Compositional Model for Calcium Silicate Hydrate (C-S-H) Gels, Their Solubilities, and Free Energies of Formation

A compositional model based on available structural evidence is proposed for amorphous calcium silicate hydrogel. It is applicable to gels in the (Ca/Si),_solid range 1.0 to 1.4 and is formulated to take account of dimeric silicate species in the solid. Its composition is represented by Ca _x H_{6−2 x} Si₂O₇· z Ca(OH)₂· n H₂O where x and z are not independently obtainable; x + z , however, is evaluated from the Ca/Si ratio. The model is applied to representative solubility data; K_sp and free energies of formation for C-S-H's in this composition range are evaluated.     

Reaction Condition for the Synthesis of Ultrafine Particles of the High-Vacancy-Content Zn(II)- Bearing Ferrites from Iron(III) Tartrate Solution

Reaction conditions for the synthesis of ultraflne particles of ferrite solid Solutions between ZnFe₂O₄ and γ-Fe₂O₃ rep-resented by x(ZnFe₂O₄)- y(Fe₃O₄)- z(γ-Fe₂O₃), where x + y + z = 1 (0.09 x 0.73, y 0.08,0.22 z 0.88) (high-vacancy-content Zn(II)- bearing ferrites), were studied using the strongly alkaline Solutions of Fe(III) tartrate con-taining Zn(II) ions at 100°C. The crystal growth of the ferrite particles was enhanced with the Zn(II) ions in the reaction solution. The number of nuclei of the ferrite was dependent on the Fe(III) or the tartrate concentration, which influenced the ultraflne particle size of the ferrite. The average particle size of the high-vacancy-content Zn(II)- bearing ferrites ranged from 7 to 38 nm. The room-temperature Mössbauer effect of the high-vacancy-content Zn(II)- bearing ferrite (x = 0.34–0.37, y 0.02, z = 0.62–0.65) revealed the superparamagnetic nature for ultrafine particle sizes less than 20 nm. The ferrite was transferred from superparamagnetic to ferrimagnetic with an increase in the particle size (>20 nm) at room temperature.     

Chemical Solution Deposition of Transparent and Metallic La0.5Sr0.5TiO3+x/2 Films Using Topotactic Reduction

Metallic and transparent La_0.5Sr_0.5TiO_{3+ x /2} films were prepared by the chemical solution deposition (CSD) method using topotactic reduction processing. The use of Si powder as the reducing agent was facile and allowed easy manipulation. It was observed that metallic (resistivity at 300 K ∼2.43 mΩ cm) and transparent (∼80% transmittance at visible light) La_0.5Sr_0.5TiO_{3+ x /2} films could be obtained with an annealing temperature of 900°C, which was significantly lower than the hydrogen reduction temperature (∼1400°C). The successful preparation of metallic and transparent La_0.5Sr_0.5TiO_{3+ x /2} films using CSD has provided a feasible route for depositing other perovskite-structured functional layers on La_0.5Sr_0.5TiO_{3+ x /2} films using this low-cost all CSD method.     

Thermal Expansion of Solid Solutions in the ZrTiO4—In2O3—M2O5 (M = Sb, Ta) System

Axial and dilatometric thermal expansions and phase transformations were studied for solid solutions having the α-PbO₂ structure in the ZrTiO₄—In₂O₃—M₂O₅ (M = Sb, Ta) system with nominal formulas of Zr _x Ti _y In _z Sb _z O₄ and Zr _x Ti _y In _z Ta _z O₄ where x + y + 2 z = 2. With increased substitution of z , the cell volume increased, the difference in the b parameters at room temperature between those quenched from 1400° and 1000°C decreased, and the thermal expansion decreased. The axial thermal expansion of ZrTi _y In _z · Ta _z O₄ with z = 0.3 was almost identical with that of HfTiO₄, and those with z = 0.4 and z = 0.45 were smaller than that of HfTiO₄. Unit-cell volumes of these compound were compared with those of single oxides to make it clear that the unit-cell volume of ZrTiO₄ was small anomalously and to distinguish the normal and abnormal substitution systems. These results were explained by the working hypothesis proposed for these compounds.     

A- and B Site Cosubstituted Ba6−3xSm8+2xTi18O54Microwave Dielectric Ceramics

Tin (Sn) substitution into the B-site and Nd/Sn cosubstitution into the A- and B-sites were investigated in a Ba _{6−3 x} Sm_{8+2 x} Ti₁₈O₅₄solid solution ( x = 2/3). A small amount of tin substitution for titanium improved the temperature coefficient of resonant frequency (τ_f) but led to a decrease of the relative dielectric constant (ɛ) and the quality factor ( Qf ). The Ba_{6−3 x} Sm_{8+2 x} (Ti_{1− z} Sn_z)₁₈O₅₄-based tungsten-bronze phase became unstable for compositions with a tin content of ≥10 mol%, where BaSm₂O₄and Sm₂(Sn,Ti)₂O₇appeared, and finally, these phases became the major phases. On the other hand, Nd/Sn cosubstitution led to a good combination of high ɛ, high Qf , and near-zero τ_f. Excellent microwave dielectric properties were achieved in Ba_{6−3 x} (Sm_{1− y} Nd _y )_{8+2 x} (Ti_{1− z} Sn _z )₁₈O₅₄ceramics with y = 0.8 and z = 0.05 sintered at 1360°C for 3 h: ɛ= 82, Qf = 10 000 GHz, and calculated τ_f=+17 ppm/°C. The tolerance factor and electronegativity difference exhibited important effects on the microwave dielectric properties, especially the Qf value. A large tolerance factor and high electronegativity difference generally led to a higher Qf value.     

Crystallization of a Rare Earth-Rich Aluminoborosilicate Glass With Varying CaO/Na2O Ratio

The effect of varying R =[CaO]/([CaO]+[Na₂O]) ratio on the crystallization of a rare earth-rich aluminoborosilicate glass (16 wt% RE₂O₃, RE=Nd or La) is investigated. The crystallization of a silicate apatite with Ca_{2+ x} RE_{8− x} (SiO₄)₆O_{2−0.5 x} composition ( x ≈0.4–0.7), is responsible for a drop of the rare earth solubility in the melt. When successive nucleation and growth stages are performed, crystallization processes change across the glass series as a consequence of glass-in-glass phase separation. An exotic phase of composition close to Ca₁₀Nd₇Si_20.75O₆₂ grows at the expense of silicate apatite.     

Phase Relations in the System MgO-V2O3-VO2 at 1200°C

Phase relations in the quasi-ternary system MgO-V₂O₃-VO₂ at 1200°C were studied using the quenching technique under controlled O₂ atmospheres. A new phase of a type z VO _y Mg_{2− x} V_{1+ x} O₄ (0< x <1, y ≥1.5, z >0) was found with a compositional region along the MgV₂O₄-Mg₂VO₄ join. Equilibrium P _{O 2} observed for Mg_{2− x} V_{1+ x} O₄ is quite different from that for V _n O_{2 n -1} with an equal ratio of V³⁺/V⁴⁺, corresponding to the V³⁺ stabilities in two types of compounds. Thus, the phase relations in the ternary system were constructed on a conventional triaxial diagram as a function of P _O2.     

Phase Transitions and Electrical Properties of (Na1−xKx)(Nb1−ySby)O3 Lead-Free Piezoelectric Ceramics With a MnO2 Sintering Aid

Lead-free piezoelectric ceramics (Na_{1− x} K _x )(Nb_{1− y} Sb _y )O₃+ z mol% MnO₂ have been prepared by a conventional solid-state sintering technique. Our results reveal that Sb⁵⁺ diffuses into the K_0.5Na_0.5NbO₃ lattices to form a solid solution with a single-phase orthorhombic perovskite structure. The partial substitution of Sb⁵⁺ for B-site ion Nb⁵⁺ decreases the paraelectric cubic-ferroelectric tetragonal phase transition ( T _c) and the ferroelectric tetragonal-ferroelectric orthorhombic phase transition ( T _O–F), and retains strong ferroelectricity. A small amount of MnO₂ is enough to improve the densification of the ceramics. The co-effects of MnO₂ doping and Sb substitution lead to significant improvements in ferroelectric and piezoelectric properties. The ceramics with x =0.45–0.525, y =0.06–0.08, and z =0.5–1 exhibit excellent ferroelectric and piezoelectric properties: d ₃₃=163–204 pC/N, k _P=0.47–0.51, k _t=0.46–0.52, ɛ=640–1053, tan δ=1.3–3.0%, P _r=18.1–22.6 μC/cm², E _c=0.72–0.98 kV/mm, and T _C=269°–314°C.     

High-Vacancy-Content Magnetites and Zinc-Bearing Ferrites from Iron(III) Tartrate in Strongly Alkaline Solution

High-vacancy-content magnetites with particle size in the range of 20 to 150 nm can be precipitated as stable products in the clear and strongly alkaline solution of iron(III) tartrate and dextrose at 100°C, although Fe(III) ions in alkaline solution have been reported previously to form only α-FeO(OH) and α-Fe₂O₃. When Zn(II) ions were present in the reaction solutions, high-vacancy-content Zn(II)-bearing ferrites represented by (ZnFe₂O₄)_x-(Fe₃O₄)_y-(γ-Fe₂O₃)_z, where x + y + z = 1, were obtained in the strongly alkaline solutions. The Fe(II) ions, which were formed by the reduction of Fe(III) ions with dextrose, accelerate the crystallization of the spinel structure.     

Synthesis of Nanosized Titanium-Chromium Oxynitride Powders by Ammonolysis of Coprecipitated TiO2/Cr2O3 Precursors

Interstitial titanium-chromium oxynitrides in the solid solution series Ti_{1− z} Cr _z (O _x N _y ) ( z = 0.2, 0.4, 0.5, 0.6, 0.8) have been obtained by ammonolysis of the TiO₂/Cr₂O₃ precursors resulting from the coprecipitation method. The precursors and the resulting oxynitrides were characterized by auger electron spectroscopy, X-ray diffraction analysis, electron probe microanalysis, transmission electron microscopy, and BET surface area techniques. Compounds in the Ti_{1− z} Cr _z (O _x N _y ) series are prepared as single phases by nitridation at 1073 K for 8 h. The as-synthesized oxynitride powders contain only Ti_{1− z} Cr _z (O _x N _y ) with cubic structure and the particle size is in the nanometer scale.     

Thermochemistry of Charge-Coupled Substitutions in Silicate Glasses: The Systems Ml/nn+ AlO2-SiO2 (M = Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Pb)

Enthalpies of solution of framework aluminosilicate glasses x M_{l/ n} ^{n +} AlO₂-(1- x )SiO₂ (M = Cs, Rb, K, Na, Li, Ba, Pb, Sr, Ca, Mg) in molten 2PbO.B₂O₃ near 973 K were measured. The sequence above represents increasing ability of the nonframework cation M to bond to the bridging oxygen. In that sequence, the enthalpy of the substitution Si⁴⁺→+ Al³⁺+ 1/ n M ^{n +} in the glass becomes less exothermic, the enthalpy of vitrification increases, and the tendency toward glass-glass immiscibility becomes more pronounced. These parameters correlate smoothly with the ionic potential, z/r , of the substituting cation.     

Study of Nonstoichiometry of 〈U1–zGdzO2±x〉

The extensive nonstoichiometry in the 〈U_{1– z} Gd _z O_{2± x} 〉 † phase was investigated experimentally and the data are represented by a chemical thermodynamic method. The experimental ranges of temperature, oxygen potential, and z were 1273 to 1773 K, 0 to −600 kJ/mol, and 0.1 to 0.8, respectively. For hypostoichiometry, ideal-solution thermodynamics for the equilibrium 3Gd_4/3O₂+ 4UO₂+ (O₂) = 6U_2/3Gd_2/3O_8/3 were used to represent the experimental data, while for hyperstoichiometry a nonideal solution was used for the equilibrium 4UO₂+ (O₂) = 2U₂O₅. The wide ranges in x and z led to an improvement of the previous analysis of literature data and led to partial molal Gibbs free energy values that are useful for any thermodynamic calculation involving the phase.     

Color and Selected Properties of PbO─BiO1.5─GaO1.5 Glasses

The density; molar volume; thermal expansion coefficient; dissolution rate in water, HC1, and NaOH; glass transition and crystallization temperatures; and the absorption edge in the ultraviolet-visible and infrared were measured for PbO─BiO1.5─GaO1.5 glasses. The range of compositions investigated was x PbO (100 − (x + y) )BiO_1.5. yGaO_1.5 for x between 20 and 60 cat% and y of 20, 25, 30, and 35 cat%. The glass-forming tendency increased with increased GaO_1.5 and decreased with increased PbO or BiO_1.5. The compositional dependence of these properties was consistent with the weight, size, charge, and bond strength of the cations. The Ga^{3 +} ions in these glasses are believed to act primarily as network-forming cations, whereas the majority of the Bi³⁺ and Pb²⁺ ions behave as network-modifying cations. It is suggested that a small friction of the lead ions are present as Pb⁴⁺. Depending upon melting conditions, these glasses ranged in color from brown to yellow. Various attempts, including containerless melting, were made to obtain colorless glasses, but no conditions were found which totally eliminated the color. The least color (pale yellow) was obtained when the glasses were melted in an air or nitrogen atmosphere in an alumina or gold crucible.     

29Si and 27Al MAS-NMR of NaOH-Activated Blast-Furnace Slag

b²⁹Si and ²⁷Al MAS-NMR were performed on NaOH-activated blast-furnace slag to better characterize the amorphous and poorly crystalline phases which occur in this system. The unreacted glass has a mainly dimeric silicate structure represented by a broad ²⁹Si peak (FWHM = 15 ppm) centered at –74.5 ppm [ Q ¹], with aluminum present exclusively in tetrahedral coordination. Upon reaction with 5M NaOH ( w/s = 0.4), three new ²⁹Si peaks with widths of ca. 2 ppm are formed at -78.5 Q ¹, –81.4 [ Q ²(1Al)J, and -84.3 [ Q ²]. Relative peak areas indicate a mostly dimeric silicate structure for the tobermorite-like C─S─H layers, with roughly a third of the bridging sites occupied by aluminum, and less than 10% by silicon. In addition to the tetrahedrally coordinated aluminum substituted in the C─S─H structure, ²⁷Al MAS-NMR reveals the presence of aluminum in octahedral sites, which is attributed to the aluminate phase (C,M)₄AH₁₃. ²⁹Si results indicate rapid initial consumption of the glass, with roughly a third of the glass reacting within the first day and another third consumed over the following 27 days.     

Substitution of Sodium and Silicon in Tricalcium Aluminate

Four types of tricalcium aluminate solid solutions with different concentrations of Na₂O and SiO₂ were prepared and examined using an electron probe microanalyzer. The atomic ratios, including those determined in a previous study, were derived from the oxide compositions and provided excellent correlations between Ca and Na + Si (i.e., Ca = 3.003 − 0.48[Na + Si]), and Al and Si (Al = 1.997 − 1.02Si). Because the replacement reactions, Ca²⁺↔ 2Na⁺ and Ca²⁺+ 2Al³⁺↔ 2Si⁴⁺, independently occur within the same crystal, these reactions have been simply combined together to generate a new formula, Na_{2 x} Ca_{3− x − y} (Al_{1− y} Si _y )₂O₆, where x is the amount of Ca substituted by Na, and y is the amount of Al substituted by Si. This formula leads to the equations Ca = 3 − 0.5[Na + Si] and Al = 2 − Si, which nicely account for the constrained chemical variation of the actual solid solutions with 0 ≤ x < 0.049 and 0 ≤ y < 0.073.     

Phase Diagram of the BaO(BaCO3)-CaO-CuO System

The phase diagram of the BaO(BaCO₃)-CaO-CuO system, especially in the barium-rich region at 900°C in air, was studied. Two new different oxycarbonates were observed: Ba₈Ca_16/15Cu_64/15O_11.20(CO₃)_2.66and a solid-solution series with a chemical composition of Ba₂Ca _{x + y} Cu_{1+( x /2)- y} O_2+delta(CO₃)_{1- z} (where 0 ≤ to x ≤ to 2/39 and 0 ≤ to y ≤ to 16 x /5). The oxycarbonate solid solution was formed in a region of the compositional triangle Ba:Ca:Cu (in moles) = (2:0:1)-(39:1:20)-(65:7:28). The solid-solution structure had P 4/ mmm symmetry, with lattice parameters a similar/congruent a _pand c similar/congruent 2 a _p, where a _prepresents the perovskite cell. The Ba₈Ca_16/15Cu_64/15O_11.20(CO₃)_2.66compound, which had Pm 3 m symmetry with a lattice parameter a = 0.8116(2) nm, had no chemical-solubility range.     

Influence of Crystal Structure on the Fatigue Properties of Pb1−xLax(Zry', Tiz)O3 Thin Films Prepared by Pulsed-Laser Deposition Technique

Lead lanthanum zirconate titanate (Pb_{1− x} La _x (Zr _y ,Ti _z )O₃, PLZT) films containing [00 l ] preferentially oriented grains were produced successfully on YBa₂Cu₃O_{7− x} -coated (YBCOcoated) SrTiO₃ (STO) or YBCO/CeO₂-coated silicon substrates; films containing randomly oriented grains were created on platinum-coated silicon substrates. The latter possessed significantly inferior ferroelectric properties, a fact ascribed to the presence of a paraelectric phase (TiO₂) at the PLZT/platinum interface. On the other hand, the PLZT/YBCO/STO films exhibited better electrical properties than did the PLZT/YBCO/CeO₂/Si films, and this phenomenon was attributed to better alignment of the grains in normal and in-plane orientations. In terms of fatigue properties, the [00l] textured films that were deposited on YBCO/CeO₂/Si substrates possessed substantially superior polarization-switching-cycle endurance versus the randomly oriented films grown on Pt(Ti)/Si substrates. Moreover, the tetragonal films behaved much more satisfactorily than did the rhombohedral PLZT films. The ferroelectric parameters of tetragonal PLZT films showed no significant degradation up to 10⁹ polarization switching cycles, whereas the remnant polarization and coercive force of the rhombohedral PLZT films had already degraded to 80% of their initial values after 10⁸ cycles.     

Review and Chemical Thermodynamic Representation of 〈U1–zCezO2±x〉 and 〈U1–zLnzO2±x); Ln = Y, La; Nd, Gd

The entire data base for the dependence of the nonstoichiometry, x , on temperature and chemical potential of oxygen (oxygen potential) in 〈U_{1– z} Ce _z O_{2+ x} 〉 and 〈U_{1– z} Ln _z O_{2+ x} 〉 was retrieved from the literature and represented by a thermodynamic method. The method reproduces the behavior of the experimental data and also results in partial molal Gibbs free energy quantities that are useful for any thermodynamic calculation involving these nonstoichiometric phases. The behavior of these systems is also compared with that for 〈U_{1– z} Pu _z O_{2± x} 〉.     

Physical Properties of Chalcogenide and Chalcohalide Glasses

The physical properties of glasses in the Ge₃₀As₁₀Se_{(60— x )}Te _x system with x = 25, 28, 30, and 35 at.% Te, the Ge₃₀As₁₀Se₃₀Te_{(30— y )}I _y system with y = 5, 10, 20, and 30 at.% I, the Ge₃₀As₁₀Se₃₅Te_{(25— z )}I _z system with z = 2, 6, 10, and 20 at.% I, and the [Ge₃₀As₁₀Se₃₀Te₃₀]_{(100— w )}I _w system with w = 0, 5, 10, and 20 at.% I have been investigated. The changes in the glass transition temperature, density, coefficient of thermal expansion, hardness, and viscosity are attributed to the delocalized metallic bonding character of Te in the substitution of Te for Se in the Ge-As-Se-Te glass system and the network-terminating role of iodine in the substitution of I for Te in the Ge-As-Se-Te-I glass system, respectively.     

Thermogravimetric Analysis and Defect Models of the Oxygen Nonstoichiometry in La2–xSrxCuO4–y

The oxygen nonstoichiometry, y, of La_{2– x} Sr _x CuO_{4– y} (0 ≤ x ≤ 1) was determined as a function of temperature (800–1050°C) and oxygen partial pressure (10^–4 to 1 atm) by a thermogravimetric technique. The results were interpreted in terms of a number of defect models. It was found that a model based on the defect reaction 4Cu^×_Cu+ 2 V ^¨_o+ O_2(g)= 4Cu^._Cu+ 2O^×_o described the results well when the x and y dependences of the partial molar enthalpy of oxygen in the solid were considered. The large defect concentrations observed in this system lead to defect interactions, possibly ordering on the oxygen sublattice.