影响盐雾试验结果的决定因素

瑞凯仪器影响盐雾试验结果的决定因素（Determiningfactorsaffectingtheresultsofsaltspraytest）1、盐溶液的浓度及密度（1,theconcentrationanddensityofthesaltsolution）盐溶液的浓度对腐蚀速度的影响与材料和覆盖层的种类有关。浓度在5%以下时钢、镍、黄铜的腐蚀速度随浓度的增加而增加；当浓度大于5%时，这些金属的腐蚀速度却随着浓度的增加而下降。上述这种现象可以用盐溶液里的氧含量来解释，盐溶液里的氧含量与盐的浓度有关，在低浓度范围内，氧含量随盐浓度的增加而增加，但是，当盐浓度增加到5%时，氧含量达到相对的饱和，如果盐浓度继续增加，氧含量则相应下降。氧含量下降，氧的去极化能力也下降即腐蚀作用减弱。但对于锌、镉、铜等金属，腐蚀速度却始终随着盐溶液浓度的增加而增加。Theinfluenceoftheconcentrationofthesaltsolutiononthecorrosionrateisrelatedtothetypeofthematerialandthecoveringlayer.Thecorrosionrateofsteel,nickelandbrassincreasedwiththeincreaseofconcentrationintheconcentrationof5%.Whentheconcentrationwasgreaterthan5%,thecorrosionrateofthesemetalsdecreasedwiththeincreaseofconcentration.Thisphenomenoncanbeexplainedbytheoxygencontentinthesaltsolution,saltsolution,theoxygencontentandsaltconcentration,inthelowconcentrationrange,thecontentofoxygenincreasedwiththeincreaseofsaltconcentration,however,whenthesaltconcentrationincreasedto5%,theoxygencontentreachedtherelativesaturation,ifthesaltconcentrationcontinuestoincrease,theoxygencontentdecreasedcorrespondingly.Theoxygencontentisdecreased,andthedepolarizationabilityofoxygenisdecreased,andthecorrosioneffectisweakened.Butthecorrosionrateofzinc,cadmium,copperandothermetalsincreasedwiththeincreaseoftheconcentrationofthesaltsolution.2、样品的放置角度及位置（2.Thepositionandangleofthesample）样品的放置角度对盐雾试验的结果有明显影响。盐雾的沉降方向是接近垂直方向的，样品水平放置时，它的投影面积最大，样品表面承受的盐雾量也最多，因此腐蚀最严重。研究结果表明：钢板与水平线成45度角时，每平方米的腐蚀失重量为250g，钢板平面与垂直线平行时，腐蚀失重量为每平方米140g。GB/T2423.17-93标准规定“平板状样品的放置方法，应该使受试面与垂直方向成30度角。Theresultsofsaltspraytesthaveobviousinfluenceonthesampleplacementangle.Saltspraydepositiondirectionisclosetotheverticaldirection,whenthesamplelevelisplaced,itisthelargestprojectionarea,theamountofsaltsprayonthesamplesurfaceisalsothemost,sothemostseriouscorrosion.Theresearchresultsshowthat:whenthesteelplateandthehorizontallineis45degreeangle,thecorrosionweightlosspersquaremeteris250g,thesteelplateplaneisparalleltotheverticalline,andthecorrosionweightlossis140gpersquaremeter.TheGB/T2423.17-93standardprovidesfortheplacementoftheplatelikespecimen,whichshouldbethe30degreeangleofthetestedsurfaceandtheverticalFangXiangcheng.瑞凯仪器3、试验的温、湿度（3,thetesttemperature,humidity）温度和相对湿度影响着盐雾的腐蚀效果作用。一般金属腐蚀的临界相对湿度大约为70%。当相对湿度达到或超过这个临界湿度时，盐将潮解而形成导电性能良好的电解液。当相对湿度降低，盐溶液浓度将增加直至析出结晶盐，腐蚀速度相应降低。试验温度越高盐雾腐蚀速度越快。国际电工委员会IEC60355：1971《ANAPPRAISALOFTHEPROBLEMSOFACCELERATEDTESTINGFORATMOSPHERICCORROSION》标准指出：“温度每升高10℃，腐蚀速度提高2～3倍，电解质的导电率增加10～20%”。这是因为温度升高，分子运动加剧，化学反应速度加快的结果。对于中性盐雾试验，大多数学者认为试验温度选在35℃较为恰当。如果试验温度过高，盐雾腐蚀机理与实际情况差别较大。Theeffectoftemperatureandrelativehumidityonthecorrosionofsaltspray.Thecriticalrelativehumidityofgeneralmetalcorrosionisabout70%.Whentherelativehumidityreachesorexceedsthecriticalhumidity,saltdeliquescenceformedgoodconductivepropertiesofelectrolyte.Whentherelativehumidityisdecreased,theconcentrationofthesaltsolutionwillincreaseuntiltheprecipitationofcrystallinesalt,thecorrosionratewillbereducedaccordingly.Thehigherthetemperatureis,thefasterthesaltspraycorrosionrateis.Every10degreesCelsiusriseintemperature,corrosionrateisimprovedby2~3times,theconductivityoftheelectrolyteincreased10%~20%pointto,accordingtotheInternationalElectrotechnicalCommissionIEC60355:1971ofanAPPRAISALtheonofACCELERATEDtestingforATMOSPHERICCORROSION.Thisisbecausethetemperatureincreases,themolecularmotionisintensified,thechemicalreactionrateisaccelerated.Fortheneutralsaltspraytest,mostscholarsbelievethatthetesttemperatureismoreappropriateat35.Ifthetesttemperatureistoohigh,thecorrosionmechanismofthesaltsprayisdifferentfromtheactualsituation.4、盐溶液的pH值（4,thepHvalueofthesaltsolution）盐溶液的pH值是影响盐雾试验结果的主要因素之一。pH值越低，溶液中氢离子浓度越高，酸性越强腐蚀性也越强。以Fe/Zn、Fe/Cd、Fe/Cu/Ni/Cr等电镀件的盐雾试验表明,盐溶液的pH值为3.0的醋酸盐雾试验(ASS)的腐蚀性比pH值为6.5～7.2的中性盐雾试验(NSS)严酷1.5～2.0倍。由于受到环境因素的影响，盐溶液的pH值会发生变化。为此国内外的盐雾试验标准对盐溶液的pH值范围都作了规定，并提出稳定试验过程中盐溶液pH值的办法,以提高盐雾试验结果的重现性。PHvalueofsaltsolutionisoneofthemainfactorsthataffecttheresultsofsaltspraytest.ThelowerthepHvalue,thehigherthehydrogenionconcentrationinthesolution,thestrongertheacidity,thestrongerthecorrosionresistance.TosaltfogtestingofFe/Zn,Fe/Cd,Fe/Cu/Ni/Cr,suchaselectroplatingshowedthatsaltsolutionofpHvaluesof3.0aceticacidsaltspraytest(ASS),corrosivethanpHvalueis6.5~7.2neutralsaltspraytest(NSS)1.5harsh~2.0times.Duetoenvironmentalfactors,thepHvalueofthesaltsolutionwillchange.SoathomeandabroadofthesaltsprayteststandardofsaltsolutionpHrangearespecified,andputsforwardmethodsofstabilitytestprocessofsaltsolutionpHvalue,inordertoimprovethereproducibilityofresultsofsaltfogtest.