Premix Solution Research Articles

Semi-Electrical Conductivity of Gelcast Alumina Sintered under Nitrogen Atmosphere

This work demonstrated an in-situ pyrolysis of gelcast alumina under reduction sintering to make alumina and carbon composite in providing semi-electrical conductivity. To increase the carbon content, the monomer was varied in the premix solution with reduction sintering in nitrogen gas. Two-probe method was used to measure electrical resistance of the sintered samples. The results revealed that the increase of monomer addition and sintering treatment were effective in reducing electrical resistance. The lowest value was 3.6×106-cm, which is a potential candidate for electrostatic shielding application. The reduction-sintered sample was re-sintered in an air in order to gain insight on the conductive path due to carbon network. Further tests such as XRD, TGA/DTA, and scanning electron microscopywere used to explain the semi-conductive property of the material.

A Synergistic Low‐Toxicity Gelcasting System by Using HEMA and PVP

A new low‐toxicity gelcasting system with a 2‐hydroxyethyl methacrylate (HEMA) monomer was applied for casting of alumina ceramics. Polyvinyl pyrrolidone (PVP) was adopted for modifying the homogeneity of the PHEMA (poly‐HEMA) gel. The rheological properties of alumina suspension in the HEMA–PVP premix solution were studied. After preparation of a concentrated alumina suspension, homogenous alumina green body with a relatively high strength of about 19 MPa could be formed through the PVP‐modified HEMA system. Dense complex‐shaped ceramic parts can be successfully produced through the system. Besides, the surface exfoliation phenomenon that seems inherent to the acrylamide gelcasting system could also be eliminated by using the PVP‐modified HEMA system. Analysis of the interaction of HEMA and PVP suggested that the improved microstructure and strength homogeneity, as well as the elimination of surface exfoliation in the new system, should be attributed to the intermolecular hydrogen bonding formed between PHEMA and PVP molecules.

A simple pen-spotting method for arraying biomolecules on solid substrates

We describe a simple, relatively inexpensive method for depositing biomolecules on a solid substrate using Rapidograph® drafting pens. The pens can be used without modification to accurately deposit spots between ∼100 and 600 μm in diameter. When mounted on a suitable microtranslation stage, the pens can be used to easily deposit tens of spots aligned with underlying substrate features such as microfabricated sensors. The pens are particularly convenient because pre-mixed solutions can be stored in the pens for multiple uses. We demonstrate the use of this approach to deposit DNA probes on a microsensor array.

Elimination of Surface Spallation of Alumina Green Bodies Prepared by Acrylamide‐Based Gelcasting via Poly(vinylpyrrolidone)

Surface spallation of gelcast alumina green bodies due to the exposure of the surface to air during gelation was successfully eliminated by adding a proper amount of poly(vinylpyrrolidone) (PVP) in aqueous acrylamide premix solution. The influences of PVP on the colloidal characteristics of alumina powder in aqueous solutions, the rheological properties of alumina slurries, the gelation process, and the properties and microstructures of the gelcast green bodies and the sintered samples were systematically investigated. Even though the addition of PVP to premix solution has slightly negative effects on the viscosity of alumina slurries, gelation and strength of green bodies, it has no obvious influence on the final structure and properties of alumina ceramics. Thus, PVP was considered an effective polymer to resolve the problem of the inhibition of gelation due to the presence of oxygen, which usually occurs in gelcasting during the formation of polymer network gel by in situ polymerization of monomers in air. The mechanism of PVP in eliminating the surface spallation problems of green bodies is also discussed.

Gelcasting of PZT

Abstract Aqueous gelcasting of PZT is discussed in this paper. Concentrated PZT suspension (50 vol.%) with low viscosity is developed by using triammonium citrate as the dispersant. Zeta potential results suggest that the effect of TAC in decreasing the viscosity of the PZT suspension may be ascribed to its electrostatic stabilization mechanism. A premix solution containing 20 wt.% of AM monomer can provide a mechanical strength of 18 MPa for the green body obtained from 50 vol.% PZT suspension. SEM photos indicate that PZT ceramics with homogeneous microstructure can be fabricated. Comparison of piezoelectric coefficients of gelcast PZT samples with those of the die pressed PZT samples indicates that the additives, including the monomer, the crosslinker and the dispersant etc., show no influence on the piezoelectric property of the PZT samples.

Gelcasting of alumina using urea–formaldehyde III. Machinable green bodies by copolymerisation with acrylic acid

The present work is an attempt to improve the gel strength, green body strength and green machinability characteristics of gelcast alumina bodies by co-polymerisation of urea-formaldehyde (UF) with acrylic acid. Methylol urea and acrylic acid in the pre-mix solution undergo simultaneous polymerisation at 80°C. The polyacrylic acid stabilises the UF condensation products through hydrogen bonding and prevent precipitation, resulting in a transparent gel. The gel when heated at 110°C forms a tough polymer which gives a peak at 1738 cm −1 in the infrared spectrum indicative of crosslinking of the methylol urea condensation products and polyacrylic acid through ester linkage. The alumina slurries prepared in the premix solution, gels within 10–15 min at 80°C. The green strength of the gelcast bodies increases with acrylic content. A binder composition containing >50% acrylic acid shows diametrical compressive strength >7 MPa. The green bodies show excellent machinability and are subjected to lathing, milling and drilling using conventional tools and equipments. The green bodies during machining show chip resistance and machined body has good surface finish. A near steady state binder removal profile is achieved by heating the samples under both dynamic and isothermal conditions. The debinderised bodies on sintering gave up to 97% theoretical density.

Physico-chemical stability of docetaxel premix solution and docetaxel infusion solutions in PVC bags and polyolefine containers.

We assessed the physical and chemical stability of docetaxel infusion solutions. Stability of the antineoplastic drug was determined 1.) after reconstitution of the injection concentrate and 2.) after further dilution in two commonly used vehicle-solutions, 0.9% sodium chloride and 5% dextrose, in PVC bags and polyolefine containers. Chemical stability was measured by using a stability-indicating HPLC assay with ultraviolet detection. Physical stability was determined by visual inspection. The stability tests revealed that reconstituted docetaxel solutions (= premix solutions) are physico-chemically stable (at a level > or = 95% docetaxel) for a minimum of four weeks, independent of the storage temperature (refrigerated, room temperature). Diluted infusion solutions (docetaxel concentration 0.3 mg/ml and 0.9 mg/ml), with either vehicle-solution, proved physico-chemically stable (at a level > or = 95% docetaxel) for a minimum of four weeks, when prepared in polyolefine containers and stored at room temperature. However, diluted infusion solutions exhibited limited physical stability in PVC bags, because docetaxel precipitation occurred irregularly, though not before day 5 of storage. In addition, time-dependent DEHP-teaching from PVC infusion bags by docetaxel infusion solutions must be considered.

Intravenous administration of large dosages of adenosine or adenosine triphosphate with minimal blood pressure fluctuation.

Hemodynamic responses, blood gas, and metabolic changes were assessed when large dosages of a pre-mixed solution of adenosine or adenosine triphosphate (ATP) with catecholamine were intravenously administered in the conscious, spontaneously breathing rabbit. The present study offers a simple and effective approach to enabling safe administration of large doses of the potent vasodilators, adenosine or ATP with minimal cardio-respiratory and metabolic changes.

Vanadia-Titania Aerogels: III. Influence of Niobia on Structure and Activity for the Selective Catalytic Reduction of No by NH 3

Niobia-doped vanadia-titania aerogels with 20 wt% nominal "V 2O 5" and 2-6 wt% nominal "Nb 2O 5" have been prepared by a two-stage sol-gel process with subsequent supercritical drying. A titania gel was synthesized by the addition of an acidic hydrolysant to tetrabutoxytitanium(IV) in methanol. The methanolic, pre-mixed solution of niobium(V) pentaethoxide and vanadium(V) oxide tri- n-propoxide was added after redispersing the titania gel. The influence of niobia loading on the morphological and chemical properties of the aerogels was studied. Similarly a ternary xerogel (20 wt% V 2O 5, 6 wt% Nb 2O 5) was prepared for comparison with the corresponding aerogel. The aero(xero-)gels were characterized by means of N 2 physisorption, X-ray diffraction, thermal analysis coupled with mass spectrometry, scanning electron microscopy, and vibrational spectroscopy. The meso- to macroporous aerogels possess BET surface areas of 176-203 m 2 g −1 calcination at temperatures ≤ 673 K and contain well-developed anatase crystallites of 7-8 nm mean size. For the calcination at 723 K niobia is suggested to retard both crystallization of the vanadia phase and phase transformation of anatase to rutile. The corresponding BET surface area is 114 m 2 g −1. In contrast, the xerogel calcined at 673 K is micro- to mesoporous, possesses a BET surface area of 117 m 2 g −1, and contains anatase as well as monoclinic TiO 2 with mean crystallite sizes of 11 and 15 nm, respectively. Crystalline V 2O 5 was only detected for the xerogel calcined at 773 K. In all other samples the vanadia phase consists of highly dispersed vanadium oxo clusters together with more extended structures, especially at temperatures ≥ 673 K. The catalytic properties of the aero(xero-)gels were tested with the selective catalytic reduction of NO by NH 3. The variation of the niobia loading from 2 to 6 wt% Nb 2O 5 did not affect the activity. An increase of the calcination temperature from 573 to 723 K led to a significant activity rise of the aerogel catalysts. The xerogel calcined at 673 K exhibited the highest activity among all catalysts tested.

Diarrhea Care in Private Practice

To the Editor.— The article by Dr Snyder, "Use and Misuse of Oral Rehydration Therapy for Diarrhea,"1 led us to review our treatment of gastroenteritis, revise our telephone protocols, and seek out rehydration solutions. Our difficulty in obtaining adequate supplies mirrored that of Dr O'Banion.2 Expense to the patient is also an important factor: commercial premixed solutions sell for $4 to $6 per quart in our area, which many families cannot pay. Our solution was to obtain from the World Health Organization the name of the US supplier of oral rehydration solution (ORS) packets and order direct from the supplier (Jianas Bros Packaging Co, 2533 SW Blvd, Kansas City, MO 64108).

Hysteresis-like behaviour in the swelling/deswelling of polystyrene based crosslinked resins using acetone/water mixtures

Five polystyrene resins nominally ∼20% crosslinked and macroporous (toluene diluent/comonomers, 2/1) have been prepared. Four of these have a nominal content of ∼5% v/v respectively of methacrylic acid, 4-vinyl pyridine, 2-hydroxyethyl methacrylate and methyl methacrylate. The swelling behaviour of each in tetrahydrofuran/water and acetone/water mixtures of 80, 60, 40 and 20% by volume has been quantified. In the former mixtures, the swelling achieved is independent of whether pre-mixed solutions are used, or whether either pure component contacts the resins first. Unique swelling/composition curves result. With acetone and water, however, the swellings using pre-mixed solutions and solutions where water contacts the resin first, are depressed relative to those where acetone contacts the resin first. Two different swelling/composition curves result for each resin, forming an hysteresis-like loop. This result is explained tentatively in terms of a kinetic effect and differences in the strengths of interaction between tetrahydrofuran and water, and acetone and water.

Uses of formal and informal knowledge in the comprehension of instructions for oral rehydration therapy in Kenya

Information for using pre-mixed oral rehydration salt solutions, which have been made widely available in rural Kenya, is normally obtained from what is printed on the packets in English and either read or explained to the purchaser. Consequently, the comprehension can be improved with simple changes in the printed text, particularly those that reinforce appropriate modern or indigenous medical knowledge. However, the knowledge involved in effectively using oral rehydration therapy is not merely an awareness of its benefits, but an understanding of the environmental and biological causes of diarrhoeal diseases and an ability to explain the course of treatment that secondary schooling seems to develop.

VELOCITY FLUCTUATIONS IN NON-HOMOGENEOUS DRAG REDUCTION

Non-homogeneous drag reduction is obtained by injecting a polymer solution thread into the center of a turbulent pipe flow. Under the proper conditions the magnitude of this non-homogeneous drag reduction is much larger than that for the same polymer molecules uniformly distributed in the flowing solvent. In this work the axial velocities and velocity fluctuations near the wall were examined in such a non-homogeneous drag reduction and also in the flow of a homogeneous (pre-mixed) solution of poly(ethylene oxide). The drag reduction and the Reynolds number were the same for both fluids. Significant differences were found in the velocity profile and in the statistical analysis of the velocity fluctuations. The skewness profile for the non-homogeneous case remained positive to a much greater distance from the wall than the skewness profile for the premix solution. In the injection case the velocity fluctuation spectra had the same sharp peak at 5−10 Hz for y + between 11 and 50. This peak corresponded to the bursting frequency measured from the short time autocorrelation. In the pre-mix case a broad increase in velocity fluctuation spectra was seen at y + = 11 which was attributed to polymer molecule rotations in the laminar shear flow near the wall. This band was absent in the non-homogeneous drag reduction, suggesting that no polymers were present at y + = 11. The observations imply that non-homogeneous drag reduction involves a modification of the large eddy structure.

Topically administered clindamycin in the treatment of acne vulgaris and other dermatologic disorders.

Clindamycin is a macrolide antibiotic that has been used orally and topically in the treatment of acne vulgaris. Unfortunately, oral administration is associated with pseudomembranous colitis in up to 10% of patients; consequently, it is no longer a generally accepted form of acne therapy. Topical application is an effective, safer alternative. Topical formulations may be extemporaneously prepared or purchased as a pre-mixed hydroalcoholic solution. Adverse effects associated with topical preparations are few and mostly minor. Topical clindamycin is also used in the treatment of erythrasma, rosacea, periorificial facial dermatitis, and folliculitis.