Review of oxidational wear: Part I: The origins of oxidational wear

This is the first part of a two-part in-depth review of the oxidational wear of metals. It discusses the parallelism between the formation of an oxide film for dry contact conditions and of other surface films for lubricated contacct. Wear modes are unified into two major classes of mild and severe wear, including both lubricated both dry and conditions. Oxidational wear is a mechanism of mild wear in which protective oxide films are formed at the real areas of contact (during the time of a contact) at the contact temperature, T_cc. When the oxide reaches a critical thickness ξ, usually 1 to 3 μm, the oxide breaks up and eventually appears as wear particles. These oxides are preferentially formed on plateaux, which alternately carry the load - as they reach their critical thickness - and are removed. Temperature is important in determining the structure of the oxide film present, which in turn affects the wear properties of the sliding interfaces. Hence, this part of the review concludes with a thorough treatment of the thermal aspects involved during the sliding of a typical laboratory simulation of the oxidational wear of steel specimens without lubrication. This treatment shows how the general surface temperature (T_s) and the division of heat (?)_at the interface can be calculated and used, in conjunction with the measured wear rate (w), to give information about a possible surface model consisting of N contracts on the (thermally expanded) operative plateau, the height of the plateau being identical to the critical oxide film thickness (ξ) mentioned above.Part II outlines recent research to determine the oxidational constant, ie the activation energy and the Arrhenius constant, relevant to oxidational wear. It is found that the Arrhenius constant for oxidational wear is different from that for static oxidation tests. Some typical values of N, ξ and T_c are calculated from oxidational wear experiments. A new oxidational wear theory designed to take into account the oxide growth which occurs at the general surface temperature, T_s (where T_s < T_c) , whilst operation plateau is out-of-contact. This theory is most relevant to weat at elevated temperatures, where it is not permissible to assume that out-of-contact oxidation is negligible. After a brief review of the small amount of work done on the effects of partial oxygen pressures on oxidational wear, Part II concludes with a discussion of the possible connection between the general oxidational wear theory for dry contacts and the wear which occurs at lubricated contacts.     

Transparent single-point turning of optical glass:: A phenomenological presentation

Single-point turning of optical glasses by continuous chip generation at elevated temperature is described in this paper: appropriate temperatures are ranged around the American softening point. Optimisation of tool-setting, depth of cut, local heat supply and other parameters resulted in transparent turning of a number of optical glasses by a process combining abrasive turning by single-point machining and viscous relaxation of the glass surface immediately after removal of the continuous chip     

Microbial spoilage of engineering materials: Part 1: The power of the microbe

Microbes are uniquely equipped to take advantage of the Chemical bond energy of organic and inorganic materials. Thousands of biotransformation reactions can be mediated at phenomenal rates at ordinary temeperatures and pressures by cellular enzymes. One manifestation of this, biodeterioration of materials used by man, represents a costly nuisance aspect of wider process, biodegration, which is essential to our life-support system. The long term control of biodetermination in industry requires integrated action from a number of progfessions. This action, if it is to be effective, must arise from a knowledge of microbial growth, nutrition, and cell structure and function.     

SEM analysis of enamel surface treated by Er:YAG laser: influence of irradiation distance

BACKGROUND: Depending on the distance of laser tip to dental surface a specific morphological pattern should be expected. However, there have been limited reports that correlate the Er:YAG irradiation distance with dental morphology. PURPOSE: To assess the influence of Er:YAG laser irradiation distance on enamel morphology, by means of scanning electron microscopy (SEM). METHODS: Sixty human third molars were employed to obtain discs (approximately =1 mm thick) that were randomly assigned to six groups (n=10). Five groups received Er:YAG laser irradiation (80 mJ/2 Hz) for 20 s, according to the irradiation distance: 11, 12, 14, 16, or 17 mm and the control group was treated with 37% phosphoric acid for 15 s. The laser-irradiated discs were bisected. One hemi-disc was separated for superficial analysis without subsequent acid etching, and the other one, received the phosphoric acid for 15 s. Samples were prepared for SEM. RESULTS: Laser irradiation at 11 and 12 mm provided an evident ablation of enamel, with evident fissures and some fused areas. At 14, 16 and 17 mm the superficial topography was flatter than in the other distances. The subsequent acid etching on the lased-surface partially removed the disorganized tissue. CONCLUSIONS: Er:YAG laser in defocused mode promoted slight morphological alterations and seems more suitable for enamel conditioning than focused irradiation. The application of phosphoric acid on lased-enamel surface, regardless of the irradiation distance, decreased the superficial irregularities.     

对ISO 14121-1:2007《机械安全风险评价第1部分:原则》的理解

本文简要介绍了ISO 14121-1:2007的主要技术内容和机械(机器)的风险评价过程,重点介绍了风险评价、机械限制的确定、危险识别、风险评估及风险评定等内容.     

Freeze-fracture cytochemistry: Review of methods

“Freeze-fracture cytochemistry” encompasses a diversity of recently developed techniques in which freeze-fracture and cytochemistry are combined. Cytochemical labeling may, in principle, be integrated into one of three basic points in the standard freeze-fracture procedure; (1) before the specimen is frozen, (2) after it has been fractured, or (3) after it has been platinum shadowed and/or carbon coated. Visualization of the labeled cellular structures can be achieved by a variety of different methodologies. For example, the markers (usually colloidal gold particles) may be viewed embedded within a replica, or attached to it via fragments of membrane (or other cellular components). Sectioning is a central strategy in a number of techniques, either in combination with or in place of replication. The different combinations of methods that have been devised are not, for the most part, alternative ways of arriving at the same result; each provides quite distinct information about specific classes of membrane component or other structure in the cell. The purpose of this review is to present, within a single article, a systematic survey of the full range of techniques currently available in freeze-fracture cytochemistry. Emphasis is placed on explaining the principles underlying the methods and on illustrating their applications. With the success recently achieved, freeze-fracture cytochemistry has moved from the phase of experimental development to a position in which it may be expected increasingly to make significant contributions across a wide spectrum of problems in cell and membrane biology.     

Erosion behavior of high silicon bainitic structures: II: High silicon steels

The erosion behavior of two austempered high silicon (2.5 wt.% Si) steels, one containing 1 wt.% Mn and the other 1 wt.% Ni, has been compared with the mechanical property variations after austempering for various times in the upper bainite temperature range (420 °C). For both steels the erosion resistance is a maximum for austempering times near the end of stage II. The erosion resistance correlates directly with the tensile toughness and with the percentage elongation divided by the percentage reduction in area and inversely with the hardness in all three stages of austempering. It is shown that the strain-hardening coefficient peaks at the minimum erosion rate and that the high strain-hardening character of the retained austenite in these austempered steels is beneficial to erosion resistance. Comparison with the austempered cast irons in Part I of this study shows that the graphite nodules of the cast irons have no significant effect upon erosion rate.     

The use of Er:YAG laser for cavity preparation: an SEM evaluation

OBJECTIVE: The purpose of this study was to evaluate morphological changes in cavities prepared by the Er:YAG laser (2.94 mum) at different parameters of irradiation and by a diamond bur. EXPERIMENTAL DESIGN: Cavities were prepared on 27 human molars (n = 3): G1, 15 Hz/160 mJ enamel/6 Hz/200 mJ dentin; G2, 15 Hz/180 mJ enamel/6 Hz/200 mJ dentin; G3, 15 Hz/160 mJ enamel/6 Hz/250 mJ dentin; G4, 15 Hz/180 mJ enamel/6 Hz/250 mJ dentin; G5, 15 Hz/180 mJ enamel/10 Hz/180 mJ dentin; G6, 15 Hz/160 mJ enamel/10 Hz/180 mJ dentin; G7, 15 Hz/160 mJ enamel/10 Hz/160 mJ dentin; G8, 15 Hz/180 mJ enamel/10 Hz/160 mJ dentin; G9, diamond bur. For SEM analysis, samples were fixed (2.5% glutaraldheyde, 12 h, 4 degrees C), dehydrated (25-100% ethanol), dried, and sputter-coated with gold. RESULTS: Despite the changes on energy and repetition-rate settings, all laser-treated samples showed no evidence of thermal damage or signs of burning and melting. Er:YAG laser ablated dental hard tissues showed exposed enamel prisms, dentin surface without smear layer, and opened dentinal tubules. CONCLUSION: Different Er:YAG laser parameters were effective for ablation of hard tissues, creating an irregular and microretentive morphological pattern without hard tissue damage.     

Part 2: Ultrastructural changes of fibrin networks during three phases of pregnancy: A qualitative investigation

Introduction: Normal pregnancy is characterized by significant alterations in the haemostatic system accompanied by an augmented risk of thrombosis. Materials and methods: The fibrin network ultrastructure of different phases of pregnancy, namely early pregnancy (week 8–14), late pregnancy (week 36–40) as well as post‐partum (week 6–8 after birth) were compared with nonpregnant fibrin networks as well as each other to establish whether differences in fibrin network morphology exist during pregnancy. Scanning electron microscopy was employed to analyse fibrin network morphology. Results: The fibrin networks from all phases of pregnancy appeared similar to each other, exhibiting prominent coagulant formation, an increase in the formation of minor, thin fibers, and the presence of granular globules. All three phases, however, differ from the typical fibrin network ultrastructure exhibited by the fibrin networks from nonpregnant individuals. The increase in estrogen associated with pregnancy may cause the increase in coagulation factors and ultimately the prothrombotic state characteristic of pregnancy. Conclusions: Since no differences were apparent between the different phases of pregnancy it suggests that activation of the coagulation system commences with pregnancy and this pro‐thrombotic state continues till at least 8 weeks after birth. These results may shed light on possible pathological mechanisms employed in the development of abnormal or ailing pregnancy. Microsc. Res. Tech. 77:602–608, 2014. © 2014 Wiley Periodicals, Inc.     

Tribological behavior of plasma-enhanced CVD a-C:H films. Part I: effect of processing parameters

A systematic study was conducted on the effect of plasma-enhanced CVD processing parameters, namely bias voltage, pressure and CH₄/Ar flow ratio, on the characteristics and tribological response of amorphous hydrogenated carbon (a-C:H) films. Film hardness, intrinsic stress, structure, composition and tribological response were characterized. Variation of processing parameters was found to produce a-C:H films with a range of characteristics with the CH₄/Ar ratio exercising a dominant effect. A low ratio produced harder films with more sp³ bonding, low hydrogen content and low wear rate; whereas a high ratio produced softer films, with more sp² bonding, higher hydrogen content and low friction. Film characteristics were found to affect the wear mechanism with softer films showing a layer-by-layer removal and harder films involving formation of fine debris. These two diverse types of films offer the opportunity to synthesize multilayered films combining desirable properties from each component.     

Quality: A cylinder of quality

Nicola Shaw and Keith Ridgway describe how Pareto analysis and a combination of plant and laboratory based experiments were used to investigate quality problems during the manufacture of high pressure gas cylinders, developing a checklist for the use of the Taguchi method.     

Treatment of port-wine stains: analysis

Port-wine stains (PWS) are bluish red skin stains that are caused by enlarged, ectatic blood vessels in the dermis. Laser treatment of PWS is analyzed from computation of the spatial distribution of heat production by direct absorption of the laser light and subsequent heat conduction. The absorption and scattering caused by oxyhemoglobin, epidermis, and dermis as a function of wavelength are utilized in this analysis. Ideal treatment is defined as coagulating the ectatic blood vessels without irreversible damage to the epidermis and dermis. The analysis shows that a millisecond pulsed, yellow dye laser at 577 nm (one of the large absorption bands in blood) is the laser of choice to treat PWS, offering as close to the "ideal treatment" as possible. The blue-green argon laser, which is currently the most frequently used laser for this purpose, is strongly recommended with irradiation times in milliseconds. Other lasers that are in clinical use, such as the red ruby and near-infrared Nd-YAG lasers, can provide selective treatment only when the epidermis is cooled concurrently. The CO2 laser, on the other hand, can coagulate the blood vessels only through heat conduction from the hot epidermis; hence, it has neither the treatment selectivity nor any other physical option to force this selectivity.     

把频率和电路变成纯音乐

德国人他们把每件器材都作为艺术品一样“精雕细琢”。柏林之声音响器材对产品高度可靠性及绝对音乐性的要求却是秉成传统,坚持手工组装,以突显人性化的调控。这是高级手表爱好者喜欢的方式。“我们对品质的要求简质是疯狂的,”柏林之声的总裁Burmester说,“我们的产品是能加上‘超’字的。”     

Characteristics of a hybrid journal bearing with one recess: Part 1: Dynamic considerations

A fluid film hybrid journal bearing with one recess, as used in tandem cold rolling mills, is studied theoretically in two ways. The dynamic response of the hybrid bearing, under isothermal conditions due to the decrease in hydrostatic pressure, is considered and presented in Part 1 of the study, while the thermal effects on the load capacity, temperature distribution, etc of the bearing will be dealt with and described in Part 2.In this paper, the dynamic behaviour of the journal due to the decrease in hydrostatic pressure is presented in the form of transient orbits and squeezed-film speeds, which are shown to be dependent on the initial equilibrium conditions. In the analysis, when the recess pressure is dropped below the hydrodynamic pressure generated by the fluid film, it is found to be difficult to obtain a convergent solution. The dynamic response of the bearing, due to the shut-off of external pressure is, therefore, simulated by the dynamic behaviour of the journal due to a series of pressure drops in arbitrary time intervals. The results show that the journal is quite stable in such conditions.