绿色化学理念在木材化学及其实验教学中的应用

随着工业化程度不断提高,环境和能源问题日益严峻。木材化学课程应将绿色化学理念贯彻于理论和实验教学中,可以采取具体措施：在木材化学理论教学中引入木材主要组分的分离和化学反应的绿色方法,试剂,做到资源的高效绿色高值化利用;在木材化学实验中利用多媒体辅助教学;提倡半微量化操作模式,对部分实验进行微型化改进;增设教学模块,改革实验内容,创新设计综合实验。通过这一系列措施在木材化学教学中引入并强化绿色化学理念,使学生在以后的工作中运用该理念,做到绿色环保、节能减排。     

Cellulose degradation in the Vasa: The role of acids and rust

Abstract

The oak timbers of the Swedish warship Vasa are deteriorating. High amounts of oxalic acid have been found along with a low pH and low molecular weight cellulose deep in the wood timbers. The iron-rich surface wood differs from the interior wood in that it displays higher pH and cellulose with higher molecular weight. The objective of this study was to determine why there is a difference in cellulose degradation, pH, and oxalic acid amount between the surface region and the interior of the Vasa timbers. Analysis of cellulose weight average molecular weight by size exclusion chromatography was performed, as well as quantification of oxalic acid and iron by high-performance anion exchange chromatography and atomic emission spectroscopy, respectively. It was found that a decrease in iron content coincides with an increase in oxalic acid concentration and a drop in pH at a certain depth from the wood surface. When iron-rich surface wood samples from the Vasa were mixed with an aqueous solution of oxalic acid, a fast increase of pH over time was observed. Neither interior wood poor in iron nor the fresh oak reference showed the same neutralizing effect during the time of measurement. This indicates that the presence of iron (rust) causes a neutralization of the wood, through the formation of iron(III) oxalato complexes, thus protecting the wood from oxalic acid hydrolysis. This effect was not observed to the same extent for other acids observed in Vasa wood (sulfuric, formic, glycolic, and acetic acids).     

Iron removal from waterlogged wood: Extraction by electrophoresis and chemical treatments

Abstract

The presence of iron oxides (lepidocrocite, goethite) in archeological wood may result in a degradation of the wood matrix. Extraction of these iron oxides is largely dependent on their solubility. In this study, balsa wood samples were impregnated with iron oxides to test extraction treatments. Additionally, archeological wood samples were also examined to determine treatment efficiency. Electrophoresis and simple immersion treatments were performed using various chemical solutions: a neutral and a conductive substance (potassium nitrate), an acid (acetic acid), three alkaline chelating agents (tri-ammonium and tri-sodium citrate and sodium oxalate), three acidic and slightly acidic chelating agents (ethylenediaminetetraacetic acid (EDTA), citric acid, and oxalic acid), and a reductant (sodium dithionite). Potassium nitrate did not extract sufficient amounts of iron, irrespective of whether the treatment was conducted by electrophoresis or simple immersion; any observable dissolution was attributed to protonation because of the acidic pH around the anode (as low as 3). Dissolution in acetic acid did not extract iron with either treatment. Strong chelating agents improved extraction, and these compounds gave the best results for simple immersion, particularly EDTA. This chemical is well adapted for use on archeological objects because of its chemical properties (stability constant, speciation based on pH). The addition of sodium dithionite to the solution improved dissolution. Even though electrophoresis improved extraction (in particular for tri-ammonium citrate), none of the tested chelating chemicals were suitable for electrophoresis because of a significant increase in temperature as well as high anode corrosion. The presence of iron sulfide in the archeological wood limited the effectiveness of the tested chemicals. A pre-treatment in sodium persulfate was expanded to include oxidized iron sulfide in oxy/hydroxide iron, which improved the extraction rate.     

两种中部切削结构的PDC钻头破岩效率研究

为提高深井钻井速度、延长钻头寿命及提高钻头破岩效率,以释放井底应力降低岩石抗钻能力为理论基础,设计并加工了中心外凸、中心内凹两种中部切削结构的PDC钻头,并与普通PDC钻头开展破岩效果对比实验.实验结果表明,与普通钻头相比,中心内凹钻头破岩钻进速度最大增幅达到了336％,中心外凸钻头破岩钻进速度最大增幅达到了89％.实...     

数控车床的试切对刀方法

工件坐标系的设定及对刀是数控机床加工中重要而关键的环节,对刀精度的高低直接影响零件的加工质量。基于数控机床的加工原理,通过对几个关键概念的具体分析,重点提出了数控车床中的试切对刀法,并对试切法对刀引起的误差进行了探讨,对提高对刀精度有一定的指导意义。     

魏晋官文书以纸代简及其启示

从公元105年东汉蔡伦发明纸张,到公元404年东晋桓玄以诏令的形式肯定纸张,沿袭上千年的简牍书写材料被纸张所代替。在这以纸代简的300年间,书信和书籍最先使用纸张,其完成时间在东汉末年。官文书以纸代简要迟缓一些,至东晋才告完成。其中案牍文书、簿籍文书分别在西晋和东晋实现了转变。一种新的官文书书写材料代替另一种官文书书写材料,需要新的书写材料性能良好、实际应用富有成效且时机成熟。这对于今天电子文件代替纸质文件也许有所启发。     

组合刀具在轴承座精加工中的应用

本文分析了柴油机轴承座加工中存在的问题,介绍了组合刀具的设计机理、安装调整方法,以及如何利用组合刀具精加工精度较高的轴承座孔、外圆柱面方法和使用效果。     

反排木鼓舞：从历史记忆到文化表征

反排木鼓舞作为文化的一种展示方式,随着时代的不同发生着文化的变迁和意义的生产,由一种族群源流与迁徙,祖先历史与记忆的隐喻和象征,逐渐转向反排文化,这种文化的展示与表征,一是通过苗族形象,二是展示和表征贵州少数民族和苗族的文化符号,从而实现文化的再生产。     

花椒硬枝扦插试验研究

以成熟的一年生花椒枝条为试材,就不同激素种类和浓度处理对扦插生根的效应进行了研究,探索出了快速、高效地培育花椒优质苗木的新方法。结果表明花椒具有较强的产生不定根的能力;不同激素种类处理对促进花椒插穗的生根均有明显的效果,其中以500mg/LNAA处理的效果最好;以50～100mg/L的IBA处理效果较好。扦插苗当年平均高度可达成1.23m,茎粗平均可达0.86cm。