In the calcination of limestones using fluidized beds coating occurring in the preheating section is a well-known problem. A series of basic experiments were carried out to determine conditions for coating formation, and based on the results, a commercial limestone calciner was smoothly operated without coating trouble. In the basic test, effects of temperature upon the adhesive force of limestone or quicklime against a glass surface were examined. Furthermore, injection tests were conducted to study the effects of particle size, injection speed, temperature, particle concentration, and water content upon coating formation. These test results were compared with data observed by the commercial plant.
Homogeneous C-S-H with a Ca/Si molar ratio of 1.0 was prepared hydrothermally at 130°C. Xonotlite was formed from C-S-H at 200°C after a rapid increase of the reaction temperature. The structural change of silicate anions on the process was investigated mainly by 29Si solid-state NMR. CP (Cross Polarization) -MAS (Magic Angle Spinning) NMR spectra of C-S-H and xonotlite were obtained quantitatively at a contact time of 4 ms because of their rich content of hydrogen nuclei. Faster CP speed of chain end groups Q1 indicates there are more hydrogen nuclei around Q1 than around middle groups Q2 and branching groups Q3 in both C-S-H and xonotlite. The chemical shift of Q2 of C-S-H changed from-84.3 to-85.6 ppm at the induction period of xonotlite formation, which suggests some of Q2 became well bonded to CaO layer and the origin of nuclei of xonotlite crystals. The mean chain length of silicate anions was estimated from Q2/Q1 and (Q2+Q3) /Q1 intensity ratios. It was clarified the silicate chain length decreased at the induction period and increased with the formation of xonotlite. The Q3/Q2 ratio corresponded well to the degree of formation of xonotlite obtained by thermogravimetry.
In this study, the influence of early hydration characteristics of ultra rapid hardening cement with different amounts of additives on hardening shrinkage crack of the paste at the temperature of 5°C was investigated by the observation of the texture of hydrates as well as characterization of early hydration and test of crack occurrence, using FE-SEM, conduction calorimetry, DSC, XRD and so on. The relationship between amounts and morphology of hydrates, and hardening shrinkage was also discussed. The results obtained are as follows : 1) Judging from the observation of occurrence of crack, the influence of H3B03 in ultra rapid hardening cement on crack is far greater than that of Na2SO4, CaSO4. Ultra rapid hardening cement paste added more than 0.5% of H3B03 has no crack due to hardening shrinkage. 2) The measured hardening shrinkage agrees well with the degree of crack by the test of crack occurrence. The degree of crack becomes larger with increase of hardening shrinkage determined by rubber method. 3) Ultra rapid hardening cement with larger amount of H3BO3 produces larger amount of ettringite in early hydration stage. The form of this ettringite is cubiform shape with aspect ratio of nearly 1.0. 4) Hardening shrinkage of ultra rapid hardening cement paste doesn't correspond to the degree of hydration directly.The amount of ettringite and its morphology are considered to be much influential to hardening shrinkage.
Magnesium bis (hydrogenorthophosphate) tetrahydrate, Mg (H2PO4) 2 4H2O, has been prepared by adding magnesium hydroxide and a small amount of calcium oxide into 60% orthophosphoric acid. Upon heating at a temperature higher than 150°C, the magnesium orthophosphate produced several kinds of chain and ring condensed phosphates. The phosphate composition of the thermal product depended on heating rate. The main thermal dehydrationcondensation reactions were concluded as follows : (at 150-300°C) Mg (H2PO4) 2→MgH2P2O7 + H2O (at a temperature higher than 300°C) 2Mg (H2P2O7) →Mg2P4O12 + 2H2O All of the magnesium orthophosphate finally converted to magnesium cyclo-tetraphosphate and the overall thermal condensation can be written : 2Mg (H2PO4) 2→Mg2P4O12+4H2O
A new method for determination of iron (II) in α-Fe2O3 for a combustible gas sensor has been developed using a flow-injection analysis (FIA) system with spectrophotometric detection which is based on the reaction of iron (II) and 2, 4, 6-tris (2-pyridyl) -s-triazine. A α-Fe2O3 sample (0.1g) was decomposed with 1 ml of 46% hydrofluoric acid and 2m1 of 4.5M sulfuric acid containing 1 x10-3 M vanadium (V), and then 25m1 of 4w/v% boric acid was added to mask excess fluoride ion, followed by diluting the solution to 200m1 by water. In the FIA system, a sample solution injected into the carrier is mixed with a stream of 2, 4, 6-tris (2-pyridyl) -s-triazine and a masking agent (sodium pyrophosphate) for iron (III) at a confluence point, and then merged downstream with a buffer solution (sodium acetate-acetic acid) for spectrophotometric detection by complex formation. The results for the analysis of various α-Fe2O3 sensor showed good reproducibility. It has also proved that the FIA system allows rapid and simple analysis; only 2min. is required for analytical measurement after sample injection and no complicated procedure is involved.
Porous hydroxyapatite (HAp) particles were prepared by sintering HAp powder mixed with carbon powder at 1150°C for 2hr. The HAp powder was synthesized by the method of precipitation from calcium nitrate and diammonium hydrogen phosphate. Ethanol fermentation using the sintered HAp as a carrier was investigated, and compared with that using a commercial carrier, porous glass. First, yeast cells were immobilized on the sintered HAp by the cultivation in a medium at 30°C, and the immobilized yeast reached a maximum 2.2×108 cells per g-carrier with a particle diameter of 2380-3360pm. Secondly, a batch ethanol fermentation with the immobilized yeast on the sintered HAp at 30°C was found to proceed more smoothly than that with immobilized yeast on the porous glass in the medium containing glucose concentration of 10% (w/v). In the medium composed of glucose more than 20% (w/v), although the fermentation with the sintered HAp had the same tendency as the above up to ethanol concentration of about 6% (w/v), the fermentation was inhibited thereafter by the calucium cation eluted from the sintered HAp. In a continuous fermentation with immobilized yeast on the sintered HAp, ethanol concentration of 7.1% (w/v) was stably produced by adjusting the pH of the medium in the reactor to 5.0 at 24hr intervals under the conditions of glucose concentration of 15% (w/v) in the medium and the residence time of 5.8hr.