Exploring the hygroscopic behavior of highly energetic oxidizer ammonium dinitramide(ADN)at different temperatures and humidities using an innovative hygroscopic modeling

Ammonium dinitramide(ADN)is a new type of green energetic oxidizer with excellent energy density and low pollution combustion characteristics.However,the strong hygroscopicity has a significant impact on its practical application.To assist in the research on moisture-proof modification of ADN materials,an innovative hygroscopic modeling approach was proposed to evaluate the hygroscopicity of ADN at various temperatures and humidities.By investigating the diffusion coefficient of water molecules in molecular dynamics processes,a visual insight into the hygroscopic process of ADN was gained.Furthermore,analyzing the non-covalent interactions between ADN and water molecules,the hygroscopicity of ADN could be evaluated qualitatively and quantitatively.The energy analysis revealed that electrostatic forces play a dominant role in the process of water adsorption by ADN,whereas van der Waals forces impede it.As a whole,the simulation results show that ADN presents the following hygroscopic law:At temperatures ranging from 273 K to 373 K and relative humidity(RH)from 10%to 100%,the hygroscopicity of ADN generally shows an increasing trend with the rise in temperature and humidity based on the results of three simulations.According to the non-hygroscopic point(298 K,52%RH)of ADN obtained by experiment in the literature,a non-hygroscopic range of temperature and humidity for ADN can be depicted when the simulation results in relative hygroscopicity is less than or equal to 17%.This study can provide effective strategies for screening anti-hygroscopic modified materials of ADN.

Studies on ammonium dinitramide and 3,4-diaminofurazan cocrystal for tuning the hygroscopicity

Ammonium dinitramide(ADN)is a promising oxidizer with high energy characteristic,which is a relatively new environmentally friendly oxidizer without halogens and carbon elements.However,ADN has high hygroscopicity when exposed to high humidity air,restricting its applications on the solid propellants.In this paper,a novel energetic cocrystal composed of ammonium dinitramide and 3,4-diaminofurazan(DAF)was proposed and successfully synthesized by antisolvent crystallization method,and the properties of the cocrystal were systematically investigated by analytical characterization and theoretical simulation calculations.The formation of the cocrystal was confirmed by powder X-ray diffraction,differential scanning calorimetry,scanning electron microscopy,infrared spectroscopy and Raman spectroscopy,indicating that the synthesized product was a cocrystal.Through theoretical studies,the ADN/DAF cocrystal structure was predicted,and the powder X-ray diffraction,morphology,water sorption capacity of ADN/DAF cocrystal were calculated,which was consistent with experimental phenomena.The results showed that newly prepared cocrystal of ADN/DAF had lower hygroscopicity compared to pure ADN,and the water sorption capacity was reduced from 15.35%to 7.90%.This may be due to the formation of N-H…O medium-strength hydrogen bonds between the ammonium ion of ADN and the O atom of DAF in the cocrystal,which prevents the binding of water molecules in the air and ammonium ions and reduces the probability of ADN binding to water molecules,leading to the reduction of cocrystal hygroscopicity.The newly prepared energetic cocrystal can provide theoretical and technical guidance for the study of the anti-hygroscopicity of ADN and advance the practical application of ADN.

Synthesis,Characterization and Water Absorption Analysis of Highly Hygroscopic Bio-based Co-polyamides 56/66

This study aims to develop highly hygroscopic bio-based co-polyamides(CPs)by melt co-polycondensation of polyamide(PA)56 salt and PA66 salt with varying molar fractions.The functional groups and the chemical structure of the prepared samples were determined by Fourier transform infrared(FTIR)spectroscopy and proton nuclear magnetic resonance(^(1)H-NMR)spectroscopy.The relative viscosity was determined with an Ubbelohde viscometer.The melting behavior and the thermal stability of CPs were investigated by differential scanning calorimetry(DSC)and thermogravimetric analysis(TGA).Furthermore,the water absorption behavior of CP hot-pressed film was studied.The results reveal that the melting point,the crystallization temperature and the crystallinity of CPs firstly decrease and then increase with the molar fraction of PA66 in CPs.The copolymerization of PA56 with PA66 leads to an obvious increase in water absorption.The CPs with PA66 molar fraction of 50%possess a high saturated water absorption rate of 17.6%,compared to 11.6%for pure PA56 and 7.8%for pure PA66.

Response of colour and hygroscopic properties of Scots pine wood to thermal treatment

The effect of heat treatment on the surface colour and hygro- scopic properties of pine wood were investigated in this study. Boards of Scots pine wood （Pinus sylvestris L.） were subjected to thermal treatment at 200℃, for 4, 6, and 8 h. The change of equilibrium moisture content and density values of the specimens in order to facilitate the understand- ing of the treated material behavior. The colour parameters L＊ a＊ and b＊, used to depict the total colour change （dE） of wood surface, were shown to change proportionally to the treatment intensity. Moreover, swelling in the tangential and radial directions and absorption of the specimens ap- peared to be enhanced in great extent by the thermal treatment process. The mean value of swelling percentage in the tangential direction de- creased 10.26%, 17.22%, and 19.60% for specimens treated for 4, 6, and 8 h, respectively, referring to the final measurement after 72 h of immer- sion. In radial direction, mean value of swelling percentage decreased 19.56%, 32.75%, and 34.65% for treated for 4, 6 and 8 h, respectively, after 72 h immersion, which attests the decrease in swelling and im- provement in the hygroscopic behavior of Scots pine wood.

In situ DRIFTS study of hygroscopic behavior of mineral aerosol

In situ diffusion reflectance infrared Fourier transform spectroscopy was used to study the water adsorption on mineral oxides （SiO2, a-Al2O3, MgO, Fe2O3, TiO2）. The results showed that all the water adsorption isotherms were well fitted with the Brunauer-Emmett-Teller （BET）-Ⅲ type equation, with the calculated monolayers occurring at 24%-30% relative humidity. It showed that about 1-5 layers of water adsorbed on oxides surfaces in ambient relative humidity （20%-90%）. The measured deliquescence relative humidity of NaCl was （74 ± 1）%, which demonstrated that DRIFTS is a useful method for the study the hygroscopic behavior of mineral dust. In addition, the limits of DRIPTS were also discussed.

Negative Thermal Expansion of (ZrMg)xY2-2xMo3O12 Ceramics with Low Hygroscopicity

(ZrMg)xY2-2xMo3O12(x=0.0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,and 1)ceramics have been synthesized to obtain less hygroscopicity and negative thermal expansion.With increasing the substitution of(ZrMg)^6+(ion radius 7.2×10^-11 m)for Y3+(ion radius 9×10^-11 m),the crystal water are reduced obviously.The linear thermal expansion coefficient is improved with increasing the content of(ZrMg)^6+.The material shows near zero thermal expansion(-0.12×10^-6 K^-1,430-870 K)with x=0.7.Meanwhile,ZrMgMo3O12 shows low non-hygroscopicity and negative thermal expansion,but low softening temperature.After substituting amount of Y^3+for(ZrMg)^6+in ZrMgMo3O12(x=0.8),the softening temperature increases remarkably(750 K to 830 K)and it presents near zero thermal expansion.

A Closure Study of Aerosol Hygroscopic Growth Factor during the 2006 Pearl River Delta Campaign

Measurements of aerosol physical, chemical and optical parameters were carried out in Guangzhou, China from 1 July to 31 July 2006 during the Pearl River Delta Campaign. The dry aerosol scattering coefficient was measured using an integrating nephelometer and the aerosol scattering coefficient for wet conditions was determined by subtracting the sum of the aerosol absorption coefficient, gas scattering coefficient and gas absorption coefficient from the atmospheric extinction coefficient. Following this, the aerosol hygroscopic growth factor, f（RH）, was calculated as the ratio of wet and dry aerosol scattering coefficients. Measurements of size-resolved chemical composition, relative humidity （RH）, and published functional relationships between particle chemical composition and water uptake were likewise used to find the aerosol scattering coe？cients in wet and dry conditions using Mie theory for internally- or externally-mixed particle species [（NH_4）_2SO_4, NH_4NO_3, NaCl, POM, EC and residue]. Closure was obtained by comparing the measured f（RH） values from the nephelometer and other in situ optical instruments with those computed from chemical composition and thermodynamics. Results show that the model can represent the observed f（RH） and is appropriate for use as a component in other higher-order models.

Reducing SU-8 hygroscopic swelling by ultrasonic treatment

The volume expansion of SU-8 resist brings serious dimensional errors to electroformed structures.Two approaches have been proposed to reduce resist distortions during electroforming:electroforming at room temperature and adding auxiliary features for mask patterns.However,the former method induces higher internal stresses in the electroformed metal layers.And the latter method makes it difficult to predict the expansion behaviors of the resists.In the paper,the thermal expansion of the SU-8 mould is calculated by ANSYS firstly,and the lower thermal expansion value indicates that hygroscopic swelling plays a leading role in SU-8 mould distortions.An original technique is presented to reduce SU-8 hygroscopic swelling by ultrasonic treatment.The dimensional errors of the electroformed structure fabricated on the ultrasonic treatment mould are 50% lower than the one without ultrasonic treatment.Simulation of hygroscopic swelling is conducted by finite element analysis,and the results indicate that the hygroscopic strain ε of SU-8 after electroforming is declined from 6.8% to 3.1% because of ultrasonic.The measurements show that ultrasonic treatment increased the water contact angle of cured SU-8 from 70.8?to 74.9?.Based on these results,the mechanism of ultrasonic effect on hygroscopic swelling is proposed from the view of ultrasonic vibration decreasing the number of hydroxyl groups in SU-8.The research presents a novel method to improve the precisions of electroformed structures.It has no influence on the internal stresses of final structures and does not increase the complexities of mask layouts.

Insight into the behavior at the hygroscopicity and interface of the hydrophobic imidazolium-based ionic liquids

How to completely remove the water from ionic liquids(ILs)is difficult for researchers because of the hygroscopicity of ILs.In order to study the hygroscopicity of ILs,two kinds of ILs,1-Butyl-3-methylimidazolium hexafluorophosphate([Bmim][PF6])and 1-Butyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)([Bmim][NTf_(2)])were investigated by molecular dynamics simulations.Although[Bmim][PF6]and[Bmim][NTf_(2)]are hydrophobic,both of the ILs could absorb water molecules from the vapor.In this work,the process of absorbing water from the vapor phase was studied,and the water molecules could disperse into the IL.Aggregation was observed with increasing the water concentration.Although the absorbed water increases obviously,the amount of free water and small cluster in the ILs does not change significantly and always stays at a certain level.The amount of free water and small cluster in[Bmim][PF6]is more than that in[Bmim][NTf_(2)],which is consistent with their hydrophobicity.In addition,the liquid-vacuum and liquid–liquid interfaces of the ILs were simulated and analyzed in detail.The number density distribution and angle distribution indicated that[Bmim]+cations arrangement regularly at the IL-vacuum interface.The butyl chain point to the vacuum,while the imidazlium ring is close to the IL phase region and perpendicular to the interface.While at the IL-water interface,the cations and anions are disordered.

Surface modification of ammonium nitrate by coating with surfactant materials to reduce hygroscopicity

Ammonium nitrate(AN)is promising oxidizer in green propellants.In this work,the physical coating method was improved to modify the surface of ammonium nitrate particles with different surfactant materials to reduce hygroscopicity.Cetylalcohoi,stearic acid,stearyl alcohol,palmic acid,lauric acid,stearsmide,tetradecylamine,dodecylamine,and tetradecanol were used as coating surfactant agents.The hygroscopicity was tested for ammonium nitrate with and without coating.Fourier transform infrared(FTIR)and scanning electron microscopy(SEM)were used to characterize the surface of coated and uncoated ammonium nitrate.The mass ratio of coating layer and decline of absorption rate of ammonium nitrate coated by cetylalcohol were 1.00%,and 28.40%,respectively.The results indicate that coating with cetylalcohol surfactant have advantages over the other surfactants in term of low mass ratio of coating layer,and high decline of moisture absorption rate.Thus,cetylalcohol would be a promising coating surfactant material for ammonium nitrate.The idea and approach presented in this study have potential to made hydrophobic layer on the surface of particles to reduce hygroscopicity of AN,and also help the researcher to improving anti-hygroscopicity of ammonium salts.

Hygroscopic Behavior of Lyophilized Powder of Grugru Palm (<i>Acrocomia aculeata</i>)

The objective of this study was to determine adsorption isotherms and hygroscopic behavior of lyophilized powder from grugru palm. The powders of grugru palm were obtained by lyophilization process without maltodextrin (T1) and with 8% matodextrin (T2). The experimental data were obtained through the static gravimetric method at temperatures (25℃, 30℃, 35℃ and 40℃), with different saturated solutions of salts. The models of GAB, BET, Henderson and Oswin were fitted to experimental data. The values obtained for hygroscopicity were 7.68% and 6.86% and the degrees of caking were 0.33% and 0.09% for T1 and T2, respectively. Mathematical models of adsorption isotherms for grugru palm powders can be classified as Type III. The GAB and Oswin models represented better the behavior of isotherms for T1 and T2. Grugru palm powder showed an increase in the humidity of the monolayer Xm along with increasing temperature. The grugru palm powder demonstrated to be a non-hygroscopic product, non-caking features.

The Effect of Hygroscopic Growth on Continental Aerosols

In this paper, the authors investigated some microphysical and optical properties of continental clean aerosols from OPAC to determine the effect of hygroscopic growth at the spectral range of 0.25 μm to 2.5 μm and eight relative humidities (RHs) (0%, 50%, 70%, 80%, 90%, 95%, 98% and 99%). The microphysical properties extracted were radii, volume mix ratio, number mix ratio and mass mix ratio as a function of RH while the optical properties are scattering and absorption coefficients and asymmetric parameters. Using the microphysical properties, growth factors of the mixtures were determined while using optical properties the enhancement parameters were determined and then parameterized using some models. We observed that the data fitted the models very well. The angstrom coefficients show that the mixture has bimodal type of distribution with the dominance of fine mode particles.

Study on Improvement of Hygroscopicity of Magnesite-Bonded Wood Wool Panel

Magnesite-bonded wood wool panel(MWWP)is an inorganic-bonded panel product in which wood excelsior is bonded with magnesite.Lowering the hygroscopicity is one of the key measures to improve the quality of the panel.In this study,moisture absorption mechanism of MWWP and measures generally applied to lower its hygroscopicity were reviewed.Three methods were then experimented to improve the dimensional stability of the panel,including adjusting the molar ratio of raw materials,adding additives and optimizing the conditioning process.The results showed that satisfying dimensional stability could be achieved when the molar ratio of MgO to MgCl_(2) was 5:1,the No.2 composite additive(aluminum powder+NH_(4)H_(2)PO_(4)+ferric alum)was adopted and a constant temperature and humidity treatment was applied in the first stage of conditioning.

Effect of model errors in ambient air humidity on the aerosol optical depth obtained via aerosol hygroscopicity in eastern China in the Atmospheric Chemistry and Climate Model Intercomparison Project datasets

This analysis of the multi-model aerosol optical depth (AOD) in eastern China using the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) datasets shows that the global models underestimate the AOD by 33% and 44% in southern and northern China, respectively, and decrease the relative humidity (RH) of the air in the surface layer to 71%–80%, which is less than the RH of 77%–92% in reanalysis meteorological datasets. This indicates that the low biases in the RH partially account for the errors in the AOD. The AOD is recalculated based on the model aerosol concentrations and the reanalysis humidity data. Improving the mean value of the RH increases the multi-model annual mean AOD by 45% in southern China and by 33% in June–August in northern China. This method of improving the AOD is successful in most of the ACCMIP models, but it is unlikely to be successful in GISS-E2-R, in which the plot of its AOD efficiency against RH strongly deviates from the rest of the models. The effect of the improvement in the modeled RH on the AOD depends on the concentration of aerosols. The shape error in the frequency distribution of the RH is likely to be more important than the error in the mean value of the RH, but this requires further research.

Hygroscopicity-resistant mechanism of an α-starch based composite binder for dry sand molds and cores

Hygroscopicity-resistance of an α-starch based composite binder for dry sand molds (cores) has been studiedexperimentally and theoretically. Focus is placed on the relationship between the hardening structure andhumidity-resistance of the composite binder. The results show that the α-starch composite binder has goodhumidity-resistance due to its special complex structure. SEM observations illustrate that the composite binder consists ofreticular matrix and a ball- or lump-shaped reinforcement phase, and the specific property of the binding membrane withheterogeneous structure is affected by humidity to a small extent. Based on the analyses on the interplays of differentingredients in the binder at hardening, the structure model and hygroscopicity-resistant mechanisms of the hardeningcomposite binder were further proposed. Moreover, the reasons for good humidity-resistance of the composite binderbonded sand are well explained by the humidity-resistant mechanisms.

黄精多糖提取工艺优化及其吸湿、保湿性能研究

目的:优化黄精多糖提取工艺,并研究其吸湿保湿性能、探索其护肤功能。方法:采用热回流法结合正交进行黄精多糖提取工艺优化;以黄精多糖为实验对象,采用重量法进行吸湿性(相对湿度分别为43%和81%)、保湿性试验,并对吸湿曲线进行模型拟合;将黄精多糖添加到市售面霜中进行皮肤水分测试。结果:实验表明黄精多糖最佳提取工艺条件为:料液比1∶25(g/mL),提取时间是150 min,提取次数为1次;黄精多糖在不同相对湿度下的吸湿均符合双指数模型;置于干硅胶环境下48 h,黄精多糖保湿率为14.00%。结论:黄精多糖具有良好的保湿性,在护肤品开发中具有一定的应用价值。

典型粉末型吸湿性催化剂的雾室及静态检测

暖云催化剂在人工影响天气暖云催化降水和暖性云雾消除方面应用前景广阔,近年开发的各类新型材料有望在暖云催化中使用,但目前仍缺少效果理想的制剂配方,亟需在相同试验条件下对比各类吸湿性催化剂的性能。2023年5月在中国气象局云降水物理与人工影响天气重点开放实验室开展催化剂雾室及静态检测试验,评估9种典型粉末型吸湿性催化剂的消雾能力及吸湿特性。结果表明:无机盐类催化剂消雾所需时间最短,多孔复合材料催化剂效果也较好,而改性淀粉、分子筛、有机膨润土及钠基膨润土消雾效果不明显。在常温常湿环境下,CaCl_(2)的静态吸湿能力最强,其次是多孔复合材料,复合盐的吸湿性也较强,其他催化剂吸湿性不明显;在高湿环境下,膨润土类催化剂及分子筛吸湿性仍不佳,NaCl、多孔复合材料的吸湿能力明显高于其他催化剂。各种催化剂在雾室与静态检测试验的性能基本一致。

使用有限数据推求土壤水分特征曲线VG模型的参数

【目的】使用一种简易方法和有限数据来获取土壤水分特征曲线VG模型的参数。【方法】选择了黑土、褐土、黄绵土、红壤和紫色土5种地带性土壤,实测了土壤饱和含水率(θ_(s))、0.33 bar土壤含水率(θ_(0.33 bar))、最大吸湿水(θ_(97%RH))和空气相对湿度为43%时的土壤吸湿水(θ_(43%RH)),并以θ_(43%RH)为残余含水率(θ_(r)),推导VG模型的参数。将推导出的参数带入到VG模型中,进行了土壤水分特征曲线的预报,并与实测的土壤含水率进行了比较。【结果】该方法能较好地模拟褐土的土壤水分特征曲线,模拟值和测定值的残差一般在0.01 cm^(3)/cm^(3)以内;也可以较好的模拟黄绵土和红壤在0.33~15 bar的土壤含水率,残差一般在±0.01 cm^(3)/cm^(3)以内;但黑土的模拟结果相对较差,在低于0.33 bar时,残差为负,在-0.03 cm^(3)/cm^(3)以内,而在0.33~15 bar,残差为正,达到0.04 cm^(3)/cm^(3);紫色土的模拟结果最差,在低于0.33 bar时,残差为负,达到了-0.07 cm^(3)/cm^(3);但在0.33~15 bar,情况有所改善,残差在0.03 cm^(3)/cm^(3)以内。通过配对t检验,认为模拟值和测定值无显著差异,二者的相关系数(r)为0.990。造成模拟值和测定值差异的原因可能是采样时紫色土密度较低,土壤中有较多的大孔隙,而黑土可能因有机质含量较高具有较好的结构性导致持水能力较强。【结论】采用土壤饱和含水率(θ_(s))、0.33 bar土壤含水率(θ_(0.33 bar))、最大吸湿水(θ_(97%RH))和空气相对湿度为43%时的土壤吸湿水(θ_(43%RH))推导的VG模型参数,可以较好地预报土壤水分特征曲线。但对土壤密度较低、存在大孔隙的土壤,及有机质量较高或结构性较好的土壤,可能会导致部分模拟值和测定值产生较明显的差异。前者可能会影响低吸力段的模拟结果(<0.33 bar),后者则可能影响土壤有效含水率段的模拟结果(0.33~15bar)。

吸附式大气集水技术的探讨、优化与应用突破

吸附式大气集水技术利用吸湿材料从空气中吸附水蒸气,通过太阳能驱动解吸,经冷凝收集生产新鲜液态水,已被公认为是干旱地区分散供水的一种有前途的技术。为尽快实现该技术在日常生活、工农业生产等方面的实际应用,进行了大量的探索和实践,并取得了一些突破。该文在简要介绍了吸附式大气集水的吸附、解吸、冷凝收集的技术过程基础上,针对解吸阶段进行了着重探讨;详细总结了吸湿材料的吸湿和解吸机理;基于材料结构和集水器设计,阐明了提高解吸能力和冷凝效果的优化策略;最后,从基础研究和实际应用方面概述太阳能驱动吸附式大气集水技术目前面临的挑战,并对其未来发展方向进行了展望。

三种PTFs方法获取的侵蚀黑土水分特征曲线的比较

采用3种土壤转换方程(PTFs)获取不同侵蚀程度黑土的土壤水分特征曲线(SWCC),并与实测数据进行了比较,以选择适合黑土SWCC间接获取的PTFs方法。以4种不同侵蚀程度的黑土为供试土壤,采用常用的PTFs计算机模型:Rosetta3、CalcPTF和以最大吸湿量为残余含水量(θ_(r))发展的PTFs方法(编号:PTFs3),进行了SWCC的van Genuchten (VG)模型参数的预报。Rosetta3模型的输入参数包括土壤机械组成、土壤密度、33 kPa压力下的土壤含水率(θ_(33 kPa))和1 500 kPa压力下土壤含水量(θ_(1 500 kPa));CalcPTF模型的输入参数包括土壤机械组成、土壤密度和有机碳含量;PTFs3的输入参数包括饱和含水量(θ_(0))、最大吸湿量(θ_(97%RH))、θ_(33 kPa)和θ_(1 500 kPa)。将上述3种方法获取的参数带入VG模型,得出供试土壤在不同水吸力下的土壤含水量,并与实测结果进行对比。结果显示,使用3种PTFs模型输出参数的VG模型预报值与实测值都有极显著的相关性,总体计算结果与实测结果也比较接近。PTFs3预报值与实测值的差值在±0.05 cm^(3)/cm^(3)内;CalcPTF-Var模型差值在-0.08~0.05 cm^(3)/cm^(3)之间;而Rosetta3模型的差值在-0.10~0.06 cm^(3)/cm^(3)之间。在土壤含水率压力小于33 kPa情况下时,SWCC差值相对较大。Rosetta3和PTFs3因为有θ_(33 kPa)和θ_(1 500 kPa)两点的水分进行校正,精确性比较可控,效果优于CalcPTF-Var。预报值与实测值差异的百分比也说明了这一点。具体到每个供试土壤样本,3种PTFs对剧烈侵蚀的黑土预报偏差百分比都较大,但PTFs3表现较优于其他两种模型。CalcPTF-Var在微度侵蚀样本S1的模拟上也出现了相对较大的偏差。综上,PTFs3模型是一种比较适合预报黑土SWCC的VG模型参数的PTFs方法。Rosetta3模型误差主要来源于较严重的低估了≤1 kPa SWCC的土壤含水量,而高估了6~33 kPa的土壤含水量。仅输入土壤理化性质的CalcPTF-Var模型需注意在部分黑土样本上的较大偏差。