Experimental study of asphaltene deposition in transparent microchannels using the light absorption method

This study focuses on an experimental investigation of asphaltene deposition in a vertical transparent microchannel. Heptane-induced asphaltene precipitation is utilized to precipitate dissolved asphaltene in crude oil into asphaltene particles at ambient temperature and standard atmospheric pressure. These asphaltene particles deposit gradually on the surface of microchannels. The key parameters that influence the mechanism of asphaltene deposition are the ratio of crude oil to n-heptane and experimental elapsed time. At a constant flowrate, the amount of asphaltene deposited on a transparent channel wall is quantified using a new flow visualization technique based on reflected light intensity and image analysis. Asphaltene precipitation and deposition strongly affect the reflected light intensity through the change of mixture color in the recorded images. Experimental results show that asphaltene deposition process follows three stages, (i) slow asphaltene particle deposition at the beginning of the experiment, (ii) a rapid and continuous deposition occurring after few hours and (iii) a slower deposition (decreasing deposition rate) at the end of the experimentation. The experimental results for different crude oil to n-heptane ratios illustrate that deposition increases with this ratio, i.e. increasing concentration of n-heptane. An empirical equation is developed to correlate the intensity of the light absorption to the thickness of the deposited asphaltene in a transparent microchannel. Non-uniform deposition along the longitudinal direction of the microchannel is characterized. Deposits decrease with increasing longitudinal distance from the inlet. This non-uniform deposition distribution is due to local mass transport limitations and asphaltene aggregation size effect.     

Scalable Wet Deposition of Zeolite AEI with a High Degree of Preferred Crystal Orientation

Producing zeolite films with controlled preferred orientation on an industrial scale is a long‐standing challenge. Herein we report on a scalable approach to the direct wet deposition of zeolite thin films and membranes while maintaining a high degree of control over the preferred crystal orientation. As a proof of concept, thin films comprising aluminophosphate zeolite AEI were cast on silicon wafer or porous alumina substrates. Electrical properties and separation performance of the zeolite thin films/membranes were engineered through controlling degree of preferred crystal orientation.     

High‐Purity Inorganic Perovskite Films for Solar Cells with 9.72 % Efficiency

All‐inorganic perovskite solar cells with high efficiency and improved stability are promising for commercialization. A multistep solution‐processing method was developed to fabricate high‐purity inorganic CsPbBr₃ perovskite films for use in efficient solar cells. By tuning the number of deposition cycles (n) of a CsBr solution, the phase conversion from CsPb₂Br₅ (n ≤3), to CsPbBr₃ (n=4), and Cs₄PbBr₆ (n≥5) was optimized to achieve vertical‐ and monolayer‐aligned grains. Upon interfacial modification with graphene quantum dots, the all‐inorganic perovskite solar cell (without a hole‐transporting layer) achieved a power conversion efficiency (PCE) as high as 9.72 % under standard solar illumination conditions. Under challenging conditions, such as 90 % relative humidity (RH) at 25 °C or 80 °C at zero humidity, the optimized device retained 87 % PCE over 130 days or 95 % over 40 days, compared to the initial efficiency.     

Gallium-containing sulfide binary and ternary materials by atomic layer deposition: precursor reactivities and growth fine chemistries

Gallium sulfide (Ga_xS) and copper gallium sulfide (Cu_xGa_yS_z) were synthetized by atomic layer deposition (ALD), using copper acetylacetonate Cu(acac)₂, hexakis(dimethylamino)digallium [Ga(NMe₂)₃]₂ and hydrogen sulfide (H₂S). Thanks to the compatibility of the Cu_xS and Ga_xS ALD windows, a supercycle strategy that combines single growth cycles of the two binary compounds was used to generate the ternary material. A wide range of compositions and properties can be obtained from Ga-rich to Cu-rich via copper gallium sulfide thin films. Structural, morphological, and optoelectronic characterizations were performed on all films. Surface and in-depth chemical compositions were determined by X-ray photoelectron spectroscopy profiling, allowing a better understanding of the chemical reactions involved during the growth process. In the case of Ga_xS films, other Ga precursors have been tested. Our experimental observations, combined with reported ones and density functional theory calculation results have highlighted the specific reactivity of alkylamido precursor in ALD chemistry. Compositional studies revealed a significant O content which origin is discussed and represents an important challenge to address in ALD of sulfide materials in general.     

Growth in a restricted solid on solid model with correlated noise

We introduce correlated growth into a restricted solid on solid model (RSOS), a stochastic deposition model with a constraint on neighboring height differences. A two-dimensional lattice model is used in which particles are deposited via horizontal Levy flight steps with a step length distribution exponentf. Though RSOS is in the same universality class as ballistic deposition for uncorrelated deposition, it appears to depart from it for strong correlations. Forf=1, the short-range limit is reached and both exponents and, which describe the dependence of surface width on time and strip length, tend to 1. Forf>1 we retreat to an enhanced algorithm, searching for growth sites which become excessively rare. We find an unusual short-time dependence, but still tends to 1. The number of growth sitesG shows saturation forf<1, while forf1 we observeG/L0 as the strip lengthL increases. Finally, we test directly the relationship of noise-noise correlation strength tof, and find that a direct comparison between correlated growth models and theoretical predictions for growth with correlated noise is so far unjustified.     

Lithium electrochemistry of NiSe2: A new kind of storage energy material

NiSe₂ thin film has been successfully fabricated by reactive pulsed laser deposition and was investigated for its electrochemistry with lithium for the first time. The reversible discharge capacities of NiSe₂/Li cells cycled between 1.0 V and 3.0 V were found in the range of 314.9–467.5 mA h g⁻¹ during the first 200 cycles. By using ex situ X-ray diffraction, transmission electron microscopy, and selected-area electron diffraction measurements, the intermediates of β-NiSe, and Ni₃Se₂ were identified during the reversible conversions of NiSe₂ into metal nickel and Li₂Se. Both cation (nickel) and anion (selenium) in NiSe₂ provide the redox active centers in its electrochemical reaction with lithium, indicating one of the features of its lithium electrochemistry. The high reversible capacity and good cycle ability of NiSe₂ electrode made it become a promising cathode material for future rechargeable lithium batteries.     

IR laser ablative decomposition and depolymerisation/repolymerisation of poly(ethylene succinate)

Pulsed IR laser ablation of poly(ethylene succinate) results in the formation of volatile products (mainly carbon oxides, hydrogen, C₁-C₄ hydrocarbons) and affords deposition of polymeric films. Composition, structure and molecular weight distribution of the latter products were examined by EDX-SEM, FTIR, UV and NMR spectroscopy and gel permeation chromatography and revealed to be virtually identical to the initial poly(ethylene succinate). The deposited films and poly(ethylene succinate) decompose in the same way, as proved by TGA analysis. The formation of the volatile products is accounted for by random cleavages of the polymer backbone. The deposition of the polymeric products is judged to be due to molecular ester group interchange and/or a sequence of the C-C bond homolysis and recombination of the produced radicals.     

A Global Model of Chemical Vapor Deposition of Silicon Dioxide by Direct-Current Corona Discharges in Dry Air Containing Octamethylcyclotetrasiloxane Vapor

A model of the electron distribution in direct current corona plasmas is combined with a global chemistry model and a two-dimensional transport model to predict the rate of chemical vapor deposition of silicon dioxide on the discharge wire in both positive and negative discharges in dry air containing octamethylcyclotetrasiloxane. The gas-phase chemistry includes reactions to form atomic oxygen (O) and additional global reactions to form gaseous silicon dioxide precursors by the impact reactions of electrons and atomic oxygen with silicone molecules. Surface chemistry is approximated by a single step global reaction from gaseous to solid silicon dioxide. The rate coefficient between atomic oxygen and octamethylcyclotetrasiloxane is estimated from prior experiments to be on the order of 10^–12 cm³/molecule-s. The effects of discharge polarity, current, wire radius and air velocity (Peclet number for mass transfer) on the deposition rate are considered. Deposition rates can be minimized by using positive coronas instead of negative coronas for Peclet number less than 18.5. At higher Peclet numbers, the deposition rate is slightly higher in positive corona discharges, but devices used indoors should continue to use the positive corona in order to minimize the production of ozone. The deposition rate in the positive corona is relatively insensitive to air velocity for velocities from 0.044 to 10 m/s^–1 . However,it may be minimized by operating the corona with the lowest current that provides adequate performance (e.g., particle charging) and the smallest wire that provides adequate mechanical strength.     

一种新型汞离子选择薄膜传感器

采用脉冲激光沉积技术,在光寻址电位传感器表面上沉积了对二价汞离子敏感的薄膜,制备了一种新型汞离子选择薄膜传感器,靶材成分为HgAgIS,基底为p型单晶硅片,金属接触层为Cr/Au。该薄膜传感器在3星期内显示了良好的重复性和稳定性;检出限为3×10-6mol/L;响应时间小于2min,适用pH范围小于2。对干扰离子和迟滞效应等也进行了研究。该传感器具有测量快速灵活、所需样品少、动态范围宽等特点,因为把电位信号转化为对光激发的交流电流信号进行测量,所以提高了灵敏度。同时也证明了脉冲激光沉积是适合制备薄膜传感器的一种新技术。