NATIONAL BUREAU OF STANDARDS REPORT

8688

PROGRESS REPORT

January 1 through March 31, 1965

PORCELAIN ENAMEL INSTITUTE RESEARCH ASSOCIATESHIP

NATIONAL BUREAU OF STANDARDS

WASHINGTON, D. C.

>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards is a principal focal point in the Federal Government for assuring

maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. Its responsibilities include development and maintenance of the national stand- ards of measurement, and the provisions of means for making measurements consistent with those standards; determination of physical constants and properties of materials; development of methods

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listing of its four Institutes and their organizational units. Institute for Basic Standards. Electricity. Metrology. Heat. Radiation Physics. Mechanics. Applied Mathematics. Atomic Physics. Physical Chemistry. Laboratory Astrophysics.'"' Radio Standards Laboratory: Radio Standards Physics; Radio Standards Engineering.'"* Office of Standard Ref- erence Data. Institute for Materials Research. Analytical Chemistry. Polymers. Metallurgy. Inorganic Materials. Reactor Radiations. Cryogenics.** Office of Standard Reference Materials. Central Radio Propagation Laboratory.** Ionosphere Research and Propagation. Troposphere

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NATIONAL iUMAU OF STANDARDS REPORT

MBS FiOJECT NBS HEPOKT

42108-11-4210180 8688

PROGRESS REPORT

January 1 through March 31, 1965

PORCELAIN ENAMEL INSTITUTE RESEARCH ASSOCIATESHIP

NATIONAL BUREAU OF STANDARDS

WASHINGTON, D. C.

IMPORTANT NOTICE NATIONAL BUREAU OF S

for use within the Government, and review. For this reason, tl whole or in part, is not authc Bureau of Standards, Washing)

the Report has been specificall

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

iss accounting documents intended

; subjected to additional evaluation

; listing of this Report, either in

le Office of the Director, National

by the Government agency for which

copies tor its own use.

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

PROGRESS REPORT

January 1 through March 31, 1965

PORCELAIN ENAMEL INSTITUTE RESEARCH ASSOCIATESHIP

NATIONAL BUREAU OF STANDARDS

Washington, D. C.

SUMMARY

A Hunter multipurpose ref lectometer was extensively modified to permit its use for detecting the amount of fluorescent soils that remain

on specimens after standard cleaning treatments. The major modifications

involved substituting an ultraviolet source for the regular lamp source

and the introduction of special filters to prevent unwanted radiation

from reaching the photocells. Preliminary trials with the modified

instrument indicated that it will perform satisfactorily over a wide

range of fluorescent intensities.

A survey of the literature was made for tests of coating continuity.

As many as 13 different tests have been used for this purpose. Investigation of five of these suggested that the high voltage spark-test

showed the most promise for porcelain enamels.

Specimens representing the new "Nature Tone" series of mat porcelain enamels on steel were installed on the weathering racks at the Kure

Beach 80-foot site. Since no rack space was available for these new

specimens it was necessary to remove several enamel types already under

test. These enamels had shown such large changes in color and gloss

after eight years that further testing would have furnished little, if

any, information on their weathering properties.
2

The initial measurements on specimens of porcelain enamels for

aluminum were completed and the exposure of these enamels is now under

way at three of the selected sites.

A comparison was made between the citric acid spot test and the

boiling acid weight changes for a large group of enamels in the PEINBS weathering program. These data showed the type of agreement that

can be expected from the two types of tests.

INTRODUCTION

I . CLEANABILITY

The report for the previous period outlined the need for an

experimental method to evaluate the "aesthetic" cleanability of

porcelain enamels. A review of the literature indicated some research

concerned with "bacterial" cleanability of various surface finishes,

but little work was found to provide guidelines for the present effort.

The work with conventional soiling agents, previously reported,

emphasized the problems involved when porcelain enamels in a wide range

of colors and surface textures were to be evaluated. These problems

have focused attention during the present report period on the use of

a soil that would fluoresce in the visible when exposed to ultraviolet

radiation. The method would be based on (1) applying the soil, (2)

subjecting the surface to a standard cleaning treatment, and, finally,

(3) determining the amount of soil remaining on the surface after

cleaning by measuring the intensity of the residual fluorescence when

the surface was exposed to a standard ultraviolet source.

Before the use of fluorescent soils could be fully investigated,

it was first necessary to develop a quantitative technique for the

estimation of the intensity of fluorescence which could be utilized in
3

a cleanability test precedure.

The phenomena of fluorescence has been extensively studied. Many

applications are found in biological pharmaceutical, medical and agricultural research. Methods for observing and measuring fluorescence

have been used in testing paints, varnishes and laquers, fuels, detergents,

^

/ and foods, as well as in criminology. Radley and Grant—, in 1939, and, more

2 / recently, Udenfriend—, have reviewed many of the instrumental systems in

past and current use for fluorescence measurements. A majority of these

instruments estimate materials in solution and some have been designed or

3/ modified to measure fluorescence from solids. Gardner and Sward — report use of the Hunter Multipurpose Ref lectometer in fluorescence analysis,

and a kit is available for conversion of the instrument for this use. The

Hunter instrument was originally designed at the suggestion of the Standards

Committee of the Porcelain Enamel Institute for the measurement of reflectance and gloss properties of porcelain enameled specimens. The specimens

required are of a convenient size. The equipment is commercially available

and, in addition, some of these instruments are undoubtedly in current use

in the porcelain enamel industry. For these reasons, the Hunter instrument

was selected for some of the preliminary trials.

RESULTS AND DISCUSSION

1. Initial Experiments.

The first attempt at measuring the residual fluorescence of soiled specimens was made using the somewhat crude device shown schematically in figure

1. Specimens soiled with anthracene [CgH^(CH)

2 ^^ ] were irradiated with

ultra-violet light to excite fluorescence. A cadmium-sulphide photocell,

fitted with a filter holder, was provided to respond to the visible radiation
4

emitted by the soiled specimens. A DC voltage which was applied to the

photocell generated a "dark current" which corresponded to the voltage

drop across the potentiometer. When the soiled specimen was radiated

with ultraviolet, visible light struck the photocell. This in turn

caused a change in resistance of the cell which was measured as a voltage

drop.

Experiments with this device showed that responses of between 0 and

8 millevolts could be generated from various specimens. However, these

responses could be attributed only partly to the fluorescence of the

anthracene that was present on the enameled specimens.

These early experiments led to the following conclusions: a) a

more intense source of ultra-violet light was needed, b) suitable

filters should be provided between the source and the specimen, as well

as between the specimen and the light-sensitive cell, c) a more sensitive photocell and measuring circuit should be sought, d) adequate

ventilation or cooling should be provided because the photocell response

was dependent on temperature, e) light-tightness should be improved, particularly if a more sensitive cell and circuit was incorporated, and f)

fluorescence measurements could not be made with the required precision

unless a more sophisticated measurement system was used.

2. Modification of Hunter Multipurpose Ref lectometer

.

A schematic drawing of the Hunter Ref lectometer is shown in figure 2.

Light from a single source is split into two beams, the reflectance beam

and the gloss beam. The reflectance beam strikes one barrier-layer photocell and the gloss beam strikes a second matched photocell. These two

cells are connected, with opposing polarities, to a sensitive galvanometer
- 5

-

which is used to indicate a null balance. The reflectance beam is incident

upon the reflectance surface at 45% and the reflectance photocell views

the surface normally. This cell is on a movable mount so that it can be

moved to a position where the light reaching it is the same as that

reaching the gloss cell. The gloss path involves reflection from a

specimen (or a mirror when measuring reflectance) placed horizontally on an

opening in the instrument top. This beam, after passing an adjustable semi

diffusing mirror, terminates on the gloss photocell which is mounted at a

fixed position.

A Hunter instrument was modified to test its suitability for

fluorescence measurements. The following changes were made:

a) A General Electric AH-4 mercury arc lamp together with a special

lamp holder and a transformer was substituted for the projection lamp

normally used.

b) An ultra-violet transmitting filter glass was substituted for one

of the tri-stimulus colored glass filters normally used in the instrument.

This primary filter passes the UV but filters out most of the unwanted

visible light that is generated by the GE AH-4 lamp.

c) A holder for a 2" x 2" filter glass was installed in front of,

but attached to, the movable reflectance photocell. This secondary filter

was required to eliminate any ultraviolet radiation reflected from the

specimen surface. Unfortunately, the photocell responds to this radiation

as well as to the visible.

d) A centimeter scale was substituted for the gloss and reflectance

scales normally used with the instruments. When a null balance is achieved

this centimeter scale is used to measure the distance from the reflectance

photocell to the vertical specimen surface on the instrument front which.
6

in turn, is an indication of the light intensity from the specimen. The

photocell is adjustable between 10 and 33.8 cm. from the specimen.

e) The black, porcelain enameled comparison surface supplied with

the instrument was replaced with a front -surface aluminum mirror. This

mirror is a part of the gloss path and rests horizontally on the top

opening of the instrument.

f) The semi-diffusing adjustable mirror in the gloss path was replaced with a flat piece of fluorescent uranium glass (Corning CS 3-73).

3. Experiments with the Modified Reflectometer .

a) Present Concept of Instrument Use.

Present plans call for measuring fluorescence by a substitutional

method. A bare specimen, before soil application, would be balanced on

the instrument with the reflectance cell in the front position, 10 centimeters from the specimen. The balance would be obtained by adjusting the

angular position of the fluorescent glass with adjusting screw to allow

the proper fraction of light to fall on the fixed photocell. After soiling

and cleaning the specimen, residual soil would be measured by replacing

the treated specimen in the test position and reestablishing a null balance, this time by moving the reflectance photocell away from the specimen

(if fluorescence was detected). The distance of the cell movement would

then be indicative of the residual soil on the specimen.

This concept of use is only one of several by which the instrument

could be used to measure residual fluorescence on specimens. One advantage

of the presently contemplated method, however, is that all measurements

would depend on an initial balance at the front position of the movable

photocell, which is the most sensitive portion of the scale. The technique

would also insure equal sensitivity when making intensity measurements on
- 7

-

specimens of different colors.

b) Filter Selection.

Numerous filters have been evaluated for use in the instruments.

Both the percentage transmission and the wavelength selectivity (band

pass) must be considered. In the case of the primary filter located

between the source and the specimen, a relatively low transmission is

not serious because of the high intensity of the UV source; however, it

is important that the filter pass little or no visible radiation. The

secondary filter, on the other hand, should have a transmission as high

as possible to permit sensitive measurement of low intensity fluorescence and at the same time it should selectively exclude UV radiation

reflected or strayed from the source.

The best results obtained so far, based on these considerations,

and confirmed by experiment, have been with a Corning CS 7-60 primary

filter and a Wratten Number 3 gelatin filter in front of the movable

photocell. No filter was required in front of the fixed photocell.

Several filters, now on order, may lead to even better filtering.

c) Adjustment of Ref lectometer for Sensitivity Equalization.

A selection of white and colored porcelain enameled specimens was

made to include the extremes of photocell response for the initial

balance. As explained above, it is desirable that all colors be balanced

in the front position of the reflectance cell. Because the filters are

not 100% efficient, some light from the UV source will be reflected by

the specimen and reach the photocell. The amount of this light will be

less for black specimens than for high reflectance white specimens. It

was found that a suitable initial balance could not be achieved with the

original diffusing mirror; hence, the fluorescent uranium glass was used
- 8

-

for this purpose.

d) Sensitivity of Multipurpose Ref lectometer

.

Experiments were performed to determine the response of the modified

instrument to the wide range of anthracene intensities that might conceivably be encountered in a cleanability test. Both black and white specimens were used. The specimens, which were in the "as manufactured"

condition, were washed with a tri-sodium phosphate solution prior to soiling. A different amount of anthracene was applied to the surface of each

specimen. This was done by first applying the material in excess and then

cleaning the specimens by light or hard rubbing either with dry or wet

disposable paper tissues. Visual ratings of the amounts of anthracene

that remained were made by inspecting the specimens under a laboratory

ultra-violet lamp. The visual ratings varied from a "large amount" to "a

very slight amount." The results of the experiment, given in table 1,

show good agreement between visual and instrumental readings. There were

differences in surface texture between the black and the white specimens,

which might, in fact, contribute to a difference in cleanability. The

results obtained with the ref lectometer suggest that this method was more

sensitive than the visual ratings and could provide a numerical basis for

assigning differences in cleanability.

FUTURE PLANS

Work for the next report period will be concerned with:

a) Development of a reproducible abrasion pretreatment for cleanability

specimens

.

b) Determination of most suitable fluorescent "soil."

c) Selection of effective and reproducible mechanical methods for soil

application and cleaning.
9

d) Improvement in the filtering of ultra-violet light to exclude all visible

wavelengths

.

e) Development of an index to express cleanability results.

f) Investigation of the degree of correlation between test results with

fluorescent soils and the cleanabilities as determined from qualitative

estimates of volunteers.
10

II. CONTINUITY OF COATING

INTRODUCTION

One of the more important reasons for applying a porcelain enamel

coating to appliances, architectural panels, or sanitary ware, is to

protect the base metal from corrosion. Thus, to insure the highest

quality, any discontinuity or defect, either on the surface or within the

layer of porcelain enamel, that might lead to early corrosion of the base

metal should be detected before an enameled part is placed in service.

It is believed obvious that a continuity of coating test that would

detect these defects would be beneficial to all parties concerned.

The first phase in the development of a continuity of coating test

was to analyze the defects that might lead to early failure of an enameled

part. Figure 3 is a schematic drawing of such defects. These include:

1. Holidays. Holidays are the largest of these defects. A

holiday may be caused by tearing, crawling, jumping, fishscaling, or

chipping. Holidays are relatively large defects and they can be detected

easily by visual observation.

2. Burnoff. Burnoff is also easily detected visually. However, it

is rarely considered a serious defect, when considering continuity of coat

ing, because the exposed edges, where burnoff usually occurs, are not

normally subjected to corrosive conditions. Therefore, burnoff does not

ordinarily shorten the life of a porcelain enamel part.

3. Cracking. Cracking or crazing can oftentimes be detected by

visual inspection. The depth of the crack is an important factor in

determining whether or not it will cause early corrosion of the base metal
11

Unfortunately it is difficult to determine visually the depth to which

the crack penetrates. Any continuity of coating test should provide

this information.

4. Pinholes and Blisters. These can oftentimes be detected

visually, but it is difficult to determine how far they penetrate into

the enamel. Pinholes and blisters which do not penetrate deeply should

not cause any special difficulties from the corrosion standpoint.

However, those that penetrate almost to the metal may well lead to an

early failure; hence, a continuity of coating test should detect this

type of defect.

5. Subsurface Pores. Subsurface pores can not be detected visually

and it is also difficult to determine whether or not they can cause

early corrosion of the base metal. It seems likely that large pores

might be detrimental. These, therefore, should be detected by a continuity of coating test.

6.

Copperheads. Copperheads of the type often times observed in

ground coat enamels may not be serious defects with respect to corrosion

protection, but more information is needed in this area.

A review of this list of defects shows that pinholes, blisters, large

sub-surface pores, and cracks are the main types that can cause corrosion

difficulties. Hence, at least the preliminary work on a continuity of

coating test should concentrate on these four defects.

RESULTS AND DISCUSSION

A review of the literature revealed that several test methods have

been used for locating discontinuities in either porcelain enamel or

organic coatings. Preliminary investigations of a few of these test
12

methods have been made. Attention was focused on ease of performing the

test, types of defects located, and reproducibility of the test method.

A brief description of the five methods investigated follows:

1. High-Voltage Methods.

An instrument for continuity testing with a high voltage probe is

the Porosity Detector, produced by Uvral.TM/ The voltage on the probe can

be adjusted at any desired level from 0-5 KV. Because of the low amperage the high voltage is harmless to humans. The operation of the

equipment is quite simple. The ware to be tested is grounded and a wire

probe searches the surface for discontinuities. When the probe passes

over a discontinuity, a discharge occurs to the base metal. The completion of the circuit is then indicated by a bell ringing and a light that

flashes in the handle of the probe and is recorded on a counter. The

type of results obtained with the high-voltage tester are dependent

both on the thickness and the dielectric strength of the enamel.

The Porosity Detector was obtained for the present study and it was

used for several preliminary tests. The resulting data indicated that

the instrument is capable of locating a wide range of discontinuities

depending on the voltage setting. It is not possible, however, to use the

whole range of voltage settings and then to repeat the same test and duplicate the results because the higher voltages used in the first probing

apparently create new discontinuities. However, the results are fairly

reproducible when several passes of the probe are made at one voltage

setting only.

It was also found that if a piece of carbon paper was placed over

the specimen prior to the test, the discharges resulted in a "mapn of

the discontinuities on the carbon paper. When the number of discontinuities
13

recorded by the instrument was compared with the number of discontinuities

on the "map," there was good agreement, except at the highest voltages where

an almost continuous discharge occured.

This high-voltage instrument seems to be capable of locating subsurface defects, as well as those that are open to the surface. A similar

instrument is also available from Pfaudler.—

The main disadvantage of the instrument is that a spark discharging

through a subsurface pore will create a tiny hole to the base metal which

may later lead to corrosion. This puncture will not occur, however, if

the voltage is not excessive.

2. Wet Chemical Test.

This test, which has been used by Western Electric,—^ consists of

soaking a filter paper in a solution consisting of 1900 ml of distilled

water, 100 ml concentrated sulfuric acid, and one gram of potassium

f erricyanide . The wet filter paper is placed on the surface to be tested

for fifteen seconds, after which it is removed and examined visually.

Areas showing dark blue discolorations represent discontinuities in the

enamel

.

Besides being messy to perform, this test was found to be sensitive

only to very large discontinuities, most of which could have been located

by visual examination.

3. Electrographic Printing.

8 9/ This method —2—— consists of first soaking a sheet of photographic

dye transfer paper and blotting paper in a solution of 5°L by weight of

potassium nitrate for 30 minutes. The method is quite involved. The excess potassium nitrate is removed by placing the papers between a sheet of
14

dry blotting paper and a sheet of plastic after which they are pressed at

300 psi. The dye transfer paper is next placed on the specimen to be

tested and the blotting paper containing the potassium nitrate is used

to back it up. The specimen and blotting papers are then placed between

two sheets of aluminum, the one under the specimen is the cathode while

the one on top of the blotting paper is the anode, and six volts are

placed across the specimen. The specimen sandwich is then placed between two sheets of rubber and pressed at 300 psi for 15-20 seconds. The

dye transfer paper is next developed in a solution containing 2.5%

potassium ferricyanide and 2.5% potassium ferrocyanide for 30 minutes.

Finally, the dye transfer paper is washed in warm water until the background color of the paper is x^hite. The discontinuities appear as dark

blue spots on the white background.

Several difficulties were encountered in using this test with porcelain enamels. The first occurred with specimens which were not completely

flat. When these specimens were pressed at 300 psi, the enamel would chip

or crack. The second difficulty was that while two successive tests on

the same specimen often yielded approximately the same number of defects,

the defects were not always in the same location. Therefore, the

reproducibility was poor. Also, it is difficult to detect the small dark

blue spots which indicate the discontinuities.

One point to remember when considering this particular test for

continuity of coatings, is that it could not be applied to most production

parts

.
1 5

4 . Swab Tests.

Swab tests-^-2-^ consist of connecting a low voltage source to

either a sponge or felt probe which has been dampened with an electrolyte.

This probe then scans the specimen surface and changes in either amperage

or voltage indicate discontinuities. It has been found in some brief

exploratory experiments that the test lacks sensitivity, in that either

no discontinuities or one continuous discontinuity was indicated. However, after a meeting with the Standards Committee it was disclosed that

many people are now using this test with satisfactory results. Therefore,

a more careful look will be given to the swab testing approach.

5. Electrified Particle Method.

The electrified particle method was developed and licensed by the

12 / Statiflux Corporation-— . The method consists of spraying the surface

with charged particles of calcium carbonate. These particles are attracted

to the base metal where a discontinuity exists. This test seems to be more

sensitive for small discontinuities, expecially cracks, than it is in

locating relatively large discontinuities. Again it is relatively hard

to see the powder deposit that forms on the top of a pin hole.

Other test methods for continuity of coating which have not been

investigated by the research associateship are:

1. X-Ray Ionization.

13/ This method -— was developed by Joeseph A. Finlayson as a thesis

project at The State University of New York State College of Ceramics at

Alfred University. The method consists of connecting two specimens, facing

each other but separated by a small airgap , to a 2200 volt DC power supply.

One of the specimens was a standard, while the other was a piece to be
- 16

tested. A volt-meter was connected in the circuit to measure the voltage

when the circuit was energized. The voltage was recorded before and after

ionizing the air by X-ray radiation and the differences in voltage gave

an indication of the discontinuities present. In the thesis it was noted

that this method was less sensitive than the wet chemical method previous-

\ - ly described. It is, therefore, not considered as a promising approach.

2.

Salt Spray Tests.

These test methods consist of exposing a specimen to a

salt spray for a standard test period and then inspecting the surface for

/ evidence of localized corrosion. Discontinuities appear as rust on the

l surface. This type of test would probably not be convenient as a coating

continuity procedure, but it might be desirable in correlating results of

) a continuity of coating test with simulated service conditions.

3. Dye Penetration. , r K-' — • > 17 / This type of test—^ consists of three steps; (1) applying a

penetrant and removing the excess, (2) developing the penetrant, and

> v s, { (3) examining the piece for discontinuities. After the penetrant has

been applied to the piece and the excess removed, the developer forms /

a thin porous layer on the surface of the specimen. Any penetrant ip a

discontinuity can return to the surface through the developer which. ’

tends to spread the dye penetrant over a larger area ahd thus make the

defect more easily visible. This method of test reveals only 'those »

1

,

defects which are open to the surface. '

./ ’

. ,

'

4. Iodine Vapor Test.

18 / In this test—'

1 iodine vapor from crystals of iodine penetrate

defects and corrode the base iron making the defect visible.
17

5. Copper Deposition.

19/ In this test — the specimens are immersed in a solution of copper

sulfate and sodium chloride. Copper deposits on the surface of the specimen where a discontinuity permits the solution to contact with iron.

6. Other methods, including the resistance test, electrolytic test,

and transformer test, are outlined in the 1951 Proceedings of the PEI

20 / Shop Practice Forum— .

PLANS FOR NEXT REPORT PERIOD

The review of possible test methods as outlined above has indicated

that one of the more promising approaches to coating continuity testing

is the high voltage discharge. However, a large amount of additional

study is required. In the work for the next report period emphasis will

be placed on a further examination of the variables that affect the test

results

.

III. EXPOSURE TEST OF PORCELAIN ENAMEL ON ALUMINUM

INTRODUCTION

An exposure test of porcelain enamels on aluminum was authorized

early in 1964. Detailed planning regarding the enamels in the test,

specimen sizes, exposure sites, selection of exposure specimens, as well

as the procedure to be followed when cleaning and measuring the gloss,

color, and acid resistance of the enamels, has been previously reported

> All specimens were installed during the present report period at Kure Beach,

Washington, and Montreal.

RESULTS AND DISCUSSION

1. Initial Measurements*

The 45° specular gloss, color, acid solubility, and acid spot test
18

rating# were determined by the procedures reported previously. The

results of these measurements for all fifty-one enamels are given in

table 2.

2. Thickness.

The thicknesses were measured with an Elcometer Minitor Thickness

Gauge. Since these values seemed low, polished cross-sections were

prepared of all the enamels and the thickness was measured with a micrometer eyepiece on a metallographic microscope. While these two thickness

values were not the same, there was a good correlation between the two t

as illustrated in Figure 4. In this figure the microscope (or true)

thickness is plotted against the thickness value determined with the

Elcometer Thickness Meter. The solid line represents the least squares

fit through the points, while the dashed line indicates where the points

would lie if the meter gave the same thickness values as the microscope.

It is planned to correct the meter readings to the microscope values by

using the equation for the least squares line, Y = 1.09X + 1.03, where Y

would be the corrected value and X would be the value determined with the

thickness meter. By correcting the thickness it will be possible to follow any changes in thickness that might possibly occur during weathering.

The corrected thickness values are included in table 2.

3. Distinctness of Image Gloss.

The distinctness of image gloss for each enamel was determined in

21 / acooidance with PEI Bulletin T-20 — , with the exception that only

six specimens were tested. The values for the distinctness of image

glo®@ for all 31 enamels are given in table 2.

4. Spall Tests.

Triplicate specimens of each enamel are being spall tested in
- 19

22 / accordance with ASTM Standard Method of Test C 486-61T —, (96 hrs. -

57, by weight NH, Cl) . Since these tests were not completed, the results

will not be reported until next quarter.

5. Installation of Exposure Specimens.

The test specimens have been installed at Kure Beach, Washington,

and Montreal. The specimens have been sent to Los Angeles for installation.

PLANS FOR NEXT REPORT PERIOD

It is planned to complete the spall testing and to install the

exposure specimens and racks at New York City during the next quarter.

IV. EXPOSURE TEST OF NATURE TONE ENAMELS

INTRODUCTION

The interest shown by architects in mat finishes has led to the

development of a series of mat enamels called "nature tones." While

these enamels meet the requirements of the architects for color, gloss,

and texture, they have not been thoroughly weather tested to ascertain

whether or not the accelerated tests developed for glossy enamels on steel

are reliable for predicting the weatherability of these new low gloss

enamels

.

23/ Since a previous exposure test — has indicated that enamels exposed

80 feet from the ocean at Kure Beach, N. C., undergo an especially severe

weathering attack, this site was selected for testing so that information

on weatherability could be obtained in the shortest possible time.

RESULTS AND DISCUSSION

Four specimens of each of thirty selected nature tone enamels were

received early in March. Two of these four were used for exposure, while
20

the other two were tested by the acid spot test and by boiling acid

solubility.

Before the exposure specimens were measured for either gloss or

color they were washed by scouring 30 strokes with calcium carbonate

on a sponge., rinsing with tap water, and wiping with a sponge moistened

with trisodium phosphate followed by rinsing with tap water, distilled

water, and alcohol. This method of washing was found to be effective

in removing dirt films while causing only very slight changes in the gloss

of the surface.

Since the enamels had low 45° specular gloss values, a gloss standard

with an assigned value of 15 was used instead of the usual standard, which

has a value of 54.3. The data for 45° specular gloss, image gloss, acid

spot test, and boiling acid solubility are given in table 3. The initial

color values; Rd, a, and b, were also determined.

The specimens were installed on the racks at Kure Beach-80 on

March 19, 1965. At the same time, 60 specimens in the current PEI-NBS

Weathering Test, now in its eighth year, were withdrawn from this site

to provide space for testing these new enamels. All of the enamels withdrawn showed color retentions of 90 or less and/or rusting of the base

metal through the enamel surface.

PLANS FOR NEXT REPORT PERIOD

The first inspection of the nature tone enamels is scheduled after

six months. Therefore, no further work on this project is scheduled

during the next report period.
- 21

V. CORRELATION OF CITRIC ACID SPOT TEST WITH BOILING

ACID SOLUBILITY

INTRODUCTION

The acid resistance of porcelain enamels has long been measured by

the citric acid spot test (PEI T-21) . Although this test has proved to

be a reasonably good indicator of acid resistance of glossy enamels, it

is not satisfactory for low-gloss enamels. The boiling acid solubility

test (ASTM C 203), however, does not suffer from this difficulty and,

in addition, it provides a more quantitative measure of acid resistance.

Because of these two advantages, there appears to be an increasing trend

for some laboratories to use the boiling acid test rather than the spot

test for evaluating acid resistance. A comparison of test results by

the two methods for a large number of enamels was, therefore, believed

of some interest.

RESULTS AND DISCUSSION

Recently, both the boiling acid solubility and the acid spot test

ratings were obtained for a group of storage specimens of 90 enamels,

which are included in the PEI-NBS weathering study. The results of

these determinations are given in table 4. It will be noted that, on

the average, an excellent correlation exists between the two tests.

However, there is considerable scatter, as indicated by either the

ranges or the high standard deviations. This high scatter suggests

that conversions from one test result to the other cannot be made with

any high degree of assurance. However, the comparison shows that for

the 75 regular enamels, those that were rated acid-resistant (AA or A)

2 by the spot test all had boiling acid solubilities of 7.0 mg/in or less.
22

At the same time 10 of the 25 enamels that were rated B and C by the

2 spot test showed acid solubilities under 7 mg/ in^ . Since these 10

enamels also had good weather resistance, it seems that they might be

termed acid-resistant enamels if it was not for their tendency to show

slight stains on exposure to room temperature acids.

This same comparison could not be made for the low-temperature

enamels, since there were no C and D enamels and only one B enamel

included in the test.

PLANS FOR NEXT REPORT PERIOD:

No further work is planned.
- 23

STANDARD REFERENCE MATERIALS

The following stock of standards was on hand April 1, 1965:

Corundum abrasive, March 1960 issue,

for subsurface abrasion 296 lb., 74 jars

Standard Pennsylvania Glass Sand, July 1963 issue,

for Surface abrasion 300 lb., 100 jars

Distinctness of image gloss standards 20 sets

Calibrated glass plates for abrasion testing 28.5 doz

.

Respectfully submitted.

M. D. Burdick

M. A. Rushmer

Research Associates

Table 1. Comparison of Visual and Instrumental Measurement

of Fluorescence Intensity from Specimens "Soiled"

with Anthracene.

iecimen Visual Estimate of Multipurpose Ref lectometer

No. Retained Anthracene Measurement of Intensity

Black Enamel White Enamel

cm. cm.

1 Large amount 23.0 16.7

2 Medium " 15.1 14.4

3 Small " 12.4 11.3

4 V. slight " 10.4 10.2

5 None 10 10

6 None 10 10

a / Modified to use AH-4 mercury lamp

Primary filter CS 7-60

Secondary filter Wratten No. 3

Technical grade anthracene (90-95 percent Purity)
Table

2.

SUMMARY

OF

THE

INITIAL

DATA

FOR

THE

ENAMELS

IN

THE

ALUMINUM

EXPOSURE

TEST

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Table 3. Summary of the Initial Data on the Nature Tone Enamels.

Specimen Color Acid Resistance

Boiling Spot

Solubility Test

mg/ in

Gloss

45° Specular Imagi

MA-3 Yellow Green 2.1 A 6.5 < 1 MA-4 Light Green 0.9 A 1.8 < 1 MA-5 Medium Gray 1.8 A 10.4 < 1 MA-6 Light Red-Brown 1.7 A 8.8 < 1 MA-12 Dark Gray 1.2 A 20.4 < 1 MB -4 Light Yellow

Green

9.0 B 8.5 < 1

MB -5 Gray 7.0 A 5.3 < 1 MC-2 Light Blue 1.2 A 22.0 < 1 MC-4 Blue 1.3 A 22.0 < 1 MC-5 Light Gray 1.1 A 25.7 < 1 MC-6 Dark Gray 1.6 A 30.2 < 1 MC-9 Red Brown 1.0 A 30.1 < 1 MG -10 Black 1.1 A 22.4 < 1 MC -12 Light Blue 3.2 A 5.5 < 1 MD-1 Peacock Blue 1.2 A 20.5 < 1 MD-3 Chocolate Brown 0.9 A 25.4 < 1 MD-4 Red Brown 0.9 A 26.6 < 1 MD-5 Dark Gray Black 1.1 A 29.6 < 1 MD-6 Medium Green 0.6 A 48.4 < 1 ME -2 Chartruse 1.7 A 17.6 < 1 ME -3 Medium Gray 0.8 A 18.7 < 1 ME -4 Slate Blue 1.0 A 36.0 < 1 ME-5 Red Brown 0.7 A 21.7 < 1 ME -6 Green 0.9 A 7.2 < 1 ME -7 Dark Gray -Green 1.2 A 12.7 < 1 ME -8 Black 1.9 A 25.6 < 1 ME -9 Steel Blue 0.7 A 20.2 < 1 ME -10 Chocolate Brown 2.6 A 19.1 < 1 ME-11 Brown 0.9 A 1.2 < 1 ME-12 Black 1.3 A 17.1 < 1
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REFERENCES

1. Radley and Grant; "Fluorescence Analysis in Ultra-Violet Light,"

D. Van Nostrand Co.; New York; 1939.

2. Sidney Udendriend; "Fluorescence Assay in Biology and Medicine;"

Academic Press; New York; 1962.

3. Gardner and Sward; "Paint Testing Manual" Distributed by Gardner

Laboratory Inc.; P. 0. Box 5728; Bethesda; 14; Maryland; Twelfth

Edition; 1962.

4. Richard S. Hunter; "A Multipurpose Photoelectric Ref lectometer ,

J. Research NBS; 25; 581-618; 1940; RP 1345.

5. Uvral Porosity Detector Type 100/5K SB/2 available from Allen P.

Webb; 24 Stone Street; New York 4; New York.

6. Pfaudlertron Testers available from Pfaudler Permutit Inc.;

Pfaudler Division; Rochester 3; New York.

7. "Inspection Instructions;" Code Number 60.125; Issue 4; 1958;

Western Electric Telephone Sales Division.

8. "Determination of the Porosity of Coatings," Research Report, Battelle

Memorial Institute, November 11, 1952.

9. Max Kronstein, Marion M. Ward, and Robert Roper, "Evaluation of

Organic Coatings by Electrographic Printing," Industrial and

Engineering Chemistry, 42 (8) 1568-1572 (1950).

10. Interim Military Specification, Porcelain Enamel Coating (for

Snorkel Exhaust Piping), Mil-P-17378 (Ships), 23 Dec. 1952.

11. Pin Hole Detector available from Perro Corporation, 4150 East

56th Street, Cleveland 5, Ohio.

12. Henry N. Staats, "Observations on the Nature of Cracks in Porcelain

Enamel," Bull. Am. Cer. Soc. 21 (2) 33 (1952).

13. Joseph A. Finlayson, Jr., "A Correlation of the Sensitivity of

Discontinuity Tests for Porcelain Enameled Steel," Bachelor of

Science Thesis, The State University of New York, College of

Ceramics at Alfred University, Alfred, New York, 1959.

14. "Acetic Acid-Salt Spray (Fog) Testing," ASTM Designation B 287-62,

Book of ASTM Standards, Vol. 7, 1964, American Society of Testing

Materials, 1916 Race Street, Philadelphia 3, Pennsylvania.

15. "Copper-Accelerated Acetic Acid Salt Spray (Fog) Testing (Cass

Test)," ASTM Designation B 368-62T, Book of ASTM Standards, Vol. 7,

1964, American Society of Testing Materials, 1916 Race Street,

Philadelphia 3, Pennsylvania.
16 . ,!Method for Salt Spray (Fog) Testing , " ASTM Designation B 117-64,

Available as a reprint, American Society of Testing Materials, 1916

Race Street, Philadelphia 3, Pennsylvania.

17. Wallace J. Ericksen and George W. Billings, Jr., "How to Use

Liquid Penetrant Tests," Nondestructive Testing for Management,

pages 51-55, American Society for Metals, Metals Park, Ohio, 1963.

18. Andrew I. Andrews, "Porcelain Enamels," page 600, The Garrard Press,

Champaign, Illinois, 2nd Edition, 1961.

19. Obtained during a conversation with Joseph C. Richmond, National

Bureau of Standards, Washington, D. C.

20. Stanley C. Orr, "Methods for Testing Enamel Coating Discontinuities,"

Proc. P.E.I. Forum, 43-52, 1951.

21. "Image-Gloss Test," PEI Bulletin T-20, Porcelain Enamel Institute,

1900 L. Street, N. W. Washington, D. C., 20036.

22. "Spalling Resistance of Porcelain Enameled Aluminum," ASTM Designation C 486-61T, Book of ASTM Standards, Vol. 13, 444, 1964,

American Society of Testing Materials, 1916 Race Street, Philadelphia

3, Pennsylvania.

23. D. G. Moore and Alan Potter, "Effect of Exposure Site on Weather

Resistance of Porcelain Enamels Exposed for Three Years," NBS

Monograph 44, April 1962. For sale by Supt. of Documents, U. S. Government Printing Office, Washington 25, D. C.
WATT.

FIG. I. PROTOTYPE FLUORIMETER AND MEASURING CIRCUIT.
\\ Gloss Surface

figure 2. Diagram of Hunter Multipurpose Ref lactometer
zzzzzzzzz h£ zz.

HOLIDAY

y Zzzzzzzzzz

PIMMOLE CRACK

BURNOFF

SUBSURFACE PORE

• i"A -

'• T- i > A :

COPPERHEAD

Figure 3. Schematic drawing of discontinuities

in porcelain enamel.
I

THICKNESS, IN MILS, OBTAINED WITH ELCOMETER M I NIT OR

THICKNESS METER

Figure 4. Correction curve for the Elcometer Thickness Meter.

USCOMM-NBS-DC