SIST EN 12698-1:2007

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Chemical analysis of nitride bonded silicon carbide refractories - Part 1: Chemical methodsKemijska analiza nitrid silicijevega karbida - 1.del: Kemijske metodeAnalyse chimique des produits réfractaires contenant du carbure de silicium a liaison nitrure - Partie 1: Méthodes chimiquesChemische Analyse von feuerfesten Erzeugnissen aus nitridgebundenem Siliciumcarbid - Teil 1: Chemische VerfahrenTa slovenski standard je istoveten z:EN 12698-1:2007SIST EN 12698-1:2007en;de71.040.40Kemijska analizaChemical analysisICS:SLOVENSKI
STANDARDSIST EN 12698-1:200701-julij-2007

EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 12698-1March 2007ICS 71.040.40 English VersionChemical analysis of nitride bonded silicon carbide refractories -Part 1: Chemical methodsAnalyse chimique des produits réfractaires contenant ducarbure de silicium à liaison nitrure - Partie 1: MéthodeschimiquesChemische Analyse von feuerfesten Erzeugnissen ausnitridgebundenem Siliciumcarbid - Teil 1: ChemischeVerfahrenThis European Standard was approved by CEN on 15 February 2007.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the CEN Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as theofficial versions.CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2007 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 12698-1:2007: E

Page Foreword.3 1 Scope.4 2 Normative references.4 3 Terms and Definitions.4 4 Methods for determination.4 5 Sampling.5 6 Determination of free aluminium.5 6.1 Principle.5 6.2 Reagents.6 6.3 Apparatus.6 6.4 Sample preparation.6 6.5 Procedure.6 6.6 Calculation and expression of results.6 7 Determination of total nitrogen.7 7.1 General.7 7.2 Determination of total nitrogen by carrier gas fusion (CGF).7 7.3 Determination of total nitrogen content by fusion decomposition.10 7.4 Determination of total nitrogen content by Kjeldahl distillation.14 7.5 Determination of total nitrogen by microwave digestion.16 8 Determination of free silicon.18 9 Determination of free silica.18 9.1 Principle.18 9.2 Reagents.18 9.3 Apparatus.19 9.4 Sample preparation.19 9.5 Procedure.19 9.6 Determination.21 9.7 Calculation and expression of SiO2 content.21 9.8 Precision.21 10 Determination of carbon.21 10.1 Determination of the total carbon,
Ct.21 10.2 Determination of free carbon, Cfree.21 11 Calculation of silicon carbide content.25 12 Determination of free alumina (Al2O3).25 12.1 Principle.25 12.2 Reagents.25 12.3 Apparatus.26 12.4 Procedure.26 12.5 Calculation and expression of results.26 12.6 Precision.26 Annex A (informative)
Determination of free carbon using the hot chromic sulfuric iodic acid method (10.2.1): Explanation for the evaluation of the different possible detection methods.27 A.1 Coulometric detection system.27 A.2 Infrared absorption detection system.29 A.3 Conductometric detection system.30 Bibliography.32

2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 12475-4:1998, Classification of dense shaped refractory products — Part:4 Special products EN 12698-2,
Chemical analysis of nitride bonded silicon carbide refractories — Part 2: XRD methods prEN ISO 21068, Chemical analysis of silicon carbide containing raw materials and refractory products ISO 836:2001, Terminology for refractories ISO 3310-1, Test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth ISO 5022, Shaped refractory products — Sampling and acceptance testing ISO 5725-1, Accuracy (trueness and precision) of measurement methods and results — Part 1: General principles and definitions
ISO 8656-1, Refractory products — Sampling of raw materials and unshaped products — Part 1: Sampling scheme 3 Terms and Definitions For the purposes of this document the terms and definitions given in ISO 836:2001, EN 12475-4:1998 and the following apply.
3.1 nitride and oxynitride bonded silicon carbide refractories
refractory products predominantly consisting of silicon carbide with minor amounts of nitride phases as a matrix component NOTE In general, metallic silicon is used as precursor material which undergoes a phase transformation in an oxygen-free nitrogen atmosphere. 4 Methods for determination A list of methods and the relevant European Standards are given in Table 1.
Carbon is determined by the evolution of carbon dioxide on combustion in a stream of oxygen at defined temperatures. Silicon carbide is calculated by the difference of total carbon (Ctotal) and free carbon (Cfree). NOTE 1 The carbon dioxide evolved can be conveniently measured coulometrically, gravimetrically by absorbtion onto soda lime, or by infrared detection.

The free aluminium content can also be determined by the evolution of hydrogen using sodium hydroxide. In this case, the volume of hydrogen evolved is corrected for the silicon content. Free iron will also evolve hydrogen; a correction is made for the iron content.
6.2
Reagents During the analysis, unless otherwise stated, use only reagents of recognized analytical grade 6.2.1 Distilled water or water which has been fully demineralized by ion exchange (deionized water) and reagents of analytical grade. 6.2.2 Dilute hydrochloric acid, 1+1 by volume. 6.3
Apparatus 6.3.1 Nitrometer, as used for determining free silicon. 6.3.2 Balance, capable of reading to the nearest 0,1 mg. 6.4
Sample preparation Dry the test sample (sampling as described in clause 5) a to constant mass at (110 ± 10) °C for a minimum of 2 h prior to analysis. 6.5
Procedure
Weigh (0,5 ± 0,01) g of sample into a clean, dry nitrometer tube. Place a dry ignition tube inside the tube and holding the nitrometer tube upright, introduce, using a long dropping pipette and without letting any touch the sample, 5 ml of dilute hydrochloric acid into the ignition tube.
Carefully fit the bung of the apparatus making sure there is good seal. Equalize the pressure and leave the three-way tap in a position that connects the sample and graduated tube. Tip the acid out of the ignition tube onto the sample. Shake the apparatus gently and allow it to stand for 15 min. Read off the volume after equalizing the pressure. Shake gently and read again after another 5 min to 10 min. Record the final volume reading when consecutive readings are the same. Also note the temperature and barometric pressure.
NOTE If this method is used frequently, it is recommended that a conical flask with airtight sample insert device, e.g. a side-on positioned ground-in connection and ground-in stopper with weighing bottle (special version) is used. The weighed sample is placed into the stopper-connected weighing bottle. The hydrochloric acid is added to the flask. After equalizing the pressure, the sample powder is added to the acid by turning the stopper. 6.6
Calculation and expression of results Correct the volume reading to the gas volume at standard temperature, V(STP) in ml, using equation (1):

()()()TppVV+×−×=273273013,251OH1STP2 (1) where V1 is the measured volume, in ml; p
is the atmospheric pressure, at time of measurement, in hPa;
OH2p is the partial pressure of water vapour at the measured temperature, in hPa; T
is the measured temperature, in °C. Calculate the percentage of free aluminium, A, using equation (2): ()mVA1008040,000STP××= (2) where
m is the mass of the sample, in g. Report the result to the nearest 0,1 %. 7 Determination of total nitrogen 7.1 General To determine total nitrogen one of the four methods given in 7.2 to 7.5 shall be used. 7.2
Determination of total nitrogen by carrier gas fusion (CGF) 7.2.1 General This method is used to determine nitrogen in silicon nitride, Si3N4, and other compounds, in the form of nitrides and oxynitrides by thermal decomposition. 7.2.2 Principle A sample, prepared as described in clause 5, is decomposed in a graphite crucible in a stream of carrier gas (helium) by heating it to above 2 400 °C in a resistance furnace (electrode furnace). The gases released are mainly nitrogen, carbon monoxide and hydrogen. The carbon monoxide and hydrogen are oxidized to carbon dioxide and water and then removed by absorption. Alternatively, formed carbon monoxide and gases other than nitrogen shall be removed, for example, using a molecular sieve. The change in thermal conductivity due to the nitrogen component is then measured.
The details of the determination procedure can vary with the type of apparatus used and it is therefore only possible to give general instructions that can be used with any type of apparatus. Using the gas calibration, the validity of the results is confirmed by analysing a reference material having similar extraction behaviour.

or water which has been fully demineralized by ion exchange (deionized water).
7.2.3.2 Helium, having a minimum purity of 99,99 %. 7.2.3.3 Nitrogen, having a minimum of 99,99 %. 7.2.3.4 Catalysts, such as copper oxide. 7.2.3.5 Sorption agents for removing water vapour and carbon dioxide, e.g. magnesium perchlorate, sodium hydroxide on a support, or a molecular sieve. 7.2.4 Apparatus 7.2.4.1 Measurement device, commercially available apparatus consisting of a resistance furnace and a measuring unit for determining nitrogen in a stream of carrier gas using a thermal conductivity cell. An example of a suitable apparatus is given in Figure 1. HeN1572349862 Key 1. Carrier gas 2. Crucible 3. Sample 4. Thermal conductivity cell 5. He plus gases from sample 6. Electrodes 7. Calibration gas 8. Apparatus for oxidizing carbon monoxide and hydrogen (CO : CO2; H2 : H2O) 9. Carbon dioxide and water vapour absorption tubes (H2O CO2) Figure 1 — Gas flow diagram for the determination of total nitrogen by carrier gas fusion
7.2.4.2 Analytical balance, capable of measuring to the nearest 0,01 mg. 7.2.4.3 Graphite crucibles, having approximately the same electrical resistance.
The crucibles shall contain concentrations of nitrogen as low as possible. The nitrogen shall be removed by out-gassing, which can be proved by blank determinations.

NOTE Reliable analytical results will only be obtained if adequate information relating to sample preparation, procedure, calibration, recalibration and checking, and apparatus maintenance is available from in-house experiments and experience. 7.2.7 Calibration and recalibration 7.2.7.1 Gas calibration Carry out gas calibration by adding a known amount of nitrogen gas. Calculate the amount of gas added, m in mg, using equation (3): ()TpVpm×+××=γρ1nNT2 (3) where p
is the corrected barometric pressure, in hPa; T
is the temperature, in °C; VT
is the gas volume added, in ml at T °C and p hPa; N2
is the density of nitrogen gas under standard conditions, i.e. 1,250 4 mg/ml; γ
is the cubic coefficient of thermal expansion of nitrogen (0,003 671 K-1);
pn
is the standard pressure, 1013,25 hPa. The linearity of the evaluation curve is fixed by this procedure. This can also be done with a computer connected to the measuring equipment. The calibration, however, will not provide any information about the efficiency of the extraction process. This can only be determined by analysing suitable reference samples. The latter approach is the only one possible for systems not designed for gas calibration. 7.2.7.2 Calibration using solids For calibration with solids, the reference material shall be analysed using widely varying sample masses covering as much as possible, the entire calibration range of the apparatus.
NOTE 1 The relative analytical error will increase if smaller sample masses are used. NOTE 2 If linearity has been found beforehand by calibration using gas addition or a reference sample, any variation is the analytical result in connection with the initial sample mass and can be unambiguously ascribed to an inefficient extraction process.

NOTE Incorrect results can be expected if replacement of the oxidation and sorption reagents it is not carried out in due time. 7.2.9 Calculation Typically, using state of the art instrumentation, the nitrogen content is automatically calculated through the calibration function in % by mass by entering the sample mass. If only nitrogen mass is indicated, calculate the nitrogen content in % by mass manually.
For older instrumentation where only a measuring category for nitrogen is indicated, it is necessary to plot a calibration curve. The concentration of the test sample is calculated from the value of the calibration samples measured via the calibration curve. 7.2.10 Precision Under the specified conditions, the values of the repeatability limit r, and the reproducibility limit R, as defined in ISO 5725-1 are:
r = 1 %;
R = 2 %. NOTE An improved reproducibility and accuracy may be expected if certified reference materials are used for calibration. 7.3
Determination of total nitrogen content by fusion decomposition 7.3.1 General This method is used to determine nitrogen in silicon nitride, Si3N4, and other compounds in the form of nitrides and oxynitrides by fusion decomposition. Analogous methods may be used to determine nitrogen in materials containing not less than 5 % by mass of nitrogen bound in the form of nitrides and oxynitrides. 7.3.2 Principle The sample is fused with lithium hydroxide at no more than 700 oC to convert the nitrogen into ammonia. A gentle stream of inert gas is used to transfer the ammonia to a receiving vessel containing boric acid solution and the amount of nitrogen is determined by titration with an acid of known concentration. 7.3.3 Reagents During the analysis, unless otherwise stated, use only reagents of recognized analytical grade. 7.3.3.1 Distilled water,
or water which has been fully demineralized by ion exchange (deionized water). 7.3.3.2 Powdered lithium hydroxide, LiOH. 7.3.3.3 Sulfuric acid, ρ = 1,84 g/ml. 7.3.3.4 Standard solution, 0,1 mol/l hydrochloric or sulfuric acid of known standardization for titration.

The reaction tube can also be a gas-tight ceramic tube with the sample inlet and borosilicate glass ground joint shown in Figure 1, which are fused on or attached by means of silicone hoses. The reaction tube shall be heated by a tubular furnace which can be maintained at (700 ± 10) °C. The still hot part of the tube outside the tubular furnace and adjacent to the absorption vessel is packed with loose vitreous silica wool which is capable of condensing any lithium hydroxide which evaporates.

4. Inert gas 5. Gas inlet tube with capillary tip 6. Sulfuric acid 7. Porcelain boat 8. Washing bottles 9. Boric acid solution 10. Absorption vessel Figure 2 — Nitrogen determination apparatus for fusion decomposition
7.3.4.3 Potentiometric titrator, with a metering volume of 50 ml and a maximum relative tolerance of 0,1 %. 7.3.5 Sample preparation Dry the test sample (sampled as described in clause 5) to constant mass at (110 ± 10) °C for a minimum of 2 h prior to analysis. 7.3.6 Procedure 7.3.6.1 Decomposition by fusion NOTE The time for complete reaction should be established before the method is applied. Coat the entire inside of the porcelain boats with 500 mg of lithium hydroxide at 600 °C and store the boats in a desiccator. Weigh 100 mg of the sample to the nearest 0,01 mg, into a coated porcelain boat and mix thoroughly with 1,5 g of lithium hydroxide. Flush the apparatus with inert gas and pour 40 ml of boric acid solution into the absorption vessel and immerse the gas inlet tube in it. Set the inert gas flow to 70 normal ml/min to 100 normal ml/min, open the ground joint closure and push the porcelain boat into the centre of the reaction tube to the point where the thermocouple is located. After closing the tube again, slowly heat the tubular furnace to 700 °C in steps to prevent the melt from spattering. For tubular furnaces that heat up rapidly, the heating phase shall not be less than 15 min. After 30 min a
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