This quantitative analysis of α- and β-hemihydrates is based on the fact that the transformation ratio of them to II CaSO₄ is remarkably different under moderate conditions of heating.
When α- and β-hemihydrates are heated at 200°C for 24 hr, they are partly transformed to II CaSO₄ with the following composition, respectively
α_II=55.0%II CaSO₄+45.0%αCaSO₄·1/2H₂O
β_II=14.8%II CaSO₄+85.2%βCaSO₄·1/2H₂O
Therefore, when a mixture of α- and β-hemihydrates is heated under the same condition, the compositions of the heat-treated mixture consist of a mixture of α_II and β_II.
The determination of each component in the mixture of α- and β-hemihydrates can be easily made by the determination of all and 1311 in the heat-treated mixture.
Using this technique, determinations of crystal water, heat of hydration and content of II CaSO₄ in the mixture of an and β_II are examined by means of TG, calorimeter and XRD.
The relative standard deviation is used as a measure of scatter of the experimental values.
The relative standard deviation is less than 2% for both crystal water and heat of hydration and 3. 74-4. 55% for content of II CaSO₄.
This indicates that the determination of both crystal water and heat of hydration can be accurately carried out on the mixture of an and β_II

View full abstract

On heating to 1000°C, gypsum expands below 100°C, and then shrinks by dehydration up to 500°C, and over 600°C shrinks strongly, remaining the derormated crystals. It was recognized that the strong shrinkage over 600°C would be originated in this deformation. Procedures to control this shrinkage by mixing refractory materials to gypsum, or by adding materials to prevent crystal deformation were tested, and following results were obtained.
Addition of glycerine, quartz, carbon, magnesia, metaphosphoric acid and chromium (III) oxide have small effect.
Addition of glycerine and quartz, silicone, ammonium dihydrogen phosphate and hydrochloric acid, magnesium chloride and ammonia water, aluminium chloride, and water : glass have respectable effect.
Addition of phosphoric acid, aluminium chloride and phosphoric acid, aluminium chloride and ammonia water, and chromium (VI) oxide have strong effect.
The gypsum samples which were added strongly effective materials expand on reheating to 1000°C and shrink on cooling both corresponding to temperature, remaining small residual shrinkage and weight loss due to the decomposition of gypsum.
X-ray analysis of these gypsum samples indicate the existence of refractory materials such as AlPO₄, 3CaO·Al₂O₃, Al₂O₃·Cr₂O₃ respectively.
ESCA analysis indicates that those refractory materials exist on the surface of gypsum crystals, and so prevent the deformation.
Compressive strength of gypsum descends to 1/2 -1/5 of that of nonadded one according to added material, and it degrades to 1/2-1/5 of each one by calcination at 260° and 500°C.

View full abstract

Applying the zeolite/aluminium-flock composite material such as one of new polutant removal reagents for the sewage treatment, the simultaneous adsorption abilities of PO₄^3- and NH₄⁺ in the sewage and the effects of the sewage constituents on the adsorption abilities were investigated. Both adsorption abilities of the sewage PO₄^3- and the sewage NH₄⁺ decreased to about 60% of its original value, and their weights of the adsorption were 9. 6 mg-PO₄^3- and 2. 6 mg-NH₄⁺ per 1g of the removal reagent. These decrease of the adsorption abilities seemed to be depending on very low concentrations of PO₄^3- and NH₄⁺ in the sewage used. In view of the experimental fact, BOD constituents, large amount of Cl^- Zn²⁺, Cu²⁺, etc. present in the sewage might be thought to have no interfering with the adsorptions for PO₄^3- and NH₄⁺.

View full abstract