1、Designation: D8091 16 An American National StandardStandard Guide forImpregnation of Graphite with Molten Salt1This standard is issued under the fixed designation D8091; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of l
2、ast 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 guide covers procedures for the impregnation ofgraphite with molten salt under a consistent pressure andtemperatur
3、e. Such procedures are necessary if the user wishesto prepare graphite specimens for testing that have beenexposed to a molten salt environment that may not necessarilyrepresent material exposed to an operating reactor environ-ment.1.2 The values stated in SI units are to be regarded asstandard. No
4、other units of measurement are included in thisguide.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility o
5、f regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C559 Test Method for Bulk Density by Physical Measure-ments of Manufactured Carbon and Graphite ArticlesD7775 Guide for Measurements on Small Graphite Speci-mens3. Terminology3.1 Definitions:3.1.1 impregnation pressure
6、(PI), nthe pressure of covergas used in the impregnation.3.1.2 impregnation temperature (TI), nthe system tem-perature before the graphite sample has been immersed in themolten salt.3.2 Definitions of Terms Specific to This Standard:3.2.1 Parameter Dprovides a measure of the extent ofpenetration of
7、the graphite porosity by the molten salt. If therewas no damage to the microstructure of the graphite duringimpregnation, then parameter D based upon open pore volumewould be unity at saturation. At high impregnation pressures,closed porosity may be broken into by the molten salt andparameter D base
8、d upon open pore volume could have valuesgreater than unity. It is therefore useful to express parameter Din terms of both open pore volume and total (open and closed)pore volume.3.2.1.1 DiscussionParameter D is based upon open porevolume (typically applicable at low impregnation pressures)and is ca
9、lculated as follows:Do5W22 W1Vo(1)where:W1= the weight of the graphite sample before impregnation,W2= the weight of the graphite sample after impregnation, = the density of molten salt, andVo= the open pore volume in the sample.3.2.1.2 DiscussionParameter D based upon total porevolume (typically at
10、high impregnation pressures) is calculatedas follows:Dt5W22 W1Vt(2)where:Vt= the total pore volume in the sample.4. Summary of Guide4.1 This guide provides guidance on the impregnation ofgraphite with molten salt. The guide gives the various factorswhich need to be considered to perform the impregna
11、tionprocedure. These include pretreatment of graphite samples,immersion of graphite in the molten salt, safe handling of themolten salt, and selection and control of the impregnationpressures and temperatures.5. Significance and Use5.1 The molten salt reactor is a nuclear reactor which usesgraphite
12、as reflector and structural material and fluoride moltensalt as coolant. The graphite components will be submerged inthe molten salt during the lifetime of the reactor. The porousstructure of graphite may lead to molten salt permeation, which1This guide is under the jurisdiction of ASTM Committee D0
13、2 on PetroleumProducts, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom-mittee D02.F0 on Manufactured Carbon and Graphite Products.Current edition approved Dec. 1, 2016. Published January 2017. DOI: 10.1520/D8091-16.2For referenced ASTM standards, visit the ASTM website, www.
14、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.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis int
15、ernational standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) C
16、ommittee.1can affect the thermal and mechanical properties of graphite.Consequently, it is important to assess the effect of impregna-tion of molten salt on the properties of the as-manufacturedgraphite material.5.2 The purpose of this guide is to report considerations thatshould be included in the
17、preparation of graphite samplesrepresentative of that after exposure to a molten salt environ-ment. The degree to which the molten salt will infiltrate thegraphite will depend upon a number of factors, including thetype of graphite and the type and extent of porosity, theproperties of the molten sal
18、t, the impregnation pressure andtemperature, and the duration of the exposure of the graphite tothe molten salt.5.3 The user of this guide will need to select impregnationparameters sufficiently representative of those in a molten saltreactor based on parameters provided by the designer.Alternativel
19、y, the user may select a standard set of impregna-tion conditions to allow comparisons across a range of graphi-tes.5.4 This guide is not intended to be prescriptive. A typicalapparatus and associated procedure is described. Some indica-tion of the sensitivity of the procedure to graphite type andim
20、pregnation conditions is given in He, et al.35.5 There are four major practical issues that must beaddressed during the impregnation process:5.5.1 The density of molten salt is greater than that ofgraphite. A specially designed tool is required to submergegraphite samples in the molten salt during t
21、he impregnationprocess.5.5.2 Some molten salts (for example, FLiBe) are poisonousand it is therefore necessary to provide containment byperforming procedures within a glove box.5.5.3 The graphite must be kept away from air to avoidoxidation at high temperature. This can be achieved byperforming the
22、impregnation process within a glove box witha controlled atmosphere.5.5.4 Pressure control of the molten salt can be difficult toachieve. A specially designed autoclave is needed to hold thesample and molten salt.5.6 In order to assess the quantity of molten salt in thegraphite, parameter D is used
23、as a variable in measuring themechanical and thermal material properties. For a low impreg-nation pressure, the parameter Dois the ratio of salt volume toopen pore volume. For a high impregnation pressure, theparameter Dtis the ratio of salt volume to total pore volume.The saturated value of Docan b
24、e greater than 1 when themolten salt impregnation takes place at high pressure. It ispostulated that the internal microstructure of graphite has beendamaged by the impregnation pressure and some closed poreshave been opened. In this case, the parameter Dtis moreappropriate to represent the impregnat
25、ion process.6. Apparatus6.1 Autoclave:6.1.1 Since fluoride molten salts are toxic and a smallamount of water can significantly affect the wetting behavior ofgraphite, the conditions for the procedure should be strictlycontrolled during molten salt impregnation. The schematicdiagram of an impregnatio
26、n setup is shown in Fig. 1.6.1.2 An autoclave is used as a sealed container and shouldmeet a leakage rate 99.99 %) is pumped into theautoclave and is used to adjust the impregnation pressure ofmolten salt. A pressure gauge should be installed to measurethe gas pressure inside the autoclave.6.2 Elect
27、ric FurnaceAn electric furnace with temperaturecontrol is used to heat the autoclave. The furnace should beable to provide the desired temperature of TIC 6 20 C.6.3 Analytical BalanceAn analytical balance is used tomeasure the weight of the graphite sample before and after theimpregnation procedure.
28、 The error of the scale should be lessthan 60.1 mg.6.4 Glove Box:6.4.1 All the testing equipment, including the autoclave, theelectric furnace, and the analytical balance should be placedinside a glove box. A hoist system may be installed inside theglove box to aid lifting the autoclave and the grap
29、hite crucible.6.4.2 The water and oxygen contents inside the glove boxshould be less than 1 ppm to prevent external contamination or3He, Zhoutong, et al., “Molten FLiNaK Salt Infiltration into Degassed NuclearGraphite Under Inert Gas Pressure,” Carbon, Vol 84, 2015, pp. 511518. FIG. 1 Schematic Diag
30、ram of the Procedural SetupD8091 162oxidation. The glove box is maintained at negative pressure toprevent release of toxic salt vapor/dust from the glove box.6.4.3 The glove box can be divided into two zones. Onezone may be used for temporary storage of graphite samplesand the weighing of graphite s
31、amples; the other contains thefurnace and the impregnation equipment.7. Procedure7.1 Graphite specimens must be individually marked (forexample, surface laser etching) or tracked.7.2 For regular specimen geometries, the volume should beevaluated from the dimensions measured in accordance withTest Me
32、thod C559. For non-regular specimen geometries, thevolume must be evaluated by another method such as immer-sion method (Guide D7775).7.3 The graphite crucible and graphite sample must be driedin an oven at a temperature above 110 C for 2 h to remove anysorbed water.7.4 Measure the open pore volume,
33、 Vo, of the graphitesample by using helium pycnometry.7.5 The weight of graphite specimen is measured at roomtemperature by using the analytical balance inside the gloveboxand recorded as W1.7.6 Calculate the total pore volume, Vt, from the differencebetween the sample bulk density and the graphite
34、crystaldensity taken as 2.24 g cm3.7.7 The autoclave should be preheated at a temperatureabove 110 C for at least 2 h.7.8 Molten salt is poured into the graphite crucible beforethe impregnation such that the level is no more than half heightof the graphite crucible. The graphite crucible is placed i
35、nto theautoclave.7.9 The specimen holder containing the graphite specimensis placed inside the graphite crucible and held by the samplerod above the molten salt level.7.10 The autoclave flange is sealed. The temperature of theautoclave is increased to the desired impregnation temperature.The sample
36、holder containing the graphite specimens is im-mersed into the molten salt by pushing the sample rod after theimpregnation temperature has been reached.7.11 High purity inert gas is used to adjust the impregnationpressure inside the autoclave. Once the impregnation pressurehas been reached, the impr
37、egnation start time is recorded andthe duration measured.7.12 The desired impregnation pressure and temperatureshould be kept constant over the whole impregnation period.7.13 Retrieve the specimen after impregnation:7.13.1 Once the target impregnation time has been reached,withdraw the sample holder
38、 to a position above the molten saltlevel.7.13.2 Turn off the furnace and allow the autoclave to cooldown to room temperature.7.13.3 Release the pressure valve and open the autoclaveflanges to retrieve the specimens.7.13.4 The weight of each graphite specimen is measured atroom temperature by using
39、the analytical balance inside theglove box and recorded as W2.NOTE 1After the test, some solidified salt may have been deposited onthe surface of graphite specimen. The user may carefully remove the salton the surface before the measurement of specimen weight. Confirm thatthe individual dimensions o
40、f the sample are within 0.5 % of the originaldimensions.7.13.5 The specimen is stored in the temporary storage zoneof the glove box for use in subsequent tests.8. Test Data Record8.1 The actual impregnation time, the specimen dimension,the specimen weight before and after the impregnation, theimpreg
41、nation pressure, and temperature should be recorded.8.2 The D parameters should be calculated as in Eq 1 or Eq2 and should be recorded.9. Report9.1 The report should include all the test data recordstogether with relevant information on graphite gradedesignation, lot number, billet number, orientati
42、on, and loca-tion. Information on the molten salt shall be provided.10. Keywords10.1 graphite; impregnation; molten saltFIG. 2 Sample Holder: Graphite Plates and Sample RodD8091 163ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item
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