Propeller mechanism

Trzaska and co-workers showed a similar propeller mechanism for the formation of helical columns from disclike metallomesogens (29-31).34 These metallomesogens also have C3 symmetry and 30 and 31 are provided with chiral side chains. In the hexagonal columnar mesophase these chiral side chains induce a Cotton effect in the chromophore of the helically arranged core. Heating the mesophase to the isotropic liquid results in the disappearance of the Cotton effect because of the loss of helical order. This effect illustrates the need for the molecules to be positionally ordered in order for the side-chain chirality to be transferred to the supramolecular column. 

The urethane reaction is particularly useful for solid propellant applications because of its quantitative nature, convenient rate which can be adjusted by proper choice of catalysts, and the availability of many suitable hydroxyl compounds which permit the tailoring of propellant mechanical properties. Despite the quantitative nature and apparent simplicity of the urethane reaction R NCO + ROH - R NHCOOR, its exact course has not been fully explored yet. It does not follow simple second-order kinetics as the above formula would suggest since its second-order rate constant depends on many factors, such as concentration of reactants and the nature of the solvent. Baker and co-workers (2) proposed that the reaction is initiated through the attack of an alkoxide ion on the carbon atom of the isocyanate group... 

Table IX. Effect of Bonding Agent on Propellant Mechanical Properties"...

Prepolymer and Propellant Quality Control. Prepolymer Control. The characterization of the functionally terminated prepolymers was an important factor in the control of these materials required to assure satisfactory reproducibility of solid propellant properties. To characterize these materials adequately, it was necessary to develop new analytical methods or to improve existing methods to provide the desired level of control. It was ultimately demonstrated that (1) propellant mechanical... 

Using the above techniques, satisfactory reproducibility of CTPB propellant mechanical properties has been achieved. The reproducibility of the mechanical properties of a production CTPB propellant which is controlled by this method is shown in Table XIX. In this case, the standard deviations of the mechanical properties shown are 10% or less of the measured values. The data include differences arising from lot-to-lot variations in raw materials (27 lots of CTPB) and two sources for the prepolymer. 

Solid Propellant Mechanical Properties Testing, Failure Criteria, and Aging... 

ICRPG Solid Propellant Mechanical Behavior Manual, CPIA, Johns... 

Lavigne, J., Lessard, P., Ahad, E., and Dubois, C. (1994) Correlation of propellant mechanical properties and branched gap synthesis parameters. 

Burning composite propellants containing ammonium perchlorate Modifications of composite propellants (Mechanical profterties Manufacture of composite propellants Shapes of the propellant grains Explosive properties of composite propellants References... 

X.P. Zheng, H.P. Zhao, L.T. Gao, J.L. Liu, S.W. Yu, X.Q. Feng, Elasticity-driven droplet movement on a microbeam with gradient stiffness a biomimetic self-propelling mechanism. J. Colloid Interface Sci. 323(1), 133-140 (2008)... 

Williams, M. L., Blatz, P. J., and Schapery, R. A., "Fundamental Studies Relations to Systems Analysis of Solid Propellants," GALCIT SM 61-S, California Institute of Technology, Pasadena, California (Feb 1961). Also published in Interagency Chemical Rocket Propulsion Group, Solid Propellant Mechanical Behavior Manual, Chemical Propulsion Information Agency Pub. No. 21, Section 2.3 (1963). 

Compressed gas systems were originally developed simply to provide a means of expelling a product from its container when the valve was depressed. SemisoHd products such as a cream, ointment, or caulking compound are dispensed as such. A Hquid concentrate and a compressed gas propellant (Fig. 3) produce a spray when a mechanical breakup actuator is used. Nitrogen, insoluble in most materials, is generally used as the propellant. 

Trimethylolethane trinitrate (metriol trinitrate) is not satisfactory as a plasticizer for nitrocellulose, and must be used with other plasticizers such as metriol triacetate. Mixtures with nitroglycerin tend to improve the mechanical properties of double-base cast propellants at high and low temperatures. Metriol trinitrate has also been used in combination with triethylene glycol dinitrate as a plasticizer for nitrocellulose. Its physical properties are Hsted in Table 7 (118-122). 

Rocket Propellants. SoHd rocket propellants are mostly based on chemically cross-linked polymeric elastomers to provide the mechanical properties required in launchings and the environmental conditions experienced in storage, shipment, and handling (see Elastomers, synthetic). Double-and triple-based nitrocellulose propellants are also employed as rocket propellants. 

Polymer-based rocket propellants are generally referred to as composite propellants, and often identified by the elastomer used, eg, urethane propellants or carboxy- (CTPB) or hydroxy- (HTPB) terrninated polybutadiene propellants. The cross-linked polymers act as a viscoelastic matrix to provide mechanical strength, and as a fuel to react with the oxidizers present. Ammonium perchlorate and ammonium nitrate are the most common oxidizers used nitramines such as HMX or RDX may be added to react with the fuels and increase the impulse produced. Many other substances may be added including metallic fuels, plasticizers, stabilizers, catalysts, ballistic modifiers, and bonding agents. Typical components are Hsted in Table 1. 

Gun Propellents. Although the stresses on individual gun propellant grains are less severe because of the small size, these propellants must withstand much higher weapon pressures and accelerations. Formulation options are usually more limited for gun propellants than for rocket propellants because the products of combustion must not foul or corrode a gun, should have a low flame temperature, and should exhibit minimum flash and smoke characteristics. Gun propellants are examined microscopically for porosity, are tested for mechanical characteristics, and fired in closed bombs to determine the burning characteristics. 

Oxidizers. The characteristics of the oxidizer affect the baUistic and mechanical properties of a composite propellant as well as the processibihty. Oxidizers are selected to provide the best combination of available oxygen, high density, low heat of formation, and maximum gas volume in reaction with binders. Increases in oxidizer content increase the density, the adiabatic flame temperature, and the specific impulse of a propellant up to a maximum. The most commonly used inorganic oxidizer in both composite and nitroceUulose-based rocket propellant is ammonium perchlorate. The primary combustion products of an ammonium perchlorate propellant and a polymeric binder containing C, H, and O are CO2, H2, O2, and HCl. Ammonium nitrate has been used in slow burning propellants, and where a smokeless exhaust is requited. Nitramines such as RDX and HMX have also been used where maximum energy is essential. 

Gun Propellents. Low sensitivity gun propeUants, often referred to as LOVA (low vulnerabUity ammunition), use RDX or HMX as the principal energy components, and desensitizing binders such as ceUulose acetate butyrate or thermoplastic elastomers (TPE) including poly acetal—polyurethane block copolymers, polystyrene—polyacrjiate copolymers, and glycidyl azide polymers (GAP) to provide the required mechanical... 

All five processes requite plasticization of the nitrocellulose to eliminate its fibrous stmcture and cause it to bum predictably in parallel layers. Mechanical working of the ingredients contributes to plasticization and uniformity of composition. The compositions of representative nitroceUulose-based gun propellants are shown in Table 7. 

S olid Propellant Mging, Mechanical Pehavior and Grain Structural Integrity, CPIA Pubhcation LS 77-27, CPIA, Johns Hopkins University, Laurel, Md., 1977. 

---