Comparative Investigation of Inhibitive Properties of Newbouldia Laevis (NL) and Azadirachta Indica

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Comparative Investigation of Inhibitive Properties of Newbouldia Laevis (NL) and Azadirachta Indica (AZI) Leaf Extracts on Corrosion of High Carbon Steel in Sulphuric Acid.

Department of Mechanical Engineering, Niger Delta University, Amasoma, Nigeria ***

ABSTRACT

Inthisstudy,theeffectivenessofthetwoextractsinpreventingcorrosiononhighcarbonsteelusingNewbouldiaLaevisand Azadirachta Indica leaf extracts in sulphuric acid medium was evaluated. In order to calculate the weight loss of the high carbonsteelwhilesubmergedinthecorrodingsolutionwithandwithouttheleafextracts,respectively,thecorrosionofhigh carbon steel was studied using the gravimetric method. Due to the relationship between weight loss and corrosion rate, the testpieceweightlossservesasagaugefortheseverityofcorrosion.Ingeneral,theweightloss decreasedwhentheextracts werepresent,provingthattheyweregoodcorrosioninhibitors.Incontrast,whentheextractswereabsent,therewasarapid weightloss thatledtoa highrate of high-carbonsteel degradation in theacidicmedium. Comparatively,the effectivenessof NewbouldiaLaevisLeafExtractasacorrosioninhibitorforhighcarbonsteelinsulphuricacidpeakedatanaverageefficiency of 88% at a concentration of 0.5g/L while Azadirachta Indica for the same conditions achieved an efficiency of 71%. This showedthatNewbouldiaLaevisLeafExtractisabettercorrosioninhibitorthanAzadirachtaIndicaLeafExtract.

Keywords: Corrosion,HighCarbonSteel,SulphuricAcid,Gravimetric,Inhibition.

1 INTRODUCTION

According to the American Society of Testing and Materials (ASTM) International, corrosion is the result of a chemical or electrochemical reaction between a substance, typically a metal, and its surroundings that accelerates the loss of the substance's qualities (Brycki et al., 2018). The International Organization for Standardization (ISO) also describes it as the physiochemical interaction between a metal and its surroundings that alters the metal's characteristics and may seriously affect the metal, the environment, or the technical system's ability to function (ISO 8044, 2015). Metal atoms are found in chemical compounds in nature, and variations in the electrolyte can cause corrosion. The oxygen, concentrations, moisture content,anddifferentionicconcentrationsareexamplesofsuchdiscrepancies(Papavinasam,2011).

Metal corrosion control has been crucial, especially in the production industry (Rani and Basu, 2012). Corrosion inhibitors have historically been regarded as the first line of defense against internal corrosion in the oil and gas production and processing industries. Corrosion can cause structural and equipment failures in plants, which are often expensive to fix, expensiveintermsoflostorpollutedoutput,expensiveintermsofenvironmentaldamage,andpossiblyexpensiveintermsof human safety. A precise evaluation of the factors influencing a structure's corrosion and rate of degradation is necessary beforemakingdecisionsaboutthefutureintegrityofthestructureoritsparts.Withthisknowledge,awisechoicecanbemade regardingthenature,expense,andurgencyofpotentialcorrectiveactions(Roberge,2008).

Total corrosion costs include design, manufacture, maintenance, repair, and rehabilitation costs as well as depreciation or replacementcosts forstructuresthathavelosttheir usefulnessdueto corrosion (Koch,2017).The maincausesofcorrosion are chemical and electrochemical reactions. Chemical corrosion occurs in non-conductive liquids and dry gases without current or electron flow. An oxide layer that develops as a result of oxidation in the air is the primary result of chemical corrosion. According to McCafferty (2010), redox reactions and the differing potentials on the surface of the corroded metal causeelectrochemicalcorrosiontooccurinsolutionbetweenmetallicmaterialsandelectrolytes.Aportionofthemetalisused asananode,whereitoxidizesandtransformsintoanion.Thecathodeisanothercomponent,wheredepolarization,primarily thereductionofoxygenandhydrogencation,takesplace(Houetal.,2017;Stewartetal.,2012).

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Corrosiveassaultonmildsteelwillstartatimperfectionsintheoxidefilmifitisexposedtoacorrosiveenvironment,suchas sulfuricacid.Theseflawscouldbecaused by natural filmdiscontinuities,suchasinclusions,grain boundaries, ordislocation networksatthesteel'ssurface,ortheycouldbetheresultofmechanicaldentslikescratches.

1.1 Material and energy

The impact of corrosion on the equipment and its surroundings deserves careful attention when a sector of the economy is beingdeveloped.Corrosion isoneofthehardestchallengestoovercomeforthemajorityof wealthycountries. Anationmay experience major material and monetary losses as a result of corrosion of tanks, pipes, metal components of machinery, bridges, ships, etc. In addition, failure brought on by corrosion may jeopardize the security of operational equipment like boilers,pressurevessels,steelstoragecontainersforhazardouschemicals,bridges,turbinebladesandrotors,vehiclesteering systems, and aircraft components. Additionally, water, electricity, and the production of metal frames are all susceptible to corrosion's harmful impacts (Li,andTrost,2008). The energyneededtomakeonetonofsteel isaboutsimilartotheenergy usedbyatypicalhouseholdovertheperiodofthreemonths,despitethefactthatonetonofsteelisbelievedtorustevery 90 seconds.Nearlyhalfofeverytonofsteelproducedworldwideisusedtoreplacecorrodedsteel(HöferandBigorra,2008).

1.2 Corrosion Implication on Human life and safety

Corrosioncanhaveaninconceivableinfluenceonhumanlifeandsafety.Asaresultofliabilityconcernsorsimplybecausethe evidencedisappearedduringthecatastrophicevent,thisdestructivephenomenahasgoneunrecognizedasthemaincauseof many fatal occurrences. The Silver Bridge collapse is among the riskiest and most well-known corrosion accidents (FioriBimbi etal.,2015). One of WestVirginia'sdarkestdays inhistory wasDecember 15, 1967. It wassadlyjust the first of many terrible days that West Virginians would endure. In 1928, the Silver Bridge, which connected Point Pleasant with Gallipolis, Ohio, was made public. It was the first bridge in the country to use a cutting-edge eyebar-link suspension technology rather thanaconventionalwire-cablesuspension.However,oneofthoseeyebarshadaminute,undetectableflaw.Outofsightfrom thegeneralpublicorbridgeinspectors,thedefectiveeyebarultimatelybrokeandstartedtorust.

The bridge collapsed on December 15 about 5 p.m. after a string of failures that started with the eyebar. The bridge was crowdedwithvehiclesbecauseitwasrushhour.Thirty-onetrucksslidintotheOhioRiver'sfrigidwaters.Although21people did not perish, 46 people did. National reforms in bridge inspection procedures were brought about after the Silver Bridge catastrophe.Another40-year-oldbridgeofthesamekindthatwaslocatedatSt.Marys,almost100milesupstreamfromPoint Pleasant,waspromptlyclosedandultimatelydestroyed(PublicbroadcastinginWestVirginia.EncyclopediaofWestVirginia. publishedat7:51AMESTonDecember15,2020).

OneofthedeadliestindustrialmishapsintermsofthenumberofpersonskilledandinjuredoccurredthenightofDecember 2–3, 1984, in Bhopal, India. At Union Carbide India Limited, an unfortunate seepage of water (500 liters) brought on by corrosion of pipelines, valves, and other safety systems led to the release of methylisocyanate (MIC) and other dangerous reaction products into the surrounding environs, there were 3000 fatalities and an estimated 500,000 injuries as a result of this tragedy (Aljourani et al., 2010). The Swimming Pool Roof Collapse in Uster, Switzerland in 1985 is another notable corrosiondisaster,whenthestainlesssteelrodssupportingthisswimmingpool'sceilingsnappedfromstresscrackcorrosion, twelvepeoplewerekilled(JingrongandYongming,2012)

2 Review of Related Work

According to some research teams, the use of naturally occurring compounds to stop metal corrosion in both acidic and alkaline conditions is on the rise. Using the weight loss method, the effect of extract from breadfruit peel on the ability of aluminum metal to resist corrosion in 0.5M H2SO4 solution was studied. It has been discovered that the extract effectively inhibitsthecorrosionofaluminumwhenusedasacorrodentinsulphuricacid.Thecreationofanadsorbedinhibitionfilmthat shields the metal surface from corrosion is thought to be the cause of the inhibition process. With an increase in inhibitor concentration,butadecreaseinsurfacecoverage(Ɵ),extractfrombreadfruitpeelshowedimprovedinhibitoryefficacy.Itwas discovered that the adsorption of breadfruit peel extract on aluminum metal surface complied with Langmuir's adsorption isotherm. The extract from breadfruit peel may be a good corrosion inhibitor because of the negative free energy value (∆Gads), which shows that the inhibitor molecule was physically adsorbed and that the reaction was spontaneous. (Orie and

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Mathew, 2015). Okra mucilage, a naturally occurring polysaccharide, is used as a cathodic type corrosion inhibitor for mild steelin0.5MH2SO4 (Amaretal.,2017).

A Schinopsis lorentzii extract's cathodic inhibition effectiveness was reported by Gerengi et al. (2012) to be "marginally" effective.Nevertheless,aninhibitormaybeanodic,cathodic,ormixed.Dependingontheenvironment,aguanidinederivative behavesdifferently,behavingcathodicallyin1MHClandmixed-typein0.5MH2SO4,accordingtoareport(Khaled,2008).

Assafecorrosioninhibitorsforironinaeratedstagnant1.0MHClsolutions,Aminetal.(2010)evaluatedtheeffectiveness of threechosenaminoacids,namelyalanine,cysteine,andS-methylcysteine.Thethreeaminoacidswereadsorbtotheelectrode surface by various methods, including physical, chemical, and H-bonding adsorption. The study employed computational analysestoevaluatetheHOMO(HighestOccupiedMolecularOrbit)-LUMO(LowestUnoccupiedMolecularOrbit)orbitals.

Otherpaperswereabletospeculativelydescribetheadsorptionmechanismand,byextension,theinhibitorymechanism,but they lacked more thorough arguments backed by theoretical and/or experimental evidence. The investigation of the Henna extract'sabilitytopreventcorrosionproducedaplausibleexplanationfortheobservedinhibitionactivitythatdidnotinclude anysoliddata support and offereda theoryonthedevelopmentof complexesrather thanan adsorption process(Chaudhari andVashi,2016).

Ostovari et al. (2009) highlighted the importance of examining the mechanism beyond the corrosion inhibition effect in another study on henna extract. To support the theory that insoluble complex compounds were formed when metal cations andadsorbedLawsonemoleculesweremixed,conductimetrictitrationwasutilizedasareliableapproach.

Theyalsodeterminedtheindividual inhibitorypotenciesofthe extract'scomponentsandtheextractitself.Amongtheother henna components, including gallic acid, glucose, and tannic acid, lawsone demonstrated the highest inhibition efficiency. It also had a higher inhibition efficiency than the henna extract itself. Streptomycin was used as an inhibitor as well, and the authorsofthestudyclaimedtohaveobtainedaninhibitioneffectthathappensduringthedrug'sadsorptiononametalsurface withoutchangingthewaycorrosionworks.However,eveninthisinstance,theprocesswasnotexamined;instead,onlyafew ideaswereprovided(Shuklaetal.,2009).

NLhasbeenstudiedforitsabilitytopreventmetalcorrosion.AccordingtoNnannaetal.(2011),boththecontentoftheplant extract and the length of time the aluminum samples were exposed to the extract-containing H2SO4 solutions affected the effectivenessoftheinhibition.TheeffectofhydrochloricacidcorrosiononmildsteelwasrevealedbyNwosuetal.(2018).The weight loss was substantially slower and the rate of chemical attack on the aluminum alloy was also slowed down by the presence of the Newbouldia leavis leaf extract. The effectiveness of the inhibitor's inhibition increases with concentration while decreasing with temperature. The addition of leaf extract modifies the metal's electrochemical behavior in an acidic environment.

Utilizing a gravimetric approach, the inhibitory effectiveness of an extract of NL leaves for the corrosion of mild steel was studied. The leaves were gathered, dried, and powdered to a micron size for gravimetric analysis. Using the ethanol reflux method,theleafextractwasobtained,andtheweightoftheextractedleaveswascalculated.Thequantitiesforvariousextract concentrations were likewise calculated, put to the acidic medium, and the mild steel coupons submerged throughout the courseoffourhours.Theinhibitoryefficiencywasestimatedafterobtainingtheweightlossvaluesforeachmetalcoupon.

Results for weight loss and corrosion rate showed that the plant extract from NL leaves functioned as an effective inhibitor, withweightlossreducingwithincreaseinconcentration(from0.0g/Lto0.5g/L)andcorrosionratedropping(from43mm/yr to 4.2mm/yr). With an increasing inhibition efficiency from 72% to 90% as inhibitor concentration increases, from the gravimetric approach employed to test the extract from Newbouldia leavis leaves, the inhibitor was found to be an effective mild steel corrosion inhibitor. Plant extracts are an excellent alternative to corrosion inhibitors due to their availability, biodegradability, low cost, and reduced risk to humans and the environment. This study has demonstrated that NL leaf extracts,whenusedintheproperconcentration,canincreasetheservicelifeofmildsteel.(Yusufetal.,2020).

ThemolecularandbiologicalcharacteristicsofAZIarenoteworthy.Itisoneamongthemosteffectiveproducersofsecondary metabolitesinnature.Todate,morethan300naturalproductshavebeenextractedfromdiversetreeparts,andthenumber

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ofsubstancesaddedtothelisteachyearisgrowing.Thecurrentworkattemptsto increasetheusabilityofplantextractsfor metallic corrosion inhibition as a contribution to the current interest in green corrosion inhibitors by specifically examining theinhibitorycapacitiesofAZIformildsteel,aluminum,andtin.ThecurrentpaperdiscussesthepotentialofAZIextractasa corrosioninhibitor on metal surfaces,in particularthoseformed of carbonsteel anditsalloys,aluminum,andtin. There has been extensive research on the chemical composition of AZI, the effect of temperature on inhibitory effectiveness, and the computational studies related to AZI adsorption on metals. This effort would enhance our comprehension of the adsorption processandthesubsequentinhibitoryeffectofplantextractonmetalcorrosion(Sanjayetal.,2015).

ThegravimetricmethodwasusedtoassesstheeffectivenessofAZIgumasamildsteelcorrosioninhibitorin1.0Mnitricacid (HNO3),sulphuricacid(H2SO4),andhydrochloricacid(HCl)solutionsat298Kand313K.Weightlosswasobservedatvarious inhibitor doses (0.50, 1.00, 1.50, 2.00, and 2.50% w/v). The weight measurements were used to determine the extent of surfacecoverageandtheefficiencyoftheinhibitor.TheGibbsfreeenergyandheat ofadsorptionwerecalculatedalongwith theactivationenergyusingtheArrheniusequationinordertoexaminethespontaneityandenthalpyofthecorrosionprocess. Langmuir, Temkin, and Fraudlish adsorption isotherms were employed to shed light on a probable adsorption mechanism (Abdulmudallibetal.,2018).

This study investigated the ability of two biological elements, AZI and an enzyme, to inhibit mild steel corrosion. Using the weightlossanalysismethod,thecorrosionrates,inhibitors'effectiveness,andsurfacecoverageofmildsteelexposed tosaline solutions with or without inhibitors for a period of 576 days were assessed. The results showed that the rate of mild steel corrosiongenerallydidnotvarysignificantlyafter400daysofcontinuousexposuretothesamesolution.Therateofmildsteel corrosion was significantly reduced when enzyme was added to low and high saline solutions as opposed to when saline solutions were used alone. It was found that the enzyme's effective concentration was 2 wt.% in both low and high saline solutions,andapplicationoftheenzymeproducedhighcorrosioninhibitionefficacy.ThecorrosioninhibitionofAZI,however, was shown to be more effective in low saline solutions, and in this environment, an optimum concentration of 2 wt.% was effective.However,agreaterconcentrationof10%isneededinhighsalinesolutionforefficientcorrosioninhibition(Udohet al.,2022).

For a very long time, there have been significant losses at high costs due to the corrosion and damage it creates in most industrial operations, particularly in the oil and gas industries. Erosion calls for long-term solutions due to the disastrous impactithasontheecosystemandtheseriousthreatitposestobothpeopleandanimals.Asaresult,thesubjectofcorrosion is covered in a ton of literature. Thus, there is a need for organic corrosion inhibitors, whether they be natural or manufactured.Theseinhibitorsarefrequentlyaccessibleandsecurebecausetheydecompose,asshownbyprevious studies. By using organic molecules with several heterogeneous atoms and double and triple bonds in their molecular structures, metals can be shielded from corrosion under a variety of corrosive situations. Each year, a large amount of research on the productionorextractionof corrosioninhibitors,aswellasontheclassificationandinhibitorymechanisms,ispublishedbya large number of academics. The current study evaluates the efficacy of various extracted or synthesized coumarins used as corrosioninhibitors,aswellasthevariousformsofcorrosion,inhibitors,methodsofaction,andassessingcorrosioninhibitor efficiency(Kadhimetal.,2021).

The ability of AZI leaf extracts to lessen corrosion in sea water was investigated using chemical methods. Mild steel didn't corrode in sea water because to AZI extracts. The extract of AZI leaves has been studied using linear polarization, electrochemicalimpedancespectroscopy(EIS),potentiodynamicpolarization,andweightloss.TheNyquistplotsshowedthat doublelayercapacitancereducedasAZIconcentrationincreasedwhilechargetransferresistanceincreased.Theefficiencyof the inhibition grew as the concentration of extract did. Higher 98% inhibitory efficiency of AZI's leaf extract was shown to exist(Sribharathyetal.,2018).

The effect of AZI seed extract in 0.5M, 1.0M, and 1.5M H2SO4 on the prevention of corrosion of mild steel and copper was investigatedusingthegasometricmethod.Zeroorder,halforder,andfirstordermodelswerefittedtothedata basedonthe amountofhydrogenevolved.Theseresultsshowthatinhibitiondecreasestheinstantaneousvolumeofhydrogenevolved(V0) and kinetic rate constant, and a zero order kinetic model may be utilized to approximate the volume of hydrogen evolved during the corrosion of mild steel and copper in an H2SO4 environment (k). The results of the gasometric approach also revealedthatmildsteel-basedsolutionsrustedmorequicklythancopper-basedones(Ekekeetal.,2019).

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3 Materials AND Method

3.1 Extraction of NL and AZI leaves.

InAba,Nigeria,theNLandAZIplants'leaveswerecollected,dried,andground.Asthecorrosivemedium,H2SO4 (1.0M)was used,by boiling weighedamountsofdriedandpowderedNL andAZIleavesinH2SO4 ata low,constantboilforthreehours, stock solutions of plant extracts were created. Once the solutions had cooled to room temperature, they were filtered. To calculate the quantity of plant materials extracted into the solutions, the weight of the dried residues was compared to the weightofthepowderedplantmaterialbeforeextraction.Inhibitortestsolutionscontaining0.1to0.5g/Lofexcesscorrodent weremadebydilutingthestocksolutions.

3.2 Metal Preparations

The experiment employed a high carbon steel (HCS) sample of grade (C-1345) with the following chemical composition: C = 0.85%, Mn = 1.71%, Si = 3.94%, Cr = 0.88%, Ti = 0.29%, Co = 0.68%, Cu = 0.07%, Mo = 0.68%, and Fe = 91.76%. The metal sheets were cut into 20 x 20 x 4mm coupons, abraded with 120, 600, and 1200 grit emery paper, cleaned with soap and ethanoltoremoveanygrease,andallowedtodryontheairbeforebeingweighed.

3.3 Gravimetric Method

The gravimetric experiment was conducted in accordance with the guidelines (American Society for Testing and Materials (ASTM) International, 2004). HCS samples with measurements of 2 cm x 2 cm x 4 cm were abraded with different grades of emerypaper(120,600,and1200),andthenrinsedwithdistilledwater,ethanol,andacetone.AMettlerweighingbalancewas thenusedtopreciselyweighthetestsamples.Afterthat,HCSsamplesweredippedintoa100mlbeakerthatcontained50ml of1.0MH2SO4 solutioninvariousdosesoftheinhibitor(0.0g/L,control,0.1g/L,0.2g/L,0.3g/L,0.4g/L,and 0.5g/L).The experimentwasperformedateachinhibitorconcentration.

The test setup was exposed to air for a variety of exposure intervals (4hrs, 8hrs, 12hrs, 16hrs, and 20 hrs.). The test componentwasremovedeveryfourhoursuntilthefinalpiecewasremovedaftertwentyhours.Thetestpiecewasdippedin nitricacidtostopthecorrosionreaction,washedinwatertoremovetheacid,dippedinethanoltoremovethewater,andthen driedentirelyinacetonetopreventcorrosionbeforeitcouldbereweighed.

Theweightloss,corrosionrate,andInhibitionefficiency(ɳgravimetric %)willbecalculatedbyEquation ∆W=W1-W2 (3.1)

Where W1 and W2 are samples weight before and after immersion in the test solution for time (t), respectively (ASTM International,2014).ΔWistheweightlossrepresentedingrams.

Basedonobtainedresults,thecorrosionratewillbeestimatedinEquation(3.2).

CorrosionRate(CR)=K∆W/Atρ (3.2)

whereKisaconstant(8.76×104)whichallowsrepresentingCRinmm/year;Aisthesurface ofthemetalsample(cm2);tistheimmersiontime(hours);ρisthedensityofthemetal(g/cm3)(ASTMInternational,2004). TheinhibitionefficiencyforthegravimetricmethodwillbecalculatedusingEquation(3.3).

(ɳgravimetric %)=(1-Wi/Wo)x100%, (3.3)

whereWiistheweightlosswheninhibitedandWoisweightlosswithoutbeinginhibited

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4. Results and Discussion

Belowaretheresultsoftheweightlossexperiment

4.1 Test Results for NL leaf extract as Corrosion Inhibitor for HCS in H2SO4

W e ig ht L oss (g )

1.4

1.2

1

0.8

0.6

0.4

0.2

High Carbon Steel

0.0g/L 0.1g/L 0.2Gg/L 0.3g/L 0.4g/L 0.5g/L

0

1.6 0 2 4 6 8 10 12 14 16 18 20 22

Exposure Time (hr.)

Figure 4.1: Plot of Weight Loss (g) versus Exposure Time (t) for HCS with NL leaf extract as inhibitor.

ThecorrosionofHCSin1.0MH2SO4 intheabsenceandpresenceofvariousdosesofNLleafextractispresentedasafunction ofweightlossversusexposuretimeinFigure4.1,whichdepictstheoutcomesofthegravimetricexperimentusingNLleafas an inhibitor for high carbon steel. As can be observed from the plots, the rate of weight loss in the controlled environment (1.0MH2SO4)increasedconsistentlyovertime;however,therewasalargeweightlossbetween16and20hours,showingthat theHCSwassuccumbingtocorrosion.Whentheleafextractinhibitorswereadministered,theweightlossdroppedandstayed the same until around 16 hours, at which point there was a slight increase, indicating that the inhibitor concentration was dwindling.

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High Caebon Steel

Corrosion Rate (mm/yr.)

3.00

2.50

2.00

1.50

1.00

0.50

0.00

3.50 0 2 4 6 8 10 12 14 16 18 20 22

Exposure Time (hr.)

0.0g/L 0.1g/L 0.2g/L 0.3g/L 0.4g/L 0.5g/L

Figure 4.2: Plot of CR (mm/yr.) (For control + various concentrations) versus Exposure Time (hr.) foe HCS with NL leaf extract as inhibitor.

A graph showing the trend of high carbon steel CR over time in the presence (control experiment) and absence of NL leaf extractisshowninfigure4.2.Theformationofaprotectivelayeroffilmonthetestpiece'ssurface,whichreducedtherateof corrosion,iswhatcausedcorrosionresistancetoexistduringthefirst16hours,asshownbythecontrolcurve.After16to 20 hours,thetestpiecesuccumbedtofurthercorrosion,provingthattheprotectivecoveringhadcompletelywornoff. Afterthe additionofvariousconcentrationsofNLLeafextracts,thecorrosiondecreasedsignificantlyandmaintainedalowertrendfor alltheconcentrations(0.1to0.5g/L),provingthatthetestpiecewasprotectedagainstdeterioration.CRvalues(forcontrol+ differentconcentrations)versusexposuretime.

Theinhibitedcorrosioncurvesalsoshowthatat0.1g/L,theCR fell continuouslyfrom0to16hours,indicatingthattheleaf has formed a protective layer on the test piece's surface and prevented the mass transfer of charges in the corrosive environment. The leaf extract concentration that produced the best CR value at 16 hours was 0.1g/L. between 16 and 20 hours,therewasalittlerise,indicatingthatthe0.1g/Lconcentrationisdeterioratingandstartingtosuccumbtocorrosion.

Althoughtherewasaslightincreasebetween16and20hours,thecorrosionrateof0.2g/Ldecreasedgraduallyfrom0to16 hours, indicating that the amount of leaf extract in the corrosive media was diminishing. At a concentration of 0.3g/L, CR increased between 8 and 12 hours but declined from 0 to 16 hours. Concentrations of 0.4g/L behaved similarly to those of 0.3g/L. The concentration of 0.5g/L showed a consistent downward trend from 0 to 20 hours, demonstrating that the leaf extractisstillactive.ThegraphshowshowNLleafextractinhibitsacidiccorrosionofHCS.

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Inhibitor efficiency

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.1 0.2 0.3 0.4 0.5

Inhibitor concentration (g/L)

Figure 4.3: Efficiency (%) versus Concentration of inhibitor (g/L) for HCS with NL

In Figure 4.3, the inhibitor's inhibitory effectiveness is plotted against the concentration of the plant extract, demonstrating thatNLleafextractisapotentinhibitorofsulphuricacidcorrosionofHCS.Astheconcentrationoftheinhibitorwasincreased, theeffectivenessofinhibitionincreased.

4.2 Test Results for AZI leaf extract as Corrosion Inhibitor for HCS in H2SO4

1.4000

1.2000

High Carbon Steel 0.0g/L 0.1g/L 0.2Gg/L 0.3g/L 0.4g/L 0.5g/L

1.0000

0.8000

0.6000

High Carbon Steel 4 hrs. 8 hrs. 12 hrs. 16 hrs. 20 hrs. 0.0000

1.6000 0 2 4 6 8 10 12 14 16 18 20 22

0.4000

0.2000

Weight Loss (g) Exposure Time (hr.)

Figure 4.4: Plot of Weight Loss (g) versus Exposure Time (t) for MCS with AZI leaf extract as inhibitor

ThegravimetricexperimentusingAZIleafasanHCSinhibitoryieldsthefindingsshowninFigure4.4.Accordingtothegraphs showingthecorrosionofHCSin1.0MH2SO4 intheabsenceandpresenceofvaryingconcentrationsofAZIleafextract,therate of weight loss in the controlled environment (1M H2SO4) increased steadily over time, though there was a significant loss

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between16and20hours,indicatingthattheHCSwill notsurviveforvery long.Weightloss droppedafteradministrationof the inhibitor leaf extracts and stayed steady for almost 16 hours before it slightly increased, indicating that the inhibitor concentrationwasdeclining.

High Carbon Steel

3.00

2.50

2.00

1.50

1.00

0.50

Corrosion Rate (mm/yr.) Exposure Time (hr.)

3.50 0 2 4 6 8 10 12 14 16 18 20 22

0.0g/L 0.1g/L 0.2g/L 0.3g/L 0.4g/L 0.5g/L

0.00

Figure 4.5: Plot of Corrosion Rate (mm/yr.) (for control + various concentrations) versus Exposure Time (hr.) for HCS with AZI leaf extract as inhibitor

The graph depicts the trend of high carbon steel CR over time in the presence and absence of AZI leaf extract (control experiment) (figure 4.5). The creation of a protective layer of film on the test piece's surface during the first 16 hours prevented corrosion, as shown by the control curve, which also showed a delay in the rate of corrosion. The test piece succumbed to further corrosion after 16 to 20 hours, indicating that the protective layer had totally disappeared. The corrosion significantly decreased and maintained a lower trend with the addition of different concentrations of AZI Leaf extracts(0.1to0.5g/L),indicatingthatthetestpieceswereshieldedagainstdeterioration.

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Hight Carbon Steel

I nhibi tor e f fic ienc y

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.1 0.2 0.3 0.4 0.5

Inhibitor concentration (g/L)

4 hrs. 8 hrs. 12 hrs. 16 hrs. 20 hrs.

Figure4.6:Efficiency(%)versusConcentrationofinhibitor(g/L)forHCSwithAZIleafextractasinhibitor

The relationship between the inhibitory effectiveness and the concentration of the plant extract is shown in Figure 4.6. It is clear that AZI leaf extract works wonders to prevent HCS from corroding in sulphuric acid with an increase in inhibitor concentration.

4.3 Comparison of Inhibitive potencies of NL and AZI

Table4.1:ValuesofInhibitionEfficienciesforNLandAZIleafextractsatvaryingInhibitorConcentrationsforHCS. ComparisonofNLandAZILeafExtractsEfficacyonInhibitionEfficiencyofHCSin H2SO4 Conc.(g/L) ExposureTime(hr.)

Average Inhibition Efficiency 4 8 12 16 20

0.1g/L-NL 78% 78% 77% 83% 88% 81% 0.1g/L-AZI 37% 47% 69% 72% 73% 60% Difference 41% 31% 7% 11% 15%

0.2g/L-NL 78% 82% 85% 82% 87% 83% 0.2g/L-AZI 40% 58% 70% 70% 77% 63% Difference 38% 24% 15% 12% 10%

0.3g/L-NL 81% 78% 84% 82% 84% 82%

0.3g/L-AZI 59% 64% 66% 80% 86% 71% Difference 22% 14% 18% 2% -2%

0.4g/L-NL 80% 84% 81% 81% 85% 82% 0.4g/L-AZI 67% 73% 83% 80% 86% 78%

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Difference 13% 11% -3% 1% -1%

0.5g/L-NL 84% 87% 89% 88% 93% 88% 0.5g/L-AZI 46% 67% 73% 79% 89% 71% Difference 38% 20% 15% 8% 5%

Table4.1displays theeffectivenessoftheleafextractsfromtheNL andAZIonthepreservationofHCSinH2SO4.Theresults showthattheNLleafextractsignificantlyincreasedthe fortificationagainstdegradationwhiletheAZIextractprotectedHCS from corrosion. According to the study of efficiency in Table 4.1, a positive difference demonstrates that NL inhibited well, whereasanegativedifferencerevealsthatAZIinhibitedbest.

Table4.1:AverageInhibitionEfficiency(%)atvariousConcentration(g/L)

Concentration (g/L) InhibitionEfficiency(%) NL AZI 0.1 81 60 0.2 83 63 0,3 82 71 0.4 82 78 0.5 88 71

The average inhibitive efficacy of NL and AZI at various concentrations is shown in Table 4.1, which further supports the conclusionthatNLperformedbetterthanAZI.

In h ib it ion E f f ic ien c y ( % )

0 10 20 30 40 50 60 70 80 90 100 0.1 0.2 0,3 0.4 0.5

Inhibitor Concentration (g/L)

NL AZI

Figure4.7:Efficiency(%)versusConcentrationofinhibitor(g/L)forHCSwithNLandAZIleafextractsasinhibitor

NLleafextractinhibitedmosteffectivelyat0.5g/Lwithanefficacyof88%,whereasAZIhaditsmaximumefficiencyat0.4g/L witha78%efficiency.Figure3.7illustratesthepatternofhowefficiencywasimprovingasinhibitorconcentrationincreased.

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5 Conclusions

The findings of this study demonstrate that the extracts of Newbouldia Laevis and Azadirachta Indica leaves significantly reduce the corrosion of high carbon steel in H2SO4 solutions. With an increase in extract concentration, plant extracts' inhibitory potencies improved. The higher concentration of phytoconstituents identified in the Newbouldia Laevis extracts thanintheAzadirachtaIndicaextractsmayexplainwhytheNewbouldiaLaevisisfoundtobeamoreeffectiveinhibitorthan theAzadirachtaIndica

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