title: Quantitative phase analysis from X-ray diffraction in Y-TZP dental ceramics: a critical evaluation.
abstract: The dentistry literature shows consensus to use the Garvie and Nicholson equation modified by Toraya to quantify the Y-TZP phase transformation. However, this method does not include the possibility of cubic phase transformation and crystallographic texture after artificial ageing, and in this case, it is possible to observe errors of quantification.
  
  
  OBJECTIVE
  The aim of this study was to evaluate a dental Y-TZP ageing kinetic of phase transformation under pressure and hydrothermal conditions (130°C, 2bar) and to compare the methods of quantification by the equation of Garvie and Nicholson modified by Toraya and the Rietveld refinement method.
  
  
  METHODS
  Discs of Y-TZP (12mm Ø×1.2mm in height) were divided into groups (n=4) according to the ageing times (in the range of 6 and 138h). The superficial characterisation was made using SEM and the XDR for crystallographic analysis.
  
  
  RESULTS
  An aggressive superficial degradation process at the beginning of phase transformation in 6-10h of ageing was observed by SEM. The phase transformation quantification showed differences between the methods. It was observed the increase and stabilisation of monoclinic phase until 80% at 40h of ageing by the Garvie and Nicholson modified by Toraya equation, compared to 60% of monoclinic phase and approximately 30% of cubic phase observed by the Rietveld method.
  
  
  CONCLUSIONS
  The Toraya equation showed an overestimated result of monoclinic quantification compared to the Rietveld method.
  
  
  CONCLUSIONS
  The overestimated result of monoclinic phase could lead to different interpretation about the dental Y-TZP ageing process.
authors.affiliation: Institute of Science and Technology, Universidade Estadual Paulista Julio de Mesquita Filho, São José dos Campos, São Paulo, Brazil; Materials Science and Technology Center (CCTM), Nuclear and Energy Research Institute - National Nuclear Energy Commission (IPEN - CNEN/SP), São Paulo, Brazil. Electronic address: anelyse@uol.com.br.
authors.forename: A
authors.initials: A
authors.lastname: Arata
authors.affiliation: Instituto Tecnológico de Aeronáutica (ITA), São José dos Campos, São Paulo, Brazil.
authors.forename: T M B
authors.initials: TM
authors.lastname: Campos
authors.affiliation: Associated Laboratory of Sensors and Materials, National Institute for Space Research (INPE), São José dos Campos, São Paulo, Brazil.
authors.forename: J P B
authors.initials: JP
authors.lastname: Machado
authors.affiliation: Materials Science and Technology Center (CCTM), Nuclear and Energy Research Institute - National Nuclear Energy Commission (IPEN - CNEN/SP), São Paulo, Brazil.
authors.forename: D R R
authors.initials: DR
authors.lastname: Lazar
authors.affiliation: Materials Science and Technology Center (CCTM), Nuclear and Energy Research Institute - National Nuclear Energy Commission (IPEN - CNEN/SP), São Paulo, Brazil.
authors.forename: V
authors.initials: V
authors.lastname: Ussui
authors.affiliation: Materials Science and Technology Center (CCTM), Nuclear and Energy Research Institute - National Nuclear Energy Commission (IPEN - CNEN/SP), São Paulo, Brazil.
authors.forename: N B
authors.initials: NB
authors.lastname: Lima
authors.affiliation: Institute of Science and Technology, Universidade Estadual Paulista Julio de Mesquita Filho, São José dos Campos, São Paulo, Brazil.
authors.forename: R N
authors.initials: RN
authors.lastname: Tango
mesh_terms: D000465:Algorithms; D017554:Carbon Compounds, Inorganic / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry*; D003461:Crystallography; D045662:Dental Etching / Q000379:methods; D003764:Dental Materials / Q000737:chemistry*; D006195:Hafnium / Q000737:chemistry; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D008956:Models, Chemical; D010087:Oxides / Q000737:chemistry; D017655:Silicon Compounds / Q000737:chemistry; D013052:Spectrometry, X-Ray Emission; D013499:Surface Properties; D013997:Time Factors; D014961:X-Ray Diffraction; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: D017554:Carbon Compounds, Inorganic; D003764:Dental Materials; D010087:Oxides; D017655:Silicon Compounds; C499362:yttria stabilized tetragonal zirconia; C545179:hafnium oxide; D015019:Yttrium; D015040:Zirconium; C028541:zirconium oxide; C022088:silicon carbide; D006195:Hafnium; C091417:yttria
keywords: Artificial ageing; Characterisation; Rietveld method; Y-TZP