Solid CaO Research Articles

Formation of Ca‐O clusters and their protonation and hydration in direct laser vaporization

AbstractCalcium oxide clusters produced in the direct laser vaporization of different precursor solid samples CaO, Ca(OH)2 and CaCO3 have been investigated by a time‐of‐flight mass spectrometer. Besides [Ca(CaO)n]+ and [(CaO)n]+ clusters, considerable protonated clusters [H(CaO)n]+ and hydrated clusters [H(CaO)n(H2O)m]+ have also been found in the TOF mass spectra. The characteristic of the abundance distribution of the clusters shows that the formation process of calcium oxide clusters should proceed along the growth course of the rock salt structure, which is further supported by the reactivity of [H(CaO)n]+ clusters with H2O produced in the direct laser vaporization.

Thermodynamics of calcium and oxygen in molten titanium and titanium-aluminum alloy

The deoxidation equilibrium of molten titanium and titanium-aluminum alloys saturated with solid CaO has been measured in the temperature range from 1823 to 2023 K. The equilibrium constant of reaction CaO (s)=Ca (mass pct in Ti,Ti-Al)+O (mass pct in Ti,Ti-Al) and the interaction parameter between calcium and oxygen were determined for Ti, TiAl, and TiAl3. The standard Gibbs energy of reaction for TiAl was obtained as follows: $$\Delta G^\circ = 279,000 - 103TJ/mol$$ The possibilities for the deoxidation of titanium and titanium-aluminum alloys by using calcium-based fluxes are discussed.

96/05233 The effect of solid CaO on the production of NOx and N2O in fluidized bed combustors: Studies using pyridine as a prototypical nitrogenous fuel

96/05233 The effect of solid CaO on the production of NOx and N2O in fluidized bed combustors: Studies using pyridine as a prototypical nitrogenous fuel

The effect of solid CaO on the production of NO x and N 2O in fluidized bed combustors: Studies using pyridine as a prototypical nitrogenous fuel

Pyridine is typical of the nitrogenous species found in coal which decompose during devolatilization to yield HCN. Hence, pyridine was burned in an electrically heated bed of sand fluidized by O 2 + N 2. One product, NO, is found to have a concentration proportional to that of the pyridine in the fluidizing gases. A second, N 2O, has a concentration proportional to the square of the pyridine concentration. The mechanistic implications of this are discussed; it turns out that the production of NO and N 2O in this system is different from in a homogeneous gas-phase system. In particular, it appears that CN radicals adsorbed on sand are oxidised relatively rapidly to NO in: − CN → − CNO → CO + NO. The presence of 2 wt.% CaO in the bed increases the yield of NO by up to a factor of 20 and decreases that of N 2O slightly, without changing the dependences of [NO] and [N 2O] on [pyridine] noted above. The effects of oxygen concentration and temperature are investigated. It appears that CaO promotes a new heterogeneous reaction, whereby species in the pool of HCN and CN radicals are converted relatively rapidly to NO, resulting in a lower yield of N 2O. Certainly, NH 3 is found to react with CaO to produce NO. Addition of NO to the fluidizing air when burning pyridine establishes that N 2O is produced by reaction between NO and an intermediate which is most probably the NCO radical. Another effect of the presence of CaO is to reduce emissions of CO. It appears that CO burns catalytically on a CaO surface. Finally, CaO probably catalyses the reduction of NO and N 2O in: CO + NO → CO 2 + 1 2 N 2 and CO + N 2O → CO 2 + N 2.

固体CaOと平衡するNi-Ca-OとNi-Ta-Ca-O融体の熱力学

固体CaOと平衡するNi-Ca-OとNi-Ta-Ca-O融体の熱力学

Kinetics of the reaction between gaseous sulfur trioxide and solid calcium oxide

Tiny particles (diameter < 100 µm) of porous CaO have been reacted with SO3 in inert N2 at atmospheric pressure and temperatures between 600 and 900 °C. These particles of CaO were well characterized by BET analysis and mercury porosimetry. Conditions were such that the kinetics of the reaction: CaO + SO3→ CaSO4, whereby one solid gives another, controlled the rate of production of CaSO4. Thus it was established that, for the initial stages of reaction, the diffusion of SO3 to a particle of CaO in the thermogravimetric balance used was relatively rapid, as was the diffusion of SO3 both inside the pores of a particle of CaO and through the layer of product, CaSO4. The reaction is first order in SO3, the rate constant (defined per unit area of solid CaO) being 3.2 ± 0.3 × 10–6 exp(–746 ± 108/T) m s–1. Thus the apparent activation energy is only 6.2 ± 0.9 kJ mol–1. The rate constant is almost identical to that for SO2 reacting with CaO to give CaSO3; in each case the steric factor is extremely low, being ca. 2 × 10–8. The diffusivity for SO3 through the product, CaSO4, is ca. 2 × 10–13 m2 s–1.

The cohesion of solid magnesium and calcium oxide: the role of in-crystal modification of the oxide ion and electron correlation

The cohesive properties of solid MgO and CaO are investigated using the fully ionic description calculating exactly, after generating the electronic wavefunctions of the ions, those portions of each inter-ionic potential energy function that do not arise from electron correlation. Three major new refinements are introduced. The modifications of each anion wavefunction that arise from the crystalline environment are described using two new methods in which the environmentally generated contribution to the potential energy acting on an anion electron is related to the cation electron density. These methods improve substantially on earlier models, shown to be inadequate for solid oxides, in which the environmental potential energy has the form of that generated by a spherical shell of charge. Density functional theory is used to evaluate the contribution of electron correlation to the oxide-ion rearrangement energy, that is the energy required to convert a free 0 - ion to an in-crystal 0 2- ion. For any oxide, this correlation term varies appreciably with crystal geometry, as well as differing significantly between different oxides at their equilibrium geometries. The present models for the in-crystal environment of the oxide ion require a new way of deriving the parameters that govern the damping of the dispersive attractions between the ions, this damping originating from ion-wavefunction overlap being too large to neglect.

Determination of CaO activity in the mixture { xCaO + (1 − x)ZrO 2} at the temperature 1270 K by a galvanic cell involving calcium-ion conducting solid electrolyte

By the use of a solid electrolyte: Ca-β″-alumina, conducting Ca 2 +ions, the CaO activities in { xCaO + (1− x)ZrO 2} at the temperature 1270 K have been determined. The cubic solid solutions CaO in ZrO 2formed in this mixture in the composition range x= 0.11 to 0.16 exhibit negative deviations from Raoult’s law. They were found to behave as regular solutions.

The influence of improved dipole-quadrupole dispersion coefficients on the predicted cohesion of ionic oxides

The coefficients governing the dipole-quadrupole dispersive attractions between all the ions in solid magnesium oxide are computed ab initio using the coupled Hartree-Fock method. These confirm for oxides the previous conclusion that the Starkschall-Gordon formula provides the most reliable values for systems not amendable to ab initio computation. Combination of the ab initio results with semiempirical estimates of the much smaller contributions from electron correlation produces improved coefficients. The cohesion predicted for MgO with the fully ionic model remains essentially unchanged on replacing the Starkschall-Gordon dipole-quadrupole dispersion coefficients with the improved values. The use of improved predictions for C8(O2-...O2-) in solid CaO, ThO2 and UO2 in place of Starkschall-Gordon values leaves essentially unchanged the cohesion predicted for CaO whilst very slightly but significantly increasing that predicted for ThO2 and UO2. Theory and experiment for ThO2 then agree as excellently as for MgO and CaO, thus showing no evidence for any covalency.

Synthesis of Boron Nitride from Boron Oxide Using Super-Critical Ammonia

Hexagonal boron nitride was synthesized from boron oxide using super critical ammonia and solid CaO below the melting point of B 2 O 3 by the following reaction: B 2 O 3 (s)+2NH 3 (super-critical fluid) + 3CaO (s)=2BN (s)+3Ca(OH) 2 (s). The experiment was carried out at 623-753 K and the initial ammonia pressure was 3.0-40.0 MPa. The mean diameter of obtained BN particles was 0.2-0.3 μm. The yield of BN increased with increasing temperature, initial ammonia pressure and the addition of CaO. The thermochemical calculation showed that the CaO addition suppressed the decomposition loss of ammonia during the reaction.

Coupled transcription of Epstein--Barr virus latent membrane protein (LMP)-1 and LMP-2B genes in nasopharyngeal carcinomas

The presence of transcripts of the Epstein-Barr virus genes for Epstein-Barr nuclear antigen (EBNA)-1 and EBNA-2 and for latent membrane protein (LMP)-1, LMP-2A and LMP-2B was investigated in 24 nasopharyngeal carcinoma (NPC) biopsies of Chinese origin and two NPC-derived solid tumour lines, CAO and C15, of Chinese and north African origin respectively, propagated by serial transplantation in nude mice. Transcripts were detected by PCR amplification of cDNA. EBNA-1 transcripts were present in all biopsies tested and originated exclusively from the FQ promoter while the C and W promoters were inactive. Using nested primers, LMP-1 and LMP-2B RNAs were found to be co-ordinately expressed in 22 of the 24 biopsies, while the two remaining tumours were negative for both. LMP-2A transcription was detected in 17 of the 22 LMP-1-positive biopsies. In summary, the following patterns of viral gene expression were observed in the tumour biopsies: (i) LMP-1-LMP-2B and LMP-2A positive (17 biopsies); (ii) LMP-1-LMP-2B positive but LMP-2A negative (five biopsies); (iii) no viral gene other than EBNA-1 expressed (two biopsies).

Structures and bonding properties of calcium oxide clusters inferred from mass spectral abundance patterns

Calcium oxide clusters were produced by a gas aggregation technique and investigated using time-of-flight mass spectrometry. Depending on the source conditions, either singly or doubly charged clusters dominate the mass spectrum. Singly charged (CaO) n Ca m + (m=0-5) clusters are observed for higher flows of inert carrier gas, whereas primarily doubly charged (CaO) n Ca 2+ (n=3-100) clusters are observed at lower flows. The mass spectral abundance patterns indicate that the clusters have cubic structures resembling pieces of the fcc lattice of solid CaO

Thermodynamic conditions for inclusions modification in calcium treated steel

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固体生石灰による溶銑脱硫の反応機構におよぼす生石灰内細孔分布の影響

It is important to understand the desulfurization mechanism by solid CaO for improving its desulfurizing power of hot metal. From the standpoint described above, desulfurization experiment of hot metal was carried out by CaO calcined under various conditions. Experimental results were discussed with CaO properties. Results obtained are as follows. No correlation between utilization factor (ηS) which has been regarded as a desulfurizing power and CaO properties was found. On the other hand, a good correlation between desulfurization efficiency (dηS /dt) defined by the authors and pore size distribution of CaO used was found, namely higher desulfurization efficiency of early stage in the reaction was given by rather lower porosity CaO having pores with wide diameter, than by higher porosity CaO having a number of pores with small diameter.

Equation of state and electronic structure of solid CaO under high pressure

The equations of state (EOSs) and the electronic structures of solid CaO both in the B1 and in the B2 structure have been calculated by using the local-density functional theory with the APW method in the muffin-tin approximation. The EOS of the B1 phase is in excellent agreement with the diamond-anvil-cell experiments. The metallization at T = 0 K is shown to occur in the B2 phase at a pressure of 480 GPa. By using the Debye temperature and the Grüneisen constant, both of which are theoretically determined, the hugoniot has also been calculated. The agreement with experiment is good for the B1 phase and is moderate for the B2 phase.

The effect of temperature on the kinetics and extent of SO 2 uptake by calcareous materials during the fluidised bed combustion of coal

Measurements have been made in laboratory scale fluidised beds of the kinetics of absorption of SO2 by calcined limestone and dolomite particles. In addition, the extent to which CaO in these particles was ultimately converted to CaSO4 has been determined. Both sets of measurements were made over a range of bed temperatures, particle sizes and oxygen concentrations. In addition, observations were made both with and without coal burning in the bed. In the latter case, the bed was fluidised with gas mixtures containing SO2 in N2, together with O2 and CO2. In some experiments, propane was fed into the middle of the bed to simulate the release of coal volatiles. Most work was carried out at atmospheric pressure, but some studies were performed at elevated pressures. The final conversion of a particle to CaSO4 shows a maximum at ∼1148 K, when a bed is fluidised by gas mixtures containing O2 and SO2. However, with coal burning in the bed, conversion to CaSO4 falls off sharply to low levels above ∼1173 K. It is clear that this is due to low [O2] in the particulate phase of the bed. The rate constant for the reaction of SO2 with solid CaO does not vary with particle size or [O2]. Absorption of SO2 actually proceeds in the absence of O2; the measured activation energy is 32.6±4.5 kJ/mol. The indications are that SO3 is not a necessary intermediate. The mechanism of absorption and the role played by O2 are discussed.

固体CaO化合物で飽和したCaO-CaF&lt;SUB&gt;2&lt;/SUB&gt;-SiO&lt;SUB&gt;2&lt;/SUB&gt;系スラグと炭素飽和溶鉄間のりんの分配平衡

固体CaO化合物で飽和したCaO-CaF&lt;SUB&gt;2&lt;/SUB&gt;-SiO&lt;SUB&gt;2&lt;/SUB&gt;系スラグと炭素飽和溶鉄間のりんの分配平衡

Dephosphorization kinetics and reaction region in hot metal during lime injection with oxygen.

To improve dephosphorization of hot metal by the lime injection process, it is necessary to clarify the dissolution mechanism of blown-in CaO in hot metal, the mechanism o f dephosphorization reaction and the region where the reaction takes place. For this purpose, a single-crystal lime lump immersion test and a lime powder injection test were made. Lime lumps after immersion tests, reaction products adhered to Al2O3 tubes immersed into hot metal and collected slag samples by steel samples were analyzed by EPMA.In hot metal, CaO starts to dissolve due to penetration o f FetO and MntO. Then, the dephosphorization reaction initiates between {CaO-Fe (Mn)tO}l and phosphorus, and the latter is fixed as (CaO-SiO2 P2O5)s in the reaction layers. Dephosphorization takes place mainly in the vicinity of the oxygen blowing nozzle.The slagging rate of solid CaO decreases with increasing distance between the nozzle and the suspending position of CaO since carbon in hot metal consumes oxygen. The dephosphorization rate also decreases with increasing distance since FetO in {CaO-Fe (Mn)tO}l is reduced by carbon.It is concluded that the increases both in the slagging rate of solid lime and oxygen potential in the bath is necessary to enhance the dephosphorization rate and in this sense, the injection of iron oxide with oxygen is effective.

The rates of desulfurization of liquid iron by solid CaO and CaO-saturated liquid iron oxide at 1600‡c

The rates of desulfurization of Fe-O-S melts by CaO crucibles and by CaO-saturated liquid iron oxide have been measured at 1600 ‡C. It was found that irons containing 1.62 wt pct and 0.64 wt pct sulfur and 0.070 wt pct oxygen are desulfurized by a reaction with the containing CaO crucible which does not involve the formation of a CaS product layer. The rate of desulfurization reaction is controlled by diffusion of sulfur in the iron melt, and a value of 6.7 ±1.7 × 10-5 cm2 per second was obtained for the diffusion coefficient of sulfur in liquid iron. Iron containing 0.088 wt pct sulfur and 0.070 wt pct oxygen is not desulfurized by solid CaO. The rate of desulfurization of liquid iron containing 0.088 wt pct sulfur and 0.070 wt pct oxygen by CaO-saturated liquid iron oxide is significantly greater than that calculated on the assumption of diffusion control in the metal phase, and evidence is presented in support of speculation that the reaction rate is enhanced by Marangoni turbulence at the slag-metal interface. The addition of 4 wt pct CaF2 to the CaO-saturated liquid iron oxide has no influence on the rate of desulfurization of the melt.

The thermal stability of calcium uranates in a hydrogen atmosphere

The stability and decomposition of CaUO 4, Ca 2UO 5, and Ca 3UO 6 on heating in hydrogen were investigated by X-ray powder diffraction and thermogravimetry. Ca 2UO 5 decomposes at 450°C into Ca 2UO 4.5 with a triclinic unit cell. At 850°C, it changes to monoclinic Ca 2(Ca 0.67U 0.33)UO 6 which loses some oxygen up to the composition Ca 2(Ca 0.67U 0.33)UO 5.83. At 1100°C, it decomposs to UO 2 solid solution and CaO. CaUO 4 decomposes at 900°C to Ca 2(Ca 0.67U 0.33)UO 5.83 and CaU 2O 6. The decomposition products of Ca 3UO 6 at 850°C are Ca 2(Ca 0.67U 0.33)UO 5.83 and CaO.