Shock Wave Mediated Plume Chemistry for Molecular Formation in

Jan 6, 2016 - Early in the plasma expansion, the generated shock wave at the plume edge acts as a barrier for the combustion process and molecular ...
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Shock Wave Mediated Plume Chemistry for Molecular Formation in Laser Ablation Plasmas Sivanandan S. Harilal,* Brian E. Brumfield, Bret D. Cannon, and Mark C. Phillips Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States S Supporting Information *

ABSTRACT: Although it is relatively straightforward to measure the ionic, atomic, molecular, and particle emission features from laser ablation plumes, the associated kinetic and thermodynamic development leading to molecular and nanocluster formation remain one of the most important topics of analytical chemistry and material science. Very little is known, for instance, about the evolutionary paths of molecular and nanocluster formation and its relation to laser plume hydrodynamics. This is, to a large extent; due to the complexity of numerous physical processes that coexist in a transient laser-plasma system. Here, we report the formation mechanisms of molecules during complex interactions of a laser-produced plasma plume expanding from a high purity aluminum metal target into ambient air. It is found that the plume hydrodynamics plays a great role in redefining the plasma thermodynamics and molecular formation. Early in the plasma expansion, the generated shock wave at the plume edge acts as a barrier for the combustion process and molecular formation is prevalent after the shock wave collapse. The temporally and spatially resolved contour mapping of atoms and molecules in laser ablation plumes highlight the formation routes and persistence of species in the plasma and their relation to plume hydrodynamics.

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gas leads to spatial confinement, aiding molecular and cluster generation.10 However, even though the LA process is extensively used in a variety of applications, it is still not fully understood when and where these molecules and particles are formed. Understanding the mechanisms of molecule and particle formation in LA plumes is crucial both from a fundamental standpoint of plasma chemistry and also for applications of analytical techniques using LA.11,12 Moreover, analysis of molecular emission from LA plumes yields higher isotopic shifts when compared to atomic species.2,13 A laser produced plasma (LPP) system generated from LA of Al provides a model system for understanding the evolution of ionic and atomic to molecular species generation,14−16 the plasma fundamentals,17,18 and plume hydrodynamics.7 An Al LPP in ambient air is also an excellent system to study the role of plasma chemistry on plume hydrodynamics or vice versa. Analysis of optical emission spectra can easily distinguish Al ions, Al neutrals, and molecular species such as AlO; combining optical spectroscopy with time- and space-dependent measurements provides insight into the temporal and spatial evolution of these species. In particular, the formation of AlO molecules during Al plasma interaction with air is an intriguing process which involves gas-phase combustion of Al with surrounding oxidizers.18−20 Although both AlO and AlN formation are possible in ambient air, emission spectra show features from

he process of laser ablation (LA) is used for numerous applications with the plasma plume expanding into environments ranging from high vacuum to liquids. Some of the well-known analytical applications of LA are laser-induced breakdown spectroscopy (LIBS),1,2 LA inductively coupledplasma mass-spectrometry (LA-ICPMS),3,4 LA-laser absorption spectroscopy (LA-LAS),5 etc. Several LA applications are performed at moderate to high vacuum conditions, while others are performed at or near atmospheric pressure levels. LA plume expansion into vacuum conditions is less complex compared to its expansion in the presence of a reactive gas like air.6 In the latter scenario, the plasma chemistry will redefine the plume hydrodynamics and evolution of the chemical composition of the plume. Moreover, the presence of a cover gas causes effects such as plume splitting, sharpening, confinement, and the formation of internal plume structures.7 Ions, atoms, molecules and nanoclusters are generated during the life of the LA plume, and their maximum concentrations in the plasma plumes are separated in time8 and strongly dependent on the nature and pressure of the cover gas. For example, the LA plumes are hotter and denser for the earliest times of expansion where emission from ions dominate (≲1 μs) followed by atoms (∼0.5−10 μs). Molecular species are generally formed at later times (∼2−50 μs), and their formation is explained as due to atomic collisions and recombination, which is prevalent when the plasma has cooled down to lower temperatures.9 Aerosols and nanoclusters are generated through a nucleation−condensation process at the end of the lifecycle of the LA process.10 It has been broadly reported that the presence of a moderate to high pressure cover © XXXX American Chemical Society

Received: November 1, 2015 Accepted: January 6, 2016

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DOI: 10.1021/acs.analchem.5b04136 Anal. Chem. XXXX, XXX, XXX−XXX

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Analytical Chemistry only AlO,15 which is consistent with the standard heat of formation being strongly exothermic for AlO and strongly endothermic for AlN.21 During Al combustion, other molecules such as Al2O and AlO2 can also be formed as intermediates, but they do not have strong emission bands in the visible region.20 Although significant efforts have been undertaken to understand the local conditions (mainly temperature) of LA plumes by analyzing molecular emission features,17−19,22,23 the kinetics of molecular formation and its relation to plasma chemistry are not well-known.11,12 In this article we report the role of plasma gas dynamics on the formation of AlO in laser-produced Al plasmas generated in air at atmospheric pressure. A multitude of plasma diagnostic tools, viz., focused shadowgraphy, monochromatic fast gated imaging, optical emission spectroscopy (OES), and time-offlight-emission spectroscopy (TOF-ES), are used to infer the roles of plume hydrodynamics and plasma chemistry on AlO formation throughout the evolution of the LA plume. Our results highlight the complex interplay between plume hydrodynamics and plasma chemistry leading to the formation of AlO and their influence on the persistence of all species in the plume.

ablation laser using two digital delay generators with a maximum temporal jitter of ≤1 ns.

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RESULTS AND DISCUSSION LA Evolution and Emission Spectroscopy. OES is often used to identify various excited species (atoms, ions, molecules) in a LA plume and to evaluate the fundamental properties of the plasma.26 Time-resolved OES studies of transient laser plasmas are also a valuable experimental tool for investigating the plasma chemistry leading to molecular formation.11 Lowresolution spectra in the wavelength range of 300−600 nm obtained from the Al plasma at various times after the onset of plasma formation are given in Figure 1A. As seen in the figure,

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EXPERIMENTAL DETAILS LA and Sample. The LA plumes on an Al target (99.999% purity) were produced using pulses from a Q-switched Nd:YAG laser (1064 nm, 6 ns full width half-maximum (fwhm)). The target disc was mounted on a motorized x-y-z translator to move the sample and avoid complications from drilling and cratering. All experiments were performed at atmospheric pressure (∼760 Torr) and at room temperature (21 °C). The laser beam is focused normal to the target surface using a plano-convex lens with an estimated spot size ∼1 mm, providing a laser fluence ∼12 J cm−2. The laser pulse is also used for cleaning the sample surface before spectral measurements. Emission Spectroscopy. Experimental details of emission spectroscopy24 can be found elsewhere. Briefly emission from the plasma was collected at right angles to the plasma expansion direction using appropriate optics and imaged onto the slit of a 0.5 m triple grating spectrograph. This imaging optical system was translated to monitor different parts of the plume with a spatial precision of ∼100 μm. The spectrograph consisted of two detectors. An intensified CCD (ICCD) was used to record the wavelength dispersed spectra while a photomultiplier tube (PMT, 2 ns rise time) was used to record the TOF or temporal evolution of various species in the plume with high time precision in conjunction with a 1 GHz storage oscilloscope. The 2-D plume imaging was accomplished by positioning an ICCD orthogonal to the plasma expansion direction. An objective lens was used to image the plasma onto the camera. Narrowband filters were positioned in front of the ICCD to discriminate emission from atoms and molecules. Shadowgraphy. Focused shadowgraphy25 was used to observe the shockwave propagation emanating from the Al laser plasmas. A frequency doubled Nd:YAG laser at 532 nm and a pulse duration of ∼4 ns fwhm was used for shadowgraphy. In this setup a relay lens was used to image the plasma plume onto a CMOS detector. To record the plasma expansion at different time windows with good spatial precision, the magnification of the shadowgram image was adjusted by using various lens combinations. The probe laser was synchronized with the

Figure 1. Time-resolved plasma spectra recorded at 0.6 mm from the target surface after the onset of plasma formation. The gate times used were 2 ns, 2 ns, 2 μs, and 20 μs for delays of 30 ns, 500 ns, 10 μs, and 50 μs, respectively. The insets in part d correspond to zoomed AlO emission spectral region.

during the initial stages, continuum emission dominates over spectral line emission. As the plasma expands, the line-tocontinuum ratios improve, and at times ∼0.1−1 μs the spectrum mainly consists of ionic and atomic lines. The recorded spectrum at 500 ns is dominated by emission from Al I and Al II with a weak background emission. At later times (≳10 μs), emission from Al I dominates but weak emission from the B2Σ − X2 Σ electronic band of AlO is also present. As time evolves, the molecular emission increases significantly relative to the atomic emission. A high resolution spectrum of AlO is given in Figure 2 which clearly shows a series of vibrational band sequences (Δν = 3,2,1,0,−1,−2) with resolved rotational structure. The physio-chemical phenomena leading to AlO formation are strongly connected to the local plasma conditions which change dynamically in a laser-plasma system. Because the emission spectra of species in the plasma are strongly influenced by changes in the fundamental properties (density and temperature) of the plasma with time, OES is an accurate and nonintrusive method for measuring various plasma properties such as the temperature, density, species distribution, ionization, and kinetics of the plume.26 We used the Stark broadened profiles of Al II at 281 nm to estimate the electron density.27 Stark broadening is a well-known method for estimating electron density during the time evolution (∼50 B

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Figure 3. Comparison between the experimental and a simulated spectrum of the Δν = −1 band sequence for the B-X electronic transition of AlO. The experimental spectrum was collected at a 25 μs delay/10 μs gate width. The simulated spectrum is the result of the least-squares fitting analysis using PGOPHER. A constant Gaussian slit function value of 0.045 nm was used for simulating the spectrum.

Figure 2. High-resolution spectrum of AlO with vibrational band sequences (Δν = 3, 2, 1, 0, −1, −2) and with resolved rotational structure. The recording parameters are 10 μs gate delay and 100 μs gate width.

μs is only 2.2 times the combined uncertainty estimates, which do not include several sources of potential error, and so are not statistically significant. Plume Hydrodynamics: Al and AlO Imaging. According to spectral features given in Figure 1, the AlO emission peaks are at very late times indicating poor initial mixing of the expanding laser ablation plume with ambient gas and attributed to combustion mechanisms.20 However, because AlO is formed through plasma chemistry when the plume interacts with the ambient air, the plume hydrodynamics may greatly control the spatiotemporal evolution of AlO formation. Fast photography in conjunction with narrow spectral band-pass interference filters provides the spatiotemporal evolution of various species in the plume, and this information is extremely useful for understanding the hydrodynamic expansion features, velocity differences, and uneven spatial distribution among various species.11,33,34 Figure 4 shows the distribution of excited AlO

ns to 10 μs) of the plasma. At very early times, continuum emission masks any line emission and hence the Stark method is not a viable technique. At later times (≳5 μs), the instrumental line width of the spectrograph dominates over the Stark broadening of the atomic line. Under the irradiation conditions used in the present experiments, the estimated densities of the plume are (8.0 ± 0.5) × 1018, (4.0 ± 0.3) × 1017, and (4.0 ± 0.3) × 1016 cm−3 at times 70 ns, 500 ns, and 7 μs, respectively. Such a rapid reduction in electron density with time was previously reported.28 The temperature estimate of the Al plasma at ambient conditions is challenging considering the limited number of transitions that are available in the visible regime; therefore, the PrismSPECT collisional radiative spectral analysis code29 was used for inferring temperature. The estimated temperatures by spectral comparison with PrismSPECT at various times are (14300 ± 1100) K and (6500 ± 700) K at 500 ns and 10 μs after the onset of plasma generation. At later times (≳10 μs), the emission intensity from AlO is sufficient for spectral analysis and least-squares contour fitting of the Δν = −1 band sequence of the B-X system is used to estimate the molecular temperature. This fitting was performed in the molecular spectra analysis program PGOPHER.30 Here the molecular temperature describes the rotational and vibrational temperature for AlO, which are based on the assumption of local thermodynamic equilibrium (LTE) under the experimental conditions.18 The model developed in the current work simulates the AlO B-X band in PGOPHER using spectroscopic constants taken from Saksena et al.31 and Hebert et al.32 For simulation, only emission from transitions in the Δν = −1 band are considered due to a complete set of spectroscopic constants and freedom from interfering emission lines. An example of the agreement between the model and an experimental spectrum is shown in Figure 3. Performing this analysis for emission spectra collected at gate delays of 10 μs, 25 μs, and 50 μs yields estimated molecular temperatures of (4940 ± 90) K, (4220 ± 50) K, and (3640 ± 40) K, respectively. The AlO molecular temperatures observed in this work are comparable to those reported for ablation from an Al target using a similar fluence.18 The uncertainties in these temperatures and those from PrismSPECT are the one standard deviation values taken from the least-squares fitting analysis and do not include uncertainties from the spectroscopic parameters. The difference between the inferred electronic temperature using PrismSPECT and the molecular temperature using PGOPHER at 10

Figure 4. Distribution of excited AlO and Al species in an Al plasma at atmospheric pressure. For recording these images, narrow band-pass filters with transmission centered at 482 nm (AlO) and 396 nm (Al) were used. The images are normalized to its maximum intensity and given in false color. The color sequence black, green, yellow, red, and white represent the range of normalized intensities from 0 to 1.

and Al species in the plasma at various times during plasma evolution. Each image given is obtained from a single laser shot and normalized to its maximum intensity. At earlier times, most of the AlO emission is seen very near to the target surface. However, at later times, especially at times ≳20 μs, the AlO species is found to propagate normal to the target surface. A void in AlO emission can also be seen closer to the target at C

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wave (R α t0.4) theory. On the basis of the shadowgraphic results, the shock wave will act as a barrier and restrict plasma chemistry induced by the cover gas. However, the shock waves eventually cease propagation when the shock front pressure equilibrates with the background pressure. When this occurs, the boundary established by the shock front will collapse, allowing an influx of O2 that will oxidize Al in the plume. An estimate for the plume stopping distance is made by employing an R−t plot and the drag model (R = R0[1 − exp(−βt)], where R0 is the stopping distance of the plume and β is the slowing coefficient). According to the drag model, the shock will eventually come to rest at 5.8 mm by ∼20 μs due to resistance from collisions with the background gas. The AlO maximum emission region is found to start moving away from the target surface after these times based on AlO monochromatic images (Figure 4); this indicates that the oxidation of the Al becomes prevalent after the collapse of the shock wave. Even though the shock wave acts as a boundary between the plume species and background air molecules, which in effect limits the oxidation of Al species, strong AlO emission can be seen near to the target surface at earlier times. Computational fluid dynamics (CFD) modeling results predict that the shock pressure is significantly higher in the normal direction (plume expansion direction) compared to that parallel to the surface of the target.36 This can be understood considering the rapid expansion of laser plasma along the target normal where most of the energetic ions are concentrated.8 So the presence of AlO emission features at early times could be due to air gas leakage to the plasma volume through the weaker shock wave boundary closer to the target periphery. This is also supported by the “disc-like” shape of the AlO emission zones observed closer to the target before the shock collapse time. However, a bright “spherical shape” emission zone is also noticeable at early times (4 and 7 μs snapshots) that may be due to other emission features, such as continuum and other interfering lines, that are present at early times in the plasma evolution and fall within the spectral window of the optical filter. This argument is supported by near absence of AlO emission in early time spectral features given in Figure 1. Comparing the AlO monochromatic images given in Figure 4 and the shadowgram images given in Figure 5, it can be concluded that the oxidation of Al species along the shock boundary is potentially weak, which is rather surprising. It can be anticipated that the high velocity ions occupied in the plume front positions at early times will be neutralized because of interaction with cold ambient gas species which should eventually lead to oxidation of Al species. Previous studies employing laser-induced fluorescence (LIF) showed an intense AlO signal along the plume front positions;16,38 however, those experiments were performed at lower O2 ambient pressures (0.5−0.075 Torr) which may lead to stronger plume-ambient species interpenetration in comparison to the atmospheric background pressure used in the present studies. Apart from that, the dynamic range of the ICCD may limit the observation of weaker AlO emission along the shock boundary which is typically confined to a very narrow spatial location. Spatiotemporal Evolution of Al and AlO. Optical timeof-flight (OTOF)24 studies employing a monochromator-PMT combination, which provides significantly higher dynamic range compared to the filtered ICCD imaging technique, was used to investigate further the spatiotemporal distributions of Al and AlO and to confirm the weak AlO emission along the shock boundary. OTOF measurements were made to generate

later times which could be due to vorticity generated by initial shockwaves.11,35 Unlike AlO, emission from Al I is found to move away from the target surface until the confinement provided by the ambient air background effectively blocks its propagation. However, both Al and AlO species show nearly identical distributions at later times (≳40 μs) though there are significant differences in their distribution at early times. Plume Hydrodynamics: Shock Waves. The present experiments were performed at 1 atm air pressure and the presence of a reactive environment like air dramatically influences the laser plasma generation, expansion features, and plume chemistry. Recent modeling and experimental studies show that under the experimental conditions used in the present work, the initial pressure of the plasma can reach ≳100 MPa and drops by more than 2 orders of magnitude within 2 μs after the plasma formation.36 The initial high plume pressure will compress the cover gas leading to the formation of shock wave in the plume interface. Since gas-phase Al is involved in the formation of AlO, the differences in Al and AlO distributions seen in Figure 4 could be related to availability of oxygen in the plasma, which is controlled by shock waves developed in the plasma−gas interface. We used focused shadowgraphy to record the shock waves generated by the Al plasma in air and results are given in Figure 5a. Different

Figure 5. (a) Shadowgrams taken at different times after the onset of plasma formation. Please note the differences in spatial scales for the series of shadowgram given in the top and bottom row. (b) The R−t plot obtained from the shadowgram is given along with spherical blast wave and drag model fits.

magnifications were used to capture shadowgrams at early (0− 600 ns) and later times (0.5−10 μs). The recorded shadowgrams show the shock waves continue to propagate out of the field of view after 10 μs. The position−time (R−t) plot obtained from the shadowgrams is given in Figure 5b along with predictions from the “blast wave” model,37 demonstrating that the experimental results agree well with a spherical blast D

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correlated to the 2D monochromatic images (Figure 4) where AlO is found to expand after the shock wave collapse (∼20 μs). However, similar to the 2D imaging, the AlO emission in the shock front region is found to be very weak or negligible even with a PMT as the detector. The persistence of both Al and AlO emissions are found to peak approximately 1 mm from the target, while a significant reduction in persistence is noticed at farther distances due to confinement effects. Plasma Chemistry Leading AlO Formation. The temporal and spatial distributions obtained for Al and AlO using fast gated imaging and OTOF mapping show that they coexist for ∼100 μs. It is well documented that due to space charge and mass effects the highly charged ions possess the largest velocity followed by neutrals and molecules, while a similar sequence is expected in persistence for the species in the plume due to various recombination mechanisms.39 Particle transport and energy exchange in plasmas are dictated by ionization and recombination rates along with collision frequency of various species in the plume which strongly depends on number density and temperatures. Since AlO is formed during the oxidation of Al species in the plasma, the collisions of Al neutrals with O neutrals and O2 molecules will be the predominant mechanism for its formation. At early times, the shock waves at the plume front effectively act as a barrier between the plume and ambient gas, restricting the interaction between O2 in the cover gas and the species in the plume thus slowing the formation of AlO. However, reaction of the neutral population with oxygen can be expected with time especially after the collapse of the shock front. So the coexistence of emission from Al and AlO in the same spatial regions of the plume out to ∼100 μs is connected directly to the chemistry for the formation and destruction of AlO. The gas phase reaction routes to AlO formation and removal in a proposed mechanism for the combustion of aluminum are20,40

spatiotemporal contour maps of Al and AlO emission, given in Figure 6. The emission lines selected for OTOF contour

Al + O2 ↔ AlO + O;

ΔH = 11.3

Al + O + M ↔ AlO + M;

kJ ; mol

ΔG = − 98.5

ΔH = −504.8

kJ ; mol

kJ mol

(1)

ΔG = 63.5

kJ mol

(2) Figure 6. Spatiotemporal contour maps of excited Al and AlO species in an Al laser produced plasma in air at atmospheric pressure levels. The emission features were obtained using 396 nm for Al and 484.2 nm 0−0 band head for AlO.

AlO + O2 ↔ AlO2 + O;

ΔH = 100.6

kJ ; mol

ΔG = 77.9

kJ mol

(3)

where the standard enthalpy and Gibbs free energy changes, ΔH and ΔG, respectively,21 have been calculated for a temperature of 5000 K. Along with the above three reactions, the recombination of atomic O is also important and is described by the following reaction pathway:

mapping are Al (396 nm, 3s23p −3s24s) and AlO (484.2 nm, 0−0 band head). The contour plots clearly show a comprehensive picture of the evolution histories of Al and AlO. Both Al and AlO show very complex spatiotemporal distributions with multimodal profiles at all distances from the target, with the coexistence of Al and AlO emission for ∼100 μs. A sharp and fast emission zone is clearly evident in the Al contour map, which has similar expansion features to Al ions, and is likely generated by recombination of those ions. Typical free expansion velocities of Al II and Al neutrals in vacuum under similar experimental conditions are ∼3 × 106 and ∼2 × 106 cm/s, respectively, and their persistence is limited to a few microseconds.27 The significant increased persistence of Al species in the contour map is caused by the effective ambient gas confinement. Both Al and AlO possess an approximately similar delayed component, though their expansion features are somewhat different at early times and at short distances. The differences in expansion dynamics at closer distances can be

O + O + M ↔ O2 + M;

ΔH = − 516.0

kJ ; mol

ΔG = 162.0

kJ mol

(4)

In high temperature environments, all the above-mentioned reactions can proceed in both directions toward an equilibrium point determined by ΔG(T), which is a function of temperature of the plume,40 and the relative partial pressures of products and reactants. At 5000 K, the product R·T is 41.6 kJ/mol and the equilibrium constants (Keq) range from about 10.7 for reaction 1 to 0.02 for reaction 4; none of these reactions strongly favors products or reactants at 5000 K except for reaction 4 which strongly favors atomic oxygen. This result is consistent with the experimental observation of the coexistence of Al and AlO emission over time scales where E

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Analytical Chemistry the estimated molecular temperature ranges from ∼3000−5000 K. Thermodynamic quantities for reactions 1−4 for producing AlO at 3000, 4000, 5000, and 6000 K are provided as Supporting Information. Using the equilibrium expressions for these four reactions and the two equations for atom conservation, at 5000 K the AlO to Al pressure ratios are 4% and 6% for initial ratios of Al to O2 of 5:1 and 1:1, respectively, at a total final pressure of 1 bar, including N2 from air. Changing only the temperature to 3000 K increases the AlO to Al ratios to 23% and 66% for the two initial reactant ratios. A full discussion of the thermodynamics of these reactions is beyond the scope here, but one feature merits discussion. Reactions 2 and 4 are both highly exothermic but have large positive ΔG values at 5000 K, which favors reactants over products. This difference in sign between ΔH and ΔG results from the entropy decrease associated with the decrease in translational degrees of freedom of the products compared to the reactants. The large negative ΔH values cause large temperature dependences for these equilibrium constants with the constants increasing with lower temperatures. A consequence of this temperature dependence is that high temperatures inhibit the formation of AlO, and AlO formation becomes prevalent when the plasma cools down and the Al + O reaction becomes favorable.

Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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REFERENCES

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CONCLUSIONS We investigated the role of the plume dynamics and plasma chemistry on AlO formation in an Al laser plasma expanding into 1 atm air. Spectroscopic results showed that emission from AlO molecules in LA plumes in air are weaker at times ≲10 μs and peaks at times ≳20 μs with a persistence ∼100 μs. Our results clearly showed that the plume hydrodynamics play a significant role in redefining plasma thermodynamics and molecular formation. The shock waves at the plume front act as a barrier keeping ambient oxygen away from the plume during early times of plasma expansion. The AlO formation is found to be prevalent after the shock wave collapse. The imaging and species mapping studies showed Al and AlO coexist in the plasma for ∼100 μs. This indicates that after the shock front collapse both Al and AlO species occupy the plume based on the chemical reactions for formation and destruction of AlO and also show collective kinetic behavior similar to one exhibited by charged particles in the plasmas. A thermodynamic analysis of the standard Gibbs energies and Keq values for the reaction pathways for the combustion of Al support the coexistence of Al and AlO over the estimated molecular temperature ranges found in this study. The present results also show that the complex plasma chemistry facilitated by plume hydrodynamics plays a critical role in molecular formation in laser ablation plumes. ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.analchem.5b04136. Thermodynamic quantities of reactions for producing AlO at various temperatures (PDF)

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ACKNOWLEDGMENTS

This work was partly supported by the Laboratory Directed Research and Development (LDRD) Program of PNNL and DOE/NNSA Office of Nonproliferation and Verification Research and Development (NA-22). Pacific Northwest National Laboratory is operated for the U.S. Department of Energy by the Battelle Memorial Institute under Contract No. DE-AC05-76RLO1830.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: 509.375.6497. F

DOI: 10.1021/acs.analchem.5b04136 Anal. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.analchem.5b04136 Anal. Chem. XXXX, XXX, XXX−XXX