Papers by Keyword: Paste

Abstract: Currently, native starch as a binder and sizing component is used extremely rarely due to its inherent disadvantages. It has been replaced everywhere with modified starches of various kinds. Studies have shown that polyelectrolyte flocculants can be created on the basis of starch if ionizable groups are introduced into the macromolecules of amylose and amylopectin. At the same time, it was found that the treatment of starch with oxidizing agents (of various natures and activities) can significantly improve the functional properties of native starch when gluing, used for surface sizing, and as a binder for corrugated cardboard. In this work, we also obtained oxidized starch in order to create an adhesive binder on its basis, and only local raw materials were used. It is shown that this method makes it possible to regulate the number of functional groups (oxidizing effect, or OE) in oxidized starch and its paste viscosity within a wide range. This is achieved by changing the molar ratio of the catalyst and oxidizer. During the oxidation process, it is possible to vary the concentration ratios of the oxidizer, catalyst, and conditions. Using FeSO₄ as a catalyzer, the oxidized starch pastes show a less pronounced pseudoplasticity and are characterized by reduced viscosity. The analysis showed that during the oxidation of corn starch with hydrogen peroxide, changes in the supramolecular structure of starch are insignificant: a certain repeated decrease in the level of crystallinity takes place, which leads to a decrease in the gelatinization temperature and also the viscosity of starch pastes.

Abstract: This paper presents the results of an experimental determination of the coefficient of thermal expansion of hardened alkali-activated slag pastes. In the experiment, three different activators were used – liquid sodium silicate, sodium carbonate and sodium hydroxide. The slag volume fraction for all paste types was set to 0.52. The specimens’ internal moisture content and shrinkage strains were plateaued at ambient laboratory conditions (temperature = 22 ± 2 °C, relative humidity = 55 ± 5 %) at the testing time. All of the specimens were wrapped into the polyethylene foil before the start of thermal dilation measurements and stored in the Q-Cell incubator in which they were subjected to temperature cycling from 5 °C to 30 °C. Length changes caused by the temperature changes were measured with dilatometers supplemented by continuous strain gauges measurement. The results show different values of the coefficient of thermal expansion depending on the activator type. Moreover, the strains recorded by the dilatometer through the steel pins embedded into the ends of specimens and by the strain gauges placed in the core of the test specimens led to different resulting values of the coefficient of thermal expansion.

Abstract: The Purpose of paper is to conduct studies to assess the possibility of increasing the hardness of the surface layer of steel St3 grade by plasma heating of the applied surface coating containing powder alloy PR-N80X13S2R. Mixtures of pasta were divided into 2 groups: for furnace chemical-thermal treatment and plasma surface melting. The study of the microstructure showed a difference in the depth of the saturated layer, depending on the processing method, during chemical-thermal treatment-1 mm, plasma fusion - 2 mm. The results of measuring the surface micro-hardness showed that, the obtained coating from a mixture of PR-N80X13S2R + Cr₂O₃ + NH₄Cl has a uniform high surface hardness (31-64 HRC), from a mixture of only PR-N80X13S2R - the surface hardness varies in a wide range (15-60 HRC). The study of the microhardness of the cross section of the surface layer showed that, the diffusion region: from a mixture of powder PR-N80X13S2R + Cr₂O₃ + NH₄Cl has uniform hardness (450-490 HV); from a mixture of PR-N80X13S2R - hardness increases in the depth of the molten region (from 300 to 600 HV), and sharply decreases in the heat affected zone (210-170 HV). The use of PR-N80X13S2R alloy powder as the main component in the composition of the paste deposited on the St3 surface during plasma treatment leads to the formation of a doped surface layer with high hardness.

Abstract: This work aims to study the feasibility of making a geopolymer cement based on dredged sediments, from the Fergoug dam (Algeria) and to evaluate their construction potential particularly interesting in the field of special cementitious materials. These sediments due to their mineralogical composition as aluminosilicates; are materials that can be used after heat treatment. Sedimentary clays were characterized before and after calcination by X-ray diffraction, ATG / ATD, spectroscopy (FTIR) and XRF analysis. The calcination was carried out on the raw material sieved at 80 μm for a temperature of 750 ° C, for 3.4 and 5 hours. The reactivity of the calcined products was measured using isothermal calorimetric analysis (DSC) on pastes prepared by mixing an alkaline solution of sodium hydroxide (NaOH) 8 M in an amount allowing to have a Na / Al ratio close to 1 (1: 1). Also, cubic mortar samples were prepared with a ratio L / S: 0.8, sealed and cured for 24 hours at 60 ° C and then at room temperature until the day they were submited to mechanical testing. to check the extent of geopolymerization. The results obtained allowed to optimize the calcination time of 5 hours for a better reactivity of these sediments, and a concentration of 8M of sodium hydroxide and more suitable to have the best mechanical performances.

Abstract: This research focuses on influence of pore structure on chloride distribution in surface layer of cement paste under cyclic wet-dry condition. The results of chloride distribution reveal that drying and wetting cycles can lead to a peak value of chloride content (C_max) occurring in surface layer of cement paste. C_max increases with the increase of W/C. While the depth (Δx) at which C_max appears does not show a regular change. Moreover, C_max should be used to predict service life of concrete structures when C_max appears in the chloride profiles. For the influence of pore structure, there exists an obvious hyperbolic relationship between chloride diffusion coefficient (D), C_max and pore structure parameters. D and C_max increase with total porosity and the most probable pore diameter, decrease with tortuosity, and stabilize gradually. And the most probable pore diameter has the most significant impact on D and C_max. In addition, XRD and SEM-EDS results indicate that the deposition of Friedel’s salt results in the formation of more inkbottle shaped pores, which may cause the appearance of C_max under cyclic drying-wetting conditions due to hysteretic moisture effect.

Abstract: Calcium phosphates (CaPs) are synthetic bone grafting materials. CaPs are an alternative to overcome the drawbacks present with autologous bone grafting and/or xenograft materials. Among the CaPs, tricalcium phosphate (TCP) stands out as a good candidate due to its physicochemical properties. The clinical performance of β-TCP has already been proven and established. Nevertheless, the format in which TCP is delivered is also important in terms of clinical handling. This work assessed the in vivo performance of TCP-based bone grafting materials with different formats. Materials studied were a TCP paste (TCP-P), a TCP foam (TCP-F) and TCP granules (TCP-G). A sheep scapula model was used to evaluate the osteogenic performance of these bone grafting materials. All materials performed well in terms of bone regenerative capacity and material resorption. However, TCP-P and TCP-F displayed a more pronounced initial material resorption and also exhibited better handling properties compared to TCP-G. TCP-based materials with improved handling properties, such as TCP-P and TCP-F, which at the same time possess the advantageous properties of β-TCP are suitable bone substitute materials for grafting and reconstruction of bone defects in numerous clinical applications.

Abstract: The carbon nanotube (CNT) paste was fabricated by a very simple method where the paste composition could be controlled precisely. We have fabricated several types of field emitters from the CNT paste mixture consisting of the thin multi-walled CNT, the nanosized inorganic fillers, the ethyl cellulose binder and the terpineol solvent. The field emission current density was found to be more than 100 mA/cm² at a field of 2.5 V/μm for the planar-type CNT emitter and ~5 A/cm² for the tip-type emitter, respectively. We also optimized the filler material in the paste to make the emitter reliable under the high-temperature conditions. The developed CNT paste had good reproducibility and the field emitters made of the paste showed excellent characteristics as the electron sources for the various applications.

Abstract: The early age drying shrinkage of cement-based materials with same the same workability staring from the initial setting time was studied. Superplasticizers (SP) were used to get the same workability. The drying shrinkage of paste was measured by clock gauge, and CABR-NES deformation instrument was used to measure the shrinkage of concrete. Temperature probes were buried into both paste and concrete specimen cores to measure the temperature curve, and temperature deformation was considered into the early shrinkage. Results show the addition of SP increases much more shrinkage than the control group, and polycarboxylate SP increases more shrinkage than naphthalene SP. The different temperature peak time of different mixtures show that the addition of SP changes the hydration process of cement, and the shrinkage of cement-based materials after temperature compensation is bigger than the measured value in the first 6 hours, but the gap is not big.

Abstract: Influence of fly ash on alkalinity of pore solution and microstructure characteristics of hardened cement pastes were investigated by means of ex-situ leaching (ESL), MIP and SEM. The results reveal that the decline of alkalinity of pore solution is not endless, even though the contents of fly ash in fly ash-cement(FC) pastes is very high(65%).The incorporation of fly ash in proper ratios could increase the ratio of harmless pores and improve the microstructure of the FC pastes. Ca(OH)2 was not consumed heavily or exhausted when cementitious material was hydrated due to the low reaction degree of fly ash.

Abstract: Pt is used as a heating resistor by sensors based on ZrO2. A heating resistor will directly influence the response rate and life expectancy of the sensor. The service life of heating resistor using pure Pt is very short , in order to improve the quality of resistor, this paper studies the addition of ceramic powder to Pt paste by intermittent thermal shock test of heating resistor slurry life, the method of square resistance test, and using SEM to observe the microstructure of Pt resistor. Then the reasonable Pt paste formula of heating resistor is obtained.