A new approach for kinetic modeling and optimization of rubber molding

Although extensive research has been carried out on the understanding of the complex vulcanization process, the influence of reversion through exposure time and temperature on the vulcanization degree remains unclear. Therefore, the main aim of this study was a novel optimization approach that can help the industrial practitioners to select the optimal operating parameters, exposure time, and molding temperature, to achieve desired vulcanization degree of selected product. Spheres of four different diameters (2.5, 5, 10, and 20 cm) were selected as test geometry for simulation and optimization of rubber molding. Obtained vulcanization rheometer data for commercially available rubber blend (NR/SBR) were fitted by a new modeling approach, dividing vulcanization curve into two fitting sets: curing and reversion. The heat transfer equations for chosen geometry were coupled with proposed kinetic model. A new temperature-dependent kinetic parameter x, as the maximal reversion degree, was introduced, enabling determination of the lowest operating molding temperature (T_min = 132.36 °C), preventing high reversion and overheating of the rubber product. The final optimization goal was assessment of the optimal temperature and vulcanization time dependence on the rubber products dimensions. Proposed models have precise prediction with R² values greater than 0.8328 and MAPE less than 2.3099%.     

Optimization of a Fabric Softener Formulation with an Electrochemical Sensor and Streaming Potential Measurements

An electrochemical, cationic, surfactant-selective sensor based on multiwalled carbon nanotubes (MWCNT) functionalized with a sulfate group and the cetylpyridinium ion (MWCNT–OSO₃⁻CP⁺) as a sensing material was used for optimization of the formulation of a fabric softener. Potentiometric titrations were performed and response measurements were obtained using four cationic surfactants (CS) of technical grade and four CS of analytical grade. The slope closest to Nernstian was obtained for di-(tallow carboxyethyl) hydroxyethyl methylammonium methosulfate (MAS) (59.5 ± 1.1 mV/decade of activity in water and 57.5 ± 1.3 mV/decade of activity in CaCl₂). When using CS as analytes in potentiometric titrations, the best accuracy (99.8%) was obtained when using MAS; therefore, it was chosen as the CS for the fabric softener formulation. Due to the better properties of fabric softeners with silicone in their formulations, four silicones at several concentration levels were used as potential additives. Based on the stability and viscosity of the system, the diquaternary polydimethylsiloxane (DPS) (w = 0.19%) was chosen for the fabric softener formulation. The pH did not significantly influence the potential when in the range of 3–8 or the recovery of potentiometric titrations when in the range of 3–7. The application profile of the CS was assessed through streaming potential measurements of reference fabrics in an electrokinetic analyzer. The obtained electrokinetic parameters indicated on lag in adsorption of model fabric softener (MFS) based on MAS (w = 9%), with the addition of silicone DPS (MFS 3), on cotton and polyester fabrics, but advantage in stability when compared with other MFS investigated.     

The addition to the ergodic theorem on probability MV-algebras with product

 This article deals with the prototype of the strong law of large numbers, with individual ergodic theorem on probability MV-algebras with product. Dedicated to Prof. Ján Jakubík on the occasion of his 80th birthday This research is supported by Grant 1/9056/02 1991 Mathematics Subject Classification: 28E10     

Magnetron sputtered Au-Pd-In alloys: microgravimetric and electrochemical characterisation in simulated physiological solutions

An electrochemical quartz crystal microbalance (EQCM) has been applied in corrosion sensing of magnetron sputtered Au-Pd-In alloy in simulated physiological solutions. The piezoelectric resonators were prepared by alloy deposition on quartz substrates by a DC magnetron-sputtering (MS) technique. X-ray photoelectron spectroscopy (XPS) analysis showed that the deposit composition was similar to that of the MS target, which was a commercially available casting alloy. X-ray diffraction indicated that the sputtered alloy has a crystalline structure. Measurements by using impedance spectroscopy and DC voltammetry showed some differences in electrochemical behaviour of both sputtered and cast alloy; however, these data did not indicate superior corrosion resistance of the sputtered specimen. Alloy corrosion has been studied by EQCM in three simulated physiological solutions: 0.9 N NaCl, 0.1 N NaCl+0.1 N lactic acid and artificial saliva. The EQCM indicated corrosion as increase in electrode mass, which was due to accumulation of corrosion products on the surface. The mass gain curves were similar in both neutral (pH 6) and acidic (pH 2.2) solutions, what implies dissolution of corrosion products in both media to be insignificant. XPS analysis showed that In₂O₃ was the main corrosion product on the surface. Corrosion current calculations from the mass curves were undertaken, which yielded the same corrosion rate assuming different oxides on the surface. The average corrosion rates in oxygenated 0.9 N NaCl and 0.1 N NaCl+0.1 N lactic acid solutions were similar and about twice as high as that in saliva.     

Decarburization of Fe-Cr-C steels during high-temperature oxidation

Isothermal oxidation treatments were carried out on Fe-Cr-C steels. The steels containing 0.08, 0.15, 0.17, 0.88, 1.51, and 12.77wt.% Cr and 0.10, 0.49, 1.19, 0.18, 1.05, and 1.63 wt.% C were oxidized in ambient air at temperatures of 900, 1000, and 1200°C. Steels containing 13.22, 12.90, 12.52, and 12.77wt.% Cr and 0.15, 0.30, 0.50, and 1.63 wt.% C were heated (1100°C/3hr) in a flowing atmosphere of O₂-N₂-He in a SETARAM thermobalance. Evidence of decarburization of the steels is given by metallographic observations, by direct measurements of carbon diffusivities from the decarburization profiles in the oxidized samples, and by the results of kinetics measurements.³ Carbon diffusion coefficients were measured by the standard sectioning method in the samples oxidized in air. A. generalized equation for carbon diffusivity in Fe-Cr-C alloys is developed in terms of N_Cr[wt.%], N_C[wt.%], and T[K].     

Preparation of TiAl15Si15 intermetallic alloy by mechanical alloying and the spark plasma sintering method

This work is devoted to the preparation of alloys based on intermetallic compounds in the Ti–Al–Si system by powder metallurgy using mechanical alloying and the spark plasma sintering (SPS) method. The aim was to describe the formation of intermetallic phases during mechanical alloying of TiAl15Si15 (wt-%) alloy and to consolidate the powder prepared by optimised conditions. Phase composition, microstructure and hardness of compacted alloy were determined. Four hours of mechanical alloying is sufficient time for preparation of pure elements free material composed only of intermetallic phases. After consolidation, the TiAl15Si15 alloy has a homogeneous structure composed of silicide (Ti₅Si₃) in aluminide (TiAl) matrix. The hardness of the material reaches 865?±?42 HV 5.     

Tough thermosetting polyurethanes and adhesives from rubber seed oil by hydroformylation

Rubber seed oil (RSO), extracted from the seeds of rubber trees, is inedible oil with high free fatty acid content. In order to add value to RSO, we prepared a polyol with primary OH groups via hydroformylation/hydrogenation. Free hydroxy fatty acids formed in the process were utilized as reactive diluents, viscosity reducers, and adhesion promoters through hydrogen bonding with the substrate. The structures of the oil and polyol were analyzed using a range of analytical methods. The polyol had a hydroxyl number of 244 mg KOH g⁻¹ and an acid number of 21 mg KOH g⁻¹. The polyurethane prepared from this polyol and diphenylmethane diisocyanate was a highly crosslinked, tough material with a glass transition at 44 °C, high tensile strength and elongation, and attractive electrical properties. When used as a wood adhesive, it displayed extraordinary shear strength characterized by substrate wood failure rather than cohesive failure of the polymer. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48509.     

Passive filler loaded polysilazane-derived glass/ceramic coating system applied to AISI 441 stainless steel,part 1: Processing and characterization

This study describes an oxidation and corrosion resistant environmental barrier coating (EBC) applied to an AISI 441 stainless steel substrate. For this purpose, four polymer-derived ceramic (PDC) coating systems were developed. These coating systems consisted of a bond coat applied by dip coating, and a top-coat that was loaded with passive fillers and deposited by spray coating. The microstructures of the coatings were investigated using optical microscopy and scanning electron microscopy, including energy dispersive spectroscopy (EDS). X-ray powder diffraction (XRD) was used to investigate the phase composition of the coatings. The optimized composite top coatings were prepared from the preceramic polymer HTT1800, filled with yttria-stabilized zirconia and a specially tailored Al₂O₃–Y₂O₃–ZrO₂ (AYZ) passive filler, and commercial barium silicate glasses were used as sealing agents. After thermal treatment in air at 750°C, uniform and crack-free composite coatings on stainless steel substrates were developed, with thicknesses of up to 93 μm. Oxidation tests, which were performed at 850°C in synthetic air, showed that every tested coating system remained undamaged by oxidation and showed good bonding to the metal substrate.     

Au implantation into various types of silicate glasses

The implantation of gold ions into three types of silicate glass was studied. The energies of the implanted Au⁺ ions were 1701 keV, and the fluences of the ions were 1 × 10¹⁴, 1 × 10¹⁵, 3 × 10¹⁵ and 1 × 10¹⁶ cm^?2. The as-implanted samples were annealed in air at two temperatures (400 and 600 °C). The Au concentration depth profiles were investigated using Rutherford Backscattering Spectrometry (RBS) and compared to simulated profiles from the SRIM. The structural changes were studied by UV–vis absorption spectroscopy. The obtained mono-mode waveguides were characterised using Dark Mode Spectroscopy at 671 nm to yield information on the refractive index changes. The results showed interesting differences depending on the type of glass and the post-implantation treatment. The obtained data were evaluated on the basis of the structure of the glass matrix, and the relations between the structural changes, waveguide properties and absorption, which are important for photonics applications, were formulated.