Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “determination”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

SU-F-T-16: Experimental Determination of Ionization Chamber Correction Factors for In-Phantom Measurements of Reference Air Kerma Rate and Absorbed Water Dose Rate of Brachytherapy 192Ir Source

Purpose: Following the method of in-phantom measurements of reference air kerma rate (Ka) at 100cm and absorbed water dose rate (Dw1) at 1cm of high-dose-rate 192Ir brachytherapy source using 60Co absorbed-dose-to-water calibrated (ND,w,60Co) ionization chamber (IC), we experimentally determined the in-phantom correction factors (kglob) of the PTW30013 (PTW, Freiburg, Germany) IC by comparing the Monte Carlo (MC)-calculated kglob of the other PTW30016 IC. Methods: The Dw1 formalism of in-phantom measurement is: M*ND,w,60Co*(kglob)Dw1, where M is the collected charges, and (kglob)Dw1 the in-phantom Dw1 correction factor. Similarly, Ka is determined by M*ND,w,60Co*(kglob)ka, where (kglob)ka the in-phantom Ka correction factor. Two thimble ICs PTW30013 and another PTW30016 having a ND,w,60Co from the German primary standard laboratory (PTB) were simultaneously exposed to the microselectron 192Ir v2 source at 8cm in a PMMA phantom. A reference well chamber (PTW33004) with a PTB transfer Ka calibration Nka was used for comparing the in-phantom measurements to derive the experimental (kglob)ka factors. We determined the experimental (kglob)Dw1 of the PTW30013 by comparing the PTW30016 measurements with MC-calculated (kglob)Dw1. Results: Ka results of the PTW30016 based on ND,w,60Co and MC-calculated (kglob)ka differ from the well chamber results based on Nka by 1.6% and from the manufacturer by 1.0%. Experimental (kglob)ka factors for the PTW30016 and two other PTW30013 are 0.00683, 0.00681 and 0.00679, and vary <0.5% with 1mm source positioning uncertainty. Experimental (kglob)Dw1 of the PTW30013 ICs are 75.3 and 75.6, and differ by 1.6% from the conversion by dose rate constant from the AAPM report 229. Conclusion: The 1.7% difference between MC and experimental (kglob)ka for the PTW30016 IC is within the PTB 2.5% expanded uncertainty in Ka calibration standard. Using a single IC with ND,w,60Co to calibrate the brachytherapy source and dose output in external radiotherapy is feasible. MC validation of the PTW30013(kglob)Dw1 is warranted.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-T-64: An Alternative Approach to Determining the Reference Air-Kerma Rate from Extrapolation Chamber Measurements

Purpose: Since 2008 the Physikalisch-Technische Bundesanstalt (PTB) has been offering the calibration of {sup 125}I-brachytherapy sources in terms of the reference air-kerma rate (RAKR). The primary standard is a large air-filled parallel-plate extrapolation chamber. The measurement principle is based on the fact that the air-kerma rate is proportional to the increment of ionization per increment of chamber volume at chamber depths greater than the range of secondary electrons originating from the electrode x{sub 0}. Methods: Two methods for deriving the RAKR from the measured ionization charges are: (1) to determine the RAKR from the slope of the linear fit to the so-called ’extrapolation curve’, the measured ionization charges Q vs. plate separations x or (2) to differentiate Q(x) and to derive the RAKR by a linear extrapolation towards zero plate separation. For both methods, correcting the measured data for all known influencing effects before the evaluation method is applied is a precondition. However, the discrepancy of their results is larger than the uncertainty given for the determination of the RAKR with both methods. Results: A new approach to derive the RAKR from the measurements is investigated as an alternative. The method was developed from the ground up, based on radiation transport theory. A conversion factor C(x{sub 1}, x{sub 2}) is applied to the difference of charges measured at the two plate separations x{sub 1} and x{sub 2}. This factor is composed of quotients of three air-kerma values calculated for different plate separations in the chamber: the air kerma Ka(0) for plate separation zero, and the mean air kermas at the plate separations x{sub 1} and x{sub 2}, respectively. The RAKR determined with method (1) yields 4.877 µGy/h, and with method (2) 4.596 µGy/h. The application of the alternative approach results in 4.810 µGy/h. Conclusion: The alternative method shall be established in the future.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

SU-F-T-73: Experimental Determination of the Effective Point of Measurement in Electron Beams Using a Commercial Scintillation Detector

Purpose: The aim of this work was to determine experimentally the effective point of measurement (EPOM) in clinical electron beams for three cylindrical ionization chambers using a commercial scintillation detector as a reference detector. Methods: Percent depth dose (PDD) curves were measured using an Exradin W1 scintillation detector and were used as a representative PDD to water. Depth dose curves were measured with the Exradin A18, A1SL, and A28 ionization chambers. The raw ionization chamber curve data were corrected by the chamber fluence perturbation correction factor and restricted mass collisional stopping power ratio at each depth to obtain a percent depth dose curve to the gas volume (PDDGV) of the detector. Ratios of the W1 PDD to the ion chamber PDDGV were calculated for each measurement depth. The W1 PDD curve was shifted by small depth increments, Δz, until the ratio of the W1 PDD to the ion chamber PDDGV was depth-independent (optimal Δz). A MATLAB routine was developed to determine the optimal Δz value. Results: The optimal Δz shift was used as an estimate of the EPOM for each chamber. The average calculated EPOM shifts (expressed as a fraction of the chamber cavity radius) for the A18, A1SL, and A28 ionization chambers were 0.21 ± 0.04, 0.10 ± 0.05, and 0.22 ± 0.03, respectively. Conclusion: The experimentally determined EPOM values for the A18 and A1SL in this work agreed with the simulated values of Muir and Rogers (MedPhys 2014). The results also indicate that the Exradin W1 scintillator is water equivalent for electron energies of 6 MeV, 9 MeV, 12 MeV, and 16 MeV. In addition, we confirmed that the AAPM TG51 recommended EPOM shift of 0.5 times the cavity radius is not accurate for the A18 and A1SL chambers.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

SU-G-201-06: Directional Low-Dose Rate Brachytherapy: Determination of the TG-43 Dose-Rate Constant Analog for a New Pd-103 Source

Purpose: The aim of this work is to determine the TG-43 dose-rate constant analog for a new directional low-dose rate brachytherapy source based on experimental methods and comparison to Monte Carlo simulations. The CivaSheet™ is a new commercially available planar source array comprised of a variable number of discrete directional source elements called “CivaDots”. Given the directional nature and non-conventional design of the source, modifications to the AAPM TG-43 protocol for dosimetry are required. As a result, various parameters of the TG-43 dosimetric formalism have to be adapted to accommodate this source. This work focuses on the dose-rate constant analog determination for a CivaDot. Methods: Dose to water measurements of the CivaDot were performed in a polymethyl methacrylate phantom (20×20×12 cm{sup 3}) using thermoluminescent dosimeters (TLDs) and Gafchromic EBT3 film. The source was placed in the center of the phantom, and nine TLD micro-cubes were irradiated along its central axis at a distance of 1 cm. For the film measurements, the TLDs were substituted by a (3×3) cm{sup 2} EBT3 film. Primary air-kerma strength measurements of the source were performed using a variable-aperture free-air chamber. Finally, the source was modeled using the Monte Carlo N-Particle Transport Code 6. Results: Dose-rate constant analog observed for a total of eight CivaDots using TLDs and five CivaDots using EBT3 film was within ±7.0% and ±2.9% of the Monte Carlo predicted value respectively. The average difference observed was −4.8% and −0.1% with a standard deviation of 1.7% and 2.1% for the TLD and the film measurements respectively, which are both within the comparison uncertainty. Conclusion: A preliminary investigation to determine the doserate constant analog for a CivaDot was conducted successfully with good agreement between experimental and Monte Carlo based methods. This work will aid in the eventual realization of a clinically-viable dosimetric framework for the CivaSheet. This work was partially supported by NCI contract (HHSN261201200052C) through CivaTech Oncology Inc.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-G-TeP3-02: Determination of Geometry-Specific Backscatter Factors for Radiobiology Studies

Purpose: Radiation biology research relies on an accurate radiation dose delivered to the biological target. Large field irradiations in a cabinet irradiator may use the AAPM TG-61 protocol. This relies on an air-kerma measurement and conversion to absorbed dose to water (Dw) on the surface of a water phantom using provided backscatter factors. Cell or small animal studies differ significantly from this reference geometry. This study aims to determine the impact of the lack of full scatter conditions in four representative geometries that may be used in radiobiology studies. Methods: MCNP6 was used to model the Dw on the surface of a full scatter phantom in a validated orthovoltage x-ray reference beam. Dw in a cylindrical mouse, 100 mm Petri dish, 6-well and 96-well cell culture dishes was simulated and compared to this full scatter geometry. A reference dose rate was measured using the TG-61 protocol in a cabinet irradiator. This nominal dose rate was used to irradiate TLDs in each phantom to a given dose. Doses were obtained based on TLDs calibrated in a NIST-traceable beam. Results: Compared to the full scattering conditions, the simulated dose to water in the representative geometries were found to be underestimated by 12-26%. The discrepancy was smallest with the cylindrical mouse geometry, which most closely approximates adequate lateral- and backscatter. TLDs irradiated in the mouse and petri dish phantoms using the TG-61 determined dose rate showed similarly lower values of Dw. When corrected for this discrepancy, they agreed with the predicted Dw within 5%. Conclusion: Using the TG-61 in-air protocol and given backscatter factors to determine a reference dose rate in a biological irradiator may not be appropriate given the difference in scattering conditions between irradiation and calibration. Without accounting for this, the dose rate is overestimated and is dependent on irradiation geometry.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

TU-H-CAMPUS-JeP3-05: Adaptive Determination of Needle Sequence HDR Prostate Brachytherapy with Divergent Needle-By-Needle Delivery

Purpose: To develop a new method which adaptively determines the optimal needle insertion sequence for HDR prostate brachytherapy involving divergent needle-by-needle dose delivery by e.g. a robotic device. A needle insertion sequence is calculated at the beginning of the intervention and updated after each needle insertion with feedback on needle positioning errors. Methods: Needle positioning errors and anatomy changes may occur during HDR brachytherapy which can lead to errors in the delivered dose. A novel strategy was developed to calculate and update the needle sequence and the dose plan after each needle insertion with feedback on needle positioning errors. The dose plan optimization was performed by numerical simulations. The proposed needle sequence determination optimizes the final dose distribution based on the dose coverage impact of each needle. This impact is predicted stochastically by needle insertion simulations. HDR procedures were simulated with varying number of needle insertions (4 to 12) using 11 patient MR data-sets with PTV, prostate, urethra, bladder and rectum delineated. Needle positioning errors were modeled by random normally distributed angulation errors (standard deviation of 3 mm at the needle’s tip). The final dose parameters were compared in the situations where the needle with the largest vs. the smallest dose coverage impact was selected at each insertion. Results: Over all scenarios, the percentage of clinically acceptable final dose distribution improved when the needle selected had the largest dose coverage impact (91%) compared to the smallest (88%). The differences were larger for few (4 to 6) needle insertions (maximum difference scenario: 79% vs. 60%). The computation time of the needle sequence optimization was below 60s. Conclusion: A new adaptive needle sequence determination for HDR prostate brachytherapy was developed. Coupled to adaptive planning, the selection of the needle with the largest dose coverage impact increases chances of reaching the clinical constraints. M. Borot de Battisti is funded by Philips Medical Systems Nederland B.V.; M. Moerland is principal investigator on a contract funded by Philips Medical Systems Nederland B.V.; G. Hautvast and D. Binnekamp are fulltime employees of Philips Medical Systems Nederland B.V.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Determination of Main Components of Glass-Forming Cu–Zr Alloys

A rapid procedure is developed for determination of copper and zirconium in their binary alloys Cu{sub 100–x}Zr{sub x} in the content ranges corresponding to the region of bulk amorphization (x = 30–70) using inductively coupled plasma atomic emission spectroscopy (ICP-AES). The spectrometer operating conditions are optimized, and the analytical spectral lines (Cu II 224.700 nm and Zr II 354.262 nm) are selected, as well as calibration method and sampling procedure: dissolution in the mixture of HNO{sub 3} and HF with addition of HCl, providing for the minimum standard deviation of the analytical signal. A procedure of oxygen determination by inert gas fusion technique and a procedure for determination of copper by spectrophotometry and zirconium by gravimetric analysis in a single sample together with quality control of ICP-AES are developed for the considered alloys. The results of analysis of Cu{sub 100–x}Zr{sub x} alloys according to the developed procedures agree well between themselves and accounting for adjustment of oxygen content agree within the error limits (not more than 0.5 wt %) with the added content of copper and zirconium upon synthesis.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Determination of Microelements in Oil by Combined Sample Preparation Technique

The determination of a wide spectrum of microelements in four oil samples from the Arlanskoye, Labaganskoye, Priobskoye, and Romashkinskoye oil fields of the Russian Federation by inductively coupled plasma mass spectrometry (ICP-MS) is described. The following two techniques have been used for the sample preparation: microwave decomposition of oil for determination of Be, Na, Mg, Al, S, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Ga, Se, Rb, Sr, Zr, Mo, Cs, Ba, W, Re, and U; and extraction concentrating with rotating helix columns (RHC) for determination of Nb, Ru, Rh, Ag, Cd, Sb, Te, Hf, Ir, Pt, Te, and rare earth elements. Concentrating of the oil microelements with RHC has been shown to result in significant improvement of the ICP-MS detection limits.

02 PETROLEUM↗
DOE OSTI2018

Determining the Size of Pores in a Partially Transparent Ceramics from Total-Reflection Spectra

A technique is proposed for determining the pore-size distribution based on measuring the dependence of total reflectance in the domain of partial transparency of a material. An assumption about equality of scattering-coefficient spectra determined by solving the inverse radiation transfer problem and by theoretical calculation with the Mie theory is used. The technique is applied to studying a quartz ceramics. The poresize distribution is also determined using mercury and gas porosimetry. All three methods are shown to produce close results for pores with diameters of <180 nm, which occupy ~90% of the void volume. In the domain of pore dimensions of >180 nm, the methods show differences that might be related to both specific procedural features and the structural properties of ceramics. The spectral-scattering method has a number of advantages over traditional porosimetry, and it can be viewed as a routine industrial technique.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Determination of a brass alloy concentration composition using calibration-free laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a technique that can provide qualitative and quantitative measurements of the characteristics of irradiated metals. In the present work, we have calculated the parameters of the plasma produced from a brass alloy sample under the action of a pulsed Nd: YAG laser operating at 1064 nm. The emission lines of copper atoms (Cu I), zinc atoms (Zn I), and lead atoms (Pb I), which are elements of a brass alloy composition, were used to investigate the parameters of the brass plasma. The spectral profiles of Cu, Zn, and Pb lines have been used to extract the electron temperature and density of the brass alloy plasma. The characteristics of Cu, Zn, and Pb were determined quantatively by the calibration-free LIBS (CF-LIBS) method considering for accurate analysis that the laser-induced ablated plasma is optically thin in local thermodynamic equilibrium conditions and the plasma ablation is stoichiometric. The Boltzmann plot method was used to evaluate the plasma temperature, and the Stark broadened profiles were used to determine the electron density. An algorithm based on the experimentally measured values of the intensity of spectral lines and the basic laws of plasma physics was developed for the determination of Cu, Zn, and Pb concentrations in the brass sample. The concentrations C{sub CF-LIBS} calculated by CF-LIBS and the certified concentrations C{sub certified} were very close.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Experimental determination of the electron effective masses and mobilities in each dimensionally-quantized subband in an In{sub x}Ga{sub 1−x}As quantum well with InAs inserts

HEMT structures with In{sub 0.53}Ga{sub 0.47}As quantum well are synthesized using molecular-beam epitaxy on InP substrates. The structures are double-side Si δ-doped so that two dimensionally-quantized subbands are occupied. The effect of the central InAs nanoinsert in the quantum well on the electron effective masses m* and mobilities in each subband is studied. For experimental determination of m*, the quantum μ{sub q} and transport μ{sub t} mobilities of the two-dimensional electron gas in each dimensionally-quantized subband, the Shubnikov-de Haas effect is measured at two temperatures of 4.2 and 8.4 K. The electron effective masses are determined by the temperature dependence of the oscillation amplitudes, separating the oscillations of each dimensionally-quantized subband. The Fourier spectra of oscillations are used to determine the electron mobilities μ{sub q} and μ{sub t} in each dimensionally-quantized subband. It is shown that m* decreases as the InAs-nanoinsert thickness d in the In{sub 0.53}Ga{sub 0.47}As quantum well and electron mobilities increase. The maximum electron mobility is observed at the insert thickness d = 3.4 nm.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Luminosity determination using Z boson production at the CMS experiment

The measurement of Z boson production is presented as a method to determine the integrated luminosity of CMS data sets. The analysis uses proton–proton collision data, recorded by the CMS experiment at the CERN LHC in 2017 at a center-of-mass energy of 13 TeV. Events with Z bosons decaying into a pair of muons are selected. The total number of Z bosons produced in a fiducial volume is determined, together with the identification efficiencies and correlations from the same data set, in small intervals of 20 pb –1 of integrated luminosity, thus facilitating the efficiency and rate measurement as a function of time and instantaneous luminosity. Using the ratio of the efficiency-corrected numbers of Z bosons, the precisely measured integrated luminosity of one data set is used to determine the luminosity of another. For the first time, a full quantitative uncertainty analysis of the use of Z bosons for the integrated luminosity measurement is performed. The uncertainty in the extrapolation between two data sets, recorded in 2017 at low and high instantaneous luminosity, is less than 0.5%. We show that the Z boson rate measurement constitutes a precise method, complementary to traditional methods, with the potential to improve the measurement of the integrated luminosity.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Determinations of Vus using inclusive hadronic τ decay data

Two methods for determining |V us | employing inclusive hadronic ττ decay data are discussed. The first is the conventional flavor-breaking sum rule determination whose usual implementation produces results ~3σ low compared to three-family unitary expectations. The second is a novel approach combining experimental strange hadronic ττ distributions with lattice light-strange current–current two-point function data. In preliminary explorations of the latter show the method promises |V us | determinations are competitive with those from K ℓ3 and Γ[π μ2 ]/Γ[π μ2 ]. For the former, systematic issues in the conventional implementation are investigated. Unphysical dependences of |V us | on the choice of sum rule weight, w, and upper limit, s 0 , of the weighted experimental spectral integrals are observed, the source of these problems identified and a new implementation which overcomes these problems developed. The lattice results are shown to provide a tool for quantitatively assessing truncation uncertainties for the slowly converging D=2 OPE series. Our results for |V us | from this new implementation are shown to be free of unphysical w- and s0-dependences, and ~0.0020 higher than those produced by the conventional implementation. With preliminary new Kπ branching fraction results as input, we find |V us | in excellent agreement with that obtained from K ℓ3 , and compatible within errors with expectations from three-family unitarity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Determination of Kinetic Properties of Ni(II) Ions in Molten LiF-NaF-KF via Voltammetry

Kinetic properties of Ni(II) in eutectic LiF-NaF-KF (FLiNaK) molten salt were determined at T = 748–823 K using cyclic voltammetry (CV), square wave voltammetry (SWV), and chronoamperometry (CA) measurements using a glassy C working electrode, Ni(II)/Ni reference electrode, and Ni counter electrode. Reduction of Ni(II) to Ni(s) was determined to be a single step, two-electron transfer process. Diffusivity values were calculated using the Berzins and Delahay equation and semi-integral electroanalysis from the CV measurements as well as using the Cottrell equation from the CA measurements. Diffusivity of Ni(II) in molten FLiNaK at T = 748–823 K was determined to be 3.27 × 10 –7 –3.04 × 10 –6 cm 2 s –1 with an activation energy of 62–104 kJ mol –1 . The estimated kinetic properties varied appreciably among methodologies possibly due to inherent assumptions in theory regarding reversibility and unit activity during Ni metal deposition on the working electrode.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Quantitative Chromatographic Determination of Dissolved Elemental Sulfur in the Non-aqueous Electrolyte for Lithium-Sulfur Batteries

A fast and reliable analytical method is reported for the quantitative determination of dissolved elemental sulfur in non-aqueous electrolytes for Li-S batteries. By using high performance liquid chromatography with a UV detector, the solubility of S in 12 different pure solvents and in 22 different electrolytes was determined. It was found that the solubility of elemental sulfur is dependent on the Lewis basicity, the polarity of solvents and the salt concentration in the electrolytes. In addition, the S content in the electrolyte recovered from a discharged Li-S battery was successfully determined by the proposed HPLC/UV method. Thus, the feasibility of the method to the online analysis for a Li-S battery is demonstrated. Interestingly, the S was found super-saturated in the electrolyte recovered from a discharged Li-S cell.

25 ENERGY STORAGE↗
DOE OSTI2018

Thermodynamic Properties of Strontium-Lead Alloys Determined by Electromotive Force Measurements

The thermodynamic properties of Sr-Pb alloys were determined by electromotive force (emf) measurements. A Sr(s)|CaF 2 -SrF 2 |Sr(in Pb) electrochemical cell was used to measure emf values at 773–1073 K for Sr-Pb alloys at mole fractions x Sr = 0.07–0.59. These emf measurements were used to determine thermodynamic properties of Sr-Pb alloys, including activity, partial molar entropy, and partial molar enthalpy. At 873 K, activity values of Sr in Pb were as low as a Sr = 1.72 &#x00d7; 10 –9 at mole fraction x Sr = 0.07, implying strong atomic interactions between Sr and Pb. Phase transition temperatures of Sr-Pb alloys, observed during emf measurements, were corroborated by thermal analysis (0.07 ≤ x Sr ≤ 0.34) by differential scanning calorimetry (DSC), and the phase constituents of Sr-Pb alloys (0.07 ≤ x Sr ≤ 0.75) were characterized using X-ray diffraction (XRD). Experimentally-determined thermodynamic properties were compared to the assessed thermodynamic properties of the Sr-Pb system, confirming the phase transition temperatures and highlighting discrepancies in solution properties (activity and excess Gibbs energy).

36 MATERIALS SCIENCE↗
DOE OSTI2016

Determining the Best Method for Estimating the Observed Level of Maximum Detrainment Based on Radar Reflectivity

Convective mass transport is the transport of mass from near the surface up to the upper troposphere and lower stratosphere (UTLS) by a deep convective updraft. This transport can alter the chemical makeup and water vapor balance of the UTLS, which affects cloud formation and the radiative properties of the atmosphere. It is therefore important to understand the exact altitudes at which mass is detrained from convection. The purpose of this study was to improve upon previously published methodologies for estimating the level of maximum detrainment (LMD) within convection using data from a single ground-based radar. Four methods were used to identify the LMD and validated against dual-Doppler derived vertical mass divergence fields for six cases with a variety of storm types. The best method for locating the LMD was determined to be the method that used a reflectivity texture technique to determine convective cores and a multi-layer echo identification to determine anvil locations. Although an improvement over previously published methods, the new methodology still produced unreliable results in certain regimes. The methodology worked best when applied to mature updrafts, as the anvil needs time to grow to a detectable size. Thus, radar reflectivity is found to be valuable in estimating the LMD, but storm maturity must also be considered for best results.

Carletta, Nicholas D.↗
DOE OSTI2020

Experimental determination of the solubility constant of kurnakovite, MgB3O3(OH)5·5H2O

In this study, I present experimental results on the equilibrium between boracite [Mg 3 B 7 O 13 C1(cr)] and kurnakovite [chemical formula, Mg 2 B 6 O 11 ·15H 2 O(cr); structural formula, MgB 3 O 3 (OH) 5 ·5H 2 O(cr)] at 22.5 ± 0.5 °C from a long-term experiment up to 1629 days, approaching equilibrium from the direction of supersaturation, Mg 3 B 7 O 13 C1(cr) + H + + 2B(OH)$^-_4$ + 18H 2 O(1) ⇌ 3MgB 3 O 3 (OH) 5 ·5H 2 O(cr) + C1 - . Based on solubility measurements, the 10-based logarithm of the equilibrium constant for the above reaction at 25 °C is determined to be 12.83 ± 0.08 (2σ). Based on the equilibrium constant for dissolution of boracite, Mg 3 B 7 O 13 C1(cr) + 15H 2 O(1) = 3Mg 2+ + 7B(OH)$^-_4$ + C1 - + 2H + at 25 °C measured previously (Xiong et al. 2018) and that for the reaction between boracite and kurnakovite determined here, the equilibrium constant for dissolution of kurnakovite, MgB 3 O 3 (OH) 5 ·5H 2 O(cr) = Mg 2+ + 3B(OH)$^-_4$ + H + + H 2 O(1) is derived as -14.11 ± 0.40 (2σ). Using the equilibrium constant for dissolution of kurnakovite obtained in this study and the experimental enthalpy of formation for kurnakovite from the literature, a set of thermodynamic properties for kurnakovite at 25 °C and 1 bar is recommended as follows: Δ H $^0_f$ = -4813.24 ± 4.92 kJ/mol, Δ G$^0_f$ = -4232.0 ± 2.3 kJ/mol, and S 0 = 414.3 ± 0.9 J/(mol·K). Among them, the Gibbs energy of formation is based on the equilibrium constant for kurnakovite determined in this study; the enthalpy of formation is from the literature (Li et al. 1997), and the standard entropy is calculated internally with the Gibbs-Helmholtz equation in this work. The thermodynamic properties of kurnakovite estimated using the group contribution method for borate minerals based on the sums of contributions from the cations, borate polyanions, and structural water to the thermodynamic properties from the literature (Li et al. 2000) are consistent, within their uncertainties, with the values listed above. Since kurnakovite usually forms in salt lakes rich in sulfate, studying the interactions of borate with sulfate is important to modeling kurnakovite in salt lakes. Finally, for this purpose, I have re-calibrated our previous model (Xiong et al. 2013) describing the interactions of borate with sulfate based on the new solubility data for borax in Na 2 SO 4 solutions presented here.

36 MATERIALS SCIENCE↗