Search

Introduction: Congenital heart defects are one of the most common malformations. Almost 50 % of patients with congenital heart defects require cardiac surgery. Nosocomial infections strongly influencing the effectiveness of postoperative rehabilitation remain among the major problems of modern health care. Objective: To establish risk factors for infectious complications in children with congenital heart defects after cardiac surgery. Materials and methods: In 2014 to 2021, we conducted a case–control study of 603 patients under the age of 18 with congenital heart defects who underwent 643 cardiac surgeries at the perinatal center. The case cohort included 134 children of both sexes having infectious complications while the control cohort included 469 children of both sexes showing no signs of nosocomial infections after cardiac surgeries. We assessed the role of endogenous and exogenous risk factors for postoperative infectious complications and the relationship between the exposure and the outcome based on the odds ratio. Testing for significance of differences was performed by hypothesis assessment with the calculation of the p-value and estimation of confidence intervals. Results: The incidence density of healthcare-associated infections was 15.6 (13.26–18.32) per 1,000 patient-days. The most significant endogenous and exogenous risk factors were identified. Conclusions: The established predictors of infectious complications indicate the need for a risk-based approach to prevention of nosocomial infections in pediatric cardiac surgery.

The research results conducted on binderless tungsten carbide (WC) ceramics obtained by Spark Plasma Sintering (SPS) of WC powders with different average particle sizes (0.095, 0.8, 3 μm) are presented. Nonuniform distribution of crystalline phases and microstructure of the WC ceramics was studied using layer-by-layer XRD analysis and SEM. Surface layers of the WC-based ceramics are characterized by nonuniform distribution of W2C crystalline phase and grain sizes, including the appearance of abnormally large grains. Thickness of the nonuniform layer was at least 50 μm. The effect under study is associated with an intense carbon diffusion from graphite foil. On the one hand, this contributed to a decrease in the intensity of W2C phase particle formation, which is transformed into α-WC phase due to the carbon. On the other hand, it caused abnormal grain growth in the layer where the carbon diffused. The obtained value of the carbon diffusion depth exceeds the values known from the literature (up to 1 μm in the case of volume diffusion even at temperature of 2370℃ and exposure time of ~ 60 h). The use of boron nitride (BN) as a protective coating on graphite mold parts did not prevent the formation of nonuniform layer on the ceramic surface.

This paper investigates the density, phase composition, microstructure and mechanical properties (microhardness, fracture toughness) of binderless WC + SiC ceramics obtained by conventional pressureless sintering (CPS) and Spark Plasma Sintering (SPS). α-WC nanopowders obtained by DC arc plasma chemical synthesis and β-SiC powders have been used as raw materials. The content of SiC particles was 1, 3, 5% wt. Excess graphite (0.3, 0.5% wt.) was added to α-WC nanopowders to decrease the volume fraction of W2C particles that negatively affect the mechanical properties of ceramics. WC + 1% wt. SiC + 0.3% wt. C ceramics are shown to have a homogeneous fine-grained microstructure, high relative density, increased microhardness and Palmquist fracture toughness. The CPS and SPS activation energies of WC + SiC nanopowders at an intensive shrinkage stage are determined using the Young-Cutler model. The effect of carbon and SiC particles on the CPS and SPS activation energies of tungsten carbide nanopowders has been analyzed. The CPS activation energies of WC, WC + C and WC + SiC + C nanopowders are shown to be closer to the carbon diffusion activation energy along α-WC grain boundaries. The SPS activation energies of WC and WC + SiC nanopowders turn out to be lower than the carbon grain boundary diffusion activation energy of α-WC.

Cardiac surgery of the aortic valve in pediatric patients is an urgent problem. Performing an open aortic commissurotomy and planar resection of the valves during the newborn period allows to obtain suboptimal results and postpone subsequent interventions indefinitely. With an unsatisfactory result of open aortic commissurotomy in children of the first years of life, the need to search for optimal surgical tactics arises. The presented article describes the technique of replacing the aortic root with a decellularized valve-containing allograft in a child of 14 months of life. A good immediate result of the operation is associated with the ability of the allograft to provide physiological hemodynamics in the aortic position. The advantages of the described technique are the reduction in the time and complexity of surgical intervention, the possibility of preserving own pulmonary valve, the probability of recellularization and the possibility of graft growth with the growth of the child. That is precisely why the presented technique should be considered as an alternative to Ross surgery, especially if there are anatomical contraindications to it.

The present work was aimed at the investigation of effect of High Energy Ball Milling (HEBM) time on the sintering kinetics, structure, and properties of heavy tungsten alloy (HTA) W-7%Ni-3%Fe. The HTA samples were obtained from the nanopowders (20-80 nm) by conventional liquid phase sintering (LPS) in hydrogen and by Spark Plasma Sintering (SPS) in vacuum. The HTA density was shown to depend on the HEBM time non-monotonously that originates from the formation of non-equilibrium solid solutions in the W-Ni-Fe systems during HEBM. The SPS kinetics of the HTA nanopowders was shown to have a two-stage character, the intensity of which depends on the Coble diffusion creep rate and on the intensity of diffusion of the tungsten atoms in the crystal lattice of the -phase. The kinetics of sintering of the initial submicron powders have a single-stage character originating from the intensity of the grain boundary diffusion in the -phase. The dependencies of the hardness and of the yield strength on the grain sizes were found to obey the Hall-Petch relation. The hardness, strength, and dynamic strength in the compression tests of the fine-grained tungsten alloys obtained by SPS and LPS were studied.

The paper describes the results of fatigue and corrosion-fatigue tests of the pseudo α titanium alloy PT-3V, which is actively used in nuclear engineering for the manufacture of heat exchange equipment for modern nuclear power plants. Alloy PT-3V has an inhomogeneous coarse-crystalline structure with precipitates of β-phase particles along the grain boundaries of the lamellar shape. It is shown that smooth specimens tested according to the bending-with-rotation loading scheme do not show a noticeable decrease in the cyclic fatigue life when exposed to a neutral corrosive environment (3 % aqueous NaCl solution). However, specimens with a notch (stress concentrator) tested according to the cantilever bending loading scheme demonstrate sensitivity to the action of a corrosive environment at the stages of initiation and growth of fatigue cracks, as evidenced by a significant decrease in the number of cycles before crack initiation, as well as before specimen failure, in comparison with tests in air. Fractographic analysis of fractures of smooth specimens and specimens with a concentrator after fatigue and corrosion-fatigue tests has been carried out. The main stages of the initiation and growth of fatigue cracks are revealed. It has been established that a decrease in the resistance to the initiation and propagation of corrosion-fatigue cracks during testing of notched specimens may be due to the effect of hydrogen embrittlement, accelerated by stress concentration.

A diffusion welding of coarse-grained and ultrafine-grained (UFG) specimens of titanium near-α alloy Ti-5Al-2V used in nuclear power engineering was made by Spark Plasma Sintering. The failure of the welded specimens in the conditions of hot salt corrosion and of electrochemical corrosion were shown to have preferentially intercrystalline character. In the case of presence of macrodefects, crevice corrosion of the welded joints was observed. The resistance of the alloys against the intercrystalline corrosion was found to be determined by the concentration of vanadium at the titanium grain boundaries, by the size and volume fraction of the β-phase particles and by the presence of micro- and macropores in the welded joints. The specimens of the welded joints of the UFG alloy have higher hardness, hot salt corrosion resistance and the electrochemical corrosion.

The conductor aluminum alloys Al-0.25wt.%Zr doped additionally with Х = Er, Si, Hf, and Nb were the objects of investigations. The fine-grained microstructure in the alloys was formed by Equal Channel Angular Pressing and Rotary Swaging. The thermal stability of the microstructure, specific electrical resistivity, and microhardness of the novel conductor aluminum alloys was investigated. The mechanisms of nucleation of the Al3(Zr,X) secondary particles during annealing the fine-grained aluminum alloys were determined using Jones-Mehl-Avrami-Kolmogorov equation. Using Zener equation, the dependencies of the mean secondary particle sizes on the annealing time were obtained on the base of analysis of the data on the grain growth in the aluminum alloys. The secondary particle nucleation during long-time low-temperature annealing (300 оC, 1000 hrs) was shown to go preferentially at the cores of the lattice dislocations. The Al-0.25%Zr-0.25%Er-0.20%Hf-0.15%Si alloy subjected to long-time annealing at 300 оC has the optimal combination of the microhardness and electrical conductivity (59.8%IACS, Hv = 480 ± 15 MPa).

The research was undertaken to study the way deformation behaves in ultrafine-grained (UFG) conducting Al-Zr alloys doped with Sc, Hf, and Yb. All in all, 8 alloys were studied with zirconium partially replaced by Sc, Hf, and/or Yb. Doping elements (X = Zr, Sc, Hf, Yb) in the alloys total 0.4 wt.%. The choice of doping elements is conditioned by possible precipitation of Al3X particles with L12 structure while annealing these alloys. Such particles provide higher thermal stability of a nonequilibrium UFG microstructure. Initial coarse-grained samples were obtained by induction casting. The UFG microstructure in the alloys was formed by Equal Channel Angular Pressing (ECAP) at 225°C. Superplasticity tests were carried out at temperatures ranging from 300 to 500 °C and strain rates varying between 3.310-4 and 3.310-1 s-1. The highest values of elongation to failure are observed in Sc-doped alloys. A UFG Al-0.2%Zr-0.1%Sc-0.1%Hf alloy has maximum ductility: at 450 °C and a strain rate of 3.310-3 s-1, relative elongation to failure reaches 765%. At the onset of superplasticity, stress–strain curves are characterized by a stage of homogeneous strain and a long stage of localized plastic flow. The dependence of homogeneous strain (eq) on test temperature in UFG Sc-doped alloys is increasing uniformly, which is not the case for other UFG alloys with eq(T) dependence peaking at 350-400 оС. Strain rate sensitivity coefficient of flow stress m is small and does not exceed 0.26-0.3 at 400-500 °C. In UFG alloys containing no scandium, m coefficient is observed to go down to 0.12-0.18 at 500 оС. It has been suggested that lower m values are driven by intensive grain growth and pore formation in large Al3X particles, which develop specifically at the ingot crystallization stage.

Al-6%Mg-Sc-Zr alloys with the total ratio of Sc + Zr = 0.32 wt.% make up the target of this research. The content of scandium and zirconium varied with an increment of 0.02%. The alloys were produced by induction casting. Their ultrafine-grained (UFG) microstructure was formed with Equal Channel Angular Pressing (ECAP). Such cast alloys have a homogeneous macrostructure formed by small equiaxed grains in the central part of the ingot and columnar crystals along the edges of the cross section. After ECAP, the average grain size in the alloy specimens is 0.5–1 µm. The average grain size does not depend on the ratio of Sc and Zr in these alloys. Superplasticity tests were performed at temperatures ranging from 300 to 500 °C and at a strain rate varying between 3.3·10-3 and 3.3·10-1 s-1. UFG Al-6%Mg-0.20%Sc-0.12%Zr and Al-6%Mg-0.18%Sc-0.14%Zr alloys exhibit the highest superplasticity. It was suggested that changes in Sc:Zr ratio affect spatial distribution and composition of the following precipitating particles: Al3Sc, Al3Zr, Al3(ScxZr1-x). An increase in Zr concentration is shown to reduce the susceptibility of UFG alloys to cavitation fracture.

Ceramic armour materials are designated to protect personnel and vehicles against ballistic damage. The main effort is now focused on developing ceramics with difficult-to-obtain properties, such as high ballistic performance and light weight. Over the past 30 years, the development of ceramic materials has led to a sustained improvement in their properties and structural homogeneity. Nevertheless, the relation of these properties with the ballistic performance of ceramics remains unclear. This paper reviews the current understanding regarding the failure stages of ceramic armour and the methods used to evaluate ballistic performance. A comparison of alumina with silicon carbide and boron carbide was performed.

The effect of scandium on the superplasticity characteristics of Al–0.5Mg–Sc conductor aluminum alloys with a submicrocrystalline (SMC) structure is investigated. Large elongation to failure (~1060%) is achieved in the SMC alloys with 0.4 and 0.5% Sc at a deformation temperature of 500°C and a strain rate of 1 × 10–1 s–1. Intense pore formation is shown to occur during the superplasticity of the Al–0.5Mg–Sc SMC alloys. The kinetics of deformation-stimulated grain growth in the Al–0.5Mg–Sc SMC alloys is found to be determined by the mobility of junction disclinations and orientation-misfit dislocations.

We have studied the hydrolytic stability of Y2.5Nd0.5Al5O12-based garnet ceramics produced by spark plasma sintering. The ceramics have been tested under hydrothermal conditions in an autoclave and, for comparison, in static mode at room temperature. The mechanisms of yttrium and neodymium leaching from the ceramics have been identified.

t—The diffusion welding of ultrafine-grained pseudo-α-titanium Ti–4.73% Al–1.88% V alloy specimens has been performed by spark plasma sintering. It has been shown that the destruction of welded joints in the ultrafine-grained (UFG) specimens under hot salt corrosion (HSC) conditions has a two-stage character: intercrystallite corrosion (ICC) is developed at the first stage to turn into pitting corrosion at the following stage. It has been established that the resistance to intercrystallite corrosion is governed by the concentration of vanadium on grain boundaries, the size and volumetric content of β-phase particles, and the existence of pores in a welded joint. It has been demonstrated that the welded joints of the ultrafine-grained specimens have higher hardness and resistance to intercrystallite corrosion as compared to coarse-grained specimens.

The Y0.95Gd0.05PO4 phosphate with the xenotime structure has been synthesized in powder form and as ceramics. Ceramics with a relative density of ~99% have been produced by spark plasma sintering. The sintering temperature was 1140°C and the sintering time was ~18 min, without isothermal holding. We have assessed the radiation resistance of the ceramics under irradiation with 132Xe26+ ions and investigated the restoration of the obtained metamict phase to a crystalline one via high-temperature heat treatment. No complete amorphization of the samples has been reached at the fluences used in this study. The calculated critical fluence is (9.2 ± 0.1) × 1014 cm–2, and the calculated latent track radius is ~2.8 nm. Hydrolytic tests have shown that the phosphate under study is stable in water under dynamic conditions. The observed Y and Gd leaching rates were Ri = 1.68 × 10–6 and 1.5 × 10–7 g/(cm2 day), respectively.

The special aspects of spark plasma sintering (SPS) of plasma-chemical nanopowders of tungsten carbide with higher oxygen content were investigated. It was demonstrated that shrinkage rate of the WC nanopowders during SPS is limited by the rate of grain-boundary diffusion with the abnormally low values of activation energy. Decrease in the activation energy of SPS is caused by the influence of oxygen on the diffusion permeability of boundaries of the tungsten carbide grains at the stage of intense densification, as well as by abnormal grain growth. Kinetics of SPS of the WC-W2C-WO3-W nanopowder compositions at the stage of severe densification is controlled by the rate of sticking together the oxide particles, with their simultaneous transformation into W2C particles, and then by the plastic flow of W2C particles in the presence of the tungsten particles at the stage of high-temperature sintering. Ceramics with a high density ratio (98–99%) and ultra-fine-grained structure (the mean grain size less than 0.3 μm) with higher hardness HV = 30.5 GPa and fracture toughness of ~6.5 MPa m1/2 were obtained using the SPS method.

The effect of severe plastic deformation by rotary forging on the mechanical properties and the corrosion resistance of a pseudo-α-titanium PT-7M alloy is studied. The corrosive character of fracture the fine-grained alloy under hot salt corrosion (HSC) conditions is found to change: pitting corrosion at the onset of recrystallization processes changes into intercrystalline corrosion. The HSC resistance of the fine-grained PT-7M titanium alloy is shown to depend on the structure–phase state of grain boundaries, whose intense migration with developing recrystallization leads to “sweeping out” of corrosion-hazardous alloying elements (aluminum, zirconium) from the crystal lattice of the titanium alloy.

New NZP-type solid solutions, Na1+2xZr2–xNix(PO4)3 and Ca0.5+xZr2–xNix(PO4)3 with x = 0.10, 0.25, and 0.50, have been prepared by solid-state reactions. The synthesized samples have been characterized by X-ray diffraction and IR spectroscopy. Crystal structure of the compound CaZr1.5Ni0.5(PO4)3 has been refined by full-profile X-ray diffraction analysis method, reliability factors is Rp = 4.78% and Rwp = 6.45%, respectively. Thermal expansion of the phosphates has been studied by high-temperature X-ray diffraction in the temperature range 25–700°C. The synthesized compounds have been shown to be intermediate- and low-thermal-expansion materials. Using SPS method we have produced ceramic samples with a high relative density (ρrel > 97%), based on phosphate powders. Strength characteristics (microhardness and fracture toughness) of the ceramics have been determined.

Features of high-speed sintering of WC–Co nanopowders with various contents of excess carbon (colloidal graphite) were studied. Powders were obtained in a process that included plasma-chemical and low-temperature syntheses and a chemical-metallurgical method of applying ultrathin cobalt layers by precipitation from a solution of salts. Powder materials were consolidated by high-speed spark plasma sintering. It was found that an increase in the concentration of free carbon (colloidal graphite) has the greatest effect on the shrinkage and the sintering rate at the stage of intense shrinkage of WC–Co nanopowders. It was revealed that the process of nanopowder compaction at the intense shrinkage stage is determined by the intensity of the plastic flow and the intensity of diffusion along the boundaries of cobalt grains. It was shown that the mechanism of plastic deformation of the cobalt-based γ phase corresponds to the Coble diffusion creep. It was found that an increase in carbon content lowers the activation energy at the stage of intense shrinkage and does not significantly affect the activation energy at stage III of sintering, where the shrinkage intensity is observed to decrease. It was shown that a decrease in the sintering activation energy is due to a decrease in the tungsten concentration in the γ phase.

The shrinkage of the WC nanopowders with increased oxygen content during Spark Plasma Sintering (SPS) was shown to be limited by the grain boundary diffusion with abnormally low activation energy. It was found that the reduction of the SPS activation energy may originate from the effect of oxygen on the diffusion permeability of the grain boundaries in tungsten carbide at the intensive compaction stage as well as from an abnormal grain growth at the high-temperature sintering stage. The kinetics of SPS of the WC-W2C–WO3–W nanopowders at the intense compaction stage is controlled by the sintering rate of the oxide particles with simultaneous transformation of these ones into the W2C particles and then, at the high-temperature sintering stage – by the plastic flow of the W2C particles in the presence of tungsten ones. The ceramic specimens with high density (98–99%) and ultrafine grained structure (mean grain size

The article discusses the features of the acceptance of garments produced for the needs of the penal system. A detailed analysis of the process of assessing the compliance of the quality indicators of clothing items with the terms of the concluded contract, which is currently an urgent issue in the activities of logistics services, was carried out. Due to the fact that in the list of clothing supplied for the needs of the penal system, most of the items are garments, they have been chosen as the object of the research. Since the generalized system of controlled objects, assessed during the procedure of acceptance and quality control of garments, has not yet been defined, in the course of the experiment a systematization was carried out and a project was proposed for grouping into six categories the quality indicators monitored during the expert examination of garments supplied for the needs of the Penal system. On their basis, the main stages of the process of acceptance of clothing items were modeled and considered in detail, recommendations were given on the organization and establishment of its compliance with the terms of the concluded contract. When evaluating the results of the study, it has been noted that the developed procedure for the acceptance of clothing items, supplied for the needs of the penitentiary system of the Russian Federation, intended for assessing the compliance with the terms of the concluded contract, does not require additional financial costs and can be recommended for practical use in institutions of the penitentiary system. Key words: penal system, employees, clothing items, garments, acceptance, quality.

The thermal stability of the grain structure, the mechanical properties, and the electrical resistivity of submicrocrystalline (SMC) Al–0.5% Mg alloys with 0.2, 0.3, 0.4, and 0.5% Sc is studied. The alloys are fabricated by induction casting and equal-channel angular pressing (ECAP). The alloys with >0.3% Sc contain submicrometer primary Al3Sc particles, the amount of which increases with the scandium content in the alloys. The precipitation kinetics of Al3Sc particles in the SMC alloys is determined by the intensity of diffusion processes along lattice dislocation cores and grain boundaries. ECAP of the alloys at a temperature of 225°C provides high thermal stability of the SMC structure: the temperature of the onset of recrystallization is 375°C. At room and elevated temperatures, the SMC alloys have a high plasticity and a good combination of strength, hardness, and electrical conductivity.

High-density (95.3–95.8%) CeO2–xα-SiC (x = 10, 20 vol %) composite ceramics have been produced for the first time by spark plasma sintering (SPS) as promising mineral-like materials for inert fuel matrices. The SPS of CeO2–SiC ceramics has been shown to be a three-stage process. The addition of α-SiC particles shifts characteristic temperatures of CeO2 sintering to higher values. SPS leads to an increase in the hardness, fracture toughness, and thermal conductivity of cerium dioxide-based ceramics.

We have synthesized Na1 ¿ xZr2(PO4)3 ¿ x(¿O4)x and ¿a0.5 ¿ xZr2(PO4)3 ¿ x(¿O4)x (X = Mo, W; 0 ¿ x ¿ 0.5) compounds with the NZP structure. Their thermal expansion has been studied in the temperature range 25¿800°C using high-temperature X-ray diffraction and shown to have a tendency to decrease as the occupancy of the extraframework sites in their structure decreases. Ceramic samples with a relative density above 97.5% have been prepared from the synthesized phosphate molybdates and phosphate tungstates by spark plasma sintering. Their strength characteristics (microhardness and fracture toughness) have been determined and they have been characterized by hydrolytic stability tests.

The thermal stability of a fine-grained aluminum wire made of Al–Mg–Zr–Sc(Yb) alloys with different zirconium and scandium (ytterbium) contents is studied. Samples are produced by induction casting and subsequent cold working by drawing. The structure and properties of fine-grained the Al–0.6Mg–Zr–Sc alloys are shown to exhibit high thermal stability due to preliminary (before drawing) annealing at 320°C for 2 h, resulting in the precipitation of intermetallic Al3(ScxZr1 – x) particles. A fine-grained homogeneous structure with an average grain size of 2.4–2.8 μm and a microhardness of 405–440 MPa is found to be retained in the Al–0.6Mg–Zr–Sc alloys after prolonged annealing at 400°C for 100 h. A fine-grained magnesium-free Al–0.33Zr–0.16Yb ytterbium alloy has a low hardness and low thermal stability. The average grain size in it after annealing at 400°C for 100 h is 4.1–4.8 μm.

The corrosion–fatigue fracture of an ultrafine-grained Ti–2.2Al–2.5Zr pseudo-α titanium alloy (PT-7M alloy), which is used in atomic power engineering, is studied. The formation of an ultrafine-grained structure by rotary forging is found to increase the corrosion–fatigue strength. The parameters in Basquin’s equation are determined, and the slope of the σa–log N fatigue curve is shown to nonmonotonically depend on the temperature of annealing of the ultrafine-grained alloy.

Spark plasma sintering and a standard sintering method are used to manufacture ceramic plates with a diameter of 30 mm from aluminum oxide powder with a fraction size approximately equal to 3 µm. Dynamic strength of the ceramics obtained is studied. Dynamic loading is carried out by a hardened steel impactor. It is shown that energy dissipation in a material obtained using spark plasma sintering is substantially larger than that in a material produced using standard sintering, which means that it is more resistant to dynamic loads.