bluuebunny/crossref_metadata_2025 huggingface dataset:
Rie Damage and Its Control in Silicon Processing
Authors: Fonash SJ , Rohatgi A
Published: December 2008

Reactive ion etching (RIE) has become a necessary tool in much of silicon device manufacturing. When employing this important etching technique, one must be aware that its use can produce damage and contamination. The types of damage and contamination that can result from RIE are discussed for several etching chemistries. Control of RIE damage can be achieved by removing it by wet chemical etching or by furnace annealing. Control of RIE damage can also be achieved by hydrogen passivation or by the use of rapid thermal anneals. These latter techniques are of considerable interest since they are compatible with micron and submicron device geometries.
The Effects of Plasma Processing of Dielectric Layers on Gallium Arsenide Integrated Circuits
Authors: Vanner KC , Cockrill JR , Turner JA
Published: December 2008

In the commercial production of GaAs I.C.s it is essential to minimise processing induced damage to the shallow semiconducting layers of the MESFET. Currently used fabrication sequences do not involve the use of highly energetic plasma processes such as RIE under conditions which may cause surface damage as a result of ion bombardment. In the development of new fabrication technologies it is essential to ensure that device performance is not degraded by the use of such plasma processes. The use of such techniques as plasma enhanced CVD to deposit passivation or interlayer dielectrics, and subsequent patterning by plasma or reactive ion etching, may adversely affect the active layer as a result of ion or radiation bombardment, or by chemical contamination of the surface.

This paper will present results from a study of the effects of plasma processing of GaAs MESFETs in MMICs. Measurements of device performance show that assessment of FET characteristics can provide a valuable complement to diode measurements and surface analysis.
Effects of Deep UV Radiation on Photoresist in Al Etch
Authors: Lee SC , Chin BL
Published: December 2008

The photoresist integrity and edge profile can be improved in Al RIE etch by exposing the patterned Al coated wafers to deep UV radiation (λ =220nm). The transmitted DUV intensity on a photoresist coated clear sapphire wafer was measured as a function of the accumulated exposure time. The transmitted DUV intensity reaches a maximum after a period which is proportional to the photoresist thickness. The surface of the DUV exposed photoresist forms a highly polymerized membrane during hard bake and is stressed by the vapor pressure from inside the photoresist. The property of this membrane was studied and reasons for the improved etch integrity are proposed.
Comparison of Impurity Profiles Generated by Spreading Resistance Probe and Secondary Ion Mass Spectrometry
Authors: Sweeney GG , Alvarez TR
Published: December 2008

Silicon wafers, implanted with As or BF2, were subjected to isochronal anneals and the resulting impurity profiles were measured with both spreading resistance probe (SRP) and secondary ion mass spectrometry (SIMS). The two measurements converged as the anneal temperature was increased. This is to be expected as SRP measures the electrically active impurity concentration, while SIMS measures the atomic concentration of the impurity present. An anomalous kink in the BF2 profile observed in SIMS measurements was not present in the SRP measurement. Junction depths measured by SRP were consistently shallower than measurements made by SIMS. The SRP and SIMS profiles were compared to those profiles simulated with SUPREM, a process modeling computer program.
Mapping Silicon Wafers by Spreading Resistance
Authors: Mazur RG
Published: December 2008

Whole wafer mapping is a useful method for studying inhomogeneities in as-grown or processed silicon. However, its usefulness has been limited to structures on which four-point-probe measurements can be made. This paper shows that the spreading resistance technique can be used for surface mapping in those situations where four-point-probe measurements are difficult or impossible. The strengths and weaknesses of the two mapping techniques are compared for the following types of samples: P on P+ or N on N+ epi wafers, low-dose ion implants, ion implants into same conductivity-type substrates, heavily-doped as-grown materials, and very thin films.
Production Monitoring of 200MM Wafer Processing
Authors: Keenan WA , Johnson WH , Smith AK
Published: December 2008

A successful transition to 200mm wafers requires careful monitoring of substrate quality and rapid feedback on process performance. Sheet resistance mapping will play a key role in this transition because it allows precise control of repeatability and uniformity for a wide range of processes. The critical role of sheet resistance mapping in the transition to larger wafers will be reviewed. Advanced, fully automated sheet resistance mapping systems, capable of measuring 200mm wafers, will also be discussed. Data obtained from 200mm wafers will be presented for various process applications, including epitaxial and metal deposition, and ion implantation.
Summary of Statistical Analyses of Specification Mortar Cube Test Results from Various Cement Suppliers, Including Four Types of Cement Approved for Corps of Engineers Projects
Authors: Poole TS
Published: December 2008

Within-plant variation in compressive strength was examined for 95 portland cement sources. Levels of variation were found to vary with test age and type of cement. Standard deviations generally increased with age and were generally higher in Type III and Type V cements. The effect of type of sampling on estimates of within-plant standard deviation in compressive strength was examined. Test samples represented by 24-h production composites exhibited measurably less variation than the same cements when represented by grab samples.
A Study of the Effects of Dry and Wet Deposition on Galvanized Steel and Weathering Steel: A Three-year Field Exposure
Authors: Spence JW , Haynie FH , Stiles DC , Edney EO
Published: December 2008

At an exposure site located at Research Triangle Park, NC an automatic covering device was installed to partition the effects of dry and wet deposition on the corrosion of galvanized steel and weathering steel samples. Mass loss was used as the measure of corrosion of both metals. Meteorological and air quality were recorded continuously during the 36-month exposure study and evaluated to eliminate errors and to estimate missing data. Models were derived to describe the corrosion of galvanized steel and weathering steel. Rainfall was found to be a significant factor for the corrosion of both metallic materials.
Risk Reduction Through Use of Closed Systems: An Attainable Goal?
Authors: Jacobs WW
Published: December 2008

Closed systems have been advanced as means for minimizing the amount of exposure received by persons who mix and transfer agricultural pesticides. The U.S. Environmental Protection Agency has considered required use of closed systems as potentially viable alternatives to cancellation of certain hazardous formulations or to mandatory use of full protective clothing outfits in hot climates. The EPA is concerned about the performance of closed systems in practice. The effectiveness of closed systems has been limited by problems in accommodating the large variety of containers used for liquid agricultural pesticides, human errors, and equipment failures. Improvements in these areas are being realized through development of higher quality, more versatile equipment that is relatively easy to operate, and through movement toward container standardization within the agrichemical industry. While currently available closed systems can reduce pesticide exposure, they do not eliminate it entirely.
Economical Pesticide Application: The Reasons for Controlled Droplet Application
Authors: Bals TE
Published: December 2008

The true costs of pesticide application are still ill-defined and frequently misconceived, despite the fact that they form a large, and growing, proportion of the costs of crop protection. Increased efficiency in the application of pesticides is vital for the achievement of maximum economic yield and is a necessary concomitant of the widespread adoption of Integrated Pest Management programs.

Controlled droplet application (CDA) represents a significant advance in the precision of pesticide application over conventional spraying techniques utilizing hydraulic nozzles. It offers advantages in the logistics of the spraying operation as well as reduced environmental contamination and greater potential operator safety. However, a massive and co-ordinated research effort is required to take full advantage of the potential benefits of CDA and to truly advance crop protection as a science.
Registration Considerations for Pesticide Formulations
Authors: Landis WR
Published: December 2008

Pesticide formulation technology affects all areas of pesticide development. The relationships between formulation and efficacy, phytotoxicity, purchasing, patents, toxicology, non-target organisms, environmental fate, and re-entry protection are discussed. Procedures for alternate inert and active registrations are presented.
Characterization of High Growth Rate Epitaxial Silicon from a New Single Wafer Reactor
Authors: Robinson MD , Lawrence LH
Published: December 2008

A new single wafer epitaxial silicon reactor, the Epsilon One, is characterized by automated cassette-to-cassette wafer handling, rapid thermal cycle, and high deposition rate for wafers up to 150 mm diameter. This paper describes the reactor, and its results in terms of epi thickness and doping uniformity, epi/substrate transition width, and epi defect density.
Nucleation and Growth Kinetics of Bulk Microdefects in Heavily Doped Epitaxial Silicon Wafers
Authors: Wijaranakula W , Matlock JH , Mollenkopf H
Published: December 2008

Nucleation and growth mechanisms of the bulk microdefects in oxygen controlled silicon substrate wafers heavily doped with boron and antimony were studied following pre- and postepitaxial enhanced precipitation annealing at various temperatures. It was observed that “grown-in” microdefects in both dopant species are nucleated by a similar mechanism during the crystal growth cooling period. Microdefect growth behavior appears, however, to be different, probably due to differing effects of the dopant species. It was also observed that the pre- and postepitaxial annealing as well as the epitaxial deposition processes have a strong impact on the growth of the bulk microdefects. Based upon this study, generic growth characteristics of the bulk microdefects of both P+ and N+ materials are established and a growth kinetics model is proposed.
On the Application of Calibration Data to Spreading Resistance Analysis
Authors: Berkowitz HL
Published: December 2008

The requirements imposed by microelectronics structures on material characterization by spreading resistance profiling (SRP) have made the development of sound calibration procedures for SRP essential. To this end, the Efficient Multilayer Analysis Program, also known as the Berkowitz-Lux technique, has been adapted to incorporate both variable probe radius and barrier resistance models. Since both models are heuristically based, two versions of each method have been tried. Numerical stability and the ability to produce reasonable results are discussed for each version.
Crack Free and Highly Reliable Double Level Metallization Process Using Plasma Oxide and Silanol-Type Sog Layers
Authors: Iwamori T , Sakata Y , Kojima H , Yatsuda Y
Published: December 2008

A double level metallization process using a sandwich structure of Plasma CVD(P-CVD) / Spin-On-Glass (SOG) / PSG oxide for an interlevel dielectric layer has been developed. A very thin phosphorus-doped silanol-type SOG is coated for planarization. The plasma-oxide which is deposited beneath the SOG film suppresses hillock growth in the 1st Al layer and together with the very thin coat of SOG prevents the SOG layer from cracking. Furthermore, silanol-type is found to be more reliable compared with siloxane-type. The surface topography is found to be planarized very well by cross-sectional SEM. The failures of 2nd Al open and short and short between 1st Al and 2nd Al are all negligible in our 2.0–1.3µm process proven by TEG (Test Element Group) evaluation. No problems have appeared in our reliability test program.
Chemical Analysis of Metallic Impurity on the Surface of Silicon Wafers
Authors: Shiraiwa T , Fujino N , Sumita S , Tanizoe Y
Published: December 2008

In silicon wafer processing, it is important to decrease the impurity on the wafer after final process. The authors report a method of analysis of impurity only on the top surface of Si wafers. In this study, wafer are contaminated with a cleaning solution containing impurity, and the impurity remains on the wafer is collected into the resulting liquid of the oxide and HF vapor. They are then analysed by atomic absorption spectrophotometer. Detection limits are Na: 5×108atoms/cm2, Fe: 2×109atoms/cm2, Al: 1×1010atoms/cm2.
The Role of Oxygen Precipitates in the Gettering of Iron in Silicon
Authors: Sinha PK , Glaunsinger WS
Published: December 2008

The gettering of iron in silicon has been reported to occur at dislocations and stacking faults in the vicinity of oxygen precipitates. The iron-containing phase has also been identified. For heat treatments between 800 °C and 1025 °C for 24 hrs, only one phase was identified in argon-implanted as well as oxygen-implanted samples. The gettered particles 30 nm to 100 nm in size were analyzed using EDS, EELS and micodiffraction, and the only phase was identified as FeSi. It is proposed that the role of oxygen precipitates in the gettering process is only to generate defects in the matrix, which ultimately getter the transition metal.
Perkin-Elmer 544 Overlay Evaluation Using Statistical Techniques
Authors: Keller GA , Waldo WG , Babasick RF
Published: December 2008

A recently developed optical overlay measurement system is used to perform factorial design statistical experiments on the Perkin-Elmer 544 Micralign. The overlay measurement system (Perkin-Elmer's OMS-1) is used to check out the operation of computer offsets and microstage scale corrections in the Micralign 544 with a half fractional factorial test for five factors. This is a resolution five experiment. OMS-1 compares a resist image to a previously etched substrate. This offers fast turnaround time and contactless measurement of product wafers. We have found that with a minimum of equipment utilization, a Perkin-Elmer scanner can be checked out for operation on many different programmable settings. Experimental data is reported in real time since the development step is the only process required before wafers are measured. Information will also be presented on the functionality of the OMS-1 with respect to reproducibility and repeatability. The Perkin-Elmer scanner is tested for stability over time using the OMS. Also, we demonstrate efficiency of the OMS in overlay measurement processing and a method to evaluate the alignment distribution offsets needed to achieve optimal registration.
Revolutionizing Semiconductor Material Specifications
Authors: Lowry RK
Published: December 2008

Statistical process control is being widely adopted to improve yields and profitability in semiconductor manufacturing. Controlling and reducing key process parameter variability is essential for yield improvement and cost control. Accordingly, statistically-controlled processes must be supplied with raw materials which are similarly statistically controlled. This need has been inadequately recognized by vendors and standards-writing groups. This paper discusses the importance of controlling materials variability. Examples from IC manufacturing are given. It is shown that raw material specifications cannot be based solely on engineering limits, but must include centered means, statistical control limits, and the requirement that vendors deliver their products from their own in-control manufacturing processes.
Economic Impact of Standards on Productivity in the Semiconductor Industry
Authors: Tassey GC , Scace RI , French JC
Published: December 2008

The generic role of standards in the development and diffusion of technology is reviewed. Examples of the economic value to the semiconductor industry of standards and the metrological research that underlies them are given to show the substantial return on investment that usually is obtained. Current metrological issues are raised to show that the present level of effort in standards development in this field is not sufficient and is cause for serious concern.
Formulations — Past, Present, and Future
Authors: Corty C
Published: December 2008

During the last 30 years there have been significant evolutionary changes in the formulation and application of agrichemical products. Crop protection is now a sophisticated task, and quality requirements for crop protection chemicals are ever increasing. With agriculture under economic stress and with intense competition between existing chemicals and newly developing products of high potency, formulation development is evolving as an increasingly scientific multidisciplinary effort increasingly closely integrated with application technology.
Philosophy of Formulation
Authors: Becher P
Published: December 2008

The principles of formulation science are presented in terms of a hypothetical formulation of an emulsifiable concentrate.
Selecting the Ideal Preservative for Aqueous Pesticide Formulations
Authors: Chasin DG
Published: December 2008

With few exceptions, pesticides formulated as aqueous solutions and suspensions (flowables) require a preservative. Even most fungicide aqueous flowables require an effective bactericide. Preservatives are primarily incorporated to prevent (1) deterioration of sensitive formulation components (eg. rheological modifiers), and (2) formation of microbial slimes which can clog spray nozzles. The many requirements imposed on preservatives include (1) broad spectrum antimicrobial activity, (2) non-reactivity with other formulation components, (3) low phytotoxicity and mammalian toxicity, (4) activity over wide pH range, (5) high temperature stability, (6) ease of assay, (7) environmental safety, and (8) broad regulatory approvals. Considerable testing is required to determine the most cost-effective preservative level in each formulation.

Covered in this paper are (1) sources and control of contaminating organisms, (2) the importance of test organism adaptation and “challenge” testing in determining microbial susceptibility and optimal preservative level, and (3) comparison of several preservatives — including formaldehyde and 1,2-benzisothiazolin-3-one (active ingredient in PROXEL® GXL) — covered by EPA regulation 40 CFR 180.1001.
Using the Predictive Powers of Triangular Co-Ordinate Plots for Designing Agricultural Formulations
Authors: Botts MF
Published: December 2008

An agricultural formulation candidate was developed with the aid of triangular co-ordinate plots. It was found that when a candidate formulation must satisfy many requirements, a plot is useful for managing the large number of variables involved.

A plot was produced which showed how emulsion stability varies with formula composition. Each point in the plot was shown to carry a large amount of information. The point describes the complete composition of the recipe it represents and by its coding it also describes the emulsion stability of the recipe.

From the coding of the first group of points produced for the plot, it was possible to predict what composition regions would most likely produce the best emulsion stability. Subsequent groups of points were added to more closely define the boundaries of the best emulsion stability region.

The preparation of triangular co-ordinate plots show promise for automation. Data for one example given were obtained by laboratory robotics. This capability makes the design of formulations with the aid of triangular co-ordinate plots quite attractive, because the numerous points required can be obtained with a laboratory robotic arm [1].
Droplet and Deposit Patterns of One Pseudoplastic and Three Newtonian Spray Mixtures Following Spray Application Under Laboratory Conditions
Authors: Sundaram A
Published: December 2008

A pseudoplastic spray mixture was prepared from fenitrothion, polymeric adjuvants and humectants. Three Newtonian spray mixtures were prepared, one each from fenitrothion, aminocarb and mexacarbate respectively, using oils, surfactants and cosolvents. The spray mixtures were sprayed over potted seedlings of balsam fir using a spinning disc atomizer, at an application rate of 1.5 L/ha. Aminocarb and mexacarbate were each sprayed at 70 g active ingredient (AI)/ha, whereas fenitrothion, at 210 g AI/ha. Spray droplets were sampled with Kromekote® cards and deposits were collected on glass plates. Foliar droplets were counted and pesticide concentrations were measured by gas-liquid-chromatography. Physical properties measured were: viscosity-shear rate relationship, surface tension and volatility. The data indicated that the presence of the polymeric adjuvants imparted pseudoplastic behavior to the spray medium. Because of this, the mixture provided a markedly larger droplet size spectrum and much greater deposit concentrations of the insecticide both on conifer foliage and on the sampling units.
Plant and Mineral Oils as Insecticide Adjuvants: Effects on Residues and Toxicity
Authors: Plapp FW
Published: December 2008

Effects were measured of combining plant and mineral oils with insecticides on residue properties of insecticides on cotton leaves. Surface residues of a relatively polar organophosphate, parathion, were increased in persistence. Little effect of oils on residue properties was found in tests with the more nonpolar synthetic pyrethroid, permethrin.

Effects of oils on insecticide toxicity were measured in tests where insects were exposed to residues on glass surfaces. All oils increased efficacy of organophosphate and pyrethroid insecticides.

Thus, oils are effective in modifying both insecticide residue life and toxicity. Polarity us test insecticides and nature of the oil are important variables in determining the effects produced.
Mechanistic Modeling of Zircaloy Deformation and Fracture in Fuel Element Analysis
Authors: Nichols FA
Published: December 2008

A review is given of the comprehensive model developed in the 1960s at the Bettis Atomic Power Laboratory to explain the creep of Zircaloy during neutron irradiation and applied to fuel element analysis and design. The in-pile softening observed at low stresses was hypothesized to be due to a combination of the growth-directed Roberts-Cottrell yielding creep originally proposed for α-uranium and the formation of point defect loops preferentially on certain planes in response to the applied stress, with the second process being of relatively greater importance. The in-pile hardening observed at high stresses (or strain-rates) was proposed to be due to the cutting by dislocations of radiation-produced obstacles. In this stress (strain-rate) region, in-pile behavior was proposed to be identical to post-irradiation behavior. At intermediate stresses (strain-rates) a mechanism of radiation-enhanced climb around obstacles was suggested as being rate-controlling. As the stress is decreased, the climb process becomes easier, and the rate was then predicted to be controlled by glide at a flow-stress characteristic of unirradiated, annealed material, where radiation-enhanced diffusion enabled climbing around the normal strain-hardening obstacles. At still lower stresses, this glide process became negligibly slow compared with the growth-connected creep mechanism that was presumed to operate independently. The overall scheme was shown to be in good agreement with all the in-pile data then available and implemented into the computer analysis of fuel element behavior.
Influence of Hydrostatic Extrusion on Properties of Zirconium and Zircaloys
Authors: Jimei S
Published: December 2008

The influence of hydrostatic extrusion on the properties and microstructure of zirconium and Zircaloys has been studied using zirconium and Zircaloy rods produced by cold hydrostatic extrusion and cold drawing. The tensile properties, ductile fracture toughness, microhardness, density, and microvoid content were determined. The microstructural investigations were carried out by metallography, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. It has been found that hydrostatic extrusion increases the strength of zirconium and Zircaloys to some extent and markedly improves their ductilities compared with conventional drawing. The ductile fracture toughness (JIc) and the tear modulus (T) of the extruded material were, respectively, 2 to 3 and 3 to 4 times greater than those of drawn material. Hydrostatic extrusion led to more uniform properties across the whole cross section of the rods and formed a stronger 〈10¯10#x232A; deformation texture, healed the microdefects in the material, increased the density with increasing reduction, formed an unusual substructure through the complete volume, and gave effects similar to those of a fine grain size.
Parametric Study of an Autoclave Test for Nodular Corrosion
Authors: Schemel JH
Published: December 2008

The use of a steam corrosion autoclave test as a quality control tool for Zircaloy products has been practiced for many years. The most common form of the test is exposure to steam at 672 K, 10.3 MPa (750°F, 1500 psi) for three days. Some years ago it was found that this test did not predict susceptibility to the occurrence nodular corrosion in boiling water reactors (BWR). A number of investigators found that a test at 723 to 773 K would produce nodular corrosion on Zircaloy products and therefore used the test as an index for research work on Zircaloy materials. More recently the test has been proposed as a quality control test on each lot of material. This study of test parameters and interlaboratory variability was undertaken as a necessary part of establishing an ASTM standard for such a test. Temperature of the test was found to be the most significant variable studied, and interlaboratory variation was relatively high when compared with the common 672 K test.
Progress in the Knowledge of Nodular Corrosion
Authors: Garzarolli F , Stehle H , Steinberg E , Weidinger H
Published: December 2008

Zircaloy in boiling water reactor (BWR) systems often exhibits, besides slight uniform corrosion, a nodular type of corrosion. Highest nodular corrosion was found with materials never β-quenched during their fabrication, whereas β-quenched materials generally showed an improved behavior. Results of nodule thickness measurements after increasing burnup were normalized by using a correlation w ∼ (BU)0.7 (w = average nodule oxide thickness, BU = burnup). The scatterband of the normalized data was different for different reactors. The statistical distribution was generally Gaussian with a tail at high values.

To find reasons for the material-inherent scatter of the in-pile corrosion behavior, archive samples were examined by electron microscopy and high-pressure steam tests. The latter led to a comparable ranking if the specimens were fully recrystallized before testing. The microstructural examinations indicate a correlation of the in-pile corrosion with the size distribution of the intermetallic precipitates and the spacing between the precipitates.

High-pressure steam tests have been used to identify the fabrication steps which influence nodular corrosion. According to these tests it is mainly the β-quenching treatment and all annealing or working steps in the upper α-phase range that have an influence.

Low nodular corrosion was achieved using quenching rates >5 K/s if the subsequent annealing stays in the low α-range. In the cold-worked condition, nodular corrosion in general was less pronounced. However, with respect to the in-reactor performance, no marked difference was found between stress-relieved and fully recrystallized cladding tubes.

For actual practice it is concluded that an appropriate β-treatment is needed and that temperature treatments of the material after its last β-quenching should stay within a range in which the distribution of the alloying elements is not affected unduly. Several in-pile programs are under way in cooperation with utilities to confirm the progress achieved.
Recent Studies of Crack Initiation During Stress Corrosion Cracking of Zirconium Alloys
Authors: Cox B , Haddad R
Published: December 2008

In order to study crack initiation, we had first to develop a technique for reproducibly obtaining large numbers of very small crack initiation regions. The previously used test methods of stressed split-rings or pressurized (or compressed) tubes gave low success rates. Specimens either showed through-wall cracks, or no cracks, with few incipient cracks being observed. This suggested that the propagation time was short compared with the incubation time. Attempts to overcome this by unloading specimens following the first acoustic emission signal still gave a low frequency of incipient cracks.

The possibility that an “active path” mechanism was the cause of the difficulties in obtaining incipient cracks reproducibly was investigated by a stress-pulse technique. The results were apparently consistent with an “active path” developing ahead of the crack tip, and cracking during the stress-pulse. Two iodine tracer techniques, one using radioactive 131I, the other using natural 127I (located by Rutherford backscattering), showed that iodine did not diffuse ahead of the crack tip. When specimens were not statically loaded, but merely given a stress-pulse, the results showed that the appearance of an “active path” mechanism resulted from the length of time taken for the chemistry inside the apparatus to reach a condition capable of initiating cracking. When the system was allowed to come to chemical and thermal equilibrium before the specimen was loaded, cracking started almost immediately (<2 min). This virtual disappearance of the incubation time with adequate equilibration of the apparatus was equally true for experiments in I2 or Cs/Cd vapours. It was concluded that, if the chemistry of the system could be rapidly equilibrated, there would probably be effectively no incubation time and cracking would start immediately.

Many small incubation sites were produced in these tests. No second-phase particles were seen at these sites in the SEM, and no local contamination of the initiation site was seen by energy dispersive X-ray analysis (EDAX). The initiation sites were individual grains (or small groups of grains) which fractured transgranularly to give a fractography otherwise identical with transgranular fracture surface produced during crack propagation in the bulk of the specimen. It was concluded that localized residual stresses, when added to the applied load, cause a few correctly oriented grains at the surface to crack immediately upon loading, given that the “correct chemistry” was present.

The presence of organic-iodine compounds (in particular methyl iodide) as impurities in the vapor phase was found to act as a promoter of crack initiation, giving a large increase in the frequency of initiation sites and an increase in crack velocity. Methyl iodide also gave a characteristic fractography which was explained as a modification of the propagation mode of the crack front.
The U.K. Approach to Dust Explosibility Assessment and Its Relevance to Explosion Prevention and Protection
Authors: Abrahamsen AR
Published: December 2008

Dust explosibility assessment in the United Kingdom is in a transitory period as traditional test methods based on the Hartmann apparatus become superceded by methods in line with European codes of practice.

The minimum explosible concentration is measured in the open Hartmann tube using a test method with severe drawbacks. Recent years have seen the use of a 15-L apparatus and the 20-L sphere as means of generating a dust cloud more representative of the industrial scale. The sensitivity to ignition of a dust cloud in relation to electrostatic hazards is represented by its minimum ignition energy. The corresponding test method is the subject of controversy in terms of the spark generating mechanism and various methods may be adopted to simulate a typical “industrial” spark.

Minimum ignition temperatures of dust clouds are measured in the Godbert-Greenwald furnace. However, this apparatus has the disadvantage of not having an independent ignition source to enable minimum explosible concentration or ignition energy measurements to be made at elevated temperatures. A 1.2-L furnace based on a U.S. Bureau of Mines design partly overcomes this problem.

The determination of explosion pressures and rates of pressure rise is essential for the optimum design of explosion protection systems. Methods for measuring these parameters have undergone radical change in recent years, and although the Hartmann bomb apparatus is still accepted in U.K. industry, its use nowadays is not recommended, the 1-m3 or 20-L sphere vessels being preferred.

The lack of a dedicated British Standard on dust explosibility testing is one of the reasons for the apparently confused attitude towards the subject which exists in many parts of industry. The use of a vessel, such as the 20-L sphere, to measure all dust explosibility parameters (except minimum ignition temperature) is strongly advocated to give data which can be reliably applied to full-scale situations, something which the small Hartmann tube cannot be expected to give.
Investigations into the Buildup and Development Conditions of Coal Dust Explosions in a 700-m Underground Gallery
Authors: Michelis J , Margenburg B , Müller G , Kleine W
Published: December 2008

To investigate the buildup and development of coal dust explosions, comprehensive tests were carried out in a 8-m2, 700-m-long explosion gallery at the Experimental Mine Tremonia. The majority of these tests were done with “Dortmund standard coal dust” (coking coal) with a mean particle size between 18 and 22 µm. The following test conditions were varied: length of the fuel zone, strength of primary initiation and secondary initiation, coal dust concentration, mean particle size of coal dust, and inert content of coal dust. The test results are discussed.
Review of Coal Pulverizer Fire and Explosion Incidents
Authors: Zalosh RG
Published: December 2008

Reports of 26 coal pulverizer fires and explosions are reviewed in order to elucidate causes and preventive measures. Most of the explosions occurred during pulverizer shutdowns or restarts. The most common ignition scenario involved coal dust accumulations in the mill spontaneously igniting and coming in contact with a flammable coal dust-air suspension during a mill shutdown or restart. Detection of spontaneous combustion by pulverizer outlet temperature alarms (and, to a lesser extent, carbon monoxide analyzers) has not been reliable. Improvements are needed in the detection of incipient mill fires and the effective use of inert gas purges to prevent destructive pulverizer explosions.
Recent Dust Explosion Experiences in the U.S. Grain Industry
Authors: Kauffman CW
Published: December 2008

After the explosions of December 1977 intense scrutiny was given to the occurrence of fires and explosions in grain handling and processing facilities in the United States.

The conditions leading to fires and explosions in these facilities—fuel, oxidizer, ignition, mixing, and confinement—had been identified immediately following World War I.

At the beginning of this decade the National Academy of Sciences investigated 14 explosion incidents, reported on the findings, and made recommendations concerning accident prevention. As the decade has progressed, however, these fires and explosions have continued with reports of investigations being available for some major incidents. The continuing critical factor in these explosions is the massive uncontrolled accumulations of fuel. In the effort to eliminate this industrial hazard, the U.S. Department of Labor has issued Draft Final Standards pertaining to safety hazards in grain-handling facilities. It is clear that it is technically feasible to eliminate fire and explosion hazards from the grain and agricultural products industry because these events do not occur as a result of unknown, unpreventable causes.
Grain Dust Probes—Calibration and Measurement
Authors: Rajendran N
Published: December 2008

In situ light attenuation and backscattering probes were designed, fabricated, and calibrated for monitoring the dust levels in grain elevators. The calibration was performed both in a dust cloud chamber using mixed grain dust and in an elevator facility with various types of grain. The true dust concentration was determined with an isokinetic sampling probe.
A Comparison of Lake Sediments and Ombrotrophic Peat Deposits as Long-Term Monitors of Atmospheric Pollution
Authors: Norton SA , Kahl JS
Published: December 2008

Ombrotrophic bogs receive all of their water and nutrients from the atmosphere. As such, these systems are potentially well suited to record the chronology and magnitude of atmospheric deposition of chemically nonmobile elements. Lakes receive focused material from their watersheds as well as directly from the atmosphere and thus may misestimate the atmospheric flux. Cores of profundal lake sediment and ombrotrophic peat from both a hummock and hollow were dated by Pb-210, utilizing the constant rate of supply (CRS) model, and analyzed for 13 major and trace elements. All cores, except the hollow, have yielded a pattern of increasing concentration of lead (Pb), zinc (Zn), and vanadium (V) since the mid-1800s. Net accumulation rates (NAR) over this period range from 0.1 to 5.0, 0.2 to 3.5, and 0.04 to 1.15 μg/cm2/year for Pb, Zn, and V, respectively, in the lakes. In the hollows, the values are 0.2 to 2.1, 0.1 to 0.86, and <0.01 to 0.11; in the hummocks, they are 0.2 to 4.1, 0.2 to 3.0, and <0.01 to 0.42. Actual atmospheric deposition rates are probably between the rates from the two sites in the bog. The possible overestimation of flux to lake sediment can be compensated for terrigenous input by normalization of trace metal flux to titanium dioxide (TiO2) flux. The adjusted ranges of atmospheric fluxes are 0 to 4.5, 0 to 2.4, and 0 to 0.4 μg/cm2/year for Pb, Zn, and V, respectively, in the lakes. The TiO2 normalization for peat chemistry is not a valid procedure, because the TiO2 content of peat is largely determined by atmospheric inputs that are erratic and that are large in relation to the background content. The large mineral TiO2 content of sediments results in a negligible atmospheric TiO2 signal in lake sediment.
General Analytical Chemistry of Beryllium
Authors: Hertz RK
Published: December 2008

A number of classical methods for the determination of beryllium are described in the literature. Gravimetric methods in which beryllium is weighed as the oxide or the pyrophosphate are employed for relatively pure materials, but careful separation of interfering elements is required. A useful volumetric method is based upon the precipitation of beryllium hydroxide, addition of fluoride to complex beryllium, and titration of the liberated hydroxide; but this method is also subject to many interferences. Spectrophotometric reagents, such as aluminon and p-nitrophenylazoorcinol, and fluorometric reagents, such as morin, have been used to determine beryllium: but for most applications atomic emission spectrometry and atomic absorption spectrophotometry have replaced these methods. The emission of neutrons by gamma-irradiated beryllium is the basis for a rapid, relatively interference-free beryllium analyzer, which requires minimal sample preparation and may be used for practically any matrix.
Quality Assurance in Metals Analysis Using the Inductively Coupled Plasma
Authors: Watters RL
Published: December 2008

The inductively coupled plasma (ICP) technique is a useful approach for multielement analysis of a wide variety of materials. Published reports have described the successful application of the ICP technique for the analysis of trace, minor, and major elements in metal alloys. When assessing the quality of analytical results using the ICP or any other technique, one must consider the contribution of various parts of the measurement process to the total error. In addition to random error, a careful evaluation of all possible sources of systematic errors must be undertaken, so that the appropriate corrections can be applied to the analytical results. Emission spectroscopists are well aware of the problems caused by spectral interferences in ferrous matrices. The inherent linearity of the ICP technique offers a correction scheme for dealing with spectral interferences, but the method of measuring correction factors and accounting for their variability warrants close examination.

Most descriptions of ICP applications report relative freedom from matrix effects. Although the magnitude of systematic errors may be less than for other spectrometric techniques, such errors can cause analytical bias, which can appreciably affect the final results. For example, it has been shown that differences in acid concentration between pure element standards and the sample can cause systematic error. This type of problem can occur when complex alloys are dissolved for ICP analysis. Examples of these kinds of errors and approaches to correcting for them are presented.
Damage Thresholds of Fused Silica, Plastics and KDP Crystals Measured with 0.6-ns 355-nm Pulses
Authors: Staggs MC , Rainer F
Published: December 2008

We used 355-nm, 0.6-ns pulses focused to a beam diameter of approximately 1 mm to measure the laser damage thresholds for surfaces of bare polished samples of several types of fused silica, for the bulk of crystals of potassium dihydrogen phosphate (KDP), and for a few plastics. Surface damage thresholds for fused silica ranged from 1–14 J/cm2, and were least for surfaces with residual subsurface polishing fractures. Thresholds for inclusion damage in KDP crystals were 2–4 J/cm2. Test volumes in these same crystals had thresholds from 2.5–7.0 J/cm2 when they were laser hardened by repeated subthreshold irradiation. FEP teflon films had thresholds of 3 J/cm2, which were the greatest threshold observed for a plastic.
Strengthening CsI Crystals for Optical Applications
Authors: Durand WW , Koepke BG , Gerberich WW
Published: December 2008

Cesium iodide (CsI) is a very useful optical material combining a low refractive index with broad spectral transparency. Unfortunately, the mechanical weakness of CsI crystals severely limits practical applicability of the material. Nearly all uses require mechanical strengthening. The strengthening treatment cannot, of course, degrade desirable single crystal optical properties. Previous work at Honeywell has involved strengthening of alkali halides having the rocksalt structure (KCl, NaCl, etc.). Processed materials have been strengthened by as much as an order of magnitude without measurable optical degradation. Direct application of these processing methods to the dissimilar structure of CsI is impossible due to the limited number of slip systems active in the material. This investigation was, therefore, concerned with development of CsI processing methods that would effectively strengthen the material without introducing cracks or other optically degrading defects. This paper describes successful uniaxial and plane strain processing methods. Detailed process parameters and strengthened CsI material properties are included.
Investigation of Window Materials for Repetitively Pulsed CO2 Lasers
Authors: Goela JS , Taylor RL , Lefebvre MJ , Price PE , Smith MJ
Published: December 2008

A need exists to develop infrared window materials for use on repetitively pulsed CO2 lasers. Data obtained on single pulse damage criteria at 10.6 μm may not be sufficient to determine the response of materials under repetitive illumination. The optical, mechanical and physical properties of all potential transmissive optical materials at 10.6 μm were collected and compared. From this list, 19 optical materials were selected for detailed analysis using a set of baseline laser parameters. This analysis included pressure induced optical distortion, fracture criteria and thermal effects from laser energy absorption. A set of figures of merit were developed for axial and planar stress due to temperature profiles in the material and optical distortion (thermal lensing). Maps were developed to demonstrate the influence of the assumed laser parameters on these figures of merit. It was shown that no one optical material met all figures of merit. The three best materials based on this analysis are CVD ZnSe, GaAs and Polytran NaCl. Samples of these materials were fabricated and tested on a REP-pulsed CO2 laser at fluences between 15–25 J/cm2 with pulse trains up to 20 pulses at 20 Hz.
Inherent Mechanical Damage in Diamond Machined Optical Surfaces
Authors: Hurt HH , Decker DL
Published: December 2008

The surface and near-surface regions in diamond machined Cu have been investigated by high resolution transmission electron microscopy, scanning electron microscopy, and scanning transmission electron microscopy. This study has revealed that the near-surface region produced by diamond machining is heavily deformed and that the temperature rise due to the deformation leads to interesting internal oxidation and dynamic recrystallization effects. Surface microstructure is shown to be related to the surface microtopography. A companion paper at this conference presents some correlation of this observed structure with optical properties of the surface including laser damage thresholds.
Surface Finish Measurements on Low-Scatter Laser Mirrors and Roughness Standards
Authors: Bennett JM , Guenther KH , Wierer PG
Published: December 2008

In assessing the surface quality of low-scatter laser mirrors, it is important to understand the advantages and limitations of various measurement methods. For example, values for the root mean square (rms) surface roughness may depend critically on the lateral resolution of the profile measuring instrument and on the surface spatial wavelength range sampled if the correlation lengths of the surface microirregularities are less than or equal to the instrumental resolution, or if appreciable long range surface waviness is present. If the surface roughness is deduced from a measurement of the total integrated scattering, the measurement wavelength, collection angles, and spatial wavelengths of the surface microroughness all have an effect. In the present study, several methods were used to measure the rms roughness of a group of samples which included low-scatter laser mirror substrates and additional samples of varying roughness, all partly coated with high reflectance dielectric multilayers and aluminum overcoatings. Measurement techniques and instruments included a diamond stylus surface profiling instrument (Talystep), Mireau heterodyne interferometer (Wyko), optical heterodyne profilometer (Lawrence Livermore National Laboratory), and total integrated scattering (Naval Weapons Center and Balzers). The roughness values thus obtained are compared and conclusions are drawn concerning the effect of the surface spatial wavelength range sampled and the instrumental lateral resolution.