Creep and Stress Rupture Behavior of an Advanced Silicon Nitride: Part I, Experimental Observations

Cylindrical buttuohead specimens of an advanced silicon nitride were tested in uniaxial tension at temperatures between 1422 and 1673 K. In the range 1477 to 1673 K, creep deformation was reliably measured using high-temperature contact probe extensometry. Extensive scanning and transmission electron microscopy has revealed the formation of lenticular cavities at two-grain junctions at all temperatures (1422–1673 K) and extensive triple-junction cavitation occurring at the higher temperatures (1644–1673 K). Cavitation is believed to be part of the net creep process. The stress rupture data show stratification of the Monkman–Grant lines with respect to temperature. Failure strain increased with increase in rupture time or temperature, or decrease in stress. Fractography showed that final failure occurred by subcritical crack growth in all specimens.     

Dynamic viscoelasticity of low‐density polyethylene/in‐situ‐grafted carbon black composite

The study on the dynamic viscoelastic properties of grafted carbon black (g‐CB) filled low‐density polyethylene (LDPE) was carried out. Because of formation of CB networking, the characteristic modulus plateau and loss tangent arc appears. Addition of grafting monomer like butyl acrylate (BA) and acroleic acid (AA) enhances the interaction between particles and matrix due to accelerated formation of micronetworking in the composites induced by forming branch chains of AA and BA with multiunit. The decrease of the temperature corresponding to α_c mechanical relaxation together with AA (BA) addition given by the position of loss tangent (tan δ) peak for LDPE is owed to the formation of long‐chain polymer grafted between CB and the matrix, which facilitates the slip of the lamella of LDPE. The influence of maleic anhydride (MA) on enhancing interaction between LDPE and CB is not so pronounced, as compared with AA and BA because of no formation of long chain between CB particle and polymer matrix. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4127–4132, 2006     

The effect of waste oil-cracking catalyst on the compressive strength of cement pastes and mortars

Epcat, one of the spent fluid catalytic cracking (FCC) catalysts from oil-cracking refineries, shows pozzolanic activity. In this study, pastes and mortars with Epcat were prepared and cured, and their compressive strengths after 3, 7 and 28 curing days were measured. The water/binder (W/B) ratios were 0.2, 0.25 and 0.3, and the replacement levels of cement by Epcat were 0, 5, 10 and 15 wt.%. Proper amount of superplasticizer was added into each mix to ensure similar workability.The results indicate that the presence of Epcat would increase the compressive strength of mortars substantially, but increase the compressive strength of the related pastes only slightly. Epcat mortars with W/B=0.25 show more strength-enhancing effect than those with W/B=0.3, and this effect increases with the catalyst content. Therefore, the mix (W/B=0.25) incorporated 15% Epcat exhibits the greatest compressive strength (92.3 MPa). For mortars with W/B=0.2, the strength-enhancing effect occurs only for those containing 5% catalyst; this effect becomes unclear when mixes containing 10% Epcat or more because high dosage of superplasticizer was added in obtaining proper workability and that affects the strength development. The improvement in the mechanical properties of mortars is attributed to the increase in the hydrated cement paste itself and, more importantly, improved bonds between the cement paste and aggregate.     

旋风分离器内颗粒运动规律的数值模拟

采用单颗粒动力学模型计算了旋风分离器内颗粒的运动轨迹。计算结果表明：进入旋风分离器的颗粒绝大多数在环形空间内就被甩向器壁；从入口上部进入的部分较小颗粒由于局部二次流作用而上升形成顶灰环；还有少量颗粒进入下部分离空间。在下部分离空间内，有灰斗返气夹带上来的颗粒，处于内旋流的颗粒则有可能随上升气流而逃逸，所以一定的分离空间高度有利用颗粒的二次再分离。     

无底柱分段崩落法采矿进路受力过程分析

在使用无底柱分段崩落法的矿山,大都存在着地压现象。其主要表现是采矿进路和联络道的变形破坏。对采矿进路在开挖和回采过程中各阶段受力情况的分析表明,进路的变形、破坏主要是受到岩体初始静应力、爆破动应力和矿柱支撑应力的综合作用的结果。     

螺带式搅拌器在假塑液中的混合及放大的研究

本文综合研究了螺带式搅拌器在假塑性液体中的混合特性及动力特性，测定了双螺带，内外螺带及螺带螺旋３种类型搅拌器的功率常数Ｋｐ和Ｍｅｔａｎｅｒ常数Ｋｓ，并得出混匀操作和传质工艺过程的放大准则。     

一缩二乙二醇二缩水甘油醚的合成

以一缩二乙二醇和环氧氯丙烷为原料、三氟化硼乙醚络合物为催化剂合成一缩二乙二醇二缩水甘油醚(DGEG)。讨论了催化剂用量、原料配比、碱金属氢氧化物以及成环反应温度对产物收率的影响。同时 ,用傅立叶红外光谱对其进行了分析与表征。当三氟化硼乙醚络合物用量为 3份、环氧氯丙烷与一缩二乙二醇的物质的量比为 8∶1、用氢氧化钾在 30℃左右进行成环反应时 ,可以得到低粘度、高收率的产物。     

炭黑品种及用量对NBR/CHR并用胶性能的影响

研究了炭黑Ｎ６６０、Ｎ６３０、Ｎ７６２、天然气半补强炭黑及喷雾炭黑对ＮＢＲ／均聚氯醚橡胶（ＣＨＲ）并用胶性能的影响。试验结果表明，这些炭黑在ＮＢＲ／ＣＨＲ并用胶中的用量达到８０份时，并用胶的加工性能仍较好。随着炭黑用量的增大，ＮＢＲ／ＣＨＲ并用胶的耐四氯化碳性能提高；压缩永久变形、压缩温升及硬度增大；扯断伸长率和回弹值下降；而拉伸强度则是先升高，当炭黑用量达到６０份时即下降；撕裂强度也是先升高，而后在不同用量处出现下降趋势。     

Demineralization of a UK bituminous coal using HF and ferric ions

A UK bituminous coal has been used to study demineralization by two-stage chemical leaching. The first-stage uses hydrofluoric acid (HF) at 65 °C and reduces the ash content from 5.30 wt% to 1.37 wt% by mainly removing Al and Si containing minerals. Subsequent leaching by ferric ions decreases the ash content further to 990 ppm by removing most of the pyrite and fluorides formed during the HF leaching. Calorific value of the coal shows no change following leaching, which suggests no oxidation is occurring to the coal carbonaceous matrix. The mercury and sulfur contents after the two-stage leaching sequence decrease by 40% and 26%, respectively.