Prof. Dr. OJ Dada | Signature EcoSystems Technologies (original) (raw)

Papers by Prof. Dr. OJ Dada

Friction Stir Welding (FSW) is one of the fastest developing welding technologies being implement... more Friction Stir Welding (FSW) is one of the fastest developing welding technologies being implemented in the transport industry today. Fracture surfaces of AA5083-H111 specimens, which were friction-stir-welded using different parameters, were studied with a scanning electron microscope (SEM). The changes in the microstructure of the weld, the location and type of defects that accompanied each stirring process determined the magnitude of reduction in strength and soundness of joints for flawed samples. The paths of crack propagation and modes of fast fracture under static loads were also determined. The sharp edges of the defects were stress concentrators, and so aided crack initiation. Understanding of the effect of microstructure and defect on failure of FSW joints will aid optimization of the process variables, tool design, weld quality assurance and decision making. On the long run, it will boost the confidence of medium scale manufacturers in the adoption and implementation this fairly new technology.

ECS Meeting Abstracts, 2015

Technological demands in HEVs, renewable systems, and electrical storage systems coupled with its... more Technological demands in HEVs, renewable systems, and electrical storage systems coupled with its mature industrial process, recyclability and low cost has furthered the interests in Lead acid (LAB) systems. The LAB Positive active materials, due to low utilization and life cycle, severely limits the competitiveness of the traditional battery. Reported attempts to optimize the lead acid system using nano-size materials including graphene and carbon nanotubes, has yielded increase in some performance metrics, but little is known about the responsible mechanisms 1,2 3. Based on the gel-crystal theory, Pavlov et al. 4–6has established that the lead acid active mass particles comprises interfaces made of intermediate amorphous molecules, within which the electrochemical reactions take place. Little or nothing is known about the effects of additives of micro- and sub-micro sizes on the redox activity in the gel zone, and how the chemistry of the active mass is improved to result in globa...

2015 IEEE 15th International Conference on Nanotechnology (IEEE-NANO), 2015

The effect of reduced graphene electro-catalysts and their the agglomerate sizes, the case in lea... more The effect of reduced graphene electro-catalysts and their the agglomerate sizes, the case in lead acid battery positive active material was done. Reduced graphene size distributions were achieved via shear induced fragmentation of graphene oxide paper followed by hydrazine reduction. Increased size of agglomerates were beneficial when conductive reduced graphene was used as an electro-catalyst, and up to 14% improvements in discharge performance were recorded.

Materials Today: Proceedings, 2016

Journal of The Electrochemical Society, 2006

The high surface area of porous silicon (PSi) makes it attractive for use in chemical and biologi... more The high surface area of porous silicon (PSi) makes it attractive for use in chemical and biological sensors. Selectivity, however, will require tailoring its interfacial characteristics with organic molecules. This paper describes in situ functionalizing of PSi during its electrochemical formation with 1-heptyne and 6-heptynoic acid. Fourier transform infrared spectroscopy (FTIR) confirmed the attachment of the organic molecules, which were able to take part in subsequent chemical reactions. However, some disadvantages of in situ functionalization were noted, such as a reduction in the thickness and porosity of the PSi layer, along with incomplete coverage of the PSi; Si-H stretches were still observed on the FTIR spectra. Nevertheless, when the in situ functionalized PSi was treated in boiling 1-decene, all the Si-H groups were converted to S-C bonds, without the 1-decene replacing the molecules attached in the in situ process. Hence, combining in situ and ex situ functionalization, or adding a mixture of organic molecules into the etching solution, may enable different organic molecules with varying chemical functional groups to be incorporated on a single PSi specimen. Finally, the possibility of using PSi functionalized with carbonyl groups as an alcohol sensor was demonstrated by using FTIR to observe reversible shifts in the frequency of the carbonyl stretch on exposure and removal of methanol vapor.

Journal of The Electrochemical Society, 2019

This work establishes that the frequency and temperature-dependent electronic and dielectric prop... more This work establishes that the frequency and temperature-dependent electronic and dielectric properties of electrochemically reduced graphene (ERGO) are higher than graphene oxide (GO) papers by 2 orders of magnitude. There is stronger polarization as a result of increased concentration of reduced clusters and thinning of graphene sheets in ERGO papers, first ever electrochemically reduced paper from GO. In GO, there is a greater dependence on frequency due to a higher percentage of interlayer O–H bonds. Dielectric permittivity increases with decreasing frequency due to stronger polarization and reduced conduction losses. At very high frequencies, greater conduction losses are responsible for lower values of dielectric permittivity of ERGO papers compared to GO papers. The “U” or “W” profile (σ vs T curves) of temperature dependent conductivity was due to thermally activated transport, residence time and ionic scattering of charge carriers. The recovery of conducting and dielectric properties at higher temperatures were due to the transition from graphene–ion–cloud to a graphene–air dielectric multi-nano-capacitor system. The latter had more sp2–carbon cluster concentration and increased electrical percolation supportive of band-like or variable range electron transport. Higher activation energies along ln σT vs T−1/2 plot are associated with delocalization of charge carriers from their potential wells, thermally activated carrier transport and frequency of the electronic field. <br>

Oluwaseun John Dada 2020 Meet. Abstr. MA2020-02 585, 2020

High performance lithium battery anode plates were made from processed arc discharge graphene. Ar... more High performance lithium battery anode plates were made from processed arc discharge graphene. Arc discharge graphene has been produced from glow electrolytic thermal arc discharging of graphite rods [1-3], different from graphene or reduced graphene prepared through other means [4-11], because it maintains high crystallinity and planar characteristics of graphite marked by low ID/IG and XRD peak (2θ = 26 ⁰C). Arc discharge Graphene was sonicated in NMP for hours until fully exfoliated and able to film coat without impediments on the rougher side of the electrode copper film. Sonicated Graphene was dried in the vacuum oven. Anode plates were prepared by homogenizing the sonicated graphene in PVDF saturated NMP (0.53% NMP; 4% superP carbon black; and 2.25wt% PVDF) for 1 hr. The anode slurry was coated on the copper plates using automatic doctor blade film coater at a speed of 100mm/min. Anode plates were dried at 80 ⁰C for and cured for 120 ⁰C for 2 hrs in vacuum oven. Coin cells of NMC//HGR were made and tested in CT2001A. The capacity of the anode cycled at 1C was ~1083mAhg-1. This very high capacity of the graphene anode represents 188.3% increase over nominal graphite anodes, and one of the highest reported in published literature.

ECS Meeting Abstracts, Volume MA2020-02, B01: Carbon Nanostructures: From Fundamental Studies to Applications and Devices, 2020

Free Standing Porous Graphene and Reduced Graphene Papers manufactured from Sedimentation of Arc ... more Free Standing Porous Graphene and Reduced Graphene Papers manufactured from Sedimentation of Arc Discharge of Graphite Rods. At SignEcoTech, novel and newer nano-carbons such as hard carbons, homogenized graphene, low defect highly crystalline graphene's, and wrinkled graphene [1-14]. Here, Graphene Oxide papers have been synthesized previously by flow-directed assembly, where the pressure of air within the assembly supports graphene oxide sheets in their nano-crystalline colloidal solution being filtered on nano-porous filter paper. However in this research, we haven't used any filter paper, or directed flow assembly, but sedimentation of the colloidal solution in ethyl alcohol in a dish. Then, the wrinkled the hierarchical GO sheets fall under gravity by sedimentation. Wrinkling in GO was enhanced by low defects, multi-layer clusters, and variegated + edge interaction amongst graphene clusters, as such the sedimented graphene papers were porous, intertwined and free standing. The composition of GO was confirmed by XPS, while the low defect level clearly marked by higher planar order and low ID/IG band. The wrinkled, multilayer clusters and carbonic surface properties of the graphene oxide sheets enhanced fast sedimentation, evaporation of the alcohol and formation of porous GO structure. The porous reduced\GO morphology is captured by optical microscope.

Keywords: Wrinkled GO Papers, Reduced Graphene, Arc Discharge, Modified Hummers Method

ECS Meeting Abstracts, Volume MA2020-02, LA: Late Presentations in Battery and Energy Storage Citation Oluwaseun John Dada 2020 Meet. Abstr. MA2020-02 3736, 2020

Abstract Low cost, low defect and high-quality graphene have been produced in three simple exfoli... more Abstract
Low cost, low defect and high-quality graphene have been produced in three simple exfoliation steps as a fully tested commercial concept. Low energy thermal arc-discharging expands the electrolytic graphite rod electrodes into hierarchical-like 3D graphene retaining the graphite structural order on a basal plane and chemical purity. Multi-size ball milling causes movement of the graphene materials in multi-shear directions, with optimized speed of the balls and lesser time. Micro-waving further separates the graphene sheets by "thermal expansion and release" mechanism utilizing thermally induced lattice vibrations. This also causes higher lattice order on basal plane improving directional and surface properties. The produced graphene (XRD 2theta = 26 degrees) has low defect (I(D)/I(G) between 0.05 and 0.2), retains chemical purity (between 0.56 and 2.4% change in oxygen content), and with comparatively optimized effective nano-sizes (ranging from 300nm to 35um). These properties make the graphene suitable for diverse applications, dispersibility in various solvents, conformability to flat semitransparent surfaces, and storable in concentrated slurries (>50 mg mL−1) or powder.

Keywords: Low Defect; 2D Planar; Arc Discharge Graphene; PPC Sonication; 5 Sec Microwaving; Exfoliation; Electronics.

ECS Meeting Abstracts, Volume MA2020-02, LB: Late Presentations in Carbon Nanostructures and Devices Citation Oluwaseun John Dada 2020 Meet. Abstr. MA2020-02 3737, 2020

This is an exceptional process on low cost, low defect and high-quality graphene which is produce... more This is an exceptional process on low cost, low defect and high-quality graphene which is produced by sonication in PPC and microwaving for just 5sec. Low energy arc-discharging process expands electrolytic graphite rods into hierarchical-like 3D-graphene retaining the basal plane carbon crystalline order and chemical purity [1-2]. Sonication in Polypropylene Carbonate causes non-covalent PPC-π bonding at graphene basal plane, aligning the graphene sheets in directions that allows efficient transmission of cavitation pressures and exfoliation; while microwave treatment for 5s separates any layered graphene, utilizing thermally induced lattice vibrations without changes on surface properties. Produced graphene (XRD 2θ = 26 ⁰C) has low defect (0.05 < ID/IG < 0.2), retainment of chemical purity (0~2.5% O2 content), with optimized effective graphene sizes (ranging from 350nm to 35 um), for diverse applications, dispersibility in diverse solvent, conformability to flat semi-transparent surfaces; storable in concentrated slurry (>50 mg mL−1). Planar graphene is suitable as 2D electronic materials applications [3], composites [4] and energy materials applications [5-10].

Keywords: Arc Discharge, Sonication, Microwave, Exfoliation, Planar, XRD, HR-SEM, HR-TEM.

Acta Materialia Turcica , 2020

Friction stir welding (FSW) is the fastest evolving joining technology and the principal prospect... more Friction stir welding (FSW) is the fastest evolving joining technology and the principal prospective technique for implementing an integral fuselage structure in aircraft manufacturing. The viability of FS welds is dependent upon mechanical properties and production turnovers, which are dependent on welding rates and tool design. Hence this review paper border on the effect of welding parameters, tool designs on microstructure, and mechanical behavior of friction stir welds. The microstructure and micro-hardness which were influenced by the welding rates determined static properties, failure locations, and residual stress minima and maxima. The study reviews the nature and distribution of material flow, grain structure, and precipitates in the aluminum FS welds and their effect on mechanical properties. Advances in the industrial application of Friction Stir Welds and further prospects are critical to this review work.

Scientific African, 2020

Friction Stir Welding (FSW) is one of the fastest developing welding technologies being implement... more Friction Stir Welding (FSW) is one of the fastest developing welding technologies being implemented in the transport industry today. Fracture surfaces of AA5083-H111 specimens, which were friction-stir-welded using different parameters, were studied with a scanning electron microscope (SEM). The changes in the microstructure of the weld, the location and type of defects that accompanied each stirring process determined the magnitude of reduction in strength and soundness of joints for flawed samples. The paths of crack propagation and modes of fast fracture under static loads were also determined. The sharp edges of the defects were stress concentrators which aided crack initiation. Understanding of the effect of microstructure and defect on the failure of FSW joints will aid optimization of the process variables, tool design, weld quality assurance and decision making. On the long run, it will boost the confidence of medium-scale manufacturers in the adoption and implementation of this fairly new technology.

SSRN Electronic Journal , 2019

In recent times, it is found that energy has received quite an appreciable attention around the w... more In recent times, it is found that energy has received quite an appreciable attention around the world. This is partly due to the gradual transition from centralized to distributed energy generation technology brought about by the widespread application of renewable energy resources. However, while this is a welcome development, it is also found that one other aspect that affects human lives, as much as energy, seems either to be neglected or given less attention in many parts of the world, especially in developing countries. This is the management of solid wastes, which has a direct impact on the health and well-being of the people in an area, a city or community. Managing domestic and industrial solid wastes is one of the major challenges facing both the industrialized and developing nations, but this has been identified as a means to also generate revenue and energy. For these reasons, there is the need to also prioritize the management of municipal wastes both from the residential and industrial premises. This paper presents improved design of a Compost Processing Plant (CPP) for managing municipal solid wastes, using an existing plant in Ondo State, Nigeria, with a throughput of 508 kg/hr as a case study. We design the various machine components to achieve an increased throughput of 875 kg/hr of compost, which is about 75% improvement in performance. We include the cost of the components of the CPP, to give the study a techno-economic outlook that can be useful for planning such a plant in developing countries, including Nigeria. The plant is not only useful for managing solid wastes, but also produces compost for agricultural purposes. Some directions for future work are also suggested.

SSRN Electronic Journal, 2019

Reduced graphene fillers were integrated into epoxy nanocomposites by solvent exchange of GO solu... more Reduced graphene fillers were integrated into epoxy nanocomposites by solvent exchange of GO solution to acetone, ethanol and DMF, and subsequent in-situ thermal reduction and curing. The comparative fracture specimens of neat epoxy, acetone-rGO/epoxy, and DMF-rGO/epoxy showed ethanol-rGO/epoxy had greater load transfer by bonding and functionalization of the rGO surface with polymer chains from the epoxy via the solvent. The TGA and DTG showed marginal drop in the stability of the nanocomposites behind the neat epoxy, and DSC heat loss magnitude showed superior chemical bonding within ethanol-rGO/epoxy. The modulus increased with rGO content from 0, 0.05, 0.1, 0.2, 0.3 and 0.4 wt%, while the highest tensile strength was at 0.2 wt%. Thereafter, the dynamic and viscoelastic mechanical characteristics of rGO-epoxy nanocomposites: while the 0.4 wt% of rGO in ethanol-rGO/epoxy exhibited the highest storage modulus of 4144 MPa 0.91 tan delta, and a marginal decrease in glass transition temperature, Tg, while highest Tg was 115 ⁰C at 0.05 wt%. The dynamic mechanical storage moduli were fairly constant with increased amplitude from 0 to 4 µm, while loss moduli and tan delta only reduced at lower amplitudes from 0-4 µm.

Keywords: DMA; Epoxy NanoComposite; rGO; Mechanical Behaviour

Suggested Citation:
Dada, Oluwaseun John, In-Situ Reduced Graphene Filled Epoxy NanoComposite With Highest Storage Modulus (April 7, 2019). Available at SSRN: https://ssrn.com/abstract=3367824 or http://dx.doi.org/10.2139/ssrn.3367824

SSRN Electronic Journal, 2019

NanoScale and Advanced Manufacturing Lab, Signature EcoSystems Technologies, DLF Center, Hong Kon... more NanoScale and Advanced Manufacturing Lab, Signature EcoSystems Technologies, DLF Center, Hong Kong.

Lithium battery anode plates were made from sugar processed into hard carbon by high temperature carbonization in an autoclave. Sucrose was dissolved in water at 60 ⁰C, mixed thereafter with naphthalene. The hard carbon is purifies with HCl and distilled water. Nano-hard carbons 1,2 are 3-dimensional and notably larger than the 2-dimensional graphenes 3-5. Anode plates were prepared by homogenizing the sonicated graphene in PVDF saturated NMP (0.53% NMP; 4% super-P carbon black; and 2.25wt% PVDF) for 1 hr. The anode slurry was coated on the copper plates using automatic doctor blade film coater at a speed of 100mm/min. Anode plates were dried at 80 ⁰C for and cured for 120 ⁰C for 2 hrs and 24 hrs respectively, in vacuum oven. Coin cells of NMC//HC were made and tested in CT2001A. The capacity of 48 µm thick and 28.2 g/m 2 anode cycled at 1C was ~49.70 mAhg-1 , which is a replaceable anode material for lithium ion batteries to 67 µm thick and 33.9 g/m 2 graphite anode with a capacity of 60.62 mAhg-1. 1. K. Sattler et al., "Ultralight carbon nanofoam from naphtalene-mediated hydrothermal sucrose carbonization" Carbon, 2015.

SSRN Electronic Journal, 2019

Miracle Adegun (https://papers.ssrn.com/sol3/cf\_dev/AbsByAuth.cfm?per\_id=3566326) affiliation not... more Miracle Adegun (https://papers.ssrn.com/sol3/cf_dev/AbsByAuth.cfm?per_id=3566326) affiliation not provided to SSRN Miracle Ogunlade (https://papers.ssrn.com/sol3/cf_dev/AbsByAuth.cfm?per_id=3566527) affiliation not provided to SSRN Ben O. Adewuyi (https://papers.ssrn.com/sol3/cf_dev/AbsByAuth.cfm?per_id=3566318) affiliation not provided to SSRN Abstract Compared with the matrix alloy, Al6061 reinforced with nano-fillers possesses higher strength, stiffness, damage tolerance properties, and wear and creep resistance in a wide temperature range hence, suitable for automotive, aerospace structures, marine and medicine. This research work entails the enhancement of the structural properties of Al6061 nanocomposite using carbon nano-particle (CNP) synthesized from pyrolysis of scrap rubber tyre. The composite Al6061/CNP samples were produced via stir casting process, with 0-2 wt% CNP added directly during mechanical hot-stirring to the molten aluminium matrix. Significant improvements in mechanical properties (tensile, stiffness and hardness) were recorded in the as-cast products machined into standard testing specimens. The major strengthening mechanism is Orowan strengthening. The 2 dimensional spherical CNP intercepts disclocation in addition to load transfer effect. However, there was a slight decrease in fracture toughness due to reduced composite ductility, by crack initiation at CNP/matrix interface.

SSRN Electronic Journal, 2019

Wrinkled Graphene Oxide has been produced from both glow electrolytic thermal arc discharging of ... more Wrinkled Graphene Oxide has been produced from both glow electrolytic thermal arc discharging of graphite rods 1,2 combined with hummer's process 3-5. Wrinkling in GO was enhanced by low defects, multilayer clusters, and variegated-edge interaction amongst graphene clusters. The composition of GO was confirmed by XPS, while the low defect level clearly marked by higher planar order and low I D /I G band. The GO morphology is captured by optical microscope and TEM. While arc discharge maintains the graphitic quality of the GO, the slightly modified hummer's process did not introduce as much defects as the GO used in previous works 5,6. The wrinkled GO dispersion is optimal for quenching for DNS biosensors, and it is also applicable for similar high volume and high storage modulus epoxy composites 7 , and other diverse materials and energy applications 8-10 .

ECS Meeting Abstracts, 2015

2015 IEEE 15th International Conference on Nanotechnology (IEEE-NANO), 2015

Materials Today: Proceedings, 2016

Journal of The Electrochemical Society, 2006

Journal of The Electrochemical Society, 2019

Oluwaseun John Dada 2020 Meet. Abstr. MA2020-02 585, 2020

ECS Meeting Abstracts, Volume MA2020-02, B01: Carbon Nanostructures: From Fundamental Studies to Applications and Devices, 2020

Keywords: Wrinkled GO Papers, Reduced Graphene, Arc Discharge, Modified Hummers Method

ECS Meeting Abstracts, Volume MA2020-02, LA: Late Presentations in Battery and Energy Storage Citation Oluwaseun John Dada 2020 Meet. Abstr. MA2020-02 3736, 2020

Keywords: Low Defect; 2D Planar; Arc Discharge Graphene; PPC Sonication; 5 Sec Microwaving; Exfoliation; Electronics.

ECS Meeting Abstracts, Volume MA2020-02, LB: Late Presentations in Carbon Nanostructures and Devices Citation Oluwaseun John Dada 2020 Meet. Abstr. MA2020-02 3737, 2020

Keywords: Arc Discharge, Sonication, Microwave, Exfoliation, Planar, XRD, HR-SEM, HR-TEM.

Acta Materialia Turcica , 2020

Scientific African, 2020

Friction Stir Welding (FSW) is one of the fastest developing welding technologies being implement... more Friction Stir Welding (FSW) is one of the fastest developing welding technologies being implemented in the transport industry today. Fracture surfaces of AA5083-H111 specimens, which were friction-stir-welded using different parameters, were studied with a scanning electron microscope (SEM). The changes in the microstructure of the weld, the location and type of defects that accompanied each stirring process determined the magnitude of reduction in strength and soundness of joints for flawed samples. The paths of crack propagation and modes of fast fracture under static loads were also determined. The sharp edges of the defects were stress concentrators which aided crack initiation. Understanding of the effect of microstructure and defect on the failure of FSW joints will aid optimization of the process variables, tool design, weld quality assurance and decision making. On the long run, it will boost the confidence of medium-scale manufacturers in the adoption and implementation of this fairly new technology.

SSRN Electronic Journal , 2019

SSRN Electronic Journal, 2019

Keywords: DMA; Epoxy NanoComposite; rGO; Mechanical Behaviour

SSRN Electronic Journal, 2019

Uitgeverij Onze Kennis (December 23, 2020), 2020

Frictie roerlassen (FSW) is de snelst evoluerende verbindingstechnologie en de belangrijkste pros... more Frictie roerlassen (FSW) is de snelst evoluerende verbindingstechnologie en de belangrijkste prospectieve techniek voor de implementatie van een integrale rompstructuur in de vliegtuigbouw. De levensvatbaarheid van FS-lassen is afhankelijk van de mechanische eigenschappen en de productieomzetten, die afhankelijk zijn van de lassnelheid en het ontwerp van het gereedschap. Vandaar dat in deze review paper het effect van lasparameters, gereedschapsontwerpen op de microstructuur en het mechanische gedrag van wrijvingsroerlassen aan bod komt. De microstructuur en de microhardheden die werden beïnvloed door de lassnelheden bepaalden de statische eigenschappen, de faallocaties en de minima en maxima van de restspanning. De studie beoordeelt de aard en de verdeling van de materiaalstroom, de korrelstructuur en de precipitaten in de aluminium FS-lassen en hun effect op de mechanische eigenschappen. De vooruitgang in de industriële toepassing van Friction Stir Welds en verdere vooruitzichten zijn van cruciaal belang voor dit beoordelingswerk.

Wydawnictwo Nasza Wiedza (December 23, 2020), 2020

Spawanie steru ciernego (FSW) jest najszybciej rozwijającą się technologią łączenia i najważniejs... more Spawanie steru ciernego (FSW) jest najszybciej rozwijającą się technologią łączenia i najważniejszą perspektywiczną techniką wdrażania zintegrowanej struktury kadłuba w konstrukcji samolotu. Żywotność spawania FSW zależy od właściwości mechanicznych i konwersji produkcji, które zależą od prędkości spawania i konstrukcji narzędzi. W związku z tym w niniejszym artykule przeglądowym omówiono wpływ parametrów spawania, konstrukcji narzędzi na mikrostrukturę oraz zachowanie mechaniczne zgrzewania tarciowego z przemieszaniem. Mikrostruktura i mikrotwardość pod wpływem prędkości spawania określała właściwości statyczne, miejsca uszkodzenia oraz minima i maksima naprężeń resztkowych. W pracy dokonano oceny charakteru i rozkładu przepływu materiału, struktury ziaren i osadów w spawaniu aluminium FS oraz ich wpływu na właściwości mechaniczne. Postępy w zakresie przemysłowego zastosowania spawania tarciowego z przemieszaniem oraz dalsze perspektywy mają kluczowe znaczenie dla niniejszej oceny.

Edições Nosso Conhecimento , 2020

Friction stir welding (FSW) é a tecnologia de junção mais rápida em evolução e a principal técnic... more Friction stir welding (FSW) é a tecnologia de junção mais rápida em evolução e a principal técnica prospectiva para implementação de uma estrutura de fuselagem integral na fabricação de aeronaves. A viabilidade das soldas FS depende das propriedades mecânicas e do volume de produção, que dependem das taxas de soldagem e do projeto da ferramenta. Por isso, este documento de revisão se debruça sobre o efeito dos parâmetros de soldagem, projetos de ferramentas na microestrutura e comportamento mecânico das soldas por fricção. A microestrutura e as microdurezas que foram influenciadas pelas taxas de soldagem determinaram as propriedades estáticas, os locais de falha e os mínimos e máximos de tensão residual. O estudo revisa a natureza e distribuição do fluxo do material, estrutura do grão e precipitações nas soldas de alumínio FS e seu efeito sobre as propriedades mecânicas. Avanços na aplicação industrial de Soldas por fricção e outras perspectivas são críticos para este trabalho de revisão.

KS Omniscriptum Publishing, 2020

Diese Arbeit stellt fest, dass die frequenz- und temperaturabhängigen elektronischen und dielektr... more Diese Arbeit stellt fest, dass die frequenz- und temperaturabhängigen elektronischen und dielektrischen Eigenschaften von elektrochemisch reduziertem Graphen (ERGO) um 2 Größenordnungen höher sind als die von Graphenoxidpapieren (GO). Es gibt eine stärkere Polarisierung als Folge einer erhöhten Konzentration von reduzierten Clustern und einer Verdünnung der Graphenblätter in ERGO-Papieren, dem ersten elektrochemisch reduzierten Papier aus GO überhaupt. Bei GO besteht aufgrund eines höheren Anteils an O-H-Zwischenschichtbindungen eine größere Abhängigkeit von der Frequenz. Die dielektrische Permittivität steigt mit abnehmender Frequenz aufgrund stärkerer Polarisierung und reduzierter Leitungsverluste. Bei sehr hohen Frequenzen sind größere Leitungsverluste für niedrigere Werte der dielektrischen Permittivität von ERGO-Papieren im Vergleich zu GO-Papieren verantwortlich. Das Profil der temperaturabhängigen Leitfähigkeit war auf thermisch aktivierten Transport, Verweilzeit und ionische Streuung von Ladungsträgern zurückzuführen. Die Erholung der leitenden und dielektrischen Eigenschaften bei höheren Temperaturen war auf den Übergang von einer Graphen-Ionen-Wolke zu einem dielektrischen Multi-Nano-Kondensatorsystem aus Graphen und Luft zurückzuführen.

KS Omniscriptum Publishing, 2020

Questo lavoro stabilisce che le proprietà elettroniche e dielettriche dipendenti dalla frequenza ... more Questo lavoro stabilisce che le proprietà elettroniche e dielettriche dipendenti dalla frequenza e dalla temperatura del grafene elettrochimicamente ridotto (ERGO) sono superiori di 2 ordini di grandezza rispetto alle carte di ossido di grafene (GO). C'è una polarizzazione più forte come risultato di una maggiore concentrazione di cluster ridotti e di assottigliamento dei fogli di grafene nelle carte ERGO, prima carta elettrochimicamente ridotta da GO. Nel GO, c'è una maggiore dipendenza dalla frequenza a causa di una maggiore percentuale di legami O-H interstrato. La permittività dielettrica aumenta con frequenza decrescente a causa della maggiore polarizzazione e delle minori perdite di conduzione. Ad altissime frequenze, maggiori perdite di conduzione sono responsabili di minori valori di permittività dielettrica delle carte ERGO rispetto alle carte GO. Il profilo di conducibilità dipendente dalla temperatura è dovuto al trasporto attivato termicamente, al tempo di permanenza e alla dispersione ionica dei portatori di carica. Il recupero delle proprietà conduttive e dielettriche a temperature più elevate era dovuto al passaggio da un sistema multi-nano-capacitore dielettrico ad aria di grafene ad un sistema multi-nano-capacitore di grafene.

KS Omniscriptum Publishing, 2020

Ce travail établit que les propriétés électroniques et diélectriques du graphène électrochimiquem... more Ce travail établit que les propriétés électroniques et diélectriques du graphène électrochimiquement réduit (ERGO), qui dépendent de la fréquence et de la température, sont supérieures de deux ordres de grandeur à celles des papiers à base d'oxyde de graphène (GO). La polarisation est plus forte en raison de la concentration accrue des grappes réduites et de l'amincissement des feuilles de graphène dans les papiers ERGO, le tout premier papier à réduction électrochimique de GO. Dans les papiers GO, il y a une plus grande dépendance de la fréquence en raison d'un pourcentage plus élevé de liaisons O-H entre les couches. La permittivité diélectrique augmente avec la diminution de la fréquence en raison d'une polarisation plus forte et de pertes de conduction réduites. À des fréquences très élevées, des pertes de conduction plus importantes sont responsables des valeurs plus faibles de la permittivité diélectrique des papiers ERGO par rapport aux papiers GO. Le profil de conductivité dépendant de la température est dû au transport activé thermiquement, au temps de séjour et à la diffusion ionique des porteurs de charge. La récupération des propriétés conductrices et diélectriques à des températures plus élevées était due à la transition du nuage d'ions de graphène à un système de multi-nano-condensateurs diélectriques graphène-air.

KS Omniscriptum Publishing, 2020

Este trabalho estabelece que as propriedades eletrônicas e dielétricas dependentes da freqüência ... more Este trabalho estabelece que as propriedades eletrônicas e dielétricas dependentes da freqüência e temperatura do grafeno reduzido eletroquimicamente (ERGO) são superiores aos papéis de óxido de grafeno (GO) em 2 ordens de grandeza. Há uma polarização mais forte como resultado do aumento da concentração de grupos reduzidos e do desbaste de folhas de grafeno em papéis ERGO, o primeiro papel reduzido eletroquimicamente a partir de GO. Em GO, há uma maior dependência de frequência devido a uma maior percentagem de títulos O-H entre camadas. A permissividade dieléctrica aumenta com a diminuição da frequência devido a uma polarização mais forte e a perdas de condução reduzidas. Em frequências muito altas, maiores perdas de condutibilidade são responsáveis por menores valores de permissividade dielétrica dos papéis ERGO em comparação com os papéis GO. O perfil de condutividade dependente da temperatura foi devido ao transporte termicamente ativado, tempo de residência e dispersão iônica dos portadores de carga. A recuperação das propriedades condutoras e dielétricas a temperaturas mais elevadas deveu-se à transição de um sistema multi-nano-capacitor dielétrico de grafite-ion-cluvem para um sistema multi-nano-capacitor de grafite-ar.

Edizioni Sapienza, 2020

Gel - Teoria del cristallo Meccanismo di precipitazione di dissoluzioneMiglioramenti dei nanofogl... more Gel - Teoria del cristallo Meccanismo di precipitazione di dissoluzioneMiglioramenti dei nanofogli di grafeneEffetto delle dimensioni e riduzione del grafeneFrammentazione indotta da taglio del grafene Interconduttività e fenomeni elettro-osmoticiNuove strategie per l'utilizzo e il miglioramento della capacità delle batterie al piombo acido Le richieste tecnologiche nei veicoli elettrici ibridi, nei depositi su larga scala e nelle centrali elettriche portatili hanno favorito un maggior numero di interessi di ricerca nel campo delle batterie al piombo (LAB), oltre al vantaggio della potenza nominale per costo. I materiali attivi positivi LAB (PAM), a causa del basso utilizzo e del basso ciclo di vita, limitano fortemente la competitività della batteria tradizionale. La combinazione di materiali catodici con additivi su misura a base di grafene. L'interazione elettrochimica dei fogli di grafene che ha cambiato la reattività dei cristalli di biossido di piombo nella zona del gel. Il modello di trasferimento ionico è stato sviluppato mostrando l'ottimizzazione del trasferimento ionico della zona del gel indotta dall'attività elettrochimica degli additivi a base di grafene. Le caratteristiche meccanicistiche interfacciali dei potenziamenti del grafene nei LAB sono state ulteriormente valutate sulla base della capacità del doppio strato e della resistenza di trasferimento della carica.

Edições Nosso Conhecimento, 2020

Gel - Teoria dos Cristais Mecanismo de Precipitação de DissoluçãoMelhorias na Nanofolha GrapheneE... more Gel - Teoria dos Cristais Mecanismo de Precipitação de DissoluçãoMelhorias na Nanofolha GrapheneEfeito do Tamanho e Redução do GrafenoFragmentação de Grafeno Induzida por Cisalhamento InterCondutividade e Fenômenos Eletro-OsmóticosNovas Estratégias de Utilização e Melhoria da Capacidade da Bateria de Ácido Chumbo As exigências tecnológicas em veículos eléctricos híbridos, armazenamento em larga escala e centrais eléctricas portáteis têm fomentado mais interesses de investigação em Baterias de Ácido Chumbo (LAB), para além da vantagem da classificação de potência por custo. O LAB materiais ativos positivos (PAM), devido à baixa utilização e ciclo de vida, limita severamente a competitividade da bateria tradicional. A combinação de materiais catódicos com aditivos à base de grafeno sob medida. A interação eletroquímica das folhas de grafeno que alterou a reatividade dos cristais de dióxido de chumbo na zona de gel. O modelo de transferência iónica foi desenvolvido mostrando a optimização da transferência iónica da zona de gel induzida pela actividade electroquímica dos aditivos do grafeno. As características interfaciais mecanicistas dos melhoramentos do grafeno em LABs foram ainda avaliadas com base na capacitância da dupla camada e na resistência de transferência de carga.

Editions Notre Savoir, 2020

Théorie du gel - cristal Mécanisme de dissolution et de précipitationAméliorations des nanofeuill... more Théorie du gel - cristal Mécanisme de dissolution et de précipitationAméliorations des nanofeuilles de graphèneEffet de la taille et de la réduction du graphèneFragmentation du graphène induite par le cisaillement Interconductivité et phénomènes électro-osmotiquesNouvelles stratégies pour l'utilisation et l'amélioration de la capacité des batteries au plomb Les exigences technologiques en matière de véhicules électriques hybrides, de stockage à grande échelle et de centrales électriques portables ont fait progresser les intérêts de la recherche sur les batteries plomb-acide (LAB), en plus de l'avantage de la puissance nominale par coût. Les matériaux actifs positifs (PAM) des LAB, en raison de leur faible utilisation et de leur cycle de vie, limitent sérieusement la compétitivité de la batterie traditionnelle. L'interaction électrochimique des feuilles de graphène qui a modifié la réactivité des cristaux de dioxyde de plomb dans la zone de gel. Un modèle de transfert d'ions a été développé, montrant l'optimisation du transfert d'ions dans la zone de gel induit par l'activité électrochimique des additifs à base de graphène. Les caractéristiques interfaciales mécanistes des améliorations du graphène dans les LAB ont été évaluées plus en détail sur la base de la capacité de la double couche et de la résistance de transfert de charge.

Wydawnictwo Nasza Wiedza, 2020

Uitgeverij Onze Kennis, 2020

Gel - Kristaltheorie Oplossingsmechanisme voor neerslagVerbeteringen aan de grafiek-NanoSheetEffe... more Gel - Kristaltheorie Oplossingsmechanisme voor neerslagVerbeteringen aan de grafiek-NanoSheetEffect van Grootte en Vermindering van GrapheneSchuifgeïnduceerde fragmentatie van grafeen Interconductiviteit en elektro-smotische verschijnselenNieuwe strategieën voor het gebruik en de capaciteitsverbetering van loodaccu's De technologische eisen in hybride elektrische voertuigen, grootschalige opslag en draagbare krachtcentrales hebben de onderzoeksinteresses in loodaccu's (LAB) bevorderd, naast het voordeel van het vermogen per kostenpost. De LAB positieve actieve materialen (PAM), als gevolg van het lage gebruik en de levenscyclus, beperken de concurrentiekracht van de traditionele batterij sterk. Elektrochemische interactie van de grafeenplaten die de reactiviteit van de looddioxidekristallen in de gelzone veranderde. Er werd een model voor ionentransfer ontwikkeld dat de optimalisatie van de ionentransfer van de gelzone, geïnduceerd door de elektrochemische activiteit van de grafeenadditieven, laat zien. De mechanistische interfaciale karakteristieken van grafeenverbeteringen in LAB's werden verder geëvalueerd op basis van de capaciteit van de dubbele laag en de weerstand tegen ladingsoverdracht.

Verlag Unser Wissen, 2020

Neuware - Gel-Kristalltheorie Auflösungs-Niederschlags-MechanismusGraphen-Nano-Blatt-Verbesserung... more Neuware - Gel-Kristalltheorie Auflösungs-Niederschlags-MechanismusGraphen-Nano-Blatt-VerbesserungenAuswirkung von Größe und Verkleinerung von GraphenScher-induzierte Fragmentierung von Graphen Interleitfähigkeit und elektro-osmotische PhänomeneNeue Strategien für die Nutzung und Kapazitätsverbesserung von Blei-Säure-Batterien Die technologischen Anforderungen an Hybrid-Elektrofahrzeuge, Großspeicher und tragbare Kraftwerke haben neben dem Vorteil der Leistung pro Kosten auch weitere Forschungsinteressen im Bereich der Blei-Säure-Batterien (LAB) gefördert. Die LAB-positiven aktiven Materialien (PAM) schränken aufgrund ihrer geringen Auslastung und Lebensdauer die Wettbewerbsfähigkeit der traditionellen Batterie stark ein. Die elektrochemische Wechselwirkung der Graphenschichten, die die Reaktivität der Bleidioxidkristalle in der Gelzone veränderte. Es wurde ein Ionentransfermodell entwickelt, das die Optimierung des Ionentransfers in der Gelzone zeigt, der durch die elektrochemische Aktivität der Graphenadditive induziert wird. Die mechanistischen Grenzflächeneigenschaften von Graphenverbesserungen in LABs wurden auf der Grundlage der Kapazität der Doppelschicht und des Ladungstransfer-Widerstands weiter evaluiert.

Editions Notre Savoir, 2020

Les soudures par friction-malaxage (FSW), une nouvelle technique de soudage pour tous les alliage... more Les soudures par friction-malaxage (FSW), une nouvelle technique de soudage pour tous les alliages métalliques et les polymères, ont montré de meilleures propriétés mécaniques que les anciennes technologies de soudage et d'assemblage, en particulier pour la structure intégrale en aluminium de la cellule afin de réduire la charge de poids et la défaillance. Cette étude paramétrique est importante pour les simulations et la programmation automatique de la fabrication, ainsi que pour la prédiction précise de la qualité et des propriétés mécaniques des soudures. L'outil Scroll Shoulder Triflat FSW possède un axe d'outil à 3 méplats équidistants, qui distribue les pressions d'écoulement plastique et la chaleur de frottement générée, de sorte que les changements de paramètres de soudure peuvent produire des changements linéaires et mesurables dans les microstructures des zones de soudure et les propriétés mécaniques. Il s'agit de la première étude à faire correspondre cette relation linéaire entre les propriétés mécaniques de l'alliage aéronautique AA6056-T4 soudé par friction-malaxage avec la vitesse de rotation et l'avance par tour.

Edizioni Sapienza, 2020

Le saldature a frizione (FSW), una nuova tecnica di saldatura per tutte le leghe metalliche e i p... more Le saldature a frizione (FSW), una nuova tecnica di saldatura per tutte le leghe metalliche e i polimeri, ha mostrato migliori proprietà meccaniche rispetto alle vecchie tecnologie di saldatura e di giunzione, specialmente per la struttura integrale in alluminio della cellula per ridurre il peso e i guasti. Questo studio parametrico è importante per le simulazioni e la programmazione automatica della produzione e per una previsione accurata della qualità e delle proprietà meccaniche delle saldature. Lo strumento Scroll Shoulder Triflat FSW ha un perno con 3 piani equidistanti, che distribuisce le pressioni del flusso di plastica e il calore per attrito generato, in modo tale che le variazioni dei parametri di saldatura possono produrre cambiamenti lineari e misurabili nelle microstrutture delle zone di saldatura e delle proprietà meccaniche. Questo è il primo studio che abbina questa relazione lineare tra le proprietà meccaniche della lega aeronautica AA6056-T4 con la velocità di rotazione e l'avanzamento per giro.

AV Akademikerverlag, 2020

Rührreibschweißnähte (Friction Stir Weldings, FSW), ein neuartiges Schweißverfahren für alle Meta... more Rührreibschweißnähte (Friction Stir Weldings, FSW), ein neuartiges Schweißverfahren für alle Metalllegierungen und Polymere, hat bessere mechanische Eigenschaften als ältere Schweiß- und Fügetechniken gezeigt, insbesondere für integrale Aluminiumstrukturen von Flugzeugzellen, um die Gewichtsbelastung und das Versagen zu reduzieren. Diese parametrische Studie ist wichtig für Simulationen und automatische Programmierung für die Fertigung sowie für die genaue Vorhersage der Qualität und der mechanischen Eigenschaften der Schweißnähte. Das Scroll Shoulder Triflat FSW-Werkzeug verfügt über einen Werkzeugstift mit 3 äquidistanten Abflachungen, der die plastischen Fließdrücke und die erzeugte Reibungswärme so verteilt, dass Änderungen der Schweißparameter lineare und messbare Änderungen der Mikrostrukturen der Schweißzonen und der mechanischen Eigenschaften bewirken können. Dies ist die erste Studie, die diese lineare Beziehung zwischen den mechanischen Eigenschaften der reibrührgeschweißten Luftfahrtlegierung AA6056-T4 mit der Rotationsgeschwindigkeit und dem Vorschub pro Umdrehung in Einklang bringt.

LAP LAMBERT Academic Publishing, 2020

Friction stir welds (FSW), a novel welding technique for all metal alloys and polymers, has shown... more Friction stir welds (FSW), a novel welding technique for all metal alloys and polymers, has shown better mechanical properties than older welding and joining technologies, especially for integral airframe aluminium structure to reduce weight burden and failure. This parametric study is important for simulations and automatic programming for manufacturing, and accurate prediction of the quality and mechanical properties of the welds. The Scroll Shoulder Triflat FSW tool has a tool pin with 3 equidistant flats, which distributes plastic flow pressures and frictional heat generated, such that changes in weld parameters can produce linear and measurable changes in microstructures of the weld zones and mechanical properties. This is the first study to match this linear relationship between Friction Stir Welded aeronautical alloy AA6056-T4 mechanical properties with the rotational speed and advance per revolution.

LAP Lambert Academic Publishing, 2020

Technological demands in HEVs, large scale storage and portable power stations has furthered more... more Technological demands in HEVs, large scale storage and portable power stations has furthered more research interests in Lead Acid Batteries (LAB), in addition to the advantage of power rating per cost. The LAB positive active materials (PAM), due to low utilization and life cycle, severely limits the competitiveness of the traditional battery. The combination of cathode materials with tailored graphene based additives: Graphene Oxide (GO-PAM), chemically converted graphene (CCG-PAM) and pristine graphene (GX-PAM) resulted in improved discharge capacity and cycle life. PAM-GO had the best performance with the highest utilization of 41.8%, followed by CCG-PAM (37.7%), control-PAM (29.7%), and GX-PAM (28.7%) at 2.5C rate. CCG-PAM had better charging performance such as lower internal resistance, but poorer cycle life compared to GO-PAM. Cycled at 2.5C rate, all samples but the control, had increasing capacity till after ~50 cycles. Electrochemical interaction of the graphene sheets which changed the of PbO2 crystals in the gel zone. Ion transfer model was developed showing the optimization of gel zone ion transfer induced by the electrochemical activity of graphene additives.

978-620-2-51862-8, 2019

ISBN-13: 978-620-2-51862-8 ISBN-10:6202518626EAN:9786202518628 Book language:English Blurb/Shortt... more ISBN-13:
978-620-2-51862-8
ISBN-10:6202518626EAN:9786202518628
Book language:English
Blurb/Shorttext:

This work establishes that the frequency and temperature-dependent electronic and dielectric properties of electrochemically reduced graphene (ERGO) are higher than graphene oxide (GO) papers by 2 orders of magnitude. There is stronger polarization as a result of increased concentration of reduced clusters and thinning of graphene sheets in ERGO papers, first ever electrochemically reduced paper from GO. In GO, there is a greater dependence on frequency due to a higher percentage of interlayer O–H bonds. Dielectric permittivity increases with decreasing frequency due to stronger polarization and reduced conduction losses. At very high frequencies, greater conduction losses are responsible for lower values of dielectric permittivity of ERGO papers compared to GO papers. The “U” or “W” profile (σ vs T curves) of temperature dependent conductivity was due to thermally activated transport, residence time and ionic scattering of charge carriers. The recovery of conducting and dielectric properties at higher temperatures were due to the transition from graphene–ion–cloud to a graphene–air dielectric multi-nano-capacitor system.Publishing house:
LAP LAMBERT Academic Publishing
Website:
https://www.lap-publishing.com/
By (author) :Oluwaseun John DadaNumber of pages:80Published on:2020-03-30Stock:AvailableCategory:
Chemistry
Price:39.90 €Keywords:Carbon, Dielectrics, graphene, Electronics, Paper, conductivity

Reduced graphene fillers were integrated into epoxy nanocomposites by solvent exchange of GO solu... more Reduced graphene fillers were integrated into epoxy nanocomposites by solvent exchange of GO solution to acetone, ethanol and DMF, and subsequent in-situ thermal reduction and curing. The comparative fracture specimens of neat epoxy, acetone-rGO/epoxy, and DMF-rGO/epoxy showed ethanol-rGO/epoxy had greater load transfer by bonding and functionalization of the rGO surface with polymer chains from the epoxy via the solvent. The TGA and DTG showed marginal drop in the stability of the nanocomposites behind the neat epoxy, and DSC heat loss magnitude showed superior chemical bonding within ethanol-rGO/epoxy. The modulus increased with rGO content from 0, 0.05, 0.1, 0.2, 0.3 and 0.4 wt%, while the highest tensile strength was at 0.2 wt%. Thereafter, the dynamic and viscoelastic mechanical characteristics of rGO-epoxy nanocomposites: while the 0.4 wt% of rGO in ethanol-rGO/epoxy exhibited the highest storage modulus of 4144 MPa 0.91 tan delta, and a marginal decrease in glass transition temperature, T g , while highest T g was 115 ⁰C at 0.05 wt%. The dynamic mechanical storage moduli were fairly constant with increased amplitude from 0 to 4 µm, while loss moduli and tan delta only reduced at lower amplitudes from 0-4 µm.

Oluwaseun John DADA, NanoScale and Advanced Manufacturing Lab, Signature EcoSystem Ltd. DLF Centr... more Oluwaseun John DADA, NanoScale and Advanced Manufacturing Lab, Signature EcoSystem Ltd.
DLF Centre, 12A Pok Man Street, Tai Kok Tsui, Hong Kong. oluwaseundd@yahoo.com; john.dada@signecotech.org (852) 5362 1400 (852) 6709 8309

1. This is the first study to exfoliate and synthesize 2D planar graphene from graphite with conformable with flat surfaces for electronic applications.
2. Also the first study to synthesize low defect Graphene with smaller domain size, unobtainable by laboratory or industrially available arc discharge graphene production. 3. Sonication in PPC happens by efficient transfer of cavitation pressures, by PPC-pi interaction at the basal planes.
4. 5 sec microwave thermal expansion and relaxation of individual graphene sheets, reduces domain size, increases pi-configuration and planar properties.

Abstract: This is an exceptional process on low cost, low defect and high quality graphene which is produced by sonication in PPC and microwaving for just 5sec. Low energy arc-discharging process expands electrolytic graphite rods into hierarchical-like 3D-graphene retaining the basal plane carbon crystalline order and chemical purity. Sonication in Polypropylene Carbonate causes non-covalent PPC-π bonding at graphene basal plane, alligning

Low cost, low defect and high-quality graphene have been produced in three simple exfoliation ste... more Low cost, low defect and high-quality graphene have been produced in three simple exfoliation steps as a fully tested commercial concept. Low energy thermal arc-discharging expands the electrolytic graphite rod electrodes into hierarchical-like 3D graphene retaining the graphite structural order on a basal plane and chemical purity. Multi-size ball milling causes movement of the graphene materials in multi-shear directions, with optimized speed of the balls and lesser time. Micro-waving further separates the graphene sheets by "thermal expansion and release" mechanism utilizing thermally induced lattice vibrations. This also causes higher lattice order on basal plane improving directional and surface properties. The produced graphene (XRD 2theta = 26 degrees) has low defect (0.05 < ID/IG < 0.2), retains chemical purity (0.56-2.4% change in oxygen content), and with comparatively optimized effective nano-sizes (ranging from 300nm to 35um).