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Scanning Auger and Xps Studies of Fracture Surfaces of B4C Hot Pressed with Excess Carbon

Published online by Cambridge University Press:  22 February 2011

Benjamin M. DeKoven ,
Eric A. Ness  and
David D. Hawn
Benjamin M. DeKoven
Affiliation:
The Dow Chemical Company, Central Research, 1776 Building, Midland, MI 48674
Eric A. Ness
Affiliation:
The Dow Chemical Company, Central Research, 1776 Building, Midland, MI 48674
David D. Hawn
Affiliation:
The Dow Chemical Company, Michigan Applied Science and Technology Laboratory, 1897 Building, Midland, MI 48674
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Abstract

A series of boron carbide materials was hot pressed with 0-7% excess carbon. The strength of each material was determined by four point bending, and found to decrease from about 600MPa to 300MPa as the carbon content increased from 0% to 7%. Diamond indentation yielded hardness values that decreased from 28.3 to 25.OGPa and toughness values that increased from 3.5 to 4.5 MPa√mover the same carbon range. Each sample was fractured in situ in ultrahigh vacuum (UHV) and examined by scanning Auger microanalysis (SAM) and XPS to determine both the elemental and chemical state distributions. For the samples with excess carbon, localized carbonrich regions are observed on fracture surfaces by SAM. XPS reveals a 50% enhancement of excess carbon on the fracture surface compared to the bulk for the sample with 7% excess carbon. A correlation was observed between surface carbon composition and the bulk toughness and hardness. The C(ls) XPS spectra were utilized to determine the nature of carbon in B4C on freshly fractured and Ne+ bombarded surfaces. Two distinct peaks were observed in the C(ls) region. Low dose ion bombardment resulted in a single broad C(ls) peak at the midpoint of the two initial peaks. It can be inferred from this data that there are C-C-C intericosahedral linkages in B4C.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 153: Symposium J – Interfaces Between Polymers, Metals, and Ceramics , 1989 , 351
Copyright
Copyright © Materials Research Society 1989

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