Tiêu chuẩn iso 21068 3 2008

Microsoft Word C043831e doc Reference number ISO 21068 3 2008(E) © ISO 2008 INTERNATIONAL STANDARD ISO 21068 3 First edition 2008 08 01 Chemical analysis of silicon carbide containing raw materials an[.]

General

For oxygen only, the IR detection method is given; for nitrogen, several different methods are described, calculated nominally as Si 3 N 4

The calculation of nitrogen as Si₃N₄ is valid only when other nitride species are either absent or present at levels too low for detection by XRD, as outlined in ISO 21068-1 In cases where other nitride species are detectable, nitrogen should be reported as total nitrogen.

Combined determination of nitrogen and oxygen by an analyser with thermal

conductivity (CR) and infrared absorption (IR) detection

The method employs inert-gas fusion analysis, where a preweighed sample is placed in a graphite crucible situated between the electrodes of an impulse furnace Typically, 5 kW of power is applied to the crucible, resulting in a temperature of around 2,800 °C.

NOTE 1 Furnace temperatures can be varied by increasing and decreasing current/voltage

The sample undergoes decomposition, releasing elemental nitrogen and oxygen, which reacts with the graphite crucible to produce carbon monoxide The gases are transported via a helium carrier gas to a rare-earth copper catalyst that converts carbon monoxide into carbon dioxide, which is then measured in an infrared cell Alternatively, the gases can be measured directly as carbon monoxide without the catalyst The gas stream is subsequently treated with sodium hydroxide to eliminate carbon dioxide and magnesium perchlorate to remove moisture, before being analyzed for nitrogen quantification using a thermal conductivity cell or another suitable analyzer.

NOTE 2 A method for the determination of oxygen contents less than 3 % is given in EN 725-3 [7]

To prevent sample loss during analysis, it is essential to enclose the powder sample in a small nickel capsule before placing it in the graphite crucible.

When materials with dissociation temperatures higher than 2 400 °C ± 25 °C are being analysed, it is recommended that a fluxing agent is also included with the sample A suitable agent would be a nickel wire basket

4.2.2.1 Nickel or tin capsule, of suitable dimensions and oxygen and nitrogen free

4.2.2.2 Nickel basket, of suitable dimensions and oxygen and nitrogen free

Ordinary laboratory apparatus and the following

4.2.3.1 Combined nitrogen/oxygen analyser, commercially available

NOTE If no combined analyser for nitrogen and oxygen is available, a separate nitrogen and/or oxygen analyser can be used

Calibration can be performed using two methods as outlined in the instrument operation manual: a) utilizing certified reference materials, ideally primary ones; and b) injecting known volumes of pure carbon dioxide and nitrogen into the detection system.

If b) is used, it is recommended that a standard reference material be analysed to verify the performance of the electrode furnace, associated chemicals and detection system

For both methods, a minimum of three calibration points and a zero shall be used to establish the calibration

Operate the instrument in accordance with the instrument operation manual

Copyright International Organization for Standardization

Dry and grind the sample (see Clause 4 of ISO 21068-1:2008) Weigh it, to the nearest 0,1 mg, into the nickel capsule and seal it, taking care to expel any air present

A typical sample mass is around 50 mg ± 1 mg, but the actual mass is influenced by the analyser's dynamic range and the concentration levels of oxygen and nitrogen present.

Put the nickel capsule into the loading-mechanism analyser

The analysis is conducted in two stages: first, heat the graphite crucible to a temperature equal to or greater than that used for the analysis, allowing enough time for any trapped oxygen and nitrogen to be expelled Next, introduce the sample into the heated graphite crucible and proceed with the analysis.

Because of the sample masses involved, report results as the mean of at least three determinations

Before analysis, any oxygen and nitrogen in the graphite crucible is eliminated; however, residual oxygen and nitrogen may still exist in the tin capsule and nickel basket To ensure accuracy, conduct blank determinations and subtract these values from the subsequent analyses, with the blank being the average of at least three determinations.

To prepare the solution, combine approximately 75 ml of acetic acid, 25 ml of nitric acid, and 1.5 ml of hydrochloric acid In a well-ventilated fume cupboard, heat the mixture to a temperature of 55 °C ± 5 °C Immerse the nickel basket in the heated solution for 30 to 60 seconds, then remove it and rinse immediately with running water Next, immerse the nickel basket in chemically pure acetone, dry it thoroughly, and finally place the cleaned nickel basket in a desiccator.

To calculate the mass fraction of nitrogen or oxygen, denoted as \$w_m\$, expressed as a percentage, use Equation (1): \$$w_m = w - b\$$ In this equation, \$w\$ represents the mass fraction of nitrogen or oxygen measured in the sample, while \$b\$ is the average blank determination of nitrogen or oxygen, also expressed as a percentage by mass.

Report the results as the mean of three determinations

5 Determination of nitrogen calculated as Si 3 N 4

General

The nitrogen content is quantified as silicon nitride, which can be determined through methods such as acid decomposition combined with pressurization, followed by steam distillation and neutralization titration.

The article discusses methods for analyzing samples containing silicon nitride with a mass percentage of less than 2% It highlights three key techniques: acid decomposition combined with pressurization and steam distillation, indophenol blue absorption spectroscopy, and the inert-gas fusion-thermal conductivity method.

The calculation of Si₃N₄ using measured nitrogen content is valid only if nitrogen is chemically bonded as silicon nitride The methods outlined in Clause 4 can be used to determine total nitrogen When employing methods 5.2 or 5.3 for this determination, results must be verified using a method from Clause 4 or 5.4 due to the high chemical resistance of nitrides, especially concerning unknown nitrides present in the sample.

Acid decomposition — Titration method

In a pressurization container, a sample is decomposed using sulfuric acid and hydrofluoric acid, converting silicon nitride into ammonium salt Boric acid is subsequently added to the mixture, which is then transferred to a distillation flask Sodium hydroxide is introduced, and steam distillation is performed, allowing the ammonia distillate to be absorbed into suitable amidosulfonic acid Finally, the excess amidosulfonic acid is titrated with sodium hydroxide.

Solutions 5.2.2.1, 5.2.2.2 and 5.2.2.7 shall be stored in plastics bottles

5.2.2.5 Ammonium sulfate, purity more than 99,9 % by mass Heat at 110 °C ± 10 °C for 3 h and cool in a desiccator

Weigh 10.0 g of high-purity amidosulfuric acid (99.99% purity) to the nearest 0.1 mg Dissolve the acid in water, then transfer the solution to a 1,000 ml volumetric flask and dilute it to the mark with water.

Calculate the factor, F, for the 0,1 mol/l amidosulfuric acid solution using Equation (2) a

F = × × (2) where m a is the mass of amidosulfuric acid, in grams;

P is the purity of amidosulfuric acid, expressed as a percentage by mass

Weigh 165 g of sodium hydroxide and dissolve it in 150 ml of carbon-dioxide-free water in a 500 ml polyethylene airtight container Allow the solution to stand for 4 to 5 days, ensuring it is shielded from carbon dioxide After this period, transfer 54 ml of the supernatant liquid to a 1 l polyethylene airtight container and add carbon-dioxide-free water to achieve the desired total volume.

1 l, mix well, and store it with a soda-lime tube attachment

To prepare a sodium hydroxide solution, pipette 100 ml of 1 mol/l sodium hydroxide into a 1,000 ml volumetric flask, then dilute it with carbon-dioxide-free water to reach a total volume of 1,000 ml Mix the solution thoroughly, transfer it to an airtight polyethylene container, and store it with a soda-lime tube attachment for optimal preservation.

Transfer precisely 50 ml of 0,1 mol/l amidosulfuric acid solution (5.2.2.6) to a 200 ml beaker, dilute to about

To conduct the titration, mix 100 ml of the solution with water and titrate using a 0.1 mol/l sodium hydroxide solution Utilize a pH meter with a glassy electrode to monitor the process The endpoint of the titration is reached when the pH measures 5.5, at which point the volume of the 0.1 mol/l sodium hydroxide solution used should be recorded.

Calculate the factor, F′, of this 0,1 mol/l sodium hydroxide solution using Equation (3)

F is the factor of 0,1 mol/l amidosulfuric acid solution;

V is the volume of titration of 0,1 mol/l sodium hydroxide, in millilitres

5.2.3.1 Pressurization vessel, for decomposition; the inner cap and the vessel are made of ethylene

4-fluoride resin and outer cap and pressure-resistant container are made of stainless steel

To avoid cross-contamination by nitrogen from other uses of the vessel, reserve pressure vessels solely for the determination of silicon nitride

5.2.3.2 Steam distillation apparatus, consisting of the elements listed in 5.2.3.2.1 to 5.2.3.2.6

The steam distillation apparatus, illustrated in Figure 1, consists of components crafted from borosilicate glass These parts are interconnected using standard ground-glass joints and secured with springs or clamps.

9 connection of rubber tube with pinchcock

10 jack a Flask (2,5 l) for generation of steam b Trap (500 ml) c Sphere and tube d Distillation flask (750 ml) e Graham condenser f Collecting vessel

Figure 1 — Example of the steam distillation apparatus

5.2.3.2.1 Flask, 2,5 l, for generation of steam, attached to a funnel with a stopcock and an outlet tube for the steam, and an electric heater (using 1 kW Nichrome wire)

5.2.3.2.2 Trap, having a rubber tube with pinchcock connected to the bottom tube on the sphere The nozzle of the inner tube for steam has several small holes

The setup consists of a sphere and tube featuring an inlet tube for steam, a funnel with a stopcock, and a trap to prevent splashing The inlet tube from the trap is appropriately sized and connected via a rubber tube to the lower inlet tube within the distillation flask, facilitating quick changes to the lower inlet tube that immerses in the NaOH solution It is essential to replace both the inlet and rubber tubes when they exhibit signs of degradation.

5.2.3.2.6 Collecting vessel, 300 ml tall beaker

The mass of test portion depends on the silicon nitride content, as shown in Table 1

Table 1 — Mass of test portion Silicon nitride content Mass of test portion

Weigh the sample into a platinum crucible (No 20), put it in a resin vessel, add 5 ml of sulfuric acid (1+1) and

10 ml of hydrofluoric acid Put the vessel into a pressure-resistant container with an inner cap, fasten an inner cap tightly, and heat at 160 °C ± 5 °C in an air bath for about 16 h

After cooling, carefully remove the outer and inner caps, then use plastic tweezers to transfer the solution into a 100 ml plastic beaker Rinse the platinum crucible, tweezers, inner cap, and resin vessel with a small amount of water, adding the washings to the beaker Finally, incorporate 5 g of boric acid and ensure it is fully dissolved.

Transfer the solution to a distillation flask and set up the distillation apparatus Add 50 ml of 0.1 mol/l amidosulfonic acid to a collecting vessel, ensuring the end of the Graham condenser is immersed in this solution Pour 50 ml of sodium hydroxide solution (500 g/l) from the funnel of the distillation flask, rinsing the funnel with water until approximately 150 ml of liquid is collected, then close the stopcock on the funnel.

Before using a new distillation apparatus or one that has been idle for an extended period, it is essential to wash the apparatus by performing a distillation without cooling water in the Graham condenser.

Begin the steam distillation process Once the liquid volume in the collecting vessel reaches 170 ml, adjust the vessel to align with the top of the Graham condenser instead of the liquid surface, and continue the distillation until a total of 200 ml is collected.

When steam generation begins, open the pinchcock on the bottom tube of the trap, and once the steam flow stabilizes between 4.5 to 5.0 ml per minute after adjusting the heater, close the pinchcock.

Wash the ends of the outer and inner sides of the Graham condenser, and the inner side of the ball joint attached to it, with a small amount of water

Titrate the distillate with a 0.1 mol/L sodium hydroxide solution, utilizing a pH meter with a glassy electrode, until reaching a pH of 5.5 as the endpoint Calculate the volume of the 0.1 mol/L sodium hydroxide solution consumed during the titration.

Weigh 0,280 g of ammonium sulfate (5.2.2.5), to the nearest 0,1 mg, into a platinum crucible (No 20), and carry out the procedure given in 5.2.5

Calculate the recovery, R, as a percentage using Equation (4) s

F is the factor of 0,1 mol/l amidosulfonic acid solution;

V is the used volume of 0,1 mol/l sodium hydroxide solution, in millilitres;

F′ is the factor of 0,1 mol/l sodium hydroxide solution; m s is the mass of ammonium sulfate weighed, in grams

Calculate the mass fraction of silicon nitride, w Si3N4 , expressed as a percentage, using Equation (5)

F is the factor of 0,1 mol/l amidosulfonic acid solution;

V is the volume of 0,1 mol/l sodium hydroxide solution used (see 5.2.2.8), in millilitres;

F′ is the factor of 0,1 mol/l sodium hydroxide solution;

R is the recovery rate in 5.2.6, in percent; m is the mass of test portion weighed, in grams.

Acid decomposition — Photometry method

A sample is treated with sulfuric acid and hydrofluoric acid in a pressurized container, converting silicon nitride into ammonium salt Boric acid is then added, and the resulting solution is transferred to a distillation flask Sodium hydroxide is introduced, followed by steam distillation, where the ammonia distillate is absorbed into sulfuric acid Finally, sodium hypochlorite and sodium phenolate are added to a portion of the absorbed solution, and the absorbance of the resulting indo-phenol blue is measured.

Dissolve 20 g of sodium hydroxide in water and dilute to 100 ml with water The reagent should be prepared freshly as required

To prepare the reagent, dissolve 25 g of phenol in 55 ml of a 200 g/l sodium hydroxide solution, then cool the mixture to room temperature Next, add 6 ml of acetone and dilute the solution to a final volume of 200 ml with water It is essential to prepare this reagent fresh for each use.

Transfer 26 g of sodium thiosulfate pentahydrate and 0,2 g of sodium carbonate into a 1 l volumetric flask, add

1 l of oxygen-free water to dissolve it, and store in an airtight container Allow to stand for 2 days before use

To prepare a potassium iodate solution for volumetric analysis, heat 0.9 to 1.1 g of high-purity potassium iodate at 130 °C for at least 2 hours, then cool in a desiccator Transfer the weighed potassium iodate into a 250 ml volumetric flask, dissolve it in the minimum amount of water, and dilute to the mark with water From this flask, pipette 25 ml into a 200 ml Erlenmeyer flask, then add 2 g of potassium iodide and 2 ml of sulfuric acid (1+1) After stoppering and gently shaking, let the mixture stand in the dark for 5 minutes Add starch solution as an indicator and titrate with 0.1 mol/l sodium thiosulfate until the solution fades to a faint yellow, indicating that the endpoint is near The endpoint is reached when the blue color of the solution disappears completely.

In a 200 ml interchangeable ground Erlenmeyer flask, combine 25 ml of water with 2 g of potassium iodide and add 2 ml of diluted sulfuric acid (1+1) After securely stoppering the flask, gently shake the mixture until fully dissolved, then let it sit for 5 minutes in a dark environment Conduct a blank test under identical conditions to adjust the volume required for titration.

Calculate the factor, F, of the 0,1 mol/l sodium thiosulfate solution using Equation (6) p 25

= × ⋅ × (6) where m p is the mass of potassium iodate weighed out, in grams;

A is the purity of potassium iodate, expressed as a percentage by mass;

0,003 566 7 is the mass of potassium iodate equivalent to 1 ml of 0,1 mol/l sodium thiosulfate solution, in grams;

V is the volume of 0,1 mol/l sodium thiosulfate solution needed for titration, in millilitres

5.3.2.5 Sodium hypochlorite solution, effective chlorine 10 g/l

Determine the effective chlorine of the sodium hypochlorite solution (effective chlorine 5 % to 12 %) and dilute to 10 g/l of effective chlorine with water The reagent should be prepared freshly as required

Determine the effective chlorine of the sodium hypochlorite solution as follows

Transfer 10 ml of sodium hypochlorite solution to a 200 ml volumetric flask and dilute to the mark with water

Transfer precisely 10 ml to a 300 ml Erlenmeyer flask with stopper and dilute to 100 ml with water Add 1 g to

To prepare the solution, mix 2 g of potassium iodide with 6 ml of acetic acid (1:1 ratio) in a stoppered container and shake well Allow the mixture to sit in the dark for 5 minutes before titrating with a 0.1 mol/l sodium thiosulfate solution As the yellow color of the solution fades, add 2 ml of starch solution as an indicator and continue titrating until the blue color of iodostarch disappears.

Separately, as a blank test, transfer 10 ml of water, carry out the same procedures as described above, and adjust the titration value using this blank test result

Calculate the effective chlorine of the sodium hypochlorite solution, N, in grams per litre, using Equation (7) t 200 1

V t is the titration volume of 0,1 mol/l sodium thiosulfate solution, in millilitres;

F is the factor of 0,1 mol/l sodium thiosulfate solution;

V is the volume of sodium hypochlorite solution, in millilitres

5.3.2.6 Ammonium ion standard solution, 1 mg NH 4 + /ml

Keep ammonium sulfate in a desiccator overnight Weigh 3,66 g of ammonium sulfate, dissolve in water, transfer to a 1 000 ml volumetric flask, and dilute to the mark with water

Use the same pressurization apparatus as described in 5.2.3.1

Carry out the procedure in 5.2.5, but adding 50 ml of sulfuric acid (0,05 mol/l) to the gathering vessel instead of 0,1 mol/l amidosulfonic acid solution

To prepare the solution, transfer the distillate into a 250 ml volumetric flask and dilute it to the mark with water Next, take an aliquot of this solution and transfer it to a 50 ml volumetric flask, diluting it to approximately 25 ml with water.

NOTE The volume of the aliquot portion of the stock solution depends on the content of silicon nitride (percent), as shown in Table 2

Table 2 — Aliquot portion of stock solution

Silicon nitride content Aliquot of stock solution

To prepare the solution, combine 10 ml of sodium phenolate with a 50 ml volumetric flask and shake well Next, add 5 ml of sodium hypochlorite solution (containing 10 g/l of effective chlorine) and dilute the mixture to the mark with water Allow the solution to stand at a temperature of 25 °C ± 2.5 °C for approximately 30 minutes.

Transfer a portion of the solution to a 10 mm cell and measure the absorbance at a wave-length around

630 nm against water as a reference

Carry out the procedure in accordance with 5.3.5 without the sample

Dilute the ammonium ion standard solution precisely 2 000 times with water, transfer a range from 0 ml to

To prepare a calibration graph for ammonium ion concentration, transfer 25 ml of the diluted solution (ranging from 0.0 mg to 0.125 mg of ammonium ion) into several 50 ml volumetric flasks and dilute each to approximately 25 ml with water Follow the procedure outlined in section 5.3.5, then plot the relationship between absorbance and the mass of ammonium ion, ensuring the curve is adjusted to pass through the origin.

Calculate the mass fraction of silicon nitride, w Si3N4 , expressed as a percentage, in the sample using

Equation (8), with the amount of ammonium ion obtained from the absorbances obtained in 5.3.5 and 5.3.6, and the calibration graph plotted in 5.3.7

A 1 is the ammonium ion amount in 5.3.5, in grams;

A 2 is the ammonium ion amount in 5.3.6, in grams;

V is the volume of the aliquot portion in 5.3.5, in millilitres; m is the mass of the test portion, in grams.

Inert-gas fusion — Thermal conductivity method

A sample is thermally fused with a co-fusion metal in an inert-gas atmosphere using the impulse method in a graphite crucible The process involves extracting nitrogen gas along with other gases Following this, the obtained hydrogen gas and carbon monoxide are oxidized to produce water and carbon dioxide, which are then absorbed The remaining gases are analyzed for thermal conductivity changes using a thermal conductivity analyzer.

5.4.2.1 Inert gas, helium above 99,99 % by volume

5.4.2.2 Capsule, made of tin or nickel and designated for each apparatus

5.4.2.3 Co-fusion metal, granular, basket-like, or pellet tin or nickel, made from a different sort of metal from the capsule metal

5.4.2.4 Calibration sample, comprising powdered standard materials, powdered silicon nitride with a known nitrogen percentage

5.4.3.1 Graphite crucible, suitable for an impulse furnace Examples are shown in Figure 2

Figure 2 — Examples of graphite crucible for impulse furnace

5.4.3.2 Nitrogen determination apparatus, composed of the components given in 5.4.3.2.1 to 5.4.3.2.3

A schematic diagram of the apparatus for inert-gas fusion thermal conductivity determination of nitride is shown in Figure 3

14 a) Nitrogen/oxygen analyser type (1 pass type) b) Nitrogen/oxygen analyser type (2 passes type) c) Nitrogen analyser type

2 deoxidizing tube with electric furnace

8 oxidizing tube with electric furnace

Figure 3 — Apparatus for inert-gas fusion thermal conductivity determination of nitrogen

5.4.3.2.1 Inert-gas refining part, composed of a deoxygenating tube (for example, reducing copper) with electric furnace, a carbon dioxide absorbing tube (soda lime) and a dehydration tube (magnesium perchlorate – for dryness)

NOTE One type of apparatus has a de-nitration tube (sponge titanium)

The gas extracting component includes a sample loading system and an impulse furnace designed for inert-gas fusion analysis This furnace features fixed upper electrodes and movable lower electrodes, both of which are cooled by a continuous flow of water.

The sample capsule is loaded into the graphite crucible of the impulse furnace using specialized equipment, all within an inert-gas atmosphere Positioned between two electrodes, the graphite crucible is heated to an impressive temperature of 3,000 °C by the impulse furnace.

5.4.3.2.3 Gas separating part, composed of a dust tube (glass wool), an oxidizing tube with electric furnace, copper(II) oxide, a carbon dioxide absorbing tube (soda lime) and a dehydration tube (magnesium perchlorate)

The extracted gas is sent to a thermal conductivity analyzer, where the electric resistance differences between the sample and reference cells are converted into nitrogen concentration based on a pre-established calibration.

The mass of the test portion depends on the content of silicon nitride , as shown in Table 3

Because of the low mass of test portion required in this determination, ensure that the sample taken is representative of the bulk

Table 3 — Mass of test portion

Silicon nitride content Mass of test portion

Carry out the determination of blank test, calculation of calibration coefficient, and measurement of sample in accordance with the manufacturer’s operating instructions and using the procedure given in 5.4.5.1 to 5.4.5.4

NOTE It is only necessary to carry out the procedures 5.4.5.1 and 5.4.5.2 once if several samples are analysed as a batch on the same day

To begin, activate the cooling water and inert gas systems, then power on the apparatus and allow it to stabilize Following this, perform a leak check on the inert gas in accordance with the manufacturer's operating instructions.

5.4.5.2 Place a new graphite crucible in the impulse furnace and de-gas it at a temperature of more than

The process involves heating to 2,900 °C under an inert gas flow, followed by idling cycles at a gas extraction temperature of 2,500 °C for 3 to 4 minutes During this time, the integrated value of thermal conductivity is measured This procedure is repeated until the integrated values stabilize at a constant level.

The temperature of the graphite crucible is regulated by modifying the electrical current or voltage It is essential to establish the correlation between temperature and current/voltage prior to utilizing the equipment for measurements Notably, the de-gas temperature is approximately 100 °C higher than the temperature used for gas extraction.

NOTE 2 The optimum gas extracting temperature is determined beforehand by using a reference material of known nitrogen content

To prepare for the experiment, follow the manufacturer's operating instructions by adding the specified amount of co-fusion metal to a new graphite crucible and inserting it into the impulse furnace Next, weigh the sample into the capsule, then use a jig to press and bend the mouth of the capsule before placing it in the sample loading device Finally, ensure inert gas is flowing and heat the setup at the de-gas temperature for 3 to 4 minutes.

NOTE In an apparatus with a feeder of co-fusion metal, co-fusion metal is de-gassed after the degassing of the graphite crucible

5.4.5.4 Insert the capsule containing the sample into the graphite crucible treated as in 5.4.5.1 and 5.4.5.3, heat at the extraction temperature and measure the integrated conductivities

It is recommended that the optimum extraction temperature be established by trials using samples with known nitrogen contents

NOTE Much equipment of the type used for this determination is fully automated, so many of the steps described above are carried out without the need for operator intervention

Carry out the procedure given in 5.4.5 without the sample Calculate the mean of the integrated values obtained from 3 to 5 consecutive measurements

Carry out the procedure given in 5.4.5 using the calibration sample Calculate the mean of the integrated values obtained from 3 to 5 consecutive measurements and calculate the calibration coefficient using Equation (9) c N

The calibration coefficient, denoted as K, is measured in grams per integrated value The mass of the calibration sample, represented as m c, is quantified in grams Additionally, the mass fraction of nitrogen in the calibration sample, indicated as w N, is expressed as a percentage.

A 0 is the integrated value of the calibration sample;

A 1 is the integrated value obtained in 5.4.6

Calculate the mass fraction of silicon nitride, w Si

3 N 4 , expressed as a percentage, using Equation (10)

A 2 is the integrated value obtained in 5.4.5;

A 1 is the integrated value obtained in 5.4.6;

K is the calibration coefficient, in grams/integrated value; m is the mass of test portion in grams.

Determination of total nitrogen

5.5.1 Determination of total nitrogen by fusion decomposition

Determine the total nitrogen content as described in 7.3 of EN 12698-1:2007

The method for determining nitrogen in silicon nitride (Si₃N₄) involves fusion decomposition Similar techniques can also be applied to analyze nitrogen in materials that contain at least 5% nitrogen, such as silicon and aluminum nitrides.

The sample is treated with lithium hydroxide at a controlled temperature of 700 °C ± 25 °C to facilitate the conversion of nitrogen into ammonia The nitrogen content is quantified through titration using an acid of known concentration.

5.5.2 Determination of total nitrogen by Kjeldahl distillation

The sample is subjected to hydrofluoric acid under pressure, allowing nitrogen to be distilled as ammonia into a receiving vessel with boric acid solution This process utilizes an ammonia distillation apparatus, and the nitrogen content is quantified through potentiometric titration.

5.5.3 Determination of total nitrogen by microwave digestion

6 Determination of free Iron by Inductively Coupled Plasma Atomic Emission

General

Free iron can be introduced during the manufacturing process or through milling apparatus with iron components, leading to interference in the analysis of silicon-carbide-based materials This interference can adversely affect the total composition calculations of a sample, necessitating accurate determination of free iron levels Key issues include: a) variable results in total iron determination via X-ray fluorescence (XRF) due to free iron alloying with platinum vessels; b) interference in free silicon measurement using the silver displacement method if samples are not acid washed to remove iron; and c) errors in weight-change measurements, such as free carbon determination according to ISO standards, caused by the oxidation of iron upon heating.

The accurate determination of free iron, while detectable by X-ray diffraction, is best achieved through chemical methods One method involves the bromine/methanol technique, where free iron in a dried sample reacts with anhydrous bromine in methanol under reflux, followed by filtration and dissolution in dilute hydrochloric acid Alternatively, the copper sulfate method extracts free iron into a copper sulfate solution by displacing copper under reflux The iron content from both methods is analyzed using ICP-AES.

The two methods for analyzing silicon-carbide-based materials yield consistent and accurate results The copper sulfate method is advantageous due to its use of fewer toxic and non-flammable reagents, eliminating the need for an evaporation stage, making it more convenient, faster, and cost-effective Conversely, the bromine/methanol method is beneficial for comparing results, especially when evaluating new materials or addressing uncertainties.

Copper sulfate method

In the analysis, free iron in the sample is reacted with copper sulfate solution under reflux conditions Following this reaction, undissolved materials are eliminated through filtration, and the iron content in the resulting solution is quantified using inductively coupled plasma optical emission spectroscopy (ICP-AES).

This procedure outlines the method for determining free iron in silicon-carbide-based materials, specifically for samples containing up to 1% iron by mass For samples with higher iron content, the sample mass can be adjusted accordingly to ensure accurate measurement.

Use only reagents of analytical grade and prepare all solutions using distilled or deionized water and store in polyethylene bottles

Nitric acid is highly corrosive and can cause serious burns; therefore, it is crucial to avoid inhaling its fumes and to prevent any contact with skin or eyes Always dilute concentrated nitric acid in a fume cupboard while wearing protective PVC gloves and a face shield for safety.

6.2.2.1 Nitric acid, concentrated, density 1,5 g/ml

6.2.2.2 Nitric acid solution, 20 % by volume

Dilute 200 ml of concentrated nitric acid to 1 l with water

6.2.2.4 Copper sulfate solution, 10 % (mass/volume)

Dissolve 50 g of copper sulfate (CuSO 4 ã5H 2 O) in 200 ml of water and dilute to 500 ml

6.2.2.5 Standard solution, containing 1 000 mg/l Fe of spectroscopic grade

Commercially available, traceable standard solutions may be used

Dissolve 30 g of copper sulfate (CuSO 4 ã5H 2 O) in 200 ml of water, add 100 ml of concentrated nitric acid (6.2.2.1) and dilute to 500 ml

In a series of six 250 ml volumetric flasks, add varying volumes of standard solution: 0.0 ml, 1.00 ml, 2.00 ml, 3.00 ml, 4.00 ml, and 5.00 ml Next, incorporate 50 ml of matrix solution into each flask and dilute to the mark at room temperature.

6.2.3.1 Conical flasks, 100 ml with a ground-glass B24 socket

6.2.3.2 Air condensers, B24 cone with 100 mm shank length

6.2.3.3 Filter apparatus, preferably the dismountable Buchner type

6.2.3.4 Inductively coupled plasma atomic emission spectrometer

The measuring parameters will be instrument dependent

NOTE The Fe 259,94 nm line is preferable

To prepare the sample, dry approximately 5 g of finely powdered material in an air oven at 110 °C ± 10 °C for a minimum of 2 hours After drying, allow the sample to cool in a desiccator Accurately weigh about 0.5 g of the dry sample, measuring to the nearest 0.1 mg, and transfer it for further analysis.

In a 100 ml conical flask, combine 30 ml of a 10% (mass/volume) copper sulfate solution with a magnetic stirrer bar and attach an air condenser Heat the mixture to boiling on a stirrer hotplate, maintaining reflux conditions for 30 minutes After cooling, filter the solution using hardened ash-less filter paper on a Buchner funnel, and thoroughly wash the residue with hot water to achieve a filtrate volume of approximately 150 ml Finally, transfer the filtrate quantitatively to a suitable container.

250 ml volumetric flask containing 50 ml of nitric acid solution, 20 % (6.2.2.2) Dilute to volume at room temperature and mix thoroughly

Repeat the procedure to provide duplicate analysis solutions for each sample

Prepare a blank solution by following the above procedure omitting the sample

To ensure accurate measurements, calibrate the ICP/AES spectrometer with calibration solutions and analyze both sample and blank solutions Finally, re-run the highest and lowest calibration standards as unknowns to adjust sample readings for any variations in instrument sensitivity during the analysis.

Calculate the mass fraction of iron, w Fe , expressed as a percentage, using Equation (11)

The equation \$\rho_s = \rho \times \left( \frac{(11 - \rho_b)}{m_d} \right)\$ represents the relationship between the observed iron concentration of a sample solution (\$\rho_s\$) and various parameters, including the blank solution concentration (\$\rho_b\$), the calibration solution concentration (\$\rho\$), and the mass of the dry sample (\$m_d\$) This formula is essential for accurately determining the iron concentration in a given sample.

Report individual values to three decimal places and mean values to two places.

Bromine/methanol method

Free iron in a dried sample is reacted with a 5% bromine solution in methanol under reflux After filtration to remove undissolved material, methanol is eliminated by boiling with a small amount of sulfuric acid The resulting residue is then dissolved in dilute hydrochloric acid, and the iron content of the solution is analyzed using ICP/AES.

This procedure outlines the method for determining free iron content in silicon-carbide-based materials, specifically for samples containing up to 2.5% iron by mass For samples with higher iron concentrations, the sample mass can be adjusted to facilitate accurate measurement.

Use only reagents of analytical grade unless stated to the contrary and prepare all solutions using distilled or deionized water and store in polyethylene bottles

Bromine is a hazardous substance that can lead to serious burns and toxicity It is essential to avoid inhaling bromine and to prevent any contact with skin and eyes Always wear appropriate protective gear, including clothing, gloves, and eye protection, and conduct all procedures within a fume cupboard to ensure safety.

WARNING — Sulfuric acid causes severe burns Prevent contact with skin and eyes Wear protective clothing, PVC gloves and face protection when diluting concentrated acid

Hydrochloric acid is hazardous, causing burns and releasing irritating vapors; therefore, it is crucial to avoid inhalation and contact with skin and eyes Always handle it in a fume cupboard, similar to the precautions taken with sulfuric acid.

Carefully add 25 ml of bromine to 475 ml of the methanol Mix and transfer to a dry stoppered vessel Prepare freshly as required

6.3.2.4 Sulfuric acid, concentrated, density 1,84 g/ml

Carefully add 50 ml of acid to 50 ml of water to a beaker cooled in a water bath Stir the mixture continuously Allow to cool and store

6.3.2.6 Hydrochloric acid, concentrated, density 1,18 g/ml

Add 25 ml of acid to 225 ml of water, mix well and store

6.3.2.8 Standard solution, containing 1 000 mg/l Fe, spectroscopic grade

Commercially available, traceable, standard solutions may be used

Prepare six 50 ml volumetric flasks by adding 0.0 ml, 1.0 ml, 2.0 ml, 3.0 ml, 4.0 ml, and 5.0 ml of the standard solution to each flask Then, add 25 ml of a (1+9) hydrochloric acid solution to each flask and dilute to the mark at room temperature.

6.3.3.1 Conical flasks, 100 ml with a ground-glass B24 socket

6.3.3.2 Air condensers, B24 cone with 100 mm shank length

6.3.3.3 Filter apparatus, preferably dismountable Buchner type

6.3.3.4 Filter paper, (hardened ash-less grade)

NOTE The Fe 259,94 nm line is preferable

To prepare the sample, dry approximately 5 g of finely powdered material in an air oven at 110 °C ± 10 °C for at least 2 hours, then cool in a desiccator Accurately weigh about 0.2 g of the dried sample and transfer it to a dry 100 ml conical flask Add 50 ml of a 5% bromine/methanol solution along with a magnetic stirrer bar, and attach an air condenser Heat the mixture to boiling and maintain reflux for 30 minutes After cooling, filter the solution through hardened ash-less filter paper using a Buchner funnel, washing the residue with dry methanol to achieve a filtrate volume of approximately 150 ml Finally, transfer the filtrate to a 250 ml beaker, add 5 drops of (1+1) sulfuric acid and some anti-bumping granules, then heat to boiling and evaporate to dryness.

To dissolve the salts, cool the beaker and add 25 ml of (1+9) hydrochloric acid, then heat it to a gentle boil Afterward, cool the mixture and transfer it quantitatively to a 250 ml volumetric flask, diluting to the desired volume and mixing thoroughly.

To ensure accurate duplicate analysis for each sample, repeat the established procedure Additionally, prepare a blank solution by following the same steps but excluding the sample Finally, calibrate the ICP-AE spectrometer using the prepared calibration solutions.

To determine the iron content in the sample solutions, record the readings from duplicate samples for each solution Use the indicated content from one of the calibration solutions to adjust the sample readings, compensating for any variations in instrument sensitivity during the analysis.

Calculate the mass fraction of iron, w Fe , expressed as a percentage, using Equation (12)

The formula for calculating the iron concentration in a sample solution is given by \$\rho_s = \rho \times \left( \frac{m_d}{\rho_0 - \rho_b} \right)\$, where \$\rho_s\$ represents the observed iron concentration of the sample solution in milligrams per litre, \$\rho_b\$ is the observed iron concentration of the blank solution, \$\rho\$ denotes the iron concentration of the calibration solution, \$\rho_0\$ is the observed iron concentration of the calibration solution, and \$m_d\$ is the mass of the dry sample in grams.

Report individual values to three decimal places and mean values to two places

7 Determination of free aluminium and free magnesium

General

The determination of free aluminum and free magnesium can be achieved through several methods, including acid decomposition with ICP-AES, acid decomposition with FAAS, and the hydrogen generating method, which is specifically applicable for free aluminum.

Methods a) and b) are not suitable for determining free aluminium or free magnesium in samples containing soluble aluminium or magnesium compounds, excluding metal forms For instance, in magnesia-graphite bricks containing metal aluminium and metal magnesium, these methods can be used to determine free aluminium but are ineffective for free magnesium due to the solubility of magnesia clinker in hydrochloric acid.

Acid decomposition — Inductively coupled plasma atomic emission spectroscopy (ICP-AES)

The determination of free aluminum and free magnesium is achieved through acid decomposition using ICP-AES This process involves dissolving the sample at room temperature with hydrochloric acid, followed by measuring the emission intensities of each element using ICP-AES.

Use only reagents of analytical grade and prepare all solutions using distilled or deionized water

7.2.2.2 Aluminium standard solution, 1,0 mg Al/ml

To prepare high-purity aluminium for analysis, first wash the surface with a hydrochloric acid solution (1:3) to remove the oxidized layer, followed by rinsing with water, 99.5% ethanol, and diethyl ether, then dry in a desiccator Next, weigh 1.000 g of aluminium on a platinum dish, cover it with a watch glass, and add 50 ml of hydrochloric acid solution (1:1), heating it on a steam bath until dissolved After cooling, transfer the solution into a 1,000 ml volumetric flask and dilute to the mark with water.

7.2.2.3 Magnesium standard solution, 1,0 mg Mg/ml

To prepare magnesium for analysis, first wash the surface of high-purity magnesium (over 99.9% by mass) with a 1:3 hydrochloric acid solution to remove the oxidized layer Rinse thoroughly with water, followed by 99.5% ethanol and diethyl ether, then dry in a desiccator Next, weigh 1.000 g of magnesium in a 200 ml beaker, cover it with a watch glass, and add 30 ml of 1:1 hydrochloric acid Heat the mixture on a steam bath until the magnesium dissolves, then allow it to cool Finally, transfer the solution to a 1,000 ml volumetric flask and dilute to the mark with water.

7.2.2.4 Mixed standard solution, 0,1 mg Al/ml, 0,05 mg Mg/ml

Transfer 20 ml of aluminium standard solution and 10 ml of magnesium standard solution into a 200 ml volumetric flask precisely and dilute to the mark with water

1,00 g of the test sample shall be weighed out for the determination

Weigh the sample into a 100 ml beaker, add 30 ml of hydrochloric acid (1+5), cover with a watch glass, and allow to stand at room temperature

After 16 h, filter with a filter paper (type 5 B) and wash completely with hydrochloric acid (1+50) Transfer the filtrate and washings into a 200 ml volumetric flask and dilute to the mark with water

If the solution becomes muddy, treat a portion of the sample solution to separate out muddy particles by using a centrifuge and use the top clear layer as the sample solution

Transfer precisely an aliquot portion of stock solution into a 100 ml volumetric flask, add 2 ml of hydrochloric acid (1+1), and dilute to the mark with water

NOTE The volume of the aliquot of the stock solution depends on the content of free aluminium and free magnesium, as shown in Table 4

Table 4 — Aliquot portions of stock solution

Al free and Mg free % by mass Free aluminium Free magnesium

To analyze the stock solution, spray a portion into the Ar plasma flame of an ICP-AE spectrometer and measure the emission intensity at specific wavelengths, such as 369.15 nm for aluminum (Al) and 279.55 nm for magnesium (Mg).

Carry out the procedure in 7.2.5 without the sample

Transfer 0 to 30 ml of the mixed standard solution, containing 0 to 3 mg of aluminum and 0 to 1.5 mg of magnesium, into separate 100 ml volumetric flasks Add 2 ml of hydrochloric acid (1+1) to each flask and dilute to the mark with water Spray these solutions similarly to the samples and measure the absorptions against the reference solution Plot the relationship between the emission intensities for each element and the mass of each metal component, and prepare the calibration graph by ensuring the curve passes through the origin.

Simultaneous measurement of calibration solutions, including both stock and blank solutions, is essential A new calibration line should be established for each measurement to ensure accuracy.

To determine the mass fractions of aluminium (\$w_{Al}\$) and magnesium (\$w_{Mg}\$) as percentages, utilize Equations (13) and (14) These calculations are based on the quantities of each metal component obtained from the emission intensities outlined in sections 7.2.5 and 7.2.6, along with the calibration details provided in section 7.2.7.

The equation \$E = -m_1 \times m_2 \times (14)\$ represents the relationship between the masses of aluminium and magnesium in specific test portions Here, \$m_1\$ denotes the mass of aluminium from section 7.2.5, \$m_2\$ is the mass of aluminium from section 7.2.6, \$m_3\$ indicates the mass of magnesium from section 7.2.5, and \$m_4\$ represents the mass of magnesium from section 7.2.6 Additionally, \$m\$ refers to the mass of the test portion, measured in grams.

V is the volume of the aliquot portion of the stock solution in 7.2.5, in millilitres.

Acid decomposition — Flame Atomic Absorption Spectrometry (FAAS)

Determination of free aluminium and free magnesium by acid decomposition using Flame Atomic Absorption Spectroscopy (FAAS)

The sample is dissolved at room temperature by adding hydrochloric acid The intensities of each element are measured by the atomic absorption spectrometer

The reagents are as specified in 7.2.2

NOTE The operating conditions will depend on the instrument used

Follow the procedures outlined in section 7.2.5, but instead of spraying a portion of the stock solution into the acetylene/dinitrogen monoxide flame of the atomic absorption spectrometer, measure the absorbance at 309.3 nm for aluminum (Al) and 285.2 nm for magnesium (Mg).

Carry out the procedure given in 7.2.5 without the sample

Transfer 0 to 30 ml of the mixed standard solution, containing 0 to 3 mg of aluminum and 0 to 1.5 mg of magnesium, into individual 100 ml volumetric flasks Add 2 ml of hydrochloric acid (1:1) to each flask and dilute with water up to the mark.

To analyze aluminum (Al) and magnesium (Mg) using an atomic absorption spectrometer, spray a portion of the solutions into the acetylene/di-nitrogen monoxide flame Measure the absorbance at 309.3 nm for Al and 285.2 nm for Mg, comparing the results against a reference solution.

Plot the relationships between the emission intensities of each element and the mass of each metal component Create a calibration graph by fitting the curve to ensure it intersects at the origin.

To determine the mass fraction of aluminium (\$w_{Al}\$) and magnesium (\$w_{Mg}\$) as percentages, utilize Equations (15) and (16) The quantities of each metal component are obtained from the emission intensities detailed in sections 7.3.4 and 7.3.5, along with the calibration information provided in section 7.3.6.

The equation \$y = -m_1 \times m_2 \times (16)\$ represents the relationship between the masses of aluminium and magnesium in specific sections of the study Here, \$m_1\$ denotes the mass of aluminium from section 7.3.4, \$m_2\$ is the mass of aluminium from section 7.3.5, \$m_3\$ indicates the mass of magnesium from section 7.3.4, and \$m_4\$ represents the mass of magnesium from section 7.3.5 Additionally, \$m\$ refers to the mass of the test portion, measured in grams.

V is the volume of the aliquot portion of the stock solution in 7.2.5, in millilitres.

Hydrogen generating method

The method described is very susceptible to failure and therefore should be handled with care

Determine the free aluminium content as described in Clause 6 of EN 12698-1:2007, using the same apparatus as used as for the determination of free silicon described Clause 8 of ISO 21068-2:2008

This method measures the volume of hydrogen generated by the action of dilute hydrochloric acid on any free aluminium in a sample

In the presence of free silicon, free aluminium is not quantifiable by this method

If the sample is known to contain carbonate, then the volume of hydrogen evolved shall be corrected for the known carbonate present

The free aluminum content can be assessed by measuring the hydrogen evolution when sodium hydroxide is used It is essential to adjust the volume of hydrogen produced based on the known silicon content, as well as to account for the free iron that also generates hydrogen, requiring a correction for the known iron content.

General

To determine the content of oxides, utilize wet chemical methods in accordance with ISO 26845 and ISO 21587-1 and ISO 21587-2 Additionally, employ FAAS and ICP-AES techniques as outlined in ISO 21587-1 and ISO 21587-3 for alumino-silica products.

ISO 10058-3 (basic products) and ISO 21079-3;

For products that contain chrome, ISO 20565-3 is applicable instead of ISO 21587-1 The XRF fusion method, following the ignition of the sample as outlined in ISO 12677, can be modified as specified Additionally, the determination of oxides should be conducted after ignition at 850 °C, as referenced in section 8.5.2.

Wet methods

Carry out the analysis of oxides as described in ISO 21587-1 and ISO 21587-2 (alumino-silica products),

ISO 10058-2 (basic products) and ISO 26845 emphasize the importance of preventing infused sample specks from directly contacting platinum ware Additionally, it is crucial to adjust the sample mass to account for the increase in mass during fusion.

The components Al₂O₃, Fe₂O₃, TiO₂, CaO, MgO, K₂O, and Na₂O can be analyzed either from the filtrate following the removal of total silica, as outlined in Clause 7 of ISO 21068-2:2008, or after the complete decomposition of the material.

Flame atomic absorption and/or inductively coupled plasma atomic emission spectrometer

Carry out the analysis as described in ISO 21587-1 and ISO 21587-3 (alumino-silica products), ISO 10058-3

(basic products) or ISO 21079-3 but decompose the sample using one of the fusion techniques described in

8.3.2 Sodium carbonate boric acid fusion method

To prepare a ground sample, take 0.5 g ± 0.001 g and place it in a platinum crucible Add 1.4 g ± 0.0001 g of a fusion mixture, consisting of 12 parts anhydrous sodium carbonate and 2 parts boric acid, which should be ground in a sling mill for 10 seconds Mix the components thoroughly and cover the crucible with a platinum lid Finally, heat the crucible on a bench heater for about 20 minutes.

To prevent significant damage to the platinum crucible, it is crucial that the majority of the silicon carbide reacts at a low temperature with sufficient air access If initial tests indicate the presence of free silicon, this process must be conducted with caution.

To prepare the sample, first, remove the crucible from the heater and place it in a muffle furnace at a temperature of 1,200 °C ± 50 °C for 25 minutes Afterward, allow the crucible to cool before adding 1.0 g of anhydrous potassium carbonate without mixing Cover the crucible with a platinum lid and return it to the muffle furnace at the same temperature for an additional 5 minutes Once removed and cooled, place the crucible and lid into a 250 ml squat beaker containing 100 ml of (1+2) HCl, and heat until the dissolution is complete Finally, pour the dissolved sample into a 250 ml volumetric flask, fill it to the mark, and mix thoroughly.

If the melt has a glassy appearance, indicating a high silicon content, modify the dissolution stage by adding

To prepare the solution, use 50 ml of distilled water in place of (1+2) HCl, covering it with a watch glass while heating and stirring continuously Next, add this solution to 65 ml of (1+1) HCl and continue heating with constant agitation until the dissolution is fully achieved.

Weigh 2 g of lithium metaborate in a clean platinum crucible and fuse it at a temperature of 1,200 °C ± 50 °C, swirling while cooling to coat the crucible walls Next, add the required sample amount to the crucible For samples with free carbon, initially heat gently to 400 °C ± 25 °C, then gradually increase the temperature to 750 °C ± 25 °C to eliminate the free carbon.

NOTE A pre-ignited sample can be used for analysis

To prepare the mixture, add 1 g of vanadium pentoxide and mix thoroughly Heat the mixture at 820 °C ± 25 °C for 1.5 hours with the crucible partially covered Then, transfer it to a furnace set at 1,200 °C ± 50 °C for 15 minutes, swirling the contents at the 5-minute and 10-minute marks During cooling, spread the fusion around the walls of the crucible to facilitate extraction.

Cool the solution to ambient temperature and mix it with 150 ml of water and 8 ml of concentrated nitric acid using a magnetic stirrer until fully dissolved Transfer the dissolved sample into a 250 ml volumetric flask, fill it to the mark, and ensure thorough mixing.

FAAS and/or ICP-AES is used to obtain the concentration of Al, Ca, Mg and Si in this solution.

XRF fusion method after ignition of the sample

Carry out the analysis of oxides as described in ISO 12677, with modifications to the methods as given in 8.4.2 to 8.4.4

Determine the loss on ignition to maximum mass loss at 750 °C ± 25 °C, making successive ignitions at

15 min intervals Samples containing carbon or other carbonaceous material will require a burning-out stage over a burner at between 400 °C ± 25 °C and 600 °C ± 25 °C, both to constant mass

NOTE The time required will vary from a few minutes for samples containing 10 % carbon to overnight or about 16 h for samples containing more than 30 % carbon

To determine the mass of the ignited sample based on the known or anticipated mass fraction of silicon carbide (SiC), it is important to note that 1 g of SiC yields 1.5 g of SiO₂ upon fusion The necessary mass of the sample for fusion, denoted as M, can be calculated using Equation (17).

+ (17) where w SiC is the expected mass fraction of SiC in the ignited sample, expressed as a percentage; m f is the normal mass of the fused sample, in grams

To protect the sample during the initial stages, line the fusion vessel with a layer of lithium tetraborate or boric oxide Sinter the well-mixed sample, combined with lithium carbonate, lanthanum oxide, or vanadium pentoxide, on top of this protective layer at a controlled temperature that allows for decomposition without melting the layer Gradually increase the heat until sintering occurs, ensuring the protective layer remains intact, and maintain this temperature until the reaction is fully complete.

The reaction between silicon carbide (SiC) and various reduced species is highly exothermic, leading to significant heat generation Additionally, silicon carbide creates a eutectic with platinum, which can result in damage to the platinum components involved in the reaction.

NOTE 2 As vanadium pentoxide might attack silicon carbide, its determination can be required

To enable analysis of samples using existing calibrations, it is essential to reconstitute the normal flux into equivalent masses of sintering agent and protective layer that match the original mass and composition of the normal flux.

1) If the flux is 7,5 g of a 1:4 mixture of lithium tetraborate:lithium metaborate, the sintering agent would be 2,228 g of lithium carbonate, and the protective layer would be 6,60 g lithium tetraborate

2) If the flux is 7,5 g of lithium tetraborate, then the sintering agent would 3,276 g of lithium carbonate and the protective layer would consist of 6,175 g of boric oxide;

3) If the flux is 10 g of 10 % lanthanum oxide in lithium tetraborate, the sintering agent would be 1,000 g of lanthanum oxide and the protective layer 9,000 g of boric oxide

After fully decomposing the sample in the sintering agent, increase the temperature to ensure thorough mixing and fusion of all components Before casting the melt, weigh the dish and its contents to calculate the dilution of the sample in the melt, allowing for adjustments to correct any deviations from the standard dilution factor.

The modified fluxes used for decomposing silicon carbide materials exhibit varying levels of impurities compared to the normal flux used in calibration To assess this, duplicate beads of pure silica and alumina will be prepared and analyzed using XRF, with any differences in blank levels recorded, whether negative or positive Corrections will be made for these blanks, as stoichiometric differences may result in slight variations in the slope factor for both silica and alumina Any changes observed will be measured and corrected, although differences in slope factors for minor constituents are expected to be insignificant.

Determination of silicon(IV) oxide, aluminium oxide, iron(III) oxide, titanium(IV) oxide,

zirconium oxide, and boron oxide

The test sample is obtained from the heat residue at 850 °C and the content of each component is determined by using analytical methods given in 8.5.3

8.5.2 Measurement of ratio on heat residue at 850 °C

Carry out the determination as described in 4.6 of ISO 21068-2:2008 and use the residue for the determination of the components as described in 8.5.3 and 8.5.4

8.5.3 Methods of determination of each component

Analytical methods are as follows: a) analytical methods for refractories, as shown in Table 5; b) ICP-AES method given in 8.3; c) XRF analysis method given in 8.4

Table 5 — Selection of analytical method according to materials Classification of refractories Method of determination

Graphite bricks containing silicon carbide ISO 21587-1

Silicon carbide bricks (including those containing silicon nitride) ISO 21587-1

Clay-based refractories containing silicon carbide and silicon nitride ISO 21587-1

Silica-based refractories containing silicon carbide and silicon nitride ISO 21587-1

High-alumina based refractories containing silicon carbide and silicon nitride ISO 21587-1

Magnesia- and dolomite-based refractories containing silicon carbide and silicon nitride ISO 10058

Chrome-magnesite-based refractories containing silicon carbide and silicon nitride ISO 20565

Zircon-zirconia-based refractories containing silicon carbide and silicon nitride ISO 21079

Alumina-zirconia-silica-based refractories containing silicon carbide and silicon nitride ISO 21079

Alumina-magnesia-based refractories containing silicon carbide and silicon nitride

Refractories containing silicon carbide and silicon nitride except those given above ISO 21587-1

Carry out the method described in 8.5.3 and determine the mass fraction, expressed as a percentage, based on the heat residue at 850 °C ± 25 °C

Convert the mass fraction of each oxide component, w M m O n , expressed as a percentage, on the residue base obtained in 8.5.2 into that on the dry base, using Equation (18) m n m n

M O M O * 100 w =w × R (18) where w M m O n * is the mass fraction of each oxide component obtained in 8.5.4, expressed as a percentage;

R is the ratio on heat residue at 850 °C ± 25 °C, expressed as a percentage by mass

To convert the mass fractions of silicon(IV) oxide (\$w_{SiO_2}\$), aluminium oxide (\$w_{Al_2O_3}\$), and magnesium oxide (\$w_{MgO}\$) from the residue base to the dry base, apply Equations (19) and (20) as outlined in section 8.5.2.

SiO SiO * SiC 1,498 Si N 1,285 Si 2,139

=⎜⎝ × ⎟⎠− × (21) where w SiO2* is the mass fraction of silicon(IV) oxide obtained in 8.5.4, expressed as a percentage;

R represents the heat residue ratio at 850 °C ± 25 °C, expressed as a percentage by mass The mass fraction of free silicon, denoted as $ w_{Si} $, is obtained from Clause 9 of ISO 21068-2:2008, also expressed as a percentage Similarly, $ w_{SiC} $ indicates the mass fraction of silicon carbide from Clause 7 of the same standard, while $ w_{Si3N4} $ refers to the mass fraction of silicon nitride from Clause 5, both expressed as percentages The mass fraction of aluminium oxide, $ w_{Al2O3^*} $, is derived from section 8.5, and $ w_{Al} $ represents the mass fraction of free aluminium from Clause 7, both expressed as percentages Additionally, $ w_{MgO^*} $ is the mass fraction of magnesium oxide from section 8.5, and $ w_{Mg} $ denotes the mass fraction of free magnesium from Clause 7, expressed as a percentage.

Express the test results in accordance with Clause 7 of ISO 21068-1:2008

NOTE Uncertainty data are given in Annex A

The test report shall be presented in accordance with Clause 8 of ISO 21068-1:2008

Statistical results obtained with analysis of refractories containing carbon and/or silicon carbide

The article discusses various materials used in industrial applications, including alumina-carbon-silicon carbide bricks (R001, R004, R006), magnesia-carbon bricks (R002), silicon carbide bricks (R003, R009), alumina-carbide bricks (R007, R010), and taphole clay (R008) Each material is identified by a specific sample number, highlighting their unique properties and uses in manufacturing processes.

Analytical results are given in Tables A.1 to A.4

Table A.1 — Total carbon, % by mass

ACS MC SC ACS ACS AC Taphole clay SC x 1 12,78 15,65 ― 37,17 10,07 4,88 3 53,51 30,82 x 2 12,81 15,88 ― 37,32 10,12 4,86 5 53,52 30,70 x 12,80 15,76 ― 37,24 10,10 4,87 4 53,52 30,76

S R 0,17 8 0,24 9 0,13 7 0,33 1 0,19 2 0,19 6 0,21 7 0,34 5 x is the average of x 1 and x 2 obtained on different days

R is the range, absolute difference of x 1 and x 2 x is the average of x of L 1 to L 9 s RW is the standard deviation within a laboratory s R is the standard deviation between laboratories

Table A.2 — Free carbon, % by mass

ACS MC SC ACS ACS AC Taphole clay SC x 1 11,25 15,84 ― 33,45 9,30 1 4,84 0 49,88 ― x 2 11,31 16,06 ― 33,60 9,32 3 4,83 0 49,95 ― x 11,28 15,95 ― 33,52 9,31 2 4,83 5 49,92 ―

Table A.3 — Silicon carbide, % by mass

ACS SC ACS ACS Taphole clay SC x 1 5,51 3 ― 12,41 2,64 5 12,16 ― x 2 5,50 4 ― 12,40 2,59 5 11,91 ― x 5,50 8 ― 12,40 2,62 0 12,04 ―

Table A.4 — Other components, % by mass

MC AC AC MC SC Taphole clay x 1 3,00 5 2,56 0 2,26 6 0,78 3 1,24 7 52,96 x 2 3,08 0 2,58 2 2,28 2 0,79 5 1,33 7 53,26 x 3,04 2 2,57 1 2,27 4 0,78 9 1,29 2 53,11

[1] ISO 1927, Prepared unshaped refractory materials (dense and insulating) — Classification

[2] ISO 10060, Dense, shaped refractory products — Test methods for products containing carbon

[3] ISO 10081-1, Classification of dense shaped refractory products — Part 1: Alumina-silica

[4] ISO 10081-2, Classification of dense shaped refractory products — Part 2: Basic products containing less than 7 % residual carbon

[5] ISO 10081-3, Classification of dense shaped refractory products — Part 3: Basic products containing from 7 % to 50 % residual carbon

[6] ISO 10081-4, Classification of dense shaped refractory products — Part 4: Special products

[7] EN 725-3, Advanced technical ceramics — Methods of test for ceramic powders — Part 3: Determination of the oxygen content of non-oxides by thermal extraction with a carrier gas

[8] JIS 2011, Methods for chemical analysis of refractories containing carbon and/or silicon-carbide

Tiêu đề	Chemical Analysis Of Silicon-Carbide-Containing Raw Materials And Refractory Products — Part 3: Determination Of Nitrogen, Oxygen And Metallic And Oxidic Constituents
Trường học	International Organization for Standardization
Chuyên ngành	Chemical Analysis
Thể loại	tiêu chuẩn
Năm xuất bản	2008
Thành phố	Geneva

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