details about different properties of ceramics, silicate structures and a little information about cement

1. Cement, silicate structures and
properties of ceramics
BY SRUTHI SUDHAKAR
Sir syed college,
Taliparamba,
Kannur,kerala

2. CERAMICS

4. A ceramic material is an inorganic, non-
metallic, often crystalline oxide, nitride or
carbide material. Some elements, such as
carbon or silicon, may be
considered ceramics. Ceramic materials
are brittle, hard, strong in compression,
weak in shearing and tension.

6. cement
• Material for bonding solids together

7. • TYPES OF CEMENTS:
• Cement may be hydraulic or non-hydraulic:
• 1)Non-hydraulic cements (e.g. gypsum plaster) must be
kept dry in order to retain their strength.
• 2)Hydraulic cements : Harden because of hydration,
chemical reactions that occur independently of the mixture's
water content; they can harden even underwater or when
constantly exposed to wet weather.
• Hydraulic cement may be: i) Portland cements ii) Natural
cements iii) Expansive cements iv) High-alumina cements

8. Composition of Cement
 Lime Calcium Oxide (CaO) = 60 – 65% (63%)
 Silica (SiO2) = 20 – 25% (22%) •
Aluminium Oxide = 4 - 8% (6%)
 Iron Oxide = 2 – 4 % (3%) •
Magnesium Oxide = 1 – 3 %
 Gypsum 1 to 4%

10. types

11. 1. Natural cement
2. Quick setting cement
3. Artificial cement
4. Rapid hardening cement
5. Sulphate resistant cement
6. Low heat cement
7. High alumina cement
8. Colored cement
9. Blast furnace slag cement
10. Hydrographic Cement
11. Air entraining cement

13. Portland cement
The invention of Portland cement usually is attributed
to Joseph Aspdin of Leeds, Yorkshire, England,
who in 1824 took out a patent for a material that
was produced from a synthetic mixture
of limestone and clay. He called the product
“PORTLAND CEMENT” because of a fancied
resemblance of the material, when set, to Portland
stone, a limestone used for building in England.

14. • Cements used in road and airport paving
are adhesive materials.
• Cement used in civil engineering
construction is Portland cement.

15. • Hydraulic calcium silicate cement
• Raw feed
Material Composition Material Composition
SiO2 15.5% Al2O3 2.5%
Fe2O3 2.0% CaO 42.0%
MgO 2.5% CO2 35.5%

16. operation
Raw materials grounded to 200 mesh in a ball mill
Burned in the cement kiln either dry or mixed with water as
slurry
After burning, clinker is grounded to 325 mesh
Blended with about 3% gypsum
Bagged and stored in large cement silos

18. percentage
C3S C2S C3A C4AF
Normal Portland 45 27 11 8
High early
strength
53 19 10 10
Sulphate
resistant
38 43 4 8

19. High Early Strength Portland Cement only requires 3 days to
show the strength that Ordinary Portland Cement shows in 7
days
High Early Strength Portland Cement is particularly suitable
for works where rapid setting and rapid hardening properties
are beneficial, for example, for urgent works being carried out
in cold weather to keep schedules.

20. The use of SRC is particularly beneficial in such
exposure/service conditions, where the concrete is exposed
to the risk of deterioration due to sulphate attack. The use of
SRC is recommended for following applications:
Foundations, piles, basements and underground structures
Sewage and Water treatment plants.
Chemical, Fertilizers, Petrochemical factories, Food
processing units.
Coastal works, construction of building along the coastal
area within 25 km from coast.

21. • Hardens by taking up water in a complex chemical
reaction – hydration
• Ca3Al2O6+6 H2O Ca3Al2(OH)12
• Ca2SiO4 + x H2O Ca2SiO4.xH2O

22. siLicate structures
Cheap and plentiful
Distinct properties which are useful in engineering applications
Portland cement is most commonly known silicate
Brick, tile, glass and vitreous enamel
Applications in chemical ware electrical insulators reinforcing
glass fibers

23. Types of silicate
structures

24. Silicon oxygen tetrahedron (SiO4)4-

25. • One silicon interstitially fits among four oxygen
• Only 7 electrons for oxygen ,so unstable
• Become stable by :
a. Taking electron from other metal like (Mg,Ca
etc)
b. Sharing an electron par with second silicon

26. Double and poly tetrahedral structures

27. • One oxygen member of 2 units
• Si2O7 unit forming (Si2O7)2-
• Pyrosilicates examples

29. • 3 or more tetrahedra unit
• Ring structure
• One oxygen member of 2 units
• (Si3O9)6-

30. Chain structure

31. • One oxygen shared in two tetrahedra and similar sharing
on other part of tetrahedra
• Double chain structure when two parallel identical chain
are polymerized by sharing oxygen to every alternate
corner
• These can be infinite in length

33. Sheet structure

34. • Double chain structure extends infinitely in 2 D plane
• Clays, micas and talc are examples
• Consequences:
1. Cleavage of mica
2. Lubricating character of talc
3. Plasticity of clay

36. Framework structure
• Extension of silicate tetrahedral in 3 D
• Low densities
• Low atomic packing factors
• Hard
• Examples are cristobalite , quartz, feldspar

37. Vitreous structure

38. • Glass is vitreous silicate
• 3 D framework with covalent bonds
• Rigid

39. Properties of ceramic materials

40. 1. Mechanical properties
Hardness and resistance to wear
Great hardness and resistance to wear makes them useful
for grinding and cutting wheels
Carborundum- 2480 knoop
Boron nitride-7000 knoop

41. Tensile strength
Low tensile strength
Ceramics fail due to stress concentration on cracks, pores
etc
Tensile strength of alumina 1900kg/cm2

42. Compressive strength
Higher compressive strength
Alumina compressive strength 19500kg/cm2- 35000
kg/cm2
For strength cement brick etc are use in compression than
in tension

43. Transverse strength
• Transverse strength of alumina- 3500kg/cm2

44. Fracture strength
• Most ceramics have low fracture strength
• So fail in a brittle manner

45. Impact strength
o Ceramic materials do face impact loading under certain
conditions
CERAMIC MATERIAL IMPACT VALUE (Nm)
Stone ware 1.1-1.3
Vitrified ware 0.7-1.2

46. Modulus of elasticity
Value ranges from 7x1010 /N/m2 to 40x 1010 N/m2

47. Electrical properties
Following factors affect the electrical properties:
Size
Texture
Composition
Density
Temperature

48. • Used as
insulators,semiconductors,thermistors,thermoelectrics,tran
sistors, piezoelectric transducers, storage cells in memory
systems

49. Electrical insulation
• Porcelain, alumina , forsterite etc are common insulators
• Minimum electrical resistivity at 20oc
Alumina- >1012
Steatite>1012
• At 200oc
1010 1011 respectively

51. Electrical conductivity
Though most are insulators some conducts well at room
temperature
Forms two types of classes of semiconductors :
NTC resistors
PTC resistors

53. • NTC stands for “Negative Temperature Coefficient”.
• Iron oxide or nickel oxide
• Resistors with a negative temperature coefficient, which
means that the resistance decreases with increasing
temperature.
• Primarily used as resistive temperature sensors and current-
limiting devices.
• NTC sensors are typically used in a range from −55°c to
200°c.
• Temperature coefficients:-2 to-6%/ 0c

55. • PTC stands for ” Positive Temperature Coefficient“.
• Resistors with a positive temperature coefficient, which means
that the resistance increases with increasing temperature.
• PTC thermistors are divided into two groups, based on the
materials used, their structure and the manufacturing process.
• The first group of PTC thermistors is comprised of Silistors,
which use silicon as the semiconductive material.
• They are used as PTC temperature sensors for their linear
characteristic.
• The second group is the Switching Type PTC Thermistor.
• This type of PTC thermistors is widely used in PTC heaters,
sensors etc.

56. • Polymer PTC thermistors, made of a special plastic, are
also in this second group, often used as resettable fuses.
• The switching type PTC thermistor has a highly nonlinear
resistance-temperature curve
• . When the switching type PTC thermistor is heated, the
resistance starts to decrease at first, until a certain critical
temperature is reached.
• As the temperature is further increased above that critical
value, the resistance increases dramatically.

58. Dielectric constant
 A quantity measuring the ability of a substance to store
electrical energy in an electric field.
 Ceramics with dielectric constant upto 100 exist which
has constant temperature coefficients and low dielectric
losses
 Porcelain mica alumina dielectric constant upto 12

59. Dielectric strength
 Electrical breakdown point of an insulator per thickness
 High alumina – 200-300 v/mil
 Fused silica glass – 410
 Forsterite - 230

60. Piezoelectric properties
Ceramics like Barium Titanate can be made piezoelectric
by treatment at high voltage
Mechanical deformations to voltage changes
Gramophone pickups , roughness meters etc

62. Magnetic ceramics
• Ferrites with iron oxides along with other oxides are
magnetic ceramics
• Ferroxccube- soft magnetic material
• Ferroxdure – hard magnetic material
• Due to high resistivity has electrical applications

63. 3.Chemical properties
• Resistant to almost all chemicals except hydrofluoric
acids and some hot caustic solutions
• Organic solvents do not affect them
• Oxidic ceramic resistant to oxidation even at high
temperature
• Magnesia , Zirconia, Porcelain etc resistant to molten
metals so used to make crucible and furnace linings

64. • Glass is used when resistance to acids, bases and solutions
are required
• Glazed porcelain for chemical vessel

65. 4.Thermal properties
• Ceramics have many favorable properties at high
temperature

66. 5.Optical properties
• Used for production of window glasses and optical lenses
• Selective transmission or absorption of certain wavelength
of light
• Index of refraction 1.46-2.0 and so used in almost all
lenses

68. 6.Nuclear properties
• Since ceramics are refractory, chemically resistant and
different composition offers different neutron capture and
scatter characteristics, they are being used as :
1. Fuel elements
2. Control
3. Shielding
4. moderators

69. Strength Properties of Ceramics
• Theoretically, the strength of ceramics should be higher
than metals because their covalent and ionic bonding
types are stronger than metallic bonding
• But metallic bonding allows for slip, the mechanism by
which metals deform plastically .
• Bonding in ceramics is more rigid and does not permit slip
under stress the inability to slip makes it much more
difficult for ceramics to absorb stresses

70. Imperfections in Crystal Structure of
Ceramics
• Ceramics contain the same imperfections in their crystal
structure as metals - vacancies, displaced atoms,
interstitials, and microscopic cracks
• Internal flaws tend to concentrate stresses, especially
tensile, bending, or impact
• Hence, ceramics fail by brittle fracture much more readily
than metals
• Strength is much less predictable due to random
imperfections and processing variations

71. More About Compressive Strength
Of Ceramics
The frailties that limit the tensile strength of ceramic
materials are not nearly so operative when compressive
stresses are applied
Ceramics are substantially stronger in compression than in
tension
For engineering and structural applications, designers use
ceramic components so that they are loaded in
compression rather than tension or bending

72. Methods to Strengthen Ceramic
Materials
• Make starting materials more uniform
• Decrease grain size in polycrystalline ceramic products
• Minimize porosity
• Introduce compressive surface stresses
• Use fibre reinforcement
• Heat treat

73. Physical Properties of Ceramics vs metals
Density – most ceramics are lighter than metals but heavier
than polymers
Melting temperatures - higher than for most metals
Some ceramics decompose rather than melt
Electrical and thermal conductivities - lower than for metals;
but the range of values is greater, so some ceramics are
insulators while others are conductors
Thermal expansion - somewhat less than for metals, but
effects are more damaging because of brittleness