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By Marcio José Cuccolo Rosales

A soldagem por brasagem a vácuo promove a união de materiais dissimilares com alto valor agregado. Este trabalho visa estudar a interação química do nitreto de boro hexagonal (h-BN) na interface de ligação brasada do par Kovar®/h-BN. As variáveis de processo são determinantes para formação da junta brasada metalurgicamente estável. O trabalho estuda a molhabilidade do h-BN quando em contato com ligas de adição do sistema eutético Ag-Cu durante a solidificação. Foram conduzidos ensaios no h-BN a fim de caracterizar sua aplicação no sensor de posição do feixe de elétrons (BPM) do projeto do Sirius, e as propriedades que influenciam o seu processamento durante a brasagem, como coeficiente de expansão térmica e molhabilidade superficial. Os ensaios de brasagem com a liga Ag-Cu-4,5Ti, mostraram boa molhabilidade e espalhamento na superfície, favorecendo a formação da junta sem descontinuidades. As reações na interface são complexas no sentido de formação de novas fases e intermetálicos e, influenciadas pela seleção dos materiais, que possuem diferentes temperaturas de fusão e coeficientes de expansão térmica. Os resultados indicam que a seleção da liga com Ti, que é o elemento de ativação, promove a interação na superfície do h-BN com os demais materiais da junta.

Oct 30, 2017

By T. S. Lundy, R. A. Padgett

The fact that cobalt diffuses in silver at a much slower rate in a region near a free surface than in bulk material has been demonstrated in a variety of experiments. Various possible mechanisms of this near-surface effect (NSE) are examined in light of experimental evidences. The tendency for surface segregation of some solute atoms appears to be a likely mechanism to explain the effect. UNIDIRECTIONAL and isothermal diffusion from a plane source of radioactive tracer into an isotropic, homogeneous medium follows the Gaussian solution to Fick's second law, or: where A(x,t) is the position and time-dependent concentration of the diffusing species, M is the quantity of diffusant per unit area initially at x = 0, and D is the diffusion coefficient. For a given time, say t = tl, one can easily see that: d In Aixji)_____1_ r2] d(x2) 4Dti Thus, if diffusion data obtained by serial sectioning are plotted as In A(x,tl) vs x2, the diffusion coefficient is obtained from Eq. [2]. The ideal behavior seldom is observed in real systems. Deviations from ideality generally occur either at small or large values of penetration distance. The overall picture is shown schematically in Fig. 1 where Regions I, 11, and 111 are due, respectively, to some near-surface effect or effects (NSE), volume diffusion, and short-circuiting effects. For different systems and conditions of specimen preparation and analysis, the relative importance of Regions I, 11, and I11 may be drastically different. Region I is completely absent in many systems and there is no NSE. In others, however, there may be considerable difficulty in determination of volume diffusion coefficients due to the overshadowing influences of Region I. Such is particularly true when indirect techniques such as the surface concentration decrease or the Gruzin method' are used to find D. In this paper several experiments which had as their goal a better understanding of near-surface effects are reported. Specifically, it is well-known that unusual penetration behavior results for the diffusion of several impurities in ilver- and that considerable controversy exists with regard to interpretation of the published diffusion data. We chose to examine those unusual results which occur for cobalt diffusion in monocrystalline silver395 primarily because knowledge of experimental procedures and materials were readily available. Both radioactive co60 and co5' could be utilized to offer a wide range of available concentration of the diffusing species. Experiments were also performed on the diffusion of AgnO in silver. They gave base-line data for the system—both for technique evaluation and for examination of the vacancy distribution near the surface. I) PROCEDURES Cylindrical-shaped specimens 1.25 cm diam and 1 to 1.25 cm long were cut from 99.999 pct Ag single crystals obtained from Monocrystals Co., Cleveland. One end surface of each specimen was polished flat and etched with a mixture of 20 ml saturated Cr03 solu-tion-20 ml H20-3 ml concentrated HC1. Radioactive tracer (co60 or co5' or Ag'lO, each having a radio-chemical purity of greater than 99 pct) was deposited onto the prepared surface either dropwise with evaporation to dryness of the solution containing the tracer (0.5 N HC1 solution for the co60 and co5' and 0.6 N HNO3 solution for the A"'), by electroplating, or by evaporation from a tantalum or tungsten filament in an evacuated bell jar. The amount of deposited cobalt was varied from many atomic layers of cobalt containing the co60 to approximately one co5' atom per lo6 surface atoms of silver. This large variation in amount of deposited cobalt yielded information about both the influence of a thick-source layer of tracer and solubility effects on the NSE. Such variations were possible because of the large differences in half-lives,

Jan 1, 1969

By Walter W. Bradley

(Three, papers included, in this discussion are classified as Mining Geology and also as one of the following-A, Metal Mining: B, Milling and Concentration: L, Geophysics. These papers are TP 2255, TP 2092 and TP 2038.) CONTENTS [PAGE Review of Fluorescence as Applied to Minerals, with Special Reference to Scheelite. (TP 1967 by J. W. VANDERWILT, Min. Tech., March 1946. Discussion by WALTER W. BRADLEY) I Geologic Interpretation of Magnetic Exploration on the Mesabi Range, Minnesota. (TP 2038 by R. B. H. JONES, Min. Tech., July 1946. Discussion by ROBERT B. SOSMAN) I A Technique for Photographing Difficult Subjects through a Petrographic Microscope. (TP 2092 by DONALD W. SCOTT, Min. Tech., Nov. 1946. Discussion by HORACE WINCHELL) 2 The Search for Concealed Deposits-a Reorientation of Philosophy. (TP 2146 by SAMUEL G. LASKY, Min. Tech., May 1947. Discussion by T. M. BRODERICK)3 Occurrence of Lead-zinc Ore at Iron King Mine, Prescott, Arizona. (TP 21 go by H. F. MILLS, Min. Tech., July 1947. Discussion by HUGH M. ROBERTS)3 Geologic Relations and New Ore Bodies of the Republic District, Washington. (TP 2197 by LAWRENCE B. WRIGHT, Min. Tech., July 1947. Discussion by AUGUSTUS LOCKE and J. A. RICHARDSON) 4 San Manuel Prospect. (TP 2255 by H. J. STEELE and G. R. RUBLY, Min. Tech., Sept. 1947. Discussion by L. KENNETH WILSON, ELDRED D. WILSON and the author) 5] Review of Fluorescence as Applied to Minerals, with Special Reference to Scheelite WALTER W. BRADLEY*-AS I recall, the first portable units for ultra-violet light of practical use with scheelite were developed at the Nevada-Massachusetts Tungsten Mine at Mill City, Nevada, and were used underground. Ultra-violet lamps are also installed there in the mill, above the gravity-concentration tables, for control observations. Geologic Interpretation of Magnetic Exploration on the Mesabi Range, Minnesota ROBERT B. SOSMAN*-When artificial precipitated magnetite is oxidized at a temperature in the vicinity of 100°C, the oxide is converted into a chocolate brown ferric oxide of the formula Fe2O3, free from ferrous iron, yet possessing the same magnetic susceptibility as the original Fe3O4. This form of Fe2O3 is variously called "ferromagnetic ferric oxide," " maghemite," or "gamma ferric oxide," and has been found as a natural mineral. If a body of magnetite in the Biwabik were to oxidize to this form, the oxidized and leached ore body might successfully conceal itself from Mr. Jones' survey by this ferromagnetic pretense. So far, gamma ferric oxide has not been found on the Minnesota iron ranges. I thought I had found some in the Hibbing pit in 1940, in a strongly magnetic specimen of soft ore differing in color from the prevailing hematite

Jan 1, 1947

By Saulo Brinco Diniz

O presente trabalho buscou explorar a influência de um tratamento térmico de ressolubilização, realizados com distintos tempos (70, 80 e 90 minutos) a uma temperatura de 510ºC, na microestrutura e na dureza de uma liga de alumínio 7475- T7351. Para verificar a influência destes tratamentos térmicos foram utilizados um durômetro (fabricante EMCOTEST, modelo Duravision 300) e um microscópio óptico (Olympus, modelo GX51). Após os resultados obtidos, pode-se evidenciar que a liga de alumínio em estudo sofre um envelhecimento natural (a temperatura ambiente), e dentre os tempos de encharque estudados, 70 minutos é o tempo que possivelmente obtém-se a maior ressolubilização dos precipitados.

Aug 17, 2017

Os mais importantes processos de redução de minério de ferro em fornos de cuba convivem, com maior ou menor intensidade, o problema de precipitação de carbono no interior de seus reatores. Para melhor conhecer os efeitos dos parâmetros operacionais desses processos sobre as cinéticas simultâneas de redução das pelotas de minério de ferro e de precipitação de carbono, foi definido um programa cooperativo entre a Samarco e o Grupo de Siderurgia da PUC-Rio. O presente trabalho é a parte 1 deste programa, que analisou o comportamento de pelotas RD nas temperaturas de 500, 700 e 900 °C, vazões de 60 e 90 NL/min e pressões de 1,2 e 2,5 atm, quando reagiram com os gases de topo e sopro típicos das regiões superiores (Zona de Redução-ZR) dos fornos de produção de ferro esponja (DRI). O tratamento dos resultados obtidos nos testes programados pelo método estatístico fatorial, permitiu identificar as cinéticas concorrentes e propor um modelo global baseado no principio da superposição. Finalmente, utilizando as curvas “Grau de Reação Global-GR versus tempo”, mostrou correlações plenamente compatíveis com os dados experimentais levantados e plena viabilidade de aplicação a outros processos de produção de ferro primário.

Aug 1, 2018

By P. C. Claspy, P. H. Smakula

The electro-optic coefficients of LiNbO, and KTao.,5Nboe3,O3 (KTN) have been experimentally determined at the HeNe laser wavelengths of 0.6328, 1.15, and 3.39 µ. The coefficients were calculated fronz the retardation induced by an applied electric field. The retardations were measured by observing one or move transmission maxima and minima as a function of the applied field, and by measuring the retardation directly with a Babinet-Soleil compensator. The values obtained agree quite well with those previo~lsly reported by others. Extinction ratios as high as 3000:l have been observed. Resistivities and Curie temperatures have also been measured. Light-induced optical inhornogeneities in LiNbO, repovted by others have been observed. CONSIDERABLE interest has recently been shown in the electro-optic properties of LiNb03 (Refs. 1 and 2) and KTN.3, 4 These crystals have a number of advantages over such well-known materials as KDP. These advantages include: 1) the infrared transmission of KTN and LiNb03 extends to 5 p whereas that of KDP cuts off at 1.5 p ; 2) driving voltages required for modulators using these materials are considerably lower than those required for KDP. After first discussing some theoretical considerations of the electro-optic effect, we will report the results of measurements of the dc electro-optic coefficients of these materials at wavelengths of 0.6328, 1.15, and 3.39 p. THEORY The generalized equation for the electro-optic effect can be written: Although lattice polarization is the fundamental variable, rather than the applied electric field, we follow the convention of expressing the linear electro-optic effect in terms of the applied field. For LiNbO the quadratic terms are negligible. Since KTN has a center of symmetry the rijk tensor is 0. After applying the usual symmetry considerations and index contractions,* the rijk and gijkl tensors can be expressed as follows: LiNbOaT If field directions are now chosen, the change in refractive index and the angle between the induced optic axes and the crystallographic axes can be found. The induced rotations of the principal axes of the index ellipsoid for fields in principal crystallographic directions are given in Table I. Since KTN is initially isotropic, the principal axes in the zero-field condition are parallel to the crystallographic axes. The induced retardations are given in Table 11. EXPERIMENTAL We obtained the various electro-optic coefficients by measuring the induced retardation as a function of

Jan 1, 1968

By D. Turk, P. Lefebvre, J. Sargent, K. Major

"Stillwater Mining Company recovers platinum and palladium from their Nye Montana operations. Mining first commenced at Nye in 1987 at a milling rate of 455 t/d (500 stpd). The plant was expanded in 1995 with the replacement of the ball mill and the addition of flotation capacity to increase mill throughput to 1820 t/d (2000 stpd). The applications for platinum and palladium have increased in recent years particularly in the automotive industry and the supply of the metals has remained fairly constant with prices for both platinum and palladium increasing and remaining very stable. In 1997 Stillwater initiated the expansion of their operations to increase production of platinum and palladium. Projects were initiated to expand production at the Nye operations, increase smelter and refining capacities at the Columbus facilities and to develop the extension of the orebody at the East Boulder site. This paper will discuss the changes at the Nye concentrator which were completed to increase production from 1820 t/d (2000 stpd) to 2730 t/d (3000 stpd) and eliminate some of the process bottlenecks.IntroductionStillwater Mining Company is mining the only significant primary source of PGMs outside of South Africa. The J-M Reef is an extensive mineralized zone containing PGMs that has been traced over a strike length of about 43 km (27 miles) in the southwest region of Montana. Stillwater controls the entire PGM mineralized zone.Johns-Manville geologists discovered palladium and platinum in the early 1970’s. In 1979, a Manville subsidiary entered into a partnership with Chevron, USA to develop the project. In 1 987, operations at the Stillwater property near Nye, Montana commenced."

Jan 1, 2000

By A. E. Dwight, A. F. Berndt

ThE published U-Ru equilibrium diagram indicates the existence of six intermetallic compounds in this system.' The structure of only two of the compounds, u2Ru2,3 and URU3,4 have been identified. This communication reports on the crystal structure and density of Uau3, which is formed by a peritectoid transformation at 1025° ± 5°C: U3Ru4 + U3Ru5 = U2Ru3. An alloy with the stoichiometric formula U2Ru3 was prepared by arc melting electrolytic uranium and ruthenium of 99.9 pct purity on a water-cooled copper hearth under an argon atmosphere. After homo-genization at 1000°C for 3 days, a metallographic examination revealed that the peritectoid transformation was complete and less than 5 pct of a second phase was present. A powdered sample, obtained by crushing the brittle compound, was annealed for 1 hr at 1000°C and air-cooled. Debye-Scherrer patterns were obtained with filtered CrKa, FeKa, CoKa, or CuKa radiation. The X-ray patterns of U2Ru3 weFe indexed as an fcc structure with a. = 12.895 0.00lA. The unit-cell constant and its standard deviation were calculated by a computer program described by Mueller, Heaton, and Miller.5 The density, measured by an immersion method, was 14.45 g cm-3. A calculated density of 14.48 g cm-3 was obtained on the assumption that twenty-four formula units (120 atoms) comprise a unit cell. The space group is either oh7 Fd3m, or the less symmetric, T4h, Fd3, since reflections indexed as hk0 with h + k + 4n are absent. All values of h2 + k2 + 12 permitted by both space groups are listed in Table I together with dc, do, and I. values. The calculated d spacings were obtained by the computer program of Mueller, Meyer, and simonsen.6 The observed d spacings above 0.77A were obtained from X-ray" patterns prepared with CuKa radiation, above 0.90A with CoKa radiaaion, above 0.98A with FeKa radiation, and above 1.16A with CrKa radiation. An attempt was made to identify the crystal structure of U2Ru3 by comparison with published data on other A2B3 compounds. A recent compilation7 of intermetallic compounds lists thirty-two structure types with the A2B3 stoichiometry. Only two of the structure types are fcc and they are Sb2O3(r), senarmontite, with 16 Sb2O3 per unit cell, and In2Te3 for which several structures have been proposed.8 However, the two cases cited do not have twenty-four formula units in the unit cell. We therefore, cannot identify UPRU3 with any of the other known A2B3 compounds. Ternary alloys were made in which 5 at. pct Os, Rh, or A1 were substituted for 5 pct of the Ru in U2Ru3. The osmium substitution increased the unit cell constant to 12.899 * .001A, which is to be expected since the atomic volume of osmium is slightly larger than

Jan 1, 1969

By Saulo Brinco Diniz

O presente trabalho buscou explorar a aplicação da nanoindentação instrumentada na caracterização microestrutural e mecânica de materiais metálicos. Para isso foi utilizado um ultramicrodurômetro (Shimadzu, modelo DUH–211S) e um microscópio (Olympus, modelo BX51M) a fim de analisar uma chapa laminada a quente de uma liga de alumínio 7475-T7351. De acordo com algumas das possibilidades apresentadas, pode-se concluir que a nanoindentação instrumentada é uma ferramenta poderosa para a caracterização de materiais metálicos.

Aug 16, 2017

By Suzana Souza da Silva Scardua

O desenvolvimento dos aços microligados representa um grande avanço tecnológico e oferece grandes vantagens econômicas para diversas áreas da engenharia. Nas últimas décadas houve um aumento expressivo na demanda mundial por tubos utilizados na construção de dutos para transporte de petróleo e gás. Neste caso são utilizados os aços ARBL (Alta Resistência e Baixa Liga) que combinam alta resistência e tenacidade necessárias para operar em altas pressões. Os tubos são produzidos a partir de placas laminadas e posteriormente soldadas atendendo a norma API 5L. Em componentes de geometria complexa, tais como juntas, acoplamentos e conexões, a laminação não é a técnica mais adequada. Para este fim, o processo de forjamento é uma alternativa, pois permite uma ampla faixa de dimensões e formas complexas com controle da microestrutura e propriedades mecânicas após tratamentos térmicos adequados. Para avaliar novas técnicas de processamento, foram fabricadas barras forjadas de um aço microligado com composição química similar à de um API 5L X70 comercial. O aço foi lingotado e forjado em barras quadradas de 35 mm de aresta. Em seguida foram retiradas amostras para tratamentos térmicos de têmpera a 920°C e 1.050°C e revenimento de 150°C a 650°C. Após analisar as microestruturas foi escolhida a similar à de um tubo comercial API 5L X70 para preparação de corpos de prova para ensaios de tração. Resultados preliminares mostram a possibilidade de obter aços com qualidade API através do forjamento.

Aug 7, 2018

By V. Beskrovnaya

Oxidised lead-bearing ores of one of the deposits of Russian Federation represent complex raw materials. Its main components are lead (3.2%~4.7%), silver (100~300 g/t) and zinc (0.7%~0.8%). The sample is characterized as oxidized ore. Silicium (37.4%) and iron (33.2%) are its main com-ponents and present in oxide form. Lead presents as cerussite, anglesite and plumbojarosite have a subject role. Zinc occurs as smithsonite. Certain part of zinc is associated with manganese minerals (psylomelane-pyrolusite). Close association of valuables with manganese-iron mineralization is ob-served. Silver is present in native finely dispersed form. Three options of flowsheets have been developed to recover valuables from the ore. 1. Hydrometallurgical flowsheet of lead and silver recovery on the basis of chloride leaching. 2. Flotation. 3. Flotation -flotation tailings cyanidation. Hydrometallurgical flowsheet of ore processing on the basis of chloride leaching (option I) al-lows to achieve recovery into saleable products of 68.8% Pb and 70.2% Ag. High quality lead concentrate with 71.7% lead and 700 g/t silver was obtained during flotation (option 2). Flotation tailings cyanidation (option 3) provides 24% silver additional recovery (from the ore). Technical and economical evaluation demonstrated that ore flotation (option 2) and flotation with subsequent flotation tailings cyanidation (option 3) are the most cost-efficient. Option II is the most cost-efficient variant of 1 tonne of ore processing (9.05 US dollars).

Jan 1, 2014

By De-qing Geng, Guang-liang Wu

The waste slag generated by the LF refining process of Q345B low alloy hot-rolled steel, still has some refining capabilities. If recycled, it can reduce environmental pollution, and save the economic costs. A research on melting Characteristics of Q345B steel LF refining waste slag was investigated by using orthogonal experimental method, and the effect laws of composition on that were analyzed. Through variance analysis and significance criterion, it is concluded that the optimum ingredient of the regenerated LF refining slag is 25%A12O3, 12%CaF2, 7%MgO and R= (CaO)/ (SiO2) =2.5. And the regression analysis is carried out by using SPSS software, to get the mathematical relationship between ingredient with high reliability and melting temperature of refining slag T=1451.3-6.25CaF2+2.36 R.

Jan 1, 2016

By Bryane Prando Brandão

Aços microligados expostos a ambientes contendo H2S e CO2 (sour gas) sofrem corrosão generalizada que promovem a entrada de hidrogênio atômico no metal, causando fragilização por hidrogênio, podendo gerar falhas graves no material. O objetivo deste trabalho é estudar o grau de fragilização, utilizando ensaio Charpy, de um tubo API 5L X65 após diferentes tempos de imersão em uma solução saturada com H2S. O eletrólito empregado foi solução A (ácido acético contendo cloreto de sódio) da norma NACE TM0284-2011, fazendo-se purga com N2 e injeções de H2S. Os corpos de prova padronizados foram imersos durante 96 e 360 horas, sendo que após doze dias do término da imersão, foram realizados os ensaios Charpy. Foram levantadas as curvas da energia absorvida em função da temperatura, para corpos de prova com e sem imersão. Os resultados mostraram que mesmo após imersão, não houve modificação significativa na temperatura de transição do material, apenas uma pequena diminuição da energia absorvida. Esse comportamento sugere que o teor de hidrogênio em solução sólida aumentou em função do tempo de imersão, levando a tais resultados. O refinamento da microestrutura e o baixo nível de inclusões estão relacionados a baixa quantidade e uniformidade da distribuição dos sítios de ancoramento de hidrogênio irreversível, o que pode explicar o desempenho obtido.

Aug 7, 2018

By Patricia Silva Madeira

Os aços molas ou mais especificamente os aços para a fabricação de molas (ASTM 5160) são basicamente aços com teores de carbono entre – 0,5% e 1,2%. O segredo do sucesso dos aços está relacionado a sua versatilidade, isto é da capacidade de se alcançar um conjunto específico de propriedade, dentro de um espectro muito amplo de possibilidades. Neste trabalho foram determinadas de maneira quantitativa as relações entre as propriedades elásticas com o tempo de recozimento variado e temperatura constante. A temperatura utilizada foi de 850°C, com tempos crescentes de 40 a 110 min. Para determinação das propriedades, os corpos de prova foram submetidos a ensaios de tração. A partir dos resultados observou-se uma redução do limite de escoamento e do módulo de resiliência do material. Decorridos 70 minutos de recozimento, essas propriedades mantiveram-se constantes. É apresentado ainda uma relação entre as propriedades de construção das molas com as propriedades do material utilizado em sua fabricação.

Aug 7, 2018

By J. I. Carroll, J. A. Walker

"Abstract - Camelback is a small (=200 000 tonnes), moderate grade (5%-7% Zn+Pb), volcanogenic massive sulfide deposit, which occurs within the Nepisiguit Falls Formation of the Ordovician Tetagouche Group. The host rocks are tuffaceous sedimentary rocks (Little Falls member) that overlie quartz-feldspar porphyritic tufflavas (Grand Falls member). The hanging-wall sequence comprises rhyolite of the Flat Landing Brook Formation, overlain by the Forty Mile Brook tholeiitic basalt. A dike of unaltered andesite was intersected beneath the massive sulfides, but was not found in the hanging-wall sequence in the vicinity of the deposit. The stratiform part of the deposit is made up of two, steeply south dipping, subparallel massive lenses that average approximately 4 m in thickness. Each lens is zoned, with an upper part consisting mainly of a pyrite and a basal part containing pyrite, sphalerite, and galena, with Ag values. The Au content in the massive sulfides is low (average = 52 ppb for 271 samples), but tends to be enriched in the massive pyrite near the top of each lens. Oxide facies iron formation is spatially associated with the massive sulfides, and has been traced up to 1800 m along strike. Footwall hydrothermal alteration is typical of VMS systems, and is characterized by depletion in K2O and Na2O, and enrichment in MgO and Fe2O3T with proximity to massive sulfides. The massive lenses are underlain by intensely chloritic, fine-grained, tuffaceous sedimentary rocks containing locally significant sulfide (chalcopyrite > pyrite > pyrrhotite) veins, which are interpreted to represent feeder zone mineralization. Unlike many VMS deposits, there is no evidence of silicification beneath the massive sulfides at the top of the feeder zone. The oxygen isotopic compositions (d18O = -1.5‰ to -0.3‰) of hydrothermal chlorite coupled with sulfur isotopic compositions (d34S ˜ 12‰) of the massive sulfides suggest that seawater was the dominant fluid in the hydrothermal system. Normalized rare earth element diagrams show flat Ce profiles and positive Eu anomalies, indicating that modified seawater was involved in ore formation; i.e., high-temperature (=350ºC), acidic, and reduced prior to entrainment into the hydrothermal cell. Although, seawater was the dominant fluid in the sulfide-forming system, d34S values of stringer zone sulfides (8.5‰) coupled with elevated Sn (400 ppm) in one massive sulfide sample indicate that there was at least some magmatic component in the hydrothermal cell."

Jan 1, 2006

By Stênio Cavalier Cabral

O diboreto de titânio (TiB2) é um material cerâmico de alta dureza com uma grande potencialidade de aplicação tecnológica. No entanto, existe uma grande dificuldade de se produzir corpos bem sinterizados desse material, quando são usadas técnicas convencionais de sinterização. Neste trabalho, foi empregada uma técnica de processamento em altas pressões e altas temperaturas para produzir compactos de TiB2 com AlN. Amostras cilíndricas, com 5 mm de diâmetro e 7 mm de altura, foram processadas durante diferentes intervalos de tempo compreendendo os ciclos de sinterização. O principal objetivo do trabalho foi à realização do ensaio de torneamento para a avaliação de desempenho dos compósitos produzidos e sua relação com a quantidade de ciclos de sinterizaçãos em condições reais de trabalho. Os resultados obtidos apresentam perspectivas interessantes de utilização do processamento em alta pressão e alta temperatura para produção de inseros para aplicação na usinagem do ferro fundido nodular.

Aug 16, 2017

A. L. FIELD, Cleveland, Ohio (written discussion*.-)In equation 2, B is used to denote the ratio of bases (lime plus magnesia ) to acids (alumina plus silica) it being stated that this ratio gives more concordant results than the ratio either of bases to silica, or of lime to silica. I find, however, that, by making use of the ratio between true CaO (CaO by analysis minus sulfur calculated to CaS) to acids, equation 2 may he modified to agree with the observed facts within an average error of 0.0041 per cent. sulfur instead of 0.0045 per cent. The revised equation is s = 0.072 + 0.01835 - 0.00061 (t - 1400) - 0.0403B where B is the ratio of true CaO to Al2O3 Plus Si02, and the other symbols have the same significance as before. I would not appear to stress too much this slightly better agreement of the revised equation with the observed sulfur. Yet I believe that the use of this ratio of true CaO to acids is to be preferred, if for no other reason than the fact that it is more in harmony with the previous findings of the Bureau of Mines with regard to the effect of magnesia and other impurities on slag viscosity.1

Jan 12, 1919

By Iara Janaína Fernandes

A casca de arroz é um resíduo amplamente gerado no mundo, é o principal subproduto do beneficiamento do arroz, e tem sido utilizada como biomassa para geração de energia, o que reduz o impacto ambiental causado pela destinação. No entanto, gera outro resíduo, a cinza de casca de arroz (CCA). A CCA é composta basicamente por sílica e carbono. Sendo os elementos traço mais comumente encontrados o sódio, potássio, cálcio, magnésio, ferro, cobre, manganês e zinco. Pelo elevado teor de sílica, é um resíduo com potencial para ser transformado em coproduto para diversas indústrias, porém, dependendo da aplicação pode ser necessária maior pureza. Assim, diversos estudos utilizaram a lixiviação ácida para reduzir o teor de contaminantes ou melhorar propriedades da CCA. Neste sentido, este trabalho teve como objetivo avaliar o beneficiamento de uma CCA residual através do processo de lixiviação ácida. Para isso, foram utilizados diferentes ácidos/concentrações, relações CCA/ácido e tempos de contato. Após estes testes utilizou-se análise elementar por FRX para caracterização química. Os resultados mostraram que o ataque ácido foi efetivo na redução ou eliminação de Fe2O3, K2O, CaO, P2O5 e ZnO para todos os ácidos e concentrações testadas. Sendo que as diferentes concentrações não afetaram a eficiência de remoção.

Aug 16, 2017

By Gisele Ferreira de Lima

Magnésio e suas ligas são promissores para armazenagem de hidrogênio devido à alta eficiência, boa reversibilidade, baixo custo e segurança. Entretanto, hidretos à base de Mg apresentam cinéticas de ab/dessorção lentas, temperaturas de operação muito altas, e alta reatividade ao ar para aplicação práticas. A moagem de alta energia (HEBM) combinada com o uso de catalisadores têm produzido nanocompósitos à base de Mg com cinéticas mais rápidas. Recentemente, processos termomecânicos e de deformação plástica severa (SPD) têm sido investigados para produzir nanocompósitos em volume com melhor resistência ao ar (processo de ativação) e que podem ser facilmente fabricados em escala industrial. No presente trabalho, amostras 2Mg-Fe foram misturadas com CNT (0-5%p.) por HEBM, e em seguida processadas por extrusão a quente (termomecânico) a 300oC e/ou laminação a frio (SPD) a temperatura ambiente. Pós com 0%p a 5%p. de CNT mostraram padrões de DRX muito similares indicando similares nanoestruturas. Todas as amostras puderam ser laminadas, mas somente amostras com menos que 2,0%p. de CNT puderam ser extrudadas, e submetidas pela combinação de extrusão-laminação. As propriedades cinéticas, medidas pelos métodos Sieverts e DSC, foram piores para as extrudadas, intermediárias para as extrudadas/laminadas e melhores para as somente laminadas. Nessas últimas, os picos de Bragg mostraram baixa intensidade e textura favorável ao longo de (002) no Mg, que possivelmente explicam esses resultados. Quanto maiores foram as quantidades de CNT melhores foram as propriedades (cinética e temperatura de dessorção).

Aug 8, 2018

By J. W. Hickman

INTRODUCTION MOST of the electron diffraction studies of oxide films which form on metals and alloys have been carried out by oxidizing the specimens in an auxiliary furnace, cooling down to room temperature and then inserting the sample in the camera and taking a diffraction photograph. Prior to the investigations at the Westinghouse Research Laboratories, no systematic study of the oxidation of any metal or alloy had been made over a wide temperature range with photographs taken at elevated temperatures except the investigation of iron by Jackson and Quarrell.1 In order to interpret the electron diffraction patterns of the oxides which may form on alloys, it seemed advisable to make a comprehensive study of the oxidation of the purest metals available in the bulk form. Thus far studies have been completed on iron,2 cobalt,2 nickel,2 chromium ,2 Copper2, tungsten,3 molybdenum,3 beryllium ,4 uranium,4 thorium4 titanium5 and zirconium5 while investigations are in progress on tantalum and columbium, The next step in the study is concerned with the investigation of the oxides which form on binary alloys. Some of the alloys consist of a single, phase while others contain more than one phase. The identification of the oxides on the surface of a binary alloy may be more difficult than on the metals since oxides containing both metals as well as those of each metal separately may form. Furthermore, it is possible that solid solutions of the various oxides may occur. In these cases the electron diffraction method may not be able to identify the oxidation products unequivocally, Examples of solid solutions which may present difficulties are MoO2 and W02, Fe3O4 and FeO-Cr2O3 since the diffraction patterns are so similar. Since electron diffraction can determine only the structure of the oxide, the chemical composition must be inferred from the diffraction data based upon X ray diffraction investigations of specimens of known composition. It is possible in some cases to decide whether a given solid phase reaction can occur on the surface of an alloy by a study of available thermodynamic data. Table I lists the equations for the formation of most of the oxides from the elements together with values of log10 KR for the several temperatures. [OF°R = -RT In KR 0 and-~75T = logi°KR] [?F°R] and KR are the free energy and equilibrium constant of the reaction. Calculations may be made using the values given in Table I to determine whether a given solid phase reaction is possible thermodynamically. For example, a solid phase reaction should occur between aluminum and chromium' oxide to form

Jan 1, 1948