national Bureau of Standards

Library, N.W. Bldg

AUG 1 1 1965 iiSn NBS MISC. PUBL. 260-6 ^

a o

Standard Reference Materials:

Methods for the Chemical Analysis of

White Cast Iron Standards

Kio-ii U.S. Department of Commerce

k»pY.t.i National Bureau of Standards
THE NATIONAL BUREAU OF STANDARDS

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Library of Congress Catalog Card Number: 65-60098
UNITED STATES DEPARTMENT OF COMMERCE . John T. Connor, Secretary NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

Standard Reference Materials:

Methods for the Chemical Analysis of

White Cast Iron Standards

J. I. Shultz

Institute for Materials Research

National Bureau of Standards Washington, D.C.

National Bureau of Standards Miscellaneous Publication 260-6

Issued July 16, 1965

For sale by the Sui>erintenuent of Documents, F.S. Government Printing Office Washington, D.C, 20102 - Price 45 cents
PREFACE

Within the framework of the NBS Institute for Materials

Research the area of standard reference materials is a broad

and important one, including the preparation, characterization and distribution of a wide variety of materials in such

diverse fields as metallurgy, polymers and inorganic

materials. In carrying out such a program there is much

interaction with representatives of industry and science,

beginning with discussions as to which primary standard

materials will do most to advance technology, the furnishing

of materials and fabrication of samples, and the characterization and certification of the materials by cooperative

efforts. The many groups participating in a standards

program are very interested in detailed information on specific aspects of the program -- but to date there has

been no publication outlet for such written discussions.

To meet this need, NBS Miscellaneous Publication 260 has

been reserved for a series of papers in the general area of

"standard reference materials". This series will present

the results of studies and investigations undertaken within

the Institute for Materials Research with emphasis on the

preparation and characterization of standard reference

materials. This subject-oriented series will provide a means

for rapid dissemination of this detailed information and we hope will stimulate the use of standard reference materials

in science and industry.

¥. Wayne Meinke, Chief

Office of Standard Reference Materials.

ii
OTHER NBS PUBLICATIONS IN THIS SERIES

NBS Misc. Publ. 260 , Standard Reference Materials:

Catalog and Price List of Standard Reference Materials

Issued by the National Bureau of Standards , January 1965.

In press ,*

(Supersedes NBS Misc. Publ. 24l, March 1962).

NBS Misc. Publ. 260-1, Standard Reference Materials:

Preparation of NBS White Cast Iron Spectrochemical

Standards , June 1964. 30 cents. * NBS Misc. Publ. 260-2, Standard Reference Materials:

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Standards , October 1964. 35 cents.

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for postage.

iii
CONTENTS

PAGE

1. INTRODUCTION 1

2. CARBON IN WHITE CAST IRON 5

3. MANGANESE IN WHITE CAST IRON 11

4. PHOSPHORUS IN WHITE CAST IRON 16

5. SULFUR IN WHITE CAST IRON 21

6. SILICON IN WHITE CAST IRON 27

7. COPPER IN WHITE CAST IRON 50

8. NICKEL IN WHITE CAST IRON 35

9. CHROMIUM IN WHITE CAST IRON 43

10. CHROMIUM AND VANADIUM IN WHITE CAST IRON 47

11. VANADIUM IN WHITE CAST IRON 53

12. MOLYBDENUM IN WHITE CAST IRON 57

LIST OF FIGURES

FIGURE NO.

1. Schematic of combustion carbon method

apparatus 10

2. Schematic of combustion-titration method for

sulfur 26

LIST OF TABLES

TABLE NO.

1. Composition limits of the ten major elements

for white cast iron . 4

2. Certified values of the ten major elements

for white cast iron 4

iv
STANDARD REFERENCE MATERIALS:

METHODS FOR THE CHEMICAL ANALYSIS OF

WHITE CAST IRON STANDARDS

J. I, Shultz

Institute for Materials Research

National Bureau of Standards

The procedures described in this publication are those used at the National Bureau of Standards in

the analysis of white cast iron standard reference

materials for the ten (10) major elements; namely , carbon., manganese , phosphorus , sulfur , silicon.,

copper, nickel, chromium, vanadium, and molybdenum.

Carbon and sulfur are determined by combustion;

manganese, chromium and vanadium by titrimetry;

phosphorus, copper, and molybdenum by photometry;

and silicon and nickel by gravimetry.

These procedures, which are slight modifications

of well-established and previously published

methods, were selected for their accuracy and

dependability

.

1. INTRODUCTION

These methods cover the procedures for the chemical

analysis of ten major elements for eight white cast iron

Standard Reference Materials 117'6-ll83 that were issued by

the National Bureau of Standards in April I96I. Details of

the planning and preparation of these alloys are given in

NBS Miscellaneous Publication 260-1 entitled, "Preparation of

NBS White Cast Iron Spectrochemicai Standards" [l]. Although

the standards contain a graded composition for twenty-one

(21) elements, they were initially analyzed and certified for

carbon, manganese, phosphorus, sulfur, silicon, copper,

nickel, chromium, vanadium, and molybdenum. The residual

1
elements having concentration ranges for which values have

more recently been determined include titanium, arsenic,

antimony, tin, cobalt, tellurium, boron, bismuth, zirconium,

lead and aluminum.

The methods of analysis used at the National Bureau of

Standards were selected or designed to give the best obtainable results. In some instances, more than one procedure was employed for an element as a cross-check on both the precision and accuracy of the composition.

The analysis is of little value unless the sampling

procedure is carefully controlled. Not only must care be

taken to assure that the sample is representative of the

whole, but it is equally important that the sample be prepared in such a manner that contamination is avoided.

Similarly, the materials to be used as composition standards

must be homogeneous and in a form suitable for use. The

homogeneity of the samples was established by metallographic

,

spectroscopic and chemical examination before sampling for

the final analysis.

Although limited in engineering applications, these

white iron standards have been prepared for the cast iron industry to meet the needs for analytical control by rapid instrumental methods. White iron represents the only metallurgical structure that would provide the requisite homogeneity

for optical emission spectroscopic analyses. In addition,

2
the fact that carbon is present in the combined form permits,

by vacuum techniques, the determination of carbon, phosphorus

and sulfur which would otherwise not be possible.

The samples for chemical analysis were prepared from

1 1/4 inch square and 3/4 inch thick solid sections by

breaking brittle segments, cut from the certified portion of

the samples, in a hardened iron mortar with an iron pestle.

The material was then sized to pass through a No. l4 sieve.

Samples for cooperative analysis were sent to five (5)

selected laboratories whose experience in the analysis of

these types of alloys is well established. Those laboratories assisting with the analysis were: The American Cast Iron

Pipe Co., Birmingham, Alabama, R. Elder and R. Deas; General

Motors Corp., Warren, Michigan, M. D. Cooper and

R. B. Loranger; Naval Research Laboratory, Washington, D. C,

D. Walter and 0. Mylting; Applied Research Laboratory,

United States Steel Corp., Pittsburgh, Pa., L. M. Melnick;

and Canton Roll and Machine Works, United States Steel Corp.,

Canton, Ohio, D. J. Henderson.

These methods cover the chemical analysis of white cast

irons having chemical compositions within the limits shown

in table 1.

3
Table 1. Composition limits of the ten major

elements for white cast iron.

Element determined Limit (* ) Carbon 1.5 - 4. 0 Manganese 0.3 - l. 5 Phosphorus .01 - o. 8 Sulfur .03 - • 2 .3 - 4. 0 Copper .1 l. 5 Nickel .01 - 3. 0 .01 3. 0 .005 - 0. 3 .01 - 1. 5

Table 2 gives the revised certified values which are based on

the results obtained at NBS and five cooperating laboratories.

Table 2. Certified values of the ten major elements

for white cast iron.

NBS No: 1176 1177 1178 1179 II80 1181 1182 1183

Type: Piston Wear Die Brake Mold Special Special Special

ring plate drum 1 2 3 Element Percent

C 3.47 i.lh 3.11 3.35 3.28 3.63 1.97 3.05 Mn 0.63 0.37 0.86 0.64* 1.12 1.32 0.45 0.91

P .42 .61 .11

5

.23 0.05

5 0.29 .85 .011

S .061 .037 .026 • 16

5 .086 .052 .046 .025 Si 3.19 .88 1.91 1.34 3.04 2.54 .31 1.76 Cu 0.76 .08

? 0.16 0.41 0.20 1.47 .49 1.01

Ni • 05

5 2.97 2.25 1.31 .044 0.11 .22 0.53

Cr .51 1.39 O.89 0.23 .14 2.04 .029 .07

7 V .17 o.oo

5 .017 •°% .26 0.11 • o6

o .080 Mo .59 1.49 .94 .31 • 15

5 .042 .01g •02

9

.1

4
2. CARBON IN WHITE CAST IRON

Carbon Is undoubtedly the most important element in

ferrous materials and the one which has greater influence on

the properties of a metal than any other, with the possible

exception of large amounts of some of the alloying elements.

As a result of this importance, many methods of analysis have

been developed [2,3,4,5] but carbon is determined most

rapidly and accurately by direct combustion in oxygen.

During the many years this method has been in general use, variations in apparatus and procedure have been introduced

to meet specific requirements.

In white cast iron, as in steels, virtually all of the

carbon exists in the combined form as Fe-^C with essentially

no free graphite present; hence, the combined carbon is

represented as total carbon.

Scope

This method is recommended for the determination of

carbon in the range of 1.5 to 4.0 percent. For this

concentration range, the relative standard deviation is 0.02 percent.

Principle of Method

The sample is burned in a stream of oxygen, and the

carbon dioxide in the evolved gases is collected in a suitable absorbent and weighed.

5
Interferences

Oxides of sulfur are removed by means of a manganese

dioxide trap, or by a. tube of platinized silica gel

heated to 440°C, followed by a tube containing ironized

asbestos and anhydrous Mg (ClO^)^.

Apparatus

Apparatus for determination of carbon by the directcombustion gravimetric method is available commercially

or may be constructed. A schematic of the apparatus for

the combustion carbon method is given in figure 1. (a) Resistance furnace, using silicon carbide

resistance elements and capable of maintaining a temperature of at least 1100°C.

(b) Miscellaneous apparatus. Additional equipment

required includes absorption bulbs, catalyst heater,

combustion tubes, sample inserters, oxygen flow indicators, oxygen pressure gages, oxygen drying and

purifying trains.

(c) Absorption bulbs. No special types of bulbs are specified, but the Fleming, Nesbitt and the Midvale

bulbs are preferred. The bulbs should be filled in such

a manner that the gas passes through the absorbent for

G0

2 and the absorbent for water, in that order. A layer

of glass wool immediately adjacent to the entrance and

exit is required to prevent plugging by particles of the

solid absorbent and to aid in diffusing the gases.

6
The absorbents should be added in increments with gentle

tapping, to compact the charge adequately.

(d) Purifying train, consisting of a carbon dioxide

absorbent and magnesium perchlorate trap, H

2 S0^ trap

and a flowmeter.

Reagents and Materials

(a) Alundum, granular (60 mesh or finer), specially

prepared for carbon determination.

(b) Boats, ceramic, clay, or nickel. Ignite in a muffle furnace, or preferably in a tube furnace in the

presence of oxygen, at 1100°C or higher for at least

1 hour before use until a constant blank is obtained.

(c) Carbon dioxide absorbent, inert base, 8 to

20 mesh impregnated with NaOH (Ascarite and Caroxite

have been found satisfactory for this purpose).

(d) Magnesium perchlorate, anhydrous (Mg(C10^)

2

). (e) Manganese dioxide (MnO^) specially prepared for

removal of oxides of sulfur.

(f) Oxygen, minimum 99.6 percent pure.

(g) Platinized silica gel.

Preparation of Apparatus

(a) Assemble the apparatus and provide for purification of the oxygen by passing it through a catalyst

heater and purifying train. Turn on the current and

adjust the furnace temperature to at least 1100°C.

7
(b) Open the stopcocks of one of the absorption

bulbs and connect it to the combustion train. If the

absorption bulb has not been in use for 8 hours or longer , condition it as follows:

(c) Transfer several grams of a sample containing

approximately 0.5 percent carbon to the combustion boat

containing alundum bedding material. Cover the boat

with a suitable cover and introduce it into the

combustion tube. Close the tube and preheat the sample

for 2 minutes. Turn on the oxygen, adjust the flow rate

to about 800 to 1000 ml per min. and maintain this rate for 8 min.

(d) Shut off the oxygen. Detach the absorption bulb,

close the stopcocks, and place the bulb in the balance

case to cool. (Note: the time allowed for the absorption bulb to cool before weighing it must be held to a definite time limit. The requirement is easily fulfilled

by employing two bulbs and by weighing the bulb just

prior to its use.) Remove the sample from the combustion tube.

(e) Repeat the steps outlined in Paragraphs (b)

through (d) inclusive with the second absorption bulb.

8
Procedure

(a) Weigh the tared absorption "bulb which has been

conditioned as described above, (b) through (d), and

attach it to the combustion train.

(b) Transfer a 1 g sample, weighed to the nearest

1 mg, to the boat containing the alundum bedding.

(c) Cover the boat and proceed as described above,

(c) and (d), collecting the evolved carbon dioxide in one of the weighed absorption bulbs.

(d) Weigh the bulb. The increase in weight

represents CC^.

Blank

Determine a blank on each absorption bulb, following

the same procedure and using the same amounts of all

materials

.

Calculation

Calculate the percentage of carbon as follows:

Carton, percent = B)x 0.2729 x 100

where

:

A = grams of C0

2 B = correction for blank, in grams, and

C = grams of sample used.

9
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5! •«= x £ O Cl i i < GO

CPc v> o

It: c o 5 o «

Q. O III I I I O O LU

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ctf ftftop

CD

10
3. MANGANESE IN WHITE CAST IRON

When correct conditions are closely observed, oxidation

with ammonium persulfate, followed by a measured reduction

with sodium arsenite, is a reliable and rapid method for the

determination of manganese, and thus is preferred to the

bismuthate method.

Manganese may also be determined gravimetrically as the

pyrophosphate or as the sulfate, and photometrically as the

colored permanganate ion. However, it is commonly determined

volumetrically by one of two methods - the persulfate or the

bismuthate methods, which terms refer to the reagents used in

oxidizing the manganese in solution [2,3,^,6] . While the bismuthate method is reliable, it is timeconsuming and requires great care to obtain accurate results.

Scope

This method is recommended for the determination of

manganese in the range of 0.3 to 1.5 percent. The

relative standard deviations at the low and high ranges

are 0.005 and 0.02 percent, respectively.

Principle of Method

Manganese ions in a sulfuric -phosphoric -nitric acid

medium are oxidized to permanganate by ammonium persulfate in the presence of silver ions. The permanganic

acid is titrated with standard sodium arsenite

solution

.

11
Interferences

Elements ordinarily present in white iron do not

interfere when the titration is performed potentiometrically. If the samples contain between 5 and 20 mg of

chromium, the background is compensated for by the

addition of potassium dichromate solution to the solution

used for standardization.

Apparatus

Apparatus for potent iometric titration is available

commercially.

Reagents

(a) Ammonium persulfate solution (250 g per liter).

Dissolve 25 g of ammonium persulfate ((NH^)

2 S2

03) in

water and dilute to 100 ml. Do not use solutions that

are more than one day old.

(b) Iron, high purity (low manganese). Determine the

manganese content of a suitably milled and well-mixed

portion of the metal by the periodate photometric method.

(c) Manganese, standard solution (1 ml = 0.0008 g Mn)

.

Transfer an amount of high-purity manganese of known

assay, equivalent to 0.8 g of manganese, weighed to the

nearest 0.1 mg, to a. 250-ml beaker. Add 15 ml of

HNO-^ (1+1) and heat gently to dissolve the metal and

expel brown fumes. Cool, transfer to a 1-liter volumetric

flask, dilute to volume, and mix.

12
(d) Mixed acids. Add 100 ml of H

2 S0i| to 525 ml of

water slowly, while stirring. Cool, add 125 ml of H^PO^

and 250 ml HNO^ , and mix.

(e) Potassium dichromate solution (1 ml = 0.001 g Cr).

Dissolve 2.830 g of potassium dichromate (K^CrgO^) in

water, transfer to a 1-liter volumetric flask, dilute to volume, and mix.

(f) Silver nitrate solution (8 g per liter).

Dissolve 8 g of silver nitrate (AgNO-^) in water and

dilute to 1 liter.

(g ) Sodium arsenite solution (54 g per liter).

Dissolve 54 g of sodium arsenite (NaAs0

2

) in water and

dilute to 1 liter.

(h) Sodium arsenite, standard solution (1 ml = 0.0008 g Mn). Dilute 100 ml of the sodium arsenite

solution described in Paragraph (g) to 1 liter and

filter, if not clear. Saturate the solution with carbon

dioxide

.

cedure

(a) Transfer a 1 g sample, weighed to the nearest

0.5 nig, to a 250-ml beaker.

(b) Add 30 ml of water, 50 ml of mixed acids and

2-3 drops of HF. Heat until dissolution of the sample

is complete, and boil the solution until brown fumes have

been expelled. Dilute to 75 ml with water, filter through

a coarse paper, collecting the filtrate in a. 500-ml

13
Erlenmeyer flask. Wash the residue with hot water , adjust the volume to 125 ml and proceed as directed in

paragraphs (d) and (e).

(c) Dissolve approximately the same weight of iron

as the weight of the sample in 30 ml of the mixed acids.

Transfer by pipet a portion of the manganese solution

(1 ml = 0.0008 g Mn) to the iron solution. The amount

of manganese added should be approximately the same amount as expected in the sample. Dilute to 130 ml with

water and proceed as directed in paragraphs (d) and (e). Use this solution for the standardization of the sodium

arsenite solution.

(d) Add 10 ml of AgNO^ solution and 15 ml of

(NH^)

2

S 2 0g solution. Heat the solution to boilings and

boil briskly for 90 sec. Cool to 5 to 10°C in an ice.

bath.

(e) Transfer the solution to a. 400-ml beaker and

rinse the flask with 50 ml of cold water (5 to 10°C).

Position the electrodes of the titrimeter in the

solution, stir vigorously, and titrate with sodium

arsenite solution until a maximum change in potential is

indicated

.

(f) Calculate the manganese equivalent of the

arsenite solution as g of manganese per ml.

14
Calculation

Calculate the percentage of manganese as follows:

AB

Manganese s percent = — x 100

where

A = milliliters of sodium arsenite solution required

to titrate the sample., B = manganese equivalent of the sodium arsenite

solution, in grams per milliliter, and

C = grams of sample used.

15
4. PHOSPHORUS IN WHITE CAST IRON

In this method, phosphorus is converted to the blue

complex by adding a solution containing hydrazine sulfate

and ammonium molybdate and heating at 98°C for several

minutes. The transmittance or absorbance is read at 65O m\±

.

Other widely used methods for the determination of

phosphorus in ferrous materials involve its precipitation

as the yellow ammonium phosphomolybdat e and subsequent

conversion to magnesium pyrophosphate or by titration of the

phosphomolybdate with standard alkali solution. These

methods are dependable, but time-consuming [j?]. More rapid and sensitive photometric methods which

utilize the molybdenum-blue reaction are generally preferred

because of their relative freedom from interferences by

alloying elements [7].

Scope

This method is recommended for the determination

of phosphorus in the range of 0.01 to 0.8 percent. The

relative standard deviations at the low and high ranges

are 0.002 and 0.01 percent, respectively.

Principle of Method

Phosphorus as the ortho acid forms a blue complex

with ammonium molybdat e-hydraz ine sulfate. Photometric

measurement is made at approximately 650 mu

.

16
Concentration Range

The recommended concentration range is from 0.001 to 0.04 mg of phosphorus in 50 ml of solution , using a. cell

path of 2 cm. Stability of Color

The color develops within 5 minutes at ^Q°C and is

stable for at least 24 hours.

Interferences

Arsenic above 0.05 percent interferes and must be

removed by volatilization with HBr. Reagents

(a) Ammonium molybdate solution (2 percent in

11 N H

2 S0^). Add 300 ml of H^SO^ (sp gr 1.84) to 500 ml

of water and cool. Dissolve 20 g of ammonium molybdate

in the acid and dilute to 1 liter with water.

(b) Hydrazine sulfate solution (0.15 percent).

Dissolve 1.5 g of hydrazine sulfate in 1 liter of water.

(c) Ammonium molybdate-hydrazine sulfate solution.

Dilute 25 ml of ammonium molybdate solution to 80 ml with

water, add 10 ml of the hydrazine sulfate solution and

dilute to 100 ml with water. Prepare this solution as needed.

(d) Sodium sulfite solution (10 percent) 0 Dissolve

100 g of anhydrous sodium sulfite in 500 ml of water and

dilute to 1 liter.

17
(e) Standard phosphorus solution (A) (l ml = 0.4 mg

of P). Dissolve 1.8312 g of Na

2HP0^_ in 200 ml of water,

add 35 ml of HNO-^ (1+1), dilute to 1 liter in a volumetric flask with water, and mix.

(f) Standard phosphorus solution (B) (l ml = 0.01 mg

of P). Transfer 5.0 ml of standard phosphorus solution

(A) with a pipet to a 200-ml volumetric flask, dilute

to the mark with water, and mix. Prepare this solution

as needed.

Preparation of Calibration Curve

(a) Transfer 0, 0.5, 1.0, 2.0, 3.0 and 4.0 ml aliquot

portions of standard phosphorus solution (B) to each of

six 125-ml Erlenmeyer flasks.

(b) Add 5 ml of HNO^ (l+l) and 3.0 ml of HCIO^

(60 percent). Evaporate the solution to fumes and fume

gently for 3 to 4 minutes to remove HNO^.

(c) Cool and add 5 ml of HBr (1+4). Evaporate to fuming and fume gently to remove HBr. Cool, wash the

wall of the flask with 5 ml of water, and evaporate to fumes. Cool somewhat and add 10 ml of water and 15 ml of

Na

2

S0-j solution. Heat the solution to boiling and boil

gently for 30 seconds. Add 20 ml of the ammonium

molybdate-hydrazine sulfate reagent, heat to about 95-98°C

and digest at this temperature for 4 to 5 minutes. Then

heat rapidly just to the boiling temperature, but do not

boil. Cool rapidly to room temperature and transfer the

18
solution to a 50 -ml volumetric flask. Wash the Erlenmeyer

flask with 2 -ml portions of a dilute solution of the

ammonium molyb date -hydrazine sulfate reagent (1+4) and

transfer the washings to the 50-ml flask. Dilute to the

mark with the diluted solution of the reagent and mix.

(d) Transfer a portion of the solution to a 2-cm

absorption cell and measure the transmittance or absorbance at about 650 mu.., using water as a reference

solution for 100 percent transmittance or zero absorbance

.

(e) Plot the transmittance values obtained against

milligrams of phosphorus in 50 ml on semi-log paper.

Calculate the phosphorus value in milligrams per

absorbance unit from the A-scale readings.

Procedure

(a) Transfer an aliquot portion s containing from

0.001 mg to 0.04 mg of phosphorus } of a solution to a 125 -ml Erlenmeyer flask. Proceed as directed in

(c) 3 and (d) of section above.

(b) Using the value obtained,, read from the

calibration curve the number of milligrams of phosphorus

present in 50 ml of the final solution.

Blank

Determine the blank correction by following the same procedure and using the same amounts of all reagents.

19
Calculation

Calculate the percentage of phosphorus as follows:

Phosphorus 3 percent = ^ ^

where

:

A = milligrams of phosphorus in 50 ml of final

solution

B = milligrams of phosphorus in 50 ml of the blanks

and

C = grams of sample in 50 ml of the final solution.

20
5. SULFUR IN WHITE CAST IRON

The combustion-titration procedure given., though not

stoichiometric , has gained widespread acceptance because of

its speed and general application. The procedure permits

various modifications in apparatus and reagents, but because

it is empirical 3 close adherence to the details of the method

is necessary to yield reproducible and accurate results [3,5].

A number of other methods are available for the

determination of sulfur in ferrous materials. The gravimetric

procedure in which the sulfur is weighed as barium sulfate;

the evolution method in which it is evolved as hydrogen

sulfide and then oxidized by a solution of Iodine or iodate;

and the combustion - titration procedure all have been widely

used. Difficulties attending to accurate determinations by

the gravimetric method are generally well known. The

evolution method is rapid, but it is empirical and the

details must be carefully worked out and followed if

satisfactory results are to be obtained [2,3,4].

Scope

This method is recommended for the determination of

sulfur in the range of 0.01 to 0.2 percent. The

relative standard deviations at the low and high ranges

are 0.002 and 0.003 percent, respectively.

Principle of Method

A major part of the sulfur in the sample is converted

to sulfur dioxide (SOg) by combustion in a stream of

21
oxygen. The SOg is absorbed in an acidified starchiodide solution and determined, during the combustion,

by titration with a potassium iodate solution. The

latter is standardized against materials similar in

composition to those being analyzed, since the percentage

of sulfur evolved as SO^ varies with different materials.

Interferences

Elements ordinarily present in white iron do not

interfere

.

Apparatus

Apparatus for determination of sulfur by combustiontitration method is available commercially or may be

constructed. A schematic of the apparatus for the

combustion sulfur method is given in figure 2. (a) Resistance furnace, using silicon carbide

resistance elements and capable of maintaining a temperature of at least l425°C.

(b) Miscellaneous apparatus. Additional equipment

required: absorption and titration apparatus, boats,

buret, combustion tube, oxygen flow indicator, oxygen

pressure gages, porous filter.

Reagents and Materials

(a) Boats and covers, ceramic. Ignite in a tube

furnace in the presence of oxygen at 1000°C or higher

for at least 1 hour before use.

22
(b) Copper , foil strips for use as an accelerator.

(c) Oxygen , minimum 99.6 percent pure.

(d) Potassium iodate, standard solution (1 ml = 0.0001 g S). Dissolve 0.207 g of KIO^ in 900 ml of

water, and dilute to 1 liter in a volumetric flask.

(Note: Experimental "work indicates that the recovery of

sulfur as sulfur dioxide is 93 to 95 percent complete

with the apparatus and procedure used. The standard

iodate solution is prepared by weighing 93 percent of the

stoichiometric amount of potassium iodate.)

(e) Starch solution (9 g per liter). Transfer 9 g of soluble starch to a small beaker,, add 5 to 10 ml of

water, and stir until a smooth paste is obtained. Pour

the mixture slowly into 500 ml of boiling water. Cool,

add 15 g of KI, and stir until the KI is dissolved.

Dilute to 1 liter.

Procedure

(a) Adjust the temperature of the furnace to 1425 to 1440°C.

(b) Add approximately 65 to 70 ml of HC1 (3+197) and

2 ml of starch solution to the titration vessel. Pass

oxygen through the system and add a small amount of

K10^ (1 ml = 0.0001 g S) until the intensity of the blue

color is that which is to be taken as the endpoint of the

final titration. Read the buret and record as the initial

reading. Turn off the oxygen.

23
(c) Transfer a 1 g sample , weighed to the nearest

1 mg, to the preignited combustion boat, spreading the

sample evenly over the length of the boat. Select as a control, a sample whose sulfur content and alloy

characteristics are similar to those of the sample being

analyzed. Cover the sample with approximately 0.2 g of

copper foil. Place a preignited cover on the boat and

introduce the boat and contents into the center of the

combustion zone of the combustion tube. Close the tube

and allow the sample to heat for 1.5 min. Start the

flow of oxygen at a rate of approximately 1.5 liters per

min.

(d) As the stream of gas begins to bubble through the

absorption solution, the blue color will fade. Titrate

continuously with standard KTO^ solution (1 ml = 0.0001 g at such a rate as to maintain as nearly as possible, the

initial intensity of the blue color. A 5 to 6 minute

combustion period will usually suffice. Near the end of

the combustion period, carefully adjust the blue color of

the endpoint to that taken initially, paragraph (b).

Read the buret and record the reading. Subtract the

initial reading. The difference is the volume of KIO^

solution required for titration of the sample.

Blank

Make a blank determination, following the same procedure and using the same amounts of all reagents.

24
Some refractory boats may contain sulfur compounds

liberated only in the presence of a burning sample,

and each lot should be checked on a low sulfur standard

to insure proper performance.

Calculation

Calculate the percentage of sulfur as follows:

0 , (A - B)C x 100 Sulfur, percent = ^_

where

:

A = milliliters of standard KIO^ solution

required for titration of the sample

B = milliliters of standard KIO^ solution

required for titration of the blank

C = sulfur equivalent of the KIO^ solution, in

grams per milliliter, and

D = grams of sample used.

25
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26
6. SILICON IN WHITE CAST IRON

The most reliable methods for the determination of

silicon in white cast iron involve solution of the sample

in a mineral acid or a mixture of these acids, dehydration

with sulfuric or perchloric acid, and final purification of

the residue by volatilizing the silica with hydrofluoric

acid [2,3,5,8].

In this method, the use of perchloric acid as the

dehydrating acid has the advantage that most anhydrous

perchlorates are readily soluble; thus, little difficulty is

encountered in dissolving the salts after the silicic acid

has been dehydrated. Since single evaporations never yield

all of the silica, double dehydrations are recommended.

Scope

This method is recommended for the determination of

silicon in the range of 0.3 to 4.0 percent. The relative

standard deviations at the low and high ranges are 0.0004 and 0.002 percent, respectively.

Principle of Method

After dissolution of the sample, silicic acid is

dehydrated by fuming with perchloric acid. The solution

is filtered, and the silica is ignited, weighed, and then

volatilized with hydrofluoric acid. The residue is

ignited and weighed. The loss in weight represents

silica (SiOp).

27
Interferences

Elements ordinarily present in white iron do not

interfere

Procedure

(a) Transfer a sample to a 400-ml beaker, selecting

the sample weight in accordance with the following table

and weighing it to the nearest 3 or 5 mg as specified.

Tolerance of

Silicon Sample Weight Sample Weight

percent g g 0.30 to 2.0 4.075 0.005

2.0 to 4.0 2.337 .003

(te) Add 40 ml of HNO-^ (3+5), cover and heat cautiously

until dissolution of the sample is complete. Raise the cover and add 40 ml of HCIO^ for a. 2.337 g sample, or

.0 ml for a 4.675 & sample. Evaporate the solution to fumes and heat at such a rate that the HCIO^ refluxes

on the sides of the beaker for 15 to 20 min.

Discontinue heating and when the solution has cooled

sufficiently add 100 ml of warm water (40 to 50°C).

Stir to dissolve the salts and heat gently, if necessary.

(c) Add pulp and filter immediately, using an 11-cm

medium paper. Collect the filtrate in a bOO-ml beaker.

Transfer the precipitate to the paper, scrubbing the

beaker thoroughly with a rubber-tipped rod. Wash the

paper and residue alternately but not more than 8 to

28
10 times with 3 to 5 ml portions of hot HC1 (5+95) and

hot water to remove the iron salts. Transfer the paper

to a. platinum crucible and reserve.

(d) Add 15 ml of HNO^ to the filtrate and evaporate

the solution as directed in paragraph (b). Filter

immediately 5 using a fine paper and wash as directed

in paragraph (c).

(e) Transfer the paper to the reserved platinum

crucible and heat carefully at 600°C until the carbon is

removed. Finally ignite for at least 50 min., or to constant weighty at 1100 to 1150°C. Cool in a desiccator , and weigh.

(f) Add enough H

2 S0^ (1+1) to moisten the Si0

2

, and

then 3 to 5 ml of HF. Evaporate to dryness and then at

a gradually increasing rate until H^SO^ is removed.

Ignite for 15 min. at 1100 to 1150o C, cool in a desiccator, and weigh.

Calculation

Calculate the percentage of silicon as follows:

Silicon, percent = ( A~ B ) * °-^675 x 100

where

:

A a initial weight , crucible and impure Si0

2

, B = final weight, crucible and residue, and

C = grams of sample used.

29
7. COPPER IN WHITE CAST IRON

Accurate methods for the determination of copper include

gravimetric , electrolytic, titrimetric and photometric

approaches. All give satisfactory results when properly

applied and carried out. All, except the photometric

procedure, generally require preliminary and time-consuming

separations of the copper, either as the sulfide or the

thiocyanate [2,3]

A rapid, one-step photometric procedure [9], specifically designed for the determination of copper in all types o of ferrous alloys, has been readily adapted to white cast

iron. In this method, citrate and ethylenediaminetetraacetate

(versene) are added as complexing agents, the copper carbamate

complex is then formed and extracted with butyl acetate. The

absorbance of the copper carbamate complex is measured at 560 m|i.

Scope

This method is recommended for the determination

of copper in the range of 0.1 to 1 .5 percent. The

relative standard deviations at the low and high range

are 0.002 and 0.02 percent, respectively.

Principle of Method

After dissolution of the sample, citric acid and

ammonium hydroxide are added. The sodium salt of

ethylenediaminetetraacetic acid is added as a complexing

agent and sodium diethyldithiocarbamate is added to form

30
the copper complex. The copper complex is extracted

with butyl acetate and the photometric measurement is

made at approximately 56O np,. Concentration Range

The recommended concentration range is from 0.002 mg

to 0.04 mg of copper in 25 ml of butyl acetate using a cell path of 2 cm. Stability of Color The color is stable for several hours.

Interfering Elements

Provision has been made to complex all commonly

encountered interfering elements.

Reagents

(a) Citric acid solution (250g per liter). Dissolve

125 g of citric acid in about 250 ml of water, add 10 ml

of H

2 S0Z| (1+1), and dilute to 500 ml with water.

(b) Disodium ethylenediaminetetraacetate solution

(40 g per liter). Dissolve 20 g of disodium ethylenediaminetetraacetate dihydrate in 400 ml of water and dilute

to 500 ml.

(c) Sodium diethyldithiocarbamate solution (1.0 g per

liter). Dissolve 0.1 g of sodium diethyldithiocarbamate

trihydrate in 100 ml of water.

(d) Standard copper solution (1 ml = 200 jag Cu) . Dissolve 100.0 mg of copper in 20 ml of H

2S0^ (1+1) and

5 to 6 drops of HN0-, by heating. Evaporate the solution
to fumes of HgSO^, cool, add 100 ml of water, and cool

to room temperature. Transfer the solution to a 500-ml

volumetric flask, dilute to the mark with water, and mix

well.

(e) Standard copper solution (1 ml = 4.00 |±g Cu) . Transfer exactly 10 ml of standard copper solution

(1 ml = 200 u.g Cu) to a 500-ml volumetric flask, dilute

to the mark with water, and mix well. Prepare this

solution as needed.

Preparation of Calibration Curve

Calibration Solutions. Transfer 0, 1.0, 3.0, 5.0,

7.0, and 10.0 ml of standard copper solution (l ml = 4.00 u.g Cu) to each of six 125 ml Erlenmeyer flasks.

Add 10 ml of H

2 S02| (1+1), dilute to 25 ml with water,

and add 10 ml of citric acid solution.

(a) Neutralize the above solution to a pH 7, using

litmus paper, with ammonium hydroxide, cooling, if

necessary, and add 3 to 5 ml in excess. Add 15 ml

ethylenediaminetetraacetate solution to the warm

solution and cool to room temperature. Transfer the

solution to a 125-ml separatory funnel, washing the

Erlenmeyer flask with 10 ml of water. Add 10 ml of

diethyldithiocarbamate solution and shake for 10 to 15 seconds. Pipet exactly 25 ml of butyl acetate into

the funnel, shake for 30 seconds and cool in running

water for 2 to 3 minutes. Repeat the shaking for

32
15 seconds, cool, and allow the layers to separate. Drain

off completely the lower aqueous layer and discard. Trans

fer the butyl acetate layer to a dry test tube and stopper

(b) Photometry. Fill the reference cell with butyl

acetate and adjust the photometer to the initial setting,

using a light band centered at approximately 56O mu.

.

While maintaining this photometric adjustment, take the

photometric readings of the calibration solutions.

(c) Calibration curve. Plot the photometric readings

of the calibration solutions against the micrograms of

copper per 25 ml of butyl acetate extract.

Procedure

(a) Transfer a 0.100 g sample, containing not more than 40 jig of copper, to a 125 -ml Erlenmeyer flask, add

15 ml of H

2 S01| (1+4), 1 to 2 drops of HF and heat until

the sample dissolves. Evaporate the solution to fumes

of H

2 S0^. Cool, (Note), add 20 ml of water and 10 ml

of citric acid solution and continue as directed in

paragraphs (a) and (b) above.

(Note) For samples containing more than 40 |ig Cu, transfer to a 100 ml volumetric flask, add 5 ml H

2 S0l (1+1)

and dilute to the mark with water. Transfer an aliquot,

containing not more than 40 |i,g of copper to a 125-ml

Erlenmeyer flask, adjust the amount of H

? S0k and water to provide a volume of 25 ml containing 5 ml of H

2S0k. Add

10 ml of citric acid solution and continue as directed

in paragraphs (a) and (b) above.
(b) By means of a calibration curve, convert the

photometric readings of the sample solutions to micrograms of copper.

Blank

Make a blank determination following the same procedure and using the same amounts of all reagents.

Calculation

Calculate the percentage of copper as follows:

A - B

Copper, percent = jr C x 10

where

A = micrograms of copper found in the 25 ml of butyl

acetate extract of the sample

B = micrograms of copper found in the 25 ml of

butyl acetate extract of the blank

C = grams of sample represented in the 25 ml of

butyl acetate extract of the sample.

54
8. NICKEL IN WHITE CAST IRON

(Nickel greater than 1 percent)

The dimethylglyoxime-gravimetric procedure , as applied to ferrous materials, is virtually specific for nickel when the

necessary precautions are observed. This procedure has the

desirable feature of requiring few, if any preliminary

separations

.

Nickel can also be determined volumetrically by titration

with silver nitrate after treatment of an oxidized solution

with potassium iodide and potassium cyanide, gravimetrically

or volumetrically after precipitation with dimethylglyoxime,

or electrolyt ically [2,3,4].

Scope

This method is recommended for the determination of

nickel in the range of 1.0 to 3.0 percent. lor this

concentration range, the relative standard deviation is

0.02 percent.

Principle of Method

After dissolution of the sample, nickel is precipitated with dimethylglyoxime, filtered and weighed.

Interferences

Interferences due to copper and cobalt are eliminated

by double precipitation of the nickel dimethylglyoxime.

Apparatus

Crucible, filtering. Fritted-glass filtering

crucibles or porous-bottom porcelain filtering crucibles

are recommended for general use.

35
Reagents

(a) Citric acid solution (250 g per liter). Dissolve

250 g of citric acid in 750 ml of water, add 20 ml of

diluted H

2 S02| (1+1), dilute to 1 liter and filter, if

necessary.

(b) Dimethylglyoxime (10 g per liter of ethyl alcohol).

Dissolve 10 g of dimethylglyoxime in 1 liter of ethyl

alcohol and filter, if necessary.

Procedure

(a) Transfer a 2 g sample to a 600-ml beaker, add

100 ml of HNO^ (1+5) > and digest until solution is

complete. Evaporate the solution to dryness. Dissolve

the residue in 20 ml of HC1 and heat gently. Add 75 ml

of hot water, and filter, using an 11 cm coarse paper

containing pulp, into a 600-ml beaker. Transfer any

insoluble material to the filter, wash alternately with

hot HC1 (5+95) and hot water until most of the iron salts

are removed and then 3 times with hot water. Dilute the

filtrate to 200 ml with water.

(b) Transfer the paper and precipitate to a platinum

crucible, ignite at 850 to 900°C, cool, and add enough

H^SO^ (1+1) to moisten the residue, and then 3 to 5 ml of

HF. Evaporate to dryness and then heat at a. gradually

increasing rate until H^SO^ is removed. Fuse the residue

in a minimum of NagSgO^ and add the fusion to the reserved

filtrate.

36
(c) Add 75 ml of citric acid solution and neutralize

with NH^OH. Add 40 ml, or a sufficient amount, of

dimethylglyoxime solution, and add a slight excess of

NH^OH. Digest for 1 hour at 60°C. Cool to room

temperature and filter through an 11 cm fine paper.

Wash the beaker and precipitate 3 times with water. Add

5 ml of dimethylglyoxime to the filtrate to determine

whether precipitation is complete.

(d) Transfer the paper and precipitate to the beaker,

add 5 ml of H^SO^ and mix thoroughly to char the paper.

Add 20 ml of HNO-^, digest until the solution is clear,

and evaporate to dense fumes of H^SO^. Continue the

fuming for 5 to 10 minutes to destroy all organic matter,

cool, and wash the sides of the beaker. Add 25 ml of

water and 5 ml of citric acid solution. Mix well, and

filter, using a 9 cm fine paper containing pulp, into

a 400-ml beaker. Wash the beaker 3 to 4 times and

finally wash the paper 12 to 15 times with hot water.

Adjust the volume to 200 ml. Discard any residue.

(e) Nearly neutralize the filtrate with NH^OH, add

40 ml, or a sufficient amount, of dimethylglyoxime

solution, and add a slight excess of NH^OH. Digest for

1 hour at 60°C. Cool to room temperature. Filter the

precipitate through a weighed fritted crucible, wash

well with water.

37
(f) Dry the precipitate at 130°C to constant weight.

Cool in a desiccator and weigh as nickel dimethylglyoxime

.

Calculation

Calculate the percentage of nickel as follows:

Nickel, percent = A x Q- 20^ 2 x 100

where

:

A = grams of nickel dimethylglyoxime } and

B = grams of sample used.

8. NICKEL IN WHITE CAST IRON

9 (Nickel less than 1 percent)

Scope

This method is recommended for the determination of

nickel in the range of 0.01 to 1.0 percent. The

relative standard deviations at the low and high ranges

are 0.003 and 0.02 percent, respectively.

Principle of Method

After dissolution of the sample, the bulk of the

iron is separated from nickel "by extraction with ether.

The nickel is then precipitated with dimethylglyoxime,

filtered and weighed.

Interferences

Interferences due to copper and cobalt are eliminated

by double precipitation of the nickel dimethylglyoxime

.

58
Apparatus

Crucible, filtering. Fritted-glass filtering

crucibles or porous-bottom porcelain filtering crucibles

are recommended for general use. Reagents

(a) Citric acid solution (250 g per liter). Dissolve

250 g of citric acid in 750 ml of water, add 20 ml of

diluted H

2 S0i| (1+1), dilute to 1 liter and filter, if

necessary.

(b) Dimethylglyoxime (10 g per liter of ethyl alcohol).

Dissolve 10 g of dimethylglyoxime in 1 liter of ethyl

alcohol and filter, if necessary.

(c) Ethyl ether.

Procedure

(a) Transfer a 10 g sample to a 600-ml beaker, add

100 ml of HC1 (1+1), and digest until solution is complete.

Cool somewhat, cautiously add 8 to 12 ml of HNO^ to oxidize the solution, and evaporate to dryness. Dissolve

the residue in 20 ml of HC1 and heat gently. Add 75 ml

of hot water, and filter using an 11 cm coarse paper con- taining pulp into a 600-ml beaker. Transfer any insoluble

material to the filter, wash alternately with hot HC1

(5+95) and hot water until most of the iron salts are removed, and then 3 times with hot water. Evaporate the

filtrate to dryness on the steam bath, cool, and dissolve

in 50 ml of HC1 (1+1)

.
(b) Transfer the paper and precipitate to a platinum

crucible, ignite at 850 to 900°C, cool, and add enough

H,->SO^ (1+1) to moisten the residue, and then 3 to 5 ml

of HF. Evaporate to dryness and then heat at a gradually

increasing rate until HgSO^ is removed. Fuse the residue

in a minimum of Na^S^Oy ancj a^ the fusion to the reserved

filtrate.

(c) Transfer the solution in paragraph (a) above

to a 600-ml cylindrical separatory funnel, rinse the

beaker several times with small portions of HC1 (1+1),

and dilute to a volume of 1^0 ml with HC1 (1+1).

Cool in an ice bath to 5 "to 10°C, add 300 ml of cooled

ethyl ether and shake thoroughly. Allow the funnel to cool 5 to 10 minutes in the ice bath, and repeat the

shaking. Allow the layers to separate, and draw off the

lower acid layer into the 600-ml beaker. Wash the funnel

with approximately 25 ml of cold HC1 (1+1) and repeat the

above operations, finally draining the lower acid layer

into the beaker. Discard the ether layer.

(d) Cautiously heat the ether-extracted acid layer

on a steam bath to remove the ether, add 3 ml of HNO^ and

finally evaporate to dryness. Dissolve in 5 ml of HC1

(1+1) and dilute to 75 ml with water. Heat gently

until the salts are in solution and adjust the volume

to 200 ml.

40
(e) Add 25 ml of citric acid solution, nearly neutralize with NH^OH, add 20 ml, or a sufficient amount, of

dimethylglyoxime solution. Add NH^OH until slightly

alkaline , and digest for 1 hour at about 60°C. Cool to room temperature. Filter using an 11-cm fine paper

containing a little pulp into a 600 ml beaker. Wash the

beaker and precipitate 3 times with water. Add 5 ml of

dimethylglyoxime to the filtrate to determine whether

precipitation is complete.

(f ) Transfer the paper and precipitate to the beaker,

add 5 ml of H^SO^, and mix thoroughly to char the paper.

Add 20 ml of HNO^, digest until the solution is clear,

and evaporate to dense fumes of H^SO^. Continue the fuming,

for 5 to 10 minutes to destroy all organic matter, cool,

and wash the sides of the beaker. Add 25 ml of water and

5 ml of citric acid solution. Mix well, and filter using

a 9 cm fine paper containing pulp into a 400-ml beaker.

Wash the beaker 3 to 4 times, and finally wash the paper

12 to 15 times with hot water. Adjust the volume to 200 ml. Discard any residue.

(g) Nearly neutralize the filtrate with NH^OH, add

20 ml, or a sufficient amount, of dimethylglyoxime

solution. Add NH^OH until slightly alkaline and digest

for 1 hour at about 60°C. Cool to room temperature.

41
Filter the precipitate through a weighed fritted crucible

wash well with water.

(h) Dry the precipitate at 130°C to constant weight.

Cool in a desiccator and weigh as nickel dimethylglyoxime

Calculation

Calculate the percentage of nickel as follows:

ivt. i -i -u Ax 0.20^2 -.^ Nickel, percent = ^ — x 100

where

A = grams of nickel dimethylglyoxime, and

B = grams of sample used.

42
9. CHROMIUM IN WHITE CAST IRON

The most satisfactory methods for determining chromi-um

in ferrous materials are volumetric and differ only in the

reagents that are used to oxidize the chromium and in the

details of titrating the oxidized chromium.

The basis for one of the most commonly used volumetric

procedures is the oxidation to hexavalent chromium with

ammonium persulfate and reduction to the trivalent form by

potentiometric titration with ferrous ammonium sulfate. Any

vanadium present is oxidized to vanadate with persulfate and

is reduced to the vanadyl state by the ferrous sulfate. This

is the basis for the determination of both chromium and

vanadium on the same sample [2 a 4 3 5].

Scope

This method is recommended for the determination of

chromium in the range of 0.2 to 3.0 percent. The

relative standard deviations at the low and high,

ranges are 0.002 and 0.02 percent, respectively.

Principle of Method

After dissolution of the sample 9 chromium is

oxidized with (NH^)

2

S 2 0g and titrated potentiometrically

with Fe(NH4 ) 2 (S04 ) 2

. Vanadium is titrated with the chromium and it must

be determined and the proper corrections applied to the chromium.
Apparatus

Apparatus for potentiometric titration.

Reagents

(a) Ammonium per sulfate solution (15 percent).

Dissolve 15 g of (NH^^Og in 85 ml of water. This

solution should be prepared as needed.

(b) Ferrous ammonium sulfate (23 g per liter).

Dissolve 23 g of Fe(NHi| ) 2 (S0i| ) 2• 6H

2 0 in 1 liter of cool

H

2 S04 (1+19).

(c) Potassium dichromate, standard solution (1 ml = 0.0010 g Cr). Dissolve 2.829 g of K

2 Cr2 0

7 in 500 ml of

water contained in a 1 liter volumetric flask, and dilute

to volume with water.

(d) Silver nitrate solution (0.25 percent). Dissolve

2.5 g of AgNO^ in 1 liter of water. Procedure

(a) Transfer a 2 g sample to a 600-ml beaker 3 add 75 ml

of water and 20 ml of H

2 S0^. Heat gently until the sample

is dissolved. Evaporate until salts separate, cool, and

dilute with about 50 ml of warm water, and digest until

the salts are dissolved.

(b) Filter, using an 11 cm coarse paper containing pulp

and collect the filtrate in a 600-ml beaker. Wash the

beaker and paper 10 to 12 times with warm H" 2S0^ (2+98).

Reserve the filtrate.

44
(c) Transfer the paper and residue to a platinum

crucible, ignite at 850 to 900°C, cool, and add enough

H

2 S0^ (1+1) to moisten the residue, and then 3 to 5 ml

of HF. Evaporate to dryness and then heat at a gradually increasing rate until H

2 S0^ is removed. Fuse

the residue in a minimum of Na

2 S2 0^ and add the fusion

to the reserved filtrate.

(d) Dilute the solution to a volume of 300 ml with

water, add 10 ml of AgNO^ solution and 20 ml of ammonium

persulfate solution. Heat to boiling and boil 20 minutes

to oxidize the chromium. At this point a pink color due

to permanganic acid should develop, indicating the

complete oxidation of the chromium (and vanadium). If

this does not occur, add more AgNO^ and (NH^)

2

S 2 0g and

continue the boiling for several minutes until a pink

color appears. Boil for 10 to 15 minutes after the last

addition of the (NH^)

2

S 2 0g. Add 5 ml of HC1 (1+3) and

boil for 10 minutes after the pink color has disappeared.

Cool to room temperature.

(e) Position the electrodes of the titrimeter in the

solution, stir vigorously and titrate the chromium with

ferrous ammonium sulfate (23 g per liter) until a maximum

change in potential is indicated. Standardize the ferrous

ammonium sulfate solution by titrating potentiometrically

an equivalent amount of chromium as potassium dichromate

45
in 300 ml of boiled and cooled HgSO^ (1+19). Vanadium

is also titrated and a correction must be applied to the chromium.

Calculation

Calculate the percentage of chromium as follows:

A = grams of sexivalent chromium used as standard

B = milliliters of Fe(NH^)

2 (S0^)

2 solution used to titrate A.

C = chromium titer , in grams , of Fe(NH^) 2(^0^)2

solution

D = milliliters of Fe(NH^)

2 (S0^)

2 solution used to titrate the sample

E = grams of sample used

C x D Chromium + (vanadium), percent = —^— x 100

In this method, vanadium is also titrated, and the

chromium value obtained must be corrected for vanadium

as follows:

C x D F Chromium, percent (corrected) =(—<g— x 100)- Og-^ff) F = Percent of vanadium in sample.

46
10. CHROMIUM AND VANADIUM IN WHITE CAST IRON

(Sodium Bicarbonate Separation)

Scope

This method is recommended for the determination of

chromium in the range of 0.01 to 0.2 percent and vanadium

in the range of 0.005 to 0.3 percent. For chromium in

this concentration range , the relative standard deviation

is 0.002 percent. For vanadium in this concentration

range, the relative standard deviations are 0.001 and

0.003 percent, respectively.

Principle of Method

After dissolution of the sample, chromium and

vanadium are separated from the bulk of the iron by

hydrolytic precipitation with NaHCO^, oxidized with

(NH^)

2

S

2 0g and titrated potentiometrically with

Fe(NH4 ) 2 (S04 ) 2

. Vanadium is titrated with the chromium and must also

be determined and the proper corrections applied to the chromium.

Apparatus

Apparatus for potentiometric titration.

Reagents

(a) Ammonium persulfate solution (15 percent).

Dissolve 15 g of (NH^J^Og in 85 ml of water. This

solution should be prepared as needed.

47
(b) Ferrous ammonium sulfate solution (8 g per liter).

Dissolve 8 g of Fe(NH4 ) 2 (S04 ) 2

,

• gH 0 in 1 liter of

cool HgSO^ (1+19)

.

(c) Ferrous ammonium sulfate solution (23 g per

liter). Dissolve 23 g of Fe (NH^)

2 (S0^) 2

,

• 6H2

0 in

1 liter of cool HgSO^ (1+19).

(d) Potassium dichromate standard solution (l ml = 0.0010 g Cr). Dissolve 2.829 g of K

2 Cr

2 0

7 in 500 ml of

water contained in a 1 liter volumetric flasks and dilute

to volume with water.

(e) Silver nitrate solution (0.25 percent). Dissolve

2.5 g of AgNO^ in 1 liter of water.

(f) Sodium bicarbonate solution (80 g per liter).

Dissolve 80 g of NaHCO^ in 900 ml of water, dilute to

1 liter and filter, if necessary.

Procedure

(a) Transfer a 10 g sample to a 500-ml Erlenmeyer

flask, add exactly 110 ml of HgSO^ (1+9), cover and heat

gently until the sample is dissolved. Dilute the

solution with 50 ml of hot water and heat to boiling.

Add the NaHCO^, solution from a buret while constantly

swirling the flask to avoid a local excess, until a slight permanent precipitate forms and then add 6 to 8 ml

in excess. Cover the flask, boil gently for several

minutes, and allow the precipitate to settle. Immediately

filter using a 12.5 cm coarse paper, decanting the

48
supernatant liquid, and finally transfer the precipitate

to the paper. Wash the flask and paper 2 to 5 times with

hot water and discard the filtrate. The filtrate may

become cloudy through oxidation and hydrolysis of the

iron, but this is of no consequence.

(b) Return the paper and precipitate to the flask,

add 20 ml of H^SO^ and swirl until the filter is in

solution. Add 25 ml of HNO-^, digest and evaporate to fumes of H^SO^. Repeat the digestion with an additional

25 ml of HNO^ and evaporate to fumes, if necessary, to destroy organic matter. Add 75 ml of water, digest until

salts are dissolved, and filter using an 11 cm coarse paper containing pulp, and collect the filtrate in a 600-ml beaker. Wash the flask and paper 10 to 12 times

with warm water. Reserve the filtrate.

(c) Transfer the paper and residue to a platinum

crucible, ignite at 850 to 900°C } cool, and add enough

H

2 S0^ (1+1) to moisten the residue, and then 3 to 5 ml

of HF. Evaporate to dryness and then heat at a gradually

increasing rate until H^SO^ is removed. Fuse the residue

in a minimum of ^£$20^ ancj a^ the fusion to the reserved

filtrate

(d) Add 3 ml of water saturated with S02

, heat to boiling, and boil 5 minutes to expel the excess SO^.

Cool somewhat and oxidize any reduced iron with 3 ml of

HNO-j. Boil to expel nitrous oxides, dilute to 200 ml,

49
and add 40 ml of HNO^. Remove the cover glass and boil

gently for at least 1 hour at such a rate that the final

volume is 125 ml. Cool, dilute to 300 ml with water and

cool to 5°C in an ice bath.

(e) Position the electrodes of the titrimeter in the

solution, stir vigorously and titrate the vanadium with

standard ferrous ammonium sulfate solution (8 g per

liter) until a maximum change in potential is indicated.

Standardize the ferrous ammonium sulfate solution by

titrating potentiometrically an equivalent amount of

potassium dichromate in 300 ml of boiled and cooled

H

2 S04 (1+19).

(f) Evaporate the solution to fumes of H^SO^ and

continue the fuming until most of the HNO-^ is expelled.

Cool, add 75 ml of water, and digest until the salts are

in solution.

(g) Dilute the solution to a volume of 300 ml with

water, add 10 ml of AgNO-^ solution and 20 ml of ammonium

persulfate solution. Heat to boiling and boil 20 minutes

to oxidize the chromium. At this point a pink color due

to permanganic acid should develop indicating the complete

oxidation of the chromium (and vanadium). If this does not occur, add 2 drops of KMnO^ solution (25 g per liter)

and additional ammonium persulfate solution until a pink

color appears. Add 5 ml of HC1 (1+3) and continue the

50
boiling for 10 minutes after the pink color has disappeared. Cool to room temperature.

(h) Position the electrodes of the titrimeter in the

solution, stir vigorously and titrate the chromium with

ferrous ammonium sulfate solution (23 g per liter)

until a maximum change in potential is indicated.

Standardize the ferrous ammonium sulfate solution by

titrating potentiometrically an equivalent amount of

chromium as potassium dichromate in 300 ml- of boiled

and cooled H^SO^ (1+19). Vanadium is also titrated and

a correction must be applied to the chromium.

Calculation

Calculate the percentage of vanadium as follows:

A = grams of sexivalent chromium used as standard

B milliliters of Fe(NH^)

2 (S0^) 2 solution to titrate A

C vanadium titer, in percent,

solution

A x 29.4

B

D milliliters of Fe(NH^)

2 (S0

2| ) 2 solution to titrate

the sample

Vanadium, percent = C x D

51
Calculate the percentage of chromium as follows:

E = grams of sexivalent chromium used as standard

F = milliliters of Fe (NH^)

2 (SO^)

2 solution to titrate E G = chromium titer, in percent, of Fe (NH^)

2 (SO^)

2 solution

n E x 10 G = —

P

H = milliliters of Fe (NH^)

2 (SO^)

2 solution to titrate the sample

( C x Chromium, percent = G x H - ' ^g

'

52
11. VANADIUM IN WHITE CAST IRON

The principal methods for the determination of vanadium

are volumetric and depend either on a measured reduction from

the pentavalent to the tetravalent state, or on a measured

oxidation from the tetravalent to the pentavalent state. The procedure utilizing the reduction of the vanadium is

preferred because it can be readily performed in solutions

at room temperature, while its oxidation, on the other hand,

does not proceed as easily and is best done at 60 to 80°C.

A number of reagents are used to oxidize vanadium to vanadate and include nitric acid, permanganate, bromate, and

hydrogen peroxide. The reduction is generally performed with

ferrous ammonium sulfate.

In this method, the use of nitric acid for the oxidation

and subsequent reduction with ferrous sulfate has the

desirable feature of a rapid, direct potentiometric titration

requiring no preliminary separations [2,4,10].

Scope

This method is recommended for the determination of

vanadium in the range of 0.1 to 0.3 percent. For this

concentration range, the relative standard deviation is

0.003 percent.

Principle of Method

After dissolution of the sample, vanadium is oxidized

with HNO-^ and titrated potentiometrically with

Fe(NH4 ) 2 (S04 ) 2

. 53
Interference

Elements ordinarily present in white iron do not interfere

Apparatus

Apparatus for potentiometric titration.

Reagents

(a) Ferrous ammonium sulfate solution (8 g per

liter). Dissolve 8 g of Fe(NH^) 2 (S0^) 2

,

• 6H

2 0 in 1 liter of cool l^SO^ (1+19).

(b) Potassium dichromate standard solution (1 ml = 0.0010 g Cr). Dissolve 2.829 g of K^Cr^ in 500 ml

of water contained in a liter volumetric flask, and

dilute to volume with water. Procedure

(a) Transfer a 2 g sample to a 600-ml beaker, and

add 100 ml of H

2 S0^ (1+4). Heat gently until the

sample is dissolved. Evaporate until salts separate,

cool, and dilute with about 50 ml of warm water, and

digest until the salts are dissolved.

(b) Add 10-15 ml of HNO^ to oxidize the iron and

any carbides that may persist. Filter, using an 11 cm

coarse paper containing pulp and collect the filtrate

in a 600-ml beaker. Wash the beaker and paper 10 to

12 times with warm H

2 S0^ (2+98). Reserve the filtrate.

(c) Transfer the paper and residue to a platinum

crucible, ignite at 850 to 900°C, cool, and add enough

54
H

2 S0^ (1+1) to moisten the residue, and then add 3 to

5 ml of HF. Evaporate to dryness and then heat at a gradually increasing rate until HgSO^ is removed.

Fuse the residue in a minimum of Na^^^ and add the

fusion to the reserved filtrate.

(d) Add 3 ml of water saturated with S02

, heat to boiling, and boil 5 minutes to expel the excess S0

2

. Cool somewhat and oxidize any reduced iron with 3 ml

of HNO-j.. Boil to expel nitrous oxides , dilute to 200 ml, and add 40 ml of HNO-^. Remove the cover glass

and boil gently for at least 1 hour at such a rate

that the final volume is 125 ml. Cool, dilute to 300 ml

with water and cool to 5°C in an ice bath.

(e) Position the electrodes of the titrimeter in

the solution, stir vigorously and titrate the vanadium

with standard ferrous ammonium sulfate solution (8 g per liter) until a maximum change in potential is

indicated. Standardize the ferrous ammonium sulfate

solution by titrating potentiometrically an equivalent

amount of potassium dichromate in 300 ml of boiled and

cooled H

2 S02| (1+19)

.

Calculation

Calculate the percentage of vanadium as follows:

A = grams of sexivalent chromium used in standard

B - milliliters of Fe (NH^)

2 (S0^)2 solution to titrate A

55
vanadium titer, in percent, of Fe (NH^)

2 (S0^)

solution

n Ax 2.94

milliliters of Fe(NH^)

2 (S0^)

2 solution to titrate the sample

grams of sample used

Vanadium, percent = C x D

56
12. MOLYBDENUM IN WHITE CAST IRON

A direct, one-step photometric procedure, readily

adapted to white cast iron, is based on the formation and

extraction of the molybdenum thiocyanate complex and

subsequent measurement at 470 mu. . Methods for the determination of molybdenum vary and

include numerous photometric, gravimetric and volumetric

approaches

.

There is little to choose between the gravimetric

methods in which the molybdenum is precipitated with alphabenzoinoxime and ignited to the oxide, or precipitated and

weighed as lead molybdate, and the volumetric method in which

it is reduced by zinc, collected under a solution of ferric

sulfate., and titrated with a standard solution of potassium

permanganate. Both methods, however, are time consuming and

require great care to obtain accurate results [4,5].

Scope

The photometric method is recommended for the determination of molybdenum in the range of 0.01 to 1.5 percent.

The relative standard deviations at the low and high

ranges are 0.002 and 0.02 percent, respectively.

Principle of Method

After dissolution of the sample, the thiocyanate

complex of the molybdenum is developed. The complex is

extracted with butyl acetate and the photometric measurement is made at approximately 470 mo.

.

57
Concentration Range

The recommended concentration range is from 0.002 mg

to 0.03 mg of molybdenum in 20 ml of butyl acetate using

a cell depth of 2 cm. Stability of Color

The intensity of the color is stable for several

hours

.

Interferences

Elements ordinarily present do not interfere.

Reagents

(a) Citric acid solution (250 g per liter). Dissolve

125 g of citric acid in about 250 ml of water, add 10 ml

of H

2S0^ (1+1), and dilute to 500 ml with water.

(b) Ferric sulfate solution (50 g per liter).

Dissolve 5 g of Fe

2 (S0^)^ -R^O in 90 ml of H

2S02| (1+9)

and dilute to 100 ml with HgSO^ (1+9).

(c) Sodium thiocyanate solution (100 g per liter).

Dissolve 50 g of NaCNS in 400 ml of water and dilute to 500 ml.

(d) Stannous chloride solution (350 g per liter).

Dissolve 175 g of SnCl

2 -2H2

0 in 100 ml of HCl (1+1) by

heating, and dilute to 500 ml with water.

(e) Standard molybdenum solution (1 ml = 150 |ig Mo).

Dissolve I89.I mg of Na^oO^ -2H

2 0 in 100 ml of H

2 S0^ (1+9),

transfer to a 500-ml volumetric flask, dilute to the mark

with water, and mix well.
(f) Standard molybdenum solution (1 ml = 3.00 \±g Mo).

Transfer exactly 10 ml of standard molybdenum solution

(1 ml = 150 |xg) to a 500-ml volumetric flasks dilute to the mark with H.^SO^ (1+99) and mix well. Prepare this

solution as needed.

Preparation of Calibration Curve

Calibration solutions. Transfer 0, 1.0, 3 0, 5.0,

7.0 and 10.0 ml of standard molybdenum solution (1 ml =

3 \ig Mo) to each of six 125-ml Erlenmeyer flasks, add

15 ml of H

2 S0^ (1+1) and dilute to 60 ml with water.

(a) Add 1 ml of ferric sulfate solution and 10 ml of

citric acid solution, heat to 80°C for 5 minutes and

cool. Transfer the solutions to 250-ml separatory funnels

and cool in running water. Add 10 ml of sodium thiocyanate solution and shake for 30 seconds. Add 10 ml of

stannous chloride solution and shake for exactly 1 minute.

Pipet exactly 20 ml of butyl acetate into the funnel,

shake for 30 seconds and cool in running water for 2 to

3 minutes. Repeat the shaking for 30 seconds and allow

the layers to separate. Drain off and discard the lower

aqueous layer. Add 50 ml of HgSO^ (1+9), 10 ml sodium

thiocyanate solution and 5 ml of stannous chloride solution. Shake for 30 seconds, let stand for 2 to 3 minutes,

repeat the shaking for 30 seconds and allow the layers to separate. Drain off and discard the lower aqueous layer.

Transfer the butyl acetate layer to a dry test tube,

59
stopper the tube, and allow to stand until the solution

is clear.

(b) Photometry. Fill the reference cell with butyl

acetate and adjust the photometer to the initial setting,

using a light band centered at approximately 470 mji

.

While maintaining this photometric adjustment, take the

photometric readings of the calibration solutions.

(c) Calibration curve. Plot the photometric readings

of the calibration solution against the micrograms of

molybdenum per 20 ml of butyl acetate extract. Procedure

(a) Transfer a 0.100 g sample, containing not more

than 30 ^g of molybdenum, to a 125 -ml Erlenmeyer flask,

add 15 ml of HpSO^ (1+1) , 1 to 2 drops of HF and heat

until the sample dissolves. Cool, add 1 ml of H^O^

(30 percent) and evaporate to fumes of H^SO^. Cool,

(Note), dilute to 60 ml with water, add 10 ml of citric

acid solution, heat to 80°C for 5 minutes and cool.

Transfer the solutions to 250-ml separatory funnels and

cool in running water. Continue the color development

and extraction as directed in paragraphs (a) and (b)

above

.

(Note) For samples containing more than 30 \ig Mo, add 5 ml of

HpSO^ (1+1), dilute to 50 ml with water, cool, transfer to a 100-ml volumetric flask, and dilute to the mark with water. Transfer an aliquot, containing not more than 30 \±g 3 to a 125-

ml Erlenmeyer flask, and adjust the amount of E^SOu to give

about 7.5 ml of H SO, in the flask, add 1 to 2 drops of HF

and heat to fumes of H^SO^. Cool, dilute to 60 ml with water

and proceed as dire cted in paragraphs (a) and (b) above.

60
(b) By means of a calibration curve 9 convert the

photometric readings of the sample solutions to micrograms of molybdenum.

Blank

Make a blank determination following the same procedure and using the same amounts of all reagents.

Calculation

Calculate the percentage of molybdenum as follows:

A - B

Molybdenum., percent = jr C x 10

where

A = micrograms of molybdenum found in the 20 ml butyl

acetate extract of the sample

B = micrograms of molybdenum found in the 20 ml butyl

acetate extract of the blank

C = grams of sample in the 20 ml butyl acetate

extract of the sample

61
•1

I REFERENCES

[l] Michaelis, R.E., Wyman, L.L.j "Standard Reference

Materials: Preparation of NBS White Cast Iron

Spectrochemical Standards" , NBS Misc. Publ. 260-1

(1964).

[2] Lundell, G.E.F., Hoffman, J.I., Bright, H.A.,

"Chemical Analysis of Iron and Steel", John Wiley

and Sons, Inc., New York, 1931.

D] Am. Soc. Testing and Materials, Philadelphia, "ASTM

Methods Chemical Analysis of Metals", i960.

[4] Hillebrand, W.F., Lundell, G.E.F., Bright, H.A.,

Hoffman, J.I., "Applied Inorganic Analysis", 2nd

edition, John Wiley and Sons, Inc., New York, 1953.

[5] Pigott, E.C., "Ferrous Analysis", 2nd edition,

John Wiley and Sons, Inc., New York, 1953.

[6] Bright, H.A., Larrabee, C.D., "Determination of

Manganese in Steel and Iron by the Persulfate-Arsenite

Method", J. Res. Natl. Bur. Std. 3, 573 (1929).

[7] Hague, J.L., Bright, H.A., " Colorimetric Determination

of Phosphorous in Steel and Cast Iron". J. Res. Natl.

Bur. Std., 26, 405 (1941).

[8] Fowler, R.M., "Determination of Silicon in Steels",

Ind. and Eng. Chem., Anal. Ed. 4, No. 4, 382 (1932).

[9] Hague, J.L., Brown, E.D., Bright, H.A., "Photometric

Determination of Copper in Iron and Steel with

Diethyldithiocarbamate" , J. Res. Natl. Bur. Std. 4j_, 5 (1951)o

[10] Westwood, W., Mayer, A., "Chemical Analysis of Cast

Iron and Foundry Materials", George Allen and Unwin

Ltd., London, 1951.

62

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