Periclase Phase Research Articles

Crystalline magnesium oxide films on soda lime glass by sol–gel processing

Well-crystallized and large-grained magnesium oxide films were deposited onto soda lime glass substrates by sol–gel technique. The films could be synthesized at a relatively low annealing temperature (∼500 °C). The films were dense and characterized by strong reflections from (200) plane for periclase phase and from (400) plane for the β-phase.

A study of slag-infiltrated magnesia-chromite refractories using hybrid microwave heating

Rebonded magnesia-chromite refractories are used in vacuum oxygen decarburisation ladles for the secondary refining of stainless steel. They suffer from acute wear due to the stringent chemical, thermal and mechanical conditions imposed. Although post-mortem investigation of worn refractories is indispensable to study the degradation mechanisms, its application is often hampered by evaluation difficulties due to crystallisation phenomena occurring during in situ cooling. To study the actual microstructures at elevated temperatures, industrially worn and virgin refractory samples were reheated and quenched in a cylindrical single-mode microwave furnace. Usage of a tubular susceptor allowed reproducible hybrid heating of the samples up to 1800°C. The quenched samples were analysed with SEM and EPMA-EDS. Concurrently, elemental line scans, X-ray mappings and quantitative image analyses were performed. This allowed the description of the ‘high-temperature inactivation’ mechanisms of the secondary chromite bonding phase: dissolution (1) in the periclase phase and (2) in the liquid slag, with (2) being predominant. Conclusions are drawn with respect to the refractoriness of the contributors to the spinel bonding phase: MgO.Cr2O3 (magnesiochromite)>MgO.Al2O3 (spinel)≫MgO.Fe2O3 (magnesioferrite). Hybrid microwave heating is shown to be an interesting alternative for conventional furnace experiments on refractory samples.

Study of MgO and Pt/MgO Systems by XRD, TPR, and 1H MAS NMR

We studied changes in magnesium oxide upon rehydration under operating conditions similar to those used in the subsequent impregnation of a metal salt on its surface. The ensuing transformations were monitored by using the XRD, TPR, and 1H MAS NMR techniques. On the basis of the results, magnesium oxide (periclase phase) is rehydrated to magnesium hydroxide (brucite phase) and dehydrated back to periclase when the calcination temperature is raised to 600 °C. At this point, the transformation occurs simultaneously with changes in the textural and basic properties of the solid. Pt/MgO catalysts prepared by impregnation of magnesium oxide exhibit variable metallic and surface properties depending on whether Pt(NH3)4(NO3)2 or H2PtCl6 is used as the impregnating salt.

Phase equilibria of the MgO-Cu 2O-CuO system

Phase equilibria of the MgO-Cu 2O-CuO system have been determined in air at temperatures ranging from 850 to 1100 °C. The starting compositions ranged from 0 to 100% Mg in (Mg 1 − xCu x)O. CuO was quite soluble in MgO. The solubility of CuO in MgO at 850 °C was about 9% and at 1050 °C was about 20%. The only known ternary Guggenite phase had a composition of Cu 2MgO 3. The Guggenite phase exists in three forms, namely, Guggenite A (G A, orthorhombic, space group Pmmn(59)), Guggenite B (G B, orthorhombic, space group I(0)), and Guggenite X (G x, monoclinic). Guggenite A was obtained as a single phase in air at X CuO = 67% (i.e., 67% CuO and 33% MgO) and 1000 °C. It undergoes a phase transition to the Guggenite X phase when it is heated above 1050 °C. The Guggenite B phase was obtained in a mixture at X CuO = 75% and at temperatures above 1050 °C. MgO was not found to be soluble in CuO. For samples with x cuo ≥ 67%, the Guggenite A phase coexisted with tenorite (CuO, monoclinic) at temperatures ≤ 1000 °C and above 1021 °C, it was in equilibrium with cuprite (Cu 2O, cubic). For CuO compositions between 20% and 67%, a mixture of Guggenite A phase and the periclase phase (MgO, cubic) was obtained at temperatures ≤ 1000 °C. The decomposition of Cu 2MgO 3 (Guggenite A) phase was determined at several oxygen partial pressures and the Gibbs free energy of formation of this phase was also calculated.

Study on the Dispersion of Nickel Ions in the NiO−MgO System by X-ray Absorption Fine Structure

NiO−MgO samples (NixMg1-xO:x = moles of Ni/(moles of Ni + moles of Mg)) were prepared by impregnation of MgO powder with an aqueous solution of Ni(NO3)2, followed by calcination at 773 K. The dispersion of Ni ions in these samples has been studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS). XPS of the depth profile of the samples shows that the atomic concentration of Ni and Mg against the depth is almost constant and close to those of bulk concentrations. The analyses by EXAFS and XANES reveal the absence of the preferential segregation of nickel oxide phase or magnesium oxide phase in all samples, suggesting the substitution of Ni ions for Mg ions. A detailed analysis by the curve-fitting method indicates that Ni ions dissolving into MgO are dispersed at random, regardless of the compositions of the samples. These results suggest that these samples form solid solutions over the entire composition range, even by calcination at 773 K.

Constitution of laser melted Al2O3–MgO–SiO2ceramics

An investigation has been made of ceramics of the Al2 O3–MgO–SiO2 system produced as pellets by laser melting of powder mixtures of the component oxides, followed by relatively rapid solidification. The phase constitution and microstructural features have been investigated using X-ray diffraction, microscopy, and differential thermal analysis. Compositions were selected with the aim of determining the solidification sequences, including certain invariant reactions involving combinations of the silica, cordierite, mullite, protoenstatite, forsterite, and periclase phases. Taking account of compositional changes that occurred during melting, and the fact that glass formation interrupted the solidification sequences, the observations were generally consistent with existing phase diagram data.MST/3120

Grain Growth of the Lime and Periclase Phases in a Synthetic Doloma

Simultaneous grain growth of the lime (CaO) and periclase (MgO) phases was studied in a synthetic, hydroxide‐derived doloma over the temperature range 1400° to 1700°C. The grain growth kinetic exponents were 5 and 6 and the activation energies 333±45 and 437±47 kJ/mol for the CaO and MgO phases, respectively. The large kinetic exponents are attributed to the topological restraints of the two phases on the growth of one another. The parameters suggest that the grain growth of the CaO may be governed by Ca2+ diffusion within the CaO phase for it is the continuous phase in the microstructure. In most instances for grain growth of the MgO phase, the Mg2+ must diffuse through the lime phase, and this process is believed to be limited by movement of associated defects involving Mg2+ within the CaO structure.

X-Ray Powder Diffraction Study of NBS Fly Ash Standard Reference Materials

AbstractThe fly ash Standard Reference Materials (SRMs) issued by the U.S. National Bureau of Standards have been studied by X-ray powder diffraction (XRD). Based on observations of large diffuse scattering maxima in their X-ray diffractograms, it was evident that all of the ashes had a high glass content. SRM 1633a and 2689, derived from the combustion of bituminous coal, contained different amounts of quartz, mullite, hematite and ferrite spinel (magnetite). SRM 2891, derived from subbituminous coal had quite a different chemical composition and a more complex crystalline phase assemblage, that included these four phases plus anhydrite, tricalcium aluminate, lime, periclase and minor phases. SRM 2690, also derived from subbituminous coal, had only quartz, mullite and ferrite spinel as detectable phases in its diffractogram. Analytical CaO is an important factor in determining the phase assemblage; SRM 2691 had 25.8 wt%, SRM-2690 had 8.0%, and the ash derived from bituminous coals had only 1.6-3.0%. The changing composition of the glass phases in the SRMs is detected in a shift in the position and shape of the diffuse scattering maximum in the diffractograms. Use of an internal intensity standard permitted quantitative comparisons of the relative amounts of crystalline phases among the four fly ash SRMs.

Comportamiento térmico y mineralógicode las dunitas serpentinizadas de la región Moa-Baracoa bajo temperaturas de hasta 1600 ºC

The purpose of this study is to determine the phase transformation and thermal performance of the serpentinized dunites of Moa-Baracoa region subjected to temperatures between 1 200 ° C and 1 600 ° C. To fulfill this purpose X-ray diffraction analysis and thermal analysis (gravimetric and differential) were carried out. Heating the dunites at such temperatures produced a stabilization of the forsterite and periclase phases, which gives important refractory properties to this material which support using this raw material in the metallurgical foundry processes.

Electrochemical determination of diffusivity and the solubility-diffusivity product of oxygen in internally oxidised copper

Diffusivity and the solubility-diffusivity product of oxygen in internally oxidised copper containing 0.22 wt% magnesium is determined by both potentiostatic and potentiometric techniques with the help of a single galvanic cell in the temperature range 750–1000°C. Internally oxidised magnesium oxide phase is found to have negligible effect on the diffusivity values.

Studies on the Interaction Between Fe<sub>2</sub>O<sub>3</sub> and MgO and It's Effect on the Sintering of MgO

The tablets consisting of chemically purest Mg(OH)2 and 0-1.5wt. per cent Fe2O3 were fired at 1000°-1550°C to examine the appearance after the firing as well as the microstructure.The firing shrinkage and the bulk density began to increase markedly from 1000° to 1200°C (Figs. 1-4). At 1200°C the coloured regions, which had developed by the diffusion of iron from Fe2O3 grains, began to spread abruptly with the remarkable growth of periclase crystals. From the results mentioned above, it may be inferred that the sintering of Mg(OH)2 occurs in two successive stages; (1) up to 1200°C the periclase crystals formed by the decomposition of Mg(OH)2 come into intimate contact each other showing the remarkable shrinkage of the specimens, and (2) in the second stage during which the growth of periclase crystals takes place with the rapid diffusion of iron from Fe2O3 through the contact points between periclase grains.The mechanism of the reaction of Fe2O3 and MgO examined by poralization microscope and X-ray diffraction may be interpreted clearly with the aid of the phase diagram of the binary system MgO and Fe2O3 (B. Phillips, S. Somiya, and A. Muan, J. Am. Ceram. Soc., 44, 169 (1961)).The reaction is a kind of the counter diffusion processes. MgO diffuses into Fe2O3 grains to form magnesioferrite. With the elevation of temperature, Fe3O4 content of the magnesioferrite becomes higher until it changes to very dark colour. On the other hand, Fe2O3 is reduced into ferrous state which duffuses into MgO to form a solid solution, magnesiowüstite. With increasing temperature the content of ferrous iron increases up to the saturation limit with a result that the further introduction of iron oxide to the periclase phase gives rise to the formation of magnesioferrite.The acicular hematite crystals are exsoluted from the magnesioferrite during cooling, which distribute between the grains of magnesioferrite, as the solid solution limit of Fe3O4 decreases with decreasing temperature. Also magnesioferrite is exsoluted from magnesiowüstite and spread throughout the periclase phase, as the solid solution limit of FeO in periclase decreases grately with decreasing temperature.The results of the experiments mentioned above suggest that the following conditions should be held in order to maintain the higher FeO content of magnesia clinker: (1) In order to enlarge the area of the solid solution limits of FeO in periclase, and of Fe3O4 in magnesioferrite, it is desirable that the firing temperature is kept as high as possible. (2) To maintain the conditions in higher temperature the clinkers should be cooled quickly. (3) To accelerate the reactions between Fe2O3 and MgO the grain size should be reduced as far as possible. In practice the refractories can not be cooled rapid enough to prevent the exsolution of FeO. If we consider only this phenomenon, it seems to be inferred that the magnesia clinker mineralized with Fe2O3 is not suitable for the fired refractories, and if the clinker mineralized with Fe2O3 is used, unburned refractories seem to be prefered rather than the fired ones.From the experimental results concerning the relation between the firing shrinkage and Fe2O3 contents, it is suggested that only a small amount of Fe2O3 would be sufficient for the mineralizer of magnesia clinker.During the heating up the growth of periclase grains proceeds gradually together with the diffusion of iron from Fe2O3 grains. Pores between the periclase grains, and perhaps the oxygen releases by the reduction of