Cold Copper Research Articles

Understanding the Antipathogenic Performance of Nanostructured and Conventional Copper Cold Spray Material Consolidations and Coated Surfaces

The role of high strain rate and severe plastic deformation, microstructure, electrochemical behavior, surface chemistry and surface roughness were characterized for two copper cold spray material consolidations, which were produced from conventionally gas-atomized copper powder as well as spray-dried copper feedstock, during the course of this work. The motivation underpinning this work centers upon the development of a more robust understanding of the microstructural features and properties of the conventional copper and nanostructured copper coatings as they relate to antipathogenic contact killing and inactivation applications. Prior work has demonstrated greater antipathogenic efficacy with respect to the nanostructured coating versus the conventional coating. Thus, microstructural analysis was performed in order to establish differences between the two coatings that their respective pathogen kill rates could be attributed to. Results from advanced laser-induced projectile impact testing, X-ray diffraction, scanning electron microscopy, electron backscatter diffraction, scanning transmission microscopy, nanoindentation, energy-dispersive X-ray spectroscopy, nanoindentation, confocal microscopy, atomic force microscopy, linear polarization, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy and copper ion release assaying were performed during the course of this research.

On the substitution of vanadium with iron in Ti–6Al–4V: Thermo-Calc simulation and processing map considerations for design of low-cost alloys

Two basic cost reducing concepts, manipulation of alloy chemistry and optimisation of the hot working process, were adopted in developing low-cost experimental titanium alloys that may be suitable for land-based applications. Iron, a low-cost beta stabilising element in titanium alloys, was used as a partial and full replacement for vanadium in ASTM grade 5 Ti–6Al–4V. Thermo-Calc simulations were first done on the Ti–6Al-xV-yFe alloy compositions (for y = 4 – x and x = 1–3) to predict the amounts of phases and the β-transus temperatures. Thereafter, the compacted powders of the different experimental alloys were melted and allowed to solidify in the electric arc furnace cold copper hearth. Optical and scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterise the alloys. Also, the hardness of the low-cost alloys was measured and compared to commercial Ti–6Al–4V. The Ti–6Al–1V–3Fe alloy was subjected to hot compression testing at various temperatures (750–950 °C) and strain rates (1-10 s-1) on a Gleeble 3500 thermomechanical simulator. Processing maps and microstructural validation were used to define the most suitable processing conditions. The stress exponent and apparent activation energy were also calculated using a hyperbolic-sine equation. The results show that the low-cost alloys with partial substitution of vanadium with iron contained only α-Ti and β-Ti phases with no TiFe phase. The hardness of the alloys increased with increase in iron addition. The stress exponent “n” value was less than 5 indicating that flow softening was not solely driven by dynamic recovery. The optimum processing conditions for hot working were found at ~900 °C and 0.1 s-1 strain rate. The alloy generally had a large processing window with the softening process controlled by mechanisms such as dynamic recovery, dynamic recrystallisation of prior beta grains, and dynamic alpha lath globularisation. In the region of 750–780 °C and 1.5–10 s−1 an area of unstable deformation was established which should be avoided during processing. This work shows that low-cost α+β titanium alloys containing iron can be manufactured using traditional ingot metallurgy techniques and loss of material due to processing-induced defects can be minimised or avoided during primary conversion process such as forging and rolling.

Thin hybrid capillary two-phase cooling system

A novel hybrid two-phase cooling system was developed that integrated a mechanically pumped two-phase loop with a capillary-driven two-phase cooling device. The latter cooling mechanism was based on evaporation/boiling from wick structures made by sintering copper particles on the interior surfaces of a copper cold plate. The cold plate provided cooling to two surfaces and each of them included four heaters in series. The novelty of the developed technology was preventing flooding of the evaporator wicks by isolating the evaporation surface from the pumped liquid flow that fed them. This arrangement allowed for a high liquid feed flow rate much greater than would be allowed by a capillary pumped system while maintaining a low thermal resistance at the evaporation surface. Using this approach, the cooling system removed over 850 W with a low pumping power below 1.0 W while using R245fa as the working fluid. The equivalent heat fluxes exceeded 970 W/cm2 over areas less than 0.12 cm2. The measured thermal resistance was as low as 0.09 K-cm2/W. The presented thermal management solution enables an increase in the power of high heat flux electronic devices beyond the state-of-the-art.

The Problem of Copper Softening During Cold Gas Dynamic Spraying

The effect of the gas-dynamic (cold) spraying of the Cu-Al2O3-Zn powder mixture on the microstructure and strength of the copper substrate is investigated. A copper cold drawn contact wire was used as a substrate. We propose using gas-dynamic cold spraying to restore the local wear of the contact wire. The study of the microstructure using the electron backscattered diffraction (EBSD) method showed the presence of grain orientation characteristics of the cold drawing of copper. Recrystallization of the surface layers of the contact wire during spraying does not occur. Using the microhardness measurement, the absence of softening of the layers of the contact wire with a depth of up to 2 mm is shown. The results of mechanical tests show that spraying does not lead to a decrease in the tensile strength of the contact wire. The results of creep tests show that spraying does not lead to a decrease in the heat resistance of the contact wire.

The Effect of Corrosion on Conventional and Nanomaterial Copper Cold Spray Surfaces for Antimicrobial Applications

The U.S. spends over $125 billion a year in prevention of touch surface infections [1-5]. Copper cold spray coatings have been identified as having greater antimicrobial effectiveness than other additive methods...

The effect of load and addition of MWCNTs on silicone based TIMs on thermal contact heat transfer across Cu/Cu interface

In the present work, the effect of thermal interface material (TIM) and load on contact heat transfer between hot and cold cylindrical copper specimens was assessed. Pristine silicone grease and multi walled carbon nanotubes (MWCNT) impregnated silicone grease was used as TIM. Copper specimens with L/D ratios of 1 and 5 were used. For copper specimens with L/D ratio of 1, the interfacial heat transfer was quantified by estimating the peak heat flux and integral heat flow using a lumped heat capacitance approach. An inverse solution to heat conduction equation was adopted for estimating heat flux transients for copper specimens with L/D ratio of 5. As the applied load increased from a no load condition to 5 kg, the peak heat flux and the corresponding integral flow increased significantly. Increasing the load above 5 kg did not result in any significant changes in the peak heat flux and integral heat flow for both sets of specimens. The effect of load on the contact heat transfer was significant in the absence of TIM. The use of 0.1 wt% MWCNT- silicone grease as TIM significantly increased the heat flow for no load condition. At higher loads, the effect of MWCNT was insignificant and caused deterioration in the heat flow parameters. Further, increasing the MWCNT content to 1 wt% in silicone grease decreased the heat flux transients at all loading conditions. The thermal contact resistance (RT) was calculated and it increased exponentially with the peak temperature difference (ΔTmax) between hot and cold specimens irrespective of the L/D ratio.

Corrosion Resistance Evaluation of Some Stainless Steels Used in Manufacture of Hydraulic Turbine Runner Blades

The paper presents corrosion resistance testing results of three stainless steels that may be used in hydropower turbine blades manufacture. Two of these have a chemical composition close to that of some other stainless steels previously employed in producing these parts, being updated steel grades of the former ones. The third one is of a new conception, having a chemical composition close to that of a maraging steel. The three materials were produced in an induction furnace with cold copper crucible under vacuum and argon atmosphere in order to obtain improved mechanical and corrosion resistance characteristics as well as an inclusion � free structure. Quenching and tempering heat treatments were subsequently applied. Tests were carried out at room temperature in normally aerated 1N Na2SO4 and 3% NaCl solutions. Corrosion rates were calculated using the Tafel slope method. All steels have a passivation tendency in a chlorine-free aqueous medium. The newly conceived steel has a more pronounced anodic field as a result of a chromium content below 12%. However, the general corrosion behavior of this material is rebalanced by the content of about 10% Ni which leads to a mainly martensitic structure in quenched state. The corrosion rate values obtained for all samples enframe the three materials in highly and very highly corrosion resistant steels. Nevertheless it must be specified that in chlorine environments the overall corrosion rate is not a sensitive indicator of corrosion resistance performance due to the local depassivation process followed by corrosion pits.

Influence of Current Waveforms on Single Discharge Crater in EDM

This paper describes the effects of the discharge-current waveform on the shape and removal volume of craters in electrical discharge machining (EDM). In EDM, it is known that removal efficiency, defined as the ratio of the removal volume to the volume molten by a single discharge, is no more than several percent. Hence, to increase the removal efficiency, the influence of the discharge current waveforms on the removal volume in a single discharge was investigated. Using cold tool steel plates and copper rods as the workpiece and tool electrode, respectively, the removal volume of workpiece with the polarity of positive was largest when a linearly increased and sharply turned off current was used with the pulse duration of 200μs.

Cavitation Erosion Resistance Tests Performed on Some Stainless Steels for Turbine Runner Blades

The paper presents cavitation erosion testing results of three stainless steels that may be used in making hydropower turbine parts. Two of these steels have a chemical composition close to that of some other stainless steels previously employed in producing these parts. They are updated steel grades of the former ones. The third one is newly conceived. Aiming better mechanical and corrosion resistance characteristics as well as an inclusion - free structural state, steels were produced in an induction furnace with cold copper crucible under vacuum and argon atmosphere. Quenching and tempering heat treatments were subsequently applied.

The strength properties dependence of aluminum materials on the ZrO2 nanoparticles concentration

New data were obtained on the effect of small additions of zirconium oxide nanoparticles on the strength properties of powder matrices based on pure aluminum, including those with the addition of 1.5% copper cold pressed and sintered in forevacuum. It is shown that even with an insignificant concentration of nano-additives, there is a noticeable increase in the mechanical properties of materials: tensile strength, bending, compression, and yield strength.

Assessment of the performance of a 20 kA REBCO current lead

In the framework of a worldwide effort investigating the design of high-current High Temperature Superconductor (HTS) current leads (CLs) composed of REBCO, a 20 kA HTS CL developed at the Karlsruhe Institute of Technology (KIT) based on the JT-60SA CL design, but replacing the Bi-2223 tapes by brass-stabilized REBCO tapes, has been recently tested in the CuLTKa facility at KIT to investigate its steady state and transient performance. The thermal-hydraulic CURLEAD code developed at KIT, recently upgraded in a collaboration between KIT and Politecnico di Torino and validated in both steady state and transient (pulsed) operation, was applied predictively, i.e. before the tests were performed, to support the test strategy of the REBCO CL, which is presented here. The prediction was used to define the set point for the steady state tests, both with and without current, while transient simulations were used to define the number of current pulses needed to reach periodic operation conditions for given current waveforms. The comparison between predictions and experimental results is presented here, showing good agreement between the two in all operating conditions. Interpretive simulations, which took into account the experimental results of parameters, like, e.g., the contact resistance of the HTS module to both the heat exchanger and the cold end copper, are finally presented, showing as expected an even better capability to reproduce the experimental traces, giving confidence in the reliability of CURLEAD for future applications.

Influence of Salinity on the Mechanism of Surface Icing: Implication to the Disappearing Freezing Singularity.

The effect of salinity on surface icing has been investigated experimentally. Water droplets with a variable salinity are deposited on a cold polished copper substrate. Distinctive two-stage freezing, which can be seen in case of pure water, is not observed in heterogeneous freezing of saltwater droplets. Interestingly, the final freezing stage commences before the initial freezing front completely traverses the saline droplet. A considerable increase in delay for heterogeneous ice nucleation is observed with the increasing salinity. The reduction in the associated degree of metastability due to the depression in the freezing point of the bulk solution and the increase in the nucleation barrier due to the appearance of the solvation shells that are formed around the ions are two possible causes of this nucleation delay. Moreover, the solidification time associated with surface icing increases considerably with the increasing salinity. Because of the insolubility of salt in ice, the salt ions are rejected to the entrapped water in the ice scaffold locally and to the bulk unfrozen water explicitly. This collective implicit and explicit modes of brine rejection contributes to the overall slowdown of freezing of the saline water droplets. From the phase diagram, it can be found that the complete solidification of water within the saline droplet is not possible when the substrate temperature is in between the eutectic temperature and the equilibrium freezing temperature. As a result, the relative magnitude of tip singularity during freezing reduces considerably with the increasing salinity due to the increase in unfrozen water content within the droplet.

Environmental radionuclides as contaminants of HPGe gamma-ray spectrometers: Monte Carlo simulations for Modane underground laboratory

The main limitation in the high-sensitive HPGe gamma-ray spectrometry has been the detector background, even for detectors placed deep underground. Environmental radionuclides such as 40K and decay products in the 238U and 232Th chains have been identified as the most important radioactive contaminants of construction parts of HPGe gamma-ray spectrometers. Monte Carlo simulations have shown that the massive inner and outer lead shields have been the main contributors to the HPGe-detector background, followed by aluminum cryostat, copper cold finger, detector holder and the lead ring with FET. The Monte Carlo simulated cosmic-ray background gamma-ray spectrum has been by about three orders of magnitude lower than the experimental spectrum measured in the Modane underground laboratory (4800 m w.e.), underlying the importance of using radiopure materials for the construction of ultra-low-level HPGe gamma-ray spectrometers.

Comparison of Copper and Graphite Crucibles for Si Extraction from TiO2 - SiO2 System at Plasma-Arc Heating

<p>Plasma arc recovery melting of the quartz-leucoxene concentrate is investigated. Experiments were made in laboratory DC plasma arc furnace in various crucibles. The best results are reached in a cold copper crucible. The temperature field of a pool is calculated in hot graphite and cold copper crucibles. It is shown that in a graphite crucible diameter of an anode spot is more, and density of current and material temperature in a spot is less, than in copper that is the reason of the worst refinements in a graphite crucible.</p>

Mirror image technique for the thermal analysis in cryoablation: Experimental setup and validation

The paper presents a set of experiments that were performed to characterize the freezing front propagation in water first, and in an agar-gel solution afterwards. The experimental setup made of Peltier devices, to emulate the cryogenic effect, and a copper cold finger, to mimic the cold probe interface, are described. We claim that by monitoring some temperatures at the generating cryodevice, several pieces of information can be derived through the cold interface to assess the outside thermodynamic changes. The employed technique, known as mirror image, allows determining the occurrence of the initial ice formation outside the cryo-probe and in the surrounding material, also with different magnitudes of the thermal contact resistance at the cold interface. For both water and agar the ice penetration was found to be non linear versus time, and proportional to the square root of time in the performed experiments. The ice drift velocity decreases according to its penetration inside the tested materials. At the beginning of ice formation, the measured drift velocities are approximately 0.11 mm/s and 0.06 mm/s for water and agar, respectively, and after the ice penetrates 2 mm, they become approximately 0.03 mm/s for both materials.

Fabrication of lamellar porous alumina with regular structure via directional solidification with multiple cold sources

Porous ceramics obtained with aqueous slurries by directional solidification have randomly distributed lamellar pore channels and thus have unstable mechanical properties. According to the anisotropic principle of ice crystal growth, the growth of lamellar ice crystals is regular when multiple cold sources are used, and porous ceramics with regular pore channels are then obtained after drying. Multiple cold sources are formed with a bottom cold plate and copper sides in rectangular molds. The copper sides are in contact with the bottom cold plate, thus forming the side cold source with temperature gradient distribution by heat transfer. The interaction between the side cold source and the bottom cold plate facilitates the regular distribution and continuous growth in parallel of ice crystals. The use of parallel copper sides of the mold results in porous ceramics with an axisymmetric pore structure and high aspect ratios of pore channel in porous alumina. The positive compressive strength of fabricated porous ceramics with an axisymmetric structure is similar with those of conventional directional solidification, but the lateral side direction compressive strength of fabricated porous ceramics with an axisymmetric structure is significantly increased.

Preparation and Characterization of Borosilicate Glass Waste Form for Immobilization of HLW from WWER Spent Nuclear Fuel Reprocessing

ABSTRACTBorosilicate glassy materials for immobilization of HLW from Russian WWER (PWR) spent nuclear fuel reprocessing were designed, synthesized in a resistive furnace, and characterized by XRD, SEM/EDS, and FTIR spectroscopy. Chemical durability was determined by PCT-A procedure and compared to EPA glass and reference data. The glasses with 20 and 25 wt.% waste loading were found to be X-ray amorphous, homogeneous and chemically durable. Glass network formally had a relatively low degree of connectedness that was increased due to embedding of different structural groups thus improving chemical durability. Boron is present primarily in trigonal oxygen coordination. The glasses with 40-45 wt.% waste loading contained minor britholite phase concentrating rare earth elements and as expected trivalent actinides. Glassy product with up to 30 wt.% waste loading was also produced by cold crucible inductive melting at the IPCE RAS lab-scale unit equipped with 56 mm inner diameter copper cold crucible and energized from a 10 kW/5.28 MHz generator. The product was composed of vitreous phase and minor britholite with average composition K0.39Sr1.99Fe0.16Nd5.50Si7.96O26.60.

Calculations and TPMC simulations of the reduction of radioactive decays of a noble gas by cryo-panels

In the KATRIN neutrino mass experiment, radioactive decays inside the large UHV chamber of the Main Spectrometer can increase the background rate considerably and thus, diminish the sensitivity for the actual signal. In particular, the amount of the short-lived radon isotopes R219n and R220n has to be reduced. Three LN2 -cooled cryogenic baffles have been installed to capture the radon atoms before they decay. However, radon does not stick to a cold surface indefinitely. It either desorbs after a limited sojourn time, or it decays into polonium.We compare two different methods which describe the radon suppression for different baffle temperatures. The first method calculates the suppression factor analytically, using the effective pumping speed and the transmission probability of the baffles simulated with the Test Particle Monte Carlo code MolFlow+. A newly introduced effective sticking coefficient takes into account the radon lifetime and its mean sojourn time on the cold copper baffles. For the second method the MolFlow+ code was extended to simulate directly the radon lifetime and sojourn time. At the end experimental data are compared to the simulations and the mean sojourn time is determined as a function of the baffle temperature.

Enhancement and Prediction of Adhesion Strength of Copper Cold Spray Coatings on Steel Substrates for Nuclear Fuel Repository

Thick copper coatings have been envisioned as corrosion protection barriers for steel containers used in repositories for nuclear waste fuel bundles. Due to its high deposition rate and low oxidation levels, cold spray is considered as an option to produce these coatings as an alternative to traditional machining processes to create corrosion protective sleeves. Previous investigations on the deposition of thick cold spray copper coatings using only nitrogen as process gas on carbon steel substrates have continuously resulted in coating delamination. The current work demonstrates the possibility of using an innovative surface preparation process, forced pulsed waterjet, to induce a complex substrate surface morphology that serves as anchoring points for the copper particles to mechanically adhere to the substrate. The results of this work show that, through the use of this surface preparation method, adhesion strength can be drastically increased, and thick copper coatings can be deposited using nitrogen. Through finite element analysis, it was shown that it is likely that the bonding created is purely mechanical, explaining the lack of adhesion when conventional substrate preparation methods are used and why helium is usually required as process gas.

Surface Catalyzed Reaction Efficiencies in Oxygen Plasmas from Laser-Induced Fluorescence Measurements

Recent advancements in laser techniques for plasma facility diagnostic applications have enabled measurements of temperature and species gradients in the reacting zone above a high-temperature material. The laser measurements, which are done with submillimeter spatial resolution, provide a direct, qualitative illustration of surface-catalyzed reaction efficiency when reactive species distributions are compared for different materials. Further analysis of the measured quantities balancing the diffusive reactant flux with the consumption of atoms by surface reactions yields quantitative values for surface-catalyzed reaction rates and catalytic efficiencies. In this work, measurements of oxygen atom distributions in plasmas are presented for reference materials of high and low catalytic efficiency. The laser measurements are then used to determine values for atomic oxygen recombination to molecular oxygen. Comparisons of the present values of the recombination efficiency ( cold copper, cold quartz, and hot quartz) with previously published data suggest that this technique provides a viable method for characterizing the catalytic behavior of high-temperature materials in plasma test facilities.