Particle refinement and graphene doping effects on thermal properties of potassium picrate

The ultrafine potassium picrate (KPA) was prepared under the action of crystalline controlling agent and modified by graphene. KPA, ultrafine FKPA, and graphene-doped GKPA were studied by the particle size analysis, DPTA, DSC, and thermal sensitivity tests. The particle size arranged in an increasing order is FKPA < GKPA < KPA. The kinetic and thermodynamic parameters of thermal decomposition are ranked as FKPA < GKPA < KPA. The results indicate that the particle refinement increases the thermal sensitivity, because the ultrafine particles have large surface area and high surface bonding energy which endow them with high reaction activity. The doped-graphene nanoparticles with larger surface area partly hinder the effective collisions of KPA particles and accelerate the heat dispersion. Thus, the graphene doping improves the thermal stability, while still preserving the ultrafine size. GKPA has better thermal stability than FKPA and higher thermal sensitivity than KPA.     

高性能镓酸镧基电解质燃料电池

制备并用多种电化学方法研究了LaGaO3基高性能中温固体氧化物燃料电池的电极和电解质材料，组装出了高性能单电池.实验发现， Co掺杂的La0.8Sr0.2Ga0.8Mg0.2O3电解质中， Co含量的增加显著提高了电解质的氧离子电导率，电解质的氧迁移数略有减小，是非常好的中、低温燃料电池电解质.钴掺杂的电解质不仅显著减小了电池的欧姆电阻，而且减小了电池的阴、阳极极化过电位.以La0.8Sr0.2Ga0.8Mg0.11Co0.09O3为电解质时电池在1073、973、873 K下的最大输出功率密度分别达到1.77、0.92、0.41 W•cm－2，是非常有前景的电池体系.     

Effect of zinc(II) doping on thermal and optical properties of potassium hydrogen phthalate (KHP) crystals

The influence of doping the transition metal Zn(II) on potassium hydrogen phthalate (KHP) crystals has been studied. A close observation of FT-IR and XRD profiles of doped and undoped samples reveals some minor structural variations. It appears that the crystal undergoes considerable lattice stress as a result of doping the bivalent zinc. Furthermore, the possibility of cation vacancies aroused owing to the substitution of K¹⁺ by Zn²⁺ could result in a defective crystal system. Energy dispersive spectra reveal the incorporation of Zn(II) in the crystalline matrix of KHP crystals. Differential scanning calorimetry (DSC) and TG-DTA studies reveal the purity of the sample and no decomposition is observed below the melting point. Small quantity additions of Zn(II) enhance the fluorescence intensity of KHP crystals. The doping results in morphological changes and significantly improves the second harmonic generation (SHG) efficiency of the host crystal.     

Stoichiometric ratio and doping effects on the thermal properties of sodium potassium sulphate crystals

The influence of stoichiometric ratio on the phase transition of sodium potassium sulphate (Na_xK_1–x)₂SO₄ crystals is investigated in the temperature range 300–500 K. The stoichiometric ratiox is chosen to bex=0.2, 0.3, 0.4, 0.8 and 0.9. The study has been carried out by using differential scanning calorimetry, DSC technique. The value of the specific heat,C _p, at the transition temperature,T _c , increases asx is increased up tox=0.4 and then decreases for higher values ofx. The change in the specific heat, C _p, is following a relation of the form C _p C _p (T–T _c /T _c )^– with = 0.12 which is in a fair agreement with the 3d Ising model. Insertion of Cu²⁺ ions into the lattice of (Na_xK_1–x)₂SO₄ crystals leads to a multiple peak in the temperature dependence ofC _p. The results are discussed from thermodynamical point of view.We would like to thank Prof. E. F. El-Wahidy, Prof. of Solid State Physics and Head of Physics Department, Faculty of Science, Alexandria University, for his interest and support of this work.     

Effect of aliovalent doping on the transport properties of lanthanum cuprates

Cuprates with perovskite-related structure and the general formula (A=Ca, Ba, Sr; B=Li; x=0.1, 0.2, 0.3; y=0, 0.1) were prepared by the citrate route. Their structures were studied by X-ray powder diffraction and their electrical conductivities (as a function of temperature) by four-point DC measurements on sintered bars. The highest values of electrical conductivity were observed for the x=0.3 Sr-doped cuprate, which showed a metallike temperature dependence. Ba-doped cuprates showed a transition from semi-conducting to metallic temperature dependence of conductivity. The extent of A-site deficiency is small and had the effect of slightly decreasing the conductivity and thermal expansion coefficient. Li solubility was also found to be small, but it reduced conductivity drastically, due in part to the disruption of the copper–oxygen conductive network. Reactions between cuprates and a typical manganite fuel cell cathode, and Pt and Pd contacts were observed at 1,000 °C.     

Effect of thermal degradation on rheological properties for poly(3-hydroxybutyrate)

Thermal degradation at processing temperature and the effect on the rheological properties for poly(3-hydroxybutyrate) have been studied by means of oscillatory shear modulus and capillary extrusion properties, with the aid of molecular weight measurements. Thermal history at processing temperature depresses the viscosity because of random chain scission. As a result, gross melt fracture hardly takes place with increasing the residence time in a capillary rheometer. Moreover, it was also found that the molecular weight distribution is independent of the residence time, whereas the inverse of the average molecular weight is proportional to the residence time. Prediction of average molecular weight with a constant molecular weight distribution makes it possible to calculate the flow curve following generalized Newtonian fluid equation proposed by Carreau as a function of temperature as well as the residence time.     

Effect of heterovalent doping on photostimulated defect formation in CsPbBr3

Two series of CsPbBr₃ perovskites doped with Bi or Ag were synthesized and investigated for photostimulated defect formation. It was demonstrated that the type and concentration of dopants strongly affect the absorption spectra and kinetics of photostimulated defect formation.     

Effects of doping on the thermal stability of spindle-shaped γ-Fe2O3 particles

Spindle-shaped α-FeOOH particles were synthesized using the chemical coprecipitation method in Fe(CO₃)_x(OH)_2(?x) suspensions system by adding metallic ions. The spindle-shaped γ-Fe₂O₃ particles were obtained by dehydration of α-FeOOH, and subsequent reduction and oxidation. Its thermal stability was investigated by differential thermal analysis (DTA). It was found that the transition temperature of γ-Fe₂O₃→α-Fe₂O₃ of samples doped with metallic ions is higher than that of the pure γ-Fe₂O₃ and increasing with increase of the size of the metallic ions, and γ-Fe₂O₃ by doping with two or more different metallic ions together has even higher thermal stability. The origin of the improved thermal stability was discussed. Additionally, the magnetic properties of γ-Fe₂O₃ were measured.     

Effect of transition metal doping and carbon doping on thermoelectric properties of YB66 single crystals

We have been investigating the high-temperature thermoelectric properties of some novel rare earth borides with a structure containing B₁₂ icosahedra. Doping effects on the TE properties in such systems were investigated for the first time. A series of Nb-doped YB₆₆ and C-doped YB₆₆ single crystals were grown by the floating zone method. The Nb-doped compounds have approximate chemical formulas ranging from YNb_0.30B₆₆ to YNb_0.33B₆₆ while the C-doped compound has a formula of YB₆₆C_0.6. The effect of Nb-doping on the thermoelectric properties was not monotonic and appears to be complex. As a result of Nb-doping, the room temperature resistivity and the characteristic temperature T₀ were considerably reduced. At room temperature the power factor of the Nb-doped YB₆₆ sample with 89% site occupancy was three times greater than that of non-doped YB₆₆. However, in the important high-temperature region, the non-doped sample actually exhibited the highest power factor for . Furthermore, owing to a structural feature of YB₆₆, thermal conductivity actually increases with doping of transition metals. Taking into account all the thermoelectric properties, transition metal doping of YB₆₆ is therefore not suitable for our purposes. On the other hand, doping of carbon, which is assumed not to go into the same sites as the transition metals, yielded a lowering of the thermal conductivity. Furthermore, contrary to Nb-doping, carbon doping did not result in a reversal of the relative magnitude of resistivity at extremely high temperatures and therefore, an increase in the figure of merit of factor 2 was realized at 1000 K.     

Effect of water release on thermal properties of polyaniline

Conducting polyaniline (PANI) was studied by thermal expansion measurement, thermogravimetric analysis and by electrical conductivity measurement. Relative elongation and coefficient of thermal expansion (CTE) were determined from room temperature to 60 °C. Various temperature profiles were used. During heating, the treatment of samples at a constant temperature higher than the room temperature, or evacuation, water was released from the samples. Water release was detected by mass and thermogravimetric analysis. Water release was connected with shrinkage of the PANI samples and apparent negative CTE in the first thermal cycle. In the following thermal cycles, it increased and reached a positive value. CTE of PANI attained values in the range of ?30 × 10^?6 K^?1 up to 20 × 10^?6 K^?1 in dependence on water content in the sample before measurement and on experimental conditions of measurement. Irreversible shrinkage of the polymer was the largest in the first thermal cycle. Water release exhibited a strong time and temperature dependence, and it was only partially reversible. The electrical conductivity was measured by a four-point van der Pauw method. Relative electrical conductivity decreased with amounts of water release. Relative decrease of electrical conductivity reached as far as 20% after evacuation 7 h at the room temperature.     

Effect of glass cullet on thermal properties of kaolinite

Waste compromises environmental preservation as well human health in many countries. Recycling is an alternative that sometimes represents the only economical activity for a significant population in the big cities. Almost 3% of waste materials in Brazil are vitreous. Ceramic production adding waste glass is possible with advantages of costs reduction associated to decrease on firing temperatures and to the raw material itself. At present paper up to 80 mass% of waste glass was added to clay. The sintering temperature decreased linearly and the shrinkage increased with glass content, an effect more pronounced for high glass amount.     

Effect of thermal treatment on interfacial properties of beta-lactoglobulin

The changes in the secondary conformation and surface hydrophobicity of beta-lactoglobulin subjected to different thermal treatments were characterized at pH values of 7, 5.5 and 4 using circular dichroism (CD) and hydrophobic dye binding. Heating resulted in a decrease in alpha-helix content with a corresponding increase in random coil at all pH values, this change being more pronounced for small heating times. Heating also resulted in an increase in surface hydrophobicity as a result of partial denaturation, this increase being more pronounced at pH 4. Thermal treatment resulted in a shift of the spread monolayer isotherm at air-water interface to smaller area per molecule due to increased flexibility and more loop formation. Thermal treatment led to an increase in interfacial shear elasticity and viscosity of adsorbed beta-lactoglobulin layer at pH 5.5 and 7. Interfacial shear elasticity, shear viscosity, stability of beta-lactoglobulin stabilized emulsion and average coalescence time of a single droplet at a planar oil-water interface with adsorbed protein layer exhibited a maximum for protein subjected to 15 min heat treatment at pH 7. At pH 5.5, the interfacial shear rheological properties and average single drop coalescence time were maximum for 15 min heat treatment whereas emulsion stability was maximum for 5 min heat treatment. At pH 7, thermal treatment was found to enhance foam stability. Analysis of thin film drainage indicated that interfacial shear rheological properties do not influence thin film drainage.     

Current-voltage characteristics of grain boundaries in polycrystalline Sr-doped LaGaO3

The oxide-ion current across grain boundaries in a polycrystalline LaGaO(3) ceramic doped with 1 mol% Sr(2+) increases non-linearly with the applied dc-bias to present a transition from ohmic to superohmic where the bias exceeds the thermal voltage, verifying that a Schottky-type potential barrier exists at the grain boundary in acceptor-doped LaGaO(3) to limit the internal current.     

Effects of Se doping on thermoelectric properties of Zn4Sb3 at low-temperatures

The thermoelectric properties of Se-doped compounds Zn₄(Sb_1?xSe_x)₃ (x = 0, 0.005, 0.01, 0.015) have been studied. The results indicate that low-temperature (T < 300 K) thermal conductivity of moderately doped Zn₄(Sb_0.99Se_0.01)₃ reduce remarkably as compared with that of Zn₄Sb₃ due to enhanced impurity (dopant) scattering of phonons. Electrical resistivity and Seebeck coefficient are found to increase and then decrease moderately with the increase in the Se content. Moreover, the lightly doped compound Zn₄(Sb_0.99Se_0.01)₃ exhibits the best thermoelectric performance due to the improvement in both its thermal conductivity and Seebeck coefficient. Its figure of merit, ZT, is about 1.3 times larger than that of pure Zn₄Sb₃ at 300 K.     

Effect of the doping of a metal oxide by platinum on its oxidizing properties

Oxidation is very slow on supported metals or oxides whose contact surface between the catalytic active phase and the carbonaceous particle to burn is poor. On the contrary, some pure oxides are more active. Oxidation by oxygen proceeds by partial reduction of the oxide and the rate-determining step of the reaction is the reoxidation of the reduced solid. Addition of a small amount of platinum catalyzes that reoxidation.     

Effect of thermal transport mechanisms on the thermal decomposition of CaCO3

Isothermal and dynamic techniques were employed to examine the rate of weight loss of CaCO₃. Thermogravimetric studies were conducted in atmospheres of He, N₂, Ar, and various percentage of CO₂ in Ar. Three methods for deriving kinetic parameters from thermogravimetric data were used and these results were then compared with data obtained from isothermal investigations done on identical samples. It was found that the higher the thermal conductivity of the atmosphere, the more repidly the reaction proceeded. Also, as the percentage of CO₂ in Ar increased, the temperature range of the decomposition became higher and narrower, resulting in a higher activation energy.