Literature on Quality aspects of Cement

What is cement and how it is made?Cement is a substance which is applied to the surface of solid bodies to make them cohere firmly or more specifically a powdered substance which is made plastic with water is used in a soft and pasty stage which hardness or drying and bind together with bricks, stones etc in building. Portland cement is a calcined material comprising lime and silicates which is Mixed with sand and stone and upon hydration forms a plastic material which Sets and hardens to a rock like material called concrete. Portland cement is manufactured in a series of process. Limestone (Calcium Carbonate) and other material containing appropriate proportions of Calcium, silicon, aluminium and iron oxides are crushed and milled to a fine Flour like stuff called “ Raw Meal “ This is preheated in a pre heater or in A rotary kiln to dis-associate calcium carbonate to active calcium oxide with The evolution of carbon dioxide and then to react calcium oxides with Other component in a Rotary Kiln to form calcium silicates and aluminates Which partially fuse at material burning temp up to 1400oC. The Reaction Product leave the kiln as a dark grayish nodules called “ Clinker “ The Clinker is finally inter ground with a small proportion of Gypsum to control The rate of hydration and the fine product is cement.

Why Gypsum is added with Clinker in the production of cement?Gypsum is added to the cement production process mainly for the purpose Of regulating its setting time. It prevents flash setting and makes the Concrete workable for hours. In addition it also influences other cement properties like grind ability, sensitivity to storage, volume stability and development of strength.

What is setting time?

It is the time required to change the stage of cement paste from fluid to a rigid One.

What is the false set of cement paste?

False set is used to describe the premature stiffening of the cement paste which some time occurs within 10-15 minutes of mixing with water which is caused by dehydration of Gypsum dehydrated due to high temp. during cement grinding process. However the plasticity of the paste is regained on remixing.

What is flash set of cement paste?

This refers to rigidity of the cement paste which some time occur Within 5-10 Minutes of mixing with water and is referred To as Irreversible rigidity. This is caused by the formation of aluminate hydrate due to high content of C3A and or a too small amount of easily soluble calcium sulphate. Cement Produced with this behavior is unsuitable to use.

What is consistency of cement paste?Consistency of cement paste is the amount of water required for preparing a workable cement paste.

What is heat of Hydration in cement paste?

When cement is mixed with water, the chemical reaction between the calcium Silicates in cement with water producing gel like calcium silicates hydrate and Calcium hydroxide is called “ Hydration of cement paste “ This hydration Reaction is an exothermic reaction which means

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heat is liberated. This is called heat of hydration in cement paste. The quantity of heat liberated in quite Appreciable and due consideration to be taken while making mass concrete construction. During cooling of the concrete after hydration reaction, cracks can develop due to thermal gradients if enough design consideration are not taken care.

What is Soundness in cement?

Soundness provides an index of potential delayed expansion caused by hydration of Calcium oxide, or Magnesium oxide, or both when present in Portland cement. This, in turn, provides information on the volume stability of concrete when Portland cement is used.

What is Shrinkage in cement?

The term ‘drying shrinkage’ can be defined as the decrease in length of the cement test specimen, where the decrease is caused by any factor other than externally applied forces under stated environmental conditions. The terms includes the net effect of a variety of phenomena, including hydration of the cement, tending to bring about both increase and decrease in length during the period in which the cement test specimens are stored under stated environmental conditions.

What is Air content of cement?

This indicates the volume of air (and other gases, if any) in a freshly mixed cement mortar, expressed as a percentage of total volume of the mortar. The test for air content is essential to assess the cement for its requirement with respect to air-entraining requirement.

What is Compressive strength?Compressive strength is the usual primary requirement of good concrete in it’s hardened state and this is an overall measure for the quality of cement and concrete. In order to ascertain the compressive strength of cement and concrete, a predetermined ratio of cement, aggregate and water are thoroughly mixed and specimens are cast. These specimens are cured and stored in specified environmental conditions prior to testing it’s compressive strength at various ages like 3 days, 7 days, 28 days etc. Many of the desirable properties of concrete like durability, impermeability, abrasion resistance etc., are highly influenced by compressive strength. Water cement ratio, workability and maximum size of aggregate also affects the compressive strength of the concrete.

What is Tensile strength?

The term is used to define the maximum tensile stress measured in force per unit cross sectional area that a cement mortar specimen can resist before it ruptures. Concrete, a mixture of loosely bonded sand and gravel has a low tensile strength because of its coarse structure and hence must be reinforced to withstand the tensile stresses encountered in structure.

What is Flexural Strength?

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Generally compressive strength is used as an overall measure for the quality of cement and concrete. However, in specific applications like roads and runways flexural strength is more important. The flexural strength of cement mortar / concrete is determined by subjecting a plain prison / beam to flexure under transverse loads. Flexural strength is more sensitive to inadequate curing and type of aggregate since the effects of non-uniform shrinkage adversely affects flexural strength.

What is Impermeability?Impermeability plays a primary role on the durability of concrete, which in turn depends on the water cement ratio. In the air entrained concrete, minute air bubbles are trapped inside, which improves the workability of the mix and also function as minute safety values by providing room for the free water in hardened concrete to escape.

Why there are so many types of special cements?Special cements are usually developed and produced to meet performance and durability requirement in particular.

- Improved strength development.- Increased resistance to chemical attack.- Improved compatibility with reactive – aggregates.- Suitability for use at elevated temperature and pressures.- Suitability for use in special application- Applicability in architectural purposes.

What is sulphate resisting cement?

Sulphate can be found in natural and industrial wastes as well as in soils. Soluble sulphates can react with lime and aluminates present in the hardened Concrete and form respectively gypsum and ettringite. Both reactions involve expansion and consequent concrete deterioration. Sulphate Resisting Cement are characterized by a low C3A content to minimize the risk of ettringite formation.

What is low heat cements?

Hydration reaction of cement develops heat. When cement is used in the Production of mass concrete, temperature gradients generate between core and surface of the mass cause strains and may eventually lead to cracking. Low heat cements have a reduced heat of hydration obtained by altering the chemical composition to have low C3S and low C3A contents. This type of cement is recommended for use for mass concrete production or for large structural sections.

What is leaching resistant cements?

Water with low salinity or a high content of carbon dioxide are capable to dissolve hydration lime presence in concrete and can damage the structure. Leaching resistant cement is produced with low C3S content which has a low development of calcium hydroxide or lime. Their use is suggested in hydraulic works like basins, river barriers and sides etc.

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What is low alkali cement?

Some aggregates may contain forms of reactive amorphous silica. In the presence of water, this can react with the soluble alkali content of cement and form locally an expansive gel that can deteriorate the concrete. In such case cements are produced to have lower content of K2O and Na2O or to add some special pozzolana or slag material which can immediately react with alkali and prevent subsequent reaction with aggregates in the concrete.

What is seawater-resisting cement?Deterioration of the concrete which is in contact with sea water takes place due to chemical attack by MgSO4, mechanical stresses by tidal waves, Crystallization pressure due to deposition of salts in the wind and water line. To absorb all these factors, sea water resisting cements are produced with moderate C3A content or as blended cements.

What is blended cement?

In blended cement production, some portion of the clinker component is replaced with a suitable pozzolana or a slag or limestone or fly ash etc. The use of these mineral will improve the durability and the pore structure of the hardened concrete by lowering its lime content and porosity as a consequence of the enhanced development of calcium silicate hydrates.

What is high early strength and rapid hardening cement?The requirement of these types of cement arise when a rapid strength development is required like if form work has to be removed or reused after a short time or when sufficient strength is required for further construction in slip forming. In all such cases the cement used should develop the required strength as soon as possible. These types of cement are made by grinding of clinker with more fines or by altering the quality of clinker with high C3S and C3A content. Since rapid strength gain is usually associated to high rate of heat development, this kind of cement should not be used in mass concrete or in large structural sections.

What is oil well cement?

Oil well cement is developed for use in oil and gas wells and is designed to set at high temperatures and pressures in well grouting. They can also be used for sealing water wells, waste disposal pits and geothermal wells. In order to meet the above requirements oil well cements are made with special composition or additives use enabling to have low permeability, good bond between rock and casing, to withstand and set under high temperature and pressure and to protect the casing against corrosion and collapse.

What is white cement?

As the name suggests the color of these cement is white and the mechanical properties are comparable to those of gray cement. It is produced with suitable selection of raw materials in which coloring elements like Iron, Chromium and manganese must be kept at the lowest possible level. In order to ease the clinker burning, addition of fluoride is used as a mineraliser. This kind of cement is used mainly for architectural purposes in white or colored concrete

What is Masonry cement?The masonry cements are those, which have low early and late strength, low shrinkage, limited water permeability, high water retention, excellent plasticity and cohesiveness in the

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fresh stage and better workability. This cement is produced by a low to medium clinker content and the use of limestone or other mineral additions and use of air entraining agents.

What is free lime in cement?During clinker formation, all the uncombined lime released from the limestone gets combined with silica, iron and alumina to make silicates, ferrite and aluminate phases. The lime left uncombined is known as free lime and it is responsible for unsoundness in cement if present in excess.

Quality of cement

The quality of cement is judged by its performance in combination with water as a binder in a material and it includes properties like setting behavior, strength development, heat development, volume stability and durability. It is very essential to ensure that the contribution to these properties of the cement is kept at a certain level and with variations as small as possible to meet the demand expressed in the standard specifications and to comply with the wishes and needs of the market.

These factors are associated with the characteristics of the materials being used for the cement viz. Clinker, Gypsum and Additives and how they are altered during grinding and storage.

Raw material components required for the manufacturing of cement

The main raw material components required for the Cement manufacturing are the “ Calcareous ” and “ Argillaeous ” materials. The Calcareous material mainly provide CaO ( Calcium Oxide ) plus some part of other oxides. Wheras Argillaeous material mainly provide SiO2 ( Silicon Di Oxide), Al2O3 ( Aluminium Oxide) and Fe2O3 ( Ferric Oxide).

In case of deficiency in any components then corrective materials rich in SiO2 like Sand, rich in Al2O3 like Bauxite and rich in Fe2O3 like Iron Ore or Laterite are added in Raw mix to meet the specification of Clinker and Cement as per International norms.

In order to regulate the setting time of the Cement, Gypsum – CaSO4.2H2O is added along with Clinker in the final cement grinding.

Typical Analysis of various types of Calcareous material available:

Designation Lime Stone High Grade

Lime Stone

Chalk Sandy

Lime Stone

Marble Calcareous

Marl

Phosphatic

Lime Stone

Dolomitic

Lime

Stone

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Loss % 42.9 42.9 42.26 35.23 43.14 30.6 42.0 37.5

SiO2 % 5.19 0.70 2.38 15.74 1.10 13.8 2.0 16.7

Al2O3 % 0.81 0.68 1.57 0.88 0.51 7.0 0.37 2.1

Fe2O3 % 0.54 0.08 0.56 0.51 0.25 4.55 0.56 0.27

CaO % 48.61 54.54 52.48 44.89 54.33 38.35 52.1 33.60

MgO % 1.90 0.59 0.59 2.54 0.48 1.32 0.76 9.3

SO3 % 0.05 0.25 0.01 0.61 0.04 0.43 0.23 0.08

K2O % 0.33 0.01 0.02 0.21 0.01 0.86 0.08 0.29

Na2O % 0.05 0.16 0.02 0.08 0.01 2.61 0.36 0.40

TiO2 % 0.06 0.01 0.01 0.05 0.02 0.21 0.01 0.07

Cr2O3 % 0.01 0.01 0.01 0.01 0.01 0.02 0.01 0.01

Mn2O3 % 0.05 0.01 0.01 0.03 0.08 0.29 0.06 0.06

P2O5 % 0.04 0.01 0.01 0.10 0.03 0.25 0.98 0.20

Cl % 0.02 0.01 0.03 0.11 0.01 0.04 0.04 0.12

F % 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01

Total % 100.11 99.97 99.97 101.0 100.16 100.34 99.57 100.71

Note: Of the above So3, K2O, Na2O, MgO and Cl components are undesirable for the Cement process and should be as

minimum as possible. As a consequence, Dolomitic Limestone is not desirable.

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Typical Analysis of various types of Argillaceous material:

Designation Shale I Shale II Siliceous

Marl

Clay

stone

Clay Sandy

Shale

Slate

Loss % 3.71 5.3 32.24 13.3 12.5 3.9 5.58

SiO2 % 61.1 64.1 22.7 48.6 45.9 70.8 56.29

Al2O3 % 16.4 13.6 3.9 19.6 23.9 10.9 19.22

Fe2O3 % 7.1 6.1 2.4 9.1 15.5 5.2 4.39

CaO % 1.1 1.8 32.9 2.5 0.72 1.3 0.09

MgO % 2.4 2.9 3.32 1.6 0.33 2.2 1.65

SO3 % 0.01 0.03 0.95 1.78 0.03 0.03 0.72

K2O % 4.8 2.7 0.59 0.54 0.01 2.2 10.85

Na2O % 1.6 1.9 0.19 1.0 0.11 2.0 0.19

TiO2 % 0.76 0.67 0.39 1.2 0.86 0.71 0.46

Cr2O3 % 0.01 0.01 0.01 0.1 0.01 0.01 0.01

Mn2O3 % 0.06 0.05 0.04 0.04 0.20 0.05 0.22

P2O5 % 0.13 0.18 0.03 0.18 0.06 0.17 0.15

Cl % 0.02 0.01 0.01 0.22 0.04 0.01 0.06

F % 0.01 0.01 0.01 0.01 0.01 0.01 0.01

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Total % 99.21 99.36 99.68 99.68 99.88 94.49 100.07

Note: Of the above So3, K2O, Na2O, MgO and Cl components are undesirable for the Cement process

and should be as minimum as possible.

Typical Analysis of Corrective Raw material Components:

Correctives Aluminum – Al2O3 Iron Oxide – Fe2O3 Silicon Di

Oxide – SiO2

Designation BauxiteType

I

BauxiteType

II

BauxiteType

III

Pyrite

Ash

Hematite Umber Iron

Slag

Sand Sand

Stone

Loss % 10.5 29.35 15.4 Nd 3.41 13.99 1.6 0.91 3.69

SiO2 % 4.3 3.3 3.1 7.8 11.0 32.1 21.5 94.7 80.2

Al2O3 % 56.0 56.6 57.6 1.0 3.1 4.3 8.8 2.9 8.37

Fe2O3 % 22.1 9.4 15.8 84.3 77.7 37.5 57.6 0.24 3.26

CaO % Nd 1.15 4.1 0.8 1.2 1.42 3.1 0.35 3.29

MgO % Nd 0.08 0.16 0.45 0.32 1.70 3.6 0.13 0.45

SO3 % Nd 0.24 0.29 11.73 2.1 0.04 2.3 0.01 0.08

K2O % Nd 0.15 0.08 0.09 0.48 0.69 Nd 1.3 1.9

Na2O % Nd 0.1 0.08 0.07 0.07 0.30 Nd 0.2 0.11

TiO2 % 3.0 Nd 2.9 0.16 0.19 3.24 Nd 0.12 0.48

Cr2O3 % Nd Nd 0.02 Nd 0.01 0.24 Nd 0.01 0.01

Mn2O3 % Nd Nd 0.03 0.04 1.31 5.75 Nd 0.03 0.01

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P2O5 % Nd Nd 0.21 Nd 0.02 0.16 Nd 0.01 0.02

Cl % Nd Nd 0.01 Nd 0.02 0.08 Nd 0.01 0.01

F % Nd Nd 0.01 Nd 0.01 0.02 Nd 0.01 0.01

Total % Nd 100.37 99.79 Nd 100.94 101.53 98.50 100.93 98.89

Note: Of the above So3, K2O, Na2O,MgO and Cl components are undesirable for the Cement process and

should be as minimum as possible.

In the Cement Manufacturing Process, the selected raw material components are blended, proportioned and finely ground to a powder form called as Raw Meal, which often have a fineness of 14 – 16 % residue on 90-micron sieve. This material is heated in stages and finally in a rotary Kiln at about 1400 Deg C. In the Kiln after the completion of chemical reactions a sintered mass is produced which is called as Clinker. This semi-finished product is again proportioned with Gypsum and then ground to a powder, which is called as Cement.

The following chemical reactions and phase transformations take place at different temperature ranges.

Temp – Deg C Process Chemical Transformation

< 100 Drying and elimination of Free water from raw

material components

H2O ( Liq) » H2O ( Gas)

100 – 400 Elimination of combined water or physically

absorbed water.

400 – 750 Decomposition of Clay minerals with the

formation of metakaolinite. Removal of

structural H2O.

Al4(OH)8Si4O10 » 2(Al2O3.2SiO2) + 4

H2O

600 – 900 Decomposition of metakaolinite to mixture of

free and reactive oxides

Al2O3.2SiO2 » Al2O3 + 2 SiO2

600 – 1000 Dissociation of limestone and formation of

intermediate products CS and CA

CaCO3 » CaO +

CO23CaO+2SiO2+Al2O3 »

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2(CaO.SiO2) + CaO.Al2O3

800 –1300 Binding of lime by CS and CA with the

formation of C2S, C3A and C4AF.Formation of

belite and liquid phases such as aluminate

and ferrite melt

CaO.SiO2+CaO » 2CaO.SiO2

2CaO+CaO+Al2O3 »

3CaO.Al2O33CaO+CaO+Al2O3+Fe2O

3 » 4CaO.Al2O3.Fe2O3

1250 – 1450 Further binding of Lime by C2S to form

C3S.Completion of reaction and

recrystallization of formed phases.

2CaO.SiO2+CaO » 3CaO.SiO2

Cooling1300 –

1240

Crystallization of liquid phase into mainly

aluminate and ferrite

Common Control factors and their influence on the property of Clinker and Cement

Parameter Empirical

Formula

Limiting

Range

Preferable

Range

Effects

(SM) - Silica

Modulus

S / (A+F) 1.9 – 3.2 2.3 – 2.7 A higher SM will: - Result in harder burning and

High fuel consumption.- Tends to cause unsoundness or

free CaO- Causes difficulty in coating

formation and hence the radiation from Kiln shell will be very high.

- Reduces the service life of refractories.

- Results in slow setting and hardening of the cement.

(AM) Alumina

Modulus.

A / F 1.5 – 2.5 A higher AM will : - Imparts harder burning and

entails higher fuel consumption.- Increases the proportion of C3A

and reduces C4AF.- Increases both C3S and C2S

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- Reduces the liquid phase and Kiln output.

- Tends to render cement quick setting and strong at early ages.

- Increases viscosity of the liquid phase at constant temperature.

- If AM is too low and raw mix is without free silica, clinker sticking and balling is high.

(LSF) – Lime

Saturation

Factor.

100 C / (2.8S

+1.65A +0.35F)

when AM is

>0.64

100C / ( 2.8 S +

1.1 A + 0.7

F )when AM <

0.64

100 (C+0.75

M) / 2.8S + 1.18

A +0.65 F when

M < 2.0

100 ( C +

1.5M) / 2.8 S +

1.8 A+0.65 F

when M > 2.0

0.66 –

1.02

0.92 – 0.96 A higher LSF will: - Makes it difficult to burn the raw

mix.- Tends to produce unsound

cement ie.high amount of free CaO presence.

- Increases the C3S content.- Reduces the C2S content- Causes slow setting with high

early strength.

Free Silica in

different

forms.

Sf 0 – 3 % As low as possible A higher Sf will: - Increases the power and fuel

consumption.- Causes difficulty in coating

formation.- Deteriorates the refractory

lining.- Increases the radiation from the

kiln shell.- Increases the kiln exit gas

temperature.

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Magnesium

Oxide (MgO)

M 0 – 5% 0 – 2 % A higher M will: - Reduces viscosity and surface

tension of clinker liquid and increase ionic mobility.

- Favors the dissolution of C2S and free CaO at higher temperature and lets C3S forms more quickly.

- Tends to ball easily in the burning zone, which affects the Kiln operation.

- Leads to unsoundness by forming periclase crystals when M > 2.0%

- Increases C3S and melt but has no effect on C2S(M < 2 %)

- Volume instability when 2>M>6

Titanium

Oxide (TiO2)

TiO2 0 – 4% 1.5 – 2.0% A higher TiO2 will: - Results in sharp reduction in C3S

content with equal gain in C3S content and appreciable variations in other phases.

- Reduces viscosity and surface tension of the melt.

- Reduces grain sizes of alite and belite.

- Causes slower setting and lower early strength.

- Forms darker color clinker.

Manganese

Oxide

Mn2O3 0 – 4% 1.5 – 2.0 % A higher content will: - Reduces the viscosity of the

melt.- Reduces the size of the alite

crystals.- Reduces early strength.

Strontium

Oxide

SrO 0 – 4 % 0.5 – 1.0 % A higher content will: 

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- Accelerates the combination reaction of CaO in solid phase.

- Lowers the apperance temperature of the liquid.

- Decreases hydraulic strength.- Tends to release free CaO by the

destruction of C3S.

Chromium

Oxide

Cr2O3 0 – 2 % 0.3 – 0.5 % A higher content will: - Reduces viscosity and surface

tension of the clinker liquid.- Forms alite rapidly and increases

its crystals.- Decomposes C3S into CaO free

and C2S.- Increases the stability of A and

decreases that of F.- Increases the initial hydraulic

activity.

Alkalies K2O + Na2O 0 – 1 % 0.2 – 0.3 % A higher content will: - Improves the burnability at lower

temperature and deteriorates at higher temperature.

- Increases liquid and coating formation.

- Lowers the solubility of CaO in the melt.

- Breaks down the alite and belite phases.

- Creates operational problems like coating and jamming in preheaters.

- Will lead to expansion when total alkali level > 0.60% in cement.

Sulfur

compounds

Su 0 – 4 % 0.5 – 2.0 % A higher content will: - Acts as an effective mineralizer

and modifier of the alkali – recycle by forming less volatile

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compounds. - Lowers the appearance

temperature of liquid phase by 100 Deg C, decreases its viscosity and surface tension and increases ionic mobility of oxides.

- Increases belite formation.- Decomposes alite at 1250 DegC

if high alkali sulphate are present.

- When SO3 . 2.5 – 4 %, causes sulphate expansion.

- Improves burning of raw mix at lower temperature and deterioate the same at higher temperatures.

- Decreases hydraulic and mechanical strength.

Phosphorous

Pentoxide

P2O5 0 – 1 % 0.3 – 0.5 % A higher content will: - Accelerates the clinkerization

reaction.- Reduces the intensity of internal

cycle.- Reduces early strength.- Reduces C3S content.

Fluoride F 0 – 0.6 % 0 .03 – 0.08 % A higher content will: - Lowers the temperature of C3S

formation.- Decreases the mechanical

strength of the clinker.

Chloride Cl 0 – 0.6 % 0 – 0.015% A higher content will: - Operational and process related

problems expected.- Increases liquid formation and

melting point of the absorbed phase is drastically changed.

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- A bypass system is required if value >0.015%

Typical Analysis of Gypsum:

Designation Gypsum I Gypsum II

Loss % 22.30 12.80

SiO2 % 1.30 9.20

Al2O3 % 0.71 2.60

Fe2O3 % 0.30 0.95

CaO % 30.60 30.30

MgO % 0.05 0.50

SO3 % 45.50 37.20

K2O % 0.08 1.18

Na2O % 0.20 0.97

TiO2 % 0.01 0.88

Cr2O3 % 0.01 0.16

Mn2O3 % Nd 0.64

P2O5 % Nd 1.52

Cl % Nd 0.16

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F % Nd 0.35

Total % 101.06 99.61

Based on the availability of different types of Raw Material components, a composite Raw Mix design to be made ( Raw Meal )which should have the following resultant chemical composition. With this composition high quality Type I OPC - clinker can be manufactured which will have the composition as mentioned in the table below.

Parameters Raw Meal Composition Clinker Quality

SiO2 % 13.6 – 14.2 21.0 – 22.0

Al2O3 % 3.2 – 3.6 4.75 – 5.25

Fe2O3 % 2.2 – 2.6 3.60 – 4.0

CaO % 43.0 – 43.80 65.0 – 67.0

MgO % 0.60 – 1.20 1.20 – 1.60

K2O % 0.15 – 0.25 0.60 – 0.80

Na2O % 0.03 – 0.06 0.12 – 0.22

SO3 % 0.03 – 0.06 0.30 – 0.60

Chlorides % 0.008 – 0.02 0.01 – 0.03

Loss On Ignition % 35.0 – 36.0 0.15 – 0.35

Lime Saturation Factor 96 + / - 1 95 +/- 1

Silica Modulus 2.45 +/- 0.10 2.50 +/- 0.10

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Alumina Modulus 1.45 +/- 0.05 1.4 +/- 0.05

Tri Calcium Silicates – C3S NA 60 +/- 2

Di Calcium Silicates – C2S NA 18 +/- 2

Tri Calcium Aluminate – C3A NA 7 +/- 1

Tetra Calcium Alumino Ferrite –

C4AF

NA 12 +/-1

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