MATERIALS PROPERTY DATA

AND MEASUREMENT METHODOLOGY Current emphasis is on the generation of numerical data which describe the physical properties of materials. Carefully prepared and highly characterized reproducible materials are used as samples. The principal aims are to provide (1) needed reference data, (2) the relationship between the physical properties and the characterization parameters and (3) measurement methodology.

Basic measurements are made on both basic and engineering materials. Also, engineering properties are determined on engineering materials. The data generated become part of the NBS data bank for which the National Standard Reference Data System serves as the outlet. The data and technology generated is quite universal, being equally applicable in industry and science. Potential standard reference materials are identified and the science and technology on which standard reference materials calibrations are based are generated under the program. This work is influenced by, and has a major impact on, the national research and development program; in addition it furnishes the data required for developing materials performance criteria required in engineering.

High Temperature Materials.-Stability of materials at high temperatures was investigated to determine decomposition pressures, species, phases, etc. These factors determine the chemical and dimensional stability and reliability of materials used in space systems and other high temperature applications.

Titanium Alloy Properties.-Stressed titanium alloys, in contact with salts (chlorides) at moderate to high temperatures, are known to fail by stress corrosion cracking. When used in supersonic aircraft, these alloys are subjected to stress conditions and failures can occur. Accordingly, NBS is subjecting specimens of these alloys to such environments to determine the mechanism, or cause, and thus be able to prevent possible catastrophic failures.

Properties of Oxygen.-NBS scientists accurately measured the density of liquid and gaseous oxygen at pressures up to 340 atm. During the measurements, a group of analysts developed an equation of state which permitted the calculation of extensive tables and charts of entropy, enthalpy and internal energy. Results could then be used immediately in effecting economy and efficiency by calculating mass rate of fuel consumption in mass reaction devices such as rockets.

International High Temperature Standards. A number of scientists in IMR are members of an international task force (including representatives from Great Britain, France, Japan, Nor

way, USA, and the USSR) organized to study high-temperature melting points. With scientific investigations and industrial technology now requiring precision measurements at higher temperatures, new reference temperatures must be provided. The melting point of alumina was chosen first to help fill a long-standing need for high-temperature reference points, in addition to those specified by the International Practical Temperature Scale of 1948. Measurements will be made by various techniques and the concerted efforts of the scientists of many countries should speed the research, improve the results and promote international acceptance of the standards.

Constant-Current Coulometry.-Constant-current coulometry has been up-graded by NBS research to the point that it now has the highest accuracy and precision of any method of chemical analysis, approaching 1 part in 100,000. Versatility has been increased through the use of additional oxidation-reduction systems.

Chromium Atomic Weight Redetermination.-A 6-inch mass spectrometer was designed and built for studies of the lighter elements. A new atomic weight of chromium was determined to be 51.9961 +0.0003 versus old mass spectrometry value of 51.996 +0.002. The atomic weight of magnesium is currently being redetermined.

Chemically Strengthened Glass.-Several mechanical properties of chemically strengthened glass were determined at elevated temperatures. Potential applications for this new glass are very interesting, for not only does it possess superior mechanical strength but it can be uniquely produced in thin cross sections which are relatively light in weight. Aircraft windshields, safety lenses, and underwater apparatus are examples of commodities for which it can be used. NBS studies provide engineers with the data needed in developing these applications.

Dental Material Tensile Strength Studied.-NBS applied a method usually used to determine the tensile strength of building materials, such as concrete, to small cylinders of dental amalgams and cements. This proved to be a simple and accurate method for following the increase in strength of dental size specimens from the time of insertion in the tooth until the material is fully hardened. The technique will be useful in the evaluation of new and presently available dental materials.

High Velocity Impact Strains in Fibers.-Performance of polymer filaments under stress due to high-velocity impact was studied. Flash photography was used to record the motion caused by rifle bullet impact. Strain distributions and time to break were

obtained. Some textile fibers were able to withstand impact by stretching significant amounts within times less than 50 millionths of a second. Such information on the behavior of polymeric materials is used in the search for materials having superior impact performance.

New Technique for Surface Studies.-A new technique called ELF for studying surface phenomena was developed. It combines the individual techniques of Ellipsometry, Low energy electron diffraction, and Field emission microscopy. These three techniques, combined in a single instrument, permit the simultaneous measurement of extremely small amounts of material absorbed on the surface, characterization of the structure of the surface and the absorbed material, and determination the thermodynamic work function, coverages, and system cleanliness.

Dynamical and Structural Properties of Materials.-Neutron elastic and inelastic scattering techniques were applied to the study of a number of inorganic and organic molecular solids.

Infrared spectra and diffraction data were obtained in several cases to supplement the neutron results. The molecular systems and problems investigated include: (a) Rotational motions in methyl-substituted organics and their correlation with solid phase transitions and crystal structures, and (b) vibration spectra of yttrium and uranium hydrides and deuterides. The results were compared in detail with structural and thermodynamic properties. (c) The molecular motions, barriers to rotation and structure of a number of inorganic salts, including several ferroelectric materials. (d) Slow neutron energy spectra in ammonium acetate, carbonate, and citrate to obtain information on the ammonium ion motions in these compounds. (e) Hydrogen bonding in inorganic crystals.

Liquid Hydrogen Flow Meters.-Flow meters for liquid hydrogen appear feasible based on observed degree of proton spin relaxation occurring between two stations spaced a suitable distance apart along a pipe. In support of such a development, the proton longitudinal relaxation time, T1, as a function of ortho-para composition and temperature was determined and published. NASA is sponsoring the commercial development of a working model flow meter based on these new data and technology. This new type of nuclear magnetic resonance meter may also be used to monitor the custody transfer (sale) of this important but difficult to measure commodity.

Precision Determination of the Coefficient of Expansion of Polyethylene. The bulk coefficient of volume expansion of polyethylene has been measured by dilatometric techniques from 70 to 373 °K. This necessitated the development of a new dilatometric technique for operation at very low temperatures. The expansion of the lattice has also been measured by x-ray techniques and shown to be significantly different from the bulk expansion.

TECHNICAL ASSISTANCE TO OTHERS

To further utilize the technology and talent developed in IMR, advisory and consulting services are provided to governmental, non-profit, and industrial organizations at important stages of their planning and execution of programs with significant materials aspects. Such services are based on comprehension of the science which supports technology. Urgently needed testing services are sometimes rendered to other Government agencies not having suitable facilities of their own. IMR outputs of data on properties of materials and measurement systems are made available to national and international standardizing bodies, and consultative services are given on utilization of this information.

Air Pollution.-NBS found that a variety of products were formed when aromatic hydrocarbons, adsorbed on particulate matter, were treated with air and light. Photochemical oxidation of polycyclic, aromatic hydrocarbons adsorbed on air-borne particles takes place readily in the atmosphere and gives rise to a variety of compounds, some of which may play an important role in air pollution. Pyrene (an important air-pollutant) adsorbed on silica gel was found to give many oxidation products. Two of these, 0.6-pyrenedione and 1.8-pyrenedione, have now been identified. Procedures for the preparation, separation and determination of these and related compounds were developed, and samples of the pure compounds were supplied as reference materials to other laboratories engaged in studies of air pollution.

NBS Report Serves as a Military Text.-An NBS report describing the results of a metallurgical examination of a fractured rod end fitting from a helicopter was prescribed for study by all military classes at the Aerospace Safety Division of the University of California.

Investigations of Fire and Explosion at Cambridge Electronic Accelerator. The AEC requested the assistance of the Cryogenics Division of IMR in the investigation and identification of the cause of the explosion and fire which demolished the Experimental Hall of the Cambridge Electronic Accelerator. The liquid hydrogen technology and safety procedures associated with a large liquid hydrogen bubble chamber were of particular concern. Design philosophy, operating procedures, and physical damage were examined in cooperation with other major national laboratories in identifying the most probable sequence of events.

Corrosion Research for the Office of Saline Water.-The Institute for Materials Research was requested by the Office of Saline Water, Department of the Interior, to establish research in relevant aspects of corrosion. Emphasis is on providing a scientific basis for the most economical selection and utilization of materials for desalination plants. Research is aimed at understanding, under practical desalination conditions, how corrosion occurs and how it may be predicted and controlled. The program is multidisciplinary in nature and will fully utilize the many years of practical experience gained at NBS through corrosion research.

Automotive Seat Belt Standards.-NBS assisted in promulgating a standard for maintaining the quality of seat belts. The Institute for Materials Research laboratories provided much of the data required to evaluate the compliance of newly manufactured belts with requirements.