SIST EN 12698-1:2007
(Main)Chemical analysis of nitride bonded silicon carbide refractories - Part 1: Chemical methods
Chemical analysis of nitride bonded silicon carbide refractories - Part 1: Chemical methods
This standard describes the methods for the analysis of all refractory products containing nitride and oxynitride bonded silicon carbide, irrespective of the silicon carbide level. It includes details of sample preparation, general principles of chemical analysis and detailed methods for the determination of carbon, silicon carbide, free aluminium, free silicon, total nitrogen and oxygen.
Chemische Analyse von feuerfesten Erzeugnissen aus nitridgebundenem Siliciumcarbid - Teil 1: Chemische Verfahren
Analyse chimique des produits réfractaires contenant du carbure de silicium a liaison nitrure - Partie 1: Méthodes chimiques
La présente norme décrit les méthodes d’analyse applicables à tous les produits réfractaires contenant du carbure de silicium à liaison nitrure et à l’oxynitrure, quelle que soit la teneur en carbure de silicium. Elle contient les détails relatifs à la préparation des échantillons, les principes généraux de l’analyse chimique ainsi que les méthodes détaillées de détermination du carbone, du carbure de silicium, de l’aluminium libre, du silicium libre, de l’azote total et de l’oxygène.
Kemijska analiza nitrid silicijevega karbida - 1.del: Kemijske metode
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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
EN 12698-1:2007 (E) 2 Contents
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
EN 12698-1:2007 (E) 3 Foreword This document (EN 12698-1:2007) has been prepared by Technical Committee CEN/TC 187 “Refractory products and materials”, the secretariat of which is held by BSI. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by September 2007, and conflicting national standards shall be withdrawn at the latest by September 2007. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: 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.
EN 12698-1:2007 (E) 4 1 Scope This standard describes the methods for the analysis of all refractory products containing nitride and oxynitride bonded silicon carbide, irrespective of the silicon carbide level. It includes details of sample preparation, general principles of chemical analysis and detailed methods for the determination of carbon, silicon carbide, free aluminium, free silicon, total nitrogen and oxygen.
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.
EN 12698-1:2007 (E) 5 Free aluminium is determined by the evolution of hydrogen on treatment with hydrochloric acid and by measuring the gas volume in a nitrometer. Free silicon shall be determined on the same sample by treatment with sodium hydroxide. Total nitrogen is determined by a variety of methods: carrier gas fusion, alkaline fusion, Kjeldal distillation or microwave digestion. NOTE 2 The nitrogen can be conveniently measured by thermal conductivity or after digestion as ammonium by titration with hydrochloric acid. Distinction between aluminium nitride and silicon nitride is made by their reaction with sodium hydroxide solution; aluminium nitride is quantitatively decomposed yielding free ammonia, while silicon nitride is unaffected. A convenient commercial apparatus for determining total oxygen consists of an induction furnace in which the sample is heated with pure carbon. Carbon dioxide and carbon monoxide are measured by infrared absorption and the integrated signals are combined to give the total oxygen content. NOTE 3 Specification of many of the constituents can often be made using XRD techniques, e.g. free silicon, silicon nitride, silicon oxynitride, quartz and cristobalite (see EN 12698-2). Table 1 — Methods and relevant European Standards Item tested European Standard Carbon and silicon carbide prEN ISO 21068 Free silicon prEN ISO 21068 Oxygen prEN ISO 21068 Free aluminium EN 12698-1 Total nitrogen EN 12698-1 Silicon nitride/oxynitride, free silica EN 12698-1 XRD prEN ISO 21068 and EN 12698-2 Sialon EN 12698-2 Free carbon prEN ISO 21068 or EN 12698-1 Total carbon prEN ISO 21068 Silicon carbide prEN ISO 21068 and EN 12698-1 Free alumina EN 12698-1 5 Sampling Sample shaped and unshaped products using the procedures given in ISO 5022 and ISO 8656-1. When sampling large fragments, take care to collect samples from different points of individual pieces. Homogenize the sample by reducing the maximum particle size to 150 µm and take the test sample from this material. 6 Determination of free aluminium 6.1 Principle The volume of hydrogen generated by the action of dilute hydrochloric acid on any free aluminium in a sample is measured.
EN 12698-1:2007 (E) 6 If the sample is known to contain carbonate, then the volume of hydrogen evolved is corrected for the known carbonate content.
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):
EN 12698-1:2007 (E) 7
()()()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.
EN 12698-1:2007 (E) 8 7.2.3 Reagents During the analysis, unless otherwise stated, use only reagents of recognized analytical grade. 7.2.3.1 Distilled water,
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.
EN 12698-1:2007 (E) 9 7.2.5 Sample preparation Dry the test sample to constant mass at (110 ± 10) °C. It is advisable to encase the sample in tin, nickel or platinum and compress it so as little air as possible is included. Using bath metals such as casing materials (capsules or foil) will ensure formation of a homogeneous melt for the extraction. NOTE The addition of bath metals, e.g. nickel or tin, may also be necessary to complete the extraction. 7.2.6 Procedure The mass of the sample depends on the type of apparatus used, but the sample shall not be less than 4 mg. The lower limit depends on the homogeneity of the sample material and the upper limit on the calibration range of the apparatus; the initial sample mass will depend on the anticipated nitrogen content. Follow the manufacturer’s operating instructions for the apparatus. Place the crucible in the furnace and de-gas it at 100 °C above the analysis temperature. Weigh the sample and record its mass to the nearest 0,01 mg. Add the sample to the crucible and heat it.
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.
EN 12698-1:2007 (E) 10 7.2.8 Checking and maintaining the apparatus Before a new apparatus is used, the manufacturer’s data on the measurement range, initial sample mass, reproducibility and stability shall be checked using suitable samples with known nitrogen contents. The manufacturer’s instructions for regular checks and maintenance shall be carried out.
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.
EN 12698-1:2007 (E) 11 7.3.3.5 Boric acid solution, prepared by dissolving 40 g of boric acid, H3BO3, in 1 l of hot water. 7.3.3.6 Inert gas, argon or nitrogen (nitrogen acts as an inert gas for this reaction), with a purity of 99,99 % as inert gas. 7.3.3.7 Sodium carbonate, Na2CO3, 99,95 % to with a purity of at least 99,95 %. 7.3.3.8 Calcium chloride, CaCl2, dried. 7.3.4 Apparatus 7.3.4.1 Analytical balance, capable of reading to the nearest 0,01 mg. 7.3.4.2 Measurement device, apparatus for releasing, carrying over and absorbing ammonia (see Figure 2), comprised of: a) flow meter; b) gas washing bottles; c) vitreous silica reaction tube with ground joints, stoppers and gas inlet; d) unglazed porcelain boats; e) tubular furnace, e.g. heated by infrared radiation, capable of being heated to, and maintained at, (700 ± 10) °C; f) vitreous silica wool; g) gas inlet tube with ground joint and capillary tip; h) absorption vessel. In this apparatus, the inert gas from a pressurized gas cylinder passes through a gas washing bottle filled with sulfuric acid with a density, ρ = 1,84 g/ml, preceded and followed by an empty washing bottle for safety reasons. NOTE 1 No gas purification is necessary if the ammonia content of the inert gas does not exceed 0,005 % by volume. The inert gas is then passed through a flow meter and into the vitreous silica reaction tube at the side gas inlet. The ground joint through which the sample is inserted is also located at this point. The other end of the reaction tube is connected by a ground joint to a gas inlet tube whose tip has been drawn out to form a capillary and extends almost to the bottom of a narrow absorption vessel. NOTE 2
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.
EN 12698-1:2007 (E) 12 12357488869101 Key 1. Tubular furnace 2. Vitreous silica wool 3. Vitreous silica tube with connections
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 at (700 ± 10) °C, the nitride nitrogen will have been quantitatively converted into ammonia. Ensure the furnace temperature does not, under any circumstances exceed 730 °C, because the lithium hydroxide will start to evaporate above that temperature.
EN 12698-1:2007 (E) 13 7.3.6.2 Standardization of titration acid Dry the sodium carbonate at 270 °C to 300 °C for 1 h, stirring occasionally, and store it in a desiccator over calcium chloride. Weigh 200 mg of dried sodium carbonat
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