Troy Munro

There is a growing field that is devoted to developing inexpensive microscopes and measurement devices by leveraging low-cost commercial parts that can be controlled using smartphones or embedded devices, such as Arduino and Raspbery Pi. Examples include the use of Blu-ray optical heads like the PHR-803T to perform cytometry, spinning disc microscopy, and lensless holographic microscopy. The modular or disposable nature of these devices means that they can also be used in contaminating and degrading environments, including radioactive environments, where replacement of device elements can be expensive. This paper presents the development and operation of a confocal microscope that uses the PHR-803T optical device in a Blu-ray reader for both imaging and detection of temperature variations with between 1.5 and 15 µm resolution. The benefits of using a PHR-803T confocal system include its relatively inexpensive design and the accessibility of the components that are used in its construction. The design of this scanning confocal thermal microscope (SCoT) was optimized based on cost, modularity, portability, spatial resolution, and ease of manufacturability using common tools (e.g., drill press, 3D printer). This paper demonstrated the ability to resolve microscale features such as synthetic spider silk and measure thermal waves in stainless steel using a system requiring <USD 1000 in material costs.

Friction stir process models are typically validated by tuning heat transfer and friction coefficients until measured temperatures in either the tool or workpiece, but rarely in both, match simulated results. A three-dimensional finite element model for a tool plunge in an AA 6061-T6 is validated for temperature predictions in both the tool and workpiece using a friction coefficient that varies with time. Peak workpiece temperatures were within 1.5% of experimental temperatures and tool temperatures were off by 80 °C. The sensitivity of the predicted temperatures with respect to the workpiece/tool heat transfer coefficient was shown to be high for the tool and low for the workpiece, while the spindle torque was slightly underpredicted in the best case. These results show that workpiece/tool interface properties must be tuned by considering predictions on both sides of the heat generation interface in order to ensure a reliable process simulation.

New microfluidic lab-on-a-chip capabilities are enabled by broadening the toolkit of devices that can be created using microfabrication processes. For example, complex geometries made possible by 3D printing can be used to approach microfluidic design and application in new or enhanced ways. In this paper, we demonstrate three distinct designs for microfluidic one-way (check) valves that can be fabricated using digital light processing stereolithography (DLP-SLA) with a poly(ethylene glycol) diacrylate (PEGDA) resin, each with an internal volume of 5–10 nL. By mapping flow rate to pressure in both the forward and reverse directions, we compare the different designs and their operating characteristics. We also demonstrate pumps for each one-way valve design comprised of two one-way valves with a membrane valve displacement chamber between them. An advantage of such pumps is that they require a single pneumatic input instead of three as for conventional 3D-printed pumps. We also characterize the achievable flow rate as a function of the pneumatic control signal period. We show that such pumps can be used to create a single-stage diffusion mixer with significantly reduced pneumatic drive complexity.

One class of neutron detectors for illicit nuclear materials are capture‐gated detectors, which use organic scintillators to slow neutrons while emitting fluorescent light and elements that have high neutron capture cross‐sections to provide a second signal. Homogeneous detectors composed of neutron capturing metallo‐organics within plastic darken due to their chemical instability, while heterogeneous detectors frequently result in non‐transparent material due to a mismatch of the refractive index. These detectors are often polymerized through bulk polymerization, but there is little data available on this process applied to mixtures of polystyrene (PS) and polyvinyl toluene (PVT), two commonly used polymers in plastic scintillators. This work presents bulk polymerization processing toward an index‐matched, heterogeneous capture‐gated neutron detector based on PS and PVT copolymers with a range of refractive indices. Specifically 1:3, 1:1, and 3:1 PS:PVT ratios were manufactured and their refractive indices, measured by refractometry, were compared to a theoretical model based on a mixture of the refractive indices of pure PS and PVT. Finally, a composite of PS/PVT and an Ohara S‐BAL42 glass was developed to confirm the index‐matching capability of the process as a step toward developing a heterogenous, capture‐gated neutron detector with high light transmission efficiencies allowed by index‐matched materials.

One class of neutron detectors for illicit nuclear materials are capture‐gated detectors, which use organic scintillators to slow neutrons while emitting fluorescent light and elements that have high neutron capture cross‐sections to provide a second signal. Homogeneous detectors composed of neutron capturing metallo‐organics within plastic darken due to their chemical instability, while heterogeneous detectors frequently result in non‐transparent material due to a mismatch of the refractive index. These detectors are often polymerized through bulk polymerization, but there is little data available on this process applied to mixtures of polystyrene (PS) and polyvinyl toluene (PVT), two commonly used polymers in plastic scintillators. This work presents bulk polymerization processing toward an index‐matched, heterogeneous capture‐gated neutron detector based on PS and PVT copolymers with a range of refractive indices. Specifically 1:3, 1:1, and 3:1 PS:PVT ratios were manufactured and their refractive indices, measured by refractometry, were compared to a theoretical model based on a mixture of the refractive indices of pure PS and PVT. Finally, a composite of PS/PVT and an Ohara S‐BAL42 glass was developed to confirm the index‐matching capability of the process as a step toward developing a heterogenous, capture‐gated neutron detector with high light transmission efficiencies allowed by index‐matched materials.

New heater geometries enabled by 3D printing provide improved spatial temperature distributions to typical heaters, validated through simulations and experiments. A first set of design rules to guide truly 3D microfluidic heater design is provided.

Reports in the literature indicate that temperature control in Friction Stir Welding (FSW) enables better weld properties and easier weld process development. However, although methods of temperature control have existed for almost two decades, industry adoption remains limited. This work examines single-loop Proportional-Integral-Derivative (PID) control on spindle speed as a comparatively simple and cost-effective method of adding temperature control to existing FSW machines. Implementation of PID-based temperature control compared to uncontrolled FSW in AA6111 at linear weld speeds of 1–2 m per minute showed improved mechanical properties and greater consistency in properties along the length of the weld under temperature control. Additionally, results indicate that a minimum spindle rpm may exist, above which tensile specimens do not fracture within the weld centerline, regardless of temperature. This work demonstrates that a straightforward, PID-based implementation of temperature control at high weld rates can produce high quality welds.

In 1974, reference correlations for the viscosity of molten LiF-NaF-KF, LiF-BeF2, and Li2CO3-Na2CO3-K2CO3 were proposed by Janz and have been extensively used since then. However, in the last 45 years, many additional measurements have been published. This is why in this paper, new reference correlations for the viscosity of these salts are proposed. All available experimental data for the viscosity of these three molten salts have been critically examined with the intention of establishing improved or new reference viscosity correlations. All experimental data have been categorized into primary and secondary data according to the quality of measurement specified by a series of criteria. The reference correlation proposed for LiF-NaF-KF, with an uncertainty of 2.9% at the 95% confidence level, expands the temperature range of the previous correlation from (770–970) K to (732–1163) K and retains its uncertainty. The correlation proposed for LiF-BeF2, with an uncertainty of 4.9% at the 95% confidence level, expands the high temperature range of the previous correlation from (740–870) K to (793–1573) K, with a slight loss in its uncertainty. It is, however, a much better correlation as it is based upon measurements not available at the time of the previous one. Finally, the reference correlation for Li2CO3-Na2CO3-K2CO3, with an uncertainty of 3%, also expands the temperature range of the previous correlation from (920–1170) K to (738–1170) K and retains its uncertainty.

In 1974, reference correlations for the viscosity of molten LiF-NaF-KF, LiF-BeF2, and Li2CO3-Na2CO3-K2CO3 were proposed by Janz and have been extensively used since then. However, in the last 45 years, many additional measurements have been published. This is why in this paper, new reference correlations for the viscosity of these salts are proposed. All available experimental data for the viscosity of these three molten salts have been critically examined with the intention of establishing improved or new reference viscosity correlations. All experimental data have been categorized into primary and secondary data according to the quality of measurement specified by a series of criteria. The reference correlation proposed for LiF-NaF-KF, with an uncertainty of 2.9% at the 95% confidence level, expands the temperature range of the previous correlation from (770–970) K to (732–1163) K and retains its uncertainty. The correlation proposed for LiF-BeF2, with an uncertainty of 4.9% at the 95% confidence level, expands the high temperature range of the previous correlation from (740–870) K to (793–1573) K, with a slight loss in its uncertainty. It is, however, a much better correlation as it is based upon measurements not available at the time of the previous one. Finally, the reference correlation for Li2CO3-Na2CO3-K2CO3, with an uncertainty of 3%, also expands the temperature range of the previous correlation from (920–1170) K to (738–1170) K and retains its uncertainty.

Over the life of nuclear fuel, inhomogeneous structures develop, negatively impacting thermal properties. New fuels are under development but require more accurate knowledge of how the properties change to model performance and determine safe operational conditions. Measurement systems capable of microscopic thermal transport measurements and low cost are necessary to measure these properties and integrate into hot cells where electronics are likely to fail during fuel investigation. This project develops a cheaper, smaller, and easily replaceable Fluorescent Scanning Thermal Microscope (FSTM) using the blue laser and focusing circuitry from an Xbox HD-DVD player that incorporates novel fluorescent thermometry methods to determine thermal diffusivity. The FSTM requires minimal sample preparation, does not require access to both sides of the sample, and components can be easily swapped out if damaged, as is likely in irradiated hot cells. Using the optical head from the Xbox for sensing temperature changes, an infrared laser diode provides periodic heating to the sample, and the blue laser induces fluorescence in Rhodamine B deposited on the sample’s surface. Thermal properties are fit to modulated temperature models based on the phase delay response at different modulated heating frequencies. With the FSTM method, the thermal diffusivity of a Nordic gold (euro) coin was found to be 21 ± 5 mm2/s. This value is compared to laser flash and thermal conductivity microscope methods, which found the thermal diffusivity to be 30.4 ± 0.1 mm2/s and 19 ± 3 mm2/s. The system shows promise as a feasible property characterization technique with future refinement and testing in progress.

As analysis systems shrink in size to microfluidic scales and devices, there is a need to improve temperature control in the microscale for temperature-sensitive processes. Technology that combines accurate temperature measurement and 3D spatial control of the temperature distribution is limited by common 2D layer-based microfluidic fabrication techniques but can be realized with 3D printed microfluidic chips. This work presents an iterative process to create a microfluidic chip using multi-material 3D printing to improve temperature sensing and create an even temperature around a target volume. Through an iterative process, verification is presented of fluorophore viability (specifically CdTe quantum dots) after being secured in place by cured PR48 3D printing resin, thus confirming the possibility of fluorescent thermometry as an accurate non-contact temperature sensing method. Numerical analyses of various geometries of chip design iterations are also presented verifying spatially even heating due to the placement of heating sources in the microfluidic chip. Combining the fluorescent thermometry and improved heating will lead to improved temperature control in microfluidic devices.

Uranium and thorium oxides have critical roles as fuels in existing nuclear power plants, as well as in proposed reactor concepts. The thermal conductivity of these materials determines their ability to transfer heat from the reactor core to the surrounding coolant. Additionally, these actinide compounds are of interest in condensed matter physics because of the 5f orbitals and unique electron interaction, coupling, and scattering events that can occur. Because of the radioactivity of thorium and uranium, thin film measurements of actinide materials are used to limit the amount of operator exposure, but standard thermal characterization methods are not well suited for thin films. This paper presents the process of depositing thin film UOx and ThOx samples of nm-μm thicknesses and the results of thermal property measurements. Thin films were deposited on silicon and glass substrates via dc-magnetron sputtering using an argon/oxygen mixture as the working gas. The thermal properties of the films were measured by the Thermal Conductivity Microscope (TCM). This uses one laser to generate thermal waves and a second laser to measure the magnitude and phases of the thermal waves to obtain the conductivity of materials. The results of the research show that the UOx film properties are lower than bulk values and that the role of the substrate has a considerable effect on determining the measured properties. Future work aims at improving the deposition process. Epitaxial film growth is planned. Additional understanding of thermal property measurements is targeted.

The processes used to create synthetic spider silk greatly affect the properties of the produced fibers. This paper investigates the effect of process variations during artificial spinning on the thermal and mechanical properties of the produced silk. Property values are also compared to the ones of the natural dragline silk of theNephila clavipesspider, and to unprocessed (as‐spun) synthetic silk. Structural characterization by scanning pyroelectric microscopy is employed to provide insight into the axial orientation of the crystalline regions of the fiber and is supported by X‐ray diffraction data. The results show that stretching and passage through liquid baths induce crystal formation and axial alignment in synthetic fibers, but with different structural organization than natural silks. Furthermore, an increase in thermal diffusivity and elastic modulus is observed with decreasing fiber diameter, trending toward properties of natural fiber. This effect seems to be related to silk fibers being subjected to a radial gradient during production.image

As a system of interest gets small, due to the influence of the sensor mass and heat leaks through the sensor contacts, thermal characterization by means of contact temperature measurements becomes cumbersome. Non-contact temperature measurement offers a suitable alternative, provided a reliable relationship between the temperature and the detected signal is available. In this work, exploiting the temperature dependence of their fluorescence spectrum, the use of quantum dots as thermomarkers on the surface of a fiber of interest is demonstrated. The performance is assessed of a series of neural networks that use different spectral shape characteristics as inputs (peak-based—peak intensity, peak wavelength; shape-based—integrated intensity, their ratio, full-width half maximum, peak normalized intensity at certain wavelengths, and summation of intensity over several spectral bands) and that yield at their output the fiber temperature in the optically probed area on a spider silk fiber. Starting from neural networks trained on fluorescence spectra acquired in steady state temperature conditions, numerical simulations are performed to assess the quality of the reconstruction of dynamical temperature changes that are photothermally induced by illuminating the fiber with periodically intensity-modulated light. Comparison of the five neural networks investigated to multiple types of curve fits showed that using neural networks trained on a combination of the spectral characteristics improves the accuracy over use of a single independent input, with the greatest accuracy observed for inputs that included both intensity-based measurements (peak intensity) and shape-based measurements (normalized intensity at multiple wavelengths), with an ultimate accuracy of 0.29 K via numerical simulation based on experimental observations. The implications are that quantum dots can be used as a more stable and accurate fluorescence thermometer for solid materials and that use of neural networks for temperature reconstruction improves the accuracy of the measurement.

Fiber thermal characterization is often accomplished by indirect means, such as embedding the fiber in a matrix, measuring the thermal response of the composite, and relating for the contributions of the fiber and matrix to the overall behavior or measuring bundles of fibers. To improve the accuracy of the composite-based or bundle-based techniques, several different contact (hot wire and dc thermal bridge) and non-contact (Raman shift and IR thermography) methods have been developed to directly measure the thermal properties of individual fibers. To improve on the shortcomings of these methods, this paper presents the experimental results of an improved transient electrothermal (TET) method, as well as a 3ω-based method that better accounts for all sources of heat transfer, particularly heat loss by radiation. The incorporation of radial radiation heat loss becomes a significant factor as the size of the fibers decrease. This work describes practical applications of the methods to measure the properties of the fibers, including sample preparation for electrically conductive and non-conductive samples, data acquisition and calibration, data analysis, and sample property determination.

Results include validation of the methods with electrically conductive (platinum) and non-conductive (glass) fibers to improve upon the initial validation of the generalized electrothermal method which focused only on short, conductive fibers. The axial thermal conductivity and diffusivity of several high performance fibers are presented. The novelty of this paper is that it serves as both a compilation of previous research on the transient electrothermal and 3ω methods [1–6], measurements of new silk fibers, and practical information associated with the methods that improve the accuracy of the measured thermal property, as well as presenting thermal properties of additional fibers (carbon fiber and natural and synthetic spider silks).

To improve upon the long sample preparation time required for the TET and 3ω methods, future work focused on the development of a quantum dot-based photothermal fluorescence method is presented.

Neural network recognition of features of the fluorescence spectrum of a thermosensitive probe is exploited in order to achieve fluorescence-based thermometry with an accuracy of 200 mK with 100 MHz bandwidth, and with high robustness against fluctuations of the probe laser intensity used. The concept is implemented on a rhodamine B dyed mixture of copper chloride and glycerol, and the temperature dependent fluorescence is investigated in the temperature range between 234 K and 311 K. The spatial dependence of the calibrated amplitude and phase of photothermally induced temperature oscillations along the axis of the excitation laser are determined at different modulation frequencies. The spatial and frequency dependence of the extracted temperature signals is well fitted by a 1D multi-layer thermal diffusion model. In a time domain implementation of the approach, the gradual temperature rise due to the accumulation of the DC component of the heat flux supplied by repetitive laser pulses as well the immediate transient temperature evolution after each single pulse is extracted from acquired temporal sequences of fluorescence spectra induced by a CW green laser. A stroboscopic implementation of fluorescence thermometry, using a pulsed fluorescence evoking probe laser, is shown to achieve remote detection of temperature changes with a time resolution of 10 ns.

Spider silk is well-known for its exceptional mechanical properties, such as strength, elasticity and flexibility. Recently, it has been reported that dragline silk from a Nephila clavipes also has an exceptionally high thermal conductivity, comparable to copper when the fiber is stretched. Synthetic spider silks have been spun from spider silk proteins produced in transgenic sources, and their production process has the optimization potential to have properties similar to or better than the natural spider silk. There is interest to measure the thermal properties of natural and synthetic silk at cryogenic temperatures for use of spider silk fibers as heat conduits in systems where component weight is an issue, such as in spacecraft. This low temperature measurement is also of particular interest because of the conformational changes in protein structures, which affect material properties, that occurs at lower temperatures for some proteins. A measurement system has been designed and is being tested to characterize the thermal properties of natural and synthetic spider silks by means of a transient electrothermal method.

Spider silks exhibit excellent strength, stiffness, and toughness simultaneously, a feat unachievable in most synthetic, structural materials. It has recently been reported that the thermal conductivity of dragline silk is comparable to copper, which is uncharacteristically high for a biomaterial. In order to develop a fundamental understanding of the high thermal properties of spider silk, further research must be made to explore how the structure and organization of spider silk proteins affects heat transfer characteristics. Synthetically produced silks created from spider silk proteins obtained from transgenic sources can be used to determine these protein structure effects by varying protein content and process treatments. This initial study determined the thermal properties of synthetic spider silk created from transgenic goat’s milk proteins using the transient electrothermal method (TET). Results show that the thermal properties of the synthetic silk are lower than the natural spider silk but vary based on the process treatment, and that the annealing of the gold film coated on the fiber has no effect on the measured thermal properties. These results provide a framework for further research on the protein content effect and its role in thermal properties.