Influence of admixtures on the crystallization and morphology of AlPO4 crystals

The influence of various uni-, bi-, tri- and tetravalent admixtures on the crystallization and morphology of AlPO₄ has been studied in detail. AlPO₄ crystals were synthesized under hydrothermal conditions. It was found that the phase formation and morphology vary with the type of admixture and its concentration. The crystals were hexagonal, rhombohedral, rounded, irregular, rod shaped and massive in habit. With an increase in the concentration of admixtures, two phases (berlinite and metaphosphates) of the respective admixtures crystallize simultaneously.     

Effect of Ag addition on crystallization in As2Se3 glasses

Differential scanning calorimetry (DSC) behaviours of glassy As₂Se₃ containing Ag up to 5 at % were measured at various heating rates. The effect of addition of Ag on crystallization of glassy As₂Se₃ was investigated. The glass transition temperature decreased with increasing Ag content. Crystallization kinetics were analysed on the basis of the two-step process model, where crystal growth takes place after nucleation. For non-doped As₂Se₃ two-dimensional growth of crystal was predominant, while for Ag-doped ones three-dimensional growth was very likely. It was supposed for all glassy Ag-doped samples that crystal nuclei exist, though micro-crystallites were not observed on X-ray diffraction traces. The activation energy for crystallization and the glass-forming tendency decreased by the addition of Ag.     

Characterization of Agx(Ge2Sb2Te5)1 − xthin film by RF magnetron sputtering

We reported the Ag adding effects on the crystallization behavior in Ge₂Sb₂Te₅ film. Ag_x(Ge₂Sb₂Te₅)_1 − x films (where x = 0–0.2) were deposited on SiO₂ wafer and glass substrate by RF magnetron co-sputtering and annealed by RTA (rapid thermal annealing) at various temperature to crystallize. The effects of Ag adding on the structural, thermal and electrical properties were measured by X-ray diffraction, X-ray reflectivity, AFM, SEM, DSC and 4-point probe analysis. It was found that the crystallization temperature increased by Ag adding in Ge₂Sb₂Te₅ films. However, the surface of Ag_x(Ge₂Sb₂Te₅)_1 − x films got rough when annealing temperature and Ag contents increased. According to the Kissinger method, the activation energy for crystallization increased as the Ag content increased. It is thought that Ag atoms in Ge₂Sb₂Te₅ act as an amorphous stabilizer and they make it hard to switch from amorphous to crystalline phase. From this study, we would show the Ag_0.06(Ge₂Sb₂Te₅)_0.94 film is suitable for phase change memory material because of its higher crystallization temperature and structural stability.     

Explosive crystallization in the course of formation of Se/Ag nanosize film structure

Results of an experimental study of explosive crystallization appearing in the process of formation of a Se/Ag nanosize film structure are presented. It is shown that explosive crystallization appears in a wide range of Se film thicknesses (70–280 nm) and occurs during a narrow time interval (2.00–4.52 s). The cooperative effect of the thermal energy of the phase transformation of Ag₂Se and the energy of elastic stress in the amorphous Se film leads to development of an explosive crystallization. It was found that, depending on the relative thicknesses of Se and Ag films, orthorhombic Ag₂Se with crystal-lattice constants a = 4.333 Å, b = 7.062 Å, and c = 7.764 Å and hexagonal Se (a = 4.3552 Å and c = 4.9495 Å) are formed in the reaction products upon the explosive crystallization.     

Alkali carbonation of calcium aluminate cements: influence of set-retarding admixtures under hydrothermal conditions

The preferential uptake of aluminium ions by lactone and carboxylic acid groups in glucuronic-6,3-lactone and gluconic acid suggested that these organic admixtures have a high potential as set-retarding admixtures of high-temperature calcium aluminate cement slurry. However, the liberation of abundant free calcium ions caused by the adsorption of aluminium ions by the admixtures, increased the carbonation rate of hydrated cement pastes after exposure to Na₂CO₃-laden water at 300 C. Using inorganic acid admixtures, such as boric acid and sodium tetraborate decahydrate, the retarding ability of colloidal Ca(BO₂)₂ ·nH₂O and aluminium hydroxide yielded by the reaction between admixture and cement was less than that of the reaction products derived from organic acid admixtures. Although Ca(BO₂)₂ ·nH₂O in hot Na₂CO₃ solution was converted into CaCO₃, the rate of alkali carbonation was almost the same as that of admixture-free calcium aluminate cement pastes.     

Oriented crystallization of AgGaS<Subscript>2</Subscript> from the melt system Ag-Ga-S

For estimating the boundaries of the homogeneity field of silver thiogallate (TGS) in the quasibinary system Ag₂S-Ga₂S₃, the oriented crystallization of three samples of the following composition (at %) was made: (1) 42.86 Ag, 14.28 Ga, 42.86 S; (2) 26.26 Ag, 24.24 Ga, 49.49 S; (3) 23.76 Ag, 25.74 Ga, 50.49 S. It was shown that the trajectories of changes in the melt composition upon crystallization on the surface of the liquidus of the system Ag-Ga-S do not lie in the plane of the section Ag₂S-Ga₂S₃. This means that the section is not quasi-binary. Our data and literature data say that the projection of the field of homogeneity of TGS onto the concentration triangle has a fairly wide interval in sulfur (from 49.5 to 51.2 at %) and less wide interval in metallic components. The sizes of the field of homogeneity of TGS decrease, while temperature fall and its boundaries come to a stoichiometric composition. This circumstance can lead to the formation of inclusions of minor phases during crystal cooling. The character of inclusions is indicated by the belonging of the melt composition to different segments of triangulation of phase diagram Ag-Ga-S.     

Phase diagram study of the formation and crystallization of Ge-metal amorphous alloy films

The Ge-Au and Ge-Ag alloy films were deposited in vacuum at room temperature and then systematically observed in the TEM. The maximum metallic concentrations in the alloy films,C _max, which form the stable amorphous alloy phases of germanium with gold and silver, were obtained. The annealed crystallization temperatureT _c, which falls with increasing metallic content in these films was also found. The structures of these films and their annealed specimens were also studied. There are various factors which influence the formation of amorphous alloy films deposited in vacuum for Ge-metal systems. A new formula forC _max has been derived. The annealed crystallization character has been explained by means of the variation of the free energy and the activation energy of crystallization. The activation energy of crystallization,E _a, can be obtained from the data values ofT _c. For Ge-Au films,E _a (Au)=E _a ^o /(–18.66C _Au ² +16.83C _Au+1)±3.3 (kcal mol^–1); for Ge-Ag films,E _a (Ag)=E _a ^o /(–2.754C _Ag ² +3.815C _Ag+ 1)±2.6 (kcal mol^–1). In order to explain all these results, two kinds of phase diagram for the alloy films have been introduced. One is the three-dimensional relationship diagrams of phase formation in semiconductor-metallic alloy films; it was introduced to explain the influencing factors. The other is the three-dimensional phase diagrams of annealed semiconductor-metallic films systems. From this diagram all the phase transitions can be found.     

A comparative study of dip coating and spray pyrolysis methods for synthesizing ITO nanolayers by using Ag colloidal sol

Indium tin oxide (ITO) films were deposited on glass substrates by dip-coating and thermal pyrolysis methods. Sn (IV) is often used in the spray method as a precursor salt, but in this research we have employed a new procedure that uses Sn (II) and In(NO₃)₃ for preparation of transparent conductive thin films. Then, colloidal Ag was deposited on the ITO layers in order to compare the two synthesis methods, and the structural and electrical properties of the resultant films were investigated by FESEM, XRD, and four-terminal resistometry. The obtained films are polycrystalline with a preferred orientation of (200). The XRD patterns of the films indicate that in both films, the Sn phase is crystallized separately from In₂O₃. The presence of a Sn peak and the overall low intensity of XRD peaks suggest relative crystallization of ITO structure. For this reason, Ag films were deposited by dip coating method using a colloidal sol. By analyzing the XRD patterns of Ag-ITO films after eliminating the Sn peak, the increased intensity of the peaks confirmed the relatively good crystallization of the ITO films. The results show that the films with a sheet resistance as low as 2 × 10^?2 Ω·cm, which is beneficial for solar cells, were achieved.     

Phase equilibria in Ag-Ga-S films and kinetics of AgGaS<Subscript>2</Subscript> crystallization

The phase compositions of films produced by coevaporation and sequential evaporation of Ag, Ga, and S have been determined. The phases identified in the films grown at room temperature are Ag₂S, GaS, Ga₂S₃, and AgGaS₂. The kinetics of phase transformations in thin amorphous AgGaS₂ films have been studied by dynamic electron diffraction. The dimensionality of growth during amorphous AgGaS₂ crystallization and the activation energies for nucleation and crystallite growth have been evaluated.     

矿物外加剂对丁苯聚合物/水泥复合胶凝材料凝结硬化过程的影响及机制

为了比较沸石、纳米二氧化硅和稻壳灰这3种矿物外加剂对丁苯聚合物/水泥复合胶凝材料凝结硬化过程作用的差异,分别采用这3种矿物外加剂为调凝材料,并从凝结时间、早期强度、水化进程以及水化产物等角度比较3种矿物外加剂对丁苯聚合物/水泥复合胶凝材料的影响。结果表明,3种矿物外加剂都能促进复合胶凝材料的凝结硬化,大幅缩短凝结时间,提高早期强度。但3种矿物外加剂的调凝效果互不相同,调凝机理也有差异:沸石对AFt的生成有较大的促进作用,它不仅能促进C3A的水化,自身也能与Ca(OH)_2反应生成AFt和CSH凝胶;而纳米二氧化硅和稻壳灰对C3S水化的促进作用较强,自身也会与Ca(OH)_2反应生成CSH凝胶。     

Influence of admixtures on strength development of Portland cement and on the microstructure of tricalcium silicate

The influence of various inorganic salts, used as additives to Portland cement paste, on strength development was studied. The salts used were: CaCl₂, CrCl₃, Cdl₂. It was found that CaCl₂ and CrCl₃ accelerate the rate of strength development, while Cdl₂ retards it compared to Portland cement without admixtures. No influence by CdCl₂ was observed. The effect of the same admixtures on the microstructure of hydrated tricalcium silicate was examined by a scanning electron microscope, and correlation between the morphology of the simple system and the mechanical behaviour of the complex cement system is discussed.     

Influence of silver addition on microstructures and transport properties of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript>:Ag<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> composites

In order to obtain high temperature coefficient of resistance (TCR) value of La_0.67Ca_0.33MnO₃:Ag _x (LCMO:Ag _x ) composites, samples with different Ag contents (x?=?0, 0.1, 0.2, 0.25, 0.3, and 0.5) were prepared by sol–gel method. X-ray diffraction analyses indicated that all samples had orthorhombic perovskite structures. As x increased, lattice parameters (a, b, c) and cell volumes underwent slight expansions. Interestingly, the addition of Ag dramatically affected TCR and magneto-resistance (MR) values. Elevated TCR value up to 53.46%·K^?1 at 277 K was observed for LCMO:Ag _x composites with added Ag at the composition of x?=?0.1. Meanwhile, MR value at 263 K reached 71% at the magnetic field of 1 T for samples with Ag composition of x?=?0.25. The increase in Mn⁴⁺/Mn³⁺ ratio and improvement in crystallization caused by added Ag was found responsible for the elevated values of TCR, MR, and T_p. These findings may have practical use in high-performance magneto-resistive manganites.     

UV–vis spectroscopic studies of CaF2 photo-thermo-refractive glass

A photo-thermo-refractive glass based on the system Na₂O/K₂O/CaO/CaF₂/Al₂O₃/ZnO/SiO₂ doped with Ag₂O, CeO₂, SnO₂, Sb₂O₃ and KBr was investigated. This glass undergoes a permanent refractive index change after UV irradiation and subsequent two step heat treatment at temperatures above Tg. This is due to the formation of Ag metal clusters which act as nucleation centers for CaF₂ crystallization. Oxidation of Ce³⁺ by UV light is the initial reaction and acts as photosensitizer in the glass. The UV–vis absorption spectra during this photo-induced crystallization process were measured. The spectral components that form the absorption spectra of cerium were studied in detail by a band separation with Gaussian functions. Deconvolution of the cerium absorption bands shows an envelope of five spectral components for the trivalent cerium due to the 4f-5d transitions and two spectral components for the tetravalent cerium caused by charge transfer transitions. The effect of different dopants and melting conditions on the photo-thermal process were studied to investigate the influence of glass technology on the photoprocess.     

Synthesis, characterization, and sintering of sol–gel derived cordierite ceramics for high-frequency MLCIs

The synthesis, characterization, and sintering of sol–gel derived cordierite ceramics are investigated in the present paper. Synthesis was carried out by optimizing two main preparation parameters. The effect of the heat-treatment schedule on crystallization and the properties of crystalline phases were analyzed. The additives B₂O₃ and P₂O₅ were utilized to promote the crystallization or transformation to -cordierite and sintering. This material has a low dielectric constant and a low dissipation factor and can be co-fired with high conductivity metals such as Au, Ag/Pd, Cu paste at low temperature (below 1000 °C), suggesting that it would be a promising material for high-frequency MLCIs.     

Low firing temperature ceramic material for high frequency multilayer chip inductors

The low firing temperature glass-ceramics of the system B₂O₃-P₂O₅-MgO-Al₂O₃-SiO₂ were investigated in the present paper. The effect of the heat-treatment schedule on crystallization and the properties of crystal phases were analyzed. This material has a low dielectric constant and a low dissipation factor and can be co-fired with high conductivity metals such as Au, Ag/Pd, Cu paste at low temperature (below 1000 °C), suggesting that it would be a promising material for high-frequency MLCIs.     

Dependence of the Structural, Electrical and Magnetic Properties of YBa2Cu3O7?δ Bulk Superconductor on the Ag Doping

The effects of Ag dopants on the superconducting properties of YBCO bulk samples, prepared under solid-state reaction method, have been studied by resistivity?Ctemperature (???CT), X-ray diffraction (XRD), scanning electron microscope (SEM), bulk density, AC susceptibility, DC magnetization measurements, and theoretical analysis. Small Ag substitutions (x??0.10) do not effect T _c of pure YBa₂Cu_3?x Ag _x O_7??? , while we observed small decreases of 1.5?K for larger doping levels (x??0.15). AC susceptibility measurements for sintered YBCO pellets have been performed as a function of temperatures at constant frequency and AC field amplitude in the absence of DC bias field. The critical current densities (J _c ) have been estimated as a function of magnetic field from the magnetization data employing Bean??s critical state model. The increase in Ag amount (x) in YBa₂Cu_3?x Ag _x O_7??? (x??0.10) system effectively decreases the intragrain critical current density, which is attributed to the reduced connectivity between the grain boundaries. In the case of small additions (x=0.05), Ag atoms fill partly the pores, leading better crystallization of the grains.     

Influence of the additive Ag for crystallization of amorphous Ge-Sb-Te thin films

We have investigated the optical and amorphous-to-crystalline transition properties in four-types of chalcogenide thin films; Ge₂Sb₂Te₅, Ge₈Sb₂Te₁₁, Ag-Ge₂Sb₂Te₅ and Ag-Ge₈Sb₂Te₁₁. Crystallization was caused by nano-pulse illumination (λ = 658 nm) with power (P) of 1-17 mW and pulse duration (t) of 10-460 ns, and the morphologies of crystallized spots were observed by SEM and microscope. It was found that the crystallized spot nearby linearly increases in size with increasing the illuminating energy (E = P ? t) and eventually ablated out by over illumination. Changes in the optical transmittance of as-deposited and annealed films were measured using a UV-vis-IR spectrophotometer. In addition, a speed of amorphous-to-crystalline transition was evaluated by detecting the reflection response signals for the nano-pulse scanning. Conclusively, the Ge₈Sb₂Te₁₁ film has a faster crystallization speed than the Ge₂Sb₂Te₅ film despite its higher crystallization temperature. The crystallization speed was largely improved by adding Ag in Ge₂Sb₂Te₅ film but not in Ge₈Sb₂Te₁₁ film. To explain these results, we considered a heat confinement by electron hopping.     

Effects of additional elements (M) on the thermal stability and structure of (Zr52.2Cu39.1Al8.7)100?xMx (M?=?Ag, Be, Gd, x?=?8, 7, 2) amorphous alloys

The effects of Ag (8 at.%), Be (7 at.%), and Gd (2 at.%) addition on structure and thermal stability, as well as bulk glass forming ability, in (Zr_52.2Cu_39.1Al_8.7)_100−x M _x (M = Ag, Be, Gd) alloys are investigated by means of X-ray diffraction and differential scanning calorimetry. The alloy containing Ag and Be have a critical diameter of more than 10 mm, with larger supercooled liquid region and atomic packing efficiency than Zr_52.2Cu_39.1Al_8.7 alloy, while the (Zr_52.2Cu_39.1Al_8.7)₉₈Gd₂ alloy only has a critical diameter of up to 5 mm and shows smaller supercooled liquid region and atomic packing density. CuZr is the main competing crystal phase with amorphous phase in the present Zr-Cu-based alloys. Ag and Be atoms in Zr_52.2Cu_39.1Al_8.7 alloy decrease the long range diffusion of Cu atoms and hinder the crystallization process under rapid solidification conditions. As a result, the glass forming ability of (Zr_52.2Cu_39.1Al_8.7)₉₂Ag₈ and (Zr_52.2Cu_39.1Al_8.7)₉₃Be₇ alloys are effectively enhanced.     

Preparation and characterization of functional fabrics from bamboo charcoal/silver and titanium dioxide/silver composite powders and evaluation of their antibacterial efficacy

Bamboo charcoal supporting silver (BC/Ag) and titanium dioxide supporting silver (TiO₂/Ag) were prepared by activation and chemical reduction. The BC/Ag and TiO₂/Ag composites were characterized by silver particle size and distribution and antibacterial properties. The pore and surface properties were studied in terms of BET volumetric measurement with nitrogen adsorption, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The antibacterial effects of the BC/Ag and TiO₂/Ag composite powders were assessed from the minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs), and an excellent antibacterial performance was discovered. Moreover, these composite powders were deposited via immersion coating onto fabrics (nonwoven and carbon fibers) to improve the antibacterial efficacy and to act as a biologically-protective material. The antibacterial activities of the fabrics supported by BC/Ag and TiO₂/Ag were studied in zone of inhibition and plate counting tests against Gram-positive Staphylococcus aureus ME/GM/TC Resistant, Bacillus subtilis, Candida albicans, Gram-negative Pseudomonas aeruginosae (CTZ&EM&GM) Res. Clin. Isol., Escherichia coli Juhl, and Klebsiella pneumoniae. The results showed that fabric-BC/Ag and fabric-TiO₂/Ag possess a strong antibacterial activity and an inhibitory effect on the growth of these bacteria and are therefore believed to have great potential for use as antibacterial fabrics.     

Crystallization of Li-Si-O-N oxynitride glasses

Effects of nitrogen incorporation on the crystallization of a 3OLi₂O · 70SiO₂ glass have been studied in terms of the glass transition and crystallization temperatures, nucleation mechanism and precipitated crystalline phases. Glass transition and crystallization temperatures rise with increasing nitrogen content. Bulk crystallization is dominant in these oxinitride glasses. Precipitated crystallization phases and their relative amounts vary with nitrogen content. The experimental results are discussed assuming the formation of an [((-O-)₃Si-)₃N] unit and its evolution to an [SiON₃] unit in the residual glassy phase during the crystal growth.On leave from the Government Industrial Development Laboratory, Hokkaido, 2-17 Tsukisamu-Higashi, Toyohira-ku, Sapporo 004, Japan.