ISO/DIS 9285-1

ISO/TC 29/SC 5

Secretariat: DIN

Date: 2026-02-02

Oxide based abrasive grains — Chemical analysis —

Voting begins on: 2026-03-30 Voting terminates on: 2026-06-22

Part 1:
Wet chemistry methods

Voting begins on: 2026-03-30 Voting terminates on: 2026-06-22

Voting begins on: 2026-03-30 Voting terminates on: 2026-06-22

Voting begins on: 2026-03-30 Voting terminates on: 2026-06-22

DIS stage

© ISO 2026

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Contents

Foreword v

Introduction vi

1 Scope 1

2 Normative references 1

3 Terms and definitions 1

4 Reagents 2

5 Apparatus 3

6 Procedure 4

6.1 Preparation of samples for analysis 4

6.2 Blank determination 4

7 Gain or loss on ignition 4

7.1 Procedure 4

7.2 Expression of results 4

8 Determination of silicon dioxide 5

8.1 Gravimetrie method 5

8.2 Colorimetric method 6

8.3 Animal gel coagulation method 8

9 Separation of iron, titanium, magnesium and calcium from aluminium 10

10 lron(III) oxide determination 11

10.1 Volumetric method 11

10.2 Colorimetric method 11

10.3 Sulfosalicylic acid colorimetric method 12

11 Titanium dioxide colorimetric determination 14

11.1 Reagents 14

11.2 Apparatus 14

11.3 Procedure 14

11.4 Expression of results 14

12 Determination of calcium oxide 15

12.1 Calcium oxide gravimetric determination 15

12.2 Volumetric method 15

13 Determination of magnesium oxide 17

13.1 Magnesium oxide gravimetric determination 17

13.2 Volumetric method 18

14 Zirconium oxide gravimetric determination 19

14.1 Precipitation of zirconium phosphate 19

14.2 Zirconium oxide, mandelic acid precipitation 20

15 Chromium oxide colorimetric determination 21

15.1 Principle 21

15.2 Reagents 21

15.3 Apparatus 21

15.4 Procedure 21

15.5 Expression of results 22

16 Aluminium oxide 22

16.1 Indirect method 22

16.2 EDTA volumetric method 22

17 Test report 25

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISO's adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 29, Small tools, Subcommittee SC 5, Grinding wheels and abrasives.

This second edition cancels and replaces the first edition (ISO 9285:2017), which has been technically revised.

The main changes compared to the previous edition are as follows:

• As part of the revision of ISO 9285:1997, the standard is divided into Part 1 and Part 2;
• Part 2 contains the methods of instrumental analysis;
• This document, Part 1, describes classical wet chemical methods for quantitative chemical analysis. In addition, some new methods are added;
• Animal gel coagulation method for silicon dioxide determination (see 8.3) is added;
• Sulfosalicylic acid colorimetric method for the determination of iron(ΙΙΙ) (see 10.3) is added;
• The volumetric method for the determination of calcium oxide (see 12.2) and magnesium oxide (see 13.2) is added;
• Chromium oxide determination (see Clause 15) is added;
• EDTA volumetric method for aluminum oxide (see 16.2) is added.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

Introduction

The International Organization for Standardization (ISO) [and/or] International Electrotechnical Commission (IEC) draw[s] attention to the fact that it is claimed that compliance with this document may involve the use of a patent.

ISO [and/or] IEC take[s] no position concerning the evidence, validity and scope of this patent right.

The holder of this patent right has assured ISO [and/or] IEC that he/she is willing to negotiate licences under reasonable and non-discriminatory terms and conditions with applicants throughout the world. In this respect, the statement of the holder of this patent right is registered with ISO [and/or] IEC. Information may be obtained from the patent database available at www.iso.org/patents.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights other than those in the patent database. ISO [and/or] IEC shall not be held responsible for identifying any or all such patent rights.

Oxide based abrasive grains — Chemical analysis —

Part 1:
Wet chemistry methods

This document deals with the chemical analysis of abrasive grains or crude based on fused aluminium oxide. lt applies to commercially available products but not necessarily to products which have been altered by use. lt includes the following determinations:

• Loss on ignition
• Silicon dioxide
• lron oxide
• Titanium dioxide
• Calcium oxide
• Magnesium oxide
• Zirconium oxide
• Aluminium oxide
• Chromium oxide

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements 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.

ISO 9138:2015, Abrasive grains — Sampling and splitting

ISO 6353-1:1982, Reagents for chemical analysis — Part 1: General test methods

ISO 6353-2:1983, Reagents for chemical analysis — Part 2: Specifications — First series

ISO 6353-2/Add.2:1986, Addendum 2 to ISO 6353-2:7983.

ISO 6353-3:1987, Reagents for chemical analysis — Part 3: Specifications — Second series

ISO 9138:2015, Abrasive grains — Sampling and splitting

No terms and definitions are listed in this document.

General

Unless otherwise indicated, it is intended that all reagents shall conform to the specifications given in ISO 6353-1, ISO 6353-2 and ISO 6353-3. Other grades may be used, provided it be first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination. Unless otherwise indicated, references to water shall be understood to mean deionized water.

Paragraphs 4.2 to 4.20 include those reagents common to two or more analytical procedures. Other reagents will be found in the section which deals with the particular method in which they are used.

WARNING — The use of this document can involve hazardous materials, operations and equipment.

WARNING — WARNING — The reagents used are partly corrosive and toxic. Safety precautions are absolutely necessary.

WARNING — WARNING — This document involves handling of hot apparatus.

Concentrated acids and ammonium hydroxide

Concentrated acids and ammonium hydroxide having the following approximate volumetric masses p, in grams per millilitre or concentrations, in percentage by mass will be required:

Hydrochloric acid (HCl): ρ=1,18 g/ml

Nitric acid (HNO₃): ρ=1,42 g/ml

Sulphuric acid (H₂SO₄): ρ=1,84 g/ml

Hydrofluoric acid (HF): 40% (m/m)

Phosphoric acid (H₃PO₄): 85% (m/m)

Ammonium hydroxide (NH₄OH): ρ=0,90 g/ml

Dilute acids and ammonium hydroxide.

The dilute acids and ammonium hydroxide referred to have varying concentrations. They shall be made up by mixing proportional volumes of the concentrated reagent and water. The dilute sulphuric acid mixtures shall be made up by slowly adding the acid to the water and stirring continuously. These dilutions are designated in the test procedures as (1+5), (1+8), etc., except for the very dilute solutions which are characterized by the percentage of reagent added. The designations in parentheses indicate the volume of the reagent added to the volume of water; for example, H₂SO₄ (1+9) contains 10 % (V/V) of H₂SO₄ (ρ=1,84 g/ml).

Ammonium acetate, 300 g/L solution.

Dissolve 300 g of NH₄C₂H₃O₂ in water. Fill to the 1 L mark with water.

Ammonium chloride (NH₄Cl).

Ammonium oxalate [(NH₄)₂C₂O₄], saturated solution.

Diammonium hydrophosphate, 100 g/l solution.

Dissolve 10 g of (NH₄)₂HPO₄ in 100 ml of water.

Barium diphenylamine sulphonate, 2 g/l solution.

Dissolve 0,5 g of the salt in 250 ml of H₂SO₄.

Hydrogen peroxide, 30 g/l solution.

Hydroxylamine hydrochloride or hydroxylammonium chloride, 100 g/l solution. Dissolve 50 g of ClNH₃OH in 500 ml of water. Filter if necessary.

Mercuric chloride (HgCl₂), saturated solution.

Methyl red indicator, 1 g/l solution.

Dissolve 0,1 g methyl red in 100 ml of methanol.

o-Phenanthroline (1,10-phenanthroline), 1 g/l solution.

Dissolve 1 g o-phenanthroline monohydrate in 15 ml of ethanol (95 %). Dilute to 1 l with water.

Potassium dichromate (K₂Cr₂O₇), 0,01 mol/l solution.

Dissolve 2,942 4 g of K₂Cr₂O₇ in water. Make up the solution to the 1 l mark of a volumetric flask. Standardize the solution against a sample with a certified iron content.

Potassium permanganate (KMnO₄), standardized solution, c (1/5 KMnO₄) = 0,01 mol/l.

Dissolve 1,580 0 g of KMnO₄ in 500 ml of water. Allow to stand for 1 d-2 d. Filter through an asbestos mat and dilute to the 1 l mark of a volumetric flask with water. Standardize against sodium oxalate.

Potassium permanganate (KMnO₄), 50 g/l solution. Dissolve 5 g KMnO₄ in 100 ml of water.

Potassium pyrosulfate (K₂S₂O₇).

Anhydrous sodium carbonate (Na₂CO₃).

Sodium tetraborate (Na₂B₄O₇).

Tin (II) chloride (SnCl₂), 50 g/l solution. Dissolve 50 g of SnCl₂ in 100 ml of HCl. Make up to the 1 l mark of a volumetric flask with water. Store the solution with metallic tin in the bottle.

Small jaw or roll crusher with hardened steel faces.

Tool steel mortar.

In situations where it is vital that iron contamination be eliminated, the crushing should be carried out in a tungsten carbide mortar.

Sieve, with mesh of 150 µm aperture size.

Sieve, with 2 mm aperture size.

Platinum crucible, weighed, 30 ml, with lid.

Scale, accuracy 0,0001g.

Scale, accuracy 0,1 g.

Spectrophotometer, wavelength range, 200 nm -1000nm.

Desiccator, add drying agent to desiccator, e.g. silica gel.

The sample shall be obtained by means of an approved sampling method according to ISO 9138:2015, is crushed in a small jaw or roll type crusher until it can be passed through a sieve having a mesh size of 2 mm; it is then mixed and divided by coning and quartering until approximately 500 g are obtained. The 500 g sample is in turn mixed and divided by coning and quartering until a sample weighing between 10 g and 20 g is obtained. This 20 g sample is then pulverized in a mortar until, unless otherwise specified, it completely passes through a sieve having a mesh size of 150 µm; it is then mixed thoroughly and placed in a container which will ensure freedom from contamination.

Precautions shall be taken in order to prevent the sample being contaminated by steel particles from the sampling and crushing equipment.

Tungsten carbide or corundum milling tools can be used to improve sample preparation, which can reduce steel particle contamination.

The sample, carefully obtained by one of the approved methods, is thoroughly mixed and divided by coning and quartering until 10 g to 20 g are obtained. lt is then crushed until, unless otherwise specified, it completely passes through a sieve having a mesh size of 150 µm; it is then carefully mixed and placed in a container which will ensure freedom from contamination (see ISO 9138).

Blank determination on the reagents shall be made for each determination and the necessary corrections applied in each case.

Weigh a 1 g sample to within 0,000 1 g and place it in a weighed platinum crucible which has been previously heated to 1 100 °C and cooled down to room temperature. Record the mass of the sample and the crucible. Heat the crucible plus sample at 1 100 °C until a constant mass is obtained. Cool the crucible in a desiccator and weigh the crucible plus sample.

Loss on ignition, expressed as a percentage, is given by the formula

(1)

where

m₁ is the mass of the crucible plus sample before ignition, in grams (g);

m₂ is the mass of crucible plus sample after ignition, in grams (g);

m₀ is the mass of sample, in grams (g).

NOTE lf the sample gains in mass, report as a gain, and use the formula:

(2)

To be used when the silicon dioxide concentration is greater than 2% (m/m) and less than 5% (m/m).

Platinium crucible, with lid.

Beaker, 400 ml.

Filterpaper, medium grade.

Desiccator.

Weigh a 1 g sample to within 0,000 1 g and place in a platinum crucible containing 3 g of Na₂C0₃ and 3 g of Na₂B₄0₇. Mix the sample and fuse mixture thoroughly. Cover the crucible with a platinum lid and fuse the mixture at 1 000 °C until the entire sample is in solution. Rotate the crucible during cooling to deposit the melt in a thin layer on the side of the crucible. Place crucible and lid in a 400 ml beaker.

Dissolve the fusion in 100 ml of H₂SO₄ (1+4). When fully dissolved, thoroughly wash crucible and lid, adding washes to main solution.

Carefully evaporate the solution to fumes of SO₃ and leave to cool. Add 100 ml of water and boil to dissolve salts. Filter using a medium grade ashless filter paper. Wash the paper and precipitate with hot H₂S0₄ (2+98). Retain the filtrate for the Fe₂O₃, TiO₂, CaO and MgO determinations. Transfer the filter paper to a platinum crucible and char at low heat. When fully charred ignite at 1 000 °C. Leave the crucible to cool in a desiccator and weigh to constant mass.

Moisten the solid mass with 1 or 2 drops of water, add 10 ml of HF acid and 2 or 3 drops of H₂SO₄ (1+1). Slowly evaporate to dryness then ignite at 1 000 °C. Cool the crucible in a desiccator and weigh to constant mass. Evaluate the loss in mass due to HF, H₂SO₄ treatment.

Silicon dioxide content, expressed as a percentage by mass, is given by the equation

(3)

where

m₁ is the mass lass due to the HF, H₂SO₄ treatment, in grams (g);

m₀ is the mass of the sample, in grams (g).

To be used when the silicon dioxide concentration is less than 2% (m/m).

Molybdic acid solution, 100 g/l.

Dissolve 100 g of ammonium molybdate [82 % (m/m) of MoO₃] in approximately 600 ml of water. Add 70 ml of H₂SO₄ (ρ= 1,84 g/ml). Filter the solution. Dilute to 1 l with water in a volumetric flask.

Reducing solution.

Dissolve 25 g of sodium hydrogen sulphite (NaHSO₃) in 25 ml of water. Dissolve 2 g of sodium sulphite (Na₂SO₃) and 0,4 g of 1-amino-2-naphthol-4-sulphonic acid in 25 ml of water.

Mix the two solutions and dilute to 250 ml with water in a volumetric flask. Note that this solution has a maximum shelf life of two weeks.

Silicon dioxide, standard solution corresponding to 0,1 mg SiO₂ per millilitre.

Melt 0,100 g of anhydrous SiO₂ and 1 g of Na₂CO₃ in a platinum crucible. Cool the molten mass. Dissolve in water and make up to 1 000 ml in a volumetric flask. Transfer to a polyethylene bottle.

Tartaric acid, 100 g/l solution.

Dissolve 100 g of tartaric acid in water. Dilute to 1 000 ml in a volumetric flask.

Fusion mixture, comprising 3 parts Na₂CO₃ or 1 part B₂O₃. (Boric oxide is the preferred reagent). Salts containing boron have varying amounts of SiO₂ giving high and frequently inconsistent blank values.)

Hydrofluoric acid, 2 % (V/V) solution (for cleaning PTFE).

Platinum crucible.

PTFE beaker, 250 ml.

Magnetic stirrer.

PTFE stirring bar.

pH-meter.

Volumetrie flask, 100 ml.

Spectrophotometer.

Sample size and dilutions

Use the Table 1 to determine appropriate sample test portions and dilution.

Preparation of test solution

Weigh 5 g of fusion mixture into a 30 ml platinum crucible then weigh the appropriate size sample (see 8.2.3.1) into the crucible and cover with an additional 5 g of fusion mixture. Place the crucible in a high-temperature furnace. Melt from room temperature to 950 °C-1 000 °C and keep for 1 h-1,5 h. Cool the melt to room temperature. Wash the outside of the crucible with water. Place the crucible in a 250 ml PTFE beaker and add enough water to cover the crucible. Bring to the boil until the melt is dissolved. Cool to room temperature and dilute to approximately 175 ml to 200 ml. Place the PTFE stirring bar in the beaker and place on a magnetic stirrer.

Using a pH-meter, adjust very carefully the pH of the solution to 1,8 using H₂SO₄ (1+1). (Do not allow pH to go below 1,8.)

lf pH goes below 1,8 polymerization of the silicic acid starts to take place and polymerized silicic acid will not react to form silicomolybdic acid capable of being reduced to form the proper colour.

Transfer the solution to a volumetric flask (see 8.2.3.1 for flask size), dilute to the mark with water and mix. Pipette an appropriate aliquot (see 8.2.3.1) into a 100 ml volumetric flask to which is added in the following order:

1. 2 ml of freshly prepared molybdic acid solution (see 8.2.1.1). Mix and allow to stand for 7 min;
2. 10 ml of tartaric acid solution (see 8.2.1.4);
3. 2 ml of reducing solution (see 8.2.1.2). Mix and allow to stand for 30 min.

Read absorbance at a wavelength of 700 nm, using 1 cm cuvette (for best accuracy, absorbance shall be in the range of 0,2 to 0,6).

Table 1

Preparation of calibration curve

Prepare a series of standard solutions to cover the expected range of silicon dioxide concentrations. Determine the absorbance of the solutions as described for the sample in 8.2.3.2. Prepare a calibration curve by plotting the absorbance values for the standard solutions against the concentration of SiO₂, in grams, per 100 ml of solution.

Silica content, expressed as a percentage by mass is given by the equation

(4)

where

d is the dilution factor (see 8.2.3.1);

m₁ is the mass, in grams (g), of silicon dioxide per 100 ml of sample solution as found by interpolation from the calibration curve;

m₀ is the mass of the sample, in grams (g).

To be used when the silicon dioxide concentration is greater than 5% (m/m).

The sample is melted and decomposed by using a mixture of sodium tetraborate and sodium carbonate flux. After leaching with a dilute hydrochloric acid solution, evaporate to a wet salt state. Add animal gel to condense the silicic acid. Filter it, and then burn the solid filter cake to a constant amount. Treated with hydrofluoric acid and sulfuric acid, and the silicon will escape as silicon tetrafluoride. Then, burn the residual to a constant amount. The mass difference before and after hydrofluoric acid treatment is the mass of silica in the solid filter cake. Determine residual silica in the filtrate by using silicon molybdenum blue spectrophotometry. The sum of these two parts are the content of silicon dioxide in the sample.

Add to the former mass of silica, and then yield the content of silicon dioxide in the sample.

The animal gel coagulation method is based on the following chemical reactions:

Gelatin, fragmented (CAS 9000-70-8).

Sodium tetraborate-sodium carbonate mixed flux, take sodium tetraborate and sodium carbonate with the mass ratio of 2:1 in an agate mortar. Mix well and store in a jar.

Ammonium molybdate solution (50 g/l), dissolve 5 g of ammonium molybdate [82 % (m/m) of MoO3] in 20 ml of water. Dilute to 100 ml with water in a volumetric flask. Place it for 24 h and filter the solution. If there is precipitation during use, stop using it.

p-nitrophenol indicator (2 g/l ethanol solution), weigh 0,2 g of p-nitrophenol and dissolve it in 95% ethanol, and dilute it to 100 ml with ethanol.

Ammonium ferrous(II) sulfate solution (60 g/l), weigh 6 g of (NH₄)₂Fe(SO₄)₂ and dissolve it in 100 ml of water. Add 5 drops of sulfuric acid (1+1) dropwise and mix well.

Oxalic acid and sulfuric acid mixed solution (1+1), take 50 g/l oxalic acid solution and sulfuric acid (1+3) by volume ratio of 1:1 and mix well.

Silicon dioxide standard solution (0,03 mg/ml), weigh 0,300 0 g of silica (high-purity reagent) burned at 1000 °C into a platinum crucible. Mix it with 3 g of anhydrous sodium carbonate (reference reagent). Mix well, cover it, slightly open the lid, and send it into a high-temperature furnace. Melt at 850 °C to 900 °C for 20 min to 30 min. Take out, and leach it in hot water in a PTFE beaker. Transfer it to a 1 000 ml volumetric flask after cooling. Dilute with water to 1 000 ml, mix well, and immediately transfer to a clean and dry plastic bottle for storage. 1ml this solution contains 0,3 mg of silica.

Pipette 100 ml the above-mentioned 0,3 mg/ml silica solution into a 1 000 ml volumetric flask. Neutralize with sulfuric acid (5+95) until slightly acidic. Dilute with water to 1 000 ml, mix well, and immediately transfer to a clean and dried plastic bottle for storage. This is the silicon dioxide standard solution. 1 ml this solution contains 0,03 mg of silicon dioxide.

Blank solution, weigh 4 g of sodium tetraborate - sodium carbonate mixed flux into a platinum crucible. Melt in a high temperature furnace at 1 000 °C for 10 min. Take out and cool. Heat and leach in 100 ml hydrochloric acid (1+4). Wash out the crucible and lid with water. Cool down and transfer to a 250 ml volumetric flask. Dilute with water to 250 ml, and mix well.

Spectrophotometer.

Determination

Weigh about 0,5 g of the test portion (m₀) into a platinum crucible, accurate to 0,0001 g. Add 3 g of sodium tetraborate-sodium carbonate mixed flux, mix well, cover with 1 g mixed flux. Cover with the lid, and slightly open the lid. Place it in a high-temperature furnace. Melt from room temperature to 1000℃±20℃ (maximum heating rate 20 ℃ per minute) and keep for 1 h to 1,5 h. Take it out, rotate the crucible making the molten material attaching to the inside of the crucible. After cooling, place it in a beaker which contains 100ml of near boiling hydrochloric acid (1+4). Heat it on a sand bath for leaching, and wash out the crucible and lid with water. When evaporating the material inside the beaker on a sand bath to a wet salt state, add 0,1 g of gelatin, stir thoroughly for 2 min to 3 min, and keep it warm for 20 min on a water bath at 60 °C to 70 °C. Take it off, add 40 ml of hot hydrochloric acid (5+95), and stir to dissolve the salt. Filter with a medium speed quantitative filter paper, wash with hot hydrochloric acid (5+95) 7 to 8 times, and then wash with water until there are no chloride ions. The filtrate flows into a 250 ml volumetric flask.

Place the silica precipitate and filter paper into a platinum crucible, carefully dry and incinerate. Transfer to a high-temperature furnace. Burn at 980 °C to 1000 °C for 1 h. Take out, and cool slightly. Place in a dryer, and cool to room temperature. Weigh, and burn to a constant amount (m₁). Wet the burned sediment with water. Add 1-2 drops of sulfuric acid (1+1) and 5 ml of hydrofluoric acid. Evaporate on a sand bath until sulfuric acid white smoke appears. Take off and cool slightly. Add 2ml to 3ml of hydrofluoric acid, and continue to evaporate until dry. Place in a high-temperature furnace and burn at 980 °C to 1000 °C for 15 min to 30 min. Take out and cool slightly. Place in a dryer, and cool to room temperature. Weigh, and burn to a constant amount (m₂).

Add 2 g of potassium pyrosulfate (analytical reagent) to the burned residue. Heat on an electric furnace to melt it. Take out and place it in a high temperature furnace at 650 °C for 10 min. Take out and cool down. Then, add an appropriate amount of hydrochloric acid (1+1) to leach it. After the residue is completely dissolved, transfer it into the 250 ml volumetric flask with the former filtrate. After cooling, dilute with water to 250 ml, and mix well. Put aside the solution A (V₀) for determining residual silicon dioxide, aluminum oxide, calcium oxide, magnesium oxide, and etc.

Pipette 5 ml (V₁) of the above solution into a 100 ml volumetric flask. Add 40 ml of water and 2 drops of p-nitrophenol indicator. Neutralize with ammonium hydroxide (density 0,90 g/ml) until yellow, and immediately add 5 ml of hydrochloric acid (1+3) and 5ml of ammonium molybdate solution. Stand for 10 min to 15 min. Operate as 8.3.4.2 to determine its absorbance. Measure the absorbance and determine the corresponding mass of silica (m₃) from the working curve.

Drawing of working curve

Take 5 ml blank solution in eight 100ml volumetric flasks respectively. Add 0,00 ml, 0,50 ml, 1,00 ml, 2,00 ml, 4,00 ml, 6,00 ml, 8,00 ml, and 10,00 ml of silica standard solution in the volumetric flasks with a micro burette sequentially. Add 10ml of water, and adjust the test solution temperature to 20 °C to 25 °C. Add 5 ml of ammonium molybdate solution, and mix well. Stand for 10 min to 15 min. Add 20 ml of oxalic acid and sulfuric acid mixed solution (1+1) while shaking. Add 5ml of ammonium ferrous(II) sulfate solution quickly. Dilute with water to 100 ml, and mix well. Using blank solution as a reference, measure the absorbance with the spectrophotometer at a wavelength of 700 nm using a 1 cm cuvette. Draw the working curve with the mass of silica as the x-axis and the absorbance of the test solution as the y-axis.

The content of silica is calculated according to the formula below.

(5)

where

m₁ is the mass of sediment and crucible before hydrofluoric acid treatment, in grams (g);

m₂ the mass of residue and crucible after hydrofluoric acid treatment, in grams (g);

m₀ is the mass of the sample, in grams (g);

m₃ is the mass of silica in the test solution according to the standard curve, in grams (g);

V₀ is the total volume of test solution, in milliliters (ml);

V₁ is the volume of the test solution, in milliliters (ml).

Evaporate the filtrate obtained from the gravimetric SiO₂ determination (see 8.1), or an aliquot of the solution from the colorimetric SiO₂ determination (see 8.2), or an aliquot of the solution from the animal gel coagulation SiO₂ determination (see 8.3) until 150 ml to 200 ml of the solution is obtained. Adjust the acidity of the solution to nearly neutral with NaOH (550 g/l).

Add NaOH (550 g/l) dropwise until the precipitate just completely dissolves. Transfer the solution into a beaker containing 150 ml of cold NaOH (150 g/l) and 1 g of Na₂CO₃. Heat the solution and allow it to digest for one hour. Cool the solution. Filter the precipitate using a medium grade filter paper which has been treated with NaOH solution (150 g/l).

Wash with Na₂CO₃ (10 g/l). Dissolve the precipitate through the paper with 25 ml of hot HCl (1+9). Wash the paper with hot HCl (2+98). Dilute approximately 150 ml. Add 5 ml of H₂O₂ [3% (V/V)]. Bring the solution to the boil. Add 1 g of ammonium chloride (NH₄Cl) and 3 drops of methyl red indicator solution. Add NH₄OH (1+1) dropwise until a persistent yellow color is produced. Then add approximately 10 extra drops in excess. Bring the solution to the boil. Allow the solution to stand for one minute. Filter using a medium grade paper. Wash the paper and the precipitate with a hot ammonium chloride solution (NH₄Cl at 20 g/l) which has been made alkaline with NH₄OH.

Return the precipitate and the paper to the original beaker. Add 100 ml HCl (1+9). Stir until the precipitate has dissolved and the paper is completely macerated. Dilute to approximately 200 ml with water. Bring the solution to the boil.

Repeat both the precipitation with NH₄OH and the filtration. Combine the filtrates from the two precipitations and retain them for the CaO and MgO determinations. Dissolve the precipitate in 50 ml of H₂SO₄ (1+4). Transfer the solution to a 100 ml volumetric flask. Bring up to the mark with water. This solution is used for volumetric method determination of iron(III) oxide and content.

To be used when the iron(III) oxide concentration is greater than 1% (m/m).

Filterpaper, medium grade.

Beaker, 250 ml.

Transfer a 50 ml of the mixed oxide solution prepared in Clause 9 to a 250 ml beaker. Add 5 ml of HCl. Evaporate the solution to about 20 ml. Add SnCl₂ solution dropwise with continual stirring until the solution is colourless. Add 1 drop in excess. Cool the solution rapidly in a water bath. Add 15 ml of HgCl₂ solution. Allow the solution to stand for 3 min. Add 15 ml of H₃PO₄ (1+1), then 3 drops of barium diphenylamine sulphonate indicator solution.

Titrate with potassium dichromate until a persistent purple end point is obtained.

lron(III) content expressed as a percentage by mass is given by the equation

(6)

where

V is the volume of potassium dichromate solution required, in millilitre (ml);

c is the actual concentration of this solution, expressed in moles of potassium dichromate per litre (mol/l);

d is the dilution factor;

m₀ is the mass of the sample, in grams (g);

479,1 is the triple of the molecular weight of iron(III) oxide, in mole per grams (g/mol);

1000 conversion between liters and milliliters.

To be used when the iron(III) oxide concentration is less than 1% (m/m).

Standard iron solution, (1 ml= 1 mg Fe₂O₃).

Dissolve 4,91 g of ferrodiammonium disulphate [Fe(NH₄)₂(SO₄)₂·6H₂O] in HCl (0,1 mol/l) or H₂SO₄ (0,05 mol/l), and dilute to the 1 l mark with the acid. Standardize the solution by titration against a solution of a standard oxidant.

Congo-red paper indicator.

1,10-Phenanthroline, 1 g/l solution.

Volumetric flask, 100 ml.

Beaker, 150 ml.

Hot plate.

Preparation of test solution

Transfer a 25 ml aliquot of the mixed oxide solution (see Clause 9) to a 150 ml beaker. Add 10 ml of hydroxylamine hydrochloride solution and 10 ml of tartaric acid solution (see 8.2.1.4). Add NH₄OH dropwise until the solution becomes alkaline to Congo-red paper. Add H₂SO₄ (1+1) dropwise until the solution just becomes acid to Congo red paper. Add the ammonium acetate solution until the solution becomes alkaline again, then add 5 ml in excess.

Add 10 ml of phenanthroline-1,10 solution. Transfer the solution to a 100 ml volumetric flask. Bring up to the mark with water.

Measure the absorbance of the solution using a wave length of approximately 500 nm. Use a blank test solution which has undergone all the successive procedures as a reference solution.

Preparation of calibration curve

Prepare a series of standard solutions to cover the expected range of iron oxide concentrations. Determine the absorbance as described for the sample solution in 10.2.3.1. Draw a calibration curve by plotting the absorbance values for the standard solution in terms of quantities, in milligrams, of Fe₂O₃ per 250 ml of solution.

From the measured absorbance of the sample solution, interpolate the amount of iron oxide in the sample solution from the calibration curve.

lron(III) oxide content, expressed as a percentage by mass is given by the equation

(7)

where

m₁ is the mass, in milligrams (mg), of iron oxide per 250 ml of sample solution, as found by interpolation;

V₁ is the volume of mixed oxide solution, in millilitres (ml);

V₀ is the volume of aliquot, in millilitres (ml);

m₀ is the mass of the sample, in grams (g);

1 000 is the conversion factor, grams to milligrams.

In an ammonium hydroxide with pH 8-11, reaction between iron(III) and sulfosalicylic acid to generate a stable yellow complex. Measure absorbance at a wavelength of 420 nm to determine the content of iron oxide.

To be used when the iron(III) oxide concentration is less than 2% (m/m).

The sulfosalicylic acid colorimetric method is based on the following chemical reactions:

Sodium tetraborate-sodium carbonate mixed flux, take sodium tetraborate and sodium carbonate with the mass ratio of 2:1 in an agate mortar. Mix well and store in a jar.

Sulfosalicylic acid solution (150 g/l), weigh 15 g of sulfosalicylic acid and dissolve it in water, dilute with water to 100 ml.

Iron oxide standard solution (0,025 0 mg/ml), weigh 0,250 0g of iron oxide (high-purity reagent) (pre-dried at 110 °C for 2 hours). Place in a 300 ml beaker. Add 40 ml of hydrochloric acid (1+1), and dissolve it at low temperature. Transfer to a 1 000 ml volumetric flask, and cool down. Dilute with water to 1 000 ml, and mix well. 1ml of this solution contains 0,250 0 mg of iron oxide.

Transfer 100 ml of the above iron oxide solution to a 1 000 ml volumetric flask, add 5 ml of sulfuric acid (1+1). Dilute with water to 1 000 ml, and mix well. This is the iron oxide standard solution. 1ml of this solution contains 0,025 0 mg of iron oxide.

Blank solution, weigh 4 g of mixed flux into a platinum crucible, melt in a high temperature furnace at 1 000 °C for 10 min. Take out and cool. Heat and leach with 100ml hydrochloric acid (1+4). Wash out the crucible and lid with water, and cool it. Transfer to a 250 ml volumetric flask. Dilute with water to 250 ml, and mix well.

Spectrophotometer.

Drawing of working curve

Take 25 ml blank solution in nine 50 ml volumetric flasks respectively. Add 0,00 ml, 0,20 ml, 0,40 ml, 1,00 ml, 2,00 ml, 4,00 ml, 6,00 ml, 8,00 ml, and 10,00 ml of the standard iron oxide solution in the volumetric flasks with a micro burette sequentially. Add 10 ml of sulfosalicylic acid solution, shake, and add ammonium hydroxide dropwise until the solution turns stable yellow, and then add 2 ml in excess. Cool to room temperature. Dilute with water to 50 ml, and mix well. Measure the absorbance in a spectrophotometer at a wavelength of 420 nm using a 1 cm cuvette. Subtract the absorbance from the blank test. Draw the working curve according to the corresponding mass of iron oxide.

Analysis steps

Pipette 25 ml of solution A (see 8.3.4.1) (V₁) into a 50 ml volumetric flask. Add 10ml of sulfosalicylic acid solution, and shake. Add ammonium hydroxide (1+1) dropwise until the solution turns stable yellow, and then add 2 ml in excess. Cool to room temperature. Dilute with water to 50 ml, and mix well. Use water as a reference. Measure its absorbance in a spectrophotometer at a wavelength of 420 nm using a 1cm cuvette. After subtracting the absorbance of the blank test, check the mass of iron oxide (m₁) on the working curve.

The content of iron oxide is calculated according to the formula below.

(8)

where

m₁ is the mass, in milligrams (g), of iron oxide per 50 ml of sample solution, as found by interpolation;

V₁ is the volume of mixed oxide solution, in millilitres (ml);

V₀ is the volume of aliquot, in millilitres (ml);

m₀ is the mass of the sample, in grams (g).

Titanium dioxide, standard solution.

Weigh 1,25 g of calcined TiO₂ and place in a platinum crucible. Fuse with 10 g of K₂S₂O₇, keeping the temperature as low as possible in order to maintain fluidity. Cool and dissolve in about 200 ml H₂SO₄ (1+1); cool. Transfer to a 1 000 ml volumetric flask. Dilute to the mark with water and mix thoroughly. Standardize the solution by precipitation with NH₄OH and ignition to TiO₂.

Platinum crucible.

Volumetric flask, 250 ml.

Volumetric flask, 1 000 ml.

Transfer a 50 ml aliquot of the mixed oxide solution (see Clause 9, 8.1.2) to a 250 ml volumetric flask. Add 50 ml of H₂SO₄ (1+1). Dilute the solution to approximately 200 ml. Add 5 ml of H₃PO₄ (1+1) and 5 ml of hydrogen peroxide [3% (V/V) H₂O₂]. Dilute to the mark with water. Measure the absorbance of the solution using a wavelength of 425 nm. Use a blank reagent solution as a reference.

Prepare a series of standard solutions to cover the expected range of titanium dioxide concentrations. Determine the absorbance of solution as described for the sample solution in 11.3.1. Draw a calibration curve by plotting the absorbance values for the standard solutions in terms of quantities (in milligrams) of TiO₂ per 250 ml of solution.

From the measured absorbance of the sample solution, interpolate the amount of titanium dioxide in the sample solution from the calibration curve (see 11.3.2).

Titanium dioxide content, expressed as a percentage by mass is given by the equation

(9)

where

m₁ is the mass of titanium oxide, in milligrams (g), per 250 mi of sample solution, as found by interpolation;

V₁ is the volume of mixed oxide solution, in millilitres (ml);

V₀ is the volume of aliquot, in millilitres (ml);

m₀ is the mass of the sample, in grams (g);

1 000 is the conversion factor, grams to milligrams (g).

To be used when the calcium oxide concentration is greater than 1% (m/m).

Filterpaper, fine grade.

Platinum crucible

Since manganese may be present in some materials and will interfere with the calcium and magnesium determinations it should be separated at this point.

Evaporate the filtrate obtained from the mixed oxide separation (see Clause 9) to approximately 100 ml. Add 10 ml of saturated bromine water, make the solution alkaline with NH₄0H and add 15 drops in excess. Leave to digest until any manganese present precipitates as Mn0₂, keeping the solution ammoniacal. Filter and wash with hot water.

Make the filtrate acidic by adding HCl to methyl red. Bring to the boil. Slowly add 10 ml of the ammonium oxalate solution. Add 5 ml of NH₄0H (1+1). Continue boiling the solution for 5 minutes. Allow the solution to digest overnight at a temperature slightly below the boiling point of the solution. Filter the precipitate on a fine paper. Wash the precipitate with the ammonium oxalate solution [0,1 % (m/m)l then dissolve the precipitate through the paper with 50 ml of HCl (1+4). Dilute the solution to approximately 100 ml. Precipitate and filter the calcium oxalate as above. Combine and retain the filtrates for the magnesium oxide determination.

Calcine the precipitate in a weighed platinum crucible at 1 000 °C until a constant mass is obtained. Weigh the precipitate as CaO.

Calcium oxide content. expressed as a percentage by mass is given by the equation

(10)

where

m₁ is the mass of the precipitate, in grams (g);

m₀ is the mass of the sample, in grams (g).

To be used when the calcium oxide concentration is greater than 1% (m/m).

Separate interfering elements such as aluminum, iron, titanium, and manganese using hexamethylenetetramine copper reagent. According to the principle that calcium ions can quantitatively form complex with EDTA at pH 8-13, this method uses a small amount of magnesium ions to form precipitate of Mg(OH)⁺ or Mg(OH)₂ when pH≥12 (not interfere with the determination). At this time, calcium ions form a purple red complex with the calcium reagent, but calcium ions can form a more stable complex with EDTA. When titrated with EDTA standard solution, calcium ions will be extracted from it. The endpoint is when the solution appears blue. Calculate the content of calcium oxide from the consumption of EDTA standard solution.

The volumetric method is based on the following chemical reactions:

Ca²⁺+H₂Y^2-→CaY^2-+2H⁺

Ca²⁺+HInd^2-→CaInd^-+H⁺

(From pure blue to purple red)

CaInd^-+H₂Y^2-→CaY^2-+HInd^2-+H⁺

(From purple red to pure blue)

Sodium diethyldithiocarbamate (copper reagent).

Hexamethylenetetramine solution (20 g/l, 150 g/l), weigh 2 g and 15 g of hexamethylenetetramine separately and dissolve them in water, then dilute with water to 100 ml.

Sodium hydroxide solution (200 g/l), weigh 20 g of sodium hydroxide and dissolve it in water, dilute with water to 100 ml.

Calcium reagent sodium carboxylate indicator (1:100), weigh 0.5 g of calcium reagent sodium carboxylate and mix with 50 g of sodium chloride.

Hydrochloric acid (1+1), take concentrated hydrochloric acid (density 1,19 g/cm³) and dilute it by volume with water with a ratio of 1:1.

EDTA standard solution (0,01 mol/l):

1. Preparation: Weigh 3,75 g of disodium ethylenediaminetetraacetic acid (EDTA) into a 400ml beaker. Add 200 ml of water, heat it to dissolve at low temperature, and cool it. Filter it into a 1 000 ml volumetric flask. Dilute with water to 1 000 ml, and mix well.
2. Calibration: Weigh 1,784 8 g of calcium carbonate (reference reagent) (pre dried at 110 °C for 2 h) and place it in a 250 ml beaker. Add 50 ml of water. Add hydrochloric acid (1+1) dropwise until completely dissolved and add of 2-3 drops in excess. Heat and boil to remove carbon dioxide. After cooling, transfer to a 1 000 ml volumetric flask, dilute with water to 1 000 ml, and mix well. This solution is the standard calcium oxide solution (1,00 mg/ml). Transfer 10ml of above calcium oxide standard solution into a 300 ml conical flask. Add 100 ml of water, add 10ml of sodium hydroxide solution. Shake, and let stand for 2 min to 3 min. Add a small amount of calcium reagent sodium carboxylate indicator, and titrate with the prepared EDTA standard solution until a persistent pure blue endpoint is obtained. Conduct blank test under the same condition.
3. Calculate according to formulas below.

(11)

(12)

where

T_CaO is the titration of EDTA standard solution to calcium oxide, in grams per milliliter (g/ml);

m is the mass of calcium oxide in the test solution, in grams (g);

V is the volume of EDTA standard solution consumed (minus blank value), in milliliters (ml);

T_MgO is the titration of EDTA standard solution for magnesium oxide, in grams per milliliter (g/ml);

k is the coefficient converting CaO to MgO, which is 0,718 8.

Pipette 50ml of solution A (8.3.4.1) in a 250 ml beaker. Add 80ml of water, and adjust to generate precipitate with sodium hydroxide solution. Then, add hydrochloric acid dropwise until the precipitate dissolves. Add 5ml of hexamethylenetetramine solution. Heat until the precipitate condenses. After cooling, add 0,3 g of copper reagent. Stand for more than 1 h, and filter in a 250 ml volumetric flask. Wash the filter cake 8 to 10 times with hexamethylenetetramine solution. Dilute with water to 250 ml, and mix well. This solution B is used to determine the amount of CaO and MgO.

Pipette 100 ml of solution B into a 300 ml conical flask. Add 20ml of sodium hydroxide solution. Stand for 5 min to 10 min. Add a small amount of calcium reagent sodium carboxylate indicator, and titrate with EDTA standard solution until a persistent pure blue endpoint is obtained. The volume of EDTA standard solution consumed by the sample test solution is V. Conduct blank test under the same condition. The volume of EDTA standard solution consumed by the blank solution is V₀.

The content of calcium oxide is calculated according to the formula below.

(13)

where

T_CaO is the titration of EDTA standard solution to calcium oxide, in grams per milliliter (g/ml);

V₁ is the volume of EDTA standard solution consumed by the test solution during titration, in millil iters (ml);

V₀ is the volume of EDTA standard solution consumed by the blank solution during titration, in milliliters (ml);

m₀ is the mass of the sample, in grams (g).

To be used when the magnesium oxide concentration is greater than 1% (m/m).

Platinum crucible.

Filterpaper, medium grade.

Filterpaper, fine grade.

Take the filtrate from the CaO determination, (see Clause 12) and make it strongly acidic with nitric acid (HNO₃). Evaporate the solution until dry.

Dissolve the residue in 200 ml of HCl (1+19). Filter the solution through a fine paper. Wash the paper with water. Make the solution alkaline by adding NH4OH dropwise, then add 10 ml in excess. Then add 20 ml of the diammonium hydrophosphate solution (see 4.7). Stir the solution vigorously for 1 min to 2 min. Allow the solution to stand overnight. Collect the precipitate on a medium grade filter paper using a filter accelerator. Wash the precipitate with ammonium nitrate solution (NH₄NO₃, 2+98). Dissolve the precipitate through the paper with 50 ml hot HCl (1+4). Make the solution alkaline by adding NH₄OH dropwise, and add a further 5 ml in excess. Add 5 ml of the ammonium phosphate solution. Stir, leave to digest, filter and wash as above.

Transfer the paper to a weighed platinum crucible. Calcine the precipitate at 1 100 °C in an oxidizing atmosphere. Weigh the precipitate as Mg₂P₂0₇.

Magnesium oxide content, expressed as a percentage by mass is given by the equation

(14)

where

m₁ is the mass of the precipitate, in grams (g);

m₀ is the mass of the sample, in grams (g).

To be used when the magnesium oxide concentration is greater than 1% (m/m).

Using a hexamethylenetetramine copper reagent to separate interfering elements such as iron, titanium, aluminum, manganese, zirconium, etc. This method is based on the principle that magnesium ions forming complex with EDTA in alkaline solutions quantitatively. At pH10, magnesium and calcium ions react with eriochrome black T to generate a purple red complex in the test solution. Titrating with EDTA standard solution, magnesium and calcium ion can form a more stable colorless complex. Thereby the eriochrome black T indicator will liberate. When the solution appears blue, it is the endpoint. Subtract the amount of EDTA standard solution consumed during calcium titration from the amount of EDTA standard solution consumed to obtain the content of magnesium oxide.

The volumetric method is based on the following chemical reactions:

Mg²⁺+H₂Y^2–→MgY^2–+2H⁺

Mg²⁺+HInd^2–→MgInd^–+H⁺

MgInd^–+ H₂Y^2–→MgY^2–+HInd^2–+H⁺

(From purple red to pure blue)

Ammonia-ammonium chloride buffer solution, pH10, weigh 67,50 g of ammonium chloride and dissolve it in 250 ml of water. Add 570 ml of ammonium hydroxide, dilute with water to 1 000 ml, and mix well.

EDTA standard solution (0,01 mol/l) (see 12.2.2.6).

Eriochrome Black T indicator (1:100), weigh 0,5 g of chromium black T and 50 g of sodium chloride. Grind and mix well.

Pipette 100 ml of solution B (see 12.2.3) into a 300 ml conical flask. Add 10 ml of ammonia ammonium chloride buffer solution (pH10). Add a small amount of chromium black T indicator, mix well. Titrate with EDTA standard solution until a persistent pure blue end point is obtained. This is the combined amount of calcium and magnesium. The volume of EDTA standard solution consumed by the sample test solution is V₂. Conduct blank test under the same condition. The volume of EDTA standard solution consumed by the blank solution is V₃.

The content of magnesium oxide is calculated according to the formula below.

(15)

where

T_MgO is the titration of EDTA standard solution to magnesium oxide, in grams per milliliter (g/ml);

V₂ is the volume of EDTA standard solution consumed by the test solution during the titration of calcium and magnesium, in milliliters (ml);

V₃ is the volume of EDTA standard solution consumed by titrating calcium magnesium white solution, in milliliters (ml);

V₁ is the volume of EDTA standard solution consumed by the test solution during calcium titration, in milliliters (ml);

V₀ is the volume of EDTA standard solution consumed by the blank solution during calcium titration, in milliliters (ml);

m₀ is the mass of the sample, in grams (g).

To be used when the zirconia concentration is less than 1,5% (m/m).

Filterpaper, medium grade.

Platinum crucible.

Meker burner.

Hot plate.

Weigh 0,5 g of sample into a 30 ml platinum crucible. Add 10 g of potassium pyrosulphate (K₂S₂O₇) to the crucible. Fuse the sample over a Meker burner until the Al₂O₃ is completely dissolved. Cool the molten mass. Dissolve the fusion in 100 ml of HCl (1+9) in a 250 ml beaker. Evaporate the solution until dry on a hot plate. Continue heating for 1 h at over 100 °C. Cool the beaker. Dissolve the solids in 100 ml of H₂SO₄ (1+10). Filter the solution through a medium filter paper. Wash the paper with hot water. Add 10 ml of H₂O₂ [3% (V/V)] then add 20 ml of (NH₄)₂HPO₄ (see 4.7). Allow the solution to digest overnight at 60°C to 80°C. Filter the precipitate on a medium filter paper. Wash the precipitate six times with the NH₄NO₃ solution (10 g/l). Place the precipitate and filter paper into a weighed platinum crucible; carefully burn off the filter paper at 1 000 °C until a constant mass is obtained. Weigh the precipitate as zirconium pyrophosphate (ZrP₂O₇).

Zirconium oxide content, expressed as a percentage by mass is given by the equation

(16)

where

m₁ is the mass of ZrP₂O₇, in grams (g);

m₀ is the mass of the sample, in grams (g).

To be used when the zirconia concentration is greater than 1,5 % (m/m).

Mandelic acid (DL-phenylglycolic acid).

Platinum crucible.

Filterpaper, fine grade.

Beaker, 400 ml.

Meker burner.

Platinum filter cone.

Hot plate.

Weigh 0,5 g of sample into a 30 ml platinum crucible. Add 5 g of a (1+1) mixture of Na₂CO₃ and Na₂B₄O₇ to the crucible. Mix the sample and fusion mixture thoroughly. Fuse over a Meker burner until completely dissolved. Cool, then place the crucible in a 400 ml beaker and cover with HCl (1+9). Add 15 ml-20 ml of concentrated HCl and boil until the fusion is completely dissolved. Cool the solution slightly, then add NaOH (25%) until a white precipitate forms.

Add 30 ml concentrated HCl and dilute the volume to the 250 ml mark. Boil the solution for 2 min to 3 min. Add 16 g-18 g mandelic acid carefully while boiling. Remove the beaker from the hot plate when foaming begins. Add paper pulp, mix well and allow the solution to digest on a warm hat plate until clear (1 h to 2 h). Add more pulp and filter by suction through a fine paper using a platinum filter cone. Keep the solution warm while filtering . Wash the paper thoroughly with a hat phenylglycolic acid solution (50 g of phenylglycolic acid per 1 l of 2 % HCl). Transfer the paper and precipitate to a weighed platinum crucible, carefully burn off the paper, and then calcine at 1 000 °C until a constant weight is obtained. Weight the precipitate as ZrO₂.

Zirconium oxide content expressed as a percentage by mass is given by the equation

(17)

where

m₁ is the mass of the precipitate, in grams (g);

m₀ is the mass of the sample, in grams (g).

The sample is melted with mixed flux and then leached with water. In an alkaline solution, the yellow color of chromate itself is used for spectrophotometric determination to determine the content of chromium oxide.

To be used when the chromium oxide concentration is less than 2,5% (m/m).

Sodium Hydroxide.

Borax sodium carbonate mixed flu, weigh two parts of borax and one part of anhydrous sodium carbonate and grind them in an agate mortar, mix well. Store them in a plastic bottle.

Chromium oxide standard solution (0,25 mg/ml), weigh 0,4839 g of potassium dichromate (reference reagent) (pre dried at 110 °C for 2 h). Place it in a 100 ml beaker, dissolve it in water. Transfer it into a 1000 ml volumetric flask. Dilute to the mark with water, and mix well. 1ml of this solution contains 0,25mg of chromium oxide.

Blank solution, take 8 g of mixed flux (15.2.2) into a platinum crucible and melt it in a high-temperature furnace under 1000 °C for 20 min. Take out and wash the outside of the crucible. Extract the molten material with hot water in 300 l beaker. Take out the crucible, add 4 g of sodium hydroxide. After cooling, transfer it to a 250 ml volumetric flask. Dilute with water to the mark, mix well.

Spectrophotometer.

Take 25 ml of blank solution and put it into seven 50 ml volumetric flasks respectively, and then add 0,00ml, 1,00ml, 2,00ml, 4,00ml, 6,00ml, 8,00ml, and 10,00ml of chromium oxide standard solution successively in the volumetric flasks with a micro burette. Dilute with water to the mark and mix well. Operate as 15.4.2 to determine its absorbance. After subtracting the absorbance of blank solution, it is relative to the corresponding chromium oxide mass. Subtract the absorbance from the blank test. Draw the working curve according to the corresponding mass of chromium oxide.

Weigh about 0,5g of the test portion (m₀), accurate to 0,0001g, and place it in a platinum crucible. Add 3g of borax sodium carbonate mixed flu. Stir evenly, and then add 1g of borax sodium carbonate mixed flu. Cover it with a lid and open the lid slightly. Put the crucible into a high-temperature furnace and melt it at 1060 °C~1100 °C for 1 h. Take out, rotate the crucible, and let the molten material adhere to the inside of the crucible. After cooling, clean the outside of the crucible and place it in a 300 ml beaker. Heat and leach the crucible with 100 ml boiling water on a sand bath. After the molten material is completely leached, wash out the crucible and lid. Add 2g of sodium hydroxide, and slightly boil it on the sand bath for 20 min. Transfer into a 250ml volumetric flask. After cooling, add water to dilute it to 250 ml, mix well (dry filter if there is sediment). Use a 1 cm cuvette at a wavelength of 420 nm. Measure the absorbance of the cuvette with water as the reference solution. Use the same method for blank test. After subtracting the absorbance of blank test, find out the mass of chromium oxide on the working curve.

Chromium oxide content expressed as a percentage by mass is given by the equation

(18)

where

w_Cr2O3 is the content of chromium oxide (Cr₂O₃), mass fraction in percent (%);

m is the mass of the test portion, in grams (g);

m₁ is the mass of chromium oxide found on the working curve in the sample solution, in grams (g);

V is the total volume of test solution, in millilitres (ml);

V₁ is the volume of the test solution, in millilitres (ml).

Calculations

Aluminium oxide content, expressed as a percentage by mass is given by the equation

(19)

where

A is the percentage by mass, loss on ignition;

B is the percentage by mass SiO₂;

C is the percentage by mass Fe₂O₃;

D is the percentage by mass TiO₂;

E is the percentage by mass CaO;

F is the percentage by mass MgO;

G is the percentage by mass ZrO₂;

H is the percentage by mass (Na₂O+K₂O+Cr₂O₃), where applicable.

In weakly acidic solutions, trivalent aluminum ions form a moderately strong complex with EDTA, which proceeds slowly and cannot be directly used for titration. Thus, the back titration is required. First, add EDTA standard solution in excess, adjust the pH value to around 2,3. When heated, trivalent aluminum ions completely chelate with EDTA. Then adjust the pH value to 5-6, using xylenol orange as an indicator, the excess EDTA will be titrated with a standard solution of Zn²⁺. The titration endpoint is when the solution changes from yellow to orange red.

Under this condition, trivalent iron ions, tetravalent titanium ions, and zirconium ions also complex with EDTA, which can be deducted during calculation.

The EDTA volumetric method is based on the following chemical reactions:

Sodium tetraborate-sodium carbonate mixed flux, take sodium tetraborate and sodium carbonate with the mass ratio of 2:1 in an agate mortar. Mix well and store in a jar.

Methyl orange indicator (0,5 g/l), weigh 0,05 g of methyl orange and dissolve it in water, dilute with water to 100 ml.

Hexamethylenetetramine solution (150 g/l), weigh 15 g of hexamethylenetetramine and dissolve it in water, dilute with water to 100 ml.

Sodium hydroxide solution (200 g/l), weigh 20 g of sodium hydroxide and dissolve it in water, dilute with water to 100 ml.

Dimethyl phenol orange indicator (1:100), weigh 0,5 g of dimethyl phenol orange indicator and 50 g of sodium chloride. Grind and mix well in an agate mortar.

Calcium reagent sodium carboxylate indicator (1:100), weigh 0,5 g of calcium reagent sodium carboxylate and 50 g of sodium chloride. Grind and mix well.

EDTA standard solution (0,05 mol/l).

1. Preparation: Weigh 18,16g of EDTA, and transfer to a 400 ml beaker. Add 200 ml of water. Heat slightly to dissolve at low temperature. Cool it, and filter it into a 1 000 ml volumetric flask. Dilute with water to 1 000 ml, and mix well.
2. Calibration: Weigh 1,784 8g of calcium carbonate (reference reagents) that has been dried at 110 °C for 2 h. Transfer it in a 250 ml beaker. Add 50 ml of water. Add hydrochloric acid (1+1) dropwise until calcium carbonate completely dissolved, and then add 2-3 drops in excess. Heat and boil to remove carbon dioxide. After cooling, transfer to a 1 000ml volumetric flask. Dilute with water to 1 000 ml, and mix well. 1ml of this solution contains 1.0000mg of calcium oxide.

Transfer 50,00 ml of calcium oxide standard solution into a 300 ml conical flask. Add 10 ml of water and 10 ml of sodium hydroxide solution. Mix well. Add an appropriate amount of calcium reagent sodium carboxylate indicator. Titrate with EDTA standard solution until a persistent pure blue end point is obtained. Conduct blank test under the same conditions.

1. The titration of EDTA standard solution to CaO is calculated according to the formula below.

(20)

where

T_CaO is the titration of EDTA standard solution to calcium oxide, in grams per milliliter (g/ml);

m is the mass of calcium oxide, in grams (g);

V is the volume of EDTA standard solution consumed (minus blank value), in milliliters (ml).

Zinc sulfate standard solution (0,025 mol/l).

1. Preparation: Weigh 7,2 g of zinc sulfate (ZnSO₄ 7H₂O, guaranteed grade) and transfer to a 250 ml beaker. Add 100 ml of water, stir and dissolve. Add sulfuric acid (1+1) dropwise to make it clear. Transfer to a 1 000 ml volumetric flask. Dilute with water to 1 000 ml, and mix well.
2. Calibration: Take 10,00 ml of EDTA standard solution (0,05 mol/l) into a 250 ml conical flask using a burette. Add 50ml of water, 5ml of hexamethylenetetramine solution, and an appropriate amount of xylenol orange indicator. Titrate the prepared zinc sulfate standard solution until it turns from yellow to slightly orange red endpoint.
3. The conversion coefficient of EDTA standard solution to zinc sulfate standard solution is calculated according to the formula below.

(21)

where

K is the volume of 1ml EDTA standard solution to zinc sulfate standard solution;

V₂ is the volume of zinc sulfate standard solution consumed for titration, in milliliters (ml);

V₁ is the volume of EDTA standard solution, in milliliters (ml).

The titration of zinc sulfate standard solution for aluminum oxide is calculated according to the formula below.

(22)

where

T_Al2O3 is the titration of zinc sulfate standard solution to aluminum oxide, in grams per milliliter (g/ml);

T_CaO is the titration of EDTA standard solution to calcium oxide, in grams per milliliter (g/ml);

k is the coefficient of converting calcium oxide to aluminum oxide, which is 0,909 1;

K is the volume of 1ml EDTA standard solution to the volume of zinc sulfate standard solution.

Weigh 0,5 g of the test portion (m₀) (accurate to 0,000 1 g) and mix it evenly in a platinum crucible which pre filled with 5 g of mixed flux. Cover it with 1 g of mixed flux. Cover it with the lid. Place the crucible in a high temperature furnace at 1 000 °C and melt for about 1 h. Take it out, rotate the crucible to make the molten substance attaching to the inside of the crucible. After cooling, wash the outside of the crucible with water. Place it in a 250 ml beaker containing 100 ml of nearly boiling H₂SO₄ (5+95). Heat it on a sand bath for leaching. Rinse the crucible and lid with water. Transfer to a 250 ml volumetric flask, and cool it. Dilute with water to 250 ml, and mix well. This is solution C.

Transfer 25,00 ml of solution C into a 250 ml conical flask. Add 50 ml of water and 25 ml of EDTA standard solution (V₁), and mix well. Heat it to 40 °C-50 °C. Add one drop of methyl orange indicator, adjust to yellow with ammonium hydroxide (1+1). Then, adjust to just a slight red with hydrochloric acid and add 2 drops in excess. Rinse the bottle inside wall with water. Heat to a slight boil for 3 min. Cool to room temperature with running water. Add 10 ml of hexamethylenetetramine solution and an appropriate amount of xylenol orange indicator. Titrate with zinc sulfate standard solution until it turns from yellow to slightly orange red endpoint. The volume of zinc sulfate standard solution consumed for titration is V₂.

The mass fraction of aluminum oxide using EDTA volumetric method is calculated according to the formula below.

(23)

where

V₁ is the volume of EDTA standard solution added, in milliliters (ml);

K is the volume of 1ml EDTA standard solution to the volume of zinc sulfate standard solution;

V₂ is the volume of zinc sulfate standard solution consumed for titration, in milliliters (ml);

T_Al2O3 is the titration of zinc sulfate standard solution to aluminum oxide, in grams per milliliter (g/ml);

m₀ is the mass of the sample, in grams (g);

k₁ is the coefficient of converting iron oxide into aluminum oxide, which is 0,638 3;

k₂ is the coefficient of converting titanium dioxide into aluminum oxide, which is 0,638 1;

k₃ is the coefficient of converting zirconia to aluminum oxide is 0,413 8.

The test report shall, in addition to the results, mention the method used (reference to this International Standard), all the test conditions and all details of procedures which are not provided for in this International Standard or which are optional, as well as all variations or observations regarding the sample likely to have an effect on the results.