Mass Change Of Samples Research Articles

Influence of the polymer matrix type on cavitation resistance of composites

Cavitation resistance of polymer matrix / basalt powder composites was determined in this work. Two types of composites were tested: epoxy resin / basalt powder composite and polyester resin / basalt powder composite. In both cases, a basalt powder was used as reinforcement in the resin (grain size 20μm, in the amount of 15 wt%). An ultrasonic vibration method with a stationary sample was used to test the cavitation resistance of composites in laboratory conditions. The change in sample mass with test time was monitored to define cavitation rate. Scanning electron microscopy was used to monitor the morphology of composites surface damage.

INFLUENCE OF MICROSPHERES ON PROPERTIES OF AGGRESSIVE RESISTANT RUBBERS

The aim of the work is to study the effect of hollow corundum, glass and pomegranate ceramic microspheres on the rheometric characteristics of aggressive resistant rubber mixtures and the physicomechanical parameters of their vulcanizates to determine of the content of fillers of this type, which provides an improvement in the priority properties of products and, as a result, an increase in their durability. The objects of research were two rubber mixtures intended for compression molding and injection molding. The compression molding mixture is based on a combination of nitrile butadiene, isoprene and butadiene-α-methyl styrene caoutchoucs with colloidal silicic acids as the main fillers. And the injection molding mixture is based on a combination of synthetic isoprene and butadiene rubbers filled with chalk, P234 carbon black and carbon 100. We used hollow corundum (HMC-L), glass (MS-V), and pomegranate ceramic (MVMD-170) microspheres. The rheometric properties of the rubber compounds were evaluated by the values of the minimum and maximum torques, the duration of the induction period, the time to reach the technological optimum, and the maximum vulcanization rate. When testing vulcanizates, conditional tensile strength, elongation at break, tear resistance, hardness, abrasion and rebound elasticity were determined. Priority indicators were also determined that correlated to the greatest extent with the durability of the products during operation - relative changes in conditional tensile strength and elongation at break, hardness after heat aging in air and standard liquid SZhR-1, change in mass of samples after swelling in industrial oil I-20A and Nefras S-80/120. For a mixture for compression molding, the effect of the type of microspheres introduced at a dosage of 5 parts by mass per 100 parts by mass caoutchoucs, on the properties of unvulcanized mixtures and vulcanizates was studied. It was found that the rubber mixture with glass microspheres is somewhat below in vulcanization activity, and its vulcanizate in terms of abrasion resistance, heat aging, especially in air, is inferior to two mixtures and rubbers with corundum and pomegranate microspheres. In the second mixture, we tested corundum microspheres with a dosage of 3.0 to 7.0 parts by mass per 100 parts by mass of caoutchoucs while reducing by the appropriate amount of carbon black. It was found that with an increase in the dosage of microspheres, a decrease in the vulcanization activity of the mixture, minimum and maximum torques, and also their difference is observed, which indicates a slight decrease in the degree of crosslinking of rubbers. The consequence is an increase in relative lengtheningof the vulcanizates. To the least extent, this effect manifests itself with the introduction of corundum microspheres in a dosage of 3 parts by mass. Thus, the advantage of rubbers with microspheres is reduced abrasion, higher tear resistance while maintaining resistance to the action of physically and chemically aggressive environments at the level of rubbers that do not contain microspheres.

Slowing down the corrosion of metal structures using polymeric materials

This article examines the resistance of corrosion-resistant polymeric materials to chemical reagents and the degree of corrosion, taking into account the direction of corrosion processes. One of the main factors that determined the corrosion rate is air humidity and dust released into the atmosphere during industrial emissions. Mixtures based on polymer materials can be used to gum up chemical apparatus and equipment; for corrosion protection, expensive materials are required. The sample is conditioned for 30 months at (23 ± 2) 0С, relative humidity (50 ± 5) %, and the thickness of the sample is determined. Resistance to chemical reagents the change in mass of samples of polymeric materials at a temperature of 35 0C for 3 months was analyzed. It was also found that by determining the corrosion rate (grade St3) by storing steel plates in a different exposure environment for 50 days. As a result, the corrosion rate of steel anti-corrosion coatings is lower than the control sample. According to the data obtained, it was found that the chloro-sulfonated polyethylene compositions are resistant to various organic solvents, acids, alkalis, oxidizing agents, and others.

Određivanje otpornosti na dejstvo kavitacije uzoraka pirofilita

The resistance under the action of cavitation of sintered pyrophillite samples was investigated. The initial sample of pyrophillite from the Parsovic-BiH deposit was ground a vibrating mill to a granulation of 20 mm, pressed and sintered at temperatures (⁰C): 100; 1100; 1200. To assess cavitation resistance, the change in sample mass as a function of cavitation time was monitored. The cavitation erosion test was performed using the ultrasonic vibratory cavitation test method according to the ASTM G-32 standard. Cavitation velocites were calculated for all samples, as a basic indicator of the resistance of the material under the action of cavitation. The change in the morphology of the surface with the test time was followed by scanning electron microscopy. Based on the values of cavitation velocity and analysis of the surface damage morphology, the cavitation resistance of the tested samples based on pyrophillite was determined. The obtained results indicate that the samples of sintered pyrophillite have satisfactory resistance to the action of cavitation and be applied in conditions of lower cavitation loads.

The moisture buffering performance of plasters when exposed to simultaneous sinusoidal temperature and RH variations

Wall constructions have the capacity to contribute to the passive regulation of indoor Relative Humidity. This property, referred to as moisture buffering, is linked to the hygroscopicity of materials, which allows materials to store and release moisture from and to the surrounding air, depending on the indoor Relative Humidity levels. Laboratory testing procedures, based on a step-response method, were introduced to quantify moisture buffering. The step response method monitors the change in mass of samples, when subjected to square wave humidity variation and constant temperature. However, those protocol's prescribed testing environmental conditions may not be representative of the materials behaviour in buildings, as the surface of walls is exposed to an indoor environment that changes with respect to the temperature and humidity daily and seasonally. This paper investigates the response of clay and gypsum plasters to quasi sinusoidal and simultaneous humidity and temperature functions. It was experimentally shown that the relative humidity influences the amount of water vapour adsorbed and desorbed by the materials, while temperature impacts the rate and the time lag response of clay and gypsum to the indoor humidity variation. The significance of the investigation is to demonstrate the joint effects of Relative Humidity and temperature on hygroscopic materials and to seek to developing a laboratory test, which can represent the real behaviour of such materials in buildings, which are exposed to sine wave-forms.

Numerical Simulation of Coupled Pyrolysis and Combustion Reactions with Directly Measured Fire Properties.

In this study, numerical simulations of coupled solid-phase reactions (pyrolysis) and gas-phase reaction (combustion) were conducted. During a fire, both charring and non-charring materials undergo a pyrolysis as well as a combustion reaction. A three-dimensional computational fluid dynamics (CFD)-based fire model (Fire Dynamics Simulator, FDS version 6.2) was used for simulating the PMMA (non-charring), pine (charring), wool (charring) and cotton (charring) flaming fire experiments conducted with a cone calorimeter at 50 and 30 kW/m2 irradiance. The inputs of chemical kinetics and the heat of reaction were obtained from sample mass change and enthalpy data in TGA and differential scanning calorimetry (DSC) tests and the flammability parameters were obtained from cone calorimeter experiments. An iso-conversional analytical model was used to obtain the kinetic triplet of the above materials. The thermal properties related to heat transfer were also mostly obtained in house. All these directly measured fire properties were inputted to FDS in order to model the coupled pyrolysis–combustion reactions to obtain the heat release rate (HRR) or mass loss. The comparison of the results from the simulations of non-prescribed fires show that experimental HRR or mass loss curve can be reasonably predicted if input parameters are directly measured and appropriately used. Some guidance to the optimization and inverse analysis technique to generate fire properties is provided.

Investigating the influence of instrumental parameters and chemical composition on pyrolysis efficiency of peat

ABSTRACT To track changes in organic matter (OM) in peat soils, analytical techniques are needed that effectively characterize their chemical components. Pyrolysis-gas chromatography/mass spectrometry is a useful method for obtaining a chemical “fingerprint” of OM. To obtain representative fingerprints, the pyrolysis process should be highly reproducible and representative of the original sample; however, these key indicators for successful volatilization are underreported in the literature. We investigated the influence of instrumental parameters (temperatures, heating rates, sample mass), original organic C and nitrogen (N) content, and instrument type (“slow” vs “flash”), on volatilization of different peat samples by monitoring sample mass loss and changes in organic C and N content before and after pyrolysis. Average percent C by mass volatilized (“C pyrolysis efficiency”) across all pyrolysis experiments conducted (mass, instrument types, and settings) was 47.8 ± 1.8%. Sample mass was not a major driver; however, instrument temperatures, heating rate, and original N content had a significant influence on pyrolysis efficiency. N pyrolysis efficiency occurred at significantly higher rates (56.7–75.8%) than C pyrolysis efficiency (45.1–51.6%). N pyrolysis efficiency was also negatively influenced by decreasing concentrations of original sample N, suggesting that N-containing compounds may undergo preferential volatilization in high pyrolysis temperatures. Our data suggest that C pyrolysis efficiency is relatively insensitive to instrumental parameters; whereas when seeking to identify N-containing compounds, appropriate temperatures and heating rates must be chosen. These results provide an expected range for pyrolysis efficiency as a reference for peat samples analyzed with this technique.

Oxidation response of additively manufactured eutectic Mo-Si-B alloys

Previous studies showed the technical feasibility of additive manufacturing (AM) of Mo-Si-B alloys using the laser powder bed fusion (L-PBF) process. The competitiveness of the properties of AM alloys was demonstrated by a comparison to literature data from conventionally processed Mo-Si-B materials. In addition to the excellent mechanical properties at ambient and elevated temperatures, the oxidation resistance in a wide temperature range is another decisive aspect for the potential use of AM Mo-Si-B alloys. The present work shows investigations on the cyclic oxidation performance of a eutectic AM Mo-16.5Si-7.5B alloy. Depending on the temperature (800 °C, 1100 °C, 1300 °C), the oxidation mechanisms are different, which is due to different reactions at the surface of the alloys accompanied with mass changes of samples. These mass changes can be explained on the basis of microstructural investigations. However, compared to a directionally solidified (DS) alloy, the AM alloy shows improved oxidation resistance.

Combustion Performance and Kinetic Analysis of Shenhua Raw Coal Mixed Coal Gasification Slag

In this paper, Shenhua coal and its gasification slag (GS) in Ordos are taken as the research objects. The thermogrmetric analyzer is used to investigate the mixed combustion characteristics of different proportions. The experimental results show that Shenhua raw coal mixed with GS can improve the overall ignition and burnout characteristics of mixed coal to some extent. With the increase of the mixing amount of GS, the combustion characteristic temperature of coal samples presents an overall trend of increase in ignition point temperature (T i) and burnout temperature (T b). When the GS content is 50%, the maximum weight loss temperature (T max) is the highest. The mixing amount of GS is not equal to the change of sample mass. The comprehensive combustion characteristic S decreases with the increase of GS content.When the mixing amount of GS was 50%, the minimum apparent activation energy obtained was 87.11kJ/mol.

DETERMINATION OF FORMATION REGIMES FOR BILAYER COBALT DYSPROSIUM INTERMETALIC SURFACE ALLOY

High tech industrial fields on modern development stage are in need of construction materials with an optimal ratio of volume and surface properties, along with low cost of material itself. As evidenced by studies, in order to give a set complex of properties to a workpiece that operates under specific conditions, it is often sufficient to only modify its surface area. Over the course of studies, by means of gravimetric, influence of technological parameters (temperature and time samples are kept in the melt) on specific mass change of cobalt samples, that act as substrate, during electroless diffusive saturation with dysprosium in eutectic melt of lithium and potassium chlorides have been studied. A mathematical dependency was established for specific mass change of cobalt samples on time spent in melt for temperature range of 873–973 K. Composition of intermetallic coats obtained on surface of cobalt samples was studied means of EDX and SEM analyses. It was discovered, that for chosen temperature range, diffusion layers formed on surface of cobalt samples consists of two structural zones that correspond to Co-Dy and Cp2Dy phases.

Oxidation kinetics of silicon carbide in steam at temperature range of 1400 to 1800 °C studied by laser heating

As expected for accident tolerant fuels, the investigation of steam oxidation for silicon carbide under beyond design basis accident scenarios is needed. Many studies focused on steam oxidation of SiC at temperatures up 1600 °C have been reported in the literature. However, behavior of SiC in steam at temperatures above 1600 °C still remains unclear. To complete this task, we have designed and manufactured a laser heating facility for steam oxidation at extreme temperatures. With the facility, we report the first results on the steam oxidation behavior of SiC in the temperature range of 1400–1800 °C for short term exposure of 1–7 h under atmospheric pressure. Based on the mass change of SiC samples, parabolic oxidation rate and linear volatilization rate were calculated to be kp=exp(1.44±1.8+−96±30kJmol−1RTK), and kl=exp(4.7±0.6+−95±10kJmol−1RTK). The oxidation layer appears to be maintained at 1800 °C in steam, but the bubble formation phenomenon suggests other volatilization reactions may limit its life.

Hygroscopic Properties of Saline Mineral Dust From Different Regions in China: Geographical Variations, Compositional Dependence, and Atmospheric Implications

AbstractSaline mineral dust particles, emitted from saline topsoil in arid and semiarid regions, contribute significantly to tropospheric aerosol particles. However, hygroscopic properties of saline mineral dust particles, especially for those found in regions other than North America, are poorly understood. In this work we investigated hygroscopic properties of 13 saline mineral dust samples collected from different locations via measuring sample mass change at different relative humidity (RH; up to 90%), and measured their chemical and mineralogical compositions using ion chromatography and X‐ray diffraction. The mass growth factors at 90% RH, defined as the sample mass at 90% RH relative to that at <1% RH, were found to display large geographical variations, spanning from ~1.02 to 6.7, and the corresponding single hygroscopicity parameters (κ) were derived to be in the range of <0.01 to >1.0. The saline components (mainly Na+, Cl−, and SO42−) contained by saline mineral dust particles largely determined their hygroscopicity, and the predicted mass growth factors at 90% RH using an aerosol thermodynamic model (ISORROPIA‐II), agreed with measured values within 20% for most of samples examined, although larger discrepancies also occurred for three samples. Our results improve our understanding in hygroscopicity of saline mineral dust particles and thus their heterogeneous chemistry and ability to serve as cloud condensation nuclei to form cloud droplets.

Kinetics of drying of certain lacquers and paints in isothermal conditions using a thermogravimetric analyser

The tools used for thermogravimetric analysis exhibit high measuring precision for three measurements: mass changes, temperature and temperature changes. This high measuring precision has contributed to the widespread use of thermogravimetric analysis in various scientific and technological fields: characterization and assessment of the thermal stability of various types of materials, composition analysis, kinetic studies, corrosion studies and industrial process simulation. The furnace of the Mettler Toledo TGA-SDTA851e equipment may be considered a mini-reactor capable of mimicking the conditions existing in an industrial reactor. Thus, 5-mm-diameter dry fir tree wooden discs were used, on which various lacquers and paints available on the market were applied. The experimental tests at constant temperature (25 °C) consisted of sample mass change analysis conducted for a period of 2 h. The findings enabled us to draw the drying curves (material moisture − drying time) and drying rate curves (drying rate − material moisture). The moisture ratio data obtained experimentally were fitted to different models, to determine the best-fit model. The drying rate curves revealed the existence of two drying periods: the constant-rate drying period (very short, lasting approximately 10 min) and the decreasing speed drying period. Thermogravimetric analysis in the air or nitrogen, in dynamic conditions, for the three types of fresh alkyd paint available on the market and the paint layer obtained after complete drying, i.e. natural ageing in laboratory conditions for 8 weeks, revealed a complex thermal decomposition mechanism including a sequence of three to six stages, with varying percentages of mass loss depending on their structure and on the working atmosphere.

Preparation of oxidation protective MoSi2–SiC coating on graphite using recycled waste MoSi2 by one-step spark plasma sintering method

In order to prepare MoSi2–SiC coating rapidly and controllably on the basis of recycling of Mo resources, waste MoSi2 heating element rods were used as raw materials to fabricate MoSi2–SiC coating on graphite substrate by SPS method through one step. Microstructural evolution and phase transformation of the coating before and after oxidation were characterized and the oxidation behaviors of deposited coating were studied in air at 1400 °C and 1200 °C. The results showed that the coating was mainly composed of MoSi2, SiC and Si, which means that the SiC phase was synthesized in a short-time sintering process. The prepared coating was about 600 μm in thickness, presenting a dense structure without any cracks. The adhesive strength of prepared coating was tested by scratch test and the adhesive strength of MoSi2–SiC coating is about 41.25 N. After high temperature oxidation, the coating surface was covered by a dense and smooth SiO2 film. The protective SiO2 film could prevent the diffusion of oxygen during oxidation. As a result, the mass change of oxidation sample followed a parabolic law and the final mass gain was 9.932 mg/cm2 after 90 h oxidation at 1400 °C.

Protective coatings for high-temperature steam oxidation in coal-fired power plants

Corrosion resistance of protective coatings on stainless steels against high-temperature steam oxidation was studied. The coatings made through the thermal diffusion process consist of aluminides, and they have a 3-layer structure or even more complex architectures when the aluminide layers are covered by thin oxide-based (e.g. Al2O3, SnO2, ZrO2) or BN layers. Oxidation behaviour of these coatings compared to bare materials (e.g. 310SS and 800H) was studied at 800 °C for 3000 h. In this work, along with determination of mass change of samples vs. time (kinetics of oxidation), structural analysis and hardness determination for the coatings and substrates were carried out. The developed multi-layered coating architectures demonstrated promising high-temperature steam oxidation performance with no breakaway degradation issues. Their performance is defined by the inertness of the aluminium intermetallides with a total thickness of protective thermal diffusion coatings of >100 μm, with strong diffusion-related bonding between the layers and with the substrate, and by the formation of the stable aluminium oxide films occurred due to surface oxidation. The additional layer from the selected oxides or BN applied on the top of the aluminized structure can provide additional corrosion protection; however, it is important to maintain a high level of bonding between this layer and the intermetallide structure. The thermal diffusion technology and obtained coating systems are applicable for protection of products with different sizes and shapes, including long tubing required in industry.

A comprehensive study of hygroscopic properties of calcium- and magnesium-containing salts: implication for hygroscopicity of mineral dust and sea salt aerosols

Abstract. Calcium- and magnesium-containing salts are important components for mineral dust and sea salt aerosols, but their physicochemical properties are not well understood yet. In this study, hygroscopic properties of eight Ca- and Mg-containing salts, including Ca(NO3)2⚫4H2O, Mg(NO3)2⚫6H2O, MgCl2⚫6H2O, CaCl2⚫6H2O, Ca(HCOO)2, Mg(HCOO)2⚫2H2O, Ca(CH3COO)2⚫H2O and Mg(CH3COO)2⚫4H2O, were investigated using two complementary techniques. A vapor sorption analyzer was used to measure the change of sample mass with relative humidity (RH) under isotherm conditions, and the deliquescence relative humidities (DRHs) for temperature in the range of 5–30 ∘C as well as water-to-solute ratios as a function of RH at 5 and 25 ∘C were reported for these eight compounds. DRH values showed large variation for these compounds; for example, at 25 ∘C DRHs were measured to be ∼ 28.5 % for CaCl2⚫6H2O and >95 % for Ca(HCOO)2 and Mg(HCOO)2⚫2H2O. We further found that the dependence of DRH on temperature can be approximated by the Clausius–Clapeyron equation. In addition, a humidity tandem differential mobility analyzer was used to measure the change in mobility diameter with RH (up to 90 %) at room temperature, in order to determine hygroscopic growth factors of aerosol particles generated by atomizing water solutions of these eight compounds. All the aerosol particles studied in this work, very likely to be amorphous under dry conditions, started to grow at very low RH (as low as 10 %) and showed continuous growth with RH. Hygroscopic growth factors at 90 % RH were found to range from 1.26 ± 0.04 for Ca(HCOO)2 to 1.79 ± 0.03 for Ca(NO3)2, and the single hygroscopicity parameter ranged from 0.09–0.13 for Ca(CH3COO)2 to 0.49–0.56 for Ca(NO3)2. Overall, our work provides a comprehensive investigation of hygroscopic properties of these Ca- and Mg-containing salts, largely improving our knowledge of the physicochemical properties of mineral dust and sea salt aerosols.

Poređenje nastajanja i razvoja kavitacionih oštećenja livenih i sinterovanih uzoraka na bazi bazalta

The paper examines the resistance to the effect of cavitation of glass-ceramics based on basalt. Two types of samples were investigated: cast and sintered samples based on basalt.The cavitation erosion test was performed using the ultrasonic vibratory method with a stationary sample. To measure the cavitation resistance, a change in sample mass in function of the cavitation time was monitored. The change in the morphology of the surface with the test time was followed by scanning electron microscopy. The level of the surface degradation of the samples was quantified using the image analysis. Samples were tested under the same conditions. A comparison of the properties of the resistance to the effect of cavitation was performed in relation to the calculated cavitation rates. The results showed the high degree of cavitation resistance of the tested samples and the possibility of their application in conditions of high cavitation loads.

Convective Drying of D Coal

The energy value of fossil fuels may be improved by changing their excess moisture content. In studying the development of heat and mass transfer in the heating of coal samples at a rate of 5°C/min in air, with the plotting of a complete differential scanning calorimetry (DSC) curve, it is found that initial heating of the coal sample is accompanied by the removal of physical moisture up to 180°C and increase in its heat content (period 1). At ~340°C, oxidation of carbon develops, with the release of excess heat (period 2). The intensity of heat emission may be judged from the change in sample mass at 460–676°C. Heating period 3 (up to 740°C) is associated with endothermal decomposition of the coal components and culminates in combustion of the combustible mass. On the basis of the kinetics of moisture removal from a weighed sample on isothermal heating at 250°C in a 2-m/s air flux, the total drying time is found to be 229 min, with increase in the rate of moisture removal for 12 min and steady drying for 20 min. According to the laws governing the motion of friable materials in a drum-type dryer, the drying time for coal with a mean moisture content of 9% is 20–28 min, with 20–25% mean filling of the working space. To prevent restoration of the moisture content of a dried coal sample in air, the total drying time cannot exceed 64–88 min, while drying must end with a residual moisture content of at least 7%.

Quantification of accessible hydroxyl groups in cellulosic pulps by dynamic vapor sorption with deuterium exchange

Dynamic vapor sorption (DVS) coupled with deuterium exchange was applied in determining the amount of hydroxyl (OH) groups accessible for deuteration in pulps and pure cellulose quantitatively. The samples studied with the method were different types of chemical pulps as well as microcrystalline and amorphous cellulose powders. The measurement sequence consisted of drying the samples first until the change in sample mass was less than 0.0005% min−1 followed by rewetting the sample with deuterium oxide (D2O) vapor at set relative humidity (RH) of 95% for 600 min and then drying the sample again the same way as the initial drying was done. The method allows determination of the absolute amount of OH groups accessible to deuterium exchange in the samples fully automatically within 1 day. In addition, the equilibrium moisture contents (EMC) of the samples were measured at RH 95% without prior drying enabling the assessment of the EMC of the samples in as-received state without the need to assess the effect of drying. The accessibilities of chemical pulps were found to vary between 54 and 61% of the theoretical maximum, whereas the accessibilities of microcrystalline cellulose and amorphous cellulose were 51 and 63%, respectively. Interestingly, it was found that the accessible OH group content and the EMC of the samples in mol kg−1 correlated with each other and that, in fact, their ratio was close to one.Graphical abstract

Mechanism of Low-Temperature Reduction Degradation of Alumina-Containing Hematite Solid Solution Below 550 °C

Low-temperature reduction degradation (LTRD) of sinter has an adverse effect on blast furnace permeability, and it is mainly caused by the stress produced in the reduction process of hematite. This stress is strongly influenced by alumina dissolved in hematite crystal lattice. In this work, the experiments were conducted to investigate the effect of alumina dissolved in hematite solid solution (Hss) on LTRD by reducing Hss below 550 °C. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), and optical microscope have been used to characterize the mass change and mineral change of samples, respectively. Jade software has been used to calculate the micro strain in magnetite for quantitatively studying the change of strain in reducing process. The results show that alumina was unfavorable to the reduction of Hss on thermodynamics, and the starting reduction temperature of Hss containing 6.0 mol pct alumina was 28 °C higher than that of pure hematite. According to the calculation on kinetics, the generation rate of stress was accelerated by dissolving alumina into hematite crystal lattice. The apparent activation energy of reduction reaction lowered from 47.89 to 28.07 kJ/mol with the increase of alumina content from 0.0 to 6.0 mol pct. The addition of alumina also increased the stress in the reduction products, and this stress was released in the form of LTRD.