@PhDThesis{Assis:2014:EsEsFa,
author = "Assis, Jo{\~a}o Marcos Kruszynski de",
title = "Estudo da estabiliza{\c{c}}{\~a}o de fases cristalinas de
cer{\^a}micas do sistema ni{\'o}bia – {\'{\i}}tria –
zirc{\^o}nia",
school = "Instituto Nacional de Pesquisas Espaciais (INPE)",
year = "2014",
address = "S{\~a}o Jos{\'e} dos Campos",
month = "2014-02-25",
keywords = "zirc{\^o}nia, {\'{\i}}tria, ni{\'o}bia, thermal barrier
coating (TBC), analise de fases, zirconia, yttria, niobia,
mechanical properties, thermal barrier coating.",
abstract = "Atualmente v{\'a}rios dopantes est{\~a}o sendo pesquisados para
utiliza{\c{c}}{\~a}o com TBC, como alternativa a
composi{\c{c}}{\~a}o utilizada comercialmente, a 7 YSZ, que
possui limita{\c{c}}{\~o}es como a temperatura de trabalho, em
aproximadamente \$1250^{o}\$C. Entre estes dopantes estudados
atualmente podemos citar a it{\'e}rbia, a tit{\^a}nia, a
gadol{\'{\i}}nea, a esc{\^a}ndia e o tantalato de
{\'{\i}}trio (adi{\c{c}}{\~a}o equimolar de {\'{\i}}tria e
t{\^a}ntala). Este {\'u}ltimo obteve resultados promissores,
como tenacidade a fratura no mesmo n{\'{\i}}vel da 7 YSZ e
aumento da temperatura de trabalho para \$1500^ {o}\$C. Este
trabalho visa estudar a estabiliza{\c{c}}{\~a}o de fases de
zirc{\^o}nia pela adi{\c{c}}{\~a}o de {\'{\i}}tria e
ni{\'o}bia, uma vez que a ni{\'o}bia possui propriedades
semelhantes as propriedades da t{\^a}ntala, al{\'e}m de serem
obtidas do mesmo mineral. Foram escolhidas tr{\^e}s
composi{\c{c}}{\~o}es de zirc{\^o}nia com adi{\c{c}}{\~a}o
equimolar de {\'{\i}}tria e ni{\'o}bia, 14,5\% mol, 16\% mol
e 17,5\% mol, de forma comparativa ao sistema zirc{\^o}nia -
{\'{\i}}tria - t{\^a}ntala, onde estas composi{\c{c}}{\~o}es
est{\~a}o dentro de um campo tetragonal n{\~a}o
transform{\'a}vel. Foram realizados estudos de
prepara{\c{c}}{\~a}o dos p{\'o}s iniciais atrav{\'e}s de
tr{\^e}s tipos de moagem, em moinhos de alta energia,
planet{\'a}rio e a ar Jet Mill, onde os p{\'o}s obtidos foram
caracterizados por distribui{\c{c}}{\~a}o de tamanhos de
part{\'{\i}}culas, {\'a}rea superficial e massa
espec{\'{\i}}fica. As cer{\^a}micas obtidas por
sinteriza{\c{c}}{\~a}o ao ar e a v{\'a}cuo, em quatro
temperaturas, foram caracterizadas por massa espec{\'{\i}}fica
aparente, microdureza Vickers e difra{\c{c}}{\~a}o de raios X. A
moagem por moinho planet{\'a}rio foi identificada como o melhor
meio de moagem, e as cer{\^a}micas obtidas neste processo e
sinterizadas em \$1550 ^{o}\$C ao ar e \$1650 ^{o}\$C {\'a}
v{\'a}cuo foram escolhidas para maior investiga{\c{c}}{\~a}o.
As cer{\^a}micas escolhidas para caracteriza{\c{c}}{\~a}o foram
analisadas por DRX utilizando o M{\'e}todo de Rietveld, MEV e
EDS, distribui{\c{c}}{\~a}o de {\'a}rea superficial, tamanhos
de gr{\~a}os e raz{\~a}o de aspecto, tenacidade {\`a} fratura
por penetra{\c{c}}{\~a}o e por entalhe, an{\'a}lise de
tens{\~a}o de ruptura na temperatura ambiente e em \$1250
^{o}\$C. A composi{\c{c}}{\~a}o 14,5\% mol foi escolhida para
deposi{\c{c}}{\~a}o por EB-PVD em substrato de a{\c{c}}o
inoxid{\'a}vel com camada intermedi{\'a}ria e analisada por MEV,
EDS e difra{\c{c}}{\~a}o de raios X de alta
resolu{\c{c}}{\~a}o em {\^a}ngulo rasante. Al{\'e}m destas
an{\'a}lises foram realizados estudos de fases obtidas
atrav{\'e}s de composi{\c{c}}{\~o}es equimolares (0 a 20\%
mol) e em composi{\c{c}}{\~o}es n{\~a}o equimolares, al{\'e}m
de difra{\c{c}}{\~a}o de raios X de alta temperatura em algumas
composi{\c{c}}{\~o}es, obtidas por moagem de alta energia. Os
resultados obtidos para as cer{\^a}micas indicam a
forma{\c{c}}{\~a}o de fase tetragonal como fase principal na
sinteriza{\c{c}}{\~a}o ao ar e forma{\c{c}}{\~a}o de fase
tetragonal e c{\'u}bica como fases principais na
sinteriza{\c{c}}{\~a}o a v{\'a}cuo. Por{\'e}m {\'e}
necess{\'a}rio estudos de tempos de sinteriza{\c{c}}{\~a}o para
obten{\c{c}}{\~a}o de maior porcentagem de fase tetragonal e
redu{\c{c}}{\~a}o da forma{\c{c}}{\~a}o de outras fases e
consequente redu{\c{c}}{\~a}o no tamanho de gr{\~a}o,
principalmente para aumento dos valores de propriedades
mec{\^a}nicas, assim como influenciaram na forma{\c{c}}{\~a}o
de camadas com diferentes composi{\c{c}}{\~o}es na
deposi{\c{c}}{\~a}o por EB-PVD. S{\~a}o descritos as
diferen{\c{c}}as e as semelhan{\c{c}}as entre os diagramas de
fases dos sistemas \$ZrO_{2}\$ - \$YO_{1,5}\$ -
\$TaO_{2,5}\$ em \$1500 ^{o}\$C e \$ZrO_{2}\$ -
\$YO_{1,5}\$ - \$NbO_{2,5}\$ em \$1550 ^{o}\$C. As
composi{\c{c}}{\~o}es com adi{\c{c}}{\~a}o at{\'e} 10\% mol
apresentaram, ap{\'o}s resfriamento, fase tetragonal e
monocl{\'{\i}}nica na difra{\c{c}}{\~a}o de raios X em alta
temperatura. Em adi{\c{c}}{\~o}es acima de 10\% mol, a
obten{\c{c}}{\~a}o de fase tetragonal e niobato de
{\'{\i}}trio est{\~a}o em concord{\^a}ncia com o sistema
dopado com {\'{\i}}tria e t{\^a}ntala com excess{\~a}o da fase
c{\'u}bica e do niobato ortorr{\^o}mbico. As
composi{\c{c}}{\~o}es com excesso de ni{\'o}bia apresentaram
fases n{\~a}o observadas no sistema comparativo e as
composi{\c{c}}{\~o}es com excesso de {\'{\i}}tria apresentaram
alta similaridade. ABSTRACT: Some dopants oxides like
\$Yb_{2}\$\$O_{3}\$, \$Sc_{2}\$\$O_{3}\$,
\$Gd_{2}\$\$O_{3}\$, \$TiO_{2}\$ and \$YTaO_{4}\$ that
stabilize the tetragonal structure of zirconia are studied to
substitute the 7 YSZ (the commercial ceramic utilized by TBC)
because of its limitation, as the work temperature at \$1250
^{o}\$C. The ceramics stabilized by \$YTaO_{4}\$ showed the
same level of fracture toughness that 7 YSZ and enhanced in work
temperature to \$1500 ^{o}\$C. The aim of this work is the
stabilization of zirconia phases by addition of \$YO_{1.5}\$ and
\$NbO_{2.5}\$ because of the similarity with the tantala. Three
compositions were chosen, 14.5 mol \%, 16 mol \% and 17.5 mol
\%, compositions that prepared with yttria and tantala are
located in the tetragonal non-transformable field in the ternary
phase diagram of \$ZrO_{2}\$ - \$YO_{1.5}\$ -\$TaO_{2.5}\$
system. Three milling methods were used, high energy ball mill,
planetary ball mill and jet mill were chosen and the powders were
analyzed by particle size distribution, superficial area and
specific mass. The ceramics obtained by air and vacuum sintering
in four temperatures, were analyzed by specific mass, Vickers
hardness and XRD. The best processing method studied was the
milling by planetary ball mill and the samples prepared by this
method and sintered in air at \$1550 ^{o}\$C and at vacuum at
\$1650 ^{o}\$C were chosen to further characterizations. The
ceramics were analyzed by XRD using Rietveld Method to phase
analysis and structures, superficial area distribution, grain size
distribution and aspect ratio distribution, fracture toughness by
identation and by SEVNB, modulus of rupture at room temperature
and at \$1250 ^{o}\$C. The composition 14.5 mol \% was chosen
to EB-PVD deposition in stainless steel substrate with an
intermediate layer and analyzed by SEM/EDS and high resolution XRD
at low angle. Other phases studies were realized, like 0 - 20 mol
\% equimolar addition and non-equimolar additions, and in some
compositions, analysis by high temperature XRD obtained by high
energy ball mill. The results showed that at air sintering,
tetragonal phase was the main phase and at vacuum sintering,
tetragonal and cubic phases were the main phases. However,
sintering times studies is required to obtain an increase of
tetragonal phase quantities with consequent decrease in grain size
to result an increase in mechanical properties and to obtain rich
\$ZrO_{2}\$ layers in EB-PVD deposition. The phase studies
showed similarities and differences between the ternary diagram
with tantala at \$1500 ^{o}\$C and the ternary diagram with
niobia at \$1550 ^{o}\$C. The compositions until 10 mol \%
addition showed, after cooling, tetragonal and monoclinic phases
in high temperature XRD. Above this tetragonal phase of zirconia
and monoclinic yttrium niobate phase are in agreement with yttria
and tantala doped system except with cubic zirconia and
ortorr{\^o}mbic niobate phases. The compositions with excess of
niobia showed not observed phases in the comparative system and
the compositions with excess of yttria showed high similarity.",
committee = "Piorino Neto, Francisco (presidente/orientador) and Nono, Maria do
Carmo de Andrade (orientador) and Melo, Francisco
Crist{\'o}v{\~a}o Louren{\c{c}}o de (orientador) and Mineiro,
S{\'e}rgio Luis and Oliveira, Rodrigo de Matos and Campos, Elson
de and Reis, Danieli Aparecida Pereira",
englishtitle = "Crystalline phases stabilization study of ceramics of the niobia -
yttria - zirconia system",
language = "pt",
pages = "251",
ibi = "8JMKD3MGP5W34M/3FPHPU5",
url = "http://urlib.net/ibi/8JMKD3MGP5W34M/3FPHPU5",
targetfile = "publicacao.pdf",
urlaccessdate = "27 abr. 2024"
}