Reactivity of Solids最新文献

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Self-diffusivity of nitrogen in γ'-iron nitride (“Fe4N”) γ′-氮化铁(“Fe4N”)中氮的自扩散率

Reactivity of Solids

Pub Date : 1989-06-01 DOI: 10.1016/0168-7336(89)80022-1

C.T. Cheung, G. Simkovich

The growth of γ'-iron nitride (“Fe₄N”) on pure iron plate samples was followed by a thermogravimetric technique in the temperature range of 450–550 ° C at various nitrogen activities (fixed by H₂/NH₃ gas mixtures). The growth kinetics were characterized by an initial stage of nucleation and growth control followed by nitrogen diffusion controlled growth. At 450 ° C, the self-diffusivity of nitrogen D^* is independent of nitrogen activities. At 500 ° C, D^* decreases with increasing nitrogen activities. At 550°C, D^* decreases to a minimum and then increases again with increasing nitrogen activities. It is suggested that the nitrogen diffusion mechanism in γ'-iron nitride is strongly related to the non-stoichiometry of this phase. At 450 and 500 ° C, the growth kinetics can be explained by a mechanism that involves the mixed control of two processes: (i) nitrogen diffusion via a small number of vacant regular sites ( $12$ , $12$ , $12$ ) and (ii) nitrogen diffusion via a large number of disordered sites ( $12$ , 0, 0), (1, $12$ , 0), (0, 0, $12$ ) as interstitials. At 550°C, the diffusion mechanism is controlled by nitrogen diffusion via the vacant regular sublattice sites at low nitrogen activities. At high nitrogen activities, the diffusion mechanism again becomes mixed control of the two diffusion processes. At the nitrogen activities of 100 and 174, D^* can be represented, respectively, by: D^* = (5.81 × 10⁻⁷cm²/s) · exp((−19.05 $kcal mole$ )/RT) and D^* = (2.45 × 10⁻⁹cm²/s) · exp((−11.16 $kcal mole$ )/RT) It appears that the activation energy of diffusion for nitrogen diffusion via the disordered sites is higher than that via the regular sites.

在450-550℃的温度范围内，采用热重法测定了γ′-氮化铁(Fe4N)在纯铁板样品上的生长，并测定了不同氮活度(由H2/NH3气体混合物固定)。生长动力学表现为初始阶段的成核和生长控制，然后是氮扩散控制生长。在450℃时，氮D*的自扩散率与氮的活性无关。在500℃时，D*随氮活性的增加而降低。在550°C时，D*降低到最小值，然后随着氮活性的增加而再次增加。结果表明，氮在γ′-氮化铁中的扩散机制与该相的非化学计量学密切相关。在450°C和500°C时，生长动力学可以用一种机制来解释，该机制涉及两个过程的混合控制:(i)氮通过少量空的规则位点(12,12,12)扩散，(ii)氮通过大量无序位点(12,0,0)，(1,12,0)，(0,0,12)作为间隙扩散。在550℃时，氮在低氮活性下通过空的规则亚晶格位扩散。在高氮活度时，扩散机制再次成为两种扩散过程的混合控制。在氮活度为100和174时，D*分别可以表示为:D* = (5.81 × 10−7cm2/s)·exp((−19.05 kcalmol)/RT)和D* = (2.45 × 10−9cm2/s)·exp((−11.16 kcalmol)/RT)。可见，氮通过无序位点扩散的活化能要高于通过规则位点扩散的活化能。

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引用次数: 3

Real space imaging of adsorbed organic molecules by STM STM吸附有机分子的实空间成像

Reactivity of Solids

Pub Date : 1989-06-01 DOI: 10.1016/0168-7336(89)80030-0

FalkoP. Netzer

引用次数: 0

Entropy of activation as a possible structure-sensitive parameter in the dehydroxylation of kaolinite 活化熵作为高岭石脱羟基反应中可能的结构敏感参数

Reactivity of Solids

Pub Date : 1989-06-01 DOI: 10.1016/0168-7336(89)80027-0

I. Horváth, G. Kranz, Yu.G. Fedorenko

The kinetics of the dehydroxylation on 14 kaolinites having varying structural disorder (crystallinity) was studied by use of an isothermal TG method. Second-order kinetics were found to control the rate of water release during the dehydroxylation with up to 60% of conversion regardless of the crystallinity and/or temperature of the isothermal heating.

There is no simple relationship between crystallinity and activation energy (E). Unexpectedly high values of E have been determined for some extremely disordered structures. To explain this, the role of intracrystalline pressure of the gaseous product as well as the character of its diffusion paths in the decomposition reaction have been considered.

The crystallinity (index HWB) and activation entropy (ΔS^≠) are related by empirical straight-line function: HWB = (0.07064 ΔS^≠) + 17.65 (correl. coeff. r = 0.873) in which ΔS^≠ values increase with decreasing of kaolinite crystallinity (index HWB increases).

采用等温热重法研究了14种不同结构无序(结晶度)高岭石的脱羟基化动力学。二级动力学被发现在脱羟基过程中控制水的释放速率，无论结晶度和/或等温加热的温度如何，转化率高达60%。结晶度和活化能(E)之间没有简单的关系。对于一些极度无序的结构，E的值出人意料地高。为了解释这一点，考虑了气体产物的晶内压力的作用及其在分解反应中的扩散路径的特征。结晶度(指数HWB)与活化熵(ΔS≠)通过经验直线函数关系:HWB = (0.07064 ΔS≠)+ 17.65 (correl。多项式系数。r = 0.873)，其中ΔS≠值随高岭石结晶度的降低而增大(指数HWB增大)。

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引用次数: 8

Calendar of forthcoming events 即将举行的活动日历

Reactivity of Solids

Pub Date : 1989-06-01 DOI: 10.1016/0168-7336(89)80035-X

引用次数: 0

Meeting report 会议报告

Reactivity of Solids

Pub Date : 1989-06-01 DOI: 10.1016/0168-7336(89)80033-6

R. Burch

引用次数: 0

Sonochemistry 声化学

Reactivity of Solids

Pub Date : 1989-06-01 DOI: 10.1016/0168-7336(89)80029-4

M. Gasgnier

引用次数: 0

Physical adsorption on heterogeneous solids 非均相固体的物理吸附

Reactivity of Solids

Pub Date : 1989-06-01 DOI: 10.1016/0168-7336(89)80031-2

M. Gasgnier

引用次数: 0

Oxidation behaviour of ytterbium sulphides 硫化镱的氧化行为

Reactivity of Solids

Pub Date : 1989-06-01 DOI: 10.1016/0168-7336(89)80024-5

L.C. Otero-Diaz, M.J. Torralvo-Fernández, R.M. Rojas ∗

Thermal studies (at up to ~1500 ° C) carried out on some ytterbium sulphides in air or under nitrogen show that complex decomposition processes undergone before the ultimate formation of the ytterbium oxide. The decompositions take place as overlapping and incomplete reactions to give mixtures of various intermediates, such as Yb₂O₂S and Yb₂O₂SO₄. Electron microscopy diffraction studies on the intermediate Yb₂O₂SO₄ reveals a complex microstructure because of intergrowth with small precipitates of cubic phase Yb₂O₃.

在空气或氮气条件下对某些硫化镱进行的热研究(温度高达~1500℃)表明，在氧化镱最终形成之前经历了复杂的分解过程。分解以重叠和不完全反应的形式发生，生成各种中间体的混合物，如Yb2O2S和Yb2O2SO4。对中间体Yb2O2SO4的电镜衍射研究表明，由于与立方相Yb2O3的小析出相共生而形成复杂的微观结构。

引用次数: 1

An alternative route to copper antimony oxide, Cu9Sb4O19 铜锑氧化物Cu9Sb4O19的替代路线

Reactivity of Solids

Pub Date : 1989-06-01 DOI: 10.1016/0168-7336(89)80028-2

Shiro Shimada, Tadao Ishii

引用次数: 7

Aluminium-Rich Metallic Glasses, by R.W. Calm (Advanced Materials, 1 (1989) 19–20) 富铝金属玻璃，R.W. Calm(先进材料，1 (1989)19-20)

Reactivity of Solids

Pub Date : 1989-06-01 DOI: 10.1016/0168-7336(89)80032-4

M. Gasgnier

引用次数: 0

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