Effects of superimposed pulse bias on TiN coating in cathodic arc deposition

Orthogonal designs are used to investigate the main factors when doing experiments in which pulse bias is superimposed on d.c. bias during cathodic are deposition of TiN. Pulse peak, duty cycle, frequency, direct voltage, are current and pressure all are investigated when coating TiN on HSS substrates. Roughness, surface micrograph, microhardness and thickness are tested. By analysis of variance, it is shown that pressure and frequency are the main factors. R-a and droplet density of the film with (d.c. + pulse) bias decrease. A simple explanation for the result is suggested.

Substrate Effects on the Micro/Nanomechanical Properties of TiN Coatings

Nanoindentation and nanoscratch tests were performed for titanium nitride (TiN) coatings on different tool steel substrates to investigate the indentation/scratch induced deformation behavior of the coatings and the adhesion of the coating–substrate interfaces and their tribological property. In this work, TiN coatings with a thickness of about 500 nm were grown on GT35, 9Cr18 and 40CrNiMo steels using vacuum magnetic-filtering arc plasma deposition. In the nanoindentation tests, the hardness and modulus curves for TiN/GT35 reduced the slowest around the film thickness 500 nm with the increase of indentation depth, followed by TiN/9Cr18 and TiN/40CrNiMo. Improving adhesion properties of coating and substrate can decrease the differences of internal stress field. The scratch tests showed that the scratch response was controlled by plastic deformation in the substrate. The substrate plays an important role in determining the mechanical properties and wear resistance of such coatings. TiN/GT35 exhibited the best load-carrying capacity and scratch/wear resistance. As a consequence, GT35 is the best substrate for TiN coatings of the substrate materials tested.

Thermocapillary Flows In Liquid Bridges Of Molten Tin With Small Aspect Ratios

Numerical simulations were conducted to study thermocapillary flows in short half-zone liquid bridges of molten tin with Prandtl number Pr = 0.009, under ramped temperature difference. The spatio-temporal structures in the thermocapillary flows in short half-zone liquid bridges with aspect ratios As = 0.6, 0.8, and 1.0 were investigated. The first critical Marangoni numbers were compared with those predicted by linear stability analyses (LSA). The second critical Marangoni numbers for As = 0.6 and 0.8 were found to be larger than that for As = 1.0. The time evolutions of the thermocapillary flows exhibited unusual features such as a change in the azimuthal wave number during the three-dimensional stationary (non-oscillating) flow regime, a change in the oscillation mode during the three-dimensional oscillatory flow regime, and the decreasing and then increasing of amplitudes in a single oscillation mode. The effects of the ramping rate of the temperature difference on the flow modes and critical conditions were studied as well. In this paper, the experimental observability of the critical conditions was also discussed. (C) 2008 Elsevier Inc. All rights reserved.

过滤电弧沉积的TiN/TiCrN/CrN/CrTiN多层膜

用过滤电弧技术在高速钢表面沉积了TiN/TiCrN/CrN/CrTiN多层膜 ,用扫描电镜 (SEM )观察了截面和断口形貌及划痕后的形貌。使用俄歇电子谱仪进行剥层成分分析 ,用纳米压痕仪测试了多层膜和单层膜的显微硬度和弹性模量。结果表明 ,在调制周期大于 10 0nm时 ,多层膜的显微硬度符合Hall Petch关系 ,在 80nm时 ,则脱离线性关系。划痕法测试多层膜的结合力达到 80N。

过滤电弧沉积TiN、ZrN和TiN／CrN多层纳米薄膜的性能比较

用过滤电弧离子镀(FAMIP)技术在高速钢基体上沉积了TiN、ZrN单层薄膜和TiN／CrN多层纳米薄膜。利用扫描电子显微镜(SEM)观察了薄膜及其划痕的表面形貌;用X射线衍射仪(XRD)分析了薄膜的相组成,结合显微探针仪、划痕试验机、金相显微镜和钻床,研究了金属陶瓷单层和多层纳米薄膜的性能并进行比较。研究结果表明:3种薄膜的临界载荷值均大于80N,多层纳米薄膜的耐磨性明显优于2种单层薄膜。

电弧离子镀中脉冲偏压对TiN,CrN薄膜性能的影响

在电弧离子镀技术中使用脉冲偏压电源是近年来发展起来的一项新技术。研究表明，在薄膜沉积过程中，以直流偏压为基础，迭加一个高脉冲电压，有助于改善薄膜的性能，并且能够在较低的沉积温度下获得结合力较强、内应力较小、表面光洁度也比较好的薄膜。通过正交设计和方差分析，本文首次研究了在电弧离子镀技术中使用脉冲偏压电源， 在高速钢和不锈钢基体上沉积TiN和CrN的过程中，对薄膜的表面粗糙度、表面形貌、结合力、显微硬度、沉积速率等性能的影响，发现：（1） 在考虑气氛、弧电流和脉冲电源的各种参数的情况下，气氛和频率是影响薄膜性能的主要因素；（2）在气氛、弧电流不变的条件下，脉冲电源的频率和占空比是影响薄膜粗糙度的主要因素；（3）在比较了直流偏压和脉冲偏压的实验结果之后，认为利用直流迭加脉冲的偏压方式，经过优化参数，能够比较显著地 降低薄膜的表面粗糙度，提高沉积速率。

Reaction of glucose catalyzed by framework and extraframework tin sites in zeolite beta

The isomerization of glucose into fructose is a large-scale reaction for the production of high-fructose corn syrup, and is now being considered as an intermediate step in the possible route of biomass conversion into fuels and chemicals. Recently, it has been shown that a hydrophobic, large pore, silica molecular sieve having the zeolite beta structure and containing framework Sn⁴⁺ (Sn-Beta) is able to isomerize glucose into fructose in aqueous media. Here, I have investigated how this catalyst converts glucose to fructose and show that it is analogous to that achieved with metalloenzymes. Specifically, glucose partitions into the molecular sieve in the pyranose form, ring opens to the acyclic form in the presence of the Lewis acid center (framework Sn⁴⁺), isomerizes into the acyclic form of fructose and finally ring closes to yield the furanose product. Akin to the metalloenzyme, the isomerization step proceeds by intramolecular hydride transfer from C2 to C1. Extraframework tin oxides located within hydrophobic channels of the molecular sieve that exclude liquid water can also isomerize glucose to fructose in aqueous media, but do so through a base-catalyzed proton abstraction mechanism. Extraframework tin oxide particles located at the external surface of the molecular sieve crystals or on amorphous silica supports are not active in aqueous media but are able to perform the isomerization in methanol by a base-catalyzed proton abstraction mechanism. Post-synthetic exchange of Na⁺ with Sn-Beta alters the glucose reaction pathway from the 1,2 intramolecular hydrogen shift (isomerization) to produce fructose towards the 1,2 intramolecular carbon shift (epimerization) that forms mannose. Na⁺ remains exchanged onto silanol groups during reaction in methanol solvent, leading to a near complete shift in selectivity towards glucose epimerization to mannose. In contrast, decationation occurs during reaction in aqueous solutions and gradually increases the reaction selectivity to isomerization at the expense of epimerization. Decationation and concomitant changes in selectivity can be eliminated by addition of NaCl to the aqueous reaction solution. Thus, framework tin sites with a proximal silanol group are the active sites for the 1, 2 intramolecular hydride shift in the isomerization of glucose to fructose, while these sites with Na-exchanged silanol group are the active sites for the 1, 2 intramolecular carbon shift in epimerization of glucose to mannose.

Formation and characterization of tin oxide aerogel derived from sol-gel process based on tetra(n-butoxy)tin(IV)

Transparent and translucent SnO2 aerogels with high specific surface area (>300m(2)/g) have been prepared by sol-gel process using tetra(n-butoxy)tin(IV) as a starting compound, and supercritical drying technique for solvent extraction. Light scattering measurements reveal that the polymeric cluster size distribution in sol system is gradually broadened during sol-gel transition. SEM images show that the aerogels are made up of the cottonlike oxide agglomerates with a large number of Pores. TEM images show that these aerogels seem to be self-similar at different magnifications. Their pore size distribution is pretty wide ranging, from mesopore to macropore especially for that of translucent aerogel. (C) 2004 Elsevier B.V. All rights reserved.