The temperature-dependence of the electrical resistance of Al-Zn 78 wt.% was measured during linear cooling of the samples in the range of eutectoidal decomposition. The resulting resistancevs. temperature curves were analysed by:deriving the temperature-dependence of the volume fractionx(T) of theη precipitate;fitting the theoretical functionx(T)=xh(T)+xc(T) following from numerical integration of the reaction rate equations for the simultaneously occurring homogeneous (H) and cellular (C) precipitation processes.
The system of sulfoaluminate ferrite belite (SAFB) clinkers premixed with Portland cement (PC) in mass ratio 85:15 in combination
with hydroxypropylmethyl cellulose (HPMC) or polyphosphates(poly-P) was used for the syntheses of Macro-Defect-Free (MDF)
materials. The subsequent moisture treatment and thermal stability of these MDF materials were investigated. The effect of
individual humidity upon the evolution of mass is more intensive than the effects of composition of MDF materials or duration
of the original MDF material synthesis. Detailed values of mass changes at 100% relative humidity (RH) and under ambient conditions
are strongly affected by the nature of polymer used. A significant improvement of moisture resistance of MDF materials is
achieved when the materials are dried after 24 h of finishing the pressure application. In the inter-phase section of MDF
material samples, the content ofC-(A,F)-S hydraulic phases, mainly tetracalcium aluminate ferrite monosulphatehydrate (AFm) decomposing by 250°C and CaCO3 decomposing at 600–700°C increase after the moisture attack, while cross-links in AFm-like section with typical thermoanalytical
traces in temperature region 250–550°C remain intact.
Authors:C. Chaudhari, K. Dubey, Y. Bhardwaj, Virendra Kumar, N. Goel, and S. Sabharwal
Radiation induced grafting of acrylonitrile (ACN) on ethylene-propene diene terpolymer (EPDM) rubber film was investigated
by mutual radiation grafting technique. Effect of experimental variables viz. radiation dose, dose rate, type of solvent and
monomer content on extent of grafting was studied. From the kinetic studies a mathematical relation Rgα[M]0.7D0.68 showing non-linear relationship for rate of grafting with monomer concentration and dose was deduced. The grafted samples
showed increased hardness and oil resistance.
The EU Chocolate Directive 2000/36/EC allows the use of the vegetable fats CBEs and CBIs up to a maximum of 5% in chocolate. Manufacturers and users must know how this has an influence on the properties of chocolate. The objective of the work reported here was to find out by systematic investigations, which effect CBEs/CBIs have on the quality parameters, hardness and heat resistance of chocolate. The influence on the hardness was tested also under extreme practical storage conditions. The quality monitoring was performed up to one year. For the determination of the heat resistance the penetrometric method was used in the temperature range 25–32 °C measuring the maximum loading force, occurring during the penetration of a cylindrical probe of 2 mm diameter with 4 mm penetration. The correlation between the average maximum loading force, relevant to the hardness of chocolate, and the temperature can be described by a linear regression at 95% confidence level. Statistical analyses (correlation analysis, residual analysis, Durban-Watson statistic) showed that it is possible to define the heat resistance of solid chocolate in the temperature range of 25–32 °C by the slope and the ordinate intercept of the regression line of the loading force vs. temperature for given parameters (composition, storage, experimental layout, etc.). For the determination of the hardness of the chocolate also the penetrometric method was used to measure the maximum loading force occurring during the penetration of a needle probe with 2 mm deformation. The hardness of the chocolate samples determined with the penetrometric method and statistical analysis (One-Way, Two-Way Analysis of Variance, Dunnett’s comparisons) is significantly dependent on the composition and storage conditions, where the storage conditions are the dominant factor. The results show that the differences in hardness between the chocolate samples with CBE/CBI and those without CBE/CBI, both stored in the cellar (cold storage), are marginal. After one week of storage the sample with CBI has nearly the same hardness as the standard sample with CB, whereas the sample with CBE was slightly softer. The differences are slightly clearer for the northern storage room (moderate temperature) and for the southern room (warm temperature). After a definite storage time the hardness of all samples increased and was in the case of the southern storage room (warm temperature) up to twice as high. The quality monitoring up to one year showed that the reason for this increase in hardness is not a special storage time but the increasing temperatures with the beginning of the warm season and the cyclic change of the temperature during day and night. So an explanation for this unexpected increase in hardness can be a thermocyclic hardening of the chocolate samples under these storage conditions.
With the aims of accounting for the effects of the internal thermal resistance of the sample holder on the parameters of recorded DTA curves, and of estimating the difference between the instrument with a thermally insulated sample holder and the gradientless model, a novel two-point method of differential thermal analysis has been developed. Its essence is that two thermoanalytical curves are recorded simultaneously, with the differential thermocouple at central and side positions relative to the sample. The theory of the method has been elaborated, and formulae are derived which allow quantitative estimation of the thermal resistance of the sample holder, depending on the manner of packing and on the state of the sample in the holder, and which also indicate the optimum manner of packing. If the packing is not dense and not uniform, the thermal resistance of the holder increases and the accuracy of instrument calibration at the tail-end of the differential curve decreases by 10–20%. Through introduction of a correction term into the formula, this effect can be eliminated. A basic formula is given for DTA calculation in the general case of a sample holder with non-zero internal thermal résistance.
Authors:R. Puchert, U. Menzel, A. Bärwolff, M. Voβ, and Ch. Lier
The thermal behaviour of high-power GaAlAs/GaAs laser arrays is described by a comprehensive thermal two-dimensional finite-element model which takes several heat sources into account. The influence of these different heat sources on the two-dimensional temperature distribution in the laser array has been investigated. The power densities of the heat sources related to the active region were calculated by an analytic description of the temperature dependent processes as spontaneous emission, Auger recombination and interface recombination. The results of our numerical calculation show, that the local distribution of the heat sources has a strong influence on the lateral temperature profile and on the maximum temperature in the active region of the array, i.e. on the thermal resistance. The calculated temperature profiles are in a good agreement with the measured lateral temperatures at different injection currents and heat sink temperatures. The difference between calculated and measured maximum temperature is lower than 0.75°C.
Authors:R. Pathak, A. Khuda Bukhsh, S. Dey, U. Ghosh, B. Sen Gupta, M. Semwal, and N. Bhattacharyya
The paper aims to investigate cytogenetic and apoptotic responses of γ-irradiation in a radio-resistant cell strain designated
as M5. Induced micronuclei, chromosomal aberrations, nuclear fragmentation and nucleosomal ladders by γ-irradiation were less
at equal doses in M5 cells in comparison with that obtained in the parental Chinese hamster V79 cells. However, at equal survival,
there were no differences in the end points studied. Results indicate that the residual damages that lead to reproductive
cell death also resulted in the cytogenetic and apoptotic responses. We speculate that the repair efficiency in M5 cells was
more efficient and increased DNA repair could be the cause of radiation resistance observed in M5 cells.
The yields of hydrogen and ethylene from the radiolysis of 15-crown-5, 18-crown-6, dibenzo-18-crown-6, and dicyclohexyl-18-crown-6 ethers have been measured. The quantities obtained are compared with the ones for PEG-300, PEG-600 and 1,4-dioxane measured under the same conditions. The hydrogen yields range from about 1 to nearly 2 molecules per 100 eV and these of ethylene range from 0.02 to 0.15 depending on the irradiation conditions. From the viewpoint of the rate of radiation decomposition, there is no much difference between crown ethers and their analogues including 1,4-dioxane, the simplest molecule in the series.
Authors:G. Vourlias, N. Pistofidis, D. Chaliambalias, K. Chrissafis, El. Pavlidou, and G. Stergioudis
Zinc coatings on ferrous substrates are possible to be applied with thermal spraying. In the present work the corrosion behavior of zinc thermal sprayed coatings deposited on low carbon steel St-37 was examined in a simulated marine atmosphere (salt spray chamber-SSC) and in a dry atmosphere at elevated temperature (400°C). The corrosion progress was examined by means of optical microscopy, scanning electron microscopy, X-ray diffraction and thermogravimetric analysis. From this investigation it was deduced that in the SSC the coating is uniformly corroded, while the main corrosion products are hydrated zinc oxides and chlorides. By contrast at 400°C only a thin, compact and continuous film of ZnO is formed on top of the coating, which remains adherent to the ferrous substrate.