1、Designation: C 831 98 (Reapproved 2003)Standard Test Methods forResidual Carbon, Apparent Residual Carbon, and ApparentCarbon Yield in Coked Carbon-Containing Brick andShapes1This standard is issued under the fixed designation C 831; the number immediately following the designation indicates the yea
2、r 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods cover the determination of residual
3、carbon content in carbon-bearing brick and shapes after aprescribed coking treatment. They provide two procedures.The first procedure is based on the combustion of carbon andits measurement as carbon dioxide. However, when using thefirst procedure for articles that contain silicon carbide or otherca
4、rbides, no distinction will be made between carbon present inthe form of a carbide and carbon present as elemental carbon.The second procedure provides a method for calculatingapparent residual carbon (on the basis of weight loss afterigniting the coked specimens), apparent carbonaceous materialcont
5、ent, and apparent carbon yield. If the second procedure isused for brick or shapes that contain metallic additives orcarbides, it must be recognized that there will be a weight gainassociated with the oxidation of the metals, or carbides, orboth. Such a weight gain can change the results substantial
6、lyand this must be kept in mind when interpreting the data.1.2 The values stated in inch-pound units are to be regardedas the standard. The values given in parentheses are forinformation only.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It
7、 is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 571 Methods for Chemical Analysis of Carbon andCarbon-Ceramic RefractoriesD 29
8、06 Practice for Statements on Precision and Bias forTextilesE 11 Specification for Wire-Cloth Sieves for Testing Pur-poses3. Significance and Use3.1 These test methods are designed for use with carbon-containing products. The residual carbon content of a cokedcarbon containing brick or shape is an i
9、ndication of how muchcarbon may be available, in service, to resist slag attack on, oroxidation loss of, that body. Apparent carbon yield gives anestimate of the relative efficiency of the total carbonaceousmatter to be retained as residual carbon.3.2 Residual carbon has a direct bearing on several
10、proper-ties of a pitch or resin containing refractory such as ignitedporosity, density, strength, and thermal conductivity.3.3 These test methods are suitable for product develop-ment, manufacturing control and specification acceptance.3.4 These test methods are very sensitive to specimen size,cokin
11、g rates, etc., therefore, strict compliance with these testmethods is critical.3.5 Appreciable amounts of reducible components, such asFe2O3, will have a noticeable effect on the results. Thus, valuesobtained by these test methods will be different when brickremoved from service is tested. This must
12、 be kept in mindwhen attempting to use these test methods in an absolute sense.3.6 Oxidizable components such as metals and carbides canhave a noticeable effect on the results. This must be kept inmind when using the second procedure, which is based onmeasuring weight loss after igniting the coked s
13、pecimens.3.7 Testing of brick or shapes that contain magnesium metalpresents special problems since this metal is highly volatile andsubstantial amounts of the magnesium can be lost from thesample during the coking procedure. This must be kept in mindwhen interpreting the results of testing of brick
14、 that containmagnesium. In addition, magnesium can react readily withatmospheric humidity. This must be kept in mind when storingbrick that contain magnesium.4. Apparatus4.1 For Coking:1These test methods are under the jurisdiction of ASTM Committee C08 onRefractories and are the direct responsibili
15、ty of Subcommittee C08.04 on ChemicalBehaviors.Current edition approved November 2003. Published January 2004. Originallyapproved in 1976. Last previous edition C 831 98.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annu
16、al Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.1.1 Gas or Electric Furnace with heating chamber ca-pable of receiving the
17、 coking box shown in Fig. 1.NOTE 1Samples should not be subjected to thermal gradients greaterthan 40F (22C) during heatup. In electric furnaces with silicon carbideheating elements, the length of the box should be parallel to theseelements.4.1.2 Inner and Outer Box, stainless steel (or equivalental
18、loy), as shown in Figs. 1-3.4.2 For CO2Absorption:4.2.1 Laboratory Pulverizer3designed to provide a sealed,dustproof grinding chamber, and having a capacity of at least50 g of sample.4.2.2 Combustion-Tube Furnace capable of operating at183F (1000C)4.2.3 CO2-Absorption Train as described in Fig. 4 an
19、d inMethod C 571NOTE 2Commercial automatic and semi-automatic carbon determi-nators may replace the apparatus described in 4.2.2 and 4.2.3.4.3 The precision obtained with these instruments shallmeet the requirements specified in Section 10.5. Preparation of Test Specimens5.1 This method assumes that
20、 the number of specimenstested will be a statistically valid sample of the entire lot ofbrick or shapes being evaluated. The exact number is usuallyarrived at by mutual agreement between parties concerned.5.2 Although sample brick from either the 412-in. (114-mm)or the 6-in. (152-mm) series may be t
21、ested, it is preferable touse the larger size for the test. Cut slices 1 6132 in. (25 6 0.8mm) in thickness perpendicular to the length at the mid-sectionof each sample brick or shape. As shown in Fig. 5, the nominal3Typical grinders are: Blueler Mill, Applied Research Laboratories, Sunland,CA; Labo
22、ratory Disc Mill, Angstrom, Inc., Bellville, MI; and Shatter Box, SpexIndustries, Inc., Metuchen, NJ.FIG. 1 Outer Coking Box (Dimensions are in Inches)C 831 98 (2003)2size of each slice shall be 1 by 3 by 6 in. (25 by 76 by 152 mm).The two 1 by 3-in. faces and the two 1 by 6-in. faces must beorigina
23、l surfaces.5.3 Test specimens may be cut wet or dry except forproducts capable of hydration, such as dolomite brick, whichmust be cut dry and stored in a dry container prior to coking.5.4 Specimens that are cut wet must be dried immediatelywith a paper or cloth towel and flash dried. For pitch-impre
24、gnated samples, flash drying should be done at a suffi-ciently low temperature to avoid “weeping” of pitch from thepores of the brick. Drying can usually be done on a forced-airdryer at 220F (105C) by limiting exposure to 5 to 10 min.Repeat if necessary. These drying procedures are especiallyimporta
25、nt for metal-containing brick because hydration of themetals can occur. Specimens containing a coating of pitch onFIG. 2 Inner Coking BoxC 831 98 (2003)3uncut surfaces, as is typical of an impregnation process, mustbe scraped clean prior to drying.5.5 Weigh all specimens after drying to constant wei
26、ght(60.2g), recording weight to the nearest 0.1 g. This weight is“as-received weight, A,” (This step may be omitted if residualcarbon is to be determined by CO2absorption, as indicated in1.1.)6. Procedure for Coking6.1 Place the test specimens randomly into the inner box,Fig. 2NOTE 3Burned pitch-imp
27、regnated magnesite brick should not becoked with tempered, tar-bonded, or dolomite brick because of carbonpickup by the impregnated samples and disruption of the bottom ofFIG. 3 Coking Box ArrangementFIG. 4 CO2-Absorption TrainC 831 98 (2003)4tempered samples. Pitch-bonded, pitch-bonded tempered mag
28、nesite brickand dolomite brick may be coked in the same box or coking run.NOTE 4The number of samples coked per run should be constantwithin a laboratory. Dummy uncoked samples consistent with Note 3 maybe used to fill any empty positions in the inner box.6.2 Place the inner box into the center of t
29、he outer box (Fig.3), on the bottom of which has first been placed a12-in.(13-mm) slab of carbon, covered with a thin layer of dust-freemetallurgical-grade coke breeze (No. 14 (1.40mm) sieve size)(Note 5). To ensure that the coke breeze is free of moisturewhich could oxidize carbon during cooking, d
30、ry the coke at400F (205C) for 24 h, and keep in a closed container at roomtemperature until needed.NOTE 5Detailed requirements for sieves are given in Specification E116.3 Place the thermocouple well into the center of the innerbox and put the lid on the inner box. The thermocouple wellmust be long
31、enough to extend above the cover of the outerbox.6.4 Cover the inner box with metallurgical-grade cokebreeze retained on a No. 14 sieve and place a loose-fitting lidover the coke breeze (see Fig. 3). Pack the coke breeze betweenthe edges of the lid and box.6.5 Place the coking-box assembly (Fig. 3)
32、into the furnace,and insert a calibrated thermocouple into the thermocouplewell.6.6 Heat the furnace so that the thermocouple within the boxregisters 250F (120C) after the first hour, then heat thefurnace so that the box is heated at a rate of 400 6 20F (220611C)/h to 1800 6 20F (980 6 11C).6.7 Hold
33、 the temperature for 3 612 h, starting from the time1780F (970C) is reached in the inner box.6.8 After completing the hold period, shut off the furnaceand allow the coking box to cool naturally within the furnace.6.9 Remove the samples from the coking box after the boxhas cooled sufficiently to hand
34、le. After removing specimensfrom the inner box, clean by brushing carefully with a nylon ornatural bristle brush to remove clinging particles. The proceedto either of the two alternatives for analyzing the specimens.NOTE 6After each run, clean the muffle and the bottom carbon plateof any adhering co
35、ke breeze.6.10 Samples that contain dolomite or aluminum metalshould be stored in a sealed container containing dessicant inthe time interval between coking and measurement of carboncontent. This is to prevent hydration of dolomite or aluminumcarbide. The aluminum carbide is formed by reaction betwe
36、enaluminum and carbon in the shape during the coking operation.Aluminum carbide can react with a water source such asatmospheric humidity to form methane. Care should be takensince methane can be an explosion hazard.CO2ABSORPTION (FIRST ALTERNATIVEPROCEDURE)7. Preparation of Sample7.1 A sample consi
37、sts of a single slice or multiple specimensof brick prepared as described in Sections 5 and 6.7.2 Crush the sample in a laboratory jaw crusher, or otherimpact-type crusher, to pass a No. 4 (4.75-mm) sieve (Note 5).Thoroughly mix the crushed sample and reduce to approxi-mately 50 g by quartering or r
38、iffling.7.3 Place the sample in the laboratory pulverizer and grindto 100 % passing a No. 100 (150 m) sieve. This takesapproximately 90 to 100 s. Promptly transfer the groundsample to a suitable airtight container.NOTE 7Extreme care must be taken during the entire sample prepa-ration to avoid loss o
39、f carbon by segregation or dusting. About 60 % of thevariance in this procedure is in this step.8. Procedure8.1 With the furnace at operating temperature, pass oxygenthrough the absorption train until the CO2-absorption bulbattains constant weight (usually 15 to 30 min). Adjust theoxygen pressure an
40、d flow rate to provide 120 to 150 bubblesper minute through the bubbling tower. Close the stopcock,remove the absorption bulb from the train, cool to roomtemperature, and weigh to the nearest 0.1 mg.8.2 Into a previously ignited combustion boat, weigh a 0.1to 1.0 g sample to the nearest 0.1 mg. Retu
41、rn the weighed CO2absorption bulb to the train and open the stopcock. Then placethe combustion boat with sample in the combustion tube andimmediately reseal the train. Adjust the flow of oxygen asbefore (8.1), heat the furnace to 1740 to 1830F (950 toFIG. 5 Location of Test SpecimenC 831 98 (2003)51
42、000C), and maintain until the CO2adsorption bulb attainsconstant weight (usually 45 to 60 min).8.3 Remove the absorption bulb from the train, close thestopcock, cool to room temperature, and reweigh. The increasein weight is the CO2won from the sample by combustion ofthe carbon.9. Calculation and Re
43、port9.1 Calculate the percentage of residual carbon in thesample as follows:Residual carbon, % 5wt of CO23 0.2729 3 100wt of sample(1)9.2 Run the determinations in duplicate. Results shall notvary by more than 60.05 % stated in terms of the wholesample as 100 %. If satisfactory checks are not obtain
44、ed, repeatthe analysis in duplicate. Report at least two individualanalyses per slice.10. Precision and Bias410.1 An interlaboratory study was conducted in 1970 usinga nested experimental design wherein a composite of severalsizes of magnesite grain and lampblack was mixed in accu-rately weighed pro
45、portions, divided into four samples, and sentto four laboratories for testing. Each laboratory split its sampleinto four specimens, ground them for analysis and made tworeplicate determinations on each. The components of variance(Note 8) of the results given in terms of standard deviationswere found
46、 to be as follows:Carbon Content , %Grand mean 4.572Between laboratories (sL) 6 0.0778Between samples (sS6 0.0987Between replicates (sR) 6 0.0161NOTE 8A procedure for calculating precision is fully described inPractice D 2906. There is no known means for determining the bias ofthese test methods.10.
47、2 On the basis of the components of variance in 10.1, wewould expect two averages of an equal number of specimenstested by this test method to be considered different at the 95% probability level if their difference exceeds the values below(for t = 1.96) (assume that two replicates are always used p
48、ertest method:Number of Samples Between Samples Between Twoin Each Average Within One Laboratory Laboratories1 0.274 0.3506 0.116 0.24512 0.085 0.23210.3 These precision data may not be applicable for sampleswith substantially higher carbon contents or for samples thatcontain metals.IGNITION LOSS (S
49、ECOND ALTERNATIVEPROCEDURE)11. Procedure11.1 Weigh all specimens to the nearest 0.1 g and record as“coked weight, B.”11.2 Place specimens on a layer of magnesia grain in a kilnor furnace.11.3 Heat specimens in an air atmosphere (preferably cir-culating) at 500 to 700F (280 to 380C)/h to a temperaturebetween 1800 and 2200F (980 to 1205C). For alumina-silicarefractories, ignition temperature should be limited to 1800F.11.4 Hold the selected temperature for a minimum of 8 h(depending on the temperature in 11.3), or until a constantweight (6 0.2
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