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NASA NTRS1999

Directional Solidification of Pure Succinonitrile and a Succinonitrile-Acetone Alloy

An experimental study of the horizontal Bridgman growth of pure succinonitrile (SCN) and of a succinonitrile-1.0 mol.% acetone alloy (SCN-1.0 mol.% ACE) has been performed. Experiments involving both a stationary thermal field (no-growth case) and a translating thermal field (growth case) were conducted. Growth rates of 2 and 40 micrometers/s were investigated. For the pure SCN experiments, the velocity field in the melt was estimated using video images of seed particles in the melt. Observations of the seed particles indicate that a primary longitudinal convective cell is formed. The maximum velocity of two different particles which traveled along similar paths was the same and equal to 1.49 +/- 0.01 mm/s. The general accuracy of velocity measurements is estimated to be +/- 0.08 mm/s, though the data shows consistency to within +/- 0.02 mm/s. The shape of the solid/liquid interface was also quantitatively determined. The solid/liquid interface was stable (non-dendritic and non-cellular) but not flat; rather it was significantly distorted by the influence of convection in (he melt and, for the growth case, by the moving temperature boundary conditions along the ampoule. It was found that the interface shape and position were highly dependent on the alignment of the ampoule in the apparatus. Consequently, the ampoule was carefully aligned for all experiments. The values for front location agree with those determined in previous experiments. For the alloy experiments, the solid/liquid interface was determined to be unstable at growth rates greater than 2.8 micrometers/s, but stable for the cases of no-growth and growth at 2 micrometers/s. When compared to the shape of the pure SCN interface, the alloy interface forms closer to the cold zone, indicating that the melting temperature decreased due to the alloying element. Extensive temperature measurements were performed on the outside of the ampoule containing pure SCN. The resulting thermal profiles are presented in detail in the results section. It is intended that the interface shape, thermal boundary condition and velocity data presented in this paper be used to test numerical simulations.

Simpson, James E.↗

NASA NTRS2000

Directional Solidification of Pure Succinonitrile and a Succinonitrile-Acetone Alloy

An experimental study of the horizontal Bridgman growth of pure succinonitrile (SCN) and of a succinonitrile-1.0 mol% acetone alloy (SCN-1.0 mol.% ACE) has been performed. Experiments involving both a stationary thermal field (no-growth case) and a translating thermal field (growth case) were conducted. Growth rates of 2 and 40 micrometers/sec were investigated. For the pure SCN experiments, the velocity field in the melt was estimated using video images of seed particles in the melt. Observations of the seed particles indicate that a primary longitudinal convective cell is formed. The maximum velocity of two different particles which traveled along similar paths was the same and equal to 1.49 +/- 0.01 mm/s. The general accuracy of velocity measurements is estimated to be +/-0.08 mm/s, though the data shows consistency to within +/- 0.02 mm/s. The shape of the solid/liquid interface was also quantitatively determined. The solid/liquid interface was stable (non-dendritic and non-cellular) but not flat: rather it was significantly distorted by the influence of connection in the melt and, for the growth case, by the moving temperature boundary conditions along the ampoule. It was found that the interface shape and position were highly dependent on the alignment of the ampoule in the apparatus. Consequently, the ampoule was carefully aligned for all experiments. The values for front location agree with those determined in previous experiments. For the alloy experiments, the solid/liquid interface was determined to be unstable at growth rates greater than 2.8 micrometers/sec, but stable for the cases of no-growth and growth at 2 micrometers/sec. When compared to the shape of the pure SCN interface, the alloy interface forms closer to the cold zone, indicating that the melting temperature decreased due to the alloying element. Extensive temperature measurements were performed on the outside of the ampoule containing pure SCN. The resulting thermal profiles are presented in detail in the results section. It is intended that the interface shape, thermal boundary condition, and velocity data presented in this paper be used to test numerical simulations.

Simpson, James E.↗

NASA NTRS2012

Joining and Assembly of Bulk Metallic Glass Composites Through Capacitive Discharge

Bulk metallic glasses (BMGs), a class of amorphous metals defined as having a thickness greater than 1 mm, are being broadly investigated by NASA for use in spacecraft hardware. Their unique properties, attained from their non-crystalline structure, motivate several game-changing aerospace applications. BMGs have low melting temperatures so they can be cheaply and repeatedly cast into complex net shapes, such as mirrors or electronic casings. They are extremely strong and wear-resistant, which motivates their use in gears and bearings. Amorphous metal coatings are hard, corrosion-resistant, and have high reflectivity. BMG composites, reinforced with soft second phases, can be fabricated into energy-absorbing cellular panels for orbital debris shielding. One limitation of BMG materials is their inability to be welded, bonded, brazed, or fastened in a convenient method to form larger structures. Cellular structures (which can be classified as trusses, foams, honeycombs, egg boxes, etc.) are useful for many NASA, commercial, and military aerospace applications, including low-density paneling and shields. Although conventional cellular structures exhibit high specific strength, their porous structures make them challenging to fabricate. In particular, metal cellular structures are extremely difficult to fabricate due to their high processing temperatures. Aluminum honeycomb sandwich panels, for example, are used widely as spacecraft shields due to their low density and ease of fabrication, but suffer from low strength. A desirable metal cellular structure is one with high strength, combined with low density and simple fabrication. The thermoplastic joining process described here allows for the fabrication of monolithic BMG truss-like structures that are 90% porous and have no heat-affected zone, weld, bond, or braze. This is accomplished by welding the nodes of stacked BMG composite panels using a localized capacitor discharge, forming a single monolithic structure. This removes many complicated and costly fabrication steps. Moreover, the cellular structures detailed in this work are among the highest- strength and most energy-absorbent materials known. This implies that a fabricated structure made from these materials would have unequaled mechanical properties compared to other metal foams or trusses. The process works by taking advantage of the electrical properties of the matrix material in the metal-matrix composite, which in this case is a metallic glass. Due to the random nanoscale arrangement of atoms (without any grain boundaries), the matrix glass exhibits a near-constant electrical resistivity as a function of temperature. By placing the composite panels between two copper electrode plates and discharging a capacitor, the entire matrix of the panel can be heated to approximately 700 C in 10 milliseconds, which is above the alloy s solidus but below the liquidus. By designing the geometry of the panels into the shape of an egg box, the electrical discharge localizes only in the tips of each pyramidal cell. By applying a forging load during discharge, the nodes of the panels can be fused together into a single piece, which then dissipates heat through radiation back into a glassy state. This means that two panels can be metallurgically fused into one panel with no heat-affected zone, creating a seamless connection between panels. During the process, the soft metal particles (dendrites) that are uniformly distributed in the glassy matrix to increase the toughness are completely unaffected by the thermoplastic joining. The novelty is that a truss (or foam-like) structure can be formed with excellent energy- absorbing capabilities without the need for machining. The technique allows for large-scale fabrication of panels, well-suited for spacecraft shields or military vehicle door panels. Crystalline metal cellular structures cannot be fabricated using the thermoplastic joining technique described here. If metal panels were te assembled into a cellular structure, they would either have to be welded, brazed, bonded, or fastened together, creating a weak spot in the structure at each connection. Welded parts require a welding material to be added to the joint and exhibit a soft and weak heat-affected zone. Brazing and bonding do not form a metallurgical joint and thus exhibit low strengths, especially when the panels are pulled apart and fasteners require high-stress-concentration holes to be drilled. No equivalent rapid heating method exists for assembling metal panels together into cellular structures, and thus, those parts must be foamed, machined, or investment cast if they are to form a monolithic structure. If the crystalline panels were to be joined using capacitive discharge, as with a spot welder, their bond would be very weak, and the panels would have to be extremely thin. In contrast, the strength of joined BMG parts has been demonstrated to have strength comparable to the parent material. This technique opens up the possibility of using large-scale BMG hardware in spacecraft, military, or commercial applications.

Hofmann, Douglas C.↗

NASA NTRS1983

Process research of non-CZ silicon material

High risk, high payoff research areas associated with the Westinghouse process for producing photovoltaic modules using non- CZ sheet material were investigated. All work was performed using dendritic web silicon. The following tasks are discussed and associated technical results are given: (1) determining the technical feasibility of forming front and back junctions in non-CT silicon using dopant techniques; (2) determining the feasibility of forming a liquid applied diffusion mask to replace the more costly chemical vapor deposited SiO2 diffusion mask; (3) determining the feasibility of applying liquid anti-reflective solutions using meniscus coating equipment; (4) studying the production of uniform, high efficiency solar cells using ion implanation junction formation techniques; and (5) quantifying cost improvements associated with process improvements.

Source record↗

NASA NTRS1984

Crystallization of Silicon Ribbons

Purity constraints for reasonable solar-cell efficiency require that silicon-ribbon growth for photovoltaics occur in a regime in which constitutional supercooling or other compositional effects on the crystallization front are not important. A major consideration in the fundamentals of crystallization is the removal of the latent heat of fusion. The direction of removal, compared with the growth direction, has a major influence on the crystallization rate and the development of localized stresses. The detailed shape of the crystallization front appears to have two forms: that required for dendritic-web growth, and that occurring in all others. After the removal of the latent heat of fusion, the thermal-mechanical behavior of all ribbons appears similar within the constraints of the exothermal gradient. The technological constraints in achieving the required thermal and mechanical conditions vary widely among the growth processes.

Leipold, M. H.↗

NASA NTRS2019

Development of Solid State Electrolytes for Li-Metal Based High Capacity Battery

NASA future missions demand safe, high specific energy (>400 Wh/kg) batteries. Current state-of-the-art (SOA) lithium-ion batteries (LIBs) can only provide ~150-200 Wh/kg in energy capacity, which is unable to meet NASA's future energy goals, and also pose safety issues due to the use of liquid flammable electrolyte. There are intense on-going development activities to increase battery energy density. The use of Li metal as an anode material has emerged as one highly attractive option for achieving high-energy, next generation batteries. This is because Li has many advantages. It is the lightest metal, but also has the highest theoretical capacity. It also has the lowest potential, which boosts whole cell voltage, and Li metal is 100% active material and requires no binder. Thus, Li metal is an ideal anode material for high energy battery chemistries. Lithium metal based advanced battery chemistries are envisioned to be mission enhancing and, in many cases, mission enabling for future space and aeronautic applications. However, the reliable use of this exceptionally high capacity anode in a commercial rechargeable battery has not been achieved due to safety and reliability concerns resulting from thermal runaway and short-circuit issues due to dendritic growth on the Li metal anode from lithium plating during charge-discharge cycles. A solid state electrolyte, such as garnet/ceramic or solid polymer nanocomposite electrolyte, is a promising approach to make Li metal safely cycling. The solid state electrolyte is non-flammable and eliminates leakage and fire hazard by replacing the liquid flammable electrolyte. However, the low-ionic conductivity and high interfacial impedance are the key issues to be overcome. In this presentation, the research activities on solid state electrolyte development funded by the NASA Advanced Energy Storage System program and by the NASA Center Innovative Fund will be presented, and the progress and results will be also discussed.

Wu, James J.↗

NASA NTRS2023

Evaluation of Ultrasonic Battery Inspection Techniques

Lithium metal batteries are prone to subtle defects such as internal dendrites, which can cause internal short circuits and lead to catastrophic ignition. These defects are often undetectable by battery management systems, prompting the need to advance nondestructive evaluation (NDE) techniques for battery applications. In this work, two ultrasonic approaches were compared to establish their relative merits for this application: local ultrasonic resonance spectroscopy, and guided wave ultrasound. Benchtop experiments on batteries seeded with lithium chips emulating plating were used to demonstrate the two techniques. The results show the ability to identify and map local changes in cell structure.

Ultrasound↗

NASA NTRS2023

Evaluation of Ultrasonic Battery Inspection Techniques

Ultrasound↗

NASA NTRS1976

Design, fabrication and test of prototype furnace for continuous growth of wide silicon ribbon

A program having the overall objective of growing wide, thin silicon dendritic web crystals quasi-continuously from a semi-automated facility is discussed. The design considerations and fabrication of the facility as well as the test and operation phase are covered; detailed engineering drawings are included as an appendix. During the test and operation phase of the program, more than eighty growth runs and numerous thermal test runs were performed. At the conclusion of the program, 2.4 cm wide web was being grown at thicknesses of 100 to 300 micrometers. As expected, the thickness and growth rate are closely related. Solar cells made from this material were tested at NASA-Lewis and found to have conversion efficiencies comparable to devices fabricated from Czochralski material.

Duncan, C. S.↗

NASA NTRS1979

Phase 2 of the array automated assembly task for the low cost solar array project

The process sequence for the fabrication of dendritic web silicon into solar panels was modified to include aluminum back surface field formation. Plasma etching was found to be a feasible technique for pre-diffusion cleaning of the web. Several contacting systems were studied. The total plated Pd-Ni system was not compatible with the process sequence; however, the evaporated TiPd-electroplated Cu system was shown stable under life testing. Ultrasonic bonding parameters were determined for various interconnect and contact metals but the yield of the process was not sufficiently high to use for module fabrication at this time. Over 400 solar cells were fabricated according to the modified sequence. No sub-process incompatibility was seen. These cells were used to fabricate four demonstration modules. A cost analysis of the modified process sequence resulted in a selling price of $0.75/peak watt.

Campbell, R. B.↗

NASA NTRS2007

Synthesis of Poly-Silicon Thin Films on Glass Substrate Using Laser Initiated Metal Induced Crystallization of Amorphous Silicon for Space Power Application

Poly-silicon thin films on glass substrates are synthesized using laser initiated metal induced crystallization of hydrogenated amorphous silicon films. These films can be used to fabricate solar cells on low cost glass and flexible substrates. The process starts by depositing 200 nm amorphous silicon films on the glass substrates. Following this, 200 nm of sputtered aluminum films were deposited on top of the silicon layers. The samples are irradiated with an argon ion cw laser beam for annealing. Laser power densities ranging from 4 to 9 W/cm2 were used in the annealing process. Each area on the sample is irradiated for a different exposure time. Optical microscopy was used to examine any cracks in the films and loss of adhesion to the substrates. X-Ray diffraction patterns from the initial results indicated the crystallization in the films. Scanning electron microscopy shows dendritic growth. The composition analysis of the crystallized films was conducted using Energy Dispersive x-ray Spectroscopy. The results of poly-silicon films synthesis on space qualified flexible substrates such as Kapton are also presented.

Abu-Safe, Husam H.↗

NASA NTRS2000

Experience-dependent development of spinal motor neurons

Locomotor activity in many species undergoes pronounced alterations in early postnatal life, and environmental cues may be responsible for modifying this process. To determine how these events are reflected in the nervous system, we studied rats reared under two different conditions-the presence or absence of gravity-in which the performance of motor operations differed. We found a significant effect of rearing environment on the size and complexity of dendritic architecture of spinal motor neurons, particularly those that are likely to participate in postural control. These results provide evidence that neurons subserving motor function undergo activity-dependent maturation in early postnatal life in a manner analogous to sensory systems.

STS-90 Shuttle Project↗

NASA NTRS1978

The impact of defects on the photovoltaic potential of RTR silicon ribbon

Silicon ribbon grown at a high rate by the ribbon-to-ribbon (RTR) method contains a variety of defects and can exhibit an unusual dendritic morphology. This paper is a study of the effect of the defect structure and dendritic morphology on the photovoltaic potential of RTR ribbon. Defects found in RTR ribbon include grain boundaries, twin planes, stacking faults and dislocations. The electrical activity of these defects is investigated by measuring the diffusion length in the ribbon; by fabricating small area diodes on the ribbon and evaluating their photoresponse; and by using a scanning electron microscope in the electron beam induced current mode. It is concluded that although grain boundaries serve very effectively as recombination centers, they do not occur frequently enough in RTR ribbons to significantly affect the generation current. Dislocation densities up to 1,000,000/sq cm can be tolerated without strongly reducing the photoresponse. Similarly, linear boundaries such as twin planes or stacking faults do not affect the cell performance up to densities of 1000/sq cm.

Baghdadi, A.↗

NASA NTRS1999

An Experimental and Computational Study of Directional Solidification in Transparent Materials

An experimental and numerical study of the horizontal Bridgman growth of pure succinonitrile (SCN) and of a succinonitrile- 1.0 mol.% acetone alloy (SCN- 1.0 mol.% ACE) has been performed. Experiments at growth rates of 0, 2 and 40 micron/s were investigated. The solid/liquid interface was stable (non-dendritic and non-cellular); however, it was not flat. Rather, it was significantly distorted by the influence of convection in the melt and, for the growth cases, by the moving temperature boundary conditions along the ampoule. For the alloy, the interface was.determined to be unstable at growth rates greater than 2.8 micron/s, but stable for the no-growth and 2 micron/s growth cases. When compared to the pure SCN interface, the alloy interface forms closer to the cold zone, indicating that the melting temperature has been suppressed by the addition of the alloying element. Two-dimensional computer simulations were performed for the no-growth case for both the pure and alloy materials. These simulations indicate that a primary longitudinal convective cell is formed in the melt. The maximum magnitude of velocity was calculated to be 1.515 mm/s for pure SCN and 1.724 mm/s for the alloy. The interface shape predicted by the computer simulation agrees well with the experimentally determined shape for the pure SCN case. In ongoing work, numerical simulations of the process during growth conditions are being performed.

Simpson, James E.↗

NASA NTRS1994

Evidence that the protocell was also a protoneuron

A blueprint for a protocell was presented in 1960 (Fox) as a consequence of the newly discovered self-ordering of amino acids and the self-organization of the resultant thermal proteins into cellular structures. The biofunctions of the laboratory protocells (proteinoid microspheres) have since been cataloged; they display roots of many phenomena of modern cells, e.g. synthesis of internucleotide and peptide bonds in aqueous media. These results are inconsistent with a popular assumption that DNA/RNA preceded protein in earliest molecular evolution. The necessity for synthetic research on molecules and cells to 'begin at the beginning' is being realized. Ivanov and Fortsch (1986) have described by analysis how the self-ordering mechanism of amino acids into informed thermal proteins was conserved in evolution from the earliest stage as modern (reverse) mechanisms assumed control. Tyagi and Ponnamperuma (1990) have negated assumptions corollary to DNA/RNA. Ponnamperuma has demonstrated the powerful effect of self-ordering of amino acids in polymerization of aminoacyl nucleotides and the irrelevance of mononucleotide residues. Excitable thermal proteins (Vaughan et al, 1987) are neurotrophic and antiaging when added to cultures of real neurons (Hefti et al, 1991) and are memory enhancers in mice (Fox and Flood, 1992). Proteinoid microspheres of dominant hydrophobic constitution form 'gap junctions', sprout axon-like outgrowths, and form dendritic networks spontaneously. In the latest studies, phenylalanine-rich equimolar proteinoid or the leucine analog (Ishima et al 1981), is found to produce electrical signals for several days when lecithin is included in the assembly with the thermal polymer.

Bi, YU↗

NASA NTRS2010

Simulated Microgravity Induces SOST/Sclerostin Upregulation in Osteocytes

Osteocytes are theorized to be the mechanosensors and transducers of mechanical forces in bone, yet the biological mechanism of this action remains elusive. Recent evidence suggests that SOST/Sclerostin is an important regulator of mechano-transduction. To investigate the molecular mechanisms of SOST/Sclerostin regulation under in-vitro and ex-vivo unloading we used the NASA Rotating Wall Vessel(RWV) Bioreactor. For in-vitro experiments, MLOY-4 osteocytic cells were seeded at a concentration of 250,000 cells onto 3D collagen scaffold (BD). Scaffolds (4 per condition) were either rotated in a vertical 50ml NASA/bioreactor vessel at 18 rpm (unloaded), cultured in a horizontal 50 ml NASA bioreactor vessel at 18 rpm (control for the sheared environment of vertical rotating vessel), or cultured in a static T-75 cm dish (static condition ) for 7days. For ex-vivo experiments, calvaria bones were harvested from 12-week old C57/Bl6 mice and sequentially digested with type I/II collagenase to remove periosteal osteoblasts. Calvaria halves (10 per condition) were then exposed to the same set of culture conditions described above. Simulated unloading, as achieved in the NASA RWV, resulted in enlarged, round osteocytes, as assessed by H&E staining, that was reminiscent of prior reports of unloading causing loss of osteocyte morphology and dendritic network connectivity. Semiquantitative realtime qPCR and immunohistochemistry from both in-vitro and ex-vivo RWV experiments demonstrated a four-fold up-regulation of SOST/Sclerostin. Furthermore, mRNA of the transcriptional SOST enhancer Mef2C was upregulated 1.4 fold in ex-vivo calvaria subjected to unloading conditions of the NASA RWV, suggesting that Mef2C might be an important regulator of mechano-sensation. These findings are consistent with results from seven day hindlimb unloading experiments, C57/B6 females, conducted in our laboratory and validate the use of the NASA RWV as a tool to study osteocyte mechanotransduction

Spatz, Jordan↗

NASA NTRSDate not supplied

Lithium Nucleation of Anode-Free Solid-State Batteries with a Dry Compressible Interlayer

Anode-free lithium batteries offer promising advantages, including increased energy density and the ability to address common mechanistic failures within the cell, thus increasing safety. One way that can make this possible is to control lithium nucleation. This could be achieved by reducing the overpotential required and implanting lithophilic nucleation sites in an anodic interlayer to aid in lithium ion transport and plating. The concept has been utilized in solid-state battery systems where electrolytes are solids with further improved safety and structural longevity. In this presentation, we discuss the use of a silver-holey graphene-based anodic interlayer that can be fabricated via direct dry compression without the use of solvent or binder. The addition of silver to the holey graphene matrix creates a route to lithium plating via a lower-energy intermediate. This idea is supported by the presence of a lithium-silver alloy that forms during the activation step. It is understood that the embedded silver acts as a nucleation site for lithium ions, thereby assisting in even plating. This control, combined with the added cushion of the holey graphene itself, can help reduce dendrite formation, ultimately increasing the safety and lifetime of the solid-state batteries.

Solid state batteries↗

NASA NTRS2000

Exploiting the Temperature Dependence of Magnetic Susceptibility to Control Convection in Fundamental Studies of Solidification Phenomena

It is well known that convection is a dominant mass transport mechanism when materials are solidified on Earth's surface. This convection is caused by gradients in density (and therefore gravitational force) that are brought about by gradients in temperature, composition or both. Diffusion of solute is therefore dwarfed by convection and the study of fundamental parameters, such as dendrite tip shape and growth velocity in the absence of convection is nearly impossible. Significant experimental work has therefore been carried out in orbiting laboratories with the intent of minimizing convection by minimizing gravity. One of the best known experiments of this kind is the Isothermal Dendritic Growth Experiment (IDGE), supported by NASA. Naturally such experiments are costly and one objective of the present investigation is to develop an experimental method whereby convection can be- halted, in solidification and other experiments, on the surface. A second objective is to use the method to minimize convection resulting from the residual accelerations suffered by experiments in microgravity. The method to be used to minimize convection relies on the dependence of the magnetic susceptibility of a fluid on temperature or composition (whichever is driving convection). All materials experience a force when placed in a magnetic field gradient. The direction and magnitude of that force depend on the magnetic susceptibility of the material. Consequently the force will vary if the susceptibility varies with temperature or composition. With a magnetic field gradient in the right direction (typically upward) and of the right magnitude, this variation in the magnetic force can be made to exactly cancel the variation in the gravitational force. Expressed another way, normal buoyancy is exactly countered by a "magnetic buoyancy". To demonstrate the principle, a solution of MnC12 in water has been used. First the variation of the susceptibility of this paramagnetic solution with temperature and concentration was measured. Then a "cell", containing this solution and 50mm long by 15mm high by 155mm wide, was placed in a superconducting magnet at Marshall Space Flight Center. The magnetic field was measured at various positions within the bore of the magnet using a Hall effect probe. In this way, a position was found where the magnetic field gradient was predominantly upward; the magnitude of the gradient could then be adjusted by adjusting the current of the magnet. The ends of the cell consisted of machined copper blocks maintained at controlled temperatures by circulating water from constant temperature baths. The walls of the cell were of rectangular section glass tubing so that the cell contents could be seen. Velocities arising from thermal gradients within the cell were measured by particle image velocimetry (PIV). Particles used for this purpose were silver-coated hollow glass spheres of micrometers diameter and nearly the same density as the solution. A central vertical plane of the cell was illuminated by a laser beam passing through a cylindrical lens. Digital images of the particles were captured on a CCD camera and fed to a computer so that frame-to-frame movements of particles traveling with the fluid were captured. These images were employed to compute velocity maps using commercial PIV software. In a typical experiment the cold end of the cell was maintained at 10C and the warm end at 30 C. With no current in the magnet, i.e.- with natural -convection allowed to occur, the fluid was observed to circulate with an average speed of approximately 0.3 millimeters per second. It was visually apparent that this circulation was diminished as the current was increased. At currents of approximately 20A the flow was halted, to within the precision of the PIV measurements. At yet higher currents the convection was reversed with the hotter solution sinking and the cooler solution rising. At 40A this reversed convection had speeds averaging 0.43 millimeters per second. The measurements of susceptibility and density allow an estimate of the field gradient necessary to halt convection in the experiment. That estimate was 7.8T (squared) per meter and the convection was observed to halt in the magnet at a current giving 7.21T (squared) per meter from the magnetic field measurements. Calculations of the flow have been carried out using the computational fluid dynamics software FLUENT and show good agreement with the measurements.

Seybert, C. D.↗