Michio Sekiya

Studies on Fluidization of Particles of Gypsum Series

The authors studied on the fluidity of particles of gypsum series such as dihydrate, hemihydrate as well as anhydrite and contributed these results to the fundamental problems concerning with the manufacturing process of various gypseous products such as plaster of Paris or Keenes cement etc.As samples the authors used gypsum of by-product from salt manufacture and natural gypsum of Rasmallap Island by origin as well as the latter calcined for each 30 min. at 180°, 500° and 800°C respectively. The above samples were sieved between 0.0300-0.0147, 0.0147-0.0104, 0.0104-0.0074cm and finer than 0.0074cm particle sizes. Then, for comparison, the Normal Sand (JIS R 5201) was used at the same procedure. As fluidizing apparatus the authors used a tube of glass, with dimensions of 5cm diameter and 1m hight. The results were as follows.The particles of gypsum series between 0.0300-0.0074cm sizes showed a good fluidization. However, they were less fluid than the Normal Sand, and dihydrate especially by-product one had very worse fluidity than hemihydrate or anhydrite. It is considered that these results were caused by the difference of particle shapes and of formation process. All finer particles than 0.0074cm (200 meshes), except the case of by-product gypsum, showed “channeling.” Moreover, it was recognized that slugging was observed for all samples when the hight of fixed bed reached to the amount more than twice of diameter of fluidizing tube. The hight of fluidizing bed was larger as the amount of samples was smaller, and also, with some exceptions, as the particle sizes larger. For the particle of gypsum series the bed hight increased as its specific gravity increased, namely, in the order, from dihydrate, himihydrate to anhydrite. But it appears that this fact was influenced by the kinds of particles. The necessary air velocity to obtain good fluidity was u>0.15um, and at this time the bed hight expanded to about 1.5-3.0 times of the hight of fixed bed.

STUDIES ON PREPARATION OF GYPSUM PLASTER BY THE SPECIAL HYDROTHERMAL METHOD (II)

In continuing the previous studies, it is the main point to studing, in the present paper, on the special hydrothermal method for making gypsum hemihydrate CaSO4⋅1/2H2O by directly crystallizing out from gypsum crystal in the solution of various electrolyte of organic and inorganic salts, as following: (1) Sodium salts of oxalic, acetic, citric and tartaricacids, and Rochelle salt or potassium and sodium tartarate, and gelatine, and (2) Sulphates as Na2SO4, K2SO4, ZnSO4, MgSO4, Al2(SO4)3, Cr2(SO4)3, Fe2(SO4)3, K2Al2(SO4)4, (NH4)2Al2(SO4)4, K2Cr2(SO4)4 and (NH4)2Fe2(SO4)4, phosphate as NaH2PO4, and borate as Na2B4O7. In the former case of organic acid salt, sodium salt of citric acid was proved to be the most suitable electrolyte in water solution of 0.1-0.01%, to obtain good crystallized tabuilar or prismatic crystal of gypsum hemihydrate. In the latter case of various inorganic salts, Al2(SO4)3 was observed to be most effective in its 5% or more concentrated solution. to obtain the hemihydrate above described.