Chemical vapor deposition was studied as early as in the years from 1922 to 1939 as a method of preparing high purity refractory metals and considerable progress in the fundamental studies and practical applications were carried out by Powell, Campbell and Gonser at The Battel Memorial Institute after 1955.
Some achievements of the auther's research have been applied already in Japan as a refractory coating for rocket nozzles and protective coating for nuclear graphites. However, chemical vapor deposition is promised to be of greater importance and interest in the future not only as the fundamentals of thermodynamics, crystalline growth but also a practical applications concerning with coating of nuclear fuel particles for fission product retention, epitaxially coated semi-conductor and whisker.
We have studied β-SiC coating by vapor-phase reaction of volatile silicon tetrachloride, toluen and hydrogen used as carrier gas which were induced onto the of surface graphite substrate heated by induction furnace. The composition of deposited layer was examined and identified mainly by X-ray powder diffraction analysis method.
The experiment was carried out under the conditions at the ratio of SiCl₄ and C₇H₈ varied between 1.3:1 and 5.0:1, the graphite substrate heated at the temperature ranging from 1200° to 1500°C and at the flow rate of 1400ml. per min.
The results obtained are summarized as follows;
1) It was found that massive vapor deposited coatings of beta silicon carbide were obtained already under proper control of conditions on graphite substrates at the temperature of about 1200°C.
2) Good adherent and metal-free β-SiC coating can be deposited at 1400° to 1450°C from a mixture of SiCl₄+C₇H₈+H₂, in which the SiCl₄:C₇H₈ ratio was maintained between 3.5:1 and 2.5:1. The layer tended to become more coarsely crystalline at the temperature up to 1450°C and the coating layers applied below 1350°C were consisted of the mixture of β-SiC and Si.
3) At the temperature of 1400°C, the rate of deposition of metal-free β-SiC coating layers was about 3.7μ per min.

抄録全体を表示

It has been well known that some carbohydrates have a injurious effect on the hydration of portland cement. Succharose, for example, acts as a retarder when present in low concentrations, but accelerates set (temporarily occurs the flash set in the strict sence of the word) when used at higher concentrations. Moreover, the development of the compressive and bending strength is lowered with the increase of the concentration of succharose, and the hardening of portland cement mortar and concrete are impossible over a few months in such higher concentrations as the flash set happens.
There are many reports about the above mentioned actions of succharose on the hydration of portland cement, but is something to be investigate.
Authors investigated the hydration of portland cement and clinker minerals from several points of view in the presence of succharose, d-glucose and dextrin, and obtained the results as following.
(1) Influences of d-glucose on the setting and hardening of portland cement are similar to that of succharose, and dextrin has also slightly similar action to the latters.
(2) The possible explanation of the flash set, which occur in higher concentrations of succharose, may be that a large amounts of gel-like lime-ssuccharose compound and aluminum hydroxide are produced by chemical reaction between succharose and tricalcium aluminate and occurs “gel set” by sudden coagulation.
The precipitation of insoluble compounds, which may be trilime-monosuccharate and higherlime-monosuccharate produced by the reaction between succharose and surface of alite particle and lime in a aq. solution, plays an important role in retarding the development of mechanical strength.
The retarding action of succharose and d-glucose etc. on the hydration of alite increase consistently with the increse of its concentrations.
(3) α-d-methylglucosid, which is produced by the reaction of H₃C- with “reducing carbon” group of glucose, does not react with lime, therefore, has only a little effect on the hydration of portland cement clinker minerals in relatively higher concentrations.
(4) The mechanism of the hydration of alite, with or without carbohydrate, are investigated by the analyzing of the heat liberation curves which were derived from hydration of alite in devised adiabatic calorimeter. The proposed mechanism shall be that hydration of alite consists of three possible processes, namely, the first process is the dissolution of alite, the second is the sprightly formation of calcium silicate hydrates and the last is diffusion process of hydration. These processes occurs orderly and continuously, and initial and final parts of each process overlap mutually.
The dissolution process is hastened by the rising of hydration temperature and addition of the accelerating reagents, on the contrary, is prolonged by the protective coating formation of gel-like lime-succharose compound on the surface of alite particles. The second process continue until the hydration rate of alite reach near 40% and after all the hydration reaction are obedient to diffusion process.

抄録全体を表示