bluuebunny/crossref_metadata_2025 huggingface dataset:
Special Calibration Systems for Reactive Gases and Other Difficult Measurements
Authors: Dorko WD , Hughes EE
Published: December 2008

The most popular method for determining a component of interest in a gas mixture is to use a detector that responds to the analyte and is calibrated directly with a cylinder gas mixture containing the analyte at the approximate concentration of interest. In many instances, however, this cannot be achieved; cylinder calibration mixtures may be unstable or the direct response detector may not be sensitive enough. The unstable cylinder mixture can be replaced by a dynamic dilution gas calibration system where the analyte can be introduced by any one of several means including permeation devices, or a higher concentration gas mixture that can be more easily stabilized. If the detector for the analyte is insensitive or difficult to calibrate, then the analyte can be converted to another compound for which there is a detector that is sufficiently sensitive and easy to calibrate.

In the case of analytical systems, such as gas chromatography, where separation occurs, a mixture of a stable gas can be used to calibrate for a reactive gas if the relative detector responses are known. There is no one particular way to either provide calibration mixtures for the analysis of all reactive gases or to provide a means for the determination of difficult compounds. Any system that will produce a mixture of the required concentration, of acceptable uncertainty, and of stability sufficient for the analysis at hand can be a special calibration system.
A Comparative Study of Dynamic Impact and Static Loading of One-Ply Roofing Assemblies
Authors: Koontz JD
Published: December 2008

In just the past few years, there has been industry-wide acceptance of the use of oneply roofing systems. This has basically involved three major groups: elastomerics, thermoplastics, and modified bitumens. The use of these different one-ply membranes over a variety of substrates has led to a virtual collage of roofing systems available on the market today.

The relative puncture resistance of these membranes, in conjunction with their substrates, has not been clearly understood. At present, several different methods of measuring static and dynamic puncture resistance are used by a variety of organizations, such as ASTM, the Canadian General Standards Board (CGSB), the European Union of Agrement (EUAtc), and various manufacturers.

This paper addresses some preliminary data relating to the dynamic and static puncture resistance of one-ply assemblies.
Coefficient of Expansion Values for Modified Bitumen Roof Membranes
Authors: Dupuis RM , Lee JW
Published: December 2008

A laboratory study was undertaken to determine the nature and the value of the coefficient of expansion for a wide variety of modified bitumen roof membranes. Tests were run from temperatures of 48.9°C (120°F) down to −40°C (−40°F) with observations being made at discrete temperature points. Regression analysis was used to establish a continuous curve for the coefficient of expansion values. This allowed for either tangent or secant coefficient of expansion values to be derived at any point (or between any two points for the secant coefficient) along the temperature range.

These data are provided as basic information on the possible range of variation in the coefficient of expansion for these materials. The range of coefficients presented in this paper has been found to be an important factor in evaluating design and performance standards for roof membranes using these sheets.
Thin Epitaxial Silicon by CVD
Authors: Fisher SM , Hammond ML , Sandler NP
Published: December 2008

Device applications for thin silicon epitaxy require sharp transition widths and uniform layers on wafers up to 200 mm diameter in production quantity. Uniform silicon epitaxy nominally 1 um thick deposited with transition widths of 0.2 – 0.3 µm over heavily doped buried layers using reduced pressure CVD technology are discussed. Both boron and arsenic buried layers can be accommodated in the 100 – 200 torr range. Thin selective epitaxy, with and without uniform polycrystalline silicon overgrowth on the oxide, is improved by reduced pressure deposition. Epitaxial lateral overgrowth is another technology based on thin epitaxy that is improved by reduced pressure CVD. Silicon-on-Sapphire requires very high growth rates at atmospheric pressure for very short times to achieve acceptable crystal quality. Some results for these thin epitaxy processes are reviewed.
Effects of Gettering on Epi Quality for CMOS Technology
Authors: Daniel Wong C-C , Borland JO , Hahn S
Published: December 2008

The quality of silicon epitaxial layer deposited on n+ substrates has been improved by applying a pre-epitaxial intrinsic gettering process to the substrates. The epilayer defect density was decreased, while the junction breakdown voltage and the product yield of 16K CMOS Static RAM were both increased. The bulk microdefects generated by the IG process were observed and believed to be the key to the quality improvement of epitaxial layer. The better quality of epitaxial layer deposited on heavily phosphorus doped substrates, compared to those deposited on heavily antimony doped substrates, was attributed to the microdefects formed close to the epi/substrate interface. Although the epi/substrate transition width of n/n+(P) is wider than that of n/n+(Sb), no significant difference in current gain of parasitic bipolar transistors has been observed.
Some Aspects of Productivity of a Low Pressure CVD Reactor
Authors: Middleman S
Published: December 2008

A mathematical model of a CVD reactor is presented, from which performance criteria such as deposition uniformity, and reactor productivity, may be obtained in terms of design and operating parameters. An example is presented in which the interwafer spacing, and the number of wafers to be processed as a single batch, are determined to maximize productivity while maintaining a constraint on uniformity.
The Bonding Structure and Compositional Analysis of Plasma Enhanced and Low Pressure Chemical Vapor Deposited Silicon Dielectric Films
Authors: Nguyen SV , Abernathey JR , Fridmann SA , Gibson ML
Published: December 2008

Silicon dielectric films such as silicon nitride, oxide and oxynitride films deposited by Plasma Enhanced and Low Pressure Chemical Vapor Deposition (PECVD and LPCVD) processes were analyzed and compared using Fourier Transform Infrared (FTIR), X-ray Photoelectron, Auger, Electron Spin Resonance Spectroscopies and Nuclear Reaction Analysis for hydrogen. The plasma deposited films exhibit a more random structure with less long-range order and contain more hydrogen as compared to those of LPCVD films. However, marked similarities were observed in the bonding and its variation in films deposited by both processes. Analysis data indicates that the silicon oxynitride films (RI-1.75–1.78), deposited by both processes, may be the most stable oxynitride where mixed silicon oxynitride tetrahedral N2-Si-O2 bonding structures are most abundant.
Influence of X-Ray Exposure Conditions on Pattern Quality
Authors: Starov V
Published: December 2008

We have examined the relationship between x-ray resist sensitivity, spectral characteristics of the x-ray sources, and resist absorption coefficient with respect to our ability to control feature size in x-ray lithography. We have derived an expression relating these properties to the edge-definition quality by estimating the mean distance between the adjacent photon absorption events. It is shown that to ensure feature-size control to 0.05µm necessary to achieve 0.5µm minimum feature size, x-ray resist sensitivity should be no greater than 8 mJ/cm2 if conventional x-ray sources are used for exposure. The effect of a controlled exposure ambient [1] on edge definition is also demonstrated and discussed.
Palladium Silicide Contact Process Development for VLSI
Authors: Singh RN
Published: December 2008

A process for forming self-aligned small-area palladium silicide ohmic contacts to shallow junction silicon is described. A number of processing steps such as thin-film deposition, thermal annealing for silicide formation, and etching of unreacted palladium are developed in conjunction with modern materials characterization techniques such as SEM, SIMS and RBS. The results indicate that palladium films of ≤500A thickness have good adherence to silicon and silicon dioxide. The metal-rich, dense, and continuous Pd2Si readily forms on reaction of silicon with palladium upon thermal annealing. The siliciding reaction disrupts the native oxide and forms an intimate silicide-silicon interface. Unreacted palladium is etched in an aqueous etching solution, but extreme care is necessary to avoid palladium oxide formation during annealing, which leads to etching difficulties. Based on these results an optimum palladium silicide contact process for VLSI is proposed. Excellent contact resistance values between 11 and 25Ω are obtained for palladium silicide contacts of 1.25µm diameter using the optimum process.
Effect of Bulk Defects in Silicon on SiO2 Film Breakdown
Authors: Suga H , Murai K
Published: December 2008

The origins of degrading the dielectric breakdown strength of silicon dioxide on silicon were analysed by controlling surface and bulk lattice defects and back side damage. As a result, two different mode of breakdown were observed. One is caused by lattice defects emerging on the silicon/silicon dioxide interface, but the degree of degradation in breakdown strength was only as much as 1 MV/cm. The other is due to low density of point like contamination. This kind of contamination was controlled with the gettering by lattice defects nearby the surface region.
Some Aspects of Spreading Resistance Profile Analysis
Authors: Albers J
Published: December 2008

The calculation of resistivity profiles (and carrier density profiles) from spreading resistance requires the use of a correction factor. The present status of the calculation of the correction factor based upon the Schumann and Gardner multilayer solution of Laplace's equation is reviewed and discussed. Recent calculations of carrier densities from atomic densities are also discussed. In particular, the numerical solutions of the semiconductor equations are reviewed and their implications in the interpretation of spreading resistance measurements for profiling shallow layers are presented. The limitations of the multilayer Laplace equation analysis of spreading resistance in VLSI profiling are also discussed.
Applications of x-ray Fluorescence Analysis to the Thin Layer on Silicon Wafers
Authors: Shiraiwa T , Ochiai T , Sano M , Tada Y , Arai T
Published: December 2008

Thin layered materials on silicon wafer were analyzed with X-ray fluorescent spectrometer which is specially designed for the analysis of semiconductor devices. The spectrochemical analysis using hard X-rays (22Ti - 92U) can be applied to the thicker layered materials (0.5 – 50µm). By soft and ultrasoft X-rays (5B - 21Sc), thinner layered materials (0 – 2µm) can be analyzed for the determination of concentration of layered material and film thickeness. In analysis of SiO2 Layer, the intensity of O-Kα X-ray was measured and the thickness was calculated by the theoretical approach. The precision of measurement is a few percent and it can distinguish the difference of natural oxide according to the cleaning method. Other experimental results of typical silicon wafer samples are informed; which are the analysis of NSG, PSG, BPSG, metal and alloy films, and As or P implanted elements.
Illinois' Experience with Cement Strength Uniformity
Authors: Oglesby JR
Published: December 2008

The development of a cement strength uniformity requirement for the Illinois Department of Transportation's portland cement acceptance program is presented. The Department's historical test data indicate that while cement manufacturers have little difficulty producing cement meeting the minimum strength requirements of ASTM Specification for Portland Cement (C 150-85a), there is significant seasonal variation in strength for some manufacturers. Although cement strength variability is but one factor affecting concrete performance, it becomes of considerable practical importance in the design of economical concrete mixes. To determine the ability of manufacturers to produce cement of uniform strength, ASTM Method for Evaluation of Cement Strength Uniformity from a Single Source (C 917-82) test data was requested from each manufacturer furnishing cement to Illinois. Information on standard deviations, coefficients of variation, and 7- and 28-day average strengths is presented. The test information was studied, and a uniformity requirement was proposed wherein the manufacturer would submit 7- and 28-day strength levels at which he proposed to furnish cement, and control limits would be used to detect significant changes in the process average or variability. Information on standard deviations, coefficients of variation, and plots of average strengths are presented and compared to test information received before enforcement of the uniformity requirement. To verify test data reported by the manufacturer, split portions of selected ASTM C 917 samples are tested by the Department. Data obtained from these samples are also evaluated to determine differences in testing between the manufacturer and Department laboratories. The t-statistic is used to test whether the mean differences are significant. Data obtained are tabulated and presented. Results indicate that cement manufacturers are capable of furnishing cements which the user can be confident will vary in strength between known limits in the long run.
Detection of Inherent Heterogeneities in Cement Strength Records by Means of Segmentation
Authors: Taerwe LR
Published: December 2008

Five series of cement strength data are analyzed by means of an appropriate segmentation technique, which makes it possible to detect inherent heterogeneities hidden in these records. This heterogeneous aspect follows from the fact that the mean strength level presents a step-wise variation in time, rather than a continuous one. It is indicated that the variation of the mean value of the segments contributes significantly to the total variance of the strength records. Finally, it is mentioned that a similar model is applicable to concrete strength records.
Variability of Cement Strength in Saudi Arabia
Authors: Taryal MS , Chowdhury MK
Published: December 2008

The variability of cement strength depends mainly on the method of test and on the quality control of the cement production. Process changes, particularly in burning and cooling, may significantly alter the crystal structure and the strength development [8]. This study was conducted to determine the variation in cement strength due to variation in the test procedures adopted in Saudi standards as compared with other standards, and to study the variability of cement strength due to quality control of production in the individual company as well as between the eight cement companies of Saudi Arabia. The periodical cement samples from the cement companies were tested for fineness and compressive strength. The test data were analyzed statistically, and this shows the frequencies and sizes of apparent changes in process parameters such as mean, standard deviation, and coefficient of variation [10]. The quality of cement produced by individual companies is uniform and satisfies the minimum requirements according to Saudi Standard SSA 143/1979 and ASTM Specification for Portland Cement (C 150-85a), although there are different grades of production among the cement companies. The results reported in this study revealed the apparent quality and variability of cement strength in Saudi Arabia.
Corrosion of Steel and Zinc in Scandinavia with Respect to the Classification of the Corrosivity of Atmospheres
Authors: Kucera V , Haagenrud S , Atteraas L , Gullman J
Published: December 2008

Exposure of steel and zinc specimens at 32 test sites in Scandinavia shows that the pollution by sulfur dioxide (SO2) and by chlorides in marine locations is of decisive importance in the corrosion attack. The differences in the corrosion rate at the six rural sites in Southern Scandinavia are very slight despite substantial variations in other environmental parameters. Dose response relations for the corrosion attack on steel and zinc, including SO2 concentration, chloride deposition rate, and time of exposure have been developed. The results may serve as a basis for a quantitative description of corrosivity classes in systems for classification of the corrosivity of atmospheres of the type which is now under development by the International Standardization Organization.
Closed System Acceptance and Use in California
Authors: Rutz R
Published: December 2008

In 1974 the California Department of Food and Agriculture (CDFA) adopted regulations pertaining to the safety of employees handling pesticides for agricultural uses and entering fields that might have pesticide residues. The regulations mandated that closed systems be developed for handling toxicity Category One liquid pesticides. While the regulations contained a general definition of closed systems, more specific criteria were not developed until some time later. The requirement for use of closed systems has been in place for several years, and debate continues over their usefulness. This paper reviews the development of California closed system criteria and the implementation problems encountered.
A System for Examination of the Pesticide Dose Transfer Process
Authors: Hall FR , Reichard DL , Alm SR
Published: December 2008

In an attempt to better understand the interaction of drop size, distribution, and dosage on the efficiency of the pesticide dose transfer process, a system for generating uniform drops in various distribution patterns was developed. The system comprised a uniform droplet generator, with a variable speed conveyor to transport leaf disks or fruit samples, a photographic and fluorometric analysis unit, and a computer image analysis device for characterizing of spray droplet distributions. In addition, a video technique was utilized to record pest behavioral responses to droplet concentration and distribution parameters. The results of some initial studies are reported and ranges of potential uses described.
Effect of Application Rate on Droplet Size Spectra and Deposit Characteristics of Dimilin® Spray Mixtures in an Aerial Spray Trial
Authors: Sundaram A , Retnakaran A , Raske AG , West RJ
Published: December 2008

The wettable powder formulation of diflubenzuron, Dimilin® WP-25, was aerially sprayed as an aqueous suspension over four 15 ha plots in conifer forests in Newfoundland using different volume and emission rates of application. A Piper Pawnee aircraft equipped with six Micronair® AU5000 atomizers delivered the spray mixtures. Plot P9-35/4.7 was treated with 35 g active ingredient (AI) in 4.7 L/ha, plots P10-70/4.7 and P16-70/4.7 with 70 g AI in 4.7 L/ha, and plot P11-30/2.0 with 30 g AI in 2.0 L/ha. The first three plots were each sprayed at an emission rate of 48.13 L/min, the fourth plot at 20.48 L/min. Spray droplets were sampled with Kromekote® cards to determine the size spectra of the spray cloud reaching the ground level. The use of a tracer dye, Erio Acid Red, facilitated droplet measurements on the sampling cards. Glass plates were used to collect deposits of the tracer dye for colorimetric determination of the percent recovery of the spray volume emitted.

The higher emission rate of 48.13 L/min used in plots P9-35/4.7, P10-70/4.7, and P16-70/4.7 resulted in large droplets, higher droplets/cm2, and greater recovery of the applied spray volume at ground level. The lower emission rate of 20.48 L/min used in plot P11-30/20 to accommodate the lower application rate resulted in smaller droplets, lower droplets/cm2, and a smaller percent recovery of the spray volume on glass plates. The smaller droplets have a tendency to linger longer near the forest tree canopy, increasing the chance of impaction on the conifer needles. The lower application rate might provide a better target coverage at canopy level, with minimum ground contamination, and warrants further field testing. The relationship between rate of application and deposit characteristics of Dimilin WP-25 is discussed.
Herbicidal Root Control in Sewer Lines Requires Unique Application Techniques
Authors: Cummings GL
Published: December 2008

Root intrusion into sewer lines creates a variety of problems. Herbicides have advantages in controlling roots, particularly in providing residual control. However, unique problems occur in applying herbicides in sewer lines. The problems and solutions will be demonstrated by tracing the evolution of the Vaporooter® product line through spraying, soaking, and foaming techniques.
Production of Granular Products by Roll Compaction
Authors: Johnson CE
Published: December 2008

Particle size enlargement of powders has become a very important process variable. A number of physical properties of powders can be altered to meet specific needs by changing particle size and bulk density.

Roll compaction is a method of agglomeration which offers some unique advantages: 1. High volume production of granules from 0.2 to 6 mm in size. 2. Controls bulk density and flow properties within the limits of the material. 3. Low consumption of energy. 4. Minimum labor requirements.

This paper discusses evaluation of powders and the elements of compacting machine designs.
Silicon Slice Fracture Analysis
Authors: Dyer LD
Published: December 2008

Slice fracture problems can occur in a host of bare slice and patterned wafer fabrication processes. Some knowledge of how to diagnose the source of the fracture can aid in timely response to such problems. The purpose of this paper is to describe some of the tools and the techniques for analyzing silicon slice fractures. Included are: 1) a review of fracture markings in silicon similar to those in glasses and ceramics, plus a new marking that appears on crystalline fracture surfaces, 2) a description of inspection techniques and equipment and, 3) mention of some simple testing techniques. Examples are given of the use of markings and techniques in deducing probable causes of fracture and in enhancing process development in wafer fabrication.
Dry Etching of Ion Implanted Silicon: Electrical Effects
Authors: Heddleson JM , Horn MW , Fonash SJ
Published: December 2008

In this paper we examine the effect of dry etching on p-type and n-type material implanted with 11B+ at 100 keV to doses of 1E12, 1E13, 1E14, 1E15, and 1E16 cm−2. Hydrogen-containing etch chemistries and typical etch parameters are simulated by Ion Beam Etching with 100% deuterium. We show that for deuteration of 1E12 and 1E13 cm−2 11B+ implants into p-type material, deep deactivation, as is observed for unimplanted material, is suppressed but still observed. Deuteration of the same low dose 11B+ implants into n-type material expose two important results. The first is that hydrogen preferentially “pairs” with boron in a compensated n-type environment. The second is that hydrogen deactivates boron acceptors not only in the absence of free holes but even when the Fermi level is near the conduction band edge.
Reaction Mechanisms and Rate Limitations in Dry Etching of Silicon Dioxide with Anhydrous Hydrogen Fluoride
Authors: Clements LD , Busse JE , Mehta J
Published: December 2008

A novel dry etching process for silicon dioxide has been developed. This process, carried out at ambient temperature and pressure, uses anhydrous hydrogen fluoride, water vapor in a nitrogen carrier, and a unique processing sequence to achieve etch rates of about 200A/second, with 5 percent or better uniformity.

The overall reaction is a complicated sequence of surface hydration and surface fluorination by adsorption, reaction, and product desorption. This paper presents two proposed reaction mechanisms and describes how experimental data from a laminar flow reactor were used to evaluate the mechanisms.
Parameters Controlling Counting Efficiency for Optical Liquid-Borne Particle Counters
Authors: Lieberman A
Published: December 2008

Present-day optical liquid-borne particle counters (OPCs) present data in digital format, frequently accepted as absolute by many users. However, counting efficiency of these devices is affected by instrument design, performance and operation. This discussion summarizes some of the pertinent parameters affecting OPC accuracy, explains effects on data and indicates means of maximizing OPC efficiency. Operation of OPCs using light extinction or scattering is described, including discussion of the pertinent optical parameters. Effects on OPC response are summarized, considering the relationships between the optical properties of the calibration material and typical contaminants with those of the liquid. It is shown that as OPC response varies with differential refractive index, then particle counts for polydisperse materials will also change.
A Correlation Study of Aluminum Film Wet Etch Uniformity with the Sputter Etch of Oxide Films
Authors: Dumesnil FM , Bruner M , Berman M
Published: December 2008

Recent research in the fabrication process of sputtered aluminum (30 ppm silicon) films for device interconnection shows a correlation between the ability to wet metal etch the film in a uniform manner, and the surface reflectance of the film. Aluminum grain notching of patterned metal lines causing subsequent open device circuits is shown to be related to the amount of residual gas incorporated into the metal film. Reflectance measurements of the deposited aluminum films exhibit lower values of reflectance for films that incorporate residual gases. Low reflectance films show a greater degree of metal grain notching than those of higher surface reflectance when wet metal etched. Removal of the sputter etched by-products from the aluminum deposition is necessary to avoid residual gas incorporation. Two methods are successful in increasing the aluminum reflectance as well as minimizing metal line width grain notching. These two methods are described and compared in their ability to optimize the uniformity of metal wet etching.
VLSI Defect Detection, Classification, and Reduction from In-Process and Post-Process Sram Inspections
Authors: Parks HG , Logan CE , Fahrenz CA
Published: December 2008

As device dimensions shrink to the order of one micron and chip sizes approach 100mm2, containing more than 105 transistors, some of the standard yield enhancement practices lose effectiveness. In particular, in-process inspections suffer as it becomes increasingly probable that defects will not be detected due to the reduced circuit dimensions and increased pattern complexity. Another area hard hit is post process probe yield failure analysis. With the greater number of components and functions per chip extremely large vector sets (thousands) must be run to adequately characterize and isolate failures at probe test. This results in long test times as well as a significant increase in the time required for data analysis to isolate circuit failures. Adoption of a static RAM (SRAM) as a yield vehicle can reinstate the effectiveness of both of these techniques for VLSI. The repetitiveness and regularity of the RAM pattern facilitates visual inspection, even at the micron level, and bit mapping provides easy test isolation of defects at post process probing. The application of a SRAM in a VLSI yield enhancement strategy for defect classification and reduction is discussed in this paper.
Process - Induced Influence on the Minority — Carrier Lifetime in Power Devices
Authors: Khanna VK , Thakur DK , Jasuja KL , Khokle WS
Published: December 2008

Carrier lifetime has been studied as a function of process conditions for power semiconductor devices. The lifetime measurements have been done to see the influence of minority-carrier lifetime on device characteristics under different process conditions such as KOH etching, DI water rinse, deep diffusions, thermal oxidation, phosphorous diffusion and gold diffusion. Open Circuit Voltage Decay (OCVD) and Surface Photovoltage (SPV) techniques have been used to measure minority-carrier lifetime.

It has been observed that the starting-wafer lifetime tends to change strongly during the course of fabrication processes and shows a dependence on the injection level. The typical curves show two-fold effects : (i) The effect of traps and (ii) The carrier density. The injection-level dependence of lifetime is attributed to heavy-doping effects in silicon, and in the absence of traps, is described by an empirical relationship.
Optimum Polysilicon Deposition on Wafer Backs for Gettering Purposes
Authors: Borionetti G , Domenici M , Ferrero G
Published: December 2008

Polysilicon deposition process parameters have been addressed for the preparation of poly layers having characteristics that increase extrinsic gettering behaviour, irrespective of oxygen enhanced precipitation, thus making them particularly suitable for relatively high device processing temperatures.

Morphological parameters that correlate with extrinsic gettering efficiency have been found to be grain sizes and their preferred orientation, so care was given to produce and consistently reproduce such characteristics by a suitable choice of the deposition process parameters.
Zirconium Activities in Europe: 1945–1984
Authors: Syre RP
Published: December 2008

The production of nuclear-grade zirconium sponge and the fabrication of zirconium-base alloys have been considered vital in some European countries, because of the need for zirconium independence for military (atomic bomb) or economic (nuclear power plant) reasons. This paper describes the various steps of this scientific and industrial development, mainly from 1950 to 1984, in which mostly the Federal Republic of Germany and France were involved. The important improvements brought by Europe to the basic processes are pointed out, and the present status of the European zirconium industry is described.
Long-Term Corrosion and Deuterium Uptake in CANDU-PHW Pressure Tubes
Authors: Urbanic VF , Cox B , Field GJ
Published: December 2008

Recent examinations of cold-worked Zircaloy-2 and cold-worked Zr-2.5Nb pressure tubes from CANDU-PHW reactors have extended the corrosion and deuteriding data for these materials up to 5600 effective full power days (efpd), the longest published exposure for these materials in reactor. The examinations have demonstrated that short-term tests to investigate irradiation and water chemistry effects must be supplemented by extended exposures in order to better understand the long-term corrosion and deuteriding behavior of zirconium alloy components with thick oxide films.

In-reactor corrosion and deuteriding of Zircaloy-2 was found to accelerate with time once the oxides exceeded a critical thickness of 15 to 20 µm. Radiolysis within these thick porous oxides, leading to a highly localized water chemistry near the metal-oxide interface, independent of the bulk water chemistry, is suggested as the probable explanation for the acceleration in kinetics. In conformance with this hypothesis, Zircaloy-2 pressure tubes developed large maxima in oxide thickness and deuterium concentration towards the outlet end where the combined effect of neutron flux and temperature was most severe.

Corrosion of Zr-2.5Nb tubes with a similar operating history was about one third that for Zircaloy-2, with no evidence of accelerating kinetics under normal operating conditions. Deuterium uptake was remarkably low, being 2 to 4% of that measured for Zircaloy-2. After 3500 efpd irradiation, the average deuteriding rate in Zr-2.5Nb tubes was only 1.5 mg/kg per year.

The observations are discussed in terms of the current understanding of corrosion and deuteriding processes.
Development of a Sensitive and Reproducible Steam Test for Zircaloy Nodular Corrosion
Authors: Cheng B , Levin HA , Adamson RB , Marlowe MO , Monroe VL
Published: December 2008

The sensitivity and reproducibility of high-temperature, high-pressure steam tests for Zircaloy nodular corrosion were studied as a function of test parameters, such as temperature, pressure, test duration, and flow rate, using a recirculating autoclave loop. Other variables, such as heat-up rate and oxygen and hydrogen gas contents, were also studied.

The effects of the test variables and gaseous species on test reproducibility are minimized by the addition of a prefilming step at 410°C for 4 to 8 h before exposing the test samples to a higher nodule-forming temperature. The prefilming treatment reduces the degree of nodular corrosion, but the reduced nodule sensitivity can be regained by controlling the second-step test temperature. A test involving a prefilming step at 410°C/1500 psig (102 bars) for 8 h and a nodule sensitivity step at 510°C/1500 psig (102 bars) for 16 h has been found to be capable of reproducibly discriminating Zircaloy cladding source materials into a broad spectrum of nodular corrosion susceptibility. Good reproducibility of the 410/510°C two-step test was demonstrated over 40 test runs using control samples. The two-step test was calibrated to in-reactor corrosion performance using pretested samples and irradiated plenum samples removed from fuel rods.
Mechanistic Studies of Zircaloy Nodular Corrosion
Authors: Cheng B , Adamson RB
Published: December 2008

The effects of alloy chemistry and thermal processing on corrosion performance of Zircaloy are shown to provide significant insights into the mechanisms governing nodular corrosion formation. Nucleation and growth behavior of nodular oxide in ex-reactor and in-reactor tests were studied phenomenologically, with the results suggesting that the behavior is similar in both environments. The sites of nodular oxide nucleation were found not to be at large precipitates or grain boundaries; rather, the sites were identified, though not unambiguously, to be free of precipitates.

Zircaloy-2 and Zircaloy-4 show significant differences in response to heat treatment in the high alpha phase region; only Zircaloy-2 shows improvement in nodular corrosion resistance. Both alloys, however, become highly resistant to nodular corrosion after receiving heat treatment in the alpha-beta or beta phase fields at temperatures above 830°C. Both the high alpha annealing improvement of Zircaloy-2 and alpha-beta or beta annealing improvement of Zircaloy-2 and -4 are attributed to a redistribution of solute elements into the Zircaloy matrix.

A nodular corrosion mechanism based on local solute depletion and its effects on the stoichiometric structure of the initial black oxide is proposed.
Influence of Variations in Early Fabrication Steps on Corrosion, Mechanical Properties, and Structure of Zircaloy-4 Products
Authors: Charquet D , Steinberg E , Millet Y
Published: December 2008

Variations in fabrication schedule, beta quenching, extrusion temperature, and intermediate and final annealing were performed in order to study the influence on workability of tube shells and technological properties of final cladding tubes. The mechanical properties of the final tubes depend on the final heat treatment and slightly on the first steps of the fabrication sequence, leading to small differences in the grain size. In addition, the nodular corrosion resistance was investigated. The nodular corrosion sensitivity of the recrystallized cladding tubes points out the influence of the early fabrication steps: The increase of the alpha annealing temperature in any fabrication step is detrimental. Among the tubes tested in this program those with the best nodular corrosion resistance in the high-pressure steam test had the worst behavior using ASTM Practice for Aqueous Corrosion Testing of Samples of Zirconium and Zirconium Alloys (G 2). During the ASTM G 2 test the weight gain of the external surface of the tubes was higher than the weight gain of the internal surface.
Influence of the Initial Material Condition on the Deformation Behavior of Zircaloy Cladding Tubes in the High-α-Phase Region
Authors: Ortlieb E , Cheliotis G , Weidinger HG
Published: December 2008

The influence of the initial material condition on the deformation behavior of Zircaloy cladding tubes at 600 and 800°C is systematically investigated by closed end creep rupture tests and transient burst tests in air. At 800°C the strain rate of the cladding tube diameter can be described by the Norton creep equation ˙ε = Aσn exp(− Q/RT) with a constant structure parameter A, stress exponent n, and activity energy Q. The structure parameter A depends on the normalized initial stress σ0/G(T) (σ0 = initial stress; G(T) = temperature-dependent shear modulus) and the initial material condition of the cladding characterized by the yield stress at 400°C and the degree of cold work during the final rocking step.

At 600°C nonstationary creep behavior is reported for the as-cold-worked and partly recrystallized material condition. The Norton creep equation can be maintained with the same constants n and Q if a time-dependent structure parameter is assumed. As a result, the structure parameter A(t) can be written as a function of (1) the “extended normalized annealing time” K(ϕ, t, T), which describes the influence of cold work ϕ, annealing time t, and temperature T on the degree of recrystallization, and (2) the creep deformation represented by the normalized true tangential stress σ(t)/G(T) of the cladding tube sample: 1A(t)−AminAmax−A(t)=a[σ(t)G(T)K(ϕ,t,T)]b where Amin, Amax = empirical minimum and maximum values of A, respectively, and a, b = empirical constants, depending on the degree of cold work.

The analytical treatment is extended to temperature transient processes by using in Eq 1 an effective temperature instead of the actual temperature. The empirical equation (1) together with the Norton creep equation enable the description of the strain rate history of a Zircaloy cladding tube in the temperature range between 600 and 800°C and the dependency on the initial material condition.
Cyclic Behavior of Zircaloy-4 at Elevated Temperatures
Authors: Armas AF , Alvarez-Armas I
Published: December 2008

The object of the present work is to study the load and strain cyclic behavior of Zircaloy-4 in the temperature range 573 to 873 K. Load cyclic tests are performed at 673 and 873 K for different values of R = σmin/σmax, keeping σmax and the load rate constant at each temperature. At 873 K the lifetime and the cyclic creep rate show a time-dependent behavior, with the mean strain being activated by the mean stress. For zero values of the mean stress (R = −1) no appreciable net strain accumulation occurs and failure by fatigue precedes failure by cyclic creep. At 673 K the mean strain is activated by the mean stress only in the range 1 > R > 0. In the 0 > R > −1 range the cyclic creep becomes faster on decreasing the mean stress up to some R value between −0.9 and −1. This effect is consistent with a dislocation model where the substructure formed in tension is unstable when the loading direction is reversed.

Strain-controlled cyclic tests with a total strain rate of 0.01 and a strain rate of 2 × 10−3s −1 are also carried out in the range 573 to 873 K. The peak tensile stress response during strain cycling shows a cyclic hardening behavior in the range 623 to 823 K. In the region 673 to 743 K this effect is more prominent and the hysteresis loops are nearly independent of temperature and strain rate. This phenomenon and the well-defined cell structure observed by transmission electron microscopy are attributed to strain aging. Below and above this temperature region (at 573 and 873 K) the total stress range remains approximately the same after a few cycles up to near fracture. The dislocation structures observed at both temperatures are consistent with the lack of cyclic hardening or softening.
A Differentiated Approach to Sizing of Dust Explosion Vents: Influence of Ignition Source Location with Particular Reference to Large, Slender Silos
Authors: Eckhoff RK
Published: December 2008

The rate of heat generation during combustion of a dust cloud in a vented industrial enclosure is influenced by several factors, including some that are entirely dependent on the actual industrial process. The key role played by the location of the ignition source in relation to the vent opening is emphasized. Recent experiments in a top-vented 236-m3 silo of length/diameter (L/D) = 6 revealed that the maximum explosion pressure increased by almost two orders of magnitude, with ignition at the silo bottom as opposed to at the top. The need for a new differentiated approach to dust explosion vent sizing is emphasized. In future, simple, general nomographs and formulas will have to be replaced by methods tailoring the vent to suit each specific application within an overall context of risk assessment. The lack of correlation between explosion violence predicted by existing closed bomb tests, and explosion violence in realistic full-scale experiments also calls for a differentiated approach to the violence testing problem.
A Multidecade Trend-Monitoring Program for Chesapeake Bay, A Temperate East Coast Estuary
Authors: Mountford K , Mackiernan GB
Published: December 2008

In the past two decades, Chesapeake Bay has experienced apparent increasing periods of deep water anoxia, poor spawning success by anadromous fish species, and unprecedented declines in submerged aquatic vegetation. These changes coincide with increased loading of nutrients and toxic materials from the surrounding 109 219 km2 drainage basin, which is experiencing significant changes in land use and population density. Concern by basin governments and citizens led ultimately to the establishment in 1984 of a 167-station monitoring network reporting to a common data bank. This program is designed to operate for at least 1.5 to 2 decades and to define trends in Bay water and sediment quality during that period. Twenty water and sediment quality parameters are monitored 20 times per year in the main stem and principal tidal tributaries. Collections link with studies of sediment organics, toxics, benthos, phyto- and zooplankton, and commercially harvested species. Data for 1984 indicate that large riverine inflows produced intense water column stratification and unusually widespread anoxia in the Bay main stem, but mixing events and wind forcing may temporarily reduce severity and promote reaeration. Early data sets indicate pulses of nutrient input into the estuary, nutrient regeneration in subpycnoclinal water, phytoplankton response to nutrients, as well as instances of potential nutrient limitation.
Gas Chromatographic Residue Patterns of Toxaphene in Fish Samples from the Great Lakes and from Rivers of the Southeastern United States
Authors: Petty JD , Schwartz TR , Stalling DL
Published: December 2008

Residues of environmentally derived toxaphene were determined in fish samples from the Great Lakes and from rivers of the southeastern United States. These analyses were performed by fused silica capillary gas chromatography with electron capture detection. Data reduction and compilation were performed using an “in-house” developed data base system. In an effort to more clearly delineate the similarity of environmentally derived toxaphene residues to technical toxaphene, SIMCA, a principal components pattern recognition technique, was used to analyze sample residues. The results of these analyses are discussed.
Rapid Dissolution of Steel Industry Materials for Chemical Analysis
Authors: Bhargava OP
Published: December 2008

This paper describes a rapid, simple technique for solubilizing a wide range of materials such as ores, sinters, slags, ferro-alloys, and other reagents and additives used in integrated steel making operations including environmental dusts and particulate matter. The procedure involves fusion of the specimen with sodium peroxide, or with a sodium peroxide-sodium carbonate mixture in a zirconium or virtreous carbon crucible. Treatment of the fused melt with water and acid yields a clear solution. It avoids the tedious operations involved in solubilizing residues left by other dissolution techniques. Losses of normally volatile elements, such as arsenic, phosphorus, lead, and zinc, do not occur. Solutions obtained by this procedure may be analyzed by a wide range of methods (for example, atomic absorption spectroscopy, photometry, redoximetric, or complexometric titrations or gravimetry) for such elements as aluminum, arsenic, calcium, chromium, copper, iron, magnesium, phosphorus, manganese, lead, titanium, vanadium, and zinc, at concentrations from trace to major. Numerous examples of methods developed employing the dissolution technique are cited, with data on accuracy and precision, to demonstrate the wide range of usefulness of the technique. Combined with automated instrumental methods such as DC and inductively couple plasma spectrometers for solution analysis, this procedure offers an attractive alternative to purely physical methods of analysis, which are often subject to matric interferences.
Applications of Automatic Titration Instruments in the Specialty Metals Industry
Authors: Dulski TR
Published: December 2008

Classical volumetric analysis remains an essential service in the modern specialty alloy industry, but now a new generation of automatic titrators can remove some of the tedium and operator-skill factors associated with the technique. Carpenter Technology's recent experience with two commercial instruments is described. The new titrators allow high-speed closed-loop electronic control of potentiometric redox or acid-base titrations in any of several fixed-endpoint or endpoint-seeking modes. Major modification of the basic chemistry of manual titration procedures is usually not required to adapt them to the automatic equipment, although sometimes minor changes are necessary. Applications for the determination of major levels of chromium, vanadium, boron, and cobalt in highly alloyed materials have demonstrated that, when properly configured, these instruments can routinely meet or exceed the performance data for the equivalent manual method in skilled hands.
Interdependence of Chemical and Instrumental Methods of Analysis
Authors: Kallmann S
Published: December 2008

Chemical methods of analysis are inherently more precise than purely instrumental methods. With the exception of trace metal determinations chemical methods are also more accurate than instrumental methods and have a wider range of application, since final measurements are absolute and do not depend on the availability of standards. The main disadvantage of the classical chemical approach is the length of time required to carry out the analysis.

It will be shown in this paper that chemical methods of analysis can be greatly simplified, and their application range enhanced by incorporating into the procedure various instrumental features. The instrument allows the analytical chemist to (1) examine filtrates for solubility products, (2) avoid reprecipitations by determining specific contaminants by instrumental means, and (3) act as final measuring device, after removing matrix elements by selective or specific separations such as ion exchange, solvent extraction, and precipitations. While the interdependence of chemical and instrumental methods is demonstrated in this paper to be particularly striking in the case of precious metal analysis, an area the author has been concentrating on during the last 15 years, examples of the applicability of the “interdependence” theme to base metal analysis are also provided.