Synthesis of Cubic Boron Nitride by Decomposition of Magnesium Boron Nitride

Cubic boron nitride ( c -BN) was synthesized by the decomposition of Mg₃BN₃ under high pressure and high temperature. The minimum pressure for c -BN synthesis was 4 GPa, which was 1 GPa lower than that of the conventional catalytic process. The decomposition of Mg₃BN₃ was observed only when H₂O was added. Therefore, the reaction was as follows: Mg₃BN₃+ 3H₂O = 3MgO + c -BN + 2NH₃. The c -BN crystals obtained were tetrahedron in shape and about 10 μ m in diameter.     

Studies on 4CaOAl2.O3.13H2O and the Related Natural Mineral Hydrocalumite

Single-crystal X-ray and electron-diffraction studies show the existence in one polymorph of 4CaO.Al₂O₃. 13H₂O of a hexagonal structural element with α= 5.74 a.u., c = 7.92 a. u. and atomic contents Ca₂(OH)₇- 3H₂O. These structural elements are stacked in a complex way and there are probably two or more poly-types as in SiC or ZnS. Hydrocalumite is closely related to 4CaO.A1₂O₃.13H₂O, from which it is derived by substitution of CO₃^2-for 20H^-+ 3H₂O once in every eight structural elements; similar substitutions explain the existence of compounds of the types 3CaO Al₂O₃.Ca Y ₂- xH₂O and 3CaO Al₂O₃ Ca Y xH₂O. On dehydration, 4CaO.Al₂O₃.13H₂O first loses molecular water and undergoes stacking changes and shrinkage along c. At 150° to 250°C., Ca(OH)₂ and 4CaO.3Al₂O₃.3H₂O are formed and, by 1000°C., CaO and 12CaO.7Al₂O₈. The dehydration of hydrocalumite follows a similar course, but no 4CaO.3Al₂O₃.3H₂O is formed.     

Electroceramics from Source Materials via Molecular Intermediates: BaTiO3 from TiO2 via (Ti(catecholate)3)2-

Rutile or anatase may be depolymerized and complexed by sequential treatment with (i) H₂SO₄/(NH₄)₂SO₄, (ii) H₂O, and (iii) catechol/NH₄OH to produce the intermediate (NH₄)₂(Ti(catecholate)₃) · 2H₂O. Treatment with Ba(OH)₂· 8H₂O leads to an acid-base reaction generating Ba(Ti(catecholate)₃) · 3H₂O, in which the Ba:Ti ratio is held at 1:1 at the molecular level. Calcination produces BaTiO₃ powder.     

Mechanochemical Changes of Weinschenkite-Type RPO4·2H2O (R = Dy, Y, Er, or Yb) by Grinding and Thermal Reactions of the Ground Specimens

It is reported that, on mechanochemical treatment, weinschenkite-type RPO₄·2H₂O (R = Dy, Y, or Er) gradually transforms into rhabdophane-type RPO₄· nH₂O (n = 0.5 to 1) and weinschenkite-type YbPO₄·2H₂O into xenotime-type YbPO₄, at room temperature in air. Rhabdophane-type YPO₄·0.8H₂O and ErPO₄·0.9H₂O obtained by grinding weinschenkite-type RPO₄·2H₂O (R=Y or Er) are new. The new rhabdophane-type YPO₄·0.8H₂O and ErPO₄·0.9H₂O gradually transform to xenotime-type YPO₄ and ErPO₄ when heated above 900°C (R = Y) and 700°C (R = Er) in air.     

The System MgO─P2O5─H2O at 25°C

The phase diagram for the ternary system MgO─P₂O₅─H₂O at 25°C has been constructed. The magnesium phosphates represented are Mg(H₂PO₄)₂· n H₂O ( n = 4, 2, 0), MgHPO₄·3H₂O, and Mg₃(PO₄)₂· m H₂O ( m = 8, 22). Because of the large differences in the solubilities of these compounds, the technique which involves plotting the mole fractions of MgO and P₂O₅ as their 10th roots has been employed. With the exception of MgHPO₄·3H₂O, the magnesium phosphates are incongruently soluble. Because incongruency is associated with a peritectic-like reaction, the phase Mg₂(PO₄)₃· 8H₂O persists metastably for an extended period.     

Electroceramics from Source Materials via Molecular Intermediates: PbTiO3 from TiO2 via [Ti(catecholate)3]2-

The precursor [NH₄]₂[Ti(catecholate)₃] · 2H₂O is known to react with Ba(OH)₂· 8H₂O in an acid/base process that generates Ba[Ti(catecholate)₃] · 3H₂O, a compound which undergoes low-temperatue calcination to produce BaTiO₃ powder. Attempts to develop similar routes to PbTiO₃ have been frustrated, since lead(II) hydroxide does not exist. The amphoteric yellow PbO and the basic oxide, Pb₆O(OH)₆⁴⁺, are both insufficiently basic to react with [NH₄]₂[Ti(catecholate)₃] · 2H₂O. Based on the large sizes of both the [Ti(catecholate)₃]^2- anion and the Pb²⁺ cation, a precipitation method has been developed in which lead nitrate and [NH₄]₂[Ti(catecholate)₃] · 2H₂O are added together in an aqueous medium causing precipitation and leaving only NH₄NO₃ in solution. The lead-titanium-catecholate complex that forms in this manner undergoes low-temperature pyrolysis to produce PbTiO₃. SEM indicates a submicrometer ultimate crystallite size.     

Formation and Transformation of WO3 Prepared from Alkoxide

Amorphous WO₃ or WO₃ or H₂O is formed by hydrolysis of tungsten ethoxide. The temperature of hydrolysis influences the crystallization of WO₃·H₂O. Tungsten hydrate (WO₃·H₂O) has an orthorhombic unit cell with a=0.5235 nm, b = 1.0688 nm, and c=0.5123 nm. Orthorhombic WO₃ crystallizes at 350° to 500°Cfrom amorphous WO₃. Cubic WO₃ is formed at 200° to 310°C with dehydration of WO₃·H₂O. WO₃ transformations are examined by high-temperature X-ray diffraction. The kinetics of formation of the cubic modification have been studied by measuring the weight decrease with a thermobalcnce. Formation isotherms can be interpreted in terms of the first-order equation –In (1–f)=kt; activation energies are 110 and 80 kJ mol⁻¹ for initial and final stages, respectively.     

Effect of Heat-Treatment on the Constitution and Mechanical Properties of Some Hydrated Aluminous Cements

The compound compositions of four aluminous cements were determined on anhydrous as well as hydrated specimens which had been heat-treated at temperatures between room temperature and 1400° C. Phases were identified by X-ray diffraction and differential thermal analysis. Specimens were also tested for transverse strength, dynamic modulus of elasticity, and thermal length change. A study of the dehydration characteristics of CaO - Al₂O₈ - 10H₂O₃ 3CaO.Al₂O₃. 6H₂O, and Al₂O₃. 3H₂O was included. The data indicated that CaO. Al₂O₃ 10H₂O was the primary crystalline hydrate formed in the cements at room temperature. At 50° C., 3 CaO Al₂O₃-6H₂O and Al₂O₃. 3H₂O were formed as by-products of the dehydration of CaO.Al₂O₃.10H₂O. When heated alone in an open system, CaO.Al₂O₃.10H₂O did not convert to 3CaO. Al₂O₃. 6H₂O and A1₂O₃. 3H₂O. A correlation between the mechanical properties and compound compositions was noted.     

Synthesis of Titanate Derivatives Using Ion-Exchange Reaction

Two types of titanate derivatives, layered hydrous titanium dioxide (H₂Ti₄O₉· n H₂O) and potassium octatitanate (K₂Ti₈O₁₇) with a tunnellike structure, were synthesized using an ion-exchange reaction. Fibrous potassium tetratitanate (K₂Ti₄O₉· n H₂O) was prepared by calcination of a mixture of K₂CO₃ and TiO₂ with a molar ratio of 2.8 at 1050°C for 3 h, followed by boiling-water treatment of the calcined products for 10 h. The material then was transformed to layered H₂Ti₄O₉· n H₂O through an exchange of K⁺ ions with H⁺ ions using HCl. K₂Ti₈O₁₇ was formed by a thermal treatment of KHTi₄O₉· n H₂O. Pure KHTi₄O₉· n H₂O phase was effectively produced by a treatment of K₂Ti₄O₉ with 0.005 M HCl solution for 30 min. Thermal treatment at 250°–500°C for 3 h resulted in formation of only K₂Ti₈O₁₇.     

Liquid Corrosion and High-Temperature Oxidation Effects on Silicon Carbide/Titanium Diboride Composites

A silicon carbide composite containing titanium diboride particulate reinforcement was subjected to room-temperature acidic corrosion in aqua regia solutions for 200 h, and 50% NaOH+50% H₂O and 10% HF+57% HNO₃+33% H₂O solutions for up to 500 h. A small increase in room-temperature strength was observed after the aqua regia exposure. Separately, this ceramic was oxidized at 1400°C for 24 h and then tested for strength retention at room temperature. Contrary to the observations reported in the literature on similar material, there was no significant room-temperature strength decrease in this particular composite.     

Encapsulation of Sn(II) and Sn(IV) Chlorides in Composite Cements

The hydration of two high replacement composite cements (3:1 blast furnace slag:ordinary Portland cement (BFS:OPC), and 3:1 pulverized fuel ash:OPC (PFA:OPC)) with the addition of both SnCl₂ and SnCl₄ has been investigated and the results from X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS) are presented. Adding 5% or 1% SnCl₂·2H₂O or SnCl₄·5H₂O to the mix water resulted in the formation of Friedel's salt, Ca₃Al₂O₆.CaCl₂·10H₂O, and calcium hydroxo-stannate CaSn(OH)₆, which also involved the consumption of calcium hydroxide. After 90 days hydration at lower levels of addition (i.e., 1%) there was no longer evidence for CaSn(OH)₆, indicating that it too had been consumed in the pozzolanic reaction due to the lack of calcium hydroxide present. Results from SEM and EDS showed that bright regions between the BFS or PFA grains were tin containing and they were incorporated into the hydrated cement matrix. The tin was, therefore, localized rather than spread throughout and intimately incorporated into the microstructure.     

Experimental Phase Diagram in the Ag-Cu2O-CuO System

Phase equilibria in the Ag-CuO-Cu₂O system were experimentally determined using thermal analysis, and structural and compositional studies. Three reactions were observed in air: (1) L₁= CuO + Ag, (2) L₂= CuO + L₁, and (3) Cu₂O = CuO + L₂. The evolution and absorption of oxygen accompanied these reactions. At oxygen partial pressures below 0.02 bar, the reactions L₁= Cu₂O + Ag and L₂= Cu₂O + L₁ were found. Based on isobaric projections in the Ag-CuO-Cu₂O system, two invariant reactions, L₁= CuO + Cu₂O + Ag and L₂= CuO + Cu₂O + L₁, were deduced.     

Dehydration Behavior of Aluminum Sulfate Hydrates

An exothermic transition is observed near 400°CC on thermal dehydration of highly crystalline AI₂(SO₄)3.16H₂O, Al₂(S0₄)₃ 14H₂O, and Al₂(S0₄)₃ 9H₂O when the early stages of heating are carried out in vacuum. Amorphous or partially crystalline hydrates do not show the exotherm. No systematic relation is apparent between the decomposition behavior and the pore volume distribution of the various anhydrous A1₂(SO₄)₃ products.     

Alternative Route for Synthesis of Barium Titanyl Oxalate: Molecular Precursor for Macrocrystalline Barium Titanate Powders

An important molecular precursor to barium titanate, namely, barium titanyl oxalate [BaTiO(C₂O₄)₂.4H₂O], has been synthesized by an alternative route. An alcoholic solution containing 1 mol of butyl titanate monomer [(C₄H₉O)₄Ti] is reacted with alcoholic solution containing 2 mol of oxalic acid (H₂C₂O₄:2H₂O) to form an intermediate soluble oxalotitanic acid [H₂TiO(C₂O₄)₂.nH₂O]. The oxalotitanic acid in alcoholic medium is subjected to cation exchange reaction with aqueous solution containing equimolar barium acetate to form an insoluble barium titanyl oxalate (BTO) in yields of 80–85% at room temperature. The pyrolysis of BTO in air at T .750°C/5 h produced barium titanate (BT) powders.     

The System Alumina-Gallia-Water

A study of the system Al₂O₃–Ga₂O₃–H₂O has resulted in the determination of equilibrium diagrams for the systems Al₂O₃–Ga₂O₃ and Al₂O₃.-H₂O–Ga₂O₃.H₂O. Extensive solid solution characterizes the α -Al₂O₃ and β -Ga₂O₃ structures at high temperatures, but it is shown that below 810°C. a compound, GaAlO₃, and a new series of (Al, Ga)₂O₃ structures are stable. Among the hydrates, a complete series of diaspore solid solutions extends from Al₂O₃.H₂O to Ga₂O₃.H₂O. Boehmite solid solutions extend to approximately the composition 70Al₂O₃.H₂O, 30Ga₂O₃.H₂O.     

Preparation of Hydroxyapatite Fibers by Electrospinning Technique

Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HA) fibers were prepared by electrospinning a precursor mixture of Ca(NO₃)₂·4H₂O and (C₂H₅O)₃PO with a polymer additive, followed by a thermal treatment. The X-ray diffraction (XRD) analysis of the annealed composite fibers revealed that pure HA phase could be obtained by annealing at 600°C for 1 h. The scanning electron microscopy (SEM) analysis showed the surface of as-electrospun composite fibers with an average diameter of 50 μm was smooth due to the amorphous nature of the polymer. However, the surface of the calcined HA fibers was rough because of the complete removal of the polymer. The pure HA fibers obtained by electrospinning in this work were up to 10 mm in length and 10–30 μm in diameter and the hydroxyapatite grain size was ∼1 μm in the HA fibers.     

Synthesis and Characterization of (Ce0.67Tb0.33)MnxMg1−xAl11O19 Phosphors Derived by Sol–Gel Processing

A (Ce_0.67Tb_0.33)Mn _x Mg_{1− x} Al₁₁O₁₉ phosphor powder was synthesized, using a simple sol–gel process, by mixing citric acid with CeO₂, Tb₄O₇, Al(NO₃)₃·9H₂O, Mg(OH)₂·4MgCO₃·6H₂O, and Mn(CH₃COO)₂. The phosphor crystallized completely at 1200°C, and the phosphor particle size was between 1 and 5 μm. The excitation spectrum was characteristic of Ce³⁺, while the emission spectrum was composed of lines from Tb³⁺ and Mn²⁺. The Mn²⁺ gave a green fluorescence band, and concentration quenching occurred when x > 0.10. The luminescent properties of the phosphor were explained by a configurational coordinate model.     

Thermal Analysis of Some Barium and Strontium Titanyl Oxalates

The thermal decompositions of BaTiO(c₂O₄)₂.- 4H₂O, BaTiO(OH)₂C₂O₄.2H₂O, SrTiO(C₂O₄)₂.- 4H₂O, and SrTiO(OH)₂C₂O₄.H₂O were investigated using TGA, DTA, and effluent gas analysis. The stoichiometry of the decompositions is discussed and it is proposed that a reduced state of titanium is formed as an intermediate.     

Dynamics of Formation of Self-Organized Mesoporous AlO(OH)·αH2O Structure in Al-Metal Surface Hydrolysis in Humid Air

In humid air, a nascent Al-metal surface (S) with a surface Hg²⁺ catalyst hydrolyzes in divided reaction centers (micelles) with a vigorous exothermic reaction, {Al + 2OH⁻}+αH₂O → AlO(OH)·αH₂O + 3e⁻+ H⁺. It yields amorphous AlO(OH)·αH₂O with a huge ∼90% porosity with α= 0.25. The primary driving forces of the reaction are the chemical potential μ_e between the reaction species, the mechanical stress ς induced in expansion of S, and the flow of the reaction species. They drive it in a common direction perpendicular to S. The heat released in it flows primarily along S. It disrupts and stops the directional hydrolysis if the local temperature in the micelle reaches a critical value T _c (hot spot). The hot spot cools to the operating value T ₀, and the reaction restarts and runs over to T _c in a periodic manner, at a time scale of Δ t _i∼ 5 s, per the dynamics of hot spots, forming a self-organized mesoporous structure of 15–50-nm diameter ellipsoidal shaped particles (halo) separated through 3–5-nm pores. A pore, in continuous formation of the sample, forms in disrupted reaction during the hot spot as it cools from T _c to T ₀. The result is modeled in terms of the microstructure and dynamics of the hot spots.     

Dehydration of Hydrous Zirconia with Methanol

The washing of hydrous zirconia with alcohols to reduce the incidence of hard agglomerates on subsequent drying is well known. The results of methanol dehydration of hydrous zirconia (zirconium hydroxide), [Zr₄(μ-OH)₈(OH)₈(H₂O)₈]˙ xH₂O, show that only μ-OH groups are unaffected. This suggests two things: First, the removal of nonbridging hydrooxo groups and water with alcohols such as methanol leads to a reduction/elimination of hard agglomerates. Second, hard agglomerate formation is associated with condensation reactions involving nonbridging hydroxo groups (Zr-OH+HO-Zr→Zr-O-Zr+H₂O).