Effect of boron oxide on the cubic-to-monoclinic phase transition in yttria-stabilized zirconia

Specimens of yttria fully stabilized zirconia with different amounts of boron oxide have been studied by X-ray diffraction at room temperature and at higher temperatures up to 1250 °C. A boron oxide-assisted cubic-to-monoclinic phase transformation was determined in the temperature range 800-1250 °C. In situ high temperature X-ray diffraction experiments gave evidences of the dependence of the phase transformation on the heating rate. The possibility of tuning the cubic-monoclinic phase ratio by suitable addition of boron oxide before pressing and sintering is proposed.     

Effect of melt-spun powder additions on the thermoelectric properties of bismuth and antimony chalcogenides

We have studied the thermoelectric properties of p-type Bi_0.5Sb_1.5Te₃ and n-type Bi₂Te_2.4Se_0.6 solid solutions prepared by vacuum hot pressing of mixtures of powders differing in particle size composition. The powders were prepared by mechanically grinding ingots and by ultrarapid melt cooling (melt spinning). Fracture surfaces of samples were examined by scanning electron microscopy. The samples consisted of large, layered particles of the major component (up to hundreds of microns in size) and small flakes (a few to tens of microns in size) of the component prepared by melt spinning. The microstructure of the materials was examined under an optical microscope. On grain boundaries in the p-type materials, we observed telluriumbased eutectic precipitates in the form of a white phase. In some of the n-type samples, the Bi₂Te_2.4Se_0.6 solid solution was found to undergo ordering, resulting in the formation of the ternary compound Bi₂Te₂Se. The Seebeck coefficient, electrical conductivity, and thermal conductivity of the materials were measured in the temperature range 100–700 K. The addition of 40 wt % powder prepared by melt spinning to hot-pressed p-type samples was shown to have no effect on their thermoelectric figure of merit (ZT)_max, which was 1.0 at 350 K. On the addition of 20 wt % powder prepared by melt spinning, we obtained (ZT)_max = 1.1 at 550 K in a hot-pressed n-type sample.     

Effect of oxide additions on the properties of plasma-sprayed Y-Ba-Cu-O coatings

Plasma-spraying is a potential technique for forming flexible tapes from the brittle highT _c oxides. It is possible to obtain superconducting YBa₂Cu₃O _x coatings by a suitable heat-treatment after spraying. In an effort to improve the critical current densities of the coatings, the effect of additions of Ag₂O, Bi₂O₃ and SnO₂ to the YBa₂Cu₃O _x powder used for spraying was studied. The maximumJ _c value of 75 A/cm² was obtained for the sample doped with 5% SnO₂.     

Single crystal fibers of yttria-stabilized cubic zirconia with ternary oxide additions

Single crystal fibers of yttria (Y2O3)-stabilized cubic zirconia (ZrO2) with ternary oxide additions were grown using the laser float zone fiber processing technique. Ternary additions to the ZrO2-Y2O3 binary system were studied aimed at increasing strength while maintaining the high coefficient of thermal expansion of the binary system. Statistical methods aided in identifying the most promising ternary oxide candidate (Ta2O5, Sc2O3, and HfO2) and optimum composition. The yttria range investigated was 14 to 24 mol% and the ternary oxide component ranged from 1 to 5 mol%. Hafnium oxide was the most promising ternary oxide component based on 816 °C tensile strength results and ease of fabrication. The optimum composition for development was 81ZrO2-14Y2O3-5HfO2 based upon the same elevated temperature strength tests. Preliminary results indicate process improvements could improve the fiber performance. We also investigated the effect of crystal orientation on strength.     

Effect of gamma irradiation on properties of hardened cement paste

Carbonation of hydrated cement paste (HCP) under γ-irradiation is researched in this paper. It is supposed that radiation-induced carbonation takes part simultaneously with “natural” carbonation. “Natural” carbonation is governed by diffusion and therefore takes part in the material close to surface only, whereas radiation-induced carbonation manifests in all irradiated material. The hypothesis has been tested by means of three sets of experiments. Within these experiments the following changes were investigated: (a) changes of composition of hydrated cement paste (transformation of portlandite to calcite), (b) changes of porous space [changes of average pore diameter (APD)], (c) changes of mechanical properties (hardness). HCP was analysed in the surface layer as well as in the centre of samples. The results show clearly that radiation at least accelerates carbonation driven by diffusion and support a hypothesis that besides natural carbonation there is also independent carbonation caused by γ-irradiation.     

Effect of gamma irradiation on the optical properties of amorphous GeSe films

We have studied the influence of gamma irradiation in a ⁶⁰Co source (1.25 MeV, gamma doses from 10² to 10⁶ Gy) and subsequent storage for a year on the structure, fundamental absorption edge, and refractive index of a-GeSe films prepared by flash evaporation in vacuum on silica substrates (T _s = 293 K). The high-energy irradiation has been shown to stimulate structural transformations and to produce changes in the electron-defect subsystem of the films.     

Effect of gamma irradiation on the optical properties of CR-39 polymer

The UV-Visible absorption spectra of virgin and gamma irradiated (20–800 kGy) CR-39 polymer have been deduced by using Shimadzu Double beam Double Monochromator UV-Visible Spectrophotometer (UV-2550). The existence of the peaks, their shifting and broadening as a result of gamma irradiation has been discussed. Finally the indirect and direct band gap in virgin and gamma irradiated CR-39 has been determined. The values of indirect band gap have been found to be lower than the corresponding values of direct band gap.     

Effect of copper oxide on the polymorphism of unstabilized and yttria-stabilized zirconia

We have studied the effect of copper oxide doping on the phase composition of unstabilized and yttria partially and fully stabilized zirconia prepared via hydroxide precipitation followed by heat treatment at different temperatures. Copper oxide is shown to stabilize cubic zirconia only in the presence of yttria. The chemical processes in the CuO-Y₂O₃-ZrO₂ system and the mechanisms of C-ZrO₂ stabilization are discussed.     

Effect of CaF2 on the electrical properties of yttria-stabilized zirconia

The effects of CaF₂ addition on the phase constitutions and electrical properties of 8 mol% yttria-stabilized zirconia were investigated. Three samples were prepared, one being doped with 10 mol% CaF₂ and sintered at 1473 K and the other two doped with 20 mol% CaF₂ and sintered at 1473 and 1673 K, respectively. Single phased fluorite-type solid solution with cubic symmetry was observed for each sample. However, F ion exists only in the sample doped with 20 mol% CaF₂ and sintered at 1273 K. Electrical measurements showed that addition of CaF₂ may enhance the ionic conductivity of the yttria-stabilized zirconia.     

Effect of gamma irradiation on the electrical and optical properties and conduction mechanism of α-SiO2

The electrical and optical properties of gamma-irradiated α-SiO₂ crystals are studied in broad dose and temperature ranges, and their lattice dynamics is analyzed using IR absorption spectroscopy. The radiation effect on the electrical conductivity of the crystals is shown to be a nonlinear function of temperature and gamma dose, characteristic of percolation systems at low temperatures. The conductivity of the crystals is shown to be proportional to T ^?1/2 in a broad temperature range. The mechanism of conduction in the crystals is discussed in terms of percolation theory.     

硼酸类复配物的固相制备及其热变色性能研究

采用固相法制备了龙胆紫-硼酸等系列可逆热致变色颜料.考察了其配比、无机填料的种类与用量、紫外线以及环境温度对其热变色性能的影响.结果表明:以龙胆紫:硼酸:氧化铝=1100:100～150制成的变色颜料变色敏锐,变色温度为65℃,复色时间为小于700s.     

γ射线辐照对PA6/PTFE合金吸水与力学性能的影响

为了探讨辐照对尼龙6(PA6)基共混材料吸水性能和力学性能的影响,制备了PA6和聚四氟乙烯(PTFE)共混合金并在室温下进行不同剂量的60Coγ射线辐照.通过吸水率测试、准静态拉伸和弯曲实验以及缺口冲击测试,研究了辐照对PA6/PTFE共混体系吸水性能以及吸收水和辐照剂量对共混合金动静态力学性能的影响.结果表明,辐照过程引发交联反应,共混合金的拉伸强度、拉伸模量和弯曲模量均随辐照剂量的增大而增大,而缺口冲击强度和吸水率则随之减小.吸收水对共混合金缺口冲击强度的影响与合金组分有关.PTFE含量较低时,吸收水抑制PTFE对合金冲击强度的减弱作用;当PTFE的质量分数大于7%时,吸收水反而加剧PTFE对材料冲击强度的减弱效应.此外,PA6/PTFE合金的吸水率随PTFE含量的增加而降低,而弯曲模量则先增后减.     

Electrical and thermoelectric properties of surfactant-assisted calcium cobalt oxide nanoparticles

Journal of Materials Science: Materials in Electronics - We are in need of clean, cost-effective and renewable energy sources because of the energy crisis and global warming. Thermoelectric...     

Effect of gamma irradiation and silver doping on YBCO superconductor

The effect of -irradiation and silver doping on the properties of YBCO superconductors has been studied by electrical resistance measurements and x-ray diffraction techniques. The zero-resistance superconducting transition temperature of (YBCO)_1–xAg _x systematically increase by about 2 K with an increase of Ag content up tox=0.04. Further increase in Ag content decreases the transition temperature. The normal-state resistance decreases up to a factor of 3.4 with an increase of Ag content. No significant change in the transition width has been observed due to silver addition up tox=0.30. Undoped YBCO and the Ag-doped specimens of (YBCO)_1.96Ag_0.04 were irradiated with-rays up to an integrated-dose of 77 MR. The normal-state resistance of the specimens gradually increases and the transition temperature slightly decreases with increase of-dose. The intensities of the x-ray diffraction peaks of the monolayers of the sample powders decrease with -irradiation without noticeable change of diffraction angles or peak widths. These observations indicate that the high-T _c supconductor YBCO is quite sensitive to-irradiation but drastic lattice expansion does not occur up to a-dose of 77 MR.     

The effects of copper and iron oxide additions on the sintering and properties of Y-TZP

Yttria-tetragonal zirconia polycrystals (Y-TZP) with a range of yttria contents were prepared from powders neutralized during processing with ammonium hydroxide and sintered at temperatures of 1300–1700 °C. Iron or copper oxide was ádded and studies made of body characteristics, mechanical properties and ageing resistance. Densification was aided by higher yttria concentrations. The effects of the oxide additives were dependent on amounts present and sintering conditions, including ramp rates and holding temperatures. Ageing resistance was significantly improved for both oxide additions fired to lower temperatures but rapid transformation to monoclinic phase was observed for materials with larger grain sizes associated with higher sintering temperatures.     

Modification of the phase transition in cesium niobate under gamma irradiation

Ultrasonic techniques are used to study the phase behavior of cesium niobate under gamma irradiation. It is shown that the irradiation shifts the anomalies of the internal friction and velocity of sound toward lower temperatures as a result of structural ordering of cesium niobate crystals. Pis’ma Zh. Tekh. Fiz. 23, 70–74 (August 12, 1997)     

Effect of PbO layers with nickel oxide and vanadium oxide additions on the thermal oxidation of InP

IR and ultrasoft x-ray emission spectroscopy data indicate that the thermal oxidation of PbO/InP structures with additions of transition-metal (nickel and vanadium) oxides leads to the formation of multicomponent layers consisting of nickel, vanadium, lead, and indium phosphates. These oxide additions to PbO nanolayers accelerate the thermal oxidation of InP. A small amount of vanadium oxide added to PbO gives rise to a significant contribution of a catalytic mechanism to the accelerated thermal oxidation of InP. The principal distinction between the PbO/InP and (PbO + NiO)/InP structures is that the thermal oxidation of the latter leads to the formation of an In_xNi_yP_z transition layer, which influences the growth rate and the composition of the resulting layer.     

Effect of thickness on the thermoelectric properties of PbS thin films

A non-monotonic dependence of the thermoelectric properties of PbS epitaxial films grown on (001)KCl substrates and covered with an EuS protective layer on the PbS layer thickness (d=2-200 nm) was detected at room temperature. The complex character of the dependence on d is attributed to a competition between percolation phenomena and size quantization. Within the framework of percolation theory on the basis of experimental data, the critical exponent for the electrical conductivity was determined. Oscillations in the thickness dependence of the kinetic coefficients are attributed to quantum size effects occurring in thin layers.