Effect on Heat Treatment and Doping of Cubic NaZn13-Type La0.7Pr0.3(Fe,Si)13 for Magnetic Refrigerator Application

Soft ferromagnetic cubic NaZn13-type La0.7Pr0.3Fe11.4Si1.6 has turned out to be a standout amongst the most fascinating compounds for investigating substantial magnetocaloric effect (MCE) on the grounds that the attractive properties of this compound shows large enough spontaneous magnetization for applications, strongly doping dependent, and as well as delicate soft ferromagnetism. These impacts can be attributed to the itinerant electron metamagnetic (IEM) transition especially around the first-order magnetic transition region. However, this compound is difficult to frame by the basic cementing process because of the inherent deficiency of the peritectic response, Υ-Fe + La → La(Fe,Si)13(τ1a), which frequently brings about a blended microstructure of α-Fe + La(Fe,Si)13(τ1a) + LaFeSi(τ4). Additionally, dependability of La(FexSi1−x)13 is no middle-of-the-road stage and common solvency amongst Fe and La in the Fe-La framework as a reality is represented by response dispersion as indicated by magnetic and electronic states’ contribution. From this point of view, the structure, attractive properties and MCE of this compound have been talked about in detail as indicated by various temperatures and times of the annealing treatment. In addition, efficiently contemplating on the doping impact from various concentrations of transition metal elements such as Copper (Cu) and Chromium (Cr) on Iron (Fe) in the La0.7Pr0.3Fe11.4Si1.6 compound is likewise discussed

Smart control and management system for hydroponic plant growth

Hydroponics is one of the cultivation methods that uses water as a plant growth medium. In this technique, a mineral solution is added to the water solvent, which enables the process of nutrient uptake by the plant. Several important parameters need to be observed to use hydroponic cultivation methods such as temperature, humidity, water, and nutrient requirements. Sunlight is also needed for the process of photosynthesis to take place. This research uses hydroponic techniques in a hydroponic growth space, with LED growth lights as an alternative to sunlight because the space is covered without sunlight. Monitoring of the output in the box was detected using a temperature sensor, a humidity sensor, an ultrasound sensor to detect the height of the plant, and a water level sensor with the height of the water measured as the plant medium. The sensor measurement results in the hydroponic growth chamber are described as follows: the fan cooler operates when the temperature is > 30oC, and the humidity > 60%. The water pump works when the water level is less than 50% of the set point. Control on the lights was carried out with the LDR sensors each reaching a setting point of >500 in bright conditions, and <500 in dark conditions. The average update / data time received in the web is 2.4 seconds

Performance and limitation of mineral oil-based carbon nanotubes nanofluid in transformer application

Transformer oil-based carbon nanotube (CNT) nanofluids which have unique dielectric behaviour, is effective as the posterity insulation fluids that can boost the performance of the transformer as they proposed inspiring, distinctive behaviour compared to existing transformer oil which is widely used in practice namely mineral oils. With this motivation, the effect of AC breakdown voltages for two sonication duration (30 min and 120 min) techniques were applied in producing nanofluids, two different diameter sizes of CNTs (20 nm) and five different weight concentrations (0.01 g/L to 0.2 g/L) are investigated. The results indicate CNT with a longer sonication process, a smaller diameter and low concentrations of CNT provides the highest breakdown values that gave a huge potential impact on the conventional transformer oil. The Weibull and Normal distributions functions are used in this paper to obtain a successful forecast of the lowest, average, and highest possibility of breakdown rates (1%, 50% and 90%). It figures out that, CNT nanofluid can reach the greatest breakdown efficiency as good insulating oil at 0.01 g/L concentration. To understand the characterization of CNT nanofluids samples in detail, Raman spectroscopy analysis, storage modulus, viscosity and heat flow of mineral oil have been evaluated accordingly as a function of increasing temperatur

Simulation studies of vibration isolation using electromagnetic damper

This paper presents the review of electromagnetic damper as a vibration/isolation material. A bunch of articles about vibration and suspension system was reviewed and the key factors that contribute to electromagnetic damper was identified. Electromagnetic damper has been given special attention from many researchers and thus being among the important research area in vibration system. Vibration concept of electromagnetic damper has been elucidated by referring to several paper that demonstrate the usage of electromagnetic damper. Finite element magnetic method (FEMM) software has been used in order to identify the best configuration of geometry in the system. A simulation in Matlab was done by considering a quarter car model with a theoretical value from the Faraday’s Law equation involved in electromagnetic damper. The slotted and cylindrical geometry configurations have been simulated using FEMM and the result clearly shows that the slotted configuration has a better effect on the electromagnetic damper system

A Review On Oil-Based Nanofluid As Next-Generation Insulation For Transformer Application

Due to the increasing demand on developing good insulation, several researchers have performed experimental studies to prove the effectiveness and capabilities of transformer oil. This is done by suspending nanosized solid particles in the oil (nanofluid) for transformer applications. In brief, this paper presents a compilation of research studies which is divided into three parts. Part I discuss the preparation of the nanofluid which involves different types of nanomaterials, the optimal amount of concentrations, and applicable synthesisation methods for producing stably suspended nanofluids. In Part II, the nanofluid’s performances including the electrical breakdown voltages, impulse tests, and thermal and dielectric behaviour are reviewed in depth and compared. Part III emphasizes the limitation of nanofluids. Most researchers have agreed that appropriate concentrations of nanomaterials and the preparation method for nanofluids mainly affect the performance of nanofluids especially in terms of electrical properties. Meanwhile, types of nanomaterials and base oil also play a vital role in producing nanofluids as a better alternative transformer oil. However, among a few researchers, there are concerns regarding the issue of agglomeration and inconsistencies of findings that need to be resolved. Therefore, a few aspects must be taken into consideration to produce the next generation of high heat dissipation insulation

Kinetic studies of few-layer graphene grown by flame deposition from the perspective of gas composition and temperature

Studies on depositions of chemical vapour deposition (CVD) diamond films have shown that flame combustion has the highest deposition rates without involving microwave plasma and direct current arc. Thus, here we report on our study of few-layer graphene grown by flame deposition. A horizontal CVD reactor was modified for the synthesis of flame deposition of few-layer graphene on a Cu substrate. It was found that graphene obtained has comparable quality to that obtained with other flame deposition setups reported in the literature as determined from Raman spectroscopy, sheet resistance, and transmission electron microscopy. Calculation of the chemical kinetics reveals a gas phase species that has a close correlation to the growth rate of graphene. This was further correlated with van't Hoff analysis of the reaction, which shows that the growth reaction has a single dominating mechanism for temperatures in the range of 400 °C to 1000 °C. Arrhenius analysis also was found to be in good agreement with this result. This study shows few-layer graphene growth proceeds through different pathways from a CVD grown graphene and also highlights flame deposition as a viable method for graphene growth

Magnetism And Thermomechanical Properties In Si Substituted MnCoGe Compounds

MnCoGe-based compounds have been increasingly studied due to their possible large magnetocaloric effect correlated to the magnetostructural coupling. In this research, a comprehensive study of structure, magnetic phase transition, magnetocaloric effect and thermomechanical properties for MnCoGe1−xSix is reported. Room temperature X-ray diffraction indicates that the MnCoGe1−xSix (x = 0, 0.05, 0.1, 0.15 and 0.2) alloys have a major phase consisting of an orthorhombic TiNiSi-type structure with increasing lattice parameter b and decreasing others (a and c) with increasing Si concentration. Along with M-T and DSC measurements, it is indicated that the Tc value increased with higher Si concentration and decreased for structural transition temperature Tstr. The temperature dependence of the magnetization curves overlaps completely, indicating that there is no thermal hysteresis, and it is shown that the transition is the second-order type. It is also shown that the decreased magnetization on the replacement of Si for Ge decreases the value of −ΔSM from −ΔSM~8.36 J kg−1 K−1 at x = 0 to −ΔSM~5.49 J kg−1 K−1 at x = 0.2 with 5 T applied field. The performed Landau theory has confirmed the second-order transition in this study, which is consistent with the Banerjee criterion. The magnetic measurement and thermomechanical properties revealed the structural transition that takes place with Si substitution of G

Magnetic phase transitions and novel materials for magnetocaloric effect

The magnetic and structural properties of some selected magnetocaloric materials such as La (Fe, Si)13 series compounds, RMn2X2 series (R=rare earth and X=Si or Ge) compounds and typical MM′X series (M, M′ = transition metal, X = Si, Ge, Sn) have been systematically investigated in this thesis with total 7 chapters being included. After a general introduction in Chapter 1, the description of theoretical aspects of the research and experimental techniques are given in Chapters 2 and 3, respectively. In Chapter 4, the investigation on structure and magnetic properties of the La0.7Pr0.3Fe11.4- xCuxSi1.6 and La0.7Pr0.3Fe11.4-xCrxSi1.6 compounds is presented. Cu substitution for Fe in La0.7Pr0.3Fe11.4-xCuxSi1.6 (x = 0, 0.06, 0.12, 0.23, 0.34) leads to a reduction in hysteresis loss, a decrease in magnetic entropy change but an increase in Curie temperature (TC). The influences of annealing processes at different temperatures on TC, magnetic hysteresis, and the magnetocaloric effect (MCE) of La0.7Pr0.3Fe11.4Si1.6 are also investigated in detail. It has been found that a short-time and high temperature annealing process has benefits for the formation of the NaZn13 types as phase compared to a long-time and low temperature annealing process. Furthermore, the effects of substitution Fe by Cr in NaZn13-type La0.7Pr0.3Fe11.4-xCrxSi1.6 (x=0, 0.06, 0.12, 0.26, and 0.34) compounds have been investigated by high intensity of X-ray and neutron diffraction, scanning electron microscopy, specific heat, and magnetization measurement. It has been found that a substitution of Cr for Fe in this compounds leads to a decrease in the lattice parameter a at room temperature and a variation on TC. While the first order nature of magnetic phase transition around TC does not change with increasing Cr content up to x=0.34. High intensity X-ray and neutron diffraction study at variable temperatures for highest Cr concentration x=0.34 confirmed the presence of strong magnetovolume effect around TC and indicated the direct evidence of coexistence of two magnetic phases across magnetic transition as characteristic of first order nature. The values of -ΔSM around TC found to decrease from 17 J kg-1K-1 for x=0 to 12 J kg-1K-1 for x=0.06 and then increases with further increasing Cr content up to 17.5 J kg-1K-1 for x=0.34 under a change of 0–5 T magnetic field. The relative cooling power (RCP) also indicated the similar behaviour which is decrease from 390 J kg-1 for x=0 to 365 J kg-1 for x=0.06 at the beginning and then increases up to 400 J kg-1 for x=0.34 at the same field applied. Chapter 5 describes the investigation on magnetic behaviour and magnetocaloric effects of RMn2X2-based materials (R=rare earth and X=Si or Ge). The RMn2X2 series has attracted significant interest in recent years due primarily to their natural layered structure in which R and Mn atoms lie in alternate layers, separated by layers of X atoms. The strong dependence of the Mn–Mn magnetic exchange interaction on the intralayer near neighbour distance, and the interplay between the magnetism of the Mn and R layers lead to a fascinating arrangement of magnetic phases for these compounds. Firstly, in order to clarify the effect of substitution Mn with other transition metal (T) in NdMn2Si2 compound, structural and magnetic properties of the intermetallic compounds NdMn2−xTxSi2 (T=Ti, Cr, Cu and V) have been studied. The Curie temperature and N´eel temperature of NdMn2Si2 decrease from TC = 36 K and TN = 380 K to TC = 14 K and TN = 360 K, respectively, on substitution of Ti (x = 0.3) for Mn. The magnetocaloric effect around TC, has been investigated in detail. Under a change of magnetic field of 0–5 T, the maximum value of the magnetic entropy change is 27 J kg-1K-1 for x = 0, reducing to 15.3 J kg-1K-1 for x = 0.1 and 10 J kg-1K-1 for x = 0.3; importantly, no thermal or field hysteresis losses occur with increase in Ti concentration. Combined with the lack of any hysteresis effects, these findings indicate that NdMn1.9Ti0.1Si2 compound offers potential as a candidate for magnetic refrigerator applications in the temperature region below 35 K. In substitution Mn with Cr in NdMn2−xCrxSi2 compound, a giant magnetocaloric effect has been observed around Curie temperature, TC~42 K, in NdMn1.7Cr0.3Si2 with no discernible thermal and magnetic hysteresis losses. Detailed study shown that below 400 K, three magnetic phase transitions take place around 380 K, 320 K and 42 K. High resolution synchrotron and neutron powder diffraction (10–400 K) analysis confirmed the magnetic phases transitions as follows: TN intra~380 K denotes the transition from paramagnetism to intralayer antiferromagnetism (AFl), TN inter~320 K represents the transition from the AFl structure to the canted antiferromagnetic spin structure (AFmc), while TC~42 K denotes the first order magnetic transition from AFmc to canted ferromagnetism (Fmc+F(Nd)) due to ordering of the Mn and Nd sub-lattices. The maximum values of the magnetic entropy change and the adiabatic temperature change, around TC for a field change of 5 T are evaluated to be -ΔSM~15.9 J kg-1K-1 and ΔTad~5 K, respectively. The first order magnetic transition associated with the low levels of hysteresis losses (thermal 1.7Cr0.3Si2 offers potential as a candidate for magnetic refrigerator applications in the temperature region below 45 K. Furthermore, the structural and magnetic properties of NdMn2-xCuxSi2 compounds (x=0–1.0) also have been investigated. Substitution of Cu for Mn leads to an increase in the lattice parameter a but a decrease in c at room temperature. Two magnetic phase transitions have been found for NdMn2-xCuxSi2 compounds with TN for the antiferromagnetic ordering of Mnsublatttice and TC for the Nd-sublattice ferromagnetic ordering. TC increases significantly with increasing Cu content from 36 K at x=0 to 100 K at x=1.0. Moreover, it is found that the order of magnetic phase transition around TC also changes from first order at xM around TC decrease with increasing x from 27 J kg-1K-1 for x=0 to 0.5 J kg-1K-1 for x=1.0 under 0–5 T field. Refinement of neutron diffraction patterns for x=0.2 confirms the magnetic states detected by magnetic study and also indicates that the lattice constants a and c show a distinct variation around TC. Moreover, further study on substitution Mn with V in NdMn2Si2 compound shown the similar behaviour with the replacement Mn by Ti. Both TC and TN are found decrease with increasing V concentration accompany with decreasing magnetic entropy change as discussed in more detail in Chapter 5. Secondly, we carry out investigations of the Pr1-xYxMn2Ge2 magnetic phase diagram as functions of both composition and Mn–Mn spacing using X-ray and neutron diffraction, magnetization and differential scanning calorimetry measurements. Pr1-xYxMn2Ge2 exhibits an extended region of re-entrant ferromagnetism around x=0.5 with re-entrant ferromagnetism at TCPr~ 50 K for Pr0.5Y0.5Mn2Ge2. The entropy values -ΔSM around the ferromagnetic transition temperatures TCinter from the layered antiferromagnetic AFl structure to the canted ferromagnetic structure Fmc (typically TCinter~330–340 K) have been derived for Pr1-xYxMn2Ge2 with x=0.0, 0.2, and 0.5 for ΔB=0–5 T. The changes in magnetic states due toY substitution for Pr are also discussed in terms of chemical pressure, external pressure, and electronic effects. Thirdly, the structural and magnetic properties of CeMn2Ge2-xSix compounds with Si concentrations in the range x = 0.0–2.0 have been investigated. Substitution of Ge with Si leads to a monotonic decrease of both a and c along with concomitant contraction of the unit cell volume and significant modifications to the magnetic states - a crossover from ferromagnetism at room temperature for Ge-rich compounds to antiferromagnetism for Sirich compounds. The magnetic phase diagram has been constructed over the full range of CeMn2Ge2-xSix compositions and co-existence of ferromagnetism and antiferromagnetism has been observed in both CeMn2Ge1.0Si1.0 and CeMn2Ge0.8Si1.2 compounds with novel insight provided by high resolution X-ray synchrotron radiation studies. This study has enabled the large variety of magnetic structures and magnetic phase transitions of CeMn2Ge2-xSix compounds and their related magnetic properties to be determined by controlling chemical concentration. Finally in Chapter 6, the MnCoGe-based materials, as a typical MM′X (M, M′ = transition metal, X = Si, Ge, Sn) compound which undergoes a second-order phase transition as well as a crystallographic phase transition from the low temperature orthorhombic TiNiSi-type to the high temperature hexagonal Ni2In-type structure have been studied. An investigation on substituting Ge by other metalloids in MnCoGe1-xTx compounds (T = Al and Si) has been implemented in this thesis and it was found that an appropriate T concentration successfully shifted the structural change and magnetic phase transition into the temperature range of interest, leading to the attainment of a high contribution to the giant magnetocaloric effect (GMCE). MnCoGe1-xTx provides the best example for control of the temperature window in order to investigate the effects of the structural and magnetic transition on the total entropy change, providing an excellent vehicle for investigation of the field-induced martensitic transformation in GMCE materials. Thus, in an effort to understand the nature of the magnetic transition in MnTiGe0.97Al0.03, critical exponent analysis in the vicinity of the ferromagnetic (FM)–paramagnetic (PM) region has been performed. The outcomes revealed that this material undergoes a structural transition at ~ 420 K as well as a second-order ferromagnetic–paramagnetic transition at ~ 350 K. Finally, a temperature dependent neutron diffraction experiment has been performed and confirmed that there is a coupling of the structural transition and the magnetic phase transition. Structural, magnetic and magnetocaloric properties of the Mn1-xTixCoGe also have been investigated using X-ray diffraction, DC magnetization and neutron diffraction measurements in order to define the effect of substitution Mn with Ti in MnCoGe compound. Substitution of Ti for Mn in the parent MnCoGe compound leads to a significant reduction in both structure change temperature, Tstr (from ~ 645 K for MnCoGe to ~ 235 K for Mn0.94Ti0.06CoGe and ~ 178 K for Mn0.9Ti0.1CoGe) and Curie temperature, TC (from ~ 345 K for MnCoGe to ~ 270 K for Mn0.94Ti0.06CoGe and ~ 280 K for Mn0.9Ti0.1CoGe). Moreover, all the critical exponents for Mn0.94Ti0.06CoGe and Mn0.9Ti0.1CoGe fulfil the Widom scaling law. The validity of the calculated critical exponents was confirmed by the scaling equation, with the magnetization, field, and temperature data obtained below and above TC collapsing onto two different curves. Thus, the scaling of the magnetization data above and below TC was obtained using the respective critical exponents, and the consistency of the values of the critical exponents determined by different methods confirm that the calculated exponents are unambiguous and intrinsic. The critical exponents determined are close to those predicted by the mean-field theory for long range interactions

Penggunaan sistem pengesanan emosi bagi melatih kemahiran komunikasi pembentangan

Ekspresi wajah memainkan peranan utama untuk mengesan emosi seseorang. Penggunaan pengesanan emosi dalam pembelajaran boleh mengesan emosi negatif pelajar terutamanya ketika mereka melaksanakan pembentangan projek. Kelemahan yang dikesan ini mampu diatasi dengan latihan bagi meningkatkan keupayaan keyakinan dan kemahiran komunikasi pembentangan. Justeru, kajian ini dijalankan bertujuan untuk mengenal pasti emosi pelajar semasa proses pembentangan kajian projek. Kajian ini menumpukan kepada dua objektif iaitu mengenalpasti elemen-elemen emosi pelajar dan valensi rangsangan muka ketika pembentangan. Melalui sistem pengesanan emosi ini, penambaikan komunikasi pembentangan telah berjaya dicapai melalui latihan menerusi sistem pengesanan emosi yang dapat mengesan ekspresi wajah pelajar. Ujian pengesanan emosi ini melibatkan 10 pelajar yang mengikuti kurus elektif iaitu Topik Terkini Kejuruteraaan Mekanikal. Walau bagaimanapun, keputusan 2 sampel pelajar lelaki dan perempuan telah dipilih untuk didokumentasi secara komprehensif dalam manuskrip ini. Pelajar lelaki mempunyai skala intensiti yang tinggi berbanding pelajar wanita. Skala intensiti yang tinggi menggambarkan kekuatan emosi yang ditionjolkan pada ekspresi wajah. Hasil keputusan menunjukkan kedua-dua pelajar lelaki dan perempuan menunjukkan kecenderungan mempamerkan emosi negatif ketika pembentangan tetapi dengan valensi berbeza antara satu sama lain. Namun proses latihan intensif telah dijalankan untuk memberi latihan komunikasi pembentangan kepada pelajar agar memberi ekspresi wajah tenang semasa pembentangan. Latihan ini berjaya memberikan impak yang positif. Diharapkan latihan pengesanan emosi yang ditindikkan dalam elemen pembentangan ini mampu memberi nilai inovasi baru yang mampu menyumbang ke arah satu keupayaan pembentangan yang lebih baik di kalangan pelajar

Influence of Nanosized CoTiO₃ Synthesized via a Solid-State Method on the Hydrogen Storage Behavior of MgH₂

Magnesium hydride (MgH2) has received outstanding attention as a safe and efficient material to store hydrogen because of its 7.6 wt.% hydrogen content and excellent reversibility. Nevertheless, the application of MgH2 is obstructed by its unfavorable thermodynamic stability and sluggish sorption kinetic. To overcome these drawbacks, ball milling MgH2 is vital in reducing the particle size that contribute to the reduction of the decomposition temperature. However, the milling process would become inefficient in reducing particle sizes when equilibrium between cold-welding and fracturing is achieved. Therefore, to further ameliorate the performance of MgH2, nanosized cobalt titanate (CoTiO3) has been synthesized using a solid-state method and was introduced to the MgH2 system. The different weight percentages of CoTiO3 were doped to the MgH2 system, and their catalytic function on the performance of MgH2 was scrutinized in this study. The MgH2 + 10 wt.% CoTiO3 composite presents the most outstanding performance, where the initial decomposition temperature of MgH2 can be downshifted to 275 °C. Moreover, the MgH2 + 10 wt.% CoTiO3 absorbed 6.4 wt.% H2 at low temperature (200 °C) in only 10 min and rapidly releases 2.3 wt.% H2 in the first 10 min, demonstrating a 23-times-faster desorption rate than as-milled MgH2 at 300 °C. The desorption activation energy of the 10 wt.% CoTiO3-doped MgH2 sample was dramatically lowered by 30.4 kJ/mol compared to undoped MgH2. The enhanced performance of the MgH2–CoTiO3 system is believed to be due to the in situ formation of MgTiO3, CoMg2, CoTi2, and MgO during the heating process, which offer a notable impact on the behavior of MgH2