NATIONAL BUREAU OF STANDARDS REPORT

7589

THE APPLICATION OF X-RAY PROJECTION MICROSCOPY

TO ROOFING ASPHALT SYSTEMS

by

Sidney H, Greenfeld

<NB§>

I). S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March 3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and maintenance of the national standards of measurement and the provision of means and methods for making measurements consistent

with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,* devices, and structures; advisory services to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; and the development of standard practices, codes, and specifications. The work includes basic

and applied research, development, engineering, instrumentation, testing, evaluation, calibration services,

and various consultation and information services. Research projects are also performed for other government

agencies when the work relates to and supplements the basic program of the Bureau or when the Bureau’s

unique competence is required. The scope of activities is suggested by the listing of divisions and sections on the inside of the back cover.

Publications

The results of the Bureau’s research are published either in the Bureau’s own series of publications or

in the journals of professional and scientific societies. The Bureau itself publishes three periodicals avail- able from the Government Printing Office: The Journal of Research, published in four separate sections,

presents complete scientific and technical papers; the Technical News Bulletin presents summary and pre- liminary reports on work in progress; and Basic Radio Propagation Predictions provides data for determining

the best frequencies to use for radio communications throughout the world. There are also five series of nonperiodical publications: Monographs, Applied Mathematics Series, Handbooks, Miscellaneous Publications,

and Technical Notes. A complete listing of the Bureau’s publications can he found in National Bureau of Standards Circular

460, Publications of the National Bureau of Standards, 1901 to June 1947 ($1.25), and the Supplement to National Bureau of Standards Circular 460, July 1947 to June 1957 ($1.50), and Miscellaneous Publication 240,

July 1957 to June 1960 (Includes Titles of Papers Published in Outside Journals 1950 to 1959) ($2.25); avail- able bom the Superintendent of Documents, Government Printing Office, Washington 25, D. C.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT MBS REPORT

1004-1 2-101 41 August 10, 1962 7589

THE APPLICATION OF X-RAY PROJECTION MICROSCOPY

TO ROOFING ASPHALT SYSTEMS

Sidney H„ Greenfeld

Research Associate

Asphalt Roofing Industry Bureau

Organic Building Materials Section

Building Research Division

Jointly Sponsored by

Asphalt Roofing Industry Bureau

and

National Bureau of Standards

IMPORTANT NOTICE

NATIONAL BUREAU OF STAh

Intended for use within the Go

to additional evaluation and rev

listing of this Report, either In the Office of the Director, Natl< however, by the Government a$ to reproduce additional copies

gress accounting documents Approved for public release by the published It is subjected „ , XTi- it 4.-^+ c production, or open-literature

Director of the National Institute of „ „ oMllnld | np

wri,|„g from Standards and Technology (NIST) ich permission is not needed, on October 9, 201 5. e Pared lf that ae

enc7 wishes

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

THE APPLICATION OF X-RAY PROJECTION MICROSCOPY

TO ROOFING ASPHALT SYSTEMS

1 „ INTRODUCTION

The ability to see within an asphalt or an asphalt product has always been

hampered by the general opacity of the materials involved. The optical

microscope has been used on very thin sections of asphalts, but its contributions have been limited primarily to surface configurations [l, 2]— and

phase separations [3], The election microscope has been applied to asphalt

problems, but it has been shown that the observations reported were largely

of artifacts introduced by specimen preparation [4, 5, 6].

X-rays have been used on asphalts in a number of types of analyses. While

normal radiology has produced little useful information because of the

transparency of asphalts to the wavelengths of x-rays normally used,

x-ray diffraction and x-ray scattering studies have produced some useful

information [7, 8], However, the patterns have been quite diffuse and the

interpretations have been questioned.

In recent years a point-projection microscope has been developed, which

can be used with soft x-rays to "see" the interior of asphalt specimens

as thick as 50 mils. Preliminary results of the application of this

technique to asphalt problems will be covered in this report. This study was made in close collaboration with Dr. S, B. Newman, who is in charge

of the microscopy laboratory at the National Bureau of Standards.

2 . APPARATUS

The point-projection x-ray microscope, shown schematically in Figure 1, was

of the Cosslett and Nixon type [9], manufactured by Micro X-Ray Laboratories

Ltd., of Surrey, London, England. It consisted of a Wehnelt type election

gun with grid bias, electromagnetic condenser and objective lenses and a series of interchangable targets. The spot size on the targets was about

one micron; however, slight scattering of the x-rays resulted in an effective x-ray source slightly larger than this. All x-ray photographs were made with an aluminum target, yielding x-rays of 8.34 A wavelength.

The election gun was evacuated by mechanical and oil diffusion pumps to

a pressure of 10“^ mm. of mercury. A complete description of this

apparatus may be found in reference [9].

Numbers in brackets refer to literature references at the end of this

report.

X-RAY PATH

PHOTOGRAPHIC PLATE

SPECIMEN

ALUMINUM TARGET

OBJECTIVE LENS

CONDENSER LENS

ELECTRON PATH

ANODE

GRID

FILAMENT

FIGURE I. SCHEMATIC OF X-RAY PROJECTION MICROSCOPE

- 2 -

3. PROCEDURE

At the beginning of each day the election gun of the x-ray projection

microscope must be evacuated and focused. The focusing is accomplished

by placing a small piece of screen grid on the aluminum target and

projecting its image on to a phosphor-coated sheet of lead glass. Adjustments are made by changing the magnetic fields in the lenses. When

the microscope is ready the specimen is placed in position, a hollow

cylinder of appropriate height to produce the desired magnification

placed concentric with the specimen, a photographic plate placed on the

cylinder and the exposure made. The plate is developed and viewed

immediately. The gun was operated at 12„5 KV and 30 pA for all of the

photographs in this report.

As seen in Figure 1, the focusing is entirely within the gun, all points

in the x-ray path are always in focus when the gun is properly focused.

Thus, the magnification is controlled by regulating the relative distances of the specimen and the plate from the x-ray source, the target

of the election gun„. All points in the specimen are in focus, but

points in different planes within the specimen are magnified to different

degrees

.

The photographs in this report are at various magnifications. No effort

was made to position the specimen or control its thickness precisely.

Thus, the results must be interpreted on a qualitative basis only.

4. RESULTS AND DISCUSSION

Figure 2 - Unexposed Asphalt

This photomicrograph is typical of many taken of commercial samples of

coating-grade asphalt. There are indications of materials of different

densities dispersed in the asphalt. These range from air bubbles, the

white, round area, to various types of debris. Some of this litter may

be introduced during specimen preparation, for dust and lint tend to

collect on the freshly cut asphalt surfaces, but the bulk of the

foreign material is in the asphalt.

FIGURE 2. A COMMERCIAL COATING-GRADE ASPHALT

3

Figure 3 - Cross Section of Asphalt Film Weathered for 88 Months on

the Roof of the Industrial Building - Magnification 1 20X

In all weathered films, a more-or-less stratified appearance has been

found. There is a surface layer, which is obviously less dense than

the rest of the coating. This layer is the "velvet" film seen on asphalts, which consists of partially oxidized organic material. The

more-comp lete ly oxidized material has been leached from this layer,

leaving a film of low density. Below this surface layer is a denser

layer; this second layer possibly consists of an accummulation of

non-diffusing materials (primarily asphaltenes) which have partially

collapsed on themselves because of a deficiency of oils. The third

layer is again less dense, possibly because the oils have diffused out,

leaving an incompletely filled, but not collapsed, asphaltene structure.

Finally, the bulk of the asphalt remains below.

This particular film is 19.5 mils thick; it had lost 6.5 mils in

thickness and 247, of its initial weight.

"’igure 4 - Cross-Section of Asphalt with 507. Dolomite Weathered 75 Months

on the Roof of the Industrial Building - Magnification 240X

Several strata of varying density are quite apparent. The surface layer seems to be almost entirely mineral matter with little asphalt to hold

it together. The specimen is unsupported; hence, the apparently detached

mineral matter is actually held in position by some material transparent

to x-rays of this wavelength.

Below the low-density surface layer is a high-density layer. This area

seems to be unusually rich in material between the dolomite particles.

The lowest layer, almost 507, of the film, is of an intermediate density.

A possible interpretation of this picture may be that the weathering

at the surface has depleted the surface of asphalt binder through

oxidation followed by solution of water-soluble end products. The

second layer is of high density because the least dense material, the

oils, have diffused to the surface and have left the more dense resins

and asphaltenes behind. The rest of the film is changed to a lesser

degree. It is more akin to the original coating.

*

FIGURE 3. AN ASPHALT FILM WEATHERED 88 MONTHS OUT

OF DOORS - 120X



4

Figure 5 - Random Sample c£ 215-pound Uniform- Thickness Asphalt Shingle - Magnification 70X

This sample of a commercial asphalt strip shingle may not be typical, but

it demonstrates vividly the value of the x-ray microscope for observing

latent failures in roofing products. The mechanical embedment of the

granules is quite evident. There is no contact (let alone adhesion) of

coating and granules in large areas of their interface.

Some coating has been brought on to the exposed surface of the granule

in the center of the photograph, possibly by rotation of the granule

during embedment. A thin spot in the coating exists just to the right

of this granule.

Regions in the saturated felt show significantly lower density than

others. If these areas are less dense because of lower saturant, it

would appear that the interfaces between coating and felt have become

depleted in saturant. The saturant could have fluxed with the coating

or could have been driven back into the felt. Small isolated areas in

the body of the felt seem to be lacking saturant as well.

The variation in thickness of back-coating and back surfacing is quite

apparent.

Figure 6 - Shingle That Has Clawed - Magnification 70X

This section taken from the center of a tab of a clawed, thick-butt

shingle shows the condition existing when extreme clawing has occurred.

The double overlay construction is apparent and still in good condition.

A thin strata of saturated felt, just below the coating, also seems to be

in good condition. (The low-saturation interface area seen in Figure 5 is not apparent here.) However, just below this layer is the bulk of

the saturated felt, largely deteriorated. The back surfacing is full of

holes and some of it has worked up into the felt. It appears that the

original shingle may have had a light back-coating.

Figure 7 - Peace River Glass Mat with Kansas Asphalt. Thickness - 42 mils.

Exposed 600 hrs to 51 -9C cycle. Magnification - 1 10X

The glass mat occupies the lower two-thirds of the total thickness of this

film. The mat is quite open and the individual fibers are surrounded by

asphalt. The asphalt surface shows some signs of weathering; it is less

dense than the interior and seems to have a fuzzy texture. The mottled

appearance of the asphalt is difficult to explain, but is not untypical.

Many asphalt specimens, before exposure, appear like this one.

FIGURE

5.

A

COMMERCIAL,

UNEXPOSED

UNIFORM-THICKNESS

ASPHALT

SHINGLE

-

70X

FIGURE 6. A THICK BUTT SHINGLE THAT HAS DEVELOPED

SEVERE CLAWING - 70X

OFFICE FILE COPY

DIVISION SECTION

PRINT FROM BUREAU OF STANDARDS

PHOTOGRAPHIC LABOR^XORY

ORDER DUPLICATE COWES

BY NUMBER

3092

A

FIGURE 7. AN ASPHALT FILM CONTAINING A PEACE RIVER

A

GLASS MAT AFTER 600 HOURS IN THE WEATHEROMETER - 110X

5

Figure 8 - Johns-Manville Glass Mat with Kansas Asphalt. Thickness - 30 mils

Exposed 600 hrs to 5 1 — 9 C cycle. Magnification 120 X.

The stratification occurring during weathering is quite apparent in this

picture. The glass mat, which is of the same weight as the one in

Figure 7, tends to be concentrated in the lowest part of the asphalt

film. Some debris is clearly seen in the asphalt.

Figure 9 - Monoform Roofing - Clay Emulsion Reinforced with Chopped Glass

Fibers on a Coated Sheet - Magnification Not Determined.

The mineral matter in the coating on the saturated felt is visible at the

bottom of the picture. The random and irregular distribution of the

glass fibers, as individuals and in clusters, throughout the clay emulsion

residue is quite apparent. Clay particles are also quite apparent.

5 . SUMMARY

The application of the x-ray point projection microscope to asphalt problems

has been demonstrated through a number of photographs. The use of soft

x-rays permits observence of variations in the asphalts as well as difference

in absorbences among asphalts and additives.

6. REFERENCES

[1] Schwarz, F., Asphalt und Strassenbau, Supplement No. 5 of Petroleum

Zeitschrift 28 (1932).

[2] Traxler, R. N. and Coombs, C. E„, Proc. ASTM _37_, II, 549 (1937).

[3] Benson, J. R., Proc. AAPT 9, 63, 102-132 (1937).

[4] Preckshot, G. W., DeLisle, N. G., Cottrell, C„ E., and Katz, D. L.,

Trans. Inst. Min. & Met. Engrs 151 , 188 (1943).

[5] Katz, D. L. and Beu, K. E., Ind. Eng. Chem. J7, 195 (1945).

[6 1 Ellis, S. H., Pet. Refiner 27, 410 (1948).

[7] Williford, C„ L., Bull. A & M College of Texas, 7_3> 7 (1943).

[8] Yen, T. F., Erdman, J„ G., and Pollack, S. S., Anal. Chem. 33,

1587 (1961).

[9] Cosslett, V. E. and Nixon, W. C., "X-Ray Microscopy", Cambridge

University Press, London (1960).

FIGURE 8. AN ASPHALT FILM CONTAINING JOHNS -MANVILLE

GLASS MAT AFTER 600 HOURS IN THE WEATHER0METER - 120X

FIGURE 9. GLASS FIBER REINFORCED CLAY EMULSION ON A

COATED BASE SHEET

U. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. As tin. Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C., and

Boulder, Colorado, is suggested in the following listing of the divisions and sections engaged in technical work.

In general, each section carries out specialized research, development, and engineering in the field indicated by

its title. A brief description of the activities, and of the resultant publications, appears on the inside of the

front cover. WASHINGTON, D. C.

Electricity. Resistance and Reactance. Electrochemistry. Electrical Instruments. Magnetic Measurements

Dielectrics. High Voltage.

Metrology. Photometry and Colorimetry. Refractometry. Photographic Research. Length. Engineering Metrology.

Mass and Scale. Volumetry and Densimetry.

Heat. Temperature Physics. Heat Measurements. Cryogenic Physics. Equation of State. Statistical Physics.

Radiation Physics. X-ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological Equipment.

Nucleonic Instrumentation. Neutron Physics.

Analytical and Inorganic Chemistry. Pure Substances. Spectrochemistry. Solution Chemistry. Standard Refer- ence Materials. Applied Analytical Research. Crystal Chemistry.

Mechanics. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Rheology. Combustion

Controls. Polymers. Macromolecules: Synthesis and Structure. Polymer Chemistry. Polymer Physics. Polymer Characterization. Polymer Evaluation and Testing. Applied Polymer Standards and Research- Dental Research.

Metallurgy. Engineering Metallurgy. Microscopy and Diffraction. Metal Reactions. Metal Physics. Electrolysis

and Metal Deposition.

Inorganic Solids. Engineering Ceramics. Glass. Solid State Chemistry. Crystal Growth. Physical Properties.

Crystallography.

Building Research. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials. Codes and Safety Standards. Heat Transfer. Inorganic Building Materials. Metallic Building Materials. Applied Mathematics. Numerical Analysis, Computation. Statistical Engineering. Mathematical Physics. Operations Research. Data Itocessing Systems. Components and Techniques. Computer Technology. Measurements Automation.

Engineering Applications. Systems Analysis.

Atomic Physics. Spectroscopy. Infrared Spectroscopy. Solid State Physics. Electron Physics. Atomic Physics.

Instrumentation. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical Instru- ments. Basic Instrumentation. Physical Chemistry. Thermochemistry. Surface Chemistry. Organic Chemistry. Molecular Spectroscopy. Molecular Kinetics. Mass Spectrometry.

Office of Weights and Measures. BOULDER, COLO.

Cryogenic Engineering Laboratory. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Cryogenic Technical Services. CENTRAL RADIO PROPAGATION LABORATORY

Ionosphere Research and Propagation. Low Frequency and Very Low Frequency Research. Ionosphere Research. Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Services. Vertical Soundings Research.

Radio Propagation Engineering. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements.

Tropospheric Analysis. Propagation-Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.

Radio Systems. Applied Electromagnetic Theory. High Frequency and Very High Frequency Research. Modulalation Research. Antenna Research. Navigation Systems.

Uppei Atmosphere and Space Physics. Upper Atmosphere and Plasma Physics. Ionosphere and Exosphere Scatter. Airglow and Aurora. Ionospheric Radio Astronomy.

RADIO STANDARDS LABORATORY

Radio Physics. Radio Broadcast Service. Radio and Microwave Materials. Atomic Frequency and Time-Interval

Standards. Millimeter-Wave Research.

Circuit Standards, High Frequency Electrical Standards. Microwave Circuit Standards. Electronic Calibration

Center.