Magnesium Zirconium Research Articles

Crystal structure of the double magnesium zirconium orthophosphate at temperatures of 298 and 1023 K

Double magnesium zirconium orthophosphate Mg0.5Zr2(PO4)3 is synthesized by the sol-gel method. The compound prepared is characterized using electron probe microanalysis and X-ray diffraction. The crystal structure of the orthophosphate is refined by the Rietveld method in space group P21/n (Z = 4) at temperatures of 298 K [a = 12.4218(2) A, b = 8.9025(2) A, c = 8.8218(2) A, β = 90.466(1)°] and 1023 K [a = 12.4273(5) A, b = 8.9453(4) A, c = 8.8405(4) A, β = 90.320(3)°]. It is demonstrated that an increase in the temperature leads to an anisotropic expansion of the unit cell of the phosphate structure, but the structural type remains unchanged.

Synthesis and characterization of ZrO 2–MgO solid solutions by citrate gel process

The zirconia–magnesia (ZrO2–x mol% MgO; x = 3–90) solid solutions were prepared by the citrate gel method. The phase identification and crystallite size of the samples were obtained using X-ray diffraction. Raman spectroscopy was performed to distinguish between cubic and tetragonal phases. The metastable tetragonal t′-form was determined in MgO-doped ZrO2 calcined at 800 °C. Samples containing up to 50 mol% MgO were revealed to be monoclinic ZrO2 solid solution and MgO when calcined at 1000 °C. Moreover, ZrO2–x mol% MgO (x = 60–90) solid solutions have metastable tetragonal t′ with MgO phase at 800 and 1000 °C, whereas no cubic phase was determined at any compositions of zirconia-based solid solutions. The prepared powders were characterized by transmission electron microscopy (TEM) to obtain the size and the morphology of the particles.

Study of the magnesia additive on the characterization of zirconia–magnesia composite sphere

Zirconia composite with varying amounts of magnesia was prepared by sol–gel technique. A series of carefully designed experiments were conducted to obtain data needed to assist the comparison of the resultant composites in terms of surface area, pore diameter, pore volume, crystalline phase and their stability to temperature. The results show that the presence of magnesia can be helpful for stabilization of zirconia composite, and different amounts of magnesia doping result in ultimate composite materials with different properties. We can tailor the structural and surface characteristics through changing the reactant ratio of magnesium chloride to zirconyl chloride to cater for its various applications, such as catalysts, chromatographic packings and so on.

Surface wear study of composite spray coated steel

In this investigation, a comparative study among different types of coating materials to improve the wear resistance of steel was conducted. There were three types of coating material, magnesium zirconate, aluminium bronze, and molybdenum, and mixtures of different percentages of them were used. The influences of load, velocity and counter surface roughness on each type were also determined. It was found that the addition of molybdenum to magnesium zirconate in a sufficient amount helped to increase its wear resistance in comparison to the wear behaviour of pure magnesium zirconate. Scanning electron microscopy and microhardness testing of longitudinal cross-sections of each of the materials were used to explore the reasons behind the interesting behaviour of these composites after abrasive wear testing. It was found that the reason behind the high wear resistance and high microhardness of the magnesium zirconate matrix after the addition of 10% molybdenum was the prevention of the pull out of magnesium zirconate particles. The abrasive wear mechanisms for the spray coated steel appear to be microcracking and microploughing.

Study on interaction between drug and membrane by using liposome coated zirconia–magnesia chromatography

The interactions between drug molecules and membrane were studied using the new chromatography stationary phase of liposome coated zirconia-magnesia. logK(s)(ZrO(2)-MgO) on this new chromatography for some drugs, compared with that on liposome coated silica chromatography and other reported data, fair correlations were observed between them when excluding effect of special adsorption. logK(s)(ZrO(2)-MgO) values for barbitalum, diazepam, benzene, benzocaine and toluene correlated well with corresponding values on liposome coated silica chromatography (R=0.99778, P<0.001; R=0.98229, P<0.003; R=0.9985, P<0.0001; R=0.99925, P<0.0001, pH value of mobile phase at pH 7.4, 7.0, 6.4 and 5.4, respectively). They also correlated well with the literature data on immobilized artificial membrane chromatography (R=0.99999, P<0.004 at pH 7.4) and liposome chromatography (R=0.99994, P<0.008) for procaine, lidocaine and bupivacaine. Liposome coated zirconia-magnesia chromatography can thus be used for studying drug-membrane interaction and prediction of drug absorption as another liposome chromatography method.

Heterogeneous nuclei size in magnesium–zirconium alloys

An investigation was made of the size distribution of zirconium particles that were observed at the centres of grains in a magnesium alloy grain-refined by zirconium. It was found that the majority of particles were in the range between 1 and 5 μm and that large zirconium particles (>5 μm) were inactive as nucleation centres.

Release Coatings on Apparatus for Fabrication of Electrodes for Chemical Power Sources

The influence exerted by the composition and properties of formulations for electrodeposition on the characteristics of release coatings on rollers for rolling of ribbon-type cathodes is described. A composition based on VUPFS-35 resin and magnesium zirconate powder is recommended for use in the formulations.

Oxidation protection of carbon-carbon composites by sol-gel ceramic coatings

Carbon-carbon composites were coated with Calcium Magnesium Zirconium Phosphate (CMZP) and Mg-doped Al2TiO5 sol-gels in order to form an oxygen barrier at temperatures above ∼650°C. The coatings were applied using a dipping technique and controlled drying procedures. It was determined that 10 coats of CMZP sol-gel fired every other coat created crack free coatings and oxidation protection. Mg-doped AlTi2O5 coatings produced were unsuccessful as oxidation barriers.

Thermal shock behavior of ZrO2:MgO solid electrolytes

Thermal shock studies have been undertaken in MgO-stabilized ZrO2 solid electrolytes prepared from powders obtained by the citrate technique. Impedance spectroscopy and X-ray diffraction analyses have been carried out in sintered pellets before and after thermal shock at 1600°C to study phase changes. Scanning electron microscopy observations have also been performed. Thermal shock leads to a large increase in the cubic(tetragonal)-to-monoclinic phase ratio with a corresponding modification in the bulk conductivity value of the zirconia–magnesia solid electrolytes.

Plasma-sprayed oxide ceramics on steel substrates

The behavior of plasma-sprayed oxide ceramic coatings on several metal substrates was investigated under different mechanical and thermal loading conditions. Metallographic evaluations were carried out to determine the structures of the coatings and interfacial regions. Some of the crystallographic transformations were detected by conducting X-ray diffraction analyses on powders and as-sprayed coatings. In alumina-based powders, most of α -Al 2 O 3 (H) always transformed to γ -Al 2 O 3 (C). In the case of magnesium zirconate powders, monoclinic zirconia, which is present in the initial composition, was completely transformed to cubic zirconia. The spraying of lime-stabilized zirconia resulted in the evaporation of CaO powder (CaCO 3 ) because of its relatively lower evaporation point, and part of the monoclinic zirconia was transformed to tetragonal structure after spraying. It was shown by tensile and three-point bending tests that ceramic coatings have a failure mechanism in which microcrack formations prevail and, as the stress level is increased, macrocrack formations start. Thermal shock and flame tests showed that ceramic coatings are resistant to high temperature gradients and they have good thermal barrier properties. However, relatively long-term heat treatment resulted in oxidation problems at the interfacial region in the case of using AISI 1015 carbon steel substrates. For AISI 304 stainless-steel substrates, the failure mechanisms appeared to be the thermal expansion mismatch and partial destabilization of the coating structure.

Can Thermal Barrier Coatings be Sealed by Metal-Organic Chemical Vapour Deposition of Silica and Alumina?

Thin Al 2 0 3 and SiO 2 films were deposited on thermal barrier coatings (TBC) by means of metal-organic chemical vapour deposition (MOCVD). The thermal barrier coatings consist of ZrC 2 , partially stabilised by MgO (Magnesium Zirconate Amdry 333) and a bond coat of NiAl (Amdry 956). Alumina films were deposited at low temperatures by low pressure MOCVD, carried out in nitrogen gas using aluminium-tri-sec-butoxide (ATSB) as the precursor. Silica films were deposited on the thermal barrier coatings by atmospheric pressure MOCVD with di-acetoxy-di-t-butoxy-silane (DADBS) as the precursor. Besides the deposition of thin oxide films on TBC, pre-oxidation experiments were performed at 600, 800 and 1000°C for 175 h. In order to evaluate the effectiveness of sealing and pre-oxidation, sulphidation experiments were carried out at 600°C for 200 h. Low pressure deposited alumina films did not show any increased protective power. Pre-oxidation of the TBC to form a dense and continuous alumina layer on the top of the bond coat also did not show any significant improvement of the protection against sulphide containing gases.

Lifetime determining factors during thermal cycling of zirconia based thermal barrier coatings

Plasma sprayed yttria stabilised zirconia (YSZ) coatings were investigated to assess the factors influencing their durability during thermal cycling. For any given powder, the best performance was found to be achieved at an optimum plasma arc current, all other spray parameters being held constant. The YSZ overlayer thickness was found to be an important lifetime determining factor. Use of a NiCoCrAlY bond coat instead of Ni–Cr led to a substantial improvement in coating lifetime, with the enhancement provided by NiCoCr AlY becoming more pronounced with increasing porosity level of the ceramic overlayer. A post-coating heat treatment was also found to be beneficial to coating longevity. The relative ranking of magnesium zirconate and YSZ coatings was found to depend upon the thermal cycle adopted during testing, which has important implications in designing accelerated tests to evaluate coating performance.

Thermochemical experiments and numerical simulation of ceramic coatings

Abstract Aluminium alloys coated by magnesium zirconate used as thermal barriers have been investigated. Thermal shocks have been conducted to evaluate the resistance of various types of coatings: cylindrical specimens were submitted to an oxyacetylene torch. Different geometries and various shock intensities were tested and special attention was paid to the influence of the thickness of the coating on the crazing phenomenon. Numerical calculations have also been performed using the finite element code Zebulon developed at the Centre des Materiaux. The temperature field was first determined and the results, introduced in the mechanical simulation, allowed the thermomechanical stresses to be calculated. Crack initiations were then predicted. The numerical and experimental results are in good accordance.

Tribochemical Synthesis of Magnesium Zirconate for Some Specific Purposes

MgZrO3 was synthesized by tribochemical and thermal treating of a mixture of MgO and ZrO2 corresponding to its stoichiometry. The gained compound is identified by chemical and X-ray analysis.

Mechanical testing of plasma-sprayed coatings of ceramics

Mechanical tests have been performed on two types of plasma-sprayed ceramic coatings: magnesium zirconate (ZM) on aluminium alloy and chromium oxide (CO) on cast iron. Tensile strength, shear strength, energy relaxation rate and crack velocity have been determined. Results obtained with double-torsion tests show good agreement with those of double-cantilever-beam tests. Fracture always occurred in the ceramic for the ZM coating and at the interface for the CO one. Finally, acoustic emission monitoring carried out during bending tests was used to point out different types of emission, and to correlate them with micrographic examinations in order to identify some damaging processes.[/p]

Vaporization behavior of a single droplet impinging on a heated surface with flame-sprayed ceramic coating.

The vaporization behavior of a single droplet impinging on a heated surface which was coated with ceramics such as alumina, magnesium zirconate and zirconium oxide was studied. This is the extension of the previous study on a vaporizing droplet on a solid surface of ceramics. The lifetime curves for some pure liquids were measured at a surface temperature up to 1100 K. We observed in detail the vaporization process of a droplet using a 16 mm high-speed motion-picture camera and high-speed video camera. It should be stressed that the ceramic-coated surface brought a wide temperature range yielding minimum vaporization times and short lifetimes in spite of its thinly coated layer, owing to its low-thermal conductivity and characteristic surface.

Growth morphology of the tetragonal phase in partially stabilized zirconia

The zirconia-rich, metastable tetragonal phase in partially stabilized zirconia—magnesia, zirconia—calcia and zirconia—yttria is examined using electron microscopy and electron and X-ray diffraction. The tetragonal phase precipitate distribution is that normally associated with homogeneously nucleated coherent precipitation. An attempt is made to explain the growth morphology of the tetragonal phase in terms of the cubic—tetragonal lattice parameter mismatch. It is found that the tetragonal phase is retained at room temperature provided coherency with the cubic matrix is retained. Once coherency is lost, due to growth strains or mechanical influences, the precipitate reverts to the room temperature stable monoclinic form.

The Preparation of a Haifnium-Free Magnesium-Zirconium Alloy by Process Separation of Hafnium

Magnesium zirconium alloy for sheathing uranium elements in gas-cooled reactors was successfully prepared from high-purity magnesiumt and zirconium produced by the magnesium reduction of a crude oxide. Hafnium separation, suggested by a higher ratio Hf to Zr in the sludge than in the melt was considered possible owing to its higher density and melting point and its isomorphous behaviour to the strongly electropositive zirconium which readily forms compounds and exhibits a two-phase melt when added in excess of 0.5 per cent. Precipitation of excess zirconium by settling was aided by the development of a flux of high density and low inclusion-flux interfacial energy. Removal of hafnium and other high neutron capture cross-section impurities was achieved.