مجله مواد و فناوری های پیشرفته
سال هفتم شماره 3 (پاییز 1397)

Bone defect is one of the important challenges of medical science in the all world. Today, the synthesis of a suitable scaffold for replace the lost tissue with the aim of repairing, recovering and restoring tissue function has been developed. The combination of protein-polysaccharide is a promissing approach in scaffolding with the ability to induce bone like apatite formation. In this paper, new bioactive composite scaffolds based on kappa-carrageenan/fibrobin nanofibers were synthesized and characterized for bone regeneration applications. The fibroin nanofibers were prepared by electrospinning, then the chopped electrospun nanofibers were incorporated to Kappa-carrageenan solution (0.5% w/v) in different ratios as a reinforcer. Finally, 3D scaffolds were fabricated by Freeze-drying. In order to evaluate the fabricated scaffold, different characterization methods have been applied to analyze structure, morphology, mechanical strength and the amount of apatite formation on the surface of the scaffolds that have been compared with the pure Kappa-Carrageenan sample. The results of scanning electron microscopy showed the highly porous structure with the interconnected porous. The porosity percentage and average pore size of the scaffolds were suitable for bone cells implantation and propagation. In addition, Energy Dispersive X ray (EDS) technique has proved Precipitation of Ca-P on the surfaces. The biocompatibility evaluation of fabricated scaffolds was done using MTT indirect assay. The results indicated no toxicity effects on cultured MG-63 osteoblast-like cells. In addition, the MG-63 osteoblast-like cells exhibited good adhesion behavior in direct contact with the scaffolds and cell attachment was observed by SEM images.

In this study, hematite nanoparticles and hematite nanoparticles doped with Ti, Sn doped have been synthesized and deposited on FTO glass for photo anode application. To make a thin layer of hematite by hydrothermal method, ammonia and ferric chloride solution react indirectly at 120 ̊C for 24 h for better adhesion of synthesized iron hydroxide on FTO glass. The   synthesized samples were calcined at 550o C. XRD analysis was confirmed that FeOOH-coated were subsequently converted to the rhombohedral structure of the a-Fe2O3.  A complete synthesis study was performed using FTIR analysis and using UV-Vis results, the bandgap energy of the samples was calculated with and without the additive. The finite structure and morphology of synthesized powders were also compared with FESEM images. The results showed that the addition of 1% wt of titanium caused the synthesis of uniform spherical nanoparticles leads to alow electrons bandgap energy of 1.85 eV.

In this study, graphitic carbon nitride (g-C3N4) was made by thermal condensation of melamine at 450 and 550 °C. Moreover, the TiO2 porous nanostructured electrode was fabricated as a substrate for the g-C3N4 deposition by anodization method on a titanium foil (Ti) and then, reduced by electrochemical method to improve electrical conductivity (Re-TiO2 NP). The graphite carbon nitride layers were deposited on the porous nanostructured electrode (Re-TiO2 NP/Ti) by electrophoretic technique and the g-C3N4/Re-TiO2 NP/Ti electrodes were used as supercapacitor electrode. Comparison of the supercapacitive properties of the g-C3N4/Re-TiO2 NP/Ti electrodes showed that the electrochemical efficiency and specific capacitance of the g-C3N4 (450)/Re-TiO2 NP/Ti electrode is higher than the g-C3N4 (550)/Re-TiO2 NP/Ti electrode due to the increased active sites and charge transfer and the enhanced hydrophilicity as result of its high nitrogen content.

In the present study thermal shock behavior of monolothic alumina and two types of micro and nano aluminum tianate composites have been studied using quench-strength method. The powders were wet mixed and the slurry dried. Then the grinded powders were formed by isostatic pressing. The composites were prepared by in-situ reaction sintering of alumina with nano and micronized TiO2 addition to formation of 20 wt.% aluminum titanate as secondary phase. Investigations were carried out by s-DT curves, X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) analysis. The results revealed fully formation of Al2TiO5 phases in the both case of micro and nano titania as a result of Al2O3 and TiO2 reaction sintering. The nano layer structure of the Al2TiO5 was formed at the triple junction of the alumina grains. Also thermal shock values of the alumina, micro and nano composites were measured about 230, 265 and 290 °C, respectively. Thermal shock increment of the composite in the comparison of the alumina can be related to the secondary phase effect on the rising toughness curve (R-curve) and microcracking of the composites.

Titanium and its alloys are used as under-load implants due to the high corrosion resistant and mechanical properties. However, they show weakness in surface and tribology behavior. In this study, the protective composite TiB/TiB2 coating mechanism towards the diffusion pack cementation method and also their osteoconduction properties have been investigated via in-vitro experience. Boriding process was performed at the different temperatures (800 and 1000 ˚C) for certain soaking time (60 min). SEM micrographs showed a gradient B concentration regard to the formation of TiB2, Ti3B4, and TiB phases. XRD analysis also confirmed the formation mechanism and indicated that boriding at 800 ˚C tends to single phase TiB, while at 1000 ˚C tends to the formation of composite TiB/TiB2 coating. In-vitro study during two weeks immersion in simulated body fluid (SBF) showed that the TiB/TiB2 coating exchanges the bio-inert titanium surface to a bio-active surface resulting in an osteoconductive material formation. SEM image of TiB/TiB2 coating after two weeks immersion revealed that bone like apatite precipitants formed a porous structure like cancellous bone tissue on the titanium surface.

In this present study, 5, 10 and 15 wt% V2O5 were added to aluminum matrix and the microstructure and mechanical properties of spark plasma sintered composites were investigated. The mixing process was conducted in ethanol media with high energy mixer mill and then the mixture was heated on the hot plate at 70°C. The sintering process was performed at the   400 and 450°C with vacuum condition and 10 and 30 MPa initial and final applied pressure, respectively. The XRD patterns showed interfacial product of Al3V and reduction-transition in oxygen content by increasing of sintering temperature. The mechanical properties investigation revealed highest bending strength of 141±11 MPa and Vickers hardness of 103±12 (VHN) for specimens with 15wt% of V2O5 and sintered at 450°C. The FESEM images showed almost uniform distribution of reinforcement and local melting area with different types of vanadium oxide.

In this research, a chemical getter with 75%wt zirconium, 22% cobalt, 1.5%wt of praseodymium and 1.5%wt neodymium was synthesized by ball milling. The effect of these elements on the adsorption/desorption properties of the getter was compared with the effect of yttrium. Due to the high activity of non-evaporable getters, oxide layers are formed on the surface. So, for activating a getter these layers must be removed. For this purpose, the samples were first placed at 100 °C for 30 minutes and then were activated at 360 °C for 80 minutes. The results of the adsorption tests in terms of pressure and temperature variations versus time indicated that the activation temperature for the yttrium sample was reduced by about 60 degrees and reached from 260 to 200 °C. The start pressure of the adsorption test in the getter chamber for all samples is 1.5 × 10-5 mmHg. While in the case of Y the final pressure of the reactor was reached to 1.3 × 10-6 mmHg. After completion of the activation process, the connection between the reactor and the vacuum pumps was disconnected to determine the time of vacuum preserving from 0.001 to 0.2 mmHg. The required time to break the vacuum for yttrium containing sample was 4955 seconds, which has the highest value. According to the results, the performance of the Pr, Nd and Y is close to each other, and all of the  these elements reduced the pressure of the system by about ten times and increased the vacuum breaking time to more than 4000 seconds.

This research has been conducted with the view of the effect of various polymeric processing aids (PPA) on the stick-slip phenomenon in polyethylene compounds. In the extrusion process of thermoplastic polymers, such as polyethylene, for proper and efficient products like wire coatings, pipes, bottles, and films, it is desirable that the final products, gain a smooth surfaces and be polished. In the industry, it is also necessary that the rate of extrusion process is as high as possible, dislike the pressure of this process is as low as possible, so that it can be used for the most part from process machines and thus reduce process costs so much as practical. In this study, MBM and MBR masterbatches (containing 35-40% carbon black) were added to high density polyethylene powder (PE100) and the effect of these masterbatches on the reduction of viscoelastic phenomenon was confirmed. In the next step, three types of PPA with commercial names of Viton, Fx and Daikin with concentrations of 50, 100 and 150 ppm were added to the PE100MBR and PE100MBM compounds to reduce the melt fracture of the samples. The capillary rheometry test determined the quantity changes in the stick-slip phenomenon. The microscopy test also showed qualitatively the changes that occurred in the extrudates. The torque meter test also determined the effect of the PPA on the ampere and the energy consumed by the extruder. Finally, samples were produced with these features due to the importance of reducing energy in the process as well as improving the quality of the extrudates. Depending on the structure of the fluoroelastomer and hyper branch polymers, it has been found that adding these kind of materials has improved processability, and finally the appearance of the product is smoother and polished.