A study of Tantalum Carbide Crystals

1
A study of Tantalum Carbide Crystals

• Arnab Kundu

2
Brief Outline

• Aims Objectives
• Description of Tantalum
• Tantalum Carbide its applications
• Structure of Transition metal carbides

• Experimental work on Tantalum Carbide
• Micro-hardness test
• Dislocation etching experiment
• Recommendation for future study

3
Introduction
4

• This study is significant because of two most
  important characteristics of transition metal
  carbides
• their hardness,
• and their highly refractory nature
• These two properties render the combination of
  carbides with metals belonging to the transition
  group highly useful in the industrial world in
  applications involving high temperature and high
  strength.

5
Aims and Objectives

• To discuss the physical characteristics exhibited
  by tantalum carbide at variable temperatures.
• To determine the degree of hardness of tantalum
  carbide crystal at room temperature by means of
  micro-indentation test.
• To study the effect of change in microstructure
  of the crystal after dislocation itching
  experiment.

6
What is Tantalum?
7
History In Greek,
Tantalos Tantalum was discovered in 1802 by
Ekeberg, but many chemists thought niobium and
tantalum were identical elements until Rowe in
1844, and Marignac, in 1866, showed that niobic
and tantalic acids were two different acids. The
early investigators only isolated the impure
metal. Von Bolton produced the first relatively
pure ductile tantalum in 1903.
8
Occurrence.Tantalum occurs
principally in the mineral columbite-tantalite.
Tantalum ores are found in Australia, Brazil,
Mozambique, Thailand, Portugal, Nigeria, Zaire,
and Canada. Separation of tantalum from
niobium requires several complicated steps.
Several methods are used to commercially
produce the element, including electrolysis of
molten potassium fluorotantalate, reduction of
potassium fluorotantalate with sodium, or
reacting tantalum carbide with tantalum oxide.
9
The essentialsName Tantalum
Symbol Ta Atomic number 73 Atomic
weight 180.9479 (1) Group in periodic table 5
Period in periodic table 6 Block in periodic
table d-block
10
PropertiesTantalum is a grey,
heavy, and very hard metal. When pure, it is
ductile and can be drawn into fine wire, which is
used as a filament for evaporating metals such as
aluminium. Tantalum is almost completely
immune to chemical attack at temperatures below
150C, and is attacked only by hydrofluoric acid,
acidic solutions containing the fluoride ion, and
free sulphur trioxide. Alkalis attack it only
slowly. At high temperatures, tantalum becomes
much more reactive. The element has a melting
point exceeded only by tungsten and rhenium.
11
UsesTantalum is
used to make a variety of alloys with desirable
properties such as high melting point, high
strength, and good ductility. Scientists at
Los Alamos have produced a tantalum carbide
graphite composite material, which is said to be
one of the hardest materials ever made. The
compound has a melting point of 3738C.
Tantalum is used to make electrolytic
capacitors and vacuum furnace parts, which
account for about 60 of its use. The metal is
also widely used to fabricate chemical process
equipment, nuclear reactors, and aircraft and
missile parts.
12
What is Tantalum Carbide?

• It is a metallic powder of a dark light-brown
  colour.
• It has a theoretical carbon content of 6.23.
• It is only slightly soluble in acids and burns in
  air with a bright flash.
• Its melting point ranges between 4730-4830oC.

13
Applications

• Though tantalum carbide (TaC) has been proposed
  for use as wound filaments in the form of wires,
  it is prohibited due to the low strength of TaC
  wires.
• It is of practical importance in the production
  of cemented multicarbide hard metals.
• In the industrial world, it can be used in
  machining-tool materials to reduce the tendency
  of welding between steel chips and tool material.

14
Structures of Transition Metal Carbides
15
Experimental work on TaCThe crystal
sample used for experimentation was grown at
Stanford Research Institute by floating zone
melting technique.Experiments performed1)
Hardness indentation measurement on the sample at
room temperature using Knoop
indenter.2) Dislocation etching experiments.
16
Micro-Hardness TestKnoop Indentations
were made on the sample surface using a Leitz
micro-hardness tester with 200grams load.The
indentations were performed throughout the
diameter of the sample at a spacing of
100µ.All indentations were made on the(001)
surface of the crystal sample.

17
Table of measured Knoop Hardness
18
Knoop hardness at different positions of
the sample
19
Dislocation Etching ExperimentAfter
etching, the crystal sample showed 4 distinct
different zones which reflect the change in
micro-structure.Micro-indentation test revealed
the variation in hardness in the 4 zones under
observation.
20
Average Knoop Hardness in 4 Different Zones
21
Variation of Hardness at 4 Different Zones