Heats of Combustion and Formation of Trimethylborane,Triethylborane, and Tri-n-butylborane

The heats of combustion at 25 °C of trimethylborane (liquid), triethylborane (liquid), and tri-n-butylborane (liquid), to form crystalline boric acid, liquid water, and gaseous carbon dioxide have been determined to be −2989.4 ±22.4 kj/mole (−714.48 ±5.36 kcal/mole), −4975.6 ±15.1 kj/mole (−1189.2 ±3.6 kcal/mole), and −8901.0 ±10.2 kj/mole (−2127.4 ±2.4 kcal/mole), respectively. These data, combined with the heats of formation of boric acid, carbon dioxide, and water give −34.79 ±5.40, −47.2 ±3.7, and −83.2 ±2.5 kcal/mole at 25 °C for the standard heats of formation of trimethylborane, triethylborane, and tri-n-butylborane, respectively. The data of other investigators are discussed briefly.     

Heat of Formation of Titanium Tetraiodide

The heat of formation of titanium tetraiodide was determined relative to that of titanium tetrabromide by comparison of their heats of hydrolysis in dilute sulfuric acid. The difference in the heats of formation may be expressed by the equation: TiI4(c)+2Br2(liq)=TiBr(c)+2I2(c),ΔH(25°C)=−230.91±0.75kj/mole(−55.19±0.18kcal/mole).By taking the heat of formation of TiBr₄(c) as −616.72 ±4.60 kj/mole, the heat of formation of TiI₄(c) is calculated to be −385.81 ±4.64 kj/mole (−91.21 ±1.11 kcal/mole). The heats of hydrolysis of TiBr₄ and TiCl₄ were similarly measured; the value obtained for the difference (186.77 ±1.34 kj/mole) is in good agreement with the difference between the directly determined heats of formation (187.11 ±5.35 kj/mole).     

Heat of Formation of Titanium Trichloride

A calorimetric comparison of the heat of hydrolysis of TiCl₄(liq) with the heat of oxidation and hydrolysis of TiCl₃(c) has been made. The following value is reported for the combination of these data according to the process: TiCl3(c)+½I2(c)+HCl(g)→TiCl4(liq)+HI(g),ΔH°(25°C)=8.37±0.30kcal/mole.A combination of this value with −192.3 ±0.7 kcal/mole for the heat of formation of TiCl₄(liq) and with the standard heats of formation of HCl(g) and HI(g) gives for TiCl₃(c), ΔHf°(25 °C) = −172.4±0.8 kcal/mole.     

Heats of Formation of Lithium Perchlorate,Ammonium Perchlorate,and Sodium Perchlorate

Calorimetric measurements of the heats of solution of LiClO₄(c), NH₄ClO₄(e), and NaClO₄(c) have been made. The results have been combined with the heats of formation of KClO₄(c), KCl(c), LiCl(c), NH₄Cl(c), and NaCl(c), to obtain the following heats of formation: LiClO4(c),ΔHf°(25°C)=−380.27±1.21kj/mole=−90.89±0.29kcal/mole,NH4ClO4(c),=−295.98±1.35kj/mole=−70.74±0.32kcal/mole,NaClO4(c),=−382.75±0.93kj/mole=−91.48±0.22kcal/mole.A brief summary of other recent data has been included.     

Heat of Combustion of Borazine,B3N3H6

The heat of combustion of liquid borazine has been determined according to the following equation: B3N3H6(liq)+15/4O2(g)+3/2H2O(liq)=3H3BO3(c)+3/2N2(g),ΔH°(25°C)=−2313.3±12.6kj/mole(−552.90±3.0kcal/mole).From this value the heat of formation of liquid borazine may be calculated as ΔHf°(25 °C) = −548.5 ± 13.4 kj/mole (−131.1 ± 3.2 kcal/mole), and for the gas, ΔHf°(25 °C) = −519.2 ± 13.4 kj/mole (−124.1 ± 3.2 kcal/mole).     

Heats of Hydrolysis and Formation of Dimethoxychloroborane

The heat of hydrolysis of dimethoxychloroborane has been measured; for the reaction, (CH3O)2BCl(liq)+3H2O(liq)=H3BO3(c)+2CH3OH(liq)+HCl(g)ΔH(25°C)=−26.6±0.8kj/mole=−6.4±0.2kcal/mole.From this, we have calculated the heat of formation of dimethoxychloroborane: for the liquid, ΔHf° (25 °C) = −782.1 ± 1.8 kj/mole (−186.9±0.4 kcal/mole), and for the gas, ΔHf° (25 °C) = −747.9 ±2.2 kj/mole (−178.8±0.5 kcal/mole).     

Mass Spectrometric Study of NF2, NF3, N2F2, and N2F4

Appearance potentia’s have been measured for selected ions from NF₂, NF₃, N₂F₂, and N₂F₄. Ionization-dissociation processes are identified and bond dissociation energies are calculated. In addition, the bond dissociation energy, D(F₂N–NF₂), has been directly measured to be 5.14±0.38 kj/mole (21.5± 1.6 kcal/mole). A summary is made of available thermochemical and mass spectrometric data for N–F compounds and some evidence is presented to support the designation of cis and trans structures for the N₂F₂ isomers.     

Heat of Decomposition of Potassium Perchlorate

The heat of decomposition of potassium perchlorate into potassium chloride and oxygen has been determined in a bomb calorimeter. The process may be represented by the equation: KClO4(c)=KCl(c)+2O2(g),ΔH°(25°C)=−4.02±0.34kj/mole,=−0.96±0.08kcal/mole.Combination of this datum with the heat of formation of KCl(c) gives −103.22 ±0.15 kcal/mole for the standard heat of formation of KClO₄(c) at 25 °C.     

Heat of Formation of Calcium Aluminate Monosulfate at 25 °C

The heat of formation of calcium aluminate monosulfate, 3CaO·Al₂O₃·CaSO₄·12H₂O, at 25 °C, and of less completely hydrated samples of the same compound, was determined by the heat-of-solution method, with 2N HCl as the solvent, and 3CaO·Al₂O₃·6H₂O(c) and CaSO₄·2H₂O(c), as the reactants. The results were as follows:

Phase Equilibria in Systems Involving the Rare Earth Oxides. Part III. The Eu2O3?In2O3 System

The equilibrium phase diagram was determined for the Eu₂O₃−In₂O₃ system. An induction furnace, having an iridium crucible as the heating element (susceptor), was used to establish the solidus and liquidus curves. The 1:1 composition melts congruently at 1745 ± 10 °C. Melting point relations suggest that the 1:1 composition is a compound with solid solution extending both to 31 mole percent In₂O₃ and 71 mole percent In₂O₃. The compound is pseudohexagonal with a_H = 3.69 A and c_H = 12.38 A. Isostructural phases also occur in the 1:1 mixtures of both Gd₂O₃ and Dy₂O₃ with In₂O₃. The melting points of Eu₂O₃ and In₂O₃ were determined to be 2,240 ± 10 °C and 1910 ± 10 °C respectively. A eutectic occurs in the Eu₂O₃−In₂O₃ system at 1,730 °C and about 73 mole percent In₂O₃. The indicated uncertainties in the melting points are conservative estimates of the overall inaccuracies of temperature measurement.     

Heats of Hydrolysis and Formation of Potassium Borohydride

The heat of reaction of potassium borohydride with 0.060 molal HCl has been measured by solution calorimetry. The heat of solution of the hydrolysis products has also been measured and combined with certain literature values to calculate the process: KBH4(c)+HCl(g)+3H2O(liq)→KCl(c)+H3BO3(c)+4H2(g),ΔH°(25°C)=−354.06±1.84kj/mole(−84.62±0.44kcal/mole).A combination of this value with literature values for the heats of formation of HCl(g), H₂O(liq), KCl(c), and H₃BO₃(c) gives for KBH₄(c): ΔHf°(25°C) = ?228.86 ± 2.30 kj/mole(?54.70 ± 0.55 kcal/mole).Other data on the heats of formation of the alkali-metal borohydrides are discussed briefly.     

Compressibility of Natural Rubber at Pressures Below 500 kg/cm2

The specific volumes of unvulcanized natural rubber and of a peroxide-cured vulcanizate of natural rubber were measured at pressures of 1–500 kg/cm² at temperatures from 0 to 25 °C. Observations on mercury-filled dilatometers were made through a window in the pressure system. No time effects or hysteresis phenomena were observed. The specific volume V in cm³/e over the range studied can be represented by V = V_0,25{1 + A(t ? 25)}{1 + [α₂₅ + k₁(t ? 25)]P + [β₂₅ + k₂(t ? 25)]P²}where P is the pressure in kg/cm², and t the temperature in °C. The constants for the unvulcanized and for the peroxide-cured samples are:

• V₀,₂₅= 1.0951 and 1.1032 cm³/g;
• 10⁴A = 6.54 and 6.36 per degree;
• 10⁶α₂₅= −50.5 and −50.4 (kg/cm²)⁻¹;
• 10⁶k₁ = −0.227 and −0.203 per degree;
• 10⁹β₂₅= 10 and 11.5 (kg/cm²)⁻²;
• and 10⁹k₂=0.048 and 0.073 per degree, respectively. The compressibility of unvulcanized natural rubber at 25° and 1 kg/cm² is thus 50.5×10⁻⁶ (kg/cm²)⁻¹ falling to 40.6×10⁻⁶ (kg/cm²) ⁻¹ at a pressure of 500 kg/cm². It is concluded that a low degree of vulcanization produces no significant changes in the constants listed. The values are not far different from those obtained by extrapolating to zero sulfur content the observations of Scott on the rubbersulfur system. Calculations of values of compressibility (and its reciprocal the bulk modulus), “internal pressure”, bulk wave velocity, difference between specific heats, and several other physical properties are in reasonable agreement with those obtained by direct observation by other workers. For the prediction of values at pressures above 500 kg/cm² the use of the Tait equation is recommended.

     

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.     

Thermodynamic Properties of Some Methylphosphonyl Dihalides From 15 to 335 °K

Measurements of the heat capacity of methylphosphonyl difluoride (CH₃POF₂), methyl phosphonyl dichloride (CH₃POCl₂), and methylphosphonyl chlorofluoride (CH₃POClF) were made from about 15 to 335 °K by means of an adiabatic calorimeter. These highly reactive and toxic substances were purified in a completely closed glass apparatus by combining slow crystallization and fractional melting procedures. The purities determined by the freezing-curve method are shown to be generally in agreement with those values obtained by the calorimetric method. From the results of the heat measurements, the triple-point temperature, heat of fusion, and their corresponding estimated uncertainties were found to be, respectively, 236.34±0.05 °K and 11,878±12 J/mole for CH₃POF₂, 306.14± 0.02 °K and 18,076±15 J/mole for CH₃POCl₂, and 250.70± 0.20 °K and 11,853±30 J/mole for CH₃POClF. Triple-point temperatures obtained by the freezing-curve method are in agreement with the above values. A table of smoothed values of heat capacity, enthalpy, enthalpy function, entropy, Gibbs free energy, and Gibbs free energy function from 0 to 335 °K was obtained from the data. The entropy and its corresponding estimated uncertainty for CH3POF2, CH3POCl2, and CH3POClF in their respective condensed phase at 298.15 °K and saturation pressure was found to be 208.3± 0.3, 164.8± 0.3, and 216.4± 0.4 J/deg mole, respectively. The entropies in the gaseous state at 298.15 °K and 1 atm pressure were found to be 312.7±3, 339.7±3, and 335.0±3 J/deg mole, respectively.     

Airflow elicits a spider's jump towards airborne prey. I. Airflow around a flying blowfly

The hunting spider Cupiennius salei uses airflow generated by flying insects for the guidance of its prey-capture jump. We investigated the velocity field of the airflow generated by a freely flying blowfly close to the flow sensors on the spider''s legs. It shows three characteristic phases (I–III). (I) When approaching, the blowfly induces an airflow signal near the spider with only little fluctuation (0.013 ± 0.006 m s⁻¹) and a strength that increases nearly exponentially with time (maximum: 0.164 ± 0.051 m s⁻¹ s.d.). The spider detects this flow while the fly is still 38.4 ± 5.6 mm away. The fluctuation of the airflow above the sensors increases linearly up to 0.037 m s⁻¹ with the fly''s altitude. Differences in the time of arrival and intensity of the fly signal at different legs probably inform the spider about the direction to the prey. (II) Phase II abruptly follows phase I with a much higher degree of fluctuation (fluctuation amplitudes: 0.114 ± 0.050 m s⁻¹). It starts when the fly is directly above the sensor and corresponds to the time-dependent flow in the wake below and behind the fly. Its onset indicates to the spider that its prey is now within reach and triggers its jump. The spider derives information on the fly''s position from the airflow characteristics, enabling it to properly time its jump. The horizontal velocity of the approaching fly is reflected by the time of arrival differences (ranging from 0.038 to 0.108 s) of the flow at different legs and the exponential velocity growth rate (16–79 s⁻¹) during phase I. (III) The air flow velocity decays again after the fly has passed the spider.     

Calcium Fluoride Precipitation and Deposition From 12 mmol/L Fluoride Solutions With Different Calcium Addition Rates

The effects of different Ca-addition rates on calcium fluoride (CaF₂) precipitation and deposition were investigated in 12 mmol/L sodium fluoride solutions to which 0.1 mol/L calcium chloride solution was continuously added at average rates of (5, 7.5, 10, 12.5, 15 or 20) mmol L⁻¹ min⁻¹. The changes in ionic fluoride and calcium concentrations, as well as turbidity, were continuously recorded by F and Ca electrodes, and a fiber optic based spectrophotometer, respectively. The F⁻ concentration decreased and turbidity increased with time indicating precipitation of CaF₂. For the systems with Ca-addition rates of (5, 7.5, 10, 12.5, 15, and 20) mmol L⁻¹ min⁻¹, the 1 min CaF₂ depositions in the model substrate (cellulose filter paper, pores 0.2 µm) expressed as mean ± SD of deposited F per substrate surface area were (3.78 ± 0.31, 11.45 ± 0.89, 9.31 ± 0.68, 8.20 ± 0.56, 6.63 ± 0.43, and 2.09 ± 0.28) µg/cm², respectively (n = 10 for each group). The 1-min F depositions did not show positive correlation to Ca-addition rates. The lowest 1-min F deposition was obtained in the systems with the highest Ca-addition rate of 20 mmol L⁻¹ min⁻¹ for which CaF₂ precipitation rate reached the maximum value of 0.31 mmol L⁻¹ s⁻¹ almost immediately after beginning of reaction (6 s). The largest 1-min F depositions were obtained from the systems with Ca addition rates of (7.5 to 12.5) mmol L⁻¹ min⁻¹ in which CaF₂ precipitation rates continuously increased reaching the maximum values of (0.13 to 0.20) mmol L⁻¹ s⁻¹ after (18 to 29) s, respectively. The 1-min F depositions were greatly enhanced in comparison with the control F solutions that did not have continuous Ca-addition. This indicates that continuous Ca addition that controls the rate of CaF₂ formation could be a critical factor for larger F depositions from F solutions. The efficacy of conventional F mouthrinses could be improved with addition of a substance that continuously releases Ca.     

Photoluminescent lead(II) coordination polymers stabilised by bifunctional organoarsonate ligands

Four lead(II) coordination polymers were isolated under hydro(solvo)thermal conditions. The applied synthetic methodology takes advantage of the coordination behaviour of a new bifunctional organoarsonate ligand, 4-(1, 2, 4-triazol-4-yl)phenylarsonic acid (H₂TPAA) and involves the variation of lead(II) reactants, metal/ligand mole ratios, and solvents. The constitutional composition of the four lead(II) coordination polymers can be formulated as [Pb₂(TPAA)(HTPAA)(NO₃)]·6H₂O (1), [Pb₂(TPAA)(HTPAA)₂]·DMF·0.5H₂O (DMF = N, N-Dimethylformamide) (2), [Pb₂Cl₂(TPAA)H₂O] (3), and [Pb₃Cl(TPAA)(HTPAA)₂H₂O]Cl (4). The compounds were characterized by single-crystal and powder x-ray diffraction techniques, thermogravimetric analyses, infra-red spectroscopy, and elemental analyses. Single-crystal x-ray diffraction reveals that 1 and 2 represent two-dimensional (2D) layered structures whilst 3 and 4 form three-dimensional (3D) frameworks. The structures of 1, 2, and 4 contain one-dimensional (1D) {Pb^II/AsO₃} substructures, while 3 is composed of 2D {Pb^II/AsO₃} arrays. Besides their interesting topologies, 1–4 all exhibit photoluminescence properties in the solid state at room temperature.     

A Double-Primary Dead-Weight Tester for Pressures (35–175) kPa in Gage Mode

Primary pressure standards in the atmospheric pressure range are often established using mercury manometers. Less frequently, controlled-clearance dead-weight testers in which one component (normally the piston) has been dimensionally measured have also been used. Recent advances in technology on two fronts i) the fabrication of large-diameter pistons and cylinders with good geometry; and ii) the ability to measure the dimensions of these components, have allowed some dead-weight testers at NIST to approach total relative uncertainties (k = 2) in dimensionally-derived effective areas near 5 × 10⁻⁶. This paper describes a single piston/cylinder assembly (NIST-PG201WC/WC) that serves as both a primary gage in which both piston and cylinder are measured dimensionally and a controlled-clearance primary gage (employing the Heydemann-Welch method). Thus it allows some previous assumptions about the modeling of dead-weight testers to be checked. For the gage described in this paper the piston/cylinder clearance obtained from the two analyses have relative differences of 4 × 10⁻⁶ to 7 × 10⁻⁶ over the pressure range 35 kPa to 175 kPa. Some implications of these results will be discussed. From the dimensional characterizations and auxiliary measurements we have determined that the effective area for this gauge at 20 °C is: A_eff,20 = 1961.0659mm²(1 + 3.75 × 10^?12P/Pa + 3.05 × 10^?12P_J/Pa), where P is the system pressure and P_J is a control pressure. The estimated relative uncertainty in effective area is 8.2 × 10⁻⁶ +1.4 × 10⁻¹¹ P/Pa (k = 2). The temperature coefficient for the area was measured and found to be (9.06 ± 0.04) × 10⁻⁶/K. Thus using the gage at a reference temperature of 23 °C yields an effective area: A_eff,23 = 1961.1192mm²(1 + 3.75 × 10^?12P/Pa + 3.05 × 10^?12P_J/Pa), with almost no increase in the uncertainty over that at 20 °C.     

Water Calorimetry: A Correction to the Heat Defect Calculations

In a recent publication, we used a reaction model (model III) to calculate the heat defect for the irradiation of aqueous solutions with ionizing radiation at 21 °C. Subsequent work has revealed that the literature value used for one of the rate constants in the model was incorrect. A revised model (model IIIR) incorporates the correct rate constant for 21 °C. Versions of models III and IIIR were created for irradiations at 4 °C. For our current water calorimetry protocol, the values of the heat defect for H₂/O₂-water (water saturated with a flow of 43 % H₂ and 57 % O₂, by volume) at 21 °C predicted by model III and model IIIR are similar but the value for 4 °C predicted by III is 30 % smaller than the value predicted by IIIR. Model IIIR predicts that the values of the heat defect at 21 °C and 4 °C lie within the range −0.023±0.002, in agreement with the values obtained from our water calorimetry measurements done using pure water and H₂-saturated water at 21 °C and 4 °C. The yields of hydrogen peroxide in H₂/O₂-water at 21 °C and 4 °C were measured and agree with the predictions of model IIIR. Our water calorimetry measurements made with pure water and H₂-saturated water are now of sufficient quality that they can be used to determine the heat defect for H₂/O₂-water better than can be done by simulations. However, consistency between the three systems continues to be an excellent check on water purity which is crucial, especially for the pure water system.     

Preparation and Calibration of Carrier-Free 209Po Solution Standards

Carrier-free ²⁰⁹Po solution standards have been prepared and calibrated. The standards, which will be disseminated by the National Institute of Standards and Technology as Standard Reference Material SRM 4326, consist of (5.1597 ±0.0024) g of a solution of polonium in nominal 2 mol · L⁻¹ hydrochloric acid (having a solution density of (1.031±0.004) g · mL⁻¹ at 22 °C) that is contained in 5 mL flame-sealed borosilicate glass ampoules, and are certified to contain a ²⁰⁹Po alpha-particle emission rate concentration of (85.42±0.29) s⁻¹ · g⁻¹ (corresponding to a ²⁰⁹Po activity concentration of (85.83 ±0.30) Bq · g⁻¹) as of the reference time of 1200 EST 15 March 1994. The calibration was based on 4πα liquid scintillation (LS) measurements with two different LS counting systems and under wide variations in measurement and sample conditions. Confirmatory measurements by 2πα gas-flow proportional counting were also performed. The only known radionuclidic impurity, based on α- and photon-emission spectrometry, is a trace quantity of ²⁰⁸Po. The ²⁰⁸Po to ²⁰⁹Po impurity ratio as of the reference time was 0.00124 ±0.00020. All of the above cited uncertainty intervals correspond to a combined standard uncertainty multiplied by a coverage factor of k = 2. Although ²⁰⁹Po is nearly a pure α emitter with only a weak electron capture branch to ²⁰⁹Bi, LS measurements of the ²⁰⁹Po a decay are confounded by an a transition to a 2.3 keV (J^π= 1/2⁻) level in ²⁰⁵Pb which was previously unknown to be a delayed isomeric state.