Carboxylates and sulfates of polysaccharides for controlled internal water release during cement hydration

Calcium and aluminium carboxylates and sulfates of polysaccharides form hydrogels. Four Al- and three Ca-salt hydrogels of such polysaccharides, which were found to be stable enough to be mixed into fresh Portland cement pastes of low initial water-to-cement ratio of 0.275, were compared with respect to their water retardation potential using non-destructively operating low-field ¹H NMR relaxometry. All of the investigated hydrogels release their water to the cement mainly during the accelerated period of cement hydration. At a degree of hydration of about 0.7 the water in the hydrogels is consumed completely by the hydration reactions. Based on Powers’ hydration model the development of the volumetric phase distribution of the investigated hydrating cement with internal curing by the hydrogels was quantified. Within the hardening cement the Ca-salt hydrogels are more stable than the Al-hydrogels which is concluded from the changes of the T₂ relaxation times during the cement hydration.     

Anwendung der Warburg-Technik für Korrosionsmessungen an Nickelproben mit und ohne Stromdurchgang

Use of the Warburg technique to measure corrosion of nickel samples with and without passage of current The use of the Warburg technique in corrosion processes makes possible the determining of the kind and extent of gas participation in the reaction. Specially in the corrosion of pure nickel in aqueous solution of hydrochloric acid containing oxygen, it may be decided how muc of the oxygen present is reduced to hydrogen peroxide or water. The relationship of both reaction products is dependent on the passage of current through the nickel electrode. The experiments were carried out under stationary conditions, i.e. conditions similar to those in practice. Surface qualities therefore influenced the results. It could be shown that this influence mainly concerns the reduction of oxyge to water and the formation of absorbed hydrogen, whilst the extent of hydrogen peroxide formation is decisively dependent on the passage of current through the electode. The maximum formation of hydrogen peroxide lies in the steady state potetial of teh nickel sample.     

Schrifttumsberichte

Ohne Zusammenfassung     

Neuromyelitis optica does not impact periventricular venous density versus healthy controls: a 7.0 Tesla MRI clinical study

Objective

To quantify the periventricular venous density in neuromyelitis optica spectrum disease (NMOSD) in comparison to that in patients with multiple sclerosis (MS) and healthy control subjects.

Materials and methods

Sixteen patients with NMOSD, 16 patients with MS and 16 healthy control subjects underwent 7.0-Tesla (7T) MRI. The imaging protocol included T₂*-weighted (T₂*w) fast low angle-shot (FLASH) and fluid-attenuated inversion recovery (FLAIR) sequences. The periventricular venous area (PVA) was manually determined by a blinded investigator in order to estimate the periventricular venous density in a region of interest-based approach.

Results

No significant differences in periventricular venous density indicated by PVA were detectable in NMOSD versus healthy controls (p = 0.226). In contrast, PVA was significantly reduced in MS patients compared to healthy controls (p = 0.013).

Conclusion

Unlike patients with MS, those suffering from NMOSD did not show reduced venous visibility. This finding may underscore primary and secondary pathophysiological differences between these two distinct diseases of the central nervous system.

     

The Role of Biodegradable Poly-(L-lactide)-Based Polymers in Blood Cell Activation and Platelet-Monocyte Interaction

The main purpose of new stent technologies is to overcome unfavorable material-related incompatibilities by producing bio- and hemo-compatible polymers with anti-inflammatory and anti-thrombogenic properties. In this context, wettability is an important surface property, which has a major impact on the biological response of blood cells. However, the influence of local hemodynamic changes also influences blood cell activation. Therefore, we investigated biodegradable polymers with different wettability to identify possible aspects for a better prediction of blood compatibility. We applied shear rates of 100 s⁻¹ and 1500 s⁻¹ and assessed platelet and monocyte activation as well as the formation of CD62P+ monocyte-bound platelets via flow cytometry. Aggregation of circulating platelets induced by collagen was assessed by light transmission aggregometry. Via live cell imaging, leukocytes were tracked on biomaterial surfaces to assess their average velocity. Monocyte adhesion on biomaterials was determined by fluorescence microscopy. In response to low shear rates of 100 s⁻¹, activation of circulating platelets and monocytes as well as the formation of CD62P+ monocyte-bound platelets corresponded to the wettability of the underlying material with the most favorable conditions on more hydrophilic surfaces. Under high shear rates, however, blood compatibility cannot only be predicted by the concept of wettability. We assume that the mechanisms of blood cell-polymer interactions do not allow for a rule-of-thumb prediction of the blood compatibility of a material, which makes extensive in vitro testing mandatory.     

NMR diffusion and relaxation studies during cement hydration—A non-destructive approach for clarification of the mechanism of internal post curing of cementitious materials

Internal post-curing of hardening cement pastes by addition of alginate spheres, which contain 98% of water, is studied by non-destructive ¹H NMR measurements of transverse relaxation time and self-diffusion. The onset and amount of water transition from the alginate gel used as additive with temporary delayed release of water to cement pastes was observed continuously during the dormant and accelerated period of cement hydration. During hydration, the water transition from the alginate into the cement matrix as well as the development of pore size is monitored quantitatively by studying the time dependence of characteristic peaks in the transverse relaxation time distribution. Comparison between samples without and with internal post curing shows that the addition of alginate gel does not influence the pore size in the micropore region. NMR diffusion studies demonstrate that the physically bound pore water has sufficient mobility to ensure homogeneous distribution of water from the alginate source into the surrounding cement matrix during the dormant and accelerated period.     

Enhancement of Efficiency in Crude Iron Production Using an Increased Amount of Pellet Feed

In order to use pellet feed, particularly iron ore with size distributions from 10 to 100 µm, in fluidized bed reactors, different binding systems for an agglomeration are evaluated. The micro agglomerates differ from each other in chemical compositions, contents, and thermal treatments. Crucial indicators for an application in a fluidized bed are reducibility as well as compressive strength. In pressure thermo gravimetric analyzer tests, micro agglomerates with lime hydrate and acid binder show the best reduction behavior, whereas micro agglomerates with inorganic binding systems reached the highest compressive strength before and after a three-step reduction process.