A study on the economic efficiency of hydrogen production from biomass residues in China

As part of Pilot Project of KIP of CAS, a feasibility study of hydrogen production system using biomass residues is conducted. This study is based on a process of oxygen-rich air gasification of biomass in a downdraft gasifier plus CO-shift. The capacity of this system is 6.4 t biomass/d. Applying this system, it is expected that an annual production of 480 billion N m(3) H-2 will be generated for domestic supply in China. The capital cost of the plant used in this study is 1328$/(N m(3)/h) H-2 out, and product supply cost is 0.15$/N m(3) H-2. The cost sensitivity analysis on this system tells that electricity and catalyst cost are the two most important factors to influence hydrogen production cost.

Hydrate dissociation conditions for gas mixtures containing carbon dioxide, hydrogen, hydrogen sulfide, nitrogen, and hydrocarbons using SAFT

A new method, a molecular thermodynamic model based on statistical mechanics, is employed to predict the hydrate dissociation conditions for binary gas mixtures with carbon dioxide, hydrogen, hydrogen sulfide, nitrogen, and hydrocarbons in the presence of aqueous solutions. The statistical associating fluid theory (SAFT) equation of state is employed to characterize the vapor and liquid phases and the statistical model of van der Waals and Platteeuw for the hydrate phase. The predictions of the proposed model were found to be in satisfactory to excellent agreement with the experimental data.

Hydrogen-rich gas production from biomass air and oxygen/steam gasification in a downdraft gasifier

Biomass gasification is an important method to obtain renewable hydrogen, However, this technology still stagnates in a laboratory scale because of its high-energy consumption. In order to get maximum hydrogen yield and decrease energy consumption, this study applies a self-heated downdraft gasifier as the reactor and uses char as the catalyst to study the characteristics of hydrogen production from biomass gasification. Air and oxygen/steam are utilized as the gasifying agents. The experimental results indicate that compared to biomass air gasification, biomass oxygen/steam gasification improves hydrogen yield depending on the volume of downdraft gasifier, and also nearly doubles the heating value of fuel gas. The maximum lower heating value of fuel gas reaches 11.11 MJ/ N m(3) for biomass oxygen/steam gasification. Over the ranges of operating conditions examined, the maximum hydrogen yield reaches 45.16 g H-2/kg biomass. For biomass oxygen/steam gasification, the content of H-2 and CO reaches 63.27-72.56%, while the content Of H2 and CO gets to 52.19-63.31% for biomass air gasification. The ratio of H-2/CO for biomass oxygen/steam gasification reaches 0.70-0.90, which is lower than that of biomass air gasification, 1.06-1.27. The experimental and comparison results prove that biomass oxygen/steam gasification in a downdraft gasifier is an effective, relatively low energy consumption technology for hydrogen-rich gas production.

Continuum structures at the second dissociation limit of hydrogen molecules

We describe near-threshold high-resolution spectra and continuum resonance dynamical behaviour of all three stable hydrogen isotopic variants, and finally obtain improved values for the dissociation energies of hydrogen molecule and its ion. The second dissociation limit is determined by analysing the onset of the vibrational continuum.

The second dissociation threshold bound levels of hydrogen molecule

The near-threshold highly bound states of all three stable isotopic variants of molecular hydrogen have been studied. Numerous perturbations and unexpected transitions are observed as far as 1cm(-1) just below the second dissociation threshold. This complex structure may arise from a combination of nonadiabatic coupling between B, B', C electronic states, perturbations due to. ne and hyperfine interactions, and strong shape resonances. The perturbed near-threshold states and vibrational continuum exhibit finegrained structure, differing greatly between isotopes because of varying nonadiabatic coupling.

Growth and characterization of InAsSb alloys by metalorganic chemical vapour deposition

Low pressure metalorganic chemical vapour deposition (LP-MOCVD) growth and characteristics of InAssb on (100) Gasb substrates are investigated. Mirror-like surfaces with a minimum lattice mismatch are obtained. The samples are studied by photoluminescence spectra, and the output is 3.17 mu m in wavelength. The surface of InAssb epilayer shows that its morphological feature is dependent on buffer layer. With an InAs buffer layer used, the best surface is obtained. The InAssb film shows to be of n-type conduction with an electron concentration of 8.52 x 10(16) cm(-3).

富钇稀土-铝合金制取的研究Study on Preparation of Yttrium-Rich RE-Al Alloys

我国江西龙南稀土矿是目前世界上储量最大的富钇稀土矿、研制具有多种用途的钇（Y）-铝（Al）或富钇混合稀土（Ymm）-铝中间合金，对于开拓我国龙南稀土矿的应用领域扩大稀土合金出口具有重要意义。基于这一背景并针对目前氟化物体系制取Ymm-Al合金时存在着电解温度高，腐蚀现象严重，电效偏低等缺点，本文系统开展了在氯化物熔盐体系中电解制取Ymm-Al合金的研究工作。本工作由三部分组成：在第一部分工作中，开展了熔盐电解所需要基本原料-无水稀土氯化物制取的工艺研究。利用化学分析和结构分析手段，弄清了干法氯化过程中YmmCl_3水解的机理，提出了减弱水解的措施，即YmmCl_3先在850-900 ℃灼烧1.5 + 0.2hr，脱掉吸附水并将碱式碳酸盐转化为氧化物，增加稀土氧化物的比表面。通过条件试验得到最佳工艺条件为：采用NH_4 Cl:Ymm_2 O_3 = 14:1（摩尔比）的配料比，每次投入氯化装置的原料量为0.26 - 0.36 kg, 在400-450 ℃氯化反应激烈开始后迅速降温至400 ℃以下，待物料粘结现象消失后，再行升温氯化。出料及后期控制温在475 ± 25 ℃。经过3.8 ± 0.2hr氯化，可制得水不溶物小于1%并符合熔盐电解要求的YmmCl_3原料。此新工艺与原有干法工艺相比，流程短，装置简单，不需密闭抽真空，成本低，适于制取任何量的优质熔盐电解所需氯化稀土原料。在第二部分工作中，利用上述YmmCl_3原料，以液态铝为阴极，在氯化物体系中进行熔盐电解，通过试验得出在小型试验规模制取Ymm-Al合金的最隹工艺条件为：电解质组成（重量比）40%YmmCl_3-1%NaF-59%等摩尔的NaCl-KCl；电解温度为790 ± 5 ℃；阴极电流密为0.7 - 0.02A/cm~2；电解电量为333 ± 5库仑/克铝，制得钇铝合金中Ymm含量为10 ± 2%。添加1%的NaF可消除阴极表面生成枝状物，减少合金中夹渣和熔盐中沉渣。在电解工作中，将方差分析应用于试验数据处理，方差分析结果表明，各种试验因素对电效有明显影响，试验数据可靠，试验误差在允许范围以内。在第三部分工作中，利用线性扫描伏安法测定了在最隹电解工艺条件下Y~（3+）和Ymm在液态铝及钼电极上的析出电位。测定结果表明：Y~（3+）和Ymm~（3+）在液态铝阴极上的析出电位比在钼阴极上偏正0.2 ～ 0.8伏，氟离子的加入要比不加氟时析出电位不有同程度的负移，但考虑到氟离了具有消渣作用，加入少量氟比物添加剂对提高电效有利。

Band crossing in isovalent semiconductor alloys with large size mismatch: First-principles calculations of the electronic structure of Bi and N incorporated GaAs

For large size- and chemical-mismatched isovalent semiconductor alloys, such as N and Bi substitution on As sites in GaAs, isovalent defect levels or defect bands are introduced. The evolution of the defect states as a function of the alloy concentration is usually described by the popular phenomenological band anticrossing (BAC) model. Using first-principles band-structure calculations we show that at the impurity limit the N-(Bi)-induced impurity level is above (below) the conduction- (valence-) band edge of GaAs. These trends reverse at high concentration, i.e., the conduction-band edge of GaAs1-xNx becomes an N-derived state and the valence-band edge of GaAs1-xBix becomes a Bi-derived state, as expected from their band characters. We show that this band crossing phenomenon cannot be described by the popular BAC model but can be naturally explained by a simple band broadening picture.

THE EFFECT OF PASSIVATION OF BORON DOPANTS BY HYDROGEN IN NANO-CRYSTALLINE AND MICROCRYSTALLINE SILICON FILMS

It is well known that the value of room-temperature conductivity sigma(RT) of boron-doped silicon films is one order lower than that of phosphorus-doped silicon films, when they are deposited in an identical plasma-enhanced chemical vapour deposition system. We use surface acoustic wave and secondary-ion mass spectrometry techniques to measure the concentration of total and electrically active boron atoms. It is shown that only 0.7% of the total amount of incorporated boron is electrically active. This is evidence that hydrogen atoms can passivate substitutional B-Si bonds by forming the neutral B-H-Si complex. By irradiating the boron-doped samples with a low-energy electron beam, the neutral B-H-Si complex converts into electrically active B-Si bonds and the conductivity can be increased by about one order of magnitude, up to the same level as that of phosphorus-doped samples.

HYDROGEN DIFFUSION IN A-SI-H/A-SI STRUCTURE UNDER ELECTRICAL BIAS

By using the technique of elastic recoil detection (ERD), we have measured the hydrogen profiles in a-Si:H/a-Si structure samples annealed at various temperatures with and without electrical bias, and investigated the influence of electrical bias on hydrogen diffusion. The results show that hydrogen diffusion in a-Si is significantly enhanced by the action of electrical bias. The existence of the excess carriers, which are introduced by electrical injection, is considered to be responsible for the enhancement of hydrogen diffusion, and the microprocess of hydrogen transport has been exploited.

CONTROLLING OF SCHOTTKY-BARRIER HEIGHTS FOR AU/N-GAAS AND TI/N-GAAS WITH HYDROGEN INTRODUCED AFTER METAL-DEPOSITION BY BIAS ANNEALING

Up to now, in most of the research work done on the effect of hydrogen on a Schottky barrier, the hydrogen was introduced into the semiconductor before metal deposition. This letter reports that hydrogen can be effectively introduced into the Schottky barriers (SBs) of Au/n-GaAs and Ti/n-GaAs by plasma hydrogen treatment (PHT) after metal deposition on [100] oriented n-GaAs substrates. The Schottky barrier height (SBH) of a SB containing hydrogen shows the zero/reverse bias annealing (ZBA/RBA) effect. ZBA makes the SBH decrease and RBA makes it increase. The variations in the SBHs are reversible. In order to obtain obvious ZBA/RBA effects, selection of the temperature for plasma hydrogen treatment is important, and it is indicated that 100-degrees-C for Au/n-GaAs and 150-degrees-C for Ti/n-GaAs are suitable temperatures. It is concluded from the analysis of experimental results that only the hydrogen located at or near the metal-semiconductor interface, rather than the hydrogen in the bulk of either the semiconductor or the metal, is responsible for the ZBA/RBA effect on SBH.

GROWTH OF WIDE-BAND GAP IMMISCIBLE II-VI ALLOYS BY METALORGANIC VAPOR-PHASE EPITAXY

Although metalorganic vapor phase epitaxy (MOVPE) is generally regarded as a non-equillibrium process, it can be assumed that a chemical equilibrium is established at the vapor-solid interface in the diffusion limited region of growth rate. In this paper, an equilibrium model was proposed to calculate the relation between vapor and solid compositions for II-VI ternary alloys. Metastable alloys in the miscibility gap may not be obtained when the growth temperature is lower than the critical temperature of the system. The influence of growth temperature, reactor pressure, input VI/II ratio, and input composition of group VI reactants has been calculated for ZnSSe, ZnSeTe and ZnSTe. The results are compared with experimental data for the ZnSSe and ZnSTe systems.

EFFECT OF TOTAL HYDROGEN CONTENT IN SILICON-NITRIDE SENSITIVE FILM ON PERFORMANCE OF ISFET

Quantitative determinations of the hydrogen content and its profile in silicon nitride sensitive films by the method of resonant nuclear reaction have been carried out. At a deposition temperature of 825-degrees-C, hydrogen exists in an LPCVD silicon nitride sensitive film and the hydrogen content on its surface is in the range (8-16) x 10(21) cm-3, depending on the different deposition processes used. This hydrogen content is larger than the (2-3) x 10(21) cm-3 in its interior part, which is homogeneous. Meanwhile, we observe separate peaks for the chemical bonding configurations of Si-H and N-H bonds, indicated by the infrared absorption bands Si-O (1106 cm-1), N-H (1200 cm-1), Si-H-3 (2258 cm-1) and N-H-2 (3349 cm-1), respectively. The worse linear range of the ISFET is caused by the presence of oxygen on the surface of the silicon nitride sensitive film. The existence of chemical bonding configurations of Si-H, N-H and N-Si on its surfaces is favourable for its pH response.

HYDROGEN-RELATED DONOR IN SILICON-CRYSTALS GROWN IN A HYDROGEN ATMOSPHERE

Neutron transmutation doped (NTD) silicon crystals grown in a hydrogen atmosphere have been investigated by infrared absorption spectroscopy at a low temperature (10 K). An effective-mass-like donor state HD0/+ has been found at 110.8 me V below the conduction band bottom after rapid thermal annealing (RTA). The HD0/+ formation mechanism after NTD and RTA is briefly discussed, and tentatively attributed to H atoms present in the vicinity of some residual irradiation defects, like a complex of a H atom and a H-saturated vacancy.