NATIONAL BUREAU OF STANDARDS REPORT

^313

Progress Report

on

ALLOYS OF GALLIUM WITH POWDERED METALS AS POSSIBLE

REPLACEMENT FOR DENTAL AMALGAM

by

Denton L. Smith

Harold J. Caul

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

0708-10-0707 December 30* 1955

NBS REPORT

4313

Progress Report

ALLOYS OF GALLIUM WITH POWDERED METALS AS POSSIBLE

REPLACEMENT FOR DENTAL AMALGAM

by

Denton L. Smith*

Harold J. Caul *

* Research Associate* American Dental Association Research

Fellowship* Dental Research Section* National Bureau of

Standards

.

This work is a part of the dental research program conducted

at the National Bureau of Standards in cooperation with the

Council on Dental Research of the American Dental Association

the Army Dental Corps* the Air Force Dental Service* the Navy

Dental Corps and the Veterans Administration.

(Task 7756-41 BV No. 55-14)

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, rr

unless permission I 25, D.C. Such pe

cal ly prepared If I

Approved for public release by the

director of the National Institute of

Standards and Technology (NIST) on October 9, 2015

' in part, is prohibited

tandards, Washington

sport has been specifieport for its own use,

ALLOYS OF GALLIUM WITH POWDERED METALS AS POSSIBLE

REPLACEMENT' FOR DENTAL AMALGAM

Abstract

The possibility of using gallium as a liquid

metal to replace mercury in dental restorations was

investigated. It was found that gallium would not

combine at room or mouth temperature with bodycentered'* cubic metals such as tantalum, chromium

and molybdenum. Gallium did combine with powdered

face-centered cubic metals such as nickel, gold,

copper, with alloys of copper and tin, and with

cobalt

With the exception of gallium-cobalt these

alloys had adequate compressive strength and hardness

but expanded excessively during hardening. Galliumcobalt had low compressive strength but exhibited

shrinkage during hardening

Gallium alloys have been made that have some

physical properties that are better than dental

amalgam. None of the alloys investigated possess

all the desired physical properties for oral

restorations

1 . INTRODUCTION

The metallic element gallium was first predicted by Mendeleff

in 1871 in his work on the correlation of the properties of the

elements with their atomic weights [1], It was also predicated

at about the same- time by de Boisbaudran who concluded, while

studying the spectral lines of the elements, that there was an

element missing between aluminum and indium in the periodic table.

Gallium was first isolated by de Boisbaudran in 1875 [2],

The amount of gallium present in the earth's crust is about

the same as lead, roughly 15 g per ton [ 3 ]. Unlike lead which is

concentrated in localized areas, gallium is widely distributed.

The low concentration of the ore and lack of demand for the metal

make gallium relatively expensive at $ 2.50 to $5 .00 per gram [ 3 ].

Gallium has several interesting physical properties . Its

melting point is 29.78°C (85.60°F) [4] while its boiling point is

1983 °C (3601°F) [4], thus giving it one of the longest liquid

ranges of the metals. The metal has a low vapor pressure even

at high temperatures, a pressure of 1 mm of mercury being attained

at 1315°C (2399°F) [4]. Gallium expands 3.4$ in volume during

solidification, the solid having a density of 5*90 g/cm3. It has

the property of wetting many materials including tooth structure.

2

The true nature of this property has not been determined but the

wetting characteristic is generally attributed to a thin oxide

film on the surface of the metal [6], It has also been reported

that gallium is essentially nontoxic [7].

This combination of physical properties indicates that gallium

instead of mercury might be used as a component in a filling

material. Some alloys of gallium begin to melt at higher temperatures than does dental amalgam. These factors make it desirable

to investigate its possible use in oral restorations. It is expected that gallium* instead of mercury* might be used as a liquid

metal to be combined with a powdered metal or alloy to form such a

filling material. To be successful the combination should readily

mix and condense* preferably using implements similar to those

already familiar to the dentist. The gallium alloy should harden

at mouth temperature within a reasonable length of time and possess

strength* dimensional stability and corrosion resistance equal to

or greater than those of dental amalgam.

2 . MATERIALS AND METHODS

Gallium metal of 99*9+$ purity was used in the experiments

described here. The powdered metals and alloys used were obtained

from laboratory supply houses* powdered metal manufacturers, or

by alloying and comminuting in the Dental Research Section at

the National Bureau of Standards. All metallic powders passed a

No. 325 sieve of the U.S. Standard Sieve Series. For laboratory

control* all mixing and condensing of specimens was at 37 °C

(98.6°F) which is above the melting point of gallium. Mixing was

accomplished either in a mortar or in a mechanical amalgamator.

All of the triturated mass was condensed. No liquid metal was

expressed prior to or during condensation with one exception as

noted.

Determinations of the dimensional change were made at 37 °C

( 98 .6°F) using unrestricted specimens 10 mm long and 5 mm in

diameter in a differential interferometer with a fiducial reading

15 minutes after mixing was started. The compressive strength

was determined at 21 °C (69.8°F) using cylinders 8 mm long and

4 mm in-:' diameter . The strength of one series of gallium-nickelsilicon alloys was determined at 37°C (98.6°F) and at 50°C

(122°F). The rate of loading of the compressive strength specimens was in all cases 80 lbs (38.3 Kg) per minute.

3 . RESULTS

Gallium-tantalum mixture . Two mixes of gallium and powdered

tantalum were made* one containing 40% gallium and the other 25%

gallium. The first was mixed with a mechanical amalgamator* the

second with a mortar and pestle. Both specimens could be easily

packed. These metals did not alloy. At room temperature the

specimens hardened by the freezing of the gallium but readily

softened when reheated to mouth temperature

- 3

- Gal Hum-chromium mixture . Gallium and finely divided chromium

did not mix well. A specimen containing 3 5$ gallium hardened by

the solidification of the free gallium present. As in the case of

the gallium-tantalum -mixture, the gallium-chromium specimen

softened by the melting of the gallium when heated to body temperature. A mix containing 50% gallium was too crumbly to pack.

When these mixtures of gallium and chromium were heated over

an open flame the two metals combined with an exothermic reaction

causing the mass suddenly to become bright red. The combination,

after cooling, was a black friable powder.

Gallium-molybdenum mixture . Powdered molybdenum was mixed

with 35* 40 and 50$ gallium, respectively, in a mortar and in a

mechanical amalgamator. The 50^ gallium mixture was too wet to

pack satisfactorily, while the 3 5$ gallium mixture was too dry to

pack well. The resultant mixtures did not harden during a 5-week

period at room temperature. Small droplets of what appeared to be

gallium were observed on the surface of the specimens.

Mixtures of gallium and molybdenum also combined exothermically when heated over- an open flame to form a brittle, black mass.

Gallium-silver-indium alloys . Silver alloys containing 22^,

30 and 34$ indium were prepared and chill cast into a steel mold.

These alloys were then comminuted on a lathe. None of these alloys

when combined with gallium hardened during storage at 37 °C (98.6°F)

for 1 month. The combinations remained soft and were easily

deformed in the hand.

Gallium-gold alloy . A mixture containing 60$ precipitated

gold powder and 40$ gallium hardened. These components react

exothermically to form the intermetallic compound AuGa2 [7].

The rate at which the reaction occurs is apparently dependent on

the temperature at which the metals are mixed. Mixing temperatures

of about 22°C (73°k) ..resulted in no appreciable heat generation;

but when the components were mixed at a temperature of approximately 55°C (131 °F) and packed into a 4 x 8 mm cylinder containing

a thermocouple, temperatures as high as 450°C (842°F) were . recorded

The blue color, characteristic of AuGa2 [7]* was noted to

extend throughout the specimen. These alloys had a linear expansion of about 12.5% during hardening.

Gallium-cobalt alloy . A mixture of 40$ gallium with cobalt

powder contracted approximately 3/^/cm in 24 hours and was stable

for 4 days thereafter-. This is the only alloy investigated that

contracted during hardening. The 7-day compressive strength of

this alloy was 12,700 psi with a standard deviation of 1,100 psi

This low compressive strength makes the gallium-cobalt alloys

unsuitable for oral use, but powdered cobalt may be introduced

into an experimental gallium-powdered metal alloy to control an

excessive expansion.

- 21 - Gal liiLm -nickel alloys. Nickel powder that passed a U.S.

Standard Sieve No . 325 combined readily with gallium in several

proportions. For practical purposes a gallium content from 20

to 40$ was desirable. Less than 20$ gallium resulted in a dry

granular material that could not be readily packed and more than

40$ gallium made a sloppy alloy that was difficult to handle.

The data on compressive strength and hardness of four galliumnickel alloys are summarized in Table 1. When triturated 70

revolutions in 30 seconds* the 35$ gallium alloy expanded from

128 to 136>d/cm at the end of 24 hours and was about constant

at 140 to l49^/cm from 2 to 5 days (Fig. 1* Curves 1 and 2).

Mixing this alloy in a mechanical amalgamator for 1 minute instead of a mortar for 30 seconds resulted in a 24-hour expansion

of about 6 0^//cm (Fig. 1* Curve 3)* This increased to about

75x/cm expansion after 3 days and remained constant for 14 days

thereafter. Increasing the amount of work done on the mix appears

to reduce the expansion and increase the compressive strength of

the 35$ gallium-nickel alloy.

Either powdered cobalt or powdered silicon reduced the large

setting expansion of gallium-nickel alloys. For example* an

alloy of 35$ gallium*. 55$ nickel* and 10$ cobalt expanded about

55-^/cm at the end of 24 hours (Fig. 1* Curve 4). It continued

to expand for about 6 days until a total expansion of approximately

70 /(/cm had occurred. No additional expansion had occurred at the

end of 16 days.. A specimen containing 36$ gallium* 62$ nickel

and 2$ silicon .expanded 37>^/cm in 24 hours. However* this method

of reducing the^ high expansion of the gallium-nickel alloys also

reduced their strength. A comparison of the 24^hour compressive

strengths is given in Table 2.

The compressive strength of the 38$ gallium* 60$ nickel and

2$ silicon alloy ..remained constant from 20°C (68°F) to 50°C

(122°F). The strength of amalgam at mouth temperature was reduced

approximately 21$ and at 50°C (122^F) the strength was decreased

about 43$ (Table- 3)

The tarnish resistance of gallium-nickel alloy was superior

to amalgam, when, exposed to ammonium polysulfide vapor. The sulfide film that did form on the gallium-nickel alloy was easily

removed by wiping with the finger* whereas the sulfide film on

amalgam was adherent

Gallium-copper and gallium-copper-tin alloys . Gallium

combined with copper and copper-tin alloys of several compositions.

Copper powder and a powdered alloy containing 90$ copper and 10$

tin were obtained from a manufacturer of powdered metals. Alloys

with compositions corresponding to the y(73$ copper-27$ tin)*

$ (68$ copper-32$ tin)* £ (62$ copper-3o$ tin) and ^(41$

copper-59$ tin) phases of the copper-tin phase diagram (Fig. 2)

[9] were made and comminuted. The compressive strengths of these*

- 5

- when combined with 35$ gallium., are shown in Figure 3. The alloy

made by the combination of gallium and speculum metal (68$ copper32$ tin) was readily mixed and packed and had good strength. This

alloy hardened slowly as shown in the strength-time curve in

Figure 4* and expanded from 46 to 50 ^/cm on hardening (Figure 5).

This expansion is less than that of the 35$ gallium-65$ nickel

alloy but is still high when compared to the expansion of dental

amalgam (3 to 13 ^/cm is the range of expansion permitted by

American Dental Association Specification No. 1 for Dental Amalgam

Alloy) [10]. The hardness of this alloy varied from 100 to 119

Brinell which corresponds to the upper range of a type II (medium)

or the lower range of n. type III (hard) inlay casting gold alloy [10].

Gallium-copper-beryllium alloys . Gallium combined with a

powdered copper-beryllium alloy (98$ copper-2$ beryllium) to form

an alloy that hardened rapidly. The compressive strength (average

of 2 specimens) of this copper-beryllium alloy when combined with

35$ gallium was 19,500 psi at 1 hour and 18*500 psi at 24 hours.

This would indicate that little or no reaction between the gallium

and copper-beryllium alloy occurred after 1 hour. This does not

agree with the data on dimensional change on hardening as shown in

Figure 6. The technique for preparing the compressive strength

specimens was the same as that for Curve 1* Figure 6. Different

trituration times used in preparing this alloy resulted in different

rates at which the expansion occurred (Figure 6) . The discrepancy

in the order of the expansion curves was not investigated because

the alloy had unsatisfactory compressive strength.

When the gallium content was increased to 40$* liquid gallium

squeezed out of a 1-hour-old specimen during crushing. This specimen had a compressive strength of 14*000 psi.

Gallium and commercial dental amalgam alloys (silver 65$ min.*

tin 25$ min.* copper 6$ max.* and zinc 2$ max

)

.

The combination

of gallium with commercial dental amalgam alloys was unsatisfactory.

The compressive strength of these alloys when mixed with gallium

varied from a maximum of 14*000 psi after 1 week for a specimen

containing 20$ gallium* with a powdered alloy containing 69 . 1$

silver* 26 . 8$ tin* 2.8$ copper and 1.4$ zinc* to a minimum of 1*000

psi after 1 day when 35$ gallium was triturated with an alloy containing 74.5$ silver* 25$ tin and 0.5$ zinc. Trituration in all

cases was in a mortar using 70 revolutions in 30 seconds with a

3 lb load on the pestle. The 1-day compressive strength of the

74.5$ silver* 25$ tin* 0.5$ zinc alloys* when combined with gallium

in this manner* decreased with an increasing gallium content as

shown in Figure 7. The compressive strength of any of these is

too low for use In the mouth.

* Composition limits for dental amalgam as per American Dental

Association Specification No. 1 for Dental Amalgam Alloys

(First revision 1934) [10].

- 6 -

4 . DISCUSSION

This investigation indicates that powdered face-centered

cubic metals such as gold, nickel, copper and some intermetallic

compounds of copper and tin will, when triturated with gallium,

harden at room or mouth temperature. Powdered body-centered cubic

metals such as tantalum, chromium and molybdenum, when triturated

with gallium, if they harden at all, do so too slowly to be of

practical value

The strength of alloys containing 35$ gallium-65^ copper,

35$ gallium-65$ speculum metal, 35$ gallium-65$ nickel Is adequate

for oral use but the expansion on hardening may be excessive as

clinical experience with alloys having a setting expansion of

about 50 >$cm ( 35$ gallium-65$ speculum metal) has not been reported . The wetting action of gallium should give good adaptation

when the alloy is condensed in a cavity. Packing a 35$ gallium65$ nickel alloy into a glass tube gave a mirror-like appearance

to the inside of the tube. This wetting action is also a handicap

when handling gallium alloys. The glass and metal mixing and

condensing instruments become coated with gallium alloy making

cleaning difficult. Since gallium does not wet wax and wax-like

materials and smooth surfaces of some resins such as Teflon and

Nylon, it may be possible to make satisfactory mechanical amalgamator capsules and pluggers from these resins.

The indication that gallium alloys retain their strength at

mouth temperature and above, whereas amalgam does not, may be

significant. Failure of amalgam at the margins of a restoration

may be due, in part, to the reduced strength of the amalgam at

body temperature

5 . SUMMARY

The following alloys of gallium with powdered metals and

alloys have been made and found to harden at room or body temperature : 40$ gallium-60$ gold, 35$ gallium-65$ nickel, 38$ gallium60^ nickel-2$ silicon, 35$ gallium-55$ nickel-10$ cobalt, 35$

gallium-65$ copper, 40$ gallium-60$ cobalt; and 35$ gallium with

the following copper-tin alloys; 90$ copper-10$ tin, 73$ copper27$ tin, 68$ copper-32$ tin (speculum metal), 62$ copper-38$ tin,

and 4l$ copper-59$ tin.

Mixtures of gallium with tantalum, chromium, molydenum and

some commercial amalgam alloys would not harden or were too weak

to be of practical value.

The 40$ gallium-gold alloy reacted exothermically under certain

conditions and was therefore impractical for oral restorations.

7

The 35$ gal Hum-nickel alloy had good strength and hardness

but expanded 140 to l49^//cm in 2 days. The expansion was reduced

to about 75 -*/cm by increasing the amount of work done on the mix

during trituration.

Cobalt powder or silicon powder added to gallium-nickel alloys

also reduced the expansion but the 1-day strength of the alloy

was decreased by this treatment.

The 3 5$ gallium-speculum metal alloy had good strength and

hardness but set slowly. Lt continued to gain strength during 10

days storage at body temperature. This alloy had a setting expansion of 46 to 50 >tf/cm.

Gallium alloys have been made with some physical properties

that are adequate for oral restorations . However, sufficient data

on the physical properties of gallium-powdered metal alloys are not

available to recommend any so far investigated as possible replacements for dental amalgam. Prior to any such recommendations the

alloy or alloys must be assessed biologically.

- 8 - BIBLIOGRAPHY

1. Mendeleeff* D. K. Die Periodische Gesetzmassigkeit

der Chemischen Elmente. Analen der Chemie und

Pharmacies Supplementband 8 Heft £:10* 1871 .

2. de Boisbaudran* L. Sur Un Nouveau., Le Gallium.

Ann. Chim. et Phys . 10:100 Jan. 1877*

3. Thompson* A. P. and Hamer* H. R. Ga: A Byproduct

Metal. J. of Metals 191:91 Feb. 1951.

4. Roeser* W. F. and Hoffman* J. I. Freezing Point of

Gallium. NBS J. Res. 13:673 Nov. 1934.

5 . Atomic Energy Commission. Liquid Metals Handbook*

Ed. 2. U. S. Government Printing Office* Washington*

D . C . * June 1952

6. Wilkinson* W. D. Properties of Gallium. Argonne

National Laboratory Report 4109* 1948.

7. Meek* S. F.* Harrold* G. C. and McCord* C. P.

Toxicity of Gallium. Industrial Med. 12:7 Jan. 1943-

8.

Zintl* E.* Harder* A. and Haucke* W. Legierungphasen

Mit Fluoritstruktur . Z. Phys. Chemie. B. 35:354,

March 1937.

9.

Raynor* G. V. Annotated Equilibrium Diagram Series

No. 2. Inst, of Metals* London 1944.

10.

Paffenbarger* G. C. and Sweeney* W. T. American Dental

Association Specifications for Dental Materials* Ed. 1.

American Dental Association* Chicago* 1955.

- 9

- TABLE 1

Compressive Strength and Brinell Hardness of Some

Gallium-nickel Alloys

Compres- Baby Brinell

^ Composition sive hardness

Gallium-Nickel Strength 15 Kg load

Wt % Wt a/o psl 1/1 6 ball Remarks

23 77 14,000 48 Triturated 2 min.

3 lb load on pestle.

Specimen 3 days old

33 87 32,000 90 Triturated 2 min.

3 lb load on pestle.

Specimen 1 day old.

35 85 49,000 90 Triturated l\ min.

3 lb load on pestle.

Specimen 1 day old

44 58 33*000 70 Triturated 2 min.

3 lb load on pestle.

Specimen 1 day old

62,000 100 As above except excess

gallium was expressed

during condensation.

Above values are individual or average of two determinations
•

•
TABLE 2

Effects of Addition of Cobalt and Silicon to the Compressive

Strength of Gallium-nickel Alloys

Composition

wt %

Compressive Strength

Average Standard Deviation

psi psi

35 gallium

65 nickel

39,600 5,500

35 gallium

584 nickel

6-J- cobalt

31,100 2,300

38 gallium

60 nickel

2 silicon

25,500 800

All specimens made by triuration in a mortar* 70 revolutions

in 30 seconds under a 3 lb load.

11

TABLE 3

Compressive strength (l day) of amalgam and an alloy of

38% gallium, 60$ nickel, and 2% silicon at 21°C, 37°C

and 50°C (70% 99°. and 122°F)

Temperature Amalgam*

38$ gallium. 60$ nickel, 2% silicon

Average Standard Deviation

°C psi psi psi

21 49,500** 25,500 800

37 39.000** 26,700 1,300

50 28,600** 2.5,200 2,000

* Alloy composition - Silver 70.3$. Copper 2.4$, Tin 25-5$

and Zinc 1 . 8$

** Average of two determinations

EXPANSION

-MICRONS

PER

CENTIMETER

SETTING EXPANSION

GALLIUM- NICKEL ALLOYS

GALLIUM-NICKEL— COBALT ALLOYS

Figure 1. Dimensional Change on Hardening of Gallium-Nickel

and Gallium-Nickel-Cobalt Alloys at 37°C (98.6°F)

Curves 1 and 2. 35# gallium-65# nickel triturated 70 revolutions

in 30 seconds at 3 lb load.

Curve 3. Same as 1 and 2 except triturated 1 minute

in a mechanical amalgamator.

35$ gallium-55$ nickel-10# cobalt triturated

75 revolutions in 30 seconds at 3 lb load.

Curve 4

EXPANSION

-MICRONS

PER

CENTIMETER

SETTING EXPANSION

GALLIUM- NICKEL ALLOYS

GALLIUM-NICKEL- COBALT ALLOYS

Figure 1. Dimensional Change on Hardening of Gallium-Nickel

and Gallium-Nickel-Cobalt Alloys at 37°C (98.6°F)

Curves 1 and 2. 35$ gallium-65$ nickel triturated 70 revolutions

in 30 seconds at 3 lb load.

Curve 3* Same as 1 and 2 except triturated 1 minute

in a mechanical amalgamator.

35$ gallium-55$ nickel -10$ cobalt triturated

75 revolutions in 30 seconds at 3 lb load.

Curve 4.

EXPANSION

-MICRONS

PER

CENTIMETER

SETTING EXPANSION

GALLIUM- NICKEL ALLOYS

GALLIUM-NICKEL- COBALT ALLOYS

Figure 1. Dimensional Change on Hardening of Gallium-Nickel

and Gallium-Nickel -Cobalt Alloys at 37°C (98.6°F)

Curves 1 and 2. 35$ gallium-65$ nickel triturated 70 revolutions

in 30 seconds at 3 lb load.

Curve 3. Same as 1 and 2 except triturated 1 minute

in a mechanical amalgamator.

35$ gallium-55$ nickel -10$ cobalt triturated

75 revolutions in 30 seconds at 3 lb load.

Curve 4.

EXPANSION

-MICRONS

PER

CENTIMETER

SETTING EXPANSION

GALLIUM-NICKEL ALLOYS

GALLIUM-NICKEL- COBALT ALLOYS

Figure 1. Dimensional Change on Hardening of Gallium-Nickel

and Gallium-Nickel -Cobalt Alloys at 37°C (98.6°F)

Curves 1 and 2. 35$ gallium-65$ nickel triturated 70 revolutions

in 30 seconds at 3 lb load.

Curve 3. Same as 1 and 2 except triturated 1 minute

in a mechanical amalgamator.

35$ gallium-55$ nickel -10$ cobalt triturated

75 revolutions in 30 seconds at 3 lb load.

Curve 4

Cu-Sn Copper-Tin

°C Atomic Percentage Tin °F

Q Figure 2. Copper-tin Constitution Diagram .

COMPRESSIVE

STRENGTH

-

PSI

COMPRESSIVE STRENGTH

GALLIUM-COPPER-TIN ALLOYS

0 Sn 10 20 30 40 50 60 Sn

POWDERED METAL COMPOSITION - WEIGHT %

Figure 3. Three-day Compressive Strength of Copper and Coppervpin

Alloys -when Combined with 35^ Gallium.

Trituration in a mortar, JO revolutions with a 3 lt> load.

Center line is average; upper and lower lines are

standard deviations
\
COMPRESSIVE

STRENGTH

—

PSI

COMPRESSIVE STRENGTH WITH TIME

GALLIUM- SPECULUM METAL

HOURS DAYS

SPECIMEN AGE

Figure 4. Compressive Strength of 35# Gallium, 65# Speculum Metal

(68# copper-32# tin).

Triturated 70 revolutions in 45 seconds with a 3 lb load.

Center line is average; upper and lower lines are

standard deviations
\
EXPANSION-MICRONS

PER

CENTIMETER

SETTING EXPANSION

GALLIUM - COPPER - Tl N ALLOY

Figure 5. Dimensional Change on Hardening of Three Specimens of

35# BIlI 1 ium-65/6 Speculum Metal (68^6 copper-32/6 tin) .

EXPANSION-MICRONS

PER

CENTIMETER

SETTING EXPANSION

Figure 6 . Dimensional Change on Hardening 35$ Gallium65$ Copper -Beryllium Alloy ( 98$ copper-2$ beryllium)

Trituration in a mortar with 3 lb load.

Curve 1 - 50 revolutions in 30 seconds.

Curve 2-70 revolutions in 45 seconds.

Curve 3

- 100 revolutions in 60 seconds.

COMPRESSIVE

STRENGTH

PSI

COMPRESSIVE STRENGTH

GALLIUM-DENTAL SILVER ALLOYS

Figure 7. Compressive Strength at 24 hours of

Gallium-Silver-Tin-Zinc Mixtures

(powdered alloy composition, silver 74.5#,

tin 25#, zinc 0.5#).

Triturated 70 revolutions in 30 seconds

with 3 It load.

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. A major portion of the Bureau’s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Reports are issued to the sponsoring agency of a particular project

or program. Published papers appear either in the Bureau’s own series of publications or in the

journals of professional and scientific societies. The Bureau itself publishes three monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

summary and preliminary reports on work in progress; and Basic Radio Propagation Predictions,

which provides data for determining the best frequencies to use for radio communications throughout

the world. There are also five series of nonperiodical publications: The Applied Mathematics

Series, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous

Publications.

Information on the Bureau’s publications can be found in NBS Circular 460, Publications of

the National Bureau of Standards ($1.25) and its Supplement ($0.75), available from the Superintendent of Documents, Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of

Standards, Washington 25, D. C.