20 research outputs found
Mechanisms and Materials for NTE
Negative thermal expansion (NTE) upon heating is an unusual property but is observed in many materials over varying ranges of temperature. A brief review of mechanisms for NTE and prominent materials will be presented here. Broadly there are two basic mechanisms for intrinsic NTE within a homogenous solid; structural and electronic. Structural NTE is driven by transverse vibrational motion in insulating frameworkâtype materials e.g., ZrW2O8 and ScF3. Electronic NTE results from thermal changes in electronic structure or magnetism and is often associated with phase transitions. A classic example is the Invar alloy, Fe0.64Ni0.36, but many exotic mechanisms have been discovered more recently such as colossal NTE driven by BiâNi charge transfer in the perovskite BiNiO3. In addition there are several types of NTE that result from specific sample morphologies. Several simple materials, e.g., Au, CuO, are reported to show NTE as nanoparticles but not in the bulk. Microstructural enhancements of NTE can be achieved in ceramics of materials with anisotropic thermal expansion such as betaâeucryptite and Ca2RuO4, and artificial NTE metamaterials can be fabricated from engineered structures of normal (positive) thermal expansion substances
Effect of sintering technology in beta-eucryptite ceramics: Influence on fatigue life and effect of microcracks
ÎČ-eucryptite ceramics with low negative or near-zero coefficient of thermal expansion
(CTE) with excellent mechanical properties, such as Youngâs modulus 100 GPa, have
attracted attention for many important industrial applications. The extremely anisotropic
thermal expansion behaviour of this material leads to thermal residual stresses, and
causes spontaneous microcracking. These microcracks cause large negative CTE with
mechanical weaknesses. The appearance of microcracks is due to different factors. The
most important are prolonged sintering time and heating source used.
The present work shows experimentally the evolution of grain microcracks and residual
stresses of the sintered -eucryptite material going through many thermal fatigue cycles
(3600). The effect of stresses applied on ÎČ-eucryptite crystals due to the thermal
cycling could be considered for explaining the small change observed of ÎČ-eucryptite to
ÎČ-spodumene phase, which is higher in the samples obtained by microwave sintering.
Therefore, the study of residual stresses has suggested that the heating source employed,
such as conventional or microwave, has a great influence on thermal fatigue life and the
final mechanical and thermal properties. The microwave heating has a significant
impact on ÎČ-eucryptite materials lifetime.A. Borrell, acknowledges the Spanish Ministry of Science and Innovation for a Juan de la Cierva contract (JCI-2011-10498) and the Polytechnic University of Valencia (UPV) for financial support received under project SP20120677. The authors would like to thank the SCSIE team of the University of Valencia.Benavente MartĂnez, R.; Salvador Moya, MD.; MartĂnez-Amesti, A.; FernĂĄndez, A.; Borrell TomĂĄs, MA. (2016). Effect of sintering technology in beta-eucryptite ceramics: Influence on fatigue life and effect of microcracks. Materials Science and Engineering: A. 651:668-674. https://doi.org/10.1016/j.msea.2015.11.013S66867465
Fabrication of near-zero thermal expansion of fully dense beta-eucryptite ceramics by microwave sintering
Microwave heating is proposed as non-conventional technique for the sintering of optimal lithium aluminosilicate compositions of β-eucryptite system. The coefficient of thermal expansion and mechanical properties of the sintered samples has been studied
under the influence of microwave heating.
The ad hoc synthesized β-eucryptite together with the microwave sintering technique developed in this work open the opportunity to produce breakthrough materials with low or negative coefficient of thermal expansion and excellent mechanical properties, as a Young s modulus of 110 GPa. The combination of rapid heating with low energy applied by the microwave technology (eco-friendly process) and the dramatic reduction in cycle time allows densification without glass phase formation.
Results of the coefficient of thermal expansion of the β-eucryptite ceramics presented here under cryogenic conditions will be of value, for example, in the future design of new composite materials for space applicationsThe authors would like to thank Dr. Emilio Rayon for performing the nanoindentation analysis in the Materials Technology institute (ITM) of the Polytechnic University of Valencia (UPV) and your financial support received of UPV under Projects SP20120621 and SP20120677 and Spanish Government through the Project MONIDIEL (TEC2008-04109). A. Borrell, acknowledges the Spanish Ministry of Science and Innovation for a Juan de la Cierva contract (JCI-2011-10498) and SCSIE of the University of Valencia.Benavente MartĂnez, R.; Borrell TomĂĄs, MA.; Salvador Moya, MD.; Garcia-Moreno, O.; Penaranda-Foix, FL.; CatalĂĄ Civera, JM. (2014). Fabrication of near-zero thermal expansion of fully dense beta-eucryptite ceramics by microwave sintering. Ceramics International. 40(1):935-941. https://doi.org/10.1016/j.ceramint.2013.06.089S93594140
Elaboration of ceramic composites with low thermal expansion coefficient for space applications
Actuellement, la qualitĂ© de lâimagerie provenant de systĂšmes optiques spatiaux est limitĂ©e par la taille de leurs miroirs et la masse des structures supportant le miroir. Le dĂ©veloppement de systĂšmes athermiques lĂ©gers (un seul matĂ©riau) constitue le principal challenge dans lâamĂ©lioration de ces systĂšmes. De matĂ©riaux lĂ©gers, rĂ©sistants mĂ©caniquement (E/Ï3 > 10, Ïf > 100 MPa) et stables thermiquement ( 10, Ïf > 100 MPa) and thermal stability (< 2.0e-6/K) are required. Within this context, our project consists in processing new ceramic composites by combining positive thermal expansion coefficient (TEC) materials having good mechanical properties (alumina or ceria doped zirconia) and negative TEC materials (zirconium tungstate or ÎČ-eucryptite) The processing of zirconium tungstate-based materials showed several decomposition and chemical reactions with some oxide matrix leading to its giving up. In the case of ÎČ-eucryptite, vermicular phenomenon occurs during sintering leading to the formation of intragranular porosity. Sintering parameters optimization can limit this porosity. The study of the thermal behavior of pure ÎČ-eucryptite materials shows that the very negative TEC results from microcracking, generated by the TEC anisotropy of its crystal lattice. This microcracking depends on the grain size and the aggregate size in the case of powder materials. Despite the fact that the TEC of its lattice (called intrinsic TE C equals to -0.4e-6/K) is very low, its bulk (or extrinsic) TEC can reach values until -10.9e-6/K according to the processing conditions. In this work, two strategies for developing composites were studied. The first one consists in decreasing the matrix TEC using an uncracked ÎČ-eucryptite powder (-0.4e-6/K) while the second one consists in elaborating near zero TEC materials from a microcracked ÎČ-eucryptite powder (-3.0e-6/K). When ceria-doped zirconia is used, ceria content must be adjusted in order to limit zirconia phase transformation. This transformation is driven by tensile stresses induced by the ÎČ-eucryptite and modifies the composite thermal behavior linearity. In both studied cases, dense composites show a modification of the ÎČ-eucryptite intrinsic TEC from -0.4e-6/K to more than +3.2e-6/K as a consequence of compressive stresses applied by the oxide matrix. An uncompleted densification of composites is required to relax these stresses. Taking into account these observations, several very low TEC composites were elaborated. However, the uncompleted densification of composites and the ÎČ-eucryptite microcracking greatly decrease the mechanical properties of these materials
Elaboration de matériaux composites céramiques à faible coefficient de dilatation thermique pour des applications spatiales
Actuellement, la qualité de l imagerie provenant de systÚmes optiques spatiaux est limitée par la taille de leurs miroirs et la masse des structures supportant le miroir. Le développement de systÚmes athermiques légers (un seul matériau) constitue le principal challenge dans l amélioration de ces systÚmes. De matériaux légers, résistants mécaniquement (E/ 3 > 10, f > 100 MPa) et stables thermiquement ( 10, f > 100 MPa) and thermal stability (< 2.0e-6/K) are required. Within this context, our project consists in processing new ceramic composites by combining positive thermal expansion coefficient (TEC) materials having good mechanical properties (alumina or ceria doped zirconia) and negative TEC materials (zirconium tungstate or b-eucryptite) The processing of zirconium tungstate-based materials showed several decomposition and chemical reactions with some oxide matrix leading to its giving up. In the case of b-eucryptite, vermicular phenomenon occurs during sintering leading to the formation of intragranular porosity. Sintering parameters optimization can limit this porosity. The study of the thermal behavior of pure b-eucryptite materials shows that the very negative TEC results from microcracking, generated by the TEC anisotropy of its crystal lattice. This microcracking depends on the grain size and the aggregate size in the case of powder materials. Despite the fact that the TEC of its lattice (called intrinsic TE C equals to -0.4e-6/K) is very low, its bulk (or extrinsic) TEC can reach values until -10.9e-6/K according to the processing conditions. In this work, two strategies for developing composites were studied. The first one consists in decreasing the matrix TEC using an uncracked b-eucryptite powder (-0.4e-6/K) while the second one consists in elaborating near zero TEC materials from a microcracked b-eucryptite powder (-3.0e-6/K). When ceria-doped zirconia is used, ceria content must be adjusted in order to limit zirconia phase transformation. This transformation is driven by tensile stresses induced by the b-eucryptite and modifies the composite thermal behavior linearity. In both studied cases, dense composites show a modification of the b-eucryptite intrinsic TEC from -0.4e-6/K to more than +3.2e-6/K as a consequence of compressive stresses applied by the oxide matrix. An uncompleted densification of composites is required to relax these stresses. Taking into account these observations, several very low TEC composites were elaborated. However, the uncompleted densification of composites and the b-eucryptite microcracking greatly decrease the mechanical properties of these materials.VILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF
Chemical Looping Combustion with Different Types of Liquid Fuels
CLC is a new promising combustion process for CO2 capture with less or even no
energy penalty compared to other processes. Up to now, most of the work performed on CLC
was conducted with gaseous or solid fuels, using methane and coal and/or pet coke. Liquid
fuels such as heavy fuels resulting from oil distillation or conversion may also be
interesting feedstocks to consider. However, liquid fuels are challenging feedstock to
deal with in fluidized beds. The objective of the present work is therefore to investigate
the feasibility of liquid feed injection and contact with oxygen carrier in CLC conditions
in order to conduct partial or complete combustion of hydrocarbons.
A batch experimental fluidized bed set-up was developed to contact alternatively oxygen
carrier with liquid fuels or air. The 20 mm i.d. fluidized bed reactor was filled up with
45 g of NiAl0.44O1.67 and pulses of 1-2 g of liquid were injected in
the bed at high temperatures up to 950ËC. Different feedstocks have been injected, from
dodecane to heavy fuel oils No.2. Results show that, during the reduction period, it is
possible to convert all the fuel injected and there is no coke remaining on particles at
the end of the reduction step. Depending upon oxygen available in the bed, either full
combustion or partial combustion can be achieved. Similar results were found with
different liquid feeds, despite their different composition and properties
Chemical Looping Combustion with Different Types of Liquid Fuels Combustion en boucle chimique avec différentes charges liquides
CLC is a new promising combustion process for CO2 capture with less or even no energy penalty compared to other processes. Up to now, most of the work performed on CLC was conducted with gaseous or solid fuels, using methane and coal and/or pet coke. Liquid fuels such as heavy fuels resulting from oil distillation or conversion may also be interesting feedstocks to consider. However, liquid fuels are challenging feedstock to deal with in fluidized beds. The objective of the present work is therefore to investigate the feasibility of liquid feed injection and contact with oxygen carrier in CLC conditions in order to conduct partial or complete combustion of hydrocarbons. A batch experimental fluidized bed set-up was developed to contact alternatively oxygen carrier with liquid fuels or air. The 20 mm i.d. fluidized bed reactor was filled up with 45 g of NiAl0.44O1.67 and pulses of 1-2 g of liquid were injected in the bed at high temperatures up to 950ËC. Different feedstocks have been injected, from dodecane to heavy fuel oils No.2. Results show that, during the reduction period, it is possible to convert all the fuel injected and there is no coke remaining on particles at the end of the reduction step. Depending upon oxygen available in the bed, either full combustion or partial combustion can be achieved. Similar results were found with different liquid feeds, despite their different composition and properties. Le CLC est un nouveau concept prometteur appliquĂ© Ă la combustion qui permet le captage de CO en minimisant la pĂ©nalitĂ© Ă©nergĂ©tique liĂ©e au captage. JusquâĂ prĂ©sent, lâessentiel des travaux de recherche dans le domaine du CLC concerne les charges gazeuses (mĂ©thane) et solides (charbon et coke). Les charges liquides, et particuliĂšrement les rĂ©sidus pĂ©troliers, sont des charges Ă©galement intĂ©ressantes Ă considĂ©rer a priori. La mise en oeuvre de ces charges en lit fluidisĂ© est cependant dĂ©licate. Lâobjet de ce travail est dâĂ©tudier la faisabilitĂ© de la combustion partielle ou totale des charges liquides dans les conditions du CLC au contact dâun matĂ©riau porteur dâoxygĂšne. Un petit rĂ©acteur en lit fluidisĂ© opĂ©rant en batch a Ă©tĂ© dĂ©veloppĂ© pour permettre alternativement le contact du matĂ©riau porteur dâoxygĂšne avec une charge liquide ou de lâair. Le rĂ©acteur de 20 mm de diamĂštre est rempli de 45 g de particules de NiAl0.44O1.67. Environ 1-2 g de charge liquide est injectĂ© par pulse dans le lit Ă des tempĂ©ratures allant jusquâĂ 950ËC. DiffĂ©rentes charges liquides ont Ă©tĂ© Ă©tudiĂ©es, du dodĂ©cane au fioul lourd nË2. Les rĂ©sultats montrent que pendant la pĂ©riode de rĂ©duction du matĂ©riau porteur dâoxygĂšne, il est possible de convertir tous les hydrocarbures injectĂ©s. Ă lâissue de cette phase, il ne subsiste pas de dĂ©pĂŽt de coke Ă la surface des particules. En fonction de la quantitĂ© dâoxygĂšne disponible dans le lit, on effectue une combustion totale ou partielle des hydrocarbures injectĂ©s. Des rĂ©sultats similaires sont obtenus pour les diffĂ©rents hydrocarbures testĂ©s, malgrĂ© leurs propriĂ©tĂ©s a priori trĂšs diffĂ©rentes
Ceramic Composite Based on BetaâEucryptite and an Oxide, and Process of Manufacturing Said Composite
US Patent App. 13/096,905no abstrac