Thermodynamic Properties of Magnesium Oxide and Beryllium Oxide from 298 to 1,200 °K

As a step in developing new standards of high-temperature heat capacity and in determining accurate thermodynamic data for simple substances, the enthalpy (heat content) relative to 273 °K, of high purity fused magnesium oxide, MgO, and of sintered beryllium oxide, BeO, was measured up to 1,173 °K. A Bunsen ice calorimeter and the drop method were used. The two samples of BeO measured had surface-to-volume ratios differing by a factor of 15 or 20, yet agreed with each other closely enough to preclude appreciable error attributable to the considerable surface area. The enthalpies found for MgO are several percent higher than most previously reported values. The values are represented within their uncertainty (estimated to average ± 0.25%) by the following empirical equations³ (cal mole⁻¹ at T °K) MgO:HT°−H273.15°=10.7409T+1.2177(10−3)T2−2.3183(10−7)T3+2.26151(105)T−1−3847.94.BeO:HT°−H273.15°=11.1084T+7.1245(10−4)T2+8.40705(105)T−1−5.31245(107)T−2−5453.21.Values of enthalpy, heat capacity, entropy, and Gibbs free-energy function are tabulated from 298.15 to 1,200 °K.     

Acid Dissociation Constant and Related Thermodynamic Quantities for Triethanolammonium Ion in Water From 0 to 50°C

Earlier studies of the dissociation constants of monoethanolammonium and diethanolammonium ions and the thermodynamic constants for the dissociation processes have been supplemented by a similar study of triethanolammonium ion from 0° to 50° C. The dissociation constant (K_bh) is given by the formula ?log K_bh = 1341.16/T + 4.6252 ? 0.0045666Twhere T is in degrees Kelvin. The order of acidic strengths of the ions is as follows: Triethanolammonium >diethanolammonium>monethanolammonium. Conversely, monoethanolamine is the strongest of the three bases. The thermodynamic constants for the dissociation of one mole of triethanolammonium ion in the standard state at 25° C are as follows: Heat content change (ΔH°) 33.450 joule mole⁻¹; entropy change (ΔS°), −36.4 joule deg⁻¹ mole⁻¹; heat-capacity change (ΔCp°), 52 joule deg⁻¹ mole⁻¹.     

Spectrophotometric Determination of the Thermodynamic pK Value of Picric Acid in Water at 25 °C

The thermodynamic pK value of picric acid was determined spectrophotometrically in water containing hydrochloric acid to repress the ionization. The pK value 0.33 (K ≈ 0.46) was obtained from data at 450 mμ. Attempts to determine the pK value by potentiometric titrations of picric acid and by spectrophotometric measurements of picric acid solutions in the near-saturation range did not yield satisfactory results. The new pK value is compared with previously published values.     

Dissociation Constant of 4-Aminopyridinium Ion in Water From 0 to 50 °C and Related Thermodynamic Quantities

The dissociation constant of 4-aminopyridinium ion in water at 11 temperatures from 0° to 50° C has been determined from electromotive force measurements of 19 approximately equimolal aqueous buffer solutions of 4-aminopyridine and 4-aminopyridinium chloride. Cells without liquid junction were used; the cell is represented as follows: Pt; H₂(g), H₂NC₅H₄N ? HCl(m₁), H₂NC₅H₄N(m₂), AgCl; Agwhere m is molality.Between 0° and 50° C, the dissociation constant (K_bh) is given as a function of temperature (T) in degrees Kelvin by −logKbh=2575.8T+0.08277+0.0013093TThe changes of Gibbs free energy (ΔG°), of enthalpy (ΔH°), of entropy (ΔS°), and of heat capacity (ΔC_p°) for the dissociation process in the standard state were calculated from the constants of this equation. At 25° C the following values were found: −logKbh=9.114,ΔG°=52,013jmole−1,ΔH°=47,090jmole−1,ΔS°=−16.5jdeg−1mole−1,ΔCp°=−15jdeg−1mole−1.Thermodynamic constants for the basic dissociation of 4-aminopyridine at 25° C were also computed.     

Multizone Furnace for Analysis of Fixed-Point Realizations in the Range from 1,000°C to 1,700°C

In this article, the development of a laboratory furnace specially designed for analysis of fixed-point plateau realizations in the range from 1,000 °C to 1,700 °C that enables control of various temperature distribution settings along the heating zone length is presented. A total of 13 thermocouples are built into the furnace tube wall to control the temperature as well as to measure the temperature distribution. The furnace is divided into seven independently controlled heating zones. Each heating zone comprises a MoSi₂ heating element and its dedicated DC power supply module. The furnace temperature is controlled by manipulating the output voltage of each power supply to control the temperature of each heating element, as estimated from its electrical resistance. The heating power and temperature measurement are fully controlled by a computer using an application written in Lab VIEW, allowing very flexible furnace control. The furnace can be used in air as well as in an inert atmosphere. Measurements of the temperature distribution of the furnace during a melting-point realization are presented.     

Effect of a temperature change from 20 to 50°C on the basic creep of HPC and HPFRC

This research was performed in order to study the basic creep of High Performance Concretes (HPC) under uniaxial compression at 20 and 50°C. The aim of this work is to contribute to a better understanding of the basic creep phenomena of HPC at moderate temperature and to provide experimental data which will be used in Thermo-Hydro-Mechanical models such as those necessary for the National project CEOS.FR (Sellier, Thermo hydro mechanical numerical modelling, invited paper at the CEOS International workshop on Control of cracking in R.C. structures: a major step towards serviceability, 2009). The article also presents the fitting of a model considering the effect of temperature via an Arrhenius law affecting its viscous modules (Sellier and Buffo-Lacarriere, Eur J Environ Civ Eng 10:1161–1182, 2009). The concretes are those envisioned for future storage structures of Intermediate Level Long-Life Nuclear Wastes. The research programme has been established with four HPC, two non fibrous and two fibrous; the kinetics and amplitude of basic creep under uniaxial compression are measured during several months at 50°C and compared to those obtained at 20°C for the same materials (Camps, PhD thesis, 2008). Experimental results show that the average creep at 50°C is about twice the creep at 20°C. Besides, results show that this amplification depends on the binder type; the sensitivity to the temperature rise is greater for blended cement based concretes than for OPC based ones. The creep increase due the temperature rise is higher for the HPC under study than for ordinary concretes inventoried in a literature survey. The creep amplitude of HPC seems correlated to their amount of secondary C–S–H. At last, the fitting of the model parameters on the experimental results shows that the values of activation energy are quite close to those obtained by other authors on ordinary concretes (Bazant et al., J Eng Mech ASCE 130(6): 691–699, 2004).     

Thermophysical Properties of Uranium-Based Niobium and Zirconium Alloys from 23 °C to 175 °C

The thermal diffusivities of uranium alloys were measured by the laser-flash method between room temperature and 448 K. In recent years, several UZrNb alloys have been studied by many researchers and it was shown that additions of niobium and zirconium improve the properties of uranium-based alloys. The purpose of this article is to summarize the thermophysical properties of two uranium alloys that have been studied by CDTN in a program of development of fuel for low-power reactors. The nominal compositions of the studied alloys are U4Zr6Nb and U3Zr9Nb. The results obtained by the original laser-flash method and by the mathematical model developed by the laboratory were compared to the literature data. The adaptive Monte Carlo method was used to obtain the endpoints of the probabilistically symmetric 95% coverage interval for estimates of the output quantities and its uncertainties.     

State Primary Standard of Temperature Unit in the Range 0–3200°C GET 34-2020: Practical Implementation of the New Definition of Kelvin

Measurement Techniques - We consider the necessity and means of modernizing the State primary standard GET 34-2007 of the unit of temperature in the range of 0–3000°С. The problem...     

Determination of the elastic moduli of a machinable ceramic over the range from room temperature to 800°C

The ultrasonic velocities of a machinable ceramic were measured using the pulse echo overlap technique. The machinable ceramic consists of 5- to 10-m crystallite blocks of mica in a boroaluminosilicate glass matrix. The elastic moduli are deduced from the sound velocities over the temperature range from room temperature to 800°C. Their temperature change is well described by a fourth-degree polynomial. Although the moduli decrease with increasing temperature, a plateau region appears at about 450°C. This anomalous behavior is explained by applying the simple rule of mixtures to constituent materials, the mica crystallites, and the glass matrix.     

Thermal-Conductivity Measurements of Aqueous Orthophosphoric Acid Solutions in the Temperature Range from (293 to 400) K and at Pressures up to 15 MPa

A new improved guarded parallel-plate thermal-conductivity cell for absolute measurements of corrosive (chemically aggressive) fluids under pressure has been developed. Using the new modified guarded parallel-plate apparatus the thermal conductivity of aqueous orthophosphoric acid solutions was measured over the temperature range from (293 to 400) K and pressures up to 15 MPa. Measurements were made for three compositions of \(\text {H}_{3}\text {PO}_{4}\) (8 mass%, 15 mass%, and 50 mass%) along three isobars of (0.101, 5, and 15) MPa. The combined expanded uncertainty of the thermal-conductivity \((\lambda )\) measurements at the 95 % confidence level with a coverage factor of \(k=2\) is estimated to be 2 %. The uncertainties of the temperature, pressure, and concentration measurements were 15 mK, 0.05 %, and 0.01 %, respectively. The temperature, concentration, and pressure dependences of the thermal conductivity of the solution were studied. The measured values of thermal conductivity were compared with the available reported data and the values calculated from various correlation and prediction models. A new wide-range correlation model (extended Jones–Dole type equation with pressure-dependent coefficients) for the \(\text {H}_{3}\text {PO}_{4}\) (aq) solution was developed using the present experimental data.     

Stability of Tungsten�CRhenium Thermocouples in the Range from 0?��C to 1500?��C

The effect of exposure up to 1500 °C on emf values of type C (95 % tungsten 5 % rhenium vs. 74 % tungsten 26 % rhenium) thermocouples were evaluated. Three thermocouples consisting of thermocouple wires of 0.5 mm diameter, twin-bore beryllia tubes, and tantalum sheaths were prepared. After three type C thermocouples were calibrated in the range from 0 °C to 1550 °C, which confirmed insignificant difference among them, the drifts of two among them were measured at the palladium?Ccarbon (Pd?CC) eutectic point (1492 °C). They indicated a similar tendency, where the emf of thermocouples increased rapidly within the first 30 h, and after that, decreased gradually. To investigate the mechanism of the drift, the inhomogeneities of thermocouples were examined at 160 °C using a water heat-pipe furnace during the drift measurements at the Pd?CC eutectic point. It was found that the increase of emf within the first 30 h exposure at around 1500 °C was caused by the emf change due to inhomogeneity above 700 °C, and after that, the decrease of emf was caused by that around 1400 °C.     

First-Class State Working Standard of Units of Wavelength in the Range from 1.25 to 20.00 μm and of Wavenumber in the Range from 500 to 8000 cm–1

Measurement Techniques - The first-class State Working Standard of units of wavelength in the range from 1.25 to 20.00 μm and of units of wavenumber in the range from 500 to 8000 cm–1...     

Localization of U(VI) on nickel hydroxide from aqueous solution in the presence of complexing anions at 25°C

Sorption and coprecipitation of U(VI) from aqueous solution containing various complexing anions (CO₃^25-, SO₄²⁻, H₂EDTA²⁻) with the Ni(OH)₂ solid phase at 25°C was studied. Uranium(VI) is not noticeably sorbed on the Ni(OH)₂ solid phase from aqueous solutions containing CO₃²⁻ and SO₄²⁻. The distribution coefficients K _d are less than 1.0 ml g⁻¹ throughout the examined range of [U(VI)]: [L] ratios (L = CO₃²⁻, SO₄²⁻) at V/m ≥ 100 ml g⁻¹ and contact time of the solid and liquid phases of 60 min. In the presence and in the absence of H₂EDTA²⁻, the degree of the U(VI) sorption is essentially the same (K _d ∼90–140 ml g⁻¹ at V/m ≥ 100 ml g⁻¹). Uranium(VI) does not coprecipitate with Ni(OH)₂ from aqueous solutions containing SO₄²⁻ and H₂EDTA²⁻. The distribution coefficients K _d are less than 0.001 ml g⁻¹ at V/m ≥ 200 ml g⁻¹ and contact time of the solid and liquid phases of 60 min. In solutions containing CO₃²⁻, the U(VI) capture by the Ni(OH)₂ precipitate depends on the [CO₃²⁻]: [U(VI)] ratio. The higher the [CO₃²⁻]: [U(VI)] ratio, the more strongly U(VI) coprecipitates with Ni(OH)₂.     

Thermal stability of mixtures of the extractant and nitric acid at temperatures from 90 to 120°С

The thermal stability of mixtures of tri-n-butyl phosphate (TBP) with HNO₃ was studied in the temperature range from 90 to 125°C. In mixtures with the irradiated extractant at 110°C, intense exothermic processes initiated by oxidation of extractant radiolysis products are possible, whereas at 90°C oxidation of the irradiated extractant is accompanied by weak heat and gas evolution. In the temperature range from 110 to 120°C, exothermic oxidation processes in nonirradiated mixtures start after long induction period (hours), develop gradually, and do not have an avalanche character. Below 110°C, heating of mixtures of the extractant with HNO₃ at the HNO₃ concentration from 8 to 15.7 M is accompanied by gas evolution without exothermic effects. On the whole, oxidation processes in extraction mixtures at temperatures below the “start” parameters of thermal explosion are not dangerous from the viewpoint of the probability of thermal explosion, even at prolonged heating.     

Structure and Mechanical Properties of ZrCr2 Intermetallic Compound within the Temperature Range 20–1300°C

We studied the properties of ZrCr₂ intermetallic compound without crystallization cracks, obtained due to the introduction of excess zirconium (up to 2 at.%) with respect to the stoichiometric composition into the alloy. The melt was poured in a copper chill mold, and specimens for mechanical compression tests within the temperature range 900–1300°C were cut out of the castings. The short-term strength of intermetallic compound was _u = 665 and 140 MPa, and fracture took place mainly along the grain boundaries: below 1100°C, it was brittle, but, at higher temperatures (1200–1300°C), the plastic strain reached 5–7% prior to crack initiation and almost 30% before fracture. Plastic deformation is not accompanied by hardening. In the case of transcrystalline fracture, its type can be attributed to venous, which is characteristic of amorphous metallic materials.     

The Viscosities of Dilute Kr,Xe, and CO$$_$$ Revisited: New Experimental Reference Data at Temperatures from 95 K to 690 K

Previously reported, but also unpublished experimental data of our group for the viscosities of dilute krypton, xenon, and carbon dioxide, obtained in the range from 295 K to a maximum of 690 K using oscillating-disk viscometers, were re-evaluated and corrected or extrapolated to the limit of zero density (\(\eta _0\)). The combined standard uncertainty of the data is 0.1 % at room temperature and 0.2 % at higher temperatures. For krypton and carbon dioxide, our \(\eta _0\) data were compared with \(\eta _0\) values theoretically calculated using the kinetic theory and highly accurate ab initio potentials for the krypton atom pair and the CO\(_2\) molecule pair, but also with recent experimental \(\eta _0\) data from the literature. Our data for krypton differ up to 690 K from the theoretical values by \(-0.10\,\%\) to \(+0.28\,\%\), whereas that of Lin et al. (Fluid Phase Equilib. 418:198, 2016) show deviations of +(0.04 to 0.20) % at temperatures from 243 K to 393 K, in each case proving that experiment and theory are in consistent agreement. The re-evaluated \(\eta _0\) data for xenon were compared with recent data from the literature and with calculated values resulting from the HFD-B potential for xenon via the corresponding-states principle to verify that they are reference values. For carbon dioxide, \(\eta _0\) values obtained from 26 re-evaluated isotherms and from eight isotherms of Schäfer et al. (J Chem Thermodyn 89:7, 2015) between 253 K and 473 K are mutually consistent with ab initio calculated and subsequently scaled viscosity values of Hellmann (Chem Phys Lett 613:633, 2014). The isotherms of Schäfer et al. are especially suitable for determining the initial density dependence of the viscosity. Concomitantly inferred reduced second viscosity virial coefficients were checked against two theoretical approaches of the Rainwater–Friend theory.     

Calibration of Radiation Thermometers and Blackbodies in the Temperature Range from 160 ��C to 420 ��C

The NMIJ has established a new calibration facility consisting of a 1.6??m radiation thermometer and three fixed-point blackbodies of indium (156.5985 °C), tin (231.928 °C), and zinc (419.527 °C) in the temperature range from 160 °C to 420 °C. The expanded uncertainties (k = 2) of the fixed-point blackbodies are estimated to be 28 mK for the In point, 22 mK for the Sn point, and 32 mK for the Zn point. The expanded uncertainties in the temperature scale of the 1.6??m radiation thermometer are estimated to be 40 mK to 77 mK. When this standard is used to calibrate devices under test to be used in industry, uncertainties (k = 2) of 61 mK for the In point, 67 mK for the Sn point, and 99 mK for the Zn point, 91 mK to 136 mK for a 1.6??m radiation thermometer, and 73 mK to 116 mK for a variable-temperature blackbody can be achieved.     

Composition-microstructure-property relationships in ceramic monofilaments resulting from the pyrolysis of a polycarbosilane precursor at 800 to 400 °C

A 15 m monofilament was extruded from a Yajima's type molten polycarbosilane, stabilized by addition of oxygen and heat-treated at 800 to 1400 °C under an argon atmosphere. Two important phenomena occur during pyrolysis. At 500 to 750 °C, an organic-inorganic state transition takes place with a first weight loss. It yields an amorphous material stable up to about 1100 °C. At this temperature, its composition is close to Si₄C₅O₂. It can be described as a continuum of SiC₄ and/or SiC_4–x O_x tetrahedral species (and possibly contains free carbon), with a homogeneity domain size less than 1 nm. The amorphous filament exhibits a high strength and semi-conducting properties. Above 1200 °C, a thermal decomposition of the amorphous material takes place with an evolution of gaseous species thought to be mainly SiO and CO, an important cross-section shrinkage and the formation of 7 to 20 nm SiC crystals which are surrounded with a poorly organized turbostratic carbon. The amorphous-crystalline state transition results in a drop in the tensile failure strength and an increase, by four orders of magnitude, in the electrical conductivity which becomes temperature independent. The former effect is due to the crystallization of the filament and the latter to a percolation phenomenon related to the intergranular carbon. The low stiffness is also due to the presence of carbon. It is anticipated that this transition is mainly related to the decomposition of the silicon oxycarbide species. Finally, a 40 to 50 nm layer of turbostratic carbon is formed at the filament surface at 1200 to 1400 °C whose origin remains uncertain. It is thought to be mainly responsible for the formation of the carbon interphase in the high-temperature processing of ceramic matrix composites.