Surface Phase Composition Research Articles

Influence of Graphite and Zirconia Addition on the Tribological Properties of Plasma-Sprayed Alumina Coatings

Al2O3, Al2O3-graphite and Al2O3-ZrO2 coatings were formed on the C45 steel rolls using atmospheric plasma spraying. The influence of graphite and zirconia addition on the surface morphology, phase composition and tribological properties under dry sliding conditions using 30 N load were analyzed. It was found that the addition of graphite or ZrO2 slightly affected the fraction of the α-Al2O3 and γ-Al2O3 phases in the alumina coatings. The highest mass loss rate (~8.84 × 10−4 g/s) was obtained for the friction pair of C45 steel roll and steel plate. The friction coefficient of the Al2O3-graphite coating was slightly lower (up to 7%) compared to the coating of Al2O3-ZrO2. However, the friction pair of Al2O3-ZrO2 coating and steel plate demonstrated the highest wear resistance under dry sliding conditions. The increase in the wear resistance of the Al2O3-graphite and Al2O3-ZrO2 coatings is due to the formation of tribofilm in the sliding contact zone.

A new strategy to prepare ammonium aluminum carbonate hydroxide using plasma electrolytic oxidation in electrolyte containing carbon nanotubes

In this work, a plasma electrolytic oxidation (PEO) technique was used to prepare ammonium aluminum carbonate hydroxide (AACH) in an electrolyte containing carbon nanotubes (CNTs). CNTs were also involved in the composite coating on the surface of 6063 aluminum alloy. The formation mechanism of AACH and effects of CNTs on the microstructure and corrosion behavior of the PEO coatings were investigated. The surface morphology, pore distribution, phase composition, functional groups and electrochemical characteristics of the PEO composite coatings were examined using scanning electron microscopy (SEM), Image Pro software, X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR) and electrochemical workstations, respectively. Results showed that the rod-like AACH was generated around the discharge channel by reacting between ammonia, carbon dioxide and AlOOH under transient high temperature and high pressure environment with the presence of CNTs. The surface micropores of the composite coatings were enlarged due to the excellent electrical conductivity of CNTs. With the by addition of CNTs of 1.5 g/L, the self-corrosion current of the coating was the smallest, and the polarization resistance Rp was larger than that of 1.0 g/L and 2.0 g/L CNTs.

Preparation of Fe3O4/NiO Nanomaterials by Electrodeposition and Their Adsorption Performance for Fluoride Ions

The high concentration of fluoride ions in industrial wastewater poses a threat to both human safety and the ecological environment. In this paper, three types of magnetic NiO nanomaterial (MNN) with nickel–iron ratios of 3:1, 2:1, and 1:2 were successfully prepared using the electrodeposition technique to eliminate fluoride ions (F−) from industrial wastewater. The surface morphology, phase composition, and chemical structure of the nanomaterials were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results demonstrate the MNN material’s exceptional adsorption capabilities for fluoride ions (F−) at a nickel–iron ratio of 3:1, with a maximum adsorption capacity of up to 58.3 mg/g. The adsorption process of fluoride on the MNN material was further examined using Langmuir and pseudo-second-order kinetic models, revealing predominantly monolayer adsorption and chemisorption characteristics. When the amount of FeSO4•9H2O added is minimal, only the distinctive peaks of NiO are visible in the product’s spectrum. However, as the Ni/Fe ratio decreases, characteristic peaks of Fe3O4 crystals begin to appear and gradually intensify, indicating an increase in Fe3O4 content within the MNN material. Additionally, the pH level significantly affects the adsorption of fluoride ions (F−) onto the MNN material, with the highest adsorption capacity observed at pH 7.

Friction and corrosion characteristics of microarc oxidation/laser cladding palygorskite coating on 6061 aluminum alloy substrates

In this study, micro arc oxidation (MAO) technology was used to surface coating of 6061 aluminum (Al) disk. Then laser is used to clad palygorskite (Pal) on the surface of the MAO coating to improve the protection of the coating against the Al substrate. The laser irradiates heat onto the Pal powder, the Pal is heated and at the same time the MAO coating is affected by the heat, and the MAO coating is cooled and cured along with the Pal to form the MAO- Pal composite coating. The surface morphology, elemental composition and phase composition of the MAO-Pal coating were analyzed using scanning electron microscopy, energy spectroscopy and X-ray diffraction. And friction experiments were performed on the MAO- Pal coating. The results showed that the coefficient of friction (COF) of the MAO-Pal coating was reduced by 27 % compared to the Al substrate and 19 % compared to the MAO coating under water lubrication conditions. Through the corrosion resistance experiments, the corrosion potential (Ecorr) of the MAO- Pal coating increased by 0.197 V compared to the Al substrate and 0.280 V compared to the MAO coating, and the corrosion current density (Icorr) simultaneously decreased by three orders of magnitude compared to the Al substrate and one order of magnitude compared to the MAO coating. The MAO- Pal coating prepared by laser cladding Pal had good wear and corrosion resistance, which improved the service life and application range of Al alloy and was expected to promote the development of Al alloy in the application field.

Ca/P in situ introduction for enhancing coating biocompatibility via plasma electrolytic oxidation in low-temperature molten salt

Plasma electrolytic oxidation (PEO) is one of the most promising methods for synthesizing ceramic coatings on metallic substrates. Recently, PEO in molten salt electrolytes was found to be advantageous due to overcoming system heating and the formation of contaminants. However, the PEO in molten salt was conducted at a high temperature (Tm∼220 °C), limiting the introduction of different components such as Ca and P. This study realizes the employment of a low-temperature electrolyte based on a ternary eutectic system of Ca(NO3)2–NaNO3–KNO3 (Tm∼130 °C) jointly with the in situ introduction of Ca/P in the form of ammonium dihydrogen phosphate (ADP). The surface morphology, phase and chemical composition, wettability, and anti-corrosion performance were examined. The results indicate improved surface performance with the addition of 1 wt% ADP to the electrolyte. This surface preferably comprises the anatase phase of TiO2 and exhibits enhanced biocompatibility and corrosion resistance in a biological environment.

Corrosion property investigation of laser-cladding copper coating in the simulated nuclear waste disposal solution

To explore the efficient corrosion protection for the nuclear waste storage containers, pure copper coatings were successfully prepared on the 20# steel pipe surface using an infrared laser system under different laser powers. The study was conducted on the copper coatings, encompassing the surface quality, defects, microstructure, elemental distribution, phase composition, and corrosion products. The electrochemical and immersion corrosion behavior of the copper coatings in simulated nuclear waste disposal solutions was analyzed. The pure copper coating prepared by 2800 W laser power has fewer amounts and smaller sizes of defects inside the coating with only a slight fusion of Cu and Fe elements at the interface, which exhibits the highest corrosion potential and the smallest self-corrosion current density. During the immersion corrosion process, pores and unfused defects inside the coating, as well as the pits formed by galvanic coupling corrosion, lead to enhanced acidity inside these defects, resulting in a higher corrosion rate. As the immersion time proceeds, the corrosion rate slows down gradually and the content of Cu2+ corrosion product increases significantly.

Characterization of an advanced bone graft material with a nanocrystalline hydroxycarbanoapatite surface and dual phase composition.

The bone formation response of ceramic bone graft materials can be improved by modifying the material's surface and composition. A unique dual-phase ceramic bone graft material with a nanocrystalline, hydroxycarbanoapatite (HCA) surface and a calcium carbonate core (TrelCor®-Biogennix, Irvine, CA) was characterized through a variety of analytical methods. Scanning electron microscopy (SEM) of the TrelCor surface (magnification 100-100,000X) clearly demonstrated a nanosized crystalline structure covering the entire surface. The surface morphology showed a hierarchical structure that included micron-sized spherulites fully covered by plate-like nanocrystals (<60 nm in thickness). Chemical and physical characterization of the material using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy Energy Dispersive X-ray Spectroscopy (SEM-EDX) showed a surface composed of HCA. Analysis of fractured samples confirmed the dual-phase composition with the presence of a calcium carbonate core and HCA surface. An in vitro bioactivity study was conducted to evaluate whether TrelCor would form a bioactive layer when immersed in simulated body fluid. This response was compared to a known bioactive material (45S5 bioactive glass - Bioglass). Following 14-days of immersion, surface and cross-sectional analysis via SEM-EDX showed that the TrelCor material elicited a bioactive response with the formation of a bioactive layer that was qualitatively thicker than the layer that formed on Bioglass. An in vivo sheep muscle pouch model was also conducted to evaluate the ability of the material to stimulate an ectopic, cellular bone formation response. Results were compared against Bioglass and a first-generation calcium phosphate ceramic that lacked a nanocrystalline surface. Histology and histomorphometric analysis (HMA) confirmed that the TrelCor nanocrystalline HCA surface stimulated a bone formation response in muscle (avg. 11% bone area) that was significantly greater than Bioglass (3%) and the smooth surface calcium phosphate ceramic (0%).

Ultrafast processing of zirconia ceramics by transient and selective laser absorption

Ultrashort-pulse lasers (USPLs) are used in the machining of zirconia ceramics (ZrO2) because of their extremely high peak intensities. However, highly efficient and high precision microprocessing of ZrO2 remains challenging. In this study, we applied a transient and selective laser (TSL) processing technique by combining a USPL and a continuous-wave (CW) laser to realize ultrafast drilling of opaque ZrO2. Ultra-high-efficiency TSL drilling of ZrO2 was achieved with a processing efficiency 1800 times higher than that of USPL drilling. The material removal mechanism, hole formation process, and parameter dependence of TSL drilling were revealed by direct observation of the internal processing phenomenon on a timescale of microseconds. The variations in the processed surface characteristics, including surface morphology, elemental composition, and phase composition, are also presented. Subsequently, the effect of different excited electron regions occurring in the picosecond timescale induced by the USPL on the TSL drilling performance is discussed. Finally, the repeatability and stability of the TSL processing were verified by fabricating microarrays of different sizes. This study will contribute to revealing the ultrafast processing mechanisms of TSL processing in ZrO2 microfabrication. Furthermore, this technique can significantly broaden the applications of ZrO2 in the advanced electronic industry by greatly improving the microprocessing efficiency.

Investigation of the Features of the Formation of Diffusion Layers During Nitrocementation of High-Chromium Steels in a Carbon Black Medium

The purpose of the work is to establish the regularities of the formation of the structure and phase composition of surface (modified) layers on 20X13 chromium stainless steel under intense saturation with carbon and nitrogen and, on this basis, to substantiate the possibility of surface hardening of parts made of high-chromium steels by nitrocementation.Methods. The studies were carried out on samples made of high–chromium steel 20X13, which were subjected to high-temperature nitrocementation in a paste-like medium including fine soot, sodium carbonate and potassium ferruginous oxide (paste-forming agent is an aqueous solution of carbomethylcellulose). The microstructure was studied using an optical metallographic microscope OLIMPUS OX 51 and a scanning electron microscope Qanta FEG-650 with an X-ray microanalysis system EDAX. The microhardness was determined on the Duramit-5 microhardometer, the phase composition on the XRD-7000S X-ray diffractometer.Results. Nitrocementation of high chromium steel 20X13 in the temperature range of 820–950°C provides the formation of diffusion layers on the surface, the structure of which is represented by three zones: a crust of solid carbonitrides on the surface, an eutectoid zone with a solid matrix and inclusions of carbonitrides under the crust and a transition zone including a solid solution enriched in carbon and nitrogen with grains of the base metal. The microhardness of the nitrocemented layers on 20X13 steel after quenching from 1050°C in oil and tempering at 600°C reaches Nm 750–800 on the surface and decreases smoothly enough in depth of the nitrocemented layer. The depth of nitrocemented layers with increased microhardness (more than 400 Nm), depending on the duration of treatment, can reach ~ 0.5 (860°C, 6 hours).Conclusion. Nitrocementation of high-chromium steel 20X13 at 820–880°C in an active carbon black paste with the addition of potassium ferrocarbon leads to an increase in the hardness of the surface layers by about 4 times the hardness of the base, which, combined with the high mechanical properties of the base, will significantly increase the service life of parts made of high-chromium stainless steels of type X13 operating under high contact conditions loads.

Effect of Process Parameters on Bismuth Ferrite Thin Films by Sol-Gel Method

&lt;p&gt;鐵酸鉍是一種無鉛多鐵性鈣鈦礦材料，本研究的目標為探討不同製程參數對使用溶膠凝膠法所製備鐵酸鉍薄膜之表面形貌與相組成的影響。研究中改變的製程參數有薄膜層數、退火時間、退火環境、基板選擇，以及旋轉塗佈轉速。當選擇銅片做為基板沉積薄膜並在真空環境下退火時，薄膜中會存在大量氧化鉍二次相。而當薄膜的退火過程選擇在大氣下進行，則發現樣品中存在大量氧化銅。選擇以鋁片做為基板沉積薄膜並在大氣環境下退火，改變旋轉塗佈轉速發現，經轉速4000rpm塗佈的薄膜表面形貌最為平整且緻密，經過XRD繞射分析後發現薄膜相組成以鐵酸鉍相為主。當薄膜的退火過程選擇在真空環境下進行，則發現樣品的薄膜表面存在大量孔洞。&lt;/p&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;&lt;p&gt;Bismuth ferrite is a lead-free multiferroic perovskite material. The objective of this study is to investigate the influence of process parameters on the surface morphology and phase composition of bismuth ferrite thin films deposited by the sol-gel method. Various process parameters were considered, including the number of film layers, the annealing time, the substrates, and the rotational speed of the spin coating machine. While copper substrates were used for thin film deposition with a vacuum annealing, a large amount of bismuth oxide phase was found in the films. In contrast, when the annealing process of the films was conducted under an ambient atmosphere, a large amount of copper oxide was detected in the thin films. For aluminum substrates with an ambient atmosphere annealing, the primary phase composition was bismuth ferrite in the X-ray diffraction (XRD) analysis of the thin films. While the rotation speed of the spin coater was increased to 4000 rpm, the films exhibited the optimal properties with smooth and dense surface morphologies. However, a significant number of pores was found on the surface of the thin films while the annealing process was performed in a vacuum environment.&lt;/p&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;

Synthesis of MgO nanomaterials using ultrasonic electrodeposition and their adsorption performance for Pb(II)

This study reports the successful synthesis of MgO nanomaterials while employing ultrasonic electrodeposition and heat treatment procedures. The capability and mechanism of these materials for removing Pb (II) from industrial soil were then investigated under ultrasonic powers of 100 W, 150 W, and 200 W. The surface morphology and phase composition of the nanomaterials were analyzed through SEM and XRD. The MgO nanomaterials prepared at 150 W displayed a high adsorption capacity for Pb (II), reaching up to 68.9 mg g−1, under conditions of pH 4.5, temperature 30 °C, Pb (II) concentration of 50 mg/L, and an optimal reaction time of 20 min. The maximum adsorption capacity of MgO nanomaterials prepared at 150 W ultrasonic power was observed to be 43.7 mg g−1 under the condition of 30 °C, Pb (Ⅱ) concentration of 50 mg/L, the optimal deposition time of 20 min, and pH 7. Analysis of the Pb (II) adsorption process on the surface of MgO nanomaterials was carried out using the pseudo-second-order kinetic and Langmuir models. The results revealed that Pb (II) adsorption on MgO nanomaterials exhibited distinct monolayer and chemical adsorption properties. Moreover, the Pb (II) adsorption capacity on MgO nanomaterials was found to be significantly influenced by temperature. The highest adsorption amount of Pb (II) by MgO nanomaterials was observed at a temperature of 30 °C. Further, the Langmuir model revealed the adsorption properties of MgO for Pb (II), with a correlation coefficient higher than 0.99. Therefore, the results confirm that ultrasonic power affects the adsorption performance of MgO nanomaterials prepared by ultrasonic electrodeposition, with the adsorption performance of MgO nanomaterials prepared at 150 W being the best.

Industrial aluminum hydroxides: Part 1. Phase composition and textural characteristics of industrial aluminum hydroxides/oxides

The most common component in the design of heterogeneous catalysts for oil refining and petrochemistry are aluminum oxides. Each type of hydrocarbon raw materials and technological process corresponds to the optimal characteristics of aluminum oxide supports and catalysts: specific surface area, pore size, phase and impurity compositions. Due to the trend towards import substitution, the research of domestic producers of aluminum hydroxide used for the synthesis of aluminum oxides is becoming more relevant. In this work, domestic industrial samples of aluminum hydroxides were studied by methods of X-ray phase analysis, thermogravimetry combined with differential scanning calorimetry, low-temperature nitrogen adsorption and elemental analysis. It is established that the objects of research are most often phase-inhomogeneous, in which impurities of iron, silicon and calcium are present. The influence of the degree of crystallization and the size of the coherent scattering regions of aluminum hydroxides, mainly with the structure of boehmite and, in some cases, containing bayerite, on the textural characteristics of the resulting aluminum oxides is shown.

Characterization of modified titanium surfaces by anodisation and immersion tests

This paper explores the features of both nanoporous and compact TiO2 films formed by titanium anodisation in two experimental conditions, given that they have completely different morphologies and properties than those found by our previous studies. After anodisation, samples have been subjected for 20 days to immersion tests in different media (H2O, H3PO4, and KOH). Surface morphology, phase composition and wettability of anodised films were investigated using FESEM, FTIR, Raman spectroscopy, contact angle measurements and XPS, and the hydrophilicity of modified surfaces was investigated by immersion tests. Nanoporous films exhibited hydrophobic surfaces, but contact angle values gradually decreased after immersing films in H2O, H3PO4 and KOH media, respectively. However, compact films produced superhydrophilic surfaces, both before and after immersion tests, with the exception of immersing the film in a H3PO4 medium due to film removal by acid attack. As for compact films, an unusual morphology revealed by the presence of cone-shaped particles might be responsible for the adsorption of –OH groups arranged so as to favour anatase phase formation.

In-situ formation Mg(OH)2-ZrO2 coating on AZ61 magnesium alloy for corrosion protection

A Mg(OH)2-ZrO2 composite coating was fabricated on AZ61 Mg alloy by a one-step in-situ methanol-assisted hydrothermal process. The surface morphology, phase composition, chemical composition, and corrosion resistance of the Mg(OH)2-ZrO2 coating were characterized. The composite coating exhibited a uniform compact homogenous structure. The electrochemical and immersion results confirmed that the corrosion resistance of the Mg(OH)2-ZrO2 coating was significantly enhanced compared with the Mg(OH)2 coating.

Catalytic activity of modified silica gel adsorbents under conditions of methanol conversion from water-methanol waste of natural gas

The work is devoted to the analysis of factors affecting the catalytic activity of modified silica gel adsorbents under conditions of methanol conversion to dimethyl ether. The objects of the study were the initial and modified silica gel adsorbents ASM, ASM VS, BASF KC-Trockenperlen H and BASF KC-Trockenperlen WS used in the purification of methanol from water‒methanol waste of natural gas. The purpose of this paper is to study the effect of the specific surface area, elemental and phase composition, and operating time of adsorbents on the catalytic activity of modified silica gel adsorbents under conditions of methanol conversion to dimethyl ether. The composition and structural characteristics of the samples were determined by X‒ray fluorescence, X-ray diffraction analysis and low-temperature nitrogen adsorption. Based on the results of IR‒spectrometric and thermal studies, changes in the structure of the surfaces of adsorbents during their operation by various components of organic origin were evaluated. The catalytic activity of silica gel adsorbents in methanol conversion was studied in a fixed bed reactor at atmospheric pressure in the range of 120-290°C and an optimized rate of methanol-saturated nitrogen flow of 1200 ml/min. The methanol conversion process was controlled by gas‒liquid chromatography. An increase of the catalytic activity of adsorbents in methanol conversion to dimethyl ether was found in the range of ASM VS &lt; BASF KC-Trockenperlen WS &lt; BASF KC-Trockenperlen H &lt; ASM. The maximum catalytic activity at 290°C was shown by the adsorbent ASM with 4.2% aluminum oxide and an amorphous structure, which significantly reduces methanol emissions into the atmosphere. For crystalline adsorbents ASM VS with an alumina content of 13.2%, the catalytic activity was minimal. It is shown that the decrease in the catalytic activity of adsorbents in gas treatment unit during operation is associated with a decrease in the value of the specific surface area of samples with a constant content of aluminum oxide and phase state, which is associated with the possible blocking of the catalytic centers of adsorbents due to the accumulation of components of organic origin in the process of natural gas purification. The establishment of factors affecting the methanol conversion to dimethyl ether on modified silica gel adsorbents will allow managing environmental risks, as well as reducing risks to humans during transportation and disposal of water-methanol waste from natural gas purification.

ZnO–Doped CaO Binary Core–Shell Catalysts for Biodiesel Production via Mexican Palm Oil Transesterification

This work investigates biodiesel production via transesterification of Mexican palm oil with methanol catalyzed by binary solid base core–shell catalysts with improved catalytic stability. A series of CaO–ZnO mixed solids were prepared using an inexpensive co–precipitation method by varying ZnO content from 5 to 20 mol%. Several factors, such as surface basicity, ZnO content, phase compositions, and thermal treatment of the catalysts, were all proven to be crucial for the production of biodiesel with good quality. Thermal treatment could effectively remove the surface adsorbed water and impurities and improved the catalytic activity. The addition of ZnO to CaO significantly enhanced the catalysts’ stability; however, it led to lower surface basicity and slightly diminished catalytic activity. ZnO doping inhibited the formation of surface Ca(OH)2 and promoted the formation of Ca–Zn–O or CaZn2(OH)6 phase as the core and a surface CaCO3 shell, which effectively decreased Ca2+ leaching by approximately 74% in methanol and 65% in a methanol–glycerol (4:1) mixture. A combined method of separation and purification for obtaining clean biodiesel with high quality was proposed. The biodiesel obtained under the control conditions exhibited properties which satisfied the corresponding standards well.

Synthesis and characterization of WC-FeCr base alloy composite produced by spark plasma sintering

This study investigates the microstructural and mechanical properties of WC-FeCr base alloy composite materials prepared using spark plasma sintering (SPS) technique. The composites with different FeCr alloy content (2% and 6%) were sintered at temperatures of 1100 °C, 1200 °C, and 1300 °C. The characterization of the sintered samples involved analyzing the surface morphology, phase composition, and grain structure of the sintered samples using scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The results indicate that the FeCr alloy content has a significant influence on the microstructural characteristics, hardness, and density of the WC-FeCr composites. Increasing FeCr alloy content results in improved surface quality and enhanced hardness. Additionally, the sintering temperature plays a crucial role in determining the microstructural features and mechanical properties of the composites.

Fabrication of a highly active β-PbO2-Co3O4 electrode for zinc electrowinning by pulse electrodeposition: Characterization and catalytic performance analysis

High oxygen evolution overpotential and low corrosion resistance are regarded as the main drawbacks of anode materials in zinc electrowinning. To improve the electrocatalytic activity of oxygen evolution reactions (OER) and reduce energy consumption in zinc electrowinning, a Co3O4 nanoparticle-modified PbO2 anode was prepared on a Ti substrate with Sn-SbOX as an interlayer through pulse electrodeposition. The surface morphology, phase composition, and electrochemical properties of the as-prepared anode were systematically investigated. The introduction of Co3O4 nanoparticles refined the crystal size of PbO2 and increased the surface roughness of the anode. Electrochemical tests suggested the excellent electrocatalytic activity of the Co3O4 nanoparticle-modified PbO2 anode. Density functional theory (DFT) calculations revealed that Co3O4 nanoparticles reduced the OER free energy (1.58 eV) and that pulse electrodeposition reduced the PbO2 crystal size and increased the active surface area of the anode. In the simulated zinc electrowinning test, an improved current efficiency (90.6 %) was achieved, and the low energy consumption (2,508.29 kW·h) for zinc production per ton was significantly reduced as compared with that for the conventional Pb-0.75 %Ag anode. The lifetime of the modified electrode is increased by approximately 36.8 %. This provides a reference for the design and development of anode materials with high oxygen evolution activity and strong corrosion resistance in zinc electrowinning systems.

Electrolyte-plasma surface hardening of hollow steel applicator needles for point injection of liquid mineral fertilizers

&lt;abstract&gt; &lt;p&gt;This paper presents the results of research on the effect of electrolyte-plasma hardening on tribological and mechanical properties of hollow needles of 12Kh18N10Т steel applicators for liquid fertilizer application. For the application of liquid fertilizers for processing and testing, the hollow needles of the applicator are made of 12Kh18N10Т steel of cylindrical shape with a diameter of 20 mm. To ensure uniformity of the hardening process, the part was rotated clockwise during the entire procedural cycle. To reveal the influence of the sample rotation speed on the uniform surface hardening, an experiment was conducted for three applicators with rotation speeds of 4, 6, and 8 rev/min. As a result of electrolyte-plasma surface hardening (EPSH), the phase composition of the specimen's surface is characterized by the presence of austenite (γ-Fe) and ferrite (α-Fe). It is revealed that the maximum value of microhardness after EPSH is 2 times higher than the initial value. According to the results of the performed works, the contract on application of tests in field conditions and revealing of perspectivity of needle applicators for liquid fertilizers application was concluded.&lt;/p&gt; &lt;/abstract&gt;

A monetite/amorphous silica complex for long-term dentine hypersensitivity treatment through the acid stability and mineralization promoting effect of silica.

Dentine hypersensitivity (DH) is often related to the exposure of dentin tubules. Mineral particles, such as hydroxyapatite and bioactive glass, can provide calcium and phosphate ions to temporarily block dentin tubules via the biomineralization process, serving as feasible alternatives for DH treatment. However, due to the acidic microenvironment caused by dietary acids, these particles are easily eroded and dissolved, making it difficult to achieve efficient dentin tubule occlusion. Given the significant stability of silica in dietary acids and its excellent ability to bond with calcium and phosphate ions to form mineralized hydroxyapatite, we proposed to develop a micron-sized monetite/amorphous silica complex (MMSi) hydrosol to effectively seal the exposed dentin tubules. In this study, we hypothesized that the MMSi hydrosol could tolerate acid erosion and concurrently provide active sites for the calcium and phosphate ions to promote biomineralization in comparison to a micron-sized monetite (MM) hydrosol. Hence, the composition and microstructure including the surface morphology, silica content and phase composition of MMSi were investigated to verify the presence of silica. The results of the ion release and in vitro biomineralization process indicated that silica did not hinder the calcium and phosphate ion release and the formation of hydroxyapatite via the biomineralization process. The acid-resistant test suggested that the MMSi hydrosol exhibited a significantly slower corrosion rate than the MM hydrosol when treated with citric acid. Notably, the silica in the MMSi hydrosol retained the ability to induce the nucleation and crystallization of hydroxyapatite during de/remineralization processes. Finally, the MMSi hydrosol was mixed with commercialized toothpaste to explore its efficacy in dentin tubule occlusion via cycling de/remineralization processes. As a result, compared to the MM hydrosol, the toothpaste containing the MMSi hydrosol presented excellent acid-resistant ability and dentin tubule occlusion outcomes, which indicated that the MMSi hydrosol could be a potential promise in the long-term treatment of DH.