Coarsening induced reverse phase transformation of hafnia in polymer-derived Si-Hf-C-N-O ceramics was studied experimentally. X-ray diffraction and high resolution transmission electron microscopy were used to obtain information regarding nanocrystalline structure. Hafnia crystallites precipitated out from the amorphous ceramic matrix on heat treatment were observed to remain as tetragonal hafnia below a critical crystallite radius of 4 nm. Prolonged heat treatment has resulted in coarsening, as explained by Lifshitz-Slyozov-Wagner model, resulting in reverse phase transformation from tetragonal to monoclinic hafnia. © 2011 The American Ceramic Society.

Ravi Kumar

Department of Metallurgical and Materials Engineering

Ravindran Sujith

Adhimoolam Bakthavachalam Kousaalya

CERAMIC MATRIX

Induced phase transformation

Nano-crystalline structures

REVERSE PHASE TRANSFORMATION

Ceramic materials

Coarsening

Crystallites

hafnium

Heat treatment

Phase Transitions

Transmission electron microscopy

X ray diffraction

High resolution transmission electron microscopy

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Journal of the American Ceramic Society

Powder particles of polymer derived SiHfCN(O) ceramics were pulsed electric current sintered at 1300 and 1500 °C to produce amorphous and partially crystalline ceramic pellets for corrosion studies in salt (NaCl or Na2SO4) and acid (HF) environments. While, sodium dramatically accelerated phase transformation and catalyzed the crystallization process, the open porosity acted as the main cause for sodium penetration in these materials. The samples, however, were completely disintegrated during fluoride acid tests. The cristobalite and HfO2 crystalline phases were severely corroded and it was found that the SiC grains were relatively stable in comparison with other phases in the system. © 2015 Elsevier Ltd and Techna Group S.r.l.

Ceramics International

Corrosion behavior of polymer-derived SiHfCN(O) ceramics in salt and acid environments

The influence of pulsed electric current sintering on the structural evolution and indentation response of hafnia incorporated silicon carbonitride polymer derived ceramics was studied. Despite the absence of any sintering additives, appreciable sintering at 1400 C with a density of ∼2.7 g/cc was observed. Sintering beyond 1300 C resulted in the phase separation and nano-crystallization of amorphous Si-Hf-C-N-O ceramic. The crystallite coarsening was insignificant and thereby the tetragonal phase of hafnia was retained in the ceramic nanocomposite. A relatively high indentation hardness and elastic modulus of ∼18 GPa and ∼313 GPa were determined by depth sensing nanoindentation technique. © 2013 Elsevier Ltd and Techna Group S.r.l.

Indentation response of pulsed electric current sintered polymer derived HfO2/Si-C-N(O) nanocomposites

Hafnium alkoxide modified polysilazane was synthesized by the drop-wise addition of hafnium tetra(n-butoxide) to polysilazane. The solid state thermolysis (SST) temperature and the ceramic yield for both the polysilazane and modified polysilazane were determined by performing thermogravimetry. Fourier transform infrared spectroscopy was performed to understand the polymer to ceramic conversion as well as the bonding characteristics of the ceramics. The modified polymer after crosslinking was subjected to SST at 800 °C at a constant heating rate of 5 °C/min for a dwell time of 2 h in atmospheric ambience. From the X-ray diffractograms, the as-thermolysed ceramics were observed to remain X-ray amorphous and on heat-treatment resulted in the crystallization of tetragonal hafnia. However, on heat-treatment at 1500 °C, reverse phase transformation from tetragonal to monoclinic hafnia was observed. Raman spectroscopy and transmission electron microscopy were employed to further understand the phase evolution. The thermal stability and the influence of amorphous matrix on the coarsening of HfO 2 were also evaluated. © 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Synthesis and phase stability of precursor derived HfO 2/Si-C-N-O nanocomposites

Polymer-Derived Ceramics: 40 Years of Research and Innovation in Advanced Ceramics

Polymer-Derived Silicon Oxycarbide/Hafnia Ceramic Nanocomposites. Part II: Stability Toward Decomposition and Microstructure Evolution at T≫1000°C

Journal of Applied Physics

Size-dependent polymorphism in HfO2 nanotubes and nanoscale thin films

Physical Review B

Combined experimental and theoretical study of thin hafnia films

Thermodynamically Stable SiwCxNyOzPolymer-Like, Amorphous Ceramics Made from Organic Precursors

Coarsening induced phase transformation of hafnia in polymer-derived Si-Hf-C-N-O ceramics

Journal	Journal of the American Ceramic Society
ISSN	00027820
Open Access	No