CO2 is a major corrosive pollutant for building materials. It enters inside materials by diffusion or osmosis process and in presence of moisture it produces H2CO3 which decrease the pH value and accelerates chemical and electrochemical reaction with building materials. The carbonation reaction produces deterioration inside and outside of building materials. The destructive attack is developed by CO2 in concrete is the main cause for its corrosion. Chemical reactions occur with concrete and mortar in presence of water. CO2 reacts with Ca(OH)2 and Mg(OH)2 to form voluminous compound CaCO3.MgCO3.H2O. This compound is increased the size of building components thus crack is developed. It also generates swelling and dissolving effect in building materials. H2CO3 creates acidic environment for reinforced iron bar in concrete and form corrosion cell with iron bar thus corrosion starts and disbonding occurs between set cement and iron bar in this way concrete detached with iron bar. Metallic bar exhibits galvanic, pitting, crevice and stress corrosion. CO2 environment corrosion of building materials is controlled by coating of octahydrodibenzo [a,d]  annulene-5,12-diphenyhydrazone and CoS filler. These compounds are developed composite barrier on interface of building materials to stop diffusion or osmosis of CO2 and that is works as anticarbonation coating. The corrosion rate of building materials was determined by gravimetric and potentiostat techniques. Octahydrodibenzo [a,d] annulene-5,12-diphenyhydrazone was synthesized and it was used as anticarbonation coating. The composite layer formation was studied by thermal parameters like activation energy, heat of adsorption, free energy, enthalpy and entropy. The results of surface coverage area and coating efficiencies are indicated that above mentioned coating and filler compounds are provided a anticorrosive composite barrier.
There are certain phenomena to give clear warning of the corrosion of building materials (Birks J W, et.al. 1993). Building is exposed in certain environment condition (R K Singh, 2009) for appreciable periods of time provide so many evidences. If sulphate rocks (Finlayson-Pitts, et.al. 2000) present in the subsoil, it is a dangerous for concrete corrosion (Houghton J T, et.al.2001). Many industrial plants (Manahan S E, et.al. 2000) like coal, petroleum, metallurgy, thermal power, hydropower, breweries, tanneries, gasworks, dye works, mines, dairies, factories making preservatives, soap, alkali or sugar, glass etching plants, paint factories, textile, medicine, pesticides, herbicides, insecticides bleach works, food processing, fertilizer, agro industry also are released waste materials which are damaged concrete (D Prakash, et.al. 2006), mortar and iron bar.
It is essential to analysis quality of water (U S E P, 2002). On this result, it is possible to differentiate between corrosive and noncorrosive waters (Feely R A C L Sabine, 2008). Such test may indicate the presence of corrosive substances (R K Singh. et.al. 20015) likely to attack concrete.
Concrete consists of cement and ballast with reinforced steel
(A S Hamdy, 2007). The ballast (GUO Xing-hue. Et.al. 2009) is usually stable against the aggressive media. Whereas, limestone and some other ballasts which are dissolved by acid water as well as ballast containing sheets of mica, in which gypsum can crystallize in the presence of sulphate and crack the concrete structure by swelling
(M Quinet, et.al. 2007).
The cement is the part of the concrete which is most easily attacked. Portland cement is one of the most important building materials (R K Singh, 2011) at the present time. It is formed when mixture of limestone and clay are strongly heated (S V Lamaka, 2007). It is mixed with small amount of water, set in few hours to a hard stone like substance. Portland cement (C M Cho, 2007) is chemically defined as the finely ground mixture of calcium aluminates and silicates of varying compositions, which hydrate when mixed with water to form a rigid solid structure with good compressive strength (SHI Hong-Wei, 2009).
It is produced from the Portland cement clinker phase by reactions with water. A typical reaction is that of tricalcium aluminate (Davidson O et.al. 2002), which forms more than 50% by weight of Portland cement. It illustrates the complicated nature of the hydration of cement;
2(3CaO.SiO2) + 6H2O ? 3CaO.2SiO2.3H2O + 3Ca(OH)2
The set cement consists of hydrated calcium silicate, calcium hydroxide and reaction products originating from calcium aluminate (e.g. hydrated tetracalcium aluminate) and calcium aluminate ferrate (Vishwanadh B, et.al 2008). Hydrated calcium silicate, in particular, gives strength to concrete, while the calcium hydroxide is the reason for the alkaline nature of the set cement ( Maruthamuthus S, et.al, 2008) (pH > 12).
The above mention pollutants are produced two types of corrosive attack in which one is materials are dissolving by corrosive attack and another is materials swelling by corrosive attack. The oxide of carbon (CO2) and oxide of sulphur (SO2) are produced two types of corrosion like dissolving and swelling corrosion with hydrated calcium silicate, calcium hydroxide, hydrated calcium aluminates and hydrated calcium aluminoferrate (R K Singh, et.al. 2009).
For the hydration of cement 30% water is required. The cement and water ratio is 0.3. After hardening, the excess water stays in capillary pores (Natesan M, et.al. 2006) of the concrete as a solution of calcium hydroxide. The cement and water ratio is greater than 0.3, the excess of porous are developed into the set cement. The inner surface of the concrete is easily penetrated by corrosive gases. The reinforcement in reinforced and prestressed concretes is normally passivated by the presence of calcium hydroxide where pH value is greater than 12. In this condition it cannot rust. The passivity of the reinforcement can be destroyed by external agents. For example, CO2 may be absorbed and the resulting carbonation of the concrete may allow corrosion of the reinforcement. The strength of the steel is reduced and the concrete which surrounds the steel can flake off.
The corrosive action of acid depends upon their strength and their concentrations. The strong acids are hydrochloric acid, sulphuric acid and nitric acid. These acids dissolve all components of set cement to form salts of calcium, aluminum and iron and silica gel (Ohtsu M, et.al. 2007). Weak acids like carbonic acid many organic acids as humic acid and lactic acid which form water soluble salts with calcium compounds. Various types of damage observe after long periods of exposure.
Hydrogen sulphide (R K Singh, et.al. 2015) is evolved as effluents during the decomposition of organic materials. It dissolves in water to give weak acid. It can be absorbed with humidity of the concrete and then oxidized to produce sulphrous and sulphric acid. In both cases an acidic attack is mainly involved.
SO2 gas (R K Singh, et.al. 2014) is present in flue gases. It can be converted into sulphrous acid (H2SO3) in presence of moisture and by oxidation into sulphuric acid. Strong acids may be present in effluents, while acids are produced by dairies, fruit juice factories, breweries, paint and dyes, drugs, food processing and preservative industries and bog waters.
Carbonic acid (R K Singh, et.al. 2011) dissolves limestone. Its ability to attack cannot be expressed by its pH value alone. It occurs in water. Even its small quantities create corrosive environment for concrete. Carbonic acid behaves like weak acids just like other weak acids and is capable of dissolving lime from concrete (R K Singh, et.al. 2018). Lime stone is partial soluble in water but its solubility is increased in presence of carbon dioxide. Addition of limestone does not prevent this from of corrosion.
CaCO3 + H2O + CO2 ? Ca (HCO3)2
(Sparingly soluble) (Very soluble)
The corrosion rate of building material components were calculated in CO2 environment by gravimetric method without and with coating of octahydrodibenzo[a,d]annulene-5,12-diphenyhydrazone and CoS filler at 2830K, 2930K, 3030K, 3130K and 3230K temperatures and that mentioned temperatures 100mM organic compound and 25mM filler were used. The formula used for corrosion rate determination is written as:
K = 13.56 W/DAt (1)
Where K = corrosion rate constant, W= weight loss (kg), D= density of material (kg/m3) t = expose time (hr)
Potentiostat 138 model used to calculate the corrosion rate, corrosion potential and corrosion current density of absence and presence of octahydrodibenzo [a,d]  annulene-5,12-diphenylhydrazone and CoS filler The corrosion current was calculated by formula:
?E/?I = ßa ßc / 2.303 Icorr (ßa + ßc) (2)
(where ?E/?I is the slope which linear polarization resistance (Rp), ßa and ßc are anodic and cathodicTafel slope respectively and I is the corrosion current density in mA/cm2 ). The corrosion of building materials components were determined by formula:
- R (mmpy) = 0.1288 X Icorr.(mA /cm2) × Eq .Wt (g) / ? (g/cm3) (3)
(where Icorr. is the corrosion current density ? is specimen density and Eq.Wt is specimen equivalent weight)
Synthesis of octahydrodibenzo[a,d]annulene-5,12-diphenylhydrazone
When 3,4-dihydronaphthalen-1(2H)-one (25gm) is added into cold solution of benzene (50gm) containing PCl5(30gm), the reaction mixture was stirred for one hour. The reaction mixture was quenched with NaHCO3 and did workup with diethyl ether. The solvent evaporated with rotator vapour. The product was purified by silica gel column chromatography and produced 89% 4-chloro-1, 2-dihydonaphthalene.
4-Chloro-1,2-dihydronaphthalene (10gm) kept in two neck round bottle flask and potassium t-butaoxide (25gm) dissolved in THF solution. This solution poured into 4-Chloro-1,2-dihydronaphthalene and reaction temperature 00C. The reaction was mixture stirring four hours after completion reaction added cyclohexene as trapping agent and again stirring reaction more two hours. After work up got adduct 90% of 1,2-didehydro-3,4-dihydronaphthalene.
When 1,2-didehydro-3,4-dihydronaphthalene was used with cyclohexene, it was trapped by 1,2-didehydro-3,4-dihydronaphthalene to yield benzo-decahydrobiphenylene.
Adduct (20gm) oxidized into benzo-decahydrobiphenylene with addition of NaIO4 (10gm) and RuO2 (15g) in the presence of solvent CH3CN and CCl4. The reaction was quenched with H2O and after workup 87% yield of octahydrodibenzo[a,d]annulene-5,12-dione was obtained.
25g of colourless phenylhydrazine hydrochloride and 25g of sodium acetate in were taken in 100ml water and added in a solution of 45g of octahydrodibenzo [a,d]  annulene-5,12-dione in a little ethanol. The mixture was shaken until a clear solution was obtained and a little more ethanol was added. Warmed on a water bath for 30 minutes the reaction mixture was cooled. The crystalline derivative was filtered off and 87% of octahydrodibenzo[a,d]  annulene-5,12-diphenylhydrazone was received.
Results and Discussion
Octahydrodibenzo[a,d]annulene-5,12-diphenyhydrazone was coated on the surface of building material components and their porosities were block CoS filler. Their corrosive activities was studied in CO2 environment at 283, 293, 303, 313 and 3230K temperatures and time mentioned 2, 5, 8, 11 and 14 days. The corrosion rates were calculated by gravimetric experiment with help of formula, K (mmpy) = 13.56W/D A t (where W = weight loss of test coupon expressed in kg, A = Area of test coupon in square meter, D = Density of the material in kg. m-3) and their results were recorded table1. The results of table1 indicated that corrosion rate reduced after coating of octahydrodibenzo[a,d]annulene-5,12-diphenyhydrazone but these values more decreased when CoS filler was used. It was clearly observed in figure1 which plotted between K(mmpy) versus t(days).
Figure2 represented graph between logK versus 1/T for octahydrodibenzo[a,d]annulene-5,12-diphenylhydrazone and CoS filler at above mentioned tempertaures. All these compounds show liner plots which depicted that corrosion rate increased without coating but its values decreased with coating and filler compounds such types of trend was observed in table1.
Figure3 plotted between log(?/1-?) versus 1/T for octahydrodibenzo [a,d]  annulene-5,12-diphenylhydrazone and CoS filler. The graph of coating and filler compounds indicated that values of log (?/1-?) increased as temperatures rise from 283 to 3230K and their values were written in table1. It was observed that coating and filler compounds reduced corrosion rate. CoS filler increased log(?/1-?) values with respect of octahydrodibenzo [a,d]  annulene-5,12-diphenylhydrazone since filler compound enhanced surface accommodation properties of coating material. The coating compound and filler material were produced highly stable composite barrier in CO2 environment.
Figure4 gave information about surface coverage areas occupied by octahydrodibenzo[a,d]annulene-5,12-diphenylhydrazone and CoS filler. The surface coverage was obtained by formula, ? = (1- K / Ko) (where K is the corrosion rate with coating and Ko is the corrosion rate without coating) and its values were mentioned in table1. Figure4 plotted between ? (surface coverage area) against T (temperature) which indicated filler compound covered more surface area with respect of coating octahydrodibenzo [a,d]  annulene-5,12-diphenylhydrazone. CoS filler enhanced surface coverage efficiency and provided strength in base materials.
Figure5 plotted between %CE (percentage coating efficiency) versus T (temperature) for octahydrodibenzo [a,d]  annulene-5,12-diphenylhydrazone and CoS filler. Coating efficiencies of both compounds were calculated by formula, %CE = (1 – K / Ko) X 100 (where CE = coating efficiency, K = Corrosion rate with coating, Ko = corrosion rate without coating) and its values were recorded in table1. Analysis of the result of table1and figure5 reflect that coating and filler compounds increased coating efficiency at lower temperatures but these values were decreased at higher temperature. Octahydrodibenzo [a,d]  annulene-5,12-diphenylhydrazone coated on outer surface of building materials and CoS filler used to block porosities. Both substances were developed composite surface barrier and nullify the attack of CO2.
Activation energy of octahydrodibenzo [a,d]  annulene-5,12-diphenylhydrazone and CoS filler were calculated by the use of figure2 and Arrhenius equation, d /dt (logK) = Ea / R T2 (where T is temperature in Kelvin, R is universal gas constant and Ea is the activation energy of the reaction) and their values were recorded in table2. Activation energy of building materials increased in case of without but its values were decreased with coating and filler compounds. Activation energy results were shown that coating and filler compounds were adhered by chemical bonding on the surface of building materials.
Heat of adsorption of octahydrodibenzo [a,d]  annulene-5,12-diphenylhydrazone and CoS filler were obtained by figure3 and Langmuir equation, log (?/ 1-?) = log (A .C) – (q/ 2.303R T) ( where T is temperature in Kelvin and q heat of adsorption). The heat of adsorption of both compounds was depicted in table2. Coating and filler compounds produced a negative sign of energies which noticed that they formed chemical bonding with base of building materials. Thermally stable composite barrier was developed by coating and filler compounds.
Free energy developed by octahydrodibenzo[a,d]annulene-5,12-diphenylhydrazone and CoS filler during nanocoating determined with formula, ?G = -2.303RT log (33.3K) (where R is universal gas constant, T be temperature and K corrosion rate). The values of free energy indicated that both compounds were attached by chemical bonding. These results gave information that coating was an exothermic process as negative sign of free energy reflected in table2.
Figure6 plotted between log(K/T) versus 1/T and transition state equation , K = R T / N h log (?S# / R) X log (-?H #/ R T) (where N is Avogadro’s constant, h is Planck’s constant, ?S# is the change of entropy activation and ?H # is the change of enthalpy activation) produced enthalpy and entropy of octahydrodibenzo[a,d]annulene-5,12-diphenylhydrazone and CoS filler and their values were mentioned in table2. Both compounds show a negative sign of enthalpy and entropy. It indicates that coating is an exothermic process. Both compounds accommodated on the surface of base materials by chemical bonding.
Table2 Thermal parameters of octahydrodibenzo[a,d]annulene-5,12-diphenylhydrazone and CoS filler in CO2 environment
Figure7 indicated plot of activation energy, heat of adsorption, free energy, enthalpy and entropy against temperatures for octahydrodibenzo[a,d]annulene-5,12-diphenylhydrazone and CoS filler compounds were occupied surface coverage area. The results of table2 confirmed that the values of thermal parameters decreased as temperature increased and surface coverage area of coating and filler compounds were enhanced. The results of all thermal parameters recorded for octahydrodibenzo[a,d]annulene-5,12-diphenylhydrazone and CoS, they indicated that coating is an exothermic process. Both compounds were adhered on the surface of base materials by chemical bonding. CoS filler increased stability of surface. Such types coating create passive composite thin film barrier that barrier is impermeable and check osmosis or diffusion process of CO2.
Potentiostat results of octahydrodibenzo [a,d]  annulene-5,12-diphenylhydrazone and CoS filler were calculated by ?E/?I = ßa ßc / 2.303 Icorr (ßa + ßc) (where ?E/?I is the slope which linear polarization resistance (Rp), ßa and ßc are anodic and cathodicTafel slope respectively and I is the corrosion current density in mA/cm2 ) and Tafel plot figure8. Electrode potentials and corrosion current densities were increased without coating but its values decreased with coating and filler compounds. Anodic current enhanced without coating whereas coating and filler reduced anodic current and increased cathodic current.
Corrosion current of octahydrodibenzo [a,d]  annulene-5,12-diphenyhyadrazone and CoS filler put in equation, C. R (mmpy) = 0.1288 I (mA /cm2) × Eq .Wt (g) / ? (g/cm3) (where I is the corrosion current density ? is specimen density and Eq.Wt is specimen equivalent weight) to give corrosion rate and their values written in table3. The corrosion rate of building materials were found to be higher but these values were lower with coating and filler compounds. Coating and filler compounds enhanced surface coverage area and percentage coating efficiency. All dates were calculated by gravimetric method for octahydrodibenzo[a,d]annulene-5,12-diphenylhydrazone and CoS satisfied the results of potentiostat.
Author is thankful for UGC-New Delhi to provide financial support for this work. Author gives his thanks to other people who provide data collection and graphs plotting.
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Rajesh Kumar Singh1, Shabana Latif2, Manjay Kumar Thakur3
1Department of Chemistry, Jagdam College, J P University, Chpara, India
2,3Research Scholar, Department of Chemistry, Jagdam College, J P University, Chpara, India