Applied Mechanics and Materials Vol. 729

Abstract: Lightweight gypsum materials foamed by the help of stone dust were investigated. Lightweight material prepared from the gypsum as a main binder and foamed by stone dust and acid agent. The materials with the bulk density are 607 kg/m³, compressive strength about 1.3 MPa and thermal conductivity was prepared. Basic physical, mechanical and thermal properties were investigated.

Abstract: The purpose of this study was to evaluate the chemical and metallurgical aspects, mechanical properties and hardness of the stainless steel of Fe-Cr alloy, the stainless steel of Fe-Cr alloys coating with Ni and Cu-Zn alloys coating with Ni alloys used for microsurgical instruments manufacturing.In dentistry are develop new materials and methods to obtain microsurgical instruments with complex form and who must to present mechanical resistance, good corrosion and a great cleaning identically like the glass. The new methods to obtain the microsurgical instruments try to realize quickly the complex form with a cost is expensive.Ni coating permit a better corrosion resistance of microsurgical instruments, because of the thin shiny layer protective, resistant and homogenous.Ni coating permit a better wear resistance of microsurgical instruments for long time.

Abstract: The structural phase transitions and electronic structures of Co are investigated by using the first-principles calculation based on density-functional theory (DFT). Our calculated equilibrium structural parameters of Co are in good agreement with the available experimental data and other theoretical results. The calculated phase transition hcp-Co → fcc-Co at ca. 125.25 GPa. The magnetic moment of hcp-Co and fcc-Co drops to zero at 155 GPa and 77 GPa, respectively.

Abstract: In order to develop a chromium-free pre-treatment method for electroless Ni-P (ENP) plating on magnesium alloy from an acidic plating bath, several various pickling and activation processes were studied in the present work. The surface morphologies of the matrix before and after etching or activation as well as the surface and cross sectional appearance of the Ni-P coatings were observed by scanning electronic microscope (SEM), while the elemental compositions were detected by energy dispersive X-ray spectroscopy (EDS). Those surface characterizations along with the scribe and grid testing results showed that the coatings obtained from etching only in H₃PO₄ solution display poor adhesion due to the existance of an interlayer between the matrix and the coatings. When fluoride was added into the pickling solution, the adhesion of the Ni-P coatings was also unsatisfactory because of the bad mechanical interlocking. By comparison, the Ni-P coatings obtained from pickling in 400 cm³·dm⁻³ H₃PO₄ solution followed by 10 cm³·dm⁻³ HF activation exhibit good characteristics in both adhesion and anti corrosion. The polarization test in 3.5wt.% NaCl aqueous solution showed that the corrosion potential (E_corr) and corrosion current density (I_corr) of the new achieved coatings increases positively from −1.65 V to −0.87 V and decreases remarkably from 2.09 mA⋅cm⁻² to 3.58 μA⋅cm⁻², respectively (both compared with the bare Mg alloy).

Abstract: In this paper, composite Al₂O₃–t-ZrO₂ ceramics (composition: 95 wt. % Al₂O₃ – 5 wt. % t-ZrO₂ and 90 wt. % Al₂O₃ – 10 wt. % t-ZrO₂) was formed by slip casting in plaster mould. After drying, green bodies were sintered in laboratory electric kiln under air environment at a temperature of 1650 °C.Erosive wear resistance of sintered monolithic Al₂O₃ and composite Al₂O₃–t-ZrO₂ ceramics was determined by SEM analysis of the sample surface morphology before and after erosion at impact angle of 90° and SiC as erodent particles. Surface morphology analysis after erosion showed that wear scars were significantly larger on Al₂O₃ than on Al₂O₃–t-ZrO₂ samples. All conducted tests showed that tribological properties of monolithic Al₂O₃ can be improved with the addition of t-ZrO₂.

Abstract: The work deals with soldering of silicon substrate with active solders designated S-Bond 220-1, 220-50 and 220-M. Soldering was performed with power ultrasound in the air without flux application at temperature 250 to 280 °C. The results of EDX analysis have shown that active elements as Ti, Ce and Mg support wetting of Si substrate and thus assure the joint formation. Strength of joints was studied by shear test. The highest strength was achieved with S-Bond 220-1 solder. The strength of joints fabricated with S-bond solders on Si substrate varied from 23 to 38 MPa.

Abstract: Guar gum grafted sodium polyacrylate have been prepared via aqueous solution graft polymerization. Furthermore, the polymers were then surface-crosslinked using trimethylolpropane triglycidyl ether (TMPTGE) to improve the properties of swollen hydrogel. Polymerization conditions were systematically optimized to achieve the optimum swelling capacity. FTIR and DSC spectra confirmed that sodium acrylate had been grafted onto guar gum chains. SEM observations showed morphology of the samples. The results confirmed that introducing guar gum into the superabsorbent could improve the swollen hydrogel mechanics performance, including hydrogel strength, resilience and dispersion, although making the water absorbency decreasing slightly. The good mechanics performance will make it feasible in hygiene application.

Abstract: This paper is the first stage of the research with the aim to identify the type of hazardous waste with the most critical production within the Czech Republic and to find the optimal composition of the cement matrix that will ensure maximum content disposal of this chosen hazardous waste. The part of the project solution will be also to define suitable testing procedure that will verify the stability of this cement composite and the impact of the inbuilt hazardous waste on the cement matrix properties.

Abstract: The aim of the research was to test basic properties of fiber reinforced concrete with PP fibers and cement matrix subjected to heat load of various intensity. Behavior of fiber reinforced concrete was observed in particular from the point of view of change of physico-mechanical properties and microstructure after exposure of test samples to different level of heat load. Volume weight, compressive strength, tensile bending strength, splitting tensile strength and strength in tension of surface layers of concrete were observed.