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.     

Dielectric properties of K2Zn2(SO4)3 and (NH4)2 Mg2(SO4)3

Dielectric constant (ɛ), dielectric loss (tan δ) and conductivity (σ) for K₂Zn₂(SO₄)₃ and (NH₄)₂ Mg₂(SO₄)₃ have been measured over the frequency range 100 Hz — 100 kHz and in temperature range 30°C — 400°C. The values of static dielectric constant at room temperature are 7.67 and 4.80 for K₂Zn₂(SO₄)₃ and (NH₄)₂ Mg₂(SO₄)₃ respectively. The plots of log σ against reciprocal temperature at different frequencies of these samples merge into a straight line beyond 250°C and the activation energies calculated in this region are found to be 0.67 eV and 1.98 eV for K₂Zn₂(SO₄)₃ and (NH₄)₂ Mg₂(SO₄)₃ respectively.     

Role of rare earth oxide coatings on oxidation resistance of chromia-forming alloys

Rare earths (RE) have been used to increase high temperature oxidation resistance of chromia and alumina forming alloys. The RE can be added as elements (or oxides) to the alloys or applied as oxide coatings to the alloy surface. This paper presents the effect of different RE oxide coatings and lanthanum chromite coatings on the high temperature oxidation behavior of Fe20Cr and Fe20Cr4Al alloys. The oxidation resistance of the Fe20Cr alloy increased with increase in ionic radius of the RE element in the coating. The RE oxides decreased chromia growth rate more than alumina growth rate. In extended cyclic oxidation tests that were carried out from peak temperatures of 900 °C, 1,000 °C and 1,100 °C to room temperature at cooling rates of 300 °C/s and 1,000 °C/s, the La₂O₃ coating increased cyclic oxidation resistance of the Fe20Cr alloy significantly more than the Pr₂O₃ coating. The role of RE in increasing overall oxidation resistance of chromia forming alloys is discussed.     

Facile Proton Transport in Ammonium Borosulfate—An Unhumidified Solid Acid Polyelectrolyte for Intermediate Temperatures

High proton conductivity is reported for unhumidified ammonium borosulfate, NH₄[B(SO₄)₂], a solid acid coordination polymer that contains 1D, hydrogen-bonded NH₄⁺···¹_∞[B(SO₄)_4/2]⁻ chains. NH₄[B(SO₄)₂] is thermally stable to 320 °C and is amenable to sintering into monolithic, polycrystalline discs at 200 °C and about 300 MPa of uniaxial pressure. Impedance spectroscopy measurements reveal ionic conductivities for sintered ammonium borosulfate of 0.1 mS cm⁻¹ at 25 °C and up to 10 mS cm⁻¹ at 180 °C in ambient air. No superprotonic transition is observed in the temperature range of 25–180 °C. Ab initio molecular dynamics simulations show these high conductivities are aided by free rotation of the NH₄⁺ units and significant gyrational mobility of the SO₄ tetrahedra, which, in turn, provide facile pathways for proton locomotion. High conductivities, a wide operational temperature window, and tolerance to both ambient and anhydrous conditions make NH₄[B(SO₄)]₂ an attractive candidate electrolyte for intermediate-temperature hydrogen fuel cells that may enable operation at temperatures as high as 300 °C without active humidification.     

Preparation of hydroxyapatite ceramics by hydrothermal hot-pressing method at 300 °C

Hydroxyapatite (HA) ceramics were prepared by a hydrothermal hot-pressing (HHP) method at a low temperature (300 °C). DCPD (CaHPO₄·2H₂O) + Ca(OH)₂, OCP (Ca₈H₂(PO₄)₆·5H₂O) + Ca(OH)₂, DCPD + NH₃·H₂O, OCP + NH₃·H₂O or α-TCP (Ca₃(PO₄)₂) + NH₃·H₂O were used as the precursors. The mixture was treated by HHP under a condition of 300 °C/40 MPa. In sample DCPD + Ca(OH)₂ and OCP + Ca(OH)₂, the HA ceramics obtained showed a porous and homogenous microstructure, and the bending strength were 9.9 MPa and 10.9 MPa, respectively. In sample α-TCP+NH₃·H₂O, rod-like HA crystals produced. When the starting materials were DCPD + NH₃·H₂O, OCP + NH₃·H₂O, the HA particles produced exhibited plate-like features. It appeared that the plate-like HA particles stacked into a lamellar structure. The formation of the lamellar structure leads to a noticeable improvement in fracture property of the HA ceramic. The bending strength and the fracture toughness of the sample prepared from OCP and ammonia water reach 90 MPa and 2.3 MPam^1/2, respectively.     

The effect of Mg(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> addition on the formation of AlN nanowire by direct nitridation

In this study AlN nanowire was produced via direct nitridation (DN) method. In order to investigate the effect of nitridation on the formation of nanowire, elemental aluminum powder and ammonium chloride (NH₄Cl) mixture was prepared with and without the addition of minor amount (0.5 wt%) of magnesium nitrate (Mg(NO₃)₂). The experiments were performed in a conventional electric resistance furnace coupled with a horizontal stainless-steel tube. Nitridation was carried out at 800–1000 °C for 2 h in N₂ atmosphere. Differential scanning calorimetry and thermal gravimetric analyses were performed to powder mixtures, in order to examine the effect of Mg(NO₃)₂ addition on the morphology of AlN nanowire. X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM) and Energy-dispersive X-ray spectroscopy (EDS) techniques were also performed to identify to formed phases after the DN method. Using this technique, it was shown that with an addition of Mg(NO₃)₂ at 950 °C in N₂ atmosphere a complete transformation to AlN nanowires was achieved having diameters of 40–45 nm.     

Book review

Abstract

Magnesium based Mg–9Al–1Zn–5RE (RE=Y, La, Nd, Ce, or Pr) alloys with or without an addition of 1%Si were rapidly solidified by chill block melt spinning and splat quenching. The base alloy AZ91 (Mg–9Al–1Zn) was also rapidly solidified. Isochronal heat treatment for 1 h at 100–400°C showed that the microhardness of the ribbon maintained a similar level to that of the as spun alloy up to 300°C but decreased when heat treated at 400°C. Isothermal heat treatment for up to 24 h at 250–350°C showed that there were aging responses for the sample treated at 250°C while above this temperature, the microhardness decreased as the treatment time increased. The addition of 5% of RE elements to AZ91 displaced the Mg₁₇Al₁₂ phase in AZ91 with fine dispersoids of Al₂RE (RE=Y or Nd) or Al₁₁RE₃ (RE=La, Nd, Ce, or Pr) in Mg–9Al–1Zn–5RE alloys. These Al–RE intermetallics remained fine and precipitated at the grain boundaries so restraining grain growth during heat treatment at up to 400°C. Although Mg₂Si precipitates were found to be present in the silicon containing alloys after heat treatment at 400°C, their size was greater than those of Al–RE intermetallics, indicating that Mg₂Si has a lower thermal stability than these Al–RE intermetallics. The relationship between microhardness and grain size is discussed.

MST/3400     

Thermolysis of Urea Complexes of Uranyl Nitrate

Quantitative parameters of thermolysis of uranyl nitrate urea complexes, [UO₂(NO₃)₂{(NH₂)₂·CO}₂], [UO₂(H₂O){(NH₂)₂CO}₄](NO₃)₂, and [UO₂(H₂O){(NH₂)₂CO}₅](NO₃)₂ at 175, 200, and 225°C were measured. Thermolysis of [UO₂(NO₃)₂{(NH₂)₂CO}₂] at 200°C affords the biuret complex of uranyl nitrate in a 90% yield. The urea ligands in the hydrated complexes completely transform into biuret at 175°C. Thermolysis of [UO₂(H₂O){(NH₂)₂CO}₅](NO₃)₂ yields the biuret-cyanurate complexes of uranyl nitrate. The features of thermolysis of the uranyl nitrate complexes originate from the chemical transformations of urea at elevated temperatures.     

Microstructural stability and creep properties of die casting Mg–4Al–4RE magnesium alloy

The AE44 (Mg–4Al–4RE) alloy was prepared by a hot-chamber die casting method. The microstructure, microstructural stability and creep properties at 175 °C were investigated. The microstructure was analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and the Rietveld method. The results show that die cast AE44 magnesium alloy consists of α-Mg, Al₁₁RE₃, Al₂RE and Al_2.12RE_0.88 phases. The Al₁₁RE₃ phase is thermally stable at 175 °C whereas the metastable Al_2.12RE_0.88 phase undergoes a transition into the equilibrium Al₂RE phase. The alloy investigated is characterized by good creep properties at temperatures of 175 °C and 200 °C.     

Surface and structural characterisation of coprecipitated CexZr1?xO2 (0?≤?x?≤?1) mixed oxides

Ce _x Zr_1−x O₂-mixed oxides with three different Ce/Zr ratios (Ce_0.8Zr_0.2O₂, Ce_0.5Zr_0.5O₂ and Ce_0.2Zr_0.8O₂) along with pure cerium and zirconium oxides were prepared by coprecipitation of the metal hydroxides in alkali media and subsequent calcinations at 500 °C, using two different cerium precursors (Ce(NO₃)₃·6H₂O or (NH₄)₂Ce(NO₃)₆). These samples were characterised by N₂ adsorption at −196 °C, XRD, Raman spectroscopy, XPS and H₂-temperature programmed reduction. Besides, the two mixed oxides with higher cerium content were calcined at higher temperature (1000 °C) with the additional purpose of studying their thermal stability and phase homogeneity. XRD and Raman spectroscopy confirm a significant improvement in the insertion of zirconium cations into the ceria lattice when the samples Ce_0.8Zr_0.2O₂ and Ce_0.5Zr_0.5O₂ are synthesised with (NH₄)₂Ce(NO₃)₆ instead of Ce(NO₃)₃·6H₂O. This is attributed to a more homogeneous coprecipitation of cerium and zirconium hydroxides, leading to mixed oxides with better bulk oxygen mobility and smaller lattice parameter. Moreover, the mixed oxides prepared with the (NH₄)₂Ce(NO₃)₆ precursor and calcined at 1000 °C exhibit a single phase whereas phase segregation occurs in the counterpart mixed oxides prepared with the Ce(NO₃)₃·6H₂O precursor. XPS analysis reveal correlations among O/(Ce + Zr) surface atomic ratio and total cerium content for both cerium precursors. Among the samples calcined at 1000 °C, Ce_0.8Zr_0.2O₂ synthesised with Ce(NO₃)₃·6H₂O is the only one that preserves the low-temperature surface reduction peak, and also shows a BET surface area slightly higher than those of the rest of samples calcined at high temperature.     

Solid-state reactions in V x O y (NH4VO3)-P2O5 and V x O y (NH4VO3)-(NH4)2HPO4 closed systems

Solid-state reactions in V _x O _y (NH₄VO₃)-P₂O₅ and V _x O _y (NH₄VO₃)-(NH₄)₂HPO₄ closed systems can be used to synthesize vanadyl hydrogen phosphate at 300°C and a variety of ammonium vanadium phosphates at lower and higher temperatures.     

Synthesis of hollow calcium carbonate particles by the bubble templating method

Hollow calcium carbonate (CaCO₃) is a potential component in many industrial fields such as plastics, rubbers, papermaking, and drug delivery. This paper described a novel approach to synthesize hollow CaCO₃ particles by using bubble as template via passing CO₂ bubbles into calcium chloride (CaCl₂) solution in the presence of ammonia (NH₃) at 27 °C. The CO₂ bubble is not only the reactive material, but also the template of hollow particles. The newly-formed primary particles attach to bubbles and form a solid shell. After filtering and drying the hollow CaCO₃ particles were obtained. Physical characteristics of the precipitate were evaluated using scanning electron microscopy (SEM) and X-ray diffraction (XRD).     

Etude du systeme KPO3-LaP3O9. Donnees cristal lographiques sur K2La(PO3)5 et (NH4)2La(PO3)5

The system KPO₃-LaP₃O₉ has been studied for the first time by differential thermal analysis and X ray diffraction. The system shows two compounds KLa(PO₃)₄ and K₂La(PO₃)₅ which melt in a peritectic decomposition at 880°C and 770°C respectively. An eutectic point appears at 705°C; The eutectic point corresponds to a concentration of 10% molar LaP₃O₉.Infra Red absorption spectra are typical of chain phosphates.The new compound K₂La(PO₃₅ is isotypic whith (NH₄)₂La(PO₃)₅ which has been synthetized for the first time. They belong to the triclinic system whith space group P1 and Z = 2. The parameters of the unit cell are: $\text{a = 7.309(4)}\text{A}\text{?}$$\text{b = 13.35(2)}\text{A}\text{?}$$\text{c = 7.155(7)}\text{A}\text{?}$α = 90°3(1) β = 109°17(7) γ = 89°90(4) for K₂La(PO₃)₅ and: $\text{a = 7.174(8)}\text{A}\text{?}$$\text{b = 13.38(2)}\text{A}\text{?}$$\text{c = 7.35(2)}\text{A}\text{?}$α = 90°6(2) β = 107°4(1) γ = 89°82(7) for (NH₄)₂La(PO₃)₅.     

Synthesis of boron nitride

The authors examine the boric oxide—ammonia route with special stress on the yield and composition of the intermediate addition compound (BN) _x (B₂O₃) _y (NH₃) _z . It has been concluded that B₂O₃ and NH₃ present in the addition compound formed between 350°C and 900°C cannot be further reacted to convert the B₂O₃ into BN and the BN yield remains at around 66%. A formula (BN)_12·7(B₂O₃)_7·5NH₃ has been suggested for the addition compound.     

Hydrothermal synthesis of cubic ferric oxide particles

Single crystalline α-Fe₂O₃ cubic particles of narrow size distribution were prepared by a hydrothermal synthesis at 130 °C from a solution of urotropine ((CH₂)N₄) and ferric chloride. About 400 nm faultless cubic particles were observed. Spheres with rough surface were synthesized at 80 °C, while pseudo cubes and some spheres were prepared at 100 °C. For the preparation of α-Fe₂O₃ cubes, 130 °C is the appropriate temperature.     

Synthesis of carbonated hydroxyapatite nanospheres through nanoemulsion

This study investigated the nanoemulsion technique as a means to synthesize carbonated hydroxyapatite (CHAp) nanospheres which could be used to produce composite tissue engineering scaffolds. CHAp nanospheres were successfully synthesized by mixing an acetone solution of Ca(NO₃)₂ · 4H₂O with an aqueous solution of (NH₄)₂HPO₄ and NH₄HCO₃. Four reaction temperatures, namely, 4, 25, 37 and 55 °C, were investigated and no surfactant was added in all nanoemulsion processes. Wet slurries of CHAp from the nanoemulsions were freeze-dried to obtain dry powders. X-ray diffraction (XRD) results showed that the as-synthesized CHAp nanoparticles were mainly in an amorphous state. After calcination at 900 °C, the apatite became well crystallized. Fourier transform infrared (FTIR) spectroscopy showed that the CHAp was B-type substitution. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the CHAp particles were spherical in shape and that their sizes were in the nanometer range. The successful synthesis of CHAp nanospheres is a critical step forward in our efforts to fabricate bone tissue engineering scaffolds using the selective laser sintering technology.     

]Electrical conductivity measurements on gel grown KDP crystals added with some ammonium compounds

Pure and impurity added [with NH₄CI, NH₄NO₃, NH4₄H₂PO₄, (NH₄)₂CO₃ and (NH₄)₂SO₄] KDP single crystals were grown by the gel method using silica gels. Electrical conductivity measurements were carried out along both the unique axis and perpendicular directions at various temperatures ranging from 28 to 140°C by the conventional two-probe method. The present study shows that the conductivity in KDP crystals, for all the five dopants considered, increases with the increase in impurity concentration and temperature. Activation energies were also determined and reported.     

Preparation process of magnesium alloys by complex salt dehydration-electrochemical codeposition

High-purity anhydrous MgCl₂-containing molten salt was directly synthesized from MgCl₂ · 6H₂O via complex salts dehydration and protection. After that, Mg-Al and Mg-Zn alloys were prepared by electrochemical codeposition. The hydrolysis processes of magnesium chloride hexahydrate in various chloride mixtures were studied. Then, the preparation process was studied and the dehydration mechanism was put forward. NH₄Cl·MgCl₂·nH₂O formed under 300°C inhibits the formation of hydrolysate during the dehydration process. KMgCl₃ and K₃NaMgCl₆ formed above 400°C can further protect the unstable anhydrous MgCl₂. Therefore, high-purity anhydrous MgCl₂-containing molten salt with w(MgO)/w(MgCl₂) being 0.016 wt.% was obtained. The current efficiency was above 81% and 97%, respectively, when preparing Mg-Al alloys and Mg-Zn alloys, and the alloying elements were distributed homogeneously in the alloy matrix.     

Synthesis and characterization of hydroxyapatite by microwave heating using CaSO<Subscript>4</Subscript>·2H<Subscript>2</Subscript>O and Ca(OH)<Subscript>2</Subscript> as calcium source

In this paper, synthesis of hydroxyapatite (HAp) in the absence or presence of 1.05 wt% magnesium oxide, as sintering additive, by heating in a microwave oven was studied. For this purpose, CaSO₄·2H₂O, Ca(OH)₂, Mg(OH)₂ and (NH₄)₂HPO₄ were used as raw materials. The total chemical reactions for all the studied compositions were observed after a 3 h microwave treatment. In case of pure hydroxyapatite, a powder with needle-like grains results. In the presence of Mg(OH)₂, the (Mg, Ca₂)·O·(HPO₄)₂·H₂O hydrated phosphate is formed besides hydroxyapatite. Pure hydroxyapatite, thermally treated at 1,200 °C, mostly transforms in β-Ca₃P₂O₈. By adding MgO into the precursor mixture, hydroxyapatite was stabilised, and found in a much greater proportion at 1,200 °C. After the thermal treatment, the hydroxyapatite, analysed by electronic microscopy, shows a prismatic morphology originating in its initial state.     

Synthesizing nano LaAlO3 powders via co-precipitation method

Co-preparation method has been applied to synthesize nano LaAlO₃ powders. By using La(NO₃)₃ and Al(NO₃)₃ as raw materials and keeping the pH≈9, the co-preparation process could be finished at room temperature. Pure LaAlO₃ nano powders with a size of about 50 nm could be obtained after calcining at 700–800 °C. These nano LaAlO₃ powders could be sintered at 1550 °C for 4 h, a high relative density of about 97% could be reached.