Role of structure and capacity for energy absorption in increasing the strength and crack resistance of refractory ceramics

Conclusions We identified the influence of the parameters of a heterogeneous structure and also of particles possessing the capacity to absorb energy of deformation on the strength _rup and the crack resistance K_lc of refractory ceramics. The proposed relationships facilitate quantitative evaluation of the influence of these factors and indicate ways of increasing the levels of _rup and K_lc. Comparison of the calculated and experimental values of _rup and K_lc obtained from tests of various types of ceramics indicate the suitability of the equations for assessing the characteristics of strength and crack resistance.Translated from Ogneupory, No. 7, pp. 8–13, July, 1987.     

The impedance of the alkaline zinc-manganese dioxide cell. II. An interpretation of the data

The impedance of small alkaline zinc-manganese dioxide cells has been interpreted in terms of a controlling charge-transfer and diffusion process at the zinc electrode throughout the early stages of discharge. After about 20% of the available charge has been removed, it becomes necessary to include the manganese dioxide electrode circuit components. This network has the circuit elements for charge transfer and a proceeding chemical reaction. The Warburg component for the manganese dioxide electrode need not be considered since the effective area considerably exceeds that of the zinc. The relative areas are confirmed by the magnitudes of the circuit element components. The decomposition of the impedance data has been successfully accomplished as far as 80% discharge; after this point cells show considerable differences from cell to cell, especially in the low-frequency range, which makes a confident interpretation difficult. It is considered that this is due to the loss of the physical definition of the system.Nomenclature C _m,C _z double-layer capacitances of MnO₂ and Zn electrodes, respectively - C _X,R _X parallel branch accounting for current density varying with fractional electrode coverage - R resistance of electrolyte - V open-circuit voltage of cell - Z, Z, Z impedance of cell,resistive component ofZ and reactive component ofZ, respectively - _m, _z transfer resistance of MnO₂ and Zn electrodes, respectively - , _R, _C in Warburg equation:Z _W = ^–1/2(1–i) orZ _W = _R^–1/2– i_Cco^–1/2     

Crack resistance of corundum refractories over a wide range of temperatures

Conclusions The ultimate bend strength _bnd and the critical stress intensity factor K_lc of a group of corundum refractories were determined over a wide range of temperatures. It was shown that the temperature dependences of _bnd and K_lc have a similar nature. In the refractories having the usual porous structure, the rate of decrease of K_lc with increasing temperature is less than that of _bnd. Owing to this, the coefficient of crack resistance K_t of the refractories increases at high temperatures.The refractories having a porous-fissured structure, exhibit an almost identical reduction of _bnd and K_lc with increasing temperature and the magnitude of K_t increases very insignificantly.Translated from Ogneupory, No. 3, pp. 8–11, March, 1987.     

Plasma-induced polymerization

Summary The plasma-induced bulk copolymerization of alphamethyl styrene (MS) with methyl methacrylate (MMA) and with acrylonitrile (AN) was studied at room temperature. The reactivity ratio values: MMA — MS r_MMA= 0.42 r_MS= 0.22 AN — MS r_AN = 0.03 r_MS= 0.14 as well as the configurational parameter = 0.21 for the first system indicate that both systems can be described by the simple terminal model, neglecting the depolymerization reactions.     

Studies on electrical conductivity of gamma irradiated polyaniline

Summary de electrical conductivity at surface of -irradiated polyaniline (PAn) has been studied. EPR spectroscopic results indicate that the variation of spin concentration is consistent with the increase of _de. Electrical conductivity (_de) versus temperature (T) characteristics of unirradiated and irradiated PAn were performed, which demonstrate that the unirradiated curve can fit to ln_deT₁, while the irradiated curve fit to ln_deT_1/4.     

Effect of the Moisture Content on the Electrical Conductivity of SiO2/LiCl Xerogels

The effect of LiCl and water in pores on the active component of the low-frequency electrical conductivity of silicon dioxide xerogels is investigated. It is found that the electrical conductivity of SiO₂/LiCl xerogels at atmospheric humidity substantially depends on the hygroscopic properties of the salt. It is demonstrated that the dependence of the electrical conductivity of SiO₂and SiO₂/LiCl xerogels on the fraction pof the pore volume filled with an ionic conductor (water or an aqueous LiCl solution) can be described by equations of the percolation theory. The dilution of the LiCl solution upon water sorption does not change the character of the power dependence (p). It is shown for the first time that the introduction of water into pores considerably (by several orders of magnitude) extends the electrical conductivity range for xerogels and shows promise as a means for increasing the sensitivity of humidity detectors and controlling their threshold response.     

Effect of production factors on the properties of siliceous ceramic concrete

Conclusions Using dinas waste as the filler (D_grav=1–40 mm) and a quartz-sand suspension as the binder, we have studied the effect of the production factors on the macrostructure and strength of a siliceous ceramic concrete in the initial (after drying at 105–110°C) state and after heat treatment. The strengthening of the ceramic concrete is not an obligatory technological operation in the case where _cc>12.5 MPa. The value of _cc of the siliceous ceramic concrete is 14.4–105.0 MPa after heat treatment at 100, 1350, or 1450°C.The regression equations which adequately describe the dependence of _cc on the technological factors investigated have been derived.Translated from Ogneupory, No. 6, pp. 36–39, June, 1981.     

Brittle-ductile transition of polymer blends

Based on the Ludwik-Davidenkov-Orowan theory, a new criterion of BDT for polymer blends is proposed. In this approach fracture stress (_b) and shear yielding stress (_y) governing the brittle-ductile transition (BDT) of polymer blends is combined into a dimensionless group as D_a = _b ²/_y ². The theory dictates that BDT occurs at a critical condition D_ac = 1, brittle fracture occurs when D_a < 1, and ductile fracture occurs when D_a > 1. It can be shown that D_a = F_g · L_ym/L_D, where L_ym measures the length of shear band of the matrix, L_D is a parameter determined by the morphology and interfacial adhesion of dispersed phase, and F_g is related to specimen geometry and other extrinsic parameters. It is suggested that the onset of BDT depends on the competition between the L_ym and L_D. With due consideration to blend morphology, interfacial adhesion and matrix properties, existing experimental evidence supports the applicability of the proposed criterion.The project supported by FORD and NSFC No. 09415312     

Effect of temperature on the solution properties in 2-ethoxyethanol of statistical copolymers of methacrylic acid and methyl methacrylate

Summary The temperature dependence of the second virial coefficient and intrinsic viscosity of statistical copolymers of methyl methacrylate and methacrylic acid in 2-ethoxyethanol was investigated. It was found that the -temperatures of copolymers are outside the temperature range given by the -values for poly(methacrylic acid) and poly(methyl methacrylate). Their dependence on the copolymer composition has a discontinuity. Simple theoretical considerations have shown that this behaviour may be expected with copolymers composed of monomer units dissolving, respectively, with absorption and evolution of heat.     

An assessment of soil tests for phosphate for the prediction of cereal yields on a sandy soil in Western Australia

Nine soil tests for phosphate were evaluated for predicting the yield and P content of wheat, barley and oats grown on a sandy soil in Western Australia: Olsen, modified Olsen 1 (soil:solution ratio 1:5), modified Olsen 2 (soil:solution ratio 1:50), Colwell, Bray 1, Bray 2, modified Bray 2T (shaking time 10 minutes), modified Bray 2C (pH 3.7) and lactate. The soil had been fertilized 5 years previously with 20 levels each of superphosphate (OSP, range 0 to 400 kg P ha^–1) and Queensland rock phosphate (QRP, range 0 to 20 000 kg P ha^–1). For each species and fertilizer taken separately, all the tests, except for lactate, gave a good prediction of yield. When data for OSP and QRP were pooled, Bray 2 and modified Bray 2T tests were unsatisfactory predictors of both yield and P content.A linear relationship (P < 0.05) between mean soil tests value () and the standard deviation ( ) of the test value was observed for each soil test. For QRP, the results for lactate were the most variable (i.e./ was greatest) followed by modified Olsen 2 > Bray 1 > Bray 2 > Olsen > modified Bray 2C > modified Olsen 1 > modified Bray 2T > Colwell. The order for OSP fertilized soil was Bray 1 > modified Bray 2T > Bray 2 > Olsen > Colwell > modified Bray 2C > modified Olsen 1 > lactate > modified Olsen 2. For combined OSP and QRP data, the results of the Olsen 1 and Colwell extractions were the least variable.Errors in the prediction of yield ( _Y ) for all crops resulting from an error in soil test values () were calculated. For OSP-fertilized soil variability in values for the Bray-1 test provided the highest error (about 16%) in the prediction of the yield, followed by Bray 2 (12%) > Bray 2T (10%) > Olsen (8%) > Colwell (7%) > modified Bray 2C (6%) > lactate (4%). Maximum error was at yields of about 65% of maximum yield. For soil fertilized with QRP, lactate provided the highest error (about 10%) in the prediction of yield, followed by the other tests (< 6%). Maximum error was at yields of about 35% of maximum yield.The Colwell soil test gave the most accurate overall prediction of yield for both fertilizers.     

Ionic conductivities and glass transition temperatures in poly(vinyl methyl ether)-salt mixtures

Summary The solubility of a number of salts in poly(vinyl methyl ether) (PVME) was tested, and several gave homogeneous solutions over a range of concentrations. When dissolution of the salts occurred, the glass transition temperature of the mixture tended to rise, reflecting the solvation of the cations by the ether oxygens which also leads to crosslinking. Ionic conductivities (/Scm^–1) were measured for some of the mixtures but the level at room temperature was low. A rise in with increase in temperature was observed reaching 10^–4 Scn^–1 at 430K for PVME/LiClO₄ mixtures at a [Li⁺]/[O] ratio of 0.25.     

Preparation of stereoregular block copolymer comprising isotactic PMMA and polyisobutylene blocks and its characterization

Summary A triblock copolymer of isotactic(it)-poly(methyl methacrylate) (PMMA) and polyisobutylene (PIB), it-PMMA-block-PIB-block-it-PMMA, was prepared by anionic polymerization of triphenylmethyl methacrylate initiated with , -dilithiated PIB diisobutyrate in tetrahydrofuran at -78°C, and subsequntt hydrolysis and methylation with diazomethane. Molecular weight distribution of the triblock copolymer was narrow, and the stereoregularity of the PMMA block was highly isotactic. Proton spin-lattice relaxation times of the block copolymer in acetone-d₆, which is non-solvent for PIB but dissolves the block copolymer, indicate the aggregation of the copolymer through PIB block. Stereocomplex formation between the it-block copolymer and syndiotactic(st)-PMMA-block-PIB-block-st-PMMA was also studied.     

Copolymerization of aromatic polyamide macromonomers with methyl methacrylate

Summary Graft copolymers of end methacrylate-functionalized[MacroAM] or styrene-functionalized[MacroAS] polyamide macromonomers with methyl methacrylate(MMA) were prepared by radical copolymerization, and their thermal, dynamic properties, and miscibility with matrix PMMA have been investigated. The glass transition temperature(Tg)s of the copolymers were significantly elevated with the increase of the macromonomer content in the copolymer. Storage modulus E of the graft copolymers began to decrease at around 85°C, which is close to Tg of PMMA, irrespective of the macromonomer content in the copolymers. As the macromonomer content and its degree of polymerization became higher, the drop in E became significant.     

Rheological investigation of form relaxation and interface relaxation processes in polymer blends

Summary Transmission electron microscopical and rheological investigations have been performed on polymer blend systems of the type A/B, A/A-b-B/B, and A/C-b-B/B, where B is poly(methyl methacrylate) as the continuous and A is polystyrene as the dispersed phase. A-b-B is the corresponding diblock copolymer, and C-b-B is a diblock copolymer with poly(cyclohexyl methacrylate) (C) being thermodynamically miscible with A. The sphere-size distribution was estimated from the TEM data and found to be monomodal for all blends. Smaller sphere sizes in the A/C-b-B/B blends compared with the A/A-b-B/B blends prove the efficiency of the enthalpic acting compatibilizer.The rheological material functions G and G were used to calculate relaxation time spectra and to determine characteristic relaxation times. The form relaxation time ₁ for the relaxation of the ellipsoidally deformed soft PS-particles back to spheres have been verified for all blends no matter whether they where compatibilized or not. An additional relaxation time was found for both types of compatibilized blends. This time is assigned to a non-isotropic interfacial stress, which may arise from relaxation processes of the block copolymers at the interface.     

Critical solution point and chain dimension of branched-polystyrene solutions

Summary Critical solution point and chain dimension were measured for branched polystyrene(BPS) in solution as a function of molecular weight(M) and compared with those for linear polystyrene(LPS). The critical concentration _c of BPS was quite different from that of LPS at a fixed M, but the same at a fixed overlap-concentration ^*, i.e., plots of _c vs. ^* fall on a single straight line for both BPS and LPS (gf_c ^*). Reduced critical temperature _c defined by gt_c=(–T_c)/ [T_c: critical temperature, : the -temperature] was related to _c as _{c c} ² for BPS, whereas _{c c} for LPS.     

Prospects for strengthening fibres and films

Conclusions A model of the orientation strengthening of polymers which is based on the concept of the existence of a network of nodes which rearrange during the stretching process has been used to calculate the limiting values of degree of stretch, , and the strength, , of fibres of polyethylene, polycaproamide, polyvinyl alcohol, polypropylene, polyacrylonitrile, and poly-p-phenyleneterephthalamide.According to calculation, increasing the molecular weight of the polymer and decreasing the concentration of the solution being spun should lead to an increase in and ; for Terlon with a molecular weight of about 250,000, =100 and =10 GPa.Translated from Khimicheskie Volokna, No. 5, pp. 33–34, September–October, 1983.     

Microcalorimetric, infrared spectroscopic and DFT studies of ethylene adsorption on Ru, Ru/Sn and Ru/Cu catalysts

Microcalorimetric measurements of the adsorption of H₂, CO and C₂H₄ were conducted on silica-supported Ru, Ru/Sn, Ru/Cu and Cu catalysts; infrared spectroscopic measurements were made of adsorbed CO and C₂H₄. The adsorption of C₂H₄ leads to formation of di--adsorbed ethylene and ethylidyne species on Ru/SiO₂ at 300 K, with an initial heat of 160 kJ/mol. Ethylene adsorption at 203 K leads to the formation of di--adsorbed ethylene, ethylidyne species and weakly adsorbed -bonded ethylene. The initial heats are 110, 95 and 75 kJ/mol on Ru/SiO₂, 5Ru/Sn/SiO₂ and Ru/Cu/SiO₂, respectively. Lower heats of CO and C₂H₄ adsorption are measured on Ru/Cu/SiO₂, primarily as a result of these adsorbates binding on both Cu and Ru. Quantum chemical calculations employing density functional theory were performed using (0001) slabs of Ru and Ru/Sn. The results of these calculations indicate that Sn weakens the interaction of -bonded ethylene, di--bonded ethylene and ethylidyne species with Ru by 41, 23 and 15 kJ/mol, respectively. This behavior is in contrast to the effect of adding Sn to Pt and Pd, for which Sn preferentially weakens the bonding of ethylidyne species to the surface.     

Anisotropy in the strength of cellulosic fibres

Conclusions It is proposed to use the equation of a lemniscate, or the Cassini curve, to determine the destructive stress at break for cellulose films in any direction. Thereupon, to determine , it is necessary to know the destructive stress along two basic directions (₀ and ₉₀).To obtain cellulosic films which are isotropic in plane, a necessary and sufficient condition is ₀=₉₀.Translated from Khimicheskie Volokna, No. 6, pp. 34–35, November–December, 1987.     

Cryochemical Synthesis of Mn-Containing Poly(p-Xylylene)

A Mn-containing polymer was produced by solid-state photopolymerization of a cocondensated mixture of p-xylylene with Mn at 80 K. It was shown that during simultaneous deposition p-xylylene and Mn formed both - and -complexes. Irradiation of the system by UV light resulted in polymerization of p-xylylene with the destruction of the unstable -complexes, while the -bonded compounds were incorporated into the polymer chains. Complexes of Mn with benzyl-type radicals of the polymerized system were also observed. Prolonged storage of the polymerized material at ambient temperature under vacuum led to the gradual decomposition of the organomanganese compounds and complexes.     

Copolymerization of 5-vinyl-2,2′-bithiophene with methyl methacrylate and n-butyl acrylate

Summary Copolymers of 5-vinyl-2,2-bithiophene with methyl methacrylate or n-butyl acrylate were synthesized. Copolymer compositions were analyzed by nuclear magnetic resonance spectroscopy and reactivity ratios were calculated using the Kelen-Tüdõs method. 5-Vinyl-2,2-bithiophene proved to be a very reactive monomer with a reactivity ratio value of greater than 3 in copolymerization reactions with methyl methacrylate and a value of greater than 4 in Copolymerization reactions with n-butyl acrylate.