ASTM_D_4517_-_15.pdf

Designation:D451715Standard Test Method forLow-Level Total Silica in High-Purity Water by FlamelessAtomic Absorption Spectroscopy1This standard is issued under the fixed designation D4517;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the determination of total silicain water.1.2 This test method is applicable in the range from 25 to250 g/L of silica as SiO2.Higher concentrations may bedetermined by decreasing the aliquot volume(see Note 6).Concentration range should not be extended by dilution.1.3 This test method determines total silica,and does notdistinguish between soluble and insoluble forms.1.4 This test method was tested on reagent water only.It isthe users responsibility to assure the validity of the testmethod for waters of other matrices.1.5 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.6 This standard does not purport to address the safetyconcerns,if any,associated with its use.It is the responsibilityof the user of this standard to establish appropriate safety andhealth practices and determine the applicability of regulatorylimitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D859 Test Method for Silica in WaterD1066 Practice for Sampling SteamD1129 Terminology Relating to WaterD1192 Guide for Equipment for Sampling Water and Steamin Closed Conduits(Withdrawn 2003)3D1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD3919 Practice for Measuring Trace Elements in Water byGraphite Furnace Atomic Absorption SpectrophotometryD4453 Practice for Handling of High Purity Water SamplesD5810 Guide for Spiking into Aqueous SamplesD5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water Analysis3.Terminology3.1 Definitions:3.1.1 For definitions of terms used in this standard,refer toTerminology D1129.4.Summary of Test Method4.1 Total silica is determined using an atomic absorptionspectrophotometer in conjunction with a graphite furnace.Asample is placed in a graphite tube,evaporated to dryness,charred,and atomized.Since the graphite furnace uses thesample much more efficiently than flame atomization,thedetection of low concentrations of elements in small samplevolumes is possible.Finally,the absorption signal duringatomization is recorded and compared to standards.A generalguide for the application of the graphite furnace is given inPractice D3919.Pretreatment of the graphite tube may be usedto enhance the sensitivity and repeatability,or both,of the test.44.2 Total silica is determined using a freshly ultrasonicallytreated and shaken aliquot of sample.4.3 This test method determines low-level total silica inhigh purity water.Refer to Test Method D859,Test Method B,for determination of molybdate-reactive silica.5.Significance and Use5.1 Control of silica in boiler feedwater and boiler water isnecessary to minimize the formation of scale-forming silicatesthat decrease heat transfer in the boiler.Volatilization and1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.03 on Sampling Water andWater-Formed Deposits,Analysis of Water for Power Generation and Process Use,On-Line Water Analysis,and Surveillance of Water.Current edition approved Aug.1,2015.Published September 2015.Originallyapproved in 1985.Last previous edition approved in 2009 as D4517 04(2009).DOI:10.1520/D4517-15.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.4Rawa,J.A.,and Henn,E.L.,“Determination of Trace Silica in IndustrialProcess Waters by Flameless Atomic Absorption Spectrometry,”AnalyticalChemistry,Vol 51,March 1979.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 carryover of silica with the steam may cause hard,glassysiliceous deposits to form on turbine blades that reduce turbineefficiency.5.2 Colloidal silica that is not removed by boiler waterpretreatment processes may be solubilized in the boiler andthus contribute to the dissolved silica concentration in theboiler.Both dissolved and total silica are of interest.6.Interferences6.1 For a complete discussion of general interferences withfurnace procedures,the analyst is referred to Practice D3919.6.2 Relatively pure waters such as demineralizer