Dry paste

A typical plot of torque versus amount of liquid (di-butyl-phthalate, DBT) added is given in Fig. 15 for a very porous sodium carbonate powder mixture. The increase in measured torque at around 25% by volume DBT and again at around 65 %, can easily be seen (the final decrease in torque upon the formation of the wet cake is not shown). These two points correspond to the condition under which the continuous network of bridges forms, at about 25% liquid present, and the formation of the dry paste, at around 65%, where enough binder is available to fill most internal voids. The amount of liquid in Fig. 15 is given as a fraction of the total volume of powder, instead... 

To 27.5 g. (0.1 mole) of crude (carbonato)bis(ethylenediamine)-cobalt(III) chloride is added 200 ml. of 1.00 N hydrochloric acid. The carbonato complex is dissolved with evolution of carbon dioxide gas and formation of a red solution consisting primarily of the corresponding cw-diaqua species. The solution is evaporated in the steam bath until an almost dry paste has been formed. The purple residue is filtered and washed with three 20-ml. portions of ice-cold water. Drying in air yields 19.5 g. of purple crystals of cu-dichlorobis(ethylenediamine)cobalt(III) chloride. The mother liquor and the washings are again evaporated almost to dryness to yield a second crop of crystals, 5.9 g. The total yield is 25.4 g. (84% based on (carbonato)bis(ethylenediamine)cobalt(III) chloride). The analysis and the visible absorption spectrum of the two fractions are identical. Anal. Calcd. for [Co(en)2Cl2 ] C1 H20 Co, 19.42 N, 18.46 C, 15.82 Cl, 35.05 H, 5.98. Found Co, 19.50 N, 18.57 C, 15.77 C1, 35.15 H, 6.01. 

To Make Slow Match.—Dissolve 1 drra. nitrate of lead in H oz. boiling water. Cut a sheet of blotting paper in six equal parts, and wet them on both sides, with a sash tool, with the solution. When dry, paste a piece all over, and upon it smoothly press another piece upon this, pasted, put a third piece and so on, till all the six form a stiff board, iky them under a heavy weight and, when dry, with a sharp knife and straight edge, cut the whole into strips a quarter of an inch broad. Four inches will burn about a quarter of an hour. Narrow tape, boiled in the solution, makes excellent slow match. 

Fig. 8.5 Relations between porosities (volume percentages) and water/ccmcnt ratio for mature Portland cement pastes. The experimental data are for pastes at least 8 months old, and the calculated curves relate to a typical cement aged 18 months. Open symbols total water porosities. Filled or half-filled symbols mercury porosities. Curve A total water porosity. Curve B free water porosity. Curve C capillary porosity. References to data O (P20) O (S77) A (F33) V (M68) (S78) (F34) 9 (019) (M68) (D3I) 3 (H4I). In the last two cases, porosities by volume were estimated from data referred in the original sources to masses of dried paste, assuming the tatter to have contained 0.23 kg of water per kg of cement having a specific volume of 3.17 x 10 m kg h...

Porosities have sometimes been reported as percentages by volume of the paste and sometimes as volumes per unit weight of dried paste. The first is the more meaningful, especially as in the latter case the water content of the material has not always been given, A similar comment applies to specific surface areas (L41). 

Powers and Brownyard (P20) found that porosities of D-dried pastes obtained using helium as the pyknometric fluid were lower than those obtained using water. Feldman (F33) confirmed this and found that a lower value was also obtained using methanol if a D-dried sample was exposed to... 

In principle, isotherms at low partial pressures of the sorbate may be used to determine specific surface areas by the Brunauer-Emmett-Teller (BET) method (G64). In this method, it is assumed that molecules of the sorbate are adsorbed on surfaces that can include the walls of pores, provided that the distance between molecules on opposing walls is large compared with molecular dimensions. From a plot derived from the isotherm, and given the effective cross-sectional area of the sorbate molecule, the specific surface area of the sorbent and the net heat of adsorption are obtained. Using water as sorbate, specific surface areas of about 200 m per g of D-dried paste have typically been obtained for mature cement pastes of normal w/c ratios... 

Using N2 sorption on samples solvent-dried by methanol exchange, Hansen and Almudaiheem (H41) found the volumes of pores with diameters smaller than 4 nm and accessible to N2 to be 0.052 ml, 0.035 ml and 0.038 ml per g of dry paste for mature pastes of w/c ratio 0.4, 0.6 and 0.75 respectively. These results correspond to volume porosities of about 9%. 5% and 4%, respectively. 

Paullinia cupana (guarana) contains the xanthines theobromine and theophylline as well as flavone glycosides. The crushed seeds of P. cupana are made into a dried paste called guarana, from which a beverage is prepared. All of its effects are directly related to its high content of caffeine-like substances. 

Guarana Dried Paste, Paullinia Cupana Brazil... 

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