Microcalorimetric analysis of methylcellulose influence on the hydration process of tricalcium aluminate,alite and their mixture

In the paper, the results of investigation concerning the influence of 0.3% addition of hydroxypropyl methylcellulose (MC) of 40 and 70 Pa s viscosity on the hydration process of main clinker phases C₃S and C₃A are presented. The course of hydration is documented using microcalorimetry, and formed phases were identified by XRD. The research indicated that methylcellulose inhibited the hydration process of clinker phases, analysed both, separately and in their mixture. Moreover, it was found that the presence of MC admixture also led to the reduction in calcium sulphate dihydrate reactivity in the system.     

Polypyrrole-palladium systems prepared in PdCl2 aqueous solutions

In the work, reactions of a partially deprotonated polypyrrole doped with hydroxide ions (PPyOH) in various PdCl₂ aqueous solutions which differed in acidity were studied. Using X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy it was established that in the PdCl₂ solutions of lower acidity PPyOH was oxidatively doped and Pd⁰ and Pd²⁺ were incorporated into the polymer matrix. Pd²⁺ formed palladium(II) hydroxy-and/or aquochlorocomplex dopant anions and/or was coordinated by nitrogen atoms of the polymer (Pd-N bond). Additionally, deprotonation of PPyOH occurred in the PdCl₂ solutions of lower acidity. It was proposed that deprotonation of PPyOH was caused by nucleophilic attack of [PdCl₃(H₂O)]⁻ on the positively charged, doped polymer chain. By comparison of the PPyOH and chloride-doped polypyrrole (PPyCl)-palladium systems prepared in similar PdCl₂ solutions of lower acidity it was shown that the type of the counterion in the starting polymer has a decisive effect on the deprotonation process.PPyOH was less reactive towards palladium species in the PdCl₂ solutions of higher acidity where [PdCl₄]²⁻ was the dominant complex. PPy-palladium systems containing exclusively Pd²⁺ were obtained in this case. It was proposed that incorporation of palladium species in these conditions proceeded via an acid-base reaction or coordination of palladium ions by the polymer chain (Pd-N bond formation).Results of the studies may serve as the basis for the preparation of a variety of polypyrrole-supported palladium catalysts.     

The studies of the effect of sulfates added as chromium(VI) reducers in portland cement

The calorimetric measurements were applied in testing the effect of some sulfates, used as Cr(VI) reducers in cement, as setting and hardening modifiers. The iron(II) sulfate is most commonly added as Cr reducer to cement on grinding. This was taken as a reference in the studies of the other potential chromium reducers, such as tin(II) and manganese(II) sulfates on cement hydration. The high percentage of admixtures was reduced steadily from very high overdosage—to find the possible effect of non-homogeneity resulted from the hygroscopic character of compounds used and to detect the possible products which can be formed—to relatively small quantity, as used in practice. The progress of cement hydration was investigated by calorimetry and chemical shrinkage measurements. The rheological properties of cement paste admixtured with iron, tin, and manganese sulfates were investigated, as well as the phase composition of hydrated pastes was studies by XRD. The compressive strength of the small paste cylinders was measured. Finally, the hydrated samples were subjected to the SEM observations. The tin sulfate showed the strongest retarding action as it was proved by calorimetry and chemical shrinkage data, as well as by strength and rheological measurements; however, at small quantities, this compound has a positive impact on setting and hardening. The detrimental effect of overdosed Mn and Fe sulfates due first of all to the formation of higher amount of ettringite at very early age was found. This can be proved additionally by the change of rheological parameters—higher yield stress and viscosity.     

Characterization of 40-year-old calcium silicate pastes by thermal methods and other techniques

Differential thermal analysis, thermogravimetry and evolved gas analysis, as well as the X-ray diffraction, were used to identify and to quantify the products of dicalcium silicate hydration. The samples were 38 years stored in laboratory conditions. The calcium hydroxide, calcium carbonate and calcium silicate hydrate contents were determined and discussed in terms of the specific properties of initial anhydrous phases used.