This paper presents a study on the thermal properties of a range of geopolymers in order to assess their suitability for high temperature applications such as thermal barriers, refractories and fire ...resistant structural members. Geopolymers were synthesised from five different fly ashes using sodium silicate and sodium aluminate solutions to achieve a set range of Si:Al compositional ratios. The thermo-physical, mechanical and microstructural properties of the geopolymers are presented and the effect of the source fly ash characteristics on the hardened product is discussed, as well as implications for high temperature applications. The amount and composition of the amorphous component (glass) of each of the fly ashes was determined by combining XRD and XRF results. It was found that the Si:Al ratio in the glass of the fly ashes strongly influenced the thermal performance of the geopolymers. Geopolymers synthesised from fly ashes with a high Si:Al (≥5) in the glass exhibited compressive strength gains and greater dimensional stability upon exposure to 1000°C, whereas geopolymers synthesised from fly ashes with low Si:Al (<2) in the glass exhibited strength losses and reduced dimensional stability upon high temperature exposure.
► Quantification of the crystalline and amorphous phases of five different fly ashes. ► Si:Al ratio in the glass of the fly ash influences the thermal performance. ► Compressive strength of geopolymers can increase by up to 5 fold after firing. ► Sodium aluminate activated geopolymers exhibit thermal stability up to 800°C. ► Sintering during thermal exposure improved inter-particle bonding.
Based on the fact that tumor cells are more thermolabile and less oxygen resistant than normal cells, a novel minimally invasive tumor treatment modality, magnetic hyperthermia (MHT) is proposed. ...However, magnetic materials, which are necessities in MHT, are toxic to human tissue if they are excessively employed. Thus, magnetic materials with higher specific absorption rate (SAR) and intrinsic loss power (ILP) values becomes imperative to minimize their clinical application while mitigating damage to normal human tissues under identical treatment temperature conditions. In this study, the incorporation of soft magnetic MnFe2O4 into hard magnetic CoFe2O4 was introduced, leveraging the exchange coupling between these materials to enhance the magnetic saturation (Ms). Subsequently, we combined these magnetic nanomaterials with graphene oxide (GO) to establish an efficient heat conduction pathway, further augmenting the specific absorption rate (SAR) value of the resulting magnetic composites. Our findings reveal that the Mn0.5Co0.5Fe2O4-1%GO composite developed in this investigation boasts superior SAR values and intrinsic loss power (ILP) of 49.7 W/g and 5.90 nHm2/kg, respectively, when compared to other magnetic materials. The nanomaterials synthesized in this study have the potential to significantly enhance the effectiveness of tumor magnetothermal therapy.
•Improve the SAR by increasing the magnetic saturation with exchange coupling between the soft and hard magnetic phases.•Combine magnetic nanomaterials with graphene oxide to construct heat transfer channels to further improve the SAR.•Investigate Mn1-xCoxFe2O4 MNPs in a wide range of Mn and Co ratios and select the best one with highest SAR value.•Investigate magnetic properties of Mn0.5Co0.5Fe2O4-GO MNPs with different GO contents in alternating magnetic field.
Bi doped 2CaO-Al.sub.2O.sub.3-SiO.sub.2 (gehlenite) glasses were prepared by conventional melting. The concentration of Bi.sup.3+ was 0, 0.25, 0.50 and 1.50 mol. %. The prepared samples were X-ray ...amorphous except of the undoped sample and the sample with the highest content of Bi.sup.3+, for which XRD records revealed traces of crystalline gehlenite.
Graphene consists of a monolayer of sp(2) bonded carbon atoms and has attracted considerable interest over recent years due to its extreme mechanical, electrical, and thermal properties. Graphene ...nanocomposites have naturally begun to be studied to capitalize upon these properties. A range of complex chemical and physical processing methods have been devised that achieve isolated graphene sheets that attempt to prevent aggregation. Here we demonstrate that the simple casting of a polymer solution containing dispersed graphene oxide, followed by thermal reduction, can produce well-isolated monolayer reduced-graphene oxide. The presence of single layer reduced-graphene oxide is quantitatively demonstrated through transmission electron microscopy and selected area electron diffraction studies and the reduction is verified by thermogravimetric, X-ray photoelectron spectroscopy, infrared spectrum, and electrical conductivity studies. These findings provide a simple, environmentally benign and commercially viable process to produce reduced-graphene oxide reinforced polymers without complex manufacturing, dispersion or reduction processes.
This study investigates the impact of incorporating TiOsub.2 nanoparticles into two types of oils at different temperatures and with varying volume fractions: transformer oil (NYTRO LIBRA) and virgin ...coconut oil (manufactured by Govi Aruna Pvt. Ltd., Gampaha, Sri Lanka). The nanofluids were prepared using a two-step method by adding CTAB (cetyltrimethylammonium bromide) surfactant. To minimize nanoparticle agglomeration, this study employed relatively low-volume fractions. Thermal properties by means of thermal conductivity, thermal diffusivity, and volumetric heat capacity were measured in accordance with ASTM (American Society for Testing and Materials) standard methods using a multifunctional thermal conductivity meter (LAMBDA thermal conductivity meter). The measured thermal conductivity values were compared with theoretical models and previous research findings. It was confirmed that the modification of thermal properties was enhanced by doping TiOsub.2 nanoparticles with different volume fractions.
Experimental investigations have been carried out for determining the thermal conductivity of three nanofluids containing aluminum oxide, copper oxide and zinc oxide nanoparticles dispersed in a base ...fluid of 60:40 (by mass) ethylene glycol and water mixture. Particle volumetric concentration tested was up to 10% and the temperature range of the experiments was from 298 to 363
K. The results show an increase in the thermal conductivity of nanofluids compared to the base fluids with an increasing volumetric concentration of nanoparticles. The thermal conductivity also increases substantially with an increase in temperature. Several existing models for thermal conductivity were compared with the experimental data obtained from these nanofluids, and they do not exhibit good agreement. Therefore, a model was developed, which is a refinement of an existing model, which incorporates the classical Maxwell model and the Brownian motion effect to account for the thermal conductivity of nanofluids as a function of temperature, particle volumetric concentration, the properties of nanoparticles, and the base fluid, which agrees well with the experimental data.
A critical synthesis of the variants within the thermophysical properties of nanofluids is presented in this work. The experimental results for the effective thermal conductivity and viscosity ...reported by several authors are in disagreement. Theoretical and experimental studies are essential to clarify the discrepancies in the results and in proper understanding of heat transfer enhancement characteristics of nanofluids. At room temperature, it is illustrated that the results of the effective thermal conductivity and viscosity of nanofluids can be estimated using the classical equations at low volume fractions. However, the classical models fail to estimate the effective thermal conductivity and viscosity of nanofluids at various temperatures. This study shows that it is not clear which analytical model should be used to describe the thermal conductivity of nanofluids. Additional theoretical and experimental research studies are required to clarify the mechanisms responsible for heat transfer enhancement in nanofluids. Correlations for effective thermal conductivity and viscosity are synthesized and developed in this study in terms of pertinent physical parameters based on the reported experimental data.
The aim of the study was to determine the effects of oven, microwave (MW), and infrared (IR) drying technology on the drying kinetics, physicochemical properties, and β-carotene retention of the ...dried orange-fleshed sweet potato flour (OFSP). Fresh OFSP slices were dried in an oven (40°C), MW (80 W), IR (250 W), MW-IR (80 W+250 W), and freeze-drying (-45°C, 100 kPa) and milled into flour. Hot air at a constant temperature was applied to all thermal drying technologies (40°C, 4.5 m/s air velocity). The drying rate of the MW-IR drying method was the fastest (45 min), followed by MW (60 min), IR (120 min), and oven (180 min). The Page model was most suitable for the oven-drying method, the Lewis model for IR drying, and Henderson and Pabis for IR and Logarithmic for the MW-IR method. The pasting and thermal properties of the flours were not significantly (p>0.05) affected by the different drying methods. However, IR- and MW-IR-dried flours showed a higher final viscosity when compared to other drying methods. MW-IR drying methods, IR, and MW showed a higher water solubility index, while the oven and freeze-drying methods showed a lower solubility index. MW-IR drying methods showed a higher retention of β-carotene (85.06%). MW also showed a higher retention of β-carotene (80.46%), followed by IR (66.04%), while oven and freeze-drying methods showed a lower retention of β-carotene. High β-carotene retention in the produced flour is due to the faster drying method, and these flours can be used in food-to-food fortification to address vitamin A deficiency.
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