Alumina

3-D microstructure of polycrystalline aluminium microstructure has been reconstructed on the basis of microscopic analysis results of actual α-Al2O3 microstructure by using Laguerre tessellation. SEM images of sintered bodies were used to calculate values of equivalent grain diameters and shape coefficient which then the Laguerre tessellation utilised for the 3D-reconstruction. The condition of periodicity has been additionally introduced for the generated domains. 3D periodical models of sizes ranging from 5 μm × 5 μm × 5 μm (61 grains content) to 30 μm × 30 μm × 30 μm (13220 grains content) were obtained in this way. Values of equivalent grain diameters and shape coefficients were determined for the synthetic microstructures. A comparison between distributions of the latter parameters and the analogous distributions originated from the polycrystalline Al2O3 SEM image analysis showed good compatibility. Dihedral angles of the synthetic microstructures also showed good compatibility with the literature reported data. The presented models will constitute the basis of further works on analysis of thermomechanical properties of polycrystalline materials.

Due to the reduction in the size of the electronic components, heat dissipation has become a major problem. In many cases, air cooling has failed to provide the required demands. The invention of nanofluid has promised to increase the efficiency of the liquid cooling system. The addition of solid nanoparticles to the liquid actually increases the thermal conductivity of the liquid because of the higher thermal conductivity of the solid particles. In this work, the thermal performance of a minichannel heat sink was analyzed using CFD for cooling of processor chipset using nanofluids instead of pure water. The effect of different mass flow rates and various volume concentrations of nanoparticles on the overall thermal performance are also analyzed. The Alumina and graphene water nanofluids are used as coolants with volume concentrations of 0.1, 0.15 and 0.2%. The cooling fluid is made to flow through an Aluminium mini channel with height 5mm and width 1mm respectively. The maximum allowable temperature that has to be maintained at the chip is below 50oC. By using the liquid cooling system with a heat sink, this temperature is reduced as low as 41.22oC. There is also an enhancement of the convective heat transfer coefficient in using graphene nanofluids when compared to alumina nanofluids. The thermal resistance of the heat sink with nanofluids is lesser than pure water.

Near-infrared (IR) spectroscopy has been used to distinguish between alumina oxo and hydroxy phases. Two near-IR spectral regions are identified for this function: (1) the high-frequency region between 6400 and 7400 cm−1, attributed to the first overtone of the hydroxyl stretching mode, and (2) the 4000–4800 cm−1 region attributed to the combination of the stretching and deformation modes of the AlOH units. Near-IR spectroscopy allows the study and differentiation of the hydroxy and oxo(hydroxy) alumina phases, since each phase has its own characteristic spectrum. The spectrum of bayerite resembles that of gibbsite, whereas the spectrum of boehmite is similar to that of diaspore. Bayerite has four characteristic near-IR bands at 7218, 7128, 6996, and 6895 cm−1. Gibbsite shows five major bands at 7151, 7052, 6958, 6898, and 6845 cm−1. Boehmite displays three near-IR bands at 7152, 7065, and 6960 cm−1. Diaspore shows a prominent band at around 7176 cm−1. The use of near-IR reflectance spectroscopy to study alumina surfaces has a wide application, particularly with thin films and surfaces. The technique is rapid and accurate. Near-IR, because of its sensitivity, can be used in reflectance mode for the on-line processing of bauxitic minerals.

The effects of doping small amounts of TiO2 up to 5 wt% on the sintering behaviour of alumina (Al2O3) was studied. Green samples were prepared and pressureless sintered in air at temperatures ranging from 1250°C to 1600°C, at a furnace ramp rate of 10°C/min. and soaking time of 2 hours. Sintered samples were characterized to determine bulk density, hardness and Young's modulus. It has been found that all the doped samples exhibited higher bulk density than the undoped samples. The bulk density increases with increasing temperature and attained a maximum value of 3.9 Mgm-3 for samples doped with 1.0 wt% TiO2 at 1450°C. The addition of 1 wt% TiO2 when sintered at 1450°C was found to be the most beneficial throughout the studied range as the samples exhibited the highest Young's modulus of 381 GPa and Vickers hardness of 16.5 GPa as compared to 256.7 GPa and 11.2 GPa for the undoped alumina. Titanium oxide doping is one economical way of improving the densification of Al2O3 without affecting mechanical properties.

http://link.springer.com/chapter/10.1007/978-3-540-69139-6_89

The ceramic shells were fabricated with ceramic slurry containing alpaha and gamma alumina as filler materials and colloidal silica binder. The shell characteristics in terms of bending strength and thermal expansion were measured. The phase transformation from gamma to alpha alumina were observed with transmission electron microscopy (TEM) and selected area electron diffraction (SAED) patterns.  The metal to mould reaction were revealed with optical microstructures and hardness distribution. The bonding mechanism in the alumina and colloidal silica binder system was due to formation siloxane bonds. The phase transition γ- → α-Al2O3 occurs in two phases, respectively in the temperature ranges of 600°C - 850°C cubic crystal structure and from 850°C - 1000°C, α-Al2O3 with corundum crystal structure. The cracks have been observed in the investment shells made of gamma alumina after 7075 Al-alloy pouring.

A study was carried out on the behavior during the sintering of Al2O3 ceramics with pre-sintering of the additives Nb2O5 and LiF at different temperatures. It was observed through XRD and DSC the formation of the LiNb3O8, Nb3O7F and LiNbO3 phases during the pre-sintering of the additive powders and the formation of the LiAl5O8, AlNbO4 phases during the sintering of the samples The samples showed densities around 91% of the theoretical density, and pre-sintered samples showed low growth in grain size.

A series of polycarboxylate ether-based copoly-mers that include acrylic acid, 2-acrylamido-2-methylpropane sulfonic acid, and polyethylene glycol-1000 was synthesized, and the performance of these copolymers as rheology modifiers in aqueous alumina suspensions was characterized. We discussed the effect of monomer feed ratio and molecular weight on dispersing ability of these copoly-mers and on extensional behavior of alumina suspensions. Results of zeta potential analysis determined that using the copolymers even at 0.5 wt.% results in all-negative zeta potentials for the entire pH range (2–12). These copolymers immensely affect the extensional rheological behavior of alu-mina suspensions—while 20 vol.% pure alumina suspension showed severe strain hardening behavior, suspensions with 1 wt.% copolymers and 35 vol.% alumina particles displayed no strain hardening. In this series, the copolymer with lowest molecular weight decreased the extensional viscosity of sus-pensions at the rupture of thread with three orders of magnitude as well.

Nanocomposites based on low-density polyethylene (LDPE), containing 0.5, 1, 2, 3, and 5 wt of nanoalumina, were prepared by melt-mixing at 125°C and hot melt-pressing to thin polymer film at 125°C. To enhance the interfacial interaction between alumina and LDPE, alumina surface was treated with silane which acts as coupling agent. The effects of alumina additions to the structure and morphology of LDPE matrix were characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), respectively. The mechanical behaviour of nanoalumina-reinforced LDPE composite was studied using tensile tests, flexural tests, and impact tests. The interfacial adhesion between nano alumina particle and LDPE matrix was investigated. The result showed that the reinforcement performance of nano alumina to LDPE matrix was attributed to the interfacial adhesion between nanoparticle and polymer matrix. The addition of 1 wt nano alumina has successfully enhanced the mechanical properties of LDPE material. © 2012 Ching Yern Chee et al.

http://dl.acm.org/citation.cfm?id=2490013

In November 2010 a keynote lecture was presented by the author on the failure of the dam of the red mud reservoir No. 10 of the Ajka Alumina Refinery in the course of the XVIII th Symposium of ICSOBA in Zhengzhou, China. Based on this lecture a paper was published. Since that time further relevant information have been made public by scientific studies, on the legal circumstances, the industrial, governmental and other actions, or their lack, which probably played role in the changes which eventually led to the dam failure. The scientific study results, the industrial and governmental actions, the activities of civil organizations, the report of a parliamentary committee, a study report of the " green party " of Hungary and a leading civil engineer' expert opinion will be summarized in this paper. The paper challenges the method of the classification of the solid materials whether they are considered to be hazardous or not, a new approach has been proposed. Though a better understanding on the probable reasons of the tragic failure of the dam has been achieved than was available a year ago, further relevant information may come up in the future.

The present work was aimed to assess the influence of Si content, superheat, modification and mould preheat temperature on the fluidity. The fluidity spirals were made using alumina filler materials and the colloidal silica binder. The fluid increases with the increase of Si content, super heat and shell mould preheat temperature, but decreases with Sr modification.

This study aimed to compare the biomechanical behaviour of functionally graded structured posts (FGSPs) and homogenous-type posts in simulated models of a maxillary central incisor. Two models of FGSPs consisting of a multilayer xTi-yHA composite design, where zirconia and alumina was added as the first layer for models A and B respectively were compared to homogenous zirconia post (model C) and a titanium post (model D). The amount of Ti and HA in the FGSP models was varied in gradations. 3D-FEA was performed on all models and stress distributions were investigated along the dental post. In addition, interface stresses between the posts and their surrounding structures were investigated under vertical, oblique, and horizontal loadings. Strain distribution along the post-dentine interface was also investigated. The results showed that FGSPs models, A and B demonstrated better stress distribution than models C and D, indicating that dental posts with multilayered structure dissipate localized and interfacial stress and strain more efficiently than homogenous-type posts.

http://www.ncbi.nlm.nih.gov/pubmed/22123011

A two-step electrochemical anodisation approach was adopted in this work to create a series of highly ordered mesopores etched with different diameter (60 to 160 nm) and uniform nanotube length in anodised aluminium oxide (AAO). The loading and release characteristics of model drug (indomethacin) and drug carriers (micelles named Pluronic F127, TPGS, PEO-PPO-PEO) were presented to investigate the influence of micelle size, pore diameter and surface modification of AAO on release studies. Surface chemistry was varied via silanation process, using AFTES and PFPTES. It was discovered that quicker release of drugs was induced by larger pore size and smaller micelles. Moreover drug release was found to favour hydrophobic surface as the release was faster in PFPTES modified AAO than the one with APTES.

A 3D model for intergranular thermal stresses in coarse polycrystalline alumina has been derived using Diffraction Contrast Tomography. Larger tensile thermal strains develop when the (0001) pole of adjacent grains lies closer to the grain boundary normal. This agrees with observations of cracked boundaries, obtained through digital image correlation of in-situ observations in fine alumina.

Doped nano alumina powders were successfully deposited as a thick film by electrophoretic deposition (EPD). A mixture of ethanol, cation salts of alumina dopants and iodine was used for dispersion system. Mg-Y-La-and Ce-salts add to ethanol and deposited with alumina powders on to substrate. The effects of suspension power loading, deposition time, electrode distance and applied potential simultaneously on density, pore size distribution and cell current density of alumina nanoparticles were examined. The weight of deposition increased with time and voltage increased and electrode distance decreased. In all applied voltages in higher suspension concentration, weight of deposition are sufficiently high but the density of the film are clearly better in low and high voltages than medium voltage. In constant suspension concentration with increasing in applied voltage, deposition rate increased and current decreased faster than medium voltage, which limits the homogeneous deposition forming and decreased density. Low applied voltages provided better pore size distribution and narrow and steep slope in middle of pore size distribution plot. High density samples with best pore size distribution achieved in lower rate deposition and assisted to better densification at sintering step in doped alumina plates.

The present invention discloses a dental post fabricated of metal-ceramic functionally graded composite material. The dental post and method of fabrication and installation of the post were devised to enable a dental post to be prefabricated, utilizing materials that have structural and compositional compatibility with the natural tooth being restored. Using a metal-ceramic functionally graded composite material to fabricate the post, high modulus of elasticity at coronal part can be achieved which is approximately similar to the crown/s and bridge abutment/s and it gradually reduced towards the apical partof the tooth. Utilization of this post will increase the fracture resistance of endodontically treated teeth. It has also been shown that when failure occurs,the failed tooth is likely to be repairable thus making root treated teeth more durable.

It has been demonstrated that carbon (C) doped aluminium oxide (Al2O3) nanocomposite (C­0.012 wt%) had greater wear resistance and lower surface grains pull out percentage when compared with monolithic Al2O3. In the present study, we investigated the physicochemical, micro­ and nano­mechanical, cell attachment, in vitro biocompatibility and osteogenic differentiation properties of Al2O3 doped carbon (0.012 wt%) nanocomposite (Al2O3/C). Data were compared to values obtained for monolithic alumina (Al2O3). The calcined Al2O3/C nanocomposite was densified using cold isostatic pressing and followed by pressureless sintering. For physicochemical and microstructural characterisation, Energy dispersive X­ray (EDX), X­ray diffraction (XRD), Raman spectroscopy, and X­ray photo­ emission spectrometer (XPS) were used. EDX, XRD peaks and Raman spectroscopy demonstrated correlating to Al2O3/C. Surface profiling and contact angle investigations demonstrated highly contoured micro­surface topography. The micro and nano­hardness indicate an improved wear resistance of the Al2O3/C when compared with monolithic Al2O3. SEM, confocal images and alamar blue reduction assay suggested good cell attachment and proliferation of human bone marrow derived mesenchymal stromal cells (hBMSCs). Osteogenic protein and gene expression indicated Al2O3/C had a significant osteogenic potential (p < 0.05) when compared with Al2O3. In conclusion, our novel Al2O3/C nanocomposite had improved mechanical properties. It also supports cell attachment and proliferation which are comparable to Al2O3. However, Al2O3/C has a significant osteogenic potential than that of Al2O3. These findings suggest that Al2O3/C nanocomposite is superior to Al2O3 and thus has a greater potential for use in orthopaedic applications. (C)

A B S T R A C T Graphene was prepared using liquid phase exfoliation and dispersed in an alumina matrix using an ultrasonication and powder processing route. Al 2 O 3 –graphene composites with up to 5 vol% content were densified (>99%) using SPS. The fracture toughness of the material increased by 40% with the addition of only 0.8 vol% graphene. However for higher graphene contents the improvement in fracture toughness was limited. Graphene changed the

Boron doped PVA/Zr-Al acetate nanofibers were prepared by electrospinning using PVA as a precursor. The effect of calcination temperature on morphology and crystal structure was investigated at 250, 500, and 800 °C. The study also establishes the effect of boron doping on the morphology of PVA/Zr-Al acetate nanofibers at various calcination temperatures. The measurements showed that the conductivity, pH, viscosity and the surface tension of the hybrid polymer solutions have increased with boron doping. In addition, the fibers were characterized by FTIR, DSC, XPS, XRD and SEM techniques. The addition of boron did not only increase the thermal stability of the fibers, but also increased the average fiber diameters, which gave stronger fibers. The DSC results indicated that the melting temperature (Tm) of the fibers was increased from 256 to 270 °C with the addition of boron. XRD peak patterns showed that after further heat treatment at 800 °C, zirconia exists in two phases of tetragonal and monoclinic modifications. Moreover, alumina does not transform into the γ-Al2O3 and θ-Al2O3 phase at 800 °C. The SEM appearance of the fibers showed that the addition of boron resulted in the formation of crosslinked bright surfaced fibers.

Os processos de síntese química podem ser descritos como sendo atos de equilíbrio manipulados de acordo com determinadas especificações para criação de materiais ou produtos, um desempenho de equilíbrio de fótons, elétrons e partículas em meio fluido para criar movimentos, fluxos ou explosões que geram materiais adequados e altamente requisitados no desenfreado avanço da tecnologia contemporânea. Existem várias peças no quebra-cabeça das sínteses químicas que vêm sendo elucidadas ao longo dos anos mediante pesquisas e adoções de novas tecnologias associadas. Algumas envolvem economia, outras, sustentabilidade, sendo que todas desempenham papéis importantes.

Este livro intitulado “Nanomateriais Cerâmicos por Reação de Combustão: Síntese e Aplicações” está intencionalmente focado nos princípios elementares e técnicos subjacentes aos aspectos tecnológicos do método da síntese química por reação de combustão, mas também envolve o seu progresso de scale-up e aplicações. A reação de combustão é vivenciada de forma trivial no Laboratório de Síntese de Materiais Cerâmicos (LabSMaC) como uma ferramenta fundamental para obtenção de pós cerâmicos que posseum as características desejadas para aplicações como em catálise, materiais absorvedores de radiação eletromagnética, biomateriais e spintrônica. Também é importante destacar a escassez de tecnologias em desenvolvimento difundidas na literatura focada nos métodos de síntese química que oferecem as vantagens de dados operacionais para oportunizar um aumento de escala, especialmente quando se trata da reação de combustão, sendo que a escalabilidade tem sido uma tendência mundial nos setores, sejam laboratoriais ou industriais, figurando uma necessidade que se torna ainda mais sobrepujante diante do contexto atual em que os inúmeros e diversos segmentos buscam se reinventar para manter competitividade e inovação, e isto ainda mais recentemente acentuado devido a pandemia de COVID-19, iniciada no ano de 2020 e causada pelo vírus SARS-CoV-2 ou Novo Coronavírus, a qual vem causando repercussões de cunho biomédico, epidemiológico, impactos sócil-econômicos, políticos, culturais e históricos.
 
Estruturamos o livro em onze capítulos dos quais os dois primeiros compilam informações gerais e conhecimentos técnico-científicos de grande relevância que podem ser aproveitados pelos leitores sobre os princípios da reação de combustão e sua scale-up, por outro lado, por exemplo, para pesquisadores com expertise neste tipo de síntese, a seção sobre o método será trivial, no entanto, este público poderá se beneficiar ao ver uma diferente abordagem que é panoramicamente apresentada sobre o tema, contendo uma metodologia em situações reais, ao passo que incentiva a imersão na leitura completa do livro. Os demais capítulos podem ser selecionados por aqueles interessados em atender as necessidades de específicas e importantes aplicações para os materiais obtidos, podendo impulsionar ou aprimorar ideias. A obra como um todo se mostra de grande relevância, principalmente para aqueles que vivenciam os desafios envolvidos na temática das sínteses químicas.

De abordagem objetiva, a obra é baseada nos estudos desenvolvidos por graduandos, pós-graduandos, pesquisadores e docentes envolvidos no grupo de pesquisa de Sínteses dos Materiais Cerâmicos e do Programa de Pós-Graduação em Ciência e Engenharia de Materiais da UFCG, e que também atuam na UFPB, UEPB, IFPB, UFRN, UFRPE, UFSCar, UNIFEI e IEAv. Seu primeiro capítulo é uma abordagem dos principais fundamentos da reação de combustão, e o segundo capítulo voltado para exemplificar como a síntese em maior escala funciona, e, ao fazê-lo, evidencia as vantagens deste processo, sendo a expectativa demonstrar a eficiência e a viabilidade técnica, como também despertar ideias para novas e eficientes estratégias de produção por parte dos interessados na área de ciências, engenharias e profissionais. Os demais capítulos são abordagens de algumas diferentes aplicações dos pós produzidos por reação de combustão, os quais ressaltam a importância do método. Por causa do perfil de abordagem fundamental, esperamos que também sirva bem àqueles que precisam entender as limitações das soluções técnicas dos processos de síntese e requerem uma compreensão científica mais direcionada e prática do que está sendo proposto, e que necessitam de forma mais particular conhecer o progresso da pesquisa nesta área.

As contribuições de todos os autores e seus colaboradores, a quem agradecemos a confiança e espírito de parceria; junto ao apoio e as excelentes sugestões dos revisores e editores, nos ajudaram muito na preparação desta obra.

Um esforço significativo foi feito por todos para a realização desta edição do livro. Assim, agradecemos a Deus, e, nós gostaríamos de receber comentários dos leitores sobre questões que possam interessar para uma próxima edição.

Agora, é hora de desejar sucesso ao livro e que seja bem difundido; e aos leitores, uma boa leitura! E, passar para o próximo Projeto.



Joelda Dantas
Ana Cristina Figueiredo de Melo Costa

Dip coating investment slurry composition is important parameter to judge the performance of ceramic shell moulding process. The paper presents the use of an industrial waste, namely coal flyash for the investment casting. Experiments have been conducted on the dip-coating slurry and shell moulds to examine their characteristics that enrich the ceramic shell moulding process from flyash. The results indicate substantial enhance in the quality of flyash shell moulds due to uniform slurry viscosity, low sedimentation rate, completion of electrostatic bonds and round particle shape.

Surface modification and characterization of engineering components using high energy beams is an ever expanding and innovative area of research. Laser surface modification of plasma sprayed alumina coatings were carried out for transforming metastable γ-Al2O3 phase predominantly present in as-sprayed coating to a thermodynamically stable α-Al2O3 phase. These laser treated coatings were characterized using laser based non-destructive techniques like laser Raman spectroscopy, laser scattering, photoluminescence and piezospectroscopy for quantitative evaluation of the phase transformation, surface roughness, densification and residual stress associated with the coatings. Raman spectroscopic studies indicated the restoration of α-Al2O3 phase and laser scattering technique was used to optimize the processing parameters to obtain superior surface finish. Photoluminescence measurements have shown a marginal decline in residual stress and significant increase in density of the laser treated coatings.

Sodium bentonite is recognized as a natural pozzolan that can improve the mechanical properties of cemented materials due to its fineness and high content of silica and alumina. When mixed with cement paste in an appropriate amount, it is capable to impart pozzolanic effect which is vital to ensure continuous strength gain of cemented materials. Besides, the fineness of sodium bentonite enables the clay to bring filler effect on cemented materials, thus refining its pore spaces and reinforcing its structures. For stabilization of highly organic soil such as peat, research works that aim to quantify these effects with sodium bentonite as a natural pozzolan are relatively few. This article focuses on laboratory investigation on the application of sodium bentonite to maximize the filler and pozzolanic effects of stabilized peat. The outcome of the laboratory investigation is an optimal mix design of stabilized peat, which can be effectively applied to improve peat in a geological condition of swampy area for highway construction. Other than sodium bentonite, calcium chloride, Portland Composite Cement (PCC) and silica sand were used as additives to stabilize the peat sampled from Sri Nadi village, which is located in the area of Klang, Malaysia. To develop the optimal mix design, specimens of stabilized peat were tested in unconfined compression, direct shear and falling head tests. Both elemental composition and microstructure of the stabilized soil were examined using energy dispersive X-ray (EDX) apparatus and scanning electron microscope (SEM). It was found that test specimen of stabilized peat containing 10% partial replacement of PCC with sodium bentonite has the maximum unconfined compressive strength at 7days of curing in water and under the application of 50kPa initial pressure. Besides peat, the test specimen was formulated with a 300kgm-3 binder dosage and a 596kgm-3 silica sand dosage. At the same mix design, test specimens of stabilized peat have high values of cohesion, high values of angle of internal friction and very low rates of permeability, which are comparable to that of intact clay with a practically impervious drainage characteristic. Also, it was discovered that after testing, the test specimens showed a progressive increase in the direct shear parameters and a continuous decrease in the rate of permeability with increasing curing time in water. In the EDX and SEM analyses, high peaks of calcium, silicon, aluminum and oxide elements, and insignificant pore spaces of the stabilized peat were observed. This proves the existence of cementation products of mainly calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH) crystals that were responsible to bind the organic and soil particles together to form stabilized peat. © 2012 Elsevier B.V.

http://ac.els-cdn.com/S0013795212003043/1-s2.0-S0013795212003043-main.pdf?_tid=a2053ce6-66e4-11e3-9514-00000aacb361&acdnat=1387261970_2f749daf097c804708e4906fc2c5f939 
http://www.sciencedirect.com/science/article/pii/S0013795212003043

ABSTRACT The three-dimensional deformation beneath a Vickers indentation in polycrystalline alumina has been measured, in situ, by digital volume correlation of high resolution synchrotron X-ray computed tomographs. The displacement fields at the peak indentation load and after unloading are used to study the shape and orientation of sub-surface cracks induced by the indentation; lateral cracking due to residual stresses, bounded by a system of radial cracks, is revealed. For the first time, it is shown that radial cracks have mixed mode opening displacements, which are affected by the relaxation of residual stresses via lateral cracking. This novel technique may find applications in the study of surface damage by abrasive wear in brittle materials.

This study investigates the effect of Alumina, Zirconia, and fly ash particles coating on the microstructure and wear behavior of EN8 steel. The wear behavior of plain EN8 steel and different particles like Alumina, Zirconia, and fly ash coatings studied systematically with respect to load, sliding speed. The wear behavior of EN8steel studied by three body abrasive wear tester. The results show that with coatings Weight loss (specific wear rate) lower than that of plain EN8steel. It is also noted that weight loss increases with increase in load and speed. Meanwhile, the wear mechanisms of EN8 steel and with different coatings (like Al2O3, ZrO2, fly-ash) percentage is described and analysed.