粮食水分的测量和电子水分仪测量不确定度的评定

介绍粮食中水分的两种测量方法：烘干称重法和电测法。同一台水分仪测量不同品种的粮食可能有不同的不确定度,一台水分仪要存入多条工作曲线用以测量不同品种粮食的含水量。介绍了电子水分仪测量不确定度的评定方法。     

Interlaboratory comparison of melt flow rate testing of moisture sensitive plastics

The current standard for melt flow rate testing, ISO 1133, does not adequately cover the measurement of materials that degrade or further polymerise at the melt flow rate test conditions. Materials such as PET, PBT and PA tend to degrade, sometimes rapidly, at melt temperatures if they contain absorbed water. This results in poor repeatability and reproducibility of melt flow rate results. The ISO Plastics Melt Rheology Working Group (TC61/SC5/WG9) is currently developing a modified melt flow rate test method for reliable measurement of moisture sensitive materials, thereby providing an alternative to intrinsic viscosity measurements. The modified method controls more tightly the time–temperature history experienced by the material during testing and, thus, the resultant variability in measured properties due to degradation.The results of an intercomparison of testing of moisture sensitive polymers using the melt volume flow rate (MVR) and melt mass flow rate (MFR) methods are reported. A polypropylene (PP), used as a benchmark material, and five moisture sensitive materials were tested by a number of laboratories measuring either MVR or MFR, or both. For standard testing of the PP material, the repeatability and reproducibility of measurements of MVR were up to 5% and 11%, respectively, and for MFR were 7% and 21%, respectively (95% confidence level, outliers excluded). For the moisture sensitive materials the repeatability and reproducibility of measurements varied significantly, with repeatability values up to 26% and reproducibility values up to 114% being obtained. By imposing moisture and temperature control criteria in accordance with the proposed testing standard, the repeatability and reproducibility limits were significantly reduced to approximately 10% and 60%, respectively. The results suggest that both the moisture and temperature criteria were important for improving the repeatability of MVR measurements. However, the moisture content criterion was more important for improving the reproducibility of MVR measurements.The need to tightly control the sample preparation, in particular the drying and subsequent sample handing procedures, and the time–temperature history of the sample throughout the test is considered critical to further improve the precision of measurements of such materials.     

Viscoelastic,dielectric, and piezoelectric behavior of solid amylose

Complex elastic, dielectric, and piezoelectric properties were measured on amylose films as a function of temperature and moisture content at 10 Hz. The real part of the complex Young's modulus of films containing a small amount of moisture was larger than that of a dry film. Peaks in the imaginary parts of these complex response functions were observed at about ?80°C. The height of these peaks decreased when the specimen absorbed a little moisture. The activation energy for this peak as determined from an Arrhenius plot of the dielectric frequency dispersion was about 9.5 kcal/mole. This peak was ascribed to methylol rotation. The real part of piezoelectric e constant was shifted downwards when the specimen absorbed moisture. This was attributed to the instantaneous response in the case of a step function excitation. The structure of amylose was thought to be stabilized by moisture absorption, probably due to hydrogen bonding. The mechanism of methylol rotation was examined by dielectric measurements.     

The Present Relationships of Sulfuric Acid Concentration to Acid Dewpoint for Flue Gases

Abstract

Interpretation of flue gas acid dewpoints in terms of sulfuric acid concentrations has relied heavily upon Mullers¹ work. A more recent work by additional authors indicates disagreement with Muller's curves. This work involves the study of the acid dewpoint-acid concentration relationship using a commercially available acid dewpoint meter. The study involves generating a steady-state, high temperature, sulfuric acid gas stream using a newly designed acid generation system. By using an absorption reference method, dewpoint as a function of acid concentration and moisture are compared with previous authors. The relationship established is then used along with the previous works to interpret some actual flue gas dewpoints to simultaneous flue gas acid measurements.     

Synthesis of Ag/SiO2 nanocomposite material by adsorption phase nanoreactor technique

Ag/SiO₂ nanocomposite was synthesized in a nanoreactor formed by adsorption layer on silica surface. Ag nanoparticles were prepared by the reduction of Ag ion with ethanol at alkaline condition. By using TEM and XRD, the effects of NaOH concentration, water and temperature on the appearance and grain size of Ag particles were analyzed, respectively. The adsorption curve of NaOH was measured by electrical conductivity meter. The experiment result revealed that Ag grain size decreased while increasing NaOH concentration or while increasing water in our system. Ag grain size increased with the increase of temperature. And Ag aggregated seriously when temperature is up to 60 °C. Finally, after exploring the optimum conditions of reaction, we successfully obtained the well-distributed Ag nanoparticles on surface of silica, and average grain size of Ag nanoparticles reached 5 nm.     

A strip resonance technique for measuring the ultrasonic viscoelastic parameters of polymeric sheets with application to cellulose

An acoustic strip resonance apparatus that measures the viscoelastic response of polymeric sheets over the temperature range of 100–400°K and at frequencies from 20 to 100 kHz is described. This is a computer-controlled instrument which uses the resonant frequency and the quality factor of standing waves in strips to calculate the ratio of complex Young's modulus to density. Results are presented for cellophane and paper samples. These are consistent with measurements reported by others at lower frequencies. That is, (1) a single predominant secondary relaxation process which corresponds to the γ relaxation occurring at 200°K and 1 Hz is found in dry samples at 260°K and 60 kHz; (2) as moisture is added, the γ relaxation weakens and a higher temperature, β, relaxation appears; and (3) at low temperature, moisture addition initially increases the mass specific Young's modulus. The effects of methanol on the viscoelastic parameters of cellulose were also measured and found to be similar to those of water.     

Simultaneous non-invasive microwave dielectric spectroscopy and dynamic mechanical analysis for studying drying processes

The aim of this paper is to describe how a dynamic mechanical analyser can be used together with the microwave coaxial line technique. This coupling enables the simultaneous recording of changes in the mechanical properties and moisture content of materials as a function of time or temperature at a selected frequency. The sample is placed either directly under the probe or clamped in the sample holder of the dynamic mechanical analyser. Sample positioning and heating is accurately controlled by the mechanical analyser and its temperature controller. Samples can be subjected to a constant static force, a frequency or both. A micro probe, recently designed for measurements on semi-rigid and rigid surfaces [1], and connected to a network analyser was used to monitor the moisture content of the samples.     

Biofuels

The article presents results of thermogravimetric measurements of the pyrolysis of dry biomass materials such as: grains and oats and triticale straw, energy plants called cukrosorgo. The initial phase of dry decomposition visible on the DTG curve is evaporation of moisture. The process of evaporation for the studied types of agro biomass occurred at temperatures of 65.9?°C (triticale straw) to 82?°C (oat grain). The next stage of the process concerned major transformations that for the studied cases were conducted in temperatures of 200?C400?°C, and the maximum speed of transformations (the second peak is visible in the DTG graph) refers to the temperature range from 299.1?°C (oat grain) to 323.9?°C (triticale straw). The last phase of the process is characterized by the absence of mass loss, which in the case of dry biomass distribution determines the conditions of carbonizate formation. The calorific values of formed process gases ranged from 4,884 to 6,302?kJ/Nm³. Gases of such calorific values are defined as low calorific, despite the fact they can be successfully used for energy purposes, this is for burning in boilers and gas turbines. Carbonizates are characterized with high-calorific values from 24,100 to 27,900?kJ/kg. This type of high-calorific fuels is recommended to be burnt in the boiler furnaces in a mix with fuels with a lower calorific value such as pulverized coal or wet biomass. In these processes, the combustible gas is obtained, which can be burned in power boilers and gas turbines.     

The pressure–volume–temperature relationship of cellulose

Pressure–volume–temperature (PVT) measurements of α-cellulose with different water contents, were performed at temperatures from 25 to 180 °C and pressures from 19.6 to 196 MPa. PVT measurements allowed observation of the combined effects of pressure and temperature on the specific volume during cellulose thermo-compression. All isobars showed a decrease in cellulose specific volume with temperature. This densification is associated with a transition process of the cellulose, occurring at a temperature defined by the inflection point T _t of the isobar curve. T _t decreases from 110 to 40 °C with pressure and is lower as moisture content increases. For isobars obtained at high pressures and high moisture contents, after attaining a minimum, an increase in volume is observed with temperature that may be related to free water evaporation. PVT α-cellulose experimental data was compared with predicted values from a regression analysis of the Tait equations of state, usually applied to synthetic polymers. Good correlations were observed at low temperatures and low pressures. The densification observed from the PVT experimental data, at a temperature that decreases with pressure, could result from a sintering phenomenon, but more research is needed to actually understand the cohesion mechanism under these conditions.     

Effect of moisture on the bulk properties of salted poly(caproamide)

The glass-transition temperature (T_g) and the elastic modulus of nylon-6 and its mixtures with 4% w/w LiCl and with 2% LiCl+3% LiBr were investigated. In one set of experiments care was taken to avoid absorption of moisture during the measurements. In another set of experiments, samples were exposed to atmospheric humidity for different lengths of time. Both unoriented and oriented specimens were investigated. The presence of 4% LiCl almost doubles the amount of moisture absorbed at equilibrium by nylon-6. The T_g was found to be greatly affected by the moisture content and by salt type. When strict precautions to exclude moisture are taken, the addition of 4% LiCl raises the T_g of nylon-6 by about 25°C. The elastic modulus of oriented samples is increased by the addition of salts provided moisture is completely absent. This beneficial effect is, however, completely eliminated when samples are allowed to equilibrate with atmospheric moisture.     

Unusual decrease in conductivity upon hydration in acceptor doped, microcrystalline ceria

The impact of hydration on the transport properties of microcrystalline Sm(0.15)Ce(0.85)O(1.925) has been examined. Dense, polycrystalline samples were obtained by conventional ceramic processing and the grain boundary regions were found, by high resolution transmission electron microscopy, to be free of impurity phases. Impedance spectroscopy measurements were performed over the temperature range 250 to 650 °C under dry, H(2)O-saturated, and D(2)O-saturated synthetic air; and over the temperature range 575 to 650 °C under H(2)-H(2)O atmospheres. Under oxidizing conditions humidification by either H(2)O or D(2)O caused a substantial increase in the grain boundary resistivity, while leaving the bulk (or grain interior) properties unchanged. This unusual behavior, which was found to be both reversible and reproducible, is interpreted in terms of the space-charge model, which adequately explains all the features of the measured data. It is found that the space-charge potential increases by 5-7 mV under humidification, in turn, exacerbating oxygen vacancy depletion in the space-charge regions and leading to the observed reduction in grain boundary conductivity. It is proposed that the heightened space-charge potential reflects a change in the relative energetics of vacancy creation in the bulk and at the grain boundary interfaces as a result of water uptake into the grain boundary core. Negligible bulk water uptake is detected under both oxidizing and reducing conditions.     

A simple in situ characterization technique for the onset of the chemical degradation of PEM fuel cells’ fluorinated membranes

The onset of the chemical degradation of the fluorinated PEM fuel cells’ membranes is characterized using an in situ novel technique. It is based upon measuring the pH of the water drained out from the cathode and the anode compartments using a flow pH meter connected to these outlets. It was found that the acidity of water increases significantly as the load increases if the cell operates at low temperature–low relative humidity (RH) condition after it was working at high temperature–high RH condition previously. Degradation rates were calculated from the pH measurements.     

Dynamic reference electrode for investigation of fluoride melts containing beryllium difluoride

Existing designs of reference electrodes for potentiometric measurements in fluoride melts do not meet basic requirements of the long exposure corrosion tests to be performed. A new diaphragm-free three-electrode meter with a nonstationary (dynamic) beryllium reference electrode for the redox potential measurements was developed. Optimum conditions of forming dynamic beryllium reference electrode were determined in the laboratory tests in isothermal cell. The device for redox potential measurement was designed and it was shown that it is highly sensitive to changes redox potential within ±5 mV. Reliability and efficiency of diaphragm-free device with dynamic reference electrode was confirmed in the thermal convection corrosion loop operating more than 1200 h with molten 15LiF-58NaF-27BeF₂ mixture (mol%) at a maximum temperature of about 700 °C.     

Effects of curing on the glass transition temperature and moisture absorption of a neat epoxy resin

Apparent glass transition temperature (T_g) measurements were made on smaples of a neat epoxy resin that had been cured at four different temperature and for four different times at each temperature. The apparent T_g data increase with cure time toward an asymptote that was dependent on cure temperature. The asymptotic dependence of T_g on cure temperature may be explained by the effect of cure temperature on the reaction rates and available reaction sites. The asymptotic increase with cure time may be understood in terms of the resin's extent of cure. Moisture-conditioning studies were also made and the amount of moisture absorbed was correlated with the extent of cure. The absorbed moisture's interaction with the resin's molecular structure was deduced to by primarily at hydroxyl sites.     

Microstructure and Magnetic Properties of Ag/Fe/Ag Pseudo-Sandwich Nanogranular Films

"Nanogranular Ag/Fe/Ag films were prepared by magnetron sputtering from a silver and an iron target onto glass substrates at room temperature and subsequent in situ annealing. The structural and magnetic properties of the films were investigated as a function of silver layer thickness and annealing temperature. X-ray diffraction shows the Fe(110) peak is formed in all the samples. Vibrating sample magnetometer measurements indicate that the magnetic moments lie well perpendicular to the film plane. Coercivityreaches the maximum in the sample annealed at 500 oC for 30 min with 3 nm Ag layer. A scanning probemicroscope was used to scan surface morphology and magnetic domain structures. In as-deposited samplesthe average grain size and the average roughness is smaller than that the annealing samples. After annealing,the grain size is larger and the contrast of domains increases, but the domain size becomes smaller."     

Intermediate temperature ionic conductivity of Sm1.92Ca0.08Ti2O7–δ pyrochlore

The results of concentration cell electromotive force methods (EMF) and electrochemical impedance spectroscopy measurements on the pyrochlore system Sm_1.92Ca_0.08Ti₂O_7–δ are presented. The data have been used to estimate total and partial conductivities and determine transport numbers for protons and oxide ions under various conditions. The EMF techniques employed include corrections for electrode polarisation resistance. The measurements were performed using wet and dry atmospheres in a wide \( {p_{{{{\rm{O}}_{{2}}}}}} \) range using mixtures of H₂, N₂, O₂, and H₂O in the temperature region where proton conductivity was expected (500–300 °C). The impedance measurements revealed the conductivity to be mainly ionic under all conditions, with the highest total conductivity measured being 0.045 S/m under wet oxygen at 500 °C. Both bulk and grain boundary conductivity was predominantly ionic, but electronic conductivity appeared to play a slightly larger part in the grain boundaries. EMF data confirmed the conductivity to be mainly ionic, with oxide ions being the major conducting species at 500 °C and protons becoming increasingly important below this temperature.

     

Intermediate temperature ionic conductivity of Sm1.92Ca0.08Ti2O7�C�� pyrochlore

The results of concentration cell electromotive force methods (EMF) and electrochemical impedance spectroscopy measurements on the pyrochlore system Sm_1.92Ca_0.08Ti₂O_7?C?? are presented. The data have been used to estimate total and partial conductivities and determine transport numbers for protons and oxide ions under various conditions. The EMF techniques employed include corrections for electrode polarisation resistance. The measurements were performed using wet and dry atmospheres in a wide $ {p_{{{{\rm{O}}_{{2}}}}}} $ range using mixtures of H₂, N₂, O₂, and H₂O in the temperature region where proton conductivity was expected (500?C300?°C). The impedance measurements revealed the conductivity to be mainly ionic under all conditions, with the highest total conductivity measured being 0.045?S/m under wet oxygen at 500?°C. Both bulk and grain boundary conductivity was predominantly ionic, but electronic conductivity appeared to play a slightly larger part in the grain boundaries. EMF data confirmed the conductivity to be mainly ionic, with oxide ions being the major conducting species at 500?°C and protons becoming increasingly important below this temperature.     

Self-diffusion of a polystyrene-polyisoprene block copolymer

Forced Rayleigh scattering (FRS) has been used to measure the self-diffusion coefficient, D, of a lamellar-forming polystyrene-polyisoprene diblock copolymer (M_PS = 1.0 X 10⁴, M_PI = 1.3 X 10⁴) as a function of temperature. The measurements traverse the order-disorder transition (ODT), which occurs at 160°C. There is no obvious change in either D or the temperature dependence of D at the ODT, in agreement with measurements on several other systems. Electron microscopy confirms that the sample in the ordered state is quenched, with no long-range orientation of lamellae, and a typical grain size well below 1 μm. In contrast to previous measurements on a similar styrene-isoprene diblock, these FRS signals are well-described by single exponential decays; this may be largely attributed to differences in average grain size. The temperature dependence of D is modeled with several empirical expressions, based on the known monomeric friction factors for pure polystyrene and pure polyisoprene, but without quantitative success. These results underscore the need for a greater understanding of the composition and temperature dependences of local friction in polymer mixtures. © 1996 John Wiley & Sons, Inc.