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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
241

An investigation of the concentration dependence of the interdiffusion coefficient in the binary liquid aluminum-copper system

Porth, Christopher 03 January 2017 (has links)
Challenges continue to exist in developing a comprehensive theory of diffusion in liquid metals, despite the advancement of several semi-empirical and theoretical models. One major difficulty in developing a theory is that experimental data are not available for many pure metals and binary metal systems, and when they do exist, data are often inaccurate. In addition to challenges with data quality, where deemed reliable, existing data are typically reported over limited temperature and concentration intervals. In this thesis research, interdiffusion data was obtained for the binary Al-Cu system using the solid wire long capillary technique (SWLC), and molecular dynamics (MD) simulation with a concentration-dependent embedded atom method (CD-EAM) interatomic potential. In the SWLC experiments the interdiffusion coefficient was determined at temperatures of 993 K, 1023 K, 1073 K, 1123 K, and 1193 K, over an Al-rich concentration range limited by the liquidus of the binary phase diagram at the given temperature. For liquid Al~100Cu~0 (tracer), Al80Cu20, and Al60Cu40, the interdiffusion coefficient is well described by the Arrhenius relationship D_AlCu=D_0*exp(-Q_0/RT) over the temperature range, with best fit parameter values of Q_0 = 20.85 ± 4.49 kJ/mol, D_0 = 8.21 (+5.4, -3.26) x 10^-8 m^2/s, Q_0 = 34.41 ± 3.71 kJ/mol, D_0 = 2.84 (+1.47, -0.97) x 10^-7 m^2/s, Q_0 = 38.74 ± 8.01 kJ/mol, D_0 = 4.03 (+5.89, -2.39) x 10^-7 m^2/s, respectively. For the MD simulations, a new Al-Cu CD-EAM interatomic potential was developed that is suitable for the study of diffusion phenomena in the liquid state. Self- and interdiffusion coefficients were determined over a temperature interval of 993-1493 K. Simulations are performed for liquid Al99.999Cu0.001 (tracer), Al80Cu20, and Al60Cu40, and interdiffusion is described by Q_0 = 22.81 ± 0.27 kJ/mol, D_0 = 1.04 (+0.03, -0.03) x 10^-7 m^2/s Q_0 = 30.15 ± 0.49 kJ/mol, D_0 = 1.78 (+0.08, -0.08) x 10^-7 m^2/s, Q_0 = 37.01 ± 1.48 kJ/mol, D_0 = 3.29 (+0.52, -0.45) x 10^-7 m^2/s, respectively. The calculated values of the interdiffusion coefficients from the MD simulation are in good agreement with those obtained using the SWLC technique, supporting the accuracy of these new experimental findings. / February 2017
242

Dual-emitting Cu-doped ZnSe/CdSe nanocrystals

Sutton, Rebecca Suzanne January 1900 (has links)
Master of Science / Department of Chemistry / Emily McLaurin / Cu-doped ZnSe/CdSe core/shell nanocrystals were synthesized using the growth doping method. Upon shell growth, the nanocrystals exhibit dual emission. The green luminescence peak is assigned as band edge emission and the broad, lower energy red peak is due to Cu dopant. Although, the oxidation state of Cu in the nanocrystals is debated, the emission is explained as recombination of a hole related to Cu²⁺ with an electron from the conduction band. The emission changed in the presence of dodecanethiol. Generally, the band edge emission intensity decreases and the Cu emission intensity increases. One explanation is the thiol acts as a hole trap, preventing hole transfer to the conduction band. Samples were obtained with varying amounts of Cd²⁺. In the presence of larger amounts of Cd²⁺, the nanocrystals had “thicker shells”, and both the band edge and Cu emission were less sensitive to thiol. The sensitivity likely decreased because the shelled, larger nanocrystals have fewer surface defects resulting in more available electrons.
243

Zeolite encapsulated metal complexes as heterogeneous catalysts for oxidation reactions

Willingh, Gavin Von January 2012 (has links)
>Magister Scientiae - MSc / This study describes the synthesis and characterisation of Cu(II) and V(IV) complexes of tri- and quadridentate ligands L1 and L2 formed by condensation of ethylenediamine with acetylacetonate in 1:1 and 1:2 molar ratio, respectively. Encapsulation of these metal complexes in the nanocage of zoilite-Y generates new heterogeneous catalysts. These catalysts were synthesized employing the flexible ligand method encapsulation technique.The structures of these encapsulated complexes were established on the basis of various physico-chemical and spectroscopic studies. The results indicated that the complexes did not hinder or modify the framework or structure of the zeolite, confirming successful immobilization of Schiff-bases through the voids of zeolite Y.These encapsulated complexes were screened as heterogeneous catalysts for various oxidation reactions such as such as phenol, benzene, styrene and cyclohexene using a green oxidant (H2O2).For comparison, the corresponding neat complexes were screened as potential homogeneous catalysts for these oxidation reactions. The results proved that the corresponding homogeneous systems described here represent an efficient and inexpensive method for oxidation of phenol, benzene, styrene and cyclohexene, having advantages over heterogeneous catalysis are its high activity and selectivity and short reaction times. Its major problem is its industrial application regarding principally the separation of the catalyst from the products.The size of the substrate has a significant effect on the conversion by encapsulated complexes such as in styrene oxidation. Therefore, it was established that steric effects of the substrates play a critical role in the poor reactive nature of the encapsulated complexes.In general, the percentage conversion decreased upon encapsulation of complexes in zeolite Y. All catalysts studied proved to be potential catalysts for the various oxidation reactions.It has been shown in this study that encapsulation can effectively improve product selectivity but requires a longer reaction time in most cases for maximum activity.Furthermore,oxovanadium complexes were more reactive than copper-based catalysts in all oxidation reactions tested in this study.A reaction mechanism study revealed that the activity of the encapsulated and neat complexes occurs through either formation of peroxovanadium (V) or hydroperoxidecopper(II) intermediate species.The studies in this thesis, therefore, conclude that the Cu(II) and V(IV) complexes encapsulated in Y-zeolite are active heterogeneous catalysts for the selective oxidation of various substrates. Encapsulation of the metal complexes in the super cages (-cages) of the zeolite matrix has the advantages of solid heterogeneous catalysts of easy separation and handling, ruggedness, thermostability, reusability (regeneration of the deactivated catalysts) as well as share many advantageous features of homogeneous catalysts.
244

Efficient and Selective Synthesis of Multifunctional Organoboron Compounds Promoted by Cu-Based N-Heterocyclic Carbene Complexes

Jang, Hwanjong January 2016 (has links)
Thesis advisor: Amir H. Hoveyda / Chapter 1. We have developed a single-vessel catalytic protocol for double protoboryl additions to terminal alkynes with B2(pin)2 promoted by Cu complex derived from chiral N-heterocyclic carbene (NHC), to achieve enantiomerically enriched versatile vicinal diborons. Since an alkenyl(pinacolato)boron, which was in situ generated by the first protoboration of a terminal alkyne, can serve as an effective substrate for the second protoboration (alkenylboron can allow delocalization of π electrons of olefin to a partially vacant p orbital on boron), single-vessel catalytic process with 2 equiv. of B2(pin)2 in the presence of sulfonate-bearing chiral NHC–Cu complex, affords enantiomerically enriched 1,2-diborons in up to 93% yield and 97.5:2.5 enantiomeric ratio (e.r.). Site-selective Pd-catalyzed cross-coupling with alkenyl bromide shows the versatility of the resulting diboron compounds, which delivers the coupling product efficiently. Interestingly, only the less hindered, primary C–B bond on vicinal diboron compound participates in the cross coupling. Chapter 2. Cu-catalyzed protocol for selective formation of α-alkenylborons has been demonstrated. With achiral NHC–Cu complex, readily prepared from commercially available imidazolinium salt, various terminal alkynes are converted to internal alkenylborons in up to 93% yield with high to exclusive α selectivity. Propargyl ethers, amides and aryl alkynes are proved to be suitable substrates. Utility of α-alkenylborons is demonstrated by conversion to methyl ketone and synthesis of cyclic alkenylboron compound. In addition, when Cu complex bearing a stronger electron-donating NHC is used, the site selectivity of protoboration reaction becomes reversed, which delivers the alternative isomer, β-alkenylboron efficiently. By altering the steric and electronic nature of NHC, site selectivity is dramatically changed. Mechanistic basis for site selectivity is presented. Chapter 3. Efficient and selective protocol for synthesis of enantiomerically enriched silylborons is described. In the presence of achiral NHC–Cu complex, site- and stereoselective protosilyl additions to terminal alkynes afford a wide range of alkyl- and aryl-substituted (E)-β-alkenylsilanes. Chiral monodentate NHC−Cu complex promotes enantioselective protoboration of alkyl- or alkenyl-bearing alkenylsilanes, delivering vicinal borosilanes with up to 96.5:3.5 e.r. When an alkene bearing both silyl and aryl groups is utilized, on the other hand, geminal silylboron is obtained with high enantio- (93:7–98.5:1.5 e.r.) and site selectivity (up to >98% geminal). In this case, we have reasoned that the electronic attribute of aryl unit is more dominant than the silyl group to control site selectivity. To demonstrate the utility of the Cu-catalyzed transformation, we have illustrated the formal synthesis of bruguierol A, natural product active against Gram-positive and also Gram-negative bacteria. The key intermediate geminal borosilane is provided by sequential NHC–Cu-catalyzed protosilylation and protoboration of terminal alkyne in 77% overall yield with 97.5:2.5 e.r. and 97% site selectivity. Additionally, stereochemical models to account for levels and trends in site- and enantioselectivity are proposed. Chapter 4. New methods for enantioselective protonation of 2-B(pin)-bearing allylcopper, which is in situ generated by site-selective Cu–B addition to 1,1-disubstituted allene, are presented. Transformations are promoted by a chiral NHC–Cu complex, affording an alkenylboron containing α-carbon stereogenic center. Enantiomerically enriched aryl-, heteroaryl- and silyl-bearing alkenylborons are generated in high yield (up to 98%) and selectivities (up to >98% site selectivity and 96.5:3.5 e.r.). To explore the utility of enantiomerically enriched alkenylborons, we have developed Cu-catalyzed enantioselective allylic alkenyl addition to allylic phosphate. A chiral NHC–Cu complex promotes the allylic substitution of enantiomerically enriched alkenylboronic acid with ally phosphate to deliver 1,4-diene in 62% yield with 96:4 d.r. (>98% stereoselectivity). Chapter 5. We have developed a single-vessel, multicomponent process to synthesize N-bearing quaternary carbon stereogenic centers with exceptional diastereo- (>98:2 d.r. for all cases) and high enantioselectivity (88:12 to >99:1 e.r. except one case). Especially, protecting group-free ketoimine (“N–H” ketoimine), which can be prepared by alkylation of a readily available nitrile, has been utilized for the study. The transformation of “N–H” ketoimine is very useful because the obtained amine has no protecting group, which allows us to avoid the deprotection step as well as to be able to choose appropriate protecting group for subsequent chemical reactions. By oxidation of α-tertiary carbamine with NaBO3, β-amino ketones (Mannich reaction product) are obtained in up to 83% yield. A stereochemical model to account for the level of diastereo- and enantioselectivity are presented using DFT calculations. To show the utility of the present method, we have synthesized a medicinally active compound, which was studied for Alzheimer’s disease. The Cu-catalyzed protocol delivers the core structure of the target molecule with exclusive diastereo- and enantioselectivity (>98:2 d.r. and 99.5:0.5 e.r.). / Thesis (PhD) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.
245

"Estudos do desenvolvimento e caracterização das ligas Cu-Ni-Pt e Cu-Ni-Sn para fins eletro-eletrônicos" / STUDIES OF THE DEVELOPMENT AND CHARACTERIZATION OF THE Cu-Ni-Pt AND Cu-Ni-Sn ALLOYS FOR ELETRO-ELECTRONIC USES

Silva, Luis Carlos Elias da 04 October 2006 (has links)
O Cu e suas ligas têm diferentes aplicações na sociedade moderna devido as excelentes propriedades elétricas, condutividade térmica, resistência à corrosão dentre outras propriedades. Estas aplicações podem ser em válvulas, tubulações, panelas para absorção de energia solar, radiadores para automóveis, condutores de corrente e eletrônico, elementos de termostatos e partes estruturais de reatores nucleares, como, por exemplo, bobinas para campo toroidal para um reator de fusão nuclear. Dentre as ligas utilizadas em reatores nucleares, podemos destacar Cu-Be, Cu-Sn e Cu-Pt. O Ni e o Co, freqüentemente são adicionados às ligas de Cu para que a solubilidade seja deslocada para temperaturas mais elevadas com relação aos sistemas binários de Cu-Sn e Cu-Pt. A adição de Ni-Pt ou Ni-Sn ao Cu em porcentagens iguais ou inferiores a 1,5 % aliado a tratamentos termos-mecânico alteram as propriedades do Cu. Estudamos neste trabalho sete diferentes ligas: três ligas de Cu-Ni-Pt 1 (97,99 % Cu - 1,55 % Ni - 0,46 % Pt), 2 (99,33 % Cu - 0,23 % Ni -0,43 % Pt) 3 (98,01 % Cu - 0,48 % Ni - 1,51 % Pt); três ligas de Cu-Ni-Sn 4 (98,31% Cu - 1,12 % Ni - 0,58 % Sn), 5 (98,79 % Cu – 0,57 % Ni - 0,65 % Sn), 6 (98,39% Cu – 0,46 % Ni – 1,16 % Sn) e Cu eletrolítico 0 (0,0058 % Pb - 0,0007 % Fe - 0,0036 % Ni - 0,0024 % Ag). As referentes ligas foram desenvolvidas a partir de um forno a arco voltaico e passaram por tratamentos termo-mecânicos pré-determinados. As microestruturas foram analisadas diretamente por microscopia óptica e microscopia eletrônica de varredura / EDS e indiretamente por medidas de dureza Vickers e condutividade elétrica. O objetivo deste trabalho, portanto, foi observar e constatar os efeitos da mudança da microestrutura em relação às propriedades dureza e condutividade elétrica. / The Cu and its alloys have different applications in the owed modern society the excellent electric properties, thermal conductivity, resistance to the corrosion and other properties. These applications can be in valves, pipes, pots for absorption of solar energy, radiators for automobiles, current driver, electronic driver, thermostats elements and structural parts of nuclear reactors, as, for example, reels for field toroidal for a reactor of nuclear coalition. The alloys used in nuclear reactors, we can highlight Cu-Be, Cu-Sn and Cu-Pt. Ni and Co frequently are added to the Cu alloys so that the solubility is moved for temperatures more elevated with relationship to the binary systems of Cu-Sn and Cu-Pt. The addition of Ni-Pt or Ni-Sn to the Cu in the same or inferior percentages to 1,5% plus thermomechanical treatments changes the properties of the copper. We studied the electric conductivity and hardness Vickers of the Cu-Ni-Pt and Cu-Ni-Sn and compared with the electrolytic Cu. In the proposed flowcharts, breaking of the obtaining of the ingot, we proceeded with thermo mechanical treatments.
246

Cu-Catalyzed Enantioselective Allylic Substitutions with Organomagnesium and Organoaluminum Reagents Promoted by N-Heterocyclic Carbenes for the Formation of Quaternary Stereogenic Centers

Mandai, Kyoko January 2010 (has links)
Thesis advisor: Amir H. Hoveyda / Chapter One: An overview of Cu-catalyzed enantioselective allylic substitutions with organometallic reagents. Chapter Two: Development of Cu-catalyzed enantioselective allylic alkylations of allylic chlorides with Grignard reagents for the formation of all-carbon quaternary stereogenic centers is disclosed. Chapter Three: Development of Cu-catalyzed enantioselective allylic substitutions of allylic phosphates with alkyl, aryl, and heterocyclic aluminum reagents for the formation of quaternary stereogenic centers is discussed. / Thesis (MS) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.
247

Site- and Enantioselective C-C and C-B Bond Forming Reactions Catalyzed by Cu-, Mg-, Zn-, or Al-based N-Heterocyclic Carbene Complexes

Lee, Yunmi January 2010 (has links)
Thesis advisor: Amir H. Hoveyda / Chapter 1. In this chapter, the ability of chiral bidentate N-heterocyclic carbenes (NHCs) to activate alkylmetal reagents directly in order to promote C&#8210;C bond forming reactions in the absence of a Cu salt is presented. Highly regio- and enantioselective Cu-free allylic alkylation reactions of di- and trisubstituted allylic substrates with organomagnesium, organozinc, and organoaluminum reagents are demonstrated. Chiral bidentate sulfonate-bearing NHC-Zn and NHC-Al complexes are isolated and fully characterized. Based on crystal structures of these catalytic complexes, mechanistic details regarding Cu-free allylic alkylations with alkylmetal reagents are proposed. Chapter 2. New methods for efficient and highly enantioselective Cu-catalyzed allylic alkylation reactions of a variety of trisubstituted allylic substrates with alkylmagnesium and alkyl-, aryl-, 2-furyl-, and 2-thiophenylaluminum reagents are presented. Transformations are promoted by a chiral NHC complex in the presence of commercially available, inexpensive and air stable CuCl2*H2O. Enantiomerically enriched compounds containing difficult-to-access all-carbon quaternary stereogenic centers are obtained. Chapter 3. New methods for highly site- and enantioselective Cu-catalyzed allylic alkylation reactions of allylic phosphates with vinylaluminum reagents are presented. The requisite vinylaluminums are prepared by reaction of readily accessible terminal alkynes with DIBAL-H and used directly without further purification. Vinyl additions are promoted in the presence of a chiral bidentate sulfonate-based NHC complex and a Cu salt. The desired SN2' products are obtained in >98% E selectivities, >98% SN2' selectivities, >98% group selectivities (<2% i-Bu addition) and high enantioselectivities. The enantioselective total synthesis of the natural product bakuchiol highlights the versatility of the one-pot hydroalumination/Cu-catalyzed enantioselective allylic vinylation process. Chapter 4. Efficient and highly site-selective Cu-catalyzed hydroboration reactions of 1,2-disubstituted aryl olefins with bis(pinacolato)diboron (B2(pin)2) are presented. Transformations are promoted by an NHC-Cu complex in the presence of MeOH, affording only secondary &#946;-boronate isomers. A Cu-catalyzed method for the synthesis of enantiomerically enriched secondary alkylboronates promoted by chiral NHC complexes is disclosed. Chapter 5. A new method for efficient and site-selective tandem Cu-catalyzed copper-boron additions to terminal alkynes with B2(pin)2 in the presence of an NHC-Cu complex is demonstrated. In a one-pot process, Cu-catalyzed hydroboration of alkynes provides vinylboronates in situ, which undergo a second site-selective hydroboration to afford vicinal diboronates. Highly Enantiomerically enriched diboronates obtained through Cu-catalyzed enantioselective dihydroboration in the presence of chiral bidentate sulfonate-based NHC-Cu complex are obtained. The control of site selectivity in the first-stage hydroboration of alkynes is critical for efficient and highly enantioselective reactions in the tandem dihydroboration. Functionalizations of the vicinal diboronates described herein underline the significance of the current method. / Thesis (PhD) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.
248

Determinação da estrutura de uma série de tri(hidroximetil) amino metano complexados com íons metálicos (Cu, Ag, Ni, Zn) / X-ray crystal structures of Cu, Ag, Ni and Zn íons with tri(hidroximetil) amino methane

Silva, Lenilda Austrilino 05 December 1986 (has links)
As estruturas do tri(hidroximetil) amino metano complexado com cobre Cu(II), Cu[NH2C(COH3)3]2+H2O e do tri(hidroximetil)amino metano dopado com prata Ag(I), Ag[NH2C(COH3)3] foram determinados por difração de raios-x. O complexo contendo íons de cobre refinou até um R de 0.034 e foram encontradas as seguintes características principais: sistema cristalino monoclínico; grupo espacial C2/c, a=12.955(2)&#197; b=10.793(1)&#197; c=10.091(2)&#197; &#946=116.62&#176; V=1261.3(6)&#1973; Z=4; xDc=1.694(2)g/cm-3; &#955(K&#945Mo)=0.71073&#197; das reflexões medidas 1441 tinham I&#62 3&#948 (I). O íon de cobre está coordenado por pares de átomos de oxigênio e nitrogênio os quais formam uma pirâmide de base quadrada, o oxigênio da molécula de água ocupa o outro vértice da pirâmide. A determinação dessa estrutura é utilizada na interpretação da formação de complexos de cobre com tri(hidroximetil) amino metano em função do pH. A estrutura do tri(hidroximetil) amino metano dopado com prata apresentou as seguintes características: sistema cristalino ortorrômbico; grupo espacial Pna21; a=7.800(2)&#197; b=8.810(3)&#197; c=8.850(2)&#197; V=608.85(4)&#1973; Dc=1.329g/cm-3; Dm=1.337g/cm-3; 435 reflexões com I&#62 3&#948 (I); R=0.13; o carbono central é coordenado tetraedricamente por três átomos de carbono do tri(hidroximetil) e um nitrogênio do grupo amino. As estruturas do tris dopado com níquel, e do tris dopado com zinco apresentam-se isomorfa com a estrutura do tris dopado com prata. / The crystal structures of the tri(hydroxymethyl) amine methane complexed with cooper Cu[NH2C(COH3)3]2+H2O and the silver Ag[NH2C(COH3)3] doped into the tri(hydroxymethyl) amine methane have been determined by x-ray diffraction. The complex involving Cu++ refined to final R-factor of 0.034, and the following main features were found: the crystal system is monoclinic and its space group is C2/c, a=12.955(2)&#197; b=10.793(1)&#197; c=10.091(2)&#197; &#946=116.62&#176; V=1261.3(6)&#1973; Z=4; Dc=1.694(2)g/cm-3; &#955(K&#945Mo)=0.71073&#197; from measures done, 1441 had I&#62 3&#948 (I). The Cu++ is coordinated by couples of atoms of oxygen and nytrogen, which form a base of a quadrangular pyramid, the pyramid vertex is formed by the oxygen of the water molecule. The determination of this structure is used to interpret the rise of tri(hydroxymethyl) amine methane and complexed with Cooper varying the pH. The silver doped into the structures of tris(hydroxymethyl) amine methane presented the following features: crystal system is orthorrombic; space group is Pna21; a=7.800(2)&#197; b=8.810(3)&#197; c=8.850(2)&#197; V=608.85(4)&#1973; Dc=1.329 g/cm-3; Dm=1.337 g/cm-3; R=0.13; 435 reflections with I&#62 3&#948 (I) the central carbon is coordinated tetrahedrally by three atoms of carbon from tri(hydroxymethyl) and a nitrogen from the amine group.
249

Engineering of Substrate Surface for the synthesis of Ultra-Thin Composite Pd and Pd-Cu Membranes for H2 Separation

Guazzone, Federico 10 January 2006 (has links)
This work describes a novel technique to prepare ultra-thin composite Pd-porous metal membranes for H2 separation. This novel technique consists of the gradual smoothing of the Porous Metal (PM) support's surface with several layers of pre-activated alumina particles of different sizes. The deposition of coarse, fine and ultra-fine alumina particles resulted in the narrowing of the PM' surface pore size distribution. The excellent surface smoothness achieved after the grading of the PM 's surface support allowed for the preparation of gas tight Pd layers as thin as 5.6?m. The Pd layers were extremely uniform due to the presence of the grade layer and strongly attached to the support. Composite Pd membranes prepared on graded supports showed H2 permeance as high as 50 m3/(m2 h bar0.5) at 500ºC and ideal selectivities (H2/He) as high as 27000. Moreover, the H2 permeance and ideal selectivity were stable over 1100 hours at 500ºC in H2 atmosphere. Composite Pd-Cu membranes showed H2 permeance as high as 30 m3/(m2 h bar0.5) at 450ºC and ideal selectivities (H2/He) as high as 900. The H2 permeance and ideal selectivity of Pd-Cu membranes were stable over 500 hours at 450ºC in H2 atmosphere. The outstanding long-term H2 permeance and ideal selectivity stability of all composite Pd and Pd-Cu membranes represented a breakthrough in composite Pd membrane synthesis. The thermal stresses arising from the mismatch in the coefficient of thermal expansion between the Pd film and the support were determined by means of x-ray diffraction. The results indicated that the release of stresses began to occur at temperatures close to 400ºC. Also, the release of stresses took place with a visible sintering of Pd clusters within the thin Pd film. The stresses due to the absorption of H2 were also studied and modeled. It was estimated that the maximum compressive stress under which these composite Pd membranes were characterized was equal to 260 MPa.
250

Efeito de adições de Ni e Mg sobre o comportamento térmico, mecânico e elétrico de ligas Al-Cu-Fe solidificadas unidirecionalmente

SOUZA, Pedro Henrique Lamarão January 2013 (has links)
Submitted by Cleide Dantas (cleidedantas@ufpa.br) on 2014-04-08T17:15:22Z No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_EfeitoAdicoesNi.pdf: 5757867 bytes, checksum: 8a77abd3b782bdae2352df421372bf23 (MD5) / Approved for entry into archive by Ana Rosa Silva (arosa@ufpa.br) on 2014-09-01T15:39:57Z (GMT) No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_EfeitoAdicoesNi.pdf: 5757867 bytes, checksum: 8a77abd3b782bdae2352df421372bf23 (MD5) / Made available in DSpace on 2014-09-01T15:39:57Z (GMT). No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_EfeitoAdicoesNi.pdf: 5757867 bytes, checksum: 8a77abd3b782bdae2352df421372bf23 (MD5) Previous issue date: 2013 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho estudou a influência dos teores dos solutos Mg e Ni na modificação das propriedades térmicas, elétricas e mecânicas de uma liga Al-Cu-Fe para aplicação como condutor de energia elétrica. Para a realização do presente estudo, as ligas foram obtidas por fundição unidirecional horizontal, a partir da base do alumínio de pureza comercial com adição dos teores 0,05%p Cu e [0,24 a 0,28]%p Fe. Tal base foi modificada em uma primeira etapa com teores de 0,45, 0,60 e 0,80%p Mg. As ligas obtidas com estes teores tiveram suas propriedades estudadas para que se selecionasse um teor de Mg para posterior adição de Ni à liga. O estudo destas propriedades na primeira etapa passou pela análise das propriedades térmicas: velocidade de solidificação (VL) e taxa de resfriamento (Ṫ). A caracterização elétrica estudou a propriedade condutividade elétrica (φ) e o levantamento das propriedades mecânicas: limite de resistência à tração (σ) e microdureza Vickers (HV). A liga com adição de Ni passou por tratamentos térmicos de envelhecimento, por 1, 4 e 8h. Estas amostras foram analisadas em um microscópio eletrônico de varredura - MEV pelos sinais de elétrons retroespalhados – ERE e espectroscopia de energia dispersiva – EDS. Como resultados do estudo, encontrou-se que adições de Mg influenciaram significativamente a viscosidade das ligas, elevando as velocidades de solidificação nos instantes finais. Os ensaios de microdureza das amostras envelhecidas mostraram que houve um acréscimo significativo de dureza na quarta hora de envelhecimento, da mesma forma que as análises de EDS mostraram que a concentração de Ni também elevou-se nesta condição de tratamento. / This work studied the influence of Mg and Ni solute content on the modification of the thermal, electrical and mechanical properties of an Al-Cu-Fe alloy for application as an electrical conductor. To realize the present study, the alloys were obtained by unidirectional horizontal casting, starting from the commercial pure aluminum with the addition of 0.05wt% Cu and [0.24 to 0.28]wt% Fe content. This basis was modified on a first stage with 0.45, 0.60 and 0.80wt% of Mg content. The alloys obtained with these contents had its properties studied for the selection of a Mg content for further Ni addition at the alloy. The study of these properties on the first stage passed through the analysis of the thermal properties: growth rate (VL) and cooling rate (Ṫ). The electrical characterization studied the electrical conductivity property (φ) and the following mechanical properties were determined: ultimate tensile strength (σ) and Vickers microhardness (HV). The alloy which has Ni additions passed through ageing heat treatments of 1, 4 and 8 hours. These samples were analyzed in a scanning electron microscope – SEM by the electrons backscattered – EBS and energy dispersive spectroscopy – EDS signals. As a result of the research, it was found that Mg additions had significantly influenced the alloys viscosity, increasing its growth rates at the final moments of the solidification. The microhardness tests for the aged samples showed that they suffered a significant gain of hardness at the fourth hour of ageing, also, the EDS analysis showed that Ni content increased at the same treating conditions.

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