Long-term relative stability of thermistors

The relative stability of four glass-bead thermistors has been analyzed for 44 months to determine if thermistors have sufficient relative stability to be used as feedback sensors for milliKelvin levels of temperature control. The thermistors were measured at 20 ± 0.1 °C using commercial two-wire instrumentation. The thermistors have a nominal resistance of 12.5 kΩ and sensitivity of −4.5%/°C at 20°C. They are nested together inside several layers of thermal resistance and capacitance, which are held at nominal 20°C with a temperature-controlled, recirculating air chamber. After correction for instrumentation drift with two high-stability reference resistors, the average relative rms drift of the thermistors is 50 ± 15 μK, with an rms fitted drift rate of 0.26 ± 0.16 μK/week.     

Long-term relative stability of thermistors: Part 2

The relative stability of four glass–bead thermistors has been analyzed for 66 months to determine if thermistors have sufficient relative stability to be used as feedback sensors for milliKelvin levels of temperature control. This paper provides additional drift data and new correlations beyond those described in a previous paper [Prec Eng, J Int Soc Prec Eng Nanotechnol 2001;25:24–8]. The thermistors were measured at 20±0.1 °C using commercial two-wire instrumentation. The thermistors have a nominal resistance of 12.5 kΩ and sensitivity of −4.5%/°C at 20 °C. They are nested together inside several layers of thermal resistance and capacitance which are held at nominal 20 °C with a heater controller that maintains the thermistor nest above the 19 °C ambient air temperature. After correction for instrumentation drift with two high-stability reference resistors, the average relative RMS drift of the thermistors is 48±16 μK, with an RMS fitted drift rate of 0.19±0.08 μK per week.     

A calibration system for PTU devices

Devices measuring pressure, temperature and humidity simultaneously are known as PTU devices. There are hardly any commercial calibration systems for the PTU devices available for low temperatures (<0 °C). To obtain more comprehensive data on the performance of PTU devices, a new calibration system is developed at MIKES. In this PTU Apparatus, pressure, temperature and humidity can be controlled simultaneously so that all combinations over the ranges are possible. The nominal ranges of the system are the following: absolute pressure 500–1100 hPa, temperature −52 °C to +80 °C and relative humidity 10–95%. The target uncertainties (k = 2) of the pressure, temperature and humidity are 10 Pa, 0,1–0,3 °C and 1–3% RH, respectively. The construction and operation as well as the results of operational tests of the PTU Apparatus are reported in this paper.     

Studies of high temperature sliding wear of metallic dissimilar interfaces II: Incoloy MA956 versus Stellite 6

The development of wear surfaces formed during limited debris retention sliding wear of Incoloy MA956 against Stellite 6 between room temperature and 750 °C, and sliding speeds of 0.314 and 0.905 m s⁻¹ (7 N applied load, 4522 m sliding distance) were investigated. At 0.314 m s⁻¹, mild oxidational wear was observed at all temperatures, due to oxidation of Stellite 6-sourced debris and transfer to the Incoloy MA956; this debris separated the Incoloy MA956 and Stellite 6 wear surfaces. Between room temperature and 450 °C, the debris mainly took the form of loose particles with limited compaction, whilst between 510 °C and 750 °C the debris were compacted and sintered together to form a Co–Cr-based, wear protective ‘glaze’ layer. The behaviour was identical to that previously observed on sliding Nimonic 80A versus Stellite 6 at 0.314 m s⁻¹.At 0.905 m s⁻¹, mild oxidational wear was only observed at room temperature and 270 °C and dominated by Incoloy MA956-sourced debris. At 390 and 450 °C, the absence of oxide debris allowed ‘metal-to-metal’ contact and resulted in intermediate temperature severe wear; losses in the form of ejected metallic debris were almost entirely Incoloy MA956-sourced. This severe wear regime was also observed from 510 up to 630 °C, but increasingly restricted to the early stages of wear by development of a wear protective Incoloy MA956-sourced ‘glaze’ layer. This ‘glaze’ layer formed so rapidly at 690 °C and 750 °C, that severe wear was all but eliminated and wear levels were kept low.The behaviour observed for Incoloy MA956 versus Stellite 6 at 0.905 m s⁻¹ contrasts sharply with that previously observed for Nimonic 80A versus Stellite 6, in that the Incoloy MA956-sourced high Fe–Cr debris formed a protective oxide ‘glaze’, whilst the Nimonic 80A-sourced Ni and Cr oxides formed an abrasive oxide that at high sliding speeds assisted wear. The data indicates that the tendency of oxide to form a ‘glaze’ is readily influenced by the chemistry of the oxides generated.     

A full factorial investigation of the erosion durability of automotive clearcoats

A full factorial experimental investigation has been carried out into factors affecting the resistance of a commercial acrylic/melamine automotive clearcoat to erosion by silica sand particles. The factor variables and their ranges were: particle size 125–425 μm; temperature 30°C–65°C; impact angle 30°–90°; particle velocity 35 m s⁻¹–55 m s⁻¹; and the baking process applied to the coating. An empirical linear regression model for the erosion response of the coating with R²_adj=97.5% was generated from the data. The regression coefficients of this model quantify the relative strengths of the effects of each of the factors. Several interactions between the factor variables were identified. In particular, the glass transition of the coating, which occurs at 40°C, has a significant effect on its response to erosion. The study has allowed the combinations of conditions that would be of most concern for automotive paint users to be identified.     

On-site calibration system for trace humidity sensors

A portable device for calibration of trace humidity sensors and an adopted calibration procedure have been developed. The calibration device is based on humidity generation by permeating water through polymeric membrane tubes. Water vapour transmission rates for various polymers were experimentally determined in order to select the most suitable polymeric material. The developed trace humidity generator consists of a gas-flow polymeric hose immersed in a water reservoir thermostated by a sensor-controlled heater. Mole fractions of water vapour between 1 μmol mol⁻¹ and 350 μmol mol⁻¹ (equivalent to frost-point temperatures from −76 °C to −31 °C) were generated by varying either the operating temperature or gas flow. The operating temperature can be varied from 20 °C to 60 °C and kept stable within 0.1 K. Uncertainty analysis indicated that the trace humidity generator produces gas flows of constant humidity amounts with a relative expanded uncertainty less than 3.4% (k = 2) of the generated value.     

基于冷镜式露点仪的湿度标准装置测量不确定度评定

高精度露点仪是一种高准确度的湿度测量仪器是国家湿度量值传递和国际比对通用的传递标准。而双压法湿度发生器能够连续输出恒湿气体,也是传递湿度量值的标准设备。本文讨论了高精度露点仪与双压法湿度发生器配套使用时,标准装置产生测量不确定度的多种因素。从双压法湿度发生器的工作原理出发,建立数学模型,并统一采用露点温度的形式,对本湿度标准装置的测量不确定度进行了评定。     

Ceramic-ceramic composite materials with improved friction and wear properties

Dry friction and wear tests were performed with self-mated couples of SiC containing 50% TiC, Si₃N₄---BN, SiC---TiB₂ and Si₃N₄ with 32% TiN at room temperature and 400°C or 800°C.Under room temperature conditions, the friction coefficient of the couple SiC---TiC/SiC---TiC is only half of that of the couple SiC/SiC and the wear is one order of magnitude smaller. At 400°C, it exceeds the friction coefficient of SiC/SiC except at the highest sliding velocity of 3 m s⁻¹. At lower sliding velocities the wear coefficient of SiC---TiC/SiC---TiC is lower than that of SiC/SiC.The couple Si₃N₄---TiN/Si₃N₄---TiN exhibits high friction coefficients under all test conditions. At room temperature the wear volume of the self-mated couples of Si₃N₄ and Si₃N₄---TiN after a sliding distance of 1000 m is similar, but Si₃N₄---TiN shows a running-in behaviour. At 800°C the wear coefficient of Si₃N₄---TiN/Si₃N₄---TiN is approximately two orders of magnitude smaller than that of Si₃N₄/Si₃N₄, and equal to those at room temperature. At 22°C the addition of BN reduces the friction of Si₃N₄. The wear coefficient is independent of sliding velocity and the self-mated couples showing running-in. Friction and wear increase with increasing temperature. The wear coefficient of SiC---TiB₂ above 0.5 m s⁻¹ at 400°C is advantageously near 10⁻⁶ mm³ (Nm)⁻¹. With the other test conditions the wear behaviour is similar to SSiC.     

The friction behavior of Ni-, SiO2- and mica sodium silicate-based solid lubrication composites

The friction behavior of Ni⁻-, SiO⁻₂- and mica sodium silicate-based lubricant composites, which included BN, WS₂ and graphite as lubricants, were examined. A ring-on-disk apparatus, in which a solid lubricant composite disk was held against a rotating stainless ring, was used as the test configuration. The tests were run with a load from 62 to 250 N in temperatures from 20 to 800°C in the laboratory environment. The wear surface was characterized by scanning electron microscope and X-ray photo spectroscopy. The major findings were that both mica sodium silicate- and SiO⁻₂-based composites failed at above 500°C due to severe wear and surface damage; in contrast, Ni⁻-based composite showed a stable friction coefficient and low wear from 20 to 800°C.     

Influence of temperature on erosion by a cavitating liquid jet

The influence of water temperature on cavitation erosion has previously been studied using a vibratory apparatus, but no researches have been conducted at a constant cavitation number in flow condition. This study deals with the influence of the water temperature on cavitation erosion using a cavitating jet apparatus. The optimum stand-off distance at 25 °C was 11, 15, 21 and 25 mm at cavitation number of σ = 0.03, 0.025, 0.02 and 0.015, respectively, and was almost the same as that of a guideline in the ASTM G134 standard. The optimum stand-off distance at 75 °C is similar to that at 25 °C. The erosion rate increases with the liquid temperature and reaches a peak, followed by a decrease. The relative temperature was defined as 0 °C for freezing temperature and 100 °C for boiling temperature of pressurized water. The peak appears at the approximate average of freezing and boiling relative temperatures. The erosion rate increases by 1%/ °C between 5 and 45 °C of relative temperatures, and decreases by 2%/ °C between 45 and 80 °C.     

High temperature erosion of Ti(Mo)C–Ni cermets

The resistance of Ti(Mo)C–Ni cermets of different binder content to solid particle erosion was evaluated at 25, 350 and 650 °C. The elevated temperature erosion of cermets containing 40, 50, 60, 70 and 80 wt.% of titanium carbides and produced from the powder of initially different ratios of Ni to Mo were tested with the help of specially designed centrifugal particle accelerator using silica as the abrasive. Erosion rate was related to both microstructure developed during sintering and materials removal mechanisms operating at the test conditions (impact angle of particles jet was 30° and 90° and velocity was 50 ms⁻¹). The erosion rate decreases with the increase of TiC and Mo contents in the composite. At 650 °C the process of tribo-oxidation affected the material performance to a great extent. The morphology of the worn surface was analyzed with SEM to determine the erosion mechanisms.     

A method for achieving effective load transfer between the inner and outer layers of a two-layer braided high-pressure hydraulic hose

A method is proposed for accommodating the misfit between two layers of a braided hose. This is achieved by laying the inner and outer braids at angles that lie symmetrically on either side of the equilibrium helix angle of tan⁻¹ 2 for a single-layer hose. The theory of the method is developed and it is shown that a difference of helix angles of 4° or more will accommodate the fractional radial misfit of 3 × 10⁻³ existing in a particular sample of hose. An analysis of the wire tensions in a pressurised hose, assuming constant inter-layer volume, revealed that seriously unequal tensions exist in the two layers if the two helix angles lie asymmetrically about tan⁻¹ 2. The process of taking up misfit, now proposed, generates asymmetry. However this asymmetry and the associated inequality of wire tension decreases as the difference of braid angles increases. Guided by this generalisation, it is demonstrated that an acceptable hose design is achieved if the inner braid is laid at an angle of 59·74° and the outer braid at 49·74°. The geometrical changes that take up the misfit at low pressures produce an extension of the hose of 0·65% and reduce the braid angles by about . The ratio of final tensions in the two layers is 0·93. The analysis in the paper leads to the conclusion that manufacturing uncertainties in the angle at which a braid is laid can generate serious inequalities of wire tension. In the specific illustrative example analysed here an uncertainty of ±1° in braid angle will cause the ratio of wire tensions to vary, but it never falls below a value of 0·63.     

Effect of diesel soot on lubricant oil viscosity

Soot related lubricant oil thickening is a primary concern for heavy-duty diesel engines. Engines which produce a relatively low level of particulate matter in exhaust emissions show a significant level of soot contamination in the lubricant. This contamination results in lubricant breakdown. The soot contaminates the lubricant and changes the chemical properties resulting in the lubricant ceasing to perform its functions. This causes an increase in viscosity of the engine oil causing pumpability problems. Hence, it is necessary to study the effects of soot and lubricant oil additives and their interactions on engine oil viscosity.Statistically designed experiments were developed to study the effect of soot contamination on engine oil viscosity. The oil samples used for the study differed in the base stock, dispersant level, and Zinc Dithiophosphate (ZDP) level. These three variables were formulated at two levels: Low (−1) and High (1), which resulted in a 2³ matrix (8 oil blends). Soot was considered as a variable at three levels: low/0% weight (−1), medium/2% by weight (0), and high/4% by weight (1). This resulted in 24 oil samples, and soot at three levels helped in determining the non-linear effect of soot on oil viscosity.Experiments were conducted at 40 and 90 °C to study the effect of the various factors on viscosity with temperature variation. The results showed that viscosity of the oil samples increased with increase in soot at both 40 and 90 °C. The analysis indicated a nonlinear behavior of viscosity as the amount of soot increased at 40 °C, whereas a linear variation at 90 °C.The results obtained were analyzed using the general linear model (GLM) procedure of the statistical analysis system (SAS) package to determine the significance of variables on viscosity. The statistical analysis system also highlighted the significance of various interactions among the variables on viscosity. The statistical analysis results at 40 and 90 °C showed that the effect of base stock and ZDP levels were negligible at 40 °C, whereas the dispersant level and soot level influenced the viscosity of the oil samples at both temperatures.     

Calibration of electronic levels using a special sine bar

Electronic levels are designated for the precise measurement of inclination angles within the range of ±3 mm/m. They are very often used for checking the straightness of machine tool guides as well as the flatness of different kinds of machine tool tables and surface plates. Typical resolution of such instruments is 1 μm/m. Electronic levels are calibrated by using very precise angle generators. One such generator is a sine bar. Sine bars are cheap and enable fast and simple calibrations. Commercial sine bars however are not precise enough. We, therefore, decided to design a special sine bar, which would be able to generate angles within an uncertainty of 1 μm/m. This sine bar was designed by the laboratory staff and manufactured in our workroom. We have also created a calibration procedure, which has already been accredited. Uncertainty analysis, including experimental measurements, shows that the planned uncertainty has been reached. The sine bar design, calibration procedure and uncertainty evaluation are presented in this article.     

Chromium oxide coatings applied to magnetic tape heads for improved wear resistance

This paper reports on an investigation of the wear of chromium oxide based very thin films. Linear data tape Advanced Digital Recording (ADR™) heads coated with 20- and 40-nm thick chromium oxide films have been tested subject to temperature/humidity matrix of 10 to 40°C/10 to 80% in order to assess the wear behaviour of the coating as a function of environment. The tested heads were analysed at various stages of wear, by use of optical microscopy (OM), atomic force microscopy (AFM) and Auger electron spectroscopy (AES). The results show that the most severe damage occurs at the highest relative humidity (80% RH) and for a given humidity, at the lowest temperature (10°C). Inversely, stain transferred from the tape to the head surface predominates at the lowest humidity (10% RH). Stain therefore appears to protect the coating against wear with the degree of protection increasing with the temperature.The wear process differs according to the coating thickness. This is attributed to the location of the maximum subsurface stress with respect to the coating/substrate interface. It is shown that this maximum stress occurs below the interface for 20 nm and at the interface for 40 nm thick coatings. This correlates to different observed wear modes.     

温湿度传感器检定装置对比实验与分析

合理选取HMP45D温湿度传感器的检定装置对提高校准质量、节约校准成本具有重要意义。文中基于本单位现有的4台温湿度检定装置,通过大量的对比实验,分析了不同装置对HMP45D温湿度传感器校准质量的差异。结果表明：恒湿盐湿度发生器和DJM10型湿度检定箱具有较高的性价比,适合作为HMP45D温湿度传感器的检定装置。具体来说,恒湿盐湿度发生器适合HMP45D温湿度传感器的现场校准工作,而湿度检定箱更适合完成室内校准任务。     

基于红外测湿传感器的湿度检定箱设计

文章介绍了一种新型湿度检定箱,其温度控制采用高效气液换热,湿度控制采用干湿气混合法反馈控制原理,湿度测量采用红外激光吸收式湿度传感器。通过实验测试,新型湿度检定箱的温度、湿度均匀度和波动度都优于目前计量测试部门使用的所有湿度检定箱,且测试室容积大,可对毛发湿度表(计)、干湿表等大型测试仪表和湿度传感器等进行检定测试,还可同时进行温度校准,具有很好地推广应用价值。     

Force, torque and plastic flow analysis in rotary upsetting of ring shaped billets

The orbital upsetting of rings has been analysed for a Mises material by using an upper bound approach. Forging forces, rocking die torques and ring profiles are calculated at each step of the process. Experiments are described in which rings made of 1045 mild steel, 52100 chromium alloyed steel and 316 stainless steel are upset at room temperature on a 1.6 MN rotary press. The main parameters are: orbital oscillation angle, 2°, upper die oscillations, 200 min⁻¹ and lower die speed, 4.10 mm s⁻¹. An experimental rocking die placed on a conventional testing machine has been used for the rotary upsetting of rings made of Plasticine as model material. The simulation parameters are: oscillation, 2°, upper die oscillations, 40 min⁻¹, speed, 98.4 mm min⁻¹. The theoretical values of forging forces, rocking torques, and ring profiles are in keeping with the experiments. So the proposed upper bound approach may be considered as a good model for rotary upsetting.     

High temperature tribology of ceramics

The friction and wear behaviour of self-mated couples of MgO---ZrO₂, Al₂O₃ and two types of SiSiC were studied under dry sliding conditions in a special pin-on-disc high temperature tribometer. The temperature was varied between 25 and 1000°C, and the sliding speed from 0.03 m s⁻¹ to 3 m s⁻¹. The morphology of the worn surfaces was studied by means of SEM, and their phase distribution by X-ray diffraction and TEM analyses. The results show that the wear coefficients of all couples mostly increase with increasing temperature and sliding velocity. The wear of MgO---ZrO₂ is influenced by tribo-induced phase transformations while α-Al₂O₃ retains its original structure for all test conditions. For SiSiC delamination and fatigue of the interface Si/ß-SiC predominate. At higher temperatures and sliding velocities tribo-oxidation is effective. The friction coefficients lie between 0.5 and 1.0 under steady-state conditions but for short test durations lower values can occur. The couple SiSiC/SiSiC has low friction coefficients at low sliding velocities and temperatures, even if the steady-state region is reached.     

Humidity-controlled preparation of frozen-hydrated biological samples for cryogenic coherent x-ray diffraction microscopy

Coherent x-ray diffraction microscopy (CXDM) has the potential to visualize the structures of micro- to sub-micrometer-sized biological particles, such as cells and organelles, at high resolution. Toward advancing structural studies on the functional states of such particles, here, we developed a system for the preparation of frozen-hydrated biological samples for cryogenic CXDM experiments. The system, which comprised a moist air generator, microscope, micro-injector mounted on a micromanipulator, custom-made sample preparation chamber, and flash-cooling device, allowed for the manipulation of sample particles in the relative humidity range of 20%-94%rh at 293 K to maintain their hydrated and functional states. Here, we report the details of the system and the operation procedure, including its application to the preparation of a frozen-hydrated chloroplast sample. Sample quality was evaluated through a cryogenic CXDM experiment conducted at BL29XUL of SPring-8. Taking the performance of the system and the quality of the sample, the system was suitable to prepare frozen-hydrated biological samples for cryogenic CXDM experiments.