Production of TiC
Transcript of Production of TiC
Introduction
This work consists of five main stages including
Historical development of titanium carbide,
General properties of titanium carbide,
The production of titanium carbide,
Application of titanium carbide,
Prices.
In this investigation, I would like to mostly emphasize the three production methods of
titanium carbide among the other production methods. And we will discuss them in detail
as much as I can.
1. Historical Development of Titanium Carbide
Titanium carbide powder has been the subject of research for over 100 years. Beginning as
early as 1887, TiC was separated from titanium-bearing cast iron. Shimer accomplished
this with treatment by hydrochloric acid. In order to isolate titanium metal, Moissan
attempted the reduction of TiO2 in the presence of carbon in an electric arc furnace,
resulting in the production of TiC. This TiC was of very low purity, but the method used
seems to be the basis for the carbothermal reduction process in use today.
Miyamoto et al. proposed high-pressure self-combustion sintering (HPCS) as a combined
process of SHS and high-pressure sintering in 1984 and demonstrated the simultaneous
synthesis and densification of TiB2.
2. General Properties of Titanium Carbide
Titanium carbide has a wide range of properties similar to both metallic and ceramic
materials. For example, TiC has very high hardness, extremely high melting point, similar
to ceramics, but still maintains very good electrical and thermal conductivity associated
with the parent metal. The unique properties of TiC are derived from its complex bonding
nature. The generally accepted bonding scheme for TiC is a combination of metallic,
covalent, and ionic bonding.
TITANIUM CARBIDE
TiC 59.89
Melting Point (ºC) 3140Boiling Point (ºC) 4820
Density (g/cm3) 4.93
Mohs Hardness
(kg/mm2, @ 20 ºC)
3200
Modulus of Elasticity(GPa)
451
Thermal Conductivity(cal/cm sec. ºK, @ 20 ºC)
0.041 – 0.074
Coefficient of Thermal Expansion(µm/m ºK)
7.7
Electrical Resistivity(Microhm-cm)
180-250
Table 1. General Properties of TiC
TiC holds an B1 NaCl crystal structure. Each titanium atom is surrounded by six carbon
atoms and each carbon atom is surrounded by six titanium atoms in a perfect lattice.
Figure 2.1. Crystal structure of TiC
The NaCl-structured transition metal carbides and nitrides are often referred to as
interstitial compounds. The structure can be viewed as an fcc lattice of Me (Ti) atoms, in
which the interstitial sites are occupied by the Y (C) atoms, as we can see from the Fig. X..
TiC is often discussed as an interstitial carbide where titanium occupies a close-packed
structure and the carbon is located on a specific interstitial sites. However, this classical
description of titanium carbide is not scientifically correct. For example, the high
temperature form of β-titanium has the bcc structure. In this case, the parent metal,
titanium, must change its structure to an fcc or hcp structure which creates octahedral sites
that are large enough to accommodate carbon atoms. This change from the bcc to the fcc
structure also causes the Ti-Ti distance between the host metal atoms to change, and
concequently is not a true interstitial structure as the initial metal framework is altered.
Titanium carbide has long been recognized as a defect structure, i.e. it contains vacancies.
These vacancies generally occur on the carbon site and to a lesser degree on the Ti site. As
a result, TiC is stable over a wide range of composition.
Under realistic experimental conditions, many of the cubic
carbides and nitrides tend to be substoichiometric (a phase
with a smaller concentration of Y atoms than of Me ones,
MeYx, where x <1:0, is called substoichiometric or
hypostoichiometric). For example, TiC most often contains at
least a few percent of C vacancies. According to the Ti-C
phase diagram in Figure, the ideally stoichiometric TiC phase
would prefer to split into substoichiometric TiCx, x ~ 0,96 –
0,97 and a pure C phase.
Figure 2.2. Phase diagram for Ti-C system
Correlation of structure and properties for TiC is difficult because of the effects of bond
strength, stoichiometry, valance, vacancies, atomic size and bond length which are still not
fully understood. Variations in all these factors give rise to the wide range of material
properties for TiC.
Figure 2.3. The binary Ti-C phase diagram
3. Production Techniques of Titanium Carbide
• Direct Carburization
• Carbothermal Reduction
• Self-propagating High Temperature Synthesis (SHS)
• Mechanical Alloying
• High Pressure Self Combustion Sintering
• Chemical Vapor Deposition
3.1. Direct Carburization
Tthe most basic TiC production method is the direct carburization of titanium. The reaction
proceeds as:
Ti + C ® TiC
Ti and C powders is used as beginning material and processed at 2500 – 3000 ºC. The
basis of the process usage of the gases that occurs in the process. The high pressure which
is made by these gases increases the reaction between Ti and C. This reaction suffers
several severe limitations. First, the cost of elemental titanium is high, and attaining
submicron particles from the titanium is a difficult prospect, as the smaller particles are
pyrophoric, making them difficult to handle. With reaction time being from 5-20 hours,
this process allows excessive grain growth to occur as well as producing strong
agglomerates, necessitating milling to produce fine TiC powders.
3.2. Carbothermal Reduction
The most widely applied method for producing TiC on a commercial scale is carbothermal
reduction. Using reaction temperatures between 1700°C and 2100°C, TiC can be produced
according to the following reaction :
TiO2 + 3C = TiC + 2CO(g)
The theoretical thermodynamic reaction temperature (when the Gibbs energy becomes
negative) for this reaction is 1289°C. Commercially, this process makes use of carbon
black mixed with titania. Unfortunately, physical mixing allows only limited contact
between the reactants. This has the effect of increasing reaction time (as long as 10 hours)
to produce powders having unreacted carbon and TiO2, a wide size distribution, and
particle agglomeration.
Figure 3.1. The Gibbs Free Energy vs. Temperature for TiC Formation Reaction
3.3. Mechanical Alloying
Mechanical alloying is a kind of milling process, and is commonly referred to high energy
ball milling. High-energy ball milling can induce structural and microstructural
modifications and produce various nonequilibrium materials: supersaturated solid solution,
amorphous alloy, nanocrystalline materials and so on.
Mechanical alloying is a potential method for producing commercial nanocrystalline
powders. During the ball milling, large particles may be plastic deformed and fragmented,
small particles may coalesce by cold-welding. Furthermore, high exothermic reaction can
be initiated by high energy ball milling. It is easy to obtain TiC with nanocrsytalline size
by using ball milling at room temperature.
Figure 3.2. Ball milling and grinding media for laboratory investigations
Figure 3.3. High efficiency ball mills in industry
TiC is able to be synthesized for a
short time at room temperature. Wider
peaks, finer grain size, longer time.
Figure 3.4. X-ray diffraction patterns of TiC
(mol)=1:1 at different milling time
a) 120 min b) 240 min c) 600 min
TiC with 20 nm crsytallites is fabricated by ball milling of Ti and C powders just after
reaction 120 min.
Figure 3.5. Nanocrsytalline Size vs. Milling Time
When the milling time reached 115 min, the
temperature of the vial increased abruptly and
reached its climax. This is associated with the
exothermic reaction of Ti and C. XRD analysis
supports this.
Figure 3.6. Temperature vs. Milling Time
We can conclude that TiC powders are able to be manufactured by mechanical alloying
after 120 minutes milling time.
Fig. X. shows the scanning electron microscopy (SEM) images of product powder
particles. Fig. Xa. shows the micrograph of a TiC powder particle just after an exothermic
reaction. Fig. Xb. shows the magnified micrograph in a typical region of a larger particle of
Fig. Xa.. The large particles appear to be agglomerates of finer particles with about 1 mm
in diameter.
Figure 3.7. SEM micrographs of milled powder at different times a) just after an
exothermic raction, 120 min b) 240 min c) 600 min
Briefly, the exothermic reaction of Ti and C can be carried out by the mechanical alloying
technique. The self propagating reaction induced by mechancial alloying takes place in a
short time. During the subsequent milling, the crystalline size decreased gradually. The
average crystalline size reached about 7 nm when ball milled for 10 h.
3.4. High Pressure Self Combustion Sintering (HPCS)
Firstly, we should introduce self-propagating high temperature synthesis (SHS), since
HPCS is a combined process of SHS. SHS process enables the synthesis of powder
materails, like TiC, in a very short time by utilizing an exothermic reaction. Moreover, it is
simple, and energy efficient.
Self-propagating High-temperature Synthesis (SHS) is a relatively novel and simple
method for making certain advanced ceramic, composites and intermetallic compounds.
This method has received considerable attention as an alternative to conventional furnace
technology.
The SHS is based on systems able to react exothermally when ignited and to sustain them
to form a combustion wave. The temperature of the combustion can be very high (as 5000
K) and the rate of wave propagation can be very rapid (as 25 cm/s), hence this process
offers the opportunity to investigate reactions in conditions of extreme thermal gradients
(as 105 K/cm).
In the typical combustion synthesis the reactants are usually fine powders, mixed and
pressed into a pellet to increase an intimate contact between these. The reactant mixture is
placed in a refractory container and ignited in vacuum or inert atmosphere. The products of
the reaction are extremely porous, typically 50% of theoretical density.
Reactions between particulate materials are an alternative way to produce various types of
materials considering the extreme simplicity of the process, relatively low energy
requirement, high purity of the products obtained, the possibility to obtain metastable
phases, and the possibility of simultaneous synthesis and densification. Higher purity of
products is the consequence of high temperature associated to the combustion, volatile
impurities are expelled as the wave propagates through the sample. The possibility of the
formation of metastable phases is based on high thermal gradients and rapid cooling rate
associated with the reaction.
Figure 3.8. Schematic diagram of SHS
Table 2. Some materials produced by SHS
A high pressure self combustion sintering (HPCS) process is applied to synthesis and
simultaneous sintering in a very short time by use of exothermic reaction under high
pressure. Dense TiC (>95% of theoretical) can be fabricated by this HPCS method.
Pressure is applied by means of a
hydraulic uniaxial press
Boron nitride die
Argon atmosphere
Ignition agent, mixture of titanium and
boron
The electrical current at 1,5 to 2,0 kV ·
A for 2 s for ignition agent is passed
through a tungsten heater
Figure 3.9. Schematic diagram of the experimental system for HPCS
Figure 3.10. X-ray powder diffraction patterns of the products by HPCS under 65 MPa
Small peaks due to titanium and carbon appeared in the X-ray diffraction pattern for the
product from the reactant mixture with C/Ti = 0.80, as shown in Fig. X. The phase diagram
of the Ti- TiC system suggests that the achievement of complete reaction for a reactant
mixture with C/Ti = 0.80 must yield a product which consists of only single-phase TiC.
Moreover, the residual carbon is available due to excessively initial carbon amount. This
situation leads to existence of unreacted carbon elements in the structure.
The lattice constant decreases with increasing pressure.
This results in producing a denser and a harder product.
As we can see from the related figures, vickers
microhardness is directly proportional to the density. The
microhardness increases with increasing density.
Figure 3.11. Lattice constant as a function of molar ratio, C/Ti
Figure 3.12. Relationship between Vickers
microhardness and Density
Combustion synthesis seems to be completed through three steps;
1. Transport elements to encounter the reaction
2. An exothermic synthesis reaction
3. Structuralization
When the reaction to form TiC occurs, the following three mechanism are possible;
1. Compund formation occurs at the boundry of the two elements in the condensed
phase, without transport of the elements through the gas phase,
2. Either element is transported to the surface of the other element through gas
phase, and then compound formation occurs,
3. Both elements impinge upon each other in the gas phase and the compound
condenses.
However, the most commonly encountered possibilities are second and third ones.
It is obvious that carbon fiber remains in the product and the combustion reaction is
incomplete, seen from the figures X. (Generally, C powders can be used in HPCS, instead
of C fibers.However, in this investigation C fibers were employed to highligt the
possibilities mentioned above).
Figure 3.13. SEM photographs of the fractured surface of the product from the reactant
mixture with C/Ti = 0.80 by HPCS under 65 MPa
Figure 3.14. SEM photograph of the carbon fiber before the production.
There is a gap between the unreacted carbon fiber and the surrounding product TiC
The diameter of the residual carbon fiber is 5µm, while the initial was 7 µm
The surface of the residual carbon fiber is very rough, while the initial was smooth
These micrographs, also, support to second and third possibilities.
A certain carrier for the transport of titanium and/or carbon should be taken into
consideration, because even under vapor pressure in equilibrium at the adiabatic
temperature (3210 ºK for TiC), a very fast combustion process such as in fabrication of
TiC cannot be explained.
Therefore, oxygen plays an important role as a carrier for carbon, since it can exist in the
starting elements and BN dies.
Carbon transport by CO is considered in the combustion reaction of titanium and carbon, if
there is sufficient oxygen available. The reaction most likely proceeds by
Briefly, the HPCS process is useful to fabricate the dense titanium carbide ceramics
directly from the constituent elements without additives. The advantage of this new
sintering process is that the synthesis and sintering of Tic can be accomplished by a simple
and extremely short-time process and with low electric power. The mixtures of Ti and C
converted entirely to the nonstoichiometric TiC, compounds in the mixing range of
C/Ti≤O.95. The maximum values of the relative density and the Vickers microhardness is
96.5% and 31 GN/m2, respectively, at room temperature.
3.5. Chemical Vapor Deposition (CVD)
Chemical vapor deposition (CVD) is a technique of modifiying properties of surface of
engineering componenets by depositing a layer or layers of another metal or compound
through chemical reactions in a gaseous medium surrounding the componenet at elevated
temperature.
In formal terms, CVD may be defined as a technique in which a mixture of gases interacts
with the surface of substrate at a relatively high temperature, resulting in the
decomposition of some of the constituents of the gas mixture and the formation of a solid
film of coating of a metal or a compound on the substrate.
Figure 3.15. Schematic diagram showing various components of a typcial chemical vapor
deposition system
1. Reactor 12. Particulate trap
2. Heating elements 13. Gas scrubber
3. Reaction chamber 14. Flow meter
4. Water-cooled end flanges 15. Flow control valves
5. Power controller 16. Gas tank regulators
6. Pressure gauge 17. Substrate support
7. Temperature sensor and controller 18. Substrate
8,10,11. Precursor gas sources
9. Metal halide (liquid) vaporizer
Figure 3.16. Process/Microstructure/Property Relationship in CVD
A modern CVD system includes a system of metering a mixture of reactive and carrier
gases, a heated reaction chamber, and a system for the treatment and disposal of exhaust
gases.
The gas mixture (which typically consists of hydrogen, nitrogen, or argon, and reactive
gases such as metal halides and hydrocarbons) is carried into a reaction chamber that is
heated to desired temperature by suitable means.
Table 3. Typical parameters in CVD
Process parametersType of precursorsGas ratioSubstrate T/ DepositionTPressureFlow rateDeposition timeReactor geometry
Coating propertiesNucleation and growthDeposition rateMicrostructureComposition/StoichiometryCoating thicknessUniformity and adhesionPhysical/chemical/electrical/ optical/magnetical/ mechanical properties
CVD phenomena Thermodynamics Chemical kinetics (gas phase/surface) Mass transport
All CVD systems require a mechanism by which the products of the chemical reaction are
treated. These products contain various reactive and potentially hazardous constituents, as
well as particulate matter, which must be trapped and neutralized before the gases are
exhausted to the atmosphere. In addition, as most CVD process are carried out at
subatmospheric pressures, the pumping equipment must be protected from relatively hot,
corrosive gases. This is usually done by using nonreactive materials for pump components.
The CVD technique is applicable for the deposition of a wide variety of materials, such as
metals, compunds, ceramics, powders, and whiskers.
Table 4. Applications of the CVD Technique
Table 5. Typical Materials Deposited by CVD
One of the most widely known and practiced applications of CVD is in the manufacture of
coated cemented carbide cutting tools.
The commonly used coatings include TiC, TiN, and Al2O3, and their combinations.
Another application in tribological coating includes refractory compounds such as
carbides, nitrides, and borides due to their extreme hardness, high elastic modulus, fracture
toughness etc.
One of the elegant applications of CVD tribological coatings is for ball bearings. Other
applications of tribological coatings include various steel components such as coating on
dies, used in molding, extrusion and similar metalworking operations.
4. Applications of TiC
TiC is an important ceramic because it has a specific strength at a high temperature,
an extremely high melting point and desirable properties of corrosion resistance.
TiC is an attractive compound for a wide range of engineering applications,
especially fusion reactors and superhard cutting devices.
Because of the wide range properties for TiC, it can be added to WC-Co as a
secondary carbide, up to 15wt.%, to avoid diffusion of WC into the steel surface
during machining operation. Moreover, it lowers density of the carbide.
Because of its hardness and wear resistance it is mainly used for cutting tool tips,
saws, dies, and wear resistant coatings.
TiC + Al2O3 ceramic inserts.
Titanium carbide coated 440C stainless steel balls.
Advantages of Titanium Carbide Coated balls:
• Extended bearing life
• Minimized adhesion and fretting wear
• Reduced race wear
• Reduced cage (retainer) wear
• Extends life of lburicant and also has high tolerance towards all types of
lubes: chemical inertia of coating
• Low coefficient of friction (3 x’s lower than steel)
• Works in low lubrication conditions
• Excellent wettability characteristics
• In contrast to ceramic balls, TiC balls exhibit the bulk properties of the steel
substrate (identical Young’s modulus, thermal expansion and hardness of
steel balls and races)
• Complete traceability
Figure 4.1. TiC cutting tools
Figure 4.2. Al2O3 ceramic inserts in white and TiC + Al2O3 ceramic inserts in black
Figure 4.3. Ball coated with TiC and ball bearing
Figure 4.4. TiC saws
5. Prices for TiC
Prices can be higher depending on the quantities of the TiC powders;
70 $ - 270 $
10 TiC inserts can be bought by
40 $
Material Name
Titanium Carbide powder, 99.7%, APS <3 m
Formula TiC
Specification99.7% (metal basis); average particle size (APS) <3 m, total C ≥19.4%, free C <0.25%, O <0.2%
Quantity & 250 g $ 48.60
Product # 22R-0601
TiC Powder, 99.7%, APS <3 m
m.p. 3140 oC, b.p. 4820 oC, density 4.93 g/cm3
Price 500 g $ 73.20
1 kg $ 112.50
2 kg $ 86.70/kg
5 kg $ 54.90/kg
10 kg $ 46.80/kg
20 kg $ 42.60/kg
50 kg $ 39.50/kg
100-500 kg -1 metric ton (1000 kg) $ 26.70/kg
2-10 tons -
References
Seiji Adachi, Takahiro Wada, and Toshihiro Mihara (Central Research Laboratory,
Matsushita Electric Industrial Co., Ltd., Moriguchi, Osaka 570, Japan), Yoshinari
Miyamoto and Mitsue Koizumi (Institute of Scientific and Industrial Research,
Osaka University, Ibaraki, Osaka 567, Japan), Osamu Yamada (College of General
Education, Osaka Industrial University, Daito, Osaka 574, Japan), “Fabrication of
Titanium Carbide Ceramics by High Pressure Self Combustion Sintering of
Titanium Powder and Carbon Fiber”, Journal of the American Ceramic Society,
1989.
Osamu Yamada (College of General Education, Osaka Industrial University, Daito,
Osaka 574, Japan),“High-pressure Self-Combustion Sintering of Titanium
Carbide”, Communications of the American Ceramic Society, 1987.
Douglas E. Wolfe, “Synthesis and characterization of TiC, TiBCN, TiB2/TiC and
TiC/CrC multilayer coatings by reactive and ion beam assisted, electron beam-
physical vapor deposition (EB-PVD)”, The Pennsylvania State University, 2001.
Zhu Xinkun, Zhao Kunyu, Cheng Baochang, Lin Qiushi, Zhang Xiuqin, Chen
Tieli, Su Yunsheng, “Synthesis of nanocrystalline TiC powder by mechanical
alloying”, Department of Materials, Kunming UniÕersity of Science and
Technology, Kunming 650093, People’s Republic of China, 2001.
Arthur A. Tracton, “COATINGS TECHNOLOGY HANDBOOK”, 2006.
Kenneth J. A. Brookes, “Hardmetals and other hard materials”, 1998.
“Properties and Selection Nonferrous Alloys”, ASM Handbook Volume 02.
http://en.wikipedia.org/
http://www.hooverprecision.com/html/hoover_-_titanium_carbide__tic.html
http://images.google.com.tr/imgres?imgurl=http://chifis1.unipv.it/materials/
images/cs1.gif&imgrefurl=http://chifis1.unipv.it/materials/HighLights/
SHS.htm&h=262&w=586&sz=8&hl=tr&start=80&um=1&tbnid=nOzxBbK4wYQ
d1M:&tbnh=60&tbnw=135&prev=/images%3Fq%3D%2522self-propagating
%2Bhigh-temperature%2Bsynthesis%2522%26start%3D60%26ndsp
%3D20%26svnum%3D10%26um%3D1%26hl%3Dtr%26sa%3DN
http://images.google.com.tr/imgres?imgurl=http://www.dicm.unica.it/~cincotti/
gruppo/instrumentation_file/image008.jpg&imgrefurl=http://www.dicm.unica.it/
~cincotti/gruppo/
instrumentation.html&h=481&w=642&sz=45&hl=tr&start=16&um=1&tbnid=jAC
MSlZCFT5AFM:&tbnh=103&tbnw=137&prev=/images%3Fq%3D%2522self-
propagating%2Bhigh-temperature%2Bsynthesis%2522%26svnum%3D10%26um
%3D1%26hl%3Dtr%26sa%3DN