Controlled growth of silicon nanowires by solid-liquid-solid method and their formation mechanism

High quality silicon nanowires (SiNWs) were grown directly from n-(111) silicon single crystal substrate by using Au film as a metallic catalyst. The diameter and length of the formed nanowires are 30-60 nm and from several micrometers to sereral tens of micrometers, respectively. The effects of Au film thickness, annealing temperature, growth time and N-2 gas flow rate on the formation of the nanowires were experimentally investigated. The results confirmed that the silicon nanowires with controlled diameter, length, shape and orientation can be obtained via reasonably choosing and optimizing various technical conditions. The formation process of the silicon nanowires is analyzed qualitatively based on solid-liquid-solid growth mechanism.

Influence of A-type Zeolite on Methane Hydrate Formation

The porous medium has an important effect on hydrate formation. In this paper, the formation process and the gas storage capacity of the methane hydrate were investigated with A-type zeolite and Sodium Dodecyl Sulfate (SDS) existing in the system. The results show that A-type zeolite can influence methane hydrate formation. At the temperature of 273.5 K and pressure of 8.3 MPa, the distilled water with A-type zeolite can form methane hydrate with gaseous methane in 12 hours. The formation process of the system with A-type zeolite was quite steady and the amount of A-type zeolite can influence the gas storage capacity significantly. The adding of A-type zeolite with 0.067 g.(g water)(-1) into 2 x 10(-3) g.g(-1) SDS-water solution can increase the gas storage capacity, and the maximum increase rate was 31%. Simultaneously the promotion effect on hydrate formation of 3A-type zeolite is much more obvious than that of 5A-type zeolite when the water adding amounts are 0.033 g.g(-1) and 0.067 g.g(-1) at the experimental conditions.

The methane hydrate formation and the resource estimate resulting from free gas migration in seeping seafloor hydrate stability zone

It is a typical multiphase flow process for hydrate formation in seeping seafloor sediments. Free gas can not only be present but also take part in formation of hydrate. The volume fraction of free gas in local pore of hydrate stable zone (HSZ) influences the formation of hydrate in seeping seafloor area, and methane flux determines the abundance and resource of hydrate-bearing reservoirs. In this paper, a multiphase flow model including water (dissolved methane and salt)-free gas hydrate has been established to describe this kind of flow-transfer-reaction process where there exists a large scale of free gas migration and transform in seafloor pore. In the order of three different scenarios, the conversions among permeability, capillary pressure, phase saturations and salinity along with the formation of hydrate have been deducted. Furthermore, the influence of four sorts of free gas saturations and three classes of methane fluxes on hydrate formation and the resource has also been analyzed and compared. Based on the rules drawn from the simulation, and combined information gotten from drills in field, the methane hydrate(MH) formation in Shenhu area of South China Sea has been forecasted. It has been speculated that there may breed a moderate methane flux below this seafloor HSZ. If the flux is about 0.5 kg m-2 a-1, then it will go on to evolve about 2700 ka until the hydrate saturation in pore will arrive its peak (about 75%). Approximately 1.47 109 m3 MH has been reckoned in this marine basin finally, is about 13 times over preliminary estimate.

Influence of 5A-Type Zeolite Powder on Tetrahydrofuran Hydrate Formation and Dissociation Process

Visual observations of tetrahydrofuran (THF) hydrate formation and dissociation processes with 5A-type zeolite powder were made at normal atmospheric conditions and below zero temperature by microscope. Results indicate that 5A-type zeolite powder can promote THF hydrate growth. At the same time, in the presence of 5A-type zeolite, agglomerated crystals and vein-like crystals of THF hydrate were also formed. SA-type zeolite powder increases the crystallization temperature and decreases the dissociation temperature. The particle size distribution of 5A-type zeolite powder influences THF hydrate formation and its dissociation characteristics significantly.

Effect of microwave on formation/decomposition of natural gas hydrate

Natural gas hydrate (NGH) reservoirs have been considered as a substantial future clean energy resource and how to recover gas from these reservoirs feasibly and economically is very important. Microwave heating will be taken as a promising method for gas production from gas hydrates for its advantages of fast heat transfer and flexible application. In this work, we investigate the formation/decomposition behavior of natural gas hydrate with different power of microwave (2450MHZ), preliminarily analyze the impact of microwave on phase equilibrium of gas hydrate,and make calculation based on van der Waals-Platteeuw model. It is found that microwave of a certain amount of power can reduce the induction time and sub-cooling degree of NGH formation, e.g., 20W microwave power can lead to a decrease of about 3A degrees C in sub-cooling degree and the shortening of induction time from 4.5 hours to 1.3 hours. Microwave can make rapid NGH decomposition, and water from NGH decomposition accelerates the decomposition of NGH with the decomposition of NGH. Under the same pressure, microwave can increase NGH phase equilibrium temperature. Different dielectric properties of each composition of NGH may cause a distinct difference in temperature in the process of NGH decomposition. Therefore, NGH decomposition by microwave can be affected by many factors.