Processing Conditions Optimization for the Synthesis and Consolidation of High-Entropy Diborides

The fabrication by Spark Plasma Sintering (SPS) of bulk high entropy ceramics from powders obtained by Self-propagating High temperature Synthesis (SHS) is addressed in this work. The effect produced by the introduction of 1 wt.% of graphite to the powders before SPS is investigated under different temperature conditions. The final density and composition of sintered (Hf0.2Mo0.2Zr0.2Ti0.2Ta0.2)B2 and (Hf0.2Mo0.2Zr0.2Ti0.2Nb0.2)B2 ceramics are found to be negatively affected by the presence of oxide impurities in the powders. While product composition can be progressively improved when the temperature is increased from 1800 to 1950 °C, residual porosities remain relatively high if using additive-free powders. In contrast, the introduction of 1 wt.%C markedly allows for oxides elimination by carbothermal reduction mechanism. Products consolidation is correspondingly enhanced so that relative densities of about 97% are attained. Other than the latter effect, surface oxides removal also makes powders more reactive, thus the synthesis of single-phase products is promoted. In particular, fully homogeneous (Hf0.2Mo0.2Zr0.2Ti0.2Ta0.2)B2 ceramics are obtained at relatively lower temperature conditions (1850 °C).

Computational Analysis of Bone Remodeling in the Proximal Tibia Under Electrical Stimulation Considering the Piezoelectric Properties

The piezoelectricity of bone is known to play a crucial role in bone adaptation and remodeling. The application of an external stimulus such as mechanical strain or electric field has the potential to enhance bone formation and implant osseointegration. Therefore, in the present study, the objective is to investigate bone remodeling under electromechanical stimulation as a step towards establishing therapeutic strategies. For the first time, piezoelectric bone remodeling in the human proximal tibia under electro-mechanical loads was analyzed using the finite element method in an open-source framework. The predicted bone density distributions were qualitatively and quantitatively assessed by comparing with the computed tomography (CT) scan and the bone mineral density (BMD) calculated from the CT, respectively. The effect of model parameters such as uniform initial bone density and reference stimulus on the final density distribution was investigated. Results of the parametric study showed that for different values of initial bone density the model predicted similar but not identical final density distribution. It was also shown that higher reference stimulus value yielded lower average bone density at the final time. The present study demonstrates an increase in bone density as a result of electrical stimulation. Thus, to minimize bone loss, for example, due to physical impairment or osteoporosis, mechanical loads during daily physical activities could be partially replaced by therapeutic electrical stimulation.

The Density of Different Local Anesthetic Solutions, Opioid Adjuvants and Their Clinically Used Combinations: An Experimental Study

Various opioids are added to local anesthetic solutions for spinal anesthesia. This may change the final density of the local anestetic (LA) mixture. This effect regarding current concepts in spinal anesthesia needs to be re-evaluated. In order to re-evaluate such effects, hyperbaric and isobaric local anesthetic (LA) solutions were mixed with opioid adjuvants (A) using the equipment available in the operating room. Ten density measurements for each composition (LA-A) were performed. The density change of 0.0006 g/mL was regarded as significant. Measured densities were also compared with theoretical values calculated using Hare’s. As a result, the addition of an opioid adjuvant caused a significant reduction in the final density of the LA-A solution. In hyperbaric LA mixtures, it did not change the baricity from hyperbaric to isobaric. However, the addition of highly hypobaric fentanyl 0.99360 g/mL (SD ± 0.00004) changes all isobaric LA solutions baricity to hypobaric. The comparison of measured and theoretical densities revealed significant differences (p > 0.05). However, the absolute reduction reached 0.0006 g/mL in only two LA-A compositions. We conclude that the addition of fentanyl to isobaric LA results in a hypobaric solution that may affect the distribution of the block. The inadequacy of LA-A in a clinical setting is unlikely to influence block characteristics.

A Study on Binder Jetting of High Dimensional Stability Alloy

This work opens a new pathway to fabricate high dimensional stability Invar36 aerospace devices with Binder Jetting technology, for applications where temperature fluctuations directly interfere in the correct performance of high sensibility systems. Since full density part fabrication is one of the main ongoing challenges for Binder Jetting, the leading objective of this work is to study and optimise the main process parameters to increase the final density of Invar36 printed parts. Microstructural analysis and obtained density and CTE values, confirmed the feasibility to fabricate Invar36 parts.

Study into the feasibility of obtaining dense materials based on AlN-SiC solid solution in one stage by SHS gasostatiс processing

The synthesis and sintering of the (AlN)x(SiC)1–x solid solution were studied under the conditions of SHS gasostatiс processing at high nitrogen gas pressures (up to 110 MPa). Phase formation during the combustion of aluminum and silicon carbide mixtures with the different amount of a combustible component (aluminum content is 35 to 60 wt.%) was studied. It was shown that the optimal amount of aluminum mixed with silicon carbide to obtain a single-phase solid solution (with the complete Al conversion to AlN and without SiC dissociation) is 45–50 wt.%. A mixture with 55–60 wt.% Al leads to excessively high temperatures, which in turn leads to the silicon carbide decomposition to Si + C elements. The optimal parameters for obtaining a dense material in one stage were determined. The measured porosity and density of materials obtained demonstrated that preforming is essential for the final density of samples containing 50 wt.% Al: maximum density was achieved at a preforming pressure of 10 MPa. It was found that the 5 wt.% yttrium oxide additive increases the material density by almost 10 %. A similar effect is also obtained by increasing the initial gas pressure from 80 to 110 MPa. The maximum density in this case reached 2.7 g/cm3, i.e. 83 % of the theoretical density. The total volumetric shrinkage of the material was 10 ± 0.5 %, and this indicator can be almost completely smoothed over by the 3 wt.% boron additive. The microhardness of samples was 2000 kg/mm2.

Impact of phenol film grammage on selected mechanical properties of plywood

Impact of phenol film grammage on chosen mechanical properties of plywood. For the purpose of this research several plywood samples with a thickness of 15 mm were produced and coated, in industrial conditions, with 5 different variants of phenol films varying in terms of grammage (40/120 g/m2, 60/145 g/m2, 60/167 g/m2, 80/220 g/m2, 2 × 80/220 g/m2). Finished plywood was tested for abrasion resistance, MOR, MOE and density. It was concluded that higher grammage of phenol film increases wear resistance and final density of plywood. Plywood coated with two-layer phenol film with grammage of 80/220 g/m2 had 4 times higher rate of abrasion resistance in comparison with plywood coated with phenol film with surface density of 40/120 g/m2. Coating plywood surface with phenol films generally decreases MOR values, in comparison with uncoated plywood. In terms of MOE, there were no evidence of conclusive relation, despite statistically significant differences between each variant.

Effect of betaine and selenium on the growth and photosynthetic pigment production in Dunaliella salina as biostimulants

ABSTRACT The aim of our study was to establish the effect of selenium and betaine on the growth of D. salina, accumulation of photosynthetic pigments and antioxidant activity of the hydrophobic fraction. This approach was an attempt to demonstrate ‘microalgae biostimulant’ effects, similar to ‘plant biostimulant’ effects, i.e. increased tolerance to abiotic stress and enhanced accumulation of bioactive compounds. A high-throughput assay was done in 24-well microplates, at 15% NaCl and different concentrations of sodium selenite (0, 0.5, 2 and 8 µM) or betaine (0, 5, 50 and 500 µM). Both selenium and betaine induced a slight delay in algae growth during the actively growing stage but the final density reached similar values to the control. Betaine significantly enhanced (50%–100%) carotenoids and chlorophyll a accumulation, in a concentration depending manner. Antioxidant activity increased almost 3-fold in extracts of algae treated with 50 µM betaine. Selenium had a much more discrete effect than betaine on pigments biosynthesis. The antioxidant activity of the extracts increased 2-fold in the presence of Se compared to the control. Our work proves that it is possible to enhance production and activity of bioactive compounds from microalgae by using ingredients, which already proved to act as plant biostimulants.

Studies on the suitability of oxidizing agents for discolouring lime and poplar wood in the first stage of transparent wood forming process

Studies on the suitability of oxidizing agents for discolouring lime and poplar wood in the first stage of transparent wood forming process. Series of lime and poplar wood samples were prepared and subjected to oxidising agent in order to decolourise wood in bulk. Sodium chlorite solution in the environment of diluted acetic acid and alkaline hydrogen peroxide solution were used as different treating agents, followed by intense rinsing in water and drying the samples. The effect of wood delignification conditions such as time of treatment and reagent used was investigated. Changes in mass and dimensions of the samples were measured, and thus density changes were calculated. Colour changes were measured with colorimeter in CIE Lab colour space. In the case of lime wood swelling of the samples was observed at the first stage, along with mass loss, leading to density decrease by 10 % after 20 h exposure. In the case of poplar wood, shrinking of the samples was observed, but due to severe mass loss, final density was similar to lime wood. Colour changes correlated mainly with lightness parameter of the samples. Significant colour differences were found even at the shortest time of treatment.

Coexistence effect of rotifer, Brachionus rotundiformis and copepod, Oithona similis in culture media on growth performance and eggs production

Suminto, Chilmawati D. 2019. Coexistence effect of rotifer, Brachionus rotundiformis and copepod, Oithona similis in culture media on growth performance and eggs production. Biodiversitas 20: 2396-2402. The effect of Brachionus rotundiformis, and Oithonasimilis coexistence in culture media on the growth performance and egg production were examined and it aims to know the best coexistence percentage which provides the highest growth performance and egg production of O. similis and B. rotundiformis. Experiment method was carried out in this research by using a completely randomized design (CRD) with 5 treatments and 4 replications. The treatments were percentage through mix culture ratio of O.similis. and B. rotundiformis whereas those treatments were with ratio of 100% and 0% (A); 90% and 10% (B); 80% and 20% (C); 70% and 30% (D); and 60% and 40% (E), respectively. The results showed that, B. rotundiformis had a significant effect (p <0.05) on final density, population growth rate and eggs production of Oithona sp.; coexistence of 60% Oithona sp. and 40% B. rotundiformis provides the best final density for Oithona sp. (27.40±0.34 ind./ml) and B. rotundiformis (30.23±0.21 ind./ml); the highest population growth rate of Oithona sp. (0.29±0.02 ind./day) and B. rotundiformis (0.36±0.03 ind./day); and the highest egg production of Oithona sp. (18.83±0.76 eggs/ind) and B. rotundiformis (3.30±0.24 eggs/ind.). However, the mix culture of O.similis. and B. Rotundiformis may be applied in co-existent semi-mass or mass culture.

Dilatometric investigations of Fe – Cr – Mo – C system

Sintering behavior in high purity nitrogen and mixture of 5% H2-95% N2 of Fe-(Cr)-(Mo)-C system was investigated. The mixtures, differ from chromium, molybdenum and carbon content were prepared in Turbula mixer. Then, using single-action pressing in a rigid die at pressing pressure 400 MPa, green compacts with density level 5.9±0.17 g/cm3 were pressed. Sintering was carried out in a horizontal push rod dilatometer Netzsch 402E at 1120 and 1250°C for 60 min. Heating and cooling rates were 10 and 20°C/min., respectively. After heating, compacts were isothermal sintered at 1120 or 1250°C for 60 minutes an cooled up to 200°C, then isothermally hold for 60 minutes and definitely cooled to the room temperature. Pure nitrogen and mixture of 5% H2-95% N2 were employed as sintering atmospheres. During investigations the influence of isothermal sintering temperature, chemical composition of sintering atmosphere, chromium, molybdenum and carbon content was followed by dilatometry. The aim of investigations was to determine transformation temperatures. It was shown that the dimensional changes occurring during heating and isothermal sintering and the final density of sintered compacts are influenced by sintering parameters and the alloying elements concentration in powder mixture.