Magnesium Vapor Research Articles

Thermochemistry of ternary liquid Cu-Mg-Si alloys

The thermodynamic properties of ternary liquid Cu-Mg-Si alloys with a constant concentration ratio of xCu/xSi=7/3 were determined using a combination of different experimental methods. Enthalpies of mixing were measured by isoperibolic calorimetry, and magnesium vapor pressures were obtained by an isopiestic method. Partial thermodynamic properties of magnesium were derived from the vapor pressure data, and the composition dependence of the magnesium activities is given for 1173 K. Integral Gibbs energies of mixing for liquid alloys were calculated by a Gibbs-Duhem integration. The agreement of the thermodynamic data obtained from different methods was found to be very good.

マグネシウムの真空蒸留精製

An investigation on vacuum distillation of magnesium was carried out to obtain high purity material for basic research use, using a Mg–20%Al electrolytic magnesium (99.93%) base alloy as a raw material. Magnesium vapor was found to be condensed at a region where the temperature ranged from 625 K to 750 K involving steep temperature rise ascribed to the latent heat of condensation. To permit the condensation to occur uniformly on the sleeve, the temperature of the condenser portion was controlled within the above range. Purified magnesium of about 3 kg was obtained from the raw material of 4 kg by a distillation for 86.4 ks at 933 K. Impurities such as Fe, Mn, Si, commonly contained in commercial magnesium, were substantially eliminated by this distillation, resulting in a purity above 99.99% that was significantly increased from that (99.93%) of electrolytic magnesium.

A study on the mechanism of reaction between refractory materials and aluminium deoxidised molten steel

The conditions of formation of inclusions in steel during ladle refining in MgO‐C lined ladles have been investigated in laboratory experiments at 1873 K in MgO‐C crucibles with 50 g iron. From both the experimental results as well those of a thermodynamic study conducted in parallel, the following conclusions can be made about the reaction mechanism between the MgO‐C refractory and aluminium deoxidised molten steel: At steelmaking temperature an internal oxidation‐reduction occurs in the MgO‐C refractory. The formation of a thin oxide layer at the interface is due to the reaction between magnesium vapour and aluminium dissolved into the molten steel and the CO(g) generated by the reaction between MgO and C in the crucible walls. The oxide inclusions formed in the steel have been shown mainly to consist of MgO, Al2O3 or mixture of them. Some of the finest inclusions are considered to be formed as secondary inclusions during cooling and solidification of the steel and they are connected only with the diffusion of magnesium from the crucible to the molten steel. The thermodynamic calculations indicate that during vacuum refining, as the pressure decreases, the chemical compatibility of carbon‐bonded magnesia for ladle lining decreases.

Investigation of the molecular species produced by the vaporization of the Group IIA metal nitrates from a graphite surface

The Group IIA metals studied exhibited similar mechanisms when atomized from graphite and tantalum lined surfaces. The vaporization of beryllium, magnesium, calcium, strontium and barium begins with the decomposition of the nitrate during drying and the deposition of the oxide on the interior of the graphite. Each metal appears to produce an early absorption by a hydroxide followed by the oxide and subsequently by the metal. The presence of carbides could not be confirmed but the graphite may play an active role in the atomization of the Group IIA nitrates, as suggested by the accelerated degradation of the furnace for most of the substances examined. The carbides did not appear to vaporize well from the graphite but did seem to react readily with water vapor from the air.

Partial thermodynamic properties of magnesium in ternary Cu-Mg-Si alloys

An investigation of the Cu-Mg-Si alloy system was carried out by measuring magnesium vapor pressures along the isopleth with a copper to silicon ratio, X Cu/ X Si = 7/3 employing a pseudo-isopiestic technique. The measurements were made in the temperature range from 1014 to 1323 K. Thermodynamic activities and partial molar enthalpies of magnesium were derived for the liquid phase. The composition dependence of the activities at 1173 K over the composition range between 20 and 80 at.% magnesium is presented.

Potential energy of magnesium atom-hydrogen molecule interaction and interdiffusion coefficient

The potential energy of intermolecular interaction is calculated by the quantum-mechanical exchange perturbation theory. The results are used to calculate the diffusion coefficient for magnesium vapor in hydrogen. The calculations agree with the experimental results.

Probing the initial stage of synthesis of Al2O3/Al composites by directed oxidation of Al-Mg alloys

In the directed oxidation of Al-Mg alloys, the amount of MgO that forms in the initial stage prior to the incubation period affects the rate of oxidation of Al to Al2O3 in the composite growth stage. The mechanism of formation of MgO and the duration of the initial stage were investigated experimentally and theoretically. The variables studied were total pressure in the reaction chamber, partial pressure of oxygen, and the nature of the diluent gas which affects the diffusion coefficients of magnesium vapor and oxygen in the gas phase. The oxidation rate in the initial stage was proportional to both the oxygen partial pressure and the diffusivity of oxygen. The duration of the initial stage decreased with the increase in oxygen pressure. To understand the role of magnesium evaporation in the oxidation behavior of the alloy, the velocity, temperature, and concentration fields in the gas phase were simulated numerically. The calculated concentration profiles of magnesium vapor and oxygen as a function of time were consistent with the experimentally measured oxidation rates and confirm reaction-enhanced gaseous diffusion-limited vaporization of magnesium in the initial stage of oxidation of Al-Mg alloys. The region where the magnesium vapor is oxidized in the gas phase moved progressively closer to the alloy surface during the initial stage of oxidation. The end of the initial stage and the start of the incubation period corresponded to the arrival of the oxygen front close to the surface when the spinel formation occurred.

Thermodynamic properties of liquid magnesium-nickel alloys

Magnesium vapor pressures were determined over liquid Mg-Ni alloys for compositionsx Mg>0.65 using an isopiestic method. Data points between 760 and 890°C were evaluated to derive corresponding partial thermodynamic properties. The composition dependence of the magnesium activities in liquid alloys is shown for a temperature of 1073 K. Additionally, it is possible to obtain the shape of the liquidus curve between about 60 and 70 at% Mg from the results of the isopiestic measurements.

The Millimeter/Submillimeter Spectrum and Rotational Rest Frequencies of MgCH[TINF]3[/TINF]([FORMULA][F][A][AC]X[/AC][AC][d5][/AC][/A][/F][/FORMULA] [TSUP]2[/TSUP][ITAL]A[/ITAL][TINF]1[/TINF

The pure rotational spectrum of the free radical MgCH3( 2A1) has been measured in the laboratory for the first time using millimeter/submillimeter direct absorption spectroscopy. The molecule was made in a DC discharge by the reaction of magnesium vapor and dimethyl mercury. Ten rotational transitions of this species were observed in the range 176-374 GHz. MgCH3 is a symmetric top molecule with net spin angular momentum. Consequently, both K structure and spin-rotation interactions were observed in every rotational transition. The data were analyzed with a2A1 Hamiltonian and rotational, centrifugal distortion, and fine-structure parameters were accurately determined. These measurements will now enable a search for this radical in interstellar and circumstellar sources to be conducted using millimeter/submillimeter telescopes.

A Model for Low-Temperature Ignition of Magnesium Particles

Abstract A new theoretical model for the low-temperature ignition process of magnesium particles is proposed. The model is based on physical-mechanical effects resulting from the buildup of oxide layers on the particle surface and their possible destruction as a result of mechanical stresses attributed to thermal and pressure expansion which are due to temperature elevation, melting and, in some instances, liberation of dissolved hydrogen and generation of magnesium vapors. The model attempts to describe and predict peculiar and unexplained phenomena, which have been observed experimentally during the low temperature ignition of magnesium particles, such as increase or pulsations in particle size, formation of hollow spheres, and fragmentation of particles

The millimeter-wave spectrum of 25MgNC and 26MgNC: bonding in magnesium isocyanides

Rotational spectra of the 25Mg and 26Mg isotopomers of MgNC have been recorded in the frequency range 298–386 GHz using millimeter/sub-millimeter direct absorption spectroscopy. The species were created in their natural isotopic ratios in a dc discharge of cyanogen gas and magnesium vapor. Rotational and fine structure parameters were determined for these radicals, as well as magnesium 25 hyperfine constants for 25MgNC. For this isotopomer, b F ≈ −298(16), indicating a large electron density at the nucleus and an ionic type Mg +NC − structure, as expected for a linear configuration. R 0 bond lengths were also derived, which are in good agreement with theoretical calculations.

Metal hyperfine structure in magnesium chloride. The millimeter-wave spectrum of 25MgCl and 26MgCl

Rotational spectra of the magnesium and chlorine isotopomers of MgCl (X 2ϵ +) have been measured in the frequency range 260–380 GHz using direct absorption techniques. The species studied ( 25Mg 35Ml, 25Mg 37Cl, and 26Mg 37Cl) were created in a dc glow discharge by the reaction of magnesium vapor with CCl 4. Several rotational transitions were recorded for each isotopomer, and fine structure, as well as hyperfine splittings due to the 25Mg nucleus, were observed. Rotational, spin—rotation and hyperfine constants were determined for these radicals. The average value of the Fermi contact terms was b F( 25Mg) = −317.8 (4.9) MHz, indicating a large electron density at the magnesium nucleus.

Thermodynamic properties of ternary liquid Cu-Mg-Ni alloys

Magnesium vapor pressures were determined over ternary Cu-Mg-Ni alloys along three isopleths with x[sub Cu]/x[sub Ni]=2.0, 1.0, and 0.5 using an isopiestic method. Data points were obtained between approximately 20 and 90 at. pct magnesium in the temperature interval from 1,050 to 1,350 K. Partial thermodynamic properties of magnesium were derived for the liquid phase, and integral Gibbs energies of formation were computed by a Gibbs-Duhem integration. The composition dependence of the activities at 1,173 K is shown for the three sections investigated. The experimental integral Gibbs energies of mixing for liquid alloys are compared with the values calculated from binary data by a geometrical formalism.

Partial thermodynamic properties of magnesium in ternary liquid CuMgNi alloys

Magnesium vapour pressures over ternary CuMgNi alloys were determined by an isopiestic method along three isopleths with χ Cu/ χ Ni = 2.0, 1.0 and 0.5 between about 20 and 90 at.% Mg. Thermodynamic activities and partial molar enthalpies of magnesium were derived from the vapour pressure data, and composite dependence of the activities at 1173 K is shown for the three sections investigated. The possibility of ordering in the ternary liquid around 33 at.% Mg is discussed.

Laboratory spectroscopy of MgNC - The first radioastronomical identification of Mg-bearing molecule

view Abstract Citations (203) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Laboratory Spectroscopy of MgNC: The First Radioastronomical Identification of Mg-bearing Molecule Kawaguchi, Kentarou ; Kagi, Eriko ; Hirano, Tsuneo ; Takano, Shuro ; Saito, Shuji Abstract The linear MgNC radical was detected, for the first time, by laboratory microwave spectroscopy, and six unidentified lines in IRC + 10216 reported by Guelin et al. (1986) were assigned to the transitions of this radical. The radical was produced in a free space absorption cell by a dc discharge in a mixture of magnesium vapor, argon, and cyanogen. Observed spectral lines in the 250-370 GHz region were analyzed by using the 2Sigma energy level expression, to give the rotational, centrifugal distortion and spin-rotation constants: B0 = 5966.8969(24) MHz, D0 = 0.004 2338(35) MHz, H0 = 0.308(16) x 10 exp -7 MHz, and gamma0 = 15.219(13) MHz, with one standard deviation in parentheses. Publication: The Astrophysical Journal Pub Date: March 1993 DOI: 10.1086/186781 Bibcode: 1993ApJ...406L..39K Keywords: Astronomical Spectroscopy; Line Spectra; Magnesium Compounds; Molecular Spectroscopy; Radio Astronomy; Electron Transitions; Molecular Spectra; Radio Spectroscopy; Stellar Envelopes; Astronomy; LINE: IDENTIFICATION; MOLECULAR DATA; RADIO LINES: STARS full text sources ADS | data products SIMBAD (1)

On temperature increase of the Mg 2 mole fraction in saturated magnesium vapour

The composition of saturated magnesium vapour is investigated in terms of the dimerization equilibrium constant and the observed saturated pressure in the temperature region 700–1000 K. The highest reported value of the dimer mole fraction x 2 in its equilibrium mixture with the monomer at the saturated pressure is quite small (0.004%). It is found that (at least in the interval 850–1000 K) the x 2 term increases with temperature. This is in agreement with recent findings of such temperature increase with other associating vapours.

Synthesis of silicon and silicon nitride powders by vapour-phase reactions

The Bureau of Mines is investigating vapour-phase reactions for syntheses of high-purity, nanometre-sized silicon and Si3N4 powders suitable for industrial applications. In this study, submicrometre-sized silicon powder was formed by a vapour-phase reaction of SiCl4, NH3, and magnesium vapor at temperatures ranging from 950–1050°C. The silicon was subsequently nitrided to form Si3N4 at 1150°C.

Photon detection based on pulsed laser-enhanced ionization and photoionization of magnesium vapour: experimental characterization

A resonance ionization detector (RID) based on the two-step laser-enhanced ionization of Mg in a miniature air–acetylene flame is described. The detector utilizes the 285.213 nm resonance absorption of Mg as the signal transition, i.e., photons to be measured. Magnesium atoms excited by absorption of photons at 285.2 nm were further excited to higher lying energy states by absorption of photons at 571.2 or 435.2 nm, from which collisional ionization could occur, or by absorption of photons at 300.9 nm, which directly ionized the excited Mg atoms via an autoionizing level above the ionization continuum. The miniature flame used (about 2 mm in diameter) had very low noise characteristics and the minimum detectable number of photons (MDP) was limited, in some instances, by the noise of the transimpedance amplifier used. The lowest MDP, obtained for the excitation scheme 3s21S (285.2 nm)→3p 1P0(435.2 nm)→6d 1D, was experimentally determined to be 1 × 103(7 × 10–16 J). The quantum efficiency of this excitation scheme, defined as the number of electrons created per photon absorbed at the signal transition (285.2 nm), was found to be 0.75. The spectral response bandwidth of the detector in the signal transition was determined to be mostly Lorentzian in nature, owing to pressure broadening in the atmospheric pressure flame, with a stray light rejection ratio of approximately 1 × 10–5 at 100 cm–1 displacement from the absorption maximum of the RID at 285.213 nm. An application of the RID is given in the detection of weak Raman scatter of carbon tetrachloride, chloroform and dimethyl sulfoxide.

Photon detection based on pulsed, laser-enhanced ionization and photoionization of magnesium vapour: quantum efficiency versus ion yield. Invited lecture

The concepts of quantum efficiency and ion yield pertinent to a photon detector consisting of an atmospheric pressure oxygen–argon–acetylene (or hydrogen) flame containing magnesium atomic vapour, and also some published experimental results obtained with this detector, are critically discussed. In these experiments, collision-induced ionization and direct photoionization of magnesium atoms are performed. In the former instance, one dye laser excites the atoms from the ground state into the 3s3p–1P10 state and another laser, in temporal and spatial coincidence with the first, brings the excited atoms into the 3s5d–1D2 state, from which collisional ionization occurs. In the last instance, direct photoionization from the 1P10 level is accomplished either with the excimer laser radiation at 308 nm or by tuning the second laser into an autoionizing resonance at 300.9 nm. It is shown that the total loss rate from the 1P10 level can be calculated by time resolving the resonance fluorescence waveform, with and without the presence of the second laser, and that, by integrating this signal over the duration of the laser pulse, the fluorescence dip obtained can be related to the ion yield of the excitation–ionization scheme. It is also stressed that, because of the presence of a metastable level which can act as a trap for the excited atoms, owing to quenching collisions in the flame, the quantum efficiency of this detector will never exceed the ‘ion branching ratio’, i.e., the ratio between the ionization rate and the total loss rate from the excited level. By evaluating several experimental results obtained with different laser systems, it is shown that, in the collision-induced ionization mode, both fluorescence and ionization measurements are necessary to derive the quantum efficiency, whereas in the direct photoionization mode, fluorescence data suffice.

Effect of magnesium on the composition, microstructure and mechanical properties of carbon fibres

This work was undertaken in order to provide more detailed information on the chemical and mechanical behaviour of carbon fibres during the elaboration of graphite-magnesium composite materials. For this purpose, PAN-based T300, pitch-based P55 and P100 carbon fibres were isothermally heat treated, at temperatures ranging from 450 to 700 °C, under a saturated vapour pressure of magnesium. The composition, microstructure and tensile strength of the resulting samples were characterized by chemical and electron probe microanalysis, Raman spectrometry, X-ray diffraction and mechanical test of single filaments. From the results obtained, it has been concluded that highly graphitized fibres such as pitch-based P55 or P100 are not affected by long-time annealing in the presence of magnesium vapour, whereas impure and disorded fibres such as PAN-based T300 undergo some chemical and microstructural modifications decreasing their mechanical properties.