Water Softening Methods PDF

Water Softening Methods 12/12/2021 1  Water Softening Methods ❖ Zeolite (Permutit process) ❖ Ion-exchange ❖ Mixed bed ion-exchange ❖ Reverse Osmosis 12/12/2021 2  Permutit or Zeolite Process o Zeolite is hydrated sodium al...

Water Softening Methods 12/12/2021 1  Water Softening Methods ❖ Zeolite (Permutit process) ❖ Ion-exchange ❖ Mixed bed ion-exchange ❖ Reverse Osmosis 12/12/2021 2  Permutit or Zeolite Process o Zeolite is hydrated sodium aluminium silicate having a general formula, Na2OAl2O3.xSiO2.yH2O. o It exchanges Na+ ions for Ca2+ and Mg2+ ions. o Common Zeolite is Na2OAl2O3.3SiO2.2H2O known as natrolith. o Other gluconites, green sand (iron potassium phyllosilicate with characteristic green colour, a mineral containing Glauconite)etc. are used for water softening. o Artificial zeolite used for water softening is Permutit. o These are porous, glassy particles having higher softening capacity compared to green sand. o They are prepared by heating china clay (hydrated aluminium silicate), feldspar (KAlSi3O8-NaAlSi3O8 – CaAl2Si2O8) are a group of rock-forming tectosilicate minerals which make up as much as 60% of the earth’s crust) and soda ash (Na2CO3) 12/12/2021 3 Natural Zeolites: 1. Natrolite - Na2O. Al2O3 4SiO2.2H 2O 2. Laumontite - CaO. Al2O3 4SiO2.4H 2O 3. Harmotome - (BaO.K2O). Al2O3 5SiO2.5H 2O - Capable of exchanging its Na ions 12/12/2021 4  Permutit or Zeolite Process o Method of softening: Na2Ze + Ca(HCO3)2 2 NaHCO3+CaZe Na2Ze + Mg(HCO3)2 2 NaHCO3+ MgZe Na2Ze + CaSO4 2 Na2SO4+CaZe Na2Ze + CaCl2 2 NaCl+CaZe o Regeneration of Zeolite: CaZe (or) MgZe + 2 NaCl Na2Ze + CaCl2 or MgCl2 Brine solution 12/12/2021 5 12/12/2021 6 12/12/2021 7  Zeolite Process o Advantages: o Residual hardness of water is about 10 ppm only o Equipment is small and easy to handle o Time required for softening of water is small o No sludge formation and the process is clean o Zeolite can be regenerated easily using brine solution o Any type of hardness can be removed without any modifications to the process o Disadvantages: o Coloured water or water containing suspended impurities cannot be used without filtration o Water containing acidic pH cannot be used for softening since acid will destroy zeolite. 12/12/2021 8  Ion-Exchange Process o Ion-exchange resins are cross linked long chain polymers with microporous structure o Functional groups present are responsible for ion-exchange properties o Acidic functional groups (-COOH, -SO3H etc.) exchange H+ for cations & o Basic functional groups (-NH2, =NH etc.) exchange OH- for anions. A. Cation-exchange Resins(RH+): - Styrene divinyl benzene copolymers - When sulphonated, capable of exchange H+ 12/12/2021 9  Ion-Exchange Process B. Anion-exchange resins (R’OH): - Styrene divinyl benzene copolymers or amine formaldehyde copolymers with NH2, QN+, QP+, QS+, groups. - On alkali treatment, capable of exchange of OH- 12/12/2021 10 12/12/2021 11 12/12/2021 12  Ion-Exchange Process The Process of Ion-exchange is: 2 RH+ + Ca2+/Mg2+ R2Ca2+/R2Mg2+ + 2 H+ (Cation exchange) R’OH- + Cl- R’+ Cl- + OH- (anion exchange) 2 R’OH- + SO42- R’2 SO42- + 2 OH- (anion exchange) 2 R’OH- + CO32- R’2 CO32- + 2 OH- (anion exchange) Finally, H+ + OH- H2 O Regeneration of exhausted resins: Saturated resins are regenerated: R2Ca2+/R2Mg2+ + 2H+ 2 RH+ + Ca2+/Mg2+ (cation) (Strong acid) (washings) R’2 SO42- + 2 OH- 2 R’OH- + SO42- (Strong base) 12/12/2021 (washings) 13  Ion-Exchange Process Note: Hard water should be first passed through the cation exchanger and then Anion exchanger to avoid hydroxides of Ca2+ and Mg2+ getting formed 12/12/2021 14 12/12/2021 15  Mixed Bed Deionizer 12/12/2021 16 12/12/2021 17  Advantages & Disadvantages of ion-exchange process o Advantages: - Can be used for highly acid and highly alkaline water - Residual hardness of water is as low as 2 ppm. - Very good for treating water for high pressure boilers o Disadvantages: - Expensive equipment and chemicals - Turbidity of water should be < 10 ppm. Otherwise output will reduce; turbidity needs to be coagulated before treatment. - Needs skilled labour 12/12/2021 18  Reverse Osmosis oWhen two solutions of unequal concentrations are separated by a Semipermeable membrane, solvent will flow from lower conc. to higher conc. oThis phenomenon can be reversed (solvent flow reversed) by applying hydrostatic pressure on the concentrated side oIn reverse osmosis, pressure of 15-40 kg/cm2 is applied to sea water. oThe water gets forced through the semipermeable membrane leaving behind the dissolved solids. 12/12/2021 19 12/12/2021 20  Module VI FUELS & COMBUSTION INTRODUCTION AND SOLID FUELS  Introduction Most chemical fuels are found in nature in the form of crude oil, natural gas, and coal. These fuels are called fossil fuels because they have been formed by the decay of vegetable and animal matter over millions of years under conditions of high pressure and temperature and absence of oxygen..  FUELS Fuel is a combustible substance which when burnt in oxygen or air, produces significant amount of heat which can be economically used for domestic and industrial purposes for generating power. In the process of combustion, the chemical energy of fuel is converted into heat energy. Fuel + Air/oxidizer  Products of combustion + Energy  Classification of Fuels Based on origin Natural / Primary Fuels Synthetic / Derived Fuels Based on physical state Based on physical state Liquid Liquid Solid Fuels Gaseous Solid Fuels Gaseous Fuels Fuels Fuels Fuels Examples Examples Examples Examples Examples Oils from Examples Charcoal Producer gas Petroleum Natural petroleum Wood Coke Water gas or Gas distillation Coal Briquettes Coal gas Crude oil Coal tar, Oil shale Shale-oil Alcohols  CHARACTERISTICS OF GOOD FUEL 1. HIGH CALORIFIC VALUE: A good fuel should have high calorific value i.e. it should produce large amount of heat on burning. CALORIFIC VALUE The quantity of heat liberated by the complete combustion of unit weight (1gm or 1kg) of the fuel in air or oxygen. Calorific Values of Important Fuels FUELS CALORIFIC VALUES (kilo joules per kg) Cow dung cake 6000 - 8000 Wood 17000 - 22000 Coal 25000 - 33000 Petrol 45000 Kerosene 45000 Methane 50000 CNG 50000 LPG 55000 Biogas 35000 - 40000 Hydrogen 150000 2. MODERATE IGNITION TEMPERATURE Ignition temperature: Lowest temperature to which fuel must be preheated so that it starts burning smoothly. If ignition temperature is low, the fuel catches fire easily. Low ignition temperature is dangerous for storage and transportation of fuel. High temperature causes difficulty in ignite. So, a good fuel should have moderate ignition temperature. IGNITION TEMPERATURES OF SELECTED FUELS Substance Ignition Temp Hydrogen 1085⁰F Carbon 925⁰F Sulphur 450⁰F Coal 750⁰F Wood 450⁰F Kerosene 490⁰F 3. LOW MOISTURE CONTENT A good fuel should have low moisture content as moisture content reduces the calorific value. 4. LOW NON-COMBUSTIBLE MATTER CONTENT A good fuel should have low contents of non-combustible material as non-combustible matter is left in form of ash which decreases the calorific value of fuel 5. MODERATE RATE OF COMBUSTION The temperature of combustion of fuel depends upon the rate of combustion. If the rate of combustion is low, then required high temperature may not be reached soon. On the other hand ,too high combustion rate causes high temperature very quickly. 6. MINIMUM SMOKE AND NON-POISONOUS GASES On burning, fuel should not give out objectionable and poisonous gases. In other words, gaseous products should not pollute the atmosphere. Examples: CO- Poisonous or toxic gas SO2, SO3, NOx - responsible for acid rain CO2 - results in global warming 7.CHEAP A good fuel should be cheap and readily available. 8. EASY TRANSPORTATION A good fuel should be easy to handle and transport at low cost  Calorific value of fuels The most important property of fuel to be taken into account is its calorific value or the capacity to supply heat. The calorific value of a fuel can be defined as "the total quantity of heat liberated when a unit mass or volume of the fuel is burnt completely". Units are Calorie/ Kilocalorie - Calorie is the amount of heat required to raise the temperature of one gram of water through one degree centigrade. Determination of Calorific Value Bomb calorimeter Higher or Gross Calorific Value (HCV or GCV) Usually, all fuels contain some hydrogen and when the calorific value of hydrogen containing fuel is determined experimentally, the hydrogen is converted to steam. If the products of combustion are condensed to room temperature (15C or 60F), the latent heat of condensation of steam also gets included in the measured heat, which is then called "higher or gross calorific value". So gross or higher calorific value may be defined as "the total amount of heat produced when one unit mass/volume of the fuel has been burnt completely and the products of combustion have been cooled to room temperature".  Lower or Net Calorific Value In actual use of fuel, the water vapour and moisture etc are not condensed and escapes as such along with hot combustion gases. Hence a lesser amount of heat is available. So, net or lower calorific value may be defined as "the net heat produced when unit mass / volume of the fuel is burnt completely and the products are permitted to escape". Net or lower calorific value can be found from GCV value NCV = GCV - Latent heat of water vapour formed = GCV - Mass of hydrogen x 9 x latent heat of steam 1 part by mass of hydrogen produces 9 parts by mass of water. The latent heat of steam is 587 k cal / kg or 1060 B. Th. U. / lb of water vapour formed at room temperature. (ie 15C).  Calculation m = mass of fuel pellet (g) W = mass of water in the calorimeter (g) w = water equivalent of calorimeter (g) t1 = initial temperature of calorimeter. t2 = final temperature of calorimeter. HCV = gross calorific value of fuel.  Water Equivalent of the calorimeter is determined by burning a fuel of known calorific value (benzoic acid (HCV = 6,325 kcal/kg) and naphthalene (HCV = 9,688 kcal/kg) If H is the percentage of hydrogen in fuel, the mass of water produced from 1 g of fuel = (9/100)×H = 0.09 H Heat taken by water in forming steam = 0.09 H× 587 cal (latent heat of steam = 587 cal/kg) LCV = HCV – Latent heat of water formed 16 1. 0.72 gram of a fuel containing 80% carbon, when burnt in a bomb calorimeter, increased the temperature of water from 27.3o to 29.1oC. If the calorimeter contains 250 grams of water and its water equivalents is 150 grams, calculate the HCV of the fuel. Give your answer in KJ/Kg. Solution. Here x= 0.72 g, W = 250g, t1 = 27.3oC, t2 = 29.1oC. HCV of fuel (L) = (W + w) (t1 - t2) Kcal/kg x = (250 + 150) × (29.1-27.3) kcal/kg = 1,000 × 4.2 kJ/Kg = 4,200 kJ/kg 0.72 17 2. On burning 0.83 of a solid fuel in a bomb calorimeter , the temperature of 3,500g of water increased from 26.5oC to 29.2oC. Water equivalent of calorimeter and latent heat of steam are 385.0g of and 587.0 cal/g respectively. If the fuel contains 0.7% hydrogen, calculate its gross and net calorific value. Solution. Here wt. of fuel (x) = 0.83 g of ; wt of water (W) = 3,500 g; water equivalent of calorimeter (w) = 385 g ; (t2 - t) = (29.2oC - 26.5oC) = 2.7oC ; percentage of hydrogen (H) = 0.7% ; latent heat of steam = 587 cal/g Gross calorific value = (W + w) (t1 - t2) cal/g x = (3,500 +385) × 2.7 = 12,638 cal/g 0.83 NCV = [GCV – 0.09 H × 587] = (12,63 8– 0.09 × 0.7 × 587) cal/g = (12,638 – 37) cal/g = 12,601 cal/g 18 1. Fuse wire correction 2. Acid correction 3. Cooling correction 19  Corrections Fuse wire correction: Heat liberated during sparking should be subtracted from calorific value 20 Acid correction: Fuels containing Sulphur and Nitrogen if oxidized, the heats of formation of H2SO4 and HNO3 should be subtracted (as the acid formations are exothermic reactions) 21 22 Cooling correction: The rate of cooling of the calorimeter from maximum temperature to room temperature is noted. From this rate of cooling (i.e., dt°/min) and the actual time taken for cooling (X min) then correction (dt × X) is called cooling correction and is added to the (t2. t1) term. 23  (W+w) (t2-t1+Cooling Correction) – (Acid + Fuse Correction) GCV = Mass of the fuel (x) 24 3. A sample of coal contains C =93%; H =6% and ash = 1%. The following data were obtained when the above coal was tested in bomb calorimeter. Wt. of coal burnt =0.92g Wt. of water taken =550g Water equivalent of calorimeter =2,200g Rise in temperature =2.42 oC Fuse wire correction =10.0 cal Acid correction =50.0 cal Calculate gross and net calorific value of the coal, assuming the latent heat of condensation of steam as 580 cal/g. Solution: Wt. of coal sample (x) = 0.92 g; wt. of water (W) =550 g; water equivalent of calorimeter (w) = 2,200g; temperature rise (t2-t1) = 2.42 oC; acid correction = 50.0cal; fuse wire correction = 10.0 cal; latent heat of steam = 580 cal/g; percentage of H =6% 25 GCV = (W + w) (t1 - t2) –[acid+fuse corrections] x = (550+2,200) × 2.42 – [50+10] cal 0.92g = 7,168.5 cal/g. NCV = [GCV – 0.09 H × latent heat steam] = (7168.5 – 0.09 × 6 × 580) cal/g = 6855.3 cal/g 26  Boy’s Calorimeter It is used for measuring the calorific value of gaseous (or) liquid fuels. Principle A known volume of gaseous fuel sample is burnt in the combustion chamber of a Boy’s calorimeter. The released heat is quantitatively absorbed by cooling water, circulated through copper coils surrounding the combustion chamber. The mass of cooling water and its rise in temperature are noted. The mass of water produced by condensation of steam is calculated. The calorific value of the fuel sample is then calculated from these data. 27 Construction Boy‘s calorimeter consists of a combustion chamber surrounded by water tube with two thermometers T1 and T2 attached. There is a burner in the chamber, which is connected to a gas tube. Working  A known volume of water is passed through the tubes.  The initial temperature is noted when the two thermometers show the same constant temperature.  A known volume of the gas (measured using a meter) is passed through the tube and burnt in the combustion chamber.  The heat liberated is absorbed by the water in the tubes.  The final temperature of water is noted.  The gaseous products are cooled and condensed into a measuring jar. 28 29 Calculation  Knocking In an internal combustion engine, a mixture of gasoline vapour and air is used as a fuel. After the initiation of the combustion reaction by spark in the cylinder, the flame should spread rapidly and smoothly through the gaseous mixture, thereby the expanding gas drives the piston down the cylinder. The ratio of the gaseous volume in the cylinder at the end of the suction-stroke to the volume at the end of compression-stroke of the piston is known as the 'compression ratio'. The efficiency of an internal combustion engine increases with the compression ratio.  Compression ratio (CR) is defined as the ratio of the cylinder volume (V1) at the end of the suction stroke to the volume (V2) at the end of the compression stroke of the piston. V1 being greater than V2, the CR is >1. The CR indicates the extent of compression of the fuel-air-mixture by the piston. However, successful high compression ratio is dependent on the nature of the constituents present in the gasoline used. In certain circumstances, due to the presence of some constituents in the gasoline used, the rate of oxidation becomes so great that the last portion of the fuel-air mixture gets ignited instantaneously producing an explosive violence, known as 'knocking'. The knocking results in loss of efficiency, since this ultimately decreases the compression ratio.  Chemical structure and knocking The tendency of fuel constituents to knock is in the following order. Straight - chain paraffins > branched - chain paraffins (isoparaffin) > olefins > cyclo paraffins (naphthenes) > aromatics. Octane number The most common way of expressing the knocking characteristics of a combustion engine fuel is by 'octane number', introduced by Edger. It has been found that n- heptance, knocks very badly and hence, its anti-knock value has arbitrarily been given zero.  Octane number Octane number is equal to the percentage by volume of iso-octane (2,2,4-trimethyl pentane) in a mixture of n-heptane and iso-octane having the same knocking tendency compared to the sample of gasoline being tested; Iso-octane has the best antiknocking properties and assigned an octane number of 100 whereas n-heptane has poor antiknocking property and assigned an octane number of zero. The hydrocarbons present influence the knocking properties of gasoline which vary according to the series: straight chain paraffin > branched chain paraffin > olefin > cycloparaffin > aromatics. The fuel which has same knocking tendency with the mixture having 80% iso-octance has octane number 80.  H H H H H H H H C C C C C C C H H H H H H H H n-heptane CH 3 CH 3 C CH 2 CH CH 3 CH 3 CH 3 Isooctane  Improvement of anti-knock characteristics of a fuel The octane number of many otherwise poor fuels can be raised by the addition of tetra ethyl lead (C2H5)4Pb or TEL and diethyl telluride (C2H5)2Te. In motor spirit (Motor fuel) about 0.5ml and in aviation fuel 1.0 - 1.5ml of TEL is added per litre of petrol. TEL is converted into a cloud of finely divided lead and lead oxide particles in the cylinder and these particles react with any hydrocarbon peroxide molecules formed, thereby slowing down the chain oxidation reaction and thus decreasing the chances of any early detonation. However deposit of lead oxide is harmful to the engine life. In order to help the simultaneous elimination of lead oxide formed from the engine, a small amount of ethylene dibromide (or ethylene dichloride) is also added to petrol. The added ethylene dibromide removes lead oxide as volatile lead bromide along with the exhaust gases. The presence of sulphur compounds in petrol reduces the effectiveness of the TEL. TEL is more effective on saturated hydrocarbons than on unsaturated ones.  Other additives Oxidation inhibitors - 2,4 - ditertiary butyl - 4 - methyl phenol. Rust inhibitors - Organic compounds of phosphorus or antimony. Ignition control additives - tricresyl phosphate which suppresses pre-ignition of the fuel due to glowing deposits on spark plug or a hot spot on the cylinder wall.  Diesel Engine Fuels Characteristics of an ideal diesel oil It should have low spontaneous ignition temperature. It should have very little sulphur, aromatic and ash content. The ignition lag should be as short as possible.  Knocking in Diesel Engines In a diesel engine, the fuel is exploded not by a spark, but by the application of heat and pressure. In the cycle of operations of a diesel engine, air is first drawn into the cylinder and compressed. Towards the end of the compression stroke, the fuel (diesel oil) is injected as a finely-divided spray into air in the cylinder heated to about 500C by compression. The oil absorbs the heat from the air and if it attains its ignition temperature the oil ignites spontaneously. The pressure of the gases is further increased by the heat accompanying the ignition of the oil. The piston is pushed by the expanding gases and this constitutes the power stroke. Fuel feed and ignition continue during this down stroke. The fuel injection stops at the exhaust stroke.  Diesel engine fuels consist of longer chain hydrocarbons than internal combustion engine fuels. The main characteristic of diesel engine fuel is that it should easily ignite below compression temperature. There should be as short an induction lag as possible. This means that it is essential that the hydrocarbon molecules in a diesel fuel should be as far as possible the straight-chain ones with a minimum admixture of aromatic and side-chain hydrocarbon molecules. The suitability of a diesel fuel is determined by its cetane value, which is the percentage of hexadecane in a mixture of hexadecane and 2-methyl naphthalene, which has the same ignition characteristics as the diesel fuel sample, under the same set of conditions. The cetane number of a diesel fuel can be raised by the addition of small quantity of certain "pre-ignition dopes" like alkyl nitrites such as ethyl nitrite, iso-amyl nitrite, acetone peroxide.  H H H H C C C H 14 H H H n-Hexadecane (Cetane No. = 100) CH3 2-Methyl naphthalene (Cetane No. = 0)  Ignition quality decreases among hydrocarbons is as follows n-alkanes > naphthalenes > alkenes > branches alkanes > aromatics Cetane number decreases Ignition quality decreases Ignition delay increases  Module 7C CORROSION CONTROL  Spontaneity of Corrosion Metal has natural tendency to go to Thermodynamically stable state Metals (thermodynamically unstable) are usually extracted from ores (thermodynamically stable) through the application of a considerable amount of energy Corrosion (oxidation) Metal Ore (metallic compd) Energy (T.D.Unstable) T.D.Stable Metallurgy (reduction) The energy required to convert ore to metallic state is returned when the metal corrodes to form the original compound. The tendency of metal to release this energy by corrosion, is reflected by the relative positions of pure metals in the electrochemical series.  Rust formation in iron 4Fe + 3O2 + 6H2O → 4Fe(OH)3 Protective coatings oProtective coating provide a physical barrier between the metal and the environment. oThey not only give corrosion protection but also add to the decorative value of the article. oCoatings are broadly divided as: a) Inorganic coatings : metallic and chemical conversion coatings b) Organic coatings : paints, varnishes, enamels, lacquers 4 Protective coatings Metallic coatings: a) Anodic coatings b) Cathodic coatings a) Anodic coatings: o Anodic coatings are given on cathodic metals using metals which are more anodic. o Zinc, aluminium, cadmium coatings on iron are anodic coatings. o If the coating breaks, then a galvanic couple is set up and corrosion rate gets enhanced. o During this process, the anodic coating gets disintegrated but it protects the cathodic base metal. o Hence, the anodic metal sacrifices itself to protect the base metal. o This type of coating is known as galvanisation. 5 Protective coatings Cathodic coatings: o Cathodic coatings are given on anodic metals using metals which are more cathodic. o Coating of tin, chromium, nickel on iron surface are cathodic coatings. o If there is a discontinuity in the coating, then galvanic couple will form with base metal as anode and the coated metal as cathode. o Then the process of corrosion will start by the base metal ions going into solution and the metal deteriorating. o To avoid this, the article is checked and re-plated periodically so that there is no discontinuity in the coating. 6 Protective coatings Methods of metallic coatings: a) Hot dipping b) Metal cladding c) Electroplating d) Electrolessplating e) PVD f) CVD a) Hot dipping: Two types of hot dipping techniques are known: i) Galvanizing: Dipping the base metal iron in molten zinc metal solution ii) Tinning : Dipping the base metal iron in molten tin metal solution. 7  Electroplating o It is a process by which a coating metal is deposited on the base metal by passing direct current through an electrolytic solution, containing the soluble salt of the coating metal. o Electroplating is done for improving a) corrosion resistance b) wear resistance c) chemical resistance d) surface hardness e) appearance o Both ferrous and non-ferrous metals are plated with Ni, Cr, Cu, Zn, Pb, Al, Ag, Au, Sn etc. o Electroplating is mainly used in automobile, aircraft, refrigerator, chemical and electrical appliances etc.  Electroplating Plating bath solution o It is a highly conducting salt solution of the metal which is to be plated. o The level of the plating bath should cover completely the cathode and sufficient area of anode. o It should be good conductor and highly soluble. o It should not undergo hydrolysis, oxidation, reduction and other chemical changes. 9  Electroplating with Nickel on Copper Copper Cathode is reduced Nickel Anode is oxidized (accepts electrons) (gives electrons) Ni2+ ions within solution become attracted to Copper cathode Important Factors of electroplating o Cleaning of the article is essential for strong adherence of the electroplating: - Scraping, grinding, sand blasting, wire brushing, solvent cleaning and acid pickling are used for surface cleaning. - A well cleaned and properly pre treated surface of any material to be electroplated is necessary for obtaining the coating of long life. o Concentration of the electrolyte is another important factor: - Low concentration of metal ions will give uniform coherent deposition. - To maintain low conc. of metal ions, complexing agents are added to the electrolyte. o Thickness of the deposition should be optimised to get a strong and adherent deposition: - For corrosion protection multiple coatings are given to get impervious coating without any discontinuity. - For decorative purpose, thin coating is given. o Current density - Current density is the current per unit area of the article being plated (amps cm-2). - The C.D should be maintained at optimal level to get uniform and adherent deposition. 11  Important Factors of electroplating o Additives to electrolytic bath - Additives to electrolyte are added in small quantities to get strong adherent deposition. - Commonly used additives are gelatin, glue, glycine, boric acid etc. and brighteners for bright plating. o pH of the bath: - For a good electrodeposit, the pH of the bath must be properly maintained. For most plating baths, pH ranges from 4 to 8. o Method of Electroplating: - Method depends upon the type of metal to be electroplated, the size and type of article to be electroplated. - Its main objectives and economics are also considered. 12  Electroless plating Electroless plating, also known as chemical or auto-catalytic plating, is a non- galvanic plating method that involves several simultaneous reactions in an aqueous solution, which occur without the use of external electrical power. The process is a chemical reaction and is autocatalytic. It is mainly different from electroplating by not using external electrical power. The deposition rate is normally 12.5 – 25 um (0.0005 – 0.001 in). The plating thickness tends to be uniform compared to electroplating due to the absence of electric fields and the associated problems in making them uniform. Typically nickel and copper are used in electroless platings. In the case of nickel, the deposits are dense, relatively hard and brittle. Electroless Nickel is not as bright as electroplated, easy to solder and braze, but difficult to weld. Autocatalytic platings are widely used for machine frames, base plates, fixtures, some machine parts where metal-to-metal wear applications are needed and the conventional oils and greases can not be used.  Theory of Autocatalytic Platings Electroless plating is the process of deposition of metal on a catalytical active surface by using suitable reducing agent without using electric current. For example; The electroless plating involving a nickel sulfate bath has the following reaction: NiSO4 + NaH2PO2 + H2O Ni + NaH2PO3 + H2SO4 Copper electroless deposition is done by reduction of alkaline solution containing copper (II) ion Stabilized by EDTA. Here formaldehyde acts as reducing agent. Electroless Plating Electroplating  CONTROL OF CORROSION BY MODIFYING THE SURFACE Modifying the surface by application of protective coatings. The coated surface isolates the underlying metal from the corroding environment. The coating applied must be chemically inert to the environment under particular condition of temp. and press. Protective coatings are Metallic coatings, Non-metallic coatings and Organic coatings  Physical Vapour Deposition o This is a process of depositing some material by atom by atom or molecule by molecule or ion by ion. Applications: 1. This process is widely used to produce decorative coatings on plastic parts those are resembling shiny metal. 2. Many automobile parts are plastic with a PVD coating of aluminium. 3. A lacquer coating is applied over the decorative coating to provide corrosion protection. 4. This process is also used to apply relatively thick (1mm) coatings of heat resistant materials on jet engine parts, A special alloy of chromium, aluminium and yttrium is used for this type of coating. 18  PVD: – 1. Thermal Evaporation Method Al and Au are quite usable in thermal evaporation system with heated crucible, for they can be melt in crucible and generate enough quantity of vapours. However, W and Ti are not suitable for their low vapour pressure. Typical deposition rates in industry is around 0.5 µm/min (~8 nm/s, for Al)19  PVD: 2 – Sputtering Method Sputtering : A popular method for adhering thin films onto a substrate. Sputtering is done by bombarding a target material with a charged gas (typically argon) which releases atoms in the target that coats the nearby substrate. It all takes place inside a magnetron vacuum chamber under low pressure. 1. High technology coatings such as ceramics, metal alloys and organic and inorganic compounds are applied by sputtering. 2. The substance to be coated is connected to a high voltage DC power supply. 3. When the vacuum chamber has been pumped down, a controlled amount of argon or another gas is introduced to establish a pressure of about 10-2 to 10-3 torr. 4. On energizing current supply, plasma is established between the work and the material to be coated. 5. The sputtering gas is often an inert gas such as argon. For efficient momentum transfer, the atomic weight of the sputtering gas should be close to the atomic weight of the target, so for sputtering light elements neon is preferable, while for heavy elements krypton or xenon are used. Reactive gases can also be used to sputter compounds. 20  PVD: 2 – Sputtering Method Sputtering is a process whereby particles are ejected from a solid target material due to bombardment of the target by energetic particles. Sputtering is done either using DC voltage (DC sputtering) for metals or using AC voltage (RF sputtering) for dielectric materials and polymers. The gas atoms are ionized and they bombard the material to be coated. The energy of imposing ions cause atoms of the target material to be sputtered off and they are transported through the plasma to form a coating. Direct current sputtering is used when the target is electrically conductive. Radio-frequency sputtering, which uses a RF power supply is used when the target is a non conductor such as polymer. 21 Figure : PVD by sputtering process  PVD: 2 – Sputtering Method Plasma is a “state of matter similar to gas in which a certain portion of the particles are ionized” The main principle is to build a vaccum chamber and fill with Argon By adding a high voltage, the argon will arc to plasma state The argon ion (Ar+) will move toward to cathode with high speed and sputter the target material (use target as cathode). The target atom or molecular will be hit to substrate surface and condense as a film. Instead of heat melting in evaporation method, the plasma Ar+ ion hit and sputter the target is the main mechanism in plasma sputtering method. The target atom is knocked out by Ar+ ion, the knock force is so big and can accelerate target atom a high speed. With such velocity, the target atom can hit and attach to substrate surface deeply. The film density is good compared to thermal evaporation.  PVD: 2 – Sputtering Method Applications of Sputtering method: o This method is used in VLSI fabrication (Very-large-scale integration (VLSI) is the process of creating an integrated circuit (IC) by combining hundreds of thousands of transistors or devices into a single chip) o Sputtering is used extensively in the semiconductor industry to deposit thin films of various materials in integrated circuit processing. o Thin antireflection coatings (MgF2 and Fluoropolymers; mesoporous silica materials; titanium nitride and niobium nitride) on glass for optical applications are also deposited by sputtering. o An important advantage of sputter deposition is that even materials with very high melting points are easily sputtered while evaporation of these materials in a resistance evaporator or Knudsen cell is problematic or impossible. Sputter deposited films have a composition close to that of the source material. 23 Sputtering offers the following advantages over other PVD methods used in VLSI fabrication: 1) Sputtering can be achieved from large-size targets, simplifying the deposition of thins with unifrom thickness over large wafers; 2) Film thickness is easily controlled by fixing the operating parameters and simply adjusting the deposition time; 3) Control of the alloy composition, as well as other film properties such as step coverage and grain structure, is more easily accomplished than by deposition through evaporation; 4) Sputter-cleaning of the substrate in vacuum prior to film deposition can be done; Sputtering, however, has the following disadvantages too: 1) High capital expenses are required; 2) The rates of deposition of some materials (such as SiO2) are relatively low; 3) Some materials such as organic solids are easily degraded by ionic bombardment; 4) Sputtering has a greater tendency to introduce impurities in the substrate than deposition by evaporation because the former operates under a lesser vacuum range than the latter. Computational chemistry is the use of computers to solve the equations of a theory or model for the properties of a chemical system. 1 Three “Pillars” of Scientific Investigation ⮚ Experiment ⮚ Theory (analytical equations) ⮚ Computational Simulation ⮚ (“theoretical experiments”) 2 ⮚Simulation is becoming a third pillar of science, along with theory and experiment. ⮚Using theory, we develop models: simplified representations of physical systems. ⮚We test the accuracy of these models in experiment, and use simulation to help refine this feedback loop. ⮚Anything that can be measured can be simulated, including properties related to energetics, structures, and spectra of chemical systems. 3  The Nobel Prize in Chemistry 1998 John A. Pople Walter Kohn The Nobel Prize in Chemistry 1998 was divided equally between Walter Kohn "for his development of the density- functional theory" and John A. Pople "for his development of computational methods in quantum chemistry". 4  2013 Nobel Prize In Chemistry "for the development of multiscale models for complex chemical systems” Martin Karplus, Université de Strasbourg, France, and Harvard University, Cambridge, MA, USA Michael Levitt, Stanford University, Los Angeles, CA, USA Arieh Warshel, University of Southern California (USC), CA, USA 5 Using computational chemistry software you can in particular perform: o Electronic structure predictions o Geometry optimizations or energy minimizations o Conformational analysis and potential energy surfaces (PES) o Frequency calculations o Finding transition structures and reaction paths o Molecular docking: Protein – Protein and Protein-Ligand interactions o Electron and charge distributions calculations o Calculations of rate constants for chemical reactions: Chemical kinetics o Thermochemistry - heat of reactions, energy of activation, etc. o Calculation of many other molecular and physical and chemical properties o Orbital energy levels and electron density o Electronic excitation energy 6  Structure of a molecule in general is how atoms are arranged in the molecule in the three dimensional space. Potential energy surface (PES) is a plot of energy with respect to various internal coordinates of a molecule such as bond length, bond angle etc. 7  The PES is the energy of a molecule as a function of the positions (coordinates). This energy of a system of two atoms depends on the distance between them. At large distances the energy is zero, meaning “no interaction”. The attractive and repulsive effects are balanced at the minimum point in the curve Potential energy for nuclear motion in a diatomic molecule 9 Potential Energy Surfaces and Mechanism 10  Conformational Analysis ⮚ Identification of all possible minimum energy structures (conformations) of a molecule is called conformational analysis. ⮚ Conformational analysis is an important step in computational chemistry studies as it is necessary to reduce time spent in the screening of compounds for properties and activities. 11 ⮚ The identified conformation could be the local minimum, global minimum, or any transition state between the minima. ⮚ Out of the several local minima on the potential energy surface of a molecule, the lowest energy conformation is known as the global minimum. Global minimum Local minima 12 Local minimum Local minimum Global minimum 13 Ethane Conformations 14 15 16 17