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.

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http://en.wikipedia.org/

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