On the blister formation in copper alloys due to the helium ion implantation

A new approach to the blister-formation phenomenon is discussed by means of the mathematical solution on a uniformly loaded circular plate with clamped edges (circular diaphragm). In the present investigation, it was found that blister formation depends on the mechanical properties of the alloys and the near-surface concentration of the implanted gas, which itself is contingent on the crystallographic orientation by means of the stopping power of the implanted atoms. The reported model is based on the fact that at certain depths from the surface, the pressure in the cavities approaches the yield stress of the metal and blistering starts. The thickness of this thin film depends on the mechanical properties of the specific metal. Once a blister cavity is formed, the deformation of the thin film to form a blister cap depends on the buildup of pressure in the cavity contingent on the implanted dose. For the present model, it is sufficient to say that the thickness of the blister's cap cannot be correlated with the projected range of the implantation, as assumed by other authors. The implanted helium concentration needed to buildup enough gas pressure to create a blister at a depth which is close to the projected range is higher by 50 times than the gas helium concentration in the cavity. Experimental results, such as the fact that the blishers have burst at the edge of the circular skin, where the maximum stresses are developed, and the fact that at high implantation energy (large projected range), the bursting of the blisters occurs by multilayer caps, suport the present model.     

Growth and configurational stability of circular,buckling-driven film delaminations

A study is presented of delamination at the interface between a thin elastic film bonded to a substrate under conditions in which the film is subject to equi-biaxial compression. The focus is on initially circular delaminations. When the initial delamination is sufficiently large it buckles away from the substrate producing a blister which in turn induces a driving force on the interface crack tip. A two-part theoretical analysis of the coupled buckling/fracture problem is conducted: the axisymmetric growth of the circular blister, and the stability of the circular blister to nonaxisymmetric perturbations of the interface crack front. A simple criterion is identified which excludes the possibility of wide-spread delamination. Experiments are reported for a model film/substrate system (mica bonded to aluminum) chosen to allow visualization of the interface and to permit compressive stresses in the film to be generated over the full range of interest by exploiting the large thermal expansion mismatch of the system. The experiments bear out the theoretical prediction of a regime of axisymmetric growth which gives way to nonaxisymmetric blisters after a blister becomes sufficiently large. The study suggests that the wavy-circular and worm-like blister morphologies which are usually observed for delaminated films are a manifestation of the configurational instability of the interface crack front.     

The extension of hydrogen blister-crack array in linepipe steels

Hydrogen induced fracture in linepipe steels is characterized by the formation of internal blisters caused by hydrogen precipitation at an inclusion-matrix interface, followed by the formation of blister-crack array by cracking the region connecting the blisters through the action of internal hydrogen pressure and external stress. The manner of extension of the hydrogen induced fracture of this type is considerably influenced by the presence of external stress: in the absence of the external stress fracture develops by linking the blisters which are formed in stacked arrays out of a plane approximately perpendicular to the external stress axis. Shear stress distribution induced around the blister is sensi-tively influenced by the external stress applied parallel to the blister plane; therefore, it is expected that the manner of extension of the blister-crack array should be influenced by the external stress. In the present paper the above mentioned influence of the external stress on the manner of extension of the hydrogen induced fracture is explained based on stress analysis around a hydrogen gas pressurized crack-like cavity under stress.     

Fracture mechanics of a new blister test with stable crack growth

A new blister test is proposed to measure the specific work of adhesion W between a thin flexible film on a rigid substrate. In contrast to the conventional blister loaded by constant fluid pressure which leads to catastrophic crack propagation, the new test is driven by an internal expansion of a fixed mass of working gas which leads tostable crack growth. The new technique is demonstrated by measuring W of an interface with a commercial sticky tape serving as the thin film and aluminium as the rigid substrate.     

Nucleation of grain boundary cavities under the combined influence of helium and applied stress

Modelling cavity nucleation at grain boundaries in structural alloys under the combined influence of helium and stress is the primary objective of this paper. The role of stress in cavity nucleation is analyzed using an extension of classical theory by taking into account grain boundary sliding to describe stress concentration buildup and relaxation at particles and triple-point junctions. Helium clustering in the matrix is modeled using rate theory. The helium flux to grain boundaries is determined by the application of sink strength theory which takes into account the various competing clustering mechanisms in the matrix. Helium clustering on grain boundaries is also theoretically investigated using rate theory. The work agrees with experimental observations showing that irradiation results in grain boundary bubble densities which are orders of magnitude larger than cavity populations observed in conventional creep experiments. It is shown that even if the total injected helium is as little as one part per million, it can result in grain boundary bubble densities on the order of 10¹³ m⁻². Such cavity population exceeds typical grain boundary cavity densities associated with creep experiments. Grain boundary bubble densities are shown to reach steady state for injected helium amounts on the order of 10 parts per million.     

Energy release rates and stability of straight-sided,thin-film delaminations

Straight-sided delamination of a thin, elastic film from an elastic substrate in analyzed. The loadings causing delamination are general in-plane stresses and a normal pressure on the film. Delamination is modelled as a crack propagation at the film/substrate interface and closed form expressions have been derived for the energy release rate and its separation into mode 1 and mode 2. The range of validity of these results is investigated by performing a stability analysis for the delamination shape considered. The results, which are related to both buckling delamination and blister tests, show strong dependence of the stability behaviour on the in-plane loading.     

Protein concentration of subcutaneous interstitial fluid in the human leg. A comparison between the wick technique and the blister suction technique

The wick technique and the blister suction technique are the most common methods for sampling of subcutaneous interstitial tissue fluid in man. The blister suction technique has the advantage of being less invasive than the wick technique, but the reliability of this method is still controversial. The aim of this study was to evaluate whether the simpler blister suction technique using large (8 mm) blisters could replace the wick technique in the investigation of patients with postreconstructive leg edema. Fifteen patients with ipsilateral leg edema following infrainguinal bypass surgery for lower limb atherosclerosis were investigated. The two different fluid sampling techniques were applied simultaneously on both legs. The concentration of total protein and albumin as well as colloid osmotic pressure of the subcutaneous interstitial tissue fluid in the leg were measured in all fluid samples. Agreement analysis was applied to compare the two methods, while the correspondence between the methods was estimated with linear regression analysis. The agreement index was found to be positive for all variables from the operated as well as from the contralateral control limb. Furthermore, all values were within the agreement limit. The best agreement between the two methods was found for colloid osmotic pressure on the operated side. According to the equation of linear regression, there was a slight overestimation of the wick values compared to the observed blister values. In conclusion, there was a good methodological agreement between the blister suction technique and the wick technique. The less invasive blister suction technique should be regarded as the method of choice for the investigation of subcutaneous interstitial tissue fluid in patients with postreconstructive leg edema.     

Cavity microstructure and kinetics during gas tungsten arc welding of helium-containing stainless steel

Helium was implanted in type 316 stainless steel, through tritium decay, to levels of 0. 18, 2. 5, 27, 105, and 256 atomic parts per million (appm). Bead-on-sheet welds were then made using the gas tungsten arc (GTA) process. Intergranular cracking occurred in the heat-affected zones (HAZs) of specimens with helium concentrations equal to or greater than 2.5 appm. No such cracking was observed in helium-free control specimens or in specimens containing the lowest helium concentration. In addition to the HAZ cracking, brittle, centerline cracking occurred in the fusion zone of specimens containing 105 and 256 appm helium. Transmission and scanning electron microscopy results indicated that both the HAZ cracking and centerline cracking in the fusion zone resulted from the stress-induced growth and coalescence of cavities initiated at helium bubbles on interfaces. For the HAZ case, the cavity growth rate is modeled and shown to predict the experimentally measured 1-second time lag between peak weld temperature and the onset of cracking.     

Gas trapping and release in polycrystalline nickel preimplanted with helium

Hydrogen profiling using nuclear reaction analysis (NRA) and a thermal desorption technique coupled with scanning electron microscopy (SEM) observations have been used to study the gas trapping and release in high-purity polycrystalline nickel. The effect of the preimplanted helium dose on both deuterium and helium desorption was investigated over a wide range of helium doses (1 x 10²¹ to 4 x 10²¹ ions/m²). A computer code, DIFFER, was used to simulate the deuterium flux curves, and the trapping characteristics were evaluated. The simulation results clearly show that a wide distribution of trapping energies exists. This can be explained using a stress-field trapping model. The effective binding energy, E _h ^eff , was estimated to be in the range of 0.4 to 0.5 eV. For samples which were irradiated with helium ions to high doses, a massive helium release was also observed. Thermal charging with deuterium was found to reduce the helium self-trapping energy as was expressed by lower temperature helium release. For the high dose samples, deuterium or hydrogen gas charging and thermal ramping were also found to induce blisters growth and surface exfoliation.     

Influence of pressure on the kinetics of synthetic llmenite reduction in hydrogen

In-situ thermogravimetric measurements were used in the hydrogen reduction of poly-granular synthetic ilmenite discs at temperatures in the range 823 to 1173 K and at pressures in the range 1.2 to 13 atm. A symmetrical beam microbalance was used, coupled with twin reactors and twin furnaces, to minimize buoyancy and drag effects. Stable operation was achieved at high gas flow rates where gas film transport effects were negligible. Polishing the ilmenite discs prior to reduction eliminated the formation of dense surface metallic iron films that can impede gas diffusion into the discs. Macroscopically, the reduction reaction proceeded topochemically and a shrinking core reaction model was found to be appropriate to predict conversion-time relationships. It was necessary to allow for water vapor adsorption onto the reacting interface in order to model the effect of pressure on the reduction kinetics. The observed reduction rate increased sharply with pressure up to approximately 3 atm and then approached a plateau with further pressure increase. The porosity in the reduced ilmenite samples was very fine, with pore diameters of typically 0.05 to 0.3 μm. Intragrain gas pressure buildup in the fine pores due to the influence of Knudsen diffusion was incorporated into the modeling of the kinetic data.     

On the methods for studying the mechanisms and bioavailability of iron

Bullous pemphigoid (BP) blisters contain several molecules, some of which spread into the blisters from the interstitial fluid, while others are produced locally and migrate into the circulation. The calculation of the ratios between blister/serum concentrations may help to distinguish between these two types of molecules. The rules regulating the diffusion of the molecules have been described only in suction blisters, where the theoretical molecular weight (MW) represents one of the principal influencing factors. The aim of the present study was to analyse the relationship between theoretical MWs and the ratios of concentrations of several molecules evaluated both in sera and in blister fluids. Eight cytokines (interleukin-2, interleukin-3, interleukin-4, interleukin-5, interleukin-10, tumor necrosis factor-alpha, oncostatin-M and vascular endothelial growth factor), two acute phase reactants (alpha-1 acid glycoprotein, haptoglobin), albumin, one soluble membrane molecule with adhesion functions (sICAM-1) and the eosinophil cathionic protein (ECP) were measured in samples from 15 patients affected with BP by means of commercially available tests. The data suggest that the MW may influence the rate of diffusion throughout the blister, both in input and output directions, despite the discontinuity observed at the basement membrane level on the BP blister floor.     

Structural Changes in the Vanadium Sample Surface Induced by Pulsed High-Temperature Deuterium Plasma and Deuterium Ion Fluxes

The structural changes in the vanadium sample surface are studied as functions of the conditions of irradiation by pulsed high-temperature deuterium plasma and deuterium ion fluxes in the Plasma Focus installation. It is found that processes of partial evaporation, melting, and crystallization of the surface layer of vanadium samples take place in the plasma flux power density range q = 10⁸–10¹⁰ W/cm² and the ion flux density range q = 10¹⁰–10¹² W/cm². The surface relief is wavelike. There are microcracks, gas-filled bubbles (blisters), and traces of fracture on the surface. The blisters are failed in the solid state. The character of blister fracture is similar to that observed during usual ion irradiation in accelerators. The samples irradiated at relatively low power density (q = 10⁷–10⁸ W/cm²) demonstrate the ejection of microparticles (surface fragments) on the side facing plasma. This process is assumed to be due to the fact that the unloading wave formed in the sample–target volume reaches its irradiated surface. Under certain irradiation conditions (sample–anode distance, the number of plasma pulses), a block microstructure with block sizes of several tens of microns forms on the sample surfaces. This structure is likely to form via directional crack propagation upon cooling of a thin melted surface layer.     

Glucose content in human skin: relationship with blood glucose levels

In order to ascertain the dynamic relationship between the extracellular glucose in upper skin layers and blood glucose, skin suction blisters were raised in six Type 1 diabetic patients during a three-step glucose clamp. Blister glucose closely paralleled venous glucose (mean of r = 0.998). However, in three patients blister glucose was constantly lower than plasma glucose and this appeared to be related to their slower formation of skin blisters. A substantial difference in skin blister suction time was noted among patients and it was found that suction time was linearly correlated to glycosylated haemoglobin (HbA1C) (n = 6, r = 0.865, p = 0.026). It is concluded that a non-invasive blood glucose monitoring system could be successfully based on measurement of alterations in skin glucose contents.     

Determination of fracture initiation in hydride blisters using acoustic emission

An experimental study based on acoustic emission techniques was carried out to determine the conditions that lead to the initiation and growth of cracks in and from zirconium hydride blisters. The stress to initiate, at room temperature, a crack in a blister previously grown on a tensile speci-men could be accurately determined using an acoustic emission (AE) method based on linear event-location techniques. It was found that the applied stress to first form a crack in an unbroken blister decreases with blister depth but also that this value is statistically distributed. This is likely due to a size distribution of microcracks or incipient flaws in the blister. The propagation, by the delayed hy-dride cracking (DHC) mechanism, of a crack from a pregrown blister at 516 K seems to require both a critical applied stress, which decreases with blister depth, and approach of the testing temperature from above. However, DHC initiation was possible at 563 K (approached from below) for blisters grown under stress, provided the applied stress was sufficiently high. The stress intensity factor,K _IB , to initiate DHC ranged from 10.7 to 15.4 MPa √m. This is above the range forK _IH the thresholdK ₁ for DHC obtained in other experiments. The characteristics of AE generated by crack propagation from a blister due to DHC always follows the same pattern. It has a low event rate both at the beginning and at the end of DHC and a maximum value in between. The DHC initiation stage has a high proportion of high amplitude events. The peak in the distribution of events with peak am-plitude shifts to lower peak amplitudes as DHC progresses. An explanation for this trend is sought in terms of the maximum hydride size required near the crack tip to propagate the crack as a func-tion ofK ₁ .     

Comparison of three different experimental methods for the assessment of peripheral compartment pharmacokinetics in humans

In many cases the concentration reached in a peripheral effect compartment rather than in plasma determines the clinical outcome of therapy. Therefore, several experimental approaches have been developed for direct assessment of drug kinetics in peripheral compartments. Particularly saliva sampling, skin blister fluid sampling, and in vivo microdialysis are frequently employed for measuring peripheral drug concentrations. However, data derived from these techniques have never been directly compared. In the present study, the tissue kinetics of theophylline were measured following single dose administration simultaneously in cantharides induced skin blisters, saliva and microdialysates of subcutaneous- and skeletal muscle- tissue and compared to plasma concentrations. Theophylline was administered to 9 healthy volunteers as an i.v. infusion of 240 mg. Mean ratio (AUCsaliva/AUCplasma) was 0.63 +/- 0.05, mean ratio (AUCblister/AUCplasma) was 0.69 +/- 0.12, mean ratio (AUCmuscle/AUCplasma) was 0.41 +/- 0.10, mean ratio (AUCsubcutaneous/AUCplasma) was 0.34 +/- 0.07. The time course of the concentration(peripheral)/concentration(plasma)-ratios showed that tissue concentrations obtained by microdialysis were closely correlated to free plasma levels, whereas saliva- and cantharides blister data overestimated the corresponding free plasma concentrations. It is concluded that microdialysis represents a reliable technique for the measurement of unbound peripheral compartment concentrations and is superior to saliva- and skin blister concentration measurements.     

双流法溶出新工艺高温碱液腐蚀与防止方法试验研究

本文报导了国家攻关项目———双流法溶出新工艺及设备研究专题中高温碱液预热器工业模拟腐蚀试验和工业腐蚀试验结果。通过分析工业腐蚀试验中高温碱液预热器的温度径向分布,得出在预热器内套管内壁处碱液因饱和蒸气压大于其静压力产生气泡,气泡因压力梯度和温度梯度的存在,在向径向移动的过程中冷却破裂,对其内壁产生巨大冲击力而发生腐蚀,即空泡腐蚀;提出了应用双流法改进流程、降低熔盐温度、提高碱液与矿浆流的比例和采用全逆流预热流程等防止腐蚀方法。通过调整工艺条件和设备参数,应用双流法溶出新工艺稳定运行800多小时,无腐蚀现象发生。     

车轮钢中的白点(一)

研究了车轮钢中白点形成的机理以及白点对断口形貌的影响.结果表明,氢和空位聚集导致鼓泡形核和长大,随着鼓泡内氢气压力的升高,裂纹从鼓泡核壁形核、扩展导致白点形成.白点的断口为准解理,和氢致滞后开裂断口相同,含白点试样的断口形貌依赖于断裂方式和试样厚度.钢中的白点除了产生二次裂纹和局部准解理断面外,对各种断口形貌均没有明显的影响.     

Kindler syndrome. Clinical and ultrastructural findings

BACKGROUND: Kindler syndrome is a genodermatosis that combines clinical features of hereditary epidermolysis bullosa and poikiloderma congenitale. The ultrastructural level of blister formation has not been well characterized. OBSERVATIONS: Two brothers with Kindler syndrome had a history of primarily acral blistering since infancy as well as photosensitivity. Blister formation was found through the basal layer. Marked tonofilament clumping was found in intact keratinocytes adjacent to the blisters. The younger brother (aged 21 years) had actinic keratoses, which have not been previously described in Kindler syndrome. CONCLUSIONS: The findings of basal layer separation in both spontaneous and induced blisters in Kindler syndrome suggest this is the true level of blister formation. The finding of actinic keratoses in a young patient with Kindler syndrome suggests that some patients may be at increased risk for early solar-induced skin disease. The presence of clumped tonofilaments in keratinocytes adjacent to blistered areas suggests an abnormality of keratin 5 or 14 could be present and may play a role in blister formation in patients with Kindler syndrome.     

Is the implantation of a second intraocular lens prior to the removal of the first implants remaining in the vitreous cavity incorrect medical treatment?

BACKGROUND: The implantation of an intraocular lens into the capsular bag is a common procedure in modern cataract surgery. In case of a break of the posterior capsule it is possible to implant the intraocular lens by rhexis-, ciliary sulcus- or pars-plana-fixation. The following case is in so far remarkable, as a second intraocular lens has been implanted while a dislocated intraocular lens was still in the vitreous cavity. PATIENT: We report on a 70-year-old patient who underwent cataract surgery. After a break in the posterior capsule the intraocular lens dislocated into the vitreous cavity. A second intraocular lens has been implanted in the ciliary sulcus. 41 days after cataract surgery the dislocated intraocular lens has been removed by pars-plana-vitrectomy without any problems. CONCLUSION: Intraocular lens implantation in the ciliary sulcus is not proved to be a hindrance with regard to the transcleral removal of a posteriorly dislocated intraocular lens, following the principles of intraocular foreign body surgery.