Estudo de sistemas vítreos para infiltração em alumina

The system in-Ceram Alumina, produced by VITA, consists in a technique of prepare of a substructure of ceramics to dental crowns. First burning is made in the alumina decanted by slip casting process under a stone die that reproduces the tooth prepared to receive a crown. In a second burning, alumina is infiltrated by vitreous system, giving to this set a high mechanic resistance. In this work, it s made a study of the composition of a new infiltrating material more used nowadays, giving to alumina desirable mechanics proprieties to its using like substructure of support to ceramic s crown used in the market today. The addition of Lanthanum oxide (frit A) and calcium oxide (frit B) was made in attempt to increase the viscosity of LZSA and to reduce fusion temperature. The frits were put over samples of alumina and took to the tubular oven to 1400ºC under vacuum for two groups (groups 1 and 2). For another two groups (groups 3 and 4) it was made a second infiltration, following the same parameters of the first. A fifth group was utilized like group of control where the samples of pure alumina were not submitted to any infiltrating process. Glasses manifested efficient both in quality and results of analysis of mechanic resistance, being perfectly compatible with oral environment in this technical requisite. The groups that made a second infiltration had he best results of fracture toughness, qualify the use in the oral cavity in this technical question. The average of results achieved for mechanic resistance to groups 1, 2, 3, 4 and 5 were respectively 98 MPa, 90 MPa, 144 MPa, 236 MPa and 23 MPa

Estudo da zircônia reforçado com alumina

Ceramics materials have good properties including chemical stability, high hardness and wear resistance. Moreover, due to its fragility, can suffer failure under relatively low levels of tension. Actually zirconia is the material of choice in metal free dental prostheses used in dentistry due its inertia in physiological environment, good bending strength, hardness and fracture toughness. The alumina and mixed tungsten and titanium carbides additions, acting as reinforcement elements in the zirconia matrix, have as their main objective the improvement of mechanical properties of this material. In this work, samples of zirconia, zirconia with 30% wt of alumina and zirconia with 30% wt mixed carbides were analyzed. The samples were sintered by uniaxial hot pressing on 30 MPa pressure, for 1 hour in an argon atmosphere. They were physically characterized by porosity and density measurements, and mechanically by 3-points bending strength and Vickers microhardness. The X-ray diffraction was used for the phase identifications and microstructure was examined by scanning electron microscopy (SEM). The addition of mixed carbides as reinforcement elements in zirconia matrix provides improvements in all properties analyzed in this work. The alumina addition has dropped the zirconia strength, although it caused improvement in other properties

Influência de tratamentos térmicos no comportamento mecânico da blenda poli(metacrilato de metila) / poli(tereftalato de etileno) reciclado

Studies indicate that a variation in the degree of crystallinity of the components of a polymer blend influences the mechanical properties. This variation can be obtained by subjecting the blend to heat treatments that lead to changes in the spherulitic structure. The aim of this work is to analyze the influence of different heat treatments on the variation of the degree of crystallinity and to establish a relationship between this variation and the mechanical behavior of poly(methyl methacrylate)/poly(ethylene terephthalate) recycled (PMMA / PETrec) with and without the use of compatibilizer agent poly(methyl methacrylate-al-glycidyl methacrylate-al-ethyl acrylate) (MMAGMA- EA). All compositions were subjected to two heat treatments. T1 heat treatment the samples were treated at 130 ° C for 30 minutes and cooled in air. In T2, the samples were treated at 230 ° C for 5 minutes and cooled to approximately -10 ° C. The variation of the degree of crystallinity was determined by the proportional relationship between crystallinity and density, with the density measured by pycnometry. The mechanical behavior was verified by tensile tests with and without the presence of notches and pre-cracks, and by method of fracture toughness in plane strain (KIC). We used the scanning electron microscopy (SEM) to analyze the fracture surface of the samples. The compositions subjected to heat treatment T1, in general, showed an increase in the degree of crystallinity in tensile strength and a tendency to decrease in toughness, while compositions undergoing treatment T2 showed that the opposite behavior. Therefore, this work showed that heat treatment can give a polymer blend further diversity of its properties, this being caused by changes in the crystal structure

Compósitos Portland-biopolímeros para cimentação de poços de petróleo

The oil production in mature areas can be improved by advanced recovery techniques. In special, steam injection reduces the viscosity of heavy oils, thus improving its flow to surrounding wells. On the other hand, the usually high temperatures and pressures involved in the process may lead to cement cracking, negatively affecting both the mechanical stability and zonal isolation provided by the cement sheath of the well. The addition of plastic materials to the cement is an alternative to prevent this scenario. Composite slurries consisting of Portland cement and a natural biopolymer were studied. Samples containing different contents of biopolymer dispersed in a Portland cement matrix were prepared and evaluated by mechanical and rheological tests in order to assess their behavior according to API (American Petroleum Institute) guidelines. FEM was also applied to map the stress distribution encountered by the cement at bottom bole. The slurries were prepared according to a factorial experiment plan by varying three parameters, i.e., cement age, contents of biopolymer and water-to-cement ratio. The results revealed that the addition of the biopolymer reduced the volume of free water and the setting time of the slurry. In addition, tensile strength, compressive strength and toughness improved by 30% comparing hardened composites to plain Portland slurries. FEM results suggested that the stresses developed at bottomhole may be 10 to 100 times higher than the strength of the cement as evaluated in the lab by unconfined mechanical testing. An alternative approach is proposed to adapt the testing methodology used to evaluate the mechanical behavior of oilwell cement slurries by simulating the confined conditions encountered at bottornhole

Influência da sequência de empilhamento nas propriedades mecânicas de laminados compósitos submetidos à tração

Composite laminates with plies in different directions finely dispersed are classified as homogenized. The expected benefits of homogenization include increased mechanical strength, toughness and resistance to delamination. The objective of this study was to evaluate the effect of stacking sequence on the tensile strength of laminates. Composite plates were fabricated using unidirectional layers of carbon/epoxy prepreg with configurations [903/303/-303]S and [90/30/-30]3S. Specimens were subjected to tensile and open hole tension (OHT) tests. According to the experimental results, the mean values of strength for the homogenized laminates [90/30/-30]3S were 140% and 120% greater for tensile and OHT tests, respectively, as compared to laminates with configuration [903/303/-303]S. The increase in tensile strength for more homogenized laminates was associated with the increment in interlaminar interfaces, which requires more energy to produce delamination, and the more complicated crack propagation through plies with different orientations. OHT strength was not affected by the presence of the hole due to the predominance of the interlaminar shear stress in relation to the stress concentration produced by the hole

Estudo da viabilidade do processo de reciclagem do material descartado do sistema Zirkonzanh® de produção de próteses dentárias

At present, the material of choice for performing aesthetic dental prosthetic work is in the ceramic. Among them, the ceramic base of stabilized zirconia with 3% yttria (3Y - TZP) stand out for having excellent physical and mechanical properties. During the machining of blocks of zirconia in the laboratory to prepare the various types of prostheses, much of the material is given off in the form of powder, which is subsequently discarded. The waste of this material results in financial loss, reflecting higher final cost treatment for patients, as well as damage to the environment, thanks to the processes involved in the manufacture and disposal of the ceramic. This research, pioneered the recycling of zirconium oxide powder obtained during milling of dental crowns and bridges, we highlight the social and environmental aspects and aims to establish a protocol for the reuse of waste (powder of zirconia Zirkonzahn® system) discarded to obtain a new block of compacted zirconia to maintain the same mechanical and microstructural properties of commercial high-cost imported material. To compare with the commercial material, samples were uniaxially (20 MPa) and isostatically (100 MPa), and its mechanical and microstructural characterization was performed through tests of density, porosity, dilatometry, X-ray diffraction (XRD), hardness, fracture toughness, resistance to fracture electron microscopy (SEM) and analysis of grain size. The results observed in the samples were isostatically pressed similiares those obtained with samples from the commercial material demonstrating the viability of the process

Avaliação do efeito da adição de resíduo de borracha de pneu e brita calcária na formulação de compósitos cimentíceos

Researches have shown that the introduction of rubber in concrete improves the features of its deformability, as well as contributes to environmental disposal of waste generated in the tire retreading process. Furthermore, there is a high availability of limestone within RN and CE country. Ignorance about this stone, does not allow its wide use as aggregate, leaving, this abundant supply idle. A composite of limestone gravel, with proportions of tire rubber waste which could be used as concrete would be an alternative to concrete for low applications. Therefore, this research aims to evaluate the characteristics of concrete containing limestone gravel and proportions of little aggregate replacement (sand) by tire rubber waste. To this goal, the material components of the concrete were characterized, concrete specimens with limestone gravel were made, from the dash 1.0: 2.5: 3.5, varying the water/cement ratio, and inserting a commercial plasticizer, without a proportion of residue, known as reference. From this, concrete with and without the presence of the additive in the same proportions were chosen, as well as these with the use of granite gravel, for being the most used. Selected the references, to these, replacements of little aggregate (sand) were added replaced by rubber waste from the tire retreading process, treated with 1M NaOH in proportions from 5.0 to 20.0 % by mass, cured and exposed to the semiarid environment. The results indicate the possibility of using limestone gravel in the concrete composition with workability correction using plasticizer. There was a decrease in the mechanical properties of the concrete with increments of waste rubber, but there is an improvement in toughness and deformability of the composite, which makes it interesting for the construction of non-structural concrete floors, as well as, the rubber waste delayed the hardening process, continuing to gain resistance after 28 days

Adição de geomanta e tecido não tecido de polipropileno em cimentos geopoliméricos de pega rápida

Geopolymers are cementing materials that depict a number of advantages compared to Portland cement. Contrary to the latter, geopolymers are synthesized at room temperature, thus significantly reducing the emission of CO2 to the atmosphere. Moreover, the composition and synthesis reactions can be tailored to adjust the setting time of the material as well as its compressive mechanical strength. It is then possible to produce geopolymeric cements with short setting times and high compressive strength, although relatively brittle. The objective of the present study was to produce and characterize composite materials by reinforcing fastsetting geopolymeric matrixes with polypropylene geosynthetics (geomats and geotextiles) in an attempt to improve the toughness and tensile strength of the cementing material. Geosynthetics have been increasingly used to reinforce engineering structures, providing higher strength and better toughness. In particular, polypropylene nonwoven and geomats depict other attractive properties such as low density, durability, impact absorption and resistance to abrasion. Fast-setting geopolymers were then synthesized and reinforced with polypropylene nonwoven and geomats. The mechanical strength of the materials, reinforced or not, was characterized. The results showed that relatively short setting times and adequate flowing behavior were achieved by adjusting the composition of the geopolymer. In addition, it is possible to improve the fracture resistance of geopolymeric cements by adding polypropylene geosynthetics. The best results were achieved by reinforcing geopolymer with polypropylene TNT

Análise do efeito do tempo da moagem de alta energia no tamanho de cristalito e microdeformação da rede cristalina do WC-Co

Hard metals are the composite developed in 1923 by Karl Schröter, with wide application because high hardness, wear resistance and toughness. It is compound by a brittle phase WC and a ductile phase Co. Mechanical properties of hardmetals are strongly dependent on the microstructure of the WC Co, and additionally affected by the microstructure of WC powders before sintering. An important feature is that the toughness and the hardness increase simultaneously with the refining of WC. Therefore, development of nanostructured WC Co hardmetal has been extensively studied. There are many methods to manufacture WC-Co hard metals, including spraying conversion process, co-precipitation, displacement reaction process, mechanochemical synthesis and high energy ball milling. High energy ball milling is a simple and efficient way of manufacturing the fine powder with nanostructure. In this process, the continuous impacts on the powders promote pronounced changes and the brittle phase is refined until nanometric scale, bring into ductile matrix, and this ductile phase is deformed, re-welded and hardened. The goal of this work was investigate the effects of highenergy milling time in the micro structural changes in the WC-Co particulate composite, particularly in the refinement of the crystallite size and lattice strain. The starting powders were WC (average particle size D50 0.87 μm) supplied by Wolfram, Berglau-u. Hutten - GMBH and Co (average particle size D50 0.93 μm) supplied by H.C.Starck. Mixing 90% WC and 10% Co in planetary ball milling at 2, 10, 20, 50, 70, 100 and 150 hours, BPR 15:1, 400 rpm. The starting powders and the milled particulate composite samples were characterized by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) to identify phases and morphology. The crystallite size and lattice strain were measured by Rietveld s method. This procedure allowed obtaining more precise information about the influence of each one in the microstructure. The results show that high energy milling is efficient manufacturing process of WC-Co composite, and the milling time have great influence in the microstructure of the final particles, crushing and dispersing the finely WC nanometric order in the Co particles

Metalização mecânica de ZrO2 com Ti para brasagem ZrO2/Aço com ligas de adição sem metal ativo

Metal/ceramic interfaces using zirconia have dominated the industrial applications in the last decade, due to the high mechanical strength and fracture toughness of zirconia, especially at temperatures below 300 ºC. Also noteworthy is the good ionic conductivity in high temperatures of this component. In this work joining between ZrO2 Y-TZP and ZrO2 Mg-PSZ with austenitic stainless steel was studied. These joints were brazed at high-vacuum after mechanical metallization with Ti using filler alloys composed by Ag-Cu and Ag-Cu-Ni. The influence of the metallization, and the affinity between the different groups (ceramic / filler alloys) was evaluated, in order to achieve strong metal/ceramic joints. Evaluation of joints and interfaces, also the characterization of base materials was implemented using various techniques, such as: x-ray diffraction, leak test, three-point flexural test and scanning electron microscopy with chemical analysis. The microstructural analysis revealed physical and chemical bonds in the metal/ceramic interfaces, providing superior leak proof joints and stress cracking, in order to a good joint in all brazed samples. Precipitation zones and reaction layers with eutetic characteristics were observed between the steel and the filler metal

Efeito da moagem de alta energia na densificação e microestrutura do compósito AI2O3-Cu

The Cu-Al2O3 composite ceramic combines the phase of alumina, which is extremely hard and durable, yet very brittle, to metallic copper phase high ductility and high fracture toughness. These characteristics make this material a strong candidate for use as a cutting tool. Al2O3-Cu composite powders nanocrystalline and high homogeneity can be produced by high energy milling, as well as dense and better mechanical structures can be obtained by liquid phase sintering. This work investigates the effect of high-energy milling the dispersion phase Al2O3, Cu, and the influence of the content of Cu in the formation of Cu-Al2O3 composite particles. A planetary mill Pulverisatte 7 high energy was used to perform the experiments grinding. Al2O3 powder and Cu in the proportion of 5, 10 and 15% by weight of Cu were placed in a container for grinding with balls of hard metal and ethyl alcohol. A mass ratio of balls to powder of 1:5 was used. All powders were milled to 100 hours, and powder samples were collected after 2, 10, 20, 50 and 70 hours of grinding. Composite powders with compact cylindrical shape of 8 mm diameter were pressed and sintered in uniaxial matrix resistive furnace to 1200, 1300 to 1350 °C for 60 minutes under an atmosphere of argon and hydrogen. The heating rate used was 10°C/min. The powders and structures of the sintered bodies were characterized by XRD, SEM and EDS. Analysis TG, DSC and particle size were also used to characterize the milled powders, as well as dilatometry was used to observe the contraction of the sintered bodies. The density of the green and sintered bodies was measured using the geometric method (mass / volume). Vickers microhardness with a load of 500 g for 10 s were performed on sintered structures. The Cu-Al2O3 composite with 5% copper density reached 61% of theoretical density and a hardness of 129 HV when sintered at 1300 ° C for 1h. In contrast, lower densities (59 and 51% of the theoretical density) and hardness (110 HV and 105) were achieved when the copper content increases to 10 and 15%.

Estudo da influência da adição de níquel em alumina pela rota da metalurgia do pó

Ceramic materials alumina basis have been widely used in structural components, mainly because owning properties such as high hardness, chemical inertness and good wear resistance, however, the low toughness is a factor that compromises its use in many other applications, featuring the addition of nickel as a possible solution to this problem, in this context, this work aims to study the addition of nickel alumina using the route of powder metallurgy processing of the material. The percentage of nickel were added 2, 4 and 6 wt%; and each composition to high energy milling in a planetary mill was performed for 2, 4, 9 and 16h. Subsequently, the samples were compacted at 300 MPa and sintered in a vacuum oven at 1400⁰C for 2h. The samples were characterized as the physical and mechanical properties, observing, in general, an improvement in sinterability of the material with increasing grinding time and nickel content, and mixing with a decrease of porosity and increase of hardness, density values above 80% of theoretical were obtained. The milling time of 4 hours and addition of 2% nickel, particularly if achieved higher hardness (HV 1068.7 +/- 32.6) and density of about 99% theoretical density.

Estudo da influência da adição de níquel em alumina pela rota da metalurgia do pó

Ceramic materials alumina basis have been widely used in structural components, mainly because owning properties such as high hardness, chemical inertness and good wear resistance, however, the low toughness is a factor that compromises its use in many other applications, featuring the addition of nickel as a possible solution to this problem, in this context, this work aims to study the addition of nickel alumina using the route of powder metallurgy processing of the material. The percentage of nickel were added 2, 4 and 6 wt%; and each composition to high energy milling in a planetary mill was performed for 2, 4, 9 and 16h. Subsequently, the samples were compacted at 300 MPa and sintered in a vacuum oven at 1400⁰C for 2h. The samples were characterized as the physical and mechanical properties, observing, in general, an improvement in sinterability of the material with increasing grinding time and nickel content, and mixing with a decrease of porosity and increase of hardness, density values above 80% of theoretical were obtained. The milling time of 4 hours and addition of 2% nickel, particularly if achieved higher hardness (HV 1068.7 +/- 32.6) and density of about 99% theoretical density.

Efeito da adição de WC e Co na sinterização e propriedades mecânicas da alumina

Composites based on alumina (Al2O3), tungsten carbide (WC) and cobalt (Co) exhibit specific properties such as low density, high oxidation resistance, high melting point and high chemical inertia. That composite shows to be a promising material for application in various fields of engineering. In this work, the mechanical properties of the composite (Al2O3 – WC – Co), particularly density and hardness, were evaluated according to the effects of the variables of powder processing parameters, green compact and sintered. Powder composites with the composition of 80 wt% Al2O3, 18 wt% WC and 2 wt% Co were processed by high energy ball milling in a planetary mill for 50 hours as well as mixed by manual mixing in a glass vessel with the same proportion. Samples were collected (2, 10, 20, 30, 40 and 50 hours) during the milling process. Then, the powders were compacted in a cylindrical die with 5 mm in diameter in a uniaxial press with pressures of 200 and 400 MPa. The sintering was in two stages: first, the solid phase sintering was performed at 1126 and 1300 °C for 1 hour with a heating rate of 10 °C/min in a resistive furnace under argon atmosphere for green samples compacted in 200 and 400 MPa; the second sintering was performed on dilatometer in solid phase at 1300 °C for green sample compacted in 200 MPa, another sintering also was performed on dilatometer, this time in liquid phase at 1550 °C for green samples compacted in 200 and 400 MPa, with the same parameters used in resistive furnace. The raw materials were characterized by X – ray diffraction (XRD), X – ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and laser particlemeter. The sintered samples were subjected to microhardness testing. The results showed that high energy milling achieved to the objectives regarding the particle size and the dispersion of composite phases. However, the hardness did not achieve to significant results, this is an indication that the composite has low fracture toughness.

Efeito da adição de WC e Co na sinterização e propriedades mecânicas da alumina

Composites based on alumina (Al2O3), tungsten carbide (WC) and cobalt (Co) exhibit specific properties such as low density, high oxidation resistance, high melting point and high chemical inertia. That composite shows to be a promising material for application in various fields of engineering. In this work, the mechanical properties of the composite (Al2O3 – WC – Co), particularly density and hardness, were evaluated according to the effects of the variables of powder processing parameters, green compact and sintered. Powder composites with the composition of 80 wt% Al2O3, 18 wt% WC and 2 wt% Co were processed by high energy ball milling in a planetary mill for 50 hours as well as mixed by manual mixing in a glass vessel with the same proportion. Samples were collected (2, 10, 20, 30, 40 and 50 hours) during the milling process. Then, the powders were compacted in a cylindrical die with 5 mm in diameter in a uniaxial press with pressures of 200 and 400 MPa. The sintering was in two stages: first, the solid phase sintering was performed at 1126 and 1300 °C for 1 hour with a heating rate of 10 °C/min in a resistive furnace under argon atmosphere for green samples compacted in 200 and 400 MPa; the second sintering was performed on dilatometer in solid phase at 1300 °C for green sample compacted in 200 MPa, another sintering also was performed on dilatometer, this time in liquid phase at 1550 °C for green samples compacted in 200 and 400 MPa, with the same parameters used in resistive furnace. The raw materials were characterized by X – ray diffraction (XRD), X – ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and laser particlemeter. The sintered samples were subjected to microhardness testing. The results showed that high energy milling achieved to the objectives regarding the particle size and the dispersion of composite phases. However, the hardness did not achieve to significant results, this is an indication that the composite has low fracture toughness.