Investigation of phase changes induced in boron nitride by mechanical milling

Thumbnail Image
Date
2001
Authors
Wheelock, Paul Brett
Major Professor
Advisor
Russell, Alan M.
Committee Member
Journal Title
Journal ISSN
Volume Title
Publisher
Authors
Research Projects
Organizational Units
Journal Issue
Is Version Of
Versions
Series
Department
Abstract
A research project was carried out in which the effects of mechanical milling on the structure of hexagonal boron nitride powder were investigated. Boron nitride has several different crystalline forms, the two most common being hexagonal and cubic. It can also have an amorphous structure with little or no crystalline order. Three different types of milling, Spex, attritor, and planetary, were performed. The milled powder was analyzed by several different methods including: x-ray diffraction, Raman spectroscopy, differential thermal analysis, and electron energy loss spectroscopy. Several experiments were also performed on the milled powders in an attempt to find a method to consolidate them into a piece large enough to measure its mechanical properties. These methods were: cold pressing, hot pressing, and sintering with an additive. Heat treatments of the milled powder were also performed to evaluate what resulting phase changes might occur. Both the x-ray diffraction and Rarnan spectroscopy analyses of the milled powders indicated that, as the powder was milled, it was becoming more amorphous. Milling conditions were found that produced a nearly amorphous powder with a minimum of contamination from the milling media and vessel. This milled powder was then used in subsequent experiments for heat treatment and consolidation. The heat treated powders seemed to retain nearly all of their amorphous characteristics, which would indicate that it is a relatively stable structure. The x-ray diffraction analysis of these powders showed that very little crystallization occurred. The consolidation experiments that were performed had limited success in producing an amorphous part with significant structural integrity. The only high strength, fully dense part produced seemed to be crystalline.
Comments
Description
Keywords
Citation
DOI
Source
Copyright