Argon Samples Research Articles

Momentum dependent flavor radiative corrections to the coherent elastic neutrino-nucleus scattering for the neutrino charge-radius determination

Despite being neutral particles, neutrinos can have a non-zero charge radius, which represents the only non-null neutrino electromagnetic property in the standard model theory. Its value can be predicted with high accuracy and its effect is usually accounted for through the definition of a radiative correction affecting the neutrino couplings to electrons and nucleons at low energy, which results effectively in a shift of the weak mixing angle. Interestingly, it introduces a flavour-dependence in the cross-section. Exploiting available neutrino-electron and coherent elastic neutrino-nucleus scattering (CEνNS) data, there have been many attempts to measure experimentally the neutrino charge radius. Unfortunately, the current precision allows one to only determine constraints on its value. In this work, we discuss how to properly account for the neutrino charge radius in the CEνNS cross-section including the effects of the non-null momentum-transfer in the neutrino electromagnetic form factor, which have been usually neglected when deriving the aforementioned limits. We apply the formalism discussed to a re-analysis of the COHERENT cesium iodide and argon samples and the NCC-1701 germanium data from the Dresden-II nuclear power plant. We quantify the impact of this correction on the CEνNS cross-section and we show that, despite being small, it can not be neglected in the analysis of data from future high-precision experiments. Furthermore, this momentum dependence can be exploited to significantly reduce the allowed values for the neutrino charge radius determination.

A numerical study on the levitation system for droplet preparation in a fuel-coolant interaction experiment

The MISTEE facility at KTH was designed to investigate the process and phenomena of a molten droplet falling into a water pool that may be encountered in fuel-coolant interactions (FCI) during a severe accident of light water reactors. An aerodynamic levitation mechanism is proposed to hold the molten droplet during its preparation (melting and heating up to a prescribed temperature) in an induction furnace. The crucible is flushed with argon through an injection nozzle at the bottom to prevent the droplet from falling out of the crucible. A numerical simulation of the aerodynamic levitation system is performed in the present study with the objective of determining and optimizing the design. The problem was simplified as an isothermal two-phase flow in an axisymmetric geometry. The simulation is realized through ANSYS Fluent v17 platform, which employs the VOF method to track interfaces between two phases and the SST k-omega model to describe turbulence flow of argon gas. The numerical model is validated against tests performed in the MISTEE facility after mesh sensitivity study. It is then applied to investigate the impacts of various parameters on the facility levitation capability and the droplet stability. According to the simulation results, stable molten droplets can be obtained in the designed experimental setup. The simulation also provides the appropriate values of argon inlet velocity and sample mass at which a stable droplet can be obtained inside the crucible before its discharge. Either higher or lower inlet velocity will destabilize the formation of the droplet. Considering the temperature-dependent melt properties, both surface tension and viscosity affect the movement and deformation of the molten droplet. The wettability of melt on the crucible wall is critical to droplet formation, and it is found that a poor wettability can ensure the levitation of droplet.

Mitigation of ion-induced desorption for accelerator components by surface treatment and annealing

Ion-induced desorption is a serious limitation for beam intensity and life time in heavy ion accelerator facilities. To investigate how gas desorption is affected by surface conditions and bulk materials, oxygen-free copper, tungsten and aluminum samples were irradiated with 4.8 MeV/u Ca and Au ions. The surfaces were pretreated by various combinations of milling, lapping, polishing and etching, while the bulk is conditioned by thermal annealing. For all tested samples desorption yields of H2, H2O, CO and CO2 are presented. Diamond milling and polishing reduce ion-induced desorption to some extent, but most pronounced effects were achieved by ex-situ thermal annealing at 400 °C for about 4 h under ultra-high vacuum conditions. The decreased desorption persists for at least 9 months of storage in atmosphere. This is a strong indication that for the mitigation of desorption stimulated by high energy ion exposure, not only the surface properties have to be optimized, but also the treatment of the bulk material plays an important role. Storage of annealed samples in argon is favorable compared to storage in atmosphere.

Preservation of high-pressure volatiles in nanostructured diamond capsules.

High pressure induces dramatic changes and novel phenomena in condensed volatiles1,2 that are usually not preserved after recovery from pressure vessels. Here we report a process that pressurizes volatiles into nanopores of type 1 glassy carbon precursors, converts glassy carbon into nanocrystalline diamond by heating and synthesizes free-standing nanostructured diamond capsules (NDCs) capable of permanently preserving volatiles at high pressures, even after release back to ambient conditions for various vacuum-based diagnostic probes including electron microscopy. As a demonstration, we perform a comprehensive study of a high-pressure argon sample preserved in NDCs. Synchrotron X-ray diffraction and high-resolution transmission electron microscopy show nanometre-sized argon crystals at around 22.0 gigapascals embedded in nanocrystalline diamond, energy-dispersive X‑ray spectroscopy provides quantitative compositional analysis and electron energy-loss spectroscopy details the chemical bonding nature of high-pressure argon. The preserved pressure of the argon sample inside NDCs can be tuned by controlling NDC synthesis pressure. To test the general applicability of the NDC process, we show that high-pressure neon can also be trapped in NDCs and that type 2 glassy carbon can be used as the precursor container material. Further experiments on other volatiles and carbon allotropes open the possibility of bringing high-pressure explorations on a par with mainstream condensed-matter investigations and applications.

Exploring the superhydrophilicity of nanosecond laser textured silicon: a Raman analysis.

We present Raman analysis of nanosecond laser textured silicon. The samples have also been characterized by field emission scanning electron microscopy (FESEM) and x ray diffraction. Contact angles (CAs) are measured to trace the hydrophilic nature. Characterization of the textured samples in argon and air shows that cleavage cracks are developed during texturing. CA measurements reveal the superhydrophilic nature of textured samples obtained in the presence of ambient oxygen and argon. In vacuum, however, the hydrophilicity is decreased. Micro-Raman analysis indicates the formation of nano-sized cleavage cracks that impart stable superhydrophilic properties to textured silicon is supported from FESEM images also. On the other hand, in vacuum textured silicon, evidence of such cracks is not noticed, which is also supported by Raman analysis. Further, the hydrophilicity is decreased. A definitive trend appears to exist between Raman signatures and hydrophilicity. We believe that the study will further the understanding of the mechanistic aspect in designing textured silicon with a high degree of self-cleaning capability.

Cathodoluminescence of intrinsic defects in films La : HfZrO

Lanthanum-doped (La:(HfZr)O2) nanometer films of a solid solution of hafnium oxide and zirconium oxide are of great interest for the development of a universal memory that combines an unlimited number of RAM reprogramming cycles and nonvolatile flash memory. This work is devoted to studying the cathodoluminescent properties of La : HfZrO thin films with different contents of lanthanum. It is shown that the cathodoluminescence spectra are dominated by two emission bands with intensity maxima at 2.7 and 2.2 eV. The blue band with an energy of 2.7 eV is due to an oxygen vacancy in La : HfZrO. The study of the influence of the lanthanum impurity and annealing of the samples in argon suggests that the yellow band with the emission maximum at 2.2 eV is related to the oxygen divacancy. Keywords: luminescence, hafnium oxide, zirconium oxide, oxygen vacancy.

Катодолюминесценция собственных дефектов в пленках La : HfZrO

Lanthanum-doped (La:(HfZr)O2) nanometer films of a solid solution of hafnium oxide and zirconium oxide are of great interest for the development of a universal memory that combines an unlimited number of RAM reprogramming cycles and nonvolatile flash memory. This work is devoted to studying the cathodoluminescent properties of La:HfZrO thin films with different contents of lanthanum. It is shown that the cathodoluminescence spectra are dominated by two emission bands with intensity maxima at 2.7 and 2.2 eV. The blue band with an energy of 2.7 eV is due to an oxygen vacancy in La:HfZrO. The study of the influence of the lanthanum impurity and annealing of the samples in argon suggests that the yellow band with the emission maximum at 2.2 eV is related to the oxygen divacancy.

Reconstruction of the atmospheric 39Ar/Ar history

The radioactive isotope 39Ar is an ideal tracer for ocean ventilation, groundwater flow, and for dating mountain glaciers. With a half-life of 269 years, it covers the age range from a few tens to about 1800 years. We evaluate the input history of the atmospheric 39Ar in the past 2500 years. By measuring the 39Ar/Ar ratios of a modern argon sample and two old argon samples collected in 1959 and 1961, respectively, the anthropogenic contribution to the atmospheric 39Ar in the past 60 years is determined to be less than 15%. The temporal variation of the atmospheric 39Ar in the past 2500 years is calculated based on a cosmic-ray record derived from ice cores and tree rings. It is found that the atmospheric 39Ar/Ar ratio has changed by as much as 17% in that period of time. This input variation has to be taken into account and corrected for in future 39Ar dating applications.

The Impact of Sintering Atmosphere and Temperature on the Phase Evolution of High Surface Area LSCF Prepared by In Situ Carbon Templating

The thermochemical stability of lanthanum strontium cobalt ferrite (LSCF) processed between 1000 °C–1200 °C via the in situ carbon templating method was studied. This method generates high surface area ceramics at traditional solid oxide fuel cell (SOFC) sintering temperatures by generating a carbon template in situ and subsequently removing the template by oxidation at 700 °C. Argon processed samples produced an amorphous carbon template, whereas nitrogen tended to form graphitic carbon. Prior to the oxidation step, nitrogen samples comprised larger La2O3 crystallites (22–40 nm) compared to argon (9–17 nm). Upon oxidation, argon samples resulted in a pure LSCF phase with surface areas in the 21–29 m2·g−1 range, whereas nitrogen samples contained significant impurities. This demonstrates that the size of La2O3 crystallites formed during inert processing limited the ability to produce a pure LSCF phase. Symmetrical cells comprising nano-LSCF electrodes generated by the templating method were compared to cells sintered directly in air. Impedance results suggest that nano-LSCF cells and cells processed in air were dominated by interfacial charge transfer resistance and gas diffusion, respectively. The results map out conditions for preparing and integrating high surface area, nanostructured LSCF into SOFC electrodes at traditional sintering temperatures. Strategies for improving the interfacial resistance of nano-LSCF electrodes are discussed.

Commissioning the ATLAS Liquid Argon Calorimeter Phase-I Upgrade

Liquid argon (LAr) sampling calorimeters are employed by ATLAS for all electromagnetic calorimetry in the pseudo-rapidity region η < 3.2, and for hadronic and forward calorimetry in the region from η = 1.5 to η = 4.9. In the first LHC run (Run-1), a total luminosity of around 26 fb-1 was collected at centre-of-mass energies of 7-8 TeV. After detector consolidation during a long shut-down, Run-2 started in 2015 and around 150 fb-1 of data at a centre-of-mass energy of 13 TeV was recorded. With the end of Run-2 in 2018, a multi-year shutdown for the Phase-I detector upgrades began. As part of the Phase-I upgrade, new trigger readout electronics of the ATLAS LAr Calorimeter have been developed. Installation be-gan at the start of the LHC shut down in 2019 and is expected to be completed in 2020. A commissioning cam-paign is underway in order to realise the capabilities of the new, higher granularity and higher precision level-1 trigger hardware in Run-3 data taking. This contribution will give an overview of the new trigger readout system and the ongoing commissioning and installation efforts.

Tailoring the NIR range optical absorption, band-gap narrowing and ferromagnetic response in defect modulated TiO2 nanocrystals by varying the annealing conditions

In this investigation, we report the influence of oxygen vacancy and Ti3+ related defects in the visible and IR range absorption as well as on the bandgap and magnetism of TiO2 nanocrystals annealed in different atmospheres. The X-ray diffraction patterns and Raman spectra indicate anatase phase formation and TEM analysis confirm the highly crystalline nature of TiO2 nanocrystals with a particle size of around ~ 9–12 nm. Significant absorption in the visible and IR region along with much-reduced bandgap is observed in argon, hydrogen and vacuum annealed samples. These samples exhibit strong visible photoluminescence associated mostly with oxygen vacancies. The room temperature ferromagnetism observed in argon annealed TiO2 nanocrystals is explained by taking into consideration the concept of bound magnetic polarons. Hence, this study reports the formation of TiO2 nanocrystals with extended absorption in visible as well as in IR region and ferromagnetism at room temperature which could have potential applications for future technologies.

(Invited) In-Situ Liquid Phase TEM Studies of Corrosion Initiation in Aluminium Alloys

Aluminium alloy 2024-T3 (AA2024-T3), widely applied in aerospace industries, may suffer from severe localized corrosion as a result of its relatively complex and heterogeneous microstructure. The corrosion initiation in such a critical alloy is governed by dynamic processes that take place at the nanoscale. A thorough understanding of the sequential stages of corrosion initiation is of pivotal importance to developing efficient inhibition strategies and demands high resolution techniques along with the ability of real-time recording of nanoscopic events.However, to date, it has not yet been possible to unambiguously show the morphological and electrochemical characteristics during local corrosion of AA2024-T3. In particular, local corrosion initiation linked to nano-/microstructural heterogeneities, intermetallic particles (IMPs), take place relatively fast and at the nanoscopic scale, rendering the study of the early stages of corrosion experimentally virtually impossible until now. Herein, we show, for the first time, the dynamic evolution of site-specific local corrosion of AAs from early surface initiation to depth propagation at the nanoscale using a dedicated in-situ liquid phase-transmission electron microscopy (LP-TEM) experimental facility.Transmission electron microscopy (TEM), capable of revealing microstructural and compositional variations in alloys at atomic and nanoscopic scale, has been applied widely in corrosion studies but mostly ex-situ and quasi in-situ. These approaches are not straightforward as artefacts and contaminations might be introduced into the system during the ex-situ and quasi in-situ experiments, including dehydration of surfaces and therefore may not fully represent the real conditions. With recent technological advances, thanks to the development of dedicated microelectronic mechanical systems (MEMS), it is now possible to fabricate components like nanoreactors (NRs) to study complicated corroding systems at the nanoscale in-situ. In fact, NRs employed in TEM studies enable to monitor morphological and compositional evolutions in materials in-situ as a result of interaction with aggressive environments like a gas or liquid.In this study, we put efforts into providing direct evidence for the nanoscopic role of intermetallics in AA2024-T3 localized corrosion through quasi in-situ TEM and in-situ LP-TEM approaches. Quasi in-situ studies were implemented by intermittently exposing the Argon ion-milled thin samples to 0.01 M NaCl solution. For in-situ LP-TEM, the real TEM specimens (lamellae) were first fabricated out of regions of interest with a FEI Helios focused ion beam. Then, the lamellae were transferred successfully to home-made NRs using an easy-lift technique. The NRs, equipped with an electrochemical set-up, were specially designed for corrosion studies. A Cs-corrected FEI Titan TEM was employed to perform real-time studies in scanning TEM (STEM) mode. Although a good resolution is still a major challenge for in-situ LP-TEM, the results revealed that intermetallic phases regardless of their types are active and prone sites to localized corrosion attack themselves and the observations finally show and elucidate initial stages of IMP-induced pitting corrosion and copper redistribution mechanisms in AA2024-T3.

ATLAS LAr calorimeter performance in LHC Run 2

Liquid argon (LAr) sampling calorimeters are employed by ATLAS for all electromagnetic calorimetry in the pseudorapidity region |η| < 3.2, and for hadronic and forward calorimetry in the region from |η| = 1.5 to |η| = 4.9. In the first LHC run a total luminosity of 27 fb−1 has been collected at center-of-mass energies of 7–8 TeV. After detector consolidation during a long shutdown, Run 2 started in 2015 and 147 fb−1 of data at a center-of-mass energy of 13 TeV have been recorded. In order to realize the level-1 trigger acceptance rate of 100 kHz in Run 2 data taking, the number of read-out samples recorded and used for the energy and the time measurement has been modified from five to four while keeping the expected performance. The well calibrated and highly granular LAr calorimeter reached its design values both in energy measurement as well as in direction resolution. This contribution gives an overview of the detector operation, hardware improvements, changes in the monitoring and data quality procedures, to cope with increased pileup, as well as the achieved performance, including the calibration and stability of the electromagnetic scale, noise level, response uniformity and time resolution.

ATLAS LAr Calorimeter performance in LHC Run 2

Liquid argon (LAr) sampling calorimeters are employed by ATLAS for all electromagnetic calorimetry and for hadronic and forward calorimetry in the region 1.5 < |η| < 4.9. In the first LHC run a total luminosity of 27 fb−1 has been collected at center-of-mass energies of 7–8 TeV . After detector consolidation during a long shutdown, Run-2 started in 2015 and 139 fb−1 of data at a center-of-mass energy of 13 TeV have been recorded. In order to accomplish the Level-1 acceptance rate of 100 kHz in Run-2 data taking, the number of read-out samples recorded and used for the energy and the time measurement has been modified from five to four while keeping the expected performance. The well calibrated and highly granular LAr Calorimeter reached its design goals, both in terms of energy and direction measurement. This contribution gives an overview of the detector operation, hardware improvements, monitoring and data quality procedures, as well as the achieved performance, including the calibration and stability of the electromagnetic scale, noise level, response uniformity and time resolution.

A new method of low-temperature cementation of stainless steel by decomposition of C2H2 in low-energy electron beam generated plasma

The method of low-temperature (400–500°C) cementation of AISI430 stainless steel by decomposition of acetylene in a wide (100 cm2) low-energy (200–300 eV) electron beam generated plasma in an Ar+C2H2 gas mixture was investigated. The composition of a beam Ar+C2H2-plasma is investigated and it is shown that the degree of decomposition of acetylene varies with the current and energy of the electron beam. It is shown that the magnitude of the flow of acetylene significantly affects the formation rate and hardness of the hardened layer. From the obtained results it can be seen that at fixed values of argon pressure ( ~ 0.8 mTorr), beam current (3.5 A), bias voltage (–120 V), sample temperature (500°C) and exposure time (3 h) increase in QC2H2 from 1 to 4–5 cm3·min−1 leads to an increase in the thickness and microhardness of the hardened layer. With a further increase in QC2H2, an abrupt decrease in the rate of formation of the hard layer occurs.

Thermal Processing of Chloride-Contaminated Plutonium Dioxide.

Over 80 heat treatment experiments have been made on samples of chloride-contaminated plutonium dioxide retrieved from two packages in storage at Sellafield. These packages dated from 1974 and 1980 and were produced in a batch process by conversion of plutonium oxalate in a furnace at around 550 °C. The storage package contained a poly(vinyl chloride) (PVC) bag between the screw top inner and outer metal cans. Degradation of the PVC has led to adsorption of hydrogen chloride together with other atmospheric gases onto the PuO2 surface. Analysis by caustic leaching and ion chromatography gave chloride contents of ∼2000 to >5000 ppm Cl (i.e., μgCl g–1 of the original sample). Although there are some subtle differences, in general, there is surprisingly good agreement in results from heat treatment experiments for all the samples from both cans. Mass loss on heating (LOH) plateaus at nearly 3 wt % above 700 °C, although samples that were long stored under an air atmosphere or preexposed to 95% relative humidity atmospheres, gave higher LOH up to ∼4 wt %. The majority of the mass loss is due to adsorbed water and other atmospheric gases rather than chloride. Heating volatilizes chloride only above ∼400 °C implying that simple physisorption of HCl is not the main cause of contamination. Interestingly, above 700 °C, >100% of the initial leachable chloride can be volatilized. Surface (leachable) chloride decreases quickly with heat treatment temperatures up to ∼600 °C but only slowly above this temperature. Storage in air atmosphere post-heat treatment apparently leads to a reequilibration as leachable chloride increases. The presence of a “nonleachable” form of chloride was thus inferred and subsequently confirmed in PuO2 samples (pre- and post-heat treatment) that were fully dissolved and analyzed for the total chloride inventory. Reheating samples in either air or argon at temperatures up to the first heat treatment temperature did not volatilize significant amounts of additional chloride. With regard to a thermal stabilization process, heat treatment in flowing air at 800 °C with cooling and packaging under dry argon appears optimal, particularly, if thinner powder beds can be maintained. From electron microscopy, heat treatment appeared to have the most effect on degrading the square platelet particles compared to those with the trapezoidal morphology.

Uranium brannerite with Tb(III)/Dy(III) ions: Phase formation, structures, and crystallizations in glass

AbstractUranium brannerite phases with terbium(III) or dysprosium(III) ions have been investigated. The precursors with molar ratio of 0.5:0.5:2 (Ln: U: Ti with Ln = Tb or Dy) were prepared and calcined at 750°C in argon. Sintering the pelletized samples in argon at 1200°C led to the formation of pyrochlore phases with TiO2 rutile and U‐rich oxides while sintering in air led to the formation of brannerite phases with the nominal composition close to Ln0.5U0.5Ti2O6 together with trace amounts of TiO2 rutile and LnUO4. Incorporating an excess of TiO2 (20 wt%) and sintering at higher temperature (1300°C) resulted in no obvious change to the phase equilibrium. As designed, pentavalent uranium has been proven to be dominant in these brannerite phases with diffuse reflectance spectroscopy. The relationships between the cell parameters and the ionic radii of the A‐site cations have been explored and rationalized from the structure point of view for a range of titanate brannerite phases (ATi2O6). In addition, the crystallization of Ln0.5U0.5Ti2O6 brannerite in glass has been achieved via heat treatment at 1200°C and confirmed with X‐ray diffraction, scanning electron microscopy‐energy dispersive spectroscopy and transmission electron microscopy–selected area electron diffraction.

Kinetic study of carbothermal reduction of zirconia under vacuum condition

In this research, formation mechanism and kinetics of vacuum carbothermal synthesis of zirconium carbide using zirconium acetate and sucrose are discussed. The study of non-isothermal reduction was conducted by thermogravimetry analysis and heating the samples in argon and vacuum conditions up to 1773 K, and then the heat exchange values of reactions were calculated. Isothermal formation mechanism of carbide phase was investigated by heating the samples at 1473 K and 1673 K in argon and vacuum atmospheres followed by X-ray diffraction and quantitative phase analysis. Results showed that in non-isothermal state, the carbothermal reduction of zirconia is a heterogeneous reaction with multiple steps. For isothermal reaction, the kinetic parameters such as activation energy and pre-exponential factor were calculated as 70.56 kJ mol−1 and 11.22 × 10−2 S−1, respectively. It was presented that the activation energy value extracted from isothermal reaction is completely in accordance with the final step of non-isothermal results.

ATLAS LAr calorimeter performance in LHC run 2 and electronics upgrades for next runs

Liquid argon (LAr) sampling calorimeters are employed by ATLAS for all electromagnetic calorimetry in the pseudo-rapidity region |η|<3.2, and for hadronic and forward calorimetry in the region from |η|=1.5 to |η|=4.9. In the LHC Run 2 about 150 fb−1 of data at a center-of-mass energy of 13 TeV have been recorded. The well calibrated and highly granular LAr Calorimeter reached its design values both in energy measurement as well as in direction resolution. Electronics developments are pursued for the trigger readout of the ATLAS LAr Calorimeter towards the Phase-I upgrade scheduled in the LHC shut-down period between December 2018 and early 2021. Trigger signals with finer spatial granularity and higher precision are needed in order to improve the identification efficiencies of electrons, photons, taus, jets and missing energy, at high background rejection rates, already at the Level-1 trigger. Following new TDAQ buffering requirements and high expected radiation doses in the pileup conditions of the high-luminosity LHC, the LAr Calorimeter electronics will be further upgraded (Phase-II) to readout the full 182,500 calorimeter cells at 40 MHz with 16 bit dynamic range. Developments of low-power preamplifiers and shapers to meet these requirements are ongoing in 130 nm CMOS. In order to digitize the analogue signals on two gains after shaping, radiation-hard, low-power 40 MHz 14-bit ADCs are developed using a SAR architecture in 65 nm CMOS. This contribution gives an overview of the detector operation, changes in the monitoring and data quality procedures, to cope with increased pileup, as well as the achieved performance. Results of ASIC developments including quality assurance and quality control (QA/QC) and radiation hardness evaluations, performances of the pre-production boards and results of the system integration tests, progress of QA/QC of final production boards are presented along with the overall system design for the Phase-I upgrade. Results of tests of the first prototypes of front-end components are presented, along with design studies on the performance of the off-detector readout system for the Phase-II upgrade.

Combustion Characteristics of Physically Mixed 40 nm Aluminum/Copper Oxide Nanothermites Using Laser Ignition.

This paper reports on the ignition and flame propagation characteristics of aluminum/copper oxide (Al/CuO) nanothermite at different packing density, manufactured from 40 nm commercial Al and CuO nanopowders. A 3.5 W continuous wave laser was used to ignite the samples in argon at atmospheric pressure, and a high speed camera captured the flame propagation. The high speed images revealed that the fast laser heating creates significant material ablation, followed by heat transfer along the heated surface. The bulk ignition occurs near the edge of the top surface, followed by the self-sustained burning. Lightly pressed powders (90% porosity) ignited in ~0.1 ms and the burning front propagated at around 200 m/s, while the dense pellets (40–60% porosity) ignited in ~1 ms and the burning front propagated at around 10 m/s. These results indicate that the reaction mechanism changes from mass convection to heat diffusion with increasing the packing density. The ignition and burn speeds of these Al/CuO nanothermites at different equivalence ratios (ERs), along with SEM images of pre- and post-combustion, illustrate that the homogeneity of the mixture is a critical parameter for optimizing the performance. The Al rich mixtures show significantly lower ignition delays and higher burn speeds.