Cement

A powder substance made by calcining lime and clay mixed with water to form mortar or mixed with sand, gravel and water to make concrete is known as cement.

Raw materials

Lime (CaO), silica (SiO₂), Alumina (Al₂O₃), Iron oxide (Fe₂O₃), magnesium oxide (MgO), sulphur trioxide (SO₃), alkalies (K₂O, Na₂O) etc.

Main steps in cement production

1. Raw material extraction / Quarry

Raw material of cement such as limestone, sand and clay, alumina are extracted from quarries by blasting, drilling or ripping using heavy machinery.

2. Crushing

Then the raw materials are crushed in a rotating cylindrical ball so that the primary crusher reduces first to 6 inches and reduced them by a secondary crusher to 3 inches.

3. Grinding

The crushed ore is mixed either in dry or wet ways and then grounded and then made homogeneous by means of compressed gas in grinding mill. The resulting material is known as slurry having 35–40% water.

4. Heating

Slurry is then introduced in a rotary kiln with the help of a “hopper”. The rotary kiln consists of a huge cylinder made of steel and lined with firebricks. In a rotary kiln the slurry is then passed through different zones of temperature. The whole process in kiln is completed in 2 to 3 hrs.

i) Preheating zone

In this zone the temp is kept to 500°C and usually the moisture is removed and clay is broken into silica, aluminium and iron oxide.

ii) Decomposition zone

Temperature is raised up to 800°C. In this zone limestone decomposes into quick lime and CO₂.

iii) Burning zone

In this zone temp is maintained up to 1250°C and the inside product in the above zone combines together and form respective silicate, aluminate and ferrite.

iv) Cooling zone

This is a last stage where the whole assembly is cooled upto 150–200°C.

5. Final grinding

The product which is obtained from rotary kiln is called clinker. The cooled clinker collected in small funnels and sent into mills. The clinker is grinded into powder in a ball mill along with 2–3% powdered gypsum to decrease the setting time of cement so that cement is adequately hardened.

6. Storage and packaging

The grinded cement is stored in silos from which it is marketed either in container load or 50 kg bags.

Some important terms

Marl

Limestone with admixture of silica, clay substance and iron oxide is called marl.

Corrective ingredients

The essential chemical component adding in the cement to make required amount of cement is known as corrective ingredients or additives. Eg: sand, high silica, clay etc.

Slurry

A mixture of raw materials and water is called slurry.

Clinker

The fused product of aluminate and silicate of calcium in the form of hard and small stone obtained by fusing limestone and clay is called clinker.

Flow sheet diagram of Portland cement

Types of cement

Cement is primarily characterized into two types:

1. Hydraulic cement
2. Non-hydraulic cement

1. Hydraulic cement

Those cement which hardens in the presence of water because of hydration is called hydraulic cement. Portland cement is the best example of it.

2. Non-hydraulic cement

This cement which doesn’t harden underwater is called non-hydraulic cement.

Differentiate between ordinary Portland cement and Pozzolana Portland cement

Quality control of cement

X-ray fluorescence (XRF) spectrometer, flame photometer and X-ray diffraction (XRD) spectrometer instrumentation can provide complete quality control of clinker and cement.

Flow chart of paper production

Stages in production of pulp and paper

1. Timbering

Timber comes from well managed forests where more trees are planted. The quality of the paper depends upon the quality of the timber.

2. De-barking

It is the process of removing the bark of trees. The bark is stripped/removed from the logs by hydraulic bark remover methods to make the pulp free from bark and dirt. Stripped bark used for fuel or soil enrichment.

3. Chipping

Stripped timber are chipped into flat chips of size 2–5 cm by knives in a massive chipping machine. Chips are then stored in huge bins temporarily.

4. Pulping

The process of converting pulp from the fibre are called pulping. It is carried out in one or more of the following process.

a) Chemical pulping

Chips from the storage bins are fed into the digester. The wood chips are then cooked to remove lignin. It is carried out in two process:

i) Sulfate process (Kraft)

It is an alkaline process in which the pulpwood is cooked in hot mixture of water, caustic soda and sodium sulphide at 170–180°C and 10 atm pressure for 2–5 hrs.

ii) Sulfite process

It is an acidic process of production of pure fibre or pulp from wood chip.

b) Mechanical pulping

Rotating steel discs with teeth are used to tear wood parts in mechanical pulping.

c) Hydropulping

The wood fibres are brought into the circular tank containing water. It has a very powerful agitator at the bottom which breaks up the bales into small pieces.

5) Blend chest

Chemicals can be added to obtain the required characteristics of the paper. Dyes are also added to get colour paper.

6) Waste paper

Waste paper is collected from waste (60–62%) paper bank and commercial dumps. It represents 67% of raw materials; paper not suitable for recycling is removed.

7) De-inking

Before the printed paper can be recycled, the ink needs to be removed. It is done by washing and floatation.

8) Refining

This is where the cellulose fibre passes through a refining process. Cellulose is stiff and inflexible before refining.

9) Screening and cleaning

Pulps contain undesirable fibrous and non-fibrous materials which should be removed. Cleaning involves removing small particles of dirt and grit using rotating screens and centrifugal cleaner.

10) Papermaking machine

A slurry of fibre is drained to create a continuous paper web. After it, the wet web passes through the press section to remove excess water and then the press web passes through a heated drying section to obtain dry and quality paper.

Factor affecting quality of paper

• Raw material quality and composition
• Nature of pulp
• Process of paper formation with finishing and converting process applied

Spectrophotometer

Characteristics of paper

• Brightness
• Finish
• Sizing
• Strength
• Clarity, opacity and transparency

Challenge in establishing paper industry

• High cost of raw material
• Lack of power supply
• Lack of skilled manpower
• Use of primitive technology

Bhrikuti pulp and paper Nepal limited was the first paper company in Nepal and was established in Gaindakot municipality in 1985.

Quality control of paper: Spectrophotometer

Brightness, whiteness, opacity and colour consistency.

Sulpha drugs

Sulpha drugs are the member of a group of synthetic antibiotics containing the sulfonamide infections.

Drug addiction

Drug addiction is a disease that affects a person brain and behaviour and leads to an inability to the use of legal or illegal drug or medication.

Pesticides

Those chemical substances which are used to kill pests are called pesticides. Pesticides are grouped according to the types of pests which they kill or control.

1. Insecticides: kill insects. Eg: DDT, BHC.
2. Herbicides: kill plants. Eg: 2,4-D / 2,4-dichlorophenoxyacetic acid.
3. Rodenticides: kill rodents (rats and mice). Eg: zinc phosphide (Zn₃P₂).
4. Bactericides: kills bacteria. Eg: oxytetracycline hydrochloride.
5. Fungicides: kills fungi. Eg: EUSBU soln. [as written in source]

c) Antibiotics

The chemical substance produced by microorganism that either inhibit or kill the pathogen are called antibiotics.

Eg: penicillin, penicillium notatum, amoxicillin etc.

Antiseptic and disinfectants

Those drugs which prevent the growth of microorganism or kill the microorganisms in injured tissues is called antiseptic.

Eg: phenol and its derivatives, 0.1% HgCl soln, 1% KMnO₄ soln etc.

Disinfectants: The chemical substances which are used to kill microorganism but they cannot be applied on living tissue are called disinfectants. Eg: chlorine water, phenol 1%, etc.

Anaesthetics

The chemicals which cause the loss of sensation of a part of the body or unconsciousness to the patients are anaesthetics. Eg: chloroform, nitrous oxide etc.

Antacid

The drug used to neutralize excess acid present in gastric juice is known as antacid.

Tranquilizer drugs

Drugs that are used to reduce anxiety, fear, tension and related state of mental disturbance are called tranquilizers. Eg: Luminal, Equanil etc.

d) Disperse dyes

They are insoluble in water and disperse in water in colloidal form.

e) Azoic / Engrain dyes

In this method of dyeing, the water insoluble azo dye is produced in the fabric itself.

Drugs (medicine)

Drugs are the chemicals which are used to modify or explore the physiological systems or pathological states for the benefit of the recipient.

Characteristics

• It should be non-toxic.
• It should not have any side effect.
• It shouldn’t disturb the physiology of the host.

Types

a) Antipyretics: The drugs which are used to reduce the body temperature in case of high fever. Eg: aspirin, paracetamol etc.

b) Analgesics: The drugs that reduce pain in body of patients without loss of consciousness are called analgesics. It is habit forming, narcotic drugs and narcotics drugs. It is also called pain killer. Eg: paracetamol and aspirin.

f) Anthraquinone

Alizarin red.

3) On the basis of application

a) Direct dyes

Those dyes which are directly applied to the fabrics is called direct dyes. Eg: Martius yellow etc.

b) Vat dyes

These are water insoluble dyes and are used in reduced colourless soluble form by treating with sodium bisulphite. Eg: Indigo.

c) Mordant dyes

Those dyes which are applied to the fabric after treating it with a metal is called mordant dye. Eg: Alizarin.

c) Nitro / Nitroso dyes

Nitro group (−N=O) as chromophore. Eg: picric acid.

d) Triphenyl methane dyes / Triaryl methane dyes

Containing triphenyl methane as chromophore.

Eg: malachite green.

e) Indigo dyes

Containing carbonyl chromophore.

Eg: Indigo.

b) Synthetic dyes

The dyes which are prepared artificially in the lab are called artificial or synthetic dyes. Eg: phenolphthalein, p-aminoazobenzene.

2) On the basis of chemical structure

a) Azo dyes

A dyes which contain nitrogen in the azo group (−N=N−) is azo dye.

• p-hydroxyazobenzene
• p-aminoazobenzene
• Methyl orange

b) Phthalein dyes

Phthalein anhydride as chromophore unit.

Eg: phenolphthalein.

c) Auxochromes

The groups or atoms which intensify the colour of the chromogens are called auxochromes. −NH₂, −NHR, −NR₂ are basic auxochromes while −OH, −COOH, −SO₃H are acidic auxochromes.

Example: p-hydroxyazobenzene (azo dye)

Classification of dyes

1) On the basis of occurrence

a) Natural dyes

The dyes which are obtained from natural sources like plants are called natural dyes.

Eg: saffron, indigo, alizarin etc.

Alizarin (Turkey red dye).

Dyes

Those substances or the compounds which are used for imparting colour to textile, silk, wool, foodstuffs, leather etc. are known as dyes.

Structural components of a dye

a) Chromophores

The unsaturated groups which are responsible for the imparting colour in textile are called chromophores. Due to chromophore such substance are linked (through) multiple bonds due to which an organic compound appears coloured.

Eg: −N=N−, −NO₂, −N=O, −N=N−, C=O (carbonyl), C=C (alkene), quinonoid.

b) Chromogens

The compound which contains chromophore are called chromogens.

Eg: azobenzene.

e) Orlon

It is also an addition polymer that is manufactured from vinyl cyanide. After heated under pressure in presence of catalysts FeSO₄ and H₂O₂.

vinyl cyanide → Orlon

Uses: It is used for making bathing suits, sweaters and other clothing.

f) Rubbers

Polyisoprene (natural rubber, neoprene) etc. are rubber used for making toys, tyres, sports goods etc.

isoprene → polyisoprene

2) Condensation polymer

a) Terylene (Dacron) (less imp)

It is prepared by heating ethylene glycol with terephthalic acid.

c) Polystyrene

It is also addition homo polymer of styrene. It is prepared by heating styrene in presence of organic peroxide (dibenzoyl peroxide).

Uses: It is used to make food container, comb, toys etc.

d) Teflon (PTFE)

It is the addition polymer of tetrafluoro ethene and is called polytetrafluoroethylene (PTFE). It is manufactured by heating tetrafluoroethene in presence of catalyst ferrous sulphate and H₂O₂.

tetrafluoroethylene → polytetrafluoroethylene (Teflon)

Uses: It is used in making gasket, valves, tooths used in water for electrical items etc.

They have density 0.901–0.905 g/cc. It is used for making pipes, buckets, electrical insulator, bottle etc.

ii) High density polythene (HDPE)

They have density 0.95–0.97 g/cc.

Uses: buckets, tanks, pipes.

Imp: Ziegler-Natta → Triethyl aluminium and titanium chloride.

b) Polyvinyl chloride (PVC)

It is the polymerization product of vinyl chloride. It is the homopolymer of vinyl chloride. It is prepared by heating vinyl chloride in presence of dibenzoyl peroxide.

vinyl chloride → polyvinylchloride

Uses: It is used in the manufacture of raincoats, handbags, blood bags, pipes, cable insulator etc.

Force are called elastomers. Eg: vulcanized rubber.

b) Fibres

The polymers in which the molecular chains are held together by means of very strong intermolecular force are called fibres. Eg: nylon 66, Orlon, Terylene polymers etc.

5) On the basis of action of heat

a) Thermoplastics

The polymers or the plastics which become soft on heating and can be moulded and remoulded into different shapes are called thermoplastics. Eg: polythene, PVC, polystyrene etc.

b) Thermosetting plastics

The polymers which don’t become soft on heating and cannot be moulded or remoulded into different shape is called thermosetting plastics. Eg: bakelite, glyptal resins etc.

Manufacture of some synthetic polymers

1) Addition polymers (chain)

a) Polythene

It is the homopolymer of ethene and it is two types:

i) Low density polythene (LDPE)

2) On the basis of monomers

a) Homopolymer

Those polymers which are made of only one type of monomer unit are called homopolymers.

Eg: polythene, teflon, PVC, orlon etc.

b) Copolymer

Those polymers which are made of more than one type of monomers in their molecules are called copolymer. Eg: Bakelite, nylon−6,6, Dacron etc.

3) On the basis of synthesis

a) Addition polymers

The polymers in which a large no of monomer molecules are added together to form polymer unit are called addition polymers. Eg: polythene, teflon, PVC etc.

b) Condensation polymer

The polymers formed by condensation between the monomer molecules are called condensation polymers. Eg: nylon, bakelite, nylon 66 etc.

4) On the basis of molecular forces

a) Elastomers

The polymers in which the molecular chains are held together by means of very weak intermolecular …

Applied chemistry

Polymers

Polymers are very large molecules that are formed by the combination of many smaller molecules and the phenomenon is known as polymerization. Teflon, nylon, polythene, PVC, plastic are some of the commonly used polymers.

Classification of polymers

1) On the basis of origin

a) Natural polymers

The polymers which are synthesized in nature are called natural polymer. Eg: proteins, starch, cellulose, rubber, resins, wool etc.

Natural rubber obtained from the latex of rubber plant is polymer of isoprene.

Isoprene / 2−methylbuta−1,3−diene

b) Synthetic polymers (artificial)

Those polymers which are synthesized from different compounds are called synthetic polymers. Eg: nylon, teflon, PVC, polythene etc.