The present investigation aims to examine characteristic properties of Ca-rich (calcian) dolomites.
For this purpose, dolomite samples from Cebu. the Philippines were studied by means of EPMA, XRD, IR techniques and TG-DTA. In addition, several samples from Kuzuu, Tochigi Pref. and a well cryrstallized, stoichiometric sample from Korea, together with synthetic dolomites and magnesian calcites were also examined for comparison.
The main results obtained are summarized as follows.
1) EPMA indicates that the Philippine samples are remarkably heterogeneous, consisting of several phases of different compositions.
2) From the relation between d₁₀₄ values or lattice parameters and chemical compositions, it is suggested that almost all samples are composed of at least two phases having different CaCO₃ contents. One of them is nearly stoichiometric (Ca/Mg=1.0-1.1) and the other is more calcian (Ca/Mg=1.3-1.4). Linear relation is observed between co parameter and CaCO₃ content in the latter phase.
3) The IR absorption intensity ratio I (730 cm^-1) /I (880 cm^-1) is found to be a good indicator of the degree of structure ordering, as well as the widely used method using X-ray intensity ratio I (015) /I (110).
4) The first endotherm of the DTA curves obtained in CO₂ flow shifts to higher temperature side by 10 to 20 degrees, compared with those of normal dolomites. Some interesting results are observed on the synthetic high Mg-calciites and disordered dolomites.

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Halogen-bearing apatites were prepared by heating the powder mixtures of hydroxyapatite and NH₄F or NH₄Cl at 1000°C for 1 hr. As for the lattice constants of the apatites so prepared, Vegard's law held across the entire ranges. The peak seperation and shift in the OH band (3572 cm-1) of IR indicated the presence of hydroxyl groups whose stretching were peturbed by the halogen atoms.
Dense sintered apatites (above 90% of the thoeretical density) were obtained by firing in the air at 1200°C for 1 hr. The apatites hot-pressed at 1100°C and 375 kg/cm² for 1 hr became more dense (94-98%) than those by ordinary sintering, and some of the hot-pressed apatites containing chloride were transparent. The values of Vickers hardness for the halogen-bearing apatites were found to be 500-700 kg/mm².

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Refractory lining of cement and lime rotary kilns is exposed, at high temperatures, to strain and shearing due to rotation of the kiln. One of the many factors influencing an increased refractory life is an increase in the latter's high temperature strength.
From this point of view, specimens consisting of the same ratio of chrome are and sea water magnesia were fired at 1750°C, 1800°C, and 1850°C. The relationship between high temperature characteristics and the microtexture of the resulting fired test pieces was studied.
High temperature characteristics was measured using an HMOR furnace with a three-point bending system and the microtexture was observed using a SEM and an EDS.
At 1200°C the silicate phase was seen to have some influence on the hot strengh on all test specimens. Those fired at 1850°C for two hours exhibited the highest value followed by those fired at 1800°C for two hours then by those fired at 1750°C for two hours. Test specimens fired at 1800°C and soaked at six hours gave lower value compared to those fired at the same temperature but soaked for two hours.
At 1400°C, the hot strength was seen to have been influenced by the spinel bonds. Again, specimens fired at 1850°C for two hours gave the highest hot strength value. But this time, those fired at 1800°C for 6 hours gave the second highest value followed by those fired at the same temperature but soaked for two hours then by the specimens fired at 1750°C for two hours.
SEM/EDS observations showed that at 1850°C firing and two hours soaking, Cr₃0₃ in the spinel bond has higher peaks compared to Fe₂0₃. A similar pattern is seen on those specimens fired at 1800°C and soaked for six hours. At 1800°C and two hours soaking, Cr203 peaks, although still higher, already approaches that of the Fe₂0₃ peak. At 1750°C, this gap is further shortened.
This high quantity of Cr₂0₃ in the spinel bond has great influence on the hot strength of the bricks. This suggests that high temperature firing in actual manufacturing process of basic refractory bricks is a very important factor.
In actual usage, the basic refractory bricks having the same texture as those exhibited by test specimens fired at 1850°C, in this study, exhibited increased refractory life.

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adhesion on the spinel-magnesia brick when it is being used in the burning zone of the rotary cement kiln, however, by adding a small amount of Fe to the bonding part of the spinel-magnesia brick, increase of coating adhesion is expected.
In this study, two types of spinel-magnesia brick, one with 0.7% of Fe₂0₃ in the bonding part and the other with 0.03% of Fe₂0₃, were used for both laboratory test and practical lining test in the rotary cement kiln to compare coating adhesion characteristic between them. Remarkable difference in the coating adhesion was observed in the laboratory test, however, it became more clearer in the rotary kiln lining test.
After 640h, 952h, 1562h and 2420h of kiln performance, kiln shell temperature was measured. From the shell temperature, the degree of coating adhesion was presumed.
As the result, the kiln shell temperature where the test brick with 0. 7% of Fe₂0₃ was located was obserbed 130°C lower than the temperature of the shell where the less Fe₂0₃ brick was lined. Remarkable difference in coating adhesion appeared in the both bricks.
Also used test brick was analyzed and the existence of C₄AF in the boundary between cement coating and the test brick was observed.

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