Influence of T4 Heat Treatment on Tribological Behavior of Za27 Alloy Under Lubricated Sliding Condition

The effects of heat treatment on the microstructure, hardness, tensile properties, and tribological behavior of ZA27 alloy were examined. The alloys were prepared by conventional melting and casting route. The heat treatment of samples included the heating up to 370 °C for 3 or 5 h, quenching in water, and natural aging. Lubricated sliding wear test were conducted on as-cast and heat-treated ZA27 samples using block-on-disc machine. The friction and wear behavior of alloys were tested in contact with steel discs using combinations of three levels of load (10, 30, and 50 N) and three levels of linear sliding speeds (0.26, 0.50, and 1.00 m/s). To determine the wear mechanisms, the worn surfaces of the samples were examined by scanning electron microscopy (SEM). The heat treatment resulted in reduction in the hardness and tensile strength but increase in elongation. The heat-treated alloy samples attained improved tribological behavior over the as-cast ones, under all combinations of sliding speeds and contact loads. The rate of improvement increased with duration of solutionizing process before quenching in water. Obtained tribological results were related to the effects of heat treatment on microstructure changes of alloy.     

Determination of 200 °C Isothermal Section of Al-Ag-Ga Phase Diagram by Microanalysis,X-ray Diffraction,Hardness and Electrical Conductivity Measurements

Ternary Al-Ag-Ga system at 200 °C was experimentally and thermodynamically assessed. Isothermal section was extrapolated using optimized thermodynamic parameters for constitutive binary systems. Microstructure and phase composition of the selected alloy samples were analyzed using light microscopy, scanning electron microscopy combined with energy-dispersive spectrometry and x-ray powder diffraction technique. The obtained experimental results were found to be in a close agreement with the predicted phase equilibria. Hardness and electrical conductivity of the alloy samples from four vertical sections Al-Ag₈₀Ga₂₀, Al-Ag₆₀Ga₄₀, Ag-Al₈₀Ga₂₀ and Ag-Al₆₀Ga₄₀ of the ternary Al-Ag-Ga system at 200 °C were experimentally determined using Brinell method and eddy current measurements. Additionally, hardness of the individual phases present in the microstructure of the studied alloy samples was determined using Vickers microhardness test. Based on experimentally obtained results, isolines of Brinell hardness and electrical conductivity were calculated for the alloys from isothermal section of the ternary Al-Ag-Ga system at 200 °C.     

Contribution of marine and continental aerosols to the content of major ions in the precipitation of the central Mediterranean

The region of the investigated receptor is situated in the southern part of the Adriatic Sea in the Mediterranean. The measuring station is located on the seashore, which, being considered as a border area, is representative for the qualitative and quantitative estimation of the influence of marine and continental aerosols on the content of major ions in precipitation. In the sampling period, precipitation in the region of the investigated receptor was more abundant during the summer and autumn than during the winter and spring. The most frequent precipitation heights were up to 20 mm, while high precipitation came exclusively from the continental region. The results of the measurements of ions readily soluble in water were used for the differentiation of marine from continental contributions of primary and secondary aerosols to their content in the precipitation. Using PCA, it was shown that main contribution of Cl(-), Na(+) and Mg(2+) came from primary marine aerosols, while the contribution from continental sources was dominant for the content of SO(4)(2-), NO(3)(-), NH(4)(+) and Ca(2+) in the precipitation. The continental origin of Ca(2+) was from a primary source, while SO(4)(2-), NO(3)(-) and NH(4)(+) were representatives of secondary aerosols produced by reactions between acid oxides and alkaline species in the atmosphere, but SO(4)(2-) and NO(3)(-) also exist in the precipitation as free acids. The origin of the trace elements Cd, Cu, Pb and Zn in the precipitation came from anthropogenic emission sources. The results obtained in this work are based on experimental data from 609 samples collected during the period 1995-2000.     

Some engineering properties of limestone: Tunnel Stra?ina case study (Croatia)

The paper presents geological and engineering geological characteristics of the Stra?ina Tunnel along the Bisko-Šestanovac section of the Zagreb-Split-Dubrovnik highway in Croatia. This paper compares the actual conditions of the rock mass during the excavation with a prediction model that preceded the excavation. From the engineering-geological viewpoint the rock mass in the tunnel was of a significantly higher quality than the prediction model. The specific geological feature of the Stra?ina Tunnel, with its right and left tunnel tube, is the passage of the right tunnel tube through a transgressive contact between Upper Cretaceous rudist limestones and Eocene foraminiferal limestones. Since this is the only tunnel in Croatia excavated through this particular transgressive contact, the geological and engineering properties of the transgression zone were up to now only assumed. Therefore, additional mineralogical, petrographical and engineering geological observations were carried out in order to determine and describe the transgression zone. The results are presented in this paper. In the left tunnel tube the contact between the mentioned litostratigraphical Units is of the fault type. This paper also briefly deals with the significance and cause of the overprofile excavation during tunneling through strongly karstified carbonate rocks. Consequently, special attention was paid to the overprofile during excavation since it can significantly affect tunneling costs.     

A CALCULATION METHOD OF OBTAINING DESORPTION ISOTHERMS OF BEECH (FAGUSMOESL4CA) WOOD

ABSTRACT

This paper presents the specific methods to obtain sorption isotherms. Sorption isotherms were first obtained experimentally for 20°C and 100°C and then, by using the presented method, isotherms were also obtained for 50°C and 80°C. The same treatment can be applied in finding any isotherm sorption in the temperature range between 20°Cand 100°C.

The experiments were carried out on beech (Fagus moesiaca) and sample dimensions were 3×3×3cm. Based on the results of the experiment, by regression analysis, the most suitable analytic formula was proposed. It relsites temperature and air humidity with the equilibrium moisture content in wood. Experimental results were compared with psychrometric tables and Bramhall's formula for desorption curves with good agreement. This proves that the method presented in this paper is precise and efficient to decrease the lime needed to obtain sorption isotherms experimentally.     

Fully-Naphthalenoid Hydrocarbons and their Conjugation Modes

Abstract

A fully-naphthalenoid hydrocarbon (FUN) is a benzenoid hydrocarbon whose all π-electrons can be (formally) grouped into disjoint naphthalene-units. The cyclic conjugation in FUNs is studied by means of the energy-effects of their various cycles. It is found that the dominant conjugation modes in FUNs are those involving the 6- and 10-membered cycles of the “full” naphthalene fragments. The cycles belonging to the “empty” domains of a FUN have significantly smaller energy-effects.     

A new method in designing compatibility and adhesion of EVA/PMMA blend by using EVA-<Emphasis Type="Italic">g</Emphasis>-PMMA with controlled graft chain length

Atom transfer free radical polymerization (ATRP) was employed in a synthesis of graft polymer EVA-g-PMMA with controlled length of side PMMA chains. Three steps of synthesis: partial hydrolysis of EVA, esterification with chloroacetyl chloride and ATRP grafting were performed to produce EVAOH, macroinitiator EVACl and grafted polymers G8020 (EVA/PMMA?=?80/20 wt%) and G6040 (EVA/PMMA?=?60/40 wt%). FTIR, Raman and NMR spectroscopy were used in the determination of the chemical structure and modification of EVA. Transmitted light and dark field microscopy showed higher affinity for coil formation of EVA-g-PMMA with longer PMMA side chains, i.e. G6040 compatibilizer. Morphological, thermal and adhesive properties of optical fiber adhesives of graft polymers and polymer blends poly(ethylene-co-vinyl acetate)-blend-poly(methyl methacrylate) (EVA/PMMA) compatibilized with 1 wt% of EVA-g-PMMA, were studied. Image analysis of SEM micrographs showed effective compatibilization with short grafted chains (G8020) that was indicated by lower porosity characteristics. TG/DTG analysis enabled determination of degree of hydrolysis and amount of chloro-functionalized groups. DSC analysis showed higher thermal stability of G8020 polymer. Single lap joint of adhesives/optical fibers were subjected to adhesive testing and obtained results for maximal force applied and adhesive failure suggested the visible influence of the length of graft chains on adhesion.     

Forward Adaptive Logarithmic Quantizer with New Lossless Coding Method for Laplacian Source

The aim of this paper is to improve the G.711 standard, which is widely used, especially in the public switched telephone network (PSTN). Two solutions are proposed. The first solution uses only lossless coder, achieving a bit-rate decrease of 0.82 bits/sample, compared to the G.711 codec. The second solution uses forward adaptation and a lossless coder, further decreasing the bit-rate (by 1.25 bits/sample) and achieving higher average signal-to-quantization noise ratio (SQNR) in comparison with the G.711 codec. Also, the second solution is more robust than the G.711 codec, which means that it has near constant SQNR for a wide range of input signal power. That is very important for signals whose input power varies with time, such as speech and video signals. Our solutions are compatible with the G.711 codec, they have little additional complexity and delay and therefore can be applied in real-time systems, such as PSTN or VoIP. They can also be used in many other systems, such as WiMax and OFDM, as a replacement or improvement of the G.711 codec. Standardization process of the G.711.1 standard (which is a wide-band extension of the G.711 standard) is largely present. Our solutions fulfill all the requirements for that new standard; therefore they can be implemented in its low-frequency part.