Excessive Void Research Articles

The role of defects on the electrochromic response time of sputter-deposited Ni oxide films

The role of defects on the electrochromic response time of sputter-deposited Ni oxide films grown by RF magnetron sputtering system was examined. In order to create an excess interstitial oxygens and voids, the sputter-deposited Ni oxides were grown at varying Ar/O 2 ambient ratios and RF power, respectively. The electrochromic response time was evaluated by an in situ transmittance measurement during a pulse potential cycling test. Although all of the sputter-deposited Ni oxide films had a similar, amorphous crystallographic structure, the excess interstitial oxygens and the voids affect the electrochromic response time, leading to a disturbance in proton intercalation/deintercalation during the coloring/bleaching processes. Moreover, the voids in the film played a more critical role on the electrochromic response time than an excess of interstitial oxygen.

Asphalt Permeability Testing in Virginia

Because of high air voids, long-lasting damp spots on pavement surfaces, and problems that other states have had with permeable coarse Superpave mixes, the Virginia Department of Transportation (VDOT) decided to investigate the permeability of its Superpave mixes. As part of this study, VDOT also tested other asphalt mixes. Falling-head permeability tests were performed on pavement cores to determine the general permeability of the mixes. The permeability of some of the pavement cores was compared with the permeability of specimens made in the laboratory through the use of mixtures sampled during construction to determine whether laboratory specimens could be used to predict pavement permeability. The primary purpose of this investigation was to determine the general magnitude of permeability for mixes being used by VDOT, with an emphasis on Superpave mixes. A large percentage of the field cores contained excessive voids, resulting in excessive permeability. Each mix had a unique voids-permeability relationship. Mixes that were composed of large aggregates required fewer voids to achieve an acceptable level of permeability. In four of five cases, the results of laboratory tests were generally quite successful in indicating field permeability. The preliminary permeability testing demonstrates the importance of achieving low voids in the field and will help in the future development of density specifications and possibly in the establishment of permeability requirements. It is recommended that the permeability test continue to be used to help set such limits.

A process for prestaging thermosetting towpreg

AbstractA method for prestaging thermosetting towpreg consisting of passing the material through a tunnel oven was developed to address the difficulties inherent in making thick‐walled thermosetting composite parts: aging, moisture uptake, and low resin viscosity during lay‐up; and residual stresses, warping, thermal degradation, resin gradients, and excessive void nucleation during the final cure. AS‐4 carbon fiber in a 3501‐6 epoxy matrix was used to test the continuous prestaging process. With prestaging, significant reductions in towpreg bulk, voids, and total enthalpy were achieved. Cure shrinkage also was achieved. The final towpreg product had good drape and greatly reduced tack. These changes addressed many of the aforementioned difficulties. A relation between residence time at 200°C (the process temperature) versus percent degree of cure (%DOC) was developed. Manufacturing characteristics such as drape, tack, and bulk were related to %DOC. A processing window of 15 to 22 %DOC yielded towpreg with optimal characteristics. Prestaged towpreg would be well suited to manufacturing with advanced fiber placement (AFP) type equipment. Initial trials in industry have been promising.

Mechanical properties of parts manufactured from prestaged thermosetting towpreg

AbstractA prestaging process consisting of passing thermoset towpreg through a tunnel oven and roller apparatus was developed to address the difficulties inherent in making thick‐walled thermosetting composite parts: aging, moisture uptake, and low resin viscosity during lay‐up; and residual stresses, warpage, thermal degradation, and excessive void nucleation during the final cure. Unidirectional laminates were fabricated from prestaged and as‐received AS4/3501‐6 towpregs to understand the relationship between the parts' mechanical properties and the amount of prestaging (degree of cure) of the towpregs. In this manner, the feasibility of manufacturing with prestaged thermosetting towpreg was confirmed. Ultrasonic nondestructive evaluation showed that the parts manufactured from prestaged towpreg were uniform and relatively low in voids as compared to parts manufactured with as‐received towpreg. This was confirmed with scanning electron microscopy. Using three‐point bending tests, a drop in mechanical properties was found in parts manufactured from towpreg prestaged beyond 19% degree of cure. However, the parts were well consolidated and had predictable mechanical properties up to approximately 40% degree of cure. The equivalent limits on degree of cure from a companion processing study are between 15% and 22%.

The Continuous Curing Process for Thermoset Polymer Composites. Part 2: Experimental Results for a Graphite/Epoxy Laminate

A new composite manufacturing method called continuous curing has been developed to alleviate problems in the processing of thick composites such as long manufacturing cycle times and material degradation due to thermal spiking. A 10 cm-thick graphite/epoxy (AS4/3501-6) laminate was fabricated using the continuous curing method. The thermal distributions were measured during the process and the final cure distribution was obtained by DSC testing. The mechanical performance of the laminate was analyzed by destructive testing of 16-ply mechanical test specimens removed from the bulk laminate. These specimens were distributed at five locations across the thickness of the laminate. Results for longitudinal compressive strength, transverse tensile strength, and interlaminar shear strength show some degradation. An attempt to quantify the factors contributing to the lower measured strengths is presented. Optical microscopy and image analysis was performed to obtain void and fiber volume distributions across the laminate thickness. Longitudinal layer waviness was measured by optical microscopy. The degradation in strength can be attributed to the high degree of layer waviness, nonuniform consolidation, and excessive voids. These manufacturing defects are attributed to less than optimal processing parameters chosen for the demonstration experiment.

Enhanced grain growth in polycrystalline CuInSe2 using rapid thermal processing

Rapid thermal processing of precursor small-grained (less than or equal to 1 μm) CuInSe2 thin films can result in enhanced grain growth on the order of 100 μm under certain processing conditions. Crystal growth was accompanied by large increases (×10) in the X-ray diffraction intensity of the (112) peak, indicating near-perfect crystal growth in the [221] direction. Single-crystal quality was verified by selected-area electron channeling. However, at present, this effect occurs in conjuction with excessive void and pinhole formation between single-crystal platelets. These voids are often decorated with relatively selenium-deficient phases.

Investigation on the influence of sulfur segregation on the adherence of protective oxide layers on high temperature materials

Oxide layers of various thicknesses have been produced on Fe-15Cr and NiAl doped with sulfur. For thin oxide layers, depth profiles demonstrated that no sulfur is enriched at the oxide-metal interface. For thick oxide layers, the interface has been made accessible by bending or scratching the specimen. Sulfur has been found on the spalled area by AES. Micrographs proved that excessive void formation is responsible for the bad adherence of the oxide layers to the substrate. Sulfur segregaton decreases the surface energy, thus reducing the radius of nucleus formation and promoting void formation. Reactive elements form refractive sulfides with sulfur, thereby improving scale adherence.

Total Bladder Replacement Using Detubularized sigmoid Colon: Technique and Results

We performed total bladder replacement with a detubularized segment of sigmoid colon in patients after cystoprostatectomy. The surgical technique and long-term results in 27 patients are reported. This neobladder configuration compared favorably with other neobladder types regarding ease of construction. The surgical complications were acceptable. Initial reservoir function was good but improved further with time. After 1 year the capacity averaged 600 cc, pressures during filling and at capacity were low (average 12 and 16cm. water) and emptying was satisfactory (residual urine 4 to 80 cc). All patients were continent during the day and 67% were continent at night without excessive voiding habits. Nighttime incontinence was further resolved in 2 patients by using the AMS 800 artificial sphincter around the bulbous urethra. The detubularized sigmoid is an excellent neobladder configuration after cystoprostatectomy.

The formation of an amorphous silicide by thermal reaction of sputter-deposited Ti and Si layers

The initial reaction in amorphous Si-Ti-amorphous Si trilayers was investigated with Auger electron spectroscopy, transmission electron microscopy, and x-ray diffraction. It was clearly demonstrated that at temperatures not exceeding 450 °C an amorphous Ti-Si alloy is formed. At temperatures of 500 °C and higher, crystalline TiSi2 with the ZrSi2 (C49) structure was found. The growth kinetics of the amorphous silicide could not be described by a simple diffusion controlled process. It was shown that at 400 °C the thickness of the amorphous silicide is limited to approximately 18 nm. Since it was found that the growth of the amorphous phase is accompanied by excessive Kirkendall void formation, it is proposed that these voids eventually suppress the growth of amorphous silicide. The composition of the amorphous phase was determined to be between TiSi0.9 and TiSi1.2, i.e., close to the composition of the monosilicide.

On theory of apparent molar volumes in concentrated aqueous solutions of strong electrolytes

On the basis of the method reported in the previous work, according to which close-packed hydration sheaths of ions are surrounded by excess voids which in the above model were replaced by contact gap of width d0 independent of temperature and concentration, it is inferred in the present study that on extrapolating the apparent volumes of strong electrolytes to zero volume fraction of water in solution, temperature-independent water-free ion volumes Φ’i are obtained. These volumes correspond to the state in which the contact gap is shifted up to the very surface of ions, without changing its width d0 = 39 ± 2 pm. The volumes Φ’i show additivity and acquire thus the properties of parameters which are applicable to calculation of the density of aqueous solutions of strong electrolytes as well as of their mixtures up to the highest possible concentrations. With Li+ and Na+ ions, the condition of temperature invariance of Φ’i results in that the hydrate nucleus is not naked cation but a species MH2O+ analogous to H3O+ ion. This explains likely the different function of Na+ and K+ ions in biological systems (especially concerning their permeation through membranes). In the case of Mg2+, Ca2+, Sr2+, and Ba2+ ions, the hard-body centre of their hydrates is formed by hexaaqua-complexes.

On theory of ionic volumes in dilute aqueous solutions of electrolytes

For purposes of calculation of densities of aqueous solutions of strong electrolytes and of their mixtures, theoretical substantiation of the formerly outlined empirical model of apparent molar ionic volumes φ in solution is presented. According to the model, the hydration sheaths of ions consisting of radially close-packed H2O molecules having effective molar volume V’w the same for all ions, are on their contact with the adjacent structure of liquid water surrounded by a layer of excess voids. This layer can bee substituted in the model by continuous gap of which d0, which again is common to all the ions and is temperature-independent. Using experimental φ values of twenty-seven strong electrolytes together with the data on electrolytic transport of water on ions, V’w = 12 cm3 mol-1 and d0 = (40 ± 2) pm were found for mono- and divalent ions in 1 mol dm-3 solutions, independently of ionic charges and crystallographic radii. The exception are small ions Li+ and Na+, the volumes of which – if interpreted on the basis of the model – correspond to hydration sheaths formed by a cluster of voluminous ice-like structure. An anomaly in this respect has been encountered also in the case of NH+4 ion.

Excess nitrogen and discontinuous precipitation in nitrided iron-chromium alloys

FeCr (1.88 and 3.61 wt % Cr) specimens were gas nitrided (10 vol % NH3/90 vol % H2 gas mixture at 833 K). The structure after nitriding was studied employing metallographic methods (optical microscopy, hardness measurements), scanning electron microscopy and X-ray diffractometry (residual macrostress determination and phase identification). Further the weight and thickness increases of the specimens during nitriding were determined. Excess nitrogen uptake, discontinuous precipitation and void formation were observed. The amount of excess nitrogen observed in an initial stage of precipitation corresponds well with the predicted amount applying thermodynamics of stressed solids. The occurrence of a discontinuous precipitation reaction at later stages of precipitation was accompanied by the loss of excess nitrogen from the supersaturated ferritic matrix. In this way void formation and changes in the residual macrostress distribution within the specimen during nitriding can be explained. As a result a model is presented for the description of the nitriding behaviour of Fe-Cr alloys.

Influence of preparation techniques on the structure of amorphous metallic alloy (Mo 0.6Ru 0.4) 82B 18

We report X-ray diffraction studies and density measurements on liquid quenched foils and sputter deposited films of the amorphous metallic alloy, (Mo 0.6Ru 0.4) 82B 18. The crystallization temperature (T x) for both the films and the foils is ∼800 ± 10°C. The density of the as-sputtered films is ∼4% less than that of the foils. The annealing of these films at ∼ T x 2 increases the density to within ∼1.7% of the value for the foils. The X-ray diffractionpatterns for both the foils and films are similar and show the amorphous nature of the samples. The reduced radial distribution functions suggest that as-sputtered films have noticably larger second and third nearest neighbor distances, probably due to excess residual stresses and voids in them.

Laser Crystallization of Deposited Silicon Films

ABSTRACTSilicon layers evaporated on crystalline Si have been crystallized by Q-switched Nd:YAG laser irradiation. A strong correlation was observed between the density of a-Si films and the quality of the epitaxial regrowth from the liquid phase. Dense films crystallized epitaxially in a wide range of laser energy densities. Layers with 20% lower density, as determined by spectroscopic ellipsometry, had higher crystallization thresholds and suffered from severe pitting of the surface. Coalescence of the excess void volume into microbubbles, stabilized by gaseous contaminants, is responsible for the surface degradation.In polycrystalline films on amorphous insulating substrates laser melting changes the grain distribution. Rapid melting and solidification of small diameter spots creates concentric rings of large crystallites. This characteristic pattern is explained by a simple model, based on the kinetics of crystallization.

Microporosity in thin films

Because a large number of vacancies and voids can be incorporated into thin films during the deposition processes the films are generally porous. The presence of excess vacancies and voids greatly influences the physical properties. In particular freshly deposited films contain a large number (up to 1%) of excess vacancies which are highly mobile at ambient temperature. These excess vacancies are readily annihilated by diffusing to various sinks available in the thin films. During the annihilation process some film properties, which are sensitive to variations in the vacancy concentration, change continuously with time until all the excess vacancies are eliminated, leading to an aging phenomenon. In this report thin film microporosity is described in terms of the vacancies and voids incorporated during the deposition processes. The origins of these vacancies and voids and their effects on the physical properties of thin films are also discussed.

The role of lithium in stabilizing some high-temperature silica phases*

Abstract High-quartz and keatite are two of the high-temperature silica phases. Both have negative thermal expansion and both can be stabilized by partial replacement of Si with Al and Li. Some current data are used in this paper to extend and refine the stabilization principle first outlined by Buerger. Based upon this study, it is the interstitial cations like Li that stabilize the high-temperature structure by effectively reducing the excess void space. Thus the high-temperature structure is buttressed and preserved by preventing it from collapsing into the low-temperature form at the transformation temperature. It is also found that Li can best stabilize the high-quartz and the keatite phases because of its unique characteristics. First, Li has the precise size to fit into the interstitial space with ease. Second, Li has the ideal combination of valence and coordination number so that it can best balance the local charge. Some structural data are presented to support these observations.

Oxidation of C 5 hydrocarbons to maleic anhydride

Low noise asphalt pavement mitigates the impact of traffic noise on the ecological environment and surrounding population to a certain extent. To explore the noise reduction characteristics of different asphalt pavements, an indoor simulation device for pavement noise reduction is developed in this paper, based on the principle of pavement noise reduction. The device simulates the process of noise reflection and interference on the surface and inside of the pavement, which consumes the sound energy to achieve the noise reduction effect. The mechanical performance of six different types of asphalt mixtures is first tested. The noise reduction performance of the asphalt mixtures is then studied using the self-made noise testing device and Kundt’s tube method to verify the accuracy of the device. The influence of surface texture on pavement noise is also analyzed, and test results show that the six types of asphalt mixtures used in this study all meet mechanical performance requirements. A strong correlation is also observed between the noise testing device and the traditional Kundt’s tube method. The noise testing device is found to accurately measure the noise reduction characteristics of asphalt mixtures. For noise of different sound pressure levels, the same type of asphalt mixture displays different noise reduction capabilities. The better the noise reduction performance, the lower the sensitivity to sound wave changes, and the more stable the noise reduction effect. Excessive air void content does not significantly improve the pavement noise reduction performance, and it is recommended that the pavement air void content is maintained within the range of 17%–24%. The density of the asphalt mixture is found to be negatively correlated with the noise reduction performance, while the air void content and the mean texture depth is positively correlated with noise reduction. The results of grey relational analysis show that air void content is the most important factor affecting the noise reduction characteristics of asphalt pavement, followed by mean texture depth. Aggregate particle size is also found to exert a significant influence on noise reduction characteristics, and the influence degree of 9.5 mm particles is found to be the greatest, with 1.18 mm and 2.36 mm particles also showing a high degree of influence. Reasonable control of aggregate particle size should therefore be carried out in the design of low noise asphalt pavement.