Key Engineering Materials Vol. 887

Abstract: The copolyesters derived from dimethyl ester of terephthalic acid, ethylene glycol, and 4-hydroxybenzoic acid (HBA) have been synthesized via catalytically promoted polycondensation omitting the acetylation step. FTIR spectroscopy results have evidenced an insertion of HBA along a polymer backbone. Of note, thermal gravimetric analysis has shown that the HBA moieties substantially improved the thermal stability of polyesters. As found by differential scanning calorimetry and polarizing microscopy, the copolyesters are capable of forming an anisotropic phase in a temperature range of 150-170 °C. Additionally, the free surface energy of the samples was determined to evaluate the compatibility of thermotropic copolyesters with other high-molecular compounds.

Abstract: Polymers modified with carbon nanomaterials exhibit enhanced electrical conductivity. The modifier, which is qualitatively distributed in the polymer matrix, actively absorbs microwave waves even with an extremely small introduced volume (up to 1.5 mass parts). Photographs obtained by scanning electron microscopy indicate a uniform distribution of carbon nanotubes in the matrix of fluoroplastic 4. The microwave treatment of the obtained composites showed a significant increase in the temperature of the samples with a heating time of up to 100 sec. even with minimal amounts of modifier added. Strength characteristics for a uniaxial plant of modified materials after microwave increase by 40-50%. The obtained modified materials based on a non-polar polymer matrix have enhanced characteristics of absorption of microwave radiation.

Abstract: 5-hydroxymethylfurfural-acetone (5-HMFA) resins are obtained on the basis of 5-hydroxymethylfurfural (5-HMF) and acetone, that is, from monomers whose source of raw materials is renewable resources (agricultural waste). The 5-HMFA condensation reaction was carried out under various experimental conditions. The synthesis conditions for 5-HMFA were selected with a yield of the desired product of 51%. The resulting resins were pressed at various curing temperatures and tested for compressive strength and absorption of water. The optimum pressing temperature was set to 180 ° C. The resulting composites have a strength not inferior to the strength of phenol-formaldehyde resin composites, but have a 3 times higher water resistance.

Abstract: This article discusses the possibility of the fabrication of a highly sensitive sensor based on single-walled boron-carbon BC₅ nanotubes surface modified with functional carboxyl groups (-COOH). The sensor potential for detection of alkali (lithium, potassium, and sodium) metals were investigated. The results of computer simulation of the interaction process between the sensor and an arbitrary surface of the modified tube containing atoms of the studied metals are presented. The carboxylated BC₅ nanotube and a similarly modified BC₃ nanotube was compared. The effect of boron atoms on sensory properties of the obtained system is concluded. The calculations were carried out within the framework of the density functional theory (DFT) method using the molecular cluster model. It has been proved that surface-modified boron-carbon nanotubes by carboxyl group show high sensitivity for the metal atoms under study and can be used as the sensor device.

Abstract: Special features of the high-damping state formation in bimetallic materials produced by explosion welding have been studied. High-damping Mn-Cu alloy was used for the damping base of the bimetallic composite and high–strength steel (grade: 30HGSA) was used to form the coating layer. The effect of planar tensile stresses (observed in the damping component of the bimetal and caused by valuable difference between coefficients of thermal expansion of components of the bimetal) is discussed. Damping properties of bimetallic materials were found to be comparable with damping characteristics of monolithic high damping alloys. High-strength steel provides high-strength characteristics of the surface layer of the bimetal, where the strength level reaches 1100MPa and the hardness is equal to 50 HRC. Obtained combination of high damping and high strength in developed bimetallic materials provides real chance for practical application of these materials in industry.

Abstract: In this work various methods of glass plate hardening are considered. These plates are used to protect defense devices. As a glass was used system R₂O-B₂O₃-SiO₂. The method of thermal hardening was considered. Technological disadvantages of this method were discovered by analyzing Newton's rings and a polarizing plate. The use of chemical hardening has shown its advantages over the thermal method. The essence of the method is the ion exchange of alkali metals between glass plates and the chemical mixture melt. The operating principle of the chemical hardening equipment and its technology were considered. As a result, hardened glass plates with preservation of planar geometry were obtained.

Abstract: Experimental titanium implants with a rough calcium phosphate (CР) coating with bio-inspired properties have been developed. The role of roughness (in the range Ra = 2.4 - 4.6 μm) of the surface CP simulating the physicochemical features of the mineral substance of regenerating bone tissue to change the growth and morphofunctional activity of mesenchymal stem cells (MSCs) was evaluated. Titanium substrates with a microrelief CP coating bearing artificial niches for stem cells was shown in vitro to have an epigenomic effect on MSCs, that contributes to their differentiation and maturation in bone cells. The results show the promise of developing and introducing a new class of medical devices with bio-inspired surfaces into clinical practice for traumatology and orthopedics.

Abstract: In this paper, the substantiation of the possibility of additive forming of nitinol billets by simultaneous surfacing of two titanium and nickel wires with an electron beam in vacuum is given. The method of mathematical modeling shows the possibility of forming several molten pools of liquid metal on the bead being deposited immediately behind the main pool for remelting the formed material. The modes of the electron beam for the formation of the main and two additional remelting pools due to the deflection of the beam are determined taking into account the technological capabilities of the installation. The residence time of the metal in the liquid state is calculated for various additive forming modes. Remelting makes it possible to increase the residence time in the liquid state by a multiple of the molten pools number. This significantly improves the conditions for mixing the raw materials and reduces the heterogeneity of the material.

Abstract: Portable electrochemical sensors based on noble metal nanoparticles (МеNPs) for the quantitative determination of hydrogen peroxide (H₂O₂) and sulfur-containing amino acids (cysteine, methionine, glutathione) are discussed. These sensors have high sensitivity (pM), with low sample requirements (<50 μl). This article discusses methods for producing sensors based on silver and gold nanoparticles and their application in voltammetry. It is shown that the sensitivity of H₂O₂ determination on a sensor based on silver nanoparticles (AgNPs) depends on their size. Their size is determined by the reducing agent. Sensors based on AgNPs of spherical shape with the smallest size from 0.5 to 17.5 nm have the highest sensitivity for determining H₂O₂, but a narrow range of determined concentrations. Sensors on medium-sized AgNPs have optimal metrological characteristics. Their size is from 10 to 55 nm, less sensitive, but with a wide range of determined concentrations from 0.1 to 1 nm H₂O₂. The linearity of the range of glutathione concentrations is 1.0-10.0 pM. The linearity of the range of determined concentrations of methionine is 1–26 рМ.