Modeling of high temperature- and diffusion-controlled die soldering in aluminum high pressure die casting

Soldering of cast alloys to the dies has been a continuing source of die surface damage in the aluminum die-casting industry. To reduce the repair and maintenance costs, an approach to modeling the damage and predicting the die lifetime is required. The aim of the present study is the estimation of the die lifetime based on a quantitative analysis of die soldering in the framework of the numerical simulations of the die-casting process.Full 3D simulations of the process, including the filling, solidification, and the die cooling, are carried out using the casting simulation software MAGMAsoft. The resulting transient temperature fields on the die surface and in the casting are then post-processed to estimate the die soldering.The present work deals only with the metallurgical/chemical kind of soldering which occurs at high temperatures and involves formation and growth of intermetallic layers. The die-soldering model combines two approaches available in literature, describing the two aspects of die soldering: the growth of the intermetallic layer, and the thermal and metallurgical conditions in the layer that lead to the die soldering. The theoretical model is then extended with the treatment of the intermetallic layer growth controlled by the idealized effective diffusivity and with the treatment of solder strength dependent on the temperature and liquid fraction within the layer. The solder strength locally on the die surface is calculated as a function of the number of die-casting cycles. This also provides the estimation of the die lifetime defined as the number of cycles until the critical solder strength level is reached.Proper validation of the model is required, and the model parameters (the critical solder strength value, among others) need to be calibrated by measurements and data from the die-casting industry.As an example, the model is applied to several cases of high pressure die casting (HPDC) where A380 alloy parts are cast in the H13 steel die. The predicted locations of the higher strength of soldering appear in the “hot spot” areas of the die surface in agreement with the reports in literature. The influence of several casting process parameters such as cooling/spraying efficiency and other parameters that control the thermal history of the die and the casting is in agreement with the expected behavior.     

Determination of the radionuclide composition and burn-up of high-burn-up WWER-1000 fuel by destructive methods

A sample of WWER-1000 spent nuclear fuel (SNF) with the burn-up of approximately 50 GW day (t U)^?1 was studied by methods of destructive analysis. Data on the content of isotopes of U, Pu, Am, Cm, Nd, and Cs are given. The methods used are briefly described. These include anion exchange and extraction chromatography, thermal ionization mass spectrometry, luminescence analysis, and ??- and ??-ray spectrometry. The main method of the study is isotope dilution followed by mass-spectrometric analysis. The data obtained will be used for developing of a low-waste and low-cost technology for preprocessing of highburn-up SNF and also for checking the accuracy of calculation of heavy actinide content in SNF and for improving computation methods and programs intended for calculation of the SNF nuclide composition in relation to the fuel burn-up in WWER-type reactors. The Nd and Cs isotopes were used as burn-up monitors.     

Isotopic composition of plutonium in the bottom deposits of the Norwegian Sea and Greenland Sea and identification of the sources of contaminationhearder

The results of measurements of the isotopic atomic ratios²³⁸Pu/²³⁹Pu,²⁴⁰Pu/²³⁹Pu,²⁴¹Pu/²³⁹Pu,²⁴²Pu/²³⁹Pu in samples of bottom deposits are presented. The role of the main sources of plutonium contamination of the region is examined. It is shown that the contribution of the α activity of industrial plutonium (^238–240Pu) in bottom sediments from the European reprocessing plants, mainly, Sellafield (Great Britain), on the background due to global fallouts is 20 to 55% of the total α activity and 70–95% for the β activity (²⁴¹Pu). No escape of reactor and weapons plutonium from the nuclear powered submarine “Komsomolets” into the environment was observed. The lower limit of sensitivity of the method is 10⁻¹⁴g of plutonium in a sample, which corresponds to a plutonium α activity of 0.02 mBq in a 10 g sample of bottom deposits, 4 tables, 26 references. Translated from Atomnaya énergiya, Vol. 87, No. 4, pp. 286–294. October, 1999.     

Determination of the isotope composition and content of U and Pu in environmental samples on the ultrasmall level by isotope dilution mass spectrometry

A procedure was developed for isolation and determination of the isotope composition and content of U and Pu on the ultrasmall level in environmental samples of technogenic origin, characterized by a small mass (up to 0.l g) and complex macrocomposition. The procedure is based on isotope dilution and mass-spectrometric measurement of the isotope ratios (IDMS). Subnanogram quantities of U and Pu were isolated using a modification of resin bead technique, involving sorption on a limited number of anion exchanger beads and allowing, after desorption, analysis of the solutions containing the selectively isolated nanogram quantities of U or 10^–12–10^–15 g of Pu. The measurements were carried out on thermal ionization mass spectrometers manufactured in Ukraine and Russia with a modernized ion registration system utilizing a position-sensitive detector based on microchannel plates. Uranium was analyzed by the laser luminescence method suitable for measuring fractions of nanograms of U accurately to within 10%. This procedure, combining highly sensitive methods of isolation of ultrasmall quantities of U and Pu with the mass-spectrometric method of analysis, is applied at the Radium Institute (acting as a national laboratory of IAEA) and at the Institute of Analytical Instrument Designing, Russian Academy of Sciences, in analysis of inspection samples submitted by IAEA for monitoring the activity of nuclear facilities under the Treaty on Nonproliferation of Nuclear Weapons.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 464–470.Original Russian Text Copyright © 2004 by Stepanov, Makarova, Domkin, Pevtsova, Aleksandruk, Nikolaeva, Chubinskii-Nadezhdin, Kulikov.     

Abnormalities in electrical and acoustic properties of thermoplastic polyurethane

The temperature dependence of ultrasonic pulse velocity C and specific volume resistance ρ_v of crystallizing thermoplastic polyurethane (TPUR) was investigated. It was revealed that under certain conditions TPUR acquired abnormally low ρ_v values and C values uncharacteristic of polymers. An explanation for the observed abnormalities could be based on the assumption of the presence of ‘hot’ electrons in TPUR.     

Adenylosuccinate synthetase of the yeast Saccharomyces cerevisiae: purification and properties

Motor and sensory nerve conduction velocities (MNCV and SNCV) were reduced in the sciatic nerve of rats after 4 weeks of untreated streptozotocin-induced diabetes, and declined further during the following 4 weeks. Treating diabetic rats with the novel peptide HP228 had no effect on the decline of MNCV after the first 4 weeks of diabetes but attenuated the decline in SNCV. HP228 treatment also prevented any further decline in MNCV or SNCV between weeks 4 and 8 of diabetes. Consequently, at the conclusion of the study, the nerve conduction velocities (NCVs) in treated rats were significantly (both P < .001) higher than in untreated diabetic rats. Reduced nerve homogenate Na+,K+-adenosine triphosphatase (ATPase) activity in diabetic rats was significantly (P < .05) increased by HP228 but remained significantly (P < .05) lower than in untreated controls. HP228 treatment also reduced nerve Na+,K+-ATPase activity of control rats compared with untreated controls (P < .05). There was no effect of HP228 on the hyperglycemia, nerve polyol accumulation, myo-inositol depletion, reduced nerve laser Doppler blood flow, thermal hypoalgesia, or reduced mean axonal caliber in diabetic rats or on any of these parameters in control rats. These data demonstrate that a novel peptide may protect against the slowing of nerve conduction in prolonged diabetes and that the mechanism of action is unrelated to aldose reductase inhibition, prevention of nerve ischemia, or axonal atrophy. HP228 may prove a potential therapeutic agent for the treatment of prolonged diabetic neuropathy.