云南省烧材消耗量探析

云南省森林采伐限额中,烧材的比重,“八五”为51.2%,“九五”为55.6%,造成烧材消耗量过大的原因,除了自然地理的原因之外,还有计算方法和调查方法上的原因,并论证了烧材的合理消耗量,以及解决途径.

关于在部分林场改变烧材结构的探讨

本文通过对以煤代木取暖、附助以煤气做饭的燃料结构及对丢弃的细小枝丫为烧材的可行性研究后 ,确认烧小枝丫方案可行 。

“四定四禁止”是云南烧材限额管理的一种好形式——禄丰县烧柴限额管理的启示

“八五”、“九五”期间云南全省烧材限额分别占总限额的 5 5 %和 5 6 % ,而实际烧材还不止这个数字。“十五”期间烧材限额占 5 9 1% ,因此形势非常严峻 ,为探索新形势下烧材管理的有效办法 ,通过对楚雄州禄丰县的调查 ,认为对烧材实行“四定”和“四禁止”是一个好办法。“四定”是“定采伐数量、定采伐地点、定采伐时间、定采伐树种”。“四禁止”是“禁止挖树根、禁止砍伐水源林及特殊地带的林木、禁止在公益林带及稀疏林内砍伐林木、禁止砍伐用材林”。

Microstructure and ablation behavior of Zr-based ultra-high-temperature gradient composites

To obtain high-performance Zr-based ultra-high-temperature composites,Zr-based ultra-high-temperature gradient composites were prepared by changing the laying method of the infiltrant via reactive melt infiltration.The effects of different infiltrant laying methods on the microstructure and ablative properties of Zr-based ultrahigh-temperature gradient composites were investigated.The results showed that the gradient structure of the Zr-based ultrahigh-temperature gradient composites differed when the composition ratio of the infiltrant was changed.When the thicknesses of the Zr/Mo/Si layers were 6/4/12 mm and 8/2/12 mm,the SiMoZrC solid solution content in the samples increased and decreased along the infiltration direction,respectively.The gradient samples were ablated in an oxyacetylene flame at 3000°C for 40 s.The ablation resistance of the sample was the highest when the infiltrant was a powder and the thickness of the Zr/Mo/Si layer was 6/4/12 mm.

Effect of ZrC-SiC content on microstructure and ablation properties of C/C composites

C/C-ZrC-SiC composites with different ZrC-SiC contents were fabricated by precursor infiltration and pyrolysis. The effect of ceramic content on the microstructure and ablation resistance was investigated. Both the C/C-SiC and C/C-ZrC-SiC composites exhibited good ablation resistance under the plasma flame above 2300℃. Withtheincreaseof ZrC content, a continuous oxide layer and a solid Zr-Si-O mesophase were formed during the ablation. And the structure of the formed oxides layer closely linked with the contents of ZrC-SiC ceramics. The solid ZrO2-ZrC and Zr-Si-O mesophase could increase the viscosity of SiO2 moderately and improve the anti-scouring ability. The continuous SiO2-ZrO2-ZrC-SiC layer would serve as a thermal and oxygen barrier for preventing the substratefrom further ablation. The C/C-ZrC-SiC composites with 27.2%ZrC and 7.56%SiC shows superior ablation resistance, and the mass and linear ablation rates are-3.51 mg/s and-1.88 μm/s, respectively.

巍山县森林资源消耗现状调查与管理对策

采取分类型抽样调查方法对云南省巍山县森林资源消耗情况进行调查。结果表明,全县森林资源消耗总量为76 760 m^3,其中县内资源63 683 m^3,县外购进商品材13 077 m^3,县内消耗中,商品性消耗11 783 m^3,占总消耗的18.5%;非商品性消耗51 466 m^3,占总消耗的80.82%,烧材消耗占消耗总量的84.50%。藉此分析消耗特点,提出降低森林资源低价值消耗的对策。

新平县森林资源现状及保护对策

根据１９９７年森林资源二类调查，新平县森林资源蓄积量１４４３５０００ｍ２，森林覆盖率（含灌木林）达７０．３５％。但还存着低价值消耗过大、本材综合利用率低，可利用资源少等问题。当前应抓住西部大开发的历史机遇，做好以下工作：严格执行森林资源限额采伐制度，制止超限额采伐；全面停止天然林采伐，加强资源保护力度；积极退耕还林；加强烧材管理，压缩农村生活烧材数量；严格控制烤烟烧材消耗；积极营造薪炭林。

Properties and microstructure of Cu/diamond composites prepared by spark plasma sintering method

Cu/diamond composites have been considered as the next generation of thermal management material for electronic packages and heat sinks applications. Cu/diamond composites with different volume fractions of diamond were successfully prepared by spark plasma sintering（SPS） method. The sintering temperatures and volume fractions（50%, 60% and 70%） of diamond were changed to investigate their effects on the relative density, homogeneity of the microstructure and thermal conductivity of the composites. The results show that the relative density, homogeneity of the microstructure and thermal conductivity of the composites increase with decreasing the diamond volume fraction; the relative density and thermal conductivity of the composites increase with increasing the sintering temperature. The thermal conductivity of the composites is a result of the combined effect of the volume fraction of diamond, the homogeneity and relative density of the composites.

Low temperature solid-phase sintering of sintered metal fibrous media with high specific surface area

A procedure of low temperature solid-phase sintering（LTSS） was carried out to fabricate sintered metal fibrous media（SMFM） with high specific surface area.Stainless steel fibers which were produced by cutting process were first plated with a coarse copper coating layer by electroless plating process.A low-temperature sintering process was then completed at about 800 °C for 1 h under the protection of hydrogen atmosphere.The results show that a novel SMFM with complex surface morphology and high specific surface area（0.2 m2/g） can be obtained in this way.The effect of sintering temperature on the surface morphology and specific surface area of SMFM was studied by means of scanning electron microscopy and Brunauer-Emmett-Teller.The damage of micro-structure during the sintering process mainly contributed to the loss of specific surface area of SMFM and the optimal sintering temperature was 800 °C.

Theoretical analysis of ultra-short pulsed laser ablation of SiO_2 material based on a Coulomb explosion model

Based on the kinetic theoretical Vlasov-Poisson equation, a surface Coulomb explosion model of SiO2 material induced by ultra-short pulsed laser radiation is established. The non-equilibrium free electron distribution resulting from the two mechanisms of multi-photon ionization and avalanche ionization is computed. A quantitative analysis is given to describe the Coulomb explosion induced by the self-consistent electric field, and the impact of the parameters of laser pulses on the surface ablation is also discussed. The results show that the electron relaxation time is not constant, but it is related to the microscopic state of the electrons, so the relaxation time approximation is not available on the femtosecond time scale. The ablation depths computed by the theoretical model are in good agreement with the experimental results in the range of pulse durations from 0 to 1 ps.

Effect of glass fibre(GF) addition on microstructure and tensile property of GF/Pb composites fabricated by powder metallurgy

GF/Pb compositeswerefabricated by the method of powder metallurgy, and the density, microstructure and tensile propertywerecharacterized considering the size and content ofglass fibre （GF）. The results show that relative densities decrease with increasing GF fraction, and the 50μm-GF reinforced specimens exhibit a better densification than the 300μm-GF reinforced ones. The GF particles distribute quite uniformly inPb matrix, and the composites fabricated at low sintering temperature （〈200℃） possess fine-grain microstructure. The addition of GF significantly improves the strength of the Pb composites, and the ultimate tensile strength of the Pb composite reinforcedwith the addition of 50μm-0.5% GF（mass fraction）is about 30MPa higher than that of GF-free sample. For all composites groups, increasing the reinforcement content from 0.5%to 2%（mass fraction）results in a decrease in both tensile strength and ductility.

Microstructure characteristics and mechanical properties of TiB/Ti-1.5Fe-2.25Mo composites synthesized in situ using SPS process

TiB/Ti-1.5Fe-2.25Mo composites were synthesized in situ using the spark plasma sintering （SPS） method at temperatures of 850-1150 °C. The effect of the sintering temperature on microstructure and mechanical properties of the composites was investigated. The results indicate that the aspect ratio of the in situ synthesized TiB whiskers in Ti alloy matrix decreases rapidly with an increase in sintering temperature. However, both the relative density of the sintered specimens and the volume content of TiB whiskers in composites increase with increasing sintering temperature. Thus, the bending strength of the composites synthesized using SPS process increases slowly with increasing the sintering temperature from 850 to 1150 °C. TiB/Ti-1.5Fe-2.25Mo composite synthesized at 1150 °C using SPS method exhibits the highest bending strength of 1596 MPa due to the formation of fine TiB whiskers in Ti alloy matrix and the dense microstructure of the composite.

Influence of porogen type and copper powder morphology on property of sintering copper porous materials

Copper porous materials have been manufactured by the method of powder metallurgy.Electrolytic copper powders and atomized copper powders are used as matrix material.Methylcellulose and paraffin are used as porogen.The influence of porogen type and copper powder morphology on the property of copper porous materials is investigated as well.The results show that copper porous materials with paraffin as porogen have lower porosity and permeability compared with materials using methylcellulose as porogen,due to the different pore-forming mechanisms.The pore forming mechanism of methylcellulose is thermal decomposition,while the pore forming mechanism of paraffin is melting–evaporation.The morphology of copper powders affects the contact state between adjacent powders,which further influence the sintering shrinkage.The porous materials using arborescent copper powders as matrix have lower porosity,smaller pore size and lower permeability,compared with materials with atomized copper powders as matrix.

Sintering behavior and mechanical properties of sintered ceramics based on spodumene tailings

In this study,ceramics was prepared by slip casting(no pressure was used during shaping step)and atmospheric pressure sintering with low-melting point glass(LPG)powder as the binding material to facilitate the transformation of spodumene flotation tailings(SFTs)into ceramics at lower temperatures.The influence of sintering temperature and mass ratio of LPG on the mechanical properties(flexural strength and compressive strength)of ceramic materials was studied by orthogonal test.The results showed that when the mass ratio of LPG powder was higher than or equal to 20 wt%and the sintering temperature was higher than or equal to 550℃,mutual adhesion between the sample particles was realised and consequently the ceramic materials could be prepared with good mechanical properties(the maximum flexural strength=19.55 MPa,the maximum compressive strength=42.25 MPa,average porosity=24.52%,average apparent density=1.66 g/cm^(3),and average water absorption=14.79%).The sintered ceramics were characterized by XRF,XRD,optical microscopy analysis,SEM,TGA-DSC and FT-IR.The formation of liquid phase at high temperature may lead to the mutual bonding between particles,which might be the main reason for the improvement of mechanical properties of ceramic materials.Overall,SFTs were successfully sintered at low temperature to prepare ceramic materials with good mechanical properties,which are crucial for energy conservation and environmental preservation.

Physico-chemical properties and microstructure of hydroxyapatite-316L stainless steel biomaterials

Sintering shrinkage, compressive strength, bending strength, metallurgical morphology, microstructure and chemical composition diffusion of hydroxyapatite-316L stainless steel(HA-316L SS) composites were investigated. The results show that the sintering shrinkage of HA-316L SS composites decreases from 27.38% to 8.87% for cylinder sample or from 27.18% to 8.62% for cuboid sample with decreasing the volume ratio of HA to 316L SS, which leads to higher sintering activity of HA compared with that of 316L SS. The compressive strength of HA-316L SS composites changes just like parabolic curve (245.3→126.3→202.8 MPa) with reducing the volume ratio of HA to 316L SS. Bending strength increases from 86.3MPa to 124. 2 MPa with increasing the content of 316L SS. Furthermore, comprehensive mechanical properties of 1.0∶3.0 (volume ratio of HA to 316L SS) composite are optimal with compressive strength and bending strength equal to 202.8 MPa and 124.2 MPa, respectively. The (microstructure) and metallurgical structure vary regularly with the volume ratio of HA to 316L SS. Some chemical reaction takes place at the interface of the composites during sintering.

Characteristics and wear behavior of cenosphere dispersed titanium matrix composite developed by powder metallurgy route

The cenosphere dispersed Ti matrix composite was fabricated by powder metallurgy route, and its wear and corrosion behaviors were investigated. The results show that the microstructure of the fabricated composite consists of dispersion of hollow cenosphere particles in a-Ti matrix. The average pore diameter varies from 50 to 150 μm. The presence of porosities is attributed to the damage of cenosphere particles due to the application of load during compaction as well as to the hollow nature of cenospheres. A detailed X-ray diffraction profile of the composites shows the presence of Al2O3, SiO2, TiO2 and α-Ti. The average microhardness of the composite （matrix） varies from HV 1100 to HV 1800 as compared with HV 240 of the as-received substrate. Wear studies show a significant enhancement in wear resistance against hardened steel ball and WC ball compared with that of commercially available Ti-6Al-4V alloy. The wear mechanism was established and presented in detail. The corrosion behavior of the composites in 3.56% NaCl （mass fraction） solution shows that corrosion potential （φcorr） shifts towards nobler direction with improvement in pitting corrosion resistance. However, corrosion rate of the cenosphere dispersed Ti matrix composite increases compared with that of the commercially available Ti-6Al-4V alloy.

Effect of porosity and interface structures on thermal and mechanical properties of SiC_p/6061Al composites with high volume fraction of SiC

50 vol.% SiCp/Al composites with high thermal and mechanical properties were successfully produced by spark plasma sintering technique. The influences of sintering temperature on the thermal conductivity, coefficient of thermal expansion and bending strength of the SiCp/Al composites were carefully investigated. The results show that the SiCp/Al composites sintered at 520℃ exhibits a thermal conductivity of 189 W/(m·K), a coefficient of thermal expansion (50.200℃) of 10.03×10^-6 K^-1 and a bending strength of 649 MPa. The high thermal and mechanical properties can be ascribed to the nearly full density and the well interfacial bonding between the alloy matrix and the SiC particles. This work provides a promising pathway for producing materials to meet the needs of high performance electronic packaging.

Phase composition, transition and structure stability of functionally graded cemented carbide with dual phase structure

The phase composition, phase transition and phase structure transformation of the wire-cut section of functionally graded WC-Co cemented carbide with dual phase structure were investigated by XRD phase analysis. It is shown that the composition of η phase in the core zone is Co_3W_3C (M_6 C type). The structure of cobalt based solid solution binder phase is fcc type. At the cooling stage of the sintering process, the phase transition of η phase, i.e. M_6C→M_12C and the martensitic phase transition of the cobalt based solid solution binder phase, i.e. fcc→hcp are suppressed, which facilitates the strengthening of the alloy. Because the instantaneous temperature of the discharge channel is as high as 10 000 ℃ during the wire cutting process, the processed surface is oxidized. Nevertheless, the oxide layer thickness is in micro grade. In the oxide film, η phase is decomposed into W_2C and CoO, and cobalt based solid solution binder is selectively oxidized, while WC remains stable due to the existence of carbon containing liquid organic cutting medium.

Effect of Si content on microstructure and properties of Si/Al composites

Si/Al composites with different Si contents for electronic packaging were prepared by spark plasma sintering （SPS） technique. Properties of the composites were investigated, including density, thermal conductivity, coefficient of thermal expansion and flexural strength. The effects of the Si content on microstructure and thermal and mechanical properties of the composites were studied. The results show that the Si/Al composites consist of Si and Al components and Al uniformly distributes among Si grains. The relative density of the Si/Al composites gradually increases with the decrease of Si content and reaches 98.0% when the Si content is 50%. The thermal conductivity, the coefficient of thermal expansion and the flexural strength of the composite all decrease with the increase of the Si content, and an optimal matching of them is obtained when the Si content is 60%（volume fraction）.