Scratch and wear resistance of nano-silica-modified silicate conversion coating on aluminium

The silicate conversion coating was modified with nano-silica and applied on the surface of AA2024 by dip-coating technique. The mechanical properties of produced modified silicate layer were investigated by the pencil scratch hardness, cross-cut and abrasion resistance tests. The characterisation of coated surface before and after the tests was studied with optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy and atomic force microscopy. Addition of nano-silica to the silicate coating caused an enhancement in the SiO₂:K₂O ratio. The results showed that the homogeneity of coating surfaces increased in the presence of nano-silica. The wear and scratch resistance of the modified silicate layer improved against the sliding conditions. In addition, the adhesion of coating layer to the substrate metal increased.     

Laser ablation protection of polymer matrix composites by adhesive inorganic coatings

Further utilization of polymer matrix composites (PMCs) in the aerospace industry is threatened by the development of laser weapons, resulting from weak oxidation resistance, low operation temperature and poor anti-laser ablation performance of the PMCs. Preparing an adhesive inorganic coating on the surface of components is an effective method to improve the laser irradiation resistance. Anti-laser ablation coatings composed of ZrO₂ as pigment and sodium silicate as binder with different curing agents (including SiO₂ and Na₂SiF₆) are fabricated on the PMCs substrate with brush painting. Influence of the different curing agents on anti-laser ablation of the coatings at the laser wavelength of 1064 nm is investigated. The rear surface temperature of substrate with coatings, containing SiO₂ and Na₂SiF₆, decreases from 240 to 60 and 70 °C, respectively, when testing at 1000 W for 5 s. After irradiation test at 1000 W for 10 s, the coating with SiO₂ as curing agent shows slight molten state on the surface, while the coating with Na₂SiF₆ is broke down, because coating containing SiO₂ possesses more compact microstructure and fewer cracks than that with Na₂SiF₆.     

Characterization and properties of CuZrAlTiNi high entropy alloy coating obtained by mechanical alloying and vacuum hot pressing sintering

CuZrAlTiNi High entropy alloy (HEA) coating was synthesized on T10 substrate using mechanical alloying (MA) and vacuum hot pressing sintering (VHPS) technique. The MA results show that the final product of as-milled powders is amorphous phase. The obtained coating sintered at 950 °C is compact and about 0.9 mm in thickness. It is composed of a couple of face-centered cubic (FCC), one body-centered cubic (BCC) solid solutions and AlNi₂Zr phase. The interface strength between coating and substrate is 355.5 MPa measured by three point bending test. Compared with T10 substrate, the corrosion resistance of CuZrAlTiNi HEA coating is enhanced greatly in the seawater solution, which is indicated by the higher corrosion potential, wider passivation region, and secondary passivation. The average microhardness of the coating reaches 943 HV_0.2, and is about 3.5 times higher than the substrate, which is mainly ascribed to the uniformly dispersed nano-size precipitates, phase boundary strengthening and solid solution strengthening. Moreover, the wear resistance of the coating is slightly improved in comparison with the substrate.     

Effects of nano-Fe2O3 powder on thermal emission property of microarc oxidation coating on titanium alloy

Abstract

A ceramic coating was formed on the titanium alloy by microarc oxidation in an electrolyte containing nano-Fe₂O₃, emulsifier OP-10 and sodium phosphate. The composition, surface and cross-sectional morphology and the element compositions of the coatings were characterised by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis system. The spectral emissivity of the coatings was measured by a Fourier transform spectrometer apparatus. The bonding strength between the coating and the titanium alloy was studied by tensile strength test. The thermal shock resistance of the coatings was also evaluated. The results showed that nano-Fe₂O₃ was incorporated into the coating, and the coating had high emission at the wavelength range of 3–20 μm. The bonding strength was 33·2 MPa, and after being subjected to severe thermal shocking for 50 cycles, little peeling-off of the coating occurred.     

Investigation on resistance to attrition of coated particles by response surface methodology

The purpose of the present study is to obtain better understanding of the influence of the coating thickness, h, coating formulation, T_g, and fluid bed temperature, T_bed, variables on the resistance to attrition of the coated sodium benzoate reference particles. Three reference coating materials (T_g = 50 – 125 – 150 °C) have been sprayed by using top spray fluid bed coater. Per each coating formulation three different coating levels (h = 1% – 5% – 9% w/w) have been obtained. The coating processes were performed at three different fluid bed temperatures (T_bed = 40 – 55 – 70 °C). The experiments have been designed according to the response surface methodology (RSM). Both single effects and interactions between single effects on the resistance to attrition (response variable) calculated by means of repeated impact tester were evaluated. From statistical analysis, the coating quantity appears to have a predominant effect on the resistance to attrition of the coated particle in these studied ranges of variables. This relationship is linear and positive, which means that an increasing quantity leads to more resistance to attrition. The interaction coating thickness – coating formulation, the interaction between the fluid bed temperature and the coating formulation and the coating formulation as well as the interaction costing thickness – fluid bed temperature were found to be very significant. On the contrary, no direct effect of the fluid bed temperature on the resistance to attrition is detected.     

Electrolytic deposition of hydroxyapatite coating on thermal treated Ti-40Zr

In this study, hydroxyapatite (HA) was coated on both thermal treated and untreated Ti-40Zr substrates by means of electrolytic deposition. It was predicted that the HA layer would increase the bioactivity and osteoconductivity of the Ti-40Zr substrate, and a thermal treatment would improve the bonding strength between the HA layer and Ti-40Zr substrate, and prevent the corrosion of the Ti-40Zr substrate. First, the Ti-40Zr samples were annealed at various temperatures (200, 300, 400, 500 and 600°C respectively). After annealing, samples were immersed in a Ca(NO₃)₂ · 4H₂O and (NH₄)₃PO₄ · 3H₂O solution for the electrolytic deposition of the HA coating. Various analyses of the coating were conducted, including surface morphology, phase structure, corrosion resistance, biocompatibility, and bond strength between HA and Ti-40Zr. Experimental results indicated that the bonding strength of the HA coating on the thermal treated Ti-40Zr was markedly improved when compared to that of the HA coating on an untreated Ti-40Zr alloy. The corrosion resistance of Ti-40Zr was also improved by the use of the thermal treatment, as shown by a potentiodynamic polarization test. Finally, osteoblast-like cells cultured on the HA coating surface were found to have proliferated on all samples.     

水玻璃的磁化改性对水玻璃砂性能的影响

研究了水玻璃流速和流量对水玻璃的磁化改性效果及磁化改性对水玻璃砂表面强度的影响。     

Combination formation in the reinforcement of metakaolin geopolymers with quartz sand

Although quartz sand is widely used as filler material in construction, a few studies investigated the incorporation of quartz sand in geopolymers. To study the incorporation of quartz sand in the reinforcement of metakaolin geopolymer not only fills this gap, but also gives a clue on using non-calcinated aluminosilicates (e.g., mine tailings) in the synthesis of geopolymers. In the presence of sodium silicate, metakaolin geopolymers were synthesized with quartz sand of various size ranges as filler material. XRD, FTIR, SEM and NMR characterizations on the geopolymers indicate the dissolution, precipitation, and the formation of combination on quartz particles that associates them into the geopolymeric gel, so as to reinforce the mechanical strength of geopolymers. The compressive strength of metakaolin geopolymers with only silicate, silicate plus quartz sand and silicate plus rutile sand is 31.2, 52.2 and 41.5 MPa, respectively. In geopolymer with silicate and quartz sand, a decreasing Si/Al ratio as increasing distance from the quartz particle is observed through an energy dispersive X-ray (EDX) mapping. The SEM images and NMR spectra suggest that the formed combination is of several micrometers with main species of polysialates (-Si-O-) such as Q⁴(2Al), Q⁴(1Al).     

金属锆微弧氧化电解液体系和氧化时问对陶瓷膜层的影响

分别用钨酸钠、偏铝酸钠、硅酸钠电解液体系在金属锆表面上制备了氧化锆陶瓷膜。探讨了电解液种类、氧化时间对膜层相结构、微观形貌和耐蚀性的影响。结果表明：氧化膜成分、组织结构、形貌和耐蚀性受电解液种类影响较大;钨酸钠、偏铝酸钠体系陶瓷膜由单斜相组成,而硅酸钠体系则形成了异常的正交相及单斜相,其膜层的耐蚀性不同程度地优于钨酸钠...     

Morphology of calcium carbonate coating on amorphous silicate powder

The amorphous silicate powders containing sodium, calcium,barium and magnesium were prepared by sol-gel and ion-exchangemethod, and calcium carbonate was coated on the powders for thepurpose of industrial re-circulation of calcium carbonate. Thecalcium carbonate powder with micro pores was obtained bycoating on amorphous CaO-SiO₂ powder, and the pore sizedistribution would be influenced by calcium on the surface ofthe powder. The coating on amorphous MgO-SiO₂ powderresulted in a hedgehog-like powder, which allowed needle-likecrystal extended radially, and the coated powder was the mixedphase of aragonite and calcite. The use of amorphousBaO-SiO₂ and Na₂O-SiO₂ powders also led to the coatingpowder with the single phase of calcite. The morphology ofcalcium carbonate coating would be ascribed to cations on thesurface of the amorphous silicate powders, because the amount ofcations that would be dissolved in soaking solution was smalland insufficient to affect the morphology.     

Effects of hydroxyapatite/Zr and bioglass/Zr coatings on morphology and corrosion behaviour of Rex-734 alloy

To improve corrosion resistance of metallic implant surfaces, Rex-734 alloy was coated with two different bio-ceramics; single-Hydroxyapatite (HA), double-HA/Zirconia(Zr) and double-Bioglass (BG)/Zr by using sol–gel method. Porous surface morphologies at low crack density were obtained after coating and sintering processes. Corrosion characteristics of coatings were determined by Open circuit potential and Potentiodynamic polarization measurements during corrosion tests. Hardness and adhesion strength of coating layers were measured and their surface morphologies before and after corrosion were characterized by scanning electron microscope (SEM), XRD and EDX. Through the SEM analysis, it was observed that corrosion caused degradation and sphere-like formations appeared with dimples on the coated surfaces. The coated substrates that exhibit high crack density, the corrosion was more effective by disturbing and transmitting through the coating layer, produced CrO₃ and Cr₃O₈ oxide formation. It was found that the addition of Zr provided an increase in adhesion strength and corrosion resistance of the coatings. However, BG/Zr coatings had lower adhesion strength than the HA/Zr coatings, but showed higher corrosion resistance.     

电场改性水玻璃固化黄土机理研究

利用正交和单因素控制实验对电场改性水玻璃加固黄土进行了研究,并通过化学组成、矿物成分和微观结构分析探讨了电场改性水玻璃加固黄土的机理。结果表明:通电电压越高,通电时间越长,改良土体的无侧限抗压强度越大;土体强度随Na2O含量、模数的增长先减小后增大,存在下极值点;X射线衍射图中出现非晶质物相峰群,随着Na2O含量的增加,非晶质先减少后增多,矿物的衍射强度先降低后升高;SEM图像表明随着电压的不断增大,生成的硅酸凝胶逐渐增多,包覆土体颗粒,填充颗粒之间的孔隙,使得骨架颗粒连接紧密,从而使得土体强度增大;BET表面积孔隙分析表明,随着通电电压的升高和通电时间的延长,黄土的小孔隙增多,孔隙体积和表面积增大,孔径分布减小,平均孔径变化不大。     

Mechanical strength and surface microstructure of partially crystallised glasses

The influence on the mechanical strength of lithia-silica glasses of heat-treatment in the temperature range (400 to 600° C), where the degree of crystallisation is small, has been studied. It was shown for a binary Li₂O-SiO₂ glass that heat-treatment led to a significant increase in the mechanical strength and that similar but less marked effects were observed for a Li₂O-SiO₂-P₂O₅ glass. From observations of the effects of abrasion upon the mechanical strength of the heat-treated glass it appeared that the strengthening effect arose from a change in surface structure of the glass. Examination by electron microscopy and X-ray diffraction revealed that a surface layer of lithium silicate crystals is formed during heat-treatment. The mechanical properties are discussed in relation to the surface structure of the glass.     

A solid-state NMR and X-ray powder diffraction investigation of the binding mechanism for self-healing cementitious materials design: The assessment of the reactivity of sodium silicate based systems

The identification of affordable healing agents for cement based materials, able to promote autonomous crack healing, is a challenge to improve the durability of building structures. In this study, a thorough investigation of the reactivity between a hydrated Portland cement and sodium silicate solutions, as healing agents, has been carried out.The goal is to quantitatively assess the chemical reactivity and actual binding capacity of sodium silicate. Mechanical recovery was evaluated by means of a healing agent strength test on hydrated cement treated with sodium silicate. XRPD and Solid-state NMR allowed the definition of reaction times, the involved species, and the nature and stability of the reaction products. Highlights show that sodium silicate reacts not only with Ca(OH)₂ (namely portlandite), but also with calcium aluminate phases (AFt, AFm, TAH) to extract calcium and/or aluminum ions, with the formation of crystalline/semi-crystalline C-S-H/C-A-S-H tobermorite phase.     

Alkali silicate binders: effect of SiO2/Na2O ratio and alkali metal ion type on the structure and mechanical properties

The influence of SiO₂:Na₂O molar ratio and the nature of an alkali metal (Na vs. K) in commercial aqueous alkali silicate on the microstructure, textural properties, phase composition, and hydrolytic stability of an alkali silicate binder have been investigated using scanning electron microscopy, nitrogen adsorption/desorption technique, X-ray diffractometry, thermal analysis, and dissolution tests. It has been found that microstructure and textural properties of the alkali silicate binder depend both on silica to alkali molar ratio and type of alkali metal (Na vs. K). Sodium silicate binder obtained from commercial silicate solution with lower SiO₂:Na₂O molar ratio (2.2) exhibits a globular microstructure of silica xerogel with high content of micropores, whereas the binder formulated with SiO₂:Na₂O molar ratio 3.2 is characterized by more open cluster structure with lower content of micropores. It is observed that surface specific area estimated by Brunauer, Emmett, and Teller method and mesopore volume obtained by the Barrett–Joyner–Halenda method for sodium silicate binder are substantially higher than those for potassium silicate binder. The ultimate hydrolytic stability of the sodium silicate binder increases slightly with increase in the silica to alkali molar ratio within the studied range. Decreasing in SiO₂:Na₂O molar ratio and replacement of sodium silicate solution by potassium silicate solution in the corresponding filled composition lead to the improvement of mechanical properties and decrease in open porosity.     

Determination of Adsorption Layers on Silicon Sorption Artifacts using the Gravimetric Method

The adsorption layers on the surface of silicon artifacts were determined experimentally as a function of relative air humidity in the range of 0.07 < h < 0.73 using the gravimetric method. 1 kg silicon sorption artifacts were fabricated with the same surface finish and material properties, but they had a very different surface area of 507.8 cm². In this experiment, an ultra-precision mass comparator and special humidity control unit were used. We found that the sorption behavior of the silicon surface was type II by BET classification with the parameters μ _m  = 0.017 μg/cm², and c _B  = 9.3 from the adsorption isotherm of water vapor on the surface of silicon with R _z  < 26.6 nm. The coefficient of water vapor adsorption in moist air was estimated as δμ/δh = 65.3 ng cm^?2 in a limited humidity range of 0.3 < h < 0.6.     

Silicate bonding of inorganic materials

The room-temperature setting process in compacts of various silicate and non-silicate mineral particles bonded with sodium silicate was found to be markedly accelerated by treatment with the acidic gases CO₂, S0₂ and H₂S, but was unaffected by neutral or alkaline gases. Strength development increases with gassing time up to a maximum value which depends on the Si to Na ratio of the sodium silicate, the nature of the mineral matter and the gas used. Longer gassing times are needed to achieve ultimate strength with sodium silicates of higher pH and gases of lower solubility in water. The chemical species formed by reaction of CO₂, S0₂ and H₂S with sodium silicate were investigated by IR spectroscopy, X-ray diffraction and 29-Si solid state NMR spectroscopy.     

Preparation of layered bioceramic hydroxyapatite/sodium titanate coatings on titanium substrates using a hybrid technique of alkali-heat treatment and electrochemical deposition

Bioceramic hydroxyapatite/sodium titanate coating on sandblasted titanium substrate was fabricated by a three-step process. At first, the sandblasted titanium substrate was coated with a flake-like sodium titanate layer by alkali-heat treatment. In the second step, the alkali-heat treated titanium substrate was hydrothermal treated at 180 °C for 4 h with calcium solutions. In the third step, the hydroxyapatite (HA) coating was deposited onto the hydrothermal treated layer via electrochemical deposition method. The surface topography and roughness of the coatings were determined by field emission scanning electron microscope (FESEM) and a mechanical contact profilometer, respectively. The surface compositions were evaluated by X-ray diffraction (XRD), energy-dispersive X-ray spectrum (EDS), and X-ray photoelectron spectroscopy (XPS). The EDS, XPS, and XRD analysis confirm the presence of element Ca, Ca²⁺, and CaTiO₃ on sodium titanate layer after hydrothermal treatment with Ca(NO₃)₂ solution, respectively. FESEM micrograph shows the rod/needle-shaped crystallites are highly densely packed on the calcium-ion-containing layer with an average size of ~50 nm in diameter. The results indicate that the sodium titanate layer containing Ca²⁺ ions possesses higher ability to induce HA formation compared with the pure sodium titanate layer. It is revealed that surface composition plays an important role in the electrochemical deposition of HA. The calcium-ion-containing layer probably makes the nucleation of HA easy and effectively promotes orientated growth of HA on flake-like sodium titanate surface. The sodium titanate layer possesses a lower corrosion current density and a higher corrosion potential than sandblasted-Ti substrate. The sodium titanate layer should act as a barrier to the release of metal ions from metallic substrate to physiological solutions and thus reducing the electrochemical reaction rate.     

超音速等离子体喷涂MoSi2涂层工艺研究

涂层技术是C/C复合材料高温抗氧化与抗烧蚀的有效手段,单一的SiC涂层很难为C/C复合材料提供有效的长寿命保护。金属间化合物MoSi2高温时会形成一层致密的SiO2保护膜,具有特别优异的高温抗氧化性能,常作为C/C复合材料的高温抗氧化涂层。本文采用超音速等离子喷涂法在带SiC涂层的C/C复合材料表面制备了MoSi2涂层,主要研究了喷涂功率、主气(Ar)流量对粉料表面温度、飞行速度、沉积率以及对涂层表面微观结构和结合强度的影响。结果表明:喷涂功率在47.5~52.5 kW之间,既能使粒子有较高的速度和温度,还能保证粉末不过熔,在喷涂功率为50 kW时,粉料的沉积率最高,氧化不高,涂层表面致密性好,截面结合紧密,结合强度高;Ar流量为65 L/min时,能够保证MoSi2粉末有较高的表面温度与较快飞行速度,沉积率最高,氧化不高,涂层表面致密,几乎没有孔隙与裂纹。因此,调控超音速等离子体喷涂工艺参数能够在带SiC涂层的C/C复合材料表面得到致密且结合良好的MoSiO2涂层。     

镁铝合金表面锶磷化膜的改性及其腐蚀性能研究

利用化学沉积法在镁铝合金表面构筑锶磷化膜,以氢氧化钠和硅酸钠为原料配制磷化膜封孔处理液,对镁合金表面锶磷化膜存在的裂纹和孔洞等缺陷进行封孔处理。通过元素分析及扫描电子显微镜发现改性膜层表面具有Sr、P、O以及Si元素,硅酸钠对锶磷化膜具有良好的封孔作用。通过膜层厚度检测,证明封孔后的锶磷化膜厚度没有发生显著变化。封孔后的锶磷化膜极化电阻比封孔前提升了4倍,而腐蚀电流仅为封孔前的1/3,封孔后膜层的耐腐蚀性能显著提升。