S. Y. Yahya

Synthesis and nucleation-growth mechanism of almost catalyst-free carbon nanotubes grown from Fe-filled sphere-like graphene-shell surface

This finding focuses on the optimization of synthesis time for the transformation of Fe-filled spherical-like graphene shell (GS) to almost catalyst-free carbon nanotube (CNT) structure using two-stage catalytic chemical vapor deposition apparatus. The camphor oil and ferrocene were used as carbon precursor and catalyst respectively, following the variety growth of graphene-family nanomaterials for 2, 4, 6, 8, 10, 30, and 60 min at 800°C synthesis temperature. The graphene-family nanomaterial properties were characterized using field emission scanning electron microscope, high resolution transmission electron microscope, micro-Raman spectrometer, thermogravimetric, and carbon-hydrogen-nitrogen-sulfur/oxygen (CHNS/O) analyzer. The result of field emission scanning electron microscopy analysis reveals that the CNTs were observed with high aspect ratio at 60-min synthesis time. The dependence of integrated intensity ratio of D-band and G-band (ID/IG) presented that ID/IG ratio sharply decreases with longer synthesis time. At higher synthesis time, thermogravimetric and CHNS/O analysis of CNT can obviously improve with decreases of non-carbonaceous material and transition metal catalyst. The nucleation-growth model of Fe-filled spherical-like GS to almost catalyst-free CNT has been highlighted to explain the change in growth mode.

Mechanical properties of thermoplastic natural rubber reinforced with multi-walled carbon nanotubes

This study investigated the mechanical properties of thermoplastic natural rubber (TPNR) nanocomposites reinforced by multi-walled carbon nanotubes (MWNTs). The TPNR nanocomposites were prepared using melt blending method from polypropylene, natural rubber, and liquid natural rubber as a compatibilizer, respectively, with 1—7 wt% of MWNTs. The tensile strength and Young’s modulus increased by almost 39% and 30%, respectively, at 3 wt% of MWNTs. The elongation at break decreased with increase in the percentage of MWNTs. The maximum impact strength was recorded at 5 wt% of MWNTs which was increased by 74% as compared with a pristine TPNR sample. The effect of MWNTs was also confirmed by DMA; it showed that the storage modulus E′, loss modulus E′′, and glass transition temperature (Tg) also increased for all MWNT reinforced samples. SEM micrographs confirm the effect of good dispersion of MWNTs and their interfacial bonding in TPNR.

Thermal behavior of MWNT-reinforced thermoplastic natural rubber nanocomposites

This article studies the thermal properties of a multi-walled carbon nanotube (MWNT)-reinforced thermoplastic natural rubber (TPNR) nanocomposite. The nanocomposite was prepared using a melt blending method. Various percentages (1, 3, 5, and 7 wt%) of MWNTs were added into TPNR to improve its thermal properties. The laser flash technique was also employed to determine the thermal conductivity, thermal diffusivity, and specific heat capacity of the nanocomposite. The DMA result showed that the glass transition temperature (Tg) increased with the increase in MWNT content. TEM micrographs also demonstrated that a good dispersion of MWNTs was achieved in the TPNR environment.

Reinforced Thermoplastic Natural Rubber (TPNR) Composites with Different Types of Carbon Nanotubes (MWNTS)

The emergence of thermoplastic elastomers (TPEs) is one of the most important developments in the area of polymer science and technology. TPEs are a new class of material that combine the properties of vulcanized rubbers with the ease of processability of thermoplastics (Abdullah & Dahlan, 1998). Thermoplastic elastomers can be prepared by blending thermoplastic and elastomers at high shear rate. Thermoplastics, for example, polypropylene (PP), polyethylene (PE) and polystyrene (PS), and elastomers, such as ethylene propylene diene monomer (EPDM), natural rubber (NR) and butyl rubber (BR), are among the materials used in thermoplastic elastomer blends. Blends of natural rubber (NR) and polypropylene (PP) have been reported widely by previous researchers (Abdullah & Dahlan, 1998; Ismail & Suryadiansyah, 2002). According to Abdullah and Dahlan (1998), polypropylene is the best choice for blending with natural rubber due to its high softening temperature (150oC) and low glass transition temperature (60oC, is Tg for NR), which makes it versatile in a wide range of temperatures. Even though NR and PP are immiscible, their chemical structure is nearly the same. Thus, stable dispersion of NR and PP is possible. Incompatibility between NR and PP can be overcome by the introduction of a compatibilizer that can induce interactions during blending. Compatibility is important as it may affect the morphology, mechanical and thermal properties of the blends. Among the commonly used compatibilizers are dicumyl peroxide (DCP), m-phenylene bismaleimide (HVA-2) and liquid natural rubber (LNR). Apart from compatibility, mixing torque and curing are interrelated in determining the homogeneity of the TPNR blend (Abdullah & Dahlan, 1998). A pioneer group of researchers in UKM has studied extensively the utilization of liquid natural rubber (LNR) as a compatibilizer on various natural rubber/polyolefin blends (Ibrahim Abdullah & Sahrim Ahmad, 1999). Liquid natural rubber was produced by photodegradation of natural rubber (NR) in toluene and exposure to ultraviolet for 6 hours (Dahlan, 1998). The LNR has the same microstructure with NR but with a short chain of polyisoprene (different in molecular weight, Mw) (Ibrahim, 2002). The Mw for LNR is around

Superconductivity of REBa2Cu3O7-δ (RE= Y, Dy, Er) ceramic synthesized via coprecipitation method

The REBa2Cu3O7-δ (RE= Y, Dy, Er) superconducting ceramics have been prepared via coprecipitation(COP) method from nearly saturated solutions of metal acetates and 2- propanol solution of oxalic acid. The metal oxalates powders were subjected to thermal treatment of 12 hours calcination at 900oC. The pelletized powder was sintered for 15 hr at 920oC. All samples showed a single step transition in the R-T curves. The TC(R=0) for samples Dy123, Y123and Er123 and were 93 K, 91 K and 90 K, respectively. XRD data showed single phase of an orthorhombic structure for all samples. SEM micrographs showed large grain sizes that are randomly distributed. These results showed that COP method using metal oxalates starting powders is very effective to synthesize high quality superconductors and shorten the sintering time required due to the formation of sub micron oxalate powders.

Improving Structural and Micro-Raman Properties of Camphor-Grown Pristine Carbon Nanotubes with Special Focus on Single-Stage Thermal Annealing System

The camphor-grown pristine carbon nanotubes (CNT) was annealed by a single-stage thermal annealing system through controlled ambient in air, argon and nitrogen, are reported. Field emission scanning electron microscopy images confirmed that the heat treatment process gives a place to re-ordering carbon nanostructures which involves: (i) an elimination of structural defects and (ii) better graphitization of the amorphous carbon phase without damaging CNT structure. The room temperature micro-Raman measurements showed that no significant changes on the D and G-line position. However, different annealing gas ambient could give different values degree of graphitization (ID/IG ratio) due to the nature of gas itself. It reveals that single-stage thermal annealing system is relatively simple and effective to obtain an ideal CNT.

Effect of Ultrasonic Treatment on The Tensile and Impact Properties of Thermoplastic Natural Rubber Nanocomposites Reinforced with Carbon Nanotubes

This study investigates the effect of ultrasonic treatment on the mechanical properties of thermoplastic natural rubber (TPNR) nanocomposites reinforced with multi‐walled nanotubes. The TPNR nanocomposites were prepared using melt blending method from polypropylene (PP), natural rubber (NR) and liquid natural rubber (LNR) as a compatibilizer, respectively, with 1% of Multi‐wall nanotubes. The nanocomposite was prepared using the indirect technique (IDT) with the optimum processing parameters at 180° C with 80 rpm mixing speed and 11 minutes processing time. The results have showed that the good dispersion on nanotubes was achieved by ultrasonic treatment. The optimization of ultrasonic time indicated that the maximum tensile and impact properties occurred with 1 h ultrasonic treatment. The Young’s modulus, tensile strength, elongation at break and impact strength have increased by almost 11%, 21%, 43% and 50%, respectively. The results from our study indicate that nanotubes have as excellent reinforcement...

Synthesis of Bi1.6Pb0.4Sr2Ca2Cu3O10+δ-(Dy2O3)x Added with Magnetic Nanoparticles Dy2O3 Dysprosium Oxide (0.0≤x≤0.1) via Co-Precipitation Method

Superconducting study present the properties of small weight percent of magnetic nanoparticles Dy2O3 from x = 0.0 to 0.10 added in Bi1.6Pb0.4Sr2Ca2Cu3O10+δ (Dy2O3)x. It is found, the form size of magnetic nanoparticles Dy2O3 is spherical, nano Dy2O3 particles will enter easily into the Bi, Pb-2223 superconductor. From here it is early to conclude the inducing of Dy atoms into the Bi, Pb-2223 crystal structure because Bi-based superconductors are known for their strong anistropic properties and extremely short coherence length (ξ) as long there are significant change in it microstructure, lattice parameter and the normal state conductivity of the system. The characterization on critical temperature (Tc) and transport critical current density (Jc) of magnetic nanoparticles Dy2O3 added to enhance the optimum amount levels added. The maximum Tc achieved Tc-(R=0) 109 K (for x = 0.4) as samples respectively compared to the pure samples. This results will discussed directly to the basis properties changes in Bi, Pb-2223 with addition of magnetic nanoparticles of Dy2O3.

Structural and Thermal Properties of ACNT by Modified Deposition Method: Growth Time Approach

The knowledge of fabrication method plays an important role in the preparation of aligned carbon nanotubes (ACNT) from natural hydrocarbon feedstock. Here ACNT were successfully synthesized by two-stage catalytic chemical vapor deposition method using organic oil (camphor oil) as a precursor. Synthesis was carried out at a fixed growth temperature of 800 °C and in different growth time: 10, 20, 30, 40, 50 and 60 minutes. The optimized condition for the growth of ACNT produced a small amount of by-product amorphous carbon and highly uniform crystal structure. The experimental results demonstrated that formation ACNT is also dependent on the growth time. The nanotubes were characterized by field emission scanning electron microscopy and micro-Raman spectroscopy. Thermal properties were evaluated by thermogravimetric analysis.

Influence of Na, Mg and Yb Substitution for Ca in Bi(Pb)-2223 Superconductor

The effect of Ca substitution by Na, Mg and Yb on the structural and transport properties of Bi1.6Pb0.4Sr2Ca2-xMxCu3Oy (M = Na, Mg and Yb) (x = 0.0 and 0.2) superconducting samples have been investigated. The samples were prepared by the coprecipitation (COP) method. The samples were characterized by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), electrical resistivity measurement and critical current density. The critical current density (Jc) and transition temperature (Tc zero) of Na, Mg and Yb substituted with x = 0.2 were found to be lower than the pure sample. Tc zero varies between 100 K and 63 K. Mg concentration was found to give the highest Tc zero of 93 K. Tc zero gradually decreased from Mg, Yb to Na corresponding to a small change in the carrier concentration. Jc decreased with Mg, Yb and Na substitution, and it was measured to be 7.4611 A/cm2, 0.0667 A/cm2, 1.4579 A/cm2 and 1.2479 A/cm2 for pure, Na, Mg and Yb substitution, respectively at 60 K. XRD analysis showed that the decrease of the volume fraction for the 2223 phase and increase of the volume fraction for the 2212 phase with substitution of Na, Mg and Yb. The proportion of Bi-2223/Bi-2212 (%) was estimated from 78.13/21.87 for pure to 51.71/48.29 for Na substitution.