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doi: 10.1002/jctb.280430102pmid: N/A
Investigations were carried out to produce an autoclaved gypsum plaster (α‐hemihydrate) by heating the naturally occurring selenite and by‐product phosphogypsum under steam pressure in an autoclave. Various factors effecting the calcination of gypsum such as pressure, time of the autoclaving process and the particle size of gypsum lumps were investigated. The formation of hemihydrate was examined by periodic differential thermal analysis and weight loss determinations. The mineralogical studies of plaster were determined using microscopy and X‐ray diffraction. The data showed that complete inversion of gypsum into hemihydrate takes place by heating gypsum of particle size 15 to 20 mm3 at 1.75 kg cm−2 steam pressure for 7 h. The microscopy of plaster revealed formation of well‐defined euhedral prismatic and tabular shaped crystals showing a higher degree of crystallinity than the conventional β‐hemihydrate. The hydraulic properties of plaster were studied and it was found to possess considerable strength (230 kg cm−2). The α‐plaster has been found suitable for making masonry mortar and fibrous plaster boards according to the relevant Indian Standards for use in construction works.
Ruggeri, Bernardo; Genon, Giuseppe
doi: 10.1002/jctb.280430103pmid: N/A
The performance of a cyclic reactor was examined using a kinetic model allowing for inhibition by the metabolic product of the growth of microorganisms and production coupled with their growth and maintenance. The reactor's stability field was investigated through a search for cyclically stable solutions giving Sf ≠ O and Xf ≠ O. The productivity pattern and substrate utilisation as functions of the operating variables were studied within this field. Comparison of these results with those obtained with a Monod‐type kinetics leads to the conclusion that they are of general validity and do not depend on the kinetic model adopted.
Al‐Ayed, Omar S.; Kunzru, Deepak
doi: 10.1002/jctb.280430104pmid: N/A
The main reaction and deactivation kinetics of cyclohexane dehydrogenation in the presence of hydrogen has been investigated at atmospheric pressure over a nickel kieselguhr catalyst in the temperature range 583–623 K. The rate of reaction for the fresh catalyst increased with increasing temperature, cyclohexane and hydrogen partial pressures whereas it decreased with an increase in the benzene partial pressure. The experimental data could be adequately modelled by a power law rate expression. The catalyst activity decreased with run time due to catalyst fouling by coke deposition. The rate of deactivation was independent of cyclohexane partial pressure, increased with increasing benzene concentration and decreased with increasing hydrogen partial pressure. It is postulated that coke is most likely formed by the successive dehydrogenation of benzene.
doi: 10.1002/jctb.280430105pmid: N/A
The effectiveness and efficiency of nine different natural oils were investigated using simulated fermentation media and several dimensionless coefficients were derived to provide a means for quantitative comparison. Furthermore, correlations between the physical and chemical properties of natural oils and of media and foam‐suppression efficiencies of natural oils were sought. It was concluded that the effectiveness of a natural oil in foam suppression greatly varies with the type of medium.
doi: 10.1002/jctb.280430106pmid: N/A
Ethanol fermentation by Saccharomyces cerevisiae was investigated in broth‐organic solvent two‐liquid phase systems with and without interphase mixing. The effect of interphase mixing with aliphatic alcohols as polar solvents and with alkanes as apolar solvents was determined from investigations in three distinct systems: a solvent‐saturated broth, a solvent‐broth dispersion system and a dispersion‐free solvent‐broth system.
Ahmed, Abd El‐Hamid N.; Abd‐Alla, Mohamed A.; El‐Zohry, Maher F.
doi: 10.1002/jctb.280430107pmid: N/A
Several new quinazolin‐4‐one containing oxadiazolin‐5‐thione moieties were synthesized and evaluated for their antibacterial activity. Esterification of 2‐substituted phenyl‐3‐carboxyalkyl‐methyl‐3,4‐dihydroquinazolin‐4‐ones (I) with absolute ethyl alcohol in the presence of sulfuric acid afforded the corresponding esters (II). Hydrazinolysis of (II) with hydrazine hydrate in ethanol gave the acid hydrazides (III). Refluxing (III) with equimolar amounts of potassium hydroxide and slight excess of carbon disulfide afforded the corresponding oxadiazolin‐5‐thione derivatives (IV). The thiones undergo Mannich reaction using a formaldehyde/secondary amines mixture whereby the 4‐substituted amino‐methyl derivatives (V) were obtained. Microanalysis, IR, NMR spectra were used to elucidate the structures of the newly synthesized compounds. All the designed compounds were tested for their antibacterial activity. The morpholino derivatives showed an encouraging antibacterial activity.
Kishimoto, Shin'ichi; Naruse, Masayoshi
doi: 10.1002/jctb.280430108pmid: N/A
It is known that rod‐like crystals of aspartame, in which several needle crystals appear to be bundled together (bundle‐like crystals), have remarkably improved physical properties compared to the crystals obtained from a conventional stirred crystallizer.
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