Mechanism Of Nodule Formation Research Articles

Mechanisms of nodule formation on Ni-Pt targets during sputtering

Mechanisms of nodule formation on Ni-Pt targets during sputtering

Silurian metalliferous nodules from the region of Asaritsa peak, West Balkan mountain – preliminary results

First data for polymetallic nodules and host sediments in Silurian sequence from the region of Asaritsa peak, West Balkan mountain are presented. The nodules are rich of Fe, Mn, Co and Ni. Both sediments and nodules have high content of REE. The described Silurian nodules and sediments show a number of similarities with modern deep-sea polymetallic nodule bearing sediments. Some differences such as probable depth of deposition, mechanism of nodule formation, degree of lithification are also established.

Growth of Nodules in Copper Electrorefining: Numerical Simulation of Natural Convection

It is well known that copper can be electrodeposited with 100 % current efficiency without hydrogen evolution. In modern copper electrorefining process, however, the current utilization rate for copper electrorefining is generally 93-98 %. This is because nodulation occurs on cathode to cause short circuits and lose currents [1]. In other words, when nodules on the cathode grow to reach anode, current can flow but electrochemical reaction can not occur. There are various studies on the mechanism of nodule formation [2], and it is considered that suspended particles (e.g. floating slime) adhering to the cathode are an origin of nodule formation or nodule outbreak (see Fig. 1a).Previously we investigated the effect of current concentration on a nodule by experiments and numerical simulations [3-5]. Based on the secondary current distribution model, i.e. without considering the effect of natural convection, it was found that the experimental growth rate cannot be explained by the effect of current concentration on nodules only.Upward and downward natural convection occurs near the cathode and anode, respectively, as the density of the electrolyte solution near the electrode changes due to electrolysis (see Fig. 1a). Although natural convection can affect mass transfer, its contribution to the nodule formation has not been clarified. In this study, we focused on the natural convection as a factor for nodule growth in the early stages of nodule formation or after nodule outbreak.We performed numerical simulations based on the tertiary current distribution model. Using the FEM simulation software COMSOL Multiphysics®, we calculated the natural convection behavior and the cupric ion concentration distribution. Cylindrical protrusions were considered to mimic the nodules. The partially simplified governing equations for electrochemical model, mass transfer and computed fluid dynamics (CFD) were solved simultaneously (see Fig. 2). In CFD, laminar flow was assumed. The calculation was performed in 3D area of the electrolyte solution between the single pair of vertical anode and cathode plates.Figures 1b and 1c confirmed that the flow behaviors changed as a function of the protrusion length. When the protrusion length was 0.2 mm or less, natural convection along the cathode surface flowed over the protrusion. By contrast, when it was about 0.5 mm or more, the flow was divided into both sides of the protrusion, implying that natural convection is weakened at the protrusion tip. It is also notable that the simulated thickness of the diffusion layer at the protrusion tip decreased as the protrusion length increased. Thus, as the protrusion length increases, more Cu2+ ions are supplied by diffusion at the protrusion tip. This effect may promote the nodule growth above a certain size under natural convection.[1] M. E. Schlesinger, M. J. King, K. C. Sole and W. G. Davenport, Extractive metallurgy of copper 5th, Elsevier (2011), pp. 251-279.[2] T. N. Andersen, C. H. Pitt and L. S. Livingston, J. Appl. Electrochem., 13(4), 429 (1983).[3] K. Adachi, Y. Nakai, A. Kitada, K. Fukami and K. Murase, TMS Annual Meeting & Exhibition, Springer, Cham (2018), pp. 215-222.[4] Y. Nakai, K. Adachi, A. Kitada, K. Fukami and K. Murase, TMS Annual Meeting & Exhibition, Springer, Cham (2018), pp. 319-323.[5] K. Adachi, Y. Nakai, S. Mitsuno, M. Miyamoto, A. Kitada, K. Fukami and K. Murase, Journal of MMIJ (in Japanese), 136(2), 8 (2020). Figure 1

Early mesangiolysis and monocyte influx observed in diabetic glomerulosclerosis: relation to nodule formation.

Lytic changes to the mesangium and subendothelial area in diabetic glomerulosclerosis were studied by electron microscopy with an emphasis on the mechanism of nodule formation. Renal biopsy specimens were obtained from 30 diabetics (11 males, 19 females; 27 NIDDM, 3 IDDM; mean age, 52.2 years) with renal involvement. Evaluations were made of the glomerular lesions, particularly the ultra-structural findings contributing to nodule formation, mainly by electron microscopy. Varying degrees of lytic change, such as a loose and edematous mesangial matrix, widening of the subendothelial space, followed by endothelial detachment, and destruction of anchor points, were observed in close association with progression of the diffuse lesions. Plasma proteins were found to infiltrate into the widened subendothelial space. Mesangial cells also protruded into the same space and encroached around the whole capillary wall. The interposed mesangial cells were occasionally separated from the basement membrane. Monocytes identified from their ultrastructure were frequently present noticed in the lytic areas, suggesting a reaction to lytic changes. These processes may occur repeatedly with direct expansion of the mesangial matrix, subsequently revealing a nodular appearance.

Pyroxenites and hornblendites from the maar-type volcanoes of the Westeifel, Federal Republic of Germany

The scoria cones of the Quarternary maarvolcanoes of the Westeifel, Federal Republic of Germany, contain abundant ultramafic nodules, among which the lherzolites of the Dreiser Weiher are very well studied. This work deals with ultramafic nodules from some other maar-type volcanoes of the same district. The nodules are pyroxenites and hornblendites. A petrographic description of the nodules and chemical analyses of their constituent phases are given. The main constituents are olivine (fo 83–91 mol %), Ti- and Al-rich salitic clinopyroxene, titaniferous pargasitic amphibole, and titaniferous phlogopite. The nodules are interpreted as low pressure cognate cumulates of an undersaturated nephelinitic magma. Clinopyroxens and olivines of some nodules, however, are presumably early high pressure, high temperature phases. The mechanism of nodule formation is discussed.

Morphological and Physiological Studis on Nodule Formation in Leguminous Crops : VI. On the factors detemining the location of nodule formation on root system in kidney bean and sword bean.

In a previous paper (KAMATA 1958a), the author reported that eighteen leguminous crops might be classified into two groups which belonged to the following types ; i. e. I-A type--nodules formed on both the primary and all the lateral roots, and I-B type--nodulation took place only on the lateral roots. This experiment was carried out to know the mechanism of nodule formation in I-B type using kidney bean (Phaseolus vulgaris L.) and sword bean (Canavalia gladiata D. C.) as materials. By the histological study, it was clearly seen that the number of the cells in primary root, which were infected with penetration of Rhzobium were similar in both cases, I-B type (kidney bean and sword bean) and I-A type (soybean and peanut), even though the nodule scarcely formed afterwards on the primary root in the former. The weak staining with HEIDENHAIN'S iron-alum hematoxylin, when examined microscopically, proved no proliferation of nodule bacterium in the first infection cells of I-B type plants. Cutting off a part of cotyledon from seed before sowing resulted to stop the development of nodule on a primery root in I-B type crops until flowering season. The nodule bacterium however, succeeded to grow, when it was cultured on RAGGIO'S complete cultural medium added with the different amount of the extract obtained by the systematic extraction method from primary, secondary and tertiary roots of I-B type plants. The fact proved that the extract contained no inhibitor, which might be a toxic or promotive substance for the growth of bacterium in primary roots of I-B type plants. In comparison of the amount of reducing sugar, non-reducing sugar and crude starch in root and rootlets of I-A type plant (soybean) and I-B type plants (kidney bean and sword bean) measured by Somogi's method, a complete parallelism was found between the concentration of available sugar, which was carbon source for growth of nodule bacterium in vitro, and the degree of nodule development. The amount of available sugar in the primary root of I-B type plants was lower and the amount of unavailable carbohydrate such as starch was higher as compared with those contained in other rootlets. Therefore, the nodule bacterium in the first infection cell might be inhibited to grow by the lack of available sugar in the primary roots in I-B type plants. If the above mentioned supposition is appropriate, nodules must appear on primary root of I-B type crops, when unavailable carbohydrate in the root is changed into available sugar. The wilting treatment was thought to be one of the useful methods for changing carbohydrate to available sugar, and such results were obtained after treatments of wilting given three times during seedling stage as incease of available sugar, decrease of crude starch and the development of nodules on the primary roots in both the case of kidney bean and sword bean.

OBSERVATIONS REGARDING ARTIFICIALLY INDUCED SUBCUTANEOUS NODULES IN RHEUMATIC FEVER PATIENTS

Subcutaneous nodules indistinguishable from spontaneously occurring nodules have been artificially induced in rheumatic patients by the subcutaneous injection of blood. The frequency, size and duration of the induced nodules correlated closely with the severity and duration of the rheumatic process. Only infrequently could nodules be induced in control subjects suffering from conditions unrelated to rheumatic fever. Although citrated blood obtained from patients with highly active rheumatic fever seemed to be more effective in inducing nodules in quiescent and mildly active rheumatic patients than did the patient's own blood, the active rheumatic blood was not more effective than blood obtained from healthy young adults. The daily injection of convalescent rheumatic serum into the site of the nodule test did not interfere with the induction of nodules. Saline, as well as blood, effectively induced nodules in certain patients, provided that it was injected with the standard traumatizing technic. It is concluded that the development of nodules results from injury to the subcutaneous fibrous tissue, the reactivity of which is altered by the rheumatic process, and that the hypothesis of a nodule-stimulating substance present in the blood of active rheumatic patients is untenable. Nodules have been induced in some rheumatic patients by the subcutaneous injection of hyaluronidase. These observations, together with the observations of others that trypsin is also an effective nodule-inducing agent, suggest that enzymes may play a role in the mechanism of nodule formation. However, it is also possible that these substances act in quite a nonspecific way and set off the nodule reaction merely by injuring the subcutaneous fibrous tissue.