0.95Ni0.40Fe0.15Mn0.3Ti0.15O2 undergoes highly reversible O3-P3-OP2 phase transitions with a small cell volume change of 2.8%, instead of complex O3-O'3-P3-P'3-P3'-O1 phase transitions in NaNi0.5Mn0.5O2. Consequently, the cathode displays a high specific capacity of 161.6 mAh g-1 with an average working voltage of 3.28 V and 81.8% capacity retention after 200 cycles at 5C. Furthermore, the cathode material remains very stable after exposure to air for 7 days and even after soaking in water for 1 h, owing to the prohibition of sodium losing by elevating redox potential and contracting sodium layer spacing. This work proposes an effective method to enhance the electrochemical performance and storage stability of O3-type layered oxide cathodes and promises advancing Na-ion batteries toward large-scale industrialization.

A New Candidate in Polyanionic Compounds for Potassium Ion Battery Anode: MXene Derived Carbon Coated π‐Ti2O(PO4)2

AbstractIntercalation‐type reaction that occurs in polyanion materials is considered to be a facile way to counter the mismatched relationship between the large K+ and compact host structure for potassium ion batteries (PIBs). However, the large “dead” weight and poor conductivity introduced by the polyanion framework severely limit the electrochemical performance of polyanion anodes. Herein, a new rigid K+ host of 1D π‐Ti2O(PO4)2 with carbon‐coated (TOP@C) is simply synthesized through a simple Ti3C2Tx‐derived method. The density functional theory (DFT) calculations and experimental results show that the potassium storage properties are unquestionably improved by the small cell volume change during cycling, the intercalation pseudo‐capacitance energy storage mechanism, and the large K‐storage tunnels with lower migration energy (0.23 eV) of TOP@C anode (134.5 mAh g‐1 after 2000 cycles at 1.0 A g‐1). The TOP@C//PTCDA full batteries, which clearly illustrate their promising application in advanced PIBs, successfully achieved a high energy density of 119.4 Wh kg‐1 and a power density up to 632.8 W kg‐1 with regard to the total mass of TOP@C and PTCDA.

High Entropy Enabling the Reversible Redox Reaction of V4+/V5+ Couple in NASICON‐Type Sodium Ion Cathode

AbstractNASICON‐type Na3VM(PO4)3 (M: transition metals) cathodes usually suffer from poor cycling stability in the voltage region of above 4 V versus Na+/Na owing to irreversible phase transition and severe structural distortion. Herein, the high entropy concept is extended to NASICONs and Na3VAl0.2Cr0.2Fe0.2In0.2Ga0.2(PO4)3 (NVMP) with high purity is obtained. The NVMP achieves a highly reversible specific capacity of 102 mAh g−1 (2.5–4.4 V vs Na+/Na) via the successive redox reaction of V3+/V4+/V5+ together with a long‐term lifespan of 5000 cycles at 20 C (a capacity retention of 86.8%). Even at an extreme temperature of −20 °C, the NVMP cathode can still provide excellent cycling performance (a capacity retention of 94.2% at 5 C after 1000 cycles). Moreover, the increased configurational entropy in the electrode renders a quite small cell volume change of 1.1%. The sodium ion storage mechanism containing solid solution‐type in the voltage range of 2.5–3.8 V and bi‐phasic in 3.8–4.4 V is revealed by ex situ XRD analysis. Pairing with a hard carbon anode, NVMP//HC cell offers a specific capacity of 81 mAh g−1 at 0.2 C based on the cathode mass. This high‐entropy engineering is expected to be widely applicable for the development of polyanionic electrode materials.

Investigation of thermal control in phase-changing ABO3 perovskites via first-principles predictions: general mechanism of emittance.

Phase-change thermal control has recently seen increased interest due to its significant potential for use in smart windows, building insulation, and optoelectronic devices in spacecraft. Tunable variation in infrared emittance can be achieved by thermally controlling the phase transitions of materials at different temperatures. A high emittance in the mid-infrared region is usually caused by resonant phonon vibrational modes. However, the fundamental mechanism of emittance variation during the phase-change process remains elusive. In this work, the electronic bandgaps, phononic structures, optical-spectrum properties, and formation energies of 76 kinds of phase-changing ABO3 perovskites were predicted based on first-principles calculations in the mid-infrared region. The variation in emittance between two phases of a single material was found to have an exponential correlation with the bandgap difference (R2 ∼ 0.92). Furthermore, a strong linear correlation (R2 ∼ 0.92) was found between the emittance variation and the formation-energy difference, and the emittance variation was also strongly correlated with the volume-distortion rate (R2 ∼ 0.90). Finally, it was concluded that a large lattice vibrational energy, a high formation energy, and a small cell volume are conducive to high emittance. This work provides a strong dataset for training machine-learning models, and it paves the way for further use of this novel methodology to seek efficient phase-change materials for thermal control.

The Lattice Distortion, Defect Evolution and Electrochemical Performance Improvement in Zn-VO2(B) Nanorods.

Cathode materials of energy storage batteries have attracted extensive attention because of the importance in deciding the rate performance and long cycle property of batteries. Herein, we report a simple and environmentally friendly solvothermal method to prepare Zn-doped VO2(B) cathode materials. The introduction of zinc ions can effectively regulate the lattice structure, surface morphology and internal defect state of Zn-VO2(B) nano materials. The sample with Zn content x = 1.5% has smaller cell volume and grain size, and higher concentration of vacancy defects. These microstructures ensure the structural stability during ion embedding process and, thus, this sample shows excellent electrochemical performances. The capacitance retention rate still maintains 88% after 1000 cycles at the current density of 0.1 A·g−1. The enhanced performances of Zn-doped VO2(B) samples may lay a foundation for the improvement of electrochemical performances of VO2(B) cathode materials for energy storage batteries in the future.

Rabi oscillation of spin-polarized rubidium in the spin-exchange relaxation-free regime.

The transient dynamics of atomic spins under oscillating and static magnetic fields have been studied in the spin-exchange relaxation-free (SERF) regime with a dual-beam configuration. The spin-relaxation rate can be accurately measured by detecting the transient response signal of the free induction decay (FID) process within several milliseconds. Leveraging this convenient method for measuring a large relaxation rate in a small cell volume, the dependence of the spin-relaxation rate on the probe intensity and ambient magnetic field was studied in the limit of low spin polarization. Moreover, by theoretical analysis of the dynamic evolution of the Rabi oscillation generated by a consecutive oscillating field and a small static magnetic field, we experimentally demonstrate that the amplitude of the Rabi oscillation is affected by the amplitude of the oscillating field in the SERF regime. According to the retrieved frequency of the FID signal and amplitude of relevant Rabi oscillation, the coil constants were 75.55 ± 0.78~nT/mA, 151.5 ± 0.9~nT/mA, and 116.6 ± 0.3~nT/mA along the x-, y-, and z-axes, respectively.

High-throughput single cell metabolomics and cellular heterogeneity exploration by inertial microfluidics coupled with pulsed electric field-induced electrospray ionization-high resolution mass spectrometry

Single cell metabolomics can obtain the metabolic profiles of individual cells and reveal cellular heterogeneity. However, high-throughput single-cell mass spectrometry (MS) analysis under physiological conditions remains a great challenge due to the presence of complex matrix and extremely small cell volumes. Herein, a serpentine channel microfluidic device which was designed to achieve continuous cell separation and inertial focusing, was coupled with a pulsed electric field-induced electrospray ionization-high resolution MS (PEF-ESI-HRMS) to achieve high-throughput single cell analysis. The pulsed square wave electric field was applied to realize on-line cell disruption and induce electrospray ionization. Single cells were analyzed under near-physiological conditions at a throughput of up to 80 cells min−1. More than 900 features were detected and approximately 120 metabolites were tentatively identified from a single cell. Further, by continually analyzing more than 3000 MCF7 and HepG2 cells, discrimination of different cancer cells based on their individual metabolic profiles was achieved by using the principal component analysis. The PEF-ESI-HRMS method was also applied for the analysis of single yeast cells, and more than 40 metabolites were annotated. This method is versatile and has good robustness, which is promising for high-throughput single cell metabolomics analysis.

Single‐Cell Metabolomics by Mass Spectrometry: Opportunities and Challenges

AbstractCellular heterogeneity is an inherent property of cell populations with a wide spectrum of biological manifestations, ranging from barely observable variations that enhance organismal adaptation, to life‐threatening differences. Single‐cell metabolomics can reveal molecular information and variations in metabolite concentrations between cells that are masked in cell‐population studies. These differences are quantitatively captured by the abundance distributions for the population and their statistical analysis can reveal the presence of latent subpopulations. In recent years, mass spectrometry (MS), combined with novel sampling and ionization techniques, has become an important tool for single‐cell metabolomics. These new techniques must contend with significant challenges in the form of small cell sizes and volumes, ultratrace metabolite amounts per cell, and potentially interfering high turnover rates and rapid diffusion. Owing to the ultrasmall sample volume, low abundance of some metabolites, and poor ionization efficiencies, metabolite detection, identification, and accurate quantitation remain a major challenge. The ability of some techniques to analyze tissue‐embedded cells opens the door for spatial metabolomics, potentially revealing cellular synergism in organ level metabolism. In this Concept article, we present a bird's eye view of these major themes in single cell metabolomics and some of the relevant MS‐based methods.

Aurantimicrobium photophilum sp. nov., a non-photosynthetic bacterium adjusting its metabolism to the diurnal light cycle and reclassification of Cryobacterium mesophilum as Terrimesophilobacter mesophilus gen. nov., comb. nov.

The aerobic primarily chemoorganotrophic actinobacterial strain MWH-Mo1T was isolated from a freshwater lake and is characterized by small cell lengths of less than 1 µm, small cell volumes of 0.05-0.06 µm3 (ultramicrobacterium), a small genome size of 1.75 Mbp and, at least for an actinobacterium, a low DNA G+C content of 54.6 mol%. Phylogenetic analyses based on concatenated amino acid sequences of 116 housekeeping genes suggested the type strain of Aurantimicrobium minutum affiliated with the family Microbacteriaceae as its closest described relative. Strain MWH-Mo1T shares with the type strain of that species a 16S rRNA gene sequence similarity of 99.6 % but the genomes of the two strains share an average nucleotide identity of only 79.3 %. Strain MWH-Mo1T is in many genomic, phenotypic and chemotaxonomic characteristics quite similar to the type strain of A. minutum. Previous intensive investigations revealed two unusual traits of strain MWH-Mo1T. Although the strain is not known to be phototrophic, the metabolism is adjusted to the diurnal light cycle by up- and down-regulation of genes in light and darkness. This results in faster growth in the presence of light. Additionally, a cell size-independent protection against predation by bacterivorous flagellates, most likely mediated by a proteinaceous cell surface structure, was demonstrated. For the previously intensively investigated aerobic chemoorganotrophic actinobacterial strain MWH-Mo1T (=CCUG 56426T=DSM 107758T), the establishment of the new species Aurantimicrobium photophilum sp. nov. is proposed.

Advanced Al2O3–SiC–SiO2–C refractories with B2O3 addition

This study investigates the effect of B2O3 addition (0.4 wt%, 0.8 wt%, 1.2 wt%, and 1.6 wt%) on the properties and microstructure of Al2O3–SiC–SiO2–C (ASSC) refractories. The results indicate that B2O3 plays an important role in accelerating mullite formation at low temperature. The substitution with Si by B in mullite crystal resulted in the formation of short and strong B–O bonds after firing at 1450 °C, causing the formation of boron-doped mullite with a smaller cell volume and leading to a decrease in the overall expansion of ASSC refractories. The addition of B2O3 to the ASSC refractories accelerated the growth of mullite along the direction parallel to the c axis, resulting in the improvement of mullite morphology (needle-like). The presence of in situ boron-doped mullite allowed the performance improvement of this class of refractory materials. The mechanical properties of the specimens improved significantly at various thermal-treatment temperatures. Moreover, the addition of B2O3 was beneficial for increasing the bulk density of the specimens, owing to the formation of a boron-rich liquid phase, which could accelerate sintering and densification. The optimal amount of B2O3 added in the specimens was <1.2 wt%, as above this value, an excessive liquid phase was formed, which degraded the high temperature performance.

Positional isomerism for strengthening intermolecular interactions: Toward monocyclic nitramino oxadiazoles with enhanced densities and energies

Development of high-density energetic materials has drawn considerable attention because the densities significantly affect their detonation performance. Herein, we propose an effective strategy based on positional isomerism for enhancing the densities of pre-existing energetic materials by optimizing their structures to reinforce intermolecular interactions. By applying this strategy, we design and synthesize 2-amino-5-nitramino-1,3,4-oxadiazole (2), a suitable isomer of 3-amino-5-nitramino-1,2,4-oxadiazole (1). This isomer is the first example of a monocyclic nitramino 1,3,4-oxadiazole reported to date. Single-crystal X-ray diffraction reveals that the isomer has a high crystal density (1.938 g cm−3 at 110 K), which is 0.083 g cm−3 greater than that of the original material (1, 1.855 g cm−3 at 110 K). Mechanistic studies confirmed that the isomer possesses stronger intermolecular hydrogen-bonding and π − π interactions, resulting in denser stacking, smaller cell volume, and thus, higher density. Remarkably, the isomer has a very short intermolecular hydrogen bond (1.956 Å), which is significantly shorter than that of 1 (2.133 Å) and other representative strongly hydrogen-bonded energetic materials such as 2,4,6-triamino-1,3,5-trinitrobenzene (TATB, 2.239 Å) and 1,1-diamino-2,2-dinitroethylene (FOX-7, 2.143 Å). Moreover, this strategy can be applied to its energetic salts. The higher densities of the isomer and its salts endow better detonation performance. Particularly, the detonation velocity of the isomer is more than 400 m s−1 higher than that of the original material (8668 m s−1 for 2 vs 8250 m s−1 for 1). Meanwhile, the hydroxylammonium salt 2b exhibits a high detonation velocity of 9087 m s−1, which is superior to that of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX).

Phase Transitions in the "Spinel-Layered" Li1+xNi0.5Mn1.5O4 (x = 0, 0.5, 1) Cathodes upon (De)lithiation Studied with Operando Synchrotron X-ray Powder Diffraction.

“Spinel-layered” Li1+xNi0.5Mn1.5O4 (x = 0, 0.5, 1) materials are considered as a cobalt-free alternative to currently used positive electrode (cathode) materials for Li-ion batteries. In this work, their electrochemical properties and corresponding phase transitions were studied by means of synchrotron X-ray powder diffraction (SXPD) in operando regime. Within the potential limit of 2.2–4.9 V vs. Li/Li+ LiNi0.5Mn1.5O4 with cubic spinel type structure demonstrates the capacity of 230 mAh·g−1 associated with three first-order phase transitions with significant total volume change of 8.1%. The Li2Ni0.5Mn1.5O4 material exhibits similar capacity value and subsequence of the phase transitions of the spinel phase, although the fraction of the spinel-type phase in this material does not exceed 30 wt.%. The main component of Li2Ni0.5Mn1.5O4 is Li-rich layered oxide Li(Li0.28Mn0.64Ni0.08)O2, which provides nearly half of the capacity with very small unit cell volume change of 0.7%. Lower mechanical stress associated with Li (de)intercalation provides better cycling stability of the spinel-layered complex materials and makes them more perspective for practical applications compared to the single-phase LiNi0.5Mn1.5O4 high-voltage cathode material.

Microstructure and Magnetic Properties of La-Ca-Co Substituted M-Type Sr-Hexaferrites with Controlled Si Diffusion

La-Ca-Co substituted M-type Sr-hexaferrites (Sr0.3Ca0.4La0.3Fe9.8Co0.2O19-δ) were prepared by a solid-state reaction using two different procedures, where the SiO2 additive was mixed either before calcination (pre-Si) or after calcination (post-Si). At the same sintering temperature, smaller cell volumes and reduced saturation magnetization (Ms) values were obtained for samples processed with the pre-Si method than those with the post-Si method. This implied that the pre-Si method resulted in a greater degree of Si substitution into the M-type lattice and increased Fe extrusion out of the lattice. The grain growth behavior was controlled by the SiO2 amount and sintering temperature. It was found that abnormal grains occur with a bimodal distribution in the 0.5 wt% SiO2 samples sintered at 1240 °C, due to the increased critical driving force for growth caused by an increased amount of SiO2 addition. The Ms and coercivity values were altered with the control of Si diffusion and abnormal grain growth. The control of the additive diffusion behavior is one of the important keys in the material design under same materials compositions.

Lipidomic profiling of single mammalian cells by infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI).

To better understand cell-to-cell heterogeneity, advanced analytical tools are in a growing demand for elucidating chemical compositions of each cell within a population. However, the progress of single-cell chemical analysis has been restrained by the limitations of small cell volumes and minute cellular concentrations. Here, we present a rapid and sensitive method for investigating the lipid profiles of isolated single cells using infrared matrix-assisted laser desorption electrospray ionization mass spectrometry (IR-MALDESI-MS). In this work, HeLa cells were dispersed onto a glass slide, and the cellular contents were ionized by IR-MALDESI and measured using a Q-Exactive HF-X mass spectrometer. Importantly, this approach does not require extraction and/or enrichment of analytes prior to MS analysis. Using this approach, 45 distinct lipid species, predominantly phospholipids, were detected and putatively annotated from the single HeLa cells. The proof-of-concept study demonstrates the feasibility and efficacy of IR-MALDESI-MS for rapid lipidomic profiling of single cells, which provides an important basis for future work on differentiation between normal and diseased cells at various developmental states, which can offer new insights into cellular metabolic pathways and pathological processes. Although not yet accomplished, we believe this approach can be readily used as an assessment tool to compare the number of identified species during source evolution and method optimization (intra-laboratory), and also disclose the complementary nature of different direct analytical approaches for the coverage of different types of endogenous analytes (inter-laboratory).Graphical abstract.

Estimating the in-operando stabilities of AlFe2B2-Based compounds for magnetic refrigeration

The in-operando stabilities of AlFe2B2-based (aka, 1-2-2) compounds were investigated by mimicking two separate operating conditions (immersion in a heat transfer fluid and magnetic field cycling) of an active magnetic regenerator (AMR) refrigerator. Parent AlFe2B2 and Ga-containing samples of nominal composition Al1.2-xGaxFe2B2 (x = 0, 0.05 and 0.1) were prepared by casting and subsequent annealing. The chemical stability of pulverized (Al,Ga)Fe2B2-based compounds subjected to water immersion at room temperature for up to 960 h was evaluated. In a separate test, the mechanical stability of dry (Al,Ga)Fe2B2 cast-disk-shaped samples was studied utilizing a device constructed to mimic the AMR field cycling process. The materials’ responses as a function of water-immersion time or of magnetic field cycles were assessed by probing the crystal structure, the microstructure, the magnetic characters and the magnetocaloric response as quantified by the magnetic entropy change ΔSmag. The water-immersed pulverized samples exhibit exponential-decay-like degradations in magnetization and in ΔSmag. The Ga-containing compound exhibits significantly smaller reductions in magnetization and in ΔSmag after 960 h of water immersion relative to those of the Ga-free composition. In the separate magnetic-field-cycling test conducted under a dry condition, the structural and the magnetocaloric responses of both the Ga-free and Ga-containing disks remain similar after ∼5 × 105 cycles in and out of a 0.5 T magnetic field. The decrease in the magnetocaloric response during water immersion is attributed to the formation of oxide and/or hydroxide phases that reduced the AlFe2B2 phase fraction. The stable structure and the constant magnetocaloric response observed after magnetic field cycling are attributed to the extremely small unit cell volume change of AlFe2B2 through its magnetic phase transition. Overall, these results demonstrate that the AlFe2B2-based compounds exhibit good chemical stability upon water immersion that is improved by small Ga additions, and robust mechanical integrity upon dry magnetic field cycling, suggesting that AlFe2B2-based compounds are promising as robust AMR magnetic refrigeration working materials.