STA Analysis Research Articles

Application of waste sorghum stem (sorghum bicolour) as a raw material for microfibre cellulose

Microfibre cellulose (MFC) is one of trending topics in advanced material researches. This work was aimed to study the characteristics of MFC produced from waste sorghum stem. To produce MFC, the amorphous part presence in the fibre such as hemicellulose and lignin had to be removed through chemical process. This study compared two methods for preparing the waste sorghum stem i.e. 1) Alkalization 1-Hydrolysis-Alkalization 2-Acetylation and 2) Alkalization-Bleaching-Acetylation. Thermal stability, crystallinity, morphology, and functional group analysis were the parameters measured in this research. The method that produce MFC with better quality was the first method. The MFC had a significant reduction of amorphous fraction with crystallinity index of 81.07%. From STA analysis it was found that the MFC product was able to endure the thermal treatment at 315°C without any significant weight loss.

The evaluation of the mechanical characteristics of the synthesized glass-ionomer cements (GICs): the effect of hydroxyapatite and fluorapatite nanoparticles and glass powders

The goal of this research is to examine the influence that incorporation of synthesized hydroxyapatite (HA) and fluorapatite (FA) nanoparticles has on the synthesis and mechanical characteristics of glass-ionomer cements (GICs). In this research, HA and FA nanoparticles were synthesized through wet-chemical precipitation method. The obtained inorganic nanoparticles were evaluated with XRD, SEM, TEM, and STA analyses. The glass powder of the GIC (G1 and G2) were synthesized with two different formulations, and in addition, the polymer of GIC, acrylic-itaconic copolymer, was prepared in this research. The synthesized GIC components were appraised employing XRD and STA (for glass component) and FTIR and H-NMR (for polymer component). HA and FA nanoparticles were then added into the powder component (G1 and G2) at 5% and 8 wt%, and unblended powder was utilized as a control. Compressive strength (CS) and diametral tensile strength (DTS) before and after 1, 7, and 28 days of storage in distilled water were investigated utilizing a universal testing machine. Surface microhardness after 1 and 7 days of storage in distilled water was measured utilizing Vickers microhardness tester. Also, setting and working time was determined as specified in the ASTM standard. The obtained results showed that the calcined HA and FA nanoparticles have an ellipsoid-like morphology, and their mean crystallite sizes were measured as 24 and 30 nm, respectively. The mechanical results of the modified GICs, following the addition of HA and FA (5 and 8 wt%) into the glass ionomer cement and 28 days storage in distilled water, exhibited statistically higher CS (64–70 and 66–72 MPa, respectively). Also, higher DTS was observed, at about 7.5–10.5 and 8.5–12 MPa, respectively. The microhardness of the GICs containing HA and FA nanoparticles (5 wt%) increased by 6.5 and 14%, respectively. In addition, the working time and setting time by adding the 5 wt% nanoparticles reduced about 12 and 19% for HA and 13.5 and 18% for FA, respectively. Finally, it can be concluded that the synthesized GICs containing HA and FA nanoparticles provide enhanced mechanical properties to restorative dental materials.

Optically stimulated luminescence characteristics of BeO nanoparticles synthesized by sol-gel method

Optically Stimulated Luminescence (OSL) properties of the sol-gel synthesized nano-powders of Beryllium Oxide (BeO) were investigated. Luminescence properties of BeO nanoparticles are dependent on the crystal structure, particle size, and morphology and therefore strongly dependent on the way of synthesis, thus the preparation was modified to enhance the OSL signal from the material. Structural, thermal and morphological properties of BeO in nanopowder and pellet forms were studied using X-Ray Diffraction (XRD), Fourier Transform Infrared Microscopy (FTIR), Simultaneous Thermal Analysis STA (Thermo Gravimetric Analysis (TGA)/Differential Scanning Calorimetry (DSC)) and Scanning Electronic Microscopy (SEM) techniques. XRD and STA analysis suggested an enhancement in crystallinity and thermal stability of the BeO with increasing sintering temperature.OSL dosimetric properties of the pellets prepared by pressing the synthesized powders were investigated in detail. Thermal stability of the signal as determined with a pulse heating experiment has shown that the OSL signal was stable up to depleted at around 300 °C, suggesting the suitability for dosimetric purposes. Dose response of OSL signals was observed to be linear in the dose range 0.1–100 Gy. The minimum detectable dose limit was estimated at around 100 μGy. Replicated measurements of the samples irradiated with the same dose indicated a good repeatability. Fading properties of the OSL signals were also studied up to 1 month. OSL signals of BeO pellets were decreased by approximately 11% at the end of 7 days and by about 17% at the end of 30 days when compared with the first readout.

The impact of Al2O3 amount on the synthesis of CASH samples and their influence on the early stage hydration of calcium aluminate cement

In this work the impact of Al2O3 amount on the synthesis (200 °C; 4–8 h) of calcium aluminium silicate hydrates (CSAH) samples and their influence on the early stage hydration of calcium aluminate cement (CAC) was examined. It was found that the amount of Al2O3 plays an important role in the formation of calcium aluminate hydrates (CAH) because in the mixtures with 2.7% Al2O3 only calcium silicate hydrates (CSH) intercalated with Al3+ ions were formed. While in the mixtures with a higher amount of Al2O3 (5.3–15.4%), calcium aluminate hydrate – C3AH6, is formed under all experimental conditions. It is worth noting that the largest quantity of mentioned compound was obtained after 4 h of hydrothermal treatment, in the mixtures with 15.4% of Al2O3. It was proved that synthesized C3AH6 remain stable up to 300 °C and at higher temperature (945 °C) recrystallized to mayenite (Ca12Al14O33), which reacted with the rest part of CaO and amorphous structure compound, resulting in the formation of gehlenite (Ca2Al2SiO7). Moreover, the synthesized C3AH6 addition induced the early stage of CAC hydration. Besides, in the samples with an addition, the induction period was effectively shortened: in a case of pure CAC (G70) paste, hydration takes about 6–6.5 h, while with addition – only 2–2.5 h. The synthesized and calcinated compounds was characterized by using XRD and STA analysis.

Fabrication, controlled release, and kinetic studies of indomethacin—layered zinc hydroxide nanohybrid and its effect on the viability of HFFF2

ABSTRACTThe intercalation of indomethacin into the interlayer gallery of layered zinc hydroxide (LZH) has been successfully executed using the simple ion exchange approaches. The synthesized intercalation compound, indomethacin-LZH nanohybrid, was characterized using PXRD, FTIR, SEM, BET, and STA. From the PXRD results, the intercalation of indomethacin anions into the interlayer gallery of LZH was successful; showing the formation of a new peak at lower 2θ with a basal spacing of 21.96 Å. FTIR analysis of the nanohybrid further supported the presence of indomethacin in the interlayer of the indomethacin-LZH nanohybrid. STA analysis confirms that the nanohybrid has higher thermal stability than pure indomethacin. The in vitro release mechanism of the indomethacin anions from the indomethacin-LZH nanohybrid showed slow release, with 95% and 78% release in phosphate buffer saline (PBS) solution at pH 4.8 and 7.4, respectively. The release behavior of indomethacin from its intercalation compounds in PBS solution at pH 4.8 and 7.4 follows the Higuchi model. In addition, the nanohybrid treated with normal fibroblast cell line shows that it reduces cell viability in a dose and time-dependent manner. This study shows that the high potential of the nanohybrid as an encapsulated material for the controlled release formulation of nonsteroidal anti-inflammatory (NASID) anions.

Thermodynamic properties of the La2 O3 -ZrO2 system by Knudsen effusion mass spectrometry at high temperature.

Zirconia doped with a lanthanum oxide system is of high interest due to its exceptional thermal stability for the development of high-performance ceramics. It possesses the beneficial properties of pure zirconia, such as heat resistance, mechanical strength and inertness, but also eliminates its main disadvantage, i.e. brittleness. At high temperatures, components of such systems may vaporize selectively, leading to significant change in composition, and hence, the thermal resistance, phase stability and performance of the ceramic materials. Therefore, information on the vaporization processes and thermodynamic properties of the La2 O3 -ZrO2 system is of great importance. Knudsen effusion mass spectrometry was used to study the vaporization processes and thermodynamic properties of solid solutions in the La2 O3 -ZrO2 system at 2110 K. Pure La2 O3 was used as a reference substance. Comprehensive characterization of the precursors and ceramics was performed via SEM, STA, XRD and PSD analysis. Zirconia-doped lanthania precursor powders and ceramics with La2 O3 of 33.3, 50, 70 and 90 mol.% content were manufactured by solid-state synthesis and the original cryochemical technique. La, LaO, ZrO and ZrO2 were found to be the main vapor species over the samples studied. The activities and thermodynamic properties of La2 O3 were calculated. Via XRD analysis it was shown that the phase composition of xLa2 O3 -(100-x)ZrO2 powders (x = 0.33, 0.5, 0.7 and 0.9 mol. fraction) significantly depends on the synthesis technique chosen. According to the XRD results combined with Rietveld refinement of the patterns, 33.3 La2 O3 -66.7 ZrO2 ceramics after solid-state synthesis are composed of well-formed cubic pyrochlore-type La2 Zr2 O7 with 5 wt.% admixture of monoclinic and cubic ZrO2 whereas 33.3 La2 O3 -66.7 ZrO2 precursor powders after cryochemical synthesis correspond to low-crystalline La(OH)3 . The components of the La2 O3 -ZrO2 system evaporate separately: there is no temperature range where lanthanum and zirconium gaseous species are present together. It was found that the activities of lanthania have low negative deviation from the ideal case.

DTA–TGA and XRD study of the formation of LISICON-type Li1+xCrxZr2−x(PO4)3 ceramic using ZrOCl2·8H2O as precursor

This contribution is devoted to thermoanalytical investigation of the mechanism of the formation of solid solutions of Li1+xCrxZr2−x(PO4)3. The samples were prepared by high-temperature solid-state reaction in the reaction mixtures of (0.5 + x/2)Li2CO3–(2 − x)ZrOCl2·8H2O–(x/2)Cr2O3–3(NH4)2HPO4. Thermal behaviour of the mixtures was characterised using STA analysis (RT-1200 °C); evolution of the phase composition during heating was analysed using powder XRD analysis. It is shown that with increase in substitution degree x from 0 to 2, the mechanism of the formation of the solid solutions changes dramatically. In general, it is influenced by the content of ZrOCl2·8H2O because its interaction with (NH4)2HPO4 is the dominant feature of the thermal transformation of the mixtures. However, with decrease in ZrOCl2·8H2O content and the corresponding increase in x, the indicated process becomes less dominant. On the other hand, unreacted amount of (NH4)2HPO4 is increased and the corresponding effect of elimination of its ammonia becomes more and more prominent. The mixture with x = 2 can be characterised with typical behaviour of the mixtures of (NH4)2HPO4 with oxides or carbonates. In general, the formation of solid solutions required calcination at 1200 °C during 6–12 h.

Influence of raw meal compaction pressure on OPC clinker mineral composition and heat flow

In this paper, the results of compaction pressure influence on ordinary Portland cement (OPC) clinker mineral formation and heat flow evaluating calcination temperature and duration were determined using the industrial initial mixture for OPC clinker burning. Raw meal samples were pressed to 4–20 MPa and calcined at temperatures of 1300, 1350, 1400, and 1450 °C for 20, 40, and 60 min. Raw materials and products were analysed by chemical, XRD, Rietveld and STA analyses. Heat release of the products during hydration reactions was determined by isothermal microcalorimetry. Sample pressing at yet low pressure (4 MPa) accelerates the synthesis of clinker minerals and decreases the amount of free CaO by ~0.5%. However, further increase in the pressure has no major influence on the clinker mineral formation. Hydration reactions of the pressed OPC clinker samples are slightly more intensive compared to powder ones; therefore, it is presumable that cement stone hardening processes would be intensified as well.

The effect of microwave and hydrothermal treatments on the properties of hydrotalcite

In this work, a comparative study of the application of direct microwave or hydrothermal synthesis for obtaining hydrotalcite from solid initial materials and the effect of these treatments (200 °C, 1–3 h) on the thermal stability of formed compounds were investigated. The molar ratios of primary mixtures Mg/Al were equal to 1 and 2, while the water/solid ratio was maintained to 10.0. It was determined that the microwave treatment was suitable for the direct synthesis of hydrotalcite, although the intensities of diffraction maximums characteristic to this compound were decreased under all experimental conditions. Furthermore, it was examined that, after 3 h of isothermal curing, the highest crystallinity of hydrotalcite was obtained. It should be noted that, in a case of microwave synthesis, the crystallite size of hydrotalcite varied in a 33.89–38.50 nm range, while, in a case of hydrothermal treatment, in a 40.06–52.45 nm region. Moreover, the method used for the synthesis of the latter compound did not influence the formation sequence of compounds during solid sintering (575 and 1000 °C, 1 h). In both cases, at 575 °C temperature, MgO and Al2O3 were formed, while at 1000 °C—magnesium and aluminium spinel-type compounds, which have a similar chemical nature, were obtained. The synthetic and calcined products were characterized by XRD, STA and SEM analyses.

Solar Selective Coatings with Enhanced Thermal and Corrosion Stability: Electrochemically Deposited Black Chrome on Stainless Steel in the Presence of Graphite Encapsulated FeCo Nanoparticles

Black chrome coatings were electrodeposited under galvanostatic conditions on SS substrates. To enhance the thermal stability of the coatings for viable usage in parabolic trough receiver tubes in solar thermal applications beyond 250°C, graphite encapsulated FeCo nanoparticles had been introduced in the electrolyte solution at different weight percentages (0.025, 0.05, 0.1). An increase in the thermal stability of the coatings in the range of 400°C to 600°C is noticed from the STA analysis. The corrosion analysis (Tafel) and cyclic voltammetric studies of the coatings in the presence and absence of nanoparticles have been carried out in 3.5% NaCl solution to understand the stability of the coating in saline environment.

Fabrication, Thermal, and Magnetic Properties of Fe2TiO5/Polyaniline Nanocomposites

Polyaniline-iron titanate nanocomposites (NCs) with two contents loading of Fe2TiO5 were successfully synthesized by sol-gel technique. FTIR, XRD, SEM, STA, and VSM were used to characterize the structure and properties of the obtained NCs. The results indicated that Fe2TiO5 NPs with particle size between 25 and 75 nm were distributed in PANI matrix. STA analysis indicates better thermal stability of the NCs than that of pure PANI, and the terminal degradation temperature of NCs (670°C) is greater than the PANI/Fe3O4 NCs (570°C). Saturation magnetizations of NCs indicated an increase of ferromagnetic interaction with more incorporation of Fe2TiO5 in PANI matrix.

Fabrication of asymmetric alumina membranes

Abstract The effect of SrO addition on the thermal stabilization of transition aluminas with the aim of producing membrane layers (supported and unsupported) has been investigated. Al 2 O 3 – x wt.% SrO composite powders ( x = 1, 3, 5, 8) were synthesized by co-precipitation of the hydroxides from solutions of AlCl 3 and Sr(NO 3 ) 2 salts using NH 4 OH as a precipitating agent. Optimum SrO dopant concentration regarding the transition aluminas stabilization effect was determined to be 5 wt.% based on XRD analysis. STA analysis showed a 30 °C shift versus higher temperatures in the transformation of final transitional alumina (θ-Al 2 O 3 ) to stable alpha phase due to addition of 5 wt.% SrO. The mechanism of transition aluminas thermal stabilization as a result of SrO addition is thoroughly discussed. Unsupported alumina membranes were prepared by drying boehmite sols at 600, 800, 1000 and 1100 °C. The effect of calcination temperature on surface area, pore size distribution of unsupported membranes containing 5 wt.% SrO has been investigated. The microstructure of unsupported and supported membranes revealed quite different. Smaller grains in the supported layers were attributed to the interaction between support and membrane.

Spatial Structure of Complex Cell Receptive Fields Measured with Natural Images

Neuronal receptive fields (RFs) play crucial roles in visual processing. While the linear RFs of early neurons have been well studied, RFs of cortical complex cells are nonlinear and therefore difficult to characterize, especially in the context of natural stimuli. In this study, we used a nonlinear technique to compute the RFs of complex cells from their responses to natural images. We found that each RF is well described by a small number of subunits, which are oriented, localized, and bandpass. These subunits contribute to neuronal responses in a contrast-dependent, polarity-invariant manner, and they can largely predict the orientation and spatial frequency tuning of the cell. Although the RF structures measured with natural images were similar to those measured with random stimuli, natural images were more effective for driving complex cells, thus facilitating rapid identification of the subunits. The subunit RF model provides a useful basis for understanding cortical processing of natural stimuli.