Strong time-dependence for strengthening a lithium disilicate parent glass and the corresponding glass-ceramic by Li+/Na+ exchange

X C Li; M Meng; D Li; R Wei; L He; S F Zhang

doi:10.1016/j.jmbbm.2019.103394

Strong time-dependence for strengthening a lithium disilicate parent glass and the corresponding glass-ceramic by Li⁺/Na⁺ exchange

J Mech Behav Biomed Mater. 2019 Dec:100:103394. doi: 10.1016/j.jmbbm.2019.103394. Epub 2019 Aug 7.

Authors

X C Li¹, M Meng², D Li¹, R Wei³, L He⁴, S F Zhang⁵

Affiliations

¹ State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, 710049, China.
² State Key Laboratory of Military Stomatology, Department of Prosthodontics, School of Stomatology, Fourth Military Medical University, Xi'an, 710032, China.
³ School of Materials Science and Engineering, Zhengzhou University, Zhengzhou, 450001, China.
⁴ State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, 710049, China. Electronic address: helin@mail.xjtu.edu.cn.
⁵ State Key Laboratory of Military Stomatology, Department of Prosthodontics, School of Stomatology, Fourth Military Medical University, Xi'an, 710032, China. Electronic address: sfzhang@fmmu.edu.cn.

PMID: 31419749
DOI: 10.1016/j.jmbbm.2019.103394

Abstract

Chemical strengthening of a lithium disilicate (LD) parent glass with stoichiometric composition and the corresponding glass-ceramic by Li⁺/Na⁺ exchange was investigated. The ion-exchange was performed in a molten NaNO₃ salt bath at 380 °C below the glass transition temperature over a wide time range from 3.75 to 480 min. It was found that strength of both the glass and glass-ceramic could be significantly enhanced after very short time treatment (3.75-15 min); however, significant strength decreases occurred similarly for the glass and glass-ceramic with further increasing the treatment time to obtain a greater ion-exchanged depth. Morphology analysis of the ion-exchanged surfaces revealed that the over-long treatment would induce surface failure for the glass, or LD crystal micro-cracking in the ion-exchanged region for the glass-ceramic. The strong time-dependence of the strengthening was attributed to dual effects of the ion-exchange. Besides the conventional "stuffing effect" of ion-exchange, the thermal expansion increase of surface layer induced by Li⁺/Na⁺ exchange might be a critical factor to be considered for strengthening the LD glass and glass-ceramic. With prolonging the processing time, the dual effects would change the surface residual stress from compressive into tensile, resulting in surface failure and undesirable strength degradation.

Keywords: Glass-ceramics; Ion-exchange; Lithium disilicate; Mechanical characterization; Residual stresses.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Calorimetry, Differential Scanning
Ceramics / chemistry*
Chromatography, Ion Exchange
Dental Porcelain / chemistry*
Ions
Materials Testing*
Models, Statistical
Sodium / chemistry*
Stress, Mechanical
Surface Properties*
Temperature
Tensile Strength
Time Factors
X-Ray Diffraction

Substances

Ions
lithia disilicate
Dental Porcelain
Glass ceramics
Sodium