The effect of gamma irradiation on mechanical,thermal and morphological properties of glass fiber reinforced polyethylene waste/reclaim rubber composites

Composites of waste polyethylene (WPE), collected from municipal solid waste/recycled waste rubber powder (RWRP) reactive compatibilizing agent, maleic anhydride (MA) and glass fiber (GF) up to 20 wt%, prepared by melting and irradiated with gamma-rays up to 150 kGy have been studied. Tensile strength (T_S), elongation at break (E_b), elastic modulus, hardness, thermal and morphological parameters of the irradiated composites were investigated. The examined mechanical properties have been found to improve largely with filler content. Interesting E_b behavior has been detected for the irradiated composites loaded up to ∼10 wt% GF and has been basically discussed in view of matrix crystallinity and morphology. TGA thermograms of unirradiated composites revealed enhanced thermal stability than that reported for the blend whereas comparatively slight improvement has been demonstrated by irradiation. Whereby insignificant alteration in T_m values was observed by loading or irradiation, yet ΔH_m maximum of 3.41 J/g, indicated for the 5 wt% GF irradiated composite with an integral dose of 75 kGy, emphasizes the influence of the relatively moderate load and dose levels on matrix stability. The phenomenon has been confirmed by the respective SEM micrographs.     

Studies on a novel bioactive glass and composite coating with hydroxyapatite on titanium based alloys: Effect of γ-sterilization on coating

A novel silicate based bioactive glass coating composition containing B₂O₃ and TiO₂ having matching thermal properties with that of Ti₆Al₄ V implants was developed and characterized. A conventional vitreous enamelling technique was used for coating small flat surface and curved surface of small rods. Hydroxyapatite (HAp) micro and nano-crystalline particles were used to prepare bioactive glass-HAp composite coating. Scratch testing was used to study the coating adhesion and its fracture behaviour under simulated conditions. As observed from scratch testing results, adhesion strength of the coating improved from 21 N normal load to 27 N and 32 N on addition of micro-HAp and nano HAp powder, respectively, to bioactive glass matrix. Further, sterilization of the coated samples with 25 kGy gamma irradiation substantially enhanced the adhesion of glass coating and HAp-composite coating.     

Effects of oxide addition on the microstructure and mechanical properties of lamellar SiC scaffolds and Al–Si–Mg/SiC composites prepared by freeze casting and pressureless infiltration

Silicate-bonded porous SiC scaffolds with lamellar structures were prepared by freeze casting and liquid-phase sintering. It was found that the viscosity and solidification velocity of SiC water-based slurries with 30 vol% solid loading decreased with increasing Al₂O₃–MgO (AM) addition. As the AM content increased from 10 to 30 wt%, the lamellae of the sintered scaffolds became denser and the porosity decreased from 69±0.5% to 62±0.5%, while the compressive strength improved from 25±2 to 51±2 MPa. The dynamics of pressureless infiltration for an Al–12 Si–10 Mg alloy on the SiC porous scaffold was measured and the composites with lamellar-interpenetrated structures were successfully produced. Both the compressive strength and the elastic modulus of the composites increased with increasing AM content. The maximum strength reached 952±24 MPa and the highest elastic modulus about 156 GPa, respectively, in a longitudinal direction, increasing about 32% and 11% as compared with those of the composites without AM.     

Multi-walled carbon nanotubes acting as free radical scavengers in gamma-irradiated ultrahigh molecular weight polyethylene composites

Multi-walled carbon nanotubes (MWCNTs) were incorporated in ultrahigh molecular weight polyethylene (UHMWPE), which is a polymer used in industrial and orthopedic applications. The composites were prepared by ball milling and thermo-compression processes at concentrations up to 3 wt.% and subsequently gamma irradiated at 90 kGy. Electrical conductivity measurements showed a low percolation threshold of 0.5 wt.%. Electron spin resonance detection of the radiation-induced radicals proved the radical scavenger behavior of MWCNTs: when the nanotube concentration increased, the number of radicals generated by the gamma irradiation process decreased. Allyl radicals seem to be the radicals most affected by the presence of nanotubes in this polymeric matrix. Fourier transformed infrared spectroscopy measurements and an accelerated ageing protocol were performed to ascertain the influence of the irradiation on the oxidation index. The results pointed to the positive contribution of the MWCNTs in increasing the oxidative stability of the composite compared to pure UHMWPE. Crosslinking density induced by gamma irradiation was obtained by swelling measurements. The findings showed that, despite the radical scavenger performance, MWCNTs are capable of maintaining the efficiency of the crosslinking density, unlike the other antioxidants, which inhibit radiation crosslinking.     

Effects of in situ synthesized mullite whiskers on compressive strength of mullite fiber brick

The method of in situ synthesis of mullite whiskers by gas-phase deposition and reaction was applied to improve the compressive strength of the mullite fiber brick. During the preparation process, silica sol, Al(NO₃)₃ solution and NH₄F solution were introduced into the fibrous brick in the form of ions or sol through vacuum impregnation and freeze drying, and the silica sol, Al(NO₃)₃ and NH₄F served as the silica sources, aluminum source and catalyst, respectively. Effects of process parameters (concentration of impregnation solutions, holding time, sintering temperature) on compressive strength and elastic modulus of the fibrous brick during the in situ toughening process were analyzed. SEM and XRD analysis results demonstrated that the mullite whiskers were synthesized on the surface of mullite fibers based on the reaction of AlOF and SiF₄. What is more, the whiskers on adjacent fibers intersected with each other and formed many unfixed lap-jointing points, resulting in the increase of compressive strength and elastic modulus. Although the density and thermal conductivity of the sample after the generation of mullite whiskers fabricated with the optimum process were 0.406 g/cm³ and 0.1262 W/(m K), respectively, which were slightly higher than that of the raw fibrous brick (0.375 g/cm³ density and 0.1069 W/(m K) thermal conductivity, respectively), the corresponding compressive strength and elastic modulus of the sample reinforced with the whiskers increased to 1.45 MPa and 42.03 MPa, respectively, which were much higher than that of the raw fibrous brick (0.39 MPa compressive strength and 6.5 MPa elastic modulus).     

Thermoluminescence response of 120 MeV Ag9+ and γ-ray exposed LiMgBO3:Dy3+ nanophosphors for dosimetry

Thermoluminescence(TL) response of LiMgBO₃:Dy³⁺ nanophosphor synthesized by combustion method was examined using γ-ray and 120 MeV Ag⁹⁺ swift heavy ion (SHI) irradiation. The LiMgBO₃:Dy³⁺ samples were exposed to 0.01 kGy −5 kGy γ-rays while for the different fluences the samples were irradiated with 120 MeV Ag⁹⁺ SHI over the range 1×10¹¹ ions cm⁻² to 1×10¹³ ions cm⁻². The prominent TL glow curve peaks appeared at 396 K and 390 K for the γ-ray and 120 MeV Ag⁹⁺ SHI irradiated samples. The glow curves for the SHI iradiated samples were more complex than those of the γ-ray exposed samples. The effect of different heating rates on the TL response was also determined. The trapping parameters (i.e. activation energy, frequency factor, order of kinetic) of all the individual peaks of the glow curves have been analysed by using Chen's formulae. The TL response curve against γ-ray exposure illustrated a good linear response upto 3 kGy and after that the response was sublinear. For the 120 MeV Ag⁹⁺ ion irradiated samples, the material exhibited a sublinear dependence against ion irradiation for the studied fluence. The good TL response against γ-ray irradiation suggested that the material can be explored for a possible application in dosimetry.     

Effect of gamma-irradiation on the mechanical properties of polyacrylonitrile-based carbon fiber

The influence of gamma-irradiation on the structure and mechanical properties of polyacrylonitrile-based carbon fibers was studied. It was observed that the Young’s modulus of the fibers irradiated increased with irradiation dose, increasing to 267 GPa at 300 kGy, a 16.1% improvement compared to that of as-received carbon fiber. However, the tensile strength increased to 5.4 GPa at 30 kGy, i.e., a 17.4% increase, and then dropped to 4.65 GPa at 300 kGy, which is almost the same as for the untreated fiber. Uniform stress model analysis and Raman spectroscopy show that the degree of covalent cross-linking between the graphene planes increased to a maximum at 30 kGy and then remained almost constant with further irradiation. The SEM images show that the degree of surface roughness increased with the increasing irradiation dose. It is believed that when the dose is less than 30 kGy, the increased cross-linking is the dominant effect, and thus improves the tensile strength. On the other hand, further irradiation generates surface flaws, which neutralizes the increase and results in a decrease of tensile strength.     

Fabrication of structure-controlled hydroxyapatite/zirconia composite

The structure-controlled hydroxyapatite/zirconia (HAp/ZrO₂) composites were fabricated. At first, cylindrical hydroxyapatite (HAp) samples were prepared by the extrusion process, and then the extruded HAp cylindrical samples were coated with 3 mol% of Y₂O₃ partially stabilized ZrO₂ slurry, dried and aligned unidirectionally to form a composite bulk. The volume fraction of ZrO₂ in the HAp/ZrO₂ composite was estimated to be about 23 vol%. Bulk density and bending strength of the composites increased with sintering temperature. Fracture energy of HAp/ZrO₂ composite sintered at 1350 °C was approximately 1.6 times higher than that of monolithic HAp. Although the bending strength of HAp/ZrO₂ composite prepared in this study was relatively low, it exhibited high fracture energy than HAp monolithic and a non-brittle fracture behavior was obtained without using fiber as the reinforcement.     

Surface modifications of activated carbon by gamma irradiation

Four commercial activated carbons with different chemical and textural characteristics were modified by gamma irradiation under five different conditions: irradiated in absence of water, in presence of ultrapure water, in ultrapure water at pH = 1.0 and 1000 mg L⁻¹ Cl⁻, in ultrapure water at pH = 7.5 and 1000 mg L⁻¹ Br⁻, and in ultrapure water at pH = 12.5 and 1000 mg L⁻¹ NO₃⁻. Changes in surface chemistry were studied by X-ray photoelectron spectroscopy; pH of point of zero charge, total acidic groups and total basic groups, which were determined by assessment with HCl and NaOH; and textural changes were determined by obtaining the corresponding adsorption isotherms of N₂ and CO₂. Outcomes show that the activated carbon surface chemistry can be modified by gamma irradiation and that the changes depend on the irradiation conditions. Modifications in the sp² hybridization of the surface carbons suggest that the irradiated carbons undergo graphitization. Measurements of structural parameters indicate that the irradiation treatment does not modify the textural properties of the carbons. Finally, studies of pristine and irradiated activated carbons using diffuse reflectance spectroscopy with the Kubelka–Munk function revealed a reduction in band gap energy in the irradiated carbons associated with an increase in sp² hybridization of the carbon atoms.     

Natural origin hydroxyapatite scaffold as potential bone tissue engineering substitute

Fish scales derived natural hydroxyapatite (FS-HAp) scaffolds were prepared through solvent casting technique, which could mimic the structure of cortical and cancellous bone tissues of body system. The hydroxyapatite (HAp) biomaterial was synthesized by thermal decomposition of chemically treated fish scales. Fabricated scaffolds were characterized through morphological analysis, volumetric shrinkage, mechanical tests, and in vitro, in vivo biological studies. The projected scaffolds successfully mimic the cancellous/cortical bone system in terms of structure, porosity, mechanical strength, and exhibit excellent bioactive behavior. The FS-HAp scaffolds manifest good mechanical behaviors with Vickers Hardness (HV) of ~0.78 GPa, 0.52 GPa compressive stress, 190 MPa tensile stress and ~35% porosity on sintering at 1200 °C. In vitro and in vivo studies suggest these nontoxic HAp scaffolds graft with osteoconductive support, facilitating new cell growth on the developed scaffold surface. The graded grafts have a great potential for application as traumatized tissue augmentation substitute, and ideal for load-bearing bone applications.     

Comparative study of hydroxyapatite/gelatin composites reinforced with bio-inert ceramic particles

Recently, nano bio-composites have emerged as an efficient strategy to upgrade the structural and functional properties of synthetic bone grafts. Bioinert ceramics have attracted wide attention because of their biocompatibility. Novel composites of nano-hydroxyapatite/GEL with incorporation of bioinert ceramics like Al₂O₃, TiO₂ and ZrO₂ for different composites as a reinforcing phase to increase its mechanical properties was prepared. The nHAp with the size of 10–50 nm in diameter and 50–100 nm in length was uniformly distributed into GEL matrix to form the composite. It was found that the composite with a high ceramic content has good homogeneity and mechanical strength, which are close to the cancellous bone. An interconnected porous material with porosity of at least 74% was achieved by phase inversion method. The formation reaction of the nHAp/GEL/bioinert ceramic nanocomposite was then investigated via FT-IR, XRD, TG/DTA and SEM. The organic–inorganic interaction between HAp nano crystallites and GEL molecules were confirmed from FT-IR and TG/DTA. The compressive strength of bioinert ceramic reinforced nanocomposites scaffolds could high up to 13.15 MPa while those of nHAp/GEL were 4.87 MPa. The nano indentation technique was used to find nano hardness and fracture toughness was evaluated by Vickers indentation.     

Microstructures and material properties of fibrous HAp/Al2O3–ZrO2 composites fabricated by multi-pass extrusion process

Fibrous HAp/Al₂O₃–ZrO₂ composites were fabricated using the multi-pass extrusion process. In the 3rd and 4th passed extrusion bodies, fibrous microstructures were obtained. The 3rd and 4th passed Al₂O₃–ZrO₂ cores used as reinforcement, were about 35 and 4.5 μm in diameter, respectively. In the bodies sintered at over 1400 °C, the HAp decomposed and was transformed to β-TCP and TTCP, in which large numbers of pores were observed. The values of bending strength, Vickers hardness and fracture toughness of the 3rd passed HAp/Al₂O₃–ZrO₂ composites were 178 MPa, 325 Hv, and 3.4 MPa m^1/2, respectively while the values of the 4th passed bodies were 190 MPa, 405 Hv and 3.8 MPa m^1/2.     

Fabrication of surface-treated BN/ETDS composites for enhanced thermal and mechanical properties

The ceramic/polymer composites based on epoxy-terminated dimethylsiloxane (ETDS) and boron nitride (BN) were prepared for use as thermal interface materials (TIMs). 250 µm-sized BN was used as a filler to achieve high-thermal-conductivity composites. To improve the interfacial adhesion between the BN particles and the ETDS matrix, the surface of BN particles were modified with silica via the sol–gel method with tetraethyl orthosilicate (TEOS). The interfacial adhesion properties of the composites were determined by the surface free energy of the particles using a contact angle test. The surface-modified BN/ETDS composites exhibited thermal conductivities ranging from 0.2 W/m K to 3.1 W/m K, exceeding those of raw BN/ETDS composites at the same weight fractions. Agari׳s model was used to analyze the measured thermal conductivity as a function of the SiO₂-BN concentration. Moreover, the storage modulus of the BN/ETDS composites was found to increase with surface modification of the BN particles.     

Effect of electron beam irradiation and degree of boric acid loading on the properties of styrene-butadiene rubber

Synthetic and totally amorphous styrene-butadiene rubber (SBR) has been loaded with varying contents of boric acid. Vulcanization of prepared composites as well as of unloaded rubber has been induced by ionizing radiation of accelerated electron beam of varying doses up to 250 kGy. Evaluation of prepared composite subjected to this range of irradiation has been followed up through the measurement of mechanical, physical, electrical and thermal properties of vulcanized composites. Mechanical properties, namely tensile strength (TS) and Young’s modulus were found to increase, whereas elongation at break (E_b) and permanent set (PS) were found to decrease with the increase in degree of boric acid loading as well as irradiation dose. On the other hand, physical properties, namely the gel content, have increased whereas the swelling number has decreased. Moreover, increase in the decomposition temperature has been attained. Also, limited increase in electrical conductivity has taken place. Data obtained indicate enhancement in thermal as well as in physico-mechanical properties of prepared composites. Moreover, 60 phr of boric acid has attained good mechanical properties.     

Characteristic reaction processes in the system brushite–NaOH solution

The reaction of brushite (CaHPO₄·2H₂O, DCPD) with NaOH solutions ranging in concentration from 0 to 40 mass% were investigated at 25 °C. At low NaOH concentrations below 20 mass%, hydroxyapatite (HAp) formed directly through the reaction (1) DCPD → HAp. At middle concentrations of 20–27 mass%, DCPD changed once into Ca(OH)₂ and then into HAp, i.e., through the consecutive reaction (2) DCPD → Ca(OH)₂ → HAp. At high concentrations above 27 mass%, the consecutive reaction (3) DCPD → HAp → Ca(OH)₂ was concluded. The boundary concentrations, i.e., singular points, between the first/second and the second/third reactions were estimated to be ca. 20 and 27 mass%, respectively. HAp particles obtained were platelet aggregates of very fine HAp microcrystals. The platelet form was compatible to the original platelet DCPD form. HAp samples prepared in this reaction system were structurally low crystalline and compositionally stoichiometric, and had a feature of large heating weight losses below 400 °C.     

Loadable TiO2 scaffolds—A correlation study between processing parameters,micro CT analysis and mechanical strength

It was shown in the present study that it is possible to produce TiO₂ scaffolds with both high mechanical strength and high porosity by using the polymer sponge method. TiO₂ scaffolds with porosity above 85% exceeded 1 MPa in compressive strength. TiO₂ scaffolds with equally high compressive strength having a fully open porosity close to 90% is not previously been reported in the literature. Reduction of porosity leads to even further reinforce the scaffolds’ mechanical structure. A statistical correlation study with 160 tested scaffolds defined the most important manufacturing steps and the governing morphological characteristics for the scaffold's increased mechanical strength. The key manufacturing factors were a holding phase during sintering time for more than 30 h (at 1500 °C) and multiple coatings of the scaffold's structure. The crucial parameters for high mechanical strength were the fractal dimensions of the struts, object surface/volume ratio, density and overall porosity.     

Mechanical properties and microstructures of 2D Cf/ZrC–SiC composites using ZrC precursor and polycarbosilane

Two-dimensional C_f/ZrC–SiC composites were fabricated through mold-pressing and polymer infiltration and pyrolysis (PIP) using T700SC plain weave fiber fabrics as reinforcements with ZrC precursor and polycarbosilane. The mechanical properties and microstructures of the composites with 34, 45, and 56% fiber fraction were investigated. All composites showed a typical non-brittle fracture behavior and a large amount of pulled-out fibers were observed on the fracture surface. The bending strength and elastic modulus of the composite with 56 vol% fiber fraction increased up to 582 ± 80 MPa and 167 ± 25 GPa, with increasing fiber fraction. The mass loss and linear recession rate of the composites during the oxy-propane torch test were 0.008 g/s and ?0.003 mm/s, respectively. The formation of a ZrSiO₄ melt on the surface of the composite significantly contributed to the excellent ablative property of the 2D C_f/ZrC–SiC composites.     

Microstructure and properties of ablative C/ZrC–SiC composites prepared by reactive melt infiltration of zirconium and vapour silicon infiltration

C/ZrC-SiC composites with a density of 3.09 g/cm³ and a porosity of 4.8% were prepared by reactive melt infiltration and vapour silicon infiltration. The flexural strength and modulus were 235 MPa and 18.3 GPa, respectively, and the fracture toughness was 7.0 MPa m^1/2. The formation of SiC and ZrSi₂ during vapour silicon infiltration, at the residual cracks and pores in the C/ZrC, enhanced the interface strength and its mechanical properties. The high flexural strength (223 MPa, c. 95% of the original value) after oxidation at 1600 °C for 10 min indicated the excellent oxidation resistance of the composites after vapour silicon infiltration. The mass loss and linear recession rate of the composites were 0.0071 g/s and 0.0047 mm/s, respectively and a fine ablation morphology was obtained.     

Aluminum titanate based ceramics from aluminum sludge waste

This work aims at obtaining aluminum titanate-based ceramics (Al₂TiO₅: AT) composites from industrial wastes. Al-sludge waste and rutile ore were used as rich sources of alumina and titania instead of pure materials. Sludge-(0–40 wt%) rutile mixtures were mixed, formed and fired at 1350 °C for various times. Phase composition, microstructure, densification, mechanical and thermal behaviors of the obtained AT composites have been investigated. Complete conversion of the starting materials to AT with bulk density of 3.199 g/cm³, compressive strength and modulus of rupture of 326.425 MPa and 30.84 MPa, respectively and very low CTE (−0.927*10⁻⁶ K⁻¹) were achieved by firing the sludge-(30 wt%) rutile at 1350 °C for 4 h. These results suggest that the obtained AT-ceramics from Al-sludge waste-rutile ore are a promising and an ecofriendly route.     

Fully reacted high strength geopolymer made with diatomite as a fumed silica alternative

Geopolymers are formed by mixing of aluminosilicate sources with alkaline meta-silicate solution at room temperature. In the current study, diatomite of Turkish origin was fully utilized as a fumed silica alternative for the preparation of geopolymer, having a typical formula of K₂O•Al₂O₃•4SiO₂•11H₂O. From XRD of this sample, a broad peak centered at 28° 2θ indicated the well-known formation of amorphous geopolymer, as well as a fully reacted microstructure of geopolymer as seen by scanning electron microscopy. Additionally, geopolymer having the same formula was made by using fumed silica, in order to compare with geopolymers prepared from diatomite. The Weibull modulus was calculated from four-point bending and compressive strength testing of both geopolymer composites. The use of diatomite as a fumed silica substitute in geopolymer production resulted in a very close flexure strength 9.2 (± 4.2 MPa) when compared to geopolymer made from fumed silica 10.2 (± 3.3 MPa). There was a significantly higher compressive strength 71 (± 13.9 MPa) and Weibull modulus (5.4), than comparable properties of geopolymer made from fumed silica, which had a compressive strength 54 (± 25.8 MPa) and Weibull modulus of 2.0. The discrepancy was attributed to some self-reinforcement of the geopolymer matrix due to unreacted diatomite.