Non-Linear Mechanical Behavior of Plasma Sprayed Alumina Under Mechanical and Thermal Loading

Mechanical response of plasma sprayed ceramic coatings to mechanical and thermal loading of various extents was studied. Coated samples were subjected to four-point bending (4PB), with coatings loaded in tension and compression, respectively. Thermal loading was provided by heating the samples, while stresses were generated by thermal mismatch between the coatings and substrates. In both cases, cyclic loading was applied. Non-linear behavior and significant hysteresis were observed, indicating inelastic phenomena taking place. The tests were complemented by structural observations in SEM and indentation tests. Relevant structural features and possible mechanisms underlying this behavior are discussed.     

Preparation of vermiculite nanoparticles using thermal hydrogen peroxide treatment

Powdered natural Mg-vermiculite (Letovice, Czech Republic), with the formula (Mg0.35K0.02Ca0.01) (Mg2.39Fe0.51(3+)Fe0.02(2+)Al0.08) (Si2.64Al1.33Ti0.03) O10(OH)2 x 4.97H2O and particle size < 5 microm, was used for the investigation of exfoliation after hydrogen peroxide and/or microwave treatment (600 W). A sample heated in the microwave oven for 40 min exhibits a 11% mass loss and reduction of the 001 peak intensity in the X-ray diffraction pattern. The basal 001 peak intensity of untreated Mg-vermiculite sample (/001 = 100%) drops to 35% in the microwave treated sample. Only the sample treated for 5 h at 80 degrees C fully rehydrated after 120 min at room temperature. A more pronounced reduction of the 001 peak intensity (to 8%) was observed after hydrogen peroxide treatment of the sample at 25 degrees C. The combination of a five-hour hydrogen peroxide treatment at 80 degrees C and subsequent microwave heating leads to an effective extinction of the 001 diffraction in the XRD pattern. The 001 diffraction profile becomes very diffuse with peak intensity less than 1%. The degree of reduction of the 001 diffraction intensity also depends on the time and temperature of hydrogen peroxide treatment and on the peroxide concentration. An even more pronounced reduction of the peak intensity is caused by exfoliation of particles to nano-domains coupled with a randomization of the c-axes.     

Improvement of the evaluation of inkjet printed silver based layers’ adhesion

This paper presents the improved method of analysis and evaluation of the silver layers’ adhesion printed by inkjet printing technology. The generally known method for adhesion measurement of layers and coatings according to the standards ASTM D3359 and ISO 2409 has been improved by development of the automatic evaluation software of achieved results from cross cut tests. The developed evaluation tool offers the possibilities of calculation the detached area, rotation of the image, setting the threshold and the automatic classification according to the mentioned standards. The inaccuracy caused by samples’ assessment by humans is mainly eliminated by using of this tool. The developed evaluation tool has been applied to experimental works oriented to analysis of the adhesion of two commercially available silver based nano-inks on two polymeric based substrates (PI and PET). For this purpose, different sintering conditions have been applied to analysed samples. The achieved results show the differences between the investigated nano-inks’ adhesion on two types of polymeric substrates. The adhesion of silver layers can be optimized by controlling the sintering conditions. By developing the software tool the simple and inaccurate method of adhesion analysis has been upgraded to the appropriate technique to the silver layers’ adhesion testing. The improved method for adhesion measurements can serve as a tool for fast and relatively simple technique for technologist.     

Evaluation of the Antimicrobial Efficacy of N-Acetyl-l-Cysteine,Rhamnolipids, and Usnic Acid—Novel Approaches to Fight Food-Borne Pathogens

In the food industry, the increasing antimicrobial resistance of food-borne pathogens to conventional sanitizers poses the risk of food contamination and a decrease in product quality and safety. Therefore, we explored alternative antimicrobials N-Acetyl-l-cysteine (NAC), rhamnolipids (RLs), and usnic acid (UA) as a novel approach to prevent biofilm formation and reduce existing biofilms formed by important food-borne pathogens (three strains of Salmonella enterica and two strains of Escherichia coli, Listeria monocytogenes, Staphylococcus aureus). Their effectiveness was evaluated by determining minimum inhibitory concentrations needed for inhibition of bacterial growth, biofilm formation, metabolic activity, and biofilm reduction. Transmission electron microscopy and confocal scanning laser microscopy followed by image analysis were used to visualize and quantify the impact of tested substances on both planktonic and biofilm-associated cells. The in vitro cytotoxicity of the substances was determined as a half-maximal inhibitory concentration in five different cell lines. The results indicate relatively low cytotoxic effects of NAC in comparison to RLs and UA. In addition, NAC inhibited bacterial growth for all strains, while RLs showed overall lower inhibition and UA inhibited only the growth of Gram-positive bacteria. Even though tested substances did not remove the biofilms, NAC represents a promising tool in biofilm prevention.     

Residual life assessment of steam turbine casing containing crack defect

In steam turbine casing made of cast steel of type 0.6Cr0.5Mo0.25V ( SN 42 2744), which run about 25% over designed life, several crack defects were found. The most serious case was represented by a crack in valve chest, which reached nearly up to one half of wall thickness. In spite of this it was necessary to operate the turbine for some time. The aim of this contribution is to describe procedures used for assessment of safe residual life.Material data necessary for this life assessment were evaluated during research of material properties of another steam turbine casing made of the same type steel whose operating time was finished after 1.23×10⁵ h. The mentioned material data are also presented.     

Surface characteristics enhancement of MWCNT alumina composites using multi-pass WEDM process

Machining of ceramic composites in electrical discharge machining process is often associated with high roughness, unwanted surface and subsurface defects. This situation is generally not desired as it will reduce the life of the ceramic components fabricated in this machining process. Thus, an improvement towards enhancement of surface characteristics is desired. Multi-pass wire electrical discharge machining process can serve as an effective means of enhancing the surface characteristics in machining of ceramic composite. The current work utilizes the multi-pass concept to improve the surface properties of multi-walled carbon nanotubes filled alumina composites. A decreasing nature of surface roughness is observed with increase in the number of machining passes. A lesser appearance of unwanted debris and cracks is observed at the end of the final pass on the machined surface. The spalling effect is found to be more dominant at the initial first pass while melting and evaporation effect is more dominating in higher passes. Also, a better subsurface characteristic with lesser porous recast layer is observed with increase in the number of passes.     

Behavioral Alterations and Decreased Number of Parvalbumin-Positive Interneurons in Wistar Rats after Maternal Immune Activation by Lipopolysaccharide: Sex Matters

Maternal immune activation (MIA) during pregnancy represents an important environmental factor in the etiology of schizophrenia and autism spectrum disorders (ASD). Our goal was to investigate the impacts of MIA on the brain and behavior of adolescent and adult offspring, as a rat model of these neurodevelopmental disorders. We injected bacterial lipopolysaccharide (LPS, 1 mg/kg) to pregnant Wistar dams from gestational day 7, every other day, up to delivery. Behavior of the offspring was examined in a comprehensive battery of tasks at postnatal days P45 and P90. Several brain parameters were analyzed at P28. The results showed that prenatal immune activation caused social and communication impairments in the adult offspring of both sexes; males were affected already in adolescence. MIA also caused prepulse inhibition deficit in females and increased the startle reaction in males. Anxiety and hypolocomotion were apparent in LPS-affected males and females. In the 28-day-old LPS offspring, we found enlargement of the brain and decreased numbers of parvalbumin-positive interneurons in the frontal cortex in both sexes. To conclude, our data indicate that sex of the offspring plays a crucial role in the development of the MIA-induced behavioral alterations, whereas changes in the brain apparent in young animals are sex-independent.