Production of Urea/Acetylated-ligninsulfonate Matrix as SRFs and Investigation the Effect of Hydrodynamic Conditions on the Release Rate Using Biot Number

Background: This study aimed to investigate the effect of the hydrodynamic condition on the release rate of urea/acetylated lignin sulfonate (Ac-LS) matrix as slow-release fertilizers (SRFs). Therefore, two models were developed using the mass transfer balance for the finite/infinite volume of fluids, solving finite integral transform/separation of a variable. In these models, the Biot number that verified the hydrodynamic condition appeared. Methods: In the experimental section, the urea/Ac-LS matrix fertilizer was produced. The morphological, thermal, chemical, and mechanical properties of the LS, Ac-LS, urea, and urea/Ac-LS matrix were analyzed using Fe-SEM, TGA, XRD, and SANTAM. Finally, the nitrogen release of the matrix fertilizer was investigated at 25°C for different impeller speeds. Results: The results showed that the thermal and mechanical resistance of urea/Ac-LS, with strong interaction, increased rather than pure urea or Ac-LS. The models were also validated using experimental data. The results further showed that in both states, the external resistance of the mass transfer decreased with increasing impeller speed, and the nitrogen release rate increased with increasing Biot number. Conclusion: It was also observed that, in a given hydrodynamic condition, initially, the release rate in the finite environment was less than the infinite; however, after a while, the type of environment did not affect the release rate

Biocompatible and Thermoresistant Hydrogels Based on Collagen and Chitosan

Hydrogels are considered good biomaterials for soft tissue regeneration. In this sense, collagen is the most used raw material to develop hydrogels, due to its high biocompatibility. However, its low mechanical resistance, thermal stability and pH instability have generated the need to look for alternatives to its use. In this sense, the combination of collagen with another raw material (i.e., polysaccharides) can improve the final properties of hydrogels. For this reason, the main objective of this work was the development of hydrogels based on collagen and chitosan. The mechanical, thermal and microstructural properties of the hydrogels formed with different ratios of collagen/chitosan (100/0, 75/25, 50/50, 25/75 and 0/100) were evaluated after being processed by two variants of a protocol consisting in two stages: a pH change towards pH 7 and a temperature drop towards 4 °C. The main results showed that depending on the protocol, the physicochemical and microstructural properties of the hybrid hydrogels were similar to the unitary system depending on the stage carried out in first place, obtaining FTIR peaks with similar intensity or a more porous structure when chitosan was first gelled, instead of collagen. As a conclusion, the synergy between collagen and chitosan improved the properties of the hydrogels, showing good thermomechanical properties and cell viability to be used as potential biomaterials for Tissue Engineering.

Effect of Corrosive Media on the Chemical and Mechanical Resistance of IPS e.max® CAD Based Li2Si2O5 Glass-Ceramics

The influence of 4% acetic acid (pH~2.4) and an alkaline solution of NaOH (pH~10) on the corrosion resistance and micromechanical properties of disilicate crystals containing glass-ceramics (LS2-GC’s) is studied. Partially crystallized lithium metasilicate crystal containing glass-ceramics (LS-GC’s) are annealed to fully LS2-GC’s using a one stage and a two-stage heating to induce nucleation. Materials with various chemical and wear resistance are prepared. The content of the crystalline phase in the material annealed in the two-stage process A is 60.0% and increases to 72.2% for the material heated in the one-stage process B. The main elements leached in the acidic medium are lithium and phosphorus, while lithium, silicon, and phosphorus leached into the alkaline environment. Material B exhibits better chemical resistance to the corrosive influence of 4% acetic acid under quasi-dynamic conditions. In the alkaline corrosion medium, silicon is leached from material A faster compared to the material B. After prolonged exposure to acidic or basic environments, both materials show evidence of surface structural changes. A decrease of the sliding wear resistance is observed after corrosion in the acidic environment under dynamic conditions. In both materials, the wear rate increases after corrosion.

‎‏FINDING PERCENTAGE OF BREAKDOWN STIMULATION OF ALUMINUM WIRES THAT OPERATES IN A CORROSIVE MEDIUM

The study of the duration of mechanical resistance to static tensile stress (withstand time) for an aluminum wire that being suffers from the corrosion effect stimulated by stray currents at different temperatures. Test device was designed and produced locally "in advance" in accordance with the specification (ASTM G103 - 97) to create static tensile stress of (1 N) on an aluminum wire of type ASTM (B231/B231M) with particular dimensions and utilized in the transmission of electrical energy, and when the wire is surrounded by a corrosive environment (NaCl solution) (3.5 % NaCl) at three different temperatures (25, 50, and 75 ° C) without any external electrical current causing corrosion; this symbolizes stray currents. Then compare the findings of that example to the results of the same wire's withstand time in the presence of an external electrical current generated by corrosion of type (D.C) by (5V & 3A). Following that, the resulting diagrams were analyzed, and it was discovered that the wire resistivity time (without the existence of stray currents and at a temperature of 25 ° C) completed (17 days), which is the longest duration of endure, and the lowest time of resistivity or resistance period (in the existence of an external electric current) is (18 hr.).Impact of (stray currents) at (75 ° C), and this is an indicator of the stray currents with corrosive environment temperatures on the resistance period (withstand duration) in the existence of static stress. The total stimulation increase is 1.9% between corrosion at 75°C and 25°C.

Analysis of the mechanical resistance of cement with aggregates of petrous endocarp from macadamia nut

This research evaluates if adding crushed macadamia nutshell to a mixture of cement and sand could result in lighter and more resistant constructive materials. The mechanical resistance under compression of cement blocks made from two different experimental mixtures, in which a certain amount of sand is replaced with crushed nutshell, is compared against two control groups. Results show that blocks made from one of the proposed mixtures got an average resistance around 50% above the controls group while being 3% lighter. Additionally, the physical dependence of the strength of the blocks on the granulometry of the aggregated endocarp fragments, and their percentage to the volume of cement, was studied thanks to contour plots developed from a factorial design of the data.

Ex vivo biomechanical testing of Funkquist B dorsal laminectomy between the sixth and seventh cervical vertebrae in dogs

ABSTRACT: Dorsal laminectomy is routinely performed for spinal cord compressions or stenosis of the cervical vertebral canal. However, despite good results, relevant complications have been described in dogs. Considering the incomplete understanding of the necessity for complementary surgical stabilization after performing laminectomies in the cervical region, this study compared the resistance and range of motion (ROM) of the cervical spinal column subjected to Funkquist B laminectomy between the sixth and seventh vertebrae in dogs. Forty-four cervical vertebral columns (C2-T1) of dogs, with an average weight of 26.2±3.8 kg, were selected using radiography and computed tomography. Four experimental groups (n=11) were established according to the mechanical test: two control groups (flexion and extension control) and two laminectomy groups (flexion and extension laminectomies). Numerical results of the maximum load for measuring the resistance and ROM of the columns of the two control groups and the two laminectomy groups were compared. The laminectomy groups showed a lower maximum load, regardless of the mechanical test performed (P<0.001). The ROM was not influenced by laminectomy, the type of mechanical test (ventral flexion or extension), or its interaction (P<0.05). There was no interaction between the effect of the laminectomy factors (yes or no) and the effect of the mechanical tests for ventral flexion or extension (P<0.05). In conclusion, Funkquist B dorsal cervical laminectomy between C6 and C7 decreases mechanical resistance with a supraphysiological loading force but does not alter the ROM, suggesting that it can be used without additional mechanical stabilization in dogs.

Evaluation of the mechanical resistance of rheophores of the means of initiation for explosive’s materials, on the basis of the resistance to abrasion determined with the OPVA 10 specialized equipment

The scientific paper presents the synthesis of research results undertaken to develop the technical and methodological infrastructure for assessing the safety of means of initiating explosives, on the abrasion resistance of rheophores of electric detonators, in order to increase the safety of their use. The state-of-the-art OPVA 10 equipment is used to test the ability of rheophores insulation to withstand the abrasion forces that may occur during normal use. This equipment with a programmable automatic ensures the testing of the rheophores of the electric detonating staples to determine the abrasion resistance under the operating conditions provided by the harmonized European standard EN 13763-4 and the technical specification of the manufacturer, the operating temperature of this equipment being between 10 ÷ 30 °C ensuring at the highest level the fulfillment of the technical requirements imposed by the European and international regulations in the field.

Stability of Polymeric Membranes to UV Exposure before and after Coating with TiO2 Nanoparticles

The combination of photocatalysis and membrane filtration in a single reactor has been proposed, since the photocatalytic treatment may degrade the pollutants retained by the membrane and reduce fouling. However, polymeric membranes can be susceptible to degradation by UV radiation and free radicals. In the present study, five commercial polymeric membranes were exposed to ultraviolet (UV) radiation before and after applying a sol–gel coating with TiO2 nanoparticles. Membrane stability was characterized by changes in hydrophilicity as well as analysis of soluble substances and nanoparticles detached into the aqueous medium, and by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and energy-dispersive X-ray spectrometry (EDS) for structural, morphological, and elemental distribution analysis, respectively. The TiO2 coating conferred photocatalytic properties to the membranes and protected them during 6 h of UV radiation exposures, reducing or eliminating chemical and morphological changes, and in some cases, improving their mechanical resistance. A selected commercial nanofiltration membrane was coated with TiO2 and used in a hybrid reactor with a low-pressure UV lamp, promoting photocatalysis coupled with cross-flow filtration in order to remove 17α-ethinylestradiol spiked into an aqueous matrix, achieving an efficiency close to 100% after 180 min of combined filtration and photocatalysis, and almost 80% after 90 min.

Fabrication and Characterization of Environmentally Friendly Biochar Anode

Electrical power generation by means of electrochemical systems utilizing wastewaters is a global energy challenge tackling technique for which a creation of novel eco-friendly electrode materials is in high relevance. For this purpose a Rhodophyta algae derived activated biochar anode bound with a flaxseeds mucilage binder (5, 10, 20, 30 wt.%) was formed and characterized by thermogravimetric, Brunauer-Emmett-Teller (BET) analysis as well as conductivity and mechanical resistance determination. Activation technique with KOH prior to carbonization at 800 °C of algae was employed to obtain biocarbon with a large surface area. The highest specific surface area of 1298.49 m2/g was obtained with the binder-free sample and had a tendency to decrease with the increase of the binder content. It was estimated that biochar anodes are thermally stable at the temperature of up to 200 °C regardless of binder concentration. The concentration of the binder on the other hand had a significant influence in anodes mechanical resistance and electrical conductance: anode with 30 wt.% of the binder had the highest compressive strength equal to 104 bar; however, the highest conductivity was estimated in anode with 5 wt.% of the binder equal to 58 S/m. It is concluded that anode with 10 wt.% mucilage binder has the optimal properties necessary in MFC utilization.

Analysis of the current scenario of Compressed Earth Block (CEB) production

The main objective of this study is to identify the parameters that influence the quality of the production of compressed earth blocks (CEB). Thus, an analysis of the performance of the materials that make up the final product was carried out, such as the binders that act as chemical stabilizers and the different types of soils, also the mechanical resistance and durability tests and finally the technical standards for its manufacturing. For this aim, a literature review was carried out in three electronic databases, Scopus, Web of Science and Scielo. The results showed environmental concerns with the use of Portland cement for stabilization, therefore, 18% of the studies used agricultural residues and 25% used mineral by-products, for partial or total replacement of Portland cement. Soils with plasticity indexes between 15% and 30% have a stabilization success rate of 69%, while soils with plasticity index less than 15% have a stabilization greater than 93%, which can be increased to 100% if the soil have a percentage of clay and silt between 21 and 35%. On the other hand, a plasticity index above 30% negatively affects stabilization. The compaction energy applied in the manufacture of CEB is an important parameter, as it influences the density, thermal conductivity and mechanical strength. Among the sustainable construction techniques, CEB is a great option, as it can be done locally and with ease of construction.