Studies on the formation of a solid solution compound in Li2O impregnated CuAl2O4 catalyst

Li₂O impregnated CuAl₂O₄ samples were calcined at two temperatures (673 K and 1173 K). X-ray analysis showed that the lattice parameter of the spinel phase decreased with increasing calcining temperature. X-ray studies on the solid solution series Cu_1?x$\text{Li}{}_{\mathrm{<mtext>x</mtext><mtext>2</mtext>}}$$\text{Al}{}_{\mathrm{<mtext>2+</mtext><mtext>x</mtext><mtext>2</mtext>}}$ O₄ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) showed that the lattice parameter decreased with increasing concentration of lithium and from the comparison of lattice parameters it appears that Cu_0.84 Li_0.08 Al_2.08 O₄ is formed in the impregnated sample calcined at 673 K. Electrical resistivity measurements are consistent with the formation of a solid solution compound.     

The existence and stability of Ca6Zr19O44 compound in the system ZrO2CaO

The development of ordered phases in the system ZrO₂CaO was studied during prolonged heating of reactive powders derived from gels. The pure phase ф₂ was obtained at 1250°C only with gels containing 24 m/o CaO which indicates that the correct composition of this phase i$\text{s}$ Ca₆Zr₁₉O₄₄. This phase has rhombohedral symmetry, space group R3c, and is analogous to the ф₂ phase in the HfO₂CaO system. The pure phase ф₁ (CaZr₄O₉) was obtained by heating gels containing 20 m/o CaO at 1180°C. This phase often appears as a precursor to the formation of the ф₂ phase. At 1355±15°C the ф₂ phase decomposes to a cubic ZrO₂ solid solution and CaZrO₃. At 1235±15°C the ф₁ phase decomposes to a cubic ZrO₂ solid solution and the phase ф₂. The inability to synthesize a phase analogous to the phase ф (Ca₂Hf₇O₁₆) in the HfO₂CaO system can be explained by the low cation diffusivity in the ZrO₂CaO system below 1150°C.     

Positions of cations and molecules in zeolites with the chabazite framework I. Dehydrated ca-exchanged chabazite

Chabazite from Bozen, Tyrol, was ion-exchanged with CaCl₂ solution to Ca_1.9Al_3.8Si_8.2O₂₄.nH₂O. After de$\text{h}$ydration at 320°C for 1 day, the crystal structure (R3m $\text{a}$ 9.442(2) Å α 93.09(1)°) was determined at room temperature. Most Ca atoms (refined to 1.88) are displaced into the large cavity from the center of a 6-ring and lie at 2.33Å to three O(4) and 2.78 to three O(3). The center of the ditrigonal prism contains 0.1 Ca apparently at 2.8Å to six O(4). All cations have O(4) as nearest neighbors leaving the other framework oxygens undersaturated. The TO bond lengths increase $\text{～0.08}\text{A}\text{?}$ per unit charge of undersaturation. The cation distribution and cell dimensions differ from those determined earlier for Ca-exchanged chabazite from Benton County, Oregon, which was dehydrated at 360°C for 4 hr.     

The use of aluminium-enriched layers on Hastelloy X against high temperature carburization in high temperature gas-cooled reactor helium

The possibility of protecting nickel-based alloys against carburization using NiAl layers is discussed. NiAl layers were produced using the chemical vapour deposition reaction: $\text{AlCl}{}_3\text{+}\text{3}\text{2}\text{H}{}_2\text{+}\text{Ni-based alloy}\text{→}\text{NiAl}\text{+3}\text{HCl}$ The kinetics of growth of an NiAl layer on nickel and the nickel-based alloys Hastelloy X, IN-738LC and IN-617 in the temperature range 1173–1373 K at total pressures ranging from 100 to 800 mbar are described.No carbon uptake occurs in the layer or in the bulk alloy, because of the formation of an α-Al₂O₃ oxide layer in CH₄H₂ gas mixtures with carbon activities from 0.2 to 0.8 and at temperatures of up to 1273 K. Al₂O₃ formation is caused by the presence of oxygen as an impurity in the CH₄H₂ gas mixtures.     

Phase relation of ternary system ZrO2CaOAl2O3

The phase relation in the ternary system ZrO₂CaOAl₂O₃ has been studied at 1,380°C in the composition range below 50 mol% CaO. The mixed oxides with various compositions have been prepared from their acidic solutions through evaporation, calcination, and heat-treatment. Nine regions have been found. In the stabilized zirconia with fluorite structure, 4 mol% Al₂O₃ is soluble. The fluorite phase also exists in equilibrium in two-phase regions (fluorite + ZrO₂, and fluorite + CaO·ZrO₂) and in three-phase regions (fluorite + ZrO₂ + CaO·2Al₂O₃, and fluorite + CaO·ZrO₂ + CaO·2Al₂O₃).     

Synthesis,structural characterization and some properties of a germanic analogue of phillipsite

Germanic phillipsite, with the chemical formula K₂O·Al₂O₃·2GeO₂·xH₂O, has been synthesized at 90°C from K⁺ containing gels. The parameters of its primitive (tetragonal) unit cell are : $\text{a}\text{=}\text{b}\text{= 14.515}\text{A}\text{?}$ and $\text{c}\text{= 9.733}\text{A}\text{?}$. IR spectroscopy shows that all the absorption bands are shifted towards longer wavelengths. The structural stability towards ion-exchange has been followed by X-ray diffraction. Adsorption isotherms of N₂ and H₂O have been measured. The pore opening of K-germanic phillipsite is approximately 3 Å.     

The preparation,characterisation and ion exchange properties of an amorphous titanium phosphate

An amorphous titanium phosphate has been synthesized and characterized by chemical analysis, thermal analysis (DTA and TGA), i,r. spectroscopy and X-ray diffraction of the product calcined at 1000 °C. It was assigned the molecular formula Ti₄O₂(HPO₄)₃(H₂PO₄)₂(OH)₄·3H₂O. Its exchange capacity in the processes $\text{H}{}^{\mathrm{+}}\text{Na}{}^{\mathrm{+}}$ and $\text{H}{}^{\mathrm{+}}\text{Cu}{}^{\mathrm{2+}}$ has been determined.     

Alkaline earth scandates

In the CaOSrOSc₂O₃ and BaOSrOSc₂O₃ systems, complete series of mixed crystals were found for (Ca,Sr)Sc₂O₄ and (Sr,Ba)₃Sc₄O₉ respectively. In the BaOCaOSc₂O₃ system a new ternary phas?e with composition Ba_x(Ca_2xSc_2?2x)Sc₆O₁₂ was detected having an incommensurate structure which may be described with a basic hexagonal unit cell ($\text{a}\text{=9.7039}\text{A}\text{?}$, $\text{c}\text{=3.1274}\text{A}\text{?}$) and a second hexagonal cell having the same basic a-axis. The c-axis of the second cell is x-dependent: $\text{c}{}^{\mathrm{x}}\text{= 3.13/}\text{x}\text{A}\text{?}$, x varying from 0.782 to 0.736, corresponding to the region from BaCa₂Sc₈O₁₅ with $\text{c}{}^{\mathrm{x}}\text{= 4.00}\text{A}\text{?}$, to BaCa₂Sc₉O_16.5 with $\text{c}{}^{\mathrm{x}}\text{= 4.25}\text{A}\text{?}$.     

Synthesis of Cu3(PO4)2 · H2O based solid solutions through Co or Ni substitution for Cu

New substitutional solid solutions have been synthesized: (Cu_{1 ? x} Co_x)₃(PO₄)₂ · H₂O (0 < x ≤ 0.20), (Cu_{1 ? x} Ni_x)₃(PO₄)₂ · H₂O (0 < x ≤ 0.12), and (Cu_{1 ? y} Co_y)₃(PO₄)₂ · H₂O (0.55 ≤ y ≤ 0.65). The first two solid solutions are isostructural with Cu₃(PO₄)₂ · H₂O (monoclinic symmetry, sp. gr. C2/c); the third solid solution also has a monoclinic structure, which is a Cu₃(PO₄)₂ · H₂O related superstructure. The lattice parameter b of (Cu_{1 ? y} Co_y)₃(PO₄)₂ · H₂O (0.55 ≤ y ≤ 0.65) is almost twice that of (Cu_{1 ? x} Co_x)₃(PO₄)₂ · H₂O (0 < x ≤ 0.20), while their a and c parameters differ little. The solid solutions have been characterized by chemical analysis, x-ray diffraction, IR spectroscopy, and thermal analysis.     

Solid-state reactions in the system CaONd2O3Fe2O3Al2O3

Inherently cementitious ceramic compositions made by sintering show promise as host materials for the containment of radioactive wastes. The distribution of lanthanons in Ca-rich compositions has been explored using Nd as a model 4f element. Phase relations in the relevant portions of the CaONd₂O₃Fe₂O₃A$\text{l}$₂O₃ system show the coexistence of calcium aluminates and ferrites with Nd-melilites, perovskites, and K₂NiF₄-type phases.     

Preparation of sodium zirconium phosphates of the type Na1+4xZr2−x (PO4)3

Sodium zirconium phosphates of the type Na_1+4x Zr_2?x (PO₄)₃ were prepared from mixtures of Na₃PO₄-ZrO₂-ZrP₂O₇ in sealed platinum tubes at temperatures of 900 – 1200°C. Stoichiometric NaZr₂ (PO₄)₃ (x = 0) was found not to exist. Instead, a solid solution in the range x = 0.02 ? 0.06 was found, with a slight difference in unit cell dimensions obtained. A second solid solution region was found with x = 0.88 – 0.93. At still higher values of x, a stoichiometric phase with hexagonal unit cell dimensions of $\text{a}\text{= 9.152(1)}\text{A}\text{?}$ and $\text{c}\text{= 21.844(1)}\text{A}\text{?}$ was obtained. Finally a phase of composition Na₇Zr_0.5 (PO₄)₃ was synthesized at the highest values of x. Attempts to prepare Na_5+x ZrSi_x-P_3?xO₁₂ always yielded NASICON and Na₇Zr_0.5 (PO₄)₃.     

Ultra-rapid quenching of laser-melted binary and unary oxides

A technique has been developed for ultra-rapid quenching of oxide materials from the liquid state. A modified Duwez splat gun combined with a continuous wave 400 watt CO₂ laser achieved quench rates estimated to be ～10⁷°C/sec. Mixed non-crystalline solid (NCS) and crystalline product phases were formed for both Al₂O₃ and MgAl₂O₄, as predicted theoretically. Moreover, mixed NCS and crystalline phases were formed in the binary systems MgOAl₂O₃, Al₂O₃Y₂O₃, Al₂O₃SiO₂ and MgOCaO.     

Synthesis and conductivity studies of Li<Subscript>1.5</Subscript>Al<Subscript>0.5</Subscript>Ge<Subscript>1.5</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> solid electrolyte

This paper describes the preparation of a lithium ion conducting solid electrolyte with the composition Li_1.5Al_0.5Ge_1.5(PO₄)₃ by a new liquid-phase method with the use of the water-soluble salts Al(NO₃)₃ · 9H₂O, LiNO₃ · 3H₂O, and (NH₄)₂HPO₄ and the germano-oxalic acid H₂[Ge(C₂O₄)₃]. The synthesized materials have been characterized by X-ray diffraction, differential scanning calorimetry, thermogravimetry, and impedance spectroscopy. The results demonstrate that sintering of the synthesized amorphous powders at a temperature of 650°C leads to the formation of phase-pure Li_1.5Al_0.5Ge_1.5(PO₄)₃. The ionic conductivity of the electrolyte measured at frequencies from 10 Hz to 2 MHz using pellets with an 86% relative density was 4.2 × 10^–4 S/cm.     

Preparation of (NH4)Zr2(PO4)3 and HZr2(PO4)3

(NH₄)Zr₂(PO₄)₃ has been prepared, hydrothermally, from α-zirconium phosphate in three different ways; (1) from amine intercalates at 300°C, (2) from mixtures of ZrOCl₂·8H₂O in excess (NH₄)H₂PO₄ and (3) reaction of NH₄Cl with Zr(NaPO₄)₂. Ammonium dizirconium triphosphate is rhombohedral with a = 8.676(1) and $\text{c}\text{= 24.288(5)}\text{A}\text{?}$. It decomposed on heating to HZr₂(PO₄)₃. Below 600°C a complex, as yet unindexed, X-ray pattern was obtained. A very similar X-ray pattern was obtained by washing LiTi_0.1Zr_1.9(PO₄)₃ with 0.3N HCl. Heating this phase or NH₄Zr₂(PO₄)₃, above 600°C resulted in the appearance of a rhombohedral phase of HZr₂(PO₄)₃ with cell dimensions a = 8.803(5) and $\text{c}\text{= 23.23(1)}\text{A}\text{?}$. The protons were not completely removed until about 1150°C. Decomposition of (NH₄)Zr₂(PO₄)₃ at 450°C yielded an acidic gas whereas at 700°C NH₃ was evolved. A possible explanation for this behavior is presented.     

Positions of cations and molecules in zeolites with the mordenite-type framework: V dehydrated Rb-mordenite

Mordenite from Challis Valley, Idaho, was ion-exchanged with RbCl₂ solution to ～Rb₈Al₈Si₄₀O₉₆·nH₂O. After dehydration at 340°C for 1 day, the crystal structure was determined at room temperature. Earlier attempts to dehydrate crystals at higher temperature led to disintegration, and even the present crystal fractured. Although this resulted in poor X-ray data, refinement in Cmcm ($\text{a}$ 18.127(7) $\text{b}$ 20.408(6) $\text{c}$ 7.463(3)Å) yielded atomic positions similar to those for dehydrated K-mordenite. Rb atoms in sites II (3.7Rb), IV (3.1Rb) and VI (0.7Rb) block most of the small channels (“side pockets”) and may hinder diffusion along the main channels. A few diffractions violating the C lattice were ignored in the refinement but indicate structural distortion similar to that in dehyrated K-mordenite which was refined in Pbcn. However the presence of a few weak diffractions violating the $\text{b}$ glide indicates even lower symmetry.     

On the proton conductor (H3O)Zr2(PO4)3

The compound HZr₂(PO₄)₃ was converted to (H₃O)Zr₂(PO₄)₃ by refluxing in water for 12 or more hours. The water is lost above 150°C to regenerate the original triphosphate. The hydronium ion phase is rhombohedral with hexagonal axes of a = 8.760(1) and $\text{c}\text{= 23.774(4)}\text{A}\text{?}$. Proton conduction in these compounds was investigated by an ac impedance method over the frequency range 5Hz – 10MHz. The activation energy for (H₃O)Zr₂(PO₄)₃ in the temperature range of 25 to 150°C was 0.56eV while the corresponding value for HZr₂(PO₄)₃ (125 – 300°C) was 0.44eV.     

Atomic carbon in magnesium oxide Part VIII: General discussion and outlook

The presence of atomic carbon in MgO and the experimentally well documented fact that an internal equilibrium exists between defect-bound OH^? and H + O^? lead to a very complex pattern of defect equilibria and defect reactions in the bulk and at the surface of the MgO crystals. The most important extrinsic bulk defects are the bare and the OH-compensated cation vacancies, [V″_$\text{Mg}$]″, |OH^· V″_$\text{Mg}$|′, and [OH^· V″_$\text{Mg}$ HO^·]^$\text{x}$ of which the latter yields [O^· (H_$\text{2}$)″_$\text{Mg}$ O^·]^$\text{x}$, interstitial hydrogen molecules (H_$\text{2}$)^$\text{x}$, interstitial C atoms C^x_i, which may enter the available cation vacancies, and the positive hole, [O^·]^?. Reactions between C atoms entering the O V″ O and [O^· V″_$\text{Mg}$|′ at the surface lead to the formation of CO_$\text{2}$ and CO molecules and to the formation of double F and single F centers respectively. The free electrons in the F centers are held responsible for the formation of Mg-organic commpounds. Reaction between the C atoms and interstitial H₂ molecules lead to hydrocarbon formation. The strain fields associated with the interstitial C atoms and the positive holes provide the driving force for segregation of the carbon into the elastically relaxed subsurface zone and for fluctuating reaction kinetics.