Effect of carbon and silicon on the structure and corrosion resistance of 18cr-8ni cast steel in concentrated nitric acid solutions

The solutions of nitric acid can be divided into two concentration ranges: range I from 0 to 60–70% and range II from 80 to 100%. The 18Cr-8Ni cast steel with about 4% Si and up to 0.12% C exhibits very good corrosion resistance in concentrated nitric acid solutions (up to 98%); however, it is slightly inferior to a corresponding 18 Cr-13 Ni grade. The investigations were concentrated on the effect of the carbon and silicon contents on structure and corrosion resistance of an 18 Cr-8 Ni cast steel in cold nitric acid solutions. The following materials were used in these studies: a cast stainless steel of type 18Cr-8Ni with 0.48–6.75% Si and 0.021–0.220% C. A detailed analysis of the main result shows that

• 1. in cold HNO₃ solutions of concentrations above 80% the silicon content in a cast steel must not be lower than 2.5-3.0%;
• 2. the 18Cr-8Ni cast steel containing more than 4% Si and up to 0.12-0.13% carbon is practically not susceptible to corrosion in cold HNO₃ over the whole range of concentrations.

     

Influence of furfuryl moulding sand on flake graphite formation in surface layer of ductile iron castings

The influence of the use of moulding sand with furan resin, prepared both with fresh sand and reclaimed matrix, on the formation of a flake graphite formation at the surface layer of ductile iron castings has been investigated. A series of experimental heats of ductile iron cast in moulds made of moulding sand characterised by different levels of surface active elements (sulphur, oxygen) were performed. The effect of the wall thickness and the initial temperature of the metal in the mould cavity on the formation of flake graphite in the surface layer of the casting is shown in the paper. Investigations carried out by means of scanning electron microscopy (energy dispersive X-ray spectroscopy and wavelength dispersive X-ray spectroscopy) showed concentration of gradient profiles of surface active elements in the castings surface layer, which are responsible for their quality. Finally, it has been shown that there exists a significant effect of the quality of the sand on the formation of the flake graphite layer and the surface characteristics of ductile iron castings.     

Investigation of the ion dose non-uniformity caused by sheath-lens focusing effect on silicon wafers

The ion dose non-uniformity induced on the wafer surface by modal and discrete focusing effects is investigated for different plasma densities and implantation parameters. Measured impact radius agrees well with values obtained by simulation. The optical pattern observed on the wafer surface is correlated with the ion dose by FT-IR measurements. The applicability of a previously proposed vertical ring is demonstrated, the ring being able to considerably improve the ion flux uniformity by shifting the discrete focusing effect out of the wafer surface and reducing the modal focusing. Experiments are performed in an inductively coupled plasma produced in hydrogen.     

Corrosion resistance of cast steel in hydroxylamine sulphate solution

In hydroxylamine sulphate production processes fittings made from cast steel 18Cr-10Ni failed after short working periods due to inadequate corrosion resistance. By means of weight loss measurements different austenitic and austenitic-ferritic grades of cast steel with higher amount of alloying elements were tested in cold hydroxylamine sulphate solution before hydrolysis and in hot solution after second reactor. Cast steel types 20Cr-25Ni and 25Cr-6Ni have shown the highest corrosion resistance. The laboratory results were verified by industrial tests where gate valves made from cast steel type 20Cr-25Ni after 4 years of working period are still in a good state.     

Cross-reactivity in HIV-infected patients switched from trimethoprim-sulfamethoxazole to dapsone

STUDY OBJECTIVE: To evaluate the cross-reactivity of dapsone after a documented hypersensitivity reaction to trimethoprim-sulfamethoxazole (TMP-SMX) during prophylaxis for Pneumocystis carinii pneumonia. DESIGN: Retrospective, chart review, cohort study. SETTING: Two university-affiliated teaching hospitals. PATIENTS: Sixty patients infected with the human immunodeficiency virus. MEASUREMENTS AND MAIN RESULTS: Thirteen patients (21.7%) had cross-reactivity to dapsone after the reaction to TMP-SMX. No significant risk factors for this response were identified. Most reactions were of mild or moderate severity and rated as possibly or probably caused by one of the agents. Of the 13 patients, 4 (30.8%) continued therapy. CONCLUSIONS: Although cross-reactivity can occur, dapsone may be considered in patients with mild hypersensitivity reactions to TMP-SMX.     

Cognitive processes related to gait velocity: Results from the Einstein aging study.

The authors examined the relationship between cognition and gait velocity, performed with and without interference, in elderly participants. Neuropsychological test scores from 186 cognitively normal elders were submitted to factor analysis that yielded 3 factors: Verbal IQ, Speed/Executive Attention, and Memory. Regression analyses revealed that these factors were significant predictors of variance in gait velocity, but the relationship varied as a function of task condition. All 3 factors predicted gait velocity without interference. However, the Speed/Executive Attention and Memory factors but not Verbal IQ predicted gait velocity in the interference condition. These findings suggest that gait velocity and cognitive function may have both shared and independent brain substrates. Future studies should explore gait velocity and cognitive function as predictors of dementia and falls. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Site-specific thermodynamics and kinetics of a coiled-coil transition by spin inversion transfer NMR

A 33-residue pseudo-wild-type GCN4 leucine zipper peptide is used to probe the equilibrium conformational population in proteins. 13Calpha-NMR shows that chain sites differ in structural content at a given temperature, and that two dimeric folded forms are evident at many sites. Spin inversion transfer experiments are reported bearing on the thermodynamics and kinetics of interconversion of the two dimeric folded forms (Fa <--> Fb) at the 13Calpha-labeled position L13. At each temperature, at conditions wherein the population of unfolded chains is quite small, inversion of the Fa spins via a tuned Gaussian pi-pulse is followed by a time interval (tau), interrogation, and recording of the free induction decay. Fifteen such inversions, with varying tau, provide the time course for recovery of equilibrium magnetization after inversion. Similar experiments follow inversion of the Fb spins. Re-equilibration is known to be modulated by four first-order rate constants: two (T1a(-1) and T1b(-1)) for spin-lattice relaxation intrinsic to the respective sites, and two (kab and kba) for the conformational change. All four follow from joint, Bayesian analysis of all the data at each temperature. The equilibrium constant at each temperature for this local transition, determined simply from the equilibrium relative magnetizations at Fa and Fb sites, agrees well with the kinetic ratio kab/kba. The standard Gibbs energies, enthalpy, and entropy follow. Activation parameters, both ways, are accessible from the rate constants and suggest a transition state with high Gibbs energy and enthalpy, but with entropy between those of Fa and Fb.     

Investigations of physicochemical properties of dusts generated in mechanical reclamation process of spent moulding sands Mth alkaline resins

Mechanical reclamation processes of spent moulding sands generate large amounts of post- reclamation dusts mainly containing rubbed spent binding agents and quartz dusts. The amount of post- reclamation dusts, depending in the reclamation system efficiency and the reclaim dedusting system, can reach 5%-10% in relation to the total reclaimed spent moulding sand. The proper utilization of such material is a big problem facing foundries these days. This study presents the results of investigations of physicochemical properties of post- reclamation dusts. All tested dusts originated from various Polish cast steel plants applying the mechanical reclamation process of moulding sands with alkaline resins, obtained from different producers. Different dusts, delivered from foundries, were tested to determine their chemical composition, granular characterization, physicochemical and energetic properties. Presented results confirmed assumptions that it is possible to utilize dusts generated during mechanical reclamation of used sands with organic resins as a source of energy.     

Structural stability of short subsequences of the tropomyosin chain

The native tropomyosin molecule is a parallel, registered, alpha-helical coiled coil made from two 284-residue chains. Long excised subsequences (> or = 95 residues) form the same structure with comparable thermal stability. Here, we investigate local stability using shorter subsequences (20-50 residues) that are chemically synthesized or excised from various regions along the protein chain. Thermal unfolding studies of such shorter peptides by CD in the same solvent medium used in extant studies of the parent protein indicate very low helix content, almost no coiled-coil formation, and high thermal lability of such secondary structure as does form. This behavior is in stark contrast to extant data on leucine-zipper peptides and short "designed" synthetic peptides, many of which have high alpha-helix content and form highly stable coiled coils. The existence of short coiled coils calls into question the older idea that short subsequences of a protein have little structure. The present study supports the older view, at least in its application to tropomyosin. The intrinsic local alpha-helical propensity and helix-helix interaction in this prototypical alpha-helical protein is sufficiently weak as to require not only dimerization, but macro-molecular amplification in order to attain its native conformation in common benign media near neutral pH.     

Effect of Reclamation on the Skin Layer of Ductile Iron Cast in Furan Molds

The paper presents the results of investigations of the influence of the quality of molding sand with furan resin hardened by paratoluenesulfonic acid, on the formation of microstructure and surface quality of ductile iron castings. Within the studies different molding sands were used: molding sand prepared with fresh sand and molding sands prepared with reclaimed sands of a different purification degree, determined by the ignition loss value. Various concentrations of sulfur and nitrogen in the sand molds as a function of the ignition loss were shown in the paper. A series of experimental melts of ductile iron in molds made of molding sand characterized by different levels of surface-active elements (e.g., sulfur) and different gas evolution rates were performed. It was shown that there exists a significant effect of the quality of the sand on the formation of the graphite degeneration layer.