Search Results
Abstract
We have examined the isotopic compositions of lead reported for 55 terrestrial and 65 lunar samples. The lead ages indicate that the 4.55 billion years generally accepted as the age of the solar system refers instead to the time of the breakup of the meteorite parent body.
Abstract
Mössbauer spectroscopy, X-ray diffractometry and microprobe analysis were used to study electrodeposited Fe−Ni−Cr (40–50% Fe, 40–47% Ni, 3–5% Cr) alloys isothermally aged at 500°C from 5 minutes to 100 hours in an inert argon gas atmosphere. The main phase of the as-deposited samples exhibits ferromagnetic microcrystalline behavior, whereas the thermally prepared samples of same composition are always paramagnetic. The dominant effect of ageing is an oxidation process which resulted in the formation of hematite and magnetite iron oxides in considerable amounts and which are attributable to the presence of oxygen inclusions in the as-electrodeposited samples.
Abstract
In this comparative study, the effect of gamma rays on the ageing characteristics of poly(ethylene-co-vinyl acetate) (EVA) and poly(ethylene-co-vinyl acetate)/carbon black mixture (EVA/CB) was investigated in terms of thermal stability. EVA, containing 13% vinyl acetate (VA), and EVA/CB, containing 13% VA and 1% carbon black (CB), were aged at 85°C in air up to 30 weeks for thermal ageing. Same substances were aged by means of UV light with a wavelength in the vicinity of 259 nm, in air, up to 400 h for UV ageing. Same substances were also irradiated with gamma rays at ambient conditions up to 400 kGy. Following these experiments, samples which had been irradiated with gamma rays, were subjected to thermal and UV ageing under the same conditions as for unirradiated samples. Dynamic thermogravimetry studies were performed for determination of the thermal stabilities of the samples. 10 and 50% mass losses were calculated for the samples from their respective curves. As a result of thermal analysis experiments, it was found that CB dramatically loses its protective property against thermal ageing of EVA after gamma irradiation. On the other hand, gamma irradiation does not have any significant effect on the UV ageing characteristics of EVA and EVA/CB in terms of thermal stability.
Abstract
The thermal degradation of new, and artificially aged fine Ulster linen and archival linen specimens from 19th century paintings were compared using thermogravimetric analysis and differential scanning calorimetry. Thermal degradation data from new and artificially aged linen were found to be similar in nature. Archival specimens showed a decreased major degradation temperature, an increase in char remaining at the end of the experiment and some evidence of a depressed glass transition temperature. These indicate natural ageing through chain scission. Evidence of a two-stage degradation process was observed in some archival specimens suggesting that an unknown additive was present.
Abstract
The authors present a kinetic investigation of the generation of manganese ferrite by the ageing of some coprecipitates in contact with the residual solution.
Thermal analysis is found to be suitable methods to investigate the electrical aging of polyethylene.
Introduction Iron Age pottery from an archeological site in the Galilee was analyzed [ 1 ]. The pottery was excavated at Tel-Hadar, on the eastern shore of the Sea of Galilee. The excavation was carried out in the framework of
Abstract
A common scepticism towards the application of many product formulations results from the fact that their long-term stability is difficult to predict. In the present study we report on a new approach of kinetic analysis of the oxidation reactions of natural rubbers with and without stabiliser in an oxygen atmosphere at moderate temperatures using CL measurements carried out on a newly-developed instrumentation. The kinetic parameters of the oxidation process, calculated from the chemiluminescence’s signals by means of the differential isoconversional method of Friedman, were subsequently applied for the simulation of the rubber aging under different temperature profiles. The presented results are the first stage of research by using the chemiluminescence method to measure the oxidative aging of rubber and predicting the life time of rubber items.
Abstract
Multilayers constituted by very thin films of Fe and Al, deposited by thermal evaporation and magnetron sputtering techniques and then aged in air at temperatures in the 300–400 K range for times up to 200 h, were analyzed by means of XRD, CEMS, XPS and AES measurements. Fe(Al) solid solutions form during evaporation because of interdiffusion phenomena at the Fe–Al interfaces, while Al undergoes oxidation during sputtering deposition and, consequently, the multilayers are constituted by Fe intercalated with Al2O3 films. Aging treatments in oxidizing environments induce no significant modification in sputtered multilayers while, on the contrary, the evaporated multilayers show the effects of both interdiffusion and oxidation phenomena.
Abstract
Thermal, chemical and rheological properties of ultraviolet aged asphalt binder were characterized by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) and dynamic shear rheometer (DSR), respectively. Asphalt binder samples were made with different film thickness (50, 100, 200 and 500 μm) and suffered different ageing time (0, 48, 96 and 144 h), at a certain UV radiant intensity of 20 w m–2 in a self-made accelerated ageing oven. The results indicate that the UV light ageing would lead to the improvement of thermal behavior and the growth of the glass transition temperature of asphalt binder. This type of ageing can be also reflected from the FTIR spectra in terms of the characteristic peaks of the carbonyl groups and sulphoxides. The UV light ageing can change some rheological parameters of asphalt binder, such as complex modulus and phase angle. The ageing degrees of asphalt binder by this type of ageing test are mainly related to the ageing time and film thickness of the sample.
