Nakamichi Yamasaki

CO2 injection to granite and sandstone in experimental rock/hot water systems

Abstract Experiments were conducted using a batch type micro-autoclave over a temperature range of 100–350 °C to understand granite and sandstone reactions in hot water in the absence or presence of excess CO 2 . Our experiments, for one-week duration, show that the dissolution of granite and sandstone, and the deposition of secondary minerals, is enhanced by the presence of excess CO 2 . Major element concentrations of the residual solution from the batch autoclave experiments were higher for the rock (granite or sandstone)/H 2 O/CO 2 system, than in the rock (granite or sandstone)/H 2 O system, but the sample weight loss was lower in the rock/H 2 O/CO 2 system than in the rock/H 2 O system. Changes in sample weight and CO 2 -gas volume content concur with the deposition of aluminium silicate and calcium-aluminosilicate secondary minerals, which indicate fixation of CO 2 in the rock. Our results suggest that it may be possible for granite and/or sandstone to ‘capture’ CO 2 , at hydrothermal conditions, and that underground disposal may be a feasible solution to reducing atmospheric emission of CO 2 .

Preparation of porous materials from hydrothermally hot pressed glass compacts

The importance of the recycling of waste materials has been recognized for sustainable development of our human life. Recently, the authors [1] proposed the recycling of used glasses for building materials using the hydrothermal hot-pressing technique (hereafter referred as HHP), which is useful for preparation of solid compacts from various inorganic powders at low temperatures below 300 ◦C [2–4]. In this paper, we focused on the preparation of porous glass compacts to develop another alternative route for the recycling of used glasses. Porous materials are very attractive because of their controlled porosity and insulating properties for numerous applications such as thermal insulators, substrates for catalyst, filter systems and building materials. A wide variety of porous materials have been produced in an industrial scale using several raw materials such ceramics, glasses, cements and organic materials [5]. The porous ceramics are traditionally produced by a combination of solid state sintering and decomposition of the organic compound or calcium carbonate during the firing process, which results in the formation of a great number of pores in the ceramic bodies. Another routes to prepare porous materials are a phase transformation and a chemical reaction [6, 7]. For the preparation of porous glasses, the phase separation and sol-gel process are commonly employed [8]. The porous glasses have a very wide range of applications such as separation membranes, catalyst precursors, packing materials for chromatography, molecular sieves, and thermal insulators [8, 9]. In general, all the methods employed to produce porous glass materials involve very high cost of fabrication, because of the high sintering temperatures and a special route for the porosity control. In the present work, we prepared porous glass compacts with closed pores for insulating materials by simply heating the glass compacts densified by HHP. A powder of the used glass of blue color was employed to prepare glass compacts by HHP. The chemical analysis [1] of the glass powder showed that it consisted of SiO2 (69.58 wt%), Na2O (14.61 wt%), CaO (10.9 wt%) and other oxides. The glass powder (10 g) with particle size between 46–53 μm was well ground in a mortar with water (5–20 wt%). The mixture was placed in the cylindrical chamber of an autoclave for HHP, with inner diameter of 20 mm, uniaxially compressed at 20 MPa, and then heated to 200 ◦C at a rate of 5 ◦C/min. The temperature and pressure were kept constant for 2 h. The glass compacts prepared by HHP were heated in air for 1 h at a temperature in the range 50–750 ◦C. All the heat treatments were conducted at a constant heating rate of 5 ◦C/min. The weight of the compacts was measured before and after the heat treatment to determine the weight loss. The bulk density of the heated specimens was also determined using the cubic samples (10 × 10 × 10 mm3) shaped from the heated specimens. The weight loss of the compacts prepared with different contents of water is shown in Fig. 1. Large weight loss was observed by heating the compacts for 1 h at temperatures up to 750 ◦C. By hydrothermal hot pressing of the glass powder, a new amorphous phase was formed surrounding the original glass particles [1]. Energy dispersive X-ray analysis conducted on both the residual original glass particles and new phase showed that both of them consisted of the same elements, though infrared spectra of the compacts demonstrated that a significant amount of water was incorporated in the compacts during the hydrothermal hot-pressing treatment [10]. The new phase may be formed by the hydrothermal reaction of the glass powder with water. The weight loss observed during heating the compacts must be caused by the release of water included in the compacts prepared by HHP. Even after the heat treatment at 850 ◦C, no crystalline phases were detected by X-ray diffraction analyses.

Potential utilization of riverbed sediments by hydrothermal solidification and its hardening mechanism.

Hydrothermal solidification of riverbed sediments (silt) has been carried out in a Teflon (PTFE) lined stainless steel hydrothermal apparatus, under saturated steam pressure at 343-473 K for 2-24 h by calcium hydrate introduction. Tobermorite was shown to be the most important strength-producing constituent of the solidified silt. A longer curing time or a higher curing temperature was shown to be favorable to the tobermorite formation, thus promoting strength development; however, overlong curing time (24 h) seemed to affect the strength development negatively. The hardening mechanism consisted of the crystal growth/morphology evolution during the hydrothermal process. The species dissolved from the silt were precipitated first as fine particles, and then some of the particles seemed to build up the rudimental morphology of calcium silicate hydrate (CSH) gel. The CSH gel, with precipitated particles, appeared to cause some reorganization within the matrix, which made the matrix denser and thus gave an initial strength development. Tobermorite, transformed inevitably from the CSH gel, reinforced the matrix with its interlocked structure, and thus further promoted the strength development.

Synthesis of Diamond Particles under Alkaline Hydrothermal Conditions

Very fine diamond powder (1-3 ~m) was readily sintered under hydrothermal conditions, with new bond formation occurring between the diamond particles in a l0M-NaOH solution at 573 K maintained at 1 GPa pressure, for 24 hours. This new bonding material can be formed by carbonization, from a chlorinated hydrocarbon such as dichloromethane and 1, 1,1–trichloroethane. The carbonized material forms a new bond between the hydrogenated diamond particles by the release of hydrogen chloride. Using Raman spectroscopy and hydrogenated cubic boron nitride substrates it was indisputably demonstrated that diamond was synthesized under these alkaline hydrothermal conditions. The surface morphology of the hydrothermal product on the cubic boron was similar to the new growth on the diamond substrates.

The possibility of diamond sintering by hydrothermal hot‐pressing

Very fine diamond was synthesized under hydrothermal conditions, with new bond formation among diamond particles, in 10M‐NaOH solution at 573K, 1GPa, for 24 hours. This new bonding material is formed by carbonization, from chlorinated hydrocarbon such as dichloromethane and 1,1,1‐trichloroethane, under alkaline hydrothermal conditions. The carbonized material forms a new bond between diamond particles by the release of hydrogen‐chloride using a hydrated diamond powder particle as the starting material. With pellet of compacted diamond, the platy materials were produced. These materials were diamond by micro‐XRD analysis. New growth materials between compacted diamonds, and each diamond particles were bonded. Therefore, it is possible that compacted diamonds is sintered by carbon‐bonds under hydrothermal synthesis. Hydrothermal hot‐pressing is technic that materials as glass, calcium silicate and calcium carbonate is solidified. Compacted materials is deformed under hydrothermal conditions, and materials i...

Hydrothermal Preparation of Porous Hydroxyapatite with Tailored Crystal Surface

Porous sheets of hydroxyapatite (Ca10(PO)4(OH)2; HA) with about 50 µm to 1 mm in thickness and porous HA granules of about 50 µm to 1 mm in size with tailored crystal surface were prepared by the hydrothermal vapor exposure method at the temperatures above 105 °C under saturated vapor pressure of pure water. Porous HA sheets with about 75 % porosity prepared at 120 °C were composed of rod-shaped crystals of about 30 µm in length. Porous HA granules prepared at 160 °C were also composed of rod-shaped crystals of about 20 µm in length with the mean aspect ratio of 30. These crystals were elongated along the c-axis. Rod-shaped HA crystals were locked together to make micro-pores of about 0.1 µm in size. Both of materials were nonstoichiometric HA with calcium deficient composition. These materials must have the advantage of adsorptive activity, because they had large specific crystal surface and much micro-pores.

Effects of NaOH Concentration on CO2 Reduction via Hydrothermal Water

The reductions of CO2 under hydrothermal conditions were investigated by using the micro autoclave (45cm3) lined with Hastelloy‐C alloy. Sodium hydrogen carbonate (NaHCO3) was used as a starting material. H2 gas was used as reducing agents. NaHCO3 powder, H2 gas and water put into the autoclave simultaneously. The autoclave was heated upto 300°C by induction heater. In this study, effects of pH value of the NaOH solution in the autoclave are investigated. Reaction products were analyzed with gas chromatographs (GC), liquid chromatographs (LC), X‐ray diffractometor (XRD) and Scanning electron microscopy (SEM). The following things were showed in this research: CO2 was reducted to HCOO− and CH4 at high conversion ratio under hydrothermal conditions. HCOO− was formed at high selectivity using Hastelloy‐C reactor in the alkaline solution with Raney Ni catalyst. Raney Ni was exellent methanation catalyst, and CH4 formation progressed via HCO3−, not via CO. It is cleared that the NaOH solution in the autoclave ...

Recycling of Organic Waste Sludge by Hydrothermal Dry Steam Aiming for Adsorbent

Global warming becomes more serious problem today. We have to develop new technology for new energy or fixation of carbon dioxide. Biomass is considered to be one of new energies. Methane fermentation is a method to make methane from biomass, such as garbage and fecal of farm animals, by methane fermentation bacteria. It has a problem, however, that bacteria are deactivated due to ammonia, which is made by itself. And much methane fermentation residue is incinerated. Therefore recycling methane fermentation residue is important for effective use of biomass. We research hydrothermal process. Dry steam means unsaturated vapor, we call. It demands a temperature less than 400 °C. And it is expected to accelerate dehydration effect, decompose and extract the organic matter, and make porous material. Thus, we try to apply the dry steam to recycling of organic waste sludge aiming for absorbent. Experiments were conducted at 250–350 °C in nitrogen atmosphere. The carbon products are analyzed by CHNS elemental ana...

Porous Hydroxyapatite with Tailored Crystal Surface Prepared by Hydrothermal Method

Porous plates of hydroxyapatite (Ca10(PO4)6(OH)2; HA) with about 0.5 to 5 mm in thickness and porous HA granules of about 40 µm to 1 mm in size with tailored crystal surface were prepared by the hydrothermal vapor exposure method at the temperatures above 105 °C under saturated vapor pressure of pure water. Porous HA plates with about 75 % porosity prepared at 120 °C were composed of rod-shaped crystals of about 20 µm in length. Porous HA granules prepared at 160 °C were also composed of rod-shaped crystals of about 20 µm in length with the mean aspect ratio of 30. These crystals were elongated along the c-axis. Rod-shaped HA crystals were locked together to make micro-pores of about 0.1 to 0.5 µm in size. Both of materials were nonstoichiometric HA with calcium deficient composition. These materials must have the advantage of adsorptive activity, because they had large specific crystal surface and much micro-pores.

Hydrothermal Detoxization of Slate Containing Asbestos and the Possibility of Application for Fertilizer of its Products

Hydrothermal decomposition of slate (building materials) containing asbestos has been attempted by using a NH4H2PO4 solution. Firstly, the alteration of chrysotile as a starting material was investigated under hydrothermal conditions of 200° C, 12 hrs of reaction time and with a phosphate solution. It was confirmed that the original fibrous form of chrysotile had been perfectly collapsed by the SEM observation. The chrysotile (asbestos) disappeared to form Mg‐Ca‐Silicate (Ca7Mg2P6O24) estimated by XRD. The composition and chemical form of reaction products (Mg‐Ca‐Silicate) was predicted to application as a fertilizer. Fertilizer effect of these resulted product on cultivations of Japanese radish (leaves), soybeans and tomatoes, was examined by using a special medium of mixed soil with a low content of N, P, K and a thermal‐treated zeolite one. The fertilizer effects of the product were compared to commercial fertilizers such as N, N‐K‐P and P types. In order to estimate the fertilizer effect, the size of ...