Accelerated Curing of Compacted Calcium Silicate Mortars on Exposure to CO2

The parameters affecting strength development in compacted cylinders of 3CaO- SiO₂ and β-2CaO- SiO₂ mortars exposed to CO₂ were investigated. Strength increased with time up to 81 min, the duration of the longest detailed study. The β-2CaO- SiO₂ develops strength more slowly initially, but both silicates achieved compressive strengths of 7,000 to 10,000 psi. The rate of increase in strength depends on both the amount of water used in molding the compact and the amount of water present in the CO₂. Increasing CO₂ pressures from 1 to 2 atm increased the rate of reaction, but a further increase to 4 atm had little additional effect. Carbonation occurs mainly in the outer portions of the cylindrical compacts. The initial reaction on exposure to CO₂ appears to be accelerated hydration of the silicates to a CaO-SiO₂-H₂O-like gel and calcite. The gel has a stoichiometry similar to that found in conventional hydration. Further reaction results in progressive carbonation of the gel, which decreases its lime content. The reaction products appear to be intimately dispersed in the microstructure.     

Synthesis and Characterization of Monosized Doped TiO2 Powders

Monosized spheroidal doped TiO² particles with an average diameter of 0.3 to 0.7 μm were prepared by the controlled cohydrolysis of mixtures of titanium alkoxide and either niobium or tantalum alkoxide. An inorganic salt precipitation technique was used to put Ba, Cu, or Sr onto the surface of singly doped TiO₂ particles. Chemical analyses by several methods demonstrated the reproducibility and reliability of the doping procedures     

Phase Transformation Kinetics in the Doped System LiAl5O8—LiFe5O8

Solid solutions of various compositions in the system LiAl₅O₈–LiFe₅O₈ were prepared by calcining mixtures of Li₂CO₃, Al₂O₃, and Fe₂O₃. Lattice parameters of the solid solutions were determined by X-ray diffraction (XRD). Samples of equimolar composition were also prepared with titanium and magnesium as dopants. The doped and undoped samples were annealed at 1050°C for up to 192 h in air. Annealing at this temperature, which is inside the miscibility gap for an equimolar composition, led to the decomposition of the originally single-phase solid solution. The extent of phase transformation was followed by XRD. The fraction transformed was estimated using integrated peak intensities. The kinetic data were analyzed in light of the conventional kinetic equation and the previously derived equation which takes into account the diffusive and the interface transfer processes. It was observed that titanium enhances and magnesium suppresses the kinetics of phase separation. These results are rationalized on the premise that the predominant point defects are Schottky defects in this spinel system.     

Crystallographic Data of a New Phase of Dicalcium Silicate

Unit-cell parameters and the space group of a new phase of dicalcium silicate (Ca₂SiO₄) were determined by using powder X-ray diffractometry and selected-area electron diffraction techniques. This phase could be synthesized via the dissociation of hydrothermally synthesized alpha-Ca₂(SiO₄H)OH at temperatures of ∼500°-920°C. Crystallographic data for the sample synthesized at 600°C were as follows: Ca₂SiO₄, monoclinic; P 2₁/ c space group; lattice parameters of a = 0.82147(9) nm, b = 0.9808(1) nm, c = 0.9741(1) nm, and β= 94.642(7)°; cell volume ( V ) of 0.7857(1) nm³; Z = 8 (where Z is the number of chemical formula units in a unit cell); and a density of 2.91 g/cm³. The crystallographic data for samples synthesized at 800°C had slightly different unit-cell parameters of a = 0.82124(6) nm, b = 0.97348(7) nm, c = 0.97935(7) nm, β= 94.831(5)°, and V = 0.7849(1) nm³. Structural relationships of the new phase with the other dicalcium silicates are discussed.     

Structural Investigations of Prehydrolyzed Precursors Used in the Sol-Gel Processing of Lead Titanate

A variety of titanate gels were prepared from lead acetate and titanium isopropoxide in methoxyethanol. In the present study, ¹H and ¹³C Fourier transform-nuclear magnetic resonance and mass spectroscopic techniques were used to identify the structure of the lead and titanium precursors formed from lead acetate and titanium isopropoxide, respectively, when refluxed in methoxyethanol. The lead and titanium precursors were determined to be Pb(OOCCH₃) (OC₂H₄OCH₃). x H₂O, where x < 0.5, and Ti₂(OC₂H₄OCH₃)₈, respectively. Similar spectroscopic procedures were applied to identify the lead titanium complex formed from the reaction between lead and titanium precursors.     

Interactions Between Cement Minerals and Hydroxycarboxylic-Acid Retarders: I, Apparent Adsorption of Salicylic Acid on Cement and Hydrated Cement Compounds

A radioisotope assay method was developed to measure the apparent adsorption of salicylic acid on cement and hydrated cement compounds at concentrations of salicylic acid in aqueous solution up to 0.2 wt%, thus including the range of concentrations used for hydroxycarboxylic-acid retarders in concrete. Previously published data were available only for concentrations below 0.01%. The results confirm that there is only limited apparent adsorption on dicalcium and tricalcium silicates, whereas apparent adsorption on paste- and bottle-hydrated products of these compounds is significant. Apparent adsorption on tricalcium aluminate is strong and is greater at intermediate concentrations than near saturation. A similar pattern was observed for apparent adsorption on "C₄AF," but the amounts removed from solution were much less. Experiments with C₄AH₁₃, C₃AH₀, and ettringite revealed that hydrated calcium aluminate and aluminate sulfate compounds also remove major amounts of salicylic acid from solution.     

Semiconducting–Insulating Transition for Highly Donor-Dopod Barium Titanate Ceramics

BaTiO₃ ceramics doped with La (0.01–0.84 at.%) were prepared only with the addition of La and stoichiometric TiO₂. As a result, even when BaTiO₃ was doped with 0.53 at.% La, it could be converted to a semiconductor by sintering at 1540°C for 2 h in air and cooled slowly in the furnace. Differential thermal analysis data clearly demonstrated that the Curie point in the materials shifted toward lower temperatures with increased content of La substituted at the Ba site up to a critical concentration that varied with the sintering temperature. The obtained results suggest that the semiconducting–insulating transition for highly donor-doped BaTiO₃ was closely related to the incorporation of donor into the grains and to the resultant grain size, which were significantly affected by the sinterability of the BaTiO₃ starting powders and sintering conditions used.     

Chemical Solution Deposition of (Pb1−xCax)TiO3 Thin Films with x∼0.5 as New Dielectrics for Tunable Components and Dynamic Random Access Memories

Calcium lead titanate ((Pb,Ca)TiO₃) thin films, with calcium contents of ∼50 at.%, have been prepared by chemical solution deposition (CSD). Different synthetic sol–gel methods have been used for the preparation of the precursor solutions. 1,3-propanediol, OH(CH₂)₃OH, and water, H₂O, were used as solvents. Lead (II) acetate trihydrate, Pb(OCOCH₃)₂·3H₂O, and titanium di-isopropoxide bis(acetylacetonate), Ti(OC₃H₇)₂(CH₃COCHCOCH₃)₂, were used as reagents of lead and titanium, respectively. Calcium was incorporated into the solutions as calcium acetate hydrate, Ca(OCOCH₃)₂· x H₂O, or as calcium acetylacetonate hydrate, Ca(CH₃COCHCOCH₃)₂· x H₂O. Only the use of calcium acetate led to precipitate-free solutions. Pb(II)–Ti(IV)–Ca(II) sols were obtained when calcium acetate was refluxed with the lead and titanium reagents in a diol–water solvent. These sols led to films with a homogeneous compositional profile. Solutions obtained by mixing a water solution of calcium acetate with a Pb(II)–Ti(IV) sol led to films with a heterogeneous compositional profile in which an interface between the film and the Pt bottom electrode is formed. The films derived from the Pb(II)–Ti(IV)–Ca(II) sols have values of dielectric constant at room temperature of ∼500, which, together with their low leakage currents, low dielectric losses, and tunability, make these films promising for dynamic random access memories and tunable devices.     

Acid-Base Equilibria in the System PbO–SiO2

The acid-base equilibria in the liquid silicates in the system PbO–SiO₂ are discussed, Data reported by Richardson and Webb, wherein the PbO activity is determined over a composition range of 0 to 60 mole % SiO₂, are used for comparison with activities computed from structural models with consideration of the acid-base equilibria. The results suggest that the liquid silicates in the system PbO–SiO₂, for the composition and temperature ranges studied, are constituted of a relatively low number of anionic species and that these anions are of a relatively small size (i.e., O_2–, SiO_4–, (SiO₃)₃⁶⁻. and (SiO_2.5)₆⁶⁻).     

Preparation of Amorphous Silicas Doped with Organic Molecules by the Sol-Gel Process

Molecular dispersions of amorphous siliceous materials doped with organic molecules were prepared by a sol-gel process in which Si(OC₂H₅)₄ was hydrolyzed in neutral or acidic solution. An amorphous silica which was doped with quinizarin on the order of 5×10⁻⁵ mol/mol SiO₂ showed photochemical hole burning at ∼4 K.     

Solid Solution of Titanium Dioxide in Aluminum Oxide

The solid solution limit of titanium dioxide in Al₂O₃ was investigated using diffuse reflectance and cathodoluminescence measurements on polycrystalline Al₂O₃ doped with 1.0 mole % or less TiO₂. The samples had been fired in air at 1300°C. The diffuse reflectance spectra indicated that the solid solubility limit is between 0.25 and 0.30 mole %. Cathodoluminescence spectra indicated that both Ti³⁺ and Ti⁴⁺ are present in air-fired samples whereas only Ti³⁺ is present in hydrogen-fired samples.     

Investigations of a Diol-based Sol-Gel Process for the Preparation of Lead Titanate Materials

Lead titanate sols were prepared by a sol-gel method from lead acetate trihydrate, Pb(OOCCH₃)₂3H₂O, and titanium di-isopropoxide bis-acetylacetonate, Ti (OC₃H₇)₂- (CH₃COCHCOCH₃)₂, in 1,3-propanediol, HO(CH₂)₃OH, as solvent. IR analysis and NMR spectroscopic techniques were used to study the reaction mechanisms and to identify possible polymer structures developed during synthesis of the solutions.     

Preparation of Hollow BaTiO3 and Anatase Spheres by the Layer-by-Layer Colloidal Templating Method

Hollow BaTiO₃ and anatase spheres were prepared from multilayered colloidal titanate particles. An inorganic precursor, titanium (IV) bis(ammonium lactate) dihydroxide (TALH) (chemical formula: [CH₃CH(O–)CO₂–NH₄]₂Ti(OH)₂) was used. First, a layer-by-layer (LBL) colloid-templating method was employed using TALH to generate monodispersed hollow titanate spheres. These spheres were then treated in a Ba(OH)₂ solution or distilled water under hydrothermal conditions to transform them into hollow BaTiO₃ or anatase spheres, respectively.     

Influence of Rare-Earth Dopants on Barium Titanate Ceramics Microstructure and Corresponding Electrical Properties

In this article, ytterbium and erbium oxides are used as doping materials for barium titanate (BaTiO₃) materials. The amphoteric behavior of these rare-earth ions leads to the increase of dielectric permittivity and decrease of dielectric losses. BaTiO₃ ceramics doped with 0.01–0.5 wt% of Yb₂O₃ and Er₂O₃ were prepared by conventional solid-state procedure and sintered at 1320°C for 4 h. In BaTiO₃ doped with a low content of rare-earth ions (0.01 wt%) the grain size ranged between 10 and 25 μm. With the higher dopant concentration of 0.5 wt%, the abnormal grain growth is inhibited and the grain size ranged between 2 and 10 μm. The measurements of capacitance and dielectric losses as a function of frequency and temperature have been carried out in order to correlate the microstructure and dielectric properties of doped BaTiO₃ ceramics. The temperature dependence of the dielectric constant as a function of dopant amount has been investigated.     

Hydrothermal Synthesis of Spherical Perovskite Oxide Powders Using Spherical Gel Powders

Spherical perovskite oxide powders, composed of fine particulates, were prepared by using spherical gel powders under hydrothermal conditions. Spherical PbTiO₃, BaTiO₃, and SrTiO₃ powders were synthesized from spherical TiO₂ gel powders, and spherical PbZrO₃ powder from spherical ZrO₂ gel powder. Spherical Pb(Zr_0.5, Ti_0.5)O₃ and Ba(Zr_0.5,Ti_0.5)O₃ powders were prepared from spherical ZrTiO₄ gel powders. Lead acetate trihydrate, barium hydroxide octahydrate, and strontium hydroxide octahydrate were used as the sources of A-site ions in each perovskite oxide (ABO₃). The spherical TiO₂ and ZrO₂ gel powders were prepared by thermal hydrolysis of titanium tetrachloride and zirconium oxychloride, respectively, and spherical ZrTiO₄ gel powder by thermal hydrolysis of a mixture of them in alcohol-water mixed solvent. During the hydrothermal treatment, the spherical gel powders retained their spherical shape to produce spherical perovskite oxide powders, composed of nanometer-sized particulates.     

Environmentally friendly coloured materials: cellulose/titanium dioxide/inorganic pigment composite spherical microbeads prepared by viscose phase-separation method

In order to develop environmentally friendly coloured materials, cellulose composite spherical microbeads hybridised with titanium dioxide (TiO₂) particles and inorganic pigment were prepared by a phase-separation method using viscose and an aqueous solution containing sodium polyacrylate. Findings regarding the relationships between cellulose xanthate and the electronic characteristics of TiO₂ particles used in the cellulose/inorganic material composite sphering process are also reported. These findings suggest that the location of TiO₂ particles in cellulose microbeads is related to electrical repulsion between the xanthate (CSS⁻) group and TiO₂. The use of TiO₂ powder as colour pigment is limited, as its colour is white. The cellulose composite spherical microbeads covered with TiO₂ and Fe₂O₃ particles were developed by addition of iron oxide (Fe₂O₃). Their surfaces were viewed by laser microscope and using SEM images. These composite microbeads retained the photocatalytic property of TiO₂. Cellulose/TiO₂/Fe₂O₃ composite spherical microbeads with both colour function and photocatalytic properties were successfully prepared.     

Aging of Lime Putty: Effects on Traditional Lime Mortar Carbonation

The influence of storing slaked lime under water for extended periods of time (i.e., aging) on Ca(OH)₂ crystal morphology, texture, and carbonation evolution of various lime mortars has been studied by the combined use of X-ray diffractometry, phenolphthalein tests, porosity measurements, electron microscopy, and ultrasonic wave propagation analyses. Mortars prepared using traditional aged lime putties (up to 14 years storage under water) show rapid, extensive carbonation, resulting in porosity reduction and ultrasonic speed increase. The aged hydrated lime mortar carbonation reaction (i.e., Ca(OH)₂+ CO₂= CaCO₃+ H₂O) follows a complex diffusive path, resulting in periodic calcite precipitation as Liesegang rings. In this case, binder:aggregate ratios >1:4 result in crack development. Nonaged commercial hydrated lime mortars show slower carbonation and need a higher binder:aggregate ratio (1:3). The carbonation of nonaged lime mortars follows a normal diffusion-limited continuous path progressing from the mortar sample surface toward the core. Differences between aged and nonaged lime mortar carbonation evolution are explained considering Ca(OH)₂ crystal shape changes (from prisms to platelike crystals) and size reduction that occurs on aging of lime putty. Implications of these results on historic building conservation using traditional lime mortars are discussed.     

Characterization and Tribological Investigation of Sol–Gel Titania and Doped Titania Thin Films

Titania (TiO₂) and doped TiO₂ ceramic thin films were prepared on a glass substrate by a sol–gel and dip-coating process from specially formulated sols, followed by annealing at 460°C. The morphologies of the original and worn surfaces of the films were analyzed with atomic force microscopy (AFM) and scanning electron microscopy. The chemical compositions of the obtained films were characterized by means of X-ray photoelectron spectroscopy (XPS). The tribological properties of TiO₂ and doped TiO₂ thin films sliding against Si₃N₄ ball were evaluated on a one-way reciprocating friction and wear tester. The AFM analysis shows that the morphologies of the resulting films are very different in nanoscale, which partly accounts for their tribological properties. XPS analysis reveals that the doped elements exist in different states, such as oxide and silicate, and diffusion took place between the film and the glass substrate. TiO₂ films show an excellent ability to reduce friction and resist wear. A friction coefficient as low as 0.18 and a wear life of 2280 sliding passes at 3 N were recorded. Unfortunately, all the doped TiO₂ films are inferior to the TiO₂ films in friction reduction and wear resistance, primarily because of their differences in structures and chemical compositions caused by the doped elements. The wear of the glass is characteristic of brittle fracture and severe abrasion. The wear of the TiO₂ thin film is characteristic of plastic deformation with slight abrasive and fatigue wear. The doped TiO₂ thin films show lower plasticity than the TiO₂ thin film, which leads to large cracks. The propagation of the cracks caused serious fracture and failure of the films.     

Physical Properties and Structure of Rf-Sputtered Amorphous Films in the System Ti02-Si02

Amorphous films in the system Ti0₂-Si0₂ were prepared by rf sputtering and their density, refractive index, and thermal expansion were measured. Also, the silicon Kα and titanium Kβ band emission spectra were obtained by X-ray emission spectroscopy in order to determine the coordination state of silicon and titanium ions in these amorphous films. The density and refractive index increased, but not proportionally, with increasing Ti0₂ content. On the other hand, a minimum was observed in the thermal expansion coefficient at =15 mol% Ti0₂. The coordination state of silicon ions in the amorphous films did not change with Ti0₂ content. However, the coordination number of titanium ions changed from 4 to 6, depending on Ti0₂ content. These results indicate that, in amorphous films in the system Ti0₂-Si0₂, the change of the coordination state of titanium ions has an important effect on physical properties, such as volume, molar refractivity, and thermal expansion.     

Cation Effects in NaPO3 Glasses Doped with Metal Nitrides and Oxides

Oxynitride glasses were prepared by doping a NaPO₃ melt with either AIN, Mg₃N₂, or Ca₃N₂ NaPO₃ glasses doped with AI₂O₃, MgO, or CaO, so as to contain the same weight percent of each cation as in the oxynitride glasses were also prepared. The dissolution rate in water and the thermal expansion coefficient both decreased while the dilatometric softening point, glass transition temperature, and refractive index increased with increasing nitride or oxide dopant concentration. The properties of the corresponding oxide- or nitride-doped glasses were essentially equal, which indicated that the cation was primarily responsible for the change in each property.